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    Generation of valley pump currents in silicene
    John Tombe Jada Marcellino, Mei-Juan Wang(王美娟), Sa-Ke Wang(汪萨克)
    Chin. Phys. B, 2019, 28 (1): 017204.   DOI: 10.1088/1674-1056/28/1/017204
    Abstract152822)   HTML    PDF (433KB)(151541)      

    We propose a workable scheme for generating a bulk valley pump current in a silicene-based device which consists of two pumping regions characterized by time-dependent strain and staggered potentials, respectively. In a one-dimension model, we show that a pure valley current can be generated, in which the two valley currents have the same magnitude but flow in opposite directions. Besides, the pumped valley current is quantized and maximized when the Fermi energy of the system locates in the bandgap opened by the two pumping potentials. Furthermore, the valley current can be finely controlled by tuning the device parameters. Our results are useful for the development of valleytronic devices based on two-dimensional materials.

    Spin and valley filter in strain engineered silicene
    Wang Sa-Ke (汪萨克), Wang Jun (汪军)
    Chin. Phys. B, 2015, 24 (3): 037202.   DOI: 10.1088/1674-1056/24/3/037202
    Abstract141790)   HTML    PDF (643KB)(141106)      
    The realization of a perfect spin or valley filtering effect in two-dimensional graphene-like materials is one of the fundamental objectives in spintronics and valleytronics. For this purpose, we study spin- and valley-dependent transport in a silicene system with spatially alternative strains. It is found that due to the valley-opposite gauge field induced by the strain, the strained silicene with a superlattice structure exhibits an angle-resolved valley and spin filtering effect when the spin-orbit interaction is considered. When the interaction that breaks the time reversal symmetry is introduced, such as the spin or valley dependent staggered magnetization, the system is shown to be a perfect spin and valley half metal in which only one spin and valley species is allowed to transport. Our findings are helpful to design both spintronic and valleytronic devices based on silicene.
    Spin and valley half metal induced by staggered potential and magnetization in silicene
    Wang Sa-Ke (汪萨克), Tian Hong-Yu (田宏玉), Yang Yong-Hong (杨永宏), Wang Jun (汪军)
    Chin. Phys. B, 2014, 23 (1): 017203.   DOI: 10.1088/1674-1056/23/1/017203
    Abstract135809)      PDF (639KB)(136615)      
    We investigate the electron transport in silicene with both staggered electric potential and magnetization; the latter comes from the magnetic proximity effect by depositing silicene on a magnetic insulator. It is shown that the silicene could be a spin and valley half metal under appropriate parameters when the spin–orbit interaction is considered; further, the filtered spin and valley could be controlled by modulating the staggered potential or magnetization. It is also found that in the spin-valve structure of silicene, not only can the antiparallel magnetization configuration significantly reduce the valve-structure conductance, but the reversing staggered electric potential can cause a high-performance magnetoresistance due to the spin and valley blocking effects. Our findings show that the silicene might be an ideal basis for the spin and valley filter analyzer devices.
    Recent advances of interface engineering in inverted perovskite solar cells
    Shiqi Yu(余诗琪), Zhuang Xiong(熊壮), Zhenhan Wang(王振涵), Haitao Zhou(周海涛), Fei Ma(马飞), Zihan Qu(瞿子涵), Yang Zhao(赵洋), Xinbo Chu(楚新波), and Jingbi You(游经碧)
    Chin. Phys. B, 2022, 31 (10): 107307.   DOI: 10.1088/1674-1056/ac8e9f
    Abstract334)   HTML8)    PDF (8178KB)(1342)      
    Perovskite solar cells (PSCs) have witnessed great achievement in the past decade. Most of previous researches focus on the n—i—p structure of PSCs with ultra-high efficiency. While the n—i—p devices usually used the unstable charge transport layers, such as the hygroscopic doped spiro-OMeTAD, which affect the long-term stability. The inverted device with the p—i—n structure owns better stability when using stable undoped organic molecular or metal oxide materials. There are significant progresses in inverted PSCs, most of them related to charge transport or interface engineering. In this review, we will mainly summarize the inverted PSCs progresses related to the interface engineering. After that, we prospect the future direction on inverted PSCs.
    Image segmentation of exfoliated two-dimensional materials by generative adversarial network-based data augmentation
    Xiaoyu Cheng(程晓昱), Chenxue Xie(解晨雪), Yulun Liu(刘宇伦), Ruixue Bai(白瑞雪), Nanhai Xiao(肖南海), Yanbo Ren(任琰博), Xilin Zhang(张喜林), Hui Ma(马惠), and Chongyun Jiang(蒋崇云)
    Chin. Phys. B, 2024, 33 (3): 030703.   DOI: 10.1088/1674-1056/ad23d8
    Abstract379)   HTML34)    PDF (1065KB)(336)      
    Mechanically cleaved two-dimensional materials are random in size and thickness. Recognizing atomically thin flakes by human experts is inefficient and unsuitable for scalable production. Deep learning algorithms have been adopted as an alternative, nevertheless a major challenge is a lack of sufficient actual training images. Here we report the generation of synthetic two-dimensional materials images using StyleGAN3 to complement the dataset. DeepLabv3Plus network is trained with the synthetic images which reduces overfitting and improves recognition accuracy to over 90%. A semi-supervisory technique for labeling images is introduced to reduce manual efforts. The sharper edges recognized by this method facilitate material stacking with precise edge alignment, which benefits exploring novel properties of layered-material devices that crucially depend on the interlayer twist-angle. This feasible and efficient method allows for the rapid and high-quality manufacturing of atomically thin materials and devices.
    Intrinsic electronic structure and nodeless superconducting gap of YBa2Cu3O7-δ observed by spatially-resolved laser-based angle resolved photoemission spectroscopy
    Shuaishuai Li(李帅帅), Taimin Miao(苗泰民), Chaohui Yin(殷超辉), Yinghao Li(李颖昊), Hongtao Yan(闫宏涛), Yiwen Chen(陈逸雯), Bo Liang(梁波), Hao Chen(陈浩), Wenpei Zhu(朱文培), Shenjin Zhang(张申金), Zhimin Wang(王志敏), Fengfeng Zhang(张丰丰), Feng Yang(杨峰), Qinjun Peng(彭钦军), Chengtian Lin(林成天), Hanqing Mao(毛寒青), Guodong Liu(刘国东), Zuyan Xu(许祖彦), Lin Zhao(赵林), and X J Zhou(周兴江)
    Chin. Phys. B, 2023, 32 (11): 117401.   DOI: 10.1088/1674-1056/acf498
    Abstract200)   HTML10)    PDF (6820KB)(470)      
    The spatially-resolved laser-based high-resolution angle resolved photoemission spectroscopy (ARPES) measurements have been performed on the optimally-doped YBa2Cu3O7-δ (Y123) superconductor. For the first time, we found the region from the cleaved surface that reveals clear bulk electronic properties. The intrinsic Fermi surface and band structures of Y123 were observed. The Fermi surface-dependent and momentum-dependent superconducting gap was determined which is nodeless and consistent with the d+is gap form.
    Switchable terahertz polarization converter based on VO2 metamaterial
    Haotian Du(杜皓天), Mingzhu Jiang(江明珠), Lizhen Zeng(曾丽珍), Longhui Zhang(张隆辉), Weilin Xu(徐卫林), Xiaowen Zhang(张小文), and Fangrong Hu(胡放荣)
    Chin. Phys. B, 2022, 31 (6): 064210.   DOI: 10.1088/1674-1056/ac4f5b
    Abstract403)   HTML2)    PDF (1582KB)(371)      
    A switchable terahertz (THz) polarization converter based on vanadium dioxide (VO2) metamaterial is proposed. It is a 5-layer structure which containing metal split-ring-resonator (SRR), the first polyimide (PI) spacer, VO2 film, the second PI spacer, and metal grating. It is an array structure and the period in x and y directions is 100 μm. The performance is simulated by using finite integration technology. The simulation results show that, when the VO2 is in insulating state, the device is a transmission polarization converter. The cross-linear polarization conversion can be realized in a broadband of 0.70 THz, and the polarization conversion rate (PCR) is higher than 99%. Under thermal stimulus, the VO2 changes from insulating state to metallic state, and the device is a reflective polarization converter. The linear-to-circular polarization conversion can be successfully realized in a broadband of 0.50 THz, and the PCR is higher than 88%.
    Measuring small longitudinal phase shifts via weak measurement amplification
    Kai Xu(徐凯), Xiao-Min Hu(胡晓敏), Meng-Jun Hu(胡孟军), Ning-Ning Wang(王宁宁), Chao Zhang(张超), Yun-Feng Huang(黄运锋), Bi-Heng Liu(柳必恒), Chuan-Feng Li(李传锋), Guang-Can Guo(郭光灿), and Yong-Sheng Zhang(张永生)
    Chin. Phys. B, 2024, 33 (3): 030602.   DOI: 10.1088/1674-1056/ad1c5a
    Abstract185)   HTML11)    PDF (1036KB)(247)      
    Weak measurement amplification, which is considered as a very promising scheme in precision measurement, has been applied to various small physical quantities estimations. Since many physical quantities can be converted into phase signals, it is interesting and important to consider measuring small longitudinal phase shifts by using weak measurement. Here, we propose and experimentally demonstrate a novel weak measurement amplification-based small longitudinal phase estimation, which is suitable for polarization interferometry. We realize one order of magnitude amplification measurement of a small phase signal directly introduced by a liquid crystal variable retarder and show that it is robust to the imperfection of interference. Besides, we analyze the effect of magnification error which is never considered in the previous works, and find the constraint on the magnification. Our results may find important applications in high-precision measurements, e.g., gravitational wave detection.
    Creation and annihilation of artificial magnetic skyrmions with the electric field
    Jun Cheng(程军), Liang Sun(孙亮), Yike Zhang(张一可), Tongzhou Ji(吉同舟), Rongxing Cao(曹荣幸), Bingfeng Miao(缪冰锋), Yonggang Zhao(赵永刚), and Haifeng Ding(丁海峰)
    Chin. Phys. B, 2024, 33 (3): 037501.   DOI: 10.1088/1674-1056/ad188f
    Abstract178)   HTML4)    PDF (1824KB)(151)      
    Recent theory and experiments show that artificial magnetic skyrmions can be stabilized at room temperature without the need for the external magnetic field, casting strong potentials for the device applications. In this work, we study the electric field manipulation of artificial magnetic skyrmions imprinted by Co disks on CoPt multilayers utilizing the micromagnetic simulations. We find that the reversible annihilation and creation of skyrmions can be realized with the electric field via the strain mediated magnetoelastic coupling. In addition, we also demonstrate controllable manipulation of individual skyrmion, which opens a new platform for constructing magnetic field-free and low-energy dissipation skyrmion based media.
    Electrostatic force of dust deposition originating from contact between particles and photovoltaic glass
    Xing-Cai Li(李兴财), Juan Wang(王娟), and Guo-Qing Su(苏国庆)
    Chin. Phys. B, 2021, 30 (10): 104101.   DOI: 10.1088/1674-1056/abeb12
    Abstract418)   HTML1)    PDF (2941KB)(267)      
    Charged photovoltaic glass produces an electrostatic field. The electrostatic field exerts an electrostatic force on dust particles, thus making more dust particles deposited on the glass. In this paper, the contact electrification between the deposited dust particles and the photovoltaic glass is studied. Meanwhile, the surface charge density model of the photovoltaic glass and the electrostatic force of charged particles are analyzed. The results show that with the increasing of the particle impact speed and the inclination angle of the photovoltaic panel, the charges on particles increase to different degrees. Under a given condition, the electrostatic forces acting on the charged particles at different positions above the glass plate form a bell-shaped distribution at a macro level, and present a maximum value in the center of the plate. As the distance between the particle and the charged glass decreases, the electrostatic force exerted on the particle increases significantly and fluctuates greatly. However, its mean value is still higher than the force caused by gravity and the adhesion force, reported by some studies. Therefore, we suggest that photovoltaic glass panels used in the severe wind-sand environment should be made of an anti-static transparent material, which can lessen the dust particles accumulated on the panels.
    Magnetoresistance hysteresis in topological Kondo insulator SmB6 nanowire
    Ling-Jian Kong(孔令剑), Yong Zhou(周勇), Hua-Ding Song(宋化鼎), Da-Peng Yu(俞大鹏), Zhi-Min Liao(廖志敏)
    Chin. Phys. B, 2019, 28 (10): 107501.   DOI: 10.1088/1674-1056/ab3a89
    Abstract651)   HTML    PDF (1379KB)(301)      
    SmB6, a topological Kondo insulator, with a gapped bulk state and metallic surface state has aroused great research interest. Here, we report an exotic hysteresis behavior of magnetoresistance in individual SmB6 nanowire in a temperature range in which both surface and bulk states contribute to the total conductance. Under a magnetic field parallel to the SmB6 nanowire, the resistance suddenly increases at the turning point from up-sweep to down-sweep of the magnetic field. The magnetoresistance hysteresis loops are well consistent with the magnetocaloric effect. Our results suggest that the SmB6 nanowires possess potential applications in the magnetic cooling technology.
    Interfaces of high-efficiency kesterite Cu2ZnSnS(e)4 thin film solar cells
    Shoushuai Gao(高守帅), Zhenwu Jiang(姜振武), Li Wu(武莉), Jianping Ao(敖建平), Yu Zeng(曾玉), Yun Sun(孙云), Yi Zhang(张毅)
    Chin. Phys. B, 2018, 27 (1): 018803.   DOI: 10.1088/1674-1056/27/1/018803
    Abstract823)   HTML    PDF (6884KB)(1124)      

    Cu2ZnSnS(e)4 (CZTS(e)) solar cells have attracted much attention due to the elemental abundance and the non-toxicity. However, the record efficiency of 12.6% for Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is much lower than that of Cu(In,Ga)Se2 (CIGS) solar cells. One crucial reason is the recombination at interfaces. In recent years, large amount investigations have been done to analyze the interfacial problems and improve the interfacial properties via a variety of methods. This paper gives a review of progresses on interfaces of CZTS(e) solar cells, including:(i) the band alignment optimization at buffer/CZTS(e) interface, (ii) tailoring the thickness of MoS(e)2 interfacial layers between CZTS(e) absorber and Mo back contact, (iii) the passivation of rear interface, (iv) the passivation of front interface, and (v) the etching of secondary phases.

    Distinction between critical current effects and intrinsic anomalies in the point-contact Andreev reflection spectra of unconventional superconductors
    Ge He(何格), Zhong-Xu Wei(魏忠旭), Jérémy Brisbois, Yan-Li Jia(贾艳丽), Yu-Long Huang(黄裕龙), Hua-Xue Zhou(周花雪), Shun-Li Ni(倪顺利), Alejandro V Silhanek, Lei Shan(单磊), Bei-Yi Zhu(朱北沂), Jie Yuan(袁洁), Xiao-Li Dong(董晓莉), Fang Zhou(周放), Zhong-Xian Zhao(赵忠贤), Kui Jin(金魁)
    Chin. Phys. B, 2018, 27 (4): 047403.   DOI: 10.1088/1674-1056/27/4/047403
    Abstract748)   HTML    PDF (6344KB)(460)      

    In this work, we discuss the origin of several anomalies present in the point-contact Andreev reflection spectra of (Li1-xFex)OHFeSe, LiTi2O4, and La2-xCexCuO4. While these features are similar to those stemming from intrinsic superconducting properties, such as Andreev reflection, electron-boson coupling, multigap superconductivity, d-wave and p-wave pairing symmetry, they cannot be accounted for by the modified Blonder-Tinkham-Klapwijk (BTK) model, but require to consider critical current effects arising from the junction geometry. Our results point to the importance of tracking the evolution of the dips and peaks in the differential conductance as a function of the bias voltage, in order to correctly deduce the properties of the superconducting state.

    Fabrication of Al/AlOx/Al Josephson junctions and superconducting quantum circuits by shadow evaporation and a dynamic oxidation process
    Wu Yu-Lin (吴玉林), Deng Hui (邓辉), Yu Hai-Feng (于海峰), Xue Guang-Ming (薛光明), Tian Ye (田野), Li Jie (李洁), Chen Ying-Fei (陈莺飞), Zhao Shi-Ping (赵士平), Zheng Dong-Ning (郑东宁)
    Chin. Phys. B, 2013, 22 (6): 060309.   DOI: 10.1088/1674-1056/22/6/060309
    Abstract859)      PDF (1978KB)(4383)      
    Besides serving as promising candidates for realizing quantum computing, superconducting quantum circuits are one of a few macroscopic physical systems in which fundamental quantum phenomena can be directly demonstrated and tested, giving rise to a vast field of intensive research work both theoretically and experimentally. In this paper we report our work on the fabrication of superconducting quantum circuits, starting from its building blocks, Al/AlOx/Al Josephson junctions. By using electron beam lithography patterning and shadow evaporation, we have fabricated aluminum Josephson junctions with a controllable critical current density (jc) and wide range of junction sizes from 0.01 μm2 up to 1 μm2. We have carried out systematical studies on the oxidation process in fabricating Al/AlOx/Al Josephson junctions suitable for superconducting flux qubits. Furthermore, we have also fabricated superconducting quantum circuits such as superconducting flux qubit and charge-flux qubit.
    Quantum spin Hall and quantum valley Hall effects in trilayer graphene and their topological structures
    Majeed Ur Rehman, A A Abid
    Chin. Phys. B, 2017, 26 (12): 127304.   DOI: 10.1088/1674-1056/26/12/127304
    Abstract595)   HTML    PDF (5174KB)(618)      

    The present study pertains to the trilayer graphene in the presence of spin orbit coupling to probe the quantum spin/valley Hall effect. The spin Chern-number Cs for energy-bands of trilayer graphene having the essence of intrinsic spin-orbit coupling is analytically calculated. We find that for each valley and spin, Cs is three times larger in trilayer graphene as compared to single layer graphene. Since the spin Chern-number corresponds to the number of edge states, consequently the trilayer graphene has edge states, three times more in comparison to single layer graphene. We also study the trilayer graphene in the presence of both electric-field and intrinsic spin-orbit coupling and investigate that the trilayer graphene goes through a phase transition from a quantum spin Hall state to a quantum valley Hall state when the strength of the electric field exceeds the intrinsic spin coupling strength. The robustness of the associated topological bulk-state of the trilayer graphene is evaluated by adding various perturbations such as Rashba spin-orbit (RSO) interaction αR, and exchange-magnetization M. In addition, we consider a theoretical model, where only one of the outer layers in trilayer graphene has the essence of intrinsic spin-orbit coupling, while the other two layers have zero intrinsic spin-orbit coupling. Although the first Chern number is non-zero for individual valleys of trilayer graphene in this model, however, we find that the system cannot be regarded as a topological insulator because the system as a whole is not gaped.

    Machine learning in materials design: Algorithm and application
    Zhilong Song(宋志龙), Xiwen Chen(陈曦雯), Fanbin Meng(孟繁斌), Guanjian Cheng(程观剑), Chen Wang(王陈), Zhongti Sun(孙中体), and Wan-Jian Yin(尹万健)
    Chin. Phys. B, 2020, 29 (11): 116103.   DOI: 10.1088/1674-1056/abc0e3
    Abstract1013)   HTML    PDF (4567KB)(849)      

    Traditional materials discovery is in ‘trial-and-error’ mode, leading to the issues of low-efficiency, high-cost, and unsustainability in materials design. Meanwhile, numerous experimental and computational trials accumulate enormous quantities of data with multi-dimensionality and complexity, which might bury critical ‘structure–properties’ rules yet unfortunately not well explored. Machine learning (ML), as a burgeoning approach in materials science, may dig out the hidden structure–properties relationship from materials bigdata, therefore, has recently garnered much attention in materials science. In this review, we try to shortly summarize recent research progress in this field, following the ML paradigm: (i) data acquisition → (ii) feature engineering → (iii) algorithm → (iv) ML model → (v) model evaluation → (vi) application. In section of application, we summarize recent work by following the ‘material science tetrahedron’: (i) structure and composition → (ii) property → (iii) synthesis → (iv) characterization, in order to reveal the quantitative structure–property relationship and provide inverse design countermeasures. In addition, the concurrent challenges encompassing data quality and quantity, model interpretability and generalizability, have also been discussed. This review intends to provide a preliminary overview of ML from basic algorithms to applications.

    Fabrication of suspended graphene devices and their electronic properties
    Li Qiang(李强), Cheng Zeng-Guang(程增光), Li Zhong-Jun(李忠军), Wang Zhi-Hua(王志华), and Fang Ying(方英)
    Chin. Phys. B, 2010, 19 (9): 097307.   DOI: 10.1088/1674-1056/19/9/097307
    Abstract1758)      PDF (1469KB)(1905)      
    Suspended graphene devices are successfully fabricated by using a novel PMMA/MMA/PMMA tri-layer resist technique. The gap between graphene and dielectric substrate can be easily controlled by the thickness of the bottom PMMA layer, and no wet-etching with hazardous hydrofluoric acid is involved in our fabrication process. Electrical characterizations on suspended graphene devices are performed in vacuum when in-situ current annealing directly leads to a significant improvement on transport properties of graphene, i.e., the increase of carrier mobility with the reduction of width of Dirac peak. Our results make a new opportunity to study intrinsic properties of graphene.
    Transfer function modeling and analysis of the open-loop Buck converter using the fractional calculus
    Wang Fa-Qiang (王发强), Ma Xi-Kui (马西奎)
    Chin. Phys. B, 2013, 22 (3): 030506.   DOI: 10.1088/1674-1056/22/3/030506
    Abstract1057)      PDF (457KB)(21017)      
    Based on the fact that the real inductor and the real capacitor are fractional order in nature and the fractional calculus, the transfer function modeling and analysis of the open-loop Buck converter in continuous conduction mode (CCM) operation are carried out in this paper. The fractional order small signal model and the corresponding equivalent circuit of the open-loop Buck converter in CCM operation are presented. The transfer functions from the input voltage to the output voltage, from the input voltage to the inductor current, from the duty cycle to the output voltage, from the duty cycle to the inductor current, and the output impedance of the open-loop Buck converter in CCM operation are derived, and their bode diagrams and step responses are calculated, respectively. It is found that all the derived fractional order transfer functions of the system are influenced by the fractional orders of the inductor and the capacitor. Finally, the realization of the fractional order inductor and the fractional order capacitor is designed, and the corresponding PSIM circuit simulation results of the open-loop Buck converter in CCM operation are given to confirm the correctness of the derivations and the theoretical analysis.
    Anomalous spin Josephson effect in spin superconductors
    Wen Zeng(曾文) and Rui Shen(沈瑞)
    Chin. Phys. B, 2024, 33 (3): 037401.   DOI: 10.1088/1674-1056/ad1982
    Abstract95)   HTML4)    PDF (634KB)(99)      
    The spin superconductor state is the spin-polarized triplet exciton condensate, which can be viewed as a counterpart of the charge superconductor state. As an analogy of the charge Josephson effect, the spin Josephson effect can be generated in the spin superconductor/normal metal/spin superconductor junctions. Here we study the spin supercurrent in the Josephson junctions consisting of two spin superconductors with noncollinear spin polarizations. For the Josephson junctions with out-of-plane spin polarizations, the possible π-state spin supercurrent appears due to the Fermi momentum-splitting Andreev-like reflections at the normal metal/spin superconductor interfaces. For the Josephson junctions with in-plane spin polarizations, the anomalous spin supercurrent appears and is driven by the misorientation angle of the in-plane polarizations. The symmetry analysis shows that the appearance of the anomalous spin Josephson current is possible when the combined symmetry of the spin rotation and the time reversal is broken.
    Preparation of Se-based solar cell using spin-coating method in ambient condition
    Menghua Zhu(朱孟花), Yaxin Deng(邓雅心), Weiwei Liu(刘伟伟), Xin Li(李欣)
    Chin. Phys. B, 2018, 27 (1): 015202.   DOI: 10.1088/1674-1056/27/1/015202
    Abstract800)   HTML    PDF (1640KB)(434)      
    A new hybrid organic-inorganic structure of FTO/TiO2/Se/HTL/Au based selenium solar cell has been fabricated through a low-cost spin-coating process in air. In this process, selenium is completely dissolved in hydrazine, to form a homogeneous precursor solution. After spin-coating the precursor solution on the TiO2 substrates, following by sintering at 200℃ for 5min, a uniform selenium film with crystalline grains is formed. The selenium based solar cell exhibits an efficiency of 1.23% under AM1.5 illumination (100 mW·cm-2), short-circuit current density of 8 mA·cm-2, open-circuit voltage of 0.55 V, and fill factor of 0.37. Moreover, the device shows a stable ability with almost the same performance after 60 days.
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