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Volume 21 Issue 6
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Original Articles
Exact Eigenstates for a Class of Models Describing Multiphoton Processes in the Presence of Six Bosonic Modes
ZHAN Zhi-Ming, LI Wei-Bin, LI Jia-Hua, YANG Wen-Xing, CHEN Ai-Xi
Chin. Phys. Lett. 2004, 21 (6): 983-986 .  
Abstract   PDF(pc) (233KB) ( 416 )
We present an efficient approach to study the spectra and eigenstates for the model describing six multiphoton processes in the presence of bosonic modes without using the assumption of the Bethe ansatz. The exact analytical results of all the eigenstates and eigenvalues are in terms of a parameter λ for a class of models describing the six-mode multiphoton processes. The parameter is determined by the roots of a polynomial and is solvable analytically or numerically.

Connection Between Quantum-Classical Correspondence and Long-Range Correlations in Quantum Spectra
LI Xi-Guo, SONG Jian-Jun
Chin. Phys. Lett. 2004, 21 (6): 987-990 .  
Abstract   PDF(pc) (283KB) ( 663 )
Based on the Berry-Tabor trace formula, a semiclassical quantization condition for the periodic orbits in a two-dimensional uncoupled oscillator system and the correspondence relation between the quantum levels and classical trajectories of the system have been studied in detail. Making use of the quantum-classical correspondence relation, it has been found that if a set of quantum levels corresponds to the periodic orbits with the same topology structure M (M1,M2), there will be long-range correlations among these quantum levels.

An Intuitive Expression for Inseparability Condition of a Two-Mode Squeezed Vacuum State in a Thermal Environment
LI Fu-Li, LI Hong-Rong
Chin. Phys. Lett. 2004, 21 (6): 991-994 .  
Abstract   PDF(pc) (208KB) ( 397 )
Considering the propagation of a two-mode optical field that is initially in a squeezed vacuum state in a thermal environment, we obtain an intuitive expression for inseparability condition of the two-mode mixed state which is given in the coherent state representation. This condition shows that the two modes have quantum entanglement if and only if the coefficient of the correlation term between the two modes is larger than that of the off-diagonal term of each mode in the density matrix. We find that even if the quantum channel is dynamically coupled to the thermal environment, the fidelity for teleporting coherent states larger than 1/2 is still the criterion for quantum teleportation. We also show that the entanglement, squeezing and quantum teleportation conditions are always consistent with each other.
Probabilistic Cloning and Quantum Computation
GAO Ting, , YAN Feng-Li, WANG Zhi-Xi
Chin. Phys. Lett. 2004, 21 (6): 995-998 .  
Abstract   PDF(pc) (266KB) ( 776 )
We discuss the usefulness of quantum cloning and present examples of quantum computation tasks for which the cloning offers an advantage which cannot be matched by any approach that does not resort to quantum cloning. In these quantum computations, we need to distribute quantum information contained in the states about which we have some partial information. To perform quantum computations, we use a state-dependent probabilistic quantum cloning procedure to distribute quantum information in the middle of a quantum computation.
Generation of Entangled Coherent States in Raman-Coupled Bose-Einstein Condensates
KUANG Le-Man, ZENG Ai-Hua, KUANG Zhen-Hua
Chin. Phys. Lett. 2004, 21 (6): 999-1002 .  
Abstract   PDF(pc) (245KB) ( 409 )
A method for producing entangled coherent states (ECSs) for atomic Bose-Einstein condensates (BECs) is presented. The proposed method involves a BEC with three internal states and two classical laser beams in a three-level Lambda configuration. We show how to generate multi-state ECSs through properly manipulating strengths of these interactions and laser detunings. A maximally entangled coherent state is obtained explicitly.
Analytical Results of Eigenstates and Eigenenergies by Mixing Models of Five Bosonic Modes
LI Wei-Bin, ZHAN Zhi-Ming, XIE Xiao-Tao, LUO Jin-Ming, WU Xuan
Chin. Phys. Lett. 2004, 21 (6): 1003-1005 .  
Abstract   PDF(pc) (209KB) ( 413 )
The analytical expressions of eigenstates and eigenenergies are demonstrated using a parameter λ without the assumption of Bethe ansatz for two kinds of five-mode mixing models. It is found that the parameter can be determined by the roots of a simple polynomial. We also illustrate the exact analytical expressions of eigenstates and energies without any unknown parameter.

Quantum Entropy of the Schwarzschild Black Hole due to Gravitational Perturbations
CHEN Song-Bai, JING Ji-Liang
Chin. Phys. Lett. 2004, 21 (6): 1006-1008 .  
Abstract   PDF(pc) (197KB) ( 405 )
The quantum entropies of the Schwarzschild black hole arising from the axial and polar gravitational perturbations are investigated by using the‘brick-wall’model. It is shown that, although the axial and polar perturbational potentials have quite different forms, the black hole entropies due to both the gravitational perturbations are equivalent. We also find that the logarithmic correction, which can be expressed in the form ln(AH4), is 30 times larger than that of the scalar field.
Horowitz-Strominger Black Hole Entropy Without Brick Wall
ZHANG Li-Chun, ZHAO Ren, LIN Hai
Chin. Phys. Lett. 2004, 21 (6): 1009-1012 .  
Abstract   PDF(pc) (206KB) ( 368 )
A Horowitz-Strominger black hole is discussed through a new equation of state density motivated by the generalized uncertainty relation in quantum gravity. There is no burst in the last stage of emission from a Horowitz-Strominger black hole. When the new equation of state density is used to investigate the entropy of bosonic field and fermionic field outside the horizon of a static Horowitz-Strominger black hole, the divergence that appears in the brick-wall model is removed without any cutoff. The entropy proportional to the horizon area is derived from the contribution in the vicinity of the horizon.

Determination of Optimal Control Strength of Delayed Feedback Control Using Time Series
YIN Hua-Wei, LU Wei-Ping, WANG Peng-Ye
Chin. Phys. Lett. 2004, 21 (6): 1013-1015 .  
Abstract   PDF(pc) (313KB) ( 365 )
We study controlling chaos using time-delayed feedback control based on chaotic time series without prior knowledge of dynamical systems, and determine the optimal control parameters for stabilizing unstable periodic orbits with maximal stability.

A Spatiotemporal-Chaos-Based Cryptosystem Taking Advantage of Both Synchronous and Self-Synchronizing Schemes
LÜ, Hua-Ping, WANG Shi-Hong, LI Xiao-Wen, TANG Guo-Ning, KUANG Jin-Yu, YE Wei-Ping, HU Gang,
Chin. Phys. Lett. 2004, 21 (6): 1016-1019 .  
Abstract   PDF(pc) (309KB) ( 423 )
Two-dimensional one-way coupled map lattices are used for cryptography where multiple space units produce chaotic outputs in parallel. One of the outputs plays the role of driving for synchronization of the decryption system while the others perform the function of information encoding. With this separation of functions the receiver can establish a self-checking and self-correction mechanism, and enjoys the advantages of both synchronous and self-synchronizing schemes. A comparison between the present system with the system of advanced encryption standard (AES) is presented in the aspect of channel noise influence. Numerical investigations show that our system is much stronger than AES against channel noise perturbations, and thus can be better used for secure communications with large channel noise.
Localized Excitations in (3+1) Dimensions: Dromions, Ring-Shape and Bubble-Like Solitons
LOU Sen-Yue
Chin. Phys. Lett. 2004, 21 (6): 1020-1023 .  
Abstract   PDF(pc) (380KB) ( 587 )
By means of infinite-dimensional Kac-Moody-Virasoro symmetry group transformation, rich localized (3+1)-dimensional excitations such as dromions, ring-shape and bubble-like excitations are obtained for a matrix system which is produced by extending the Lax pair of the celebrated self-dual Yang-Mills field. Abundant (3+1)-dimensional localized excitations can also be found in other types of nonlinear systems.

Structure of the πg7/2 [404] 7/2+ Band in Odd Proton Nucleus 123I
WANG Shou-Yu, MA Ying-Jun, T. Komatsubara, LIU Yun-Zuo, ZHANG Yu-Hu, K. Furuno, T. Hayakawa, J. Mukai, Y. Iwata, T. Morikawa, G. B. Hagemann, G. Sletten, J. Nyberg, D. Jerrestam, H. J. Jensen, J. Espino, J. Gascon, N. GjФrup, B. Cederwall, P. O. TjФm
Chin. Phys. Lett. 2004, 21 (6): 1024-1026 .  
Abstract   PDF(pc) (443KB) ( 376 )
High spin states of the odd proton nucleus 123I have been populated in the reaction 116Cd(14N, 5n2p) at a beam energy of 65 MeV. Two previously known positive-parity ΔI = 2 sequences have been extended up to 31/2+ and 41/2+. In addition, a number of ΔI = 1 transitions linking the two ΔI = 2 sequences have been observed. It is suggested that both the ΔI = 2 sequences are built upon the oblate πg7/2[404]7/2+ Nilsson configuration.
Density Dependence of the Beta Decay Width in Astronuclear Matter
YUAN Wei, LIU Yu-Xin, ,
Chin. Phys. Lett. 2004, 21 (6): 1027-1030 .  
Abstract   PDF(pc) (217KB) ( 399 )
By combining the four-fermion interaction theory and the linear σ-ω model, we propose an approach to describe the density dependence of the β-decay width (the half-life time of the decay) in infinite and charge-neutral nuclear matter. We find that the half-life time of the β-decay decreases rapidly with the increase of the nuclear matter density.
Baryonic Effect on XcJ Suppression in Au+Au Collisions at RHIC Energies
PENG Ru, XU Xiao-Ming, ZHOU Dai-Cui
Chin. Phys. Lett. 2004, 21 (6): 1031-1034 .  
Abstract   PDF(pc) (421KB) ( 373 )
We predict that XcJ mesons at low transverse momentum in the central rapidity region are almost dissociated by nucleons and antinucleons in hadronic matter produced in central Au+Au collisions at relativistic high-ion collider (RHIC) energies √sNN = 130 and 200 GeV. In the calculations the nucleon and antinucleon distributions in hadronic matter are results of evolution from their freeze-out distributions which well fit the experimental transverse momentum spectra of proton and antiproton.

Effect of Nickel Alloying Layer on Hydrogen Absorption Ability of Zr-Al Getter Material
LIU Chao-Zhuo, SHI Li-Qun
Chin. Phys. Lett. 2004, 21 (6): 1035-1038 .  
Abstract   PDF(pc) (636KB) ( 734 )
By using ion beam sputtering, an 85-Å thick nickel layer was deposited on the Zr-Al alloy (non-evaporable getter) to improve the characteristic of the hydrogen absorption. The presputtering for 15 min to clean the surface passivation layer and the vacuum heating treatment of the sample at 750°C for 1 h for surface alloying can improve the ability of the gas absorption. The gas absorption experiments show fast absorption kinetics of the hydrogen pumping and good durability against contaminable gases. The Rutherford-back-scattering spectra and the secondary ion mass spectroscopy demonstrate the formation of an alloy of Zr, Al, and Ni in the near-surface area after the thermal process. The elastic recoil detection analysis indicates that the sample holds the original high capacity of hydrogen.

Synchronization of an Ultrafast Ti:Sapphire Laser to the S-Band Microwave
LIU Sheng-Guang, WANG Ming-Kai, SUN Da-Rui, DAI Jian-Ping, LI Yong-Gui
Chin. Phys. Lett. 2004, 21 (6): 1039-1040 .  
Abstract   PDF(pc) (361KB) ( 735 )
We have synchronized a 102-MHz ultrafast self-mode-locked Ti:sapphire laser to a 2856-MHz rf source with the sample-locking technology. The relative root-mean-square time-jitter is 0.57 ps and the maximum time jitter is 2.60 ps. This is the first time that synchronization between the ultrafast laser pulse and the s-band microwave has been accomplished in China. Potential applications include synchronization of lasers and rf power sources in particle accelerator experiments and high-resolution pump-probe experiments.
Generation of a Collimated Doughnut-Beam for Atom Trapping Using a Single-Cone Axicon
QIAN Yong, ZHANG Yu, WEI Rong, WANG Yu-Zhu
Chin. Phys. Lett. 2004, 21 (6): 1041-1043 .  
Abstract   PDF(pc) (377KB) ( 683 )
We propose a novel method to generate a collimated doughnut-beam (DB) using only one single-cone axicon and realize it experimentally. The diameter of the DB is estimated by ray optics and is in good agreement with the experimental results. The CCD image of the DB and the radial light intensity distribution are experimentally obtained. The light intensity of the DB dark inner region is about 1% of the peak intensity of the DB. The far-field divergent angle is about 6 mrad and seems to be well-collimated. With optimum values of the power and the positive detuning of the laser field, the optical dipole potential of the DB can be chosen to be very large as a good confinement for atom trapping.
Collisional Reactions of Energetic Methane Molecules with Single-Walled Carbon Nanotubes
LI Feng, XIA Yue-Yuan, ZHAO Ming-Wen, LIU Xiang-Dong, HUANG Bo-Da, TAN Zhen-Yu, JI Yan-Ju
Chin. Phys. Lett. 2004, 21 (6): 1044-1047 .  
Abstract   PDF(pc) (540KB) ( 399 )
We study the collisions of energetic methane molecules with single-walled carbon nanotubes in the incident energy range from 5 to 100 eV using classical molecular dynamics simulations combined with ab initio calculations. The methane molecules can be decomposed into different hydrocarbon radicals, e.g. CHn (n = 1-3), in the collisions depending on the incident energy. Chemical functionalization of the single-walled carbon nanotubes resulting from the chemical adsorption of these hydrocarbon radicals on the outside wall of single-walled carbon nanotubes can be achieved simultaneously. Some stable adsorption configurations of hydrocarbon-functionalized single-walled carbon nanotubes are also presented based on ab initio calculations.
Intermolecular Interaction Potentials of CH4-Ne Complex Calculated with Local Density Approximation Methods
BAI Yu-Lin, CHENG Xiao-Hong, CHEN Xiang-Rong, YANG Xiang-Dong, ZHU Jun
Chin. Phys. Lett. 2004, 21 (6): 1048-1050 .  
Abstract   PDF(pc) (254KB) ( 511 )
The intermolecular interactions potentials for two configurations of CH4-Ne complex are calculated with local density approximation methods in the frame of density functional theory. It is found that the calculated potentials have two minima when the distance between the carbon atom of CH4 and the Ne atom takes R = 5.80 a.u. and 6.20 a.u. for both the two configurations. For the edge configuration, the corresponding depth of the potential is 0.0669536 eV and 0.0671416 eV. For the face configuration, the corresponding depth of the potential is 0.0737956 eV and 0.0645506 eV. The global minimum occurs at R = 5.80 a.u. for the face configuration with a depth of the potential 0.0737956 eV. The depths of our calculation are in better agreement with the experimental data than the quantum chemical calculation approach, while the position of minimum potential for our calculation is underestimated.
Range Distribution Parameters and Electronic Stopping Power for 19F+ Ions in SnO2, Indium-Tin Oxide, AgGaSe2 and AgGaS2: Comparison Between Theory and Experiment
XIA Hui-Hao, LIU Xiang-Dong
Chin. Phys. Lett. 2004, 21 (6): 1051-1054 .  
Abstract   PDF(pc) (418KB) ( 385 )
Range distributions of fluorine for 19F+ implantation into SnO2, indium--tin oxide, AgGaS2 and AgGaSe2 are measured by using the 19F(p,α γ)16O resonant nuclear reactions. The electronic stopping cross sections for 19F ions in these materials are derived from the measured range distributions. These experimental results are compared with those obtained from the newest version of stopping and range computer code, SRIM2003. The values of projected range predicted by the SRIM2003 agree well with the measured values for AgGaS2 and AgGaSe2 substrates. However, the values given by the SRIM2003 substantially deviate from the experimental values for the oxide materials SnO2 and ITO.
Single-Electron Detachment for Transition Elements Cr- and Fe- in Collision with He
WU Shi-Min, HUANG Yong-Yi, ZHANG Xue-Mei, LI Guang-Wu, LU Fu-Quan, YANG Fu-Jia
Chin. Phys. Lett. 2004, 21 (6): 1055-1056 .  
Abstract   PDF(pc) (212KB) ( 447 )
Single-electron detachment (SED) cross-sections for Cr- and Fe- in collisions with He have been obtained in the energy region of 10-30keV for the first time. In the present energy range the magnitude of the Cr- + He SED cross-sections is close to that of Fe- + He, although the electron affinity of Fe- (0.16 eV) and Cr- (0.668 eV) are different. It is found that the cross-sections for Cr- and Fe- in collisions with He exhibit nearly the same dependence on anions impact velocity.

Properties of Speckle Intensities in Near-Field Optical Regions by Numerical Solutions of Wave Equations
CHENG Chuan-Fu, REN Xiao-Rong, LIU Chun-Xiang, ZHANG Ning-Yu, TENG Shu-Yun, XU Zhi-Zhan
Chin. Phys. Lett. 2004, 21 (6): 1057-1060 .  
Abstract   PDF(pc) (480KB) ( 323 )
Starting from the electromagnetic wave equations and boundary conditions and using Green’s integral theorem, we implement the rigorous numerical solutions of the speckle field produced by scattering of dielectric random surfaces in the optical near-field. The average sizes of speckle granules are enlarged very quickly with the increase of the distance in the range less than a wavelength. It is found that the speckle contrast in the near-field and in the neighbourhood region is inversely proportional to the square of lateral correlation length at its large values and linearly decreases with the roughness exponent.

Fabrication of Dammann Gratings Inside Glasses by a Femtosecond Laser
NAKAYA Takayuki QIU Jian-Rong, ZHOU Chang-He, HIRAO Kazuyuki,
Chin. Phys. Lett. 2004, 21 (6): 1061-1063 .  
Abstract   PDF(pc) (348KB) ( 425 )
Dammann grating is useful in information technology as an optical splitter. It is usually fabricated through complicated processes. Here we report on the direct fabrication of a 6 x 6 Dammann grating in a silica glass by an 800 nm femtosecond laser. We also discuss the relationship between diffraction efficiency of 1 x 2 Dammann grating and laser irradiation conditions.

Silica-Based Arrayed Waveguide Grating with Flattened Spectral Response Using a Multimode Interference Coupler
TANG Yan-Zhe, JIA Ke-Miao, LI Bai-Yang, YANG Jian-Yi, JIANG Xiao-Qing, WU Ya-Ming, WANG Yue-Lin,
Chin. Phys. Lett. 2004, 21 (6): 1064-1066 .  
Abstract   PDF(pc) (488KB) ( 390 )
We designed and fabricated an arrayed waveguide grating based on silica-on-silicon materials with flattened spectral response by adding a multimode interference coupler in the input region. The theoretical analysis and calculation are given. The device has worked effectively and has been tested with the passband 0.43 nm at 1 dB, 0.72 nm at 3 dB and 1.56 nm at 20 dB respectively, at a cost of power penalty of about 1.5 dB. The crosstalk is less than -30 dB, owing to the high-resolution photomask and well-controlled fabrication processes.

Numerical Analysis of Three-Dimensional Object Recognition with Digital Holography
DING De-Hua, HE Qing-Sheng, WANG Jian-Gang, WU Min-Xian, JIN Guo-Fan
Chin. Phys. Lett. 2004, 21 (6): 1067-1070 .  
Abstract   PDF(pc) (439KB) ( 476 )
We describe an intrinsic correlation peak of three-dimensional (3D) pattern recognition, which is higher than that of the two-dimensional (2D) pattern recognition and whose difference can reach up to five orders of magnitude in our numerical simulation. The relationship between the 3D objects and their recognition result is formalized and the comparison between the 3D and 2D pattern recognitions as well as the former's independency of the reconstruction distance is presented. Finally, the augmentation of the 3D pattern recognition sensitivity with the increasing surface complexity of the 3D object is also demonstrated.
Entropy and Entanglement of the Electromagnetically Induced Transparency System
LIU Xiao-Juan, , FANG Mao-Fa, ZHOU Qing-Ping,
Chin. Phys. Lett. 2004, 21 (6): 1071-1074 .  
Abstract   PDF(pc) (325KB) ( 413 )
We study the entropy and the entanglement of an electromagnetically induced transparency system. The quantum entanglement between the atom and the two quantized laser fields is discussed by using quantum reduced entropy and that between the two quantized laser fields by using quantum relative entropy. We also examine whether influences of EIT on entropy and quantum entanglement of the system considered occur or not. Our results show that the minimum value of the atomic reduced entropy may be regarded as an entropy criterion on the electromagnetically induced transparency occurring.

Four-Wave Mixing Scheme in a Four-Level Ladder-Type Atomic System Based on Electromagnetically Induced Transparency
LI Jia-Hua CHEN Ai-Xi, PENG Ju-Cun
Chin. Phys. Lett. 2004, 21 (6): 1075-1078 .  
Abstract   PDF(pc) (313KB) ( 502 )
A nonlinear optical four-wave mixing scheme is presented and analysed for the generation of coherent light in a nearly four-level ladder-type atomic system in the context of electromagnetically induced transparency (EIT). We find that EIT can suppress nonlinear photon absorption and the peak of the generated mixing field is located at the centre of the transparency window where the loss is minimal, though there is a dip in the centre. Such a nonlinear optical process can also be used for generating coherent short-wavelength radiation.
Gain Saturation Effects of a Flowing Chemical Oxygen-Iodine Laser
GAO Zhi, SHEN Yi-Qing, FAN An-Fu,
Chin. Phys. Lett. 2004, 21 (6): 1079-1082 .  
Abstract   PDF(pc) (294KB) ( 400 )
A new oxygen-iodine medium gain model is developed to include pumping and deactivation of the upper laser levels of the iodine atoms, hyperfine and translation relaxation, as well as the flowing effect. The rate equations for gain of a supersonic flowing cw oxygen-iodine laser (COIL) are described when the medium is stimulated by a single-mode field. The general solution of the self-consistency integral equation is obtained. The result shows that the saturation behaviour in low pressure of the COIL differs from both the inhomogeneous and homogeneous broadening, and exhibits an ‘anomalous’saturation phenomenon.

A 115-W Ytterbium-Doped Fibre Laser
ZHOU Jun, LOU Qi-Hong, KONG Ling-Feng, WU Zhong-Lin, XUE Dong, DONG Jing-Xing, WEI Yun-Rong, YE Zhen-Huan, ZHU Jian-Qiang, WANG Zhi-Jiang
Chin. Phys. Lett. 2004, 21 (6): 1083-1085 .  
Abstract   PDF(pc) (313KB) ( 767 )
We report a highly efficient ytterbium-doped double-clad fibre laser, one-end pumped by a 975-nm diode stack source and generating up to 115.6 W of cw output power at 1.1 μm. The maximum optical-to-optical conversion efficiency with respect to the launched pump power is 79% at 65-W output power, and the overall slope efficiency is about 69%.

Modulation Instability in Biased Photorefractive-Photovoltaic Crystals
LU Ke-Qing, ZHAO Wei, YANG Yan-Long, SUN Chuan-Dong, GAO Hong-Wen, LI Jin-Ping, ZHANG Yan-Peng
Chin. Phys. Lett. 2004, 21 (6): 1086-1088 .  
Abstract   PDF(pc) (294KB) ( 408 )
We show the modulation instability of broad optical beams in biased photorefractive-photovoltaic crystals under steady-state conditions. This modulation instability growth rate depends on the external bias field, the bulk photovoltaic effect, and the ratio of the optical beam intensity to that of the dark irradiance. Under appropriate conditions, this modulation instability growth rate is the modulation instability growth rate studied previously in biased photorefractive-nonphotovoltaic crystals, and the modulation instability growth rate in open- and closed-circuit photorefractive-photovoltaic crystals can be predicted.

Enhancement of Supercontinuum Spectrum Generation in a Dispersion-Decreasing Fibre with a Concave Dispersion Profile
XU Wen-Cheng, JIN Wei, XU Yong-Zhao, CUI Hu, LIU Song-Hao
Chin. Phys. Lett. 2004, 21 (6): 1089-1092 .  
Abstract   PDF(pc) (422KB) ( 380 )
A new approach is proposed to enhance supercontinuum (SC) spectrum generation in A dispersion-decreasing optical fibre with a new dispersion profile. The chromatic dispersion D(λ,z) is a concave function of wavelengths and has no zero-dispersion wavelengths over the whole or part of the fibre as D(λ,z) is positive. A flatter and much broader spectrum can be produced based on the scheme. The general criteria parameters are obtained for characterizing SC shapes in the optical fibres.

Supercontinuum Generation in a Photonic Crystal Fibre
YAN Pei-Guang, RUAN Shuang-Chen, LIN Hao-Jia, DU Chen-Lin, YU Yong-Qin, LU Ke-Cheng, YAO Jian-Quan
Chin. Phys. Lett. 2004, 21 (6): 1093-1095 .  
Abstract   PDF(pc) (378KB) ( 515 )
Nearly 1000-nm broad continuum from 390 nm to 1370 nm is generated in a 2-m long photonic crystal fibre. The maximum total power of supercontinuum is measured to be 60 mW with the pumping power of 800 mW output from a 200-fs Ti:sapphire laser. The evolution of the pumping light into supercontinuum is experimentally studied in detail. It is found that the mechanism for supercontinuum generation has direct relations with Raman effect and soliton effect, and the four-wave mixing plays an important role in the last phase of the supercontinuum generation.

Crystallization Kinetics of Amorphous In44Sb20Te36 Phase-Change Optical Recording Films on a Nanosecond Scale
ZHANG Xue-Ru, WUTTIG Mattias
Chin. Phys. Lett. 2004, 21 (6): 1096-1099 .  
Abstract   PDF(pc) (337KB) ( 542 )
We propose a simple method to investigate the crystallization kinetics of amorphous In44Sb20Te36 films on a nanosecond scale, based on local reflectivity measurements of the nanosecond laser-induced crystallization using a static tester. The pulse condition in terms of laser power and pulse width required for the onset of crystallization is established. Applying this pulse condition and Kissinger's analysis, an activation energy of 0.57 eV is estimated for the crystallization. This value deviates substantially from the activation energy determined at lower sample temperatures where crystallization proceeds in a time scale of seconds rather than nanoseconds.

A Broadband Geoacoustic Inversion Scheme
LI Zheng-Lin, ZHANG Ren-He
Chin. Phys. Lett. 2004, 21 (6): 1100-1103 .  
Abstract   PDF(pc) (498KB) ( 584 )
A geoacoustic inversion scheme, which combines several inversion methods together to invert for the bottom parameters, has been proposed based on the fact that the bottom acoustic parameters have different sensitivities to the different physical parameters of acoustic field. Firstly, the characteristic impedance of the bottom is inverted by measuring the vertical bottom reflective coefficients. Secondly, the derived bottom characteristic impedance is used as a constrained condition in another inversion procedure, which is very sensitive to the bottom sound speed but less sensitive to the attenuation, to inverse the bottom sound speed and bottom density. Lastly, the bottom attenuation can be estimated from methods such as transmission loss data, the vertical correlation of propagation data, and the normal mode attenuation. To obtain the characteristic impedance of the bottom accurately, vacuum glass spheres (VGS) are used as broadband sound sources, and a special mechanism is designed to trigger the VGS imploded at the preset depth. The inversion scheme has been successfully used for a set of sea experimental data. It shows that the inverted bottom parameters could distinguish the atlas marked bottom type quite well. The excellent comparison of the numerical results with the experimental data shows the validity of the inverted parameters.
Transportation Characteristics for a Class of Generalized N-Diffusion Equation with Convection
ZHENG Lian-Cun, ZHANG Xin-Xin, HE Ji-Cheng
Chin. Phys. Lett. 2004, 21 (6): 1104-1107 .  
Abstract   PDF(pc) (551KB) ( 345 )
A suitable similarity transformation group is used to reduce the power law parabolic partial equation to a class of singular nonlinear boundary value problems. Analytical solutions and numerical solutions both are presented for the specific power law index N, conductivity and convective functions, and the associated transportation characteristics are discussed in detail.

Sedimentation of a Single Charged Elliptic Cylinder in a Newtonian Fluid by Lattice Boltzmann Method
ZHANG Chao-Ying, SHI Juan, TAN Hui-Li, LIU Mu-Ren, KONG Ling-Jiang
Chin. Phys. Lett. 2004, 21 (6): 1108-1110 .  
Abstract   PDF(pc) (366KB) ( 524 )
We simulate the sedimentation of single charged and single uncharged elliptic cylinders in a Newtonian fluid by using the lattice Boltzmann method. Due to the polarizing effects and non-axial symmetry shape, there are the Coulomb force and corresponding torque exerted on the charged elliptic cylinder during the sedimentation, which significantly change the horizontal translation and rotation of the cylinder. When the dielectric constant of the liquid is smaller than that of the wall, the direction of the Coulomb force is opposite to that of the hydrodynamic force. Therefore there appears to be a critical linear charge density qc at which the elliptic cylinder will fall vertically off the centreline.
A New Low-Impedance High Power Microwave Source
HE Jun-Tao, ZHONG Hui-Huang, LIU Yong-Gui
Chin. Phys. Lett. 2004, 21 (6): 1111-1113 .  
Abstract   PDF(pc) (522KB) ( 445 )
We propose a new low-impedance high power microwave source based on the axial transit time effect, i.e. a low-impedance axial transit-time oscillator. The analysis and simulation are carried out to investigate the characteristics of this new configuration. In the numerical simulation, the microwave output peak power of 6 GW is obtained with an electron beam in the electron energy 580 keV and in the beam current 20 kA. The diode impedance is 29Ω. The power of the input electron beam is 11.6 GW. The beam-to-microwave power conversion efficiency is 51.7%. The frequency is 3.9 GHz by numerical simulation.

Shadow Effect and Its Revisal in Grid-Enhanced Plasma Source with Ion Implantation Method
ZHANG Gu-Ling, WANG Jiu-Li, LIU Yuan-Fu, LI Xue-Ming, WU Xing-Fang, FAN Song-Hua, LIU Chi-Zi, YANG Si-Ze
Chin. Phys. Lett. 2004, 21 (6): 1114-1116 .  
Abstract   PDF(pc) (390KB) ( 414 )
The implanting voltage, gas pressure and the grid electrode radius are the key parameters influencing the surface grid shadow effect that has been observed in our grid-enhanced plasma source ion implantation experiment. To reduce the shadow effect and obtain a corresponding better implantation uniformity of sample surfaces, we need to use lower implanting voltage, higher gas pressure and smaller grid radius. Furthermore, we apply an axial magnetic field to increase the plasma density inside the tube and to mix the plasma outside the grid, so that the shadow effect of sample surfaces can be weakened.

Molecular Dynamics for Elastic and Plastic Deformation of a Single-Walled Carbon Nanotube Under Nanoindentation
FANG Te-Hua, JIAN Sheng-Rui, CHUU Der-San
Chin. Phys. Lett. 2004, 21 (6): 1117-1119 .  
Abstract   PDF(pc) (355KB) ( 612 )
Mechanical characteristics of a suspended (10,10) single-walled carbon nanotube (SWCNT) during atomic force microscopy (AFM) nanoindentation are investigated at different temperatures by molecular dynamics simulations. The results indicate that the Young modulus of the (10,10) SWCNT under temperatures of 300-600 K is 1.2-1.3 TPa. As the temperature increases, the Young modulus of the SWCNT increases, but the axial strain of the SWCNT decreases. The strain-induced spontaneous formation of the Stone-Wales defects and the rippled behaviour under inhomogeneous stress are studied. The rippled behaviour of the SWCNT is enhanced with the increasing axial strain. The adhesive phenomenon between the probe and the nanotube and the elastic recovery of the nanotube during the retraction are also investigated.

Droplet Undercooling During Containerless Processing in a Drop Tube
WANG Nan, WEI Bing-Bo
Chin. Phys. Lett. 2004, 21 (6): 1120-1123 .  
Abstract   PDF(pc) (322KB) ( 1057 )
The droplet undercooling prior to crystallization during containerless processing in a drop tube is calculated on the basis of nucleation theory and processing parameters. The influences of droplet size, wetting angle, and cooling rate on undercooling are also evaluated under the situation of heterogeneous nucleation. An experimental study of containerless solidification is performed on Ag28.1Cu41.4Ge30.5 ternary alloy in comparison with the theoretical analysis. It is revealed that, in the case of heterogeneous catalysis, the droplet size is only an ostensible parameter to influence undercooling, whereas the wetting angle is the essentially dominating factor. The different cooling rates in such a case also have an effect on droplet undercooling, but this effect is not significant. The calculated results will agree well with the experimental data if the inverse relationship between wetting angle and droplet size is given.

Blue Upconversion Emission in Yb3+ and Tm3+ Codoped Lead-Germanate-Tellurite Glasses
YANG Zhong-Min, XU Shi-Qing, WEN Lei, JIANG Zhong-Hong
Chin. Phys. Lett. 2004, 21 (6): 1124-1127 .  
Abstract   PDF(pc) (352KB) ( 458 )
Intense blue and red upconversion emissions have been observed in Yb3+/Tm3+ co-doped 0.05 K2O-0.1ZnO-0.1BaO-0.2PbO-0.2GeO2-0.35TeO2 glasses under the pump of 976-nm laser diode. The dependence of the intensity of the upconversion emissions on the Tm3+ concentration has been studied in order to determine the ion concentration and the involved mechanism. The blue emission centred at 476 nm decreases and the 792-nm red emission increases with the increasing Tm3+ concentration. Subsequently, the dependence of upconversion emission intensity on the excitation power is investigated. It is found that the intensity ratio between the 792-nm red and 476-nm blue emissions decreases with the increasing pump energy.

Investigation of Microstructures of AlAs Oxides Before and After Oxidation
WANG Yong, JIA Hai-Qiang, MAI Zhen-Hong, JIA Quan-Jie, JIANG Xiao-Ming
Chin. Phys. Lett. 2004, 21 (6): 1128-1130 .  
Abstract   PDF(pc) (441KB) ( 410 )
The effect of lateral oxidation on microstructures of the GaAs/AlAs/GaAs heterostructure was studied by x-ray specular reflectivity, nonspecular scattering and diffraction. The GaAs/Al2O3/GaAs multilayer was obtained after oxidation of the GaAs/AlAs/GaAs sample. The results show that, before oxidation, there are two 40-Å-thick intermixing layers, one located between the AlAs sublayer and the GaAs substrate, and the other between the AlAs sublayer and the upper GaAs sublayer. After oxidation, these two intermixing sublayers disappear. The AlAs was oxidized into amorphous Al2O3 totally. The surface and interface roughnesses of the sample also decrease after oxidation.
V-F and V+K Aggregate Colour Centres: Origin of the Room-Temperature 350 nm Absorption Band in PbWO4
ZHANG Qi-Ren, LIU Ting-Yu, YAN Fei-Nan
Chin. Phys. Lett. 2004, 21 (6): 1131-1134 .  
Abstract   PDF(pc) (436KB) ( 359 )
A PbWO4 (PWO) single crystal has been grown by the advanced Bridgman method. The as-grown PWO crystal exhibits a weak band at 350 nm. This band was fitted into two overlapping bands peaking at 330 nm and 360 nm respectively. The absorption spectra of the as-grown crystal sample on un-polarized light and polarized light are measured respectively. The formation mechanism of colour centres in the as-grown PWO crystal is discussed and the 330 nm and 360 nm bands are ascribed to V-F and V+K centres respectively. The structure models of V-F and V+K centres are illustrated. The configuration terms, absorption transitions between the energy terms, the absorption spectral features on polarized light and the distributions of V-F and V+K centres in PWO are systematically studied.
Applications of Cubic MgZnO Thin Films in Metal-Insulator-Silicon Structures
LIANG Jun, WU Hui-Zhen, LAO Yan-Feng, QIU Dong-Jiang, CHEN Nai-Bo, XU Tian-Ning
Chin. Phys. Lett. 2004, 21 (6): 1135-1138 .  
Abstract   PDF(pc) (471KB) ( 1010 )
Cubic Mg0.55Zn0.45O thin film alloys have been deposited on Si substrates at low growth temperature. The topography of the cross section of the epitaxial film by scanning electronic microscope demonstrates good morphology and high interfacial quality. The high (001) orientation and wide band-gap (Eg > 5.5 eV) of the cubic Mg0.55Zn0.45O thin films accord with the guidelines for metal-insulator-silicon (MIS) device applications. Using the cubic ternary thin films as insulators, MIS structures have been fabricated. The capacitance-voltage measurements show the flat band voltage shift VFB of 11.8 V and mobile ion density Dmc of 5.57 x 1010cm-2 for the MIS structure. Leakage current density as low as ~ 10-7 A/cm2 is obtained at E = 700 kV/cm by the current-voltage measurements. These unique structural and electrical properties of the fabricated MIS devices indicate that cubic MgZnO materials could become a new candidate for high-k dielectrics used in silicon integrated circuit technologies.

Structural and Electrical Properties of Barium Strontium Titanate Thin Film on Conductive La1-xSrxMnO3 Bottom Layer
MIAO Jun, CHEN Wei-Ran, CHEN Bin, YANG Hao, PENG Wei, ZHONG Jian-Pin, WU Hao, YUAN Jie, XU Bo, QIU Xiang-Gang, CAO Li-Xin, ZHAO Bai-Ru
Chin. Phys. Lett. 2004, 21 (6): 1139-1142 .  
Abstract   PDF(pc) (573KB) ( 877 )
Ferroelectrics and colossal magnetoresistance heterostructure Ba1-xSrxTiO3(BST)/La1-xSrxMnO3 (LSMO) have been fabricated on a LaAlO3 substrate by the pulse laser deposition method. The dielectric measurements show that at room temperature and 100 kHz, the dielectric constant and loss tangent are about 990 and 0.012, respectively; the highest tunability is about 45 % near 200 K under the applied electric field of 200 kV/cm. Further study indicates that the leakage current for the BST/LSMO heterostructure obeys the Schottky emission mechanism in the electric field region higher than 100 kV/cm at room temperature.

Effect of Annealing Temperature on the Microstructure and Resistivity of Ge2Sb2Te5 Films
LIU Bo, SONG Zhi-Tang, FENG Song-Lin, CHEN Bomy
Chin. Phys. Lett. 2004, 21 (6): 1143-1146 .  
Abstract   PDF(pc) (351KB) ( 413 )
The effect of annealing temperature on crystallization of amorphous Ge2Sb2Te5 films with thickness of 40 nm is studied by TEM and AFM methods. The relationship between microstructure and resistivity of the Ge2Sb2Te5 film is investigated. From the TEM measurements, the grain size of crystallites increases gradually as the annealing temperature increases. When the annealing temperature is too high, voids are formed, which may originate from evaporation of the Ge2Sb2Te5 film at the elevated temperatures, formation of sink, being nucleated by residual vacancies, and surface roughness. The resistivity of the Ge2Sb2Te5 film decreases with the increasing annealing temperature and has slight changes when the temperature is higher than 400°C. Phase transitions and scattering of crystallite boundaries may be the major factors affecting the resistivity of the Ge2Sb2Te5 film.
Infrared-to-Visible Upconversion and 1.53-μm Emission of Er3+-Doped Al(PO3)3-Based Fluorophosphate Glass
LI Tao, ZHANG Qin-Yuan, LIU Yue-Hui, ZHANG Jun-Jie, DENG Zai-De, JIANG Zhong-Hong,
Chin. Phys. Lett. 2004, 21 (6): 1147-1149 .  
Abstract   PDF(pc) (418KB) ( 486 )
We investigate the spectroscopic properties of the 1.53-μm emission from the 4I13/24I15/2 transition of Er3+ ions in Al(PO3)3-based fluorophosphate glass for applications in broadband fibre amplifiers. The emission peak locates at ~1530 nm with a full width at half-maximum of ~65 nm. The measured lifetime and the calculated emission cross-section of this transition are ~8.1 ms and ~7.6 x 10-21cm2, respectively. Frequency upconversion to the 4F7/2 state occurs simultaneously upon excitation of the 1.53-μm emission with a 977-nm laser diode. Three infrared-to-visible upconversion emissions centred at around 524, 546 and 668 nm have been clearly observed. The quadratic dependence of fluorescence on excitation laser power confirms the fact that a two-photon process will contribute to the infrared-to-visible upconversion emissions.

A Novel Buffer Layer of Alq3 in Organic Electroluminescent Devices
ZHANG Zhi-Feng, DENG Zhen-Bo, LIANG Chun-Jun, LIN Peng, ZHANG Meng-Xin, XU Deng-Hui
Chin. Phys. Lett. 2004, 21 (6): 1150-1152 .  
Abstract   PDF(pc) (521KB) ( 502 )
Inserting the Alq3 layer in the ITO/NPB interface as the buffer layer can improve the organic electroluminescent devices. The current density efficiency and power efficiency of the device with the Alq3 buffer layer rises to 6.5 cd/A and 1.21 m/W at the current density of 120 mA/cm2, respectively. The improvement is mostly attributed to the balance of the hole and the electron injections.
Observation of Photovoltaic Effects in Bright Red Organic Electroluminescent Diodes Doped with Red Dopant
WEI Han-Zhi, LI Wen-Lian, WANG Dong-Yue, CHU Bei, LI Ming-Tao, ZHANG Zhi-Qiang, HU Zhi-Zhi
Chin. Phys. Lett. 2004, 21 (6): 1153-1156 .  
Abstract   PDF(pc) (359KB) ( 651 )
Photovoltaic (PV) effects for red bright organic light-emitting diodes (OLEDs) in which the red light emitted from the dopant 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) have been observed. The OLEDs show organic photovoltaic properties. At the optimum doping concentration, the main eletroluminescence parameters including the maximum brightness and the maximum luminous efficiency under current density of 20 mA/cm2 are 3280 cd/m2 and 1.54 cd/A, respectively. When irradiated by a 365-nm UV-light (4 mW/cm2), the device exhibits the PV parameters of the open-circuit voltage 1.4 V, short-circuit current 2.9 μA/cm2, fill factor 0.22, and power conversion efficiency 0.022%. Effects of every organic layer, especially the doped DCJTB on the PV performance, are also discussed. It is expected that the research for the PV property of the small molecular doping OLEDs will be of benefit for flat panel display technology in the future.

Terahertz-Induced Changes of Optical Spectra in GaAs Quantum Wells
MI Xian-Wu, CAO Jun-Cheng
Chin. Phys. Lett. 2004, 21 (6): 1157-1160 .  
Abstract   PDF(pc) (431KB) ( 525 )
We have theoretically investigated optical absorption spectra in GaAs quantum well (QW) driven by both a strong terahertz (THz) field and a near-infrared field within the theory of density matrix. In presence of a strong THz field, the optical transitions in the QW subbands are altered by the THz field. The alteration has a direct impact on the optical absorption and results in the Autler-Townes splitting and the sidebands generation, which is in agreement with the experiments.
Properties of Diamond Film/Alumina Composites for Integrated Circuits with Ultra-High Speed and High Power
WANG Lin-Jun, XIA Yi-Ben, FANG Zhi-Jun, ZHANG Ming-Long, SHEN Hu-Jiang
Chin. Phys. Lett. 2004, 21 (6): 1161-1163 .  
Abstract   PDF(pc) (328KB) ( 810 )
We report the properties of the diamond film/alumina composites which were thought of as promising substrate materials for integrated circuits with ultra-high speed and high power. The measurement results of dielectric properties of diamond film/alumina composites show that the coating of CVD diamond films could effectively reduce the dielectric constant of the composite. Carbon ion implantation into alumina substrates prior to the diamond deposition can reduce the dielectric loss of the composite from 5 x 10-3 to 2 x 10-3, and can give the composite better frequency stability. The thermal conductivity of composites could be obviously increased by coating CVD diamond film. The composite has a dielectric constant of 6.5 and a thermal conductivity of 3.98 W/(cmK) when the thickness of diamond film is up to 100 μm.
Nd3+, Yb3+ and Ho3+ Codoped Oxyfluoride Glass Ceramics with High Efficient Green Upconversion Luminescence
ZHANG Jun-Jie, KAWAMOTO Yoji, DAI Shi-Xun, ZHANG Li-Yan, HU Li-Li
Chin. Phys. Lett. 2004, 21 (6): 1164-1167 .  
Abstract   PDF(pc) (466KB) ( 585 )
New oxyfluoride glasses and glass ceramic codoped with Nd3+, Yb3+ and Ho3+ were prepared. The x-ray diffraction analysis revealed that the heat treatments of the oxyfluoride glasses could cause the precipitation of (Nd3+, Yb3+, Ho3+)-doped fluorite-type crystals. Very strong green up-conversion luminescence due to the Ho3+: (5F4, 5S2) → 5I8 transition under 800-nm excitation was observed in these transparent glass ceramics. The intensity of the green up-conversion luminescence in a 1-mol% YbF3-containing glass ceramic was found to be about 120 times stronger than that in the precursor oxyfluoride glass. The reason for the highly efficient Ho3+ up-conversion luminescence in the oxyfluoride glass ceramics is discussed.

Fast Growth of Polycrystalline Film in SiCl4/H2 Plasma
HUANG Rui, LIN Xuan-Ying, YU Yun-Peng, LIN Kui-Xun, WEI Jun-Hong, YU Chu-Ying, WANG Zhao-Kui
Chin. Phys. Lett. 2004, 21 (6): 1168-1170 .  
Abstract   PDF(pc) (413KB) ( 534 )
We report the discovery of fast growth of polycrystalline silicon films under low temperature of 200-300°C from SiCl4/H2 mixture gases by plasma enhanced chemical vapour deposition technique. The deposition rate strongly depends not only on the rf power and the flow ratio of H2/SiCl4, but also on the substrate temperature, while the crystalline fraction is mainly affected by both the rf power and the flow ratio of H2/SiCl4. The high film-growth rate is due to the enhancement of the gas-phase reaction in SiCl4/H2 plasma. By means of adjusting the matching relation between the flow ratio of H2/SiCl4 and rf power, and optimizing the substrate temperature, we obtain the polycrystalline silicon films deposited at a higher deposition rate over 3.5Å/s, with a crystalline fraction of 75% and an average crystallite size of 400-500 nm in diameter.

Effect of Ballistic-Type Hot Atom Adsorption Mechanism on the Phase Diagram of Monomer-Dimer CO-O2 Surface Catalytic Reaction: A Monte Carlo Simulation
M. Khalid, K. M. Khan, A. U. Qaisrani, Q. N. Malik
Chin. Phys. Lett. 2004, 21 (6): 1171-1174 .  
Abstract   PDF(pc) (347KB) ( 452 )
We investigate the effect of the ballistic mechanism on the phase diagram using a square surface. While using this mechanism whenever an O2 molecule hits a randomly vacant selected site, the molecule breaks up into atomic form and then executes a ballistic flight. The paths of the two oxygen atoms are taken exactly to be opposite to each other, i.e. anti-parallel, and the ranges of the atoms are taken to be equal, i.e.~they may fly up to 1 or 1.414 or 2 of the atomic spacing from the site of impact. Four cases have been studied on the basis of the range of hot atoms. The range of the hot oxygen atoms executing a ballistic flight might be up to the first nearest neighbourhood (1 atomic spacing from the site of impact), the second nearest neighbourhood (1.414 atomic spacing from the site of impact), the third nearest neighbourhood (2 atomic spacing from the site of impact), known as cases a, b, and c, respectively, while for case d the range of the oxygen atoms executing the ballistic flight might be up to 1 atomic spacing or 1.414 atomic spacing or 2 atomic spacing from the site of impact. The steady reactive window is observed and the continuous transition disappears. As soon as the CO partial pressure departs from zero, the production of CO2 is observed, which clearly verifies the experimental observation.

Effective Depletion Potential of Colloidal Spheres
LI Wei-Hua, MA Hong-Ru
Chin. Phys. Lett. 2004, 21 (6): 1175-1178 .  
Abstract   PDF(pc) (318KB) ( 407 )
A new semianalytical method, which is a combination of the density functional theory with Rosenfeld density functional and the Ornstein-Zernike equation, is proposed for the calculation of the effective depletion potentials between a pair of big spheres immersed in a small hard sphere fluid. The calculated results are almost identical to the integral equation method with the Percus-Yevick approximation, and are also in agreement well with the Monte Carlo simulation results.

Star Counts and Galactic Structure
DU Cui-Hua, ZHOU Xu, MA Jun, CHEN Jian-Sheng
Chin. Phys. Lett. 2004, 21 (6): 1179-1182 .  
Abstract   PDF(pc) (363KB) ( 303 )
We use a model of the Galactic stellar distribution to analyse the BATC star count data toward two high Galactic latitude fields. Since star counts at high Galactic latitudes are not strongly related to the radial distribution, they are very suitable for the study of the vertical distribution of the Galaxy. The vertical density distribution of the stars shows the contribution of the thin disc, the thick disc and the stellar halo of the Galaxy. We give quantitative descriptions of these components in terms of exponential discs and a de Vaucouleurs halo. We find that the observed counts support an axial ratio of c/a ~ 0.5, implying a more flattened halo. We consider that it is possible that the halo has two subpopulations, i.e. a flattened inner halo and a spherical outer halo in the Milky Way.

Dark Energy Coupled with Dark Matter in the Accelerating Universe
Chin. Phys. Lett. 2004, 21 (6): 1183-1186 .  
Abstract   PDF(pc) (249KB) ( 450 )
To model the observed Universe containing both dark energy and dark matter, we study the effective Yang- Mills condensate model of dark energy and add a non-relativistic matter component as the dark matter, which is generated out of the decaying dark energy at a constant rate Γ, a parameter of our model. For the Universe driven by these two components, the dynamic evolution still has asymptotic behaviour: the expansion of the Universe is accelerating with an asymptotically constant rate H, and the densities of both components approach to finite constant values. Moreover, ΩΛ 0.7 for dark energy and Ωm 0.3 for dark matter are achieved if the decay rate Γ is chosen such that Γ/H ~ 1.
A Possible Origin of Dark Energy
T. D. Lee
Chin. Phys. Lett. 2004, 21 (6): 1187-1188 .  
Abstract   PDF(pc) (157KB) ( 423 )
We discuss the possibility that the existence of dark energy may be due to the presence of a spin zero field Ф(x), either elementary or composite. In the presence of other matter field, the transformation Ф(x) → Ф(x) + constant can generate a negative pressure, like the cosmological constant. In this picture, our universe can be thought as a very large bag, similar to the much smaller MIT bag model for a single nucleon.

58 articles