Vol. 55, No. 1 (2006)
2006, 55 (1): 1-5. doi: 10.7498/aps.55.1
Part of results of research on satellite heat control under the Harvest Project of the National 973 Program is reported.In accordance with the “minimized nucleus” requirement of the satellite,the thermal conductivity of the dielectric FCC argon-crystal nano-film in the normal direction is predicted using the equilibrium molecular dynamic (EMD) and non-equilibrium molecular dynamic (NEMD) methods. The calculated results are compared with the experimental value of the bulk cryastal.Our calculation shows that the thermal conductivity of the thin films is much lower than that of its bulk conterpart,and the size-effect is significant;it increses nearly linearly with increasing thickness in the thickness range of 2.124—5.310nm.
2006, 55 (1): 6-9. doi: 10.7498/aps.55.6
A sea-air oscillator model of the nonlinear coupling system is studied.Using the variational iteration principle,a series of corresponding functional is constructed.Then the Lagrange operators are selected.Finally,using the generalized variational iteration method,the approximate sequences of a series of solutions for the sea-air oscillator model are obtained.
We present a field method for solving the Whittaker equations.One of the field variables is considered as a function of other variables and time,and the fundamental partial differential equation for the function is established.If the complete integral of the partial differential equation can be obtained,the solution of the Whittaker equations are obtained by solving the algebraic equations.
New exact solitary wave solutions for nonlinear wave equation with fifth-order strong nonlinear term constructed by hyperbolic function type of auxiliary equation
2006, 55 (1): 13-18. doi: 10.7498/aps.55.13
Based on the method of auxiliary equation,the paper uses two auxiliary equations with function-transformation and one auxiliary equation of hyperbolic function type to construct an important model in mechanics,which has solutions of new trigonometric function type of wave equation with fifth-order strong nonlinear term and the exact solitary wave solutions of hyperbolic function type, obtained via the symbolic calculation system of Mathematica.The method has general meanings in searching for other new exact solutions to the nonlinear evolution equation with fifth-order strong nonlinear term.
2006, 55 (1): 19-23. doi: 10.7498/aps.55.19
In this paper, we use the solution of the Fokker-Planck equation for non-degenerate parametric amplification to deduce the condition of demonstration of the EPR paradox. The numerical simulation shows that the optimum realization of EPR paradox can be achieved by adjusting the degree of squeezing, and this is the best condition for demonstrating the EPR paradox for a given finite loss k.
2006, 55 (1): 24-28. doi: 10.7498/aps.55.24
The polarization tracking principle is analyzed by using a half-wave plate in satellite quantum key distribution and the polarization “zero” direction can be corrected by rotation of the half-wave plate. The transforms of six photon polarization states in three conjugative bases are given and the quantum key coding principle based on the polarization tracking is analyzed for the BB84 protocol and B92 protocol.
2006, 55 (1): 29-34. doi: 10.7498/aps.55.29
In this paper, the nonlinear dynamical behaviors and bifurcation series of complex systems are studied. Numerical simulation and theoretical inference show that there are chaotic attractors in complex chaotic system which are sensitive to the initial states and are short of a boundary line.
2006, 55 (1): 35-41. doi: 10.7498/aps.55.35
This paper investigates the synchronization design for a class of chaotic systems with uncertainties in which all state variables are not measured. The design makes use of an observer with a controller. Assuming the boundedness of chaotic attractors and limited cycles, the approach, which is both global and not relying on complete knowledge of the systems involved, is rigorously proved by means of Lyapunov theory. Computer simulation results illustrate the validity of the method.
The multiplication of chaotic maps is analyzed theoretically in this paper. The result of our computer simulation shows that the new chaotic map, combined by several chaotic maps, still has chaos attractors and is sensitive to the initial states.The concept of multiplication of chaotic maps is important in theory and applications.
2006, 55 (1): 47-53. doi: 10.7498/aps.55.47
This article reports a crisis in a system described by a concatenation of a conservative and a dissipative mapping. The special feature of the crisis lies in its special escaping hole. A fat fractal forbidden net, induced by interaction between discontinuous and noninvertible properties, introduces rippled-like attraction basins of two periodic attractors, which appear after the crisis when a chaotic attractor suddenly loses stability. There are small areas, which serve as escaping holes and are dominated by strong dissipation as well as confined by the boundary of forbidden region only in the vicinity of each periodic point. To our knowledge, the crisis has not been reported before.
2006, 55 (1): 54-59. doi: 10.7498/aps.55.54
Recent investigation has shown that the permanent magnet synchronous motor(PMSM) may have chaotic behaviors for cortain values of parameters or under certain working conditions,which threatens the secure and stable operation of motor-driven.Hence,it is important to study methods of controlling or suppressing chaos in PMSM.Using the exact linearization theory of differential geometry,a law of controlling chaos in PMSM is deduced in this paper, and then,the process of controlling is simulated and analyzed.Theoretical analysis and simulation results show that the deduced control law is effective and its control property is better than that of other methods.Our results may help to maintain the system's secure operation.
2006, 55 (1): 60-67. doi: 10.7498/aps.55.60
This paper discusses the degree distribution of a type of social networks and some technological networks with similar topological structures. Firstly, we propose a most simplified model and try to show analytically that the degree distribution and the act degree distribution are well consistent, but the distribution of the number of the nodes inside an act have much smaller influence on the degree distribution. Secondly, we perform numerical simulations in a more general situation of the model, so as to show that the above mentioned conclusion is rather universal. This model leads to a conclusion that these generalized collaboration networks usually have a degree distribution between the power law and the exponential function. In the last part of the article, we introduce very briefly the results of the empirical statistical investigation on some practical collaboration networks to show that the model is valid for generalized collaboration networks.
2006, 55 (1): 68-75. doi: 10.7498/aps.55.68
In this paper the time characteristics of soft X-ray diode (XRD) is studied. XRD is the importance component of soft X-ray spectrometer,which measures the soft X-ray spectrum emited by laser-plasma.The experiment utilizes the 200TW laser facility with energy ～6J and pulse width ～30fs at the Laser Fusion Research Center of CAEP.The Au foil target irradiated by laser pulse produced X-ray emission, the filter(Al)-XRD system measures the X-ray signal.The high frequency cable (SUJ-50) transmits the electrical signal, a broad band oscillograph (TDS694C and TDS6604B) registers the signal.Linearity fit and comparison analysis of experimental data are performed.
The density ρ and surface tension γ of lithium tetraborate melt have been systematically measured from 1100K up to about 1500K.The experimental results indicate that the melt density and surface tension decreased linearly with increasing temperature.The relationship of Li2Ｏ-２Ｂ２Ｏ３ melt density with temperature is ρ(T)=2.574-4.89×１０－４T.The density of Li2Ｏ-２Ｂ２Ｏ３ melt is 1.992g/cm3 at melting point.The temperature dependence of the surface tension of Li2Ｏ-２Ｂ２Ｏ３ melt is γ=262.8-4.59×10-2T.
2006, 55 (1): 80-83. doi: 10.7498/aps.55.80
Applicable nano metric titanium-titanium oxide line-titanium tunneling junction was fabricated with dual-facing target sputtering,micro-electronic optical lithography and atomic force microscope anodic oxidation.The thickness of titanium film of the fabricated junction was 3nm and the width of the titanium oxide line was 60.5nm.The I-V curve of the tunneling junction at room temperature clearly indicates the Coulomb blockade effect.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2006, 55 (1): 84-90. doi: 10.7498/aps.55.84
In the framework of the finite temperature Brueckner-Hartree-Fock approach including the contribution of the microscopic three-body force, the single nuclear potential and the nucleon effective mass in hot nuclear matter at various temperatures and densities have been calculated by using the hole-line expansion for mass operator, and the effects of the three-body forces and the ground state correlations on the single nucleon potential have been investigated. It is shown that both the ground state correlations and the three-body force affect considerably the density and temperature dependence of the single nucleon potential. The rearrangement correction in the single nucleon potential is repulsive and it reduces remarkably the attraction of the single nucleon potential in the low-momentum region. The rearrangement contribution due to the ground state correlations becomes smaller as the temperature rises up and becomes larger as the density increases. The effect of the three-body force on the ground state correlations is to reduce the contribution of rearrangement. At high densities, the single nucleon potential containing both the rearrangement correction and the contribution of the three-body force becomes more repulsive as the temperature increases.
Entrance channel effects on the role of isospin-dependent momentum interaction in isospin fractionation in heavy ion collisions
2006, 55 (1): 91-97. doi: 10.7498/aps.55.91
An isospin degree of freedom is inserted into the momentum dependent interaction in the quantum molecular dynamics model to obtain an isospin dependent momentum interaction given in a form practically usable in isospin dependent quantum molecular dynamics model. We investigate the entrance channel effects for the role of isospin momentum dependent interaction on the isospin fractionation ratio and its dynamical mechanism in the intermediate energy heavy ion collisions. It is found that the isospin dependent momentum interaction induces a significant reduction of isospin fractionation ratio under all entrance channel conditions. However the strong dependence of isospin fractionation ratio on the symmetry potential is preserved after considering the isospin degree of freedom in the momentum dependent interaction.
2006, 55 (1): 98-101. doi: 10.7498/aps.55.98
Using high-deposition-pressure technique, high-quality microcrystalline silicon film was prepared by radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) combined with rapid thermal treatment. The volume fractions of the amorphous and microcrystalline phases and optical properties of microcrystalline silicon were carefully studied by Raman spectra, reflectance spectra and transmittance spectra. The results show a red shift of the absorption edge of microcrystalline silicon, which can be due to the increase in the volume fractions of the amorphous and microcrystalline phase and decrease in the band tail states.
ATOMIC AND MOLECULAR PHYSICS
2006, 55 (1): 102-106. doi: 10.7498/aps.55.102
Structure and properties of the ground states and low-lying excited electronic states of CH, NH and OH radicals are reported in this paper using CCSD(T) method and aug-cc-pVTZ basis set.Their analytic potential energy functions are in good agreement with the Murrell-Sorbie function, and the ground states are X2Π for CH, X3Σ- for NH and X2Π for OH radicals, and the adiabatic excitation energies of a4Σ- and 6Σ- for CH, a1Δ and 5Σ- for NH, a4Σ- and 6Σ- for OH are 0.705, 7.669, 1.895, 3.492, 4.535 and 14.041eV, respectively.
Theoretical studies of dielectronic recombination and resonant transfer excitation for highly ionized Cu18+ ions
2006, 55 (1): 107-111. doi: 10.7498/aps.55.107
The dielectronic recombination cross sections of Cu18+ ions are calculated using a quasi-relativistic theory. The effects of configuration interaction to the cross sections are analysed. Base on the calculated data, the resonant transfer excitation cross sections of Cu18+ with H2 targets are estimated by using the convolution of Compton profile of the target electron in the impulse approximation. Good agreement of the present calculation with new experimental observation is achieved.
2006, 55 (1): 112-118. doi: 10.7498/aps.55.112
Based on the multiconfiguration Dirac-Fock method, a new program was developed for the calculation of cross sections of dielectronic recombination (DR). As an example, the decay rates and the corresponding DR cross sections have been systematically calculated for the doubly excited state 1s2l2l′ of C3+, Ar15+, Kr33+ and U89+ ions. For C4+, Ar16+ and Kr34+ ions, a good agreement has been found between the present calculations and the previous theoretical and experimental results; for U90+ ion, the effect of the Breit interation on the DR cross sections has been emphasized especially.
High efficiency organic red electrophosphorescence devices with changing thickness of the emitting layer
2006, 55 (1): 119-124. doi: 10.7498/aps.55.119
Devices using red phosphorescent dye as dopant with exciton blocking layer were constructed. The device structure is ITO/CuPc/NPB/TPBi:Btp2Ir(acac)/TPBi/Alq/LiF/Al. The EL spectra, luminance-current, efficiency-current characteristics of the device have been investigated. At the CIE coordinates x=0.62，y=0.35，efficiency 2.43cd /A has been achieved. At 20mA/cm2 and 400mA/cm2, luminance is 431cd/m2 and 4798 cd/m2, respectively. The effects of the emitting layer thickness on efficiency and EL spectra of the device have been studied also. With the decrease of the emitting layer thickness, efficiency decreases and the blue band of the El spectra increases. For the thickness d2Ir(acac) HOMO energy level. For the thickness d>20nm, the decrease of the efficiency is attributed to the added invalid emitting-layer and more annihilation centers.
2006, 55 (1): 125-129. doi: 10.7498/aps.55.125
Our study indicates that the number of trapped Rb atoms in a magneto-optical trap (MOT) strongly depends on the trapping laser intensity and detuning, the repumping laser intensity and the magnetic gradient. We estimate the trapped-atom numbers changing with the trapping laser intensity and detuning, using a two-level system model. The theoretical results are in qualitative agreement with the experimental results. The experimental results also show an obvious dependence of the trapped-atom numbers on repumping laser intensity and the magnetic gradient, which the simple theory cannot account for. These studies are helpful for selecting suitable experimental parameters to achieve larger numbers of cold atoms.
Theoretical analysis of evanescent-wave atomic (molecular) guide using a bundle of four single-mode optical fibers
2006, 55 (1): 130-136. doi: 10.7498/aps.55.130
In this paper, we propose a new scheme to guide cold atoms (or cold molecules) using a bundle of four single-mode optical fibers with a sub-micrometer size, and calculate the evanescent-wave field in the hollow region of four-fiber bundle and its optical potential for 85Rb atoms. Our study shows that such a blue-detuned hollow evanescent-wave field can also be used to realize the laser waveguide of cold atoms (or cold molecules), and, compared with the traditional atomic guiding scheme using a hollow optical fiber, our scheme is not only simple and cheap, but also easier to realize the single-mode waveguide of cold atomic matter-wave with high efficiency.
2006, 55 (1): 137-141. doi: 10.7498/aps.55.137
The photoionization and photodissociation processes of C2Cl4 were investigated under the supersonic molecular beam conditions by using a reflectron-time-of-flight mass spectrometer (TOF-MS) and vacuum ultraviolet (VUV) photons from synchrotron radiation source. The photoionization mass spectrum and the photoionization efficiency (PIE) curves of the parent ion and some fragment ions were measured. The appearance potentials of these ions are obtained from their PIE curves. The formation enthalpies of some major ions and the dissociation energy of C2Cl4 have been evaluated from these data. According to the experimental results and the energy calculated by G1 theory, the main possible channels of dissociative photoionization of C2Cl4 have been discussed. In the future, we can detect C2Cl4 with single photon ionization(SPI)-TOFMS technique using 118.0nm laser radiation. This is based on the mass spectrum obtained at the wavelenth by using synchrotron radiation source.
2006, 55 (1): 142-147. doi: 10.7498/aps.55.142
First principles calculations have been used to study the various surface reconstructions, local density of states of surface atoms, and the local magnetic moments of the Mn constituents in Mn/GaAs(001) surface. It is found that the Mn atoms will act as donors and donate as many electrons as required by the GaAs surface. The local magnetic moment of Mn being an important factor in surface magnetic properties can be deduced directly from the reconstruction by electron counting.
2006, 55 (1): 148-154. doi: 10.7498/aps.55.148
Electron beam lithography has high sensitivity since it is free from limitation from diffraction effect. It will be the mostcommon technique of the next generation lithography to replace the conventional optical lithography. The proximity effect is the most important limitation of the sensitivity of lithography,which is simulated with Monte Carlo method in this paper.The influence on proximity effect of the shape and energy of electron beam and the material and depth of substrate is analyzed. The simulation results are compared with the experimental data and are found to fit well. It is found that, the proximity effect shown by Gaussian shaped electron beam is much larger than that by ideal electron beam, and lager atomic number, thicker substrate and lower energy of the electron beam will cause lager proximity effect independently.
By combining the self-consistent field theory for polymers with the Helfrich elasticity theory of membrane, the polymer anchored infinite membrane is investigated. Both the density distribution of the polymer and deformation of the membrane are obtained. Close to the anchoring site,the membrane has the conical shape and bends away from the polymer due to the membrane's impenetrability to the polymer and the confined space for the polymer, which is consistent with previous theoretical results and Monte Carlo simulations. Moreover, the interaction between the membrane and polymer chain length, and the effects of bending rigidity and surface tension on the deformation of the membrane are investigated.
Optimum valence bond scheme: theoretical study of small clusters of elements in the second and third row of periodic table
2006, 55 (1): 162-170. doi: 10.7498/aps.55.162
Using optimum valence bond scheme which reduces the computation effort, we study systematically the properties of the critical structures (critical points) of small clusters (up to four atoms) of elements in the second and third row of the periodic table. We also show the evolution process of the clusters from two atoms to four atoms. By examining the electronic structures of all clusters, we can understand why the four-atom clusters for specific elements can have three-dimensional structures with Td symmetry. More interestingly, comparing the variation of the binding energy of such small clusters with the melting points and boiling points of corresponding pure element materials, we can understand the effect of the critical structures in the melting and boiling processes.
2006, 55 (1): 171-178. doi: 10.7498/aps.55.171
Possible geometrical structures and relative stability of MgmBn(m=1,2;n=1—4) clusters are studied by using the hybrid density functional theory(B3LYP) with 6-31G basis sets. For the most stable isomers of MgmBn(m=1,2;n=1—4) clusters, the electronic structure, vibrational properties, bond properties, ionization potential, polarizability and hyperpolarizability are analyzed. The calculated results show that most of the optimized MgmBn(m=1,2;n=1—4) clusters have planar structure, the B-B and B-Mg bonds are coexisting in the cluster, but the Mg-Mg bonds are infrequent in the clusters. The bond length of B-B is about 0.153—0.182nm and that of Mg-B is 0.221—0.231nm. The outcome of population analysis suggests that there is an electronegative center in the cluster, the other B and Mg atoms with positive charge are located at apexes of the cluster.
CLASSICAL AREA OF PHENOMENOLOGY
Negative effective refraction index in guided wave mode for periodic layered ferrite-dielectric/metallic film composites
2006, 55 (1): 179-183. doi: 10.7498/aps.55.179
We have studied the effective refraction index of the guided wave mode in periodic layered ferrite-dielectric/metal film composites. Using the equivalent transmission line approach we have analyzed and calculated the dispersion characters and then the effective refraction index of the composites. We have found that the effective refraction index of the composites will be negative within a certain frequencies only when the wave is in TE mode. The loss of the composite is closely related to the dielectric layers, which can be effectively reduced by decrease the dielectric loss. However, too small dielectric loss results in disappearing of the negative refraction index.
Experimental investigation of phase detection and compensation in coherent combining of fiber laser array
2006, 55 (1): 184-187. doi: 10.7498/aps.55.184
Recently, the coherent combining of high power fiber laser array has become a hotspot of research internationally, and the phase control electronics contributed greatly to the success of the coherent combining. A high-speed wavefront sensor is introduced to sample the wavefront and actively control the phase state of each individual optical fiber in a high average power fiber laser array,and accordingly the phase-locked output of the whole system is achieved.A single signal lightwave is taken as example in the paper,the research results are presented.We conclude from the research results that when closing the phase control feedback loop the phasefront can be locked to the quiescent state of phase.
2006, 55 (1): 188-191. doi: 10.7498/aps.55.188
The effect of number of unit cells of the fcc photonic crystals on the property of the band gaps was investigated experimentally. Fcc photonic crystals with different numbers of cells were fabricated by using recording materials of different thickness in holography. Their transmitted spectra of the band gaps were measured. A guiding rule was given: a photonic crystal which can be practically used should have 50 unit cells at least.
2006, 55 (1): 192-196. doi: 10.7498/aps.55.192
We study the nonclassical feature of the field in the two-atom Tavis-Cummings model with atomic motion using the quantum theory. The influence of atomic motion, the field mode structure and the field initial states on the properties of the light squeezing and the photon antibunching are discussed.
2006, 55 (1): 197-201. doi: 10.7498/aps.55.197
Based on the kinetic process of UV Cu+ laser in longitudinal nanosecond-pulsed discharge, the necessary condition for the population inversion between the upper and lower laser levels has been obtained. The experimental phenomenon that the laser power increases rapidly with the decrease of the discharge tube aperture has been analyzed theoretically. It is pointed out that the radiation trapping of lower laser level could be restrained effectively by reducing the tube radius, resulting in the increase of depopulation rate of lower laser level and the laser power.
Influence of cataphoresis on metal vapor distribution in high repetition rate pulsed discharge metal vapor lasers
2006, 55 (1): 202-205. doi: 10.7498/aps.55.202
A theoretic model has been established to describe the cataphoresis dynamics in high repetition rate (HRR) pulsed discharge metal vapor lasers (MVLs). The analytic solutions for transient and steady-state diffusion equations of metal vapor concentration are obtained. The axial distribution processes of metal vapors in HRR pulsed discharge He-Sr+ and He-Cd+ lasers have been calculated. It shows that the axial metal vapor distribution between the metal source and the cathode reaches sufficient homogeneity in about 2s, thus ensuring the stable output characteristics of cataphoresis MVLs.
2006, 55 (1): 206-210. doi: 10.7498/aps.55.206
It is reported that fluorescent microtubules may break under irradiation. However, the process and mechanism are not well understood. In this paper, we study the process of light-induced microtubule breaking by optical tweezers and find the breakup of protofilaments in microtubule is not simultaneous but proceeds step-by-step. After a series of biological experiments, we confirm that free radicals are the main reason for the photosensitive breaking of microtubule. According to the results of optical tweezers experiments, the mechanism of free radicals acting on microtubule is infered.
2006, 55 (1): 211-216. doi: 10.7498/aps.55.211
Ultra-short optical pulse source is one of key components in optical time-division multiplexing(OTDM) system. In this paper, a wavelength and repetition rato tunable actively mode-locked fiber ring laser based on cross-gain modulation in a reflective Semiconductor Optical Amplifier(SOA) is demonstrated. Theoretical model for this scheme is also established and output characteristics are calculated. Stable picosecond pulse trains with high extinction ratio at 10—40 GHz repetition rato are obtained. 30nm wavelength tuning range is also achieved in our proposed actively mode-locked laser.
2006, 55 (1): 217-220. doi: 10.7498/aps.55.217
Single-shot damage morphology of magnesium fluoride induced by femtosecond laser pulse was studied with scanning electron microscope (SEM). The laser pulses used were 800 nm central wavelength. By the linear relationship between the area of damage spot and the logarithm of the laser energy, we measured the dependence of damage threshold on the pulse duration ranging from 55 femtosecond (fs) to 750 fs. We have calculated the two-photon absorption in the conduction band and improved the multiple-equation model (Phys. Rev. Lett. 92 187401, 2004). The experimental results are well explained by our model.
Observation of Rydberg series of neutral barium by two-photon resonent nondegenerate four-wave mixing
2006, 55 (1): 221-225. doi: 10.7498/aps.55.221
We have applied two-photon resonant nondegenerate four-wave mixing (NFWM) with a resonant intermediate state to measure the energy levels of the Ba even-parity J=0 and J=2 series. Differing from other experiment techniques, our method is a pure optical technique. Instead of detecting electrons or ions, the signal here is a coherent light. Two-photon resonant NFWM is a Doppler-free spectroscopy when the incident laser beams have narrow bandwidths.
2006, 55 (1): 226-229. doi: 10.7498/aps.55.226
A new design of metamaterials of one dimensional periodic structure is presented in this paper and the transmission parameters are measured. The experiment results indicate that when the bias voltage rises the left-hand passband will move toward higher frequencies. Based on transmission line theory, the dispersive equation of the tunable metamaterials is given. The results of the theory agree very well with those of the experiments.
Theoretical analysis of optimum parameters for complete forbidden bands of three-dimensional photonic crystals with typical lattice structures
2006, 55 (1): 230-237. doi: 10.7498/aps.55.230
Based on plane wave expansion method, the influence of factors such as lattice structure, dielectric constant ratio and filling ratio on three-dimensional photonic crystals with fcc, diamond and woodpile structures is studied. Of these structures, the fcc structure, owing to its high symmetry, is only fit for close-packed lattice prepared by inverted-opal method. The diamond structure easily generates good complete band gaps with high band gap ratio, and also the complete forbidden band that is needed can be obtained by adjusting some parameters in the experiment. The woodpile structure can produce big band gaps in a wider parameter range than the other two structures, which offers convenience for preparing three-dimensional photonic crystals in the laboratory. For all three kinds of three-dimensional photonic crystal structures, their band gap width and band gap ratio can be improved with the increase of dielectric constant ratio. In this paper, some interesting phenomena not noticed in the former papers are also presented.
Numerical simulation of square-lattice photonic crystal fiber with high birefringence and low confinement loss
2006, 55 (1): 238-243. doi: 10.7498/aps.55.238
In this paper a square-lattice photonic crystal fiber with gradually increasing air-holes in a silica matrix has been put forward for the first time. The model field, dispersion, birefringence and confinement loss of the fibre fundamental mode are simulated by multipole method. It is found that low confinement loss can be realized under condition of fewer rings of air holes. Simulation shows that birefringence and dispersion of this square-lattice PCF are dominated by inner-ring air holes in the fibre. The simulation results of this paper are highly instructive for the fabrication of birefringent photonic crystal fibers.
2006, 55 (1): 244-248. doi: 10.7498/aps.55.244
A novel spectral phase interferometry reconstruction for ultrashort optical pulse measurement with high accuracy is presented to overcome the shortcomes of conventional SPIDER. The measured pulse and its two chirped and delayed replicas are mixed synchronously to generate a fringe-free interference pattern. By introducing a suitable small delay into the interference pattern the spectral phase of the measured pulse is retrieved directly and uniquely without using Fourier transformation. This technique is capable of characterizing pulses with long duration or/and complex phase structure.
2006, 55 (1): 249-253. doi: 10.7498/aps.55.249
A high sensitivity fiber-optic torsion sensor is described,which measures twist rate and determines twist direction simultaneously by using a novel ultra long-period fiber grating (ULPFG) with periods of up to several millimeters fabricated by high frequency CO2 laser pulses. The torsion characteristics of a ULPFG are analyzed based on the coupling theory and birefringence phenomena. The experimental results show that a higher torsion sensitivity of 0.2244nm/(rad/m) for high order resonant modes was obtained, which is four times higher than that of the long-period fiber grating written by high frequency CO2 laser pulses. Finally, an intensity-type demodulation approach for the realization of real-time torsion measurement is proposed and demonstrated based on the edge filtering effect of the ULPFG.
Quasi-vectorial analysis of the optical characteristics of rib waveguides and directional couplers based on InGaAs/InAlAs multiple quantum wells
2006, 55 (1): 254-260. doi: 10.7498/aps.55.254
A new three-dimensional quasi-vectorial beam propagation method based on the series expansion (SE-QV-BPM) is proposed for simulating the optical rib waveguide and directional coupler based on InGaAs/InAlAs multiple quantum wells. For the same etched-depth, the confinement of TM mode in horizontal direction is shown to be stronger than that of TE mode, and the singular behaviors for TM modes at the corners are clearly observed. For the same gap width, the coupling length of TM mode for directional coupler is larger than that of TE mode. The effective indices and modal profiles of the quasi-vectorial fundamental TE and TM modes for shallow- and deep-etched rib waveguides and directional couplers are obtained. Besides, the evolution of the injected field with propagation distance through the directional coupler is demonstrated. The calculation has good efficiency due to the small size of the resulting matrix, and the rib structures can be conveniently dealt with since the sinusoidal functions are selected as the basis functions. Moreover, the variable transformation is introduced to avoid the boundary truncation.
10 GHz optical short pulse generation using tandem electroabsorption modulators monolithically integrated with distributed feedback laser by ultra-low-pressure selective area growth
2006, 55 (1): 261-266. doi: 10.7498/aps.55.261
In this work, a novel light source of tandem InGaAsP/InGaAsP multiple quantum well electroabsoption modulator(EAM) monolithically integrated with distributed feedback laser is fabricated by ultra-low-pressure (22×１０２Pa) selective area growth metal-organic chemical vapor diposition technique. Superior device performances have been obtained, such as low threshold current of 19 mA, output light power of 4.5 mW, and over 20 dB extinction ratio at 5 V applied voltage when coupled into a single mode fiber. Over 10 GHz 3dB bandwidth in EAM part is developed with a driving voltage of 2 V. Using this sinusoidal voltage driven integrated device, 10GHz repetition rate pulse with an actual width of 13.7 ps without any compression elements is obtained due to the gate operation effect of tandem EAMs.
Formulation of the acoustically-induced electromagnetic field in a porous formation in terms of Hertz vectors and simulation of the borehole electromagnetic field excited by an acoustic multipole source
2006, 55 (1): 267-274. doi: 10.7498/aps.55.267
The electromagnetic field induced by acoustic waves in a porous formation is investigated. By supposing the acoustic field is not influenced by its induced electromagnetic field, the governing equations for the coupled acoustic and electromagnetic fields are reduced to a set of Maxwell equations with a propagation current source. The Maxwell equations are then transformed into inhomogeneous vector Helmholtz equations by introducing Hertz vectors. Finally the electromagnetic field is formulated in terms of the solutions to the Helmholtz equations. This method is used to evaluate the electromagnetic field during seismoelectric logging in a porous formation. The full waveforms of the acoustic field and the electromagnetic field in the borehole are calculated when the borehole acoustic sources are respectively a monopole, a dipole and a quadrupole.
2006, 55 (1): 275-280. doi: 10.7498/aps.55.275
A genetic algorithm (GA) with adaptive crossover and mutation probability is developed to design a two-dimensional phononic crystal of a square lattice with maximal absolute band gap. The composites of Pb cylinders in epoxy matrix are studied with GA method connection with plane-wave expansion approach. We find that GA method is effective to find out excellent topology of unit cell with a widest absolute band gap.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2006, 55 (1): 281-286. doi: 10.7498/aps.55.281
To meet the requirement of plasma shape control running mode on experimental advanced superconducting tokamak(EAST), this paper studies the quick identification algorithm of plasma discharge shape and gives the results of reconstruction simulation. Moreover, the code is checked by the equilibrium reconstruction code EFIT provided by GA in U.S.A. Results show that we can identify the shape quickly by using external magnetic measurements and appropriate current profile in conjunction with real time equilibrium reconstruction algorithm.
2006, 55 (1): 287-293. doi: 10.7498/aps.55.287
The thickness of target for X-ray sources with approximate Planck's spectral distribution from laser-produced plasmas is optimized using a one-dimensional radiation hydrodynamics code MULTI. The effect of X-ray radiation field with Planck's distribution on the processes of excitation and ionization in a plasma is stadied using a non-LTE ionized material package NIMP. These results are very important in the future experimental design to study the influence of X-ray emission from accretion disks on interstellar matter.
2006, 55 (1): 294-298. doi: 10.7498/aps.55.294
The transport of runaway electrons in hot plasma can be comparatively easily measured by steady state or perturbation experiments, which provide runaway electron diffusivity Dr. The runaway diffusion coefficient has been obtained using four methods: (1) Dr is deduced from Plasma shift experiment; (2) Dr is deduced from its sawteeth oscillations behaviors of HXR flux and of SXR intensity; (3) Dr is deduced from microwave radiation intensity sawtoothing behaviors; (4) Dr is deduced from hard-X-ray bremsstrahlung spectra. The diffusivity can be interpreted in terms of a magnetic fluctuation level. The internal magnetic fluctuations level (b～r/BT) is estimated to be about (2—4)×10-4 in the HL-1M plasma. The results presented here demonstrate the effectiveness of using runaway transport techniques for determining internal magnetic fluctuations. A profile of the magnetic fluctuation level in the HL-1M can be estimated from Dr.
2006, 55 (1): 299-303. doi: 10.7498/aps.55.299
A plasma channel up to 80 Rayleigh lengths is formed when intense femtosecond laser pulses propagate in air. Two methods, fluorescence measurement and acoustic diagnostics, are used to probe the plasma channel simultaneously. Both methods reveal the evolution of the channel in detail. Compared with the fluorescence measurement, the acoustic method is a convenient approach having higher sensitivity and higher spatial resolution in detecting long plasma channels.
2006, 55 (1): 304-309. doi: 10.7498/aps.55.304
The laser light propagation inside the conical target has been studied by three-dimensional particle-in-cell simulations. It is found that the existence of under-dense plasma significantly affects the light propagation and the generation of relativistic electrons. The laser light can be focused at the tip of the cone and the intensity increases up to tens of times in the focal spot. With the under-dense plasma the laser light focused intensity is decreased. The existence of under-dense plasmas favors the relativistic electron generation in the laser conical target interaction in enhancing the number and energy of relativistic electrons.
2006, 55 (1): 310-320. doi: 10.7498/aps.55.310
Effects of plasma density distributions on self-focusing of intense laser pulses propagating in an underdense cold plasma are investigated, where the laser intensity has a Gaussian distribution and the initial plasma density is cylindrical-symmetrically distributed. An evaluation function is derived to judge which type of plasma density distribution is more beneficial for the occurrence of self-focusing. Through analyzing and calculating the evaluation function, it is found that for a given laser field and with fixed initial plasma density along the central axis, which coincides with the axis of the laser beam, increasing plasma density with the distance from the axis favors self-focusing. Furthermore, the greater the density gradient, the more favorable. It is also found that the combined action of both relativistic and ponderomotive effects is of more advantage to self-focusing than that of relativistic effect alone. Numerical simulation confirms that the evaluation function is capable of accurately predicting the favorable role of plasma density distribution in producing laser self-focusing.
2006, 55 (1): 321-325. doi: 10.7498/aps.55.321
Gyrotron traveling wave amplifier is a very important high power millimeter wave source for radar applications. By studying the absolute instability, the gyrotron backward wave oscillation and the interaction between the electron beam and wave, the stability of amplifier and the suppression of spurious oscillations are discussed. The simulation results of W-band TE01 gyrotron traveling wave amplifier are given. The PIC simulation results show that this amplifier can generate 250kW at 94GHz with 28% efficiency and 50dB gain and 5% bandwidth at 100kV,10A electron beam input.
2006, 55 (1): 326-330. doi: 10.7498/aps.55.326
The plasmas generated in the laser interacting with targets can be used as a new propulsive source. In this paper, the effects of the target configuration on the laser plasma momentum-coupling coefficient are investigated. Results show that, compared with planar targets, the momentum-coupling coefficient is enhanced five times by the cavity target, and over ten times for the confined planar target. It is found that effectively confined plasma expansion is the main reason for the enhancement of the momentum-coupling coefficient.
2006, 55 (1): 331-336. doi: 10.7498/aps.55.331
In a multi-pin to multi-sphere plane DC negative corona discharge configuration at atmospheric pressure, stable and diffuse glow discharge has been obtained. The effect of the air flow velocity, the gap distance and the electrode structure on the discharge mode transition and the stabilization of the glow discharge is investigated by means of electric measurements and emission recording. The stabilization mechanism of the glow discharge is discussed. It is found that there is a transition phase characterized by Trichel pulse with DC component between corona and glow discharge.
2006, 55 (1): 337-343. doi: 10.7498/aps.55.337
When an intense laser pulse propagates in a gaseous target, an ionization front is produced at the leading edge of the laser pulse, which moves at the speed of light. By use of a one-dimensional particle-in-cell code with the field ionization included, we simulate the interaction between the laser pulse and its ionization front. It is found that, because of the discontinunities in atomic ionization potentials for different ionization orders, a flat-top region of the electron density appears inside the ionization front at the beginning. The ionization induces blue shif in the laser frequency, which modifies the laser pulse into a step-like profile. This new pulse profile in turn shortens the flat-top region in the ionization front. Generally the ionization front evolves into several parts, corresponding to different ionization orders, with different plasma density gradients. The effects of different gas elements and initial gas densities on the produced ionization fronts have been investigated. The conditions ith regard to the laser intensity and gas species to produce steep density gradients in ionization fronts have been studied for applications in frequency up-conversion by use of counter-propagating light pulses. Finally, the spectrum evolution of the ionizing pulse is investigated and the resulting fine spectrum structure located between the fundamental and the second harmonic is analyzed.
2006, 55 (1): 344-350. doi: 10.7498/aps.55.344
An easy-operated and effective scheme is presented to generate a novel kind of atmospheric cold plasma millimeter jet. The jet operates with many kinds of working gas at atmosphere pressure, such as Ar, He and N2, in a capillary quartz dielectric barrier discharge (DBD) system powered by a pulsed power source with a frequency of 33kHz and variable voltage of 1—12kV. Via an CCD imager, the initial discharge filaments in the DBD gap are found to be transformed into diffusion discharge or glow-like discharge by the flowing gas through the DBD gap, and a plasma jet formed in the outlet of the capillary is viewed simultaneously. The critical velocity of the gas flow for the plasma jet formation is determined to be 3—8m/s for different working gases by a well-designed enthalpy probe. The jet range for a special gas can be changed by the increase of the gas flow velocity while the jet range for different gases varies a lot and the helium jet takes the longest range of about 44mm when the helium flows at a elocity of about 20m/s. Beyond the velocity limit of 20m/s for laminar helium flow, the jet of helium plasma becomes torrent and unstable and its range turns shorter. Based on the OES analysis of He plasma jets, it is determined that the excitation temperature of He jets lay in the range 2000K—3000K, which is much lower than the excitation temperature of a normal arc plasma torch and hints that the jet is cold especially when compared to the arc plasma torch.
2006, 55 (1): 351-356. doi: 10.7498/aps.55.351
Using self-fabricated equipment, new type carbon films with unfamiliar properties, high hardness and good electric conductivity were deposited on 1Cr18Ni9Ti substrate under deposition parameters of ion energy 2keV, pressure 2Pa, and methane ratio in hydrogen 10%. Process review shows that the substrate material is the key factor for the carbon films deposition, and the parameters of ion energy, pressure and methane ratio are impotent also. The grain size is less than 100nm and the film is smooth, dense and uniform as tested by AFM. Raman spectra show that there is only one broaden peak around 1580cm－1. The sheet resistance of the film is 1.6×104Ω/cm2 as measured with the ohmmeter. The micro-hardness of the film is 21.38GPa and the bulk elasticity is 420.65GPa as tested by nano-indenter. It is concluded that there may be carbon chain structure in this film.
2006, 55 (1): 357-361. doi: 10.7498/aps.55.357
A long plasma channel can be formed when ultra-intense femtosecond laser pulse propagate, in air. We measured the value of the resistivity of the plasma channel and the contact resistance between the plasma channel and the electrodes. We also investigated the main factors affecting the resistivity of the plasma channel.
Square and hexagon pattern formation in dielectric barrier discharge in argon at atmospheric pressure
2006, 55 (1): 362-366. doi: 10.7498/aps.55.362
Pattern formations in dielectric barrier discharge in argon at atmospheric pressure under different discharge conditions are investigated. Patterns undergo the transition sevies of hexagonal-square-square with glow background-hexagonal with glow background as the applied voltage is increased, and the spatial wavelength and the filament density change also. When the glow background appears under a certain discharge condition, the spatial wavelength and the filaments density remain constant and the number of discharge pulses of each filament in half cycle changes from one to two.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2006, 55 (1): 367-371. doi: 10.7498/aps.55.367
The structure, transport and magnetic properties of half doped Sm0.5Ca0.5MnO3 manganite has been systamatically studied. The results show that Sm0.5Ca0.5MnO3 compound has the O′orthorhombic structure and shows typical Jahn-Teller distortion. Throughout the temperature range used, the electric transport shows semiconducting behavior and there are no I-M transition and CMR effect. Meanwhile, it is found that the charge-order and antiferromagnetic transition temperatures of the system are around 270K and 200K, respectively, whereas at lower temperature there appears a typical spin-glass state around 41K with reentrant behavior. The negative magnetization is also observed in this compound. All these phenomena indicate that for the ground state of Sm0.5Ca0.5MnO3, there exists the competition mechanism of several complex magnetic interactions. Present study may provide abundant experimental information for understandig the mechanism of the strongly electron correlated system.
2006, 55 (1): 372-377. doi: 10.7498/aps.55.372
Three-dimensional molecular dynamics simulation of epitaxial growth of fcc aluminum film with a negative misfit of 0.05, under atomic deposition, has been carried out. An embedded atom method (EAM) potential is employed for computing atomic interaction in aluminum. Formation of misfit dislocation appears in the simulated growth process. Atomistic analysis of the film shows that, in the beginning the misfit dislocation consists of two Shockley partial dislocations with a stacking fault zone between them. The Burgers vectors of the two partial dislocations are of 〈211〉/6 type, and the width of the stacking fault is ～1.8 nm, which agrees well with theoretical calculation. During further deposition growth, the dislocation pair can slide, but their distance remains stable. Further analysis shows that the dislocation pair forms in a local surface disordering-ordering process, like the local melting-crystallization. Atomic scale squeezed-out tetrahedrons are found to form near the surface and soon slide back in the anor of statistical fluctuation. Under some circumstances, however, a squeezed-out tetrahedron causes disorder of its neighboring atoms, and developes into the observed local disorder zone, which later becomes the nucleation site for the formation of the Shockley dislocation pair.
2006, 55 (1): 378-385. doi: 10.7498/aps.55.378
The present paper investigates the formation and composition characteristics of Cu-based bulk metallic glasses (BMGs) in the inter-transition metal system Cu-Zr-Ti by using an “e/a-variant criterion” which is relevant to clusters. Three such composition lines, (Cu9/13Zr4/13)100-xTix, (Cu０.618Zr０.382)１００-xTix and (Cu０.56Zr０.4４)100-xTix, are defined in the Cu-Zr-Ti system. Among them, Cu９Zr4, Cu61.８Zr38.2 and Cu56Zr44 are specific Cu-Zr binary cluster compositions. Alloy compositions are designed along these three composition lines, and alloy rods with diameter of 3mm are prepared by copper mould casting. X-ray and TEM analysis show that BMGs are formed within Ti content range of x=7.5%—15%, x=7.5%—12.5% and x=5%—12% respectively along these three lines. Thermal analysis results further indicate that these BMGs have igher thermodynamic Tg,Tx,Tg/Tl and γ values, and these values of BMGs on every composition line decrease with increasing Ti content. The optimum BMG composition in this system is Cu64Zr28.５Ti7.5 on the (Cu９/13Zr4/13)１00-xTix series, which also has the highest hardness and activation energy of crystallization. The characteristic parameters of this BMG are Tg＝736K, Tx＝769K, Tg/Tl=0.627,γ=0.403, Hν= 6.74GPa and ΔE=3.88 eV, which are all superior to those of the reported BMG Cu6０Zr3０Ti１０.
2006, 55 (1): 386-392. doi: 10.7498/aps.55.386
We have simulated the end structures of perfect single-walled carbon nanotube at temperatures from 2000 K to 3500 K using tight binding molecular dynamics method. Our calculations suggest that the effect of temperature on the ends of the nanotubes is important. The two ends of a perfect single-walled carbon nanotube closes in turn at 3000 K and 3500 K within 15 ps. As the temperature increases, the two ends of a perfect single-walled carbon nanotube will close more quickly. Both processes of closing of two ends are accompanied by the lowing of the system energy. Moreover, the ends of armchair-type carbon nanotube close easier than those of zigzag carbon nanotube with the same diameter due to the lower strain energy of the former.
2006, 55 (1): 393-397. doi: 10.7498/aps.55.393
The stacking fault energies of fcc metals have been calculated by the embedded-atom method for 10 fcc metals, Cu, Ag, Au, Ni, Al, Rh, Ir, Pd, Pt and Pb. The calculated values are in good agreement with experimental results, that of Rh and Ir excepted.
2006, 55 (1): 398-402. doi: 10.7498/aps.55.398
Two-dimension numerical research has been carried out on the ablation of metal Ti target irradiated by intense pulsed ion beam(IPIB) produced by TEMP Ⅱ accelerator. Spatial and temporal evolution of the ablation process of the target during the pulse time has been obtained. Melting and evaporation processes begin from the surface of the target and the ablation process of target is layer by layer while the target is irradiated by IPIB. Meanwhile, we have also obtained the result that the average ablation velocity in center region of the target is about 10m/s, which is far lower than the ejection velocity of the plume plasma formed during the pulse time. The effects have been compared for different ratios of two kinds of ions in the pulsed beams produced by using different kinds of materials as the anode of magneto-isolated diosts during the irradiation time.
A large signal equivalent circuit model for SiGe HBT is established based on the physical model of the transistor. The quasi saturation effect and the self-heating effect are taken into account in this equivalent circuit model. The model is composed of the intrinsic and the extrinsic parts, and has the features of clear physical meaning and simple topology. The model is embedded in the DEVEQ(Device Equations Developer) of PSPICE and simulated and analyzed by the PSPICE. The results conform to the theoretically analyzed conclusion and are in accordance with the published results in the literature.
The effect of solution treatment on the spatial behavior of the Portevin-Le Chatelier effect in Al-Cu alloys
2006, 55 (1): 409-412. doi: 10.7498/aps.55.409
The effect of solution treatment on the spatial behavior of the Portevin-Le Chatelier effect in Al-Cu alloys is investigated under constant applied driving velocity. During the initial stage of plastic deformation, the PLC deformation band nucleates in the neighborhood of the middle of the transverse direction of specimen. And multiple bands will exist simultaneously in the specimen when deformation develops, whose width is narrower and incline at a larger angle than those in annealing treated material. At high applied velocity, the PLC deformation band propagates continuously first, and then nucleates randomly in the specimen.
2006, 55 (1): 413-418. doi: 10.7498/aps.55.413
The order-disorder phase transitions of the fcc AB alloy thin films in (001) direction are studied numerically by the cluster variation method. The computation results show that the order-disorder phase transitions of thin films are determined by the parity of the layer number of films. The thin films with different parity will show different phase structures and thermodynamic properties. When the surface field is weak, for films with even number of layers, in the chemical potential region corresponding to the bulk concentration x=0.5, there appears the middle-temperature phase as well as the wetting phenomenon due to the missing of symmetry of the films. While for films with odd number of layers, the order-disorder phase transitions are similar with that of the bulk materials. When the surface field is strong, for films with odd number of layers, in the chemical potential region corresponding to the bulk concentration x=0.5, there is an AB(AB)nA phase which does not show order-disorder phase transtion with the increase of temperature due to the combined effect of the surface field and finite size.
2006, 55 (1): 419-423. doi: 10.7498/aps.55.419
The surface tension of supercooled liquid Ni-15%Sn alloy was measured by the electromagnetic oscillating drop method over a wide temperature range from 1368 to 1915K. The maximum supercooling of 265K(0.16TL) was achieved. Over the temperature range investigated, the measured surface tension shows a linear property expressed by σNi-15%Sn=1316.7-1.01(T-TL)mN/m. On the basis of experimental data, the viscosity and the diffusion coefficient of Ni-15%Sn melt were derived, and we also analyzed the activation energy for viscous flow and diffusion.
2006, 55 (1): 424-429. doi: 10.7498/aps.55.424
A kinetic Monte Carlo model describing the three-dimensional thin film growth on heterogeneous substrates is presented, in which the diffusion of adatoms on substrates, along the island edges and between various layers, as well as the heterogeneity of adsorptive energy, are taken into account. Three growth modes, namely the Layer-by-layer mode, Stranski-Krastanovs mode and 3D mode, and the morphology of multiple layer growth of thin films are simulated. The relationship between thin film growth modes and growth conditions is established by taking into account the distribution of deposited atoms on various layers and the surface roughness of thin films.
2006, 55 (1): 430-436. doi: 10.7498/aps.55.430
ZnO thin films with strong c-axis prefered orientation have been successfully deposited on Si(100) substrate at 750℃ by using reactive radio frequency magnetron sputtering. The influence of annealing temperature ranging from 600 to 1000℃on the microstructure and photoluminescence (PL) properties of ZnO films was investigated by Ｘ-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence measurement at room temperature. The XRD and TEM results show that the grain size of ZnO film increases and the residual stress in the film is tensile and remains constant at about 1 GPa with the increase of annealing temperature below 900℃. After annealed at 1000℃, the grain size decreases and the residual stress in the film changes into compressive with the value about -2 GPa. The PL spectra of the ZnO films show two emission bands, namely that originating from ultraviolet (UV) exciton transition and the visible defect photoluminescence. The intensity of UV PL spectrum and the relative intensity of fferent exciton emission are dependent on the grain size and defects in the ZnO film. The red shift of UV PL spectrum results from the change of the relative intensity of different exciton emission with annealing temperature. The visible PL spectrum is sensitive to the change of annealing temperature. The relationship between PL spectra and microstructure and defects in the films is discussed.
2006, 55 (1): 437-440. doi: 10.7498/aps.55.437
MgxZn1-xO films(x=0.16) have been prepared at 80℃ by radio frequency magnetron sputtering. The effect of the annealing temperature on the structure and optical properties of the films are studied using XRD, photoluminescence and the transmittance spectra. The results indicate that the thin films have hexagonal wurtzite single phase structure and a prefered orientation with the c axis perpendicular to the substrate. With increasing annealing temperature the intensities of the XRD (002) peaks increase, the grain size and intensity of the UV photoluminescence peaks also increase, while the FWHM of (002) peaks decreases, which demonstrates that high quality MgxZn1-xO films deposited by RF magnetron sputtering can be obtained by properly controlling the annealing temperature.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2006, 55 (1): 441-445. doi: 10.7498/aps.55.441
The nonlinear differential equation for charge density wave(CDW) proposed by Grüner is analyzed in this paper. According to a periodic solution of the equation suggested in this paper at first, it follows naturally that the sliding of CDW obeys the Ohms law. Many results such as the threshold of starting field and sliding velocity of a single segment are also derived, and the defect of neglecting the first term in the equation is avoided. Applying the result to the model of multiple segments of the CDW, the exponential law of the conductivity and the threshold of applied field, as well as the “narrow-band" noise are obtained simply, which are consistent with the experimental formula. To describe the connection of a multiple segment of CDW system, the mechanism of “elastic connection" is treated as an internal force, which clarifies the vagueness in primary Portis model.
2006, 55 (1): 446-449. doi: 10.7498/aps.55.446
The photoluminescence spectrum of ZnO film with high crystal quality has been measured. The peak of near-ultraviolet emission located at 389 nm has been observed. For the ZnO film treated by ultrasonic, not only the ultraviolet peak of ZnO, but also the strong green peak at 508 nm have been observed. It is also found that the intensity of the green peak (508 nm) is stronger than that of the ultraviolet peak. The ultraviolet peak also appears to have red-shift. The intensity of the green peak (508 nm) increases sharply with further heating. The crystal quality of ZnO films is changed by the ultrasonic treatment and oxygen vacancies are produced. The lattice vibration of film is aggravated in the treatment process. When the lattice vibration arrives at certain degree, the lattice oxygen leaves the lattice site to form oxygen vacancy, and the green peak (about 510 nm) is attributed to oxygen vacancies in the crystal. The density of oxygen vacancies depends on the ZnO film temperature. The higher the film temperaure, the greater the density of oxygen vacancy and the stronger the intensity of the green peak.
2006, 55 (1): 450-455. doi: 10.7498/aps.55.450
The magnetic and microstructural properties of Ta/FePt/C thin films after annealing at various temperatures have been investigated. The results indicate that for a very thin Ta buffer with amorphous structure and relatively large roughness, defects and grain boundaries of high density are formed in the FePt film grown on it, which effectively lowers the energy barrier of the ordering with Ta interdiffusion into the grain boundaries of the FePt film during the annealing process. The formation of the L10 phase of FePt thin films is thus greatly promoted with the ordering temperature of FePt significantly reduced by introducing a thin Ta buffer layer. On the other hand, when Ta layer is relatively thick, its roughness accordingly reduces, and most of the interfacial Ta atoms are finally bounded with the advent of the crystalline structure of the Ta buffer. Therefore, Ta buffer layer at this thickness range has little effect on the ordering of FePt films.
2006, 55 (1): 456-459. doi: 10.7498/aps.55.456
We report what we believe to be the first demonstration of laser operation with a novel laser material of Yb3+-doped Gd2SiO2(Yb:GSO)pumped by a laser diode at 940 nm. We obtained a low lasing threshold of 1.27 kW/cm2 with the center wavelength of 1090 nm, which is lower than the value of 1.53 kW/cm2 predicted for Yb:YAG. The maximal output power of 360 mW was obtained with a 2% output, which corresponds to a slope efficiency up to 19%.
2006, 55 (1): 460-464. doi: 10.7498/aps.55.460
In this paper, using Monte Carlo simulation, we obtain different structures of chromatin fibers with different ionic concentration. The result shows that as the ionic concentration is increased, the fiber undergoes a conformational change from sawtooth state to super-helix state. The structural parameters obtained by simulation agree well with the experimental results, indicating that our model is useful in explaining the conformational change of chromatin fibers in different ionic solutions.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Thermodynamic explanation of solid-state reactions in synthesis process of CoSb3 via mechanical alloying
2006, 55 (1): 465-471. doi: 10.7498/aps.55.465
CoSb3 powders were synthesized by mechanical alloying (MA) with Co and Sb powders as starting materials. The influence of milling speed and duration on the solid reaction were systematically studied. The XRD results indicated that the CoSb3 phase increased with prolonged MA-time, but extensive MA resulted in the appearance of CoSb2 and the decomposition of CoSb3 to CoSb2 and amorphous Sb at a constant MA-speed. Increasing the MA-speed can shorten the incubation time of the reaction, but doesn't influence the MA solid reactions themselves. For MA processes that give a specific state of alloying, the MA-speed and the MA-time should satisfy the relationship: ω3.8t=C(constant), which expresses the relationship of equivalency between MA-speed and MA-time, indicating that the supplied energy is being accumulated during MA. The MA mechanism concerning the formation of CoSb3 has been discussed on the basis of MA from a viewpoint of non-equilbrium thermodynamics.
2006, 55 (1): 472-476. doi: 10.7498/aps.55.472
Grain fragmentation and property modification of nanocrystalline ZnO under high pressure were studied on CS-1B 6×8000 kN cubic high pressure apparatus. Grain size and microstructure of the samples have been characterized by X-ray diffraction and field emission scanning electron microscopy. The results show that the significant grain fragmentation phenomenon occurs inside the crystallites. Experimental results on hardness and the current-voltage characteristics indicate that micro-hardness of the samples after high pressure is 2.3 times that of the samples sintered at atmospheric pressure and the nonlinear current-voltage characteristics is obviously better than that of the latter.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Analysis of features of climate change of Huabei area and the global climate change based on heuristic segmentation algorithm
2006, 55 (1): 477-484. doi: 10.7498/aps.55.477
Global change science is a new research field, and one of the most important topics of which is the climate change study, to which great importance is attached by all governments of the world, and climatic abrupt change is one of manifestations of climate changes. Nowadays, research of climate change is mainly based on climatic proxy using traditional statistical method. However, climatic system is nonlinear, non-stationary and hierarchical, which makes even harder to detect and analyze abrupt climate changes. As well known, climatic system is made up of several sub-systems, and there may be inherent connections between them; however, there is only a few research methods and theories in this field. This article introduces a new detecting method, the heuristic segmentation algorithm, which is well fitted to nonlinear and non-stationary time series. Then, dealing with northern hemisphere tree rings and Beijing stalagmite based on high and low frequency series, we try to distinguish abrupt changes in different sles and disclose its physial mechanism. Defining a new physical quantity, the abrupt density, and analyzing the distribution characteristics of abrupt changes before and after 1000 a, We take Huabei area's climatic change as an example to explore the inherent connections between local and global areas.