Analysis of an optical mm-wave generation scheme with frequency octupling using two cascaded Mach-Zehnder modulators

We propose a novel method to generate optical mm-wave signals with frequency octupling using two cascaded Mach-Zehnder modulators (MZMs). First, the scheme is investigated both theoretically and by simulation, and results show that an 80 GHz mm-wave is generated by a 10 GHz RF oscillator. Then, an analytical expression is developed to describe the performance of the scheme. The influences caused by non-ideal factors are discussed in detail, and undesired sidebands suppression ratios are plotted and analyzed. At last a RoF system using the mm-wave generation scheme is demonstrated and its BER curves indicate that the performance of the system is still good even if the parameters deviate from the ideal values to a certain degree.     

A novel chaos synchronization of uncertain mechanical systems with parameter mismatchings, external excitations, and chaotic vibrations

In this paper, a new concept of chaos synchronization, which is superior to generalized exponential synchronization, generalized virtual synchronization, and generalized complete synchronization, is firstly introduced and the chaos synchronization of a pair of Duffing-Holmes oscillators with parameter mismatchings, external excitations, and chaotic vibrations is investigated. Based on the time-domain approach with differential inequality, a feedback control is proposed to realize generalized synchronization (generalized exponential synchronization, respectively) for a pair of Duffing-Holmes oscillators without uncertainties (with uncertainties, respectively). In addition, not only the guaranteed exponential convergence rate can be arbitrarily pre-specified but also the critical time can be correctly estimated. Finally, a numerical example is provided to illustrate the feasibility and effectiveness of the obtained result.     

Small scale effect on vibrational response of single-walled carbon nanotubes with different boundary conditions based on nonlocal beam models

The free vibration response of single-walled carbon nanotubes (SWCNTs) is investigated in this work using various nonlocal beam theories. To this end, the nonlocal elasticity equations of Eringen are incorporated into the various classical beam theories namely as Euler-Bernoulli beam theory (EBT), Timoshenko beam theory (TBT), and Reddy beam theory (RBT) to consider the size-effects on the vibration analysis of SWCNTs. The generalized differential quadrature (GDQ) method is employed to discretize the governing differential equations of each nonlocal beam theory corresponding to four commonly used boundary conditions. Then molecular dynamics (MD) simulation is implemented to obtain fundamental frequencies of nanotubes with different chiralities and values of aspect ratio to compare them with the results obtained by the nonlocal beam models. Through the fitting of the two series of numerical results, appropriate values of nonlocal parameter are derived relevant to each type of chirality, nonlocal beam model, and boundary conditions. It is found that in contrast to the chirality, the type of nonlocal beam model and boundary conditions make difference between the calibrated values of nonlocal parameter corresponding to each one.     

IrTi合金晶格动力学的第一性原理研究

利用密度泛函理论的平面波赝势方法研究了IrTi合金的晶格动力学行为. 声子谱计算表明四方(L1₀)结构动力学不稳定,通过冷冻不稳定声子模式, 发现IrTi会发生从四方(L1₀)到正交的结构相变.进一步分析软模对应的原子振动, 得到了具有正交对称性,空间群为Cmmm,相对于四方(L1₀)相能量更低、更稳定的结构. 这种正交新相(Cmmm)弹性稳定和动力学稳定,而且其结构参数与实验上观察到的低温结构有限的晶格参数相符合,表明IrTi合金的低温相是正交结构(Cmmm). 从理论上肯定了IrTi合金立方到四方再到正交的相变机制, 解决了实验上关于相变机制和低温相结构形式的争议.     

Dynamic motion of whirling rods with Coriolis effect

Longitudinal vibrations coupled with transverse vibrations of whirling rods are investigated. It is known that longitudinal and transverse vibrations are governed by second and fourth order differential equations, respectively. Due to the Coriolis effect, a system of equations that governs the longitudinal and transverse displacements will be constructed by coupling these two equations together. Solutions of the equations assume small oscillations of vibration being superimposed on the steady state of the whirling rod. Exact and approximate solutions are obtained from the proposed governing equations, where the approximate solutions on displacements and natural frequencies are acquired by neglecting the Coriolis effect. A proposed numerical scheme known as complete function collocation method is implemented to solve the governing equations coupled with longitudinal and transverse displacements. The approximate results on both longitudinal and transverse natural frequencies show that natural frequencies are decreasing while the angular velocity of the rod is increasing. Exact and numerical results on both longitudinal and transverse natural frequencies show that there are no predictable trends whether natural frequencies are increasing or decreasing while the angular velocity of the rod is increasing.     

Investigation of the Raman spectra of CuxAgl−xGaS2 solid solutions

Raman spectra in (┴, ┴) and (║, ║) polarizations are investigated on crystals of CuGaS₂, AgGaS₂ compounds and Cu_xAg_l−xGaS₂ solid solutions. The frequencies of longitudinal and transverse optical phonons are determined, their concentration dependences are constructed, and the behavior of the vibrational modes in Cu_xAg_l−xGaS₂ solid solutions is established. Belarusian State University of Information Science and Radioelectronics, 6P, Brovka St., 220069, Minsk, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 447–449, May–June. 1998.     

A quantum field theory of lattice dynamics and melting in compounds

Summary A unified theory on the lattice dynamics and the melting in compounds is presented by taking into account the Coulomb interaction. The melting temperature is determined by the mean value of the eigenfrequencies of the atoms. The theory is applied to zincblende and rock salt structure crystals.

---

Riassunto Si presenta una teoria unificata sulla dinamica dei reticoli e sulla fusione nei composti considerando l’interazione di Coulomb. La temperatura di fusione è determinata dal valore medio delle autofrequenze degli atomi. Si applica la teoria alla zinco-blenda e a cristalli con struttura del tipo di sali di rocca.

---

Резюме Предлагается теория динамики решетки и плавления в химических соединениях, которя учитывает кулоновское взаимодействие. Температупа плавления определяется, как средияя величина собстенных чатстот атомов. Предложенная теория применяется к кристаллам со структурой цинковой обманки и кчменной соли.

     

Nonlinear Translational Vibrations of a Solid with a Gravity–Friction Seismic Damper

A mathematical model of variable structure is constructed to describe translational motions of a solid on a fixed spherical support with regard for gravity forces and Coulomb friction. Generalized velocities determining transitions from one mathematical model to another are determined. The translational acceleration amplification factor is plotted against the natural period of vibrations of the solid under damped multifrequency disturbance