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An Approach to Enhance the Efficiency of a Brownian Heat Engine
ZHANG Yan-Ping, HE Ji-Zhou**, XIAO Yu-Ling
Chin. Phys. Lett. 2011, 28 (10):
100506
.
DOI: 10.1088/0256-307X/28/10/100506
A Brownian microscopic heat engine, driven by temperature difference and consisting of a Brownian particle moving in a sawtooth potential with an external load, is investigated. The heat flows, driven by both potential and kinetic energies, are taken into account. Based on the master equation, the expressions for efficiency and power output are derived analytically, and performance characteristic curves are plotted. It is shown that the heat flow via the kinetic energy of the particle decreases. The efficiency of the engine is enhanced, but the power output reduces as the α shape parameter of the sawtooth potential increases. The influence of the α shape parameter on efficiency and power output is then analyzed in detail.
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Contribution of the LHT Model to Zc
WANG Ya-Bin, LI Xiang-Dong, HAN Jin-Zhong, YANG Bing-Fang, **
Chin. Phys. Lett. 2011, 28 (10):
101202
.
DOI: 10.1088/0256-307X/28/10/101202
In the littlest Higgs model with T-parity (LHT), some new particles, such as the T-odd mirror quarks and goldstone bosons, can contribute to various observables. We calculate their contribution to Zcc coupling. Some observables are related to Zcc coupling, for example, the effective vector and axial−vector Zcc coupling constants (gVc,gAc) and c−quark forward-backward asymmetry (AcFB). We give our predictions about gVc,gAc in the LHT model and show the allowed regions of the mirror quark masses based on the experimental data of gVc−gAc. Then, we present an explanation of AcFB.
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Tensor Effect on Bubble Nuclei
WANG Yan-Zhao, GU Jian-Zhong, **, ZHANG Xi-Zhen, DONG Jian-Min,
Chin. Phys. Lett. 2011, 28 (10):
102101
.
DOI: 10.1088/0256-307X/28/10/102101
In the framework of the Hartree–Fock–Bogoliubov (HFB) approach with Skyrme interactions SLy5+T, SLy5+Tw and several sets of TIJ parametrizations, i.e. the Skyrme interaction parametrizations including the tensor terms, the proton density distribution in 34Si and 46Ar nuclei is calculated with and without the tensor force. It is shown that the bubble effect in 34Si does not depend a great deal on the Skyrme parametrization and the proton density distribution in 34Si is hardly influenced by the tensor force. As to 46Ar, the SLy5+Tw parametrization favors the formation of the bubble structure due to the inversion between the 2s1/2 and 1d3/2 orbits (2s1/2–1d3/2 inversion). The inversion mechanism induced by the SLy5+Tw interaction is analyzed based on the proton single−particle spectra obtained from the SLy5 and SLy5+Tw interactions as well as the wave functions of the 2s1/2 and 1d3/2 states.
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Two Diode Lasers Simultaneously Optically Locked by Orthogonal Polarizations of a Monolithic Confocal Cavity
PENG Yu, **, ZHAO Yang, LI Ye, YANG Tao, CAO Jian-Ping, FANG Zhan-Jun, ZANG Er-Jun
Chin. Phys. Lett. 2011, 28 (10):
104208
.
DOI: 10.1088/0256-307X/28/10/104208
We demonstrate two self-injection locking extended cavity diode lasers (ECDLs) using resonant optical feedback independently from s- and p-polarizations of a monolithic folded Fabry–Perot confocal cavity (MFC). The relative frequency shift of adjacent axial modes of s resonance and p resonance of MFC is around 1.030 GHz. Beat note measurements between the two ECDLs are performed and present a relative linewidth of 4 kHz. With the help of a narrow-linewidth reference laser, the linewidth of s-component and p-component ECDLs are measured to be about 32 kHz and 40 kHz, respectively.
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Seven Odd-Order Multi-Wave Mixing Spectra in a Five-Level Atomic System
ZHANG Ru-Yi, LI Liang, LI Jin, LI Ning, WU Zhen-Kun, LIU Hua, WANG Zhi-Guo, ZHENG Huai-Bin, ZHANG Yan-Peng**
Chin. Phys. Lett. 2011, 28 (10):
104215
.
DOI: 10.1088/0256-307X/28/10/104215
In a K-type five-level atomic system, seven odd-order multi-wave mixing (MWM) processes are considered. We can distinguish the MWM signals by selectively blocking different laser beams and changing frequency detuning. We study the interaction in seven odd-order MWM processes in a five-level atomic system and demonstrate the existence of mutual suppression of seven odd-order MWM processes by setting dual electromagnetically induced transparency windows as separated or merged.
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Quantum Discord Dynamics in Two Different Non-Markovian Reservoirs
DING Bang-Fu**, WANG Xiao-Yun**, LIU Jing-Feng, YAN Lin, ZHAO He-Ping
Chin. Phys. Lett. 2011, 28 (10):
104216
.
DOI: 10.1088/0256-307X/28/10/104216
The quantum discord dynamics of two non-coupled two-level atoms independently interacting with their reservoir is studied under two kinds of non-Markovian conditions, namely, an off-resonant case with atomic transition frequency and a photonic band gap. In the first case, the phenomenon of the quantum discord loss and the oscillatory behavior of the quantum discord can occur by changing the detuning quantity and reducing the spectral coupling width for any initial Bell state. Under the second condition, the trapping phenomenon of the quantum discord can be presented by adjusting the width of gap, that is, the quantum discord of two atoms keep a nonzero constant for a long time.
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Transmission Characteristics in Tubular Acoustic Metamaterials Studied with Fluid Impedance Theory
FAN Li**, ZHANG Shu-Yi, ZHANG Hui
Chin. Phys. Lett. 2011, 28 (10):
104301
.
DOI: 10.1088/0256-307X/28/10/104301
Tubular acoustic metamaterials with negative densities composed of periodical membranes set up along pipes are studied with the fluid impedance theory. In addition to the conventional forbidden bands induced by the Bragg-scattering due to the periodic distributions of different acoustic impedances, the low-frequency forbidden band (LFB) with the low-frequency limit of zero Hertz is studied, in which the LFB is explained with acoustic impedance matching and the Bloch theory. Furthermore, the influences of the structural parameters of the tubular acoustic metamaterials on the transmission characteristics, such as the transmission coefficients, dispersion curves, widths of forbidden and pass bands, fluctuations in pass bands, etc., are evaluated, which can be used in the optimization of the acoustic insulation ability of the metamaterials.
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Mechanical Properties and Defect Evolution of Kr-Implanted 6H-SiC
XU Chao-Liang, **, ZHANG Chong-Hong, ZHANG Yong, ZHANG Li-Qing, YANG Yi-Tao, JIA Xiu-Jun, LIU Xiang-Bing, HUANG Ping, WANG Rong-Shan
Chin. Phys. Lett. 2011, 28 (10):
106103
.
DOI: 10.1088/0256-307X/28/10/106103
Specimens of silicon carbide (6H-SiC) were irradiated with 5 MeV Kr ions (84Kr19+) for three fluences of 5×1013, 2×1014 and 1×1015 ions/cm2, and subsequently annealed at room temperature, 500 °C, 700 °C and 1000 °C, respectively. The strain of the specimens was investigated with high resolution XRD and different defect evolution processes are revealed. An interpretation of the defect evolution and migration is given to explain the strain variation. The mechanical properties of the specimens were studied by using a nano−indentation technique in continuous stiffness measurement (CSM) mode with a diamond Berkovich indenter. For specimens irradiated with fluences of 5×1013 or 2×1014 ions/cm2, hardness values exceed that of un−implanted SiC. However, hardness sharply degrades for specimens irradiated with the highest fluence of 1×1015 ions/cm2. The specimens with fluences of 5×1013 and 2×1014 ions/cm2 and subsequently annealed at 700 °C and 500 °C, respectively, show the maximum hardness value.
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Optical Properties and Photocatalytic Activity of Marokite-Type CaMn2O4
WU Xue-Wei, ZHANG Hai-Xin, LIU Xiao-Jun**, ZHANG Xing-Gan**
Chin. Phys. Lett. 2011, 28 (10):
107101
.
DOI: 10.1088/0256-307X/28/10/107101
The optical properties and electronic structure of marokite-type CaMn2O4 are investigated by using UV−vis spectroscopy and the local-spin-density approximation plus the Hubbard-U (LSDA+U) method. Four absorption bands are observed at 638 nm (1.94 eV), 512 nm (2.42 eV), 377 nm (3.29 eV) and 248 nm (5.00 eV), which are ascribed to the charge transfer transitions O2p↑→Mn3d eg↑, O2p↓→Mn3d eg↑, Mn3d eg↑→Mn3d t2g ↓ and O2p↑→Mn3d t2g↓, respectively. We further use CaMn2O4 as a photocatalyst to decompose an azo-dye acid orange 7 (AO7) under irradiation of visible light and find that the decomposition ratio of AO7 reaches 15.9% under the irradiation of visible light for two hours.
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Reproduced Giant Localization Length of Two-Side Surface Disordered Nanowires with Long-Range Correlation
ZHAO Wei**, DING Jian-Wen
Chin. Phys. Lett. 2011, 28 (10):
107102
.
DOI: 10.1088/0256-307X/28/10/107102
We numerically investigate the normalized localization length of two-side rough nanowires as functions of energy, magnetic field and correlation strength by using modular recursive Green's function method. It is found that in the absence of correlation, while in the presence of magnetic field, the localization length increases linearly for two-side roughness, which is different to diverging exponentially for one-side roughness. Moreover, the localization of electrons is suppressed in the low energy region, but enhanced in the high energy region. In the presence of correlation, especially, an exponential enhancement in the localization length resumes in high energy region, in contrast to that in low energy region, the long-range correlations abnormally enhance the localization of electrons. A competitive mechanism is proposed to explain this behavior.
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A High Breakdown Voltage AlGaN/GaN MOSHEMT Using Thermal Oxidized Al-Ti as the Gate Insulator
ZHOU Bin, WANG Jin-Yan**, MENG Di, LIN Shu-Xun, FANG Min, DONG Zhi-Hua, YU Min, HAO Yi-Long, Cheng P. WEN
Chin. Phys. Lett. 2011, 28 (10):
107303
.
DOI: 10.1088/0256-307X/28/10/107303
Direct oxidation of composite Al/Ti metal films as gate insulators for AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistors (MOSHEMTs/HEMTs) is successfully realized. The devices fabricated with this novel process exhibit four orders of magnitude reduction in gate leakage current and remarkable breakdown voltage (V br=490 V vs 88 V for normal HEMT) improvement, compared with conventional Schottky-gate HEMTs. Furthermore, the transconductance of the MOSHEMT is only slightly lower (2.6%) than that of Schottky-gate HEMTs and have a wider full width of half maximum. The notable enhancement in device performance renders this new process highly promising for GaN-based microwave power amplifier applications in communication and radar systems.
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Reversible and Reproducible Giant Universal Electroresistance Effect
SYED Rizwan, ZHANG Sen, YU Tian, ZHAO Yong-Gang, ZHANG Shu-Feng, HAN Xiu-Feng**
Chin. Phys. Lett. 2011, 28 (10):
107308
.
DOI: 10.1088/0256-307X/28/10/107308
After the prediction of the giant electroresistance effect, much work has been carried out to find this effect in practical devices. We demonstrate a novel way to obtain a large electroresistance (ER) effect in the multilayer system at room temperature. The current-in-plane (CIP) electric transport measurement is performed on the multilayer structure consisting of (011)-Pb(Mg1/3Nb2/3)O3−PbTiO3(PMN−PT)/Ta/Al-O/metal. It is found that the resistance of the top metallic layer shows a hysteretic behavior as a function electric field, which corresponds well with the substrate polarization versus electric field (P–E) loop. This reversible hysteretic R–E behavior is independent of the applied magnetic field as well as the magnetic structure of the top metallic layer and keeps its memory state. This novel memory effect is attributed to the polarization reversal induced electrostatic potential, which is felt throughout the multilayer stack and is enhanced by the dielectric Al-O layer producing unique hysteretic, reversible, and reproducible resistance switching behavior. This novel universal electroresistance effect will open a new gateway to the development of future multiferroic memory devices operating at room temperature.
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Electric and Magnetic Field Tunable Rectification and Magnetoresistance in FexGe1−x/Ge Heterojunction Diodes
QIN Yu-Feng, YAN Shi-Shen, KANG Shi-Shou, XIAO Shu-Qin, LI Qiang, DAI Zheng-Kun, SHEN Ting-Ting, DAI You-Yong**, LIU Guo-Lei, CHEN Yan-Xue, MEI Liang-Mo, ZHANG Ze
Chin. Phys. Lett. 2011, 28 (10):
107501
.
DOI: 10.1088/0256-307X/28/10/107501
FexGe1−x/Ge amorphous heterojunction diodes with p-FexGe1−x ferromagnetic semiconductor layers are grown on single-crystal Ge substrates of p-type, n-type and intrinsic semiconductors, respectively. The I–V curves of p−Fe0.4Ge0.6/p−Ge diodes only show slight changes with temperature or with magnetic field. For the p-Fe0.4Ge0.6/n−Ge diode, good rectification is maintained at room temperature. More interestingly, the I–V curve of the p−Fe0.4Ge0.6/i-Ge diode can be tuned by the magnetic field, indicating a large positive magnetoresistance. The resistances of the junctions decrease with the increasing temperature, suggesting a typical semiconductor transport behavior. The origin of the positive magnetoresistance is discussed based on the effect of the electric and magnetic field on the energy band structures of the interface.
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Effect of Porous Structure on the Magnetic Properties of NixMgyZn1−x-yFe2O4 Magnetic Materials
QI Xin, ZHOU Xin, SHU Di, ZHAO Jing-Jing, WANG Wei, CHEN Juan**
Chin. Phys. Lett. 2011, 28 (10):
107502
.
DOI: 10.1088/0256-307X/28/10/107502
We deal with the preparation of NiMgZnFeIII−SO4 layered double hydroxides (LDHs) with the layered precursor method and introduce excessive ZnO into the NiMgZnFeIII−SO4 LDHs to produce NixMgyZn1−x-yFe2O4 ferrites that contain massive ZnO. Then the NixMgyZn1−x-yFe2O4 ferrites are treated with NaOH solution to remove ZnO to produce the porous NixMgyZn1−x-yFe2O4 magnetic material: when y=0, porous NiZnFe2O4 ferrite magnetic materials are obtained; when y≠0, porous NiMgZnFe2O4 ferrite magnetic materials are obtained. From analyses of these two ferrites, their pore−forming mechanism and comparison of their properties before and after they undergo the alkali treatment, we find that after being treated by the NaOH solution, NiZnFe2O4/ NiMgZnFe2O4 have better uniform-structure pores, which will greatly expand their pore volume, widen their application scope and improve their magnetic properties.
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MWCNTs/SiO2 Composite System: Carrier Transmission, Twin-Percolation and Dielectric Properties
CAO Wen-Qiang, , LU Ming-Ming, WEN Bo, CHEN Yuan-Lu, LI Hong-Bo, YUAN Jie**, CAO Mao-Sheng**
Chin. Phys. Lett. 2011, 28 (10):
107701
.
DOI: 10.1088/0256-307X/28/10/107701
We synthesize composite systems of multi-wall carbon nanotubes (MWCNTs)/SiO2 by using the sol−gel method. The dielectric properties of the systems with different-concentration MWCNTs are studied. In our MWCNTs/SiO2 inorganic systems, the twin−percolation phenomenon exists when the concentrations of MWCNTs are 5–10% and 15–20%. The permittivity and conductivity have jumping changes. The twin−percolation phenomenon is attributed to the special transfer mechanism of MWCNTs in the system, determined by hopping and migrating electrons. Variations of dielectric properties and conductance of the MWCNTs/SiO2 systems are conformed to the percolation theory. The special percolation phenomenon and electric properties of MWCNTs/SiO2 can help us comprehend the conductivity mechanism of the MWCNTs/SiO2 systems effectively, and promote the development of a high performance function composite system.
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Rectifying the Current−Voltage Characteristics of a LiNbO3 Film/GaN Heterojunction
HAO Lan-Zhong, **, LIU Yun-Jie, ZHU Jun**, LEI Hua-Wei, LIU Ying-Ying, TANG Zheng-Yu, ZHANG Ying, ZHANG Wan-Li, LI Yan-Rong
Chin. Phys. Lett. 2011, 28 (10):
107703
.
DOI: 10.1088/0256-307X/28/10/107703
Epitaxial LiNbO3 (LNO) films are grown on n−type GaN semiconductor substrates, forming LNO/GaN p-n junctions. The current-voltage (I–V) and capacitance−voltage (C–V) characteristics of the junctions are studied. The I–V curve shows a clear rectifying property with a turn−on voltage of 2.4 V. For the forward voltages, the conduction mechanism transits from Schottky thermionic emission for low voltages to space-charge-limited current for large voltages. Reverse C–V characteristics exhibit a linear 1/C2 versus V plot, from which a built-in potential of 0.34 V is deduced. These results are explained using the energy-band structure of the LNO/GaN junction.
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Frequency Response of Modulated Electroluminescence of Light-Emitting Diodes
FENG Lie-Feng**, LI Yang, LI Ding, WANG Cun-Da, ZHANG Guo-Yi, YAO Dong-Sheng, LIU Wei-Fang, XING Peng-Fei
Chin. Phys. Lett. 2011, 28 (10):
107801
.
DOI: 10.1088/0256-307X/28/10/107801
Frequency responses of modulated electroluminescence (EL) of light-emitting diodes were measured using a testing setup. With increasing frequency of the ac signal, the relative light intensity (RLI) clearly decreases. Furthermore, a peculiar asynchrony between the RLI and ac small-signal is observed. At frequencies higher than 10 kHz, the RLI clearly lags behind the ac signal and the absolute value of the lagging angle is nearly proportional to the signal frequency. Using the classical recombination model of light-emitting diodes under ac small-signal modulation, these abnormal characteristics of modulated EL can be clearly explained.
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Nonlinear Optical Studies of [(C4H9)4N][Ni(dmit)2] by Z-Scan Technique
SUN Jing**, ZHAO Yi-Kun, WANG Xin-Qiang, REN Quan, CHEN Jing-Wei, ZHANG Guang-Hui, XU Dong, WANG He-Zhou
Chin. Phys. Lett. 2011, 28 (10):
107803
.
DOI: 10.1088/0256-307X/28/10/107803
Nonlinear optical properties of an organo-metallic compound [(C4H9)4N][Ni(dmit)2] (dmit=2−thioxo-1,3-dithiole-4,5-dithiolate), abbreviated as BuNi, dissolved in acetone, are investigated using the Z-scan technique with a 40 ps pulse width at 1064 nm and a 1 ns and 15 ns pulse width at 1053 nm. Strong saturable absorption is found when the sample solution is irradiated by 40 ps and 1 ns laser pulses. When irradiated with a 15 ns laser pulse, a stronger reverse saturable absorption is found. The nonlinear optical absorption coefficients are -1.06×10-11, −2.02×10-11 and 2.73×10−10 m/W, respectively. All the results suggest that BuNi may be a promising candidate in the application of laser pulse compression in the near-infrared waveband.
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Ultraviolet-Visible Electroluminescence of a p-ZnO:As/n-Si Device Formed by the GaAs Interlayer Doping Method
XIA Xiao-Chuan, WANG Hui, ZHAO Yang, WANG Jin, ZHAO Jian-Ze, SHI Zhi-Feng, LI Xiang-Ping, LIANG Hong-Wei, ZHANG Bao-Lin, DU Guo-Tong, **
Chin. Phys. Lett. 2011, 28 (10):
108101
.
DOI: 10.1088/0256-307X/28/10/108101
Arsenic doped p-type ZnO films were grown on n-type silicon substrates using the GaAs interlayer doping method. Under our growth conditions the main doping element is arsenic, which was confirmed by x-ray photoelectroscopy. X-ray diffraction measurements revealed that the p-ZnO:As film was still in the (002) preferred orientation. The Hall test showed that the hole concentration of the p-ZnO:As film was 2.6 × 1017 cm−3. The acceptor level was located at 135 meV above the valance band maximum, according to the low-temperature photoluminescence results. We then fabricated a p-ZnO:As/n-Si heterojunction light-emitting device. Its current-voltage curve showed the typical rectifying behavior of a p–n diode. At forward current injections, the electroluminescence peaks, which cover the ultraviolet-to-visible region, could be clearly detected.
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The Preparation and Characteristics of InxGa1−xN (0.06≤x≤0.58) Films Deposited by ECR-PEMOCVD
LIU Xing-Long, QIN Fu-Wen, **, BIAN Ji-Ming, ZHANG Dong, CHEN Wei-Ji, ZHOU Zhi-Feng, ZHI An-Bo, YU Bo, WU Ai-Min, JIANG Xin,
Chin. Phys. Lett. 2011, 28 (10):
108104
.
DOI: 10.1088/0256-307X/28/10/108104
We investigate the structural property and surface morphology of InxGa1−xN films for In compositions ranging from 0.06 to 0.58, which are deposited by electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). The results of x-ray diffraction (XRD) in InGaN films confirm that they have excellent c−axis orientation. The In content in the InGaN epilayers is checked by electron probe microanalysis (EPMA), which reveals that In fractions determined by XRD are in good agreement with the EPMA results. Atomic force microscopy measurements reveal that the grown films have a surface roughness that varies between 4.16 and 8.14 nm. The results suggest that it is possible to deposit high-c-axis-orientation InGaN films with different In contents.
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82 articles
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