Influence of supercurrents on the stability of superconducting magnets

Supercurrents were recently identified as a source of reduced magnet stability which can explain the measured ramp rate limitation in large superconducting magnets. They also explain an unexpected periodic field modulation along the axes of superconducting accelerator dipoles. Supercurrents are extra coupling currents between the strands of a cable which are induced by a variable field sweep rate (x) along the length of the cable. They flow over the whole cable length and have time constants many orders of magnitudes larger than ‘normal' interstrand coupling currents. Supercurrents may lead to a highly inhomogeneous current distribution and to additional coupling losses (‘supercurrent losses'), even in magnet sections with =0. Both effects can drastically reduce the magnet stability during fast ramping up. The complete solution of the space and time dependence is given for a two-strand model cable. The theory of supercurrents can explain typical results of ramp rate limitation in large magnets.     

Influence of cesium on the stability of a GaAs photocathode

The stability of a reflection-mode GaAs photocathode has been investigated by monitoring the photocurrent and the spectral response at room temperature.We observe the photocurrent of the cathode decaying with time in the vacuum system under the action of Cs current,and find that the Cs atoms residing in the vacuum system are helpful in prolonging the life of the cathode.We examine the evolution and analyse the influence of the barrier on the spectral response of the cathode.Our results support the double dipolar model for the explanation of the negative electron affinity effect.     

Influence of Doppler broadening on the stability of monomode ring lasers

We consider a single running mode in a ring gas laser where inhomogenous Doppler broadening is dominant. The analytic linear stability analysis of the stationary solution leads to the conclusion that in the bad cavity limit a second threshold exists; a salient property is that it occurs at low intensity in contradistinction to homogeneously broadened media where it occurs at high intensity.     

Influence of Lorentz broadening on the stability of monomode ring lasers

We carry out a linear stability analysis of the stationary solutions describing in the frame of the semiclassical theory a Lorentz broadened single running mode in a ring laser. We seek the conditions of destabilization via a Hopf bifurcation and prove that it can occur only in a bad cavity. The threshold intensity is very high when homogeneous broadening dominates, it is of the order of a few saturation intensities when homogeneous and inhomogenous widths are comparable and it tends to zero as the inhomogeneous width increases well beyond the homogeneous width.     

柔性基础对ICF装置稳定性的影响

 为探讨土-结构相互作用（SSI）对惯性约束聚变（ICF）装置在地脉动作用下响应的影响,建立了某ICF装置刚性地基和柔性地基两种有限元模型。通过设置人工虚拟边界的弹簧单元和阻尼装置来考虑SSI效应,并且通过设置具有概率意义的弹簧刚度和阻尼系数,来模拟岩土特性参数的不确定性。两个模型地脉动随机响应结果的对比分析,揭示了柔性地基条件下SSI效应及岩土地基参数不确定性对装置的影响。研究表明,考虑岩性地基的柔性时,ICF装置主要部位的位移响应和转角响应分别放大了1.24和1.49倍。     

Impact on short length bars

A finite element method for the solution of an axisymmetric wave propagation problem of a bar of finite length is proposed. The results are obtained for a uniform bar with (i) a displacement input and (ii) a stress input. Also results are obtained for a discontinuous bar with stress input. They are compared with the existing finite difference solutions and experimental results. It is observed that the results are in close agreement. The study is then extended to the case of bars with an hemispherical end. The advantage of using the finite element method for such problems is indicated. Finally the results for a composite bar comprising a hallow cylinder and hemisphere are obtained by using the finite element method. Experiments are conducted to verify these results.     

Influence of the interphasal surface energy on the stability of solid disperse systems

The extension of the size-distribution function of dispersed particles and the dependence of their individual radii on the time permitted going over to the solution of a problem on the stability of different dispersed systems in its more general formulation. It is shown that the conditions of growth, solution, and transformation of the size distribution of microparticles are substantially determined by the kind of dependence of the interphasal surface energy on the radius. Possibilities of the experimental detection of established, unknown earlier, kinetic regularities of the growth and solution of microparticles are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 7–12, November, 1978.     

Influence of radiation losses on the stability of premixed flames on a porous-plug burner

Analysis of the planar premixed flames on a porous plug was performed numerically for finite activation energy within the diffusive-thermal model. The paper is focused on the influence of radiation heat loses on the flame standoff distance and its linear stability. We show that the presence of volumetric heat losses limits the range of the mass flow range as well as it can promote the flame instabilities of different kinds, both oscillatory and cellular. The oscillatory instability, which for freely propagating flames can be usually observed for the Lewis number larger than one, in the porous-plug case occurs also for flames with unity and lower than unity Lewis number. For flames with Le < 1 both cellular and oscillatory instabilities can be observed simultaneously in a certain range of the mass flow rate.     

Influence of impurities on phase stability of martensites in titanium

The influence of H, C, N and O impurities on the phase stability of titanium was studied by first principles total energy calculations. The occupation energies of the impurities were estimated to identify their site preferences. All impurities considered prefer to occupy the octahedral site except for H, which tends to occupy the tetrahedral site in the β phase. Electronic structures were analyzed to clarify the intrinsic influence mechanisms of impurity on the stability of martensitic phases. It was found that the density of states around the Fermi energy, which was affected dramatically by impurity, and the bonding interactions between impurity and titanium were connected to the phase stability of Ti. Elastic constants of impurity-containing systems were estimated from curves of energy against strain to evaluate the mechanical stability of these systems. It was shown that the α″ phase can not be stabilized by impurities considered here, while the α′ phase (regardless of the impurities) and H- and C-containing β phase are thermodynamically stable and also satisfy the mechanical stability criteria.     

An influence of the electrodes on the frequency of piezoelectric bars

An influence of the vacuum deposited electrodes on the frequency of longitudinally vibrating piezoelectric quartz bars was studied. Both theoretical considerations and measurements show a linear dependence of the frequency on the mass and elastic properties of the electrodes. The influence of the electrodes on the frequency can be eliminated for certain ratio of the length of electrodes to the length of bar (l₁/l₀)₀. A discrepancy between the theoretical and experimental value of this ratio is ascribed to various values of Young's modulus of the bulk metal and a vacuum deposited layer.Devoted to Professor V. Petrílka on his sixty-fifth birthday.     

Influence of the exciton blocking layer on the stability of layered organic solar cells

The life-time of multi-layer organic solar cells based on the couple donor acceptor copper phthalocyanine/fullerene is studied as a function of the nature of the exciton blocking layer (EBL). It is shown that organic EBL are more efficient than are the inorganic In₂S₃ EBLs. Moreover among the organic EBL, Alq₃ is the most efficient EBL protecting layer. An organic solar cell’s lifetime depends on oxygen- and water-contamination of the organic materials. The solar cell’s degradation may correspond to bulk or interface phenomena. Using equivalent electrical schemes of solar cell diodes, we show that the structure degradation is mainly related to bulk modification. It is proposed that oxygen- and water-diffusion into the C₆₀ induce a large increase in its resistivity and, therefore an increase in the series resistance, which decreases the solar cell efficiency. In the case of In₂S₃ EBLs, the degradation law predicts that with time two different phenomena will be present. The classical oxygen- and water-diffusion into the organic material, during the first hour of air exposure, leads to a modification in the In₂S₃ EBL/organic interface properties.     

Influence of micro-explosions on the stability of laminar premixed water-in-fuel emulsion spray flames

A model is presented for a one-dimensional laminar premixed flame, propagating into a rich, off-stoichiometric, fresh homogenous mixture of water-in-fuel emulsion spray, air and inert gas. Due to its relatively large latent heat of vaporisation, the water vapour acts to cool the flame that is sustained by the prior release of fuel vapour. To simplify the inherent complexity that characterises the analytic solution of multi-phase combustion processes, the analysis is restricted to fuel-rich laminar premixed water-in-fuel flames, and assumes a single-step global chemical reaction mechanism. The main purpose is to investigate the steady-state burning velocity and burnt temperature as functions of parameters such as initial water content in the emulsified droplet and total liquid droplet loading. In particular, the influence of micro-explosion of the spray’s droplets on the flame’s characteristics is highlighted for the first time. Steady-state analytical solutions are obtained and the sensitivity of the flame temperature and the flame propagating velocity to the initial water content of the micro-exploding emulsion droplets is established. A linear stability analysis is also performed and reveals the manner in which the micro-explosions influence the neutral stability boundaries of both cellular and pulsating instabilities.     

Study on the beam shaping of high-power laser diode bars

Based on the Collins form, the intensity distribution of the resulting beam is derived when Gaussian beams of a high-power laser diode bar pass through a paraxial optical system. Then flattop beam profiles are obtained by a concave cylindrical lens, and the propagation properties are discussed in detail, such as the peak-intensity axis inclined at an angle γi. In addition, an expression to calculate beam angular width is presented.     

Influence of the composition and ionizing radiation on the stability of combustion of composite propellants

The results of an experimental study of the acoustic admittance of the burning surface of composite propellants performed with the use of a two-end combustion chamber (T-chamber) are presented. The effects of the composition of the composite propellant (type of fuel-binder, content of aluminum powder, burning rate catalysts) and of ionizing γ-radiation on the acoustic admittance, which characterizes the tendency of the combustion chamber to high-frequency instability, are analyzed.     

Influence of porous-coating thickness on the stability and transition of flat-plate supersonic boundary layer

In the present study, we examined, both experimentally and theoretically, the influence of porouscoating thickness on the stability and laminar-turbulent transition of flat-plate supersonic boundary layer at free-stream Mach number M_∞ = 2. A qualitative agreement between the data calculated by the linear theory of stability and the experimental data on the transition obtained for models with different porous-coating thicknesses was established. We show that with decreasing (within a certain interval) the porouscoating thickness the boundary layer becomes more stable to perturbations, and the laminar-turbulent transition, more delayed.     

Influence of gravitational potential on the thermodynamic stability of pure and mixed clathrate hydrates

Clathrate hydrates are an ice-like material consisting of gas molecules confined within cavities in a crystalline water lattice. Phase equilibria of clathrate hydrates systems was described using the statistical mechanical theory of van der Waals and Platteeuw. This theory makes use of the fractional occupancy of cavities within the clathrate hydrate lattice in the determination of chemical equilibria. Classical density functional theory with intermolecular interactions restricted to the first hydration shell was employed to determine the fractional occupancy. In addition to the external field describing the gas-water interactions, the effect of a gravitational field was introduced. The results of the calculations show that although the gravitational potential term may be orders of magnitude smaller than the thermal kinetic energy of the gas species or the hydrogen-bond energy holding the clathrate lattice together, it can nevertheless influence the phase equilibrium of the clathrate hydrate system to some degree. The effect of the magnitudes of both the gravitational potential and the local gravitational field are considered too.     

Influence of the exchange interaction on the stability of the charged excitons in CuCl and CuBr

We show that in CuCl and CuBr the electron-hole exchange interaction treated as a perturbation does not destroy the exciton-electron or exciton-hole bound states.