An Analytical Approach to Determining the Influence of Thermal Noise on the Mean Frequency and Amplitude of a Spin-Transfer Nano-Oscillator

An axisymmetric model of a spin-transfer nano-oscillator (STNO) under the action of statistically isotropic magnetic-field fluctuations is considered. An expression for the stationary probability-density distribution of the angular coordinates of magnetization vector is analytically derived and used for determining dependences of the mean value and standard deviation of the amplitude and the mean oscillation frequency on the magnitude of current. The phenomenon of noise-induced shifts of the mean values of STNO amplitude and frequency is discovered. The latter effect qualitatively explains the experimentally observed dependences of the generation frequency on the STNO current.     

Noise-induced binary synchronization in nonlinear systems

The phenomenon of noise-induced binary synchronization has been discovered in two independent dynamical systems generating aperiodic binary signals under the action of a common noise source. The presence of a synchronous regime was confirmed by the calculation of Lyapunov exponents for the two systems. The mechanism of development of the noise-induced binary synchronization regime has been found. A relation of the observed regime to binary generalized synchronization is established.

     

近场地震作用下RC框架鲁棒性分析

基于地震作用下结构的受力的特征,提出构件易损性及重要性系数的改进计算方法,以此定量分析结构在近场地震作用下的鲁棒性。通过分析比较RC框架在近场有无速度脉冲两组地震动,不同强度下的构件易损性系数、重要性系数和结构鲁棒性系数,揭示了RC框架结构在近场地震作用下抗连续倒塌鲁棒性的特点,并依此提出增强结构鲁棒性的措施。研究表明：相比于层间位移角等结构的整体响应指标,鲁棒性则更能具体地反应出结构在近场地震下的状态;与近场无速度脉冲型地震动相比,速度脉冲型地震动会对结构构件的易损性与重要性造成更为明显的影响,从而降低了整体结构的鲁棒性,对结构安全存在更为不利的影响。     

Prelase stabilization of the polarization state and frequency of a Q-switched, diode-pumped, Nd:YAG laser

We present an experimental investigation of the energy statistics of the linear polarization components of pulses from a Nd:YAG laser that is repetitively Q-switched with an acousto-optic modulator. Varying the modulator-induced diffraction losses leads to changes in the pulse polarization state and the energy statistics of the polarization components. For conventional Q-switching there is no laser oscillation during the low-Q intervals, and we find that the orthogonal components of the pulses can display large relative energy fluctuations even though the total pulse energy is quite stable. In the prelase mode, a weak continuous-wave background seeds the Q-switched pulses and results in the emission of highly linearly polarized, single-longitudinal-mode pulses with small relative energy fluctuations.     

Scintillation index of a multiwavelength beam in turbulent atmosphere

We characterize the scintillation index of a multiwavelength plane-wave optical beam that is subjected to a turbulent optical channel. It is assumed that the level of turbulence in the atmosphere ensures a weak-turbulence scenario and that the turbulence is due to the fluctuations in the index of refraction of the medium. It is assumed that the propagation path is nearly horizontal and that the heights of the transmitter and receiver justify a near-ground propagation assumption.     

Noise-induced effects in an active medium with periodic boundary conditions

A model of an active medium with periodic boundary conditions in which the elementary cell is represented by a FitzHugh-Nagumo oscillator has been studied. Depending on the system parameters, the elementary cell can occur in either auto-oscillatory or excitable state. In both cases, an autonomous medium in the absence of noise performs sustained oscillations and exhibits the phenomenon of multistability. A method for diagnostics of the character of medium with the aid of external noise is proposed, specific features in behavior of the system near the point of transition from the excitable to auto-oscillatory state are considered, and the phenomena of coherent resonance and noise-induced switching are described.     

Noise-induced transitions in a system of coagulating particles

Rigorously solvable models of the system of coagulating particles in a stochastic medium are proposed. It is demonstrated that such systems are featuring additional noise-induced stationary states. The results are considered from the standpoint of using this phenomenon for evaluating the effective parameters of the medium.     

Generation of chaotic microwave pulses in broadband self-oscillating ring system with ferromagnetic film under the action of external pulse-modulated microwave signal

We have experimentally studied specific features of the generation of chaotic microwave pulse trains in a self-oscillating ring system with nonlinear delay line on surface magnetostatic waves, bandpass filter, and power amplifier on GaAs field-effect transistors under the action of an external pulse-modulated microwave signal occurring outside the band of the generated chaotic signal. It is established that a decrease in the off/duty ratio in the external pulse-modulated microwave signal leads to an increase in this ratio for the chaotic microwave pulses. The integral power of the chaotic microwave signal generated under the pulsed external signal action is increased as compared to the power of signal generated in the autonomous regime.     

Excitation of Nonlinear Spin Oscillations in an Antiferromagnet under the Action of Pulsed Terahertz Pumping

Technical Physics Letters - We present a model of excitation of nonlinear spin oscillations in an antiferromagnet under the action of terahertz pulses of an electromagnetic field. It is shown that,...     

Methane conversion in a plasma created by a periodic-pulsed electron beam and non-self-sustained discharge

The process of methane conversion in a mixture modeling the natural gas under the action of a periodic nanosecond pulsed electron beam and an electron-beam-induced non-self-sustained discharge has been numerically simulated and studied in experiment. The possibility of methane conversion under the action of electric pulses without significant heating of the processed gas mixture is demonstrated for the first time. The main conversion products in experiment were hydrogen, ethylene, and acetylene.     

Response of cracks to impact by caustics

A study of the behaviour of notched plexiglas specimens under stress pulses created from an air-gun was undertaken. It was concluded that the initial notch is propagated by steps under the action only of tensile stress pulses, while the compressive stress pulses do not have any influence on crack propagation. It was also found that the maximum crack propagation velocity depends on the magnitude of the applied stress pulse, as well as on the initial notch length. Furthermore, the dependence of the crack-tip stress intensity factor on the crack propagation velocity was established and the critical strain energy release rate was determined. Finally, a comparison of the results of the present paper with the corresponding theoretical or experimental data of previous investigations was made.     

High-current-density subnanosecond electron beams formed in a gas-filled diode at low pressures

The formation of electron beams in a gas diode filled with various gases at low and medium pressures under the action of nanosecond voltage pulses has been studied. It is shown that subnanosecond pulses of the beam current in helium, hydrogen, neon, nitrogen, argon, methane, sulfur hexafluoride, krypton, and xenon can be obtained both at atmospheric pressure and at a pressure of several units or dozens of Torr. In particular, a beam current density above 2 kA/cm² behind the foil at a pulse duration (FWHM) of 250 ps has been obtained in helium-filled diode. On the passage from the regime of ultrashort avalanche electron beam formation to the vacuum diode regime, the beam current pulse amplitude decreases, while both the beam pulse duration (FWHM) and the pulse front width increase.     

Nonequilibrium phase transitions induced by external noise in distributed systems

A formalism is proposed to describe nonequilibrium phase transitions induced by external multiplicative noise in distributed systems. This approach can reduce the problem to an investigation of a regular differential equation whose roots correspond to possible phase states in the system. By means of this theory the relative probability of the existence of one state can be compared with another and the number of possible states identified, and the genesis of the system under the action of fluctuations of the external medium can be traced. Pis’ma Zh. Tekh. Fiz. 25, 91–95 (February 26, 1999)     

Propagation of cracks in structural alloys at a temperature of 4.2 K

We study distinctive features of the process of crack propagation in structural materials under conditions of discontinuous yield and under the action of pulses of electric current at a temperature of 4.2 K. The kinetics of fracture processes in steel under the indicated conditions is studied by the method of stereofractographic analysis. We investigate the applicability of approaches to the evaluation of the characteristics of the crack-growth resistance of materials that take into account the effect of discontinuous yield and pulses of electric current on the process of formation of a plastic zone at a crack tip.     

Generation of single chaotic microwave pulses in a self-oscillating ring system with ferromagnetic film under the action of external noise

The generation of single chaotic microwave pulses in a self-oscillating ring system with ferromagnetic film under the action of external narrow-band noise microwave signal occurring outside the band of frequencies of the chaotic microwave signal was observed. Chaotic generation emerged due to the parametric instability of the magnetostatic surface wave in the ferromagnetic film, whereas formation of single chaotic microwave pulses was caused by the absence of complete suppression of chaos under the action of narrowband noise.     

Analysis of the effect of turbulence on thermal radiation transfer in a nonscattering medium

The effect of temperature fluctuations on thermal radiation transfer under conditions of isotropic turbulence is analyzed. Simple analytical dependences are given for estimating the fluctuations of radiation intensity and of radiation flux in a plane layer of nonscattering medium. The solution of model problem is given for microwave radiation of cloud layer in the Earth atmosphere.     

基于粒子群算法的劣化桥面铺装多目标组合维护策略优化研究

发展了维护导致的间接维护成本改进模型,基于改进的桥面铺装劣化模型推导了在组合维护策略下其状态指标评估公式,建立了多目标组合维护优化模型.使用自适应粒子群优化算法,根据寿命期内维护成本现值最小化和状态指标最大化的原则,满足性能要求和预算限制约束下,优化出寿命期内成本和性能都满足要求的维护策略.以劣化水泥混凝土桥面铺装为数...     

Laser-induced thermal breakdown of a semiconductor in the presence of mutually correlated noises

The laser-induced thermal breakdown in a semiconductor plate under the joint action of an external multiplicative noise (laser radiation energy density fluctuations) correlated with an internal additive noise is studied theoretically. The correlated additive noise is demonstrated to increase the degree of bistability of the crystal temperature hysteresis.     

Pulsed cyclic heating of copper surface using high-power 30-GHz free-electron maser

Thermal fatigue of the surface of copper subjected to multiply repeated pulsed microwave heating has been studied in order to estimate the maximum permissible acceleration rate for the CLIC collider at CERN. For this purpose, the damage of copper rings in a test cavity of the JINR-IAP facility was traced under the action of 10⁴–10⁵ microwave pulses at a temperature rise up to 190–250 K in every pulse. The test cavity was loaded by pulses of a high-power 30-GHz free-electron maser. Data on the dynamics of damage developed on the copper surface under the action of a strong electromagnetic field in the cavity are presented.     

Light-induced EMF in silver-palladium film resistors

We have studied the generation of nanosecond emf pulses in silver-palladium film resistors under the action of radiation of a Q-switched laser. The samples were fabricated using the technology of thick film resistors on dielectric substrates, based on fusing a resistive paste that contains palladium, silver oxide, glass, and an organic binder into the substrate at 880 K. The amplitude of detected pulses exhibits linear growth with the power of incident laser radiation, depends on the angle of light incidence (vanishes at the normal incidence) onto the film and the angle of film rotation about the normal to its surface, and changes its sign with that of the incidence angle. The duration of the generated emf pulses is several times that of the incident laser pulses. The signal is not of a thermoelectric nature and can be related to the current generation by means of the surface photogalvanic effect and the photon quasi-momentum transfer to charge carriers during light absorption by the film material.