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Exact Solution to Rate Equation with Time-Dependent Coefficients: Its Application in InGaAsP Lasers
WANG Gang, LUO Bin, PAN Wei, WU Shao-Quan, HOU Bang-Pin
Chin. Phys. Lett. 2006, 23 (3):
535-538
.
By using the algebraic dynamics method, we obtain exact analytical solutions of rate equations with time-dependent coefficients, which might present an effective description of the physical mechanism of the practical semiconductor lasers. Based on the exact solutions, we investigate the dynamic behaviour and the emitted properties of the InGaAsP laser, which has been commonly used in long wavelength optical communication systems. It is found that when the cavity length varies with time exponentially, the output power of the laser will drop and approach its asymptote. When the cavity length is a sinusoid function of time, the intensity of the emitted optical pulses can be controlled by the amplitude of this function.
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Highest Occupied Molecular Orbital of Cyclopentanone by Binary (e, 2e) Spectroscopy
ZHANG Shu-Feng, NING Chuan-Gang, DENG Jing-Kang, REN Xue-Guang, SU Guo-Lin, YANG Tie-Cheng, HUANG Yan-Ru
Chin. Phys. Lett. 2006, 23 (3):
583-596
.
We report the first measurements of the momentum profiles of highest occupied molecular orbital (HOMO) and the complete valence shell binding energy spectra of cyclopentanone with impact energies of 600 and 1200eV by a binary (e, 2e) spectrometer. The experimental momentum profiles of the HOMO orbital are compared with the theoretical momentum distribution calculated using the Hartree--Fock and density functional theory methods with various basis sets. However, none of these calculations gives a completely satisfactory description of the momentum distributions of the HOMO 7b2. The inadequacy of the calculations could result in the intensity difference of the second maximum at p~1.2a.u. between the experiment and the theory. The discrepancy between experimental and theoretical data in the low-momentum region is explained with the distorted wave effect.
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State-Selective Electron Capture for keV He2+ Ions on Helium Collisions Studied by Recoil Momentum Spectroscopy
ZHU Xiao-Long, MA Xin-Wen, LI Bin, LIU Hui-Ping, CHEN Lan-Fang, ZHANG Shao-Feng, QIAN Dong-Bin, FENG Wen-Tian, CAO Shi-Ping, SHA Shan, ZHANG Da-Cheng,
Chin. Phys. Lett. 2006, 23 (3):
587-590
.
State-selective single electron capture cross sections are measured by recoil ion momentum spectroscopy technique for He2+ on He at 30keV incident energy. The cross sections for capture into ground and excited states are obtained and compared to classical model calculations as well as to the quantum mechanical calculations. The experimental results are in good agreement with quantum mechanical results.
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High-Order Temporal Corrected Fields of Ultra-Short Laser Pulses and Laser-Driven Acceleration
XIE Yong-Jie, HUO Yu-Kun, KONG Qing, WANG Ping-Xiao, CHEN Zhao, LIU Jing-Ru
Chin. Phys. Lett. 2006, 23 (3):
599-602
.
Up to third-order temporal correction in terms of a small dimensionless temporal parameter ε =1/(ω0 t0) (ω0 = ck0 the central oscillatory frequency, t0 the pulse duration of half period), the field expressions of ultra-short focused laser pulses are explicitly presented. To evaluate the correction efficacy, electric amplitudes of zeroth-order and higher-order corrected fields are compared for different pulse durations. Furthermore, electron interaction with ultra-short laser pulses is simulated using both the zeroth-order and higher-order corrected field equations. Our simulation results show that the third-order correction terms should be considered for investigating the interaction if the laser pulse duration decreases to a few optical periods.
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Comparison between Two Kinds of Semiconductor Absorbers for Mode-Locking in Nd:YVO4 Laser
WANG Cui-Luan, WANG Yong-Gang, MA Xiao-Yu, LIU Yang, SUN Li-Qun, TIAN Qian, ZANG Zhi-Gang, WANG Qin-Yue
Chin. Phys. Lett. 2006, 23 (3):
616-618
.
We have demonstrated passive mode-locking in a diode-end-pumped Nd:YVO4 laser using two kinds of semiconductor absorbers whose relaxation region comes from In0.25Ga0.75As grown at low temperature (LT) and GaAs/air interface respectively. Mode-locking, using absorbers of the GaAs/air interface relaxation region, has the characteristics of less Q-switching tendency and higher average output power than that using absorbers of LT In0.25Ga0.75As relaxation region, but is not as stable as the latter.
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Diode-Pumped Passive Q-Switched 946nm Nd:YAG Laser with a GaAs Saturable Absorber
WANG Su-Mei, ZHANG Qiu-Lin, ZHANG Ling, ZHANG Chun-Yu, ZHANG Dong-Xiang, FENG Bao-Hua, ZHANG Zhi-Guo
Chin. Phys. Lett. 2006, 23 (3):
619-621
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We report, for the first time to our knowledge, a diode-pumped passive Q-switched 946nm Nd:YAG laser by using a GaAs as saturable absorber. The maximum average output power is 1.24W at an incident pump power of 15W, corresponding to a slope efficiency of 10%. Laser pulses with pulse duration of 70ns and repetition rate of 330kHz are generated.
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Effect of Distribution Pattern of Molecular Dipoles on Microscopic Second-Harmonic Generation
DENG Xiao-Yuan, WANG Xian-Ju, LIU Han-Ping, ZHUANG Zheng-Fei, GUO Zhou-Yi
Chin. Phys. Lett. 2006, 23 (3):
629-632
.
We set up a model for dealing with the second-harmonic generation (SHG) from molecular dipoles in a line alignment pattern rather than a planar distribution under a microscope. Because of this model, it is possible to perform a flexibly quantitative investigation of SHG from collagen fibres at a molecular level. The line alignment pattern induces more significant modifications in both the angular dipole distribution structure A(θ,ψ) and the second-harmonic power structure θy (θ,ψ), compared to a planar distribution. Also, the line alignment angle t has strong effect on A(θ,ψ) and θy(θ,ψ), resulting in an irregular SHG angular power distribution. That is to say, it is unnecessary for SHG emission to present two well-defined off-axis lobes. The total SHG power shows two symmetrical peaks at angles of t=50° and t =130° while a drop at t=90°. The weakest SHG signals can be measured at t=0° and t=180°.
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A Novel Lattice Boltzmann Model For Reactive Flows with Fast Chemistry
CHEN Sheng, LIU Zhao-Hui, HE Zhu, ZHANG Chao, TIAN Zhi-Wei, SHI Bao-Chang, ZHENG Chu-Guang
Chin. Phys. Lett. 2006, 23 (3):
656-659
.
A novel lattice Boltzmann model, in which we take the ratio of temperature difference in the temperature field to the environment one to be more than one order of magnitude than before, is developed to simulate two-dimensional reactive flows with fast chemistry. Different from the hybrid scheme for reactive flows [Comput. Phys. Commun. 129(2000)267], this scheme is strictly in a pure lattice Boltzmann style (i.e., we solve the flow, temperature, and concentration fields using the lattice Boltzmann method only). Different from the recent non-coupled lattice Boltzmann scheme [Int. J. Mod. Phys. B 17(2003)197], the fluid density in our model is coupled directly with the temperature. Excellent agreement between the present results and other numerical data shows that this scheme is an efficient numerical method for practical reactive flows with fast chemistry.
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Detailed Radiative Opacity Studies of a High-Temperature Gold Plasma
ZENG Jiao-Long, ZHAO Gang, YUAN Jian-Min,
Chin. Phys. Lett. 2006, 23 (3):
660-663
.
The radiative opacity of a gold plasma at a temperature of 360eV and a density of 0.01g/cm3 has been studied using a detailed level accounting (DLA) method. Under this plasma condition, the average ionization degree is 50.2. Dominant ion types in the plasma are Au+49, Au+50 and Au+51, which account for 18.3%, 33.1% and 32.6%, respectively. The spectrally resolved opacity shows complex fine structures. The result obtained by the DLA method is compared with that of the average atom model. Detailed analyses are carried out to study the strongest absorption peaks caused by 3d-4f transitions near the photon energy of 2600eV. To better understand the value of the Rosseland mean opacity, the radiative opacity around the energy region of the maximal Rosseland weighting function is also discussed in detail.
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Relativistic Electromagnetic Solitary Wave in a Cylindrical Magnetized Plasma
WANG Yun-Liang, ZHOU Zhong-Xiang, JIANG Xiang-Qian, YUAN Cheng-Xun, WANG Hai-Feng, ZHANG Hai-Feng, HOU Chun-Feng, JIANG Yong-Yuan, SUN Xiu-Dong, QIN Ru-Hu
Chin. Phys. Lett. 2006, 23 (3):
664-667
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In the presence of an applied static and uniform magnetic field, a cylindrical Kadomtsev--Petviashivili equation is derived for a relativistic electromagnetic solitary wave propagating in collisionless plasma consisting electrons, positrons, and ions in the case of weak relativistic limit. This equation is solved in a stationary frame to obtain explicit expression for the velocity, amplitude and width of solitons. The amplitude of the solitary wave has a maximum value at a critical αc of the ratio of the ion equilibrium density to the electron one, and it increases as the applied magnetic field becomes larger.
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Energy Variable Slow Positron Beam Study of Li+-Implantation-Induced Defects in ZnO
CHEN Zhi-Quan, M. Maekawa, A. Kawasuso
Chin. Phys. Lett. 2006, 23 (3):
675-677
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ZnO films grown on sapphire substrates are implanted with 100-keV Li ions up to a total dose of 1×10-16 cm-2. Vacancy-type defects, mostly vacancy clusters, are observed by positron annihilation measurements after implantation. Upon annealing, they first have an agglomeration process which leads to the growth in the vacancy size. After annealing at about 500°C, vacancy clusters grow into microvoids, which is indicated by the positronium formation. With annealing temperature increases to above 500°C, the microvoids begin to recover, and finally all the implantation-induced vacancy defects are removed at 1000°C. No Li nanoclusters can be observed after Li+ implantation.
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Compositional and Structural Properties of TiO2-xNx Thin Films Deposited by Radio-Frequency Magnetron Sputtering
JING Shi-Wei, LIU Yi-Chun, LIANG Yu, MA Jian-Gang, LU You-Ming, SHEN De-Zhen, ZHANG Ji-Ying, FAN Xi-Wu, MU Ri-Xiang
Chin. Phys. Lett. 2006, 23 (3):
682-685
.
TiO2-xNx thin films are deposited onto Si(100) and quartz substrates by a rf magnetron sputtering method using a titanium metal disc as a target in Ar, N2, and O2 atmospheres. The substrate temperature is kept at 300°C. The O2 and Ar gas flow rates are kept to be constants and the N gas flow rate is varied. TiO2-xNx films with different N contents are characterized by x-ray diffraction and x-ray photoelectron spectroscopy. The results indicate that the TiO2-xNx thin films can be obtained at 13% N and 15% N contents in the film, and the films with mixed TiO2 and TiN crystal can be obtained at 13% N and 15% N contents in the film. In terms of the results of x-ray photoelectron spectroscopy, N 1s of β-N (396eV) is the main component in the TiO2-xNx thin films. Because the energy level of β-N is positioned above the valence-band maximum of TiO2, an effective optical-energy gap decreases from 2.8eV (for pure TiO2 film deposited by the same rf sputtering system) to 2.3eV, which is verified by the optical-absorption spectra.
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Fabrication of Syringe-Shaped GaN Nanorods
XUE Cheng-Shan, WU Yu-Xin, ZHUANG Hui-Zhao, TIAN De-Heng, LIU Yi-An, HE Jian-Ting, AI Yu-Jie, SUN Li-Li, WANG Fu-Xue, CAO Yu-Ping
Chin. Phys. Lett. 2006, 23 (3):
686-688
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Syringe-shaped GaN nanorods are synthesized on Si(111) substrates by annealing sputtered Ga2O3/BN films under flowing ammonia at temperature of 950°C. Most of the nanorods consist of a main rod and a top needle, looking like a syringe. X-ray diffraction and selected-area electron diffraction confirm that the syringe-shaped nanorods are hexagonal wurtzite GaN. Scanning electron microscopy and high-resolution transmission electron microscopy reveal that these nanorods are as long as several micrometres, with diameters ranging from 100 to 300nm. In addition to the BN intermediate layer, the proper annealing temperature has been demonstrated to be a crucial factor for the growth of syringe-shaped nanorods by this method.
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Photoconductive Properties of MEH-PPV/CuS-Nanoparticle Composites
JIN Hui, HOU Yan-Bing, TANG Ai-Wei, MENG Xian-Guo, TENG Feng
Chin. Phys. Lett. 2006, 23 (3):
693-696
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Photoconductive properties of photodiodes based on composites of CuS nanoparticles and Poly[2-methoxy,5-(2’-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) are investigated. By comparing composite devices with different MEH-PPV:CuS weight ratios of 1:1 (D2-1), 1:1.25 (D2-2), 1:2.5 (D2-3) and 1:5 (D2-4), it is found that the device D2-3 exhibited the best performance: the short-circuit current density of 17μA/cm2 with the light intensity of 16.7 mW/cm2, the highest open-circuit voltage of 0.83V, and the photosensitivity of 132 at reverse bias of -1 V. The photosensitivity is improved by a factor of 5 compared with the undoped MEH-PPV device.
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Pregelation Behaviour of Coagulation Processes with the Constant-Reaction-Number Kernel
KE Jian-Hong, LIN Zhen-Quan, CHEN Xiao-Shuang
Chin. Phys. Lett. 2006, 23 (3):
720-723
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We propose an irreversible binary coagulation model with a constant-reaction-number kernel, in which, among all the possible binary coagulation reactions, only p reactions are permitted to take place at every time. By means of the generalized rate equation we investigate the kinetic behaviour of the system with the reaction rate kernel K(i;j)=(ij)ω (0≤ ω <1/2), at which an i-mer and a j-mer coagulate together to form a large one. It is found that for such a system there always exists a gelation transition at a finite time tc, which is in contrast to the ordinary binary coagulation with the same rate kernel. Moreover, the pre-gelation behaviour of the cluster size distribution near the gelation point falls in a scaling regime and the typical cluster size grows as (tc-t)-1/(1-2ω). On the other hand, our model can also provide some predictions for the evolution of the cluster distribution in multicomponent complex networks.
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Empirical Study on the Volatility of the Hang-Seng Index
CAI Shi-Min, ZHOU Pei-Ling, YANG Hui-Jie, YANG Chun-Xia, WANG Bing-Hong, ZHOU Tao,
Chin. Phys. Lett. 2006, 23 (3):
754-757
.
We study the statistical properties of volatility of price fluctuation for the Hang-Seng index in the Hong Kong stock market, they are measured by locally averaging over a time window T, the absolute value of price change over a short time interval Δt. The data include minute-by-minute records of the Hang-Seng index from 3 January 1994 to 28 May 1997. We find that the cumulative distribution of the volatility is consistent with the asymptotic power-law behaviour, characterized by the power exponent μ=2.12 ± 0.04, different from that found in the previous studies as μ approx 3. The volatility distribution remains the same asymptotic power-law behaviour for the time scales from T=10 min to T=80 min. Furthermore, we investigate the volatility correlations by using the power spectrum analysis and detrended fluctuation analysis. Both the methods show a long-range power-law decay with the exponent α=0.636±0.002.
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65 articles
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