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Simulation of Helium Behaviour in Titanium Crystals Using Molecular Dynamics
WANG Jun, HOU Qing, SUN Tie-Ying, WU Zhong-Cheng, LONG Xing-Gui, WU Xing-Chun, LUO Shun-Zhong
Chin. Phys. Lett. 2006, 23 (7):
1666-1669
.
The behaviour of helium in Ti crystals at 300K has been investigated by means of the molecular dynamics. The study is focused on the influences of He--Ti interaction on the aggregation of helium atoms in the substrate. When a Born--Mayer potential is used to describe the He--Ti interaction, the He atoms are unable to cluster with each other due to the weak bridge barrier that cannot trap the helium atoms, Whereas using a He--Ti potential that is constructed by fitting the ab initio pairwise He--Ti potential, the clustering of He atoms can be observed. The results indicate that suitable He--Ti potential plays an important role in the formation of He clusters in metals. Moreover, it is noted that the shape of the formed He cluster is irregular, and the produced defect prefers to congregating on one side of the He cluster rather than spreading symmetrically around it.
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Multiparty Quantum Secret Report
DENG Fu-Guo, , LI Xi-Han, LI Chun-Yan, ZHOU Ping, LIANG Yu-Jie, ZHOU Hong-Yu,
Chin. Phys. Lett. 2006, 23 (7):
1676-1679
.
A multiparty quantum secret report scheme is proposed with quantum encryption. The boss Alice and her M agents first share a sequence of (M+1)-particle Greenberger--Horne--Zeilinger (GHZ) states that only Alice knows which state each (M+1)-particle quantum system is in. Each agent exploits a controlled-not (CNot) gate to encrypt the travelling particle by using the particle in the GHZ state as the control qubit. The boss Alice decrypts the travelling particle with a CNot gate after performing a σx operation on her particle in the GHZ state or not. After the GHZ states (the quantum key) are used up, the parties check whether there is a vicious eavesdropper, say Eve, monitoring the quantum line, by picking out some samples from the GHZ states shared and measuring them with two measuring bases. After confirming the security of the quantum key, they use the remaining GHZ states repeatedly for the next round of quantum communication. This scheme has the advantage of high intrinsic efficiency for the qubits and total efficiency.
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Stochastic Resonance in an Over-Damped Bias Linear System with Dichotomous Noise
GUO Feng, ZHOU Yu-Rong, JIANG Shi-Qi, GU Tian-Xiang
Chin. Phys. Lett. 2006, 23 (7):
1705-1708
.
The stochastic resonance in an over-damped bias linear system subject to multiplicative and additive dichotomous noise (DN) is investigated. By using the linear-response theory and the properties of the DN, the exact expressions are found for the signal-to-noise ratio (SNR). It is shown that the SNR is a non-monotonic function of the correlation time of the additive DN, and it varies non-monotonically with the bias of the external field, the intensity and asymmetry of the multiplicative DN, as well as the external field frequency. Moreover, the SNR depends on the bias of the system, as well as the strength and asymmetry of the additive DN.
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Annihilation of Antiprotons in Light Nuclei
M. A. Rana, E. U. Khan, M. I. Shahzad, I. E. Qureshi, F. Malik, G. Sher, S. Manzoor, H. A. Khan
Chin. Phys. Lett. 2006, 23 (7):
1716-1718
.
CR-39 detectors have been exposed to a 5.9-MeV antiproton beam using the low energy antiproton ring (LEAR) facility at CERN. At this energy, tracks of antiprotons appear in a CR-39 detector after 135min of etching in 6M NaOH at 70°C. Fluence of the antiproton beam has been determined using track density. We have also found tracks in the etched CR-39 detector at different depths (250--500μm). These tracks have resulted from the annihilation of antiprotons with the constituents (H, C and O) of the CR-39 detector. The goal of the experiment is to develop a simple and low-cost method to study properties of antiparticles and those formed after annihilation of these particles with the target matter.
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Properties of the πh9/2 otimes νi13/2 Oblate Band in 188Tl
MA Long, ZHOU Xiao-Hong, XING Ye-Bing, ZHANG Yu-Hu, GUO Ying-Xing, LEI Xiang-Guo, XIE Chen-Ying, Oshima M., Toh Y., Koizumi M., Osa A., Hatsukawa Y., Sugawara M.
Chin. Phys. Lett. 2006, 23 (7):
1727-1730
.
High spin states in 188Tl have been investigated via the 157Gd(35Cl,4n) reaction at beam energy of 170MeV. A rotational band built on the πh9/2 otimes νi13/2 configuration with oblate deformation has been established. Considering the similarity between the band structure observed in odd--odd Tl nuclei, spin values have been tentatively proposed for the new band in 188Tl. The πh9/2 otimes νi13/2 oblate band in 188Tl shows low-spin signature inversion, and it can be interpreted qualitatively by the two quasiparticle plus rotor model including a J-dependent p--n residual interaction.
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Exotic Behaviour of Angular Dispersion of Weakly Bound Nucleus 17F at Small Angles
WANG Qi, HAN Jian-Long, XIAO Zhi-Gang, XU Hu-Shan, SUN Zhi-Yu, HU Zheng-Guo, ZHANG Xue-Ying, WANG Hong-Wei,
MAO Rui-Shi, YUAN Xiao-Hua, XU Zhi-Guo, ZHAO Tie-Cheng, ZHANG Hong-Bin, XU Hua-Gen, QI Hui-Rong, WANG Yue, JIA Fei, WU Li-Jie, DING Xian-Li, GAO Qi, GAO Hui, LI Song-Lin, BAI Zhen, XIAO Guo-Qing, JIN Gen-Ming, REN Zhong-Zhou, ZHOU Shan-Gui, SERGEY Yu-Kun,
Chin. Phys. Lett. 2006, 23 (7):
1731-1733
.
The differential cross sections of 17F and 17O elastic scattering products on 208Pb have been measured at the Radioactive Ion Beam Line at Lanzhou (RIBLL). Two angular dispersion plots of ln(dσ/dθ) versus θ2 are obtained from the angular distribution of the elastic scattering differential cross sections. The angular dispersion plot exhibits a clear turning point for 17F in the range of small scattering angles 6--20° due to its exotic structure, but for 17O, the turning point is not observed in the same angular range. The experimental results have been compared with previous data of other groups. Systematical analysis on the available data supports the above conclusion that there is an exotic behaviour of the angular dispersion plot of weakly bound nuclei with halo or skin structure as compared with that of the ordinary nuclei near stable line. Therefore the turning point of the angular dispersion plot appears at small angle for weakly bound nuclei with halo or skin structure, and can be used as a new probe to investigate the halo and skin phenomena of weakly bound nuclei.
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Alpha Decay Half-Lives of New Superheavy Elements through Quasimolecular Shapes
ZHANG Hong-Fei, LI JUN-Qing, ZUO Wei, CHEN Bao-Qiu, MA Zhong-Yu, Soojae Im, Royer Guy
Chin. Phys. Lett. 2006, 23 (7):
1734-1737
.
The lifetimes of α decays of the recently produced isotopes of the elements 112, 114, 116 and the element 294118 and of some decay products have been calculated theoretically within the Wentzel--Kramers--Brillouin approximation. The α decay barriers have been determined in the quasimolecular shape path within a generalized liquid drop model including the proximity effects between nuclei in a neck, the mass and charge asymmetry and the precise nuclear radius. These calculations provide reasonable estimates for the observed α decay lifetimes. The calculated results have been compared with the results of the density-dependent M3Y effective interaction and the experimental data. It is indicated that the theoretical foundation of the generalized liquid drop model is as good as that of the microscopic DDM3Y model, at least in the sense of predicting the T1/2 values as long as one uses a correct α decay energy. The half lives of these new nuclei are well tested from the consistence of the macroscopic, the microscopic and the experimental data.
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Assignment of Photoelectron Spectra of MC2 (M= V, Cr, Fe, and Co)
YUAN Yong-Bo, DENG Kai-Ming, LIU Yu-Zhen, TANG Chun-Mei
Chin. Phys. Lett. 2006, 23 (7):
1761-1764
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Hybrid density functional theory (DFT) calculations are performed to study MC2 (M= V, Cr, Fe and Co) clusters in the neutral and anionic charge states. We find that the equilibrium geometries of MC2 and their anions are all cyclic structures with C2v symmetry, which agrees well with the previous theoretical studies. The Mulliken charge and spin populations of MC2 clusters and their anions are also calculated, and it is found that the electron charge transformations from anions to neutral molecules mainly take place on the M atoms. Time-dependent DFT is used to calculate the excited states, and a theoretical assignment for the features in the experimental photoelectron spectrum is given, which are in good agreement with the available experimental data.
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Multi-Wavelength Erbium-Doped Fibre Lasers on Assistance of High-Nonlinear Photonic-Crystal Fibres
LIU Xue-Ming, ZHAO Wei, ZHANG Tong-Yi, LU Ke-Qing, SUN Chuan-Dong, WANG Yi-Shan, OUYANG Xian, HOU Xun, CHEN Guo-Fu
Chin. Phys. Lett. 2006, 23 (7):
1787-1789
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On the basis of self-stability effect of four-wave mixings (FWMs) in high-nonlinear photonic-crystal fibres, a novel multi-wavelength erbium-doped fibre (EDF) laser is proposed and demonstrated experimentally at room temperature. The proposed lasers have the capacity of switching and tuning with excellent uniformity and stability. By means of adjusting the attenuators, the triple-, four-, or five-wavelength EDF lasers can be lasing simultaneously. With the assistance of the FWM self-stability function, the multi-wavelength spectrum is excellently stabilized with uniformity less than 0.9dB.
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Kilohertz Electro-Optic Q-Switched Nd:YAG Ceramic Laser
WANG Chun-Yu, JI Jiang-Hua, QI Yun-Feng, LOU Qi-Hong, ZHU Xiao-Lei, LU Yu-Tian
Chin. Phys. Lett. 2006, 23 (7):
1797-1802
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We investigate the lasing characteristics of a laser-diode-array side-pumped electro-optic Q-switched Nd:Y3Al5O12 ceramic laser operating at 1000Hz pulse repetition rate. Using a YAG polycrystalline rod with Nd3+ concentration of 1at.% as the gain medium, pumping with 808nm laser-diode-arrays, the Q-switched laser output at 1064nm wavelength with 23mJ pulse energy and less than 12ns FWHM pulse width are obtained at a pumping power of about 400W, the slope efficiency is around 15%, the output beam divergence angle is about 1.2mrad.
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High Efficiency Infrared-to-Visible Upconversion Emission in Er3+,Yb3+, and Ho3+ Codoped Tellurite Glasses
DAI Shi-Xun, ZHANG Xiang-Hua, XU Tie-Feng, SHEN Xiang, WANG Xun-Shi, NIE Qiu-Hua
Chin. Phys. Lett. 2006, 23 (7):
1810-1812
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A novel method of codoping the Er3+, Yb3+, and Ho3+ ions in tellurite glasses is demonstrated to obtain a high efficiency of infrared-to-visible upconversion. Three intense emission bands observed in Er3+, Yb3+, and Ho3+ codoped tellurite glasses centred at 525, 547, and 657nm correspond to Er3+: 2H11/2 → 4I15/2, Er3+: 4S3/2 → 4I15/2+Ho3+: 5S2(5F4) → 5 I8, and Er3+: 4 S3/20 → 4I15/2+Ho3+: 5F5 → 5I8 transitions, respectively. No visible upconversion quenching phenomenon is observed when three rare-earth ions are codoped together in tellurite glasses. In contrast, the upconversion intensity of red and green emissions in Er3+, Yb3+, and Ho3+ codoped glasses is enhanced largely when compared with Er3+/Yb3+-codoped glasses. The dependence of upconversion intensities on excitation power and the possible upconversion mechanisms are evaluated. The three emissions are based on two-photon absorption processes.
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Transmission Loss due to Modes Conversion Caused by Random Surface Imperfections in Left-Handed-Material Slab Waveguides
ZHANG Gao-Ming, PENG Jing-Cui, JIAN Zhi-Jian, HUANG Xiao-Yi
Chin. Phys. Lett. 2006, 23 (7):
1826-1829
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Based on the orthogonality relations among the modes in left-handed-material (LHM) slab waveguides (SWGs), we derive the coupled equations among the modes caused by imperfect surfaces, and compute the transmission loss due to mode conversion. The computation shows that the transmission loss is very large, which is due to three facts: (1) there exist slow waves in the LHM SWG, whose electric field is mainly distributed in the surface; (2) the absence of fundamental node-less modes, so the fundamental modes have a node, whose electric field is also mainly distributed in the surface; and (3) the different focusing effects of the random RHM and LHM imperfections cause the electric field to suffer from severe deformations aggravated by the electric field distribution of the guided wave and the slow wave, which of course dissipates the power carried by the guided wave more severely. Therefore, we can safely conclude that the LHM SWG is unsuitable for transmitting the fundamental modes with a node.
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Lattice Bhatnagar--Gross--Krook Simulations of Hydromagnetic Double-Diffusive Convection in a Rectangular Enclosure with Opposing Temperature and Concentration Gradients
MA Chang-Feng, , SHI Bao-Chang
Chin. Phys. Lett. 2006, 23 (7):
1842-1845
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The temperature-concentration lattice Bhatnagar--Gross--Krook (TCLBGK) model with a robust boundary scheme is developed for two-dimensional hydromagnetic double-diffusive convective flow of a binary gas mixture in a rectangular enclosure, in which the upper and lower walls are insulated, while the left and right walls are constant temperature and constant concentration, and a uniform magnetic field is applied in the x-direction. In the model the velocity, temperature and concentration fields are solved by three independent LBGK equations, which are combined into a coupled equation for the whole system. In our simulations, we take the Prandtl number Pr=1.0, the Lewis number Le=2.0, the thermal Rayleigh number RaT=105, and the aspect ratio A=2 for the enclosure. The numerical results are found to be in good agreement with those of previous studies.
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Simulation of Z-Pinch Processes of Nested Tungsten Wire-Array on Angara-5-1 Facility
NING Cheng, DING Ning, LIU Quan, YANG Zhen-Hua, FAN Wen-Bin, ZHANG Yang
Chin. Phys. Lett. 2006, 23 (7):
1857-1860
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Based on the hydrodynamic shell-on-shell collision model, the Z-pinch processes of nested tungsten wire-array in Sino-Russian joint experiments on Angara-5-1 facility are simulated by means of our one-dimensional three-temperature radiation magneto-hydrodynamic code. The results show the evolutions of x-ray radiation burst, implosion trajectories of interfaces, current transfer in inner and outer wire-array plasmas, and the temporal and spatial changes of magnetic field and current density in the process. About 20% of the total driven current is transferred into the inner wire-array plasma by convection and diffusion of magnetic field when the two shells are pinched closest. Compared to the measured x-ray power, the simulated full width at half maximum and time at the strongest radiation agree approximately with the measured values. It is also demonstrated in our simulation that the radiation of nested wire-array Z-pinch is enhanced. The effects of fluctuations of driven current on yields of x-ray are also investigated.
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Spontaneous Hillock Growth on Indium Film Surface
WEI He-Lin, ZHANG Xi-Xiang, HUANG Han-Chen
Chin. Phys. Lett. 2006, 23 (7):
1880-1883
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Uniformly distributed indium hillocks are grown on silicon substrates by dc magnetron sputtering. The morphologies and the microstructures have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray diffraction (XRD). From the TEM and SEM images, we find that, at the earlier stage, the grain coalescent process dominates. This coalescent process induces a larger compressive stress. We believe that the drive force for hillock growth comes from this compressive stress. Under this compressive stress, the grain locating in the middle of several grains are extruded from these grains, and then a hillock forms with the increasing deposition time. For low melting point and high diffusion coefficient metal, such as bismuth and indium, this spontaneous-hillock growth mechanism can be used to fabricate well aligned nanostructures.
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Optical Properties of Pr3+-Doped Y2SiO5 Crystals
SUN Cheng-Lin, LI Jian-Fu, HU Chang-Hong, JIANG Zhan-Kui,
Chin. Phys. Lett. 2006, 23 (7):
1915-1918
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Optical properties of Pr3+ doped in Y2SiO5, including absorption spectra, emission spectra, and fluorescence decay, have been investigated with a special attention in the UV region. Broad band (270--350nm) UV fluorescence assigned to the transitions 4f5d → 4f2 3HJ, 3FJ is found. The spontaneous transition probabilities in the 4f2 intraconfiguration are calculated by utilizing the Judd--Ofelt theory, by which three phenomenological parameters (Ω2, Ω4, Ω6,) are obtained by fitting the absorption spectra. For the evaluation of transition probability of the interconfiguration 4f5d → 4f2, a formula for electric dipole transition is employed. In comparison of the measured fluorescence lifetime with the calculated spontaneous radiative lifetime, the fluorescence quantum efficiency is deduced.
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Photoluminescence from Electron-Beam Deposited CeO2 Thin Film after High Temperature Thermal Annealing
FANG Ying-Cui, ZHANG Zhuang-Jian, SHEN Jie, LU Ming
Chin. Phys. Lett. 2006, 23 (7):
1919-1922
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CeOx films are deposited onto the surface of a SiO2 matrix embedded with Si nanocrystals (nc-Si/SiO2) by electron-beam evaporation of CeO2 powder in high vacuum. By tuning the thickness of the CeOx film, photoluminescence (PL) spectra centred at 330, 358, 378, 388, 400, and 450nm, respectively, are observed. It has been identified that the PL centred at 358, 388 and 400nm are from cerium silicide compounds, and those centred at 330nm, 378nm are due to Ce3 ions, while the 450nm PL is from the defects in the SiO2 matrix.
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Characterization of Al2O3 Thin Films on GaAs Substrate Grown by Atomic Layer Deposition
LU Hong-Liang, LI Yan-Bo, XU Min, DING Shi-Jin, SUN Liang, ZHANG Wei, WANG Li-Kang
Chin. Phys. Lett. 2006, 23 (7):
1929-1931
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Al2O3 thin films are grown by atomic layer deposition on GaAs substrates at 300°C. The structural properties of the Al2O3 thin film and the Al2O3/GaAs interface are characterized using x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and x-ray photoelectron spectroscopy (XPS). The XRD results show that the as-deposited Al2O3 film is amorphous. For 30 atomic layer deposition growth cycles, the thicknesses of the Al2O3 thin film and the interface layer from the HRTEM are 3.3nm and 0.5nm, respectively. XPS analyses reveal that the Al2O3/GaAs interface is almost free from As2O3.
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Inductance of Long Intrinsic Josephson Junction Arrays Composed of Misaligned Tl2Ba2CaCu2O8 Thin Films
ZHOU Tie-Ge, YAN Shao-Lin, FANG Lan, ZUO Xu, LI Song, JI Lu, ZHAO Xin-Jie
Chin. Phys. Lett. 2006, 23 (7):
1939-1938
.
We observe and measure the inductance of long intrinsic Josephson junction arrays composed of misaligned Tl2Ba2CaCu2O8 thin films grown on LaAlO3 substrates. The array consists of about 9.1×103 intrinsic Josephson junctions, where 90° phase shift between ac voltage across the array and ac current flowing through has been measured. Furthermore, the voltage is proportional to the frequency of the current. The measured inductance values of the intrinsic Josephson junction arrays are basically consistent with the theoretically calculated results, confirming that the inductance is mainly due to the Josephson effect. The dependence of the array inductance on its critical current is also discussed.
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Fabrication Process of Sol-Gel Spin Coating for SrBi2Ta2O9 Films Applied to FeRAM
JIA Ze, REN Tian-Ling, ZHANG Zhi-Gang, LIU Tian-Zhi, WEN Xin-Yi, XIE Dan, LIU Li-Tian
Chin. Phys. Lett. 2006, 23 (7):
1943-1946
.
We investigate SrBi2Ta2O9 (SBT) films prepared by the sol-gel spin method with different spin rates or different anneal conditions for the first layer of SBT, as promising ferroelectric layer materials applied to ferroelectric random access memory (FeRAM). All the specimens in this experiment have similar SBT crystal orientations of (115), (020), (220), and (135). The Pt/SBT/Pt capacitor with coating of 3000rpm spin rate has a perfect rectangle shape of hysteresis loops, remanent polarization of 7.57μC/cm2 and coercive voltage of 0.816V at 5V voltage amplitude. These characteristics are better than those with coating of 3500rpm spin rate, which is attributed to the influence for thickness and grain size of the film from depressed spin rate. Slow-rate anneal in the furnace for the first layer of SBT can improve the crystallization processes and properties for SBT layers slightly, compared with rapid thermal annealing. The ion damage from etching for the top electrode can influence leakage current characteristics of the Pt/SBT/Pt capacitor at positive voltage bias.
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83 articles
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