Small- and strong-signal dielectric response in a single-crystal film of partially deuterated betaine phosphite

Poly- and single-crystal films of betaine phosphite deuterated to ∼20% have been grown by evaporation on NdGaO₃ (001) substrates with a preliminarily deposited planar interdigital structure of electrodes. The small-signal dielectric response in the 0.1–100.0-kHz frequency range has revealed a strong anomaly in capacitance upon the transition of the films to the ferroelectric state. Application of a bias field brings about suppression and a slight shift of the dielectric anomaly toward higher temperatures. The strong-signal dielectric response has been studied by the Sawyer-Tower method over the frequency range 0.06–3.00 kHz both in the para- and ferroelectric phases. In contrast to the case of a plane-parallel capacitor, in the planar structure studied, the dielectric hysteresis loops exhibit a very small coercivity at low frequencies, which grows with increasing frequency. This difference should be assigned to different domain structures formed in a planeparallel capacitor and in a planar structure in a saturating field. The growth of hysteresis with increasing frequency in a planar structure is considered to be associated with the domain wall motion.     

Transition from transient response to steady state for a layered medium

The transition from transient response to steady-state for a layered medium subjected to antiplane loadings is studied. The steady-state formula for a layered medium is derived and the solutions for a layered half-space are then expressed explicitly in the form of wave number integrals. The transient response solutions for a layered half-space are obtained by the convolution of time harmonic loading function with transient response formula derived analytically from an effective matrix method. Two layered half-spaces with different ratios of wave velocities in the layer and half-space are considered and investigated by means of extensive numerical results to show their quite different transition behavior. The numerical results indicate that transient responses will approach steady state after certain characteristic times when the transient effects die away. The transition phenomena and characteristic times are investigated in detail through the responses from near field to far field as well as from low frequency to high frequency.     

Fast primary store based on an Arkad’ev-Marx generator

We describe the design of an Arkad’ev-Marx generator with the capacitors discharging energy into the magnetic field within a time less than 1 μsec. We give the equivalent circuit of the generator and calculations for the transient for different firing circuits. We present the results of an experimental study of a generator consisting of 10 stages. Institute of High-Current Electronics, Siberian Branch, Russian Academy of Sciences. Centre d’Etudes de Gramat, France. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 17–24, December, 1997.     

Transient fields for W ions traversing Fe hosts and for Os ions traversing Fe and Ni hosts

Transient field strengths were measured for^{184, 186}W ions traversing thin, magnetized Fe foils with velocities in the range 1.8 ≲ υ/υ₀ ≲ 5.7 (υ₀ = Bohr velocity) and for^{188, 190, 192}Os ions traversing polarized Ni hosts with average velocities 〈υ/υ₀〉 ∼ 4. The present measured transient field strengths, together with previously measured results for W, Os ions, are compared with transient field strength parametrizations, and discussed in terms of microscopic models of the transient field.     

Optimising dislocation-engineered silicon light-emitting diodes

This article presents a study of the possibilities of optimising the electroluminescence (EL) efficiency of dislocation-engineered silicon light-emitting diodes (DELEDs). The diodes were produced by implantation of boron in n-type (100)Si wafers, at a constant ion energy and fluence, of 30 keV and 1×10¹⁵ ions/cm², respectively. The density and the areal coverage by dislocation loops were varied by applying different annealing times in a rapid thermal processing, from 30 s to 60 min. It is shown that the EL efficiency is directly correlated to the number and areal coverage by the loops. The highest population of loops, ∼5×10⁹ /cm², and an areal coverage of around 50% were achieved for 1–5 min annealing. This loop distribution results in optimal DELEDs, having the highest EL response and the largest increase of EL intensity with operating temperature (80–300 K). The results of this work confirm a previously introduced model of charge-carrier spatial confinement by a local stress induced by the edge of the dislocation loops, preventing carrier diffusion to non-radiative recombination centres and enhancing radiative transitions at the silicon band edge. PACS 85.60.Jb; 78.60.Fi; 61.72.Tt     

Magnetization curves for non-elliptic cylindrical samples in a transverse field

Using recent results for the surface current density on cylindrical surfaces of arbitrary cross-section producing uniform interior magnetic field and an assumed set of flux-fronts, solutions of Bean’s critical state model for cylindrical samples with non-elliptic cross-section are presented. Magnetization hysteresis loops for two cross-sections with different aspect ratios are obtained. A comparison with some exact results shows the limitations of this approach.     

Scanning probe microscopy investigation of ferroelectric properties of barium strontium niobate crystals

The ferroelectric properties of relaxor ferroelectric materials Sr _x Ba_{1 − x} Nb₂O₆ of different compositions have been investigated using scanning probe microscopy and macroscopic polarization methods. An analysis of the results obtained from microscopic and macroscopic measurements of the hysteresis loops has demonstrated that a frequency dependence of the coercive field E _c is observed at frequencies f in the range from 0.03 to 250 Hz, so that the coercive field E _c regularly decreases with decreasing frequency. The observation of the kinetics of domains under a direct-current voltage applied to the probe of the atomic force microscope has revealed a lateral motion of domain walls in response to electric fields E ≪ E _c . This result qualitatively explains a slow polarization relaxation occurring for a giant time in Sr _x Ba_{1 − x} Nb₂O₆.     

Conformally invariant pomeron interaction in perturbative QCD with large Nc

An effective non-local quantum field theory is constructed, which describes the interaction of pomerons in high-colored QCD. The theory includes both splitting and merging triple pomeron vertexes and diagrams with pomeronic loops. The Schwinger–Dyson equations for the ‘physical’ pomeron are written. Conformal invariance allows one to reduce the theory to the old-fashioned Gribov pomeron theory with an infinite number of pomerons, one of which is supercritical.     

On the effect of an elastic shear stress upon the magnetization of ferromagnetic sheets

When an elastic shear stress and a cyclical magnetic field, parallel to each other, are applied in the plane of a ferromagnetic sheet, magnetization changes perpendicular to the field are induced in the sample. “Transverse” hysteresis loops, i.e. transverse magnetization plotted as a function of the longitudinal field, were studied in various materials. The characteristic shape of the loop and the differences in sign and magnitude of the “transverse” magnetization have been qualitatively explained in terms of magnetic domain theory. Work supported by G.N.S.M. (CNR).     

Control of amplification without inversion in H2 and LiH molecules: Dependence on relative magnitude of probe and coherent field Rabi frequencies in three-level Λ system

Dependence of amplification without inversion (AWI) on the relative strength of probe and coherent field Rabi frequencies has been studied in H₂ and LiH molecules for three-level Λ configuration. We have derived exact analytical expressions for coherences and populations keeping all the orders of probe field Rabi frequency (G) and coherent field Rabi frequency. (Θ) in the steady state limit. Previously, first-order approximation (i.e. keeping only the first-order term in G) was used and hence AWI was studied for the condition Θ>>G. Here, by using the exact analytical expressions of coherences and populations, we have shown that AWI is maximum when Θ is within the same order of probe field Rabi frequency G irrespective of the choice of different ro-vibrational transitions in both the molecules. However, the shape of the gain profile and the maximum value of gain on the probe field and the absorption on coherent field depend on the choice of different ro-vibrational levels as the upper lasing levels. Effect of bidirectional pumping, homogeneous and inhomogeneous broadening on AWI process has been studied. By solving the density matrix equations numerically it has been shown that both the transient and the steady state AWI can be obtained and the numerical values of coherences and populations at large time are in very good agreement with exact analytical values in the steady state limit. It has been shown that in molecules AWI can be obtained on probe field of smaller wavelength than that of the coherent field which has not been observed in atoms so far.     

On the Fluctuation Relation for Nosé-Hoover Boundary Thermostated Systems

We discuss the transient and steady state fluctuation relation for a mechanical system in contact with two deterministic thermostats at different temperatures. The system is a modified Lorentz gas in which the fixed scatterers exchange energy with the gas of particles, and the thermostats are modelled by two Nosé-Hoover thermostats applied at the boundaries of the system. The transient fluctuation relation, which holds only for a precise choice of the initial ensemble, is verified at all times, as expected. Times longer than the mesoscopic scale, needed for local equilibrium to be settled, are required if a different initial ensemble is considered. This shows how the transient fluctuation relation asymptotically leads to the steady state relation when, as explicitly checked in our systems, the condition found in (D.J. Searles, et al., J. Stat. Phys. 128:1337, 2007), for the validity of the steady state fluctuation relation, is verified. For the steady state fluctuations of the phase space contraction rate Λ and of the dissipation function Ω, a similar relaxation regime at shorter averaging times is found. The quantity Ω satisfies with good accuracy the fluctuation relation for times larger than the mesoscopic time scale; the quantity Λ appears to begin a monotonic convergence after such times. This is consistent with the fact that Ω and Λ differ by a total time derivative, and that the tails of the probability distribution function of Λ are Gaussian.     

架空及埋地多导体线缆对HEMP辐照的瞬态响应

针对瞬态电磁场辐照多导体电缆问题,首先介绍了一种用于计算架空及埋地线缆瞬态响应的高效时域宏模型。该模型基于传输线理论,利用广义特征线法和SPICE求解器中集成的模拟行为建模库,在时域内实现建模过程中涉及的频率相关参数和卷积计算。该方法适用性广泛,可同时用于架空及埋地线缆的场线耦合建模仿真;与现有时域有限差分法相比,不需要对时间和空间进行离散,以及对频率相关参数进行矢量匹配或数值逆傅里叶变换,因此可简化建模步骤,提高建模及仿真计算的效率;该宏模型计算效率不受线缆长度限制,适用于研究多导体长距离线缆。其次,在时域和频域分别研究了高空电磁脉冲(HEMP)的环境及特点。最后,利用算例验证了所提宏模型计算架空及埋地线缆响应的有效性,并利用该方法分别研究了架空地线对三相输电线路瞬态响应的影响以及埋地电力电缆金属护套在端接线性及非线性保护器件时对HEMP的瞬态响应。结果表明,宏模型法可在时域内高效地计算入射场耦合架空输电线及埋地电力电缆的瞬态响应,特别是对于带有非线性器件的长多导体线缆。     

Dispersive and absorptive properties of a <Emphasis Type="Italic">Λ</Emphasis>-type atomic system with two fold lower-levels

The dispersion and the absorption properties of a driven four-level Λ-type atomic system is investigated. It is found that the interaction of double-dark states lead to controllable group velocity of the weak probe field by the intensity of driving field and the relative phase between applied fields. Moreover, the transient dispersion, absorption and the group index are also discussed. The required switching time for switching the group velocity of a weak probe field from subluminal to superluminal pulse propagation is then discussed.     

An assessment of coherent coupling through radiation fields in time varying slab waveguides

This paper presents an analytical methodology for analysing two-dimensional, dielectric slab waveguides where the guiding region is subject to abrupt and arbitrary temporal changes in permittivity. The methodology solves Maxwell’s equations in the frequency domain and recovers the solutions for the guided and radiation fields in the time domain using the Laplace transformation (LT). Explicit separation of the complete field solution into a set of guided modes and a radiation field continuum provides a clearer insight into the transient effects present in time-varying dielectric waveguides. In particular, the method is used to assess and quantify the impact of coherent radiation field coupling for arbitrary time variation of the waveguide permittivity.     

Linear response of layered superconductors with d pairing to a longitudinal electric field

Simple expressions are obtained for the current and charge densities in layered superconductors with d pairing. The conductivities describing the response to solenoidal and potential electric fields are determined by the momentum relaxation time and the imbalance time of the populations of the branches of the quasiparticle spectrum and exhibit a different frequency dependence. The collective modes associated with the oscillations of the potential electric field are investigated. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 4, 311–316 (25 February 1997)     

Transient response of infrared photoconductors: The roles of contacts and space charge

The transient response of an extrinsic photoconductor, with two implanted ohmic contacts, has been calculated by solving the full continuity equation using a variable finite difference technique. For a step function in photon flux under constant voltage bias, transient times ranging from 10^–4 to 10^–2 s have been determined for 20 to 200 m thick detectors under the low background fluxes typical of infrared astronomy. The transient response consists of a fast and a slow component, with their relative magnitudes dependent on the ratio of diffusion and drift lengths to the device length. The characteristic time for the fast component is determined, as expected, by the carrier lifetime, but a slower transient response is also present which is controlled by out-diffusion and sweep-out and the establishment of a counteracting electric field barrier. The effects of material and operating parameters have been investigated, and an analytical model is presented for estimating transient response times for any extrinsic photoconductor. Contact-limited transient response will be most limiting for operation of thin device structures under very low photon backgrounds.     

Dynamical properties of magnetization reversal in an ultrathin AuCo film

We present a dynamical study of hysteresis loops of a MoS₂/[Au/Co/Au] sandwich performed by surface magneto-optical Kerr effect with a field variation rate up to 1.2 MOe/s. An interpretation of dynamical effects at room temperature is proposed, using a modelization of the magnetization reversal. We discuss simulations which describe two different processes of the magnetization reversal to interpret the evolution of the hysteresis loops for several rates of variation of the magnetic field. For a first range of field variation rates lower than 180 kOe/s, the predominant mechanism seems to be wall motion and beyond 180 kOe/s, an expression for the magnetization is given, which supposes micro-domains reversal as a prevailing process. Finally, the general behaviour of the relaxation time, depending on the magnetic field, is investigated.     

Wilson loops,geometric operators and fermions in 3d group field theory

Group field theories whose Feynman diagrams describe 3d gravity with a varying configuration of Wilson loop observables and 3d gravity with volume observables at each vertex are defined. The volume observables are created by the usual spin network grasping operators which require the introduction of vector fields on the group. We then use this to define group field theories that give a previously defined spin foam model for fermion fields coupled to gravity, and the simpler “quenched” approximation, by using tensor fields on the group. The group field theory naturally includes the sum over fermionic loops at each order of the perturbation theory.     

Comment on: X-ray production by Pt and Os projectiles moving in thick Fe targets withE p=17–30 MeV

In a recent paper, Pakou et al. concluded that if the transient field for PtFe is weaker than that of OsFe, the reduction “cannot be accounted for by the sharing of vacancies between the 4s and 2p shells”. However, such a firm conclusion does not follow from their results. Rather, the vacancy-sharing picture is consistent with available data pertaining to the behaviour of the transient field in this region.