Experimental investigation of graphite explosive-emission cathodes operating in a periodic pulse regime

We have studied the electron emission from graphite cathodes under the action of voltage pulses with an amplitude of up to 300 kV, a pulse duration of 10^?9 s, and a pulse repetition frequency of 1–3.5 kHz. The magnetically insulated electron beam had a peak power of up to 600 MW at an average power of 1–3 kW. The dynamics of emission current delay was studied in relation to the charge transferred by the beam and to the state of the cathode surface (studied by scanning electron microscopy). It is established that smoothening of the microrelief leads to degradation of the cathode emissivity, which can be compensated by increasing the pulse repetition rate above a certain critical level.     

Generation of a train of ultrashort pulses using periodic waves in tapered photonic crystal fibres

We consider a light wave propagation in tapered photonic crystal fibres (PCFs) wherein the wave propagation is described by the variable coefficient nonlinear Schrödinger equation. We solve it directly by means of the theta function identities and Hirota bilinear method in order to obtain the exact periodic waves of sn, cn and dn types. These chirped period waves demand exponential variations in both dispersion and nonlinearity. Besides, we analytically demonstrate the generation of a train of ultrashort pulses using the periodic waves by exploiting the exponentially varying optical properties of the tapered PCFs. As a special case, we discuss the chirped solitary pulses under long wave limit of these periodic waves. In addition, we derive these types of periodic waves using the self-similar analysis and compare the results.     

Generation of a periodic sequence of powerful ultrashort pulses in a traveling wave tube with bleachable absorber in the feedback loop

It is shown that a periodic series of ultrashort pulses can be formed in electron microwave generators with a bleachable absorber in the feedback loop. The peak power of such radiation is considerably higher than radiation power in stationary modes. The pulsed generation method is analogous to the method of passive synchronization of waves, which is widely used in laser physics.     

Excitation and suppression of oscillations in a chain of unidirectionally coupled elements with neuron-like dynamics

The propagation of pulses in a model chain of Hindmarsh-Rose neurons with unidirectional coupling has been studied in the presence of intrinsic dynamics in chain elements. The main regimes of oscillations in the model chain are determined as dependent on the coupling parameter. The mechanisms of activation and suppression of oscillations in the model chain under the action of rectangular pulses are explained using the results of a detailed analysis of the basins of attraction of a stable immobile point and a periodic attractor of a model neuron.     

Pulse propagation in a linear and nonlinear diatomic periodic chain: effects of acoustic frequency band-gap

One-dimensional nonlinear phononic crystals have been assembled from periodic diatomic chains of stainless steel cylinders alternated with Polytetrafluoroethylene spheres. This system allows dramatic changes of behavior (from linear to strongly nonlinear) by application of compressive forces practically without changes of geometry of the system. The relevance of classical acoustic band-gap, characteristic for chain with linear interaction forces and derived from the dispersion relation of the linearized system, on the transformation of single and multiple pulses in linear, nonlinear and strongly nonlinear regimes are investigated with numerical calculations and experiments. The limiting frequencies of the acoustic band-gap for investigated system with given precompression force are within the audible frequency range (20–20,000 Hz) and can be tuned by varying the particle’s material properties, mass and initial compression. In the linear elastic chain the presence of the acoustic band-gap was apparent through fast transformation of incoming pulses within very short distances from the chain entrance. It is interesting that pulses with relatively large amplitude (nonlinear elastic chain) exhibit qualitatively similar behavior indicating relevance of the acoustic band gap also for transformation of nonlinear signals. The effects of an in situ band-gap created by a mean dynamic compression are observed in the strongly nonlinear wave regime.     

Thermal mode of a lamp operating in the pulse mode

A method of computing the thermal modes of lamps is proposed and the passage to the analysis of thermooptical distortions occurring in their active elements is realized.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 1, pp. 112–118, July, 1981.     

Laser-parameter effects on the generation of ultrabroad harmonic and ultrashort attosecond pulse in a long-plus-short scheme

By numerically solving the time-dependent Schrödinger equation for helium gas in a special two-color laser field, which is synthesized by a long (9?fs) driving pulse and a short (6?fs) controlling pulse, we discuss the influence of the carrier-envelope phase, frequency, and the intensity of the controlling pulse on the generation of harmonic spectra and isolated attosecond pluses. In the cutoff region, two or three plateaus can be controlled by optimizing these laser parameters, and an ultrabroad supercontinuum harmonic spectrum with a bandwidth of 800?eV can be produced, which can support an ultrashort isolated 4.5 as pulse generation by Fourier transformation. Furthermore, using classical ionizing and returning energy maps, time–frequency analyses are presented to explain the underlying physical mechanisms.     

Simulation of heat and aerodynamic processes in regenerators of continuous and periodic operation. II. Investigation of the parameters of a gas-turbine plant regenerator operating in dynamic and quasi-stationary regimes

A mathematical model for investigating the processes in regenerative heat exchangers is described. A finite-difference scheme of numerical integration is proposed for solving the conjugate problem on unsteady heat exchange between one-dimensional flows and a two-dimensional matrix wall. Test calculations were compared with the known data of other authors. The quasi-stationary and dynamic processes in a gas-turbine plant regenerator with a matrix packed with gauzes have been investigated. The optimum design parameters of such a regenerator and rotational speeds of its rotor that which provide a maximum heat efficiency of the regenerator at a minimum aerodynamic drag in it have been determined.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 77, No. 6, pp. 38–45, November–December, 2004.     

The flow of a compressible dust-gas medium in tubes,in several thermal and structural regimes

We examine the one-dimensional motion of a compressible dust-gas medium in tubes in the case of critical pressure differences and great flow-rate concentrations of a finely dispersed material, with the latter exhibiting various distribution structures in the flow.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 16, No. 5, pp. 826–834, May, 1969.     

粗氩塔工况周期性恶化分析及处理

简述 6 0 0 0m3 /h空分设备粗氩塔运转 1～ 3个月后就出现工况周期性恶化的故障 ;经过分析检查 ,原因为管道变形、珠光砂进入所致 ;经 4项整改措施 ,粗氩塔工况恢复正常。     

Origin and effect of high-order dispersion in ultrashort pulse multiphoton microscopy in the 10 fs regime

Short pulses can induce high nonlinear excitation, and thus they should be favorable for use in multiphoton microscopy. However, the large spectral dispersion can easily destroy the advantages of the ultrashort pulse if there is no compensation. The group delay dispersion (GDD), third-order dispersion, and their effects on the intensity and bandwidth of second-harmonic generation (SHG) signal were analyzed. We found that the prism pair used for compensating the GDD of the two-photon microscope actually introduces significant negative high-order dispersion (HOD), which dramatically narrowed down the two-photon absorption probability for ultrashort pulses. We also investigated the SHG signal after GDD and HOD compensation for different pulse durations. Without HOD compensation, the SHG efficiency dropped significantly for a pulse duration below 20 fs. We experimentally compared the SHG and two-photon excited fluorescence (TPEF) signal intensity for 11 fs versus 50 fs pulses, a pulse duration close to that commonly used in conventional multiphoton microscopy. The result suggested that after adaptive phase compensation, the 11fs pulse can yield a 3.2- to 6.0-fold TPEF intensity and a 5.1-fold SHG intensity, compared to 50 fs pulses.     

Two-phase flow regimes in round, square and rectangular tubes during condensation of refrigerant R134a

An experimental investigation of two-phase flow mechanisms during condensation of refrigerant R134a in six small diameter round (4.91 mm), square (D_h=4 mm, α=1), and rectangular (4×6 and 6×4 mm: D_h=4.8 mm, α=0.67 and 1.5; 2×4 and 4×2 mm: D_h=2.67 mm, α =0.5 and 2) was conducted. Unique experimental techniques and test sections were developed to enable the documentation of the flow mechanisms during phase change. For each tube under consideration, flow mechanisms were recorded over the entire range of qualities for five different refrigerant mass fluxes between 150 and 750 kg m⁻² s⁻¹. The flow mechanisms were categorized into four different flow regimes: intermittent flow, wavy flow, annular flow, and dispersed flow. In addition, the large amount of data enabled the delineation of several different flow patterns within each flow regime, which provides a clearer understanding of the different modes of two-phase flow. Transition lines between the respective flow patterns and regimes on these maps were established based on the experimental data. It was found that for similar hydraulic diameters, flow regime transitions are not very strongly dependent on tube shape or aspect ratio. These maps and the transition lines can be used to predict the particular flow pattern or regime that will be established for a given mass flux, quality and tube geometry.     

The effect of the absolute phase on the spectrum of a femtosecond pulse propagating in a nonlinear medium

It is shown that the spectrum of a femtosecond light pulse propagating in a nonlinear medium depends on the absolute phase. As the propagation distance increases, the effect of the absolute phase of the light pulse on its spectrum may either decrease or increase.     

Bifurcation sequences in the interaction of resonances in a model deriving from nonlinear rotordynamics: the zipper

Using numerical continuation we show a new bifurcation scenario involving resonant periodic orbits in a parametrized four-dimensional autonomous system deriving from nonlinear rotordynamics. The scenario consists of a carefully orchestrated sequence of transcritical bifurcations in which branches of periodic solutions are exchanged. Collectively, the bifurcations resemble the action of a zipper. An underlying governing mechanism clearly exists but still has to be uncovered. For a range of parameter values the sequence of bifurcations forms a global connection between a Sil'nikov bifurcation and (partial) mode-locking. The homoclinic bifurcation is introduced into the system by a Takens-Bogdanov bifurcation. The system also features an interaction between two chaotic Sil'nikov bifurcations.     

Interaction of masses in the operating process of pulse jet engines as a means of increasing their thrust efficiency

Experimental and calculational-theoretical studies have been made of the operating process of pulse jet engines. With certain combinations of parameters of the operating pulsations, the interaction of cyclic gas masses among themselves or with the external medium (with and without the ejector channel alike) is possible, which provides an increase in the thrust efficiency of the engine. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 3, pp. 85–90, May–June, 2006.     

Application of the “double pulse” method for the suppression of thermal waves in a semiconductor injection laser

A theoretical foundation is given for the feasibility of eliminating unwanted temperature peaks in the active zone of a pulsed injection laser by the input of a prepulse.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 1, pp. 140–145, July, 1989.     

Influence of nonlinear interactions and boundary effects on the propagation of energy in a one-dimensional particle chain

A one-dimensional system (chain) of particles interacting with each other and with the substrate has been investigated by the method of computer modeling. Particles at the boundaries of the chain, which are considered separately, represent self-oscillating systems. The influence of the parameters of a system on the transfer of energy by the chain has been studied; the behavior of the system in the transient and steady-state regimes of motion has been investigated. It has been shown that the stationary states of the system are characterized by a nonuniform distribution of the average particle velocities (temperatures) squared over the chains length. A correlation between the increase in the thermal resistance of a system and the enhancement of its structurization has been established.__________Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 1, pp. 94–100, January–February, 2005.     

Modelling and analysis of coupled nonlinear oscillations of a floating body in two degrees of freedom

Summary We describe a mathematical model to investigate the effect of coupled nonlinear oscillations of a floating body in time domain under the influence of sinusoidal waves. To account for hydrodynamic forces, a mathematical formulation for added mass moments of inertia, damping and restoring moments is presented for roll and yaw. Using perturbation technique, we obtain order wise solutions in the normalized domain wherein the assumption on small distortion holds. On applying Laplace transform, a zeroth-order solution is obtained in closed form whereas for higher order solutions we resort to the Runge-Kutta method with adaptive step size algorithm. For analyzing the model result we perform numerical experiments for a vessel of mass 19190 tons under the action of a beam wave of frequency 0.74 rad/sec and 1.0 m wave height. The validity of the numerical scheme is checked by comparing with the analytical solution for uncoupled zeroth-order roll and then we proceed to examine the effect of coupled behavior of roll and yaw for higher-order approximations. The inter-dependence between wave frequency (ω), system frequency (β) and damping factor (ζ) is obtained to reveal system stability. Model results indicate an artificial increase in amplitude for uncoupled roll, and also emphasize the contribution of viscous damping in roll in contrast to added mass in yaw.