Vol. 53, No. 11 (2004)
2004, 53 (11): 3627-3631. doi: 10.7498/aps.53.3627
In the paper, an open cavity is divided into two parts: closed part and open part. The closed part means the closed cavity, and the open part is equi valent to the absorbing traveling boundary. According to Maxwell theory, there exists a coupling equation between the modes of the closed cavity and those of the open part.Utilizing the method, the X-band six-cavity transit time oscill ator is calculated; the calculated frequency and the Q value of the working mode are very close to the measured values.
This paper reports the study on p-n GaInP2/GaAs tandem cells. The cell samples were produced by metal-organic chemical vapor deposition at a low gas pressure. In order to optimize the device configuration, numerical modeling has been performed for the impacts of a fieldaided collection on the performances of the top cells. On the basis of modeling results, a modified configuration of top cells is introduced, using p+-p—n—n+ structure instead of p+n structure. This modification has brought about much improved photovoltaic performance of the top and tandem cells, with the conversion efficiency Eff=14.26% and 23.82% (AMO, 25℃, 2×2cm2), respectively.
Numerical simulation and analysis on the mechanical behaviors of the single-crystalline and poly-crystalline nano-Cu film
2004, 53 (11): 3637-3643. doi: 10.7498/aps.53.3637
Molecular dynamics simulation and analysis are performed on the mechanical properties of mono-and poly-crystalline nano-Cu film. Computational results indicate that the temperature effects are very significant on the tensile strength and the deformation mechanism of the mono-crystalline Cu-film. The strength of the sample is much higher at absolute zero temperature than at normal temperature. The plastic deformation at zero temperature is induced by the short-distantce sliding of the particles while it is caused by the long-distance propagation of dislocations at normal temperature. The strength of polycrystalline Cu-film increases with the decrease of grain size. In the process of strain accretion, grain boundary sliding dominates the plastic deformation. Dislocations originating from grain boundaries propagate toward grains. The area of the grain boundary enlarges and the grain size shrinks with the development of plastic deformation. However, the shapes of the basic grains have no remarkable change even at very large strain.
2004, 53 (11): 3644-3647. doi: 10.7498/aps.53.3644
This paper gives a new type of conserved quantities for Birkhoffian systems. First, the equations of motion of the systems are established, and the definitions and criterions of Mei symmetries are given. Next, an existence theorem for the n ew type of conserved quantities of the systems is given, and the generalized Killing equations used to determine the infinitesimal generators are deduced. Finally, the inverse theorem of the conservation law is established.
2004, 53 (11): 3648-3651. doi: 10.7498/aps.53.3648
In this paper, the third order Lagrange equation is obtained, by which can be obtained motion equation of a body. This equation contains third order rate of change of generalized coordinates and the rate of change of force. In addition, the third order Lagrange equation and the fraditional Lagrange equation are used to solve the same problem of the motion of a body, and their results are discussed. Finally, it is pointed out that the third order Lagrange equation provides a method of obtaining equation of motion which is different from that of the traditional Lagrange equation.
The variable separation approach and study on solving the variable-coefficient nonlinear Schr?dinger equation
2004, 53 (11): 3652-3656. doi: 10.7498/aps.53.3652
In this paper, a variable separation approach is proposed and successfully extended to the (1+1)dimensional physics models. The new exact solution of two classes of variable-coefficient nonlinear Schrdinger equations are obtained. As a specific example, the envelope soliton solution for nonlinear Schr?dinger equations are a by-product, which is somewhat different in form, from the present result.
2004, 53 (11): 3657-3662. doi: 10.7498/aps.53.3657
Using the Kinani-Daoud method we have constructed the Gazeau-Klauder(GK) and KlauderPerelomov(KP) coherent states for the anharmonic oscillator. It is shown that the two types of coherent states have totally different forms in their expressions. We have also discussed the resolution of unity of the two coherent states and the Hilbert space of each state. The study of Mandel Q pa rameter of the states shows that GK coherent state coincides with the sub-Poissonian and KP coherent state coincides with the super-Poissonian statistical distributions.
2004, 53 (11): 3663-3667. doi: 10.7498/aps.53.3663
For the general time-dependent linear potential, the exact and complete solution of the Schr?dinger equation was obtained by assuming a form of wave function. Meanwhile, it was pointed out that the matrices φ(t)〉和ψ(t)〉 defined by the two wave functions 〈φ(t)xψ(t)〉和〈φ(t)pψ(t)〉 satisfy classical equations of motion. According to the ensemble theory of quantum mechanics, such classical equations describe the motion of fluid. A further research shows that similar conclusions apply to any linear system.
2004, 53 (11): 3668-3672. doi: 10.7498/aps.53.3668
Based upon the Heisenberger's uncertainty relations for mixed states, the minimu muncertainty and squeezing effects are studies. Although all minimum uncertainty states must be pure states, the nucertainty of one dynamical variable can be squeezed in some pure states or mixed states, even if they are not minimum uncert ainty states for the pair of dynamical variables. In addition, we present the ge neral uncertainty relation of statistics, which has the similar mathmatical stru cture of Heisenberg's indeterminacy principle, but has no relation with quantum interfernce.
2004, 53 (11): 3673-3675. doi: 10.7498/aps.53.3673
The partition functions of bosonic and fermionic field in Barriola-Vilenkin blac k hole are directly derived by using the method of quantum statistics. Then the entropy of the Barriola-Vilenkin black hole is calculated by using the improved brick-wall method in the frame of membrane model.
Application of resonant parametric perturbation to the chaos control in Boost converter and its optimization
2004, 53 (11): 3676-3683. doi: 10.7498/aps.53.3676
The method of resonant parametric perturbation is a simple non-feedback chaos control means. It is such a suitable control method for controlling chaos in non-autonomous systems that we are inspired to study its applications for chaos control in current controlled Boost converter. Furthermore, the method of resonant parametric perturbation is optimized by selecting the best perturbation phase, so as to achieve the best chaos control results. These relative applications (with or without optimization) in Boost converter can be analyzed theoretically, and the influence induced by variable circuit parameters on the effective perturbation can also be calculated or predicted.
2004, 53 (11): 3684-3689. doi: 10.7498/aps.53.3684
A nonuniform ratchet model with Gauss-transition rates is proposed to discuss the directional motion of Brownian particles in an asymmetrical periodic potential. It is assumed that the particles experience several internal states in a single mechanical-chemical circle. In this model, the transition rates between diff erent states are position-dependent, which have the form of Gaussian function. For any internal states, the probability distribution as a function of time and position may be expanded near the transition points to any rank if necessary. Fin ally, the focus of our study is concentrated on a two-state model, in which we choose (M, K)=(2, 2) and calculate the average current as a function of the transition width, temperature and transition rate. It is revealed that the trans ition width influences the current greatly.
2004, 53 (11): 3690-3694. doi: 10.7498/aps.53.3690
Using the Monte Carlo method, we have investigated the effect of the external noise on the phase-separation dynamics in binary mixtures. It is found that the addition of the fluctuation has speeded up the pattern growth, and driven the system to form［1,1］oriented tilted strip formation. When the noise intensity is fixed and the noise acting probability is less thanp=0.015, the noise will erase the effect of the deep quench, and the system will avoid being frozen.With the increase of the noise acting probability, the structure factor will grow linearly. If the noise intensity is adequate, in an appropriate noise acting probability region, the system can form a high-oriented tilted strip pattern.
2004, 53 (11): 3695-3700. doi: 10.7498/aps.53.3695
The average path length of Internet with power law degree distribution is stud ied in this paper. The main work is to give a formula to compute the average pat h length . The essential of Internet or many other complex networks is to realize the least cost (the smallest total number of edges) and the best benefi t (the short average path length), which can be expressed as two optimization fa ctors to minimize the average degree and the average path length . By analyzing the main factor affecting , we find the main property of p ath length distribution P(l), and then give a formula of P(l) only inclu ding one parameter α. This work shows that P(l) and a direct relation with P(k),and α represent the effective link between nodes and the tota l number of networks on . This formula makes it possible that if we get the α of P(k)～k-α, we can calculate easily. The simulati on shows the formula is quite exact. Our method is successful. In the end, we di scuss that the parameter αis very important for Internet design.
2004, 53 (11): 3701-3705. doi: 10.7498/aps.53.3701
Based on the continuous feedback control idea,a novel nonlinear dynamics of map and control method for a symmetric chaotic system is presented.Different from t he periodical orbit method,the basis to choose controlling parameters has been g iven.Only by appropriately adjusting feedback parameters,any periodical orbit can be reached.This method is applied to Logistic map,and good results have been o btained.
A method for controlling hyperchaos of Er-doped fiber laser——Nonlinear time-delay feedback modulating-parameter
2004, 53 (11): 3706-3709. doi: 10.7498/aps.53.3706
We present a method of nonlinear time-delay feedback modulating/parameter to control chaos/hyperchaos.A scheme of controlling the hyperchaotic dualring Er-doped fiber laser by using this method is proposed.Numerical simulation shows th at a hyperchaotic dual-ring Er-doped fiber laser can be successfully controlle d into different periodic states by this method only when the delay time and fee dback intensity are suitably matching.
2004, 53 (11): 3710-3715. doi: 10.7498/aps.53.3710
The spectral responsibility of 6H-SiC pn junction ultraviolet photode tector has been simulated by 2D numerical model. The effect of different impurity concentration and different junction-depth on the responsibility is discussed in this paper. For p+n device, the responsibility can be as high as 167.2 mA/ W when the width of p+ layer is about 0.2μm, and the impurity concentrations are about 9×10.18cm-3and 1×10.6 cm-3 in p+layer and nlayer, re spectively. For n+p device, the responsibility is as high as 183.5 mA/W when the width of n+-layer is about 0.2μm, and the impurity concentrations are abo ut 9× 10.18cm-3 and 1×10.6cm-3in n+-layer and p-layer, respe ctively. It is shown that the result of simulation agrees with the experimental data very well.
ATOMIC AND MOLECULAR PHYSICS
2004, 53 (11): 3716-3723. doi: 10.7498/aps.53.3716
We report on the establishment of Fourier transform step-scan time-resolved photoconductivity spectroscopy to study the solar cell's minority carrier lifetime ,which has close relationship with its conversion efficiency.Three typical Si so lar cells are selected in our experiments,including both the monocrystalline and polycrystalline silicon samples.We find that the rise and decay curves of the t ransient photoconductivity can be well described by two simple exponential funct ions.Due to the participation of recombination centers,the recombination minorit y carrier lifetimes are generally smaller than those of generation.In order to p rove the reliability of our experimental results,we extract the bulk lifetime an d the effective diffusion length of the three samples.Furthermore,we analyze the correlation of the minority lifetime with the shortcircuit current,open volta ge and conversion efficiency,by the aid of the investigation of solar cells' dark I-V characteristics and load characteristics.In addition,we also discuss in detail other applications of the established stepscan time-resolved spect roscopy.
CLASSICAL AREA OF PHENOMENOLOGY
2004, 53 (11): 3724-3728. doi: 10.7498/aps.53.3724
By using the vector Rayleigh diffraction integrals, an analytical expression for the diffraction of nonparaxial vector Gaussian beams at a circular screen is de rived. The diffracted on-axis field and farfield expressions and free-space pro pagation equation of nonparaxial vector Gaussian beams, as well as the paraxial Fresnel and Fraunhofer diffraction formulae of Gaussian beams diffracted at a ci rcular aperture are treated in a unified way as special cases of our general res ult. Numerical comparative examples are given to illustrate the intensity distri butions and far-field behavior of nonparaxial vector Gaussian beams. It is show n that for the diffraction at the circular screen both the f-parameter and truncation parameter affect the beam nonparaxiality.
2004, 53 (11): 3729-3732. doi: 10.7498/aps.53.3729
Based on our previous work, with the aid of the numerical method, the phase pro bability distributions of Roy-type even and odd nonlinear coherent states are in vestigated. It is shown that the distributions for the states are rather different, and unlike the case of ordinary even and odd coherent states the Pegg-Barnett distribution clearly reflects the different characters of quantum interference in the case of Roy-type even and odd nonlinear coherent states.
Entanglement swapping in the process of two-level atoms interacting with cavity fields of coherent states*
2004, 53 (11): 3733-3738. doi: 10.7498/aps.53.3733
From the viewpoint of quantum information theory, a multiatom and muticavity system was investigated. In the system the interaction between the atoms and the fi elds in the cavities is described by the intensity-dependent coupling Jaynes-Cummings model. It is found that the atomic maximal entangled state can be transformed into the maximal odd-even-like coherent entangled state, whereas the maximal odd-even-like coherent entangled state also can be transfor med into the atomic maximal entangled state.
Cavity field spectra of two different atoms interacting with a Two-mode field through Raman process
2004, 53 (11): 3739-3743. doi: 10.7498/aps.53.3739
The cavity field spectra of two different atoms interacting with two-mode field s through Raman process are studied.The effects of relative coupling constant R=g2/g1 on the spectrum structure are discussed.It is found thatR pla ys a different role in the syectrum for vacuum,weak or strong initial field.Dege nerate spectrum structure appears usually forR=1 orR=0.A complicated a symmetric multipeak structure appears when R is between 0 and 1.When the f ield of upper frequency mode is vacuum,its spectrum is influenced sensitively by the field intensity of the other mode for fixed R.
2004, 53 (11): 3744-3747. doi: 10.7498/aps.53.3744
In this paper, a simulation software with a direct coupling in quasi-three-di mensions for the gain-waveguide vertical-cavity surface-emitting lasers has b een realized. The electrical field, carrier density, optical-field and temperature distributions in the vertical-cavity surface-emitting lasers are given. The proper threshold characteristics are shown only when the potentia ls in the p-type and n-type DBR layers are studied together.
Influence of hydrogen additive and excitation circuits on the output performance of barium vapor laser
2004, 53 (11): 3748-3751. doi: 10.7498/aps.53.3748
The output performances of barium vapor laser with and without hydrogen additive excited by pulsed discharge with Blumlein circuit were experimentally investiga ted. The result indicates that the laser output power increases two times with 1.5% hydrogen mixed into the neon buffer gas. Based on this experimental result,this paper further compares the working characteristics of barium vapor laser w ith interactive circuit and Blumlein circuit, and finds that the interactive cir cuit can greatly improve the laser output power and its efficiency. The maximum laser power of 3W and efficiency of 0.4% have been obtained at 1.5μm laser line. The dependence of laser power on working parameters is measured and discuss ed, and the mechanisms of hydrogen additive and interactive circuit for impr ovement of the laser performance are qualitatively analyzed.
The experimental studies of Ni-like Ta x-ray laser at near “water window" on Shenguang Ⅱ laser facility were reported. By using a new scheme of united driving of fundamental- and double-frequency laser, the distinct spectrum signal of N i-like Ta x-ray laser at 4.48 nm was obtained under the total drive energy of 400J. The efficient gain-length product was about 5.5
Influence of external electric field on photorefractive two-wave coupling in SBN:Cr crystal and its applications
2004, 53 (11): 3756-3760. doi: 10.7498/aps.53.3756
The properties and applications of the photorefractive two-wave coupling in con gruent SBN:Cr(Sr0.61Ba0.39Nb2O.6:Cr)crystal under external dc e lectric field are experimentally investigated in this paper.The variation of the intensity gain coefficient of the two-wave coupling with the external field is analyzed,and the measurement results are presented.It is found that the photore fractive two-wave coupling gain and response rapidity can be both increased,by applying appropriate external electric field to the crystal.Further study indica tes this electric response property of SBN:Cr crystal is useful to some applicat ions,such as improving the image edge-enhancement and the image edge-enhanceme nt joint-transform correlator based on the nonlinear energy transfer of photore fractive two-wave coupling in the crystal.
2004, 53 (11): 3761-3765. doi: 10.7498/aps.53.3761
The linear and nonlinear optical properties,as well as phase-matching of mixed Cd0.35Hg0.65Ga2S4 nonlinear crystal are investigated. Da mage threshold is determined in comparison with the widely used middle IR crystal under identical experimental conditions. CO2 laser second harmonic generatio n (SHG) is realized in this crystal at a phase-matching angle in well coi ncidence with estimation.
2004, 53 (11): 3766-3770. doi: 10.7498/aps.53.3766
Based on the coupled wave equations of nonlinear optics, a two-dimensional p hysics model is established to describe transverse stimulated Brilluoin satteri ng (TSBS) in large-aperture optics of a high-power laser system. The temporal and spatial profile of the stress induced by TSBS is evaluated numerically, and the damage characteristics of optical components is presented, which agrees well with the experimental phenomenon observed at LLN laboratory. The energy loss induced by TSBS are calculated to be up to 20%, sho wing that TSBS may have strong influence on routine operation of high-power las er systems.
2004, 53 (11): 3771-3776. doi: 10.7498/aps.53.3771
In this paper,a research work is done on two optical beams co-propagating in opp osite directions in two-dimensional self-defocusing nonlinear media.Numerical re sults show that the probe beam can be induced to focus due to cross-phase modula tion by the pump beam under certain conditions.We also discuss the effect on the focusing of the probe beam from the four parameters:the specimen length,the ini tial amplitudes of the pump beam and the probe beam,and the initial transversal distance between the centers of the two beams.We find that some of them have opt imum values,which result in the strongest focusing.
2004, 53 (11): 3777-3785. doi: 10.7498/aps.53.3777
The parallel interaction between two photovoltaic spatial solitons of dark and dark as well as dark and bright with different wavelengths is investigated by numerical method. Our numerical study indicates that the dark solitons can both remain as quasi soliton form in certain distance while they propagate coaxially. H owever,they attract each other while closely overlapping. And they have a conver gent effect on each other at the slowly varying region of optical field while in larger separations. For the case of interaction between dark and bright, the br igh t one may experience compression, expansion or energy transfer depending on thei r mutual separation.The physical interpretation of this solitons interaction is also given in terms of the refractive index waveguide they jointly induce.
2004, 53 (11): 3786-3793. doi: 10.7498/aps.53.3786
Proton exchange waveguides in MgO:LiNbO.3 and LiNbO.3 crystals were fabricated , and the diffusion coefficients for the proton exchange process are obtained. The evolution characteristics of the waveguide index profile in the annealing process are studied. The structural deformation of the proton exchange waveguides in Mg O:LiNbO.3 and LiNbO.3 and the restoration effect of annealing are also studied tho roughly by the x-ray diffraction method and the OH-infrared absorption method. The optical and structural characteristics of annealed proton exchange waveguides in MgO:LiNbO.3 and LiNbO.3 are analysed and compared with eath other.
Wavelength demultiplexer using the spatial dispersion of repeated-period double-chirped structures*
2004, 53 (11): 3794-3799. doi: 10.7498/aps.53.3794
Based on the rudimentary double-chirped stack, exploiting wavelength-dependent penetration depth, repeated-period double-chirped structures, in which each couple of Bragg layers is repeated for different times, are presented to increase the spatial linear shift and the beam shifting with different incident wavelength, thus allowing the design of compact thin-film spatial wavelength demultiplexer. We compare the improved structure repeated for n times with the directly double -chirped structure with the same layer number, finding that the former has not only more advantages in theoretical design but a higher tolerance in experiment al fabrication. Besides, we have given the qualitative analysis for the strongosc illation appearing in the spatial dispersion curves when the repeated times of improved double-chirped structure or the wavelength of incident beam are relatively large.
2004, 53 (11): 3800-3805. doi: 10.7498/aps.53.3800
Growth dynamics and spatiotemporal evolutions of one-dimensional tra veling-wave pattern in a binary-fiuid-mixture Reylaigh-Benard convection with extremely weak through-flows are investigated by numerically simulating basic hydr odynamic equations. We show that the system exhibits repeated dynamics of trave lingwave convection, and their repeating periods depend sensitively on the strength of through-flow。
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2004, 53 (11): 3806-3813. doi: 10.7498/aps.53.3806
The magnetohydrodynamic model,which describes the plasma flows inside the D.C.ar c plasma torch,is presented.By numerical simulations,the plasma flow characteris tics inside the plasma torch and the turbulence effects on the flows are studied in detail.Then the parameter studies are carried out.At last,comparisons betwee n the numerically predicated results and the experimental data are made in detail.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2004, 53 (11): 3814-3817. doi: 10.7498/aps.53.3814
Based on the theory of electrical spin injection into semiconductors, by conside ring the car riers of spin polarons and spinless bipolarons in organic polymers, we suggested a model of spin injection into organic polymers. It was found that a high curre nt polarization can be obtained by adjusting the spin current polarization in the ferromagnetic layer or the conductivities of the ferromagnetic and organic layers. Effect of the proportion of polarons to carriers on the spin current polarization was discussed.
Low temperature fabrication of nanostructured Si-SiOx and Si-SiNx composite films and their photoluminescence features
2004, 53 (11): 3818-3822. doi: 10.7498/aps.53.3818
Silicon nanoparticles were fabricated in both silicon oxide and nitride matrices by using plasmaenhanced chemical vapor deposition, for which a low substrate t emperature belowo 50℃ has been found most favorable. High-density (up to 4.0 ×1012cm-2, from TEM micrograph) amorphous silicon nanoparticles with an averaged size down to 3 nm have been obtained. Strong roomtemperature photoluminescence was observed in the whole visible light range from the deposits that were postannealed at 500 ℃ for two minutes. Careful comparison shows that the Si-SiNx films provoke a significantly more effective photoluminescence than Si-SiOx films f abricated with similar processing parameters, especially in the green and blue light range. Theis low- temperature procedure for fabricationg light-emitting silicon structures opens up the possibility of manufacturing silicon-based tunable high-efficiency light-e mitting devices.
2004, 53 (11): 3823-3828. doi: 10.7498/aps.53.3823
Ti and C ions extracted from a metal vapor vacuum arc ion source were implanted into H13 steel, with an implantation dose of 3×1017cm-2,an extractio n acceleration 48kV,and an average ion beam flux between 20 and 47μAcm-2. Rutherf ord backscattering (RBS) spectrum was used to measure the Ti concentration depth profile in H13 steel after Ti ion implantation. The surface microstructure observation was carried out using glancing xray diffraction analysis(GXRD). Wear test results showed that the wear rate of the implanted layer dropped by about 40% for Ti ，C dual implantation. In addition, the Ti implantation was found to significant ly reduce the friction coefficient of steel H13. The wear mechanisms of the impl anted layer were discussed by results of RBS and GXRD.
2004, 53 (11): 3829-3833. doi: 10.7498/aps.53.3829
Three internal friction peaks were found around 180℃ (termed as P1),340℃ (termed as P2) and 510℃(termed as P3) in rapidly cooled Fe71Al29 alloy,while only the P3 peak can be observed in slowly cooled sp ecimens.Only the P1 and P2 peaks were investigated using a computer- controlled inverted torsion pendulum in the present study.The P1 and P2 peaks in air-cooled specimens disappear during cooling or after long term ag eing at 350℃.They decline even disappear with increasing ageing time.Both the P1 and P2 peaks have relaxation features and their activation energy values are H1=1．03±0．08eVfor the P1 peak and H2=1．64±0．05eV for the P2 peak.It is suggested that P1 peak originates from the nearestneighbor jumps of Al atoms within tetrahedral lattices and P2 peak from the next-nearest-neighbor jumps of Al atoms within tetrahedral lattices in quenched alloys.
2004, 53 (11): 3834-3838. doi: 10.7498/aps.53.3834
There exists a low-frequency relaxation internal friction peak in La2NiO4+δwithδ=0.071, 0.110, 0.135 and 0.140, the peak position shifting to higher temperatu re, when more excess oxygen is incorporated. At δ=0.087 two peaks were obse rved which may be attributed to the jump of the interstitial oxygen atoms in the diff erent kind of the one-dimensional ordering phase formed by phase separation. At δ=0.038 two peaks were also observed which may be attributed to the jump of the i nterstitial oxygen atoms in the low-temperature tetragonal phase and the one-dimensional ordering phase formed by phase separation.
2004, 53 (11): 3839-3844. doi: 10.7498/aps.53.3839
The kinetic property during the glass transition process of Zr_Al_Ni_Cu (Nb,Ti) amorphous alloys was systematically investigated by differential scanning calorimetry method. The activation energy (ΔE) at the glass transition temperature was much smaller than tradition amorphous alloys and have different magnitude compared to ΔEvalue at Tx. These reveal that the bulk amorphous alloys show special structure characteristics and that is the reason of its big glass_forming ability. The Vogel_Fulcher_Tammann fits to the experimenta l data are given by the full curves and the fragility parameter mvalue was calculated to be about 30, reflecting its “strong" liquid property in deep_unde rcooled region. The B value of Lasocka function，atom activation energy and glass fragility parameter reveal a close relationship between kinetic behavior at glass transition and the glass_forming ability. So it could be used as an impor tant judgment for glass_forming ability.
Diffusion of Co in Zr＿46.75Ti＿8.25Cu＿7.5Ni＿10Be＿27.5 bulk metallic glass in supercooled liquid region under high pressure
2004, 53 (11): 3845-3848. doi: 10.7498/aps.53.3845
Diffusion of Co in Zr＿46.75Ti＿8.25Cu＿7.5Ni＿10Be＿27.5 bulk metallic glass under high pressure is investigated in supercooled liquid regio n by ion implantation combined with secondary ion mass spectroscopy.Before impla ntation of Co atoms,the amorphous samples were annealed and relaxed in supercool ed liquid region.Diffusion coefficients of Co at 603K in the relaxed samples are found to increase with increasing pressure.And the activation volume for diffus ion is obtained to be -1.236Ω,where Ω is the mean atomic volume of the alloy.The result shows that diffusion of Co in this case is in an interstitial way.
2004, 53 (11): 3849-3852. doi: 10.7498/aps.53.3849
Ag/TCNQ bi-layer films with different thickness were prepared on glass substrates by alternating vacuum deposition of Ag and TCNQ. The transport behavior in the film was studied using transmission spectrum to monitor the process. An ab normal accelerated transport phenomenon was observed when the film was ultra thin and a tunneling model was proposed to explain this phenomenon.
2004, 53 (11): 3853-3857. doi: 10.7498/aps.53.3853
The temperature dependence of thermal conductivity (K),resistivity (ρ) and low field ac susceptibility (χ) of perovskite nick elates Nd＿2-xSr＿xNiO＿4(x =0.33,1.35) have been measured at temperatures from 77 to 300 K. The thermal conductivity an omalies associated with charge_order (CO) and spin_order (SO) are observed simultaneously in Nd＿1.67Sr0.33NiO＿4 for the firs t time so far as we know. The thermal conductivity is enhanced belowT_CO , but is suppressed near T＿SO. There is also response to CO and S O in the χ-Τ curve. Only CO is observed in the ρ-Τ curve. In contrast, th ere are no anomalies in K-Τ, ρ-Τ andχ-Τ of Nd＿1.67Sr0.33NiO＿4. The anomalous phonon thermal conductivi ty in Nd＿1.67Sr0.33NiO＿4 indicates that there are strong charg e_phonon interaction and the spin_phonon interaction in this compound.
Theoretical study on the atomic structure, electronic states, and STM image of c(2×2) Cu(001)/O surface
2004, 53 (11): 3858-3862. doi: 10.7498/aps.53.3858
Abstract In this article we have studied the surface structure, rel axation, and oxygen absorbed c(2×2) Cu(001) surface by using ab initio projector augmented wave and Car-Parinello method. It i s concluded that the bond length between oxygen and surface Cu atom is 0.194nm which yields a perpendicular distance of 0.069nm from O to Cu(S). The absor ption of oxygen produces a hybridized band and yields the well localized surface states a t 6.7 eV below E＿F. The calculated work function for this absorbed sur face is 5.29 eV. We also calculate the scanning tunneling microscope images in the Tersoff-Hamann approach and make comparison with available experimental observ ations.
2004, 53 (11): 4015-4020. doi: 10.7498/aps.53.4015
The thermal stability of Mn12-Ac[Mn12(CH3COO)16(H2O)4O12]52CH3COOH54H2O magnetic molecular crystals was investigated by TG-DTA from room temperature to 270℃. According to the results of XRD and TG,we found that Mn12-Ac lost the crystal water and the acetic acid molecules of solvation which were located between the adjacent molecules in the temperature range from 25℃ to 1 10℃. At the same time, 4H2O which were linked with 4 Mn3+ were lost. The crystalline structure of Mn12-Ac single crystal was destroyed during this course. However, the core structure in the molecule was well preserved. From 180℃ to 230℃, a further transformatio n took place, Mn12-Ac lost all the CH3COO- ions and turned intoγ-Mn2O3, with a little amount of Mn3O4.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Oxide overlayer effect on the measurement of the parameters of interband critical point: A fractional-dimensional space approach*
2004, 53 (11): 3863-3867. doi: 10.7498/aps.53.3863
The fractional-dimensional space approach and analysis of spectroscopic ellipsometry are used to study an oxide overlayer effect on the measurement of the parameters of interband critical point (CP) of Si by a Si-SiO＿2 model. There sults of the calculation show that the oxide overlayer effect can influence the calculated CP parameters derived from an optical spectrum by decreasing t he ampl itude and dimensionality, and increasing the lifetime broadening. Moreover, the effect is enhanced with increasing thickness of the overlayer. However, this eff ect on threshold energy is shown to be very small and can be ignored.
2004, 53 (11): 3868-3872. doi: 10.7498/aps.53.3868
InSb is an important non-carbon-bearing anode material for lithium (ion) batteri es. An ab initiomethod with first-principles pseudopotentials based on the density functional theory has been used to calculate the total energies, formation energies and equi librium volumes of Li intercalations in InSb in 125 possible cases. Comp aring with the experimental voltage profile curve, we have picked out the possib le reaction routes of Li insertions in InSb and a theoretical voltage pr ofile curve is reached. Our results show that, from bulk InSb to bulk Li＿3Sb, the re are no possible reaction routes undergoing five or more intermediate ph ases. The most favored route for undergoing only one intermediate phase is Li+In＿4Sb＿4→Li＿1In＿4Sb＿4,11Li+Li＿1In＿4Sb＿4→Li＿12Sb＿4+4In；whereas there exists only one reaction route for undergoing four intermediate phases, that is, Li+In＿4Sb＿4→Li＿1In＿4Sb＿4,2Li+Li＿1In＿4Sb＿4→ Li＿3In＿4Sb＿4,4Li+Li＿3In＿4Sb＿4→Li＿7In＿3Sb＿4+In,3Li+Li＿7In＿3Sb＿4→Li＿10In＿2Sb＿4+In,2Li+Li＿10In＿2Sb＿4→Li＿12Sb＿4+2In..
2004, 53 (11): 3873-3876. doi: 10.7498/aps.53.3873
We have investigated the electronic structure of HoNiO_3 perovskit e using first principles based on the density_functional theory. A comparison of elec tron_density map between orthorhombic and monoclinic structures indicated that there is only one type of Ni^3+state in the orthorhombic_metallic phase (space group Pbnm), and there are two types of Ni^(3-δ)+ and Ni^(3+δ) + states in the monoclinic_insulating phase ( space group P2_1/n). The characteristic parameter of charge di sproportionation δis concerned with the non_bonding t_2g band of partial density of states of Ni3d electron. δis calculated to be 0. 34±0.01， based on the changes of t_2gband from orthorhombic to monoclinic phase.
The variable metric algorithm for ground state energy of ionized-donor-bound excitons in semiconductors
2004, 53 (11): 3877-3881. doi: 10.7498/aps.53.3877
We present an optimization method, called the variable metric algorithm, to calc ulate the ground-state energies of excitons. The ground-state energ ies of two-dimensional ionized-donor-bound excitons(D＾+,X)have been calcu lated variationally for all values of effective electron-to-hole mass ratioб. They are compared with those obtained by the variational method. The results show that the proposed method is simple in software programming, acc urate, and has more advantages than the traditional variational method for the g round-state energies. The method is especially fitted for complex systems.
2004, 53 (11): 3882-3887. doi: 10.7498/aps.53.3882
Using the bosonization technique and Gaussian wave functional method, we investi gate the low-energy excitations of a spin-Peierls chain where the spins interact with quantum phonons. The results show that the energy gap of the one- and two- particle excitation states decrease gradually when spin-phonon coupling constant decreases or the phonon frequency increases. A quantum phase transition from a gapless spin-fluid phase to a gapped dimerized phase occurs at a nonzero critica l value of the spin-phonon coupling. Our results indicate that the two-particle excitation spectrum is much more sensitive to spin-phonon coupling constant than the one-particle excitation spectrum.
2004, 53 (11): 3888-3894. doi: 10.7498/aps.53.3888
The charge trap states of AlN_Si(111) grown by metal_organic chemical, vapor dep osition are studied by the c apacitance spectroscopy of Al_AlN_Si MIS structure. The interface charge trap st ates of AlN_Si heterostructure and discrete trap center in AlN films are studied . The discrete trap center 2.55eV about E_v in AlN film is found. The dist ribution of interface states is continuous in the energy range of Si. The lowest state density N_ss is 8×10^11eＶ^-1cm^-2in the middle of the band gap. The corresponding time constantτ is 8×10^-4s and the cap ture cross section σnis 1.58×10^-14cm^2. T here are three kinds of trap states in the boundary layer of AlN film which caus es the frequency dispersion in the accumulation region of Al_AlN_Si MIS structure.
2004, 53 (11): 3895-3901. doi: 10.7498/aps.53.3895
Magnetic tunnel junctions (MTJs) with different sizes from 5μm×5μm to 15μm×60μm were fabricated on 4_inch Si/SiO_2 substrates. Their mag netoelectronic properties were investigated using the four_probe measuring system. The typical values of junction resistance_area product and tunneling mag netoresistance (TMR) ratio of the MTJs are 16 kΩμm^2and 18% respectively. The absolut eerrors of junction resistance_area product and TMR ratio are within 10% and 7% respectively for all the MTJs. All of the MTJs fabricated and measured show a good uniformity. Our experimental results show that such MTJs can be used to fabrica te the prototype demonstration devices for magnetoresistive random access memory .
Effects of proximity coupling and substitutions for Ba-sites on the transition temperature and ARPES of high-T＿c superconductors
2004, 53 (11): 3902-3908. doi: 10.7498/aps.53.3902
Abstract Taking into account the proximity effects of the CuO chain on the hig h-T＿c superconductivity, we introduce an S-N (superconducting-normal) model with d-wave Cooper pairing in the S layer. The hopping interaction between the S and N layers shows the suppression effect on the transition temperature T＿c from the Green's function obtained in the Nambu space. Based on this model, we investigat e the negative effects of the substitution for Ba-site on the transition tempera ture T＿c in the Y-Ba-Cu-O system. Experimental observations are qualita tively con sistent with our theoretical results. Finally, the hump/dip/peak structure in th e line shapes of the angle-resolved photoemission of the high-T＿c supercond uctors has also been discussed in the framework of the S-N model.
Thickness and strain effects on electronic transport and Curie temperature in La_0.67Ca0.33MnO_3 films
2004, 53 (11): 3909-3915. doi: 10.7498/aps.53.3909
La_0.67Ca_0.33Mn_O.3 films with thickness between 25 and 400nm were fabricated on (001)SrTiO_3 and (001)LaAlO_3 substrates, using pulsed laser deposition. The magnetization and resistivity ρ of the fil ms were studied as functions of thickness. The reduction of t causes the decrease of the Curie temperature T_C in addition to the increase of ρ of the films. Com pared with the compressive strain in the La_0.67Ca_0.33Mn_O.3/La AlO_3 films, the tensile strain in the La_0.67Ca_0.33Mn_O.3/SrTiO_3 films causes a faster reduction of T_C with t, and a larger value of ρ_０. The low_temperature ρ is found to follow well ρ=ρ_0+Bω_s/sin h^2(ω_s/2/k_BT)+CT^n， with ρ_０ being the residual resistivity. The second term arises fro m the scattering by a soft optical phonon mode, and the third term denotes the other possible transp ort mechanisms. B, ω_s(the frequency of a soft optical mode) and C are fitting parameters. At temperatures higher than T_C, ρ of all the films show activated conduction with ρ=DT×exp（E_a/k_BT）. Here, E_a is the activation energy. Based on the investigation of ρ_０, ω_s and E_a, the thickness and strain effect s in the films are discussed, separately. Further study shows that the variation of T_C is mai nly associated with E_a and ω_s, confirming the crucial role of the electron_phonon coupling in the strain effects on T_C.
2004, 53 (11): 3916-3919. doi: 10.7498/aps.53.3916
Analyzing the effectivity of "forbidden" 3-magnon processes locally excitated in magneto-ordered crystals, we successfully constructed the corresponding effe ctive 4-magnon interaction terms by the unitary transformations.
2004, 53 (11): 3920-3923. doi: 10.7498/aps.53.3920
The antiferromagnetic coupling in Fe/Si multilayers was investigated with spa cers varying from pure Si to heavy-doped n-type and p-type Si. It was found that interlayer diffusion between Fe and Si occurred even though the multilayers sho wed well-defined layer structure, and the diffusion dominated the hea vy-doped Si, which made no difference at all for the antiferromagnetic coupl ing with different type of Si. Furthermore, the antiferromagnetic coupling in Fe/Si multi lay ers still goes on while the diffusion between Fe and Si layers enhanced and the layer structure was degraded to some extent after annealing.
2004, 53 (11): 3924-3928. doi: 10.7498/aps.53.3924
A series of ZnxMg1-xO films are prepared with electro phoresis deposition. The x-ray diffraction of the film is consistent with that of the multicrystal ZnO, it shows the structure of the ZnxMg1-xO film agree with the polycrystal of ZnO. The photoluminescence study of the ZnxMg1-xO film shows that there are two promine nt peaks in the ultraviolet region of the emission spectra, corresponding to the light emission of free and bound excitons, respectively. The intensity of the emi ssion spectra is invariable in the visible region, and no new peaks including the green band exist. This phenomenon indicates that the oxygen in the film keeps a fine stoichiometry with other elements, and restrains the emission of the green band based on the oxygen vacancies. On the other hand, the blue shift of the UV peaks in the photoluminescence spectra is found to be associated with increasing Mg content in ZnxMg1-xO films, and the intensity of peaks is also reinforced significantly with increasing annealing temperature.
2004, 53 (11): 3929-3933. doi: 10.7498/aps.53.3929
The Raman spectra of lanthanum-doped intergrowt h ferroelectric ceramics Bi_4-xLa_xTi_3O_12-SrBi_4-yLayTi_4O_15［BLT-SBLT(x+y),x+y= 0.00, 0.25,0.50,0.75,1.00,1.25,1.50］achieved at room temperature were inve stiga ted. The results show that La was substituted the Bi ions in the pseudo-perovski te blocks when La content is lower than 0.50 When La content is higher than 0.50, so me of La ions are incorporated into the (Bi_2O_2)^2+ blocks. The inco rporation of La ions into the (Bi_2O_2)^2+ layers would change th e structure of (Bi_2O_2)^2+ and destroy its functions as the insu lating layers and the space charge storage, which leads to the decrease of the remnant polarization. The relaxation characteristics observed in BLT-SBLT(1.50) are consistent with the softening of the mode lower than 30 cm^-1. This in dicates that La-doping may bring about the structural phase transition.
2004, 53 (11): 3934-3939. doi: 10.7498/aps.53.3934
In this paper, the properties of fluorescence were studied of the thin films with different component ratios of polyvinyl carbazole(PVK)and Alq3. The energy transfer between PVK and Alq3 was studied through analysis of absorption spectra, excitated spectra, emission spectra of the thin films. When the content of Alq3 was high enough，the peak of Alq3 was quite evident in the abs orption spectra and excitated spectra, at the same time the emission spectra was the characteristic emission band of Alq3.When the content of PVK was high enough, the peak value of PVK is much greater than that of Alq3. At this time the extraordinary strong characteristic emission band of Alq3 and the feeble charac teristic emission band of PVK was observed. It is proved that the energy can transfer from PVK to Alq3 in a wide concentration range and it is most efficient at the concentration of 1∶7. A model Hamitonian based on single chain model including the dopant was put forward to simulate the experiment .This model can explain the experimental results very well.
2004, 53 (11): 3940-3944. doi: 10.7498/aps.53.3940
The 3D thermoluminescence(TL) spectra were used to study the defect structure and luminescence mechanism produced by neutron irradiation in sapphire:Mn. The TL spectra of sapphire:Mn irradiated with 1000 Gy60Co γ-rays before n eutron irradiation show a broad wavelength band around 680nm at about 350℃ which may be related to the Mn2+ ions emission, and there is the 695 nm line spectrum which superposes to 680 nm broad band that is emitted from Cr3+ ions. Comparison between the spectra of undopedα-Al2O3 crystal and that of sapphire:Mn shows that the emission spectra of undopedα-Al2O3 at 416nm at about 207℃ related to the relaxation of an electron from the excited 3P state to the ground state 1S of the F center, is seriously suppressed. After neutron irradiation with fluence 1017cm-2, new glow peaks occur at about 150℃,at wavelengths 416 nm, 680 nm and 695 nm. The intensity of the glow peak at 150℃, 695 nm is greatly enhanced compared to that before neutron irradiation. The glow peaks at wavelength 520 nm at about 150℃, 190℃ and 250℃ emitted probably from Mn2+ ions are observed after 1018cm-2 fluence neutron irradiation. This indicates that neutron irradiation produces a quite amount shallow traps and F centers, and that 3D spectra are useful for studying the trap structures and luminescence mechanism.
2004, 53 (11): 3945-3949. doi: 10.7498/aps.53.3945
The spectral properties of nanoparticles Gd2O3:Eu3+ have been investigated by using Judd Ofelt theory at 77K. Intensity parameters Ωλ(λ＝2，4) were calculated using the experimental data of 5D0→7F2 and 5D0→7F4 transitions by taking the magnetic dipole transition 5D0→7F1 as reference. The intensity of the transition is almost completely unaffected by the local environment. It is indicated that intensity parameter Ωλ changes with the variation of diameter of nanoparticles Gd2O3:Eu3+,dramatically different from that of the bulk material.With decreasing diameter of the nanoparticles Gd2O3:Eu3+ from 135 to 15nm,the quantum efficiency of the emitting level 5D0 reduces from 23.6% to 4.6%. The smaller the diameter of nanoparticles Gd2O3:Eu3+, the bigger the ratio of surface to volume and the more the surface defect.It is the enhancing of the non radiation channels that results in the decrease of the quantum efficiency. The other two non radiation channels, charge (Eu3+-O2-) transfer state and multiphonon nonradiative re excitaton, were also studied.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2004, 53 (11): 3950-3955. doi: 10.7498/aps.53.3950
Polycrystalline silicon thin films were prepared at high-speed by plasma-enhanced chemical vapor deposition technique at low temperatures using SiCl4 and H2 as source gases. It was found that the grain growth is strongly affected by the relative concentration of different active radicals in the gas-phase space. On the other hand, the relative concentration depends on the deposition conditions. With the decrease of the rf power and the H2/ SiCl4 flow ratio, and the increase in the reaction pressure, the grain size increases. By changing the deposition conditions, variations of the relative concentration were analyzed. It is suggested that the “gas-phase crystalline" is of crucial importance to the grain growth.
2004, 53 (11): 3956-3960. doi: 10.7498/aps.53.3956
Transparent and integral U:CaF2 single crystals with diameter of 75mm were successfully grown by temperature gradient technique. The distribution coefficient of uranium in Ca F2 is equal to 0.53, which was calculated using the formula, K0=Cs/Cl.The calculated concentrations of uranium in CaF2 according to general distribution equation, Cs=K0C0(1-g)K0-1, are consistent with the measured values, indicating that the process of crystal growth was nearly in equilibrium. Unit cell paramenters and optical absorption spectra of U:CaF2 crystals grown under different conditions have been analyzed. Results indicate that the growth atmospheres determine the valences of uranium ions and the mechanism of charge compensation: the uranium ion is U4+ with green color in the absence of Pb F2; uranium is apt to form U3+with radius most close to that of Ca2+ in the presence of Pb F2 as a scavenger. From the beginning part to the end of U3+:Ca F2 crystal, only optical densities of all absorption bands gradually increase with the concentration of uranium. With increasing concentration of doped uranium, the color of the as grown U:Ca F2 crystals change from pink to brownish. The 5mm thickness periphery of the U3+:Ca F2 crystal with a yellow color was confirmed to contain mixed valences of U2+ and U3+, as a result of the reduction effect of graphite crucible.
Large scale synthesis of single-walled carbon nanotubes by an arc-discharge method at controlled temperatures
2004, 53 (11): 3961-3965. doi: 10.7498/aps.53.3961
Large amounts of single-wall carbon nanotubes(SWNTs) deposited on all the wall of the chamber have been obtained in helium and nitrogen mixed atmosphere using Co-Ni alloy catalyst with a modified arc furnace which can control the temperature during arcing process. Additionally, there are many weblike deposition products located between the cathode and anode. By twostep purification:the as-grown SWNT was heated in air at 500℃ for 30min, then soaked in 37% hydrochloric acid for 72h and filtered with deionized water. Microanalysis was carried out by Transmission electron microscopy(TEM), high-resolution TEM and Raman spectroscopy. The results obtained indicate that the purified SWNTs have high purity (higher than 95%) and uniform diameter (from 1.24 to 1.38nm).This experiment indicates that the temperature strongly affects the production of SWNT; the production and purity of SWNT increase with temperature. When the temperature is 600℃, the purity is about 70% and the production of SWNT is 12g/h.
2004, 53 (11): 3966-3970. doi: 10.7498/aps.53.3966
The investigation on the nucleation mechanism of Au-containing glass in an electric field By means of x-ray diffraction, scanning electron microscopy and absorption spec troscopy, we have studied Au-containing glass which is heat-treated under a n a pplied electric field. The experimental results are consistent with the conclusi ons obtained from a new thermodynamic model, which is proposed based on the static electromagnetic theory and thermodynamic theory in order to describe the nucl eation process of glass doped with metals. As a key factor in the model, the ele ctric energy change is calculated by two methods in this study. One is based on some approximation treatment, and the other the finite element method. The resul ts obtained by the two methods are similar and can explain the experimental results fairly well.
Time-dependent interface stability during directional solidification of a single phase alloy(Ⅰ) Theoritical
2004, 53 (11): 3971-3977. doi: 10.7498/aps.53.3971
The initial transient solute redistribution during directional solidification is systematically investigated by carefully comparing the current theoreltical models with experimental results. It is shown that at the transient front solute redistribution generally meets an exponential profile no matter whether there exi sts liquid convection or pure diffusion in front of the liquid/solid interface.The profile can be described by a unified formula. Based on this, a general time-dependent linear dynamic analysis of the morphological instability of a solidifying planar interface during directional solidification is carried out. It is found that the timedependent instability solution has the same form as the steadystate solution described by Mullins and Sekerka, but the timedependent concentration gradient GtC, interface velocity Vi and diffusion length l should replace the corresponding steadystate concentration gradi ent GC，interface velocity V，diffusion length DL/V in Mulli ns and Sekerka solution.
A time-dependent interface stability during directional solidification of a single phase alloy(Ⅱ)Comparison with experimental results
2004, 53 (11): 3978-3983. doi: 10.7498/aps.53.3978
In situ observation on the interface instability and the solute transport boundary layer in front of the solid/liquid interface is carried out during the di rectional solidification of SCN-1.5at%Salol. Based on this, and in combination with the experimental results of SCN-1.1 wt%Eth, SCN-0.43wt%C152 alloys, the morp hological instability of a solidifying planar interface is systematically invest igated during directional solidification with and without the convection. It is found that the interface stability analysis in our previous paper describes corr ectly the time-dependent evolution of interface instability. Both the incubation time ti for instability and the incubation time tb for breakdown of the planar interface can be determined from the time-dependent instability so lution, and the convection obviously shortens the incubation time ti for i nstability and the incubation time tb for breakdown of the planar interface. The steady-state instability solution overestimates the unit amplitude devel oping rate by an order of magnitude, as compared to the experimental value, while the time-dependent solution underestimates the experimental result.
2004, 53 (11): 3984-3989. doi: 10.7498/aps.53.3984
Highly monodispersed colloidal silica particles in sizes ranging from 700 to 1300 nm were synthesized by a two-step method. The transmission electron microscope images showed that the mean standard deviation of these particles is less than 5%. Silica particle size range for self-assembly in the gravitational sedimentation was broadened through adjusting the viscosity of media in silica suspensions. The synthetic opals with particle diameters ranging from 700 to 1300 nm were obtained,and their optical characteristics were examined. Scanning electron microscope images showed that the synthetic opals have a face-centered-cubic structure and have partial photonic band-gaps. This provides the foundation for the study of complete photonic crystals with wavelengths within near-infrared and infrared regions and for the fabrication of other macroporous materials.
2004, 53 (11): 3990-3995. doi: 10.7498/aps.53.3990
Pulse shortening is an universal phenomenon in highpower microwave tubes, which hinders the improvement of microwave output energy. So far, it is also an unres olved problem in the field of high-power microwave devices. In this paper, the relativistic backward wave tube (RBWO) is treated as an example to study the pul se shortening phenomena. The influences of explosive emission in the inner surface of RBWO and fluctuation of the relativistic electron beam on the pulse width and output power are investigated by means of the particle in cell(PIC) method .Through the simulation results, some useful conclusions have been drawn. The explosive emission in the surface of the slow wave structure due to intense elec tric field is one of the most important factors causing pulse shortening in high-power microwave tube. The fluctuation of the electron beam can also lead to pulse shortening. Some methods to overcome pulse shortening are given in this paper.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Effect of atmospheric turbulence on the propagation properties of spatially partially coherent polychromatic light
2004, 53 (11): 3996-4001. doi: 10.7498/aps.53.3996
Based on the propagation law of partially coherent light, the longdistance pro pagation of the spatially partially coherent polychromatic light through the atm osphere is studied. It is shown that the atmospheric turbulence gives rise to sp ectral shift and to beam spreading of spatially partially coherent polychromatic-light whether the scaling law is satisfied or not. The influence of turbulence on beam spreading of the spatially partially coherent polychromatic light is sma ller than that of spatially fully coherent polychromatic light. However, the inf luence of bandwidth on the intensity distribution is relatively small.
2004, 53 (11): 4002-4006. doi: 10.7498/aps.53.4002
Applying the generalized uncertainty relation to the thin film brick wall model, the method of calculating black hole entropy without cutoff was first proposed in 2002. However, it was then only determined that the upper bound of entropy is proportional to the event horizon. Since the method is studied more deeply, the entropy itself is found proportional to the horizon too. The relation between the ratio coefficient and the second-order uncertainty parameter is also discusse d. Moreover, the non-spherical Rindler horizon is studied, and the expected res ult is given. It is apparent that the cut-off in the brick wall model is something related to the quantum theory of gravity.
Discussion on the characteristics of the quantumradiation of unstationary and slowly-changing Reissner-Nordstr?m black hole
2004, 53 (11): 4007-4014. doi: 10.7498/aps.53.4007
Taking into account the case that the mass M and charge Q of Reissner-Nordstr?m black hole varying slowly with time t, the discussion on the quant um radiation characteristics of the black hole shows that the thermal radiation spectrum of charged Dirac particles is connected with the black hole's evaporati on rate together with the factors M(t), Q(t) etc. changing with time, and that the maximum energy of the quantum nonthermal radiation of nonstationary and slowly-changing Reissner-Nordstr?m black hole is equal to the chemical potential in the quantum thermal radiation spectrum.