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Shock Waves (shock + wave)
Terms modified by Shock Waves Selected AbstractsLongitudinal Dust Lattice Shock Wave in a Strongly Coupled Complex Dusty PlasmaCONTRIBUTIONS TO PLASMA PHYSICS, Issue 8 2008S. Ghosh Abstract The effect of hydrodynamical damping that arises due to the irreversible processes within the system have been studied on 1D nonlinear longitudinal dust lattice wave (LDLW) in homogeneous strongly coupled complex (dusty) plasma. Analytical investigation shows that the nonlinear wave is governed by Korteweg-de Vries Burgers' equation. This hydrodynamical damping induced dissipative effect is responsible for the Burgers' term that causes the generation of shock wave in dusty plasma crystal. Numerical investigation on the basis of the glow-discharge plasma parameters reveal that LDLW exhibits both oscillatory and monotonic shock. The shock is compressive in nature and its strength decreases (increases) with the increase of the shielding parameter , (characteristic length L). The effects of dust-neutral collision are also discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Shock wave induced cytoskeletal and morphological deformations in a human renal carcinoma cell lineCANCER SCIENCE, Issue 4 2006S. Fatemeh Moosavi-Nejad Effects of shock waves on the morphology and cytoskeleton of a human renal carcinoma cell line (ACHN) were investigated in vitro. ACHN monolayer cultured on a cover slide glass was treated with 10 shots of focused underwater shock waves, with 16 MPa peak pressure at the focal area of a piezoceramic shock wave generator. After exposure to the shock wave, based on the severity of morphological deformations of the treated cells, the monolayer was divided into three morphological areas; focal, marginal and intact. Morphological deformations were found to be associated with disorganization of the intracellular cytoskeletal filaments. Deformation of the cytoskeletal proteins in the treated cells were separately studied with respect to the location of the cells within the three morphological areas. Among three major cytoskeletal proteins, actin and tubulin, but not vimentin, were affected by the shock waves. The deformed cells reorganized their cytoskeletal network within 3 h with a pattern similar to the control, indicating the transient characteristic of the shock wave induced cytoskeletal damage in the surviving cells. The remaining cell fragments on the slide glass, which contained short actin filaments, indicated the important role of shear stress in damaging the cytoskeletal fibers by shock waves. (Cancer Sci 2006; 97: 296,304) [source] Shock waves,Phenomenology, experimental, and numerical simulationMETEORITICS & PLANETARY SCIENCE, Issue 9-10 2005Klaus Thoma First, the principal phenomena of shock wave generation and propagation, predominantly in solid media, are presented, and then analytical and numerical mathematical treatment of shock wave processes on the basis of mass, momentum, and energy conservation laws will be described and discussed. Experimental methods of shock wave investigations by means of impact and explosive techniques are summarized, including hypervelocity acceleration facilities and high-pressure explosive devices. Shock pressure barometry by means of mineralogical evidence of distinct material phase transitions and characteristic shock structures is also discussed. [source] Collisionless Plasma Expansion in the Presence of a Dipole Magnetic FieldCONTRIBUTIONS TO PLASMA PHYSICS, Issue 6 2009H. B. Nersisyan Abstract The collisionless interaction of an expanding high,energy plasma cloud with a magnetized background plasma in the presence of a dipole magnetic field is examined in the framework of a 2D3V hybrid (kinetic ions and massless fluid electrons) model. The retardation of the plasma cloud and the dynamics of the perturbed electromagnetic fields and the background plasma are studied for high Alfvén,Mach numbers using the particle,in,cellmethod. It is shown that the plasma cloud expands excluding the ambient magnetic field and the background plasma to form a diamagnetic cavity which is accompanied by the generation of a collisionless shock wave. The energy exchange between the plasma cloud and the background plasma is also studied and qualitative agreement with the analytical model suggested previously is obtained (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Longitudinal Dust Lattice Shock Wave in a Strongly Coupled Complex Dusty PlasmaCONTRIBUTIONS TO PLASMA PHYSICS, Issue 8 2008S. Ghosh Abstract The effect of hydrodynamical damping that arises due to the irreversible processes within the system have been studied on 1D nonlinear longitudinal dust lattice wave (LDLW) in homogeneous strongly coupled complex (dusty) plasma. Analytical investigation shows that the nonlinear wave is governed by Korteweg-de Vries Burgers' equation. This hydrodynamical damping induced dissipative effect is responsible for the Burgers' term that causes the generation of shock wave in dusty plasma crystal. Numerical investigation on the basis of the glow-discharge plasma parameters reveal that LDLW exhibits both oscillatory and monotonic shock. The shock is compressive in nature and its strength decreases (increases) with the increase of the shielding parameter , (characteristic length L). The effects of dust-neutral collision are also discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Numerical simulation on operation of closed-loop experimental facility with subsonic MHD generatorELECTRICAL ENGINEERING IN JAPAN, Issue 1 2008Hidemasa Takana Abstract The operating characteristics and operation procedure of the closed-loop experimental facility under subsonic power generation have been investigated by means of time-dependent quasi-one-dimensional numerical simulations. Two ways of operation for subsonic power generation were found: (1) subsonic operation both under nonpower and power generation and (2) supersonic operation under nonpower generation and subsonic operation under power generation. For operation (1), Mach number at channel inlet decreases to ,0.6, therefore it is required to generate plasma under this Mach number. On the other hand, if the plasma cannot be generated, operation (2) needs to be carried out. In this case, a shock wave appears in the generator channel, then the influence of a large pressure change and a vibration caused by a shock wave in the generator channel needs to be considered. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(1): 25,33, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20399 [source] Assessment of flooding in urbanized ungauged basins: a case study in the Upper Tiber area, ItalyHYDROLOGICAL PROCESSES, Issue 10 2005T. Moramarco Abstract The reliability of a procedure for investigation of flooding into an ungauged river reach close to an urban area is investigated. The approach is based on the application of a semi-distributed rainfall,runoff model for a gauged basin, including the flood-prone area, and that furnishes the inlet flow conditions for a two-dimensional hydraulic model, whose computational domain is the urban area. The flood event, which occurred in October 1998 in the Upper Tiber river basin and caused significant damage in the town of Pieve S. Stefano, was used to test the approach. The built-up area, often inundated, is included in the gauged basin of the Montedoglio dam (275 km2), for which the rainfall,runoff model was adapted and calibrated through three flood events without over-bank flow. With the selected set of parameters, the hydrological model was found reasonably accurate in simulating the discharge hydrograph of the three events, whereas the flood event of October 1998 was simulated poorly, with an error in peak discharge and time to peak of ,58% and 20%, respectively. This discrepancy was ascribed to the combined effect of the rainfall spatial variability and a partial obstruction of the bridge located in Pieve S. Stefano. In fact, taking account of the last hypothesis, the hydraulic model reproduced with a fair accuracy the observed flooded urban area. Moreover, incorporating into the hydrological model the flow resulting from a sudden cleaning of the obstruction, which was simulated by a ,shock-capturing' one-dimensional hydraulic model, the discharge hydrograph at the basin outlet was well represented if the rainfall was supposed to have occurred in the region near the main channel. This was simulated by reducing considerably the dynamic parameter, the lag time, of the instantaneous unit hydrograph for each homogeneous element into which the basin is divided. The error in peak discharge and time to peak decreased by a few percent. A sensitivity analysis of both the flooding volume involved in the shock wave and the lag time showed that this latter parameter requires a careful evaluation. Moreover, the analysis of the hydrograph peak prediction due to error in rainfall input showed that the error in peak discharge was lower than that of the same input error quantity. Therefore, the obtained results allowed us to support the hypothesis on the causes which triggered the complex event occurring in October 1998, and pointed out that the proposed procedure can be conveniently adopted for flood risk evaluation in ungauged river basins where a built-up area is located. The need for a more detailed analysis regarding the processes of runoff generation and flood routing is also highlighted. Copyright © 2005 John Wiley & Sons, Ltd. [source] Flow characteristics of a cold helium arc-jet plasma along open field linesIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 3 2009Kazuyuki Yoshida Member Abstract We experimentally study plasma parameters including ion acoustic Mach number of expanding cold helium plasma jet with an electron temperature of less than 1 eV flowing along open field lines. It is experimentally found that the ion Mach number increases from 1 to 3, and that the plasma potential decreases by about 1 V. We discuss the experimental results based on a quasi one-dimensional flow model in which the plasma is assumed to be quasi-neutral and in a state of thermodynamic equilibrium. Our model describes the ion acceleration, the axial profiles of the potential drop, and the electron temperature/density. The model also shows that the helium ions are accelerated both by the electric field and by the increasing cross-sectional area of the transonic flow. After the ion acceleration, the ion Mach number decreases and the electron temperature increases. These phenomena are discussed in terms of a shock wave. It is noted that the electron density decreases even in the shock wave. This is discussed in terms of rapid recombination because of the low electron temperature. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] On the computation of steady-state compressible flows using a discontinuous Galerkin methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2008Hong Luo Abstract Computation of compressible steady-state flows using a high-order discontinuous Galerkin finite element method is presented in this paper. An accurate representation of the boundary normals based on the definition of the geometries is used for imposing solid wall boundary conditions for curved geometries. Particular attention is given to the impact and importance of slope limiters on the solution accuracy for flows with strong discontinuities. A physics-based shock detector is introduced to effectively make a distinction between a smooth extremum and a shock wave. A recently developed, fast, low-storage p -multigrid method is used for solving the governing compressible Euler equations to obtain steady-state solutions. The method is applied to compute a variety of compressible flow problems on unstructured grids. Numerical experiments for a wide range of flow conditions in both 2D and 3D configurations are presented to demonstrate the accuracy of the developed discontinuous Galerkin method for computing compressible steady-state flows. Copyright © 2007 John Wiley & Sons, Ltd. [source] A spectral-element method for modelling cavitation in transient fluid,structure interactionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 15 2004M. A. Sprague Abstract In an underwater-shock environment, cavitation (boiling) occurs as a result of reflection of the shock wave from the free surface and/or wetted structure causing the pressure in the water to fall below its vapour pressure. If the explosion is sufficiently distant from the structure, the motion of the fluid surrounding the structure may be assumed small, which allows linearization of the governing fluid equations. In 1984, Felippa and DeRuntz developed the cavitating acoustic finite-element (CAFE) method for modelling this phenomenon. While their approach is robust, it is too expensive for realistic 3D simulations. In the work reported here, the efficiency and flexibility of the CAFE approach has been substantially improved by: (i) separating the total field into equilibrium, incident, and scattered components, (ii) replacing the bilinear CAFE basis functions with high-order Legendre-polynomial basis functions, which produces a cavitating acoustic spectral element (CASE) formulation, (iii) employing a simple, non-conformal coupling method for the structure and fluid finite-element models, and (iv) introducing structure,fluid time-step subcycling. Field separation provides flexibility, as it admits non-acoustic incident fields that propagate without numerical dispersion. The use of CASE affords a significant reduction in the number of fluid degrees of freedom required to reach a given level of accuracy. The combined use of subcycling and non-conformal coupling affords order-of-magnitude savings in computational effort. These benefits are illustrated with 1D and 3D canonical underwatershock problems. Copyright © 2004 John Wiley & Sons, Ltd. [source] A computational model for impact failure with shear-induced dilatancyINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2003Z. Chen Abstract It has been observed in plate impact experiments that some brittle solids may undergo elastic deformation at the shock wave front, and fail catastrophically at a later time when they are shocked near but below the apparent Hugoniot elastic limit. Because this phenomenon appears to have features different from those of usual inelastic waves, it has been interpreted as the failure wave. To design an effective numerical procedure for simulating impact failure responses, a three-dimensional computational damage model is developed in this paper. The propagation of the failure wave behind the elastic shock wave is described by a non-linear diffusion equation. Macroscopic shear-induced dilatancy is assumed and treated as a one-to-one measure of the mean intensity of microcracking. The damage evolution in time is determined based on the assumption that the deviatoric strain energy in the elastically compressed material (undamaged) is converted, through the damaging process, into the volumetric potential energy in the comminuted and dilated material. For the ease in large-scale simulations, the coupled damage diffusion equation and the stress wave equation are solved via a staggered manner in a single computational domain. Numerical solutions by using both the finite element method and the material point method, i.e. with and without a rigid mesh connectivity, are presented and compared with the experimental data available. It is shown that the model simulations capture the essential features of the failure wave phenomenon observed in shock glasses, and that the numerical solutions for localized failure are not mesh-dependent. Copyright © 2003 John Wiley & Sons, Ltd. [source] Numerical simulation of a single bubble by compressible two-phase fluidsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2010Siegfried Müller Abstract The present work deals with the numerical investigation of a collapsing bubble in a liquid,gas fluid, which is modeled as a single compressible medium. The medium is characterized by the stiffened gas law using different material parameters for the two phases. For the discretization of the stiffened gas model, the approach of Saurel and Abgrall is employed where the flow equations, here the Euler equations, for the conserved quantities are approximated by a finite volume scheme, and an upwind discretization is used for the non-conservative transport equations of the pressure law coefficients. The original first-order discretization is extended to higher order applying second-order ENO reconstruction to the primitive variables. The derivation of the non-conservative upwind discretization for the phase indicator, here the gas fraction, is presented for arbitrary unstructured grids. The efficiency of the numerical scheme is significantly improved by employing local grid adaptation. For this purpose, multiscale-based grid adaptation is used in combination with a multilevel time stepping strategy to avoid small time steps for coarse cells. The resulting numerical scheme is then applied to the numerical investigation of the 2-D axisymmetric collapse of a gas bubble in a free flow field and near to a rigid wall. The numerical investigation predicts physical features such as bubble collapse, bubble splitting and the formation of a liquid jet that can be observed in experiments with laser-induced cavitation bubbles. Opposite to the experiments, the computations reveal insight to the state inside the bubble clearly indicating that these features are caused by the acceleration of the gas due to shock wave focusing and reflection as well as wave interaction processes. While incompressible models have been used to provide useful predictions on the change of the bubble shape of a collapsing bubble near a solid boundary, we wish to study the effects of shock wave emissions into the ambient liquid on the bubble collapse, a phenomenon that may not be captured using an incompressible fluid model. Copyright © 2009 John Wiley & Sons, Ltd. [source] Simple efficient algorithm (SEA) for shallow flows with shock wave on dry and irregular bedsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2008Alireza Zia Abstract An explicit Godunov-type solution algorithm called SEA (simple efficient algorithm) has been introduced for the shallow water equations. The algorithm is based on finite volume conservative discretisation method. It can deal with wet/dry and irregular beds. Second-order accuracy, in both time and space, is achieved using prediction and correction steps. A very simple and efficient flux limiting technique is used to equip the algorithm with total variation dimensioning property for shock capturing purposes. In order to make sure about the balance between the flux gradient and the bed slope, treatment of the source term has been done using a new procedure inspired mainly by the physical rather than mathematical consideration. SEA has been applied to one-dimensional problems, although it can equally be applied to multi-dimensional problems. In order to assess the capability of proposed algorithm in dealing with practical applications, several test cases have been examined. Copyright © 2007 John Wiley & Sons, Ltd. [source] A numerical scheme for strong blast wave driven by explosionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2006Kaori Kato Abstract After the detonation of a solid high explosive, the material has extremely high pressure keeping the solid density and expands rapidly driving strong shock wave. In order to simulate this blast wave, a stable and accurate numerical scheme is required due to large density and pressure changes in time and space. The compressible fluid equations are solved by a fractional step procedure which consists of the advection phase and non-advection phase. The former employs the Rational function CIP scheme in order to preserve monotone signals, and the latter is solved by interpolated differential operator scheme for achieving the accurate calculation. The procedure is categorized into the fractionally stepped semi-Lagrangian. The accuracy of our scheme is confirmed by checking the one-dimensional plane shock tube problem with 103 times initial density and pressure jump in comparison with the analytic solution. The Sedov,Taylor blast wave problem is also examined in the two-dimensional cylindrical coordinate in order to check the spherical symmetry and the convergence rates. Two- and three-dimensional simulations for the blast waves from the explosion in the underground magazine are carried out. It is found that the numerical results show quantitatively good agreement with the experimental data. Copyright © 2006 John Wiley & Sons, Ltd. [source] Adaptive strategy of the supersonic turbulent flow over a backward-facing stepINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2004Shih-Ying YangArticle first published online: 16 MAR 200 Abstract An adaptive strategy incorporating mesh remeshing and refining is developed to study the supersonic turbulent flow over a backward-facing step on a mixed quadrilateral,triangular mesh. In the Cartesian co-ordinate system, the unsteady Favre-averaged Navier,Stokes equations with a low-Reynolds-number k,,turbulence model are solved using a locally implicit scheme with an anisotropic dissipation model. In the present adaptive strategy, two error indicators for both mesh remeshing and refining, respectively, are presented. The remeshing error indicator incorporates unified magnitude of substantial derivative of pressure and that of vorticity magnitude, whereas the refining error indicator incorporates unified magnitude of substantial derivative of pressure and that of weighted vorticity magnitude. To assess the present approach, the transonic turbulent flow around an NACA 0012 airfoil is performed. Based on the comparison with the experimental data, the accuracy of the present approach is confirmed. According to the high-resolutional result on the adaptive mesh, the structure of backstep corner vortex, expansion wave and oblique shock wave is distinctly captured. Copyright © 2004 John Wiley & Sons, Ltd. [source] Weighted average flux method and flux limiters for the numerical simulation of shock waves in rigid porous mediaINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2002R. Torrens Abstract The one-dimensional flow field generated by the passage of a shock wave in a rigid, thermoelastic porous foam has been simulated using a two-phase mathematical model. The work presented here makes use of the weighted average flux method to solve the system of six equations that govern the problem. Spurious oscillations are eliminated through the application of total variation diminishing limiting methods. Four different limiters were tested: van Leer, SuperA, MinA and van Albada. Numerical tests were carried out to verify the performance of each flux limiter in terms of accuracy. The results were compared to analytical and previously obtained data to assess the performance of the mathematical model. Excellent agreement was obtained. Copyright © 2002 John Wiley & Sons, Ltd. [source] Some recent finite volume schemes to compute Euler equations using real gas EOSINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2002T. Gallouët Abstract This paper deals with the resolution by finite volume methods of Euler equations in one space dimension, with real gas state laws (namely, perfect gas EOS, Tammann EOS and Van Der Waals EOS). All tests are of unsteady shock tube type, in order to examine a wide class of solutions, involving Sod shock tube, stationary shock wave, simple contact discontinuity, occurrence of vacuum by double rarefaction wave, propagation of a one-rarefaction wave over ,vacuum', , Most of the methods computed herein are approximate Godunov solvers: VFRoe, VFFC, VFRoe ncv (,, u, p) and PVRS. The energy relaxation method with VFRoe ncv (,, u, p) and Rusanov scheme have been investigated too. Qualitative results are presented or commented for all test cases and numerical rates of convergence on some test cases have been measured for first- and second-order (Runge,Kutta 2 with MUSCL reconstruction) approximations. Note that rates are measured on solutions involving discontinuities, in order to estimate the loss of accuracy due to these discontinuities. Copyright © 2002 John Wiley & Sons, Ltd. [source] Metal Objects Mapping After Small Charge Explosions.JOURNAL OF FORENSIC SCIENCES, Issue 3 2006A Study on AISI 304Cu Steel with Two Different Grain Sizes ABSTRACT: Evidence of exposure of a metal component to a small charge explosion can be detected by observing microstructural modifications; they may be present even if the piece does not show noticeable overall plastic deformations. Particularly, if an austenitic stainless steel (or another metal having a face-centered cubic structure and a low stacking fault energy) is exposed to an explosive shock wave, high-speed deformation induces primarily mechanical twinning, whereas, in nonexplosive events, a lower velocity plastic deformation first induces slip. The occurrence of mechanical twins can be detected even if the surface is damaged or oxidized in successive events. In the present research, optical metallography (OM) and scanning electron microscopy (SEM), and scanning tunneling microscopy (STM) were used to detect microstructural modifications caused on AISI 304Cu steel disks by small-charge explosions. Spherical charges of 54.5 or 109 g TNT equivalent mass were used at explosive-to-target distances from 6.5 to 81.5 cm, achieving peak pressures from 160 to 0.5 MPa. Explosions induced limited or no macro-deformation. Two alloy grain sizes were tested. Surface OM and SEM evidenced partial surface melting, zones with recrystallization phenomena, and intense mechanical twinning, which was also detected by STM and X-ray diffraction. In the samples' interior, only twins were seen, up to some distance from the explosion impinged surface and again, at the shortest charge-to-sample distances, in a thin layer around the reflecting surface. For forensic science locating purposes after explosions, the maximum charge-to-target distance at which the phenomena disappear was singled out for each charge or grain size and related to the critical resolved shear stress for twinning. [source] Evaluating planetesimal bow shocks as sites for chondrule formationMETEORITICS & PLANETARY SCIENCE, Issue 11 2004Fred J. CIESLA The formation of such shocks is modeled using a piecewise parabolic method (PPM) code under a variety of conditions. The results of this modeling are used as a guide to study chondrule formation in a one-dimensional, finite shock wave. This model considers a mixture of chondrule-sized particles and micron-sized dust and models the kinetic vaporization of the solids. We found that only planetesimals with a radius of ,1000 km and moving at least ,8 km/s with respect to the nebular gas can generate shocks that would allow chondrule-sized particles to have peak temperatures and cooling rates that are generally consistent with what has been inferred for chondrules. Planetesimals with smaller radii tend to produce lower peak temperatures and cooling rates that are too high. However, the peak temperatures of chondrules are only matched for low values of chondrule wavelength-averaged emissivity. Very slow cooling (<,100s of K/hr) can only be achieved if the nebular opacity is low, which may result after a significant amount of material has been accreted into objects that are chondrule-sized or larger, or if chondrules formed in regions of the nebula with small dust concentrations. Large shock waves of approximately the same scale as those formed by gravitational instabilities or tidal interactions between the nebula and a young Jupiter do not require this to match the inferred thermal histories of chondrules. [source] Space very long baseline interferometry observations of polarization in the jet of 3C 380MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006A. Papageorgiou ABSTRACT A comparison between low-frequency space very long baseline interferometry (VLBI) and high-frequency ground-based VLBI images can, in principle, be used to detect small variations in rotation measure (RM) on fine angular scales inaccessible to ground arrays alone. This paper reports an attempt to perform such a comparison using the jet in the quasar 3C 380. Observations made with the VSOP antenna HALCA together with a ground array at wavelength 1.6 GHz provide total intensity and polarization images of comparable resolution to those from the ground array alone at 5 GHz. The results provide an image showing derotated magnetic vector position angle of somewhat higher resolution than that available earlier. The results show variations in an RM around component A of the order of 10 rad m,2 that could not have been detected with the ground array alone. It is concluded that satellite VLBI observations provide a promising means to study the distribution of matter and magnetic fields around parsec-scale jets. The ground observations used here follow the steady outward drift of component A, which has approximately doubled its distance from the core since the first observations in 1982. They also reveal total intensity and polarization structure associated with a bright knot 0.7 arcsec from the core which is reminiscent of that expected for a conical shock wave. [source] Star formation triggered by SN explosions: an application to the stellar association of , PictorisMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006C. Melioli ABSTRACT In the present study, considering the physical conditions that are relevant in interactions between supernova remnants (SNRs) and dense molecular clouds for triggering star formation we have built a diagram of SNR radius versus cloud density in which the constraints above delineate a shaded zone where star formation is allowed. We have also performed fully 3D radiatively cooling numerical simulations of the impact between SNRs and clouds under different initial conditions in order to follow the initial steps of these interactions. We determine the conditions that may lead either to cloud collapse and star formation or to complete cloud destruction and find that the numerical results are consistent with those of the SNR,cloud density diagram. Finally, we have applied the results above to the , Pictoris stellar association which is composed of low-mass post-T Tauri stars with an age of 11 Myr. It has been recently suggested that its formation could have been triggered by the shock wave produced by an SN explosion localized at a distance of about 62 pc that may have occurred either in the Lower Centaurus Crux or in the Upper Centaurus Lupus which are both nearby older subgroups of that association (Ortega and co-workers). Using the results of the analysis above we have shown that the suggested origin for the young association at the proposed distance is plausible only for a very restricted range of initial conditions for the parent molecular cloud, that is, a cloud with a radius of the order of 10 pc and density of the order of 20 cm,3 and a temperature of the order of 50,100 K. [source] Anisotropic mass ejection in binary mergersMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006T. Morris ABSTRACT We investigate the mass loss from a rotationally distorted envelope following the early, rapid in-spiral of a companion star inside a common envelope. For initially wide, massive binaries (M1+M2= 20 M,, P, 10 yr), the primary has a convective envelope at the onset of mass transfer and is able to store much of the available orbital angular momentum in its expanded envelope. Three-dimensional smoothed particle hydrodynamics calculations show that mass loss is enhanced at mid-latitudes due to shock reflection from a torus-shaped outer envelope. Mass ejection in the equatorial plane is completely suppressed if the shock wave is too weak to penetrate the outer envelope in the equatorial direction (typically when the energy deposited in the star is less than about one-third of the binding energy of the envelope). We present a parameter study to show how the geometry of the ejecta depends on the angular momentum and the energy deposited in the envelope during a merging event. Applications to the nearly axisymmetric, but very non-spherical nebulae around SN 1987A and Sheridan 25 are discussed, as well as possible links to RY Scuti and the Small Magellanic Cloud object R4. [source] G.W. Bush and North Korea: A Levels of Analysis ViewPACIFIC FOCUS, Issue 1 2007Curtis H. Martin This study describes and evaluates, from the perspective of pertinent system, state, and individual level theory, the unfolding of the Bush administration's strategy for addressing the North Korea nuclear issue up to the February 2007 Beijing agreement on first steps toward denuclearization of the Korean peninsula. It will explore whether that policy has been "effective harmony of different goals," as the administration has claimed, or something far less coherent and effective. At its inception, the administration's policy was grounded in a strong, though by no means universally held,preference for "asphyxiation" rather than "oxygen," for pressure and isolation rather than for rewards. However, this default policy was constrained at almost every turn by system and state level realities that drove the United States to eschew forceful unilateral action and to pursue its objectives through multilateral regional diplomacy. And yet throughout the years of six-party talks, the strong preference of core decision makers for isolation continued,pending what they hoped would be a more propitious environment to pursue a forward leaning policy,to rein in U.S. negotiators. As a result, U.S. policy often appeared to exhibit characteristics of "temporary appeasement,""hawk engagement" and "malign neglect" in which negotiations assume a primarily tactical role rather than a wholehearted effort to engage the DPRK. The apparent success of financial sanctions, coupled with the international shock wave that followed North Korea's missile and nuclear tests, might have been expected to give administration hawks the long-awaited opportunity to pursue their default policy. Despite the successes enjoyed by new financial sanctions, however, U.S. policy remained as constrained as ever by the grave deterioration of the United States' position in the Middle East and the unanticipated shift of power in congress. These constraints may in part explain the dramatic about-face in the administration's position that led ultimately to the February 13, 2007 agreement to offer the DPRK an "early harvest" in exchange for initial steps toward denuclearization. [source] Instrumentation for Simultaneous Gas and Particle Velocity Measurements at Mach,5,PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 6 2002Francis Micheli Abstract This study deals with re-entry vehicles passing through high-altitude clouds of ice particles. The particles disturb the flow field and are erosive, thereby increasing the turbulent heat flux considerably. Measurements were performed in a blow-down wind tunnel to analyze the effects of a particle field on the flow. The wind tunnel flow was seeded by two aerosols. The first was used for LDV flow velocity measurements. Its size was checked by the analysis of its passage through a plane shock wave. The second aerosol was made of uniform micro-spheres of 200,,m diameter, used to simulated the water droplets. The velocity, feeding and scattering of the latter aerosol need to be accurately measured. The velocities of the flow field and of the micro-spheres were measured simultaneously by laser velocimetry. This paper describes the instruments used to seed, ascertain and measure this flow with two aerosols. [source] The Decomposition of some RDX and HMX Based Materials in the One Dimensional Time to Explosion Apparatus.PROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 1 2007Part 2. Abstract Various methods of assessment have been applied to the One Dimensional Time to Explosion (ODTX) apparatus and experiments with the aim of allowing an estimate of the comparative violence of the explosion event to be made. Non-mechanical methods used were a simple visual inspection, measuring the increase in the void volume of the anvils following an explosion and measuring the velocity of the sound produced by the explosion over 1 metre. Mechanical methods used included monitoring piezo-electric devices inserted in the frame of the machine and measuring the rotational velocity of a rotating bar placed on the top of the anvils after it had been displaced by the shock wave. This last method, which resembles original Hopkinson Bar experiments, seemed the easiest to apply and analyse, giving relative rankings of violence and the possibility of the calculation of a "detonation" pressure. [source] The Effects of Containment on Detonation VelocityPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 1 2004Clark Souers Abstract Reactive flow cylinder code runs on six explosives were made with rate constants varying from 0.03 to 70,,s,1. Six unconfined/steel sets of original ANFO and dynamite data are presented. A means of comparing confinement effects both at constant radius and at constant detonation velocity is presented. Calculations show two qualitatively different modes of behavior. For Us/Co,1.2, where Us is the detonation velocity and Co the zero-pressure sound speed in steel, we find a sharp shock wave in the metal. The shock passes through the steel and the outer wall has a velocity jump-off. For Us/Co,1.04, we find a pressure gradient that moves at the detonation velocity. A precursor pulse drives in the explosive ahead of the detonation front. The outer wall begins to move outward at the same time the shock arrives in the explosive, and the outer wall slowly and continuously increases in velocity. The Us/Co,1.2 cylinders saturate in detonation velocity for thick walls but the Us/Co<<1.04 case does not. The unconfined cylinder shows an edge lag in the front that approximately equals the reaction zone length, but the highly confined detonation front is straight and contains no reaction zone information. The wall thickness divided by the reaction zone length yields a dimensionless wall thickness, which allows comparison of explosives with different detonation rates. Even so, a rate effect is found in the detonation velocities, which amounts to the inverse 0.15,0.5 power. [source] Shock wave induced cytoskeletal and morphological deformations in a human renal carcinoma cell lineCANCER SCIENCE, Issue 4 2006S. Fatemeh Moosavi-Nejad Effects of shock waves on the morphology and cytoskeleton of a human renal carcinoma cell line (ACHN) were investigated in vitro. ACHN monolayer cultured on a cover slide glass was treated with 10 shots of focused underwater shock waves, with 16 MPa peak pressure at the focal area of a piezoceramic shock wave generator. After exposure to the shock wave, based on the severity of morphological deformations of the treated cells, the monolayer was divided into three morphological areas; focal, marginal and intact. Morphological deformations were found to be associated with disorganization of the intracellular cytoskeletal filaments. Deformation of the cytoskeletal proteins in the treated cells were separately studied with respect to the location of the cells within the three morphological areas. Among three major cytoskeletal proteins, actin and tubulin, but not vimentin, were affected by the shock waves. The deformed cells reorganized their cytoskeletal network within 3 h with a pattern similar to the control, indicating the transient characteristic of the shock wave induced cytoskeletal damage in the surviving cells. The remaining cell fragments on the slide glass, which contained short actin filaments, indicated the important role of shear stress in damaging the cytoskeletal fibers by shock waves. (Cancer Sci 2006; 97: 296,304) [source] The Fall and Renewal of the Commission: Accountability, Contract and Administrative OrganisationEUROPEAN LAW JOURNAL, Issue 2 2000Paul Craig The fall of the Santer Commission, prompted by the Report of the Committee of Independent Experts, sent shock waves throughout the entire Community. This article seeks to examine the nature of the problems which beset the Commission, to place these within the broader context of decision-making by public bodies, and to consider also the responsibilities of the Council and European Parliament for the delivery of agreed Community policies. The article analyses in detail the Reports of the Committee of Independent Experts, and the subsequent reforms initiated by the Prodi Commission, in order to assess the prospects for improved service delivery in the future. [source] Microstructures and adiabatic shear bands formed by ballistic impact in steels and tungsten alloyFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2003Z. Q. DUAN ABSTRACT Projectiles of sintered tungsten alloy were fired directly at two kinds of steel target plates. The microstructures near the perforation of a medium, 0.45% carbon steel target plate can be identified along the radial direction as: melted and rapidly solidified layer, recrystallized fine-grained layer, deformed fine-grained layer, deformed layer and normal matrix. The adiabatic shear bands cannot be found in this intermediate strength steel. The microstructures along the radial direction of perforation of 30CrMnMo steel target plate are different from that of the medium carbon steel. There was a melted and rapidly solidified layer on the surface of the perforation, underneath there was a diffusing layer, and then fine-grained layer appeared as streamlines. Several kinds of adiabatic shear bands were found in this higher strength steel; they had different directions and widths, which were relative to the shock waves, as well as the complex deformation process of penetration. The deformation of the projectiles was rather different when they impacted on target plates of medium carbon steel and 30CrMnMo steel. The projectile that impacted on the medium carbon steel target plate was tamped and its energy dissipated slowly, while that which impacted on the 30CrMnMo steel target plate was sheared and the energy dissipated quickly. [source] Observation of neutral density variations accompanying streamer progression across air gapsIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 1 2009Tetsuo Fukuchi Member Abstract Neutral density variations accompanying progression of streamers across needle-to-rod air gaps of length 0.75 and 1 m were observed with the use of a laser shadowgraph system consisting of astronomical telescopes for beam expansion and reduction, and an acousto-optic laser deflector for high-speed imaging. The system had a spatial resolution of about 1 mm over an annular observation region of outer diameter 28 cm and inner diameter 11 cm, and a temporal resolution in the order of microseconds. The system was also used to observe neutral density variations accompanying shock waves which resulted from a spark discharge. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] | |||||||||||||||||||||||||||||||||||||||||||