Shock tunnel experiments on control of shock induced large separation bubble using boundary layer bleed

Shock-Boundary Layer Interaction (SBLI) often occurs in supersonic/hypersonic flow fields. Especially when accompanied by separation (termed strong interaction), the SBLI phenomena largely affect the performance of the systems where they occur, such as scramjet intakes, thus often demanding the control of the interaction. Experiments on the strong interaction between impinging shock wave and boundary layer on a flat plate at Mach 5.96 are carried out in IISc hypersonic shock tunnel HST-2. The experiments are performed at moderate flow total enthalpy of 1.3 MJ/kg and freestream Reynolds number of 4 million/m. The strong shock generated by a wedge (or shock generator) of large angle 30.96 degrees to the freestream is made to impinge on the flat plate at 95 mm (inviscid estimate) from the leading edge, due to which a large separation bubble of length (75 mm) comparable to the distance of shock impingement from the leading edge is generated. The experimental simulation of such large separation bubble with separation occurring close to the leading edge, and its control using boundary layer bleed (suction and tangential blowing) at the location of separation, are demonstrated within the short test time of the shock tunnel (similar to 600 mu s) from time resolved schlieren flow visualizations and surface pressure measurements. By means of suction - with mass flow rate one order less than the mass flow defect in boundary layer - a reduction in separation length by 13.33% was observed. By the injection of an array of (nearly) tangential jets in the direction of mainstream (from the bottom of the plate) at the location of separation - with momentum flow rate one order less than the boundary layer momentum flow defect - 20% reduction in separation length was observed, although the flow field was apparently unsteady. (C) 2014 Elsevier Masson SAS. All rights reserved.

Effect of small-angle scattering on the integer quantum Hall plateau

A GaAs/AlGaAs two-dimensional electron gas (2 DEG) structure with the high mobility of mu(2K) = 1.78 x 10(6) cm(2)/Vs has been studied by low-temperature Hall and Shubnikov de Hass (SdH) measurements. Quantum lifetimes related to all-angle scattering events reduced from 0.64 ps to 0.52 ps after illuminating by Dingle plots, and transport lifetimes related to large-angle scattering events increasing from 42.3 ps to 67.8 ps. These results show that small-angle scattering events become stronger. It is clear that small-angle scattering events can cause the variation of the widths of the quantum Hall plateaus.

Shock tunnel study of spiked aerodynamic bodies flying at hypersonic Mach numbers

A three-component accelerometer balance system is used to study the drag reduction effect of an aerodisc on large angle blunt cones flying at hypersonic Mach numbers. Measurements in a hypersonic shock tunnel at a freestream Mach number of 5.75 indicate more than 50% reduction in the drag coefficient for a 120degrees apex angle blunt cone with a forward facing aerospike having a flat faced aerodisc at moderate angles of attack. Enhancement of drag has been observed for higher angles of attack due to the impingement of the flow separation shock on the windward side of the cone. The flowfields around the large angle blunt cone with aerospike assembly flying at hypersonic Mach numbers are also simulated numerically using a commercial CFD code. The pressure and density levels on the model surface, which is under the aerodynamic shadow of the flat disc tipped spike, are found very low and a drag reduction of 64.34% has been deduced numerically.

Cyclic Deformation Of Nanocrystalline And Ultrafine-Grained Nickel

The cyclic deformation behavior Of ultrafine-grained (UFG) Ni samples synthesized by the electrodeposition method was studied. Different from those made by severely plastic deformation, the UFG samples used in this study are characterized by large-angle grain boundaries. Behaviors from nanocrystalline Ni and coarse-grained Ni samples were compared with that Of Ultrafine-grained Ni. With in situ neutron diffraction. unusual evolutions of residual lattice strains as well as cyclic hardening and softening behavior were demonstrated during the cyclic deformation. The microstructural changes investigated by TEM are discussed with respect to the unusual lattice strain and cyclic hardening/softening. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

适用于中等耦合等离子体的碰撞算子

完全电离等离子体中，当试探粒子分布函数fα是关于试探粒子速度vα的偶函数时，导出了一个新的动力学方程的碰撞算子．该碰撞算子同时包括了大角散射（库仑近碰撞）和小角散射（库仑远碰撞）的二体碰撞的贡献，因此，该碰撞算子同时适用于弱耦合（库仑对数ln∧≥10）和中等耦合（库仑对数2≤ln∧≤10）等离子体．而且经过修改的碰撞算子和Rosenbluth势有直接的联系，当试探粒子和场粒子满足条件mα＜mβ（如电子-离子碰撞或Lorentz气体模型）和｜vα｜〉｜vβ｜时，经约化的电子-离子碰撞算子同最初的Fokker

基于掺镧锆钛酸铅电光材料的光学相控阵光束扫描器

基于掺镧锆钛酸铅(PLZT)电光陶瓷材料的光学特性,提出了一种具有上下电极结构的光学相控阵高速光束扫描器。在理论上,分析了具有这种结构的光学相控阵的光束电光偏转特性和机制;在实验上,分析了掺镧锆钛酸铅材料的相位调制特性和损耗特性,制作了相关的光学相控阵器件,并构建了相应的测试系统,获得了光束在空间的角度偏转,与理论分析结果相符。

TEM study of dislocations in ZnTe/GaAs heterostructure grown by hot-wall epitaxy

A ZnTe layer grown on GaAs substrate by hot-wall epitaxy (HWE) was studied using transmission electron microscopy (TEM). For a (110) cross-sectional specimen, its (001) ZnTe/GaAs interface was analysed by large angle stereo-projection (LASP) and high resolution electron microscopy (HREM). In the LASP, a double diffraction occurred and moire fringes were formed, meanwhile misfit dislocations were revealled clearly by weak beam technique. In HREM, not only Lomer and 60 degrees types of misfit dislocations were observed, but also two types of stacking faults were analysed. The residual strain was estimated by both methods.

MATRIX DESCRIPTION OF DYNAMIC HOLZ DIFFRACTION TESTED ON THE STRAINED LAYER SUPERLATTICE SI/GESI

A matrix formulation has been developed and applied to simulate large-angle convergent-beam electron diffraction (LACBED) patterns from the Si/GexSi1-x strained layer superlattice (SLS). Good quantitative agreement has been achieved between experimental and simulated patterns. By utilizing dynamical HOLZ line patterns, we demonstrate that an accuracy of better than 0.1% can be achieved in the determination of the averaged lattice constant of a SLS, and the averaged number of layers of atoms within one period of SLS can be determined up to a single monolayer.

CONVERGENT-BEAM ELECTRON-DIFFRACTION STUDY OF GE0.5SI0.5/SI STRAINED-LAYER SUPERLATTICES GROWN BY MOLECULAR-BEAM EPITAXY

Side bands due to purely composition and combined composition-strain modulation in plan-view specimens of a nominally Ge0.5Si0.5(5nm)/Si(25nm) superlattice have been obtained by large-angle convergent-beam electron diffraction. The intensities of the side bands have been calculated from a periodic tension-compression model of the superlattice bilayer using the kinematical theory of electron diffraction. Accurate values of elastic strains in the bilayer and of the Ge content can be obtained in this way.

Evidence of strong projectile-target-core interaction in single ionization of neon by electron impact

The momentum distributions of recoil ions were measured in the single ionization of neon by electron impact at incident energies between 80 and 2300 eV. It was found that there are a noticeable number of recoil ions carrying large momenta, and the relative contributions of these ions becomes more pronounced with the further decrease of incident electron energy. These observed behaviors indicate that there is a strong projectile-target-core interaction in the single-ionization reaction. By comparing our results with those of electron-neon elastic scattering, we concluded that the elastic scattering of the projectile electron on the target core plays an important role at low and intermediate collision energies.

Probing UPD-induced surface atomic rearrangement of polycrystalline gold nanofilms with surface plasmon resonance spectroscopy and cyclic voltammetry

Silver underpotential deposition (UPD)-induced surface atomic rearrangement of polycrystalline gold nanofilms was probed with use of surface plasmon resonance spectroscopy (SPRs) as a novel probe tool in combination with cyclic voltammetry. Interestingly, upon repetitive electrochemical UPD and stripping of Ag, the surface structure of the resulting bare Au film is rearranged due to strong adatom-substrate interactions, which causes a large angle shift of SPR R-theta curves, in a good linear relationship with the number of UPDs, to a lower SPR angle. The n, K values of the surfacial Au monolayers before and after the repetitive Ag UPD and stripping for 27 times are found to be 0.133, 3.60 and 0.565, 9.39, respectively, corresponding to the huge shift of 1.61degrees to the left of the SPR minima. Cyclic voltammetry experiments in 0.10 M H2SO4 are carried out before and after the UPD treatment to examine the quality of the whole electrode surface and confirmed this change. To correlate the angle change in SPRs with the profile change in the cyclic voltammogram, the UPD treatment was also performed on a Au(111) textured thin film. It was therefore confirmed that the resonance position of the SPR spectrum is very sensitive to the surface crystallographic orientation of the bare Au substrates. Some surface atomic rearrangement can cause a pronounced SPR angle shift.

复杂介质中地震波场数值模拟研究——基于广义正交多项式迭积微分算子法

In this paper, we propose a new numerical modeling method – Convolutional Forsyte Polynomial Differentiator (CFPD), aimed at simulating seismic wave propagation in complex media with high efficiency and accuracy individually owned by short-scheme finite differentiator and general convolutional polynomial method. By adjusting the operator length and optimizing the operator coefficient, both global and local informations can be easily incorporated into the wavefield which is important to invert the undersurface geological structure. The key issue in this paper is to introduce the convolutional differentiator based on Forsyte generalized orthogonal polynomial in mathematics into the spatial differentiation of the first velocity-stress equation. To match the high accuracy of the spatial differentiator, this method in the time coordinate adopts staggered grid finite difference instead of conventional finite difference to model seismic wave propagation in heterogeneous media. To attenuate the reflection artifacts caused by artificial boundary, Perfectly Matched Layer (PML) absorbing boundary is also being considered in the method to deal with boundary problem due to its advantage of automatically handling large-angle emission. The PML formula for acoustic equation and first-order velocity-stress equation are also derived in this paper. There is little difference to implement the PML boundary condition in all kind of wave equations, but in Biot media, special attenuation factors should be taken. Numerical results demonstrate that the PML boundary condition is better than Cerjan absorbing boundary condition which makes it more suitable to hand the artificial boundary reflection. Based on the theories of anisotropy, Biot two-phase media and viscous-elasticity, this paper constructs the constitutive relationship for viscous-elastic and two-phase media, and further derives the first-order velocity-stress equation for 3D viscous-elastic and two-phase media. Numerical modeling using CFPD method is carried out in the above-mentioned media. The results modeled in the viscous-elastic media and the anisotropic pore elastic media can better explain wave phenomena of the true earth media, and can also prove that CFPD is a useful numerical tool to study the wave propagation in complex media.

Interaction between coronal mass ejections and the solar wind

Jones, R. A.; Breen, A. R.; Fallows, R. A.; Canals, A.; Bisi, M. M.; Lawrence, G. (2007). Interaction between coronal mass ejections and the solar wind, Journal of Geophysical Research, 112, Issue A8 RAE2008

Simulations of magnetic microstructure in thin film elements used for programmable motion of magnetic particles

The results of two-dimensional micromagnetic modeling of magnetization patterns in Permalloy ellipses under the influence of rotating constant-amplitude magnetic fields are discussed. Ellipses of two different lateral sizes have been studied, 0.5m x 1.5m and 1m x 3m. The amplitude of the rotating magnetic field was varied between simulations with the condition that it must be large enough to saturate or nearly saturate the ellipse with the field applied along the long axis of the ellipse. For the smaller ellipse size it is found that the magnetization pattern forms an S state and the direction of the net magnetization lags behind the direction of the applied field. At a critical angle of the rotating magnetic field the direction of the magnetization switches by a large angle to a new S state. Both the critical angle and the angle interval of the switch depend on field amplitude. For this new state, it is instead the applied field direction that lags behind the magnetization direction. The transient magnetization patterns correspond to multi-domain patterns including two vortices, but this state never exists for the equilibrated magnetization patterns. The behavior of the larger ellipse in rotating field is different. With the field applied along the long-axis of the ellipse, the magnetization of the ellipse is nearly saturated with a vortex close to each apex of the ellipse. As the field is rotated, this magnetization pattern remains and the net-magnetization direction lags behind the direction of the field until for a certain angle of the applied field an equilibrium multi-domain state is created. Comparisons are made with corresponding experimental results obtained by performing in-field magnetic force microscopy on Permalloy ellipses.

Location and characteristics of the reconnection X line deduced from low-altitude satellite and ground-based observations: 2. Defense Meteorological Satellite Program and European Incoherent Scatter data

We present an analysis of a cusp ion step, observed by the Defense Meteorological Satellite Program (DMSP) F10 spacecraft, between two poleward moving events of enhanced ionospheric electron temperature, observed by the European Incoherent Scatter (EISCAT) radar. From the ions detected by the satellite, the variation of the reconnection rate is computed for assumed distances along the open-closed field line separatrix from the satellite to the X line, do. Comparison with the onset times of the associated ionospheric events allows this distance to be estimated, but with an uncertainty due to the determination of the low-energy cutoff of the ion velocity distribution function, ƒ(ν). Nevertheless, the reconnection site is shown to be on the dayside magnetopause, consistent with the reconnection model of the cusp during southward interplanetary magnetic field (IMF). Analysis of the time series of distribution function at constant energies, ƒ(ts), shows that the best estimate of the distance do is 14.5±2 RE. This is consistent with various magnetopause observations of the signatures of reconnection for southward IMF. The ion precipitation is used to reconstruct the field-parallel part of the Cowley D ion distribution function injected into the open low-latitude boundary layer in the vicinity of the X line. From this reconstruction, the field-aligned component of the magnetosheath flow is found to be only −55±65 km s−1 near the X line, which means either that the reconnection X line is near the stagnation region at the nose of the magnetosphere, or that it is closely aligned with the magnetosheath flow streamline which is orthogonal to the magnetosheath field, or both. In addition, the sheath Alfvén speed at the X line is found to be 220±45 km s−1, and the speed with which newly opened field lines are ejected from the X line is 165±30 km s−1. We show that the inferred magnetic field, plasma density, and temperature of the sheath near the X line are consistent with a near-subsolar reconnection site and confirm that the magnetosheath field makes a large angle (>58°) with the X line.