Vol. 45, No. 1 (1996)
1996, 45 (1): 1-12. doi: 10.7498/aps.45.1
The nonlinear variations of the eigenvectors are discussed on the basis of Ref. [1, 2]. It is shown that relative to a steady wave the nonlinear eigen frequency allows for both forward and backward transports. Their eigenvectors deflect in the Fourier space as compared to the linear case. The positive (P-) and negative (N-) energy modes can be defined in the nonlinear case according to the relative strength of the forward and backward eigenvectors of the perturbations. Based on this definition the effect of N-mode on the nonlinear instabilities is further studied. The results are in consistency with the conclusion in Ref. [1,2]. The bista-bility of wavepacket is associated with the transition of a resonance N-mode to a p-mode, in particular its eigenvector is discontinuous in the parameter space; The Hop f bifurcation of a steady wavepacket is associated with the resonance of a N-mode to a p-mode. As a result re-connections occur between their eigenvectors of forward and backward perturbations respec-tively. With the increase of nonlinearity, the p-mode first and the N-mode following next change their energy types. Consequently there exists a parameter regime where both modes become N-type. This regime coincides with that of the Hopf bifurcation. This fact strongly supports the conjecture that the excitation of N-modes induces the nonlinear (Hopf) bifurcation.
ATOMIC AND MOLECULAR PHYSICS
1996, 45 (1): 13-19. doi: 10.7498/aps.45.13
As an extension of theoretical study of transition from an initial state to a final channel,the initial states with same angular momentum form varied initial channels. By defining anew renormalized matrix element, the atomic radiative processes from an initial channel to afinal channel can be treated in an unified manner. As an example, we present here the renor-malized matrix element of Rb atom between initial and final channels.
LIE ALGEBRAIC APPROACH TO THE MITLTIPHOTON EXCITATION OF VIBRATIONAL STATES OF DIATOMIC MOLECULES IN INTENSE LASER FIELDS
1996, 45 (1): 20-28. doi: 10.7498/aps.45.20
The multiphoton vibration excilation of diatomic molecules in intense laser fields arestudied by using the simulated poltjnllal-Lie Algebra. It is calculated that the transition prob-abilities of the molecule change with the external field frequencies and time. The effect of two laser fields on the probabilities is discussed.
1996, 45 (1): 29-36. doi: 10.7498/aps.45.29
The collisional energy pooling process in a sodium vapor [ Na(3PJ)+Na(3PJ′)→Na(nLJ″)+Na(3S1/2)] is experimentally investigated. At sufficiently low sodium densities,such that only the optically excited 3PJ state is significantly populated, the ratios of nLJ″ fluorescence intensities and the relative density of Na(3P1/2) versus the density of Na(3P3/2) are measured. The ratios of rate coefficients k(nLJ′)(J, J′) relative to k5S(3/2,3/2) are given for nLJ″= 4D3/2, 4D5/2, 4F5/2, 4F7/2, and 5S1/2, each for J = J′ =1/2 and 3/2. At high sodium densities, the 3P states are populated in nearly statistical ratios, the ratios of the k(nLJ″)(1/2,3/2) relative to k5S(3/2,3/2) are obtained.
CLASSICAL AREA OF PHENOMENOLOGY
EFFECTS OF AC STARK SHIFTS ON COHERENT POPUALTION TRAPPING IN THE NONDEGENERATE TWO-PHOTON JAYNES-CUMMINGS MODEL
1996, 45 (1): 37-45. doi: 10.7498/aps.45.37
We have studied the population trapping properties in the nondegenerate two - photon Jaynes-Cummings model in the presence of ac Stark shifts. The important influences of ac Stark shifts on the field inducing the atom to be trapped (called inducing trapping field) are pointed out and the properties of this field are analyzed.
1996, 45 (1): 46-51. doi: 10.7498/aps.45.46
The generalized Maxwell-Bloch equations are reduced via the centre-manifold theory inthe good cavity limit. In comparison with the adiabatic elimination technique, it causes asmall correction. The numerical results show that the correction does not change the main dy-namical behavior or the system.
According to the Weizsacker-Williams approximation, FEL Is simulated by collision between the relativistic electron and the pseudophoton, and the photon is scattered by the electron. According to this physical model, we studied the energy conversion between the electron and the photon, and obtained the relation between the energy of scattered photon and the energy of photon before collision:εp=4γ2εp(0). Increase of the energy of the scattered photon is at the price of the energy that the electron consumes. We calculated the scale of the energy conversion. In FEL, the maximum energy conversion efficiency is 50 %.
1996, 45 (1): 58-64. doi: 10.7498/aps.45.58
In order to evaluate the attenuation in fiber reinforced composites due to scattering, the multiple scattering should be taken into account when the volume concentration of fibers is large. This paper presents a method for calculating the effective incident wave field in the composites. The contribution of the scattered transverse waves to the incident longitudinalwave propagating perpendicularly to the fiber axis is shown to be zero. An explicit expression for ultrasonic attenuation coefficient with the multiple scattering included is derived. The influence of multiple scattering on the attenuation coefficient is numerically evaluated in a fiber/aluminum composite.
1996, 45 (1): 65-72. doi: 10.7498/aps.45.65
It is proved experimentally and theoretically that the electrorheology effect (ER) dominantly depends on the electrical conductivity. The mechanism of electrorheology includes not only the body and the interface polarizations but also the ion polarization of double electric layers. Under direct and low-frequency alternate electric field, the ER fluid exhibiting out standing ER effect requires σp＞σf and εp＞εf. It is beneficial to improve rheological proper ties of ER fluids by increasing the σf and the static electric interaction of the ion layers. But it must work under a low electric current and low Joule heat and low electric power input.
THE EFFECT OF GEOMETRICAL FACTOR OF DISPERSED PHASE PARTICLES ON THE RESPONSE TIME OF ELECTRORHEOLOGICAL FLUID
1996, 45 (1): 73-79. doi: 10.7498/aps.45.73
Instantaneous response time is an important parameter of electrorheological (ER) fluids.Based on the expetiment and theoretical analyses, a model of response time of ER fluid re garding the geometrical factor of dispersed phase particles is established. According to the model, for the same particle volume of the dispersed phase particles the response time of the ER fluid which consists of prolate ellipsoid particles is shorter than that of the ER fluid which consists of sphere-like particles, while the response time of the ER fluid which consists of oblate ellipsoid or laminar-like particles is longer than that of the ER fluid which consists of sphere-like particles, and the response time of the ER fluid which contains rod-like particles is shorter or longer than that of the ER fluid which contains sphere-like particles depending on the value of εp/εf. The relationship between the response time and the size of particles isthat (1) with the increase of the particle volume, the response time of ER fluids containing different shape particles decrease; (2 ) under the same volume, with the increase of the prolateradius ratio, the response time of ER fluid containing prolate ellipsoid particles decreases,while the response time of ER fluid containing oblate ellipsoid or larninar-like particles in creases, and the response time of ER fluid containing rod-like particles increases or decreasesin accordance with the value of εp/εf. In order to get ER fluid with short response time, be sides sphere-like particles other shapes such as prolate ellipsoid and rod-like particles with a given size can be choosed at a low Reynold number.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1996, 45 (1): 80-87. doi: 10.7498/aps.45.80
A study of the Mg-ion indiffusion of lithium niobate single crystal substrate is made by MgF2 as a diffusion source. By means of electron probe microanalysis, the Mg-ion concentra tion of the Mg diffused layer is obtained, which is approximately a half parabolic and step profiles. The activation energy of Mg-ion indiffusion is 104 kJ/mol. It is found by X-ray diffraction analysis that in the Mg diffused layer LiNb3O8 compound appears with Mg-ion in diffusion beyond a certain extent. The appearance of LiNb3O8 compound is related to the Li ion outdiffusion from the bulk of lithium niobate and existence of a great deal of F-ion at the diffused surface. It is observed by scanning electron microscopy that the F-ion is in the form of LiF and LiF will go away from the surface of the Mg diffused layer with increasing of Mg ion indiffusion degree.
1996, 45 (1): 88-93. doi: 10.7498/aps.45.88
Textured diamond films were depsited on (100) Si substrates via microwave plasma CVD (MWCVD) with bias - enhanced nucleation or without substrate bias. The samples were identified by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD) to be textured. The nucleation and growth process of textured diamond films were investigated, the mechanism of nucleation and growth were discussed.
1996, 45 (1): 94-100. doi: 10.7498/aps.45.94
The behaviour of the fractal crystallization in Pd, Ge thin film system of various ratios of thickness (or composition) after annealing have been investigated by transmission electron microscopy (TEM). It was difficult for the coevaporated Pd-Ge films to realize the fractal crystallization. The production of the fractal structure in Pd/a-Ge bilayers was easier than that in a-Ge/Pd bilayers. The fractal crystallizations were restrainted because of the formation of the compounds (Pd2Ge and PdGe) in Pd, Ge bilayers. The growting of the fractal struc ture depends on the competition of the two precesses of a-Ge crystallization and compound formation.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1996, 45 (1): 101-106. doi: 10.7498/aps.45.101
Using effective media theory to calculate far-infrared absorption in small metal partiele insulator composite, when there is a uniform and continuous shape distribution in the small metal particles, the absorption spectrum of the surface plasma in the small metal particles,which widens the absorption peak of the composite. This effect can lead to the anomalous far infrared absorption.
1996, 45 (1): 107-112. doi: 10.7498/aps.45.107
This paper presents a theoretical determination of valence-band offsets (VBO' s) on (001 ) and (110) interfaces for St/Ge system under different strain conditions, by making use of an average bond energy theory in conjunction with a deformation potential method. The quantitative relationship between the VBO's and the strain condition (characterized by the composition x in substrate Si1-xGex ) is demonstrated. It is shown that the discontinuity be tween the two average valence-band energies is affected little by the strain condition, while,the discontinuity between the two tops of valence-band has a sensitive dependance on the strain condition, and this effect is mainly due to the alteration of the valence-band structure induced by the uniaxial stress. It is found that the VBO value on (110) interface is somewhat smaller than those on (001 ) interface. i. e., there is a weak relevance to the lattice orienta tion. Present results of VBO's are 0. 74 eV for Ge on St(001 ) and 0. 22 eV for St on Ge(001 ), in very good agreement with experimental data:(0. 74 + 0. 13) eV and (0. 17 + 0. 13)eV, respectively.
PHENOMENOLOGICAL CALCULATIONS OF THE DEPENDENCES OF THE MAGNETORESISTANCE IN FM/NM MULTILAYERS ON THE THICKNESSES OF FM AND NM
1996, 45 (1): 113-120. doi: 10.7498/aps.45.113
Based on the phenomenological theory in which the mixed layer composed of the ferro magnetic and nonmagnetic materials is introduced in lieu of the interface, we calculate the dependences of the giant magnetoresistance (GMR) in Fe/Cr multilayers on the thicknesses of ferromagnetic (FM) layers and non-magnetic (NM) layers. Good agreement of the calculated resutls with experimental ones is found. The two-variable function of the GMR respect to the thicknesses of FM and NM is plotted.
1996, 45 (1): 121-125. doi: 10.7498/aps.45.121
We have sysmatically studied the porous silicon (PS) that emits blue light with a peak energy at 2.7 eV; measuring its time-resoluted photoluminescence (PL) spectra and the local vibration mode absorption, and studying the Gamma ray lrradlatlon effect on its PL spectra and comparing the effect with that for the PS which emits red or yellow light. We have also studied the stabability of the blue light emission from PS after long term storage in air and irradiation with laser and ultroviolet light. our experimental resuits and those in other references for blue light emission from PS are contradictory with the quantum confinement model, but can be explained by the quantum confintjnlent/luminescence centers model. We consider that the blue light emission originates from some characteristic luminescence centers in the SiOx layer covering nanoscale silicon in PS.
THE VALENCE BAND STRUCTURES AND OPTICAL PROPERTIES OF STRAINED GaAs LAYERS GROWN ON THE GexSi1-x(001) SUBSTRATES
1996, 45 (1): 126-132. doi: 10.7498/aps.45.126
The valence band structures and third order nonlinear optical susceptibility of strained GaAs layers grown on the GexSi1-x(001) substrates were calculated in tight-binding frame.The results show that the strain makes the effective mass of holes as well as the dentity of state for the valence band decrease and makes the nonlinear optical susceptibility with polarity in (001) plane xxxxx(3) grow.
1996, 45 (1): 133-139. doi: 10.7498/aps.45.133
Using generalized Parisi's replica symmetry breaking scheme, the quantum spin glass theory proposed by our previous work is extended to the first-step replica symmetry breaking. A set of new self-consistent equations of spin self-interact ions and spin glass order parameters are obtained. The corresponding local susceptibility is reduced. It is found that the replica symmetry solution for vector spin glass model at low temperature must be broken through calculating the free-energy of the replica symmetry breaking.
The magnetic properties investigated by experiment on the Ni/NiO interface of Ni/NiO multi-thin layers and surface-NiO-coated Ni ultra fine particles are reported. At temperatures below 80 K, an abnormal enhanced magnetization under external magnetic field (H = 40kOe) was found. The enhanced magnetization decreases quickly with temperature increasing.The high field (5-65 kOe) magnetization (approching to saturation) of ultrafine particles and multi-thin layers were also measured. The fit results for experimental data indicate that the interface Ni/NiO in Ni/NiO UFP and Ni/NiO ML have inhomogenous spin structure.
1996, 45 (1): 146-152. doi: 10.7498/aps.45.146
Vacuum sublimed Snpc films with a-form and β-form polycrystalline structures were prepared and characterized by optical absorption spectrum and X-ray diffraction measurements. Films grown on anisotropic substrates were measured for polarization absorption. The partially oriented β-SnPc film was found to possess large linear dichroism and the dichromatic absorption axis rotated over 90 degrees when going from the blue side to the red side of the Q exciton band. A new band near 530 urn was observed which was believed to be an inter-molecular charge-transfer excitation band.
INVESTIGATIONS OF THE STRUCTURAL AND CONDUCTIVE PROPERTIES OF CONDUCTING POLYMER PEU BY POSITRON ANNIHILATION
1996, 45 (1): 153-160. doi: 10.7498/aps.45.153
Positron annihilation lifetime spectra have been measured for polymer electrolyte poly (ether urethane) (PEU). The variations of the positron annihilation parameters as a function of Li - dopant concentration show that the Li - dopants diffuse mostly into the amorphous regions. The temperature dependances of the o - Ps lifetime and its intensity give the information about the structural transition of PEU and PEU - LiClO4. The relation between the conductivity of PEU - LiClO4 and temperature can be explained by the theory of free volume.
SIMULATIONS OF INTERACTIONS BETWEEN GOLD CLUSTERS AND GOLD THIN FILMS WITH A MANY-BODY POTENTIAL(Ⅰ)──SURFACE DAMAGES INDUCED BY GOLD CLUSTERS
1996, 45 (1): 161-168. doi: 10.7498/aps.45.161
A hybrid potential, which is the combination of the Molters with a semiempirical tight-binding potential has been developed in this paper. The collision dynamics between gold clusters and gold thin films has been simulated by means of molecular dynamics simulations. The hybrid potential is applied in the simulation. The clusters bombard on An(100) surfaces at the energy of 3250 eV per cluster. Radiation damages of the gold thin films at atomic scale have been studied. The changes of crystalline structures and the craters on the surface have been predicted. The collective nature of the interactions between clusters and thin films has been discussed.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
1996, 45 (1): 169-176. doi: 10.7498/aps.45.169
This work was undertaken to study deep underccoling of Al65Cu20Fe15 alloy melt in Al- Cu - Fe system by cyclic superheating and cooling method. By means of the denucleating technique, Al65Cu20Fe15 alloy melt has been undercooled to 98 K under its melting point, and Al - Cu - Fe icosahedral quasicrystalline ball of 6 mm in diameter was produced. Moreover,the first phase to nucleate will change with the degree of underccoling in alloy melt. It was confirmed that quasicrystal forming ability can be enhanced by increasing the level of denu-cleating in Al65Cu20Fe15 alloy.