Dynamics of bi-periodic structures

Many structures considered for space applications are bi-periodic in their construction. Bi-periodicity means that two types of structural subassemblies, alternating in one or more directions, make up the structure. To gain insight into the dynamics of bi-periodic space structures a variety of one and two dimensional bi-periodic structures are considered. Results indicate that bands in which natural frequencies lie for periodic structures are further subdivided as a consequence of the bi-periodicity. Analytical solutions for the modes and frequencies of finite length one dimensional bi-periodic structures are obtained for general boundary conditions. A transmission method is developed to simplify the application of boundary conditions. It is found that some modes occur at frequencies which are outside the frequency bands predicted for bi-periodic structures. Two dimensional bi-periodic crossed beam grillage and truss structures are considered in this study. For cases where a separation of variables solution is possible the two dimensional structures exhibit similar properties to the one dimensional bi-periodic structures. Analytical solutions for the one and two dimensional bi-periodic structures considered above lead to a compact solution form similar to that of periodic structures analysis.     

Transference of squeezing in coupled oscillators

We examine the possibility of obtaining the transference of the squeezing effect between two coupled oscillators, one of them described by a quadratic Hamiltonian in terms of the ladder operators, the other one being a linear harmonic oscillator, plus an interaction term. We obtain an exact solution for the time evolution of our coupled system which allows us to find the variances for one and two-mode oscillations. It is shown that the squeezing generated in one of the oscillators may or may not spread to the other oscillator, depending on the choice of the involved parameters. Other interesting features exhibited for the one- and two-mode oscillations are also discussed.     

Bistability effects of the brownian motion in periodic potentials

In the stationary state the equation of motion for particles moving in a periodic potential has two solutions, a locked one and a running one, for low and intermediate damping constants and for suitable external forces. The effect of an additional Langevin force to this bistable behaviour is investigated. For finite noise strength, the mobility depends continuously on the external force, whereas in the limit of vanishing strength of the noise force one gets a sharp transition between the locked and the running solution at a critical external force. This critical force is calculated exactly in the low friction limit and approximately for intermediate friction constants. Furthermore the temperature dependence for various forces including the critical one is shown in the low friction limit.     

退火对ZnO薄膜结构及发光特性的影响

生长在蓝宝石C面上的ZnO薄膜是通过等离子体金属有机物化学汽相淀积方法获得的，由其X光衍射得知，生长过程中分段退火和最后退火在薄膜中分别引入了张应力和压应力。通过对样品光致发光光谱研究表明：分段退火样品在380nm附近出现了单一激子发射峰，而最后退火样品却出现了与应变有关的Γ5和Γ6两激子发射峰，同时在两者的光致发光光谱中与深能级有关的荧光峰都未出现。     

Expansion of the Madelung parameter in terms of multipole moments and as a function of the ratio of two lattice parameters

A method is derived to expand the Madelung parameters of non-cubic crystals as a function of the ratio of two lattice parameters and in terms of multipole moments. Only one expansion of this kind is necessary to evaluate the Madelung constants for a series of compounds of one type of structure either containing polyatomic ions or spherical ions at positions slightly varying from one compound to the other. This method also allows the minimisation of the lattice energy with respect to one particular lattice parameter, leaving invariant all internal distances in the polyatomic ions.     

On the geometry of master-slave synchronization

In 1990, Pecora and Carroll reported the observation that one can synchronize the orbits of two identical dynamical systems, which may be chaotic, by feeding state variables of one of them to the other one with no feedback, a phenomenon often called master-slave synchronization. We report here some results on the theory of master-slave synchronization for maps and flows, which are all inspired by a similar geometric and coordinate independent point of view to the one introduced in master-slave synchronization by Tresser, Worfolk, and Bass. Our results are variations on the theme that projection often can compensate for expansion.(c) 2002 American Institute of Physics.     

Spontaneous ionization of bound exciton complexes

Within the framework of the effective mass method a formula for the computation of the probability of the following non-radiative transition in a semiconductor- or insulator crystal was deduced: two holes and one electron or two electrons and one hole are trapped on a crystal lattice defect, one electron recombines with one hole and the energy released thereby is taken up by the remaining quasiparticle which is thus set free and a free carier is formed. The deduced formula is applied to a Cu₂O-crystal with a copper-ion vacancy as the crystal lattice defect.The author wishes to express his gratitute to Dr. M. Trlifaj for pointing out this interesting problem and for his valuable comments.     

Transport properties of Dirac electrons in graphene based double velocity-barrier structures in electric and magnetic fields

Using transfer matrix method, transport properties in graphene based double velocity-barrier structures under magnetic and electric fields are numerically studied. It is found that velocity barriers for the velocity ratio (the Fermi velocity inside the barrier to that outside the barrier) less than one (or for the velocity ratio greater than one) have properties similar to electrostatic wells (or barriers). The velocity barriers for the velocity ratio greater than one significantly enlarge the resonant tunneling region of electrostatic barriers. In the presence of magnetic field, the plateau width of the Fano factor with a Poissonian value shortens (or broadens) for the case of the velocity ratio less than one (or greater than one). When the Fermi energy is equal to the electrostatic barrier height, for different values of the velocity ratio, both the conductivities and the Fano factors remain fixed.     

Belle实验发现新粲重子存在的迹象

粲重子是含有粲夸克的一类重子。粲重子存在很丰富的激发态,粲重子谱的研究对理解轻夸克在含重夸克系统中的动力学行为,以及检验重夸克对称性和轻夸克手征对称性具有重要意义。Λ⁺_c是质量最轻的粲重子,它是由一个粲夸克、一个上夸克和一个下夸克构成的同位旋单态。最近,日本的Belle实验利用在Υ(4S)中心质量采集的772×10⁶对B相似文献   

Relaxation in cooperative systems: Use of mixture virial coefficients

The coefficients in power series in the variable time that describe relaxation in a cooperative system can be calculated using a combinatorial approach where one considers how many ways one can introduce a given number of properly defined events in a system. The coefficients obtained in this manner can be related to the equilibrium virial coefficients for a mixture. If one assumes rapid internal equilibration, the relaxation process can be expressed completely in terms of the viral coefficients for a mixture with at most one solute particle, or, in some cases, just the virial coefficients for a single-component system. Thus, equilibrium virial coefficients can give useful information about the time evolution of processes in cooperative systems.     

Spin eigen-states of Dirac equation for quasi-two-dimensional electrons

Dirac equation for electrons in a potential created by quantum well is solved and the three sets of the eigen-functions are obtained. In each set the wavefunction is at the same time the eigen-function of one of the three spin operators, which do not commute with each other, but do commute with the Dirac Hamiltonian. This means that the eigen-functions of Dirac equation describe three independent spin eigen-states. The energy spectrum of electrons confined by the rectangular quantum well is calculated for each of these spin states at the values of energies relevant for solid state physics. It is shown that the standard Rashba spin splitting takes place in one of such states only. In another one, 2D electron subbands remain spin degenerate, and for the third one the spin splitting is anisotropic for different directions of 2D wave vector.     

Electrodynamic calculation of spirals contacting the cavity ends

We calculate the eigenfrequencies of a cylindrical cavity with spirals contacting its ends. Explicit expressions are obtained for the case of a long cavity with one spiral contacting both ends and for the case of a cavity with one short spiral contacting one end. Calculations are also performed for the structures without constraints on the length and for a cavity with both spirals having close eigenfrequencies.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 47, No. 9, pp. 761–768, September, 2004.     

An ultrasonic method for determination of elastic moduli, density, attenuation and thickness of a polymer coating on a stiff plate

An ultrasonic method proposed by us for determination of the complete set of acoustical and geometrical properties of a thin isotropic layer between semispaces (J. Acoust. Soc. Am. 102 (1997) 3467) is extended to determination of the properties of a coating on a thin plate. The method allows simultaneous determination of the coating thickness, density, elastic moduli and attenuation (longitudinal and shear) from normal and oblique incidence reflection (transmission) frequency spectra. Reflection (transmission) from the coated plate is represented as a function of six nondimensional parameters of the coating which are determined from two experimentally measured spectra: one at normal and one at oblique incidence. The introduction of the set of nondimensional parameters allows one to transform the reconstruction process from one search in a six-dimensional space to two searches in three-dimensional spaces (one search for normal incidence and one for oblique). Thickness, density, and longitudinal and shear elastic moduli of the coating are calculated from the nondimensional parameters determined. The sensitivity of the method to individual properties and its stability against experimental noise are studied and the inversion algorithm is accordingly optimized. An example of the method and experimental measurement for comparison is given for a polypropylene coating on a steel foil.     

晶体级联方式宽带三倍频方案的参数优化

 针对时间位相调制的宽带激光,采用分步离散傅里叶变换及四阶龙格－库塔算法进行数值模拟计算。讨论了采用KDP晶体级联方式时,入射基频光的光强、带宽以及晶体厚度对三倍频转换效率的影响。对采用一块РⅠ类二倍频晶体、一块Ⅱ类和一块Ⅰ类双混频晶体的级联宽带三倍频方式进行了晶体参数的优化。研究结果表明,使用两块级联的KDP晶体作为混频晶体,不仅能有效地提高带宽较宽条件下三倍频光的转换效率,还可以显著增大宽带三倍频的动态范围。经优化后,带宽1.11 nm时入射基频光强在3～8 GW/cm²范围内的三倍频转换效率可保持在60％～70％,比采用单倍频单混频方案时增大了30％～40％。     

Splitting of vibrational mode of CO isotopic species in the unstable trapping site in argon matrix

FTIR spectra of the antisymmetric stretch and symmetric bending vibrational modes of isotopic species of CO₂ trapped in argon matrix are recorded at 5 K with a resolution of . A splitting of the mode is observed for the different species in the trapping site termed unstable. Considering this splitting and the width of the line observed for this unstable site, one expects this site to be larger than the stable one. A theoretical model is elaborated to interpret this splitting. Calculations performed at harmonic level of approximation for vibrational modes in a single substitutional site (S1) and a double substitutional one (S2) in a fcc distorted argon lattice to minimize the free energy of the molecule-matrix system, show the splitting to occur in the larger site. The latter result leads us to invert former attribution of the sites: the stable site is a single substitutional one, whereas the unstable site is a double substitutional one. Received: 27 January 1998 / Revised: 30 July 1998 / Accepted: 17 August 1998     

Conformation of ethylene glycol from the rotational spectra of the nontunneling O-monodeuterated species

The microwave spectrum of the two possible O-monodeuterated species has been measured in a mixture containing roughly 25% of each of the four possible OH/OH, OH/OD, OD/OH, and OD/OD isotopic species. Both spectra follow a semirigid rotor model without effects due to the tunneling of the two hydroxyl protons. Only one conformer has been detected: one oxygen is gauche with respect to the other; one hydroxyl hydrogen participates in the hydrogen bond, while the second one is trans with respect to the C---C bond. Precise values for the quartic centrifugal distortion constants have been obtained for both species. A measure of the dipole moment is given.     

First and second derivatives of internal combustion engine cylinder pressure diagrams

Approximate formulae are proposed for estimating natural frequencies of isotropic and specially orthotropic skew plates with clamped sides. It has been shown previously that one can estimate a natural frequency of a generally orthotropic skew plate with clamped sides by using an approximate formula for the isotropic plate which one can relate to the orthotropic one by applying a previously described reduction method. The accuracy of the proposed approximate formulae is demonstrated by comparing numerical and experimental results for several typical cases.     

Mass spectra of dual strings

Dual strings seem to correspond uniquely to certain subgroups of the modular group. From three axioms, one of which is a tentative simplicity assumption, a finite number of possible mass spectra is derived, but not yet the corresponding amplitudes. Above space-time dimension 8, this approach yields just the mass spectra of the known models, plus one additional candidate for 10 dimensions. Further models exist probably for dimensions 8, 6, and 4, and perhaps for dimensions 5 and 3. The mass spectrum of one candidate for the “correct model” is determined. It yields only mesons of charge zero, but otherwise the agreement with experiment is amazing.     

Features in constructing a certificate of strength of extraterrestrial material by the example of the Chelyabinsk meteorite

The mechanical properties of various components of the Chelyabinsk meteorite are studied. A measurement technique allowing one to obtain a strength certificate of the material by a minimum necessary number of samples with allowance for defectiveness is developed. Universal expressions for the chondritic component and impact melting have been obtained. The expressions allow one to make general estimates of the strength boundaries for LL type meteorites.