Observation of bistability in a CO2 laser exhibiting passive Q-switching

Optical bistability has been investigated experimentally in a CO₂ laser containing CF₃Br as a saturable absorber. The frequency dependence of the hysteresis cycle of this laser containing a saturable absorber (LSA) has been studied. It has also been shown that the LSA may undergo simultaneously hysteresis cycles and Q-switching. The phase diagram of the LSA has been extended towards regions where this behavior has been observed.     

Deflagration-to-detonation transition in spiral channels

The deflagration-to-detonation transition in hydrogen–air mixtures that fill spiral channels has been studied. A spiral channel has been produced in a cylindrical detonation tube with a twisted ribbon inside. The gas mixture has been ignited by means of a spark gap switch. The predetonation distance versus the twisted ribbon configuration and molar ratio between the gas mixture components has been determined. A pulling force exerted by the detonation tube after a single event of hydrogen–air mixture burnout has been found for four configurations of the twisted ribbon. Conditions under which the use of a spiral tube can be more effective (increase the pulling force) have been formulated.     

Specific features of the structure of detonation nanodiamonds from results of electron microscopy investigations

The experimental results of a comprehensive investigation of the structure of detonation synthesis nanodiamonds by electron microscopy methods have been presented. The morphology of diamond nanoparticles has been investigated and the microdiffraction patterns have been analyzed. The method of characteristic fast electron energy loss spectroscopy in transmission electron microscopy has been used. The local density of structural components of a nanodiamond (diamond core and fullerene-like shell) has been obtained. The shape of the shell surrounding the nanocrystal has been determined using model calculations. A hypothesis explaining the charging of the nanodiamond surface has been proposed.     

Evaporation waves in a metastable single-component liquid

In this paper, evaporation waves appearing at rapid depressurization of a vessel filled with liquid Freon R11 have been investigated experimentally. Regimes with a high-speed evaporation front have been revealed. It has been shown that the disintegration of a metastable liquid takes place in the form of a surface evaporation wave with a cellular structure of the front and anomalously high values of the coefficient of heat transfer from the liquid. The dependence of the evaporation front velocity on the initial temperature of the liquid has been obtained. A critical temperature value below which evaporation waves are not observed has been determined. Visualization of the evaporation front structure and dynamics with the use of a high-speed video camera has been performed. It has been found that the evaporation front motion has a pulsatory character. A method to calculate the surface evaporation wave with a quasi-plane interphase boundary has been developed. It is based on a model of nonequilibrium evaporation of the liquid and experimentally measured coefficients of the heat transfer from the liquid.     

Spatial Temporal Analysis of Electrically-Addressable Phase-Only Spatial Light Modulator

An optically addressed parallel-aligned nematic-liquid-crystal spatial light modulator (PAL-SLM) has been studied as a dynamic phase-only modulation device. A computer control feature of the spatial light modulator is strongly desired for practical applications. For those demands, an electrically-addressable phase-only spatial light modulator has been developed to combine a liquid crystal display (LCD) with a PAL-SLM (LCD-coupled PAL-SLM) and its performance has been reported. However, a temporal characteristic especially two-dimensional (2D) response has not been discussed before. In this paper, 2D response analysis system has been constructed by using a high-speed complementary Metal-Oxide-Semiconductor (CMOS) camera (1000 frames/sec) and the 2D-modulation characteristic of the LCD-coupled PAL-SLM has been observed. As a result, the LCD has a spatially non-uniform modulation characteristic due to a scanning addressing. It has the potential to cause problems in high speed switching for a computer generated hologram. On the other hand, the spatial non-uniformity has not been observed with the LCD-coupled PAL-SLM.     

稀土和锕系化合物中重费密子行为

本文采用周期Anderson哈密顿量研究了稀土和锕系化合物中的重费密子行为。对f电子间库仑关联项做了平均场近似并引入自能项反映多体作用的效应。对自能项采用了单格位近似,在准粒子表象中讨论了系统的性质,通过对f电子平均占据数的自洽计算,得到了准粒子有效质量,讨论了形成重费密子的条件,以及相应的磁性的变化,并做了数值计算。所得结果与最近的实验进行了比较。 关键词：     

Study of the interaction of a palladium nanocontact with a hydrogen molecule

The interaction of a palladium nanocontact with a hydrogen molecule has been studied using molecular static method. The influence of impurity on the atomic structure and mechanical properties of the palladium nanocontact has been demonstrated. The characteristic interatomic distance has been determined in this contact. It has been found that the hydrogen molecule dissociates by interaction with nanocontact atoms.     

Magnetization and transport characteristics of layered high-temperature superconductors with different anisotropy parameters

The magnetization of a layered high-temperature superconductor with different anisotropy parameters has been calculated using the Monte Carlo method in the framework of a modified three-dimensional Lawrence–Doniach model with actual boundary conditions. The penetration of a magnetic flux into a bulk sample from the boundary has been simulated, and the curves of magnetization reversal of a high-temperature superconductor by an external magnetic field have been calculated for different anisotropy parameters γ and types of defects in the sample. It has been found that there are significant differences in the magnetization curves and transport properties of superconductors with different anisotropy parameters γ. The influence of tilted columnar defects on the critical current has been analyzed. A decreasing dependence of the critical current on the tilt angle of defects with respect to the c axis has been obtained. It has been shown that, as the anisotropy parameter increases, this dependence weakens and, for a specific value of γ, disappears. An explanation of the mechanism responsible for the disappearance of the dependence has been proposed.     

Calculation of the energy losses of charged particles upon motion near a nanotube within dielectric formalism

A carbon nanotube has been simulated in the form of a cylindrical layer with a given dielectric function, taking into account the temporal dispersion of the medium. Quantization of the intrinsic electrical oscillations of a carbon nanotube electron subsystem has been performed. The polarization potential, which arises when a charged particle moves near a carbon nanotube, has been calculated and the energy loss caused by the excitation of surface plasmons has been obtained.     

Bistability of a “chevron” smectic C* liquid crystal in an external electric field

The system of nonlinear equations describing a surface-stabilized ferroelectric smectic C* liquid crystal in the chevron geometry has been investigated by numerical methods in the framework of the continuum model of liquid crystals. Stable orientational and structural configurations have been studied, and the results obtained have been compared with those derived using simplified models. The height of the potential barrier separating two stable configurations has been determined, and the transition between them under the action of the external electric field has been examined. It has been demonstrated that this effect has a threshold character. The dependence of the threshold field on the film thickness has been analyzed.     

Maximally Entangled States of a Two-Qubit System

Entanglement has been explored as one of the key resources required for quantum computation, the functional dependence of the entanglement measures on spin correlation functions has been established, correspondence between evolution of maximally entangled states (MES) of two-qubit system and representation of SU(2) group has been worked out and the evolution of MES under a rotating magnetic field has been investigated. Necessary and sufficient conditions for the general two-qubit state to be maximally entangled state (MES) have been obtained and a new set of MES constituting a very powerful and reliable eigen basis (different from magic bases) of two-qubit systems has been constructed. In terms of the MES constituting this basis, Bell’s States have been generated and all the qubits of two-qubit system have been obtained. It has shown that a MES corresponds to a point in the SO(3) sphere and an evolution of MES corresponds to a trajectory connecting two points on this sphere. Analysing the evolution of MES under a rotating magnetic field, it has been demonstrated that a rotating magnetic field is equivalent to a three dimensional rotation in real space leading to the evolution of a MES.     

Viscosity and electric properties of water aerosols

The flow of water mist in a narrow duct has been studied experimentally. The profile of the velocity of drops has been measured, and the viscosity of the mist has been calculated using the Navier–Stokes equation. It has been found that at low gradients of the rate of shear the viscosity of the mist can exceed that of clean air by tens and even hundreds of times. The electric charge of the drops has been measured. It has been found that the viscosity of the mist differs from that of clean air at gradients of the rate of shear that are less than the frequency of the establishment of electric equilibrium between the drops. A comparative analysis of the viscosities of the mist and a drop cluster has been carried out, and the dependence of the viscosity of the water aerosol on the radius and the charge of the drops has been predicted. The possible role of aerosols that contain submicron drops in the known “clear air turbulence” problem has been shown.     

Analysis and design of ring-resonator integrated hemi-elliptical lens antenna at terahertz frequency

In this paper, a novel lens integrated ring-resonator microstrip antenna is analyzed and simulated at 600 GHz. A mathematical model to compute the directivity of this kind of the antenna has been developed and the directivity of the antenna has been computed which is 18 dBi. The proposed model has been simulated by using CST Microwave Studio a commercially available simulator based on finite integral technique and similar result has been obtained. Further, the directivity of the antenna has also been computed by using the techniques reported in the literature and in this case also we have obtained the similar result. Later, a probe-fed patch integrated lens antenna has also been investigated to validate the correctness of the numerical method. To find the potential advantages of this kind of the structure, the ? 10 dB impedance bandwidth of the antenna has been compared to a lens-integrated probe-fed microstrip patch antenna and a significant enhancement in the bandwidth has been observed.     

Family of graphene-based superconducting devices

A family of highly sensitive devices based on a graphene nanobridge and superconducting electrodes has been developed, manufactured, and examined. These devices can be used to create a graphene-based integral receiver. A cold-electron bolometer prototype with superconductor-insulator-normal metal tunnel junctions has been studied. Its response to a change in the temperature and external microwave radiation has been measured. A superconducting quantum interferometer with a graphene strip as a weak coupling between superconducting electrodes has been examined. The corresponding modulation of the voltage by a magnetic field at a given current has been measured. The effect of the gate voltage on the resistance of graphene has been analyzed for these samples. To confirm that graphene is single-layer, measurements with the reference samples were performed in high magnetic fields, displaying the half-integer quantum Hall effect.     

Quantum model of the prolate spheroidal Thomson hydrogen atom

In a uniformly charged prolate spheroidal Thomson hydrogen atom the electron states have been investigated. It has been shown from the mathematical point of view that the problem is equivalent to a spheroidal hydrogen atom in a parabolic potential with the cylindrical symmetry. In the framework of adiabatic approximation, the energy of ground state has been calculated. Comparison with the case of uncharged spheroidal quantum dot has been made, and the analytical form of wave function of electron has been also obtained.     

Approximate radiative solutions of the Einstein equations

In this paper the external field of a bounded source emitting gravitational radiation has been considered. A successive approximation method has been used to integrate the Einstein equations in Bondi's coordinates. A method of separation of angular variables has been worked out and the approximate Einstein equations have been reduced to the key equations (3.8)–(3.10). The losses of mass, momentum, and angular momentum due to gravitational multipole radiation have been found. It has been demonstrated that in the case of proper treatment a real mass occurs instead of a mass aspect in a solution of the Einstein equations. In Appendix C Bondi's news function has been given in terms of sources.     

Electron Spectrum of Nonlinear Cold Emission from a Metal under the Action of a Laser Shot

The nonlinear emission of electrons from a metal under the action of a femtosecond moderate-intensity laser pulse (laser shot) has been studied. A theoretical model of the process has been constructed based on the 1D nonstationary Schrödinger equation in the vacuum half-space with given boundary conditions for the electron wavefunction. This equation has been solved using the Laplace transformation. It has been assumed that the states of free electrons in a metal, which are described by the Sommerfeld theory of metals, are insignificantly influenced by the laser field. The energy spectrum of emitted electrons has been obtained, and its dependence on the parameters of the lased shot has been found. The calculated spectrum of nonlinear electron emission from a tungsten nanotip under the action of a 6.5-fs-long laser shot generating a field of 9.26 V/nm agrees with the experimental data.     

To the theory of adsorption on epitaxial graphene: Model approach

A model of adsorption on epitaxial graphene has been constructed in two stages: first, the density of states of a graphene monolayer adsorbed on a solid substrate has been found and then an adsorbed atom has been placed on the epitaxial graphene thus formed. Metallic and semiconductor substrates have been considered. Charge transfer between the adatom and epitaxial graphene has been calculated. The roles of the substrate and graphene layer in the formation of the electronic state of adatoms have been estimated.     

Influence of the external mechanical load on the formation of nanopores in an optical fiber under pulsed UV light

The joint action of an external tensile mechanical stress applied to a fiber and high-power UV light pulses on a photosensitive optical fiber has been investigated. The mechanism of formation of fiber Bragg gratings of the type IIA in photosensitive optical fibers has been revealed, and a theoretical model of their formation has been constructed. This mechanism has been confirmed by a series of experiments on the formation of fiber gratings. It has been established that the actions of UV light pulses on stressed and unstressed fibers differ fundamentally. The critical value of the tensile stress of the fiber at which structural defects intensively nucleate in the fiber under the joint action of the irradiation and external load has been determined. This stress coincides with the breaking stress in our experiments.     

High-sensitivity microwave detector based on a Josephson heterostructure

The possibility of using the Josephson heterostructure composed of a nanoscale metallic absorber separated from superconducting strips by thin insulating layers as a high-sensitivity microwave detector has been considered theoretically. The inductive response of such a detector has been calculated and the influence of the nonequilibrium of the electron subsystem of the metallic absorber on its response has been analyzed. The limiting sensitivity of the proposed detector has been found.