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Efficient collinear frequency tripling of femtosecond laser with compensation of group velocity delay Wang Yan-Ling, Zhou Xu-Gui, Wu Hong, Ding Liang-En Chin. Phys. B, 2009, 18 (10): 4308-4313.   DOI: 10.1088/1674-1056/18/10/036 Abstract （1573）      PDF （708KB）（98477）       Knowledge map    This paper demonstrates an approach that negative uniaxial crystal has a relative anomalous dispersion effect which can compensate group velocity delay, and applies this approach to nonlinear frequency conversion of an ultrafast laser field. High efficiency of the third harmonic generation is experimentally fulfilled by adopting a collinear configuration of doubing-compensation-tripling system. Through finely adjusting the incident angle and optical axis direction of the compensation plate, it obtains ultraviolet (UV) output energy of 0.32~mJ centered at 270~nm with spectral bandwidth of 2~nm when input beam at 800~nm was 70~fs pulse duration and 6~mJ pulse energy which was extracted from Ti:sapphire laser system by a diaphragm, corresponding to an 800-to-270~nm conversion efficiency of 5.3% and a factor-of-1.6 improvement in the third harmonic generation of UV band in comparison with a general conventional configuration. Furthermore, when the full energy of 18~mJ from a Ti:sapphire laser system was used and optimized, the UV emission could reach 0.83~mJ.

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Compression of the self-Q-switching in semiconductor disk lasers with single-layer graphene saturable absorbers Yu Zhen-Hua, Tian Jin-Rong, Song Yan-Rong Chin. Phys. B, 2014, 23 (9): 094206.   DOI: 10.1088/1674-1056/23/9/094206 Abstract （3603）      PDF （2034KB）（83277）       Knowledge map    We demonstrate the first use of single layer graphene for compressing self-Q-switching pulses in semiconductor disk lasers. The gain region of the semiconductor disk laser used InGaAs quantum wells with a central wavelength of 1030 nm. Due to self saturable absorption of the quantum wells, the disk laser emitted at the self-Q-switching state with a pulse width of 13 μs. By introducing the single layer graphene as a saturable absorber into the V-shaped laser cavity, the pulse width of the self-pulse was compressed to 2 μs with a lower pump power of 300 mW. As the pump power was increased, multiple pulses with the pulse width of 1.8 μs appeared. The compression factor was about 7.2.

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High performance pentacene organic field-effect transistors consisting of biocompatible PMMA/silk fibroin bilayer dielectric Li Hai-Qiang, Yu Jun-Sheng, Huang Wei, Shi Wei, Huang Jiang Chin. Phys. B, 2014, 23 (3): 038505.   DOI: 10.1088/1674-1056/23/3/038505 Abstract （560）      PDF （492KB）（62400）       Knowledge map    Pentacene organic field-effect transistors (OFETs) based on single-or double-layer biocompatible dielectrics of poly(methyl methacrylate) (PMMA) and/or silk fibroin (SF) are fabricated. Compared with those devices based on single PMMA or SF dielectric or SF/PMMA bilayer dielectric, the OFETs with biocompatible PMMA/SF bilayer dielectric exhibit optimal performance with a high field-effect mobility of 0.21 cm2/Vs and a current on/off ratio of 1.5×104. By investigating the surface morphology of the pentacene active layer through atom force microscopy and analyzing the electrical properties, the performance enhancement is mainly attributed to the crystallization improvement of the pentacene and the smaller interface trap density at the dielectric/organic interface. Meanwhile, a low contact resistance also indicates that a good electrode/organic contact is formed, thereby assisting the performance improvement of the OFET.

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Coherence transfer from 1064 nm to 578 nm using an optically referenced frequency comb Fang Su, Jiang Yan-Yi, Chen Hai-Qin, Yao Yuan, Bi Zhi-Yi, Ma Long-Sheng Chin. Phys. B, 2015, 24 (7): 074202.   DOI: 10.1088/1674-1056/24/7/074202 Abstract （581）   HTML    PDF （487KB）（62233）       Knowledge map    A laser at 578 nm is phase-locked to an optical frequency comb (OFC) which is optically referenced to a subhertz-linewidth laser at 1064 nm. Coherence is transferred from 1064 nm to 578 nm via the OFC. By comparing with a cavity-stabilized laser at 578 nm, the absolute linewidth of 1.1 Hz and the fractional frequency instability of 1.3× 10-15 at an averaging time of 1 s for each laser at 578 nm have been determined, which is limited by the performance of the reference laser for the OFC.

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A population-level model from the microscopic dynamics in Escherichia coli chemotaxis via Langevin approximation He Zhuo-Ran, Wu Tai-Lin, Ouyang Qi, Tu Yu-Hai Chin. Phys. B, 2012, 21 (9): 098701.   DOI: 10.1088/1674-1056/21/9/098701 Abstract （822）      PDF （7039KB）（48662）       Knowledge map    Recent extensive studies of Escherichia coli (E. coli) chemotaxis have achieved a deep understanding of its microscopic control dynamics. As a result, various quantitatively predictive models have been developed to describe the chemotactic behavior of E. coli motion. However, a population-level partial differential equation (PDE) that rationally incorporates such microscopic dynamics is still insufficient. Apart from the traditional Keller-Segel (K-S) equation, many existing population-level models developed from the microscopic dynamics are integro-PDEs. The difficulty comes mainly from cell tumbles which yield a velocity jumping process. Here, we propose a Langevin approximation method that avoids such a difficulty without appreciable loss of precision. The resulting model not only quantitatively reproduces the results of pathway-based single-cell simulators, but also provides new inside information on the mechanism of E. coli chemotaxis. Our study demonstrates a possible alternative in establishing a simple population-level model that allows for the complex microscopic mechanisms in bacterial chemotaxis.

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Effect of following strength on pedestrian counter flow Kuang Hua, Li Xing-Li, Wei Yan-Fang, Song Tao, Dai Shi-Qiang Chin. Phys. B, 2010, 19 (7): 070517.   DOI: 10.1088/1674-1056/19/7/070517 Abstract （1299）      PDF （2420KB）（42236）       Knowledge map    This paper proposes a modified lattice gas model to simulate pedestrian counter flow by considering the effect of following strength which can lead to appropriate responses to some complicated situations. Periodic and open boundary conditions are adopted respectively. The simulation results show that the presented model can reproduce some essential features of pedestrian counter flows, e.g., the lane formation and segregation effect. The fundamental diagrams show that the complete jamming density is independent of the system size only when the width W and the length L are larger than some critical values respectively, and the larger asymmetrical conditions can better avoid the occurrence of deadlock phenomena. For the mixed pedestrian flow, it can be found that the jamming cluster is mainly caused by those walkers breaking the traffic rules, and the underlying mechanism is analysed. Furthermore, the comparison of simulation results and the experimental data is performed, it is shown that this modified model is reasonable and more realistic to simulate and analyse pedestrian counter flow.

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Nanoscale guiding for cold atoms based on surface plasmons alongtips of metallic wedges Wang Zheng-Ling, Tang Wei-Min, Zhou Ming, Gao Chuan-Yu Chin. Phys. B, 2013, 22 (7): 073701.   DOI: 10.1088/1674-1056/22/7/073701 Abstract （282）      PDF （2707KB）（41300）       Knowledge map    We propose a novel scheme to guide neutral cold atoms in a nanoscale region based on surface plasmons (SPs) of one pair and two pairs of tips of metallic wedges with locally enhanced light intensity and sub-optical wavelength resolution. We analyze the near-field intensity distribution of the tip of the metallic wedge by the FDTD method, and study the total intensity as well as the total potential of optical potentials and van der Waals potentials for 87Rb atoms in the light field of one pair and two pairs of tips of metallic wedges. It shows that the total potentials of one pair and two pairs of tips of metallic wedges can generate a gravito-optical trap and a dark closed trap for nanoscale guiding of neutral cold atoms. Guided atoms can be cooled with efficient intensity-gradient Sisyphus cooling by blue-detuned light field. This provides an important step towards the generation of hybrid systems consisting of isolated atoms and solid devices.

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Kink effect in current–voltage characteristics of a GaN-based high electron mobility transistor with an AlGaN back barrier Ma Xiao-Hua, Lü Min, Pang Lei, Jiang Yuan-Qi, Yang Jing-Zhi, Chen Wei-Wei, Liu Xin-Yu Chin. Phys. B, 2014, 23 (2): 027302.   DOI: 10.1088/1674-1056/23/2/027302 Abstract （348）      PDF （409KB）（33615）       Knowledge map    The kink effect in current–voltage (IV) characteristic s seriously deteriorates the performance of a GaN-based HEMT. Based on a series of direct current (DC) IV measurements in a GaN-based HEMT with an AlGaN back barrier, a possible mechanism with electron-trapping and detrapping processes is proposed. Kink-related deep levels are activated by a high drain source voltage (Vds) and located in a GaN channel layer. Both electron trapping and detrapping processes are accomplished with the help of hot electrons from the channel by impact ionization. Moreover, the mechanism is verified by two other DC IV measurements and a model with an expression of the kink current.

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Conservation laws of the generalized short pulse equation Zhang Zhi-Yong, Chen Yu-Fu Chin. Phys. B, 2015, 24 (2): 020201.   DOI: 10.1088/1674-1056/24/2/020201 Abstract （514）   HTML    PDF （192KB）（28325）       Knowledge map    We show that the generalized short pulse equation is nonlinearly self-adjoint with differential substitution. Moreover, any adjoint symmetry is a differential substitution of nonlinear self-adjointness, and vice versa. Consequently, the general conservation law formula is constructed and new conservation laws for some special cases are found.

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The consistent Riccati expansion and new interaction solution for a Boussinesq-type coupled system Ruan Shao-Qing, Yu Wei-Feng, Yu Jun, Yu Guo-Xiang Chin. Phys. B, 2015, 24 (6): 060201.   DOI: 10.1088/1674-1056/24/6/060201 Abstract （404）   HTML    PDF （271KB）（26061）       Knowledge map    Starting from the Davey–Stewartson equation, a Boussinesq-type coupled equation system is obtained by using a variable separation approach. For the Boussinesq-type coupled equation system, its consistent Riccati expansion (CRE) solvability is studied with the help of a Riccati equation. It is significant that the soliton–cnoidal wave interaction solution, expressed explicitly by Jacobi elliptic functions and the third type of incomplete elliptic integral, of the system is also given.

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Analysis of the breakdown mechanism for an ultra high voltage high-side thin layer silicon-on-insulator p-channel lateral double-diffused metal oxide semiconductor Zhuang Xiang,Qiao Ming,Zhang Bo,Li Zhao-Ji Chin. Phys. B, 2012, 21 (3): 037305.   DOI: 10.1088/1674-1056/21/3/037305 Abstract （843）      PDF （1679KB）（24099）       Knowledge map    This paper discusses the breakdown mechanism and proposes a new simulation and test method of breakdown voltage (BV) for an ultra-high-voltage (UHV) high-side thin layer silicon-on-insulator (SOI) p-channel lateral double-di?used metal oxide semiconductor (LDMOS). Compared with the conventional simulation method, the new one is more accordant with the actual conditions of a device that can be used in the high voltage circuit. The BV of the SOI p-channel LDMOS can be properly represented and the effect of reduced bulk field can be revealed by employing the new simulation method. Simulation results show that the off-state (on-state) BV of the SOI p-channel LDMOS can reach 741 (620) V in the 3-μm-thick buried oxide layer, 50-μm-length drift region, and at -400 V back-gate voltage, enabling the device to be used in a 400 V UHV integrated circuit.

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Adsorption of sodium ions and hydrated sodium ions on a hydrophobic graphite surface via cation-π interactions Shi Guo-Sheng, Wang Zhi-Gang, Zhao Ji-Jun, Hu Jun, Fang Hai-Ping Chin. Phys. B, 2011, 20 (6): 068101.   DOI: 10.1088/1674-1056/20/6/068101 Abstract （1325）      PDF （3011KB）（22538）       Knowledge map    Using density functional theory computation, we show that sodium ions and hydrated sodium ions can be strongly adsorbed onto a hydrophobic graphite surface via cation-π interactions. The key to this cation-π interaction is the coupling of the delocalized π states of graphite and the empty orbitals of sodium ions. This finding implies that the property of the graphite surface is extremely dependent on the existence of the ions on the surface, suggesting that the hydrophobic property of the graphite surface may be affected by the existence of the sodium ions.

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Transfer function modeling and analysis of the open-loop Buck converter using the fractional calculus Wang Fa-Qiang, Ma Xi-Kui Chin. Phys. B, 2013, 22 (3): 030506.   DOI: 10.1088/1674-1056/22/3/030506 Abstract （601）      PDF （457KB）（20572）       Knowledge map    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.

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Adaptive backstepping control of the uncertain Lü system Yu Yong-Guang, Zhang Suo-Chun Chin. Phys., 2002, 11 (12): 1249-1253.   DOI: 10.1088/1009-1963/11/12/006 Abstract （748）      PDF （232KB）（17459）       Knowledge map    In this paper we investigate further the method for controlling the uncertain Lü system via adaptive backstepping. The Lü system is transformed into the so-called general strict-feedback form. Then a novel control method is designed for controlling the uncertain Lü system. Especially, this method can overcome the singularity problem. Numerical simulations show the effectiveness and feasibility of this approach.

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Theoretical investigation of band-gap and mode characteristics of anti-resonance guiding photonic crystal fibres Yuan Jin-Hui, Sang Xin-Zhu, Yu Chong-Xiu, Xin Xiang-Jun, Zhang Jin-Long, Zhou Gui-Yao, Li Shu-Guang, Hou Lan-Tian Chin. Phys. B, 2011, 20 (2): 024213.   DOI: 10.1088/1674-1056/20/2/024213 Abstract （1045）      PDF （3374KB）（15122）       Knowledge map    With the full-vector plane-wave method (FVPWM) and the full-vector beam propagation method (FVBPM), the dependences of the band-gap and mode characteristics on material index and cladding structure parameter in anti-resonance guiding photonic crystal fibres (ARGPCFs) are sufficiently analysed. An ARGPCF operating in the near-infrared wavelength is shown. The influences of the high index cylinders, glass interstitial apexes and silica structure on the characteristics of band-gaps and modes are deeply investigated. The equivalent planar waveguide theory is used for analysing such an ARGPCF filled by the isotropic materials, and the resonance and the anti-resonance characteristics can be well predicted.

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Silicon nanoparticles：Preparation, properties, and applications Chang Huan, Sun Shu-Qing Chin. Phys. B, 2014, 23 (8): 088102.   DOI: 10.1088/1674-1056/23/8/088102 Abstract （323）      PDF （2101KB）（15094）       Knowledge map    Silicon nanoparticles have attracted great attention in the past decades because of their intriguing physical properties, active surface state, distinctive photoluminescence and biocompatibility. In this review, we present some of the recent progress in preparation methodologies and surface functionalization approaches of silicon nanoparticles. Further, their promising applications in the fields of energy and electronic engineering are introduced.

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Magnetic iron oxide nanoparticles：Synthesis and surface coating techniques for biomedical applications Sun Sheng-Nan, Wei Chao, Zhu Zan-Zan, Hou Yang-Long, Subbu S Venkatraman, Xu Zhi-Chuan Chin. Phys. B, 2014, 23 (3): 037503.   DOI: 10.1088/1674-1056/23/3/037503 Abstract （1441）      PDF （4676KB）（14617）       Knowledge map    Iron oxide nanoparticles are the most popular magnetic nanoparticles used in biomedical applications due to their low cost, low toxicity, and unique magnetic property. Magnetic iron oxide nanoparticles, including magnetite (Fe3O4) and maghemite (γ-Fe2O3), usually exhibit a superparamagnetic property as their size goes smaller than 20 nm, which are often denoted as superparamagnetic iron oxide nanoparticles (SPIONs) and utilized for drug delivery, diagnosis, therapy, and etc. This review article gives a brief introduction on magnetic iron oxide nanoparticles in terms of their fundamentals of magnetism, magnetic resonance imaging (MRI), and drug delivery, as well as the synthesis approaches, surface coating, and application examples from recent key literatures. Because the quality and surface chemistry play important roles in biomedical applications, our review focuses on the synthesis approaches and surface modifications of iron oxide nanoparticles. We aim to provide a detailed introduction to readers who are new to this field, helping them to choose suitable synthesis methods and to optimize the surface chemistry of iron oxide nanoparticles for their interests. Cited: Web of science (68)

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Switching properties of bi-OPE-monothiol molecular junctions: Substituent effects and improvement of open-close ratio Fu Xiao-Xiao, Zhang Li-Xia, Li Zong-Liang, Wang Chuan-Kui Chin. Phys. B, 2013, 22 (2): 028504.   DOI: 10.1088/1674-1056/22/2/028504 Abstract （460）      PDF （559KB）（14529）       Knowledge map    The electronic transport properties of a new kind of molecular switches -bi-OPE-monothiol molecular switches -were studied by applying first-principles calculations and generalized elastic scattering Green's function. The numerical results show that, for a bi-OPE-molecule junction, the offset face-to-face configuration induces more delocalized molecular orbitals, and results in higher conductivity than the parallel face-to-face configuration, so it can be used as a molecular switch. The side substituent groups containing more delocalized electrons can strengthen the intermolecular coupling and raise the conductivities of bi-OPE-monothiol molecular devices. On the basis of the investigations, we find a scheme to enhance the open-close ratios of bimolecular switches.

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A simple model of suppressing stimulated Brillouin scattering in optical fiber with frequency-modulated laser Hu Xiao-Yang, Chen Wei, Tu Xiao-Bo, Meng Zhou Chin. Phys. B, 2014, 23 (12): 124208.   DOI: 10.1088/1674-1056/23/12/124208 Abstract （294）      PDF （317KB）（13045）       Knowledge map    A simple model is developed to study the mechanism of stimulated Brillouin scattering (SBS) suppression with frequency-modulated laser in optical fiber. By taking into account the laser frequency distribution along the fiber induced by frequency modulation, the average effective Brillouin gain is calculated to determine the SBS threshold. Experimental results show agreement with the numerical analysis. The application for SBS suppression in interferometric fiber sensing system is also discussed in this paper. The results show that the maximum input power can be increased effectively by frequency modulation method.

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Structure and electronic structure of S-doped graphitic C3N4 investigated by density functional theory Chen Gang, Gao Shang-Peng Chin. Phys. B, 2012, 21 (10): 107101.   DOI: 10.1088/1674-1056/21/10/107101 Abstract （770）      PDF （3695KB）（12232）       Knowledge map    The structures of the heptazine-based graphitic C3N4 and the S-doped graphitic C3N4 are investigated by using the density functional theory with a semi-empirical dispersion correction for the weak long-range interaction between layers. The corrugated structure is found to be energetically favorable for both the pure and the S-doped graphitic C3N4. The S doptant is prone to substitute the N atom bonded with only two nearest C atoms. The band structure calculation reveals that this kind of S doping causes a favorable red shift of the light absorption threshold and can improve the electroconductibility and the photocatalytic activity of the graphitic C3N4.