Numerical investigation of flow over two sweepback wedges at M = 4 and 6

Results of numerical simulation are discussed: simulation was carried out for a configuration of two wedges with sweepback leading edges placed on a pre-compression ramp in a way that skewed surfaces of the wedges deflect the compressed flows in the opposite directions. It was demonstrated that this configuration produces a flow with irregular interaction in the plane of symmetry for shock waves produced by sweepback wedges. The shock waves formed by the skew wedges induce 3D boundary layer separations along sweepback leading edges of the wedges. Flows in the separation zones are directed toward the plane of symmetry of this configuration; they interact and produce in the central part a “swollen” zone of separation flow with a typical S-shaped profile of velocity. Simulation data was obtained for the free stream flow with Mach number M = 4 and 6 and based upon Navier—Stokes equations and k-ωSST turbulence model using FLUENT computation code. Inviscid flow described by Euler equations was considered as well.     

Motion of nanodroplets near edges and wedges

Nanodroplets residing near wedges or edges of solid substrates exhibit a disjoining pressure induced dynamics. Our nanoscale hydrodynamic calculations reveal that nonvolatile droplets are attracted or repelled from edges or wedges depending on details of the corresponding laterally varying disjoining pressure generated, e.g., by a possible surface coating.     

Understanding the performance of CMS calorimeter

The performance of the CMS hadron calorimeter is studied using test beam facilities at CERN. Two wedges of brass-scintillator calorimeter are exposed to negative and positive beams with momenta between 3 and 300 GeV/c. Light produced in the scintillators are collected using wavelength shifting fibres and read out using hybrid photodiodes. Each of the wedges has 17 layers of scintillators. In one of these wedges signal from all 17 layers are grouped together while in the other each layer is read out separately. The response, energy resolution, longitudinal and lateral shower profiles are measured. on behalf of the CMS Collaboration     

精确放射治疗中改进的楔形挡板剂量修正算法

在精确放射治疗中,精确计算楔形挡板的楔形因子是精确修正加入楔形挡板后剂量值的关键。提出了基于衰减系数法思想的改进楔形野剂量修正算法,首先计算了楔形挡板材料的线性衰减系数,再根据楔形挡板的实际剖面尺寸,建立了线性拟合公式计算射线束穿过楔形挡板的实际厚度,精确计算楔形因子,并以AAPM55号报告提供的45°楔形挡板进行了验证。该方法在保证计算精度的同时减少了大量离轴测量数据,减轻了物理师的负担,可以作为一种有效的楔形挡板修正算法应用于放射治疗计划系统中。     

Coupled edge plasmon modes of metal/dielectric multi-wedges

We present a metallic/dielectric multi-wedge model to investigate the coupled edge plasmon modes （CEPMs）, where all wedges have a common edge and the wave propagates along the edge direction. A general theoretical method valid to many practical structures is presented. The analytical dispersion relations of CEPMs in these structures are obtained and the CEPM properties are discussed with numerical results and the dispersion relations. For all structures mentioned in this paper, we find that the structures containing an even number of metallic wedges have four CEPMs and those with an odd-number of metallic wedges have two CEPMs. Further, the periodic structures containing any odd number of periods and any even number of periods possess their common CEPMs, respectively.     

Construction of an anechoic chamber for aeroacoustic experiments and examination of its acoustic parameters

The acoustic parameters of a new anechoic chamber constructed at Perm National Research Polytechnic University (PNRPU) are presented. This chamber is designed to be used, among other things, for measuring noise from aerodynamic sources. Sound-absorbing wedges lining the walls of the chamber were studied in an interferometer with normal wave incidence. The results are compared to the characteristics of sound-absorbing wedges of existing anechoic facilities. Metrological examination of the acoustic parameters of the PNRPU anechoic chamber demonstrates that free field conditions are established in it, which will make it possible to conduct quantitative acoustic experiments.     

Observation of wedge waves and their mode transformation by laser ultrasonic technique

Wedge waves (WWs) in wedges, including their dispersion characteristics and mode transformation, are investigated using the laser ultrasound technique. Pulsed laser excitation and optical deflection beam method for detection are used to record WWs. Numerous WWs are detected by scanning the excitation laser along the wedge tip. Dispersions of WWs are obtained by using the two-dimensional (2D) Fourier transformation method, and different WW orders are revealed on the wedges. Mode transformation is determined by fixing the distance between the excitation and detection position, as well as by scanning the samples along the normal direction of the wedge tip.     

多视场电视观瞄具的光轴调校技术

针对如何实现多视场电视观瞄具光轴平行性和稳定性的调校,根据其光机系统结构,提出了CCD靶面与双光楔相结合的调校技术方案,通过设计和搭建安装基面与光轴平行的装调装置,用平行光管自准直法建立了统一的装调基准。通过分析双光楔调校原理,对调校技术方案进行优化,添加了双光楔配对和粗调误差控制的工艺要求。经过装调、测试验证,光轴平行性可达0.1 mrad,光轴稳定性可达0.05 mrad。     

Isotope studies of hydrogen and oxygen in ground ice-experiences with the equilibration technique

Equilibration technique suitable for a large amount of samples is described for hydrogen and oxygen isotope analyses of ground ice, especially ice wedges, including the sampling strategy and the analytical procedure as well as the calibration of the Finnigan MAT Delta-S mass spectrometer in June, 1999. Since for future analyses of ice wedges, a higher sampling resolution with limited sample volume is required, the limit of the equilibration technique for small water sample sizes of between 0.05 and 5 ml was checked. For water samples smaller than 1 ml, corresponding to a molar ratio [H2O]/[H2] of smaller than 0.994, a balance correction has to be applied. The experimental errors due to partial evaporation during evacuation, the balance calculation of the isotope equilibration process, the linearity as well as memory effects of the mass spectrometer for samples with large differences in delta18O and deltaD are tackled in this paper. In the polar regions of Northern Siberia without Late Pleistocene and Holocene glaciation, ground ice is used as an archive for paleoclimate studies. First results of stable isotope measurements on ice wedges clearly show a shift towards heavier isotopes and thus warmer winter temperatures as well as a change in the source of the precipitation between Late Pleistocene and Holocene. These results indicate the high potential of ground ice for paleoclimate studies.     

Nanoscale guiding for cold atoms based on surface plasmons along the tips of metallic wedges

We propose a novel scheme to guide neutral cold atoms in a nanoscale region based on surface plasmons (SPs) of one pair and two pairs of tips of metallic wedges with locally enhanced light intensity and sub-optical wavelength resolution. We analyze the near-field intensity distribution of the tip of the metallic wedge by the FDTD method, and study the total intensity as well as the total potential of optical potentials and van der Waals potentials for 87 Rb atoms in the light field of one pair and two pairs of tips of metallic wedges. It shows that the total potentials of one pair and two pairs of tips of metallic wedges can generate a gravito-optical trap and a dark closed trap for nanoscale guiding of neutral cold atoms. Guided atoms can be cooled with efficient intensity-gradient Sisyphus cooling by blue-detuned light field. This provides an important step towards the generation of hybrid systems consisting of isolated atoms and solid devices.     

Localized vibration modes in free anisotropic wedges

Propagation of flexural localized vibration modes along edges of anisotropic wedges is considered in the framework of the geometrical-acoustics approach. Its application allows for straightforward evaluation of the wedge-mode velocities in the general case of arbitrary elastic anisotropy. The velocities depend on the wedge apex angle and on the mode number in the same way as in the isotropic case, but there appears to be additional dependence on elastic coefficients. The velocities in tetragonal wedges (with the midplane orthogonal to the four-fold axis) and in "weakly" monoclinic wedges are explicitly calculated and analyzed. Bounds of the wedge-wave velocity variation in tetragonal materials are established.     

Influence of the Spatial Model of Lithospheric Plates on an Initial Earthquake

The boundary-value problem for a block structure consisting of an elastic half-space that occupies the lower part of a Cartesian coordinate system and interacts with two block elements in the form of unbounded wedges with right angles at the vertices is considered. The horizontal boundaries of the wedges are rigidly connected with the half-space boundary, and vertical ones are parallel planes. We consider the antiplane problem for cases where the distance between the vertical boundaries of block elements is present or absent. By the example of a three-dimensional problem degenerating into a two-dimensional one, it is shown that an initial earthquake is possible, like in the case of using Kirchhoff plates instead of three-dimensional block elements.     

旋转双光楔折射特性与二维扫描轨迹的分析

 为实现旋转双光楔二维扫描的可控操作,利用几何光学和光的标量衍射理论,对双光楔的折光特性进行了数学分析。研究发现：绕固定轴以不同角速度旋转的双光楔可等效为一个折射棱角和主截面都变化的单光楔。以该双光楔系统作为衍射屏,对通过双光楔的光束在观察面的衍射光场分布作了理论分析,得到了夫琅和费衍射下,光束经转动双光楔在像平面上的衍射光斑随转角变化的规律：光斑的横坐标与两光楔转角正弦值的差成正比,纵坐标与两光楔转角余弦值的和成正比。     

Sound diffraction by multiple wedges and thin screens

A theoretical formula that is based on the geometrical theory of diffraction (GTD) is proposed for computing sound diffraction by multiple wedges, barriers, and polygonal-like shapes. The formula can treat both convex and concave edges, where edges may or may not be inter-connected. Comparisons of theoretical predictions with other results done by the BEM or experiments for scaled model confirm the accuracy of the present formula. Numerical examples such as double wedges and doubly inclined barrier show that when there exist several diffraction paths for given source and receiver positions, the insertion loss is dominated by the diffraction associated with the shortest propagation path. It is also found that although the partially inclined barrier increases the shadow zone as compared to the simple screen type of the same total height, it does not necessarily increase the insertion loss at all heights.     

Generation of higher-order optical vortices by a dielectric wedge

Diffraction of a Gaussian beam with a system of successively located optical wedges is considered. It is shown that the system is able to form higher-order optical vortices.     

Laser-based linear and nonlinear guided elastic waves at surfaces (2D) and wedges (1D)

The characteristic features and applications of linear and nonlinear guided elastic waves propagating along surfaces (2D) and wedges (1D) are discussed. Laser-based excitation, detection, or contact-free analysis of these guided waves with pump–probe methods are reviewed. Determination of material parameters by broadband surface acoustic waves (SAWs) and other applications in nondestructive evaluation (NDE) are considered. The realization of nonlinear SAWs in the form of solitary waves and as shock waves, used for the determination of the fracture strength, is described. The unique properties of dispersion-free wedge waves (WWs) propagating along homogeneous wedges and of dispersive wedge waves observed in the presence of wedge modifications such as tip truncation or coatings are outlined. Theoretical and experimental results on nonlinear wedge waves in isotropic and anisotropic solids are presented.     

Isotope Studies of Hydrogen and Oxygen in Ground Ice - Experiences with the Equilibration Technique

Abstract

Equilibration technique suitable for a large amount ofsamples is described for hydrogen and oxygen isotope analyses of ground ice, especially ice wedges, including the sampling strategy and the analytical procedure as well as the calibration of the Finnigan MAT Delta-S mass spectrometer in June, 1999. Since for future analyses of ice wedges, a higher sampling resolution with limited sample volume is required, the limit of the equliibration technique for small water samples size of between 0.05 and 5 ml was checked. For water samples smaller than 1ml, corresponding to a molar ratio [H₂O]/[H₂] of smaller than 0.994, a balance correction has to be applied. The experimental errors due to partial evaporation during evacuation, the balance calcultion of the isotope equilibration process, the linearity as well as memory effects of the mass spectrometer for smaples with large differences in δ¹⁸O and δD are tackled in this paper. In the polar regions of Northern Siberia without Late Pleistocene and Holocene glaciation, ground ice is used as an archive for paleoclimate studies. First results of stable isotope measurements on ice wedges clearly show a shift towards heavier isotopes and thus warmer winter temperatures as well as a change in the source of the precipitation between Late Pleistocene and Holocene. These results indicate the high potential of ground ice for paleoclimate studies.     

Sound attenuation by multiple barriers

A method (tentatively called ‘the method of equivalent sound source’) of predicting the sound attenuation achieved by multiple barriers with knife edges and/or right-angled wedges is proposed. This paper shows that the sound pressure level in the shadow region behind the multiple barriers can be obtained by successively setting imaginary sound sources for respective edges and/or wedges. The locations of the imaginary sound sources are determined by means of the traditional solution for sound attenuation by a single edge. The calculated results for several kinds of small-scale model, obtained by ‘the method of equivalent sound source’, are compared with experimental results.     

Elastic Waves in Cylindrical Metal Wedges with Different Geometries

Acoustical Physics - The article presents results of numerical simulation and experimental studies of elastic wedge wave propagation in cylindrical wedges with positive and negative curvature in...     

Numerical modelling of free interaction of shock waves in corner flows

The inviscid supersonic flows in corners between intersecting compression wedges were studied numerically. Under usual conditions, the flows in such corner configurations are conically self-similar. Besides, shock waves formed by wedges are plane and they interact with one another in these flows and the downstream development of the shock interaction structure at that occurs in a region which is bounded in cross-sectional directions by the walls and contracts towards the corner rib, and in this sense the above interaction of shocks may be subjected to influence of the rib. The corner flows of another type with an interaction of shocks not subjected to the “rib effect”, in other words free, were considered. This was ensured by that the corner configurations were designed with a gradually expanding gap along the rib in a way that the reflected shocks arising as a result of interaction passed through the gap without falling onto the walls. This eliminated the influence of a local flow near the corner rib on the interaction of plane shock waves formed by the wedges. The inviscid flows symmetric with respect to the bisector plane of the corner dihedral angle were considered. The computations showed that, in the gapped corner configurations with the free interaction of shocks, if these interactions were irregular, the cross-flow patterns were practically the same as in the original corner configurations without a gap. The conditions for the flows over corner configurations were also considered under which the interaction of shocks corresponded to the Neumann criterion of mechanical equilibrium. These conditions are equivalent to those, which take place in two-dimensional steady flows, when a hysteresis phenomenon is possible, which manifests itself in changing the moment of transition from a regime of regular reflection of shocks to an irregular one and conversely at a direct and inverse courses of varying the flow parameters—the Mach number and the inclination angle of the wedges. The conducted computations showed that a hysteresis is possible for considered corner flows in gapped configurations, but it must be followed by a detachment of shocks from the corner apex and a breakdown of the conical flow structure.