深水域近水面水下爆炸水柱形态及演变实验研究

 为研究不同起爆深度的水下爆炸水柱形态及演变特征,进行了1 kg球形RDX装药在不同起爆深度下的海上爆炸实验,通过高速摄像机记录装药起爆后水柱的形成和成长过程,获得了喷射水柱形态的演变特征以及水柱高度、直径、水柱突出水面时间等参数的变化规律,并与Cole、Hole和Swisdak等人的研究结果进行对比分析。研究结果表明：对于深水域近水面水下爆炸,水柱以垂直喷射形态为主,当气泡在膨胀阶段到达水面时水柱存在微弱的径向飞散现象;水柱最大高度随起爆深度呈脉动变化,水柱直径随起爆深度线性减小;Swisdak关于水柱最大高度的计算公式不适用深水域近水面水下爆炸情况。     

Ultraviolet fluorescence of water and highly diluted aqueous media

Light scattering spectra at the wavelength of excitation and fluorescence spectra of water and highly diluted aqueous media were measured. Long-term (several hours and/or days) changes in the spectral parameters after shaking, ultraviolet irradiation, and other actions on the aqueous medium were detected. It was found that melt water is significantly more sensitive to physical actions and adding various compounds.     

Barrier properties of celluloses microfibers (CMF)/ethylene-co-vinyl acetate (EVA)/composites

The effect of celluloses microfibers (CMF) reinforcement in ethylene-vinyl acetate (EVA) on its barrier properties was evaluated using xylene, toluene, and benzene as penetrant molecule. CMF were obtained from Hibiscus sabdariffa by steam explosion technique and was reinforced in EVA by melt extrusion. The barrier properties of the composites were found to be improved with CMF loading. This has been attributed to good interfacial interaction between CMF and EVA which is further confirmed using Kraus equation. Arrhenius activation parameters for the diffusion, permeation, and thermodynamic parameters were also estimated from the sorption data. The mode of the transport was found to follow regular Fickian trend.     

压缩产生等离子体强光源辐射功率计算方法

强光辐射技术是一项技术复杂、特点突出的高新尖端技术,在红外对抗中有着重要的应用。在爆炸激励等离子体产生强光辐射时,发光工质材料及其初始参数的选择成为一项关键技术,他们对辐射功率有着重要的影响。介绍了爆炸激励等离子体产生强光辐射功率的计算方法,用这种计算方法对各种发光工质的辐射功率进行计算,选择出了一种合适的发光工质的材料。分析了在产生强光辐射过程中发光工质的材料、初始参数对辐射功率的影响。推导出辐射功率与这些参数的函数关系,绘制了相应的关系曲线,通过特性曲线分析选择出适宜的初始参数。     

Thermal explosion in a stirred medium

The critical conditions of a thermal explosion in a cylindrical chemical reactor with several symmetrically positioned agitators for creating a forced convection of the reaction mixture are examined. The analysis is carried out for an arbitrary Peclet number on the assumption that the flow of the fluid is laminar. The critical value of the thermal explosion parameter (Frank-Kamenetskii parameter) is determined as a function of the number of agitators, Peclet number, and the distances between the axes of the agitators and the reactor axis. In contrast to the previous studies, the dependence of the thermal explosion parameter on the rate of stirring of the medium is considered. Calculations show that, as the number of agitators and mixing rate increases, the thermal explosion probability decreases, so that the critical value of the thermal explosion parameter can be several times greater than its classical value. It is demonstrated that, depending on the values of the parameters, the problem can have four stationary solutions, two of which are stable.     

Features of electrical explosion alloying of metals and alloys

The kinetics of the electrical explosion of foils has been investigated and the parameters of the plasma jet, the radius of the plasma-affected zone, the pressure and temperature of the plasma in the shock-compressed layer near the irradiated surface, and the accepted power density at the jet axis have been calculated in relation to the dimensions of the plasma accelerator, the distance from the nozzle exit section to the irradiated surface, and the charge voltage of the energy store. Modes of electrical explosion alloying of metals have been determined experimentally which are associated with surface melting, splashing of melt, effects of convective heat and mass transfer, aftereffect, and also with physicochemical and physicomechanical features of the materials used. Methods of optical, scanning, and transmission electron diffraction microscopy have been used to examine the relief, phase composition, and defect substructure of the surface layers of metals after various types of one-and two-component electrical explosion alloying. A multilayer structure has been revealed which is characterized by the degree of variation of the phase-structure state and of the material mechanical characteristics. Based on the features of the multiphase jet that serves as a tool for affecting the surface, some propositions have been made on the physical nature of the processes occurring in a material subject to electrical explosion alloying. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 71–83, May, 2008.     

舰船水下接触爆炸数值研究

计及船体外板的材料强度,基于SPH算法建立水下接触爆炸数值模型,提出混合密度、广义光滑长度等解决数值模拟中计算崩溃的问题,对舰船的水下接触爆炸进行数值模拟,计算结果和冲击波基本理论及接触爆炸试验吻合良好.结果表明,接触爆炸时钢结构会产生圆形冲塞破口,其破口大小和炸药的厚度接近,当板与炸药的正则化厚度达1.8时,板仅会发生较大的塑性变形而不会冲塞破坏.并得到钢的反射系数约为1.2,及接触爆炸钢板的近似变形公式.     

Numerical calculation of the current specific action integral at the electrical explosion of wires

The electrical explosion of aluminum wires is numerically simulated in the magnetohydrodynamic approximation for the current density ranging from 10⁷ to 10¹⁰ A/cm² and times to explosion varying from 10^?10 to 10^?6 s. It is shown that, at current densities of 10⁸?10⁹ A/cm², low-temperature explosion conditions change to high-temperature ones, when inertial forces preventing the wire dispersion play a decisive role. This transition is accompanied by a sharp change in the thermodynamic parameters (the temperature and the energy deposited into the wire by the instant of explosion increase by several times), and the action integral for this transition increases smoothly approximately threefold as the explosion characteristics (current density and time to explosion) change by two orders of magnitude. The instant of transition from the low-temperature explosion to the high-temperature one depends on the radial dimensions of an exploding wire and does not depend on the properties of the environment.     

Kinetics of adhesive contact formation between thermoplastic melts and solid surfaces: Effect on bond strength

Formation of an adhesive contact between a polymer melt (or solution) and reinforcing fibers is considered from the viewpoint of kinetics. A two-stage model of this process has been proposed, and an expression for the interfacial bond strength as a function of time and temperature is derived. Experimental data on bond strength in adhesive joints between thermoplastic polymers and reinforcing fibers formed under various conditions were obtained, and the concept of activation energy was used to analyze them. Since the process is controlled by the stage having the larger activation energy, the adhesive contact formation between fibers and polymer solutions is governed by the rate of adhesive bonding, whereas that between fibers and polymer melts is governed by the rate of the melt spreading.     

Contact melting of alkali halides with high-melting compounds

Contact melting has been examined for several alkali halide crystals with some refractory compounds via the formation of a contact melt and subsequent crystallization as eutectic structures or dendrites. Mutual solusolubility occurs during contact melting, the low-melting component being highly soluble in the high-melting one.The authors wish to thank D. D. Saratovkin and V. N. Zhdanova for discussions.     

Structures of BiInSn nanoparticles formed through laser ablation

The eutectic alloy of BiInSn was ablated in water by UV pulsed radiation. Electron microscopy of the ablated material shows spherical particles that fall into three size regimes: those with diameters of ～0.5 μm, crystalline and amorphous particles with dimensions of ～30 nm, and amorphous particles that are approximately 1 nm across. The 30-nm amorphous particles are homogeneous, while there are two types of 30-nm crystalline particles, those that separate into three phases and those that are homogeneous. The existence of different characteristic sizes is explained by two mechanisms: phase explosion and Rayleigh instability of the ejected melt.     

MODES OF CONTACT AND UNIQUENESS OF SOLUTIONS FOR SYSTEMS WITH FRICTION-AFFECTED SLIDERS

The kinetic equations of planar multi-body systems with friction-affected sliding joints are reformulated for the computation of closed-form solutions for the kinetic parameters. The state of such systems is characterized not only by the position parameters and velocities, but in addition, the modes of contact in the sliding joints must be specified. Then the cases with one or several sets of solutions, obtained for the same position parameters, velocities, active forces and friction parameters, can be related to positions of the system with different modes of contact between sliders and guiding surfaces. They are physical unequivocal states and can be interpreted as unique solutions for the kinetic problem with specified configuration of the system. If no solutions exist, then the friction parameters considered are too large and exceed limiting values, for which friction locking occurs.     

Contact angle and surface morphology of KCl crystal-melt interface studied by the “bubble method”

The validity of the “bubble method” is discussed for the measurements of contact angles between a crystal and its own melt and for the observations of interface morphology. Experiments were done on KCl crystals pulled in various directions. Gold decoration technique was employed to observe the surface morphology. The measurement of the contact angle a is valid for the 〈100〉 axis of pulling but lacks accuracy for the other directions. The {100} interface shows two dimensional nucleation, curved growth fronts and no trace of a liquid layer. The {110}, {310}and {111} interfaces show steps and pyramids constituted by {100} facets, completely stripped of the melt, and “structureless” regions resulting from freely frozen liquid surface.     

Molecular simulation study of the adhesion work for water droplets on water monolayer at room temperature

The wetting phenomenon of water droplets coexisting with the ordered water monolayer termed an unexpected phenomenon of "water that does not wet a water monolayer" at room temperature has been found on several solid surfaces.Although the hydrogen bond saturation inside the monolayer can qualitatively describe this phenomenon, whether the Young–Dupré equation still holds under this unconventional wetting framework is still not answered. In this work, we have calculated the contact angle values of the droplets as well as the work of adhesion between the droplets and the monolayer based on an extended phantom-wall method. The results show that similar to the conventional solid–liquid interface,classical Young–Dupré equation is also applicable for the interface of liquid water and ordered water monolayer.     

Al‐density variation as one driving force for void formation in PERC solar cells

The reduction of void formation in local Al contact structures is of high interest in studies dealing with passivated emitter and rear contact (PERC) solar cells. So far, several processing parameters and their impact on local contact formation were investigated in detail. However, up to now density variation of Al in dependence on temperature and Si content in the melt were not taken into account as a principal reason for void formation. In this context the current assumption of a constant volume of the Al paste particles is discussed in more detail. Based on the results of energy dispersive X‐ray spectroscopy, void formation implies either an expansion of paste particles or their burst during contact formation.

     

Influence of initial micro-porosity of target on material ejection under nanosecond laser pulses

Heating and explosive destruction of the near surface volume of metal with initial micro-porosity under nanosecond laser pulse is simulated. It is shown that presence of initial micro-porosity may influence and modify the ejection mechanisms from melt and from solid phase. Thermal and gas dynamic processes in a gas bubble growing in laser irradiated melt are analysed. Experiments show rather different surface morphology defined by micro-explosions and melt ejection for different metals. Possible explosion of micro-pores and solid particles release under nanosecond laser irradiation is analysed for metals with high melting point. It is shown that the stress attains the values that are close to the damage threshold.     

Mechanism of negative ion emission from surfaces of ferroelectrics

Experimental studies of the mechanism of negative ion and cluster ion emission from surfaces of ferroelectrics are described. The emission was produced by negative voltage pulses with the amplitude of about 400 V, with a rapid rise-time (below 10 ns) and a slow decay‐time (several μs). The pulses were applied between the back side of the ferroelectric sample and the metal tip touching the front emitting side. The surface of the ferroelectrics could be cleaned in situ by 1 keV Ar⁺ bombardment. The morphologic changes around the tip were observed with an atomic force microscope (AFM). Mostly negative ions and cluster ions were emitted and studied in our experiments. Positive ions were detected with much lower probability and are produced by an entirely different microscopic process than negative ions. Masses as well as energies of emitted ions were measured with a time-of-flight (TOF) spectrometer and compared with available spontaneous desorption (SD) spectra and Cs‐SIMS spectra in order to clarify the mechanism of the emission. The trajectory of ions emitted from the sample was studied by computer simulation. The conclusion of these studies is that the negative ion emission is caused by the Coulomb explosion of a polarization cloud rapidly formed at the front edge of the pulse. The explosion takes place in the vicinity of the tip-sample contact at distances several tens of μm from the contact where the stabilizing effect of the positively charged tip is already small.     

d-wave collapse and explosion of a dipolar bose-einstein condensate

We investigate the collapse dynamics of a dipolar condensate of 52Cr atoms when the s-wave scattering length characterizing the contact interaction is reduced below a critical value. A complex dynamics, involving an anisotropic, d-wave symmetric explosion of the condensate, is observed. The atom number decreases abruptly during the collapse. We find good agreement between our experimental results and those of a numerical simulation of the three-dimensional Gross-Pitaevskii equation, including contact and dipolar interactions as well as three-body losses. The simulation indicates that the collapse induces the formation of two vortex rings with opposite circulations.     

汉石桥湿地水质参数光谱分析与遥感反演

水质可见光近红外遥感监测是通过研究水体反射光谱特征与水质参数之间的关系,建立水质参数反演算法进行的。与传统水质监测方法相比,遥感技术监测水质可以快速反映区域水质在空间和时间上的分布情况和变化。文章以汉石桥湿地水体水质为研究对象,通过在可见光近红外波段分析光谱仪和ASTER遥感影像的水质参数特征光谱,建立了水质参数与最佳波段及其组合的多元线性回归方程。研究结果表明,基于地面光谱仪的光谱特征分析可为航天遥感特征波段的选择提供依据,但估算模型不能通用。基于AS-TER遥感的水质参数特征光谱其波段比值相对向长波方向移动,研究最终在分析ASTER遥感特征波段基础上,构建水质参数估算模型,并通过该模型得到目标水质参数空间分布图,实现了对湿地水质时空变异的遥感监测。     

Grain boundary wetting in the Al-Mg system and synthesis of magnesium diboride in contact with melt

The interaction between a Mg-containing melt and B under conditions of partial and complete wetting of Al/Al grain boundaries by Al-Mg melt has been investigated. The study was performed on Al polycrystals with Mg contents of 5, 10, 15, 18, and 25 wt %. Correspondingly, the Mg content in the melt was determined by the liquidus line and was in the range from 5 to 30 wt %. The obtained metal-matrix composites were investigated by light and scanning electron microscopy, electron-probe microanalysis, and X-ray diffraction. The possibility of synthesizing MgB₂ in the contact with a melt having a relatively low Mg content (from 15 to 30 wt %) has been demonstrated.