Vol. 54, No. 7 (2005)

A non-collapsing solution of a uniform-density ball of dust in the discrete spacetime
Chen Guang
2005, 54 (7): 2971-2976. doi: 10.7498/aps.54.2971
Abstract +
A discrete function theory is found based on the continuous function theory and the discretization of real numbers, which is used to express the classical general relativity and analyse the collapse of a uniform-density ball of dust. It i s shown that the intrinsic and extrinsic geometrices do not actually match at th e join between the Friedmann interior and the Schwarzschild exterior for the Opp enheimer and Snyder solution as a continuum. With the discrete function theory, we can extend and discretize the solution to form a complete non-collapsing solution of the ball of dust, thereby eliminate the gravitational singularity and reveal the deep nature of the discretization of spacetime.
A singularity-free solution of Friedmann universe in the discrete spacetime
Chen Guang
2005, 54 (7): 2977-2979. doi: 10.7498/aps.54.2977
Abstract +
An idealized Friedmann cosmological model in the discrete spacetime is consist of collection of dust particles obtained in paper[1] and proved to be singu larity-free.
Symmetries and Mei conserved quantities for systems of generalized classical mechanics
Zhang Yi
2005, 54 (7): 2980-2984. doi: 10.7498/aps.54.2980
Abstract +
In this paper, the symmetries and a new type of conserved quantities called Mei conserved quantities for systems of generalized classical mechanics are studied. In the high-dimensional extended phase space, the differential equations of motion of the systems are established, and the criteria for Mei symmetries, Noethe r symmetries and Lie symmetries of the systems are given. The conditions, under which the above three symmetries can respectively lead to the Mei conserved qu antities, and the form of the Mei conserved quantities are obtained. Finally, an example is given to illustrate the application of the results.
Symmetry and stability of a relativistic birkhoff system
Zhang Kai, Feng Jun
2005, 54 (7): 2985-2989. doi: 10.7498/aps.54.2985
Abstract +
Relationships among the three symmetries——Noether symmetry,Lie symmetry and M ei symmetry of a relativistic Birkhoff system have been obtained. Some stabilit y criteria are given by using Liapunov method. Finally the conservation quanti ty and the stability of the relativistic Birkhoff system are correlated by the Energy-Casimir functional, and an example is given, to illustrate the applicat ion of the method.
New variable separation excitations, rectangle-like solitons and fractal solitons in the Boiti-Leon-Pempinelli system
Fang Jian-Ping, Zhu Jia-Min, Zheng Chun-Long
2005, 54 (7): 2990-2995. doi: 10.7498/aps.54.2990
Abstract +
Using an extended Riccati mapping approach,we obtain a new type of varable separation solutions for the (2+1)-dimensional Boiti-Leon-Pempinelli system.Based on the derived solutions,two new kinds of soliton excitations,i.e.rectangle-like soliton and fractal soliton are constructed in this paper.
Visualization of the solution of Jacobi elliptic expanding function
Zheng Qiang, Yue Ping, Gong Lun-Xun
2005, 54 (7): 2996-2999. doi: 10.7498/aps.54.2996
Abstract +
Thanks to the powerful software MATLAB, this paper gets the beautiful figures of a kind of Jacobi elliptic function-sn(x,k);and as an example, we also d raw the figures of solution of Jacobi expanding function of KdV equation in two different parameters.
Theoretical model of laser-induced dispersion optical filter
Zhang Yun-Dong, Sun Xu-Tao, He Zhu-Song
2005, 54 (7): 3000-3004. doi: 10.7498/aps.54.3000
Abstract +
The semi-classical theory was utilized to establish the theoretical model of la ser-induced dispersion optical filter (LIDOF). By solving the density matrix equ ations, we gained the susceptibility. The theoretical transmission curve of K- 694nm LIDOF was obtained, which agrees basically with the experimental result.
Statistical entropy of Kerr-Newman-de Sitter black hole
Li Gu-Qiang
2005, 54 (7): 3005-3008. doi: 10.7498/aps.54.3005
Abstract +
The partition functions of bosonic and fermionic field in Kerr-Newman-de Sitter black hole are derived directly by using the method of quantum statistics. Th en the entropy of the Kerr-Newman-de Sitter black hole is calculated by using the improved brick-wall method with the membrane model.
Prediction of the chaotic time series using support vector machines for fuzzy rule-based modeling
Cui Wan-Zhao, Zhu Chang-Chun, Bao Wen-Xing, Liu Jun-Hua
2005, 54 (7): 3009-3018. doi: 10.7498/aps.54.3009
Abstract +
Based on the powerful nonlinear mapping ability of support vector machines and the characteristics of fuzzy logic which can combine a prior knowledge into fuzzy rules, the forecasting model of the support vector machine for fuzzy rules-bas ed model in combination with Takens' delay coordinate phase reconstruction of ch aotic time series has been established; and the least squares method for large-s cale problems is used to train this model. Moreover, based on this model, relati onships among the prediction performances of this model, the embedding dimension and the delay time are discussed. Finally, the Mackey-Glass equation and the t ime series that Lorenz systems generate are applied to test this model, respecti vely, and the results show that the support vector machine for fuzzy rule-based modeling can not only acquire knowledge and generate fuzzy rules from the given data, reduce the number of support vectors greatly, but also predict chaotic ti me series accurately, and even if the embedding dimension is unknown and the del ay time is appropriately selected, the predicted results are satisfactory. These results imply the support vector machine for fuzzy rule-based modeling is a go od tool to study chaotic time series in practice.
Improving the efficiency of time-delayed feedback control of chaos through linear invertible transform
Zhang Ru-Yuan, Zhang Xiao-Ming, Peng Jian-Hua
2005, 54 (7): 3019-3026. doi: 10.7498/aps.54.3019
Abstract +
A scheme,which can be used to effectively improve the quality of time-delayed feedback control of chaos,was proposed based on linear invertible transform.Through transforming parts of state variables of the system in the corresponding sub-space,we can successfully control chaos by a single time-delayed feedback signal instead of multi-signals in the original system before the transformation.Therefore,the conditions for stabilizing the system can be found theoretically.The numerical simulation results show that this chaos control method is commendably effective and feasible.
A note on the exponent of dynamical cross-correlation factor
Wu Lian-Wen, Cheng Qian-Sheng
2005, 54 (7): 3027-3028. doi: 10.7498/aps.54.3027
Abstract +
Tthis paper argues with a counter example that the exponent of dynamical cross-correlation factor used in a paper published in Acta Phys. Sin. vol 52,p2114 is ill defined and gives the correct definition.
Synchronization of symmetrically nonlinear-coupled chaotic systems
Yu Hong-Jie, Liu Yan-Zhu
2005, 54 (7): 3029-3033. doi: 10.7498/aps.54.3029
Abstract +
The synchronization of two symmetrical nonlinear-coupled chaotic systems is discussed. A special nonlinear-coupled term is constructed by suitable separation between linear and nonlinear terms of the chaotic system. The phenomenon of stab le chaotic synchronization has been found in a certain region of the coupled str ength α=05. The stability of the synchronous state is examined by the sta bility criterion of linear systems and the conditional Lyapunov exponent. The Lo renz system and the hyper-chaotic Rssler system are treated as numerical exam ples. It is shown that the proposed method is effective for chaotic synchronizat ion of time-continued systems and hyper-chaotic systems.
Methods of finding periodic orbit in chaotic systems
Wang Pei-Jie, Wu Guo-Zhen
2005, 54 (7): 3034-3043. doi: 10.7498/aps.54.3034
Abstract +
The dynamics of a chaotic system is full of chaotic orbits, especially for highe r levels where resonances are strong enough to destroy most periodic and/or quas iperiodic trajectories.Though the remnant periodic orbits are scarce,they are no t to be neglected because they form the invariant skeleton of the dynamical phas e space.For instance,we can quantize a nonintegrable system by its periodic orbi ts,which implies the important role of periodic orbits.Therefore,the locating of periodic orbits becomes one of the key points in the study of the dynamics of c haotic systems.Based on explicit examples,we list three methods for locating the periodic orbits in this paper,and conclude that the Newton method is the optima l choice.
A study of a main-road traffic flow model with turning-probability under open-bound condition
Huang Ping-Hua, Tan Hui-Li, Kong Ling-Jiang, Liu Mu-Ren
2005, 54 (7): 3044-3050. doi: 10.7498/aps.54.3044
Abstract +
A main-road cellular automata traffic flow model with turning-probability in t erms of rules of the improved Nagel-Schreckenberg is presented under the open b oundary condition. The different characteristics of the phase transition led to by the turning probability and the open boundary condition are studied for the improvement on the traffic flow.
Phase-shift algorithm research based on multiple-beam interference principle
Luo Zhi-Yong, Yang Li-Feng, Chen Yun-Chang
2005, 54 (7): 3051-3057. doi: 10.7498/aps.54.3051
Abstract +
Aiming at the application of precision measurement of length, the phase-shift a lgorithm including algorithm error and optimum range of the phase-shift step wa s studied by using the multiple-beam interference principle in this paper. We have derived an accurate formula for the intensity distribution of multiple-be am interference (multiple reflection by and transmission through the optical s urface) in the basic principle of interference optics. Based on this formula and the numerical analysis technique, we have found the optimum value of the phase-shift step and the applicable range of the initial phase difference between in terference beams by using the precision measurement of length with Fizeau inter ferometer.We also found the respective relationships between the original phase error and the phase of four-step algorithm (and of the five-step algorithm) d ue to the intensity error from cosine dependence. We have assessed the uncertain ty from several main error sources of the multiple-beam interference.
Study on the three-dimensional theory of super thin multi-layered films irradiated by the continuously modulated laser
Yan Chang-Chun, Xue Guo-Gang, Liu Cheng, Gao Shu-Mei
2005, 54 (7): 3058-3062. doi: 10.7498/aps.54.3058
Abstract +
On the basis of heat conduction equations and under special boundary conditions,the temperatute fields of multilayered heated uniaxial films can be acquired in the cylindrical coordinate system by Hankel transformation and retransformation.As an example with specific parameters,the special growth conditions for three-layered films are discussed.The larger are the lognitudinal heat conductions vs transverse ones of thin films for higher thermal diffusivity,the larger are chan ges of phases of the temperature fields in the thin films.However,it is faintly influencing for the lognitudinal heat conductions vs transverse ones of thin fil ms for lower thermal diffusivity,and the smaller is light absorbing coefficient, the more evident is the influence on phases because of frequency change.
A new method for analysis of electro-optic detection for THz radiation
Zheng Guo-Liang, Wu Dan-Dan, She Wei-Long
2005, 54 (7): 3063-3068. doi: 10.7498/aps.54.3063
Abstract +
A new method for description of electro-optic detection for THz radiation, using wave coupling theory of linear electro-optic effect,is presented in this paper. This method is not only useable in all optically isotropic detection crystals,bu t also usable in the situation that the probe beam propagates along the optical axis of uniaxial crystals.Also,the description method can be used for all possib le polarization directions of the probe beam and for arbitrary direction of the electric field of THz radiation.The description does not need complex coordinate transform,and the calculation is very simple.Finally,some conclusions have been drawn.
Theoretical study of graded-index coatings prepared by glancing angle deposition
Shao Jian-Da, Wang Ying-Jian, Fan Zheng-Xiu, Shen Zi-Cai
2005, 54 (7): 3069-3074. doi: 10.7498/aps.54.3069
Abstract +
Relationship between refractive index and packing density of coatings prepared by glancing angle deposition is analyzed and three expressions are given firstly. And then optical characteristics of the graded-index coating, which is deposi ted as the linear changing of packing density, are discussed from some aspects a s positive or negative change,integral periods or have hale period,different per iods etc, and more over, the influences of different refractive-index theories on the optical characteristics are compared. Finelly, the preparation method,ap plications and some problem in preparation of the graded coating are discussed s eparately.
CDW-EIS calculation in He2++H impact ionization
He Bin, Liu Chun-Lei, Yan Jun, Wang Jian-Guo, Ning Ye
2005, 54 (7): 3075-3081. doi: 10.7498/aps.54.3075
Abstract +
The He2++H Impact Ionization process is investigated using a continu um distorted wave method with the eikonal initial-state(CDW-EIS) approximation.The total,single- and double-differential cross sections are obtained in the projectile energy ranges from 30keV/u to 2000keV/u.The total cross sections are compared with the existing theoretical and experimental data.When the projectile energy is larger than 100keV/u,our results are in good agreement with the experimental measurements,while about 50% less than experimental data in the lower energy range.The ionization mechanism of soft-collisions,electron captured to continuum states and binary-encounter collisions are also displayed.
The isospin effect of momentum-dependent interaction in heavy ion collisions
Guo Wen-Jun, Xing Yong-Zhong, Liu Jian-Ye
2005, 54 (7): 3082-3086. doi: 10.7498/aps.54.3082
Abstract +
We introduce the isospin degree of freedom into the momentum-dependent interaction to obtain an isospin and momentum dependent interaction given in a form practically usable in isospin-dependent quantum molecular dynamics model.We investigate the isospin effect of momentum-dependent interaction on the observable in the intermediate-energy heavy ion collisions.It is found that momentum-dependent interactions with and without isospin dependence,lead to significant different predictions on the nuclear stopping(momentum dissipation) and isospin fractionation ratio.In particular,the momentum-dependent interaction with the isospin degree of freedom induces the reduction for the strong dependence of isospin fractiona tion ratio on the symmetric potential.However,it does not change obviously the a bove feature for the isospin fractionation ratio as the good probe of symmetric potential respectively.The isospin dependence of momentum-dependent interaction is thus important for studying accurately the equation of state of isospin asym metry nuclear matter.
Study on the effect of external electric field excitation on methane
Xu Guo-Liang, Zhu Zheng-He, Ma Mei-Zhong, Xie An-Dong
2005, 54 (7): 3087-3093. doi: 10.7498/aps.54.3087
Abstract +
The present paper is devoted to the calculation of transition wavelengths, os cillator strengths f, Einstein An0 and B0n coefficients of methane from ground state X~lAl to the first six di fferent excited states by employing density functional theory and single substitute con figuration interaction (CIS) approach with basis sets 6-311++G**. At the same time, the excited states of methane under an external electric field are i nvestigated. It is shown that the total energy of the system has little change d, and simultaneously the HOMO-LUMO gaps become small and the Fermi levels dec lines slightly as the external electric field intensity become strong. The trans ition between ground state X~lAl and the high-excited state of methane is easy bring about.
THz spectrum of aromatic amino acid
Yue Wei-Wei, Wang Wei-Ning, Zhao Guo-Zhong, Zhang Cun-Lin, Yan Hai-Tao
2005, 54 (7): 3094-3099. doi: 10.7498/aps.54.3094
Abstract +
We have studied the optical properties of three kinds of aromatic amino acids including tyrosine, tryptophane and phenylalanine using THz time domain spectroscopy between 0.2 and 1.6 THz.Comparing their absorption spectra,we find that tyros ine and tryptophane have sharp absorption peaks at 0.976THz and 1.465THz respect ively,while phenylalanine does not have absorption peak in this range.This resul t shows the capability of THz time domain spectroscopy to distinguish different molecules.Calculating by density functional,we found that the absorption peaks a re caused by the rotation and torsion of the molecules.The average refractive in dexes of these three amino acids are also obtained:they are 1.507,1.526 and 1.68 6 respectively.This work not only is significant for the research of molecular s tructure and molecular dynamics,but can also provide reference for studying othe r large biological molecules by THz time domain spectroscopy.
Method for fabricating Fe3O4 nanoparticles using H2O2 and its comparison with coprecipitation method
Li Fa-Shen, Wang Tao, Wang Ying
2005, 54 (7): 3100-3105. doi: 10.7498/aps.54.3100
Abstract +
Fe3O4 nanoparticles were successfully synthesized from an aqueous Fe (OH)2 colloid under nearly neutral condition by oxidizing it with H2O2. The m orphology, structure, and magnetic properties were characterized and measured by transmission electron microscopy (TEM), x-ray diffraction (XRD), vibrating sam ple magnetometer, and superconducting quantum interference devices (SQUID). The TEM image shows that the sample consists of well-dispersed spherical particles with diameter about 18nm, and has a cubic spinel structure according to XRD. The mssbauer spectrum at room temperature is fitted using two sextet spectrum cor responding to Fe ions at A site and B site, and the results show that th e hyperfine field of the sample is a little smaller than that of bulk value, and crystalline defects exist in the sample. The saturation magnetization of the sa mple fabricated by using H2O2 is 67×10-3A·m 2/g, and the Ver wey transition was observed at 20K, but the magnetization of the sample fabricat ed by coprecipitation is only 46×10-3A·m2/g when the app lied field is 1 Tesla, and the Verwey transition was not observed in our temperature range of measurement. In addition, the superparamagnetic blocking temperature of the s ample fabricated by coprecipitation was observed at 178K.
The geometrical structure of B2H6 molecule
Zhu Zheng-He, Yan Shi-Ying, Ma Mei-Zhong
2005, 54 (7): 3106-3110. doi: 10.7498/aps.54.3106
Abstract +
The possible geometrical configuration of B2H6 molecule of D3d,D3h,D2d and planar or stereo D2h have long been argued about.In this work different methods of B3P86,BP86,B3LYP,BLYP,UHF,HF and LSDA in Gaussian 98 program have been used to optimize the structure of B2H 6.Our result shwos that the ground state geometrical configuration for B2H6 molecules is stereo D2h,i.e.,the three-center two bridge hydrogen structure,in wh ich two boron and four hydrogen atoms lie in a plane while the other two bridge hydrogen atoms lie in a plane perpendicular to it.This three-center two bridge hydrogen structure is more stable than two-center two-electron bond structure.
Transmission technigue of repetition pulse and intense current electron-beam
Zhou Chuan-Ming, Xiang Fei, Gan Yan-Qing, Chang An-Bi, Liu Zhong, Zhang Yong-Hui, Ma Qiao-Sheng
2005, 54 (7): 3111-3115. doi: 10.7498/aps.54.3111
Abstract +
The stability condition of intense annular electron beam transmission is analyzed and deduced. Based on the static electric-magnetic field simulation, the position and configuration of the guide magnetic-field and its magnitude as well as its power supply are designed. Then the experiments of repetitive rate and inte nse current electron-beam diode are carried out on CHP01 generator, and the ima ge of the intense annular electron beam is measured too. The results show that t he designed 1-s magnetic field satisfies to the stability condition of intense annular electron beam transmission. It can stably transmit intense current elect ron-beam pulse of 800kV/8kA, pulse width 40ns, repetition rate 100Hz. And now t he 1-s magnetic-field system is successfully used on CHP01 accelerator.
Spectral time evolution of quasistate modes in two-dimensional random media
Liu Jin-Song, Liu Hai, Wang Chun
2005, 54 (7): 3116-3122. doi: 10.7498/aps.54.3116
Abstract +
The spectral time evolution of optical modes in planar random media is analyzed by using the finite difference time domain method to numerically solve Maxwell equations. The character of random media can be described by some factors, including the random constitution of scattering particles, medium parameters (such as the surface-filling fraction and the size of particle), and the shape of me dium. Such factors determine the frequency property and number of optical modes in random medium under quasi-stable state. However, the media with different f actors have approximately the same character and rate for the generation, sele ction and evolution of optical modes. Such cold cavity properties of planar rand om media are similar to that in conventional optical cavities.
Near Gaussian approximation for light propagation in the intermittent atmospheric turbulence
Chen Shi-Gang, Wang Guang-Rui, Chen Jing-Yuan
2005, 54 (7): 3123-3131. doi: 10.7498/aps.54.3123
Abstract +
Intermittency is an essential property of turbulent atmosphere, and is one of the core content in modern turbulence theory. But, when we consider the problem of wave propagation in turbulent atmosphere, we always evade this property and use the assumption of a Gaussian probability distribution of dielectric permittivity fluctuation. In this paper, we discussed the intermittent effects on light propagation in turbulent atmosphere. According to the fact that the variance of dielectric permittivity fluctuation is very small, we explicitly expanded the equations of optical statistical moments to the fourth-order cumulant functions and considered their solutions. As for the second-order moment which is important i n optical applications, we have analyzed it emphatically by the hierarchical str uctures model. Our results indicate that the optical effects of turbulent interm ittency are negligible and the conventional Gaussian assumption is rational.
Applications of a simplified non-Gaussian field model to wave propagation in turbulent media
Chen Shi-Gang, Wang Guang-Rui, Chen Jing-Yuan
2005, 54 (7): 3132-3139. doi: 10.7498/aps.54.3132
Abstract +
In order to study the optical effects of turbulent intermittency,a simplified non-Gaussian random field model has been constructed,which can model atmospheric dielectric permittivity(or refractive-index) fluctuation approximately.Four arbitrary functions enter into the characteristic functional of this model.Using the properties of the atmospheric turbulence,such as the statistical homogeneity,the single-point probability distribution and the spectrum of the refractive-index fluctuations,these functions can be selected or determined.With these given functions,we have studied the statistical properties,especially the mean field adn the mutual coherence function,of a plane partially coherent incident wave.A simple example of numerical simulation has also been presented.
Study on gain fluence curve of a laser pulse amplifier
Liu Ren-Hong, Cai Xi-Jie, Yang Lin, Zhang Zhi-Xiang, Bi Ji-Jun
2005, 54 (7): 3140-3143. doi: 10.7498/aps.54.3140
Abstract +
This paper discusses a method of characterizing the gain of the laser pulse amplifier using its gain fluence curves,and studies gain fluence curves of a single amplifier.These help us to understand the characteristics of the amplifier and provide a powerful tool for the investigation of the power balance.
Investigation of the precision of curved surface fitting in the measurement of near-cylindrical surfaces’ mid-wavelength deformations
Lu Zhen-Wu, Li Feng-You, Xie Ben-Chao
2005, 54 (7): 3144-3148. doi: 10.7498/aps.54.3144
Abstract +
The application of curved surface fitting for the disposal of the wavefront aberrations got in the measurement of certain paraboloid and hyperboloid is studied. It is found that,for mid-wavelength deformations with an amplitude of 01λ, results can be obtained with RMS error smaller than 0015λ and 0013λ separately. The existence of a special fitting order which leads to the smallest RMS e rror is affirmed. To find out the special fitting order,we work out two methods which help us get the order's value successfully.
A kinetics model for metastable-metastable transition laser in Sr atom vapor
Feng Jian, Chen Gang, Pan Bai-Liang, Yao Zhi-Xin
2005, 54 (7): 3149-3153. doi: 10.7498/aps.54.3149
Abstract +
A self-consistent physical model has been developed to simulate the kinetics in a high-repetition frequency, discharge-excited Sr atom metastable-metastable transition laser. The main pumping mechanism for each upper laser level has bee n clarified: the upper level of 301μm is pumped mainly by the spontaneous and stimulated emissions from the higher levels in early discharge pulses, while th e upper levels of the other 3 laser lines are chiefly populated through the reco mbination between the univalent Sr ions and electrons in the afterglow, and the collision mixing between neutral He and Sr atoms in compound triplet. The quant itative results predicted by the model are found to be in good agreement with th e previous experimental results. Furthermore, the temporal behavior of each lase r pulse is explained successfully by the simulation results.
Dynamic behavior analysis of the 3μm and 2μm cascade Ho3+:ZBLAN fiber lasers
Zhan Sheng-Bao, Dong Shu-Fu, Chen Guo-Fu, Wang Xian-Hua
2005, 54 (7): 3154-3158. doi: 10.7498/aps.54.3154
Abstract +
A numerical study of the transient behavior, including upper level ions and laser power relaxation oscillation, of Ho3+:ZBLAN fiber laser is presente d based on the propagation-rate equations. The power propagation equations for pump a nd signal have been treated differently by neglecting the z-dependence of t he fiber laser parameters, for the sake of numerical simplicity. The results sho w that upper level ions of 5I6 and 5I7 manifolds relax alternati vely and go to steady state after the first relaxation oscillation and monotonou s decline. Similarly, the 3μm and 2μm laser powers relax alternatively first, then the 3μm laser power declines monotonously while the 2μm laser power incre ases monotonously, both of them go to steady state after the second relaxation o scillation. Moreover, peak powers of the 3 μm and 2 μm lasers in the course of relaxation oscillation are far larger than that when steady state is reached.
Experimental investigation on temporal and spectral characteristics of femtosecond-scaled ultra-broadband Ti:sapphire oscillator
Wang Qing-Yue, Wang Zhuan, Chai Lu, Zhang Wei-Li, Xie Xu-Dong
2005, 54 (7): 3159-3163. doi: 10.7498/aps.54.3159
Abstract +
In this letter, we systematically investigated the temporal and spectral characteristic of ultra-broad band Ti:sapphire oscillator in femtosecond regime. Pulse formation in temporal regime was observed while the spectral shape evolved fro m hyperbolic secant shape into multi-peak one and the bandwidth increased from 40 to 180nm. Experimental results showed that pulse shortening mainly occurred n ot at its bottom part but at its central section while the spectrum was broadene d, and at the same time the relative energy at the bottom part increased.
Influence of pump laser parameters on stimulated Brillouin scattering
Deng Shao-Yong, Guo Shao-Feng, Lu Qi-Sheng, Cheng Xiang-Ai
2005, 54 (7): 3164-3172. doi: 10.7498/aps.54.3164
Abstract +
Numerical simulation was performed to study the stimulated Brillouin scattering(SBS) amplifier of self-Stokes-seeding. Chracteristic parameters such as Stokes laser,energy reflectivity,evolvement and distribution of maximum stress,pulse compression and SBS fidelity in fused silica were discussed for different Stokes ratio,wavelength,energy,pulse duration and interaction time.The focused Gaussia n pump laser was used.We got conclusions that the damage in near-front side of SBS medium was the characteristic of SBS; tuning parameters of pump laser, super -sonic stress formed in SBS process would damage the SBS medium not only on the front side, but also the damage near the focus;and the damage near the focus wo uld be made earlier when both parts were damaged.
Third harmonic generation in plasma channels in air induced by intense femtosecond laser pulses
Hao Zuo-Qiang, Zhang Jie, Zhang Zhe, Xi Ting-Ting, Zheng Zhi-Yuan, Wang Zhao-Hua, Yuan Xiao-Hui
2005, 54 (7): 3173-3177. doi: 10.7498/aps.54.3173
Abstract +
Strong third-order harmonic (TH) emission is observed from long plasma channels formed when intense femtosecond laser pulses propagate in air. The conversion efficiency between the fundamental wave and the TH emission is roughly constant over the length of the plasma channels. The divergence angle of the TH emission in the conical emission of the plasma channels is also investigated, which is in good agreement with calculations.
Analytical solution in the Hermite-Gaussian form of the beam propagating in the strong nonlocal media
Zhang Xia-Ping, Guo Qi
2005, 54 (7): 3178-3182. doi: 10.7498/aps.54.3178
Abstract +
In this paper, it is discussed that the optical beam with a suitable input powe r propagates in the nonlocal nonlinear media,which is governed by the nonlocal nonlinear Schrdinger equation (NNLSE).A new approxiamate linear model for the NNLSE is presented for the strong nonlocal media with the spatially symmetrica l real response functions by use of Taylor expansion. An exact analytical solut ion with the Hermite-Gaussian form is obtained.It is shown that the solution in the Gaussian form is the lowest-order mode.It is found that the anisomer ousty spatial soliton exists in the strong nonlocal media.
The propagation properties of the elliptic Gaussian beam in strongly nonlocal nonlinear media
Guo Qi, Wang Xing-Hua
2005, 54 (7): 3183-3188. doi: 10.7498/aps.54.3183
Abstract +
In this paper,the propagation properties of a paraxial elliptic Gaussian beam in strongly nonlocal nonlinear media are discussed.We obtain a set of evolution equations for the param eters of the elliptic Gaussian beam,and also their exact analytical solutions.When the beam propagates in the media,the beam widths in the two trasverse directions oscillate generally along a propagation direction.What ever an intial power is,the elliptic Gaussian beam will evolve into the circular ly symmetrical Gaussian beam,then evolve back to the elliptic Gaussian beam agai n,but with the change of its major axis into the minor axis.This process is peri odic.For a certern initial power,the beam width in one trasverse direction can k eep constant,which is an optical soliton state,while the width in the other tran sverse direction vibrates.
Photoinduced birefringence in an azo-dye-doped polymer
Qi Sheng-Wen, Yang Xiu-Qin, Chen Kuan, Zhang Chun-Ping, Zhang Lian-Shun, Wang Xin-Yu, Xu Tang, Liu Yong-Liang, Zhang Guang-Yin
2005, 54 (7): 3189-3193. doi: 10.7498/aps.54.3189
Abstract +
Under varying intensities and polarization of the exciting light, the photoinduced birefringence of azo dye polymer film placed between a pair of orthogonal po larizers is studied by measuring the transmitted intensity. It is concluded that the saturation and stable values of the transmitted intensity are all proportio nal to the intensity of the exciting light. Both values are also related to the polarization direction of the exciting light, and when the angle θ between the polarization directions of the probe intensity and the exciting light is lag er than 10°, the saturation and stable values of the transmitted light are all proportional to sin22θ. In addition, the differences in birefringenc es of the sample were measured accurately by using a compensator and 1.11×10-3 (before excitated) and 3.57×10-3 (after excitated) are obtaine d.
Band structures of three-dimensional photonic crystals consisting of dielectric spheres: a plane-wave approach
Wang Jing, Dong Hui-Yuan, Liu Mei, Wu Zong-Han, Wang Zhen-Lin
2005, 54 (7): 3194-3199. doi: 10.7498/aps.54.3194
Abstract +
Using the plane-wave method, we calculate the band structures and transmission characteristics of the three-dimensional fcc photonic crystals. For a SiO2 opa l photonic crystal, we calculate the energy spectrum and the transmission featu re of electromagnetic waves along the [111] direction using both the plane-wave method and the transfer-matrix method, the obtained results are consistent wit h each other. For a full band gap studies of the inverse-opal structure, the co nvergence effect in the plane-wave method on the calculation is discussed. For an fcc lattice of core-shell sphere, it is shown that the relative L-gap width of a suitable coating of dielectric spheres of a lower dielectric material can increase by 50% as compared with that of homogeneous high-dielectric spheres. We also find that the optimum radius ratio between interior and entire spheres is 0.69.
Spin dynamics of GaAs(100) by two-photon photoemission
Wüstenberg Jan-Peter, Oleksiy Andreyev, Bauer Michael, Aeschlimann Martin, Guo Li-Jun
2005, 54 (7): 3200-3205. doi: 10.7498/aps.54.3200
Abstract +
On p-doped GaAs(100) surface, the band bending arising from Fermi-level pinning significantly affects the carrier and spin dynamics. In this paper, we report th e dynamics of spin polarization of p-doped GaAs(100) by using the time-resolve d and the energy-resolved two-photon photoemission techniques. By measuring the spin and energy relaxation of electrons emitted from the GaAs(100) surfaces, th e dynamics of spin polarization were observed and the mechanism of spin relaxati on was discussed as well. The experimental measurements together with the theore tical results indicate that the Bir-Aronov-Pikus (BAP) mechanism plays a dominan t role for spin polarization decay, especially in band bending region of GaAs(10 0).
CTMC calculation of Si2+ + H impact ionization
He Bin, Ning Ye, Yan Jun, Wang Jian-Guo, Liu Chun-Lei
2005, 54 (7): 3206-3212. doi: 10.7498/aps.54.3206
Abstract +
The Si2+ + H collision ionization is studied using classical trajecto ry Mo nte-Carlo (CTMC) method. The total cross section as functions of the energy of i ncident projectile, single differential cross section and double differential cr oss section as a functions of the energy and the angle of the ejected electron a re calculated. The ionization mechanisms of soft collision, electron capture to the continuum state,binary encounter collision are demonstrated. The effect of “saddle point" is also discussed by calculating the ejected electron distributi on depending on the ratios of distances between electron and target and between electron and projectile.
Comparison of wakefield and relativistic effects on the self-phase modulation and frequency shift of intense laser pulse propagation
Guo Hong, Wu Guo-Hua, Deng Dong-Mei, Liu Shi-Xiong, Liu Ming-Wei
2005, 54 (7): 3213-3220. doi: 10.7498/aps.54.3213
Abstract +
The relativistic effect and wakefield effect on the propagation of an intense laser pulse in plasma are compared in the resonant and non-resonant cases in detai l. The effect of wakefield, which depends on the initial pulse shape and width, leads to the asymmetry of pulse self-phase modulation. In the long pulse limit, the wakefield effect is negligible compared to the relativistic effect; in the short pulse limit, it balances the relativistic effect. Under the resonant cond ition, most of the photons within the pulse decelerates.
Maser instability driven by an electron beam with losscone-beam distribution
Wang Chuan-Bing, Chen Yan-Ping, Zhou Guo-Cheng
2005, 54 (7): 3221-3227. doi: 10.7498/aps.54.3221
Abstract +
The studies of the main characterestics of the maser-instability driven by elec trons with a losscone-beam distribution are carried out on the basis of the the oretical model of Chen et al (2002, Phys. Plasmas 9,2816; 2003, Acta Phys. S in.52,421). This kind of electrons may be created by the reconnection near the chromosphere of the sun. The electrons have the characters of both losscone and beam. The results show that it can excite the fundamental and harmonic radiatio n of extraordinary and ordinary modes in an appropriate region of plasma freque ncy over the gyrofrequency with the characters of both losscone and beam distri bution, and with much stronger growth rate. It enriches the fundamental content of the plasma instabilities. It is expected to be applicable widely in the stud y of solar and celestial emission mechanism.
Low-frequency electromagnetic instabilities in a collisionless current sheet:magnetohydrodynamic model
Zhou Guo-Cheng, Cao Jin-Bin, Wei Xin-Hua, Li Liu-Yuan
2005, 54 (7): 3228-3235. doi: 10.7498/aps.54.3228
Abstract +
Low-frequency electromagnetic instabilities in a collisionless current sheet are discussed by using the 3-dimensional,collisionless and compressible magnetohydrodynamic model with the isotropic pressure.The linear dispersion relations are numerically solved at the middle plane (z=0) and edges (z=1) of the current sheet for modes of 2-and 3-dimensional propagation.The main results are as follows.(1) For 2-dimensional disturbed propagation (kz=0),at the middl e plane (z=0),the growth rate of Alfven waves is maximum,and the frequency and the wavenumber region of unstable waves are widest.The farther the distance from the middle plane,the smaller the growth rate and the wavenumber region.As the ion-inertial length becomes longer,the growth rate of Alfven waves becomes larger.(2)For 3-dimensional disturbed propagation (kz≠0),whistler waves are unstable.At the current sheet middle plane,whistler waves have an obvious growth rate.Outside the ion-inertial region,the growth rate of whistler waves becomes larger.(3)At the middle plane (z=0),low-frequency waves are mainly excited by the current-driven instabilities.At places far from the middle plane,the gradient instabilities of the current,density and pressure become more important.
Calculation of the wave reflecting characteristics of magnetized plasma surface
Yang Juan, Zhu Liang-Ming, Su Wei-Yi, Mao Gen-Wang
2005, 54 (7): 3236-3240. doi: 10.7498/aps.54.3236
Abstract +
The total wave energy reflectance of the interface between the magnetized plasma before a conductor plate and the atmosphere or vacuum can be calculated by usin g the equivalent input impedance method. The result is that the reflection chara cteristics can be affected by electron numerical density, magnetized plasma thic kness, incidence wave frequency and magnetic intensity. Magnetic field can reduc e wave energy reflectance obviously only when the electron numerical density is of an appropriate value. The increased frequency of the incident wave must accom pany the augmented magnetic intensity, which is the condition that magnetized pl asma will absorb more energy of the electromagnetic wave.
Structure and tribology properties of diamond-like carbon films prepared by microwave electron cyclotron resonance plasma source ion implantation
Gao Peng, Xu Jun, Deng Xin-Lu, Wang De-He, Dong Chuang
2005, 54 (7): 3241-3246. doi: 10.7498/aps.54.3241
Abstract +
Diamond-like carbon(DLC) films were prepared on silicon (100) wafer by microwave electron cyclotron resonance(MW-ECR) plasma source ion implantation(PSII). Th e results showed that the films had typical properties of DLC. The films was den se and homogeneous, and the roughness and friction coefficient was low. The conn ection between the properties of the films and the flow ratio of hydrogen was cl osely. With the increase of the flow ratio of hydrogen to methane, the depositio n rate and the roughness of the films decreased. The sp3 bond obtaine d was mor e likely diamond like, which had low surface energy, consequently making the fri ction coefficient of the films decrease rapidly.
The measurement and analysis of the prolonged lifetime of the plasma channel formed by short pulse laser in air
Dong Quan-Li, Yan Fei, Zhang Jie, Jin Zhan, Yang Hui, Hao Zuo-Qiang, Chen Zheng-Lin, Li Yu-Tong, Wei Zhi-Yi, Sheng Zheng-Ming
2005, 54 (7): 3247-3250. doi: 10.7498/aps.54.3247
Abstract +
The Tikhonov regularization method is applied to analyze the lifetime of the pl asma channel produced by femtosecond laser pulses propagating in air. Experiment s show that by using double laser pulses separated by several nanoseconds, the lifetime of the plasma channel can be prolonged by 5 times that of only using o ne laser pulse.
Simulation of step response of silane low-temperature pasma(1)
Yang Jing, Li Jing-Zhen, Sun Xiu-Quan, Gong Xiang-Dong
2005, 54 (7): 3251-3256. doi: 10.7498/aps.54.3251
Abstract +
Understanding of the transient response of electronegative radio-frequency glow plasmas is important for process control, better selectivity etch technology and charge free etching. We have investigated the step responses of RF(1356MHz) silane gas plasmas at a pressure of 05 Torr(05×10333Pa). The result showed that, when the power voltage changed stepwise from 550V to 350V, a steady sta te pulsed plasma oscillation at a few kHz appeared. The transient behavior and o scillation were interpreted in terms of the transport and chemistry of charge ca rriers in the plasma.
Zr-N films prepared by MW-ECR PE-UNB alanced magnetron sputtering: plasma diagnostics and structure evolution
Zhang Zhi-Guo, Liu Tian-Wei, Xu Jun, Deng Xin-Lu, Dong Chuang
2005, 54 (7): 3257-3262. doi: 10.7498/aps.54.3257
Abstract +
ZrN films were prepared using microwave electron cyclotron resonance (MW-ECR) plasma enhanced unbalanced magnetron sputtering (PE-UMS) technique. The plasma characteristics near the holder were diagnosed by Langmuir probe for various depo sition conditions and the films obtained were characterized by electron probe mi croanalysis x-ray diffraction and micro-hardness. As the N2 flow rate increas es from 2 to 20sccm, the ion density initially increases from 807×109 to 8 31×109cm-3 and then decreases to 752×109c m-3, while the N +2 ion density increases monotonically from 312×10 -8 to 335×109cm-3 and the electron temperature does not va ry much. The N concentration in t he films increases and the grain size decreases as the N+2 ion density increases. And the films become more and more amorphous as the N/Zr ratio is above 1 4 The corresponding microhardness of the deposited films increases from 22 5GPa to the maximum of 2678GPa, and then decreases linearly to 1982GPa as th e N2 flow rate increases from 8 to 14sccm. The mechanism of the influ ence of t he plasma characteristics on the microstructure and mechanical properties of the deposited films were discussed.
Preparation of Al2O3 ceramic coating by electrolytic plasma processing and its properties
Shen De-Jiu, Wang Yu-Lin, Chen Guang-Liang, Feng Wen-Ran, Zhang Gu-Ling, Liu Chi-Zi, Yang Si-Ze, Gu Wei-Chao
2005, 54 (7): 3263-3267. doi: 10.7498/aps.54.3263
Abstract +
Metallurgically bonded Al2O3 ceramic coating was prepared on steel surface with the combined method of arc spraying and electrolytic plasma processing. The composition and microstructure of the ceramic coating were analyzed by x-ray dif fraction, scanning electron microscony and EDS. The corrosion resistance and wea r resistance of the ceramic coating were measured. The results show that the cer amic coating is compact and mainly composed of α-Al2O3, γ-Al2O3, θ-Al2O3 and a little of a morphous phase. The duplex coating shows favorable corrosion resistance and wear resistance properties.
Study on the electrical characteristic of different modes of dielectric barrier discharge in argon
Dong Li-Fang, Mao Zhi-Guo, Ran Jun-Xia
2005, 54 (7): 3268-3272. doi: 10.7498/aps.54.3268
Abstract +
Three modes of discharges, including diffuse, streamer, and patterned discharges , are achieved in dielectric barrier discharge in argon at 40 kPa gas pressure b y using a dielectric barrier discharge device with water electrodes. The electri cal and optical characteristics of the discharges are investigated. The voltage drop across discharge gap is obtained by measuring the voltage drop across the t est capacitor. Results show that the moment of discharge initiation is shifted e arlier and duty ratio of the discharge increases as the applied voltage increase s. At the moment of discharge initiation, the voltage drop across the discharge gap decreases and the transported charges abruptly increase. So the waveforms of the voltage drop across the discharge gap and the transported charges deviate from sinusoidal. The relationship between the voltage drops across the discharg e gap and the transported charges is nonlinear. Also the relationship between th e voltage drops across the discharge gap corresponding to zero applied voltage a nd the applied voltage is given. The function of wall charges and the influence of them on the voltage drops across the discharge gap and the transported charge s are discussed.
Experimental investigation of insensitive explosive C6H6N6O6 by small angle x-ray scattering technique
Xia Qing-Zhong, Chen Bo, Zeng Gui-Yu, Luo Sun-Huo, Dong Hai-Shan, Rong Li-Xia, Dong Bao-Zhong
2005, 54 (7): 3273-3277. doi: 10.7498/aps.54.3273
Abstract +
Synchrotron radiation small-angle x-ray scattering (SAXS) technique was employed to investigate the pores in the insensitive high explosive C6H 6N6O6(TA TB) manufactured by different methods. The microstructure parameters of the por es such as diameter distribution, fractal character, Porod constant, interface parameter and so on were obtained from SAXS results. Analyses of variations of the microstructure parameters were also made. It is shown that there is an obvio us microstructure feature for each TATB sample.
Conditions for formation of misfit dislocation in epitaxial films — a molecular dynamics study
Zhou Nai-Gen, Zhou Lang
2005, 54 (7): 3278-3283. doi: 10.7498/aps.54.3278
Abstract +
Molecular dynamics simulations for the formation of misfit dislocation in compre ssive epitaxial aluminum films have been carried out. The potential in an embed ded atom method (EAM) is employed. The results show that, in long relaxation at 500K, the films with a perfect surface remain dislocation-free in thickness ran ge of 9—80 atomic layers, which corresponds to 3—40 times of its thermodynami c critical thickness. However, with the presence of small boss or pit of one-at om high and three-atom wide on surface, misfit dislocations form readily in film s of 15 atomic layer thick. In dynamic growth of a preset 9 atomic layer thick film, under deposition, the surface develops significant roughness naturally, l eading to rapid formation of misfit dislocation. The dislocations formed under the three conditions are all complete edge dislocations, with their Burgers vec tors parallel to the axis of misfit. Analysis revealed that, under compression , the micro-boss induces squeezing-out of atoms beside, leading to nucleation of a dislocation, and the micro-pit is directly reshaped to a nucleus of dislocat ion semi-loop.
CuZr-based bulk metallic glasses with good glass-forming ability prepared by Al addition
Bai Hai-Yang, Tang Mei-Bo, Wang Wei-Hua, Wang Wan-Lu, Yu Peng
2005, 54 (7): 3284-3289. doi: 10.7498/aps.54.3284
Abstract +
Based on the fabrication of CuZr binary bulk metallic glass(BMG), we have produced a series of CuZr-based BMGs prepared by Al addition using a copper mold casting method. CuZr-based BMGs with good glass-forming ability (GFA) have a broad g lass-forming composition range. When Al content changes from 4% to 8%, CuZr-bas ed BMGs can be produced in cylindrical rods with a diameter of at least 5mm. The physical reason of the good GFA in the alloys is analyzed. CuZr-based BMGs have a simple structure and are lower cost, so it is very possible to have potential application. At the same time, the way that we explored the CuZr-based BMGs is an effective route for designing and obtaining new multicomponent BMGs.
Multifractal spectra of growing clusters in nanoscale characterized by small angle x-ray scattering
Shao Yuan-Zhi, Zhong Wei-Rong, Ren Shan, Cai Zhi-Su, Gong Lei
2005, 54 (7): 3290-3296. doi: 10.7498/aps.54.3290
Abstract +
Small angle x-ray scattering (SAXS) method was adopted to investigate the characteristics of growth fractal of two sorts of typical nanoscaled clusters, i.e. g rowing in both ultrafine Ni powders synthesized by chemical reaction and Finemet (Fe73.5Cu1Nb3Si13.5B9) a morphous ribbon by physical crystal lization annealing. The SAXS measurement discloses definitely the existence of d istinct mass multifractal patterns within ultrafine Ni granules and crystallizin g Finemet ribbon. The multifractal spectra of the clusters mentioned above sugge st the occurrence of inhomogeneous distribution of constituent elements and grow th fractal during the formation of those nanoscale clusters. The multifractal sp ectra of ultrafine Ni powders prepared using a variety of procedures take on an obvious difference in shape, indicating the substantial influence of preparation process on diffusion of constituent elements and the growth mechanism of cluste rs. The crystallization annealing processes, however, affect the multifractal sp ectra of Finemet alloy slightly.
Vertically aligned carbon nanotubes grown on Au/Ni films and the role of Au in the grown process
Wang Bi-Ben, Chen Shu-Xia, Lü Xian-Yi, Jin Zeng-Sun, Gu Chang-Zhi, Li Hai-Jun, Li Jun-Jie
2005, 54 (7): 3297-3301. doi: 10.7498/aps.54.3297
Abstract +
The vertically aligned carbon nanotubes( CNTs) were synthesized on Au/Ni catalyst films by plasma enhanced hot filament chemical vapor deposition( PE-HFCVD) me thod at 96% concentration of hydrogen. The growing process of CNTs on Au/Ni film was discussed. The realization of the vertically aligned CNTs grown at high hyd rogen concentration can be attributed to the adoption of the Au/Ni catalyst film s. The element Au promoted the diffusion of the carbon and improved the activity of carbon in catalyst. By comparing with the use of only Ni as catalyst, the Au in Au/Ni catalyst film can increase the carbon absorption, so carbon could be e asily saturated in the catalyst and the vertically aligned CNTs were achieved at a high hydrogen concentration.
Characterisation of the crystal structure of La0.4FeCo3Sb12 by means of x-ray and electron diffractions
Xu Min, Sheng Wen, Gao Zhan, Zhao Liang-Lei, Jiang Bei, Yang Lei, Zhang Lan-Ting
2005, 54 (7): 3302-3306. doi: 10.7498/aps.54.3302
Abstract +
The crystal structure and its evolution of an n-type La20.4FeCo3 Sb12 compound have been characterized by the Rietveld refinemen t and TEM observation. An interstitial site 01980nm in radius has been found in the lattice of t he binary Skutterudite compound. Filling this interstitial site by rare earth at om mainly results in a change of lattice coordinates of the Sb atom in the compo und. Thermal vibration parameter of the rare earth atom is larger than those of other atoms. The electron diffraction patterns confirm the bcc structure of this compound. The intensities of diffraction from different crystallographic planes correspond well between electron and powder x-ray diffractions.
Studies on dynamical behavior in reaction limited aggregation model
Tang Jun, Yang Xian-Qing, Qiu Kang
2005, 54 (7): 3307-3311. doi: 10.7498/aps.54.3307
Abstract +
Based on reaction limited aggregation model, we have investigated the dynamical process of film epitaxial growth in the presence of surfactant. The results ind icate that there are differences between the growth processes of fractal island and compact island. The growth exponents of fractal islands are greater than 1, which that of compact islands are less than 1. On the other hand, “dead" atom d ensity increases linearly with the coverage in the process of the fractal island growth, but the relations between the density and the coverage are nonlinear in the compact island situation.
Influences of the period of repeating thickness on the stress of alternative high and low refractivity ZrO2/SiO2 multilayers
Fan Zheng-Xiu, Shao Jian-Da, Shao Shu-Ying
2005, 54 (7): 3312-3316. doi: 10.7498/aps.54.3312
Abstract +
The effect of period of repeating thickness on the stress is studied in ZrO 2/SiO2 multilayers deposited by electron beam evaporation on BK7 glass a nd fused silica substrates, separately. The results show that the residual stress in the multilayers is compressive, and with the increase of the period of repeating thickness the residual stress in multilayers decrease in both BK7 and fused silica substrates. At the same time, the residual stress in multilayers deposited on BK7 glass substrates is less than that in the samples deposited on fused silica substrates. The variation of the microstructure examined by the x-ray diffraction shows that the microscopic deformation does not correspond to the macroscopic stress, which may be due to the variation of the interface stress.
The study on the Peierls phase transition of TTF-TCNQ
Zhang Hong-Qun, Liu Shao-Jun, Li Rong-Wu
2005, 54 (7): 3317-3320. doi: 10.7498/aps.54.3317
Abstract +
According to Peierls phase transition theory on the basis of the electron-phonon interaction, the Peierls phase transition temperature of a one-dimensional organic conductor TTF-TCNQ is computed by using the deformation potential model with the data calculated by using a semi-empirical crystal orbital method. The result indicates that the Peierls phase transition temperature of TTF chains is lower than that of TCNQ chains, which demonstrate that the electron-phonon coupling interaction in TTF chains is weaker than that in TCNQ chains, and the metal-insulator phase transition in TTF-TCNQ at 54K mainly takes place in TCNQ chains.
Influence of process parameters on the electrical properties of n-type and p-type Bi2Te3-based pseudo-ternary thermoelectric materials by the hot-pressing method
Rong Jian-Ying, Zhang Hong-Chen, Hu Jian-Min, Xin Jiang-Bo, Lü Qiang, Zhao Lei
2005, 54 (7): 3321-3326. doi: 10.7498/aps.54.3321
Abstract +
Seebeck coefficient and electrical conductivity of the N-type and P-type Bi 2Te3-based alloys prepared by melting/grinding/hot-pressing met hod for different process parameters (temperature and pressure of hot-pressing)were measured,and the effects of process parameters were analyzed.It has been found that the temperature and pressure of hot-pressing play very important roles in enhancing both Seebeck coefficient and electrical conductivity of the Bi2Te3-based alloys.The phenomena are different from those of Bi2Te3 single cry stal and its oriented crystal in the electrical properties.Better electrical properties may be obtained.
Transition films from amporphous to microcrystalline silicon and solar cells
Kong Guang-Lin, Zeng Xiang-Bo, Xu Ying, Diao Hong-Wei, Liao Xian-Bo, Hao Hui-Ying
2005, 54 (7): 3327-3331. doi: 10.7498/aps.54.3327
Abstract +
A series of hydrogenated silicon films near the threshold of crystallinity was p repared by very high frequency plasma-enhanced chemical vapor deposition (VHF-PE CVD)from a mixture of SiH4 diluted in H2. The effect of h ydrogen di lution ratios R= [H2]/[SiH4] on the microstructure o f the films was investigated. The photoelectronic properties and stability of the film s were studied as a function of crystalline fraction. The results show that t he diphasic films gain both the fine photoelectric properties like a-Si:H an d high stability like μc-Si:H. By using the diphasic silicon films as the intrinsic layer, p-i-n junction solar cells were prepared. Current-voltage (J-V) characteristics and stability of the solar cells were measured under an AM15 solar simulator. We observed a light-induced increase of 52% in the ope n-circuit voltage (Voc) and a light-induced degradation of ~29% in efficiency.
Influence of double-percolation phenomenon on shielding effectiveness of Ni-based conductive silicone rubber
Li Peng, Liu Shun-Hua, Chen Guang-Yun
2005, 54 (7): 3332-3336. doi: 10.7498/aps.54.3332
Abstract +
By measuring the electrical resistivity of RTV silicone rubber with Ni powder, t he percolation threshold of Ni-based conductive silicone rubber was determined. When N234 was filled in Ni-based conductive silicone rubber,double-percolation p henomenon was found other than percolation law. After fitting of the experimenta l results,the mechanism of the double-percolation phenomenon was presumed. As fo r the shielding effectiveness of high conductive silicone rubber, the result sh ows that it can be described well with the Schelkunoff theory.The influence of double-percolation phenomenon on shielding effectiveness of the rubber was investigated.
Piezomodulated-reflectivity study of GaAs/Al0.29Ga0.71As single quantum well
Wang Chong, Chen Ping-Ping, Zhou Xu-Chang, Xia Chang-Sheng, Wang Shao-Wei, Chen Xiao-Shuang, Lu Wei
2005, 54 (7): 3337-3341. doi: 10.7498/aps.54.3337
Abstract +
We report here that we have built a set of piezomodulated-reflectivity measureme nt system, and obtained piezomodulated-reflectivity spectra of two GaAs/Al0 .29 Ga0.71As single quantum well samples in which the well widths a re 5 and 25nm respectively. From these spectra, the transitions between electron and heavy and light hole subbands can be easily identified. Furthermore, we have ob served the optical transition related to spin-orbit split-off of GaAs buffer. Ef fective mass theory is applied to calculate the transition energy between electr on and hole subbands. Then the spectral structures are assigned based on the cal culated results. It is found that these calculated results agree with experiment al ones very well.
Electron transport in multi-terminal quantum chain systems based on the Green’s functions
Ni Jun, Dai Zhen-Hong
2005, 54 (7): 3342-3345. doi: 10.7498/aps.54.3342
Abstract +
We have introduced a method for the calculation of electron transport in a multi-terminal quantum system based on the recursive Green's function technique. The corresponding transport equation is presented by scattering matrix, which is exp ressed by Green's function. Using this method, the multi-terminal device can be simplified as a standard two-terminal device, which is convenient in treating th e mesoscopic device. It is found that the transmission and reflection probabilit ies of the two multi-terminal quantum systems show complex spectra. The results show that the special node can destroy the symmetrical conductance spectra, and there is a new conductance peak in the low-energy region. This method can also b e applied to the study of electron transport of complex mesoscopic structures.
Influence of electron-phonon interaction on single electron tunneling in a quantum dot molecule
Wu Zhuo-Jie, Zhu Ka-Di, Yuan Xiao-Zhong, Zheng Hang
2005, 54 (7): 3346-3350. doi: 10.7498/aps.54.3346
Abstract +
The dynamics of electron tunneling between double quantum dots is investigated t heoretically in terms of a perturbation method based on a unitary transformation . Considering electron coupling with phonons, the dynamical tunneling current is obtained analytically. The phonon-induced decoherence is studied in detail. A possible decoupling mechanism is proposed.
Magnetoresistance effect of double-barrier magnetic tunneling junction applied in spin transistors
Zeng Zhong-Ming, Han Xiu-Feng, Du Guan-Xiang, Zhan Wen-Shan, Wang Yong, Zhang Ze
2005, 54 (7): 3351-3356. doi: 10.7498/aps.54.3351
Abstract +
The multilayer films of the double-barrier magnetic tunneling junctions (DBMTJs) were deposited by magnetron sputtering. The AlOx insulator was forme d by plasma oxidizing aluminium. The photolithographic pattering procedure combin ed with Ar ion milling was used to microfabricate the DBMTJs with an ellipse of  π×3×6μm2. Magnetic transport properties of DBMTJs were invest igate d. The junctions show a resistance-area product about 136 kΩ·μm2 and 175 kΩ·μm2, a high tunneling magnetoresistance of 27% and 422% at 3 00 K and 42 K, respectively. A tunneling magnetoresistance oscillation phenome non with respect to the bias voltage was first observed in this experiment. We d esigned a few kind of spin transistors based on the spin-dependent resonant tunn eling effect of the DBMTJs.
Analysis of surface leakage and 1/f noise on long-wavelength infrared HgCdTe photodiodes
Sun Tao, Chen Xing-Guo, Hu Xiao-Ning, Li Yan-Jin
2005, 54 (7): 3357-3362. doi: 10.7498/aps.54.3357
Abstract +
The long-wavelength infrared Hg1-xCdxTe photovoltaic dete ctors with x=0217 passivated by single ZnS layer and dual (CdTe+ZnS) layers were fabricated in the same wafer. The fabricated devices were characterized by meas urements of dark currents and 1/f noise. The diode passivated by dual (CdTe+ ZnS) layers showed a higher performance compared to the diode passivated by the single ZnS layer at high reverse bias, and modeling of diode dark current mechan isms indicated that the performance of the diode passivated by single ZnS was st rongly affected by tunneling current related to the surface defects, which was r esponsible for the dark currents and 1/f noise characteristics. By the analy sis of x-ray reciprocal space map (RSM), it was found that the Qy dir e ction broadening of HgCdTe epitaxial layer passivated by ZnS was wider after pas sivation, which confirmed the existence of defects in the surface of HgCdTe epit axial layer passivated by ZnS. In order to investigate the effect of surface pas sivation on the stability of two kinds of diodes, dark currents and 1/f nois e of the diodes were measured after vacuum baking for 10 h at 80℃. The dark cur rent mechanisms indicated that the performance of the diode passivated by single ZnS was strongly affected by the surface defects. By the analysis of RSM, It wa s found that the Qy direction broadening of HgCdTe epitaxial layer pa s sivated by ZnS was wider after high-temperature baking, which also confirmed the existence of defects in the surface of HgCdTe epitaxial layer passivated by ZnS after baking.
Low-temperature metal-induced unilateral crystallized polycrystalline silicon thin-film transistor and gate-modulated lightly-doped drain structure
Meng Zhi-Guo, Wu Chun-Ya, Li Juan, Xiong Shao-Zhen, Kwok Hoi S., Man Wong
2005, 54 (7): 3363-3369. doi: 10.7498/aps.54.3363
Abstract +
In this paper the low-temperature metal-induced unilaterally crystallized (MIUC ) polycrystalline silicon thin-film transistors (TFTs) have been developed and c haracterized. These TFTs have higher field-effect mobility, lower off-state curr ent and better spatial uniformity. A new structure of gate-modulated lightly dop ed drain of TFT was proposed. It is very effective to lower gate-induced drain-l eakage current of the TFTs when a higher source drain voltage is applied to it. This type MIUC TFT is suitable to fabricate active matrices for liquid crystal and organic light-emitting diode flat-panel displays on large area glass substr ates.
Computer simulation of a-Si:H/μc-Si:H diphasic silicon solar cells
Kong Guang-Lin, Zeng Xiang-Bo, Xu Ying, Diao Hong-Wei, Liao Xian-Bo, Hao Hui-Ying
2005, 54 (7): 3370-3374. doi: 10.7498/aps.54.3370
Abstract +
Based on our experimental research on diphasic silicon films, the parameters suc h as absorption coefficient, mobility life- time product and bandgap were estima ted by means of effective-medium theory. And then computer simulation of a-Si:H/ μc-Si:H diphasic thin film solar cells was performed. It was shown that the mor e crystalline fraction in the diphasic silicon films, the higher short circuit d ensity, the lower open-circuit voltage and the lower efficiency. From the spectr al response, we can see that the response in long wave region was improved signi ficantly with increasing crystalline fraction in the silicon films. Taking Lamb ertian back refraction into account, the diphasic silicon films with 40%—50% cr ystalline fraction was considered to be the best intrinsic layer for the bottom solar cell in micromorph tandem.
Studies on surface dry treatment for improving the performance of RF superconducting cavities
Hao Jian-Kui, Jiao Fei, Huang Sen-Lin, Zhu Feng, Zhao Kui
2005, 54 (7): 3375-3379. doi: 10.7498/aps.54.3375
Abstract +
RF superconducting (SC) cavities are more frequently used in particle accelerators with excellent performance which cannot be substituted by normal conducting cavities. The surface status of superconducting cavities directly affects the properties of the cavity. In order to improve the accelerating performance of superconducting cavities, Peking University made researches and developments on a “dry treatment method” on the surface of SC cavities. It uses argon ion cleaning technique in ultra-high vacuum. Compared with the traditional wet methods (Chemical polishing and electrical polishing), dry method has special advantages. It might become a new surface treatment method to improve the performances of SC cavities. Further researches are in progress.
The oxygen in- and out-diffusion behavior in melt-textured YBCO measured by thermogravimetry
Jin Yan-Ping, Zhang Yu-Long, Yao Xin, Zhang Hong
2005, 54 (7): 3380-3385. doi: 10.7498/aps.54.3380
Abstract +
The chemical oxygen in- and out-diffusion in melt-textured YBa2Cu 3O7-δ(YBCO)is investigated by thermogravimetry. The weight relaxations resulting from the sudden change of temperature at a fixed oxygen partial pressure of 033×105Pa are recorded. By fitting the isothermal curves, the chemical diffusion coefficients at 375—600℃ are determined. It is found that the resultant numerical values for melt-textured YBCO are larger than that of crushed single crystal YBCO obtained in our previous study by about 50%, whereas all of them are of the order of 10-10cm2s-1 . The activation energies for both samples are estimated as ~1eV. It is believed that those values represent the nature of the lattice diffusion. The oxygen diffusion in me lt-textured-grown-YBCO is attributed to the YBCO matrix and the micro-cracks are responsible for the huge diffusion coefficients. Moreover, the same kinetics o f in- and out-diffusion is confirmed to be intrinsic, and it suggests that the d ifferent in- and out-diffusion coefficients measured in other works are controll ed by the large concentration gradient and the shell effect.
Magnetism and transport properties of Heuser alloy Cu2VAl
Wang Ben-Yang, Qian Zheng-Nan, Sui Yu, Liu Yu-Qiang, Su Wen-Hui, Zhang Ming, Liu Zhu-Hong, Liu Guo-Dong, Wu Guang-Heng
2005, 54 (7): 3386-3390. doi: 10.7498/aps.54.3386
Abstract +
We have investigated magnetic and transport properties of Heusler alloy Cu2 VAl. Magnetic measurements confirm that the magnetic transition from ferro magn etism to paramagnetism arises near 210K for Cu2VAl sample, which is a weak ferromagnet. Resistance curves show that there is a small jump of 1% in resista nce caused by the localized impurity superconduction phase transition around 7K. The scattering between electron-phonon is the main scattering mechanism. Furthe rmore, extraordinary Hall effect exists for side jump at temperatures below T C and the phase transition leads to Hall resistivity changing abnorma lly at 7K.
Circular magnetization processes in amorphous and nanocrystalline soft magnetic wires
Vázquez M., Li Yin-Feng, Yin Shi-Zhong
2005, 54 (7): 3391-3396. doi: 10.7498/aps.54.3391
Abstract +
The changes of circular permeability with the circular magnetic field and frequency, in amorphous and nanocrystalline soft magnetic wires with different magnetic strucutre, have been determined from the measurements of impedance. The circular magnetization curve was obtained by using the Chen et als formulas. We found that these formulas are not suitable for the process with very large magnetic losses, so a general expression has been developed. Additionally, different circular coercivity mechanisms in the wires with longitudinal or transversal domain strucutre were deduced from analyzing the circular-field-dependent complex circular permeability. Finally, the frequency effect is also discussed.
The spin excitation delay for granular film swith ferromagnetic granules
Zheng Rui-Lun, Wu Qiang
2005, 54 (7): 3397-3401. doi: 10.7498/aps.54.3397
Abstract +
With the s-d commutative operation model and under the condition of the approximate single-loop of s-d commutative reciprocity for spin Green functio n, we worked out the spin excitation delay for granular films with ferromagnetic granules, and using the (α-C:H)1-xCox granular film as a n ex ample, we explored the rules that spin excitation delay changes with temperature . As a result, the process of the spin excitation delay through spin-polarized excitation is not related to temperature; however, the process through thermal e xcitation is temperature-dependent.
Coercivity mechanism of segmented (A/B)m composite nanowire arrays
Shi Hui-Gang, Si Ming-Su, Xue De-Sheng
2005, 54 (7): 3402-3407. doi: 10.7498/aps.54.3402
Abstract +
Based on the symmetric fanning mechanism of the sphere-chain model,a systematic study on the hysteresis loops for hexagonal arrays of segmented composite magnetic nanowires fabricated by electrochemical deposition is performed by taking into account the interfacial exchange coupling effect between the segments. The coercivity variation rule with the change of the segments is presented. It is found that the exchange coupling effect between the segments plays an important role for magnetization reversal in the segmented composite nanowire arrays.
Influence of grain alignment degree on the magnetic properties for single-phase nanocrystalline Pr2Fe14B magnets
He Shu-Li, Zhang Hong-Wei, Rong Chuan-Bing, Chen Ren-Jie, Sun Ji-Rong, Shen Bao-Gen
2005, 54 (7): 3408-3413. doi: 10.7498/aps.54.3408
Abstract +
The single-phase nanocrystalline Pr2Fe14B magnets composed of cubic-shaped and irregular-shaped grains is built. The magnetic hysteresis loops are simulated by micromagnetism finite element method. The remanence, coercivity and maximum energy product decrease with deteriorated grain alignment. Attributed to strong intergrain exchange coupling (IGEC), the variation of magnetic proper ties with alignment degree is significantly affected by the average grain size i n nanocrystalline magnets. The investigation shows the increase of coercivity wi th improved grain alignment in nanocrystalline magnets, which is completely diff erent from the phenomena in sintered magnets.
Effect of annealing and polarizing temperature on the trap level distribution in nylon 11 film electrets
Zhu Jun, Zhang Xing-Yuan, Lu Hong-Bo
2005, 54 (7): 3414-3417. doi: 10.7498/aps.54.3414
Abstract +
The effect of annealing and polarizing temperature on the trap level distribution in nylon 11 film electrets has been studied by thermally stimulated depolariza tion current (TSDC) technique. It was found that there were four detrapping curr ent peaks of space charge in TSDC spectra of the quenched nylon 11 film electret , while two in that of the annealed one. Using multi-point method to fit the ex perimental curves, the detrapping current peaks could be separated and the trap depth was obtained. The results further proved that there were four trap levels of space charge in a quenched electret and the trap level distribution changed l ittle when the polarization temperature increased; while after annealing, there were only two trap levels in the electret. The results also showed that the shal lower trap level was obviously close to the deeper trap level when the polarizat ion temperature increased.
Influence of concentration of Er3+ ions on luminescence and fluorescence lifetime in TeO2-ZnO-Na2O-K2O glasses
Chen Bing-Yan, Liu Yue-Hui, Chen Dong-Dan, Jiang Zhong-Hong
2005, 54 (7): 3418-3423. doi: 10.7498/aps.54.3418
Abstract +
Absorption spectra, emission spectra and fluorescence lifetime of Er3+ions were measured for TeO2-ZnO-Na2O-K2O glasses w ith different doping concentrations of Er3+ and the emission cross section σe of Er3+ was calculated. Dependence of luminescence intensity and fluorescence lifetime on concentration of Er3+ were analyzed. The influence of concentratio n of Er3+ ions on luminescence intensity and fluorescence lifetime was unc onspi cuous in the case of low doping level of Er3+. However, high concentr ation of Er3+ ions resulted in the concentration quenching, which reduced the l uminescence intensity and fluorescence lifetime. The optimum concentration of Er3+ ions was determined for TeO2-ZnO-Na2O-K 2O glasses, and the mechanism of concentration quenching was also discussed and explained in detail.
High-efficiency red-phosphorescent 6CPt electroluminescence
Xie Yu-Qing, Peng Jun-Biao, Cao Yong, Guo Jian-Hua, Wang Yue
2005, 54 (7): 3424-3428. doi: 10.7498/aps.54.3424
Abstract +
High-efficiency red polymer phosphorescent light-emitting diodes(PLEDs) have been fabricated based on czrbazole-substituted porphyrin platinum(6CPt)complex and PBD-doped PFO(poss). The best external quantum efficiency of 5.68% has been achieved. The effect of PBD on the device performance was analyzed. We found that PBD improves the energy transfer of excitons from host PFO to guest triplet complex 6CPt.
Optical nonlinearities of iron films prepared by pulsed laser deposition
Wang Wei-Tian, Guan Dong-Yi, Zhou Yue-Liang, Lü Hui-Bin, Chen Zheng-Hao
2005, 54 (7): 3429-3433. doi: 10.7498/aps.54.3429
Abstract +
Thin films of iron were fabricated on MgO(100) substrates using pulsed laser dep osition technique. The crystalline property and surface roughness of the films w ere investigated by x-ray diffraction and atomic force microscopy, respectively . It is found that the Fe films deposited at 500 and 800℃ are of single phase, and no diffraction from randomly oriented grains or impurity phases can be obser ved. The nonlinear optical properties of continuous 9 nm-thick iron film were d etermined using the z-scan method. The results show that the ultra-thin ir on film exhibits large nonlinear refractive coefficient, n2= 709×1 0-5cm2/kW, and nonlinear absorption coefficient, β=-552×10 -3(cm/W), at the wavelength of 532 nm.
Study on temperature dependence and e+ irradiation time dependence of positron annihilation parameters about SEBS triblocks copolymer
Xia Yuan-Fu, Jiang Zhong-Ying, Yu Wei-Zhong
2005, 54 (7): 3434-3438. doi: 10.7498/aps.54.3434
Abstract +
Positron annihilation lifetime spectroscopy was used to study e+ self -irradiation effect of 22Na on positron annihilation parameters of SEBS, tem perature dependence of free volume hole radius and free volume hole fractional, based on the classic model of Eldrup, presenting the linear variation of fractional free volume versus temperature in vacuum the range below Tg and ab ove Tg, respectively. We also discuss the thermal expansion coefficient a nd the constant A in free volume fractional formula by combining the free volume theory of WLF and the classical model of Eldrup.
Numerical simulation and characteristic comparison of Spindt type and diamond film field emisson
Liu Jun-Qiao, Zhan Jie-Min
2005, 54 (7): 3439-3443. doi: 10.7498/aps.54.3439
Abstract +
By using the electromagnetic particle-in-cell(PIC) MAGIC code, the process of field emission is simulated. The simulation includes two representative field emission devices(Spindt-type field emitter and diamond film field emitter). For Spindt-type field emitter, the relation between the characteristics and the radius of curvature of the emitter tip , the relative height between the emitter tip and the gate are studied. As regards the diamond film field emitter, the characteristics of field emission microtriodes and microtetrodes are compared with each other and the influence of the area of diamond film is investigated. The resul ts show that the characteristics of diamond film field emitter has an advantage over Spindt-type field emitter.
Electrical property of rapidly solidified Co-Cu peritectic alloys
Xu Jin-Feng, Wei Bing-Bo
2005, 54 (7): 3444-3450. doi: 10.7498/aps.54.3444
Abstract +
The microstructure formation and phase selection characteristics of Co-Cu peritectic alloys during rapid solidification are investigated experimentally. The re lationships between such physical factors as cooling rate, microstructure morpho logy, crystal orientation, and alloy resistivity are further analyzed. The exper imental results show that rapid solidification makes the Co solubility in (Cu) p hase extend up to 20%Co. If Cu concentration is more than 80%Cu, the peritectic transformation L+αCo→(Cu) is suppressed, and the (Cu) phase can directly preci pitate from the undercooled alloy melt. When the Cu concentration is in the rang e of 40%-70%Cu, the liquid phase separation of the alloys is also suppressed, and the microstructure in the direction of ribbon thickness consists of two crysta l zones. In the fine crystal zone, the αCo and (Cu) phases nucleate and grow co mpetitively, the tiny equiaxed (Cu) dendrites are distributed in the αCo matrix homogeneously, whereas in the coarse crystal zone the αCo is the leading phase , where Cu-rich phase exists in the grain boundary of αCo dendrites. With the increase of cooling rate, the microstructure is refined and the amount of grain boundary increases, resulting in the rise of alloy resistivity. If the grain bou ndary reflection coefficient r=0996—0999, the electrical resistivity o f Co-Cu peritectic alloys can be predicted theoretically.
Photon absorption of conduction band electronsand impact ionization under irradiation of few-cycle ultrashort laser pulses
Wang Xiao-Feng, Jia Tian-Qing, Xu Zhi-Zhan
2005, 54 (7): 3451-3456. doi: 10.7498/aps.54.3451
Abstract +
We discuss the limitation of classical Drude Model, solve the kinematics equation for electrons in the few-cycle laser field, and calculate the photon absorpti on of conduction-band electrons(CBE) and impact ionization under irradiation of few-cycle ultrashort laser pulses. The effects of laser intensity, carrier-en velope-phase on impact ionization are discussed.
Study on nonlinear characteristics of two synchronizing uncoupled Hindmarsh-Rose neurons
He Dai-Hai, Wu Ying, Xu Jian-Xue, Jin Wu-Yin
2005, 54 (7): 3457-3464. doi: 10.7498/aps.54.3457
Abstract +
Modulating the current input of two uncoupled Hindmarsh-Rose neurons by using the membrane potential of Hindmarsh-Rose neuron under different initial conditions, the evolution mechanism of synchronization process of the two neurons is revealed by analyzing interspike interval sequences. When periodic stimulation is u sed, the full synchronization is realized in two identical neurons, and the sync hronized response of modulated neurons can be different from the stimulation sig nal; and phase synchronization can be obtained in two neurons with different par ameters:two neurons with small parameter mismatch can be synchronized to the per iodic response different from the stimulation signal, and two neurons with big p arameter mismatch can only be synchronized to the response in phase synchronizat ion with stimulation signal. When chaotic stimulation is used, two systems can o nly be synchronized to the response being in phase synchronization with stimulat ion signal. Obviously, chaotic stimulation is more helpful in encoding and deco ding information. Analyzing the relation between the largest condition Lyapunov exponents and the stimulation strength shows that when the largest condition Lya punov exponents of the two systems are both negative is the necessary condition for synchronization. The chaotic stimulation signal can more easily synchronize two neurons than periodic stimulation signal, implying that the effect of chaoti c stimulation is stronger than periodic one, and the experiments also confirm th is conclusion.
A harmonized multi-time difference scheme and its stability
Qian Wei-Hong, Gao Xin-Quan, Chou Ji-Fan, Zhang Li-Xin
2005, 54 (7): 3465-3472. doi: 10.7498/aps.54.3465
Abstract +
In this paper, a harmonized multi-time difference scheme is established, which can be easily constructed on any numerical difference scheme of ordinary differential equations. A sufficiently stable condition is proved in mathematics. If the memorial coefficients determined by an improved method of least square, it is expected that this new scheme can integrate stably in a longer period, and a better result can be achieved.