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1

Relativistic blast waves in two dimensions. I - The adiabatic case

NASA Technical Reports Server (NTRS)

Approximate solutions are presented for the dynamical evolution of strong adiabatic relativistic blast waves which result from a point explosion in an ambient gas in which the density varies both with distance from the explosion center and with polar angle in axisymmetry. Solutions are analytical or quasi-analytical for the extreme relativistic case and numerical for the arbitrarily relativistic case. Some general properties of nonplanar relativistic shocks are also discussed, including the incoherence of spherical ultrarelativistic blast-wave fronts on angular scales greater than the reciprocal of the shock Lorentz factor, as well as the conditions for producing blast-wave acceleration.

Shapiro, P. R.

1979-01-01

2

Self-similar relativistic blast waves with energy injection

NASA Astrophysics Data System (ADS)

A sufficiently powerful astrophysical source with power-law luminosity in time will give rise to a self-similar relativistic blast wave with a reverse shock travelling into the ejecta and a forward shock moving into the surrounding medium. Once energy injection ceases and the last energy is delivered to the shock front, the blast wave will transit into another self-similar stage depending only on the total amount of energy injected. I describe the effect of limited duration energy injection into environments with density depending on radius as a power law, emphasizing optical/X-ray Gamma-ray Burst afterglows as applications. The blast wave during injection is treated analytically, the transition following last energy injection with one-dimensional simulations. Flux equations for synchrotron emission from the forward and reverse shock regions are provided. The reverse shock emission can easily dominate, especially with different magnetizations for both regions. Reverse shock emission is shown to support both the reported X-ray and optical correlations between afterglow plateau duration and end time flux, independently of the luminosity power-law slope. The model is demonstrated by application to bursts 120521A and 090515, and can accommodate their steep post-plateau light-curve slopes.

van Eerten, Hendrik

2014-08-01

3

Dynamics and stability of relativistic gamma-ray-bursts blast waves

NASA Astrophysics Data System (ADS)

Aims: In gamma-ray-bursts (GRBs), ultra-relativistic blast waves are ejected into the circumburst medium. We analyse in unprecedented detail the deceleration of a self-similar Blandford-McKee blast wave from a Lorentz factor 25 to the nonrelativistic Sedov phase. Our goal is to determine the stability properties of its frontal shock. Methods: We carried out a grid-adaptive relativistic 2D hydro-simulation at extreme resolving power, following the GRB jet during the entire afterglow phase. We investigate the effect of the finite initial jet opening angle on the deceleration of the blast wave, and identify the growth of various instabilities throughout the coasting shock front. Results: We find that during the relativistic phase, the blast wave is subject to pressure-ram pressure instabilities that ripple and fragment the frontal shock. These instabilities manifest themselves in the ultra-relativistic phase alone, remain in full agreement with causality arguments, and decay slowly to finally disappear in the near-Newtonian phase as the shell Lorentz factor drops below 3. From then on, the compression rate decreases to levels predicted to be stable by a linear analysis of the Sedov phase. Our simulations confirm previous findings that the shell also spreads laterally because a rarefaction wave slowly propagates to the jet axis, inducing a clear shell deformation from its initial spherical shape. The blast front becomes meridionally stratified, with decreasing speed from axis to jet edge. In the wings of the jetted flow, Kelvin-Helmholtz instabilities occur, which are of negligible importance from the energetic viewpoint. Conclusions: Relativistic blast waves are subject to hydrodynamical instabilities that can significantly affect their deceleration properties. Future work will quantify their effect on the afterglow light curves.

Meliani, Z.; Keppens, R.

2010-09-01

4

Nonlinear collisionless damping of Weibel turbulence in relativistic blast waves

NASA Astrophysics Data System (ADS)

The Weibel/filamentation instability is known to play a key role in the physics of weakly magnetized collisionless shock waves. From the point of view of high energy astrophysics, this instability also plays a crucial role because its development in the shock precursor populates the downstream with a small-scale magneto-static turbulence which shapes the acceleration and radiative processes of suprathermal particles. The present work discusses the physics of the dissipation of this Weibel-generated turbulence downstream of relativistic collisionless shock waves. It calculates explicitly the first-order nonlinear terms associated to the diffusive nature of the particle trajectories. These corrections are found to systematically increase the damping rate, assuming that the scattering length remains larger than the coherence length of the magnetic fluctuations. The relevance of such corrections is discussed in a broader astrophysical perspective, in particular regarding the physics of the external relativistic shock wave of a gamma-ray burst.

Lemoine, Martin; Lemoine

2015-01-01

5

NASA Technical Reports Server (NTRS)

A relativistic blast-wave version of a signal-screen model is developed which can adequately explain the details of the flux-density and structural variations of compact extragalactic radio sources. The relativistic motion implied by flux variations is analyzed with respect to the synchrotron spectrum of the BL Lac object AO 0235+164 observed during outbursts, and a signal-screen model for rapidly expanding shells produced by ultrarelativistic blast waves is examined. The approximate observed structure of the blast wave at three stages in its evolution is illustrated, each stage is described, and the model is applied to the flux density outburst in AO 0235+164 observed in late 1975. The results show that a relativistic blast-wave model can in general reproduce the main features of the observed flux variations in compact sources. Some problems with the proposed model are briefly discussed.

Marscher, A. P.

1978-01-01

6

Ultra-high-energy cosmic ray acceleration by relativistic blast waves

We consider the acceleration of charged particles at the ultra-relativistic shocks, with Lorentz factors \\Gamma_s >> 1 relative to the upstream medium, arising in relativistic fireball models of gamma-ray bursts (GRBs). We show that for Fermi-type shock acceleration, particles initially isotropic in the upstream medium can gain a factor of order \\Gamma_s^2 in energy in the first shock crossing cycle, but that the energy gain factor for subsequent shock crossing cycles is only of order 2, because for realistic deflection processes particles do not have time to re-isotropise upstream before recrossing the shock. We evaluate the maximum energy attainable and the efficiency of this process, and show that for a GRB fireball expanding into a typical interstellar medium, these exclude the production of ultra-high-energy cosmic rays (UHECRs), with energies in the range 10^{18.5} - 10^{20.5} eV, by the blast wave. We propose, however, that in the context of neutron star binaries as the progenitors of GRBs, relativistic ions from the pulsar wind bubbles produced by these systems could be accelerated by the blast wave. We show that if the known binary pulsars are typical, the maximum energy, efficiency, and spectrum in this case can account for the observed population of UHECRs.

Yves A. Gallant; Abraham Achterberg

1999-03-01

7

Revisiting the Emission from Relativistic Blast Waves in a Density-jump Medium

NASA Astrophysics Data System (ADS)

Re-brightening bumps are frequently observed in gamma-ray burst afterglows. Many scenarios have been proposed to interpret the origin of these bumps, of which a blast wave encountering a density-jump in the circumburst environment has been questioned by recent works. We develop a set of differential equations to calculate the relativistic outflow encountering the density-jump by extending the work of Huang et al. This approach is a semi-analytic method and is very convenient. Our results show that late high-amplitude bumps cannot be produced under common conditions, rather only a short plateau may emerge even when the encounter occurs at an early time (<104 s). In general, our results disfavor the density-jump origin for those observed bumps, which is consistent with the conclusion drawn from full hydrodynamics studies. The bumps thus should be caused by other scenarios.

Geng, J. J.; Wu, X. F.; Li, Liang; Huang, Y. F.; Dai, Z. G.

2014-09-01

8

The particle production of Kaon and $\\Lambda$ are studied in nucleus-nucleus collisions at relativistic energy based on a chemical equilibrium blast-wave model. The transverse momentum spectra of Kaon and $\\Lambda$ at the kinetic freeze-out stage from our model are in good agreement with the experimental results. The kinetic freeze-out parameters of temperature ($T_{kin}$) and radial flow parameter $\\rho_{0}$ are presented for the FOPI, RHIC and LHC energies. And the resonance decay effect is also discussed. The systematic study for beam energy dependence of the strangeness particle production will help us to better understand the properties of the matter created in heavy-ion collisions at the kinetic freeze-out stage.

Song Zhang; Yu-Gang Ma; Jin-Hui Chen; Chen Zhong

2014-11-06

9

Curved characteristics behind blast waves.

NASA Technical Reports Server (NTRS)

The behavior of nonisentropic flow behind a propagating blast wave is theoretically studied. Exact solutions, expressed in closed form in terms of elementary functions, are presented for three sets of curved characteristicseind a self-similar, strong blast wave.

Laporte, O.; Chang, T. S.

1972-01-01

10

Blast waves in rotating media.

NASA Technical Reports Server (NTRS)

The model investigated involves a cylindrically symmetric blast wave generated by an infinitely long line explosion in a cold and homogeneous gas rotating rigidly in its self-gravitational field. It is found that within the context of rotation in a gravitational field a blast wave will not adopt the one-zone form familiar from similarity solutions but, rather, a two-zone form. The inner compression zone arises as a response to the presence of the restoring force, which drives a rarefaction wave into the outer compression zone.

Rossner, L. F.

1972-01-01

11

Simulation of Blast Waves with Headwind

NASA Technical Reports Server (NTRS)

The blast wave resulting from an explosion was simulated to provide guidance for models estimating risks for human spacecraft flight. Simulations included effects of headwind on blast propagation, Blasts were modelled as an initial value problem with a uniform high energy sphere expanding into an ambient field. Both still air and cases with headwind were calculated.

Olsen, Michael E.; Lawrence, Scott W.; Klopfer, Goetz H.; Mathias, Dovan; Onufer, Jeff T.

2005-01-01

12

Cygnus Loop Supernova Blast Wave

NASA Technical Reports Server (NTRS)

This is an image of a small portion of the Cygnus Loop supernova remnant, which marks the edge of a bubble-like, expanding blast wave from a colossal stellar explosion, occurring about 15,000 years ago. The HST image shows the structure behind the shock waves, allowing astronomers for the first time to directly compare the actual structure of the shock with theoretical model calculations. Besides supernova remnants, these shock models are important in understanding a wide range of astrophysical phenomena, from winds in newly-formed stars to cataclysmic stellar outbursts. The supernova blast is slamming into tenuous clouds of insterstellar gas. This collision heats and compresses the gas, causing it to glow. The shock thus acts as a searchlight revealing the structure of the interstellar medium. The detailed HST image shows the blast wave overrunning dense clumps of gas, which despite HST's high resolution, cannot be resolved. This means that the clumps of gas must be small enough to fit inside our solar system, making them relatively small structures by interstellar standards. A bluish ribbon of light stretching left to right across the picture might be a knot of gas ejected by the supernova; this interstellar 'bullet' traveling over three million miles per hour (5 million kilometres) is just catching up with the shock front, which has slowed down by ploughing into interstellar material. The Cygnus Loop appears as a faint ring of glowing gases about three degrees across (six times the diameter of the full Moon), located in the northern constellation, Cygnus the Swan. The supernova remnant is within the plane of our Milky Way galaxy and is 2,600 light-years away. The photo is a combination of separate images taken in three colors, oxygen atoms (blue) emit light at temperatures of 30,000 to 60,000 degrees Celsius (50,000 to 100,000 degrees Farenheit). Hydrogen atoms (green) arise throughout the region of shocked gas. Sulfur atoms (red) form when the gas cools to around 10,000 degrees Celsius (18,000 degrees Farenheit).

1993-01-01

13

On the Propagation and Interaction of Spherical Blast Waves

NASA Technical Reports Server (NTRS)

The characteristics and the scaling laws of isolated spherical blast waves have been briefly reviewed. Both self-similar solutions and numerical solutions of isolated blast waves are discussed. Blast profiles in the near-field (strong shock region) and the far-field (weak shock region) are examined. Particular attention is directed at the blast overpressure and shock propagating speed. Consideration is also given to the interaction of spherical blast waves. Test data for the propagation and interaction of spherical blast waves emanating from explosives placed in the vicinity of a solid propellant stack are presented. These data are discussed with regard to the scaling laws concerning the decay of blast overpressure.

Kandula, Max; Freeman, Robert

2007-01-01

14

Isothermal blast wave model of supernova remnants

NASA Technical Reports Server (NTRS)

The validity of the 'adiabatic' assumption in supernova-remnant calculations is examined, and the alternative extreme of an isothermal blast wave is explored. It is concluded that, because of thermal conductivity, the large temperature gradients predicted by the adiabatic model probably are not maintained in nature. Self-similar solutions to the hydrodynamic equations for an isothermal blast wave have been found and studied. These solutions are then used to determine the relationship between X-ray observations and inferred parameters of supernova remnants. A comparison of the present results with those for the adiabatic model indicates differences which are less than present observational uncertainties. It is concluded that most parameters of supernova remnants inferred from X-ray measurements are relatively insensitive to the specifics of the blast-wave model.

Solinger, A.; Buff, J.; Rappaport, S.

1975-01-01

15

Computation of blast wave-obstacle interactions

NASA Technical Reports Server (NTRS)

Numerical simulations of the interaction of a planar blast wave with various obstacles are presented. These obstacles are either ground structures or vehicles flying in the atmosphere. For a structure on the ground, the blast wave encounter is side-on, while for the flying vehicles the encounter is either head-on or oblique. Second-order accurate, finite-difference, and shock-capturing procedures are employed to solve the two-dimensional, axisymmetric, and three-dimensional unsteady Euler equations. Results are presented for the flow field consisting of blast wave striking obstacles that are at rest, moving subsonically and moving supersonically. Comparison of the numerical results with experimental data for a configuration at rest substantiates the validity of this approach and its potential as a flow analysis tool.

Champney, J. M.; Chaussee, D. S.; Kutler, P.

1982-01-01

16

Blast wave simulation with ground surface effect

NASA Astrophysics Data System (ADS)

Unsteady flowfield generated by the finite strength of a shock wave is computationally simulated with the discretization method. The results indicate that the overpressure depends on the ground surface geometry as well as the distance from the point of explosion. The present approach using the new computational-fluid-dynamic technology may improve the existing theory for estimating the unsteady motion and decay of blast waves and eventually lead to better estimation of the safety distance for rocket launching.

Fujii, Kozo; Shimizu, Fumio; Tamura, Yoshiaki; Higashino, Fumio; Hinada, Motoki; Akiba, Ryojiro

17

Boundary-layer theory for blast waves

NASA Technical Reports Server (NTRS)

It is profitable to consider the blast wave as a flow field consisting of two regions: the outer, which retains the properties of the inviscid solution, and the inner, which is governed by flow equations including terms expressing the effects of heat transfer and, concomitantly, viscosity. The latter region thus plays the role of a boundary layer. Reported here is an analytical method developed for the study of such layers, based on the matched asymptotic expansion technique combined with patched solutions.

Kim, K. B.; Berger, S. A.; Kamel, M. M.; Korobeinikov, V. P.; Oppenheim, A. K.

1975-01-01

18

Biologic response to complex blast waves

Small, bare charges were detonated inside an M59 armored personnel carrier (APC) in an attempt to simulate the complex blast waves generated by the jets from shaped-charge warheads penetrating into armored vehicles. Anesthetized sheep were placed inside the APC at 92- and 122-cm ranges from 57- or 113-g pentolite charges. Pressure-time was measured by pressure transducers either mounted on the animals or free standing at comparable ranges on the opposite side of the vehicle. In general, the waveforms were characterized by an initial shock wave of less than 1-msec duration followed by repeated reflections of decreasing magnitude. No deaths nor lung hemorrhages were observed, but all the animals sustained severe ear injury. Animals subjected to peak overpressures of 1.2 to 2.3 bar from the 113-g explosions also received slight non-auditory blast injuries to the upper respiratory and gastrointestinal tracts; those exposed to peak overpressures of just under 1 bar from the 57-g charges did not. The non-auditory blast injuries inside the APC were more severe than those sustained by sheep at comparable distances from 113-g charges in the open. The results suggested that the biological consequences of a complex wave of the type encountered in this study can be equated approximately to a Friedlander wave with a peak overpressure equal to that of the complex wave and with a total impulse equal to the impulse over the first 2 to 3 msec of the complex wave. 9 refs., 7 figs., 1 tab.

Richmond, D.R.; Yelverton, J.T.; Fletcher, E.R.; Phillips, Y.Y.

1985-01-01

19

Computation of viscous blast wave flowfields

NASA Technical Reports Server (NTRS)

A method to determine unsteady solutions of the Navier-Stokes equations was developed and applied. The structural finite-volume, approximately factored implicit scheme uses Newton subiterations to obtain the spatially and temporally second-order accurate time history of the interaction of blast-waves with stationary targets. The inviscid flux is evaluated using MacCormack's modified Steger-Warming flux or Roe flux difference splittings with total variation diminishing limiters, while the viscous flux is computed using central differences. The use of implicit boundary conditions in conjunction with a telescoping in time and space method permitted solutions to this strongly unsteady class of problems. Comparisons of numerical, analytical, and experimental results were made in two and three dimensions. These comparisons revealed accurate wave speed resolution with nonoscillatory discontinuity capturing. The purpose of this effort was to address the three-dimensional, viscous blast-wave problem. Test cases were undertaken to reveal these methods' weaknesses in three regimes: (1) viscous-dominated flow; (2) complex unsteady flow; and (3) three-dimensional flow. Comparisons of these computations to analytic and experimental results provided initial validation of the resultant code. Addition details on the numerical method and on the validation can be found in the appendix. Presently, the code is capable of single zone computations with selection of any permutation of solid wall or flow-through boundaries.

Atwood, Christopher A.

1991-01-01

20

Non-equilibrium ionized blast wave

NASA Technical Reports Server (NTRS)

The structure of a cylindrical blast wave with ionization at non-LTE conditions was calculated using equations previously developed by Wu and Fu (1970). The degree of ionization was predicted by a modified Saha equation. Temperature profiles show that the temperature at non-LTE conditions is lower than at LTE near the shock front. This corresponds to a higher degree of ionization for the non-LTE limit, which indicates that the neutral gas absorption is much more efficient at non-LTE than at the LTE limit. The decaying velocity under non-LTE is approximately 15% less than under LTE.

Wu, S. T.

1974-01-01

21

Cosmic ray origins in supernova blast waves

NASA Astrophysics Data System (ADS)

We extend the self-similar solution derived by Chevalier for a Sedov blast wave accelerating cosmic rays (CR) to show that the Galactic CR population can be divided into (A) CR with energies above ˜200 GeV released upstream during CR acceleration by supernova remnants (SNR), (B) CR advected into the interior of the SNR during expansion and then released from the SNR at the end of its life to provide the Galactic CR component below ˜200 GeV. The intersection between the two populations may correspond to a measured change in the Galactic CR spectral index at this energy.

Bell, A. R.

2015-03-01

22

STUDY OF BLAST WAVE IMPACT ON CONCRETE AJIT GEEVARGHESE JOHN

STUDY OF BLAST WAVE IMPACT ON CONCRETE by AJIT GEEVARGHESE JOHN Presented to the Faculty on numerous occasions to run my experiments. I would also express my gratitude to Kenneth without whom I would OF BLAST WAVE IMPACT ON CONCRETE Publication No. ______ Ajit Geevarghese John, M.S. The University of Texas

Texas at Arlington, University of

23

ERIC Educational Resources Information Center

The Lorentz transformation applies directly to the kinematics of moving particles viewed as geometric points. Wave propagation, on the other hand, involves moving planes which are extended objects defined by simultaneity. By treating a plane wave as a geometric object moving at the phase velocity, novel results are obtained that illustrate the…

Houlrik, Jens Madsen

2009-01-01

24

On the Interaction and Coalescence if Spherical Blast Waves

NASA Technical Reports Server (NTRS)

The scaling and similarity laws concerning the propagation of isolated spherical blast waves are briefly reviewed. Both point source explosions and high pressure gas explosions are considered. Test data on blast overpressure from the interaction and coalescence of spherical blast waves emanating from explosives in the form of shaped charges of different strength placed in the vicinity of a solid propellant stack are presented. These data are discussed with regard to the scaling laws concerning the decay of blast overpressure. The results point out the possibility of detecting source explosions from far-field pressure measurements.

Kandula, Max; Freeman, Robert J.

2005-01-01

25

Evolution of blast wave profiles in simulated air blasts: experiment and computational modeling

NASA Astrophysics Data System (ADS)

Shock tubes have been extensively used in the study of blast traumatic brain injury due to increased incidence of blast-induced neurotrauma in Iraq and Afghanistan conflicts. One of the important aspects in these studies is how to best replicate the field conditions in the laboratory which relies on reproducing blast wave profiles. Evolution of the blast wave profiles along the length of the compression-driven air shock tube is studied using experiments and numerical simulations with emphasis on the shape and magnitude of pressure time profiles. In order to measure dynamic pressures of the blast, a series of sensors are mounted on a cylindrical specimen normal to the flow direction. Our results indicate that the blast wave loading is significantly different for locations inside and outside of the shock tube. Pressure profiles inside the shock tube follow the Friedlander waveform fairly well. Upon approaching exit of the shock tube, an expansion wave released from the shock tube edges significantly degrades the pressure profiles. For tests outside the shock tube, peak pressure and total impulse reduce drastically as we move away from the exit and majority of loading is in the form of subsonic jet wind. In addition, the planarity of the blast wave degrades as blast wave evolves three dimensionally. Numerical results visually and quantitatively confirm the presence of vortices, jet wind and three-dimensional expansion of the planar blast wave near the exit. Pressure profiles at 90° orientation show flow separation. When cylinder is placed inside, this flow separation is not sustained, but when placed outside the shock tube this flow separation is sustained which causes tensile loading on the sides of the cylinder. Friedlander waves formed due to field explosives in the intermediate-to far-field ranges are replicated in a narrow test region located deep inside the shock tube.

Chandra, N.; Ganpule, S.; Kleinschmit, N. N.; Feng, R.; Holmberg, A. D.; Sundaramurthy, A.; Selvan, V.; Alai, A.

2012-09-01

26

Reactive Blast Waves from Composite Charges

Investigated here is the performance of composite explosives - measured in terms of the blast wave they drive into the surrounding environment. The composite charge configuration studied here was a spherical booster (1/3 charge mass), surrounded by aluminum (Al) powder (2/3 charge mass) at an initial density of {rho}{sub 0} = 0.604 g/cc. The Al powder acts as a fuel but does not detonate - thereby providing an extreme example of a 'non-ideal' explosive (where 2/3 of the charge does not detonate). Detonation of the booster charge creates a blast wave that disperses the Al powder and ignites the ensuing Al-air mixture - thereby forming a two-phase combustion cloud embedded in the explosion. Afterburning of the booster detonation products with air also enhances and promotes the Al-air combustion process. Pressure waves from such reactive blast waves have been measured in bomb calorimeter experiments. Here we describe numerical simulations of those experiments. A Heterogeneous Continuum Model was used to model the dispersion and combustion of the Al particle cloud. It combines the gasdynamic conservation laws for the gas phase with a dilute continuum model for the dispersed phase, as formulated by Nigmatulin. Inter-phase mass, momentum and energy exchange are prescribed by phenomenological models of Khasainov. It incorporates a combustion model based on mass conservation laws for fuel, air and products; source/sink terms are treated in the fast-chemistry limit appropriate for such gasdynamic fields, along with a model for mass transfer from the particle phase to the gas. The model takes into account both the afterburning of the detonation products of the booster with air, and the combustion of the Al particles with air. The model equations were integrated by high-order Godunov schemes for both the gas and particle phases. Adaptive Mesh Refinement (AMR) was used to capture the energy-bearing scales of the turbulent flow on the computational grid, and to track/resolve reaction zones. Numerical simulations of the explosion fields from 1.5-g and 10-kg composite charges were performed. Computed pressure histories (red curve) are compared with measured waveforms (black curves) in Fig. 1. Comparison of these results with a waveform for a non-combustion case in nitrogen (blue curve) demonstrates that a reactive blast wave was formed. Cross-sectional views of the temperature field at various times are presented in Fig. 2, which shows that the flow is turbulent. Initially, combustion occurs at the fuel-air interface, and the energy release rate is controlled by the rate of turbulent mixing. Eventually, oxidizer becomes distributed throughout the cloud via ballistic mixing of the particles with air; energy release then occurs in a distributed combustion mode, and Al particle kinetics controls the energy release rate. Details of the Heterogeneous Continuum Model and results of the numerical simulations of composite charge explosions will be described in the paper.

Kuhl, A L; Bell, J B; Beckner, V E

2009-10-16

27

Investigation of ultrafast laser-driven radiative blast waves.

We have examined the evolution of cylindrically symmetric blast waves produced by the deposition of femtosecond laser pulses in gas jets. In high- Z gases radiative effects become important. We observe the production of an ionization precursor ahead of the shock front and deceleration parameters below the adiabatic value of 1/2 (for a cylinder), an effect expected when the blast wave loses energy by radiative cooling. Despite significant radiative cooling, the blast waves do not appear to develop thin shell instabilities expected for strongly radiative waves. This is believed to be due to the stabilizing effect of a relatively thick blast wave shell resulting in part from electron thermal conduction effects. PMID:11497951

Edwards, M J; MacKinnon, A J; Zweiback, J; Shigemori, K; Ryutov, D; Rubenchik, A M; Keilty, K A; Liang, E; Remington, B A; Ditmire, T

2001-08-20

28

Ponderomotive acceleration by relativistic waves

NASA Astrophysics Data System (ADS)

In the extreme high intensity regime of electromagnetic (EM) waves in plasma, the acceleration process is found to be dominated by the ponderomotive acceleration (PA). While the wakefields driven by the ponderomotive force of the relativistic intensity EM waves are important, they may be overtaken by the PA itself in the extreme high intensity regime when the dimensionless vector potential a0 of the EM waves far exceeds unity. The energy gain by this regime (in 1D) is shown to be (approximately) proportional to a0 2 . Before reaching this extreme regime, the coexistence of the PA and the wakefield acceleration is observed where the wave structures driven by the wakefields show the phenomenon of multiple and folded wave breakings. Investigated are various signatures of the acceleration processes such as the dependence on the mass ratio for the energy gain as well as the energy spectral features. The relevance to high energy cosmic ray acceleration and to the relativistic laser acceleration is considered.

Lau, C. K.; Yeh, P. C.; Luk, O.; McClenaghan, J.; Ebisuzaki, T.; Tajima, T.

2015-02-01

29

Characterising the acceleration phase of blast wave formation

NASA Astrophysics Data System (ADS)

Intensely heated, localised regions in uniform fluids will rapidly expand and generate an outwardly propagating blast wave. The Sedov-Taylor self-similar solution for such blast waves has long been studied and applied to a variety of scenarios. A characteristic time for their formation has also long been identified using dimensional analysis, which by its very nature, can offer several interpretations. We propose that, rather than simply being a characteristic time, it may be interpreted as the definitive time taken for a blast wave resulting from an intense explosion in a uniform media to contain its maximum kinetic energy. A scaling relation for this measure of the acceleration phase, preceding the establishment of the blast wave, is presented and confirmed using a 1D planar hydrodynamic model.

Fox, T. E.; Robinson, A. P. L.; Schmitz, H.; Pasley, J.

2014-10-01

30

Numerical solutions for unsteady laminar boundary layers behind blast waves

NASA Astrophysics Data System (ADS)

The paper presents the similarity solutions obtained for laminar boundary layers behind a power-law shock associated with a blast wave. A finite-difference method based on Blottner's numerical scheme (1970) is used. The results are valid, at all times, in the entire flow region between the shock front and the immediate vicinity of the blast-wave origin provided the boundary layer remains laminar.

Liu, S. W.; Mirels, H.

1980-04-01

31

Visualization of blast waves created by exploding bridge wires

Blast waves created by small exploding bridge wires are used as a test bed for the development of a particle image velocimetry\\u000a (PIV) technique that uses polymers, seeded with scattering particles, as dynamic witness plates. Combined with pulsed, incoherent\\u000a schlieren photography, the PIV method permits visualization of the instantaneous velocity vector field in a plane cutting\\u000a through the blast wave.

M. J. Murphy; R. J. Adrian; D. S. Stewart; G. S. Elliott; K. A. Thomas; J. E. Kennedy

2005-01-01

32

Simple waves in relativistic fluids.

We consider the Riemann problem for relativistic flows of polytropic fluids and find relations for the flow characteristics. Evolution of physical quantities takes especially simple form for the case of cold magnetized plasmas. We find exact explicit analytical solutions for one-dimensional expansion of magnetized plasma into vacuum, valid for arbitrary magnetization. We also consider expansion into cold unmagnetized external medium both for stationary initial conditions and for initially moving plasma, as well as reflection of rarefaction wave from a wall. We also find self-similar structure of three-dimensional magnetized outflows into vacuum, valid close to the plasma-vacuum interface. PMID:21230574

Lyutikov, Maxim

2010-11-01

33

NO FLARES FROM GAMMA-RAY BURST AFTERGLOW BLAST WAVES ENCOUNTERING SUDDEN CIRCUMBURST DENSITY CHANGE

Afterglows of gamma-ray bursts are observed to produce light curves with the flux following power-law evolution in time. However, recent observations reveal bright flares at times on the order of minutes to days. One proposed explanation for these flares is the interaction of a relativistic blast wave with a circumburst density transition. In this paper, we model this type of interaction computationally in one and two dimensions, using a relativistic hydrodynamics code with adaptive mesh refinement called RAM, and analytically in one dimension. We simulate a blast wave traveling in a stellar wind environment that encounters a sudden change in density, followed by a homogeneous medium, and compute the observed radiation using a synchrotron model. We show that flares are not observable for an encounter with a sudden density increase, such as a wind termination shock, nor for an encounter with a sudden density decrease. Furthermore, by extending our analysis to two dimensions, we are able to resolve the spreading, collimation, and edge effects of the blast wave as it encounters the change in circumburst medium. In all cases considered in this paper, we find that a flare will not be observed for any of the density changes studied.

Gat, Ilana; Van Eerten, Hendrik; MacFadyen, Andrew [Center for Cosmology and Particle Physics, Physics Department, New York University, New York, NY 10003 (United States)

2013-08-10

34

Measurement of Blast Waves from Bursting Pressureized Frangible Spheres

NASA Technical Reports Server (NTRS)

Small-scale experiments were conducted to obtain data on incident overpressure at various distances from bursting pressurized spheres. Complete time histories of blast overpressure generated by rupturing glass spheres under high internal pressure were obtained using eight side-on pressure transducers. A scaling law is presented, and its nondimensional parameters are used to compare peak overpressures, arrival times, impulses, and durations for different initial conditions and sizes of blast source. The nondimensional data are also compared, whenever possible, with results of theoretical calculations and compiled data for Pentolite high explosive. The scaled data are repeatable and show significant differences from blast waves generated by condensed high-explosives.

Esparza, E. D.; Baker, W. E.

1977-01-01

35

Laminar boundary layers behind blast and detonation waves

NASA Astrophysics Data System (ADS)

Boundary layer flows in air behind nonuniform strong blast waves and in the burned gas of a stoichiometric mixture of hydrogen and oxygen behind uniform Chapman-Jouguet detonation waves were investigated. The results show that the Prandtl number profoundly influences boundary layer flow. For a blast wave and Pr less than unity it controls a boundary layer velocity overshoot which decreases with increasing Prandtl number. For a Chapman-Jouguet detonation wave similar results are obtained for a Pr = 0.72; however, for an actual Pr = 2.26, a flow reversal occurs away from the wave where the inviscid flow velocity approaches a small value. The viscous exponent was found to have a significant effect on the wall shear stresses and heat transfer. The effect of the wall temperature is small. Velocity profiles were computed for spherical and planar detonation waves. Because of the rapid decrease in density behind a blast wave, the boundary layer thickness becomes very much larger than their detonation wave counterparts at the same wave velocity (but different physical conditions). The velocity boundary layer thickness in air behind a quasistationary planar shock wave is somewhat more than for a planar detonation wave at the same wave velocity (but in different gases). The heat transfer to the wall behind a planar detonation wave was calculated.

Du, X.; Liu, W. S.; Glass, I. I.

1982-08-01

36

3D Tomographic imaging of colliding cylindrical blast waves

NASA Astrophysics Data System (ADS)

The interaction of strong shocks & radiative blast waves is believed to give rise to the turbulent, knotted structures commonly observed in extended astrophysical objects. Modeling these systems is however extremely challenging due to the complex interplay between hydrodynamics, radiation and atomic physics. As a result we have been developing laboratory scale blast wave collision experiments to provide high quality data for code benchmarking, & to improve our physical understanding. We report on experimental & numerical investigations of the collision dynamics of counter propagating strong (>Mach 50) cylindrical thin-shelled blast waves driven by focusing intense laser pulses into an extended medium of atomic clusters. In our test system the blast wave collision creates strongly asymmetric electron density profiles, precluding the use of Abel inversion methods. In consequence we have employed a new tomographic imaging technique, allowing us to recover the full 3D, time framed electron density distribution. Tomography & streaked Schlieren imaging enabled tracking of radial & longitudinal mass flow & the investigation of Mach stem formation as pairs of blast waves collided. We have compared our experimental system to numerical simulations by the 3D magnetoresistive hydrocode GORGON.

Smith, R. A.; Lazarus, J.; Hohenberger, M.; Robinson, J.; Marocchino, A.; Chittenden, J.; Dunne, M.; Moore, A.; Gumbrell, E.

2007-11-01

37

Rapid miniature fiber optic pressure sensors for blast wave measurements

NASA Astrophysics Data System (ADS)

Traumatic brain injury (TBI) is a serious potential threat to soldiers who are exposed to explosions. Since the pathophysiology of TBI associated with a blast wave is not clearly defined, it is crucial to have a sensing system to accurately quantify the blast wave dynamics. This paper presents an ultra-fast fiber optic pressure sensor based on Fabry-Perot (FP) interferometric principle that is capable of measuring the rapid pressure changes in a blast event. The blast event in the experiment was generated by a starter pistol blank firing at close range, which produced a more realistic wave profile compared to using compressed air driven shock tubes. To the authors' knowledge, it is also the first study to utilize fiber optic pressure sensors to measure the ballistics shock wave of a pistol firing. The results illustrated that the fiber optic pressure sensor has a rise time of 200 ns which demonstrated that the sensor has ability to capture the dynamic pressure transient during a blast event. Moreover, the resonant frequency of the sensor was determined to be 4.11 MHz, which agrees well with the specific designed value.

Zou, Xiaotian; Wu, Nan; Tian, Ye; Niezrecki, Christopher; Chen, Julie; Wang, Xingwei

2013-02-01

38

Some properties of adiabatic blast waves in preexisting cavities

NASA Technical Reports Server (NTRS)

Cox and Anderson (1982) have conducted an investigation regarding an adiabatic blast wave in a region of uniform density and finite external pressure. In connection with an application of the results of the investigation to a study of interstellar blast waves in the very hot, low-density matrix, it was found that it would be desirable to examine situations with a positive radial density gradient in the ambient medium. Information concerning such situations is needed to learn about the behavior of blast waves occurring within preexisting, presumably supernova-induced cavities in the interstellar mass distribution. The present investigation is concerned with the first steps of a study conducted to obtain the required information. A review is conducted of Sedov's (1959) similarity solutions for the dynamical structure of any explosion in a medium with negligible pressure and power law density dependence on radius.

Cox, D. P.; Franco, J.

1981-01-01

39

Quick reproduction of blast-wave flow-field properties of nuclear, TNT, and ANFO explosions

In many instances, extensive blast-wave flow-field properties are required in gasdynamics research studies of blast-wave loading and structure response, and in evaluating the effects of explosions on their environment. This report provides a very useful computer code, which can be used in conjunction with the DNA Nuclear Blast Standard subroutines and code, to quickly reconstruct complete and fairly accurate blast-wave

C. P. T. Groth

1986-01-01

40

Relativistic Bernstein waves in a degenerate plasma

Bernstein mode for a relativistic degenerate electron plasma is investigated. Using relativistic Vlasov-Maxwell equations, a general expression for the conductivity tensor is derived and then employing Fermi-Dirac distribution function a generalized dispersion relation for the Bernstein mode is obtained. Two limiting cases, i.e., non-relativistic and ultra-relativistic are discussed. The dispersion relations obtained are also graphically presented for some specific values of the parameters depicting how the propagation characteristics of Bernstein waves as well as the Upper Hybrid oscillations are modified with the increase in plasma number density.

Ali, Muddasir; Hussain, Azhar [Department of Physics, G.C. University, Lahore 54000 (Pakistan); Salam Chair in Physics, G.C. University, Lahore 54000 (Pakistan); Murtaza, G. [Salam Chair in Physics, G.C. University, Lahore 54000 (Pakistan)

2011-09-15

41

A systematic exposition of the conservation equations for blast waves.

NASA Technical Reports Server (NTRS)

In order to provide a rational background for the analysis of experimental observations of blast wave phenomena, the conservation equations governing their nonsteady flow field are formulated in a general manner, without the usual restrictions imposed by an equation of state, and with proper account taken, by means of source terms, of other effects which, besides the inertial terms that conventionally dominate these equations, can affect the flow. Taking advantage of the fact that a blast wave can be generally considered as a spatially one-dimensional flow field whose nonsteady behavior can be regarded, consequently, as a function of just two independent variables, two generalized blast wave coordinates are introduced, one associated with the front of the blast wave and the other with its flow field. The conservation equations are accordingly transformed into this coordinate system, acquiring thereby a comprehensive character, in that they refer then to any frame of reference, being applicable, in particular, to problems involving either space or time profiles of the gas-dynamic parameters in the Eulerian system, or time profiles in the Lagrangian system.

Oppenheim, A. K.; Lundstrom, E. A.; Kuhl, A. L.; Kamel, M. M.

1971-01-01

42

Relativistic electron acceleration by oblique whistler waves

Test-particle simulations of electrons interacting with finite-amplitude, obliquely propagating whistler waves are carried out in order to investigate the acceleration of relativistic electrons by these waves. According to the present findings, an efficient acceleration of relativistic electrons requires a narrow range of oblique propagation angles, close to the whistler resonance cone angle, when the wave amplitude is held constant at relatively low value. For a constant wave propagation angle, it is found that a range of oblique whistler wave amplitudes permits the acceleration of relativistic electrons to O(MeV) energies. An initial distribution of test electrons is shown to form a power-law distribution when plotted in energy space. It is also found that the acceleration is largely uniform in electron pitch-angle space.

Yoon, Peter H. [Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States) [Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States); School of Space Research, Kyung Hee University, Yongin-Si, Gyeonggi-Do 446-701 (Korea, Republic of); Pandey, Vinay S. [National Institute of Technology Delhi, Dwarka, Delhi—110077 (India)] [National Institute of Technology Delhi, Dwarka, Delhi—110077 (India); Lee, Dong-Hun [School of Space Research, Kyung Hee University, Yongin-Si, Gyeonggi-Do 446-701 (Korea, Republic of)] [School of Space Research, Kyung Hee University, Yongin-Si, Gyeonggi-Do 446-701 (Korea, Republic of)

2013-11-15

43

Blast wave reflection trajectories from a height of burst

Consideration is given to an explosive charge (TNT) detonated at various heights of burst above a perfect reflecting planar surface in air. Variations of the incident shock Mach number M(s) of the spherical blast wave front as it decays, and the corresponding wedge angle theta(w), are plotted on a two-dimensional shock wave reflection transition map in the M(s), theta(w) plane.

T. C. J. Hu; I. I. Glass

1986-01-01

44

Blast waves in atomic cluster media using intense laser pulses.

NASA Astrophysics Data System (ADS)

We report on the progress of experimental and numerical investigations of the dynamics of strong (>Mach 50) blast waves driven by focusing sub-ps laser pulses into an extended medium of atomic clusters. A gas of atomic clusters is an extraordinarily efficient absorber of intense laser light and can be used to create high energy density plasmas with tabletop laser systems. These HED plasmas can launch shocks and strongly radiative blast waves with dimensionless parameters scalable to astrophysical objects such as supernova remnants, and have been used by us in a number of shock evolution and collision studies. To date such experiments have been conducted with modest laser energies of <1J. In order to study processes such as the Vishniac overstability and cooling instability in these systems significantly more input energy may be required due to the weak variation of blast wave velocity with deposited energy Vb E^1/4. We report on the scaling of cluster blast wave experiments to laser energies up 0.5kJ using the Vulcan laser at RAL. An extensive suite of diagnostics including multi-frame optical probe systems, streaked Schlieren imaging and keV imaging and spectroscopy was fielded in order to study the growth of spatial and temporal instabilities. To better match astrophysical scenarios with strong radiative pre-heat of material upstream of the shock an additional radiation field was also introduced using a secondary laser heated gold foil target and grazing incidence XUV guiding structure. This allowed us to compare blast wave propagation into cold versus hot ionized upstream gases. These experimental systems provide a useful test bed against which to benchmark numerical simulations, and have been compared to the 3D magnetoresistive hydrocode GORGON and radiation-hydrodynamics code NYM.

Smith, Roland

2008-04-01

45

Simulation of blast-induced, early-time intracranial wave physics leading to traumatic brain injury.

U.S. soldiers are surviving blast and impacts due to effective body armor, trauma evacuation and care. Blast injuries are the leading cause of traumatic brain injury (TBI) in military personnel returning from combat. Understanding of Primary Blast Injury may be needed to develop better means of blast mitigation strategies. The objective of this paper is to investigate the effects of blast direction and strength on the resulting mechanical stress and wave energy distributions generated in the brain.

Taylor, Paul Allen; Ford, Corey C. (University of New Mexico, Albuquerque, NM)

2008-04-01

46

Reverse shock wave in relativistic explosions

NASA Astrophysics Data System (ADS)

The dynamical evolution of a relativistic explosion in a homogeneous medium is studied by means of a time-dependent, hydrodynamic code. When the expanding velocity of the shock front reduces to the sound velocity in the relativistic fluid, the reverse shock wave propagating inward through the expanding material is generated. The radius of the turning point of the reverse shock wave is proportional to the explosion energy and hardly depends on the mass of the explosion products. In the case of the non-relativistic explosion, the reverse shock wave is generated just after the free expansion stage. The radius of the turning point of the reverse shock wave is proportional to the mass of the explosion products and little depends on the explosion energy. In both cases of the non-relativistic and relativistic explosion, the reverse shock wave is strong in a spherical explosion and weak in a cylindrical one. The plane symmetric explosion does not generate the reverse shock wave.

Yokosawa, M.

1984-12-01

47

Barnacle Equivalence Structure in Relativistic Wave Equations

Relativistic wave equations for spin s particles (-i beta \\\\cdot partial + m) psi = 0 transforming under a representation Lambda mapsto T(Lambda) of SL(2, C), can have structural properties that make them physically equivalent to similar wave equations. This equivalence extends to all the standard external field interactions. There are T(Lambda)'s which cannot lead to theories different from simpler

M. A. K. Khalil

1978-01-01

48

A $55 Shock Tube for Simulated Blast Waves

Shock tubes are commonly employed to test candidate armor materials, validate numerical models, and conduct simulated blast experiments in animal models. As DoD interests desire to field wearable sensors as blast dosimeters, shock tubes may also serve for calibration and testing of these devices. The high blast pressures needed for experimental testing of candidate armors are unnecessary to test these sensors. An inexpensive, efficient, and easily available way of testing these pressure sensors is desirable. It is known that releasing compressed gas suddenly can create a repeatable shock front, and the pressures can be finely tuned by changing the pressure to which the gas is compressed. A Crosman 0.177 caliber air pistol was used (without loading any pellets) to compress and release air in one end of a 24 inch long 3/4 inch diameter standard pipe nipple to simulate a blast wave at the other end of the tube. A variable number of pumps were used to vary the peak blast pressure. As expected, the trials where 10...

Courtney, Elijah; Courtney, Michael

2015-01-01

49

Resonance shift in relativistic traveling wave amplifiers

We examine analytically the linear operation of relativistic traveling wave tube amplifiers. In this regime it is found that the maximum growth rate occurs at a beam velocity below that expected on the basis of resonance with the cold dispersion relation of the slow wave structure. The maximum growth rate can be much larger than that at the resonance condition. These results have significance when extending Pierce{close_quote}s theory to traveling wave amplifiers driven by relativistic electron beams. {copyright} {ital 1996 The American Physical Society.}

Naqvi, S.A.; Kerslick, G.S.; Nation, J.A. [School of Electrical Engineering & Laboratory of Plasma Studies, Cornell University, Ithaca, New York 14853 (United States)] [School of Electrical Engineering & Laboratory of Plasma Studies, Cornell University, Ithaca, New York 14853 (United States); Schaechter, L. [Department of Electrical Engineering, Technion--Israel Institute of Technology, Haifa 32000 (Israel)] [Department of Electrical Engineering, Technion--Israel Institute of Technology, Haifa 32000 (Israel)

1996-04-01

50

High-speed photography of microscale blast wave phenomena

NASA Astrophysics Data System (ADS)

High-speed photography has been a primary tool for the study of blast wave phenomena, dating from the work of Toepler, even before the invention of the camera! High-speed photography was used extensively for the study of blast waves produced by nuclear explosions for which, because of the large scale, cameras running at a few hundred frames per second were adequate to obtain sharp images of the supersonic shock fronts. For the study of the blast waves produced by smaller explosive sources, ever-increasing framing rates were required. As a rough guide, for every three orders of magnitude decrease in charge size a ten-fold increase of framing rate was needed. This severely limited the use of photography for the study of blast waves from laboratory-scale charges. There are many techniques for taking single photographs of explosive phenomena, but the strongly time-dependent development of a blast wave, requires the ability to record a high-speed sequence of photographs of a single event. At ICHSPP25, Kondo et al of Shimadzu Corporation demonstrated a 1 M fps video camera that provides a sequence of up to 100 high-resolution frames. This was subsequently used at the Shock Wave Research Center of Tohoku University to record the blast waves generated by an extensive series of silver azide charges ranging in size from 10 to 0.5mg. The resulting images were measured to provide radius-time histories of the primary and secondary shocks. These were analyzed with techniques similar to those used for the study of explosions from charges with masses ranging from 500 kg to 5 kt. The analyses showed the cube-root scaling laws to be valid for the very small charges, and provided a detailed record of the peak hydrostatic pressure as a function of radius for a unit charge of silver azide, over a wide range of scaled distances. The pressure-radius variation was compared to that from a unit charge of TNT and this permitted a detailed determination of the TNT equivalence of silver azide as a function of peak pressure and radius. The availability of the Shimadzu high-speed framing camera has made it possible to perform experiments at the laboratory scale that previously could be done only on large-scale field trials. At the laboratory scale, many experiments can be performed on the same day, as compared to the months or even years required for the preparation of large-scale field experiments. The economic savings are even greater.

Dewey, John M.; Kleine, Harald

2005-03-01

51

The Use of Cantilevers as Blast Wave Gauges.

NASA Astrophysics Data System (ADS)

A study has been made of the response of elastic -plastic and brittle cantilevers when subjected to blast wave loading with a view to using such devices as passive blast wave gauges, and of using the deformation of cantilevers to assess the characteristics of accidental explosions. The study was restricted to cantilevers that were circular in cross-section and made of readily available materials. A cantilever, when loaded by a blast wave, either deforms plastically, in which case the amount of deformation is the critical parameter, or fractures, in which case the failing or not failing of the cantilever provides the required information. Two numerical models were developed to describe the deformation of a dynamically loaded cantilever. Both models assume that the plastic deformation is localized in a region near the fixed end, and that the loading force was a function of the dynamic pressure time history and a variable drag coefficient, dependent on the Reynolds number, Mach number and angle of attack. The first numerical model assumed a rigid-plastic response of the cantilevers. The model accurately described the response only of cantilevers made of 50/50 lead/tin alloy. It overestimated the deformation of cantilevers made of other materials exposed in both high explosive and shock tube experiments. The second model assumed an elastic-plastic response for the blast loaded cantilever with strain hardening effects included. The algorithm was based on the premise that the elastic curvature of the cantilever was limited by the plastic yield stress of the material and that as the curvature approached this limit the cantilever was rotated by the necessary amount to keep the curvature constant and equal to this maximum. The amount of rotation was determined by fitting a fourth order polynomial with a constrained second derivative based on the maximum allowed curvature. The rotation angle were found from the angle derived from the slope of the fitted function at the origin. A rotation by this angle yields a minimum in curvature in the rotated reference frame. This model improved the predictions for cantilevers constructed of aluminum and steel. The numerical models were evaluated by studying the response of cantilevers exposed to shock waves produced in a shock tube, and to blast waves produced by the detonation of two large high-explosive chemical sources. The response of the cantilevers to the shock tube flows was recorded by high-speed photography which showed good agreement between the observed modes of deformation and those predicted by the model. The models which were finally developed also provided good predictions of the deformation or fracture of a wide range of cantilevers exposed to the free-field blast waves. These models were also used to detect any non-radial flows and to study the boundary layers in the blast wave over different surfaces. Finally, it is demonstrated how the numerical modelling can be used to determine the type of cantilever that might be used as a passive gauge for monitoring the blast wave from an explosive event, and for evaluating the deformation of a cantilever exposed to the blast wave from an accidental explosion so as to characterize that explosion.

van Netten, Alexander Antony

1995-01-01

52

Relativistically modulational instability by strong Langmuir waves

Based on the set of nonlinear coupling equations, which has considered the relativistic effects of electrons, modulational instability by strong Langmuir waves has been investigated in this paper. Both the characteristic scale and maximum growth rate of the Langmuir field will enhance with the increase in the electron relativistic effect. The numerical results indicate that longitudinal perturbations induce greater instability than transverse perturbations do, which will lead to collapse and formation of the pancake-like structure.

Liu, X. L.; Liu, S. Q. [Department of Physics, Nanchang University, Jiangxi, Nanchang 330031 (China); Li, X. Q. [Department of Physics, Nanjing Normal University, Nanjing 210097 (China)

2012-09-15

53

A thoracic mechanism of mild traumatic brain injury due to blast pressure waves

The mechanisms by which blast pressure waves cause mild to moderate traumatic\\u000abrain injury (mTBI) are an open question. Possibilities include acceleration of\\u000athe head, direct passage of the blast wave via the cranium, and propagation of\\u000athe blast wave to the brain via a thoracic mechanism. The hypothesis that the\\u000ablast pressure wave reaches the brain via a thoracic

A. C. Courtney; Michael Courtney

2009-01-01

54

Resonant Amplification of Turbulence by the Blast Waves

NASA Astrophysics Data System (ADS)

We discuss the idea of whether spherical blast waves can amplify by a nonlocal resonant hydrodynamic mechanism inhomogeneities formed by turbulence or phase segregation in the interstellar medium. We consider the problem of a blast-wave-turbulence interaction in the Linear Interaction Approximation. Mathematically, this is an eigenvalue problem for finding the structure and amplitude of eigenfunctions describing the response of the shock-wave flow to forced oscillations by external perturbations in the ambient interstellar medium. Linear analysis shows that the blast wave can amplify density and vorticity perturbations for a wide range of length scales with amplification coefficients of up to 20, with increasing amplification the larger the length. There also exist resonant harmonics for which the gain becomes formally infinite in the linear approximation. Their orbital wavenumbers are within the range of macro- (l ~ 1), meso- (l ~ 20), and microscopic (l > 200) scales. Since the resonance width is narrow (typically, ?l < 1), resonance should select and amplify discrete isolated harmonics. We speculate on a possible explanation of an observed regular filamentary structure of regularly shaped round supernova remnants such as SNR 1572, 1006, or 0509-67.5. Resonant mesoscales found (l ? 18) are surprisingly close to the observed scales (l ? 15) of ripples in the shell's surface of SNR 0509-67.5.

Zankovich, A. M.; Kovalenko, I. G.

2015-02-01

55

Simulation of the Reflected Blast Wave froma C-4 Charge

The reflection of a blast wave from a C4 charge detonated above a planar surface is simulated with our ALE3D code. We used a finely-resolved, fixed Eulerian 2-D mesh (167 {micro}m per cell) to capture the detonation of the charge, the blast wave propagation in nitrogen, and its reflection from the surface. The thermodynamic properties of the detonation products and nitrogen were specified by the Cheetah code. A programmed-burn model was used to detonate the charge at a rate based on measured detonation velocities. Computed pressure histories are compared with pressures measured by Kistler 603B piezoelectric gauges at 8 ranges (GR = 0, 2, 4, 8, 10, and 12 inches) along the reflecting surface. Computed and measured waveforms and positive-phase impulses were similar, except at close-in ranges (GR < 2 inches), which were dominated by jetting effects.

Howard, W M; Kuhl, A L; Tringe, J W

2011-08-01

56

Impact of complex blast waves on the human head: a computational study.

Head injuries due to complex blasts are not well examined because of limited published articles on the subject. Previous studies have analyzed head injuries due to impact from a single planar blast wave. Complex or concomitant blasts refer to impacts usually caused by more than a single blast source, whereby the blast waves may impact the head simultaneously or consecutively, depending on the locations and distances of the blast sources from the subject, their blast intensities, the sequence of detonations, as well as the effect of blast wave reflections from rigid walls. It is expected that such scenarios will result in more serious head injuries as compared to impact from a single blast wave due to the larger effective duration of the blast. In this paper, the utilization of a head-helmet model for blast impact analyses in Abaqus(TM) (Dassault Systemes, Singapore) is demonstrated. The model is validated against studies published in the literature. Results show that the skull is capable of transmitting the blast impact to cause high intracranial pressures (ICPs). In addition, the pressure wave from a frontal blast may enter through the sides of the helmet and wrap around the head to result in a second impact at the rear. This study recommended better protection at the sides and rear of the helmet through the use of foam pads so as to reduce wave entry into the helmet. The consecutive frontal blasts scenario resulted in higher ICPs compared with impact from a single frontal blast. This implied that blast impingement from an immediate subsequent pressure wave would increase severity of brain injury. For the unhelmeted head case, a peak ICP of 330?kPa is registered at the parietal lobe which exceeds the 235?kPa threshold for serious head injuries. The concurrent front and side blasts scenario yielded lower ICPs and skull stresses than the consecutive frontal blasts case. It is also revealed that the additional side blast would only significantly affect ICPs at the temporal and parietal lobes when compared with results from the single frontal blast case. By analyzing the pressure wave flow surrounding the head and correlating them with the consequential evolution of ICP and skull stress, the paper provides insights into the interaction mechanics between the concomitant blast waves and the biological head model. PMID:25132676

Tan, Long Bin; Chew, Fatt Siong; Tse, Kwong Ming; Chye Tan, Vincent Beng; Lee, Heow Pueh

2014-12-01

57

Interactions between Blast Waves and V-Shaped and Cone-Shaped Structures

A 2-D numerical model of interactions between a blast wave and a V-shaped or a cone-shaped structure is developed. The model simulates the blast wave reflection from a V-shaped or a cone-shaped structure, the movement of the structure due to the blast impact and the induced shock wave behind the structure. Elliptic grid generation and coordinate transformation are utilized to

W. Peng; Z. Y. Zhang; G. Gogos; G. Gazonas

2011-01-01

58

Relativistic Shock Waves in Viscous Gluon Matter

We solve the relativistic Riemann problem in viscous gluon matter employing a microscopic parton cascade. We demonstrate the transition from ideal to viscous shock waves by varying the shear viscosity to entropy density ratio eta/s from zero to infinity. We show that an eta/s ratio larger than 0.2 prevents the development of well-defined shock waves on time scales typical for ultrarelativistic heavy-ion collisions. Comparisons with viscous hydrodynamic calculations confirm our findings.

Bouras, I.; Xu, Z.; El, A.; Fochler, O.; Greiner, C. [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, Max-von-Laue-Strasse 1, D-60438 Frankfurt am Main (Germany); Molnar, E.; Niemi, H. [Frankfurt Institute for Advanced Studies, Ruth-Moufang-Strasse 1, D-60438 Frankfurt am Main (Germany); Rischke, D. H. [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, Max-von-Laue-Strasse 1, D-60438 Frankfurt am Main (Germany); Frankfurt Institute for Advanced Studies, Ruth-Moufang-Strasse 1, D-60438 Frankfurt am Main (Germany)

2009-07-17

59

A parametric study of self-similar blast waves.

NASA Technical Reports Server (NTRS)

Comprehensive examination of self-similar blast waves with respect to two parameters, one describing the front velocity and the other the variation of the ambient density immediately ahead of the front. All possible front trajectories are taken into account, including limiting cases of the exponential and logarithmic form. The structure of the waves is analyzed by means of a phase plane defined in terms of two reduced coordinates. Loci of extrema of the integral curves in the phase plane are traced, and loci of singularities are determined on the basis of their intersections. Boundary conditons are introduced for the case where the medium into which the waves propagate is at rest. Representative solutions, pertaining to all the possible cases of blast waves bounded by shock fronts propagating into an atmosphere of uniform density, are obtained by evaluating the integral curves and determining the corresponding profiles of the gasdynamic parameters. Particular examples of integral curves for waves bounded by detonations are given, and all the degenerate solutions corresponding to cases where the integral curve is reduced to a point are delineated.

Oppenheim, A. K.; Kuhl, A. L.; Lundstrom, E. A.; Kamel, M. M.

1972-01-01

60

Blast wave simulation with ground surface effect

Unsteady flowfield generated by the finite strength of a shock wave is computationally simulated with the discretization method. The results indicate that the overpressure depends on the ground surface geometry as well as the distance from the point of explosion. The present approach using the new computational-fluid-dynamic technology may improve the existing theory for estimating the unsteady motion and decay

Kozo Fujii; Fumio Shimizu; Yoshiaki Tamura; Fumio Higashino; Motoki Hinada; Ryojiro Akiba

1990-01-01

61

Interactions between Blast Waves and V-Shaped and Cone-Shaped Structures

NASA Astrophysics Data System (ADS)

A 2-D numerical model of interactions between a blast wave and a V-shaped or a cone-shaped structure is developed. The model simulates the blast wave reflection from a V-shaped or a cone-shaped structure, the movement of the structure due to the blast impact and the induced shock wave behind the structure. Elliptic grid generation and coordinate transformation are utilized to solve the flow fields in the irregular physical domain. Different types of blast wave reflections, such as normal reflection, oblique reflection and Mach stem reflection, are captured by the numerical model. It is found that the reflected pressure and impulse transmitted to the structure decrease with the increase of incident angle. On the other hand, with the increase of incident angle, the effects of fluid structure interactions (FSI) in reducing the blast loads decreases. The FSI coupled with oblique or Mach stem reflection improves the blast wave mitigation.

Peng, W.; Zhang, Z. Y.; Gogos, G.; Gazonas, G.

2011-09-01

62

Relativistic Wave Equations: An Operational Approach

The use of operator methods of algebraic nature is shown to be a very powerful tool to deal with different forms of relativistic wave equations. The methods provide either exact or approximate solutions for various forms of differential equations, such as relativistic Schr\\"odinger, Klein-Gordon and Dirac. We discuss the free particle hypotheses and those relevant to particles subject to non-trivial potentials. In the latter case we will show how the proposed method leads to easily implementable numerical algorithms.

G. Dattoli; E. Sabia; K. Górska; A. Horzela; K. A. Penson

2015-02-02

63

Relativistic wave equations: an operational approach

NASA Astrophysics Data System (ADS)

The use of operator methods of an algebraic nature is shown to be a very powerful tool to deal with different forms of relativistic wave equations. The methods provide either exact or approximate solutions for various forms of differential equations, such as relativistic Schrödinger, Klein–Gordon, and Dirac. We discuss the free-particle hypotheses and those relevant to particles subject to non-trivial potentials. In the latter case we will show how the proposed method leads to easily implementable numerical algorithms.

Dattoli, G.; Sabia, E.; Górska, K.; Horzela, A.; Penson, K. A.

2015-03-01

64

Electron cyclotron wave generation by relativistic electrons

NASA Technical Reports Server (NTRS)

We show that an energetic electron distribution which has a temperature anisotropy (T perpendicular to b is greater than T parallel to b), or which is gyrating about a DC magnetic field, can generate electron cyclotron waves with frequencies below the electron cyclotron frequency. Relativistic effects are included in solving the dispersion equation and are shown to be quantitatively important. The basic idea of the mechanism is the coupling of the beam mode to slow waves. The unstable electron cyclotron waves are predominantly electromagnetic and right-hand polarized. For a low-density plasma in which the electron plasma frequency is less than the electron cyclotron frequency, the excited waves can have frequencies above or below the electron plasma frequency, depending upon the parameters of the energetic electron distribution. This instability may account for observed Z mode waves in the polar magnetosphere of the Earth and other planets.

Wong, H. K.; Goldstein, M. L.

1994-01-01

65

Human exposure to blast waves without any fragment impacts can still result in primary blast-induced traumatic brain injury (bTBI). To investigate the mechanical response of human brain to primary blast waves and to identify the injury mechanisms of bTBI, a three-dimensional finite element head model consisting of the scalp, skull, cerebrospinal fluid, nasal cavity, and brain was developed from the imaging data set of a human female. The finite element head model was partially validated and was subjected to the blast waves of five blast intensities from the anterior, right lateral, and posterior directions at a stand-off distance of one meter from the detonation center. Simulation results show that the blast wave directly transmits into the head and causes a pressure wave propagating through the brain tissue. Intracranial pressure (ICP) is predicted to have the highest magnitude from a posterior blast wave in comparison with a blast wave from any of the other two directions with same blast intensity. The brain model predicts higher positive pressure at the site proximal to blast wave than that at the distal site. The intracranial pressure wave invariably travels into the posterior fossa and vertebral column, causing high pressures in these regions. The severities of cerebral contusions at different cerebral locations are estimated using an ICP based injury criterion. Von Mises stress prevails in the cortex with a much higher magnitude than in the internal parenchyma. According to an axonal injury criterion based on von Mises stress, axonal injury is not predicted to be a cause of primary brain injury from blasts. PMID:25409326

Wang, Chenzhi; Pahk, Jae Bum; Balaban, Carey D; Miller, Mark C; Wood, Adam R; Vipperman, Jeffrey S

2014-01-01

66

Human exposure to blast waves without any fragment impacts can still result in primary blast-induced traumatic brain injury (bTBI). To investigate the mechanical response of human brain to primary blast waves and to identify the injury mechanisms of bTBI, a three-dimensional finite element head model consisting of the scalp, skull, cerebrospinal fluid, nasal cavity, and brain was developed from the imaging data set of a human female. The finite element head model was partially validated and was subjected to the blast waves of five blast intensities from the anterior, right lateral, and posterior directions at a stand-off distance of one meter from the detonation center. Simulation results show that the blast wave directly transmits into the head and causes a pressure wave propagating through the brain tissue. Intracranial pressure (ICP) is predicted to have the highest magnitude from a posterior blast wave in comparison with a blast wave from any of the other two directions with same blast intensity. The brain model predicts higher positive pressure at the site proximal to blast wave than that at the distal site. The intracranial pressure wave invariably travels into the posterior fossa and vertebral column, causing high pressures in these regions. The severities of cerebral contusions at different cerebral locations are estimated using an ICP based injury criterion. Von Mises stress prevails in the cortex with a much higher magnitude than in the internal parenchyma. According to an axonal injury criterion based on von Mises stress, axonal injury is not predicted to be a cause of primary brain injury from blasts. PMID:25409326

Wang, Chenzhi; Pahk, Jae Bum; Balaban, Carey D.; Miller, Mark C.; Wood, Adam R.; Vipperman, Jeffrey S.

2014-01-01

67

Wave kinetics of relativistic quantum plasmas

A quantum kinetic equation, valid for relativistic unmagnetized plasmas, is derived here. This equation describes the evolution of a quantum quasi-distribution, which is the Wigner function for relativistic spinless charged particles in a plasma, and it is exactly equivalent to a Klein-Gordon equation. Our quantum kinetic equation reduces to the Vlasov equation in the classical limit, where the Wigner function is replaced by a classical distribution function. An approximate form of the quantum kinetic equation is also derived, which includes first order quantum corrections. This is applied to electron plasma waves, for which a new dispersion relation is obtained. It is shown that quantum recoil effects contribute to the electron Landau damping with a third order derivative term. The case of high frequency electromagnetic waves is also considered. Its dispersion relation is shown to be insensitive to quantum recoil effects for equilibrium plasma distributions.

Mendonca, J. T. [IPFN, Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal)

2011-06-15

68

Millimeter-Wave HF Relativistic Electron Oscillators

A review of the experimental study of single-mode oscillators based on stimulated bremsstrahlung and Cerenkov radiation of high-current relativistic electron beams is given. Three types of Cerenkov oscillators are investigated in detail: orotrons, surface wave oscillators and a flimatron (free electron maser (FEM) based on Smith-Purcell radiation). The bremsstrahlung oscillators studied are gyrotrons with TM modes, a ubitron operating at

V. L. Bratman; G. G. Denisov; M. M. Ofitserov; S. D. Korovin; S. D. Polevin; V. V. Rostov

1987-01-01

69

Heating of X-Ray Hot Gas in Groups by Blast Waves

In order to find the conditions which determine whether X-Ray hot gas in galaxy groups (intragroup gas; IGG) is heated externally or internally, we investigate the evolution of blast waves in galaxy groups growing on a hierarchical clustering scenario. We find that the blast waves driven by quasars are confined in groups and heat the IGG internally at z~ 1, they expel the IGG from groups; the expelled gas may fall back into the groups later as externally heated gas. Moreover, this may explain the observed low metal abundance of IGG. For blast waves driven by strong starbursts, the shift of the fate of blast waves occurs at z~ 3. On the other hand, although blast waves driven by weak starbursts do not expel IGG from groups, the heating efficiency decreases at z>~ 3 because of radiative cooling. It will be useful to compare these results with XMM-Newton observations.

Yutaka Fujita

2001-02-13

70

High resolution imaging of colliding blast waves in cluster media

NASA Astrophysics Data System (ADS)

Strong shocks and blast wave collisions are commonly observed features in astrophysical objects such as nebulae and supernova remnants. Numerical simulations often underpin our understanding of these complex systems, however modelling of such extreme phenomena remains challenging, particularly so for the case of radiative or colliding shocks. This highlights the need for well-characterized laboratory experiments both to guide physical insight and to provide robust data for code benchmarking. Creating a sufficiently high-energy-density gas medium for conducting scaled laboratory astrophysics experiments has historically been problematic, but the unique ability of atomic cluster gases to efficiently couple to intense pulses of laser light now enables table top scale (1 J input energy) studies to be conducted at gas densities of >1019 particles cm-3 with an initial energy density >5 × 109 J g-1. By laser heating atomic cluster gas media we can launch strong (up to Mach 55) shocks in a range of geometries, with and without radiative precursors. These systems have been probed with a range of optical and interferometric diagnostics in order to retrieve electron density profiles and blast wave trajectories. Colliding cylindrical shock systems have also been studied, however the strongly asymmetric density profiles and radial and longitudinal mass flow that result demand a more complex diagnostic technique based on tomographic phase reconstruction. We have used the 3D magnetoresistive hydrocode GORGON to model these systems and to highlight interesting features such as the formation of a Mach stem for further study.

Smith, Roland A.; Lazarus, James; Hohenberger, Matthias; Marocchino, Alberto; Robinson, Joseph S.; Chittenden, Jeremy P.; Moore, Alastair S.; Gumbrell, Edward T.; Dunne, Mike

2007-12-01

71

Self-similar blast waves incorporating deflagrations of variable speed

NASA Technical Reports Server (NTRS)

The present investigation is concerned with the development of a systematic approach to the problem of self-similar blast waves incorporating nonsteady flames. The regime covered by the presented solutions is bounded on one side by an adiabatic strong explosion and, on the other, by deflagration propagating at an infinite acceleration. Results for a representative set of accelerations are displayed, taking into account the full range of propagation speeds from zero to velocities corresponding to the Chapman-Jouguet deflagration. It is found that the distribution of stored energy in the undisturbed medium determines the acceleration of the deflagration-shock wave system. The obtained results reveal the existence of a simple relation between the location of the deflagration and its Mach number.

Guirguis, R. H.; Kamel, M. M.; Oppenheim, A. K.

1983-01-01

72

A Thoracic Mechanism of Mild Traumatic Brain Injury Due to Blast Pressure Waves

The mechanisms by which blast pressure waves cause mild to moderate traumatic brain injury (mTBI) are an open question. Possibilities include acceleration of the head, direct passage of the blast wave via the cranium, and propagation of the blast wave to the brain via a thoracic mechanism. The hypothesis that the blast pressure wave reaches the brain via a thoracic mechanism is considered in light of ballistic and blast pressure wave research. Ballistic pressure waves, caused by penetrating ballistic projectiles or ballistic impacts to body armor, can only reach the brain via an internal mechanism and have been shown to cause cerebral effects. Similar effects have been documented when a blast pressure wave has been applied to the whole body or focused on the thorax in animal models. While vagotomy reduces apnea and bradycardia due to ballistic or blast pressure waves, it does not eliminate neural damage in the brain, suggesting that the pressure wave directly affects the brain cells via a thoracic mechanism. ...

Courtney, Amy; 10.1016/j.mehy.2008.08.015

2008-01-01

73

Relativistic nonlinear plasma waves in a magnetic field

NASA Technical Reports Server (NTRS)

Five relativistic plane nonlinear waves were investigated: circularly polarized waves and electrostatic plasma oscillations propagating parallel to the magnetic field, relativistic Alfven waves, linearly polarized transverse waves propagating in zero magnetic field, and the relativistic analog of the extraordinary mode propagating at an arbitrary angle to the magnetic field. When the ions are driven relativistic, they behave like electrons, and the assumption of an 'electron-positron' plasma leads to equations which have the form of a one-dimensional potential well. The solutions indicate that a large-amplitude superluminous wave determines the average plasma properties.

Kennel, C. F.; Pellat, R.

1975-01-01

74

Blast wave simulation with a discretization method towards the estimation of safety distance

NASA Astrophysics Data System (ADS)

Unsteady flow fields generated by a blast wave are computationally simulated with a discretization method. The result indicates that pressure rise due to the frontal shock wave strongly depends on the local ground surface geometry as well as the distance from the center of explosion. Overset zonal method with moving grid is developed to enhance the accuracy of the simulations for the quantitative estimation of the blast wave strength. The present approach using new computational fluid dynamic technology may improve the existing theory for the estimation of the unsteady motion and decay of the blast wave, leading to the better estimation of the safety distance for accidental explosions.

Shimizu, Fumio; Fujii, Kozo; Higashino, Fumio

75

Blast wave fits to elliptic flow data at ?{sNN}=7.7 - 2760 GeV

NASA Astrophysics Data System (ADS)

We present blast wave fits to elliptic flow [v2(pT) ] data in minimum bias collisions from ?{sNN}=7.7 - 200 GeV at the BNL Relativistic Heavy Ion Collider, and also at the CERN Large Hadron Collider energy of 2.76 TeV. The fits are performed separately for particles and corresponding antiparticles. The mean transverse velocity parameter ? shows an energy-dependent difference between particles and corresponding antiparticles, which increases as the beam energy decreases. Possible effects of feed down, baryon stopping, antiparticle absorption, and early production times for antiparticles are discussed.

Sun, X.; Masui, H.; Poskanzer, A. M.; Schmah, A.

2015-02-01

76

Prospects for studying how high-intensity compression waves cause damage in human blast injuries

NASA Astrophysics Data System (ADS)

Blast injuries arising from improvised explosive devices are often complex leading to long-term disability in survivors. There is an urgent need to mitigate against the effects of blast that lead to these injuries, and to also improve post-traumatic therapeutic treatments related to problems associated with damage and healing processes and infections. We have initiated multidisciplinary studies to develop experimental facilities and strategies for analyzing the effects blast waves upon the human body, from cellular through to skeletal functions.

Brown, Katherine; Bo, Chiara; Ramaswamy, Arul; Masouros, Spiros; Newell, Nicolas; Hill, Adam; Clasper, Jon; Bull, Anthony; Proud, William

2011-06-01

77

A Numerical Study on the Screening of Blast-Induced Waves for Reducing Ground Vibration

Blasting is often a necessary part of mining and construction operations, and is the most cost-effective way to break rock,\\u000a but blasting generates both noise and ground vibration. In urban areas, noise and vibration have an environmental impact,\\u000a and cause structural damage to nearby structures. Various wave-screening methods have been used for many years to reduce blast-induced\\u000a ground vibration. However,

Byungkyu Jeon; Seokwon Jeon

2009-01-01

78

Energy conversion in a glass-laser-induced blast wave in air

NASA Astrophysics Data System (ADS)

Near-infrared solid laser-induced blast waves were investigated using a Q-switched Nd:glass laser oscillating at 1053 nm wavelength, up to 2.0 J/pulse laser energy Ei, and 33 ns pulse duration (full width at half maximum). Half-shadowgraph half-self-emission visualization elucidated laser detonation waves and blast waves. Laser output and transmission through the waves were measured using pairs of a photodetectors and energy meters. Results show volumetric absorption in this near-infrared region, which is mainly attributable to low inverse-Bremsstrahlung absorption coefficients at short wavelengths. Some input laser energy was converted into blast wave energy: 59% at Ei=1.0 J/pulse, which approximates that of CO2 laser-induced blast waves.

Wang, Bin; Komurasaki, Kimiya; Yamaguchi, Toshikazu; Shimamura, Kohei; Arakawa, Yoshihiro

2010-12-01

79

Supernova blast wave within a stellar cluster outflow

NASA Astrophysics Data System (ADS)

In this paper, we develop a semi-analytic model of a supernova which goes off in the centre of a stellar cluster. The supernova remnant interacts with a stratified, pre-existent outflow produced by the winds of the cluster stars. We compare our semi-analytic model with numerical simulations using the spherically symmetric Euler equations with appropriate mass and energy source terms. We find good agreement between these two approaches, and we find that for typical parameters the blast wave is likely to reach the Taylor-Sedov regime outside the cluster radius. We also calculate the predicted X-ray luminosity of the flow as a function of time, and we obtain its dependence on the outer radius and the number of stars of the cluster.

Rodríguez-Ramírez, J. C.; Raga, A. C.; Velázquez, P. F.; Rodríguez-González, A.; Toledo-Roy, J. C.

2014-11-01

80

A non-similar solution for blast waves driven by an asymptotic piston expansion

A blast wave is formed when the contact surface of an expanding gas moves faster than the speed of sound in the stagnant medium ahead of it. Solutions to this type of problem are of interest in a variety of practical problems such as the rupture of pressurized vessels or the blast from high energy explosives. The self-similar model used

M. L. Bundy

1983-01-01

81

SPIKE PENETRATION IN BLAST-WAVE-DRIVEN INSTABILITIES

The problem of interest is the unstable growth of structure at density transitions affected by blast waves, which arise in natural environments such as core-collapse supernovae and in laboratory experiments. The resulting spikes of dense material, which penetrate the less dense material, develop broadened tips, but the degree of broadening varies substantially across both experiments and simulations. The variable broadening presumably produces variations in the drag experienced by the spike tips as they penetrate the less dense material. The present work has used semianalytic theory to address the question of how the variation in drag might affect the spike penetration, for cases in which the post-shock interface deceleration can be described by a power law in a normalized time variable. It did so by following the evolution of structure on the interface through the initial shock passage, the subsequent small-amplitude phase of Rayleigh-Taylor instability growth, and the later phase in which the spike growth involves the competition of buoyancy and drag. In all phases, the expansion of the system during its evolution was accounted for and was important. The calculated spike length is strongly affected by the drag attributed to spike tip broadening. One finds from such a calculation that it is not unreasonable for narrow spikes to keep up with the shock front of the blast wave. The implication is that the accuracy of prediction of spike penetration and consequent structure by simulations very likely depends on how accurately they treat the broadening of the spike tips and the associated drag. Experimental validation of spike morphology in simulations would be useful.

Drake, R. P., E-mail: rpdrake@umich.edu [Atmospheric, Oceanic, and Space Science, and Applied Physics, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109 (United States)

2012-01-10

82

Spike morphology in blast-wave-driven instability experiments

The laboratory experiments described in the present paper observe the blast-wave-driven Rayleigh-Taylor instability with three-dimensional (3D) initial conditions. About 5 kJ of energy from the Omega laser creates conditions similar to those of the He-H interface during the explosion phase of a supernova. The experimental target is a 150 {mu}m thick plastic disk followed by a low-density foam. The plastic piece has an embedded, 3D perturbation. The basic structure of the pattern is two orthogonal sine waves where each sine wave has an amplitude of 2.5 {mu}m and a wavelength of 71 {mu}m. In some experiments, an additional wavelength is added to explore the interaction of modes. In experiments with 3D initial conditions the spike morphology differs from what has been observed in other Rayleigh-Taylor experiments and simulations. Under certain conditions, experimental radiographs show some mass extending from the interface to the shock front. Current simulations show neither the spike morphology nor the spike penetration observed in the experiments. The amount of mass reaching the shock front is analyzed and potential causes for the spike morphology and the spikes reaching the shock are discussed. One such hypothesis is that these phenomena may be caused by magnetic pressure, generated by an azimuthal magnetic field produced by the plasma dynamics.

Kuranz, C. C.; Drake, R. P.; Grosskopf, M. J.; Fryxell, B.; Budde, A. [Department of Atmospheric, Oceanic and Space Science, Center for Radiative Shock Hydrodynamics, University of Michigan, 2455 Hayward Street, Ann Arbor, Michigan 48109 (United States); Hansen, J. F.; Miles, A. R. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550 (United States); Plewa, T. [Department of Scientific Computing, Florida State University, 400 Dirac Science Library, Tallahassee, Florida 32306 (United States); Hearn, N. [Center for Astrophysical Thermonuclear Flashes, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637 (United States); Knauer, J. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States)

2010-05-15

83

Relativistic nonlinear plasma waves in a magnetic field

NASA Technical Reports Server (NTRS)

An investigation is conducted of five relativistic plane nonlinear waves, taking into account circularly polarized waves and electrostatic plasma oscillations propagating parallel to the magnetic field, relativistic Alfven waves, linearly polarized transverse waves propagating in zero magnetic field, and the relativistic analog of the extraordinary mode propagating at an arbitrary angle to the magnetic field. It is found that a large-amplitude superluminous wave determines the average plasma properties, and not vice versa. Attention is given to the implications of the obtained results for the acceleration of cosmic rays in pulsar magnetospheres.

Kennel, C. F.; Pellat, R.

1976-01-01

84

Ex vivo Characterization of Blast Wave Impact and Spinal Cord Tissue Deformation

NASA Astrophysics Data System (ADS)

Primary blast injury on central nervous system is responsible for many of the war related casualties and mortalities. An ex vivo model system is developed to introduce a blast wave, generated from a shock tube, directly to spinal cord tissue sample. A high-speed shadowgraph system is utilized to visualize the development of the blast wave and its interaction with tissue sample. Surface deformation of the tissue sample is also measured for the analysis of internal stress and possible injury occurred within the tissue sample. Understanding the temporal development of the blast-tissue interaction provides valuable input for modeling blast-induced neurotrauma. Tracking the sample surface deformation as a function of time provides realistic boundary conditions for numerical simulation of injury process.

Chen, Jun; Gao, Jian; Connell, Sean; Shi, Riyi

2010-11-01

85

Spatially-resolved X-ray scattering measurements of a planar blast wave

NASA Astrophysics Data System (ADS)

We present X-ray scattering measurements characterizing the spatial temperature and ionization profile of a blast wave driven in a near-solid density foam. Several-keV X-rays scattered from a laser-driven blast wave in a carbon foam. We resolved the scattering in high resolution in space and wavelength to extract the plasma conditions along the propagation direction of the blast wave. We infer temperatures of 20-40 eV and ionizations of 2-4 in the shock and rarefaction regions of the blast wave. This range of measured ionization states allows for a detailed comparison between different models for the bound-free scattering. FLYCHK simulations of the temperature-ionization balance generally agree with the experimental values in the shocked region while consistently underestimating the ionization in the rarefaction.

Gamboa, E. J.; Keiter, P. A.; Drake, R. P.; Falk, K.; Montgomery, D. S.; Benage, J. F.

2014-06-01

86

Rankine-Hugoniot Relations in Relativistic Combustion Waves

NASA Astrophysics Data System (ADS)

As a foundational element describing relativistic reacting waves of relevance to astrophysical phenomena, the Rankine-Hugoniot relations classifying the various propagation modes of detonation and deflagration are analyzed in the relativistic regime, with the results properly degenerating to the non-relativistic and highly relativistic limits. The existence of negative-pressure downstream flows is noted for relativistic shocks, which could be of interest in the understanding of the nature of dark energy. Entropy analysis for relativistic shock waves is also performed for relativistic fluids with different equations of state (EoS), denoting the existence of rarefaction shocks in fluids with adiabatic index ? < 1 in their EoS. The analysis further shows that weak detonations and strong deflagrations, which are rare phenomena in terrestrial environments, are expected to exist more commonly in astrophysical systems because of the various endothermic reactions present therein. Additional topics of relevance to astrophysical phenomena are also discussed.

Gao, Yang; Law, Chung K.

2012-12-01

87

Relativistic Jet Response to Precession and Wave-Wave Interactions

NASA Astrophysics Data System (ADS)

Three dimensional numerical simulations of the response of a 0.916c relativistic jet to three different precession frequencies have been performed. Low, moderate and high precession frequencies have been chosen relative to the maximally unstable frequency predicted by a Kelvin-Helmholtz stability analysis. Transverse motion and velocity decreases as the precession frequency increases. Although helical displacement of the jet decreases in amplitude as the precession frequency increases, a significant spiral pressure wave is generated in the medium external to the jet at all precession frequencies. Complex pressure and velocity structure inside the jet is shown to be produced by a combination of the helical surface and first body modes predicted by a normal mode analysis of the relativistic hydrodynamic equations. The surface and first body modes have different wave speed and wavelength, are launched in phase by the periodic precession, and exhibit beat patterns in synthetic emission images. Wave (pattern) speeds range from 0.62c to 0.86c but beat patterns remain stationary. Thus, we find a mechanism that can produce moving and stationary features in the jet. P. Hardee, A. Rosen and E. Gomez acknowledge support from the National Science Foundation through grant AST-9802955 to the University of Alabama. P. Hughes acknowledges support from the National Science Foundation through grant AST-9617032 to the University of Michigan.

Hardee, P. E.; Hughes, P. A.; Rosen, A.; Gomez, E.

2000-12-01

88

Blast shock wave mitigation using the hydraulic energy redirection and release technology.

A hydraulic energy redirection and release technology has been developed for mitigating the effects of blast shock waves on protected objects. The technology employs a liquid-filled plastic tubing as a blast overpressure transformer to transfer kinetic energy of blast shock waves into hydraulic energy in the plastic tubings. The hydraulic energy is redirected through the plastic tubings to the openings at the lower ends, and then is quickly released with the liquid flowing out through the openings. The samples of the specifically designed body armor in which the liquid-filled plastic tubings were installed vertically as the outer layer of the body armor were tested. The blast test results demonstrated that blast overpressure behind the body armor samples was remarkably reduced by 97% in 0.2 msec after the liquid flowed out of its appropriate volume through the openings. The results also suggested that a volumetric liquid surge might be created when kinetic energy of blast shock wave was transferred into hydraulic energy to cause a rapid physical movement or displacement of the liquid. The volumetric liquid surge has a strong destructive power, and can cause a noncontact, remote injury in humans (such as blast-induced traumatic brain injury and post-traumatic stress disorder) if it is created in cardiovascular system. The hydraulic energy redirection and release technology can successfully mitigate blast shock waves from the outer surface of the body armor. It should be further explored as an innovative approach to effectively protect against blast threats to civilian and military personnel. PMID:22745740

Chen, Yun; Huang, Wei; Constantini, Shlomi

2012-01-01

89

Blast Shock Wave Mitigation Using the Hydraulic Energy Redirection and Release Technology

A hydraulic energy redirection and release technology has been developed for mitigating the effects of blast shock waves on protected objects. The technology employs a liquid-filled plastic tubing as a blast overpressure transformer to transfer kinetic energy of blast shock waves into hydraulic energy in the plastic tubings. The hydraulic energy is redirected through the plastic tubings to the openings at the lower ends, and then is quickly released with the liquid flowing out through the openings. The samples of the specifically designed body armor in which the liquid-filled plastic tubings were installed vertically as the outer layer of the body armor were tested. The blast test results demonstrated that blast overpressure behind the body armor samples was remarkably reduced by 97% in 0.2 msec after the liquid flowed out of its appropriate volume through the openings. The results also suggested that a volumetric liquid surge might be created when kinetic energy of blast shock wave was transferred into hydraulic energy to cause a rapid physical movement or displacement of the liquid. The volumetric liquid surge has a strong destructive power, and can cause a noncontact, remote injury in humans (such as blast-induced traumatic brain injury and post-traumatic stress disorder) if it is created in cardiovascular system. The hydraulic energy redirection and release technology can successfully mitigate blast shock waves from the outer surface of the body armor. It should be further explored as an innovative approach to effectively protect against blast threats to civilian and military personnel. PMID:22745740

Chen, Yun; Huang, Wei; Constantini, Shlomi

2012-01-01

90

A Blast Wave from the 1843 Eruption of Eta Carinae

Very massive stars shed much of their mass in violent precursor eruptions as luminous blue variables (LBVs) before reaching their most likely end as supernovae, but the cause of LBV eruptions is unknown. The 19th century eruption of Eta Carinae, the prototype of these events, ejected about 12 solar masses at speeds of 650 km/s, with a kinetic energy of almost 10^50 ergs. Some faster material with speeds up to 1000-2000 km/s had previously been reported but its full distribution was unknown. Here I report observations of much faster material with speeds up to 3500-6000 km/s, reaching farther from the star than the fastest material in earlier reports. This fast material roughly doubles the kinetic energy of the 19th century event, and suggests that it released a blast wave now propagating ahead of the massive ejecta. Thus, Eta Car's outer shell now mimics a low-energy supernova remnant. The eruption has usually been discussed in terms of an extreme wind driven by the star's luminosity, but fast material reported here suggests that it was powered by a deep-seated explosion rivalling a supernova, perhaps triggered by the pulsational pair instability. This may alter interpretations of similar events seen in other galaxies.

Nathan Smith

2008-09-09

91

Computation of viscous blast wave solutions with an upwind finite volume method

NASA Technical Reports Server (NTRS)

A fully conservative, viscous, implicit, upwind, finite-volume scheme for the thin-layer Navier-Stokes equations is described with application to blast wave flow fields. In this scheme, shocks are captured without the oscillations typical of central differencing techniques and wave speeds are accurately predicted. The finite volume philosophy ensures conservation and since boundary conditions are also treated conservatively, accurate reflections of waves from surfaces are assured. Viscous terms in the governing equations are treated in a manner consistent with the finite volume philosophy, resulting in very accurate prediction of boundary layer quantities. Numerical results are presented for four viscous problems: a steady boundary layer, a shock-induced boundary layer, a blast wave/cylinder interaction and a blast wave/supersonic missile interaction. Comparisons of the results with an established boundary layer code, similarity solution, and experimental data show excellent agreement.

Molvik, Gregory A.

1987-01-01

92

Relativistic Jet Response to Precession and Wave-Wave Interactions

NASA Astrophysics Data System (ADS)

Three-dimensional numerical simulations of the response of a Lorentz factor 2.5 relativistic jet to precession at three different frequencies have been performed. Low-, moderate-, and high-precession frequencies have been chosen relative to the maximally unstable frequency predicted by a Kelvin-Helmholtz stability analysis. The transverse motion and velocity decreases as the precession frequency increases. Although the helical displacement of the jet decreases in amplitude as the precession frequency increases, a helical shock is generated in the medium external to the jet at all precession frequencies. Complex pressure and velocity structure inside the jet are shown to be produced by a combination of the helical surface and first-body modes predicted by a normal mode analysis of the relativistic hydrodynamic equations. The surface and first-body modes have different wave speeds and wavelengths, are launched in phase by the periodic precession, and exhibit beat patterns in synthetic emission images. Wave (pattern) speeds range from 0.41c to 0.86c, but the beat patterns remain stationary. Thus, we find a mechanism that can produce differentially moving and stationary features in the jet.

Hardee, Philip E.; Hughes, Philip A.; Rosen, Alexander; Gomez, Enrique A.

2001-07-01

93

Rankine-Hugoniot Relations in Relativistic Combustion Waves

As a foundational element describing relativistic reacting waves of relevance to astrophysical phenomena, the Rankine-Hugoniot relations classifying the various propagation modes of detonation and deflagration are analyzed in the relativistic regime, with the results properly degenerating to the non-relativistic and highlyrelativistic limits. The existence of negative-pressure downstream flows is noted for relativistic shocks, which could be of interest in the understanding of the nature of dark energy. Entropy analysis for relativistic shock waves are also performed for relativistic fluids with different equations of state (EoS), denoting the existence of rarefaction shocks in fluids with adiabatic index \\Gamma < 1 in their EoS. The analysis further shows that weak detonations and strong deflagrations, which are rare phenomena in terrestrial environments, are expected to exist more commonly in astrophysical systems because of the various endothermic reactions present therein. Additional topics of relevanc...

Gao, Yang

2012-01-01

94

Experimental investigations into the dynamics of cylindrical, laser-driven, high-Mach-number shocks are used to study the thermal cooling instability predicted to occur in astrophysical radiative blast waves. A streaked Schlieren technique measures the full blast-wave trajectory on a single-shot basis, which is key for observing shock velocity oscillations. Electron density profiles and deceleration parameters associated with radiative blast waves were recorded, enabling the calculation of important blast-wave parameters including the fraction of radiated energy, {epsilon}, as a function of time for comparison with radiation-hydrodynamics simulations.

Moore, A. S.; Gumbrell, E. T.; Lazarus, J.; Hohenberger, M.; Robinson, J. S.; Smith, R. A.; Plant, T. J. A.; Symes, D. R.; Dunne, M. [Plasma Physics Division, AWE Aldermaston, RG7 4PR. United Kingdom (United Kingdom); Laser Consortium, Blackett Laboratory, Imperial College, London SW7 2BZ. United Kingdom (United Kingdom); Ministry of Defence, Foxhill, Bath BA1 5AB. United Kingdom (United Kingdom); Central Laser Facility, Rutherford Appleton Laboratory, Oxfordshire OX11 0QX. United Kingdom (United Kingdom)

2008-02-08

95

NASA Astrophysics Data System (ADS)

Injuries to the tympanic membrane (ear drum) are particularly common in individuals subjected to blast overpressure such as military personnel engaged in conflict. Here, the interaction between blast wave and reticulated foams of varying density and thickness has been investigated using shock tube apparatus. The degree of mitigation afforded by the foam samples is discussed in relation to an injury threshold which has been suggested by others for the tympanic membrane.

Wilgeroth, J. M.; Nguyen, T.-T. N.; Proud, W. G.

2014-05-01

96

Analysis of reflected blast wave pressure profiles in a confined room

NASA Astrophysics Data System (ADS)

To understand the blast effects of confined explosions, it is necessary to study the characteristic parameters of the blast wave in terms of overpressure, impulse and arrival time. In a previous study, experiments were performed using two different scales of a pyrotechnic workshop. The main purpose of these experiments was to compare the TNT equivalent for solid and gaseous explosives in terms of mass to define a TNT equivalent in a reflection field and to validate the similitude between real and small scales. To study the interactions and propagations of the reflected shock waves, the present study was conducted by progressively building a confined volume around the charge. In this way, the influence of each wall and the origins of the reflected shock waves can be determined. The purpose of this paper is to report the blast wave interactions that resulted from the detonation of a stoichiometric propane-oxygen mixture in a confined room.

Sauvan, P. E.; Sochet, I.; Trélat, S.

2012-05-01

97

DYNAMICS AND AFTERGLOW LIGHT CURVES OF GAMMA-RAY BURST BLAST WAVES WITH A LONG-LIVED REVERSE SHOCK

We perform a detailed study on the dynamics of a relativistic blast wave with the presence of a long-lived reverse shock (RS). Although a short-lived RS has been widely considered, the RS is believed to be long-lived as a consequence of a stratification expected on the ejecta Lorentz factors. The existence of a long-lived RS causes the forward shock (FS) dynamics to deviate from a self-similar Blandford-McKee solution. Employing the ''mechanical model'' that correctly incorporates the energy conservation, we present an accurate solution for both the FS and RS dynamics. We conduct a sophisticated calculation of the afterglow emission. Adopting a Lagrangian description of the blast wave, we keep track of an adiabatic evolution of numerous shells between the FS and RS. An evolution of the electron spectrum is also followed individually for every shell. We then find the FS and RS light curves by integrating over the entire FS and RS shocked regions, respectively. Exploring a total of 20 different ejecta stratifications, we explain in detail how a stratified ejecta affects its blast wave dynamics and afterglow light curves. We show that, while the FS light curves are not sensitive to the ejecta stratifications, the RS light curves exhibit much richer features, including steep declines, plateaus, bumps, re-brightenings, and a variety of temporal decay indices. These distinctive RS features may be observable if the RS has higher values of the microphysics parameters than the FS. We discuss possible applications of our results in understanding the gamma-ray burst afterglow data.

Uhm, Z. Lucas; Zhang Bing [Department of Physics and Astronomy, University of Nevada-Las Vegas, 4505 South Maryland Parkway, Las Vegas, NV 89154 (United States); Hascoeet, Romain; Daigne, Frederic; Mochkovitch, Robert [Institut d'Astrophysique de Paris, UMR 7095 Universite Pierre et Marie Curie-CNRS, 98 bis Boulevard Arago, F-75014 Paris (France); Park, Il H., E-mail: uhm@physics.unlv.edu [Department of Physics, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

2012-12-20

98

Spectral properties of blast-wave models of gamma-ray burst sources

NASA Technical Reports Server (NTRS)

We calculate the spectrum of blast-wave models of gamma-ray burst sources, for various assumptions about the magnetic field density and the relativistic particle acceleration efficiency. For a range of physically plausible models we find that the radiation efficiency is high and leads to nonthermal spectra with breaks at various energies comparable to those observed in the gamma-ray range. Radiation is also predicted at other wavebands, in particular at X-ray, optical/UV, and GeV/TeV energies. We discuss the spectra as a function of duration for three basic types of models, and for cosmological, halo, and galactic disk distances. We also evaluate the gamma-ray fluences and the spectral characteristics for a range of external densities. Impulsive burst models at cosmological distances can satisfy the conventional X-ray paucity constraint S(sub x)/S(sub gamma)less than a few percent over a wide range of durations, but galactic models can do so only for bursts shorter than a few seconds, unless additional assumptions are made. The emissivity is generally larger for bursts in a denser external environment, with the efficiency increasing up to the point where all the energy input is radiated away.

Meszaros, P.; Rees, M. J.; Papathanassiou, H.

1994-01-01

99

POLYCYCLIC AROMATIC HYDROCARBON PROCESSING IN THE BLAST WAVE OF THE SUPERNOVA REMNANT N132D

We present Spitzer Infrared Spectrograph 14-36 {mu}m mapping observations of the supernova remnant N132D in the Large Magellanic Cloud. This study focuses on the processing of polycyclic aromatic hydrocarbons (PAHs) that we previously identified in the southern blast wave. The mid-infrared spectra show strong continuum emission from shock-heated dust and a unique, nearly featureless plateau in the 15-20 {mu}m region, which we attribute to PAH molecules. The typical PAH emission bands observed in the surrounding interstellar medium ahead of the blast wave disappear, which indicates shock processing of PAH molecules. The PAH plateau appears most strongly at the outer edge of the blast wave and coincides with diffuse X-ray emission that precedes the brightest X-ray and optical filaments. This suggests that PAH molecules in the surrounding medium are swept up and processed in the hot gas of the blast wave shock, where they survive the harsh conditions long enough to be detected. We also observe a broad emission feature at 20 {mu}m appearing with the PAH plateau. We speculate that this feature is either due to FeO dust grains or connected to the processing of PAHs in the supernova blast wave shock.

Tappe, A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-72, Cambridge, MA 02138 (United States); Rho, J. [SOFIA Science Mission Operations/USRA, NASA Ames Research Center, MS 211-3, Moffett Field, CA 94035 (United States); Boersma, C. [NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035 (United States); Micelotta, E. R., E-mail: atappe@cfa.harvard.edu [Department of Physics and Astronomy, Western University, 1151 Richmond Street, London, Ontario N6A 3K7 (Canada)

2012-08-01

100

Relativistic electron beam acceleration by Compton scattering of extraordinary waves

Relativistic transport equations, which demonstrate that relativistic and nonrelativistic particle acceleration along and across a magnetic field and the generation of an electric field transverse to the magnetic field, are induced by nonlinear wave-particle scattering (nonlinear Landau and cyclotron damping) of almost perpendicularly propagating electromagnetic waves in a relativistic magnetized plasma were derived from the relativistic Vlasov-Maxwell equations. The relativistic transport equations show that electromagnetic waves can accelerate particles in the k{sup ''} direction (k{sup ''}=k-k{sup '}). Simultaneously, an intense cross-field electric field, E{sub 0}=B{sub 0}xv{sub d}/c, is generated via the dynamo effect owing to perpendicular particle drift to satisfy the generalized Ohm's law, which means that this cross-field particle drift is identical to the ExB drift. On the basis of these equations, acceleration and heating of a relativistic electron beam due to nonlinear wave-particle scattering of electromagnetic waves in a magnetized plasma were investigated theoretically and numerically. Two electromagnetic waves interact nonlinearly with the relativistic electron beam, satisfying the resonance condition of {omega}{sub k}-{omega}{sub k{sup '}}-(k{sub perpendicular}-k{sub perpendicula=} r{sup '})v{sub d}-(k{sub parallel}-k{sub parallel}{sup '})v{sub b}{approx_equal}m{omega}{sub ce}, where v{sub b} and v{sub d} are the parallel and perpendicular velocities of the relativistic electron beam, respectively, and {omega}{sub ce} is the relativistic electron cyclotron frequency. The relativistic transport equations using the relativistic drifted Maxwellian momentum distribution function of the relativistic electron beam were derived and analyzed. It was verified numerically that extraordinary waves can accelerate the highly relativistic electron beam efficiently with {beta}m{sub e}c{sup 2} < or approx. 1 GeV, where {beta}=(1-v{sub b}{sup 2}/c{sup 2}){sup -1/2}.

Sugaya, R. [Department of Physics, Faculty of Science, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577 (Japan)

2006-05-15

101

GRB X-ray light curves display rapid declines followed by a gradual steepening or plateau phase in >~ 30% of GRBs in the Swift sample. Treating the standard relativistic blastwave model in a uniform circumburst medium, it is shown that if GRBs accelerate ultra-high energy cosmic rays through a Fermi mechanism, then the hadronic component can be rapidly depleted by means of photopion processes on time scales ~100 - 10^4 s after the GRB explosion. While discharging the hadronic energy in the form of ultra-high energy cosmic ray neutrals and escaping cosmic-ray ions, the blast wave goes through a strongly radiative phase, causing the steep declines observed with Swift. Following the discharge, the blast wave recovers its adiabatic behavior, forming the observed plateaus or slow declines. These effects are illustrated by calculations of model bolometric light curves. The results show that steep X-ray declines and plateau features occur when GRB sources take place in rather dense media, with n >~ 100 cc out to >~ 10^17 cm.

Charles D. Dermer

2007-04-22

102

Blast wave formation of the extended stellar shells surrounding elliptical galaxies

NASA Technical Reports Server (NTRS)

The existence of stellar shells at large distances from isolated elliptical galaxies is explained in terms of a blast wave associated with an active nucleus phase early in the history of the galaxy. The blast wave sweeps the initial interstellar medium out of the galaxy into an expanding shell which radiatively cools behind its leading shock front. Cooling of the shell following turnoff of the nucleus activity, which keeps the shell photoionized, leads to a brief epoch of star formation which is terminated by heating of the shell from supernovae and UV radiation from massive stars. The stars so formed follow similar, highly radial, bound orbits, moving in phase with each other and spending much of their time near apogalacteum, thus taking on the appearance of a shell. Multiple shells may be produced when conditions allow repeated episodes of shell cooling and supernovae heating to occur in the blast wave.

Williams, R. E.; Christiansen, W. A.

1985-01-01

103

Matter Density and Relativistic Models of Wave Function Collapse

NASA Astrophysics Data System (ADS)

Mathematical models for the stochastic evolution of wave functions that combine the unitary evolution according to the Schrödinger equation and the collapse postulate of quantum theory are well understood for non-relativistic quantum mechanics. Recently, there has been progress in making these models relativistic. But even with a fully relativistic law for the wave function evolution, a problem with relativity remains: Different Lorentz frames may yield conflicting values for the matter density at a space-time point. We propose here a relativistic law for the matter density function. According to our proposal, the matter density function at a space-time point x is obtained from the wave function ? on the past light cone of x by setting the i-th particle position in |?|2 equal to x, integrating over the other particle positions, and averaging over i. We show that the predictions that follow from this proposal agree with all known experimental facts.

Bedingham, Daniel; Dürr, Detlef; Ghirardi, GianCarlo; Goldstein, Sheldon; Tumulka, Roderich; Zanghì, Nino

2013-08-01

104

Wave-breaking phenomena in a relativistic magnetized plasma.

We study the wave-breaking phenomenon of relativistic upper-hybrid (UH) oscillations in a cold magnetoplasma. For our purposes, we use the electron continuity and relativistic electron momentum equations, together with Maxwell's equations, as well as introduce Lagrangian coordinates to obtain an exact nonstationary solution of the governing nonlinear equations. It is found that bursts in the electron density appear in a finite time as a result of relativistic electron mass variations in the UH electric field, indicating a phase mixing or breaking of relativistic UH oscillations. We highlight the relevance of our investigation of the UH wave phase-mixing or UH wave-breaking process to electron energization and plasma particle heating. PMID:23745888

Maity, Chandan; Sarkar, Anwesa; Shukla, Padma Kant; Chakrabarti, Nikhil

2013-05-24

105

Effects of internal heat transfer on the structure of self-similar blast waves

NASA Technical Reports Server (NTRS)

An analysis of the problem of self-similar, nonadiabatic blast waves, where both conduction and radiation are allowed to take place, show the problem to be reducible to the integration of a system of six coupled nonlinear ordinary differential equations. Consideration of these equations shows that although radiation tends to produce uniform fields through temperature gradient attenuation, all the energy carried by radiation is deposited on the front and the bounding shock becomes increasingly overdriven. When conduction is taken into account, the distribution of gasdynamic parameters in blast waves in the case of Rosseland diffusion radiation is more uniform than in the case of the Planck emission radiation.

Ghoniem, A. F.; Berger, S. A.; Oppenheim, A. K.; Kamel, M. M.

1982-01-01

106

Radiative blast waves were created by irradiating a krypton cluster source from a supersonic jet with a high intensity femtosecond laser pulse. It was found that the radiation from the shock surface is absorbed in the optically thick upstream medium creating a radiative heat wave that travels supersonically ahead of the main shock. As the blast wave propagates into the heated medium, it slows and loses energy, and the radiative heat wave also slows down. When the radiative heat wave slows down to the transonic regime, a secondary shock in the ionization precursor is produced. This paper presents experimental data characterizing both the initial and secondary shocks and numerical simulations to analyze the double-shock dynamics.

Kim, I.; Quevedo, H. J.; Feldman, S.; Bang, W.; Serratto, K.; McCormick, M.; Aymond, F.; Dyer, G.; Bernstein, A. C.; Ditmire, T. [Center for High Energy Density Science, Department of Physics, The University of Texas at Austin, C1510, Austin, Texas 78712 (United States)] [Center for High Energy Density Science, Department of Physics, The University of Texas at Austin, C1510, Austin, Texas 78712 (United States)

2013-12-15

107

Extended adiabatic blast waves and a model of the soft X-ray background. [interstellar matter

NASA Technical Reports Server (NTRS)

An analytical approximation is generated which follows the development of an adiabatic spherical blast wave in a homogeneous ambient medium of finite pressure. An analytical approximation is also presented for the electron temperature distribution resulting from coulomb collisional heating. The dynamical, thermal, ionization, and spectral structures are calculated for blast waves of energy E sub 0 = 5 x 10 to the 50th power ergs in a hot low-density interstellar environment. A formula is presented for estimating the luminosity evolution of such explosions. The B and C bands of the soft X-ray background, it is shown, are reproduced by such a model explosion if the ambient density is about .000004 cm, the blast radius is roughly 100 pc, and the solar system is located inside the shocked region. Evolution in a pre-existing cavity with a strong density gradient may, it is suggested, remove both the M band and OVI discrepancies.

Cox, D. P.; Anderson, P. R.

1981-01-01

108

Relativistic electromagnetic waves in an electron-ion plasma

NASA Technical Reports Server (NTRS)

High power laser beams can drive plasma particles to relativistic energies. An accurate description of strong waves requires the inclusion of ion dynamics in the analysis. The equations governing the propagation of relativistic electromagnetic waves in a cold electron-ion plasma can be reduced to two equations expressing conservation of energy-momentum of the system. The two conservation constants are functions of the plasma stream velocity, the wave velocity, the wave amplitude, and the electron-ion mass ratio. The dynamic parameter, expressing electron-ion momentum conversation in the laboratory frame, can be regarded as an adjustable quantity, a suitable choice of which will yield self-consistent solutions when other plasma parameters were specified. Circularly polarized electromagnetic waves and electrostatic plasma waves are used as illustrations.

Chian, Abraham C.-L.; Kennel, Charles F.

1987-01-01

109

RELATIVISTIC ELECTRON LOSSES RELATED TO PROTON PRECIPITATION AND EMIC WAVES

NASA Astrophysics Data System (ADS)

Observations of loss of relativistic electrons to the atmosphere is presented and related to SW parameters. It is shown that the L-region of relativistic electron loss matched the anisotropic proton zone. In this zone the pitch angle distribution of the protons are unstable and can generate/amplify EMIC waves which in turn scatter the electrons into the atmosphere. In spatial limited regions, located close to the plasma pause, there can be enhanced losses of protons (sometime completely filling the loss cone). These regions of proton losses (spikes) are shown to give rise to EMIC waves leading to enhance scattering of the relativistic electrons. In the main phase of the storm the proton spikes are located in the midnight/evening sector, but in the storm recovery phase they are located at all MLTs. The anisotropic proton zone and proton spikes are observed in all storms, but not all storms contain an elevated flux of relativistic electrons.

Soraas, F.; Sandanger, M. I.; Aarsnes, K.; Oksavik, K.; Evans, D. S.

2009-12-01

110

Linear Wave Propagation in Mildly Relativistic Thermal Pair Plasmas

We present dispersion relations and eigenmodes for linear waves propagating in fluid-like mildly relativistic thermal pair plasmas For any given wavevector, four modes are possible: two with sound wave-like properties, and two that are isobaric and essentially non-propagating. One of the isobaric modes strongly perturbs the pair balance, while the other does so much more weakly. Short-wavelength sound waves propagate

Paola Pietrini; Julian H. Krolik

1994-01-01

111

Negative energy waves and quantum relativistic Buneman instabilities.

The quantum relativistic Buneman instability is investigated theoretically using a collective Klein-Gordon model for the electrons and a cold fluid model for the ions. The growth rate and unstable wave spectrum is investigated in different parameter regimes corresponding to various degrees of relativistic and quantum effects. The results may be important for streaming instabilities involving ion dynamics in very dense plasmas. PMID:23031033

Haas, F; Eliasson, B; Shukla, P K

2012-09-01

112

Simulation of a blast wave in a shock tube by using perforated plates in the driver

The simulation of a blast wave in a conventional air-driven shock tube by means of judiciously positioning perforated plates in the driver with porosities judiciously selected is investigated both numerically and experimentally. For the numerical study the random-choice method is used in a much improved and extended form. Most notable in terms of the anaysis, which is presented and explained

K. Y. Zhang; J. J. Gottlieb

1986-01-01

113

12. Blast waves and supernova remnants 12.1 Self-similarity and scales

12. Blast waves and supernova remnants 12.1 Self-similarity and scales In galaxies one finds a many can arise from strong stellar winds and from stellar explosions, supernova. Supernovae are caused by run-away thermonuclear reactions that occur when stellar cores collapse. A type I supernova involves

Pohl, Martin Karl Wilhelm

114

Electron cyclotron waves and current drive in a relativistic plasma

NASA Astrophysics Data System (ADS)

The importance of relativistic effects on wave damping for electron cyclotron waves has been established for the electromagnetic X and O modes [1], and for the electrostatic Bernstein mode [2]. We have developed a numerical code R2D2 to solve the dispersion relation for EC waves in a fully relativistic plasma [2]. The wave polarization, energy flow density, and density of power absorbed are also calculated. We investigate, in detail, the effects of relativity on EC wave damping and propagation. R2D2 is coupled to a kinetic code DKE [3] which solves the fully relativistic Fokker-Planck equation. Two different current drive mechanisms using EC waves -- the Fisch-Boozer and the Ohkawa schemes -- are studied. The importance of relativistic effects on these current drive mechanisms is determined. [1] I.P. Shkarofsky, Phys. Fluids 9, 561 (1966). [2] A.K. Ram, J. Decker, and Y. Peysson, J. Plasma Phys. 71, 675 (2005). [3] J. Decker and Y. Peysson, Euratom-CEA Rep. EUR-CEA-FC-1736 (2004).

Decker, J.; Ram, A. K.

2006-10-01

115

Nonlinear hydrodynamic Langmuir waves in fully degenerate relativistic plasma

NASA Astrophysics Data System (ADS)

The combined effect of special relativity and electron degeneracy on Langmuir waves is analyzed by utilizing a rigorous fully relativistic hydrodynamic model. Assuming a traveling wave solution form, a set of conservation laws is identified, together with a pseudo-potential function depending on the relativistic parameter pF/(m c) (where pF is the Fermi momentum, m is the mass of the charge carriers and c the speed of light), as well as on the amplitude of the electrostatic energy perturbation.

Haas, F.; Kourakis, I.

2015-04-01

116

NASA Astrophysics Data System (ADS)

A Free-Lagrange numerical procedure for the simulation of two-dimensional inviscid compressible flow is described in detail. The unsteady Euler equations are solved on an unstructured Lagrangian grid based on a density-weighted Voronoi mesh. The flow solver is of the Godunov type, utilising either the HLLE (2 wave) approximate Riemann solver or the more recent HLLC (3 wave) variant, each adapted to the Lagrangian frame. Within each mesh cell, conserved properties are treated as piece-wise linear, and a slope limiter of the MUSCL type is used to give non-oscillatory behaviour with nominal second order accuracy in space. The solver is first order accurate in time. Modifications to the slope limiter to minimise grid and coordinate dependent effects are described. The performances of the HLLE and HLLC solvers are compared for two test problems; a one-dimensional shock tube and a two-dimensional blast wave confined within a rigid cylinder. The blast wave is initiated by impulsive heating of a gas column whose centreline is parallel to, and one half of the cylinder radius from, the axis of the cylinder. For the shock tube problem, both solvers predict shock and expansion waves in good agreement with theory. For the HLLE solver, contact resolution is poor, especially in the blast wave problem. The HLLC solver achieves near-exact contact capture in both problems.

Ball, G. J.

1996-02-01

117

Shock Tube Design for High Intensity Blast Waves for Laboratory Testing of Armor and Combat Materiel

Shock tubes create simulated blast waves which can be directed and measured to study blast wave effects under laboratory conditions. It is desirable to increase available peak pressure from ~1 MPa to ~5 MPa to simulate closer blast sources and facilitate development and testing of personal and vehicle armors. Three methods were investigated to increase peak simulated blast pressure produced by an oxy-acetylene driven shock tube while maintaining suitability for laboratory studies. The first method is the addition of a Shchelkin spiral priming section which works by increasing the turbulent flow of the deflagration wave, thus increasing its speed and pressure. This approach increased the average peak pressure from 1.17 MPa to 5.33 MPa while maintaining a relevant pressure-time curve (Friedlander waveform). The second method is a bottleneck between the driving and driven sections. Coupling a 79 mm diameter driving section to a 53 mm driven section increased the peak pressure from 1.17 MPa to 2.25 MPa. Using a 1...

Courtney, Elijah; Courtney, Michael

2015-01-01

118

Prospects for studying how high-intensity compression waves cause damage in human blast injuries

NASA Astrophysics Data System (ADS)

Since World War I, explosions have accounted for over 70% of all injuries in conflict. With the development of improved personnel protection of the torso, improved medical care and faster aeromedical evacuation, casualties are surviving with more severe injuries to the extremities. Understanding the processes involved in the transfer of blast-induced shock waves through biological tissues is essential for supporting efforts aimed at mitigating and treating blast injury. Given the inherent heterogeneities in the human body, we argue that studying these processes demands a highly integrated approach requiring expertise in shock physics, biomechanics and fundamental biological processes. This multidisciplinary systems approach enables one to develop the experimental framework for investigating the material properties of human tissues that are subjected to high compression waves in blast conditions and the fundamental cellular processes altered by this type of stimuli. Ultimately, we hope to use the information gained from these studies in translational research aimed at developing improved protection for those at risk and improved clinical outcomes for those who have been injured from a blast wave.

Brown, Katherine; Bo, Chiara; Masouros, Spyros; Ramasamy, Arul; Newell, Nicolas; Bonner, Timothy; Balzer, Jens; Hill, Adam; Clasper, Jon; Bull, Anthony; Proud, William

2012-03-01

119

We consider wave packets of free particles with a general energy-momentum dispersion relation E(p). The spreading of the wave packet is determined by the velocity v={partial_derivative}{sub p}E. The position-velocity uncertainty relation {delta}x{delta}v{>=}1/2 |<{partial_derivative}{sub p}{sup 2}E>| is saturated by minimal uncertainty wave packets {phi}(p)=Aexp(-{alpha}E(p)+{beta}p). In addition to the standard minimal Gaussian wave packets corresponding to the non-relativistic dispersion relation E(p)=p{sup 2}/2m, analytic calculations are presented for the spreading of wave packets with minimal position-velocity uncertainty product for the lattice dispersion relation E(p)=-cos(pa)/ma{sup 2} as well as for the relativistic dispersion relation E(p)={radical}(p{sup 2}+m{sup 2}). The boost properties of moving relativistic wave packets as well as the propagation of wave packets in an expanding Universe are also discussed.

Al-Hashimi, M.H. [Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, Bern University, Sidlerstrasse 5, CH-3012 Bern (Switzerland)], E-mail: hashimi@itp.unibe.ch; Wiese, U.-J. [Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, Bern University, Sidlerstrasse 5, CH-3012 Bern (Switzerland)

2009-12-15

120

Bernstein wave in relativistic plasma with arbitrary energy anisotropy

NASA Astrophysics Data System (ADS)

The Bernstein wave (BW) in a magnetized relativistic plasma is discussed in detail for a particular choice of distribution function1 that permits an exact analytical reduction of the dispersion relation for arbitrary energy anisotropy. The resulting dispersion relation is solved numerically in order to highlight the effect of energy anisotropy and the relativistic effects on the propagation characteristics of BW. The oscillatory character of the Bessel function appears due to the particular choice of the distribution function and thus changes the propagation characteristics significantly for short wavelengths (i.e., perpendicular wavelength is smaller than Larmour radius k?>1 ). However, for longer wavelengths, these characteristics show a trend similar to the Maxwellian distribution. The dispersion relations for the non-relativistic and ultra-relativistic regimes are also obtained. The anisotropy provides a free energy to make the Bernstein wave unstable satisfying the threshold condition due to oscillatory character of the Bessel functions. Our result may prove useful for a wide range of applications e.g., for magnetized relativistic plasma environments such as astrophysical and space plasmas, laboratory plasmas with intense rf heating and for relativistic electron beams used for microwave generation. 1. P. H. Yoon and R.C. Davidson, Phys. Rev. A, 35, 2619 (1987).

Bashir, M.; Hirose, A.; Murtaza, G.; Noreen, N.; Tahir, I.

2012-12-01

121

Surfatron acceleration of a relativistic particle by electromagnetic plane wave

We study motion of a relativistic charged particle in a plane slow electromagnetic wave and background uniform magnetic field. The wave propagates normally to the background field. Under certain conditions, the resonance between the wave and the Larmor motion of the particle is possible. Capture into this resonance results in acceleration of the particle along the wave front (surfatron acceleration). We analyse the phenomenon of capture and show that a captured particle never leaves the resonance and its energy infinitely grows. Scattering on the resonance is also studied. We find that this scattering results in diffusive growth of the particle energy. Finally, we estimate energy losses due to radiation by an accelerated particle.

A. I. Neishtadt; A. A. Vasiliev; A. V. Artemyev

2010-11-09

122

THE EARLY BLAST WAVE OF THE 2010 EXPLOSION OF U SCORPII

Three-dimensional hydrodynamic simulations exploring the first 18 hr of the 2010 January 28 outburst of the recurrent nova U Scorpii have been performed. Special emphasis was placed on capturing the enormous range in spatial scales in the blast. The pre-explosion system conditions included the secondary star and a flared accretion disk. These conditions can have a profound influence on the evolving blast wave. The blast itself is shadowed by the secondary star, which itself gives rise to a low-temperature bow shock. The accretion disk is completely destroyed in the explosion. A model with a disk gas density of 10{sup 15} cm{sup -3} produced a blast wave that is collimated and with clear bipolar structures, including a bipolar X-ray emitting shell. The degree of collimation depends on the initial mass of ejecta, energy of explosion, and circumstellar gas density distribution. It is most pronounced for a model with the lowest explosion energy (10{sup 43} erg) and mass of ejecta (10{sup -8} M {sub sun}). The X-ray luminosities of three of six models computed are close to, but consistent with, an upper limit to the early blast X-ray emission obtained by the Swift satellite, the X-ray luminosity being larger for higher circumstellar gas density and higher ejecta mass. The latter consideration, together with estimates of the blast energy from previous outbursts, suggests that the mass of ejecta in the 2010 outburst was not larger than 10{sup -7} M {sub sun}.

Drake, J. J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Orlando, S. [INAF-Osservatorio Astronomico di Palermo 'G.S. Vaiana', Piazza del Parlamento 1, 90134 Palermo (Italy)

2010-09-10

123

Gravitational Wave Science: Challenges for Numerical Relativistic Astrophysics

NASA Technical Reports Server (NTRS)

Gravitational wave detectors on earth and in space will open up a new observational window on the universe. The new information about astrophysics and fundamental physics these observations will bring is expected to pose exciting challenges. This talk will provide an overview of this emerging area of gravitational wave science, with a focus on the challenges it will bring for numerical relativistic astrophysics and a look at some recent results.

Cenrella, Joan

2005-01-01

124

Loss of relativistic electrons at geosynchronous orbit by EMIC waves

NASA Astrophysics Data System (ADS)

There are several loss mechanisms for relativistic electrons in the Earth's outer radiation belt. They are associated with adiabatic and/or non-adiabatic processes. Adiabatic processes do not produce a real loss of radiation belt particles because the relativistic particle flux variations are modulated by the change in the magnetic field strength. That is, the flux decrease is due to the field decrease, and the flux recovers when the field returns. Secondly, non-adiabatic processes produce irreversible losses; in other words, particles are lost permanently. Unlike adiabatic processes, non-adiabatic processes lead to a permanent loss. One of them is atmospheric precipitation associated with wave-particle interactions or magnetic moment scattering due to field stretching. The other is the loss through the magnetopause, called magnetopause shadowing. Recently, it has been suggested that EMIC waves are responsible for relativistic electron loss. In this study we selected several intervals showing relativistic flux dropouts at geosynchronous orbit. Around the intervals, geosynchronous spacecraft observed well-defined EMIC waves. We examine if the EMIC waves are a major factor to control the flux dropouts at geosynchronous orbit. We also discuss the effect of other non-adiabatic mechanisms for the flux dropouts.

Hyun, K.; Kim, K.; Lee, E.; Lee, D.

2013-12-01

125

Relativistic particle motion in nonuniform electromagnetic waves

NASA Technical Reports Server (NTRS)

It is shown that a charged particle moving in a strong nonuniform electromagnetic wave suffers a net acceleration in the direction of the negative intensity gradient of the wave. Electrons will be expelled perpendicularly from narrow laser beams and various instabilities can result.

Schmidt, G.; Wilcox, T.

1973-01-01

126

into an external medium and on the other by the thermal pressure of hot gas inside the blast wave. Ryu and Vishniac 500 m diameter nylon target pin immersed in 10 Torr of nitrogen gas. The resulting explosion from

Ditmire, Todd

127

The physical properties of the blast wave produced by a stoichiometric propane/oxygen explosion

NASA Astrophysics Data System (ADS)

The trajectory of the primary shock produced by the explosion of a nominal 18.14 t (20 tn) hemispherical propane/oxygen charge was analysed previously to provide the physical properties immediately behind the shock, but gave no information about the time-resolved properties throughout the blast wave. The present study maps all the physical properties of the wave throughout and beyond the positive durations for a range of distances from about 1.6-18 m scaled to a 1 kg charge at NTP. The physical properties were calculated using a hydro-code to simulate the flow field produced by a spherical piston moving with a specific trajectory. This technique has been used extensively to determine the physical properties of blast waves from a variety of sources for which the piston path was determined by high-speed photography of smoke tracers established close to the charges immediately before detonation. In the case of the propane/oxygen explosion, smoke tracer data were not available to determine the trajectory of the spherical piston. An arbitrary piston path was used and its trajectory iteratively adjusted until it produced a blast wave with a primary shock whose trajectory exactly matched the measured trajectory from the propane/oxygen explosion. Throughout the studied flow field the time histories of hydrostatic pressure, density and particle velocity are well described by fits to the modified Friedlander equation. The properties are presented as functions of scaled radius and are compared with the properties of the blast wave from a 1 kg TNT surface burst explosion, and with other measurements of the same explosion.

Dewey, M. C.; Dewey, J. M.

2014-07-01

128

The physical properties of the blast wave produced by a stoichiometric propane/oxygen explosion

NASA Astrophysics Data System (ADS)

The trajectory of the primary shock produced by the explosion of a nominal 18.14 t (20 tn) hemispherical propane/oxygen charge was analysed previously to provide the physical properties immediately behind the shock, but gave no information about the time-resolved properties throughout the blast wave. The present study maps all the physical properties of the wave throughout and beyond the positive durations for a range of distances from about 1.6-18 m scaled to a 1 kg charge at NTP. The physical properties were calculated using a hydro-code to simulate the flow field produced by a spherical piston moving with a specific trajectory. This technique has been used extensively to determine the physical properties of blast waves from a variety of sources for which the piston path was determined by high-speed photography of smoke tracers established close to the charges immediately before detonation. In the case of the propane/oxygen explosion, smoke tracer data were not available to determine the trajectory of the spherical piston. An arbitrary piston path was used and its trajectory iteratively adjusted until it produced a blast wave with a primary shock whose trajectory exactly matched the measured trajectory from the propane/oxygen explosion. Throughout the studied flow field the time histories of hydrostatic pressure, density and particle velocity are well described by fits to the modified Friedlander equation. The properties are presented as functions of scaled radius and are compared with the properties of the blast wave from a 1 kg TNT surface burst explosion, and with other measurements of the same explosion.

Dewey, M. C.; Dewey, J. M.

2014-11-01

129

Jet and vortex flow induced by anisotropic blast wave: experimental and computational study

NASA Astrophysics Data System (ADS)

This paper discusses gas-dynamic aspects of intense explosions in uniform environments. In experiments, the energy of a laser is almost instantaneously released in a volume of air shaped as either a flattened or stretched cylinder generating a blast wave. Its shape evolves in time and ultimately becomes spherical. But momentum transferred to the air when the blast wave is strongly nonspherical is anisotropic. As a result, a subsonic jet and a vortex are induced and propagate along the symmetry axis or along the perpendicular plane, depending on the initial configuration of the blast wave. Simulations based on a free-Lagrangian method for a nonviscous gas are in good agreement with the experiments. Velocities, circulation, and positions of fluid particles found in computations give an insight into the causes and details of the flow. Two simultaneous and contrary processes take place - vorticity production by the anisotropic shock wave and baroclinical generation of vorticity at the boundary of the heated gas - which give rise to net circulation.

Svetsov, V.; Popova, M.; Rybakov, V.; Artemiev, V.; Medveduk, S.

130

Relativistic collision operators for modeling noninductive current drive by waves

A weakly relativistic Fokker-Planck operator for electron-electron collision was first used by Karney and Fisch to calculate the efficiencies of current drive by waves with fast phase velocity [C. F. F. Karney and N. J. Fisch, Phys. Fluids 28, 116 (1985)]. The present work extends Karney and Fisch's work by expressing the weakly relativistic collision operator in potential form, and working out a general Legendre expansion of the potential functions. This general Legendre expansion reproduces the results in Karney and Fisch's paper and is useful in implementing the weakly relativistic operator in Fokker-Planck codes. To justify the use of the weakly relativistic collision operator for current drive applications under ITER conditions, a comparison is made of current drive efficiencies predicted by this operator and a fully relativistic collision operator. Good agreement between efficiencies predicted by these two models is found. This suggests that the weakly relativistic collision operator is sufficiently precise for modeling the current drive schemes under ITER conditions.

Hu, Y. J.; Hu, Y. M. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui 230031, China and Center for Magnetic Fusion Theory, Chinese Academy of Sciences, Hefei, Anhui 230031 (China); Lin-Liu, Y. R. [Department of Physics and Center for Mathematics and Theoretical Physics, National Central University, Taiwan (China)

2011-02-15

131

Channeling of relativistic laser pulses, surface waves, and electron acceleration.

The interaction of a high-energy relativistic laser pulse with an underdense plasma is studied by means of 3-dimensional particle in cell simulations and theoretical analysis. For powers above the threshold for channeling, the laser pulse propagates as a single mode in an electron-free channel during a time of the order of 1 picosecond. The steep laser front gives rise to the excitation of a surface wave along the sharp boundaries of the ion channel. The surface wave first traps electrons at the channel wall and preaccelerates them to relativistic energies. These particles then have enough energy to be further accelerated in a second stage through an interplay between the acceleration due to the betatron resonance and the acceleration caused by the longitudinal part of the surface wave electric field. It is necessary to introduce this two-stage process to explain the large number of high-energy electrons observed in the simulations. PMID:22463415

Naseri, N; Pesme, D; Rozmus, W; Popov, K

2012-03-01

132

Relativistic solitary waves modulating long laser pulses in plasmas

This article discusses the existence of solitary electromagnetic waves trapped in a self-generated Langmuir wave and embedded in an infinitely long circularly polarized electromagnetic wave propagating through a plasma. From the mathematical point of view they are exact solutions of the 1-dimensional relativistic cold fluid plasma model with nonvanishing boundary conditions. Under the assumption of traveling wave solutions with velocity $V$ and vector potential frequency $\\omega$, the fluid model is reduced to a Hamiltonian system. The solitary waves are homoclinic (grey solitons) or heteroclinic (dark solitons) orbits to fixed points. By using a dynamical systems description of the Hamiltonian system and a spectral method, we identify a great variety of solitary waves, including asymmetric ones, discuss their disappearance for certain parameter values, and classify them according to: (i) grey or dark character, (ii) the number of humps of the vector potential envelope and (iii) their symmetries. The solution...

Sánchez-Arriaga, G; Lefebvre, E

2011-01-01

133

NASA Astrophysics Data System (ADS)

We investigate the dynamics and afterglow light curves of gamma-ray burst blast waves that encounter various density structures (such as bumps, voids, or steps) in the surrounding ambient medium. We present and explain the characteristic response features that each type of density structure in the medium leaves on the forward shock (FS) and reverse shock (RS) dynamics for blast waves with either a long-lived or short-lived RS. We show that when the ambient medium density drops, the blast waves exhibit in some cases a period of an actual acceleration (even during their deceleration stage) due to adiabatic cooling of blast waves. Comparing numerical examples that have different shapes of bumps or voids, we propose a number of consistency tests that must be satisfied by correct modeling of blast waves. Our model results successfully pass these tests. Employing a Lagrangian description of blast waves, we perform a sophisticated calculation of afterglow emission. We show that as a response to density structures in the ambient medium, the RS light curves produce more significant variations than the FS light curves. Some observed features (such as rebrightenings, dips, or slow wiggles) can be more easily explained within the RS model. We also discuss the origin of these different features imprinted on the FS and RS light curves.

Uhm, Z. Lucas; Zhang, Bing

2014-07-01

134

Nonlinear growth of dynamical overstabilities in blast waves. [effects on supernova remnants

NASA Technical Reports Server (NTRS)

The numerical gasdynamics code ZEUS-2D is used to directly model the dynamical overstabilities in blast waves. The linear analysis is confirmed by perturbing a blast wave with a low-amplitude eigenfunction of the overstability. The amplitude of the perturbations is increased in order to determine the nonlinear behavior of the overstabilities. The overstability is found to saturate due to weak transverse shocks in the shell. Transverse velocities in the dense shell reach the postshock sound speed, and high-density regions with sizes of the order of the shell thickness form. Transverse oscillations continue even after saturation. This confirms and explains the damping of the overstability experimentally discovered by Grun et al. (1991).

Mac Low, Mordecai-Mark; Norman, Michael L.

1993-01-01

135

On self-similar blast waves headed by the Chapman-Jouguet detonation.

NASA Technical Reports Server (NTRS)

Consideration of the whole class of self-similar solutions for blast waves bounded by Chapman-Jouguet detonations that propagate into a uniform, quiescent, zero counterpressure atmosphere of a perfect gas with constant specific heats. Since such conditions can be approached quite closely by some actual chemical systems at NTP, this raises the interesting possibility of the existence of Chapman-Jouguet detonations of variable velocity. The principal virtue of the results presented is, however, more of theoretical significance. They represent the limiting case for all the self-similar blast waves headed by gasdynamic discontinuities associated with a deposition of finite amounts of energy, and they exhibit some unique features owing to the singular nature of the Chapman-Jouguet condition.

Oppenheim, A. K.; Kuhl, A. L.; Kamel, M. M.

1972-01-01

136

Most of middle-aged supernova remnants (SNRs) have a distorted and complicated appearance which cannot be explained in the framework of the Sedov-Taylor model. We consider three typical examples of such SNRs (Vela SNR, MSH 15-52, G 309.2-00.6) and show that their structure could be explained as a result of interaction of a supernova (SN) blast wave with the ambient medium preprocessed by the action of the SN progenitor's wind and ionized emission.

V. V. Gvaramadze

1999-12-24

137

Calculation of wing response to gusts and blast waves with vortex lift effect

NASA Technical Reports Server (NTRS)

A numerical study of the response of aircraft wings to atmospheric gusts and to nuclear explosions when flying at subsonic speeds is presented. The method is based upon unsteady quasi-vortex-lattice method, unsteady suction analogy, and Pade approximate. The calculated results, showing vortex lag effect, yield reasonable agreement with experimental data for incremental lift on wings in gust penetration and due to nuclear blast waves.

Chao, D. C.; Lan, C. E.

1983-01-01

138

The time development of a blast wave with shock-heated electrons

NASA Technical Reports Server (NTRS)

Accurate approximations are presented for the time development of both edge conditions and internal structures of a blast wave with shock heated electrons, and equal ion and electron temperatures at the shock. The cases considered evolve in cavities with power law ambient densities (including the uniform ambient density case) and have negligible external pressure. Account is taken of possible saturation of the thermal conduction flux. The structures evolve smoothly to the adiabatic structures.

Edgar, R. J.; Cox, D. P.

1984-01-01

139

Calculation of wing response to gusts and blast waves with vortex lift effect

NASA Technical Reports Server (NTRS)

A numerical study of the response of aircraft wings to atmospheric gusts and to nuclear explosions when flying at subsonic speeds is presented. The method is based upon unsteady quasi-vortex lattice method, unsteady suction analogy and Pade approximant. The calculated results, showing vortex lag effect, yield reasonable agreement with experimental data for incremental lift on wings in gust penetration and due to nuclear blast waves.

Chao, D. C.; Lan, C. E.

1983-01-01

140

The time development of a blast wave with shock heated electrons

NASA Technical Reports Server (NTRS)

Accurate approximations are presented for the time development of both edge conditions and internal structures of a blast wave with shock heated electrons, and equal ion and electron temperatures at the shock. The cases considered evolve in cavities with power law ambient densities (including the uniform ambient density case) and have negligible external pressure. Account is taken of possible saturation of the thermal conduction flux. The structures evolve smoothly to the adiabatic structures.

Edgar, R. J.; Cox, D. P.

1983-01-01

141

Rarefaction wave in relativistic steady magnetohydrodynamic flows

We construct and analyze a model of the relativistic steady-state magnetohydrodynamic rarefaction that is induced when a planar symmetric flow (with one ignorable Cartesian coordinate) propagates under a steep drop of the external pressure profile. Using the method of self-similarity, we derive a system of ordinary differential equations that describe the flow dynamics. In the specific limit of an initially homogeneous flow, we also provide analytical results and accurate scaling laws. We consider that limit as a generalization of the previous Newtonian and hydrodynamic solutions already present in the literature. The model includes magnetic field and bulk flow speed having all components, whose role is explored with a parametric study.

Sapountzis, Konstantinos, E-mail: ksapountzis@phys.uoa.gr; Vlahakis, Nektarios, E-mail: vlahakis@phys.uoa.gr [Faculty of Physics, University of Athens, 15784 Zografos, Athens (Greece)

2014-07-15

142

Constraints on the non-thermal emission from ? Carinae's blast wave of 1843

NASA Astrophysics Data System (ADS)

Non-thermal hard X-ray and high-energy (HE; 1 MeV < E < 100 GeV) ?-ray emission in the direction of ? Carinae has been recently detected using the INTEGRAL, AGILE and Fermi satellites. This emission has been interpreted either in the framework of particle acceleration in the colliding wind region between the two massive stars or in the very fast moving blast wave which originates in the historical 1843 "great eruption". Archival Chandra data has been reanalysed to search for signatures of particle acceleration in ? Carinae's blast wave. No shell-like structure could be detected in hard X-rays and a limit has been placed on the non-thermal X-ray emission from the shell. The time dependence of the target radiation field of the Homunculus is used to develop a single zone model for the blast wave. Attempting to reconcile the X-ray limit with the HE ?-ray emission using this model leads to a very hard electron injection spectrum dN/dE ? E - ? with ? < 1.8, harder than the canonical value expected from diffusive shock acceleration.

Skilton, J. L.; Domainko, W.; Hinton, J. A.; Jones, D. I.; Ohm, S.; Urquhart, J. S.

2012-03-01

143

Influence of ambient air pressure on the energy conversion of laser-breakdown induced blast waves

NASA Astrophysics Data System (ADS)

Influence of ambient pressure on energy conversion efficiency from a Nd?:?glass laser pulse (? = 1.053 µm) to a laser-induced blast wave was investigated at reduced pressure. Temporal incident and transmission power histories were measured using sets of energy meters and photodetectors. A half-shadowgraph half-self-emission method was applied to visualize laser absorption waves. Results show that the blast energy conversion efficiency ?bw decreased monotonically with the decrease in ambient pressure. The decrease was small, from 40% to 38%, for the pressure change from 101 kPa to 50 kPa, but the decrease was considerable, to 24%, when the pressure was reduced to 30 kPa. Compared with a TEA-CO2-laser-induced blast wave (? = 10.6 µm), higher fraction absorption in the laser supported detonation regime ?LSD of 90% was observed, which is influenced slightly by the reduction of ambient pressure. The conversion fraction ?bw/?LSD?90% was achieved at pressure >50 kPa, which is significantly higher than that in a CO2 laser case.

Wang, Bin; Komurasaki, Kimiya; Arakawa, Yoshihiro

2013-09-01

144

Extended adiabatic blast waves and a model of the soft X-ray background

NASA Technical Reports Server (NTRS)

The suggestion has been made that much of the soft X-ray background observed in X-ray astronomy might arise from being inside a very large supernova blast wave propagating in the hot, low-density component of the interstellar (ISM) medium. An investigation is conducted to study this possibility. An analytic approximation is presented for the nonsimilar time evolution of the dynamic structure of an adiabatic blast wave generated by a point explosion in a homogeneous ambient medium. A scheme is provided for evaluating the electron-temperature distribution for the evolving structure, and a procedure is presented for following the state of a given fluid element through the evolving dynamical and thermal structures. The results of the investigation show that, if the solar system were located within a blast wave, the Wisconsin soft X-ray rocket payload would measure the B and C band count rates that it does measure, provided conditions correspond to the values calculated in the investigation.

Cox, D. P.; Anderson, P. R.

1982-01-01

145

Relativistic Effects in Electron Bernstein Wave Heating and Current Drive

NASA Astrophysics Data System (ADS)

The NSTX plasma provides an interesting opportunity for heating and current drive by electron Bernstein waves (EBW). We have been studying the propagation characteristics of EBWs and their interaction with electrons using fully relativistic formulations. The numerical studies make use of a dispersion relation and ray tracing code (R2D2) and Fokker-Planck codes (DKE and BANDIT). We find that there is a significant difference between relativistic and non-relativistic description of EBW propagation for NSTX plasmas. The consequential effect on the EBW generated plasma current is being studied. EBWs drive Ohkawa current effectively in the outer half of the plasma and Fisch-Boozer current in the core. Thus, EBWs could be used for modifying the current profile. Details of these studies will be presented.

Ram, A. K.; Decker, J.; McGregor, D. E.; Cairns, R. A.; Lashmore-Davies, C. N.; O'Brien, M.

2004-11-01

146

Parametric instability of a relativistically strong electromagnetic wave.

NASA Technical Reports Server (NTRS)

The stability of a circularly polarized electromagnetic wave that is strong enough to make plasma electrons, but not ions, relativistic is studied. Small perturbations are considered which propagate parallel to the large-amplitude driver. A relativistically strong wave can be unstable on time scales as short as twice its own oscillation period, and decays into a forward-going plasma oscillation and either one or two electromagnetic waves. Ion motion introduces an additional instability which can be important at short perturbation wavelengths, where the driver would otherwise be stable. The unstable ion and electron modes both have potential for producing anomalously large acceleration of relativistic particles, as well as significant amounts of backscattered light. These effects may be important in two applications: (1) the use of intense lasers to heat or compress plasma, and (2) the plasma surrounding a pulsar, if the pulsar is losing energy by radiation of electromagnetic waves at its rotation frequency. Instability persists in the nonrelativistic regime, reducing to stimulated Raman scattering as a special case.

Max, C. E.

1973-01-01

147

Electron acceleration by young supernova remnant blast waves

NASA Technical Reports Server (NTRS)

Some general considerations regarding relativistic particle acceleration by young supernova remnants are reviewed. Recent radio observations of supernova remnants apparently locate the bounding shock and exhibit large electron density gradients which verify the presence of strong particle scattering. The radio 'rim' in Tycho's remnant has been found to contain a predominantly radial magnetic field. This may be attributable to an instability of the shock surface and a progress report on an investigation of the stability of strong shocks in partially ionized media is presented.

Blandford, R. D.

1992-01-01

148

Detonation of a high-explosive produces shock-blast wave, shrapnel, and gaseous products. While direct exposure to blast is a concern near the epicenter, shock-blast can affect subjects, even at farther distances. When a pure shock-blast wave encounters the subject, in the absence of shrapnels, fall, or gaseous products the loading is termed as primary blast loading and is the subject of this paper. The wave profile is characterized by blast overpressure, positive time duration, and impulse and called herein as shock-blast wave parameters (SWPs). These parameters in turn are uniquely determined by the strength of high explosive and the distance of the human subjects from the epicenter. The shape and magnitude of the profile determine the severity of injury to the subjects. As shown in some of our recent works (1–3), the profile not only determines the survival of the subjects (e.g., animals) but also the acute and chronic biomechanical injuries along with the following bio-chemical sequelae. It is extremely important to carefully design and operate the shock tube to produce field-relevant SWPs. Furthermore, it is vital to identify and eliminate the artifacts that are inadvertently introduced in the shock-blast profile that may affect the results. In this work, we examine the relationship between shock tube adjustable parameters (SAPs) and SWPs that can be used to control the blast profile; the results can be easily applied to many of the laboratory shock tubes. Further, replication of shock profile (magnitude and shape) can be related to field explosions and can be a standard in comparing results across different laboratories. Forty experiments are carried out by judiciously varying SAPs such as membrane thickness, breech length (66.68–1209.68?mm), measurement location, and type of driver gas (nitrogen, helium). The effects SAPs have on the resulting shock-blast profiles are shown. Also, the shock-blast profiles of a TNT explosion from ConWep software is compared with the profiles obtained from the shock tube. To conclude, our experimental results demonstrate that a compressed-gas shock tube when designed and operated carefully can replicate the blast time profiles of field explosions accurately. Such a faithful replication is an essential first step when studying the effects of blast induced neurotrauma using animal models. PMID:25520701

Sundaramurthy, Aravind; Chandra, Namas

2014-01-01

149

Chaotic Motion of Relativistic Electrons Driven by Whistler Waves

NASA Technical Reports Server (NTRS)

Canonical equations governing an electron motion in electromagnetic field of the whistler mode waves propagating along the direction of an ambient magnetic field are derived. The physical processes on which the equations of motion are based .are identified. It is shown that relativistic electrons interacting with these fields demonstrate chaotic motion, which is accompanied by the particle stochastic heating and significant pitch angle diffusion. Evolution of distribution functions is described by the Fokker-Planck-Kolmogorov equations. It is shown that the whistler mode waves could provide a viable mechanism for stochastic energization of electrons with energies up to 50 MeV in the Jovian magnetosphere.

Khazanov, G. V.; Telnikhin, A. A.; Kronberg, Tatiana K.

2007-01-01

150

X band bifrequency coaxial relativistic backward wave oscillator

NASA Astrophysics Data System (ADS)

An idea of azimuthally dividing the slow wave structure (SWS) of a relativistic backward wave oscillator (RBWO) into two parts is introduced to realize a bifrequency oscillation. To enhance the stability of this device, two sectorial waveguides are inserted into the SWS specially. The synchronization condition that is necessary to get a sustainable microwave output is derived. In Particle in cell simulation, bifrequency microwave at frequencies of 9.7 GHz and 9.87 GHz is generated with average power of 0.66 GW, conversion efficiency is 15.8% when beam voltage is 520 kV and current 8 kA.

Wang, Dong; Qin, Fen; Chen, Dai-Bing; Wen, Jie; Jin, Xiao

2011-12-01

151

Whistler wave generation by non-gyrotropic, relativistic, electron beams

Particle-in-cell code, EPOCH, is used for studying features of the wave component evident to propagate backwards from the front of the non-gyrotropic, relativistic beam of electrons injected in the Maxwellian, magnetised background plasma with decreasing density profile. According to recent findings presented in Tsiklauri [Phys. Plasmas 18, 052903 (2011)], Schmitz and Tsiklauri [Phys. Plasmas 20, 062903 (2013)], and Pechhacker and Tsiklauri [Phys. Plasmas 19, 112903 (2012)], in a 1.5-dimensional magnetised plasma system, the non-gyrotropic beam generates freely escaping electromagnetic radiation with properties similar to the Type-III solar radio bursts. In this study, the backwards propagating wave component evident in the perpendicular components of the electromagnetic field in such a system is presented for the first time. Background magnetic field strength in the system is varied in order to prove that the backwards propagating wave's frequency, prescribed by the whistler wave dispersion relation, is proportional to the specified magnetic field. Moreover, the identified whistlers are shown to be generated by the normal Doppler-shifted relativistic resonance. Large fraction of the energy of the perpendicular electromagnetic field components is found to be carried away by the whistler waves, while a small but sufficient fraction is going into L- and R-electromagnetic modes.

Skender, M.; Tsiklauri, D. [School of Physics and Astronomy, Queen Mary University of London, 327 Mile End Road, London E1 4NS (United Kingdom)] [School of Physics and Astronomy, Queen Mary University of London, 327 Mile End Road, London E1 4NS (United Kingdom)

2014-04-15

152

On plane waves in diluted relativistic cold plasmas

We briefly report on some exact results [G. Fiore, arXiv:1312.4665 preprint, to appear in J. Phys. A] regarding plane waves in a relativistic cold plasma. If the plasma, initially at rest, is reached by a transverse plane electromagnetic travelling-wave, then its motion has a very simple dependence on this wave in the limit of zero density, otherwise can be determined by an iterative procedure whose accuracy decreases with time or the plasma density. Thus one can describe in particular the impact of a very intense and short laser pulse onto a plasma and determine conditions for the "slingshot effect" [G. Fiore, R. Fedele, U. De Angelis, arXiv:1309.1400 preprint] to occur. The motion in vacuum of a charged test particle subject to a wave of the same kind is also determined, for any initial velocity.

Gaetano Fiore

2014-05-01

153

Low-cost rapid miniature optical pressure sensors for blast wave measurements.

This paper presents an optical pressure sensor based on a Fabry-Perot (FP) interferometer formed by a 45° angle polished single mode fiber and an external silicon nitride diaphragm. The sensor is comprised of two V-shape grooves with different widths on a silicon chip, a silicon nitride diaphragm released on the surface of the wider V-groove, and a 45° angle polished single mode fiber. The sensor is especially suitable for blast wave measurements: its compact structure ensures a high spatial resolution; its thin diaphragm based design and the optical demodulation scheme allow a fast response to the rapid changing signals experienced during blast events. The sensor shows linearity with the correlation coefficient of 0.9999 as well as a hysteresis of less than 0.3%. The shock tube test demonstrated that the sensor has a rise time of less than 2 µs from 0 kPa to 140 kPa. PMID:21643336

Wu, Nan; Wang, Wenhui; Tian, Ye; Zou, Xiaotian; Maffeo, Michael; Niezrecki, Christopher; Chen, Julie; Wang, Xingwei

2011-05-23

154

Modelling the 2010 blast wave of the symbiotic-like nova V407 Cygni

NASA Astrophysics Data System (ADS)

The symbiotic-like binary Mira and nova V407 Cyg was observed in outburst in 2010 March and monitored in several wavelength bands. The outburst had, to some extent, characteristics similar to those observed during other nova eruptions, such as that occurred recently in RS Oph and U Sco, suggesting that the blast wave interacted with the giant companion and propagated through a dense circumstellar medium enveloping the binary system. Here we report on multidimensional hydrodynamic simulations describing the 2010 outburst of V407 Cyg, exploring the first 60 d of evolution. The model takes into account thermal conduction (including the effects of heat flux saturation) and radiative cooling; the pre-explosion system conditions included the companion star and a circumbinary density enhancement that are believed to influence the evolution and morphology of the blast wave. The simulations showed that the blast and the ejecta distribution are both aspherical due to the inhomogeneous circumstellar medium in which they expand; in particular, they are significantly collimated in polar directions (producing a bipolar shock morphology) if the circumstellar envelope is characterized by an equatorial density enhancement. The blast is partially shielded by the Mira companion, producing a wake with dense and hot post-shock plasma on the rear side of the companion star; most of the X-ray emission produced during the evolution of the blast arises from this plasma structure. The observed X-ray light curve can be reproduced, assuming values of outburst energy and ejected mass similar to those of RS Oph and U Sco, if a circumbinary gas density enhancement is included in the model. In particular, our 'best-fitting' model predicts that the 2010 blast propagated through a circumbinary gas density enhancement with radius of the order of 40 au and gas density ?106 cm-3 and that the mass of ejecta in the outburst was Mej? 2 × 10-7 M? with an explosion energy E0? 2 × 1044 erg. Alternatively, the model can produce a similar X-ray light curve without the need of a circumbinary gas density enhancement only if the outburst energy and ejected mass were similar to those at the upper end of ranges for classical novae, namely Mej? 5 × 10-5 M? and E0? 5 × 1046 erg.

Orlando, Salvatore; Drake, Jeremy J.

2012-01-01

155

A parametric study was conducted to delineate the efficacy of personal protective equipment (PPE), such as ballistic faceshields and advanced combat helmets, in the case of a blast. The propagations of blast waves and their interactions with an unprotected head, a helmeted one, and a fully protected finite element head model (FEHM) were modeled. The biomechanical parameters of the brain were recorded when the FEHM was exposed to shockwaves from the front, back, top, and bottom. The directional dependent tissue response of the brain and the variable efficiency of PPE with respect to the blast orientation were two major results of this study. PMID:25413615

Sarvghad-Moghaddam, Hesam; Jazi, Mehdi Salimi; Rezaei, Asghar; Karami, Ghodrat; Ziejewski, Mariusz

2015-12-01

156

Application of blast wave theory to explosive propulsion. [system performance analysis

NASA Technical Reports Server (NTRS)

An analysis was carried out by using blast wave theory to delineate the important aspects of detonating explosives in nozzles, such as flow and wave phenomena, characteristic length and time scales, and the parameters on which the specific impulse is dependent. The propulsive system utilizes the momentum of the ambient gas set into motion in the nozzle by the explosion. A somewhat simplified model was considered for the situation where the mass of ambient gas in the nozzle is much greater than the mass of gas produced in the explosion, a condition of interest for dense atmospheres, e.g., near the surface of Venus. Instantaneous detonation and energy release was presumed to occur at the apex of a conical nozzle, and the shock wave generated by the explosion was taken to propagate as a spherical wave, thereby setting the ambient gas in the nozzle into one-dimensional radially outward motion.

Back, L. H.

1975-01-01

157

A Numerical Study on the Screening of Blast-Induced Waves for Reducing Ground Vibration

NASA Astrophysics Data System (ADS)

Blasting is often a necessary part of mining and construction operations, and is the most cost-effective way to break rock, but blasting generates both noise and ground vibration. In urban areas, noise and vibration have an environmental impact, and cause structural damage to nearby structures. Various wave-screening methods have been used for many years to reduce blast-induced ground vibration. However, these methods have not been quantitatively studied for their reduction effect of ground vibration. The present study focused on the quantitative assessment of the effectiveness in vibration reduction of line-drilling as a screening method using a numerical method. Two numerical methods were used to analyze the reduction effect toward ground vibration, namely, the “distinct element method” and the “non-linear hydrocode.” The distinct element method, by particle flow code in two dimensions (PFC 2D), was used for two-dimensional parametric analyses, and some cases of two-dimensional analyses were analyzed three-dimensionally using AUTODYN 3D, the program of the non-linear hydrocode. To analyze the screening effectiveness of line-drilling, parametric analyses were carried out under various conditions, with the spacing, diameter of drill holes, distance between the blasthole and line-drilling, and the number of rows of drill holes, including their arrangement, used as parameters. The screening effectiveness was assessed via a comparison of the vibration amplitude between cases both with and without screening. Also, the frequency distribution of ground motion of the two cases was investigated through fast Fourier transform (FFT), with the differences also examined. From our study, it was concluded that line-drilling as a screening method of blast-induced waves was considerably effective under certain design conditions. The design details for field application have also been proposed.

Park, Dohyun; Jeon, Byungkyu; Jeon, Seokwon

2009-06-01

158

Development of production scheme for the blast-wave loading of metal to harden bolt holes in rails

1.Bolt holes in rails should be blast-hardened without residual deformation or with the aim of minimal deformation; metal settlement above 3% causes macro- and microfailure of the surface and a reduction in longevity.2.In the absence of failure of the treated surface of the bolt hole, efficiency of loading by blast wave is determined by the magnitude of the hardening gradient

I. A. Churyumova; S. G. Dov'ysh

1993-01-01

159

PeV-EeV neutrinos from GRB blast waves in IceCube and future neutrino telescopes

NASA Astrophysics Data System (ADS)

Ultrahigh-energy cosmic rays (UHECRs), if accelerated in the gamma-ray burst (GRB) blast wave, are expected to produce PeV-EeV neutrinos by interacting with long-lived GRB afterglow photons. Detailed spectral and temporal properties of the flux of these neutrinos depend on the GRB blast wave evolution scenario, but can last for days to years time scale in contrast to the seconds to minutes time scale for "burst" neutrino flux contemporaneous with the prompt gamma-ray emission and which has been constrained by IceCube in the ˜50 TeV -2 PeV range. We compute expected neutrino events in IceCube in the PeV-EeV range from the blast wave of long-duration GRBs, both for the diffuse flux and for individual GRBs in the nearby universe. We show that IceCube will be able to detect the diffuse GRB blast wave neutrino flux after 5 years in operation, and will be able to distinguish it from the cosmogenic neutrino flux arising from the Greisen-Zatsepin-Kuzmin process in case the ultrahigh-energy cosmic rays are heavy nuclei. We also show that EeV neutrinos from the blast wave of an individual GRB can be detected with long-term monitoring by a future high-energy extension of IceCube for redshift up to z ˜0.5 .

Razzaque, Soebur; Yang, Lili

2015-02-01

160

Theoretical analysis of a relativistic travelling wave tube filled with plasma

A cold and uniform plasma-filled travelling wave tube with sinusoidally corrugated slow wave structure is driven by a finite thick annular intense relativistic electron beam with the entire system immersed in a strong longitudinal magnetic field. By means of the linear field theory, the dispersion relation for the relativistic travelling wave tube (RTWT) is derived. By numerical computation, the dispersion

Hong-Quan Xie; Pu-Kun Liu

2007-01-01

161

Relativistic solitary waves modulating long laser pulses in plasmas

NASA Astrophysics Data System (ADS)

This paper discusses the existence of solitary electromagnetic waves trapped in a self-generated Langmuir wave and embedded in an infinitely long circularly polarized electromagnetic wave propagating through a plasma. From a mathematical point of view they are exact solutions of the one-dimensional relativistic cold fluid plasma model with nonvanishing boundary conditions. Under the assumption of travelling wave solutions with velocity V and vector potential frequency ?, the fluid model is reduced to a Hamiltonian system. The solitary waves are homoclinic (grey solitons) or heteroclinic (dark solitons) orbits to fixed points. Using a dynamical systems description of the Hamiltonian system and a spectral method, we identify a large variety of solitary waves, including asymmetric ones, discuss their disappearance for certain parameter values and classify them according to (i) grey or dark character, (ii) the number of humps of the vector potential envelope and (iii) their symmetries. The solutions come in continuous families in the parametric V-? plane and extend up to velocities that approach the speed of light. The stability of certain types of grey solitary waves is investigated with the aid of particle-in-cell simulations that demonstrate their propagation for a few tens of the inverse of the plasma frequency.

Sánchez-Arriaga, G.; Siminos, E.; Lefebvre, E.

2011-04-01

162

Blast wave in a nozzle for propulsive applications

NASA Technical Reports Server (NTRS)

The reported investigation has been conducted in connection with studies concerning the development of a propulsion system based on the use of a detonating fluid propellant. Measurements have been made of the pressure and shock wave velocity in a conical nozzle at various ambient pressures and at an ambient temperature of 25 C. In the experiments a small amount of explosive was placed at the end wall of a conical aluminum nozzle and detonated by a microdetonator inside the nozzle. Differences regarding the characteristics of conventional chemical propulsion and detonation propulsion are illustrated with the aid of a graph. One- and two-dimensional numerical flow calculations were performed and compared with the experimental data.

Varsi, G.; Back, L. H.; Kim, K.

1976-01-01

163

THE Blast-Wave-Driven Instability as a Vehicle for Understanding Supernova Explosion Structure

NASA Astrophysics Data System (ADS)

Blast-wave-driven instabilities play a rich and varied role in supernovae (SNe) evolution from explosion to remnant, but interpreting their role is difficult due to the enormous complexity of stellar systems. We consider the simpler idealized problem of an interface between two constant-density fluids perturbed from spherical and driven by a central blast wave. Where valid, the existence of unified solutions suggests that general conclusions can be drawn about the likely asymptotic structure of the mixing zone. To this end, we apply buoyancy-drag and bubble merger models that include effects of divergence and compressibility. In general, these effects preclude the true self-similar evolution of classical Rayleigh-Taylor (RT), but can be incorporated into a quasi-self-similar growth model. Loss of memory of initial conditions (ICs) can occur in the model, but requires pre-explosion mode numbers higher than predicted for Type II SNe, suggesting that their late-time structure is influenced by details of the initial perturbations. Where low modes dominate, as in the Type Ia Tycho remnant, they result from initial perturbations rather than generation from smaller scales. Therefore, the structure observed now contains direct information about the explosion process. When large-amplitude modes exist in the ICs, the contribution from the Richtmyer-Meshkov (RM) instability is significant compared to RT. Such RM growth can yield proximity of the forward shock to the growing spikes and structure that strongly resembles that observed in Tycho. Laser-driven laboratory experiments offer a promising avenue for testing model and simulation descriptions of blast-wave-driven instabilities and making connections to their astrophysical counterparts.

Miles, Aaron R.

2009-05-01

164

The Blast-Wave-Driven Instability as a Vehicle for Understanding Supernova Explosion Structure

Blast-wave-driven instabilities play a rich and varied role throughout the evolution of supernovae from explosion to remnant, but interpreting their role is difficult due to the enormous complexity of the stellar systems. We consider the simpler and fundamental hydrodynamic instability problem of a material interface between two constant-density fluids perturbed from spherical and driven by a divergent central Taylor-Sedov blast wave. The existence of unified solutions at high Mach number and small density ratio suggests that general conclusions can be drawn about the likely asymptotic structure of the mixing zone. To this end we apply buoyancy-drag and bubble merger models modified to include the effects of divergence and radial velocity gradients. In general, these effects preclude the true self-similar evolution of classical Raleigh-Taylor, but can be incorporated into a quasi-self-similar growth picture. Loss of memory of initial conditions can occur in the quasi-self-similar model, but requires initial mode numbers higher than those predicted for pre-explosion interfaces in Type II SNe, suggesting that their late-time structure is likely strongly influenced by details of the initial perturbations. Where low-modes are dominant, as in the Type Ia Tycho remnant, they result from initial perturbations rather than generation from smaller scales. Therefore, structure observed now contains direct information about the explosion process. When large-amplitude modes are present in the initial conditions, the contribution to the perturbation growth from the Richtmyer-Meshkov instability is significant or dominant compared to Rayleigh-Taylor. Such Richtmyer-Meshkov growth can yield proximity of the forward shock to the growing spikes and structure that strongly resembles that observed in the Tycho. Laser-driven high-energy-density laboratory experiments offer a promising avenue for testing model and simulation descriptions of blast-wave-driven instabilities and making connections to their astrophysical counterparts.

Miles, A R

2008-05-27

165

Electrostatic rogue-waves in relativistically degenerate plasmas

In this paper, we investigate the modulational instability and the possibility of electrostatic rogue-wave propagations in a completely degenerate plasma with arbitrary degree of degeneracy, i.e., relativistically degenerate plasma, ranging from solid density to the astrophysical compact stars. The hydrodynamic approach along with the perturbation method is used to reduce the governing equations to the nonlinear Schrödinger equation from which the modulational instability, the growth rate of envelope excitations and the occurrence of rogue as well as super-rogue waves in the plasma, is evaluated. It is observed that the modulational instability in a fully degenerate plasma can be quite sensitive to the plasma number-density and the wavenumber of envelop excitations. It is further revealed that the relativistically degeneracy plasmas (R{sub 0}?>?1) are almost always modulationally unstable. It is found, however, that the highly energetic sharply localized electrostatic rogue as well as super-rogue waves can exist in the astrophysical compact objects like white dwarfs and neutron star crusts. The later may provide a link to understand many physical processes in such stars and it may lead us to the origin of the random-localized intense short gamma-ray bursts, which “appear from nowhere and disappear without a trace” quite similar to oceanic rogue structures.

Akbari-Moghanjoughi, M. [Department of Physics, Faculty of Sciences, Azarbaijan Shahid Madani University, 51745-406 Tabriz, Iran and International Centre for Advanced Studies in Physical Sciences and Institute for Theoretical Physics, Ruhr University Bochum, D-44780 Bochum (Germany)

2014-10-15

166

The soft X-ray background as a supernova blast wave viewed from inside: Solar abundance models

NASA Technical Reports Server (NTRS)

A model of the soft X-ray background is presented in which the Sun is assumed to be inside an active supernova blast wave. The blast wave evolves in a preexisting cavity. The broad band surface brightnesses is explained by such a blast wave with an explosion energy of E sub approx. 5 x 10 to the 50th power ergs and radius 80 to 100 pc, using solar abundances. An approach to treating the problem of large anisotropies in the ambient medium is also explored, accommodating the observed anticorrelation between the soft X-ray surface brightness and the 21 cm column density. It is found that only for post shock temperatures below 10 6 K a shock propagating into a density enhancement will be dimmer than a similar shock in a lower density region.

Edgar, R. J.

1984-01-01

167

The soft X-ray background as a supernova blast wave viewed from inside - Solar abundance models

NASA Technical Reports Server (NTRS)

A model of the soft X-ray background is presented in which the sun is assumed to be inside an active supernova blast wave. The blast wave evolves in a preexisting cavity. The broad band surface brightnesses is explained by such a blast wave with an explosion energy of E sub approximately 5 x 10 to the 50th power ergs and radius 80 to 100 pc, using solar abundances. An approach to treating the problem of large anisotropies in the ambient medium is also explored, accommodating the observed anticorrelation between the soft X-ray surface brightness and the 21 cm column density. It is found that only for post shock temperatures below 10 to the 6 power K a shock propagating into a density enhancement will be dimmer than a similar shock in a lower density region.

Edgar, R. J.

1986-01-01

168

The objective of this modeling and simulation study was to establish the role of stress wave interactions in the genesis of traumatic brain injury (TBI) from exposure to explosive blast. A high resolution (1 mm{sup 3} voxels), 5 material model of the human head was created by segmentation of color cryosections from the Visible Human Female dataset. Tissue material properties were assigned from literature values. The model was inserted into the shock physics wave code, CTH, and subjected to a simulated blast wave of 1.3 MPa (13 bars) peak pressure from anterior, posterior and lateral directions. Three dimensional plots of maximum pressure, volumetric tension, and deviatoric (shear) stress demonstrated significant differences related to the incident blast geometry. In particular, the calculations revealed focal brain regions of elevated pressure and deviatoric (shear) stress within the first 2 milliseconds of blast exposure. Calculated maximum levels of 15 KPa deviatoric, 3.3 MPa pressure, and 0.8 MPa volumetric tension were observed before the onset of significant head accelerations. Over a 2 msec time course, the head model moved only 1 mm in response to the blast loading. Doubling the blast strength changed the resulting intracranial stress magnitudes but not their distribution. We conclude that stress localization, due to early time wave interactions, may contribute to the development of multifocal axonal injury underlying TBI. We propose that a contribution to traumatic brain injury from blast exposure, and most likely blunt impact, can occur on a time scale shorter than previous model predictions and before the onset of linear or rotational accelerations traditionally associated with the development of TBI.

Ford, Corey C. (University of New Mexico, Albuquerque, NM); Taylor, Paul Allen

2008-02-01

169

Analysis of coaxial ridged disk-loaded slow-wave structures for relativistic traveling wave tubes

The coaxial ridged disk-loaded structure which is a new disk-loaded periodic system is presented and analyzed in this paper. As an all-metal slow-wave circuit, it has properties that can be used in high-power traveling wave tubes (TWT) and relativistic TWTs. The dispersion equation and coupling impedance of the structure are investigated in the first part of this paper. The results

Lingna Yue; Wenxiang Wang; Yubin Gong; Keqian Zhang

2004-01-01

170

NASA Technical Reports Server (NTRS)

An analysis is conducted regarding the properties of cylindrically symmetric self-similar blast waves propagating away from a line source into a medium whose density and magnetic field (with components in both the phi and z directions) both vary as r to the -(omega) power (with omega less than 1) ahead of the blast wave. The main results of the analysis can be divided into two classes, related to a zero azimuthal field and a zero longitudinal field. In the case of the zero longitudinal field it is found that there are no physically acceptable solutions with continuous postshock variations of flow speed and gas density.

Lerche, I.

1981-01-01

171

Numerical analysis of blast-induced wave propagation using FSI and ALEmulti-material formulations

As explosive blasts continue to cause casualties in both civil and military environments, there is a need to identify the dynamic interaction of blast loading with structures, to know the shock mitigating mechanisms and, most importantly, to identify the mechanisms of blast trauma. This paper examines the air-blast simulation using Arbitrary Lagrangian Eulerian (ALE) multi-material formulation. It will explain how

Mehdi Sotudeh Chafi; Ghodrat Karami; Mariusz Ziejewski

2009-01-01

172

A powerful reflector in relativistic backward wave oscillator

An improved TM{sub 021} resonant reflector is put forward. Similarly with most of the slow wave structures used in relativistic backward wave oscillator, the section plane of the proposed reflector is designed to be trapezoidal. Compared with the rectangular TM{sub 021} resonant reflector, such a structure can depress RF breakdown more effectively by weakening the localized field convergence and realizing good electrostatic insulation. As shown in the high power microwave (HPM) generation experiments, with almost the same output power obtained by the previous structure, the improved structure can increase the pulse width from 25?ns to over 27?ns and no obvious surface damage is observed even if the generated HPM pulses exceed 1000 shots.

Cao, Yibing, E-mail: caoyibing@nint.ac.cn; Sun, Jun; Teng, Yan; Zhang, Yuchuan; Zhang, Lijun; Shi, Yanchao; Ye, Hu; Chen, Changhua [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an, Shaanxi 710024 (China)

2014-09-15

173

Parametric decay of an extraordinary electromagnetic wave in relativistic plasma

NASA Astrophysics Data System (ADS)

Parametric instability of an extraordinary electromagnetic wave in plasma preheated to a relativistic temperature is considered. A set of self-similar nonlinear differential equations taking into account the electron "thermal" mass is derived and investigated. Small perturbations of the parameters of the heated plasma are analyzed in the linear approximation by using the dispersion relation determining the phase velocities of the fast and slow extraordinary waves. In contrast to cold plasma, the evanescence zone in the frequency range above the electron upper hybrid frequency vanishes and the asymptotes of both branches converge. Theoretical analysis of the set of nonlinear equations shows that the growth rate of decay instability increases with increasing initial temperature of plasma electrons. This result is qualitatively confirmed by numerical simulations of plasma heating by a laser pulse injected from vacuum.

Dorofeenko, V. G.; Krasovitskiy, V. B.; Turikov, V. A.

2015-03-01

174

A powerful reflector in relativistic backward wave oscillator

NASA Astrophysics Data System (ADS)

An improved TM021 resonant reflector is put forward. Similarly with most of the slow wave structures used in relativistic backward wave oscillator, the section plane of the proposed reflector is designed to be trapezoidal. Compared with the rectangular TM021 resonant reflector, such a structure can depress RF breakdown more effectively by weakening the localized field convergence and realizing good electrostatic insulation. As shown in the high power microwave (HPM) generation experiments, with almost the same output power obtained by the previous structure, the improved structure can increase the pulse width from 25 ns to over 27 ns and no obvious surface damage is observed even if the generated HPM pulses exceed 1000 shots.

Cao, Yibing; Sun, Jun; Teng, Yan; Zhang, Yuchuan; Zhang, Lijun; Shi, Yanchao; Ye, Hu; Chen, Changhua

2014-09-01

175

Stimulated Compton conversion of Langmuir waves by relativistic electron beams

NASA Astrophysics Data System (ADS)

The scattering of a Langmuir wave by a relativistic electron to produce a transversely polarized high-frequency EM wave by an inverse Compton process is investigated theoretically. The results of numerical computations are presented in diagrams and graphs, and it is shown that although net growth rates are predicted for several classes of Langmuir spectra, they are at least several orders of magnitude too small to account for the intense high-frequency emission seen in recent beam-plasma experiments (Benford et al., 1980; Kato et al., 1983) unless some unknown coherence mechanism is focusing the inverse-Compton emission. The implications of the mechanism for astrophysical beam-plasma systems such as quasars and radio galaxies are indicated.

Newman, D. L.

1985-05-01

176

Relativistic shock waves and the excitation of plerions

The shock termination of a relativistic magnetohydrodynamic wind from a pulsar is the most interesting and viable model for the excitation of the synchrotron sources observed in plerionic supernova remnants. We have studied the structure of relativistic magnetosonic shock waves in plasmas composed purely of electrons and positrons, as well as those whose composition includes heavy ions as a minority constituent by number. We find that relativistic shocks in symmetric pair plasmas create fully thermalized distributions of particles and fields downstream. Therefore, such shocks are not good candidates for the mechanism which converts rotational energy lost from a pulsar into the nonthermal synchrotron emission observed in plerions. However, when the upstream wind contains heavy ions which are minority constituent by number density, but carry the bulk of the energy density, much of the energy of the shock goes into a downstream, nonthermal power law distribution of positrons with energy distribution N(E)dE {proportional to}E{sup {minus}s}. In a specific model presented in some detail, s = 3. These characteristics are close to those assumed for the pairs in macroscopic MHD wind models of plerion excitation. The essential mechanism is collective synchrotron emission of left-handed extraordinary modes by the ions in the shock front at high harmonics of the ion cyclotron frequency, with the downstream positrons preferentially absorbing almost all of this radiation, mostly at their fundamental (relativistic) cyclotron frequencies. Possible applications to models of plerions and to constraints on theories of energy loss from pulsars are briefly outlines. 27 refs., 5 figs.

Arons, J. (California Univ., Berkeley, CA (USA)); Gallant, Y.A. (California Univ., Berkeley, CA (USA). Dept. of Physics); Hoshino, Masahiro; Max, C.E. (California Univ., Livermore, CA (USA). Inst. of Geophysics and Planetary Physics); Langdon, A.B. (Lawrence Livermore National Lab., CA (USA))

1991-01-07

177

TWO-DIMENSIONAL BLAST-WAVE-DRIVEN RAYLEIGH-TAYLOR INSTABILITY: EXPERIMENT AND SIMULATION

This paper shows results from experiments diagnosing the development of the Rayleigh-Taylor instability with two-dimensional initial conditions at an embedded, decelerating interface. Experiments are performed at the Omega Laser and use {approx}5 kJ of energy to create a planar blast wave in a dense, plastic layer that is followed by a lower density foam layer. The single-mode interface has a wavelength of 50 {mu}m and amplitude of 2.5 {mu}m. Some targets are supplemented with additional modes. The interface is shocked then decelerated by the foam layer. This initially produces the Richtmyer-Meshkov instability followed and then dominated by Rayleigh-Taylor growth that quickly evolves into the nonlinear regime. The experimental conditions are scaled to be hydrodynamically similar to SN1987A in order to study the instabilities that are believed to occur at the He/H interface during the blast-wave-driven explosion phase of the star. Simulations of the experiment were performed using the FLASH hydrodynamics code.

Kuranz, C. C.; Drake, R. P.; Harding, E. C.; Grosskopf, M. J. [University of Michigan, MI (United States); Robey, H. F.; Remington, B. A.; Edwards, M. J.; Miles, A. R.; Perry, T. S. [Lawrence Livermore National Laboratory, University of California, P.O. Box 5508, L-487, Livermore, CA 94550 (United States); Blue, B. E. [General Atomics, San Diego, CA (United States); Plewa, T. [Department of Scientific Computing, Florida State University, Dirac Science Library Tallahassee, FL 32306-4120 (United States); Hearn, N. C. [ASC/Alliances Center for Astrophysical Thermonuclear Flashes, University of Chicago, IL (United States); Knauer, J. P. [Laboratory of Laser Energetics, University of Rochester, Rochester, NY (United States); Arnett, D. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Leibrandt, D. R. [Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)

2009-05-01

178

Rapid energization of relativistic electrons by nonlinear wave trapping

NASA Astrophysics Data System (ADS)

We utilize a self-consistent particle code to investigate the acceleration of relativistic electrons via nonlinear wave trapping by whistler-mode chorus emissions. Whistler-mode chorus is a group of narrowband electromagnetic emissions with rising tones observed in the dawn side of the inner magnetosphere. It is well known that the activity of chorus enhances during geomagnetically disturbed periods, while the energy source of chorus is considered to be supplied by energetic electrons transferred into the inner magnetosphere through earthward particle injections during substorms. Although a number of theories have been proposed to explain the generation mechanism of chorus, the detailed physics how coherent rising tones are generated from the narrowband seed waves has not been clarified yet. Recently we have reproduced the generation process of chorus emissions by a large-scale self-consistent particle simulation [1]. The simulation result exhibited important keys to understand essential physics of the chorus generation process [2]. We have also found in the simulations that the majority of electrons lose energy, contributing to the generation of chorus emissions, while a fraction of resonant electrons having large pitch-angles are simultaneously energized through nonlinear wave trapping by the chorus emissions [3]. Highly accelerated electrons show a characteristic behavior which is explained by the relativistic turning acceleration (RTA) process [4,5]. Furthermore, accelerated relativistic electrons undergo efficient energization as a result of the ultra-relativistic acceleration (URA) process [6] followed by RTA. We discuss the characteristics of efficiently energized electrons in the simulation results, and we present evidence for rapid electron acceleration by the sequence of RTA and URA interactions. [1] Katoh, Y. and Y. Omura (2007), Geophys. Res. Lett., 34, L03102, doi:10.1029/2006GL028594. [2] Omura, Y., Y. Katoh, and D. Summers, J. Geophys. Res., in press. [3] Katoh, Y. and Y. Omura (2007), Geophys. Res. Lett., 34, L13102, doi:10.1029/2007GL029758. [4] Omura Y., N. Furuya, and D. Summers (2007), J. Geophys. Res., 112, A06236, doi:10.1029/2006JA012243. [5] Furuya, N., Y. Omura, and D. Summers, J. Geophys. Res., in press. [6] Summers D., Y. Omura (2007), Geophys. Res. Lett., 34, L24205, doi:10.1029/2007GL032226.

Katoh, Yuto; Omura, Yoshiharu; Summers, Danny

179

Steady-state solutions for relativistically strong electromagnetic waves in plasmas.

NASA Technical Reports Server (NTRS)

New steady-state solutions are derived which describe electromagnetic waves strong enough to make plasma ions and electrons relativistic. A two-fluid model is used throughout. The following solutions are studied: (1) linearly polarized waves with phase velocity much greater than c; (2) arbitrarily polarized waves with phase velocity near c, in a cold uniform plasma; (3) circularly polarized waves in a uniform plasma characterized by a scalar pressure tensor. All of these waves are capable of propagating in normally overdense plasmas, due to nonlinearities introduced by relativistic effects. The propagation of relativistically strong waves in a density gradient is examined, for the example of a circularly polarized wave strong enough to make electrons but not ions relativistic. It is shown that such a wave propagates at constant energy flux despite the nonlinearity of the system.

Max, C. E.

1973-01-01

180

Numerical experiment on relativistic Cherenkov backward wave oscillator

A simple time-dependent PIC-code has been used to study physical phenomena within a BWO. In this code, the electromagnetic field is represented separately by its potential part, and by self waves of a corrugated waveguide, corresponding to the operating mode. The excitation of each of these waves was described separately by the 1D time-dependent differential equation. The motion of macroparticles was described using either 1D or 3D relativistic ballistic equations. The Green function technique was used to solve the Poisson equation on the electrostatic potential within the rippled waveguide. The BWO full-scale time-dependent numerical experiments have been performed with the use of 2.5D version of 2.5 and 3D, fully electromagnetic PIC-code KARAT. The results are compared with data from experiments on moderately relativistic, high current, short-pulse BWO (3--5 kA, 400--650 keV, 12 ns). Agreement was obtained both in the frequency of generation and in output power for different configurations of tubes and various values of guiding magnetic field.

Pegel, I.V. [Univ. of New Mexico, Albuquerque, NM (United States); Korovin, S.D. [Inst. of High Current Electronics, Tomsk (Russian Federation)

1994-12-31

181

During magnetic storms, relativistic electrons execute nearly circular orbits about the Earth and traverse a spatially confined zone within the duskside plasmapause where electromagnetic ion cyclotron (EMIC) waves are preferentially excited. We examine the mechanism of electron pitch-angle diffusion by gyroresonant interaction with EMIC waves as a cause of relativistic electron precipitation loss from the outer radiation belt. Detailed calculations

Danny Summers; Richard M. Thorne

2003-01-01

182

Asymmetric modes decomposition in an overmoded relativistic backward wave oscillator

Most of the investigated overmoded relativistic backward wave oscillators (RBWOs) are azimuthally symmetric; thus, they are designed through two dimensional (2-D) particle-in-cell (PIC) simulations. However, 2-D PIC simulations cannot reveal the effect of asymmetric modes on beam-wave interaction. In order to investigate whether asymmetric mode competition needs to be considered in the design of overmoded RBWOs, a numerical method of determining the composition of both symmetric and asymmetric modes in three dimensional (3-D) PIC simulations is introduced in this paper. The 2-D and 3-D PIC simulation results of an X-band overmoded RBWO are analyzed. Our analysis indicates that the 2-D and 3-D PIC simulation results of our device are quite different due to asymmetric mode competition. In fact, asymmetric surface waves, especially EH{sub 11} mode, can lead to serious mode competition when electron beam propagates near the surface of slow wave structures (SWSs). Therefore, additional method of suppressing asymmetric mode competition, such as adjusting the reflections at both ends of SWSs to decrease the Q-factor of asymmetric modes, needs to be utilized in the design of overmoded RBWOs. Besides, 3-D PIC simulation and modes decomposition are essential for designing overmoded RBWOs.

Zhang, Dian; Zhang, Jun, E-mail: zhangjun@nudt.edu.cn; Zhong, Huihuang; Jin, Zhenxing; Ju, Jinchuan [College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2014-09-15

183

Numerical simulation of the fluid-structure interaction between air blast waves and soil structure

NASA Astrophysics Data System (ADS)

Normally, an explosion threat on free field especially from high explosives is very dangerous due to the ground shocks generated that have high impulsive load. Nowadays, explosion threats do not only occur in the battlefield, but also in industries and urban areas. In industries such as oil and gas, explosion threats may occur on logistic transportation, maintenance, production, and distribution pipeline that are located underground to supply crude oil. Therefore, the appropriate blast resistances are a priority requirement that can be obtained through an assessment on the structural response, material strength and impact pattern of material due to ground shock. A highly impulsive load from ground shocks is a dynamic load due to its loading time which is faster than ground response time. Of late, almost all blast studies consider and analyze the ground shock in the fluid-structure interaction (FSI) because of its influence on the propagation and interaction of ground shock. Furthermore, analysis in the FSI integrates action of ground shock and reaction of ground on calculations of velocity, pressure and force. Therefore, this integration of the FSI has the capability to deliver the ground shock analysis on simulation to be closer to experimental investigation results. In this study, the FSI was implemented on AUTODYN computer code by using Euler-Godunov and the arbitrary Lagrangian-Eulerian (ALE). Euler-Godunov has the capability to deliver a structural computation on a 3D analysis, while ALE delivers an arbitrary calculation that is appropriate for a FSI analysis. In addition, ALE scheme delivers fine approach on little deformation analysis with an arbitrary motion, while the Euler-Godunov scheme delivers fine approach on a large deformation analysis. An integrated scheme based on Euler-Godunov and the arbitrary Lagrangian-Eulerian allows us to analyze the blast propagation waves and structural interaction simultaneously.

Umar, S.; Risby, M. S.; Albert, A. Luthfi; Norazman, M.; Ariffin, I.; Alias, Y. Muhamad

2014-03-01

184

NASA Astrophysics Data System (ADS)

To combat the problem of traumatic brain injury (TBI), a signature injury of the current military conflicts, there is an urgent need to design head protection systems with superior blast/ballistic impact mitigation capabilities. Toward that end, the blast impact mitigation performance of an advanced combat helmet (ACH) head protection system equipped with polyurea suspension pads and subjected to two different blast peak pressure loadings has been investigated computationally. A fairly detailed (Lagrangian) finite-element model of a helmet/skull/brain assembly is first constructed and placed into an Eulerian air domain through which a single planar blast wave propagates. A combined Eulerian/Lagrangian transient nonlinear dynamics computational fluid/solid interaction analysis is next conducted in order to assess the extent of reduction in intra-cranial shock-wave ingress (responsible for TBI). This was done by comparing temporal evolutions of intra-cranial normal and shear stresses for the cases of an unprotected head and the helmet-protected head and by correlating these quantities with the three most common types of mild traumatic brain injury (mTBI), i.e., axonal damage, contusion, and subdural hemorrhage. The results obtained show that the ACH provides some level of protection against all investigated types of mTBI and that the level of protection increases somewhat with an increase in blast peak pressure. In order to rationalize the aforementioned findings, a shockwave propagation/reflection analysis is carried out for the unprotected head and helmet-protected head cases. The analysis qualitatively corroborated the results pertaining to the blast-mitigation efficacy of an ACH, but also suggested that there are additional shockwave energy dissipation phenomena which play an important role in the mechanical response of the unprotected/protected head to blast impact.

Grujicic, M.; Bell, W. C.; Pandurangan, B.; Glomski, P. S.

2011-08-01

185

Whistler wave generation by non-gyrotropic, relativistic, electron beams

NASA Astrophysics Data System (ADS)

Super-thermal electron beams travelling away from the Sun on the open magnetic field lines are widely accepted to be the source of the Type-III bursts. The earliest idea of the generation of the Type-III bursts was based on the plasma emission mechanism. A fast moving electron beam excites Langmuir waves at the local plasma frequency, ?p. The Langmuir waves are partially transformed via scattering at ?p and 2?p, with ion sound and oppositely propagating Langmuir waves, respectively, into electromagnetic waves. As the electron beam propagates away from the Sun, through less dense coronal and interplanetary environment, the frequency of the emitted electromagnetic radiation decreases, because plasma frequency is a function of the square root of the plasma density. Type-III bursts have been subject of theoretical, observational and numerical studies. The first detailed theory of the Type-III emission invoked coherent plasma waves, generated by a stream of fast particles, which are due to Rayleigh and combination scattering at ?p and 2?p subsequently transformed into radio waves. Stochastic growth of the density irregularities was invoked in order to produce stochastically generated clumpy Langmuir waves, where the ambient density perturbations cause the beam to fluctuate around marginal stability. Other theories on the mechanism which generates the Type-III emission include: linear mode conversion of Langmuir waves, Langmuir waves producing electromagnetic radiation as antennas and non-gyroptropic electron beam emission [1] of commensurable properties to the Type-III bursts. In Refs. [2,3] it was found that the non-gyrotropic beam excites electromagnetic radiation by the current transverse to the magnetic field, which results in (?,k)-space drift while propagating along the 1-dimensional spatial domain throughout the decreasing plasma density profile. The role of the electron beam pitch angle and the background density gradient profile was investigated in [4]. In this study [5], for the first time, the backwards propagating wave component evident in the perpendicular components of the electromagnetic field in such a system is presented. Features of the wave component propagating backwards from the front of the non-gyrotropic, relativistic, beam of electrons injected in the Maxwellian, magnetised background plasma with decreasing density profile are studied by using the Particle-In-Cell code EPOCH. Magnetic field in the 1.5-dimensional system is varied in order to prove that the backwards propagating wave is harmonic of the electron cyclotron frequency. The analysis has lead to the identification of the backwards travelling waves as whistlers. Moreover, the whistlers are shown to be generated by the normal and anomalous Doppler resonance. Large fraction of the energy of the perpendicular electromagnetic field components is found to be carried away by the whistler waves. [1] D. Tsiklauri, Phys. Plasmas 18, 052903 (2011). [2] D. Tsiklauri, H. Schmitz, Geophys. Res. Abs. 15, EGU2013-5403 (2013). [3] H. Schmitz, D. Tsiklauri, Phys. Plasmas 20, 062903 (2013). [4] R. Pechhacker, D. Tsiklauri, Phys. Plasmas 19, 112903 (2012). [5] M. Skender, D. Tsiklauri, submitted to Phys. Plasmas (2013): http://astro.qmul.ac.uk/ tsiklauri/

Skender, Marina; Tsiklauri, David

2014-05-01

186

Ion-acoustic solitary waves in fully relativistic electron-ion plasmas

NASA Astrophysics Data System (ADS)

The possibility of ion-acoustic solitary waves in a fully relativistic plasma comprised of electrons and ions is investigated by the pseudopotential method. Applying the gas-dynamic approach developed by McKenzie [Phys. Plasmas 9, 800 (2002)] to the energy conservation laws, it is shown that, as in nonrelativistic plasmas, only compressive ion-acoustic solitary waves are possible in two-component relativistic plasmas in the case where the ions are supersonic and electrons are subsonic. It is also shown that, by introducing the relativistic ion-acoustic velocity, various existence conditions for the solitary waves in relativistic two-fluid plasmas can be cast into forms that are identical to the nonrelativistic counterparts found by the gas-dynamic approach. It can be suggested that the method presented in this study can be extended for the investigation of other kinds of electrostatic solitary waves in relativistic multicomponent plasmas.

Lee, Nam C.

2008-02-01

187

Ion-acoustic solitary waves in fully relativistic electron-ion plasmas

The possibility of ion-acoustic solitary waves in a fully relativistic plasma comprised of electrons and ions is investigated by the pseudopotential method. Applying the gas-dynamic approach developed by McKenzie [Phys. Plasmas 9, 800 (2002)] to the energy conservation laws, it is shown that, as in nonrelativistic plasmas, only compressive ion-acoustic solitary waves are possible in two-component relativistic plasmas in the case where the ions are supersonic and electrons are subsonic. It is also shown that, by introducing the relativistic ion-acoustic velocity, various existence conditions for the solitary waves in relativistic two-fluid plasmas can be cast into forms that are identical to the nonrelativistic counterparts found by the gas-dynamic approach. It can be suggested that the method presented in this study can be extended for the investigation of other kinds of electrostatic solitary waves in relativistic multicomponent plasmas.

Lee, Nam C. [Department of Physics, Pusan National University, Busan 609-735 (Korea, Republic of)

2008-02-15

188

Anomalous skin effects in relativistic parallel propagating weakly magnetized electron plasma waves

Fully relativistic analysis of anomalous skin effects for parallel propagating waves in a weakly magnetized electron plasma is presented and general expressions for longitudinal and transverse permittivites are derived. It is found that the penetration depth for R- and L-waves increases as we move from non-relativistic to highly relativistic regime. The ambient magnetic field reduces/enhances the skin effects for R-wave/L-wave as the strength of the field is increased. In general, the weak magnetic field effects are pronounced for the weakly relativistic regime as compared with other relativistic cases. The results are also graphically illustrated. On switching off the magnetic field, previous results for field free case are retrieved [A. F. Alexandrov, A. S. Bogdankevich, and A. A. Rukhadze, Priniples of Plasma Electrodynamics (Springer-Verlag, Berlin, Heidelberg, 1984), Vol. 9, p. 106].

Abbas, Gohar; Bashir, M. F. [Salam Chair in Physics, G. C. University, Lahore 54000 (Pakistan); Department of Physics, G. C. University, Lahore 54000 (Pakistan); Murtaza, G. [Salam Chair in Physics, G. C. University, Lahore 54000 (Pakistan)

2011-10-15

189

A three-phase soil model for simulating stress wave propagation due to blast loading

NASA Astrophysics Data System (ADS)

A three-phase soil model is proposed to simulate stress wave propagation in soil mass to blast loading. The soil is modelled as a three-phase mass that includes the solid particles, water and air. It is considered as a structure that the solid particles form a skeleton and their voids are filled with water and air. The equation of state (EOS) of the soil is derived. The elastic-plastic theory is adopted to model the constitutive relation of the soil skeleton. The damage of the soil skeleton is also modelled. The Drucker-Prager strength model including the strain rate effect is used to describe the strength of the soil skeleton. The model is implemented into a hydrocode Autodyn. The recorded results obtained by explosion tests in soil are used to validate the proposed model. Copyright

Wang, Zhongqi; Hao, Hong; Lu, Yong

2004-01-01

190

Study of radiative blast waves generated on the Z-beamlet laser.

This document describes the original goals of the project to study the Vishniac Overstability on blast waves produced using the Z-Beamlet laser facility as well as the actual results. The proposed work was to build on earlier work on the facility and result in the best characterized set of data for such phenomena in the laboratory. To accomplish the goals it was necessary to modify the existing probe laser at the facility so that it could take multiple images over the course of 1-2 microseconds. Troubles with modifying the probe laser are detailed as well as the work that went into said modifications. The probe laser modification ended up taking the entire length of the project and were the major accomplishment of the research.

Edens, Aaron D.; Schwarz, Jens

2012-02-01

191

ON THE AMPLIFICATION OF MAGNETIC FIELD BY A SUPERNOVA BLAST SHOCK WAVE IN A TURBULENT MEDIUM

We have performed extensive two-dimensional magnetohydrodynamic simulations to study the amplification of magnetic fields when a supernova blast wave propagates into a turbulent interstellar plasma. The blast wave is driven by injecting high pressure in the simulation domain. The interstellar magnetic field can be amplified by two different processes, occurring in different regions. One is facilitated by the fluid vorticity generated by the 'rippled' shock front interacting with the background turbulence. The resulting turbulent flow keeps amplifying the magnetic field, consistent with earlier work. The other process is facilitated by the growth of the Rayleigh-Taylor instability at the contact discontinuity between the ejecta and the shocked medium. This can efficiently amplify the magnetic field and tends to produce the highest magnetic field. We investigate the dependence of the amplification on numerical parameters such as grid-cell size and on various physical parameters. We show that the magnetic field has a characteristic radial profile such that the downstream magnetic field gets progressively stronger away from the shock. This is because the downstream magnetic field needs a finite time to reach the efficient amplification, and will get further amplified in the Rayleigh-Taylor region. In our simulation, we do not observe a systematic strong magnetic field within a small distance to the shock. This indicates that if the magnetic-field amplification in supernova remnants indeed occurs near the shock front, other processes such as three-dimensional instabilities, plasma kinetics, and/or cosmic ray effect may need to be considered to explain the strong magnetic field in supernova remnants.

Guo Fan; Li Shengtai; Li Hui; Li, David [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Giacalone, Joe; Jokipii, J. R. [Department of Planetary Sciences and Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721 (United States)

2012-03-10

192

A high efficiency relativistic uniform backward wave oscillator

A recent numerical calculation predicts efficiencies of 25--30% for uniform BWOs over a wider range of beam parameters than for nonuniform BWOs. This new model includes the interaction between the electron beam and the reflected forward traveling wave. For efficient BWO operation, it is important that the backward traveling wave and the reflected forward traveling wave are properly matched at the cutoff neck and the adiabatic transition into the output waveguide. A uniform BWO based on the principles described in the above model was investigated using the Sinus-6 relativistic electron beam accelerator. Cathode voltages from 400 kV to 650 kV and beam currents from 2.5 kA to 5 kA were obtained by varying the pressure in the Sinus-6 spark gap switch. The RF pulse was 10 ns long at 9.6 GHz. A peak power of 250 MW was measured in the far field with a corresponding efficiency of 20%. At higher beam parameters significant air breakdown was observed in front of the 15 cm diameter conical horn aperture. The TM{sub 01} mode pattern was observed and photographed in the plasma formed by the air breakdown. A mode converter was used to convert the TM{sub 01} mode into a TE{sub 11} mode with the corresponding air breakdown pattern observed. A standing wave was created by placing a metal mirror 1.5 meter from the aperture. PIC code simulations of this BWO were made with KARAT and TWOQUICK. Power and frequency measurements are compared with the experiment.

Roitman, A.M.; Moreland, L.D.; Schamiloglu, E.; Pegel, I.V. [Univ. of New Mexico, Albuquerque, NM (United States); Lemke, R.W. [Sandia National Labs., Albuquerque, NM (United States)

1994-12-31

193

We report an oversized K-band backward wave oscillator (BWO) operating above 20 GHz in the weakly relativistic region less than 100 kV. It is very important to prevent microwave from going into the beam diode, since intense microwaves will harmfully affect beam generation. A weakly relativistic oversized BWO is demonstrated using a Bragg reflector at the beam entrance of slow

Kazuo Ogura; Yushi Miyazawa; Hidekazu Tanaka; Yutaka Kiuchi; Satoshi Aoyama; Akira Sugawara

2008-01-01

194

A repetitive 0.14 THz relativistic surface wave oscillator

Preliminary experimental results of a repetitive 0.14 THz overmoded relativistic surface wave oscillator (RSWO) are presented in this paper. The repetitive RSWO is developed by using a rectangularly corrugated slow-wave structure with overmoded ratio of 3 and a foilless diode emitting annular electron beam with thickness of 0.5 mm. The high quality electron beams at the repetition rate of 10 are obtained over a wide range of diode voltage (180 kV < U < 240 kV) and current (700 A < I < 1.2 kA). The generation experiments of RSWO are conducted at an axial pulsed magnetic field whose maximum strength and duration can reach about 2.7 T and 1 s, respectively. The experimental results show that the RSWO successfully produces reasonable uniform terahertz pulses at repetition rate of 10, and the pulse duration, frequency, and power of a single pulse are about 1.5 ns, 0.154 THz, and 2.6 MW, respectively, whereas the dominated radiation mode of the RSWO is TM{sub 02}.

Wang Guangqiang; Tong Changjiang; Li Xiaoze; Wang Xuefeng; Li Shuang; Lu Xicheng [Northwest Institute of Nuclear Technology, P.O. Box 69-1, Xi'an 710024 (China); Wang Jianguo [Northwest Institute of Nuclear Technology, P.O. Box 69-1, Xi'an 710024 (China); School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an 710049 (China)

2013-04-15

195

A repetitive 0.14 THz relativistic surface wave oscillator

NASA Astrophysics Data System (ADS)

Preliminary experimental results of a repetitive 0.14 THz overmoded relativistic surface wave oscillator (RSWO) are presented in this paper. The repetitive RSWO is developed by using a rectangularly corrugated slow-wave structure with overmoded ratio of 3 and a foilless diode emitting annular electron beam with thickness of 0.5 mm. The high quality electron beams at the repetition rate of 10 are obtained over a wide range of diode voltage (180 kV < U < 240 kV) and current (700 A < I < 1.2 kA). The generation experiments of RSWO are conducted at an axial pulsed magnetic field whose maximum strength and duration can reach about 2.7 T and 1 s, respectively. The experimental results show that the RSWO successfully produces reasonable uniform terahertz pulses at repetition rate of 10, and the pulse duration, frequency, and power of a single pulse are about 1.5 ns, 0.154 THz, and 2.6 MW, respectively, whereas the dominated radiation mode of the RSWO is TM02.

Wang, Guangqiang; Wang, Jianguo; Tong, Changjiang; Li, Xiaoze; Wang, Xuefeng; Li, Shuang; Lu, Xicheng

2013-04-01

196

ELECTRON INJECTION BY WHISTLER WAVES IN NON-RELATIVISTIC SHOCKS

Electron acceleration to non-thermal, ultra-relativistic energies ({approx}10-100 TeV) is revealed by radio and X-ray observations of shocks in young supernova remnants (SNRs). The diffusive shock acceleration (DSA) mechanism is usually invoked to explain this acceleration, but the way in which electrons are initially energized or 'injected' into this acceleration process starting from thermal energies is an unresolved problem. In this paper we study the initial acceleration of electrons in non-relativistic shocks from first principles, using two- and three-dimensional particle-in-cell (PIC) plasma simulations. We systematically explore the space of shock parameters (the Alfvenic Mach number, M{sub A} , the shock velocity, v{sub sh}, the angle between the upstream magnetic field and the shock normal, {theta}{sub Bn}, and the ion to electron mass ratio, m{sub i} /m{sub e} ). We find that significant non-thermal acceleration occurs due to the growth of oblique whistler waves in the foot of quasi-perpendicular shocks. This acceleration strongly depends on using fairly large numerical mass ratios, m{sub i} /m{sub e} , which may explain why it had not been observed in previous PIC simulations of this problem. The obtained electron energy distributions show power-law tails with spectral indices up to {alpha} {approx} 3-4. The maximum energies of the accelerated particles are consistent with the electron Larmor radii being comparable to that of the ions, indicating potential injection into the subsequent DSA process. This injection mechanism, however, requires the shock waves to have fairly low Alfenic Mach numbers, M{sub A} {approx}< 20, which is consistent with the theoretical conditions for the growth of whistler waves in the shock foot (M{sub A} {approx}< (m{sub i} /m{sub e}){sup 1/2}). Thus, if the whistler mechanism is the only robust electron injection process at work in SNR shocks, then SNRs that display non-thermal emission must have significantly amplified upstream magnetic fields. Such field amplification is likely achieved by the escaping cosmic rays, so electron and proton acceleration in SNR shocks must be interconnected.

Riquelme, Mario A. [Astronomy Department, University of California, Berkeley, CA 94720 (United States); Spitkovsky, Anatoly, E-mail: marh@astro.berkeley.edu, E-mail: anatoly@astro.princeton.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

2011-05-20

197

NASA Astrophysics Data System (ADS)

We study operation of a relativistic backward-wave oscillator driven by an external electromagnetic signal. Such operation regimes as hard excitation of self-oscillations and amplification of the external signal are implemented experimentally. The conditions for possible synchronization of the relativistic backward-wave oscillator by an external signal is discussed. The possibility of accelerating the onset of oscillations by the action of an external signal is confirmed experimentally. The conditions of realization of the amplification regime and the main effects, which limit the amplification coefficient, are determined. The obtained results can be used to optimize the parameters of generators and amplifiers based on relativistic backward-wave oscillators.

Abubakirov, É. B.; Denisenko, A. N.; Konyushkov, A. P.; Soluyanov, E. I.; Yastrebov, V. V.

2014-10-01

198

Small amplitude waves in a hot relativistic two-fluid plasma

NASA Technical Reports Server (NTRS)

The dispersion relation for small amplitude waves in a hot relativistic plasma embedded in a uniform magnetic field is derived. Four plasma modes exist for propagation oblique to the magnetic field, and the mode properties are summarized in a hot relativistic generalization of the cold plasma pond diagram of Stix (1962). The two-fluid approximation is considered, and two-fluid equations are applied in this procedure which summarizes properties of linear waves in an unbounded magnetized relativistic plasma by means of a parameter-space diagram of wave phase velocity.

Hyun, S.; Kennel, C. F.

1978-01-01

199

Comparison of weak-shock reflection factors for wedges, cylinders and blast waves

Ernst Mach (1838--1916) was the first to discover an irregular reflection phenomenon of shock waves, as is well known in our community. In fact, this occurred in 1875 -- three years earlier than usually assumed in the literature. A facsimile of the paper in which he mentioned a special shock wave behavior is shown in a figure. However, it is correct that Mach gave the physical interpretation of this phenomenon in 1878. Since Mach's discovery of an irregular shock reflection pattern 117 years ago, new shock configurations have been discovered -- one of the most recent examples is the so-called [open quotes]von Neumann reflection[close quotes] for weak shocks as reported by Colella and Henderson in 1990. Due to active research efforts related to shock reflection, especially in the last two decades, we now have a relatively detailed understanding of reflection phenomena and of transition conditions from one reflection configuration to another. The purpose of this paper is to compare reflection factors for weak shocks from various surfaces, and to focus attention on some unsolved questions. Three different cases are considered: (1) square-wave planar shock reflection from wedges, (2) square-wave planar shock reflection from cylinders and (3) spherical blast wave reflection from a planar surface. The authors restrict themselves to weak shocks. Following Henderson's definition, shocks with a Mach number of M[sub 0] < 1.56 in air or with an overpressure of [Delta]p[sub I] < 25 psi (1.66 bar) under normal ambient conditions are called weak.

Reichenbach, H. (Fraunhofer-Institut fuer Kurzzeitdynamik - Ernst-Mach-Institut (EMI), Freiburg im Breisgau (Germany)); Kuhl, A.L. (Lawrence Livermore National Lab., CA (United States))

1992-07-01

200

Comparison of weak-shock reflection factors for wedges, cylinders and blast waves

Ernst Mach (1838--1916) was the first to discover an irregular reflection phenomenon of shock waves, as is well known in our community. In fact, this occurred in 1875 -- three years earlier than usually assumed in the literature. A facsimile of the paper in which he mentioned a special shock wave behavior is shown in a figure. However, it is correct that Mach gave the physical interpretation of this phenomenon in 1878. Since Mach`s discovery of an irregular shock reflection pattern 117 years ago, new shock configurations have been discovered -- one of the most recent examples is the so-called {open_quotes}von Neumann reflection{close_quotes} for weak shocks as reported by Colella and Henderson in 1990. Due to active research efforts related to shock reflection, especially in the last two decades, we now have a relatively detailed understanding of reflection phenomena and of transition conditions from one reflection configuration to another. The purpose of this paper is to compare reflection factors for weak shocks from various surfaces, and to focus attention on some unsolved questions. Three different cases are considered: (1) square-wave planar shock reflection from wedges, (2) square-wave planar shock reflection from cylinders and (3) spherical blast wave reflection from a planar surface. The authors restrict themselves to weak shocks. Following Henderson`s definition, shocks with a Mach number of M{sub 0} < 1.56 in air or with an overpressure of {Delta}p{sub I} < 25 psi (1.66 bar) under normal ambient conditions are called weak.

Reichenbach, H. [Fraunhofer-Institut fuer Kurzzeitdynamik - Ernst-Mach-Institut (EMI), Freiburg im Breisgau (Germany); Kuhl, A.L. [Lawrence Livermore National Lab., CA (United States)

1992-07-01

201

Small viscosity method and criteria for shock wave existence in relativistic magnetic hydrodynamics

We obtain criteria for shock wave (SW)existence in relativistic magnetic hydrodynamics with no suppositions about convexity of the equation of state. Method of derivation involves consideration of a continuous SW profile in presence of Landau-Lifshitz relativistic viscosity tensor with both non-zero viscosity coefficients.

V. I. Zhdanov; M. S. Borshch

2005-08-22

202

Traumatic brain injury (TBI) caused by an explosive blast (blast-TBI) is postulated to result, in part, from transvascular transmission to the brain of a hydrodynamic pulse (a.k.a., volumetric blood surge, ballistic pressure wave, hydrostatic shock, or hydraulic shock) induced in major intrathoracic blood vessels. This mechanism of blast-TBI has not been demonstrated directly. We tested the hypothesis that a blast wave impacting the thorax would induce a hydrodynamic pulse that would cause pathological changes in the brain. We constructed a Thorax-Only Blast Injury Apparatus (TOBIA) and a Jugular-Only Blast Injury Apparatus (JOBIA). TOBIA delivered a collimated blast wave to the right lateral thorax of a rat, precluding direct impact on the cranium. JOBIA delivered a blast wave to the fluid-filled port of an extracorporeal intravenous infusion device whose catheter was inserted retrograde into the jugular vein, precluding lung injury. Long Evans rats were subjected to sublethal injury by TOBIA or JOBIA. Blast injury induced by TOBIA was characterized by apnea and diffuse bilateral hemorrhagic injury to the lungs associated with a transient reduction in pulse oximetry signals. Immunolabeling 24 h after injury by TOBIA showed up-regulation of tumor necrosis factor alpha, ED-1, sulfonylurea receptor 1 (Sur1), and glial fibrillary acidic protein in veins or perivenular tissues and microvessels throughout the brain. The perivenular inflammatory effects induced by TOBIA were prevented by ligating the jugular vein and were reproduced using JOBIA. We conclude that blast injury to the thorax leads to perivenular inflammation, Sur1 up-regulation, and reactive astrocytosis resulting from the induction of a hydrodynamic pulse in the vasculature. PMID:24673157

Simard, J Marc; Pampori, Adam; Keledjian, Kaspar; Tosun, Cigdem; Schwartzbauer, Gary; Ivanova, Svetlana; Gerzanich, Volodymyr

2014-07-15

203

Modeling blast waves, gas and particles dispersion in urban and hilly ground areas.

The numerical simulation of shock and blast waves as well as particles dispersion in highly heterogeneous media such as cities, urban places, industrial plants and part of countries is addressed. Examples of phenomena under study are chemical gas products dispersion from damaged vessels, gas dispersion in urban places under explosion conditions, shock wave propagation in urban environment. A three-dimensional simulation multiphase flow code (HI2LO) is developed in this aim. To simplify the consideration of complex geometries, a heterogeneous discrete formulation is developed. When dealing with large scale domains, such as countries, the topography is considered with the help of elevation data. Meteorological conditions are also considered, in particular regarding complex temperature and wind profiles. Heat and mass transfers on sub-scale objects, such as buildings, trees and other obstacles are considered as well. Particles motion is addressed through a new turbulence model involving a single parameter to describe accurately plumes. Validations against experiments in basic situations are presented as well as examples of industrial and environmental computations. PMID:25199503

Hank, S; Saurel, R; Le Métayer, O; Lapébie, E

2014-09-15

204

NASA Astrophysics Data System (ADS)

A model for the nonlinear properties of obliquely propagating electron acoustic solitary waves in a two-electron populated relativistically quantum magnetized plasma is presented. By using the standard reductive perturbation technique, the Zakharov-Kuznetsov (ZK) equation is derived and this equation gives the solitary wave solution. It is observed that the relativistic effects, the ratio of the cold to hot electron unperturbed number density and the magnetic field normalized by electron cyclotron frequency significantly influence the solitary structures.

Zhu, Zhenni; Wu, Zhengwei; Li, Chunhua; Yang, Weihong

2014-11-01

205

ccsd00001789, Dispersion relation of nite amplitude Alfv en wave in a relativistic electron-positron

in a relativistic electron-positron plasma T. Hada a , S. Matsukiyo a and V. Mu~noz a;b a Department of Earth System of a #12;nite amplitude, parallel, circularly polarized Alfv#19;en wave in a relativistic electron-positron=2 is the electron/positron plasma frequency), and an Alfv#19;en wave, with high frequency cuto#11; at the positron

206

Electromagnetic ion cyclotron (EMIC) waves which propagate at frequencies below the proton gyrofrequency can undergo cyclotron resonant interactions with relativistic electrons in the outer radiation belt and cause pitch-angle scattering and electron loss to the atmosphere. Typical storm-time wave amplitudes of 1–10 nT cause strong diffusion scattering which may lead to significant relativistic electron loss at energies above the minimum

Nigel P. Meredith; Richard M. Thorne; Richard B. Horne; Danny Summers; Brian J. Fraser; Roger R. Anderson

2003-01-01

207

NASA Technical Reports Server (NTRS)

Accurate approximations are presented for the self-similar structures of nonradiating blast waves with adiabatic ions, isothermal electrons, and equation ion and electron temperatures at the shock. The cases considered evolve in cavities with power law ambient densities (including the uniform density case) and have negligible external pressure. The results provide the early time asymptote for systems with shock heating of electrons and strong thermal conduction. In addition, they provide analytical results against which two fluid numerical hydrodynamic codes can be checked.

Cox, D. P.; Edgar, R. J.

1982-01-01

208

Waves in general relativistic two-fluid plasma around a Schwarzschild black hole

NASA Astrophysics Data System (ADS)

Waves propagating in the relativistic electron-positron or ions plasma are investigated in a frame of two-fluid equations using the 3+1 formalism of general relativity developed by Thorne, Price and Macdonald (TPM). The plasma is assumed to be freefalling in the radial direction toward the event horizon due to the strong gravitational field of a Schwarzschild black hole. The local dispersion relations for transverse and longitudinal waves have been derived, in analogy with the special relativistic formulation as explained in an earlier paper, to take account of relativistic effects due to the event horizon using WKB approximation.

Rahman, M. Atiqur

2012-10-01

209

NASA Technical Reports Server (NTRS)

We present multi-satellite observations of large amplitude radiation belt whistler-mode waves and relativistic electron precipitation. On separate occasions during the Wind petal orbits and STEREO phasing orbits, Wind and STEREO recorded intense whistler-mode waves in the outer nightside equatorial radiation belt with peak-to-peak amplitudes exceeding 300 mV/m. During these intervals of intense wave activity, SAMPEX recorded relativistic electron microbursts in near magnetic conjunction with Wind and STEREO. This evidence of microburst precipitation occurring at the same time and at nearly the same magnetic local time and L-shell with a bursty temporal structure similar to that of the observed large amplitude wave packets suggests a causal connection between the two phenomena. Simulation studies corroborate this idea, showing that nonlinear wave.particle interactions may result in rapid energization and scattering on timescales comparable to those of the impulsive relativistic electron precipitation.

Kersten, K.; Cattell, C. A.; Breneman, A.; Goetz, K.; Kellogg, P. J.; Wygant, J. R.; Wilson, L. B., III; Blake, J. B.; Looper, M. D.; Roth, I.

2011-01-01

210

Phase mixing of relativistically intense waves in a cold homogeneous plasma.

We report on spatiotemporal evolution of relativistically intense longitudinal electron plasma waves in a cold homogeneous plasma, using the physically appealing Dawson sheet model. Calculations presented here in the weakly relativistic limit clearly show that under very general initial conditions, a relativistic wave will always phase mix and eventually break at arbitrarily low amplitudes, in a time scale omegapetaumix approximately {3/64(omegape2delta3/c2k2)|Deltak/k|(|1+Deltak/k|)](1+1|1+Deltak/k|)}(-1). We have verified this scaling with respect to amplitude of perturbation delta and width of the spectrum (Deltakk) using numerical simulations. This result may be of relevance to ultrashort, ultraintense laser pulse-plasma interaction experiments where relativistically intense waves are excited. PMID:19391852

Sengupta, Sudip; Saxena, Vikrant; Kaw, Predhiman K; Sen, Abhijit; Das, Amita

2009-02-01

211

Causal Wave Propagation for Relativistic Massive Particles: Physical Asymptotics in Action

ERIC Educational Resources Information Center

Wavepackets representing relativistic quantum particles injected into a half-space, from a source that is switched on at a definite time, are represented by superpositions of plane waves that must include negative frequencies. Propagation is causal: it is a consequence of analyticity that at time t no part of the wave has travelled farther than…

Berry, M. V.

2012-01-01

212

Relativistic electron losses related to EMIC waves during CIR and CME storms

Âparticle interactions with electromagnetic ion-cyclotron (EMIC) waves during corotating interaction region (CIR) stormsRelativistic electron losses related to EMIC waves during CIR and CME storms M.I. Sandanger a,Ã?, F o Article history: Accepted 14 July 2008 Available online 30 July 2008 PACS: 94.30.Lr 94.30.cb 94

Bergen, Universitetet i

213

Experimental studies of the cross-excitation instability in a relativistic backward-wave oscillator

Our group first reported the operation of a relativistic backward wave oscillator (BWO) in the so-called `cross- excitation' regime in 1998. This instability, whose general properties were predicted earlier through numerical studies, was a consequence of using a particularly shallow rippled- wall waveguide (slow wave structure--SWS) that was installed in the experiment to diagnose pulse shortening in a long pulse

Frank Hegeler; Michael D. Partridge; Edl Schamiloglu; Chaouki T. Abdallah; N. Islam

2000-01-01

214

General Relativistic Shock Waves that Extend the Oppenheimer-Snyder Model

General Relativistic Shock Waves that Extend the Oppenheimer-Snyder Model JOELOEL SMOLLERMOLLER. These shock waves extend the celebrated Oppenheimer-Snyder result to the case of non-zero pressure. Our shock of a Friedmann- Robertson-Walker metric (a cosmological model for the expanding universe) to an Oppenheimer

Temple, Blake

215

Summary form only given, as follows. Previous analyses of the stimulated Raman forward scattering (SRFS) and the relativistic modulational instability (RMI) of light waves have treated these instabilities separately. In a rarefied plasma, however, they are closely linked branches of the same instability. A unified analysis of SRFS and RMI has been performed, and their consequences for beat-wave particle acceleration

C. J. McKinstrie; L. Mu; M. Yu; R. Bingham

1990-01-01

216

In this paper, small but finite amplitude electrostatic solitary waves in a relativistic degenerate magnetoplasma, consisting of relativistically degenerate electrons and non-degenerate cold ions, are investigated. The Zakharov-Kuznetsov equation is derived employing the reductive perturbation technique and its solitary wave solution is analyzed. It is shown that only compressive electrostatic solitary structures can propagate in such a degenerate plasma system. The effects of plasma number density, ion cyclotron frequency, and direction cosines on the profiles of ion acoustic solitary waves are investigated and discussed at length. The relevance of the present investigation vis-a-vis pulsating white dwarfs is also pointed out.

Ata-ur-Rahman,; Qamar, A. [Institute of Physics and Electronics, University of Peshawar, Peshawar 25000 (Pakistan) [Institute of Physics and Electronics, University of Peshawar, Peshawar 25000 (Pakistan); National Centre for Physics, QAU Campus, Shahdrah Valley Road, Islamabad 44000 (Pakistan); Masood, W. [National Centre for Physics, QAU Campus, Shahdrah Valley Road, Islamabad 44000 (Pakistan) [National Centre for Physics, QAU Campus, Shahdrah Valley Road, Islamabad 44000 (Pakistan); COMSATS, Institute of Information Technology, Park Road, Chak Shahzad, Islamabad 44000 (Pakistan); Eliasson, B. [Physics Department, University of Strathclyde, Glasgow G4 0NG, Scotland (United Kingdom)] [Physics Department, University of Strathclyde, Glasgow G4 0NG, Scotland (United Kingdom)

2013-09-15

217

NASA Astrophysics Data System (ADS)

In this paper, small but finite amplitude electrostatic solitary waves in a relativistic degenerate magnetoplasma, consisting of relativistically degenerate electrons and non-degenerate cold ions, are investigated. The Zakharov-Kuznetsov equation is derived employing the reductive perturbation technique and its solitary wave solution is analyzed. It is shown that only compressive electrostatic solitary structures can propagate in such a degenerate plasma system. The effects of plasma number density, ion cyclotron frequency, and direction cosines on the profiles of ion acoustic solitary waves are investigated and discussed at length. The relevance of the present investigation vis-a-vis pulsating white dwarfs is also pointed out.

Ata-ur-Rahman; Masood, W.; Eliasson, B.; Qamar, A.

2013-09-01

218

Plasma waves in a relativistic, strongly anisotropic plasma propagated along a strong magnetic field

NASA Technical Reports Server (NTRS)

The dispersion properties of plasma waves in a relativistic homogeneous plasma propagated along a strong magnetic field are studied. It is shown that the non-damping plasma waves exist in the frequency range omega sub p or = omega or = omega sub L. The values of omega sub p and omega sub L are calculated for an arbitrary homogeneous relativistic function of the particle distribution. In the case of a power ultrarelativistic distribution, it is shown that, if the ultrarelativistic tail of the distribution drops very rapidly, slightly damping plasma waves are possible with the phase velocity (omega/K)c.

Onishchenko, O. G.

1980-01-01

219

The Construction of a 'Relativistic' Wave-Particle: The Soliton.

ERIC Educational Resources Information Center

Although most waves studied by students satisfy the linear equation, particle physicists have become interested in nonlinear waves--those not satisfying the superposition principle. A mechanical wave system, satisfying the sine-Gordon equation, can be constructed using a modified transverse wave system to demonstrate nonlinear wave-particle…

Isenberg, Cyril

1982-01-01

220

NASA Astrophysics Data System (ADS)

In this paper, the dispersion relation of the relativistic travelling-wave tube (RTWT) and relativistic backward-wave oscillator (RBWO) filled with plasma is obtained in the presence of an annular electron beam and solved by an exact numerical solution. The interaction of the beam with the waveguide modes is clearly identified and beam line splitting into the slow and fast waves is observed. In addition, the growth rates of each structure are investigated. The results show that the effect of plasma on the temporal growth rate of the TM01 mode in the RBWO is negligible and the higher modes are not affected. Conversely, the spatial growth rate in the RTWT increases significantly with the plasma density.

Bayat, Sajad; Babanejad, Saeed; Hasheminejad, Seyed Mohammad; Milad Vahabi, Seyed

2014-12-01

221

We study the self-modulation of a circularly polarized Alfvén wave in a strongly magnetized relativistic electron-positron plasma with finite temperature. This nonlinear wave corresponds to an exact solution of the equations, with a dispersion relation that has two branches. For a large magnetic field, the Alfvén branch has two different zones, which we call the normal dispersion zone (where d?/dk>0) and the anomalous dispersion zone (where d?/dk<0). A nonlinear Schrödinger equation is derived in the normal dispersion zone of the Alfvén wave, where the wave envelope can evolve as a periodic wave train or as a solitary wave, depending on the initial condition. The maximum growth rate of the modulational instability decreases as the temperature is increased. We also study the Alfvén wave propagation in the anomalous dispersion zone, where a nonlinear wave equation is obtained. However, in this zone the wave envelope can evolve only as a periodic wave train. PMID:24032950

López, Rodrigo A; Asenjo, Felipe A; Muñoz, Víctor; Chian, Abraham C-L; Valdivia, J A

2013-08-01

222

Skull Flexure from Blast Waves: A New Mechanism for Brain Injury with Implications for Helmet Design

Traumatic brain injury [TBI] has become the signature injury of current military conflicts. The debilitating effects of TBI on society are long-lasting and costly. Although the mechanisms by which impacts cause TBI have been well researched, the mechanisms by which blasts cause TBI are not understood. Various mechanisms, including impacts caused by the blast, have been investigated, but blast-induced deformation of the skull has been neglected. Through the use of hydrodynamical numerical simulations, we have discovered that non-lethal blasts can induce sufficient flexure of the skull to generate potentially damaging loads in the brain, even if no impact occurs. This mechanism has implications for the diagnosis of TBI in soldiers and the design of protective equipment such as helmets.

Moss, William C; Blackman, Eric G

2008-01-01

223

Configuration mixing of angular-momentum projected triaxial relativistic mean-field wave functions

The framework of relativistic energy density functionals is extended to include correlations related to the restoration of broken symmetries and to fluctuations of collective variables. The generator coordinate method is used to perform configuration mixing of angular-momentum projected wave functions, generated by constrained self-consistent relativistic mean-field calculations for triaxial shapes. The effects of triaxial deformation and of $K$-mixing is illustrated in a study of spectroscopic properties of low-spin states in $^{24}$Mg.

J. M. Yao; J. Meng; P. Ring; D. Vretenar

2010-04-07

224

Configuration mixing of angular-momentum-projected triaxial relativistic mean-field wave functions

The framework of relativistic energy-density functionals is extended to include correlations related to the restoration of broken symmetries and to fluctuations of collective variables. The generator coordinate method is used to perform configuration mixing of angular-momentum-projected wave functions, generated by constrained self-consistent relativistic mean-field calculations for triaxial shapes. The effects of triaxial deformation and of K mixing is illustrated in a study of spectroscopic properties of low-spin states in {sup 24}Mg.

Yao, J. M. [School of Physical Science and Technology, Southwest University, Chongqing 400715 (China); State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); Physik-Department der Technischen Universitaet Muenchen, D-85748 Garching (Germany); Meng, J. [State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); School of Physics and Nuclear Energy Engineering, Beihang University, Beijing 100191 (China); Ring, P. [Physik-Department der Technischen Universitaet Muenchen, D-85748 Garching (Germany); Vretenar, D. [Physics Department, Faculty of Science, University of Zagreb, 10000 Zagreb (Croatia)

2010-04-15

225

Extracting the spectral function of 4He from a relativistic plane-wave treatment

The spectral function of 4He is extracted from a plane-wave approximation to the (e,e'p) reaction using a fully relativistic formalism. We take advantage of both an algebraic ``trick'' and a general relativistic formalism for quasifree processes developed earlier to arrive at transparent, analytical expressions for all quasifree (e,e'p) observables. An observable is identified for the clean and model-independent extraction of

Laith Abu-Raddad; Jorge Piekarewicz

2001-01-01

226

The shock wave generated by an explosion ("blast wave") may cause injury in any or all of the following: (1) direct impact on the tissues of variations in environmental pressure; (2) flying glass and other debris set in motion by it; (3) propulsion of the body. Injuries in the first category affect gas-containing organs (ears, lungs and intestines), and acute death is attributed to air forced into the coronary vessels via damaged pulmonary alveoli. It is estimated that overpressure sufficient to cause lung injury may occur up to five miles from a 20-megaton nuclear explosion. The greatest single hazard from blast is, however, flying glass, and serious wounding from this cause is possible up to 12 miles from an explosion of this magnitude. PMID:6015742

de Candole, C A

1967-01-28

227

The shock wave generated by an explosion (“blast wave”) may cause injury in any or all of the following: (1) direct impact on the tissues of variations in environmental pressure; (2) flying glass and other debris set in motion by it; (3) propulsion of the body. Injuries in the first category affect gas-containing organs (ears, lungs and intestines), and acute death is attributed to air forced into the coronary vessels via damaged pulmonary alveoli. It is estimated that overpressure sufficient to cause lung injury may occur up to five miles from a 20-megaton nuclear explosion. The greatest single hazard from blast is, however, flying glass, and serious wounding from this cause is possible up to 12 miles from an explosion of this magnitude. PMID:6015742

de Candole, C. A.

1967-01-01

228

Weakly Relativistic Quantum Effects in a Two-Dimensional Electron Gas: Dispersion of Langmuir Waves

NASA Astrophysics Data System (ADS)

A weakly-relativistic quantum-hydrodynamic model for charged spinless particles applied to low-dimensional systems is described in detail. The equations are constructed in the self-consistent field approximation. The Darwin term, the current-current interaction, and the weakly relativistic correction to the kinetic energy, all described by the Breit Hamiltonian, are considered together with the Coulomb interaction. The contributions of the described effects and also of relativistic-temperature effects to the dispersion of the Langmuir waves in a two-dimensional electron gas are calculated. A comparison with the corresponding formula for a three-dimensional system of particles is presented.

Andreev, P. A.; Ivanov, A. Yu.

2015-01-01

229

Weakly relativistic quantum kinetic theory for electrostatic wave modes in magnetized plasmas

We have derived the electrostatic dispersion relation in a magnetized plasma using a recently developed quantum kinetic model based on the Dirac equation. The model contains weakly relativistic spin effects such as Thomas precession, the polarization currents associated with the spin and the spin-orbit coupling. It turns out that for strictly electrostatic perturbations the non-relativistic spin effects vanish, and the modification of the classical dispersion relation is solely associated with the relativistic terms. Several new wave modes appear due the electron spin effects, and an example for astrophysical plasmas are given.

Hussain, Azhar [Department of Physics, GC University Lahore, 54000 Lahore (Pakistan)] [Department of Physics, GC University Lahore, 54000 Lahore (Pakistan); Stefan, Martin; Brodin, Gert [Department of Physics, Umeå University, SE-901 87 Umeå (Sweden)] [Department of Physics, Umeå University, SE-901 87 Umeå (Sweden)

2014-03-15

230

NASA Technical Reports Server (NTRS)

An exact nonlinear solution is found to the relativistic kinetic and electrodynamic equations (in their hydromagnetic limit) that describes the large-amplitude fast-mode magnetoacoustic wave propagating normal to the magnetic field in a collisionless, previously uniform plasma. It is pointed out that a wave of this kind will be generated by transverse compression of any collisionless plasma. The solution is in essence independent of the detailed form of the particle momentum distribution functions. The solution is obtained, in part, through the method of characteristics; the wave exhibits the familiar properties of steepening and shock formation. A detailed analysis is given of the ultrarelativistic limit of this wave.

Barnes, A.

1983-01-01

231

Blast-wave model description of the Hanbury-Brown–Twiss radii in pp collisions at LHC energies

NASA Astrophysics Data System (ADS)

The blast wave model is applied to the recent data on Hanbury-Brown–Twiss radii in pp collisions, measured by the ALICE Collaboration. A reasonable description of data is obtained for a rather low temperature of the kinetic freeze-out, T? 100 MeV, and the transverse profile corresponding to the emission from a shell of a fairly small width 2? ˜ 1.5 fm. The size and the life-time of the produced system are determined for various multiplicities of the produced particles.

Bialas, Andrzej; Florkowski, Wojciech; Zalewski, Kacper

2015-04-01

232

Recoil nucleon transferred polarization observables in coincidence quasielastic electron scattering are studied within the relativistic distorted wave impulse approximation. Results for response functions and polarization asymmetries are discussed for proton knockout from $p_{1/2}$, $p_{3/2}$ and $s_{1/2}$ shells in $^{16}$O. The impact of spinor distortion is examined by comparing the fully relativistic calculation with results obtained by projecting out the negative-energy components. In particular, a careful analysis of effects linked to the description of the bound and scattered relativistic nucleon wave functions is presented. The high sensitivity of some polarization observables to the dynamical enhancement of the lower components, already shown within the relativistic plane wave impulse approximation, is proven to be maintained in the relativistic distorted wave approach. Semi-relativistic approaches based on the effective momentum approximation are also studied. Finally, comparison with experimental data and a brief analysis of effects linked to medium modified form factors is presented.

M. C. Martínez; J. R. Vignote; J. A. Caballero; T. W. Donnelly; E. Moya de Guerra; J. M. Udías

2003-12-17

233

Two dimensional electrostatic shock waves in relativistic electron positron ion plasmas

Ion-acoustic shock waves (IASWs) are studied in an unmagnetized plasma consisting of electrons, positrons and hot ions. In this regard, Kadomtsev-Petviashvili-Burgers (KPB) equation is derived using the small amplitude perturbation expansion method. The dependence of the IASWs on various plasma parameters is numerically investigated. It is observed that ratio of ion to electron temperature, kinematic viscosity, positron concentration, and the relativistic ion streaming velocity affect the structure of the IASW. Limiting case of the KPB equation is also discussed. Stability of KPB equation is also presented. The present investigation may have relevance in the study of electrostatic shock waves in relativistic electron-positron-ion plasmas.

Masood, W.; Rizvi, H. [Theoretical Plasma Physics Division, PINSTECH, P.O. Nilore, Islamabad 54000 (Pakistan)

2010-05-15

234

Relativistic backward-wave tube with mechanically tunable generation frequency over a 14% range

NASA Astrophysics Data System (ADS)

A tunable-frequency low-magnetic-field relativistic microwave oscillator is realized experimentally based on a relativistic backward-wave tube with a modulating resonance reflector. The generated frequency is tuned mechanically by moving the oscillator slow-wave structure relative to the reflector. At fixed parameters of the corrugations and of the electron bunch, a frequency tuning range of about 14% measured between -3-dB (relative to the maximum peak generated microwave power) points is realized. The maximum pulse power of 3.4 ± 0.7 GW was obtained at a carrier frequency of 3.65 GHz in a magnetic field of 0.44 T.

Tot'meninov, E. M.; Vykhodtsev, P. V.; Kitsanov, S. A.; Klimov, A. I.; Rostov, V. V.

2011-07-01

235

On the stability of accelerating relativistic shock waves

We consider the corrugation instability of the self-similar flow with an accelerating shock in the highly relativistic regime. We derive the correct dispersion relation for the proper modes in the self-similar regime, and conclude that this solution is unstable.

Giuseppe Palma; Mario Vietri

2006-09-04

236

Relativistic description of the interaction of electron Bernstein waves with electrons

NASA Astrophysics Data System (ADS)

In the electron cyclotron range of frequencies (ECRF), Bernstein waves (EBW) are useful in spherical tokamaks (NSTX) and stellarators for imparting external wave energy and momentum to electrons. Previous theoretical studies on ECRF X and O modes have noted the importance of including relativistic effects in the propagation and damping of these waves. We find that, in order to properly describe EBWs and their interaction with electrons, a relativistic treatment is necessary. Relativistic effects are found to be important for temperatures which are routinely attained in present day laboratory fusion plasmas. A description of the changes in wave propagation characteristics and in the exchange of momentum and energy between EBWs and electrons will be discussed. For steady state, high-? operation of NSTX type spherical tokamaks non-inductive current drive is needed. ECRF waves can generate currents either by the Ohkawa or by the Fisch-Boozer schemes. We will elucidate the two current drive schemes as applied to NSTX. Results from two coupled codes, one which solves the fully relativistic plasma dielectric tensor (R2D2) and the other which solves the drift kinetic equation for electrons (DKE), will be presented.

Ram, A. K.; Decker, J.

2006-10-01

237

Skull flexure from blast waves: a mechanism for brain injury with implications for helmet design

Traumatic brain injury [TBI] has become a signature injury of current military conflicts. The debilitating effects of TBI are long-lasting and costly. Although the mechanisms by which impacts cause TBI have been well researched, the mechanisms by which blasts cause TBI are not understood. Various possibilities have been investigated, but blast-induced deformation of the skull has been neglected. From numerical hydrodynamic simulations, we have discovered that nonlethal blasts can induce sufficient flexure of the skull to generate potentially damaging loads in the brain, even if no impact occurs. The possibility that this mechanism may contribute to TBI has implications for the diagnosis of soldiers and the design of protective equipment such as helmets.

Moss, W C; King, M J; Blackman, E G

2009-04-14

238

Nonlinear ion-acoustic cnoidal waves in a dense relativistic degenerate magnetoplasma

NASA Astrophysics Data System (ADS)

The complex pattern and propagation characteristics of nonlinear periodic ion-acoustic waves, namely, ion-acoustic cnoidal waves, in a dense relativistic degenerate magnetoplasma consisting of relativistic degenerate electrons and nondegenerate cold ions are investigated. By means of the reductive perturbation method and appropriate boundary conditions for nonlinear periodic waves, a nonlinear modified Korteweg-de Vries (KdV) equation is derived and its cnoidal wave is analyzed. The various solutions of nonlinear ion-acoustic cnoidal and solitary waves are presented numerically with the Sagdeev potential approach. The analytical solution and numerical simulation of nonlinear ion-acoustic cnoidal waves of the nonlinear modified KdV equation are studied. Clearly, it is found that the features (amplitude and width) of nonlinear ion-acoustic cnoidal waves are proportional to plasma number density, ion cyclotron frequency, and direction cosines. The numerical results are applied to high density astrophysical situations, such as in superdense white dwarfs. This research will be helpful in understanding the properties of compact astrophysical objects containing cold ions with relativistic degenerate electrons.

El-Shamy, E. F.

2015-03-01

239

Relativistic surface-wave generators based on two-dimensional periodic structures

NASA Astrophysics Data System (ADS)

In order to increase the integral output radiation power of relativistic surface-wave generators, it is suggested to use two-dimensional (2D) periodic slow-wave systems. Numerical simulations of dynamics of a new variant of these generators showed that additional wave beams, which appear in the 2D structure and propagate in the transverse direction, are capable of synchronizing radiation from a wide sheet electron beam. This circumstance makes it possible to implement surface-wave generators operating in the millimeter wavelength range at a gigawatt power level—e.g., based on the ELMI high-current accelerator at the Institute of Nuclear Physics (Novosibirsk).

Ginzburg, N. S.; Zaslavskii, V. Yu.; Malkin, A. M.; Sergeev, A. S.

2012-02-01

240

Skull Flexure from Blast Waves: A Mechanism for Brain Injury with Implications for Helmet Design

Traumatic brain injury [TBI] has become a signature injury of current military conflicts, with debilitating, costly, and long-lasting effects. Although mechanisms by which head impacts cause TBI have been well-researched, the mechanisms by which blasts cause TBI are not understood. From numerical hydrodynamic simulations, we have discovered that non-lethal blasts can induce sufficient skull flexure to generate potentially damaging loads in the brain, even without a head impact. The possibility that this mechanism may contribute to TBI has implications for injury diagnosis and armor design.

Moss, W C; King, M J; Blackman, E G

2009-04-30

241

Skull flexure from blast waves: a mechanism for brain injury with implications for helmet design.

Traumatic brain injury (TBI) has become a signature injury of current military conflicts, with debilitating, costly, and long-lasting effects. Although mechanisms by which head impacts cause TBI have been well researched, the mechanisms by which blasts cause TBI are not understood. From numerical hydrodynamic simulations, we have discovered that nonlethal blasts can induce sufficient skull flexure to generate potentially damaging loads in the brain, even without a head impact. The possibility that this mechanism may contribute to TBI has implications for injury diagnosis and armor design. PMID:19792349

Moss, William C; King, Michael J; Blackman, Eric G

2009-09-01

242

Spatio-temporal evolution of relativistically intense longitudinal space charge waves in a cold homogeneous plasma is studied analytically as well as numerically, as an initial value problem, using Dawson sheet model. It is found that, except for very special initial conditions which generates the well known longitudinal Akhiezer-Polovin mode, for all other initial conditions, the waves break through a novel mechanism called phase mixing at an amplitude well below the Akhiezer-Polovin limit. An immediate consequence of this is, that Akhiezer-Polovin waves break when subjected to arbitrarily small longitudinal perturbations. We demonstrate this by performing extensive numerical simulations. This result may be of direct relevance to ultrashort, ultraintense laser/beam pulse-plasma interaction experiments where relativistically intense waves are routinely excited.

Sengupta, Sudip, E-mail: sudip@ipr.res.in [Institute for Plasma Research, Bhat , Gandhinagar - 382428 (India)

2014-02-11

243

NASA Astrophysics Data System (ADS)

Spatio-temporal evolution of relativistically intense longitudinal space charge waves in a cold homogeneous plasma is studied analytically as well as numerically, as an initial value problem, using Dawson sheet model. It is found that, except for very special initial conditions which generates the well known longitudinal Akhiezer-Polovin mode, for all other initial conditions, the waves break through a novel mechanism called phase mixing at an amplitude well below the Akhiezer-Polovin limit. An immediate consequence of this is, that Akhiezer-Polovin waves break when subjected to arbitrarily small longitudinal perturbations. We demonstrate this by performing extensive numerical simulations. This result may be of direct relevance to ultrashort, ultraintense laser/beam pulse-plasma interaction experiments where relativistically intense waves are routinely excited.

Sengupta, Sudip

2014-02-01

244

Relativistic electron losses related to EMIC waves during CIR and CME storms

of radiation belt electrons to the atmosphere due to waveÂparticle interactions with electromagnetic ionRelativistic electron losses related to EMIC waves during CIR and CME storms M.I. Sandanger a,Ã?, F o Article history: Accepted 14 July 2008 PACS: 94.30.Lr 94.30.cb 94.30.Xy 94.30.cv 94.20.wj 94.30.Ny

Bergen, Universitetet i

245

Enhanced frequency agility of high-power relativistic backward wave oscillators

This paper describes how finite length effects in high-power backward wave oscillators can be exploited in a controlled manner to achieve enhanced frequency agility. Experiments were performed using a Sinus-6 high-power relativistic repetitively pulsed electron beam accelerator. A uniform slow wave structure was used in these studies and its parameters were fixed. Sections of smooth-walled circular waveguide of varying lengths

L. D. Moreland; E. Schamiloglu; R. W. Lemke; A. M. Roitman; S. D. Korovin; V.V. Rostov

1996-01-01

246

Studies of relativistic backward-wave oscillator operation in the cross-excitation regime

We first reported the operation of a relativistic backward-wave oscillator (BWO) in the so-called cross-excitation regime in 1998. This instability, whose general properties were predicted earlier through numerical studies, resulted from the use of a particularly shallow rippled-wall waveguide [slow wave structure (SWS)] that was installed in an experiment to diagnose pulse shortening in a long-pulse electron beam-driven high-power microwave

Frank Hegeler; Michael D. Partridge; Edl Schamiloglu; Chaouki T. Abdallah

2000-01-01

247

The linear and nonlinear theory of a plasma-filled relativistic Cherenkov generator with coaxial slow-wave structure (SWS) is developed. Linear analysis includes the space-charge limiting current, dispersion relations, dispersion curves, and coupling impedance. In nonlinear theory, the electron beam space-charge effect, nonsynchronous interaction, and complex reflection coefficients of the electromagnetic wave at the boundaries of the SWS are taken into account.

Xiao Renzhen; Lin Yuzheng; Song Zhimin; Chen Changhua; Liu Guozhi

2007-01-01

248

A compact P-band coaxial relativistic backward wave oscillator with three periods slow wave structure was investigated experimentally. The experimental results show that the frequency of the P-band coaxial relativistic backward wave oscillator is 897 MHz and the microwave power is 1.47 GW with an efficiency of about 32% in the case in which the diode voltage is 572 kV, the beam current is 8.0 kA, and the guide magnetic field is about 0.86 T. In addition, the device can generate a 3.14 GW microwave radiation as the guide magnetic field increases to 1.2 T at the diode voltage of 997 kV and the beam current of 15.3 kA. The experimental results are in good agreement with those obtained earlier by numerical simulations.

Gao Liang; Qian Baoliang; Ge Xingjun; Zhang Xiaoping; Jin Zhenxing [College of Optoelectric Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2012-08-15

249

Smooth Light Curves from a Bumpy Ride: Relativistic Blast Wave Encounters a Density Jump

Some GRB afterglow light curves show significant variability, which often includes episodes of rebrightening. This was attributed in several cases to large fluctuations in the external density. Here we examine the effect of a sharp increase in the external density on the light curve by considering, for the first time, a full treatment of both the hydrodynamic evolution and the radiation in this scenario. To this end we develop a semi-analytic model for the light curve and carry out several elaborate numerical simulations using a 1D hydrodynamic code together with a synchrotron radiation code.Two spherically symmetric cases are explored in detail: a density jump in a uniform external medium, and a wind termination shock. Contrary to previous works, we find that even a sharp (step function) and large (by a factor of $a>>1$) increase in the external density does not produce sharp features in the light curve, and cannot account for significant temporal variability. For a wind termination shock, the light curve smoothly transitions between the asymptotic power-laws over about one decade in time, and there is no rebrightening in the optical or X-rays to serve as a clear observational signature. For a sharp jump in a uniform density we find that the maximal deviation $\\Delta\\alpha_max$ of the temporal decay index $\\alpha$ from its asymptotic value, is bounded (e.g., $\\Delta\\alpha_max <0.4$ for $a=10$); $\\Delta\\alpha_max$ slowly increases with $a$, converging to $\\Delta\\alpha_{max} \\approx 1$ at very large $a$ values. Therefore, no optical rebrightening is expected here as well. In the X-rays, while the asymptotic flux is unaffected by the density jump, the fluctuations in $\\alpha$ are found to be comparable to those in the optical. Finally, we discuss the implications of our results for the origin of the fluctuations in several afterglows.

Ehud Nakar; Jonathan Granot

2006-06-01

250

A high efficient relativistic backward wave oscillator with coaxial nonuniform slow-wave structures (SWSs) and depth-tunable extractor is presented. The physical mechanism to increase the power efficiency is investigated theoretically and experimentally. It is shown that the nonuniform SWSs, the guiding magnetic field distribution, and the coaxial extractor depth play key roles in the enhancement of the beam-wave power conversion efficiency. The experimental results show that a 1.609 GHz, 2.3 GW microwave can be generated when the diode voltage is 890 kV and the beam current is 7.7 kA. The corresponding power efficiency reaches 33.6%.

Ge Xingjun; Zhong Huihuang; Zhang Jun; Qian Baoliang [College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2013-02-15

251

NASA Astrophysics Data System (ADS)

A high efficient relativistic backward wave oscillator with coaxial nonuniform slow-wave structures (SWSs) and depth-tunable extractor is presented. The physical mechanism to increase the power efficiency is investigated theoretically and experimentally. It is shown that the nonuniform SWSs, the guiding magnetic field distribution, and the coaxial extractor depth play key roles in the enhancement of the beam-wave power conversion efficiency. The experimental results show that a 1.609 GHz, 2.3 GW microwave can be generated when the diode voltage is 890 kV and the beam current is 7.7 kA. The corresponding power efficiency reaches 33.6%.

Ge, Xingjun; Zhong, Huihuang; Zhang, Jun; Qian, Baoliang

2013-02-01

252

A relativistic beam-plasma system with electromagnetic waves E. G. Evstatiev, P. J. Morrison, and W multiwave model that describes the interaction of an electron beam, plasma waves, and electromagnetic waves, and electrostatic and electromagnetic waves. The model obtained is finite dimensional, and allows for efficient

Morrison, Philip J.,

253

Versatile gas gun target assembly for studying blast wave mitigation in materials

NASA Astrophysics Data System (ADS)

Traumatic brain injury (TBI) has become a serious problem for military personnel returning from recent conflicts. This has increased interest in investigating blast mitigating materials for use in helmets. In this paper we describe a new versatile target assembly that is used with an existing gas gun for studying these materials.

Bartyczak, S.; Mock, W., Jr.

2012-03-01

254

Macro-mechanical modeling of blast-wave mitigation in foams. Part III: verification of the models

NASA Astrophysics Data System (ADS)

Three different approaches to macro-mechanical modeling of blast-wave mitigation in foam namely: the single-phase effective gas flow model, the two-phase mixture model and the single bubble/shock wave interaction model are critically reviewed. The nature and extent of the approximations inherent in the formulation of the first two models were examined in Part I of this study. In this part, the applicability of the aforementioned approaches is verified based on a comparison of experimental pressure records obtained in shock tube tests with the results of numerical predictions that used the models under consideration. Deficiencies and inconsistencies that are found during this comparison are clarified and possible improvements are suggested. It is emphasized that both the single-phase and the two-phase approaches predict well the refraction of the incident shock at the air/foam interface while they do not uniquely determine the relaxation process and the shape of the transmitted shock wave front. Various flexibilities that are exploited to better describe the inter-phase interactions do not improve the results significantly. The single bubble model is examined with particular attention paid to the manner in which it predicts the shape of the shock wave front. Connections between the flow viscosity and the transient dynamics of the bubble compression that occur at scales of the shock wave front thickness are explored.

Britan, A.; Shapiro, H.; Liverts, M.; Ben-Dor, G.

2014-05-01

255

NASA Astrophysics Data System (ADS)

We discuss the scheme of a high-power relativistic backward-wave oscillator operating with a high-current explosive-emission electron beam. The radiation output from the tube is based on reflection of the operating wave into a fast cyclotron wave which transmits the energy of the high-frequency field towards the collector. At the collector, reverse conversion into the output electromagnetic wave takes place. The proposed scheme allows one to increase electric strength, as well as the transverse size of the working space of the backward-wave oscillator. It is shown that within the proposed scheme, one can reduce the focusing magnetic field without decreasing the power of the output radiation.

Goykhman, M. B.; Gromov, A. V.; Kladukhin, V. V.; Kovalev, N. F.; Kolganov, N. G.; Palitsin, A. V.

2014-09-01

256

The operation in the cross-excitation instability regimes for relativistic backward wave oscillators has been reported and studied in some earlier papers. In the experiment of a relativistic Cerenkov generator with coaxial slow wave structure (CRCG), the cross-excitation instability has also been observed by us. In this paper, experimental results for the CRCG operating in this regime are given, and an explanation is provided to account for the appearance of the instability. Based on this explanation, two types of reflectors, i.e., coaxial Bragg reflectors and cutoff necks, are adopted to restrain the cross-excitation instability by increasing the reflection coefficient at the entrance of the coaxial slow wave structure.

Xiao Renzhen; Zhang Lijun; Liang Tiezhu; Teng Yan; Chen Changhua; Shao Hao; Liu Guozhi [Northwest Institute of Nuclear Technology, Xi'an 710024 (China); Lin Yuzheng [Tsinghua University, Beijing 100084 (China)

2008-05-15

257

Compression-related EMIC waves and associated precipitation of relativistic electrons

NASA Astrophysics Data System (ADS)

With conjugate observations of the NOAA 15 satellite and ground-based magnetometer, we present observations of solar wind compression-related dayside electromagnetic ion cyclotron (EMIC) waves and associated precipitation of relativistic electrons in geoquiescence on Jan 1, 2007. Associated with the enhanced solar wind compression, a dayside Pc1 pulsation was observed by the OUL station. Such a Pc1 pulsation can be considered as a signature of an EMIC wave propagating from the geomagnetic equatorial plane to lower altitudes. Simultaneously, within the proton anisotropic zone the NOAA 15 satellite registered an enhancement of precipitating electrons count rates with energies >3 MeV, which can be interpreted by the theoretical calculation of the pitch angle diffusion coefficients. Our observations suggest that after an enhancement of solar wind pressure, the compression-related EMIC waves can cause a loss of relativistic electrons and play an important role in the evolution of radiation belt electrons.

Wang, D.; Yuan, Z.; Deng, X.; Zhou, M.; Huang, S.; Li, M.; Li, H.; Raita, T.; Pang, Y.

2013-12-01

258

Relativistic electron precipitation events driven by electromagnetic ion-cyclotron waves

We adopt a canonical approach to describe the stochastic motion of relativistic belt electrons and their scattering into the loss cone by nonlinear EMIC waves. The estimated rate of scattering is sufficient to account for the rate and intensity of bursty electron precipitation. This interaction is shown to result in particle scattering into the loss cone, forming ?10?s microbursts of precipitating electrons. These dynamics can account for the statistical correlations between processes of energization, pitch angle scattering, and relativistic electron precipitation events, that are manifested on large temporal scales of the order of the diffusion time ?tens of minutes.

Khazanov, G., E-mail: george.v.khazanov@nasa.gov; Sibeck, D. [NASA Goddard Space FlightCenter, Greenbelt, Maryland 20771 (United States); Tel'nikhin, A.; Kronberg, T. [Department of Physics and Technology, Altai State University, Barnaul (Russian Federation)

2014-08-15

259

The dispersion relation for circularly polarized electromagnetic waves propagating in the direction of an external magnetic field in a relativistic electron-positron plasma with arbitrary constant drift velocities is obtained for constant temperature in the homentropic regime. This result is an exact solution of the nonlinear magnetofluid unification field formalism introduced by S. Mahajan [Phys. Rev. Lett. 90, 035001 (2003)], where the electromagnetic and fluid fields are coupled through the relativistic enthalpy density. The behavior of electromagnetic and Alfven branches of the dispersion relation are discussed for different temperatures.

Asenjo, Felipe A.; Munoz, Victor; Valdivia, Juan Alejandro [Departamento de Fisica, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile); Hada, Tohru [Department of Earth System Science and Technology, Kyushu University, Fukuoka 816-8580 (Japan)

2009-12-15

260

Relativistic solitary waves with phase modulation embedded in long laser pulses in plasmas

We investigate the existence of nonlinear phase-modulated relativistic solitary waves embedded in an infinitely long circularly polarized electromagnetic wave propagating through a plasma. These states are exact nonlinear solutions of the 1-dimensional Maxwell-fluid model for a cold plasma composed of electrons and ions. The solitary wave, which consists of an electromagnetic wave trapped in a self-generated Langmuir wave, presents a phase modulation when the group velocity V and the phase velocity V{sub ph} of the long circularly polarized electromagnetic wave do not match the condition VV{sub ph} = c{sup 2}. The main properties of the waves as a function of their group velocities, wavevectors, and frequencies are studied, as well as bifurcations of the dynamical system that describes the waves when the parameter controlling the phase modulation changes from zero to a finite value. Such a transition is illustrated in the limit of small amplitude waves where an analytical solution for a grey solitary wave exists. The solutions are interpreted as the stationary state after the collision of a long laser pulse with an isolated solitary wave.

Sanchez-Arriaga, G.; Siminos, E.; Lefebvre, E. [CEA, DAM, DIF, 91297 Arpajon (France)

2011-08-15

261

Radiation from highly relativistic geodesics. [gravitational wave generation

NASA Technical Reports Server (NTRS)

A number of recent works are reviewed concerning the generation and emission of gravitational waves. It is shown that at high frequencies, the generation of gravitational radiation is a local phenomenon. Two examples are described illustrating this generation when a high-energy particle collides against the space-time curvature. One, after Matzner and Nutku, uses a method of virtual photons; the other, after Chrzanowski and Misner, is based on the W.K.B. approximation, corresponding to geometric optics, for the inhomogeneous wave equation. This method uses a factorized integral representation of the Green function which is valid asymptotically to infinity in space.

Misner, C. W.

1974-01-01

262

Electrostatic ion acoustic solitary waves are studied in a plasma system comprising of relativistic ions, kappa distributed electrons, and positrons. The increase in the relativistic streaming factor and positron and electron kappa parameters cause the soliton amplitude to thrive. However, the soliton amplitude diminishes as the positron concentration is increased in the system. Our results are general and may be helpful, in understanding nonlinear phenomena in the presence of kappa distibuted electrons, positrons, and relativistically streaming ions.

Shah, Asif; Mahmood, S.; Haque, Q. [Theoretical Plasma Physics Division, PINSTECH, P.O. Nilore, Islamabad (Pakistan)

2011-11-15

263

Relativistic wave functions and energies for nonzero angular momentum states in light-front dynamics

Light-front dynamics (LFD) is a powerful approach to the theory of relativistic composite systems (hadrons in the quark models and relativistic nucleons in nuclei). Its explicitly covariant version has been recently applied with success to describe the new CEBAF/TJNAF data on the deuteron electromagnetic form factors. The solutions used in were however not obtained from solving exactly the LFD equations but by means of a perturbative calculation with respect to the non relativistic wave function. Since, a consequent effort has been made to obtain exact solutions of LFD equations. The first results concerning J=0 states in a scalar model have been published in nucl-th/9912050. The construction of $J \

V. A. Karmanov; M. Mangin-Brinet; J. Carbonell

2000-08-31

264

NASA Astrophysics Data System (ADS)

The initial experimental results of an L-band relativistic backward wave oscillator with a coaxial slow-wave structure are presented. The asymmetric-mode-competition mechanism in the device is investigated theoretically and experimentally. It is shown that the diode voltage, guiding-magnetic field, and concentricity play a key role in the suppression and excitation of the asymmetric-mode (coaxial quasi-TE11 mode). In the experiments, the asymmetric-mode with a frequency of 2.05 GHz is suppressed and excited, which is in good agreement with the theoretical results.

Ge, Xingjun; Zhong, Huihuang; Qian, Baoliang; Zhang, Jun; Liu, Lie; Gao, Liang; Yuan, Chengwei; He, Juntao

2010-12-01

265

Blast-wave impact-mitigation capability of polyurea when used as helmet suspension-pad material

, as well as exposure to elec- tromagnetic and thermal radiation [6]. Due to the fact that blast can often propel the soldier and result in a head impact, early blast-induced TBI mitigation efforts were mainly

Grujicic, Mica

266

NASA Astrophysics Data System (ADS)

The simulation of trajectories, angular and spatial distributions of relativistic electrons and positrons (155 MeV - 1500 MeV) penetrating through an ultra-thin crystal (half-wave crystal - HWC) has been performed taking into account initial angular beam divergence. The results show similarities and differences with non-relativistic protons channeling in a HWC.

Pivovarov, Yu L.; Tukhfatullin, T. A.

2014-05-01

267

Infrared and X-Ray Evidence for Circumstellar Grain Destruction by the Blast Wave of Supernova 1987A

NASA Technical Reports Server (NTRS)

Multiwavelength observations of supernova remnant (SNR) 1987A show that its morphology and luminosity are rapidly changing at X-ray, optical, infrared, and radio wavelengths as the blast wave from the explosion expands into the circumstellar equatorial ring, produced by mass loss from the progenitor star. The observed infrared (IR) radiation arises from the interaction of dust grains that formed in mass outflow with the soft X-ray emitting plasma component of the shocked gas. Spitzer IRS spectra at 5 - 30 microns taken on day 6190 since the explosion show that the emission arises from approx. 1.1 x 10(exp -6) solar mass of silicate grains radiating at a temperature of approx. 180+/-(15-20) K. Subsequent observations on day 7137 show that the IR flux had increased by a factor of 2 while maintaining an almost identical spectral shape. The observed IR-to-X-ray flux ratio (IRX) is consistent with that of a dusty plasma with standard LMC dust abundances. This flux ratio has decreased by a factor of approx. 2 between days 6190 and 7137, providing the first direct observation of the ongoing destruction of dust in an expanding SN blast wave on dynamic time scales. Detailed models consistent with the observed dust temperature, the ionization fluence of the soft X-ray emission component, and the evolution of IRX suggest that the radiating si1icate grains are immersed in a 3.5 x 10(exp 6) K plasma with a density of (0.3 - 1) x 10(exp 4)/cu cm, and have a size distribution that is confined to a narrow range of radii between 0.02 and 0.2 microns. Smaller grains may have been evaporated by the initial UV flash from the supernova.

Dwek, Eliahu; Arendt, Richard G.; Bouchet, Patrice; Burrows, David N.; Challis, Peter; Danziger, John; DeBuizer James M.; Gehrz, Robert D.; Kirshner, Robert P.; McCray, Richard; Park, Sangwok; Polomski, Elisha; Woodward, Charles

2007-01-01

268

Materials have been applied to the thoracic wall of anaesthetised experimental animals exposed to blast overpressure to investigate the coupling of direct stress waves into the thorax and the relative contribution of compressive stress waves and gross thoracic compression to lung injury. The ultimate purpose of the work is to develop effective personal protection from the primary effects of blast overpressure--efficient protection can only be achieved if the injury mechanism is identified and characterized. Foam materials acted as acoustic couplers and resulted in a significant augmentation of the visceral injury; decoupling and elimination of injury were achieved by application of a high acoustic impedance layer on top of the foam. In vitro experiments studying stress wave transmission from air through various layers into an anechoic water chamber showed a significant increase in power transmitted by the foams, principally at high frequencies. Material such as copper or resin bonded Kevlar incorporated as a facing upon the foam achieved substantial decoupling at high frequencies--low frequency transmission was largely unaffected. An acoustic transmission model replicated the coupling of the blast waves into the anechoic water chamber. The studies suggest that direct transmission of stress waves plays a dominant role in lung parenchymal injury from blast loading and that gross thoracic compression is not the primary injury mechanism. Acoustic decoupling principles may therefore be employed to reduce the direct stress coupled into the body and thus reduce the severity of lung injury--the most simple decoupler is a high acoustic impedance material as a facing upon a foam, but decoupling layers may be optimized using acoustic transmission models. Conventional impacts producing high body wall velocities will also lead to stress wave generation and transmission--stress wave effects may dominate the visceral response to the impact with direct compression and shear contributing little to the aetiology of the injury. PMID:2050704

Cooper, G J; Townend, D J; Cater, S R; Pearce, B P

1991-01-01

269

Method of accelerating photons by a relativistic plasma wave

Photons of a laser pulse have their group velocity accelerated in a plasma as they are placed on a downward density gradient of a plasma wave of which the phase velocity nearly matches the group velocity of the photons. This acceleration results in a frequency upshift. If the unperturbed plasma has a slight density gradient in the direction of propagation, the photon frequencies can be continuously upshifted to significantly greater values.

Dawson, John M. (Pacific Palisades, CA); Wilks, Scott C. (Santa Monica, CA)

1990-01-01

270

Analysis of the Cross-Excitation Instability in a Relativistic Backward Wave Oscillator

NASA Astrophysics Data System (ADS)

The cross-excitation instability in a relativistic backward wave oscillator (BWO) was first observed by our group in 1998.^1 This instability resulted from the use of a particularly shallow rippled-wall waveguide that we had installed in our experiment to accomodate laser interferometry measurements during the course of microwave generation in a high power BWO. Since those early experiments we have analyzed a considerable amount of data to better understand this operating regime. We have invoked joint time-frequency analysis as well as wavelets to interpret the heterodyned signals of the radiated power measurements. We will discuss the interpretation of the data, as well as the methodology used to analyze the data. ^1 C. Grabowski, E. Schamiloglu, C.T. Abdallah, and F. Hegeler, ``Observation of the cross-excitation instability in a relativistic backward wave oscillator,'' Phys. Plasmas 5, 3490 (1998).

Schamiloglu, Edl; Hegeler, Frank; Abdallah, Chaouki; Partridge, Michael

1999-11-01

271

Exact relativistic expressions for wave refraction in a generally moving fluid.

The law for the refraction of a wave when the two fluids and the interface are moving with relativistic velocities is given in an exact form, at the same time correcting a first order error in a previous paper [Cavalleri and Tonni, Phys. Rev. E 57, 3478 (1998)]. The treatment is then extended to a generally moving fluid with variable refractive index, ready to be applied to the refraction of acoustic, electromagnetic, or magnetohydrodynamic waves in the atmosphere of rapidly rotating stars. In the particular case of a gas cloud receding because of the universe expansion, our result can be applied to predict observable micro- and mesolensings. The first order approximation of our exact result for the deviation due to refraction of the light coming from a further quasar has a relativistic dependence equal to the one obtained by Einsteins' linearized theory of gravitation. PMID:23679540

Cavalleri, G; Tonni, E; Barbero, F

2013-04-01

272

NASA Technical Reports Server (NTRS)

Incident overpressure data from frangible spheres pressurized with a flash-evaporating fluid in liquid and vapor form were obtained in laboratory experiments. Glass spheres under higher than ambient internal pressure of Freon-12 were purposely burst to obtain time histories of overpressure. Nondimensional peak pressures, arrival and duration times, and impulses are presented, and whenever possible plotted and compared with compiled data for Pentolite high-explosive. The data are generally quite repeatable and show differences from blast data produced by condensed high-explosives.

Esparaza, E. D.; Baker, W. E.

1977-01-01

273

We study the strong-coupling limit of some relativistic wave equations describing bound states of oppositely charged fermions or bosons 1 and 2, of arbitrary mass. Using both numerical and analytic momentum-space methods we find the value gammamax of gamma=-e1e2\\/4pi for which the lowest-lying bound state disappears from the spectrum, as well as the smaller value gammadec for which 2 becomes

G. Hardekopf; J. Sucher

1985-01-01

274

Resonant diffusion curves for electron cyclotron resonance with field-aligned electromagnetic R mode and L mode electromagnetic ion cyclotron (EMIC) waves are constructed using a fully relativistic treatment. Analytical solutions are derived for the case of a single-ion plasma, and a numerical scheme is developed for the more realistic case of a multi-ion plasma. Diffusion curves are presented for plasma parameters

Danny Summers; Richard M. Thorne; Fuliang Xiao

1998-01-01

275

Relativistic Covariance and Quark-Diquark Wave Functions

We derive covariant wave functions for hadrons composed of two constituents for arbitrary Lorentz boosts. Focussing explicitly on baryons as quark-diquark systems, we reduce their manifestly covariant Bethe-Salpeter equation to covariant 3-dimensional forms by projecting on the relative quark-diquark energy. Guided by a phenomenological multi gluon exchange representation of covariant confining kernels, we derive explicit solutions for harmonic confinement and for the MIT Bag Model. We briefly sketch implications of breaking the spherical symmetry of the ground state and the transition from the instant form to the light cone via the infinite momentum frame.

M. Dillig

2006-04-24

276

A generic nonparaxial model for pulse envelopes is presented. Classic Schrödinger-type descriptions of wave propagation have their origins in slowly-varying envelopes combined with a Galilean boost to the local time frame. By abandoning these two simplifications, a picture of pulse evolution emerges in which frame-of-reference considerations and space-time transformations take center stage. A wide range of effects, analogous to those in special relativity, then follows for both linear and nonlinear systems. Explicit demonstration is presented through exact bright and dark soliton pulse solutions. PMID:22400744

Christian, J M; McDonald, G S; Hodgkinson, T F; Chamorro-Posada, P

2012-01-20

277

Observation of relativistic plasma waves generated by the beat-wave with 1 micron lasers

NASA Astrophysics Data System (ADS)

An experiment to generate a plasma wave by the beat wave process is described. The beat wave is generated by mixing two copropagating intense laser beams at 1.053 microns and 1.064 microns. The plasma wave is observed by monitoring the sideband generated by the interaction of the plasma wave with a third copropagating laser beam at 0.526 microns. Plasma waves with an electric field of 3 x 10 to the 6th V/cm are observed.

Dangor, A. E.; Dymoke-Bradshaw, A. K. L.; Dyson, A. E.

1990-01-01

278

The klystron-like relativistic backward wave oscillator (RBWO) combines the transition radiation with Cerenkov radiation and has demonstrated microwave output of high power and high efficiency. The coaxial slow wave structure device can produce microwave with a lower frequency in a smaller cross section. For the purpose of high efficiency, low frequency, and miniaturization, a coaxial klystron-like RBWO with a premodulation cavity is presented. Particle-in-cell simulations show that a microwave with power of 1.15 GW and frequency of 2.1 GHz is generated with conversion efficiency of 48%, whereas for the device with a reflector, the efficiency is 38%.

Xiao Renzhen; Teng Yan; Chen Changhua; Sun Jun [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024 (China)

2011-11-15

279

NASA Astrophysics Data System (ADS)

Smith-Purcell (SP) radiations of weakly relativistic oversized backward wave oscillator (BWO) are examined experimentally. A bunching section composed of a coaxial slow wave structure with inner K-band corrugation is placed upstream from the oversized BWO. An annular beam less than 100 kV is self-bunched in the bunching section and then excites the oversized BWO. SP radiations are examined by using 25.5- and 45.0-GHz oversized BWOs. The beam is too far away from the walls of the oversized BWO for SP radiation to occur without the self-bunching. When the corrugation parameters of the bunching section are the same as those of the oversized BWO, enhanced SP radiations in the frequency region above the surface wave are observed even when the beam propagates outside the interaction region of the surface wave.

Iwasaki, Takayuki; Ogura, Kazuo; Magori, Shota; Kojima, Junpei; Yambe, Kiyoyuki

2014-10-01

280

Enhanced frequency agility of high-power relativistic backward wave oscillators

This paper describes how finite length effects in high-power backward wave oscillators can be exploited in a controlled manner to achieve enhanced frequency agility. Experiments were performed using a Sinus-6 high-power relativistic repetitively pulsed electron beam accelerator. A uniform slow wave structure was used in these studies and its parameters were fixed. Sections of smooth-walled circular waveguide of varying lengths were inserted both before and after the slow wave structure. Variations in the length of smooth-walled waveguide on the order of a quarter-wavelength of the generated electromagnetic radiation were found to significantly affect both microwave frequency and radiation efficiency in a periodic-like manner. The experimental results were reproduced in TWOQUICK electromagnetic particle-in-cell simulations. A bandwidth of about 500 MHz centered around 9.5 GHz at hundreds of MW power levels has been achieved with constant beam and slow wave structure parameters.

Moreland, L.D.; Schamiloglu, E. [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Electrical and Computer Engineering] [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Electrical and Computer Engineering; Lemke, R.W. [Sandia National Labs., Albuquerque, NM (United States)] [Sandia National Labs., Albuquerque, NM (United States); Roitman, A.M.; Korovin, S.D.; Rostov, V.V. [Russian Academy of Sciences, Tomsk (Russian Federation). High Current Electronics Inst.] [Russian Academy of Sciences, Tomsk (Russian Federation). High Current Electronics Inst.

1996-06-01

281

Rapid startup in relativistic backward wave oscillator by injecting external backward signal

Investigation on accelerating the building up of oscillation and achieving a rapid startup in powerful relativistic backward wave oscillator by injecting a weak external backward signal is carried out in this paper. Synchronizing the signal with the backward wave excited by intense electron beam extracting with slow wave structure, the initial noise is greatly reduced and mode competition is restrained. The analysis is demonstrated by high power X-band backward wave oscillator experiment, in which a plasma switch is designed to realize the backward signal injection. The results show that the significant reduction of microwave output delay is attained and the start time of oscillation is ahead of 10 ns with the energy conversion efficiency increases about 62%.

Song, W.; Teng, Y.; Zhang, Z. Q.; Li, J. W.; Sun, J.; Chen, C. H.; Zhang, L. J. [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an, Shanxi 710024 (China)

2012-08-15

282

NASA Astrophysics Data System (ADS)

We have examined relativistic electron flux losses at geosynchronous orbit under quiet geomagnetic conditions. One 3 day period, from 11 to 13 October 2007, was chosen for analysis because geomagnetic conditions were very quiet (3 day average of Kp< 1), and significant losses of geosynchronous relativistic electrons were observed. During this interval, there was no geomagnetic storm activity. Thus, the loss processes associated with geomagnetic field modulations caused by ring current buildup can be excluded. The >2 MeV electron flux at geosynchronous orbit shows typical diurnal variations with a maximum near noon and a minimum near midnight for each day. The flux level of the daily variation significantly decreased from first day to third day for the 3 day period by a factor of >10. The total magnetic field strength (BT) of the daily variation on the third day, however, is comparable to that on the first day. Unlike electron flux decreases, the flux of protons with energies between 0.8 and 4 MeV adiabatically responses to the daily variation of BT. That is, there is no significant decrease of the proton flux when the electron flux decreases. During the interval of quiet geomagnetic conditions, well-defined electromagnetic ion cyclotron (EMIC) waves were detected at geosynchronous spacecraft. Low-altitude polar-orbiting spacecraft observed the precipitation of energetic protons and relativistic electrons in the interval of EMIC waves enhancement. From these observations, we suggest that the EMIC waves at geosynchronous orbit cause pitch angle scattering and relativistic electron losses to the atmosphere under quiet geomagnetic conditions.

Hyun, K.; Kim, K.-H.; Lee, E.; Kwon, H.-J.; Lee, D.-H.; Jin, H.

2014-10-01

283

Derivation of the lattice Boltzmann model for relativistic hydrodynamics

A detailed derivation of the lattice Boltzmann scheme for relativistic fluids recently proposed in M. Mendoza, B. Boghosian, H. Herrmann, and S. Succi, Phys. Rev. Lett. 105, 014502 (2010) is presented. The method is numerically validated and applied to the case of two quite different relativistic fluid-dynamic problems, namely, shock-wave propagation in quark-gluon plasmas and the impact of a supernova blast wave on massive interstellar clouds. Close to second-order convergence with the grid resolution, as well as linear dependence of computational time on the number of grid points and time steps, are reported.

Mendoza, M.; Herrmann, H. J. [Computational Physics for Engineering Materials, Institute for Building Materials, ETH Zuerich, Schafmattstrasse 6, HIF, CH-8093 Zuerich (Switzerland); Boghosian, B. M. [Department of Mathematics, Tufts University, Bromfield-Pearson, Medford, Massachusetts 02155 (United States); Succi, S. [Istituto per le Applicazioni del Calcolo C.N.R., Via dei Taurini, 19 00185, Rome, Italy, and Freiburg Institute for Advanced Studies, Albertstrasse, 19, D-79104, Freiburg (Germany)

2010-11-15

284

NASA Technical Reports Server (NTRS)

One-dimensional self-similar isothermal flow behind a blast wave propagating in a medium whose density varies with distance is investigated for the cases of one-dimensional and two-dimensional flow. The isothermal flow model is adopted as an alternative to adiabatic models of self-similar flow, which neglect heat flux. The topology of the one-dimensional flow solutions, the singularities, and the influence of boundary conditions are discussed; the instability of the isothermal blast waves against nonself-similar perturbations is also considered. The number of critical points in the two-dimensional solutions is found to vary from the number in the one-dimensional problem.

Lerche, I.

1978-01-01

285

The detailed mechanism of blast-induced traumatic brain injury (bTBI) has not been revealed yet. Thus, reliable laboratory animal models for bTBI are needed to investigate the possible diagnosis and treatment for bTBI. In this study, we used laser-induced shock wave (LISW) to induce TBI in rats and investigated the histopathological similarities to actual bTBI. After craniotomy, the rat brain was

Ben Hatano; Yoshihisa Matsumoto; Naoki Otani; Daizoh Saitoh; Shinichi Tokuno; Yasushi Satoh; Hiroshi Nawashiro; Yoshitaro Matsushita; Shunichi Sato

2011-01-01

286

Optimal design method of high-power microwave source using particle simulation and parallel genetic algorithms is presented in this paper. The output power, simulated by the fully electromagnetic particle simulation code UNIPIC, of the high-power microwave device is given as the fitness function, and the float-encoding genetic algorithms are used to optimize the high-power microwave devices. Using this method, we encode the heights of non-uniform slow wave structure in the relativistic backward wave oscillators (RBWO), and optimize the parameters on massively parallel processors. Simulation results demonstrate that we can obtain the optimal parameters of non-uniform slow wave structure in the RBWO, and the output microwave power enhances 52.6% after the device is optimized.

Chen, Zaigao; Wang, Jianguo [Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 (China) [Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 (China); Northwest Institute of Nuclear Technology, P.O. Box 69-12, Xi'an, Shaanxi 710024 (China); Wang, Yue; Qiao, Hailiang; Zhang, Dianhui [Northwest Institute of Nuclear Technology, P.O. Box 69-12, Xi'an, Shaanxi 710024 (China)] [Northwest Institute of Nuclear Technology, P.O. Box 69-12, Xi'an, Shaanxi 710024 (China); Guo, Weijie [Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 (China)] [Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 (China)

2013-11-15

287

Ion-acoustic solitary waves in ultra-relativistic degenerate pair-ion plasmas

The arbitrary and the small amplitude ion-acoustic solitary waves (IASWs) have been studied. The former is studied by using the Sagdeev pseudo-potential approach in a plasma consisting of the degenerate ultrarelativistic electrons, positrons, and the non-relativistic classical ions. It is seen that only compressive solitary waves can propagate through such plasmas. The numerical calculations show that the region of existence of the ion-acoustic solitary waves depends upon the positron (ion) number density and the plasma thermal temperature. This study is appropriate for applications in inertial confinement fusion laboratory research as well as the study of astrophysical dense objects such as white dwarf and dense neutron stars.

Rasheed, A.; Tsintsadze, N. L. [Department of Physics, G.C. University, Lahore 54000 (Pakistan); Salam Chair in Physics, G.C. University, Lahore 54000 (Pakistan); Murtaza, G. [Salam Chair in Physics, G.C. University, Lahore 54000 (Pakistan)

2011-11-15

288

Observation of Self-Sustaining Relativistic Ionization Wave Launched by a Sheath Field

NASA Astrophysics Data System (ADS)

We present experimental evidence supported by simulations of a relativistic ionization wave launched into a surrounding gas by the sheath field of a plasma filament with high energy electrons. Such a filament is created by irradiating a clustering gas jet with a short pulse laser (115 fs) at a peak intensity of 5×1017 W/cm2. We observe an ionization wave propagating radially through the gas for about 2 ps at 0.2-0.5 c after the laser has passed, doubling the initial radius of the filament. The gas is ionized by the sheath field, while the longevity of the wave is explained by a moving field structure that traps the high energy electrons near the boundary, maintaining a strong sheath field despite the significant expansion of the plasma.

McCormick, M.; Arefiev, A. V.; Quevedo, H. J.; Bengtson, R. D.; Ditmire, T.

2014-01-01

289

We have studied the propagation of ion acoustic shock waves involving planar and non-planar geometries in an unmagnetized plasma, whose constituents are non-degenerate ultra-cold ions, relativistically degenerate electrons, and positrons. By using the reductive perturbation technique, Korteweg-deVries Burger and modified Korteweg-deVries Burger equations are derived. It is shown that only compressive shock waves can propagate in such a plasma system. The effects of geometry, the ion kinematic viscosity, and the positron concentration are examined on the ion acoustic shock potential and electric field profiles. It is found that the properties of ion acoustic shock waves in a non-planar geometry significantly differ from those in planar geometry. The present study has relevance to the dense plasmas, produced in laboratory (e.g., super-intense laser-dense matter experiments) and in dense astrophysical objects.

Ata-ur-Rahman,; Qamar, A. [Institute of Physics and Electronics, University of Peshawar, Peshawar 25000 (Pakistan); National Centre for Physics, QAU Campus, Shahdrah Valley Road, Islamabad 44000 (Pakistan); Ali, S. [National Centre for Physics, QAU Campus, Shahdrah Valley Road, Islamabad 44000 (Pakistan); Mirza, Arshad M. [Theoretical Plasma Physics Group, Physics Department, Quaid-i-Azam University, Islamabad 45320 (Pakistan)

2013-04-15

290

Amplification of a high-frequency electromagnetic wave by a relativistic plasma

NASA Technical Reports Server (NTRS)

The amplification of a high-frequency transverse electromagnetic wave by a relativistic plasma component, via the synchrotron maser process, is studied. The background plasma that supports the transverse wave is considered to be cold, and the energetic component whose density is much smaller than that of the background component has a loss-cone feature in the perpendicular momentum space and a finite field-aligned drift speed. The ratio of the background plasma frequency squared to the electron gyrofrequency squared is taken to be sufficiently larger than unity. Such a parameter regime is relevant to many space and astrophysical situations. A detailed study of the amplification process is carried out over a wide range of physical parameters including the loss-cone index, the ratio of the electron mass energy to the temperature of the energetic component, the field-aligned drift speed, the normalized density, and the wave propagation angle.

Yoon, Peter H.

1990-01-01

291

Observation of self-sustaining relativistic ionization wave launched by a sheath field.

We present experimental evidence supported by simulations of a relativistic ionization wave launched into a surrounding gas by the sheath field of a plasma filament with high energy electrons. Such a filament is created by irradiating a clustering gas jet with a short pulse laser (115??fs) at a peak intensity of 5×10(17)??W/cm2. We observe an ionization wave propagating radially through the gas for about 2 ps at 0.2-0.5 c after the laser has passed, doubling the initial radius of the filament. The gas is ionized by the sheath field, while the longevity of the wave is explained by a moving field structure that traps the high energy electrons near the boundary, maintaining a strong sheath field despite the significant expansion of the plasma. PMID:24580461

McCormick, M; Arefiev, A V; Quevedo, H J; Bengtson, R D; Ditmire, T

2014-01-31

292

Relativistic modulational instability of electron-acoustic waves in an electron-pair ion plasma

The modulational instability of finite amplitude electron-acoustic waves (EAWs) along the external magnetic field is studied in an electron-pair ion plasma. Accounting for the relativistic electron mass variation nonlinearity and the Boltzmann distribution of both positive and negative ions, new regimes for the relativistic modulational instability (MI) for the low frequency (below the electron gyrofrequency) short-wavelength (in comparison with the ion gyroradius) modes are obtained numerically. It is found that the presence of a significant fraction of negative ions suppresses the MI growth/decay rate for the modulated EAW packets. The results could be of important for understanding the origin of amplitude modulated EAW packets in space (e.g., Earth's magnetotail) as well as in laboratory plasmas.

Misra, A. P. [Department of Mathematics, Siksha Bhavana, Visva-Bharati University, Santiniketan-731 235 (India); Shukla, P. K. [Institut fuer Theoretische Physik IV and Centre for Plasma Science and Astrophysics, Fakultaet fuer Physik and Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum, Germany and School of Physics, University of KwaZulu-Natal, 4000 Durban (South Africa)

2008-12-15

293

Wave front for a reaction-diffusion system and relativistic Hamilton-Jacobi dynamics.

The problem of wave-front propagation for the n-dimensional reaction-diffusion system involving Kolmogorov-Petrovskii-Piskunov kinetics and the diffusion transport with a finite velocity has been considered. By using a scaling procedure we have given an asymptotic derivation of the equation governing the evolution of a reaction front in the long-time large-distance limit. It has been found that this equation is identical in form to the relativistic Hamilton-Jacobi equation. In the case of a constant value of chemical rate function we have derived exact formulas for the position of reaction front and the speed of propagation by using relativistic mechanics techniques. PMID:11969459

Fedotov, S

1999-05-01

294

Cylindrical and Spherical Ion-Acoustic Shock Waves in a Relativistic Degenerate Multi-Ion Plasma

NASA Astrophysics Data System (ADS)

A rigorous theoretical investigation has been made to study the existence and basic features of the ion-acoustic (IA) shock structures in an unmagnetized, collisionless multi-ion plasma system (containing degenerate electron fluids, inertial positively as well as negatively charged ions, and arbitrarily charged static heavy ions). This investigation is valid for both non-relativistic and ultra-relativistic limits. The reductive perturbation technique has been employed to derive the modified Burgers equation. The solution of this equation has been numerically examined to study the basic properties of shock structures. The basic features (speed, amplitude, width, etc.) of these electrostatic shock structures have been briefly discussed. The basic properties of the IA shock waves are found to be significantly modified by the effects of arbitrarily charged static heavy ions and the plasma particle number densities. The implications of our results in space and interstellar compact objects like white dwarfs, neutron stars, black holes, and so on have been briefly discussed.

Hossen, M. R.; Nahar, L.; Mamun, A. A.

2014-12-01

295

The issue of factorization within the context of coincidence quasi-elastic electron scattering is reviewed. Using a relativistic formalism for the entire reaction mechanism and restricting ourselves to the case of plane waves for the outgoing proton, we discuss the meaning of factorization in the cross section and the role of the small components of the bound nucleon wave function.

J. A. Caballero; T. W. Donnelly; E. Moya de Guerra; J. M. Udias

1997-10-16

296

The long-term cyclotron dynamics of relativistic wave packets: spontaneous collapse and revival

In this work we study the effects of collapse and revival as well as {\\it Zitterbewegung} (ZB) phenomenon, for the relativistic electron wave packets, which are a superposition of the states with quantum numbers sharply peaked around some level $n_0$ of the order of few tens. The probability densities as well as average velocities of the packet center and the average spin components were calculated analytically and visualized. Our computations demonstrate that due to dephasing of the states for times larger than the cyclotron period the initial wave packet (which includes the states with the positive energy only) loses the spatial localization so that the evolution can no longer be described classically. However, at the half-revival time $t=T_R/2$ its reshaping takes place firstly. The behavior of the wave packet containing the states of both energy bands (with $E_n>0$ and $E_ncyclotron frequency in the opposite directions and meet each other every one-half of the cyclotron period. At these moments their wave functions have significant overlap that leads to ZB. At the time of fractional revival each of two sub-packets is decomposed into few packets-fractions. However, at $t=T_R$ each of the two sub-packets (with positive or negative energy) restores at various points of the cyclotron orbit, that makes it impossible reshaping of initial wave packet entirely unlike the wave packet which consists of states with energies $E_n>0$ only. Obtained results can be useful for the description of electromagnetic radiation and absorption in relativistic plasma on astrophysics objects, where super high magnetic field has the value of the order $10^8-10^9$T, as well as for interpretation of experiments with trapped ions.

V. Ya. Demikhovskii; G. M. Maksimova; A. A. Perov; A. V. Telezhnikov

2011-11-23

297

We develop a nonlinear theory for self-modulation of a circularly polarized electromagnetic wave in a relativistic hot weakly magnetized electron-positron plasma. The case of parallel propagation along an ambient magnetic field is considered. A nonlinear Schrödinger equation is derived for the complex wave amplitude of a self-modulated wave packet. We show that the maximum growth rate of the modulational instability decreases as the temperature of the pair plasma increases. Depending on the initial conditions, the unstable wave envelope can evolve nonlinearly to either periodic wave trains or solitary waves. This theory has application to high-energy astrophysics and high-power laser physics. PMID:22680585

Asenjo, Felipe A; Borotto, Felix A; Chian, Abraham C-L; Muñoz, Víctor; Valdivia, J Alejandro; Rempel, Erico L

2012-04-01

298

NASA Technical Reports Server (NTRS)

We consider the effect of oblique EMIC waves on relativistic electron scattering in the outer radiation belt using simultaneous observations of plasma and wave parameters from CRRES. The main findings can be s ummarized as follows: 1. In 1comparison with field-aligned waves, int ermediate and highly oblique distributions decrease the range of pitc h-angles subject to diffusion, and reduce the local scattering rate b y an order of magnitude at pitch-angles where the principle absolute value of n = 1 resonances operate. Oblique waves allow the absolute va lue of n > 1 resonances to operate, extending the range of local pitc h-angle diffusion down to the loss cone, and increasing the diffusion at lower pitch angles by orders of magnitude; 2. The local diffusion coefficients derived from CRRES data are qualitatively similar to the local results obtained for prescribed plasma/wave parameters. Conseq uently, it is likely that the bounce-averaged diffusion coefficients, if estimated from concurrent data, will exhibit the dependencies similar to those we found for model calculations; 3. In comparison with f ield-aligned waves, intermediate and highly oblique waves decrease th e bounce-averaged scattering rate near the edge of the equatorial lo ss cone by orders of magnitude if the electron energy does not excee d a threshold (approximately equal to 2 - 5 MeV) depending on specified plasma and/or wave parameters; 4. For greater electron energies_ ob lique waves operating the absolute value of n > 1 resonances are more effective and provide the same bounce_averaged diffusion rate near the loss cone as fiel_aligned waves do.

Gamayunov, K. V.; Khazanov, G. V.

2007-01-01

299

NASA Technical Reports Server (NTRS)

We constrain blast wave parameters and the circumburst media ofa subsample of 10 BeppoSAX gamma-ray bursts (GRBs). For this sample we derive the values of the injected electron energy distribution index, p, and the density structure index of the circumburst medium, k, from simultaneous spectral fits to their X-ray, optical, and NIR afterglow data. The spectral fits have been done in count space and include the effects ofmetallicity, and are compared with the previously reported optical and X-ray temporal behavior. Using the blast wave model and some assumptions which include on-axis viewing and standard jet structure, constant blast wave energy, and no evolution of the microphysical parameters, we find a mean value ofp for the sample as a whole of 9.... oa -0.003.0" 2 a_ statistical analysis of the distribution demonstrates that the p-values in this sample are inconsistent with a single universal value forp at the 3 _ level or greater, which has significant implications for particle acceleration models. This approach provides us with a measured distribution ofcircumburst density structures rather than considering only the cases of k ----0 (homogeneous) and k - 2 (windlike). We find five GRBs for which k can be well constrained, and in four of these cases the circumburst medium is clearly windlike. The fifth source has a value of 0 < k < 1, consistent with a homogeneous circumburst medium.

Starling, R. L. C.; vanderHorst, A. J.; Rol, E.; Wijers, R. A. M. J.; Kouveliotou, C.; Wiersema, K.; Curran, P. A.; Weltervrede, P.

2008-01-01

300

The experimental investigation described in this dissertation demonstrates the feasibility of generating long (greater than or equal to 50 nsec) pulses of high-power (greater than or equal to 100 MW), X-band frequency microwaves. In these experiments, a relativistic Backward Wave Oscillator (BWO) is used in tandem with a Traveling Wave Tube (TWT) amplifier to generate microwave radiation. The tandem BWO

Gilberto Barreto

1992-01-01

301

... DVBIC & TBI Educational Materials Research DVBIC Locations Press Blast Injuries (U.S. Army photo by Sgt. Gustavo Olgiati) ... games. More Information: 04/12/11: Research Examines Blast Impact on Human Brain 04/06/09: Military ...

302

Calculation of the process of blast wave diffraction in a cylindrical channel

NASA Astrophysics Data System (ADS)

We performed a numerical investigation of the process of transition of a spherical leading front into a plane one in a cylindrical channel. The processes of the collision of reflected shock waves, formation of a nonstationary grating-like structure of flow, and of the overtaking interaction of shock waves are investigated. We found that in the presence of hot gas layers on the walls of the channel a plane head front is not formed.

Andrushchenko, V. A.; Meshcheryakov, M. V.

1995-07-01

303

A Free-Lagrange numerical procedure for the simulation of two-dimensional inviscid compressible flow is described in detail.\\u000a The unsteady Euler equations are solved on an unstructured Lagrangian grid based on a density-weighted Voronoi mesh. The flow\\u000a solver is of the Godunov type, utilising either the HLLE (2 wave) approximate Riemann solver or the more recent HLLC (3 wave)\\u000a variant, each adapted

G. J. Ball

1996-01-01

304

A Free-Lagrange numerical procedure for the simulation of two-dimensional inviscid compressible flow is described in detail. The unsteady Euler equations are solved on an unstructured Lagrangian grid based on a density-weighted Voronoi mesh. The flow solver is of the Godunov type, utilising either the HLLE (2 wave) approximate Riemann solver or the more recent HLLC (3 wave) variant, each adapted

G. J. Ball

1996-01-01

305

Pulsar Timing Sensitivities to Gravitational Waves from Relativistic Metric Theories of Gravity

Pulsar timing experiments aimed at the detection of gravitational radiation have been performed for decades now. With the forthcoming construction of large arrays capable of tracking multiple millisecond pulsars, it is very likely we will be able to make the first detection of gravitational radiation in the nano-Hertz band, and test Einstein's theory of relativity by measuring the polarization components of the detected signals. Since a gravitational wave predicted by the most general relativistic metric theory of gravity accounts for {\\it six} polarization modes (the usual two Einstein's tensor polarizations as well as two vector and two scalar wave components), we have estimated the single-antenna sensitivities to these six polarizations. We find pulsar timing experiments to be significantly more sensitive, over their entire observational frequency band ($\\approx 10^{-9} - 10^{-6}$ Hz), to scalar-longitudinal and vector waves than to scalar-transverse and tensor waves. At $10^{-7}$ Hz and with pulsars at a distance of $1$ kpc, for instance, we estimate an average sensitivity to scalar-longitudinal waves that is more than two orders of magnitude better than the sensitivity to tensor waves. Our results imply that a direct detection of gravitational radiation by pulsar timing will result into a test of the theory of general relativity that is more stringent than that based on monitoring the decay of the orbital period of a binary system.

Marcio Eduardo da Silva Alves; Massimo Tinto

2011-02-23

306

NASA Technical Reports Server (NTRS)

By analyzing CRRES and GOES observations on Aug. 27 1991, Tan et al. [2004] reported evidence of magnetospheric relativistic electron acceleration by resonant interactions with PC5 ULF waves. The event showed strong ULF wave activities after a storm sudden commencement (SSC) and energetic electron fluxes were enhanced in 2 hours. The electron flux peak observed in energy channels (0.6 - 1.1 MeV) were modulated by local electric field observed by CRRES. In this study, we set up a drift-resonant interaction model between ULF wave and magnetospheric relativistic electrons to model the observed electron flux in the event. In this model, the poloidal mode wave is concentrated in the dayside and the toroidal mode wave is concentrated in two flanks. The toroidal mode waves in the dawn and dusk flanks are in anti-phase. We found that electron can be accelerated jointly by the poloidal wave in the dayside and toroidal wave in flanks. The dayside poloidal wave serves as the dominant source of electron acceleration. The simulated electron flux variations agree well with observations both in fine details and long period behavior. These agreements in electron behavior indicate that the ULF wave plays an important role in accelerating MeV relativistic electrons around the geosynchronous orbit.

Fung, Shing

2007-01-01

307

A compact P-band coaxial relativistic backward wave oscillator (BWO) with only three periods slow wave structure (SWS) is investigated both theoretically and numerically. The characteristics of the coaxial SWS are analyzed when the SWS is changed from the structure with only outer conductor ripple to the structure with both inner and outer conductor ripples. It is found that the existence of the inner conductor ripple can reduce the period length of coaxial SWS to maintain the same operating frequency of the BWO and can largely increase the temporal growth rate and the spatial growth rate of the device. Then, the effects of SWS period numbers on the generation of the microwave in the P-band relativistic BWO are studied by PIC simulations. The results show that three periods SWS cannot only make the device more compact but also has a wide region of single-frequency operation and relatively large efficiency and output power in a wide range of the diode voltage. Typical simulation results show that, with a 585 kV and 7.85 kA electron beam guided by a 0.8 T solenoidal field, the microwave of 1.65 GW is generated at the frequency of 900 MHz, and the interaction efficiency is about 36%. Compared with the conventional P-band coaxial relativistic BWO with five periods SWS, the axial length of the SWS is reduced by about one half, which is only 38.4 cm, and the saturation time of the microwave signal is reduced by about 10 ns.

Gao Liang; Qian Baoliang; Ge Xingjun [College of Optoelectric Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2011-10-15

308

Gravitational waves from relativistic neutron-star mergers with microphysical equations of state.

The gravitational wave (GW) emission from a set of relativistic neutron-star (NS) merger simulations is analyzed and characteristic signal features are identified. The distinct peak in the GW energy spectrum that is associated with the formation of a hypermassive merger remnant has a frequency that depends strongly on the properties of the nuclear equation of state (EOS) and on the total mass of the binary system, whereas the mass ratio and the NS spins have a weak influence. If the total mass can be determined from the inspiral chirp signal, the peak frequency of the post-merger signal is a sensitive indicator of the EOS. PMID:17930492

Oechslin, R; Janka, H-T

2007-09-21

309

Perturbations on an interface driven by a strong blast wave grow in time due to a combination of Rayleigh-Taylor, Richtmyer-Meshkov, and decompression effects. In this paper, results from three-dimensional numerical simulations of such a system under drive conditions to be attainable on the National Ignition Facility [E. M. Campbell, Laser Part. Beams, 9(2), 209 (1991)] are presented. Using the multi-physics, adaptive mesh refinement, higher order Godunov Eulerian hydrocode, Raptor [L. H. Howell and J.A. Greenough, J. Comp. Phys. 184, 53 (2003)], the late nonlinear instability evolution, including transition to turbulence, is considered for various multimode perturbation spectra. The 3D post-transition state differs from the 2D result, but the process of transition proceeds similarly in both 2D and 3D. The turbulent mixing transition results in a reduction in the growth rate of the mixing layer relative to its pre-transition value and, in the case of the bubble front, relative to the 2D result. The post-transition spike front velocity is approximately the same in 2D and 3D. Implications for hydrodynamic mixing in core-collapse supernova are discussed.

Miles, A R; Edwards, M J; Greenough, J A

2004-11-08

310

In this work, we examine the hydrodynamics of high-energy-density (HED) shear flows. Experiments, consisting of two materials of differing density, use the OMEGA-60 laser to drive a blast wave at a pressure of ?50 Mbar into one of the media, creating a shear flow in the resulting shocked system. The interface between the two materials is Kelvin-Helmholtz unstable, and a mixing layer of growing width develops due to the shear. To theoretically analyze the instability's behavior, we rely on two sources of information. First, the interface spectrum is well-characterized, which allows us to identify how the shock front and the subsequent shear in the post-shock flow interact with the interface. These observations provide direct evidence that vortex merger dominates the evolution of the interface structure. Second, simulations calibrated to the experiment allow us to estimate the time-dependent evolution of the deposition of vorticity at the interface. The overall result is that we are able to choose a hydrodynamic model for the system, and consequently examine how well the flow in this HED system corresponds to a classical hydrodynamic description.

Di Stefano, C. A., E-mail: carlosds@umich.edu; Kuranz, C. C.; Klein, S. R.; Drake, R. P. [Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan 48109 (United States)] [Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan 48109 (United States); Malamud, G. [Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan 48109 (United States) [Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan 48109 (United States); Department of Physics, Nuclear Research Center-Negev, Beer-Sheva (Israel); Henry de Frahan, M. T.; Johnsen, E. [Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States)] [Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States); Shimony, A.; Shvarts, D. [Department of Physics, Nuclear Research Center-Negev, Beer-Sheva (Israel) [Department of Physics, Nuclear Research Center-Negev, Beer-Sheva (Israel); Department of Physics, Ben-Gurion University, Beer-Sheva (Israel); Smalyuk, V. A.; Martinez, D. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (United States)] [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551 (United States)

2014-05-15

311

Why galactic gamma-ray bursts might depend on environment: Blast waves around neutron stars

NASA Technical Reports Server (NTRS)

Although galactic models for gamma-ray bursts are hard to reconcile with the isotropy data, the issue is still sufficiently open that both options should be explored. The most likely 'triggers' for bursts in our Galaxy would be violent disturbances in the magnetospheres of neutron stars. Any event of this kind is likely to expel magnetic flux and plasma at relativistic speed. Such ejecta would be braked by the interstellar medium (ISM), and a gamma-ray flash may result from this interaction. The radiative efficiency, of this mechanism would depend on the density of the circumstellar ISM. Therefore, even if neutron stars were uniformly distributed in space (at least within 1-2 kpc of the Sun), the observed locations of bursts would correlate with regions of above-average ISM density.

Rees, Martin J.; Meszaros, Peter; Begelman, Mitchell C.

1994-01-01

312

Shock wave synthesis of ?-Si3[O,N]4 in the new Freiberg blasting facility under different conditions

NASA Astrophysics Data System (ADS)

The new subterranean blasting facility at the TU Bergakademie Freiberg allows experiments at elevated capacities of 20 kg C4-equivalent. The new installation permits the investigation of phase transitions of ? Si3N4 under dynamic loading. We studied the influence of plate thickness (shock duration) and different precursor-pressure powder (Cu, NaCl) mixtures at charge masses between 2000 and 20.000 g C4. Systematic studies showed that the Mach-reflection (so called "upstreaming jetting phenomena") is of vital importance for the synthesis success, due to the fact that the T-p ratio will increase dramatically [Milyavskii et al., 2006]. We synthesized pure ?-Si3[O,N]4 from H-bearing precursors at pressures > 25 GPa [Schlothauer et al., 2011]. The phase transition Si2N2NH into ?-Si3[O,N]4 is completely reconstructive and requires a high temperature-pressure-ratio of 176 K/GPa at pressures up to 35 GPa. Despite the high energy density during the shock wave synthesis process it will be inevitable to prepare the samples under an inert nitrogen atmosphere. References Milyavskii, V. V., V. E. Fortov, A. A. Frolova, K. V. Khishchenko, A. A. Charakhch'yan, and L. V. Shurshalov (2006), Calculation of shock compression of porous media in conical solid-state targets with an outlet hole, Computational Mathematics and Mathematical Physics, 46(5), 873 890. Schlothauer, T., M. R. Schwarz, M. Ovidiu, E. Brendler, R. Moeckel, E. Kroke, and G. Heide (2011), Shock wave synthesis of oxygen-bearing spinel-type silicon nitride (g-Si3(O,N)4 in the pressurerange from 30 to 72 GPa with high purity, in Minerals as Advanced Materials II, edited by S. V. Krivovichev, pp. 389 401, Springer. Berlin Heidelberg.

Renno, A. D.; Schlothauer, T.; Schwarz, M. R.; Heide, G.; Kroke, E.

2011-12-01

313

Mild traumatic brain injury (mTBI) resulting from exposure to blast shock waves (BSWs) is one of the most predominant causes of illnesses among veterans who served in the recent Iraq and Afghanistan wars. Such mTBI can also happen to civilians if exposed to shock waves of bomb attacks by terrorists. While cognitive problems, memory dysfunction, depression, anxiety and diffuse white matter injury have been observed at both early and/or delayed time-points, an initial brain pathology resulting from exposure to BSWs appears to be the dysfunction or disruption of the blood-brain barrier (BBB). Studies in animal models suggest that exposure to relatively milder BSWs (123 kPa) initially induces free radical generating enzymes in and around brain capillaries, which enhances oxidative stress resulting in loss of tight junction (TJ) proteins, edema formation, and leakiness of BBB with disruption or loss of its components pericytes and astrocyte end-feet. On the other hand, exposure to more intense BSWs (145–323 kPa) causes acute disruption of the BBB with vascular lesions in the brain. Both of these scenarios lead to apoptosis of endothelial and neural cells and neuroinflammation in and around capillaries, which may progress into chronic traumatic encephalopathy (CTE) and/or a variety of neurological impairments, depending on brain regions that are afflicted with such lesions. This review discusses studies that examined alterations in the brain milieu causing dysfunction or disruption of the BBB and neuroinflammation following exposure to different intensities of BSWs. Furthermore, potential of early intervention strategies capable of easing oxidative stress, repairing the BBB or blocking inflammation for minimizing delayed neurological deficits resulting from exposure to BSWs is conferred. PMID:25165433

Shetty, Ashok K.; Mishra, Vikas; Kodali, Maheedhar; Hattiangady, Bharathi

2014-01-01

314

Underwater blast wave pressure sensor based on polymer film fiber Fabry-Perot cavity.

This paper describes the theoretical and experimental aspects of an optical underwater shock wave sensor based on a polymer film optical fiber Fabry-Perot cavity manufactured by vacuum deposition technology. The transduction mechanism of the sensor involves a normally incident acoustic stress wave that changes the thickness of the polymer film, thereby giving rise to a phase shift. This transient interferometric phase is interrogated by a three-phase-step algorithm. Theoretically, the sensor-acoustic-field interaction principle is analyzed, and the phase modulation sensitivity based on the theory of waves in the layered media is calculated. Experimentally, a static calibration test and a dynamic calibration test are conducted using a piston-type pressure calibration machine and a focusing-type electromagnetic shock wave. Results indicate that the repeatability, hysteresis, nonlinearity, and the overall measurement accuracy of the sensor within the full pressure range of 55 MPa are 1.82%, 0.86%, 1.81%, and 4.49%, respectively. The dynamic response time is less than 0.767 ?s. Finally, three aspects that need further study for practical use are pointed out. PMID:25322237

Wang, Junjie; Wang, Meng; Xu, Jian; Peng, Li; Yang, Minghong; Xia, Minghe; Jiang, Desheng

2014-10-01

315

The postbounce oscillations of newly-born relativistic stars are expected to lead to gravitational-wave emission through the excitation of nonradial oscillation modes. At the same time, the star is oscillating in its radial modes, with a central density variation that can reach several percent. Nonlinear couplings between radial oscillations and polar nonradial modes lead to the appearance of combination frequencies (sums and differences of the linear mode frequencies). We study such combination frequencies using a gauge-invariant perturbative formalism, which includes bilinear coupling terms between different oscillation modes. For typical values of the energy stored in each mode we find that gravitational waves emitted at combination frequencies could become detectable in galactic core-collapse supernovae with advanced interferometric or wideband resonant detectors.

Passamonti, Andrea; Stergioulas, Nikolaos [Department of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki (Greece); Nagar, Alessandro [Dipartimento di Fisica, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Turin (Italy) and INFN, Sezione di Torino, Via Pietro Giuria 1, Turin (Italy)

2007-04-15

316

NASA Technical Reports Server (NTRS)

The theoretical properties of relativistic, transverse, magnetosonic collisionless shock waves in electron-positron-heavy ion plasmas of relevance to astrophysical sources of synchrotron radiation are investigated. Both 1D electromagnetic particle-in-cell simulations and quasi-linear theory are used to examine the spatial and kinetic structure of these nonlinear flows. A new process of shock acceleration of nonthermal positrons, in which the gyrating reflected heavy ions dissipate their energy in the form of collectively emitted, left-handed magnetosonic waves which are resonantly absorbed by the positrons immediately behind the ion reflection region, is described. Applications of the results to the termination shocks of pulsar winds and to the termination shocks of jets emanating from the AGN are outlined.

Hoshino, Masahiro; Arons, Jonathan; Gallant, Yves A.; Langdon, A. B.

1992-01-01

317

An overmoded relativistic backward wave oscillator with efficient dual-mode operation

A dual-mode operation mechanism in an overmoded relativistic backward wave oscillator is presented. The electron beam interacts with the ?1st space harmonic of TM{sub 01} mode synchronously in the slow wave structure. Then the backward propagating TM{sub 01} mode is converted to the forward propagating TM{sub 02} mode. As the phase velocity of the volume harmonic of TM{sub 02} mode is about twice that of the surface harmonic of TM{sub 01} mode, the TM{sub 02} mode also plays an important role in the high-power microwave generation. Particle-in-cell simulation shows that an efficiency of 48% and a significant improvement of the power capacity have been obtained.

Xiao, Renzhen; Li, Jiawei; Bai, Xianchen; Song, Zhimin; Teng, Yan; Ye, Hu; Li, Xiaoze; Sun, Jun; Chen, Changhua [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024 (China); Zhang, Xiaowei [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024 (China); Key Laboratory of Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an 710049 (China)

2014-03-03

318

A compact relativistic backward-wave oscillator with metallized plastic components

NASA Astrophysics Data System (ADS)

This letter presents the mechanism and realization of a compact relativistic backward-wave oscillator with metallized plastic components. The physical idea, specific structure, and the main testing results are presented. The three periods slow-wave structures with both inner and outer ripples and the coaxial extractor are designed to reduce the volume and increase the efficiency of the device. The metallized plastic components replacing the stainless steel components in the high power microwave (HPM) sources are put forward to reduce the device weight. In the initial experiment, a microwave with frequency of 1.54 GHz, power of 1.97 GW, efficiency of 33.5%, and pulse duration above 47 ns is generated, which proves that this technical route is feasible. Undoubtedly, the technical route can provide a guide to design other types of HPM sources and be benefit to the practical application of the compact HPM systems.

Ge, Xingjun; Zhang, Jun; Zhong, Huihuang; Qian, Baoliang

2014-09-01

319

A repetitive S-band long-pulse relativistic backward-wave oscillator.

This paper presents both numerical and experimental studies of a repetitive S-band long-pulse relativistic backward-wave oscillator. The dispersion relation curve of the main slow-wave structure is given by the numerical calculation. Experimental results show that a 1 GW microwaves with pulse duration of about 100 ns (full width of half magnitude) under 10 Hz repetitive operation mode are obtained. The microwave frequency is 3.6 GHz with the dominant mode of TM(01), and power conversion efficiency is about 20%. The single pulse energy is about 100 J. The experimental results are in good agreement with the simulation ones. By analyzing the experimental phenomenon, we obtain the conclusion that the explosive emission on the surface of the electrodynamics structure in intense radio frequency field mainly leads to the earlier unexpected termination of microwave output. PMID:21895263

Jin, Zhenxing; Zhang, Jun; Yang, Jianhua; Zhong, Huihuang; Qian, Baoliang; Shu, Ting; Zhang, Jiande; Zhou, Shengyue; Xu, Liurong

2011-08-01

320

A repetitive S-band long-pulse relativistic backward-wave oscillator

NASA Astrophysics Data System (ADS)

This paper presents both numerical and experimental studies of a repetitive S-band long-pulse relativistic backward-wave oscillator. The dispersion relation curve of the main slow-wave structure is given by the numerical calculation. Experimental results show that a 1 GW microwaves with pulse duration of about 100 ns (full width of half magnitude) under 10 Hz repetitive operation mode are obtained. The microwave frequency is 3.6 GHz with the dominant mode of TM01, and power conversion efficiency is about 20%. The single pulse energy is about 100 J. The experimental results are in good agreement with the simulation ones. By analyzing the experimental phenomenon, we obtain the conclusion that the explosive emission on the surface of the electrodynamics structure in intense radio frequency field mainly leads to the earlier unexpected termination of microwave output.

Jin, Zhenxing; Zhang, Jun; Yang, Jianhua; Zhong, Huihuang; Qian, Baoliang; Shu, Ting; Zhang, Jiande; Zhou, Shengyue; Xu, Liurong

2011-08-01

321

NASA Astrophysics Data System (ADS)

We study the nonlinear interaction between relativistic electrons and a coherent Electromagnetic Ion Cyclotron (EMIC) wave. We assume a coherent rising-tone emission as found in recent spacecraft observations of EMIC waves[1,2]. Considering the frequency variation, we derive the second-order resonance condition for interaction between a relativistic electron and a coherent EMIC wave[3]. The second-order resonance condition controlling nonlinear wave trapping of resonant electrons depends on an inhomogeneity factor S which is a function of the frequency sweep rate, the gradient of the magnetic field, and the wave amplitude. There occurs nonlinear trappin g of electrons by the wave potential, if |S|<1. A non-zero value of S induces very effective pitch angle scattering. When an EMIC triggered emission is generated near the equator and propagates toward the high latitude, both the spatial inhomogeneity and the rising-tone frequency result in enhanced precipitation of relativistic electrons with the time scale of EMIC triggered emission (tens of seconds), which is a possible cause of the relativistic electron microbursts observed at low altitudes. [1] J. S. Pickett,, B. Grison, Y. Omura, M. J. Engebretson, I. Dandouras, A. Masson, M. L. Adrian, O. Santolik, P. M. E. Decreau, N. Cornilleau-Wehrlin, and D. Constantinescu, Cluster observations of EMIC triggered emissions in association with Pc1 waves near Earth's plasmapause, Geophys. Res. Lett., 37, L09104, doi:10.1029/2010GL042648, 2010. [2] Y. Omura, J. S. Pickett, B. Grison, O. Santolik, I. Dandouras, M. Engebretson, P. M. E. Decreau, A. Masson, Theory and observation of electromagnetic ion cyclotron triggered emissions in the magnetosphere, J. Geophys. Res., 115, A07234, doi:10.1029/2010JA015300, 2010. [3] Y. Omura and Q. Zhao, Nonlinear pitch-angle scattering of relativistic electrons by EMIC waves in the inner magnetosphere, J. Geophys. Res., in press.

Omura, Y.; Zhao, Q.

2012-12-01

322

Hubble-like flows in relativistic heavy-ion collisions

We study the dynamical appearance of scaling solutions in relativistic hydrodynamics. The phase transition effects are included through the temperature dependent sound velocity. If a pre-equilibrium transverse flow is included in the initial conditions, then it may reach the form of the asymptotic Hubble flow, r/t, in short evolution times, 7-15 fm. The numerical solutions are found to support to the freeze-out models (Blast-Wave, Buda-Lund, Cracow).

M. Chojnacki

2006-01-30

323

An h-adaptive solution of the spherical blast wave problem

Shock waves and contact discontinuities usually appear in compressible flows, requiring a fine mesh in order to achieve an acceptable accuracy of the numerical solution. The usage of a mesh adaptation strategy is convenient as uniform refinement of the whole mesh becomes prohibitive in three-dimensional (3D) problems. An unsteady h-adaptive strategy for unstructured finite element meshes is introduced. Non-conformity of

Gustavo A. Ríos Rodriguez; Mario A. Storti; Ezequiel J. López; Sofía S. Sarraf

2011-01-01

324

Interaction of a strong blast wave with a free surface. [at ocean surface

NASA Technical Reports Server (NTRS)

When a point source explosion is initiated at the ocean surface, the shock propagated into the water is reflected at the surface as a centered expansion wave. The solution in the neighborhood of the interaction point is obtained by writing the equations of motion in the appropriate similarity variables and then changing the independent variables to polar coordinates based at the interaction point. From the zero-order solution of the resulting equations the slopes of boundaries at the interaction point are obtained. A first-order perturbation of this solution provides more accurate representation of the flow variables and the curvature of the shock surface near the interaction point.

Falade, A.; Holt, M.

1978-01-01

325

NASA Astrophysics Data System (ADS)

A weakly nonlinear analysis is carried out to derive a Korteweg-de Vries-Burgers-like equation for small, but finite amplitude, ion-acoustic waves in a dissipative plasma consisting of weakly relativistic ions, thermal positrons and nonextensive electrons. The travelling wave solution has been acquired by employing the tangent hyperbolic method. Our results show that in a such plasma, ion-acoustic shock waves, the strength and steepness of which are significantly modified by relativistic, nonextensive and dissipative effects, may exist. Interestingly, we found that because of ion kinematic viscosity, an initial solitonic profile develops into a shock wave. This later evolves towards a monotonic profile (dissipation-dominant case) as the electrons deviate from their Maxwellian equilibrium. Our investigation may help to understand the dissipative structures that may occur in high-energy astrophysical plasmas.

Tribeche, Mouloud; Pakzad, Hamid Reza

2012-06-01

326

The laboratory simulation of unmagnetized supernova remnants Absence of a blast wave

NASA Technical Reports Server (NTRS)

Supernova remnants are experimentally simulated by irradiating spherical targets with eight-beam carbon dioxide laser in a chamber containing finite amounts of neutral gas, the gas being ionized by radiation from the hot target. The expansion velocities of the target plasmas are approximately the same as the expansion velocities of supernova ejecta and the experiment is successfully scaled to the case of a supernova remnant in an unmagnetized, low-density, interstellar medium. No sweep-up of the ambient plasma is detected, indicating that no hydrodynamic shock wave is formed to couple the target ejecta to the ambient gas. The experiment implies that if supernova ejecta couple to the interstellar medium, magnetic-field effects may be crucial to the physical description.

Borovsky, J. E.; Pongratz, M. B.; Roussel-Dupre, R. A.; Tan, T.-H.

1984-01-01

327

Dirac's equation in the field of a circularly polarized electromagnetic wave and constant magnetic field has exact localized non-stationary solutions. The solutions corresponds relativistic fermions only. Among them singular solutions with energy eigenvalues close to each other are found. The solutions are most practicable and can be separated by means of the phase matching between the momentum of the electromagnetic wave and spinor. Characteristic parameters of the singular states are defined.

Boris V. Gisin

2012-03-24

328

Considering relativistic wave equations in the first-order form, wherein the transformation of the wavefunction under the proper Lorentz group involves a certain number of inequivalent irreducible representations (IIRS) repeated an arbitrary number of times, the authors note some of the restrictions (on the skeleton matrix of the matrices beta mu occurring in the equation and on the spin blocks of

P. M. Mathews; B. Vijayalakshmi; M. Seetharman; Y. Takahashi

1981-01-01

329

The experimental investigation described in this dissertation demonstrates the feasibility of generating long (>=50 nsec) pulses of high-power (>=100 MW), X-band frequency microwaves. In these experiments, a relativistic Backward Wave Oscillator (BWO) is used in tandem with a Traveling Wave Tube (TWT) amplifier to generate microwave radiation. The tandem BWO-TWT system is driven in the TM_{01 } mode by a

Gilberto Barreto

1992-01-01

330

A Ka-band TM02 mode relativistic backward wave oscillator with cascaded resonators

NASA Astrophysics Data System (ADS)

By combining the Cerenkov-type generator with the cascaded resonators, this paper proposes a Ka-band relativistic backward wave oscillator operating under the guide magnetic field 1.0 T with high power handling capability and high conversion efficiency. It is found that TM02 can be selected as the operation mode in order to increase the power handling capability and provide sufficient coupling with the electron beam. In slow wave structure (SWS), ripples composed of semicircle on top of the rectangle enhance the wave-beam interaction and decrease the intensity of the electric field on the metallic surface. Taking advantage of the resonator cascades, the output power and the conversion efficiency are promoted greatly. The front cascaded resonators efficiently prevent the power generated in SWS from leaking into the diode region, and quicken the startup of the oscillation due to the premodulation of the beam. However, the post cascade slightly postpones the startup because of the further energy extraction from the electron beam. The numerical simulation shows that generation with power 514 MW and efficiency 41% is obtained under the diode voltage 520 kV and current 2.4 kA. And the microwave with the pure frequency spectrum of 29.35 GHz radiates in the pure TM01 mode.

Teng, Yan; Cao, Yinbin; Song, Zhimin; Ye, Hu; Shi, Yanchao; Chen, Changhua; Sun, Jun

2014-12-01

331

Investigation of an improved relativistic backward wave oscillator in efficiency and power capacity

Investigation of relativistic backward wave oscillator with high efficiency and power capacity is presented in this paper. To obtain high power and high efficiency, a TM{sub 021} mode resonant reflector is used to reduce the pulse shortening and increase power capacity to about 1.7 times. Meanwhile, an extraction cavity at the end of slow wave structure is employed to improve the efficiency from less than 30% to over 40%, through the beam-wave interaction intensification and better energy conversion from modulated electron beam to the electromagnetic field. Consistent with the numerical results, microwave with a power of 3.2 GW, a frequency of 9.75 GHz, and a pulse width of 27 ns was obtained in the high power microwave generation experiment, where the electron beam energy was configured to be {approx}910 kV and its current to be {approx}8.6 kA. The efficiency of the RBWO exceeds 40% at a voltage range of 870 kV-1000 kV.

Song, W.; Chen, C. H.; Sun, J.; Zhang, X. W.; Shao, H.; Song, Z. M.; Huo, S. F.; Shi, Y. C.; Li, X. Z. [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an, Shaanxi 710024 (China)

2012-10-15

332

Controlling blast wave generation in a shock tube for biological applications

NASA Astrophysics Data System (ADS)

The shock tube is a versatile apparatus used in a wide range of scientific research fields. In this case, we are developing a system to use with biological specimens. The process of diaphragm rupture is closely linked to the shock wave generated. Experiments were performed on an air-driven shock tube with Mylar® and aluminium diaphragms of various thicknesses, to control the output. The evolution of shock pressure was measured and the diaphragm rupture process investigated. Single-diaphragm and double-diaphragm configurations were employed, as were open or closed tube configurations. The arrangement was designed to enable high-speed photography and pressure measurements. Overall, results are highly reproducible, and show that the double-diaphragm system enables a more controllable diaphragm burst pressure. The diaphragm burst pressure was linearly related to its thickness within the range studied. The observed relationship between the diaphragm burst pressure and the generated shock pressure presents a noticeable difference compared to the theoretical ideal gas description. Furthermore, the duration of the primary shock decreased proportionally with the length of the high-pressure charging volume. Computational modelling of the diaphragm breakage process was carried out using the ANSYS software package.

Nguyen, T.-T. N.; Wilgeroth, J. M.; Proud, W. G.

2014-05-01

333

Exit from Inflation with a First-Order Phase Transition and a Gravitational Wave Blast

In double-field inflation, which exploits two scalar fields, one of the fields rolls slowly during inflation whereas the other field is trapped in a meta-stable vacuum. The nucleation rate from the false vacuum to the true one becomes substantial enough that triggers a first order phase transition and ends inflation. We revisit the question of first order phase transition in an "extended" model of hybrid inflation, realizing the double-field inflationary scenario, and correctly identify the parameter space that leads to a first order phase transition at the end of inflation. We compute the gravitational wave profile which is generated during this first order phase transition. Assuming instant reheating, the peak frequency falls in the $1$ GHz to $10$ GHz frequency band and the amplitude varies in the range $10^{-8}\\lesssim \\Omega_{\\rm GW} h^2 \\lesssim 10^{-11}$, depending on the value of the cosmological constant in the false vacuum. The signature could be observed by the planned Chongqing high frequency grav...

Ashoorioon, Amjad

2015-01-01

334

NASA Astrophysics Data System (ADS)

Shock waves in molecular clouds heat, compress, accelerate, and chemically alter the gas they encounter. Despite their crucial role in determining the physical state of the dense interstellar medium and despite their making possible direct observations of H_2, molecular shocks are still poorly understood, as evidenced by the many discrepancies between theory and observations. In my dissertation, I use the supernova remnant IC 443 as a laboratory to test our understanding of shock -excited H_2 emission. By examining roughly 20 separate 2-4 ?m Ha transitions, I find the non-uniform temperature structure essentially reproduces that found in Orion Peak 1, and so is consistent with the partially dissociating J-shock model presented by Brand and collaborators. Subsequent mid-infrared observations of the pure rotational S(2) transition at 12 mu m strengthens these conclusions. Velocity resolved line profiles of the strong 1-0 S(1) transition uncover a relationship between the remnant's large-scale geometry and the line profile's full-width at 10% intensity, centroid, and shape. The relationship contradicts any model requiring local bow geometries to explain broad H_2 line widths. Comparing the 1-0 S(1) data with similar observations of the 2-1 S(1) line, I demonstrate that the excitation temperature in the shocked gas depends primarily on position, not velocity. Taken together, the identical velocity extent of the 1-0 S(1) and the 2-1 S(1) lines and their upper state energy separation of E/k ~ 6000 K proves the H_2 -emitting gas reaches its full velocity dispersion prior to cooling below roughly 1500 K. Finally, I compare, with similar spatial and spectral resolution, H_2 and HCO^+ J = 1 - 0 and find evidence for temperature gradients as a result of both preshock density inhomogeneities and postshock cooling.

Richter, Matthew Joseph

1995-01-01

335

Exit from Inflation with a First-Order Phase Transition and a Gravitational Wave Blast

In double-field inflation, which exploits two scalar fields, one of the fields rolls slowly during inflation whereas the other field is trapped in a meta-stable vacuum. The nucleation rate from the false vacuum to the true one becomes substantial enough that triggers a first order phase transition and ends inflation. We revisit the question of first order phase transition in an "extended" model of hybrid inflation, realizing the double-field inflationary scenario, and correctly identify the parameter space that leads to a first order phase transition at the end of inflation. We compute the gravitational wave profile which is generated during this first order phase transition. Assuming instant reheating, the peak frequency falls in the $1$ GHz to $10$ GHz frequency band and the amplitude varies in the range $10^{-8}\\lesssim \\Omega_{\\rm GW} h^2 \\lesssim 10^{-11}$, depending on the value of the cosmological constant in the false vacuum. The signature could be observed by the planned Chongqing high frequency gravitational probe. For a narrow band of vacuum energies, the first order phase transition can happen after the end of inflation via the violation of slow-roll, with a peak frequency that varies from $1$ THz to $100$ THz. For smaller values of cosmological constant, even though inflation can end via slow-roll violation, the universe gets trapped in a false vacuum whose energy drives a second phase of eternal inflation. This range of vacuum energies do not lead to viable inflationary models, unless the value of the cosmological constant is compatible with the observed value, $M\\sim 10^{-3}$ eV.

Amjad Ashoorioon

2015-02-02

336

By using a quasi-optical approach, we study propagation of evanescent waves along a periodically corrugated surface and their excitation by relativistic electron beams. Under assumption of a shallow (in the scale of period) corrugation, the dispersion equation for normal waves is derived and two particular cases are studied. In the first case, the wave frequency is far from the Bragg resonance; therefore, the evanescent wave propagation can be described by using the impedance approximation with deceleration of the zeroth spatial harmonic. The second case takes place at the frequencies close to the Bragg resonance. There, the field can be represented as two counter-propagating quasi-optical wave beams, which are coupled on the corrugated surface and form an evanescent normal wave. With regard to the interaction with an electron beam, the first case corresponds to the convective instability that can be used for amplification of radiation, while the second case corresponds to the absolute instability used in surface-wave oscillators. This paper is focused on studying main features of amplifier schemes, such as the increments, electron efficiency, and formation of a self-consistent spatial structure of the radiated field. For practical applications, the feasibility of realization of relativistic surface-wave amplifiers in the submillimeter wavelength range is estimated.

Ginzburg, N. S.; Malkin, A. M.; Zheleznov, I. V.; Sergeev, A. S. [Institute of Applied Physics of the Russian Academy of Sciences, 46, Ul'yanov St., Nizhny Novgorod (Russian Federation)] [Institute of Applied Physics of the Russian Academy of Sciences, 46, Ul'yanov St., Nizhny Novgorod (Russian Federation)

2013-06-15

337

A klystron-like relativistic backward wave oscillator with a ratio of transverse dimension to free-space wavelength being about four is presented. In the beam-wave interaction region, the electron beam interacts with surface wave and volume wave simultaneously. The cathode holder plays an important role in the reflection of backward waves. A guard electrode, an electron collector ring, and a reflection ring are used to optimize the beam-wave interaction. The particle in cell simulation results reveal that microwaves with a power of 2 GW and a frequency of 12.3 GHz are generated with an efficiency of 42% when the diode voltage is 400 kV, the beam current 12 kA, and the magnetic field 0.48 T.

Xiao Renzhen; Tan Weibing; Li Xiaoze; Song Zhimin; Sun Jun; Chen Changhua [National Key Laboratory of Science and Technology on High Power Microwave, Northwest Institute of Nuclear Technology, Xi'an 710024 (China)

2012-09-15

338

NASA Astrophysics Data System (ADS)

In this paper, we analyze the factors that affect the microwave pulse duration in a klystron-like relativistic backward wave oscillator (RBWO), including the diode voltage, the guiding magnetic field, the electron beam collector, the extraction cavity, and the gap between the electron beam and the slow wave structure (SWS). The results show that the microwave pulse duration increases with the diode voltage until breakdown occurs on the surface of the extraction cavity. The pulse duration at low guiding magnetic field is generally 5-10 ns smaller than that at high magnetic field due to the asymmetric electron emission and the larger energy spread of the electron beam. The electron beam collector can affect the microwave pulse duration significantly because of the anode plasma generated by bombardment of the electron beam on the collector surface. The introduction of the extraction cavity only slightly changes the pulse duration. The decrease of the gap between the electron beam and the SWS can increase the microwave pulse duration greatly.

Xiao, Renzhen; Zhang, Xiaowei; Zhang, Ligang; Li, Xiaoze; Zhang, Lijun

2012-07-01

339

Purification of the output modes of overmoded relativistic backward wave oscillators

Successful suppression of mode competition in the beam-wave interaction process of overmoded relativistic backward wave oscillators (RBWOs) cannot ensure the output modes purity. Optimizing the magnitude and the phase of the mode conversion coefficients in the devices is significant for purifying the output modes. A universal method of purifying the TM{sub 01} and TM{sub 02} mixed modes output by overmoded RBWOs without decreasing the total output power is presented in this paper. With this method, we purify the TM{sub 01} and TM{sub 02} mixed modes generated in an X-band overmoded RBWO (D/????2.6) operated at the constant diode voltage of 730?kV. Dependence of modes purification effect on the variation of diode voltage is also analyzed in particle-in-cell simulation. Our analysis indicates that when the diode voltage is in the range of (730 ± 60) kV, the percentage of output power carried by TM{sub 01} mode will be higher than 95%.

Zhang, Dian; Zhang, Jun; Zhong, Huihuang; Jin, Zhenxing; Yuan, Yuzhang [College of Optoelectric Science and Engineering, National University of Defense Technology, Changsha 410073 (China)] [College of Optoelectric Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2014-02-15

340

In this paper, we analyze the factors that affect the microwave pulse duration in a klystron-like relativistic backward wave oscillator (RBWO), including the diode voltage, the guiding magnetic field, the electron beam collector, the extraction cavity, and the gap between the electron beam and the slow wave structure (SWS). The results show that the microwave pulse duration increases with the diode voltage until breakdown occurs on the surface of the extraction cavity. The pulse duration at low guiding magnetic field is generally 5-10 ns smaller than that at high magnetic field due to the asymmetric electron emission and the larger energy spread of the electron beam. The electron beam collector can affect the microwave pulse duration significantly because of the anode plasma generated by bombardment of the electron beam on the collector surface. The introduction of the extraction cavity only slightly changes the pulse duration. The decrease of the gap between the electron beam and the SWS can increase the microwave pulse duration greatly.

Xiao Renzhen; Zhang Xiaowei; Zhang Ligang; Li Xiaoze; Zhang Lijun [National Key Laboratory of Science and Technology on High Power Microwave, Northwest Institute of Nuclear Technology, Xi'an 710024 (China)

2012-07-15

341

On plane-wave relativistic electrodynamics in plasmas and in vacuum

We revisit the exact microscopic equations (in differential, and equivalent integral form) ruling a relativistic cold plasma after the plane-wave Ansatz, without customary approximations. We show that in the Eulerian description the motion of a very diluted plasma initially at rest and excited by an arbitrary transverse plane electromagnetic travelling-wave has a very simple and explicit dependence on the transverse electromagnetic potential; for a non-zero density plasma the above motion is a good approximation of the real one as long as the back-reaction of the charges on the electromagnetic field can be neglected, i.e. for a time lapse decreasing with the plasma density, and can be used as initial step in an iterative resolution scheme. As one of many possible applications, we use these results to describe how the ponderomotive force of a very intense and short plane laser pulse hitting normally the surface of a plasma boosts the surface electrons into the ion background. Because of this penetration the electrons are then pulled back by the electric force exerted by the ions and may leave the plasma with high energy in the direction opposite to that of propagation of the pulse [G. Fiore, R. Fedele, U. De Angelis, "The slingshot effect: a possible new laser-driven high energy acceleration mechanism for electrons", arXiv:1309.1400].

Gaetano Fiore

2014-05-02

342

Gravitational waves and the deformation of compact objects: Topics in relativistic astrophysics

NASA Astrophysics Data System (ADS)

In this dissertation, we present various theoretical investigations of sources of gravitational waves, relevant to interpreting the data from current and planned gravitational wave detectors; an idee fixe is the deformation of compact objects. We begin in the strong field, vacuum regime, with a construction of initial data for the numerical simulation of black hole binaries (specializing to the case of nonspinning holes in a quasicircular orbit). The data we construct contain more of the binary's expected physics than any other current data set. In particular, they contain both the binary's outgoing radiation and the expected tidal deformations of the holes. Such improved initial data will likely be necessary for simulations to achieve the accuracy required to supply advanced gravitational wave detectors with templates for parameter estimation. We end in the weak field, hydrodynamic regime with a calculation of the expected accuracy with which one can combine standard electromagnetic and gravitational wave observations of white dwarf binaries to measure the masses of the binary's components. In particular, we show that this measurement will not be contaminated by finite size effects for realistic sources observed by LISA, though such effects could be important for exceptional sources and/or advanced mHz gravitational wave detectors. In the middle, we make a detour into the messy and poorly constrained realm of the physics of neutron star interiors, calculating the shear modulus of hadron--quark mixed phase in hybrid stars. Here we include a rough treatment of charge screening, dimensional continuation of the lattice, and the contributions from changing the cell volume when shearing lowerdimensional lattices. We find that the last of these contributions is necessary to stabilize the lattice for those dimensions, where it makes a considerable contribution to the shear modulus. We then move back to sounder theoretical footing in making a general relativistic calculation of the maximum elastic quadrupole deformation that could be sustained by a star with a known shear modulus and breaking strain (provided by, e.g., the hadron--quark mixed phase in the core, or the more standard lattice of nuclei in the crust). We find that the standard Newtonian calculation considerably overestimates the quadrupole, particularly for massive, compact stars. We also present the dimensionally continued Poisson summation formula we discovered while performing the shear modulus calculation, and thought interesting enough to prove rigorously. Our method of proof also provides a new way of proving other (Voronoi) summation formulae obtained from functions satisfying modular transformations, and allows one to relax certain of the standard hypotheses.

Johnson-McDaniel, Nathan Kieran

343

The effects of ion mobility and positron fraction on the solitary waves of the laser field envelope and the potential of the electrostatic field in weak relativistic electron-positron-ion plasma are investigated. The parameter region for the existence of solitary waves is obtained analytically, and a reasonable choice of parameters is clarified. Both cases of mobile and immobile ions are considered. It is found that the amplitudes of solitary waves in the former case are larger compared to the latter case. For small plasma density, the localized solitary wave solutions in terms of the approximate perturbation analytical method are very consistent with those by exact numerical calculations. However, as the plasma density increases the analytical method loses its validity more and more. The influence of the positron fraction on the amplitudes of solitary waves shows a monotonous increasing relation. The implications of our results to particle acceleration are also discussed briefly. PMID:24125373

Lu, Ding; Li, Zi-Liang; Xie, Bai-Song

2013-09-01

344

... more susceptible to blast effects. Existing meteorological conditions. Wind speed and direction will affect arrival time of ... from a nuclear explosion may be carried by wind currents for hundreds of miles if the right ...

345

We analyze the solutions of the Klein–Gordon and Dirac equations describing a charged particle in an electromagnetic plane wave combined with a magnetic field parallel to the direction of propagation of the wave. It is shown that the Klein–Gordon equation admits coherent states as solutions, while the corresponding solutions of the Dirac equation are superpositions of coherent and displaced-number states. Particular attention is paid to the resonant case in which the motion of the particle is unbounded. -- Highlights: •We study a relativistic electron in a particular electromagnetic field configuration. •New exact solutions of the Klein–Gordon and Dirac equations are obtained. •Coherent and displaced number states can describe a relativistic particle.

Colavita, E. [Colegio de Ciencia y Tecnología, Universidad Autónoma de la Ciudad de México, México, D.F., 09790 (Mexico)] [Colegio de Ciencia y Tecnología, Universidad Autónoma de la Ciudad de México, México, D.F., 09790 (Mexico); Hacyan, S., E-mail: hacyan@fisica.unam.mx [Instituto de Física, Universidad Nacional Autónoma de México, A. P. 20-364, México D. F., 01000 (Mexico)

2014-03-15

346

The propagation of circularly polarized electromagnetic waves along a constant background magnetic field in an electron-positron plasma is calculated by means of both a fluid and a kinetic theory treatment. In the fluid theory, relativistic effects are included in the particle motion, the wave field, and in the thermal motion by means of a function f, which depends only on the plasma temperature. In this work we analyze the consistency of the fluid results with those obtained from a kinetic treatment, based on the relativistic Vlasov equation. The corresponding kinetic dispersion relation is numerically studied for various temperatures, and results are compared with the fluid treatment. Analytic expressions for the Alfvén velocity are obtained for the fluid and kinetic models, and it is shown that, in the kinetic treatment, the Alfvén branch is suppressed for large temperatures. PMID:23004888

Domínguez, Macarena; Muñoz, Víctor; Valdivia, Juan Alejandro

2012-05-01

347

Photographs of Blast Effects on Structures

NSDL National Science Digital Library

This photograph collection shows a wood-frame house located 1,100 meters from ground zero, exposed to a nuclear blast at the Nevada Test Site. The test was Upshot-Knothole Annie, a 16 Kt tower shot, on March 17, 1953. Exposure to thermal radiation was 25 cal/cm2, about one-quarter of that experienced at ground zero in Hiroshima. The blast over pressure was 5 psi, and the blast wave created surface winds of 160 mph.

Christopher Griffith

348

Summary form only given. A great deal has been learned regarding the operation of intense relativistic electron beam-driven backward wave oscillators (BWO's) over the last few years. The issue of pulse shortening seems to be better understood, although its complete remediation has yet to be demonstrated. The energies radiated in X-band have yet to reach the kiloJoule level, although reliable

E. Schamiloglu; F. Hegeler; C. T. Abdallah; K. Hahn; S. Choi

2000-01-01

349

Mode conversion of high-power electromagnetic microwave (HPEM) was successfully accomplished using a coaxial-beam rotating antenna (COBRA) in an X-band relativistic backward-wave oscillator (RBWO). The mode conversion from the TM01 mode to the circularly polarized TE11-likeness mode was identified by both cold test and hot test. To observe whether mode conversion is effective or not, the radiation pattern of TE11-likeness mode

Sun-Hong Min; Hoe-Chun Jung; Gun-Sik Park; Jihwan Ahn; Sang Heun Lee; Young Joong Yoon; Junyeon Kim; Jun-Ho Choi; Joonho So

2010-01-01

350

The aim of this study was to elaborate identification method of crew overload as a result of trinitrotoluene charge explosion under the military wheeled vehicle. During the study, an experimental military ground research was carried out. The aim of this research was to verify the mine blast resistance of the prototype wheeled vehicle according to STANG 4569 as well as the anti-explosive seat. Within the work, the original methodology was elaborated along with a prototype research statement. This article presents some results of the experimental research, thanks to which there is a possibility to estimate the crew's lives being endangered in an explosion through the measurement of acceleration as well as the pressure on the chest, head and internal organs. On the basis of our acceleration results, both effectiveness and infallibility of crew protective elements along with a blast mitigation seat were verified. PMID:25307173

Krzysta?a, Edyta; M??yk, Arkadiusz; Kciuk, S?awomir

2014-10-13

351

NASA Technical Reports Server (NTRS)

We have used the Spitzer satellite to monitor the laid-IR evolution of SN 1987A over a 5 year period spanning the epochs between days 6000 and 8000 since the explosion. The supernova (SN) has evolved into a supernova remnant (SNR) and its radiative output, is dominated by the interaction of the SN blast wave with the pre-existing equatorial ring (ER). The mid-IR spectrum is dominated by emission from approximately 180 K silicate dust, collisionally-heated by the hot X-ray emitting gas with a temperature and density of 5 x 10(exp 6) K and approximately 3 x 10(exp 4) per cubic centimeter, respectively. The mass of the radiating dust is approximately 1.2 x 10(exp -6) solar mass on day 7554, and scales linearly with IR flux. Comparison of the IR data with the soft X-ray flux derived from Chandra observations shows that the IR-to-X-ray flux ratio, IRX, is roughly constant with a value of 2.5. Gas-grain collisions therefore dominate the cooling of the shocked gas. The constancy of IRX is most consistent with the scenario that very little grain processing or gas cooling have occurred throughout this epoch. The shape of the dust spectrum remained unchanged during the observations while the total flux increased by a factor of approximately 5 with a time dependence of t(sup '0.87 plus or minus 0.20), t' being the time since the first encounter between the blast wave and the ER. These observations are consistent with the transitioning of the blast wave from free expansion to a Sedov phase as it propagates into the main body of the ER, as also suggested by X-ray observations. The constant spectral shape of they IR, emission provides strong constraints on the density and temperature of the shocked gas in which the interaction takes place. The IR spectra also suggest the presence of a secondary population of very small, hot (T greater than or equal to 350 K), featureless dust. If these grains spatially coexists with the silicates, then they must have shorter lifetimes. The data show slightly different rates of increase of their respective fluxes, lending some support to this hypothesis. However, the origin of this emission component and the exact nature of its relation to the silicate emission is still a major unsolved puzzle.

Dwek, Eli; Arendt, Richard G.; Bouchet, Patrice; Burrows, David N.; Challis, Peter; Danziger, I. John; De Buizer, James M.; Gehrz, Robert D.; Park, Sangwook; Polomski, Elisha F.; Slavin, Jonathan D.; Woodward, Charles E.

2010-01-01

352

We have used the Spitzer satellite to monitor the mid-IR evolution of SN 1987A over a five year period spanning the epochs between days {approx}6000 and 8000 since the explosion. The supernova (SN) has evolved into a supernova remnant and its radiative output is dominated by the interaction of the SN blast wave with the pre-existing equatorial ring (ER). The mid-IR spectrum is dominated by emission from {approx}180 K silicate dust, collisionally heated by the hot X-ray emitting gas with a temperature and density of {approx}5 x 10{sup 6} K and {approx}3 x 10{sup 4} cm{sup -3}, respectively. The mass of the radiating dust is {approx}1.2 x 10{sup -6} M{sub sun} on day 7554 and scales linearly with IR flux. Comparison of the IR data with the soft X-ray flux derived from Chandra observations shows that the IR-to-X-ray flux ratio, IRX, is roughly constant with a value of 2.5. Gas-grain collisions therefore dominate the cooling of the shocked gas. The constancy of IRX is most consistent with the scenario that very little grain processing or gas cooling has occurred throughout this epoch. The shape of the dust spectrum remained unchanged during the observations while the total flux increased by a factor of {approx}5 with a time dependence of t'{sup 0.87{+-}0.20}, t' being the time since the first encounter between the blast wave and the ER. These observations are consistent with the transitioning of the blast wave from free expansion to a Sedov phase as it propagates into the main body of the ER, as also suggested by X-ray observations. The constant spectral shape of the IR emission provides strong constraints on the density and temperature of the shocked gas in which the interaction takes place. Silicate grains, with radii of {approx}0.2 {mu}m and temperature of T {approx} 180 K, best fit the spectral and temporal evolution of the {approx}8-30 {mu}m data. The IR spectra also show the presence of a secondary population of very small, hot (T {approx}> 350 K), featureless dust. If these grains spatially coexist with the silicates, then they must have shorter lifetimes. The data show slightly different rates of increase of their respective fluxes, lending some support to this hypothesis. However, the origin of this emission component and the exact nature of its relation to the silicate emission is still a major unsolved puzzle.

Dwek, Eli [Observational Cosmology Lab., Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Arendt, Richard G. [CRESST/UMBC, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Bouchet, Patrice [DSM/DAPNIA/Service d'Astrophysique, CEA/Saclay, F-91191 Gif-sur-Yvette (France); Burrows, David N.; Park, Sangwook [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Challis, Peter; Slavin, Jonathan D. [Harvard-Smithsonian, CfA, 60 Garden Street, MS-19, Cambridge, MA 02138 (United States); Danziger, I. John [Osservatorio Astronomico di Trieste, Via Tiepolo 11, Trieste (Italy); De Buizer, James M. [Gemini Observatory, Southern Operations Center, c/o AURA, Casilla 603, La Serena (Chile); Gehrz, Robert D.; Woodward, Charles E. [Department of Astronomy, University of Minnesota, 116 Church Street, SE, Minneapolis, MN 55455 (United States); Polomski, Elisha F., E-mail: eli.dwek@nasa.go, E-mail: Patrice.Bouchet@cea.f [University of Wisconsin, Eau Claire, WI 54702 (United States)

2010-10-10

353

NASA Astrophysics Data System (ADS)

Only a handful of supernovae (SNe) have been studied in multiwavelengths from the radio to X-rays, starting a few days after the explosion. The early detection and classification of the nearby Type IIb SN 2011dh/PTF 11eon in M51 provides a unique opportunity to conduct such observations. We present detailed data obtained at one of the youngest phase ever of a core-collapse SN (days 3-12 after the explosion) in the radio, millimetre and X-rays; when combined with optical data, this allows us to explore the early evolution of the SN blast wave and its surroundings. Our analysis shows that the expanding SN shock wave does not exhibit equipartition (?e/?B ˜ 1000), and is expanding into circumstellar material that is consistent with a density profile falling like R-2. Within modelling uncertainties we find an average velocity of the fast parts of the ejecta of 15 000 ± 1800 km s-1, contrary to previous analysis. This velocity places SN 2011dh in an intermediate blast wave regime between the previously defined compact and extended SN Type IIb subtypes. Our results highlight the importance of early (˜1 d) high-frequency observations of future events. Moreover, we show the importance of combined radio/X-ray observations for determining the microphysics ratio ?e/?B.

Horesh, Assaf; Stockdale, Christopher; Fox, Derek B.; Frail, Dale A.; Carpenter, John; Kulkarni, S. R.; Ofek, Eran O.; Gal-Yam, Avishay; Kasliwal, Mansi M.; Arcavi, Iair; Quimby, Robert; Cenko, S. Bradley; Nugent, Peter E.; Bloom, Joshua S.; Law, Nicholas M.; Poznanski, Dovi; Gorbikov, Evgeny; Polishook, David; Yaron, Ofer; Ryder, Stuart; Weiler, Kurt W.; Bauer, Franz; Van Dyk, Schuyler D.; Immler, Stefan; Panagia, Nino; Pooley, Dave; Kassim, Namir

2013-12-01

354

Challenges in Computing Thermal and Non-thermal Emission from Relativistic Outflows

NASA Astrophysics Data System (ADS)

Multi-wavelength emission from relativistic outflows (e.g., jets and blast waves) provides us with valuable information about the physical conditions of the emitting plasma, its fluid dynamics and about the process which generates the outflows (i.e., the central engine). We use the relativistic hydrodynamics (RHD) code MRGENESIS coupled to a radiative transfer code SPEV to simulate the dynamics and emission of relativistic jets in two astrophysical scenarios, one involving non-thermal synchrotron emission in radio, and the other where thermal emission in optical is predominant. We give an overview of the structure of two codes and explain how they are coupled to compute the time-dependent emission from the evolving relativistic fluid. A considerable attention is given to the computational challenges that we face when applying SPEV to compute the light curves and spectra of relativistic jets.

Mimica, P.; Aloy, M. A.; Cuesta-Martínez, C.; Aloy, C.

2014-09-01

355

The mechanism and realization of a band-agile coaxial relativistic backward-wave oscillator

The mechanism and realization of a band-agile coaxial relativistic backward-wave oscillator (RBWO) are presented. The operation frequency tuning can be easily achieved by merely altering the inner-conductor length. The key effects of the inner-conductor length contributing to the mechanical frequency tunability are investigated theoretically and experimentally. There is a specific inner-conductor length where the operation frequency can jump from one mode to another mode, which belongs to a different operation band. In addition, the operation frequency is tunable within each operation band. During simulation, the L-band microwave with a frequency of 1.61 GHz is radiated when the inner-conductor length is 39?cm. Meanwhile, the S-band microwave with a frequency of 2.32 GHz is radiated when the inner-conductor length is 5?cm. The frequency adjustment bandwidths of L-band and S-band are about 8.5% and 2%, respectively. Moreover, the online mechanical tunability process is described in detail. In the initial experiment, the generated microwave frequencies remain approximately 1.59 GHz and 2.35?GHz when the inner-conductor lengths are 39?cm and 5?cm. In brief, this technical route of the band-agile coaxial RBWO is feasible and provides a guide to design other types of band-agile high power microwaves sources.

Ge, Xingjun; Zhang, Jun; Zhong, Huihuang; Qian, Baoliang; Wang, Haitao [College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2014-11-03

356

Diffusive cosmic ray acceleration at relativistic shock waves with magnetostatic turbulence

The analytical theory of diffusive cosmic ray acceleration at parallel stationary shock waves with magnetostatic turbulence is generalized to arbitrary shock speeds $V_s=\\beta_1c$, including in particular relativistic speeds. This is achieved by applying the diffusion approximation to the relevant Fokker-Planck particle transport equation formulated in the mixed comoving coordinate system. In this coordinate system the particle's momentum coordinates $p$ and $\\mu =p_{\\parallel }/p$ are taken in the rest frame of the streaming plasma, whereas the time and space coordinates are taken in the observer's system. For magnetostatic slab turbulence the diffusion-convection transport equation for the isotropic (in the rest frame of the streaming plasma) part of the particle's phase space density is derived. For a step-wise shock velocity profile the steady-state diffusion-convection transport equation is solved. For a symmetric pitch-angle scattering Fokker-Planck coefficient $D_{\\mu \\mu }(-\\mu )=D_{\\mu \\mu }(\\mu )$ t...

Schlickeiser, Reinhard

2015-01-01

357

The mechanism and realization of a band-agile coaxial relativistic backward-wave oscillator

NASA Astrophysics Data System (ADS)

The mechanism and realization of a band-agile coaxial relativistic backward-wave oscillator (RBWO) are presented. The operation frequency tuning can be easily achieved by merely altering the inner-conductor length. The key effects of the inner-conductor length contributing to the mechanical frequency tunability are investigated theoretically and experimentally. There is a specific inner-conductor length where the operation frequency can jump from one mode to another mode, which belongs to a different operation band. In addition, the operation frequency is tunable within each operation band. During simulation, the L-band microwave with a frequency of 1.61 GHz is radiated when the inner-conductor length is 39 cm. Meanwhile, the S-band microwave with a frequency of 2.32 GHz is radiated when the inner-conductor length is 5 cm. The frequency adjustment bandwidths of L-band and S-band are about 8.5% and 2%, respectively. Moreover, the online mechanical tunability process is described in detail. In the initial experiment, the generated microwave frequencies remain approximately 1.59 GHz and 2.35 GHz when the inner-conductor lengths are 39 cm and 5 cm. In brief, this technical route of the band-agile coaxial RBWO is feasible and provides a guide to design other types of band-agile high power microwaves sources.

Ge, Xingjun; Zhang, Jun; Zhong, Huihuang; Qian, Baoliang; Wang, Haitao

2014-11-01

358

NASA Astrophysics Data System (ADS)

Earth's outer radiation belt is a highly dynamic region of the magnetosphere composed of relativistic electrons with often unpredictable variations in energy and spatial extent. Understanding this variable radiation environment is critical for protecting both spacecraft and humans in space. A number of competing acceleration and loss processes combine to produce net enhancements or depletions of the outer radiation belt. Electron precipitation into the atmosphere is a critical part of this loss, and quantified understanding of this mechanism is needed in order to understand and ultimately predict radiation belt dynamics. In the following work, we investigate the contribution of electron precipitation to radiation belt losses, looking at what times precipitation is important and at how much loss it contributes. Through a combination of long-term existing data sets as well as new CubeSat measurements we perform both statistical and detailed event studies to better understand the nature and extent of MeV electron loss to the atmosphere. We analyze measurements of precipitating electrons directly as well as electromagnetic waves that may be causing this precipitation. Our studies provide a more cohesive picture of outer radiation belt dynamics and the relationship between precipitating energetic electrons and global magnetospheric conditions.

Blum, Lauren W.

359

NASA Astrophysics Data System (ADS)

A dual-cavity TM02-TM01 mode converter is designed for a dual-mode operation over-moded relativistic backward-wave oscillator. With the converter, the fundamental mode output is achieved. Particle-in-cell simulation shows that the efficiency of beam-wave conversion was over 46% and a pureTM01 mode output was obtained. Effects of end reflection provided by the mode converter were studied. Adequate TM01 mode feedback provided by the converter enhances conversion efficiency. The distance between the mode converter and extraction cavity critically affect the generation of microwaves depending on the reflection phase of TM01 mode feedback.

Li, Jiawei; Xiao, Renzhen; Bai, Xianchen; Zhang, Yuchuan; Zhang, Xiaowei; Zhu, Qi; Shao, Hao; Chen, Changhua; Huang, Wenhua

2015-03-01

360

It is shown that the interaction of the superstrong laser radiation with an isotropic plasma leads to the generation of low frequency electromagnetic (EM) waves and in particular a quasistationary magnetic field. When the relativistic circularly polarized transverse EM wave propagates along z-axis, it creates a ponderomotive force, which affects the motion of particles along the direction of its propagation. On the other hand, motion of the particles across the direction of propagation is defined by the ponderomotive potential. The dispersion relation for the transverse EM wave using a special distribution function, which has an anisotropic form, is derived. The dispersion relation is subsequently investigated for a number of special cases. In general, it is shown that the growth rate of the EM wave strongly depends upon its intensity.

Gillani, S. S. A.; Shah, H. A. [Department of Physics, Government College University, Lahore 54000 (Pakistan); Tsintsadze, N. L. [Department of Physics, Government College University, Lahore 54000 (Pakistan); Salam Chair in Physics, Government College University, Lahore 54000 (Pakistan); Institute of Physics, Tbilisi 380077 (Georgia); Razzaq, M. [Department of Physics, Government College University, Lahore 54000 (Pakistan); Salam Chair in Physics, Government College University, Lahore 54000 (Pakistan)

2010-08-15

361

NASA Astrophysics Data System (ADS)

In this communication, the combined effect of relativistic and ponderomotive nonlinearities on the generation of electron plasma wave by cross focusing of two intense laser beams at difference frequency ( ?? ? ? 1 - ? 2 ? ? p) and acceleration of electrons in laser produced homogeneous plasma is analysed in the non-paraxial region. On account of these nonlinearities, two laser beams affect the dynamics of each other, and cross focusing takes place. It is observed that the focusing of laser beams becomes fast in the non-paraxial region by expanding the eikonal and other relevant quantities up to the fourth power of the radial distance ( r). Modified coupled equations for the beam width of laser beams, electric field amplitude of the excited electron plasma wave and energy gain at beat wave frequency are derived, when relativistic and ponderomotive nonlinearities are operative. These coupled equations are solved analytically and numerically to study the cross focusing of two intense laser beams in plasma and its effect on the variation of the amplitude of the electron plasma wave and energy gain. It is observed from the results that both nonlinearities significantly affect the amplitude of plasma wave excitation and particle acceleration in the non-paraxial region in comparison to the paraxial region.

Rawat, Priyanka; Singh, Ram Kishor; Sharma, Ram Pal; Purohit, Gunjan

2014-03-01

362

[The characteristics of blast traumatic brain injury].

With the increase in terrorist activity in recent times, the number of blast injuries has also increased in civilian and military settings. In a recent war, the number of patients who suffered blast traumatic brain injury (bTBI) increased, so treatment of bTBI is currently a very important issue. Blast injury is complicated and can be divided into 4 categories: primary, secondary, tertiary, and quaternary. Primary blast injury results from exposure to blast waves; secondary blast injury is trauma caused by fragments of explosive devices; tertiary blast injury is the result of collision with objects; and quaternary blast injury is the result of exposure to toxic and other substances. Blast waves mainly injure air-containing organs such as the lung, bowel, and ear. The brain may also be affected by blast waves. From the clinical perspective, hyperemia and severe cerebral edema occur frequently in patients who sustain significant bTBI. Penetrating or closed head injury caused by the explosion may be associated with vasospasm and pseudoaneurysm formation. Mild traumatic brain injury during war can be associated with posttraumatic stress disorder. To elucidate the mechanism of bTBI, many research works using animal models and computer analysis are underway. Such studies have so far shown that blast waves can cause damage to the brain tissue and cognitive deficits; however, detailed investigations on this topic are still required. Treatment of bTBI patients may require clinical knowledge and skills related to intensive care, neurology, and neurosurgery. Moreover, further research is required in this field. PMID:20697143

Matsumoto, Yoshihisa; Hatano, Ben; Matsushita, Yoshitaro; Nawashiro, Hiroshi; Shima, Katsuji

2010-08-01

363

The primary energy exchange in a relativistic backward wave oscillator (BWO) occurs between the electron beam and the backward traveling wave within the slow wave structure (SWS). In most high power BWOs the backward traveling wave is reflected by a cutoff neck at the entrance of the SWS and radiation is extracted in the direction of the electron beam. Recently, researchers have investigated the effect of the forward traveling wave on the energy exchange between the electron bunches and the backward wave and the effect of multiple end reflections and cavity effects on the efficiency of microwave generation. This poster paper presents detailed measurements of the interaction of the electron beam with the forward traveling wave, and the effect of end reflections on the radiation frequency and efficiency. Numerical simulation results are found to be in agreement with the experimental measurements. These experiments suggest an enhanced frequency agility of high power BWOs by adjusting the phase of reflections within the SWS. A research program is underway to use control strategies to both optimize BWO performance and allow for enhanced frequency agility (100s of MHz) at moderate power levels (100s of MW).

Moreland, L.D.; Schamiloglu, E. [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Electrical and Computer Engineering; Lemke, R.W. [Sandia National Labs., Albuquerque, NM (United States); Roitman, A.M. [Inst. of High Current Electronics, Tomsk (Russian Federation)

1995-12-31

364

Membrane characteristics for biological blast overpressure testing using blast simulators.

Blast simulators often use passive-rupture membranes to generate shock waves similar to free-field blasts. The purpose of this study was to compare rupture patterns and pressure traces of three distinct membrane materials for biological and biomechanical blast studies. An Advanced Blast Simulator (ABS) located at the Center for Injury Biomechanics at Virginia Tech was used to test membrane characteristics. Acetate, Mylar, and aluminum sheets with different thicknesses were used to obtain pressures between 70?210 kPa. Static pressure was measured inside the tube at the test section using piezoelectric pressure sensors. Peak overpressure, positive duration, and positive impulse were calculated for each test. Rupture patterns and characteristic pressure traces were unique to each membrane type and thickness. Shock wave speed ranged between 1.2-1.8 Mach for static overpressures of 70?210 kPa. Acetate membranes fragmented sending pieces down the tube, but produced ideal (Friedlander) pressure traces. Mylar membranes bulged without fragmenting, but produced less-than-ideal pressure traces. Aluminum membranes did not fragment and produced ideal pressure traces. However, the cost of manufacturing and characterizing aluminum membranes should be considered during membrane selection. This study illustrates the advantages and disadvantages of using Mylar, acetate, and aluminum for passive rupture membranes for blast simulators. PMID:25405432

Alphonse, Vanessa D; Siva Sai Sujith Sajja, Venkata; Kemper, Andrew R; Rizel, Dave V; Duma, Stefan M; VandeVord, Pamela J

2014-01-01

365

NASA Astrophysics Data System (ADS)

We investigated by theory and simulations how fast a relativistically transparent channel is opened by a linearly polarized relativistic laser pulse in an overdense plasma, which is classically opaque. The relativistic transparency has been well known: the dispersion relations were revealed for various steady states. However, as long as we understand, the answer to the question `how the relativistic channel is formed dynamically from an opaque plasma' has not been so clear. In this work, we focused on finding analytically the speed of such a channel opening. By employing the `channel-opening-time' concept, we could derive semi-analytically a simple formula, which showed excellent agreement with the one-dimensional PIC simulations. The theory was successfully applied in predicting the pulse shape after the interaction of an ultraintense linear polarized laser pulse and a thin foil both in one- and two-dimensional systems.

Hur, Min Sup; Kim, Young-Kuk; Kulagin, Victor; Suk, Hyyong

2011-11-01

366

Parametric decays of a left-handed circularly polarized Alfvén wave propagating along a constant background magnetic field in a relativistic thermal electron-positron plasma are studied by means of a one dimensional relativistic particle-in-cell simulation. Relativistic effects are included in the Lorentz equation for the momentum of the particles and in their thermal motion, by considering a Maxwell-Jüttner velocity distribution function for the initial condition. In the linear stage of the simulation, we find many instabilities that match the predictions of relativistic fluid theory. In general, the growth rates of the instabilities increase as the pump wave amplitude is increased, and decrease with a raise in the plasma temperatures. We have confirmed that for very high temperatures the Alfvén branch is suppressed, consistent with analytical calculations.

López, Rodrigo A., E-mail: rlopez186@gmail.com; Muñoz, Víctor [Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile)] [Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile); Viñas, Adolfo F. [NASA Goddard Space Flight Center, Heliophysics Science Division, Geospace Physics Laboratory, Mail Code 673, Greenbelt, Maryland 20771 (United States)] [NASA Goddard Space Flight Center, Heliophysics Science Division, Geospace Physics Laboratory, Mail Code 673, Greenbelt, Maryland 20771 (United States); Alejandro Valdivia, J. [Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile) [Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago (Chile); Centro para el Desarrollo de la Nanociencia y la Nanotecnología, CEDENNA, Santiago (Chile)

2014-03-15

367

Near-term development of the existing PHERMEX standing-wave linac would provide a 40 to 60 MeV electron beam with a current of 3 kA capable of answering a number of fundamental issues concerning endoatmospheric, ultra-relativistic electron beam propagation. Inherent high-repetition rate and multiple-pulse capability would allow alternative propagation scenarios to be investigated. Much of the theoretical expertise required to support the technology development and time-resolved beam propagation experiments presently resides within the Theoretical Applications Division.

Moir, D.C.; Faehl, R.J.; Newberger, B.S.; Thode, L.E.

1981-01-01

368

NASA Astrophysics Data System (ADS)

The basic features and multi-dimensional instability of electrostatic (EA) solitary waves propagating in an ultra-relativistic degenerate dense magnetized plasma (containing inertia-less electrons, inertia-less positrons, and inertial ions) have been theoretically investigated by reductive perturbation method and small-k perturbation expansion technique. The Zakharov-Kuznetsov (ZK) equation has been derived, and its numerical solutions for some special cases have been analyzed to identify the basic features (viz. amplitude, width, instability, etc.) of these electrostatic solitary structures. The implications of our results in some compact astrophysical objects, particularly white dwarfs and neutron stars, are briefly discussed.

Masum Haider, M.; Akter, Suraya; Duha, Syed; Mamun, Abdullah

2012-10-01

369

NASA Astrophysics Data System (ADS)

The basic features and multi-dimensional instability of electrostatic (EA) solitary waves propagating in an ultra-relativistic degenerate dense magnetized plasma (containing inertia-less electrons, inertia-less positrons, and inertial ions) have been theoretically investigated by reductive perturbation method and small- k perturbation expansion technique. The Zakharov-Kuznetsov (ZK) equation has been derived, and its numerical solutions for some special cases have been analyzed to identify the basic features (viz. amplitude, width, instability, etc.) of these electrostatic solitary structures. The implications of our results in some compact astrophysical objects, particularly white dwarfs and neutron stars, are briefly discussed.

Masum Haider, M.; Akter, Suraya; Duha, Syed S.; Mamun, Abdullah A.

2012-10-01

370

Particle Acceleration at Ultra-Relativistic Shocks and the Spectra of Relativistic Fireballs

We examine Fermi-type acceleration at relativistic shocks, and distinguish between the initial boost of the first shock crossing cycle, where the energy gain per particle can be very large, and the Fermi process proper with repeated shock crossings, in which the typical energy gain is of order unity. We calculate by means of numerical simulations the spectrum and angular distribution of particles accelerated by this Fermi process, in particular in the case where particle dynamics can be approximated as small-angle scattering. We show that synchrotron emission from electrons or positrons accelerated by this process can account remarkably well for the observed power-law spectra of GRB afterglows and Crab-like supernova remnants. In the context of a decelerating relativistic fireball, we calculate the maximum particle energy attainable by acceleration at the external blast wave, and discuss the minimum energy for this acceleration process and its consequences for the observed spectrum.

Yves A. Gallant; Abraham Achterberg; John G. Kirk; Axel W. Guthmann

2000-01-28

371

A nonlinear quantum theory of stimulated Cherenkov radiation of transverse electromagnetic waves from a low-density relativistic electron beam in an isotropic dielectric medium is presented. A quantum model based on the Klein-Gordon equation is used. The growth rates of beam instabilities caused by the effect of stimulated Cherenkov radiation have been determined in the linear approximation. Mechanisms of the nonlinear saturation of relativistic quantum Cherenkov beam instabilities have been analyzed and the corresponding analytical solutions have been obtained.

Bobylev, Yu. B.; Kuzelev, M. V. [Moscow State University, Faculty of Physics (Russian Federation)

2012-06-15

372

NASA Astrophysics Data System (ADS)

We have measured absolute cross sections for the K-shell ionization of medium- and high-Z targets of Sb, Gd, Yb, Au, and Bi induced by low- to intermediate-velocity F ions having energies between 2.5 and 5.8 MeV/u. Our main interest is to see the effect of the relativistic nature of the K-shell electrons of these target atoms on the ionization cross sections. The information on the degree of relativistic effect has been obtained by comparing the measured data with different theoretical calculations with and without including the relativistic corrections. A comparative study of the two different models such as SCA (semiclassical approximation) and ECPSSR [perturbed stationary state (PSS) including the corrections for energy (E) loss, Coulomb (C) deflection, and relativistic (R) effects] is presented. It is shown that the SCA calculations with the relativistic wave function predict an ionization cross section that is at least an order of magnitude higher compared to that given by the nonrelativistic calculation for Bi target. This factor is reduced to about 2 in the case of Sb. The ECPSSR, however, predicts lower ratios for the relativistic to nonrelativistic calculations. The experimental results, in general, are in good agreement with the SCA calculations using relativistic wave functions as well as with the ECPSSR model. For high-Z targets the SCA gives slightly better agreement with the data compared to the ECPSSR. In addition, it is shown that in the ECPSSR formalism the ionization cross sections of high-Z (with large relativistic effect) as well as low-Z targets (with less relativistic effect) can be scaled approximately to follow a universal curve after including the relativistic correction.

Mitra, D.; Singh, Yeshpal; Tribedi, Lokesh C.; Tandon, P. N.; Trautmann, D.

2001-07-01

373

NASA Astrophysics Data System (ADS)

Within the framework of a quasi-optical approach, we develop 2D and 3D self-consistent theory of relativistic surface-wave oscillators. Presenting the radiation field as a sum of two counter-propagating wavebeams coupled on a shallow corrugated surface, we describe formation of an evanescent slow wave. Dispersion characteristics of the evanescent wave following from this method are in good compliance with those found from the direct cst simulations. Considering excitation of the slow wave by a sheet electron beam, we simulate linear and nonlinear stages of interaction, which allows us to determine oscillation threshold conditions, electron efficiency, and output coupling. The transition from the model of surface-wave oscillator operating in the ?-mode regime to the canonical model of relativistic backward wave oscillator is considered. We also described a modified scheme of planar relativistic surface-wave oscillators exploiting two-dimensional periodic gratings. Additional transverse propagating waves emerging on these gratings synchronize the emission from a wide sheet rectilinear electron beam allowing realization of a Cherenkov millimeter-wave oscillators with subgigawatt output power level.

Ginzburg, N. S.; Malkin, A. M.; Sergeev, A. S.; Zaslavsky, V. Yu.

2013-11-01

374

With the efficiency increase of a klystron-like relativistic backward wave oscillator, the maximum axial electric field and harmonic current simultaneously appear at the end of the beam-wave interaction region, leading to a highly centralized energy exchange in the dual-cavity extractor and a very high electric field on the cavity surface. Thus, we present a method of distributed energy extraction in this kind of devices. Particle-in-cell simulations show that with the microwave power of 5.1?GW and efficiency of 70%, the maximum axial electric field is decreased from 2.26 MV/cm to 1.28 MV/cm, indicating a threefold increase in the power capacity.

Xiao, Renzhen; Chen, Changhua; Cao, Yibing; Sun, Jun [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024 (China)

2013-12-07

375

This paper presents an efficient approach to realizing the frequency tunability of a relativistic backward wave oscillator (RBWO) over three frequency bands by mode transition without changing the slow wave structure (SWS). It is figured out that the transition of the operation mode in the RBWO can be efficiently achieved by using the strong end reflection of the SWS. This mode transition results in the tunability of the RBWO over three frequency bands at high power and high efficiency without changing the SWS. In numerical simulation, the output frequency of the RBWO can jump over 7.9?GHz in C-band, 9.9?GHz in X-band, and 12.4?GHz in Ku-band with output power exceeding 3.0?GW and conversion efficiency higher than 35% by just reasonably transforming the structures of the front and post resonant reflectors which provide the strong end reflection for the SWS.

Wu, Ping; Deng, Yuqun [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China); Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024 (China); Fan, Juping; Teng, Yan; Shi, Yanchao; Sun, Jun [Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024 (China)

2014-10-15

376

NASA Astrophysics Data System (ADS)

The wave-particle interaction (WPI) is very likely the most studied physical mechanism in plasmas in general, and space plasmas in particular. This mechanism is best studied when the wave propagation is assumed parallel to the background magnetic field. However, oblique wave propagation is more realistic and changes the nature of the WPI as far as its impact on transport is concerned. The goal of this report is to present a synthesis of analytical and numerical studies of the wave-particle interaction for obliquely propagating waves and its effect on the particle's dynamics (physical trapping, acceleration) and distribution functions (beam generation). Initially, the classical WPI, in the case of a homogeneous background magnetic field, was treated using a dynamical systems approach [1]. Most notably, it was shown that the introduction of an electric field parallel to the background magnetic field results in physical trapping of particles. Using Liouville's theorem of phase-space density conservation, particle distribution functions were constructed by following phase-space trajectories. It was further shown that the WPI, in the oblique propagation case, provides a quantitative explanation to the kinetic distortions of proton distribution functions observed in fast streams of the solar wind (beams, tails)[2]. We have extended this work to the case of relativistic protons interacting with obliquely propagating electromagnetic waves; a dynamical system governing the WPI has been derived. The results of the numerical integration will be presented for the case where the background magnetic field is homogeneous, and for the special case of a dipolar magnetic field. We will also attempt to complete the study by running the model for relativistic electrons and comparing the results to observations of radiation belt electrons. [1] Hamza, A. M., K. Meziane, C. Mazelle, (2006) Oblique Propagation and nonlinear wave-particle processes, J. Geophys. Res., 111, A04,104, doi:10.1029/2005JA011410 [2] Osmane, A., A. M. Hamza, and K. Meziane, (2010), On the Generation of Proton Beams in Fast Solar Wind in the Presence of obliquely propagating Alfven waves., J. Geophys. Res., doi:10.1029/2009JA014655, in press.

Osmane, Adnane; Hamza, A. M.; Meziane, Karim

377

Overview of Intense Beam-Driven Relativistic Backward Wave Oscillators and their Use in

manner. By this we mean that, by appropriately setting the diode voltage for a fixed slow wave structure-section (overmoded) slow-wave structure with a unique profile of wall radius specifically designed to support surhce

378

Blast exposure is associated with traumatic brain injury (TBI), neuropsychiatric symptoms, and long-term cognitive disability. We examined a case series of postmortem brains from U.S. military veterans exposed to blast and/or concussive injury. We found evidence of chronic traumatic encephalopathy (CTE), a tau protein-linked neurodegenerative disease, that was similar to the CTE neuropathology observed in young amateur American football players and a professional wrestler with histories of concussive injuries. We developed a blast neurotrauma mouse model that recapitulated CTE-linked neuropathology in wild-type C57BL/6 mice 2 weeks after exposure to a single blast. Blast-exposed mice demonstrated phosphorylated tauopathy, myelinated axonopathy, microvasculopathy, chronic neuroinflammation, and neurodegeneration in the absence of macroscopic tissue damage or hemorrhage. Blast exposure induced persistent hippocampal-dependent learning and memory deficits that persisted for at least 1 month and correlated with impaired axonal conduction and defective activity-dependent long-term potentiation of synaptic transmission. Intracerebral pressure recordings demonstrated that shock waves traversed the mouse brain with minimal change and without thoracic contributions. Kinematic analysis revealed blast-induced head oscillation at accelerations sufficient to cause brain injury. Head immobilization during blast exposure prevented blast-induced learning and memory deficits. The contribution of blast wind to injurious head acceleration may be a primary injury mechanism leading to blast-related TBI and CTE. These results identify common pathogenic determinants leading to CTE in blast-exposed military veterans and head-injured athletes and additionally provide mechanistic evidence linking blast exposure to persistent impairments in neurophysiological function, learning, and memory. PMID:22593173

Goldstein, Lee E; Fisher, Andrew M; Tagge, Chad A; Zhang, Xiao-Lei; Velisek, Libor; Sullivan, John A; Upreti, Chirag; Kracht, Jonathan M; Ericsson, Maria; Wojnarowicz, Mark W; Goletiani, Cezar J; Maglakelidze, Giorgi M; Casey, Noel; Moncaster, Juliet A; Minaeva, Olga; Moir, Robert D; Nowinski, Christopher J; Stern, Robert A; Cantu, Robert C; Geiling, James; Blusztajn, Jan K; Wolozin, Benjamin L; Ikezu, Tsuneya; Stein, Thor D; Budson, Andrew E; Kowall, Neil W; Chargin, David; Sharon, Andre; Saman, Sudad; Hall, Garth F; Moss, William C; Cleveland, Robin O; Tanzi, Rudolph E; Stanton, Patric K; McKee, Ann C

2012-05-16

379

Blast exposure is associated with traumatic brain injury (TBI), neuropsychiatric symptoms, and long-term cognitive disability. We examined a case series of postmortem brains from U.S. military veterans exposed to blast and/or concussive injury. We found evidence of chronic traumatic encephalopathy (CTE), a tau protein–linked neurodegenerative disease, that was similar to the CTE neuropathology observed in young amateur American football players and a professional wrestler with histories of concussive injuries. We developed a blast neurotrauma mouse model that recapitulated CTE-linked neuropathology in wild-type C57BL/6 mice 2 weeks after exposure to a single blast. Blast-exposed mice demonstrated phosphorylated tauopathy, myelinated axonopathy, microvasculopathy, chronic neuroinflammation, and neurodegeneration in the absence of macroscopic tissue damage or hemorrhage. Blast exposure induced persistent hippocampal-dependent learning and memory deficits that persisted for at least 1 month and correlated with impaired axonal conduction and defective activity-dependent long-term potentiation of synaptic transmission. Intracerebral pressure recordings demonstrated that shock waves traversed the mouse brain with minimal change and without thoracic contributions. Kinematic analysis revealed blast-induced head oscillation at accelerations sufficient to cause brain injury. Head immobilization during blast exposure prevented blast-induced learning and memory deficits. The contribution of blast wind to injurious head acceleration may be a primary injury mechanism leading to blast-related TBI and CTE. These results identify common pathogenic determinants leading to CTE in blast-exposed military veterans and head-injured athletes and additionally provide mechanistic evidence linking blast exposure to persistent impairments in neurophysiological function, learning, and memory. PMID:22593173

Goldstein, Lee E.; Fisher, Andrew M.; Tagge, Chad A.; Zhang, Xiao-Lei; Velisek, Libor; Sullivan, John A.; Upreti, Chirag; Kracht, Jonathan M.; Ericsson, Maria; Wojnarowicz, Mark W.; Goletiani, Cezar J.; Maglakelidze, Giorgi M.; Casey, Noel; Moncaster, Juliet A.; Minaeva, Olga; Moir, Robert D.; Nowinski, Christopher J.; Stern, Robert A.; Cantu, Robert C.; Geiling, James; Blusztajn, Jan K.; Wolozin, Benjamin L.; Ikezu, Tsuneya; Stein, Thor D.; Budson, Andrew E.; Kowall, Neil W.; Chargin, David; Sharon, Andre; Saman, Sudad; Hall, Garth F.; Moss, William C.; Cleveland, Robin O.; Tanzi, Rudolph E.; Stanton, Patric K.; McKee, Ann C.

2013-01-01

380

Perturbations on an interface driven by a strong blast wave grow in time due to a combination of Rayleigh-Taylor, Richtmyer-Meshkov, and decompression effects. In this paper, results from three-dimensional (3D) numerical simulations of such a system under drive conditions to be attainable on the National Ignition Facility [E. M. Campbell, Laser Part. Beams 9, 209 (1991)] are presented. Using the multiphysics, adaptive mesh refinement, higher order Godunov Eulerian hydrocode, Raptor [L. H. Howell and J. A. Greenough, J. Comput. Phys. 184, 53 (2003)], the late nonlinear instability evolution, including transition to turbulence, is considered for various multimode perturbation spectra. The 3D post-transition state differs from the 2D result, but the process of transition proceeds similarly in both 2D and 3D. The turbulent mixing transition results in a reduction in the growth rate of the mixing layer relative to its pretransition value and, in the case of the bubble front, relative to the 2D result. The post-transition spike front velocity is approximately the same in 2D and 3D. Implications for hydrodynamic mixing in core-collapse supernovae are discussed.

Miles, A.R.; Blue, B.; Edwards, M.J.; Greenough, J.A.; Hansen, J.F.; Robey, H.F.; Drake, R.P.; Kuranz, C.; Leibrandt, D.R. [Lawrence Livermore National Laboratory, L-021, 7000 East Avenue, P.O. Box 808, Livermore, California 94551 (United States); University of Michigan, 2455 Hayward Street, Ann Arbor, Michigan 48109 (United States)

2005-05-15

381

NASA Astrophysics Data System (ADS)

The detailed mechanism of blast-induced traumatic brain injury (bTBI) has not been revealed yet. Thus, reliable laboratory animal models for bTBI are needed to investigate the possible diagnosis and treatment for bTBI. In this study, we used laser-induced shock wave (LISW) to induce TBI in rats and investigated the histopathological similarities to actual bTBI. After craniotomy, the rat brain was exposed to a single shot of LISW with a diameter of 3 mm at various laser fluences. At 24 h after LISW exposure, perfusion fixation was performed and the extracted brain was sectioned; the sections were stained with hematoxylin-eosin. Evans blue (EB) staining was also used to evaluate disruption of the blood brain barrier. At certain laser fluence levels, neural cell injury and hemorrhagic lesions were observed in the cortex and subcortical region. However, injury was limited in the tissue region that interacted with the LISW. The severity of injury increased with increasing laser fluence and hence peak pressure of the LISW. Fluorescence originating from EB was diffusively observed in the injuries at high fluence levels. Due to the grade and spatial controllability of injuries and the histological observations similar to those in actual bTBI, brain injuries caused by LISWs would be useful models to study bTBI.

Hatano, Ben; Matsumoto, Yoshihisa; Otani, Naoki; Saitoh, Daizoh; Tokuno, Shinichi; Satoh, Yasushi; Nawashiro, Hiroshi; Matsushita, Yoshitaro; Sato, Shunichi

2011-03-01

382

June 7 Ballistic Blast Results in Solar Tsunami - Duration: 0:08.

In addition to the magnificent blast, SDO detected a shadowy shock wave issuing from the blast site on the June 7, 2011 event. The 'solar tsunami' propagated more than halfway across the sun, visib...

383

NASA Astrophysics Data System (ADS)

Electromagnetic ion cyclotron (EMIC) waves were observed at multiple observatory locations for several hours on 17 January 2013. During the wave activity period, a duskside relativistic electron precipitation (REP) event was observed by one of the Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) balloons and was magnetically mapped close to Geostationary Operational Environmental Satellite (GOES) 13. We simulate the relativistic electron pitch angle diffusion caused by gyroresonant interactions with EMIC waves using wave and particle data measured by multiple instruments on board GOES 13 and the Van Allen Probes. We show that the count rate, the energy distribution, and the time variation of the simulated precipitation all agree very well with the balloon observations, suggesting that EMIC wave scattering was likely the cause for the precipitation event. The event reported here is the first balloon REP event with closely conjugate EMIC wave observations, and our study employs the most detailed quantitative analysis on the link of EMIC waves with observed REP to date.

Li, Zan; Millan, Robyn M.; Hudson, Mary K.; Woodger, Leslie A.; Smith, David M.; Chen, Yue; Friedel, Reiner; Rodriguez, Juan V.; Engebretson, Mark J.; Goldstein, Jerry; Fennell, Joseph F.; Spence, Harlan E.

2014-12-01

384

Concussive brain injury from explosive blast

Objective Explosive blast mild traumatic brain injury (mTBI) is associated with a variety of symptoms including memory impairment and posttraumatic stress disorder (PTSD). Explosive shock waves can cause hippocampal injury in a large animal model. We recently reported a method for detecting brain injury in soldiers with explosive blast mTBI using magnetic resonance spectroscopic imaging (MRSI). This method is applied in the study of veterans exposed to blast. Methods The hippocampus of 25 veterans with explosive blast mTBI, 20 controls, and 12 subjects with PTSD but without exposure to explosive blast were studied using MRSI at 7 Tesla. Psychiatric and cognitive assessments were administered to characterize the neuropsychiatric deficits and compare with findings from MRSI. Results Significant reductions in the ratio of N-acetyl aspartate to choline (NAA/Ch) and N-acetyl aspartate to creatine (NAA/Cr) (P < 0.05) were found in the anterior portions of the hippocampus with explosive blast mTBI in comparison to control subjects and were more pronounced in the right hippocampus, which was 15% smaller in volume (P < 0.05). Decreased NAA/Ch and NAA/Cr were not influenced by comorbidities – PTSD, depression, or anxiety. Subjects with PTSD without blast had lesser injury, which tended to be in the posterior hippocampus. Explosive blast mTBI subjects had a reduction in visual memory compared to PTSD without blast. Interpretation The region of the hippocampus injured differentiates explosive blast mTBI from PTSD. MRSI is quite sensitive in detecting and localizing regions of neuronal injury from explosive blast associated with memory impairment. PMID:25493283

de Lanerolle, Nihal C; Hamid, Hamada; Kulas, Joseph; Pan, Jullie W; Czlapinski, Rebecca; Rinaldi, Anthony; Ling, Geoffrey; Bandak, Faris A; Hetherington, Hoby P

2014-01-01

385

Exit of a blast wave from a conical nozzle. [flow field calculations by Eulerian computer code DORF

NASA Technical Reports Server (NTRS)

The Eulerian computer code DORF was used in the analysis of a two-dimensional, unsteady flow field resulting from semi-confined explosions for propulsive applications. Initially, the ambient gas inside the conical shaped nozzle is set into motion due to the expansion of the explosion product gas, forming a shock wave. When this shock front exits the nozzle, it takes almost a spherical form while a complex interaction between the nozzle and compression and rarefaction waves takes place behind the shock. The results show an excellent agreement with experimental data.

Kim, K.; Johnson, W. E.

1976-01-01

386

NASA Astrophysics Data System (ADS)

Multi-instrument observations of two filament eruptions on 24 February and 11 May 2011 suggest the following updated scenario for eruptive flare, coronal mass ejection (CME), and shock wave evolution. An initial destabilization of a filament results in stretching out of the magnetic threads belonging to its body that are rooted in the photosphere along the inversion line. Their reconnection leads to i) heating of parts of the filament or its environment, ii) an initial development of the flare cusp, arcade, and ribbons, iii) an increasing similarity of the filament to a curved flux rope, and iv) to its acceleration. Then the pre-eruption arcade enveloping the filament becomes involved in reconnection according to the standard model and continues to form the flare arcade and ribbons. The poloidal magnetic flux in the curved rope developing from the filament progressively increases and forces its toroidal expansion. This flux rope impulsively expands and produces a magnetohydrodynamical disturbance, which rapidly steepens into a shock. The shock passes through the arcade that expands above the filament and then freely propagates for some time ahead of the CME like a decelerating blast wave. If the CME is slow, then the shock eventually decays. Otherwise, the frontal part of the shock changes into the bow-shock regime. This was observed for the first time in the 24 February 2011 event. When reconnection ceases, the flux rope relaxes and constitutes the CME core-cavity system. The expanding arcade develops into the CME frontal structure. We also found that reconnection in the current sheet of a remote streamer forced by the shock passage results in a running flare-like process within the streamer responsible for a type II burst. The development of dimming and various associated phenomena are discussed.

Grechnev, V. V.; Uralov, A. M.; Kuzmenko, I. V.; Kochanov, A. A.; Chertok, I. M.; Kalashnikov, S. S.

2015-01-01

387

The recently developed structure model that uses the generator coordinate method to perform configuration mixing of angular-momentum projected wave functions, generated by constrained self-consistent relativistic mean-field calculations for triaxial shapes (3DAMP+GCM), is applied in a systematic study of ground states and low-energy collective states in the even-even magnesium isotopes $^{20-40}$Mg. Results obtained using a relativistic point-coupling nucleon-nucleon effective interaction in the particle-hole channel, and a density-independent $\\delta$-interaction in the pairing channel, are compared to data and with previous axial 1DAMP+GCM calculations, both with a relativistic density functional and the non-relativistic Gogny force. The effects of the inclusion of triaxial degrees of freedom on the low-energy spectra and E2 transitions of magnesium isotopes are examined.

J. M. Yao; H. Mei; H. Chen; J. Meng; P. Ring; D. Vretenar

2010-06-08

388

NASA Technical Reports Server (NTRS)

Automatic grit-blasting machine removes melted-layer residue from electrical-discharge-machined surfaces of turbine blades. Automatic control system of machine provides steady flow of grit and maintains blast nozzles at proper distance and in correct orientation perpendicular to surface being blasted, regardless of contour. Eliminates localized excessive blasting and consequent excessive removal of underlying material, blasting of adjacent surfaces, and missed areas.

Pickett, Isaiah R.; Yulfo, Alyce R.

1992-01-01

389

The amplification (attenuation) factor of an electromagnetic wave during the scattering of a relativistic electron by a nucleus\\u000a in a moderately strong field of a circularly polarized electromagnetic wave is studied theoretically. The effect of amplification\\u000a of an electromagnetic field is discovered in a certain interval of polar angles of the incident electron; this interval of\\u000a angles essentially depends on

S. P. Roshchupkin; V. A. Tsybul’nik

2005-01-01

390

Relativistic scattering coherence

Wave propagation through inhomogeneous, turbulent media is investigated for the case where the signal and inhomogeneities move relativistically. Although in classical treatments the mean-square angular deviations grow as the path length, this is found not to be true relativistically. Special attention is given to the problem of light propagating through a cosmological background of gravitational waves.

Linder, E.V.

1986-09-15

391

We report the results of 1D particle-in-cell simulations of ultrarelativistic shock waves in proton-electron-positron plasmas. We consider magnetized shock waves, in which the upstream medium carries a large scale magnetic field, directed transverse to the flow. Relativistic cyclotron instability of each species as the incoming particles encounter the increasing magnetic field within the shock front provides the basic plasma heating mechanism. The most significant new results come from simulations with mass ratio $m_p/m_\\pm = 100$. We show that if the protons provide a sufficiently large fraction of the upstream flow energy density (including particle kinetic energy and Poynting flux), a substantial fraction of the shock heating goes into the formation of suprathermal power-law spectra of pairs. Cyclotron absorption by the pairs of the high harmonic ion cyclotron waves, emitted by the protons, provides the non-thermal acceleration mechanism. As the proton fraction increases, the non-thermal efficiency increases and the pairs' power-law spectra harden. We suggest that the varying power law spectra observed in synchrotron sources powered by magnetized winds and jets might reflect the correlation of the proton to pair content enforced by the underlying electrodynamics of these sources' outflows, and that the observed correlation between the X-ray spectra of rotation powered pulsars with the X-ray spectra of their nebulae might reflect the same correlation.

Elena Amato; Jonathan Arons

2006-09-01

392

Nineteen-Foot Diameter Explosively Driven Blast Simulator

This report describes the 19-foot diameter blast tunnel at Sandia National Laboratories. The blast tunnel configuration consists of a 6 foot diameter by 200 foot long shock tube, a 6 foot diameter to 19 foot diameter conical expansion section that is 40 feet long, and a 19 foot diameter test section that is 65 feet long. Therefore, the total blast tunnel length is 305 feet. The development of this 19-foot diameter blast tunnel is presented. The small scale research test results using 4 inch by 8 inch diameter and 2 foot by 6 foot diameter shock tube facilities are included. Analytically predicted parameters are compared to experimentally measured blast tunnel parameters in this report. The blast tunnel parameters include distance, time, static, overpressure, stagnation pressure, dynamic pressure, reflected pressure, shock Mach number, flow Mach number, shock velocity, flow velocity, impulse, flow duration, etc. Shadowgraphs of the shock wave are included for the three different size blast tunnels.

VIGIL,MANUEL G.

2001-07-01

393

NASA Astrophysics Data System (ADS)

We investigate the structural and thermodynamic properties of cerium in ? phase by using the first-principles plane wave method with a relativistic analytic pseudopotential of Hartwigsen, Goedcker and Hutter (HGH) scheme in the frame of local density approximation (LDA). The obtained lattice constant and bulk modulus are consistent with the available experimental data. Moreover, dependences of the normalized primitive volume V/V0 on pressure and the thermodynamic quantities (including the Grüneisen constant ? and thermal expansion ?) on temperature and pressure are obtained. The obtained linear thermal expansion parameter ? (9.857 × 10-6 K-1 at 293.15K and 0GPa) is slightly larger than the experimental value (6.3 × 10-6 K-1). All the results indicate that we provide an effective method to deal with the ground properties of the strongly interacting d- and/or f-electron systems.

Sun, Li-Li; Ji, Guang-Fu; Chen, Xiang-Rong; Gou, Qing-Quan

2009-01-01

394

The Dirac equation, in the field of a traveling circularly polarized electromagnetic wave and a constant magnetic field, has singular solutions, corresponding the expansion of energy in vicinity of some singular point. These solutions described relativistic fermions. States relating to these solutions are not stationary. The temporal change of average energy, momentum and spin for single and mixed states is studied in the paper. A distinctive feature of the states is the disappearance of the longitudinal component of the average spin. Another feature is the equivalence of the condition of fermion minimal energy and the classical condition of the magnetic resonance. Finding such solutions assumes the use of a transformation for rotating and co-moving frames of references. Comparison studies of solutions obtained with the Galilean and non-Galilean transformation shown that some parameters of the non-Galilean transformation may be measured in high-energy physics.

Boris V. Gisin

2014-05-13

395

NASA Astrophysics Data System (ADS)

A phenomenological study of the process occurring when a plane shock wave reflected off an aqueous foam column filling the test section of a vertical shock tube has been undertaken. The experiments were conducted with initial shock wave Mach numbers in the range 1.25le {M}_s le 1.7 and foam column heights in the range 100-450 mm. Miniature piezotrone circuit electronic pressure transducers were used to record the pressure histories upstream and alongside the foam column. The aim of these experiments was to find a simple way to eliminate a spatial averaging as an artifact of the pressure history recorded by the side-on transducer. For this purpose, we discuss first the common behaviors of the pressure traces in extended time scales. These observations evidently quantify the low frequency variations of the pressure field within the different flow domains of the shock tube. Thereafter, we focus on the fronts of the pressure signals, which, in turn, characterize the high-frequency response of the foam column to the shock wave impact. Since the front shape and the amplitude of the pressure signal most likely play a significant role in the foam destruction, phase changes and/or other physical factors, such as high capacity, viscosity, etc., the common practice of the data processing is revised and discussed in detail. Generally, side-on pressure measurements must be used with great caution when performed in wet aqueous foams, because the low sound speed is especially prone to this effect. Since the spatial averaged recorded pressure signals do not reproduce well the real behaviors of the pressure rise, the recorded shape of the shock wave front in the foam appears much thicker. It is also found that when a thin liquid film wet the sensing membrane, the transducer sensitivity was changed. As a result, the pressure recorded in the foam could exceed the real amplitude of the post-shock wave flow. A simple procedure, which allows correcting this imperfection, is discussed in detail.

Britan, A.; Liverts, M.; Shapiro, H.; Ben-Dor, G.

2013-02-01

396

Note: A table-top blast driven shock tube

NASA Astrophysics Data System (ADS)

The prevalence of blast-induced traumatic brain injury in conflicts in Iraq and Afghanistan has motivated laboratory scale experiments on biomedical effects of blast waves and studies of blast wave transmission properties of various materials in hopes of improving armor design to mitigate these injuries. This paper describes the design and performance of a table-top shock tube that is more convenient and widely accessible than traditional compression driven and blast driven shock tubes. The design is simple: it is an explosive driven shock tube employing a rifle primer that explodes when impacted by the firing pin. The firearm barrel acts as the shock tube, and the shock wave emerges from the muzzle. The small size of this shock tube can facilitate localized application of a blast wave to a subject, tissue, or material under test.

Courtney, Michael W.; Courtney, Amy C.

2010-12-01

397

blast X-ray emission obtained by the Swift satellite, the X-ray luminosity being larger for higher whose evolution was followed by RXTE, Swift and Chandra (Sokoloski et al. 2006; Bode et al. 2006; Nelson

398

Relativistic breather-type solitary waves with linear polarization in cold plasmas

NASA Astrophysics Data System (ADS)

Linearly polarized solitary waves, arising from the interaction of an intense laser pulse with a plasma, are investigated. Localized structures, in the form of exact numerical nonlinear solutions of the one-dimensional Maxwell-fluid model for a cold plasma with fixed ions, are presented. Unlike stationary circularly polarized solitary waves, the linear polarization gives rise to a breather-type behavior and a periodic exchange of electromagnetic energy and electron kinetic energy at twice the frequency of the wave. A numerical method based on a finite-differences scheme allows us to compute a branch of solutions within the frequency range ?minwaves and their main properties as a function of ? is presented. Small-amplitude oscillations appearing in the tail of the solitary waves, a consequence of the linear polarization and harmonic excitation, are explained with the aid of the Akhiezer-Polovin system. Direct numerical simulations of the Maxwell-fluid model show that these solitary waves propagate without change for a long time.

Sánchez-Arriaga, G.; Siminos, E.; Saxena, V.; Kourakis, I.

2015-03-01

399

Conversion of piston-driven shocks from powerful solar flares to blast waves in the solar wind

NASA Technical Reports Server (NTRS)

Published observational data on 39 combined type-II/type-IV solar radio bursts from the period 1972-1982 are analyzed, with a focus on the potential use of the type-IV burst duration to predict the time of arrival at earth of piston-driven shock waves (extending and modifying the prediction method proposed by Smart and Shea, 1985). The data and analysis results are presented in tables and graphs and characterized in detail. It is found that a typical shock of this type leaves the solar flare at velocity 1560 km/sec and continues for a distance of 0.12 AU, decelerates as it is convected by the solar wind, and has a travel time of about 48.5 h. The mean deviation between predicted and measured arrival times is 1.40 h, with standard deviation 1.25 h.

Pinter, S.; Dryer, M.

1990-01-01

400

We present a new periodic all-metal slow wave structure, a coaxial step-disc-loaded system and the dispersion characteristics of the structure. By using the field-matching method, the dispersion equation and the coupling impedance of this structure are obtained. The coaxial structure makes the bandwidth broader than that of the non-coaxial one. Compared with the coaxial disc-loaded and ridged-disc-loaded structures, the pass-band

Ling-Na Yue; Wen-Xiang Wang; Yan-Yu Wei; Yu-Bin Gong

2005-01-01

401

NASA Astrophysics Data System (ADS)

The late afterglow of gamma-ray burst is believed to be due to progressive deceleration of the forward shock wave driven by the gamma-ray burst ejecta propagating in the interstellar medium. We study the dynamic effect of interstellar turbulence on shock wave propagation. It is shown that the shock wave decelerates more quickly than previously assumed without the turbulence. As an observational consequence, an earlier jet break will appear in the light curve of the forward shock wave. The scatter of the jet-corrected energy release for gamma-ray burst, inferred from the jet-break, may be partly due to the physical uncertainties in the turbulence/shock wave interaction. This uncertainties also exist in two shell collisions in the well-known internal shock model proposed for gamma-ray burst prompt emission. The large scatters of known luminosity relations of gamma-ray burst may be intrinsic and thus gamma-ray burst is not a good standard candle. We also discuss the other implications.

Liu, Xue-Wen

2012-11-01

402

Ion trajectories in a space-charge wave on a relativistic electron beam

NASA Technical Reports Server (NTRS)

The motion of an ion in a space-charge wave on a strongly magnetized electron beam is investigated. The motions of the ion perpendicular and parallel to the beam direction are coupled by a nonlinear term in the ion Hamiltonian that is proportional to the wave amplitude, and this coupling causes the motion of the ion to deviate significantly from that of a linear harmonic oscillator in certain resonant regions of phase space. A sequence of canonical transformations is employed to investigate the motion of the ion in these regions. It is determined that wave amplitudes that are too small to trap beam electrons are too small to cause these resonances to overlap. When this overlap does not occur, the motion is found not to be discernibly ergodic in any three-dimensional subspace of the energy hypersurface because there exists a third constant of the motion in addition to the total energy and angular momentum. The numerically integrated ion trajectories are studied using surface-of-section techniques in order to verify these findings. It is found that the third constant of the motion constrains an ion initially trapped in a potential well of the wave to remain trapped in this well. It is concluded that ergodic behavior poses no threat at attempts at collective ion acceleration in space-charge waves on an electron beam.

Russell, D. A.; Ott, E.

1983-01-01

403

NASA Astrophysics Data System (ADS)

The method for calculating the dispersion relations of the slow-wave structures (SWSs) with arbitrary geometrical structures is studied in detail by using the Fourier series expansion. In addition, dispersive characteristics and longitudinal resonance properties of the SWSs with the cosinusoidal, trapezoidal, and rectangular corrugations are analyzed by numerical calculation. Based on the above discussion, a comparison on an L-band coaxial relativistic backward wave oscillator (BWO) and an L-band coaxial BWO with a coaxial extractor is investigated in detail with particle-in-cell KARAT code (V. P. Tarakanov, Berkeley Research Associates, Inc., 1992). Furthermore, experiments are carried out at the TORCH-01 accelerator under the low guiding magnetic field. At diode voltage of 647 kV, beam current of 9.3 kA, and guiding magnetic field strength of 0.75 T, the microwave is generated with power of 1.07 GW, mode of TM01, and frequency of 1.61 GHz. That is the first experimental report of the L-band BWO.

Ge, Xingjun; Zhong, Huihuang; Qian, Baoliang; Zhang, Jun; Fan, Yuwei; Shu, Ting; Liu, Jinliang

2009-11-01

404

The method for calculating the dispersion relations of the slow-wave structures (SWSs) with arbitrary geometrical structures is studied in detail by using the Fourier series expansion. In addition, dispersive characteristics and longitudinal resonance properties of the SWSs with the cosinusoidal, trapezoidal, and rectangular corrugations are analyzed by numerical calculation. Based on the above discussion, a comparison on an L-band coaxial relativistic backward wave oscillator (BWO) and an L-band coaxial BWO with a coaxial extractor is investigated in detail with particle-in-cell KARAT code (V. P. Tarakanov, Berkeley Research Associates, Inc., 1992). Furthermore, experiments are carried out at the TORCH-01 accelerator under the low guiding magnetic field. At diode voltage of 647 kV, beam current of 9.3 kA, and guiding magnetic field strength of 0.75 T, the microwave is generated with power of 1.07 GW, mode of TM{sub 01}, and frequency of 1.61 GHz. That is the first experimental report of the L-band BWO.

Ge Xingjun; Zhong Huihuang; Qian Baoliang; Zhang Jun; Fan Yuwei; Shu Ting; Liu Jinliang [College of Photoelectric Science and Engineering, National University of Defense Technology, Changsha 410073 (China)

2009-11-15

405

Modelling human eye under blast loading.

Primary blast injury (PBI) is the general term that refers to injuries resulting from the mere interaction of a blast wave with the body. Although few instances of primary ocular blast injury, without a concomitant secondary blast injury from debris, are documented, some experimental studies demonstrate its occurrence. In order to investigate PBI to the eye, a finite element model of the human eye using simple constitutive models was developed. The material parameters were calibrated by a multi-objective optimisation performed on available eye impact test data. The behaviour of the human eye and the dynamics of mechanisms occurring under PBI loading conditions were modelled. For the generation of the blast waves, different combinations of explosive (trinitrotoluene) mass charge and distance from the eye were analysed. An interpretation of the resulting pressure, based on the propagation and reflection of the waves inside the eye bulb and orbit, is proposed. The peculiar geometry of the bony orbit (similar to a frustum cone) can induce a resonance cavity effect and generate a pressure standing wave potentially hurtful for eye tissues. PMID:23521031

Esposito, L; Clemente, C; Bonora, N; Rossi, T

2015-01-01

406

Blast design is a necessary part of design for more buildings in the United States. Blast design is no longer limited to underground shelters and sensitive military sites, buildings used by the general public daily must ...

Kieval, Tamar S. (Tamar Shoshana), 1980-

2004-01-01

407

A fully general relativistic numerical simulation code for spherically symmetric matter

NASA Astrophysics Data System (ADS)

We present a fully general relativistic open-source code that can be used for simulating a system of spherically symmetric perfect fluid matter. It is based on the Arnowitt-Deser-Misner 3+1 formalism with maximal slicing and isotropic spatial coordinates. For hydrodynamic matter High Resolution Shock Capturing (HRSC) schemes with a monotonized central-difference limiter and approximated Riemann solvers are used in the Eulerian viewpoint. The accuracy and the convergence of our numerical code are verified by performing several test problems. These include a relativistic blast wave, relativistic spherical accretion of matter into a black hole, Tolman-Oppenheimer-Volkoff (TOV) stars and Oppenheimer-Snyder (OS) dust collapses. In particular, a dynamical code test is done for the OS collapse by explicitly performing numerical coordinate transformations between our coordinate 8system and the one used for the analytic solution. Finally, some TOV star solutions are presented for the Eddington-inspired Born-Infeld gravity theory.

Park, Dong-Ho; Cho, Inyong; Kang, Gungwon; Lee, Hyung Mok

2013-02-01

408

Electron acceleration to relativistic energies at a strong quasi-parallel shock wave

Electrons can be accelerated to ultrarelativistic energies at strong (high-Mach number) collisionless shock waves that form when stellar debris rapidly expands after a supernova. Collisionless shock waves also form in the flow of particles from the Sun (the solar wind), and extensive spacecraft observations have established that electron acceleration at these shocks is effectively absent whenever the upstream magnetic field is roughly parallel to the shock surface normal (quasi-parallel conditions). However, it is unclear whether this magnetic dependence of electron acceleration also applies to the far stronger shocks around young supernova remnants, where local magnetic conditions are poorly understood. Here we present Cassini spacecraft observations of an unusually strong solar system shock wave (Saturn's bow shock) where significant local electron acceleration has been confirmed under quasi-parallel magnetic conditions for the first time, contradicting the established magnetic dependence of electron accele...

Masters, A; Fujimoto, M; Schwartz, S J; Sergis, N; Thomsen, M F; Retinò, A; Hasegawa, H; Lewis, G R; Coates, A J; Canu, P; Dougherty, M K

2013-01-01

409

We develop a Markov process theory of charged particle scattering from stationary, transverse, magnetic waves. We examine approximations that lead to quasilinear theory, in particular the resonant diffusion approximation. We find that, when appropriate, the resonant diffusion approximation simplifies the result of the weak turbulence approximation without significant further restricting the regime of applicability. We also explore a theory generated by expanding drift and diffusion rates in terms of a presumed small correlation time. This small correlation time expansion leads to results valid for relatively small pitch angle and large wave energy density - a regime that may govern pitch angle scattering of high-energy electrons into the geomagnetic loss cone.

Lemons, Don S. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2012-01-15

410

NASA Astrophysics Data System (ADS)

The nonlinear propagation of quantum ion acoustic wave (QIAW) is investigated in a four-component plasma composed of warm classical positive ions and negative ions, as well as inertialess relativistically degenerate electrons and positrons. A nonlinear Schrödinger equation is derived by using the reductive perturbation method, which governs the dynamics of QIAW packets. The modulation instability analysis of QIAWs is considered based on the typical parameters of the white dwarf. The results exhibit that both in the weakly relativistic limit and in the ultrarelativistic limit, the modulational instability regions are sensitively dependent on the ratios of temperature and number density of negative ions to those of positive ions respectively, and on the relativistically degenerate effect as well. Project supported by the National Natural Science Foundation of China (Grant No. 11104012) and the Fundamental Research Funds for the Central Universities (Grant Nos. FRF-TP-09-019A and FRF-BR-11-031B).

Liu, Tie-Lu; Wang, Yun-Liang; Lu, Yan-Zhen

2015-02-01

411

The problem of structure formation in relativistic dissipative fluids was analyzed in a previous work within Eckart's framework, in which the heat flux is coupled to the hydrodynamic acceleration, additional to the usual temperature gradient term. It was shown that in such case, the pathological behavior of fluctuations leads to the disapperance of the gravitational instability responsible for structure formation. In the present work the problem is revisited now using a constitutive equation derived from relativistic kinetic theory. The new relation, in which the heat flux is not coupled to the hydrodynamic acceleration, leads to a consistent first order in the gradients formalism. In this case the gravitational instability remains, and only relativistic corrections to the Jeans wave number are obtained. In the calculation here shown the non-relativistc limit is recovered, opposite to what happens in Eckart's case.

J. H. Mondragon-Suarez; A. Sandoval-Villalbazo; A. L. Garcia-Perciante

2012-01-21

412

NASA Astrophysics Data System (ADS)

We present a new periodic all-metal slow wave structure, a coaxial step-disc-loaded system and the dispersion characteristics of the structure. By using the field-matching method, the dispersion equation and the coupling impedance of this structure are obtained. The coaxial structure makes the bandwidth broader than that of the non-coaxial one. Compared with the coaxial disc-loaded and ridged-disc-loaded structures, the pass-band of coaxial step-disc-loaded structure is the broadest. The calculation results show that increasing the step width and decreasing the step thickness can improve the bandwidth.

Yue, Ling-Na; Wang, Wen-Xiang; Wei, Yan-Yu; Gong, Yu-Bin

2005-03-01

413

Linearly polarized waves with constant phase velocity in relativistic T. C. Pescha

relations for wave propagation that are valid in the whole regime from weak up to ultrarelativistic laser-critical density plasmas. The relationship of the present results with previous work is discussed in detail. One major result is the demonstration of symmetry breaking of the orbit in the transition regime between low

Kull, Hans-Jörg

414

The framework of relativistic self-consistent mean-field models is extended to include correlations related to the restoration of broken symmetries and to fluctuations of collective variables. The generator coordinate method is used to perform configuration mixing of angular-momentum and particle-number projected relativistic wave functions. The geometry is restricted to axially symmetric shapes, and the intrinsic wave functions are generated from the solutions of the relativistic mean-field+Lipkin-Nogami BCS equations, with a constraint on the mass quadrupole moment. The model employs a relativistic point-coupling (contact) nucleon-nucleon effective interaction in the particle-hole channel, and a density-independent {delta}-interaction in the pairing channel. Illustrative calculations are performed for {sup 24}Mg, {sup 32}S, and {sup 36}Ar, and compared with results obtained employing the model developed in the first part of this work, i.e., without particle-number projection, as well as with the corresponding nonrelativistic models based on Skyrme and Gogny effective interactions.

Niksic, T.; Vretenar, D.; Ring, P. [Physics Department, Faculty of Science, University of Zagreb (Croatia) and Physik-Department der Technischen Universitaet Muenchen, D-85748 Garching (Germany); Physik-Department der Technischen Universitaet Muenchen, D-85748 Garching (Germany)

2006-12-15

415

Initial studies of a long-pulse relativistic backward-wave oscillator utilizing a disk cathode

One of the major issues in high-power microwave device operation is pulse shortening, which often limits microwave pulses to less than 100 ns. This has been the focus of many studies on the long-pulse backward-wave oscillator (BWO) at the University of New Mexico. Previous diagnostics have indicated that significant plasma is produced by a graphite knife-edge or \\

Kelly Hahn; Mikhail I. Fuks; Edl Schamiloglu

2002-01-01

416

Relativistic distorted-wave collision strengths have been calculated for the 49 ?n=0 optically allowed transitions with n=2 in the 67 B-like ions with nuclear charge number Z in the range 26?Z?92. The calculations were made for the four final, or scattered, electron energies E{sup ?}=0.20, 0.42, 0.80, and 1.40, where E{sup ?} is in units of Z{sub eff}{sup 2} Ry with Z{sub eff}=Z?3.33. In the present calculations, an improved “top-up” method, which employs relativistic plane waves, was used to obtain the high partial-wave contribution for each transition, in contrast to the partial-relativistic Coulomb–Bethe approximation used in previous work by Zhang and Sampson [H.L. Zhang and D.H. Sampson, At. Data Nucl. Data Tables 56 (1994) 41]. In that earlier work, collision strengths were also provided for B-like ions, but for a more comprehensive data set consisting of all 105 ?n=0 transitions, six scattered energies and the 85 ions with Z in the range 8?Z?92. The collision strengths covered in the present work should be more accurate than the corresponding data given by Zhang and Sampson [H.L. Zhang and D.H. Sampson, At. Data Nucl. Data Tables 56 (1994) 41] and are presented here to replace those earlier results.

Fontes, Christopher J., E-mail: cjf@lanl.gov; Zhang, Hong Lin

2014-05-15

417

The reductive perturbation method is used to derive a generic form of nonlinear Schroedinger equation (NLSE) that describes the nonlinear evolution of electrostatic (ES)/electromagnetic (EM) waves in fully relativistic two-fluid plasmas. The matrix eigenvector analysis shows that there are two mutually exclusive modes of waves, each mode involving only either one of two electric potentials, A and {phi}. The general result is applied to the electromagnetic mode in electron-ion plasmas with relativistically high electron temperature (T{sub e} Much-Greater-Than m{sub e}c{sup 2}). In the limit of high frequency (ck Much-Greater-Than {omega}{sub e}), the NLSE predicts bump type electromagnetic soliton structures having width scaling as {approx}kT{sub e}{sup 5/2}. It is shown that, in electron-positron pair plasmas with high temperature, dip type electromagnetic solitons can exist. The NLSE is also applied to electrostatic (Langmuir) wave and it is shown that dip type solitons can exist if k{lambda}{sub D} Much-Less-Than 1, where {lambda}{sub D} is the electron's Debye length. For the k{lambda}{sub D} Much-Greater-Than 1, however, the solution is of bump type soliton with width scaling as {approx}1/(k{sup 5}T{sub e}). It is also shown that dip type solitons can exist in cold plasmas having relativistically high streaming speed.

Lee, Nam C. [Department of Physics, Pusan National University, Busan 609-735 (Korea, Republic of)

2012-08-15

418

This paper discusses the role of the discovery and analysis of the first binary pulsar in settling the long-running quadrupole formula controversy over the status of gravitational waves as a prediction of general relativity. It also discusses how we should understand the resolution of this controversy in the context of the so-called science wars. In other words it discusses whether concepts such as interpretive flexibility and the experimenters' regress can shed light on what can also be seen as a classical confirmation of realist expectations, in which a theoretical controversy is settled by a conclusive experiment.

Kennefick, Daniel

2014-01-01

419

We solve the relativistic Riemann problem in viscous matter using the relativistic Boltzmann equation and the relativistic causal dissipative fluid-dynamical approach of Israel and Stewart. Comparisons between these two approaches clarify and point out the regime of validity of second-order fluid dynamics in relativistic shock phenomena. The transition from ideal to viscous shocks is demonstrated by varying the shear viscosity to entropy density ratio {eta}/s. We also find that a good agreement between these two approaches requires a Knudsen number Kn<1/2.

Bouras, I.; El, A.; Fochler, O.; Greiner, C. [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, Max-von-Laue-Strasse 1, D-60438 Frankfurt am Main (Germany); Molnar, E. [Frankfurt Institute for Advanced Studies, Ruth-Moufang-Strasse 1, D-60438 Frankfurt am Main (Germany); KFKI, Research Institute of Particle and Nuclear Physics, H-1525 Budapest, P.O. Box 49 (Hungary); Niemi, H. [Frankfurt Institute for Advanced Studies, Ruth-Moufang-Strasse 1, D-60438 Frankfurt am Main (Germany); Xu, Z.; Rischke, D. H. [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, Max-von-Laue-Strasse 1, D-60438 Frankfurt am Main (Germany); Frankfurt Institute for Advanced Studies, Ruth-Moufang-Strasse 1, D-60438 Frankfurt am Main (Germany)

2010-08-15

420

Cosmological shells and blast waves

NASA Technical Reports Server (NTRS)

It is argued that cosmic explosions could have produced significant amounts of large-scale structure in the cosmic microwave background (CMB). Observations appear to indicate the presence of bubblelike structures with radii suggesting that positive energy perturbations were more prevalent than negative energy perturbations, since the latter would produce a prevalence of clusterlke irregularities. Energy input from processes occurring during galaxy formation and releasing about 10 to the 61st-62nd ergs per event would not overly disturb the CMB. The merging of bubbles typically resulting in bubbles with radii of roughly (10-20)/h x Mpc also would not affect the CMB. If much larger bubbles of radii 50-100 Mpc exist, a different energy input is likely to be the cause.

Ostriker, Jeremiah P.

1986-01-01

421

Blast wave from buried charges

While much airblast data are available for height-of-burst (HOB) effects, systematic airblast data for depth-of-burst (DOB) effects are more limited. It is logical to ask whether the spherical 0.5-g Nitropenta charges that, proved to be successful for HOB tests at EMI are also suitable for experiments with buried charges in the laboratory scale; preliminary studies indicated in the alternative. Of special interest is the airblast environment generated by detonations just above or below the around surface. This paper presents a brief summary of the test results.

Reichenbach, H.; Behrens, K. [Fraunhofer-Institut fuer Kurzzeitdynamik - Ernst-Mach-Institut (EMI), Freiburg im Breisgau (Germany); Kuhl, A.L. [Lawrence Livermore National Lab., El Segundo, CA (United States)

1993-08-01

422

A multi-mode shock tube for investigation of blast-induced traumatic brain injury.

Blast-induced mild traumatic brain injury (bTBI) has become increasingly common in recent military conflicts. The mechanisms by which non-impact blast exposure results in bTBI are incompletely understood. Current small animal bTBI models predominantly utilize compressed air-driven membrane rupture as their blast wave source, while large animal models use chemical explosives. The pressure-time signature of each blast mode is unique, making it difficult to evaluate the contributions of the different components of the blast wave to bTBI when using a single blast source. We utilized a multi-mode shock tube, the McMillan blast device, capable of utilizing compressed air- and compressed helium-driven membrane rupture, and the explosives oxyhydrogen and cyclotrimethylenetrinitramine (RDX, the primary component of C-4 plastic explosives) as the driving source. At similar maximal blast overpressures, the positive pressure phase of compressed air-driven blasts was longer, and the positive impulse was greater, than those observed for shockwaves produced by other driving sources. Helium-driven shockwaves more closely resembled RDX blasts, but by displacing air created a hypoxic environment within the shock tube. Pressure-time traces from oxyhydrogen-driven shockwaves were very similar those produced by RDX, although they resulted in elevated carbon monoxide levels due to combustion of the polyethylene bag used to contain the gases within the shock tube prior to detonation. Rats exposed to compressed air-driven blasts had more pronounced vascular damage than those exposed to oxyhydrogen-driven blasts of the same peak overpressure, indicating that differences in blast wave characteristics other than peak overpressure may influence the extent of bTBI. Use of this multi-mode shock tube in small animal models will enable comparison of the extent of brain injury with the pressure-time signature produced using each blast mode, facilitating evaluation of the blast wave components contributing to bTBI. PMID:21083431

Reneer, Dexter V; Hisel, Richard D; Hoffman, Joshua M; Kryscio, Richard J; Lusk, Braden T; Geddes, James W

2011-01-01

423

A Multi-Mode Shock Tube for Investigation of Blast-Induced Traumatic Brain Injury

Abstract Blast-induced mild traumatic brain injury (bTBI) has become increasingly common in recent military conflicts. The mechanisms by which non-impact blast exposure results in bTBI are incompletely understood. Current small animal bTBI models predominantly utilize compressed air-driven membrane rupture as their blast wave source, while large animal models use chemical explosives. The pressure-time signature of each blast mode is unique, making it difficult to evaluate the contributions of the different components of the blast wave to bTBI when using a single blast source. We utilized a multi-mode shock tube, the McMillan blast device, capable of utilizing compressed air- and compressed helium-driven membrane rupture, and the explosives oxyhydrogen and cyclotrimethylenetrinitramine (RDX, the primary component of C-4 plastic explosives) as the driving source. At similar maximal blast overpressures, the positive pressure phase of compressed air-driven blasts was longer, and the positive impulse was greater, than those observed for shockwaves produced by other driving sources. Helium-driven shockwaves more closely resembled RDX blasts, but by displacing air created a hypoxic environment within the shock tube. Pressure-time traces from oxyhydrogen-driven shockwaves were very similar those produced by RDX, although they resulted in elevated carbon monoxide levels due to combustion of the polyethylene bag used to contain the gases within the shock tube prior to detonation. Rats exposed to compressed air-driven blasts had more pronounced vascular damage than those exposed to oxyhydrogen-driven blasts of the same peak overpressure, indicating that differences in blast wave characteristics other than peak overpressure may influence the extent of bTBI. Use of this multi-mode shock tube in small animal models will enable comparison of the extent of brain injury with the pressure-time signature produced using each blast mode, facilitating evaluation of the blast wave components contributing to bTBI. PMID:21083431

Reneer, Dexter V.; Hisel, Richard D.; Hoffman, Joshua M.; Kryscio, Richard J.; Lusk, Braden T.

2011-01-01

424

NASA Astrophysics Data System (ADS)

Relativistic jets can be modeled as magnetohydrodynamic flows. We analyze the related equations and discuss the involved acceleration mechanisms, their relation to the collimation, to the jet confinement by its environment, and to possible rarefaction waves triggered by pressure imbalances.

Vlahakis, Nektarios

425

MONTE CARLO SIMULATIONS OF NONLINEAR PARTICLE ACCELERATION IN PARALLEL TRANS-RELATIVISTIC SHOCKS

We present results from a Monte Carlo simulation of a parallel collisionless shock undergoing particle acceleration. Our simulation, which contains parameterized scattering and a particular thermal leakage injection model, calculates the feedback between accelerated particles ahead of the shock, which influence the shock precursor and 'smooth' the shock, and thermal particle injection. We show that there is a transition between nonrelativistic shocks, where the acceleration efficiency can be extremely high and the nonlinear compression ratio can be substantially greater than the Rankine-Hugoniot value, and fully relativistic shocks, where diffusive shock acceleration is less efficient and the compression ratio remains at the Rankine-Hugoniot value. This transition occurs in the trans-relativistic regime and, for the particular parameters we use, occurs around a shock Lorentz factor ?{sub 0} = 1.5. We also find that nonlinear shock smoothing dramatically reduces the acceleration efficiency presumed to occur with large-angle scattering in ultra-relativistic shocks. Our ability to seamlessly treat the transition from ultra-relativistic to trans-relativistic to nonrelativistic shocks may be important for evolving relativistic systems, such as gamma-ray bursts and Type Ibc supernovae. We expect a substantial evolution of shock accelerated spectra during this transition from soft early on to much harder when the blast-wave shock becomes nonrelativistic.

Ellison, Donald C.; Warren, Donald C. [Physics Department, North Carolina State University, Box 8202, Raleigh, NC 27695 (United States); Bykov, Andrei M., E-mail: don_ellison@ncsu.edu, E-mail: ambykov@yahoo.com [Ioffe Institute for Physics and Technology, 194021 St. Petersburg (Russian Federation)

2013-10-10

426

Porcine head response to blast

Recent studies have shown an increase in the frequency of traumatic brain injuries related to blast exposure. However, the mechanisms that cause blast neurotrauma are unknown. Blast neurotrauma research using computational ...

Nyein, Michelle K.

427

Experimental work is underway by a SLAC-LLNL-LBL collaboration to investigate the feasibility of using relativistic klystrons as a power source for future high gradient accelerators. Two different relativistic klystron configurations have been built and tested to date: a high grain multicavity klystron at 11.4 GHz and a low gain two cavity subharmonic buncher driven at 5.7 GHz. In both configurations power is extracted at 11.4 GHz. In order to understand the basic physics issues involved in extracting RF from a high power beam, we have used both a single resonant cavity and a multi-cell traveling wave structure for energy extraction. We have learned how to overcome our previously reported problem of high power RF pulse shortening, and have achieved peak RF power levels of 170 MW with the RF pulse of the same duration as the beam current pulse. 6 refs., 3 f