Vol. 53, No. 12 (2004)
2004-06-20
GENERAL
2004, 53 (12): 4021-4025.
doi: 10.7498/aps.53.4021
Abstract +
This paper deals with a non-Noether conserved quantity constructed directly by u sing the form invariance for the Nielsen equation of a non-conservative mechanic al system. The definition and the criterion of a non-point form invariance of th e equation, of which the Noether conserved quantity is studied, are established by relying on the total time derivative along the trajectory of the equation. T he condition under which the form invariance can lead to a non-Noether conserved quantity and the form of the conserved quantity are deduced, and three corollar ies in special cases are presented. Two examples are finally given to illustrate the application of the results.
2004, 53 (12): 4026-4028.
doi: 10.7498/aps.53.4026
Abstract +
This paper studies the geometric foundations of Hojman theorem for Brikhoffian s y stems. The differential equations of motion and the Hojman conservation law of t he systems are established. A proof of Hojman theorem of Birkhoffian systems is given by use of the modern differential geometry.
2004, 53 (12): 4029-4036.
doi: 10.7498/aps.53.4029
Abstract +
The special solutions of the Kirchhoff equations, which are those rela tive to fixed coordinate system, principal coordinate system of a cross section of the rod, and Frenet coordinate system of the central line of the rod, respect ively, are derived in this paper. Lyapunov stability of these solutions is disc us sed by use of theory on the first-approximation stability, and at the same time stability area in parameter's plane is given.
2004, 53 (12): 4037-4040.
doi: 10.7498/aps.53.4037
Abstract +
In this paper, we study the non-Noether conserved quantity of Lie symmetry for m echanical systems with variable mass under a general infinitesimal transformatio n. The Hojman theorem is further generalized. The non-Noether conserved qu antity o f a general form for mechanical systems with variable mass is obtained. An examp le is given to illustrate the application of the result.
2004, 53 (12): 4041-4044.
doi: 10.7498/aps.53.4041
Abstract +
In this paper, we study the Hojman conserved quantity of Lie symmetry for mechan ical systems with variable mass in phase space under a general infinitesimal tra ns formation. The determining equations and Hojman conservation theorem of Lie symm etry of the system in phase space are obtained. An example is given to illustrat e the application of the result.
2004, 53 (12): 4045-4051.
doi: 10.7498/aps.53.4045
Abstract +
F-expansion method proposed recently is extended to construct more exact solutio ns of nonlinear evolution equations. To be more precise, it means that instead o f the first-order ordinary differential equation(ODE) and finite power series of one variable in F-expansion met hod, we introduce similar first-order ODEs and finite power series of two varia b les, each one of which is the component of solution to ODEs. As an illust rat ive example, using this extended F-expansion method we solve nonlinear Schrdin g er(NLS) equation, an abundance of envelope solutions, especially the solutions expressed by two different Jacobi elliptic functions, to the NLS equation have b een obtai ned. Obviously, the extended F-expansion method can be applied to solve other ty pe of nonlinear evolution equations as well.
2004, 53 (12): 4052-4060.
doi: 10.7498/aps.53.4052
Abstract +
In this paper, several new exact solitary wave solutions to the BBM and the m BBM equations are constructed explicitly by combined use of a hyperbolic functio n assumption and a new auxiliary ordinary differential equation. This method also can be used to find new solitary wave solutions to other nonlinear evolution equ ations.
2004, 53 (12): 4061-4064.
doi: 10.7498/aps.53.4061
Abstract +
Using the homotopic theory, an approximate solution for a class of nonlinear pro blems is first discussed.Then,the precision is raised by using variational inter active methods.Finally, a combustion model is applied and the approximate soluti on is obtained.
2004, 53 (12): 4065-4069.
doi: 10.7498/aps.53.4065
Abstract +
In this paper, we find periodic solutions with different periods and velocities to the (2+1)-dimensional general Schdinger and Boussinesq equations by making approprite linear superpositions of known periodic travelling wave solutions in volving Jacobi elliptic functions.It is noteworthy that this linear superpositio n procedure works by virtue of some remarkable new identities involving elliptic functions.
2004, 53 (12): 4070-4074.
doi: 10.7498/aps.53.4070
Abstract +
The system of steady state photorefractive spatial optical solitons can be descr ibed by a singular Lagrangian.To our knowledge,the commutation relations and qua ntum equations of motion are given by using corresponding principle, however it is not satisfactory since the constraints are ignored.In this paper,the commutat ion relations and quantum equations of motion are derived based on the Dirac the ory of constrained systems.The perturbation solution in screening soliton case i s found and the squeezing properties are discussed.
2004, 53 (12): 4075-4079.
doi: 10.7498/aps.53.4075
Abstract +
Expressions for critical temperature of Bose-Einstein condensation (BEC) in an e xternal potential, which are different from published results in the literatur e, are presente d. The results reveal the relation between the critical temperature of BECgas and the external potential, and demonstrates proporti onality of critical temperature in external potential to the value T0c at which th e potential is absent. In addition, a criterion for the validity of potential is also prese nted, which is based on the comparison between the potential and the product kT 0c. This comparison shows that only when the external potential is nearly eq ual to or larg er than kT0c, the increase of critical temperature is significant. A s the potential is much smaller than kT０c, the potential has no effects on the BEC gas.
2004, 53 (12): 4080-4086.
doi: 10.7498/aps.53.4080
Abstract +
A novel adaptive radial basis function(RBF) neural network sliding mode strat egy is developed to con trol Lorenz chaos with parametric uncertainties and external disturbances. Based on the controllable canonical form of system state error at its unstable equili brium, a sliding surface is defined as the only input to the RBF controller. Onl y seven RBFs are required for the controller and their weights ar e trained on-line based on the sliding surface approaching condition. The simula tio n results show that this method is feasible and effective, and the robustness to parametric uncertainties and external disturbance is provided.
2004, 53 (12): 4087-4091.
doi: 10.7498/aps.53.4087
Abstract +
A novel direct adaptive fuzzy neural networks(FNNs)controller for a class of unc ertain nonlinear chaotic system is presented.Takagi-Sugeno fuzzy logic systems a re applied to estimate the unknown function of the chaotic system,then the param eters of adaptive FNNs control law are on-line tuned so that the tracking prob le m is realized,i.e.to force the solutions of the chaotic plant to follow a certai n given trajectory under the condition that all signals involved are uniformly b ounded.Simulation results show the validity of the obtained result.
2004, 53 (12): 4092-4097.
doi: 10.7498/aps.53.4092
Abstract +
Based on the usual chaotic-weighting first-rank local-region forecas ting model, a modification is made for the predictor in matrix and vector simulation instead of single variant. Then the modified forec asting model is applied to pr edict silicon content in molten iron of the medium-sized blast furnace in China, and good results are obtained. Finally, we find that the value of Kolmogo rov entropy has a great effect on the hitting accuracy of the prediction .
2004, 53 (12): 4098-4110.
doi: 10.7498/aps.53.4098
Abstract +
The phenomenon of measure synchronization is an important property in coupl ed Hamiltonian systems. In this paper, we investigate the measure synchronizati on in a chaotic system, and the regularity of phase difference is also discusse d in the regular coupled systems and the chaotic coupled system.A new method is proposed for determining the critical coupled strength of transition to the mea sure synchronization. At the same time, we have studied the influence of Gaussi an white noise on the measure synchronization. It is significant to investigate the conservative system using the property of measure synchronization.
2004, 53 (12): 4111-4119.
doi: 10.7498/aps.53.4111
Abstract +
A new type of chaotic generator is studied by constructing a three_segment piec ewise_linear odd function with variable breakpoint α. The characteristic of the chaotic generator presented is that when the breakpoint α varies in th e range of 0<α≤1, there is a route to chaos through period_doubling bifurcations, and the doubl e_ layer single spiral, single_layer single spiral, double_layer double spiral and single_layer double spiral chaotic attractors can be generated. In particular, the double-layer single spiral and double-layer double spiral are found in our circuit experiment for the first time so far as we know. The b ifurca tion diagram, Lyap unov exponents λ_1,λ_2,λ_3, maximal Lyapunov exponent λ_maxand the spectrum of the single_layer double spiral and double-layer double spiral are also investigated. The associated electronic circuit is designed and the experimental result is given, which is ver ified by computer simulation and circuit experiment.
2004, 53 (12): 4120-4125.
doi: 10.7498/aps.53.4120
Abstract +
Due to the interactions among coupled spatio_temporal subsystems and th e model uncertainties, it is difficult to achieve tracking control for coupled s patio_temporal chaos with uncertain model. However, every subsystem of the coupl e d spatio_temporal chaos is approximated by a set of fuzzy models. Considering th at the st ates of the subsystems are not all available, a set of fuzzy observers are propo sed to estimate these states. Because it is very difficult to exactly eliminate many parameters and dynamic characters of the chaotic system, that is to say, the s yst em model is uncertain, there can be deviation between the fuzzy models and the real chaotic system due to approximation error. Based on these fuzzy models and observers, considering the model uncertainties, a H∞ fuzzy tracking contro l scheme is proposed, and the robust tracking control for the coupled spatio_tem pora l chaos with the uncertain model is achieved by the above scheme. A linear matri x inequali ty is employed to represent the feedback controller, the parameters of the contr oller being obtained by using the convex optimization techniques of linear matri x inequalites. The stability of the system is guaranteed and the tracking performances are tested by a simul ation example.
2004, 53 (12): 4126-4130.
doi: 10.7498/aps.53.4126
Abstract +
The ionic beam which exhibits a Kapchinsky_Vladimirsky distribution is studied in this paper. Not only the halo is found, but also the ionic radial den sity which has changed is discovered when the ionic beam is in accelerator chan nels. By delay feedback control method, the halo is removed. Moreover as long as the proper parameters are chosen, the density uniformity can be found at beam' s center.
2004, 53 (12): 4131-4137.
doi: 10.7498/aps.53.4131
Abstract +
In this paper, the magnetic field parametric switching method for controlling t he beam_halo chaos in the period_focusing channel(PFC) is studied. The law of t he parametrical switching control is presented . The simulation results demonstr ated that the chaotic envelo pe of the ion beam can be controlled well by this method. Then the method is app lied to the multi_particle model with the period_focusing magnetic field channel . The PFC simulation results show that beam halo_chaos for five different kinds of beams can be controlled well. The beam halos and its regeneration can be eliminated. This method is easy to realize in experiment.The research offers a valuable reference for the design of the PFCs in the high_current linea r proton accelerators.
2004, 53 (12): 4138-4144.
doi: 10.7498/aps.53.4138
Abstract +
Considering that the maximum velocities for different types of vehicles ar e not the same and drivers may adopt different randomization brake probabilities , we pro posed a one_dimensional sensitive driving cellular automaton model for mixed tra ffic flow based on the NS model. We presented the fundamental diagrams for diff erent parameters by using computer numerical simulation, which show that the flu x is h igher than that of the NS model and the SDNS model. Moreover, some complicated b ehaviors of the model such as the metastable state and the separation of phases are also observed. Compared with the real traffic, the characters of this model are shown and analyzed.
2004, 53 (12): 4145-4150.
doi: 10.7498/aps.53.4145
Abstract +
Considering the effects of different factors on the stochastic delay probability , we have classified the delay probability into three cases. The first case, cor responding to the deceleration state, has a large delay probability if anticipan t veloc ity is larger than the gap between the successive cars. The second one, correspo nding to the leader following stably, has an intermediate delay probability if t he anticipant velocity is equal to the gap. The last is the one with acceleratio n with the minimum delay probability. The fundamental diagram obtained by the nu merical simulation shows the different properties compared with that by the NaSc h model, in which there exist two different jamming regions corresponding to the coexistent congestion and jamming with different properties of shock wave.
ATOMIC AND MOLECULAR PHYSICS
2004, 53 (12): 4151-4156.
doi: 10.7498/aps.53.4151
Abstract +
In this paper the semi-classic theory of coherent excitation of a two-level atom was modified and applied to a two-level atom with a hyperfine structure. The im portant result of calculation is as follows: when the exciting laser power is la rge enough, due to the power broadening effect, a narrow-band laser can excite a two-level atom with a hyperfine structure effectively. So it is not necessary t o use a broad-band laser to guarantee excitation efficiency for an atom with hyp erfine split levels.
2004, 53 (12): 4157-4162.
doi: 10.7498/aps.53.4157
Abstract +
In this paper, we propose a new scheme to cool and trap neutral ato ms by using a blue-detuned localized hollow beam (LHB), and studied the dynamica l process of intensity-gradient cooling of the trapped atoms in the LHB by means of Monte-Carlo simulations. Our study shows that an ultracold atomic sample wit h a temperature of ～5 μK and an atomic density of 1012—1013/cm 3 can be obtained in our single LHB, and this atomic density can be con trolled by changing the relative aperture of the lens system. So, such a LHB can be used to realize an all-optical atomic Bose-Einstein condensation.
2004, 53 (12): 4163-4172.
doi: 10.7498/aps.53.4163
Abstract +
In this paper, we propose a novel scheme to form a controllable doublewell opt i cal trap for cold atoms or molecules by using a system composed of a binary π phase plate and a lens illuminated by a plane light wave. We calculate the int ensi ty distribution of the doublewell trap, and study the evolution process of th e optical trap from two wells to a single well, and derive the analytical relation between the characteristic parameters of the doublewell trap (includi ng g eometric parameters, the intensity distributions, intensity gradients and their curvatures) and the parameters of optical system. We find that our doublewell trap can be continuously changed into a singlewell trap by moving the πphas e pl ate along the x direction, and the relation between the distance of the trap ping centers of the two wells and the moving distance of the πphase plate is obt ain ed by data fitting. In addition, our doublewell scheme is not only simple and c onvenient, but also has some important and wide applications in the fields of at omic physics, atom optics, molecule optics and quantum optics and so on.
CLASSICAL AREA OF PHENOMENOLOGY
2004, 53 (12): 4173-4180.
doi: 10.7498/aps.53.4173
Abstract +
This paper proposes a new set of alternative direction implicit finite_di fference time_domain (ADI_FDTD) equations. In conventional ADI_FDTD, the update equation is related to several field components in cells nearby, which will lead to some difficulties in two regions:1) around the boundary region between the p erfectly ma tched layer (PML) and the scattering field; 2) around the adjacent bounda ry. Especially, in the region around the adjacent boundary, owing to the inciden t wave, we shou ld make a judgment about the situation of every component and modify the update equation. It is potential to make a solution to one_dimensional or two_dimension al problem. However, in three_dimensional (3D) analysis, one equation concerns w ith el even components and there exist several tens of cases to be modified. This makes the scheme very tedious and impossible to realize. This paper adopts the spli t field difference formation in the whole computation regime to analyse the sca ttering problem. Because the equations in the scattering field region have the same expr essi ons as those in PML absorber except for some coefficients, the boundary in the r egion mentioned above can be ignored. Due to simplicity of the split field equation, the new ADI_FDTD formula in 3D problem has only five compon ents to be cons idered and four modifications at the adjacent boundary to be made. Finally, we utilize this new method to compute some electromagnetic scattering numerical examples, and the results are in excellent agreement with those ob tained w ith other algorithm and the measured data. Moreover, the new method have 6-7 tim es higher efficiency in terms of the CPU time.
The complete analytical form and analysis on angular dispersion formula of two-dimensional grating
2004, 53 (12): 4181-4188.
doi: 10.7498/aps.53.4181
Abstract +
On the basis of the vector diffraction theory, the equation o f two_dimensional grating in arbitrary angle of incidence is given, the complet e analytical form of angular dispersion formula of two_dimensional grating is f irst ly deduced, and the concept of angular dispersion of diffractive polar angle (AD DPA)(the first kind angular dispersion) and angular dispersion of diffractive az imuthal angle (ADDAA) (the second kind angular dispersion) are established. In addition, according to theoretical analysis and numerical method on ADDPA and AD DAA of two_dimensional grating, the mechanism that diffraction spot array gener at es distortion is explained when the incidence wave has an angular deviation from the grating normal. Moreover, the conditions for causing mutation of ADDAA and l eading to the dramatic change of diffraction spot array are also determined. Thi s work, therefore, is of great importance in basic theory research. In practical ap plication, taking x_ray diffraction, low_energy electron diffraction and reflect ion high_energy electron diffraction of crystal and quantum d ot for example, we may take advantage of the above formula to test, analyz e and explain the structure of a crystal lattice and the crystal growth process, then we can find new methods of characterizing crystal structure.
2004, 53 (12): 4189-4193.
doi: 10.7498/aps.53.4189
Abstract +
Power balance between laser beams is important for high_power l aser system. This paper uses a calculation method as an exact solution for laser-amplification to simulate the output pulse shape of “Shenguang Ⅱ" laser facility. The results are preferable, as compared with the results of the experiments .
2004, 53 (12): 4194-4201.
doi: 10.7498/aps.53.4194
Abstract +
In this paper, analytical and numerical methods are used t o study cross_phase modulational instability. Firstly, by use of coup led nonlinear Schrdinger equation, we have studied the cross_phase modulation i nstability in the normal and anomalous dispersion fiber links of wavelength divi sion multiplexed system with an active amplifier, when the amplitude is perturbed. Se condly, m aking use of the split step Fourier transform and Monte_Carlo method, we simulat ed the cross_phase modulation instability in active normal and anomalous dispers ion fibers with fluctuation of phase noise. Comparison between the above met hods shows that the results agree with each other.
2004, 53 (12): 4202-4210.
doi: 10.7498/aps.53.4202
Abstract +
Symmetry in spectrum space of isotonic oscillators is studied, and a distinct fi gure is given by appropriate parametric substitution. An analytic expression of normalized eigenfunction is obtained. It is proven that linear oscillator is a degeneration of isotonic oscillator. It is revealed that an isotonic oscillator is a two_photon parametric model. Coherent state of that model is given, and that coherent state includes odd_coherent state and even_coherent state constru cted by Glauber coherent states in a natural way.
2004, 53 (12): 4211-4217.
doi: 10.7498/aps.53.4211
Abstract +
Theoretical analysis and a full numerical simulation of the electromagnet ically induced transparency model are performed under detuning conditions for a closed three_level ultracold atomic system in which a signal field can be stored and retrieved. Numerical results confirm the theory that the system can be prep ared in dark states only under resonant conditions between the fields and the a tomic transitions. The signal field is partially stored in the ultracold atomic medium with the increase of detuning and an enhanced negative group velocity of t he physically vanishing signal pulse appears. In the case of a symmetrical detun ing (red or blue detuning), no remarkable changes of the storage process occur.
2004, 53 (12): 4218-4223.
doi: 10.7498/aps.53.4218
Abstract +
The coupled equations of four_wave mixing by femtosecond pulses in gas_filled capillary are derived. Based on the equation s, the in fluence of the walk_off and phase modulation is investigated. It is found that t he discrepancy between the theoretical and experimental results decreases when t he influence of the walk_off and phase modulation is taken into account. At the same time, it is also found that taking the influence of the 3rd harmonic gener ated by the idler light into account is necessary for reducing the discrepancy b etween the theoretical and experimental results.
2004, 53 (12): 4224-4228.
doi: 10.7498/aps.53.4224
Abstract +
Laser phenomena in random media have been studied bas ed on the localized theory for optical waves in finite random media. The relatio n ship between spatial localization and amplification for quasi_state modes ha s been investigated by use of the finite difference time domain method. T he spatial profile and the spectra characteristics of quasi_state modes are dete r mined by analyzing the localized processes of optical light beams in random medi a without gain. The amplification and threshold of quasi_state modes are analyze d in random media with gain. Results show that the quasi_state mode with a stron ger spatial localization has lower threshold and can be amplified preferentially .
2004, 53 (12): 4229-4235.
doi: 10.7498/aps.53.4229
Abstract +
We have experimentally studied the Brillouin-Rayleigh scat tering in dispersion compensation fibers under Raman pump of different po we rs, and analyzed the characteristics of output spectra and the variation of th e spectra with pump power in detail. Then, based on the known theoretical model of the first-order stimulated Brillouin scattering, we deduce the theoretica l model for multi-order Brillouin-Rayleigh scattering. By this model, we have ma de numerical simulation, and the results show that theory and experiment are consiste nt at lower pump power, but have great differences at higher pump power.Moreove r, we analyze carefully the differences between theory and experiment. Finally,from theoretical calculation and experimental results, we obtain the saturation charac teristics of Brillouin-Rayleigh scattering at higher pump power, so that we can easily explain the cause of flat multi-order Brillouin-Rayleigh scattering at a certain higher Raman pump power.
2004, 53 (12): 4236-4242.
doi: 10.7498/aps.53.4236
Abstract +
Bacteriorhodopsin film has a special property of complementary suppression modulated transmission of yellow and blue beams. Resolving the transmission rate equ ations of the yellow and blue beams, the analytical formulae are obtained and gr aphic results are shown. We put forward a multilateralsystem computational mod el of digital optical matrix addition and subtraction operations without carry a nd abdication respectively. The novel model and frame of basic optical computati on are constructed, and the optimized project of digital optical matrix addition and subtraction operations are designed.
2004, 53 (12): 4243-4247.
doi: 10.7498/aps.53.4243
Abstract +
An experimental study of supercontinuum generation in a photonic crystal fiber with zero dispersion wavelength 780?nm by femtosecond laser and its dependence factor is presented. Supercontinuum light with a spectrum more than one octave broad (500-1100?nm) was generated in a photonic crystalfiber by femtosecond pulses from a selfstarting, selfmode locked Ti:sapphire oscillator running at center wavelength of 810-840?nm. Different supercontinuums were generated by the 35?fs pulses with different power, central wavelength, prechirp, and the continuous noise in the femtosecond pulses. Some reasonable analysis result is obtained from the comparisons of the experimental results, and the mechanism of the supercontinuum generation is analyzed.
2004, 53 (12): 4248-4252.
doi: 10.7498/aps.53.4248
Abstract +
A random distributed microstructure fiber in which strong asymmetry was introduced around a puresilica core was reported. Femtosecond laser pulses with duration of 35?fs from a Ti:sapphire laser oscillator were coupled into this fiber, and then periodic color rings were observed from the side of the fiber when the supercontinuum light propagated along the fiber. We attributed this phenomenon to
the polarization beating of the supercontinuum light in this highly birefringent microstructure fiber. Measurement showed that the fiber had a beat length of approximately 1?mm at a central wavelength of 600?nm, which is in good agreement with the result of calculation. A new method is proposed to measure the beat length directly in a highly birefringent microstructure fiber.
2004, 53 (12): 4253-4256.
doi: 10.7498/aps.53.4253
Abstract +
A novel fiber Bragg grating thermal tuning scheme is proposed, theoretically analyzed and experimentally studied. The device made from this scheme is named doubleshoulder beam (DSB). Experimental results demonstrate that DSB is an effective thermal tuning technique. A thermal sensitivity of 0436?nm/℃, 50 times that of the bare fiber grating, is experimentally achieved. To our knowledge, this is the largest thermal sensitivity ever demonstrated. The repeatability and lin
earity of the technique is very well. The most important advantage of DSB, as a breakthrough to conventional thermal tuning technique, is its great flexibility. It makes the thermaltuning efficiency of fiber grating no longer limited by the thermalexpansion coefficient of the drive materials, but can be designed according to practical requirements. This technique is expected to have a vast application in fields such as laser tuning, high sensitivity temperature sensing, sensor demultiplexing and so forth.
2004, 53 (12): 4257-4261.
doi: 10.7498/aps.53.4257
Abstract +
The compressivelystrained quantum wells, tensilestrained quantum wells and the combination of tensilestrained and compressivelystrained quantum wells were grown by metal organic vapor phase epitaxy, the materials properties were meas ured by photoluminescence spectra and x-ray doublecrystal diffraction. A polarizationinsensitive multiplequantumwell optical amplifier for 1310nm wavelength employing both compressively strained wells and tensilestrained wells in active region is reported. The amplifier was fabricated to ridge waveguide structure with 7° tilted cavity, the two facets were coated with antireflection thin films. The amplifier exhibited an excellent polarization insensitivity (less than 0.6dB) over the entire range of wavelength (1.28-1.34μm) and a fiber to fiber gain of 21.5B at bias current of 200mA.
2004, 53 (12): 4262-4267.
doi: 10.7498/aps.53.4262
Abstract +
Fiber Bragg grating (FBG) was successfully fabricated in a Yb3+ doped double clad fiber with D-shaped inner-cladding by using phase mask method. Based on the FBG, a stable narrow line width double clad fiber laser was successfully demonstrated which resolved the output instability caused by mode-competition in common double-clad fiber lasers. The maximum output power is 570?mW at the wavelength 1058.2nm with 0.196nm line-band. Based on rate equations, the relationship between output power and pump power, the reflectivity of the FBG and the optimized length of the fiber were analyzed, which were in good agreement with the experimental results.
2004, 53 (12): 4268-4276.
doi: 10.7498/aps.53.4268
Abstract +
The study on the holographic reconstruction and prediction of a semifree field is valuable for the practical applications of the acoustic holography technique. On the basis of the proposed holographic reconstruction and prediction method of semifree field in the inverse distributed source boundary point method,an experiment is carried out in a semifree field. The reconstructed and predicted results in the proposed method are compared with those in the conventional method. The influence of the reflected sound in the reconstruction procedure is analyzed, and the effectiveness and correctness of the proposed method are validated. In addition, considering the sensitivity of the system equations to the measurement errors of pressures on the hologram surface in the experiment, the truncated singular value decomposition method and the Tikhonov regularization method are adopted to stabilize the problem. By choosing the appropriate regularization parameters and filter factors, the influence of errors can be decreased to the least, and the reconstructed and predicted quantities of acoustic field and the reliability of the holographic images are improved.
2004, 53 (12): 4277-4281.
doi: 10.7498/aps.53.4277
Abstract +
In this paper, we use the molecular dynamics simulation to study the phenomena that the granular flow changes from dilute flow to dense flow by increasing the channel width at a fixed orifice of 9.5d (d is the diameter of grains). In the area over the orifice, the density of flow increases and the granular temperatur edecreases with the increase of channel width. The change from dilute flow to dense flow begins at a channel width of 24d, a lower granular temperature( T/m＝0.05 J/kg) and a larger coordination number of 1.2 The mechanism is a structural change in the granular flow, since a wider channel results in more horizontal chains of particles and a lower temperature makes these chains more stable.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2004, 53 (12): 4282-4286.
doi: 10.7498/aps.53.4282
Abstract +
In order to tackle the key problems in the experimental study on the microwave plasma thruster, of which the whole system operates under the vacuum condition, and remove the unnecessary energy loss, an electro microwave device operating under atmosphere and vacuum condition has been developed by applying the design technology of the nonlinear power supply, the integration of attenuator and detector, liquid cooling, and after resolving the gas breakdown problems of electro and microwave apparatus. The experimental study on the device with argon and helium as propellant has been carried out. The results show that the output power of microwave is stable， the device can operate under vacuum and atmosphere condition reliably.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2004, 53 (12): 4287-4292.
doi: 10.7498/aps.53.4287
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In this paper, the quantum theory is used to study the microscopic mechanism of cholesteric liquid crystals. It is proven that the form of the chrial potential can induce the cholesteric phase exactly.The expression of pitch is derived also
2004, 53 (12): 4293-4298.
doi: 10.7498/aps.53.4293
Abstract +
The method of pulsed laser induced nucleation combined with furnace annealing for crystal growth is successfully performed to fabricate uniform silicon nanocrys tals with high density from initial hydrogen amorphous silicon(aSi:H) ultra th in film, deposited by a plasmaenhanced chemical vapor deposition system. Ato mic force microscopy was employed to characterize the morphological modifications of samples. It is shown that the size of ncSi is increased as the laser fluence increased. Nano crystal silicon dots with lateral sizes of～10 nm in dia meter, size deviation less than 20% and with surface density about 10.11/cm2 are obtained. The growth mechanism of ncSi dots is also briefly discus sed.
2004, 53 (12): 4299-4302.
doi: 10.7498/aps.53.4299
Abstract +
The geometric structure of carbon nanotubes (CNTs) is introduced, the symmetry of zigzag and armchair CNTs is analyzed and these symmetry elements are abstracted and summarized. The series of point groups Dnh which the symmetry elements of zigzag and armchair CNTs belongs to are discussed.
2004, 53 (12): 4303-4307.
doi: 10.7498/aps.53.4303
Abstract +
We prepared aSi:H/SiO2 multilayer by using layer by layer deposition of aSi:H sublayer and insitu plasma oxidation in the plasmaenhanced chemical vapor deposition system. Based on the constrained crystallization principle of aSi:H sublayer, we employed krF excimer laser to irradiate aSi:H sublayer and crystallize it. The results of Raman scattering spectroscopy and electron diffraction show that nanocrystal silicon (ncSi) has been formed within the asdeposited aSi:H/SiO2 multilayer, and that the size of ncSi can be controlled precisely according to the thickness of aSi:H sublayer. We also studied the photoluminescence(PL) property of the sample and the effect of laser energy density on PL.
2004, 53 (12): 4308-4313.
doi: 10.7498/aps.53.4308
Abstract +
The stress and strain distributions of simplified and idealized two, one and zero dimensional semiconductor materials,i.e. quantum well, quantum wire and quantum dot are investigated based on the isotropic theory of elasticity, and the differences among the stress, strain and strain energy distributions for the materials are discussed. The results can help us to understand qualitatively the stress, strain and strain energy distributions of the more complicated shapes and structures of lowdimensional semiconductor materials.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2004, 53 (12): 4314-4318.
doi: 10.7498/aps.53.4314
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In this paper, static state and quasistatic state models of quantum well channel hole sheet density of SiGe pmetaloxidesemiconductor with δ doping layer are established and analyzed. The relations between hole sheet density and δ dopinglayer concentration, between holesheetdensity and undoping layer hickness at static state are also discussed, and the relations of the threshold voltage to the δ doping layer concentration, the quantum well channel hole sheet density and the thickness of the undoping layer are discussed. At last, the relation of the quantumwell channel hole sheet density to gate voltage for the quasistatic state is discussed.
2004, 53 (12): 4319-4324.
doi: 10.7498/aps.53.4319
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Due to the damping action during the magnetic moment precession, the magnetic flux generated by a pulsed magnetic field commonly will lag behind the field,so the phase of the pulsed magnetic field lags behind after it penetrates a coated metal. For the nonferromagnetic metal, the phaselag is very faint, and owing to the influence of conductor skin effect and eddy current, it can hardly be detected. An experimental method and the result obtained have been presented in this paper.In this method by using an ultrathin coating with zonal stripe to isolate and select an appropriate position to measure, thus the influences of conductor skin effect and eddy current have been reduced to a minimum. An analysis has been presented in this paper.
2004, 53 (12): 4325-4329.
doi: 10.7498/aps.53.4325
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In this paper, taking commercial Teflon FEP films of Du Pont Co. as an example, the influence of sample thickness on deposited charge density, the internal electrical field of film electrets charged at room and elevated temperatures, and on their bulk conductivity and c harge storage stability is discussed by means of heat pulse technique, measurement of isothermal surface potential decay and analysis of open circuit thermally stimulated discharge current spectra. The influence of the thickness on the shift of mean charge depth of the deposited charge layer under different temperature conditions is also investigated by the measurements of heat pulse technique in combination with conductivity glow curve. The results indicate that under the same charging conditions and with the decrease of the sample thickness, charge density increases, but at the same time charge storage stability is decreased gradually. Therefore, the charge storage capability and charge stability can be optimized by reasonably regulating the thickness of the sample.
2004, 53 (12): 4330-4333.
doi: 10.7498/aps.53.4330
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In doped SnO2 thin films were prepared on quartz substrates by sol-gel dipcoating technique.X-ray diffraction results show that In doped SnO2 films a re of rutile structure.Ultraviolet-visible absorption results show that In_do ped SnO2 films have an optical band gap of about 3.8eV. Hall effect measur ement results show that the hole concentration and the mobility are dependent on both the processing temperature and the In/Sn atomic ratio. It is found that 5.25℃ is the optimum processing temperature to get the highest hole concentration . For an In/Sn atomic ratio between 0.05 and 0.20, hole concentration is almo st proportional to the In/Sn ratio.
2004, 53 (12): 4334-4340.
doi: 10.7498/aps.53.4334
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In a specially designed three barrier double well tunneling structure, elect ron injecting from the emitter in combination with escaping through a resonant tunneling structure were used to adjust and control the filling of electrons in different subbands. It was observed that the occupation in the first excited electron state can result in a suppression to quantum confinement Stark effect. Mo reover, at very low bias, a series of intrigue photoluminescence peaks appeared as a small quantity of excess electron was filled in the ground state of the qua ntum well, that cannot be explained by the theory of band to band transition in the framework of single electron picture.
2004, 53 (12): 4341-4346.
doi: 10.7498/aps.53.4341
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The influence of microstructure on magnetic properties of Sm(Co,Cu,Fe,Zr)z magnets is investigated by micromagnetic finite_element method. The demagnetization curves at different temperatures are also simulated. The calculated results show that the saturation polarization Js depends on the relative proportions of 2∶17 phase and 1∶5 phase. The coercivity and the maximum energy product increase with increasing 2∶17type cell size, while they decrease wi th increasing width of 1∶5type cell boundary. The coercivity analysis shows t hat the magnetization reversa l in Sm(Co,Cu,Fe,Zr)z magnets is mainly controlled by nucleation at cell bounda ry. The abnormal temperature dependence of coercivity is due to the fact that the cell boundary becomes less magnetic even nonmagnetic and the nucleation is difficult with increasing temperature.
2004, 53 (12): 4347-4352.
doi: 10.7498/aps.53.4347
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The microstructure with which a hard magnetic phase precipitates from the soft magne ticmatrix, is observed in nanocomposite Pr2Fe14B-αFe. The magnetic hysteresis loo ps are simulated by micromagnetic finite element method. The dependence of reman ence, coercivity and maximum energy product on the width of soft phase are discu ssed in detail. Although a single hard magnetic phase behavior is observed, the coercivity decreases monotonically with the increase of soft phase width from 0 to 12 nm. The obtained maximum energy products are 184 and 674 kJ/m3 for isotropic and anisotropic magnets, respectively.
2004, 53 (12): 4353-4358.
doi: 10.7498/aps.53.4353
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The initial curves, demagnetization curves and recoil curves of Pr2Fe14B and Pr2Fe14B-α Fe nanocrystalline permanent magnets have been calculated by micromagnetic finite_element method. The validity of δm(H)curves, which can be used to determine the strength of intergrain exchange coupling interaction (IGEC), is approved by the calculated results. It is found that IGEC weakens with increasing grain size D for single-phase nanocrystalline and nanocomposite permanent magnets. Thus, the demagnetization curve shows a two-phase behavior and the δm(H) curve shows two peaks for the nanocomposite sample with D=20nm.The peak at small field can be attributed to the exchange interaction between the magnetic hard and soft grains, while the peak at large field may be due to the IGEC among hard grains.
2004, 53 (12): 4359-4363.
doi: 10.7498/aps.53.4359
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FeCoBSiO2 nano-granular films were fabricated by alternately deposited mu ltilayers using radio frequency magnetron sputtering. Microstructures and morpho logy were analyzed by x-ray diffraction, scanning probe microscope and transmis sionelectron microscope.Magnetic parameters were measured by vibrating sample magnetometer.The electrical resistivity was measured by a direct current four probe method,and the complex permeability was measured by microwave resonance cavity.The mechanism of the effect of microstructures and content of SiO2 on electromagnetic characteristics was also discussed. Results show that these films have good performance at high frequencies.μ′can be larger than 70 at 2GHz.Thus,the films may be applied to the micromagnetic devices or microwave absorbers in the GHz range.
2004, 53 (12): 4364-4368.
doi: 10.7498/aps.53.4364
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The dielectric, piezoelectric and some elastic constants of the Ca3NbGa3Si2O14 crystal had been determined by using Ycut and (yxl)30°cut crystal samples.The calculated piezoelectric constants as functions of cut a ngle of (yxl)θ cut were also given. The Ca3NbGa3Si2O14 crystal showed superior piezoelectric properties with relatively large piezoelectric constants (d11=7.93×10-12C/N，d14=-5.88×10-12 C/N) compared with La3Ga5SiO14 crystal.
2004, 53 (12): 4369-4372.
doi: 10.7498/aps.53.4369
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By using a microsecond pulse field, we succeeded in fabricating a uniform submic ron domain pattern with a period of 1.7μm in LiNbO3- doped 5mol% MgO. And the depth of these domain strips is, typically, about 30 to 50μm. When a pol ed field with a pulse width of 100ms is applied, the domain- inverted structure with a width of 0.5μm was obtained. Using the spontaneous domains backswitc hing and domain side- grown effects, we can explain the mechanism of the submicro n domains evolution.
2004, 53 (12): 4373-4377.
doi: 10.7498/aps.53.4373
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Optical bistability has been investigated in granular metal-dielectric composite media at high temperatures. Based on Maxwell-Garnett approximation and the spe ctralrepresentation, we calculate numerically the electric field as a function of the applied electric field E２０,and thus the opticalbistability can be studied.We show that the width of optical bistability decreases with increasing temperature.Furthermore, we study the dependence of the refractive index and the extinction coefficient on the temperature.
2004, 53 (12): 4378-4381.
doi: 10.7498/aps.53.4378
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We compared the lifetime values of the upconversion state for Er3+doped tellurite glass with and without halide ions as determined by direct excitation mechanism, with the results measured by upconversion excitation method. The results indicate that upconversion excitation lengthens the lifetime value largely compared with the direct excitation. The intensity of the upconversion fluorescen ce of the two kinds of glasses was discussed, which showed that it becomes stron ger with the addition of the halide ions than that without the halide ions. The upconversion mechanisms and power-dependent intensities were also determined and explained.
2004, 53 (12): 4382-4386.
doi: 10.7498/aps.53.4382
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This paper reports the excited-state upconversion of Pr(0.5):ZBLAN glass under two-color excitation. It is found that the fluorescence of upconversion-emiss ion spectrum is the same as that of common-emission spectrum. It is found also that there are three obvious peaks on upconversionexcitation spectrum under twocolor excitation, which corresponds to the 788.5nm 1G4→3P2,850.5nm 1G4→1I6,and 805.0nm 3H6→1D2 excited state absorpt ion transitions res pectively. The large 850.5nm peak of upconversion-excitation spectrum results from the large 1G4(Pr3+ )→1I6(Pr3+) (Pr3+) oscil lator strength f=23.04×10-6. It illustrates the excited state absorp tion upconve rsion from 1G4 level, especially the 1G4(Pr3+)→1I6(Pr3+) upconversion process is large. It results in the upcon version luminescence of Pr(0.5):ZBLAN under two-color excitation.
2004, 53 (12): 4387-4391.
doi: 10.7498/aps.53.4387
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Based on the layer-optimized method, the devices of sandwiched structure are pr oduced by compounding MEH-PPV and SiO2 In three different voltage regions of alternating current, the devices luminesce differently. When the voltage is low, red emission is obtained; and if the voltage is high, blue emission is acquired. The superposition of the above two emissions is obtained when the voltage is moderate. The red or blue emission belongs to the solidstate cathodoluminesc ence, it originates from the accelerated electrons in SiO2, which bombard the organic layers. By the study on the optic characteristics of the devices, the sc opes and regulations of spectra shift are analyzed.
2004, 53 (12): 4392-4397.
doi: 10.7498/aps.53.4392
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Arrays of multi-walled carbon nanotube (MWCNT) were bombarded with argon ions a nd studied with transmission electron microscopy and x-ray photoelectron spectr oscopy. Our preliminary results show that after 35min ion bombardment, most of the MWCNT curls and the iron catalyst particles residing at the top end of the tube were knocked out. Although no obvious change in its emission images is obse rved, its field emission current considerably decreases. During spontaneous cool ing down from an elevated temperature (480℃), its emission current decreases sh arply. Interesting finding is that the coating of phosphor powder on the tin-oxide-coated glass anode significantly affects the emission current measurement . For example, the phosphor coating reduces the measured current by over 30?tim es and increases the turnon field from 1.0 to 2.0V/μm.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2004, 53 (12): 4398-4404.
doi: 10.7498/aps.53.4398
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Using the atomic force microscopy, we have studied the effect of sputtering particle energy on the growth and microstructures of Mo thin films prepared on borosilicate glass (BK7) substrates with ion beam sputtering technique. With specially designed fixture, all samples were prepared in the same run, which diminished the effect of multi-runs on the growth of thin films. Furthermore,the morphology of Mo thin films was studied quantitatively based on numerical analy sis. The morphology of Mo thin films is typically fractal, and the surface para meters of thin films such as fractal dimensions, lateral correlation length and interface width are all obtained. Compared with the thin films prepared under the screen grid voltages of 300 and 700V, the interface width and lateral correlation length of the thin films prepared under the screen grid voltage of 500 V show two times large difference. All the fractal dimensions of thin films are n ear 2 and the growth process of Mo thin films can be described using Mullins diffus ion model. Besides, by using the technique of Auger electron spectroscopy, the atomic concentrations can be obtained in the depth profile.
2004, 53 (12): 4405-4409.
doi: 10.7498/aps.53.4405
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Pb0.72La0.28TiO.3(PLT28) thin films have been prepared on Pt/Ti/SiO2/Si substrates by pulsed laser deposition under various oxygen pressu re. Experimental study indicated that the oxygen pressure exerts a strong impact on the microstructure and the dielectric properties of the thin films. The film deposited under an oxygen pressure of 2Pa had a larger dielectric constant an d kept a low dielectric loss. At 10kHz frequency, the dielectric constant was approximately 852 and the dielectric loss was 0.0110 Meanwhile, we found that other La- modified PbTiO3 films have the same relation between dielectric con stant and pressure as the above. Possible explanation is given for this.
2004, 53 (12): 4410-4413.
doi: 10.7498/aps.53.4410
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Boron-doped (B-doped) silicon nanowires have been successfully synthesi zed by plasma-enhanced chemical vapor deposition (PECVD) at 440℃ using silane as the Si source, diborane(（B2H6）) as the dopant gas and Au as the catalyst. It is desirable to extend this technique to the growth of silicon nanowire pn jun ctions because PECVD enables immense chemical reactivity.
2004, 53 (12): 4414-4419.
doi: 10.7498/aps.53.4414
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On the basis of our previous elastic model which is related to the salt ion conc entration, we put forth a new model of B-DNA to Z-DNA transition by considerin g interactions of the hydrogen-bond and base-stacking in Z-DNA, and discuss the effects of salt concentration on the structure transition of B-Z and obtain the force extension curves, the probability distribution curve of the folding angle and the critical torque of B-Z transition at various salt concentrations. The results show that Z-DNA appears when salt concentration reaches 2.4mol/L,and the probability of Z-form begins to increase and the torsion of B-Z trans ition decreases with the increase of salt concentration.
2004, 53 (12): 4420-4427.
doi: 10.7498/aps.53.4420
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How to extract the magnetocardiography (MCG) signals from the background noises and attenuate the noise is the key element of MCG signal processing. From the aspect of software technique, a new adaptive algorithm is proposed to suppress the environmental magnetic noise of MCG in this paper. The propo sed algorithm is called improved complementary pair normalized least mean square algorithm. This adaptive structure is designed for MCG. This new algorithm prov ides the faster convergence speed and smaller steady-state error. In order to test the performance of this algorithm, the result of the simulated experiment and real MCG signal is analyzed. This method bring about the effective noise atten uation. Meanwhile, this algorithm is suitable for noise cancellation of other non-stationary signals.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
2004, 53 (12): 4428-4434.
doi: 10.7498/aps.53.4428
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When a seismic signal propagates through a realistic medium in the Earth, in add ition to anisotropy, the layers may show intrinsic viscoelastic behavior. Thus, an accurate description of wave propagation requires a rheology that accounts for the anisotropic and viscoelastic behavior of rocks. On this basis, the pseudo spectral recursive formulae of viscoelastic and azimuthally anisotropic media are derived. Wavefield forward modeling with the pseudo-spectral method was car ried out in viscoelastic and azimuthally anisotropic media. The numerical results from the pseudo-spectral method clearly show that seismic wavefield is closely related with the viscoelasticity and the azimuth of the principal axes of anis otropy.
2004, 53 (12): 4435-4438.
doi: 10.7498/aps.53.4435
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In this paper, in the two-parameter five-dimensional(5D) rotating black hole, we discuss the thermodynamic parameters corresponding to the black hole's horizon and the thermodynamic parameters corresponding to the cosmological horizon. It is obtained that the entropy of cosmological horizon can be written in the form of Cardy-Verlinde formula. However, if we want to write the entropy of the bla ck hole's horizon in the form of Cardy-Verlinde formula, we have to use the met hods offered by Abbott and Deser to calculate the mass of the 5D black hole with double- spinning parameter. Through the research, we can give the relation among the thermodynamic parameters of the 5D black hole, that is, the differential ex pression of the first law of thermodynamics.
