Splash formation by a spherical body plunging into water

Splashes caused by a spherical body plunging into water were investigated experimentally using a high speed CMOS camera. We categorized types of splash according to impact velocities of the sphere. Three types of splash were found: Type-I is a thin spire-type splash, Type-II is a mushroom-type splash with many droplets, and Type-III is a crown-type splash with many droplets. The reaction to the concave water surface attached to the sinking sphere is a cause of the Type-I splash. The film flow climbing up the sphere is a dominant cause of the Type-II splash. The velocity of the film flow, which is proportional to the impact velocity of the sphere, affects the fingers of the film flow, detaching of droplets, and maximum height of the Type-II splash. The Type-III crown-type splash is characterized by water jets with many droplets. A bulky air column in water is formed behind the sinking sphere, and longitudinal ridges and ripples on the surface of the air column were observed.     

Influence of the trailing-edge shape of a bluff body on the main resonant-regime characteristics

The main characteristics of an acoustic resonance developing in a channel flow past flat bluff bodies with different trailing-edge shapes have been experimentally examined. It is shown that the range of flow velocities at which the resonance is observed is wider for a model with sharp trailing edge compared to a plate with blunt trailing edge.     

Influence of cluster formation on localization of optical phonons in two-dimensional pseudobinary substitutional solid solutions

The influence of the composition and short-range order of the cluster formation type on optical phonon localization in two-dimensional pseudobinary substitutional solid solutions is studied. Direct numerical calculations of the so-called inverse participation ration (IPR) are carried out, and the scaling of this parameter is studied for the fundamental modes of the spectral density of states at the Brillouin zone center of the averaged crystal. It is shown that cluster formation promotes phonon delocalization, although the nature of this effect is different for resonant and local (in the low-concentration limit) modes. The influence of the ionicity of a solid solution on localization is considered. It is shown that the Coulomb interaction neutralizes the effect of cluster formation while simultaneously decreasing the observed IPR. Based on the form of the distribution of local site absorption of an external electromagnetic field, a new physical criterion is suggested, which allows one to analyze the localization degree of phonon modes in ionic alloys.     

Effect of instability of body shape on magnetoacoustic shock

The formation of magnetoacoustic shock waves excited by an axially symmetric thin body of unstable shape moving in a plasma is investigated.St. Petersburg State University. Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 12, pp. 1499–1502, December, 1994.     

Influence of shape variation on capacitance matrices

We theoretically determine the per-unit-of-length N × N capacitance matrix of a set of N conductors w.r.t. a reference conductor, obtained when expanding the cross-section of one or more of these conductors w.r.t. some nominal configuration. It is shown that certain relationships between the individual matrix elements of the nominal and of the expanded configuration exist. For the N ≤ 2 case, the expansion leads to the increase of the absolute value of all matrix elements. For N > 2 no such general conclusion is shown to exist. The results remain valid in three dimensions. A number of numerical examples illustrate the theory.     

Experimental study of the dynamics of penetration of a solid body into a soil medium

An experimental system is developed to determine the main parameters of the impact and penetration of a solid deformable body into a soft soil medium. This system is based on the technique of an inverse experiment with a measuring rod and the technique of a direct experiment with photo recording and the application of a shadow picture of the interaction of a striker with a soil target. To verify these techniques, the collision of a solid body with soil is studied by a numerical calculation and the time intervals in which the change of the resistance force is proportional to the penetration velocity squared are determined. The penetration resistance coefficients determined in direct and inverse experiments are shown to agree with each other in the collision velocity range 80–400 m/s, which supports the validity of the techniques and the reliability of measuring the total load.     

Effect of solid surface on the formation of thin confined lubricating film of water with micro-content of oil

The formation of confined film between two contacting surfaces is significant for evaluating the lubricating ability of liquid. A micro-content of oil in water was experimentally demonstrated to be significantly effective to the film formation of water, which was much thicker than predicted by elastohydrodynamic lubrication theory. The effect of solid surface characteristics on the liquid film confined in a nanogap has been investigated. The film forming performances of such films were presented. The work of adhesion between two different phases was calculated, and the competitive wetting behaviours of water and oil on different solid surfaces were employed to understand the film formation mechanism.     

Effects of water plasma immersion ion implantation on surface electrochemical behavior of NiTi shape memory alloys in simulated body fluids

Water plasma immersion ion implantation (PIII) was conducted on orthopedic NiTi shape memory alloy to enhance the surface electrochemical characteristics. The surface composition of the NiTi alloy before and after H₂O-PIII was determined by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) was utilized to determine the roughness and morphology of the NiTi samples. Potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) were carried out to investigate the surface electrochemical behavior of the control and H₂O-PIII NiTi samples in simulated body fluids (SBF) at 37 °C as well as the mechanism. The H₂O-PIII NiTi sample showed a higher breakdown potential (E_b) than the control sample. Based on the AFM results, two different physical models with related equivalent electrical circuits were obtained to fit the EIS data and explain the surface electrochemical behavior of NiTi in SBF. The simulation results demonstrate that the higher resistance of the oxide layer produced by H₂O-PIII is primarily responsible for the improvement in the surface corrosion resistance.     

光学窗口外形对气动光学效应的影响

流场求解采用3维雷诺平均N-S方程,分别利用ROE格式和二阶中心格式对对流通量和粘性通量进行离散处理;用高斯-赛德尔隐式格式对方程进行时间推进求解,采用k-ε两方程模型用于湍流的数值模拟。采用几何光学结合物理光学方法分析平均流动和湍流对光场的影响。计算结果表明:由于窗口外形曲面的曲率不同,两种窗口外部流场存在较大区别,气流速度、密度的分布情况各不相同。曲率较大的窗口外形对气流的压缩程度较大,导致气流绕过窗口顶端中心区域时流速快,密度梯度大,因而窗口空气阻力较大,光束在该窗口流场中传输受气流影响的影响也较大。     

Research on detection and azimuth estimation for the splash sound of target's water entry based on empirical mode decomposition

The splash sound of target＇s water entry is an instantaneous signal, consisting of impact component and bubble components. It is difficult to detect and estimate the azimuth of this signal by traditional azimuth estimation methods using a single vector sensor, especially when the SNR is low. Empirical mode decomposition is a nonlinear analysis method that can emphasize signals＇ instantaneous characteristic. In this paper, the pressure and particle velocities are decomposed into different intrinsic mode functions （IMF）, and the MAIA （mode acoustic intensity averager） method can realize the instantaneous signals＇ detection and azimuth estimation. The lake experiment and sea trial results show that this method can decompose water-entry sound and ambient interference into different IMFs, so as to detect the starting time of water-entry sound signal and estimate its azimuth effectively.     

On the formation of periodic structures on solid surfaces

A model is proposed to explain the formation of periodic structures produced on solid surfaces by laser radiation. The model gives rise to a system of two linear integrodifferential equations with difference kernels for temperature correction due to the specific absorption of electromagnetic energy at a certain solid surface profile and at a surface profile formed due to heat expansion resulting from temperature correction. The solution of this system reveals, that, first, periodic structures are formed as a result of the propagation of periodic profiles generated from a certain original non-periodic profile over the body surface. Second, the amplitudes of these waves grow with time only for a laser density exceeding certain critical value, i.e. the formation of periodic structures is a threshold effect relative to the laser density.     

Study into the shape of oxide lines formed by LAO - Influence of an oxidized material

Linear oxide patterns were formed by local anodic oxidation (LAO) using an atomic force microscope (AFM) on an n-doped GaAs substrate, a 10-nm-thick titanium layer, and on shallow GaAs/AlGaAs-based heterostructures capped either with a 5-nm-thick undoped GaAs layer or a 2-nm-thick undoped InGaP layer. Each heterostructures had a 2DEG buried at a specific depth between 22 and 45 nm. LAO was performed in contact and non-contact AFM modes with the aim to explain the phenomenon of single and double line formation depending on material oxidized. The occurrence of the phenomenon was also simulated. The results showed that the occurrence of the double lines is linked with the thickness of native oxides.     

On the quantization of solid body rotation

A general method for solving the problem of quantization of a top is proposed that allows for finding the Hamiltonian eigenfunctions in the form of polynomials of various degree n in the Cartesian coordinates with the use of the Lamé functions. All three coordinates x, y, and z are equivalently involved in computations, as well as their relations with ellipsoidal coordinates, which makes the computations symmetric.     

Study on formation and shape of carbon nanotips depending on ion bombardment

Carbon nanotips were grown from carbon film deposited on silicon substrate by plasma-enhanced hot filament chemical vapor deposition. The carbon film and carbon nanotips were investigated by scanning electron microscopy and micro-Raman spectrometry, respectively. The results indicate that the carbon film is composed of amorphous carbon and the carbon nanotips are characteristic of nanographite, and their formation and shapes depend on ion bombardment strongly. Simultaneously, the number of forming the carbon nanotips is increased by the ion bombardment. Because there are ion deposition and sputtering-etching in the process of growing of the carbon nanotips, the theory related to ion deposition and sputtering was used to obtain their formation condition and analyze effects of the ion bombardment on their shapes and the number of forming them.     

基于经验模态分解的物体入水声检测及测向研究

物体入水声是一种瞬态信号,其波形由击水声和若干气泡脉动组成。传统的矢量信号处理方法对此类瞬态信号的检测和测向会出现困难,尤其是在信噪比较低时检测不到入水声信号。经验模态分解是一种突出信号局部瞬态特性的非线性分析方法,将矢量传感器接收的声压、振速信息分解为不同的固有模态函数,利用文中提出的模态声强器的方位估计算法,可以实现瞬态信号的检测和测向。湖试和海试结果表明该方法能把本地干扰和入水声分解到不同的模态函数中,利用模态声强器可以在本地强干扰下有效检测到入水声信号出现的时间,并可以实现测向。     

荧光再吸收对固体荧光制冷的影响

 建立了荧光再吸收的蒙特卡罗计算模型,对不同尺寸的Yb³⁺:ZBLANP玻璃材料的荧光再吸收作用进行了数值计算,给出了由于再吸收作用引起的荧光平均波长红移与界面反射和材料尺寸的关系。对于立方体形状,当材料尺寸较小时由界面全反射引起的荧光平均波长红移量占主要部分;随着尺寸的变大,界面全反射的影响相对变小;材料尺寸在0.1~1.0 cm时,由于荧光再吸收作用导致的荧光平均波长红移量在2.6~5.0 nm范围内。随激发光波长的变化绝对制冷效率和单位长度的制冷功率均存在极大值,荧光平均波长红移使制冷效率明显下降,通过减小材料尺寸、改变材料形状等措施可减小荧光再吸收作用对激光冷却固体的不利的影响。     

激光脉冲波形对烧蚀Si靶表面温度的影响

利用双温方程对激光烧蚀Si靶的过程进行了数值模拟,并结合合适的初始条件和边界条件,研究了在飞秒、皮秒激光作用下,脉冲波形（矩形、梯形、三角形和高斯形）对Si靶表面载流子和晶格温度分布的影响。结果表明：激光功率密度是影响载流子温升的主要因素,矩形脉冲激光烧蚀Si靶表面载流子的峰值温度最高,而高斯分布的脉冲引起靶面载流子峰值温度最低。可见,激光脉冲波形对Si靶表面载流子的温度分布具有重要影响。所得结果可为制备高质量的薄膜提供理论依据。     

激光脉冲波形对烧蚀Si靶表面温度的影响

利用双温方程对激光烧蚀Si靶的过程进行了数值模拟,并结合合适的初始条件和边界条件,研究了在飞秒、皮秒激光作用下,脉冲波形(矩形、梯形、三角形和高斯形)对Si靶表面载流子和晶格温度分布的影响。结果表明:激光功率密度是影响载流子温升的主要因素,矩形脉冲激光烧蚀Si靶表面载流子的峰值温度最高,而高斯分布的脉冲引起靶面载流子峰值温度最低。可见,激光脉冲波形对Si靶表面载流子的温度分布具有重要影响。所得结果可为制备高质量的薄膜提供理论依据。