Vol. 50, No. 3 (2001)
2001, 50 (3): 369-376. doi: 10.7498/aps.50.369
Starting from bilinear form of integrable models, one can obtain a dromion solution that is localized in all directions or a “Solitoff” solution that decays exponentially in all directions except a preferred one for the physical field or a suitable potential. The interactions between dromions, dromion and “Solitoff”, solitons are studied in detail through the method of figure analysis for two KdV type equations. Some interactive properties between two dromions (solitons) are revealed for two models. The interactions between two dromions(solitions) may be elastic or inelastic for different form of solutions.
THE STABILITY OF THE CRYSTAL GROWTH FACE IN A MODEL FOR CRYSTAL GROWTH FROM SOLUTION UNDER MICROGRAVITY
2001, 50 (3): 377-382. doi: 10.7498/aps.50.377
The stability of the crystal growth face in a two-dimensional mathematical model of-crystal growth from solution under microgravity is studied.The growth rate of a crystal is calculated for various tilt angles of the crystal growth face.It is known from the results of calculation that there exists possibly a stable growth face of the crystal. This face should be a suitably shaped curve with the upper end of the face tilting backwards.
2001, 50 (3): 383-389. doi: 10.7498/aps.50.383
The basic theory of relativistic Birkhoffian dynamics of rotational system is constructed,and the Birkhoffian,Birkhoff's functions,Pfaff action,Pfaff-Birkhoff principle,Pfaff-Birkhoff-D'Alembert principle and Birkhoffian equations are given.The relations among relativistic Lagrangian mechanics,Hamiltonian mechanics and relativistic Birkhoffian dynamics of rotational system are studied.It is proved that the holonomic conserved and holonomic non-conserved rotational relativistic systems can all belong to the rotational relativistic Birkhoffian system.
2001, 50 (3): 390-393. doi: 10.7498/aps.50.390
The d'Alembert principle and the differential equations of motion of relativistic rotational variable mass system are given. By using the invariance of the differential equations under the infinitesimal transformations, the determining equations of the Lie symmetries of relativistic rotational variable mass system are built, and the structure equation and the conserved quantities of the Lie symmetries are obtained. An example is given to illustrate the application of the result.
2001, 50 (3): 394-397. doi: 10.7498/aps.50.394
The damping force and the external electric field caused the kink soliton excitation in a hydrogen-bonded chain with asymmetric double-well potentials. The formula of the soliton mobility was derived, from which we obtained the result of the φ4 chain as well.
2001, 50 (3): 398-401. doi: 10.7498/aps.50.398
A.Gordon first studied solitonic coductivity in some hydrogen-bonded ferroelectric materials, using the hydrogen-bonded chain model with asymmetric double-well potential, and gave the kink solution and expression for its mobility. However, kink solitons making contribution to proton-solitonic conductivity should be the solitons corresponding to proton transfer between two wells. For this reason, we suggest revising Gordon’s result, giving a low-energy-state kink solution and a new expression for its mobility. With the asymmertic double-well potential transforming to the symmetric one, this expression is reduced exactly to the same form as previous research result. This expression shows that the phase-transision critical index is 1.
2001, 50 (3): 402-405. doi: 10.7498/aps.50.402
With the aid of Wu Wen-jun characteristic-set method in nonlinear algebraic equations-solving, and using the symbolic manipulation system, the exact solitary wave and soliton solutions to a class of fifth-order nonlinear evolution equation with general coefficients are obtained, which modifies and perfects the known results.
2001, 50 (3): 406-410. doi: 10.7498/aps.50.406
Based on the theory of deformed Lie algebra, we construct a nonlinear spectrum-generating algebra for the first P?schl-Teller potential by use of the Hamiltonian and the natural operators. This nonlinear algebra can determine the energy spectrum and the complete set of eigenfunctions, and can be converted into the harmonic oscillator algebra through a nonlinear transformation, which shows there is a new symmetry in the system.
TWO DIFFERENT METHODS OF DERIVING ARNO WITT-DESER MISNER CONSTRAINT EQUATIONS FOR EINSTEIN'S GRAVITATIONAL FIELDS
2001, 50 (3): 411-415. doi: 10.7498/aps.50.411
In this paper,two different methods are given,by which the famous Arnowitt-Deser-Misner (ADM) constraint equations for Einstein's gravitational fields can be derived.One method is to construct an action of gravitational fields with a parameter in the specetimes of Lorentzian sgnature.Thus,ADM constraints with a parameter can be obtained and the familiar ADM constraint equations can be naturally derived by adjusting the value of this parameter.The other is to apply the double complex function theory to gravitational fields in Hamiltonian formulation.Hence,the double constraints can be obtained,in which the well-known ADM constraint equations are included as a special case.In addition,the Lorentzian and Euclidean gravitational theory can be expressed in a unified way by use of these two different methods.
2001, 50 (3): 416-421. doi: 10.7498/aps.50.416
Under the framework of nonlinear quantum field theory,we show the total Hamiltonian operator Htot for the interaction between an electron field and a photon field,and study the contribution of the nonlinear term A2 in the strong laser field.In this paper,we describe electrons with the Schr?dinger quantum wave field of Fermi-Dirac statistics.By applying “self-consistent mean field”,“effective mass” approximation and the displaced harmonic oscillator coherent theory,we derive the Lee-Low-Pines expression f(b+) of electron wave-photon field operator function.Then using the differential formula of f(b+) b+,we derive some relevant calculating formulas,including detailed expressions of electron energy Ek and wave field parameter βw.Furthermore,we also derive self-energy Ek=0 and renormalized mass m of electrons according to these expressions.
2001, 50 (3): 422-427. doi: 10.7498/aps.50.422
A modification to the 13-speed lattice Bhatnagar-Gross-Krook model is presented.The single relaxation time τ and the free parameter k are suitably chosen so that the transport coefficients become energy-dependent only and the Prandtl number is tunable.Simulations for various boundary cavities under high Reynold number are presented with the model.
2001, 50 (3): 428-434. doi: 10.7498/aps.50.428
A method of injected-feelback control of chaotic systems in Chai's circuits is put forward. By the method,the chaotic systems can be controlled in predetermined equilibrium states and the vibrational cyclical trajectories. With the change of control parameters,typical variation of physical state is studied to extend the applications of chau's circuits chaotic systems in Chai's circuits.
2001, 50 (3): 435-439. doi: 10.7498/aps.50.435
The wavelet function feedback method is proposed for controlling beam halo-chaos for high intensity proton beam in a periodic-focusing channel.After control for four different primary proton distributions,the halo intensity factor become zero,other statistical physical quantities (such as rrms and P2av) and relative average emittances are more than doubly reduced.Simulation results show that the method is very effective and has its prospect for application.
2001, 50 (3): 440-444. doi: 10.7498/aps.50.440
An adaptive fuzzy control scheme is presented to control model unknown coupled spatio-temporal chaos composed of high-dimensional continuous-time subsystems. This method integrates the merits of approximate ability of adaptive fuzzy system and robustness of the sliding control. By using Lyapunov method we have proved the stability of the scheme. The effectiveness and the feasibility of the proposed method are demonstrated through simulations on the continuous time coupled Duffing oscillator spatio-temoral chaos.
AN IMPROVED ONE-DIMENSIONAL CELLULAR AUTOMATON MODEL OF TRAFFIC FLOW AND THE EFFECT OF DECELERATION PROBABILITY
2001, 50 (3): 445-449. doi: 10.7498/aps.50.445
Based upon the single-lane traffic cellular automaton (CA) model introduced by Negel and Schreckenberg, an improved single-lane traffic CA model has been proposed by the consideration of the relative motion of vehicles and the relation of deceleration probability with the density. Numerical simulations have been carried out.The results show the complicated evolution process of traffic flow.The flow of vehicles can be controlled by the definition of the relation between deceleration probability and the exponet v of density pnoise～ρv.Different values of v have different effect on the critical point from free phase to jam phase.The simulation agrees with the measurement as v is about 0.75.With the increase of vehicles and the evolution process of traffic flow,the free and jam phases will become unsteady and appear alternatively, similiar to the propagation of wave.
2001, 50 (3): 450-452. doi: 10.7498/aps.50.450
VO2 thin films are used for uncooled microbolometer due to their high temperature coefficient of resistance.In this paper,on the basis of fabricating the uncooled bolometer based on VO2 sputtered thin films,the responsivity for the spectral range of 8-12μm region dependence on bias current and chopper frequency is studied.The result indicates that the responsivity is over 17kV/W and up to 10kV/W at a chopper frequency of 10 and 30Hz,respectively.The device having a detectivity D of exceeding 1.0×108cm (Hz)1/2/W and a thermal time constant of 0.011 seconds has been realized.
ATOMIC AND MOLECULAR PHYSICS
MEASUREMENT OF ISOTOPE SHIFTS AMONG 142—146,148,150Nd+ BY USING COLLINEAR FAST-ION-BEAM LASER SPECTROSCOPY
2001, 50 (3): 453-456. doi: 10.7498/aps.50.453
In atomic spectroscopy, the subject of isotope shifts is one of the few problems that links atomic and nuclear physics. The isotope shifts among all the seven stable isotopes in Nd Ⅱ were measured by means of collinear fast-ion-beam laser spectroscopy.Compared with the data that have been published,our experimental accuracy is improved by one order of magnitude and some of the results are obtained for the first time, as far as we know.
2001, 50 (3): 457-461. doi: 10.7498/aps.50.457
Energy absorption by Xe,Ar,He atomic clusters are investigated using laser pulses with 5mJ energy in 150fs duration.Experimental results show that the size of cluster and laser absorption efficiency are strongly dependent on several factors,such as the working pressure of pulse valve,atomic number Z of the gas.Absorption fraction of Xe clusters is as high as 45% at a laser intensity of 1×1015W/cm2 with 20×105Pa gas jet backing pressure.Absorption of the atomic clusters is greatly reduced by introducing pre-pulses.Ion energy measurements confirm that the efficient energy deposition results in a plasma with very high ion temperature.
CLASSICAL AREA OF PHENOMENOLOGY
2001, 50 (3): 462-466. doi: 10.7498/aps.50.462
Due to the birefringence effect of the quantum well laser and the collimating lens in a low temperature cryostat, the polarization of the output light was changed, therefore the photon number fluctuation of the output individual linearly polarized mode was increased. By compensating the birefringence with a quarter wave plate, and utilizing an inphase external weak feedback to laser diode laser by means of residuary reflection from the two surfaces of a half wave plate, we obtained the output light of 24mW with the photon number fluctuation 2.8dB below the Standard Quantum Limit at the pump current of 34.65mA.
2001, 50 (3): 467-472. doi: 10.7498/aps.50.467
A quantum optical true random number generator based on splitting a beam of photons at a 50/50 beamsplitter has been demonstrated. A continuous stream of random numbers at a rate of 200 kbit/s can be generated. A mathematical method (Huffman coding and data compressing) is used to improve the ratio of 0 and 1 bits in the original random number arrays.
2001, 50 (3): 473-477. doi: 10.7498/aps.50.473
The squeezing and coherence properties of the light produced by the Raman interaction of single-mode squeezed vacuum field with two coupling atoms are studied by means of quantum theory. Using the numerical method, the relation between the quantum properties of the light and the coupling parameter and initial state of the system is discussed.
2001, 50 (3): 478-482. doi: 10.7498/aps.50.478
The enhancement mechanism of the optimized CVL by a genetic algorithm are presented in this paper. With a small storage capacitance and a small peaking capacitance, the input power increases due to the improved impedance matching between the laser head and the discharging LC circuit by the optimization. The lasing population increases as a result of the increased tube-wall temperature. The plasma electron temperature increases more rapidly during the period of the discharge, and the electron density increases obviously after the optimization.
DYNAMIC CONVERSION FROM SELF-DEFOCUSING TO EQUIVALENT “SELF-FOCUSING” IN PHOTOVOLTAIC LiNbO3:Fe CRYSTALS
2001, 50 (3): 483-488. doi: 10.7498/aps.50.483
We experimentally studied the dynamic behavior of conversion from self-defocusing to equivalent “self-focusing” in LiNbO3:Fe crystal under certain experiment conditions. Its physical mechanism is the consequence of both the double-Phase conjugate Fabry-Perot interference cavity and photorefractive effect. It is possible to form bright spatial solitons in self-defocusing medium by the effect of dynamic conversion.
2001, 50 (3): 489-495. doi: 10.7498/aps.50.489
On the basis of coupled-mode theory we find a class of solitary solutions for the electromagnetic wave propagating in an infinite one-dimensional periodic structure with an intensity-dependent refractive index. We show that the amplitude of the solitary wave is dependent of the incident frequency and the pulse width. In the Bragg resonance limit, the solitary wave can be simplified to a soliton-like solution which was named as “gap soliton” or “slow Bragg soliton”.
A photovoltaic spatial soliton theory of duotone signal beam with monochrone background beam is presented, and a solution of bright soliton has been obtained by a numberical method. We have observed bright photovoltaic spatial solitons of polychromatic signal beam with monochrome background beam in a Cu:KNSBN crystal.
2001, 50 (3): 501-506. doi: 10.7498/aps.50.501
The steady state temperature field in human body generated by concave spherical surface focused ultrasound transducer for hyperthermia has been studied through solving bioheat conduction equation by the difference method in this paper.The influence of parameters of the transducer and biological tissue properties on the effective treated area has been analyzed through introducing the heat focal distance and isotherms, and characteristics of the sound field and temperature field are studied thoroughly.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2001, 50 (3): 507-511. doi: 10.7498/aps.50.507
This paper has studied plasma transport in scrape-off layer(SOL), by using ‘two-point’ mode and particles continuity equation. We have calculated plasma density distribution, temperature distribution, impurity radiation power loss in SOL with friction.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2001, 50 (3): 512-516. doi: 10.7498/aps.50.512
We report here the studies of electron spin resonance (ESR) and its related defect states in doped nanocrystalline silicon films (nc-Si∶H). The samples used, which was prepared by plasma enhanced CVD method, are of two phases in structure, i. e., nanocrystallites embedded in the amorphous matrix. For phosphorus doped nc-Si∶H samples, the measured ESR g-values are 1.9990—1.9991, the line width ΔHpp(40—42)×10-4T, and the ESR density Nss is of order of 1017cm-3. For boron doped nc-Si∶H samples, the measured ESR g-values are 2.0076—2.0078, ΔHpp is about 18×10-4T, and Nss is of order of 1016cm-3. Considering the micro-structural and conducting characteristics of these kinds of films, we discuss and give explanations to the ESR sources, their ΔHpp and Nss as well. We ascribe the ESR signals in phosphorus doped nc-Si∶H to the unpaired electrons in the high density defect states located in the interfaces of nanocrystallites/amorphous matrix , and that in boron doped ones to the unpaired electrons in the valence band-tail states in the a-Si∶H tissue of their amorphous matrix.
2001, 50 (3): 517-522. doi: 10.7498/aps.50.517
The growth of Si on silicon nitride surfaces has been studied using in situ STM, low energy electron diffraction and Auger electron spectroscopy. In the early stage(T=350—1075 K), Si nano-clusters can appear on different substrates. These clusters are round with sizes in the range of several nanometers.They are also rather stable when the substrate temperature changes (or annealing). As these clusters grow continually, crystalline facets start to form. On the crystalline Si3N4(0001)/Si(111), Si islands with (111) oriented top facets grow faster than others, and they are aligned with the original Si(111) substrate. Finally, Si(111) became the dominant feature on the whole surface. In contrast, on the amorphous Si3N4 surface, Si islands grow in random orientation. Low-index facets, such as (111) and (100), and high-index facets, such as (113), coexist. Some discussions are given to explain the above growth procedures.
2001, 50 (3): 523-527. doi: 10.7498/aps.50.523
Using the X-ray diffraction techniques, the intensity, structure factor, pair distribution function and the nearest neighbor distance of non-crystalline alloy Mg70Zn30 were obtained. The experimental results show that there is a visible pre-peak on the structure factor of non-crystalline alloy Mg70Zn30 in the small Q region. According to the characters of the pre-peak, an atomic model of Mg70Zn30 melt was constructed, namely, a bcc structure with one Mg atom locates at the center and other eight Zn atoms lie on the vertexes. Combined with shared vertex, it can meet the requirement for the distance of Mg-Mg atoms. The origin of the pre-peak on the structure factor of non-crystalline alloy Mg70Zn30 is caused by the correlation between the central Mg atoms in neighboring clusters.
2001, 50 (3): 528-531. doi: 10.7498/aps.50.528
Using a Fr?hlich Hamiltonian for the electron-lattice interaction, an expression for the Peierls phase transition temperature( TP)of metallic helical carbon nanotube (n1,n2)has been derived. As an illustration, the formula is used to estimate TP of metallic(n1,n2). The results indicate metallic(n1,n2)are stable against the Peierls distortion and preserve metallic property at and far bellow room temperature.
THE TRANSITION FROM Eu3+TO Eu2+ IN SiO2(Eu) THIN FILMS PREPARED BY ION IMPLANTATION AND CO-SPUTTERING
2001, 50 (3): 532-535. doi: 10.7498/aps.50.532
Eu ions doped SiO2 thin films, SiO2(Eu), were prepared by co-sputtering of SiO2 and Eu2O3 and Eu ion implantation into thermally grown SiO2 films. The Eu-L3-edge X-ray absorption near edge structure (XANES) spectra of SiO2(Eu) films show a doublet absorption peak structure with energy difference of 7 eV, which indicates the conversion of Eu3+ to Eu2+ at-high annealing temperature in N2. The strong blue luminescence of SiO2(Eu) films prepared by ions implantation after films annealed above 1100 ℃ confirms the above argument.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Photocurrent spectrum of GaAs/AlGaAs superlattice at T=77K was measured.A strong photocurrent peak at ν=1589cm-1 and several weak peaks at ν=1779,2129 and 2401cm-1 were observed.It was believed that these photocurrent peaks are relevant to waving of electron in superlattice.The calculated positions of peaks of photocurrent on the basis of the theory of electron waving are in good agreement with experimental results.
2001, 50 (3): 540-543. doi: 10.7498/aps.50.540
We have carried out preliminary investigations about the magnetic and transport properties of the double perovskite Sr2CrWO6. The polycrystalline sample was fabricated using solid-state reactions in an Ar atmosphere and evacuated silica capsules. The X-ray diffraction studies show that the sample is composed of Sr2CrWO6 and a small amount of impurity SrWO4. The Curie temperature, determined by the thermal magnetization measurements, is around 480 K. The electric resistivity increases with the drop of temperature and exhibits insulator behavior. A large intergrain magnetoresistance (MR) up to 20% at a low temperature (25 K) and a field of 5 T is observed. And the MR decreases to zero with increasing temperature toward 300 K. The large coercive force (5.97×104 A/m) and the low-field deviation of MR from high-field linear behavior indicate that there probably exists a large magnetic anisotropy in the compound.
2001, 50 (3): 544-549. doi: 10.7498/aps.50.544
The diffusion,aggregation and crystallization characteristics of gold atoms deposited on molten glass surfaces are studied.Experimental results indicate that the gold atoms first form a characteristic web-shaped Au film on the colloid glass surface,and the average diameter of the crystal grains in the film is about 20 nm.The area of the meshes gradually increases and then the whole film tatters.Thus the compact clusters are formed.The saturated diameter of the compact clusters is about 1.2μm and its diffusion coefficient D is of the order of 107—108cm2/s.The compact clusters diffuse on the molten glass surface quickly and quasi-randomly,and finally large ramified aggregates with diameter of about 50 μm from.
STUDY OF THE SYNTHESIS PROCESS AND STRUCTURAL DEFECTS IN Y-123 SUPERCONDUCTING SYSTEMS BY POSITRON EXPERIMENT
2001, 50 (3): 550-555. doi: 10.7498/aps.50.550
Using positron annihilation,X-ray diffraction and scanning electron microscopy experiments,the structural characteristics and preparation techniques for YBa2Cu3O7-δ systems are systematically studied.The results show that,for the samples sintered at 950℃,the orthorhombic disorder increases with the duration of sintering time.On the whole,with the increase of sintering temperature and time,the positron lifetime increases until it reaches a saturation value.It is proved that,under the condition of 920—950℃ for 12—72 h,the structural characteristics and superconductivity of Y-123 have good stability.The changes of defect with the sintering temperature and time are also discussed.This experimental results indicate that the positron experiment shows good stability and reliability.
2001, 50 (3): 556-560. doi: 10.7498/aps.50.556
Taking into account the spin polarized and interface roughness scattering effect, within scattering formalism, we calculate the shot noise in the ferromagnet-superconductor tunneling junction. It is found that the ferromagnetic exchange interaction gives rise to decrease of the average current and the shot-noise power, but the interface roughness can give rise to increase of the average current and the shot-noise power.
OPTICAL ABSORPTION OF Ag-BaO THIN FILM IN THE VISIBLE AND NEAR-INFRARED REGION WITH APPLIED ELECTRIC FIELD
2001, 50 (3): 561-565. doi: 10.7498/aps.50.561
The optical absorption properties of Ag-BaO composite thin film with excess barium were measured while a vertical electric field was applied on the film surface.Total two absorption peaks were observed in the visible and near-infrared region,and only the peak that lies in the near-infrared region was dependent on the applied electric filed,i.e.,the absorption intensity was decreased with the increasing electric field.The dominant peak in the visible region is attributed to the surface plasmons resonance of Ag ultrafine particles embedded into the BaO semiconductor matrix.However,the weaker one in the near-infraed region is considered to arise from the transition of bound electrons at impurity energy level of the BaO semiconductor matrix,and such an impurity energy level is related to the negative ion vacancies caused by the excess braium in the BaO crystal.When the external surface electric field was applied,some of the impurities in the BaO Semiconductor matrix were ionized,and which further resulted in a decrease of the density of bound electrons at the impurity energy level.So that,part of the optical absorption owing to the impurity energy level was decreased with the enhanced electric field.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
CHEMICAL BONDING STRUCTURE OF FLUORINATED AMORPHOUS CARBON FILMS PREPARED BY ELECTRON CYCLOTRON RESONANCE PLASMA CHEMICAL VAPOR DEPOSITION
2001, 50 (3): 566-571. doi: 10.7498/aps.50.566
The a-C∶Fx films with low dielectric constant has been studied,considering that they can be used for interlayer dielectric in ultra-large integrated circuits.These films were deposited by using electron cyclotron resonance plasma reactor with CHF3 and C6H6 mixture as source gas.The effects of microwave power,pressure and CHF3/C6H6 ratios on the film deposition rates have been investigated.The fluorocarbon and hydrocarbon radical species in the plasma discharges were monitored by the optical emission spectra.The structural properties of the films were characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.A relationship between the radical species in the discharge plasma and bonding structure of the films is analysed.It demonstrates that CF2,CF and CH radicals play the important roles in the forming of films.
A DISCUSSION ABOUT THE PAPER “DETERMINISTIC PROPERTIES CONTAINER IN QUANTUM SYSTEMS WITH CONTINUOUS SPECTRUM”
2001, 50 (3): 572-576. doi: 10.7498/aps.50.572
For a single particle system with continuous energy spectrum, the paper “Deterministic Properties Contained in Quantum Systems with Continuous Spectrum” uses the “double wave functions” to describe the quantum behavior of each particle in the ensemble staying in an energy eigenstate. And the “equivalence theorem” in the paper points out that the double wave description will become the classical mechanics description in the classical limit. However, the statistical distribution of results of measurement of a physical quantity predicted by the double wave description for the ensemble is very different from that predicted by the usual quantum mechanics. And the proof given in the paper for the “equivalence theorem” is incorrect. Actually, this theorem is not true.