Particle acceleration at shocks in the inner heliosphere

NASA Astrophysics Data System (ADS)

Parker, Linda Neergaard

This dissertation describes a study of particle acceleration at shocks via the diffusive shock acceleration mechanism. Results for particle acceleration at both quasi-parallel and quasi-perpendicular shocks are presented to address the question of whether there are sufficient particles in the solar wind thermal core, modeled as either a Maxwellian or kappa- distribution, to account for the observed accelerated spectrum. Results of accelerating the theoretical upstream distribution are compared to energetic observations at 1 AU. It is shown that the particle distribution in the solar wind thermal core is sufficient to explain the accelerated particle spectrum downstream of the shock, although the shape of the downstream distribution in some cases does not follow completely the theory of diffusive shock acceleration, indicating possible additional processes at work in the shock for these cases. Results show good to excellent agreement between the theoretical and observed spectral index for one third to one half of both quasi-parallel and quasi-perpendicular shocks studied herein. Coronal mass ejections occurring during periods of high solar activity surrounding solar maximum can produce shocks in excess of 3-8 shocks per day. During solar minimum, diffusive shock acceleration at shocks can generally be understood on the basis of single independent shocks and no other shock necessarily influences the diffusive shock acceleration mechanism. In this sense, diffusive shock acceleration during solar minimum may be regarded as Markovian. By contrast, diffusive shock acceleration of particles at periods of high solar activity (e.g. solar maximum) see frequent, closely spaced shocks that include the effects of particle acceleration at preceding and following shocks. Therefore, diffusive shock acceleration of particles at solar maximum cannot be modeled on the basis of diffusive shock acceleration as a single, independent shock and the process is essentially non-Markovian. A multiple shock model is developed based in part on the box model of (Protheroe and Stanev, 1998; Moraal and Axford, 1983; Ball and Kirk, 1992; Drury et al. 1999) that accelerates particles at multiple shocks and decompresses the particles between shocks via two methods. The first method of decompression is based on the that used by Melrose and Pope (1993), which adiabatically decompresses particles between shocks. The second method solves the cosmic ray transport equation and adiabatically decompresses between shocks and includes the loss of particles through convection and diffusion. The transport method allows for the inclusion of a temporal variability and thus allows for a more representative frequency distribution of shocks. The transport method of decompression and loss is used to accelerate particles at seventy-three shocks in a thirty day time period. Comparisons with observations taken at 1 AU during the same time period are encouraging as the model is able to reproduce the observed amplitude of the accelerated particles and in part the variability. This work provides the basis for developing more sophisticated models that can be applied to a suite of observations

A comparison/validation of a fractional derivative model with an empirical model of non-linear shock waves in swelling shales

NASA Astrophysics Data System (ADS)

Droghei, Riccardo; Salusti, Ettore

2013-04-01

Control of drilling parameters, as fluid pressure, mud weight, salt concentration is essential to avoid instabilities when drilling through shale sections. To investigate shale deformation, fundamental for deep oil drilling and hydraulic fracturing for gas extraction ("fracking"), a non-linear model of mechanic and chemo-poroelastic interactions among fluid, solute and the solid matrix is here discussed. The two equations of this model describe the isothermal evolution of fluid pressure and solute density in a fluid saturated porous rock. Their solutions are quick non-linear Burger's solitary waves, potentially destructive for deep operations. In such analysis the effect of diffusion, that can play a particular role in fracking, is investigated. Then, following Civan (1998), both diffusive and shock waves are applied to fine particles filtration due to such quick transients , their effect on the adjacent rocks and the resulting time-delayed evolution. Notice how time delays in simple porous media dynamics have recently been analyzed using a fractional derivative approach. To make a tentative comparison of these two deeply different methods,in our model we insert fractional time derivatives, i.e. a kind of time-average of the fluid-rocks interactions. Then the delaying effects of fine particles filtration is compared with fractional model time delays. All this can be seen as an empirical check of these fractional models.

CRASH: A BLOCK-ADAPTIVE-MESH CODE FOR RADIATIVE SHOCK HYDRODYNAMICS-IMPLEMENTATION AND VERIFICATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van der Holst, B.; Toth, G.; Sokolov, I. V.

We describe the Center for Radiative Shock Hydrodynamics (CRASH) code, a block-adaptive-mesh code for multi-material radiation hydrodynamics. The implementation solves the radiation diffusion model with a gray or multi-group method and uses a flux-limited diffusion approximation to recover the free-streaming limit. Electrons and ions are allowed to have different temperatures and we include flux-limited electron heat conduction. The radiation hydrodynamic equations are solved in the Eulerian frame by means of a conservative finite-volume discretization in either one-, two-, or three-dimensional slab geometry or in two-dimensional cylindrical symmetry. An operator-split method is used to solve these equations in three substeps: (1)more » an explicit step of a shock-capturing hydrodynamic solver; (2) a linear advection of the radiation in frequency-logarithm space; and (3) an implicit solution of the stiff radiation diffusion, heat conduction, and energy exchange. We present a suite of verification test problems to demonstrate the accuracy and performance of the algorithms. The applications are for astrophysics and laboratory astrophysics. The CRASH code is an extension of the Block-Adaptive Tree Solarwind Roe Upwind Scheme (BATS-R-US) code with a new radiation transfer and heat conduction library and equation-of-state and multi-group opacity solvers. Both CRASH and BATS-R-US are part of the publicly available Space Weather Modeling Framework.« less

Driven waves in a two-fluid plasma

NASA Astrophysics Data System (ADS)

Roberge, W. G.; Ciolek, Glenn E.

2007-12-01

We study the physics of wave propagation in a weakly ionized plasma, as it applies to the formation of multifluid, magnetohydrodynamics (MHD) shock waves. We model the plasma as separate charged and neutral fluids which are coupled by ion-neutral friction. At times much less than the ion-neutral drag time, the fluids are decoupled and so evolve independently. At later times, the evolution is determined by the large inertial mismatch between the charged and neutral particles. The neutral flow continues to evolve independently; the charged flow is driven by and slaved to the neutral flow by friction. We calculate this driven flow analytically by considering the special but realistic case where the charged fluid obeys linearized equations of motion. We carry out an extensive analysis of linear, driven, MHD waves. The physics of driven MHD waves is embodied in certain Green functions which describe wave propagation on short time-scales, ambipolar diffusion on long time-scales and transitional behaviour at intermediate times. By way of illustration, we give an approximate solution for the formation of a multifluid shock during the collision of two identical interstellar clouds. The collision produces forward and reverse J shocks in the neutral fluid and a transient in the charged fluid. The latter rapidly evolves into a pair of magnetic precursors on the J shocks, wherein the ions undergo force-free motion and the magnetic field grows monotonically with time. The flow appears to be self-similar at the time when linear analysis ceases to be valid.

Modeling of Particle Acceleration at Multiple Shocks via Diffusive Shock Acceleration: Preliminary Results

NASA Technical Reports Server (NTRS)

Parker, L. Neergaard; Zank, G. P.

2013-01-01

Successful forecasting of energetic particle events in space weather models require algorithms for correctly predicting the spectrum of ions accelerated from a background population of charged particles. We present preliminary results from a model that diffusively accelerates particles at multiple shocks. Our basic approach is related to box models in which a distribution of particles is diffusively accelerated inside the box while simultaneously experiencing decompression through adiabatic expansion and losses from the convection and diffusion of particles outside the box. We adiabatically decompress the accelerated particle distribution between each shock by either the method explored in Melrose and Pope (1993) and Pope and Melrose (1994) or by the approach set forth in Zank et al. (2000) where we solve the transport equation by a method analogous to operator splitting. The second method incorporates the additional loss terms of convection and diffusion and allows for the use of a variable time between shocks. We use a maximum injection energy (E(sub max)) appropriate for quasi-parallel and quasi-perpendicular shocks and provide a preliminary application of the diffusive acceleration of particles by multiple shocks with frequencies appropriate for solar maximum (i.e., a non-Markovian process).

Modeling of Particle Acceleration at Multiple Shocks Via Diffusive Shock Acceleration: Preliminary Results

NASA Technical Reports Server (NTRS)

Parker, Linda Neergaard; Zank, Gary P.

2013-01-01

We present preliminary results from a model that diffusively accelerates particles at multiple shocks. Our basic approach is related to box models (Protheroe and Stanev, 1998; Moraal and Axford, 1983; Ball and Kirk, 1992; Drury et al., 1999) in which a distribution of particles is diffusively accelerated inside the box while simultaneously experiencing decompression through adiabatic expansion and losses from the convection and diffusion of particles outside the box (Melrose and Pope, 1993; Zank et al., 2000). We adiabatically decompress the accelerated particle distribution between each shock by either the method explored in Melrose and Pope (1993) and Pope and Melrose (1994) or by the approach set forth in Zank et al. (2000) where we solve the transport equation by a method analogous to operator splitting. The second method incorporates the additional loss terms of convection and diffusion and allows for the use of a variable time between shocks. We use a maximum injection energy (Emax) appropriate for quasi-parallel and quasi-perpendicular shocks (Zank et al., 2000, 2006; Dosch and Shalchi, 2010) and provide a preliminary application of the diffusive acceleration of particles by multiple shocks with frequencies appropriate for solar maximum (i.e., a non-Markovian process).

Monte Carlo simulations of particle acceleration at oblique shocks: Including cross-field diffusion

NASA Technical Reports Server (NTRS)

Baring, M. G.; Ellison, D. C.; Jones, F. C.

1995-01-01

The Monte Carlo technique of simulating diffusive particle acceleration at shocks has made spectral predictions that compare extremely well with particle distributions observed at the quasi-parallel region of the earth's bow shock. The current extension of this work to compare simulation predictions with particle spectra at oblique interplanetary shocks has required the inclusion of significant cross-field diffusion (strong scattering) in the simulation technique, since oblique shocks are intrinsically inefficient in the limit of weak scattering. In this paper, we present results from the method we have developed for the inclusion of cross-field diffusion in our simulations, namely model predictions of particle spectra downstream of oblique subluminal shocks. While the high-energy spectral index is independent of the shock obliquity and the strength of the scattering, the latter is observed to profoundly influence the efficiency of injection of cosmic rays into the acceleration process.

Diffusive shock acceleration - Acceleration rate, magnetic-field direction and the diffusion limit

NASA Technical Reports Server (NTRS)

Jokipii, J. R.

1992-01-01

This paper reviews the concept of diffusive shock acceleration, showing that the acceleration of charged particles at a collisionless shock is a straightforward consequence of the standard cosmic-ray transport equation, provided that one treats the discontinuity at the shock correctly. This is true for arbitrary direction of the upstream magnetic field. Within this framework, it is shown that acceleration at perpendicular or quasi-perpendicular shocks is generally much faster than for parallel shocks. Paradoxically, it follows also that, for a simple scattering law, the acceleration is faster for less scattering or larger mean free path. Obviously, the mean free path can not become too large or the diffusion limit becomes inapplicable. Gradient and curvature drifts caused by the magnetic-field change at the shock play a major role in the acceleration process in most cases. Recent observations of the charge state of the anomalous component are shown to require the faster acceleration at the quasi-perpendicular solar-wind termination shock.

Implications of pressure diffusion for shock waves

NASA Technical Reports Server (NTRS)

Ram, Ram Bachan

1989-01-01

The report deals with the possible implications of pressure diffusion for shocks in one dimensional traveling waves in an ideal gas. From this new hypothesis all aspects of such shocks can be calculated except shock thickness. Unlike conventional shock theory, the concept of entropy is not needed or used. Our analysis shows that temperature rises near a shock, which is of course an experimental fact; however, it also predicts that very close to a shock, density increases faster than pressure. In other words, a shock itself is cold.

Modeling Particle Acceleration and Transport at a 2-D CME-Driven Shock

NASA Astrophysics Data System (ADS)

Hu, Junxiang; Li, Gang; Ao, Xianzhi; Zank, Gary P.; Verkhoglyadova, Olga

2017-11-01

We extend our earlier Particle Acceleration and Transport in the Heliosphere (PATH) model to study particle acceleration and transport at a coronal mass ejection (CME)-driven shock. We model the propagation of a CME-driven shock in the ecliptic plane using the ZEUS-3D code from 20 solar radii to 2 AU. As in the previous PATH model, the initiation of the CME-driven shock is simplified and modeled as a disturbance at the inner boundary. Different from the earlier PATH model, the disturbance is now longitudinally dependent. Particles are accelerated at the 2-D shock via the diffusive shock acceleration mechanism. The acceleration depends on both the parallel and perpendicular diffusion coefficients κ|| and κ⊥ and is therefore shock-obliquity dependent. Following the procedure used in Li, Shalchi, et al. (k href="#jgra53857-bib-0045"/>), we obtain the particle injection energy, the maximum energy, and the accelerated particle spectra at the shock front. Once accelerated, particles diffuse and convect in the shock complex. The diffusion and convection of these particles are treated using a refined 2-D shell model in an approach similar to Zank et al. (k href="#jgra53857-bib-0089"/>). When particles escape from the shock, they propagate along and across the interplanetary magnetic field. The propagation is modeled using a focused transport equation with the addition of perpendicular diffusion. We solve the transport equation using a backward stochastic differential equation method where adiabatic cooling, focusing, pitch angle scattering, and cross-field diffusion effects are all included. Time intensity profiles and instantaneous particle spectra as well as particle pitch angle distributions are shown for two example CME shocks.

Magnetic Fields Recorded by Chondrules Formed in Nebular Shocks

NASA Astrophysics Data System (ADS)

Mai, Chuhong; Desch, Steven J.; Boley, Aaron C.; Weiss, Benjamin P.

2018-04-01

Recent laboratory efforts have constrained the remanent magnetizations of chondrules and the magnetic field strengths to which the chondrules were exposed as they cooled below their Curie points. An outstanding question is whether the inferred paleofields represent the background magnetic field of the solar nebula or were unique to the chondrule-forming environment. We investigate the amplification of the magnetic field above background values for two proposed chondrule formation mechanisms, large-scale nebular shocks and planetary bow shocks. Behind large-scale shocks, the magnetic field parallel to the shock front is amplified by factors of ∼10–30, regardless of the magnetic diffusivity. Therefore, chondrules melted in these shocks probably recorded an amplified magnetic field. Behind planetary bow shocks, the field amplification is sensitive to the magnetic diffusivity. We compute the gas properties behind a bow shock around a 3000 km radius planetary embryo, with and without atmospheres, using hydrodynamics models. We calculate the ionization state of the hot, shocked gas, including thermionic emission from dust, thermal ionization of gas-phase potassium atoms, and the magnetic diffusivity due to Ohmic dissipation and ambipolar diffusion. We find that the diffusivity is sufficiently large that magnetic fields have already relaxed to background values in the shock downstream where chondrules acquire magnetizations, and that these locations are sufficiently far from the planetary embryos that chondrules should not have recorded a significant putative dynamo field generated on these bodies. We conclude that, if melted in planetary bow shocks, chondrules probably recorded the background nebular field.

An experimental investigation of compressible three-dimensional boundary layer flow in annular diffusers

NASA Technical Reports Server (NTRS)

Om, Deepak; Childs, Morris E.

1987-01-01

An experimental study is described in which detailed wall pressure measurements have been obtained for compressible three-dimensional unseparated boundary layer flow in annular diffusers with and without normal shock waves. Detailed mean flow-field data were also obtained for the diffuser flow without a shock wave. Two diffuser flows with shock waves were investigated. In one case, the normal shock existed over the complete annulus whereas in the second case, the shock existed over a part of the annulus. The data obtained can be used to validate computational codes for predicting such flow fields. The details of the flow field without the shock wave show flow reversal in the circumferential direction on both inner and outer surfaces. However, there is a lag in the flow reversal between the inner nad the outer surfaces. This is an interesting feature of this flow and should be a good test for the computational codes.

The Advanced Composition Explorer Shock Database and Application to Particle Acceleration Theory

NASA Technical Reports Server (NTRS)

Parker, L. Neergaard; Zank, G. P.

2015-01-01

The theory of particle acceleration via diffusive shock acceleration (DSA) has been studied in depth by Gosling et al. (1981), van Nes et al. (1984), Mason (2000), Desai et al. (2003), Zank et al. (2006), among many others. Recently, Parker and Zank (2012, 2014) and Parker et al. (2014) using the Advanced Composition Explorer (ACE) shock database at 1 AU explored two questions: does the upstream distribution alone have enough particles to account for the accelerated downstream distribution and can the slope of the downstream accelerated spectrum be explained using DSA? As was shown in this research, diffusive shock acceleration can account for a large population of the shocks. However, Parker and Zank (2012, 2014) and Parker et al. (2014) used a subset of the larger ACE database. Recently, work has successfully been completed that allows for the entire ACE database to be considered in a larger statistical analysis. We explain DSA as it applies to single and multiple shocks and the shock criteria used in this statistical analysis. We calculate the expected injection energy via diffusive shock acceleration given upstream parameters defined from the ACE Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) data to construct the theoretical upstream distribution. We show the comparison of shock strength derived from diffusive shock acceleration theory to observations in the 50 keV to 5 MeV range from an instrument on ACE. Parameters such as shock velocity, shock obliquity, particle number, and time between shocks are considered. This study is further divided into single and multiple shock categories, with an additional emphasis on forward-forward multiple shock pairs. Finally with regard to forward-forward shock pairs, results comparing injection energies of the first shock, second shock, and second shock with previous energetic population will be given.

The Advanced Composition Explorer Shock Database and Application to Particle Acceleration Theory

NASA Technical Reports Server (NTRS)

Parker, L. Neergaard; Zank, G. P.

2015-01-01

The theory of particle acceleration via diffusive shock acceleration (DSA) has been studied in depth by Gosling et al. (1981), van Nes et al. (1984), Mason (2000), Desai et al. (2003), Zank et al. (2006), among many others. Recently, Parker and Zank (2012, 2014) and Parker et al. (2014) using the Advanced Composition Explorer (ACE) shock database at 1 AU explored two questions: does the upstream distribution alone have enough particles to account for the accelerated downstream distribution and can the slope of the downstream accelerated spectrum be explained using DSA? As was shown in this research, diffusive shock acceleration can account for a large population of the shocks. However, Parker and Zank (2012, 2014) and Parker et al. (2014) used a subset of the larger ACE database. Recently, work has successfully been completed that allows for the entire ACE database to be considered in a larger statistical analysis. We explain DSA as it applies to single and multiple shocks and the shock criteria used in this statistical analysis. We calculate the expected injection energy via diffusive shock acceleration given upstream parameters defined from the ACE Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) data to construct the theoretical upstream distribution. We show the comparison of shock strength derived from diffusive shock acceleration theory to observations in the 50 keV to 5 MeV range from an instrument on ACE. Parameters such as shock velocity, shock obliquity, particle number, and time between shocks are considered. This study is further divided into single and multiple shock categories, with an additional emphasis on forward-forward multiple shock pairs. Finally with regard to forwardforward shock pairs, results comparing injection energies of the first shock, second shock, and second shock with previous energetic population will be given.

A hybrid numerical fluid dynamics code for resistive magnetohydrodynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Jeffrey

2006-04-01

Spasmos is a computational fluid dynamics code that uses two numerical methods to solve the equations of resistive magnetohydrodynamic (MHD) flows in compressible, inviscid, conducting media[1]. The code is implemented as a set of libraries for the Python programming language[2]. It represents conducting and non-conducting gases and materials with uncomplicated (analytic) equations of state. It supports calculations in 1D, 2D, and 3D geometry, though only the 1D configuation has received significant testing to date. Because it uses the Python interpreter as a front end, users can easily write test programs to model systems with a variety of different numerical andmore » physical parameters. Currently, the code includes 1D test programs for hydrodynamics (linear acoustic waves, the Sod weak shock[3], the Noh strong shock[4], the Sedov explosion[5], magnetic diffusion (decay of a magnetic pulse[6], a driven oscillatory "wine-cellar" problem[7], magnetic equilibrium), and magnetohydrodynamics (an advected magnetic pulse[8], linear MHD waves, a magnetized shock tube[9]). Spasmos current runs only in a serial configuration. In the future, it will use MPI for parallel computation.« less

Multidimensional FEM-FCT schemes for arbitrary time stepping

NASA Astrophysics Data System (ADS)

Kuzmin, D.; Möller, M.; Turek, S.

2003-05-01

The flux-corrected-transport paradigm is generalized to finite-element schemes based on arbitrary time stepping. A conservative flux decomposition procedure is proposed for both convective and diffusive terms. Mathematical properties of positivity-preserving schemes are reviewed. A nonoscillatory low-order method is constructed by elimination of negative off-diagonal entries of the discrete transport operator. The linearization of source terms and extension to hyperbolic systems are discussed. Zalesak's multidimensional limiter is employed to switch between linear discretizations of high and low order. A rigorous proof of positivity is provided. The treatment of non-linearities and iterative solution of linear systems are addressed. The performance of the new algorithm is illustrated by numerical examples for the shock tube problem in one dimension and scalar transport equations in two dimensions.

Modeling of Particle Acceleration at Multiple Shocks Via Diffusive Shock Acceleration: Preliminary Results

NASA Astrophysics Data System (ADS)

Parker, L. N.; Zank, G. P.

2013-12-01

Successful forecasting of energetic particle events in space weather models require algorithms for correctly predicting the spectrum of ions accelerated from a background population of charged particles. We present preliminary results from a model that diffusively accelerates particles at multiple shocks. Our basic approach is related to box models (Protheroe and Stanev, 1998; Moraal and Axford, 1983; Ball and Kirk, 1992; Drury et al., 1999) in which a distribution of particles is diffusively accelerated inside the box while simultaneously experiencing decompression through adiabatic expansion and losses from the convection and diffusion of particles outside the box (Melrose and Pope, 1993; Zank et al., 2000). We adiabatically decompress the accelerated particle distribution between each shock by either the method explored in Melrose and Pope (1993) and Pope and Melrose (1994) or by the approach set forth in Zank et al. (2000) where we solve the transport equation by a method analogous to operator splitting. The second method incorporates the additional loss terms of convection and diffusion and allows for the use of a variable time between shocks. We use a maximum injection energy (Emax) appropriate for quasi-parallel and quasi-perpendicular shocks (Zank et al., 2000, 2006; Dosch and Shalchi, 2010) and provide a preliminary application of the diffusive acceleration of particles by multiple shocks with frequencies appropriate for solar maximum (i.e., a non-Markovian process).

Radiation- and pair-loaded shocks

NASA Astrophysics Data System (ADS)

Lyutikov, Maxim

2018-06-01

We consider the structure of mildly relativistic shocks in dense media, taking into account the radiation and pair loading, and diffusive radiation energy transfer within the flow. For increasing shock velocity (increasing post-shock temperature), the first important effect is the efficient energy redistribution by radiation within the shock that leads to the appearance of an isothermal jump, whereby the flow reaches the final state through a discontinuous isothermal transition. The isothermal jump, on scales much smaller than the photon diffusion length, consists of a weak shock and a quick relaxation to the isothermal conditions. Highly radiation-dominated shocks do not form isothermal jump. Pair production can mildly increase the overall shock compression ratio to ≈10 (4 for matter-dominated shocks and 7 of the radiation-dominated shocks).

Diffusive shock acceleration at non-relativistic highly oblique shocks

NASA Astrophysics Data System (ADS)

Meli, Athina; Biermann, P. L.

2004-10-01

Our aim here is to evaluate the rate of the maximum energy and the acceleration rate that Cosmic Rays (CRs) acquire in the non-relativistic diffusive shock acceleration as it could apply during their lifetime in various astrophysical sites. We examine numerically (using Monte Carlo simulations) the effect of the diffusion coefficients on the energy gain and the acceleration rate, by testing the role between the obliquity of the magnetic field at the shock normal, and the significance of both perpendicular cross-field diffusion and parallel diffusion coefficients to the aceleration rate. We find (and justify previous analytical work -Jokipii 1987) that in highly oblique shocks the smaller the perpendicular diffusion gets compared to the parallel diffusion coefficient values, the greater the energy gain of the CRs to be obtained. An explanation of the Cosmic Ray Spectrum in High Energies, between 1015 and 1018eV is claimed, as we estimate the upper limit of energy that CRs could gain in plausible astrophysical regimes; interpreted by the scenario of CRs which are injected by three different kind of sources, (i) supernovae (SN) which explode into the interstellar medium (ISM), (ii) Red Supergiants (RSG), and (iii) Wolf-Rayet stars (WR), where the two latter explode into their pre-SN winds Biermann (2001); Sina (2001).

On the cosmic ray diffusion in a violent interstellar medium

NASA Technical Reports Server (NTRS)

Bykov, A. M.; Toptygin, I. N.

1985-01-01

A variety of the available observational data on the cosmic ray (CR) spectrum, anisotropy and composition are in good agreement with a suggestion on the diffusion propagation of CR with energy below 10(15) eV in the interstellar medium. The magnitude of the CR diffusion coefficient and its energy dependence are determined by interstellar medium (ISM) magnetic field spectra. Direct observational data on magnetic field spectra are still absent. A theoretical model to the turbulence generation in the multiphase ISM is resented. The model is based on the multiple generation of secondary shocks and concomitant large-scale rarefactions due to supernova shock interactions with interstellar clouds. The distribution function for ISM shocks are derived to include supernova statistics, diffuse cloud distribution, and various shock wave propagation regimes. This permits calculation of the ISM magnetic field fluctuation spectrum and CR diffusion coefficient for the hot phase of ISM.

On Multi-Dimensional Unstructured Mesh Adaption

NASA Technical Reports Server (NTRS)

Wood, William A.; Kleb, William L.

1999-01-01

Anisotropic unstructured mesh adaption is developed for a truly multi-dimensional upwind fluctuation splitting scheme, as applied to scalar advection-diffusion. The adaption is performed locally using edge swapping, point insertion/deletion, and nodal displacements. Comparisons are made versus the current state of the art for aggressive anisotropic unstructured adaption, which is based on a posteriori error estimates. Demonstration of both schemes to model problems, with features representative of compressible gas dynamics, show the present method to be superior to the a posteriori adaption for linear advection. The performance of the two methods is more similar when applied to nonlinear advection, with a difference in the treatment of shocks. The a posteriori adaption can excessively cluster points to a shock, while the present multi-dimensional scheme tends to merely align with a shock, using fewer nodes. As a consequence of this alignment tendency, an implementation of eigenvalue limiting for the suppression of expansion shocks is developed for the multi-dimensional distribution scheme. The differences in the treatment of shocks by the adaption schemes, along with the inherently low levels of artificial dissipation in the fluctuation splitting solver, suggest the present method is a strong candidate for applications to compressible gas dynamics.

Unmagnetized diffusion for azimuthally symmetric wave and particle distributions

NASA Technical Reports Server (NTRS)

Dusenbery, P. B.; Lyons, L. R.

1988-01-01

The quasi-linear diffusion of particles from resonant interactions with a spectrum of electrostatic waves is investigated theoretically, extending results obtained for no magnetic field and for strong magnetic fields to cases where the ambient magnetic field which organizes azimuthally symmetric wave and particle distributions does not have to be taken into consideration in evaluating the local interaction. The derivation of the governing equations is explained, and numerical results are presented in extensive graphs and characterized in detail. Slow-mode ion-acoustic waves are shown to be unstable under the plasma conditions studied, and the dependence of resonant-ion diffusion rates with pitch angle, speed, and the distribution of wave energy in wavenumber space is explored. The implications of the present findings for theoretical models of the earth bow shock and plasma-sheet boundary layer are indicated.

Search for low-frequency diffuse radio emission around a shock in the massive galaxy cluster MACS J0744.9+3927

NASA Astrophysics Data System (ADS)

Wilber, A.; Brüggen, M.; Bonafede, A.; Rafferty, D.; Savini, F.; Shimwell, T.; van Weeren, R. J.; Botteon, A.; Cassano, R.; Brunetti, G.; De Gasperin, F.; Wittor, D.; Hoeft, M.; Birzan, L.

2018-05-01

Merging galaxy clusters produce low-Mach-number shocks in the intracluster medium. These shocks can accelerate electrons to relativistic energies that are detectable at radio frequencies. MACS J0744.9+3927 is a massive [M500 = (11.8 ± 2.8) × 1014 M⊙], high-redshift (z = 0.6976) cluster where a Bullet-type merger is presumed to have taken place. Sunyaev-Zel'dovich maps from MUSTANG indicate that a shock, with Mach number M = 1.0-2.9 and an extension of ˜200 kpc, sits near the centre of the cluster. The shock is also detected as a brightness and temperature discontinuity in X-ray observations. To search for diffuse radio emission associated with the merger, we have imaged the cluster with the LOw Frequency ARray (LOFAR) at 120-165 MHz. Our LOFAR radio images reveal previously undetected AGN emission, but do not show clear cluster-scale diffuse emission in the form of a radio relic nor a radio halo. The region of the shock is on the western edge of AGN lobe emission from the brightest cluster galaxy. Correlating the flux of known shock-induced radio relics versus their size, we find that the radio emission overlapping the shocked region in MACS J0744.9+3927 is likely of AGN origin. We argue against the presence of a relic caused by diffusive shock acceleration and suggest that the shock is too weak to accelerate electrons from the intracluster medium.

Low-energy ion acceleration at quasi-perpendicular shocks: Transverse diffusion

NASA Technical Reports Server (NTRS)

Giacalone, J.; Jokipii, J. R.

1995-01-01

The problem of ion injection and acceleration at quasi perpendicular shocks has been the subject of some debate over the past two decades. It is widely known that these shocks efficiently accelerate particles that are well in the high-energy tail of the distribution. However, the issue of injection, or the acceleration of low-energy ions, has yet to reach a consensus. The fundamental issue is whether there is enough diffusion normal to the magnetic field for the particles to remain near the shock. Since transverse diffusion is a physical process that is not well understood in space plasmas, this is an important, and difficult issue to address. In this report, we will investigate the ion injection problem by performing test particle orbit integrations using synthesized turbulent fields. These fields are fully three-dimensional so that transverse diffusion is possible (cross-field diffusion is not possible in geometries where the electromagnetic fields are less than three dimensional). The synthesized fields are produced by superimposing a three-dimensional wave field on a background field. For completeness, we will compare the results from this model with the more well-established theories, such as the diffusive approximation and scatter-free shock drift acceleration. We will also compare these results with other numerical simulation techniques such as the well known hybrid simulation, and other test-particle calculations in which the shock fields are specified to have less than three dimensions. We will also discuss some recent relevant observations and how these compare with our results.

Time-dependent diffusive acceleration of test particles at shocks

NASA Astrophysics Data System (ADS)

Drury, L. O'C.

1991-07-01

A theoretical description is developed for the acceleration of test particles at a steady plane nonrelativistic shock. The mean and the variance of the acceleration-time distribution are expressed analytically for the condition under which the diffusion coefficient is arbitrarily dependent on position and momentum. The formula for an acceleration rate with arbitrary spatial variation in the diffusion coefficient developed by Drury (1987) is supplemented by a general theory of time dependence. An approximation scheme is developed by means of the analysis which permits the description of the spectral cutoff resulting from the finite shock age. The formulas developed in the analysis are also of interest for analyzing the observations of heliospheric shocks made from spacecraft.

Rapid innovation diffusion in social networks.

PubMed

Kreindler, Gabriel E; Young, H Peyton

2014-07-22

Social and technological innovations often spread through social networks as people respond to what their neighbors are doing. Previous research has identified specific network structures, such as local clustering, that promote rapid diffusion. Here we derive bounds that are independent of network structure and size, such that diffusion is fast whenever the payoff gain from the innovation is sufficiently high and the agents' responses are sufficiently noisy. We also provide a simple method for computing an upper bound on the expected time it takes for the innovation to become established in any finite network. For example, if agents choose log-linear responses to what their neighbors are doing, it takes on average less than 80 revision periods for the innovation to diffuse widely in any network, provided that the error rate is at least 5% and the payoff gain (relative to the status quo) is at least 150%. Qualitatively similar results hold for other smoothed best-response functions and populations that experience heterogeneous payoff shocks.

Rapid innovation diffusion in social networks

PubMed Central

Kreindler, Gabriel E.; Young, H. Peyton

2014-01-01

Social and technological innovations often spread through social networks as people respond to what their neighbors are doing. Previous research has identified specific network structures, such as local clustering, that promote rapid diffusion. Here we derive bounds that are independent of network structure and size, such that diffusion is fast whenever the payoff gain from the innovation is sufficiently high and the agents’ responses are sufficiently noisy. We also provide a simple method for computing an upper bound on the expected time it takes for the innovation to become established in any finite network. For example, if agents choose log-linear responses to what their neighbors are doing, it takes on average less than 80 revision periods for the innovation to diffuse widely in any network, provided that the error rate is at least 5% and the payoff gain (relative to the status quo) is at least 150%. Qualitatively similar results hold for other smoothed best-response functions and populations that experience heterogeneous payoff shocks. PMID:25024191

Myocardial oxygen delivery after experimental hemorrhagic shock.

PubMed Central

Archie, J P; Mertz, W R

1978-01-01

The two components of myocardial oxygen delivery, coronary blood flow to capillaries and diffusion from capillaries to mitochondria, were studied in six dogs, (1) prior to shock, (2) after three hours of hemorrhage shock at a mean systemic arterial pressure of 40 torr, (3) after reinfusion of shed blood, and (4) during the irreversible late posttransfusion stage. There was a maldistribution of left ventricular coronary flow during late shock consistent with subendocardial ischemia. Cardiac performance was significantly impaired after resuscitation and all dogs became irreversible. Total and regional left ventricular coronary blood flow and myocardial oxygen delivery to capillaries were significantly greater than preshock values in (3) but not different from preshock values in (4). However, the myocardial oxygen diffusion area to distance ratio was significantly lower than preshock values in (3), and slightly lower in (4). These data suggest that myocardial oxygen diffusion may be impaired in the early post transfusion period, (3). Accordingly, the probable etiology of left ventricular dysfunction and possibly irreversibility after resuscitation from hemorrhagic shock is subendocardial ischemia during shock with either post-resuscitation impairment of myocardial oxygen diffusion, or in cellular oxygen utilization, or both. PMID:629622

A Numerical Method for the Simulation of Skew Brownian Motion and its Application to Diffusive Shock Acceleration of Charged Particles

NASA Astrophysics Data System (ADS)

McEvoy, Erica L.

Stochastic differential equations are becoming a popular tool for modeling the transport and acceleration of cosmic rays in the heliosphere. In diffusive shock acceleration, cosmic rays diffuse across a region of discontinuity where the up- stream diffusion coefficient abruptly changes to the downstream value. Because the method of stochastic integration has not yet been developed to handle these types of discontinuities, I utilize methods and ideas from probability theory to develop a conceptual framework for the treatment of such discontinuities. Using this framework, I then produce some simple numerical algorithms that allow one to incorporate and simulate a variety of discontinuities (or boundary conditions) using stochastic integration. These algorithms were then modified to create a new algorithm which incorporates the discontinuous change in diffusion coefficient found in shock acceleration (known as Skew Brownian Motion). The originality of this algorithm lies in the fact that it is the first of its kind to be statistically exact, so that one obtains accuracy without the use of approximations (other than the machine precision error). I then apply this algorithm to model the problem of diffusive shock acceleration, modifying it to incorporate the additional effect of the discontinuous flow speed profile found at the shock. A steady-state solution is obtained that accurately simulates this phenomenon. This result represents a significant improvement over previous approximation algorithms, and will be useful for the simulation of discontinuous diffusion processes in other fields, such as biology and finance.

Enhanced Scattering of Diffuse Ions on Front of the Earth's Quasi-Parallel Bow Shock: a Case Study

NASA Astrophysics Data System (ADS)

Kis, A.; Matsukiyo, S.; Otsuka, F.; Hada, T.; Lemperger, I.; Dandouras, I. S.; Barta, V.; Facsko, G. I.

2017-12-01

In the analysis we present a case study of three energetic upstream ion events at the Earth's quasi-parallel bow shock based on multi-spacecraft data recorded by Cluster. The CIS-HIA instrument onboard Cluster provides partial energetic ion densities in 4 energy channels between 10 and 32 keV.The difference of the partial ion densities recorded by the individual spacecraft at various distances from the bow shock surface makes possible the determination of the spatial gradient of energetic ions.Using the gradient values we determined the spatial profile of the energetic ion partial densities as a function of distance from the bow shock and we calculated the e-folding distance and the diffusion coefficient for each event and each ion energy range. Results show that in two cases the scattering of diffuse ions takes place in a normal way, as "by the book", and the e-folding distance and diffusion coefficient values are comparable with previous results. On the other hand, in the third case the e-folding distance and the diffusion coefficient values are significantly lower, which suggests that in this case the scattering process -and therefore the diffusive shock acceleration (DSA) mechanism also- is much more efficient. Our analysis provides an explanation for this "enhanced" scattering process recorded in the third case.

Modeling of ion acceleration through drift and diffusion at interplanetary shocks

NASA Technical Reports Server (NTRS)

Decker, R. B.; Vlahos, L.

1986-01-01

A test particle simulation designed to model ion acceleration through drift and diffusion at interplanetary shocks is described. The technique consists of integrating along exact particle orbits in a system where the angle between the shock normal and mean upstream magnetic field, the level of magnetic fluctuations, and the energy of injected particles can assume a range of values. The technique makes it possible to study time-dependent shock acceleration under conditions not amenable to analytical techniques. To illustrate the capability of the numerical model, proton acceleration was considered under conditions appropriate for interplanetary shocks at 1 AU, including large-amplitude transverse magnetic fluctuations derived from power spectra of both ambient and shock-associated MHD waves.

On the acceleration of charged particles at relativistic shock fronts

NASA Technical Reports Server (NTRS)

Kirk, J. G.; Schneider, P.

1987-01-01

The diffusive acceleration of highly relativistic particles at a shock is reconsidered. Using the same physical assumptions as Blandford and Ostriker (1978), but dropping the restriction to nonrelativistic shock velocities, the authors find approximate solutions of the particle kinetic equation by generalizing the diffusion approximation to higher order terms in the anisotropy of the particle distribution. The general solution of the transport equation on either side of the shock is constructed, which involves the solution of an eigenvalue problem. By matching the two solutions at the shock, the spectral index of the resulting power law is found by taking into account a sufficiently large number of eigenfunctions. Low-order truncation corresponds to the standard diffusion approximation and to a somewhat more general method described by Peacock (1981). In addition to the energy spectrum, the method yields the angular distribution of the particles and its spatial dependence.

Synchronized shocks in an inhomogeneous exclusion process

NASA Astrophysics Data System (ADS)

Arita, Chikashi

2015-11-01

We study an exclusion process with 4 segments, which was recently introduced by T. Banerjee, N. Sarkar and A. Basu (J. Stat. Mech. (2015) P01024). The segments have hopping rates 1, r(<1) , 1 and r, respectively. In a certain parameter region, two shocks appear, which are not static but synchronized. We explore dynamical properties of each shock and correlation of shocks, by means of the so-called second-class particle. The mean-squared displacement of shocks has three diffusive regimes, and the asymptotic diffusion coefficient is different from the known formula. In some time interval, it also exhibits sub-diffusion, being proportional to t1/2 . Furthermore we introduce a correlation function and a crossover time, in order to quantitatively characterize the synchronization. We numerically estimate the dynamical exponent for the crossover time. We also revisit the 2-segment case and the open boundary condition for comparison.

Diffusive Cosmic-Ray Acceleration at Shock Waves of Arbitrary Speed with Magnetostatic Turbulence. I. General Theory and Correct Nonrelativistic Speed Limit

NASA Astrophysics Data System (ADS)

Schlickeiser, R.; Oppotsch, J.

2017-12-01

The analytical theory of diffusive acceleration of cosmic rays at parallel stationary shock waves of arbitrary speed with magnetostatic turbulence is developed from first principles. The theory is based on the diffusion approximation to the gyrotropic cosmic-ray particle phase-space distribution functions in the respective rest frames of the up- and downstream medium. We derive the correct cosmic-ray jump conditions for the cosmic-ray current and density, and match the up- and downstream distribution functions at the position of the shock. It is essential to account for the different particle momentum coordinates in the up- and downstream media. Analytical expressions for the momentum spectra of shock-accelerated cosmic rays are calculated. These are valid for arbitrary shock speeds including relativistic shocks. The correctly taken limit for nonrelativistic shock speeds leads to a universal broken power-law momentum spectrum of accelerated particles with velocities well above the injection velocity threshold, where the universal power-law spectral index q≃ 2-{γ }1-4 is independent of the flow compression ratio r. For nonrelativistic shock speeds, we calculate for the first time the injection velocity threshold, settling the long-standing injection problem for nonrelativistic shock acceleration.

Analysis and design of numerical schemes for gas dynamics. 2: Artificial diffusion and discrete shock structure

NASA Technical Reports Server (NTRS)

Jameson, Antony

1994-01-01

The effect of artificial diffusion on discrete shock structures is examined for a family of schemes which includes scalar diffusion, convective upwind and split pressure (CUSP) schemes, and upwind schemes with characteristics splitting. The analysis leads to conditions on the diffusive flux such that stationary discrete shocks can contain a single interior point. The simplest formulation which meets these conditions is a CUSP scheme in which the coefficients of the pressure differences is fully determined by the coefficient of convective diffusion. It is also shown how both the characteristic and CUSP schemes can be modified to preserve constant stagnation enthalpy in steady flow, leading to four variants, the E and H-characteristic schemes, and the E and H-CUSP schemes. Numerical results are presented which confirm the properties of these schemes.

Mathematical analysis of thermal diffusion shock waves

NASA Astrophysics Data System (ADS)

Gusev, Vitalyi; Craig, Walter; Livoti, Roberto; Danworaphong, Sorasak; Diebold, Gerald J.

2005-10-01

Thermal diffusion, also known as the Ludwig-Soret effect, refers to the separation of mixtures in a temperature gradient. For a binary mixture the time dependence of the change in concentration of each species is governed by a nonlinear partial differential equation in space and time. Here, an exact solution of the Ludwig-Soret equation without mass diffusion for a sinusoidal temperature field is given. The solution shows that counterpropagating shock waves are produced which slow and eventually come to a halt. Expressions are found for the shock time for two limiting values of the starting density fraction. The effects of diffusion on the development of the concentration profile in time and space are found by numerical integration of the nonlinear differential equation.

Effect of field-aligned-beam in parallel diffusion of energetic particles in the Earth's foreshock

NASA Astrophysics Data System (ADS)

Matsukiyo, S.; Nakanishi, K.; Otsuka, F.; Kis, A.; Lemperger, I.; Hada, T.

2016-12-01

Diffusive shock acceleration (DSA) is one of the plausible acceleration mechanisms of cosmic rays. In the standard DSA model the partial density of the accelerated particles, diffused into upstream, exponentially decreases as the distance to the shock increases. Kis et al. (GRL, 31, L20801, 2004) examined the density gradients of energetic ions upstream of the bow shock with high accuracy by using Cluster data. They estimated the diffusion coefficients of energetic ions for the event in February 18, 2003 and showed that the obtained diffusion coefficients are significantly smaller than those estimated in the past statistical study. This implies that particle acceleration at the bow shock can be more efficient than considered before. Here, we focus on the effect of the field-aligned-beam (FAB) which is often observed in the foreshock, and examine how the FAB affects the efficiency of diffusion of the energetic ions by performing test particle simulations. The upstream turbulence is given by the superposition of parallel Alfven waves with power-law energy spectrum with random phase approximation. In the spectrum we further add a peak corresponding to the waves resonantly generated by the FAB. The dependence of the diffusion coefficient on the presence of the FAB as well as total energy of the turbulence, power-law index of the turbulence, and intensity of FAB oriented waves are discussed.

A comparison of the effect of convection against diffusion in hemodynamics and cytokines clearance in an experimental model of septic shock.

PubMed

Herrera-Gutiérrez, Manuel E; Seller-Pérez, Gemma; Arias-Verdú, Dolores; Granados, Maria M; Dominguez, Juan M; Navarrete, Rocío; Morgaz, Juán; Gómez-Villamandos, Rafael

2012-10-01

Replacement therapies based on the use of convection have value for the removal of inflammatory mediators. Such therapies have been proposed for the management of septic shock, but diffusion has not proved useful in this scenario, unless high-flow membranes are used. The exact role of diffusion in these cases remains to be clarified because continuous replacement therapies are usually delivered with low-flow membranes and mixed convection-diffusion modalities. However, studies specifically addressing this problem have not been performed. Our aim was to define the efficacy of hemofiltration (convection) and hemodialysis (diffusion) in cytokine clearance and hemodynamic improvement in an experimental model of septic shock. Shock was induced in 15 beagle dogs (weight 10-15 kg) by infusion of 1 mg/kg of ultrapure Escherichia coli lipopolysaccharide diluted in 20 mL saline for 10 minutes. Five animals were followed without interventions (controls), five animals were treated with convection (100 mL kg h) for 6 hours, and five animals were treated with diffusion (100 mL kg h) for 6 hours. All subjects in the control group died during the study, whereas all treated subjects survived. Mean arterial pressure, cardiac output, systolic variability volume, systemic vascular resistances, dPMax, and pulmonary compliance improved in treated subjects. However, the differences in mean arterial pressure and cardiac output were significant only in the convection group and not in the diffusion-treated group.Tumor necrosis factor α rose equally in all groups and decreased only in treated subjects. Interleukin 6 rose in the three groups but decreased only in the convection group and remained unchanged in the control and diffusion groups. Convection and diffusion improved survival and hemodynamic parameters in a septic shock model. Improvement was more pronounced with convection, a difference that may be explained by convective clearance of cytokines.

Deionization shocks in microstructures

NASA Astrophysics Data System (ADS)

Mani, Ali; Bazant, Martin Z.

2011-12-01

Salt transport in bulk electrolytes is limited by diffusion and advection, but in microstructures with charged surfaces (e.g., microfluidic devices, porous media, soils, or biological tissues) surface conduction and electro-osmotic flow also contribute to ionic fluxes. For small applied voltages, these effects lead to well known linear electrokinetic phenomena. In this paper, we predict some surprising nonlinear dynamics that can result from the competition between bulk and interfacial transport at higher voltages. When counterions are selectively removed by a membrane or electrode, a “deionization shock” can propagate through the microstructure, leaving in its wake an ultrapure solution, nearly devoid of coions and colloidal impurities. We elucidate the basic physics of deionization shocks and develop a mathematical theory of their existence, structure, and stability, allowing for slow variations in surface charge or channel geometry. Via asymptotic approximations and similarity solutions, we show that deionization shocks accelerate and sharpen in narrowing channels, while they decelerate and weaken, and sometimes disappear, in widening channels. These phenomena may find applications in separations (deionization, decontamination, biological assays) and energy storage (batteries, supercapacitors) involving electrolytes in microstructures.

Linear analysis of the Richtmyer-Meshkov instability in shock-flame interactions

NASA Astrophysics Data System (ADS)

Massa, L.; Jha, P.

2012-05-01

Shock-flame interactions enhance supersonic mixing and detonation formation. Therefore, their analysis is important to explosion safety, internal combustion engine performance, and supersonic combustor design. The fundamental process at the basis of the interaction is the Richtmyer-Meshkov instability supported by the density difference between burnt and fresh mixtures. In the present study we analyze the effect of reactivity on the Richtmyer-Meshkov instability with particular emphasis on combustion lengths that typify the scaling between perturbation growth and induction. The results of the present linear analysis study show that reactivity changes the perturbation growth rate by developing a pressure gradient at the flame surface. The baroclinic torque based on the density gradient across the flame acts to slow down the instability growth of high wave-number perturbations. A gasdynamic flame representation leads to the definition of a Peclet number representing the scaling between perturbation and thermal diffusion lengths within the flame. Peclet number effects on perturbation growth are observed to be marginal. The gasdynamic model also considers a finite flame Mach number that supports a separation between flame and contact discontinuity. Such a separation destabilizes the interface growth by augmenting the tangential shear.

Global Regularity for the Fractional Euler Alignment System

NASA Astrophysics Data System (ADS)

Do, Tam; Kiselev, Alexander; Ryzhik, Lenya; Tan, Changhui

2018-04-01

We study a pressureless Euler system with a non-linear density-dependent alignment term, originating in the Cucker-Smale swarming models. The alignment term is dissipative in the sense that it tends to equilibrate the velocities. Its density dependence is natural: the alignment rate increases in the areas of high density due to species discomfort. The diffusive term has the order of a fractional Laplacian {(-partial _{xx})^{α/2}, α \\in (0, 1)}. The corresponding Burgers equation with a linear dissipation of this type develops shocks in a finite time. We show that the alignment nonlinearity enhances the dissipation, and the solutions are globally regular for all {α \\in (0, 1)}. To the best of our knowledge, this is the first example of such regularization due to the non-local nonlinear modulation of dissipation.

An artificial nonlinear diffusivity method for supersonic reacting flows with shocks

NASA Astrophysics Data System (ADS)

Fiorina, B.; Lele, S. K.

2007-03-01

A computational approach for modeling interactions between shocks waves, contact discontinuities and reactions zones with a high-order compact scheme is investigated. To prevent the formation of spurious oscillations around shocks, artificial nonlinear viscosity [A.W. Cook, W.H. Cabot, A high-wavenumber viscosity for high resolution numerical method, J. Comput. Phys. 195 (2004) 594-601] based on high-order derivative of the strain rate tensor is used. To capture temperature and species discontinuities a nonlinear diffusivity based on the entropy gradient is added. It is shown that the damping of 'wiggles' is controlled by the model constants and is largely independent of the mesh size and the shock strength. The same holds for the numerical shock thickness and allows a determination of the L2 error. In the shock tube problem, with fluids of different initial entropy separated by the diaphragm, an artificial diffusivity is required to accurately capture the contact surface. Finally, the method is applied to a shock wave propagating into a medium with non-uniform density/entropy and to a CJ detonation wave. Multi-dimensional formulation of the model is presented and is illustrated by a 2D oblique wave reflection from an inviscid wall, by a 2D supersonic blunt body flow and by a Mach reflection problem.

Nonlinear theory of diffusive acceleration of particles by shock waves

NASA Astrophysics Data System (ADS)

Malkov, M. A.; Drury, L. O'C.

2001-04-01

Among the various acceleration mechanisms which have been suggested as responsible for the nonthermal particle spectra and associated radiation observed in many astrophysical and space physics environments, diffusive shock acceleration appears to be the most successful. We review the current theoretical understanding of this process, from the basic ideas of how a shock energizes a few reactionless particles to the advanced nonlinear approaches treating the shock and accelerated particles as a symbiotic self-organizing system. By means of direct solution of the nonlinear problem we set the limit to the test-particle approximation and demonstrate the fundamental role of nonlinearity in shocks of astrophysical size and lifetime. We study the bifurcation of this system, proceeding from the hydrodynamic to kinetic description under a realistic condition of Bohm diffusivity. We emphasize the importance of collective plasma phenomena for the global flow structure and acceleration efficiency by considering the injection process, an initial stage of acceleration and, the related aspects of the physics of collisionless shocks. We calculate the injection rate for different shock parameters and different species. This, together with differential acceleration resulting from nonlinear large-scale modification, determines the chemical composition of accelerated particles. The review concentrates on theoretical and analytical aspects but our strategic goal is to link the fundamental theoretical ideas with the rapidly growing wealth of observational data.

Evolution of the Magnetic Field during Chondrule Formation in Planetary Bow Shocks

NASA Astrophysics Data System (ADS)

Mai, Chuhong; Desch, Steven; Boley, Aaron C.

2016-10-01

Recent laboratory efforts (Fu et al., 2014, 2015) have constrained the remanent magnetizations of chondrules and the magnetic field strengths they were exposed to as they cooled below their Curie points. An outstanding question is whether these fields represent the background magnetic field of the solar nebula or were unique to the chondrule-forming environment. We investigate the amplification of the magnetic field above background values in a planetary bow shock, which is one proposed mechanism for chondrule formation. We use a hydrodynamic code to model the temperature and pressure around a 3000 km-radius planetary embryo as it moves supersonically through the nebula gas. We calculate the ionization of hot, shocked gas considering thermionic emission of electrons and ions from grains and thermal ionization of potassium. We calculate the magnetic diffusion rate, including Ohmic dissipation and ambipolar diffusion (assuming a magnetic field strength comparable to 0.5 G). We compute the steady-state magnetic field around in the bow shock and find that behind the planet the field is amplified, but everywhere else it quickly diffuses out of the shocked region and recovers the background value. We consider the trajectories taken by chondrules behind the shock and present likely values of the magnetic field amplification experienced by chondrules as they cool after melting in the shock.

Dynamics of Solar Energetic Particles in the Presence of a Shock Wave

NASA Astrophysics Data System (ADS)

Timofeev, V. E.; Petukhov, Ivan; Petukhov, Stanislav; Starodubtsev, Sergei

2003-07-01

From the analysis of problem solutions on the solar energetic particle propagation in the presence of a plane shock wave described by the diffusion convective transport equation, the condition and manifestations for the influence of a shock wave on the SEP propagation in the solar wind have been determined. Solar energetic particles (SEP) in gradual events are generated by shock waves (see, for example, [1] and references there). The SEP generation region is limited, on the whole, by the solar corona. Proton fluxes of 470 MeV to 21 GeV energies, a maximum of which occur at a time when the shock in the atmosphere of the Sun reaches heights equal to 5 10 solar radii [2] indicate to it. It is also confirmed by the significant advancing of the occurrence time of maximum in the SEP intensity with kinetic energies more than 10 MeV relative to the shock front arrival moment to Earth's orbit. model calculations for the particles acceleration by the diffusive mechanism in conditions, typical for the solar corona, show that the time taken to pass the solar atmosphere by the shock is quite sufficient to form the particle spectrum corresponding to the SEP characteristics observed [3,4]. Lee and Ryan [5] investigated the problem of SEP gradual event generation, propagation and confirmed the close association between the diffusive acceleration mechanism and SEP events. The absence of depending of particle diffusion coefficients on the energy is a lack of this model. As an extension of preceding investigations, in this work the temporal dynamics of the particle spectrum in the presence of a plane shock for diffusion coefficients depending on the particle energy and also their change in time is studied. The SEP event from a moment of arising of a shock to a moment of it's arrival on the Earth's orbit can be divided on two stages: the first stage (duration is ˜ 1 hour) is a generation of SEP in the solar corona, the second stage (duration is ˜ 1 day) is a propagation in interplanetary space in the presence of a shock. Here we consider the second stage only which as believed to be began with the injection of the particle spectrum formed during the first stage.

Steady state and dynamical structure of a cosmic-ray-modified termination shock

NASA Technical Reports Server (NTRS)

Donohue, D. J.; Zank, G. P.

1993-01-01

A hydrodynamic model is developed for the structure of a cosmic-ray-modified termination shock. The model is based on the two-fluid equations of diffuse shock acceleration (Drury and Volk, 1981). Both the steady state structure of the shock and its interaction with outer heliospheric disturbances are considered. Under the assumption that the solar wind is decelerated by diffusing interstellar cosmic rates, it is shown that the natural state of the termination shock is a gradual deceleration and compression, followed by a discontinuous jump to a downstream state which is dominated by the pressure contribution of the cosmic rays. A representative model is calculated for the steady state which incorporates both interstellar cosmic ray mediation and diffusively accelerated anomalous ions through a proposed thermal leakage mechanism. The interaction of large-scale disturbances with the equilibrium termination shock model is shown to result in some unusual downstream structure, including transmitted shocks and cosmic-ray-modified contact discontinuities. The structure observed may be connected to the 2-kHz outer heliospheric radio emission (Cairns et al., 1992a, b). The time-dependent simulations also demonstrate that interaction with solar wind compressible turbulence (e.g., traveling interplanetary shocks, etc.) could induce the termination shock to continually fluctuate between cosmic-ray-dominated and gas-dynamic states. This fluctuation may represent a partial explanation of the galactic cosmic ray modulation effect and illustrates that the Pioneer and Voyager satellites will encounter an evolving shock whose structure and dynamic properties are strongly influence by the mediation of interstellar and anomalous cosmic rays.

Steady state and dynamical structure of a cosmic-ray-modified termination shock

NASA Astrophysics Data System (ADS)

Donohue, D. J.; Zank, G. P.

1993-11-01

A hydrodynamic model is developed for the structure of a cosmic-ray-modified termination shock. The model is based on the two-fluid equations of diffuse shock acceleration (Drury and Volk, 1981). Both the steady state structure of the shock and its interaction with outer heliospheric disturbances are considered. Under the assumption that the solar wind is decelerated by diffusing interstellar cosmic rates, it is shown that the natural state of the termination shock is a gradual deceleration and compression, followed by a discontinuous jump to a downstream state which is dominated by the pressure contribution of the cosmic rays. A representative model is calculated for the steady state which incorporates both interstellar cosmic ray mediation and diffusively accelerated anomalous ions through a proposed thermal leakage mechanism. The interaction of large-scale disturbances with the equilibrium termination shock model is shown to result in some unusual downstream structure, including transmitted shocks and cosmic-ray-modified contact discontinuities. The structure observed may be connected to the 2-kHz outer heliospheric radio emission (Cairns et al., 1992a, b). The time-dependent simulations also demonstrate that interaction with solar wind compressible turbulence (e.g., traveling interplanetary shocks, etc.) could induce the termination shock to continually fluctuate between cosmic-ray-dominated and gas-dynamic states. This fluctuation may represent a partial explanation of the galactic cosmic ray modulation effect and illustrates that the Pioneer and Voyager satellites will encounter an evolving shock whose structure and dynamic properties are strongly influence by the mediation of interstellar and anomalous cosmic rays.

Anomalous Transport of Cosmic Rays in a Nonlinear Diffusion Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Litvinenko, Yuri E.; Fichtner, Horst; Walter, Dominik

2017-05-20

We investigate analytically and numerically the transport of cosmic rays following their escape from a shock or another localized acceleration site. Observed cosmic-ray distributions in the vicinity of heliospheric and astrophysical shocks imply that anomalous, superdiffusive transport plays a role in the evolution of the energetic particles. Several authors have quantitatively described the anomalous diffusion scalings, implied by the data, by solutions of a formal transport equation with fractional derivatives. Yet the physical basis of the fractional diffusion model remains uncertain. We explore an alternative model of the cosmic-ray transport: a nonlinear diffusion equation that follows from a self-consistent treatmentmore » of the resonantly interacting cosmic-ray particles and their self-generated turbulence. The nonlinear model naturally leads to superdiffusive scalings. In the presence of convection, the model yields a power-law dependence of the particle density on the distance upstream of the shock. Although the results do not refute the use of a fractional advection–diffusion equation, they indicate a viable alternative to explain the anomalous diffusion scalings of cosmic-ray particles.« less

International Conference on Computing Methods in Applied Sciences and Engineering (9th) Held in Paris, France on 29 January-2 February 1990

DTIC Science & Technology

1990-02-02

National Aero-Space Plane NTC no time counter TSS-2 Tethered Satellite System - 2 VHS variable hard sphere VSL viscous shock-layer Introduction With...required at each time step to evaluate the mass fractions Yi+’ it is shown in [21] that the matrix of this linear system is an M-matrix (see e.g. [42]), and...first rewrite system (4.7)- (4.8) under the following form, separating the time -dependent, convective, diffusive and reactive terms: VW’ + F(W)r + G(,W

Nonrelativistic grey S n -transport radiative-shock solutions

DOE PAGES

Ferguson, J. M.; Morel, J. E.; Lowrie, R. B.

2017-06-01

We present semi-analytic radiative-shock solutions in which grey Sn-transport is used to model the radiation, and we include both constant cross sections and cross sections that depend on temperature and density. These new solutions solve for a variable Eddington factor (VEF) across the shock domain, which allows for interesting physics not seen before in radiative-shock solutions. Comparisons are made with the grey nonequilibrium-diffusion radiative-shock solutions of Lowrie and Edwards [1], which assumed that the Eddington factor is constant across the shock domain. It is our experience that the local Mach number is monotonic when producing nonequilibrium-diffusion solutions, but that thismore » monotonicity may disappear while integrating the precursor region to produce Sn-transport solutions. For temperature- and density-dependent cross sections we show evidence of a spike in the VEF in the far upstream portion of the radiative-shock precursor. We show evidence of an adaptation zone in the precursor region, adjacent to the embedded hydrodynamic shock, as conjectured by Drake [2, 3], and also confirm his expectation that the precursor temperatures adjacent to the Zel’dovich spike take values that are greater than the downstream post-shock equilibrium temperature. We also show evidence that the radiation energy density can be nonmonotonic under the Zel’dovich spike, which is indicative of anti-diffusive radiation flow as predicted by McClarren and Drake [4]. We compare the angle dependence of the radiation flow for the Sn-transport and nonequilibriumdiffusion radiation solutions, and show that there are considerable differences in the radiation flow between these models across the shock structure. Lastly, we analyze the radiation flow to understand the cause of the adaptation zone, as well as the structure of the Sn-transport radiation-intensity solutions across the shock structure.« less

Injection of thermal and suprathermal seed particles into coronal shocks of varying obliquity

NASA Astrophysics Data System (ADS)

Battarbee, M.; Vainio, R.; Laitinen, T.; Hietala, H.

2013-10-01

Context. Diffusive shock acceleration in the solar corona can accelerate solar energetic particles to very high energies. Acceleration efficiency is increased by entrapment through self-generated waves, which is highly dependent on the amount of accelerated particles. This, in turn, is determined by the efficiency of particle injection into the acceleration process. Aims: We present an analysis of the injection efficiency at coronal shocks of varying obliquity. We assessed injection through reflection and downstream scattering, including the effect of a cross-shock potential. Both quasi-thermal and suprathermal seed populations were analysed. We present results on the effect of cross-field diffusion downstream of the shock on the injection efficiency. Methods: Using analytical methods, we present applicable injection speed thresholds that were compared with both semi-analytical flux integration and Monte Carlo simulations, which do not resort to binary thresholds. Shock-normal angle θBn and shock-normal velocity Vs were varied to assess the injection efficiency with respect to these parameters. Results: We present evidence of a significant bias of thermal seed particle injection at small shock-normal angles. We show that downstream isotropisation methods affect the θBn-dependence of this result. We show a non-negligible effect caused by the cross-shock potential, and that the effect of downstream cross-field diffusion is highly dependent on boundary definitions. Conclusions: Our results show that for Monte Carlo simulations of coronal shock acceleration a full distribution function assessment with downstream isotropisation through scatterings is necessary to realistically model particle injection. Based on our results, seed particle injection at quasi-parallel coronal shocks can result in significant acceleration efficiency, especially when combined with varying field-line geometry. Appendices are available in electronic form at http://www.aanda.org

Nonrelativistic grey S n -transport radiative-shock solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferguson, J. M.; Morel, J. E.; Lowrie, R. B.

We present semi-analytic radiative-shock solutions in which grey Sn-transport is used to model the radiation, and we include both constant cross sections and cross sections that depend on temperature and density. These new solutions solve for a variable Eddington factor (VEF) across the shock domain, which allows for interesting physics not seen before in radiative-shock solutions. Comparisons are made with the grey nonequilibrium-diffusion radiative-shock solutions of Lowrie and Edwards [1], which assumed that the Eddington factor is constant across the shock domain. It is our experience that the local Mach number is monotonic when producing nonequilibrium-diffusion solutions, but that thismore » monotonicity may disappear while integrating the precursor region to produce Sn-transport solutions. For temperature- and density-dependent cross sections we show evidence of a spike in the VEF in the far upstream portion of the radiative-shock precursor. We show evidence of an adaptation zone in the precursor region, adjacent to the embedded hydrodynamic shock, as conjectured by Drake [2, 3], and also confirm his expectation that the precursor temperatures adjacent to the Zel’dovich spike take values that are greater than the downstream post-shock equilibrium temperature. We also show evidence that the radiation energy density can be nonmonotonic under the Zel’dovich spike, which is indicative of anti-diffusive radiation flow as predicted by McClarren and Drake [4]. We compare the angle dependence of the radiation flow for the Sn-transport and nonequilibriumdiffusion radiation solutions, and show that there are considerable differences in the radiation flow between these models across the shock structure. Lastly, we analyze the radiation flow to understand the cause of the adaptation zone, as well as the structure of the Sn-transport radiation-intensity solutions across the shock structure.« less

Brain lesions in septic shock: a magnetic resonance imaging study.

PubMed

Sharshar, Tarek; Carlier, Robert; Bernard, Francis; Guidoux, Céline; Brouland, Jean-Philippe; Nardi, Olivier; de la Grandmaison, Geoffroy Lorin; Aboab, Jérôme; Gray, Françoise; Menon, David; Annane, Djillali

2007-05-01

Understanding of sepsis-induced brain dysfunction remains poor, and relies mainly on data from animals or post-mortem studies in patients. The current study provided findings from magnetic resonance imaging of the brain in septic shock. Nine patients with septic shock and brain dysfunction [7 women, median age 63 years (interquartile range 61-79 years), SAPS II: 48 (44-56), SOFA: 8 (6-10)] underwent brain magnetic resonance imaging including gradient echo T1-weighted, fluid-attenuated inversion recovery (FLAIR), T2-weighted and diffusion isotropic images, and mapping of apparent diffusion coefficient. Brain imaging was normal in two patients, showed multiple ischaemic strokes in two patients, and in the remaining patients showed white matter lesions at the level of the centrum semiovale, predominating around Virchow-Robin spaces, ranging from small multiple areas to diffuse lesions, and characterised by hyperintensity on FLAIR images. The main lesions were also characterised by reduced signal on diffusion isotropic images and increased apparent diffusion coefficient. The lesions of the white matter worsened with increasing duration of shock and were correlated with Glasgow Outcome Score. This preliminary study showed that sepsis-induced brain lesions can be documented by magnetic resonance imaging. These lesions predominated in the white matter, suggesting increased blood-brain barrier permeability, and were associated with poor outcome.

Black Hole Scrambling from Hydrodynamics.

PubMed

Grozdanov, Sašo; Schalm, Koenraad; Scopelliti, Vincenzo

2018-06-08

We argue that the gravitational shock wave computation used to extract the scrambling rate in strongly coupled quantum theories with a holographic dual is directly related to probing the system's hydrodynamic sound modes. The information recovered from the shock wave can be reconstructed in terms of purely diffusionlike, linearized gravitational waves at the horizon of a single-sided black hole with specific regularity-enforced imaginary values of frequency and momentum. In two-derivative bulk theories, this horizon "diffusion" can be related to late-time momentum diffusion via a simple relation, which ceases to hold in higher-derivative theories. We then show that the same values of imaginary frequency and momentum follow from a dispersion relation of a hydrodynamic sound mode. The frequency, momentum, and group velocity give the holographic Lyapunov exponent and the butterfly velocity. Moreover, at this special point along the sound dispersion relation curve, the residue of the retarded longitudinal stress-energy tensor two-point function vanishes. This establishes a direct link between a hydrodynamic sound mode at an analytically continued, imaginary momentum and the holographic butterfly effect. Furthermore, our results imply that infinitely strongly coupled, large-N_{c} holographic theories exhibit properties similar to classical dilute gases; there, late-time equilibration and early-time scrambling are also controlled by the same dynamics.

Black Hole Scrambling from Hydrodynamics

NASA Astrophysics Data System (ADS)

Grozdanov, Sašo; Schalm, Koenraad; Scopelliti, Vincenzo

2018-06-01

We argue that the gravitational shock wave computation used to extract the scrambling rate in strongly coupled quantum theories with a holographic dual is directly related to probing the system's hydrodynamic sound modes. The information recovered from the shock wave can be reconstructed in terms of purely diffusionlike, linearized gravitational waves at the horizon of a single-sided black hole with specific regularity-enforced imaginary values of frequency and momentum. In two-derivative bulk theories, this horizon "diffusion" can be related to late-time momentum diffusion via a simple relation, which ceases to hold in higher-derivative theories. We then show that the same values of imaginary frequency and momentum follow from a dispersion relation of a hydrodynamic sound mode. The frequency, momentum, and group velocity give the holographic Lyapunov exponent and the butterfly velocity. Moreover, at this special point along the sound dispersion relation curve, the residue of the retarded longitudinal stress-energy tensor two-point function vanishes. This establishes a direct link between a hydrodynamic sound mode at an analytically continued, imaginary momentum and the holographic butterfly effect. Furthermore, our results imply that infinitely strongly coupled, large-Nc holographic theories exhibit properties similar to classical dilute gases; there, late-time equilibration and early-time scrambling are also controlled by the same dynamics.

Fringe localization requirements for three-dimensional flow visualization of shock waves in diffuse-illumination double-pulse holographic interferometry

NASA Technical Reports Server (NTRS)

Decker, A. J.

1982-01-01

A theory of fringe localization in rapid-double-exposure, diffuse-illumination holographic interferometry was developed. The theory was then applied to compare holographic measurements with laser anemometer measurements of shock locations in a transonic axial-flow compressor rotor. The computed fringe localization error was found to agree well with the measured localization error. It is shown how the view orientation and the curvature and positional variation of the strength of a shock wave are used to determine the localization error and to minimize it. In particular, it is suggested that the view direction not deviate from tangency at the shock surface by more than 30 degrees.

Energetic particle diffusion coefficients upstream of quasi-parallel interplanetary shocks

NASA Technical Reports Server (NTRS)

Tan, L. C.; Mason, G. M.; Gloeckler, G.; Ipavich, F. M.

1989-01-01

The properties of about 30 to 130-keV/e protons and alpha particles upstream of six quasi-parallel interplanetary shocks that passed by the ISEE 3 spacecraft during 1978-1979 were analyzed, and the values for the upstream energegic particle diffusion coefficient, kappa, in these six events were deduced for a number of energies and upstream positions. These observations were compared with predictions of Lee's (1983) theory of shock acceleration. It was found that the observations verified the prediction of the A/Q dependence (where A and Q are the particle atomic mass and ionization state, respectively) of kappa for alpha and proton particles upstream of the quasi-parallel shocks.

Ringwoodite rim around olivine core in shock-induced melt veins of Antarctic chondrite : Mechanisms of transformation and Fe-Mg diffusion

NASA Astrophysics Data System (ADS)

Xie, Z.; Li, X.; Sharp, T. G.; de Carli, P. S.

2009-12-01

Introduction: High-pressure minerals, produced by shock metamorphism, are common in and around melt veins in highly shocked chondrites. The shock duration can be constrained by using transformation kinetics, such as the crystallization rate of the melt-vein matrix[1-2], or growth rate of the high-pressure minerals [3-4], or using elements diffusion rate between two minerals [5]. Using transformation kinetics to constrain shock duration de-pend on the details of the transformation mechanism. For example, growth of topotaxial ringwoodite in olivine with coherent interfaces is slower than growth of inclusions with incoherent interfaces [4-5]. Similarly, diffusion-controlled growth, where rates are determined by long-range diffusion, is generally much slower than interface-controlled growth, which is only dependent on diffusion across the interface [6-8]. The occurrences of the high-pressure mineral rims were recently reported in shock-induced melt veins in several heavily shocked (S6) chondrites, ALH78003, Peace River and GRV052049 [9-11]. Here we report EMAP and Raman results of the ringwoodite rims around olivine cores in shock veins of the Antarctic chondrites GRV 022321, and to elucidate the mechanisms of transformation and Mg-Fe diffusion of the olivine to ringwoodite. Results: GRV022321 has a network of black veins which enclose abundant host-rock fragments. The enclosed fragments have sizes ranging from 5 µm to 30 µm, with a brighter rim up to several µm wide and a dark core in reflected light and BSE image. The Raman data reveal that the rim mineral is ringwoodite signature, and the core minerals are dominated by olivine and mixed minor ringwoodite. EMAP data confirm that the ringwoodite in rim is richer in faylite (Fa) than the olivine core. The Fa values range from 50 to 10 with the outer rim having highest Fa value, and the inside darker area with a lower value. Discussion: The occurrence of the rounded shape grains with smooth edges embedded in the fine matrix in shock-induced melt veins suggest that they are enclosed host-rock fragments and that the ringwoodite in the rim was transformed by solid-state transformation from previous olivine. The variable extent of transformation is likely a result of temperature variations during shock, with the hottest outer olivine forming the ringwoodite rim. The outer hotter ringwoodite attract more Fe than inside cooler olivine, and Mg-Fe diffusion occurs in rapid transformation at high pressure and temperature over up to 10 µm distance. The sample is unique because we can test and double check different shock duration constraints in future work. References: [1] Langenhorst and Poirier (2000) EPSL 184, 37-55. [2] Xie, Z. et al. (2006) GCA, 70. 504-515. [3] Ohtani et al. (2004) EPSL 227(3-4), 505-515. [4] Xie and Sharp (2007), EPLS, 433-445. [5] Beck, et al. (2005) Nature 435, 1071-1074. [6] Kerschhofer et al. (1996) Science 274 (5284), 79-81. [7] Kerschhofer et al. (2000) PEPI 121, 59-76. [8] Sharp and DeCarli (2006) MESS II, 653-677. [9] Ohtani et al. (2006), Shock Waves, 16:45-52. [10] Miyahara et al. (2008) Proceedings. of NAS 105,8542-8547. [11] Feng et al. (2007), MAPS 42, A45.

Time-dependent simulation of oblique MHD cosmic-ray shocks using the two-fluid model

NASA Technical Reports Server (NTRS)

Frank, Adam; Jones, T. W.; Ryu, Dongsu

1995-01-01

Using a new, second-order accurate numerical method we present dynamical simulations of oblique MHD cosmic-ray (CR)-modified plane shock evolution. Most of the calculations are done with a two-fluid model for diffusive shock acceleration, but we provide also comparisons between a typical shock computed that way against calculations carried out using the more complete, momentum-dependent, diffusion-advection equation. We also illustrate a test showing that these simulations evolve to dynamical equilibria consistent with previously published steady state analytic calculations for such shocks. In order to improve understanding of the dynamical role of magnetic fields in shocks modified by CR pressure we have explored for time asymptotic states the parameter space of upstream fast mode Mach number, M(sub f), and plasma beta. We compile the results into maps of dynamical steady state CR acceleration efficiency, epsilon(sub c). We have run simulations using constant, and nonisotropic, obliquity (and hence spatially) dependent forms of the diffusion coefficient kappa. Comparison of the results shows that while the final steady states achieved are the same in each case, the history of CR-MHD shocks can be strongly modified by variations in kappa and, therefore, in the acceleration timescale. Also, the coupling of CR and MHD in low beta, oblique shocks substantially influences the transient density spike that forms in strongly CR-modified shocks. We find that inside the density spike a MHD slow mode wave can be generated that eventually steepens into a shock. A strong layer develops within the density spike, driven by MHD stresses. We conjecture that currents in the shear layer could, in nonplanar flows, results in enhanced particle accretion through drift acceleration.

DIFFUSIVE PARTICLE ACCELERATION IN SHOCKED, VISCOUS ACCRETION DISKS: GREEN'S FUNCTION ENERGY DISTRIBUTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Becker, Peter A.; Das, Santabrata; Le, Truong, E-mail: pbecker@gmu.edu, E-mail: sbdas@iitg.ernet.in, E-mail: truong.le@nhrec.org

2011-12-10

The acceleration of relativistic particles in a viscous accretion disk containing a standing shock is investigated as a possible explanation for the energetic outflows observed around radio-loud black holes. The energy/space distribution of the accelerated particles is computed by solving a transport equation that includes the effects of first-order Fermi acceleration, bulk advection, spatial diffusion, and particle escape. The velocity profile of the accreting gas is described using a model for shocked viscous disks recently developed by the authors, and the corresponding Green's function distribution for the accelerated particles in the disk and the outflow is obtained using a classicalmore » method based on eigenfunction analysis. The accretion-driven, diffusive shock acceleration scenario explored here is conceptually similar to the standard model for the acceleration of cosmic rays at supernova-driven shocks. However, in the disk application, the distribution of the accelerated particles is much harder than would be expected for a plane-parallel shock with the same compression ratio. Hence the disk environment plays a key role in enhancing the efficiency of the shock acceleration process. The presence of the shock helps to stabilize the disk by reducing the Bernoulli parameter, while channeling the excess binding energy into the escaping relativistic particles. In applications to M87 and Sgr A*, we find that the kinetic power in the jet is {approx}0.01 M-dot c{sup 2}, and the outflowing relativistic particles have a mean energy {approx}300 times larger than that of the thermal gas in the disk at the shock radius. Our results suggest that a standing shock may be an essential ingredient in accretion onto underfed black holes, helping to resolve the long-standing problem of the stability of advection-dominated accretion disks.« less

Instability of isolated planar shock waves

DTIC Science & Technology

2007-06-07

Note that multi-mode perturbations can be treated by the inclusion of additional terms in Eq. (4), but owing to the linear independence of the... Volterra equation Figure 4 shows five examples of the evolution of the amplitude of a linear sinusoidal perturbation on a shock front obtained by...showing the evolution of the amplitude of a linear sinusoidal perturbation on a shock front obtained by numerically solving the Volterra equation in

Shock metamorphism of Elephant Moraine A79001: Implications for olivine-ringwoodite transformation and the complex thermal history of heavily shocked Martian meteorites

NASA Astrophysics Data System (ADS)

Walton, Erin L.

2013-04-01

Lithology A of Martian meteorite Elephant Moraine (EET) A79001 contains fragments entrained within a 100 μm-thick shear-induced shock vein. These fragments, the shock vein matrix and walls of olivine along the vein, as well as shock deformation and transformation in rock-forming minerals in the bulk rock, were investigated using scanning electron microscopy, the electron microprobe and Raman spectroscopy. The presence of ringwoodite, the spinel-structured high-pressure (Mg,Fe)2SiO4 polymorph, has been confirmed in EETA79001 for the first time. Ringwoodite occurs within and around the shock vein, exhibiting granular and lamellar textures. In both textures ringwoodite consists of ˜500 nm size distinct grains. Ringwoodite lamellae are 115 nm to 1.3 μm wide. Planar fractures in olivine provided sites for heterogeneous nucleation of ringwoodite. Analyses performed on the largest grains (⩾1 μm) show that ringwoodite is consistently higher in iron (Fa27.4-32.4) relative to surrounding olivine (Fa25.1-267.7), implying that there was Fe-Mg exchange during their transformation, and therefore their growth was diffusion-controlled. In the shock environment, diffusion takes place dynamically, i.e., with concurrent deformation and grain size reduction. This results in enhanced diffusion rates (⩾10-8 m2/s) over nm - μm distances. Shock deformation in host rock minerals including strong mosaicism, pervasive fracturing, polysynthetic twinning (pyroxene only), extensive shock melting, local transformation of olivine to ringwoodite, and complete transformation of plagioclase to maskelynite in the bulk rock, indicate that EETA79001 was strongly shocked. The short shock duration (0.01 s) combined with a complex thermal history, resulted in crystallization of the 100 μm thick shock vein in EETA79001 during the pressure release, and partial back-transformation of ringwoodite to olivine. Based on the pressure stabilities of clinopyroxene + ringwoodite, crystallization at the shock vein margin began at ˜18 GPa. Olivine and clinopyroxene crystallized at <14 GPa closer to the shock vein center. These represent a minimum limit to the shock pressure loading experienced by EETA79001.

High pulse number thermal shock tests on tungsten with steady state particle background

NASA Astrophysics Data System (ADS)

Wirtz, M.; Kreter, A.; Linke, J.; Loewenhoff, Th; Pintsuk, G.; Sergienko, G.; Steudel, I.; Unterberg, B.; Wessel, E.

2017-12-01

Thermal fatigue of metallic materials, which will be exposed to severe environmental conditions e.g. plasma facing materials in future fusion reactors, is an important issue in order to predict the life time of complete wall components. Therefore experiments in the linear plasma device PSI-2 were performed to investigate the synergistic effects of high pulse number thermal shock events (L = 0.38 GW m-2, Δt = 0.5 ms) and stationary D/He (6%) plasma particle background on the thermal fatigue behavior of tungsten. Similar to experiments with pure thermal loads, the induced microstructural and surface modifications such as recrystallization and roughening as well as crack formation become more pronounced with increasing number of thermal shock events. However, the amount of damage significantly increases for synergistic loads showing severe surface roughening, plastic deformation and erosion resulting from the degradation of the mechanical properties caused by bombardment and diffusion of D/He to the surface and the bulk of the material. Additionally, D/He induced blistering and bubble formation were observed for all tested samples, which could change the thermal and mechanical properties of near surface regions.

Three-temperature plasma shock solutions with gray radiation diffusion

DOE PAGES

Johnson, Bryan M.; Klein, Richard I.

2016-04-19

Here we discuss the effects of radiation on the structure of shocks in a fully ionized plasma are investigated by solving the steady-state fluid equations for ions, electrons, and radiation. The electrons and ions are assumed to have the same bulk velocity but separate temperatures, and the radiation is modeled with the gray diffusion approximation. Both electron and ion conduction are included, as well as ion viscosity. When the material is optically thin, three-temperature behavior occurs. When the diffusive flux of radiation is important but radiation pressure is not, two-temperature behavior occurs, with the electrons strongly coupled to the radiation.more » Since the radiation heats the electrons on length scales that are much longer than the electron–ion Coulomb coupling length scale, these solutions resemble radiative shock solutions rather than plasma shock solutions that neglect radiation. When radiation pressure is important, all three components are strongly coupled. Results with constant values for the transport and coupling coefficients are compared to a full numerical simulation with a good match between the two, demonstrating that steady shock solutions constitute a straightforward and comprehensive verification test methodology for multi-physics numerical algorithms.« less

Three-temperature plasma shock solutions with gray radiation diffusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Bryan M.; Klein, Richard I.

Here we discuss the effects of radiation on the structure of shocks in a fully ionized plasma are investigated by solving the steady-state fluid equations for ions, electrons, and radiation. The electrons and ions are assumed to have the same bulk velocity but separate temperatures, and the radiation is modeled with the gray diffusion approximation. Both electron and ion conduction are included, as well as ion viscosity. When the material is optically thin, three-temperature behavior occurs. When the diffusive flux of radiation is important but radiation pressure is not, two-temperature behavior occurs, with the electrons strongly coupled to the radiation.more » Since the radiation heats the electrons on length scales that are much longer than the electron–ion Coulomb coupling length scale, these solutions resemble radiative shock solutions rather than plasma shock solutions that neglect radiation. When radiation pressure is important, all three components are strongly coupled. Results with constant values for the transport and coupling coefficients are compared to a full numerical simulation with a good match between the two, demonstrating that steady shock solutions constitute a straightforward and comprehensive verification test methodology for multi-physics numerical algorithms.« less

Modeling a Single SEP Event from Multiple Vantage Points Using the iPATH Model

NASA Astrophysics Data System (ADS)

Hu, Junxiang; Li, Gang; Fu, Shuai; Zank, Gary; Ao, Xianzhi

2018-02-01

Using the recently extended 2D improved Particle Acceleration and Transport in the Heliosphere (iPATH) model, we model an example gradual solar energetic particle event as observed at multiple locations. Protons and ions that are energized via the diffusive shock acceleration mechanism are followed at a 2D coronal mass ejection-driven shock where the shock geometry varies across the shock front. The subsequent transport of energetic particles, including cross-field diffusion, is modeled by a Monte Carlo code that is based on a stochastic differential equation method. Time intensity profiles and particle spectra at multiple locations and different radial distances, separated in longitudes, are presented. The results shown here are relevant to the upcoming Parker Solar Probe mission.

Observational discrimination between modes of shock propagation in interstellar clouds: Predictions of CH+ and SH+ column densities in diffuse clouds

NASA Technical Reports Server (NTRS)

Flower, D. R.; Desforets, G. P.; Roueff, E.; Hartquist, T. W.

1986-01-01

Considerable effort in recent years has been devoted to the study of shocks in the diffuse interstellar medium. This work has been motivated partly by the observations of rotationally excited states of H2, and partly by the realization that species such as CH(+), OH and H2O might be formed preferentially in hot, post-shock gas. The problem of CH(+) and the difficulties encountered when trying to explain the high column densities, observed along lines of sight to certain hot stars, have been reviewed earlier. The importance of a transverse magnetic field on the structure of an interstellar shock was also demonstrated earlier. Transverse magnetic fields above a critical strength give rise to an acceleration zone or precursor, in which the parameters on the flow vary continuously. Chemical reactions, which change the degree of ionization of the gas, also modify the structure of the shock considerably. Recent work has shown that large column densities of CH(+) can be produced in magnetohydrodynamic shock models. Shock speeds U sub s approx. = 10 km/s and initial magnetic field strengths of a few micro G are sufficient to produce ion-neutral drift velocities which can drive the endothermic C(+)(H2,H)CH(+) reaction. It was also shown that single-fluid hydrodynamic models do not generate sufficiently large column densities of CH(+) unless unacceptably high shock velocities (u sub s approx. 20 km/s) are assumed in the models. Thus, the observed column densities of CH(+) provide a constraint on the mode of shock propagation in diffuse clouds. More precisely, they determine a lower limit to the ion-neutral drift velocity.

Ion dynamics at supercritical quasi-parallel shocks: Hybrid simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Su Yanqing; Lu Quanming; Gao Xinliang

2012-09-15

By separating the incident ions into directly transmitted, downstream thermalized, and diffuse ions, we perform one-dimensional (1D) hybrid simulations to investigate ion dynamics at a supercritical quasi-parallel shock. In the simulations, the angle between the upstream magnetic field and shock nominal direction is {theta}{sub Bn}=30 Degree-Sign , and the Alfven Mach number is M{sub A}{approx}5.5. The shock exhibits a periodic reformation process. The ion reflection occurs at the beginning of the reformation cycle. Part of the reflected ions is trapped between the old and new shock fronts for an extended time period. These particles eventually form superthermal diffuse ions aftermore » they escape to the upstream of the new shock front at the end of the reformation cycle. The other reflected ions may return to the shock immediately or be trapped between the old and new shock fronts for a short time period. When the amplitude of the new shock front exceeds that of the old shock front and the reformation cycle is finished, these ions become thermalized ions in the downstream. No noticeable heating can be found in the directly transmitted ions. The relevance of our simulations to the satellite observations is also discussed in the paper.« less

Solutions for Reacting and Nonreacting Viscous Shock Layers with Multicomponent Diffusion and Mass Injection. Ph.D. Thesis - Virginia Polytechnic Inst. and State Univ.

NASA Technical Reports Server (NTRS)

Moss, J. N.

1971-01-01

Numerical solutions are presented for the viscous shocklayer equations where the chemistry is treated as being either frozen, equilibrium, or nonequilibrium. Also the effects of the diffusion model, surface catalyticity, and mass injection on surface transport and flow parameters are considered. The equilibrium calculations for air species using multicomponent: diffusion provide solutions previously unavailable. The viscous shock-layer equations are solved by using an implicit finite-difference scheme. The flow is treated as a mixture of inert and thermally perfect species. Also the flow is assumed to be in vibrational equilibrium. All calculations are for a 45 deg hyperboloid. The flight conditions are those for various altitudes and velocities in the earth's atmosphere. Data are presented showing the effects of the chemical models; diffusion models; surface catalyticity; and mass injection of air, water, and ablation products on heat transfer; skin friction; shock stand-off distance; wall pressure distribution; and tangential velocity, temperature, and species profiles.

Diffuse gamma-ray emission from self-confined cosmic rays around Galactic sources

NASA Astrophysics Data System (ADS)

D'Angelo, Marta; Morlino, Giovanni; Amato, Elena; Blasi, Pasquale

2018-02-01

The propagation of particles accelerated at supernova remnant shocks and escaping the parent remnants is likely to proceed in a strongly non-linear regime, due to the efficient self-generation of Alfvén waves excited through streaming instability near the sources. Depending on the amount of neutral hydrogen present in the regions around the sites of supernova explosions, cosmic rays may accumulate an appreciable grammage in the same regions and get self-confined for non-negligible times, which in turn results in an enhanced rate of production of secondaries. Here we calculate the contribution to the diffuse gamma-ray background due to the overlap along lines of sight of several of these extended haloes as due to pion production induced by self-confined cosmic rays. We find that if the density of neutrals is low, the haloes can account for a substantial fraction of the diffuse emission observed by Fermi-Large Area Telescope (LAT), depending on the orientation of the line of sight with respect to the direction of the Galactic Centre.

Acute encephalopathy with biphasic seizures and late reduced diffusion associated with staphylococcal toxic shock syndrome caused by burns.

PubMed

Yokochi, Takaoki; Sakanishi, Shinpei; Ishidou, Yuuki; Kawano, Go; Matsuishi, Toyojiro; Akita, Yukihiro; Obu, Keizo

2016-10-01

We report a case of acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) associated with toxic shock syndrome caused by burns. A one-year-old girl was admitted to our hospital for treatment of severe burns. On day 3, she exhibited a fever, generalized rash and multiple organ failure. She was diagnosed with toxic shock syndrome after burns. She had seizures with fever twice on the same day, followed by secondary seizures on day 8 and transient deterioration of the gross motor functions involved in sitting alone and rolling over. On day 9, MRI diffusion-weighted images showed bright tree appearance (BTA). We conclude that she developed AESD. Copyright © 2016 The Japanese Society of Child Neurology. Published by Elsevier B.V. All rights reserved.

Selfsimilar time dependent shock structures

NASA Astrophysics Data System (ADS)

Beck, R.; Drury, L. O.

1985-08-01

Diffusive shock acceleration as an astrophysical mechanism for accelerating charged particles has the advantage of being highly efficient. This means however that the theory is of necessity nonlinear; the reaction of the accelerated particles on the shock structure and the acceleration process must be self-consistently included in any attempt to develop a complete theory of diffusive shock acceleration. Considerable effort has been invested in attempting, at least partially, to do this and it has become clear that in general either the maximum particle energy must be restricted by introducing additional loss processes into the problem or the acceleration must be treated as a time dependent problem (Drury, 1984). It is concluded that stationary modified shock structures can only exist for strong shocks if additional loss processes limit the maximum energy a particle can attain. This is certainly possible and if it occurs the energy loss from the shock will lead to much greater shock compressions. It is however equally possible that no such processes exist and we must then ask what sort of nonstationary shock structure develops. The ame argument which excludes stationary structures also rules out periodic solutions and indeed any solution where the width of the shock remains bounded. It follows that the width of the shock must increase secularly with time and it is natural to examine the possibility of selfsimilar time dependent solutions.

Selfsimilar time dependent shock structures

NASA Technical Reports Server (NTRS)

Beck, R.; Drury, L. O.

1985-01-01

Diffusive shock acceleration as an astrophysical mechanism for accelerating charged particles has the advantage of being highly efficient. This means however that the theory is of necessity nonlinear; the reaction of the accelerated particles on the shock structure and the acceleration process must be self-consistently included in any attempt to develop a complete theory of diffusive shock acceleration. Considerable effort has been invested in attempting, at least partially, to do this and it has become clear that in general either the maximum particle energy must be restricted by introducing additional loss processes into the problem or the acceleration must be treated as a time dependent problem (Drury, 1984). It is concluded that stationary modified shock structures can only exist for strong shocks if additional loss processes limit the maximum energy a particle can attain. This is certainly possible and if it occurs the energy loss from the shock will lead to much greater shock compressions. It is however equally possible that no such processes exist and we must then ask what sort of nonstationary shock structure develops. The ame argument which excludes stationary structures also rules out periodic solutions and indeed any solution where the width of the shock remains bounded. It follows that the width of the shock must increase secularly with time and it is natural to examine the possibility of selfsimilar time dependent solutions.

Perpendicular relativistic shocks in magnetized pair plasma

NASA Astrophysics Data System (ADS)

Plotnikov, Illya; Grassi, Anna; Grech, Mickael

2018-07-01

Perpendicular relativistic (γ0= 10) shocks in magnetized pair plasmas are investigated using two-dimensional Particle-in-Cell simulations. A systematic survey, from unmagnetized to strongly magnetized shocks, is presented accurately capturing the transition from Weibel-mediated to magnetic-reflection-shaped shocks. This transition is found to occur for upstream flow magnetizations 10-3 < σ < 10-2 at which a strong perpendicular net current is observed in the precursor, driving the so-called current-filamentation instability. The global structure of the shock and shock formation time are discussed. The magnetohydrodynamics shock jump conditions are found in good agreement with the numerical results, except for 10-4 < σ < 10-2 where a deviation up to 10 per cent is observed. The particle precursor length converges towards the Larmor radius of particles injected in the upstream magnetic field at intermediate magnetizations. For σ > 10-2, it leaves place to a purely electromagnetic precursor following from the strong emission of electromagnetic waves at the shock front. Particle acceleration is found to be efficient in weakly magnetized perpendicular shocks in agreement with previous works, and is fully suppressed for σ > 10-2. Diffusive shock acceleration is observed only in weakly magnetized shocks, while a dominant contribution of shock drift acceleration is evidenced at intermediate magnetizations. The spatial diffusion coefficients are extracted from the simulations allowing for a deeper insight into the self-consistent particle kinematics and scale with the square of the particle energy in weakly magnetized shocks. These results have implications for particle acceleration in the internal shocks of active galactic nucleus jets and in the termination shocks of pulsar wind nebulae.

Perpendicular relativistic shocks in magnetized pair plasma

NASA Astrophysics Data System (ADS)

Plotnikov, Illya; Grassi, Anna; Grech, Mickael

2018-04-01

Perpendicular relativistic (γ0 = 10) shocks in magnetized pair plasmas are investigated using two dimensional Particle-in-Cell simulations. A systematic survey, from unmagnetized to strongly magnetized shocks, is presented accurately capturing the transition from Weibel-mediated to magnetic-reflection-shaped shocks. This transition is found to occur for upstream flow magnetizations 10-3 < σ < 10-2 at which a strong perpendicular net current is observed in the precursor, driving the so-called current-filamentation instability. The global structure of the shock and shock formation time are discussed. The MHD shock jump conditions are found in good agreement with the numerical results, except for 10-4 < σ < 10-2 where a deviation up to 10% is observed. The particle precursor length converges toward the Larmor radius of particles injected in the upstream magnetic field at intermediate magnetizations. For σ > 10-2, it leaves place to a purely electromagnetic precursor following from the strong emission of electromagnetic waves at the shock front. Particle acceleration is found to be efficient in weakly magnetized perpendicular shocks in agreement with previous works, and is fully suppressed for σ > 10-2. Diffusive Shock Acceleration is observed only in weakly magnetized shocks, while a dominant contribution of Shock Drift Acceleration is evidenced at intermediate magnetizations. The spatial diffusion coefficients are extracted from the simulations allowing for a deeper insight into the self-consistent particle kinematics and scale with the square of the particle energy in weakly magnetized shocks. These results have implications for particle acceleration in the internal shocks of AGN jets and in the termination shocks of Pulsar Wind Nebulae.

Effects of Anomalous Cosmic Rays on the Structure of the Outer Heliosphere

NASA Astrophysics Data System (ADS)

Guo, Xiaocheng; Florinski, Vladimir; Wang, Chi

2018-06-01

Based on Voyager 1 observations, some anomalous cosmic rays (ACRs) may have crossed the heliopause and escaped into the interstellar medium, providing a mechanism of energy transfer between the inner and outer heliosheaths that is not included in conventional magnetohydrodynamics (MHD) models. In this paper, we study the effect of energetic particles’ escape through the heliopause on the size and shape of the heliosphere using a simple model that includes diffusive transport of cosmic rays. We show that the presence of ACRs significantly changes the heliosphere structure, including the location of the heliopause and termination shock. It was found that the heliopause would contract for certain values of the ACR diffusion coefficients when the diffusive particles’ pressure is comparable to the pressure of the plasma background. The difference in Voyager 1 and 2 observations of energetic particles during their respective termination shock crossings is interpreted here as due to the differences in diffusion environments during the different phases of the solar cycle. The shorter period of enhanced ACR intensities upstream of the shock measured by Voyager 2 may have been caused by weaker radial diffusive transport compared with the time of Voyager 1 crossing. We conclude that ACR diffusive effects could be prominent and should be included in MHD models of the heliosphere.

Hot chemistry in the diffuse medium: spectral signature in the H2 rotational lines

NASA Astrophysics Data System (ADS)

Verstraete, L.; Falgarone, E.; Pineau des Forets, G.; Flower, D.; Puget, J. L.

1999-03-01

Most of the diffuse interstellar medium is cold, but it must harbor pockets of hot gas to explain the large observed abundances of molecules like CH+ and HCO+. Because they dissipate locally large amounts of kinetic energy, MHD shocks and coherent vortices in turbulence can drive endothermic chemical reactions or reactions with large activation barriers. We predict the spectroscopic signatures in the H2 rotational lines of MHD shocks and vortices and compare them to those observed with the ISO-SWS along a line of sight through the Galaxy which samples 20 magnitudes of mostly diffuse gas.

Growth rate of the linear Richtmyer-Meshkov instability when a shock is reflected

NASA Astrophysics Data System (ADS)

Wouchuk, J. G.

2001-05-01

An analytic model is presented to calculate the growth rate of the linear Richtmyer-Meshkov instability in the shock-reflected case. The model allows us to calculate the asymptotic contact surface perturbation velocity for any value of the incident shock intensity, arbitrary fluids compressibilities, and for any density ratio at the interface. The growth rate comes out as the solution of a system of two coupled functional equations and is expressed formally as an infinite series. The distinguishing feature of the procedure shown here is the high speed of convergence of the intermediate calculations. There is excellent agreement with previous linear simulations and experiments done in shock tubes.

Dynamics of Mesoscale Magnetic Field in Diffusive Shock Acceleration

NASA Astrophysics Data System (ADS)

Diamond, P. H.; Malkov, M. A.

2007-01-01

We present a theory for the generation of mesoscale (krg<<1, where rg is the cosmic-ray gyroradius) magnetic fields during diffusive shock acceleration. The decay or modulational instability of resonantly excited Alfvén waves scattering off ambient density perturbations in the shock environment naturally generates larger scale fields. For a broad spectrum of perturbations, the physical mechanism of energy transfer is random refraction, represented by the diffusion of Alfvén wave packets in k-space. The scattering field can be produced directly by the decay instability or by the Drury instability, a hydrodynamic instability driven by the cosmic-ray pressure gradient. This process is of interest to acceleration since it generates waves of longer wavelength, and so enables the confinement and acceleration of higher energy particles. This process also limits the intensity of resonantly generated turbulent magnetic fields on rg scales.

Analytic study of 1D diffusive relativistic shock acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keshet, Uri, E-mail: ukeshet@bgu.ac.il

2017-10-01

Diffusive shock acceleration (DSA) by relativistic shocks is thought to generate the dN / dE ∝ E{sup −p} spectra of charged particles in various astronomical relativistic flows. We show that for test particles in one dimension (1D), p {sup −1}=1−ln[γ{sub d}(1+β{sub d})]/ln[γ{sub u}(1+β{sub u})], where β{sub u}(β{sub d}) is the upstream (downstream) normalized velocity, and γ is the respective Lorentz factor. This analytically captures the main properties of relativistic DSA in higher dimensions, with no assumptions on the diffusion mechanism. Unlike 2D and 3D, here the spectrum is sensitive to the equation of state even in the ultra-relativistic limit, andmore » (for a J(üttner-Synge equation of state) noticeably hardens with increasing 1« less

Interaction of a shock with a longitudinal vortex

NASA Technical Reports Server (NTRS)

Erlebacher, Gordon; Hussaini, M. Y.; Shu, Chi-Wang

1996-01-01

In this paper we study the shock/longitudinal vortex interaction problem in axisymmetric geometry. Linearized analysis for small vortex strength is performed, and compared with results from a high order axisymmetric shock-fitted Euler solution obtained for this purpose. It is confirmed that for weak vortices, predictions from linear theory agree well with results from nonlinear numerical simulations at the shock location. To handle very strong longitudinal vortices, which may ultimately break the shock, we use an axisymmetric high order essentially non-oscillatory (ENO) shock capturing scheme. Comparison of shock-captured and shock-fitted results are performed in their regions of common validity. We also study the vortex breakdown as a function of Mach number ranging from 1.3 to 10, thus extending the range of existing results. For vortex strengths above a critical value. a triple point forms on the shock and a secondary shock forms to provide the necessary deceleration so that the fluid velocity can adjust to downstream conditions at the shock.

A Theoretical Basis for the Scaling Law of Broadband Shock Noise Intensity in Supersonic Jets

NASA Technical Reports Server (NTRS)

Kandula, Max

2011-01-01

A theoretical basis for the scaling of broadband shock noise intensity In supersonic jets was formulated considering linear shock-shear wave interaction. Modeling of broadband shock noise with the aid of shock-turbulence interaction with special reference to linear theories is briefly reviewed. An hypothesis has been postulated that the peak angle of incidence (closer to the critical angle) for the shear wave primarily governs the generation of sound in the interaction process with the noise generation contribution from off-peak incident angles being relatively unimportant. The proposed hypothesis satisfactorily explains the well-known scaling law for the broadband shock-associated noise in supersonic jets.

Internal Shocks in the Magnetic Reconnection Jet in Solar Flares: Multiple Fast Shocks Created by the Secondary Tearing Instability

NASA Astrophysics Data System (ADS)

Tanuma, S.; Shibata, K.

2005-07-01

Space solar missions such as Yohkoh and RHESSI observe the hard X- and gamma-ray emission from energetic electrons in impulsive solar flares. Their energization mechanism, however, is unknown. In this Letter, we suggest that the internal shocks are created in the reconnection jet and that they are possible sites of particle acceleration. We examine how magnetic reconnection creates the multiple shocks by performing two-dimensional resistive magnetohydrodynamic simulations. In this Letter, we use a very small grid to resolve the diffusion region. As a result, we find that the current sheet becomes thin due to the tearing instability, and it collapses to a Sweet-Parker sheet. The thin sheet becomes unstable to the secondary tearing instability. Fast reconnection starts by the onset of anomalous resistivity immediately after the secondary tearing instability. During the bursty, time-dependent magnetic reconnection, the secondary tearing instability continues in the diffusion region where the anomalous resistivity is enhanced. As a result, many weak shocks are created in the reconnection jet. This situation produces turbulent reconnection. We suggest that multiple fast shocks are created in the jet and that the energetic electrons can be accelerated by these shocks.

The physics of interstellar shock waves

NASA Technical Reports Server (NTRS)

Shull, J. Michael; Draine, Bruce T.

1987-01-01

This review discusses the observations and theoretical models of interstellar shock waves, in both diffuse cloud and molecular cloud environments. It summarizes the relevant gas dynamics, atomic, molecular and grain processes, radiative transfer, and physics of radiative and magnetic precursors in shock models. It then describes the importance of shocks for observations, diagnostics, and global interstellar dynamics. It concludes with current research problems and data needs for atomic, molecular and grain physics.

Thermophysical Properties of Matter - The TPRC Data Series. Volume 3. Thermal Conductivity - Nonmetallic Liquids and Gases

DTIC Science & Technology

1970-01-01

design and experimentation. I. The Shock- Tube Method Smiley [546] introduced the use of shock waves...one of the greatest disadvantages of this technique. Both the unique adaptability of the shock tube method for high -temperature measurement of...Line-Source Flow Method H. The Hot-Wire Thermal Diffusion Column Method I. The Shock- Tube Method J. The Arc Method K. The Ultrasonic Method .

INJECTION TO RAPID DIFFUSIVE SHOCK ACCELERATION AT PERPENDICULAR SHOCKS IN PARTIALLY IONIZED PLASMAS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohira, Yutaka, E-mail: ohira@phys.aoyama.ac.jp

2016-08-10

We present a three-dimensional hybrid simulation of a collisionless perpendicular shock in a partially ionized plasma for the first time. In this simulation, the shock velocity and upstream ionization fraction are v {sub sh} ≈ 1333 km s{sup −1} and f {sub i} ∼ 0.5, which are typical values for isolated young supernova remnants (SNRs) in the interstellar medium. We confirm previous two-dimensional simulation results showing that downstream hydrogen atoms leak into the upstream region and are accelerated by the pickup process in the upstream region, and large magnetic field fluctuations are generated both in the upstream and downstream regions.more » In addition, we find that the magnetic field fluctuations have three-dimensional structures and the leaking hydrogen atoms are injected into the diffusive shock acceleration (DSA) at the perpendicular shock after the pickup process. The observed DSA can be interpreted as shock drift acceleration with scattering. In this simulation, particles are accelerated to v ∼ 100 v {sub sh} ∼ 0.3 c within ∼100 gyroperiods. The acceleration timescale is faster than that of DSA in parallel shocks. Our simulation results suggest that SNRs can accelerate cosmic rays to 10{sup 15.5} eV (the knee) during the Sedov phase.« less

Investigation of Shock Diffusers at Mach Number 1.85. 1 - Projecting Single Shock Cones

DTIC Science & Technology

1947-06-17

cylindrical simulated combustion chamber was used to vary the outlet area of the flow through the diffuser. The pitot -static rake , located as shown in the...Simulated combustion u chamber A 90° W •—Conical damper S Static-pressure orifice ps pitot -static "" rake ’ NATIONAL ADVISORY...recoveries were obtained with subsonic entrance flow. INTRODCJCTION For efficient conversion of the kinetic energy of a supersonic air stream into ram

Superthermal (0.5- 100 keV) Electrons near the ICME-driven shocks

NASA Astrophysics Data System (ADS)

Yang, L.; Wang, L.; Li, G.; Tao, J.; He, J.; Tu, C.

2016-12-01

We present a survey of the 0.5 - 100 keV electrons associated with ICME-driven shocks at 1 AU, using the WIND/3DP electron measurements from 1995 to 2014. We select 66 good ICME-driven shocks, and use the "Rankine-Hugoniot" shock fitting technique to obtain the shock normal, shock velocity Vs, shock compression ratio r and magnetosonic Mach number Ms. We average the electron data in the 1-hour interval immediately after the shock front to obtain the sheath electron fluxes and in the 4-hour quiet-time interval before the shock to obtain the pre-event electron fluxes. Then we subtract the pre-event electron fluxes from the sheath electron fluxes to obtain the enhanced electron fluxes at the shock. We find that the enhanced electron fluxes are positively correlated with Vs and Ms, and generally fit well to a double power-law spectrum, J E-β. At 0.5 - 2 keV, the fitted spectral index β1 ranges from 2.1 to 5.9, negatively correlated with r and Ms. At 2 - 100 keV, the fitted index β2 is smaller than β1, with values ( 1.9 to 3.4) similar to the spectral indexes of quiet-time superhalo electrons in the solar wind. β2 shows no obvious correlation with r and Ms. Neither of β1 or β2 is in agreement with the diffusive shock theoretical predication. These results suggest that electron acceleration by interplanetary shocks may be more significant at a few keVs and the interplanetary shock acceleration can contribute to the production of solar wind superhalo electrons. However, a revision of the diffusive shock acceleration theory would be needed for the electron acceleration.

Effects of Alfvénic Drift on Diffusive Shock Acceleration at Weak Cluster Shocks

NASA Astrophysics Data System (ADS)

Kang, Hyesung; Ryu, Dongsu

2018-03-01

Non-detection of γ-ray emission from galaxy clusters has challenged diffusive shock acceleration (DSA) of cosmic-ray (CR) protons at weak collisionless shocks that are expected to form in the intracluster medium. As an effort to address this problem, we here explore possible roles of Alfvén waves self-excited via resonant streaming instability during the CR acceleration at parallel shocks. The mean drift of Alfvén waves may either increase or decrease the scattering center compression ratio, depending on the postshock cross-helicity, leading to either flatter or steeper CR spectra. We first examine such effects at planar shocks, based on the transport of Alfvén waves in the small amplitude limit. For the shock parameters relevant to cluster shocks, Alfvénic drift flattens the CR spectrum slightly, resulting in a small increase of the CR acceleration efficiency, η. We then consider two additional, physically motivated cases: (1) postshock waves are isotropized via MHD and plasma processes across the shock transition, and (2) postshock waves contain only forward waves propagating along with the flow due to a possible gradient of CR pressure behind the shock. In these cases, Alfvénic drift could reduce η by as much as a factor of five for weak cluster shocks. For the canonical parameters adopted here, we suggest η ∼ 10‑4–10‑2 for shocks with sonic Mach number M s ≈ 2–3. The possible reduction of η may help ease the tension between non-detection of γ-rays from galaxy clusters and DSA predictions.

A New Numerical Scheme for Cosmic-Ray Transport

NASA Astrophysics Data System (ADS)

Jiang, Yan-Fei; Oh, S. Peng

2018-02-01

Numerical solutions of the cosmic-ray (CR) magnetohydrodynamic equations are dogged by a powerful numerical instability, which arises from the constraint that CRs can only stream down their gradient. The standard cure is to regularize by adding artificial diffusion. Besides introducing ad hoc smoothing, this has a significant negative impact on either computational cost or complexity and parallel scalings. We describe a new numerical algorithm for CR transport, with close parallels to two-moment methods for radiative transfer under the reduced speed of light approximation. It stably and robustly handles CR streaming without any artificial diffusion. It allows for both isotropic and field-aligned CR streaming and diffusion, with arbitrary streaming and diffusion coefficients. CR transport is handled explicitly, while source terms are handled implicitly. The overall time step scales linearly with resolution (even when computing CR diffusion) and has a perfect parallel scaling. It is given by the standard Courant condition with respect to a constant maximum velocity over the entire simulation domain. The computational cost is comparable to that of solving the ideal MHD equation. We demonstrate the accuracy and stability of this new scheme with a wide variety of tests, including anisotropic streaming and diffusion tests, CR-modified shocks, CR-driven blast waves, and CR transport in multiphase media. The new algorithm opens doors to much more ambitious and hitherto intractable calculations of CR physics in galaxies and galaxy clusters. It can also be applied to other physical processes with similar mathematical structure, such as saturated, anisotropic heat conduction.

COMPARISON OF IMPLICIT SCHEMES TO SOLVE EQUATIONS OF RADIATION HYDRODYNAMICS WITH A FLUX-LIMITED DIFFUSION APPROXIMATION: NEWTON–RAPHSON, OPERATOR SPLITTING, AND LINEARIZATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tetsu, Hiroyuki; Nakamoto, Taishi, E-mail: h.tetsu@geo.titech.ac.jp

Radiation is an important process of energy transport, a force, and a basis for synthetic observations, so radiation hydrodynamics (RHD) calculations have occupied an important place in astrophysics. However, although the progress in computational technology is remarkable, their high numerical cost is still a persistent problem. In this work, we compare the following schemes used to solve the nonlinear simultaneous equations of an RHD algorithm with the flux-limited diffusion approximation: the Newton–Raphson (NR) method, operator splitting, and linearization (LIN), from the perspective of the computational cost involved. For operator splitting, in addition to the traditional simple operator splitting (SOS) scheme,more » we examined the scheme developed by Douglas and Rachford (DROS). We solve three test problems (the thermal relaxation mode, the relaxation and the propagation of linear waves, and radiating shock) using these schemes and then compare their dependence on the time step size. As a result, we find the conditions of the time step size necessary for adopting each scheme. The LIN scheme is superior to other schemes if the ratio of radiation pressure to gas pressure is sufficiently low. On the other hand, DROS can be the most efficient scheme if the ratio is high. Although the NR scheme can be adopted independently of the regime, especially in a problem that involves optically thin regions, the convergence tends to be worse. In all cases, SOS is not practical.« less

Particle acceleration and turbulence in cosmic Ray shocks: possible pathways beyond the Bohm limit

NASA Astrophysics Data System (ADS)

Malkov, M. A.; Diamond, P. H.

2007-08-01

Diffusive shock acceleration is discussed in terms of its potential to accelerate cosmic rays (CR) to 1018 eV (beyond the ``knee,'' as observations suggest) and in terms of the related observational signatures (spectral features). One idea to reach this energy is to resonantly generate a turbulent magnetic field via accelerated particles much in excess of the background field. We identify difficulties with this scenario and suggest two separate mechanisms that can work in concert with one another leading to a significant acceleration enhancement. The first mechanism is based on a nonlinear modification of the flow ahead of the shock supported by particles already accelerated to some specific (knee) momentum. The particles gain energy by bouncing off converging magnetic irregularities frozen into the flow in the shock precursor and not so much by re-crossing the shock itself. The acceleration rate is determined by the gradient of the flow velocity and turns out to be formally independent of the particle mean free path. The velocity gradient is set by the knee-particles. The acceleration rate of particles above the knee does not decrease with energy, unlike in the linear acceleration regime. The knee (spectrum steepening) forms because particles above it are effectively confined to the shock only if they are within limited domains in the momentum space, while other particles fall into ``loss-islands'', similar to the ``loss-cone'' of magnetic traps. This also maintains the steep velocity gradient and high acceleration rate. The second mechanism is based on the generation of Alfven waves at the gyroradius scale at the background field level, with a subsequent transfer to longer scales via interaction with strong acoustic turbulence in the shock precursor. The acoustic turbulence in turn, may be generated by Drury instability or by parametric instability of the Alfven (A) waves.

SIMULATION OF ENERGETIC PARTICLE TRANSPORT AND ACCELERATION AT SHOCK WAVES IN A FOCUSED TRANSPORT MODEL: IMPLICATIONS FOR MIXED SOLAR PARTICLE EVENTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kartavykh, Y. Y.; Dröge, W.; Gedalin, M.

2016-03-20

We use numerical solutions of the focused transport equation obtained by an implicit stochastic differential equation scheme to study the evolution of the pitch-angle dependent distribution function of protons in the vicinity of shock waves. For a planar stationary parallel shock, the effects of anisotropic distribution functions, pitch-angle dependent spatial diffusion, and first-order Fermi acceleration at the shock are examined, including the timescales on which the energy spectrum approaches the predictions of diffusive shock acceleration theory. We then consider the case that a flare-accelerated population of ions is released close to the Sun simultaneously with a traveling interplanetary shock formore » which we assume a simplified geometry. We investigate the consequences of adiabatic focusing in the diverging magnetic field on the particle transport at the shock, and of the competing effects of acceleration at the shock and adiabatic energy losses in the expanding solar wind. We analyze the resulting intensities, anisotropies, and energy spectra as a function of time and find that our simulations can naturally reproduce the morphologies of so-called mixed particle events in which sometimes the prompt and sometimes the shock component is more prominent, by assuming parameter values which are typically observed for scattering mean free paths of ions in the inner heliosphere and energy spectra of the flare particles which are injected simultaneously with the release of the shock.« less

Combining Diffusive Shock Acceleration with Acceleration by Contracting and Reconnecting Small-scale Flux Ropes at Heliospheric Shocks

NASA Astrophysics Data System (ADS)

le Roux, J. A.; Zank, G. P.; Webb, G. M.; Khabarova, O. V.

2016-08-01

Computational and observational evidence is accruing that heliospheric shocks, as emitters of vorticity, can produce downstream magnetic flux ropes and filaments. This led Zank et al. to investigate a new paradigm whereby energetic particle acceleration near shocks is a combination of diffusive shock acceleration (DSA) with downstream acceleration by many small-scale contracting and reconnecting (merging) flux ropes. Using a model where flux-rope acceleration involves a first-order Fermi mechanism due to the mean compression of numerous contracting flux ropes, Zank et al. provide theoretical support for observations that power-law spectra of energetic particles downstream of heliospheric shocks can be harder than predicted by DSA theory and that energetic particle intensities should peak behind shocks instead of at shocks as predicted by DSA theory. In this paper, a more extended formalism of kinetic transport theory developed by le Roux et al. is used to further explore this paradigm. We describe how second-order Fermi acceleration, related to the variance in the electromagnetic fields produced by downstream small-scale flux-rope dynamics, modifies the standard DSA model. The results show that (I) this approach can qualitatively reproduce observations of particle intensities peaking behind the shock, thus providing further support for the new paradigm, and (II) stochastic acceleration by compressible flux ropes tends to be more efficient than incompressible flux ropes behind shocks in modifying the DSA spectrum of energetic particles.

COMBINING DIFFUSIVE SHOCK ACCELERATION WITH ACCELERATION BY CONTRACTING AND RECONNECTING SMALL-SCALE FLUX ROPES AT HELIOSPHERIC SHOCKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Le Roux, J. A.; Zank, G. P.; Webb, G. M.

2016-08-10

Computational and observational evidence is accruing that heliospheric shocks, as emitters of vorticity, can produce downstream magnetic flux ropes and filaments. This led Zank et al. to investigate a new paradigm whereby energetic particle acceleration near shocks is a combination of diffusive shock acceleration (DSA) with downstream acceleration by many small-scale contracting and reconnecting (merging) flux ropes. Using a model where flux-rope acceleration involves a first-order Fermi mechanism due to the mean compression of numerous contracting flux ropes, Zank et al. provide theoretical support for observations that power-law spectra of energetic particles downstream of heliospheric shocks can be harder thanmore » predicted by DSA theory and that energetic particle intensities should peak behind shocks instead of at shocks as predicted by DSA theory. In this paper, a more extended formalism of kinetic transport theory developed by le Roux et al. is used to further explore this paradigm. We describe how second-order Fermi acceleration, related to the variance in the electromagnetic fields produced by downstream small-scale flux-rope dynamics, modifies the standard DSA model. The results show that (i) this approach can qualitatively reproduce observations of particle intensities peaking behind the shock, thus providing further support for the new paradigm, and (ii) stochastic acceleration by compressible flux ropes tends to be more efficient than incompressible flux ropes behind shocks in modifying the DSA spectrum of energetic particles.« less

Heat Diffusion in Gases, Including Effects of Chemical Reaction

NASA Technical Reports Server (NTRS)

Hansen, C. Frederick

1960-01-01

The diffusion of heat through gases is treated where the coefficients of thermal conductivity and diffusivity are functions of temperature. The diffusivity is taken proportional to the integral of thermal conductivity, where the gas is ideal, and is considered constant over the temperature interval in which a chemical reaction occurs. The heat diffusion equation is then solved numerically for a semi-infinite gas medium with constant initial and boundary conditions. These solutions are in a dimensionless form applicable to gases in general, and they are used, along with measured shock velocity and heat flux through a shock reflecting surface, to evaluate the integral of thermal conductivity for air up to 5000 degrees Kelvin. This integral has the properties of a heat flux potential and replaces temperature as the dependent variable for problems of heat diffusion in media with variable coefficients. Examples are given in which the heat flux at the stagnation region of blunt hypersonic bodies is expressed in terms of this potential.

A linearized Euler analysis of unsteady flows in turbomachinery

NASA Technical Reports Server (NTRS)

Hall, Kenneth C.; Crawley, Edward F.

1987-01-01

A method for calculating unsteady flows in cascades is presented. The model, which is based on the linearized unsteady Euler equations, accounts for blade loading shock motion, wake motion, and blade geometry. The mean flow through the cascade is determined by solving the full nonlinear Euler equations. Assuming the unsteadiness in the flow is small, then the Euler equations are linearized about the mean flow to obtain a set of linear variable coefficient equations which describe the small amplitude, harmonic motion of the flow. These equations are discretized on a computational grid via a finite volume operator and solved directly subject to an appropriate set of linearized boundary conditions. The steady flow, which is calculated prior to the unsteady flow, is found via a Newton iteration procedure. An important feature of the analysis is the use of shock fitting to model steady and unsteady shocks. Use of the Euler equations with the unsteady Rankine-Hugoniot shock jump conditions correctly models the generation of steady and unsteady entropy and vorticity at shocks. In particular, the low frequency shock displacement is correctly predicted. Results of this method are presented for a variety of test cases. Predicted unsteady transonic flows in channels are compared to full nonlinear Euler solutions obtained using time-accurate, time-marching methods. The agreement between the two methods is excellent for small to moderate levels of flow unsteadiness. The method is also used to predict unsteady flows in cascades due to blade motion (flutter problem) and incoming disturbances (gust response problem).

Nonlinear reflection of shock shear waves in soft elastic media.

PubMed

Pinton, Gianmarco; Coulouvrat, François; Gennisson, Jean-Luc; Tanter, Mickaël

2010-02-01

For fluids, the theoretical investigation of shock wave reflection has a good agreement with experiments when the incident shock Mach number is large. But when it is small, theory predicts that Mach reflections are physically unrealistic, which contradicts experimental evidence. This von Neumann paradox is investigated for shear shock waves in soft elastic solids with theory and simulations. The nonlinear elastic wave equation is approximated by a paraxial wave equation with a cubic nonlinear term. This equation is solved numerically with finite differences and the Godunov scheme. Three reflection regimes are observed. Theory is developed for shock propagation by applying the Rankine-Hugoniot relations and entropic constraints. A characteristic parameter relating diffraction and non-linearity is introduced and its theoretical values are shown to match numerical observations. The numerical solution is then applied to von Neumann reflection, where curved reflected and Mach shocks are observed. Finally, the case of weak von Neumann reflection, where there is no reflected shock, is examined. The smooth but non-monotonic transition between these three reflection regimes, from linear Snell-Descartes to perfect grazing case, provides a solution to the acoustical von Neumann paradox for the shear wave equation. This transition is similar to the quadratic non-linearity in fluids.

A theoretical perspective on particle acceleration by interplanetary shocks and the Solar Energetic Particle problem

NASA Astrophysics Data System (ADS)

Verkhoglyadova, Olga P.; Zank, Gary P.; Li, Gang

2015-02-01

Understanding the physics of Solar Energetic Particle (SEP) events is of importance to the general question of particle energization throughout the cosmos as well as playing a role in the technologically critical impact of space weather on society. The largest, and often most damaging, events are the so-called gradual SEP events, generally associated with shock waves driven by coronal mass ejections (CMEs). We review the current state of knowledge about particle acceleration at evolving interplanetary shocks with application to SEP events that occur in the inner heliosphere. Starting with a brief outline of recent theoretical progress in the field, we focus on current observational evidence that challenges conventional models of SEP events, including complex particle energy spectra, the blurring of the distinction between gradual and impulsive events, and the difference inherent in particle acceleration at quasi-parallel and quasi-perpendicular shocks. We also review the important problem of the seed particle population and its injection into particle acceleration at a shock. We begin by discussing the properties and characteristics of non-relativistic interplanetary shocks, from their formation close to the Sun to subsequent evolution through the inner heliosphere. The association of gradual SEP events with shocks is discussed. Several approaches to the energization of particles have been proposed, including shock drift acceleration, diffusive shock acceleration (DSA), acceleration by large-scale compression regions, acceleration by random velocity fluctuations (sometimes known as the "pump mechanism"), and others. We review these various mechanisms briefly and focus on the DSA mechanism. Much of our emphasis will be on our current understanding of the parallel and perpendicular diffusion coefficients for energetic particles and models of plasma turbulence in the vicinity of the shock. Because of its importance both to the DSA mechanism itself and to the particle composition of SEP events, we address in some detail the injection problem. Although steady-state models can improve our understanding of the diffusive shock acceleration mechanism, SEP events are inherently time-dependent. We therefore review the time-dependent theory of DSA in some detail, including estimating possible maximum particle energies and particle escape from the shock complex. We also discuss generalizations of the diffusive transport approach to modeling particle acceleration by considering a more general description based on the focused transport equation. The escape of accelerated particles from the shock requires that their subsequent transport in the interplanetary medium be modeled and the consequence of interplanetary transport can lead to the complex spectra and compositional profiles that are observed frequently. The different approaches to particle transport in the inner heliosphere are reviewed. The various numerical models that have been developed to solve the gradual SEP problem are reviewed. Explicit comparisons of modeling results with observations of large SEP events are discussed. A summary of current progress and the outlook on the SEP problem and remaining open questions conclude the review.

Hugoniot and refractive indices of bromoform under shock compression

NASA Astrophysics Data System (ADS)

Liu, Q. C.; Zeng, X. L.; Zhou, X. M.; Luo, S. N.

2018-01-01

We investigate physical properties of bromoform (liquid CHBr3) including compressibility and refractive index under dynamic extreme conditions of shock compression. Planar shock experiments are conducted along with high-speed laser interferometry. Our experiments and previous results establish a linear shock velocity-particle velocity relation for particle velocities below 1.77 km/s, as well as the Hugoniot and isentropic compression curves up to ˜21 GPa. Shock-state refractive indices of CHBr3 up to 2.3 GPa or ˜26% compression, as a function of density, can be described with a linear relation and follows the Gladstone-Dale relation. The velocity corrections for laser interferometry measurements at 1550 nm are also obtained.

Diffusive Shock Acceleration and Reconnection Acceleration Processes

NASA Astrophysics Data System (ADS)

Zank, G. P.; Hunana, P.; Mostafavi, P.; Le Roux, J. A.; Li, Gang; Webb, G. M.; Khabarova, O.; Cummings, A.; Stone, E.; Decker, R.

2015-12-01

Shock waves, as shown by simulations and observations, can generate high levels of downstream vortical turbulence, including magnetic islands. We consider a combination of diffusive shock acceleration (DSA) and downstream magnetic-island-reconnection-related processes as an energization mechanism for charged particles. Observations of electron and ion distributions downstream of interplanetary shocks and the heliospheric termination shock (HTS) are frequently inconsistent with the predictions of classical DSA. We utilize a recently developed transport theory for charged particles propagating diffusively in a turbulent region filled with contracting and reconnecting plasmoids and small-scale current sheets. Particle energization associated with the anti-reconnection electric field, a consequence of magnetic island merging, and magnetic island contraction, are considered. For the former only, we find that (i) the spectrum is a hard power law in particle speed, and (ii) the downstream solution is constant. For downstream plasmoid contraction only, (i) the accelerated spectrum is a hard power law in particle speed; (ii) the particle intensity for a given energy peaks downstream of the shock, and the distance to the peak location increases with increasing particle energy, and (iii) the particle intensity amplification for a particular particle energy, f(x,c/{c}0)/f(0,c/{c}0), is not 1, as predicted by DSA, but increases with increasing particle energy. The general solution combines both the reconnection-induced electric field and plasmoid contraction. The observed energetic particle intensity profile observed by Voyager 2 downstream of the HTS appears to support a particle acceleration mechanism that combines both DSA and magnetic-island-reconnection-related processes.

Simulations of the Richtmyer-Meshkov Instability in a two-shock vertical shock tube

NASA Astrophysics Data System (ADS)

Ferguson, Kevin; Olson, Britton; Jacobs, Jeffrey

2017-11-01

Simulations of the Richtmyer-Meshkov Instability (RMI) in a new two-shock vertical shock tube configuration are presented. The simulations are performed using the ARES code at Lawrence-Livermore National Laboratory (LLNL). Two M=1.2 shock waves travel in opposing directions and impact an initially stationary interface formed by sulfur hexaflouride (SF6) and air. The delay between the two shocks is controlled to achieve a prescribed temporal separation in shock wave arrival time. Initial interface perturbations and diffusion profiles are generated in keeping with previously gathered experimental data. The effect of varying the inter-shock delay and initial perturbation structure on instability growth and mixing parameters is examined. Information on the design, construction, and testing of a new two-shock vertical shock tube are also presented.

DIFFUSIVE SHOCK ACCELERATION SIMULATIONS OF RADIO RELICS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Hyesung; Ryu, Dongsu; Jones, T. W., E-mail: kang@uju.es.pusan.ac.kr, E-mail: ryu@canopus.cnu.ac.kr, E-mail: twj@msi.umn.edu

2012-09-01

Recent radio observations have identified a class of structures, so-called radio relics, in clusters of galaxies. The radio emission from these sources is interpreted as synchrotron radiation from GeV electrons gyrating in {mu}G-level magnetic fields. Radio relics, located mostly in the outskirts of clusters, seem to associate with shock waves, especially those developed during mergers. In fact, they seem to be good structures to identify and probe such shocks in intracluster media (ICMs), provided we understand the electron acceleration and re-acceleration at those shocks. In this paper, we describe time-dependent simulations for diffusive shock acceleration at weak shocks that aremore » expected to be found in ICMs. Freshly injected as well as pre-existing populations of cosmic-ray (CR) electrons are considered, and energy losses via synchrotron and inverse Compton are included. We then compare the synchrotron flux and spectral distributions estimated from the simulations with those in two well-observed radio relics in CIZA J2242.8+5301 and ZwCl0008.8+5215. Considering that CR electron injection is expected to be rather inefficient at weak shocks with Mach number M {approx}< a few, the existence of radio relics could indicate the pre-existing population of low-energy CR electrons in ICMs. The implication of our results on the merger shock scenario of radio relics is discussed.« less

On the Absence of Non-thermal X-Ray Emission around Runaway O Stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Toalá, J. A.; Oskinova, L. M.; Ignace, R.

Theoretical models predict that the compressed interstellar medium around runaway O stars can produce high-energy non-thermal diffuse emission, in particular, non-thermal X-ray and γ -ray emission. So far, detection of non-thermal X-ray emission was claimed for only one runaway star, AE Aur. We present a search for non-thermal diffuse X-ray emission from bow shocks using archived XMM-Newton observations for a clean sample of six well-determined runaway O stars. We find that none of these objects present diffuse X-ray emission associated with their bow shocks, similarly to previous X-ray studies toward ζ Oph and BD+43°3654. We carefully investigated multi-wavelength observations ofmore » AE Aur and could not confirm previous findings of non-thermal X-rays. We conclude that so far there is no clear evidence of non-thermal extended emission in bow shocks around runaway O stars.« less

Investigation of charge weight and shock factor effect on non-linear transient structural response of rectangular plates subjected to underwater explosion (UNDEX) shock loading

NASA Astrophysics Data System (ADS)

Demir, Ozgur; Sahin, Abdurrahman; Yilmaz, Tamer

2012-09-01

Underwater explosion induced shock loads are capable of causing considerable structural damage. Investigations of the underwater explosion (UNDEX) effects on structures have seen continuous developments because of security risks. Most of the earlier experimental investigations were performed by military since the World War I. Subsequently; Cole [1] established mathematical relations for modeling underwater explosion shock loading, which were the outcome of many experimental investigations This study predicts and establishes the transient responses of a panel structure to underwater explosion shock loads using non-linear finite element code Ls-Dyna. Accordingly, in this study a new MATLAB code has been developed for predicting shock loading profile for different weight of explosive and different shock factors. Numerical analysis was performed for various test conditions and results are compared with Ramajeyathilagam's experimental study [8].

The effect of stochastic re-acceleration on the energy spectrum of shock-accelerated protons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Afanasiev, Alexandr; Vainio, Rami; Kocharov, Leon

2014-07-20

The energy spectra of particles in gradual solar energetic particle (SEP) events do not always have a power-law form attributed to the diffusive shock acceleration mechanism. In particular, the observed spectra in major SEP events can take the form of a broken (double) power law. In this paper, we study the effect of a process that can modify the power-law spectral form produced by the diffusive shock acceleration: the stochastic re-acceleration of energetic protons by enhanced Alfvénic turbulence in the downstream region of a shock wave. There are arguments suggesting that this process can be important when the shock propagatesmore » in the corona. We consider a coronal magnetic loop traversed by a shock and perform Monte Carlo simulations of interactions of shock-accelerated protons with Alfvén waves in the loop. The wave-particle interactions are treated self-consistently, so the finiteness of the available turbulent energy is taken into account. The initial energy spectrum of particles is taken to be a power law. The simulations reveal that the stochastic re-acceleration leads either to the formation of a spectrum that is described in a wide energy range by a power law (although the resulting power-law index is different from the initial one) or to a broken power-law spectrum. The resulting spectral form is determined by the ratio of the energy density of shock-accelerated protons to the wave energy density in the shock's downstream region.« less

Shock Wave Dynamics in Weakly Ionized Plasmas

NASA Technical Reports Server (NTRS)

Johnson, Joseph A., III

1999-01-01

An investigation of the dynamics of shock waves in weakly ionized argon plasmas has been performed using a pressure ruptured shock tube. The velocity of the shock is observed to increase when the shock traverses the plasma. The observed increases cannot be accounted for by thermal effects alone. Possible mechanisms that could explain the anomalous behavior include a vibrational/translational relaxation in the nonequilibrium plasma, electron diffusion across the shock front resulting from high electron mobility, and the propagation of ion-acoustic waves generated at the shock front. Using a turbulence model based on reduced kinetic theory, analysis of the observed results suggest a role for turbulence in anomalous shock dynamics in weakly ionized media and plasma-induced hypersonic drag reduction.

Shock recovery of a magnesium-silicate spinelloid

NASA Astrophysics Data System (ADS)

Tschauner, O. D.; Asimow, P. D.; Ahrens, T. J.; Kostandova, N.

2009-12-01

Previously it was believed that some high pressure polymorphs (e.g. of framework silicates) form under shock via growth from shock-induced precursor microscopic melt zones. Since diffusion in the melt was assumed to control crystallization rates, absence of shock recovery of any of those minerals was attributed to the short duration of laboratory shock (0.1 to 1 microsecond) experiments. In contrast to laboratory experiments, grains of high pressure polymorphs of 1 - 100 micrometer diameter have been found in melt veins of shocked meteorites and were widely believed to have formed via diffusion-controlled growth that occurred over seconds to minute time scales. Recently we reported formation of wadsleyite from a shock-generated melt in a laboratory shock experiment by analysis of the recovery products [1]. The growth rate of wadsleyite crystals at the experimental temperature of 2000 to 3000 K was estimated to be several m/s suggesting that diffusion was not the dominant factor in this ultra-rapid crystal growth. Consequently, S6 shock events in chondrites may not always be related to long shock duration and large impactors. Here we report formation of another high-pressure magnesium silicate polymorph in a shock experiment. The starting materials for this 30 GPa shot was single-crystal synthetic forsterite in a NIST 1157 tool-steel chamber. The recovered material was analyzed by micro-Raman spectroscopy and by synchrotron-based micro-X ray diffraction. Diffraction experiments were conducted in Gandolfi-geometry at station B2, CHESS, using a MAR345 image plate detector and a primary beam of 25 keV energy. Melted regions of the sample contained a spinelloid isotypic to a magnesium-gallium germanate spinelloid synthesized at ambient pressure [2]. As in the previous study [1] we observe oxidation of iron from melted metal of the recovery chamber wall entrained by the silicate melt while silicon is partially reduced. The new high-pressure silicate may have formed at less than the peak pressure experienced by the sample. [1]: O.Tschauner, P.D. Asimow, N. Kostandova,T.J. Ahrens, C. Ma, S. Sinogeikin, Z. Liu, S. Fakra, N. Tamura, Proc. Nat. Acad. Sci. USA 106, 13691-5 (2009) , [2]: Barbier, J., Hyde, B.G.,Acta Cryst. B 43, 34-40 (1987).

Jet oscillations caused by vorticity interactions with shock waves

NASA Technical Reports Server (NTRS)

Parthasarathy, S. P.; Harstad, K.; Massier, P. F.

1981-01-01

A linear theory is developed for the amplification of disturbances along a jet containing shock waves. The theory indicates that near grazing angles (i.e., wave angles near 90 deg) horizontal vorticity is greatly amplified after passing through the two shock waves that exist in a shock cell. The cumulative amplification and the mode that is amplified most can be obtained if the changes in shock parameters from cell to cell are known. Rapid rates of growth of disturbances are exhibited by shadowgraphs and rates of angular displacement of about 10 are observed. The linear two-dimensional theory also indicates that such rates of amplification occur, and that the behavior of a two-dimensional jet is qualitatively similar to that of a round jet.

Effect of ploidy on scale-cover pattern in linear ornamental (koi) common carp Cyprinus carpio.

PubMed

Gomelsky, B; Schneider, K J; Glennon, R P; Plouffe, D A

2012-09-01

The effect of ploidy on scale-cover pattern in linear ornamental (koi) common carp Cyprinus carpio was investigated. To obtain diploid and triploid linear fish, eggs taken from a leather C. carpio female (genotype ssNn) and sperm taken from a scaled C. carpio male (genotype SSnn) were used for the production of control (no shock) and heat-shocked progeny. In heat-shocked progeny, the 2 min heat shock (40° C) was applied 6 min after insemination. Diploid linear fish (genotype SsNn) demonstrated a scale-cover pattern typical for this category with one even row of scales along lateral line and few scales located near operculum and at bases of fins. The majority (97%) of triploid linear fish (genotype SssNnn) exhibited non-typical scale patterns which were characterized by the appearance of additional scales on the body. The extent of additional scales in triploid linear fish was variable; some fish had large scales, which covered almost the entire body. Apparently, the observed difference in scale-cover pattern between triploid and diploid linear fish was caused by different phenotypic expression of gene N/n. Due to incomplete dominance of allele N, triploids Nnn demonstrate less profound reduction of scale cover compared with diploids Nn. © 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles.

Investigation of Three-Dimensional Unsteady Flow Characteristics in Transonic Diffusers

NASA Astrophysics Data System (ADS)

Proshchanka, Dzianis; Yonezawa, Koichi; Tsujimoto, Yoshinobu

Three-dimensional characteristics of unsteady flow in supercritical transonic diffuser are investigated. For various pressure ratios three-dimensional flow containing a normal shock/turbulent boundary layer interaction regions with shockwave and pseudo-shockwaves fluctuating in longitudinal and spanwise directions is observed. Experimental and numerical investigations show details of the flowfield in the vicinity of terminal shock, interaction regions and downstream turbulent unsteady flow. Spectral analysis of pressure fluctuations reveals existence of two characteristic frequencies attributed to the shockwave fluctuation in longitudinal direction for the lower frequency case and acoustic resonance in spanwise direction for the higher one. Vortices appear at each corner in transversal sections modifying the core flow. As a result, size and depth of longitudinal and vertical penetration of separation regions impelled by the terminal shock is either increased or decreased.

Simulating cosmic ray physics on a moving mesh

NASA Astrophysics Data System (ADS)

Pfrommer, C.; Pakmor, R.; Schaal, K.; Simpson, C. M.; Springel, V.

2017-03-01

We discuss new methods to integrate the cosmic ray (CR) evolution equations coupled to magnetohydrodynamics on an unstructured moving mesh, as realized in the massively parallel AREPO code for cosmological simulations. We account for diffusive shock acceleration of CRs at resolved shocks and at supernova remnants in the interstellar medium (ISM) and follow the advective CR transport within the magnetized plasma, as well as anisotropic diffusive transport of CRs along the local magnetic field. CR losses are included in terms of Coulomb and hadronic interactions with the thermal plasma. We demonstrate the accuracy of our formalism for CR acceleration at shocks through simulations of plane-parallel shock tubes that are compared to newly derived exact solutions of the Riemann shock-tube problem with CR acceleration. We find that the increased compressibility of the post-shock plasma due to the produced CRs decreases the shock speed. However, CR acceleration at spherically expanding blast waves does not significantly break the self-similarity of the Sedov-Taylor solution; the resulting modifications can be approximated by a suitably adjusted, but constant adiabatic index. In first applications of the new CR formalism to simulations of isolated galaxies and cosmic structure formation, we find that CRs add an important pressure component to the ISM that increases the vertical scaleheight of disc galaxies and thus reduces the star formation rate. Strong external structure formation shocks inject CRs into the gas, but the relative pressure of this component decreases towards halo centres as adiabatic compression favours the thermal over the CR pressure.

XMM-Newton Observations of the Southeastern Radio Relic in Abell 3667

NASA Astrophysics Data System (ADS)

Storm, Emma; Vink, Jacco; Zandanel, Fabio; Akamatsu, Hiroki

2018-06-01

Radio relics, elongated, non-thermal, structures located at the edges of galaxy clusters, are the result of synchrotron radiation from cosmic-ray electrons accelerated by merger-driven shocks at the cluster outskirts. However, X-ray observations of such shocks in some clusters suggest that they are too weak to efficiently accelerate electrons via diffusive shock acceleration to energies required to produce the observed radio power. We examine this issue in the merging galaxy cluster Abell 3667 (A3667), which hosts a pair of radio relics. While the Northwest relic in A3667 has been well studied in the radio and X-ray by multiple instruments, the Southeast relic region has only been observed so far by Suzaku, which detected a temperature jump across the relic, suggesting the presence of a weak shock. We present observations of the Southeastern region of A3667 with XMM-Newton centered on the radio relic. We confirm the existence of an X-ray shock with Mach number of about 1.8 from a clear detection of temperature jump and a tentative detection of a density jump, consistent with previous measurements by Suzaku. We discuss the implications of this measurement for diffusive shock acceleration as the main mechanism for explaining the origin of radio relics. We then speculate on the plausibility of alternative scenarios, including re-acceleration and variations in the Mach number along shock fronts.

Modeling the effect of orientation on the shock response of a damageable composite material

NASA Astrophysics Data System (ADS)

Lukyanov, Alexander A.

2012-10-01

A carbon fiber-epoxy composite (CFEC) shock response in the through thickness orientation and in one of the fiber directions is significantly different. The hydrostatic pressure inside anisotropic materials depends on deviatoric strain components as well as volumetric strain. Non-linear effects, such as shock effects, can be incorporated through the volumetric straining in the material. Thus, a new basis is required to couple the anisotropic material stiffness and strength with anisotropic shock effects, associated energy dependence, and damage softening process. This article presents these constitutive equations for shock wave modeling of a damageable carbon fiber-epoxy composite. Modeling the effect of fiber orientation on the shock response of a CFEC has been performed using a generalized decomposition of the stress tensor [A. A. Lukyanov, Int. J. Plast. 24, 140 (2008)] and Mie-Grüneisen's extrapolation of high-pressure shock Hugoniot states to other thermodynamics states for shocked CFEC materials. The three-wave structure (non-linear anisotropic, fracture, and isotropic elastic waves) that accompanies damage softening process is also proposed in this work for describing CFEC behavior under shock loading which allows to remove any discontinuities observed in the linear case for relation between shock velocities and particle velocities [A. A. Lukyanov, Eur. Phys. J. B 74, 35 (2010)]. Different Hugoniot stress levels are obtained when the material is impacted in different directions; their good agreement with the experiment demonstrates that the anisotropic equation of state, strength, and damage model are adequate for the simulation of shock wave propagation within damageable CFEC material. Remarkably, in the through thickness orientation, the material behaves similar to a simple polymer whereas in the fiber direction, the proposed in this paper model explains an initial ramp, before at sufficiently high stresses, and a much faster rising shock above it. The numerical results for shock wave modeling using proposed constitutive equations are presented, discussed, and future studies are outlined.

The structure of mass-loading shocks. [interaction of solar wind with cometary coma or local interstellar medium using two-fluid model

NASA Technical Reports Server (NTRS)

Zank, G. P.; Khabibrakhmanov, I. KH.; Story, T.

1993-01-01

A new two-fluid model which describes mass loading in the solar wind (e.g., the interaction of the solar wind with a cometary coma or the local interstellar medium) is presented. The self-consistent back-reaction of the mass-loaded ions is included through their effective scattering in low-frequency MHD turbulence and the invocation of a diffusive approximation. Such an approximation has the advantage of introducing self-consistent dissipation coefficients into the governing equations, thereby facilitating the investigation of the internal structure of shocks in mass-loading environments. To illustrate the utility of the new model, we consider the structure of cometary shocks in the hypersonic one-dimensional limit, finding that the incoming solar wind is slowed by both mass loading and the development of a large cometary ion pressure gradient. The shock is broadened and smoothed by the cometary ions with a thickness of the order of the cometary ion diffusion scale.

Theoretical and Observational Analysis of Particle Acceleration Mechanisms at Astrophysical Shocks

NASA Astrophysics Data System (ADS)

Lever, Edward Lawrence

We analytically and numerically investigate the viability of Shock Surfing as a pre-injection mechanism for Diffusive Shock Acceleration, believed to be responsible for the production of Cosmic Rays. We demonstrate mathematically and from computer simulations that four critical conditions must be satisfied for Shock Surfing to function; the shock ramp must be narrow, the shock front must be smooth, the magnetic field angle must be very nearly perpendicular and, finally, these conditions must persist without interruption over substantial time periods and spatial scales. We quantify these necessary conditions, exhibit predictive functions for velocity maxima and accelerated ion fluxes based on observable shock parameters, and show unequivocally from current observational evidence that all of these necessary conditions are violated at shocks within the heliosphere, at the heliospheric Termination Shock, and also at Supernovae.

Laser Interferometry Measurements of Cold-Sprayed Copper Thermite Shocked to 30 GPa

NASA Astrophysics Data System (ADS)

Neel, Christopher; Lacina, David

2015-06-01

Plate impact experiments were conducted on a cold-sprayed Al-CuO thermite at peak stresses varying between 5-30 GPa to determine the Hugoniot and characterize any shock induced energetic reaction. Photon Doppler Velocimetry (PDV) measurements were used to obtain particle velocity histories and shock speed information for both the shock loading and unloading behavior of the material. Low stress experiments (<20GPa) exhibited a linearly increasing shock speed with increasing particle velocity. However, an obvious change in slope (i.e. a ``kink'') is present in the Hugoniot at stresses above ~ 20 GPa which follow a linear increase up to the highest stresses attained in this work. The change in Hugoniot curve suggests a volume-increasing reaction occurs in this shocked Al-CuO thermite near 20 GPa, but an analysis of the measured particle velocity histories does not support this assertion. To better characterize any shock-induced thermite reactions, emission spectroscopy measurements were obtained at stresses above and below 20 GPa.

Shock-induced CO2 loss from CaCO3: Implications for early planetary atmospheres

NASA Technical Reports Server (NTRS)

Lange, M. A.; Ahrens, T. J.

1984-01-01

Recovered samples from shock recovery experiments on single crystal calcite were subjected to thermogravimetric analysis to determine the amount of post-shock CO2, the decarbonization interval and the activation energy, for the removal of remaining CO2 in shock-loaded calcite. Comparison of post-shock CO2 with that initially present determines shock-induced CO2 loss as a function of shock pressure. Incipient to complete CO2 loss occurs over a pressure range of approximately 10 to approximately 70 GPa. Optical and scanning electron microscopy reveal structural changes, which are related to the shock-loading. The occurrence of dark, diffuse areas, which can be resolved as highly vesicular areas as observed with a scanning electron microscope are interpreted as representing quenched partial melts, into which shock-released CO2 was injected. The experimental results are used to constrain models of shock-produced, primary CO2 atmospheres on the accreting terrestrial planets.

Shock drift acceleration in the presence of waves

NASA Technical Reports Server (NTRS)

Decker, R. B.; Vlahos, L.

1985-01-01

Attention is given to the initial results of a model designed to study the modification of the scatter-free, shock drift acceleration of energetic test particles by wave activity in the vicinity of a quasi-perpendicular, fast-mode MHD shock. It is emphasized that the concept of magnetic moment conservation is a valid approximation only in the perpendicular and nearly perpendicular regimes, when the angle theta-Bn between the shock normal and the upstream magnetic field vector is in the range from 70 deg to 90 deg. The present investigation is concerned with one step in a program which is being developed to combine the shock drift and diffusive processes at a shock of arbitrary theta-Bn.

Fluid displacement between two parallel plates: a non-empirical model displaying change of type from hyperbolic to elliptic equations

NASA Astrophysics Data System (ADS)

Shariati, M.; Talon, L.; Martin, J.; Rakotomalala, N.; Salin, D.; Yortsos, Y. C.

2004-11-01

We consider miscible displacement between parallel plates in the absence of diffusion, with a concentration-dependent viscosity. By selecting a piecewise viscosity function, this can also be considered as ‘three-fluid’ flow in the same geometry. Assuming symmetry across the gap and based on the lubrication (‘equilibrium’) approximation, a description in terms of two quasi-linear hyperbolic equations is obtained. We find that the system is hyperbolic and can be solved analytically, when the mobility profile is monotonic, or when the mobility of the middle phase is smaller than its neighbours. When the mobility of the middle phase is larger, a change of type is displayed, an elliptic region developing in the composition space. Numerical solutions of Riemann problems of the hyperbolic system spanning the elliptic region, with small diffusion added, show good agreement with the analytical outside, but an unstable behaviour inside the elliptic region. In these problems, the elliptic region arises precisely at the displacement front. Crossing the elliptic region requires the solution of essentially an eigenvalue problem of the full higher-dimensional model, obtained here using lattice BGK simulations. The hyperbolic-to-elliptic change-of-type reflects the failing of the lubrication approximation, underlying the quasi-linear hyperbolic formalism, to describe the problem uniformly. The obtained solution is analogous to non-classical shocks recently suggested in problems with change of type.

Control of a Normal Shock Boundary Layer Interaction with Ramped Vanes of Various Sizes

NASA Astrophysics Data System (ADS)

Lee, Sang; Loth, Eric

2017-11-01

A novel vortex generator design positioned upstream of a normal shock and a subsequent diffuser was investigated using large eddy simulations. In particular, ``ramped-vane'' flow control devices with three difference heights relative to the incoming boundary layer thickness (0.34 δ 0.52 δ and 0.75 δ were placed in a supersonic boundary layer with a freestream Mach number of 1.3 and a Reynolds number of 2,400 based on momentum thickness. These devices are similar to subsonic vanes but are designed to be more mechanically robust while having low wave drag. The devices generated strong streamwise vortices that entrained high momentum fluid to the near-wall region and increased turbulent mixing. The devices also decreased shock-induced flow separation, which resulted in a higher downstream skin friction in the diffuser. In general, the largest ramped-vane (0.75 δ) produced the largest reductions in flow separation, shape factor and overall unsteadiness. However, the medium-sized ramped vane (0.52 δ) was able to also reduce both the separation area and the diffuser displacement thickness. The smallest device (0.34 δ) had a weak impact of the flow in the diffuser, though a 10% reduction in the shape factor was achieved.

Passive Rocket Diffuser Testing: Reacting Flow Performance of Four Second-Throat Geometries

NASA Technical Reports Server (NTRS)

Jones, Daniel R.; Allgood, Daniel C.; Saunders, Grady P.

2016-01-01

Second-throat diffusers serve to isolate rocket engines from the effects of ambient back pressure. As one of the nation's largest rocket testing facilities, the performance and design limitations of diffusers are of great interest to NASA's Stennis Space Center. This paper describes a series of tests conducted on four diffuser configurations to better understand the effects of inlet geometry and throat area on starting behavior and boundary layer separation. The diffusers were tested for a duration of five seconds with a 1455-pound thrust, LO2/GH2 thruster to ensure they each reached aerodynamic steady state. The effects of a water spray ring at the diffuser exits and a water-cooled deflector plate were also evaluated. Static pressure and temperature measurements were taken at multiple axial locations along the diffusers, and Computational Fluid Dynamics (CFD) simulations were used as a tool to aid in the interpretation of data. The hot combustion products were confirmed to enable the diffuser start condition with tighter second throats than predicted by historical cold-flow data or the theoretical normal shock method. Both aerodynamic performance and heat transfer were found to increase with smaller diffuser throats. Spray ring and deflector cooling water had negligible impacts on diffuser boundary layer separation. CFD was found to accurately capture diffuser shock structures and full-flowing diffuser wall pressures, and the qualitative behavior of heat transfer. However, the ability to predict boundary layer separated flows was not consistent.

Computational Analyses in Support of Sub-scale Diffuser Testing for the A-3 Facility. Part 2; Unsteady Analyses and Risk Assessment

NASA Technical Reports Server (NTRS)

Ahuja, Vineet; Hosangadi, Ashvin; Allgood, Daniel

2008-01-01

Simulation technology can play an important role in rocket engine test facility design and development by assessing risks, providing analysis of dynamic pressure and thermal loads, identifying failure modes and predicting anomalous behavior of critical systems. This is especially true for facilities such as the proposed A-3 facility at NASA SSC because of a challenging operating envelope linked to variable throttle conditions at relatively low chamber pressures. Design Support of the feasibility of operating conditions and procedures is critical in such cases due to the possibility of startup/shutdown transients, moving shock structures, unsteady shock-boundary layer interactions and engine and diffuser unstart modes that can result in catastrophic failure. Analyses of such systems is difficult due to resolution requirements needed to accurately capture moving shock structures, shock-boundary layer interactions, two-phase flow regimes and engine unstart modes. In a companion paper, we will demonstrate with the use of CFD, steady analyses advanced capability to evaluate supersonic diffuser and steam ejector performance in the sub-scale A-3 facility. In this paper we will address transient issues with the operation of the facility especially at startup and shutdown, and assess risks related to afterburning due to the interaction of a fuel rich plume with oxygen that is a by-product of the steam ejectors. The primary areas that will be addressed in this paper are: (1) analyses of unstart modes due to flow transients especially during startup/ignition, (2) engine safety during the shutdown process (3) interaction of steam ejectors with the primary plume i.e. flow transients as well as probability of afterburning. In this abstract we discuss unsteady analyses of the engine shutdown process. However, the final paper will include analyses of a staged startup, drawdown of the engine test cell pressure, and risk assessment of potential afterburning in the facility. Unsteady simulations have been carried out to study the engine shutdown process in the facility and understand the physics behind the interactions between the steam ejectors, the test cell and the supersonic diffuser. As a first approximation, to understand the dominant unsteady mechanisms in the engine test cell and the supersonic diffuser, the turning duct in the facility was removed. As the engine loses power a rarefaction wave travels downstream that disrupts the shock cell structure in the supersonic diffuser. Flow from the test cell is seen to expand into the supersonic diffuser section and re-pressurizes the area around the nozzle along with a upstream traveling compression wave that emanates from near the first stage ejectors. Flow from the first stage ejector expands to the center of the duct and a new shock train is formed between the first and second stage ejectors. Both stage ejectors keep the facility pressurized and prevent any large amplitude pressure fluctuations from affecting the engine nozzle. The resultant pressure loads the nozzle experiences in the shutdown process are small.

High-Speed Edge-Detecting Line Scan Smart Camera

NASA Technical Reports Server (NTRS)

Prokop, Norman F.

2012-01-01

A high-speed edge-detecting line scan smart camera was developed. The camera is designed to operate as a component in a NASA Glenn Research Center developed inlet shock detection system. The inlet shock is detected by projecting a laser sheet through the airflow. The shock within the airflow is the densest part and refracts the laser sheet the most in its vicinity, leaving a dark spot or shadowgraph. These spots show up as a dip or negative peak within the pixel intensity profile of an image of the projected laser sheet. The smart camera acquires and processes in real-time the linear image containing the shock shadowgraph and outputting the shock location. Previously a high-speed camera and personal computer would perform the image capture and processing to determine the shock location. This innovation consists of a linear image sensor, analog signal processing circuit, and a digital circuit that provides a numerical digital output of the shock or negative edge location. The smart camera is capable of capturing and processing linear images at over 1,000 frames per second. The edges are identified as numeric pixel values within the linear array of pixels, and the edge location information can be sent out from the circuit in a variety of ways, such as by using a microcontroller and onboard or external digital interface to include serial data such as RS-232/485, USB, Ethernet, or CAN BUS; parallel digital data; or an analog signal. The smart camera system can be integrated into a small package with a relatively small number of parts, reducing size and increasing reliability over the previous imaging system..

Why is solar cycle 24 an inefficient producer of high-energy particle events?

NASA Astrophysics Data System (ADS)

Vainio, Rami; Raukunen, Osku; Tylka, Allan J.; Dietrich, William F.; Afanasiev, Alexandr

2017-08-01

Aims: The aim of the study is to investigate the reason for the low productivity of high-energy SEPs in the present solar cycle. Methods: We employ scaling laws derived from diffusive shock acceleration theory and simulation studies including proton-generated upstream Alfvén waves to find out how the changes observed in the long-term average properties of the erupting and ambient coronal and/or solar wind plasma would affect the ability of shocks to accelerate particles to the highest energies. Results: Provided that self-generated turbulence dominates particle transport around coronal shocks, it is found that the most crucial factors controlling the diffusive shock acceleration process are the number density of seed particles and the plasma density of the ambient medium. Assuming that suprathermal populations provide a fraction of the particles injected to shock acceleration in the corona, we show that the lack of most energetic particle events as well as the lack of low charge-to-mass ratio ion species in the present cycle can be understood as a result of the reduction of average coronal plasma and suprathermal densities in the present cycle over the previous one.

The cosmic-ray shock structure problem for relativistic shocks

NASA Technical Reports Server (NTRS)

Webb, G. M.

1985-01-01

The time asymptotic behaviour of a relativistic (parallel) shock wave significantly modified by the diffusive acceleration of cosmic-rays is investigated by means of relativistic hydrodynamical equations for both the cosmic-rays and thermal gas. The form of the shock structure equation and the dispersion relation for both long and short wavelength waves in the system are obtained. The dependence of the shock acceleration efficiency on the upstream fluid spped, long wavelength Mach number and the ratio N = P sub co/cP sub co+P sub go)(Psub co and P sub go are the upstream cosmic-ray and thermal gas pressures respectively) are studied.

Shock Wave Structure Mediated by Energetic Particles

NASA Astrophysics Data System (ADS)

Mostafavi, P.; Zank, G. P.; Webb, G. M.

2016-12-01

Energetic particles such as cosmic rays, Pick Up Ions (PUIs), and solar energetic particles can affect all facets of plasma physics and astrophysical plasma. Energetic particles play an especially significant role in the dissipative process at shocks and in determining their structure. The very interesting recent observations of shocks in the inner heliosphere found that many shocks appear to be significantly mediated by solar energetic particles which have a pressure that exceeds considerably both the thermal gas pressure and the magnetic field pressure. Energetic particles contribute an isotropic scalar pressure to the plasma system at the leading order, as well as introducing dissipation via a collisionless heat flux (diffusion) at the next order and a collisionless stress tensor (viscosity) at the second order. Cosmic-ray modified shocks were discussed by Axford et al. (1982), Drury (1983), and Webb (1983). Zank et al. (2014) investigated the incorporation of PUIs in the supersonic solar wind beyond 10AU, in the inner Heliosheath and in the Very Local Interstellar Medium. PUIs do not equilibrate collisionally with the background plasma in these regimes. In the absence of equilibration between plasma components, a separate coupled plasma description for the energetic particles is necessary. This model is used to investigate the structure of shock waves assuming that we can neglect the magnetic field. Specifically, we consider the dissipative role that both the energetic particle collisionless heat flux and viscosity play in determining the structure of collisionless shock waves. We show that the incorporation of both energetic particle collisionless heat flux and viscosity is sufficient to completely determine the structure of a shock. Moreover, shocks with three sub-shocks converge to the weak sub-shocks. This work differs from the investigation of Jokipii and Williams (1992) who restricted their attention to a cold thermal gas. For a cold thermal non-magnetized gas, all shocks are smoothed by cosmic ray diffusion and therefore viscosity is not an important process.

Ion Thermal Decoupling and Species Separation in Shock-Driven Implosions

DOE PAGES

Rinderknecht, Hans G.; Rosenberg, M. J.; Li, C. K.; ...

2015-01-14

Here, anomalous reduction of the fusion yields by 50% and anomalous scaling of the burn-averaged ion temperatures with the ion-species fraction has been observed for the first time in D 3He-filled shock-driven inertial confinement fusion implosions. Two ion kinetic mechanisms are used to explain the anomalous observations: thermal decoupling of the D and 3He populations and diffusive species separation. The observed insensitivity of ion temperature to a varying deuterium fraction is shown to be a signature of ion thermal decoupling in shock-heated plasmas. The burn-averaged deuterium fraction calculated from the experimental data demonstrates a reduction in the average core deuteriummore » density, as predicted by simulations that use a diffusion model. Accounting for each of these effects in simulations reproduces the observed yield trends.« less

Particle Acceleration and Radiative Losses at Relativistic Shocks

NASA Astrophysics Data System (ADS)

Dempsey, P.; Duffy, P.

A semi-analytic approach to the relativistic transport equation with isotropic diffusion and consistent radiative losses is presented. It is based on the eigenvalue method first introduced in Kirk & Schneider [5]and Heavens & Drury [3]. We demonstrate the pitch-angle dependence of the cut-off in relativistic shocks.

Effect of Upstream ULF Waves on the Energetic Ion Diffusion at the Earth's Foreshock. I. Theory and Simulation

NASA Astrophysics Data System (ADS)

Otsuka, Fumiko; Matsukiyo, Shuichi; Kis, Arpad; Nakanishi, Kento; Hada, Tohru

2018-02-01

Field-aligned diffusion of energetic ions in the Earth’s foreshock is investigated by using the quasi-linear theory (QLT) and test particle simulation. Non-propagating MHD turbulence in the solar wind rest frame is assumed to be purely transverse with respect to the background field. We use a turbulence model based on a multi-power-law spectrum including an intense peak that corresponds to upstream ULF waves resonantly generated by the field-aligned beam (FAB). The presence of the ULF peak produces a concave shape of the diffusion coefficient when it is plotted versus the ion energy. The QLT including the effect of the ULF wave explains the simulation result well, when the energy density of the turbulent magnetic field is 1% of that of the background magnetic field and the power-law index of the wave spectrum is less than 2. The numerically obtained e-folding distances from 10 to 32 keV ions match with the observational values in the event discussed in the companion paper, which contains an intense ULF peak in the spectra generated by the FAB. Evolution of the power spectrum of the ULF waves when approaching the shock significantly affects the energy dependence of the e-folding distance.

Statistics of peak overpressure and shock steepness for linear and nonlinear N-wave propagation in a kinematic turbulence.

PubMed

Yuldashev, Petr V; Ollivier, Sébastien; Karzova, Maria M; Khokhlova, Vera A; Blanc-Benon, Philippe

2017-12-01

Linear and nonlinear propagation of high amplitude acoustic pulses through a turbulent layer in air is investigated using a two-dimensional KZK-type (Khokhlov-Zabolotskaya-Kuznetsov) equation. Initial waves are symmetrical N-waves with shock fronts of finite width. A modified von Kármán spectrum model is used to generate random wind velocity fluctuations associated with the turbulence. Physical parameters in simulations correspond to previous laboratory scale experiments where N-waves with 1.4 cm wavelength propagated through a turbulence layer with the outer scale of about 16 cm. Mean value and standard deviation of peak overpressure and shock steepness, as well as cumulative probabilities to observe amplified peak overpressure and shock steepness, are analyzed. Nonlinear propagation effects are shown to enhance pressure level in random foci for moderate initial amplitudes of N-waves thus increasing the probability to observe highly peaked waveforms. Saturation of the pressure level is observed for stronger nonlinear effects. It is shown that in the linear propagation regime, the turbulence mainly leads to the smearing of shock fronts, thus decreasing the probability to observe high values of steepness, whereas nonlinear effects dramatically increase the probability to observe steep shocks.

Numerical Simulation of Focused Shock Shear Waves in Soft Solids and a Two-Dimensional Nonlinear Homogeneous Model of the Brain

PubMed Central

Giammarinaro, B.; Coulouvrat, F.; Pinton, G.

2016-01-01

Shear waves that propagate in soft solids, such as the brain, are strongly nonlinear and can develop into shock waves in less than one wavelength. We hypothesize that these shear shock waves could be responsible for certain types of traumatic brain injuries (TBI) and that the spherical geometry of the skull bone could focus shear waves deep in the brain, generating diffuse axonal injuries. Theoretical models and numerical methods that describe nonlinear polarized shear waves in soft solids such as the brain are presented. They include the cubic nonlinearities that are characteristic of soft solids and the specific types of nonclassical attenuation and dispersion observed in soft tissues and the brain. The numerical methods are validated with analytical solutions, where possible, and with self-similar scaling laws where no known solutions exist. Initial conditions based on a human head X-ray microtomography (CT) were used to simulate focused shear shock waves in the brain. Three regimes are investigated with shock wave formation distances of 2.54 m, 0.018 m, and 0.0064 m. We demonstrate that under realistic loading scenarios, with nonlinear properties consistent with measurements in the brain, and when the shock wave propagation distance and focal distance coincide, nonlinear propagation can easily overcome attenuation to generate shear shocks deep inside the brain. Due to these effects, the accelerations in the focal are larger by a factor of 15 compared to acceleration at the skull surface. These results suggest that shock wave focusing could be responsible for diffuse axonal injuries. PMID:26833489

Injection of κ-like suprathermal particles into diffusive shock acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Hyesung; Petrosian, Vahé; Ryu, Dongsu

2014-06-20

We consider a phenomenological model for the thermal leakage injection in the diffusive shock acceleration (DSA) process, in which suprathermal protons and electrons near the shock transition zone are assumed to have the so-called κ-distributions produced by interactions of background thermal particles with pre-existing and/or self-excited plasma/MHD waves or turbulence. The κ-distribution has a power-law tail, instead of an exponential cutoff, well above the thermal peak momentum. So there are a larger number of potential seed particles with momentum, above that required for participation in the DSA process. As a result, the injection fraction for the κ-distribution depends on themore » shock Mach number much less severely compared to that for the Maxwellian distribution. Thus, the existence of κ-like suprathermal tails at shocks would ease the problem of extremely low injection fractions, especially for electrons and especially at weak shocks such as those found in the intracluster medium. We suggest that the injection fraction for protons ranges 10{sup –4}-10{sup –3} for a κ-distribution with 10 ≲ κ {sub p} ≲ 30 at quasi-parallel shocks, while the injection fraction for electrons becomes 10{sup –6}-10{sup –5} for a κ-distribution with κ {sub e} ≲ 2 at quasi-perpendicular shocks. For such κ values the ratio of cosmic ray (CR) electrons to protons naturally becomes K {sub e/p} ∼ 10{sup –3}-10{sup –2}, which is required to explain the observed ratio for Galactic CRs.« less

Electron Surfing Acceleration in High Mach Number Shocks

NASA Astrophysics Data System (ADS)

Hoshino, M.; Amano, T.; Matsumoto, Y.

2016-12-01

Many energetic events associated with shock waves have been argued in this context of the diffusive shock acceleration (DSA), and the origin of high-energy particles observed in astrophysical shocks are believed to be attributed to DSA. However, electron nonthermal acceleration still remains an unresolved issue of considerable interest. While cosmic rays of supernova remnant shocks with power-law spectra are believed to be produced by DSA, energetic electrons with a power-law energy spectrum are rarely ever observed at interplanetary shocks and at planetary bow shocks (e.g., Lario et al. 2003), and the diffusive-type acceleration seems to be necessarily malfunctioning in the heliosphere. The malfunctioning reason is thought to be a lack of pre-acceleration mechanism of supra-thermal electrons.In this presentation, we propose that the supra-thermal electrons can be generated by the mechanism of shock surfing acceleration (SSA) in a high Mach number magnetosonic shock. In the surfing mechanism, a series of large-amplitude electrostatic waves are excited by Buneman instability in the foot region under the interaction between the reflected ions and the incoming electrons, and it is argued that the electrons trapped in the electrostatic waves can be accelerated up to a relativistic energy (Hoshino and Shimada, 2002). Since the electron SSA has been studied based on one- or two-dimensional PIC simulations so far, SSA in three-dimensional system is questionable and remains an open question. We discuss based on our theoretical model and three-dimensional PIC simulation with a high-performance computing that the efficiency of SSA in three-dimensional system remains amazingly strong and plays an important role on the electron pre-acceleration/injection problem.

Dynamic transition in the structure of an energetic crystal during chemical reactions at shock front prior to detonation.

PubMed

Nomura, Ken-Ichi; Kalia, Rajiv K; Nakano, Aiichiro; Vashishta, Priya; van Duin, Adri C T; Goddard, William A

2007-10-05

Mechanical stimuli in energetic materials initiate chemical reactions at shock fronts prior to detonation. Shock sensitivity measurements provide widely varying results, and quantum-mechanical calculations are unable to handle systems large enough to describe shock structure. Recent developments in reactive force-field molecular dynamics (ReaxFF-MD) combined with advances in parallel computing have paved the way to accurately simulate reaction pathways along with the structure of shock fronts. Our multimillion-atom ReaxFF-MD simulations of l,3,5-trinitro-l,3,5-triazine (RDX) reveal that detonation is preceded by a transition from a diffuse shock front with well-ordered molecular dipoles behind it to a disordered dipole distribution behind a sharp front.

A powerful double radio relic system discovered in PSZ1 G108.18-11.53: evidence for a shock with non-uniform Mach number?

DOE PAGES

de Gasperin, F.; Intema, H. T.; van Weeren, R. J.; ...

2015-09-09

Diffuse radio emission in the form of radio haloes and relics has been found in a number of merging galaxy clusters. These structures indicate that shock and turbulence associated with the merger accelerate electrons to relativistic energies. We report the discovery of a radio relic + radio halo system in PSZ1 G108.18-11.53 (z = 0.335). This cluster hosts the second most powerful double radio relic system ever discovered. We observed PSZ1 G108.18-11.53 with the Giant Meterwave Radio Telescope and the Westerbork Synthesis Radio Telescope. We obtained radio maps at 147, 323, 607 and 1380 MHz. We also observed the cluster with the Keck telescope, obtaining the spectroscopic redshift for 42 cluster members. From the injection index, we obtained the Mach number of the shocks generating the two radio relics. For the southern shock, we foundmore » $M$ = 2.33 $$+0.19\\atop{-0.26}$$ while the northern shock Mach number goes from $M$2.20 $$+0.07\\atop{-0.14}$$ in the north part down to $M$ = 200 $$+0.03\\atop{-0.08}$$ in the southern region. Finally, if the relation between the injection index and the Mach number predicted by diffusive shock acceleration theory holds, this is the first observational evidence for a gradient in the Mach number along a galaxy cluster merger shock.« less

Discontinuous Galerkin method for multicomponent chemically reacting flows and combustion

NASA Astrophysics Data System (ADS)

Lv, Yu; Ihme, Matthias

2014-08-01

This paper presents the development of a discontinuous Galerkin (DG) method for application to chemically reacting flows in subsonic and supersonic regimes under the consideration of variable thermo-viscous-diffusive transport properties, detailed and stiff reaction chemistry, and shock capturing. A hybrid-flux formulation is developed for treatment of the convective fluxes, combining a conservative Riemann-solver and an extended double-flux scheme. A computationally efficient splitting scheme is proposed, in which advection and diffusion operators are solved in the weak form, and the chemically stiff substep is advanced in the strong form using a time-implicit scheme. The discretization of the viscous-diffusive transport terms follows the second form of Bassi and Rebay, and the WENO-based limiter due to Zhong and Shu is extended to multicomponent systems. Boundary conditions are developed for subsonic and supersonic flow conditions, and the algorithm is coupled to thermochemical libraries to account for detailed reaction chemistry and complex transport. The resulting DG method is applied to a series of test cases of increasing physico-chemical complexity. Beginning with one- and two-dimensional multispecies advection and shock-fluid interaction problems, computational efficiency, convergence, and conservation properties are demonstrated. This study is followed by considering a series of detonation and supersonic combustion problems to investigate the convergence-rate and the shock-capturing capability in the presence of one- and multistep reaction chemistry. The DG algorithm is then applied to diffusion-controlled deflagration problems. By examining convergence properties for polynomial order and spatial resolution, and comparing these with second-order finite-volume solutions, it is shown that optimal convergence is achieved and that polynomial refinement provides advantages in better resolving the localized flame structure and complex flow-field features associated with multidimensional and hydrodynamic/thermo-diffusive instabilities in deflagration and detonation systems. Comparisons with standard third- and fifth-order WENO schemes are presented to illustrate the benefit of the DG scheme for application to detonation and multispecies flow/shock-interaction problems.

Ion radial diffusion in an electrostatic impulse model for stormtime ring current formation

NASA Technical Reports Server (NTRS)

Chen, Margaret W.; Schulz, Michael; Lyons, Larry R.; Gorney, David J.

1992-01-01

Two refinements to the quasi-linear theory of ion radial diffusion are proposed and examined analytically with simulations of particle trajectories. The resonance-broadening correction by Dungey (1965) is applied to the quasi-linear diffusion theory by Faelthammar (1965) for an individual model storm. Quasi-linear theory is then applied to the mean diffusion coefficients resulting from simulations of particle trajectories in 20 model storms. The correction for drift-resonance broadening results in quasi-linear diffusion coefficients with discrepancies from the corresponding simulated values that are reduced by a factor of about 3. Further reductions in the discrepancies are noted following the averaging of the quasi-linear diffusion coefficients, the simulated coefficients, and the resonance-broadened coefficients for the 20 storms. Quasi-linear theory provides good descriptions of particle transport for a single storm but performs even better in conjunction with the present ensemble-averaging.

A cosmic ray driven instability

NASA Technical Reports Server (NTRS)

Dorfi, E. A.; Drury, L. O.

1985-01-01

The interaction between energetic charged particles and thermal plasma which forms the basis of diffusive shock acceleration leads also to interesting dynamical phenomena. For a compressional mode propagating in a system with homogeneous energetic particle pressure it is well known that friction with the energetic particles leads to damping. The linear theory of this effect has been analyzed in detail by Ptuskin. Not so obvious is that a non-uniform energetic particle pressure can addition amplify compressional disturbances. If the pressure gradient is sufficiently steep this growth can dominate the frictional damping and lead to an instability. It is important to not that this effect results from the collective nature of the interaction between the energetic particles and the gas and is not connected with the Parker instability, nor with the resonant amplification of Alfven waves.

Analysis and Modeling of a Two-Phase Jet Pump of a Flow Boiling Test Facility for Aerospace Applications

NASA Technical Reports Server (NTRS)

Sherif, S. A.; Steadham, Justin M.

1996-01-01

Jet pumps are devices capable of pumping fluids to a higher pressure employing a nozzle/diffuser/mixing chamber combination. A primary fluid is usually allowed to pass through a converging-diverging nozzle where it can accelerate to supersonic speeds at the nozzle exit. The relatively high kinetic energy that the primary fluid possesses at the nozzle exit is accompanied by a low pressure region in order to satisfy Bernoulli's equation. The low pressure region downstream of the nozzle exit permits a secondary fluid to be entrained into and mixed with the primary fluid in a mixing chamber located downstream of the nozzle. Several combinations may exist in terms of the nature of the primary and secondary fluids in so far as whether they are single or two-phase fluids. Depending on this, the jet pump may be classified as gas/gas, gas/liquid, liquid/liquid, two-phase/liquid, or similar combinations. The mixing chamber serves to create a homogeneous single-phase or two-phase mixture which enters a diffuser where the high kinetic energy of the fluid is converted into pressure energy. If the fluid mixture entering the diffuser is in the supersonic flow regime, a normal shock wave usually develops inside the diffuser. If the fluid mixture is one that can easily change phase, a condensation shock would normally develop. Because of the overall rise in pressure in the diffuser as well as the additional rise in pressure across the shock layer, condensation becomes more likely. Associated with the pressure rise across the shock is a velocity reduction from the supersonic to the subsonic range. If the two-phase flow entering the diffuser is predominantly gaseous with liquid droplets suspended in it, it will transform into a predominantly liquid flow containing gaseous bubbles (bubbly flow) somewhere in the diffuser. While past researchers have been able to model the two-phase flow jet pump using the one-dimensional assumption with no shock waves and no phase change, there is no research known to the authors apart from that of Anand (1992) which accounted for condensation shocks. One of the objectives of this research effort is to develop a comprehensive model in which the effects of phase slip and inter-phase heat transfer as well as the wall friction and shock waves are accounted for. While this modeling effort is predominantly analytical in nature and is primarily intended to provide a parametric understanding of the jet pump performance under different operating scenarios, another parallel effort employing a commercial CFD code is also implemented. The latter effort is primarily intended to model an axisymmetric counterpart of the problem in question. The viability of using the CFD code to model a two-phase flow jet pump will be assessed by attempting to recreate some of the existing performance data of similar jet pumps. The code will eventually be used to generate the jet pump performance characteristics of several scenarios involving jet pump geometries as well as flow regimes in order to be able to determine an optimum design which would be suitable for a two-phase flow boiling test facility at NASA-Marshall. Because of the extensive nature of the analytical model developed, the following section will only provide very brief highlights of it, while leaving the details to a more complete report submitted to the NASA colleague. This report will also contain some of the simulation results obtained using the CFD code.

Evaluation of diffuse-illumination holographic cinematography in a flutter cascade

NASA Technical Reports Server (NTRS)

Decker, A. J.

1986-01-01

Since 1979, the Lewis Research Center has examined holographic cinematography for three-dimensional flow visualization. The Nd:YAG lasers used were Q-switched, double-pulsed, and frequency-doubled, operating at 20 pulses per second. The primary subjects for flow visualization were the shock waves produced in two flutter cascades. Flow visualization was by diffuse-illumination, double-exposure, and holographic interferometry. The performances of the lasers, holography, and diffuse-illumination interferometry are evaluated in single-window wind tunnels. The fringe-contrast factor is used to evaluate the results. The effects of turbulence on shock-wave visualization in a transonic flow are discussed. The depth of field for visualization of a turbulent structure is demonstrated to be a measure of the relative density and scale of that structure. Other items discussed are the holographic emulsion, tests of coherence and polarization, effects of windows and diffusers, hologram bleaching, laser configurations, influence and handling of specular reflections, modes of fringe localization, noise sources, and coherence requirements as a function of the pulse energy. Holography and diffuse illumination interferometry are also reviewed.

An Investigation of Convergent-Divergent Diffusers at Mach Number 1.85

NASA Technical Reports Server (NTRS)

Wyatt, Demarquis D; Hunczak, Henry R

1947-01-01

An investigation has been conducted in the Cleveland 18- by 18-inch supersonic tunnel at a Mach number of 1.85 and angles of attack from 0 deg to 5 deg to determine optimum design configurations for a convergent-divergent type of supersonic diffuser with a subsonic diffuser of 5 deg included divergence angle. Total pressure recoveries in excess of theoretical recovery across a normal shock at a free-stream Mach number of 1.85 wore obtained with several configurations. The highest recovery for configurations without a cylindrical throat section was obtained with an inlet having an included convergence angle of 20 deg. Insertion of a 2-inch throat section between a 10 deg included angle inlet and the subsonic diffuser stabilized the shock inside the diffuser and resulted in recoveries as high as 0.838 free-stream total pressure at an angle of attack of 0 deg, corresponding to recovery of 92.4 percent of the kinetic energy of the free air stream. Use of the throat section also lessened the reduction in recovery of all configurations due to angle of attack.

Analytical scalings of the linear Richtmyer-Meshkov instability when a shock is reflected.

PubMed

Campos, F Cobos; Wouchuk, J G

2016-05-01

When a planar shock hits a corrugated contact surface between two fluids, hydrodynamic perturbations are generated in both fluids that result in asymptotic normal and tangential velocity perturbations in the linear stage, the so called Richtmyer-Meshkov instability. In this work, explicit and exact analytical expansions of the asymptotic normal velocity (δv_{i}^{∞}) are presented for the general case in which a shock is reflected back. The expansions are derived from the conservation equations and take into account the whole perturbation history between the transmitted and reflected fronts. The important physical limits of weak and strong shocks and the high/low preshock density ratio at the contact surface are shown. An approximate expression for the normal velocity, valid even for high compression regimes, is given. A comparison with recent experimental data is done. The contact surface ripple growth is studied during the linear phase showing good agreement between theory and experiments done in a wide range of incident shock Mach numbers and preshock density ratios, for the cases in which the initial ripple amplitude is small enough. In particular, it is shown that in the linear asymptotic phase, the contact surface ripple (ψ_{i}) grows as ψ_{∞}+δv_{i}^{∞}t, where ψ_{∞} is an asymptotic ordinate different from the postshock ripple amplitude at t=0+. This work is a continuation of the calculations of F. Cobos Campos and J. G. Wouchuk, [Phys. Rev. E 90, 053007 (2014)PLEEE81539-375510.1103/PhysRevE.90.053007] for a single shock moving into one fluid.

Hugoniot equation of state of rock materials under shock compression

PubMed Central

Braithwaite, C. H.; Zhao, J.

2017-01-01

Two sets of shock compression tests (i.e. conventional and reverse impact) were conducted to determine the shock response of two rock materials using a plate impact facility. Embedded manganin stress gauges were used for the measurements of longitudinal stress and shock velocity. Photon Doppler velocimetry was used to capture the free surface velocity of the target. Experimental data were obtained on a fine-grained marble and a coarse-grained gabbro over a shock pressure range of approximately 1.5–12 GPa. Gabbro exhibited a linear Hugoniot equation of state (EOS) in the pressure–particle velocity (P–up) plane, while for marble a nonlinear response was observed. The EOS relations between shock velocity (US) and particle velocity (up) are linearly fitted as US = 2.62 + 3.319up and US = 5.4 85 + 1.038up for marble and gabbro, respectively. This article is part of the themed issue ‘Experimental testing and modelling of brittle materials at high strain rates’. PMID:27956506

Shocks in fragile matter

NASA Astrophysics Data System (ADS)

Vitelli, Vincenzo

2012-02-01

Non-linear sound is an extreme phenomenon typically observed in solids after violent explosions. But granular media are different. Right when they unjam, these fragile and disordered solids exhibit vanishing elastic moduli and sound speed, so that even tiny mechanical perturbations form supersonic shocks. Here, we perform simulations in which two-dimensional jammed granular packings are continuously compressed, and demonstrate that the resulting excitations are strongly nonlinear shocks, rather than linear waves. We capture the full dependence of the shock speed on pressure and compression speed by a surprisingly simple analytical model. We also treat shear shocks within a simplified viscoelastic model of nearly-isostatic random networks comprised of harmonic springs. In this case, anharmonicity does not originate locally from nonlinear interactions between particles, as in granular media; instead, it emerges from the global architecture of the network. As a result, the diverging width of the shear shocks bears a nonlinear signature of the diverging isostatic length associated with the loss of rigidity in these floppy networks.

Hydrogen-Helium shock Radiation tests for Saturn Entry Probes

NASA Technical Reports Server (NTRS)

Cruden, Brett A.

2016-01-01

This paper describes the measurement of shock layer radiation in Hydrogen/Helium mixtures representative of that encountered by probes entering the Saturn atmosphere. Normal shock waves are measured in Hydrogen-Helium mixtures (89:11% by volume) at freestream pressures between 13-66 Pa (0.1-0.5 Torr) and velocities from 20-30 km/s. Radiance is quantified from the Vacuum Ultraviolet through Near Infrared. An induction time of several centimeters is observed where electron density and radiance remain well below equilibrium. Radiance is observed in front of the shock layer, the characteristics of which match the expected diffusion length of Hydrogen.

THE CHANDRA X-RAY SURVEY OF PLANETARY NEBULAE (CHANPLANS): PROBING BINARITY, MAGNETIC FIELDS, AND WIND COLLISIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kastner, J. H.; Montez, R. Jr.; Rapson, V.

2012-08-15

We present an overview of the initial results from the Chandra Planetary Nebula Survey (CHANPLANS), the first systematic (volume-limited) Chandra X-Ray Observatory survey of planetary nebulae (PNe) in the solar neighborhood. The first phase of CHANPLANS targeted 21 mostly high-excitation PNe within {approx}1.5 kpc of Earth, yielding four detections of diffuse X-ray emission and nine detections of X-ray-luminous point sources at the central stars (CSPNe) of these objects. Combining these results with those obtained from Chandra archival data for all (14) other PNe within {approx}1.5 kpc that have been observed to date, we find an overall X-ray detection rate ofmore » {approx}70% for the 35 sample objects. Roughly 50% of the PNe observed by Chandra harbor X-ray-luminous CSPNe, while soft, diffuse X-ray emission tracing shocks-in most cases, 'hot bubbles'-formed by energetic wind collisions is detected in {approx}30%; five objects display both diffuse and point-like emission components. The presence (or absence) of X-ray sources appears correlated with PN density structure, in that molecule-poor, elliptical nebulae are more likely to display X-ray emission (either point-like or diffuse) than molecule-rich, bipolar, or Ring-like nebulae. All but one of the point-like CSPNe X-ray sources display X-ray spectra that are harder than expected from hot ({approx}100 kK) central stars emitting as simple blackbodies; the lone apparent exception is the central star of the Dumbbell nebula, NGC 6853. These hard X-ray excesses may suggest a high frequency of binary companions to CSPNe. Other potential explanations include self-shocking winds or PN mass fallback. Most PNe detected as diffuse X-ray sources are elliptical nebulae that display a nested shell/halo structure and bright ansae; the diffuse X-ray emission regions are confined within inner, sharp-rimmed shells. All sample PNe that display diffuse X-ray emission have inner shell dynamical ages {approx}< 5 Multiplication-Sign 10{sup 3} yr, placing firm constraints on the timescale for strong shocks due to wind interactions in PNe. The high-energy emission arising in such wind shocks may contribute to the high excitation states of certain archetypical 'hot bubble' nebulae (e.g., NGC 2392, 3242, 6826, and 7009).« less

Viscous regularization of the full set of nonequilibrium-diffusion Grey Radiation-Hydrodynamic equations

DOE PAGES

Delchini, Marc O.; Ragusa, Jean C.; Ferguson, Jim

2017-02-17

A viscous regularization technique, based on the local entropy residual, was proposed by Delchini et al. (2015) to stabilize the nonequilibrium-diffusion Grey Radiation-Hydrodynamic equations using an artificial viscosity technique. This viscous regularization is modulated by the local entropy production and is consistent with the entropy minimum principle. However, Delchini et al. (2015) only based their work on the hyperbolic parts of the Grey Radiation-Hydrodynamic equations and thus omitted the relaxation and diffusion terms present in the material energy and radiation energy equations. Here in this paper, we extend the theoretical grounds for the method and derive an entropy minimum principlemore » for the full set of nonequilibrium-diffusion Grey Radiation-Hydrodynamic equations. This further strengthens the applicability of the entropy viscosity method as a stabilization technique for radiation-hydrodynamic shock simulations. Radiative shock calculations using constant and temperature-dependent opacities are compared against semi-analytical reference solutions, and we present a procedure to perform spatial convergence studies of such simulations.« less

A test of Lee's quasi-linear theory of ion acceleration by interplanetary traveling shocks

NASA Technical Reports Server (NTRS)

Kennel, C. F.; Coroniti, F. V.; Scarf, F. L.; Livesey, W. A.; Russell, C. T.; Smith, E. J.

1986-01-01

Lee's (1983) quasi-linear theory of ion acceleration is tested using ISEE-3 measurements of the November 12, 1978 quasi-parallel interplanetary shock. His theory accounts with varying degrees of precision for the energetic proton spatial profiles; the dependence of the spectral index of the power law proton velocity distribution upon the shock compression ratio; the power law dependence of the upstream proton scalelength upon energy; the absolute magnitude of the upstream proton scale length; the behavior of the energetic proton anisotropy upstream and downstream of the shock; the behavior of the alpha-particle proton ratio upstream; the equality of the spatial scale lengths at the shock of the upstream waves and of the protons that resonate with them; and the dependence of the integrated wave energy density upon the proton energy density at the shock. However, the trace magnetic field frequency spectra disagree with his theory in two ways. The part of the spectrum that can resonate with the observed protons via first-order cyclotron resonance is flat, whereas Lee's theory predicts an f exp - 7/4 frequency dependence for the November 12 shock. Higher frequency waves, which could not resonate with the observed upstream protons, increased in amplitude as the shock approached, suggesting that they too were generated by the shock.

Interstellar Pickup Ion Acceleration in the Turbulent Magnetic Field at the Solar Wind Termination Shock Using a Focused Transport Approach

NASA Astrophysics Data System (ADS)

Ye, Junye; le Roux, Jakobus A.; Arthur, Aaron D.

2016-08-01

We study the physics of locally born interstellar pickup proton acceleration at the nearly perpendicular solar wind termination shock (SWTS) in the presence of a random magnetic field spiral angle using a focused transport model. Guided by Voyager 2 observations, the spiral angle is modeled with a q-Gaussian distribution. The spiral angle fluctuations, which are used to generate the perpendicular diffusion of pickup protons across the SWTS, play a key role in enabling efficient injection and rapid diffusive shock acceleration (DSA) when these particles follow field lines. Our simulations suggest that variation of both the shape (q-value) and the standard deviation (σ-value) of the q-Gaussian distribution significantly affect the injection speed, pitch-angle anisotropy, radial distribution, and the efficiency of the DSA of pickup protons at the SWTS. For example, increasing q and especially reducing σ enhances the DSA rate.

Reconnection in the Post-impulsive Phase of Solar Flares

NASA Astrophysics Data System (ADS)

Forbes, Terry G.; Seaton, Daniel B.; Reeves, Katharine K.

2018-05-01

Using a recently developed analytical procedure, we determine the rate of magnetic reconnection in the “standard” model of eruptive solar flares. During the late phase, the neutral line is located near the lower tip of the reconnection current sheet, and the upper region of the current sheet is bifurcated into a pair of Petschek-type shocks. Despite the presence of these shocks, the reconnection rate remains slow if the resistivity is uniform and the flow is laminar. Fast reconnection is achieved only if there is some additional mechanism that can shorten the length of the diffusion region at the neutral line. Observations of plasma flows by the X-ray telescope on Hinode imply that the diffusion region is, in fact, quite short. Two possible mechanisms for reducing the length of the diffusion region are localized resistivity and MHD turbulence.

On force-deflection diagrams of airplane shock absorber struts : first, second, and third partial reports

NASA Technical Reports Server (NTRS)

Schlaefke, Karlhans

1954-01-01

This paper, which is presented in three parts, is an analytical study of the behavior of landing gear shock struts, with various types of assumptions for the shock-strut characteristics. The effects of tire springing are neglected. The first part compares the behavior of struts with linear and quadratic damping. The second part considers struts with nonlinear spring characteristics and linear or quadratic damping. The third part treats the oleo-pneumatic strut with air-compression springing without damping and with damping proportional to velocity. It is indicated how the damping factor can be determined by experiment.

Dhofar 378 Martian shergottite: Evidence of early shock melting

NASA Astrophysics Data System (ADS)

Park, Jisun; Bogard, Donald D.; Mikouchi, Takashi; McKay, Gordon A.

2008-08-01

Shock heating of the Dhofar 378 (Dho 378) Martian shergottite produced melting, vesiculation, and flow of the plagioclase, which upon cooling recrystallized into complex textures. Heating experiments on the similar Zagami shergottite indicate that Dho 378 was shock heated to 1000-1100°C and was cooled at ~2.5°C/h. An 39Ar-40Ar analysis of Dho 378 plagioclase indicates different Ar diffusion domains and K/Ca ratios. The lower-temperature phase defines an Ar-Ar isochron age of 141 +/- 32 Ma. The higher-temperature phase released more 40Ar but does not define an age. The meteorite's thermal history was examined by constructing a generic model to compare cooling rates for objects of different sizes against fractional diffusion loss of Ar for different cooling times. Using gas diffusion parameter values measured for Dho 378, this model indicates that it is improbable that the major shock heating event occurred at the time that Dho 378 was ejected from Mars ~3 Ma ago. Rather, we suggest that the time of shock heating is probably given by its Ar-Ar age. For Dho 378 to cool sufficiently fast not to lose most of its 40Ar ~3 Ma ago would require it to have been ejected into space as an impossibly small object. Larger and more reasonable Mars ejection sizes indicate that Dho 378 should have lost most of its 40Ar. On the basis of plagioclase texture and Ar data, we suggest that a major impact event ~141 Ma ago melted Dho 378 plagioclase, degassed most of its 40Ar, and deposited it in crater ejecta to cool. A smaller and later impact ejected it into space ~3 Ma ago.

VLA Radio Observations of the HST Frontier Fields Cluster Abell 2744: The Discovery of New Radio Relics

NASA Astrophysics Data System (ADS)

Pearce, C. J. J.; van Weeren, R. J.; Andrade-Santos, F.; Jones, C.; Forman, W. R.; Brüggen, M.; Bulbul, E.; Clarke, T. E.; Kraft, R. P.; Medezinski, E.; Mroczkowski, T.; Nonino, M.; Nulsen, P. E. J.; Randall, S. W.; Umetsu, K.

2017-08-01

Cluster mergers leave distinct signatures in the intracluster medium (ICM) in the form of shocks and diffuse cluster radio sources that provide evidence for the acceleration of relativistic particles. However, the physics of particle acceleration in the ICM is still not fully understood. Here we present new 1-4 GHz Jansky Very Large Array (VLA) and archival Chandra observations of the HST Frontier Fields Cluster Abell 2744. In our new VLA images, we detect the previously known ˜2.1 Mpc radio halo and ˜1.5 Mpc radio relic. We carry out a radio spectral analysis from which we determine the relic’s injection spectral index to be {α }{inj}=-1.12+/- 0.19. This corresponds to a shock Mach number of { M }={2.05}-0.19+0.31 under the assumption of diffusive shock acceleration. We also find evidence for spectral steepening in the post-shock region. We do not find evidence for a significant correlation between the radio halo’s spectral index and ICM temperature. In addition, we observe three new polarized diffuse sources and determine two of these to be newly discovered giant radio relics. These two relics are located in the southeastern and northwestern outskirts of the cluster. The corresponding integrated spectral indices measure -1.81 ± 0.26 and -0.63 ± 0.21 for the SE and NW relics, respectively. From an X-ray surface brightness profile we also detect a possible density jump of R={1.39}-0.22+0.34 co-located with the newly discovered SE relic. This density jump would correspond to a shock front Mach number of { M }={1.26}-0.15+0.25.

Comparison of LFM-test particle simulations and radial diffusion models of radiation belt electron injection into the slot region

NASA Astrophysics Data System (ADS)

Chu, F.; Hudson, M.; Kress, B.

2008-12-01

The physics-based Lyon-Fedder-Mobarry (LFM) code simulates Earth's magnetospheric topology and dynamics by solving the equations of ideal MHD using input solar wind parameters at the upstream boundary. Comparison with electron phase space density evolution during storms using a radial diffusion code, as well as spacecraft measurements where available, will tell us when diffusion is insufficiently accurate for radiation belt simulation, for example, during CME-shock injection events like March 24, 1991, which occurred on MeV electron drift time scales of minutes (Li et al., 1993). The 2004 July and 2004 November storms, comparable in depth of penetration into the slot region to the Halloween 2003 storm, have been modeled with both approaches. The November 8, 2004 storm was preceded by a Storm Sudden Commencement produced by a CME-shock followed by minimum Dst = -373 nT, while the July 23 to July 28 storm interval had milder consecutive drops in Dst, corresponding to multiple CME shocks and southward IMF Bz turnings. We have run the November and July storms with LFM using ACE data as upstream input, running the July storm with lower temporal resolution over a longer time interval. The November storm was different because the SCC shock was unusually intense, therefore the possibility of drift time scale acceleration by the associated magnetosonic impulse produced by the shock exists, as in March 1991 and also Halloween 2003 events (Kress et al., 2007). It can then take a short time (minutes) for electrons to be transported to low L shell while conserving their first invariant, resulting in a peak in energy and phase space density in the slot region. Radial diffusion suffices for some storm periods like the July 2004 sequence of three storms, while the guiding center test particle simulation in MHD fields is necessary to describe prompt injections which occur faster than diffusive time scales, for which November 2004 is a likely candidate. Earlier examples have been studied, including the Kress et al., 2007 study of the Halloween 2003 storm and Li et al., 1993 study of the March 24, 1991 injection event with MHD simulation carried out by Elkington et al. (2002) for this event. Radial diffusion remains the best approach for extended relatively quiet periods like the two month interval following the March 1991 prompt injection. Strong shocks will inject particles into lower L shell within a few minutes violating the third adiabatic invariant, so the diffusion mechanism cannot be adopted for sudden commencements, when Dst increases then decreases drastically; however particle tracing in time-dependent MHD fields will give an accurate estimation, so radial diffusion and particle tracing in MHD fields complement each other in radiation belt studies. Elkington, S. R., M.K. Hudson, M.J. Wiltberger, J.G. Lyon (2002) JASTP, 64, p. 607-615; Kress B. T., M. K. Hudson, M. D. Looper, J. Albert, J. G. Lyon, C. C. Goodrich (2007), J. Geophys. Res., 112, A09215, doi:10.1029/2006JA012218; Li, X., I. Roth, M. Temerin, J. R. Wygant, M. K. Hudson, and J. B. Blake (1993), Geophys. Res. Lett., 20, p. 2423-2426.

The origin of cosmic rays

NASA Technical Reports Server (NTRS)

Eichler, D.

1986-01-01

Data related to the development of cosmic rays are discussed. The relationship between cosmic ray production and the steady-state Boltzmann equation is analyzed. The importance of the power-law spectrum, the scattering rate, the theory of shock acceleration, anisotropic instabilities, and cosmic ray diffusion in the formation of cosmic rays is described. It is noted that spacecraft observations at the earth's bow shock are useful for studying cosmic rays and that the data support the collisionless shock-wave theory of cosmic ray origin.

Diffusive Shock Acceleration and Turbulent Reconnection

NASA Astrophysics Data System (ADS)

Garrel, Christian; Vlahos, Loukas; Isliker, Heinz; Pisokas, Theophilos

2018-05-01

Diffusive Shock Acceleration (DSA) cannot efficiently accelerate particles without the presence of self-consistently generated or pre-existing strong turbulence (δB/B ˜ 1) in the vicinity of the shock. The problem we address in this article is: if large amplitude magnetic disturbances are present upstream and downstream of a shock then Turbulent Reconnection (TR) will set in and will participate not only in the elastic scattering of particles but also in their heating and acceleration. We demonstrate that large amplitude magnetic disturbances and Unstable Current Sheets (UCS), spontaneously formed in the strong turbulence in the vicinity of a shock, can accelerate particles as efficiently as DSA in large scale systems and on long time scales. We start our analysis with "elastic" scatterers upstream and downstream and estimate the energy distribution of particles escaping from the shock, recovering the well known results from the DSA theory. Next we analyze the additional interaction of the particles with active scatterers (magnetic disturbances and UCS) upstream and downstream of the shock. We show that the asymptotic energy distribution of the particles accelerated by DSA/TR has very similar characteristics with the one due to DSA alone, but the synergy of DSA with TR is much more efficient: The acceleration time is an order of magnitude shorter and the maximum energy reached two orders of magnitude higher. We claim that DSA is the dominant acceleration mechanism in a short period before TR is established, and then strong turbulence will dominate the heating and acceleration of the particles. In other words, the shock serves as the mechanism to set up a strongly turbulent environment, in which the acceleration mechanism will ultimately be the synergy of DSA and TR.

Cosmic Ray Acceleration by a Versatile Family of Galactic Wind Termination Shocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bustard, Chad; Zweibel, Ellen G.; Cotter, Cory, E-mail: bustard@wisc.edu

2017-01-20

There are two distinct breaks in the cosmic ray (CR) spectrum: the so-called “knee” around 3 × 10{sup 15} eV and the so-called “ankle” around 10{sup 18} eV. Diffusive shock acceleration (DSA) at supernova remnant (SNR) shock fronts is thought to accelerate galactic CRs to energies below the knee, while an extragalactic origin is presumed for CRs with energies beyond the ankle. CRs with energies between 3 × 10{sup 15} and 10{sup 18} eV, which we dub the “shin,” have an unknown origin. It has been proposed that DSA at galactic wind termination shocks, rather than at SNR shocks, maymore » accelerate CRs to these energies. This paper uses the galactic wind model of Bustard et al. to analyze whether galactic wind termination shocks may accelerate CRs to shin energies within a reasonable acceleration time and whether such CRs can subsequently diffuse back to the Galaxy. We argue for acceleration times on the order of 100 Myr rather than a few billion years, as assumed in some previous works, and we discuss prospects for magnetic field amplification at the shock front. Ultimately, we generously assume that the magnetic field is amplified to equipartition. This formalism allows us to obtain analytic formulae, applicable to any wind model, for CR acceleration. Even with generous assumptions, we find that very high wind velocities are required to set up the necessary conditions for acceleration beyond 10{sup 17} eV. We also estimate the luminosities of CRs accelerated by outflow termination shocks, including estimates for the Milky Way wind.« less

Radio observations of the double-relic galaxy cluster Abell 1240

NASA Astrophysics Data System (ADS)

Hoang, D. N.; Shimwell, T. W.; van Weeren, R. J.; Intema, H. T.; Röttgering, H. J. A.; Andrade-Santos, F.; Akamatsu, H.; Bonafede, A.; Brunetti, G.; Dawson, W. A.; Golovich, N.; Best, P. N.; Botteon, A.; Brüggen, M.; Cassano, R.; de Gasperin, F.; Hoeft, M.; Stroe, A.; White, G. J.

2018-05-01

We present LOFAR 120 - 168 MHz images of the merging galaxy cluster Abell 1240 that hosts double radio relics. In combination with the GMRT 595 - 629 MHz and VLA 2 - 4 GHz data, we characterised the spectral and polarimetric properties of the radio emission. The spectral indices for the relics steepen from their outer edges towards the cluster centre and the electric field vectors are approximately perpendicular to the major axes of the relics. The results are consistent with the picture that these relics trace large-scale shocks propagating outwards during the merger. Assuming diffusive shock acceleration (DSA), we obtain shock Mach numbers of M=2.4 and 2.3 for the northern and southern shocks, respectively. For M≲ 3 shocks, a pre-existing population of mildly relativistic electrons is required to explain the brightness of the relics due to the high (>10 per cent) particle acceleration efficiency required. However, for M≳ 4 shocks the required efficiency is ≳ 1% and ≳ 0.5%, respectively, which is low enough for shock acceleration directly from the thermal pool. We used the fractional polarization to constrain the viewing angle to ≥53 ± 3° and ≥39 ± 5° for the northern and southern shocks, respectively. We found no evidence for diffuse emission in the cluster central region. If the halo spans the entire region between the relics (˜1.8 Mpc) our upper limit on the power is P1.4GHz = (1.4 ± 0.6) × 1023 W Hz-1 which is approximately equal to the anticipated flux from a cluster of this mass. However, if the halo is smaller than this, our constraints on the power imply that the halo is underluminous.

Characteristics of Perforated Diffusers at Free-stream Mach Number 1.90

NASA Technical Reports Server (NTRS)

Hunczak, Henry R; Kremzier, Emil J

1950-01-01

An investigation was conducted at Mach number 1.90 to determine pressure recovery and mass-flow characteristics of series of perforated convergent-divergent supersonic diffusers. Pressure recoveries as high as 96 percent were obtained, but at reduced mass flows through the diffuser. Theoretical considerations of effect of perforation distribution on shock stability in converging section of diffuser are presented and correlated with experimental data. A method of estimating relative importance of pressure recovery and mass flow on internal thrust coefficient basis is given and a comparison of various diffusers investigated is made.

Numerical computation of linear instability of detonations

NASA Astrophysics Data System (ADS)

Kabanov, Dmitry; Kasimov, Aslan

2017-11-01

We propose a method to study linear stability of detonations by direct numerical computation. The linearized governing equations together with the shock-evolution equation are solved in the shock-attached frame using a high-resolution numerical algorithm. The computed results are processed by the Dynamic Mode Decomposition technique to generate dispersion relations. The method is applied to the reactive Euler equations with simple-depletion chemistry as well as more complex multistep chemistry. The results are compared with those known from normal-mode analysis. We acknowledge financial support from King Abdullah University of Science and Technology.

Point-source and diffuse high-energy neutrino emission from Type IIn supernovae

NASA Astrophysics Data System (ADS)

Petropoulou, M.; Coenders, S.; Vasilopoulos, G.; Kamble, A.; Sironi, L.

2017-09-01

Type IIn supernovae (SNe), a rare subclass of core collapse SNe, explode in dense circumstellar media that have been modified by the SNe progenitors at their last evolutionary stages. The interaction of the freely expanding SN ejecta with the circumstellar medium gives rise to a shock wave propagating in the dense SN environment, which may accelerate protons to multi-PeV energies. Inelastic proton-proton collisions between the shock-accelerated protons and those of the circumstellar medium lead to multimessenger signatures. Here, we evaluate the possible neutrino signal of Type IIn SNe and compare with IceCube observations. We employ a Monte Carlo method for the calculation of the diffuse neutrino emission from the SN IIn class to account for the spread in their properties. The cumulative neutrino emission is found to be ˜10 per cent of the observed IceCube neutrino flux above 60 TeV. Type IIn SNe would be the dominant component of the diffuse astrophysical flux, only if 4 per cent of all core collapse SNe were of this type and 20-30 per cent of the shock energy was channeled to accelerated protons. Lower values of the acceleration efficiency are accessible by the observation of a single Type IIn SN as a neutrino point source with IceCube using up-going muon neutrinos. Such an identification is possible in the first year following the SN shock breakout for sources within 20 Mpc.

Evidence for self-refraction in a convergence zone: NPE (Nonlinear progressive wave equation) model results

NASA Technical Reports Server (NTRS)

Mcdonald, B. Edward; Plante, Daniel R.

1989-01-01

The nonlinear progressive wave equation (NPE) model was developed by the Naval Ocean Research and Development Activity during 1982 to 1987 to study nonlinear effects in long range oceanic propagation of finite amplitude acoustic waves, including weak shocks. The NPE model was applied to propagation of a generic shock wave (initial condition provided by Sandia Division 1533) in a few illustrative environments. The following consequences of nonlinearity are seen by comparing linear and nonlinear NPE results: (1) a decrease in shock strength versus range (a well-known result of entropy increases at the shock front); (2) an increase in the convergence zone range; and (3) a vertical meandering of the energy path about the corresponding linear ray path. Items (2) and (3) are manifestations of self-refraction.

Diffusive Electron Acceleration at Interplanetary CME Shocks: Comparison between events on 21 Feb 1994 and 15 July 2000

NASA Astrophysics Data System (ADS)

Terasawa, T.; Shimada, N.; Takei, Y.; Kawada, S.; Oka, M.; Den, M.; Mukai, T.; Saito, Y.

2001-12-01

While the diffusive shock acceleration (DSA) process of electrons has significant astrophysical importance, reports of in situ observations of such process accompanying with interplanetary CME shocks at 1 AU have been limited to several big events, such as those on 21 Feb 1994 and 15 July 2000 [Shimada et al., ASS, 1999; Terasawa et al., ICRC, 2001]. In this presentation, we will present the results of comparative studies of these important events based on the GEOTAIL measurements. Common features of these events are, (1) high average propagation speeds from the sun to 1AU ( ~1300 km/s and ~1500 km/s), (2) high local propagation speeds at 1 AU ( ~920 km/s and ~1100 km/s), (3) exponential upstream time profiles of nonthermal electrons (up to 40 keV), and (4) nearly power-law energy spectrum. Despite these similarities, one noticeable difference among them was the relative flux increases of accelerated electrons: In the energy range of several keV to 20 keV nearly two-order of magnitude flux increases were observed at the former shock, while the corresponding increase at the latter shock was only a factor of ~3. We are now trying to identify the origin of this difference: One possibility is the different shock angles ( ~68 deg for the former, and ~48 deg for the latter). Further search for the difference in scattering agents of these electrons is also under way (For the former shock, intensification of whistler waves of several Hz was identified.)

Anomalous diffusion with linear reaction dynamics: from continuous time random walks to fractional reaction-diffusion equations.

PubMed

Henry, B I; Langlands, T A M; Wearne, S L

2006-09-01

We have revisited the problem of anomalously diffusing species, modeled at the mesoscopic level using continuous time random walks, to include linear reaction dynamics. If a constant proportion of walkers are added or removed instantaneously at the start of each step then the long time asymptotic limit yields a fractional reaction-diffusion equation with a fractional order temporal derivative operating on both the standard diffusion term and a linear reaction kinetics term. If the walkers are added or removed at a constant per capita rate during the waiting time between steps then the long time asymptotic limit has a standard linear reaction kinetics term but a fractional order temporal derivative operating on a nonstandard diffusion term. Results from the above two models are compared with a phenomenological model with standard linear reaction kinetics and a fractional order temporal derivative operating on a standard diffusion term. We have also developed further extensions of the CTRW model to include more general reaction dynamics.

Pediatric Diabetic Ketoacidosis With Hypotensive Shock and Rash-An Unusual Presentation.

PubMed

Pasternak, Yehonatan; Niv, Omer; Waisman, Yehezkel Hezi

2018-05-15

We describe a previously healthy adolescent boy who presented with respiratory distress, hypotensive shock, and a diffuse erythematous rash. The final diagnosis was diabetic ketoacidosis. Caregivers should be alert to this unusual combination of symptoms in the emergency department setting in order to improve the recognition and management of children with new-onset diabetes.

The Statistical Studies of 0.5-100 keV Electrons Near The ICME-drivens At 1 AU

NASA Astrophysics Data System (ADS)

Yang, L.; Wang, W.; Wang, L.; Li, G.; Wimmer-Schweingruber, R. F.; He, J.; Tu, C. Y.; Bale, S. D.

2017-12-01

We present a statistical survey of the 0.5 - 100 keV electrons near the ICME-driven shocks at 1 AU, using the WIND/3DP electron measurements from 1995 to 2014. We select 74 good ICME-driven shocks, and use the "Rankine-Hugoniot" shock fitting technique to obtain the shock normal, θBn, magnetic compression ratio rB, and magnetosonic Mach number Ms. After averaging the electron data in the 10-minute interval immediately after the shock to obtain the sheath electron fluxes, Jsheath, and in the 2-hour quiet-time interval before the shock to obtain the pre-event electron fluxes, Jpre-event, we calculate the flux ratio, α, of Jsheath over Jpre-event. We find that, in the 59 quasi-perpendicular shocks, both Jsheath and Jpre-event are positively correlated with Ms and α is positively correlated with rB. In the 15 quasi-parallel cases, α is positively correlated with Ms, while neither Jsheath nor Jpre-event has any correlation with the shock parameters. Furthermore, we find that both the pre-event and sheath electron fluxes generally fit well to a double power-law spectrum, . At 0.5 - 2 keV, the fitted spectral index β1 ranges from 2.1 to 5.9, and it becomes larger in the sheah than in the pre-event in nearly a half of the 74 cases and remains the same in the other half of the cases. At 2 - 100 keV, the fitted index β2 ranges from 1.9 to 3.4, similar to the spectral indexes of solar wind superhalo electrons at quiet times (Wang et al., 2015). And β2 becomes larger in the sheah than in the pre-event in over half of the cases. In addition, neither β1 nor β2 is consistent with the diffusive shock theoretical predication. These results suggest that the shock drift acceleration may play a more important role in electron acceleration than the diffusive shock acceleration near 1 AU, and the interplanetary shock acceleration can contribute to the production of solar wind superhalo electrons.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ro, Stephen; Matzner, Christopher D., E-mail: ro@astro.utoronto.ca

Wave-driven outflows and non-disruptive explosions have been implicated in pre-supernova outbursts, supernova impostors, luminous blue variable eruptions, and some narrow-line and superluminous supernovae. To model these events, we investigate the dynamics of stars set in motion by strong acoustic pulses and wave trains, focusing on nonlinear wave propagation, shock formation, and an early phase of the development of a weak shock. We identify the shock formation radius, showing that a heuristic estimate based on crossing characteristics matches an exact expansion around the wave front and verifying both with numerical experiments. Our general analytical condition for shock formation applies to one-dimensionalmore » motions within any static environment, including both eruptions and implosions. We also consider the early phase of shock energy dissipation. We find that waves of super-Eddington acoustic luminosity always create shocks, rather than damping by radiative diffusion. Therefore, shock formation is integral to super-Eddington outbursts.« less

Transmission and Emission of Solar Energetic Particles in Semi-transparent Shocks

NASA Astrophysics Data System (ADS)

Kocharov, Leon; Laitinen, Timo; Usoskin, Ilya; Vainio, Rami

2014-06-01

While major solar energetic particle (SEP) events are associated with coronal mass ejection (CME)-driven shocks in solar wind, accurate SEP measurements reveal that more than one component of energetic ions exist in the beginning of the events. Solar electromagnetic emissions, including nuclear gamma-rays, suggest that high-energy ions could also be accelerated by coronal shocks, and some of those particles could contribute to SEPs in interplanetary space. However, the CME-driven shock in solar wind is thought to shield any particle source beneath the shock because of the strong scattering required for the diffusive shock acceleration. In this Letter, we consider a shock model that allows energetic particles from the possible behind-shock source to appear in front of the shock simultaneously with SEPs accelerated by the shock itself. We model the energetic particle transport in directions parallel and perpendicular to the magnetic field in a spherical shock expanding through the highly turbulent magnetic sector with an embedded quiet magnetic tube, which makes the shock semi-transparent for energetic particles. The model energy spectra and time profiles of energetic ions escaping far upstream of the shock are similar to the profiles observed during the first hour of some gradual SEP events.

Seed population for about 1 MeV per nucleon heavy ions accelerated by interplanetary shocks

NASA Technical Reports Server (NTRS)

Tan, L. C.; Mason, G. M.; Klecker, B.; Hovestadt, D.

1989-01-01

Data obtained between 1977 and 1982 by the ISEE 1 and ISEE 3 satellites on the composition of heavy ions of about 1 MeV per nucleon, accelerated in interplanetary shock events which followed solar flare events, are examined. It was found that the average relative abundances for C, O, and Fe in the shock events were very close to those found for energetic ions in the solar flares, suggesting that, at these energies, the shock accelerated particles have the solar energetic particles as their seed population. This hypothesis is supported by the fact that the Fe/O ratio in the solar particle events is very strongly correlated with the Fe/O ratio in associated diffusive shock events.

Monte Carlo simulation of steady state shock structure including cosmic ray mediation and particle escape

NASA Technical Reports Server (NTRS)

Ellison, D. C.; Jones, F. C.; Eichler, D.

1983-01-01

Both hydrodynamic calculations (Drury and Volk, 1981, and Axford et al., 1982) and kinetic simulations imply the existence of thermal subshocks in high-Mach-number cosmic-ray-mediated shocks. The injection efficiency of particles from the thermal background into the diffusive shock-acceleration process is determined in part by the sharpness and compression ratio of these subshocks. Results are reported for a Monte Carlo simulation that includes both the back reaction of accelerated particles on the inflowing plasma, producing a smoothing of the shock transition, and the free escape of particles allowing arbitrarily large overall compression ratios in high-Mach-number steady-state shocks. Energy spectra and estimates of the proportion of thermal ions accelerated to high energy are obtained.

Monte Carlo simulation of steady state shock structure including cosmic ray mediation and particle escape

NASA Astrophysics Data System (ADS)

Ellison, D. C.; Jones, F. C.; Eichler, D.

1983-08-01

Both hydrodynamic calculations (Drury and Volk, 1981, and Axford et al., 1982) and kinetic simulations imply the existence of thermal subshocks in high-Mach-number cosmic-ray-mediated shocks. The injection efficiency of particles from the thermal background into the diffusive shock-acceleration process is determined in part by the sharpness and compression ratio of these subshocks. Results are reported for a Monte Carlo simulation that includes both the back reaction of accelerated particles on the inflowing plasma, producing a smoothing of the shock transition, and the free escape of particles allowing arbitrarily large overall compression ratios in high-Mach-number steady-state shocks. Energy spectra and estimates of the proportion of thermal ions accelerated to high energy are obtained.

Modelling Solar Energetic Particle Events Using the iPATH Model

NASA Astrophysics Data System (ADS)

Li, G.; Hu, J.; Ao, X.; Zank, G. P.; Verkhoglyadova, O. P.

2016-12-01

Solar Energetic Particles (SEPs) is the No. 1 space weather hazard. Understanding how particles are energized and propagated in these events is of practical concerns to the manned space missions. In particular, both the radial evolution and the longitudinal extent of a gradual solarenergetic particle (SEP) event are central topics for space weather forecasting. In this talk, I discuss the improved Particle Acceleration and Transport in the Heliosphere (iPATH) model. The iPATH model consists of three parts: (1) an updated ZEUS3D V3.5 MHD module that models thebackground solar wind and the initiation of a CME in a 2D domain; (2) an updated shock acceleration module where we investigate particle acceleration at different longitudinal locations along the surface of a CME-driven shock. Accelerated particle spectrum are obtained at the shock under the diffusive shock acceleration mechanism. Shock parameters and particle distributions are recorded and used as inputs for the later part. (3) an updated transport module where we follow the transport of accelerated particles from the shock to any destinations (Earth and/or Mars, e.g.) using a Monte-Carlo method. Both pitch angle scattering due to MHD turbulence and perpendicular diffusion across magnetic field are included. Our iPATH model is therefore intrinsically 2D in nature. The model is capable of generating time intensity profiles and instantaneous particle spectra atvarious locations and can greatly improve our current space weather forecasting capability.

Numerical simulations of unsteady transonic flow in diffusers

NASA Technical Reports Server (NTRS)

Liou, M.-S.; Coakley, T. J.

1982-01-01

Forced and naturally occurring, self-sustaining oscillations of transonic flows in two-dimensional diffusers were computed using MacCormack's hybrid method. Depending upon the shock strengths and the area ratios, the flow was fully attached or separated by either the shock or the adverse pressure gradient associated with the enlarging diffuser area. In the case of forced oscillations, a sinusoidal plane pressure wave at frequency 300 Hz was prescribed at the exit. A sufficiently large amount of data were acquired and Fourier analyzed. The distrbutions of time-mean pressures, the power spectral density, and the amplitude with phase angle along the top wall and in the core region were determined. Comparison with experimental results for the forced oscillation generally gave very good agreement; some success was achieved for the case of self-sustaining oscillation despite substantial three-dimensionality in the test. An observation of the sequence of self-sustaining oscillations was given.

Anomalous Transport of High Energy Cosmic Rays in Galactic Superbubbles

NASA Technical Reports Server (NTRS)

Barghouty, Nasser F.

2014-01-01

High-energy cosmic rays may exhibit anomalous transport as they traverse and are accelerated by a collection of supernovae explosions in a galactic superbubble. Signatures of this anomalous transport can show up in the particles' evolution and their spectra. In a continuous-time-random- walk (CTRW) model assuming standard diffusive shock acceleration theory (DSA) for each shock encounter, and where the superbubble (an OB stars association) is idealized as a heterogeneous region of particle sources and sinks, acceleration and transport in the superbubble can be shown to be sub-diffusive. While the sub-diffusive transport can be attributed to the stochastic nature of the acceleration time according to DSA theory, the spectral break appears to be an artifact of transport in a finite medium. These CTRW simulations point to a new and intriguing phenomenon associated with the statistical nature of collective acceleration of high energy cosmic rays in galactic superbubbles.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Wei-long; Bassett, Will P.; Christensen, James M.

The emission lifetimes of rhodamine 6G (R6G), were measured under shock compression to 9.1 GPa, with the dual intent of better understanding molecular photophysics in extreme environments and assessing the usefulness of fluorescence lifetime microscopy to measure spatially-dependent pressure distributions in shocked microstructured media. R6G was studied as free dye dissolved in poly-methyl methacrylate (PMMA), or dye encapsulated in silica microparticles suspended in PMMA. Thin layers of these materials in impedance-matched geometries were subjected to planar single-stage shocks created by laser-driven flyer plates. A synchronized femtosecond laser excited the dye at selected times relative to flyer plate arrival and themore » emission lifetimes were measured with a streak camera. Lifetimes decreased when shocks arrived. The lifetime decrease was attributed to a shock-induced enhancement of R6G nonradiative relaxation. At least part of the relaxation involved shock-enhanced intersystem crossing. For free dye in PMMA, the lifetime decrease during the shock was shown to be a linear function of shock pressure from 0-9 GPa, with a slope of -0.22 ns·GPa -1. Furthermore, the linear relationship makes it simple to convert lifetimes into pressures. Lifetime measurements in shocked microenvironments may be better than emission intensity measurements, since lifetimes are sensitive to the surrounding environment, but insensitive to intensity variations associated with the motion and optical properties of a dynamically changing structure.« less

Application of quadratic optimization to supersonic inlet control.

NASA Technical Reports Server (NTRS)

Lehtinen, B.; Zeller, J. R.

1972-01-01

This paper describes the application of linear stochastic optimal control theory to the design of the control system for the air intake, the inlet, of a supersonic air-breathing propulsion system. The controls must maintain a stable inlet shock position in the presence of random airflow disturbances and prevent inlet unstart. Two different linear time invariant controllers are developed. One is designed to minimize a nonquadratic index, the expected frequency of inlet unstart, and the other is designed to minimize the mean square value of inlet shock motion. The quadratic equivalence principle is used to obtain a linear controller that minimizes the nonquadratic index. The two controllers are compared on the basis of unstart prevention, control effort requirements, and frequency response. It is concluded that while controls designed to minimize unstarts are desirable in that the index minimized is physically meaningful, computation time required is longer than for the minimum mean square shock position approach. The simpler minimum mean square shock position solution produced expected unstart frequency values which were not significantly larger than those of the nonquadratic solution.

Detonation Shock Dynamics Calibration for Non-Ideal He: Anfo

NASA Astrophysics Data System (ADS)

Short, Mark; Salyer, Terry R.; Aslam, Tariq D.; Kiyanda, Charles B.; Morris, John S.; Zimmerly, Tony

2009-12-01

Linear Dn-κ detonation shock dynamics (DSD) fitting forms are obtained for four ammonium nitrate-fuel oil (ANFO) mixtures involving variations in the ammonium nitrate prill properties and ANFO stoichiometries.

Emission lifetimes of a fluorescent dye under shock compression

DOE PAGES

Liu, Wei-long; Bassett, Will P.; Christensen, James M.; ...

2015-10-15

The emission lifetimes of rhodamine 6G (R6G), were measured under shock compression to 9.1 GPa, with the dual intent of better understanding molecular photophysics in extreme environments and assessing the usefulness of fluorescence lifetime microscopy to measure spatially-dependent pressure distributions in shocked microstructured media. R6G was studied as free dye dissolved in poly-methyl methacrylate (PMMA), or dye encapsulated in silica microparticles suspended in PMMA. Thin layers of these materials in impedance-matched geometries were subjected to planar single-stage shocks created by laser-driven flyer plates. A synchronized femtosecond laser excited the dye at selected times relative to flyer plate arrival and themore » emission lifetimes were measured with a streak camera. Lifetimes decreased when shocks arrived. The lifetime decrease was attributed to a shock-induced enhancement of R6G nonradiative relaxation. At least part of the relaxation involved shock-enhanced intersystem crossing. For free dye in PMMA, the lifetime decrease during the shock was shown to be a linear function of shock pressure from 0-9 GPa, with a slope of -0.22 ns·GPa -1. Furthermore, the linear relationship makes it simple to convert lifetimes into pressures. Lifetime measurements in shocked microenvironments may be better than emission intensity measurements, since lifetimes are sensitive to the surrounding environment, but insensitive to intensity variations associated with the motion and optical properties of a dynamically changing structure.« less

Acceleration of Particles Near Earth's Bow Shock

NASA Astrophysics Data System (ADS)

Sandroos, A.

2012-12-01

Collisionless shock waves, for example, near planetary bodies or driven by coronal mass ejections, are a key source of energetic particles in the heliosphere. When the solar wind hits Earth's bow shock, some of the incident particles get reflected back towards the Sun and are accelerated in the process. Reflected ions are responsible for the creation of a turbulent foreshock in quasi-parallel regions of Earth's bow shock. We present first results of foreshock macroscopic structure and of particle distributions upstream of Earth's bow shock, obtained with a new 2.5-dimensional self-consistent diffusive shock acceleration model. In the model particles' pitch angle scattering rates are calculated from Alfvén wave power spectra using quasilinear theory. Wave power spectra in turn are modified by particles' energy changes due to the scatterings. The new model has been implemented on massively parallel simulation platform Corsair. We have used an earlier version of the model to study ion acceleration in a shock-shock interaction event (Hietala, Sandroos, and Vainio, 2012).

Ignition-and-Growth Modeling of NASA Standard Detonator and a Linear Shaped Charge

NASA Technical Reports Server (NTRS)

Oguz, Sirri

2010-01-01

The main objective of this study is to quantitatively investigate the ignition and shock sensitivity of NASA Standard Detonator (NSD) and the shock wave propagation of a linear shaped charge (LSC) after being shocked by NSD flyer plate. This combined explosive train was modeled as a coupled Arbitrary Lagrangian-Eulerian (ALE) model with LS-DYNA hydro code. An ignition-and-growth (I&G) reactive model based on unreacted and reacted Jones-Wilkins-Lee (JWL) equations of state was used to simulate the shock initiation. Various NSD-to-LSC stand-off distances were analyzed to calculate the shock initiation (or failure to initiate) and detonation wave propagation along the shaped charge. Simulation results were verified by experimental data which included VISAR tests for NSD flyer plate velocity measurement and an aluminum target severance test for LSC performance verification. Parameters used for the analysis were obtained from various published data or by using CHEETAH thermo-chemical code.

Shock-turbulence interaction in core-collapse supernovae

NASA Astrophysics Data System (ADS)

Abdikamalov, Ernazar; Zhaksylykov, Azamat; Radice, David; Berdibek, Shapagat

2016-10-01

Nuclear shell burning in the final stages of the lives of massive stars is accompanied by strong turbulent convection. The resulting fluctuations aid supernova explosion by amplifying the non-radial flow in the post-shock region. In this work, we investigate the physical mechanism behind this amplification using a linear perturbation theory. We model the shock wave as a one-dimensional planar discontinuity and consider its interaction with vorticity and entropy perturbations in the upstream flow. We find that, as the perturbations cross the shock, their total turbulent kinetic energy is amplified by a factor of ˜2, while the average linear size of turbulent eddies decreases by about the same factor. These values are not sensitive to the parameters of the upstream turbulence and the nuclear dissociation efficiency at the shock. Finally, we discuss the implication of our results for the supernova explosion mechanism. We show that the upstream perturbations can decrease the critical neutrino luminosity for producing explosion by several per cent.

On the origin of ultra high energy cosmic rays: subluminal and superluminal relativistic shocks

NASA Astrophysics Data System (ADS)

Meli, A.; Becker, J. K.; Quenby, J. J.

2008-12-01

Aims: The flux of ultra high energy cosmic rays (UHECRs) at E > 1018.5 eV is believed to arise in plasma shock environments in extragalactic sources. In this paper, we present a systematic study of cosmic ray (CR) particle acceleration by relativistic shocks, in particular concerning the dependence on bulk Lorentz factor and the angle between the magnetic field and the shock flow. The contribution to the observed diffuse CR spectrum provided by the accelerated particles is discussed. Methods: For the first time, Monte Carlo simulations for super- and subluminal shocks are extended to boost factors up to Γ = 1000 and systematically compared. The source spectra derived are translated into the expected diffuse proton flux from astrophysical sources by folding the spectra with the spatial distribution of active galactic nuclei (AGN) and gamma ray bursts (GRBs). Results of these predictions are compared with UHECR data. Results: While superluminal shocks are shown to be inefficient at providing acceleration to the highest energies (E > 1018.5 eV), subluminal shocks may provide particles up to 1021 eV, limited only by the Hillas-criterion. In the subluminal case, we find that mildly-relativistic shocks, thought to occur in jets of AGN (Γ ~ 10-30), yield energy spectra of dN/dE ~ E-2. Highly relativistic shocks expected in GRBs (100 < Γ < 1000), on the other hand, produce spectra as flat as ~ E-1.0 above 109.5 GeV. The model results are compared with the measured flux of CRs at the highest energies and it is shown that, while AGN spectra provide an excellent fit, GRB spectra are too flat to explain the observed flux. The first evidence of a correlation between the CR flux above 5.7 × 1010 GeV and the distribution of AGN provided by Auger are explained by our model. Although GRBs are excluded as the principle origin of UHECRs, neutrino production is expected in these sources either in mildly or highly relativistic shocks. In particular, superluminal shocks in GRBs may be observable via neutrino and photon fluxes, rather than as protons.

Shock wave oscillation driven by turbulent boundary layer fluctuations

NASA Technical Reports Server (NTRS)

Plotkin, K. J.

1972-01-01

Pressure fluctuations due to the interaction of a shock wave with a turbulent boundary layer were investigated. A simple model is proposed in which the shock wave is convected from its mean position by velocity fluctuations in the turbulent boundary layer. Displacement of the shock is assumed limited by a linear restoring mechanism. Predictions of peak root mean square pressure fluctuation and spectral density are in excellent agreement with available experimental data.

Prediction of Undsteady Flows in Turbomachinery Using the Linearized Euler Equations on Deforming Grids

NASA Technical Reports Server (NTRS)

Clark, William S.; Hall, Kenneth C.

1994-01-01

A linearized Euler solver for calculating unsteady flows in turbomachinery blade rows due to both incident gusts and blade motion is presented. The model accounts for blade loading, blade geometry, shock motion, and wake motion. Assuming that the unsteadiness in the flow is small relative to the nonlinear mean solution, the unsteady Euler equations can be linearized about the mean flow. This yields a set of linear variable coefficient equations that describe the small amplitude harmonic motion of the fluid. These linear equations are then discretized on a computational grid and solved using standard numerical techniques. For transonic flows, however, one must use a linear discretization which is a conservative linearization of the non-linear discretized Euler equations to ensure that shock impulse loads are accurately captured. Other important features of this analysis include a continuously deforming grid which eliminates extrapolation errors and hence, increases accuracy, and a new numerically exact, nonreflecting far-field boundary condition treatment based on an eigenanalysis of the discretized equations. Computational results are presented which demonstrate the computational accuracy and efficiency of the method and demonstrate the effectiveness of the deforming grid, far-field nonreflecting boundary conditions, and shock capturing techniques. A comparison of the present unsteady flow predictions to other numerical, semi-analytical, and experimental methods shows excellent agreement. In addition, the linearized Euler method presented requires one or two orders-of-magnitude less computational time than traditional time marching techniques making the present method a viable design tool for aeroelastic analyses.

A level set approach for shock-induced α-γ phase transition of RDX

NASA Astrophysics Data System (ADS)

Josyula, Kartik; Rahul; De, Suvranu

2018-02-01

We present a thermodynamically consistent level sets approach based on regularization energy functional which can be directly incorporated into a Galerkin finite element framework to model interface motion. The regularization energy leads to a diffusive form of flux that is embedded within the level sets evolution equation which maintains the signed distance property of the level set function. The scheme is shown to compare well with the velocity extension method in capturing the interface position. The proposed level sets approach is employed to study the α-γphase transformation in RDX single crystal shocked along the (100) plane. Example problems in one and three dimensions are presented. We observe smooth evolution of the phase interface along the shock direction in both models. There is no diffusion of the interface during the zero level set evolution in the three dimensional model. The level sets approach is shown to capture the characteristics of the shock-induced α-γ phase transformation such as stress relaxation behind the phase interface and the finite time required for the phase transformation to complete. The regularization energy based level sets approach is efficient, robust, and easy to implement.

Chemical Enhancements in Shock-Accelerated Particles: Ab initio Simulations.

PubMed

Caprioli, Damiano; Yi, Dennis T; Spitkovsky, Anatoly

2017-10-27

We study the thermalization, injection, and acceleration of ions with different mass/charge ratios, A/Z, in nonrelativistic collisionless shocks via hybrid (kinetic ions-fluid electrons) simulations. In general, ions thermalize to a postshock temperature proportional to A. When diffusive shock acceleration is efficient, ions develop a nonthermal tail whose extent scales with Z and whose normalization is enhanced as (A/Z)^{2} so that incompletely ionized heavy ions are preferentially accelerated. We discuss how these findings can explain observed heavy-ion enhancements in Galactic cosmic rays.

Notes on the Prediction of Shock-induced Boundary-layer Separation

NASA Technical Reports Server (NTRS)

Lange, Roy H.

1953-01-01

The present status of available information relative to the prediction of shock-induced boundary-layer separation is discussed. Experimental results showing the effects of Reynolds number and Mach number on the separation of both laminar and turbulent boundary layer are given and compared with available methods for predicting separation. The flow phenomena associated with separation caused by forward-facing steps, wedges, and incident shock waves are discussed. Applications of the flat-plate data to problems of separation on spoilers, diffusers, and scoop inlets are indicated for turbulent boundary layers.

The tracer diffusion coefficient of soft nanoparticles in a linear polymer matrix

DOE PAGES

Imel, Adam E.; Rostom, Sahar; Holley, Wade; ...

2017-03-09

The diffusion properties of nanoparticles in polymer nanocomposites are largely unknown and are often difficult to determine experimentally. To address this shortcoming, we have developed a novel method to determine the tracer diffusion coefficient of soft polystyrene nanoparticles in a linear polystyrene matrix. Monitoring the interdiffusion of soft nanoparticles into a linear polystyrene matrix provides the mutual diffusion coefficient of this system, from which the tracer diffusion coefficient of the soft nanoparticle can be determined using the slow mode theory. Utilizing this protocol, the role of nanoparticle molecular weight and rigidity on its tracer diffusion coefficient is provided. These resultsmore » demonstrate that the diffusive behavior of these soft nanoparticles differ from that of star polymers, which is surprising since our recent studies suggest that the nanoparticle interacts with a linear polymer similarly to that of a star polymer. It appears that these deformable nanoparticles mostly closely mimic the diffusive behavior of fractal macromolecular architectures or microgels, where the transport of the nanoparticle relies on the cooperative motion of neighboring linear chains. Finally, the less cross-linked, and thus more deformable, nanoparticles diffuse faster than the more highly crosslinked nanoparticles, presumably because the increased deformability allows the nanoparticle to distort and fit into available space.« less

On the Spectral Hardening at gsim300 keV in Solar Flares

NASA Astrophysics Data System (ADS)

Li, G.; Kong, X.; Zank, G.; Chen, Y.

2013-05-01

It has long been noted that the spectra of observed continuum emissions in many solar flares are consistent with double power laws with a hardening at energies gsim300 keV. It is now widely believed that at least in electron-dominated events, the hardening in the photon spectrum reflects an intrinsic hardening in the source electron spectrum. In this paper, we point out that a power-law spectrum of electrons with a hardening at high energies can be explained by the diffusive shock acceleration of electrons at a termination shock with a finite width. Our suggestion is based on an early analytical work by Drury et al., where the steady-state transport equation at a shock with a tanh profile was solved for a p-independent diffusion coefficient. Numerical simulations with a p-dependent diffusion coefficient show hardenings in the accelerated electron spectrum that are comparable with observations. One necessary condition for our proposed scenario to work is that high-energy electrons resonate with the inertial range of the MHD turbulence and low-energy electrons resonate with the dissipation range of the MHD turbulence at the acceleration site, and the spectrum of the dissipation range ~k -2.7. A ~k -2.7 dissipation range spectrum is consistent with recent solar wind observations.

Understanding the radio spectral indices of galaxy cluster relics by superdiffusive shock acceleration

NASA Astrophysics Data System (ADS)

Zimbardo, Gaetano; Perri, Silvia

2018-06-01

Galaxy cluster merger shocks are the likely source of relativistic electrons, but many observations do not fit into the standard acceleration models. In particular, there is a long-standing discrepancy between the radio derived Mach numbers M_radio and the Mach numbers derived from X-ray measurements, M_X. Here, we show how superdiffusive electron transport and superdiffusive shock acceleration (SSA) can help to solve this problem. We present a heuristic derivation of the superlinear time growth of the mean square displacement of particles, ⟨Δx2⟩∝tβ, and of the particle energy spectral index in the framework of SSA. The resulting expression for the radio spectral index α is then used to determine the superdiffusive exponent β from the observed values of α and of the compression ratio for a number of radio relics. Therefore, the fact that M_radio>M_X can be explained by SSA without the need to make assumptions on the energy spectrum of the seed electrons to be re-accelerated. We also consider the acceleration times obtained in the diffusive case, based both on the Bohm diffusion coefficient and on the quasilinear diffusion coefficient. While in the latter case the acceleration time is consistent with the estimated electron energy loss time, the former case it is much shorter.

The acceleration of particles at propagating interplanetary shocks

NASA Astrophysics Data System (ADS)

Prinsloo, P. L.; Strauss, R. D. T.

2017-12-01

Enhancements of charged energetic particles are often observed at Earth following the eruption of coronal mass ejections (CMEs) on the Sun. These enhancements are thought to arise from the acceleration of those particles at interplanetary shocks forming ahead of CMEs, propagating into the heliosphere. In this study, we model the acceleration of these energetic particles by solving a set of stochastic differential equations formulated to describe their transport and including the effects of diffusive shock acceleration. The study focuses on how acceleration at halo-CME-driven shocks alter the energy spectra of non-thermal particles, while illustrating how this acceleration process depends on various shock and transport parameters. We finally attempt to establish the relative contributions of different seed populations of energetic particles in the inner heliosphere to observed intensities during selected acceleration events.

Simulations of high Mach number perpendicular shocks with resistive electrons

NASA Technical Reports Server (NTRS)

Quest, K. B.

1986-01-01

A simulation code which models the ions as microparticles and the electrons as a resistive massless fluid is employed to study the structure of high Mach number perpendicular shocks. It is found that stable stationary shock solutions can be obtained for Alfven Mach numbers (M sub A) between 5 and 60 for upstream plasmas where the ratio of the plasma pressure to the magnetic pressure is 1, providing that the upstream resistive diffusion length is much smaller than the ion inertial length. For much larger resistive diffusion lengths, the magnetic field overshoot is damped, and the imbalance in the electron momentum equation results in a periodic fluctuation of the fraction of reflected ions. In the limit of M sub A of less than 10, the magnetic overshoot and the fraction of reflected ions increase with increasing M sub A, while at higher Mach numbers the fraction of reflected ions peaks at about 40 percent and the magnetic field overshoot increases at a much slower rate. Electron inertial effects are also considered.

Entropy-based artificial viscosity stabilization for non-equilibrium Grey Radiation-Hydrodynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Delchini, Marc O., E-mail: delchinm@email.tamu.edu; Ragusa, Jean C., E-mail: jean.ragusa@tamu.edu; Morel, Jim, E-mail: jim.morel@tamu.edu

2015-09-01

The entropy viscosity method is extended to the non-equilibrium Grey Radiation-Hydrodynamic equations. The method employs a viscous regularization to stabilize the numerical solution. The artificial viscosity coefficient is modulated by the entropy production and peaks at shock locations. The added dissipative terms are consistent with the entropy minimum principle. A new functional form of the entropy residual, suitable for the Radiation-Hydrodynamic equations, is derived. We demonstrate that the viscous regularization preserves the equilibrium diffusion limit. The equations are discretized with a standard Continuous Galerkin Finite Element Method and a fully implicit temporal integrator within the MOOSE multiphysics framework. The methodmore » of manufactured solutions is employed to demonstrate second-order accuracy in both the equilibrium diffusion and streaming limits. Several typical 1-D radiation-hydrodynamic test cases with shocks (from Mach 1.05 to Mach 50) are presented to establish the ability of the technique to capture and resolve shocks.« less

Simultaneous Modeling of Gradual SEP Events at the Earth and the Mars

NASA Astrophysics Data System (ADS)

Hu, J.; Li, G.

2017-12-01

Solar Energetic Particles (SEP) event is the number one space hazard for spacecraft instruments and astronauts' safety. Recent studies have shown that both longitudinal and radial extent of SEP events can be very significant. In this work, we use the improved Particle Acceleration and Transport in the Heliosphere (iPATH) model to simulate gradual SEP events that have impacts upon both the Earth and the Mars. We follow the propagation of a 2D CME-driven shock. Particles are accelerated at the shock via the diffusive shock acceleration (DSA) mechanism. Transport of the escaped particles to the Earth and the Mars is then followed using a backward stochastic differential equation method. Perpendicular diffusion is considered in both the DSA and the transport process. Model results such as time intensity profile and energetic particle spectrum at the two locations are compared to understand the spatial extent of an SEP event. Observational data at the Earth and the Mars are also studied to validate the model.

Particle Acceleration in Two Converging Shocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xin; Wang, Na; Shan, Hao

2017-06-20

Observations by spacecraft such as ACE , STEREO , and others show that there are proton spectral “breaks” with energy E {sub br} at 1–10 MeV in some large CME-driven shocks. Generally, a single shock with the diffusive acceleration mechanism would not predict the “broken” energy spectrum. The present paper focuses on two converging shocks to identify this energy spectral feature. In this case, the converging shocks comprise one forward CME-driven shock on 2006 December 13 and another backward Earth bow shock. We simulate the detailed particle acceleration processes in the region of the converging shocks using the Monte Carlomore » method. As a result, we not only obtain an extended energy spectrum with an energy “tail” up to a few 10 MeV higher than that in previous single shock model, but also we find an energy spectral “break” occurring on ∼5.5 MeV. The predicted energy spectral shape is consistent with observations from multiple spacecraft. The spectral “break,” then, in this case is caused by the interaction between the CME shock and Earth’s bow shock, and otherwise would not be present if Earth were not in the path of the CME.« less

SPECTRAL EVOLUTION OF ANOMALOUS COSMIC RAYS AT VOYAGER 1 BEYOND THE TERMINATION SHOCK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Senanayake, U. K.; Florinski, V.; Cummings, A. C.

When the Voyager 1 spacecraft crossed the termination shock (TS) on 2004 December 16, the energy spectra of anomalous cosmic rays (ACRs) could not have been produced by steady-state diffusive shock acceleration. However, over the next few years, in the declining phase of the solar cycle, the spectra began to evolve into the expected power-law profile. Observations at the shock led to a broad range of alternative theories for ACR acceleration. In spite of that, in this work we show that the observations could be explained by assuming ACRs are accelerated at the TS. In this paper, we propose thatmore » the solar cycle had an important effect on the unrolling of the spectra in the heliosheath. To investigate the spectral evolution of ACRs, a magnetohydrodynamic background model with stationary solar-wind inner boundary conditions was used to model the transport of helium and oxygen ions. We used a backward-in-time stochastic integration technique where phase-space trajectories are integrated until the so-called “injection energy” is reached. Our simulation results were compared with Voyager 1 observations using three different diffusion models. It is shown that the spectral evolution of ACRs in the heliosheath at Voyager 1 could be explained by an increase in the source strength and an enhancement in diffusion as a result of a decrease of the turbulent correlation length in the declining phase of the solar cycle. At the same time, drift effects seem to have had a smaller effect on the evolution of the spectra.« less

Do oil shocks predict economic policy uncertainty?

NASA Astrophysics Data System (ADS)

Rehman, Mobeen Ur

2018-05-01

Oil price fluctuations have influential role in global economic policies for developed as well as emerging countries. I investigate the role of international oil prices disintegrated into structural (i) oil supply shock, (ii) aggregate demand shock and (iii) oil market specific demand shocks, based on the work of Kilian (2009) using structural VAR framework on economic policies uncertainty of sampled markets. Economic policy uncertainty, due to its non-linear behavior is modeled in a regime switching framework with disintegrated structural oil shocks. Our results highlight that Indian, Spain and Japanese economic policy uncertainty responds to the global oil price shocks, however aggregate demand shocks fail to induce any change. Oil specific demand shocks are significant only for China and India in high volatility state.

Atomistic simulations of shock-induced alloying reactions in Ni /Al nanolaminates

NASA Astrophysics Data System (ADS)

Zhao, Shijin; Germann, Timothy C.; Strachan, Alejandro

2006-10-01

We employ molecular dynamics simulations with a first principles-based many body potential to characterize the exothermic alloying reactions of nanostructured Ni /Al multilayers induced by shock loading. We introduce a novel technique that captures both the initial shock transit as well as the subsequent longer-time-scale Ni3Al alloy formation. Initially, the softer Al layers are shock heated to a higher temperature than the harder Ni layers as a result of a series of shock reflections from the impedance-mismatched interfaces. Once initiated, the highly exothermic alloying reactions can propagate in a self-sustained manner by mass and thermal diffusion. We also characterize the role of voids on the initiation of alloying. The interaction of the shock wave with the voids leads not only to significant local heating (hot spots) but also directly aids the intermixing between Al and Ni; both of these phenomena contribute to a significant acceleration of the alloying reactions.

Ultrafast Fiber Bragg Grating Interrogation for Sensing in Detonation and Shock Wave Experiments.

PubMed

Rodriguez, George; Gilbertson, Steve M

2017-01-27

Chirped fiber Bragg grating (CFBG) sensors coupled to high speed interrogation systems are described as robust diagnostic approaches to monitoring shock wave and detonation front propagation tracking events for use in high energy density shock physics applications. Taking advantage of the linear distributed spatial encoding of the spectral band in single-mode CFBGs, embedded fiber systems and associated photonic interrogation methodologies are shown as an effective approach to sensing shock and detonation-driven loading processes along the CFBG length. Two approaches, one that detects spectral changes in the integrated spectrum of the CFBG and another coherent pulse interrogation approach that fully resolves its spectral response, shows that 100-MHz-1-GHz interrogation rates are possible with spatial resolution along the CFBG in the 50 µm to sub-millimeter range depending on the combination of CFBG parameters (i.e., length, chirp rate, spectrum) and interrogator design specifics. Results from several dynamic tests are used to demonstrate the performance of these high speed systems for shock and detonation propagation tracking under strong and weak shock pressure loading: (1) linear detonation front tracking in the plastic bonded explosive (PBX) PBX-9501; (2) tracking of radial decaying shock with crossover to non-destructive CFBG response; (3) shock wave tracking along an aluminum cylinder wall under weak loading accompanied by dynamic strain effects in the CFBG sensor.

Ultrafast Fiber Bragg Grating Interrogation for Sensing in Detonation and Shock Wave Experiments

PubMed Central

Rodriguez, George; Gilbertson, Steve M.

2017-01-01

Chirped fiber Bragg grating (CFBG) sensors coupled to high speed interrogation systems are described as robust diagnostic approaches to monitoring shock wave and detonation front propagation tracking events for use in high energy density shock physics applications. Taking advantage of the linear distributed spatial encoding of the spectral band in single-mode CFBGs, embedded fiber systems and associated photonic interrogation methodologies are shown as an effective approach to sensing shock and detonation-driven loading processes along the CFBG length. Two approaches, one that detects spectral changes in the integrated spectrum of the CFBG and another coherent pulse interrogation approach that fully resolves its spectral response, shows that 100-MHz–1-GHz interrogation rates are possible with spatial resolution along the CFBG in the 50 μm to sub-millimeter range depending on the combination of CFBG parameters (i.e., length, chirp rate, spectrum) and interrogator design specifics. Results from several dynamic tests are used to demonstrate the performance of these high speed systems for shock and detonation propagation tracking under strong and weak shock pressure loading: (1) linear detonation front tracking in the plastic bonded explosive (PBX) PBX-9501; (2) tracking of radial decaying shock with crossover to non-destructive CFBG response; (3) shock wave tracking along an aluminum cylinder wall under weak loading accompanied by dynamic strain effects in the CFBG sensor. PMID:28134819

Ultrafast Fiber Bragg Grating Interrogation for Sensing in Detonation and Shock Wave Experiments

DOE PAGES

Rodriguez, George; Gilbertson, Steve Michael

2017-01-27

Chirped fiber Bragg grating (CFBG) sensors coupled to high speed interrogation systems are described as robust diagnostic approaches to monitoring shock wave and detonation front propagation tracking events for use in high energy density shock physics applications. Taking advantage of the linear distributed spatial encoding of the spectral band in single-mode CFBGs, embedded fiber systems and associated photonic interrogation methodologies are shown as an effective approach to sensing shock and detonation-driven loading processes along the CFBG length. Two approaches, one that detects spectral changes in the integrated spectrum of the CFBG and another coherent pulse interrogation approach that fully resolvesmore » its spectral response, shows that 100-MHz–1-GHz interrogation rates are possible with spatial resolution along the CFBG in the 50 µm to sub-millimeter range depending on the combination of CFBG parameters (i.e., length, chirp rate, spectrum) and interrogator design specifics. In conclusion, results from several dynamic tests are used to demonstrate the performance of these high speed systems for shock and detonation propagation tracking under strong and weak shock pressure loading: (1) linear detonation front tracking in the plastic bonded explosive (PBX) PBX-9501; (2) tracking of radial decaying shock with crossover to non-destructive CFBG response; (3) shock wave tracking along an aluminum cylinder wall under weak loading accompanied by dynamic strain effects in the CFBG sensor.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodriguez, George; Gilbertson, Steve Michael

Chirped fiber Bragg grating (CFBG) sensors coupled to high speed interrogation systems are described as robust diagnostic approaches to monitoring shock wave and detonation front propagation tracking events for use in high energy density shock physics applications. Taking advantage of the linear distributed spatial encoding of the spectral band in single-mode CFBGs, embedded fiber systems and associated photonic interrogation methodologies are shown as an effective approach to sensing shock and detonation-driven loading processes along the CFBG length. Two approaches, one that detects spectral changes in the integrated spectrum of the CFBG and another coherent pulse interrogation approach that fully resolvesmore » its spectral response, shows that 100-MHz–1-GHz interrogation rates are possible with spatial resolution along the CFBG in the 50 µm to sub-millimeter range depending on the combination of CFBG parameters (i.e., length, chirp rate, spectrum) and interrogator design specifics. In conclusion, results from several dynamic tests are used to demonstrate the performance of these high speed systems for shock and detonation propagation tracking under strong and weak shock pressure loading: (1) linear detonation front tracking in the plastic bonded explosive (PBX) PBX-9501; (2) tracking of radial decaying shock with crossover to non-destructive CFBG response; (3) shock wave tracking along an aluminum cylinder wall under weak loading accompanied by dynamic strain effects in the CFBG sensor.« less

Multilevel Preconditioners for Reaction-Diffusion Problems with Discontinuous Coefficients

DOE PAGES

Kolev, Tzanio V.; Xu, Jinchao; Zhu, Yunrong

2015-08-23

In this study, we extend some of the multilevel convergence results obtained by Xu and Zhu, to the case of second order linear reaction-diffusion equations. Specifically, we consider the multilevel preconditioners for solving the linear systems arising from the linear finite element approximation of the problem, where both diffusion and reaction coefficients are piecewise-constant functions. We discuss in detail the influence of both the discontinuous reaction and diffusion coefficients to the performance of the classical BPX and multigrid V-cycle preconditioner.

Transonic Shock-Wave/Boundary-Layer Interactions on an Oscillating Airfoil

NASA Technical Reports Server (NTRS)

Davis, Sanford S.; Malcolm, Gerald N.

1980-01-01

Unsteady aerodynamic loads were measured on an oscillating NACA 64A010 airfoil In the NASA Ames 11 by 11 ft Transonic Wind Tunnel. Data are presented to show the effect of the unsteady shock-wave/boundary-layer interaction on the fundamental frequency lift, moment, and pressure distributions. The data show that weak shock waves induce an unsteady pressure distribution that can be predicted quite well, while stronger shock waves cause complex frequency-dependent distributions due to flow separation. An experimental test of the principles of linearity and superposition showed that they hold for weak shock waves while flows with stronger shock waves cannot be superimposed.

Collisionless shock formation, spontaneous electromagnetic fluctuations, and streaming instabilities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bret, A.; Instituto de Investigaciones Energeticas y Aplicaciones Industriales, Campus Universitario de Ciudad Real, 13071 Ciudad Real; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-51 Cambridge, Massachusetts 02138

2013-04-15

Collisionless shocks are ubiquitous in astrophysics and in the lab. Recent numerical simulations and experiments have shown how they can arise from the encounter of two collisionless plasma shells. When the shells interpenetrate, the overlapping region turns unstable, triggering the shock formation. As a first step towards a microscopic understanding of the process, we analyze here in detail the initial instability phase. On the one hand, 2D relativistic Particle-In-Cell simulations are performed where two symmetric initially cold pair plasmas collide. On the other hand, the instabilities at work are analyzed, as well as the field at saturation and the seedmore » field which gets amplified. For mildly relativistic motions and onward, Weibel modes govern the linear phase. We derive an expression for the duration of the linear phase in good agreement with the simulations. This saturation time constitutes indeed a lower-bound for the shock formation time.« less

Pickup water group ions at Comet Grigg-Skjellerup

NASA Astrophysics Data System (ADS)

Coates, A. J.; Johnstone, A. D.; Huddleston, D. E.; Wilken, B.; Jockers, K.; Borg, H.; Amata, E.; Formisano, V.; Bavassano-Cattaneo, M. B.; Winningham, J. D.; Gurgiolo, C.; Neubauer, F. M.

1993-03-01

The density and velocity distribution of cometary water group ions was measured by the Giotto spacecraft in the regions upstream and downstream of the 'bow shock' at Comet Grigg-Skjellerup. The results show that the distributions of ions are ring-like until quite close to the shock, the timescales for pitch angle and energy diffusion appear similar and the ion density follows a r exp -2 dependence.

Diffusion by one wave and by many waves

NASA Astrophysics Data System (ADS)

Albert, J. M.

2010-03-01

Radiation belt electrons and chorus waves are an outstanding instance of the important role cyclotron resonant wave-particle interactions play in the magnetosphere. Chorus waves are particularly complex, often occurring with large amplitude, narrowband but drifting frequency and fine structure. Nevertheless, modeling their effect on radiation belt electrons with bounce-averaged broadband quasi-linear theory seems to yield reasonable results. It is known that coherent interactions with monochromatic waves can cause particle diffusion, as well as radically different phase bunching and phase trapping behavior. Here the two formulations of diffusion, while conceptually different, are shown to give identical diffusion coefficients, in the narrowband limit of quasi-linear theory. It is further shown that suitably averaging the monochromatic diffusion coefficients over frequency and wave normal angle parameters reproduces the full broadband quasi-linear results. This may account for the rather surprising success of quasi-linear theory in modeling radiation belt electrons undergoing diffusion by chorus waves.

Weighted linear least squares estimation of diffusion MRI parameters: strengths, limitations, and pitfalls.

PubMed

Veraart, Jelle; Sijbers, Jan; Sunaert, Stefan; Leemans, Alexander; Jeurissen, Ben

2013-11-01

Linear least squares estimators are widely used in diffusion MRI for the estimation of diffusion parameters. Although adding proper weights is necessary to increase the precision of these linear estimators, there is no consensus on how to practically define them. In this study, the impact of the commonly used weighting strategies on the accuracy and precision of linear diffusion parameter estimators is evaluated and compared with the nonlinear least squares estimation approach. Simulation and real data experiments were done to study the performance of the weighted linear least squares estimators with weights defined by (a) the squares of the respective noisy diffusion-weighted signals; and (b) the squares of the predicted signals, which are reconstructed from a previous estimate of the diffusion model parameters. The negative effect of weighting strategy (a) on the accuracy of the estimator was surprisingly high. Multi-step weighting strategies yield better performance and, in some cases, even outperformed the nonlinear least squares estimator. If proper weighting strategies are applied, the weighted linear least squares approach shows high performance characteristics in terms of accuracy/precision and may even be preferred over nonlinear estimation methods. Copyright © 2013 Elsevier Inc. All rights reserved.

Thermally driven film climbing a vertical cylinder

NASA Astrophysics Data System (ADS)

Smolka, Linda

2017-11-01

The dynamics of a Marangoni driven film climbing the outside of a vertical cylinder is examined in numerical simulations of a thin film model. The model has three parameters: the scaled cylinder radius R̂, upstream film height h∞ and downstream precursor film thickness b , and reduces to the model for Marangoni driven film climbing a vertical plate when R̂ -> ∞ . The advancing front displays dynamics similar to that along a vertical plate where, depending on h∞ , the film forms a Lax shock, an undercompressive double shock or a rarefaction-undercompressive shock. A linear stability analysis of the Lax shock reveals the number of fingers that form along the contact line increases linearly with cylinder circumference while no fingers form below R̂ 1.15 with b = 0.1 . The substrate curvature controls the Lax shock height, bounds on h∞ that define the three solutions and the maximum growth rate of perturbations when R̂ = O (1) , whereas the shape of solutions and the stability of the Lax shock converge to the behavior on a vertical plate when R̂ >= O (10) . The azimuthal curvatures of the base state and perturbation, arising from the annular geometry of the film, promote instability of the advancing contact line.

A Strong Merger Shock in Abell 665

NASA Technical Reports Server (NTRS)

Dasadia, S.; Sun, M.; Sarazin, C.; Morandi, A.; Markevitch, M.; Wik, D.; Feretti, L.; Giovannini, G.; Govoni, F.

2016-01-01

Deep (103 ks) Chandra observations of Abell 665 have revealed rich structures in this merging galaxy cluster, including a strong shock and two cold fronts. The newly discovered shock has a Mach number of M =?3.0 +/- 0.6, propagating in front of a cold disrupted cloud. This makes Abell 665 the second cluster, after the Bullet cluster, where a strong merger shock of M is approximately 3 has been detected. The shock velocity from jump conditions is consistent with (2.7 +/- 0.7) × 10(exp 3) km s(exp -1). The new data also reveal a prominent southern cold front with potentially heated gas ahead of it. Abell 665 also hosts a giant radio halo. There is a hint of diffuse radio emission extending to the shock at the north, which needs to be examined with better radio data. This new strong shock provides a great opportunity to study the reacceleration model with the X-ray and radio data combined.

Semi-transparent shock model for major solar energetic particle events

NASA Astrophysics Data System (ADS)

Kocharov, Leon

2014-05-01

Production of solar energetic particles in major events typically comprises two stages: (i) the initial stage associated with shocks and magnetic reconnection in solar corona and (ii) the main stage associated with the CME-bow shock in solar wind. The coronal emission of energetic particles from behind the interplanetary shock wave continues for about one hour , being not shielded by the CME shock in solar wind and having the prompt access to particle detectors at 1 AU. On occasion of two well-separated solar eruptions from the same active region, the newly accelerated solar particles may be emitted well behind the previous CME, and those solar particles may penetrate through the interplanetary shock of the previous CME to arrive at the Earth's orbit without significant delay, which is another evidence that high-energy particles from the solar corona can penetrate through travelling interplanetary shocks. Diffusive shock acceleration is fast only if the particle mean free path near the shock is small. The small mean free path (high turbulence level), however, implies that energetic particles from coronal sources could not penetrate through the interplanetary shock, and even the particles accelerated by the interplanetary shock itself could not escape to its far upstream region. If so, they could not be promptly observed at 1 AU. However, high-energy particles in major solar events are detected well before the shock arrival at 1 AU. The theoretical difficulty can be obviated in the framework of the proposed model of a "semitransparent" shock. As in situ plasma observations indicate, the turbulence energy levels in neighboring magnetic tubes of solar wind may differ from each other by more than one order of magnitude. Such an intermittence of coronal and solar wind plasmas can affect energetic particle acceleration in coronal and interplanetary shocks. The new modeling incorporates particle acceleration in the shock front and the particle transport both in parallel to the magnetic field and in perpendicular to the magnetic field directions. The modeling suggests that the perpendicular diffusion is always essential for the energetic particle production, because particles can be accelerated in tubes with a high turbulence level and then escape to far upstream of the shock via neighboring, less turbulent tubes. We have modeled both the transmission of high-energy (>50 MeV) protons from coronal sources through the interplanetary shock wave and the interplanetary shock acceleration of ~1-10 MeV protons with subsequent transport to far upstream of the shock. The modeling results imply that presence of the fast transport channels penetrating the shock and the cross-field transport of accelerated particles to those channels may play a key role in the high-energy particle emission from distant shocks and can explain the prompt onset of major solar energetic particle events observed near the Earth's orbit.

Isolator-combustor interaction in a dual-mode scramjet engine

NASA Technical Reports Server (NTRS)

Pratt, David T.; Heiser, William H.

1993-01-01

A constant-area diffuser, or 'isolator', is required in both the ramjet and scramjet operating regimes of a dual-mode engine configuration in order to prevent unstarts due to pressure feedback from the combustor. Because the nature of the combustor-isolator interaction is different in the two operational modes, however, attention is presently given to the use of thermal vs kinetic energy coordinates for these interaction processes' visualization. The results of the analysis thus conducted indicate that the isolator requires severe flow separation at combustor entry, and that its entropy-generating characteristics are more severe than an equivalent oblique shock. A constant-area diffuser is only marginally able to contain the equivalent normal shock required for subsonic combustor entry.

Particle accelerators in the hot spots of radio galaxy 3C 445, imaged with the VLT.

PubMed

Prieto, M Almudena; Brunetti, Gianfranco; Mack, Karl-Heinz

2002-10-04

Hot spots (HSs) are regions of enhanced radio emission produced by supersonic jets at the tip of the radio lobes of powerful radio sources. Obtained with the Very Large Telescope (VLT), images of the HSs in the radio galaxy 3C 445 show bright knots embedded in diffuse optical emission distributed along the post-shock region created by the impact of the jet into the intergalactic medium. The observations reported here confirm that relativistic electrons are accelerated by Fermi-I acceleration processes in HSs. Furthermore, both the diffuse emission tracing the rims of the front shock and the multiple knots demonstrate the presence of additional continuous re-acceleration processes of electrons (Fermi-II).

The effects of micro-vortex generators on normal shock wave/boundary layer interactions

NASA Astrophysics Data System (ADS)

Herges, Thomas G.

Shock wave/boundary-layer interactions (SWBLIs) are complex flow phenomena that are important in the design and performance of internal supersonic and transonic flow fields such as engine inlets. This investigation was undertaken to study the effects of passive flow control devices on normal shock wave/boundary layer interactions in an effort to gain insight into the physics that govern these complex interactions. The work concentrates on analyzing the effects of vortex generators (VGs) as a flow control method by contributing a greater understanding of the flowfield generated by these devices and characterizing their effects on the SWBLI. The vortex generators are utilized with the goal of improving boundary layer health (i.e., reducing/increasing the boundary-layer incompressible shape factor/skin friction coefficient) through a SWBLI, increasing pressure recovery, and reducing flow distortion at the aerodynamic interface plane while adding minimal drag to the system. The investigation encompasses experiments in both small-scale and large-scale inlet testing, allowing multiple test beds for improving the characterization and understanding of vortex generators. Small-scale facility experiments implemented instantaneous schlieren photography, surface oil-flow visualization, pressure-sensitive paint, and particle image velocimetry to characterize the effects of an array of microramps on a normal shock wave/boundary-layer interaction. These diagnostics measured the time-averaged and instantaneous flow organization in the vicinity of the microramps and SWBLI. The results reveal that a microramp produces a complex vortex structure in its wake with two primary counter-rotating vortices surrounded by a train of Kelvin- Helmholtz (K-H) vortices. A streamwise velocity deficit is observed in the region of the primary vortices in addition to an induced upwash/downwash which persists through the normal shock with reduced strength. The microramp flow control also increased the spanwise-averaged skin-friction coefficient and reduced the spanwise-averaged incompressible shape factor, thereby improving the health of the boundary layer. The velocity in the near-wall region appears to be the best indicator of microramp effectiveness at controlling SWBLIs. Continued analysis of additional micro-vortex generator designs in the small-scale facility revealed reduced separation within a subsonic diffuser downstream of the normal shock wave/boundary layer interaction. The resulting attached flow within the diffuser from the micro-vortex generator control devices reduces shock wave position and pressure RMS fluctuations within the diffuser along with increased pressure recovery through the shock and at the entrance of the diffuser. The largest effect was observed by the micro-vortex generators that produce the strongest streamwise vortices. High-speed pressure measurements also indicated that the vortex generators shift the energy of the pressure fluctuations to higher frequencies. Implementation of micro-vortex generators into a large-scale, supersonic, axisymmetric, relaxed-compression inlet have been investigated with the use of a unique and novel flow-visualization measurement system designed and successfully used for the analysis of both upstream micro-VGs (MVGs) and downstream VGs utilizing surface oil-flow visualization and pressure-sensitive paint measurements. The inlet centerbody and downstream diffuser vortex-generator regions were imaged during wind-tunnel testing internally through the inlet cowl with the diagnostic system attached to the cowl. Surface-flow visualization revealed separated regions along the inlet centerbody for large mass-flow rates without vortex generators. Upstream vortex generators did reduce separation in the subsonic diffuser, and a unique perspective of the flowfield produced by the downstream vortex generators was obtained. In addition, pressure distributions on the inlet centerbody and vortex generators were measured with pressure-sensitive paint. At low mass-flow ratios the onset of buzz occurs in the large-scale low-boom inlet. Inlet buzz and how it is affected by vortex generators was characterized using shock tracking through high-speed schlieren imaging and pressure fluctuation measurements. The analysis revealed a dominant low frequency oscillation at 21.0 Hz for the single-stream inlet, corresponding with the duration of one buzz cycle. Pressure oscillations prior to the onset of buzz were not detected, leaving the location where the shock wave triggers large separation on the compression spike as the best indicator for the onset of buzz. The driving mechanism for a buzz cycle has been confirmed as the rate of depressurization and repressurization of the inlet as the buzz cycle fluctuates between an effectively unstarted (blocked) inlet and supercritical operation (choked flow), respectively. High-frequency shock position oscillations/pulsations (spike buzz) were also observed throughout portions of the inlet buzz cycle. The primary effect of the VGs was to trigger buzz at a higher mass-flow ratio.

Radiation hydrodynamics of triggered star formation: the effect of the diffuse radiation field

NASA Astrophysics Data System (ADS)

Haworth, Thomas J.; Harries, Tim J.

2012-02-01

We investigate the effect of including diffuse field radiation when modelling the radiatively driven implosion of a Bonnor-Ebert sphere (BES). Radiation-hydrodynamical calculations are performed by using operator splitting to combine Monte Carlo photoionization with grid-based Eulerian hydrodynamics that includes self-gravity. It is found that the diffuse field has a significant effect on the nature of radiatively driven collapse which is strongly coupled to the strength of the driving shock that is established before impacting the BES. This can result in either slower or more rapid star formation than expected using the on-the-spot approximation depending on the distance of the BES from the source object. As well as directly compressing the BES, stronger shocks increase the thickness and density in the shell of accumulated material, which leads to short, strong, photoevaporative ejections that reinforce the compression whenever it slows. This happens particularly effectively when the diffuse field is included as rocket motion is induced over a larger area of the shell surface. The formation and evolution of 'elephant trunks' via instability is also found to vary significantly when the diffuse field is included. Since the perturbations that seed instabilities are smeared out elephant trunks form less readily and, once formed, are exposed to enhanced thermal compression.

Shapes of strong shock fronts in an inhomogeneous solar wind

NASA Technical Reports Server (NTRS)

Heinemann, M. A.; Siscoe, G. L.

1974-01-01

The shapes expected for solar-flare-produced strong shock fronts in the solar wind have been calculated, large-scale variations in the ambient medium being taken into account. It has been shown that for reasonable ambient solar wind conditions the mean and the standard deviation of the east-west shock normal angle are in agreement with experimental observations including shocks of all strengths. The results further suggest that near a high-speed stream it is difficult to distinguish between corotating shocks and flare-associated shocks on the basis of the shock normal alone. Although the calculated shapes are outside the range of validity of the linear approximation, these results indicate that the variations in the ambient solar wind may account for large deviations of shock normals from the radial direction.

Shock wave equation of state of muscovite

NASA Technical Reports Server (NTRS)

Sekine, Toshimori; Rubin, Allan M.; Ahrens, Thomas J.

1991-01-01

Shock wave data were obtained between 20 and 140 GPa for natural muscovite obtained from Methuen Township (Ontario), in order to provide a shock-wave equation of state for this crustal hydrous mineral. The shock equation of state data could be fit by a linear shock velocity (Us) versus particle velocity (Up) relation Us = 4.62 + 1.27 Up (km/s). Third-order Birch-Murnaghan equation of state parameters were found to be K(OS) = 52 +/-4 GPa and K-prime(OS) = 3.2 +/-0.3 GPa. These parameters are comparable to those of other hydrous minerals such as brucite, serpentine, and tremolite.

Shock Radiation Tests for Saturn and Uranus Entry Probes

NASA Technical Reports Server (NTRS)

Cruden, Brett A.; Bogdanoff, David W.

2017-01-01

This paper describes a test series in the Electric Arc Shock Tube at NASA Ames Research Center with the objective of quantifying shock-layer radiative heating magnitudes for future probe entries into Saturn and Uranus atmospheres. Normal shock waves are measured in Hydrogen-Helium mixtures (89:11 by volume) at freestream pressures between 13-66 Pa (0.1-0.5 Torr) and velocities from 20-30 kms. No shock layer radiation is detected within measurement limits below 25 kms, a finding consistent with predictions for Uranus entries. Between 25-30 kms, radiance is quantified from the Vacuum Ultraviolet through Near Infrared, with focus on the Lyman-a and Balmer series lines of Hydrogen. Shock profiles are analyzed for electron number density and electronic state distribution. The shocks do not equilibrate over several cm, and in many cases the state distributions are non-Boltzmann. Radiation data are compared to simulations of Decadal Survey entries for Saturn and shown to be as much as 8x lower than predicted with the Boltzmann radiation model. Radiance is observed in front of the shock layer, the characteristics of which match the expected diffusion length.

On the maximum energy achievable in the first order Fermi acceleration at shocks

NASA Astrophysics Data System (ADS)

Grozny, I.; Diamond, P.; Malkov, M.

2002-11-01

Astrophysical shocks are considered as the sites of cosmic ray (CR) production. The primary mechanism is the diffusive shock (Fermi) acceleration which operates via multiple shock recrossing by a particle. Its efficiency, the rate of energy gain, and the maximum energy are thus determined by the transport mechanisms (confinement to the shock) of these particles in a turbulent shock environment. The turbulence is believed to be generated by accelerated particles themselves. Moreover, in the most interesting case of efficient acceleration the entire MHD shock structure is dominated by their pressure. This makes this problem one of the challenging strongly nonlinear problems of astrophysics. We suggest a physical model that describes particle acceleration, shock structure and the CR driven turbulence on an equal footing. The key new element in this scheme is nonlinear cascading of the MHD turbulence on self-excited (via modulational and Drury instability) sound-like perturbations which gives rise to a significant enrichment of the long wave part of the MHD spectrum. This is critical for the calculation of the maximum energy.

Reversible electron heating vs. wave-particle interactions in quasi-perpendicular shocks

NASA Technical Reports Server (NTRS)

Veltri, P.; Mangeney, A.; Scudder, J. D.

1992-01-01

The energy necessary to explain the electron heating in quasi-perpendicular collisionless shocks can be derived either from the electron acceleration in the d.c. cross shock electric potential, or by the interactions between the electrons and the waves existing in the shock. A Monte Carlo simulation has been performed to study the electron distribution function evolution through the shock structure, with and without particle diffusion on waves. This simulation has allowed us to clarify the relative importance of the two possible energy sources; in particular it has been shown that the electron parallel temperature is determined by the d.c. electromagnetic field and not by any wave-particle-induced heating. Wave particle interactions are effective in smoothing out the large gradients in phase space produced by the 'reversible' motion of the electrons, thus producing a 'cooling' of the electrons.

The Prediction of Scattered Broadband Shock-Associated Noise

NASA Technical Reports Server (NTRS)

Miller, Steven A. E.

2015-01-01

A mathematical model is developed for the prediction of scattered broadband shock-associated noise. Model arguments are dependent on the vector Green's function of the linearized Euler equations, steady Reynolds-averaged Navier-Stokes solutions, and the two-point cross-correlation of the equivalent source. The equivalent source is dependent on steady Reynolds-averaged Navier-Stokes solutions of the jet flow, that capture the nozzle geometry and airframe surface. Contours of the time-averaged streamwise velocity component and turbulent kinetic energy are examined with varying airframe position relative to the nozzle exit. Propagation effects are incorporated by approximating the vector Green's function of the linearized Euler equations. This approximation involves the use of ray theory and an assumption that broadband shock-associated noise is relatively unaffected by the refraction of the jet shear layer. A non-dimensional parameter is proposed that quantifies the changes of the broadband shock-associated noise source with varying jet operating condition and airframe position. Scattered broadband shock-associated noise possesses a second set of broadband lobes that are due to the effect of scattering. Presented predictions demonstrate relatively good agreement compared to a wide variety of measurements.

A possible explanation of the knee of cosmic light component spectrum from 100 TeV to 3 PeV

NASA Astrophysics Data System (ADS)

Lin, Wen-Hui; Bao, Bi-Wen; Jiang, Ze-Jun; Zhang, Li

2017-10-01

A mixed hydrogen and helium (H + He) spectrum with a clear steepening at ∼ 700 TeV has been detected by the ARGO-YBJ experiments. In this paper, we demonstrate that the observed H + He spectrum can be reproduced well with a model of cosmic rays escaping from the supernova remnants (SNRs) in our Galaxy. In this model, particles are accelerated in a SNR through a non-linear diffusive shock acceleration mechanism. Three components of high energy light nuclei escaped from the SNR are considered. It should be noted that the proton spectrum observed by KASCADE can be also explained by this model given a higher acceleration efficiency. Supported by the National Natural Science Foundation of China (11433004, 11363006, 11103016, 11173020), Top Talents Program of Yunnan Province (2015HA030) and the Natural Science Foundation of Yunnan Province(2015FB103)

The solution of non-linear hyperbolic equation systems by the finite element method

NASA Technical Reports Server (NTRS)

Loehner, R.; Morgan, K.; Zienkiewicz, O. C.

1984-01-01

A finite-element method for the solution of nonlinear hyperbolic systems of equations, such as those encountered in non-self-adjoint problems of transient phenomena in convection-diffusion or in the mixed representation of wave problems, is developed and demonstrated. The problem is rewritten in moving coordinates and reinterpolated to the original mesh by a Taylor expansion prior to a standard Galerkin spatial discretization, and it is shown that this procedure is equivalent to the time-discretization approach of Donea (1984). Numerical results for sample problems are presented graphically, including such shallow-water problems as the breaking of a dam, the shoaling of a wave, and the outflow of a river; compressible flows such as the isothermal flow in a nozzle and the Riemann shock-tube problem; and the two-dimensional scalar-advection, nonlinear-shallow-water, and Euler equations.

Pyrotechnic shock: A literature survey of the Linear Shaped Charge (LSC)

NASA Technical Reports Server (NTRS)

Smith, J. L.

1984-01-01

Linear shaped charge (LSC) literature for the past 20 years is reviewed. The following topics are discussed: (1) LSC configuration; (2) LSC usage; (3) LSC induced pyroshock; (4) simulated pyrotechnic testing; (5) actual pyrotechnic testing; (6) data collection methods; (7) data analysis techniques; (8) shock reduction methods; and (9) design criteria. Although no new discoveries have been made in LSC research, charge shapes are improved to allow better cutting performance, testing instrumentation is refined, and some new explosives, for use in LSC, are formulated.

Jet noise suppression

NASA Astrophysics Data System (ADS)

Gliebe, P. R.; Brausch, J. F.; Majjigi, R. K.; Lee, R.

1991-08-01

The objectives of this chapter are to review and summarize the jet noise suppression technology, to provide a physical and theoretical model to explain the measured jet noise suppression characteristics of different concepts, and to provide a set of guidelines for evolving jet noise suppression designs. The underlying principle for all jet noise suppression devices is to enhance rapid mixing (i.e., diffusion) of the jet plume by geometric and aerothermodynamic means. In the case of supersonic jets, the shock-cell broadband noise reduction is effectively accomplished by the elimination or mitigation of the shock-cell structure. So far, the diffusion concepts have predominantly concentrated on jet momentum and energy (kinetic and thermal) diffusion, in that order, and have yielded better noise reduction than the simple conical nozzles. A critical technology issue that needs resolution is the effect of flight on the noise suppression potential of mechanical suppressor nozzles. A more thorough investigation of this mechanism is necessary for the successful development and design of an acceptable noise suppression device for future high-speed civil transports.

Improved Solver Settings for 3D Exploding Wire Simulations in ALEGRA

DTIC Science & Technology

2016-08-01

expanding plasma and shock wave resulting from the wire burst can extend to tens of cen- timeters. The elliptic nature of the magnetic diffusion...such simulations were prohibitively slow due in part to unoptimized (matrix) solver settings. In this report, we address that by varying 6 parameters...distribution is unlimited. simulation code developed by SNL for modeling high-deformation solid dynam- ics, shock -hydrodynamics, magnetohydrodynamics

Compressible instability of rapidly expanding spherical material interfaces

NASA Astrophysics Data System (ADS)

Mankbadi, Mina Reda

The focus herein is on the instability of a material interface formed during an abrupt release of concentrated energy as in detonative combustion, explosive dispersals, and inertial-confinement fusion. These applications are modeled as a spherical shock-tube in which high-pressure gas initially contained in a small spherical shell is suddenly released. A forward-moving shock and an inward-moving secondary shock are formed, and between them a material interface develops that separates high-density fluid from the low-density one. The wrinkling of this interface controls mixing and energy release. The interface's stability is studied with and without the inclusion of metalized particulates. A numerical scheme is developed to discretize the full nonlinear equations of the base flow, and the 3D linearized perturbed flow equations. Linearization is followed by spherical harmonic decomposition of the disturbances, thereby reducing the 3D computational domain to one-dimensional radial domain. The 3D physical nature of the disturbances is maintained throughout the procedure. An extended Roe-Pike scheme coupled with a WENO scheme is developed to capture the discontinuities and accurately predict the disturbances. In Chapter 2, the contact interface's stability is analyzed in the inviscid single-phase. The disturbances grow exponentially and the growth rate is insensitive to the radial initial-disturbance profile. For wave numbers less than 100, the results are in accordance with previous theories but clarify that compressibility reduces the growth rate. Unlike the classical RTI, the growth rate reaches saturation at high wavenumbers. The parametric studies show that for specific ratios of initial pressure and temperature, the instability can be eliminated altogether. Chapter 3 discusses the full effects of viscosity and thermal diffusivity. Although Prandtl number effects are minimal, viscous effects dampen the high-wave numbers. For a given Reynolds number there is a peak wave number at which the disturbances are most amplified. In Chapter 4, the multiphase case with metalized particles is investigated. The quasi steady gas-particle interaction forces and heat transfer decelerate the contact interface and reduce its Atwood number, which results in reducing the growth of the interfacial instabilities. A parametric study of the multiphase instability is presented to assist in controlling the instability.

The enigmatic nature of the circumstellar envelope and bow shock surrounding Betelgeuse as revealed by Herschel. I. Evidence of clumps, multiple arcs, and a linear bar-like structure

NASA Astrophysics Data System (ADS)

Decin, L.; Cox, N. L. J.; Royer, P.; Van Marle, A. J.; Vandenbussche, B.; Ladjal, D.; Kerschbaum, F.; Ottensamer, R.; Barlow, M. J.; Blommaert, J. A. D. L.; Gomez, H. L.; Groenewegen, M. A. T.; Lim, T.; Swinyard, B. M.; Waelkens, C.; Tielens, A. G. G. M.

2012-12-01

Context. The interaction between stellar winds and the interstellar medium (ISM) can create complex bow shocks. The photometers on board the Herschel Space Observatory are ideally suited to studying the morphologies of these bow shocks. Aims: We aim to study the circumstellar environment and wind-ISM interaction of the nearest red supergiant, Betelgeuse. Methods.Herschel PACS images at 70, 100, and 160 μm and SPIRE images at 250, 350, and 500 μm were obtained by scanning the region around Betelgeuse. These data were complemented with ultraviolet GALEX data, near-infrared WISE data, and radio 21 cm GALFA-HI data. The observational properties of the bow shock structure were deduced from the data and compared with hydrodynamical simulations. Results: The infrared Herschel images of the environment around Betelgeuse are spectacular, showing the occurrence of multiple arcs at ~6-7' from the central target and the presence of a linear bar at ~9'. Remarkably, no large-scale instabilities are seen in the outer arcs and linear bar. The dust temperature in the outer arcs varies between 40 and 140 K, with the linear bar having the same colour temperature as the arcs. The inner envelope shows clear evidence of a non-homogeneous clumpy structure (beyond 15''), probably related to the giant convection cells of the outer atmosphere. The non-homogeneous distribution of the material even persists until the collision with the ISM. A strong variation in brightness of the inner clumps at a radius of ~2' suggests a drastic change in mean gas and dust density ~32 000 yr ago. Using hydrodynamical simulations, we try to explain the observed morphology of the bow shock around Betelgeuse. Conclusions: Different hypotheses, based on observational and theoretical constraints, are formulated to explain the origin of the multiple arcs and the linear bar and the fact that no large-scale instabilities are visible in the bow shock region. We infer that the two main ingredients for explaining these phenomena are a non-homogeneous mass-loss process and the influence of the Galactic magnetic field. The hydrodynamical simulations show that a warm interstellar medium, reflecting a warm neutral or partially ionized medium, or a higher temperature in the shocked wind also prevent the growth of strong instabilities. The linear bar is probably an interstellar structure illuminated by Betelgeuse itself. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices (including movies) are available in electronic form at http://www.aanda.org

THE ROLE OF THE DIFFUSIVE PROTONS IN THE GAMMA-RAY EMISSION OF SUPERNOVA REMNANT RX J1713.7–3946—A TWO-ZONE MODEL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xiao; Chen, Yang

2016-04-10

RX J1713.7−3946 is a prototype in the γ-ray-bright supernova remnants (SNRs) and is in continuing debates on its hadronic versus leptonic origin of the γ-ray emission. We explore the role played by the diffusive relativistic protons that escape from the SNR shock wave in the γ-ray emission, apart from the high-energy particles’ emission from the inside of the SNR. In the scenario that the SNR shock propagates in a clumpy molecular cavity, we consider that the γ-ray emission from the inside of the SNR may arise either from the inverse Compton scattering or from the interaction between the trapped energetic protons and themore » shocked clumps. The dominant origin between them depends on the electron-to-proton number ratio. The diffusive protons that escaped from the shock wave during the expansion history can provide an outer hadronic γ-ray component by bombarding the surrounding dense matter. The broadband spectrum can be well explained by this two-zone model, in which the γ-ray emission from the inside governs the TeV band, while the outer emission component substantially contributes to the GeV γ-rays. The two-zone model can also explain the TeV γ-ray radial brightness profile that significantly stretches beyond the nonthermal X-ray-emitting region. In the calculation, we present a simplified algorithm for Li and Chen's “accumulative diffusion” model for escaping protons and apply the Markov Chain Monte Carlo method to constrain the physical parameters.« less

Different Types of Ion Populations Upstream of the 2013 October 8 Interplanetary Shock

NASA Astrophysics Data System (ADS)

Kajdič, Primož; Hietala, Heli; Blanco-Cano, Xóchitl

2017-11-01

We show for the first time that different types of suprathermal ion distributions may exist upstream of a single interplanetary shock. ACE and the two ARTEMIS satellites observed a shock on 2013 October 8. The ARTEMIS P1 and P2 spacecraft first observed field-aligned ions (P1) and gyrating ions (P2) arriving from the shock. These were followed by intermediate ions and later by a diffuse population. At the location of the P2 the shock exhibited an Alfvénic Mach number of M A = 5.7 and was marginally quasi-perpendicular ({θ }{Bn}=47^\\circ ). At P1 spacecraft the shock was weaker (M A = 4.9) and more perpendicular ({θ }{Bn}=61^\\circ ). Consequently, the observed suprathermal ion and ultra-low-frequency wave properties were somewhat different. At P2 the ultra-low-frequency waves are more intense and extend farther upstream from the shock. The energies of field-aligned and gyrating ions in the shock rest-frame were ˜20 keV, which is much more than in the case of the stronger (M A = 6-7) Earth’s bow shock, where they are less than 10 keV.

Molecular Diagnostics of Diffusive Boundary Layers

NASA Astrophysics Data System (ADS)

Rawlings, J. M. C.; Hartquist, T. W.

1997-10-01

We have examined the chemistry in thin (<~0.01 pc) boundary layers between dark star-forming cores and warm, shocked T Tauri winds on the assumption that turbulence-driven diffusion occurs within them. The results indicate that emissions from C+, CH, OH, H2O and the J = 6 --> 5 transition of CO, among others, may serve as diagnostics of the boundary layers.

Shock loading predictions from application of indicial theory to shock-turbulence interactions

NASA Technical Reports Server (NTRS)

Keefe, Laurence R.; Nixon, David

1991-01-01

A sequence of steps that permits prediction of some of the characteristics of the pressure field beneath a fluctuating shock wave from knowledge of the oncoming turbulent boundary layer is presented. The theory first predicts the power spectrum and pdf of the position and velocity of the shock wave, which are then used to obtain the shock frequency distribution, and the pdf of the pressure field, as a function of position within the interaction region. To test the validity of the crucial assumption of linearity, the indicial response of a normal shock is calculated from numerical simulation. This indicial response, after being fit by a simple relaxation model, is used to predict the shock position and velocity spectra, along with the shock passage frequency distribution. The low frequency portion of the shock spectra, where most of the energy is concentrated, is satisfactorily predicted by this method.

Relationship of Interplanetary Shock Micro and Macro Characteristics: A Wind Study

NASA Technical Reports Server (NTRS)

Szabo, Adam; Koval, A

2008-01-01

The non-linear least squared MHD fitting technique of Szabo 11 9941 has been recently further refined to provide realistic confidence regions for interplanetary shock normal directions and speeds. Analyzing Wind observed interplanetary shocks from 1995 to 200 1, macro characteristics such as shock strength, Theta Bn and Mach numbers can be compared to the details of shock micro or kinetic structures. The now commonly available very high time resolution (1 1 or 22 vectors/sec) Wind magnetic field data allows the precise characterization of shock kinetic structures, such as the size of the foot, ramp, overshoot and the duration of damped oscillations on either side of the shock. Detailed comparison of the shock micro and macro characteristics will be given. This enables the elucidation of shock kinetic features, relevant for particle energization processes, for observations where high time resolution data is not available. Moreover, establishing a quantitative relationship between the shock micro and macro structures will improve the confidence level of shock fitting techniques during disturbed solar wind conditions.

Acceleration and Transport of Solar Energetic Particles in 'Semi-transparent' Shocks

NASA Astrophysics Data System (ADS)

Kocharov, L. G.

2013-12-01

Production of solar energetic particles in major events typically comprises two stages: (i) an initial stage associated with shocks and magnetic reconnection in solar corona and (ii) the main stage associated with the CME-bow shock in solar wind (e.g., Figure 1 of Kocharov et al., 2012, ApJ, 753, 87). As far as the second stage production is ascribed to interplanetary shocks, the first stage production should be attributed to coronal sources. Coronal emission of energetic particles from behind the interplanetary shock wave continues for about one hour (Figures 4-6 of Kocharov et al, 2010, ApJ, 725, 2262). The coronal particles are not shielded by the CME-bow shock in solar wind and have a prompt access to particle detectors at 1 AU. On non-exceptional occasion of two successive solar eruptions from the same active region, the newly accelerated solar particles may be emitted well behind the previous CME, and those solar particles may penetrate through the interplanetary shock of the previous CME to arrive at the Earth's orbit without significant delay (Al-Sawad et al., 2009, Astron. & Astrophys., 497, L1), which is another evidence that high-energy particles from the solar corona can penetrate through travelling interplanetary shocks. Diffusive shock acceleration is fast only if the particle mean free path in the shock is small. A small mean free path (high turbulence level), however, implies that energetic particles from the solar corona could not penetrate through the interplanetary shock and could not escape to its far upstream region. If so, they could not produce a prompt event at 1 AU. However, solar high-energy particle events are observed very far from the shocks. The theoretical difficulty can be obviated in the framework of the new model of a "semi-transparent" shock. As in situ plasma observations indicate, the turbulence energy levels in neighboring magnetic tubes of solar wind may differ from each other by more than one order of magnitude. Such an intermittence of coronal and solar wind plasmas can affect energetic particle acceleration in coronal and interplanetary shocks. The new modeling incorporates particle acceleration in the shock front and the particle transport both in parallel to the magnetic field and in perpendicular to the magnetic field directions. The modeling suggests that the perpendicular diffusion is always essential for the energetic particle production, because particles can be accelerated in tubes with a high turbulence level and then escape to far upstream of the shock via neighboring, less turbulent tubes. Considered are both the penetration of the high-energy (>50 MeV) solar protons through the interplanetary shock and the interplanetary shock acceleration to lower energies (~1-10 MeV). The modeling results are compared with data of spaceborne particle instruments (SOHO. STEREO) and data of neutron monitors.

Local bounds preserving stabilization for continuous Galerkin discretization of hyperbolic systems

NASA Astrophysics Data System (ADS)

Mabuza, Sibusiso; Shadid, John N.; Kuzmin, Dmitri

2018-05-01

The objective of this paper is to present a local bounds preserving stabilized finite element scheme for hyperbolic systems on unstructured meshes based on continuous Galerkin (CG) discretization in space. A CG semi-discrete scheme with low order artificial dissipation that satisfies the local extremum diminishing (LED) condition for systems is used to discretize a system of conservation equations in space. The low order artificial diffusion is based on approximate Riemann solvers for hyperbolic conservation laws. In this case we consider both Rusanov and Roe artificial diffusion operators. In the Rusanov case, two designs are considered, a nodal based diffusion operator and a local projection stabilization operator. The result is a discretization that is LED and has first order convergence behavior. To achieve high resolution, limited antidiffusion is added back to the semi-discrete form where the limiter is constructed from a linearity preserving local projection stabilization operator. The procedure follows the algebraic flux correction procedure usually used in flux corrected transport algorithms. To further deal with phase errors (or terracing) common in FCT type methods, high order background dissipation is added to the antidiffusive correction. The resulting stabilized semi-discrete scheme can be discretized in time using a wide variety of time integrators. Numerical examples involving nonlinear scalar Burgers equation, and several shock hydrodynamics simulations for the Euler system are considered to demonstrate the performance of the method. For time discretization, Crank-Nicolson scheme and backward Euler scheme are utilized.

The Shock and Vibration Bulletin. Part 3. Shock Testing, Shock Analysis

DTIC Science & Technology

1974-08-01

APPROXIMATE TRANSFORMATION C.S. O’Hearne and J.W. Shipley, Martin Marietta Aerospace, Orlando, Florida LINEAR LUMPED-MASS MODELING TECHNIQUES FOR BLAST LOADED...Leppert, B.K. Wada, Jet Propulsion Laboratory, Pasadena, California, and R. Miyakawa, Martin - Marietta Aerospace, Denver, Colorado (assigned to the Jet...Wilmington, Delaware Vibration Testing and Analysis DEVELOPMENT OF SAM-D MISSILE RANDOM VIBRATION RESPONSE LOADS P.G. Hahn, Martin Marietta Aerospace

Magnetic ramp scale at supercritical perpendicular collisionless shocks: Full particle electromagnetic simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Zhongwei; SOA Key Laboratory for Polar Science, Polar Research Institute of China, Shanghai, 200136; Lu, Quanming

2013-09-15

Supercritical perpendicular collisionless shocks are known to exhibit foot, ramp, and overshoot structures. The shock ramp structure is in a smaller scale in contrast to other microstructures (foot and overshoot) within the shock front. One-dimensional full particle simulations of strictly perpendicular shocks over wide ranges of ion beta β{sub i}, Alfvén Mach number M{sub A}, and ion-to-electron mass ratio m{sub i}/m{sub e} are presented to investigate the impact of plasma parameters on the shock ramp scale. Main results are (1) the ramp scale can be as small as several electron inertial length. (2) The simulations suggest that in a regimemore » below the critical ion beta value, the shock front undergoes a periodic self-reformation and the shock ramp scale is time-varying. At higher ion beta values, the shock front self-reformation is smeared. At still higher ion beta value, the motion of reflected ions is quite diffuse so that they can lead to a quasi-steady shock ramp. Throughout the above three conditions, the shock ramp thickness increases with β{sub i}. (3) The increase (decrease) in Mach number and the decrease (increase) in the beta value have almost equivalent impact on the state (i.e., stationary or nonstationary) of the shock ramp. Both of front and ramp thicknesses are increased with M{sub A}.« less

Upstream gyrophase bunched ions - A mechanism for creation at the bow shock and the growth of velocity space structure through gyrophase mixing

NASA Technical Reports Server (NTRS)

Gurgiolo, C.; Parks, G. K.; Mauk, G. H.

1983-01-01

The conditions necessary for the production of gyrophase bunched ions at the bow shock are developed. The conditions are applied to the reflection mechanism presented by Paschmann et al. (1980), showing that when in their model a portion of the incident parallel velocity is converted into reflected perpendicular velocity, the reflected particles are gyrophase bunched. The growth of velocity space structure in the gyrophase bunched distribution through gyrophase mixing is also explored. The structure is found to be similar to that reported in diffuse and dispersed ion events. This together with the close correlation of the observation of gyrophase bunched ions with diffuse and dispersed ions has led us to speculate that these two populations may be closely related.

Shock-wave-like structures induced by an exothermic neutralization reaction in miscible fluids

NASA Astrophysics Data System (ADS)

Bratsun, Dmitry; Mizev, Alexey; Mosheva, Elena; Kostarev, Konstantin

2017-11-01

We report shock-wave-like structures that are strikingly different from previously observed fingering instabilities, which occur in a two-layer system of miscible fluids reacting by a second-order reaction A +B →S in a vertical Hele-Shaw cell. While the traditional analysis expects the occurrence of a diffusion-controlled convection, we show both experimentally and theoretically that the exothermic neutralization reaction can also trigger a wave with a perfectly planar front and nearly discontinuous change in density across the front. This wave propagates fast compared with the characteristic diffusion times and separates the motionless fluid and the area with anomalously intense convective mixing. We explain its mechanism and introduce a new dimensionless parameter, which allows to predict the appearance of such a pattern in other systems. Moreover, we show that our governing equations, taken in the inviscid limit, are formally analogous to well-known shallow-water equations and adiabatic gas flow equations. Based on this analogy, we define the critical velocity for the onset of the shock wave which is found to be in the perfect agreement with the experiments.

Simulation of Shock-Shock Interaction in Parsec-Scale Jets

NASA Astrophysics Data System (ADS)

Fromm, Christian M.; Perucho, Manel; Ros, Eduardo; Mimica, Petar; Savolainen, Tuomas; Lobanov, Andrei P.; Zensus, J. Anton

The analysis of the radio light curves of the blazar CTA 102 during its 2006 flare revealed a possible interaction between a standing shock wave and a traveling one. In order to better understand this highly non-linear process, we used a relativistic hydrodynamic code to simulate the high energy interaction and its related emission. The calculated synchrotron emission from these simulations showed an increase in turnover flux density, Sm, and turnover frequency, νm, during the interaction and decrease to its initial values after the passage of the traveling shock wave.

On the Scaling Law for Broadband Shock Noise Intensity in Supersonic Jets

NASA Technical Reports Server (NTRS)

Kanudula, Max

2009-01-01

A theoretical model for the scaling of broadband shock noise intensity in supersonic jets was formulated on the basis of linear shock-shear wave interaction. An hypothesis has been postulated that the peak angle of incidence (closer to the critical angle) for the shear wave primarily governs the generation of sound in the interaction process rather than the noise generation contribution from off-peak incident angles. The proposed theory satisfactorily explains the well-known scaling law for the broadband shock -associated noise in supersonic jets.

Crack propagation in functionally graded strip under thermal shock

NASA Astrophysics Data System (ADS)

Ivanov, I. V.; Sadowski, T.; Pietras, D.

2013-09-01

The thermal shock problem in a strip made of functionally graded composite with an interpenetrating network micro-structure of Al2O3 and Al is analysed numerically. The material considered here could be used in brake disks or cylinder liners. In both applications it is subjected to thermal shock. The description of the position-dependent properties of the considered functionally graded material are based on experimental data. Continuous functions were constructed for the Young's modulus, thermal expansion coefficient, thermal conductivity and thermal diffusivity and implemented as user-defined material properties in user-defined subroutines of the commercial finite element software ABAQUS™. The thermal stress and the residual stress of the manufacturing process distributions inside the strip are considered. The solution of the transient heat conduction problem for thermal shock is used for crack propagation simulation using the XFEM method. The crack length developed during the thermal shock is the criterion for crack resistance of the different graduation profiles as a step towards optimization of the composition gradient with respect to thermal shock sensitivity.

Point-of-care optical tool to detect early stage of hemorrhage and shock

NASA Astrophysics Data System (ADS)

Gurjar, Rajan S.; Riccardi, Suzannah L.; Johnson, Blair D.; Johnson, Christopher P.; Paradis, Norman A.; Joyner, Michael J.; Wolf, David E.

2014-02-01

There is a critical unmet clinical need for a device that can monitor and predict the onset of shock: hemorrhagic shock or bleeding to death, septic shock or systemic infection, and cardiogenic shock or blood flow and tissue oxygenation impairment due to heart attack. Together these represent 141 M patients per year. We have developed a monitor for shock based on measuring blood flow in peripheral (skin) capillary beds using diffuse correlation spectroscopy, a form of dynamic light scattering, and have demonstrated proof-of-principle both in pigs and humans. Our results show that skin blood flow measurement, either alone or in conjunction with other hemodynamic properties such as heart rate variability, pulse pressure variability, and tissue oxygenation, can meet this unmet need in a small self-contained patch-like device in conjunction with a hand-held processing unit. In this paper we describe and discuss the experimental work and the multivariate statistical analysis performed to demonstrate proof-of-principle of the concept.

A Study of Fundamental Shock Noise Mechanisms

NASA Technical Reports Server (NTRS)

Meadows, Kristine R.

1997-01-01

This paper investigates two mechanisms fundamental to sound generation in shocked flows: shock motion and shock deformation. Shock motion is modeled numerically by examining the interaction of a sound wave with a shock. This numerical approach is validated by comparison with results obtained by linear theory for a small-disturbance case. Analysis of the perturbation energy with Myers' energy corollary demonstrates that acoustic energy is generated by the interaction of acoustic disturbances with shocks. This analysis suggests that shock motion generates acoustic and entropy disturbance energy. Shock deformation is modeled numerically by examining the interaction of a vortex ring with a shock. These numerical simulations demonstrate the generation of both an acoustic wave and contact surfaces. The acoustic wave spreads cylindrically. The sound intensity is highly directional and the sound pressure increases with increasing shock strength. The numerically determined relationship between the sound pressure and the Mach number is found to be consistent with experimental observations of shock noise. This consistency implies that a dominant physical process in the generation of shock noise is modeled in this study.

Application of cosmic-ray shock theories to the Cygnus Loop - An alternative model

NASA Technical Reports Server (NTRS)

Boulares, Ahmed; Cox, Donald P.

1988-01-01

Steady state cosmic-ray shock models are investigated here in the light of observations of the Cygnus Loop supernova remnant. The predicted downstream temperature is derived for each model. The Cygnus Loop data and the application of the models to them, including wave dissipation, are presented. Heating rate and ionization fraction structures are provided along with an estimate of the cosmic-ray diffusion coefficient. It is found that the model of Voelk, Drury, and McKenzie (1984), in which the plasma waves are generated by the streaming instability of the cosmic rays and are dissipated into the gas, can be made consistent with some observed characteristics of the Cygnus Loop shocks. The model is used to deduce upstream densities and shock velocities and, compared to the usual pure gas shock interpretation, it is found that lower densities and approximately three times higher velocities are required.

SHORT ACCELERATION TIMES FROM SUPERDIFFUSIVE SHOCK ACCELERATION IN THE HELIOSPHERE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perri, S.; Zimbardo, G., E-mail: silvia.perri@fis.unical.it

2015-12-10

The analysis of time profiles of particles accelerated at interplanetary shocks allows particle transport properties to be inferred. The frequently observed power-law decay upstream, indeed, implies a superdiffusive particle transport when the level of magnetic field variance does not change as the time interval from the shock front increases. In this context, a superdiffusive shock acceleration (SSA) theory has been developed, allowing us to make predictions of the acceleration times. In this work we estimate for a number of interplanetary shocks, including the solar wind termination shock, the acceleration times for energetic protons in the framework of SSA and wemore » compare the results with the acceleration times predicted by standard diffusive shock acceleration. The acceleration times due to SSA are found to be much shorter than in the classical model, and also shorter than the interplanetary shock lifetimes. This decrease of the acceleration times is due to the scale-free nature of the particle displacements in the framework of superdiffusion. Indeed, very long displacements are possible, increasing the probability for particles far from the front of the shock to return, and short displacements have a high probability of occurrence, increasing the chances for particles close to the front to cross the shock many times.« less

Radial Diffusion study of the 1 June 2013 CME event using MHD simulations.

NASA Astrophysics Data System (ADS)

Patel, M.; Hudson, M.; Wiltberger, M. J.; Li, Z.; Boyd, A. J.

2016-12-01

The June 1, 2013 storm was a CME-shock driven geomagnetic storm (Dst = -119 nT) that caused a dropout affecting all radiation belt electron energies measured by the Energetic Particle, Composition and Thermal Plasma Suite (ECT) instrument on Van Allen Probes at higher L-shells following dynamic pressure enhancement in the solar wind. Lower energies (up to about 700 keV) were enhanced by the storm while MeV electrons were depleted throughout the belt. We focus on depletion through radial diffusion caused by the enhanced ULF wave activity due to the CME-shock. This study utilities the Lyon-Fedder-Mobarry (LFM) model, a 3D global magnetospheric simulation code based on the ideal MHD equations, coupled with the Magnetosphere Ionosphere Coupler (MIX) and Rice Convection Model (RCM). The MHD electric and magnetic fields with equations described by Fei et al. [JGR, 2006] are used to calculate radial diffusion coefficients (DLL). These DLL values are input into a radial diffusion code to recreate the dropouts observed by the Van Allen Probes. The importance of understanding the complex role that ULF waves play in radial transport and the effects of CME-driven storms on the relativistic energy electrons in the radiation belts can be accomplished using MHD simulations to obtain diffusion coefficients, initial phase space density and the outer boundary condition from the ECT instrument suite and a radial diffusion model to reproduce observed fluxes which compare favorably with Van Allen Probes ECT measurements.

Formation of wadsleyite in a shock experiment - implications for the duration of shock events in meteorite parent bodies

NASA Astrophysics Data System (ADS)

Tschauner, O.; Asimow, P. D.; Ahrens, T. J.; Kostandova, N.; Sinogeikin, S.

2007-12-01

We report the first observation of the high-pressure silicate phase wadsleyite in the recovery products of a shock experiment. Wadsleyite was detected by micro-X ray diffraction and EBSD. Wadsleyite grew from melt which formed by chemical reaction of periclase and silica during shock. Our findings show that the growth rate of high pressure silicate phases in shock-generated melts can be of the order of m/s and is probably not diffusion controlled. Our finding has important implications for the time scale of shock events recorded by meteorites and indicates that the presence of high pressure silicates found in shocked meteorites does not necessarily imply large impactor sizes. This work was supported by the NNSA Cooperative Agreement DOE-FC88-01NV14049 and NASA/Goddard grants under awards NNG04GP57G and NNG04GI07G. Use of the HPCAT facility was supported by DOE-BES, DOE-NNSA, NSF, DOD -TACOM, and the W.M. Keck Foundation. APS is supported by DOE-BES under Contract No. W-31-109-Eng-38.

Propagation of economic shocks in input-output networks: A cross-country analysis

NASA Astrophysics Data System (ADS)

Contreras, Martha G. Alatriste; Fagiolo, Giorgio

2014-12-01

This paper investigates how economic shocks propagate and amplify through the input-output network connecting industrial sectors in developed economies. We study alternative models of diffusion on networks and we calibrate them using input-output data on real-world inter-sectoral dependencies for several European countries before the Great Depression. We show that the impact of economic shocks strongly depends on the nature of the shock and country size. Shocks that impact on final demand without changing production and the technological relationships between sectors have on average a large but very homogeneous impact on the economy. Conversely, when shocks change also the magnitudes of input-output across-sector interdependencies (and possibly sector production), the economy is subject to predominantly large but more heterogeneous avalanche sizes. In this case, we also find that (i) the more a sector is globally central in the country network, the larger its impact; (ii) the largest European countries, such as those constituting the core of the European Union's economy, typically experience the largest avalanches, signaling their intrinsic higher vulnerability to economic shocks.

Modeling magnetic field amplification in nonlinear diffusive shock acceleration

NASA Astrophysics Data System (ADS)

Vladimirov, Andrey

2009-02-01

This research was motivated by the recent observations indicating very strong magnetic fields at some supernova remnant shocks, which suggests in-situ generation of magnetic turbulence. The dissertation presents a numerical model of collisionless shocks with strong amplification of stochastic magnetic fields, self-consistently coupled to efficient shock acceleration of charged particles. Based on a Monte Carlo simulation of particle transport and acceleration in nonlinear shocks, the model describes magnetic field amplification using the state-of-the-art analytic models of instabilities in magnetized plasmas in the presence of non-thermal particle streaming. The results help one understand the complex nonlinear connections between the thermal plasma, the accelerated particles and the stochastic magnetic fields in strong collisionless shocks. Also, predictions regarding the efficiency of particle acceleration and magnetic field amplification, the impact of magnetic field amplification on the maximum energy of accelerated particles, and the compression and heating of the thermal plasma by the shocks are presented. Particle distribution functions and turbulence spectra derived with this model can be used to calculate the emission of observable nonthermal radiation.

Particle Acceleration at a Twin CME at 1 AU

NASA Astrophysics Data System (ADS)

Parker, L. N.; Li, G.

2017-12-01

We present results from both the Particle Acceleration and Transport in the Heliosphere (PATH) and Particle Acceleration at Multiple Shocks (PAMS) models for a twin CME scenario. The PATH model follows a CME using a numerical MHD module and solves the Parker transport equation at the shock yielding the accelerated particle spectrum, while PAMS solves the steady-state cosmic ray transport equation at an individual shock analytically to yield the diffusive shock acceleration (DSA) spectrum. We address the injection of an upstream particle distribution into the acceleration process for a two shock system at 1 AU. Only those particles that exceed a theoretically motivated prescribed injection energy, Einj, and up to a maximum injection energy (Emax) appropriate for quasi-parallel and quasi-perpendicular shocks (Zank et al., 2000, 2006; Dosch and Shalchi, 2010) are injected. Results from PAMS are then compared to observations at 1 AU from the Advanced Composition Explorer (ACE) spacecraft. In addition, we test the concept of electron acceleration at low injection energies for a single and multiple shock system using the same method as in Neergaard Parker and Zank, 2012 and Neergaard Parker et al., 2014.

A quantitative comparison of numerical methods for the compressible Euler equations: fifth-order WENO and piecewise-linear Godunov

NASA Astrophysics Data System (ADS)

Greenough, J. A.; Rider, W. J.

2004-05-01

A numerical study is undertaken comparing a fifth-order version of the weighted essentially non-oscillatory numerical (WENO5) method to a modern piecewise-linear, second-order, version of Godunov's (PLMDE) method for the compressible Euler equations. A series of one-dimensional test problems are examined beginning with classical linear problems and ending with complex shock interactions. The problems considered are: (1) linear advection of a Gaussian pulse in density, (2) Sod's shock tube problem, (3) the "peak" shock tube problem, (4) a version of the Shu and Osher shock entropy wave interaction and (5) the Woodward and Colella interacting shock wave problem. For each problem and method, run times, density error norms and convergence rates are reported for each method as produced from a common code test-bed. The linear problem exhibits the advertised convergence rate for both methods as well as the expected large disparity in overall error levels; WENO5 has the smaller errors and an enormous advantage in overall efficiency (in accuracy per unit CPU time). For the nonlinear problems with discontinuities, however, we generally see both first-order self-convergence of error as compared to an exact solution, or when an analytic solution is not available, a converged solution generated on an extremely fine grid. The overall comparison of error levels shows some variation from problem to problem. For Sod's shock tube, PLMDE has nearly half the error, while on the peak problem the errors are nearly the same. For the interacting blast wave problem the two methods again produce a similar level of error with a slight edge for the PLMDE. On the other hand, for the Shu-Osher problem, the errors are similar on the coarser grids, but favors WENO by a factor of nearly 1.5 on the finer grids used. In all cases holding mesh resolution constant though, PLMDE is less costly in terms of CPU time by approximately a factor of 6. If the CPU cost is taken as fixed, that is run times are equal for both numerical methods, then PLMDE uniformly produces lower errors than WENO for the fixed computation cost on the test problems considered here.

Inferring Pre-shock Acoustic Field From Post-shock Pitot Pressure Measurement

NASA Astrophysics Data System (ADS)

Wang, Jian-Xun; Zhang, Chao; Duan, Lian; Xiao, Heng; Virginia Tech Team; Missouri Univ of Sci; Tech Team

2017-11-01

Linear interaction analysis (LIA) and iterative ensemble Kalman method are used to convert post-shock Pitot pressure fluctuations to static pressure fluctuations in front of the shock. The LIA is used as the forward model for the transfer function associated with a homogeneous field of acoustic waves passing through a nominally normal shock wave. The iterative ensemble Kalman method is then employed to infer the spectrum of upstream acoustic waves based on the post-shock Pitot pressure measured at a single point. Several test cases with synthetic and real measurement data are used to demonstrate the merits of the proposed inference scheme. The study provides the basis for measuring tunnel freestream noise with intrusive probes in noisy supersonic wind tunnels.

Stall flutter experiment in a transonic oscillating linear cascade

NASA Technical Reports Server (NTRS)

Boldman, D. R.; Buggele, A. E.; Michalson, G. M.

1981-01-01

Two dimensional biconvex airfoils were oscillated at reduced frequencies up to 0.5 based on semi-chord and a free stream Mach number of 0.80 to simulate transonic stall flutter in rotors. Steady-state periodicity was confirmed through end-wall pressure measurements, exit flow traverses, and flow visualization. The initial flow visualization results from flutter tests indicated that the oscillating shock on the airfoils lagged the airfoil motion by as much as 80 deg. These initial data exhibited an appreciable amount of scatter; however, a linear fit of the results indicated that the greatest shock phase lag occurred at a positive interblade phase angle. Photographs of the steady-state and unsteady flow fields reveal some of the features of the lambda shock wave on the suction surface of the airfoils.

Direct Numerical Simulation of Acoustic Waves Interacting with a Shock Wave in a Quasi-1D Convergent-Divergent Nozzle Using an Unstructured Finite Volume Algorithm

NASA Technical Reports Server (NTRS)

Bui, Trong T.; Mankbadi, Reda R.

1995-01-01

Numerical simulation of a very small amplitude acoustic wave interacting with a shock wave in a quasi-1D convergent-divergent nozzle is performed using an unstructured finite volume algorithm with a piece-wise linear, least square reconstruction, Roe flux difference splitting, and second-order MacCormack time marching. First, the spatial accuracy of the algorithm is evaluated for steady flows with and without the normal shock by running the simulation with a sequence of successively finer meshes. Then the accuracy of the Roe flux difference splitting near the sonic transition point is examined for different reconstruction schemes. Finally, the unsteady numerical solutions with the acoustic perturbation are presented and compared with linear theory results.

Disentangling X-Ray Emission Processes in Vela-Like Pulsars

NASA Technical Reports Server (NTRS)

Gaensler, Bryan; Mushotzky, Richard (Technical Monitor)

2003-01-01

We present a deep observation with the X-Ray Multimirror Mission of PSR B1823-13, a young pulsar with similar properties to the Vela pulsar. We detect two components to the X-ray emission associated with PSR B1823-13: an elongated core of extent 30 min immediately surrounding the pulsar embedded in a fainter, diffuse component of emission 5 sec in extent, seen only on the southern side of the pulsar. The pulsar itself is not detected, either as a point source or through its pulsations. Both components of the X-ray emission are well fitted by a power-law spectrum, with photon index Gamma approx. 1.6 and X-ray luminosity (0.5-10 keV) L(sub X) approx. 9 x 10(exp 32) ergs/s for the core and Gamma approx. 2.3 and L(sub X) approx. 3 x 10(exp 33) ergs/s for the diffuse emission, for a distance of 4 kpc. We interpret both components of emission as corresponding to a pulsar wind nebula, which we designate G18.0-0.7. We argue that the core region represents the wind termination shock of this nebula, while the diffuse component indicates the shocked downstream wind. We propose that the asymmetric morphology of the diffuse emission with respect to the pulsar is the result of a reverse shock from an associated supernova remnant, which has compressed and distorted the pulsar-powered nebula. Such an interaction might be typical for pulsars at this stage in their evolution. The associated supernova remnant is not detected directly, most likely being too faint to be seen in existing X-ray and radio observations.

Comparison of femtosecond laser ablation of aluminum in water and in air by time-resolved optical diagnosis.

PubMed

Hu, Haofeng; Liu, Tiegen; Zhai, Hongchen

2015-01-26

The dynamic process of material ejection and shock wave evolution during one single femtosecond laser pulse ablation of aluminum target in water and air is experimentally investigated by employing pump-probe technique. Shadowgraphs and digital holograms with high temporal resolution are recorded, which intuitively reveal the characteristics of femtosecond laser ablation in the water-confined environment. The experimental result indicates that the liquid significantly restrict the diffusion of the ejected material, and it has a considerable effect on the attenuation of the shock wave. In addition, the expansion Mach wave generated by the ultrasonic expansion of the shock wave is observed.

Instrument to detect syncope and the onset of shock

NASA Astrophysics Data System (ADS)

McAdams, Daniel R.; Kolodziejski, Noah J.; Stapels, Christopher J.; Fernandez, Daniel E.; Podolsky, Matthew J.; Farkas, Dana; Christian, James F.; Joyner, Michael J.; Johnson, Christopher P.; Paradis, Norman A.

2016-03-01

Currently the diagnosis of hemorrhagic shock is essentially clinical, relying on the expertise of nurses and doctors. One of the first measurable physiological changes that marks the onset of hemorrhagic shock is a decrease in capillary blood flow. Diffuse correlation spectroscopy (DCS) quantifies this decrease. DCS collects and analyzes multiply scattered, coherent, near infrared light to assess relative blood flow. This work presents a preliminary study using a DCS instrument with human subjects undergoing a lower body negative pressure (LBNP) protocol. This work builds on previous successful DCS instrumentation development and we believe it represents progress toward understanding how DCS can be used in a clinical setting.

A framework to analyze cerebral mean diffusivity using surface guided diffusion mapping in diffusion tensor imaging

PubMed Central

Kwon, Oh-Hun; Park, Hyunjin; Seo, Sang-Won; Na, Duk L.; Lee, Jong-Min

2015-01-01

The mean diffusivity (MD) value has been used to describe microstructural properties in Diffusion Tensor Imaging (DTI) in cortical gray matter (GM). Recently, researchers have applied a cortical surface generated from the T1-weighted volume. When the DTI data are analyzed using the cortical surface, it is important to assign an accurate MD value from the volume space to the vertex of the cortical surface, considering the anatomical correspondence between the DTI and the T1-weighted image. Previous studies usually sampled the MD value using the nearest-neighbor (NN) method or Linear method, even though there are geometric distortions in diffusion-weighted volumes. Here we introduce a Surface Guided Diffusion Mapping (SGDM) method to compensate for such geometric distortions. We compared our SGDM method with results using NN and Linear methods by investigating differences in the sampled MD value. We also projected the tissue classification results of non-diffusion-weighted volumes to the cortical midsurface. The CSF probability values provided by the SGDM method were lower than those produced by the NN and Linear methods. The MD values provided by the NN and Linear methods were significantly greater than those of the SGDM method in regions suffering from geometric distortion. These results indicate that the NN and Linear methods assigned the MD value in the CSF region to the cortical midsurface (GM region). Our results suggest that the SGDM method is an effective way to correct such mapping errors. PMID:26236180

Nitrogen-rich heterocycles as reactivity retardants in shocked insensitive explosives.

PubMed

Manaa, M Riad; Reed, Evan J; Fried, Laurence E; Goldman, Nir

2009-04-22

We report the first quantum-based multiscale simulations to study the reactivity of shocked perfect crystals of the insensitive energetic material triaminotrinitrobenzene (TATB). Tracking chemical transformations of TATB experiencing overdriven shock speeds of 9 km/s for up to 0.43 ns and 10 km/s for up to 0.2 ns reveal high concentrations of nitrogen-rich heterocyclic clusters. Further reactivity of TATB toward the final decomposition products of fluid N(2) and solid carbon is inhibited due to the formation of these heterocycles. Our results thus suggest a new mechanism for carbon-rich explosive materials that precedes the slow diffusion-limited process of forming the bulk solid from carbon clusters and provide fundamental insight at the atomistic level into the long reaction zone of shocked TATB.

Diffuse Galactic gamma rays from shock-accelerated cosmic rays.

PubMed

Dermer, Charles D

2012-08-31

A shock-accelerated particle flux is proportional to p(-s), where p is the particle momentum, follows from simple theoretical considerations of cosmic-ray acceleration at nonrelativistic shocks followed by rigidity-dependent escape into the Galactic halo. A flux of shock-accelerated cosmic-ray protons with s≈2.8 provides an adequate fit to the Fermi Large Area Telescope γ-ray emission spectra of high-latitude and molecular cloud gas when uncertainties in nuclear production models are considered. A break in the spectrum of cosmic-ray protons claimed by Neronov, Semikoz, and Taylor [Phys. Rev. Lett. 108, 051105 (2012)] when fitting the γ-ray spectra of high-latitude molecular clouds is a consequence of using a cosmic-ray proton flux described by a power law in kinetic energy.

Effects of shock strength on shock turbulence interaction

NASA Technical Reports Server (NTRS)

Lee, Sangsan

1993-01-01

Direct numerical simulation (DNS) and linear analysis (LIA) of isotropic turbulence interacting with a shock wave are performed for several upstream shock normal Mach numbers (M(sub 1)). Turbulence kinetic energy (TKE) is amplified across the shock wave, but this amplification tends to saturate beyond M(sub 1) = 3.0. TKE amplification and Reynolds stress anisotropy obtained in DNS are consistent with LIA predictions. Rapid evolution of TKE immediate downstream of the shock wave persists for all shock strengths and is attributed to the transfer between kinetic and potential modes of turbulence energy through acoustic fluctuations. Changes in energy spectra and various length scales across the shock wave are predicted by LIA, which is consistent with DNS results. Most turbulence length scales decrease across the shock. Dissipation length scale (rho-bar q(exp 3) / epsilon), however, increases slightly for shock waves with M(sub 1) less than 1.65. Fluctuations in thermodynamic variables behind the shock wave stay nearly isentropic for M(sub 1) less than 1.2 and deviate significantly from isentropy for the stronger shock waves due to large entropy fluctuation generated through the interaction.

Compaction by impact of unconsolidated lunar fines

NASA Technical Reports Server (NTRS)

Ahrens, T. J.

1975-01-01

New Hugoniot and release adiabat data for 1.8 g/cu cm lunar fines in the approximately 2 to 70 kbar range demonstrate that upon shock compression intrinsic crystal density (approximately 3.1 g/cu cm) is achieved under shock stress of 15 to 20 kbar. Release adiabat determinations indicate that measurable irreversible compaction occurs upon achieving shock pressures above approximately 4 kbar. For shocks in the approximately 7 to 15 kbar range, the inferred post-shock specific volumes observed decrease nearly linearly with increasing peak shock pressures. Upon shocking to approximately 15 kbar the post-shock density is approximately that of the intrinsic minerals. If the present data are taken to be representative of the response to impact of unconsolidated regolith material on the moon, it is inferred that the formation of appreciable quantities of soil breccia can be associated with the impact of meteoroids or ejecta at speeds as low as approximately 1 km/sec.

Physical Conditions in Shocked Interstellar Gas Interacting with the Supernova Remnant IC 443

NASA Astrophysics Data System (ADS)

Ritchey, Adam M.; Federman, Steven Robert; Jenkins, Edward B.; Caprioli, Damiano; Wallerstein, George

2018-06-01

We present the results of a detailed investigation into the physical conditions in interstellar material interacting with the supernova remnant IC 443. Our analysis is based on an examination of high-resolution HST/STIS spectra of two stars probing predominantly neutral gas located both ahead of and behind the supernova shock front. The pre-shock neutral gas is characterized by densities and temperatures typical of diffuse interstellar clouds, while the post-shock material exhibits a range of more extreme physical conditions, including high temperatures (>104 K) in some cases, which may require a sudden heating event to explain. The ionization level is enhanced in the high-temperature post-shock material, which could be the result of enhanced radiation from shocks or from an increase in cosmic-ray ionization. The gas-phase abundances of refractory elements are also enhanced in the high-pressure gas, suggesting efficient destruction of dust grains by shock sputtering. Observations of highly-ionized species at very high velocity indicate a post-shock temperature of 107 K for the hot X-ray emitting plasma of the remnant’s interior, in agreement with studies of thermal X-ray emission from IC 443.

Shock Loading of Granular Ni/Al Composites. Part 1. Mechanics of Loading

DOE PAGES

Cherukara, Mathew J.; Germann, Timothy C.; Kober, Edward M.; ...

2014-10-16

We present molecular dynamics simulations of the thermomechanical response under shock loading of a granular material consisting of laminated Ni/Al grains. We observe two regimes: At low piston velocities (up ≲ 1km/s), the shock wave is diffuse, and the width of the shock front decreases with increasing piston velocity. Beyond a critical shock strength, however, the width remains relatively constant at approximately the mean grain radius. This change in behavior follows from an evolution of the mechanism of compaction with increasing insult strength. Furthermore, the mechanism evolves from plastic deformation-mediated pore collapse for relatively weak shocks, to solid extrusion andmore » fluid ejecta filling pores ahead of the shock front at intermediate strengths, and finally to atomic jetting into the pore for very strong shocks (up ≳ 2 km/s). High-energy fluid ejecta into pores leads to the formation of flow vorticity and can result in a large fraction of the input energy localizing into translational kinetic energy components including the formation of hot spots. This has implications for the mechanical mixing of Ni and Al in these reactive composites.« less

EVOLUTION OF HIGH-ENERGY PARTICLE DISTRIBUTION IN MATURE SHELL-TYPE SUPERNOVA REMNANTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zeng, Houdun; Xin, Yuliang; Liu, Siming

Multi-wavelength observations of mature supernova remnants (SNRs), especially with recent advances in γ -ray astronomy, make it possible to constrain energy distribution of energetic particles within these remnants. In consideration of the SNR origin of Galactic cosmic rays and physics related to particle acceleration and radiative processes, we use a simple one-zone model to fit the nonthermal emission spectra of three shell-type SNRs located within 2° on the sky: RX J1713.7−3946, CTB 37B, and CTB 37A. Although radio images of these three sources all show a shell (or half-shell) structure, their radio, X-ray, and γ -ray spectra are quite different,more » offering an ideal case to explore evolution of energetic particle distribution in SNRs. Our spectral fitting shows that (1) the particle distribution becomes harder with aging of these SNRs, implying a continuous acceleration process, and the particle distributions of CTB 37A and CTB 37B in the GeV range are harder than the hardest distribution that can be produced at a shock via the linear diffusive shock particle acceleration process, so spatial transport may play a role; (2) the energy loss timescale of electrons at the high-energy cutoff due to synchrotron radiation appears to be always a bit (within a factor of a few) shorter than the age of the corresponding remnant, which also requires continuous particle acceleration; (3) double power-law distributions are needed to fit the spectra of CTB 37B and CTB 37A, which may be attributed to shock interaction with molecular clouds.« less

Quasi 1D Modeling of Mixed Compression Supersonic Inlets

NASA Technical Reports Server (NTRS)

Kopasakis, George; Connolly, Joseph W.; Paxson, Daniel E.; Woolwine, Kyle J.

2012-01-01

The AeroServoElasticity task under the NASA Supersonics Project is developing dynamic models of the propulsion system and the vehicle in order to conduct research for integrated vehicle dynamic performance. As part of this effort, a nonlinear quasi 1-dimensional model of the 2-dimensional bifurcated mixed compression supersonic inlet is being developed. The model utilizes computational fluid dynamics for both the supersonic and subsonic diffusers. The oblique shocks are modeled utilizing compressible flow equations. This model also implements variable geometry required to control the normal shock position. The model is flexible and can also be utilized to simulate other mixed compression supersonic inlet designs. The model was validated both in time and in the frequency domain against the legacy LArge Perturbation INlet code, which has been previously verified using test data. This legacy code written in FORTRAN is quite extensive and complex in terms of the amount of software and number of subroutines. Further, the legacy code is not suitable for closed loop feedback controls design, and the simulation environment is not amenable to systems integration. Therefore, a solution is to develop an innovative, more simplified, mixed compression inlet model with the same steady state and dynamic performance as the legacy code that also can be used for controls design. The new nonlinear dynamic model is implemented in MATLAB Simulink. This environment allows easier development of linear models for controls design for shock positioning. The new model is also well suited for integration with a propulsion system model to study inlet/propulsion system performance, and integration with an aero-servo-elastic system model to study integrated vehicle ride quality, vehicle stability, and efficiency.

Fourth order Douglas implicit scheme for solving three dimension reaction diffusion equation with non-linear source term

NASA Astrophysics Data System (ADS)

Hasnain, Shahid; Saqib, Muhammad; Mashat, Daoud Suleiman

2017-07-01

This research paper represents a numerical approximation to non-linear three dimension reaction diffusion equation with non-linear source term from population genetics. Since various initial and boundary value problems exist in three dimension reaction diffusion phenomena, which are studied numerically by different numerical methods, here we use finite difference schemes (Alternating Direction Implicit and Fourth Order Douglas Implicit) to approximate the solution. Accuracy is studied in term of L2, L∞ and relative error norms by random selected grids along time levels for comparison with analytical results. The test example demonstrates the accuracy, efficiency and versatility of the proposed schemes. Numerical results showed that Fourth Order Douglas Implicit scheme is very efficient and reliable for solving 3-D non-linear reaction diffusion equation.

Characterization of a signal recording system for accurate velocity estimation using a VISAR

NASA Astrophysics Data System (ADS)

Rav, Amit; Joshi, K. D.; Singh, Kulbhushan; Kaushik, T. C.

2018-02-01

The linearity of a signal recording system (SRS) in time as well as in amplitude are important for the accurate estimation of the free surface velocity history of a moving target during shock loading and unloading when measured using optical interferometers such as a velocity interferometer system for any reflector (VISAR). Signal recording being the first step in a long sequence of signal processes, the incorporation of errors due to nonlinearity, and low signal-to-noise ratio (SNR) affects the overall accuracy and precision of the estimation of velocity history. In shock experiments the small duration (a few µs) of loading/unloading, the reflectivity of moving target surface, and the properties of optical components, control the amount of input of light to the SRS of a VISAR and this in turn affects the linearity and SNR of the overall measurement. These factors make it essential to develop in situ procedures for (i) minimizing the effect of signal induced noise and (ii) determine the linear region of operation for the SRS. Here we report on a procedure for the optimization of SRS parameters such as photodetector gain, optical power, aperture etc, so as to achieve a linear region of operation with a high SNR. The linear region of operation so determined has been utilized successfully to estimate the temporal history of the free surface velocity of the moving target in shock experiments.

Performance of a low-pressure-ratio centrifugal compressor with four diffuser designs

NASA Technical Reports Server (NTRS)

Klassen, H. A.

1973-01-01

A low-pressure-ratio centrifugal compressor was tested with four different diffuser configurations. One diffuser had airfoil vanes. Two were pipe diffusers. One pipe diffuser had 7.5 deg cone diffusing passages. The other had trumpet-shaped passages designed for linear static-pressure rise from throat to exit. The fourth configuration had flat vanes with elliptical leading edges similar to those of pipe diffusers. The side walls were contoured to produce a linear pressure rise. Peak compressor efficiencies were 0.82 with the airfoil vane and conical pipe diffusers, 0.80 with the trumpet, and 0.74 with the flat-vane design. Surge margin and useful range were greater for the airfoil-vane diffuser than for the other three.

Quantitative understanding of Forbush decrease drivers based on shock-only and CME-only models using global signature of February 14, 1978 event

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raghav, Anil; Lotekar, Ajay; Bhaskar, Ankush

We have studied the Forbush decrease (FD) event that occurred on February 14, 1978 using 43 neutron monitor observatories to understand the global signature of FD. We have studied rigidity dependence of shock amplitude and total FD amplitude. We have found almost the same power law index for both shock phase amplitude and total FD amplitude. Local time variation of shock phase amplitude and maximum depression time of FD have been investigated which indicate possible effect of shock/CME orientation. We have analyzed rigidity dependence of time constants of two phase recovery. Time constants of slow component of recovery phase showmore » rigidity dependence and imply possible effect of diffusion. Solar wind speed was observed to be well correlated with slow component of FD recovery phase. This indicates solar wind speed as possible driver of recovery phase. To investigate the contribution of interplanetary drivers, shock and CME in FD, we have used shock-only and CME-only models. We have applied these models separately to shock phase and main phase amplitudes respectively. This confirms presently accepted physical scenario that the first step of FD is due to propagating shock barrier and second step is due to flux rope of CME/magnetic cloud.« less

Molecular Diagnostics of Diffusive Boundary Layers

NASA Astrophysics Data System (ADS)

Rawlings, J. M. C.; Hartquist, T. W.

1995-11-01

We have assessed the role of diffusion in determining chemical abundances in molecular interface regions. Chemical models have been developed which include the appropriate diffusion terms and that are appropriate to a narrow diffusion region (˜0.01pc) that may exist at the interface between a dark core and a hot, shocked T-Tauri wind. We have assumed pressure balance throughout and have calculated the chemical abundances as functions of time and position through the interface. The results show that significant enhancements of detectable molecules/transitions are expected (e.g. CO J=6→5, OH and CH). Using a realistic value of the diffusion coefficient a diffusive region of dimension 0.01pc may be established within about 104 years. In general it seems likely that diffusion processes are highly significant on these and smaller lengthscales.

Investigation of Shock Diffusers at Mach Number 1.85. 2 - Projecting Double-Shock Cones

DTIC Science & Technology

1947-06-17

pitot - static rake located as shown in figure 1(a). Total-pressure recoveries were measured for a series of tip projections varied in minimum steps...is shown. The position of the pitot -static rake with which these distributions were .measured is shown in figure 1(a). The data points correspond...Schroeder SUMMARY An Investigation has "been undertaken in the Cleveland 18- by 18-Inch, supersonic tunnel to determine the total-pressure

Toxic shock syndrome in two dogs.

PubMed

Slovak, Jennifer E; Parker, Valerie J; Deitz, Krysta L

2012-01-01

Two young, unrelated, spayed female Labrador retrievers were evaluated for severe, diffuse, generalized erythema and edema of the skin. Both dogs exhibited signs of disseminated intravascular coagulopathy and were euthanized. On postmortem examination, toxic shock syndrome (TSS) was diagnosed based on histopathology and supported by skin cultures. TSS is a rarely reported disease in veterinary medicine and can cause acute and profound clinical signs. Rapid recognition of this disease process and immediate treatment may improve the clinical outcome.

Analysis of the dynamic response of a supersonic inlet to flow-field perturbations upstream of the normal shock

NASA Technical Reports Server (NTRS)

Cole, G. L.; Willoh, R. G.

1975-01-01

A linearized mathematical analysis is presented for determining the response of normal shock position and subsonic duct pressures to flow-field perturbations upstream of the normal shock in mixed-compression supersonic inlets. The inlet duct cross-sectional area variation is approximated by constant-area sections; this approximation results in one-dimensional wave equations. A movable normal shock separates the supersonic and subsonic flow regions, and a choked exit is assumed for the inlet exit condition. The analysis leads to a closed-form matrix solution for the shock position and pressure transfer functions. Analytical frequency response results are compared with experimental data and a method of characteristics solution.

On Large Time Behavior and Selection Principle for a Diffusive Carr-Penrose Model

NASA Astrophysics Data System (ADS)

Conlon, Joseph G.; Dabkowski, Michael; Wu, Jingchen

2016-04-01

This paper is concerned with the study of a diffusive perturbation of the linear LSW model introduced by Carr and Penrose. A main subject of interest is to understand how the presence of diffusion acts as a selection principle, which singles out a particular self-similar solution of the linear LSW model as determining the large time behavior of the diffusive model. A selection principle is rigorously proven for a model which is a semiclassical approximation to the diffusive model. Upper bounds on the rate of coarsening are also obtained for the full diffusive model.

Diffraction of a Shock Wave on a Wedge in a Dusty Gas

NASA Astrophysics Data System (ADS)

Surov, V. S.

2017-09-01

Within the framework of one- and multivelocity dusty-gas models, the author has investigated, on a curvilinear grid, flow in reflection of a shock wave from the wedge-shaped surface in an air-droplet mixture using the Godunov method with a linearized Riemannian solver.

Application of quadratic optimization to supersonic inlet control

NASA Technical Reports Server (NTRS)

Lehtinen, B.; Zeller, J. R.

1971-01-01

The application of linear stochastic optimal control theory to the design of the control system for the air intake (inlet) of a supersonic air-breathing propulsion system is discussed. The controls must maintain a stable inlet shock position in the presence of random airflow disturbances and prevent inlet unstart. Two different linear time invariant control systems are developed. One is designed to minimize a nonquadratic index, the expected frequency of inlet unstart, and the other is designed to minimize the mean square value of inlet shock motion. The quadratic equivalence principle is used to obtain the best linear controller that minimizes the nonquadratic performance index. The two systems are compared on the basis of unstart prevention, control effort requirements, and sensitivity to parameter variations.

Existence and Stability of Viscoelastic Shock Profiles

NASA Astrophysics Data System (ADS)

Barker, Blake; Lewicka, Marta; Zumbrun, Kevin

2011-05-01

We investigate existence and stability of viscoelastic shock profiles for a class of planar models including the incompressible shear case studied by Antman and Malek-Madani. We establish that the resulting equations fall into the class of symmetrizable hyperbolic-parabolic systems, hence spectral stability implies linearized and nonlinear stability with sharp rates of decay. The new contributions are treatment of the compressible case, formulation of a rigorous nonlinear stability theory, including verification of stability of small-amplitude Lax shocks, and the systematic incorporation in our investigations of numerical Evans function computations determining stability of large-amplitude and nonclassical type shock profiles.

Distribution in energies and acceleration times in DSA, and their effect on the cut-off

NASA Astrophysics Data System (ADS)

Brooks, A.; Protheroe, R. J.

2001-08-01

We have conducted Monte Carlo simulations of diffusive shock acceleration (DSA) to determine the distribution of times since injection taken to reach energy E > E0. This distribution of acceleration times for the case of momentum dependent diffusion is compared with that given by Drury and Forman (1983) based on extrapolation of the exact result (Toptygin 1980) for the case of the diffusion coefficient being independent of momentum. As a result of this distribution we find, as suggested by Drury et al. (1999), that Monte Carlo simulations result in smoother cut-offs and pile-ups in spectra of accelerated particles than expected from simple "box model" treatments of shock acceleration (e.g., Protheroe and Stanev 1999, Drury et al. 1999). This is particularly so for the case synchrotron pile-ups, which we find are replaced by a small bump at an energy about a factor of 2 below the expected cut-off, followed by a smooth cut-off with particles extending to energies well beyond the expected cut-off energy.

Modified chloride diffusion model for concrete under the coupling effect of mechanical load and chloride salt environment

NASA Astrophysics Data System (ADS)

Lei, Mingfeng; Lin, Dayong; Liu, Jianwen; Shi, Chenghua; Ma, Jianjun; Yang, Weichao; Yu, Xiaoniu

2018-03-01

For the purpose of investigating lining concrete durability, this study derives a modified chloride diffusion model for concrete based on the odd continuation of boundary conditions and Fourier transform. In order to achieve this, the linear stress distribution on a sectional structure is considered, detailed procedures and methods are presented for model verification and parametric analysis. Simulation results show that the chloride diffusion model can reflect the effects of linear stress distribution of the sectional structure on the chloride diffusivity with reliable accuracy. Along with the natural environmental characteristics of practical engineering structures, reference value ranges of model parameters are provided. Furthermore, a chloride diffusion model is extended for the consideration of multi-factor coupling of linear stress distribution, chloride concentration and diffusion time. Comparison between model simulation and typical current research results shows that the presented model can produce better considerations with a greater universality.

Observation of dust acoustic shock wave in a strongly coupled dusty plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Sumita K., E-mail: sumita-sharma82@yahoo.com; Boruah, A.; Nakamura, Y.

2016-05-15

Dust acoustic shock wave is observed in a strongly coupled laboratory dusty plasma. A supersonic flow of charged microparticles is allowed to perturb a stationary dust fluid to excite dust acoustic shock wave. The evolution process beginning with steepening of initial wave front and then formation of a stable shock structure is similar to the numerical results of the Korteweg-de Vries-Burgers equation. The measured Mach number of the observed shock wave agrees with the theoretical results. Reduction of shock amplitude at large distances is also observed due to the dust neutral collision and viscosity effects. The dispersion relation and themore » spatial damping of a linear dust acoustic wave are also measured and compared with the relevant theory.« less

Concepts for radically increasing the numerical convergence rate of the Euler equations

NASA Technical Reports Server (NTRS)

Nixon, David; Tzuoo, Keh-Lih; Caruso, Steven C.; Farshchi, Mohammad; Klopfer, Goetz H.; Ayoub, Alfred

1987-01-01

Integral equation and finite difference methods have been developed for solving transonic flow problems using linearized forms of the transonic small disturbance and Euler equations. A key element is the use of a strained coordinate system in which the shock remains fixed. Additional criteria are developed to determine the free parameters in the coordinate straining; these free parameters are functions of the shock location. An integral equation analysis showed that the shock is located by ensuring that no expansion shocks exist in the solution. The expansion shock appears as oscillations in the solution near the sonic line, and the correct shock location is determined by removing these oscillations. A second objective was to study the ability of the Euler equation to model separated flow.

The Fisher-KPP problem with doubly nonlinear diffusion

NASA Astrophysics Data System (ADS)

Audrito, Alessandro; Vázquez, Juan Luis

2017-12-01

The famous Fisher-KPP reaction-diffusion model combines linear diffusion with the typical KPP reaction term, and appears in a number of relevant applications in biology and chemistry. It is remarkable as a mathematical model since it possesses a family of travelling waves that describe the asymptotic behaviour of a large class solutions 0 ≤ u (x , t) ≤ 1 of the problem posed in the real line. The existence of propagation waves with finite speed has been confirmed in some related models and disproved in others. We investigate here the corresponding theory when the linear diffusion is replaced by the "slow" doubly nonlinear diffusion and we find travelling waves that represent the wave propagation of more general solutions even when we extend the study to several space dimensions. A similar study is performed in the critical case that we call "pseudo-linear", i.e., when the operator is still nonlinear but has homogeneity one. With respect to the classical model and the "pseudo-linear" case, the "slow" travelling waves exhibit free boundaries.

The Strongest 40 keV Electron Acceleration By ICME-driven Shocks At 1 AU

NASA Astrophysics Data System (ADS)

Yang, L.; Wang, L.; Li, G.; Wimmer-Schweingruber, R. F.; He, J.; Tu, C. Y.; Bale, S. D.

2017-12-01

Here we present a comprehensive case study of the in situ electron acceleration at the two ICME-driven shocks observed by WIND/3DP on February 11, 2000 and July 22, 2004. For the 11 February 2000 shock (the 22 July 2004 shock), the shocked electrons in the downstream show significant flux enhancements over the ambient solar wind electrons at energies up to 40 keV (66 keV) with a 6.0 times (1.9 times) ehancment at 40 keV, the strongest among all the quasi-perpendicular (quasi-parallel) ICME-driven shocks observed by the WIND spacecraft at 1 AU from 1995 through 2014. We find that in both shocks, the shocked electron fluxes at 0.5-40 keV fit well to a double power-law spectrum, J ˜ E-β, bending up at ˜2 keV. In the downstream, these shocked electrons show stronger fluxes in the anti-sunward direction, but their enhancement over the ambient fluxes peaks near 90° pitch angle (PA). For the 11 February 2000 shock, the electron spectral index, β, appears to not vary with the electron PA, while for the 22 July 2004 shock, β roughly decreases from the anti-sunward PA direction to the sunward PA direction. All of these spectral indexes are strongly larger than the theoretical prediction of diffusive shock acceleration. At energies above (below) 2 keV, however, the shocked electron β is similar to the solar wind superhalo (halo) electrons observed at quiet times. These results suggest that the electron acceleration at the ICME-driven shocks at 1 AU may favor the shock drift acceleration, and the superthermal electrons accelerated by the interplanetary shocks may contribute to the formation of the halo and superhalo electron populations in the solar wind.

Quantitative model of diffuse speckle contrast analysis for flow measurement.

PubMed

Liu, Jialin; Zhang, Hongchao; Lu, Jian; Ni, Xiaowu; Shen, Zhonghua

2017-07-01

Diffuse speckle contrast analysis (DSCA) is a noninvasive optical technique capable of monitoring deep tissue blood flow. However, a detailed study of the speckle contrast model for DSCA has yet to be presented. We deduced the theoretical relationship between speckle contrast and exposure time and further simplified it to a linear approximation model. The feasibility of this linear model was validated by the liquid phantoms which demonstrated that the slope of this linear approximation was able to rapidly determine the Brownian diffusion coefficient of the turbid media at multiple distances using multiexposure speckle imaging. Furthermore, we have theoretically quantified the influence of optical property on the measurements of the Brownian diffusion coefficient which was a consequence of the fact that the slope of this linear approximation was demonstrated to be equal to the inverse of correlation time of the speckle.

S{sub 2}SA preconditioning for the S{sub n} equations with strictly non negative spatial discretization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bruss, D. E.; Morel, J. E.; Ragusa, J. C.

2013-07-01

Preconditioners based upon sweeps and diffusion-synthetic acceleration have been constructed and applied to the zeroth and first spatial moments of the 1-D S{sub n} transport equation using a strictly non negative nonlinear spatial closure. Linear and nonlinear preconditioners have been analyzed. The effectiveness of various combinations of these preconditioners are compared. In one dimension, nonlinear sweep preconditioning is shown to be superior to linear sweep preconditioning, and DSA preconditioning using nonlinear sweeps in conjunction with a linear diffusion equation is found to be essentially equivalent to nonlinear sweeps in conjunction with a nonlinear diffusion equation. The ability to use amore » linear diffusion equation has important implications for preconditioning the S{sub n} equations with a strictly non negative spatial discretization in multiple dimensions. (authors)« less

Numerical and experimental investigation of VG flow control for a low-boom inlet

NASA Astrophysics Data System (ADS)

Rybalko, Michael

The application of vortex generators (VGs) for shock/boundary layer interaction flow control in a novel external compression, axisymmetric, low-boom concept inlet was studied using numerical and experimental methods. The low-boom inlet design features a zero-angle cowl and relaxed isentropic compression centerbody spike, resulting in defocused oblique shocks and a weak terminating normal shock. This allows reduced external gas dynamic waves at high mass flow rates but suffers from flow separation near the throat and a large hub-side boundary layer at the Aerodynamic Interface Plane (AIP), which marks the inflow to the jet engine turbo-machinery. Supersonic VGs were investigated to reduce the shock-induced flow separation near the throat while subsonic VGs were investigated to reduce boundary layer radial distortion at the AIP. To guide large-scale inlet experiments, Reynolds-Averaged Navier-Stokes (RANS) simulations using three-dimensional, structured, chimera (overset) grids and the WIND-US code were conducted. Flow control cases included conventional and novel types of vortex generators at positions both upstream of the terminating normal shock (supersonic VGs) and downstream (subsonic VGs). The performance parameters included incompressible axisymmetric shape factor, post-shock separation area, inlet pressure recovery, and mass flow ratio. The design of experiments (DOE) methodology was used to select device size and location, analyze the resulting data, and determine the optimal choice of device geometry. Based on the above studies, a test matrix of supersonic and subsonic VGs was adapted for a large-scale inlet test to be conducted at the 8'x6' supersonic wind tunnel at NASA Glenn Research Center (GRC). Comparisons of RANS simulations with data from the Fall 2010 8'x6' inlet test showed that predicted VG performance trends and case rankings for both supersonic and subsonic devices were consistent with experimental results. For example, experimental surface oil flow visualization revealed a significant post-shock separation bubble with flow recirculation for the baseline (no VG) case that was substantially broken up in the micro-ramp VG case, consistent with simulations. Furthermore, the predicted subsonic VG performance with respect to a reduction in radial distortion (quantified in terms of axisymmetric incompressible shape factor) was found to be consistent with boundary layer rake measurements. To investigate the unsteady turbulent flow features associated with the shock-induced flow separation and the hub-side boundary layer, a detached eddy simulation (DES) approach using the WIND-US code was employed to model the baseline inlet flow field. This approach yielded improved agreement with experimental data for time-averaged diffuser stagnation pressure profiles and allowed insight into the pressure fluctuations and turbulent kinetic energy distributions which may be present at the AIP. In addition, streamwise shock position statistics were obtained and compared with experimental Schlieren results. The predicted shock oscillations were much weaker than those seen experimentally (by a factor of four), which indicates that the mechanism for the experimental shock oscillations was not captured. In addition, the novel supersonic vortex generator geometries were investigated experimentally (prior to the large-scale inlet 8'x6' wind tunnel tests) in an inlet-relevant flow field containing a Mach 1.4 normal shock wave followed by a subsonic diffuser. A parametric study of device height and distance upstream of the normal shock was undertaken for split-ramp and ramped-vane geometries. Flow field diagnostics included high-speed Schlieren, oil flow visualization, and Pitot-static pressure measurements. Parameters including flow separation, pressure recovery, centerline incompressible boundary layer shape factor, and shock stability were analyzed and compared to the baseline uncontrolled case. While all vortex generators tested eliminated centerline flow separation, the presence of VGs also increased the significant three-dimensionality of the flow via increased side-wall interaction. The stronger streamwise vorticity generated by ramped-vanes also yielded improved pressure recovery and fuller boundary layer velocity profiles within the subsonic diffuser. (Abstract shortened by UMI.)

A network model of successive partitioning-limited solute diffusion through the stratum corneum.

PubMed

Schumm, Phillip; Scoglio, Caterina M; van der Merwe, Deon

2010-02-07

As the most exposed point of contact with the external environment, the skin is an important barrier to many chemical exposures, including medications, potentially toxic chemicals and cosmetics. Traditional dermal absorption models treat the stratum corneum lipids as a homogenous medium through which solutes diffuse according to Fick's first law of diffusion. This approach does not explain non-linear absorption and irregular distribution patterns within the stratum corneum lipids as observed in experimental data. A network model, based on successive partitioning-limited solute diffusion through the stratum corneum, where the lipid structure is represented by a large, sparse, and regular network where nodes have variable characteristics, offers an alternative, efficient, and flexible approach to dermal absorption modeling that simulates non-linear absorption data patterns. Four model versions are presented: two linear models, which have unlimited node capacities, and two non-linear models, which have limited node capacities. The non-linear model outputs produce absorption to dose relationships that can be best characterized quantitatively by using power equations, similar to the equations used to describe non-linear experimental data.

Highly linear, sensitive analog-to-digital converter

NASA Technical Reports Server (NTRS)

Cox, J.; Finley, W. R.

1969-01-01

Analog-to-digital converter converts 10 volt full scale input signal into 13 bit digital output. Advantages include high sensitivity, linearity, low quantitizing error, high resistance to mechanical shock and vibration loads, and temporary data storage capabilities.

Shock Dynamics for particle-laden thin film

NASA Astrophysics Data System (ADS)

Wang, Li; Bertozzi, Andrea

2013-11-01

We study the shock dynamics for a recently proposed system of conservation laws (Murisic et al. [J. Fluid Mech. 2013]) describing gravity-driven thin film flow of a suspension of particles down an incline. When the particle concentration is above a critical value, singular shock solutions can occur. We analyze the Hugoniot topology associated with the Riemann problem for this system, describing in detail how the transition from a double shock to a singular shock happen. We also derive the singular shock speed based on a key observation that the particles pilling up at the maximum packing fraction near the contact line. These results are further applied to constant volume case to generate a rarefaction-singular shock solution. The particle/fluid front are shown to move linearly to the leading order with time to the one-third power as predicted by the Huppert solution for clear fluid.

Molecular origins of anisotropic shock propagation in crystalline and amorphous polyethylene

NASA Astrophysics Data System (ADS)

O'Connor, Thomas C.; Elder, Robert M.; Sliozberg, Yelena R.; Sirk, Timothy W.; Andzelm, Jan W.; Robbins, Mark O.

2018-03-01

Molecular dynamics simulations are used to analyze shock propagation in amorphous and crystalline polyethylene. Results for the shock velocity Us are compared to predictions from Pastine's equation of state and hydrostatic theory. The results agree with Pastine at high impact velocities. At low velocities the yield stress becomes important, increasing the shock velocity and leading to anisotropy in the crystalline response. Detailed analysis of changes in atomic order reveals the origin of the anisotropic response. For shock along the polymer backbone, an elastic front is followed by a plastic front where chains buckle with a characteristic wavelength. Shock perpendicular to the chain backbone can produce plastic deformation or transitions to different orthorhombic or monoclinic structures, depending on the impact speed and direction. Tensile loading does not produce stable shocks: Amorphous systems craze and fracture while for crystals the front broadens linearly with time.

Stability and modal analysis of shock/boundary layer interactions

NASA Astrophysics Data System (ADS)

Nichols, Joseph W.; Larsson, Johan; Bernardini, Matteo; Pirozzoli, Sergio

2017-02-01

The dynamics of oblique shock wave/turbulent boundary layer interactions is analyzed by mining a large-eddy simulation (LES) database for various strengths of the incoming shock. The flow dynamics is first analyzed by means of dynamic mode decomposition (DMD), which highlights the simultaneous occurrence of two types of flow modes, namely a low-frequency type associated with breathing motion of the separation bubble, accompanied by flapping motion of the reflected shock, and a high-frequency type associated with the propagation of instability waves past the interaction zone. Global linear stability analysis performed on the mean LES flow fields yields a single unstable zero-frequency mode, plus a variety of marginally stable low-frequency modes whose stability margin decreases with the strength of the interaction. The least stable linear modes are grouped into two classes, one of which bears striking resemblance to the breathing mode recovered from DMD and another class associated with revolving motion within the separation bubble. The results of the modal and linear stability analysis support the notion that low-frequency dynamics is intrinsic to the interaction zone, but some continuous forcing from the upstream boundary layer may be required to keep the system near a limit cycle. This can be modeled as a weakly damped oscillator with forcing, as in the early empirical model by Plotkin (AIAA J 13:1036-1040, 1975).

Essays in the Application of Linear and Non-linear Bayesian VAR Models to the Macroeconomic Impacts of Energy Price Shocks

NASA Astrophysics Data System (ADS)

Nguyen, Bao H.

This thesis is a collection of five self contained empirical macroeconomic papers on the asymmetric effects of energy price shocks on various economies. Chapter 1 formally determines the number of regime changes in the US natural gas market by employing a MS-VAR model. Estimated using Bayesian methods, three regimes are identified for the period 1980 - 2016, namely, before the Decontrol Act, after the Decontrol Act and the Recession. The results show that the natural gas market tends to be much more sensitive to market fundamental shocks occurring in a Recession regime than in the other regimes. Augmenting the model by incorporating the price of crude oil, the results reveal that the impacts of oil price shocks on natural gas prices are relatively small. Chapter 2 provides new empirical evidence on the asymmetric reactions of the U.S. natural gas market and the U.S. economy to its market fundamental shocks in different phases of the business cycle. To this end, we employ a ST-VAR model to capture the asymmetric responses depending on economic conditions. Our results indicate that in contrast to the prediction made by a linear VAR model, the STVAR model provides a plausible explanation to the behavior of the U.S. natural gas market, which asymmetrically reacts in bad times and good times. Chapter 3 examines the relationship between China's economic growth and global oil market fluctuations between 1992Q1 and 2015Q3. We find that: (1) the time varying parameter VAR with stochastic volatility provides a better fit as compared to it's constant counterparts; (2) the impacts of intertemporal global oil price shocks on China's output are often small and temporary in nature; (3) oil supply and specific oil demand shocks generally produce negative movements in China's GDP growth whilst oil demand shocks tend to have positive effects; (4) domestic output shocks have no significant impact on price or quantity movements within the global oil market. Chapter 4 examines the effects of world energy price shocks on China's macroeconomy. We propose a new index of primary commodity energy prices which accurately reflects both the structure of China's energy expenditure shares, as well as intertemporal fluctuations in international energy prices. The index is then in employed a sufficiently rich set of time varying BVARs, identified by a new set of agnostic sign restrictions. Uniformly sized positive energy price shocks are shown to consistently generate economic stagflation over the past two decades. Chapter 5 compares the macroeconomic effects of global oil and iron ore price shocks on the Australian economy. The main results suggest that, over the period 1990Q1 to 2014Q4, the oil shock has a relative larger impact than that of the iron ore shock on output and inflation while the iron ore shock is the dominant source of interest and exchange rate movements. The effects crucially depend on the underlying sources of oil or iron ore price shifts.

Digital-computer normal shock position and restart control of a Mach 2.5 axisymmetric mixed-compression inlet

NASA Technical Reports Server (NTRS)

Neiner, G. H.; Cole, G. L.; Arpasi, D. J.

1972-01-01

Digital computer control of a mixed-compression inlet is discussed. The inlet was terminated with a choked orifice at the compressor face station to dynamically simulate a turbojet engine. Inlet diffuser exit airflow disturbances were used. A digital version of a previously tested analog control system was used for both normal shock and restart control. Digital computer algorithms were derived using z-transform and finite difference methods. Using a sample rate of 1000 samples per second, the digital normal shock and restart controls essentially duplicated the inlet analog computer control results. At a sample rate of 100 samples per second, the control system performed adequately but was less stable.

Lack of anomalous diffusion in linear translationally-invariant systems determined by only one initial condition

NASA Astrophysics Data System (ADS)

Khorrami, Mohammad; Shariati, Ahmad; Aghamohammadi, Amir; Fatollahi, Amir H.

2012-01-01

It is shown that as far as the linear diffusion equation meets both time- and space-translational invariance, the time dependence of a moment of degree α is a polynomial of degree at most equal to α, while all connected moments are at most linear functions of time. As a special case, the variance is an at most linear function of time.

Electron acceleration by wave turbulence in a magnetized plasma

NASA Astrophysics Data System (ADS)

Rigby, A.; Cruz, F.; Albertazzi, B.; Bamford, R.; Bell, A. R.; Cross, J. E.; Fraschetti, F.; Graham, P.; Hara, Y.; Kozlowski, P. M.; Kuramitsu, Y.; Lamb, D. Q.; Lebedev, S.; Marques, J. R.; Miniati, F.; Morita, T.; Oliver, M.; Reville, B.; Sakawa, Y.; Sarkar, S.; Spindloe, C.; Trines, R.; Tzeferacos, P.; Silva, L. O.; Bingham, R.; Koenig, M.; Gregori, G.

2018-05-01

Astrophysical shocks are commonly revealed by the non-thermal emission of energetic electrons accelerated in situ1-3. Strong shocks are expected to accelerate particles to very high energies4-6; however, they require a source of particles with velocities fast enough to permit multiple shock crossings. While the resulting diffusive shock acceleration4 process can account for observations, the kinetic physics regulating the continuous injection of non-thermal particles is not well understood. Indeed, this injection problem is particularly acute for electrons, which rely on high-frequency plasma fluctuations to raise them above the thermal pool7,8. Here we show, using laboratory laser-produced shock experiments, that, in the presence of a strong magnetic field, significant electron pre-heating is achieved. We demonstrate that the key mechanism in producing these energetic electrons is through the generation of lower-hybrid turbulence via shock-reflected ions. Our experimental results are analogous to many astrophysical systems, including the interaction of a comet with the solar wind9, a setting where electron acceleration via lower-hybrid waves is possible.

Supernova shock breakout through a wind

NASA Astrophysics Data System (ADS)

Balberg, Shmuel; Loeb, Abraham

2011-06-01

The breakout of a supernova shock wave through the progenitor star's outer envelope is expected to appear as an X-ray flash. However, if the supernova explodes inside an optically thick wind, the breakout flash is delayed. We present a simple model for estimating the conditions at shock breakout in a wind based on the general observable quantities in the X-ray flash light curve; the total energy EX, and the diffusion time after the peak, tdiff. We base the derivation on the self-similar solution for the forward-reverse shock structure expected for an ejecta plowing through a pre-existing wind at large distances from the progenitor's surface. We find simple quantitative relations for the shock radius and velocity at breakout. By relating the ejecta density profile to the pre-explosion structure of the progenitor, the model can also be extended to constrain the combination of explosion energy and ejecta mass. For the observed case of XRO08109/SN2008D, our model provides reasonable constraints on the breakout radius, explosion energy and ejecta mass, and predicts a high shock velocity which naturally accounts for the observed non-thermal spectrum.

Numerical Study of Richtmyer-Meshkov Instability with Re-Shock

NASA Astrophysics Data System (ADS)

Wong, Man Long; Livescu, Daniel; Lele, Sanjiva

2017-11-01

The interaction of a Mach 1.45 shock wave with a perturbed planar interface between two gases with an Atwood number 0.68 is studied through 2D and 3D shock-capturing adaptive mesh refinement (AMR) simulations with physical diffusive and viscous terms. The simulations have initial conditions similar to those in the actual experiment conducted by Poggi et al. [1998]. The development of the flow and evolution of mixing due to the interactions with the first shock and the re-shock are studied together with the sensitivity of various global parameters to the properties of the initial perturbation. Grid resolutions needed for fully resolved and 2D and 3D simulations are also evaluated. Simulations are conducted with an in-house AMR solver HAMeRS built on the SAMRAI library. The code utilizes the high-order localized dissipation weighted compact nonlinear scheme [Wong and Lele, 2017] for shock-capturing and different sensors including the wavelet sensor [Wong and Lele, 2016] to identify regions for grid refinement. First and third authors acknowledge the project sponsor LANL.

Injection Efficiency of Low-energy Particles at Oblique Shocks with a Focused Transport Model

NASA Astrophysics Data System (ADS)

Zuo, P.; Zhang, M.; Rassoul, H.

2013-12-01

There is strong evidence that a small portion of thermal and suprathermal particles from hot coronal material or remnants of previous solar energetic particle (SEP) events serve as the source of large SEP events (Desai et al. 2006). To build more powerful SEP models, it is necessary to model the detailed particle injection and acceleration process for source particles especially at lower energies. We present a test particle simulation on the injection and acceleration of low-energy suprathermal particles by Laminar nonrelativistic oblique shocks in the framework of the focused transport theory, which is proved to contain all necessary physics of shock acceleration, but avoid the limitation of diffusive shock acceleration (DSA). The injection efficiency as a function of Mach number, obliquity, injection speed, shock strength, cross-shock potential and the degree of turbulence is calculated. This test particle simulation proves that the focused transport theory is an extension of DSA theory with the capability of predicting the efficiency of particle injection. The results can be applied to modeling the SEP acceleration from source particles.

Effects of cavity size on the control of transonic internal flow around a biconvex circular arc airfoil

NASA Astrophysics Data System (ADS)

Rahman, M. Mostaqur; Hasan, A. B. M. Toufique; Rabbi, M. S.

2017-06-01

In transonic flow conditions, self-sustained shock wave oscillation on biconvex airfoils is initiated by the complex shock wave boundary layer interaction which is frequently observed in several modern internal aeronautical applications such as inturbine cascades, compressor blades, butterfly valves, fans, nozzles, diffusers and so on. Shock wave boundary layer interaction often generates serious problems such as unsteady boundary layer separation, self-excited shock waveoscillation with large pressure fluctuations, buffeting excitations, aeroacoustic noise, nonsynchronous vibration, high cycle fatigue failure and intense drag rise. Recently, the control of the self-excited shock oscillation around an airfoil using passive control techniques is getting intense interest. Among the passive means, control using open cavity has found promising. In this study, the effect of cavity size on the control of self-sustained shock oscillation was investigated numerically. The present computations are validated with available experimental results. The results showed that the average root mean square (RMS) of pressure oscillation around the airfoil with open cavity has reduced significantly when compared to airfoil without cavity (clean airfoil).

Fulminant streptococcal toxic shock syndrome.

PubMed

Zavala, S; Arias, M; Legua, P

2018-03-01

We present a case of a previously healthy 37-year-old male who developed fever, nausea, vomiting, diarrhoea, and hypovolaemia. Within 5.5 h he presented with tachycardia, tachypnoea, became hypotensive and displayed a diffuse erythematous rash. In the following hours he developed persistent hypotension, acute respiratory distress syndrome, liver failure, kidney failure and disseminated intravascular coagulation. A diagnosis of toxic shock syndrome was made, but despite antibiotic therapy, immunoglobulin administration, and supportive measures, the patient died 50 h after presentation. Streptococcus pyogenes was isolated from blood cultures.

Combustor Modelling

DTIC Science & Technology

1980-02-01

resto A faire . Connaissant lea conditions do fonctionnoment ot los performances du foyer recherch6os, 1e motoristo va, A partir d’un certain nombre de...shock. How precisely do you manage to obtain the required good definition of the shock %ave ,itlth a finite ifference tedinique. Author’s Reply Actually...turbulent ..diffusion -lamos. ’Comb. S6i.. and Tech. 14, 229 #3. 6. A.C,, Styles and; N.A. Chigier . Combustion of air blast atomiz’d spray flames. 16th

Observations at the planet Mercury by the plasma electron experiment - Mariner 10

NASA Technical Reports Server (NTRS)

Ogilvie, K. W.; Scudder, J. D.; Vasyliunas, V. M.; Hartle, R. E.; Siscoe, G. L.

1977-01-01

Two nightside encounters with Mercury's magnetosphere by Mariner 10 revealed bow shock and magnetosheath signatures in the plasma electron data that are entirely consistent with the geometry expected for an interaction between a planet-centered magnetic dipole and the solar wind. The geometrically determined distance between the planet's center and the solar wind stagnation point is 1.4 plus or minus 0.1 R sub M. Both diffuse and sharp shock crossings were observed on the two magnetosphere encounters.

On the cross-field diffusion of ions in one- and two-dimensional hybrid simulations of collisionless shocks

NASA Technical Reports Server (NTRS)

Giacalone, Joe

1994-01-01

It can be demonstrated analytically that under certain geometries used in numerical simulations of collisionless shocks in which there is at least one ignorable spatial coordinate, the transport of particles across the magnetic field is essentially zero. This notion is tested using one- and two-dimensional hybrid simulations (kinetic ions/fluid electrons). We find, as the theorem predicts, the particles treated kinetically are tied to the same field line on which they start.

Measurements of Amplified Magnetic Field and Cosmic-Ray Content in Supernova Remnants

NASA Astrophysics Data System (ADS)

Uchiyama, Yasunobu

Supernova explosions drive collisionless shocks in the interstellar (or circumstellar) medium. Such shocks are mediated by plasma waves, resulting in the shock transition on a scale much smaller than the collisional mean free path. Galactic cosmic rays are widely considered to be accelerated at collisionless shocks in supernova remnants via diffusive shock acceleration. New high-energy data coming from the X-ray and gamma-ray satellites and from imaging air Cerenkov telescopes are making possible to study physics of particle acceleration at supernova shocks, such as magnetic field amplification which is considered to be realized as part of shock acceleration process and the energy content of cosmic-ray particles in the supernova shell. In particular, GeV observations with the Fermi Gamma-ray Space Telescope offer the prime means to establish the origin of the gamma-rays, and to measure the cosmic-ray content. Moreover they provide a new opportunity to learn about how particle acceleration responds to environ-mental effects. I will present recent observational results from the Chandra and Suzaku X-ray satellites and new results from the LAT onboard Fermi, and discuss their implications to the origin of galactic cosmic rays.

On the meaning of the diffusion layer thickness for slow electrode reactions.

PubMed

Molina, A; González, J; Laborda, E; Compton, R G

2013-02-21

A key concept underpinning electrochemical science is that of the diffusion layer - the zone of depletion around an electrode accompanying electrolysis. The size of this zone can be found either from the simulated or measured concentration profiles (yielding the 'true' diffusion layer thickness) or, in the case of the Nernst ('linear') diffusion layer by extrapolating the concentration gradient at the electrode surface to the distance at which the concentration takes its bulk value. The latter concept is very well developed in the case of fast (so-called reversible) electrode processes, however the study of the linear diffusion layer has received scant attention in the case of slow charge transfer processes, despite its study being of great interest in the analysis of the influence of different experimental variables which determine the electrochemical response. Analytical explicit solutions for the concentration profiles, surface concentrations and real and linear diffusion layers corresponding to the application of a potential step to a slow charge transfer process are presented. From these expressions the dependence of the diffusion layer thickness on the potential, pulse time, heterogeneous rate constant and ratio of bulk concentrations of electroactive species and of diffusion coefficients is quantified. A profound influence of the reversibility degree of the charge transfer on the diffusion layer thickness is clear, showing that for non-reversible processes the real and linear diffusion layers reveal a minimum thickness which coincides with the equilibrium potential of the redox couple in the former case and with the reversible half-wave potential in the latter one.

SUPG Finite Element Simulations of Compressible Flows for Aerothermodynamic Applications

NASA Technical Reports Server (NTRS)

Kirk, Benjamin S.

2007-01-01

This viewgraph presentation reviews the Streamline-Upwind Petrov-Galerkin (SUPG) Finite Element Simulation. It covers the background, governing equations, weak formulation, shock capturing, inviscid flux discretization, time discretization, linearization, and implicit solution strategies. It also reviews some applications such as Type IV Shock Interaction, Forward-Facing Cavity and AEDC Sharp Double Cone.

Experimentally validated multiphysics computational model of focusing and shock wave formation in an electromagnetic lithotripter.

PubMed

Fovargue, Daniel E; Mitran, Sorin; Smith, Nathan B; Sankin, Georgy N; Simmons, Walter N; Zhong, Pei

2013-08-01

A multiphysics computational model of the focusing of an acoustic pulse and subsequent shock wave formation that occurs during extracorporeal shock wave lithotripsy is presented. In the electromagnetic lithotripter modeled in this work the focusing is achieved via a polystyrene acoustic lens. The transition of the acoustic pulse through the solid lens is modeled by the linear elasticity equations and the subsequent shock wave formation in water is modeled by the Euler equations with a Tait equation of state. Both sets of equations are solved simultaneously in subsets of a single computational domain within the BEARCLAW framework which uses a finite-volume Riemann solver approach. This model is first validated against experimental measurements with a standard (or original) lens design. The model is then used to successfully predict the effects of a lens modification in the form of an annular ring cut. A second model which includes a kidney stone simulant in the domain is also presented. Within the stone the linear elasticity equations incorporate a simple damage model.

Experimentally validated multiphysics computational model of focusing and shock wave formation in an electromagnetic lithotripter

PubMed Central

Fovargue, Daniel E.; Mitran, Sorin; Smith, Nathan B.; Sankin, Georgy N.; Simmons, Walter N.; Zhong, Pei

2013-01-01

A multiphysics computational model of the focusing of an acoustic pulse and subsequent shock wave formation that occurs during extracorporeal shock wave lithotripsy is presented. In the electromagnetic lithotripter modeled in this work the focusing is achieved via a polystyrene acoustic lens. The transition of the acoustic pulse through the solid lens is modeled by the linear elasticity equations and the subsequent shock wave formation in water is modeled by the Euler equations with a Tait equation of state. Both sets of equations are solved simultaneously in subsets of a single computational domain within the BEARCLAW framework which uses a finite-volume Riemann solver approach. This model is first validated against experimental measurements with a standard (or original) lens design. The model is then used to successfully predict the effects of a lens modification in the form of an annular ring cut. A second model which includes a kidney stone simulant in the domain is also presented. Within the stone the linear elasticity equations incorporate a simple damage model. PMID:23927200

X-ray Observations of Cosmic Ray Acceleration

NASA Technical Reports Server (NTRS)

Petre, Robert

2012-01-01

Since the discovery of cosmic rays, detection of their sources has remained elusive. A major breakthrough has come through the identification of synchrotron X-rays from the shocks of supernova remnants through imaging and spectroscopic observations by the most recent generation of X-ray observatories. This radiation is most likely produced by electrons accelerated to relativistic energy, and thus has offered the first, albeit indirect, observational evidence that diffusive shock acceleration in supernova remnants produces cosmic rays to TeV energies, possibly as high as the "knee" in the cosmic ray spectrum. X-ray observations have provided information about the maximum energy to which these shOCks accelerate electrons, as well as indirect evidence of proton acceleration. Shock morphologies measured in X-rays have indicated that a substantial fraction of the shock energy can be diverted into particle acceleration. This presentation will summarize what we have learned about cosmic ray acceleration from X-ray observations of supernova remnants over the past two decades.

DYNAMICS OF HIGH ENERGY IONS AT A STRUCTURED COLLISIONLESS SHOCK FRONT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gedalin, M.; Dröge, W.; Kartavykh, Y. Y., E-mail: gedalin@bgu.ac.il

2016-07-10

Ions undergoing first-order Fermi acceleration at a shock are scattered in the upstream and downstream regions by magnetic inhomogeneities. For high energy ions this scattering is efficient at spatial scales substantially larger than the gyroradius of the ions. The transition from one diffusive region to the other occurs via crossing the shock, and the ion dynamics during this crossing is mainly affected by the global magnetic field change between the upstream and downstream region. We study the effects of the fine structure of the shock front, such as the foot-ramp-overshoot profile and the phase-standing upstream and downstream magnetic oscillations. Wemore » also consider time dependent features, including reformation and large amplitude coherent waves. We show that the influence of the spatial and temporal structure of the shock front on the dependence of the transition and reflection on the pitch angle of the ions is already weak at ion speeds five times the speed of the upstream flow.« less

The Accuracy of Shock Capturing in Two Spatial Dimensions

NASA Technical Reports Server (NTRS)

Carpenter, Mark H.; Casper, Jay H.

1997-01-01

An assessment of the accuracy of shock capturing schemes is made for two-dimensional steady flow around a cylindrical projectile. Both a linear fourth-order method and a nonlinear third-order method are used in this study. It is shown, contrary to conventional wisdom, that captured two-dimensional shocks are asymptotically first-order, regardless of the design accuracy of the numerical method. The practical implications of this finding are discussed in the context of the efficacy of high-order numerical methods for discontinuous flows.

Shock formation in Ne, Ar, Kr, and Xe on deuterium gas puff implosions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Narkis, J.; Rahman, H. U.; Ney, P.

2016-12-29

1- and 2-D simulations of 1-cm radius, gas-puff liners of Ne, Ar, Kr, and Xe imploding onto a deuterium target are conducted using the discharge parameters for the Zebra (1 MA, 130 ns) driver using the resistive MHD code MACH2. This is an implementation of the Staged Z-pinch concept, in which the target is driven to high-energy-density first by shock compression launched by a diffused azimuthal magnetic field (J×B force), and then by the adiabatic compression as the liner converges on axis. During the run-in phase, the initial shock heating preheats the deuterium plasma, with a subsequent stable, adiabatic compressionmore » heating the target to high energy density. Shock compression of the target coincides with the development of a J×B force at the target/liner interface. Stronger B-field transport and earlier shock compression increases with higher-Z liners, which results in an earlier shock arrival on axis. As a result, delayed shock formation in lower-Z liners yields a relative increase in shock heating, however, the 2-D simulations show an increased target isolation from magneto-Rayleigh-Taylor instability penetration, suggesting that an optimal balance between these two effects is reached in an Ar or Kr liner, rather than with Xe.« less

Observation of Dispersive Shock Waves, Solitons, and Their Interactions in Viscous Fluid Conduits.

PubMed

Maiden, Michelle D; Lowman, Nicholas K; Anderson, Dalton V; Schubert, Marika E; Hoefer, Mark A

2016-04-29

Dispersive shock waves and solitons are fundamental nonlinear excitations in dispersive media, but dispersive shock wave studies to date have been severely constrained. Here, we report on a novel dispersive hydrodynamic test bed: the effectively frictionless dynamics of interfacial waves between two high viscosity contrast, miscible, low Reynolds number Stokes fluids. This scenario is realized by injecting from below a lighter, viscous fluid into a column filled with high viscosity fluid. The injected fluid forms a deformable pipe whose diameter is proportional to the injection rate, enabling precise control over the generation of symmetric interfacial waves. Buoyancy drives nonlinear interfacial self-steepening, while normal stresses give rise to the dispersion of interfacial waves. Extremely slow mass diffusion and mass conservation imply that the interfacial waves are effectively dissipationless. This enables high fidelity observations of large amplitude dispersive shock waves in this spatially extended system, found to agree quantitatively with a nonlinear wave averaging theory. Furthermore, several highly coherent phenomena are investigated including dispersive shock wave backflow, the refraction or absorption of solitons by dispersive shock waves, and the multiphase merging of two dispersive shock waves. The complex, coherent, nonlinear mixing of dispersive shock waves and solitons observed here are universal features of dissipationless, dispersive hydrodynamic flows.

Theory of the corrugation instability of a piston-driven shock wave.

PubMed

Bates, J W

2015-01-01

We analyze the two-dimensional stability of a shock wave driven by a steadily moving corrugated piston in an inviscid fluid with an arbitrary equation of state. For h≤-1 or h>h(c), where h is the D'yakov parameter and h(c) is the Kontorovich limit, we find that small perturbations on the shock front are unstable and grow--at first quadratically and later linearly--with time. Such instabilities are associated with nonequilibrium fluid states and imply a nonunique solution to the hydrodynamic equations. The above criteria are consistent with instability limits observed in shock-tube experiments involving ionizing and dissociating gases and may have important implications for driven shocks in laser-fusion, astrophysical, and/or detonation studies.

Shock effects on hydrous minerals and implications for carbonaceous meteorites

NASA Technical Reports Server (NTRS)

Lange, M. A.; Ahrens, T. J.; Lambert, P.

1985-01-01

The effect of shock loading over the pressure range of 29-59 GPa on the shock-recovered specimens of antigorite serpentine, Mg3Si2O5(OH)4, were investigated employing infrared (IR) spectroscopy, thermogravimetric analysis, and optical and scanning electron microscopy. With increasing shock pressure, there was an increase in H2O IR absorption peaks at the expense of OH peaks, while the changes in SiO bond vibration modes were identical to those seen for other, nonhydrous minerals. Thermogravimetric results on vented assembly samples showed linear relationships between the shock pressure and both the length of dehydration interval and the effective activation energy for releasing post-shock structural water. Optical and scanning electron microscopy revealed gas bubbles, which appeared to be injected into zones of partial melting, and vesicular dark veins distributed throughout the shocked samples. It is suggested that shock loading of hydrous minerals would release and redistribute free water in the regoliths of carbonaceous chondrite parent bodies, giving rise to observed hydrous alterations.

Accuracy Study of the Space-Time CE/SE Method for Computational Aeroacoustics Problems Involving Shock Waves

NASA Technical Reports Server (NTRS)

Wang, Xiao Yen; Chang, Sin-Chung; Jorgenson, Philip C. E.

1999-01-01

The space-time conservation element and solution element(CE/SE) method is used to study the sound-shock interaction problem. The order of accuracy of numerical schemes is investigated. The linear model problem.govemed by the 1-D scalar convection equation, sound-shock interaction problem governed by the 1-D Euler equations, and the 1-D shock-tube problem which involves moving shock waves and contact surfaces are solved to investigate the order of accuracy of numerical schemes. It is concluded that the accuracy of the CE/SE numerical scheme with designed 2nd-order accuracy becomes 1st order when a moving shock wave exists. However, the absolute error in the CE/SE solution downstream of the shock wave is on the same order as that obtained using a fourth-order accurate essentially nonoscillatory (ENO) scheme. No special techniques are used for either high-frequency low-amplitude waves or shock waves.

Shock-induced fine-grained recrystallization of olivine - Evidence against subsolidus reduction of Fe/2+/

NASA Technical Reports Server (NTRS)

Ahrens, T. J.; Tsay, F.-D.; Live, D. H.

1976-01-01

Electron spin resonance (ESR) studies have been carried out on three single grains of terrestrial olivine (Fo90) shock loaded along the 010 line to peak pressures of 280, 330, and 440 kbar. The results indicate that neither metallic Fe similar to that observed in returned lunar soils nor paramagnetic Fe(3+) caused by oxidation of Fe(2+) has been produced in these shock experiments. Trace amounts of Mn (2+) have been detected in both shocked and unshocked olivine. The ESR signals of Mn(2+) show spectral features which are found to correlate with the degree of shock-induced recrystallization observed petrographically. The increasing mass fraction of recrystallized olivine correlates with increasing shock pressures. This phenomenon is modelled assuming it results from the progressive effect of the shock-induced transformation of the olivine to a yet unknown high-pressure phase and its subsequent reversion to the low-pressure olivine phase. The mass fraction of recrystallized material is predicted to be nearly linear with shock pressure.

Dynamics of a thermally driven film climbing the outside of a vertical cylinder

NASA Astrophysics Data System (ADS)

Smolka, Linda B.

2017-10-01

The dynamics of a film climbing the outside of a vertical cylinder under the competing effects of a thermally driven surface tension gradient and gravity is examined through numerical simulations of a thin-film model for the film height. The model, including boundary conditions, depends on three parameters, the scaled cylinder radius R ̂, the upstream film height h∞, and the downstream precursor film thickness b , and reduces to the model for Marangoni driven film climbing a vertical plate in the limit R ̂→∞ . The axisymmetric advancing front displays dynamics similar to that found along a vertical plate where, depending on h∞, the film forms a single Lax shock, an undercompressive double shock, or a rarefaction-undercompressive shock. A linear stability analysis of the Lax shock reveals the number of fingers that form along the contact line increases linearly with cylinder circumference while no fingers form for sufficiently small cylinders (below R ̂≈1.15 when b =0.1 ). The substrate curvature controls the height of the Lax shock, bounds on h∞ that define the three distinct solutions, and the maximum growth rate of contact line perturbations to the Lax shock when R ̂=O (1 ) , whereas the three solutions and the stability of the Lax shock converge to the behavior one observes on a vertical plate when R ̂≥O (10 ) . An energy analysis reveals that the azimuthal curvatures of the base state and perturbation, which arise from the annular geometry of the film, promote instability of the advancing contact line.

Dynamics of a thermally driven film climbing the outside of a vertical cylinder.

PubMed

Smolka, Linda B

2017-10-01

The dynamics of a film climbing the outside of a vertical cylinder under the competing effects of a thermally driven surface tension gradient and gravity is examined through numerical simulations of a thin-film model for the film height. The model, including boundary conditions, depends on three parameters, the scaled cylinder radius R[over ̂], the upstream film height h_{∞}, and the downstream precursor film thickness b, and reduces to the model for Marangoni driven film climbing a vertical plate in the limit R[over ̂]→∞. The axisymmetric advancing front displays dynamics similar to that found along a vertical plate where, depending on h_{∞}, the film forms a single Lax shock, an undercompressive double shock, or a rarefaction-undercompressive shock. A linear stability analysis of the Lax shock reveals the number of fingers that form along the contact line increases linearly with cylinder circumference while no fingers form for sufficiently small cylinders (below R[over ̂]≈1.15 when b=0.1). The substrate curvature controls the height of the Lax shock, bounds on h_{∞} that define the three distinct solutions, and the maximum growth rate of contact line perturbations to the Lax shock when R[over ̂]=O(1), whereas the three solutions and the stability of the Lax shock converge to the behavior one observes on a vertical plate when R[over ̂]≥O(10). An energy analysis reveals that the azimuthal curvatures of the base state and perturbation, which arise from the annular geometry of the film, promote instability of the advancing contact line.

Conserved linear dynamics of single-molecule Brownian motion.

PubMed

Serag, Maged F; Habuchi, Satoshi

2017-06-06

Macromolecular diffusion in homogeneous fluid at length scales greater than the size of the molecule is regarded as a random process. The mean-squared displacement (MSD) of molecules in this regime increases linearly with time. Here we show that non-random motion of DNA molecules in this regime that is undetectable by the MSD analysis can be quantified by characterizing the molecular motion relative to a latticed frame of reference. Our lattice occupancy analysis reveals unexpected sub-modes of motion of DNA that deviate from expected random motion in the linear, diffusive regime. We demonstrate that a subtle interplay between these sub-modes causes the overall diffusive motion of DNA to appear to conform to the linear regime. Our results show that apparently random motion of macromolecules could be governed by non-random dynamics that are detectable only by their relative motion. Our analytical approach should advance broad understanding of diffusion processes of fundamental relevance.

Conserved linear dynamics of single-molecule Brownian motion

PubMed Central

Serag, Maged F.; Habuchi, Satoshi

2017-01-01

Macromolecular diffusion in homogeneous fluid at length scales greater than the size of the molecule is regarded as a random process. The mean-squared displacement (MSD) of molecules in this regime increases linearly with time. Here we show that non-random motion of DNA molecules in this regime that is undetectable by the MSD analysis can be quantified by characterizing the molecular motion relative to a latticed frame of reference. Our lattice occupancy analysis reveals unexpected sub-modes of motion of DNA that deviate from expected random motion in the linear, diffusive regime. We demonstrate that a subtle interplay between these sub-modes causes the overall diffusive motion of DNA to appear to conform to the linear regime. Our results show that apparently random motion of macromolecules could be governed by non-random dynamics that are detectable only by their relative motion. Our analytical approach should advance broad understanding of diffusion processes of fundamental relevance. PMID:28585925

Conserved linear dynamics of single-molecule Brownian motion

NASA Astrophysics Data System (ADS)

Serag, Maged F.; Habuchi, Satoshi

2017-06-01

Macromolecular diffusion in homogeneous fluid at length scales greater than the size of the molecule is regarded as a random process. The mean-squared displacement (MSD) of molecules in this regime increases linearly with time. Here we show that non-random motion of DNA molecules in this regime that is undetectable by the MSD analysis can be quantified by characterizing the molecular motion relative to a latticed frame of reference. Our lattice occupancy analysis reveals unexpected sub-modes of motion of DNA that deviate from expected random motion in the linear, diffusive regime. We demonstrate that a subtle interplay between these sub-modes causes the overall diffusive motion of DNA to appear to conform to the linear regime. Our results show that apparently random motion of macromolecules could be governed by non-random dynamics that are detectable only by their relative motion. Our analytical approach should advance broad understanding of diffusion processes of fundamental relevance.

X-Ray Emission from Supernovae in Dense Circumstellar Matter Environments: A Search for Collisionless Shock

NASA Technical Reports Server (NTRS)

Ofek, E.O; Fox, D.; Cenko, B.; Sullivan, M.; Gnat, O.; Frail A.; Horesh, A.; Corsi, A; Quimby, R. M.; Gehrels, N.;

Physical lumping methods for developing linear reduced models for high speed propulsion systems

NASA Technical Reports Server (NTRS)

Immel, S. M.; Hartley, Tom T.; Deabreu-Garcia, J. Alex

1991-01-01

In gasdynamic systems, information travels in one direction for supersonic flow and in both directions for subsonic flow. A shock occurs at the transition from supersonic to subsonic flow. Thus, to simulate these systems, any simulation method implemented for the quasi-one-dimensional Euler equations must have the ability to capture the shock. In this paper, a technique combining both backward and central differencing is presented. The equations are subsequently linearized about an operating point and formulated into a linear state space model. After proper implementation of the boundary conditions, the model order is reduced from 123 to less than 10 using the Schur method of balancing. Simulations comparing frequency and step response of the reduced order model and the original system models are presented.

Management of massive diffuse alveolar hemorrhage in a child with systemic lupus erythematosus.

PubMed

Kimura, Dai; Shah, Samir; Briceno-Medina, Mario; Sathanandam, Shyam; Haberman, Brent; Zhang, Jie; Myers, Linda; Kumar, Tk Susheel; Knott-Craig, Christopher

2015-01-01

Diffuse alveolar hemorrhage (DAH) from systemic lupus erythematosus (SLE) is a rare but potentially life-threatening condition. We report the case of a 14-year-old female with SLE who developed hypoxia and shock secondary to severe alveolar hemorrhage. She was successfully managed by placement on extracorporeal membrane oxygenation (ECMO) followed by emergent pulmonary lobectomy and medical treatment including high-dose methylprednisolone, cyclophosphamide, intravenous immunoglobulin, and plasmapheresis.

Abstract Reference List: Reviews of Pertinent Literature in Shock. Volume I.

DTIC Science & Technology

1981-05-18

7:149-161 (1980). 9 23. MARROW CULTURE IN DIFFUSION CHAMGERS IN RABBITS: iii. EFFECT " OF ENDOTOXIN AND LEUKOCYTE PRODUCTS ON CELL PRODUCTION. R...269-286 (1979) ..... ............... ... 22 54. EXPERIMENTAL STUDIES ON COAGULATION-FIBRINOLYTIC ACTIVITY OF WHITE BLOOD CELLS INFLUENCED BY ENL)QTOXIN...Diffusion Chambers in Rabbits: III. Effect of Endo- toxin and Leukocyte Products on Cell Production. R Willemze, RI Walker, JC Herion, and JG Palmer. Am. J

Strong shock implosion, approximate solution

NASA Astrophysics Data System (ADS)

Fujimoto, Y.; Mishkin, E. A.; Alejaldre, C.

1983-01-01

The self-similar, center-bound motion of a strong spherical, or cylindrical, shock wave moving through an ideal gas with a constant, γ= cp/ cv, is considered and a linearized, approximate solution is derived. An X, Y phase plane of the self-similar solution is defined and the representative curved of the system behind the shock front is replaced by a straight line connecting the mappings of the shock front with that of its tail. The reduced pressure P(ξ), density R(ξ) and velocity U1(ξ) are found in closed, quite accurate, form. Comparison with numerically obtained results, for γ= {5}/{3} and γ= {7}/{5}, is shown.

On magnetic field amplification and particle acceleration near non-relativistic collisionless shocks: Particles in MHD Cells simulations

NASA Astrophysics Data System (ADS)

Casse, F.; van Marle, A. J.; Marcowith, A.

2018-01-01

We present simulations of magnetized astrophysical shocks taking into account the interplay between the thermal plasma of the shock and supra-thermal particles. Such interaction is depicted by combining a grid-based magneto-hydrodynamics description of the thermal fluid with particle-in-cell techniques devoted to the dynamics of supra-thermal particles. This approach, which incorporates the use of adaptive mesh refinement features, is potentially a key to simulate astrophysical systems on spatial scales that are beyond the reach of pure particle-in-cell simulations. We consider non-relativistic super-Alfénic shocks with various magnetic field obliquity. We recover all the features from previous studies when the magnetic field is parallel to the normal to the shock. In contrast with previous particle-in-cell and hybrid simulations, we find that particle acceleration and magnetic field amplification also occur when the magnetic field is oblique to the normal to the shock but on larger timescales than in the parallel case. We show that in our oblique shock simulations the streaming of supra-thermal particles induces a corrugation of the shock front. Such oscillations of both the shock front and the magnetic field then locally helps the particles to enter the upstream region and to initiate a non-resonant streaming instability and finally to induce diffuse particle acceleration.

Exact travelling wave solutions for a diffusion-convection equation in two and three spatial dimensions

NASA Astrophysics Data System (ADS)

Elwakil, S. A.; El-Labany, S. K.; Zahran, M. A.; Sabry, R.

2004-04-01

The modified extended tanh-function method were applied to the general class of nonlinear diffusion-convection equations where the concentration-dependent diffusivity, D( u), was taken to be a constant while the concentration-dependent hydraulic conductivity, K( u) were taken to be in a power law. The obtained solutions include rational-type, triangular-type, singular-type, and solitary wave solutions. In fact, the profile of the obtained solitary wave solutions resemble the characteristics of a shock-wave like structure for an arbitrary m (where m>1 is the power of the nonlinear convection term).

ION ACCELERATION AT THE QUASI-PARALLEL BOW SHOCK: DECODING THE SIGNATURE OF INJECTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sundberg, Torbjörn; Haynes, Christopher T.; Burgess, D.

Collisionless shocks are efficient particle accelerators. At Earth, ions with energies exceeding 100 keV are seen upstream of the bow shock when the magnetic geometry is quasi-parallel, and large-scale supernova remnant shocks can accelerate ions into cosmic-ray energies. This energization is attributed to diffusive shock acceleration; however, for this process to become active, the ions must first be sufficiently energized. How and where this initial acceleration takes place has been one of the key unresolved issues in shock acceleration theory. Using Cluster spacecraft observations, we study the signatures of ion reflection events in the turbulent transition layer upstream of the terrestrial bowmore » shock, and with the support of a hybrid simulation of the shock, we show that these reflection signatures are characteristic of the first step in the ion injection process. These reflection events develop in particular in the region where the trailing edge of large-amplitude upstream waves intercept the local shock ramp and the upstream magnetic field changes from quasi-perpendicular to quasi-parallel. The dispersed ion velocity signature observed can be attributed to a rapid succession of ion reflections at this wave boundary. After the ions’ initial interaction with the shock, they flow upstream along the quasi-parallel magnetic field. Each subsequent wavefront in the upstream region will sweep the ions back toward the shock, where they gain energy with each transition between the upstream and the shock wave frames. Within three to five gyroperiods, some ions have gained enough parallel velocity to escape upstream, thus completing the injection process.« less

Atomic-level deformation of CuxZr100-x metallic glasses under shock loading

NASA Astrophysics Data System (ADS)

Demaske, Brian J.; Wen, Peng; Phillpot, Simon R.; Spearot, Douglas E.

2018-06-01

Plastic deformation mechanisms in CuxZr100-x bulk metallic glasses (MGs) subjected to shock are investigated using molecular dynamics simulations. MGs with Cu compositions between 30 and 70 at. % subjected to shock waves generated via piston velocities that range from 0.125 to 2.0 km/s are considered. In agreement with prior studies, plastic deformation is initiated via formation of localized regions of high von Mises shear strain, known as shear transformation zones (STZs). At low impact velocities, but above the Hugoniot elastic limit, STZ nucleation is dispersed behind the shock front. As impact velocity is increased, STZ nucleation becomes more homogeneous, eventually leading to shock-induced melting, which is identified in this work via high atomic diffusivity. The shear stress necessary to initiate plastic deformation within the shock front is independent of composition at shock intensities near the elastic limit but increases with increasing Cu content at high shock intensities. By contrast, both the flow stress in the plastically deformed MG and the critical shock pressure associated with melting behind the shock front are found to increase with increasing Cu content over the entire range of impact velocities. The evolution of the short-range order in the MG samples during shock wave propagation is analyzed using a polydisperse Voronoi tessellation method. Cu-centered polyhedra with full icosahedral symmetry are found to be most resistant to change under shock loading independent of the MG composition. A saturation is observed in the involvement of select Cu-centered polyhedra in the plastic deformation processes at a piston velocity around 0.75 km/s.

Analytical scalings of the linear Richtmyer-Meshkov instability

NASA Astrophysics Data System (ADS)

Cobos, Francisco; Wouchuk, Juan Gustavo

2017-11-01

In the linear Richtmyer-Meshkov instability (RMI), hydrodynamic perturbations are generated behind the transmitted and reflected rippled fronts. The contact surface reaches an asymptotic normal velocity and two different tangential velocities at each side, which are always different for moderate to strong levels of compression, depending on the amount of vorticity generated by the corrugated shocks. We show analytical scaling laws for the ripple velocity (δvi∞)in different physical limits and approximate formulas are provided, valid for arbitrary initial pre-shock parameters. An asymptotic growth for the contact surface ripple of the form ψi(t) ψ∞ + δ vi∞t is obtained. The quantity ψ∞ is in general different from the initial post-shock ripple amplitude, in agreement with the early finding of. Comparison to simulations and experimental work is shown. F.C. acknowledges support from UCLM for a predoctoral fellowship. This work has received support from MINECO, JCCM, and UCLM (Spain).

High-Order Residual-Distribution Schemes for Discontinuous Problems on Irregular Triangular Grids

NASA Technical Reports Server (NTRS)

Mazaheri, Alireza; Nishikawa, Hiroaki

2016-01-01

In this paper, we develop second- and third-order non-oscillatory shock-capturing hyperbolic residual distribution schemes for irregular triangular grids, extending our second- and third-order schemes to discontinuous problems. We present extended first-order N- and Rusanov-scheme formulations for hyperbolic advection-diffusion system, and demonstrate that the hyperbolic diffusion term does not affect the solution of inviscid problems for vanishingly small viscous coefficient. We then propose second- and third-order blended hyperbolic residual-distribution schemes with the extended first-order Rusanov-scheme. We show that these proposed schemes are extremely accurate in predicting non-oscillatory solutions for discontinuous problems. We also propose a characteristics-based nonlinear wave sensor for accurately detecting shocks, compression, and expansion regions. Using this proposed sensor, we demonstrate that the developed hyperbolic blended schemes do not produce entropy-violating solutions (unphysical stocks). We then verify the design order of accuracy of these blended schemes on irregular triangular grids.

Quantitative body DW-MRI biomarkers uncertainty estimation using unscented wild-bootstrap.

PubMed

Freiman, M; Voss, S D; Mulkern, R V; Perez-Rossello, J M; Warfield, S K

2011-01-01

We present a new method for the uncertainty estimation of diffusion parameters for quantitative body DW-MRI assessment. Diffusion parameters uncertainty estimation from DW-MRI is necessary for clinical applications that use these parameters to assess pathology. However, uncertainty estimation using traditional techniques requires repeated acquisitions, which is undesirable in routine clinical use. Model-based bootstrap techniques, for example, assume an underlying linear model for residuals rescaling and cannot be utilized directly for body diffusion parameters uncertainty estimation due to the non-linearity of the body diffusion model. To offset this limitation, our method uses the Unscented transform to compute the residuals rescaling parameters from the non-linear body diffusion model, and then applies the wild-bootstrap method to infer the body diffusion parameters uncertainty. Validation through phantom and human subject experiments shows that our method identify the regions with higher uncertainty in body DWI-MRI model parameters correctly with realtive error of -36% in the uncertainty values.

Diffusion phenomenon for linear dissipative wave equations in an exterior domain

NASA Astrophysics Data System (ADS)

Ikehata, Ryo

Under the general condition of the initial data, we will derive the crucial estimates which imply the diffusion phenomenon for the dissipative linear wave equations in an exterior domain. In order to derive the diffusion phenomenon for dissipative wave equations, the time integral method which was developed by Ikehata and Matsuyama (Sci. Math. Japon. 55 (2002) 33) plays an effective role.

Stream interfaces and energetic ions II: Ulysses test of Pioneer results

NASA Technical Reports Server (NTRS)

Intriligator, Devrie S.; Siscoe, George L.; Wibberenz, Gerd; Kunow, Horst; Gosling, John T.

1995-01-01

Ulysses measurements of energetic and solar wind particles taken near 5 AU between 20 and 30 degrees south latitude during a well-developed recurring corotating interaction region (CIR) show that the CIR's corotating energetic ion population (CEIP) associated with the trailing reverse shock starts within the CIR at the stream interface. This is consistent with an earlier result obtained by Pioneers 10 and 11 in the ecliptic plane between 4 and 6 AU. The Ulysses/Pioneer finding is noteworthy since the stream interface is not magnetically connected to the reverse shock, but lies 12-17 corotation hours from it. Thus, the finding seems to be inconsistent with the basic model that generates CEIP particles at the reverse shock and propagates them along field lines. Eliminating the inconsistency probably entails an extension of the standard model such as cross-field diffusion or a non-shock energization process operating near the stream interface closer to the sun.

Cosmic Ray Acceleration from Multiple Galactic Wind Shocks

NASA Astrophysics Data System (ADS)

Cotter, Cory; Bustard, Chad; Zweibel, Ellen

2018-01-01

Cosmic rays still have an unknown origin. Many mechanisms have been suggested for their acceleration including quasars, pulsars, magnetars, supernovae, supernova remnants, and galactic termination shocks. The source of acceleration may be a mixture of these and a different mixture in different energy regimes. Using numerical simulations, we investigate multiple shocks in galactic winds as potential cosmic rays sources. By having shocks closer to the parent galaxy, more particles may diffuse back to the disk instead of being blown out in the wind, as found in Bustard, Zweibel, and Cotter (2017, ApJ) and also Merten, Bustard, Zweibel, and Tjus (to be submitted to ApJ). Specifically, this flux of cosmic rays could contribute to the unexplained "shin" region between the well-known "knee" and "ankle" of the cosmic ray spectrum. We would like to acknowledge support from the National Science Foundation (NSF) Graduate Research Fellowship Program under grant No. DGE-125625 and NSF grant No. AST-1616037.

Solar-flare-induced Forbush decreases - Dependence on shock wave geometry

NASA Technical Reports Server (NTRS)

Thomas, B. T.; Gall, R.

1984-01-01

It is argued that the principal mechanism for the association of Forbush decreases with the passage of a solar flare shock wave is prolonged containment of cosmic ray particles behind the flare compression region, which acts as a semipermeable obstacle to particle motion along the field lines, leading to additional adiabatic cooling of the particles. Liouville's theorem is used to calculate the instantaneous distribution function at 1 AU for each particle arriving at the earth. By averaging over a large number of individual estimates, a representative estimate of the omnidirectional phase space density and the corresponding particle intensity is obtained. The energy change of individual particles at the shocks is found to be small in comparison to the energy lost by adiabatic cooling of the cosmic rays between the shock wave and the sun. The effects of particle rigidity, diffusion coefficient, and flare longitude on the magnitude of the Forbush decrease are quantitatively investigated.

Quantum molecular dynamics simulation of shock-wave experiments in aluminum

NASA Astrophysics Data System (ADS)

Minakov, D. V.; Levashov, P. R.; Khishchenko, K. V.; Fortov, V. E.

2014-06-01

We present quantum molecular dynamics calculations of principal, porous, and double shock Hugoniots, release isentropes, and sound velocity behind the shock front for aluminum. A comprehensive analysis of available shock-wave data is performed; the agreement and discrepancies of simulation results with measurements are discussed. Special attention is paid to the melting region of aluminum along the principal Hugoniot; the boundaries of the melting zone are estimated using the self-diffusion coefficient. Also, we make a comparison with a high-quality multiphase equation of state for aluminum. Independent semiempirical and first-principle models are very close to each other in caloric variables (pressure, density, particle velocity, etc.) but the equation of state gives higher temperature on the principal Hugoniot and release isentropes than ab initio calculations. Thus, the quantum molecular dynamics method can be used for calibration of semiempirical equations of state in case of lack of experimental data.

Quantum molecular dynamics simulation of shock-wave experiments in aluminum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minakov, D. V.; Khishchenko, K. V.; Fortov, V. E.

2014-06-14

We present quantum molecular dynamics calculations of principal, porous, and double shock Hugoniots, release isentropes, and sound velocity behind the shock front for aluminum. A comprehensive analysis of available shock-wave data is performed; the agreement and discrepancies of simulation results with measurements are discussed. Special attention is paid to the melting region of aluminum along the principal Hugoniot; the boundaries of the melting zone are estimated using the self-diffusion coefficient. Also, we make a comparison with a high-quality multiphase equation of state for aluminum. Independent semiempirical and first-principle models are very close to each other in caloric variables (pressure, density,more » particle velocity, etc.) but the equation of state gives higher temperature on the principal Hugoniot and release isentropes than ab initio calculations. Thus, the quantum molecular dynamics method can be used for calibration of semiempirical equations of state in case of lack of experimental data.« less

A theoretical signal processing framework for linear diffusion MRI: Implications for parameter estimation and experiment design.

PubMed

Varadarajan, Divya; Haldar, Justin P

2017-11-01

The data measured in diffusion MRI can be modeled as the Fourier transform of the Ensemble Average Propagator (EAP), a probability distribution that summarizes the molecular diffusion behavior of the spins within each voxel. This Fourier relationship is potentially advantageous because of the extensive theory that has been developed to characterize the sampling requirements, accuracy, and stability of linear Fourier reconstruction methods. However, existing diffusion MRI data sampling and signal estimation methods have largely been developed and tuned without the benefit of such theory, instead relying on approximations, intuition, and extensive empirical evaluation. This paper aims to address this discrepancy by introducing a novel theoretical signal processing framework for diffusion MRI. The new framework can be used to characterize arbitrary linear diffusion estimation methods with arbitrary q-space sampling, and can be used to theoretically evaluate and compare the accuracy, resolution, and noise-resilience of different data acquisition and parameter estimation techniques. The framework is based on the EAP, and makes very limited modeling assumptions. As a result, the approach can even provide new insight into the behavior of model-based linear diffusion estimation methods in contexts where the modeling assumptions are inaccurate. The practical usefulness of the proposed framework is illustrated using both simulated and real diffusion MRI data in applications such as choosing between different parameter estimation methods and choosing between different q-space sampling schemes. Copyright © 2017 Elsevier Inc. All rights reserved.

Chemistry in Magnetohydrodynamic Shock Waves in Diffuse Molecular Clouds

NASA Astrophysics Data System (ADS)

Peimbert, Antonio

1998-09-01

Absorption observations of the CH+ molecule with column densities of up to 1014 cm-2 in diffuse molecular clouds in many lines of sight are reviewed, and compared to the reddening and to abundances and velocity shifts of molecules like CH. Special attention is placed on the observations of the line of sight towards ς Ophiuchi where high quality observations of many chemical species are available. The problem of the required CH+ is described, and many formation mechanisms from the literature are reviewed, finding that none of them is particularly apt at describing the observations towards ς-Oph. Two fluid J-type shock models are studied as an alternative. The necessary conditions for their formation are discussed, and it is shown how they are expected to be present widely in the interstellar medium. Plane parallel numerical integrations, for the particular case in which the magnetic field is perpendicular to the shock velocity, are employed to study the region of phase-space of initial conditions that will produce 2 fluid shocks. A chemical network is developed and formation of key molecules like CH+, CH and OH, along with the excited roto-vibrational levels of H2, are studied under the shock dynamics. These models are then compared to the observations of the different lines of sight, showing they are capable of reproducing the features of the observations towards most of those clouds. An attempt to model the line of sight towards ς-Oph is done, finding that a shock with a shock speed vs = 9.0km/s going through a cloud with a density of nH = 14cm-3 with a magnetic field of B = 4.7μG does a reasonable job at satisfying most of the observations with the exception of the highest rotational excited states of molecular hydrogen for which observations are available. There is a small family of solutions capable of explaining the observed results which make specific predictions for the velocity profiles of the H2 lines of various excited levels. New observations with the Interstellar Medium Absorption Profile Spectrograph (IMAPS) camera would be useful in confirming or rejecting these models.

Numerical Simulation of the Interaction of an Air Shock Wave with a Surface Gas-Dust Layer

NASA Astrophysics Data System (ADS)

Surov, V. S.

2018-05-01

Within the framework of the one-velocity and multivelocity models of a dust-laden gas with the use of the Godunov method with a linearized Riemann solver, the problem of the interaction of a shock wave with a dust-laden gas layer located along a solid plane surface has been studied.

Numerical Simulation of the Interaction of an Air Shock Wave with a Surface Gas-Dust Layer

NASA Astrophysics Data System (ADS)

Surov, V. S.

2018-03-01

Within the framework of the one-velocity and multivelocity models of a dust-laden gas with the use of the Godunov method with a linearized Riemann solver, the problem of the interaction of a shock wave with a dust-laden gas layer located along a solid plane surface has been studied.

PAINeT: An object-oriented software package for simulations of flow-field, transport coefficients and flux terms in non-equilibrium gas mixture flows

NASA Astrophysics Data System (ADS)

Istomin, V. A.

2018-05-01

The software package Planet Atmosphere Investigator of Non-equilibrium Thermodynamics (PAINeT) has been devel-oped for studying the non-equilibrium effects associated with electronic excitation, chemical reactions and ionization. These studies are necessary for modeling process in shock tubes, in high enthalpy flows, in nozzles or jet engines, in combustion and explosion processes, in modern plasma-chemical and laser technologies. The advantages and possibilities of the package implementation are stated. Within the framework of the package implementation, based on kinetic theory approximations (one-temperature and state-to-state approaches), calculations are carried out, and the limits of applicability of a simplified description of shock-heated air flows and any other mixtures chosen by the user are given. Using kinetic theory algorithms, a numerical calculation of the heat fluxes and relaxation terms can be performed, which is necessary for further comparison of engineering simulation with experi-mental data. The influence of state-to-state distributions over electronic energy levels on the coefficients of thermal conductivity, diffusion, heat fluxes and diffusion velocities of the components of various gas mixtures behind shock waves is studied. Using the software package the accuracy of different approximations of the kinetic theory of gases is estimated. As an example state-resolved atomic ionized mixture of N/N+/O/O+/e- is considered. It is shown that state-resolved diffusion coefficients of neutral and ionized species vary from level to level. Comparing results of engineering applications with those given by PAINeT, recommendations for adequate models selection are proposed.

The Multi-Dimensional Structure of Radiative Shocks: Suppressed Thermal X-rays and Relativistic Ion Acceleration

NASA Astrophysics Data System (ADS)

Steinberg, Elad; Metzger, Brian D.

2018-06-01

Radiative shocks, behind which gas cools faster than the dynamical time, play a key role in many astrophysical transients, including classical novae and young supernovae interacting with circumstellar material. The dense layer behind high Mach number M ≫ 1 radiative shocks is susceptible to thin-shell instabilities, creating a "corrugated" shock interface. We present two and three-dimensional hydrodynamical simulations of optically-thin radiative shocks to study their thermal radiation and acceleration of non-thermal relativistic ions. We employ a moving-mesh code and a specialized numerical technique to eliminate artificial heat conduction across grid cells. The fraction of the shock's luminosity Ltot radiated at X-ray temperatures kT_sh ≈ (3/16)μ m_p v_sh2 expected from a one-dimensional analysis is suppressed by a factor L(>T_sh/3)/L_tot ≈ 4.5/M^{4/3} for M ≈ 4-36. This suppression results in part from weak shocks driven into under-pressured cold filaments by hot shocked gas, which sap thermal energy from the latter faster than it is radiated. Combining particle-in-cell simulation results for diffusive shock acceleration with the inclination angle distribution across the shock (relative to an upstream magnetic field in the shock plane-the expected geometry for transient outflows), we predict the efficiency and energy spectrum of ion acceleration. Though negligible acceleration is predicted for adiabatic shocks, the corrugated shock front enables local regions to satisfy the quasi-parallel magnetic field geometry required for efficient acceleration, resulting in an average acceleration efficiency of ɛnth ˜ 0.005 - 0.02 for M ≈ 12-36, in agreement with modeling of the gamma-ray nova ASASSN-16ma.

Nonequilibrium transition and pattern formation in a linear reaction-diffusion system with self-regulated kinetics

NASA Astrophysics Data System (ADS)

Paul, Shibashis; Ghosh, Shyamolina; Ray, Deb Shankar

2018-02-01

We consider a reaction-diffusion system with linear, stochastic activator-inhibitor kinetics where the time evolution of concentration of a species at any spatial location depends on the relative average concentration of its neighbors. This self-regulating nature of kinetics brings in spatial correlation between the activator and the inhibitor. An interplay of this correlation in kinetics and disparity of diffusivities of the two species leads to symmetry breaking non-equilibrium transition resulting in stationary pattern formation. The role of initial noise strength and the linear reaction terms has been analyzed for pattern selection.

The role of nanoparticle rigidity on the diffusion of linear polystyrene in a polymer nanocomposite

DOE PAGES

Miller, Brad; Imel, Adam E.; Holley, Wade; ...

2015-11-12

The impact of the inclusion of a nanoparticle in a polymer matrix on the dynamics of the polymer chains is an area of recent interest. In this article, we describe the role of nanoparticle rigidity or softness on the impact of the presence of that nanoparticle on the diffusive behavior of linear polymer chains. The neutron reflectivity results clearly show that the inclusion of 10 nm soft nanoparticles in a polymer matrix (R g ~ 20 nm) increases the diffusion coefficient of the linear polymer chain. Surprisingly, thermal analysis shows that these nanocomposites exhibit an increase in their glass transitionmore » temperature, which is incommensurate with an increase in free volume. Therefore, it appears that this effect is more complex than a simple plasticizing effect. Results from small-angle neutron scattering of the nanoparticles in solution show a structure that consists of a gel like core with a corona of free chain ends and loops. Furthermore, the increase in linear polymer diffusion may be related to an increase in constraint release mechanisms in the reptation of the polymer chain, in a similar manner to that which has been reported for the diffusion of linear polymer chains in the presence of star polymers.« less

The role of nanoparticle rigidity on the diffusion of linear polystyrene in a polymer nanocomposite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, Brad; Imel, Adam E.; Holley, Wade

The impact of the inclusion of a nanoparticle in a polymer matrix on the dynamics of the polymer chains is an area of recent interest. In this article, we describe the role of nanoparticle rigidity or softness on the impact of the presence of that nanoparticle on the diffusive behavior of linear polymer chains. The neutron reflectivity results clearly show that the inclusion of 10 nm soft nanoparticles in a polymer matrix (R g ~ 20 nm) increases the diffusion coefficient of the linear polymer chain. Surprisingly, thermal analysis shows that these nanocomposites exhibit an increase in their glass transitionmore » temperature, which is incommensurate with an increase in free volume. Therefore, it appears that this effect is more complex than a simple plasticizing effect. Results from small-angle neutron scattering of the nanoparticles in solution show a structure that consists of a gel like core with a corona of free chain ends and loops. Furthermore, the increase in linear polymer diffusion may be related to an increase in constraint release mechanisms in the reptation of the polymer chain, in a similar manner to that which has been reported for the diffusion of linear polymer chains in the presence of star polymers.« less

Understanding Coupling of Global and Diffuse Solar Radiation with Climatic Variability

NASA Astrophysics Data System (ADS)

Hamdan, Lubna

Global solar radiation data is very important for wide variety of applications and scientific studies. However, this data is not readily available because of the cost of measuring equipment and the tedious maintenance and calibration requirements. Wide variety of models have been introduced by researchers to estimate and/or predict the global solar radiations and its components (direct and diffuse radiation) using other readily obtainable atmospheric parameters. The goal of this research is to understand the coupling of global and diffuse solar radiation with climatic variability, by investigating the relationships between these radiations and atmospheric parameters. For this purpose, we applied multilinear regression analysis on the data of National Solar Radiation Database 1991--2010 Update. The analysis showed that the main atmospheric parameters that affect the amount of global radiation received on earth's surface are cloud cover and relative humidity. Global radiation correlates negatively with both variables. Linear models are excellent approximations for the relationship between atmospheric parameters and global radiation. A linear model with the predictors total cloud cover, relative humidity, and extraterrestrial radiation is able to explain around 98% of the variability in global radiation. For diffuse radiation, the analysis showed that the main atmospheric parameters that affect the amount received on earth's surface are cloud cover and aerosol optical depth. Diffuse radiation correlates positively with both variables. Linear models are very good approximations for the relationship between atmospheric parameters and diffuse radiation. A linear model with the predictors total cloud cover, aerosol optical depth, and extraterrestrial radiation is able to explain around 91% of the variability in diffuse radiation. Prediction analysis showed that the linear models we fitted were able to predict diffuse radiation with efficiency of test adjusted R2 values equal to 0.93, using the data of total cloud cover, aerosol optical depth, relative humidity and extraterrestrial radiation. However, for prediction purposes, using nonlinear terms or nonlinear models might enhance the prediction of diffuse radiation.

Using hybrid implicit Monte Carlo diffusion to simulate gray radiation hydrodynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cleveland, Mathew A., E-mail: cleveland7@llnl.gov; Gentile, Nick

This work describes how to couple a hybrid Implicit Monte Carlo Diffusion (HIMCD) method with a Lagrangian hydrodynamics code to evaluate the coupled radiation hydrodynamics equations. This HIMCD method dynamically applies Implicit Monte Carlo Diffusion (IMD) [1] to regions of a problem that are opaque and diffusive while applying standard Implicit Monte Carlo (IMC) [2] to regions where the diffusion approximation is invalid. We show that this method significantly improves the computational efficiency as compared to a standard IMC/Hydrodynamics solver, when optically thick diffusive material is present, while maintaining accuracy. Two test cases are used to demonstrate the accuracy andmore » performance of HIMCD as compared to IMC and IMD. The first is the Lowrie semi-analytic diffusive shock [3]. The second is a simple test case where the source radiation streams through optically thin material and heats a thick diffusive region of material causing it to rapidly expand. We found that HIMCD proves to be accurate, robust, and computationally efficient for these test problems.« less

Nanoparticle Motion in Entangled Melts of Linear and Nonconcatenated Ring Polymers

PubMed Central

2017-01-01

The motion of nanoparticles (NPs) in entangled melts of linear polymers and nonconcatenated ring polymers are compared by large-scale molecular dynamics simulations. The comparison provides a paradigm for the effects of polymer architecture on the dynamical coupling between NPs and polymers in nanocomposites. Strongly suppressed motion of NPs with diameter d larger than the entanglement spacing a is observed in a melt of linear polymers before the onset of Fickian NP diffusion. This strong suppression of NP motion occurs progressively as d exceeds a and is related to the hopping diffusion of NPs in the entanglement network. In contrast to the NP motion in linear polymers, the motion of NPs with d > a in ring polymers is not as strongly suppressed prior to Fickian diffusion. The diffusion coefficient D decreases with increasing d much slower in entangled rings than in entangled linear chains. NP motion in entangled nonconcatenated ring polymers is understood through a scaling analysis of the coupling between NP motion and the self-similar entangled dynamics of ring polymers. PMID:28392603

Comparison of three large-eddy simulations of shock-induced turbulent separation bubbles

NASA Astrophysics Data System (ADS)

Touber, Emile; Sandham, Neil D.

2009-12-01

Three different large-eddy simulation investigations of the interaction between an impinging oblique shock and a supersonic turbulent boundary layer are presented. All simulations made use of the same inflow technique, specifically aimed at avoiding possible low-frequency interferences with the shock/boundary-layer interaction system. All simulations were run on relatively wide computational domains and integrated over times greater than twenty five times the period of the most commonly reported low-frequency shock-oscillation, making comparisons at both time-averaged and low-frequency-dynamic levels possible. The results confirm previous experimental results which suggested a simple linear relation between the interaction length and the oblique-shock strength if scaled using the boundary-layer thickness and wall-shear stress. All the tested cases show evidences of significant low-frequency shock motions. At the wall, energetic low-frequency pressure fluctuations are observed, mainly in the initial part of interaction.

Distinguishing shocked from tectonically deformed quartz by the use of the SEM and chemical etching

USGS Publications Warehouse

Gratz, A.J.; Fisler, D.K.; Bohor, B.F.

1996-01-01

Multiple sets of crystallographically-oriented planar deformation features (PDFs) are generated by high-strain-rate shock waves at pressures of > 12 GPa in naturally shocked quartz samples. On surfaces, PDFs appear as narrow (50-500 nm) lamellae filled with amorphosed quartz (diaplectic glass) which can be etched with hydrofluoric acid or with hydrothermal alkaline solutions. In contrast, slow-strain-rate tectonic deformation pressure produces wider, semi-linear and widely spaced arrays of dislocation loops that are not glass filled. Etching samples with HF before examination in a scanning electron microscope (SEM) allows for unambiguous visual distinction between glass-filled PDFs and glass-free tectonic deformation arrays in quartz. This etching also reveals the internal 'pillaring' often characteristic of shock-induced PDFs. This technique is useful for easily distinguishing between shock and tectonic deformation in quartz, but does not replace optical techniques for characterizing the shock features.

Refractive index of r-cut sapphire under shock pressure range 5 to 65 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, Xiuxia; Li, Jiabo; Li, Jun

2014-09-07

High-pressure refractive index of optical window materials not only can provide information on electronic polarizability and band-gap structure, but also is important for velocity correction in particle-velocity measurement with laser interferometers. In this work, the refractive index of r-cut sapphire window at 1550 nm wavelength was measured under shock pressures of 5–65 GPa. The refractive index (n) decreases linearly with increasing shock density (ρ) for shock stress above the Hugoniot elastic limit (HEL): n = 2.0485 (± 0.0197) − 0.0729 (± 0.0043)ρ, while n remains nearly a constant for elastic shocks. This behavior is attributed to the transition from elastic (below HEL) to heterogeneous plastic deformationmore » (above HEL). Based on the obtained refractive index-density relationship, polarizability of the shocked sapphire was also obtained.« less

Photoacoustic shock wave emission and cavitation from structured optical fiber tips

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohammadzadeh, M.; Gonzalez-Avila, S. R.; Ohl, C. D., E-mail: cdohl@ntu.edu.sg

Photoacoustic waves generated at the tip of an optical fiber consist of a compressive shock wave followed by tensile diffraction waves. These tensile waves overlap along the fiber axis and form a cloud of cavitation bubbles. We demonstrate that shaping the fiber tip through micromachining alters the number and direction of the emitted waves and cavitation clouds. Shock wave emission and cavitation patterns from five distinctively shaped fiber tips have been studied experimentally and compared to a linear wave propagation model. In particular, multiple shock wave emission and generation of strong tension away from the fiber axis have been realizedmore » using modified fiber tips. These altered waveforms may be applied for novel microsurgery protocols, such as fiber-based histotripsy, by utilizing bubble-shock wave interaction.« less

Non-linear shipboard shock analysis of the Tomahawk missile shock isolation system

NASA Technical Reports Server (NTRS)

Leifer, Joel; Gross, Michael

1987-01-01

The identification, quantification, computer modeling and verification of the Tomahawk nonlinear liquid spring shock isolation system in a surface ship Vertical Launch System (VLS) are discussed. The isolation system hardware and mode of operation is detailed in an effort to understand the nonlinearities. These nonlinearities are then quantified and modeled using the MSC/NASTRAN finite element code. The model was verified using experimental data from the Navel Ordnance Systems Center MIL-S-901 medium weight shock tests of August 1986. The model was then used to predict the Tomahawk response to the CG-53 USS Mobile Bay shock trials of May-June 1987. Results indicate that the model is an accurate mathematical representation of the physical system either functioning as designed or in an impaired condition due to spring failure.

A Simple Mathematical Model Inspired by the Purkinje Cells: From Delayed Travelling Waves to Fractional Diffusion.

PubMed

Dipierro, Serena; Valdinoci, Enrico

2018-07-01

Recently, several experiments have demonstrated the existence of fractional diffusion in the neuronal transmission occurring in the Purkinje cells, whose malfunctioning is known to be related to the lack of voluntary coordination and the appearance of tremors. Also, a classical mathematical feature is that (fractional) parabolic equations possess smoothing effects, in contrast with the case of hyperbolic equations, which typically exhibit shocks and discontinuities. In this paper, we show how a simple toy-model of a highly ramified structure, somehow inspired by that of the Purkinje cells, may produce a fractional diffusion via the superposition of travelling waves that solve a hyperbolic equation. This could suggest that the high ramification of the Purkinje cells might have provided an evolutionary advantage of "smoothing" the transmission of signals and avoiding shock propagations (at the price of slowing a bit such transmission). Although an experimental confirmation of the possibility of such evolutionary advantage goes well beyond the goals of this paper, we think that it is intriguing, as a mathematical counterpart, to consider the time fractional diffusion as arising from the superposition of delayed travelling waves in highly ramified transmission media. The case of a travelling concave parabola with sufficiently small curvature is explicitly computed. The new link that we propose between time fractional diffusion and hyperbolic equation also provides a novelty with respect to the usual paradigm relating time fractional diffusion with parabolic equations in the limit. This paper is written in such a way as to be of interest to both biologists and mathematician alike. In order to accomplish this aim, both complete explanations of the objects considered and detailed lists of references are provided.

Collisionless Shocks and Particle Acceleration.

NASA Astrophysics Data System (ADS)

Malkov, M.

2016-12-01

Collisionless shocks emerged in the 50s and 60s of the last century as an important branch of plasma physics and have remained ever since. New applications pose new challenges to our understanding of collisionless shock mechanisms. Particle acceleration in astrophysical settings, primarily studied concerning the putative origin of cosmic rays (CR) in supernova remnant (SNR) shocks, stands out with the collisionless shock mechanism being the key. Among recent laboratory applications, a laser-based tabletop proton accelerator is an affordable compact alternative to big synchrotron accelerators. The much-anticipated proof of cosmic ray (CR) acceleration in supernova remnants is hindered by our limited understanding of collisionless shock mechanisms. Over the last decade, dramatically improved observations were puzzling the theorists with unexpected discoveries. The difference between the helium/carbon and proton CR rigidity (momentum to charge ratio) spectra, seemingly inconsistent with the acceleration and propagation theories, and the perplexing positron excess in the 10-300 GeV range are just two recent examples. The latter is now also actively discussed in the particle physics and CR communities as a possible signature of decay or annihilation of hypothetical dark matter particles. By considering an initial (injection) phase of a diffusive shock acceleration mechanism, including particle reflection off the shock front - where an elemental similarity of particle dynamics does not apply - I will discuss recent suggestions of how to address the new data from the collisionless shock perspective. The backreaction of accelerated particles on the shock structure, its environment, and visibility across the electromagnetic spectrum from radio to gamma rays is another key aspect of collisionless shock that will be discussed.

HIGH-TEMPERATURE PROCESSING OF SOLIDS THROUGH SOLAR NEBULAR BOW SHOCKS: 3D RADIATION HYDRODYNAMICS SIMULATIONS WITH PARTICLES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boley, A. C.; Morris, M. A.; Desch, S. J.

2013-10-20

A fundamental, unsolved problem in solar system formation is explaining the melting and crystallization of chondrules found in chondritic meteorites. Theoretical models of chondrule melting in nebular shocks have been shown to be consistent with many aspects of thermal histories inferred for chondrules from laboratory experiments; but, the mechanism driving these shocks is unknown. Planetesimals and planetary embryos on eccentric orbits can produce bow shocks as they move supersonically through the disk gas, and are one possible source of chondrule-melting shocks. We investigate chondrule formation in bow shocks around planetoids through three-dimensional radiation hydrodynamics simulations. A new radiation transport algorithmmore » that combines elements of flux-limited diffusion and Monte Carlo methods is used to capture the complexity of radiative transport around bow shocks. An equation of state that includes the rotational, vibrational, and dissociation modes of H{sub 2} is also used. Solids are followed directly in the simulations and their thermal histories are recorded. Adiabatic expansion creates rapid cooling of the gas, and tail shocks behind the embryo can cause secondary heating events. Radiative transport is efficient, and bow shocks around planetoids can have luminosities ∼few× 10{sup –8} L{sub ☉}. While barred and radial chondrule textures could be produced in the radiative shocks explored here, porphyritic chondrules may only be possible in the adiabatic limit. We present a series of predicted cooling curves that merit investigation in laboratory experiments to determine whether the solids produced by bow shocks are represented in the meteoritic record by chondrules or other solids.« less

Thermo-Mechanical and Thermal behavior of High-Temperature Structural Materials.

DTIC Science & Technology

1982-12-31

34-’- Mr. 3. D. SilboldMr-J-..ibl Columbus, OH 43201 Coor Porcelain Company 17750 W. 32nd Avenue Dr. R. E. Engdahl Golden, CO 80401 Deposits and Composites ...number) Thermal shock, thermal stress, thermal diffusivity, thermal conductivity; refractories, composites , radiation heat transfer, cyclic heating...Hasselman and R. Ruh, "Effect of Hot-Pressing 4 -; Temperature on the Thermal Diffusivity/Conductivity of SiC-AIN Composites ." III M. A. Bucknam, L. D

Network diffusion accurately models the relationship between structural and functional brain connectivity networks

PubMed Central

Abdelnour, Farras; Voss, Henning U.; Raj, Ashish

2014-01-01

The relationship between anatomic connectivity of large-scale brain networks and their functional connectivity is of immense importance and an area of active research. Previous attempts have required complex simulations which model the dynamics of each cortical region, and explore the coupling between regions as derived by anatomic connections. While much insight is gained from these non-linear simulations, they can be computationally taxing tools for predicting functional from anatomic connectivities. Little attention has been paid to linear models. Here we show that a properly designed linear model appears to be superior to previous non-linear approaches in capturing the brain’s long-range second order correlation structure that governs the relationship between anatomic and functional connectivities. We derive a linear network of brain dynamics based on graph diffusion, whereby the diffusing quantity undergoes a random walk on a graph. We test our model using subjects who underwent diffusion MRI and resting state fMRI. The network diffusion model applied to the structural networks largely predicts the correlation structures derived from their fMRI data, to a greater extent than other approaches. The utility of the proposed approach is that it can routinely be used to infer functional correlation from anatomic connectivity. And since it is linear, anatomic connectivity can also be inferred from functional data. The success of our model confirms the linearity of ensemble average signals in the brain, and implies that their long-range correlation structure may percolate within the brain via purely mechanistic processes enacted on its structural connectivity pathways. PMID:24384152

SH Observations In and Toward Sgr B2(N): Linking the Missing Sulfur

NASA Astrophysics Data System (ADS)

McCarthy, Michael

Where is the missing sulfur in the molecular reservoir of the interstellar medium (ISM)? In the warm gas phase ISM, the abundance of sulfur is nearly equivalent to its solar value, but in the cold, diffuse clouds which span the space between stars, sulfur is depleted by several orders of magnitude. Our inability to account for this depletion represents a significant gap in our understanding of the fundamental chemical and physical processes occurring in the primordial reservoirs of gas and dust in the ISM. Central to this chemistry is SH, a radical for which few observations presently exist, and for which SOFIA is uniquely capable of accessing in its ground rotational state. We propose observations of SH in the cold, shocked molecular shell surrounding Sgr B2(N), and, simultaneously, in diffuse and translucent clouds along the line of sight to Sgr B2(N). We will constrain the abundance of SH, and compare it to previous measurements of SO, CS, C_2S, HCS(+) , H_2CS, and H_2S in these sources which span the evolutionary timescale from diffuse clouds to dense, cold shocked regions.

Solution of the nonlinear Poisson-Boltzmann equation: Application to ionic diffusion in cementitious materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arnold, J.; Kosson, D.S., E-mail: david.s.kosson@vanderbilt.edu; Garrabrants, A.

2013-02-15

A robust numerical solution of the nonlinear Poisson-Boltzmann equation for asymmetric polyelectrolyte solutions in discrete pore geometries is presented. Comparisons to the linearized approximation of the Poisson-Boltzmann equation reveal that the assumptions leading to linearization may not be appropriate for the electrochemical regime in many cementitious materials. Implications of the electric double layer on both partitioning of species and on diffusive release are discussed. The influence of the electric double layer on anion diffusion relative to cation diffusion is examined.

Parallel collisionless shocks forming in simulations of the LAPD experiment

NASA Astrophysics Data System (ADS)

Weidl, Martin S.; Jenko, Frank; Niemann, Chris; Winske, Dan

2016-10-01

Research on parallel collisionless shocks, most prominently occurring in the Earth's bow shock region, has so far been limited to satellite measurements and simulations. However, the formation of collisionless shocks depends on a wide range of parameters and scales, which can be accessed more easily in a laboratory experiment. Using a kJ-class laser, an ongoing experimental campaign at the Large Plasma Device (LAPD) at UCLA is expected to produce the first laboratory measurements of the formation of a parallel collisionless shock. We present hybrid kinetic/MHD simulations that show how beam instabilities in the background plasma can be driven by ablating carbon ions from a target, causing non-linear density oscillations which develop into a propagating shock front. The free-streaming carbon ions can excite both the resonant right-hand instability and the non-resonant firehose mode. We analyze their respective roles and discuss optimizing their growth rates to speed up the process of shock formation.

The microphysics of collisionless shock waves.

PubMed

Marcowith, A; Bret, A; Bykov, A; Dieckman, M E; Drury, L O'C; Lembège, B; Lemoine, M; Morlino, G; Murphy, G; Pelletier, G; Plotnikov, I; Reville, B; Riquelme, M; Sironi, L; Novo, A Stockem

2016-04-01

Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebulæ, active galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space. It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in situ observations, analytical and numerical developments. A particular emphasis is made on the different instabilities triggered during the shock formation and in association with particle acceleration processes with regards to the properties of the background upstream medium. It appears that among the most important parameters the background magnetic field through the magnetization and its obliquity is the dominant one. The shock velocity that can reach relativistic speeds has also a strong impact over the development of the micro-instabilities and the fate of particle acceleration. Recent developments of laboratory shock experiments has started to bring some new insights in the physics of space plasma and astrophysical shock waves. A special section is dedicated to new laser plasma experiments probing shock physics.

The microphysics of collisionless shock waves

NASA Astrophysics Data System (ADS)

Marcowith, A.; Bret, A.; Bykov, A.; Dieckman, M. E.; O'C Drury, L.; Lembège, B.; Lemoine, M.; Morlino, G.; Murphy, G.; Pelletier, G.; Plotnikov, I.; Reville, B.; Riquelme, M.; Sironi, L.; Stockem Novo, A.

2016-04-01

Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebulæ, active galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space. It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in situ observations, analytical and numerical developments. A particular emphasis is made on the different instabilities triggered during the shock formation and in association with particle acceleration processes with regards to the properties of the background upstream medium. It appears that among the most important parameters the background magnetic field through the magnetization and its obliquity is the dominant one. The shock velocity that can reach relativistic speeds has also a strong impact over the development of the micro-instabilities and the fate of particle acceleration. Recent developments of laboratory shock experiments has started to bring some new insights in the physics of space plasma and astrophysical shock waves. A special section is dedicated to new laser plasma experiments probing shock physics.

Tailoring the Blast Exposure Conditions in the Shock Tube for Generating Pure, Primary Shock Waves: The End Plate Facilitates Elimination of Secondary Loading of the Specimen

PubMed Central

Misistia, Anthony; Kahali, Sudeepto; Sundaramurthy, Aravind; Chandra, Namas

2016-01-01

The end plate mounted at the mouth of the shock tube is a versatile and effective implement to control and mitigate the end effects. We have performed a series of measurements of incident shock wave velocities and overpressures followed by quantification of impulse values (integral of pressure in time domain) for four different end plate configurations (0.625, 2, 4 inches, and an open end). Shock wave characteristics were monitored by high response rate pressure sensors allocated in six positions along the length of 6 meters long 229 mm square cross section shock tube. Tests were performed at three shock wave intensities, which was controlled by varying the Mylar membrane thickness (0.02, 0.04 and 0.06 inch). The end reflector plate installed at the exit of the shock tube allows precise control over the intensity of reflected waves penetrating into the shock tube. At the optimized distance of the tube to end plate gap the secondary waves were entirely eliminated from the test section, which was confirmed by pressure sensor at T4 location. This is pronounced finding for implementation of pure primary blast wave animal model. These data also suggest only deep in the shock tube experimental conditions allow exposure to a single shock wave free of artifacts. Our results provide detailed insight into spatiotemporal dynamics of shock waves with Friedlander waveform generated using helium as a driver gas and propagating in the air inside medium sized tube. Diffusion of driver gas (helium) inside the shock tube was responsible for velocity increase of reflected shock waves. Numerical simulations combined with experimental data suggest the shock wave attenuation mechanism is simply the expansion of the internal pressure. In the absence of any other postulated shock wave decay mechanisms, which were not implemented in the model the agreement between theory and experimental data is excellent. PMID:27603017

Tailoring the Blast Exposure Conditions in the Shock Tube for Generating Pure, Primary Shock Waves: The End Plate Facilitates Elimination of Secondary Loading of the Specimen.

PubMed

Kuriakose, Matthew; Skotak, Maciej; Misistia, Anthony; Kahali, Sudeepto; Sundaramurthy, Aravind; Chandra, Namas

2016-01-01

The end plate mounted at the mouth of the shock tube is a versatile and effective implement to control and mitigate the end effects. We have performed a series of measurements of incident shock wave velocities and overpressures followed by quantification of impulse values (integral of pressure in time domain) for four different end plate configurations (0.625, 2, 4 inches, and an open end). Shock wave characteristics were monitored by high response rate pressure sensors allocated in six positions along the length of 6 meters long 229 mm square cross section shock tube. Tests were performed at three shock wave intensities, which was controlled by varying the Mylar membrane thickness (0.02, 0.04 and 0.06 inch). The end reflector plate installed at the exit of the shock tube allows precise control over the intensity of reflected waves penetrating into the shock tube. At the optimized distance of the tube to end plate gap the secondary waves were entirely eliminated from the test section, which was confirmed by pressure sensor at T4 location. This is pronounced finding for implementation of pure primary blast wave animal model. These data also suggest only deep in the shock tube experimental conditions allow exposure to a single shock wave free of artifacts. Our results provide detailed insight into spatiotemporal dynamics of shock waves with Friedlander waveform generated using helium as a driver gas and propagating in the air inside medium sized tube. Diffusion of driver gas (helium) inside the shock tube was responsible for velocity increase of reflected shock waves. Numerical simulations combined with experimental data suggest the shock wave attenuation mechanism is simply the expansion of the internal pressure. In the absence of any other postulated shock wave decay mechanisms, which were not implemented in the model the agreement between theory and experimental data is excellent.

Shock wave compression of iron-silicate garnet.

NASA Technical Reports Server (NTRS)

Graham, E. K.; Ahrens, T. J.

1973-01-01

Shock wave compression data to over 650 kb are presented for single-crystal almandine garnet. The data indicate the initiation of a phase transformation near 200 kb. Total transition to the high-pressure polymorph occurs at approximately 300 kb. The elastic properties of the high-pressure phase are calculated from the metastable Hugoniot data by using the linear shock velocity-particle velocity relationships. The overall results obtained strongly suggest that upper mantle minerals are likely to occur in the ilmenite structure over a substantial part of the lower mantle.

The Shock and Vibration Bulletin. Part 4. Vibration Testing, Instrumentation, Loads and Environments, Tracked Vehicles

DTIC Science & Technology

1978-09-01

self with a nonlinear (thermocouple) function, the limits X os nu 2O being: x Enables Temperature Controller to command heat 0 Code Temnperature ___6...34 Shock and Vi- bration Bulletin 42, 1970. (2) R.T. Fandrich, " Self -Tuning Re- • sonant Fixtures", 47th Shock andVibration Symposium, October 1976. . " (3...is given in Fig. 4. timTit for "ysem From the shape of some of these it is apparent linear respose that in some tests dampino ratios of the order 0 of

Derivation of an applied nonlinear Schroedinger equation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pitts, Todd Alan; Laine, Mark Richard; Schwarz, Jens

We derive from first principles a mathematical physics model useful for understanding nonlinear optical propagation (including filamentation). All assumptions necessary for the development are clearly explained. We include the Kerr effect, Raman scattering, and ionization (as well as linear and nonlinear shock, diffraction and dispersion). We explain the phenomenological sub-models and each assumption required to arrive at a complete and consistent theoretical description. The development includes the relationship between shock and ionization and demonstrates why inclusion of Drude model impedance effects alters the nature of the shock operator. Unclassified Unlimited Release

System for determining position of normal shock in supersonic flow

NASA Technical Reports Server (NTRS)

Iverson, Jr., Donald G. (Inventor); Daiber, Troy D. (Inventor)

1991-01-01

Light from a plurality of light emitting diodes is transmitted through optical cables (12) to a lens system. The lenses (56, 58) expand and collimate the light and project it in a sheet (16) across the supersonic inlet of an aircraft power plant perpendicular to incoming airflow. A normal shock bends a portion of the sheet of light (16). A linear array of a multiplicity of optical fiber ends collects discrete samples of light. The samples are processed and compared to a predetermined profile to determine the shock location.

The Shock and Vibration Bulletin: Proceedings on the Symposium on ShocK and Vibration (52nd) Held in New Orleans, Louisiana on 26-28 October 1981. Part 3. Environmental Testing and Simulation, Flight Environments.

DTIC Science & Technology

1982-05-01

signal generation history can then be generated. These opera- processes generally consisted of recording tions work quite well electromagnetic ex...fninduerointe gualinicharactestics I PLOTTER MULTI CHANNEL TAPE RECORDER TEST ITEM 71T RESPONSE MOTIO ANALOG SIGNAL SHOCK CONDITIONING SPECTRUM ANALYZER...of TM to the EM. The exciter displacement producing a drive signal with excessive actua- drive signal is generated fron the linear sm tor stroke

The Acceleration of Thermal Protons and Minor Ions at a Quasi-Parallel Interplanetary Shock

NASA Astrophysics Data System (ADS)

Giacalone, J.; Lario, D.; Lepri, S. T.

2017-12-01

We compare the results from self-consistent hybrid simulations (kinetic ions, massless fluid electrons) and spacecraft observations of a strong, quasi-parallel interplanetary shock that crossed the Advanced Composition Explorer (ACE) on DOY 94, 2001. In our simulations, the un-shocked plasma-frame ion distributions are Maxwellian. Our simulations include protons and minor ions (alphas, 3He++, and C5+). The interplanetary shock crossed both the ACE and the Wind spacecraft, and was associated with significant increases in the flux of > 50 keV/nuc ions. Our simulation uses parameters (ion densities, magnetic field strength, Mach number, etc.) consistent with those observed. Acceleration of the ions by the shock, in a manner similar to that expected from diffusive shock acceleration theory, leads to a high-energy tail in the distribution of the post-shock plasma for all ions we considered. The simulated distributions are directly compared to those observed by ACE/SWICS, EPAM, and ULEIS, and Wind/STICS and 3DP, covering the energy range from below the thermal peak to the suprathermal tail. We conclude from our study that the solar wind is the most significant source of the high-energy ions for this event. Our results have important implications for the physics of the so-called `injection problem', which will be discussed.

Mathematics of thermal diffusion in an exponential temperature field

NASA Astrophysics Data System (ADS)

Zhang, Yaqi; Bai, Wenyu; Diebold, Gerald J.

2018-04-01

The Ludwig-Soret effect, also known as thermal diffusion, refers to the separation of gas, liquid, or solid mixtures in a temperature gradient. The motion of the components of the mixture is governed by a nonlinear, partial differential equation for the density fractions. Here solutions to the nonlinear differential equation for a binary mixture are discussed for an externally imposed, exponential temperature field. The equation of motion for the separation without the effects of mass diffusion is reduced to a Hamiltonian pair from which spatial distributions of the components of the mixture are found. Analytical calculations with boundary effects included show shock formation. The results of numerical calculations of the equation of motion that include both thermal and mass diffusion are given.

Characteristics of solar and heliospheric ion populations observed near earth

NASA Technical Reports Server (NTRS)

Gloeckler, G.

1984-01-01

The composition and spectra of ions in solar-energetic-particle and energetic-storm-particle events, of diffuse ions upstream of the earth bow shock, and of ions in deep-geomagnetic-tail plasmoids are characterized in a summary of in situ observations. Data are presented in graphs and tables, and remarkable similarities are noted in the distribution functions of the heliospheric ion populations. The solar wind, acting through acceleration mechanisms associated with shocks and turbulence, is identified as the major plasma source of suprathermal and energetic particles.

Numerical studies of electron dynamics in oblique quasi-perpendicular collisionless shock waves

NASA Technical Reports Server (NTRS)

Liewer, P. C.; Decyk, V. K.; Dawson, J. M.; Lembege, B.

1991-01-01

Linear and nonlinear electron damping of the whistler precursor wave train to low Mach number quasi-perpendicular oblique shocks is studied using a one-dimensional electromagnetic plasma simulation code with particle electrons and ions. In some parameter regimes, electrons are observed to trap along the magnetic field lines in the potential of the whistler precursor wave train. This trapping can lead to significant electron heating in front of the shock for low beta(e). Use of a 64-processor hypercube concurrent computer has enabled long runs using realistic mass ratios in the full particle in-cell code and thus simulate shock parameter regimes and phenomena not previously studied numerically.

Acceleration of low-energy protons and alpha particles at interplanetary shock waves

NASA Technical Reports Server (NTRS)

Scholer, M.; Hovestadt, D.; Ipavich, F. M.; Gloeckler, G.

1983-01-01

The low-energy protons and alpha particles in the energy range 30 keV/charge to 150 keV/charge associated with three different interplanetary shock waves in the immediate preshock and postshock region are studied using data obtained by the ISEE 3. The spatial distributions in the preshock and postshock medium are presented, and the dependence of the phase space density at different energies on the distance from the shock and on the form of the distribution function of both species immediately at the shock is examined. It is found that in the preshock region the particles are flowing in the solar wind frame of reference away from the shock and in the postshock medium the distribution is more or less isotropic in this frame of reference. The distribution function in the postshock region can be represented by a power law in energy which has the same spectral exponent for both protons and alpha particles. It is concluded that the first-order Fermi acceleration process can consistently explain the data, although the spectra of diffuse bow shock associated particles are different from the spectra of the interplanetary shock-associated particles in the immediate vicinity of the shock. In addition, the mean free path of the low energy ions in the preshock medium is found to be considerably smaller than the mean free path determined by the turbulence of the background interplanetary medium.

Permeabilization of the plasma membrane of L1210 mouse leukemia cells using lithotripter shock waves.

PubMed

Gambihler, S; Delius, M; Ellwart, J W

1994-09-01

Permeabilization of L1210 cells by lithotripter shock waves in vitro was monitored by evaluating the accumulation of fluorescein-labeled dextrans with a relative molecular mass ranging from 3,900-2,000,000. Incubation with labeled dextran alone caused a dose- and time-dependent increase in cellular fluorescence as determined by flow cytometry, with a vesicular distribution pattern in the cells consistent with endocytotic uptake. Shock wave exposure prior to incubation with labeled dextran revealed similar fluorescence intensities compared to incubation with labeled dextran alone. When cells were exposed to shock waves in the presence of labeled dextran, mean cellular fluorescence was further increased, indicating additional internalization of the probe. Confocal laser scanning microscopy confirmed intracellular fluorescence of labeled dextran with a diffuse distribution pattern. Fluorescence-activated cell sorting with subsequent determination of proliferation revealed that permeabilized cells were viable and able to proliferate. Permeabilization of the membrane of L1210 cells by shock waves in vitro allowed loading of dextrans with a relative molecular mass up to 2,000,000. Permeabilization of tumor cells by shock waves provides a useful tool for introducing molecules into cells which might be of interest for drug targeting in tumor therapy in vivo.

Emergence of power-law scalings in shock-driven mixing transition

NASA Astrophysics Data System (ADS)

Vorobieff, Peter; Wayne, Patrick; Olmstead, Dell; Simons, Dylan; Truman, C. Randall; Kumar, Sanjay

2016-11-01

We present an experimental study of transition to turbulence due to shock-driven instability evolving on an initially cylindrical, diffuse density interface between air and a mixture of sulfur hexafluoride (SF6) and acetone. The plane of the shock is at an initial angle θ with the axis of the heavy-gas cylinder. We present the cases of planar normal (θ = 0) and oblique (θ =20°) shock interaction with the initial conditions. Flow is visualized in two perpendicular planes with planar laser-induced fluorescence (PLIF) triggered in acetone with a pulsed ultraviolet laser. Statistics of the flow are characterized in terms of the second-order structure function of the PLIF intensity. As instabilities in the flow evolve, the structure functions begin to develop power-law scalings, at late times manifesting over a range of scales spanning more than two orders of magnitude. We discuss the effects of the initial conditions on the emergence of these scalings, comparing the fully three-dimensional case (oblique shock interaction) with the quasi-two-dimensional case (planar normal shock interaction). We also discuss the flow anisotropy apparent in statistical differences in data from the two visualization planes. This work is funded by NNSA Grant DE-NA0002913.

DSMC Shock Simulation of Saturn Entry Probe Conditions

NASA Technical Reports Server (NTRS)

Higdon, Kyle J.; Cruden, Brett A.; Brandis, Aaron; Liechty, Derek S.; Goldstein, David B.; Varghese, Philip L.

2016-01-01

This work describes the direct simulation Monte Carlo (DSMC) investigation of Saturn entry probe scenarios and the influence of non-equilibrium phenomena on Saturn entry conditions. The DSMC simulations coincide with rarefied hypersonic shock tube experiments of a hydrogen-helium mixture performed in the Electric Arc Shock Tube (EAST) at NASA Ames Research Center. The DSMC simulations are post-processed through the NEQAIR line-by-line radiation code to compare directly to the experimental results. Improved collision cross-sections, inelastic collision parameters, and reaction rates are determined for a high temperature DSMC simulation of a 7-species H2-He mixture and an electronic excitation model is implemented in the DSMC code. Simulation results for 27.8 and 27.4 kms shock waves are obtained at 0.2 and 0.1 Torr respectively and compared to measured spectra in the VUV, UV, visible, and IR ranges. These results confirm the persistence of non-equilibrium for several centimeters behind the shock and the diffusion of atomic hydrogen upstream of the shock wave. Although the magnitude of the radiance did not match experiments and an ionization inductance period was not observed in the simulations, the discrepancies indicated where improvements are needed in the DSMC and NEQAIR models.

DSMC Shock Simulation of Saturn Entry Probe Conditions

NASA Technical Reports Server (NTRS)

Higdon, Kyle J.; Cruden, Brett A.; Brandis, Aaron M.; Liechty, Derek S.; Goldstein, David B.; Varghese, Philip L.

2016-01-01

This work describes the direct simulation Monte Carlo (DSMC) investigation of Saturn entry probe scenarios and the influence of non-equilibrium phenomena on Saturn entry conditions. The DSMC simulations coincide with rarefied hypersonic shock tube experiments of a hydrogen-helium mixture performed in the Electric Arc Shock Tube (EAST) at the NASA Ames Research Center. The DSMC simulations are post-processed through the NEQAIR line-by-line radiation code to compare directly to the experimental results. Improved collision cross-sections, inelastic collision parameters, and reaction rates are determined for a high temperature DSMC simulation of a 7-species H2-He mixture and an electronic excitation model is implemented in the DSMC code. Simulation results for 27.8 and 27.4 km/s shock waves are obtained at 0.2 and 0.1 Torr, respectively, and compared to measured spectra in the VUV, UV, visible, and IR ranges. These results confirm the persistence of non-equilibrium for several centimeters behind the shock and the diffusion of atomic hydrogen upstream of the shock wave. Although the magnitude of the radiance did not match experiments and an ionization inductance period was not observed in the simulations, the discrepancies indicated where improvements are needed in the DSMC and NEQAIR models.

Acceleration of low-energy ions at parallel shocks with a focused transport model

DOE PAGES

Zuo, Pingbing; Zhang, Ming; Rassoul, Hamid K.

2013-04-10

Here, we present a test particle simulation on the injection and acceleration of low-energy suprathermal particles by parallel shocks with a focused transport model. The focused transport equation contains all necessary physics of shock acceleration, but avoids the limitation of diffusive shock acceleration (DSA) that requires a small pitch angle anisotropy. This simulation verifies that the particles with speeds of a fraction of to a few times the shock speed can indeed be directly injected and accelerated into the DSA regime by parallel shocks. At higher energies starting from a few times the shock speed, the energy spectrum of acceleratedmore » particles is a power law with the same spectral index as the solution of standard DSA theory, although the particles are highly anisotropic in the upstream region. The intensity, however, is different from that predicted by DSA theory, indicating a different level of injection efficiency. It is found that the shock strength, the injection speed, and the intensity of an electric cross-shock potential (CSP) jump can affect the injection efficiency of the low-energy particles. A stronger shock has a higher injection efficiency. In addition, if the speed of injected particles is above a few times the shock speed, the produced power-law spectrum is consistent with the prediction of standard DSA theory in both its intensity and spectrum index with an injection efficiency of 1. CSP can increase the injection efficiency through direct particle reflection back upstream, but it has little effect on the energetic particle acceleration once the speed of injected particles is beyond a few times the shock speed. This test particle simulation proves that the focused transport theory is an extension of DSA theory with the capability of predicting the efficiency of particle injection.« less

The Strongest Acceleration of >40 keV Electrons by ICME-driven Shocks at 1 au

NASA Astrophysics Data System (ADS)

Yang, Liu; Wang, Linghua; Li, Gang; Wimmer-Schweingruber, Robert F.; He, Jiansen; Tu, Chuanyi; Tian, Hui; Bale, Stuart D.

2018-01-01

We present two case studies of the in-situ electron acceleration during the 2000 February 11 shock and the 2004 July 22 shock, with the strongest electron flux enhancement at 40 keV across the shock, among all the quasi-perpendicular and quasi-parallel ICME-driven shocks observed by the WIND 3DP instrument from 1995 through 2014 at 1 au. We find that for this quasi-perpendicular (quasi-parallel) shock on 2000 February 11 (2004 July 22), the shocked electron differential fluxes at ∼0.4–50 keV in the downstream generally fit well to a double-power-law spectrum, J ∼ E ‑β , with an index of β ∼ 3.15 (4.0) at energies below a break at ∼3 keV (∼1 keV) and β ∼ 2.65 (2.6) at energies above. For both shock events, the downstream electron spectral indices appear to be similar for all pitch angles, which are significantly larger than the index prediction by diffusive shock acceleration. In addition, the downstream electron pitch-angle distributions show the anisotropic beams in the anti-sunward-traveling direction, while the ratio of the downstream over ambient fluxes appears to peak near 90° pitch angles, at all energies of ∼0.4–50 keV. These results suggest that in both shocks, shock drift acceleration likely plays an important role in accelerating electrons in situ at 1 au. Such ICME-driven shocks could contribute to the formation of solar wind halo electrons at energies ≲2 keV, as well as the production of solar wind superhalo electrons at energies ≳2 keV in interplanetary space.

Multigrid approaches to non-linear diffusion problems on unstructured meshes

NASA Technical Reports Server (NTRS)

Mavriplis, Dimitri J.; Bushnell, Dennis M. (Technical Monitor)

2001-01-01

The efficiency of three multigrid methods for solving highly non-linear diffusion problems on two-dimensional unstructured meshes is examined. The three multigrid methods differ mainly in the manner in which the nonlinearities of the governing equations are handled. These comprise a non-linear full approximation storage (FAS) multigrid method which is used to solve the non-linear equations directly, a linear multigrid method which is used to solve the linear system arising from a Newton linearization of the non-linear system, and a hybrid scheme which is based on a non-linear FAS multigrid scheme, but employs a linear solver on each level as a smoother. Results indicate that all methods are equally effective at converging the non-linear residual in a given number of grid sweeps, but that the linear solver is more efficient in cpu time due to the lower cost of linear versus non-linear grid sweeps.

Burnett-Cattaneo continuum theory for shock waves.

PubMed

Holian, Brad Lee; Mareschal, Michel; Ravelo, Ramon

2011-02-01

We model strong shock-wave propagation, both in the ideal gas and in the dense Lennard-Jones fluid, using a refinement of earlier work, which accounts for the cold compression in the early stages of the shock rise by a nonlinear, Burnett-like, strain-rate dependence of the thermal conductivity, and relaxation of kinetic-temperature components on the hot, compressed side of the shock front. The relaxation of the disequilibrium among the three components of the kinetic temperature, namely, the difference between the component in the direction of a planar shock wave and those in the transverse directions, particularly in the region near the shock front, is accomplished at a much more quantitative level by a rigorous application of the Cattaneo-Maxwell relaxation equation to a reference solution, namely, the steady shock-wave solution of linear Navier-Stokes-Fourier theory, along with the nonlinear Burnett heat-flux term. Our new continuum theory is in nearly quantitative agreement with nonequilibrium molecular-dynamics simulations under strong shock-wave conditions, using relaxation parameters obtained from the reference solution. ©2011 American Physical Society

Shock-driven transition to turbulence: Emergence of power-law scaling

DOE PAGES

Olmstead, D.; Wayne, P.; Simons, D.; ...

2017-05-25

Here, we consider two cases of interaction between a planar shock and a cylindrical density interface. In the first case (planar normal shock), the axis of the gas cylinder is parallel to the shock front and baroclinic vorticity deposited by the shock is predominantly two dimensional (directed along the axis of the cylinder). In the second case, the cylinder is tilted, resulting in an oblique shock interaction and a fully-three-dimensional shock-induced vorticity field. Furthermore, the statistical properties of the flow for both cases are analyzed based on images from two orthogonal visualization planes, using structure functions of the intensity mapsmore » of fluorescent tracer premixed with heavy gas. And at later times, these structure functions exhibit power-law-like behavior over a considerable range of scales. Manifestation of this behavior is remarkably consistent in terms of dimensionless time τ defined based on Richtmyer's linear theory within the range of Mach numbers from 1.1 to 2.0 and the range of gas cylinder tilt angles with respect to the plane of the shock front (0–30°).« less

Collisionless Electrostatic Shock Modeling and Simulation

DTIC Science & Technology

2016-10-21

unlimited. PA#16490 Dissipation Controls Wave Train Under- and Over-damped Shocks – Under-damped: • Dissipation is weak, ripples persist. • High...Density Position – Over-damped: ● Strong dissipation damps ripples . ● Low Density Position 12 Position Distribution A. Approved for public release...distribution unlimited. PA#16490 Model Verification Comparison with Linearized Solution – Evolution of the First Ripple Wavelength: • Simulated

Kinetic theory for the ion humps at the foot of the Earth's bow shock

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jovanovic, D.; Krasnoselskikh, V. V.

2009-10-15

The nonlinear kinetic theory is presented for the ion acoustic perturbations at the foot of the Earth's quasiperpendicular bow shock, that is characterized by weakly magnetized electrons and unmagnetized ions. The streaming ions, due to the reflection of the solar wind ions from the shock, provide the free energy source for the linear instability of the acoustic wave. In the fully nonlinear regime, a coherent localized solution is found in the form of a stationary ion hump, which is traveling with the velocity close to the phase velocity of the linear mode. The structure is supported by the nonlinearities comingmore » from the increased population of the resonant beam ions, trapped in the self-consistent potential. As their size in the direction perpendicular to the local magnetic field is somewhat smaller that the electron Larmor radius and much larger that the Debye length, their spatial properties are determined by the effects of the magnetic field on weakly magnetized electrons. These coherent structures provide a theoretical explanation for the bipolar electric pulses, observed upstream of the shock by Polar and Cluster satellite missions.« less

Impact on the deuterium retention of simultaneous exposure of tungsten to a steady state plasma and transient heat cycling loads

NASA Astrophysics Data System (ADS)

Huber, A.; Sergienko, G.; Wirtz, M.; Steudel, I.; Arakcheev, A.; Brezinsek, S.; Burdakov, A.; Dittmar, T.; Esser, H. G.; Kreter, A.; Linke, J.; Linsmeier, Ch; Mertens, Ph; Möller, S.; Philipps, V.; Pintsuk, G.; Reinhart, M.; Schweer, B.; Shoshin, A.; Terra, A.; Unterberg, B.

2016-02-01

The impact on the deuterium retention of simultaneous exposure of tungsten to a steady-state plasma and transient cyclic heat loads has been studied in the linear PSI-2 facility with the main objective of qualifying tungsten (W) as plasma-facing material. The transient heat loads were applied by a high-energy laser, a Nd:YAG laser (λ = 1064 nm) with an energy per pulse of up to 32 J and a duration of 1 ms. A pronounced increase in the D retention by a factor of 13 has been observed during the simultaneous transient heat loads and plasma exposure. These data indicate that the hydrogen clustering is enhanced by the thermal shock exposures, as seen on the increased blister size due to mobilization and thermal production of defects during transients. In addition, the significant increase of the D retention during the simultaneous loads could be explained by an increased diffusion of D atoms into the W material due to strong temperature gradients during the laser pulse exposure and to an increased mobility of D atoms along the shock-induced cracks. Only 24% of the retained deuterium is located inside the near-surface layer (d<4 μm). Enhanced blister formation has been observed under combined loading conditions at power densities close to the threshold for damaging. Blisters are not mainly responsible for the pronounced increase of the D retention.

Precipitation and Release of Solar Energetic Particles from the Solar Coronal Magnetic Field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Ming; Zhao, Lulu, E-mail: mzhang@fit.edu

Most solar energetic particles (SEPs) are produced in the corona. They propagate through complex coronal magnetic fields subject to scattering and diffusion across the averaged field lines by turbulence. We examine the behaviors of particle transport using a stochastic 3D focused transport simulation in a potential field source surface model of coronal magnetic field. The model is applied to an SEP event on 2010 February 7. We study three scenarios of particle injection at (i) the compact solar flare site, (ii) the coronal mass ejection (CME) shock, and (iii) the EUV wave near the surface. The majority of particles injectedmore » on open field lines are able to escape the corona. We found that none of our models can explain the observations of wide longitudinal SEP spread without perpendicular diffusion. If the perpendicular diffusion is about 10% of what is derived from the random walk of field lines at the rate of supergranular diffusion, particles injected at the compact solar flare site can spread to a wide range of longitude and latitude, very similar to the behavior of particles injected at a large CME shock. Stronger pitch-angle scattering results in a little more lateral spread by holding the particles in the corona for longer periods of time. Some injected particles eventually end up precipitating onto the solar surface. Even with a very small perpendicular diffusion, the pattern of the particle precipitation can be quite complicated depending on the detailed small-scale coronal magnetic field structures, which could be seen with future sensitive gamma-ray telescopes.« less

Precipitation and Release of Solar Energetic Particles from the Solar Coronal Magnetic Field

NASA Astrophysics Data System (ADS)

Zhang, Ming; Zhao, Lulu

2017-09-01

Most solar energetic particles (SEPs) are produced in the corona. They propagate through complex coronal magnetic fields subject to scattering and diffusion across the averaged field lines by turbulence. We examine the behaviors of particle transport using a stochastic 3D focused transport simulation in a potential field source surface model of coronal magnetic field. The model is applied to an SEP event on 2010 February 7. We study three scenarios of particle injection at (I) the compact solar flare site, (II) the coronal mass ejection (CME) shock, and (III) the EUV wave near the surface. The majority of particles injected on open field lines are able to escape the corona. We found that none of our models can explain the observations of wide longitudinal SEP spread without perpendicular diffusion. If the perpendicular diffusion is about 10% of what is derived from the random walk of field lines at the rate of supergranular diffusion, particles injected at the compact solar flare site can spread to a wide range of longitude and latitude, very similar to the behavior of particles injected at a large CME shock. Stronger pitch-angle scattering results in a little more lateral spread by holding the particles in the corona for longer periods of time. Some injected particles eventually end up precipitating onto the solar surface. Even with a very small perpendicular diffusion, the pattern of the particle precipitation can be quite complicated depending on the detailed small-scale coronal magnetic field structures, which could be seen with future sensitive gamma-ray telescopes.

Electron injection by whistler waves in non-relativistic shocks

NASA Astrophysics Data System (ADS)

Riquelme, Mario A.; Spitkovsky, Anatoly

2012-04-01

Radio and X-ray observations of shocks in young supernova remnants (SNRs) reveal electron acceleration to non-thermal, ultra-relativistic energies (~ 10-100 TeV). This acceleration is usually assumed to happen via the diffusive shock acceleration (DSA) mechanism. However, the way in which electrons are initially energized or 'injected' into this acceleration process is an open question and the main focus of this work. We present our study of electron acceleration in nonrelativistic shocks using 2D and 3D particle-in-cell (PIC) plasma simulations. Our simulations show that significant non-thermal acceleration happens due to the growth of oblique whistler waves in the foot of quasi-perpendicular shocks. The obtained electron energy distributions show power law tails with spectral indices up to α ~ 3-4. Also, 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 requires the shock waves to have fairly low Alfvénic Mach numbers, MA <20, which is consistent with the theoretical conditions for the growth of whistler waves in the shock foot (MA <(mi/me)1/2). Thus, if this 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 accelerated ions in these environments, so electron and ion acceleration in SNR shocks must be interconnected.

The role of cross-shock potential on pickup ion shock acceleration in the framework of focused transport theory

DOE PAGES

Zuo, Pingbing; Zhang, Ming; Rassoul, Hamid K.

2013-10-03

The focused transport theory is appropriate to describe the injection and acceleration of low-energy particles at shocks as an extension of diffusive shock acceleration (DSA). In this investigation, we aim to characterize the role of cross-shock potential (CSP) originated in the charge separation across the shock ramp on pickup ion (PUI) acceleration at various types of shocks with a focused transport model. The simulation results of energy spectrum and spatial density distribution for the cases with and without CSP added in the model are compared. With sufficient acceleration time, the focused transport acceleration finally falls into the DSA regime withmore » the power-law spectral index equal to the solution of the DSA theory. The CSP can affect the shape of the spectrum segment at lower energies, but it does not change the spectral index of the final power-law spectrum at high energies. It is found that the CSP controls the injection efficiency which is the fraction of PUIs reaching the DSA regime. A stronger CSP jump results in a dramatically improved injection efficiency. Our simulation results also show that the injection efficiency of PUIs is mass-dependent, which is lower for species with a higher mass. Additionally, the CSP is able to enhance the particle reflection upstream to produce a stronger intensity spike at the shock front. Lastly, we conclude that the CSP is a non-negligible factor that affects the dynamics of PUIs at shocks.« less

On magnetic field amplification and particle acceleration near non-relativistic astrophysical shocks: particles in MHD cells simulations

NASA Astrophysics Data System (ADS)

van Marle, Allard Jan; Casse, Fabien; Marcowith, Alexandre

2018-01-01

We present simulations of magnetized astrophysical shocks taking into account the interplay between the thermal plasma of the shock and suprathermal particles. Such interaction is depicted by combining a grid-based magnetohydrodynamics description of the thermal fluid with particle in cell techniques devoted to the dynamics of suprathermal particles. This approach, which incorporates the use of adaptive mesh refinement features, is potentially a key to simulate astrophysical systems on spatial scales that are beyond the reach of pure particle-in-cell simulations. We consider in this study non-relativistic shocks with various Alfvénic Mach numbers and magnetic field obliquity. We recover all the features of both magnetic field amplification and particle acceleration from previous studies when the magnetic field is parallel to the normal to the shock. In contrast with previous particle-in-cell-hybrid simulations, we find that particle acceleration and magnetic field amplification also occur when the magnetic field is oblique to the normal to the shock but on larger time-scales than in the parallel case. We show that in our simulations, the suprathermal particles are experiencing acceleration thanks to a pre-heating process of the particle similar to a shock drift acceleration leading to the corrugation of the shock front. Such oscillations of the shock front and the magnetic field locally help the particles to enter the upstream region and to initiate a non-resonant streaming instability and finally to induce diffuse particle acceleration.

Conical Lens for 5-Inch/54 Gun Launched Missile

DTIC Science & Technology

1981-06-01

Propagation, Interferenceand Diffraction of Light, 2nd ed. (revised), p. 121-124, Pergamon Press, 1964. 10. Anton , Howard, Elementary Linear Algebra , p. 1-21...equations is nonlinear in x, but is linear in the coefficients. Therefore, the techniques of linear algebra can be used on equation (F-13). The method...This thesis assumes the air to be homogenous, isotropic, linear , time indepen- dent (HILT) and free of shock waves in order to investigate the

Downstream boundary effects on the frequency of self-excited oscillations in transonic diffuser flows

NASA Astrophysics Data System (ADS)

Hsieh, T.

1986-10-01

Investigation of downstream boundary effects on the frequency of self-excited oscillations in two-dimensional, separated transonic diffuser flows were conducted numerically by solving the compressible, Reynolds-averaged, thin-layer Navier-Stokes equation with two equation turbulence models. It was found that the flow fields are very sensitive to the location of the downstream boundary. Extension of the diffuser downstream boundary significantly reduces the frequency and amplitude of oscillations for pressure, velocity, and shock. The existence of a suction slot in the experimental setpup obscures the physical downstream boundary and therefore presents a difficulty for quantitative comparisons between computation and experiment.

A computationally efficient scheme for the non-linear diffusion equation

NASA Astrophysics Data System (ADS)

Termonia, P.; Van de Vyver, H.

2009-04-01

This Letter proposes a new numerical scheme for integrating the non-linear diffusion equation. It is shown that it is linearly stable. Some tests are presented comparing this scheme to a popular decentered version of the linearized Crank-Nicholson scheme, showing that, although this scheme is slightly less accurate in treating the highly resolved waves, (i) the new scheme better treats highly non-linear systems, (ii) better handles the short waves, (iii) for a given test bed turns out to be three to four times more computationally cheap, and (iv) is easier in implementation.

On solutions of the fifth-order dispersive equations with porous medium type non-linearity

NASA Astrophysics Data System (ADS)

Kocak, Huseyin; Pinar, Zehra

2018-07-01

In this work, we focus on obtaining the exact solutions of the fifth-order semi-linear and non-linear dispersive partial differential equations, which have the second-order diffusion-like (porous-type) non-linearity. The proposed equations were not studied in the literature in the sense of the exact solutions. We reveal solutions of the proposed equations using the classical Riccati equations method. The obtained exact solutions, which can play a key role to simulate non-linear waves in the medium with dispersion and diffusion, are illustrated and discussed in details.

Linear diffusion model dating of cinder cones in Central Anatolia, Turkey

NASA Astrophysics Data System (ADS)

O'Sadnick, L. G.; Reid, M. R.; Cline, M. L.; Cosca, M. A.; Kuscu, G.

2013-12-01

The progressive decrease in slope angle, cone height and cone height/width ratio over time provides the basis for geomorphic dating of cinder cones using linear diffusion models. Previous research using diffusion models to date cinder cones has focused on the cone height/width ratio as the basis for dating cones of unknown age [1,2]. Here we apply linear diffusion models to dating cinder cones. A suite of 16 cinder cones from the Hasandağ volcano area of the Neogene-Quaternary Central Anatolian Volcanic Zone, for which samples are available, were selected for morphologic dating analysis. New 40Ar/39Ar dates for five of these cones range from 62 × 4 to 517 × 9 ka. Linear diffusion models were used to model the erosional degradation of each cone. Diffusion coefficients (κ) for the 5 cinder cones with known ages were constrained by comparing various modeled slope profiles to the current slope profile. The resulting κ is 7.5×0.5 m2kyr-1. Using this κ value, eruption ages were modeled for the remaining 11 cinder cones and range from 53×3 to 455×30 ka. These ages are within the range of ages previously reported for cinder cones in the Hasandağ region. The linear diffusion model-derived ages are being compared to additional new 40Ar/39Ar dates in order to further assess the applicability of morphological dating to constrain the ages of cinder cones. The relatively well-constrained κ value we obtained by applying the linear diffusion model to cinder cones that range in age by nearly 500 ka suggests that this model can be used to date cinder cones. This κ value is higher than the well-established value of κ =3.9 for a cinder cone in a similar climate [3]. Therefore our work confirms the importance of determining appropriate κ values from nearby cones with known ages. References 1. C.A. Wood, J. Volcanol. Geotherm. Res. 8, 137 (1980) 2. D.M. Wood, M.F. Sheridan, J. Volcanol. Geotherm. Res. 83, 241 (1998) 3. J.D. Pelletier, M.L. Cline, Geology 35, 1067 (2007)

Lack of thermal energy in superbubbles: hint of cosmic rays?

NASA Astrophysics Data System (ADS)

Gupta, Siddhartha; Nath, Biman B.; Sharma, Prateek; Eichler, David

2018-01-01

Using analytic methods and 1D two-fluid simulations, we study the effect of cosmic rays (CRs) on the dynamics of interstellar superbubbles (ISBs) driven by multiple supernovae (SNe)/stellar winds in OB associations. In addition to CR advection and diffusion, our models include thermal conduction and radiative cooling. We find that CR injection at the reverse shock or within a central wind-driving region can affect the thermal profiles of ISBs and hence their X-ray properties. Even if a small fraction (10-20 per cent) of the total mechanical power is injected into CRs, a significant fraction of the ram pressure at the reverse shock can be transferred to CRs. The energy transfer becomes efficient if (1) the reverse shock gas Mach number exceeds a critical value (Mth ≳ 12) and (2) the CR acceleration time-scale τacc ∼ κcr/v2 is shorter than the dynamical time, where κcr is a CR diffusion coefficient and v is the upstream velocity. We show that CR affected bubbles can exhibit a volume-averaged hot gas temperature 1-5 × 106 K, lower by a factor of 2 - 10 than without CRs. Thus, CRs can potentially solve the long-standing problem of the observed low ISB temperatures.

Simulation of Cosmic Ray Acceleration, Propagation and Interaction in SNR Environment

NASA Astrophysics Data System (ADS)

Lee, S. H.; Kamae, T.; Ellison, D. C.

2007-07-01

Recent studies of young supernova remnants (SNRs) with Chandra, XMM, Suzaku and HESS have revealed complex morphologies and spectral features of the emission sites. The critical question of the relative importance of the two competing gamma-ray emission mechanisms in SNRs; inverse-Compton scattering by high-energy electrons and pion production by energetic protons, may be resolved by GLAST-LAT. To keep pace with the improved observations, we are developing a 3D model of particle acceleration, diffusion, and interaction in a SNR where broad-band emission from radio to multi-TeV energies, produced by shock accelerated electrons and ions, can be simulated for a given topology of shock fronts, magnetic field, and ISM densities. The 3D model takes as input, the particle spectra predicted by a hydrodynamic simulation of SNR evolution where nonlinear diffusive shock acceleration is coupled to the remnant dynamics (e.g., Ellison, Decourchelle & Ballet; Ellison & Cassam-Chenai Ellison, Berezhko & Baring). We will present preliminary models of the Galactic Ridge SNR RX J1713-3946 for selected choices of SNR parameters, magnetic field topology, and ISM density distributions. When constrained by broad-band observations, our models should predict the extent of coupling between spectral shape and morphology and provide direct information on the acceleration efficiency of cosmic-ray electrons and ions in SNRs.

Thermal and ultrasonic evaluation of porosity in composite laminates

NASA Technical Reports Server (NTRS)

Johnston, Patrick H.; Winfree, William P.; Long, Edward R., Jr.; Kullerd, Susan M.; Nathan, N.; Partos, Richard D.

1992-01-01

The effects of porosity on damage incurred by low-velocity impact are investigated. Specimens of graphite/epoxy composite were fabricated with various volume fractions of voids. The void fraction was independently determined using optical examination and acid resin digestion methods. Thermal diffusivity and ultrasonic attenuation were measured, and these results were related to the void volume fraction. The relationship between diffusivity and fiber volume fraction was also considered. The slope of the ultrasonic attenuation coefficient was found to increase linearly with void content, and the diffusivity decreased linearly with void volume fraction, after compensation for an approximately linear dependence on the fiber volume fraction.

ION INJECTION AT QUASI-PARALLEL SHOCKS SEEN BY THE CLUSTER SPACECRAFT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johlander, A.; Vaivads, A.; Khotyaintsev, Yu. V.

2016-01-20

Collisionless shocks in space plasma are known to be capable of accelerating ions to very high energies through diffusive shock acceleration (DSA). This process requires an injection of suprathermal ions, but the mechanisms producing such a suprathermal ion seed population are still not fully understood. We study acceleration of solar wind ions resulting from reflection off short large-amplitude magnetic structures (SLAMSs) in the quasi-parallel bow shock of Earth using in situ data from the four Cluster spacecraft. Nearly specularly reflected solar wind ions are observed just upstream of a SLAMS. The reflected ions are undergoing shock drift acceleration (SDA) andmore » obtain energies higher than the solar wind energy upstream of the SLAMS. Our test particle simulations show that solar wind ions with lower energy are more likely to be reflected off the SLAMS, while high-energy ions pass through the SLAMS, which is consistent with the observations. The process of SDA at SLAMSs can provide an effective way of accelerating solar wind ions to suprathermal energies. Therefore, this could be a mechanism of ion injection into DSA in astrophysical plasmas.« less

Studies of ion kinetic effects in OMEGA shock-driven implosions using fusion burn imaging

NASA Astrophysics Data System (ADS)

Rosenberg, M. J.; Seguin, F. H.; Rinderknecht, H. G.; Sio, H.; Zylstra, A. B.; Gatu Johnson, M.; Frenje, J. A.; Li, C. K.; Petrasso, R. D.; Amendt, P. A.; Wilks, S. C.; Zimmerman, G.; Hoffman, N. M.; Kagan, G.; Molvig, K.; Glebov, V. Yu.; Stoeckl, C.; Marshall, F. J.; Seka, W.; Delettrez, J. A.; Sangster, T. C.; Betti, R.; Meyerhofer, D. D.; Atzeni, S.; Nikroo, A.

2014-10-01

Ion kinetic effects have been inferred in a series of shock-driven implosions at OMEGA from an increasing yield discrepancy between observations and hydrodynamic simulations as the ion-ion mean free path increases. To more precisely identify the nature and impact of ion kinetic effects, spatial burn profile measurements of DD and D3He reactions in these D3He-filled shock-driven implosions are presented and contrasted to both purely hydrodynamic models and models that include ion kinetic effects. It is shown that in implosions where the ion mean free path is equal to or greater than the size of the fuel region, purely hydrodynamic models fail to capture the observed burn profiles, while a model that includes ion diffusion is able to recover the observed burn profile shape. These results further elucidate the ion kinetic mechanisms that are present under long mean-free-path conditions after shock convergence in both shock-driven and ablatively-driven implosions. This work was supported in part by the U.S. DOE, NLUF, LLE, and LLNL.

X-ray Emission from Supernovae in Dense Circumstellar Matter Environments: a Search for Collisionless Shocks

NASA Technical Reports Server (NTRS)

Ofek, E. O.; Fox, D.; Cenko, Stephen B.; Sullivan, M; Gnat, O.; Frail, D. A.; Horesh, A.; Corsi, A.; Quimby, R. M.; Gehrels, N.;

Systematic search for high-energy gamma-ray emission from bow shocks of runaway stars

DOE PAGES

Schulz, A.; Ackermann, M.; Buehler, R.; ...

2014-05-01

Context. It has been suggested that the bow shocks of runaway stars are sources of high-energy gamma rays (E > 100 MeV). Theoretical models predicting high-energy gamma-ray emission from these sources were followed by the first detection of non-thermal radio emission from the bow shock of BD+43°3654 and non-thermal X-ray emission from the bow shock of AE Aurigae. Aims. We perform the first systematic search for MeV and GeV emission from 27 bow shocks of runaway stars using data collected by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope (Fermi). Methods. We analysed 57 months of Fermi-LATmore » data at the positions of 27 bow shocks of runaway stars extracted from the Extensive stellar BOw Shock Survey catalogue (E-BOSS). A likelihood analysis was performed to search for gamma-ray emission that is not compatible with diffuse background or emission from neighbouring sources and that could be associated with the bow shocks. Results. None of the bow shock candidates is detected significantly in the Fermi-LAT energy range. We therefore present upper limits on the high-energy emission in the energy range from 100MeV to 300 GeV for 27 bow shocks of runaway stars in four energy bands. For the three cases where models of the high-energy emission are published we compare our upper limits to the modelled spectra. Our limits exclude the model predictions for ζ Ophiuchi by a factor ≈ 5.« less

VLF waves in the foreshock

NASA Technical Reports Server (NTRS)

Strangeway, R. J.; Crawford, G. K.

1995-01-01

Plasma waves observed in the VLF range upstream of planetary bow shocks not only modify the particle distributions, but also provide important information about the acceleration processes that occur at the bow shock. Electron plasma oscillations observed near the tangent field line in the electron foreshock are generated by electrons reflected at the bow shock through a process that has been referred to as Fast Fermi acceleration. Fast Fermi acceleration is the same as shock-drift acceleration, which is one of the mechanisms by which ions are energized at the shock. We have generated maps of the VLF emissions upstream of the Venus bow shock, using these maps to infer properties of the shock energization processes. We find that the plasma oscillations extend along the field line up to a distance that appears to be controlled by the shock scale size, implying that shock curvature restricsts the flux and energy of reflected electrons. We also find that the ion acoustic waves are observed in the ion foreshock, but at Venus these emissions are not detected near the ULF forshock boundary. Through analogy with terrestrial ion observations, this implies that the ion acoustic waves are not generated by ion beams, but are instead generated by diffuse ion distributions found deep within the ion foreshock. However, since the shock is much smaller at Venus, and there is no magnetosphere, we might expect ion distributions within the ion foreshock to be different than at the Earth. Mapping studies of the terrestrial foreshock similar to those carried out at Venus appear to be necessary to determine if the inferences drawn from Venus data are applicable to other foreshocks.

Experimental dynamic response of a two-dimensional, Mach 2.7, mixed compression inlet

NASA Technical Reports Server (NTRS)

Baumbick, R. J.; Neiner, G. H.; Cole, G. L.

1972-01-01

A test program was conducted on a two-dimensional supersonic inlet. Internal disturbances in diffuser exit mass flow were produced by oscillating overboard bypass doors. Open-loop dynamic responses of shock position, throat exit and diffuser exit static pressures are presented. The steady-state and dynamic coupling between ducts were also obtained. The experimental results from the two-dimensional inlet are compared to results from a similar size axisymmetric inlet and also to a transfer function synthesis program.

Transmission of singularities through a shock wave and the sound generation

NASA Technical Reports Server (NTRS)

Ting, L.

1974-01-01

The interaction of a plane shock wave of finite strength with a vortex line, point vortex, doublet or quadrupole of weak strength is studied. Based upon the physical condition that a free vortex line cannot support a pressure difference, rules are established which define the change of the linear intensity of the segment of the vortex line after its passage through the shock. The rules for point vortex, doublet, and quadrupole are then established as limiting cases. These rules can be useful for the construction of the solution of the entire flow field and for its physical interpretation. However, the solution can be obtained directly by the technique developed for shock diffraction problems. Explicit solutions and the associated sound generation are obtained for the passage of a point vortex through the shock wave.

Shock ion acceleration by an ultrashort circularly polarized laser pulse via relativistic transparency in an exploded target.

PubMed

Kim, Young-Kuk; Cho, Myung-Hoon; Song, Hyung Seon; Kang, Teyoun; Park, Hyung Ju; Jung, Moon Youn; Hur, Min Sup

2015-10-01

We investigated ion acceleration by an electrostatic shock in an exploded target irradiated by an ultrashort, circularly polarized laser pulse by means of one- and three-dimensional particle-in-cell simulations. We discovered that the laser field penetrating via relativistic transparency (RT) rapidly heated the upstream electron plasma to enable the formation of a high-speed electrostatic shock. Owing to the RT-based rapid heating and the fast compression of the initial density spike by a circularly polarized pulse, a new regime of the shock ion acceleration driven by an ultrashort (20-40 fs), moderately intense (1-1.4 PW) laser pulse is envisaged. This regime enables more efficient shock ion acceleration under a limited total pulse energy than a linearly polarized pulse with crystal laser systems of λ∼1μm.

Enhanced kidney stone fragmentation by short delay tandem conventional and modified lithotriptor shock waves: a numerical analysis.

PubMed

Tham, Leung-Mun; Lee, Heow Pueh; Lu, Chun

2007-07-01

We evaluated the effectiveness of modified lithotriptor shock waves using computer models. Finite element models were used to simulate the propagation of lithotriptor shock waves in human renal calculi in vivo. Kidney stones were assumed to be spherical, homogeneous, isotropic and linearly elastic, and immersed in a continuum fluid. Single and tandem shock wave pulses modified to intensify the collapse of cavitation bubbles near the stone surface to increase fragmentation efficiency and suppress the expansion of intraluminal bubbles for decreased vascular injury were analyzed. The effectiveness of the modified shock waves was assessed by comparing the states of loading in the renal calculi induced by these shock waves to those produced by conventional shock waves. Our numerical simulations revealed that modified shock waves produced marginally lower stresses in spherical renal calculi than those produced by conventional shock waves. Tandem pulses of conventional or modified shock waves produced peak stresses in the front and back halves of the renal calculi. However, the single shock wave pulses generated significant peak stresses in only the back halves of the renal calculi. Our numerical simulations suggest that for direct stress wave induced fragmentation modified shock waves should be as effective as conventional shock waves for fragmenting kidney stones. Also, with a small interval of 20 microseconds between the pulses tandem pulse lithotripsy using modified or conventional shock waves could be considerably more effective than single pulse lithotripsy for fragmenting kidney stones.

Computational Analyses in Support of Sub-scale Diffuser Testing for the A-3 Facility. Part 1; Steady Predictions

NASA Technical Reports Server (NTRS)

Allgood, Daniel C.; Graham, Jason S.; Ahuja, Vineet; Hosangadi, Ashvin

2008-01-01

Simulation technology can play an important role in rocket engine test facility design and development by assessing risks, providing analysis of dynamic pressure and thermal loads, identifying failure modes and predicting anomalous behavior of critical systems. Advanced numerical tools assume greater significance in supporting testing and design of high altitude testing facilities and plume induced testing environments of high thrust engines because of the greater inter-dependence and synergy in the functioning of the different sub-systems. This is especially true for facilities such as the proposed A-3 facility at NASA SSC because of a challenging operating envelope linked to variable throttle conditions at relatively low chamber pressures. Facility designs in this case will require a complex network of diffuser ducts, steam ejector trains, fast operating valves, cooling water systems and flow diverters that need to be characterized for steady state performance. In this paper, we will demonstrate with the use of CFD analyses s advanced capability to evaluate supersonic diffuser and steam ejector performance in a sub-scale A-3 facility at NASA Stennis Space Center (SSC) where extensive testing was performed. Furthermore, the focus in this paper relates to modeling of critical sub-systems and components used in facilities such as the A-3 facility. The work here will address deficiencies in empirical models and current CFD analyses that are used for design of supersonic diffusers/turning vanes/ejectors as well as analyses for confined plumes and venting processes. The primary areas that will be addressed are: (1) supersonic diffuser performance including analyses of thermal loads (2) accurate shock capturing in the diffuser duct; (3) effect of turning duct on the performance of the facility (4) prediction of mass flow rates and performance classification for steam ejectors (5) comparisons with test data from sub-scale diffuser testing and assessment of confidence levels in CFD based flowpath modeling of the facility. The analyses tools used here expand on the multi-element unstructured CFD which has been tailored and validated for impingement dynamics of dry plumes, complex valve/feed systems, and high pressure propellant delivery systems used in engine and component test stands at NASA SSC. The analyses performed in the evaluation of the sub-scale diffuser facility explored several important factors that influence modeling and understanding of facility operation such as (a) importance of modeling the facility with Real Gas approximation, (b) approximating the cluster of steam ejector nozzles as a single annular nozzle, (c) existence of mixed subsonic/supersonic flow downstream of the turning duct, and (d) inadequacy of two-equation turbulence models in predicting the correct pressurization in the turning duct and expansion of the second stage steam ejectors. The procedure used for modeling the facility was as follows: (i) The engine, test cell and first stage ejectors were simulated with an axisymmetric approximation (ii) the turning duct, second stage ejectors and the piping downstream of the second stage ejectors were analyzed with a three-dimensional simulation utilizing a half-plane symmetry approximation. The solution i.e. primitive variables such as pressure, velocity components, temperature and turbulence quantities were passed from the first computational domain and specified as a supersonic boundary condition for the second simulation. (iii) The third domain comprised of the exit diffuser and the region in the vicinity of the facility (primary included to get the correct shock structure at the exit of the facility and entrainment characteristics). The first set of simulations comprising the engine, test cell and first stage ejectors was carried out both as a turbulent real gas calculation as well as a turbulent perfect gas calculation. A comparison for the two cases (Real Turbulent and Perfect gas turbulent) of the Ma Number distribution and temperature distributions are shown in Figures 1 and 2 respectively. The Mach Number distribution shows small yet distinct differences between the two cases such as locations of shocks/shock reflections and a slightly different impingement point on the wall of the diffuser from the expansion at the exit of the nozzle. Similarly the temperature distribution indicates different flow recirculation patterns in the test cell. Both cases capture all the essential flow phenomena such as the shock-boundary layer interaction, plume expansion, expansion of the first stage ejectors, mixing between the engine plume and the first stage ejector flow and pressurization due to the first stage ejectors. The final paper will discuss thermal loads on the walls of the diffuser and cooling mechanisms investigated.

Stochastic field-line wandering in magnetic turbulence with shear. I. Quasi-linear theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shalchi, A.; Negrea, M.; Petrisor, I.

2016-07-15

We investigate the random walk of magnetic field lines in magnetic turbulence with shear. In the first part of the series, we develop a quasi-linear theory in order to compute the diffusion coefficient of magnetic field lines. We derive general formulas for the diffusion coefficients in the different directions of space. We like to emphasize that we expect that quasi-linear theory is only valid if the so-called Kubo number is small. We consider two turbulence models as examples, namely, a noisy slab model as well as a Gaussian decorrelation model. For both models we compute the field line diffusion coefficientsmore » and we show how they depend on the aforementioned Kubo number as well as a shear parameter. It is demonstrated that the shear effect reduces all field line diffusion coefficients.« less

Reaction-diffusion systems coupled at the boundary and the Morse-Smale property

NASA Astrophysics Data System (ADS)

Broche, Rita de Cássia D. S.; de Oliveira, Luiz Augusto F.

We study an one-dimensional nonlinear reaction-diffusion system coupled on the boundary. Such system comes from modeling problems of temperature distribution on two bars of same length, jointed together, with different diffusion coefficients. We prove the transversality property of unstable and stable manifolds assuming all equilibrium points are hyperbolic. To this end, we write the system as an equation with noncontinuous diffusion coefficient. We then study the nonincreasing property of the number of zeros of a linearized nonautonomous equation as well as the Sturm-Liouville properties of the solutions of a linear elliptic problem.

Is the acceleration of anomalous cosmic rays affected by the geometry of the termination shock?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Senanayake, U. K.; Florinski, V., E-mail: uks0001@uah.edu, E-mail: vaf0001@uah.edu

2013-12-01

Historically, anomalous cosmic rays (ACRs) were thought to be accelerated at the solar-wind termination shock (TS) by the diffusive shock acceleration process. When Voyager 1 crossed the TS in 2004, the measured ACR spectra did not match the theoretical prediction of a continuous power law, and the source of the high-energy ACRs was not observed. When the Voyager 2 crossed the TS in 2007, it produced similar results. Several possible explanations have since appeared in the literature, but we follow the suggestion that ACRs are still accelerated at the shock, only away from the Voyager crossing points. To investigate thismore » hypothesis closer, we study ACR acceleration using a three-dimensional, non-spherical model of the heliosphere that is axisymmetric with respect to the interstellar flow direction. We then compare the results with those obtained for a spherical TS. A semi-analytic model of the plasma and magnetic field backgrounds is developed to permit an investigation over a wide range of parameters under controlled conditions. The model is applied to helium ACRs, whose phase-space trajectories are stochastically integrated backward in time until a pre-specified, low-energy boundary, taken to be 0.5 MeV n{sup –1} (the so-called injection energy), is reached. Our results show that ACR acceleration is quite efficient on the heliotail-facing part of the TS. For small values of the perpendicular diffusion coefficient, our model yields a positive intensity gradient between the TS and about midway through the heliosheath, in agreement with the Voyager observations.« less

Apparent diffusion coefficient measurement in a moving phantom simulating linear respiratory motion.

PubMed

Kwee, Thomas C; Takahara, Taro; Muro, Isao; Van Cauteren, Marc; Imai, Yutaka; Nievelstein, Rutger A J; Mali, Willem P T M; Luijten, Peter R

2010-10-01

The aim of this study was to examine the effect of simulated linear respiratory motion on apparent diffusion coefficient (ADC) measurements. Six rectangular test tubes (14 × 92 mm) filled with either water, tomato ketchup, or mayonnaise were positioned in a box containing agarose gel. This box was connected to a double-acting pneumatic cylinder, capable of inducing periodic linear motion in the long-axis direction of the magnetic bore (23-mm stroke). Diffusion-weighted magnetic resonance imaging was performed for both the static and moving phantoms, and ADC measurements were made in the six test tubes in both situations. In the three test tubes whose long axes were parallel to the direction of motion, ADCs agreed well between the moving and static phantom situations. However, in two test tubes that were filled with fluids that had a considerably lower diffusion coefficient than the surrounding agarose gel, and whose long axes were perpendicular to the direction of motion, the ADCs agreed poorly between the moving and static phantom situations. ADC measurements of large homogeneous structures are not affected by linear respiratory motion. However, ADC measurements of inhomogeneous or small structures are affected by linear respiratory motion due to partial volume effects.

Nanoparticle Motion in Entangled Melts of Linear and Nonconcatenated Ring Polymers [Nanoparticle Motion in Entangled Melts of Non-Concatenated Ring Polymers].

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ge, Ting; Kalathi, Jagannathan T.; Halverson, Jonathan D.

The motion of nanoparticles (NPs) in entangled melts of linear polymers and non-concatenated ring polymers are compared by large-scale molecular dynamics simulations. The comparison provides a paradigm for the effects of polymer architecture on the dynamical coupling between NPs and polymers in nanocomposites. Strongly suppressed motion of NPs with diameter d larger than the entanglement spacing a is observed in a melt of linear polymers before the onset of Fickian NP diffusion. This strong suppression of NP motion occurs progressively as d exceeds a, and is related to the hopping diffusion of NPs in the entanglement network. In contrast tomore » the NP motion in linear polymers, the motion of NPs with d > a in ring polymers is not as strongly suppressed prior to Fickian diffusion. The diffusion coefficient D decreases with increasing d much slower in entangled rings than in entangled linear chains. NP motion in entangled non-concatenated ring polymers is understood through a scaling analysis of the coupling between NP motion and the self-similar entangled dynamics of ring polymers.« less

Nanoparticle Motion in Entangled Melts of Linear and Nonconcatenated Ring Polymers [Nanoparticle Motion in Entangled Melts of Non-Concatenated Ring Polymers].

DOE PAGES

Ge, Ting; Kalathi, Jagannathan T.; Halverson, Jonathan D.; ...

2017-02-13

The motion of nanoparticles (NPs) in entangled melts of linear polymers and non-concatenated ring polymers are compared by large-scale molecular dynamics simulations. The comparison provides a paradigm for the effects of polymer architecture on the dynamical coupling between NPs and polymers in nanocomposites. Strongly suppressed motion of NPs with diameter d larger than the entanglement spacing a is observed in a melt of linear polymers before the onset of Fickian NP diffusion. This strong suppression of NP motion occurs progressively as d exceeds a, and is related to the hopping diffusion of NPs in the entanglement network. In contrast tomore » the NP motion in linear polymers, the motion of NPs with d > a in ring polymers is not as strongly suppressed prior to Fickian diffusion. The diffusion coefficient D decreases with increasing d much slower in entangled rings than in entangled linear chains. NP motion in entangled non-concatenated ring polymers is understood through a scaling analysis of the coupling between NP motion and the self-similar entangled dynamics of ring polymers.« less

Universal shocks in the Wishart random-matrix ensemble.

PubMed

Blaizot, Jean-Paul; Nowak, Maciej A; Warchoł, Piotr

2013-05-01

We show that the derivative of the logarithm of the average characteristic polynomial of a diffusing Wishart matrix obeys an exact partial differential equation valid for an arbitrary value of N, the size of the matrix. In the large N limit, this equation generalizes the simple inviscid Burgers equation that has been obtained earlier for Hermitian or unitary matrices. The solution, through the method of characteristics, presents singularities that we relate to the precursors of shock formation in the Burgers equation. The finite N effects appear as a viscosity term in the Burgers equation. Using a scaling analysis of the complete equation for the characteristic polynomial, in the vicinity of the shocks, we recover in a simple way the universal Bessel oscillations (so-called hard-edge singularities) familiar in random-matrix theory.

Shock Waves Propagation in Scope of the Nonlocal Theory of Dynamical Plasticity

NASA Astrophysics Data System (ADS)

Khantuleva, Tatyana A.

2004-07-01

From the point of view of the modern statistical mechanics the problems on shock compression of solids require a reformulation in terms of highly nonequilibrium effects arising inside the wave front. The self-organization during the multiscale and multistage momentum and energy exchange are originated by the correlation function. The theory of dynamic plasticity has been developed by the author on the base of the self-consistent nonlocal hydrodynamic approach had been applied to the shock wave propagation in solids. Nonlocal balance equations describe both the reversible wave type transport at the initial stage and the diffusive (dissipative) one in the end. The involved inverse influence of the mesoeffects on the wave propagation makes the formulation of problems self-consistent and involves a concept of the cybernetic control close-loop.

Terminal-shock and restart control of a Mach 2.5, axisymmetric, mixed compression inlet with 40 percent internal contraction. [wind tunnel tests

NASA Technical Reports Server (NTRS)

Baumbick, R. J.

1974-01-01

Results of experimental tests conducted on a supersonic, mixed-compression, axisymmetric inlet are presented. The inlet is designed for operation at Mach 2.5 with a turbofan engine (TF-30). The inlet was coupled to either a choked orifice plate or a long duct which had a variable-area choked exit plug. Closed-loop frequency responses of selected diffuser static pressures used in the terminal-shock control system are presented. Results are shown for Mach 2.5 conditions with the inlet coupled to either the choked orifice plate or the long duct. Inlet unstart-restart traces are also presented. High-response inlet bypass doors were used to generate an internal disturbance and also to achieve terminal-shock control.

Downstream energetic proton and alpha particles during quasi-parallel interplanetary shock events

NASA Technical Reports Server (NTRS)

Tan, L. C.; Mason, G. M.; Gloeckler, G.; Ipavich, F. M.

1988-01-01

This paper considers the energetic particle populations in the downstream region of three quasi-parallel interplanetary shock events, which was explored using the ISEE 3 Ultra Low Energy Charge Analyzer sensor, which unambiguously identifies protons and alpha particles using the electrostatic deflection versus residual energy technique. The downstream particles were found to exhibit anisotropies due largely to convection in the solar wind. The spectral indices of the proton and the alpha-particle distribution functions were found to be remarkably constant during the downstream period, being generally insensitive to changes in particle flux levels, magnetic field direction, and solar wind densities. In two of the three events, the proton and the alpha spectra were the same throughout the entire downstream period, supporting the prediction of diffusive shock acceleration theory.

The Shock and Vibration Digest. Volume 18, Number 12

DTIC Science & Technology

1986-12-01

practical msthods for fracture mechanics analysis. Linear elastic methods can yield useful results. Elas- dc-plasdc methods are becoming useful with...geometry factors. Fracture mechanics analysis based on linear elastic concepts developed in the 1960s has become established during the last decade as...2) is slightly conservative [2,3]. Materials that ran be treated with linear elastic fracture mechanics usually belong in this category. No

Existence regimes for shocks in inhomogeneous magneto-plasmas having entropy

NASA Astrophysics Data System (ADS)

Iqbal, Javed; Yaqub Khan, M.

2018-04-01

The finding of connection of plasma density and temperature with entropy gives an incitement to study different plasma models with respect to entropy. Nonlinear dissipative one- and two-dimensional structures (shocks) are investigated in nonuniform magnetized plasma with respect to entropy. The dissipation comes in the medium through ion-neutral collisions. The linear dispersion relation is derived. The Korteweg-deVries-Burgers and Kadomtsev-Petviashvili-Burgers equations are derived for nonlinear drift waves in 1-D and 2-D by employing the drift approximation. It is found that vd/u ( vd is the diamagnetic drift velocity and u is the velocity of nonlinear structure) plays a significant role in the shock formation. It is also found that entropy has a significant effect on the strength of shocks. It is noticed that v d/u determines the rarefactive and compressive nature of the shocks. It is observed that upper and lower bounds exist for the shock velocity. It is also observed that the existing regimes for both one- and two-dimensional shocks for kappa distributed electrons are different from shocks with Cairns distributed electrons. Both rarefactive and compressive shocks are found for the 1-D drift waves with kappa distributed electrons. Interestingly, it is noticed that entropy enhances the strength of one- and two-dimensional shocks.

Accretion shock geometries in the magnetic variables

NASA Technical Reports Server (NTRS)

Stockman, H. S.

1988-01-01

The first self consistent shock models for the AM Herculis-type systems successfully identified the dominant physical processes and their signatures. These homogenous shock models predict unpolarized, Rayleigh-Jeans optical spectra with sharp cutoffs and rising polarizations as the shocks become optically thin in the ultraviolet. However, the observed energy distributions are generally flat with intermediate polarizations over a broad optical band. These and other observational evidence support a non-homogenous accretion profile which may extend over a considerable fraction of the stellar surface. Both the fundamental assumptions underlying the canonical 1-D shock model and the extension of this model to inhomogenous accretion shocks were identified, for both radial and linear structures. The observational evidence was also examined for tall shocks and little evidence was found for relative shock heights in excess of h/R(1) greater than or equal to 0.1. For several systems, upper limits to the shock height can be obtained from either x ray or optical data. These lie in the region h/R(1) is approximately 0.01 and are in general agreement with the current physical picture for these systems. The quasi-periodic optical variations observed in several magnetic variables may eventually prove to be a major aid in further understanding their accretion shock geometries.

[Shock shape representation of sinus heart rate based on cloud model].

PubMed

Yin, Wenfeng; Zhao, Jie; Chen, Tiantian; Zhang, Junjian; Zhang, Chunyou; Li, Dapeng; An, Baijing

2014-04-01

The present paper is to analyze the trend of sinus heart rate RR interphase sequence after a single ventricular premature beat and to compare it with the two parameters, turbulence onset (TO) and turbulence slope (TS). Based on the acquisition of sinus rhythm concussion sample, we in this paper use a piecewise linearization method to extract its linear characteristics, following which we describe shock form with natural language through cloud model. In the process of acquisition, we use the exponential smoothing method to forecast the position where QRS wave may appear to assist QRS wave detection, and use template to judge whether current cardiac is sinus rhythm. And we choose some signals from MIT-BIH Arrhythmia Database to detect whether the algorithm is effective in Matlab. The results show that our method can correctly detect the changing trend of sinus heart rate. The proposed method can achieve real-time detection of sinus rhythm shocks, which is simple and easily implemented, so that it is effective as a supplementary method.

Hydrogen Lines in Mira Stars Through Interferometry and Polarimetry

NASA Astrophysics Data System (ADS)

Fabas, N.; Chiavassa, A.; Millour, F.; Wittkowski, M.

2015-12-01

Balmer lines in emission are the most prominent features in Mira stars spectra and have a strong potential as a proxy to study the lower atmosphere's dynamics. In Fabas et al. ([1]), we accumulated spectropolarimetric observations of Balmer lines in emission. As the shock is propagating outwards, linear polarization rate increases and the angle of this polarization evolves. Assuming that linear polarization arises from anisotropic scattering, it has the potential of telling us about the geometric structure of the shock as it propagates and the study of such atmospheric structures can typically be performed with interferometry. In 2012, AMBER data on the Mira star omicron Ceti were collected in which the Brackett γ line is studied. The data show signatures in the interferometric observables around this line. Olivier Chesneau was in the jury evaluating the PhD thesis of N. Fabas and he was seduced by the idea to study these shock waves with interferometry and use polarimetry as a complementary study.

A steady and oscillatory kernel function method for interfering surfaces in subsonic, transonic and supersonic flow. [prediction analysis techniques for airfoils

NASA Technical Reports Server (NTRS)

Cunningham, A. M., Jr.

1976-01-01

The theory, results and user instructions for an aerodynamic computer program are presented. The theory is based on linear lifting surface theory, and the method is the kernel function. The program is applicable to multiple interfering surfaces which may be coplanar or noncoplanar. Local linearization was used to treat nonuniform flow problems without shocks. For cases with imbedded shocks, the appropriate boundary conditions were added to account for the flow discontinuities. The data describing nonuniform flow fields must be input from some other source such as an experiment or a finite difference solution. The results are in the form of small linear perturbations about nonlinear flow fields. The method was applied to a wide variety of problems for which it is demonstrated to be significantly superior to the uniform flow method. Program user instructions are given for easy access.

Contribution to study of interfaces instabilities in plane, cylindrical and spherical geometry

NASA Astrophysics Data System (ADS)

Toque, Nathalie

1996-12-01

This thesis proposes several experiments of hydrodynamical instabilities which are studied, numerically and theoretically. The experiments are in plane and cylindrical geometry. Their X-ray radiographies show the evolution of an interface between two solid media crossed by a detonation wave. These materials are initially solid. They become liquide under shock wave or stay between two phases, solid and liquid. The numerical study aims at simulating with the codes EAD and Ouranos, the interfaces instabilities which appear in the experiments. The experimental radiographies and the numerical pictures are in quite good agreement. The theoretical study suggests to modelise a spatio-temporal part of the experiments to obtain the quantitative development of perturbations at the interfaces and in the flows. The models are linear and in plane, cylindrical and spherical geometry. They preceed the inoming study of transition between linear and non linear development of instabilities in multifluids flows crossed by shock waves.

A numerical study of fundamental shock noise mechanisms. Ph.D. Thesis - Cornell Univ.

NASA Technical Reports Server (NTRS)

Meadows, Kristine R.

1995-01-01

The results of this thesis demonstrate that direct numerical simulation can predict sound generation in unsteady aerodynamic flows containing shock waves. Shock waves can be significant sources of sound in high speed jet flows, on helicopter blades, and in supersonic combustion inlets. Direct computation of sound permits the prediction of noise levels in the preliminary design stage and can be used as a tool to focus experimental studies, thereby reducing cost and increasing the probability of a successfully quiet product in less time. This thesis reveals and investigates two mechanisms fundamental to sound generation by shocked flows: shock motion and shock deformation. Shock motion is modeled by the interaction of a sound wave with a shock. During the interaction, the shock wave begins to move and the sound pressure is amplified as the wave passes through the shock. The numerical approach presented in this thesis is validated by the comparison of results obtained in a quasi-one dimensional simulation with linear theory. Analysis of the perturbation energy demonstrated for the first time that acoustic energy is generated by the interaction. Shock deformation is investigated by the numerical simulation of a ring vortex interacting with a shock. This interaction models the passage of turbulent structures through the shock wave. The simulation demonstrates that both acoustic waves and contact surfaces are generated downstream during the interaction. Analysis demonstrates that the acoustic wave spreads cylindrically, that the sound intensity is highly directional, and that the sound pressure level increases significantly with increasing shock strength. The effect of shock strength on sound pressure level is consistent with experimental observations of shock noise, indicating that the interaction of a ring vortex with a shock wave correctly models a dominant mechanism of shock noise generation.

Frontiers in Anisotropic Shock-Wave Modeling

DTIC Science & Technology

2012-02-01

Nowadays, some models incorporate a user-defined subroutine within the commercial software (e.g., ABAQUS ) to take into account either a homogenous...and temperature on the mass density. The specific internal energy can be decomposed into potentials describing the cold compression, ec (ρ, S); thermal ...Taylor’s series expansion of the Hugoniot pressure P . Assume that the linear approximation between the shock velocity US 24 and particle velocity up

Linear analysis on the growth of non-spherical perturbations in supersonic accretion flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takahashi, Kazuya; Yamada, Shoichi, E-mail: ktakahashi@heap.phys.waseda.ac.jp

We analyzed the growth of non-spherical perturbations in supersonic accretion flows. We have in mind an application to the post-bounce phase of core-collapse supernovae (CCSNe). Such non-spherical perturbations have been suggested by a series of papers by Arnett, who has numerically investigated violent convections in the outer layers of pre-collapse stars. Moreover, Couch and Ott demonstrated in their numerical simulations that such perturbations may lead to a successful supernova even for a progenitor that fails to explode without fluctuations. This study investigated the linear growth of perturbations during the infall onto a stalled shock wave. The linearized equations are solvedmore » as an initial and boundary value problem with the use of a Laplace transform. The background is a Bondi accretion flow whose parameters are chosen to mimic the 15 M {sub ☉} progenitor model by Woosley and Heger, which is supposed to be a typical progenitor of CCSNe. We found that the perturbations that are given at a large radius grow as they flow down to the shock radius; the density perturbations can be amplified by a factor of 30, for example. We analytically show that the growth rate is proportional to l, the index of the spherical harmonics. We also found that the perturbations oscillate in time with frequencies that are similar to those of the standing accretion shock instability. This may have an implication for shock revival in CCSNe, which will be investigated in our forthcoming paper in more detail.« less

Note on the single-shock solutions of the Korteweg-de Vries-Burgers equation

NASA Astrophysics Data System (ADS)

Kourakis, Ioannis; Sultana, Sharmin; Verheest, Frank

2012-04-01

The well-known shock solutions of the Korteweg-de Vries-Burgers equation are revisited, together with their limitations in the context of plasma (astro)physical applications. Although available in the literature for a long time, it seems to have been forgotten in recent papers that such shocks are monotonic and unique, for a given plasma configuration, and cannot show oscillatory or bell-shaped features. This uniqueness is contrasted to solitary wave solutions of the two parent equations (Korteweg-de Vries and Burgers), which form a family of curves parameterized by the excess velocity over the linear phase speed.

THE IMPLICIT CONTRIBUTION OF SLAB MODES TO THE PERPENDICULAR DIFFUSION COEFFICIENT OF PARTICLES INTERACTING WITH TWO-COMPONENT TURBULENCE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shalchi, A., E-mail: andreasm4@yahoo.com

2016-10-20

We explore the transport of energetic particles in two-component turbulence in which the stochastic magnetic field is assumed to be a superposition of slab and two-dimensional modes. It is known that in magnetostatic slab turbulence, the motion of particles across the mean magnetic field is subdiffusive. If a two-dimensional component is added, diffusion is recovered. It was also shown before that in two-component turbulence, the slab modes do not explicitly contribute to the perpendicular diffusion coefficient. In the current paper, the implicit contribution of slab modes is explored and it is shown that this contribution leads to a reduction ofmore » the perpendicular diffusion coefficient. This effect improves the agreement between simulations and analytical theory. Furthermore, the obtained results are relevant for investigations of diffusive shock acceleration.« less

Focal Points, Endogenous Processes, and Exogenous Shocks in the Autism Epidemic

PubMed Central

Liu, Kayuet; Bearman, Peter S.

2014-01-01

Autism prevalence has increased rapidly in the United States during the past two decades. We have previously shown that the diffusion of information about autism through spatially proximate social relations has contributed significantly to the epidemic. This study expands on this finding by identifying the focal points for interaction that drive the proximity effect on subsequent diagnoses. We then consider how diffusion dynamics through interaction at critical focal points, in tandem with exogenous shocks, could have shaped the spatial dynamics of autism in California. We achieve these goals through an empirically calibrated simulation model of the whole population of 3- to 9-year-olds in California. We show that in the absence of interaction at these foci—principally malls and schools—we would not observe an autism epidemic. We also explore the idea that epigenetic changes affecting one generation in the distal past could shape the precise spatial patterns we observe among the next generation. PMID:26166907

Hexavalent Chromium Removal from Model Water and Car Shock Absorber Factory Effluent by Nanofiltration and Reverse Osmosis Membrane

PubMed Central

Bejaoui, Imen; Mouelhi, Meral; Hamrouni, Béchir

2017-01-01

Nanofiltration and reverse osmosis are investigated as a possible alternative to the conventional methods of Cr(VI) removal from model water and industrial effluent. The influences of feed concentration, water recovery, pH, and the coexisting anions were studied. The results have shown that retention rates of hexavalent chromium can reach 99.7% using nanofiltration membrane (NF-HL) and vary from 85 to 99.9% using reverse osmosis membrane (RO-SG) depending upon the composition of the solution and operating conditions. This work was also extended to investigate the separation of Cr(VI) from car shock absorber factory effluent. The use of these membranes is very promising for Cr(VI) water treatment and desalting industry effluent. Spiegler-Kedem model was applied to experimental results in the aim to determine phenomenological parameters, the reflection coefficient of the membrane (σ), and the solute permeability coefficient (Ps). The convective and diffusive parts of the mass transfer were quantified with predominance of the diffusive contribution. PMID:28819360

Bulk properties and velocity distributions of water group ions at Comet Halley - Giotto measurements

NASA Astrophysics Data System (ADS)

Coates, A. J.; Wilken, B.; Johnstone, A. D.; Jockers, K.; Glassmeier, K.-H.; Huddleston, D. E.

1990-07-01

In the region upstream of Comet Halley, pickup heavy ions of cometary origin were directly observed by the implanted ion spectrometer on Giotto. Diffusion of this population in pitch angle and in energy, during the approach to the comet and on the outbound leg is discussed. The two data sets are compared and qualitative ideas on scattering timescales are inferred. In addition the bulk parameters of these distributions have been computed and a comparison of the observed speed in the solar wind frame and the observed density with expectations is presented. Pitch angle scattering occurs more slowly than expected with filled shells appearing at 2,500,000 km, and significant energy diffusion does not occur until the bow shock region. Also the shell distributions downstream of the shock flow at the bispherical bulk speed (related to the Alfven speed) along the magnetic field with respect to the solar wind in accordance with conservation of energy between the pickup ions and the wave turbulence.

Three-dimensional implementation of the Low Diffusion method for continuum flow simulations

NASA Astrophysics Data System (ADS)

Mirza, A.; Nizenkov, P.; Pfeiffer, M.; Fasoulas, S.

2017-11-01

Concepts of a particle-based continuum method have existed for many years. The ultimate goal is to couple such a method with the Direct Simulation Monte Carlo (DSMC) in order to bridge the gap of numerical tools in the treatment of the transitional flow regime between near-equilibrium and rarefied gas flows. For this purpose, the Low Diffusion (LD) method, introduced first by Burt and Boyd, offers a promising solution. In this paper, the LD method is revisited and the implementation in a modern particle solver named PICLas is given. The modifications of the LD routines enable three-dimensional continuum flow simulations. The implementation is successfully verified through a series of test cases: simple stationary shock, oblique shock simulation and thermal Couette flow. Additionally, the capability of this method is demonstrated by the simulation of a hypersonic nitrogen flow around a 70°-blunted cone. Overall results are in very good agreement with experimental data. Finally, the scalability of PICLas using LD on a high performance cluster is presented.

The Stormy Life of Galaxy Clusters

NASA Astrophysics Data System (ADS)

Rudnick, Lawrence

2018-01-01

Galaxy clusters, the largest gravitationally bound structures, hold the full history of their baryonic evolution, serve as important cosmological tools and allow us to probe unique physical regimes in their diffuse plasmas. With characteristic dynamical timescales of 107-109 years, these diffuse thermal and relativistic media continue to evolve, as dark matter drives major mergers and more gentle continuing accretion. The history of this assembly is encoded in the plasmas, and a wide range of observational and theoretical investigations are aimed at decoding their signatures. X-ray temperature and density variations, low Mach number shocks, and "cold front" discontinuities all illuminate clusters' continued evolution. Radio structures and spectra are passive indicators of merger shocks, while radio galaxy distortions reveal the complex motions in the intracluster medium. Deep in cluster cores, AGNs associated with brightest cluster galaxies provide ongoing energy, and perhaps even stabilize the intracluster medium. In this talk, we will recount this evolving picture of the stormy ICM, and suggest areas of likely advance in the coming years.

Assessment of numerical methods for the solution of fluid dynamics equations for nonlinear resonance systems

NASA Technical Reports Server (NTRS)

Przekwas, A. J.; Yang, H. Q.

1989-01-01

The capability of accurate nonlinear flow analysis of resonance systems is essential in many problems, including combustion instability. Classical numerical schemes are either too diffusive or too dispersive especially for transient problems. In the last few years, significant progress has been made in the numerical methods for flows with shocks. The objective was to assess advanced shock capturing schemes on transient flows. Several numerical schemes were tested including TVD, MUSCL, ENO, FCT, and Riemann Solver Godunov type schemes. A systematic assessment was performed on scalar transport, Burgers' and gas dynamic problems. Several shock capturing schemes are compared on fast transient resonant pipe flow problems. A system of 1-D nonlinear hyperbolic gas dynamics equations is solved to predict propagation of finite amplitude waves, the wave steepening, formation, propagation, and reflection of shocks for several hundred wave cycles. It is shown that high accuracy schemes can be used for direct, exact nonlinear analysis of combustion instability problems, preserving high harmonic energy content for long periods of time.

Stream interfaces and energetic ions 2: Ulysses test of Pioneer results

NASA Technical Reports Server (NTRS)

Intriligator, Devrie S.; Siscoe, George L.; Wibberez, Gerd; Kunow, Horst; Gosling, John T.

1995-01-01

Ulysses measurements of energetic and solar wind particles taken near 5 AU between 20 and 30 degrees south latitude during a well-developed recurring corotating interaction region (CIR) show that the CIR's corotating energetic ion population (CEIP) associated with the trailing reverse shock starts within the CIR at the stream interface. This is consistent with an earlier result obtained by Pioneers 10 and 11 in the ecliptic plane between 4 and 6 AU. The Ulysses/Pioneer finding noteworthy since the stream interface is not magnetically connected to the reverse shock but lies 12-17 corotation hours from it. Thus, the finding to be inconsistent with the basic model that generates CEIP particles at the reverse shock and propagates them along field lines Eliminating the inconsistency probably entails an extension of the standard model. We consider two possible extensions cross-field diffusion and energetic particles generation closer to the sun in the gap between the stream interface and the reverse shock.

Ar-40/Ar-39 age of the Shergotty achondrite and implications for its post-shock thermal history

NASA Technical Reports Server (NTRS)

Bogard, D. D.; Nyquist, L. E.; Husain, L.

1979-01-01

Ar-40/Ar-39 measurements are used to determine the age of the Shergotty achondrite and the chronology of the shock event responsible for the complete conversion of its plagioclase to maskelynite is discussed. Apparent ages are found to vary between 240 and 640 million years for the whole rock sample, with a plateau age of 254 million years for a maskelynite separate. The Rb-Sr age of 165 million years determined by Nyquist at al (1978) suggests that the maskelynite as well as the whole rock was incompletely degassed. Argon diffusion characteristics indicate a post-shock cooling time greater than 1000 years and a burial depth greater than 300 m for a thermal model of a cooling ejecta blanket of variable thickness. It is concluded that the shock event which degassed the argon and reset the Rb-Sr systematics occurred between 165 and 250 million years ago when the parent body experienced a collision in the asteroid belt.

Thermal Shock Damage and Microstructure Evolution of Thermal Barrier Coatings on Mar-M247 Superalloy in a Combustion Gas Environment

NASA Astrophysics Data System (ADS)

Mei, Hui

2012-06-01

The effect of preoxidation on the thermal shock of air plasma sprayed thermal barrier coatings (TBCs) was completely investigated in a combustion gas environment by burning jet fuel with high speed air. Results show that with increasing cycles, the as-oxidized TBCs lost more weight and enlarged larger spallation area than the as-sprayed ones. Thermally grown oxide (TGO) growth and thermal mismatch stress were proven to play critical roles on the as-oxidized TBC failure. Two types of significant cracks were identified: the type I crack was vertical to the TGO interface and the type II crack was parallel to the TGO interface. The former accelerated the TGO growth to develop the latter as long as the oxidizing gas continuously diffused inward and then oxidized the more bond coat (BC). The preoxidation treatment directly increased the TGO thickness, formed the parallel cracks earlier in the TGO during the thermal shocks, and eventually resulted in the worse thermal shock resistance.

Magnetogasdynamics shock waves in a rotational axisymmetric non-ideal gas with increasing energy and conductive and radiative heat-fluxes

NASA Astrophysics Data System (ADS)

Nath, Gorakh

2016-07-01

Self-similar solutions are obtained for one-dimensional adiabatic flow behind a magnetogasdynamics cylindrical shock wave propagating in a rotational axisymmetric non ideal gas with increasing energy and conductive and radiative heat fluxes in presence of an azimuthal magnetic field. The fluid velocities and the azimuthal magnetic field in the ambient medium are assume to be varying and obeying power laws. In order to find the similarity solutions the angular velocity of the ambient medium is taken to be decreasing as the distance from the axis increases. The heat conduction is expressed in terms of Fourier's law and the radiation is considered to be the diffusion type for an optically thick grey gas model. The thermal conductivity and the absorption coefficient are assumed to vary with temperature and density. The effects of the presence of radiation and conduction, the non-idealness of the gas and the magnetic field on the shock propagation and the flow behind the shock are investigated.

Particle acceleration and magnetic field generation in SNR shocks

NASA Astrophysics Data System (ADS)

Suslov, M.; Diamond, P. H.; Malkov, M. A.

2006-04-01

We discuss the diffusive acceleration mechanism in SNR shocks in terms of its potential to accelerate CRs to 10^18 eV, as observations imply. One possibility, currently discussed in the literature, is to resonantly generate a turbulent magnetic field via accelerated particles in excess of the background field. We analyze some problems of this scenario and suggest a different mechanism, which is based on the generation of Alfven waves at the gyroradius scale at the background field level, with a subsequent transfer to longer scales via interaction with strong acoustic turbulence in the shock precursor. The acoustic turbulence in turn, may be generated by Drury instability or by parametric instability of the Alfven (A) waves. The essential idea is an A->A+S decay instability process, where one of the interacting scatterers (i.e. the sound, or S-waves) are driven by the Drury instability process. This rapidly generates longer wavelength Alfven waves, which in turn resonate with high energy CRs thus binding them to the shock and enabling their further acceleration.

Generation of mesoscale magnetic fields and the dynamics of Cosmic Ray acceleration

NASA Astrophysics Data System (ADS)

Diamond, P. H.; Malkov, M. A.

The problem of the cosmic ray origin is discussed in connection with their acceleration in supernova remnant shocks. The diffusive shock acceleration mechanism is reviewed and its potential to accelerate particles to the maximum energy of (presumably) galactic cosmic rays (1018eV ) is considered. It is argued that to reach such energies, a strong magnetic field at scales larger than the particle gyroradius must be created as a result of the acceleration process, itself. One specific mechanism suggested here is based on the generation of Alfven wave at the gyroradius scale with a subsequent transfer to longer scales via interaction with strong acoustic turbulence in the shock precursor. The acoustic turbulence in turn, may be generated by Drury instability or by parametric instability of the Alfven waves. The generation mechanism is modulational instability of CR generated Alfven wave packets induced, in turn, by scattering off acoustic fluctuations in the shock precursor which are generated by Drury instability.

Experimental evidence for superionic water ice using shock compression

NASA Astrophysics Data System (ADS)

Millot, Marius; Hamel, Sebastien; Rygg, J. Ryan; Celliers, Peter M.; Collins, Gilbert W.; Coppari, Federica; Fratanduono, Dayne E.; Jeanloz, Raymond; Swift, Damian C.; Eggert, Jon H.

2018-03-01

In stark contrast to common ice, Ih, water ice at planetary interior conditions has been predicted to become superionic with fast-diffusing (that is, liquid-like) hydrogen ions moving within a solid lattice of oxygen. Likely to constitute a large fraction of icy giant planets, this extraordinary phase has not been observed in the laboratory. Here, we report laser-driven shock-compression experiments on water ice VII. Using time-resolved optical pyrometry and laser velocimetry measurements as well as supporting density functional theory-molecular dynamics (DFT-MD) simulations, we document the shock equation of state of H2O to unprecedented extreme conditions and unravel thermodynamic signatures showing that ice melts near 5,000 K at 190 GPa. Optical reflectivity and absorption measurements also demonstrate the low electronic conductivity of ice, which, combined with previous measurements of the total electrical conductivity under reverberating shock compression, provides experimental evidence for superionic conduction in water ice at planetary interior conditions, verifying a 30-year-old prediction.

Computational Analysis of the Effect of Porosity on Shock Cell Strength at Cruise

NASA Technical Reports Server (NTRS)

Massey, Steven J.; Elmiligui, Alaa A.; Pao, S. Paul; Abdol-Hamid, Khaled S.; Hunter, Craig A.

2006-01-01

A computational flow field analysis is presented of the effect of core cowl porosity on shock cell strength for a modern separate flow nozzle at cruise conditions. The goal of this study was to identify the primary physical mechanisms by which the application of porosity can reduce shock cell strength and hence the broadband shock associated noise. The flow is simulated by solving the asymptotically steady, compressible, Reynoldsaveraged Navier-Stokes equations on a structured grid using an implicit, up-wind, flux-difference splitting finite volume scheme. The standard two-equation k - epsilon turbulence model with a linear stress representation is used with the addition of a eddy viscosity dependence on total temperature gradient normalized by local turbulence length scale. Specific issues addressed in this study were the optimal area required to weaken a shock impinging on the core cowl surface and the optimal level of porosity and placement of porous areas for reduction of the overall shock cell strength downstream. Two configurations of porosity were found to reduce downstream shock strength by approximately 50%.

Thermal infrared spectroscopy and modeling of experimentally shocked basalts

USGS Publications Warehouse

Johnson, J. R.; Staid, M.I.; Kraft, M.D.

2007-01-01

New measurements of thermal infrared emission spectra (250-1400 cm-1; ???7-40 ??m) of experimentally shocked basalt and basaltic andesite (17-56 GPa) exhibit changes in spectral features with increasing pressure consistent with changes in the structure of plagioclase feldspars. Major spectral absorptions in unshocked rocks between 350-700 cm-1 (due to Si-O-Si octahedral bending vibrations) and between 1000-1250 cm-1 (due to Si-O antisymmetric stretch motions of the silica tetrahedra) transform at pressures >20-25 GPa to two broad spectral features centered near 950-1050 and 400-450 cm-1. Linear deconvolution models using spectral libraries composed of common mineral and glass spectra replicate the spectra of shocked basalt relatively well up to shock pressures of 20-25 GPa, above which model errors increase substantially, coincident with the onset of diaplectic glass formation in plagioclase. Inclusion of shocked feldspar spectra in the libraries improves fits for more highly shocked basalt. However, deconvolution models of the basaltic andesite select shocked feldspar end-members even for unshocked samples, likely caused by the higher primary glass content in the basaltic andesite sample.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Olmstead, D.; Wayne, P.; Simons, D.

Here, we consider two cases of interaction between a planar shock and a cylindrical density interface. In the first case (planar normal shock), the axis of the gas cylinder is parallel to the shock front and baroclinic vorticity deposited by the shock is predominantly two dimensional (directed along the axis of the cylinder). In the second case, the cylinder is tilted, resulting in an oblique shock interaction and a fully-three-dimensional shock-induced vorticity field. Furthermore, the statistical properties of the flow for both cases are analyzed based on images from two orthogonal visualization planes, using structure functions of the intensity mapsmore » of fluorescent tracer premixed with heavy gas. And at later times, these structure functions exhibit power-law-like behavior over a considerable range of scales. Manifestation of this behavior is remarkably consistent in terms of dimensionless time τ defined based on Richtmyer's linear theory within the range of Mach numbers from 1.1 to 2.0 and the range of gas cylinder tilt angles with respect to the plane of the shock front (0–30°).« less

Mach 5 bow shock control by a nanosecond pulse surface dielectric barrier discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishihara, M.; Takashima, K.; Rich, J. W.

2011-06-15

Bow shock perturbations in a Mach 5 air flow, produced by low-temperature, nanosecond pulse, and surface dielectric barrier discharge (DBD), are detected by phase-locked schlieren imaging. A diffuse nanosecond pulse discharge is generated in a DBD plasma actuator on a surface of a cylinder model placed in air flow in a small scale blow-down supersonic wind tunnel. Discharge energy coupled to the actuator is 7.3-7.8 mJ/pulse. Plasma temperature inferred from nitrogen emission spectra is a few tens of degrees higher than flow stagnation temperature, T = 340 {+-} 30 K. Phase-locked Schlieren images are used to detect compression waves generatedmore » by individual nanosecond discharge pulses near the actuator surface. The compression wave propagates upstream toward the baseline bow shock standing in front of the cylinder model. Interaction of the compression wave and the bow shock causes its displacement in the upstream direction, increasing shock stand-off distance by up to 25%. The compression wave speed behind the bow shock and the perturbed bow shock velocity are inferred from the Schlieren images. The effect of compression waves generated by nanosecond discharge pulses on shock stand-off distance is demonstrated in a single-pulse regime (at pulse repetition rates of a few hundred Hz) and in a quasi-continuous mode (using a two-pulse sequence at a pulse repetition rate of 100 kHz). The results demonstrate feasibility of hypersonic flow control by low-temperature, repetitive nanosecond pulse discharges.« less

Understanding large SEP events with the PATH code: Modeling of the 13 December 2006 SEP event

NASA Astrophysics Data System (ADS)

Verkhoglyadova, O. P.; Li, G.; Zank, G. P.; Hu, Q.; Cohen, C. M. S.; Mewaldt, R. A.; Mason, G. M.; Haggerty, D. K.; von Rosenvinge, T. T.; Looper, M. D.

2010-12-01

The Particle Acceleration and Transport in the Heliosphere (PATH) numerical code was developed to understand solar energetic particle (SEP) events in the near-Earth environment. We discuss simulation results for the 13 December 2006 SEP event. The PATH code includes modeling a background solar wind through which a CME-driven oblique shock propagates. The code incorporates a mixed population of both flare and shock-accelerated solar wind suprathermal particles. The shock parameters derived from ACE measurements at 1 AU and observational flare characteristics are used as input into the numerical model. We assume that the diffusive shock acceleration mechanism is responsible for particle energization. We model the subsequent transport of particles originated at the flare site and particles escaping from the shock and propagating in the equatorial plane through the interplanetary medium. We derive spectra for protons, oxygen, and iron ions, together with their time-intensity profiles at 1 AU. Our modeling results show reasonable agreement with in situ measurements by ACE, STEREO, GOES, and SAMPEX for this event. We numerically estimate the Fe/O abundance ratio and discuss the physics underlying a mixed SEP event. We point out that the flare population is as important as shock geometry changes during shock propagation for modeling time-intensity profiles and spectra at 1 AU. The combined effects of seed population and shock geometry will be examined in the framework of an extended PATH code in future modeling efforts.

Broadband Observations and Modeling of the Shell-Type Supernova Remnant G347.3-0.5

NASA Technical Reports Server (NTRS)

Ellison, Donald C.; Slane, Patrick O.; Gaensler, Bryan M.

2002-01-01

The supernova remnant G347.3-0.5 emits a featureless power law in X-rays, thought to indicate shock acceleration of electrons to high energies. We here produce a broadband spectrum of the bright northwest limb of this source by combining radio observations from the Australia Telescope Compact Array (ATCA), X-ray observations from the Advanced Satellite for Cosmology and Astrophysics (ASCA), and TeV gamma-ray observations from the CANGAROO imaging Cerenkov telescope. We assume that this emission is produced by an electron population generated by diffusive shock acceleration at the remnant forward shock. The nonlinear aspects of the particle acceleration force a connection between the widely different wavelength bands and between the electrons and the unseen ions, presumably accelerated simultaneously with the electrons. This allows us to infer the relativistic proton spectrum and estimate ambient parameters such as the supernova explosion energy, magnetic field, matter density in the emission region, and efficiency of the shock acceleration process. We find convincing evidence that the shock acceleration is efficient, placing greater than 25% of the shock kinetic energy flux into relativistic ions. Despite this high efficiency, the maximum electron and proton energies, while depending somewhat on assumptions for the compression of the magnetic field in the shock, are well below the observed 'knee' at 10(exp 15) eV in the Galactic cosmic-ray spectrum.

Renormalized Two-Fluid Hydrodynamics of Cosmic-Ray--modified Shocks

NASA Astrophysics Data System (ADS)

Malkov, M. A.; Voelk, H. J.

1996-12-01

A simple two-fluid model of diffusive shock acceleration, introduced by Axford, Leer, & Skadron and Drury & Völk, is revisited. This theory became a chief instrument in the studies of shock modification due to particle acceleration. Unfortunately its most intriguing steady state prediction about a significant enhancement of the shock compression and a corresponding increase of the cosmic-ray production violates assumptions which are critical for the derivation of this theory. In particular, for strong shocks the spectral flattening makes a cutoff-independent definition of pressure and energy density impossible and therefore causes an additional closure problem. Confining ourselves for simplicity to the case of plane shocks, assuming reacceleration of a preexisting cosmic-ray population, we argue that also under these circumstances the kinetic solution has a rather simple form. It can be characterized by only a few parameters, in the simplest case by the slope and the magnitude of the momentum distribution at the upper momentum cutoff. We relate these parameters to standard hydrodynamic quantities like the overall shock compression ratio and the downstream cosmic-ray pressure. The two-fluid theory produced in this way has the traditional form but renormalized closure parameters. By solving the renormalized Rankine-Hugoniot equations, we show that for the efficient stationary solution, most significant for cosmic-ray acceleration, the renormalization is needed in the whole parameter range of astrophysical interest.

Linear response theory and transient fluctuation relations for diffusion processes: a backward point of view

NASA Astrophysics Data System (ADS)

Liu, Fei; Tong, Huan; Ma, Rui; Ou-Yang, Zhong-can

2010-12-01

A formal apparatus is developed to unify derivations of the linear response theory and a variety of transient fluctuation relations for continuous diffusion processes from a backward point of view. The basis is a perturbed Kolmogorov backward equation and the path integral representation of its solution. We find that these exact transient relations could be interpreted as a consequence of a generalized Chapman-Kolmogorov equation, which intrinsically arises from the Markovian characteristic of diffusion processes.

In-situ Plasma Analysis of Ion Kinetics in the Solar Wind and Hermean Magnetosphere

NASA Astrophysics Data System (ADS)

Tracy, Patrick J.

The heating of the solar wind and its interaction with the unique planetary magnetosphere of Mercury is the primary focus of this work. The first aspect of this study focused on the heavy ion population of the solar wind (A > 4 amu), and how well the signature of the heating process responsible for creating the solar wind is preserved in this heavy ion population. We found that this signature in the heavy ion population is primarily erased (thermalized) via Coulomb collisional interactions with solar wind protons. The heavy ions observed in collisionally young solar wind reveal a clear, stable dependence on mass, along with non-thermal heating that is not in agreement with current predictions based on turbulent transport and kinetic dissipation. Due to its weak magnetic dipole, the solar wind can impinge on the surface of Mercury, one of the processes contributing to the desorption of neutrals and, through ionization, ions that make up the planet's exosphere. Differentiating between surface mechanisms and analyzing magnetospheric plasma dynamics requires the quantification of a variety of ion species. A detailed forward model and a robust statistical method were created to identify new ion signatures in the measurement space of the FIPS instrument, formerly orbiting Mercury onboard the MESSENGER spacecraft. The recovery of new heavy ions species, including Al, Ne, Si, and Mg, along with tentative recoveries of S, Ar, K, and C, enable in depth studies of the plasma dynamics in the Hermean magnetosphere. The interaction of the solar wind with the bow shock of the Hermean magnetosphere leads to the creation of a foreshock region. New tools and methods were created to enable the analysis of the diffuse and Field Aligned Beam (FAB) populations in unique parameter regime of the Hermean foreshock. One result suggests that the energization process for the observed FABs can be explained by Shock Drift Acceleration, and not limited by the small spatial size of Mercury's bow shock. Analysis of diffuse populations shows that a connection time limited diffusive shock acceleration is likely responsible for the behavior of the observed energy distributions.

Nonequilibrium radiation and chemistry models for aerocapture vehicle flowfields

NASA Technical Reports Server (NTRS)

Carlson, Leland A.

1994-01-01

The primary accomplishments of the project were as follows: (1) From an overall standpoint, the primary accomplishment of this research was the development of a complete gasdynamic-radiatively coupled nonequilibrium viscous shock layer solution method for axisymmetric blunt bodies. This method can be used for rapid engineering modeling of nonequilibrium re-entry flowfields over a wide range of conditions. (2) Another significant accomplishment was the development of an air radiation model that included local thermodynamic nonequilibrium (LTNE) phenomena. (3) As part of this research, three electron-electronic energy models were developed. The first was a quasi-equilibrium electron (QEE) model which determined an effective free electron temperature and assumed that the electronic states were in equilibrium with the free electrons. The second was a quasi-equilibrium electron-electronic (QEEE) model which computed an effective electron-electronic temperature. The third model was a full electron-electronic (FEE) differential equation model which included convective, collisional, viscous, conductive, vibrational coupling, and chemical effects on electron-electronic energy. (4) Since vibration-dissociation coupling phenomena as well as vibrational thermal nonequilibrium phenomena are important in the nonequilibrium zone behind a shock front, a vibrational energy and vibration-dissociation coupling model was developed and included in the flowfield model. This model was a modified coupled vibrational dissociation vibrational (MCVDV) model and also included electron-vibrational coupling. (5) Another accomplishment of the project was the usage of the developed models to investigate radiative heating. (6) A multi-component diffusion model which properly models the multi-component nature of diffusion in complex gas mixtures such as air, was developed and incorporated into the blunt body model. (7) A model was developed to predict the magnitude and characteristics of the shock wave precursor ahead of vehicles entering the Earth's atmosphere. (8) Since considerable data exists for radiating nonequilibrium flow behind normal shock waves, a normal shock wave version of the blunt body code was developed. (9) By comparing predictions from the models and codes with available normal shock data and the flight data of Fire II, it is believed that the developed flowfield and nonequilibrium radiation models have been essentially validated for engineering applications.

Shocks in the Early Universe.

PubMed

Pen, Ue-Li; Turok, Neil

2016-09-23

We point out a surprising consequence of the usually assumed initial conditions for cosmological perturbations. Namely, a spectrum of Gaussian, linear, adiabatic, scalar, growing mode perturbations not only creates acoustic oscillations of the kind observed on very large scales today, it also leads to the production of shocks in the radiation fluid of the very early Universe. Shocks cause departures from local thermal equilibrium as well as create vorticity and gravitational waves. For a scale-invariant spectrum and standard model physics, shocks form for temperatures 1  GeV

An experimental nonlinear low dynamic stiffness device for shock isolation

NASA Astrophysics Data System (ADS)

Francisco Ledezma-Ramirez, Diego; Ferguson, Neil S.; Brennan, Michael J.; Tang, Bin

2015-07-01

The problem of shock generated vibration is very common in practice and difficult to isolate due to the high levels of excitation involved and its transient nature. If not properly isolated it could lead to large transmitted forces and displacements. Typically, classical shock isolation relies on the use of passive stiffness elements to absorb energy by deformation and some damping mechanism to dissipate residual vibration. The approach of using nonlinear stiffness elements is explored in this paper, focusing in providing an isolation system with low dynamic stiffness. The possibilities of using such a configuration for a shock mount are studied experimentally following previous theoretical models. The model studied considers electromagnets and permanent magnets in order to obtain nonlinear stiffness forces using different voltage configurations. It is found that the stiffness nonlinearities could be advantageous in improving shock isolation in terms of absolute displacement and acceleration response when compared with linear elastic elements.

Ion-impact-induced multifragmentation of liquid droplets★

NASA Astrophysics Data System (ADS)

Surdutovich, Eugene; Verkhovtsev, Alexey; Solov'yov, Andrey V.

2017-11-01

An instability of a liquid droplet traversed by an energetic ion is explored theoretically. This instability is brought about by the predicted shock wave induced by the ion. An observation of multifragmentation of small droplets traversed by ions with high linear energy transfer is suggested to demonstrate the existence of shock waves. A number of effects are analysed in effort to find the conditions for such an experiment to be signifying. The presence of shock waves crucially affects the scenario of radiation damage with ions since the shock waves significantly contribute to the thermomechanical damage of biomolecules as well as the transport of reactive species. While the scenario has been upheld by analyses of biological experiments, the shock waves have not yet been observed directly, regardless of a number of ideas of experiments to detect them were exchanged at conferences. Contribution to the Topical Issue "Dynamics of Systems at the Nanoscale", edited by Andrey Solov'yov and Andrei Korol.

Adaptive magnetorheological seat suspension for shock mitigation

NASA Astrophysics Data System (ADS)

Singh, Harinder J.; Wereley, Norman M.

2013-04-01

An adaptive magnetorheological seat suspension (AMSS) was analyzed for optimal protection of occupants from shock loads caused by the impact of a helicopter with the ground. The AMSS system consists of an adaptive linear stroke magnetorheological shock absorber (MRSA) integrated into the seat structure of a helicopter. The MRSA provides a large controllability yield force to accommodate a wide spectrum for shock mitigation. A multiple degrees-of-freedom nonlinear biodynamic model for a 50th percentile male occupant was integrated with the dynamics of MRSA and the governing equations of motion were investigated theoretically. The load-stroke profile of MRSA was optimized with the goal of minimizing the potential for injuries. The MRSA yield force and the shock absorber stroke limitations were the most crucial parameters for improved biodynamic response mitigation. An assessment of injuries based on established injury criteria for different body parts was carried out.

Quantitative evaluation of the mechanical strength of titanium/composite bonding using laser-generated shock waves

NASA Astrophysics Data System (ADS)

Ducousso, M.; Bardy, S.; Rouchausse, Y.; Bergara, T.; Jenson, F.; Berthe, L.; Videau, L.; Cuvillier, N.

2018-03-01

Intense acoustic shock waves were applied to evaluate the mechanical strength of structural epoxy bonds between a TA6V4 titanium alloy and a 3D woven carbon/epoxy composite material. Two bond types with different mechanical strengths were obtained from two different adhesive reticulations, at 50% and 90% of conversion, resulting in longitudinal static strengths of 10 and 39 MPa and transverse strengths of 15 and 35 MPa, respectively. The GPa shock waves were generated using ns-scale intense laser pulses and reaction principles to a confined plasma expansion. Simulations taking into account the laser-matter interaction, plasma relaxation, and non-linear shock wave propagation were conducted to aid interpretation of the experiments. Good correlations were obtained between the experiments and the simulation and between different measurement methods of the mechanical strength (normalized tests vs laser-generated shock waves). Such results open the door toward certification of structural bonding.

Magnetic Diagnostics on the Magnetized Shock Experiment (MSX)

NASA Astrophysics Data System (ADS)

Hutchinson, T. M.; Weber, T. E.; Boguski, J. C.; Intrator, T. P.; Smith, R. J.; Dunn, J. P.

2013-10-01

The Magnetized Shock Experiment (MSX) at Los Alamos National Laboratory was built to investigate the physics of high-Alfvénic, supercritical, magnetized shocks through the acceleration and subsequent stagnation of a Field Reversed Configuration (FRC) plasmoid against a magnetic mirror and/or plasma target. An array of high-bandwidth, multi-axis, robust, internal magnetic probes has been constructed to characterize flux compression ratios, instability formation, and turbulent macro-scale features of the post-shock plasma. The mirror magnet is mounted on a linear translation stage, providing a capability to axially move the shock layer through the probe field of view. An independent, external probe array also provides conventional information on the FRC shape, velocity, and total pressure during the formation and acceleration phases. Probe design, characterization, configuration, and initial results are presented. This work is supported by the DOE OFES and NNSA under LANS contract DE-AC52-06NA25369. LA-UR-13-25189.

Advanced Computational Modeling Approaches for Shock Response Prediction

NASA Technical Reports Server (NTRS)

Derkevorkian, Armen; Kolaini, Ali R.; Peterson, Lee

2015-01-01

Motivation: (1) The activation of pyroshock devices such as explosives, separation nuts, pin-pullers, etc. produces high frequency transient structural response, typically from few tens of Hz to several hundreds of kHz. (2) Lack of reliable analytical tools makes the prediction of appropriate design and qualification test levels a challenge. (3) In the past few decades, several attempts have been made to develop methodologies that predict the structural responses to shock environments. (4) Currently, there is no validated approach that is viable to predict shock environments overt the full frequency range (i.e., 100 Hz to 10 kHz). Scope: (1) Model, analyze, and interpret space structural systems with complex interfaces and discontinuities, subjected to shock loads. (2) Assess the viability of a suite of numerical tools to simulate transient, non-linear solid mechanics and structural dynamics problems, such as shock wave propagation.

Simulations and experiments of ejecta generation in twice-shocked metals

NASA Astrophysics Data System (ADS)

Karkhanis, Varad; Ramaprabhu, Praveen; Buttler, William; Hammerberg, James; Cherne, Frank; Andrews, Malcolm

2016-11-01

Using continuum hydrodynamics embedded in the FLASH code, we model ejecta generation in recent target experiments, where a metallic surface was loaded by two successive shock waves. The experimental data were obtained from a two-shockwave, high-explosive tool at Los Alamos National Laboratory, capable of generating ejecta from a shocked tin surface in to a vacuum. In both simulations and experiment, linear growth is observed following the first shock event, while the second shock strikes a finite-amplitude interface leading to nonlinear growth. The timing of the second incident shock was varied systematically in our simulations to realize a finite-amplitude re-initialization of the RM instability driving the ejecta. We find the shape of the interface at the event of second shock is critical in determining the amount of ejecta, and thus must be used as an initial condition to evaluate subsequent ejected mass using a source model. In particular, the agreement between simulations, experiments and the mass model is improved when shape effects associated with the interface at second shock are incorporated. This work was supported in part by the (U.S.) Department of Energy (DOE) under Contract No. DE-AC52-06NA2-5396.

Extracorporeal shock wave therapy in orthopedics, basic research, and clinical implications

NASA Astrophysics Data System (ADS)

Hausdorf, Joerg; Jansson, Volkmar; Maier, Markus; Delius, Michael

2005-04-01

The molecular events following shock wave treatment of bone are widely unknown. Nevertheless patients with osteonecrosis and non unions are already treated partly successful with shock waves. Concerning the first indication, the question of the permeation of the shock wave into the bone was addressed. Therefore shockwaves were applied to porcine femoral heads and the intraosseous pressure was measured. A linear correlation of the pressure to the intraosseous distance was found. Approximately 50% of the pressure are still measurable 10 mm inside the femoral head. These findings should encourage continued shock wave research on this indication. Concerning the second indication (non union), osteoblasts were subjected to 250 or 500 shock waves at 25 kV. After 24, 48, and 72 h the levels of the bone and vascular growth factors bFGF, TGFbeta1, and VEGF were examined. After 24 h there was a significant increase in bFGF levels (p<0.05) with significant correlation (p<0.05) to the number of impulses. TGFbeta1, and VEGF showed no significant changes. This may be one piece in the cascade of new bone formation following shock wave treatment and may lead to a more specific application of shock waves in orthopedic surgery.

Computational considerations for the simulation of shock-induced sound

NASA Technical Reports Server (NTRS)

Casper, Jay; Carpenter, Mark H.

1996-01-01

The numerical study of aeroacoustic problems places stringent demands on the choice of a computational algorithm, because it requires the ability to propagate disturbances of small amplitude and short wavelength. The demands are particularly high when shock waves are involved, because the chosen algorithm must also resolve discontinuities in the solution. The extent to which a high-order-accurate shock-capturing method can be relied upon for aeroacoustics applications that involve the interaction of shocks with other waves has not been previously quantified. Such a study is initiated in this work. A fourth-order-accurate essentially nonoscillatory (ENO) method is used to investigate the solutions of inviscid, compressible flows with shocks in a quasi-one-dimensional nozzle flow. The design order of accuracy is achieved in the smooth regions of a steady-state test case. However, in an unsteady test case, only first-order results are obtained downstream of a sound-shock interaction. The difficulty in obtaining a globally high-order-accurate solution in such a case with a shock-capturing method is demonstrated through the study of a simplified, linear model problem. Some of the difficult issues and ramifications for aeroacoustics simulations of flows with shocks that are raised by these results are discussed.

Code Verification Results of an LLNL ASC Code on Some Tri-Lab Verification Test Suite Problems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, S R; Bihari, B L; Salari, K

As scientific codes become more complex and involve larger numbers of developers and algorithms, chances for algorithmic implementation mistakes increase. In this environment, code verification becomes essential to building confidence in the code implementation. This paper will present first results of a new code verification effort within LLNL's B Division. In particular, we will show results of code verification of the LLNL ASC ARES code on the test problems: Su Olson non-equilibrium radiation diffusion, Sod shock tube, Sedov point blast modeled with shock hydrodynamics, and Noh implosion.

Internal Flow and Burning Characteristics of 16-inch Ram Jet Operating in a Free Jet at Mach Numbers of 1.35 and 1.73

NASA Technical Reports Server (NTRS)

Perchonok, Eugene; Farley, John M

1951-01-01

The effects of mass-flow ratio on the additive drag and normal-shock position of a single oblique-shock diffuser are presented. Also evaluated is the variation with operating condition of the velocity distribution at the combustion-chamber inlet. A comparison with connected-pipe data is included. Burner performance with a corrugated gutter-grid flame holder is discussed. It is shown that the total-pressure drop across the combustion chamber can be predicted with reasonable accuracy from the computed flame holder and combustion momentum pressure losses.

Trehalose: a biophysics approach to modulate the inflammatory response during endotoxic shock.

PubMed

Minutoli, Letteria; Altavilla, Domenica; Bitto, Alessandra; Polito, Francesca; Bellocco, Ersilia; Laganà, Giuseppina; Fiumara, Tiziana; Magazù, Salvatore; Migliardo, Federica; Venuti, Francesco Saverio; Squadrito, Francesco

2008-07-28

We evaluated the effects of trehalose against endotoxic shock, a condition in which the loss of bio-membrane integrity plays a pivotal role. In addition we performed a biophysics experiment by quasi elastic neutron scattering (QENS) study, to investigate whether the membrane stability effect of trehalose might be correlated with its high capability to switch-off the water diffusive dynamics and, hence, the kinetic mechanisms of interaction. Endotoxic shock was induced in male rats by a single injection of Salmonella enteritidis lipopolysaccharide (LPS; 20 mg/kg/i.p.). Thirty minutes before and 2 h after LPS injection, the animals were randomized to receive vehicle (1 ml/kg/i.p. 0.9%NaCl), sucrose (1 g/kg/i.p.) or trehalose (1 g/kg/i.p.). Mean arterial blood pressure, nuclear factor-kappaB (NF-kappaB) binding activity, Ikappa-Balpha and toll-like receptor-4 (TLR-4) activation were evaluated in both liver and lung. Plasmatic tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1), interleukin-6 (IL-6) and malondialdehyde (MDA) were also investigated. We studied liver injury by means of blood alanine aminotransferase activity (ALT); inducible nitric oxide synthase (iNOS) expression, myeloperoxidase (MPO) activity and tissue edema evaluation. Lung injury was investigated by means of tissue monocyte chemoattractant protein-1 (MCP-1) levels, MPO activity, iNOS expression and edema formation. Trehalose reduced hypotension, NF-kappaB binding activity, IkappaBalpha protein loss and TLR-4 activation. In addition trehalose reduced TNF-alpha, IL-1, IL-6 and MDA levels. Trehalose also blunted liver and lung injury. QENS measurements showed also that trehalose possesses a high "switching off" capability. Sucrose did not modify endotoxic shock-induced sequelae. Trehalose blocked the inflammatory cascade triggered by endotoxin shock, stabilizing the bio-membranes and switching off the water diffusive dynamics.

Total and Linearly Polarized Synchrotron Emission from Overpressured Magnetized Relativistic Jets

NASA Astrophysics Data System (ADS)

Fuentes, Antonio; Gómez, José L.; Martí, José M.; Perucho, Manel

2018-06-01

We present relativistic magnetohydrodynamic (RMHD) simulations of stationary overpressured magnetized relativistic jets, which are characterized by their dominant type of energy: internal, kinetic, or magnetic. Each model is threaded by a helical magnetic field with a pitch angle of 45° and features a series of recollimation shocks produced by the initial pressure mismatch, whose strength and number varies as a function of the dominant type of energy. We perform a study of the polarization signatures from these models by integrating the radiative transfer equations for synchrotron radiation using as inputs the RMHD solutions. These simulations show a top-down emission asymmetry produced by the helical magnetic field and a progressive confinement of the emission into a jet spine as the magnetization increases and the internal energy of the non-thermal population is considered to be a constant fraction of the thermal one. Bright stationary components associated with the recollimation shocks appear, presenting a relative intensity modulated by the Doppler boosting ratio between the pre-shock and post-shock states. Small viewing angles show a roughly bimodal distribution in the polarization angle, due to the helical structure of the magnetic field, which is also responsible for the highly stratified degree of linear polarization across the jet width. In addition, small variations of the order of 26° are observed in the polarization angle of the stationary components, which can be used to identify recollimation shocks in astrophysical jets.

Cosmic ray diffusion: Report of the Workshop in Cosmic Ray Diffusion Theory

NASA Technical Reports Server (NTRS)

Birmingham, T. J.; Jones, F. C.

1975-01-01

A workshop in cosmic ray diffusion theory was held at Goddard Space Flight Center on May 16-17, 1974. Topics discussed and summarized are: (1) cosmic ray measurements as related to diffusion theory; (2) quasi-linear theory, nonlinear theory, and computer simulation of cosmic ray pitch-angle diffusion; and (3) magnetic field fluctuation measurements as related to diffusion theory.

Fatal streptococcal toxic shock syndrome from an intrauterine device.

PubMed

Cho, Elizabeth E; Fernando, Dinali

2013-04-01

The occurrence of toxic shock syndrome from an intrauterine device (IUD) is very rare. To raise awareness of the risk of toxic shock syndrome caused by an IUD, to educate others about when to suspect this complication, and to provide treatment recommendations. A 49-year-old woman presented to the Emergency Department in septic shock after complaining of 5 days of nausea, vomiting, and diarrhea. Physical examination findings included a diffusely tender and rigid abdomen with free fluid on bedside sonogram. She was found, on computed tomography of her abdomen and pelvis, to have an IUD with moderate ascites. The IUD was removed, and both her IUD and her blood cultures grew out group A Streptococcus. Despite aggressive medical management, which included multiple vasopressors and broad-spectrum antibiotics, she died from group A streptococcal sepsis, with the IUD as her most likely source. Her clinical presentation and laboratory findings meet the Centers for Disease Control and Prevention diagnostic criteria for streptococcal toxic shock syndrome. Her diagnosis was confirmed by autopsy. IUDs should be considered as a possible source of infection in patients with an IUD who present with symptoms consistent with toxic shock syndrome. These patients need to be aggressively managed with early surgical intervention. Copyright © 2013. Published by Elsevier Inc.

Low-Energy Ions Injection and Acceleration at Oblique Shocks with Focused Transport Model

NASA Astrophysics Data System (ADS)

Zuo, P.; Zhang, M.; Feng, X. S.

2017-12-01

There is strong evidence that a small portion of suprathermal particles from hot coronal material or remnants of previous solar energetic particle (SEP) events serve as the source of large SEP events. Here we present a test particle simulation on the injection and acceleration of low-energy suprathermal particles by Laminar nonrelativistic oblique shocks in the framework of the focused transport theory, which is proved to contain all necessary physics of shock acceleration, but avoid the limitation of diffusive shock acceleration (DSA). We first characterize the role of cross-shock potential (CSP) on pickup ions (PUIs) acceleration. The CSP can affect the shape of the spectrum segment at lower energies, but it does not change the spectral index of the final power-law spectrum at high energies. It is found that a stronger CSP jump results in a dramatically improved injection efficiency. Our simulation results also show that the injection efficiency of PUIs is mass-dependent, which is lower for species with a higher mass. The injection efficiency as the function of Mach number, obliquity, injection speed, and shock strength is also calculated. It can be proved that the focused transport theory is an extension of DSA theory with the capability of predicting the efficiency of source particle injection.

Traveling waves in Hall-magnetohydrodynamics and the ion-acoustic shock structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hagstrom, George I.; Hameiri, Eliezer

Hall-magnetohydrodynamics (HMHD) is a mixed hyperbolic-parabolic partial differential equation that describes the dynamics of an ideal two fluid plasma with massless electrons. We study the only shock wave family that exists in this system (the other discontinuities being contact discontinuities and not shocks). We study planar traveling wave solutions and we find solutions with discontinuities in the hydrodynamic variables, which arise due to the presence of real characteristics in Hall-MHD. We introduce a small viscosity into the equations and use the method of matched asymptotic expansions to show that solutions with a discontinuity satisfying the Rankine-Hugoniot conditions and also anmore » entropy condition have continuous shock structures. The lowest order inner equations reduce to the compressible Navier-Stokes equations, plus an equation which implies the constancy of the magnetic field inside the shock structure. We are able to show that the current is discontinuous across the shock, even as the magnetic field is continuous, and that the lowest order outer equations, which are the equations for traveling waves in inviscid Hall-MHD, are exactly integrable. We show that the inner and outer solutions match, which allows us to construct a family of uniformly valid continuous composite solutions that become discontinuous when the diffusivity vanishes.« less