Spectroscopic and structural studies of a pulse discharge with a localized channel

The spectroscopic characteristics of various structural formations arising in a pulse discharge through a short capillary with centrally positioned electrodes were investigated. The axisymmetrical regions of the channel lying between the bright zones adjacent to the electrodes and the sections of the capillary not reached by the electrode flame were found to be of the greatest interest. The temperature in the axial portions of these regions reached 10⁵ °K. This makes them suitable sources for exciting lines of high-multiplicity ions of various elements at atmospheric pressure.In conclusion, the authors wish to express their since appreciation to M. A. El'yashevich for his interest in the study.     

A novel system for optically localized soliton pulse in a nano-waveguide

We propose a novel optical system that can be used to trap (store) light coherently. The system consists of two micro and a nano-ring resonators that can be integrated into a single system, which can be employed to generate the large bandwidth by a soliton pulse within a Kerr type nonlinear medium. The balance between dispersion and nonlinear lengths of the soliton pulse exhibits the soliton behavior known as self-phase modulation, which introduces the optical output (i.e. gain) constant, which means that light pulse can be trapped, i.e. localized coherently within the nano-waveguide. The time independent soliton pulse is adiabatically localized within the nano-ring device. Results obtained have shown that the trapping of the localized temporal and spatial soliton pulses is achieved.     

有矩形脉冲内热源的平板中非傅里叶导热研究

 对矩形激光短脉冲能量以内热源形式在有限厚绝热平板内释放所导致的非傅里叶导热过程进行了理论研究，利用格林函数与有限积分变换方法求得了绝热平板内温度分布的解析解,分析了平板内热波传播与反射行为以及温度场的特征。研究结果表明，温度波动频率取决于平板厚度和材料的热弛豫时间，而其幅值则与内热源释放区域的大小和脉冲宽度的长短有关。     

Deconvolution of heat pulse transients

We point out that heat pulse transients must be deconvolved to separate the heat flux transient from the transient response of the local excitation density.     

Pressure dynamics in a supersonic flow during initiation of pulse surface sliding discharges

The supersonic air flow at Mach numbers of 1.1–1.6 in a shock tube is experimentally investigated during initiation of nanosecond pulse surface sliding discharges. The shadow images of the flow field after discharge initiation, which characterize the dynamics of shock waves propagating from the discharge area, are obtained. Periodic pressure pulsations on the shock tube channel wall are recorded. The pressure dynamics is shown to correspond to both the motion of shock waves from the discharge area and a supersonic flow of the discharge-excited gas near the channel wall. The pressure increase on the shock tube channel wall was 6–18%, as compared to the pressure in an unperturbed flow. Original Russian Text ? D.F. Latfullin, I.V. Mursenkova, N.N. Sysoev, 2009, published in Vestnik Moskovskogo Universiteta. Fizika, 2009, No. 3, pp. 114–116.     

Propagation of a heat pulse in a bounded conducting medium: Thermoelectric detection

The one-dimensional, non-steady thermal field on the surface of a bounded conducting sample arising from the absorption of a square heat pulse of arbitrary duration is calculated. It is shown that the spatial temperature distributions for long and short pulses are fundamentally different: After a short heat pulse is “switched off” regions of local heating arise; such regions do not occur in the case of a long pulse. The thermoelectric response is calculated and it is shown that data on the thermal conductivity and thermal diffusivity can be obtained in a single experiment. Fiz. Tverd. Tela (St. Petersburg) 41, 606–611 (April 1999)     

Airy pulse—A new member of family of localized waves

By making use of the recently found expression for finite-energy 2-dimensional paraxial Airy beam, three types of ultrashort Airy pulses have been derived and numerically simulated. They differ in frequency dependences of their parameters and exhibit different spatial profiles and propagation features. Some startling properties of the pulses and their physical nature are discussed.     

Sound radiation by a plane localized vortex

A classical problem on small-scale fluctuations of the Rankine vortex in a compressible gas has been numerically simulated. Euler equations for a compressible gas have been solved by the CABARET method. Simulation results well predict the value of the eigenfrequency of the boundary fluctuations for the azimuthal harmonic n = 2 and almost coincide with the analytic solution. The value of the acoustic instability increment has been quantitatively predicted despite the fact that it is small and it has been revealed at a fluctuation number higher than 100.     

Sound scattering and localized heat deposition of pulse-driven microbubbles

The sound scattering of free microbubbles released from strongly driven ultrasound contrast agents with brittle shell (e.g., Sonovist) is studied numerically. At high peak pressure of the driving pulses, the bubbles respond nonlinearly with cross sections pronouncedly larger than in the linear case; a large portion of the energy is radiated into high frequency ultrasound. Subsequent absorption of these high frequencies in the surrounding liquid (blood) diminishes the effective scattering cross section drastically. The absorption results in highly localized heating, with a substantial temperature rise within the first few microm from the bubble surface. The maximum heating in 1 microm distance is strongly dependent on driving pressure. Temperature elevations of more than 100 K can be achieved for amplitudes of Pa approximately 30 atm, which coincides with the highest pressures used in ultrasound diagnostics. The perfectly spherical collapses assumed here occur rarely, and the heating is highly localized and transient (approximately 10 micros). Therefore, a thermal hazard would only be expected at driving pressures beyond the diagnostic range.     

A mathematical method for the analysis of heat capacity and thermal conductivity measurements by the heat pulse technique

We present a new mathematical method for the analysis of heat capacity and thermal conductivity measurements by the heat pulse technique for the case of samples of finite length with a one-dimensional heat flow. In these experiments a heat pulse is produced by a heater, and the temperature is measured as a function of time at a different location on the sample. Finite length effects are taken care of in a natural way, and the thermal conductivity is obtained very simply. In addition, this method is capable of separating the heat capacities of the sample, of the heater and of the thermometer, which may be of practical importance for the case of thin samples with a small heat capacity. The mathematical analysis is based on Laplace transform techniques similar to those used for electrical transmission lines. The analysis of the experimental data is performed by calculating several moments of the temperature rise in the thermometer as a function of time. The method is particularly suitable for on-line computer experiments.     

重复频率脉冲下环氧树脂电树枝引发特性

脉冲功率设备中绝缘材料的电老化特性影响它运行的可靠性、安全性及寿命。在最大幅值约34 kV、脉冲上升时间约40 ns、半高宽约70 ns的纳秒脉冲下,进行了环氧树脂在不同脉冲重复频率下(1,25,50,100,300和500 Hz)的电树枝引发特性研究。实验得出环氧树脂电树枝老化的引发电压随频率变化的规律：随着频率的升高,环氧树脂材料老化产生电树枝的形态有所变化,高频下丛林状电树枝明显增多;材料的引发电压基本随频率升高而降低,正脉冲作用下E44环氧树脂的引发电压高于负脉冲作用下的;负脉冲下E44环氧树脂的引发电压高于有机玻璃材料的。讨论分析了各种因素随频率变化对环氧树脂材料电树枝引发特性的影响,高频时空间电荷的作用明显增强。     

重复频率脉冲下环氧树脂电树枝引发特性

脉冲功率设备中绝缘材料的电老化特性影响它运行的可靠性、安全性及寿命。在最大幅值约34 kV、脉冲上升时间约40 ns、半高宽约70 ns的纳秒脉冲下,进行了环氧树脂在不同脉冲重复频率下(1,25,50,100,300和500 Hz)的电树枝引发特性研究。实验得出环氧树脂电树枝老化的引发电压随频率变化的规律:随着频率的升高,环氧树脂材料老化产生电树枝的形态有所变化,高频下丛林状电树枝明显增多;材料的引发电压基本随频率升高而降低,正脉冲作用下E44环氧树脂的引发电压高于负脉冲作用下的;负脉冲下E44环氧树脂的引发电压高于有机玻璃材料的。讨论分析了各种因素随频率变化对环氧树脂材料电树枝引发特性的影响,高频时空间电荷的作用明显增强。     

Simulation of rippled structure adjustments based on localized transient electron dynamics control by femtosecond laser pulse trains

This study investigates the effects of pulse energy distributions on subwavelength ripple structures (the ablation shapes and subwavelength ripples) using the plasma model with the consideration of laser particle–wave duality. In the case studies, the laser pulse (800 nm, 50 fs) trains consist of double pulses within a train with the energy ratios of 1:2, 1:1, and 2:1. Localized transient electron densities, material optical properties, and surface plasmon generation are strongly affected by the energy distributions. Hence, the adjustment of the ablation shape and subwavelength ripples can be achieved based on localized transient electron dynamics control during femtosecond laser pulse train processing of dielectrics. The simulation results show that better, more uniform structures, in terms of ablation shapes and subwavelength ripples, can be easily formed at a lower fluence or subpulse energy ratio of 1:1 with a fixed fluence. It is also found that pulse trains at a 1:1 energy ratio are preferred for drilling high-aspect-ratio microholes or microchannels.     

Detonation initiation by a hot corrugated wall

A numerical simulation of premixed gas combustion spreading from a hot corrugated wall is performed. It is found that sufficiently deep corrugations may trigger an abrupt transition from deflagrative to detonative combustion. The effect is found to be highly sensitive to the flame’s normal speed and the reaction rate pressure dependence, favoring fast flames and high-order reactions.     

Study of characteristics of ultrasound pulse generated by a laser pulse

I.IntroductionThegenerationofacousticpulsebylaserirradiationofametalsurfacewasfirstsuggestcdbyWhitein1963[1l.SincethatdateLaserU1trasoundtechniquchasbeendcvclopedrapidly.Becausethistechniquehasanumberoftechnicalfcatures,suchasnon-contact,highbandwidth,highhme-spacia1resolution,quantitativeteshng,generationoflongitudinal,shcarandRay1cighwaves(simu1taniously),andsoon,ithasbccnwidelyapp1icdtomcasurementsofmatcrialproperties,detectionofdefects,andcalibrationoftransd.ccrsl'-'o].Inordertodcve1opth…     

附加谐波脉冲生成强的39阿秒孤立脉冲

采用多周期800 nm激光组合它的27次谐波脉冲生成超短、宽频的孤立阿秒脉冲.研究表明,脉宽为1 fs的27次谐波脉冲可以有效地控制电子动力学过程.将其加入到单色激光场的特定时域,可以控制电离概率在半个光学周期内迅速提升,使得谐波的转化效率相对于单色场情形增强4个数量级,并实现单一的短量子路径选择,出现频宽为108 eV的超连续辐射谱,叠加该连续谱140次到210次谐波获得了脉宽为39as的强、短孤立脉冲.与文献[7]中采用5 fs/800 nm激光附加紫外阿秒脉冲的方法相比,该方案生成的连续谱频带增宽一 关键词： 组合激光脉冲 连续辐射谱 阿秒脉冲     

Bessel-Gauss pulse as an appropriate mathematical model for optically realizable localized waves

We show that the field of the optically feasible luminal localized wave solutions of the scalar homogeneous wave equation can be modeled by means of Bessel-Gauss pulses. As the Bessel-Gauss pulses have a closed-form expression, this fact may be of great value in numerical simulations of various experimental situations.     

Pressure–heat release measurements during start-up conditions in a pulse combustor

An experimental study focusing on the temporal evolution of the global OH heat release (q′) and dynamic pressure (p′) from ignition to limit cycle conditions in an aerovalved pulse combustor has been carried out. The motivation of the work was to investigate how the thermo-acoustic relationships evolve, as very little is understood regarding how pressure and heat release couplings develop prior to establishing limit cycle conditions. The start-up experiments demonstrated that the total start-up sequences occurred within 100 ms and can be subdivided into three regimes: (i) ignition and decay; (ii) instability growth; and (iii) onset of limit cycle operation. The main results showed that upon ignition the high amplitude impulse pressure wave corresponded to the natural frequency of the pulse combustor at ambient gas temperature and was verified by an acoustic model. The pressure field over the growth period exhibited two main trends, either steady amplitude growth or a short delay interval followed by steady amplitude growth to limit cycle conditions. Overall, no reproducibility in frequency or phase during the growth period was observed pointing to the influence of strong non-linear interactions. When operating under limit cycle conditions, the heat release and pressure oscillations were in phase, possessed high levels of coherence, and exhibited narrow band frequency response at the operating frequency and several harmonics.     

基于脉冲复制的单脉冲激光对比度测量

为测量超短单脉冲激光的时间波形以及对比度信息,基于三阶强度相关原理,结合光脉冲复制技术,提出了基于脉冲复制的测量方法。对测量原理进行了详尽的理论分析。利用分步傅里叶和龙格库塔数值计算方法对测量方案做了模拟验证。基于脉冲复制的测量法能同时进行多窗口测量。通过拼接测量时间窗口,可以有效解决测量分辨率与测量时间窗口不能兼顾的问题,同时实现大时间窗口和高分辨率测量。通过将主脉冲与预脉冲分离到不同的测量窗口,避免了梯度衰减片的使用,且具有高对比度测量能力。     

基于脉冲复制的单脉冲激光对比度测量

为测量超短单脉冲激光的时间波形以及对比度信息,基于三阶强度相关原理,结合光脉冲复制技术,提出了基于脉冲复制的测量方法。对测量原理进行了详尽的理论分析。利用分步傅里叶和龙格库塔数值计算方法对测量方案做了模拟验证。基于脉冲复制的测量法能同时进行多窗口测量。通过拼接测量时间窗口,可以有效解决测量分辨率与测量时间窗口不能兼顾的问题,同时实现大时间窗口和高分辨率测量。通过将主脉冲与预脉冲分离到不同的测量窗口,避免了梯度衰减片的使用,且具有高对比度测量能力。