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  • Spin dynamics of the potassium magnetometer in spin-exchange relaxation free regime

    Ji-Qing Fu(伏吉庆), Peng-Cheng Du(杜鹏程), Qing Zhou(周庆), Ru-Quan Wang(王如泉)
    Chin. Phys. B 2016, 25 (1): 010302
    The laser-pumped potassium spin-exchange relaxation free (SERF) magnetometer is the most sensitive detector of magnetic field and has many important applications. We present the experimental results of our potassium SERF magnetometer. A pump-probe approach is used to identify the unique spin dynamic...

     
  • Long-distance super-exchange and quantum magnetic relaxation in a hybrid metal-organic framework

    Ying Tian(田英), Shipeng Shen(申世鹏), Junzhuang Cong(丛君状), Liqin Yan(闫丽琴), Yisheng Chai(柴一晟), Young Sun(孙阳)
    Chin. Phys. B 2016, 25 (1): 017601
    The hybrid metal-organic framework [(CH3)2NH2]Fe(HCOO)3 with a perovskite-like structure exhibits a variety of unusual magnetic behaviors at low temperatures. While the long-distance super-exchange through the Fe-O-CH-O-Fe exchange path leads to a canted antiferromagnetic ordering at TN ~ 19 K, a se...

     
  • Unexpected low thermal conductivity and large power factor in Dirac semimetal Cd3As2

    Cheng Zhang(张成), Tong Zhou(周通), Sihang Liang(梁斯航), Junzhi Cao(曹钧植),Xiang Yuan(袁翔), Yanwen Liu(刘彦闻), Yao Shen(沈瑶), Qisi Wang(王奇思),Jun Zhao(赵俊), Zhongqin Yang(杨中芹), Faxian Xiu(修发贤)
    Chin. Phys. B 2016, 25 (1): 017202
    Thermoelectrics has long been considered as a promising way of power generation for the next decades. So far, extensive efforts have been devoted to the search of ideal thermoelectric materials, which require both high electrical conductivity and low thermal conductivity. Recently, the emerging Dira...

     
Chin. Phys. B  
  Chin. Phys. B--2016, Vol.25, No.1
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TOPICAL REVIEW—Fundamental physics research in lithium batteries

Entropy and heat generation of lithium cells/batteries

Songrui Wang(王松蕊)
Chin. Phys. B, 2016, 25 (1): 010509 doi: 10.1088/1674-1056/25/1/010509
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The methods and techniques commonly used in investigating the change of entropy and heat generation in Li cells/batteries are introduced, as are the measurements, calculations and purposes. The changes of entropy and heat generation are concomitant with the use of Li cells/batteries. In order to improve the management and the application of Li cells/batteries, especially for large scale power batteries, the quantitative investigations of the change of entropy and heat generating are necessary.

Mechanics of high-capacity electrodes in lithium-ion batteries

Ting Zhu
Chin. Phys. B, 2016, 25 (1): 014601 doi: 10.1088/1674-1056/25/1/014601
Full Text: [PDF 1247 KB] (Downloads:582) RICH HTML
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Rechargeable batteries, such as lithium-ion batteries, play an important role in the emerging sustainable energy landscape. Mechanical degradation and resulting capacity fade in high-capacity electrode materials critically hinder their use in high-performance lithium-ion batteries. This paper presents an overview of recent advances in understanding the electrochemically-induced mechanical behavior of the electrode materials in lithium-ion batteries. Particular emphasis is placed on stress generation and facture in high-capacity anode materials such as silicon. Finally, we identify several important unresolved issues for future research.

Li-ion batteries: Phase transition

Peiyu Hou(侯配玉), Geng Chu(褚赓), Jian Gao(高健), Yantao Zhang(张彦涛), Lianqi Zhang(张联齐)
Chin. Phys. B, 2016, 25 (1): 016104 doi: 10.1088/1674-1056/25/1/016104
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Progress in the research on phase transitions during Li+ extraction/insertion processes in typical battery materials is summarized as examples to illustrate the significance of understanding phase transition phenomena in Li-ion batteries. Physical phenomena such as phase transitions (and resultant phase diagrams) are often observed in Li-ion battery research and already play an important role in promoting Li-ion battery technology. For example, the phase transitions during Li+ insertion/extraction are highly relevant to the thermodynamics and kinetics of Li-ion batteries, and even physical characteristics such as specific energy, power density, volume variation, and safety-related properties.

Soft x-ray spectroscopy for probing electronic and chemical states of battery materials

Wanli Yang(杨万里) and Ruimin Qiao(乔瑞敏)
Chin. Phys. B, 2016, 25 (1): 017104 doi: 10.1088/1674-1056/25/1/017104
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The formidable challenge of developing high-performance battery system stems from the complication of battery operations, both mechanically and electronically. In the electrodes and at the electrode-electrolyte interfaces, chemical reactions take place with evolving electron states. In addition to the extensive studies of material synthesis, electrochemical, structural, and mechanical properties, soft x-ray spectroscopy provides unique opportunities for revealing the critical electron states in batteries. This review discusses some of the recent soft x-ray spectroscopic results on battery binder, transition-metal based positive electrodes, and the solid-electrolyte-interphase. By virtue of soft x-ray's sensitivity to electron states, the electronic property, the redox during electrochemical operations, and the chemical species of the interphases could be fingerprinted by soft x-ray spectroscopy. Understanding and innovating battery technologies need a multimodal approach, and soft x-ray spectroscopy is one of the incisive tools to probe the chemical and physical evolutions in batteries.

Electrochromic & magnetic properties of electrode materials for lithium ion batteries

Zheng-Fei Guo(郭正飞), Kun Pan(潘坤), Xue-Jin Wang(王学进)
Chin. Phys. B, 2016, 25 (1): 017801 doi: 10.1088/1674-1056/25/1/017801
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Progress in electrochromic lithium ion batteries (LIBs) is reviewed, highlighting advances and possible research directions. Methods for using the LIB electrode materials' magnetic properties are also described, using several examples. Li4Ti5O12 (LTO) film is discussed as an electrochromic material and insertion compound. The opto-electrical properties of the LTO film have been characterized by electrical measurements and UV-Vis spectra. A prototype bi-functional electrochromic LIB, incorporating LTO as both electrochromic layer and anode, has also been characterized by charge-discharge measurements and UV-Vis transmittance. The results show that the bi-functional electrochromic LIB prototype works well. Magnetic measurement has proven to be a powerful tool to evaluate the quality of electrode materials. We introduce briefly the magnetism of solids in general, and then discuss the magnetic characteristics of layered oxides, spinel oxides, olivine phosphate LiFePO4, and Nasicon-type Li3Fe2(PO4)3. We also discuss what kind of impurities can be detected, which will guide us to fabricate high quality films and high performance devices.

Interfacial transport in lithium-ion conductors

Shaofei Wang(王少飞) and Liquan Chen(陈立泉)
Chin. Phys. B, 2016, 25 (1): 018202 doi: 10.1088/1674-1056/25/1/018202
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Physical models of ion diffusion at different interfaces are reviewed. The use of impedance spectroscopy (IS), nuclear magnetic resonance (NMR), and secondary ion mass spectrometry (SIMS) techniques are also discussed. The diffusion of ions is fundamental to the operation of lithium-ion batteries, taking place not only within the grains but also across different interfaces. Interfacial ion transport usually contributes to the majority of the resistance in lithium-ion batteries. A greater understanding of the interfacial diffusion of ions is crucial to improving battery performance.

Size effects in lithium ion batteries

Hu-Rong Yao(姚胡蓉), Ya-Xia Yin(殷雅侠), Yu-Guo Guo (郭玉国)
Chin. Phys. B, 2016, 25 (1): 018203 doi: 10.1088/1674-1056/25/1/018203
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Size-related properties of novel lithium battery materials, arising from kinetics, thermodynamics, and newly discovered lithium storage mechanisms, are reviewed. Complementary experimental and computational investigations of the use of the size effects to modify electrodes and electrolytes for lithium ion batteries are enumerated and discussed together. Size differences in the materials in lithium ion batteries lead to a variety of exciting phenomena. Smaller-particle materials with highly connective interfaces and reduced diffusion paths exhibit higher rate performance than the corresponding bulk materials. The thermodynamics is also changed by the higher surface energy of smaller particles, affecting, for example, secondary surface reactions, lattice parameter, voltage, and the phase transformation mechanism. Newly discovered lithium storage mechanisms that result in superior storage capacity are also briefly highlighted.

Understanding oxygen reactions in aprotic Li-O2 batteries

Shunchao Ma(马顺超), Yelong Zhang(张业龙), Qinghua Cui(崔清华), Jing Zhao(赵婧), Zhangquan Peng(彭章泉)
Chin. Phys. B, 2016, 25 (1): 018204 doi: 10.1088/1674-1056/25/1/018204
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Although significant progress has been made in many aspects of the emerging aprotic Li-O2 battery system, an in-depth understanding of the oxygen reactions is still underway. The oxygen reactions occurring in the positive electrode distinguish Li-O2 batteries from the conventional Li-ion cells and play a crucial role in the Li-O2 cell's performance (capacity, rate capability, and cycle life). Recent advances in fundamental studies of oxygen reactions in aprotic Li-O2 batteries are reviewed, including the reaction route, kinetics, morphological evolution of Li2O2, and charge transport within Li2O2. Prospects are also provided for future fundamental investigations of Li-O2 chemistry.

Strategies to curb structural changes of lithium/transition metal oxide cathode materials & the changes' effects on thermal & cycling stability

Xiqian Yu(禹习谦), Enyuan Hu(胡恩源), Seongmin Bak,Yong-Ning Zhou(周永宁), Xiao-Qing Yang(杨晓青)
Chin. Phys. B, 2016, 25 (1): 018205 doi: 10.1088/1674-1056/25/1/018205
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Structural transformation behaviors of several typical oxide cathode materials during a heating process are reviewed in detail to provide in-depth understanding of the key factors governing the thermal stability of these materials. We also discuss applying the information about heat induced structural evolution in the study of electrochemically induced structural changes. All these discussions are expected to provide valuable insights for designing oxide cathode materials with significantly improved structural stability for safe, long-life lithium ion batteries, as the safety of lithium-ion batteries is a critical issue; it is widely accepted that the thermal instability of the cathodes is one of the most critical factors in thermal runaway and related safety problems.

Physics of electron and lithium-ion transport in electrode materials for Li-ion batteries

Musheng Wu(吴木生), Bo Xu(徐波), Chuying Ouyang(欧阳楚英)
Chin. Phys. B, 2016, 25 (1): 018206 doi: 10.1088/1674-1056/25/1/018206
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The physics of ionic and electrical conduction at electrode materials of lithium-ion batteries (LIBs) are briefly summarized here, besides, we review the current research on ionic and electrical conduction in electrode material incorporating experimental and simulation studies. Commercial LIBs have been widely used in portable electronic devices and are now developed for large-scale applications in hybrid electric vehicles (HEV) and stationary distributed power stations. However, due to the physical limits of the materials, the overall performance of today's LIBs does not meet all the requirements for future applications, and the transport problem has been one of the main barriers to further improvement. The electron and Li-ion transport behaviors are important in determining the rate capacity of LIBs.

Wavy structures for stretchable energy storage devices: Structural design and implementation

Lei Wen(闻雷), Ying Shi(石颖), Jing Chen(陈静), Bin Yan(严彬), Feng Li(李峰)
Chin. Phys. B, 2016, 25 (1): 018207 doi: 10.1088/1674-1056/25/1/018207
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The application of wavy structures in stretchable electrochemical energy storage devices is reviewed. First, the mechanical analysis of wavy structures, specific to flexible electronics, is introduced. Second, stretchable electrochemical energy storage devices with wavy structures are discussed. Finally, the present problems and challenges are reviewed, and possible directions for future research are outlined.

High-throughput theoretical design of lithium battery materials

Shi-Gang Ling(凌仕刚), Jian Gao(高健), Rui-Juan Xiao(肖睿娟), Li-Quan Chen(陈立泉)
Chin. Phys. B, 2016, 25 (1): 018208 doi: 10.1088/1674-1056/25/1/018208
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The rapid evolution of high-throughput theoretical design schemes to discover new lithium battery materials is reviewed, including high-capacity cathodes, low-strain cathodes, anodes, solid state electrolytes, and electrolyte additives. With the development of efficient theoretical methods and inexpensive computers, high-throughput theoretical calculations have played an increasingly important role in the discovery of new materials. With the help of automatic simulation flow, many types of materials can be screened, optimized and designed from a structural database according to specific search criteria. In advanced cell technology, new materials for next generation lithium batteries are of great significance to achieve performance, and some representative criteria are: higher energy density, better safety, and faster charge/discharge speed.

Surface structure evolution of cathode materials for Li-ion batteries

Yingchun Lyu(吕迎春), Yali Liu(刘亚利), Lin Gu(谷林)
Chin. Phys. B, 2016, 25 (1): 018209 doi: 10.1088/1674-1056/25/1/018209
Full Text: [PDF 3172 KB] (Downloads:938) RICH HTML
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Lithium ion batteries are important electrochemical energy storage devices for consumer electronics and the most promising candidates for electrical/hybrid vehicles. The surface chemistry influences the performance of the batteries significantly. In this short review, the evolution of the surface structure of the cathode materials at different states of the pristine, storage and electrochemical reactions are summarized. The main methods for the surface modification are also introduced.

Brief overview of electrochemical potential in lithium ion batteries

Jian Gao(高健), Si-Qi Shi(施思齐), Hong Li(李泓)
Chin. Phys. B, 2016, 25 (1): 018210 doi: 10.1088/1674-1056/25/1/018210
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The physical fundamentals and influences upon electrode materials' open-circuit voltage (OCV) and the spatial distribution of electrochemical potential in the full cell are briefly reviewed. We hope to illustrate that a better understanding of these scientific problems can help to develop and design high voltage cathodes and interfaces with low Ohmic drop. OCV is one of the main indices to evaluate the performance of lithium ion batteries (LIBs), and the enhancement of OCV shows promise as a way to increase the energy density. Besides, the severe potential drop at the interfaces indicates high resistance there, which is one of the key factors limiting power density.

Lithium-ion transport in inorganic solid state electrolyte

Jian Gao(高健), Yu-Sheng Zhao(赵予生), Si-Qi Shi(施思齐), Hong Li(李泓)
Chin. Phys. B, 2016, 25 (1): 018211 doi: 10.1088/1674-1056/25/1/018211
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An overview of ion transport in lithium-ion inorganic solid state electrolytes is presented, aimed at exploring and designing better electrolyte materials. Ionic conductivity is one of the most important indices of the performance of inorganic solid state electrolytes. The general definition of solid state electrolytes is presented in terms of their role in a working cell (to convey ions while isolate electrons), and the history of solid electrolyte development is briefly summarized. Ways of using the available theoretical models and experimental methods to characterize lithium-ion transport in solid state electrolytes are systematically introduced. Then the various factors that affect ionic conductivity are itemized, including mainly structural disorder, composite materials and interface effects between a solid electrolyte and an electrode. Finally, strategies for future material systems, for synthesis and characterization methods, and for theory and calculation are proposed, aiming to help accelerate the design and development of new solid electrolytes.

Multi-scale computation methods: Their applications in lithium-ion battery research and development

Siqi Shi(施思齐), Jian Gao(高健), Yue Liu(刘悦), Yan Zhao(赵彦), Qu Wu(武曲), Wangwei Ju(琚王伟), Chuying Ouyang(欧阳楚英), Ruijuan Xiao(肖睿娟)
Chin. Phys. B, 2016, 25 (1): 018212 doi: 10.1088/1674-1056/25/1/018212
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Based upon advances in theoretical algorithms, modeling and simulations, and computer technologies, the rational design of materials, cells, devices, and packs in the field of lithium-ion batteries is being realized incrementally and will at some point trigger a paradigm revolution by combining calculations and experiments linked by a big shared database, enabling accelerated development of the whole industrial chain. Theory and multi-scale modeling and simulation, as supplements to experimental efforts, can help greatly to close some of the current experimental and technological gaps, as well as predict path-independent properties and help to fundamentally understand path-independent performance in multiple spatial and temporal scales.

Redox-assisted Li+-storage in lithium-ion batteries

Qizhao Huang(黄启昭) and Qing Wang(王庆)
Chin. Phys. B, 2016, 25 (1): 018213 doi: 10.1088/1674-1056/25/1/018213
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Interfacial charge transfer is the key kinetic process dictating the operation of lithium-ion battery. Redox-mediated charge propagations of the electronic (e- and h+) and ionic species (Li+) at the electrode-electrolyte interface have recently gained increasing attention for better exploitation of battery materials. This article briefly summarises the energetic and kinetic aspects of lithium-ion batteries, and reviews the recent progress on various redox-assisted Li+ storage approaches. From molecular wiring to polymer wiring and from redox targeting to redox flow lithium battery, the role of redox mediators and the way of the redox species functioning in lithium-ion batteries are discussed.

Editorial

Hong Li, Liquan Chen
Chin. Phys. B, 2016, 25 (1): 018214 doi: 10.1088/1674-1056/25/1/018214
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Scientific and technological challenges toward application of lithium-sulfur batteries

Ya-Xia Yin(殷雅侠), Hu-Rong Yao(姚胡蓉), Yu-Guo Guo(郭玉国)
Chin. Phys. B, 2016, 25 (1): 018801 doi: 10.1088/1674-1056/25/1/018801
Full Text: [PDF 704 KB] (Downloads:615) RICH HTML
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Recent progress in improving Li-S batteries' cathodes, anodes, and electrolytes via different approaches is summarized. The poor conductivity of sulfur cathodes, the dissolution of polysulfide intermediates, and the high reactivity of metal Li anodes currently motivate a great deal of research. Urgent challenges concerning Li anodes are also emphasized.

All-solid-state lithium batteries with inorganic solid electrolytes: Review of fundamental science

Xiayin Yao(姚霞银), Bingxin Huang(黄冰心), Jingyun Yin(尹景云), Gang Peng(彭刚), Zhen Huang(黄祯), Chao Gao(高超), Deng Liu(刘登), Xiaoxiong Xu(许晓雄)
Chin. Phys. B, 2016, 25 (1): 018802 doi: 10.1088/1674-1056/25/1/018802
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The scientific basis of all-solid-state lithium batteries with inorganic solid electrolytes is reviewed briefly, touching upon solid electrolytes, electrode materials, electrolyte/electrode interface phenomena, fabrication, and evaluation. The challenges and prospects are outlined as well.

TOPICAL REVIEW—8th IUPAP International Conference on Biological Physics

Ab initio path-integral molecular dynamics and the quantum nature of hydrogen bonds

Yexin Feng(冯页新), Ji Chen(陈基), Xin-Zheng Li(李新征), Enge Wang(王恩哥)
Chin. Phys. B, 2016, 25 (1): 013104 doi: 10.1088/1674-1056/25/1/013104
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The hydrogen bond (HB) is an important type of intermolecular interaction, which is generally weak, ubiquitous, and essential to life on earth. The small mass of hydrogen means that many properties of HBs are quantum mechanical in nature. In recent years, because of the development of computer simulation methods and computational power, the influence of nuclear quantum effects (NQEs) on the structural and energetic properties of some hydrogen bonded systems has been intensively studied. Here, we present a review of these studies by focussing on the explanation of the principles underlying the simulation methods, i.e., the ab initio path-integral molecular dynamics. Its extension in combination with the thermodynamic integration method for the calculation of free energies will also be introduced. We use two examples to show how this influence of NQEs in realistic systems is simulated in practice.

A new understanding of inert gas narcosis

Meng Zhang(张萌), Yi Gao(高嶷), Haiping Fang(方海平)
Chin. Phys. B, 2016, 25 (1): 013602 doi: 10.1088/1674-1056/25/1/013602
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Anesthetics are extremely important in modern surgery to greatly reduce the patient's pain. The understanding of anesthesia at molecular level is the preliminary step for the application of anesthetics in clinic safely and effectively. Inert gases, with low chemical activity, have been found to cause anesthesia for centuries, but the mechanism is unclear yet. In this review, we first summarize the progress of theories about general anesthesia, especially for inert gas narcosis, and then propose a new hypothesis that the aggregated rather than the dispersed inert gas molecules are the key to trigger the narcosis to explain the steep dose-response relationship of anesthesia.

Uncovering the underlying physical mechanisms of biological systems via quantification of landscape and flux

Li Xu(徐丽), Xiakun Chu(楚夏昆), Zhiqiang Yan(晏致强), Xiliang Zheng(郑喜亮), Kun Zhang(张坤), Feng Zhang(张锋), Han Yan(闫晗), Wei Wu(吴畏), Jin Wang(汪劲)
Chin. Phys. B, 2016, 25 (1): 016401 doi: 10.1088/1674-1056/25/1/016401
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In this review, we explore the physical mechanisms of biological processes such as protein folding and recognition, ligand binding, and systems biology, including cell cycle, stem cell, cancer, evolution, ecology, and neural networks. Our approach is based on the landscape and flux theory for nonequilibrium dynamical systems. This theory provides a unifying principle and foundation for investigating the underlying mechanisms and physical quantification of biological systems.

Self-assembly of block copolymers grafted onto a flat substrate: Recent progress in theory and simulations

Zheng Wang(王铮) and Bao-Hui Li(李宝会)
Chin. Phys. B, 2016, 25 (1): 016402 doi: 10.1088/1674-1056/25/1/016402
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Block copolymers are a class of soft matter that self-assemble to form ordered morphologies on the scale of nanometers, making them ideal materials for various applications. These applications directly depend on the shape and size of the self-assembled morphologies, and hence, a high degree of control over the self-assembly is desired. Grafting block copolymer chains onto a substrate to form copolymer brushes is a versatile method to fabricate functional surfaces. Such surfaces demonstrate a response to their environment, i.e., they change their surface topography in response to different external conditions. Furthermore, such surfaces may possess nanoscale patterns, which are important for some applications; however, such patterns may not form with spun-cast films under the same condition. In this review, we summarize the recent progress of the self-assembly of block copolymers grafted onto a flat substrate. We mainly concentrate on the self-assembled morphologies of end-grafted AB diblock copolymers, junction point-grafted AB diblock copolymers (i.e., Y-shaped brushes), and end-grafted ABA triblock copolymers. Special emphasis is placed on theoretical and simulation progress.

Development of mean-field electrical double layer theory

Yike Huang(黄一珂), Xiaohong Liu(刘晓红), Shu Li(李姝), Tianying Yan(言天英)
Chin. Phys. B, 2016, 25 (1): 016801 doi: 10.1088/1674-1056/25/1/016801
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In order to understand the electric interfacial behavior, mean field based electric double layer (EDL) theory has been continuously developed over the past 150 years. In this article, we briefly review the development of the EDL model, from the dimensionless Gouy-Chapman model to the symmetric Bikerman-Freise model, and finally toward size-asymmetric mean field theory models. We provide the general derivations within the framework of Helmholtz free energy of the lattice-gas model, and it can be seen that the above-mentioned models are consistent in the sense that the interconversion among them can be achieved by reducing the basic assumptions.

Modeling the temperature-dependent peptide vibrational spectra based on implicit-solvent model and enhance sampling technique

Tianmin Wu (吴天敏), Tianjun Wang (王天骏), Xian Chen(陈娴), Bin Fang(方彬), Ruiting Zhang(张睿挺), Wei Zhuang(庄巍)
Chin. Phys. B, 2016, 25 (1): 018201 doi: 10.1088/1674-1056/25/1/018201
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We herein review our studies on simulating the thermal unfolding Fourier transform infrared and two-dimensional infrared spectra of peptides. The peptide-water configuration ensembles, required forspectrum modeling, aregenerated at a series of temperatures using the GBOBC implicit solvent model and the integrated tempering sampling technique. The fluctuating vibrational Hamiltonians of the amide I vibrational band are constructed using the Frenkel exciton model. The signals are calculated using nonlinear exciton propagation. The simulated spectral features such as the intensity and ellipticity are consistent with the experimental observations. Comparing the signals for two beta-hairpin polypeptides with similar structures suggests that this technique is sensitive to peptide folding landscapes.

Hierarchical processes in β -sheet peptide self-assembly from the microscopic to the mesoscopic level

Li Deng(邓礼) and Hai Xu(徐海)
Chin. Phys. B, 2016, 25 (1): 018701 doi: 10.1088/1674-1056/25/1/018701
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Under appropriate physicochemical conditions, short peptide fragments and their synthetic mimics have been shown to form elongated cross-β nanostructures through self-assembly. The self-assembly process and the resultant peptide nanostructures are not only related to neurodegenerative diseases but also provide inspiration for the development of novel bionanomaterials. Both experimental and theoretical studies on peptide self-assembly have shown that the self-assembly process spans multiple time and length scales and is hierarchical. β -sheet self-assembly consists of three sub-processes from the microscopic to the mesoscopic level: β -sheet locking, lateral stacking, and morphological transformation. Detailed atomistic simulation studies have provided insight into the early stages of peptide nanostructure formation and the interplay between different non-covalent interactions at the microscopic level. This review gives a brief introduction of the hierarchical peptide self-assembly process and focuses on the roles of various non-covalent interactions in the sub-processes based on recent simulation, experimental, and theoretical studies.

Computational design of proteins with novel structure and functions

Wei Yang(杨为) and Lu-Hua Lai(来鲁华)
Chin. Phys. B, 2016, 25 (1): 018702 doi: 10.1088/1674-1056/25/1/018702
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Computational design of proteins is a relatively new field, where scientists search the enormous sequence space for sequences that can fold into desired structure and perform desired functions. With the computational approach, proteins can be designed, for example, as regulators of biological processes, novel enzymes, or as biotherapeutics. These approaches not only provide valuable information for understanding of sequence-structure-function relations in proteins, but also hold promise for applications to protein engineering and biomedical research. In this review, we briefly introduce the rationale for computational protein design, then summarize the recent progress in this field, including de novo protein design, enzyme design, and design of protein-protein interactions. Challenges and future prospects of this field are also discussed.

Flexibility of nucleic acids: From DNA to RNA

Lei Bao(鲍磊), Xi Zhang(张曦), Lei Jin(金雷), Zhi-Jie Tan(谭志杰)
Chin. Phys. B, 2016, 25 (1): 018703 doi: 10.1088/1674-1056/25/1/018703
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The structural flexibility of nucleic acids plays a key role in many fundamental life processes, such as gene replication and expression, DNA-protein recognition, and gene regulation. To obtain a thorough understanding of nucleic acid flexibility, extensive studies have been performed using various experimental methods and theoretical models. In this review, we will introduce the progress that has been made in understanding the flexibility of nucleic acids including DNAs and RNAs, and will emphasize the experimental findings and the effects of salt, temperature, and sequence. Finally, we will discuss the major unanswered questions in understanding the flexibility of nucleic acids.

Amyloid-β peptide aggregation and the influence of carbon nanoparticles

Wen-Hui Xi(郗文辉) and Guang-Hong Wei(韦广红)
Chin. Phys. B, 2016, 25 (1): 018704 doi: 10.1088/1674-1056/25/1/018704
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Soluble peptides or proteins can self-aggregate into insoluble, ordered amyloid fibrils under appropriate conditions. These amyloid aggregates are the hallmarks of several human diseases ranging from neurodegenerative disorders to systemic amyloidoses. In this review, we first introduce the common structural features of amyloid fibrils and the amyloid fibrillation kinetics determined from experimental studies. Then, we discuss the structural models of Alzheimer's amyloid-β (Aβ) fibrils derived from solid-state nuclear magnetic resonance spectroscopy. On the computational side, molecular dynamics simulations can provide atomic details of structures and the underlying oligomerization mechanisms. We finally summarize recent progress in atomistic simulation studies on the oligomerization of Aβ (including full-length Aβ and its fragments) and the influence of carbon nanoparticles.

Improvements in continuum modeling for biomolecular systems

Yu Qiao(乔瑜) and Ben-Zhuo Lu(卢本卓)
Chin. Phys. B, 2016, 25 (1): 018705 doi: 10.1088/1674-1056/25/1/018705
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Modeling of biomolecular systems plays an essential role in understanding biological processes, such as ionic flow across channels, protein modification or interaction, and cell signaling. The continuum model described by the Poisson-Boltzmann (PB)/Poisson-Nernst-Planck (PNP) equations has made great contributions towards simulation of these processes. However, the model has shortcomings in its commonly used form and cannot capture (or cannot accurately capture) some important physical properties of the biological systems. Considerable efforts have been made to improve the continuum model to account for discrete particle interactions and to make progress in numerical methods to provide accurate and efficient simulations. This review will summarize recent main improvements in continuum modeling for biomolecular systems, with focus on the size-modified models, the coupling of the classical density functional theory and the PNP equations, the coupling of polar and nonpolar interactions, and numerical progress.

Computational investigations on polymerase actions in gene transcription and replication: Combining physical modeling and atomistic simulations

Jin Yu(喻进)
Chin. Phys. B, 2016, 25 (1): 018706 doi: 10.1088/1674-1056/25/1/018706
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Polymerases are protein enzymes that move along nucleic acid chains and catalyze template-based polymerization reactions during gene transcription and replication. The polymerases also substantially improve transcription or replication fidelity through the non-equilibrium enzymatic cycles. We briefly review computational efforts that have been made toward understanding mechano-chemical coupling and fidelity control mechanisms of the polymerase elongation. The polymerases are regarded as molecular information motors during the elongation process. It requires a full spectrum of computational approaches from multiple time and length scales to understand the full polymerase functional cycle. We stay away from quantum mechanics based approaches to the polymerase catalysis due to abundant former surveys, while addressing statistical physics modeling approaches along with all-atom molecular dynamics simulation studies. We organize this review around our own modeling and simulation practices on a single subunit T7 RNA polymerase, and summarize commensurate studies on structurally similar DNA polymerases as well. For multi-subunit RNA polymerases that have been actively studied in recent years, we leave systematical reviews of the simulation achievements to latest computational chemistry surveys, while covering only representative studies published very recently, including our own work modeling structure-based elongation kinetic of yeast RNA polymerase II. In the end, we briefly go through physical modeling on elongation pauses and backtracking activities of the multi-subunit RNAPs. We emphasize on the fluctuation and control mechanisms of the polymerase actions, highlight the non-equilibrium nature of the operation system, and try to build some perspectives toward understanding the polymerase impacts from the single molecule level to a genome-wide scale.

Multiscale molecular dynamics simulations of membrane remodeling by Bin/Amphiphysin/Rvs family proteins

Chun Chan(陈骏), Haohua Wen(文豪华), Lanyuan Lu(鲁兰原), Jun Fan(范俊)
Chin. Phys. B, 2016, 25 (1): 018707 doi: 10.1088/1674-1056/25/1/018707
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Membrane curvature is no longer thought of as a passive property of the membrane; rather, it is considered as an active, regulated state that serves various purposes in the cell such as between cells and organelle definition. While transport is usually mediated by tiny membrane bubbles known as vesicles or membrane tubules, such communication requires complex interplay between the lipid bilayers and cytosolic proteins such as members of the Bin/Amphiphysin/Rvs (BAR) superfamily of proteins. With rapid developments in novel experimental techniques, membrane remodeling has become a rapidly emerging new field in recent years. Molecular dynamics (MD) simulations are important tools for obtaining atomistic information regarding the structural and dynamic aspects of biological systems and for understanding the physics-related aspects. The availability of more sophisticated experimental data poses challenges to the theoretical community for developing novel theoretical and computational techniques that can be used to better interpret the experimental results to obtain further functional insights. In this review, we summarize the general mechanisms underlying membrane remodeling controlled or mediated by proteins. While studies combining experiments and molecular dynamics simulations recall existing mechanistic models, concurrently, they extend the role of different BAR domain proteins during membrane remodeling processes. We review these recent findings, focusing on how multiscale molecular dynamics simulations aid in understanding the physical basis of BAR domain proteins, as a representative of membrane-remodeling proteins.

In vitro three-dimensional cancer metastasis modeling: Past, present, and future

Wei-jing Han(韩伟静), Wei Yuan(袁伟), Jiang-rui Zhu(朱江瑞), Qihui Fan(樊琪慧), Junle Qu(屈军乐), Li-yu Liu(刘雳宇), on behalf of the U.S.--China Physical Sciences-Oncology Alliance
Chin. Phys. B, 2016, 25 (1): 018709 doi: 10.1088/1674-1056/25/1/018709
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Metastasis is the leading cause of most cancer deaths, as opposed to dysregulated cell growth of the primary tumor. Molecular mechanisms of metastasis have been studied for decades and the findings have evolved our understanding of the progression of malignancy. However, most of the molecular mechanisms fail to address the causes of cancer and its evolutionary origin, demonstrating an inability to find a solution for complete cure of cancer. After being a neglected area of tumor biology for quite some time, recently several studies have focused on the impact of the tumor microenvironment on cancer growth. The importance of the tumor microenvironment is gradually gaining attention, particularly from the perspective of biophysics. In vitro three-dimensional (3-D) metastatic models are an indispensable platform for investigating the tumor microenvironment, as they mimic the in vivo tumor tissue. In 3-D metastatic in vitro models, static factors such as the mechanical properties, biochemical factors, as well as dynamic factors such as cell-cell, cell-ECM interactions, and fluid shear stress can be studied quantitatively. With increasing focus on basic cancer research and drug development, the in vitro 3-D models offer unique advantages in fundamental and clinical biomedical studies.

Recent technical advancements enabled atomic resolution CryoEM

Xueming Li(李雪明)
Chin. Phys. B, 2016, 25 (1): 018710 doi: 10.1088/1674-1056/25/1/018710
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With recent breakthroughs in camera and image processing technologies single-particle electron cryo-microscopy (CryoEM) has suddenly gained the attention of structural biologists as a powerful tool able to solve the atomic structures of biological complexes and assemblies. Compared with x-ray crystallography, CryoEM can be applied to partially flexible structures in solution and without the necessity of crystallization, which is especially important for large complexes and assemblies. This review briefly explains several key bottlenecks for atomic resolution CryoEM, and describes the corresponding solutions for these bottlenecks based on the recent technical advancements. The review also aims to provide an overview about the technical differences between its applications in biology and those in material science.

SPECIAL TOPIC—Fundamental physics research in lithium batteries

FT-Raman spectroscopy study of solvent-in-salt electrolytes

Liumin Suo(索鎏敏), Zheng Fang(方铮), Yong-Sheng Hu(胡勇胜), Liquan Chen(陈立泉)
Chin. Phys. B, 2016, 25 (1): 016101 doi: 10.1088/1674-1056/25/1/016101
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Cation-anion interaction with different ratios of salt to solvent is investigated by FT-Raman spectroscopy. The fitting result of the C-N-C bending vibration manifests that the cation-anion coordination structure changes tremendously with the variation of salt concentration. It is well known that lithium-ion transport in ultrahigh salt concentration electrolyte is dramatically different from that in dilute electrolyte, due to high viscosity and strong cation-anion interaction. In ultrahigh salt concentrated “solvent-in-salt” electrolyte (SIS-7#), we found, on one hand, that the cation and anion in the solution mainly formed cation-anion pairs with a high Li+ coordination number ( ≥ 1), including intimate ion pairs (20.1%) and aggregated ion pairs (79.9%), which not only cause low total ionic conductivity but also cause a high lithium transference number (0.73). A possible lithium transport mechanism is proposed: in solvent-in-salt electrolytes, lithium ions' direct movement presumably depends on Li-ion exchange between aggregated ion pairs and solvent molecules, which repeats a dissolving and re-complexing process between different oxygen groups of solvent molecules.
GENERAL

A new six-component super soliton hierarchy and its self-consistent sources and conservation laws

Han-yu Wei(魏含玉) and Tie-cheng Xia(夏铁成)
Chin. Phys. B, 2016, 25 (1): 010201 doi: 10.1088/1674-1056/25/1/010201
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A new six-component super soliton hierarchy is obtained based on matrix Lie super algebras. Super trace identity is used to furnish the super Hamiltonian structures for the resulting nonlinear super integrable hierarchy. After that, the self-consistent sources of the new six-component super soliton hierarchy are presented. Furthermore, we establish the infinitely many conservation laws for the integrable super soliton hierarchy.

Denoising of chaotic signal using independent component analysis and empirical mode decomposition with circulate translating

Wen-Bo Wang(王文波), Xiao-Dong Zhang(张晓东), Yuchan Chang(常毓禅), Xiang-Li Wang(汪祥莉), Zhao Wang(王钊), Xi Chen(陈希), Lei Zheng(郑雷)
Chin. Phys. B, 2016, 25 (1): 010202 doi: 10.1088/1674-1056/25/1/010202
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In this paper, a new method to reduce noises within chaotic signals based on ICA (independent component analysis) and EMD (empirical mode decomposition) is proposed. The basic idea is decomposing chaotic signals and constructing multidimensional input vectors, firstly, on the base of EMD and its translation invariance. Secondly, it makes the independent component analysis on the input vectors, which means that a self adapting denoising is carried out for the intrinsic mode functions (IMFs) of chaotic signals. Finally, all IMFs compose the new denoised chaotic signal. Experiments on the Lorenz chaotic signal composed of different Gaussian noises and the monthly observed chaotic sequence on sunspots were put into practice. The results proved that the method proposed in this paper is effective in denoising of chaotic signals. Moreover, it can correct the center point in the phase space effectively, which makes it approach the real track of the chaotic attractor.

Birkhoffian symplectic algorithms derived from Hamiltonian symplectic algorithms

Xin-Lei Kong(孔新雷), Hui-Bin Wu(吴惠彬), Feng-Xiang Mei(梅凤翔)
Chin. Phys. B, 2016, 25 (1): 010203 doi: 10.1088/1674-1056/25/1/010203
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In this paper, we focus on the construction of structure preserving algorithms for Birkhoffian systems, based on existing symplectic schemes for the Hamiltonian equations. The key of the method is to seek an invertible transformation which drives the Birkhoffian equations reduce to the Hamiltonian equations. When there exists such a transformation, applying the corresponding inverse map to symplectic discretization of the Hamiltonian equations, then resulting difference schemes are verified to be Birkhoffian symplectic for the original Birkhoffian equations. To illustrate the operation process of the method, we construct several desirable algorithms for the linear damped oscillator and the single pendulum with linear dissipation respectively. All of them exhibit excellent numerical behavior, especially in preserving conserved quantities.

Atomic-scale simulations of material behaviors and tribology properties for BCC metal film

H D Aristizabal, P A Parra, P López, E Restrepo-Parra
Chin. Phys. B, 2016, 25 (1): 010204 doi: 10.1088/1674-1056/25/1/010204
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This work has two main purposes: (i) introducing the basic concepts of molecular dynamics analysis to material scientists and engineers, and (ii) providing a better understanding of instrumented indentation measurements, presenting an example of nanoindentation and scratch test simulations. To reach these purposes, three-dimensional molecular dynamics (MD) simulations of nanoindentation and scratch test technique were carried out for generic thin films that present BCC crystalline structures. Structures were oriented in the plane (100) and placed on FCC diamond substrates. A pair wise potential was employed to simulate the interaction between atoms of each layer and a repulsive radial potential was used to represent a spherical tip indenting the sample. Mechanical properties of this generic material were obtained by varying the indentation depth and dissociation energy. The load-unload curves and coefficient of friction were found for each test; on the other hand, dissociation energy was varied showing a better mechanical response for films that present grater dissociation energy. Structural change evolution was observed presenting vacancies and slips as the depth was varied.

Multi-symplectic variational integrators for nonlinear Schrödinger equations with variable coefficients

Cui-Cui Liao(廖翠萃), Jin-Chao Cui(崔金超), Jiu-Zhen Liang(梁久祯), Xiao-Hua Ding(丁效华)
Chin. Phys. B, 2016, 25 (1): 010205 doi: 10.1088/1674-1056/25/1/010205
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In this paper, we propose a variational integrator for nonlinear Schrödinger equations with variable coefficients. It is shown that our variational integrator is naturally multi-symplectic. The discrete multi-symplectic structure of the integrator is presented by a multi-symplectic form formula that can be derived from the discrete Lagrangian boundary function. As two examples of nonlinear Schrödinger equations with variable coefficients, cubic nonlinear Schrödinger equations and Gross-Pitaevskii equations are extensively studied by the proposed integrator. Our numerical simulations demonstrate that the integrator is capable of preserving the mass, momentum, and energy conservation during time evolutions. Convergence tests are presented to verify that our integrator has second-order accuracy both in time and space.

Solution of Dirac equation for Eckart potential and trigonometric Manning Rosen potential using asymptotic iteration method

Resita Arum Sari, A Suparmi, C Cari
Chin. Phys. B, 2016, 25 (1): 010301 doi: 10.1088/1674-1056/25/1/010301
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The Dirac equation for Eckart potential and trigonometric Manning Rosen potential with exact spin symmetry is obtained using an asymptotic iteration method. The combination of the two potentials is substituted into the Dirac equation, then the variables are separated into radial and angular parts. The Dirac equation is solved by using an asymptotic iteration method that can reduce the second order differential equation into a differential equation with substitution variables of hypergeometry type. The relativistic energy is calculated using Matlab 2011. This study is limited to the case of spin symmetry. With the asymptotic iteration method, the energy spectra of the relativistic equations and equations of orbital quantum number l can be obtained, where both are interrelated between quantum numbers. The energy spectrum is also numerically solved using the Matlab software, where the increase in the radial quantum number nr causes the energy to decrease. The radial part and the angular part of the wave function are defined as hypergeometry functions and visualized with Matlab 2011. The results show that the disturbance of a combination of the Eckart potential and trigonometric Manning Rosen potential can change the radial part and the angular part of the wave function.

Spin dynamics of the potassium magnetometer in spin-exchange relaxation free regime Hot!

Ji-Qing Fu(伏吉庆), Peng-Cheng Du(杜鹏程), Qing Zhou(周庆), Ru-Quan Wang(王如泉)
Chin. Phys. B, 2016, 25 (1): 010302 doi: 10.1088/1674-1056/25/1/010302
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The laser-pumped potassium spin-exchange relaxation free (SERF) magnetometer is the most sensitive detector of magnetic field and has many important applications. We present the experimental results of our potassium SERF magnetometer. A pump-probe approach is used to identify the unique spin dynamics of the atomic ensemble in the SERF regime. A single channel sensitivity of 8 f· THz-1/2 is achieved with our SERF magnetometer.

Entanglement and non-Markovianity of a multi-level atom decaying in a cavity

Zi-Long Fan(范子龙), Yu-Kun Ren(任玉坤), Hao-Sheng Zeng(曾浩生)
Chin. Phys. B, 2016, 25 (1): 010303 doi: 10.1088/1674-1056/25/1/010303
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We present a paradigmatic method for exactly studying non-Markovian dynamics of a multi-level V-type atom interacting with a zero-temperature bosonic bath. Special attention is paid to the entanglement evolution and the dynamical non-Markovianity of a three-level V-type atom. We find that the entanglement negativity decays faster and non-Markovianity is smaller in the resonance regions than those in the non-resonance regions. More importantly, the quantum interference between the dynamical non-Markovianities induced by different transition channels is manifested, and the frequency domains for constructive and destructive interferences are found.

Tunable ponderomotive squeezing induced by Coulomb interaction in an optomechanical system

Qin Wu(吴琴)
Chin. Phys. B, 2016, 25 (1): 010304 doi: 10.1088/1674-1056/25/1/010304
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We investigate the properties of the ponderomotive squeezing in an optomechanical system coupled to a charged nanomechanical oscillator (NMO) nearby via Coulomb force. We find that the introduction of Coulomb interaction allows the generation of squeezed output light from this system. Our numerical results show that the degree of squeezing can be tuned by the Coulomb coupling strength, the power of laser, and the frequencies of NMOs. Furthermore, the squeezing generated in our approach can be used to measure the Coulomb coupling strength.

Passive decoy-state quantum key distribution for the weak coherent photon source with finite-length key

Yuan Li(李源), Wansu Bao(鲍皖苏), Hongwei Li(李宏伟), Chun Zhou(周淳), Yang Wang(汪洋)
Chin. Phys. B, 2016, 25 (1): 010305 doi: 10.1088/1674-1056/25/1/010305
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Passive decoy-state quantum key distribution systems, proven to be more desirable than active ones in some scenarios, also have the problem of device imperfections like finite-length keys. In this paper, based on the WCP source which can be used for the passive decoy-state method, we obtain the expressions of single-photon error rates, single-photon counts, and phase error rates. According to the information of smooth min-entropy, we calculate the key generation rate under the condition of finite-length key. Key generation rates with different numbers of pulses are compared by numerical simulations. From the results, it can be seen that the passive decoy-state method can have good results if the total number of pulses reaches 1010. We also simulate the passive decoy-state method with different probabilities of choosing a pulse for parameter estimation when the number of pulses is fixed.

Detection efficiency characteristics of free-running InGaAs/InP single photon detector using passive quenching active reset IC

Fu Zheng(郑福), Chao Wang(王超), Zhi-Bin Sun(孙志斌), Guang-Jie Zhai(翟光杰)
Chin. Phys. B, 2016, 25 (1): 010306 doi: 10.1088/1674-1056/25/1/010306
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InGaAs/InP avalanche photodiodes (APD) are rarely used in a free-running regime for near-infrared single photon detection. In order to overcome the detrimental afterpulsing, we demonstrate a passive quenching active reset integrated circuit. Taking advantage of the inherent fast passive quenching process and active reset to reduce reset time, the integrated circuit is useful for reducing afterpulses and is also area-efficient. We investigate the free-running single photon detector's afterpulsing effect, de-trapping time, dark count rate, and photon detection efficiency, and also compare with gated regime operation. After correction for deadtime and afterpulse, we find that the passive quenching active reset free-running single photon detector's performance is consistent with gated operation.

Effects of a finite number of particles on the thermodynamic properties of a harmonically trapped ideal charged Bose gas in a constant magnetic field

Duan-Liang Xiao(肖端亮), Meng-Yun Lai(赖梦云), Xiao-Yin Pan(潘孝胤)
Chin. Phys. B, 2016, 25 (1): 010307 doi: 10.1088/1674-1056/25/1/010307
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We investigate the thermodynamic properties of an ideal charged Bose gas confined in an anisotropic harmonic potential and a constant magnetic field. Using an accurate density of states, we calculate analytically the thermodynamic potential and consequently various intriguing thermodynamic properties, including the Bose-Einstein transition temperature, the specific heat, magnetization, and the corrections to these quantities due to the finite number of particles are also given explicitly. In contrast to the infinite number of particles scenarios, we show that those thermodynamic properties, particularly the Bose-Einstein transition temperature depends upon the strength of the magnetic field due to the finiteness of the particle numbers, and the collective effects of a finite number of particles become larger when the particle number decreases. Moreover, the magnetization varies with the temperature due to the finiteness of the particle number while it keeps invariant in the thermodynamic limit N→∞.

Quantum walks with coins undergoing different quantum noisy channels

Hao Qin(秦豪) and Peng Xue(薛鹏)
Chin. Phys. B, 2016, 25 (1): 010501 doi: 10.1088/1674-1056/25/1/010501
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Quantum walks have significantly different properties compared to classical random walks, which have potential applications in quantum computation and quantum simulation. We study Hadamard quantum walks with coins undergoing different quantum noisy channels and deduce the analytical expressions of the first two moments of position in the long-time limit. Numerical simulations have been done, the results are compared with the analytical results, and they match extremely well. We show that the variance of the position distributions of the walks grows linearly with time when enough steps are taken and the linear coefficient is affected by the strength of the quantum noisy channels.

Complex dynamics of an archetypal self-excited SD oscillator driven by moving belt friction

Zhi-Xin Li(李志新), Qing-Jie Cao(曹庆杰), Léger Alain
Chin. Phys. B, 2016, 25 (1): 010502 doi: 10.1088/1674-1056/25/1/010502
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We propose an archetypal self-excited system driven by moving belt friction, which is constructed with the smooth and discontinuous (SD) oscillator proposed by the Cao et al. and the classical moving belt. The moving belt friction is modeled as the Coulomb friction to formulate the mathematical model of the proposed self-excited SD oscillator. The equilibrium states of the unperturbed system are obtained to show the complex equilibrium bifurcations. Phase portraits are depicted to present the hyperbolic structure transition, the multiple stick regions, and the friction-induced asymmetry phenomena. The numerical simulations are carried out to demonstrate the friction-induced vibration of multiple stick-slip phenomena and the stick-slip chaos in the perturbed self-excited system. The results presented here provide an opportunity for us to get insight into the mechanism of the complex friction-induced nonlinear dynamics in mechanical engineering and geography.

Memcapacitor model and its application in a chaotic oscillator

Guang-Yi Wang(王光义), Bo-Zhen Cai(蔡博振), Pei-Pei Jin(靳培培), Ti-Ling Hu(胡体玲)
Chin. Phys. B, 2016, 25 (1): 010503 doi: 10.1088/1674-1056/25/1/010503
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A memcapacitor is a new type of memory capacitor. Before the advent of practical memcapacitor, the prospective studies on its models and potential applications are of importance. For this purpose, we establish a mathematical memcapacitor model and a corresponding circuit model. As a potential application, based on the model, a memcapacitor oscillator is designed, with its basic dynamic characteristics analyzed theoretically and experimentally. Some circuit variables such as charge, flux, and integral of charge, which are difficult to measure, are observed and measured via simulations and experiments. Analysis results show that besides the typical period-doubling bifurcations and period-3 windows, sustained chaos with constant Lyapunov exponents occurs. Moreover, this oscillator also exhibits abrupt chaos and some novel bifurcations. In addition, based on the digital signal processing (DSP) technology, a scheme of digitally realizing this memcapacitor oscillator is provided. Then the statistical properties of the chaotic sequences generated from the oscillator are tested by using the test suit of the National Institute of Standards and Technology (NIST). The tested randomness definitely reaches the standards of NIST, and is better than that of the well-known Lorenz system.

Effects of abnormal excitation on the dynamics of spiral waves

Min-Yi Deng(邓敏艺), Xue-Liang Zhang(张学良), Jing-Yu Dai(戴静娱)
Chin. Phys. B, 2016, 25 (1): 010504 doi: 10.1088/1674-1056/25/1/010504
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The effect of physiological and pathological abnormal excitation of a myocyte on the spiral waves is investigated based on the cellular automaton model. When the excitability of the medium is high enough, the physiological abnormal excitation causes the spiral wave to meander irregularly and slowly. When the excitability of the medium is low enough, the physiological abnormal excitation leads to a new stable spiral wave. On the other hand, the pathological abnormal excitation destroys the spiral wave and results in the spatiotemporal chaos, which agrees with the clinical conclusion that the early after depolarization is the pro-arrhythmic mechanism of some anti-arrhythmic drugs. The mechanisms underlying these phenomena are analyzed.

Parrondo's paradox for chaos control and anticontrol of fractional-order systems

Marius-F Danca and Wallace K S Tang
Chin. Phys. B, 2016, 25 (1): 010505 doi: 10.1088/1674-1056/25/1/010505
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We present the generalized forms of Parrondo's paradox existing in fractional-order nonlinear systems. The generalization is implemented by applying a parameter switching (PS) algorithm to the corresponding initial value problems associated with the fractional-order nonlinear systems. The PS algorithm switches a system parameter within a specific set of N≥2 values when solving the system with some numerical integration method. It is proven that any attractor of the concerned system can be approximated numerically. By replacing the words “winning” and “loosing” in the classical Parrondo's paradox with “order” and “chaos”, respectively, the PS algorithm leads to the generalized Parrondo's paradox: chaos1+chaos2+…+chaosN=order and order1+order2+…+orderN=chaos. Finally, the concept is well demonstrated with the results based on the fractional-order Chen system.

The Wronskian technique for nonlinear evolution equations

Jian-Jun Cheng(成建军) and Hong-Qing Zhang(张鸿庆)
Chin. Phys. B, 2016, 25 (1): 010506 doi: 10.1088/1674-1056/25/1/010506
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The investigation of the exact traveling wave solutions to the nonlinear evolution equations plays an important role in the study of nonlinear physical phenomena. To understand the mechanisms of those physical phenomena, it is necessary to explore their solutions and properties. The Wronskian technique is a powerful tool to construct multi-soliton solutions for many nonlinear evolution equations possessing Hirota bilinear forms. In the process of utilizing the Wronskian technique, the main difficulty lies in the construction of a system of linear differential conditions, which is not unique. In this paper, we give a universal method to construct a system of linear differential conditions.

Kuznetsov-Ma soliton and Akhmediev breather of higher-order nonlinear Schrödinger equation

Zai-Dong Li(李再东), Xuan Wu(吴璇), Qiu-Yan Li(李秋艳), P B He(贺鹏斌)
Chin. Phys. B, 2016, 25 (1): 010507 doi: 10.1088/1674-1056/25/1/010507
Full Text: [PDF 540 KB] (Downloads:402) RICH HTML
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In terms of Darboux transformation, we have exactly solved the higher-order nonlinear Schrödinger equation that describes the propagation of ultrashort optical pulses in optical fibers. We discuss the modulation instability (MI) process in detail and find that the higher-order term has no effect on the MI condition. Under different conditions, we obtain Kuznetsov-Ma soliton and Akhmediev breather solutions of higher-order nonlinear Schrödinger equation. The former describes the propagation of a bright pulse on a continuous wave background in the presence of higher-order effects and the soliton's peak position is shifted owing to the presence of a nonvanishing background, while the latter implies the modulation instability process that can be used in practice to produce a train of ultrashort optical soliton pulses.

Study on bi-directional pedestrian movement using ant algorithms

Sibel Gokce and Ozhan Kayacan
Chin. Phys. B, 2016, 25 (1): 010508 doi: 10.1088/1674-1056/25/1/010508
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A cellular automata model is proposed to simulate bi-directional pedestrian flow. Pedestrian movement is investigated by using ant algorithms. Ants communicate with each other by dropping a chemical, called a pheromone, on the substrate while crawling forward. Similarly, it is considered that oppositely moving pedestrians drop ‘visual pheromones' on their way and the visual pheromones might cause attractive or repulsive interactions. This pheromenon is introduced into modelling the pedestrians' walking preference. In this way, the decision-making process of pedestrians will be based on ‘the instinct of following'. At some densities, the relationships of velocity-density and flux-density are analyzed for different evaporation rates of visual pheromones. Lane formation and phase transition are observed for certain evaporation rates of visual pheromones.
RAPID COMMUNICATION

Unexpected low thermal conductivity and large power factor in Dirac semimetal Cd3As2 Hot!

Cheng Zhang(张成), Tong Zhou(周通), Sihang Liang(梁斯航), Junzhi Cao(曹钧植),Xiang Yuan(袁翔), Yanwen Liu(刘彦闻), Yao Shen(沈瑶), Qisi Wang(王奇思),Jun Zhao(赵俊), Zhongqin Yang(杨中芹), Faxian Xiu(修发贤)
Chin. Phys. B, 2016, 25 (1): 017202 doi: 10.1088/1674-1056/25/1/017202
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Thermoelectrics has long been considered as a promising way of power generation for the next decades. So far, extensive efforts have been devoted to the search of ideal thermoelectric materials, which require both high electrical conductivity and low thermal conductivity. Recently, the emerging Dirac semimetal Cd3As2, a three-dimensional analogue of graphene, has been reported to host ultra-high mobility and good electrical conductivity as metals. Here, we report the observation of unexpected low thermal conductivity in Cd3As2, one order of magnitude lower than the conventional metals or semimetals with a similar electrical conductivity, despite the semimetal band structure and high electron mobility. The power factor also reaches a large value of 1.58 mW·m-1·K-2 at room temperature and remains non-saturated up to 400 K. Corroborating with the first-principles calculations, we find that the thermoelectric performance can be well-modulated by the carrier concentration in a wide range. This work demonstrates the Dirac semimetal Cd3As2 as a potential candidate of thermoelectric materials.

Fabrication of superconducting NbN meander nanowires by nano-imprint lithography

Mei Yang(杨美), Li-Hua Liu(刘丽华), Lu-Hui Ning(宁鲁慧), Yi-Rong Jin(金贻荣), Hui Deng(邓辉), Jie Li(李洁), Yang Li(李阳), Dong-Ning Zheng(郑东宁)
Chin. Phys. B, 2016, 25 (1): 017401 doi: 10.1088/1674-1056/25/1/017401
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Superconducting nanowire single photon detector (SNSPD), as a new type of superconducting single photon detector (SPD), has a broad application prospect in quantum communication and other fields. In order to prepare SNSPD with high performance, it is necessary to fabricate a large area of uniform meander nanowires, which is the core of the SNSPD. In this paper, we demonstrate a process of patterning ultra-thin NbN films into meander-type nanowires by using the nano-imprint technology. In this process, a combination of hot embossing nano-imprint lithography (HE-NIL) and ultraviolet nano-imprint lithography (UV-NIL) is used to transfer the meander nanowire structure from the NIL Si hard mold to the NbN film. We have successfully obtained a NbN nanowire device with uniform line width. The critical temperature (Tc) of the superconducting NbN meander nanowires is about 5 K and the critical current (Ic) is about 3.5 μA at 2.5 K.

Long-distance super-exchange and quantum magnetic relaxation in a hybrid metal-organic framework Hot!

Ying Tian(田英), Shipeng Shen(申世鹏), Junzhuang Cong(丛君状), Liqin Yan(闫丽琴), Yisheng Chai(柴一晟), Young Sun(孙阳)
Chin. Phys. B, 2016, 25 (1): 017601 doi: 10.1088/1674-1056/25/1/017601
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The hybrid metal-organic framework [(CH3)2NH2]Fe(HCOO)3 with a perovskite-like structure exhibits a variety of unusual magnetic behaviors at low temperatures. While the long-distance super-exchange through the Fe-O-CH-O-Fe exchange path leads to a canted antiferromagnetic ordering at TN ~ 19 K, a second transition of magnetic blocking develops at TB ~ 9 K. The stair-shaped magnetization hysteresis loops below TB resemble the behaviors of resonant quantum tunneling of magnetization in single-molecular quantum magnets. Moreover, the magnetic relaxation also exhibits several features of resonant quantum relaxation, such as the exponential law with a single characteristic relaxation time, and the nonmonotonic dependence of relaxation rate on the applied magnetic field with a much faster relaxation around the resonant fields. The origin of quantum tunneling behaviors in the [(CH3)2NH2]Fe(HCOO)3 metal-organic framework is discussed in terms of magnetic phase separation due to the modification of hydrogen bonding on the long-distance super-exchange interaction.

ATOMIC AND MOLECULAR PHYSICS

Correlation effects on the fine-structure splitting within the 3d9 ground configuration in highly-charged Co-like ions

Xue-Ling Guo(郭学玲), Min Huang(黄敏), Jun Yan(颜君), Shuang Li(李双),Kai Wang(王凯), Ran Si(司然), Chong-Yang Chen(陈重阳)
Chin. Phys. B, 2016, 25 (1): 013101 doi: 10.1088/1674-1056/25/1/013101
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A comprehensive theoretical study of correlation effects on the fine-structure splitting within the ground configuration 3d9 of the Co-like Hf45+, Ta46+, W47+, and Au52+ ions is performed by employing the multi-configuration Dirac-Hartree-Fock method in the active space approximation. It shows that the core-valence correlation with the inner-core 2p electron is more significant than with the outer 3p and 3s electrons, and the correlation with the 2s electron is also noticeable. The core-core correlation seems to be small and can be ignored. The calculated 2 D3/2,5/2 splitting energies agree with the recent electron-beam ion-trap measurements [Phys. Rev. A 83 032517 (2011), Eur. Phys. J. D 66 286 (2012)] to within the experimental uncertainties.

Accurate spectroscopic constants of the lowest two electronic states in S2 molecule with explicitly correlated method

Changli Wei(魏长立), Xiaomei Zhang(张晓美), Dajun Ding(丁大军), Bing Yan(闫冰)
Chin. Phys. B, 2016, 25 (1): 013102 doi: 10.1088/1674-1056/25/1/013102
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A computational scheme for accurate spectroscopic constants was presented in this work and applied to the lowest two electronic states of sulfur dimer. A high-level ab initio calculation utilizing explicitly correlated multireference configuration interaction method (MRCI-F12) was performed to compute the potential energy curves (PECs) of the ground triplet X3Σg- and first excited singlet a1Δg states of sulfur dimer with cc-pCVXZ-F12(X=m T, Q) basis sets. The effects of Davidson modification, core-valence correlation correction, and scalar relativistic correction on the spectroscopic constants were examined. The vibration-rotation spectra of the two electronic states were provided. Our computational results show excellent agreement with existing available experimental values, and the errors of main spectroscopic constants are within 0.1% order of magnitude. The present computational scheme is cheap and accurate, which is expected for extensive investigations on the potential energy curves or surfaces of other molecular systems.

Phase equilibrium of Cd1-xZnxS alloys studied by first-principles calculations and Monte Carlo simulations

Fu-Zhen Zhang(张付珍), Hong-Tao Xue(薛红涛), Fu-Ling Tang(汤富领), Xiao-Kang Li(李小康), Wen-Jiang Lu(路文江), Yu-Dong Feng(冯煜东)
Chin. Phys. B, 2016, 25 (1): 013103 doi: 10.1088/1674-1056/25/1/013103
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The first-principles calculations based on density functional theory combined with cluster expansion techniques and Monte Carlo (MC) simulations were used to study the phase diagrams of both wurtzite (WZ) and zinc-blende (ZB) Cd1-xZnxS alloys. All formation energies are positive for WZ and ZB Cd1-xZnxS alloys, which means that the Cd1-xZnxS alloys are unstable and have a tendency to phase separation. For WZ and ZB Cd1-xZnxS alloys, the consolute temperatures are 655 K and 604 K, respectively, and they both have an asymmetric miscibility gap. We obtained the spatial distributions of Cd and Zn atoms in WZ and ZB Cd0.5Zn0.5S alloys at different temperatures by MC simulations. We found that both WZ and ZB phases of Cd0.5Zn0.5S alloy exhibit phase segregation of Cd and Zn atoms at low temperature, which is consistent with the phase diagrams.

New developments in the multiscale hybrid energy density computational method

Min Sun(孙敏), Shanying Wang(王山鹰), Dianwu Wang(王殿武), Chongyu Wang(王崇愚)
Chin. Phys. B, 2016, 25 (1): 013105 doi: 10.1088/1674-1056/25/1/013105
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Further developments in the hybrid multiscale energy density method are proposed on the basis of our previous papers. The key points are as follows. (i) The theoretical method for the determination of the weight parameter in the energy coupling equation of transition region in multiscale model is given via constructing underdetermined equations. (ii) By applying the developed mathematical method, the weight parameters have been given and used to treat some problems in homogeneous charge density systems, which are directly related with multiscale science. (iii) A theoretical algorithm has also been presented for treating non-homogeneous systems of charge density. The key to the theoretical computational methods is the decomposition of the electrostatic energy in the total energy of density functional theory for probing the spanning characteristic at atomic scale, layer by layer, by which the choice of chemical elements and the defect complex effect can be understood deeply. (iv) The numerical computational program and design have also been presented.

Stark effect of the hyperfine structure of ICl in its rovibronic ground state: Towards further molecular cooling

Qing-Hui Wang(王庆辉), Xu-Ping Shao(邵旭萍), Xiao-Hua Yang(杨晓华)
Chin. Phys. B, 2016, 25 (1): 013301 doi: 10.1088/1674-1056/25/1/013301
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Hyperfine structures of ICl in its vibronic ground state due to the nuclear spin and electric quadruple interactions are determined by diagonalizing the effective Hamiltonian matrix. Furthermore, the Stark sub-levels are precisely determined as well. The results are helpful for electro-static manipulation (trapping or further cooling) of cold ICl molecules. For example, an electric field of 1000 V/cm can trap ICl molecules less than 637 μK in the lowest hyperfine level.

Numerical analyses on optical limiting performances of chloroindium phthalocyanines with different substituent positions

Yu-Jin Zhang(张玉瑾), Xing-Zhe Li(李兴哲), Ji-Cai Liu(刘纪彩), Chuan-Kui Wang(王传奎)
Chin. Phys. B, 2016, 25 (1): 013302 doi: 10.1088/1674-1056/25/1/013302
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Optical limiting properties of two soluble chloroindium phthalocyanines with α-and β -alkoxyl substituents in nanosecond laser field have been studied by solving numerically the coupled singlet-triplet rate equation together with the paraxial wave field equation under the Crank-Nicholson scheme. Both transverse and longitudinal effects of the laser field on photophysical properties of the compounds are considered. Effective transfer time between the ground state and the lowest triplet state is defined in reformulated rate equations to characterize dynamics of singlet-triplet state population transfer. It is found that both phthalocyanines exhibit good nonlinear optical absorption abilities, while the compound with α -substituent shows enhanced optical limiting performance. Our ab-initio calculations reveal that the phthalocyanine with α -substituent has more obvious electron delocalization and lower frontier orbital transfer energies, which are responsible for its preferable photophysical properties.

Triple differential cross sections of magnesium in doubly symmetric geometry

S Y Sun(孙世艳), X Y Miao(苗向阳), Xiang-Fu Jia(贾祥富)
Chin. Phys. B, 2016, 25 (1): 013401 doi: 10.1088/1674-1056/25/1/013401
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A dynamically screened three-Coulomb-wave (DS3C) method is applied to study the single ionization of magnesium by electron impact. Triple differential cross sections (TDCS) are calculated in doubly symmetric geometry at incident energies of 13.65, 17.65, 22.65, 27.65, 37.65, 47.65, 57.65, and 67.65 eV. Comparisons are made with experimental data and theoretical predictions from a three-Coulomb-wave function (3C) approach and distorted-wave Born approximation (DWBA). The overall agreement between the predictions of the DS3C model and the DWBA approach with the experimental data is satisfactory.

Mobility of large clusters on a semiconductor surface: Kinetic Monte Carlo simulation results

M Esen, A T Tüzemen, M Ozdemir
Chin. Phys. B, 2016, 25 (1): 013601 doi: 10.1088/1674-1056/25/1/013601
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The mobility of clusters on a semiconductor surface for various values of cluster size is studied as a function of temperature by kinetic Monte Carlo method. The cluster resides on the surface of a square grid. Kinetic processes such as the diffusion of single particles on the surface, their attachment and detachment to/from clusters, diffusion of particles along cluster edges are considered. The clusters considered in this study consist of 150-6000 atoms per cluster on average. A statistical probability of motion to each direction is assigned to each particle where a particle with four nearest neighbors is assumed to be immobile. The mobility of a cluster is found from the root mean square displacement of the center of mass of the cluster as a function of time. It is found that the diffusion coefficient of clusters goes as D= A(T)Nα where N is the average number of particles in the cluster, A(T) is a temperature-dependent constant and α is a parameter with a value of about -0.64< α <-0.75. The value of α is found to be independent of cluster sizes and temperature values (170-220 K) considered in this study. As the diffusion along the perimeter of the cluster becomes prohibitive, the exponent approaches a value of -0.5. The diffusion coefficient is found to change by one order of magnitude as a function of cluster size.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Cavity linewidth narrowing with dark-state polaritons

Gong-Wei Lin(林功伟), Jie Yang(杨洁), Yue-Ping Niu(钮月萍), Shang-Qing Gong(龚尚庆)
Chin. Phys. B, 2016, 25 (1): 014201 doi: 10.1088/1674-1056/25/1/014201
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We present a quantum-theoretical treatment of cavity linewidth narrowing with intracavity electromagnetically induced transparency (EIT). By means of intracavity EIT, the photons in the cavity are in the form of cavity polaritons: bright-state polariton and dark-state polariton. Strong coupling of the bright-state polariton to the excited state induces an effect known as vacuum Rabi splitting, whereas the dark-state polariton decoupled from the excited state induces a narrow cavity transmission window. Our analysis would provide a quantum theory of linewidth narrowing with a quantum field pulse.

Steady-state linear optical properties and Kerr nonlinear optical response of a four-level quantum dot with phonon-assisted transition

Yan-Chao She(佘彦超), Ting-Ting Luo(罗婷婷), Wei-Xi Zhang(张蔚曦),Mao-Wu Ran(冉茂武), Deng-Long Wang(王登龙)
Chin. Phys. B, 2016, 25 (1): 014202 doi: 10.1088/1674-1056/25/1/014202
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The linear optical properties and Kerr nonlinear optical response in a four-level loop configuration GaAs/AlGaAs semiconductor quantum dot are analytically studied with the phonon-assisted transition (PAT). It is shown that the changes among a single electromagnetically induced transparency (EIT) window, a double EIT window and the amplification of the probe field in the absorption curves can be controlled by varying the strength of PAT κ. Meanwhile, double switching from the anomalous dispersion regime to the normal dispersion regime can likely be achieved by increasing the Rabi energy of the external optical control field. Furthermore, we demonstrate that the group velocity of the probe field can be practically regulated by varying the PAT and the intensity of the optical control field. In the nonlinear case, it is shown that the large SPM and XPM can be achieved as linear absorption vanishes simultaneously, and the PAT can suppress both third-order self-Kerr and the cross-Kerr nonlinear effect of the QD. Our study is much more practical than its atomic counterpart due to its flexible design and the controllable interference strength, and may provide some new possibilities for technological applications.

Stationary entanglement between two nanomechanical oscillators induced by Coulomb interaction

Qin Wu(吴琴), Yin Xiao(肖银), Zhi-Ming Zhang(张智明)
Chin. Phys. B, 2016, 25 (1): 014203 doi: 10.1088/1674-1056/25/1/014203
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We propose a scheme for entangling two nanomechanical oscillators by Coulomb interaction in an optomechanical system. We find that the steady-state entanglement of two charged nanomechanical oscillators can be obtained when the coupling between them is stronger than a critical value which relies on the detuning. Remarkably, the degree of entanglement can be controlled by the Coulomb interaction and the frequencies of the two charged oscillators.

Fiber fuse behavior in kW-level continuous-wave double-clad field laser

Jun-Yi Sun(孙骏逸), Qi-Rong Xiao(肖起榕), Dan Li(李 丹), Xue-Jiao Wang(王雪娇), Hai-Tao Zhang(张海涛), Ma-Li Gong(巩马理), Ping Yan(闫平)
Chin. Phys. B, 2016, 25 (1): 014204 doi: 10.1088/1674-1056/25/1/014204
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In this study, original experimental data for fiber fuse in kW-level continuous-wave (CW) high power double-clad fiber (DCF) laser are reported. The propagating velocity of the fuse is 9.68 m/s in a 3.1-kW Yb-doped DCF laser. Three other cases in Yb-doped DCF are also observed. We think that the ignition of fiber fuse is caused by thermal mechanism, and the formation of bullet-shaped tracks is attributed to the optical discharge and temperature gradient. The inducements of initial fuse and formation of bullet-shaped voids are analyzed. This investigation of fiber fuse helps better understand the fiber fuse behavior, in order to avoid the catastrophic destruction caused by fiber fuse in high power fiber laser.

Frequency doubled femtosecond Ti:sapphire laser with an assisted enhancement cavity

Jin-Wei Zhang(张金伟), Hai-Nian Han(韩海年), Lei Hou(侯磊), Long Zhang(张龙),Zi-Jiao Yu(于子蛟), De-Hua Li(李德华), Zhi-Yi Wei(魏志义)
Chin. Phys. B, 2016, 25 (1): 014205 doi: 10.1088/1674-1056/25/1/014205
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We report an enhancement cavity for femtosecond Ti:sapphire laser at the repetition rate of 170 MHz. An enhancement factor of 24 is obtained when the injecting pulses have an average power of 1 W and a pulse duration of 80 fs. By placing a BBO crystal at the focus of the cavity, we obtain a 392-mW intracavity doubled-frequency laser, corresponding to a conversion efficiency of 43%. The output power has a long-term stability with a root mean square (RMS) of 0.036%.

Joint transfer of time and frequency signals and multi-point synchronization via fiber network

Nan Cheng(程楠), Wei Chen(陈炜), Qin Liu(刘琴), Dan Xu(徐丹), Fei Yang(杨飞), You-Zhen Gui(桂有珍), Hai-Wen Cai(蔡海文)
Chin. Phys. B, 2016, 25 (1): 014206 doi: 10.1088/1674-1056/25/1/014206
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A system of jointly transferring time signals with a rate of 1 pulse per second (PPS) and frequency signals of 10 MHz via a dense wavelength division multiplex-based (DWDM) fiber is demonstrated in this paper. The noises of the fiber links are suppressed and compensated for by a controlled fiber delay line. A method of calibrating and characterizing time is described. The 1PPS is synchronized by feed-forward calibrating the fiber delays precisely. The system is experimentally examined via a 110 km spooled fiber in laboratory. The frequency stabilities of the user end with compensation are 1.8× 10-14 at 1 s and 2.0× 10-17 at 104 s average time. The calculated uncertainty of time synchronization is 13.1 ps, whereas the direct measurement of the uncertainty is 12 ps. Next, the frequency and 1PPS are transferred via a metropolitan area optical fiber network from one central site to two remote sites with distances of 14 km and 110 km. The frequency stabilities of 14 km link reach 3.0× 10-14 averaged in 1 s and 1.4× 10-17 in 104 s respectively; and the stabilities of 110 km link are 8.3× 10-14 and 1.7× 10-17, respectively. The accuracies of synchronization are estimated to be 12.3 ps for the 14 km link and 13.1 ps for the 110 km link, respectively.

Tunable femtosecond near-infrared source based on a Yb:LYSO-laser-pumped optical parametric oscillator

Wen-Long Tian(田文龙), Zhao-Hua Wang(王兆华), Jiang-Feng Zhu(朱江峰), Zhi-Yi Wei(魏志义)
Chin. Phys. B, 2016, 25 (1): 014207 doi: 10.1088/1674-1056/25/1/014207
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We demonstrate a widely tunable near-infrared source from 767 nm to 874 nm generated by the intracavity second harmonic generation (SHG) in an optical parametric oscillator pumped by a Yb:LYSO solid-state laser. The home-made Yb:LYSO oscillator centered at 1035 nm delivers an average power of 2 W and a pulse duration as short as 351 fs. Two MgO doped periodically poled lithium niobates (MgO:PPLN) with grating periods of 28.5-31.5 μ in steps of 0.5 μ and 19.5-21.3 μ in steps of 0.2 μ are used for the OPO and intracavity SHG, respectively. The maximum average output power of 180 mW at 798 nm was obtained and the output pulses have pulse duration of 313 fs at 792 nm if a sech2-pulse shape was assumed. In addition, tunable signal femtosecond pulses from 1428 nm to 1763 nm are also realized with the maximum average power of 355 mW at 1628 nm.

Tunable, continuous-wave single-resonant optical parametric oscillator with output coupling for resonant wave

Xiong-Hua Zheng(郑雄桦), Bao-Fu Zhang(张宝夫), Zhong-Xing Jiao(焦中兴), Biao Wang(王彪)
Chin. Phys. B, 2016, 25 (1): 014208 doi: 10.1088/1674-1056/25/1/014208
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We present a continuous-wave singly-resonant optical parametric oscillator with 1.5% output coupling of the resonant signal wave, based on an angle-polished MgO-doped periodically poled lithium niobate (MgO:PPLN), pumped by a commercial Nd:YVO4 laser at 1064 nm. The output-coupled optical parametric oscillator delivers a maximum total output power of 4.19 W with 42.8% extraction efficiency, across a tuning range of 1717 nm in the near-and mid-infrared region. This indicates improvements of 1.87 W in output power, 19.1% in extraction efficiency and 213 nm in tuning range extension in comparison with the optical parametric oscillator with no output coupling, while at the expense of increasing the oscillation threshold by a factor of ~ 2. Moreover, it is confirmed that the finite output coupling also contributes to the reduction of the thermal effects in crystal.

Optimization of the idler wavelength tunable cascaded optical parametric oscillator based on chirp-assisted aperiodically poled lithium niobate crystal

Tao Chen(陈滔), Rong Shu(舒嵘), Ye Ge(葛烨), Zhuo Chen(陈卓)
Chin. Phys. B, 2016, 25 (1): 014209 doi: 10.1088/1674-1056/25/1/014209
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We present the numerical results for the optimization of the pump-to-idler conversion efficiencies of nanosecond idler wavelength tunable cascaded optical parametric oscillators (OPO) in different wavelength tuning ranges, where the primary signals from the OPO process are recycled to enhance the pump-to-idler conversion efficiencies via the simultaneous difference frequency generation (DFG) process by monolithic aperiodically poled, magnesium oxide doped lithium niobate (APMgLN) crystals. The APMgLN crystals are designed with different chirp parameters for the DFG process to broaden their thermal acceptance bandwidths to different extents. The idler wavelength tuning of the cascaded OPO is realized by changing the temperature of the designed APMgLN crystal and the cascaded oscillation is achieved in a single pump pass singly resonant linear cavity. The pump-to-idler conversion efficiencies with respect to the pump pulse duration and ratio of OPO coefficient to DFG coefficient are calculated by numerically solving the coupled wave equations. The optimal working conditions of the tunable cascaded OPOs pumped by pulses with energies of 350 μJ and 700 μJ are compared to obtain the general rules of optimization. It is concluded that the optimization becomes the interplay between the ratio of OPO coefficient to DFG coefficient and the pump pulse duration when the idler wavelength tuning range and the pump pulse energy are fixed. Besides, higher pump pulse energy is beneficial for reaching higher optimal pump-to-idler conversion efficiency as long as the APMgLN crystal is optimized according to this pump condition. To the best of our knowledge, this is the first numerical analysis of idler wavelength tunable cascaded OPOs based on chirp-assisted APMgLN crystals.

Numerical simulation of modulation to incident laser by submicron to micron surface contaminants on fused silica

Liang Yang(杨亮), Xia Xiang(向霞), Xin-Xiang Miao(苗心向), Li Li(李莉), Xiao-Dong Yuan(袁晓东), Zhong-Hua Yan(晏中华), Guo-Rui Zhou(周国瑞), Hai-Bing Lv(吕海兵), Wan-Guo Zheng(郑万国), Xiao-Tao Zu(祖小涛)
Chin. Phys. B, 2016, 25 (1): 014210 doi: 10.1088/1674-1056/25/1/014210
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Modulation caused by surface/subsurface contaminants is one of the important factors for laser-induced damage of fused silica. In this work, a three-dimensional finite-difference time-domain (3D-FDTD) method is employed to simulate the electric field intensity distribution in the vicinity of particulate contaminants on fused silica surface. The simulated results reveal that the contaminant on both the input and output surfaces plays an important role in the electric field modulation of the incident laser. The influences of the shape, size, embedded depth, dielectric constant (εr), and the number of contaminant particles on the electric field distribution are discussed in detail. Meanwhile, the corresponding physical mechanism is analyzed theoretically.

Data point selection for weighted least square fitting of cavity decay time constant

Xing He(何星), Hu Yan(晏虎), Li-Zhi Dong(董理治), Ping Yang(杨平), Bing Xu(许冰)
Chin. Phys. B, 2016, 25 (1): 014211 doi: 10.1088/1674-1056/25/1/014211
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For the accurate extraction of cavity decay time, a selection of data points is supplemented to the weighted least square method. We derive the expected precision, accuracy and computation cost of this improved method, and examine these performances by simulation. By comparing this method with the nonlinear least square fitting (NLSF) method and the linear regression of the sum (LRS) method in derivations and simulations, we find that this method can achieve the same or even better precision, comparable accuracy, and lower computation cost. We test this method by experimental decay signals. The results are in agreement with the ones obtained from the nonlinear least square fitting method.

Non-Noether symmetries of Hamiltonian systems withconformable fractional derivatives

Lin-Li Wang (王琳莉) and Jing-Li Fu(傅景礼)
Chin. Phys. B, 2016, 25 (1): 014501 doi: 10.1088/1674-1056/25/1/014501
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In this paper, we present the fractional Hamilton's canonical equations and the fractional non-Noether symmetry of Hamilton systems by the conformable fractional derivative. Firstly, the exchanging relationship between isochronous variation and fractional derivatives, and the fractional Hamilton principle of the system under this fractional derivative are proposed. Secondly, the fractional Hamilton's canonical equations of Hamilton systems based on the Hamilton principle are established. Thirdly, the fractional non-Noether symmetries, non-Noether theorem and non-Noether conserved quantities for the Hamilton systems with the conformable fractional derivatives are obtained. Finally, an example is given to illustrate the results.

Two kinds of generalized gradient representationsfor holonomic mechanical systems

Feng-Xiang Mei(梅凤翔) and Hui-Bin Wu(吴惠彬)
Chin. Phys. B, 2016, 25 (1): 014502 doi: 10.1088/1674-1056/25/1/014502
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Two kinds of generalized gradient systems are proposed and the characteristics of the two systems are studied. The conditions under which a holonomic mechanical system can be considered as one of the two generalized gradient systems are obtained. The characteristics of the generalized gradient systems can be used to study the stability of the holonomic system. Some examples are given to illustrate the application of the results.

Analytical study of Cattaneo-Christov heat flux model for a boundary layer flow of Oldroyd-B fluid

F M Abbasi, M Mustafa, S A Shehzad, M S Alhuthali, T Hayat
Chin. Phys. B, 2016, 25 (1): 014701 doi: 10.1088/1674-1056/25/1/014701
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We investigate the Cattaneo-Christov heat flux model for a two-dimensional laminar boundary layer flow of an incompressible Oldroyd-B fluid over a linearly stretching sheet. Mathematical formulation of the boundary layer problems is given. The nonlinear partial differential equations are converted into the ordinary differential equations using similarity transformations. The dimensionless velocity and temperature profiles are obtained through optimal homotopy analysis method (OHAM). The influences of the physical parameters on the velocity and the temperature are pointed out. The results show that the temperature and the thermal boundary layer thickness are smaller in the Cattaneo-Christov heat flux model than those in the Fourier's law of heat conduction.

Three-dimensional multi-relaxation-time lattice Boltzmann front-tracking method for two-phase flow

Hai-Qiong Xie(谢海琼), Zhong Zeng(曾忠), Liang-Qi Zhang(张良奇)
Chin. Phys. B, 2016, 25 (1): 014702 doi: 10.1088/1674-1056/25/1/014702
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We developed a three-dimensional multi-relaxation-time lattice Boltzmann method for incompressible and immiscible two-phase flow by coupling with a front-tracking technique. The flow field was simulated by using an Eulerian grid, an adaptive unstructured triangular Lagrangian grid was applied to track explicitly the motion of the two-fluid interface, and an indicator function was introduced to update accurately the fluid properties. The surface tension was computed directly on a triangular Lagrangian grid, and then the surface tension was distributed to the background Eulerian grid. Three benchmarks of two-phase flow, including the Laplace law for a stationary drop, the oscillation of a three-dimensional ellipsoidal drop, and the drop deformation in a shear flow, were simulated to validate the present model.

Predetermined control of turbulent boundary layer with a piezoelectric oscillator

Xiao-Bo Zheng(郑小波), Nan Jiang(姜楠), Hao Zhang(张浩)
Chin. Phys. B, 2016, 25 (1): 014703 doi: 10.1088/1674-1056/25/1/014703
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With a piezoelectric (PZT) oscillator, the predetermined controls of the turbulent boundary layer (TBL) are effective in reducing the drag force. The stream-wise velocities in the TBL are accurately measured downstream of the oscillator driven by an adjustable power source. The mean velocity profiles in the inner and outer scales are reported and the skin friction stresses with different voltage parameters are compared. Reduction of integral spatial scales in the inner region below y+ of 30 suggests that the oscillator at work breaks up the near-wall stream-wise vortices responsible for high skin friction. For the TBL at Reθ of 2183, the controls with a frequency of 160 Hz are superior among our experiments and a relative drag reduction rate of 26.83% is exciting. Wavelet analyses provide a reason why the controls with this special frequency perform best.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Optimized calculation of the synergy conditions between electron cyclotron current drive and lower hybrid current drive on EAST

Wei Wei(韦维), Bo-Jiang Ding(丁伯江), Y Peysson, J Decker, Miao-Hui Li(李妙辉),Xin-Jun Zhang(张新军), Xiao-Jie Wang(王晓洁), Lei Zhang(张磊)
Chin. Phys. B, 2016, 25 (1): 015201 doi: 10.1088/1674-1056/25/1/015201
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The optimized synergy conditions between electron cyclotron current drive (ECCD) and lower hybrid current drive (LHCD) with normal parameters of the EAST tokamak are studied by using the C3PO/LUKE code based on the understanding of the synergy mechanisms so as to obtain a higher synergistic current and provide theoretical reference for the synergistic effect in the EAST experiment. The dependences of the synergistic effect on the parameters of two waves (lower hybrid wave (LHW) and electron cyclotron wave (ECW)), including the radial position of the power deposition, the power value of the LH and EC waves, and the parallel refractive indices of the LHW (N||) are presented and discussed.

Numerical study of the effect of water content on OH production in a pulsed-dc atmospheric pressure helium-air plasma jet

Mu-Yang Qian(钱沐杨), Cong-Ying Yang(杨从影), Zhen-dong Wang(王震东), Xiao-Chang Chen(陈小昌), San-Qiu Liu(刘三秋), De-Zhen Wang(王德真)
Chin. Phys. B, 2016, 25 (1): 015202 doi: 10.1088/1674-1056/25/1/015202
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A numerical study of the effect of water content on OH production in a pulsed-dc atmospheric pressure helium-air plasma jet is presented. The generation and loss mechanisms of the OH radicals in a positive half-cycle of the applied voltage are studied and discussed. It is found that the peak OH density increases with water content in air (varying from 0% to 1%) and reaches 6.3× 1018 m-3 when the water content is 1%. Besides, as the water content increases from 0.01% to 1%, the space-averaged reaction rate of three-body recombination increases dramatically and is comparable to those of main OH generation reactions.

Effects of q-profiles of a weak magnetic shear on energetic ion excited q=1 mode in tokamak plasmas

Ze-Yu Li(李泽宇), Xian-Qu Wang(王先驱), Xiao-Gang Wang(王晓钢)
Chin. Phys. B, 2016, 25 (1): 015203 doi: 10.1088/1674-1056/25/1/015203
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In this paper, we study the effect of safety factor profiles, particularly with a very weak magnetic shear, on the m/n=1 mode excited by energetic ions in tokamak plasmas. It is found that the profile plays a significant role in the onset of the mode, and the thresholds for the instability are also derived. The numerical results for configurations with conventional or reversed non monotonic magnetic shears are discussed. The effects of radial location of rational surfaces, edge q value, and flatness of q-profile on the energetic ion excited mode are further analyzed in detail.

Conversion of an atomic to a molecular argon ion and low pressure argon relaxation

M N Stankov, A P Jovanović, V Lj Marković, S N Stamenković
Chin. Phys. B, 2016, 25 (1): 015204 doi: 10.1088/1674-1056/25/1/015204
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The dominant process in relaxation of DC glow discharge between two plane parallel electrodes in argon at pressure 200 Pa is analyzed by measuring the breakdown time delay and by analytical and numerical models. By using the approximate analytical model it is found that the relaxation in a range from 20 to 60 ms in afterglow is dominated by Ar2+ ions, produced by atomic-to-molecular conversion of Ar+ ions in the first several milliseconds after the cessation of the discharge. This conversion is confirmed by the presence of double-Gaussian distribution for the formative time delay, as well as conversion maxima in a set of memory curves measured in different conditions. Finally, the numerical one-dimensional (1D) model for determining the number densities of dominant particles in stationary DC glow discharge and two-dimensional (2D) model for the relaxation are used to confirm the previous assumptions and to determine the corresponding collision and transport coefficients of dominant species and processes.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Evolution of structure and physical properties in Al-substituted Ba-hexaferrites

Alex Trukhanov, Larisa Panina, Sergei Trukhanov, Vitalii Turchenko, Mohamed Salem
Chin. Phys. B, 2016, 25 (1): 016102 doi: 10.1088/1674-1056/25/1/016102
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The investigations of the crystal and magnetic structures of the BaFe12-xAlxO19 (x=0.1-1.2) solid solutions have been performed with powder neutron diffractometry. Magnetic properties of the BaFe12-xAlxO19 (x=0.1-1.2) solid solutions have been measured by vibration sample magnetometry at different temperatures under different magnetic fields. The atomic coordinates and lattice parameters have been Rietveld refined. The invar effect is observed in low temperature range (from 4.2 K to 150 K). It is explained by the thermal oscillation anharmonicity of atoms. The increase of microstress with decreasing temperature is found from Rietveld refinement. The Curie temperature and the change of total magnetic moment per formula unit are found for all compositions of the BaFe12-xAlxO19 (x=0.1-1.2) solid solutions. The magnetic structure model is proposed. The most likely reasons and the mechanism of magnetic structure formation are discussed.

A new family of sp3-hybridized carbon phases

Ning Xu(徐宁), Jian-Fu Li(李建福), Bo-Long Huang(黄勃龙), Bao-Lin Wang(王保林)
Chin. Phys. B, 2016, 25 (1): 016103 doi: 10.1088/1674-1056/25/1/016103
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A new family of superhard carbon allotropes C48(2i+1) is constructed by alternating even 4 and 8 membered rings. These new carbon allotropes are of a spatially antisymmetrical structure, compared with the symmetrical structures of bct-C4, Z-carbon, and P-carbon. Our calculations show that bulk moduli of C48(2i+1) are larger than that of c-BN and smaller than that of cubic-diamond. C48(2i+1) are transparent superhard materials possessing large Vicker hardness comparable to diamond. This work can help us understand the structural phase transformations of cold-compression graphite and carbon nanotubes.

Phonon dispersion on Ag (100) surface: A modified analytic embedded atom method study

Xiao-Jun Zhang(张晓军) and Chang-Le Chen(陈长乐)
Chin. Phys. B, 2016, 25 (1): 016301 doi: 10.1088/1674-1056/25/1/016301
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Within the harmonic approximation, the analytic expression of the dynamical matrix is derived based on the modified analytic embedded atom method (MAEAM) and the dynamics theory of surface lattice. The surface phonon dispersions along three major symmetry directions Γ X, Γ M, and XM are calculated for the clean Ag (100) surface by using our derived formulas. We then discuss the polarization and localization of surface modes at points X and M by plotting the squared polarization vectors as a function of the layer index. The phonon frequencies of the surface modes calculated by MAEAM are compared with the available experimental and other theoretical data. It is found that the present results are generally in agreement with the referenced experimental or theoretical results, with a maximum deviation of 10.4%. The agreement shows that the modified analytic embedded atom method is a reasonable many-body potential model to quickly describe the surface lattice vibration. It also lays a significant foundation for studying the surface lattice vibration in other metals.

Ab initio investigation of photoinduced non-thermal phase transition in β -cristobalite

Shi-Quan Feng(冯世全), Hua-Ping Zang(臧华平), Yong-Qiang Wang(王永强), Xin-Lu Cheng(程新路), Jin-Sheng Yue(岳金胜)
Chin. Phys. B, 2016, 25 (1): 016701 doi: 10.1088/1674-1056/25/1/016701
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Using the linear-response method, we investigate the phonon properties of β -cristobalite crystal under electronic excitation effect. We find that the transverse-acoustic phonon frequency becomes imaginary as the electron temperature is increased, which means that the lattice of β -cristobalite becomes unstable under intense laser irradiation. In addition, for the optic phonon mode, the LO(H)-TO(H) splitting disappears when the electronic temperature reaches a certain value, corresponding to the whole transverse-acoustic phonon branches becoming negative. It means that the electronic excitation destroys the macroscopic electric field of β -cristobalite. Based on the calculated phonon band structures, some thermodynamic properties are calculated as a function of temperature at different electronic temperatures. These investigations provide evidence that non-thermal melting takes place during a femtosecond pulse laser interaction with β -cristobalite.

Vortices in dipolar Bose-Einstein condensates in synthetic magnetic field

Qiang Zhao(赵强) and Qiang Gu(顾强)
Chin. Phys. B, 2016, 25 (1): 016702 doi: 10.1088/1674-1056/25/1/016702
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We study the formation of vortices in a dipolar Bose-Einstein condensate in a synthetic magnetic field by numerically solving the Gross-Pitaevskii equation. The formation process depends on the dipole strength, the rotating frequency, the potential geometry, and the orientation of the dipoles. We make an extensive comparison with vortices created by a rotating trap, especially focusing on the issues of the critical rotating frequency and the vortex number as a function of the rotating frequency. We observe that a higher rotating frequency is needed to generate a large number of vortices and the anisotropic interaction manifests itself as a perceptible difference in the vortex formation. Furthermore, a large dipole strength or aspect ratio also can increase the number of vortices effectively. In particular, we discuss the validity of the Feynman rule.

Phase transition and critical behavior ofspin-orbital coupled spinel ZnV2O4

Li Wang(王理), Rong-juan Wang(王蓉娟), Yuan-yuan Zhu(朱媛媛), Zhi-hong Lu(卢志红),Rui Xiong(熊锐), Yong Liu(刘雍), Jing Shi(石兢)
Chin. Phys. B, 2016, 25 (1): 016802 doi: 10.1088/1674-1056/25/1/016802
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We present the temperature-dependent susceptibility and specific heat measurement of spinel ZnV2O4. The structural transition with orbital ordering and the antiferromagnetic transition with spin ordering were observed at 50 K and 37 K, respectively. By analysis of the hysteresis behavior between the specific heat curves obtained in warming and cooling processes, the structural transition was confirmed to be the first-order transition, while the antiferromagnetic transition was found to be of the second-order type. At the structural transition, the latent heat and entropy change were calculated from the excess specific heat, and the derivative of pressure with respect to temperature was obtained using the Clausius-Clapayron equation. At the magnetic transition, the width of the critical fluctuation region was obtained to be about 0.5 K by comparing with Gaussian fluctuations. In the critical region, the critical behavior was analyzed by using renormalization-group theory. The critical amplitude ratio A+ /A-=1.46, which deviates from the 3D Heisenburg model; while the critical exponent α is -0.011, which is close to the 3D XY model. We proposed that these abnormal critical behaviors can be attributed to strong spin-orbital coupling accompanied with the antiferromagnetic transition. Moreover, in the low temperature range (2-5 K), the Fermi energy, the density of states near the Fermi surface, and the low limit of Debye temperature were estimated to be 2.42 eV, 2.48 eV-1, and 240 K, respectively.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Characteristics of Li diffusion on silicene and zigzag nanoribbon

Yan-Hua Guo(郭艳华), Jue-Xian Cao(曹觉先), Bo Xu(徐波)
Chin. Phys. B, 2016, 25 (1): 017101 doi: 10.1088/1674-1056/25/1/017101
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We perform a density functional study on the adsorption and diffusion of Li atoms on silicene sheet and zigzag nanoribbons. Our results show that the diffusion energy barrier of Li adatoms on silicene sheet is 0.25 eV, which is much lower than on graphene and Si bulk. The diffusion barriers along the axis of zigzag silicene nanoribbon range from 0.1 to 0.25 eV due to an edge effect, while the diffusion energy barrier is about 0.5 eV for a Li adatom to enter into a silicene nanoribbon. Our calculations indicate that using silicene nanoribbons as anodes is favorable for a Li-ion battery.

Heterogeneous fragmentation of metallic liquid microsheet with high velocity gradient

An-Min He(何安民), Pei Wang(王裴), Jian-Li Shao(邵建立)
Chin. Phys. B, 2016, 25 (1): 017102 doi: 10.1088/1674-1056/25/1/017102
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Large-scale molecular dynamics simulations are performed to study the fragmentation of metallic liquid sheets with high velocity gradient. Dynamic fragmentation of the system involves the formation of a network of fragments due to the growth and coalescence of holes, decomposition of the network into filaments, and further breakup of the filaments into spherical clusters. The final size distribution of the fragmented clusters in the large volume limit is found to obey a bilinear exponential form, which is resulted from the heterogeneous breakup of quasi-cylindrical filaments. The main factors contributing to fragmentation heterogeneity are introduced, including strain rate inhomogeneity and matter distribution nonuniformity of fragments produced during decomposition of the network structure.

Spin texturing in quantum wires with Rashba and Dresselhaus spin-orbit interactions and in-plane magnetic field

B Gisi, S Sakiroglu, İ Sokmen
Chin. Phys. B, 2016, 25 (1): 017103 doi: 10.1088/1674-1056/25/1/017103
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In this work, we investigate the effects of interplay of spin-orbit interaction and in-plane magnetic fields on the electronic structure and spin texturing of parabolically confined quantum wire. Numerical results reveal that the competing effects between Rashba and Dresselhaus spin-orbit interactions and the external magnetic field lead to a complicated energy spectrum. We find that the spin texturing owing to the coupling between subbands can be modified by the strength of spin-orbit couplings as well as the magnitude and the orientation angle of the external magnetic field.

Characterization of vertical Au/β -Ga2O3 single-crystal Schottky photodiodes with MBE-grown high-resistivity epitaxial layer

X Z Liu(刘兴钊), C Yue(岳超), C T Xia(夏长泰), W L Zhang(张万里)
Chin. Phys. B, 2016, 25 (1): 017201 doi: 10.1088/1674-1056/25/1/017201
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High-resistivity β -Ga2O3 thin films were grown on Si-doped n-type conductive β -Ga2O3 single crystals by molecular beam epitaxy (MBE). Vertical-type Schottky diodes were fabricated, and the electrical properties of the Schottky diodes were studied in this letter. The ideality factor and the series resistance of the Schottky diodes were estimated to be about 1.4 and 4.6× 106 Ω . The ionized donor concentration and the spreading voltage in the Schottky diodes region are about 4× 1018 cm-3 and 7.6 V, respectively. The ultra-violet (UV) photo-sensitivity of the Schottky diodes was demonstrated by a low-pressure mercury lamp illumination. A photoresponsivity of 1.8 A/W and an external quantum efficiency of 8.7× 102% were observed at forward bias voltage of 3.8 V, the proper driving voltage of read-out integrated circuit for UV camera. The gain of the Schottky diode was attributed to the existence of a potential barrier in the i-n junction between the MBE-grown highly resistive β -Ga2O3 thin films and the n-type conductive β -Ga2O3 single-crystal substrate.

Manipulating coupling state and magnetism of Mn-doped ZnO nanocrystals by changing the coordination environment of Mn via hydrogen annealing

Yan Cheng(程岩), Wen-Xian Li(李文献), Wei-Chang Hao(郝维昌), Huai-Zhe Xu(许怀哲), Zhong-Fei Xu(徐忠菲), Li-Rong Zheng(郑离荣), Jing Zhang(张静),Shi-Xue Dou(窦士学), Tian-Min Wang(王天民)
Chin. Phys. B, 2016, 25 (1): 017301 doi: 10.1088/1674-1056/25/1/017301
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Mn-doped ZnO nanocrystals are synthesized by a wet chemical route and treated in H2/Ar atmosphere with different H2/Ar ratios. It is found that hydrogen annealing could change the coordination environment of Mn in ZnO lattice and manipulate the magnetic properties of Mn-doped ZnO. Mn ions initially enter into interstitial sites and a Mn3+O6 octahedral coordination is produced in the prepared Mn-doped ZnO sample, in which the nearest neighbor Mn3+ and O2 ions could form a Mn3+-O2--Mn3+ complex. After H2 annealing, interstitial Mn ions can substitute for Zn to generate the Mn2+O4 tetrahedral coordination in the nanocrystals, in which neighboring Mn2+ ions and H atoms could form a Mn2+-O2--Mn2+ complex and Mn-H-Mn bridge structure. The magnetic measurement of the as-prepared sample shows room temperature paramagnetic behavior due to the Mn3+-O2--Mn3+ complex, while the annealed samples exhibit their ferromagnetism, which originates from the Mn-H-Mn bridge structure and the Mn-Mn exchange interaction in the Mn2+-O2--Mn2+ complex.

Modulating doping and interface magnetism ofepitaxial graphene on SiC(0001)

Pan Zhou(周攀) and Da-Wei He(何大伟)
Chin. Phys. B, 2016, 25 (1): 017302 doi: 10.1088/1674-1056/25/1/017302
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On the basis of first principles calculations, we report that the type and density of charge carriers of epitaxial graphene on SiC(0001) can be deliberately controlled by decorating the buffer layer with specific atoms (i.e., F, Cl, O, or N). More importantly, a fine tuning of the doping behavior from intrinsic n-type to charge neutrality to p-type and interface magnetism is achieved via increasing the doping concentration of F atoms on the buffer layer. Our results suggest an interesting avenue to the application of epitaxial graphene in nanoscale electronic and spintronic devices.

Reverse blocking characteristics and mechanisms in Schottky-drainAlGaN/GaN HEMT with a drain field plate and floating field plates

Wei Mao(毛维), Wei-Bo She(佘伟波), Cui Yang(杨翠), Jin-Feng Zhang(张金风), Xue-Feng Zheng(郑雪峰), Chong Wang(王冲), Yue Hao(郝跃)
Chin. Phys. B, 2016, 25 (1): 017303 doi: 10.1088/1674-1056/25/1/017303
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In this paper, a novel AlGaN/GaN HEMT with a Schottky drain and a compound field plate (SD-CFP HEMT) is presented for the purpose of better reverse blocking capability. The compound field plate (CFP) consists of a drain field plate (DFP) and several floating field plates (FFPs). The physical mechanisms of the CFP to improve the reverse breakdown voltage and to modulate the distributions of channel electric field and potential are investigated by two-dimensional numerical simulations with Silvaco-ATLAS. Compared with the HEMT with a Schottky drain (SD HEMT) and the HEMT with a Schottky drain and a DFP (SD-FP HEMT), the superiorities of SD-CFP HEMT lie in the continuous improvement of the reverse breakdown voltage by increasing the number of FFPs and in the same fabrication procedure as the SD-FP HEMT. Two useful optimization laws for the SD-CFP HEMTs are found and extracted from simulation results. The relationship between the number of the FFPs and the reverse breakdown voltage as well as the FP efficiency in SD-CFP HEMTs are discussed. The results in this paper demonstrate a great potential of CFP for enhancing the reverse blocking ability in AlGaN/GaN HEMT and may be of great value and significance in the design and actual manufacture of SD-CFP HEMTs.

In-situ SAXS study on PET/ PMMT composites during tensile tests

Wei-Dong Cheng(程伟东), Xiao-Hua Gu(顾晓华), Xue Song(宋雪), Peng Zeng(曾鹏), Zhao-Jun Wu(吴昭君), Xue-Qing Xing(邢雪青), Guang Mo(默广), Zhong-Hua Wu(吴忠华)
Chin. Phys. B, 2016, 25 (1): 017802 doi: 10.1088/1674-1056/25/1/017802
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The nanostructures during the tensile drawing of poly(ethylene terephthalate) (PET)/hexadecyl triphenyl phosphonium bromide montmorillonite (PMMT) nanocomposites were studied by in-situ small angle x-ray scattering. For strain higher than the yield point, the scattering intensity increases dramatically due to the nucleation and growth of nanovoids and crystals. The nanovoids and crystals are significantly dependent on the heating temperature. The effective filling of PMMT in the PET matrix provokes a strong restriction to the long period. The peaks of the long period disappear gradually with the deformation strain increasing from 0% to 34%.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Effect of fluence and ambient environment on the surface and structural modification of femtosecond laser irradiated Ti

Umm-i-Kalsoom, Shazia Bashir Nisar Ali, M Shahid Rafique, Wolfgang Husinsky, Chandra S R Nathala, Sergey V Makarov, Narjis Begum
Chin. Phys. B, 2016, 25 (1): 018101 doi: 10.1088/1674-1056/25/1/018101
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Under certain conditions, ultrafast pulsed laser interaction with matter leads to the formation of self-organized conical as well as periodic surface structures (commonly reffered to as, laser induced periodic surface structures, LIPSS). The purpose of the present investigations is to explore the effect of fsec laser fluence and ambient environments (Vacuum & O2) on the formation of LIPSS and conical structures on the Ti surface. The surface morphology was investigated by scanning electron microscope (SEM). The ablation threshold with single and multiple (N=100) shots and the existence of an incubation effect was demonstrated by SEM investigations for both the vacuum and the O2 environment. The phase analysis and chemical composition of the exposed targets were performed by x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS), respectively. SEM investigations reveal the formation of LIPSS (nano & micro). FFT d-spacing calculations illustrate the dependence of periodicity on the fluence and ambient environment. The periodicity of nano-scale LIPSS is higher in the case of irradiation under vacuum conditions as compared to O2. Furthermore, the O2 environment reduces the ablation threshold. XRD data reveal that for the O2 environment, new phases (oxides of Ti) are formed. EDS analysis exhibits that after irradiation under vacuum conditions, the percentage of impurity element (Al) is reduced. The irradiation in the O2 environment results in 15% atomic diffusion of oxygen.

Superior material qualities and transport properties of InGaN channel heterostructure grown by pulsed metal organicchemical vapor deposition

Ya-Chao Zhang(张雅超), Xiao-Wei Zhou(周小伟), Sheng-Rui Xu (许晟瑞), Da-Zheng Chen(陈大正), Zhi-Zhe Wang(王之哲), Xing Wang(汪星), Jin-Feng Zhang(张金风), Jin-Cheng Zhang(张进成), Yue Hao(郝跃)
Chin. Phys. B, 2016, 25 (1): 018102 doi: 10.1088/1674-1056/25/1/018102
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Pulsed metal organic chemical vapor deposition is introduced into the growth of InGaN channel heterostructure for improving material qualities and transport properties. High-resolution transmission electron microscopy imaging shows the phase separation free InGaN channel with smooth and abrupt interface. A very high two-dimensional electron gas density of approximately 1.85 × 1013 cm-2 is obtained due to the superior carrier confinement. In addition, the Hall mobility reaches 967 cm2/V·s, owing to the suppression of interface roughness scattering. Furthermore, temperature-dependent Hall measurement results show that InGaN channel heterostructure possesses a steady two-dimensional electron gas density over the tested temperature range, and has superior transport properties at elevated temperatures compared with the traditional GaN channel heterostructure. The gratifying results imply that InGaN channel heterostructure grown by pulsed metal organic chemical vapor deposition is a promising candidate for microwave power devices.

Detection and formation mechanism of micro-defects in ultrafine pitch Cu–Cu direct bonding

Zi-Yu Liu(刘子玉), Jian Cai(蔡坚), Qian Wang(王谦), Yu Chen(陈瑜)
Chin. Phys. B, 2016, 25 (1): 018103 doi: 10.1088/1674-1056/25/1/018103
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In this paper, Cu-Cu interconnects with ultrafine pad pitches of 6 μ m, 8 μ m, and 15 μ m are implemented on the 12 inch wafers by a direct bonding process. Defects are not found by traditional non-destructive (NDT) c-mode scanning acoustic microscopy (c-SAM). However, cross sectional observation of bonding interfaces reveals that micro-defects such as micro seams are located at SiO2 bonding interfaces. In order to examine the micro-defects in the ultra-fine pitch direct bonding process by the NDT technology, a novel “defect-enlarged approach” is proposed. The bonded dies are first annealed in an N2 oven at 300 ℃ for a few hours and then cooled quickly in air. The c-SAM scanning images show large defects at the place where nothing can be detected by c-SAM before this treatment. Cross sectional observation of the bonding interfaces indicates that these defects consist of large size micro seams at the SiO2 bonding interface, especially near Cu pads with an ultrafine pitch of 6 μ m. However, these large defects disappear after several hours at room temperature, observed by c-SAM. It is inferred that the disappearance of these defects inspected by the “defect-enlarged approach” results from the combination of intrinsic micro seams and “weak” bonds in the silicon oxide layer. Then the underlying physical mechanism of these micro-defects is proposed, which is influenced by Cu pad surface topology and bonding models.

Improved double-gate armchair silicene nanoribbon field-effect-transistor at large transport bandgap

Mohsen Mahmoudi, Zahra Ahangari, Morteza Fathipour
Chin. Phys. B, 2016, 25 (1): 018501 doi: 10.1088/1674-1056/25/1/018501
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The electrical characteristics of a double-gate armchair silicene nanoribbon field-effect-transistor (DG ASiNR FET) are thoroughly investigated by using a ballistic quantum transport model based on non-equilibrium Green's function (NEGF) approach self-consistently coupled with a three-dimensional (3D) Poisson equation. We evaluate the influence of variation in uniaxial tensile strain, ribbon temperature and oxide thickness on the on-off current ratio, subthreshold swing, transconductance and the delay time of a 12-nm-length ultranarrow ASiNR FET. A novel two-parameter strain magnitude and temperature-dependent model is presented for designing an optimized device possessing balanced amelioration of all the electrical parameters. We demonstrate that employing HfO2 as the gate insulator can be a favorable choice and simultaneous use of it with proper combination of temperature and strain magnitude can achieve better device performance. Furthermore, a general model power (GMP) is derived which explicitly provides the electron effective mass as a function of the bandgap of a hydrogen passivated ASiNR under strain.

Quantum dynamics of charge transfer on the one-dimensional lattice: Wave packet spreading and recurrence

V N Likhachev, O I Shevaleevskii, G A Vinogradov
Chin. Phys. B, 2016, 25 (1): 018708 doi: 10.1088/1674-1056/25/1/018708
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The wave function temporal evolution on the one-dimensional (1D) lattice is considered in the tight-binding approximation. The lattice consists of N equal sites and one impurity site (donor). The donor differs from other lattice sites by the on-site electron energy E and the intersite coupling C. The moving wave packet is formed from the wave function initially localized on the donor. The exact solution for the wave packet velocity and the shape is derived at different values E and C. The velocity has the maximal possible group velocity v = 2. The wave packet width grows with time ~ t1/3 and its amplitude decreases ~ t-1/3. The wave packet reflects multiply from the lattice ends. Analytical expressions for the wave packet front propagation and recurrence are in good agreement with numeric simulations.

GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Application of long-range correlation and multi-fractal analysis for the depiction of drought risk

Wei Hou(侯威), Peng-Cheng Yan(颜鹏程), Shu-Ping Li(李淑萍), Gang Tu(涂刚), Jing-Guo Hu(胡经国)
Chin. Phys. B, 2016, 25 (1): 019201 doi: 10.1088/1674-1056/25/1/019201
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Show Abstract
By using the multi-fractal detrended fluctuation analysis method, we analyze the nonlinear property of drought in southwestern China. The results indicate that the occurrence of drought in southwestern China is multi-fractal and long-range correlated, and these properties are indifferent to timescales. A power-law decay distribution well describes the return interval of drought events and the auto-correlation. Furthermore, a drought risk exponent based on the multi-fractal property and the long-range correlation is presented. This risk exponent can give useful information about whether the drought may or may not occur in future, and provide a guidance function for preventing disasters and reducing damage.
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