WorldWideScience

Sample records for shock acceleration mechanism

  1. Acceleration mechanisms flares, magnetic reconnection and shock waves

    Colgate, S.A.

    1979-01-01

    Several mechanisms are briefly discussed for the acceleration of particles in the astrophysical environment. Included are hydrodynamic acceleration, spherically convergent shocks, shock and a density gradient, coherent electromagnetic acceleration, the flux tube origin, symmetries and instabilities, reconnection, galactic flares, intergalactic acceleration, stochastic acceleration, and astrophysical shocks. It is noted that the supernova shock wave models still depend critically on the presupernova star structure and the assumption of highly compact presupernova models for type I supernovae. 37 references

  2. Dissipation Mechanisms and Particle Acceleration at the Earth's Bow Shock

    Desai, M. I.; Burch, J. L.; Broll, J. M.; Genestreti, K.; Torbert, R. B.; Ergun, R.; Wei, H.; Giles, B. L.; Russell, C. T.; Phan, T.; Chen, L. J.; Lai, H.; Wang, S.; Schwartz, S. J.; Allen, R. C.; Mauk, B.; Gingell, I.

    2017-12-01

    NASA's Magnetospheric Multiscale (MMS) mission has four spacecraft equipped with identical state-of-the-art instruments that acquire magnetic and electric field, plasma wave, and particle data at unprecedented temporal resolution to study the fundamental physics of magnetic reconnection in the Earth's magnetosphere. During Phase 1a, MMS also encountered and crossed the Earth's bow shock more than 300 times. We use burst data during 2 bow shock crossings to shed new light on key open questions regarding the formation, evolution, and dissipation mechanisms at collisionless shocks. Specifically, we focus on two events that exhibit clear differences in the ion and electron properties, the associated wave activity, and, therefore in the nature of the dissipation. In the case of a quasi-perpendicular, low beta shock crossing, we find that the dissipation processes are most likely associated with field-aligned electron beams that are coincident with high frequency electrostatic waves. On the other hand, the dissipation processes at an oblique, high beta shock crossing are largely governed by the quasi-static electric field and generation of magnetosonic whistler waves that result in perpendicular temperature anisotropy for the electrons. We also discuss the implications of these results for ion heating, reflection, and particle acceleration.

  3. Unlimited Relativistic Shock Surfing Acceleration

    Ucer, D.; Shapiro, V. D.

    2001-01-01

    Nonrelativistic shock surfing acceleration at quasiperpendicular shocks is usually considered to be a preacceleration mechanism for slow pickup ions to initiate diffusive shock acceleration. In shock surfing, the particle accelerates along the shock front under the action of the convective electric field of the plasma flow. However, the particle also gains kinetic energy normal to the shock and eventually escapes downstream. We consider the case when ions are accelerated to relativistic velocities. In this case, the ions are likely to be trapped for infinitely long times, because the energy of bounce oscillations tends to decrease during acceleration. This suggests the possibility of unlimited acceleration by shock surfing

  4. Relativistic Shock Acceleration

    Duffy, P.; Downes, T.P.; Gallant, Y.A.; Kirk, J.G.

    1999-01-01

    In this paper we briefly review the basic theory of shock waves in relativistic hydrodynamics and magneto-hydrodynamics, emphasising some astrophysically interesting cases. We then present an overview of the theory of particle acceleration at such shocks describing the methods used to calculate the spectral indices of energetic particles. Recent results on acceleration at ultra-relativistic shocks are discussed. (author)

  5. Experimental Insights into the Mechanisms of Particle Acceleration by Shock Waves

    Scolamacchia, T.; Scheu, B.; Dingwell, D. B.

    2011-12-01

    The generation of shock waves is common during explosive volcanic eruptions. Particles acceleration following shock wave propagation has been experimentally observed suggesting the potential hazard related to this phenomenon. Experiments and numerical models focused on the dynamics of formation and propagation of different types of shock waves when overpressurized eruptive mixtures are suddenly released in the atmosphere, using a pseudo-gas approximation to model those mixtures. Nevertheless, the results of several studies indicated that the mechanism of coupling between a gas and solid particles is valid for a limited grain-size range, which at present is not well defined. We are investigating particle acceleration mechanisms using a vertical shock tube consisting of a high-pressure steel autoclave (450 mm long, 28 mm in diameter), pressurized with argon, and a low-pressure 140 mm long acrylic glass autoclave, with the same internal diameter of the HP reservoir. Shock waves are generated by Ar decompression at atmospheric pressures at Pres/Pamb 100:1 to 150:1, through the failure of a diaphragm. Experiments were performed either with empty autoclave or suspending solid analogue particles 150 μm in size inside the LP autoclave. Incident Mach number varied from 1.7 to 2.1. Absolute and relative pressure sensors monitored P histories during the entire process, and a high-speed camera recorded particles movement at 20,000 to 30,000 fps. Preliminary results indicate pressure multiplication at the contact between shock waves and the particles in a time lapse of 100s μs, suggesting a possible different mechanism with respect to gas-particle coupling for particle acceleration.

  6. Reaction effects in diffusive shock acceleration

    Drury, L.Oc.

    1984-01-01

    The effects of the reaction of accelerated particles back on the shock wave in the diffusive-shock-acceleration model of cosmic-ray generation are investigated theoretically. Effects examined include changes in the shock structure, modifications of the input and output spectra, scattering effects, and possible instabilities in the small-scale structure. It is pointed out that the latter two effects are applicable to any spatially localized acceleration mechanism. 14 references

  7. Stochastic shock response spectrum decomposition method based on probabilistic definitions of temporal peak acceleration, spectral energy, and phase lag distributions of mechanical impact pyrotechnic shock test data

    Hwang, James Ho-Jin; Duran, Adam

    2016-08-01

    Most of the times pyrotechnic shock design and test requirements for space systems are provided in Shock Response Spectrum (SRS) without the input time history. Since the SRS does not describe the input or the environment, a decomposition method is used to obtain the source time history. The main objective of this paper is to develop a decomposition method producing input time histories that can satisfy the SRS requirement based on the pyrotechnic shock test data measured from a mechanical impact test apparatus. At the heart of this decomposition method is the statistical representation of the pyrotechnic shock test data measured from the MIT Lincoln Laboratory (LL) designed Universal Pyrotechnic Shock Simulator (UPSS). Each pyrotechnic shock test data measured at the interface of a test unit has been analyzed to produce the temporal peak acceleration, Root Mean Square (RMS) acceleration, and the phase lag at each band center frequency. Maximum SRS of each filtered time history has been calculated to produce a relationship between the input and the response. Two new definitions are proposed as a result. The Peak Ratio (PR) is defined as the ratio between the maximum SRS and the temporal peak acceleration at each band center frequency. The ratio between the maximum SRS and the RMS acceleration is defined as the Energy Ratio (ER) at each band center frequency. Phase lag is estimated based on the time delay between the temporal peak acceleration at each band center frequency and the peak acceleration at the lowest band center frequency. This stochastic process has been applied to more than one hundred pyrotechnic shock test data to produce probabilistic definitions of the PR, ER, and the phase lag. The SRS is decomposed at each band center frequency using damped sinusoids with the PR and the decays obtained by matching the ER of the damped sinusoids to the ER of the test data. The final step in this stochastic SRS decomposition process is the Monte Carlo (MC

  8. Cosmic ray acceleration mechanisms

    Cesarsky, C.J.

    1982-09-01

    We present a brief summary of some of the most popular theories of cosmic ray acceleration: Fermi acceleration, its application to acceleration by shocks in a scattering medium, and impulsive acceleration by relativistic shocks

  9. Particle acceleration in modified shocks

    Drury, L.O'C.; Axford, W.I.; Summers, D.

    1982-01-01

    Efficient particle acceleration in shocks must modify the shock structure with consequent changes in the particle acceleration. This effect is studied and analytic solutions are found describing the diffusive acceleration of particles with momentum independent diffusion coefficients in hyperbolic tangent type velocity transitions. If the input particle spectrum is a delta function, the shock smoothing replaces the truncated power-law downstream particle spectrum by a more complicated form, but one which has a power-law tail at high momenta. For a cold plasma this solution can be made completely self-consistent. Some problems associated with momentum dependent diffusion coefficients are discussed. (author)

  10. Particle acceleration in modified shocks

    Drury, L.O' C. (Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany, F.R.)); Axford, W.I. (Max-Planck-Institut fuer Aeronomie, Katlenburg-Lindau (Germany, F.R.)); Summers, D. (Memorial Univ. of Newfoundland, St. John' s (Canada))

    1982-03-01

    Efficient particle acceleration in shocks must modify the shock structure with consequent changes in the particle acceleration. This effect is studied and analytic solutions are found describing the diffusive acceleration of particles with momentum independent diffusion coefficients in hyperbolic tangent type velocity transitions. If the input particle spectrum is a delta function, the shock smoothing replaces the truncated power-law downstream particle spectrum by a more complicated form, but one which has a power-law tail at high momenta. For a cold plasma this solution can be made completely self-consistent. Some problems associated with momentum dependent diffusion coefficients are discussed.

  11. Role of drifts in diffusive shock acceleration

    Decker, R.B.

    1988-01-01

    The role played by shock-associated drifts during the diffusive acceleration of charged particles at collisionless MHD shocks is evaluated. In the rest frame of the shock, the total energy gained by a particle is shown to result from two coupled acceleration mechanisms, the usual first-order Fermi mechanism and the drift mechanism. When averaged over a distribution of particles, the ratio of the drift-associated energy gain to the total energy is found to be independent of the total energy at a given theta1 (the angle between the shock normal and the unperturbed upstream magnetic field) in agreement with theoretical predictions. No evidence is found for drift-associated deceleration, suggesting that drifts always augment acceleration. 35 references

  12. Diffusive Shock Acceleration and Turbulent Reconnection

    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.

  13. Relativistic shocks and particle acceleration

    Heavens, A.F.

    1988-01-01

    In this paper, we investigate the fluid dynamics of relativistic shock waves, and use the results to calculate the spectral index of particles accelerated by the Fermi process in such shocks. We have calculated the distributions of Fermi-accelerated particles at shocks propagating into cold proton-electron plasma and also cold electron-positron plasma. We have considered two different power spectra for the scattering waves, and find, in contrast to the non-relativistic case, that the spectral index of the accelerated particles depends on the wave power spectrum. On the assumption of thermal equilibrium both upstream and downstream, we present some useful fits for the compression ratio of shocks propagating at arbitrary speeds into gas of any temperature. (author)

  14. Particle Acceleration in Two Converging Shocks

    Wang, Xin; Wang, Na; Shan, Hao [Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi 830011 (China); Giacalone, Joe [Lunar and Planetary Laboratory, University of Arizona, Tucson AZ 85721 (United States); Yan, Yihua [CAS Key Laboratory of Solar Activity, National Astronomical Observatories, Beijing 100012 (China); Ding, Mingde, E-mail: wangxin@xao.ac.cn [Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University) Ministry of Education, Nanjing 210093 (China)

    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 Carlo 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.

  15. Simulation of mechanical shock environments

    Lalanne, Christian.

    1975-07-01

    Shocks can produce a severe mechanical environment which must be taken into account when designing and developing new equipments. After some mathematical (Laplace and Fourier transforms) and mechanical recalls (response of a one degree freedom system to a sinusoidal excitation), different analysis methods are compared, these methods being the most used now to compare relative severities of tests and establish specifications. A few chapter deal with the different properties of simple, easy to produce, shock shapes. Then some now-in-use programmators or shock-machines specifications are shown. A final chapter concerns acceleration transducers [fr

  16. Cosmic ray acceleration by large scale galactic shocks

    Cesarsky, C.J.; Lagage, P.O.

    1987-01-01

    The mechanism of diffusive shock acceleration may account for the existence of galactic cosmic rays detailed application to stellar wind shocks and especially to supernova shocks have been developed. Existing models can usually deal with the energetics or the spectral slope, but the observed energy range of cosmic rays is not explained. Therefore it seems worthwhile to examine the effect that large scale, long-lived galactic shocks may have on galactic cosmic rays, in the frame of the diffusive shock acceleration mechanism. Large scale fast shocks can only be expected to exist in the galactic halo. We consider three situations where they may arise: expansion of a supernova shock in the halo, galactic wind, galactic infall; and discuss the possible existence of these shocks and their role in accelerating cosmic rays

  17. Particle acceleration at shocks in the inner heliosphere

    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

  18. A FOCUSED TRANSPORT APPROACH TO THE TIME-DEPENDENT SHOCK ACCELERATION OF SOLAR ENERGETIC PARTICLES AT A FAST TRAVELING SHOCK

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

    2012-01-01

    Some of the most sophisticated models for solar energetic particle (SEP) acceleration at coronal mass ejection driven shocks are based on standard diffusive shock acceleration theory. However, this theory, which only applies when SEP pitch-angle anisotropies are small, might have difficulty in describing first-order Fermi acceleration or the shock pre-heating and injection of SEPs into first-order Fermi acceleration accurately at lower SEP speeds where SEP pitch-angle anisotropies upstream near the shock can be large. To avoid this problem, we use a time-dependent focused transport model to reinvestigate first-order Fermi acceleration at planar parallel and quasi-parallel spherical traveling shocks between the Sun and Earth with high shock speeds associated with rare extreme gradual SEP events. The focused transport model is also used to investigate and compare three different shock pre-heating mechanisms associated with different aspects of the nonuniform cross-shock solar wind flow, namely, the convergence of the flow (adiabatic compression), the shear tensor of the flow, and the acceleration of the flow, and a fourth shock pre-heating mechanism associated with the cross-shock electric field, to determine which pre-heating mechanism contributes the most to injecting shock pre-heated source particles into the first-order Fermi acceleration process. The effects of variations in traveling shock conditions, such as increasing shock obliquity and shock slowdown, and variations in the SEP source with increasing shock distance from the Sun on the coupled processes of shock pre-heating, injection, and first-order Fermi acceleration are analyzed. Besides the finding that the cross-shock acceleration of the solar wind flow yields the dominant shock pre-heating mechanism at high shock speeds, we find that first-order Fermi acceleration at fast traveling shocks differs in a number of respects from the predictions and assumptions of standard steady-state diffusive shock

  19. Energetic ion acceleration at collisionless shocks

    Decker, R. B.; Vlahos, L.

    1985-01-01

    An example is presented from a test particle simulation designed to study ion acceleration at oblique turbulent shocks. For conditions appropriate at interplanetary shocks near 1 AU, it is found that a shock with theta sub B n = 60 deg is capable of producing an energy spectrum extending from 10 keV to approx. 1 MeV in approx 1 hour. In this case total energy gains result primarily from several separate episodes of shock drift acceleration, each of which occurs when particles are scattered back to the shock by magnetic fluctuations in the shock vicinity.

  20. Energetic ion acceleration at collisionless shocks

    Decker, R.B.; Vlahos, L.

    1985-01-01

    An example is presented from a test particle simulation designed to study ion acceleration at oblique turbulent shocks. For conditions appropriate at interplanetary shocks near 1 AU, it is found that a shock with theta sub B n = 60 deg is capable of producing an energy spectrum extending from 10 keV to approx 1 MeV in approx 1 hour. In this case total energy gains result primarily from several separate episodes of shock drift acceleration, each of which occurs when particles are scattered back to the shock by magnetic fluctuations in the shock vicinity

  1. Mechanical shock absorber

    Vrillon, Bernard.

    1973-01-01

    The mechanical shock absorber described is made of a constant thickness plate pierced with circular holes regularly distributed in such a manner that for all the directions along which the strain is applied during the shock, the same section of the substance forming the plate is achieved. The shock absorber is made in a metal standing up to extensive deformation before breaking, selected from a group comprising mild steels and austenitic stainless steels. This apparatus is used for handling pots of fast neutron reactor fuel elements [fr

  2. Cosmic-ray shock acceleration in oblique MHD shocks

    Webb, G. M.; Drury, L. OC.; Volk, H. J.

    1986-01-01

    A one-dimensional, steady-state hydrodynamical model of cosmic-ray acceleration at oblique MHD shocks is presented. Upstream of the shock the incoming thermal plasma is subject to the adverse pressure gradient of the accelerated particles, the J x B force, as well as the thermal gas pressure gradient. The efficiency of the acceleration of cosmic-rays at the shock as a function of the upstream magnetic field obliquity and upstream plasma beta is investigated. Astrophysical applications of the results are briefly discussed.

  3. Electromagnetic Structure and Electron Acceleration in Shock–Shock Interaction

    Nakanotani, Masaru [Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasuga-Koen, Kasuga, Fukuoka, 816-8580 (Japan); Matsukiyo, Shuichi; Hada, Tohru [Faculty of Engineering Sciences, Kyushu University, 6-1 Kasuga-Koen, Kasuga, Fukuoka, 816-8580 (Japan); Mazelle, Christian X., E-mail: nakanot@esst.kyushu-u.ac.jp [IRAP, Université Paul Sabatier Toulouse III-CNRS, F-31028 Toulouse Cedex 4 (France)

    2017-09-10

    A shock–shock interaction is investigated by using a one-dimensional full particle-in-cell simulation. The simulation reproduces the collision of two symmetrical high Mach number quasi-perpendicular shocks. The basic structure of the shocks and ion dynamics is similar to that obtained by previous hybrid simulations. The new aspects obtained here are as follows. Electrons are already strongly accelerated before the two shocks collide through multiple reflection. The reflected electrons self-generate waves upstream between the two shocks before they collide. The waves far upstream are generated through the right-hand resonant instability with the anomalous Doppler effect. The waves generated near the shock are due to firehose instability and have much larger amplitudes than those due to the resonant instability. The high-energy electrons are efficiently scattered by the waves so that some of them gain large pitch angles. Those electrons can be easily reflected at the shock of the other side. The accelerated electrons form a power-law energy spectrum. Due to the accelerated electrons, the pressure of upstream electrons increases with time. This appears to cause the deceleration of the approaching shock speed. The accelerated electrons having sufficiently large Larmor radii are further accelerated through the similar mechanism working for ions when the two shocks are colliding.

  4. Particle acceleration and injection problem in relativistic and nonrelativistic shocks

    Hoshino, M.

    2008-01-01

    Acceleration of charged particles at the collisionless shock is believed to be responsible for production of cosmic rays in a variety of astrophysical objects such as supernova, AGN jet, and GRB etc., and the diffusive shock acceleration model is widely accepted as a key process for generating cosmic rays with non-thermal, power-law energy spectrum. Yet it is not well understood how the collisionless shock can produce such high energy particles. Among several unresolved issues, two major problems are the so-called '' injection '' problem of the supra-thermal particles and the generation of plasma waves and turbulence in and around the shock front. With recent advance of computer simulations, however, it is now possible to discuss those issues together with dynamical evolution of the kinetic shock structure. A wealth of modern astrophysical observations also inspires the dynamical shock structure and acceleration processes along with the theoretical and computational studies on shock. In this presentation, we focus on the plasma wave generation and the associated particle energization that directly links to the injection problem by taking into account the kinetic plasma processes of both non-relativistic and relativistic shocks by using a particle-in-cell simulation. We will also discuss some new particle acceleration mechanisms such as stochastic surfing acceleration and wakefield acceleration by the action of nonlinear electrostatic fields. (author)

  5. Electron acceleration in a wavy shock front

    Vandas, Marek; Karlický, Marian

    2011-01-01

    Roč. 531, July (2011), A55/1-A55/8 ISSN 0004-6361 R&D Projects: GA AV ČR(CZ) IAA300030701; GA MŠk(CZ) ME09009; GA ČR GA205/09/0170; GA ČR GAP209/10/1680 Grant - others:EU(XE) EC FP7 SWIFF 263340 Institutional research plan: CEZ:AV0Z10030501 Keywords : shock waves * acceleration of particles * magnetic fields * solar radio radiation Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.587, year: 2011

  6. Turbulent energy generated by accelerations and shocks

    Mikaelian, K.O.

    1986-01-01

    The turbulent energy generated at the interface between two fluids undergoing a constant acceleration or a shock is calculated. Assuming linear density profiles in the mixed region we find E/sub turbulent//E/sub directed/ = 2.3A 2 % (constant acceleration) and 9.3A 2 % (shock), where A is the Atwood number. Diffusion models predict somewhat less turbulent energy and a density profile with a tail extending into the lower density fluid. Eddy sizes are approximately 27% (constant acceleration) and 17% (shock) of the mixing depth into the heavier fluid. 6 refs., 3 figs

  7. Nonlinear theory of diffusive acceleration of particles by shock waves

    Malkov, M.A. [University of California at San Diego, La Jolla, CA (United States)]. E-mail: mmalkov@ucsd.edu; Drury, L. O' C. [Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2 (Ireland)

    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. (author)

  8. Particle acceleration and shock wave structure

    DRURY, L.O'C.

    1989-01-01

    A significant determinant in the large-scale structure and evolution of strong collisionless shocks under astrophysical conditions is probably the acceleration of charged particles. The reaction of these particles on the dynamical structure of the shock wave is discussed both theoretically and in the light of recent numerical calculations. Astrophysical implications for the evolution of supernova remnants, are considered. (author). 15 refs

  9. New particle accelerations by magnetized plasma shock waves

    Takeuchi, Satoshi

    2005-01-01

    Three mechanisms concerning particle accelerations are proposed to account for the high energy of cosmic rays. A model of magnetized plasma clouds is used to simulate a shock-type wave. The attainable energies of test particles colliding with the moving magnetic clouds are investigated by analytical and numerical methods for the three mechanisms. The magnetic trapping acceleration is a new type of particle trapping and acceleration in which, in principle, the test particle is accelerated indefinitely; hence, this mechanism surpasses the Fermi-type acceleration. In the single-step acceleration, the test particle obtains a significant energy gain even though it only experiences a single collision. Lastly, there is the bouncing acceleration by which the test particle is substantially accelerated due to repeated collisions

  10. Preferential acceleration in collisionless supernova shocks

    Hainebach, K.; Eichler, D.; Schramm, D.

    1979-01-01

    The preferential acceleration and resulting cosmic ray abundance enhancements of heavy elements (relative to protons) are calculated in the collisionless supernova shock acceleration model described by Eichler in earlier work. Rapidly increasing enhancements up to several tens times solar ratios are obtained as a function of atomic weight over charge at the time of acceleration. For material typical of hot phase interstellar medium, good agreement is obtained with the observed abundance enhancements

  11. Monte Carlo study of neutrino acceleration in supernova shocks

    Kazanas, Demosthenes; Ellison, D.C.; National Aeronautics and Space Administration, Greenbelt, MD

    1981-01-01

    The first order Fermi acceleration mechanism of cosmic rays in shocks may be at work for neutrinos in supernova shocks when the latter are at densities rho>10 13 g cm -3 at which the core material is opaque to neutrinos. A Monte Carlo approach to study this effect is employed and the emerging neutrino power law spectra are presented. The increased energy acquired by the neutrinos may facilitate their detection in supernova explosions and provide information about the physics of collapse

  12. Effects of Shock and Turbulence Properties on Electron Acceleration

    Qin, G.; Kong, F.-J.; Zhang, L.-H.

    2018-06-01

    Using test particle simulations, we study electron acceleration at collisionless shocks with a two-component model turbulent magnetic field with slab component including dissipation range. We investigate the importance of the shock-normal angle θ Bn, magnetic turbulence level {(b/{B}0)}2, and shock thickness on the acceleration efficiency of electrons. It is shown that at perpendicular shocks the electron acceleration efficiency is enhanced with the decrease of {(b/{B}0)}2, and at {(b/{B}0)}2=0.01 the acceleration becomes significant due to a strong drift electric field with long time particles staying near the shock front for shock drift acceleration (SDA). In addition, at parallel shocks the electron acceleration efficiency is increasing with the increase of {(b/{B}0)}2, and at {(b/{B}0)}2=10.0 the acceleration is very strong due to sufficient pitch-angle scattering for first-order Fermi acceleration, as well as due to the large local component of the magnetic field perpendicular to the shock-normal angle for SDA. On the other hand, the high perpendicular shock acceleration with {(b/{B}0)}2=0.01 is stronger than the high parallel shock acceleration with {(b/{B}0)}2=10.0, the reason might be the assumption that SDA is more efficient than first-order Fermi acceleration. Furthermore, for oblique shocks, the acceleration efficiency is small no matter whether the turbulence level is low or high. Moreover, for the effect of shock thickness on electron acceleration at perpendicular shocks, we show that there exists the bendover thickness, L diff,b. The acceleration efficiency does not noticeably change if the shock thickness is much smaller than L diff,b. However, if the shock thickness is much larger than L diff,b, the acceleration efficiency starts to drop abruptly.

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

    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).

  14. Observational test of shock drift and Fermi acceleration on a seed particle population upstream of earth's bow shock

    Anagnostopoulos, G. C.; Sarris, E. T.; Krimigis, S. M.

    1988-01-01

    The efficiency of proposed shock acceleration mechanisms as they operate at the bow shock in the presence of a seed energetic particle population was examined using data from simultaneous observations of energetic solar-origin protons, carried out by the IMP 7 and 8 spacecraft in the vicinity of the quasi-parallel (dawn) and quasi-perpendicular (dusk) regions of the earth's bow shock, respectively. The results of observations (which include acceleration effects in the intensities of the energetic protons with energies as high as 4 MeV observed at the vicinity of the dusk bow shock, but no evidence for any particle acceleration at the energy equal to or above 50 keV at the dawn side of the bow shock) indicate that the acceleration of a seed particle population occurs only at the quasi-perpendicular bow shock through shock drift acceleration and that the major source of observed upstream ion populations is the leakage of magnetospheric ions of energies not less than 50 keV, rather than in situ acceleration.

  15. Resonant ion acceleration by collisionless magnetosonic shock waves

    Ohsawa, Y.

    1985-01-01

    Resonant ion acceleration ( the ν/sub rho/xΒ acceleration ) in laminar magnetosonic shock waves is studied by theory and simulation. Theoretical analysis based on a two-fluid model shows that, in laminar shocks, the electric field strength in the direction of the wave normal is about (m/sub i/m/sub e/) 1 2 times large for quasi-perpendicular shocks than that for the quasi-parallel shocks, which is a reflection of the fact that the width of quasi-perpendicular shocks is much smaller than that of the quasi-parallel shocks. Trapped ions can be accelerated up to the speed about ν/sub A/(m/sub i/m/sub e/) 1 2(M/sub A/-1) 3 2 in quasi-perpendicular shocks. Time evolution of self-consistent magnetosonic shock waves is studied by using a 2-12 dimensional fully relativistic, fully electromagnetic particle simulation with full ion and electron dynamics. Even a low-Mach-number shock wave can significantly accelerate trapped ions by the ν/sub rho/xΒ acceleration. The resonant ion acceleration occurs more strongly in quasi-perpendicular shocks, because the magnitude of this acceleration is proportional to the electric field strength

  16. An introduction to acceleration mechanisms

    Palmer, R.B.

    1987-05-01

    This paper discusses the acceleration of charged particles by electromagnetic fields, i.e., by fields that are produced by the motion of other charged particles driven by some power source. The mechanisms that are discussed include: Ponderamotive Forces, Acceleration, Plasma Beat Wave Acceleration, Inverse Free Electron Laser Acceleration, Inverse Cerenkov Acceleration, Gravity Acceleration, 2D Linac Acceleration and Conventional Iris Loaded Linac Structure Acceleration

  17. Drift mechanism for energetic charged particles at shocks

    Webb, G.M.; Axford, W.I.; Terasawa, T.

    1983-01-01

    The energy changes of energetic charged particles at a plane shock due to the so-called drift mechanism are analyzed by using the ''adiabatic treatment.'' The analysis shows that for a fast MHD shock, particles lose energy owing to acceleration (curvature) drift in the magnetic field at the shock with the drift velocity being antiparallel to the electric field, and they gain energy owing to gradient drift parallel to the electric field. It is shown that particles with pitch angles aligned along the magnetic field which pass through the shock tend to lose energy owing to acceleration drift, whereas particles with pitch angles nonaligned to the magnetic field gain energy owing to gradient drift. Particles that are reflected by the shock always gain energy. Slow-mode shocks may be similarly analyzed, but in this case curvature drifts give rise to particle energy gains, and gradient drifts result in particle energy losses

  18. Non-thermal electron acceleration in low Mach number collisionless shocks. II. Firehose-mediated Fermi acceleration and its dependence on pre-shock conditions

    Guo, Xinyi; Narayan, Ramesh [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Sironi, Lorenzo [NASA Einstein Postdoctoral Fellow. (United States)

    2014-12-10

    Electron acceleration to non-thermal energies is known to occur in low Mach number (M{sub s} ≲ 5) shocks in galaxy clusters and solar flares, but the electron acceleration mechanism remains poorly understood. Using two-dimensional (2D) particle-in-cell (PIC) plasma simulations, we showed in Paper I that electrons are efficiently accelerated in low Mach number (M{sub s} = 3) quasi-perpendicular shocks via a Fermi-like process. The electrons bounce between the upstream region and the shock front, with each reflection at the shock resulting in energy gain via shock drift acceleration. The upstream scattering is provided by oblique magnetic waves that are self-generated by the electrons escaping ahead of the shock. In the present work, we employ additional 2D PIC simulations to address the nature of the upstream oblique waves. We find that the waves are generated by the shock-reflected electrons via the firehose instability, which is driven by an anisotropy in the electron velocity distribution. We systematically explore how the efficiency of wave generation and of electron acceleration depend on the magnetic field obliquity, the flow magnetization (or equivalently, the plasma beta), and the upstream electron temperature. We find that the mechanism works for shocks with high plasma beta (≳ 20) at nearly all magnetic field obliquities, and for electron temperatures in the range relevant for galaxy clusters. Our findings offer a natural solution to the conflict between the bright radio synchrotron emission observed from the outskirts of galaxy clusters and the low electron acceleration efficiency usually expected in low Mach number shocks.

  19. Heavy ion acceleration at parallel shocks

    V. L. Galinsky

    2010-11-01

    Full Text Available A study of alpha particle acceleration at parallel shock due to an interaction with Alfvén waves self-consistently excited in both upstream and downstream regions was conducted using a scale-separation model (Galinsky and Shevchenko, 2000, 2007. The model uses conservation laws and resonance conditions to find where waves will be generated or damped and hence where particles will be pitch-angle scattered. It considers the total distribution function (for the bulk plasma and high energy tail, so no standard assumptions (e.g. seed populations, or some ad-hoc escape rate of accelerated particles are required. The heavy ion scattering on hydromagnetic turbulence generated by both protons and ions themselves is considered. The contribution of alpha particles to turbulence generation is important because of their relatively large mass-loading parameter Pα=nαmα/npmp (mp, np and mα, nα are proton and alpha particle mass and density that defines efficiency of wave excitation. The energy spectra of alpha particles are found and compared with those obtained in test particle approximation.

  20. The acceleration of particles at propagating interplanetary shocks

    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.

  1. Shock-drift accelerated electrons and n-distribution

    Vandas, Marek; Karlický, Marian

    2016-01-01

    Roč. 591, July (2016), A127/1-A127/6 ISSN 0004-6361 R&D Projects: GA ČR(CZ) GA14-19376S; GA ČR GA15-17490S; GA ČR GAP209/12/0103 Grant - others:EC(XE) 295272; EC(XE) 606862 Program:FP7; FP7 Institutional support: RVO:67985815 Keywords : shock waves * acceleration of particles * Sun flares Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.378, year: 2014

  2. Collisionless shocks in space plasmas structure and accelerated particles

    Burgess, David

    2015-01-01

    Shock waves are an important feature of solar system plasmas, from the solar corona out to the edge of the heliosphere. This engaging introduction to collisionless shocks in space plasmas presents a comprehensive review of the physics governing different types of shocks and processes of particle acceleration, from fundamental principles to current research. Motivated by observations of planetary bow shocks, interplanetary shocks and the solar wind termination shock, it emphasises the physical theory underlying these shock waves. Readers will develop an understanding of the complex interplay between particle dynamics and the electric and magnetic fields that explains the observations of in situ spacecraft. Written by renowned experts in the field, this up-to-date text is the ideal companion for both graduate students new to heliospheric physics and researchers in astrophysics who wish to apply the lessons of solar system shocks to different astrophysical environments.

  3. Radiography for a Shock-accelerated Liquid Layer

    P. Meekunnasombat J.G. Oakley/inst M.H. Anderson R. Bonazza

    2005-01-01

    This program supported the experimental study of the interaction of planar shock waves with both solid structures (a single cylinder or a bank of cylinders) and single and multiple liquid layers. Objectives of the study included: characterization of the shock refraction patterns; measurements of the impulsive loading of the solid structures; observation of the response of the liquid layers to shock acceleration; assessment of the shock-mitigation effects of single and multiple liquid layers. The uploaded paper is intended as a final report for the entire funding period. The poster described in the paper won the Best Poster Award at the 25 International Symposium on Shock Waves

  4. The acceleration of cosmic ray by shock waves

    Axford, W.I.; Leer, E.; Skadron, G.

    1977-01-01

    The acceleration of cosmic rays in flows involving shocks and other compressional waves is considered in terms of one-dimensionl, steady flows and the diffusion approximation. The results suggest that very substantial energy conversion can occur. (author)

  5. Acceleration of cosmic rays in SNR shock waves

    Drury, L.O'C.; Markiewicz, W.J.; Voelk, H.J.

    1988-01-01

    The time dependence of the energy density of cosmic rays accelerated in the outer shock of a supernova is studied in simple nonlinear models. The solutions are classified in their dependence on the parameters of the system. (orig.)

  6. Cosmic Rays Accelerated at Cosmological Shock Waves Renyi Ma1 ...

    Cosmic Rays Accelerated at Cosmological Shock Waves. Renyi Ma1,2,∗ ... ratio of CR to thermal energy in the ICM and WHIM based on numerical simulations and diffusive shock ... Hence, the nonthermal radiation of CRs may provide us a.

  7. Particle acceleration by coronal and interplanetary shock waves

    Pesses, M.E.

    1982-01-01

    Utilizing many years of observation from deep space and near-earth spacecraft a theoretical understanding has evolved on how ions and electrons are accelerated in interplanetary shock waves. This understanding is now being applied to solar flare-induced shock waves propagating through the solar atmosphere. Such solar flare phenomena as gamma-ray line and neutron emissions, interplanetary energetic electron and ion events, and Type II and moving Type IV radio bursts appear understandable in terms of particle acceleration in shock waves

  8. Shock Isolation Elements Testing for High Input Loadings. Volume III. Mechanical Shock Isolation Elements.

    SHOCK ABSORBERS ), (*GUIDED MISSILE SILOS, SHOCK ABSORBERS ), (*SPRINGS, (*SHOCK(MECHANICS), REDUCTION), TORSION BARS, ELASTOMERS, DAMPING, EQUATIONS OF MOTION, MODEL TESTS, TEST METHODS, NUCLEAR EXPLOSIONS, HARDENING.

  9. Compact all-fiber interferometer system for shock acceleration measurement

    Zhao, Jiang; Pi, Shaohua; Hong, Guangwei; Zhao, Dong; Jia, Bo

    2013-08-01

    Acceleration measurement plays an important role in a variety of fields in science and engineering. In particular, the accurate, continuous and non-contact recording of the shock acceleration profiles of the free target surfaces is considered as a critical technique in shock physics. Various kinds of optical interferometers have been developed to monitor the motion of the surfaces of shocked targets since the 1960s, for instance, the velocity interferometer system for any reflector, the fiber optic accelerometer, the photonic Doppler velocimetry system and the displacement interferometer. However, most of such systems rely on the coherent quasi-monochromatic illumination and discrete optic elements, which are costly in setting-up and maintenance. In 1996, L. Levin et al reported an interferometric fiber-optic Doppler velocimeter with high-dynamic range, in which fiber-coupled components were used to replace the discrete optic elements. However, the fringe visibility of the Levin's system is low because of the coupled components, which greatly limits the reliability and accuracy in the shock measurement. In this paper, a compact all-fiber interferometer system for measuring the shock acceleration is developed and tested. The advantage of the system is that not only removes the non-interfering light and enhances the fringe visibility, but also reduces polarization induced signal fading and the polarization induced phase shift. Moreover, it also does not require a source of long coherence length. The system bases entirely on single-mode fiber optics and mainly consists of a polarization beam splitter, a faraday rotator, a depolarizer and a 3×3 single-mode fiber coupler which work at 1310 nm wavelength. The optical systems of the interferometer are described and the experimental results compared with a shock acceleration calibration system with a pneumatic exciter (PneuShockTM Model 9525C by The Modal Shop) are reported. In the shock acceleration test, the

  10. PARTICLE ACCELERATION AT THE HELIOSPHERIC TERMINATION SHOCK WITH A STOCHASTIC SHOCK OBLIQUITY APPROACH

    Arthur, Aaron D.; Le Roux, Jakobus A.

    2013-01-01

    Observations by the plasma and magnetic field instruments on board the Voyager 2 spacecraft suggest that the termination shock is weak with a compression ratio of ∼2. However, this is contrary to the observations of accelerated particle spectra at the termination shock, where standard diffusive shock acceleration theory predicts a compression ratio closer to ∼2.9. Using our focused transport model, we investigate pickup proton acceleration at a stationary spherical termination shock with a moderately strong compression ratio of 2.8 to include both the subshock and precursor. We show that for the particle energies observed by the Voyager 2 Low Energy Charged Particle (LECP) instrument, pickup protons will have effective length scales of diffusion that are larger than the combined subshock and precursor termination shock structure observed. As a result, the particles will experience a total effective termination shock compression ratio that is larger than values inferred by the plasma and magnetic field instruments for the subshock and similar to the value predicted by diffusive shock acceleration theory. Furthermore, using a stochastically varying magnetic field angle, we are able to qualitatively reproduce the multiple power-law structure observed for the LECP spectra downstream of the termination shock

  11. GYROSURFING ACCELERATION OF IONS IN FRONT OF EARTH's QUASI-PARALLEL BOW SHOCK

    Kis, Arpad; Lemperger, Istvan; Wesztergom, Viktor; Agapitov, Oleksiy; Krasnoselskikh, Vladimir; Khotyaintsev, Yuri V.; Dandouras, Iannis

    2013-01-01

    It is well known that shocks in space plasmas can accelerate particles to high energies. However, many details of the shock acceleration mechanism are still unknown. A critical element of shock acceleration is the injection problem; i.e., the presence of the so called seed particle population that is needed for the acceleration to work efficiently. In our case study, we present for the first time observational evidence of gyroresonant surfing acceleration in front of Earth's quasi-parallel bow shock resulting in the appearance of the long-suspected seed particle population. For our analysis, we use simultaneous multi-spacecraft measurements provided by the Cluster spacecraft ion (CIS), magnetic (FGM), and electric field and wave instrument (EFW) during a time period of large inter-spacecraft separation distance. The spacecraft were moving toward the bow shock and were situated in the foreshock region. The results show that the gyroresonance surfing acceleration takes place as a consequence of interaction between circularly polarized monochromatic (or quasi-monochromatic) transversal electromagnetic plasma waves and short large amplitude magnetic structures (SLAMSs). The magnetic mirror force of the SLAMS provides the resonant conditions for the ions trapped by the waves and results in the acceleration of ions. Since wave packets with circular polarization and different kinds of magnetic structures are very commonly observed in front of Earth's quasi-parallel bow shock, the gyroresonant surfing acceleration proves to be an important particle injection mechanism. We also show that seed ions are accelerated directly from the solar wind ion population.

  12. GYROSURFING ACCELERATION OF IONS IN FRONT OF EARTH's QUASI-PARALLEL BOW SHOCK

    Kis, Arpad; Lemperger, Istvan; Wesztergom, Viktor [Research Centre for Astronomy and Earth Sciences, Geodetic and Geophysical Institute, Sopron (Hungary); Agapitov, Oleksiy; Krasnoselskikh, Vladimir [LPC2E/CNRS, F-45071 Orleans (France); Khotyaintsev, Yuri V. [Swedish Institute of Space Physics, SE- 751 21 Uppsala (Sweden); Dandouras, Iannis, E-mail: akis@ggki.hu, E-mail: Kis.Arpad@csfk.mta.hu [CESR, F-31028 Toulouse (France)

    2013-07-01

    It is well known that shocks in space plasmas can accelerate particles to high energies. However, many details of the shock acceleration mechanism are still unknown. A critical element of shock acceleration is the injection problem; i.e., the presence of the so called seed particle population that is needed for the acceleration to work efficiently. In our case study, we present for the first time observational evidence of gyroresonant surfing acceleration in front of Earth's quasi-parallel bow shock resulting in the appearance of the long-suspected seed particle population. For our analysis, we use simultaneous multi-spacecraft measurements provided by the Cluster spacecraft ion (CIS), magnetic (FGM), and electric field and wave instrument (EFW) during a time period of large inter-spacecraft separation distance. The spacecraft were moving toward the bow shock and were situated in the foreshock region. The results show that the gyroresonance surfing acceleration takes place as a consequence of interaction between circularly polarized monochromatic (or quasi-monochromatic) transversal electromagnetic plasma waves and short large amplitude magnetic structures (SLAMSs). The magnetic mirror force of the SLAMS provides the resonant conditions for the ions trapped by the waves and results in the acceleration of ions. Since wave packets with circular polarization and different kinds of magnetic structures are very commonly observed in front of Earth's quasi-parallel bow shock, the gyroresonant surfing acceleration proves to be an important particle injection mechanism. We also show that seed ions are accelerated directly from the solar wind ion population.

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

    Ohira, Yutaka, E-mail: ohira@phys.aoyama.ac.jp [Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1 Fuchinobe, Sagamihara 252-5258 (Japan)

    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. 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.

  14. Shock-Wave Acceleration of Protons on OMEGA EP

    Haberberger, D.; Froula, D. H.; Pak, A.; Link, A.; Patel, P.; Fiuza, F.; Tochitsky, S.; Joshi, C.

    2015-11-01

    Recent experimental results using shock-wave acceleration (SWA) driven by a CO2 laser in a H2 gas-jet plasma have shown the possibility of producing proton beams with energy spreads emission from a UV ablated material. The desired characteristics optimal for SWA are met: (a) peak plasma density is overcritical for the 1- μm main pulse and (b) the plasma profile exponentially decays over a long scale length on the rear side. Results will be shown using a 4 ω probe to experimentally characterize the plasma density profile. Scaling from simulations of the SWA mechanism shows that ion energies in the range of 100 MeV/amu are achievable with a focused a0 of 5 from the OMEGA EP Laser System. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

  15. The application of front tracking to the simulation of shock refractions and shock accelerated interface mixing

    Sharp, D.H.; Grove, J.W.; Yang, Y.; Boston, B.; Holmes, R.; Zhang, Q.; Glimm, J.

    1993-01-01

    The mixing behavior of two or more fluids plays an important role in a number of physical processes and technological applications. The authors consider two basic types of mechanical (i.e., non-diffusive) fluid mixing. If a heavy fluid is suspended above a lighter fluid in the presence of a gravitational field, small perturbations at the fluid interface will grow. This process is known as the Rayleigh-Taylor instability. One can visualize this instability in terms of bubbles of the light fluid rising into the heavy fluid, and fingers (spikes) of the heavy fluid falling into the light fluid. A similar process, called the Richtmyer-Meshkov instability occurs when an interface is accelerated by a shock wave. These instabilities have several common features. Indeed, Richtmyer's approach to understanding the shock induced instability was to view that process as resulting from an acceleration of the two fluids by a strong gravitational field acting for a short time. Here, the authors report new results on the Rayleigh-Taylor and Richtmyer-Meshkov instabilities. Highlights include calculations of Richtmyer-Meshkov instabilities in curved geometries without grid orientation effects, improved agreement between computations and experiments in the case of Richtmyer-Meshkov instabilities at a plane interface, and a demonstration of an increase in the Rayleigh-Taylor mixing layer growth rate with increasing compressibility, along with a loss of universality of this growth rate. The principal computational tool used in obtaining these results was a code based on the front tracking method

  16. Cosmic-ray acceleration at stellar wind terminal shocks

    Webb, G.M.; Forman, M.A.; Axford, W.I.

    1985-01-01

    Steady-state, spherically symmetric, analytic solutions of the cosmic-ray transport equations, applicable to the problem of acceleration of cosmic rays at the terminal shock to a stellar wind, are studied. The spectra, gradients, and flow patterns of particle modulated and accelerated by the stellar wind and shock are investigated by means of monoenergetic-source solutions at finite radius, as well as solutions with monoenergetic and power-law Galactic spectra. The solutions obtained apply in the test particle limit in which the cosmic rays do not modify the background flow. The solutions show a characteristic power-law momentum spectrum for accelerated particles and a more complex spectrum of particles that are decelerated in the stellar wind. The power-law spectral index depends on the compression ratio of the shock and on the modulation parameters characterizing propagation conditions in the upstream and downstream regions of the shock. Solutions of the transport equations for the total density N (integrated over all energies), pressure P/sub c/, and energy flux F/sub c/ of Galactic cosmic rays interacting with a stellar wind and shock are also studied. The density N(r) increases with radius r, and for strong shocks with large enough modulation parameters, there may be a significant enhancement of the pressure of weakly relativistic particles near the shock compared to the cosmic-ray background pressure P/sub infinity/. The emergent energy flux at infinity is of the order of 4π R 2 V 1 P/sub infinity/ (V 1 is wind velocity upstream of the shock, R is shock radius)

  17. Analytic study of 1D diffusive relativistic shock acceleration

    Keshet, Uri, E-mail: ukeshet@bgu.ac.il [Physics Department, Ben-Gurion University of the Negev, POB 653, Be' er-Sheva 84105 (Israel)

    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, and (for a J(üttner-Synge equation of state) noticeably hardens with increasing 1<γ{sub u}<57, before logarithmically converging back to p (γ{sub u→∞})=2. The 1D spectrum is sensitive to drifts, but only in the downstream, and not in the ultra-relativistic limit.

  18. Shock drift acceleration in the presence of waves

    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.

  19. Particle injection and cosmic ray acceleration at collisionless parallel shocks

    Quest, K.B.

    1987-01-01

    The structure of collisionless parallel shocks is studied using one-dimensional hybrid simulations, with emphasis on particle injection into the first-order Fermi acceleration process. It is argued that for sufficiently high Mach number shocks, and in the absence of wave turbulence, the fluid firehose marginal stability condition will be exceeded at the interface between the upstream, unshocked, plasma and the heated plasma downstream. As a consequence, nonlinear, low-frequency, electromagnetic waves are generated and act to slow the plasma and provide dissipation for the shock. It is shown that large amplitude waves at the shock ramp scatter a small fraction of the upstream ions back into the upstream medium. These ions, in turn, resonantly generate the electromagnetic waves that are swept back into the shock. As these waves propagate through the shock they are compressed and amplified, allowing them to non-resonantly scatter the bulk of the plasma. Moreover, the compressed waves back-scatter a small fraction of the upstream ions, maintaining the shock structure in a quasi-steady state. The back-scattered ions are accelerated during the wave generation process to 2 to 4 times the ram energy and provide a likely seed population for cosmic rays. 49 refs., 7 figs

  20. Advanced and Exploratory Shock Sensing Mechanisms.

    Nelsen, Nicholas H. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Kolb, James D. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Kulkarni, Akshay G. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Sorscher, Zachary [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Habing, Clayton D. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Mathis, Allen [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Beller, Zachary J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2017-09-01

    Mechanical component response to shock environments must be predictable in order to ensure reliability and safety. Whether the shock input results from accidental drops during transportation to projectile impact scenarios, the system must irreversibly transition into a safe state that is incapable of triggering the component . With this critical need in mind, the 2017 Nuclear Weapons Summer Product Realization Institute (NW SPRINT) program objective sought the design of a passive shock failsafe with emphasis on additively manufactured (AM) components. Team Advanced and Exploratory (A&E) responded to the challenge by designing and delivering multiple passive shock sensing mech anisms that activate within a prescribed mechanical shock threshold. These AM failsafe designs were tuned and validated using analytical and computational techniques including the shock response spectrum (SRS) and finite element analysis (FEA). After rapid prototyping, the devices experienced physical shock tests conducted on Sandia drop tables to experimentally verify performance. Keywords: Additive manufacturing, dynamic system, failsafe, finite element analysis, mechanical shock, NW SPRINT, shock respon se spectrum

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

    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.

  2. Time-dependent diffusive acceleration of test particles at shocks

    Drury, L.O' C. (Dublin Inst. for Advanced Studies (Ireland))

    1991-07-15

    The acceleration of test particles at a steady plane non-relativistic shock is considered. Analytic expressions are found for the mean and the variance of the acceleration time distribution in the case where the diffusion coefficient has an arbitrary dependence on position and momentum. These expressions are used as the basis for an approximation scheme which is shown, by comparison with numerical solutions, to give an excellent representation of the time-dependent spectrum. (author).

  3. Time-dependent diffusive acceleration of test particles at shocks

    Drury, L.O'C.

    1991-01-01

    The acceleration of test particles at a steady plane non-relativistic shock is considered. Analytic expressions are found for the mean and the variance of the acceleration time distribution in the case where the diffusion coefficient has an arbitrary dependence on position and momentum. These expressions are used as the basis for an approximation scheme which is shown, by comparison with numerical solutions, to give an excellent representation of the time-dependent spectrum. (author)

  4. Particle acceleration at quasi-perpendicular shock waves: Theory and observations at 1 AU

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

    2014-01-01

    The injection of particles into the diffusive shock acceleration mechanism at highly perpendicular (where θ Bn > 70°) interplanetary shocks is investigated. This extends the previous study of Neergaard Parker and Zank which focused on the injection problem at quasi-parallel interplanetary shocks. We use observations at 1 AU to construct upstream Maxwellian and κ-distributions that are then diffusively accelerated by the shock, thus yielding the downstream accelerated particle distribution. We compare the theoretical accelerated particle distribution to observations at 1 AU using Advanced Composition Explorer data. We classify our results for quasi-perpendicular shocks into three subcategories: those with ratios of the theoretical spectral index to observed power law of >1, ∼ 1, and <1, and compare the magnetic power spectral density plots of these categories. We find that in general the assumed upstream particle distribution that best fits the energetic particle observations is best represented by a κ-distribution, with κ = 4. The magnetic field fluctuations were representative of quasi-perpendicular shocks and showed no particular bias toward our spectral ratio subcategories. The subcategory with spectral ratio <0.9 yielded the largest injection energies for all groups. In all but two of the cases in this study, there were enough particles in the solar wind thermal core to account for the accelerated distribution, thereby giving a lower limit to the required injection energy needed to diffusively accelerate particles at a quasi-perpendicular interplanetary shock. In the remaining two cases, an additional population of particles was required to match the appropriate amplitude of the spectral index. For these cases, we used a low energy (1-50 keV) v –5 spectrum advocated by Fisk and Gloeckler.

  5. Dynamics of particles accelerated by head-on collisions of two magnetized plasma shocks

    Takeuchi, Satoshi

    2018-02-01

    A kinetic model of the head-on collision of two magnetized plasma shocks is analyzed theoretically and in numerical calculations. When two plasmas with anti-parallel magnetic fields collide, they generate magnetic reconnection and form a motional electric field at the front of the collision region. This field accelerates the particles sandwiched between both shock fronts to extremely high energy. As they accelerate, the particles are bent by the transverse magnetic field crossing the magnetic neutral sheet, and their energy gains are reduced. In the numerical calculations, the dynamics of many test particles were modeled through the relativistic equations of motion. The attainable energy gain was obtained by multiplying three parameters: the propagation speed of the shock, the magnitude of the magnetic field, and the acceleration time of the test particle. This mechanism for generating high-energy particles is applicable over a wide range of spatial scales, from laboratory to interstellar plasmas.

  6. Experimental and numerical investigation of reactive shock-accelerated flows

    Bonazza, Riccardo [Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics

    2016-12-20

    The main goal of this program was to establish a qualitative and quantitative connection, based on the appropriate dimensionless parameters and scaling laws, between shock-induced distortion of astrophysical plasma density clumps and their earthbound analog in a shock tube. These objectives were pursued by carrying out laboratory experiments and numerical simulations to study the evolution of two gas bubbles accelerated by planar shock waves and compare the results to available astrophysical observations. The experiments were carried out in an vertical, downward-firing shock tube, 9.2 m long, with square internal cross section (25×25 cm2). Specific goals were to quantify the effect of the shock strength (Mach number, M) and the density contrast between the bubble gas and its surroundings (usually quantified by the Atwood number, i.e. the dimensionless density difference between the two gases) upon some of the most important flow features (e.g. macroscopic properties; turbulence and mixing rates). The computational component of the work performed through this program was aimed at (a) studying the physics of multi-phase compressible flows in the context of astrophysics plasmas and (b) providing a computational connection between laboratory experiments and the astrophysical application of shock-bubble interactions. Throughout the study, we used the FLASH4.2 code to run hydrodynamical and magnetohydrodynamical simulations of shock bubble interactions on an adaptive mesh.

  7. Experimental and numerical investigation of reactive shock-accelerated flows

    Bonazza, Riccardo

    2016-01-01

    The main goal of this program was to establish a qualitative and quantitative connection, based on the appropriate dimensionless parameters and scaling laws, between shock-induced distortion of astrophysical plasma density clumps and their earthbound analog in a shock tube. These objectives were pursued by carrying out laboratory experiments and numerical simulations to study the evolution of two gas bubbles accelerated by planar shock waves and compare the results to available astrophysical observations. The experiments were carried out in an vertical, downward-firing shock tube, 9.2 m long, with square internal cross section (25x25 cm"2). Specific goals were to quantify the effect of the shock strength (Mach number, M) and the density contrast between the bubble gas and its surroundings (usually quantified by the Atwood number, i.e. the dimensionless density difference between the two gases) upon some of the most important flow features (e.g. macroscopic properties; turbulence and mixing rates). The computational component of the work performed through this program was aimed at (a) studying the physics of multi-phase compressible flows in the context of astrophysics plasmas and (b) providing a computational connection between laboratory experiments and the astrophysical application of shock-bubble interactions. Throughout the study, we used the FLASH4.2 code to run hydrodynamical and magnetohydrodynamical simulations of shock bubble interactions on an adaptive mesh.

  8. Particle Acceleration, Magnetic Field Generation, and Emission in Relativistic Shocks

    Nishikawa, Ken-IchiI.; Hededal, C.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G.

    2004-01-01

    Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (m) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient parallel magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. New simulations with an ambient perpendicular magnetic field show the strong interaction between the relativistic jet and the magnetic fields. The magnetic fields are piled up by the jet and the jet electrons are bent, which creates currents and displacement currents. At the nonlinear stage, the magnetic fields are reversed by the current and the reconnection may take place. Due to these dynamics the jet and ambient electron are strongly accelerated in both parallel and perpendicular directions.

  9. Particle Acceleration, Magnetic Field Generation in Relativistic Shocks

    Nishikawa, Ken-Ichi; Hardee, P.; Hededal, C. B.; Richardson, G.; Sol, H.; Preece, R.; Fishman, G. J.

    2005-01-01

    Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient parallel magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. New simulations with an ambient perpendicular magnetic field show the strong interaction between the relativistic jet and the magnetic fields. The magnetic fields are piled up by the jet and the jet electrons are bent, which creates currents and displacement currents. At the nonlinear stage, the magnetic fields are reversed by the current and the reconnection may take place. Due to these dynamics the jet and ambient electron are strongly accelerated in both parallel and perpendicular directions.

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

    Verkhoglyadova, Olga P. [Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL35899 (United States); Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA91109 (United States); Zank, Gary P.; Li, Gang [Department of Space Science, UAH, Huntsville, AL35899 (United States); Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL35899 (United States)

    2015-02-12

    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

  11. Cosmic ray acceleration by shock waves in a diffusion medium. Research of high energies

    Lagage, P.O.

    1982-06-01

    The problem of galactic cosmic-ray acceleration is presented with the study of a new acceleration mechanism by supernova shock waves in a diffusive medium. The question is: do supernova shocks have enough time to accelerate cosmic rays beyond 10 4 -10 5 GeV. A firm upper limit to the energy that can be acquired by particles is established and it is considered that the mean free path of the particle has its lowest possible value and the most favorable model of supernova evolution. The diffusion coefficients which are relevant for the determination of the high energy cut off are investigated. The effect of the spatial dependence of the diffusion coefficient on the rate of acceleration of particles is examined. A more realistic cut off energy is calculated. We find E max = 2 10 4 GeV [fr

  12. Shock mitigation for the PFLs at the SATURN accelerator

    Craven, R.E.

    1997-06-01

    Accelerometer measurements were made on the SATURN pulse forming lines (PFL) to determine the mechanism responsible for severe metal deformation around the water switch openings and cracking of welded seams. A reason for this problem and a solution were established. A simple shock mitigating pad under the support stand for the PFL provides more than adequate protection from shock damage and will greatly extend the useful life of the power flow sections of SATURN

  13. Plasma acceleration by magnetic nozzles and shock waves

    Hattori, Kunihiko; Murakami, Fumitake; Miyazaki, Hiroyuki; Imasaki, Atsushi; Yoshinuma, Mikirou; Ando, Akira; Inutake, Masaaki

    2001-01-01

    We have measured axial profiles of ion acoustic Mach number, M i , of a plasma flow blowing off from an MPD (magneto-plasma-dynamic) arc-jet in various magnetic configurations. It is found that the Mach number increases in a divergent nozzle up to 3, while it stays at about unity in a uniform magnetic channel. When a magnetic bump is added in the exit of the divergent magnetic nozzle, the Mach number suddenly decreases below unity, due to an occurrence of shock wave. The subsonic flow after the shock wave is re-accelerated to a supersonic flow through a magnetic Laval nozzle. This behavior is explained well by the one-dimensional isotropic flow model. The shock wave is discussed in relation to the Rankine-Hugoniot relation. (author)

  14. Collisionless shock formation and the prompt acceleration of solar flare ions

    Cargill, P. J.; Goodrich, C. C.; Vlahos, L.

    1988-01-01

    The formation mechanisms of collisionless shocks in solar flare plasmas are investigated. The priamry flare energy release is assumed to arise in the coronal portion of a flare loop as many small regions or 'hot spots' where the plasma beta locally exceeds unity. One dimensional hybrid numerical simulations show that the expansion of these 'hot spots' in a direction either perpendicular or oblique to the ambient magnetic field gives rise to collisionless shocks in a few Omega(i), where Omega(i) is the local ion cyclotron frequency. For solar parameters, this is less than 1 second. The local shocks are then subsequently able to accelerate particles to 10 MeV in less than 1 second by a combined drift-diffusive process. The formation mechanism may also give rise to energetic ions of 100 keV in the shock vicinity. The presence of these energetic ions is due either to ion heating or ion beam instabilities and they may act as a seed population for further acceleration. The prompt acceleration of ions inferred from the Gamma Ray Spectrometer on the Solar Maximum Mission can thus be explained by this mechanism.

  15. Surfing and drift acceleration at high mach number quasi-perpendicular shocks

    Amano, T.

    2008-01-01

    Electron acceleration in high Mach number collisionless shocks relevant to supernova remnant is discussed. By performing one- and two-dimensional particle-in-cell simulations of quasi-perpendicular shocks, we find that energetic electrons are quickly generated in the shock transition region through shock surfing and drift acceleration. The electron energization is strong enough to account for the observed injection at supernova remnant shocks. (author)

  16. Mechanical vibration and shock analysis, sinusoidal vibration

    Lalanne, Christian

    2014-01-01

    Everything engineers need to know about mechanical vibration and shock...in one authoritative reference work! This fully updated and revised 3rd edition addresses the entire field of mechanical vibration and shock as one of the most important types of load and stress applied to structures, machines and components in the real world. Examples include everything from the regular and predictable loads applied to turbines, motors or helicopters by the spinning of their constituent parts to the ability of buildings to withstand damage from wind loads or explosions, and the need for cars to m

  17. Accelerated testing of space mechanisms

    Murray, S. Frank; Heshmat, Hooshang

    1995-01-01

    This report contains a review of various existing life prediction techniques used for a wide range of space mechanisms. Life prediction techniques utilized in other non-space fields such as turbine engine design are also reviewed for applicability to many space mechanism issues. The development of new concepts on how various tribological processes are involved in the life of the complex mechanisms used for space applications are examined. A 'roadmap' for the complete implementation of a tribological prediction approach for complex mechanical systems including standard procedures for test planning, analytical models for life prediction and experimental verification of the life prediction and accelerated testing techniques are discussed. A plan is presented to demonstrate a method for predicting the life and/or performance of a selected space mechanism mechanical component.

  18. ELECTRON ACCELERATIONS AT HIGH MACH NUMBER SHOCKS: TWO-DIMENSIONAL PARTICLE-IN-CELL SIMULATIONS IN VARIOUS PARAMETER REGIMES

    Matsumoto, Yosuke [Department of Physics, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522 (Japan); Amano, Takanobu; Hoshino, Masahiro, E-mail: ymatumot@astro.s.chiba-u.ac.jp [Department of Earth and Planetary Science, University of Tokyo, Hongo 1-33, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2012-08-20

    Electron accelerations at high Mach number collisionless shocks are investigated by means of two-dimensional electromagnetic particle-in-cell simulations with various Alfven Mach numbers, ion-to-electron mass ratios, and the upstream electron {beta}{sub e} (the ratio of the thermal pressure to the magnetic pressure). We find electrons are effectively accelerated at a super-high Mach number shock (M{sub A} {approx} 30) with a mass ratio of M/m = 100 and {beta}{sub e} = 0.5. The electron shock surfing acceleration is an effective mechanism for accelerating the particles toward the relativistic regime even in two dimensions with a large mass ratio. Buneman instability excited at the leading edge of the foot in the super-high Mach number shock results in a coherent electrostatic potential structure. While multi-dimensionality allows the electrons to escape from the trapping region, they can interact with the strong electrostatic field several times. Simulation runs in various parameter regimes indicate that the electron shock surfing acceleration is an effective mechanism for producing relativistic particles in extremely high Mach number shocks in supernova remnants, provided that the upstream electron temperature is reasonably low.

  19. Complex flow morphologies in shock-accelerated gaseous flows

    Kumar, S.; Vorobieff, P.; Orlicz, G.; Palekar, A.; Tomkins, C.; Goodenough, C.; Marr-Lyon, M.; Prestridge, K. P.; Benjamin, R. F.

    2007-11-01

    A Mach 1.2 planar shock wave impulsively and simultaneously accelerates a row of three heavy gas (SF 6) cylinders surrounded by a lighter gas (air), producing pairs of vortex columns. The heavy gas cylinders (nozzle diameter D) are initially equidistant in the spanwise direction (center to center spacing S), with S/D=1.5. The interaction of the vortex columns is investigated with planar laser-induced fluorescence (PLIF) in the plane normal to the axes of the cylinders. Several distinct post-shock morphologies are observed, apparently due to rather small variations of the initial conditions. We report the variation of the streamwise and spanwise growth rates of the integral scales for these flow morphologies.

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

    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.

  1. Experimental particle acceleration by water evaporation induced by shock waves

    Scolamacchia, T.; Alatorre Ibarguengoitia, M.; Scheu, B.; Dingwell, D. B.; Cimarelli, C.

    2010-12-01

    Shock waves are commonly generated during volcanic eruptions. They induce sudden changes in pressure and temperature causing phase changes. Nevertheless, their effects on flowfield properties are not well understood. Here we investigate the role of gas expansion generated by shock wave propagation in the acceleration of ash particles. We used a shock tube facility consisting of a high-pressure (HP) steel autoclave (450 mm long, 28 mm in internal diameter), pressurized with Ar gas, and a low-pressure tank at atmospheric conditions (LP). A copper diaphragm separated the HP autoclave from a 180 mm tube (PVC or acrylic glass) at ambient P, with the same internal diameter of the HP reservoir. Around the tube, a 30 cm-high acrylic glass cylinder, with the same section of the LP tank (40 cm), allowed the observation of the processes occurring downstream from the nozzle throat, and was large enough to act as an unconfined volume in which the initial diffracting shock and gas jet expand. All experiments were performed at Pres/Pamb ratios of 150:1. Two ambient conditions were used: dry air and air saturated with steam. Carbon fibers and glass spheres in a size range between 150 and 210 μm, were placed on a metal wire at the exit of the PVC tube. The sudden decompression of the Ar gas, due to the failure of the diaphragm, generated an initial air shock wave. A high-speed camera recorded the processes between the first 100 μsec and several ms after the diaphragm failure at frame rates ranging between 30,000 and 50,000 fps. In the experiments with ambient air saturated with steam, the high-speed camera allowed to visualize the condensation front associated with the initial air shock; a maximum velocity of 788 m/s was recorded, which decreases to 524 m/s at distance of 0.5 ±0.2 cm, 1.1 ms after the diaphragm rupture. The condensation front preceded the Ar jet front exhausting from the reservoir, by 0.2-0.5 ms. In all experiments particles velocities following the initial

  2. An introduction to the theory of diffusive shock acceleration of energetic particles in tenuous plasmas

    Drury, L.O'C.

    1983-01-01

    The central idea of diffusive shock acceleration is presented from microscopic and macroscopic viewpoints; applied to reactionless test particles in a steady plane shock the mechanism is shown to produce a power law spectrum in momentum with a slope which, to lowest order in the ratio of plasma to particle speed, depends only on the compression in the shock. The associated time scale is found (also by a macroscopic and a microscopic method) and the problems of spherical shocks, as exemplified by a point explosion and a stellar-wind terminator, are treated by singular perturbation theory. The effect of including the particle reaction is then studied. It is shown that if the scattering is due to resonant waves these can rapidly grow with unknown consequences. The possible steady modified shock structures are classified and generalised Rankine-Hugoniot conditions found. Modifications of the spectrum are discussed on the basis of an exact, if rather artificial, solution, a high-energy asymptotic expansion and a perturbation expansion due to Blandford. It is pointed out that no steady solution can exist for very strong shocks; the possible time dependence is briefly discussed. (author)

  3. Introduction to the theory of diffusive shock acceleration of energetic particles in tenuous plasmas

    Drury, L.O. (Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany, F.R.))

    1983-08-01

    The central idea of diffusive shock acceleration is presented from microscopic and macroscopic viewpoints; applied to reactionless test particles in a steady plane shock the mechanism is shown to produce a power law spectrum in momentum with a slope which, to lowest order in the ratio of plasma to particle speed, depends only on the compression in the shock. The associated time scale is found (also by a macroscopic and a microscopic method) and the problems of spherical shocks, as exemplified by a point explosion and a stellar-wind terminator, are treated by singular perturbation theory. The effect of including the particle reaction is then studied. It is shown that if the scattering is due to resonant waves these can rapidly grow with unknown consequences. The possible steady modified shock structures are classified and generalized Rankine-Hugoniot conditions found. Modifications of the spectrum are discussed on the basis of an exact, if rather artificial, solution, a high-energy asymptotic expansion and a perturbation expansion due to Blandford. It is pointed out that no steady solution can exist for very strong shocks; the possible time dependence is briefly discussed.

  4. Introduction to the theory of diffusive shock acceleration of energetic particles in tenuous plasmas

    Drury, L.Oc.

    1983-08-01

    The central idea of diffusive shock acceleration is presented from microscopic and macroscopic viewpoints applied to reactionless test particles in a steady plane shock. The mechanism is shown to produce a power law spectrum in momentum with a slope which, to lowest order in the ratio of plasma to particle speed, depends only on the compression in the shock. The associated time scale is found (also by a macroscopic and a microscopic method) and the problems of spherical shocks, as exemplified by a point explosion and a stellar-wind terminator, are treated by singular perturbation theory. The effect of including the particle reaction is then studied. It is shown that if the scattering is due to resonant waves these can rapidly grow with unknown consequences. The possible steady modified shock structures are classified and generalized Rankine-Hugoniot conditions found. Modifications of the spectrum are discussed on the basis of an exact, if rather artificial, solution, a high-energy asymptotic expansion and a perturbation expansion due to Blandford. It is pointed out that no steady solution can exist for very strong shocks. The possible time dependence is briefly discussed. 75 references.

  5. Response of the seated human body to whole-body vertical vibration: discomfort caused by mechanical shocks.

    Zhou, Zhen; Griffin, Michael J

    2017-03-01

    The frequency dependence of discomfort caused by vertical mechanical shocks has been investigated with 20 seated males exposed to upward and downward shocks at 13 fundamental frequencies (1-16 Hz) and 18 magnitudes (±0.12 to ±8.3 ms -2 ). The rate of growth of discomfort with increasing shock magnitude depended on the fundamental frequency of the shocks, so the frequency dependence of equivalent comfort contours (for both vertical acceleration and vertical force measured at the seat) varied with shock magnitude. The rate of growth of discomfort was similar for acceleration and force, upward and downward shocks, and lower and higher magnitude shocks. The frequency dependence of discomfort from shocks differs from that of sinusoidal vibrations having the same fundamental frequencies. This arises in part from the frequency content of the shock. Frequency weighting W b in BS 6841:1987 and ISO 2631-1:1997 provided reasonable estimates of the discomfort caused by the shocks investigated in this study. Practitioner Summary: No single frequency weighting can accurately predict the discomfort caused by mechanical shocks over wide ranges of shock magnitude, but vibration dose values with frequency weighting W b provide reasonable estimates of discomfort caused by shocks similar to those investigated in this study with peak accelerations well below 1 g.

  6. Particle magnetic moment conservation and resonance in a pure magnetohydrodynamic shock and field inclination influence on diffusive shock acceleration

    Lieu, R.; Quenby, J.J.

    1990-01-01

    Computational and analytical methods have been used in a study of particle acceleration by MHD shocks. Numerical simulations of single-particle trajectories indicate that magnetic moment is conserved quite accurately for an encounter with a near-perpendicular shock, and for all pitch angles except the very small ones. Acceleration is most effective for particles which are reflected by the shock at small pitch angles. If future encounters with the shock are possible, large acceleration will be repeated only for relativistic plasma flow velocities. Results for the pure MHD shock are then considered within the context of a diffusion model (hence a diffusive MHD shock). The microscopic approach is employed whereby one follows the history of a test particle and explicitly takes into account the possibility of reflection by the shock. Exact analytical solutions are currently available to order V/c, where V is the plasma flow speed, and are found to be in complete agreement with diffusion theory. More specifically, the presence of electromagnetic effects leads to a shortening of acceleration time scale but does not change the steady state spectrum of energetic particles. 7 refs

  7. The acceleration of electrons at a spherical coronal shock in a streamer-like coronal field

    Kong, Xiangliang, E-mail: kongx@sdu.edu.cn; Chen, Yao, E-mail: yaochen@sdu.edu.cn [Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, and Institute of Space Sciences, Shandong University, Weihai, Shandong 264209 (China); Guo, Fan, E-mail: guofan.ustc@gmail.com [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2016-03-25

    We study the effect of large-scale coronal magnetic field on the electron acceleration at a spherical coronal shock using a test-particle method. The coronal field is approximated by an analytical solution with a streamer-like magnetic field featured by partially open magnetic field and a current sheet at the equator atop the closed region. It shows that the closed field plays the role of a trapping agency of shock-accelerated electrons, allowing for repetitive reflection and acceleration, therefore can greatly enhance the shock-electron acceleration efficiency. It is found that, with an ad hoc pitch-angle scattering, electron injected in the open field at the shock flank can be accelerated to high energies as well. In addition, if the shock is faster or stronger, a relatively harder electron energy spectrum and a larger maximum energy can be achieved.

  8. Collisionless Weibel shocks: Full formation mechanism and timing

    Bret, A. [ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain); Instituto de Investigaciones Energéticas y Aplicaciones Industriales, Campus Universitario de Ciudad Real, 13071 Ciudad Real (Spain); Stockem, A. [GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisbon (Portugal); Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum (Germany); Narayan, R. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-51 Cambridge, Massachusetts 02138 (United States); Silva, L. O. [GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Lisbon (Portugal)

    2014-07-15

    Collisionless shocks in plasmas play an important role in space physics (Earth's bow shock) and astrophysics (supernova remnants, relativistic jets, gamma-ray bursts, high energy cosmic rays). While the formation of a fluid shock through the steepening of a large amplitude sound wave has been understood for long, there is currently no detailed picture of the mechanism responsible for the formation of a collisionless shock. We unravel the physical mechanism at work and show that an electromagnetic Weibel shock always forms when two relativistic collisionless, initially unmagnetized, plasma shells encounter. The predicted shock formation time is in good agreement with 2D and 3D particle-in-cell simulations of counterstreaming pair plasmas. By predicting the shock formation time, experimental setups aiming at producing such shocks can be optimised to favourable conditions.

  9. Computational and experimental investigation of plasma deflagration jets and detonation shocks in coaxial plasma accelerators

    Subramaniam, Vivek; Underwood, Thomas C.; Raja, Laxminarayan L.; Cappelli, Mark A.

    2018-02-01

    We present a magnetohydrodynamic (MHD) numerical simulation to study the physical mechanisms underlying plasma acceleration in a coaxial plasma gun. Coaxial plasma accelerators are known to exhibit two distinct modes of operation depending on the delay between gas loading and capacitor discharging. Shorter delays lead to a high velocity plasma deflagration jet and longer delays produce detonation shocks. During a single operational cycle that typically consists of two discharge events, the plasma acceleration exhibits a behavior characterized by a mode transition from deflagration to detonation. The first of the discharge events, a deflagration that occurs when the discharge expands into an initially evacuated domain, requires a modification of the standard MHD algorithm to account for rarefied regions of the simulation domain. The conventional approach of using a low background density gas to mimic the vacuum background results in the formation of an artificial shock, inconsistent with the physics of free expansion. To this end, we present a plasma-vacuum interface tracking framework with the objective of predicting a physically consistent free expansion, devoid of the spurious shock obtained with the low background density approach. The interface tracking formulation is integrated within the MHD framework to simulate the plasma deflagration and the second discharge event, a plasma detonation, formed due to its initiation in a background prefilled with gas remnant from the deflagration. The mode transition behavior obtained in the simulations is qualitatively compared to that observed in the experiments using high framing rate Schlieren videography. The deflagration mode is further investigated to understand the jet formation process and the axial velocities obtained are compared against experimentally obtained deflagration plasma front velocities. The simulations are also used to provide insight into the conditions responsible for the generation and sustenance of

  10. Periodic heat shock accelerated the chondrogenic differentiation of human mesenchymal stem cells in pellet culture.

    Jing Chen

    Full Text Available Osteoarthritis (OA is one of diseases that seriously affect elderly people's quality of life. Human mesenchymal stem cells (hMSCs offer a potential promise for the joint repair in OA patients. However, chondrogenic differentiation from hMSCs in vitro takes a long time (∼ 6 weeks and differentiated cells are still not as functionally mature as primary isolated chondrocytes, though chemical stimulations and mechanical loading have been intensively studied to enhance the hMSC differentiation. On the other hand, thermal stimulations of hMSC chondrogenesis have not been well explored. In this study, the direct effects of mild heat shock (HS on the differentiation of hMSCs into chondrocytes in 3D pellet culture were investigated. Periodic HS at 41 °C for 1 hr significantly increased sulfated glycosaminoglycan in 3D pellet culture at Day 10 of chondrogenesis. Immunohistochemical and Western Blot analyses revealed an increased expression of collagen type II and aggrecan in heat-shocked pellets than non heat-shocked pellets on Day 17 of chondrogenesis. In addition, HS also upregulated the expression of collagen type I and X as well as heat shock protein 70 on Day 17 and 24 of differentiation. These results demonstrate that HS accelerated the chondrogenic differentiation of hMSCs and induced an early maturation of chondrocytes differentiated from hMSCs. The results of this study will guide the design of future protocols using thermal treatments to facilitate cartilage regeneration with human mesenchymal stem cells.

  11. Pressure and intracorporal acceleration measurements in pigs exposed to strong shock waves in a free field

    Vassout, P.; Franke, R.; Parmentier, G.; Evrard, G.; Dancer, A.

    1987-01-01

    A theoretical study on the propagation of a pressure wave in a diphasic medium, when compared to the onset mechanism of pulmonary lesions in subjects exposed to strong shock waves, shows an increase in the incident overpressure at the interface level. Using hydrophones, intracorporal pressure was measured in pigs. The authors recorded the costal wall acceleration on the side directly exposed to the shock wave and calculated the displacement of the costal wall after a shock wave passed by. These experiments were conducted for shock waves in a free field, at an overpressure peak level ranging from 26 kFPa to 380 kPa and for a first positive phase lasting 2 ms. Sensors placed in an intracorporal position detected no increase of the overpressure level for any value of the incident pressure. A comparison of the costal wall displacement, measured experimentally, relative to the theoretical displacement of the entire animal mass indicates that the largest relative displacement of the costal wall could be the origin of the pulmonary lesions found. 5 refs., 13 figs

  12. Electron bulk acceleration and thermalization at Earth's quasi-perpendicular bow shock

    Chen, L.-J.; Wang, S.; Wilson, L. B., III; Schwartz, S. J.; Bessho, N.; Moore, T. E.; Gershman, D. J.; Giles, B. L.; Malaspina, D. M.; Wilder, F. D.; Ergun, R. E.; Hesse, M.; Lai, H.; Russell, C. T.; Strangeway, R. J.; Torbert, R. B.; Vinas, A. F.-; Burch, J. L.; Lee, S.; Pollock, C.; Dorelli, J.; Paterson, W. R.; Ahmadi, N.; Goodrich, K. A.; Lavraud, B.; Le Contel, O.; Khotyaintsev, Yu. V.; Lindqvist, P.-A.; Boardsen, S.; Wei, H.; Le, A.; Avanov, L. A.

    2018-05-01

    Electron heating at Earth's quasiperpendicular bow shock has been surmised to be due to the combined effects of a quasistatic electric potential and scattering through wave-particle interaction. Here we report the observation of electron distribution functions indicating a new electron heating process occurring at the leading edge of the shock front. Incident solar wind electrons are accelerated parallel to the magnetic field toward downstream, reaching an electron-ion relative drift speed exceeding the electron thermal speed. The bulk acceleration is associated with an electric field pulse embedded in a whistler-mode wave. The high electron-ion relative drift is relaxed primarily through a nonlinear current-driven instability. The relaxed distributions contain a beam traveling toward the shock as a remnant of the accelerated electrons. Similar distribution functions prevail throughout the shock transition layer, suggesting that the observed acceleration and thermalization is essential to the cross-shock electron heating.

  13. Ion acceleration at the earth's bow shock: A review of observations in the upstream region

    Gosling, J.T.; Asbridge, J.R.; Bame, S.J.; Feldman, W.C.

    1979-01-01

    Positive ions are accelerated at or near the earth's bow shock and propagate into the upstream region. Two distinctly different population of these ions, distinguished by their greatly different spectral and angular widths, can be identified there. The type of ion population observed in the upstream region is strongly correlated with the presence or absence of long-period compresive waves in the solar wind. Very few ions are accelerated in the vicinity of the shock to energies much above about 100 keV. It is not yet clear whether the most energetic ions (i.e. those near 100 keV) are accelerated at the shock or in the broad disturbed region upstream from the shock. In either case stochastic acceleration by turbulent electrostatic fields seems to be the most viable candidate for the acceleration of the most energetic particles

  14. Ion acceleration at the earth's bow shock: a review of observations in the upstream region

    Gosling, J.T.; Asbridge, J.R.; Bame, S.J.; Feldman, W.C.

    1979-01-01

    Positive ions are accelerated at or near the earth's bow shock and propagate into the upstream region. Two distinctly different populations of these ions, distinguished by their greatly different spectral and angular widths, can be identified there. The type of ion population observed in the upstream region is strongly correlated with the presence or absence of long-period compressive waves in the solar wind. Very few ions are accelerated in the vicinity of the shock to energies much above about 100 keV. It is not yet clear whether the most energetic ions (i.e., those near 100 keV) are accelerated at the shock or in broad disturbed region upstream from the shock. In either case stochastic acceleration by turbulent electrostatic fields seems to be the most viable candidate for the acceleration of the most energetic particles

  15. Intense laser driven collision-less shock and ion acceleration in magnetized plasmas

    Mima, K.; Jia, Q.; Cai, H. B.; Taguchi, T.; Nagatomo, H.; Sanz, J. R.; Honrubia, J.

    2016-05-01

    The generation of strong magnetic field with a laser driven coil has been demonstrated by many experiments. It is applicable to the magnetized fast ignition (MFI), the collision-less shock in the astrophysics and the ion shock acceleration. In this paper, the longitudinal magnetic field effect on the shock wave driven by the radiation pressure of an intense short pulse laser is investigated by theory and simulations. The transition of a laminar shock (electro static shock) to the turbulent shock (electromagnetic shock) occurs, when the external magnetic field is applied in near relativistic cut-off density plasmas. This transition leads to the enhancement of conversion of the laser energy into high energy ions. The enhancement of the conversion efficiency is important for the ion driven fast ignition and the laser driven neutron source. It is found that the total number of ions reflected by the shock increases by six time when the magnetic field is applied.

  16. Formation of GEMS from shock-accelerated crystalline dust in Superbubbles

    Westphal, A; Bradley, J P

    2004-01-01

    Interplanetary dust particles (IDPs) contain enigmatic sub-micron components called GEMS (Glass with Embedded Metal and Sulfides). The compositions and structures of GEMS indicate that they have been processed by exposure to ionizing radiation but details of the actual irradiation environment(s) have remained elusive. Here we propose a mechanism and astrophysical site for GEMS formation that explains for the first time the following key properties of GEMS; they are stoichiometrically enriched in oxygen and systematically depleted in S, Mg, Ca and Fe (relative to solar abundances), most have normal (solar) oxygen isotopic compositions, they exhibit a strikingly narrow size distribution (0.1-0.5 (micro)m diameter), and some of them contain ''relict'' crystals within their silicate glass matrices. We show that the compositions, size distribution, and survival of relict crystals are inconsistent with amorphization by particles accelerated by diffusive shock acceleration. Instead, we propose that GEMS are formed from crystalline grains that condense in stellar outflows from massive stars in OB associations, are accelerated in encounters with frequent supernova shocks inside the associated superbubble, and are implanted with atoms from the hot gas in the SB interior. We thus reverse the usual roles of target and projectile. Rather than being bombarded at rest by energetic ions, grains are accelerated and bombarded by a nearly monovelocity beam of atoms as viewed in their rest frame. Meyer, Drury and Ellison have proposed that galactic cosmic rays originate from ions sputtered from such accelerated dust grains. We suggest that GEMS are surviving members of a population of fast grains that constitute the long-sought source material for galactic cosmic rays. Thus, representatives of the GCR source material may have been awaiting discovery in cosmic dust labs for the last thirty years

  17. Modeling of ion acceleration through drift and diffusion at interplanetary shocks

    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.

  18. The role of magnetic loops in particle acceleration at nearly perpendicular shocks

    Decker, R. B.

    1993-01-01

    The acceleration of superthermal ions is investigated when a planar shock that is on average nearly perpendicular propagates through a plasma in which the magnetic field is the superposition of a constant uniform component plus a random field of transverse hydromagnetic fluctuations. The importance of the broadband nature of the transverse magnetic fluctuations in mediating ion acceleration at nearly perpendicular shocks is pointed out. Specifically, the fluctuations are composed of short-wavelength components which scatter ions in pitch angle and long-wavelength components which are responsible for a spatial meandering of field lines about the mean field. At nearly perpendicular shocks the field line meandering produces a distribution of transient loops along the shock. As an application of this model, the acceleration of a superthermal monoenergetic population of seed protons at a perpendicular shock is investigated by integrating along the exact phase-space orbits.

  19. First-order Fermi acceleration of the diffuse ion population near the earth's bow shock

    Forman, M. A.

    1981-01-01

    The flux of 30-65 keV particles observed by the ISEE-3 200 earth radii upstream is shown to be an upstream escape of the energetic ions in the earth's bow shock. A formal solution to the transport equation for the distribution function of energetic particles upstream from an isotropic monoenergetic source of particles/sq cm at a plane shock where the plasma changes speed is found, and escape conditions are defined. The efficiency of the acceleration is calculated to depend on the charge/particle, and fluxes near and far upstream of the shock are described analytically. Any model which takes into account shock acceleration by diffusive scattering with significant escape losses produces the observed spectrum close to the shock. The escape loss upstream is demonstrated to control the spectrum and the variation of flux and anisotropy with distance from the shock.

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

    Sundberg, Torbjörn; Haynes, Christopher T.; Burgess, D. [School of Physics and Astronomy, Queen Mary University of London, London, E1 4NS (United Kingdom); Mazelle, Christian X. [IRAP, Université Paul Sabatier Toulouse III-CNRS, 31028 Toulouse Cedex 4 (France)

    2016-03-20

    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 bow 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.

  1. RAPID COSMIC-RAY ACCELERATION AT PERPENDICULAR SHOCKS IN SUPERNOVA REMNANTS

    Takamoto, Makoto; Kirk, John G., E-mail: mtakamoto@eps.s.u-tokyo.ac.jp, E-mail: john.kirk@mpi-hd.mpg.de [Max-Planck-Institut für Kernphysik, Postfach 103980, D-69029 Heidelberg (Germany)

    2015-08-10

    Perpendicular shocks are shown to be rapid particle accelerators that perform optimally when the ratio u{sub s} of the shock speed to the particle speed roughly equals the ratio 1/η of the scattering rate to the gyro frequency. We use analytical methods and Monte-Carlo simulations to solve the kinetic equation that governs the anisotropy generated at these shocks, and find, for ηu{sub s} ≈ 1, that the spectral index softens by unity and the acceleration time increases by a factor of two compared to the standard result of the diffusive shock acceleration theory. These results provide a theoretical basis for the 30 year old conjecture that a supernova exploding into the wind of a Wolf–Rayet star may accelerate protons to an energy exceeding 10{sup 15} eV.

  2. An in situ Comparison of Electron Acceleration at Collisionless Shocks under Differing Upstream Magnetic Field Orientations

    Masters, A.; Dougherty, M. K. [The Blackett Laboratory, Imperial College London, Prince Consort Road, London, SW7 2AZ (United Kingdom); Sulaiman, A. H. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States); Stawarz, Ł. [Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Krakow (Poland); Reville, B. [School of Mathematics and Physics, Queens University Belfast, Belfast BT7 1NN (United Kingdom); Sergis, N. [Office of Space Research and Technology, Academy of Athens, Soranou Efesiou 4, 11527 Athens (Greece); Fujimoto, M. [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Burgess, D. [School of Physics and Astronomy, Queen Mary University of London, London E1 4NS (United Kingdom); Coates, A. J., E-mail: a.masters@imperial.ac.uk [Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Holmbury St. Mary, Dorking RH5 6NT (United Kingdom)

    2017-07-10

    A leading explanation for the origin of Galactic cosmic rays is acceleration at high-Mach number shock waves in the collisionless plasma surrounding young supernova remnants. Evidence for this is provided by multi-wavelength non-thermal emission thought to be associated with ultrarelativistic electrons at these shocks. However, the dependence of the electron acceleration process on the orientation of the upstream magnetic field with respect to the local normal to the shock front (quasi-parallel/quasi-perpendicular) is debated. Cassini spacecraft observations at Saturn’s bow shock have revealed examples of electron acceleration under quasi-perpendicular conditions, and the first in situ evidence of electron acceleration at a quasi-parallel shock. Here we use Cassini data to make the first comparison between energy spectra of locally accelerated electrons under these differing upstream magnetic field regimes. We present data taken during a quasi-perpendicular shock crossing on 2008 March 8 and during a quasi-parallel shock crossing on 2007 February 3, highlighting that both were associated with electron acceleration to at least MeV energies. The magnetic signature of the quasi-perpendicular crossing has a relatively sharp upstream–downstream transition, and energetic electrons were detected close to the transition and immediately downstream. The magnetic transition at the quasi-parallel crossing is less clear, energetic electrons were encountered upstream and downstream, and the electron energy spectrum is harder above ∼100 keV. We discuss whether the acceleration is consistent with diffusive shock acceleration theory in each case, and suggest that the quasi-parallel spectral break is due to an energy-dependent interaction between the electrons and short, large-amplitude magnetic structures.

  3. Shock Acceleration of Electrons and Synchrotron Emission from the Dynamical Ejecta of Neutron Star Mergers

    Lee, Shiu-Hang; Maeda, Keiichi; Kawanaka, Norita

    2018-05-01

    Neutron star mergers (NSMs) eject energetic subrelativistic dynamical ejecta into circumbinary media. Analogous to supernovae and supernova remnants, the NSM dynamical ejecta are expected to produce nonthermal emission by electrons accelerated at a shock wave. In this paper, we present the expected radio and X-ray signals by this mechanism, taking into account nonlinear diffusive shock acceleration (DSA) and magnetic field amplification. We suggest that the NSM is unique as a DSA site, where the seed relativistic electrons are abundantly provided by the decays of r-process elements. The signal is predicted to peak at a few 100–1000 days after the merger, determined by the balance between the decrease of the number of seed electrons and the increase of the dissipated kinetic energy, due to the shock expansion. While the resulting flux can ideally reach the maximum flux expected from near-equipartition, the available kinetic energy dissipation rate of the NSM ejecta limits the detectability of such a signal. It is likely that the radio and X-ray emission are overwhelmed by other mechanisms (e.g., an off-axis jet) for an observer placed in a jet direction (i.e., for GW170817). However, for an off-axis observer, to be discovered once a number of NSMs are identified, the dynamical ejecta component is predicted to dominate the nonthermal emission. While the detection of this signal is challenging even with near-future facilities, this potentially provides a robust probe of the creation of r-process elements in NSMs.

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

    Bustard, Chad; Zweibel, Ellen G. [Physics Department, University of Wisconsin–Madison, 1150 University Avenue, Madison, WI 53706 (United States); Cotter, Cory, E-mail: bustard@wisc.edu [Department of Astronomy, University of Wisconsin–Madison, 2535 Sterling Hall, 475 N. Charter Street, Madison, WI 53706 (United States)

    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, may 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.

  5. Shock-acceleration of a pair of gas inhomogeneities

    Navarro Nunez, Jose Alonso; Reese, Daniel; Oakley, Jason; Rothamer, David; Bonazza, Riccardo

    2014-11-01

    A shock wave moving through the interstellar medium distorts density inhomogeneities through the deposition of baroclinic vorticity. This process is modeled experimentally in a shock tube for a two-bubble interaction. A planar shock wave in nitrogen traverses two soap-film bubbles filled with argon. The two bubbles share an axis that is orthogonal to the shock wave and are separated from one another by a distance of approximately one bubble diameter. Atomization of the soap-film by the shock wave results in dispersal of droplets that are imaged using Mie scattering with a laser sheet through the bubble axis. Initial condition images of the bubbles in free-fall (no holder) are taken using a high-speed camera and then two post-shock images are obtained with two laser pulses and two cameras. The first post-shock image is of the early time compression stage when the sphere has become ellipsoidal, and the second image shows the emergence of vortex rings which have evolved due to vorticity depostion by the shock wave. Bubble morphology is characterized with length scale measurements.

  6. Effect of losses on acceleration of energetic particles by diffusive scattering through shock waves

    Voelk, H.J.; Morfill, G.E.; Forman, M.A.

    1981-01-01

    The effect of local losses on the acceleration of energetic particles by shocks is discussed considering both energy losses of individual particles and damping processes for the scattering hydromagnetic waves. The calculations are all time asymptotic and steady state. For locally plane and infinitely extended shocks, the requirement for acceleration is that the loss time exceed the acceleration time. The resulting modifications of the spatial structure and of the momentum dependence of the cosmic-ray distribution are described. For acceleration to be a local effect within the Galaxy, the local scattering mean free path must be small compared to the effective overall galactic mean free path as deduced from the cosmic-ray escape time. The required strengths of the scattering wave fields are such that neutral molecular clouds do not allow acceleration; in a partially ionized, warm interstellar medium, quite large shock strengths are needed. Such strong shock discontinuities are surrounded by an ionization layer within which Alfven wave damping is presumably negligible. Given the spatial extent of the layer for strong shocks propagating into neutral interstellar clouds, the possibility of localized diffusive acceleration is investigated. The estimated strength and extent of the scattering region is not large enough to confine acceleration within the layer. Rather, it will extend across the whole cloud, whose integrated losses then determine the efficiency

  7. Mechanisms of shock-induced dynamic friction

    Winter, R E; Ball, G J; Keightley, P T

    2006-01-01

    The mechanism of shock-induced dynamic friction has been explored through an integrated programme of experiments and numerical simulations. A novel experimental technique has been developed for observing the sub-surface deformation in aluminium when sliding against a steel anvil at high velocity and pressure. The experimental observations suggest that slight differences in conditions at the interface between the metals affect frictional behaviour even at the very high-velocity, high-pressure regime studied here. However, a clear finding from the experimental work is the presence of two distinct modes of deformation termed deep and shallow. The deep deformation is observed in a region of the aluminium specimen where the interfacial velocity is relatively low and the shallow deformation is observed in a region where the interfacial velocity is higher. A 1D numerical treatment is presented which predicts the existence of two mechanisms for dynamic friction termed 'asymptotic melting' and 'slide-then-lock'. In both modes there is a warm-up phase in which the interface temperature is increased by frictional heating. For high initial sliding velocity, this is followed by the onset of the asymptotic melting state, in which the temperature is almost constant and melting is approached asymptotically. This mechanism produces low late-time frictional stress and shallow deformation. For lower initial sliding velocity, the warm-up terminates in a violent work hardening event that locks the interface and launches a strong plastic shear wave into the weaker material. This slide-then-lock mechanism is characterized by sustained high frictional stress and deep plastic deformation. These predicted mechanisms offer a plausible and consistent explanation for the abrupt transitions in the depth of sub-surface deformation observed in the experiments. A key conclusion arising from the current work is that the frictional stress does not vary smoothly with pressure or sliding velocity

  8. Nonlinear Monte Carlo model of superdiffusive shock acceleration with magnetic field amplification

    Bykov, Andrei M.; Ellison, Donald C.; Osipov, Sergei M.

    2017-03-01

    Fast collisionless shocks in cosmic plasmas convert their kinetic energy flow into the hot downstream thermal plasma with a substantial fraction of energy going into a broad spectrum of superthermal charged particles and magnetic fluctuations. The superthermal particles can penetrate into the shock upstream region producing an extended shock precursor. The cold upstream plasma flow is decelerated by the force provided by the superthermal particle pressure gradient. In high Mach number collisionless shocks, efficient particle acceleration is likely coupled with turbulent magnetic field amplification (MFA) generated by the anisotropic distribution of accelerated particles. This anisotropy is determined by fast particle transport, making the problem strongly nonlinear and multiscale. Here, we present a nonlinear Monte Carlo model of collisionless shock structure with superdiffusive propagation of high-energy Fermi accelerated particles coupled to particle acceleration and MFA, which affords a consistent description of strong shocks. A distinctive feature of the Monte Carlo technique is that it includes the full angular anisotropy of the particle distribution at all precursor positions. The model reveals that the superdiffusive transport of energetic particles (i.e., Lévy-walk propagation) generates a strong quadruple anisotropy in the precursor particle distribution. The resultant pressure anisotropy of the high-energy particles produces a nonresonant mirror-type instability that amplifies compressible wave modes with wavelengths longer than the gyroradii of the highest-energy protons produced by the shock.

  9. Mechanical Properties of Shock-Damaged Rocks

    He, Hongliang; Ahrens, T. J.

    1994-01-01

    Stress-strain tests were performed both on shock-damaged gabbro and limestone. The effective Young's modulus decreases with increasing initial damage parameter value, and an apparent work-softening process occurs prior to failure. To further characterize shock-induced microcracks, the longitudinal elastic wave velocity behavior of shock-damaged gabbro in the direction of compression up to failure was measured using an acoustic transmission technique under uniaxial loading. A dramatic increase in velocity was observed for the static compressive stress range of 0-50 MPa. Above that stress range, the velocity behavior of lightly damaged (D(sub 0) less than 0.1) gabbro is almost equal to unshocked gabbro. The failure strength of heavily-damaged (D(sub 0) greater than 0.1) gabbro is approx. 100-150 MPa, much lower than that of lightly damaged and unshocked gabbros (approx. 230-260 MPa). Following Nur's theory, the crack shape distribution was analyzed. The shock-induced cracks in gabbro appear to be largely thin penny-shaped cracks with c/a values below 5 x 10(exp -4). Moreover, the applicability of Ashby and Sammis's theory relating failure strength and damage parameter of shock-damaged rocks was examined and was found to yield a good estimate of the relation of shock-induced deficit in elastic modulus with the deficit in compressive strength.

  10. First order and second order fermi acceleration of energetic charged particles by shock waves

    Webb, G.M.

    1983-01-01

    Steady state solutions of the cosmic ray transport equation describing first order Fermi acceleration of energetic charged particles at a plane shock (without losses) and second order Fermi acceleration in the downstream region of the shock are derived. The solutions for the isotropic part of the phase space distribution function are expressible as eigenfunction expansions, being superpositions of series of power law momentum spectra, with the power law indices being the roots of an eigenvalue equation. The above exact analytic solutions are for the case where the spatial diffusion coefficient kappa is independent of momentum. The solutions in general depend on the shock compression ratio, the modulation parameters V 1 L/kappa 1 , V 2 L/kappa 2 (V is the plasma velocity, kappa is the energetic particle diffusion coefficient, and L a characteristic length over which second order Fermi acceleration is effective) in the upstream and downstream regions of the shock, respectively, and also on a further dimensionless parameter, zeta, characterizing second order Fermi acceleration. In the limit as zeta→0 (no second order Fermi acceleration) the power law momentum spectrum characteristic of first order Fermi acceleration (depending only on the shock compression ratio) obtained previously is recovered. Perturbation solutions for the case where second order Fermi effects are small, and for realistic diffusion coefficients (kappainfinityp/sup a/, a>0, p = particle momentum), applicable at high momenta, are also obtained

  11. Transforming in-situ observations of CME-driven shock accelerated protons into the shock's reference frame.

    I. M. Robinson

    2005-07-01

    Full Text Available We examine the solar energetic particle event following solar activity from 14, 15 April 2001 which includes a "bump-on-the-tail" in the proton energy spectra at 0.99 AU from the Sun. We find this population was generated by a CME-driven shock which arrived at 0.99 AU around midnight 18 April. As such this population represents an excellent opportunity to study in isolation, the effects of proton acceleration by the shock. The peak energy of the bump-on-the-tail evolves to progressively lower energies as the shock approaches the observing spacecraft at the inner Lagrange point. Focusing on the evolution of this peak energy we demonstrate a technique which transforms these in-situ spectral observations into a frame of reference co-moving with the shock whilst making allowance for the effects of pitch angle scattering and focusing. The results of this transform suggest the bump-on-the-tail population was not driven by the 15 April activity but was generated or at least modulated by a CME-driven shock which left the Sun on 14 April. The existence of a bump-on-the-tail population is predicted by models in Rice et al. (2003 and Li et al. (2003 which we compare with observations and the results of our analysis in the context of both the 14 April and 15 April CMEs. We find an origin of the bump-on-the-tail at the 14 April CME-driven shock provides better agreement with these modelled predictions although some discrepancy exists as to the shock's ability to accelerate 100 MeV protons.

    Keywords. Solar physics, astrophysics and astronomy (Energetic particles; Flares and mass ejections – Space plasma physics (Transport processes

  12. Mechanical Design of Superconducting Accelerator Magnets

    Toral, F

    2014-01-01

    This paper is about the mechanical design of superconducting accelerator magnets. First, we give a brief review of the basic concepts and terms. In the following sections, we describe the particularities of the mechanical design of different types of superconducting accelerator magnets: solenoids, costheta, superferric, and toroids. Special attention is given to the pre-stress principle, which aims to avoid the appearance of tensile stresses in the superconducting coils. A case study on a compact superconducting cyclotron summarizes the main steps and the guidelines that should be followed for a proper mechanical design. Finally, we present some remarks on the measurement techniques

  13. Mechanical Design of Superconducting Accelerator Magnets

    Toral, Fernando

    2014-07-17

    This paper is about the mechanical design of superconducting accelerator magnets. First, we give a brief review of the basic concepts and terms. In the following sections, we describe the particularities of the mechanical design of different types of superconducting accelerator magnets: solenoids, costheta, superferric, and toroids. Special attention is given to the pre-stress principle, which aims to avoid the appearance of tensile stresses in the superconducting coils. A case study on a compact superconducting cyclotron summarizes the main steps and the guidelines that should be followed for a proper mechanical design. Finally, we present some remarks on the measurement techniques.

  14. Mechanical Design of Superconducting Accelerator Magnets

    Toral, F [Madrid, CIEMAT (Spain)

    2014-07-01

    This paper is about the mechanical design of superconducting accelerator magnets. First, we give a brief review of the basic concepts and terms. In the following sections, we describe the particularities of the mechanical design of different types of superconducting accelerator magnets: solenoids, costheta, superferric, and toroids. Special attention is given to the pre-stress principle, which aims to avoid the appearance of tensile stresses in the superconducting coils. A case study on a compact superconducting cyclotron summarizes the main steps and the guidelines that should be followed for a proper mechanical design. Finally, we present some remarks on the measurement techniques.

  15. The Acceleration of Charged Particles at a Spherical Shock Moving through an Irregular Magnetic Field

    Giacalone, J. [Department of Planetary Sciences, University of Arizona, Tucson, AZ (United States)

    2017-10-20

    We investigate the physics of charged-particle acceleration at spherical shocks moving into a uniform plasma containing a turbulent magnetic field with a uniform mean. This has applications to particle acceleration at astrophysical shocks, most notably, to supernovae blast waves. We numerically integrate the equations of motion of a large number of test protons moving under the influence of electric and magnetic fields determined from a kinematically defined plasma flow associated with a radially propagating blast wave. Distribution functions are determined from the positions and velocities of the protons. The unshocked plasma contains a magnetic field with a uniform mean and an irregular component having a Kolmogorov-like power spectrum. The field inside the blast wave is determined from Maxwell’s equations. The angle between the average magnetic field and unit normal to the shock varies with position along its surface. It is quasi-perpendicular to the unit normal near the sphere’s equator, and quasi-parallel to it near the poles. We find that the highest intensities of particles, accelerated by the shock, are at the poles of the blast wave. The particles “collect” at the poles as they approximately adhere to magnetic field lines that move poleward from their initial encounter with the shock at the equator, as the shock expands. The field lines at the poles have been connected to the shock the longest. We also find that the highest-energy protons are initially accelerated near the equator or near the quasi-perpendicular portion of the shock, where the acceleration is more rapid.

  16. On the stability of shocks modified by particle acceleration

    Drury, L.O' C.; Falle, S.A.E.G.

    1986-11-15

    It is shown, using a two-fluid approximation, that sound waves in a gas containing cosmic rays can be amplified if the scale height of the cosmic rays is less than a critical scale of order of the ratio of the cosmic-ray diffusion coefficient to the gas sound speed. The non-linear development has been calculated numerically and it is found that sound waves can grow into strong gas shocks. The instability is likely to have important effects on cosmic-ray modified shocks.

  17. On the stability of shocks modified by particle acceleration

    Drury, L.O'C.; Falle, S.A.E.G.

    1986-01-01

    It is shown, using a two-fluid approximation, that sound waves in a gas containing cosmic rays can be amplified if the scale height of the cosmic rays is less than a critical scale of order of the ratio of the cosmic-ray diffusion coefficient to the gas sound speed. The non-linear development has been calculated numerically and it is found that sound waves can grow into strong gas shocks. The instability is likely to have important effects on cosmic-ray modified shocks. (author)

  18. Particle Acceleration and Radiative Losses at Relativistic Shocks

    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.

  19. Injection and acceleration of H+ and He2+ at Earth's bow shock

    K.-H. Trattner

    Full Text Available We have performed a number of one-dimensional hybrid simulations (particle ions, massless electron fluid of quasi-parallel collisionless shocks in order to investigate the injection and subsequent acceleration of part of the solar wind ions at the Earth's bow shock. The shocks propagate into a medium containing magnetic fluctuations, which are initially superimposed on the background field, as well as generated or enhanced by the electromagnetic ion/ion beam instability between the solar wind and backstreaming ions. In order to study the mass (M and charge (Q dependence of the acceleration process He2+ is included self-consistently. The upstream differential intensity spectra of H+ and He2+ can be well represented by exponentials in energy. The e-folding energy Ec is a function of time: Ec increases with time. Furthermore the e-folding energy (normalized to the shock ramming energy Ep increases with increasing Alfvén Mach number of the shock and with increasing fluctuation level of the initially superimposed turbulence. When backstreaming ions leave the shock after their first encounter they exhibit already a spectrum which extends to more than ten times the shock ramming energy and which is ordered in energy per charge. From the injection spectrum it is concluded that leakage of heated downstream particles does not contribute to ion injection. Acceleration models that permit thermal particles to scatter like the non-thermal population do not describe the correct physics.Key words. Interplanetary physics (planetary bow shocks · Space plasma physics (charged particle motion and acceleration; numerical simulation studies

  20. Injection and acceleration of H+ and He2+ at Earth's bow shock

    M. Scholer

    1999-05-01

    Full Text Available We have performed a number of one-dimensional hybrid simulations (particle ions, massless electron fluid of quasi-parallel collisionless shocks in order to investigate the injection and subsequent acceleration of part of the solar wind ions at the Earth's bow shock. The shocks propagate into a medium containing magnetic fluctuations, which are initially superimposed on the background field, as well as generated or enhanced by the electromagnetic ion/ion beam instability between the solar wind and backstreaming ions. In order to study the mass (M and charge (Q dependence of the acceleration process He2+ is included self-consistently. The upstream differential intensity spectra of H+ and He2+ can be well represented by exponentials in energy. The e-folding energy Ec is a function of time: Ec increases with time. Furthermore the e-folding energy (normalized to the shock ramming energy Ep increases with increasing Alfvén Mach number of the shock and with increasing fluctuation level of the initially superimposed turbulence. When backstreaming ions leave the shock after their first encounter they exhibit already a spectrum which extends to more than ten times the shock ramming energy and which is ordered in energy per charge. From the injection spectrum it is concluded that leakage of heated downstream particles does not contribute to ion injection. Acceleration models that permit thermal particles to scatter like the non-thermal population do not describe the correct physics.Key words. Interplanetary physics (planetary bow shocks · Space plasma physics (charged particle motion and acceleration; numerical simulation studies

  1. Classical mechanics and electromagnetism in accelerator physics

    Stupakov, Gennady

    2018-01-01

    This self-contained textbook with exercises discusses a broad range of selected topics from classical mechanics and electromagnetic theory that inform key issues related to modern accelerators. Part I presents fundamentals of the Lagrangian and Hamiltonian formalism for mechanical systems, canonical transformations, action-angle variables, and then linear and nonlinear oscillators. The Hamiltonian for a circular accelerator is used to evaluate the equations of motion, the action, and betatron oscillations in an accelerator. From this base, we explore the impact of field errors and nonlinear resonances. This part ends with the concept of the distribution function and an introduction to the kinetic equation to describe large ensembles of charged particles and to supplement the previous single-particle analysis of beam dynamics. Part II focuses on classical electromagnetism and begins with an analysis of the electromagnetic field from relativistic beams, both in vacuum and in a resistive pipe. Plane electromagne...

  2. The Mechanism of Microcirculatory Failure in Shock.

    1979-05-01

    response to regional and systemic shock. Surgery 77:268, 1975. 10. Weksler BB, et al: Synthesis of PGI2 (prostacyclin) by cultured human and bovine ... bovine blood platelets. J Biol Chem 252:5871, 1977. -. . Q •( 14. Roth GJ and Mejerus PW: Acetylation of prostaglandin synthetase by aspirin. Proc Natl...gases were determined every 30 minutes and metabolic acidosis was treated with sodium bicarbonate. After 90 minutes the animals were resuscitated by

  3. Acceleration of galactic cosmic rays in shock waves

    Lagage, P.O.

    1981-06-01

    The old problem of the origin of cosmic rays has triggered off fresh interest owing to the discovery of a new model which enables a lot of energy to be transferred to a small number of particles on the one hand and the discovery of the coronal environment in which this transfer occurs, on the other. In this paper, interest is taken in the galactic cosmic rays and an endeavour is made to find out if the model can reveal the existence of cosmic rays over a wide energy range. The existence of an energy break, predicted by the model, was recognized fairly early but, in the literature, it varies from 30 GeV ro 10 6 GeV according to the authors. A study has been made of the two main causes of an energy break: the sphericity of the shock and the life time of the shock wave [fr

  4. 3-D Model of Broadband Emission from Supernova Remnants Undergoing Non-linear Diffusive Shock Acceleration

    Lee, Shiu-Hang; Kamae, Tuneyoshi; Ellison, Donald C.

    2008-07-02

    We present a 3-dimensional model of supernova remnants (SNRs) where the hydrodynamical evolution of the remnant is modeled consistently with nonlinear diffusive shock acceleration occurring at the outer blast wave. The model includes particle escape and diffusion outside of the forward shock, and particle interactions with arbitrary distributions of external ambient material, such as molecular clouds. We include synchrotron emission and cooling, bremsstrahlung radiation, neutral pion production, inverse-Compton (IC), and Coulomb energy-loss. Boardband spectra have been calculated for typical parameters including dense regions of gas external to a 1000 year old SNR. In this paper, we describe the details of our model but do not attempt a detailed fit to any specific remnant. We also do not include magnetic field amplification (MFA), even though this effect may be important in some young remnants. In this first presentation of the model we don't attempt a detailed fit to any specific remnant. Our aim is to develop a flexible platform, which can be generalized to include effects such as MFA, and which can be easily adapted to various SNR environments, including Type Ia SNRs, which explode in a constant density medium, and Type II SNRs, which explode in a pre-supernova wind. When applied to a specific SNR, our model will predict cosmic-ray spectra and multi-wavelength morphology in projected images for instruments with varying spatial and spectral resolutions. We show examples of these spectra and images and emphasize the importance of measurements in the hard X-ray, GeV, and TeV gamma-ray bands for investigating key ingredients in the acceleration mechanism, and for deducing whether or not TeV emission is produced by IC from electrons or pion-decay from protons.

  5. Shock loading influence on mechanical behavior of high purity iron

    Buy, Francois; Voltz, Christophe

    2004-01-01

    This paper proposes the analysis of shock wave effects for high purity iron. The method developed is based on the characterization of the mechanical behavior of as received and shocked material. Shock effect is generated through plate impact tests performed in the range of 4 GPa to 39 GPa on a single stage light gas gun or a powder gun. Therefore, as-received and impacted materials are characterized. A formalism proposed by J.R.Klepaczko and based on physical relations has been adopted to describe stress strain curves

  6. Experimental measurement of unsteady drag on shock accelerated micro-particles

    Bordoloi, Ankur; Martinez, Adam; Prestridge, Katherine

    2016-11-01

    The unsteady drag history of shock accelerated micro-particles in air is investigated in the Horizontal Shock Tube (HST) facility at Los Alamos National laboratory. Drag forces are estimated based on particle size, particle density, and instantaneous velocity and acceleration measured on hundreds of post-shock particle tracks. We use previously implemented 8-frame Particle Tracking Velocimetry/Anemometry (PTVA) diagnostics to analyze particles in high spatiotemporal resolution from individual particle trajectories. We use a simultaneous LED based shadowgraph to register shock location with respect to a moving particle in each frame. To measure particle size accurately, we implement a Phase Doppler Particle Analyzer (PDPA) in synchronization with the PTVA. In this presentation, we will corroborate with more accuracy our earlier observation that post-shock unsteady drag coefficients (CD(t)) are manifold times higher than those predicted by theoretical models. Our results will also show that all CD(t) measurements collapse on a master-curve for a range of particle size, density, Mach number and Reynolds number when time is normalized by a shear velocity based time scale, t* = d/(uf-up) , where d is particle diameter, and uf and up are post-shock fluid and particle velocities.

  7. The Acceleration of Thermal Protons and Minor Ions at a Quasi-Parallel Interplanetary Shock

    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.

  8. Shock-wave proton acceleration from a hydrogen gas jet

    Cook, Nathan; Pogorelsky, Igor; Polyanskiy, Mikhail; Babzien, Marcus; Tresca, Olivier; Maharjan, Chakra; Shkolnikov, Peter; Yakimenko, Vitaly

    2013-04-01

    Typical laser acceleration experiments probe the interaction of intense linearly-polarized solid state laser pulses with dense metal targets. This interaction generates strong electric fields via Transverse Normal Sheath Acceleration and can accelerate protons to high peak energies but with a large thermal spectrum. Recently, the advancement of high pressure amplified CO2 laser technology has allowed for the creation of intense (10^16 Wcm^2) pulses at λ˜10 μm. These pulses may interact with reproducible, high rep. rate gas jet targets and still produce plasmas of critical density (nc˜10^19 cm-3), leading to the transference of laser energy via radiation pressure. This acceleration mode has the advantage of producing narrow energy spectra while scaling well with pulse intensity. We observe the interaction of an intense CO2 laser pulse with an overdense hydrogen gas jet. Using two pulse optical probing in conjunction with interferometry, we are able to obtain density profiles of the plasma. Proton energy spectra are obtained using a magnetic spectrometer and scintillating screen.

  9. Radio evidence for shock acceleration of electrons in the solar corona

    Cane, H. V.; Stone, R. G.; Fainberg, J.; Steinberg, J. L.; Hoang, S.; Stewart, R. T.

    1981-01-01

    It is pointed out that the new class of kilometer-wavelength solar radio bursts observed with the ISEE-3 Radio Astronomy Experiment occurs at the reported times of type II events, which are indicative of a shock wave. An examination of records from the Culgoora Radio Observatory reveals that the associated type II bursts have fast drift elements emanating from them; that is, a herringbone structure is formed. It is proposed that this new class of bursts is a long-wavelength continuation of the herringbone structure, and it is thought probable that the electrons producing the radio emission are accelerated by shocks. These new events are referred to as shock-accelerated events, and their characteristics are discussed.

  10. Improvements in or relating to the protection of thermoelectric devices against shocks and accelerations

    Brown, M.H.; Myatt, J.

    1979-01-01

    Heart pacemakers are protected against shock and acceleration by surrounding the heat source, but not in contact with the source or the thermoelectric unit, with a plurity of spring fingers. These arrest the radioactive source in the event of movement on its resilient mounting of the thermoelectric unit relative to the casing in excess of a predetermined amount. (UK)

  11. Mechanical analysis of a heat-shock induced developmental defect

    Crews, Sarah M.; McCleery, W. Tyler; Hutson, M. Shane

    2014-03-01

    Embryonic development in Drosophila is a complex process involving coordinated movements of mechanically interacting tissues. Perturbing this system with a transient heat shock can result in a number of developmental defects. In particular, a heat shock applied during the earliest morphogenetic movements of gastrulation can lead to apparent recovery, but then subsequent morphogenetic failure 5-6 hours later during germ band retraction. The process of germ band retraction requires an intact amnioserosa - a single layered extra-embryonic epithelial tissue - and heat shock at gastrulation can induce the later opening of holes in the amnioserosa. These holes are highly correlated with failures of germ band retraction. These holes could be caused by a combination of mechanical weakness in the amnioserosa or local increases in mechanical stress. Here, we assess the role of mechanical stress using confocal imaging to compare cell and tissue morphology in the amnioserosa of normal and heat-shocked embryos and laser hole drilling to map the stress field around the times and locations at which heat-shock induced holes open.

  12. COLLISIONLESS SHOCKS IN A PARTIALLY IONIZED MEDIUM. III. EFFICIENT COSMIC RAY ACCELERATION

    Morlino, G.; Blasi, P.; Bandiera, R.; Amato, E. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, I-50125 Firenze (Italy); Caprioli, D. [Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544 (United States)

    2013-05-10

    In this paper, we present the first formulation of the theory of nonlinear particle acceleration in collisionless shocks in the presence of neutral hydrogen in the acceleration region. The dynamical reaction of the accelerated particles, the magnetic field amplification, and the magnetic dynamical effects on the shock are also included. The main new aspect of this study, however, consists of accounting for charge exchange and the ionization of a neutral hydrogen, which profoundly change the structure of the shock, as discussed in our previous work. This important dynamical effect of neutrals is mainly associated with the so-called neutral return flux, namely the return of hot neutrals from the downstream region to upstream, where they deposit energy and momentum through charge exchange and ionization. We also present the self-consistent calculation of Balmer line emission from the shock region and discuss how to use measurements of the anomalous width of the different components of the Balmer line to infer cosmic ray acceleration efficiency in supernova remnants showing Balmer emission: the broad Balmer line, which is due to charge exchange of hydrogen atoms with hot ions downstream of the shock, is shown to become narrower as a result of the energy drainage into cosmic rays, while the narrow Balmer line, due to charge exchange in the cosmic-ray-induced precursor, is shown to become broader. In addition to these two well-known components, the neutral return flux leads to the formation of a third component with an intermediate width: this too contains information on ongoing processes at the shock.

  13. FLARE VERSUS SHOCK ACCELERATION OF HIGH-ENERGY PROTONS IN SOLAR ENERGETIC PARTICLE EVENTS

    Cliver, E. W.

    2016-01-01

    Recent studies have presented evidence for a significant to dominant role for a flare-resident acceleration process for high-energy protons in large (“gradual”) solar energetic particle (SEP) events, contrary to the more generally held view that such protons are primarily accelerated at shock waves driven by coronal mass ejections (CMEs). The new support for this flare-centric view is provided by correlations between the sizes of X-ray and/or microwave bursts and associated SEP events. For one such study that considered >100 MeV proton events, we present evidence based on CME speeds and widths, shock associations, and electron-to-proton ratios that indicates that events omitted from that investigation’s analysis should have been included. Inclusion of these outlying events reverses the study’s qualitative result and supports shock acceleration of >100 MeV protons. Examination of the ratios of 0.5 MeV electron intensities to >100 MeV proton intensities for the Grechnev et al. event sample provides additional support for shock acceleration of high-energy protons. Simply scaling up a classic “impulsive” SEP event to produce a large >100 MeV proton event implies the existence of prompt 0.5 MeV electron events that are approximately two orders of magnitude larger than are observed. While classic “impulsive” SEP events attributed to flares have high electron-to-proton ratios (≳5 × 10 5 ) due to a near absence of >100 MeV protons, large poorly connected (≥W120) gradual SEP events, attributed to widespread shock acceleration, have electron-to-proton ratios of ∼2 × 10 3 , similar to those of comparably sized well-connected (W20–W90) SEP events.

  14. Shocks, singularities and oscillations in nonlinear optics and fluid mechanics

    Santo, Daniele; Lannes, David

    2017-01-01

    The book collects the most relevant results from the INdAM Workshop "Shocks, Singularities and Oscillations in Nonlinear Optics and Fluid Mechanics" held in Rome, September 14-18, 2015. The contributions discuss recent major advances in the study of nonlinear hyperbolic systems, addressing general theoretical issues such as symmetrizability, singularities, low regularity or dispersive perturbations. It also investigates several physical phenomena where such systems are relevant, such as nonlinear optics, shock theory (stability, relaxation) and fluid mechanics (boundary layers, water waves, Euler equations, geophysical flows, etc.). It is a valuable resource for researchers in these fields. .

  15. Prompt acceleration of ions by oblique turbulent shocks in solar flares

    Decker, R. B.; Vlahos, L.

    1985-01-01

    Solar flares often accelerate ions and electrons to relativistic energies. The details of the acceleration process are not well understood, but until recently the main trend was to divide the acceleration process into two phases. During the first phase elctrons and ions are heated and accelerated up to several hundreds of keV simultaneously with the energy release. These mildly relativistic electrons interact with the ambient plasma and magnetic fields and generate hard X-ray and radio radiation. The second phase, usually delayed from the first by several minutes, is responsible for accelerating ions and electrons to relativistic energies. Relativistic electrons and ions interact with the solar atmosphere or escape from the Sun and generate gamma ray continuum, gamma ray line emission, neutron emission or are detected in space by spacecraft. In several flares the second phase is coincident with the start of a type 2 radio burst that is believed to be the signature of a shock wave. Observations from the Solar Maximum Mission spacecraft have shown, for the first time, that several flares accelerate particles to all energies nearly simultaneously. These results posed a new theoretical problem: How fast are shocks and magnetohydrodynamic turbulence formed and how quickly can they accelerate ions to 50 MeV in the lower corona? This problem is discussed.

  16. Prompt acceleration of ions by oblique turbulent shocks in solar flares

    Decker, R.B.; Vlahos, L.

    1985-01-01

    Solar flares often accelerate ions and electrons to relativistic energies. The details of the acceleration process are not well understood, but until recently the main trend was to divide the acceleration process into two phases. During the first phase elctrons and ions are heated and accelerated up to several hundreds of keV simultaneously with the energy release. These mildly relativistic electrons interact with the ambient plasma and magnetic fields and generate hard x-ray and radio radiation. The second phase, usually delayed from the first by several minutes, is responsible for accelerating ions and electrons to relativistic energies. Relativistic electrons and ions interact with the solar atmosphere or escape from the Sun and generate gamma ray continuum, gamma ray line emission, neutron emission or are detected in space by spacecraft. In several flares the second phase is coincident with the start of a type 2 radio burst that is believed to be the signature of a shock wave. Observations from the Solar Maximum Mission spacecraft have shown, for the first time, that several flares accelerate particles to all energies nearly simultaneously. These results posed a new theoretical problem: How fast are shocks and magnetohydrodynamic turbulence formed and how quickly can they accelerate ions to 50 MeV in the lower corona. This problem is discussed

  17. Elastic-plastic fracture mechanics study of thermal shock cracking

    Hirano, K.; Kobayashi, H.; Nakazawa, H.

    1980-01-01

    This paper describes thermal shock experiments conducted on a nuclear pressure vessel steel (A533 Grade B Class 1), an AISI304 steel and a tool steel (JIS SKD62) using both a new thermal shock test facility and method. Analysis of their quasi-static thermal stress intensity factors is performed on the basis of linear-elastic fracture mechanics; and a thermal shock fracture toughness value, Ksub(tsc) is evaluated. Then elastic-plastic fracture toughness tests are carried out in the same high temperature range of the thermal shock experiment, and a relation between the stretched zone width, SZW, formed as a result of the fatigue precrack tip plastic blunting and the J-integral is clarified. An elastic-plastic thermal shock fracture toughness value, Jsub(tsc), is evaluated from a critical value of the stretched zone width, SZWsub(tsc), at the initiation of the thermal shock cracking by using the relation between SZW and J. The Jsub(tsc) value is compared with an elastic-plastic fracture toughness value, Jsub(Ic), and the difference between these Jsub(tsc) and Jsub(Ic) values is discussed on the basis of fractography. (author)

  18. The acceleration rate of cosmic rays at cosmic ray modified shocks

    Saito, Tatsuhiko; Hoshino, Masahiro; Amano, Takanobu

    It is a still controversial matter whether the production efficiency of cosmic rays (CRs) is relatively efficient or inefficient (e.g. Helder et al. 2009; Hughes et al. 2000; Fukui 2013). In upstream region of SNR shocks (the interstellar medium), the energy density of CRs is comparable to a substantial fraction of that of the thermal plasma (e.g. Ferriere 2001). In such a situation, CRs can possibly exert a back-reaction to the shocks and modify the global shock structure. These shocks are called cosmic ray modified shocks (CRMSs). In CRMSs, as a result of the nonlinear feedback, there are almost always up to three steady-state solutions for given upstream parameters, which are characterized by CR production efficiencies (efficient, intermediate and inefficient branch). We evaluate qualitatively the efficiency of the CR production in SNR shocks by considering the stability of CRMS, under the effects of i) magnetic fields and ii) injection, which play significant roles in efficiency of acceleration. By adopting two-fluid model (Drury & Voelk, 1981), we investigate the stability of CRMSs by means of time-dependent numerical simulations. As a result, we show explicitly the bi-stable feature of these multiple solutions, i.e., the efficient and inefficient branches are stable and the intermediate branch is unstable, and the intermediate branch transit to the inefficient one. This feature is independent of the effects of i) shock angles and ii) injection. Furthermore, we investigate the evolution from a hydrodynamic shock to CRMS in a self-consistent manner. From the results, we suggest qualitatively that the CR production efficiency at SNR shocks may be the least efficient.

  19. Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks

    Nishikawa, K.-I.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.

    2005-01-01

    Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel, and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a three-dimensional relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. New simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. Furthermore, the nonlinear fluctuation amplitudes of densities, currents, and electric and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at a comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. In addition, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by tine Weibel instability scale proportionally to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields, which contribute to the electron s (positron s) transverse deflection behind the jet head. This

  20. Laboratory studies of magnetized collisionless flows and shocks using accelerated plasmoids

    Weber, T. E.; Smith, R. J.; Hsu, S. C.

    2015-11-01

    Magnetized collisionless shocks are thought to play a dominant role in the overall partition of energy throughout the universe, but have historically proven difficult to create in the laboratory. The Magnetized Shock Experiment (MSX) at LANL creates conditions similar to those found in both space and astrophysical shocks by accelerating hot (100s of eV during translation) dense (1022 - 1023 m-3) Field Reversed Configuration (FRC) plasmoids to high velocities (100s of km/s); resulting in β ~ 1, collisionless plasma flows with sonic and Alfvén Mach numbers of ~10. The FRC subsequently impacts a static target such as a strong parallel or anti-parallel (reconnection-wise) magnetic mirror, a solid obstacle, or neutral gas cloud to create shocks with characteristic length and time scales that are both large enough to observe yet small enough to fit within the experiment. This enables study of the complex interplay of kinetic and fluid processes that mediate cosmic shocks and can generate non-thermal distributions, produce density and magnetic field enhancements much greater than predicted by fluid theory, and accelerate particles. An overview of the experimental capabilities of MSX will be presented, including diagnostics, selected recent results, and future directions. Supported by the DOE Office of Fusion Energy Sciences under contract DE-AC52-06NA25369.

  1. Acceleration of Solar Energetic Particles at a Fast Traveling Shock in Non-uniform Coronal Conditions

    Le Roux, J. A.; Arthur, A. D.

    2017-09-01

    Time-dependent solar energetic particle (SEP) acceleration is investigated at a fast, nearly parallel spherical traveling shock in the strongly non-uniform corona by solving the standard focused transport equation for SEPs and transport equations for parallel propagating Alfvén waves that form a set of coupled equations. This enables the modeling of self-excitation of Alfvén waves in the inertial range by SEPs ahead of the shock and its role in enhancing the efficiency of the diffusive shock acceleration (DSA) of SEPs in a self-regulatory fashion. Preliminary results suggest that, because of the highly non-uniform coronal conditions that the shock encounters, both DSA and wave excitation are highly time-dependent processes. Thus, DSA spectra of SEPs strongly deviate from the simple power-law prediction of standard steady-state DSA theory and initially strong wave excitation weakens rapidly. Consequently, the ability of DSA to produce high energy SEPs in the corona of ∼1 GeV, as observed in the strongest gradual SEP events, appears to be strongly curtailed at a fast nearly parallel shock, but further research is needed before final conclusions can be drawn.

  2. Role of failure-mechanism identification in accelerated testing

    Hu, J. M.; Barker, D.; Dasgupta, A.; Arora, A.

    1993-01-01

    Accelerated life testing techniques provide a short-cut method to investigate the reliability of electronic devices with respect to certain dominant failure mechanisms that occur under normal operating conditions. However, accelerated tests have often been conducted without knowledge of the failure mechanisms and without ensuring that the test accelerated the same mechanism as that observed under normal operating conditions. This paper summarizes common failure mechanisms in electronic devices and packages and investigates possible failure mechanism shifting during accelerated testing.

  3. Coupled hydromagnetic wave excitation and ion acceleration upstream of the earth's bow shock

    Lee, M.A.

    1982-01-01

    A self-consistent theory is presented for the excitation of hydromagnetic waves and the acceleration of diffuse ions upstream of the earth's bow shock in the quasi-equilibrium that results when the solar wind velocity and the interplanetary magnetic field are nearly parallel. For the waves the quasi-equilibrium results from a balance between excitation by the ions, which stream relative to the solar wind plasma, and convective loss to the magnetosheath. For the diffuse ions the quasi-equilibrium results from a balance between injection at the shock front, confinement to the foreshock by pitch angle scattering on the waves, acceleration by compression at the shock front, loss to the magnetosheath, loss due to escape upstream of the foreshock, and loss via diffusion perpendicular to the average magnetic field onto field lines that do not connect to the shock front. Diffusion equations describing the ion transport and wave kinetic equations describing the hydromagnetic wave transport are solved self-consistently to yield analytical expressions for the differential wave intensity spectrum as a function of frequency and distance from the bow shock z and for the ion omnidirectional distribution functions and anisotropies as functions of energy and z, In quantitative agreement with observations, the theory predicts (1) exponential spectra at the bow shock in energy per charge, (2) a decrease in intensity and hardening of the ion spectra with increasing z, (3) a 30-keV proton anisotropy parallel to z increasing from -0.28 at the bow shock to +0.51 as z→infinity (4) a linearly polarized wave intensity spectrum with a minimum at approx.6 x 10 -3 Hz and a maximum at approx.2--3 x 10 -2 Hz, (5) a decrease in the wave intensity spectrum with increasing z, (6) a total energy density in protons with energies >15 keV about eight times that in the hydromagnetic waves

  4. Thin Foil Acceleration Method for Measuring the Unloading Isentropes of Shock-Compressed Matter

    Asay, J.R.; Chhabildas, L.C.; Fortov, V.E.; Kanel, G.I.; Khishchenko, K.V.; Lomonosov, I.V.; Mehlhorn, T.; Razorenov, S.V.; Utkin, A.V.

    1999-01-01

    This work has been performed as part of the search for possible ways to utilize the capabilities of laser and particle beams techniques in shock wave and equation of state physics. The peculiarity of these techniques is that we have to deal with micron-thick targets and not well reproducible incident shock wave parameters, so all measurements should be of a high resolution and be done in one shot. Besides the Hugoniots, the experimental basis for creating the equations of state includes isentropes corresponding to unloading of shock-compressed matter. Experimental isentrope data are most important in the region of vaporization. With guns or explosive facilities, the unloading isentrope is recovered from a series of experiments where the shock wave parameters in plates of standard low-impedance materials placed behind the sample are measured [1,2]. The specific internal energy and specific volume are calculated from the measured p(u) release curve which corresponds to the Riemann integral. This way is not quite suitable for experiments with beam techniques where the incident shock waves are not well reproducible. The thick foil method [3] provides a few experimental points on the isentrope in one shot. When a higher shock impedance foil is placed on the surface of the material studied, the release phase occurs by steps, whose durations correspond to that for the shock wave to go back and forth in the foil. The velocity during the different steps, connected with the knowledge of the Hugoniot of the foil, allows us to determine a few points on the isentropic unloading curve. However, the method becomes insensitive when the low pressure range of vaporization is reached in the course of the unloading. The isentrope in this region can be measured by recording the smooth acceleration of a thin witness plate foil. With the mass of the foil known, measurements of the foil acceleration will give us the vapor pressure

  5. Energy-harvesting shock absorber with a mechanical motion rectifier

    Li, Zhongjie; Zuo, Lei; Kuang, Jian; Luhrs, George

    2013-02-01

    Energy-harvesting shock absorbers are able to recover the energy otherwise dissipated in the suspension vibration while simultaneously suppressing the vibration induced by road roughness. They can work as a controllable damper as well as an energy generator. An innovative design of regenerative shock absorbers is proposed in this paper, with the advantage of significantly improving the energy harvesting efficiency and reducing the impact forces caused by oscillation. The key component is a unique motion mechanism, which we called ‘mechanical motion rectifier (MMR)’, to convert the oscillatory vibration into unidirectional rotation of the generator. An implementation of a MMR-based harvester with high compactness is introduced and prototyped. A dynamic model is created to analyze the general properties of the motion rectifier by making an analogy between mechanical systems and electrical circuits. The model is capable of analyzing electrical and mechanical components at the same time. Both simulation and experiments are carried out to verify the modeling and the advantages. The prototype achieved over 60% efficiency at high frequency, much better than conventional regenerative shock absorbers in oscillatory motion. Furthermore, road tests are done to demonstrate the feasibility of the MMR shock absorber, in which more than 15 Watts of electricity is harvested while driving at 15 mph on a smooth paved road. The MMR-based design can also be used for other applications of vibration energy harvesting, such as from tall buildings or long bridges.

  6. Energy-harvesting shock absorber with a mechanical motion rectifier

    Li, Zhongjie; Zuo, Lei; Kuang, Jian; Luhrs, George

    2013-01-01

    Energy-harvesting shock absorbers are able to recover the energy otherwise dissipated in the suspension vibration while simultaneously suppressing the vibration induced by road roughness. They can work as a controllable damper as well as an energy generator. An innovative design of regenerative shock absorbers is proposed in this paper, with the advantage of significantly improving the energy harvesting efficiency and reducing the impact forces caused by oscillation. The key component is a unique motion mechanism, which we called ‘mechanical motion rectifier (MMR)’, to convert the oscillatory vibration into unidirectional rotation of the generator. An implementation of a MMR-based harvester with high compactness is introduced and prototyped. A dynamic model is created to analyze the general properties of the motion rectifier by making an analogy between mechanical systems and electrical circuits. The model is capable of analyzing electrical and mechanical components at the same time. Both simulation and experiments are carried out to verify the modeling and the advantages. The prototype achieved over 60% efficiency at high frequency, much better than conventional regenerative shock absorbers in oscillatory motion. Furthermore, road tests are done to demonstrate the feasibility of the MMR shock absorber, in which more than 15 Watts of electricity is harvested while driving at 15 mph on a smooth paved road. The MMR-based design can also be used for other applications of vibration energy harvesting, such as from tall buildings or long bridges. (paper)

  7. Use of noninvasive and invasive mechanical ventilation in cardiogenic shock

    Hongisto, Mari; Lassus, Johan; Tarvasmaki, Tuukka

    2017-01-01

    BACKGROUND: Despite scarce data, invasive mechanical ventilation (MV) is widely recommended over non-invasive ventilation (NIV) for ventilatory support in cardiogenic shock (CS). We assessed the real-life use of different ventilation strategies in CS and their influence on outcome focusing on the...

  8. Dominant acceleration processes of ambient energetic protons (E>= 50 keV) at the bow shock: conditions and limitations

    Anagnostopoulos, G.C.; Sarris, E.T.

    1983-01-01

    Energetic proton (Esub(p)>= 50 keV) and magnetic field observations during crossings of the Earth's Bow Shock by the IMP-7 and 8 spacecraft are incorporated in this work in order to examine the effect of the Bow Shock on a pre-existing proton population under different ''interplanetary magnetic field-Bow Shock'' configurations, as well as the conditions for the presence of the Bow Shock associated energetic proton intensity enhancements. The presented observations indicate that the dominant process for the efficient acceleration of ambient energetic particles to energies exceeding approximately 50 keV is by ''gradient-B'' drifting parallel to the induced electric field at quasi-perpendicular Bow Shocks under certain well defined limitations deriving from the finite and curved Bow Shock surface. It is shown that the proton acceleration at the Bow Shock is most efficient for high values of the upstream magnetic field (in general B 1 > 8#betta#), high upstream plasma speed and expanded Bow Shock fronts, as well as for direction of the induced electric field oriented almost parallel to the flanks of the Bow Shock, i.e. when the drift distance of protons parallel to the electric field at the shock front is considerably smaller than the local radius of curvature of the Bow Shock. The implications of the presented observations of Bow Shock crossings as to the source of the energetic proton intensity enhancements are discussed. (author)

  9. Mechanic- and hydraulic shock-absorbers - layout, construction, operation experience

    Kluge, M.

    1981-01-01

    The problem lies in the protection of the flexible supported power plant components against undesired sudden movements. Various shock absorbing systems are at disposal in this case: Mechanical and hydraulic shock absorbers, whose functioning systems are shown in figures. The operation experience showed a series of deficiencies, as demonstrated on various figures. In order to avoid them, some important recommendations are given. Requirements and layout are demonstrated according to todays' state-of-the-art. The admissible stresses, resulting from the summary of various specifications for the analytical evidence will be described. Development and construction will be explained in detail by means of pictures with cross sections of original shock absorbers. Todays' construction characteristics will be summarized. The final remark includes a request for generally valid guidelines. (orig.) [de

  10. THE EFFECT OF LARGE-SCALE MAGNETIC TURBULENCE ON THE ACCELERATION OF ELECTRONS BY PERPENDICULAR COLLISIONLESS SHOCKS

    Guo Fan; Giacalone, Joe

    2010-01-01

    We study the physics of electron acceleration at collisionless shocks that move through a plasma containing large-scale magnetic fluctuations. We numerically integrate the trajectories of a large number of electrons, which are treated as test particles moving in the time-dependent electric and magnetic fields determined from two-dimensional hybrid simulations (kinetic ions and fluid electron). The large-scale magnetic fluctuations effect the electrons in a number of ways and lead to efficient and rapid energization at the shock front. Since the electrons mainly follow along magnetic lines of force, the large-scale braiding of field lines in space allows the fast-moving electrons to cross the shock front several times, leading to efficient acceleration. Ripples in the shock front occurring at various scales will also contribute to the acceleration by mirroring the electrons. Our calculation shows that this process favors electron acceleration at perpendicular shocks. The current study is also helpful in understanding the injection problem for electron acceleration by collisionless shocks. It is also shown that the spatial distribution of energetic electrons is similar to in situ observations. The process may be important to our understanding of energetic electrons in planetary bow shocks and interplanetary shocks, and explaining herringbone structures seen in some type II solar radio bursts.

  11. Acceleration in Perpendicular Relativistic Shocks for Plasmas Consisting of Leptons and Hadrons

    Stockem, A.; Fiúza, F.; Fonseca, R. A.; Silva, L. O.

    2012-08-01

    We investigate the acceleration of light particles in perpendicular shocks for plasmas consisting of a mixture of leptonic and hadronic particles. Starting from the full set of conservation equations for the mixed plasma constituents, we generalize the magnetohydrodynamical jump conditions for a multi-component plasma, including information about the specific adiabatic constants for the different species. The impact of deviations from the standard model of an ideal gas is compared in theory and particle-in-cell simulations, showing that the standard MHD model is a good approximation. The simulations of shocks in electron-positron-ion plasmas are for the first time multi-dimensional, transverse effects are small in this configuration, and one-dimensional (1D) simulations are a good representation if the initial magnetization is chosen high. 1D runs with a mass ratio of 1836 are performed, which identify the Larmor frequency ω ci as the dominant frequency that determines the shock physics in mixed component plasmas. The maximum energy in the non-thermal tail of the particle spectra evolves in time according to a power law vpropt α with α in the range 1/3 Drury and Gargaté & Spitkovsky, which predict an acceleration time vpropγ and the theory for small wavelength scattering by Kirk & Reville, which predicts a behavior rather as vpropγ2. Furthermore, we compare different magnetic field orientations with B 0 inside and out of the plane, observing qualitatively different particle spectra than in pure electron-ion shocks.

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

    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.

  13. A DATA-DRIVEN ANALYTIC MODEL FOR PROTON ACCELERATION BY LARGE-SCALE SOLAR CORONAL SHOCKS

    Kozarev, Kamen A. [Smithsonian Astrophysical Observatory (United States); Schwadron, Nathan A. [Institute for the Study of Earth, Oceans, and Space, University of New Hampshire (United States)

    2016-11-10

    We have recently studied the development of an eruptive filament-driven, large-scale off-limb coronal bright front (OCBF) in the low solar corona, using remote observations from the Solar Dynamics Observatory ’s Advanced Imaging Assembly EUV telescopes. In that study, we obtained high-temporal resolution estimates of the OCBF parameters regulating the efficiency of charged particle acceleration within the theoretical framework of diffusive shock acceleration (DSA). These parameters include the time-dependent front size, speed, and strength, as well as the upstream coronal magnetic field orientations with respect to the front’s surface normal direction. Here we present an analytical particle acceleration model, specifically developed to incorporate the coronal shock/compressive front properties described above, derived from remote observations. We verify the model’s performance through a grid of idealized case runs using input parameters typical for large-scale coronal shocks, and demonstrate that the results approach the expected DSA steady-state behavior. We then apply the model to the event of 2011 May 11 using the OCBF time-dependent parameters derived by Kozarev et al. We find that the compressive front likely produced energetic particles as low as 1.3 solar radii in the corona. Comparing the modeled and observed fluences near Earth, we also find that the bulk of the acceleration during this event must have occurred above 1.5 solar radii. With this study we have taken a first step in using direct observations of shocks and compressions in the innermost corona to predict the onsets and intensities of solar energetic particle events.

  14. Strong ion accelerating by collisionless magnetosonic shock wave propagating perpendicular to a magnetic field

    Ohsawa, Yukiharu.

    1984-12-01

    A 2-1/2 dimensional fully relativistic, fully electromagnetic particle code is used to study a time evolution of nonlinear magnetosonic pulse propagating in the direction perpendicular to a magnetic field. The pulse is excited by an instantaneous piston acceleration, and evolves totally self-consistently. Large amplitude pulse traps some ions and accelerates them parallel to the wave front. They are detrapped when their velocities become of the order of the sum of the ExB drift velocity and the wave phase velocity, where E is the electric field in the direction of wave propagation. The pulse develops into a quasi-shock wave in a collisionless plasma by a dissipation due to the resonant ion acceleration. Simple nonlinear wave theory for a cold plasma well describes the shock properties observed in the simulation except for the effects of resonant ions. In particular, magnitude of an electric potential across the shock region is derived analytically and is found to be in good agreement with our simulations. The potential jump is proportional to B 2 , and hence the ExB drift velocity of the trapped ions is proportional to B. (author)

  15. Blast-Induced Acceleration in a Shock Tube: Distinguishing Primary and Tertiary Blast Injury

    2016-10-01

    injury conditions (blast and acceleration vs acceleration alone) undergo neurobehavioral and histopathological assessments to comprehensively... reversal . To facilitate mid-air blasts, a release mechanism was devised. Balls were attached to the bail of the mechanism. The blast wave would cause

  16. Vorticity generation and evolution in shock-accelerated density-stratified interfaces

    Yang, X.; Chern, I.; Zabusky, N.J.; Samtaney, R.; Hawley, J.F.

    1992-01-01

    The results of direct numerical simulations of inviscid planar shock-accelerated density-stratified interfaces in two dimensions are presented and compared with shock tube experiments of Haas [(private communication, 1988)] and Sturtevant [in Shock Tubes and Waves, edited by H. Gronig (VCH, Berlin, 1987), p. 89] . Heavy-to-light (''slow/fast or s/f) and light-to-heavy (''fast/slow,'' or f/s) gas interfaces are examined and early-time impulsive vorticity deposition and the evolution of coherent vortex structures are emphasized and quantified. The present second-order Godunov scheme yields excellent agreement with shock-polar analyses at early time. A more physical vortex interpretation explains the commonly used (i.e., linear paradigm) designations of ''unstable'' and ''stable'' for the f/s and s/f interfaces, respectively. The later time events are Rayleigh--Taylor like and can be described in terms of the evolution of a vortex layer (large-scale translation and rotation): asymmetric tip vortex ''roll-up'' and ''binding;'' layer ''instability;'' convective mixing; and baroclinic vorticity generation from secondary shock--interface interactions

  17. Comparison of accelerated ion populations observed upstream of the bow shocks at Venus and Mars

    M. Yamauchi

    2011-03-01

    Full Text Available Foreshock ions are compared between Venus and Mars at energies of 0.6~20 keV using the same ion instrument, the Ion Mass Analyser, on board both Venus Express and Mars Express. Venus Express often observes accelerated protons (2~6 times the solar wind energy that travel away from the Venus bow shock when the spacecraft location is magnetically connected to the bow shock. The observed ions have a large field-aligned velocity compared to the perpendicular velocity in the solar wind frame, and are similar to the field-aligned beams and intermediate gyrating component of the foreshock ions in the terrestrial upstream region. Mars Express does not observe similar foreshock ions as does Venus Express, indicating that the Martian foreshock does not possess the intermediate gyrating component in the upstream region on the dayside of the planet. Instead, two types of gyrating protons in the solar wind frame are observed very close to the Martian quasi-perpendicular bow shock within a proton gyroradius distance. The first type is observed only within the region which is about 400 km from the bow shock and flows tailward nearly along the bow shock with a similar velocity as the solar wind. The second type is observed up to about 700 km from the bow shock and has a bundled structure in the energy domain. A traversal on 12 July 2005, in which the energy-bunching came from bundling in the magnetic field direction, is further examined. The observed velocities of the latter population are consistent with multiple specular reflections of the solar wind at the bow shock, and the ions after the second reflection have a field-aligned velocity larger than that of the de Hoffman-Teller velocity frame, i.e., their guiding center has moved toward interplanetary space out from the bow shock. To account for the observed peculiarity of the Martian upstream region, finite gyroradius effects of the solar wind protons compared to the radius of the bow shock curvature and

  18. A Critical Shock Mach Number for Particle Acceleration in the Absence of Pre-existing Cosmic Rays: M = √5

    Vink, J.; Yamazaki, R.

    2014-01-01

    It is shown that, under some generic assumptions, shocks cannot accelerate particles unless the overall shock Mach number exceeds a critical value M > √5. The reason is that for M ≤ √5 the work done to compress the flow in a particle precursor requires more enthalpy flux than the system can sustain.

  19. Interbank funding as insurance mechanism for (persistent) liquidity shocks

    Bluhm, Marcel

    2015-01-01

    The interbank market is important for the efficient functioning of the financial system, transmission of monetary policy and therefore ultimately the real economy. In particular, it facilitates banks' liquidity management. This paper aims at extending the literature which views interbank markets as mutual liquidity insurance mechanism by taking into account persistence of liquidity shocks. Following a theory of long-term interbank funding a financial system which is modeled as a micro-founded...

  20. Control rod drive mechanism with shock absorber for nuclear reactor

    Chevereau, G.

    1989-01-01

    The mechanism usable in a PWR has a shaft carrying the bar vertically displaceable in the reactor internals and a dash pot with a hydraulic cylinder and a piston. The cylinder has a large diameter perforated upper section to the cylinder, a small diameter lower section, a piston traversed by the control rod sized to fit into the upper section and forced downwards when the control descends. The shock absorbing chamber is defined between the piston and the upper section [fr

  1. Effective Acceleration Model for the Arrival Time of Interplanetary Shocks driven by Coronal Mass Ejections

    Paouris, Evangelos; Mavromichalaki, Helen

    2017-12-01

    In a previous work (Paouris and Mavromichalaki in Solar Phys. 292, 30, 2017), we presented a total of 266 interplanetary coronal mass ejections (ICMEs) with as much information as possible. We developed a new empirical model for estimating the acceleration of these events in the interplanetary medium from this analysis. In this work, we present a new approach on the effective acceleration model (EAM) for predicting the arrival time of the shock that preceds a CME, using data of a total of 214 ICMEs. For the first time, the projection effects of the linear speed of CMEs are taken into account in this empirical model, which significantly improves the prediction of the arrival time of the shock. In particular, the mean value of the time difference between the observed time of the shock and the predicted time was equal to +3.03 hours with a mean absolute error (MAE) of 18.58 hours and a root mean squared error (RMSE) of 22.47 hours. After the improvement of this model, the mean value of the time difference is decreased to -0.28 hours with an MAE of 17.65 hours and an RMSE of 21.55 hours. This improved version was applied to a set of three recent Earth-directed CMEs reported in May, June, and July of 2017, and we compare our results with the values predicted by other related models.

  2. Numerical simulation of particle jet formation induced by shock wave acceleration in a Hele-Shaw cell

    Osnes, A. N.; Vartdal, M.; Pettersson Reif, B. A.

    2018-05-01

    The formation of jets from a shock-accelerated cylindrical shell of particles, confined in a Hele-Shaw cell, is studied by means of numerical simulation. A number of simulations have been performed, systematically varying the coupling between the gas and solid phases in an effort to identify the primary mechanism(s) responsible for jet formation. We find that coupling through drag is sufficient for the formation of jets. Including the effect of particle volume fraction and particle collisions did not alter the general behaviour, but had some influence on the length, spacing and number of jets. Furthermore, we find that the jet selection process starts early in the dispersal process, during the initial expansion of the particle layer.

  3. ACCELERATION IN PERPENDICULAR RELATIVISTIC SHOCKS FOR PLASMAS CONSISTING OF LEPTONS AND HADRONS

    Stockem, A.; Fiúza, F.; Fonseca, R. A.; Silva, L. O.

    2012-01-01

    We investigate the acceleration of light particles in perpendicular shocks for plasmas consisting of a mixture of leptonic and hadronic particles. Starting from the full set of conservation equations for the mixed plasma constituents, we generalize the magnetohydrodynamical jump conditions for a multi-component plasma, including information about the specific adiabatic constants for the different species. The impact of deviations from the standard model of an ideal gas is compared in theory and particle-in-cell simulations, showing that the standard MHD model is a good approximation. The simulations of shocks in electron-positron-ion plasmas are for the first time multi-dimensional, transverse effects are small in this configuration, and one-dimensional (1D) simulations are a good representation if the initial magnetization is chosen high. 1D runs with a mass ratio of 1836 are performed, which identify the Larmor frequency ω ci as the dominant frequency that determines the shock physics in mixed component plasmas. The maximum energy in the non-thermal tail of the particle spectra evolves in time according to a power law ∝t α with α in the range 1/3 2 . Furthermore, we compare different magnetic field orientations with B 0 inside and out of the plane, observing qualitatively different particle spectra than in pure electron-ion shocks.

  4. ANALYSIS OF THE MECHANICAL STRENGTH OF A DRIVING MECHANISM CALLED SHOCK

    Dan ILINCIOIU

    2015-05-01

    Full Text Available It evaluates the maximum static and dynamic stresses produced in the elements of a quadrilateral mechanism transporting a vehicle in the storage in an urban park. Determine multiplier shock hazard if the mechanism freezes and increases mechanical stress.

  5. Control of quasi-monoenergetic electron beams from laser-plasma accelerators with adjustable shock density profile

    Tsai, Hai-En; Swanson, Kelly K.; Barber, Sam K.; Lehe, Remi; Mao, Hann-Shin; Mittelberger, Daniel E.; Steinke, Sven; Nakamura, Kei; van Tilborg, Jeroen; Schroeder, Carl; Esarey, Eric; Geddes, Cameron G. R.; Leemans, Wim

    2018-04-01

    The injection physics in a shock-induced density down-ramp injector was characterized, demonstrating precise control of a laser-plasma accelerator (LPA). Using a jet-blade assembly, experiments systematically varied the shock injector profile, including shock angle, shock position, up-ramp width, and acceleration length. Our work demonstrates that beam energy, energy spread, and pointing can be controlled by adjusting these parameters. As a result, an electron beam that was highly tunable from 25 to 300 MeV with 8% energy spread (ΔEFWHM/E), 1.5 mrad divergence, and 0.35 mrad pointing fluctuation was produced. Particle-in-cell simulation characterized how variation in the shock angle and up-ramp width impacted the injection process. This highly controllable LPA represents a suitable, compact electron beam source for LPA applications such as Thomson sources and free-electron lasers.

  6. Time-dependent shock acceleration of energetic electrons including synchrotron losses

    Fritz, K.; Webb, G.M.

    1990-01-01

    The present investigation of the time-dependent particle acceleration problem in strong shocks, including synchrotron radiation losses, solves the transport equation analytically by means of Laplace transforms. The particle distribution thus obtained is then transformed numerically into real space for the cases of continuous and impulsive injections of particles at the shock. While in the continuous case the steady-state spectrum undergoes evolution, impulsive injection is noted to yield such unpredicted features as a pile-up of high-energy particles or a steep power-law with time-dependent spectral index. The time-dependent calculations reveal varying spectral shapes and more complex features for the higher energies which may be useful in the interpretation of outburst spectra. 33 refs

  7. Ion acceleration in electrostatic collisionless shock: on the optimal density profile for quasi-monoenergetic beams

    Boella, E.; Fiúza, F.; Stockem Novo, A.; Fonseca, R.; Silva, L. O.

    2018-03-01

    A numerical study on ion acceleration in electrostatic shock waves is presented, with the aim of determining the best plasma configuration to achieve quasi-monoenergetic ion beams in laser-driven systems. It was recently shown that tailored near-critical density plasmas characterized by a long-scale decreasing rear density profile lead to beams with low energy spread (Fiúza et al 2012 Phys. Rev. Lett. 109 215001). In this work, a detailed parameter scan investigating different plasma scale lengths is carried out. As result, the optimal plasma spatial scale length that allows for minimizing the energy spread while ensuring a significant reflection of ions by the shock is identified. Furthermore, a new configuration where the required profile has been obtained by coupling micro layers of different densities is proposed. Results show that this new engineered approach is a valid alternative, guaranteeing a low energy spread with a higher level of controllability.

  8. High energy emission of supernova sn 1987a. Cosmic rays acceleration in mixed shocks

    Lehoucq, Roland

    1992-01-01

    In its first part, this research thesis reports the study of the high energy emission of the sn 1987 supernova, based on a Monte Carlo simulation of the transfer of γ photons emitted during disintegration of radioactive elements (such as "5"6Ni, "5"6Co, "5"7Co and "4"4Ti) produced during the explosion. One of the studied problems is the late evolution (beyond 1200 days) of light curvature which is very different when it is powered by the radiation of a central object or by radioactivity. The second part reports the study of acceleration of cosmic rays in two-fluid shock waves in order to understand the different asymmetries noticed in hot spots of extragalactic radio-sources. This work comprises the resolution of structure equations of a shock made of a conventional fluid and a relativistic one, in presence or absence of a magnetic field [fr

  9. The collective acceleration mechanism of solar cosmic rays

    Gershtein, S.S.

    1978-01-01

    The collective acceleration mechanism of protons and nuclei in solar flares, which lies in the fact that nuclei are trapped by electron bunches moving along the opened lines of force of the decreasing magnetic field of solar sports, is discussed. The proposed mechanism explains in a natural way the electron and nucleus energy ratio observed during flares. Electron acceleration in the current layers up to energies of the order of a MeV is discussed as a mechanism of electron pulsed injection. The collective acceleration mechanism can be realized at a comparatively small density of accelerated electrons nsub(e) approximately equal to 10 2 10 4 cm -3

  10. Pannus-Related Mechanical Valve Dysfunction Leading to Hemodynamic Shock

    Manabu Shiraishi

    2012-02-01

    Full Text Available Mechanical prosthetic valve dysfunction caused by pannus formation is rare. Pannus restricts movement of prosthetic valve leaflets, resulting in severe aortic regurgitation. We describe the case of a 77-year-old woman who presented to the emergency room with increasing dyspnea, ischemia, and shock secondary to mechanical aortic valve dysfunction. Transesophageal echocardiography showed a blockade of the leaflets of the mechanical aortic valve, with severe aortic regurgitation. She underwent emergent cardiac surgery for aortic valve replacement. Pannus formation should be considered as a potential cause of acute severe aortic regurgitation in a patient with a small-sized mechanical aortic prosthesis in the supra-annular position. On a pathological exam, extensive pannus was found on the ventricular side of the prosthetic valve, extending from the ring into the central orifice. [Arch Clin Exp Surg 2012; 1(1.000: 50-53

  11. Design of the hydraulic shock absorbers characteristics using the acceleration of the sprung mass

    Polach P.

    2007-10-01

    Full Text Available The force-velocity characteristics of the air-pressure-controlled shock absorbers produced in BRANO a.s. were designed on the basis of the relative deflections of the air springs. These characteristics are verified by means of another approach – the acceleration of the sprung mass criterion. The reference vehicle is the same as in the previous case – the SOR C 12 intercity bus. The bus multibody models created in the alaska simulation tool are used for the designed characteristics verification. The results of both approaches are compared.

  12. An approach to incorporate the detonation shock dynamics into the calculation of explosive acceleration of metals

    Li Qingzhong; Sun Chengwei; Zhao Feng; Gao Wen; Wen Shanggang; Liu Wenhan

    1999-11-01

    The generalized geometrical optics model for the detonation shock dynamics (DSD) has been incorporated into the two dimensional hydro-code WSU to form a combination code ADW for numerical simulation of explosive acceleration of metals. An analytical treatment of the coupling conditions at the nodes just behind the detonation front is proposed. The experiments on two kinds of explosive-flyer assemblies with different length/diameter ratio were carried out to verify the ADW calculations, where the tested explosive was HMX or TATB based. It is found that the combination of DSD and hydro-code can improve the calculation precision, and has advantages in larger meshes and less CPU time

  13. ANALYSIS OF IMPACT OF CHANGING THE SHOCK ABSORBER RESISTANCE FACTOR ON ACCELERATING THE VEHICLE SPRUNG MASS

    P. Rozhkov

    2017-12-01

    Full Text Available The change of acceleration of the vehicle sprung mass while changing the coefficient of resistance of the adaptive pendant shock absorber has been analyzed. Presentation of disturbing influence is taken as a harmonic function containing the initial phase. Solution of the system of differential equations is carried out taking into account the initial conditions. The mathematical modeling of the impact of the vehicle sprung mass vibrations at various moments of time of forming the actuating signal on the change of the coefficient of resistance allowed to formulate requirements to the system of adaptive suspension control.

  14. Mechanical response of shock conditioned HPNS-5 (R-1) grout

    Plannerer, H.N.

    1997-01-01

    HPNS-5 (R-1) grout is a portland cement formulated mix designed for use as a rigid containment plug in vertical boreholes at the Nevada Test Site. Coincident with field testing of this grout in 1991 and 1992 , two arums of the grout mix were collected and positioned in the by pass drift of the DISTANT ZENITH event to expose the grout to passage of a nuclear driven stress wave. The drums were later retrieved to determine the mechanical behavior of the shock conditioned grout. Sealed hollow tubes positioned within the grout-filled drums to detect ductile flow on passage of the stress wave were found partially to completely filled with HPNS-5 grout following the experiment. Static mechanical tests support the evidence for ductile flow and place the transition from brittle fracture failure to ductile behavior in the shock conditioned grout at a confining stress between ambient and 5 MPa (725 psi). Uniaxial and triaxial tests delineated a stress-strain field for interstice collapse that interposes between the mechanics of linear elastic deformation and dilatancy. Hydrostatic stress loading between 25 MPa (3.6 ksi) and 60 MPa (8.7 ksi) results in a significant change of permanent set from 1% to greater than 15% volume strain

  15. Foot strike pattern differently affects the axial and transverse components of shock acceleration and attenuation in downhill trail running.

    Giandolini, Marlene; Horvais, Nicolas; Rossi, Jérémy; Millet, Guillaume Y; Samozino, Pierre; Morin, Jean-Benoît

    2016-06-14

    Trail runners are exposed to a high number of shocks, including high-intensity shocks on downhill sections leading to greater risk of osseous overuse injury. The type of foot strike pattern (FSP) is known to influence impact severity and lower-limb kinematics. Our purpose was to investigate the influence of FSP on axial and transverse components of shock acceleration and attenuation during an intense downhill trail run (DTR). Twenty-three trail runners performed a 6.5-km DTR (1264m of negative elevation change) as fast as possible. Four tri-axial accelerometers were attached to the heel, metatarsals, tibia and sacrum. Accelerations were continuously recorded at 1344Hz and analyzed over six sections (~400 steps per subject). Heel and metatarsal accelerations were used to identify the FSP. Axial, transverse and resultant peak accelerations, median frequencies and shock attenuation within the impact-related frequency range (12-20Hz) were assessed between tibia and sacrum. Multiple linear regressions showed that anterior (i.e. forefoot) FSPs were associated with higher peak axial acceleration and median frequency at the tibia, lower transverse median frequencies at the tibia and sacrum, and lower transverse peak acceleration at the sacrum. For resultant acceleration, higher tibial median frequency but lower sacral peak acceleration were reported with forefoot striking. FSP therefore differently affects the components of impact shock acceleration. Although a forefoot strike reduces impact severity and impact frequency content along the transverse axis, a rearfoot strike decreases them in the axial direction. Globally, the attenuation of axial and resultant impact-related vibrations was improved using anterior FSPs. Copyright © 2016 Elsevier Ltd. All rights reserved.

  16. A numerical study of shock-acceleration of a diffuse helium cylinder. Revision 1

    Greenough, J.A.; Jacobs, J.W.

    1995-08-01

    The development of a shock-accelerated diffuse Helium cylindrical inhomogeneity is investigated using a new numerical method. The new algorithm is a higher-order Godunov implementation of the so-called multi-fluid equations. This system correctly models multiple component mixtures by accounting for differential compressibility effects. This base integrator is embedded in an implementation of adaptive mesh refinement (AMR) that allows efficient increase in resolution by concentrating the computational effort where high accuracy, or increased resolution, are required. Qualitative and quantitative comparison with previous experimental data is excellent. The simulations show that counter-sign vortex blobs are deposited in the jet core by baroclinic generation of the curved shock wave as it traverses the jet. This vorticity deposition occurs over timescales that scale with the shock passage time (∼ 10microsec). Three phases of development are identified and characterized. The first is the weak deformation (WD) phase, where there is weak distortion of the Helium jet due to weak vorticity induced velocity effects. The second phase is the strong deformation (SD) phase where there is large distortion for the jet and the vortex blobs due to large induced velocity effects. The last is a relaxation/reorganization (RR) phase where the vorticity field is reorganized into point-like vortex pair. This class of problem has applications in such disparate fields as inertial confinement fusion (ICF) and high-speed combustion

  17. A numerical study of shock-acceleration of a diffuse helium cylinder

    Greenough, J.A.; Bell, J.; Colella, P.

    1995-08-01

    The development of a shock-accelerated diffuse Helium cylindrical inhomogeneity is investigated using a new numerical method. The new algorithm is a higher-order Godunov implementation of the so-called multi-fluid equations. This system correctly models multiple component mixtures by accounting for differential compressibility effects. This base integrator is embedded in an implementation of adaptive mesh refinement (AMR) that allows efficient increase in resolution where the computational effort is concentrated where high accuracy, or increased resolution, are required. Qualitative and quantitative comparison with previous experimental data is excellent. The simulations show that counter-sign vortex blobs are deposited in the jet core by baroclinic generation of the curved shock wave as it traverses the jet. This vorticity deposition occurs over timescales that scale with the shock passage time (∼ 10μsec). Three phases of development are identified and characterized. The first is the weak deformation (WD) phase, where there is weak distortion of the Helium jet due to weak vorticity induced velocity effects. The second phase is the strong deformation (SD) phase where there is large distortion for the jet and the vortex blobs due to large induced velocity effects. The last is a relaxation/reorganization (RR) phase where the vorticity field reorganizes into point-like vortex pair

  18. COLLISIONLESS SHOCKS IN A PARTIALLY IONIZED MEDIUM. I. NEUTRAL RETURN FLUX AND ITS EFFECTS ON ACCELERATION OF TEST PARTICLES

    Blasi, P.; Morlino, G.; Bandiera, R.; Amato, E. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, I-50125 Firenze (Italy); Caprioli, D. [Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08540 (United States)

    2012-08-20

    A collisionless shock may be strongly modified by the presence of neutral atoms through the processes of charge exchange between ions and neutrals and ionization of the latter. These two processes lead to exchange of energy and momentum between charged and neutral particles both upstream and downstream of the shock. In particular, neutrals that suffer a charge exchange downstream with shock-heated ions generate high-velocity neutrals that have a finite probability of returning upstream. These neutrals might then deposit heat in the upstream plasma through ionization and charge exchange, thereby reducing the fluid Mach number. A consequence of this phenomenon, which we refer to as the neutral return flux, is a reduction of the shock compression factor and the formation of a shock precursor upstream. The scale length of the precursor is determined by the ionization and charge-exchange interaction lengths of fast neutrals moving toward upstream infinity. In the case of a shock propagating in the interstellar medium, the effects of ion-neutral interactions are especially important for shock velocities <3000 km s{sup -1}. Such propagation velocities are common among shocks associated with supernova remnants, the primary candidate sources for the acceleration of Galactic cosmic rays. We then investigate the effects of the return flux of neutrals on the spectrum of test particles accelerated at the shock. We find that, for shocks slower than {approx}3000 km s{sup -1}, the particle energy spectrum steepens appreciably with respect to the naive expectation for a strong shock, namely, {proportional_to}E{sup -2}.

  19. Multiple-shock initiation via statistical crack mechanics

    Dienes, J.K.; Kershner, J.D.

    1998-12-31

    Statistical Crack Mechanics (SCRAM) is a theoretical approach to the behavior of brittle materials that accounts for the behavior of an ensemble of microcracks, including their opening, shear, growth, and coalescence. Mechanical parameters are based on measured strain-softening behavior. In applications to explosive and propellant sensitivity it is assumed that closed cracks act as hot spots, and that the heating due to interfacial friction initiates reactions which are modeled as one-dimensional heat flow with an Arrhenius source term, and computed in a subscale grid. Post-ignition behavior of hot spots is treated with the burn model of Ward, Son and Brewster. Numerical calculations using SCRAM-HYDROX are compared with the multiple-shock experiments of Mulford et al. in which the particle velocity in PBX 9501 is measured with embedded wires, and reactions are initiated and quenched.

  20. The microstructural mechanism for mechanical property of LY2 aluminum alloy after laser shock processing

    Luo, Kai-yu; Lu, Jin-zhong; Zhang, Ling-feng; Zhong, Jun-wei; Guan, Hai-bing; Qian, Xiao-ming

    2010-01-01

    This paper described nanoindentation techniques for measuring thin films mechanical properties, including elastic modulus and nano-hardness. The effects of laser shock processing (LSP) on elastic modulus and nano-hardness of the sample manufactured by LY2 aluminum alloy were experimentally investigated by nanoindentation techniques. Transmission electron microscope (TEM) observations of the microstructures in different regions after LSP are carried out. Experimental results showed that the values of nano-hardness and elastic modulus in the laser-shocked region were obviously increased by 58.13% and 61.74% compared to those in the non-shocked region, respectively. The influences of LSP on microstructure and grain size of LY2 aluminum alloy were discussed, and the enhancement mechanism of LSP on nano-hardness and elastic modulus was also addressed.

  1. Kinetic mix mechanisms in shock-driven inertial confinement fusion implosions

    Rinderknecht, H. G.; Sio, H.; Li, C. K.; Zylstra, A. B.; Rosenberg, M. J.; Frenje, J. A.; Gatu Johnson, M.; Séguin, F. H.; Petrasso, R. D. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Hoffman, N.; Kagan, G.; Molvig, K. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Betti, R.; Yu Glebov, V.; Meyerhofer, D. D.; Sangster, T. C.; Seka, W.; Stoeckl, C. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States); Bellei, C.; Amendt, P. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); and others

    2014-05-15

    Shock-driven implosions of thin-shell capsules, or “exploding pushers,” generate low-density, high-temperature plasmas in which hydrodynamic instability growth is negligible and kinetic effects can play an important role. Data from implosions of thin deuterated-plastic shells with hydroequivalent D{sup 3}He gas fills ranging from pure deuterium to pure {sup 3}He [H. G. Rinderknecht et al., Phys. Rev. Lett. 112, 135001 (2014)] were obtained to evaluate non-hydrodynamic fuel-shell mix mechanisms. Simulations of the experiments including reduced ion kinetic models support ion diffusion as an explanation for these data. Several additional kinetic mechanisms are investigated and compared to the data to determine which are important in the experiments. Shock acceleration of shell deuterons is estimated to introduce mix less than or comparable to the amount required to explain the data. Beam-target mechanisms are found to produce yields at most an order of magnitude less than the observations.

  2. Molecular Mechanisms in the shock induced decomposition of FOX-7

    Mishra, Ankit; Tiwari, Subodh C.; Nakano, Aiichiro; Vashishta, Priya; Kalia, Rajiv; CACS Team

    Experimental and first principle computational studies on FOX 7 have either involved a very small system consisting of a few atoms or they did not take into account the decomposition mechanisms under extreme conditions of temperature and pressure. We have performed a large-scale reactive MD simulation using ReaxFF-lg force field to study the shock decomposition of FOX 7. The chemical composition of the principal decomposition products correlates well with experimental observations. Furthermore, we observed that the production of N2 and H2O was inter molecular in nature and was through different chemical pathways. Moreover, the production of CO and CO2 was delayed due to production of large stable C,O atoms cluster. These critical insights into the initial processes involved in the shock induced decomposition of FOX-7 will greatly help in understanding the factors playing an important role in the insensitiveness of this high energy material. This research is supported by AFOSR Award No. FA9550-16-1-0042.

  3. A numerical study of fundamental shock noise mechanisms. Ph.D. Thesis - Cornell Univ.

    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.

  4. Shock Mechanism Analysis and Simulation of High-Power Hydraulic Shock Wave Simulator

    Xiaoqiu Xu

    2017-01-01

    Full Text Available The simulation of regular shock wave (e.g., half-sine can be achieved by the traditional rubber shock simulator, but the practical high-power shock wave characterized by steep prepeak and gentle postpeak is hard to be realized by the same. To tackle this disadvantage, a novel high-power hydraulic shock wave simulator based on the live firing muzzle shock principle was proposed in the current work. The influence of the typical shock characteristic parameters on the shock force wave was investigated via both theoretical deduction and software simulation. According to the obtained data compared with the results, in fact, it can be concluded that the developed hydraulic shock wave simulator can be applied to simulate the real condition of the shocking system. Further, the similarity evaluation of shock wave simulation was achieved based on the curvature distance, and the results stated that the simulation method was reasonable and the structural optimization based on software simulation is also beneficial to the increase of efficiency. Finally, the combination of theoretical analysis and simulation for the development of artillery recoil tester is a comprehensive approach in the design and structure optimization of the recoil system.

  5. Physical mechanisms in shock-induced turbulent separated flow

    Dolling, D. S.

    1987-12-01

    It has been demonstrated that the flow downstream of the moving shock is separated and that the foot of the shock is effectively the instantaneous separation point. The shock induced turbulent separation is an intermittant process and the separation line indicated by surface tracer methods, such as kerosene-lampblack, is a downstream boundary of a region of intermittent separation.

  6. Focusing mechanisms in the Pulselac CU accelerator

    Johnson, D.J.; Lockner, T.R.

    1986-06-01

    The post-acceleration of a 400 keV, 10 kA proton beam by a 200 kV magnetically insulated gap is investigated. The deflection from self and applied E and B fields are measured and compared to calculated values. We find that the beam is inadequately space-charge neutralized without gas puffs in regions of applied-B field to allow efficient transport. The beam is also non-current neutralized in these regions leading to self-magnetic deflection. The applied-B field is used to focus the beam both directly as a solenoidal lens and indirectly by defining the equipotential surfaces in the accelerating gap. It is also pointed out how azimuthal asymmetries in the beam current density and cathode plasma cause beam self-field asymmetries that lead to emittance growth. 4 refs., 4 figs

  7. Phase space quantum mechanics and maximal acceleration

    Caianiello, E.

    1989-01-01

    My presentation is a synopsis of work done since 1979 in search of connections among information theory, systems theory, quantum mechanics and other matters. The aim was 'to extract geometry from quantum mechanics'. (orig./HSI)

  8. Part I. Mechanisms of injury associated with extracorporeal shock wave lithotripsy; Part II. Exsolution of volatiles

    Howard, Danny Dwayne

    Part I - Shock waves are focused in extracorporeal shock wave lithotripsy (ESWL) machines to strengths sufficient to fracture kidney stones. Substantial side effects-most of them acute-have resulted from this procedure, including injury to soft tissue. The focusing of shock waves through various layers of tissue is a complex process which stimulates many bio-mechano-chemical responses.This thesis presents results of an in vitro study of the initial mechanical stimulus. Planar nitrocellulose membranes of order 10 um thick were used as models of thin tissue structures. Two modes of failure were recorded: Failure due to cavitation collapsing on or near the membranes, and failure induced by altering the structure of shock waves. Tests were done in water at and around F2 to characterize the extent of cavitation damage, and was found to be confined within the focal region, 1.2 cm along the axis of focus.Scattering media were used to simulate the effects of acoustic nonuniformity of tissue and to alter the structure of focusing shock waves. 40 um diameter (average) hollow glass spheres were added to ethylene glycol, glycerine and castor oil to vary the properties of the scattering media. Multiple layer samples of various types of phantom tissue were tested in degassed castor oil to gauge the validity of the scattering media. The scattering media and tissue samples increased the rise time decreased strain rate in a similar fashion. Membranes were damaged by the decreased strain rate and accumulated effects of the altered structure: After about 20 or so shocks immersed in the scattering media and after about 100 shocks behind the tissue samples. The mode of failure was tearing with multiple tears in some cases from about .1 cm to about 3 cm depending of the number of shocks and membrane thickness.Part II - This work examines the exsolution of volatiles-carbon dioxide from water-in a cylindrical test cell under different pressure conditions. Water was supersaturated with

  9. Selfsimilar time dependent shock structures

    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 same 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

  10. Selfsimilar time dependent shock structures

    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.

  11. ELECTRON ACCELERATION IN PULSAR-WIND TERMINATION SHOCKS: AN APPLICATION TO THE CRAB NEBULA GAMMA-RAY FLARES

    Kroon, John J.; Becker, Peter A.; Dermer, Charles D. [Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030-4444 (United States); Finke, Justin D., E-mail: jkroon@gmu.edu, E-mail: pbecker@gmu.edu, E-mail: charlesdermer@outlook.com, E-mail: justin.finke@nrl.navy.mil [Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States)

    2016-12-20

    The γ -ray flares from the Crab Nebula observed by AGILE and Fermi -LAT reaching GeV energies and lasting several days challenge the standard models for particle acceleration in pulsar-wind nebulae because the radiating electrons have energies exceeding the classical radiation-reaction limit for synchrotron. Previous modeling has suggested that the synchrotron limit can be exceeded if the electrons experience electrostatic acceleration, but the resulting spectra do not agree very well with the data. As a result, there are still some important unanswered questions about the detailed particle acceleration and emission processes occurring during the flares. We revisit the problem using a new analytical approach based on an electron transport equation that includes terms describing electrostatic acceleration, stochastic wave-particle acceleration, shock acceleration, synchrotron losses, and particle escape. An exact solution is obtained for the electron distribution, which is used to compute the associated γ -ray synchrotron spectrum. We find that in our model the γ -ray flares are mainly powered by electrostatic acceleration, but the contributions from stochastic and shock acceleration play an important role in producing the observed spectral shapes. Our model can reproduce the spectra of all the Fermi -LAT and AGILE flares from the Crab Nebula, using magnetic field strengths in agreement with the multi-wavelength observational constraints. We also compute the spectrum and duration of the synchrotron afterglow created by the accelerated electrons, after they escape into the region on the downstream side of the pulsar-wind termination shock. The afterglow is expected to fade over a maximum period of about three weeks after the γ -ray flare.

  12. Shock wave effects in copper: Design of an experimental device for post recovery mechanical testing

    Buy, Francois; Llorca, Fabrice

    2002-01-01

    The mechanical behavior of metals may prove high changes with strain rate and pressure loading history. In order to investigate the effect of a shock on the ulterior mechanical behavior of high purity copper, we set up an experimental device inspired from G. T. Gray III's works. This device, based on the trapping of shock waves after a plane plate impact is validated by numerical simulations. The aim of these simulations is the evaluation of the heterogeneity of plastic deformation. Shock pressures up to 10 GPa have been investigated. The plastic strain levels subsequent to the shock are between 0.08 and 0.15 in the sample

  13. Can diffusive shock acceleration in supernova remnants account for high-energy galactic cosmic rays?

    Hillas, A M

    2005-01-01

    Diffusive shock acceleration at the outer front of expanding supernova remnants has provided by far the most popular model for the origin of galactic cosmic rays, and has been the subject of intensive theoretical investigation. But several problems loomed at high energies-how to explain the smooth continuation of the cosmic-ray spectrum far beyond 10 14 eV, the very low level of TeV gamma-ray emission from several supernova remnants, and the very low anisotropy of cosmic rays (seeming to conflict with the short trapping times needed to convert a E -2 source spectrum into the observed E -2.7 spectrum of cosmic rays). However, recent work on the cosmic ray spectrum (especially at KASCADE) strongly indicates that about half of the flux does turn down rather sharply near 3 x 10 15 V rigidity, with a distinct tail extending to just beyond 10 17 V rigidity; whilst a plausible description (Bell and Lucek) of the level of self-generated magnetic fields at the shock fronts of young supernova remnants implies that many SNRs in varying environments might very well generate spectra extending smoothly to just this 'knee' position, and a portion of the exploding red supergiants could extend the spectrum approximately as needed. At low energies, recent progress in relating cosmic ray compositional details to modified shock structure also adds weight to the belief that the model is working on the right lines, converting energy into cosmic rays very efficiently where injection can occur. The low level of TeV gamma-ray flux from many young SNRs is a serious challenge, though it may relate to variations in particle injection efficiency with time. The clear detection of TeV gamma rays from SNRs has now just begun, and predictions of a characteristic curved particle spectrum give a target for new tests by TeV observations. However, the isotropy seriously challenges the assumed cosmic-ray trapping time and hence the shape of the spectrum of particles released from SNRs. There is

  14. Studies on mechanisms of the laser particle acceleration

    Aurand, Bastian

    2012-01-01

    Within the last decade, many developments towards higher energies and particle numbers paved the way of particle acceleration performed by high intensity laser systems. Up to now, the process of a field-induced acceleration process (Target-Normal-Sheath-Acceleration (TNSA)) is investigated the most. Acceleration occurs as a consequence of separation of charges on a surface potential. Here, the broad energy spectrum is a problem not yet overcome although many improvements were achieved. Calculations for intensities higher than 10 20..21 W/cm 2 give hint that Radiation-Pressure-Acceleration (RPA) may lead to a sharper, monoenergetic energy spectrum. Within the framework of this thesis, the investigation of the acceleration mechanism is studied experimentally in the intensity range of 10 19 W/cm 2 . Suitable targets were developed and applied for patent. A broad range of parameters was scanned by means of high repetition rates together with an adequate laser system to provide high statistics of several thousands of shots, and the dependence of target material, intensity, laser polarisation and pre plasma-conditions was verified. Comparisons with 2-d numeric simulations lead to a model of the acceleration process which was analyzed by several diagnostic methods, giving clear evidence for a new, not field-induced acceleration process. In addition, a system for a continuous variation of the polarization based on reflective optics was developed in order to overcome the disadvantages of retardation plates, and their practicability of high laser energies can be achieved.

  15. PLANETARY EMBRYO BOW SHOCKS AS A MECHANISM FOR CHONDRULE FORMATION

    Mann, Christopher R.; Boley, Aaron C. [Department of Physics and Astronomy University of British Columbia Vancouver, BC V6T 1Z1 (Canada); Morris, Melissa A. [Physics Department State University of New York at Cortland Cortland, NY 13045 (United States)

    2016-02-20

    We use radiation hydrodynamics with direct particle integration to explore the feasibility of chondrule formation in planetary embryo bow shocks. The calculations presented here are used to explore the consequences of a Mars-size planetary embryo traveling on a moderately excited orbit through the dusty, early environment of the solar system. The embryo’s eccentric orbit produces a range of supersonic relative velocities between the embryo and the circularly orbiting gas and dust, prompting the formation of bow shocks. Temporary atmospheres around these embryos, which can be created via volatile outgassing and gas capture from the surrounding nebula, can non-trivially affect thermal profiles of solids entering the shock. We explore the thermal environment of solids that traverse the bow shock at different impact radii, the effects that planetoid atmospheres have on shock morphologies, and the stripping efficiency of planetoidal atmospheres in the presence of high relative winds. Simulations are run using adiabatic and radiative conditions, with multiple treatments for the local opacities. Shock speeds of 5, 6, and 7 km s{sup −1} are explored. We find that a high-mass atmosphere and inefficient radiative conditions can produce peak temperatures and cooling rates that are consistent with the constraints set by chondrule furnace studies. For most conditions, the derived cooling rates are potentially too high to be consistent with chondrule formation.

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

    Kartavykh, Y. Y.; Dröge, W. [Institut für Theoretische Physik und Astrophysik, Universität Würzburg, D-97074 Würzburg (Germany); Gedalin, M. [Department of Physics, Ben-Gurion Unversity of the Negev, Beer-Sheva (Israel)

    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 for 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.

  17. Diagnostics for studies of novel laser ion acceleration mechanisms

    Senje, Lovisa; Aurand, Bastian; Wahlström, Claes-Göran [Department of Physics, Lund University, P. O. Box 118, S-221 00 Lund (Sweden); Yeung, Mark; Kuschel, Stephan; Rödel, Christian [Helmholtz-Institut Jena, D-07743 Jena (Germany); Wagner, Florian; Roth, Markus [Technische Universität Darmstadt, D-64289 Darmstadt (Germany); Li, Kun; Neumayer, Paul [ExtreMe Matter Institut, D-64291 Darmstadt (Germany); Dromey, Brendan; Jung, Daniel [Department of Physics and Astronomy, Queen' s University, Belfast BT7 1NN (United Kingdom); Bagnoud, Vincent [Helmholtz-Institut Jena, D-07743 Jena (Germany); GSI Helmholtzzentrum für Schwerionenforschung GmbH, D-64291 Darmstadt (Germany); Zepf, Matthew [Helmholtz-Institut Jena, D-07743 Jena (Germany); Department of Physics and Astronomy, Queen' s University, Belfast BT7 1NN (United Kingdom); Kuehl, Thomas [ExtreMe Matter Institut, D-64291 Darmstadt (Germany); GSI Helmholtzzentrum für Schwerionenforschung GmbH, D-64291 Darmstadt (Germany); Universität Mainz, D-55099 Mainz (Germany)

    2014-11-15

    Diagnostic for investigating and distinguishing different laser ion acceleration mechanisms has been developed and successfully tested. An ion separation wide angle spectrometer can simultaneously investigate three important aspects of the laser plasma interaction: (1) acquire angularly resolved energy spectra for two ion species, (2) obtain ion energy spectra for multiple species, separated according to their charge to mass ratio, along selected axes, and (3) collect laser radiation reflected from and transmitted through the target and propagating in the same direction as the ion beam. Thus, the presented diagnostic constitutes a highly adaptable tool for accurately studying novel acceleration mechanisms in terms of their angular energy distribution, conversion efficiency, and plasma density evolution.

  18. Diagnostics for studies of novel laser ion acceleration mechanisms

    Senje, Lovisa; Aurand, Bastian; Wahlström, Claes-Göran; Yeung, Mark; Kuschel, Stephan; Rödel, Christian; Wagner, Florian; Roth, Markus; Li, Kun; Neumayer, Paul; Dromey, Brendan; Jung, Daniel; Bagnoud, Vincent; Zepf, Matthew; Kuehl, Thomas

    2014-01-01

    Diagnostic for investigating and distinguishing different laser ion acceleration mechanisms has been developed and successfully tested. An ion separation wide angle spectrometer can simultaneously investigate three important aspects of the laser plasma interaction: (1) acquire angularly resolved energy spectra for two ion species, (2) obtain ion energy spectra for multiple species, separated according to their charge to mass ratio, along selected axes, and (3) collect laser radiation reflected from and transmitted through the target and propagating in the same direction as the ion beam. Thus, the presented diagnostic constitutes a highly adaptable tool for accurately studying novel acceleration mechanisms in terms of their angular energy distribution, conversion efficiency, and plasma density evolution

  19. Low Mach-number collisionless electrostatic shocks and associated ion acceleration

    Pusztai, I.; TenBarge, J. M.; Csapó, A. N.; Juno, J.; Hakim, A.; Yi, L.; Fülöp, T.

    2018-03-01

    The existence and properties of low Mach-number (M≳ 1) electrostatic collisionless shocks are investigated with a semi-analytical solution for the shock structure. We show that the properties of the shock obtained in the semi-analytical model can be well reproduced in fully kinetic Eulerian Vlasov-Poisson simulations, where the shock is generated by the decay of an initial density discontinuity. Using this semi-analytical model, we study the effect of the electron-to-ion temperature ratio and the presence of impurities on both the maximum shock potential and the Mach number. We find that even a small amount of impurities can influence the shock properties significantly, including the reflected light ion fraction, which can change several orders of magnitude. Electrostatic shocks in heavy ion plasmas reflect most of the hydrogen impurity ions.

  20. Creation of ultra-high-pressure shocks by the collision of laser-accelerated disks: experiment and theory

    Rosen, M.D.; Phillion, D.W.; Price, R.H.; Campbell, E.M.; Obenschain, S.P.; Whitlock, R.R.; McLean, E.A.; Ripin, B.H.

    1983-01-01

    We have used the SHIVA laser system to accelerate carbon disks to speeds in excess of 100 km/sec. The 3KJ/3 ns pulse, on a 1 mm diameter spot of a single disk produced a conventional shock of about 5 MB. The laser energy can, however, be stored in kinetic motion of this accelerated disk and delivered (reconverted to thermal energy) upon impact with another carbon disk. This collision occurs in a time much shorter than the 3 ns pulse, thus acting as a power amplifier. The shock pressures measured upon impact are estimated to be in the 20 MB range, thus demonstrating the amplification power of this colliding disk technique in creating ultra-high pressures. Theory and computer simulations of this process will be discussed, and compared with the experiment

  1. INTERSTELLAR PICKUP ION ACCELERATION IN THE TURBULENT MAGNETIC FIELD AT THE SOLAR WIND TERMINATION SHOCK USING A FOCUSED TRANSPORT APPROACH

    Ye, Junye; Roux, Jakobus A. le; Arthur, Aaron D. [Department of Space Science, University of Alabama in Huntsville, Huntsville, AL 35899 (United States)

    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.

  2. Shock-induced electrical activity in polymeric solids. A mechanically induced bond scission model

    Graham, R.A.

    1979-01-01

    When polymeric solids are subjected to high-pressure shock loading, two anomalous electrical phenomena, shock-induced conduction and shock-induced polarization, are observed. The present paper proposes a model of mechanically induced bond scission within the shock front to account for the effects. An experimental study of shock-induced polarization in poly(pyromellitimide) (Vespel SP-1) is reported for shock compressions from 17 to 23% (pressures from 2.5 to 5.4 GPa). Poly(pyromellitimide) is found to be a strong generator of such polarization and the polarization is found to reflect an irreversible or highly hysteretic process. The present measurements are combined with prior measurements to establish a correlation between monomer structure and strength of shock-induced polarization; feeble signals are observed in the simpler monomer repeat units of poly(tetrafluoroethylene) and polyethylene while the strongest signals are observed in more complex monomers of poly(methyl methacrylate) and poly(pyromellitimide). It is also noted that there is an apparent correlation between shock-induced conduction and shock-induced polarization. Such shock-induced electrical activity is also found to be well correlated with the propensity for mechanical bond scission observed in experiments carried out in conventional mechanochemical studies. The bond scission model can account for characteristics observed for electrical activity in shock-loaded polymers and their correlation to monomer structure. Localization of elastic energy within the monomer repeat unit or along the main chain leads to the different propensities for bond scission and resulting shock-induced electrical activity

  3. Discrimination of Thermal versus Mechanical Effects of Shock on Rock Magnetic Properties of Spherically Shocked up to 10-160 GPa Basalt and Diabase

    Bezaeva, N. S.; Swanson-Hysell, N.; Tikoo, S.; Badyukov, D. D.; Kars, M. A. C.; Egli, R.; Chareev, D. A.; Fairchild, L. M.

    2016-12-01

    Understanding how shock waves generated during hypervelocity impacts affect rock magnetic properties is key for interpreting the paleomagnetic records of lunar rocks, meteorites, and cratered planetary surfaces. Laboratory simulations of impacts show that ultra-high shocks may induce substantial post-shock heating of the target material. At high pressures (>10 GPa), shock heating occurs in tandem with mechanical effects, such as grain fracturing and creation of crystallographic defects and dislocations within magnetic grains. This makes it difficult to conclude whether shock-induced changes in the rock magnetic properties of target materials are primarily associated with mechanical or thermal effects. Here we present novel experimental methods to discriminate between mechanical and thermal effects of shock on magnetic properties and illustrate it with two examples of spherically shocked terrestrial basalt and diabase [1], which were shocked to pressures of 10 to >160 GPa, and investigate possible explanations for the observed shock-induced magnetic hardening (i.e., increase in remanent coercivity Bcr). The methods consist of i) conducting extra heating experiments at temperatures resembling those experienced during high-pressure shock events on untreated equivalents of shocked rocks (with further comparison of Bcr of shocked and heated samples) and ii) quantitative comparison of high-resolution first-order reversal curve (FORC) diagrams (field step: 0.5-0.7 mT) for shocked, heated and untreated specimens. Using this approach, we demonstrated that the shock-induced coercivity hardening in our samples is predominantly due to solid-state, mechanical effects of shock rather than alteration associated with shock heating. Indeed, heating-induced changes in Bcr in the post-shock temperature range were minor. Visual inspection of FORC contours (in addition to detailed analyses) reveals a stretching of the FORC distribution of shocked sample towards higher coercivities

  4. Neutron-decay Protons from Solar Flares as Seed Particles for CME-shock Acceleration in the Inner Heliosphere

    Murphy, Ronald J. [Code 7650, Naval Research Laboratory, Washington, DC 20375 (United States); Ko, Yuan-Kuen, E-mail: ronald.murphy@nrl.navy.mil, E-mail: yuan-kuen.ko@nrl.navy.mil [Code 7680, Naval Research Laboratory, Washington, DC 20375 (United States)

    2017-09-01

    The protons in large solar energetic particle events are accelerated in the inner heliosphere by fast shocks produced by coronal mass ejections. Unless there are other sources, the protons these shocks act upon would be those of the solar wind (SW). The efficiency of the acceleration depends on the kinetic energy of the protons. For a 2000 km s{sup −1} shock, the most effective proton energies would be 30–100 keV; i.e., within the suprathermal tail component of the SW. We investigate one possible additional source of such protons: those resulting from the decay of solar-flare-produced neutrons that escape from the Sun into the low corona. The neutrons are produced by interactions of flare-accelerated ions with the solar atmosphere. We discuss the production of low-energy neutrons in flares and their decay on a interplanetary magnetic field line near the Sun. We find that even when the flaring conditions are optimal, the 30–100 keV neutron-decay proton density produced by even a very large solar flare would be only about 10% of that of the 30–100 keV SW suprathermal tail. We discuss the implication of a seed-particle source of more frequent, small flares.

  5. Characteristics of Acceleration and Acoustic Emission Signals from Mechanical Seals

    Lee, Do Hwan; Ha, Che Woong

    2015-01-01

    Based on these results, the applicability of acceleration signals for condition monitoring of mechanical seals is examined in the present study. Mechanical seals are used for pumps to prevent excessive leakage that might be occurred between rotational and stationary parts. The mechanical seals account for the major pump component failures. In spite of its importance, there have been few studies on condition monitoring of the components. Recently, some researchers have paid attention to the application of acoustic emission (AE) sensors for the fault detection of seals. The characteristics of acceleration and AE signals obtained from various defects are investigated. In order to prevent excessive leakage from mechanical seals, a condition monitoring technique is necessary. Based on the previous studies on AE techniques for seal monitoring, the signal characteristics from accelerometer

  6. Characteristics of Acceleration and Acoustic Emission Signals from Mechanical Seals

    Lee, Do Hwan; Ha, Che Woong [KHNP Central Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    Based on these results, the applicability of acceleration signals for condition monitoring of mechanical seals is examined in the present study. Mechanical seals are used for pumps to prevent excessive leakage that might be occurred between rotational and stationary parts. The mechanical seals account for the major pump component failures. In spite of its importance, there have been few studies on condition monitoring of the components. Recently, some researchers have paid attention to the application of acoustic emission (AE) sensors for the fault detection of seals. The characteristics of acceleration and AE signals obtained from various defects are investigated. In order to prevent excessive leakage from mechanical seals, a condition monitoring technique is necessary. Based on the previous studies on AE techniques for seal monitoring, the signal characteristics from accelerometer.

  7. Robust design of microelectronics assemblies against mechanical shock, temperature and moisture effects of temperature, moisture and mechanical driving forces

    Wong, E-H

    2015-01-01

    Robust Design of Microelectronics Assemblies Against Mechanical Shock, Temperature and Moisture discusses how the reliability of packaging components is a prime concern to electronics manufacturers. The text presents a thorough review of this important field of research, providing users with a practical guide that discusses theoretical aspects, experimental results, and modeling techniques. The authors use their extensive experience to produce detailed chapters covering temperature, moisture, and mechanical shock induced failure, adhesive interconnects, and viscoelasticity. Useful progr

  8. Analysis and Mitigation of Mechanical Shock Effects on High Speed Planing Boats

    Keams, Sean

    2001-01-01

    .... Operation of these boats, particularly in rough seas, exposes the occupants to severe mechanical shock exposure that has been linked to significant increase in the rates of acute and chronic injury...

  9. Evaluating the Mechanism of Oil Price Shocks and Fiscal Policy Responses in the Malaysian Economy

    Bekhet, Hussain A; Yusoff, Nora Yusma Mohamed

    2013-01-01

    The paper aims to explore the symmetric impact of oil price shock on economy, to understand its mechanism channel and how fiscal policy response towards it. The Generalized Impulse Response Function and Variance Decomposition under the VAR methodology were employed. The empirical findings suggest that symmetric oil price shock has a positive and direct impact on oil revenue and government expenditure. However, the real GDP is vulnerable in a short-term but not in the long term period. These results would confirm that fiscal policy is the main mechanism channel that mitigates the adverse effects oil price shocks to the economy.

  10. Evaluating the Mechanism of Oil Price Shocks and Fiscal Policy Responses in the Malaysian Economy

    Bekhet, Hussain A.; Yusoff, Nora Yusma Mohamed

    2013-06-01

    The paper aims to explore the symmetric impact of oil price shock on economy, to understand its mechanism channel and how fiscal policy response towards it. The Generalized Impulse Response Function and Variance Decomposition under the VAR methodology were employed. The empirical findings suggest that symmetric oil price shock has a positive and direct impact on oil revenue and government expenditure. However, the real GDP is vulnerable in a short-term but not in the long term period. These results would confirm that fiscal policy is the main mechanism channel that mitigates the adverse effects oil price shocks to the economy.

  11. SHOCK-CLOUD INTERACTION AND PARTICLE ACCELERATION IN THE SOUTHWESTERN LIMB OF SN 1006

    Miceli, M.; Orlando, S.; Bocchino, F. [INAF-Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134 Palermo (Italy); Acero, F. [ORAU/NASA Goddard Space Flight Center, Astrophysics Science Division, Code 661, Greenbelt, MD 20771 (United States); Dubner, G. [Instituto de Astronomía y Física del Espacio (IAFE), UBA-CONICET, CC 67, Suc. 28, 1428 Buenos Aires (Argentina); Decourchelle, A., E-mail: miceli@astropa.unipa.it [Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu-CNRS-Université Paris Diderot, CE-Saclay, F-91191 Gif-sur-Yvette (France)

    2014-02-20

    The supernova remnant SN 1006 is a powerful source of high-energy particles and evolves in a relatively tenuous and uniform environment despite interacting with an atomic cloud in its northwestern limb. The X-ray image of SN 1006 reveals an indentation in the southwestern part of the shock front and the H I maps show an isolated (southwestern) cloud, having the same velocity as the northwestern cloud, whose morphology fits perfectly in the indentation. We performed spatially resolved spectral analysis of a set of small regions in the southwestern nonthermal limb and studied the deep X-ray spectra obtained within the XMM-Newton SN 1006 Large Program. We also analyzed archive H I data, obtained by combining single-dish and interferometric observations. We found that the best-fit value of N {sub H} derived from the X-ray spectra significantly increases in regions corresponding to the southwestern cloud, while the cutoff energy of the synchrotron emission decreases. The N {sub H} variation corresponds perfectly with the H I column density of the southwestern cloud, as measured from the radio data. The decrease in the cutoff energy at the indentation clearly reveals that the back side of the cloud is actually interacting with the remnant. The southwestern limb therefore presents a unique combination of efficient particle acceleration and high ambient density, thus being the most promising region for γ-ray hadronic emission in SN 1006. We estimate that such emission will be detectable with the Fermi telescope within a few years.

  12. SHOCK-CLOUD INTERACTION AND PARTICLE ACCELERATION IN THE SOUTHWESTERN LIMB OF SN 1006

    Miceli, M.; Orlando, S.; Bocchino, F.; Acero, F.; Dubner, G.; Decourchelle, A.

    2014-01-01

    The supernova remnant SN 1006 is a powerful source of high-energy particles and evolves in a relatively tenuous and uniform environment despite interacting with an atomic cloud in its northwestern limb. The X-ray image of SN 1006 reveals an indentation in the southwestern part of the shock front and the H I maps show an isolated (southwestern) cloud, having the same velocity as the northwestern cloud, whose morphology fits perfectly in the indentation. We performed spatially resolved spectral analysis of a set of small regions in the southwestern nonthermal limb and studied the deep X-ray spectra obtained within the XMM-Newton SN 1006 Large Program. We also analyzed archive H I data, obtained by combining single-dish and interferometric observations. We found that the best-fit value of N H derived from the X-ray spectra significantly increases in regions corresponding to the southwestern cloud, while the cutoff energy of the synchrotron emission decreases. The N H variation corresponds perfectly with the H I column density of the southwestern cloud, as measured from the radio data. The decrease in the cutoff energy at the indentation clearly reveals that the back side of the cloud is actually interacting with the remnant. The southwestern limb therefore presents a unique combination of efficient particle acceleration and high ambient density, thus being the most promising region for γ-ray hadronic emission in SN 1006. We estimate that such emission will be detectable with the Fermi telescope within a few years

  13. Acceleration{endash}deceleration process of thin foils confined in water and submitted to laser driven shocks

    Romain, J.P.; Auroux, E. [Laboratoire de Combustion et de Detonique (UPR 9028 CNRS), ENSMA, BP 109, Teleport 2, Chasseneuil du Poitou, 86960 Futuroscope Cedex (France)

    1997-08-01

    An experimental, numerical, and analytical study of the acceleration and deceleration process of thin metallic foils immersed in water and submitted to laser driven shocks is presented. Aluminum and copper foils of 20 to 120 {mu}m thickness, confined on both sides by water, have been irradiated at 1.06 {mu}m wavelength by laser pulses of {approximately}20ns duration, {approximately}17J energy, and {approximately}4GW/cm{sup 2} incident intensity. Time resolved velocity measurements have been made, using an electromagnetic velocity gauge. The recorded velocity profiles reveal an acceleration{endash}deceleration process, with a peak velocity up to 650 m/s. Predicted profiles from numerical simulations reproduce all experimental features, such as wave reverberations, rate of increase and decrease of velocity, peak velocity, effects of nature, and thickness of the foils. A shock pressure of about 2.5 GPa is inferred from the velocity measurements. Experimental points on the evolution of plasma pressure are derived from the measurements of peak velocities. An analytical description of the acceleration{endash}deceleration process, involving multiple shock and release waves reflecting on both sides of the foils, is presented. The space{endash}time diagrams of waves propagation and the successive pressure{endash}particle velocity states are determined, from which theoretical velocity profiles are constructed. All characteristics of experimental records and numerical simulations are well reproduced. The role of foil nature and thickness, in relation with the shock impedance of the materials, appears explicitly. {copyright} {ital 1997 American Institute of Physics.}

  14. On the mechanism of high-voltage discharge initiation in high-voltage accelerator accelerating tubes

    Zheleznikov, F.G.

    1983-01-01

    Experimental investigation into physical natupe of discharge processes in high-voltage accelerator accelerating tubes in the absence of the accelerated particle beam are conducted. The installation for the study of the mechanism of initiating vacuum isolation conductivity is used in the experiments. The vacuum chamber of the installation is made of steel and sealed with rubber packings. Electrodes 300-360 mm in diameter are made of stainless steel. Two variants of cleaning technology were used before electrode assembling: 1) degreasing by organic solvents; 2) cleaning by fine grinding cloth with successive washing by rectificated alcohol. Analysis of the obtained data shows that forma. tion of background flux of charged particles in interelectrode gap is caused by external photoelectric effect, excited by X radiation, which initiates the formation of intensive internal field in microfilms of non-conducting impurities on the electrode surfaces. The secondary electron emission plays the minor role at that

  15. Electron Acceleration in Supernovae and Millimeter Perspectives

    Keiichi Maeda

    2014-12-01

    Full Text Available Supernovae launch a strong shock wave by the interaction of the expanding ejecta and surrounding circumstellar matter (CSM. At the shock, electrons are accelerated to relativistic speed, creating observed synchrotron emissions in radio wavelengths. In this paper, I suggest that SNe (i.e., < 1 year since the explosion provide a unique site to study the electron acceleration mechanism. I argue that the eciency of the acceleration at the young SN shock is much lower than conventionally assumed, and that the electrons emitting in the cm wavelengths are not fully in the Diffusive Shock Acceleration (DSA regime. Thus radio emissions from young SNe record information on the yet-unresolved 'injection' mechanism. I also present perspectives of millimeter (mm observations of SNe - this will provide opportunities to uniquely determine the shock physics and the acceleration efficiency, to test the non-linear DSA mechanism and provide a characteristic electron energy scale with which the DSA start dominating the electron acceleration.

  16. Nonstationarity of a two-dimensional perpendicular shock: Competing mechanisms

    Lembège, B.; Savoini, P.; Hellinger, Petr; Trávníček, Pavel M.

    2009-01-01

    Roč. 114, A03217 (2009), A03217/1-A03217/21 ISSN 0148-0227 R&D Pro jects: GA AV ČR IAA300420702; GA AV ČR IAA300420602 Institutional research plan: CEZ:AV0Z30420517 Keywords : Collisionless shocks * self-reformation * nonlinear waves Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 3.082, year: 2009

  17. Numerical Study of Erosion, Heating, and Acceleration of the Magnetic Cloud as Impacted by Fast Shock

    Mao, Shoudi; He, Jiansen; Yang, Liping; Wang, Linghua; Zhang, Lei

    2017-01-01

    The impact of an overtaking fast shock on a magnetic cloud (MC) is a pivotal process in CME–CME (CME: coronal mass ejection) interactions and CME–SIR (SIR: stream interaction region) interactions. MC with a strong and rotating magnetic field is usually deemed a crucial part of CMEs. To study the impact of a fast shock on an MC, we perform a 2.5 dimensional numerical magnetohydrodynamic simulation. Two cases are run in this study: without and with impact by fast shock. In the former case, the MC expands gradually from its initial state and drives a relatively slow magnetic reconnection with the ambient magnetic field. Analyses of forces near the core of the MC as a whole body indicates that the solar gravity is quite small compared to the Lorentz force and the pressure gradient force. In the second run, a fast shock propagates, relative to the background plasma, at a speed twice that of the perpendicular fast magnetosonic speed, catches up with and takes over the MC. Due to the penetration of the fast shock, the MC is highly compressed and heated, with the temperature growth rate enhanced by a factor of about 10 and the velocity increased to about half of the shock speed. The magnetic reconnection with ambient magnetic field is also sped up by a factor of two to four in reconnection rate as a result of the enhanced density of the current sheet, which is squeezed by the forward motion of the shocked MC.

  18. Numerical Study of Erosion, Heating, and Acceleration of the Magnetic Cloud as Impacted by Fast Shock

    Mao, Shoudi; He, Jiansen; Yang, Liping; Wang, Linghua [School of Earth and Space Sciences, Peking University No. 5 Yiheyuan Road, Haidian District Beijing, 100871 (China); Zhang, Lei, E-mail: jshept@gmail.com [SIGMA Weather Group, State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences No.1 Nanertiao, Zhongguancun, Haidian district Beijing, 100190 (China)

    2017-06-20

    The impact of an overtaking fast shock on a magnetic cloud (MC) is a pivotal process in CME–CME (CME: coronal mass ejection) interactions and CME–SIR (SIR: stream interaction region) interactions. MC with a strong and rotating magnetic field is usually deemed a crucial part of CMEs. To study the impact of a fast shock on an MC, we perform a 2.5 dimensional numerical magnetohydrodynamic simulation. Two cases are run in this study: without and with impact by fast shock. In the former case, the MC expands gradually from its initial state and drives a relatively slow magnetic reconnection with the ambient magnetic field. Analyses of forces near the core of the MC as a whole body indicates that the solar gravity is quite small compared to the Lorentz force and the pressure gradient force. In the second run, a fast shock propagates, relative to the background plasma, at a speed twice that of the perpendicular fast magnetosonic speed, catches up with and takes over the MC. Due to the penetration of the fast shock, the MC is highly compressed and heated, with the temperature growth rate enhanced by a factor of about 10 and the velocity increased to about half of the shock speed. The magnetic reconnection with ambient magnetic field is also sped up by a factor of two to four in reconnection rate as a result of the enhanced density of the current sheet, which is squeezed by the forward motion of the shocked MC.

  19. Diagnostics for studies of novel laser ion acceleration mechanisms

    Senje, Lovisa; Yeung, Mark; Aurand, Bastian; Kuschel, Stephan; Rödel, Christian; Wagner, Florian; Li, Kun; Dromey, Brendan; Bagnoud, Vincent; Neumayer, Paul; Roth, Markus; Wahlström, Claes-Göran; Zepf, Matthew; Kuehl, Thomas; Jung, Daniel

    2014-01-01

    Diagnostic for investigating and distinguishing different laser ion acceleration mechanisms has been developed and successfully tested. An ion separation wide angle spectrometer can simultaneously investigate three important aspects of the laser plasma interaction: (1) acquire angularly resolved energy spectra for two ion species, (2) obtain ion energy spectra for multiple species, separated according to their charge to mass ratio, along selected axes, and (3) collect laser radiation reflecte...

  20. Acceleration mechanisms for energetic particles in the earth's magnetosphere

    Schiferl, S.; Fan, C.Y.; Hsieh, K.C.; Erickson, K.N.; Gloeckler, G.; Hovestadt, D.

    1982-01-01

    By analyzing data on energetic particle fluxes measured simultaneously with detector systems on several earth satellites, we searched for signatures of different acceleration mechanisms for these particles. One of the samples is an event observed on ATS-6 and IMP-7. IMP-7 was in the dusk quarter at 38 Rsub(E) while ATS-6 was located at local midnight at a distance of 6.6 Rsub(E). Although the flux variations as observed on the two spacecraft both showed 1.5 min. periodicity, there was a 40-second time lag with IMP-7 behind. The results indicate that the particles are accelerated by magnetic field line annihilation, with the ''x-point'' located at approximately 10 Rsub(E)

  1. Accelerated Testing of Polymeric Composites Using the Dynamic Mechanical Analyzer

    Abdel-Magid, Becky M.; Gates, Thomas S.

    2000-01-01

    Creep properties of IM7/K3B composite material were obtained using three accelerated test methods at elevated temperatures. Results of flexural creep tests using the dynamic mechanical analyzer (DMA) were compared with results of conventional tensile and compression creep tests. The procedures of the three test methods are described and the results are presented. Despite minor differences in the time shift factor of the creep compliance curves, the DMA results compared favorably with the results from the tensile and compressive creep tests. Some insight is given into establishing correlations between creep compliance in flexure and creep compliance in tension and compression. It is shown that with careful consideration of the limitations of flexure creep, a viable and reliable accelerated test procedure can be developed using the DMA to obtain the viscoelastic properties of composites in extreme environments.

  2. Thermal chemical-mechanical reactive flow model of shock initiation in solid explosives

    Nicholls, A.L. III; Tarver, C.M.

    1998-01-01

    The three dimensional Arbitrary Lagrange Eulerian hydrodynamic computer code ALE3D with fully coupled thermal-chemical-mechanical material models provides the framework for the development of a physically realistic model of shock initiation and detonation of solid explosives. The processes of hot spot formation during shock compression, subsequent ignition of reaction or failure to react, growth of reaction in individual hot spots, and coalescence of reacting hot spots during the transition to detonation can now be modeled using Arrhenius chemical kinetic rate laws and heat transfer to propagate the reactive flow. This paper discusses the growth rates of reacting hot spots in HMX and TATB and their coalescence during shock to detonation transition. Hot spot deflagration rates are found to be fast enough to consume explosive particles less than 10 mm in diameter during typical shock duration times, but larger particles must fragment and create more reactive surface area in order to be rapidly consumed

  3. Smartphone application for mechanical quality assurance of medical linear accelerators.

    Kim, Hwiyoung; Lee, Hyunseok; Park, Jong In; Choi, Chang Heon; Park, So-Yeon; Kim, Hee Jung; Kim, Young Suk; Ye, Sung-Joon

    2017-06-07

    Mechanical quality assurance (QA) of medical linear accelerators consists of time-consuming and human-error-prone procedures. We developed a smartphone application system for mechanical QA. The system consists of two smartphones: one attached to a gantry for obtaining real-time information on the mechanical parameters of the medical linear accelerator, and another displaying real-time information via a Bluetooth connection with the former. Motion sensors embedded in the smartphone were used to measure gantry and collimator rotations. Images taken by the smartphone's high-resolution camera were processed to evaluate accuracies of jaw-positioning, crosshair centering and source-to-surface distance (SSD). The application was developed using Android software development kit and OpenCV library. The accuracy and precision of the system was validated against an optical rotation stage and digital calipers, prior to routine QA measurements of five medical linear accelerators. The system accuracy and precision in measuring angles and lengths were determined to be 0.05  ±  0.05° and 0.25  ±  0.14 mm, respectively. The mean absolute errors (MAEs) in QA measurements of gantry and collimator rotation were 0.05  ±  0.04° and 0.05  ±  0.04°, respectively. The MAE in QA measurements of light field was 0.39  ±  0.36 mm. The MAEs in QA measurements of crosshair centering and SSD were 0.40  ±  0.35 mm and 0.41  ±  0.32 mm, respectively. In conclusion, most routine mechanical QA procedures could be performed using the smartphone application system with improved precision and within a shorter time-frame, while eliminating potential human errors.

  4. The ''injection problem'' for quasiparallel shocks

    Zank, G. P.; Rice, W. K. M.; le Roux, J. A.; Cairns, I. H.; Webb, G. M.

    2001-01-01

    For a particle to be accelerated diffusively at a shock by the first-order Fermi acceleration mechanism, the particle must be sufficiently energetic that it can scatter across all the micro- and macrostructure of the shock, experiencing compression between the converging upstream and downstream states. This is the well-known ''injection problem.'' Here the interaction of ions with the ramp of a quasiparallel shock is investigated. Some ions incident on the shock experience specular reflection, caused either by the cross-shock electrostatic potential or by mirroring as the magnetic field is bent and compressed through the ramp. Scattering of reflected ions by self-generated and pre-existing turbulence in the region upstream of the shock then acts to trap backstreaming ions and return them to the ramp, where some experience further reflections. Such repeated reflections and scattering energize a subpopulation of ions up to energies sufficiently large that they can be diffusively shock accelerated. Two ion distributions are considered: pickup ions which are assumed to be described by a shell distribution, are thermal solar wind ions which may be described by a kappa distribution. Injection efficiencies are found analytically to be very high for pickup ions and much lower for thermal solar wind ions, suggesting that this injection mechanism, stochastic reflected ion or SRI acceleration, is a natural precursor for the acceleration of the anomalous cosmic ray component at a quasiparallel shock. While significantly less efficient, SRI acceleration is also viable for thermal solar wind ions described by a kappa distribution

  5. Considerations on Velocities and Accelerations in Higher Pairs Mechanisms

    Florina-Carmen Ciornei

    2015-12-01

    Full Text Available The paper proposes a method for finding the velocities and accelerations in the pairs from a mechanism with higher pairs in the case when the curvature radii of the curves achieving the higher pair are finite. There are obtained the characteristic equations of the motion in the higher pair for the case that one of the curves has zero curvature radius, condition characteristic to the knife edge follower. The relations are required to justify the difference between the particular cases of knife edge follower and flat face follower. The methodology is exemplified through an actual example.

  6. A PLL based automated magnetron tuning mechanism for electron accelerators

    Khan, A M; Mahfooz, Mohammed; Sanjeev, Ganesh

    2008-01-01

    In this paper we report on a control system developed to tune the magnetron frequency to get the maximum beam pulse in a Microtron (an electron accelerator facility at Mangalore University). The control system so designed consists of a Microcontroller Unit (MCU), a Phase Locked Loop (PLL) and a Digital to Analog Converter (DAC) to track and tune the magnetron frequency. A PLL is used to track the deviation of the magnetron output frequency, and by monitoring the reflected wave voltage level, the microcontroller unit tunes the magnetron with the help of a tuner mechanism connected through a stepper motor.

  7. A PLL based automated magnetron tuning mechanism for electron accelerators

    Khan, A M; Mahfooz, Mohammed [Dept. of Electronics, Mangalore University, Mangalagangotri, Karnataka State, India - 574 199 (India); Sanjeev, Ganesh [Microtron Centre, Mangalore University, Mangalagangotri, Karnataka State, India - 574 199 (India)], E-mail: mahfooz_81@yahoo.com

    2008-09-15

    In this paper we report on a control system developed to tune the magnetron frequency to get the maximum beam pulse in a Microtron (an electron accelerator facility at Mangalore University). The control system so designed consists of a Microcontroller Unit (MCU), a Phase Locked Loop (PLL) and a Digital to Analog Converter (DAC) to track and tune the magnetron frequency. A PLL is used to track the deviation of the magnetron output frequency, and by monitoring the reflected wave voltage level, the microcontroller unit tunes the magnetron with the help of a tuner mechanism connected through a stepper motor.

  8. Thermal shock effect on Mechanical and Physical properties of pre-moisture treated GRE composite

    Chakraverty, A. P.; Panda, A. B.; Mohanty, U. K.; Mishra, S. C.; Biswal, B. B.

    2018-03-01

    Many practical situations may be encountered under which a GFRP (Glass fibre reinforced polymer) composite, during its service life, is exposed to the severities of sudden temperature fluctuations. Moisture absorption of GRE (Glass fibre reinforced epoxy) composites followed by various gradients of temperature fluctuations may cause thermo- mechanical degradation. It is on this context, the hand layed GRE composite samples are exposed to up-thermal shock (-40°C to +50°C) and down-thermal shock (+50°C to -40°C) for various time interval after several periods of moisture (hydrothermal/hygrothermal) conditioning. The thermally shocked GRE specimens are put to 3-point bend test to divulge inter laminar shear strength (ILSS). Least ILSS values are recorded for the samples with maximum period of moisture treatments under with both up-thermal and down-thermal shock conditions. Lower glass transition temperature (Tg) values, as revealed through the low temperature DSC test, are exhibited at maximum durations of both up-thermal and down-thermal shock for the samples with higher periods of hygrothermal/hydrothermal treatments. SEM fractographs of representative GRE specimens after optimum period of moisture treatments and thermal shock show the various modes of failures.

  9. Study on the Shock-transmission Mechanism of Stock Price among China, Russia and India

    Menggen Chen

    2014-08-01

    Full Text Available Researchers pay more and more attention on the price comovement-effect among international stock markets. This paper deals with the transmission mechanism of price shocks among three stock markets of China, Russia and India, with a sample of weekly returns. The results showed that the price fluctuation of each market has an influence on other markets, although the price behavior is significantly independent. The impact of external price innovations will last 5 or 6 weeks usually and disappear after about 8 weeks. The pattern of transmission-mechanism for the price shocks is very different from each other. Besides, a further study revealed that the influence of external shocks on the domestic stock price increased significantly among the three markets after the 2008 international financial crisis.

  10. Enhanced shock wave generation via pre-breakdown acceleration using water electrolysis in negative streamer pulsed spark discharges

    Lee, Kern; Chung, Kyoung-Jae; Hwang, Y. S.

    2018-03-01

    This paper presents a method for enhancement of shock waves generated from underwater pulsed spark discharges with negative (anode-directed) subsonic streamers, for which the pre-breakdown process is accelerated by preconditioning a gap with water electrolysis. Hydrogen microbubbles are produced at the cathode by the electrolysis and move towards the anode during the preconditioning phase. The numbers and spatial distributions of the microbubbles vary with the amplitude and duration of each preconditioning pulse. Under our experimental conditions, the optimum pulse duration is determined to be ˜250 ms at a pulse voltage of 400 V, where the buoyancy force overwhelms the electric force and causes the microbubbles to be swept out from the water gap. When a high-voltage pulse is applied to the gap just after the preconditioning pulse, the pre-breakdown process is significantly accelerated in the presence of the microbubbles. At the optimum preconditioning pulse duration, the average breakdown delay is reduced by 87% and, more importantly, the energy consumed during the pre-breakdown period decreases by 83%. This reduced energy consumption during the pre-breakdown period, when combined with the morphological advantages of negative streamers, such as thicker and longer stalks, leads to a significant improvement in the measured peak pressure (˜40%) generated by the underwater pulsed spark discharge. This acceleration of pre-breakdown using electrolysis overcomes the biggest drawback of negative subsonic discharges, which is slow vapor bubble formation due to screening effects, and thus enhances the efficiency of the shock wave generation process using pulsed spark discharges in water.

  11. A mechanical analysis of woodpecker drumming and its application to shock-absorbing systems

    Yoon, Sang-Hee; Park, Sungmin

    2011-01-01

    A woodpecker is known to drum the hard woody surface of a tree at a rate of 18 to 22 times per second with a deceleration of 1200 g, yet with no sign of blackout or brain damage. As a model in nature, a woodpecker is studied to find clues to develop a shock-absorbing system for micromachined devices. Its advanced shock-absorbing mechanism, which cannot be explained merely by allometric scaling, is analyzed in terms of endoskeletal structures. In this analysis, the head structures (beak, hyoid, spongy bone, and skull bone with cerebrospinal fluid) of the golden-fronted woodpecker, Melanerpes aurifrons, are explored with x-ray computed tomography images, and their shock-absorbing mechanism is analyzed with a mechanical vibration model and an empirical method. Based on these analyses, a new shock-absorbing system is designed to protect commercial micromachined devices from unwanted high-g and high-frequency mechanical excitations. The new shock-absorbing system consists of close-packed microglasses within two metal enclosures and a viscoelastic layer fastened by steel bolts, which are biologically inspired from a spongy bone contained within a skull bone encompassed with the hyoid of a woodpecker. In the experimental characterizations using a 60 mm smoothbore air-gun, this bio-inspired shock-absorbing system shows a failure rate of 0.7% for the commercial micromachined devices at 60 000 g, whereas a conventional hard-resin method yields a failure rate of 26.4%, thus verifying remarkable improvement in the g-force tolerance of the commercial micromachined devices.

  12. A novel regenerative shock absorber with a speed doubling mechanism and its Monte Carlo simulation

    Zhang, Ran; Wang, Xu; Liu, Zhenwei

    2018-03-01

    A novel regenerative shock absorber has been designed and fabricated. The novelty of the presented work is the application of the double speed regenerative shock absorber that utilizes the rack and pinion mechanism to increase the magnet speed with respect to the coils for higher power output. The simulation models with parameters identified from finite element analysis and the experiments are developed. The proposed regenerative shock absorber is compared with the regenerative shock absorber without the rack and pinion mechanism, when they are integrated into the same quarter vehicle suspension system. The sinusoidal wave road profile displacement excitation and the random road profile displacement excitation with peak amplitude of 0.035 m are applied as the inputs in the frequency range of 0-25 Hz. It is found that with the sinusoidal and random road profile displacement input, the proposed innovative design can increase the output power by 4 times comparing to the baseline design. The proposed double speed regenerative shock absorber also presents to be more sensitive to the road profile irregularity than the single speed regenerative shock absorber as suggested by Monte Carlo simulation. Lastly the coil mass and amplification factor are studied for sensitivity analysis and performance optimization, which provides a general design method of the regenerative shock absorbers. It shows that for the system power output, the proposed design becomes more sensitive to either the coil mass or amplification factor depending on the amount of the coil mass. With the specifically selected combination of the coil mass and amplification factor, the optimized energy harvesting performance can be achieved.

  13. Response of the seated human body to whole-body vertical vibration: biodynamic responses to mechanical shocks.

    Zhou, Zhen; Griffin, Michael J

    2017-03-01

    The biodynamic response of the seated human body has been investigated with 20 males exposed to upward and downward shocks at 13 fundamental frequencies (1-16 Hz) and 18 magnitudes (up to ±8.3 ms -2 ). For 1- and 2- degree-of-freedom models, the stiffness and damping coefficients were obtained by fitting seat acceleration waveforms predicted from the measured force to the measured seat acceleration waveform. Stiffness and damping coefficients were also obtained in the frequency domain with random vibration. The optimum stiffness and damping coefficients varied with the magnitude and the frequency of shocks. With both upward and downward shocks, the resonance frequency of the models decreased from 6.3 to 4 Hz as the vibration dose values of the shocks increased from 0.05 to 2.0 ms -1.75 . The stiffness and damping obtained from responses to shocks were correlated with, and similar to, the stiffness and damping obtained with random vibration. Practitioner Summary: When modelling the dynamic response of the seated human body to vertical acceleration less than 1 g, the relation between force and acceleration can be well represented by a single degree-of-freedom model although the optimum stiffness and damping depend on the magnitude and frequency of sinusoidal, random or shock motion.

  14. Plastic deformation mechanism of polycrystalline copper foil shocked with femtosecond laser

    Ye, Y.X.; Feng, Y.Y.; Lian, Z.C.; Hua, Y.Q.

    2014-01-01

    Plastic deformation mechanism of polycrystalline copper foil shocked with femtosecond (fs) laser has been characterized through optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Experiments of ns laser shocking copper (Cu) and fs laser shocking aluminum (Al) were also conducted for comparison. Dislocations arranged in multiple forms, profuse twins and stacking faults (SFs) coexist in the fs laser shocked copper. At small strain condition, dislocation slip is the dominant deformation mode and small amount of SFs act as complementary mechanism. With strain increasing, profuse twins and SFs form to accommodate the plastic deformation. Furthermore, new formed SFs incline to locate around the old ones because the dislocation densities there are more higher. So there is a high probability for new SFs overlapping on old ones to form twins, or connecting old ones to lengthen them, which eventually produce the phenomena that twins connect with each other or twins connect with SFs. Strain greatly influences the dislocation density. Twins and SFs are more dependent on strain rate and shock pressure. Medium stacking fault energy (SFE) of copper helps to extend partial dislocations and provides sources for forming SFs and twins.

  15. Using Quantum Mechanics to Predict Shock Properties of Explosives

    Romero, N. A; Mattson, W. D; Rice, B. M

    2006-01-01

    .... As little as ten years ago, quantum mechanical calculations were restricted to predictions of static properties of systems containing tens of atoms, thus limiting first principles explorations to gas...

  16. Smartphone application for mechanical quality assurance of medical linear accelerators

    Kim, Hwiyoung; Lee, Hyunseok; In Park, Jong; Choi, Chang Heon; Park, So-Yeon; Kim, Hee Jung; Kim, Young Suk; Ye, Sung-Joon

    2017-06-01

    Mechanical quality assurance (QA) of medical linear accelerators consists of time-consuming and human-error-prone procedures. We developed a smartphone application system for mechanical QA. The system consists of two smartphones: one attached to a gantry for obtaining real-time information on the mechanical parameters of the medical linear accelerator, and another displaying real-time information via a Bluetooth connection with the former. Motion sensors embedded in the smartphone were used to measure gantry and collimator rotations. Images taken by the smartphone’s high-resolution camera were processed to evaluate accuracies of jaw-positioning, crosshair centering and source-to-surface distance (SSD). The application was developed using Android software development kit and OpenCV library. The accuracy and precision of the system was validated against an optical rotation stage and digital calipers, prior to routine QA measurements of five medical linear accelerators. The system accuracy and precision in measuring angles and lengths were determined to be 0.05  ±  0.05° and 0.25  ±  0.14 mm, respectively. The mean absolute errors (MAEs) in QA measurements of gantry and collimator rotation were 0.05  ±  0.04° and 0.05  ±  0.04°, respectively. The MAE in QA measurements of light field was 0.39  ±  0.36 mm. The MAEs in QA measurements of crosshair centering and SSD were 0.40  ±  0.35 mm and 0.41  ±  0.32 mm, respectively. In conclusion, most routine mechanical QA procedures could be performed using the smartphone application system with improved precision and within a shorter time-frame, while eliminating potential human errors.

  17. Quasi-monoenergetic ion beam acceleration by laser-driven shock and solitary waves in near-critical plasmas

    Zhang, W. L.; Qiao, B.; Huang, T. W.; Shen, X. F.; You, W. Y.; Yan, X. Q.; Wu, S. Z.; Zhou, C. T.; He, X. T.

    2016-01-01

    Ion acceleration in near-critical plasmas driven by intense laser pulses is investigated theoretically and numerically. A theoretical model has been given for clarification of the ion acceleration dynamics in relation to different laser and target parameters. Two distinct regimes have been identified, where ions are accelerated by, respectively, the laser-induced shock wave in the weakly driven regime (comparatively low laser intensity) and the nonlinear solitary wave in the strongly driven regime (comparatively high laser intensity). Two-dimensional particle-in-cell simulations show that quasi-monoenergetic proton beams with a peak energy of 94.6 MeV and an energy spread 15.8% are obtained by intense laser pulses at intensity I_0 = 3 × 10"2"0" W/cm"2 and pulse duration τ = 0.5 ps in the strongly driven regime, which is more advantageous than that got in the weakly driven regime. In addition, 233 MeV proton beams with narrow spread can be produced by extending τ to 1.0 ps in the strongly driven regime.

  18. Quasi-monoenergetic ion beam acceleration by laser-driven shock and solitary waves in near-critical plasmas

    Zhang, W. L.; Qiao, B., E-mail: bqiao@pku.edu.cn; Huang, T. W.; Shen, X. F.; You, W. Y. [Center for Applied Physics and Technology, HEDPS, and State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006 (China); Yan, X. Q. [Center for Applied Physics and Technology, HEDPS, and State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); Wu, S. Z. [Institute of Applied Physics and Computational Mathematics, Beijing 100094 (China); Zhou, C. T.; He, X. T. [Center for Applied Physics and Technology, HEDPS, and State Key Laboratory of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China); Institute of Applied Physics and Computational Mathematics, Beijing 100094 (China)

    2016-07-15

    Ion acceleration in near-critical plasmas driven by intense laser pulses is investigated theoretically and numerically. A theoretical model has been given for clarification of the ion acceleration dynamics in relation to different laser and target parameters. Two distinct regimes have been identified, where ions are accelerated by, respectively, the laser-induced shock wave in the weakly driven regime (comparatively low laser intensity) and the nonlinear solitary wave in the strongly driven regime (comparatively high laser intensity). Two-dimensional particle-in-cell simulations show that quasi-monoenergetic proton beams with a peak energy of 94.6 MeV and an energy spread 15.8% are obtained by intense laser pulses at intensity I{sub 0} = 3 × 10{sup 20 }W/cm{sup 2} and pulse duration τ = 0.5 ps in the strongly driven regime, which is more advantageous than that got in the weakly driven regime. In addition, 233 MeV proton beams with narrow spread can be produced by extending τ to 1.0 ps in the strongly driven regime.

  19. Behavioral Outcomes Differ Between Rotational Acceleration and Blast Mechanisms of Mild Traumatic Brain Injury

    Brian D. Stemper

    2016-03-01

    Full Text Available Mild traumatic brain injury (mTBI can result from a number of mechanisms, including blunt impact, head rotational acceleration, exposure to blast, and penetration of projectiles. Mechanism is likely to influence the type, severity, and chronicity of outcomes. The objective of this study was to determine differences in the severity and time-course of behavioral outcomes following blast and rotational mTBI. The Medical College of Wisconsin (MCW Rotational Injury model and a shock tube model of primary blast injury were used to induce mTBI in rats and behavioral assessments were conducted within the first week, as well as 30 and 60 days following injury. Acute recovery time demonstrated similar increases over protocol-matched shams, indicating acute injury severity equivalence between the two mechanisms. Post-injury behavior in the elevated plus maze demonstrated differing trends, with rotationally injured rats acutely demonstrating greater activity, whereas blast-injured rats had decreased activity that developed at chronic time points. Similarly, blast-injured rats demonstrated trends associated with cognitive deficits that were not apparent following rotational injuries. These findings demonstrate that rotational and blast injury result in behavioral changes with different qualitative and temporal manifestations. Whereas rotational injury was characterized by a rapidly emerging phenotype consistent with behavioral disinhibition, blast injury was associated with emotional and cognitive differences that were not evident acutely, but developed later, with an anxiety-like phenotype still present in injured animals at our most chronic measurements.

  20. Mechanical Properties and Thermal Shock Resistance Analysis of BNNT/Si3N4 Composites

    Wang, Shouren; Wang, Gaoqi; Wen, Daosheng; Yang, Xuefeng; Yang, Liying; Guo, Peiquan

    2018-04-01

    BNNT/Si3N4 ceramic composites with different weight amount of BNNT fabricated by hot isostatic pressing were introduced. The mechanical properties and thermal shock resistance of the composites were investigated. The results showed that BNNT-added ceramic composites have a finer and more uniform microstructure than that of BNNT-free Si3N4 ceramic because of the retarding effect of BNNT on Si3N4 grain growth. The addition of 1.5 wt.% BNNT results in simultaneous increase in flexural strength, fracture toughness, and thermal shock resistance. The analysis of the results indicates that BNNT brings many thermal transport channels in the microstructure, increasing the efficiency of thermal transport, therefore results in increase of thermal shock resistance. In addition, BNNT improves the residual flexural strength of composites by crack deflection, bridging, branching and pinning, which increase the crack propagation resistance.

  1. Classifying the mechanisms of electrochemical shock in ion-intercalation materials

    Woodford, William; Carter, W. Craig; Chiang, Yet-Ming

    2014-01-01

    “Electrochemical shock” – the electrochemical cycling-induced fracture of materials – contributes to impedance growth and performance degradation in ion-intercalation batteries, such as lithium-ion. Using a combination of micromechanical models and acoustic emission experiments, the mechanisms of electrochemical shock are identified, classified, and modeled in targeted model systems with different composition and microstructure. A particular emphasis is placed on mechanical degradation occurr...

  2. A child in a state of shock in emercency department: classification, mechanisms and treatment

    Равіч Maрцін

    2015-06-01

    Full Text Available Paediatric shock is a life-threatening condition that can often be difficult to recognize in the emergency department, especially in early stages. Once recognized, the emphasis of therapy is to correct cellular metabolism and gas exchange by increasing oxygen and other substrate delivery to tissue beds. This review discusses various mechanisms and aetiology of shock are discussed, among them hypoxia in infancy, hypovolaemia, impaired distribution, obstruction of the cardiac outflow and sepsis.In septic shock providing oxygen, improving tissue perfusion through restoration in the intravascular volume, augmentation of cardiac output, preservation of kidney function, and administering antibiotics in a timely manner have all been shown to significantly improve outcomes in children. Simple  algorithms for first aid in emergency room are given, emphasizes the importance of effective surveillance and timely recognition of this disease process, to significantly reduce morbidity and mortality. The review indicates how to identify specific markers of septic shock, lays out the essential components of goal-directed therapy, and ways to avoid the devastating consequences of shock in paediatric patients

  3. Simultaneous density-field visualization and PIV of a shock-accelerated gas curtain

    Prestridge, K.; Rightley, P.M.; Vorobieff, P. [Los Alamos Nat. Lab., NM (United States). Dynamic Exp. Div.; Benjamin, R.F.; Kurnit, N.A.

    2000-10-01

    We describe a highly-detailed experimental characterization of the Richtmyer-Meshkov instability (the impulsively driven Rayleigh-Taylor instability) (Meshkov 1969; Richtmyer 1960). In our experiment, a vertical curtain of heavy gas (SF{sub 6}) flows into the test section of an air-filled, horizontal shock tube. The instability evolves after a Mach 1.2 shock passes through the curtain. For visualization, we pre-mix the SF{sub 6} with a small ({proportional_to}10{sup -5}) volume fraction of sub-micron-sized glycol/water droplets. A horizontal section of the flow is illuminated by a light sheet produced by a combination of a customized, burst-mode Nd:YAG laser and a commercial pulsed laser. Three CCD cameras are employed in visualization. The ''dynamic imaging camera'' images the entire test section, but does not detect the individual droplets. It produces a sequence of instantaneous images of local droplet concentration, which in the post-shock flow is proportional to density. The gas curtain is convected out of the test section about 1 ms after the shock passes through the curtain. A second camera images the initial conditions with high resolution, since the initial conditions vary from test to test. The third camera, ''PIV camera,'' has a spatial resolution sufficient to detect the individual droplets in the light sheet. Images from this camera are interrogated using particle image velocimetry (PIV) to recover instantaneous snapshots of the velocity field in a small (19 x 14 mm) field of view. The fidelity of the flow-seeding technique for density-field acquisition and the reliability of the PIV technique are both quantified in this paper. In combination with wide-field density data, PIV measurements give us additional physical insight into the evolution of the Richtmyer-Meshkov instability in a problem which serves as an excellent test case for general transition-to-turbulence studies. (orig.)

  4. Relationship between mechanical characteristics and thermal shock stability of refractories

    Volkov-Husovic, T.; Raic, K.

    2003-01-01

    Thermal stability of the refractory material with the content of 60 % Al 2 O 3 was investigated. Water quench test (JUS.B.D8.319) was applied as experimental method for thermal stability testing. Damage of porous materials is commonly related to a modification of strength that is mostly a reduction. This is linked with characteristics related to pore space. Mechanical characteristics are considered such as compressive strength, dynamic modulus of elasticity and resistance parameters resulting from resonance frequency measurements, as well as ultrasonic velocity. (Original)

  5. A Lever Coupling Mechanism in Dual-Mass Micro-Gyroscopes for Improving the Shock Resistance along the Driving Direction

    Yang Gao

    2017-04-01

    Full Text Available This paper presents the design and application of a lever coupling mechanism to improve the shock resistance of a dual-mass silicon micro-gyroscope with drive mode coupled along the driving direction without sacrificing the mechanical sensitivity. Firstly, the mechanical sensitivity and the shock response of the micro-gyroscope are theoretically analyzed. In the mechanical design, a novel lever coupling mechanism is proposed to change the modal order and to improve the frequency separation. The micro-gyroscope with the lever coupling mechanism optimizes the drive mode order, increasing the in-phase mode frequency to be much larger than the anti-phase one. Shock analysis results show that the micro-gyroscope structure with the designed lever coupling mechanism can notably reduce the magnitudes of the shock response and cut down the stress produced in the shock process compared with the traditional elastic coupled one. Simulations reveal that the shock resistance along the drive direction is greatly increased. Consequently, the lever coupling mechanism can change the gyroscope’s modal order and improve the frequency separation by structurally offering a higher stiffness difference ratio. The shock resistance along the driving direction is tremendously enhanced without loss of the mechanical sensitivity.

  6. Shock Isolation Elements Testing for High Input Loadings. Volume II. Foam Shock Isolation Elements.

    SHOCK ABSORBERS ), (*GUIDED MISSILE SILOS, SHOCK ABSORBERS ), (*EXPANDED PLASTICS, (*SHOCK(MECHANICS), REDUCTION), TEST METHODS, SHOCK WAVES, STRAIN(MECHANICS), LOADS(FORCES), MATHEMATICAL MODELS, NUCLEAR EXPLOSIONS, HARDENING.

  7. Statistical characteristics of mechanical heart valve cavitation in accelerated testing.

    Wu, Changfu; Hwang, Ned H C; Lin, Yu-Kweng M

    2004-07-01

    Cavitation damage has been observed on mechanical heart valves (MHVs) undergoing accelerated testing. Cavitation itself can be modeled as a stochastic process, as it varies from beat to beat of the testing machine. This in-vitro study was undertaken to investigate the statistical characteristics of MHV cavitation. A 25-mm St. Jude Medical bileaflet MHV (SJM 25) was tested in an accelerated tester at various pulse rates, ranging from 300 to 1,000 bpm, with stepwise increments of 100 bpm. A miniature pressure transducer was placed near a leaflet tip on the inflow side of the valve, to monitor regional transient pressure fluctuations at instants of valve closure. The pressure trace associated with each beat was passed through a 70 kHz high-pass digital filter to extract the high-frequency oscillation (HFO) components resulting from the collapse of cavitation bubbles. Three intensity-related measures were calculated for each HFO burst: its time span; its local root-mean-square (LRMS) value; and the area enveloped by the absolute value of the HFO pressure trace and the time axis, referred to as cavitation impulse. These were treated as stochastic processes, of which the first-order probability density functions (PDFs) were estimated for each test rate. Both the LRMS value and cavitation impulse were log-normal distributed, and the time span was normal distributed. These distribution laws were consistent at different test rates. The present investigation was directed at understanding MHV cavitation as a stochastic process. The results provide a basis for establishing further the statistical relationship between cavitation intensity and time-evolving cavitation damage on MHV surfaces. These data are required to assess and compare the performance of MHVs of different designs.

  8. Degradation mechanisms and accelerated testing in PEM fuel cells

    Borup, Rodney L [Los Alamos National Laboratory; Mukundan, Rangachary [Los Alamos National Laboratory

    2010-01-01

    The durability of PEM fuel cells is a major barrier to the commercialization of these systems for stationary and transportation power applications. Although there has been recent progress in improving durability, further improvements are needed to meet the commercialization targets. Past improvements have largely been made possible because of the fundamental understanding of the underlying degradation mechanisms. By investigating component and cell degradation modes; defining the fundamental degradation mechanisms of components and component interactions new materials can be designed to improve durability. Various factors have been shown to affect the useful life of PEM fuel cells. Other issues arise from component optimization. Operational conditions (such as impurities in either the fuel and oxidant stream), cell environment, temperature (including subfreezing exposure), pressure, current, voltage, etc.; or transient versus continuous operation, including start-up and shutdown procedures, represent other factors that can affect cell performance and durability. The need for Accelerated Stress Tests (ASTs) can be quickly understood given the target lives for fuel cell systems: 5000 hours ({approx} 7 months) for automotive, and 40,000 hrs ({approx} 4.6 years) for stationary systems. Thus testing methods that enable more rapid screening of individual components to determine their durability characteristics, such as off-line environmental testing, are needed for evaluating new component durability in a reasonable turn-around time. This allows proposed improvements in a component to be evaluated rapidly and independently, subsequently allowing rapid advancement in PEM fuel cell durability. These tests are also crucial to developers in order to make sure that they do not sacrifice durability while making improvements in costs (e.g. lower platinum group metal [PGM] loading) and performance (e.g. thinner membrane or a GDL with better water management properties). To

  9. Modeling of a new electron-streamer acceleration mechanism

    Ihaddadene, K. M. A.; Dwyer, J. R.; Liu, N.; Celestin, S. J.

    2017-12-01

    Lightning stepped leaders and laboratory spark discharges in air are known to produce X-rays [e.g., Dwyer et al., Geophys. Res. lett., 32, L20809, 2005; Kochkin et al., J. Phys. D: Appl. Phys., 45, 425202, 2012]. However, the processes behind the production of these X-rays are still not very well understood. During discharges, encounters between streamers of different polarities are very common. For example, during the formation of a new leader step, the negative streamer zone around the tip of a negative leader and the positive streamers initiated from the posiive part of a bidirectional space leader strongly interact. In laboratory experiments, when streamers are approaching a sharp electrode, streamers with the opposite polarity are initiated from the electrode and collide with the former streamers. Recently, the encounter between negative and positive streamers has been proposed as a plausible mechanism for the production of X-rays by spark discharges [Cooray et la., JASTP, 71, 1890, 2009; Kochkin et al., J. Phys. D: Appl. Phys., 45, 425202, 2012], but modeling results have shown later that the increase of the electric field involved in this process, which is above the conventional breakdown threshold field, is accompanied by a strong increase of the electron density. The resulting increase in the conductivity, in turn, causes this electric field to collapse over a few tens of picoseconds, preventing the electrons reaching high energies and producing significant X-ray emissions [e.g., Ihaddadene and Celestin, Geophys. Res. Lett., 45, 5644, 2015]. In this work, we will present simulation results of a new electron acceleration mechanism for producing runaway electron energies above hundred keV. The mechanism couples multiple single streamers and streamer head-on collisions, similar to a laboratory discharge, and is suitable for explaining the high-energy X-rays produced by discharges in air and by lightning stepped leaders.

  10. Design and fabrication of a eccentric wheels based motorised alignment mechanism for cylindrical accelerator components

    Mundra, G.; Jain, V.; Karmarkar, Mangesh; Kotaiah, S.

    2006-01-01

    Precision alignment mechanisms with long term stability are required for accelerator components. For some of the components motorised and remotely operable alignment mechanism are required. An eccentric wheel mechanism based alignment system is very much suitable for such application. One such alignment system is designed, a prototype is machined/fabricated for SFDTL type accelerating structure and preliminary trial experiments have been done. (author)

  11. Vertebral deformity arising from an accelerated "creep" mechanism.

    Luo, Jin; Pollintine, Phillip; Gomm, Edward; Dolan, Patricia; Adams, Michael A

    2012-09-01

    Vertebral deformities often occur in patients who recall no trauma, and display no evident fracture on radiographs. We hypothesise that vertebral deformity can occur by a gradual creep mechanism which is accelerated following minor damage. "Creep" is continuous deformation under constant load. Forty-five thoracolumbar spine motion segments were tested from cadavers aged 42-92 years. Vertebral body areal BMD was measured using DXA. Specimens were compressed at 1 kN for 30 min, while creep in each vertebral body was measured using an optical MacReflex system. After 30 min recovery, each specimen was subjected to a controlled overload event which caused minor damage to one of its vertebrae. The creep test was then repeated. Vertebral body creep was measurable in specimens with BMD Creep was greater anteriorly than posteriorly (p creep by 800 % (anteriorly), 1,000 % (centrally) and 600 % (posteriorly). In 34 vertebrae with complete before-and-after data, anterior wedging occurring during the 1st creep test averaged 0.07° (STD 0.17°), and in the 2nd test (after minor damage) it averaged 0.79° (STD 1.03°). The increase was highly significant (P creep test was proportional to the severity of damage, as quantified by specimen height loss during the overload event (r (2) = 0.51, p creep to such an extent that it makes a substantial contribution to vertebral deformity.

  12. Observation of energy-time dispersed ion structures in the magnetosheath by CLUSTER: possible signatures of transient acceleration processes at shock

    P. Louarn

    Full Text Available We analyse energy-time dispersed ion signatures that have been observed by CLUSTER in the dayside magnetosheath. These events are characterized by sudden increases in the ion flux at energies larger than 10 keV. The high energy ions (30 keV are first detected, with the transition to the low energy ions (5 keV lasting about 100 s. These injections are often associated with transient plasma structures of a few minutes in duration, characterized by a hotter, less dense plasma and a diverted flow velocity, thus presenting similarities with "hot flow anomalies". They also involve modifications of the magnetic field direction, suggesting that the shock interacts with a solar wind discontinuity at the time of the event. The injections can originate from the magnetosphere or the shock region. Studying in detail a particular event, we discuss this last hypothesis. We show that the observed energy/time dispersion can be explained by combining a time-of-flight effect with a drift of the source of energetic particles along the shock. We propose that the acceleration results from a Fermi process linked to the interaction of the discontinuity with a quasi-perpendicular shock. This model explains the observed pitch-angle selection of the accelerated particles. The Fermi process acting on the beam of ions reflected from the shock appears to be sufficiently efficient to accelerate over short time scales (less than 30 s particles at energies above 30 keV.

    Key words. Magnetospheric physics (solar-wind-magnetosphere interaction; magnetosheath – Space plasma physics (shock waves

  13. Exposure to whole-body vibration and mechanical shock: a field study of quad bike use in agriculture.

    Milosavljevic, Stephan; McBride, David I; Bagheri, Nasser; Vasiljev, Radivoj M; Mani, Ramakrishnan; Carman, Allan B; Rehn, Borje

    2011-04-01

    The purpose of this study was to determine exposure to whole-body vibration (WBV) and mechanical shock in rural workers who use quad bikes and to explore how personal, physical, and workplace characteristics influence exposure. A seat pad mounted triaxial accelerometer and data logger recorded full workday vibration and shock data from 130 New Zealand rural workers. Personal, physical, and workplace characteristics were gathered using a modified version of the Whole Body Vibration Health Surveillance Questionnaire. WBVs and mechanical shocks were analysed in accordance with the International Standardization for Organization (ISO 2631-1 and ISO 2631-5) standards and are presented as vibration dose value (VDV) and mechanical shock (S(ed)) exposures. VDV(Z) consistently exceeded European Union (Guide to good practice on whole body vibration. Directive 2002/44/EC on minimum health and safety, European Commission Directorate General Employment, Social Affairs and Equal Opportunities. 2006) guideline exposure action thresholds with some workers exceeding exposure limit thresholds. Exposure to mechanical shock was also evident. Increasing age had the strongest (negative) association with vibration and shock exposure with body mass index (BMI) having a similar but weaker effect. Age, daily driving duration, dairy farming, and use of two rear shock absorbers created the strongest multivariate model explaining 33% of variance in VDV(Z). Only age and dairy farming combined to explain 17% of the variance for daily mechanical shock. Twelve-month prevalence for low back pain was highest at 57.7% and lowest for upper back pain (13.8%). Personal (age and BMI), physical (shock absorbers and velocity), and workplace characteristics (driving duration and dairy farming) suggest that a mix of engineered workplace and behavioural interventions is required to reduce this level of exposure to vibration and shock.

  14. Effects of high shock pressures and pore morphology on hot spot mechanisms in HMX

    Springer, H. K.; Tarver, C. M.; Bastea, S.

    2017-01-01

    The shock initiation and detonation behavior of heterogeneous solid explosives is governed by its microstructure and reactive properties. New additive manufacturing techniques offer unprecedented control of explosive microstructures previously impossible, enabling us to develop novel explosives with tailored shock sensitivity and detonation properties. Since microstructure-performance relationships are not well established for explosives, there is little material design guidance for these manufacturing techniques. In this study, we explore the effects of high shock pressures (15-38 GPa) with long shock durations and different pore morphologies on hot spot mechanisms in HMX. HMX is chosen as the model material because we have experimental data on many of the chemical-thermal-mechanical properties required for pore collapse simulations. Our simulations are performed using the multi-physics arbitrary Lagrangian Eulerian finite element hydrocode, ALE3D, with Cheetah-based models for the unreacted and the product equation-of-states. We use a temperature-dependent specific heat with the unreacted equation-of-state and a temperature-dependent viscosity model to ensure accurate shock temperatures for subsequent chemistry. The Lindemann Law model is used for shock melting in HMX. In contrast to previous pore collapse studies at lower shock pressures (≤10 GPa) in HMX and shorter post-collapse burning times, our calculations show that shock melting occurs above 15 GPa due to higher bulk heating and a prominent elongated ("jet-like") hot spot region forms at later times. The combination of the elongated, post-collapse hot spot region and the higher bulk heating with increasing pressure dramatically increases the growth rate of reaction. Our calculations show that the reaction rate, dF/dt, increases with increasing shock pressure. We decompose the reaction rate into ignition ((dF/dt)ig) and growth ((dF/dt)gr) phases to better analyze our results. We define the ignition phase

  15. Research on Formation Mechanism of Dynamic Response and Residual Stress of Sheet Metal Induced by Laser Shock Wave

    Feng, Aixin; Cao, Yupeng; Wang, Heng; Zhang, Zhengang

    2018-01-01

    In order to reveal the quantitative control of the residual stress on the surface of metal materials, the relevant theoretical and experimental studies were carried out to investigate the dynamic response of metal thin plates and the formation mechanism of residual stress induced by laser shock wave. In this paper, the latest research trends on the surface residual stress of laser shock processing technology were elaborated. The main progress of laser shock wave propagation mechanism and dynamic response, laser shock, and surface residual stress were discussed. It is pointed out that the multi-scale characterization of laser and material, surface residual stress and microstructure change is a new hotspot in laser shock strengthening technology.

  16. Oxidized Metal Powders for Mechanical Shock and Crush Safety Enhancers; TOPICAL

    GARINO, TERRY J.

    2002-01-01

    The use of oxidized metal powders in mechanical shock or crush safety enhancers in nuclear weapons has been investigated. The functioning of these devices is based on the remarkable electrical behavior of compacts of certain oxidized metal powders when subjected to compressive stress. For example, the low voltage resistivity of a compact of oxidized tantalum powder was found to decrease by over six orders of magnitude during compaction between 1 MPa, where the thin, insulating oxide coatings on the particles are intact, to 10 MPa, where the oxide coatings have broken down along a chain of particles spanning the electrodes. In this work, the behavior of tantalum and aluminum powders was investigated. The low voltage resistivity during compaction of powders oxidized under various conditions was measured and compared. In addition, the resistivity at higher voltages and the dielectric breakdown strength during compaction were also measured. A key finding was that significant changes in the electrical properties persist after the removal of the stress so that a mechanical shock enhancer is feasible. This was verified by preliminary shock experiments. Finally, conceptual designs for both types of enhancers are presented

  17. The influence of peak stress on the mechanical behavior and the substructural evolution in shock-prestrained zirconium

    Cerreta, E.; Gray, G.T. III; Henrie, B.L.; Brown, D.W.; Hixson, R.S.; Rigg, P.A.

    2004-01-01

    The post shock mechanical behavior and substructure evolution of zirconium (Zr) under shock prestrained at 5.8 and 8 GPa, above and below the pressure induced α-ω phase transition, has been quantified. The reload yield stress of Zr shock prestrained to 8 GPa was found to exhibit enhanced shock hardening when compared to the flow stress measured quasi-statically at an equivalent strain. In contrast, the reload yield behavior of Zr specimens shocked to 5.8 GPa did not exhibit enhanced shock hardening. The microstructure of the as-annealed and shock prestrained materials were examined. The presence of a reduced available glide distance due to a relatively more well developed dislocation substructure and increased twinning over quasi-static specimens deformed to comparable strains correlates with the increased yield stresses after shock prestraining at 8 GPa. Additionally, the retention of ∼ 40% by volume metastable high-pressure ω-phase in specimens shocked to 8 GPa and its absence in the 5.8 GPa specimen, is thought to contribute to the increased yield stress in the 8 GPa specimens

  18. Acceleration control system for semi-active in-car crib with joint application of regular and inverted pendulum mechanisms

    Kawashima, T.

    2016-09-01

    To reduce the risk of injury to an infant in an in-car crib (or in a child safety bed) collision shock during a car crash, it is necessary to maintain a constant force acting on the crib below a certain allowable value. To realize this objective, we propose a semi-active in-car crib system with the joint application of regular and inverted pendulum mechanisms. The arms of the proposed crib system support the crib like a pendulum while the pendulum system itself is supported like an inverted pendulum by the arms. In addition, the friction torque of each arm is controlled using a brake mechanism that enables the proposed in-car crib to decrease the acceleration of the crib gradually and maintain it around the target value. This system not only reduces the impulsive force but also transfers the force to the infant's back using a spin control system, i.e., the impulse force acts is made to act perpendicularly on the crib. The spin control system was developed in our previous work. This work focuses on the acceleration control system. A semi-active control law with acceleration feedback is introduced, and the effectiveness of the system is demonstrated using numerical simulation and model experiment.

  19. Acceleration control system for semi-active in-car crib with joint application of regular and inverted pendulum mechanisms

    Kawashima, T

    2016-01-01

    To reduce the risk of injury to an infant in an in-car crib (or in a child safety bed) collision shock during a car crash, it is necessary to maintain a constant force acting on the crib below a certain allowable value. To realize this objective, we propose a semi-active in-car crib system with the joint application of regular and inverted pendulum mechanisms. The arms of the proposed crib system support the crib like a pendulum while the pendulum system itself is supported like an inverted pendulum by the arms. In addition, the friction torque of each arm is controlled using a brake mechanism that enables the proposed in-car crib to decrease the acceleration of the crib gradually and maintain it around the target value. This system not only reduces the impulsive force but also transfers the force to the infant's back using a spin control system, i.e., the impulse force acts is made to act perpendicularly on the crib. The spin control system was developed in our previous work. This work focuses on the acceleration control system. A semi-active control law with acceleration feedback is introduced, and the effectiveness of the system is demonstrated using numerical simulation and model experiment. (paper)

  20. Impact of Isothermal Aging and Testing Temperature on Large Flip-Chip BGA Interconnect Mechanical Shock Performance

    Lee, Tae-Kyu; Chen, Zhiqiang; Guirguis, Cherif; Akinade, Kola

    2017-10-01

    The stability of solder interconnects in a mechanical shock environment is crucial for large body size flip-chip ball grid array (FCBGA) electronic packages. Additionally, the junction temperature increases with higher electric power condition, which brings the component into an elevated temperature environment, thus introducing another consideration factor for mechanical stability of interconnection joints. Since most of the shock performance data available were produced at room temperature, the effect of elevated temperature is of interest to ensure the reliability of the device in a mechanical shock environment. To achieve a stable␣interconnect in a dynamic shock environment, the interconnections must tolerate mechanical strain, which is induced by the shock wave input and reaches the particular component interconnect joint. In this study, large body size (52.5 × 52.5 mm2) FCBGA components assembled on 2.4-mm-thick boards were tested with various isothermal pre-conditions and testing conditions. With a heating element embedded in the test board, a test temperature range from room temperature to 100°C was established. The effects of elevated temperature on mechanical shock performance were investigated. Failure and degradation mechanisms are identified and discussed based on the microstructure evolution and grain structure transformations.

  1. Reliability assessment of competing risks with generalized mixed shock models

    Rafiee, Koosha; Feng, Qianmei; Coit, David W.

    2017-01-01

    This paper investigates reliability modeling for systems subject to dependent competing risks considering the impact from a new generalized mixed shock model. Two dependent competing risks are soft failure due to a degradation process, and hard failure due to random shocks. The shock process contains fatal shocks that can cause hard failure instantaneously, and nonfatal shocks that impact the system in three different ways: 1) damaging the unit by immediately increasing the degradation level, 2) speeding up the deterioration by accelerating the degradation rate, and 3) weakening the unit strength by reducing the hard failure threshold. While the first impact from nonfatal shocks comes from each individual shock, the other two impacts are realized when the condition for a new generalized mixed shock model is satisfied. Unlike most existing mixed shock models that consider a combination of two shock patterns, our new generalized mixed shock model includes three classic shock patterns. According to the proposed generalized mixed shock model, the degradation rate and the hard failure threshold can simultaneously shift multiple times, whenever the condition for one of these three shock patterns is satisfied. An example using micro-electro-mechanical systems devices illustrates the effectiveness of the proposed approach with sensitivity analysis. - Highlights: • A rich reliability model for systems subject to dependent failures is proposed. • The degradation rate and the hard failure threshold can shift simultaneously. • The shift is triggered by a new generalized mixed shock model. • The shift can occur multiple times under the generalized mixed shock model.

  2. Global Mechanical Response and Its Relation to Deformation and Failure Modes at Various Length Scales Under Shock Impact in Alumina AD995 Armor Ceramic

    Dandekar, D. P; McCauley, J. W; Green, W. H; Bourne, N. K; Chen, M. W

    2008-01-01

    ... maps relating the experimentally measured global mechanical response of a material through matured shock wave diagnostics to the nature of concurrent deformation and damage generated at varying length scales under shock wave loading.

  3. Shock tube Multiphase Experiments

    Middlebrooks, John; Allen, Roy; Paudel, Manoj; Young, Calvin; Musick, Ben; McFarland, Jacob

    2017-11-01

    Shock driven multiphase instabilities (SDMI) are unique physical phenomena that have far-reaching practical applications in engineering and science. The instability is present in high energy explosions, scramjet combustors, and supernovae events. The SDMI arises when a multiphase interface is impulsively accelerated by the passage of a shockwave. It is similar in development to the Richtmyer-Meshkov (RM) instability however, particle-to-gas coupling is the driving mechanism of the SDMI. As particle effects such as lag and phase change become more prominent, the SDMI's development begins to significantly deviate from the RM instability. We have developed an experiment for studying the SDMI in our shock tube facility. In our experiments, a multiphase interface is created using a laminar jet and flowed into the shock tube where it is accelerated by the passage of a planar shockwave. The interface development is captured using CCD cameras synchronized with planar laser illumination. This talk will give an overview of new experiments conducted to examine the development of a shocked cylindrical multiphase interface. The effects of Atwood number, particle size, and a second acceleration (reshock) of the interface will be discussed.

  4. Quantitative evaluation of the mechanical strength of titanium/composite bonding using laser-generated shock waves

    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.

  5. Mechanical to electrical energy conversion by shock wave effect in a ferro-electric material

    David, Jean

    1977-01-01

    The shock wave propagation through a polarized ferroelectric ceramic changes or destroys remanent polarization and this way allows to get, in adequate electrical circuit, a volume energy of about 2 J/ cm 3 , during a time of the order of 0,4 μs; which corresponds to a peak - power of 5 MW/cm 3 . The present report has for objective to specify the optimum working conditions of this mechanical to electrical conversion from ceramic characteristics, load circuit connected to its electrodes and from the characteristics of the pressure wave which travels through the materials which constitute the converter. After a few lines about the ferroelectric materials and about the shock waves, the shock generator, the used setting and measures are described. A mathematical model which exhibits the transducer operation and a computation of the allowable electrical energy are given. For ending, the released electrical energies by industrial and laboratory ceramics are compared to the estimated computations and a thermodynamical balance is carried out. (author) [fr

  6. High temperature mechanical properties and surface fatigue behavior improving of steel alloy via laser shock peening

    Ren, N.F.; Yang, H.M.; Yuan, S.Q.; Wang, Y.; Tang, S.X.; Zheng, L.M.; Ren, X.D.; Dai, F.Z.

    2014-01-01

    Highlights: • The properties of 00C r 12 were improved by laser shock processing. • A deep layer of residual compressive stresses was introduced. • Fatigue life was enhanced about 58% at elevated temperature up to 600 °C. • The pinning effect is the reason of prolonging fatigue life at high temperature. - Abstract: Laser shock peening was carried out to reveal the effects on ASTM: 410L 00C r 12 microstructures and fatigue resistance in the temperature range 25–600 °C. The new conception of pinning effect was proposed to explain the improvements at the high temperature. Residual stress was measured by X-ray diffraction with sin 2 ψ method, a high temperature extensometer was utilized to measure the strain and control the strain signal. The grain and precipitated phase evolutionary process were observed by scanning electron microscopy. These results show that a deep layer of compressive residual stress is developed by laser shock peening, and ultimately the isothermal stress-controlled fatigue behavior is enhanced significantly. The formation of high density dislocation structure and the pinning effect at the high temperature, which induces a stronger surface, lower residual stress relaxation and more stable dislocation arrangement. The results have profound guiding significance for fatigue strengthening mechanism of components at the elevated temperature

  7. Electron velocity distributions near collisionless shocks

    Feldman, W.C.

    1984-01-01

    Recent studies of the amount of electron heating and of the shapes of electron velocity distributions across shocks near the earth are reviewed. It is found that electron heating increases with increasing shock strength but is always less than the ion heating. The scale length of electron heating is also less than that for the ions. Electron velocity distributions show characteristic shapes which depend on the strength of the shocks. At the weaker shocks, electron heating is mostly perpendicular to the ambient magnetic field, bar B, and results in Gaussian-shaped velocity distributions at low-to-moderate energies. At the stronger shocks, parallel heating predominates resulting in flat-topped velocity distributions. A reasonable interpretation of these results indicates that at the weaker shocks electron heating is dominated by a tendency toward conservation of the magnetic moment. At the stronger fast-mode shocks, this heating is thought to be dominated by an acceleration parallel to bar B produced by the macroscopic shock electric field followed by beam driven plasma instabilities. Some contribution to the heating at the stronger shocks from conservation of the magnetic moment and cross-field current-driven instabilities cannot be ruled out. Although the heating at slow-mode shocks is also dominated by instabilities driven by magnetic field-aligned electron beams, their acceleration mechanism is not yet established

  8. A primary standard for low-g shock calibration by laser interferometry

    Sun, Qiao; Wang, Jian-lin; Hu, Hong-bo

    2014-07-01

    This paper presents a novel implementation of a primary standard for low-g shock acceleration calibration by laser interferometry based on rigid body collision at National Institute of Metrology, China. The mechanical structure of the standard device and working principles involved in the shock acceleration exciter, laser interferometers and virtual instruments are described. The novel combination of an electromagnetic exciter and a pneumatic exciter as the mechanical power supply of the standard device can deliver a wide range of shock acceleration levels. In addition to polyurethane rubber, two other types of material are investigated to ensure a wide selection of cushioning pads for shock pulse generation, with pulse shapes and data displayed. A heterodyne He-Ne laser interferometer is preferred for its precise and reliable measurement of shock acceleration while a homodyne one serves as a check standard. Some calibration results of a standard acceleration measuring chain are shown in company with the uncertainty evaluation budget. The expanded calibration uncertainty of shock sensitivity of the acceleration measuring chain is 0.8%, k = 2, with the peak acceleration range from 20 to 10 000 m s-2 and pulse duration from 0.5 to 10 ms. This primary shock standard can meet the traceability requirements of shock acceleration from various applications of industries from automobile to civil engineering and therefore is used for piloting the ongoing shock comparison of Technical Committee of Acoustics, Ultrasound and Vibration (TCAUV) of Asia Pacific Metrology Program (APMP), coded as APMP.AUV.V-P1.

  9. Preliminary electrostatic and mechanical design of a SINGAP-MAMuG compatible accelerator

    Grando, L. [Consorzio RFX, Associazione EURATOM-ENEA sulla Fusione, Corso Stati Uniti 4, I-35127 Padova (Italy)], E-mail: luca.grando@igi.cnr.it; Dal Bello, S.; De Lorenzi, A. [Consorzio RFX, Associazione EURATOM-ENEA sulla Fusione, Corso Stati Uniti 4, I-35127 Padova (Italy); Pilan, N. [DIE, Universita di Padova, Via Gradenigo 6A, I-35100 Padova (Italy); Rizzolo, A.; Zaccaria, P. [Consorzio RFX, Associazione EURATOM-ENEA sulla Fusione, Corso Stati Uniti 4, I-35127 Padova (Italy)

    2009-06-15

    Each ITER NB injector shall provide 16.5 MW auxiliary power by accelerating a deuterium beam across a voltage of -1 MV. At present two possible alternatives for the accelerator are considered: the reference design, based on MAMuG electrostatic accelerator, where the total voltage is graded using five grids at intermediate steps of 200 kV, and the alternative concept, the SINGAP accelerator, for which the total voltage is held by one single gap. This paper focuses a preliminary feasibility study of integration of SINGAP accelerator grids into the support structure of a MAMuG type accelerator; the review or design of new electrostatic shields to improve the voltage withstanding capability of the system and the preliminary design of electrical and hydraulic connections routing from the bushing to the accelerator are also discussed. Electrostatic and mechanical analyses carried out to support the design are described in detail.

  10. Elastic-plastic Fracture Mechanics Assessment of nozzle corners submitted to thermal shock loading

    Chapuliot, S.; Marie, S.

    2016-01-01

    This paper focuses on the development of a simplified analytical scheme for the elastic-plastic Fracture Mechanics Assessment of large nozzle corners. Within that frame, following the specific numerical effort performed for the definition of a Stress Intensity Factor compendium, complementary elastic-plastic developments are proposed here for the consideration of the thermal shock loading in the elastic-plastic domain: this type of loading is a major loading for massive structures such as nozzle corners of large components. Thus, an important numerical was performed in order to extend the applicability domain of existing analytical schemes to those complex geometries. The final formulation is a simple one, applicable to a large variety of materials and geometrical configurations as long as the structure is large and the defect remains small in comparison to the internal radius of the nozzle. - Highlights: • Fracture Mechanics Assessment of large nozzle corners. • Elastic-plastic Stress Intensity Factor determination under thermal shock loading. • Semi-analytical schemes for J calculation.

  11. The strengthening mechanism of a nickel-based alloy after laser shock processing at high temperatures

    Li, Yinghong; Zhou, Liucheng; He, Weifeng; He, Guangyu; Wang, Xuede; Nie, Xiangfan; Wang, Bo; Luo, Sihai; Li, Yuqin

    2013-01-01

    We investigated the strengthening mechanism of laser shock processing (LSP) at high temperatures in the K417 nickel-based alloy. Using a laser-induced shock wave, residual compressive stresses and nanocrystals with a length of 30–200 nm and a thickness of 1 μm are produced on the surface of the nickel-based alloy K417. When the K417 alloy is subjected to heat treatment at 900 °C after LSP, most of the residual compressive stress relaxes while the microhardness retains good thermal stability; the nanocrystalline surface has not obviously grown after the 900 °C per 10 h heat treatment, which shows a comparatively good thermal stability. There are several reasons for the good thermal stability of the nanocrystalline surface, such as the low value of cold hardening of LSP, extreme high-density defects and the grain boundary pinning of an impure element. The results of the vibration fatigue experiments show that the fatigue strength of K417 alloy is enhanced and improved from 110 to 285 MPa after LSP. After the 900 °C per 10 h heat treatment, the fatigue strength is 225 MPa; the heat treatment has not significantly reduced the reinforcement effect. The feature of the LSP strengthening mechanism of nickel-based alloy at a high temperature is the co-working effect of the nanocrystalline surface and the residual compressive stress after thermal relaxation. (paper)

  12. Betatron emission as a diagnostic for injection and acceleration mechanisms in laser plasma accelerators

    Corde, S; Thaury, C; Phuoc, K Ta; Lifschitz, A; Lambert, G; Lundh, O; Brijesh, P; Sebban, S; Rousse, A; Faure, J; Malka, V; Arantchuk, L

    2012-01-01

    Betatron x-ray emission in laser plasma accelerators is a promising compact source that may be an alternative to conventional x-ray sources, based on large scale machines. In addition to its potential as a source, precise measurements of betatron emission can reveal crucial information about relativistic laser–plasma interaction. We show that the emission length and the position of the x-ray emission can be obtained by placing an aperture mask close to the source, and by measuring the beam profile of the betatron x-ray radiation far from the aperture mask. The position of the x-ray emission gives information on plasma wave breaking and hence on the laser non-linear propagation. Moreover, the measurement of the longitudinal extension helps one to determine whether the acceleration is limited by pump depletion or dephasing effects. In the case of multiple injections, it is used to retrieve unambiguously the position in the plasma of each injection. This technique is also used to study how, in a capillary discharge, the variations of the delay between the discharge and the laser pulse affect the interaction. The study reveals that, for a delay appropriate for laser guiding, the x-ray emission only occurs in the second half of the capillary: no electrons are injected and accelerated in the first half. (paper)

  13. High-energy cosmic-ray acceleration

    Bustamante, M; Carrillo Montoya, G; de Paula, W; Duarte Chavez, J A; Gago, A M; Hakobyan, H; Jez, P; Monroy Montañez, J A; Ortiz Velasquez, A; Padilla Cabal, F; Pino Rozas, M; Rodriguez Patarroyo, D J; Romeo, G L; Saldaña-Salazar , U J; Velasquez, M

    2010-01-01

    We briefly review the basics of ultrahigh-energy cosmic-ray acceleration. The Hillas criterion is introduced as a geometrical criterion that must be fulfilled by potential acceleration sites, and energy losses are taken into account in order to obtain a more realistic scenario. The different available acceleration mechanisms are presented, with special emphasis on Fermi shock acceleration and its prediction of a power-law cosmic-ray energy spectrum. We conclude that first-order Fermi accelera...

  14. A Massively Parallel Solver for the Mechanical Harmonic Analysis of Accelerator Cavities

    2015-01-01

    ACE3P is a 3D massively parallel simulation suite that developed at SLAC National Accelerator Laboratory that can perform coupled electromagnetic, thermal and mechanical study. Effectively utilizing supercomputer resources, ACE3P has become a key simulation tool for particle accelerator R and D. A new frequency domain solver to perform mechanical harmonic response analysis of accelerator components is developed within the existing parallel framework. This solver is designed to determine the frequency response of the mechanical system to external harmonic excitations for time-efficient accurate analysis of the large-scale problems. Coupled with the ACE3P electromagnetic modules, this capability complements a set of multi-physics tools for a comprehensive study of microphonics in superconducting accelerating cavities in order to understand the RF response and feedback requirements for the operational reliability of a particle accelerator. (auth)

  15. Accelerators

    CERN. Geneva

    2001-01-01

    The talk summarizes the principles of particle acceleration and addresses problems related to storage rings like LEP and LHC. Special emphasis will be given to orbit stability, long term stability of the particle motion, collective effects and synchrotron radiation.

  16. Basic thermal–mechanical properties and thermal shock, fatigue resistance of swaged + rolled potassium doped tungsten

    Zhang, Xiaoxin; Yan, Qingzhi, E-mail: qzyan@ustb.edu.cn; Lang, Shaoting; Xia, Min; Ge, Changchun

    2014-09-15

    Highlights: • The potassium doped tungsten grade was achieved via swaging + rolling process. • The cracking threshold of the W–K alloy was in the range of 0.44–0.66 GW/m{sup 2}. • Recrystallization occurred at 0.66–1.1 GW/m{sup 2} during the thermal shock tests. • No cracks emerged during the thermal fatigue tests (0.44 GW/m{sup 2}, 1000 cycles). • Recrystallization occurred after 1000 cycles during the thermal fatigue tests. - Abstract: The potassium doped tungsten (W–K) grade was achieved via swaging + rolling process. The swaged + rolled W–K alloy exhibited acceptable thermal conductivity of 159.1 W/m K and ductile-to-brittle transition temperature of about 873 K while inferior mechanical properties attributed to the coarse pores and small deformation degree. Then the thermal shock, fatigue resistance of the W–K grade were characterized by an electron beam facility. Thermal shock tests were conducted at absorbed power densities varied from 0.22 to 1.1 GW/m{sup 2} in a step of 0.22 GW/m{sup 2}. The cracking threshold was in the range of 0.44–0.66 GW/m{sup 2}. Furthermore, recrystallization occurred in the subsurface of the specimens tested at 0.66–1.1 GW/m{sup 2} basing on the analysis of microhardness and microstructure. Thermal fatigue tests were performed at 0.44 GW/m{sup 2} up to 1000 cycles and no cracks emerged throughout the tests. Moreover, recrystallization occurred after 1000 cycles.

  17. Applying an overstress principle in accelerated testing of absorbing mechanisms

    Tsyss, V. G.; Sergaeva, M. Yu; Sergaev, A. A.

    2018-04-01

    The relevance of using overstress test as a forced one to determine the pneumatic absorber lifespan was studied. The obtained results demonstrated that at low load overstress the relative error for the absorber lifespan evaluation is no more than 3%. This means that the test results spread has almost no effect on the lifespan evaluation, and this effect is several times less than that at high load overstress tests. Accelerated testing of absorbers with low load overstress is more acceptable since the relative error for the lifespan evaluation is negligible.

  18. Space Mechanisms Lessons Learned and Accelerated Testing Studies

    Fusaro, Robert L.

    1997-01-01

    A number of mechanism (mechanical moving component) failures and anomalies have recently occurred on satellites. In addition, more demanding operating and life requirements have caused mechanism failures or anomalies to occur even before some satellites were launched (e.g., during the qualification testing of GOES-NEXT, CERES, and the Space Station Freedom Beta Joint Gimbal). For these reasons, it is imperative to determine which mechanisms worked in the past and which have failed so that the best selection of mechanically moving components can be made for future satellites. It is also important to know where the problem areas are so that timely decisions can be made on the initiation of research to develop future needed technology. To chronicle the life and performance characteristics of mechanisms operating in a space environment, a Space Mechanisms Lessons Learned Study was conducted. The work was conducted by the NASA Lewis Research Center and by Mechanical Technologies Inc. (MTI) under contract NAS3-27086. The expectation of the study was to capture and retrieve information relating to the life and performance of mechanisms operating in the space environment to determine what components had operated successfully and what components had produced anomalies.

  19. Pressurized thermal shock probabilistic fracture mechanics sensitivity analysis for Yankee Rowe reactor pressure vessel

    Dickson, T.L.; Cheverton, R.D.; Bryson, J.W.; Bass, B.R.; Shum, D.K.M.; Keeney, J.A.

    1993-08-01

    The Nuclear Regulatory Commission (NRC) requested Oak Ridge National Laboratory (ORNL) to perform a pressurized-thermal-shock (PTS) probabilistic fracture mechanics (PFM) sensitivity analysis for the Yankee Rowe reactor pressure vessel, for the fluences corresponding to the end of operating cycle 22, using a specific small-break-loss- of-coolant transient as the loading condition. Regions of the vessel with distinguishing features were to be treated individually -- upper axial weld, lower axial weld, circumferential weld, upper plate spot welds, upper plate regions between the spot welds, lower plate spot welds, and the lower plate regions between the spot welds. The fracture analysis methods used in the analysis of through-clad surface flaws were those contained in the established OCA-P computer code, which was developed during the Integrated Pressurized Thermal Shock (IPTS) Program. The NRC request specified that the OCA-P code be enhanced for this study to also calculate the conditional probabilities of failure for subclad flaws and embedded flaws. The results of this sensitivity analysis provide the NRC with (1) data that could be used to assess the relative influence of a number of key input parameters in the Yankee Rowe PTS analysis and (2) data that can be used for readily determining the probability of vessel failure once a more accurate indication of vessel embrittlement becomes available. This report is designated as HSST report No. 117

  20. Basic thermal-mechanical properties and thermal shock, fatigue resistance of swaged + rolled potassium doped tungsten

    Zhang, Xiaoxin; Yan, Qingzhi; Lang, Shaoting; Xia, Min; Ge, Changchun

    2014-09-01

    The potassium doped tungsten (W-K) grade was achieved via swaging + rolling process. The swaged + rolled W-K alloy exhibited acceptable thermal conductivity of 159.1 W/m K and ductile-to-brittle transition temperature of about 873 K while inferior mechanical properties attributed to the coarse pores and small deformation degree. Then the thermal shock, fatigue resistance of the W-K grade were characterized by an electron beam facility. Thermal shock tests were conducted at absorbed power densities varied from 0.22 to 1.1 GW/m2 in a step of 0.22 GW/m2. The cracking threshold was in the range of 0.44-0.66 GW/m2. Furthermore, recrystallization occurred in the subsurface of the specimens tested at 0.66-1.1 GW/m2 basing on the analysis of microhardness and microstructure. Thermal fatigue tests were performed at 0.44 GW/m2 up to 1000 cycles and no cracks emerged throughout the tests. Moreover, recrystallization occurred after 1000 cycles.

  1. Wireless acceleration sensor of moving elements for condition monitoring of mechanisms

    Sinitsin, Vladimir V.; Shestakov, Aleksandr L.

    2017-09-01

    Comprehensive analysis of the angular and linear accelerations of moving elements (shafts, gears) allows an increase in the quality of the condition monitoring of mechanisms. However, existing tools and methods measure either linear or angular acceleration with postprocessing. This paper suggests a new construction design of an angular acceleration sensor for moving elements. The sensor is mounted on a moving element and, among other things, the data transfer and electric power supply are carried out wirelessly. In addition, the authors introduce a method for processing the received information which makes it possible to divide the measured acceleration into the angular and linear components. The design has been validated by the results of laboratory tests of an experimental model of the sensor. The study has shown that this method provides a definite separation of the measured acceleration into linear and angular components, even in noise. This research contributes an advance in the range of methods and tools for condition monitoring of mechanisms.

  2. Wireless acceleration sensor of moving elements for condition monitoring of mechanisms

    Sinitsin, Vladimir V; Shestakov, Aleksandr L

    2017-01-01

    Comprehensive analysis of the angular and linear accelerations of moving elements (shafts, gears) allows an increase in the quality of the condition monitoring of mechanisms. However, existing tools and methods measure either linear or angular acceleration with postprocessing. This paper suggests a new construction design of an angular acceleration sensor for moving elements. The sensor is mounted on a moving element and, among other things, the data transfer and electric power supply are carried out wirelessly. In addition, the authors introduce a method for processing the received information which makes it possible to divide the measured acceleration into the angular and linear components. The design has been validated by the results of laboratory tests of an experimental model of the sensor. The study has shown that this method provides a definite separation of the measured acceleration into linear and angular components, even in noise. This research contributes an advance in the range of methods and tools for condition monitoring of mechanisms. (paper)

  3. Energy convergence of shock waves and its destruction mechanism in cone-roof combustion chambers

    Xu, Han; Yao, Anren; Yao, Chunde; Gao, Jian

    2016-01-01

    Highlights: • Experiments with simulations are designed to probe into engine severe knock. • Energy convergence at central and edge region is observed in closed-limited space. • Modes with different intensities and mechanism of energy convergence are revealed. • Chamber shape and equivalence ratio can affect the energy convergence. • The destruction effects of energy convergence on pistons are recognized. - Abstract: Energy convergence is considered as an important phenomenon in internal combustion engines under severe knock, in which shock waves caused by violent combustion may aggregate the energy released by fuel burning to damage engine parts like pistons and spark plugs easily. In order to reveal such convergence mechanism and its destruction effects, a novel detonation bomb experiment combined with numerical simulations are conducted. In bomb experiments, a detonation wave is forcibly introduced into a clearance-variable cone-roof combustion chamber by a high energy spark ignition. Four pressure transducers were installed in different positions to monitor the energy convergence. Combined with the experiments, numerical simulations were conducted to reveal the convergence modes and mechanisms. Finally, destruction samples were presented to validate this research. It’s found that the energy convergence of shock waves always occurs in middle and edge region, which are vulnerable to be damaged. Three modes of energy convergence are concluded for middle region while several ways of energy convergence are concluded for edge region, which are all related with the chamber shape and may result in different levels of convergence. It’s also found that though detonation strength (knock intensity) can be changed by both equivalence ratios and initial pressures, only the equivalence ratios can change the convergence modes while the initial pressures cannot.

  4. Multiscale modeling of beryllium: quantum mechanics and laser-driven shock experiments using novel diagnostics

    Swift, D.C.; Paisley, Dennis L.; Kyrala, George A.; Hauer, Allan

    2002-01-01

    Ab initio quantum mechanics was used to construct a thermodynamically complete and rigorous equation of state for beryllium in the hexagonal and body-centred cubic structures, and to predict elastic constants as a function of compression. The equation of state agreed well with Hugoniot data and previously-published equations of state, but the temperatures were significantly different. The hexagonal/bcc phase boundary agreed reasonably well with published data, suggesting that the temperatures in our new equation of state were accurate. Shock waves were induced in single crystals and polycrystalline foils of beryllium, by direct illumination using the TRIDENT laser at Los Alamos. The velocity history at the surface of the sample was measured using a line-imaging VISAR, and transient X-ray diffraction (TXD) records were obtained with a plasma backlighter and X-ray streak cameras. The VISAR records exhibited elastic precursors, plastic waves, phase changes and spall. Dual TXD records were taken, in Bragg and Laue orientations. The Bragg lines moved in response to compression in the uniaxial direction. Because direct laser drive was used, the results had to be interpreted with the aid of radiation hydrodynamics simulations to predict the loading history for each laser pulse. In the experiments where there was evidence of polymorphism in the VISAR record, additional lines appeared in the Bragg and Laue records. The corresponding pressures were consistent with the phase boundary predicted by the quantum mechanical equation of state for beryllium. A model of the response of a single crystal of beryllium to shock loading is being developed using these new theoretical and experimental results. This model will be used in meso-scale studies of the response of the microstructure, allowing us to develop a more accurate representation of the behaviour of polycrystalline beryllium.

  5. Numerical simulation of the structure of collisionless supercritical shocks

    Lipatov, A.S.

    1990-01-01

    Research on the structure of a collisionless shock wave and on acceleration of charged particles is important for analyzing the processes accompanying solar flares, and also for studying the shock waves which are excited in the interaction of the solar wind with planets, comets and interstellar gas, the mechanisms for the acceleration of cosmic rays, the processes accompanying magnetic field reconnection, explosion of Supernova. The study of the shock is also important for studying the processes in the active experiments in space. In the present report only supercritical shocks are considered, when partial ion reflection plays a controlling roll in shock formation. One- and two-dimensional simulations of the perpendicular shocks are presented. (R.P.) 33 refs.; 4 figs

  6. Generation of ultra-high-pressure shocks by collision of a fast plasma projectile driven in the laser-induced cavity pressure acceleration scheme with a solid target

    Badziak, J.; Rosinski, M.; Krouský, Eduard; Kucharik, M.; Liska, R.; Ullschmied, Jiří

    2015-01-01

    Roč. 22, č. 3 (2015), s. 1-11, č. článku 032709. ISSN 1070-664X R&D Projects: GA MŠk(CZ) LD14089; GA MŠk LM2010014 EU Projects: European Commission(XE) 284464 - LASERLAB-EUROPE Institutional support: RVO:68378271 ; RVO:61389021 Keywords : laser-produced plasma * ultra-high-pressure shocks * laser-induced cavity pressure acceleration Subject RIV: BL - Plasma and Gas Discharge Physics OBOR OECD: Fluids and plasma physics (including surface physics) Impact factor: 2.207, year: 2015

  7. A fracture mechanics method of evaluating structural integrity of a reactor vessel due to thermal shock effects following LOCA condition

    Ramani, D.T.

    1977-01-01

    The importance of knowledge of structural integrity of a reactor vessel due to thermal shock effects, is related to safety and operational requirements in assessing the adequacy and flawless functioing of the nuclear power systems. Followig a loss-of-coolant accident (LOCA) condition the integrity of the reactor vessel due to a sudden thermal shock induced by actuation of emergency core cooling system (ECCS), must be maintained to ensure safe and orderly shutdown of the reactor and its components. The paper encompasses criteria underlaying a fracture mechanics method of analysis to evaluate structural integrity of a typical 950 MWe PWR vessel as a result of very drastic changes in thermal and mechanical stress levels in the reactor vessel wall. The main object of this investigation therefore consists in assessing the capability of a PWR vessel to withstand the most critical thermal shock without inpairing its ability to conserve vital coolant owing to probable crack propagation. (Auth.)

  8. Effects of laser shock processing on mechanical properties and micro-structure of ANSI 304 austenitic stainless steel

    Luo, K.Y.; Lu, J.Z.; Zhang, Y.K.; Zhou, J.Z.; Zhang, L.F.; Dai, F.Z.; Zhang, L.; Zhong, J.W.; Cui, C.Y.

    2011-01-01

    Highlights: → Effects of LSP on mechanical properties of stainless steel ANSI 304 are evaluated. → LSP can clearly enhance the values of mechanical properties in the shocked region. → Martensite transformation does not take place in the surface layer subjected to LSP. → Enhancement mechanisms of LSP on mechanical property of stainless steel are revealed. → The results can provide some insights on the surface modification of stainless steel. - Abstract: The aim of this article is to address the effects of a single laser shock processing (LSP) impact on the nano-hardness, elastic modulus, residual stress and phase transformation of ANSI 304 austenitic stainless steel. Residual stress distribution of the LSP-shocked region is determined by X-ray diffraction (XRD) with sin 2 ψ method, and the micro-structural features in the near-surface layer are characterized by using cross-sectional optical microscopy (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). By comparing with the untreated samples, LSP can clearly improve nano-hardness, elastic modulus, and residual stress in the LSP-shocked region. The underlying enhancement mechanisms of LSP on nano-hardness, elastic modulus and residual stress of stainless steel ANSI 304 are also revealed. These studies may provide some important insights into surface modification for metal materials.

  9. Delayed and accelerated aging share common longevity assurance mechanisms

    Schumacher, B.; van der Pluijm, I.; Moorhouse, M.J.; Kosteas, T.; Robinson, A.R.; Suh, Y.; Breit, T.M.; van Steeg, H.; Niedernhofer, L.J.; van IJcken, W.; Bartke, A.; Spindler, S.R.; Hoeijmakers, J.H.J.; van der Horst, G.T.J.; Garinis, G.A.

    2008-01-01

    Mutant dwarf and calorie-restricted mice benefit from healthy aging and unusually long lifespan. In contrast, mouse models for DNA repair-deficient progeroid syndromes age and die prematurely. To identify mechanisms that regulate mammalian longevity, we quantified the parallels between the

  10. Delayed and accelerated aging share common longevity assurance mechanisms

    B. Schumacher (Björn); I. van der Pluijm (Ingrid); M.J. Moorhouse (Michael); T. Kosteas (Theodore); A.R. Robinson (Andria Rasile); Y. Suh (Yousin); T.M. Breit (Timo); H. van Steeg (Harry); L.J. Niedernhofer (Laura); W.F.J. van IJcken (Wilfred); A. Bartke (Andrzej); S.R. Spindler (Stephen); J.H.J. Hoeijmakers (Jan); G.T.J. van der Horst (Gijsbertus); G.A. Garinis (George)

    2008-01-01

    textabstractMutant dwarf and calorie-restricted mice benefit from healthy aging and unusually long lifespan. In contrast, mouse models for DNA repair-deficient progeroid syndromes age and die prematurely. To identify mechanisms that regulate mammalian longevity, we quantified the parallels between

  11. Mutant p53 - heat shock response oncogenic cooperation: a new mechanism of cancer cell survival

    Evguenia eAlexandrova

    2015-04-01

    Full Text Available The main tumor suppressor function of p53 as a ‘guardian of the genome’ is to respond to cellular stress by transcriptional activation of apoptosis, growth arrest or senescence in damaged cells. Not surprisingly, mutations in the p53 gene are the most frequent genetic alteration in human cancers. Importantly, mutant p53 (mutp53 proteins not only lose their wild-type tumor suppressor activity, but also can actively promote tumor development. Two main mechanisms accounting for mutp53 proto-oncogenic activity are inhibition of the wild-type p53 in a dominant-negative fashion and gain of additional oncogenic activities known as gain-of-function (GOF. Here we discuss a novel mechanism of mutp53 GOF, which relies on its oncogenic cooperation with the heat shock machinery. This coordinated adaptive mechanism renders cancer cells more resistant to proteotoxic stress and provides both, a strong survival advantage to cancer cells and a promising means for therapeutic intervention.

  12. High-energy cosmic-ray acceleration

    Bustamante, M; de Paula, W; Duarte Chavez, J A; Gago, A M; Hakobyan, H; Jez, P; Monroy Montañez, J A; Ortiz Velasquez, A; Padilla Cabal, F; Pino Rozas, M; Rodriguez Patarroyo, D J; Romeo, G L; Saldaña-Salazar , U J; Velasquez, M; von Steinkirch, M

    2010-01-01

    We briefly review the basics of ultrahigh-energy cosmic-ray acceleration. The Hillas criterion is introduced as a geometrical criterion that must be fulfilled by potential acceleration sites, and energy losses are taken into account in order to obtain a more realistic scenario. The different available acceleration mechanisms are presented, with special emphasis on Fermi shock acceleration and its prediction of a power-law cosmic-ray energy spectrum. We conclude that first-order Fermi acceleration, though not entirely satisfactory, is the most promising mechanism for explaining the ultra-high-energy cosmic-ray flux.

  13. Influence of additives on microstructures, mechanical properties and shock-induced reaction characteristics of Al/Ni composites

    Xiong, Wei; Zhang, Xianfeng, E-mail: lynx@mail.njust.edu.cn; Wu, Yang; He, Yong; Wang, Chuanting; Guo, Lei

    2015-11-05

    Granular composites containing aluminum (Al) and nickel (Ni) are typical structural energetic materials, which possess ideal combination of both mechanical properties and energy release capability. The influence of two additives, namely Teflon (PTFE) and copper (Cu), on mechanical properties and shock-induced chemical reaction (SICR) characteristics of Al/Ni material system has been investigated. Three composites, namely Al/Ni, Al/Ni/PTFE and Al/Ni/Cu with same volumetric ratio of Al powder to Ni powder, were processed by means of static pressing. Scanning electron microscopy was used to study the microstructure of the mentioned three composites. Quasi static compression tests were also conducted to determine the mechanical properties and fracture behavior of the mentioned three composites. It was shown that the additives affected both compressive strength and fracture mode of the three composites. Impact initiation experiments on the mentioned three composites were performed to determine their shock-induced chemical reaction characteristics by considering pressure histories measured in the test chamber. The experimental results showed that the additives had significant effects on critical initiation velocity, reaction rate, reaction efficiency and post-reaction behavior. - Highlights: • .Al/Ni, Al/Ni/PTFE and Al/Ni/Cu were processed by means of static pressing. • .Microstructures, mechanical properties and shock-induced reactions were studied. • .Microstructures affect both compressive strength and fracture mode. • .Impact velocity is an important factor in shock-induced chemical characteristics. • .Each additive has significant effects on energy release behavior.

  14. Influence of additives on microstructures, mechanical properties and shock-induced reaction characteristics of Al/Ni composites

    Xiong, Wei; Zhang, Xianfeng; Wu, Yang; He, Yong; Wang, Chuanting; Guo, Lei

    2015-01-01

    Granular composites containing aluminum (Al) and nickel (Ni) are typical structural energetic materials, which possess ideal combination of both mechanical properties and energy release capability. The influence of two additives, namely Teflon (PTFE) and copper (Cu), on mechanical properties and shock-induced chemical reaction (SICR) characteristics of Al/Ni material system has been investigated. Three composites, namely Al/Ni, Al/Ni/PTFE and Al/Ni/Cu with same volumetric ratio of Al powder to Ni powder, were processed by means of static pressing. Scanning electron microscopy was used to study the microstructure of the mentioned three composites. Quasi static compression tests were also conducted to determine the mechanical properties and fracture behavior of the mentioned three composites. It was shown that the additives affected both compressive strength and fracture mode of the three composites. Impact initiation experiments on the mentioned three composites were performed to determine their shock-induced chemical reaction characteristics by considering pressure histories measured in the test chamber. The experimental results showed that the additives had significant effects on critical initiation velocity, reaction rate, reaction efficiency and post-reaction behavior. - Highlights: • .Al/Ni, Al/Ni/PTFE and Al/Ni/Cu were processed by means of static pressing. • .Microstructures, mechanical properties and shock-induced reactions were studied. • .Microstructures affect both compressive strength and fracture mode. • .Impact velocity is an important factor in shock-induced chemical characteristics. • .Each additive has significant effects on energy release behavior

  15. A new collective-field acceleration mechanism using a powerful laser

    Willis, W.J.

    1975-01-01

    Performance estimates for a linear accelerator for positive ions are presented. Focusing and acceleration is performed by means of a local, strong modulation of a relativistic electron beam using the electromagnetic field of a laser. For high-power laser beams of 1010 watts per square wavelength, the accelerating field strength can be several GV/m, assuming free electrons. Various interaction mechanisms of the laser beam with the electron beam are briefly discussed, notably inverse bremsstrahlung and interaction with the self-magnetic field of the electron beam. Finally, coherent effects and the injection of ions are dealt with. (author)

  16. Studies on mechanisms of the laser particle acceleration; Untersuchungen zu Mechanismen der Laser-Teilchenbeschleunigung

    Aurand, Bastian

    2012-06-20

    Within the last decade, many developments towards higher energies and particle numbers paved the way of particle acceleration performed by high intensity laser systems. Up to now, the process of a field-induced acceleration process (Target-Normal-Sheath-Acceleration (TNSA)) is investigated the most. Acceleration occurs as a consequence of separation of charges on a surface potential. Here, the broad energy spectrum is a problem not yet overcome although many improvements were achieved. Calculations for intensities higher than 10{sup 20..21} W/cm{sup 2} give hint that Radiation-Pressure-Acceleration (RPA) may lead to a sharper, monoenergetic energy spectrum. Within the framework of this thesis, the investigation of the acceleration mechanism is studied experimentally in the intensity range of 10{sup 19} W/cm{sup 2}. Suitable targets were developed and applied for patent. A broad range of parameters was scanned by means of high repetition rates together with an adequate laser system to provide high statistics of several thousands of shots, and the dependence of target material, intensity, laser polarisation and pre plasma-conditions was verified. Comparisons with 2-d numeric simulations lead to a model of the acceleration process which was analyzed by several diagnostic methods, giving clear evidence for a new, not field-induced acceleration process. In addition, a system for a continuous variation of the polarization based on reflective optics was developed in order to overcome the disadvantages of retardation plates, and their practicability of high laser energies can be achieved.

  17. Probabilistic fracture mechanics analysis of reactor vessel for pressurized thermal shock: the effect of residual stress and fracture toughness

    Jung, Sung Gyu; Jin, Tae Eun; Jhung, Myung Jo; Choi, Young Hwan

    2003-01-01

    The structural integrity of the reactor vessel with the approaching end of life must be assured for pressurized thermal shock. The regulation specifies the screening criteria for this and requires that specific analysis be performed for the reactor vessel which is anticipated to exceed the screening criteria at the end of plant life. In case the screening criteria is exceeded by the deterministic analysis, probabilistic analysis must be performed to show that failure probability is within the limit. In this study, probabilistic fracture mechanics analysis of the reactor vessel for pressurized thermal shock is performed and the effects of residual stress and master curve on the failure probability are investigated

  18. Mechanisms Involved in Secondary Cardiac Dysfunction in Animal Models of Trauma and Hemorrhagic Shock.

    Wilson, Nick M; Wall, Johanna; Naganathar, Veena; Brohi, Karim; De'Ath, Henry D

    2017-10-01

    Clinical evidence reveals the existence of a trauma-induced secondary cardiac injury (TISCI) that is associated with poor patient outcomes. The mechanisms leading to TISCI in injured patients are uncertain. Conversely, animal models of trauma hemorrhage have repeatedly demonstrated significant cardiac dysfunction following injury, and highlighted mechanisms through which this might occur. The aim of this review was to provide an overview of the animal studies describing TISCI and its pathophysiology.Basic science models of trauma show evidence of innate immune system activation via Toll-like receptors, the exact protagonists of which remain unclear. Shortly following trauma and hemorrhage, cardiomyocytes upregulate gene regulatory protein and inflammatory molecule expression including nuclear factor kappa beta, tumor necrosis factor alpha, and interleukin-6. This is associated with expression of membrane bound adhesion molecules and chemokines leading to marked myocardial leukocyte infiltration. This cell activation and infiltration is linked to a rise in enzymes that cause oxidative and nitrative stress and subsequent protein misfolding within cardiomyocytes. Such protein damage may lead to reduced contractility and myocyte apoptosis. Other molecules have been identified as cardioprotective following injury. These include p38 mitogen-activated protein kinases and heat shock proteins.The balance between increasing damaging mediators and a reduction in cardio-protective molecules appears to define myocardial function following trauma. Exogenous therapeutics have been trialled in rodents with promising abilities to favorably alter this balance, and subsequently lead to improved cardiac function.

  19. Effect of thermal shock on mechanical properties of injection-molded thermoplastic denture base resins.

    Takahashi, Yutaka; Hamanaka, Ippei; Shimizu, Hiroshi

    2012-07-01

    This study investigated the effect of thermal shock on the mechanical properties of injection-molded thermoplastic denture base resins. Four thermoplastic resins (two polyamides, one polyethylene terephthalate, one polycarbonate) and, as a control, a conventional heat-polymerized polymethyl methacrylate (PMMA), were tested. Specimens of each denture base material were fabricated according to ISO 1567 and were either thermocycled or not thermocycled (n = 10). The flexural strength at the proportional limit (FS-PL), the elastic modulus and the Charpy impact strength of the denture base materials were estimated. Thermocycling significantly decreased the FS-PL of one of the polyamides and the PMMA and it significantly increased the FS-PL of one of the polyamides. In addition, thermocycling significantly decreased the elastic modulus of one of the polyamides and significantly increased the elastic moduli of one of the polyamides, the polyethylene terephthalate, polycarbonate and PMMA. Thermocycling significantly decreased the impact strength of one of the polyamides and the polycarbonate. The mechanical properties of injection-molded thermoplastic denture base resins changed after themocycling.

  20. Mechanism of flow choking at shock boiling-up of a liquid

    Labuntsov, D.A.; Avdeev, A.A.

    1982-01-01

    The theory of the outflow of a saturated or non-heated liquid with thermodynamic parameters reaching the critical point from diaphragms and short nozzles has been developed basing on the concept of the boiling-up jump. Three characteristic flow conditions have been revealed: hydraulic, conditions when boiling-up jump is formed, and conditions of radial expansion of the flow. If the initial flow's parameters are low, the hydraulic conditions are realized. The expansion of the flow-passage cross-section of flow small jets by the final value takes place when the spinoidal overheating is reached near the exit cut-off at a small distance equal to the thickness of the boiling-up zone; and that causes the intensive jet dispersion in the radial direction. In case of overheatings close to the thermodynamic critical point, a boiling-up jump is formed inside the channel. The mechanism of flow choking has been analyzed; recommendations on calculation of the critical flow rate of a boiling-up liquid are given. The studied mechanism of flow choking at shock boiling-up of the flow permits to draw a rather detailed physical picture of the phenomenon and to give an explanation of the majority of experimentally-observed effects

  1. Fracture-mechanics data deduced from thermal-shock and related experiments with LWR pressure-vessel material

    Cheverton, R.D.; Canonico, D.A.; Iskander, S.K.; Bolt, S.E.; Holz, P.P.; Nanstad, R.K.; Stelzman, W.J.

    1982-01-01

    Pressurized water reactors (PWRs) are susceptible to certain types of hypothetical accidents that can subject the reactor pressure vessel to severe thermal shock, that is, a rapid cooling of the inner surface of the vessel wall. The thermal-shock loading, coupled with the radiation-induced reduction in the material fracture toughness, introduces the possibility of propagation of preexistent flaws and what at one time were regarded as somewhat unique fracture-oriented conditions. Several postulated reactor accidents have been analyzed to discover flaw behavior trends; seven intermediate-scale thermal-shock experiments with steel cylinders have been conducted; and corresponding materials characterization studies have been performed. Flaw behavior trends and related fracture-mechanics data deduced from these studies are discussed

  2. The mechanisms by which polyamines accelerate tumor spread

    Soda Kuniyasu

    2011-10-01

    Full Text Available Abstract Increased polyamine concentrations in the blood and urine of cancer patients reflect the enhanced levels of polyamine synthesis in cancer tissues arising from increased activity of enzymes responsible for polyamine synthesis. In addition to their de novo polyamine synthesis, cells can take up polyamines from extracellular sources, such as cancer tissues, food, and intestinal microbiota. Because polyamines are indispensable for cell growth, increased polyamine availability enhances cell growth. However, the malignant potential of cancer is determined by its capability to invade to surrounding tissues and metastasize to distant organs. The mechanisms by which increased polyamine levels enhance the malignant potential of cancer cells and decrease anti-tumor immunity are reviewed. Cancer cells with a greater capability to synthesize polyamines are associated with increased production of proteinases, such as serine proteinase, matrix metalloproteinases, cathepsins, and plasminogen activator, which can degrade surrounding tissues. Although cancer tissues produce vascular growth factors, their deregulated growth induces hypoxia, which in turn enhances polyamine uptake by cancer cells to further augment cell migration and suppress CD44 expression. Increased polyamine uptake by immune cells also results in reduced cytokine production needed for anti-tumor activities and decreases expression of adhesion molecules involved in anti-tumor immunity, such as CD11a and CD56. Immune cells in an environment with increased polyamine levels lose anti-tumor immune functions, such as lymphokine activated killer activities. Recent investigations revealed that increased polyamine availability enhances the capability of cancer cells to invade and metastasize to new tissues while diminishing immune cells' anti-tumor immune functions.

  3. Structure, phase content and mechanical properties of aluminium with hard particles after shock-wave compaction

    Kulkov, S; Vorozhtsov, S; Turuntaev, I

    2015-01-01

    The possibilities to combine metal and metal oxide powders in various compositions open a broad range of mechanical and thermal behavior. When using in nanostructured components the resulting materials might exhibit even more interesting properties, like product effectiveness, tensile strength, wear resistance, endurance and corrosion resistance. Intermetallics like TiAl could be obtained as TiAl x in a quality similar to that obtained from melting where only eutectic mixture can be produced. Similar effects are possible when compacting nanoceramic powders whereas these can be combined with intermetallics. Currently, it is very difficult to produce wires and special shaped parts from high temperature superconducting materials. The compacting by explosives could solve this problem.The present paper uses explosion compacting of Al nanoparticles to create nanocomposite with increased physico-mechanical properties. Russian civil explosive Uglenit was chosen as high energy material (HEM) for shock-wave compaction. The different schemes and conditions were suggested to run the explosion process. Al nanoparticles as produced by electric wire explosion contain 8-10% of aluminum oxide. That aluminum oxide can serve as strengthening material in the final nanocomposite which may be generated in various compositions by explosive compacting. Further modifications of nanocomposites were obtained when including nanodiamonds into the mixture with aluminum nanoparticles with different percentages. The addition of nanodiamonds results in a substantial strengthening effect.The experiments with compacting aluminum nanoparticles by explosives are described in detail including the process variations and conditions. The physico-mechanical properties of the nanocomposites are determined and discussed by considering the applied conditions. Especially, microstructure and phases of the obtained nanocomposites are analyzed by X-ray diffraction. (paper)

  4. Structure, phase content and mechanical properties of aluminium with hard particles after shock-wave compaction

    Kulkov, S.; Vorozhtsov, S.; Turuntaev, I.

    2015-04-01

    The possibilities to combine metal and metal oxide powders in various compositions open a broad range of mechanical and thermal behavior. When using in nanostructured components the resulting materials might exhibit even more interesting properties, like product effectiveness, tensile strength, wear resistance, endurance and corrosion resistance. Intermetallics like TiAl could be obtained as TiAlx in a quality similar to that obtained from melting where only eutectic mixture can be produced. Similar effects are possible when compacting nanoceramic powders whereas these can be combined with intermetallics. Currently, it is very difficult to produce wires and special shaped parts from high temperature superconducting materials. The compacting by explosives could solve this problem.The present paper uses explosion compacting of Al nanoparticles to create nanocomposite with increased physico-mechanical properties. Russian civil explosive Uglenit was chosen as high energy material (HEM) for shock-wave compaction. The different schemes and conditions were suggested to run the explosion process. Al nanoparticles as produced by electric wire explosion contain 8-10% of aluminum oxide. That aluminum oxide can serve as strengthening material in the final nanocomposite which may be generated in various compositions by explosive compacting. Further modifications of nanocomposites were obtained when including nanodiamonds into the mixture with aluminum nanoparticles with different percentages. The addition of nanodiamonds results in a substantial strengthening effect. The experiments with compacting aluminum nanoparticles by explosives are described in detail including the process variations and conditions. The physico-mechanical properties of the nanocomposites are determined and discussed by considering the applied conditions. Especially, microstructure and phases of the obtained nanocomposites are analyzed by X-ray diffraction.

  5. Nonlinear Alfvén waves, discontinuities, proton perpendicular acceleration, and magnetic holes/decreases in interplanetary space and the magnetosphere: intermediate shocks?

    B. T. Tsurutani

    2005-01-01

    Full Text Available Alfvén waves, discontinuities, proton perpendicular acceleration and magnetic decreases (MDs in interplanetary space are shown to be interrelated. Discontinuities are the phase-steepened edges of Alfvén waves. Magnetic decreases are caused by a diamagnetic effect from perpendicularly accelerated (to the magnetic field protons. The ion acceleration is associated with the dissipation of phase-steepened Alfvén waves, presumably through the Ponderomotive Force. Proton perpendicular heating, through instabilities, lead to the generation of both proton cyclotron waves and mirror mode structures. Electromagnetic and electrostatic electron waves are detected as well. The Alfvén waves are thus found to be both dispersive and dissipative, conditions indicting that they may be intermediate shocks. The resultant 'turbulence' created by the Alfvén wave dissipation is quite complex. There are both propagating (waves and nonpropagating (mirror mode structures and MDs byproducts. Arguments are presented to indicate that similar processes associated with Alfvén waves are occurring in the magnetosphere. In the magnetosphere, the 'turbulence' is even further complicated by the damping of obliquely propagating proton cyclotron waves and the formation of electron holes, a form of solitary waves. Interplanetary Alfvén waves are shown to rapidly phase-steepen at a distance of 1AU from the Sun. A steepening rate of ~35 times per wavelength is indicated by Cluster-ACE measurements. Interplanetary (reverse shock compression of Alfvén waves is noted to cause the rapid formation of MDs on the sunward side of corotating interaction regions (CIRs. Although much has been learned about the Alfvén wave phase-steepening processfrom space plasma observations, many facets are still not understood. Several of these topics are discussed for the interested researcher. Computer simulations and theoretical developments will be particularly useful in making further progress in

  6. A detailed examination of laser-ion acceleration mechanisms in the relativistic transparency regime using tracers

    Stark, David J.; Yin, Lin; Albright, Brian J.; Nystrom, William; Bird, Robert

    2018-04-01

    We present a particle-in-cell study of linearly polarized laser-ion acceleration systems, in which we use both two-dimensional (2D) and three-dimensional (3D) simulations to characterize the ion acceleration mechanisms in targets which become transparent to the laser pulse during irradiation. First, we perform a target length scan to optimize the peak ion energies in both 2D and 3D, and the predictive capabilities of 2D simulations are discussed. Tracer analysis allows us to isolate the acceleration into stages of target normal sheath acceleration (TNSA), hole boring (HB), and break-out afterburner (BOA) acceleration, which vary in effectiveness based on the simulation parameters. The thinnest targets reveal that enhanced TNSA is responsible for accelerating the most energetic ions, whereas the thickest targets have ions undergoing successive phases of HB and TNSA (in 2D) or BOA and TNSA (in 3D); HB is not observed to be a dominant acceleration mechanism in the 3D simulations. It is in the intermediate optimal regime, both when the laser breaks through the target with appreciable amplitude and when there is enough plasma to form a sustained high density flow, that BOA is most effective and is responsible for the most energetic ions. Eliminating the transverse laser spot size effects by performing a plane wave simulation, we can isolate with greater confidence the underlying physics behind the ion dynamics we observe. Specifically, supplemented by wavelet and FFT analyses, we match the post-transparency BOA acceleration with a wave-particle resonance with a high-amplitude low-frequency electrostatic wave of increasing phase velocity, consistent with that predicted by the Buneman instability.

  7. The crucifixion of Jesus: review of hypothesized mechanisms of death and implications of shock and trauma-induced coagulopathy.

    Bergeron, Joseph W

    2012-04-01

    The crucifixion of Jesus is arguably the most well-known and controversial execution in history. Christian faithful, dating back to the time of Jesus, have believed that Jesus was executed by crucifixion and later returned physically to life again. Others have questioned whether Jesus actually died by crucifixion, at all. From review of medical literature, physicians have failed to agree on a specific mechanism of Jesus' death. A search of Medline/Pubmed was completed with respect to crucifixion, related topics, and proposed mechanisms of Jesus' death. Several hypotheses for the mechanism of Jesus' death have been presented in medical literature, including 1) Pulmonary embolism 2) Cardiac rupture 3) Suspension trauma 4) Asphyxiation 5) Fatal stab wound, and 6) Shock. Each proposed mechanism of Jesus' death will be reviewed. The events of Jesus' execution are described, as they are pertinent to development of shock. Traumatic shock complicated by trauma-induced coagulopathy is proposed as a contributing factor, and possibly the primary mechanism, of Jesus' death by crucifixion. Copyright © 2011 Elsevier Ltd and Faculty of Forensic and Legal Medicine. All rights reserved.

  8. Constraining sources of ultrahigh energy cosmic rays and shear acceleration mechanism of particles in relativistic jets

    Liu, Ruoyu

    2015-06-10

    Ultrahigh energy cosmic rays are extreme energetic particles from outer space. They have aroused great interest among scientists for more than fifty years. However, due to the rarity of the events and complexity of the process of their propagation to Earth, they are still one of the biggest puzzles in modern high energy astrophysics. This dissertation is dedicated to study the origin of ultrahigh energy cosmic rays from various aspects. Firstly, we discuss a possible link between recently discovered sub-PeV/PeV neutrinos and ultrahigh energy cosmic rays. If these two kinds of particles share the same origin, the observation of neutrinos may provide additional and non-trivial constraints on the sources of ultrahigh energy cosmic rays. Secondly, we jointly employ the chemical composition measurement and the arrival directions of ultrahigh energy cosmic rays, and find a robust upper limit for distances of sources of ultrahigh energy cosmic rays above ∝55 EeV, as well as a lower limit for their metallicities. Finally, we study the shear acceleration mechanism in relativistic jets, which is a more efficient mechanism for the acceleration of higher energy particle. We compute the acceleration efficiency and the time-dependent particle energy spectrum, and explore the feature of synchrotron radiation of the accelerated particles. The possible realizations of this mechanism for acceleration of ultrahigh energy cosmic rays in different astrophysical environments is also discussed.

  9. FAVOR: A new fracture mechanics code for reactor pressure vessels subjected to pressurized thermal shock

    Dickson, T.L.

    1993-01-01

    This report discusses probabilistic fracture mechanics (PFM) analysis which is a major element of the comprehensive probabilistic methodology endorsed by the NRC for evaluation of the integrity of Pressurized Water Reactor (PWR) pressure vessels subjected to pressurized-thermal-shock (PTS) transients. It is anticipated that there will be an increasing need for an improved and validated PTS PFM code which is accepted by the NRC and utilities, as more plants approach the PTS screening criteria and are required to perform plant-specific analyses. The NRC funded Heavy Section Steel Technology (HSST) Program at Oak Ridge National Laboratories is currently developing the FAVOR (Fracture Analysis of Vessels: Oak Ridge) PTS PFM code, which is intended to meet this need. The FAVOR code incorporates the most important features of both OCA-P and VISA-II and contains some new capabilities such as PFM global modeling methodology, the capability to approximate the effects of thermal streaming on circumferential flaws located inside a plume region created by fluid and thermal stratification, a library of stress intensity factor influence coefficients, generated by the NQA-1 certified ABAQUS computer code, for an adequate range of two and three dimensional inside surface flaws, the flexibility to generate a variety of output reports, and user friendliness

  10. Investigation of ion acceleration mechanism through laser-matter interaction in femtosecond domain

    Altana, C., E-mail: altana@lns.infn.it [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, Via S. Sofia 62, 95123 Catania (Italy); Dipartimento di Fisica e Astronomia, Università degli Studi di Catania, Via S. Sofia 64, 95123 Catania (Italy); Muoio, A. [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, Via S. Sofia 62, 95123 Catania (Italy); Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Messina, Viale F.S. D’Alcontres 31, 98166 Messina (Italy); Lanzalone, G. [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, Via S. Sofia 62, 95123 Catania (Italy); Università degli Studi di Enna “Kore”, Via delle Olimpiadi, 94100 Enna (Italy); Tudisco, S. [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, Via S. Sofia 62, 95123 Catania (Italy); Brandi, F. [CNR, Intense Laser Irradiation Laboratory, Via G. Moruzzi 1, 56124 Pisa (Italy); Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova (Italy); Cirrone, G.A.P. [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, Via S. Sofia 62, 95123 Catania (Italy); Cristoforetti, G. [CNR, Intense Laser Irradiation Laboratory, Via G. Moruzzi 1, 56124 Pisa (Italy); Fazzi, A. [Energy Department, Polytechnic of Milan and INFN, Milan (Italy); Ferrara, P.; Fulgentini, L. [CNR, Intense Laser Irradiation Laboratory, Via G. Moruzzi 1, 56124 Pisa (Italy); Giove, D. [Energy Department, Polytechnic of Milan and INFN, Milan (Italy); Koester, P. [CNR, Intense Laser Irradiation Laboratory, Via G. Moruzzi 1, 56124 Pisa (Italy); Labate, L. [CNR, Intense Laser Irradiation Laboratory, Via G. Moruzzi 1, 56124 Pisa (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, Largo B. Pontecorvo 3, 56127 Pisa (Italy); and others

    2016-09-01

    An experimental campaign aiming to investigate the ion acceleration mechanisms through laser-matter interaction in the femtosecond domain has been carried out at the ILIL facility at a laser intensity of up to 2×10{sup 19} W/cm{sup 2}. A Thomson Parabola Spectrometer was used to identify different ion species and measure the energy spectra and the corresponding temperature parameters. We discuss the dependence of the protons spectra upon the structural characteristics of the targets (thickness and atomic mass) and the role of surface versus target bulk during acceleration process. - Highlights: • Ion acceleration mechanism in TNSA regime was investigated. • The energy spectra and the corresponding temperature parameters were measured. • Dependence of the spectra upon the target structural characteristics was discussed.

  11. Extracorporeal shock wave therapy in inflammatory diseases: molecular mechanism that triggers anti-inflammatory action.

    Mariotto, Sofia; de Prati, Alessandra Carcereri; Cavalieri, Elisabetta; Amelio, Ernesto; Marlinghaus, Ernst; Suzuki, Hisanori

    2009-01-01

    Shock waves (SW), defined as a sequence of single sonic pulses characterised by high peak pressure (100 MPa), a fast rise in pressure (conveyed by an appropriate generator to a specific target area at an energy density ranging from 0.03 to 0.11 mJ/mm(2). Extracorporeal SW (ESW) therapy was first used on patients in 1980 to break up kidney stones. During the last ten years, this technique has been successfully employed in orthopaedic diseases such as pseudoarthosis, tendinitis, calcarea of the shoulder, epicondylitis, plantar fasciitis and several inflammatory tendon diseases. In particular, treatment of the tendon and muscle tissues was found to induce a long-time tissue regeneration effect in addition to having a more immediate anthalgic and anti-inflammatory outcome. In keeping with this, an increase in neoangiogenesis in the tendons of dogs was observed after 4-8 weeks of ESW treatment. Furthermore, clinical observations indicate an immediate increase in blood flow around the treated area. Nevertheless, the biochemical mechanisms underlying these effects have yet to be fully elucidated. In the present review, we briefly detail the physical properties of ESW and clinical cases treated with this therapy. We then go on to describe the possible molecular mechanism that triggers the anti-inflammatory action of ESW, focusing on the possibility that ESW may modulate endogenous nitric oxide (NO) production either under normal or inflammatory conditions. Data on the rapid enhancement of endothelial NO synthase (eNOS) activity in ESW-treated cells suggest that increased NO levels and the subsequent suppression of NF-kappaB activation may account, at least in part, for the clinically beneficial action on tissue inflammation.

  12. A fast-starting mechanical fish that accelerates at 40 m s-2

    Conte, J; Modarres-Sadeghi, Y; Watts, M N; Hover, F S; Triantafyllou, M S

    2010-01-01

    We have built a simple mechanical system to emulate the fast-start performance of fish. The system consists of a thin metal beam covered by a urethane rubber, the fish body and an appropriately shaped tail. The body form of the mechanical fish was modeled after a pike species and selected because it is a widely-studied fast-start specialist. The mechanical fish was held in curvature and hung in water by two restraining lines, which were simultaneously released by a pneumatic cutting mechanism. The potential energy in the beam was transferred into the fluid, thereby accelerating the fish. We measured the resulting acceleration, and calculated the efficiency of propulsion for the mechanical fish model, defined as the ratio of the final kinetic energy of the fish and the initially stored potential energy in the body beam. We also ran a series of flow visualization tests to observe the resulting flow patterns. The maximum start-up acceleration was measured to be around 40 m s -2 , with the maximum final velocity around 1.2 m s -1 . The form of the measured acceleration signal as function of time is quite similar to that of type I fast-start motions studied by Harper and Blake (1991 J. Exp. Biol. 155 175-92). The hydrodynamic efficiency of the fish was found to be around 10%. Flow visualization of the mechanical fast-start wake was also analyzed, showing that the acceleration peaks are associated with the shedding of two vortex rings in near-lateral directions.

  13. Impact of Shock Front Rippling and Self-reformation on the Electron Dynamics at Low-Mach-number Shocks

    Yang, Zhongwei; Lu, Quanming; Liu, Ying D.; Wang, Rui

    2018-04-01

    Electron dynamics at low-Mach-number collisionless shocks are investigated by using two-dimensional electromagnetic particle-in-cell simulations with various shock normal angles. We found: (1) The reflected ions and incident electrons at the shock front provide an effective mechanism for the quasi-electrostatic wave generation due to the charge-separation. A fraction of incident electrons can be effectively trapped and accelerated at the leading edge of the shock foot. (2) At quasi-perpendicular shocks, the electron trapping and reflection is nonuniform due to the shock rippling along the shock surface and is more likely to take place at some locations accompanied by intense reflected ion-beams. The electron trapping process has a periodical evolution over time due to the shock front self-reformation, which is controlled by ion dynamics. Thus, this is a cross-scale coupling phenomenon. (3) At quasi-parallel shocks, reflected ions can travel far back upstream. Consequently, quasi-electrostatic waves can be excited in the shock transition and the foreshock region. The electron trajectory analysis shows these waves can trap electrons at the foot region and reflect a fraction of them far back upstream. Simulation runs in this paper indicate that the micro-turbulence at the shock foot can provide a possible scenario for producing the reflected electron beam, which is a basic condition for the type II radio burst emission at low-Mach-number interplanetary shocks driven by Coronal Mass Ejections (CMEs).

  14. Mechanical design and construction of a 200 mA, 100 keV, DC, negative ion accelerator

    Purgalis, P.; Anderson, O.A.; Cooper, W.S.; Cummings, C.; Koehler, G.W.; Matuk, C.A.; Wells, R.P.

    1987-01-01

    A volume production source and a 100 keV, dc, accelerator together with an additional, modular, 100 keV, electro static focused accelerator provide a starting point for a high energy H - /D - beamline (200 keV to 800 keV), intended for fusion energy applications. The 100 keV accelerator tests started in June 1987. The mechanical design and construction of the accelerator is described

  15. MIGRE: an Expert System as an aid for loose part diagnosis and mechanical shocks interpretation in nuclear plant

    Monnier, B.; Puyal, C.; Fernandes, A.; Martin, C.

    1990-01-01

    This paper presents an application of the expert system technique to one of the functions which participate to the surveillance of the primary circuit of water-pressurized reactors: the detection of loose parts and the interpretation of mechanical shocks. First, we describe the domain of expertise and the context in which this expert system will be used. Then we deal with the principles and the different levels involved in the knowledge modeling and with the structure of the expert system

  16. Particle acceleration in the interplanetary medium

    Engelmann, J.J.

    1987-07-01

    Variations in solar wind properties are dominated by a number of high speed streams. By interacting with the quiet wind, the fast streams give rise in the first case to a travelling shock wave, in the second case to a pair of forward and backward shock waves, by which the interaction region, corotating with the sun, is bounded. Two acceleration mechanisms are invoked to account for the energetic ion flux increases: 1) The first order Fermi process, whereby particles increase their energy by compression between converging magnetic scattering centers, located upstream and downstream of the shock. 2) The shock drift mechanism. The composition and the spectrum of the accelerated ions suggest that they probably originate from the suprathermal tail of the solar wind distribution [fr

  17. Molecular mechanisms of the angiogenic effects of low-energy shock wave therapy: roles of mechanotransduction.

    Hatanaka, Kazuaki; Ito, Kenta; Shindo, Tomohiko; Kagaya, Yuta; Ogata, Tsuyoshi; Eguchi, Kumiko; Kurosawa, Ryo; Shimokawa, Hiroaki

    2016-09-01

    We have previously demonstrated that low-energy extracorporeal cardiac shock wave (SW) therapy improves myocardial ischemia through enhanced myocardial angiogenesis in a porcine model of chronic myocardial ischemia and in patients with refractory angina pectoris. However, the detailed molecular mechanisms for the SW-induced angiogenesis remain unclear. In this study, we thus examined the effects of SW irradiation on intracellular signaling pathways in vitro. Cultured human umbilical vein endothelial cells (HUVECs) were treated with 800 shots of low-energy SW (1 Hz at an energy level of 0.03 mJ/mm(2)). The SW therapy significantly upregulated mRNA expression and protein levels of vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS). The SW therapy also enhanced phosphorylation of extracellular signal-regulated kinase 1/2 (Erk1/2) and Akt. Furthermore, the SW therapy enhanced phosphorylation of caveolin-1 and the expression of HUTS-4 that represents β1-integrin activity. These results suggest that caveolin-1 and β1-integrin are involved in the SW-induced activation of angiogenic signaling pathways. To further examine the signaling pathways involved in the SW-induced angiogenesis, HUVECs were transfected with siRNA of either β1-integrin or caveolin-1. Knockdown of either caveolin-1 or β1-integrin suppressed the SW-induced phosphorylation of Erk1/2 and Akt and upregulation of VEGF and eNOS. Knockdown of either caveolin-1 or β1-integrin also suppressed SW-induced enhancement of HUVEC migration in scratch assay. These results suggest that activation of mechanosensors on cell membranes, such as caveolin-1 and β1-integrin, and subsequent phosphorylation of Erk and Akt may play pivotal roles in the SW-induced angiogenesis. Copyright © 2016 the American Physiological Society.

  18. FAVOR: A new fracture mechanics code for reactor pressure vessels subjected to pressurized thermal shock

    Dickson, T.L.

    1993-01-01

    Probabilistic fracture mechanics (PFM) analysis is a major element of the comprehensive probabilistic methodology endorsed by the Nuclear Regulatory Commission (NRC) for evaluation of the integrity of pressurized water reactor pressure vessels subjected to pressurized-thermal-shock (PTS) transients. OCA-P and VISA-II are PTS PFM computer codes that are currently referenced in Regulatory Guide 1.154 as acceptable codes for performing plant-specific analyses. These codes perform PFM analyses to estimate the increase in vessel failure probability as the vessel accumulates radiation damage over the operating life of the vessel. Experience with the application of these codes in the last few years has provided insights into areas where they could be improved. As more plants approach the PTS screening criteria and are required to perform plant-specific analyses, there will be an increasing need for an improved and validated PTS PFM code that is accepted by the NRC and utilities. The NRC funded Heavy Section Steel Technology Program (HSST) at the Oak Ridge National Laboratory is currently developing the FAVOR (Fracture Analysis of Vessels: Oak Ridge) code, which is expected to meet this need. The FAVOR code incorporates the most important features of both OCA-P and VISA-II and contains some new capabilities such as (1) a PFM global modeling methodology; (2) the calculation of the axial stress component associated with coolant streaming beneath an inlet nozzle; (3) a library of stress intensity factor influence coefficients, generated by the NQA-1 certified ABAQUS computer code, for an appropriate range of two and three dimensional inner-surface flaws; (4) the flexibility to generate a variety of output reports; and (5) enhanced user friendliness

  19. Characterization of shocked beryllium

    Papin P.A.

    2012-08-01

    Full Text Available While numerous studies have investigated the low-strain-rate constitutive response of beryllium, the combined influence of high strain rate and temperature on the mechanical behavior and microstructure of beryllium has received limited attention over the last 40 years. In the current work, high strain rate tests were conducted using both explosive drive and a gas gun to accelerate the material. Prior studies have focused on tensile loading behavior, or limited conditions of dynamic strain rate and/or temperature. Two constitutive strength (plasticity models, the Preston-Tonks-Wallace (PTW and Mechanical Threshold Stress (MTS models, were calibrated using common quasi-static and Hopkinson bar data. However, simulations with the two models give noticeably different results when compared with the measured experimental wave profiles. The experimental results indicate that, even if fractured by the initial shock loading, the Be remains sufficiently intact to support a shear stress following partial release and subsequent shock re-loading. Additional “arrested” drive shots were designed and tested to minimize the reflected tensile pulse in the sample. These tests were done to both validate the model and to put large shock induced compressive loads into the beryllium sample.

  20. Method for the mechanical axis alignment of the linear induction accelerator

    Li Hong; China Academy of Engineering Physics, Mianyang; Yao Jin; Liu Yunlong; Zhang Linwen; Deng Jianjun

    2004-01-01

    Accurate mechanical axis alignment is a basic requirement for assembling a linear induction accelerator (LIA). The total length of an LIA is usually over thirty or fifty meters, and it consists of many induction cells. By using a laser tracker a new method of mechanical axis alignment for LIA is established to achieve the high accuracy. This paper introduces the method and gives implementation step and point position measure errors of the mechanical axis alignment. During the alignment process a 55 m-long alignment control survey net is built, and the theoretic revision of the coordinate of the control survey net is presented. (authors)

  1. Assembly Test of Elastic Averaging Technique to Improve Mechanical Alignment for Accelerating Structure Assemblies in CLIC

    Huopana, J

    2010-01-01

    The CLIC (Compact LInear Collider) is being studied at CERN as a potential multi-TeV e+e- collider [1]. The manufacturing and assembly tolerances for the required RF-components are important for the final efficiency and for the operation of CLIC. The proper function of an accelerating structure is very sensitive to errors in shape and location of the accelerating cavity. This causes considerable issues in the field of mechanical design and manufacturing. Currently the design of the accelerating structures is a disk design. Alternatively it is possible to create the accelerating assembly from quadrants, which favour the mass manufacturing. The functional shape inside of the accelerating structure remains the same and a single assembly uses less parts. The alignment of these quadrants has been previously made kinematic by using steel pins or spheres to align the pieces together. This method proved to be a quite tedious and time consuming method of assembly. To limit the number of different error sources, a meth...

  2. Release of Bacterial Spores from the Inner Walls of a Stainless Steel Cup Subjected to Thermal Stresses and Mechanical Shock

    Wolochow, H.; Chatigny, M.; Hebert, J.

    1973-01-01

    The release and fallout of particulates from surfaces afforded thermal or impact stress is of concern for control of contamination of Mars from planetary landing vehicles. A metal vessel contaminated by aerosols of spores was used as a model system and the fallout of spores as affected by various mechanisms was examined. Thermal stresses simulating those expected on the Mars lander dislodged approximately .01% of the aerosol deposited surface burden as did a landing shock of 8 to 10G deceleration. Spores imprinted by finger or swab contact yielded similar results. In all cases where repeated cycling of temperature, motion, or shock were employed the majority of fallout occurred in the first cycle. Particles released from the surface were predominantly in the size range 1 to 5 microns.

  3. Thermo-mechanical design of the SINGAP accelerator grids for ITER NB injectors

    Agostinetti, P. [Consorzio RFX, Euratom-ENEA Association, Corso Stati Uniti 4, I35127 Padova (Italy)], E-mail: piero.agostinetti@igi.cnr.it; Dal Bello, S.; Dalla Palma, M.; Zaccaria, P. [Consorzio RFX, Euratom-ENEA Association, Corso Stati Uniti 4, I35127 Padova (Italy)

    2007-10-15

    The SINGle Aperture-SINgle GAP (SINGAP) accelerator for ITER neutral beam injector foresees four grids for the extraction and acceleration of negative ions, instead of the seven grids of the Multi-Aperture Multi-Grid (MAMuG) reference configuration. The grids have to fulfil specific requirements coming from ion extraction, beam optics and thermo-mechanical issues. This paper focuses on the thermo-hydraulic and thermo-mechanical design of the grids carried out by Consorzio RFX for the design of the first ITER NB injector and the ITER NB Test Facility. The cooling circuit design (position and shape of the channels) and the cooling parameters (water coolant temperatures, pressure and velocity) were optimized with sensitivity analyses in order to satisfy the grid functional requirements (temperatures, stresses, in plane and out of plane deformations). The design required a complete modelling of the grids and their support frames by means of 3D FE and CAD models.

  4. Signal of Acceleration and Physical Mechanism of Water Cycle in Xinjiang, China

    Feng, Guo-Lin; Wu, Yong-Ping

    2016-01-01

    Global warming accelerates water cycle with features of regional difference. However, little is known about the physical mechanism behind the phenomenon. To reveal the links between water cycle and climatic environment, we analyzed the changes of water cycle elements and their relationships with climatic and environmental factors. We found that when global warming was significant during the period of 1986-2003, the precipitation in Tarim mountains as well as Xinjiang increased rapidly except ...

  5. Mechanical properties of electrospun PCL scaffold under in vitro and accelerated degradation conditions

    Løvdal, Alexandra Liv Vest; Vange, Jakob; Nielsen, Lene Feldskov

    2014-01-01

    Within recent years, researchers have looked into using polycaprolactone (PCL) as a synthetic biodegradable scaffold for tissue engineering purposes. This study investigated the mechanical properties of an electrospun PCL, while being exposed to physiological fluids at 37C (in vitro conditions) w...... in buffer (pH 12). The accelerated study showed a linear decrease in both elastic modulus and yield stress as a function of degradation time....

  6. Controlled by the Corporate Narrative: Obama's Education Policy, the Shock Doctrine, and Mechanisms of Capitalist Power

    Lea, Virginia

    2011-01-01

    This article aims to illuminate how and why public schools have been sustained and/or strengthened as hierarchical, inequitable, and undemocratic sites that serve the corporate capitalist state. In doing so, the author draws on three theoretical ideas: the "shock doctrine," described vividly by Naomi Klein (2007); "critical…

  7. A primary standard for low-g shock calibration by laser interferometry

    Sun, Qiao; Wang, Jian-lin; Hu, Hong-bo

    2014-01-01

    This paper presents a novel implementation of a primary standard for low-g shock acceleration calibration by laser interferometry based on rigid body collision at National Institute of Metrology, China. The mechanical structure of the standard device and working principles involved in the shock acceleration exciter, laser interferometers and virtual instruments are described. The novel combination of an electromagnetic exciter and a pneumatic exciter as the mechanical power supply of the standard device can deliver a wide range of shock acceleration levels. In addition to polyurethane rubber, two other types of material are investigated to ensure a wide selection of cushioning pads for shock pulse generation, with pulse shapes and data displayed. A heterodyne He–Ne laser interferometer is preferred for its precise and reliable measurement of shock acceleration while a homodyne one serves as a check standard. Some calibration results of a standard acceleration measuring chain are shown in company with the uncertainty evaluation budget. The expanded calibration uncertainty of shock sensitivity of the acceleration measuring chain is 0.8%, k = 2, with the peak acceleration range from 20 to 10 000 m s −2  and pulse duration from 0.5 to 10 ms. This primary shock standard can meet the traceability requirements of shock acceleration from various applications of industries from automobile to civil engineering and therefore is used for piloting the ongoing shock comparison of Technical Committee of Acoustics, Ultrasound and Vibration (TCAUV) of Asia Pacific Metrology Program (APMP), coded as APMP.AUV.V-P1. (paper)

  8. Cavitation behavior observed in three monoleaflet mechanical heart valves under accelerated testing conditions.

    Lo, Chi-Wen; Liu, Jia-Shing; Li, Chi-Pei; Lu, Po-Chien; Hwang, Ned H

    2008-01-01

    Accelerated testing provides a substantial amount of data on mechanical heart valve durability in a short period of time, but such conditions may not accurately reflect in vivo performance. Cavitation, which occurs during mechanical heart valve closure when local flow field pressure decreases below vapor pressure, is thought to play a role in valve damage under accelerated conditions. The underlying flow dynamics and mechanisms behind cavitation bubble formation are poorly understood. Under physiologic conditions, random perivalvular cavitation is difficult to capture. We applied accelerated testing at a pulse rate of 600 bpm and transvalvular pressure of 120 mm Hg, with synchronized videographs and high-frequency pressure measurements, to study cavitation of the Medtronic Hall Standard (MHS), Medtronic Hall D-16 (MHD), and Omni Carbon (OC) valves. Results showed cavitation bubbles between 340 and 360 micros after leaflet/housing impact of the MHS, MHD, and OC valves, intensified by significant leaflet rebound. Squeeze flow, Venturi, and water hammer effects each contributed to cavitation, depending on valve design.

  9. Quality control methods for linear accelerator radiation and mechanical axes alignment.

    Létourneau, Daniel; Keller, Harald; Becker, Nathan; Amin, Md Nurul; Norrlinger, Bernhard; Jaffray, David A

    2018-06-01

    The delivery accuracy of highly conformal dose distributions generated using intensity modulation and collimator, gantry, and couch degrees of freedom is directly affected by the quality of the alignment between the radiation beam and the mechanical axes of a linear accelerator. For this purpose, quality control (QC) guidelines recommend a tolerance of ±1 mm for the coincidence of the radiation and mechanical isocenters. Traditional QC methods for assessment of radiation and mechanical axes alignment (based on pointer alignment) are time consuming and complex tasks that provide limited accuracy. In this work, an automated test suite based on an analytical model of the linear accelerator motions was developed to streamline the QC of radiation and mechanical axes alignment. The proposed method used the automated analysis of megavoltage images of two simple task-specific phantoms acquired at different linear accelerator settings to determine the coincidence of the radiation and mechanical isocenters. The sensitivity and accuracy of the test suite were validated by introducing actual misalignments on a linear accelerator between the radiation axis and the mechanical axes using both beam steering and mechanical adjustments of the gantry and couch. The validation demonstrated that the new QC method can detect sub-millimeter misalignment between the radiation axis and the three mechanical axes of rotation. A displacement of the radiation source of 0.2 mm using beam steering parameters was easily detectable with the proposed collimator rotation axis test. Mechanical misalignments of the gantry and couch rotation axes of the same magnitude (0.2 mm) were also detectable using the new gantry and couch rotation axis tests. For the couch rotation axis, the phantom and test design allow detection of both translational and tilt misalignments with the radiation beam axis. For the collimator rotation axis, the test can isolate the misalignment between the beam radiation axis

  10. Contributions to the study of astrophysical plasmas. From accretion-ejection flows to particle acceleration in shocks

    Casse, Fabien

    2013-01-01

    After having outlined that the study of turbulence is a point of convergence between mathematics and physics, and that magnetic turbulence is omnipresent in astrophysical plasmas and also present in the interstellar medium, in stars and in their environment, in accretion disks, at the vicinity of shocks, and so on, the author proposes an overview of his research works which started with a research thesis on magnetised accretion disks and transport of relativistic particles in a magnetic turbulence. So, in this report for an accreditation to supervise research (HDR), he first focuses on physics of systems in accretion, and particularly on magnetised accretion-ejection structures. He evokes his work on a stationary modelling of these structures, on magnetohydrodynamics digital simulation of these systems, and on some instabilities in accretion disks and their interest in astrophysics. In a second part, the author reports his works on numerical assessment of coefficients of spatial diffusion of cosmic rays in a magnetic turbulence, and the description of multi-scale environments such as supernovae debris or different regions of extra-galactic jets.

  11. Generation of mesoscale magnetic fields and the dynamics of Cosmic Ray acceleration

    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.

  12. Intra-pulse transition between ion acceleration mechanisms in intense laser-foil interactions

    Padda, H.; King, M.; Gray, R. J.; Powell, H. W.; Gonzalez-Izquierdo, B.; Wilson, R.; Dance, R. J.; MacLellan, D. A.; Butler, N. M. H.; Capdessus, R.; McKenna, P., E-mail: paul.mckenna@strath.ac.uk [SUPA Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Stockhausen, L. C. [Centro de Laseres Pulsados (CLPU), Parque Cientifico, Calle del Adaja s/n. 37185 Villamayor, Salamanca (Spain); Carroll, D. C. [Central Laser Facility, STFC Rutherford Appleton Laboratory, Oxfordshire OX11 0QX (United Kingdom); Yuan, X. H. [Key Laboratory for Laser Plasmas (Ministry of Education) and Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of IFSA (CICIFSA), Shanghai Jiao Tong University, Shanghai 200240 (China); Borghesi, M. [Centre for Plasma Physics, Queens University Belfast, Belfast BT7 1NN (United Kingdom); Neely, D. [SUPA Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Central Laser Facility, STFC Rutherford Appleton Laboratory, Oxfordshire OX11 0QX (United Kingdom)

    2016-06-15

    Multiple ion acceleration mechanisms can occur when an ultrathin foil is irradiated with an intense laser pulse, with the dominant mechanism changing over the course of the interaction. Measurement of the spatial-intensity distribution of the beam of energetic protons is used to investigate the transition from radiation pressure acceleration to transparency-driven processes. It is shown numerically that radiation pressure drives an increased expansion of the target ions within the spatial extent of the laser focal spot, which induces a radial deflection of relatively low energy sheath-accelerated protons to form an annular distribution. Through variation of the target foil thickness, the opening angle of the ring is shown to be correlated to the point in time transparency occurs during the interaction and is maximized when it occurs at the peak of the laser intensity profile. Corresponding experimental measurements of the ring size variation with target thickness exhibit the same trends and provide insight into the intra-pulse laser-plasma evolution.

  13. Effects and mechanisms of cavidine protecting mice against LPS-induced endotoxic shock

    Li, Weifeng, E-mail: liwf@mail.xjtu.edu.cn; Zhang, Hailin; Niu, Xiaofeng, E-mail: niuxf@mail.xjtu.edu.cn; Wang, Xiumei; Wang, Yu; He, Zehong; Yao, Huan

    2016-08-15

    LPS sensitized mice are usually considered as an experimental model of endotoxin shock. The present study aims to evaluate effects of cavidine on LPS-induced endotoxin shock. Mice were intraperitoneally administrated with cavidine (1, 3 and 10 mg/kg) or DEX (5 mg/kg) at 1 and 12 h before injecting LPS (30 mg/kg) intraperitoneally. Blood samples, liver, lung and kidney tissues were harvested after LPS injection. The study demonstrated that pretreatment with cavidine reduced the mortality of mice during 72 h after endotoxin injection. In addition, cavidine administration significantly attenuated histological pathophysiology features of LPS-induced injury in lung, liver and kidney. Furthermore, cavidine administration inhibited endotoxin-induced production of pro-inflammatory cytokines including TNF-α, IL-6 and HMGB1. Moreover, cavidine pretreatment attenuated the phosphorylation of mitogen-activated protein kinase primed by LPS. In summary, cavidine protects mice against LPS-induced endotoxic shock via inhibiting early pro-inflammatory cytokine TNF-α, IL-6 and late-phase cytokine HMGB1, and the modulation of HMGB1 may be related with MAPK signal pathway. - Highlights: • Cavidine significantly reduced mortality in mice during 72 h after LPS injection. • Cavidine attenuated histopathological changes in lung, liver and kidney. • Cavidine decreased the level of early inflammatory cytokine TNF-α, IL-6 in LPS- stimulated mice. • Cavidine inhibited late inflammatory cytokine HMGB1 through MAPK pathway.

  14. Microstructural response and grain refinement mechanism of commercially pure titanium subjected to multiple laser shock peening impacts

    Lu, J.Z.; Wu, L.J.; Sun, G.F.; Luo, K.Y.; Zhang, Y.K.; Cai, J.; Cui, C.Y.; Luo, X.M.

    2017-01-01

    The microstructural response and grain subdivision process in commercially pure (CP) titanium subjected to multiple laser shock peening (LSP) impacts were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. The micro-hardness curves as a function of the impact time were also determined. The deformation-induced grain refinement mechanism of the close-packed hexagonal (hcp) material by laser shock wave was subsequently analyzed. Experimental results showed that uniform equiaxed grains with an average size of less than 50 nm were generated due to the ultra-high plastic strain induced by multiple LSP impacts. Special attention was paid to four types of novel deformation-induced microstructural features, including a layered slip band in the tension deformation zone, and inverse-transformation martensite, micro-twin grating and micro-twin collision in the compression deformation zone. Furthermore, the grain refinement mechanism in the near-surface layer of CP titanium subjected to multiple LSP impacts contains two types of simultaneous subdivision modes: multi-directional mechanical twin (MT)-MT intersections at (sub)micrometer scale, and the intersection between longitudinal secondary MTs and transverse dislocation walls at nanometer scale. In addition, both grain refinement (nanocrystallization) and the existence of a small amount of inverse-transformation martensite induced by multiple LSP impacts contribute to an increase in the micro-hardness of the near-surface layer.

  15. Mechanical design of recirculating accelerator experiments for heavy-ion fusion

    Karpenko, V.

    1995-01-01

    Recirculating induction accelerators have been studied as a potential low cost driver for inertial fusion energy. At LLNL, we are developing a small (4.5-m diameter), scaled, experimental machine which will demonstrate many of the engineering solutions of a full scale driver. The small recirculator will accelerate singly ionized potassium ions from 80 to 320 keV and 2 to 8 mA, using electric dipoles for bending and permanent magnet quadrupoles for focusing in a compact periodic lattice. While very compact, and low cost, this design allows the investigation of most of the critical physics issues associated with space-charge-dominated beams in future IFE power plant drivers. This report describes the recirculator, its mechanical design, its vacuum design, and the process for aligning it. Additionally, a straight magnetic transport experiment is being carried out to test diagnostics and magnetic transport in preparation for the recirculator

  16. Thermo-mechanical design of the SINGAP accelerator grids for ITER NB Injectors

    Agostinetti, P.; Dal Bello, S.; Palma, M.D.; Zaccaria, P.

    2006-01-01

    The SINGle Aperture - SINgle GAP (SINGAP) accelerator for ITER neutral beam injector foresees four grids for the extraction and acceleration of negative ions, instead of the seven grids of the Multi Aperture Multi Grid (MAMuG) reference configuration. Optimized geometry of the SINGAP grids (plasma, extraction, pre-acceleration, and grounded grid) was identified by CEA Association considering specific requirements for ions extraction and beam generation referring to experimental data and code simulations. This paper focuses on the thermo-hydraulic and thermo-mechanical design of the grids carried out by Consorzio RFX for the design of the first ITER NB Injector and the ITER NB Test Facility. The cooling circuit design (position and shape of the channels) and the cooling parameters (water coolant temperatures, pressure and velocity) were optimized with thermo-hydraulic and thermo-mechanical sensitivity analyses in order to satisfy the grid functional requirements (temperatures, in plane and out of plane deformations). A complete and detailed thermo-structural design assessment of the SINGAP grids was accomplished applying the structural design rules for ITER in-vessel components and considering both the reference load conditions and the maximum load provided by the power supplies. The design required a complete modelling of the grids and their support frames by means of 3D FE and CAD models. The grids were finally integrated with the support and cooling systems inside the beam source vessel. The main results of the thermo-hydraulic and thermo-mechanical analyses are presented. The open issues are then reported, mainly regarding the material properties characterization (static and fatigue tests) and the qualification of technologies for OFHC copper electro-deposition, brazing, and welding of heterogeneous materials. (author)

  17. An overview of low back pain and occupational exposures to whole-body vibration and mechanical shocks.

    Bovenzi, Massimo; Schust, Marianne; Mauro, Marcella

    2017-12-14

    This paper offers an overview of the relation of low back pain (LBP) to occupational exposures to whole-body vibration (WBV) and mechanical shocks. LBP is a condition of multifactorial origin and is a very common health problem in the general population. Among occupational risk factors, epidemiological studies of driving occupations have provided evidence for strong associations between LBP and occupational exposures to WBV and mechanical shocks. Since it is hard to separate the contribution of WBV exposure to disorders in the lower back from that of other individual, ergonomic or psychosocial risk factors, a quantitative exposure-response relationship for WBV cannot be outlined precisely. Experimental research has provided biodynamic support to the findings of epidemiological studies, showing that in controlled laboratory conditions exposure to WBV can cause mechanical overload to the human spine. The EU Directive on mechanical vibration has established daily exposure action and limit values to protect the workers against the risk from WBV. There is some evidence that the EU exposure limit values are excessive, so much so that an elevated risk of LBP has been found for WBV exposures beneath the EU limit values. In the Italian arm of the EU VIBRISKS prospective cohort study of professional drivers, measures of internal lumbar load (compressive and shear peak forces), calculated by means of anatomy-based finite-element models, were found better predictors of the occurrence over time of low back disorders than the metrics of external exposure suggested by the EU Directive on mechanical vibration. Further biodynamic and epidemiological studies are needed to validate the findings of the VIBRISKS study.

  18. Members of the heat-shock protein 70 family promote cancer cell growth by distinct mechanisms

    Rohde, Mikkel; Daugaard, Mads; Jensen, Mette Hartvig

    2005-01-01

    Whereas the stress-inducible heat-shock protein 70 (Hsp70) has gained plenty of attention as a putative target for tumor therapy, little is known about the role of other Hsp70 proteins in cancer. Here we present the first thorough analysis of the expression and function of the cytosolic Hsp70...... proteins in human cancer cells and identify Hsp70-2, a protein essential for spermatogenesis, as an important regulator of cancer cell growth. Targeted knock-down of the individual family members by RNA interference revealed that both Hsp70 and Hsp70-2 were required for cancer cell growth, whereas...

  19. A “slingshot” laser-driven acceleration mechanism of plasma electrons

    Fiore, Gaetano, E-mail: gaetano.fiore@na.infn.it [Dip. di Matematica e Applicazioni, Università “Federico II”, Complesso Universitario M. S. Angelo, Via Cintia, 80126 Napoli (Italy); INFN, Sezione di Napoli, Complesso Universitario M. S. Angelo, Via Cintia, 80126 Napoli (Italy); De Nicola, Sergio [SPIN-CNR, Complesso Universitario M. S. Angelo, Via Cintia, 80126 Napoli (Italy); INFN, Sezione di Napoli, Complesso Universitario M. S. Angelo, Via Cintia, 80126 Napoli (Italy)

    2016-09-01

    We briefly report on the recently proposed Fiore et al. [1] and Fiore and De Nicola [2] electron acceleration mechanism named “slingshot effect”: under suitable conditions the impact of an ultra-short and ultra-intense laser pulse against the surface of a low-density plasma is expected to cause the expulsion of a bunch of superficial electrons with high energy in the direction opposite to that of the pulse propagation; this is due to the interplay of the huge ponderomotive force, huge longitudinal field arising from charge separation, and the finite size of the laser spot.

  20. Mechanical design considerations of a standing wave s-band accelerator with on-axis couplers

    Hodge, S.B.; Funk, L.W.; Schriber, S.O.

    1976-01-01

    The mechanical design of S-band standing wave accelerator structures with on-axis coupling cells includes material selection, cavity design, segment production, rf tuning and brazing procedures. Pre-assembly tuning operations have been minimized by determining segment dimensions and tolerances so that segments can easily be fabricated in a near-finished condition by a commercial machining firm. Final tuning, if necessary, is easily achieved by removal of material from the cavity wall or drift tube nose. Considerations in choosing brazing procedures were vacuum integrity, resistivity of brazing alloy, joint thickness, alignment of the structure assembly and restriction of grain growth. (author)

  1. VDE characteristics during disruption process and its underlying acceleration mechanism in the ITER-EDA tokamak

    Nakamura, Yukiharu; Nishio, Satoshi; Yoshino, Ryuji; Kessel, C.E.; Jardin, S.C.

    1996-01-01

    The dynamic behavior of vertical displacement events (VDEs) during a disruption and acceleration mechanisms that govern VDEs in the ITER-EDA tokamak are investigated using the Tokamak Simulation Code. A sudden plasma pressure drop (β p collapse) does not accelerate VDEs for the ITER tokamak. The geometry of the ITER resistive shell is shown to be suitable for preventing a β p collapse-induced VDE, because the magnetic field decay n-index after the β p collapse does not considerably degrade. On the other hand, it is shown that the plasma current quench (I p quench) following the energy quench can accelerate VDEs due to the vertical imbalance of the attractive force arising from the up-down asymmetric shell. The vertical location of the neutral point where the I p quench-induced VDE almost disappears is found to lie at ∼22 cm below the plasma magnetic axis of the nominal equilibrium (Z = 1.44 m). An upward and moderate I p quench-induced VDE can be expected for the nominal configuration in the ITER-EDA tokamak. It is shown that the ITER tokamak has an advantage of avoiding the fatal damage of the complicated structures of the bottom-divertor. (author)

  2. Training-induced acceleration of oxygen uptake kinetics in skeletal muscle: the underlying mechanisms.

    Zoladz, J A; Korzeniewski, B; Grassi, B

    2006-11-01

    It is well known that the oxygen uptake kinetics during rest-to-work transition (V(O2) on-kinetics) in trained subjects is significantly faster than in untrained individuals. It was recently postulated that the main system variable that determines the transition time (t(1/2)) of the V(O2) on-kinetics in skeletal muscle, at a given moderate ATP usage/work intensity, and under the assumption that creatine kinase reaction works near thermodynamic equilibrium, is the absolute (in mM) decrease in [PCr] during rest-to-work transition. Therefore we postulate that the training-induced acceleration of the V(O2) on-kinetics is a marker of an improvement of absolute metabolic stability in skeletal muscles. The most frequently postulated factor responsible for enhancement of muscle metabolic stability is the training-induced increase in mitochondrial proteins. However, the mechanism proposed by Gollnick and Saltin (1982) can improve absolute metabolic stability only if training leads to a decrease in resting [ADP(free)]. This effect is not observed in many examples of training causing an acceleration of the V(O2) on-kinetics, especially in early stages of training. Additionally, this mechanism cannot account for the significant training-induced increase in the relative (expressed in % or as multiples of the resting values) metabolic stability at low work intensities, condition in which oxidative phosphorylation is not saturated with [ADP(free)]. Finally, it was reported that in the early stage of training, acceleration in the V(O2) on-kinetics and enhancement of muscle metabolic stability may precede adaptive responses in mitochondrial enzymes activities or mitochondria content. We postulate that the training-induced acceleration in the V(O2) on-kinetics and the improvement of the metabolite stability during moderate intensity exercise in the early stage of training is mostly caused by an intensification of the "parallel activation" of ATP consumption and ATP supply pathways

  3. Computerized simulation of the mechanical behavior of wood-filled shock absorbers of radioactive materials transport casks

    Neumann, Martin; Wille, Frank

    2011-01-01

    In Germany the mechanical component inspection of transport containers for radioactive materials is performed by BAM (Bundesanstalt fuer Materialforschung und -pruefung) under consideration of national and international standards and guidelines. Experimental and calculative (analytical and numerical) techniques combined with material and/or component testing are the basis of assessment concepts according the state of the art. The authors describe the experiences of BAM concerning assessment and description of the mechanical behavior of shock absorbing components, including modeling strategies, material models, drop tests and experiment-calculation comparison. Energy absorbing components are used to reduce the impact forces at the container in case of a transport accident. In Germany wood filled thin-walled constructions are used. The deformation behavior of the wood is a main part of the calculative simulation procedures in comparison with experimental tests.

  4. Effect of mechanical ventilation on systemic oxygen extraction and lactic acidosis during early septic shock in rats.

    Griffel, M I; Astiz, M E; Rackow, E C; Weil, M H

    1990-01-01

    We studied the effect of mechanical ventilation on systemic oxygen extraction and lactic acidosis in peritonitis and shock in rats. Sepsis was induced by cecal ligation and perforation. After tracheostomy, rats were randomized to spontaneous breathing (S) or mechanical ventilation with paralysis (V). Five animals were studied in each group. The V animals were paralyzed with pancuronium bromide to eliminate respiratory effort. Mechanical ventilation consisted of controlled ventilation using a rodent respirator with periodic adjustment of minute ventilation to maintain PaCO2 and pH within normal range. Arterial and central venous blood gases and thermodilution cardiac output were measured at baseline before abdominal surgery, and sequentially at 0.5, 3.5, and 6 h after surgery. At 6 h, cardiac output was 193 +/- 30 ml/kg.min in S animals and 199 +/- 32 ml/kg.min in V animals (NS). The central venous oxygen saturation was 27.4 +/- 4.7% in S animals and 30.0 +/- 6.4% in V animals (NS). Systemic oxygen extraction was 70 +/- 5% in S animals and 67 +/- 6% in V animals (NS). Arterial lactate was 2.4 +/- 0.4 mmol/L in S animals and 2.2 +/- 0.5 mmol/L in V animals (NS). The S animals developed lethal hypotension at 6.6 +/- 0.4 h compared to 6.8 +/- 0.4 h in V animals (NS). These data suggest that mechanical ventilation does not decrease systemic oxygen extraction or ameliorate the development of lactic acidosis during septic shock.

  5. Computational methods for fracture mechanics analysis of pressurized-thermal-shock experiments

    Bass, B.R.; Bryan, R.H.; Bryson, J.W.; Merkle, J.G.

    1984-01-01

    Extensive computational analyses are required to determine material parameters and optimum pressure-temperature transients compatible with proposed pressurized-thermal-shock (PTS) test scenarios and with the capabilities of the PTS test facility at the Oak Ridge National Laboratory (ORNL). Computational economy has led to the application of techniques suitable for parametric studies involving the analysis of a large number of transients. These techniques, which include analysis capability for two- and three-dimensional (2-D and 3-D) superposition, inelastic ligament stability, and upper-shelf arrest, have been incorporated into the OCA/USA computer program. Features of the OCA/USA program are discussed, including applications to the PTS test configuration

  6. Computational methods for fracture mechanics analysis of pressurized-thermal-shock experiments

    Bass, B.R.; Bryan, R.H.; Bryson, J.W.; Merkle, J.G.

    1984-01-01

    Extensive computational analyses are required to determine material parameters and optimum pressure-temperature transients compatible with proposed pressurized-thermal-shock (PTS) test scenarios and with the capabilities of the PTS test facility at the Oak Ridge National Laboratory (ORNL). Computational economy has led to the application of techniques suitable for parametric studies involving the analysis of a large number of transients. These techniques, which include analysis capability for two- and three-dimensional (2-D and 3-D) superposition, inelastic ligament stability, and upper-shelf arrest, have been incorporated into the OCA/ USA computer program. Features of the OCA/USA program are discussed, including applications to the PTS test configuration. (author)

  7. Relativistic Electrons Produced by Foreshock Disturbances Observed Upstream of Earth's Bow Shock

    Wilson, L. B., III; Sibeck, D. G.; Turner, D. L.; Osmane, A.; Caprioli, D.; Angelopoulos, V.

    2016-01-01

    Charged particles can be reflected and accelerated by strong (i.e., high Mach number) astrophysical collisionless shock waves, streaming away to form a foreshock region in communication with the shock. Foreshocks are primarily populated by suprathermal ions that can generate foreshock disturbances-largescale (i.e., tens to thousands of thermal ion Larmor radii), transient (approximately 5-10 per day) structures. They have recently been found to accelerate ions to energies of several keV. Although electrons in Saturn's high Mach number (M > 40) bow shock can be accelerated to relativistic energies (nearly 1000 keV), it has hitherto been thought impossible to accelerate electrons beyond a few tens of keV at Earth's low Mach number (1 =M foreshock disturbances to energies up to at least approximately 300 keV. Although such energetic electrons have been previously observed, their presence has been attributed to escaping magnetospheric particles or solar events. These relativistic electrons are not associated with any solar or magnetospheric activity. Further, due to their relatively small Larmor radii (compared to magnetic gradient scale lengths) and large thermal speeds (compared to shock speeds), no known shock acceleration mechanism can energize thermal electrons up to relativistic energies. The discovery of relativistic electrons associated with foreshock structures commonly generated in astrophysical shocks could provide a new paradigm for electron injections and acceleration in collisionless plasmas.

  8. Shock Geometry and Spectral Breaks in Large SEP Events

    Li, G.; Zank, G. P.; Verkhoglyadova, Olga; Mewaldt, R. A.; Cohen, C. M. S.; Mason, G. M.; Desai, M. I.

    2009-09-01

    Solar energetic particle (SEP) events are traditionally classified as "impulsive" or "gradual." It is now widely accepted that in gradual SEP events, particles are accelerated at coronal mass ejection-driven (CME-driven) shocks. In many of these large SEP events, particle spectra exhibit double power law or exponential rollover features, with the break energy or rollover energy ordered as (Q/A)α, with Q being the ion charge in e and A the ion mass in units of proton mass mp . This Q/A dependence of the spectral breaks provides an opportunity to study the underlying acceleration mechanism. In this paper, we examine how the Q/A dependence may depend on shock geometry. Using the nonlinear guiding center theory, we show that α ~ 1/5 for a quasi-perpendicular shock. Such a weak Q/A dependence is in contrast to the quasi-parallel shock case where α can reach 2. This difference in α reflects the difference of the underlying parallel and perpendicular diffusion coefficients κ|| and κbottom. We also examine the Q/A dependence of the break energy for the most general oblique shock case. Our analysis offers a possible way to remotely examine the geometry of a CME-driven shock when it is close to the Sun, where the acceleration of particle to high energies occurs.

  9. Shock Waves

    Jiang, Z

    2005-01-01

    The International Symposium on Shock Waves (ISSW) is a well established series of conferences held every two years in a different location. A unique feature of the ISSW is the emphasis on bridging the gap between physicists and engineers working in fields as different as gas dynamics, fluid mechanics and materials sciences. The main results presented at these meetings constitute valuable proceedings that offer anyone working in this field an authoritative and comprehensive source of reference.

  10. Comparison of mechanical concepts for $Nb_3Sn$ high field accelerator magnets

    AUTHOR|(CDS)2084469; Peter, Schmolz

    Several magnets using Nb$_{3}$Sn as conductor are currently developed at CERN; these magnets are either slated for future updates of the LHC or for research purposes relating to future accelerators. The mechanical structure is one of the challenging aspects of superconducting high-field magnets. The main purpose of the mechanical structure is to keep the coils in compression till the emergence of the highest electromagnetic forces that are developed in the ultimate field of the magnet. Any loss of pre-compression during the magnet’s excitation would cause too large deformation of the coil and possibly a quench in the conductor owing to relative movements of strands in contact associated with excessive local heat release. However, too high pre-compression would overstrain the conductor and thereby limit the performance of the magnet. This thesis focuses on the mechanical behaviour of three of these magnets. All of them are based on different mechanical designs, “bladder and key” and “collar-based”, ...

  11. Integration of a linear accelerator into a production line of mechanically deboned separated poultry meat

    Sadat, Theo; Volle, Christophe

    2000-01-01

    Linear accelerators, commonly called Linacs, are being used for different industrial processes. This kind of machine produces high power electron beams and can treat many products with a high throughput. The main application of a Linac is the sterilization of medical disposable devices, polymerization and decontamination of food products. Salmonella commonly contaminates poultry. Thanks to E-beam treatment, it eradicates the pathogen quickly and permits the use of meat that should have been thrown away because of its infection. The world's first Linac dedicated to treat mechanically deboned poultry meat is located in Brittany at the Societe des Proteines Industrielles. It is a Thomson CSF Linac product, the CIRCE II, with an energy of 10 MeV and a power of 10 kW. This Linac has been used for more than 8 years, and its technology is fully proven. (author)

  12. Accelerating the implementation of the clean development mechanism in South African industry

    G Little

    2014-05-01

    Full Text Available One of the responses to the threat of global warming is the Kyoto Protocol and the associated Clean Development Mechanism (CDM to reduce greenhouse gases. South Africa is an ideal country for the implementation of industrial CDM projects, yet lags behind many other countries. This qualitative research determines the factors that cause South Africa to lag other developing countries in the implementation of industrial CDM projects and the interventions that will have the most impact on accelerating implementation. The research involved interviews with 30 experts involved in the South African CDM process. The results identify the factors perceived to be facilitating and inhibiting the use of CDM opportunities and a framework for CDM practitioners to develop an implementation strategy within South African industry is established.

  13. Improvement of the Error-detection Mechanism in Adults with Dyslexia Following Reading Acceleration Training.

    Horowitz-Kraus, Tzipi

    2016-05-01

    The error-detection mechanism aids in preventing error repetition during a given task. Electroencephalography demonstrates that error detection involves two event-related potential components: error-related and correct-response negativities (ERN and CRN, respectively). Dyslexia is characterized by slow, inaccurate reading. In particular, individuals with dyslexia have a less active error-detection mechanism during reading than typical readers. In the current study, we examined whether a reading training programme could improve the ability to recognize words automatically (lexical representations) in adults with dyslexia, thereby resulting in more efficient error detection during reading. Behavioural and electrophysiological measures were obtained using a lexical decision task before and after participants trained with the reading acceleration programme. ERN amplitudes were smaller in individuals with dyslexia than in typical readers before training but increased following training, as did behavioural reading scores. Differences between the pre-training and post-training ERN and CRN components were larger in individuals with dyslexia than in typical readers. Also, the error-detection mechanism as represented by the ERN/CRN complex might serve as a biomarker for dyslexia and be used to evaluate the effectiveness of reading intervention programmes. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

  14. Mechanical Behavior of Stainless Steel Fiber-Reinforced Composites Exposed to Accelerated Corrosion

    O’Brien, Caitlin; McBride, Amanda; E. Zaghi, Arash; Burke, Kelly A.; Hill, Alex

    2017-01-01

    Recent advancements in metal fibers have introduced a promising new type of stainless steel fiber with high stiffness, high failure strain, and a thickness corrosion. The main goal of this study is to compare the impact of corrosion on the mechanical properties of steel fiber-reinforced composites with those of conventional types of stainless steel. By providing experimental evidences, this study may promote the application of steel fiber-reinforced composite as a viable alternative to conventional metals. Samples of steel fiber-reinforced polymer and four different types of stainless steel were subjected to 144 and 288 h of corrosion in ferric chloride solution to simulate accelerated corrosion conditions. The weight losses due to corrosion were recorded. The corroded and control samples were tested under monotonic tensile loading to measure the ultimate stresses and strains. The effect of corrosion on the mechanical properties of the different materials was evaluated. The digital image correlation (DIC) technique was used to investigate the failure mechanism of the corrosion-damaged specimens. Overall, steel fiber-reinforced composites had the greatest corrosion resistance. PMID:28773132

  15. Mechanical Behavior of Nanostructured and Ultrafine Grained Materials under Shock Wave Loadings. Experimental Data and Results of Computer Simulation.

    Skripnyak, Vladimir

    2011-06-01

    Features of mechanical behavior of nanostructured (NS) and ultrafine grained (UFG) metal and ceramic materials under quasistatic and shock wave loadings are discussed in this report. Multilevel models developed within the approach of computational mechanics of materials were used for simulation mechanical behavior of UFG and NS metals and ceramics. Comparisons of simulation results with experimental data are presented. Models of mechanical behavior of nanostructured metal alloys takes into account a several structural factors influencing on the mechanical behavior of materials (type of a crystal lattice, density of dislocations, a size of dislocation substructures, concentration and size of phase precipitation, and distribution of grains sizes). Results show the strain rate sensitivity of the yield stress of UFG and polycrystalline alloys is various in a range from 103 up to 106 1/s. But the difference of the Hugoniot elastic limits of a UFG and coarse-grained alloys may be not considerable. The spall strength, the yield stress of UFG and NS alloys are depend not only on grains size, but a number of factors such as a distribution of grains sizes, a concentration and sizes of voids and cracks, a concentration and sizes of phase precipitation. Some titanium alloys with grain sizes from 300 to 500 nm have the quasi-static yield strength and the tensile strength twice higher than that of coarse grained counterparts. But the spall strength of the UFG titanium alloys is only 10 percents above than that of coarse grained alloys. At the same time it was found the spall strength of the bulk UFG aluminium and magnesium alloys with precipitation strengthening is essentially higher in comparison of coarse-grained counterparts. The considerable decreasing of the strain before failure of UFG alloys was predicted at high strain rates. The Hugoniot elastic limits of oxide nanoceramics depend not only on the porosity, but also on sizes and volume distribution of voids.

  16. A 20-year multicentre outcome analysis of salvage mechanical circulatory support for refractory cardiogenic shock after cardiac surgery

    Maziar Khorsandi

    2016-11-01

    Full Text Available Abstract Background Refractory post-cardiotomy cardiogenic shock (PCCS is a relatively rare phenomenon that can lead to rapid multi-organ dysfunction syndrome and is almost invariably fatal without advanced mechanical circulatory support (AMCS, namely extra-corporeal membrane oxygenation (ECMO or ventricular assist devices (VAD. In this multicentre observational study we retrospectively analyzed the outcomes of salvage venoarterial ECMO (VA ECMO and VAD for refractory PCCS in the 3 adult cardiothoracic surgery centres in Scotland over a 20-year period. Methods The data was obtained through the Edinburgh, Glasgow and Aberdeen cardiac surgery databases. Our inclusion criteria included any adult patient from April 1995 to April 2015 who had received salvage VA ECMO or VAD for PCCS refractory to intra-aortic balloon pump (IABP and maximal inotropic support following adult cardiac surgery. Results A total of 27 patients met the inclusion criteria. Age range was 34–83 years (median 51 years. There was a large male predominance (n = 23, 85 %. Overall 23 patients (85 % received VA ECMO of which 14 (61 % had central ECMO and 9 (39 % had peripheral ECMO. Four patients (15 % were treated with short-term VAD (BiVAD = 1, RVAD = 1 and LVAD = 2. The most common procedure-related complication was major haemorrhage (n = 10. Renal failure requiring renal replacement therapy (n = 7, fatal stroke (n = 5, septic shock (n = 2, and a pseudo-aneurysm at the femoral artery cannulation site (n = 1 were also observed. Overall survival to hospital discharge was 40.7 %. All survivors were NYHA class I-II at 12 months’ follow-up. Conclusion AMCS for refractory PCCS carries a survival benefit and achieves acceptable functional recovery despite a significant complication rate.

  17. Structural VAR analysis of monetary transmission mechanism and central bank’s response to equity volatility shock in Taiwan

    Lo, Chi-Sheng

    2016-01-01

    This research applies recursive Structural Vector Auto Regression (SVAR) model with short-run restriction into two kinds of shocks: monetary and volatility. The first SVAR estimates the shock of contractionary monetary policy on Taiwan’s key monthly macroeconomic variables including exports, CPI, exchange rate, money supply, and Taiwan Weighted Stock Exchange (TWSE) Index. The second SVAR estimates the shock of Generalized Autoregressive Conditional Heteroskedasticity (GARCH) volatility of TW...

  18. Experimental analysis on physical and mechanical properties of thermal shock damage of granite

    He Xiao

    2017-01-01

    Full Text Available The purpose of this study was to explore the changes of mechanical and physical properties of granite under different thermal loading effects. Uniaxial compression experiments studying the rules of the influence of temperature load on mechanical properties of granite were carried out. After high-temperature heating at above 600 °C, granite tended to have stronger ductility and plasticity as well as declined peak stress and compressive strength. Thermogravimetry - differential scanning calorimetry (TG-DSC analysis results showed that, thermal load at different temperatures induced reactions such as water loss, oxidation and crystallization in the microstructure of granite, which led to physical changes of granite. Hence it is concluded that, heating can significantly weaken the mechanical performance of granite, which provides an important support for the optimization of heating assisted processing of granite. It also reveals that, heating assisted cutting technique can effectively lower energy consumption and improve processing efficiency.

  19. Microstructure and mechanical properties of composite resins subjected to accelerated artificial aging.

    dos Reis, Andréa Cândido; de Castro, Denise Tornavoi; Schiavon, Marco Antônio; da Silva, Leandro Jardel; Agnelli, José Augusto Marcondes

    2013-01-01

    The aim of this study was to investigate the influence of accelerated artificial aging (AAA) on the microstructure and mechanical properties of the Filtek Z250, Filtek Supreme, 4 Seasons, Herculite, P60, Tetric Ceram, Charisma and Filtek Z100. composite resins. The composites were characterized by Fourier-transform Infrared spectroscopy (FTIR) and thermal analyses (Differential Scanning Calorimetry - DSC and Thermogravimetry - TG). The microstructure of the materials was examined by scanning electron microscopy. Surface hardness and compressive strength data of the resins were recorded and the mean values were analyzed statistically by ANOVA and Tukey's test (α=0.05). The results showed significant differences among the commercial brands for surface hardness (F=86.74, p<0.0001) and compressive strength (F=40.31, p<0.0001), but AAA did not affect the properties (surface hardness: F=0.39, p=0.53; compressive strength: F=2.82, p=0.09) of any of the composite resins. FTIR, DSC and TG analyses showed that resin polymerization was complete, and there were no differences between the spectra and thermal curve profiles of the materials obtained before and after AAA. TG confirmed the absence of volatile compounds and evidenced good thermal stability up to 200 °C, and similar amounts of residues were found in all resins evaluated before and after AAA. The AAA treatment did not significantly affect resin surface. Therefore, regardless of the resin brand, AAA did not influence the microstructure or the mechanical properties.

  20. The fastest disk wind in APM 08279+5255 and its acceleration mechanism

    Hagino, K.; Done, C.; Odaka, H.; Watanabe, S.; Takahashi, T.

    2017-10-01

    The luminous high-z quasar APM 08279+5255 has the most powerful ultra-fast outflow (UFO), which is claimed as the fastest disk wind with velocity of 0.7c. This extreme velocity is very important for constraining the physical mechanism to launch the UFOs because only magnetic driving mechanism can accelerate the winds up to velocities above 0.3c, at which radiation drag effects prevent radiation driving. We reanalyze all the observed data of this source with our spectral model of highly ionized disk winds constructed by 3D Monte Carlo radiation transfer simulation. This was applied to an archetypal disk wind in PDS 456, and successfully reproduced all the spectra observed with Suzaku in spite of their strong spectral variability. By applying our spectral model to APM 08279+5255, all the spectra observed with XMM-Newton, Chandra and Suzaku are explained with less extreme outflow velocities of 0.1-0.2c. In our analysis, the high energy absorption features, which were previously interpreted as absorption lines with extremely fast velocities, are produced by iron-K absorption edges from moderately ionized clumps embedded in the highly ionized wind. We also investigate the broadband SED, and find that it is X-ray weak and UV bright, which prefers the radiation driving.

  1. On the Effects of Viscosity on the Shock Waves for a Hydrodynamical Case—Part I: Basic Mechanism

    Huseyin Cavus

    2013-01-01

    Full Text Available The interaction of shock waves with viscosity is one of the central problems in the supersonic regime of compressible fluid flow. In this work, numerical solutions of unmagnetised fluid equations, with the viscous stress tensor, are investigated for a one-dimensional shock wave. In the algorithm developed the viscous stress terms are expressed in terms of the relevant Reynolds number. The algorithm concentrated on the compression rate, the entropy change, pressures, and Mach number ratios across the shock wave. The behaviour of solutions is obtained for the Reynolds and Mach numbers defining the medium and shock wave in the supersonic limits.

  2. Thermo-mechanical analysis of an acceleration grid for the international thermonuclear experimental reactor-neutral beam injection system

    Fujiwara, Yukio; Hanada, Masaya; Okumura, Yoshikazu; Suzuki, Satoshi; Watanabe, Kazuhiro

    2001-01-01

    In the engineering design of a negative-ion beam source for a high-power neutral beam injection (NBI) system, one of the most important issues is thermo-mechanical design of acceleration grids for producing several tens of MW ion beams. An acceleration grid for the international thermonuclear experimental reactor-neutral beam injection (ITER-NBI) system will be subjected to the heat loading as high as 1.5 MW. In the present paper, thermo-mechanical characteristics of the acceleration grid for the ITER-NBI system were analyzed. Numerical simulation indicated that maximum aperture-axis displacement of the acceleration grid due to thermal expansion would be about 0.7 mm for the heat loading of 1.5 MW. From the thin lens theory of beam optics, beamlet deflection angle by the aperture-axis displacement was estimated to be about 2 mrad, which is within the requirement of the engineering design of the ITER-NBI system. Numerical simulation also indicated that no melting on the acceleration grid would occur for a heat loading of 1.5 MW, while local plastic deformation would happen. To avoid the plastic deformation, it is necessary to reduce the heat loading onto the acceleration grid to less than 1 MW

  3. Fracture mechanics analysis of reactor pressure vessel under pressurized thermal shock - The effect of elastic-plastic behavior and stainless steel cladding -

    Joo, Jae Hwang; Kang, Ki Ju; Jhung, Myung Jo

    2002-01-01

    Performed here is an assessment study for deterministic fracture mechanics analysis of a pressurized thermal shock (PTS). The PTS event means an event or transient in pressurized water reactors (PWRs) causing severe overcooling (thermal shock) concurrent with or followed by significant pressure in the reactor vessel. The problems consisting of two transients and 10 cracks are solved and maximum stress intensity factors and maximum allowable nil-ductility reference temperatures are calculated. Their results are compared each other to address the general characteristics between transients, crack types and analysis methods. The effects of elastic-plastic material behavior and clad coating on the inner surface are explored

  4. Electron acceleration by wave turbulence in a magnetized plasma

    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.

  5. Shock-induced mechanical response and spall fracture behavior of an extra-low interstitial grade Ti–6Al–4V alloy

    Ren, Yu; Wang, Fuchi [School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); National Key Laboratory of Science and Technology on Materials Under Shock and Impact, Beijing Institute of Technology, Beijing 100081 (China); Tan, Chengwen, E-mail: tanchengwen@126.com [School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); National Key Laboratory of Science and Technology on Materials Under Shock and Impact, Beijing Institute of Technology, Beijing 100081 (China); Wang, Shuyou [State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081 (China); Yu, Xiaodong [School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); National Key Laboratory of Science and Technology on Materials Under Shock and Impact, Beijing Institute of Technology, Beijing 100081 (China); Jiang, Jianwei [State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081 (China); Ma, Honglei [China Astronaut Research and Training Center, Beijing 100094 (China); Cai, Hongnian [School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081 (China); National Key Laboratory of Science and Technology on Materials Under Shock and Impact, Beijing Institute of Technology, Beijing 100081 (China)

    2013-08-20

    The mechanical response and spall fracture behavior of an extra-low interstitial (ELI) grade Ti–6Al–4V alloy are systemically investigated during one-dimensional shock loading. The effects of oxygen content on the shock response and dynamic failure characteristic of Ti–6Al–4V are also shown through the comparison of the obtained results with those for commercial Ti–6Al–4V. The measured Hugoniot elastic limit (HEL) of Ti–6Al–4V ELI is lower than that of commercial Ti–6Al–4V. While the fitted shock parameters and the measured Hugoniot in the stress-particle velocity space of Ti–6Al–4V ELI are found to be almost identical to those of commercial Ti–6Al–4V. These results indicate that the oxygen content can significantly affect the HEL of Ti–6Al–4V, but has little or no influence on the shock response of this alloy beyond the HEL. The postshock Ti–6Al–4V ELI does not display shock-induced strengthening during quasistatic and dynamic compression tests. Transmission electron microscopy (TEM) analyses reveal that the lack of high density dislocations or dislocation cells limits the shock-induced strengthening effect, although dislocation multiplication and tangles lead to increased yield strength and strain hardening rate of the reloaded material. Finally, Ti–6Al–4V ELI is demonstrated to spall in a ductile manner, and has similar spall strengths to those of commercial Ti–6Al–4V under different shock loading conditions. The oxygen content exerts no effect on the spall fracture manner of Ti–6Al–4V, although reducing the oxygen content enables this alloy to endure more micro-damages.

  6. Shock-induced mechanical response and spall fracture behavior of an extra-low interstitial grade Ti–6Al–4V alloy

    Ren, Yu; Wang, Fuchi; Tan, Chengwen; Wang, Shuyou; Yu, Xiaodong; Jiang, Jianwei; Ma, Honglei; Cai, Hongnian

    2013-01-01

    The mechanical response and spall fracture behavior of an extra-low interstitial (ELI) grade Ti–6Al–4V alloy are systemically investigated during one-dimensional shock loading. The effects of oxygen content on the shock response and dynamic failure characteristic of Ti–6Al–4V are also shown through the comparison of the obtained results with those for commercial Ti–6Al–4V. The measured Hugoniot elastic limit (HEL) of Ti–6Al–4V ELI is lower than that of commercial Ti–6Al–4V. While the fitted shock parameters and the measured Hugoniot in the stress-particle velocity space of Ti–6Al–4V ELI are found to be almost identical to those of commercial Ti–6Al–4V. These results indicate that the oxygen content can significantly affect the HEL of Ti–6Al–4V, but has little or no influence on the shock response of this alloy beyond the HEL. The postshock Ti–6Al–4V ELI does not display shock-induced strengthening during quasistatic and dynamic compression tests. Transmission electron microscopy (TEM) analyses reveal that the lack of high density dislocations or dislocation cells limits the shock-induced strengthening effect, although dislocation multiplication and tangles lead to increased yield strength and strain hardening rate of the reloaded material. Finally, Ti–6Al–4V ELI is demonstrated to spall in a ductile manner, and has similar spall strengths to those of commercial Ti–6Al–4V under different shock loading conditions. The oxygen content exerts no effect on the spall fracture manner of Ti–6Al–4V, although reducing the oxygen content enables this alloy to endure more micro-damages

  7. Collision of two shock waves as a hypothetical mechanism of producing drifting radio bursts in the 400-500 MHz range

    Karlicky, M.

    1978-01-01

    After the proton flare of July 3, 1974 a hitherto unclassified phenomenon with a diffusion ''banner'' and with a considerably decelerating drift within the type II and III burst drifts range was observed in the radio dynamic spectrum between 410 and 470 MHz. The hypothesis is presented that the phenomenon is due to the collision of two shock waves, propagating against one another, during which the flux of electromagnetic radiation is considerably enhanced relative to the sum of the fluxes of the electromagnetic radiation of the individual shock waves. The Newkirk 4-density model of the corona is used to describe the phenomenon, the mechanism of plasmon-plasmon conversion in electromagnetic radiation with a double plasma frequency is considered and, according to the parameters derived from the dynamic spectrum, the velocities, radii of curvature and direction of propagation of the anticipated shock waves are analysed in a simplifed symmetric case. (author)

  8. Sierra/SolidMechanics 4.48 User's Guide: Addendum for Shock Capabilities.

    Plews, Julia A.; Crane, Nathan K; de Frias, Gabriel Jose; Le, San; Littlewood, David John; Merewether, Mark Thomas; Mosby, Matthew David; Pierson, Kendall H.; Porter, Vicki L.; Shelton, Timothy; Thomas, Jesse David; Tupek, Michael R.; Veilleux, Michael; Xavier, Patrick G.

    2018-03-01

    This is an addendum to the Sierra/SolidMechanics 4.48 User's Guide that documents additional capabilities available only in alternate versions of the Sierra/SolidMechanics (Sierra/SM) code. These alternate versions are enhanced to provide capabilities that are regulated under the U.S. Department of State's International Traffic in Arms Regulations (ITAR) export-control rules. The ITAR regulated codes are only distributed to entities that comply with the ITAR export-control requirements. The ITAR enhancements to Sierra/SM in- clude material models with an energy-dependent pressure response (appropriate for very large deformations and strain rates) and capabilities for blast modeling. Since this is an addendum to the standard Sierra/SM user's guide, please refer to that document first for general descriptions of code capability and use.

  9. Experimental Investigation on Shock Mechanical Properties of Red Sandstone under Preloaded 3D Static Stresses

    Niu Yong

    2015-11-01

    Full Text Available Triaxial impact mechanical performance experiment was performed to study the mechanical properties of red sandstone subjected to three-dimensional (3D coupled static and dynamic loads, i.e., three confining pressures (0, 5, and 10 MPa and three axial pressures (11, 27, and 43 MPa. A modified 3D split Hopkinson pressure bar testing system was used. The change trend in the deformation of red sandstone and the strength and failure modes under axial pressures and confining pressures were analyzed. Results show that, when the confining pressure is constant, the compressive strength, secant modulus, and energy absorbed per unit volume of red sandstone initially increases and subsequently decreases, whereas the average strain rate exhibits an opposite trend. When the axial pressure is constant, both the compressive strength and secant modulus of red sandstone are enhanced, but the average strain rate is decreased with increasing confining pressure. The energy absorbed per unit volume is initially increased and subsequently decreased as the confining pressure increases. Red sandstone exhibits a cone-shaped compression–shear failure mode under the 3D coupled static and dynamic loads. The conclusions serve as theoretical basis on the mechanical properties of deep medium-strength rock under a high ground stress and external load disturbance condition

  10. On the Optimally Controlled Hydrostatic Mechanical Drive in Case of Flywheel Acceleration

    V. A. Korsunskii

    2016-01-01

    Full Text Available An improving dynamic quality of vehicles and enhanced fuel efficiency are gained thanks to the combined power system (CPS, comprising a main energy source - internal combustion engine (ICE with an attained level of the power source - and an auxiliary energy source, i.e. an energy storage device (a flywheel.To solve this problem was developed a mathematical model of CPS comprising internal combustion engine and flywheel energy storage (FES with stepless drive.The stepless drive of the flywheel is made to be hydrostatic mechanical to raise the system efficiency. To reduce the drive weight and simplify the control system in the hydraulic part of the flywheel drive is used only one hydraulic unit being controlled.The paper presents a kinematic diagram of the track-type vehicle equipped with the CPS that has a hydrostatic mechanical drive of the flywheel and a mechanical transmission.A mathematical model of the system comprising an ICE, hydrostatic mechanical drive, and FES with stepless drive has been developed. This mathematical model was used to study the influence of ICE and flywheel drive parameters on the dynamic characteristics of the system.The paper estimates the impact of flywheel energy consumption, pressure in the hydraulic system, and control parameter of hydrostatic mechanical drive on the charging time of FES.The obtained piecewise linear law to control the regulation parameter of the hydraulic unit allows us to minimize the charging time of the flywheel at the short-term stops and in the parking area of a tracked vehicle equipped with a CPS.The causes affecting the performance of ‘ICE – drive – flywheel’ system in the course of the flywheel acceleration are a restricted maximum power of the engine, as well as a limited generating capacity, and a maximum flywheel drive hydro-system pressure.The obtained results allow us to determine rational parameters of the flywheel and the laws of drive control to provide their further

  11. Material studies in the frame of CLIC Accelerating structures production conducted within the Mechanics program together with Metso Oy

    Nurminen, Janne

    2012-01-01

    MeChanICs (Marie Curie Linking Industry to CERN) is an Industry to Academia Partnership and Pathways (IAPP) platform for precision manufacturing knowledge exchange bringing together five Finnish manufacturing companies with Helsinki Insitute of Physics (HIP) and CERN. The scientific objective of MeChanICs project is to contribute to the manufacturing RTD of CLIC enabling technologies. The focus is on the design, materials, machining, brazing and assembly of A CLIC accelerating structure. This study deals with the materials work package of the program and wants to explore the following items: 1) producing copper accelerating structures for CLIC from raw copper powder by near net shape hot isostatic pressing (HIP). 2) The feasibility to use HIP diffusion bonding of the accelerator structures as a function of surface quality and applied temperature and pressure. 3) Brazing for CLIC AS auxiliary systems, like water cooling or damping manifolds, to the disc stack by coating one of the brazing partners with an enab...

  12. Documentation of probabilistic fracture mechanics codes used for reactor pressure vessels subjected to pressurized thermal shock loading: Parts 1 and 2. Final report

    Balkey, K.; Witt, F.J.; Bishop, B.A.

    1995-06-01

    Significant attention has been focused on the issue of reactor vessel pressurized thermal shock (PTS) for many years. Pressurized thermal shock transient events are characterized by a rapid cooldown at potentially high pressure levels that could lead to a reactor vessel integrity concern for some pressurized water reactors. As a result of regulatory and industry efforts in the early 1980's, a probabilistic risk assessment methodology has been established to address this concern. Probabilistic fracture mechanics analyses are performed as part of this methodology to determine conditional probability of significant flaw extension for given pressurized thermal shock events. While recent industry efforts are underway to benchmark probabilistic fracture mechanics computer codes that are currently used by the nuclear industry, Part I of this report describes the comparison of two independent computer codes used at the time of the development of the original U.S. Nuclear Regulatory Commission (NRC) pressurized thermal shock rule. The work that was originally performed in 1982 and 1983 to compare the U.S. NRC - VISA and Westinghouse (W) - PFM computer codes has been documented and is provided in Part I of this report. Part II of this report describes the results of more recent industry efforts to benchmark PFM computer codes used by the nuclear industry. This study was conducted as part of the USNRC-EPRI Coordinated Research Program for reviewing the technical basis for pressurized thermal shock (PTS) analyses of the reactor pressure vessel. The work focused on the probabilistic fracture mechanics (PFM) analysis codes and methods used to perform the PTS calculations. An in-depth review of the methodologies was performed to verify the accuracy and adequacy of the various different codes. The review was structured around a series of benchmark sample problems to provide a specific context for discussion and examination of the fracture mechanics methodology

  13. Heating and generation of suprathermal particles at collisionless shocks

    Thomsen, M.F.

    1985-01-01

    Collisionless plasma shocks are different from ordinary collisional fluid shocks in several important respects. They do not in general heat the electrons and ions equally, nor do they produce Maxwellian velocity distributions downstream. Furthermore, they commonly generate suprathermal particles which propagate into the upstream region, giving advance warning of the presence of the shock and providing a ''seed'' population for further acceleration to high energies. Recent space observations and theory have revealed a great deal about the heating mechanisms which occur in collisionless shocks and about the origin of the various suprathermal particle populations which are found in association with them. An overview of the present understanding of these subjects is presented herein. 83 refs., 8 figs

  14. Molecular Dynamics Simulation Connections and Mechanical Properties of Cu/Al Explosion Shock Interface

    ZHANG Yan

    2017-10-01

    Full Text Available Based on the molecular dynamics (MD method, transient explosive welding process of Cu/Al junction point was revealed from the microscopic aspect, and mechanical properties and machinability of the Cu/Al nano-weldment were studied. The results show that kinetic energy is converted into internal energy in the system after the collision. The heterogeneous atoms penetrate into each other and the diffusion effect of copper atoms is better than aluminium atoms. The elastic modulus of the nano-weldment is 64.56 GPa, which is between copper's and aluminium's; however, its yield strength is less than those of the two monocrystals. Interactions between dislocations and disordered lattices cause the stress strengthening in the plastic deformation stage, which causes that the stress values of the weldment is larger than those of the two monocrystals. This strengthening mechanism is also reflected in the cutting process, and the weldment has the highest average cutting force 117.80 nN. A mass of dislocations nucleate in the disordered lattice areas of the weldment, and they spread at 45¯ to the cutting direction. However, dislocations pile up when their propagation is hindered by the disordered lattices and interface, which leads to the work hardening effect.

  15. Vp x B acceleration

    Sugihara, Ryo.

    1987-05-01

    A unique particle acceleration by an electrostatic (ES) wave, a magnetosonic shock wave as well as an electromagnetic (EM) wave is reviewed. The principle of the acceleration is that when a charged particle is carried across an external magnetic field the charge feels a DC field (the Lorentz force) and is accelerated. The theory for the ES wave acceleration is experimentally verified thought it is semi-quantitative. The shock acceleration is extensively studied theoretically and in a particle simulation method and the application is extended to phenomena in interplanetary space. The EM wave acceleration is based on a trapping in a moving neutral sheet created by the wave magnetic field and the external magnetic field, and the particle can be accelerated indefinitely. A brief sketch on a slow-wave-structure for this acceleration will be given. (author)

  16. Conception and realization of an expert system to help the interpretation of the mechanical shocks in a nuclear power plant

    Brunet, E.

    1988-01-01

    The computer system MIGRE, developed with the aim of helping the understanding of mechanical shocks in the nuclear power plant primary circuit. The MIGRE system allows the description of a study domain, the acquisition and exploitation of operational knowledges. The structural organization of the system is submitted to two constraints: in the first place, the system's operation depends on the accomplishment and development of an application, and on a diagnostic's research; the second constraint is the fact that the work space of PROLOG, on Macintoch, is restricted. A specific configuration is associated to each one of the work environments. The organization principle (in ''hierarchical Worlds'') of a program by PROLOG, allows to reach easily this kind of architecture. This principle makes a modular organization easy and allows to distinguish statical from dynamical steps of the system. The selection of the system different functions takes place by menus. The transition from one configuration to another is automatically effectuated and unseen by the user. Problems applying the Knowledge acquisition and the wandering bodies function, are also considered [fr

  17. STEREO interplanetary shocks and foreshocks

    Blanco-Cano, X.; Kajdič, P.; Aguilar-Rodríguez, E.; Russell, C. T.; Jian, L. K.; Luhmann, J. G.

    2013-01-01

    We use STEREO data to study shocks driven by stream interactions and the waves associated with them. During the years of the extended solar minimum 2007-2010, stream interaction shocks have Mach numbers between 1.1-3.8 and θ Bn ∼20-86°. We find a variety of waves, including whistlers and low frequency fluctuations. Upstream whistler waves may be generated at the shock and upstream ultra low frequency (ULF) waves can be driven locally by ion instabilities. The downstream wave spectra can be formed by both, locally generated perturbations, and shock transmitted waves. We find that many quasiperpendicular shocks can be accompanied by ULF wave and ion foreshocks, which is in contrast to Earth's bow shock. Fluctuations downstream of quasi-parallel shocks tend to have larger amplitudes than waves downstream of quasi-perpendicular shocks. Proton foreshocks of shocks driven by stream interactions have extensions dr ≤0.05 AU. This is smaller than foreshock extensions for ICME driven shocks. The difference in foreshock extensions is related to the fact that ICME driven shocks are formed closer to the Sun and therefore begin to accelerate particles very early in their existence, while stream interaction shocks form at ∼1 AU and have been producing suprathermal particles for a shorter time.

  18. STEREO interplanetary shocks and foreshocks

    Blanco-Cano, X. [Instituto de Geofisica, UNAM, CU, Coyoacan 04510 DF (Mexico); Kajdic, P. [IRAP-University of Toulouse, CNRS, Toulouse (France); Aguilar-Rodriguez, E. [Instituto de Geofisica, UNAM, Morelia (Mexico); Russell, C. T. [ESS and IGPP, University of California, Los Angeles, 603 Charles Young Drive, Los Angeles, CA 90095 (United States); Jian, L. K. [NASA Goddard Space Flight Center, Greenbelt, MD and University of Maryland, College Park, MD (United States); Luhmann, J. G. [SSL, University of California Berkeley (United States)

    2013-06-13

    We use STEREO data to study shocks driven by stream interactions and the waves associated with them. During the years of the extended solar minimum 2007-2010, stream interaction shocks have Mach numbers between 1.1-3.8 and {theta}{sub Bn}{approx}20-86 Degree-Sign . We find a variety of waves, including whistlers and low frequency fluctuations. Upstream whistler waves may be generated at the shock and upstream ultra low frequency (ULF) waves can be driven locally by ion instabilities. The downstream wave spectra can be formed by both, locally generated perturbations, and shock transmitted waves. We find that many quasiperpendicular shocks can be accompanied by ULF wave and ion foreshocks, which is in contrast to Earth's bow shock. Fluctuations downstream of quasi-parallel shocks tend to have larger amplitudes than waves downstream of quasi-perpendicular shocks. Proton foreshocks of shocks driven by stream interactions have extensions dr {<=}0.05 AU. This is smaller than foreshock extensions for ICME driven shocks. The difference in foreshock extensions is related to the fact that ICME driven shocks are formed closer to the Sun and therefore begin to accelerate particles very early in their existence, while stream interaction shocks form at {approx}1 AU and have been producing suprathermal particles for a shorter time.

  19. Reaction mechanism of the acidic hydrolysis of highly twisted amides: Rate acceleration caused by the twist of the amide bond.

    Mujika, Jon I; Formoso, Elena; Mercero, Jose M; Lopez, Xabier

    2006-08-03

    We present an ab initio study of the acid hydrolysis of a highly twisted amide and a planar amide analogue. The aim of these studies is to investigate the effect that the twist of the amide bond has on the reaction barriers and mechanism of acid hydrolysis. Concerted and stepwise mechanisms were investigated using density functional theory and polarizable continuum model calculations. Remarkable differences were observed between the mechanism of twisted and planar amide, due mainly to the preference for N-protonation of the former and O-protonation of the latter. In addition, we were also able to determine that the hydrolytic mechanism of the twisted amide will be pH dependent. Thus, there is a preference for a stepwise mechanism with formation of an intermediate in the acid hydrolysis, whereas the neutral hydrolysis undergoes a concerted-type mechanism. There is a nice agreement between the characterized intermediate and available X-ray data and a good agreement with the kinetically estimated rate acceleration of hydrolysis with respect to analogous undistorted amide compounds. This work, along with previous ab initio calculations, describes a complex and rich chemistry for the hydrolysis of highly twisted amides as a function of pH. The theoretical data provided will allow for a better understanding of the available kinetic data of the rate acceleration of amides upon twisting and the relation of the observed rate acceleration with intrinsic differential reactivity upon loss of amide bond resonance.

  20. Prediction of strong acceleration motion depended on focal mechanism; Shingen mechanism wo koryoshita jishindo yosoku ni tsuite

    Kaneda, Y; Ejiri, J [Obayashi Corp., Tokyo (Japan)

    1996-10-01

    This paper describes simulation results of strong acceleration motion with varying uncertain fault parameters mainly for a fault model of Hyogo-ken Nanbu earthquake. For the analysis, based on the fault parameters, the strong acceleration motion was simulated using the radiation patterns and the breaking time difference of composite faults as parameters. A statistic waveform composition method was used for the simulation. For the theoretical radiation patterns, directivity was emphasized which depended on the strike of faults, and the maximum acceleration was more than 220 gal. While, for the homogeneous radiation patterns, the maximum accelerations were isotopically distributed around the fault as a center. For variations in the maximum acceleration and the predominant frequency due to the breaking time difference of three faults, the response spectral value of maximum/minimum was about 1.7 times. From the viewpoint of seismic disaster prevention, underground structures including potential faults and non-arranging properties can be grasped using this simulation. Significance of the prediction of strong acceleration motion was also provided through this simulation using uncertain factors, such as breaking time of composite faults, as parameters. 4 refs., 4 figs., 1 tab.

  1. The cosmic-ray shock structure problem for relativistic shocks

    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.

  2. Particle Acceleration, Magnetic Field Generation and Emission from Relativistic Jets

    Nishikawa, K.-I.; Hardee, P.; Hededal, C.; Mizuno, Yosuke; Fishman, G. Jerry; Hartmann, D. H.

    2006-01-01

    Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), supernova remnants, and Galactic microquasar systems usually have power-law emission spectra. Fermi acceleration is the mechanism usually assumed for the acceleration of particles in astrophysical environments. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that particle acceleration occurs within the downstream jet, rather than by the scattering of particles back and forth across the shock as in Fermi acceleration. Shock acceleration' is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different spectral properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. We will review recent PIC simulations of relativistic jets and try to make a connection with observations.

  3. Finite element method (FEM) model of the mechanical stress on phospholipid membranes from shock waves produced in nanosecond electric pulses (nsEP)

    Barnes, Ronald; Roth, Caleb C.; Shadaram, Mehdi; Beier, Hope; Ibey, Bennett L.

    2015-03-01

    The underlying mechanism(s) responsible for nanoporation of phospholipid membranes by nanosecond pulsed electric fields (nsEP) remains unknown. The passage of a high electric field through a conductive medium creates two primary contributing factors that may induce poration: the electric field interaction at the membrane and the shockwave produced from electrostriction of a polar submersion medium exposed to an electric field. Previous work has focused on the electric field interaction at the cell membrane, through such models as the transport lattice method. Our objective is to model the shock wave cell membrane interaction induced from the density perturbation formed at the rising edge of a high voltage pulse in a polar liquid resulting in a shock wave propagating away from the electrode toward the cell membrane. Utilizing previous data from cell membrane mechanical parameters, and nsEP generated shockwave parameters, an acoustic shock wave model based on the Helmholtz equation for sound pressure was developed and coupled to a cell membrane model with finite-element modeling in COMSOL. The acoustic structure interaction model was developed to illustrate the harmonic membrane displacements and stresses resulting from shockwave and membrane interaction based on Hooke's law. Poration is predicted by utilizing membrane mechanical breakdown parameters including cortical stress limits and hydrostatic pressure gradients.

  4. Mechanisms of force production during linear accelerations in bluegill sunfish Lepomis macrochirus

    Tytell, Eric D.; Wise, Tyler N.; Boden, Alexandra L.; Sanders, Erin K.; Schwalbe, Margot A. B.

    2016-11-01

    In nature, fish rarely swim steadily. Although unsteady behaviors are common, we know little about how fish change their swimming kinematics for routine accelerations, and how these changes affect the fluid dynamic forces and the wake produced. To study force production during acceleration, particle image velocimetry was used to quantify the wake of bluegill sunfish Lepomis macrochirus and to estimate the pressure field during linear accelerations and steady swimming. We separated "steady" and "unsteady" trials and quantified the forward acceleration using inertial measurement units. Compared to steady sequences, unsteady sequences had larger accelerations and higher body amplitudes. The wake consisted of single vortices shed during each tail movement (a '2S' wake). The structure did not change during acceleration, but the circulation of the vortices increased, resulting in larger forces. A fish swimming unsteadily produced significantly more force than the same fish swimming steadily, even when the accelerations were the same. This increase is likely due to increased added mass during unsteady swimming, as a result of the larger body amplitude. Pressure estimates suggest that the increase in force is correlated with more low pressure regions on the anterior body. This work was supported by ARO W911NF-14-1-0494 and NSF RCN-PLS 1062052.

  5. Collisionless shock waves

    Sagdeev, R.Z.; Kennel, C.F.

    1991-01-01

    Collisionless shocks cannot occur naturally on the earth, because nearly all matter here consists of electrically neutral atoms and molecules. In space, however, high temperatures and ultraviolet radiation from hot stars decompose atoms into their constituent nuclei and electrons, producing a soup of electrically charged particles known as a plasma. Plasma physicists proposed that the collective electrical and magnetic properties of plasmas could produce interactions that take the place of collisions and permit shocks to form. In 1964 the theoretical work found its first experimental confirmation. Norman F. Ness and his colleagues at the Goddard Space Flight Center, using data collected from the iMP-1 spacecraft, detected clear signs that a collisionless shock exists where the solar wind encounters the earth's magnetic field. More recent research has demonstrated that collisionless shocks appear in a dazzling array of astronomical settings. For example, shocks have been found in the solar wind upstream (sunward) of all the planet and comets that have been visited by spacecraft. Violent flares on the sun generate shocks that propagate to the far reaches of the solar system; tremendous galactic outbursts create disruptions in the intergalactic medium that are trillions of times larger. In addition, many astrophysicists think that shocks from supernova explosions in our galaxy accelerate cosmic rays, a class of extraordinarily energetic elementary particles and atomic nuclei that rain down on the earth from all directions

  6. Shock and vibration effects on performance reliability and mechanical integrity of proton exchange membrane fuel cells: A critical review and discussion

    Haji Hosseinloo, Ashkan; Ehteshami, Mohsen Mousavi

    2017-10-01

    Performance reliability and mechanical integrity are the main bottlenecks in mass commercialization of PEMFCs for applications with inherent harsh environment such as automotive and aerospace applications. Imparted shock and vibration to the fuel cell in such applications could bring about numerous issues including clamping torque loosening, gas leakage, increased electrical resistance, and structural damage and breakage. Here, we provide a comprehensive review and critique of the literature focusing on the effects of mechanically harsh environment on PEMFCs, and at the end, we suggest two main future directions in FC technology research that need immediate attention: (i) developing a generic and adequately accurate dynamic model of PEMFCs to assess the dynamic response of FC devices, and (ii) designing effective and robust shock and vibration protection systems based on the developed models in (i).

  7. Role of the calcaneal heel pad and polymeric shock absorbers in attenuation of heel strike impact.

    Noe, D A; Voto, S J; Hoffmann, M S; Askew, M J; Gradisar, I A

    1993-01-01

    The capacity of the calcaneal heel pad, with and without augmentation by a polymeric shock absorbing material (Sorbothane 0050), to attenuate heel strike impulses has been studied using five fresh human cadaveric lower leg specimens. The specimens, instrumented with an accelerometer, were suspended and impacted with a hammer; a steel rod was similarly suspended and impacted. The calcaneal heel pad attenuated the peak accelerations by 80%. Attenuations of up to 93% were achieved by the shock absorbing material when tested against the steel rod; however, when tested in series with the calcaneal heel pad, the reduction in peak acceleration due to the shock absorbing material dropped to 18%. Any evaluation of the effectiveness of shock absorbing shoe materials must take into account their mechanical interaction with the body.

  8. Illustrated instructions for mechanical quality assurance of a medical linear accelerator.

    Court, Laurence; Wang, He; Aten, David; Brown, Derek; MacGregor, Hannelie; du Toit, Monique; Chi, Melinda; Gao, Song; Yock, Adam; Aristophanous, Michalis; Balter, Peter

    2018-03-03

    The purpose of this study was to develop and test a set of illustrated instructions for effective training for mechanical quality assurance (QA) of medical linear accelerators (linac). Illustrated instructions were created for mechanical QA and underwent several steps of review, testing, and refinement. Eleven testers with no recent QA experience were then recruited from our radiotherapy department (one student, two computational scientists, and eight dosimetrists). This group was selected because they have experience of radiation therapy but no preconceived ideas about how to do QA. The following parameters were progressively decalibrated on a Varian C-series linac: Group A = gantry angle, ceiling laser position, X1 jaw position, couch longitudinal position, physical graticule position (five testers); Group B = Group A + wall laser position, couch lateral and vertical position, collimator angle (three testers); Group C = Group B + couch angle, wall laser angle, and optical distance indicator (three testers). Testers were taught how to use the linac and then used the instructions to try to identify these errors. An experienced physicist observed each session, giving support on machine operation as necessary. Testers were able to follow the instructions. They determined gantry, collimator, and couch angle errors within 0.4°, 0.3°, and 0.9° of the actual changed values, respectively. Laser positions were determined within 1 mm and jaw positions within 2 mm. Couch position errors were determined within 2 mm and 3 mm for lateral/longitudinal and vertical errors, respectively. Accessory-positioning errors were determined within 1 mm. Optical distance indicator errors were determined within 2 mm when comparing with distance sticks and 6 mm when using blocks, indicating that distance sticks should be the preferred approach for inexperienced staff. Inexperienced users were able to follow these instructions and catch errors within the criteria suggested

  9. Evaluation of seismic acceleration responses of base-isolated and nonisolated structures varying with mechanical characteristics of foundations

    You, Bong; Lee, Jae Han; Ku, Kyung Hoi [Korea Atomic Energy Research Institute, Daeduk (Korea, Republic of)

    1996-05-01

    The evaluation of acceleration responses of isolated and nonisolated structures according to mechanical features of soils is important. The kinds of soils taken in analyses are soft, medium and hard rocks, and a fixed base condition is also taken for the comparison. The horizontal isolation frequency used is 0.5 Hz. The time history analyses of reference power plant using 1940 El Centro horizontal (NS) and vertical earthquakes are performed to investigate the seismic responses varying with soil characteristics for isolated and nonisolated structures. The horizontal acceleration responses of the horizontal isolated-structures show almost similar values irrespective of the various kinds of soils and are largely decreased in the frequency ranges above 2 hz. The vertical natural frequency, 21Hz of high damping rubber bearing does not affect the vertical acceleration responses in case of soft rock, but largely affects in hard rock condition. For nonisolated structures, the acceleration responses are decreased in both horizontal and vertical directions by taking into account the soils in the analysis model. The extent of reduction of acceleration responses is larger in vertical direction than in horizontal one, as the stiffness of rock becomes softer. 8 tabs., 21 figs., 8 refs. (Author) .new.

  10. Evaluation of seismic acceleration responses of base-isolated and nonisolated structures varying with mechanical characteristics of foundations

    You, Bong; Lee, Jae Han; Ku, Kyung Hoi

    1996-05-01

    The evaluation of acceleration responses of isolated and nonisolated structures according to mechanical features of soils is important. The kinds of soils taken in analyses are soft, medium and hard rocks, and a fixed base condition is also taken for the comparison. The horizontal isolation frequency used is 0.5 Hz. The time history analyses of reference power plant using 1940 El Centro horizontal (NS) and vertical earthquakes are performed to investigate the seismic responses varying with soil characteristics for isolated and nonisolated structures. The horizontal acceleration responses of the horizontal isolated-structures show almost similar values irrespective of the various kinds of soils and are largely decreased in the frequency ranges above 2 hz. The vertical natural frequency, 21Hz of high damping rubber bearing does not affect the vertical acceleration responses in case of soft rock, but largely affects in hard rock condition. For nonisolated structures, the acceleration responses are decreased in both horizontal and vertical directions by taking into account the soils in the analysis model. The extent of reduction of acceleration responses is larger in vertical direction than in horizontal one, as the stiffness of rock becomes softer. 8 tabs., 21 figs., 8 refs. (Author) .new

  11. Some discussion on the acceleration mechanism of particles in the type-I plasma comet

    Li Zhongyuan; Guo Sheyu.

    1991-07-01

    Earlier, the large acceleration of plasma (300 cm/s 2 ) were already observed in type-I tail. Recently, the direct measurements for comet G-Z showed that the energy of particle reaches 2x10 5 eV, an energy much higher than the initial energy of comet particles (≤ 2x10 4 eV). So there should be an accelerated process in the comet. 14 refs, 3 figs

  12. Mechanical engineering and design criteria for the Magnetically Insulated Transmission Experiment Accelerator

    Staller, G.E.; Hamilton, I.D.; Aker, M.F.; Fifer, H.G.

    1978-02-01

    A single-unit electron beam accelerator was designed, fabricated, and assembled in Sandia's Technical Area V to conduct magnetically insulated transmission experiments. Results of these experiments will be utilized in the future design of larger, more complex accelerators. This design makes optimum use of existing facilities and equipment. When designing new components, possible future applications were considered as well as compatibility with existing facilities and hardware

  13. Perpendicular relativistic shocks in magnetized pair plasma

    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 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.

  14. Review of Acceleration Methods for Seismic Analysis of Through-Wall Cracked Piping from the Viewpoint of Linear Elastic Fracture Mechanics

    Kim, Jong Sung; Kim, Yong Woo [Sunchon National University, Suncheon (Korea, Republic of)

    2014-10-15

    Two acceleration methods, an effective force method (or inertia method) and a large mass method, have been applied for performing time history seismic analysis. The acceleration methods for uncracked structures have been verified via previous studies. However, no study has identified the validity of these acceleration methods for cracked piping. In this study, the validity of the acceleration methods for through-wall cracked piping is assessed via time history implicit dynamic elastic seismic analysis from the viewpoint of linear elastic fracture mechanics. As a result, it is identified that both acceleration methods show the same results for cracked piping if a large mass magnitude and maximum time increment are adequately selected.

  15. Review of Acceleration Methods for Seismic Analysis of Through-Wall Cracked Piping from the Viewpoint of Linear Elastic Fracture Mechanics

    Kim, Jong Sung; Kim, Yong Woo

    2014-01-01

    Two acceleration methods, an effective force method (or inertia method) and a large mass method, have been applied for performing time history seismic analysis. The acceleration methods for uncracked structures have been verified via previous studies. However, no study has identified the validity of these acceleration methods for cracked piping. In this study, the validity of the acceleration methods for through-wall cracked piping is assessed via time history implicit dynamic elastic seismic analysis from the viewpoint of linear elastic fracture mechanics. As a result, it is identified that both acceleration methods show the same results for cracked piping if a large mass magnitude and maximum time increment are adequately selected

  16. Shock Prevention

    1978-01-01

    The electrician pictured is installing a General Electric Ground Fault Interrupter (GFI), a device which provides protection against electrical shock in the home or in industrial facilities. Shocks due to defective wiring in home appliances or other electrical equipment can cause severe burns, even death. As a result, the National Electrical Code now requires GFIs in all new homes constructed. This particular type of GFI employs a sensing element which derives from technology acquired in space projects by SCI Systems, Inc., Huntsville, Alabama, producer of sensors for GE and other manufacturers of GFI equipment. The sensor is based on the company's experience in developing miniaturized circuitry for space telemetry and other spacecraft electrical systems; this experience enabled SCI to package interruptor circuitry in the extremely limited space available and to produce sensory devices at practicable cost. The tiny sensor measures the strength of the electrical current and detects current differentials that indicate a fault in the functioning of an electrical system. The sensing element then triggers a signal to a disconnect mechanism in the GFI, which cuts off the current in the faulty circuit.

  17. Modelling socio-metabolic transitions: The historical take-off, the acceleration of fossil fuel use, and the 1970s oil price shock - the first trigger of a future decline?

    Wiedenhofer, Dominik; Rovenskaya, Elena; Krausmann, Fridolin; Haas, Willi; Fischer-Kowalski, Marina

    2013-04-01

    By talking about socio-metabolic transitions, we talk about changes in the energy base of socio-economic systems, leading to fundamental changes in social and environmental relations. This refers to the historical shift from a biomass-based (agrarian) economy to a fossil fuel based (industrial) economy just as much as to a future shift from fossil fuels to renewable energy carriers. In our presentation, • We will first show that this pattern of transition can be identified for most high income industrial countries: the later the transition started, the faster it proceeded, and the turning point to stabilization of metabolic rates in all of them happened in the early 1970ies. Due to the inherent non-linearity of this process, two approaches will be aplied to estimate parameters for the starting point, transition speed and saturation level: firstly a combination of an expontential and a generalized logistic function and secondly a Gompertz function. For both an iterative test procedure is applied to find the global minimum of the residual error for the whole function and all its parameters. This theory-based approach allows us to apply a robust methodology across all cases, thereby yielding results which can be generalized. • Next, we will show that this was not just a "historical" socio-ecological transition, however. Currently, a substantial number of countries comprising more than half of the world's population are following a similar transitional pathway at an ever accelerating pace. Based on empirical data on physical resource use and the above sketched methodology, we can show that these so-called emerging economies are currently in the take-off or acceleration phase of the very same transition. • Apart from these "endogenous" processes of socio-metabolic transition, we will investigate the effect of external shocks and their impact on the dynamics of energy and materials use. The first such shock we will explore is the oil crisis of 1972 that possibly

  18. Setting accelerated dissolution test for PLGA microspheres containing peptide, investigation of critical parameters affecting drug release rate and mechanism.

    Tomic, I; Vidis-Millward, A; Mueller-Zsigmondy, M; Cardot, J-M

    2016-05-30

    The objective of this study was development of accelerated in vitro release method for peptide loaded PLGA microspheres using flow-through apparatus and assessment of the effect of dissolution parameters (pH, temperature, medium composition) on drug release rate and mechanism. Accelerated release conditions were set as pH 2 and 45°C, in phosphate buffer saline (PBS) 0.02M. When the pH was changed from 2 to 4, diffusion controlled phases (burst and lag) were not affected, while release rate during erosion phase decreased two-fold due to slower ester bonds hydrolyses. Decreasing temperature from 45°C to 40°C, release rate showed three-fold deceleration without significant change in release mechanism. Effect of medium composition on drug release was tested in PBS 0.01M (200 mOsm/kg) and PBS 0.01M with glucose (380 mOsm/kg). Buffer concentration significantly affected drug release rate and mechanism due to the change in osmotic pressure, while ionic strength did not have any effect on peptide release. Furthermore, dialysis sac and sample-and-separate techniques were used, in order to evaluate significance of dissolution technique choice on the release process. After fitting obtained data to different mathematical models, flow-through method was confirmed as the most appropriate for accelerated in vitro dissolution testing for a given formulation. Copyright © 2016 Elsevier B.V. All rights reserved.

  19. Insight into the labeling mechanism of acceleration selective arterial spin labeling

    Schmid, Sophie; Petersen, Esben T; Van Osch, Matthias J P

    2017-01-01

    OBJECTIVES: Acceleration selective arterial spin labeling (AccASL) is a spatially non-selective labeling technique, used in traditional ASL methods, which labels spins based on their flow acceleration rather than spatial localization. The exact origin of the AccASL signal within the vasculature......-ASL, combined AccASL and VS-ASL signal, and signal from one module with crushing from the other. RESULTS: The label created with AccASL has an overlap of approximately 50% in the vascular region with VS-ASL, but also originates from smaller vessels closer to the capillaries. CONCLUSION: AccASL is able to label...

  20. Heat shock protein 70 inhibits shrinkage-induced programmed cell death via mechanisms independent of effects on cell volume-regulatory membrane transport proteins

    Nylandsted, J; Jäättelä, M; Hoffmann, E K

    2004-01-01

    Cell shrinkage is a ubiquitous feature of programmed cell death (PCD), but whether it is an obligatory signalling event in PCD is unclear. Heat shock protein 70 (Hsp70) potently counteracts PCD in many cells, by mechanisms that are incompletely understood. In the present investigation, we found...... that severe hypertonic stress greatly diminished the viability of murine fibrosarcoma cells (WEHI-902) and immortalized murine embryonic fibroblasts (iMEFs). This effect was attenuated markedly by Hsp70 over-expression. To determine whether the protective effect of Hsp70 was mediated via an effect on volume...... regulatory ion transport, we compared regulatory volume decrease (RVD) and increase (RVI) in control WEHI-902 cells and after increasing Hsp70 levels by heat shock or over-expression (WEHI-912). Hsp70 levels affected neither RVD, RVI nor the relative contributions of the Na(+)/H(+)-exchanger (NHE1) and Na...

  1. Ergonomic assessment of brake and accelerator mechanisms of MF285 and MF399 tractors using electromyography method

    A Nikkhah

    2016-04-01

    Full Text Available Introduction: Too many people are working in the agricultural sector and therefore, pay more attention to the safety and health at work in the agricultural sector is important. This issue is more important in developing industrial countries where the level of the ergonomic working condition is less than that of developed countries. Attention to ergonomic condition of agricultural machinery drivers is one of the goals of agricultural mechanization. Therefore, in this study the ergonomic conditions of brake and accelerator mechanisms for MF285 and MF399 tractor's drivers were investigated using a new method. Materials and Methods: 25 people were selected for experiment. The electrical activity of Medialis gastrocnemius, Lateralis gastrocnemius, Vastus medialis, Vastus lateralis, Quadratus Lumborum and Trapezius muscles of drivers before and during pressing the pedal and after rest time were recorded using Biovision device. Measurements were performed for each person on each muscle 30 seconds before pressing the pedal, 60 seconds after pressing the pedal and after 60 seconds of rest. For all drivers, the muscles on the right side (brake and accelerator side have been selected and tested. The measurements were performed in compliance with appropriate time intervals between the measurements. Results and Discussion: Ergonomic assessment of brake pedal: The results showed that the RMS electrical activity of muscles of Vastus medialis and Medial gastrocnemius, during 60 seconds braking were 2.47 and 1.97. So, Vastus medialis and Medial gastrocnemius had the highest stress during pressing the MF399 tractor's brake pedal. Moreover, the Medial gastrocnemius and Lateral gastrocnemius with RMS electrical activity ratio of 2.47 and 1.74 had the highest RMS electrical activity ratio respectively, during 60 seconds braking compared to before braking of MF285 tractor. The comparison of results showed that the Vastus medialis and Trapezius had the higher stress

  2. ION INJECTION AT QUASI-PARALLEL SHOCKS SEEN BY THE CLUSTER SPACECRAFT

    Johlander, A.; Vaivads, A.; Khotyaintsev, Yu. V.; Retinò, A.; Dandouras, I.

    2016-01-01

    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) and 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

  3. Restriction of cosmic-ray acceleration, mechanisms by high-energy Be7/Be data

    Orth, C.D.; Buffington, A.; Mast, T.S.

    1979-01-01

    New high-energy cosmic-ray Be data indicate that the ratio Be 7 /Be drops by approximately a factor of two between 200 and 1500 MeV/nucleon. This result may provide a severe constraint for theories of cosmic-ray acceleration

  4. Gamma-ray emission from internal shocks in novae

    Martin, P.; Dubus, G.; Jean, P.; Tatischeff, V.; Dosne, C.

    2018-04-01

    Context. Gamma-ray emission at energies ≥100 MeV has been detected from nine novae using the Fermi Large Area Telescope (LAT), and can be explained by particle acceleration at shocks in these systems. Eight out of these nine objects are classical novae in which interaction of the ejecta with a tenuous circumbinary material is not expected to generate detectable gamma-ray emission. Aim. We examine whether particle acceleration at internal shocks can account for the gamma-ray emission from these novae. The shocks result from the interaction of a fast wind radiatively-driven by nuclear burning on the white dwarf with material ejected in the initial runaway stage of the nova outburst. Methods: We present a one-dimensional model for the dynamics of a forward and reverse shock system in a nova ejecta, and for the associated time-dependent particle acceleration and high-energy gamma-ray emission. Non-thermal proton and electron spectra are calculated by solving a time-dependent transport equation for particle injection, acceleration, losses, and escape from the shock region. The predicted emission is compared to LAT observations of V407 Cyg, V1324 Sco, V959 Mon, V339 Del, V1369 Cen, and V5668 Sgr. Results: The ≥100 MeV gamma-ray emission arises predominantly from particles accelerated up to 100 GeV at the reverse shock and undergoing hadronic interactions in the dense cooling layer downstream of the shock. The emission rises within days after the onset of the wind, quickly reaches a maximum, and its subsequent decrease reflects mostly the time evolution of the wind properties. Comparison to gamma-ray data points to a typical scenario where an ejecta of mass 10-5-10-4 M⊙ expands in a homologous way with a maximum velocity of 1000-2000 km s-1, followed within a day by a wind with a velocity values of which result in the majority of best-fit models having gamma-ray spectra with a high-energy turnover below 10 GeV. Our typical model is able to account for the main

  5. Particle acceleration near Halley's comet

    Somogyi, Antal

    1987-01-01

    Vega and Giotto space probes observed energetic ions of cometary origin near Halley's comet. The water molecules evaporating from the cometary nucleus were ionized by the solar UV radiation. These 'standing' ions were accelerated from 1 km/s to a few 1000 km/s. Present paper analyses the possible mechanisms of acceleration based on the data of TUENDE detector (constructed by CRIP, Hungary) working on board of Vega probes. The basic mechanism is the ExB Lorentz acceleration by interplanetary magnetic field and electric field induced by magnetic field frozen into solar wind plasma. It is followed by an acceleration caused by the adiabatic compression of the plasma at shock wave front. These processes can not explain the observed velocity of ions. It is shown that the second order Fermi acceleration which dissipates the ion distribution in the velocity space can lead to the observed velocities. The circumstances required to the occurrence of this process are present at the cometary environment. (D.G.) 2 figs

  6. On the Radio-emitting Particles of the Crab Nebula: Stochastic Acceleration Model

    Tanaka, Shuta J. [Department of Physics, Faculty of Science and Engineering, Konan University, 8-9-1 Okamoto, Kobe, Hyogo 658-8501 (Japan); Asano, Katsuaki, E-mail: sjtanaka@center.konan-u.ac.jp [Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa City, Chiba, 277-8582 (Japan)

    2017-06-01

    The broadband emission of pulsar wind nebulae (PWNe) is well described by non-thermal emissions from accelerated electrons and positrons. However, the standard shock acceleration model of PWNe does not account for the hard spectrum in radio wavelengths. The origin of the radio-emitting particles is also important to determine the pair production efficiency in the pulsar magnetosphere. Here, we propose a possible resolution for the particle energy distribution in PWNe; the radio-emitting particles are not accelerated at the pulsar wind termination shock but are stochastically accelerated by turbulence inside PWNe. We upgrade our past one-zone spectral evolution model to include the energy diffusion, i.e., the stochastic acceleration, and apply the model to the Crab Nebula. A fairly simple form of the energy diffusion coefficient is assumed for this demonstrative study. For a particle injection to the stochastic acceleration process, we consider the continuous injection from the supernova ejecta or the impulsive injection associated with supernova explosion. The observed broadband spectrum and the decay of the radio flux are reproduced by tuning the amount of the particle injected to the stochastic acceleration process. The acceleration timescale and the duration of the acceleration are required to be a few decades and a few hundred years, respectively. Our results imply that some unveiled mechanisms, such as back reaction to the turbulence, are required to make the energies of stochastically and shock-accelerated particles comparable.

  7. Shocks near Jamming

    Gómez, Leopoldo R.; Turner, Ari M.; van Hecke, Martin; Vitelli, Vincenzo

    2012-02-01

    Nonlinear sound is an extreme phenomenon typically observed in solids after violent explosions. But granular media are different. Right when they jam, these fragile and disordered solids exhibit a vanishing rigidity and sound speed, so that even tiny mechanical perturbations form supersonic shocks. Here, we perform simulations in which two-dimensional jammed granular packings are dynamically compressed and demonstrate that the elementary excitations are strongly nonlinear shocks, rather than ordinary phonons. We capture the full dependence of the shock speed on pressure and impact intensity by a surprisingly simple analytical model.

  8. Topical Erythropoietin Treatment Accelerates the Healing of Cutaneous Burn Wounds in Diabetic Pigs Through an Aquaporin-3-Dependent Mechanism.

    Hamed, Saher; Ullmann, Yehuda; Egozi, Dana; Keren, Aviad; Daod, Essam; Anis, Omer; Kabha, Hoda; Belokopytov, Mark; Ashkar, Manal; Shofti, Rona; Zaretsky, Asaph; Schlesinger, Michal; Teot, Luc; Liu, Paul Y

    2017-08-01

    We have previously reported that the topical application of erythropoietin (EPO) to cutaneous wounds in rats and mice with experimentally induced diabetes accelerates their healing by stimulating angiogenesis, reepithelialization, and collagen deposition, and by suppressing the inflammatory response and apoptosis. Aquaporins (AQPs) are integral membrane proteins whose function is to regulate intracellular fluid hemostasis by enabling the transport of water and glycerol. AQP3 is the AQP that is expressed in the skin where it facilitates cell migration and proliferation and re-epithelialization during wound healing. In this report, we provide the results of an investigation that examined the contribution of AQP3 to the mechanism of EPO action on the healing of burn wounds in the skin of pigs with experimentally induced type 1 diabetes. We found that topical EPO treatment of the burns accelerated their healing through an AQP3-dependent mechanism that activates angiogenesis, triggers collagen and hyaluronic acid synthesis and the formation of the extracellular matrix (ECM), and stimulates reepithelialization by keratinocytes. We also found that incorporating fibronectin, a crucial constituent of the ECM, into the topical EPO-containing gel, can potentiate the accelerating action of EPO on the healing of the burn injury. © 2017 by the American Diabetes Association.

  9. Effect of Slag Content and Hardening Accelerator Dosage on the Physico Mechanical Properties of Cement and Concrete

    Derabla, R.; Mokrani, I.; Benmalek, M.L.

    2011-01-01

    Our contribution consists at the study of the effect of (0 %, 0.2 % and 0.34 %) dosage of an hardening accelerating plasticizer (Plastocrete 160, produced by Sika Aldjazair) on the properties of normal mortar and concretes prepared with portland cement artificial of Hadjar Soud cement factory (Skikda - Algeria) with addition of (10 % and 20 %) of granulated blast furnace slag finely crushed of the El Hadjar blast furnace (Annaba - Algeria). The tests are focused to the physical and mechanical characteristics of elaborated materials to knowing: setting time, porosity, water absorption capacity and the test of compressive strength at 2, 7 and 28 days. The results obtained show clearly the reliability of the additive used to accelerate the hardening and to obtain high strengths at early age, which increase by increasing of the additive dosage. For the slag, its low hydraulic capacity does not make it profitable than at the long term (beyond 28 days). (author)

  10. Mechanical Design of a High Energy Beam Absorber for the Advanced Superconducting Test Accelerator (ASTA) at Fermilab

    Baffes, C.; Church, M.; Leibfritz, J.; Oplt, S.; Rakhno, I.; /Fermilab

    2012-05-10

    A high energy beam absorber has been built for the Advanced Superconducting Test Accelerator (ASTA) at Fermilab. In the facility's initial configuration, an electron beam will be accelerated through 3 TTF-type or ILC-type SRF cryomodules to an energy of 750MeV. The electron beam will be directed to one of multiple downstream experimental and diagnostic beam lines and then deposited in one of two beam absorbers. The facility is designed to accommodate up to 6 cryomodules, which would produce a 75kW beam at 1.5GeV; this is the driving design condition for the beam absorbers. The beam absorbers consist of water-cooled graphite, aluminum and copper layers contained in a helium-filled enclosure. This paper describes the mechanical implementation of the beam absorbers, with a focus on thermal design and analysis. The potential for radiation-induced degradation of the graphite is discussed.

  11. Study of the electronics architecture for the mechanical stabilisation of the quadrupoles of the CLIC linear accelerator

    Artoos, K; Fernandez Carmona, P; Guinchard, M; Hauviller, C; Janssens, S; Kuzmin, A; Slaathaug, A

    2010-01-01

    To reach a sufficient luminosity, the transverse beam sizes and emittances in future linear particle accelerators should be reduced to the nanometer level. Mechanical stabilisation of the quadrupole magnets is of the utmost importance for this. The piezo actuators used for this purpose can also be used to make fast incremental orientation adjustments with a nanometer resolution. The main requirements for the CLIC stabilisation electronics is a robust, low noise, low delay, high accuracy and resolution, low band and radiation resistant feedback control loop. Due to the high number of controllers (about 4000) a cost optimization should also be made. Different architectures are evaluated for a magnet stabilisation prototype, including the sensors type and configuration, partition between software and hardware for control algorithms, and optimization of the ADC/DAC converters. The controllers will be distributed along the 50 km long accelerator and a communication bus should allow external control. Furthermore, o...

  12. Sprint Acceleration Mechanics: The Major Role of Hamstrings in Horizontal Force Production

    Morin, Jean-Benoît; Gimenez, Philippe; Edouard, Pascal; Arnal, Pierrick; Jiménez-Reyes, Pedro; Samozino, Pierre; Brughelli, Matt; Mendiguchia, Jurdan

    2015-01-01

    Recent literature supports the importance of horizontal ground reaction force (GRF) production for sprint acceleration performance. Modeling and clinical studies have shown that the hip extensors are very likely contributors to sprint acceleration performance. We experimentally tested the role of the hip extensors in horizontal GRF production during short, maximal, treadmill sprint accelerations. Torque capabilities of the knee and hip extensors and flexors were assessed using an isokinetic dynamometer in 14 males familiar with sprint running. Then, during 6-s sprints on an instrumented motorized treadmill, horizontal and vertical GRF were synchronized with electromyographic (EMG) activity of the vastus lateralis, rectus femoris, biceps femoris, and gluteus maximus averaged over the first half of support, entire support, entire swing and end-of-swing phases. No significant correlations were found between isokinetic or EMG variables and horizontal GRF. Multiple linear regression analysis showed a significant relationship (P = 0.024) between horizontal GRF and the combination of biceps femoris EMG activity during the end of the swing and the knee flexors eccentric peak torque. In conclusion, subjects who produced the greatest amount of horizontal force were both able to highly activate their hamstring muscles just before ground contact and present high eccentric hamstring peak torque capability. PMID:26733889

  13. Sprint acceleration mechanics: the major role of hamstrings in horizontal force production

    Jean-Benoit eMORIN

    2015-12-01

    Full Text Available Recent literature supports the importance of horizontal ground reaction force (GRF production for sprint acceleration performance. Modeling and clinical studies have shown that the hip extensors are very likely contributors to sprint acceleration performance. We experimentally tested the role of the hip extensors in horizontal GRF production during short, maximal, treadmill sprint accelerations. Torque capabilities of the knee and hip extensors and flexors were assessed using an isokinetic dynamometer in 14 males familiar with sprint running. Then, during 6-s sprints on an instrumented motorized treadmill, horizontal and vertical GRF were synchronized with electromyographic (EMG activity of the vastus lateralis, rectus femoris, biceps femoris and gluteus maximus averaged over the first half of support, entire support, entire swing and end-of-swing phases. No significant correlations were found between isokinetic or EMG variables and horizontal GRF. Multiple linear regression analysis showed a significant relationship (P = 0.024 between horizontal GRF and the combination of biceps femoris EMG activity during the end of the swing and the knee flexors eccentric peak torque. In conclusion, subjects who produced the greatest amount of horizontal force were both able to highly activate their hamstring muscles just before ground contact and present high eccentric hamstring peak torque capability.

  14. Shock Heating of the Merging Galaxy Cluster A521

    Bourdin, H.; Mazzotta, P.; Markevitch, M.; Giacintucci, S.; Brunetti, G.

    2013-01-01

    A521 is an interacting galaxy cluster located at z = 0.247, hosting a low-frequency radio halo connected to an eastern radio relic. Previous Chandra observations hinted at the presence of an X-ray brightness edge at the position of the relic, which may be a shock front. We analyze a deep observation of A521 recently performed with XMM-Newton in order to probe the cluster structure up to the outermost regions covered by the radio emission. The cluster atmosphere exhibits various brightness and temperature anisotropies. In particular, two cluster cores appear to be separated by two cold fronts. We find two shock fronts, one that was suggested by Chandra and that is propagating to the east, and another to the southwestern cluster outskirt. The two main interacting clusters appear to be separated by a shock-heated region, which exhibits a spatial correlation with the radio halo. The outer edge of the radio relic coincides spatially with a shock front, suggesting that this shock is responsible for the generation of cosmic-ray electrons in the relic. The propagation direction and Mach number of the shock front derived from the gas density jump, M = 2.4 +/- 0.2, are consistent with expectations from the radio spectral index, under the assumption of Fermi I acceleration mechanism.

  15. Short-term mechanical circulatory support as a bridge to durable left ventricular assist device implantation in refractory cardiogenic shock: a systematic review and meta-analysis.

    den Uil, Corstiaan A; Akin, Sakir; Jewbali, Lucia S; Dos Reis Miranda, Dinis; Brugts, Jasper J; Constantinescu, Alina A; Kappetein, Arie Pieter; Caliskan, Kadir

    2017-07-01

    Short-term mechanical circulatory support (MCS) is increasingly used as a bridge to decision in patients with refractory cardiogenic shock. Subsequently, these patients might be bridged to durable MCS either as a bridge to candidacy/transplantation, or as destination therapy. The aim of this study was to review support duration and clinical outcome of short-term MCS in cardiogenic shock, and to analyse application of this technology as a bridge to long-term cardiac support (left ventricular assist device, LVAD) from 2006 till June 2016. Using Cochrane Register of Trials, Embase and Medline, a systematic review was performed on patients with cardiogenic shock from acute myocardial infarction, end-stage cardiomyopathy, or acute myocarditis, receiving short-term MCS. Studies on periprocedural, post-cardiotomy and cardiopulmonary resuscitation support were excluded. Thirty-nine studies, mainly registries of heterogeneous patient populations (n = 4151 patients), were identified. Depending on the device used (intra-aortic balloon pump, TandemHeart, Impella 2.5, Impella 5.0, CentriMag and peripheral veno-arterial extracorporeal membrane oxygenation), mean support duration was (range) 1.6-25 days and the mean proportion of short-term MCS patients discharged was (range) 45-66%. The mean proportion of bridge to durable LVAD was (range) 3-30%. Bridge to durable LVAD was most frequently performed in patients with end-stage cardiomyopathy (22 [12-35]%). We conclude that temporary MCS can be used to bridge patients with cardiogenic shock towards durable LVAD. Clinicians are encouraged to share their results in a large multicentre registry in order to investigate optimal device selection and best duration of support. © The Author 2017. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.

  16. Shock wave interaction with turbulence: Pseudospectral simulations

    Buckingham, A.C.

    1986-01-01

    Shock waves amplify pre-existing turbulence. Shock tube and shock wave boundary layer interaction experiments provide qualitative confirmation. However, shock pressure, temperature, and rapid transit complicate direct measurement. Computational simulations supplement the experimental data base and help isolate the mechanisms responsible. Simulations and experiments, particularly under reflected shock wave conditions, significantly influence material mixing. In these pseudospectral Navier-Stokes simulations the shock wave is treated as either a moving (tracked or fitted) domain boundary. The simulations assist development of code mix models. Shock Mach number and pre-existing turbulence intensity initially emerge as key parameters. 20 refs., 8 figs

  17. Nonlinear Weibel Instability and Turbulence in Strong Collisionless Shocks

    Medvedev, Mikhail M.

    2008-01-01

    This research project was devoted to studies of collisionless shocks, their properties, microphysics and plasma physics of underlying phenomena, such as Weibel instability and generation of small-scale fields at shocks, particle acceleration and transport in the generated random fields, radiation mechanisms from these fields in application to astrophysical phenomena and laboratory experiments (e.g., laser-plasma and beam-plasma interactions, the fast ignition and inertial confinement, etc.). Thus, this study is highly relevant to astrophysical sciences, the inertial confinement program and, in particular, the Fast Ignition concept, etc. It makes valuable contributions to the shock physics, nonlinear plasma theory, as well as to the basic plasma science, in general

  18. ATF1 Modulates the Heat Shock Response by Regulating the Stress-Inducible Heat Shock Factor 1 Transcription Complex

    Takii, Ryosuke; Fujimoto, Mitsuaki; Tan, Ke; Takaki, Eiichi; Hayashida, Naoki; Nakato, Ryuichiro; Shirahige, Katsuhiko

    2014-01-01

    The heat shock response is an evolutionally conserved adaptive response to high temperatures that controls proteostasis capacity and is regulated mainly by an ancient heat shock factor (HSF). However, the regulation of target genes by the stress-inducible HSF1 transcription complex has not yet been examined in detail in mammalian cells. In the present study, we demonstrated that HSF1 interacted with members of the ATF1/CREB family involved in metabolic homeostasis and recruited them on the HSP70 promoter in response to heat shock. The HSF1 transcription complex, including the chromatin-remodeling factor BRG1 and lysine acetyltransferases p300 and CREB-binding protein (CBP), was formed in a manner that was dependent on the phosphorylation of ATF1. ATF1-BRG1 promoted the establishment of an active chromatin state and HSP70 expression during heat shock, whereas ATF1-p300/CBP accelerated the shutdown of HSF1 DNA-binding activity during recovery from acute stress, possibly through the acetylation of HSF1. Furthermore, ATF1 markedly affected the resistance to heat shock. These results revealed the unanticipated complexity of the primitive heat shock response mechanism, which is connected to metabolic adaptation. PMID:25312646

  19. Thermo-hydraulic-mechanical analysis of the SS-050 sodium loop during a thermal shock of 2000C/s

    Jesus Miranda, C.A. de; Gebrin, A.N.

    1988-01-01

    An analytical thermo-hydraulic model was developed to obtain the temperature of the sodium flowing between the mixing tank TM of constant volume and the drain tank of the SS-050 sodium test facility. The piping connecting these two tanks is considered in the analysis. The sodium enters in the TM through a tube with lateral holes immersed in the TM's sodium. The model and relative computer program were tested and a typical situation was studied: a thermal shock with -200 0 C/s of thermal gradient in the test section. The sodium temperature time-histories along the piping length are presented. For the thermal shock situation, the temperature field in the TM bottom and outlet nozzle was calculated and the stresses were evaluated. The final thermal stresses will allow a detailed verification of the circuit design. (author) [pt

  20. Quasilinear simulations of interplanetary shocks and Earth's bow shock

    Afanasiev, Alexandr; Battarbee, Markus; Ganse, Urs; Vainio, Rami; Palmroth, Minna; Pfau-Kempf, Yann; Hoilijoki, Sanni; von Alfthan, Sebastian

    2016-04-01

    We have developed a new self-consistent Monte Carlo simulation model for particle acceleration in shocks. The model includes a prescribed large-scale magnetic field and plasma density, temperature and velocity profiles and a self-consistently computed incompressible ULF foreshock under the quasilinear approximation. Unlike previous analytical treatments, our model is time dependent and takes full account of the anisotropic particle distributions and scattering in the wave-particle interaction process. We apply the model to the problem of particle acceleration at traveling interplanetary (IP) shocks and Earth's bow shock and compare the results with hybrid-Vlasov simulations and spacecraft observations. A qualitative agreement in terms of spectral shape of the magnetic fluctuations and the polarization of the unstable mode is found between the models and the observations. We will quantify the differences of the models and explore the region of validity of the quasilinear approach in terms of shock parameters. We will also compare the modeled IP shocks and the bow shock, identifying the similarities and differences in the spectrum of accelerated particles and waves in these scenarios. The work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 637324 (HESPERIA). The Academy of Finland is thanked for financial support. We acknowledge the computational resources provided by CSC - IT Centre for Science Ltd., Espoo.

  1. On Modeling Risk Shocks

    Dorofeenko, Victor; Lee, Gabriel; Salyer, Kevin; Strobel, Johannes

    2016-01-01

    Within the context of a financial accelerator model, we model time-varying uncertainty (i.e. risk shocks) through the use of a mixture Normal model with time variation in the weights applied to the underlying distributions characterizing entrepreneur productivity. Specifically, we model capital producers (i.e. the entrepreneurs) as either low-risk (relatively small second moment for productivity) and high-risk (relatively large second moment for productivity) and the fraction of both types is...

  2. Hyperglycemia adversely modulates endothelial nitric oxide synthase during anesthetic preconditioning through tetrahydrobiopterin- and heat shock protein 90-mediated mechanisms.

    Amour, Julien; Brzezinska, Anna K; Jager, Zachary; Sullivan, Corbin; Weihrauch, Dorothee; Du, Jianhai; Vladic, Nikolina; Shi, Yang; Warltier, David C; Pratt, Phillip F; Kersten, Judy R

    2010-03-01

    Endothelial nitric oxide synthase activity is regulated by (6R-)5,6,7,8-tetrahydrobiopterin (BH4) and heat shock protein 90. The authors tested the hypothesis that hyperglycemia abolishes anesthetic preconditioning (APC) through BH4- and heat shock protein 90-dependent pathways. Myocardial infarct size was measured in rabbits in the absence or presence of APC (30 min of isoflurane), with or without hyperglycemia, and in the presence or absence of the BH4 precursor sepiapterin. Isoflurane-dependent nitric oxide production was measured (ozone chemiluminescence) in human coronary artery endothelial cells cultured in normal (5.5 mm) or high (20 mm) glucose conditions, with or without sepiapterin (10 or 100 microm). APC decreased myocardial infarct size compared with control experiments (26 +/- 6% vs. 46 +/- 3%, respectively; P < 0.05), and this action was blocked by hyperglycemia (43 +/- 4%). Sepiapterin alone had no effect on infarct size (46 +/- 3%) but restored APC during hyperglycemia (21 +/- 3%). The beneficial actions of sepiapterin to restore APC were blocked by the nitric oxide synthase inhibitor N (G)-nitro-L-arginine methyl ester (47 +/- 2%) and the BH4 synthesis inhibitor N-acetylserotonin (46 +/- 3%). Isoflurane increased nitric oxide production to 177 +/- 13% of baseline, and this action was attenuated by high glucose concentrations (125 +/- 6%). Isoflurane increased, whereas high glucose attenuated intracellular BH4/7,8-dihydrobiopterin (BH2) (high performance liquid chromatography), heat shock protein 90-endothelial nitric oxide synthase colocalization (confocal microscopy) and endothelial nitric oxide synthase activation (immunoblotting). Sepiapterin increased BH4/BH2 and dose-dependently restored nitric oxide production during hyperglycemic conditions (149 +/- 12% and 175 +/- 9%; 10 and 100 microm, respectively). The results indicate that tetrahydrobiopterin and heat shock protein 90-regulated endothelial nitric oxide synthase activity play a central

  3. Accelerated stress testing of terrestrial solar cells

    Lathrop, J. W.; Hawkins, D. C.; Prince, J. L.; Walker, H. A.

    1982-01-01

    The development of an accelerated test schedule for terrestrial solar cells is described. This schedule, based on anticipated failure modes deduced from a consideration of IC failure mechanisms, involves bias-temperature testing, humidity testing (including both 85-85 and pressure cooker stress), and thermal-cycle thermal-shock testing. Results are described for 12 different unencapsulated cell types. Both gradual electrical degradation and sudden catastrophic mechanical change were observed. These effects can be used to discriminate between cell types and technologies relative to their reliability attributes. Consideration is given to identifying laboratory failure modes which might lead to severe degradation in the field through second quadrant operation. Test results indicate that the ability of most cell types to withstand accelerated stress testing depends more on the manufacturer's design, processing, and worksmanship than on the particular metallization system. Preliminary tests comparing accelerated test results on encapsulated and unencapsulated cells are described.

  4. MO-FG-303-04: A Smartphone Application for Automated Mechanical Quality Assurance of Medical Accelerators

    Kim, H; Lee, H; Choi, K; Ye, S

    2015-01-01

    Purpose: The mechanical quality assurance (QA) of medical accelerators consists of a time consuming series of procedures. Since most of the procedures are done manually – e.g., checking gantry rotation angle with the naked eye using a level attached to the gantry –, it is considered to be a process with high potential for human errors. To remove the possibilities of human errors and reduce the procedure duration, we developed a smartphone application for automated mechanical QA. Methods: The preparation for the automated process was done by attaching a smartphone to the gantry facing upward. For the assessments of gantry and collimator angle indications, motion sensors (gyroscope, accelerator, and magnetic field sensor) embedded in the smartphone were used. For the assessments of jaw position indicator, cross-hair centering, and optical distance indicator (ODI), an optical-image processing module using a picture taken by the high-resolution camera embedded in the smartphone was implemented. The application was developed with the Android software development kit (SDK) and OpenCV library. Results: The system accuracies in terms of angle detection error and length detection error were < 0.1° and < 1 mm, respectively. The mean absolute error for gantry and collimator rotation angles were 0.03° and 0.041°, respectively. The mean absolute error for the measured light field size was 0.067 cm. Conclusion: The automated system we developed can be used for the mechanical QA of medical accelerators with proven accuracy. For more convenient use of this application, the wireless communication module is under development. This system has a strong potential for the automation of the other QA procedures such as light/radiation field coincidence and couch translation/rotations

  5. MO-FG-303-04: A Smartphone Application for Automated Mechanical Quality Assurance of Medical Accelerators

    Kim, H [Interdisciplinary Program in Radiation applied Life Science, College of Medicine, Seoul National University, Seoul (Korea, Republic of); Lee, H; Choi, K [Program in Biomedical Radiation Sciences, Department of Transdisciplinary Studies, Graduate School of Convergence Science and Technology, Seoul National University, Seoul (Korea, Republic of); Ye, S [Interdisciplinary Program in Radiation applied Life Science, College of Medicine, Seoul National University, Seoul (Korea, Republic of); Program in Biomedical Radiation Sciences, Department of Transdisciplinary Studies, Graduate School of Convergence Science and Technology, Seoul National University, Seoul (Korea, Republic of); Department of Radiation Oncology, Seoul National University Hospital, Seoul (Korea, Republic of)

    2015-06-15

    Purpose: The mechanical quality assurance (QA) of medical accelerators consists of a time consuming series of procedures. Since most of the procedures are done manually – e.g., checking gantry rotation angle with the naked eye using a level attached to the gantry –, it is considered to be a process with high potential for human errors. To remove the possibilities of human errors and reduce the procedure duration, we developed a smartphone application for automated mechanical QA. Methods: The preparation for the automated process was done by attaching a smartphone to the gantry facing upward. For the assessments of gantry and collimator angle indications, motion sensors (gyroscope, accelerator, and magnetic field sensor) embedded in the smartphone were used. For the assessments of jaw position indicator, cross-hair centering, and optical distance indicator (ODI), an optical-image processing module using a picture taken by the high-resolution camera embedded in the smartphone was implemented. The application was developed with the Android software development kit (SDK) and OpenCV library. Results: The system accuracies in terms of angle detection error and length detection error were < 0.1° and < 1 mm, respectively. The mean absolute error for gantry and collimator rotation angles were 0.03° and 0.041°, respectively. The mean absolute error for the measured light field size was 0.067 cm. Conclusion: The automated system we developed can be used for the mechanical QA of medical accelerators with proven accuracy. For more convenient use of this application, the wireless communication module is under development. This system has a strong potential for the automation of the other QA procedures such as light/radiation field coincidence and couch translation/rotations.

  6. Physical mechanism causing rapid changes in ultrarelativistic electron pitch angle distributions right after a shock arrival: Evaluation of an electron dropout event: Drift Shell Splitting on the Dayside

    Zhang, X.-J.; University of California, Los Angeles, CA; Li, W.; Boston University, MA; Thorne, R. M.

    2016-01-01

    Three mechanisms have been proposed to explain relativistic electron flux depletions (dropouts) in the Earth's outer radiation belt during storm times: adiabatic expansion of electron drift shells due to a decrease in magnetic field strength, magnetopause shadowing and subsequent outward radial diffusion, and precipitation into the atmosphere (driven by EMIC wave scattering). Which mechanism predominates in causing electron dropouts commonly observed in the outer radiation belt is still debatable. In the present study, we evaluate the physical mechanism that may be primarily responsible for causing the sudden change in relativistic electron pitch angle distributions during a dropout event observed by Van Allen Probes during the main phase of the 27 February 2014 storm. During this event, the phase space density of ultrarelativistic (>1MeV) electrons was depleted by more than 1 order of magnitude over the entire radial extent of the outer radiation belt (3 < L* < 5) in less than 6 h after the passage of an interplanetary shock. We model the electron pitch angle distribution under a compressed magnetic field topology based on actual solar wind conditions. Although these ultrarelativistic electrons exhibit highly anisotropic (peaked in 90°), energy-dependent pitch angle distributions, which appear to be associated with the typical EMIC wave scattering, comparison of the modeled electron distribution to electron measurements indicates that drift shell splitting is responsible for this rapid change in electron pitch angle distributions. This further indicates that magnetopause loss is the predominant cause of the electron dropout right after the shock arrival.

  7. Laboratory investigation of physical mechanisms of auroral charged particle acceleration in the field-aligned currents layers

    Gavrilov, B.; Zetzer, J.; Sobyanin, D.; Podgorny, I.

    One of the major topics of space weather research is to understand auroral structure and the processes that guide, accelerate, and otherwise control particle precipitation and produce auroral substorms. Navigation, communications and radars in the high latitude regions are severely affected through the effects on the ionosphere. It has long been recognized that the direct cause of the aurora is the precipitation of energetic electrons and ions into the atmosphere leading to excitation of the ambient atmospheric gases. Observations of the ionospheric ionization profiles and auroral precipitation characteristics have shown that field-aligned potential drops are formed to create this effect. The problem is that it is not clear the structure of the regions of magnetic field-aligned electric fields and how they are supported in the magnetospheric plasma. The objective of this research is to study the physical mechanisms of these phenomena in a laboratory experiment. It should be achieved by simulating the charged particle acceleration due to field-aligned electrical field generation in all totality of the interconnected events: generation of a plasma flow, its evolution in the magnetic field, polarization of plasma, generation of the field-aligned currents, development of instabilities in the plasma and current layers, double layers or anomalous resistance regions appearance, electrons acceleration. Parameters of the laboratory simulation and preliminary results of the experiment are discussed.

  8. Mechanical Design and Analysis of a 200 MHz, Bolt-together RFQ forthe Accelerator Driven Neutron Source

    Virostek, Steve; Hoff, Matt; Li, Derun; Staples, John; Wells,Russell

    2007-06-20

    A high-yield neutron source to screen sea-land cargocontainers for shielded Special Nuclear Materials (SNM) has been designedat LBNL [1,2]. The Accelerator-Driven Neutron Source (ADNS) uses theD(d,n)3He reaction to create a forward directed neutron beam. Keycomponents are a high-current radio-frequency quadrupole (RFQ)accelerator and a high-power target capable of producing a neutron fluxof>107 n/(cm2 cdot s) at a distance of 2.5 m. The mechanical designand analysis of the four-module, bolt-together RFQ will be presentedhere. Operating at 200 MHz, the 5.1 m long RFQ will accelerate a 40 mAdeuteron beam to 6 MeV. At a 5 percent duty factor, the time-average d+beam current on target is 1.5 mA. Each of the 1.27 m long RFQ moduleswill consist of four solid OFHC copper vanes. A specially designed 3-DO-ring will provide vacuum sealing between both the vanes and themodules. RF connections are made with canted coil spring contacts. Aseries of 60 water-cooled pi-mode rods provides quadrupole modestabilization. A set of 80 evenly spaced fixed slug tuners is used forfinal frequency adjustment and local field perturbationcorrection.

  9. Mechanical Design and Analysis of a 200 MHz, Bolt-together RFQ for the Accelerator Driven Neutron Source

    Virostek, Steve; Hoff, Matt; Li, Derun; Staples, John; Wells, Russell

    2007-01-01

    A high-yield neutron source to screen sea-land cargo containers for shielded Special Nuclear Materials (SNM) has been designed at LBNL [1,2]. The Accelerator-Driven Neutron Source (ADNS) uses the D(d,n)3He reaction to create a forward directed neutron beam. Key components are a high-current radio-frequency quadrupole (RFQ) accelerator and a high-power target capable of producing a neutron flux of >107 n/(cm2 cdot s) at a distance of 2.5 m. The mechanical design and analysis of the four-module, bolt-together RFQ will be presented here. Operating at 200 MHz, the 5.1 m long RFQ will accelerate a 40 mA deuteron beam to 6 MeV. At a 5 percent duty factor, the time-average d+beam current on target is 1.5 mA. Each of the 1.27 m long RFQ modules will consist of four solid OFHC copper vanes. A specially designed 3-DO-ring will provide vacuum sealing between both the vanes and the modules. RF connections are made with canted coil spring contacts. A series of 60 water-cooled pi-mode rods provides quadrupole mode stabilization. A set of 80 evenly spaced fixed slug tuners is used for final frequency adjustment and local field perturbation correction

  10. Acceleration mechanism of vertical displacement event and its amelioration in tokamak disruptions

    Nakamura, Yukiharu; Yoshino, Ryuji; Pomphrey, N.; Jardin, S.C.

    1996-01-01

    Vertical displacement events (VDEs), which are frequently observed in disruptive discharges of elongated tokamaks, are investigated using the Tokamak Simulation Code. We show that disruption events such as a sudden plasma pressure drop (β p collapse) and the subsequent plasma current quench (I p quench) can accelerate VDEs due to the adverse destabilizing effect of the resistive shell, which has previously been thought to stabilize VDEs. In a tokamak with a surrounding shell which is asymmetric with respect to the geometric midplane, the I p quench also causes an additional VDE acceleration due to the vertical imbalance of the attractive force. While the shell-geometry characterizes the VDE dynamics, the growth rate of VDEs depends strongly on the magnitude of the β p collapse, the speed of the I p quench and the n-index of the plasma equilibrium just before the disruption. An amelioration of I p quench-induced VDEs was experimentally established in the JT-60U tokamak by optimizing the vertical location of the plasma just prior to the disruption. The JT-60U vacuum vessel is shown to be suitable for preventing the β p collapse-induced VDE. (author)

  11. Shock absorber

    Nemeth, J.D.

    1981-01-01

    A shock absorber for the support of piping and components in a nuclear power plant is described. It combines a high degree of stiffness under sudden shocks, e.g. seismic disturbances, with the ability to allow for thermal expansion without resistance when so required. (JIW)

  12. Risk shocks and housing markets

    Dorofeenko, Viktor; Lee, Gabriel S.; Salyer, Kevin D.

    2010-01-01

    Abstract: This paper analyzes the role of uncertainty in a multi-sector housing model with financial frictions. We include time varying uncertainty (i.e. risk shocks) in the technology shocks that affect housing production. The analysis demonstratesthat risk shocks to the housing production sector are a quantitatively important impulse mechanism for the business cycle. Also, we demonstrate that bankruptcy costs act as an endogenous markup factor in housing prices; as a consequence, the volati...

  13. Concentrated ion beam emitted from an enlarged cylindrical-anode-layer Hall plasma accelerator and mechanism

    Geng, S. F.; Wang, C. X. [Southwestern Institute of Physics, Chengdu 610041 (China); Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon (Hong Kong); Tang, D. L.; Qiu, X. M. [Southwestern Institute of Physics, Chengdu 610041 (China); Chu, Paul K. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon (Hong Kong)

    2013-01-28

    An enlarged cylindrical-anode-layer Hall plasma accelerator with an outlet diameter of 150 mm is experimentally demonstrated to produce a concentrated ion beam, especially at a high discharge voltage, with a high current utilization efficiency of up to {approx}0.9. Numerical investigation based on the three-dimensional particle-in-cell method is performed to study the ion dynamics and elucidate the origin of the ion beam characteristics. The simulation results reveal that the equipotential lines play an important role in the surface near the anode emitting the ions. The ion emitting surface is determined by the magnetic field lines near the anode and the magnetic mirror contributes to the concentrated beam significantly. The high current utilization efficiency results from the appropriate obliquity of the magnetic mirror.

  14. Constant pH Accelerated Molecular Dynamics Investigation of the pH Regulation Mechanism of Dinoflagellate Luciferase.

    Donnan, Patrick H; Ngo, Phong D; Mansoorabadi, Steven O

    2018-01-23

    The bioluminescence reaction in dinoflagellates involves the oxidation of an open-chain tetrapyrrole by the enzyme dinoflagellate luciferase (LCF). The activity of LCF is tightly regulated by pH, where the enzyme is essentially inactive at pH ∼8 and optimally active at pH ∼6. Little is known about the mechanism of LCF or the structure of the active form of the enzyme, although it has been proposed that several intramolecularly conserved histidine residues in the N-terminal region are important for the pH regulation mechanism. Here, constant pH accelerated molecular dynamics was employed to gain insight into the conformational activation of LCF induced by acidification.

  15. Accelerator and Technical Sector Seminar: Mechanical stabilization and positioning of CLIC quadrupoles with sub-nanometre resolution

    2011-01-01

    Thursday 24 November 2010 Accelerator and Technical Sector Seminar at 14:15  -  BE Auditorium, bldg. 6 (Meyrin) – please note unusual place Mechanical stabilization and positioning of CLIC quadrupoles with sub-nanometre resolution Stef Janssens /EN-MME Abstract: To reach the required luminosity at the CLIC interaction point, about 4000 quadrupoles are needed to obtain a vertical beam size of 1 nm at the interaction point. The mechanical jitter of the quadrupole magnets will result in an emittance growth. An active vibration isolation system is required to reduce vibrations from the ground and from external forces to about 1.5 nm integrated root mean square (r.m.s.) vertical displacement at 1 Hz. A short overview of vibration damping and isolation strategies will be presented as well as a comparison of existing systems. The unprecedented resolution requirements and the instruments enabling these measurements will be discussed. The vibration sources from which the magnets need to...

  16. The Flexible Acceleration Mechanism of China’s Capital Adjustment with the Goal of Consumption-Driven Sustainable Growth

    Peng Su

    2018-03-01

    Full Text Available China has had an investment-led growth pattern that is unsustainable. It is struggling to shift to a consumption-driven economy, and capital adjustment is crucial to the transition. In response, the principal objective of this study is to analyze the internal market mechanism of China’s capital adjustment. Due to the imperfections of the market, we use the flexible acceleration model, which we put in an IS (Investment – Saving equation–LM (Liquidity preference – Money supply equation framework in order to reflect the guiding role of demand. The results show that the flexible acceleration model fits China’s investment well, and the demand-oriented market mechanism of capital adjustment has been formed; however, China’s market adjustment ability is not strong. The adjustment coefficient is only 0.22, and shows a decreasing trend. So, in the capital optimization process, relying on the market alone is not realistic. Furthermore, the calculated replacement rate is up to 0.429, which indicates that China’s capital is less efficient, and there are duplicated assets, idle assets, and wasted investments. The error correction model’s results show that the impact of the interest rate on the investments is not significant in the short term, so the existence of invalid capital is more likely to stem from the soft budget constraints, which require attention.

  17. High shock load testing of lithium-thionyl chloride batteries

    Epstein, J.; Marincic, N.

    1983-10-01

    Low rate cylindrical cells have been developed, capable of withstanding mechanical shocks up to 23,000 g's for one millisecond. The cells were based on the lithium-thionyl chloride battery system and totally hermetic stainless steel hardware incorporating a glass sealed positive terminal. Four cells in series were required to deliver 25 mA pulses at a minimum voltage of 10 V before and after such exposure to one mechanical shock. Batteries were contained in a hardened steel housing and mounted within a projectile accelerated by means of a gas gun. The velocity of the projectile was measured with electronic probes immediately before impact and the deceleration was effected using a special aluminum honeycomb structure from which the g values were calculated. A high survival rate for the cells was achieved in spite of some mechanical damage to the battery housing still present.

  18. Mechanical properties and thermal shock performance of W-Y2O3 composite prepared by high-energy-rate forging

    Lian, Youyun; Liu, Xiang; Feng, Fan; Song, Jiupeng; Yan, Binyou; Wang, Yingmin; Wang, Jianbao; Chen, Jiming

    2017-12-01

    The effects of the addition of Y2O3 and hot-deformation on the mechanical properties of tungsten (W) have been studied. The processing route comprises a doping technique for the distribution of Y2O3 particles in a tungsten matrix, conventional sintering in a hydrogen environment, and high-energy-rate forging (HERF). The microstructure of the composite was characterized by using transmission electron microscopy and electron backscattering diffraction imaging technique, and its mechanical properties were studied by means of tensile testing. The thermal shock response of the HERF processed W-Y2O3 was evaluated by applying edge-localized mode-like loads (100 pulses) with a pulse duration of 1 ms and an absorbed power density of up to 1 GW m-2 at various temperatures between room temperature and 200 °C. HERF processing has produced elongated W grains with preferred orientations and a high density of structure defects in the composite. The composite material exhibits high tensile strength and good ductility, and a thermal shock cracking threshold lower than 100 °C.

  19. Effect of nano-ZrO2 addition on microstructure, mechanical property and thermal shock behaviour of dense chromic oxide refractory material

    Lu, Lixia; Ding, Chunhui; Zhanga, Chi; Yanga, De'an; Di, Lizhi

    2015-01-01

    To obtain a good performance hot-face lining material in gasifier, nano-ZrO 2 , up to 5 wt %, was added into chromic oxide powder with 3 wt % TiO 2 followed by sintering at 1500°C for 2.5 h. The effect of nano-ZrO 2 addition on microstructure, mechanical property and thermal shock behaviour was studied. ZrO 2 promoted densification at contents higher than 1 wt %. Microcracks and phase transformation toughened the dense chromic oxide refractory material. The main reason for decrease of strength was the existence microcracks in specimens and weakening of intergranular fracture. Dense chromic oxide refractory material with 2∼3 wt % nano-ZrO 2 possessed good densification, uniform microstructure, normal mechanical property and proper thermal shock resistance. The rupture strength retention ratio was nearly twice than that of chromic oxide material without ZrO 2 after three cycles of quenching test from 950°C to cold water. (author)

  20. demystifying the shock of shocking

    (with a pulse), atrial fibrillation and atrial flutter. The energy dose in cardioversion is less (0.5. - 2 J/kg) than in defibrillation (2 - 4 J/kg). In cardioversion the shock is discharged synchronously with the native R wave of the patient. Without synchronisation,. VF can be induced if a shock is delivered during the refractory period ...

  1. Study of mechanism of cancer caused by carcinogenic substances with accelerator mass spectrometry

    Jiang Shan; He Ming; Wu Shaoyong; You Qubo; Xu Guoji; Wang Qien; Liu Shijie

    2001-01-01

    Full text: It is reported that most of the cancerous patients were caused by cancerogenic substances. The research in recent years shows that carcinogenesis is related with Ca in the cells. In normal cells, the level of free Ca 2+ is very stable, the Ca 2+ as messenger plays an important role to keep normal function of cells. However, the level of free Ca 2+ in cells increases when the cells are exposed to cancerogenic substances such as cigarette smoking solution and chrysotile. But where do the increased Ca 2+ come from? There are three possibilities: 1) from outside of cell membrane; 2) from inside of nucleus; or 3) from both outside and inside of cells. By using external cultivation of cells 41 Ca as tracer and accelerator mass spectrometry (AMS) as measurement method, we investigate the origin of the increased Ca 2+ when the cells are exposed to cigarette smoking solution or chrysoltile is being undertaken. Several results as below have been gotten. 1. 41 Ca synthesis. A high purification of isotope of 40 Ca (99.95%) in form of CaO was irradiated by thermal neutron with a heavy water reactor at the China Institute of Atomic Energy (CIAE). The irradiation time and neutron flux were 988h and 4.9x10 13 , respectively. A 41 Ca/ 40 Ca ratio of 7x10 -5 was obtained. The conversion efficiency of Ca metal to CaH 2 was 80% to 90%. 2. CaH 2 sample preparation. There are two steps for CaH 2 sample preparation in AMS measurement. In the first step, CaO is reduced to metallic calcium via vacuum distillation and in the second, the CaO is converted into a hybrid. 3. 41 Ca AMS measurement. The first 41 Ca AMS measurement was performed with Hl-13 tandem AMS system in the CIAE. By using a 41 Ca blank sample, 30 nA of CaH 3 - ions from ion source can be obtained. Ions were accelerated with a terminal voltage of 7.8 and Ca 8+ (E=69.7 MeV) ions were selected. From the measurement, a 41 Ca/ 40 Ca ratio of about 10 -14 was deduced. (author)

  2. The effect of artificial accelerated weathering on the mechanical properties of maxillofacial polymers PDMS and CPE.

    Eleni, P N; Krokida, M K; Polyzois, G L

    2009-06-01

    The effect of UVA-UVB irradiation on the mechanical properties of three different industrial types of polydimethylsiloxane and chlorinated polyethylene samples, used in maxillofacial prostheses, was investigated in this study. Mechanical properties and thermal analysis are commonly used to determine the structural changes and mechanical strength. An aging chamber was used in order to simulate the solar radiation and assess natural aging. Compression and tensile tests were conducted on a Zwick testing machine. Durometer Shore A hardness measurements were carried out in a CV digital Shore A durometer according to ASTM D 2240. Glass transition temperature was evaluated with a differential scanning calorimeter. Simple mathematical models were developed to correlate the measured properties with irradiation time. The effect of UVA-UVB irradiation on compressive behavior affected model parameters. Significant deterioration seems to occur due to irradiation in samples.

  3. Analysis of the microstructure and mechanical performance of composite resins after accelerated artificial aging.

    De Oliveira Daltoé, M; Lepri, C Penazzo; Wiezel, J Guilherme G; Tornavoi, D Cremonezzi; Agnelli, J A Marcondes; Reis, A Cândido Dos

    2013-03-01

    Researches that assess the behavior of dental materials are important for scientific and industrial development especially when they are tested under conditions that simulate the oral environment, so this work analyzed the compressive strength and microstructure of three composite resins subjected to accelerated artificial aging (AAA). Three composites resins of 3M (P90, P60 and Z100) were analyzed and were obtained 16 specimens for each type (N.=48). Half of each type were subjected to UV-C system AAA and then were analyzed the surfaces of three aged specimens and three not aged of each type through the scanning electron microscope (SEM). After, eight specimens of each resin, aged and not aged, were subjected to compression test. After statistical analysis of compressive strength values, it was found that there was difference between groups (α aged P60 presented lower values of compressive strength statistically significant when compared to the not subject to the AAA. For the other composite resins, there was no difference, regardless of aging, a fact confirmed by SEM. The results showed that the AAA influenced the compressive strength of the resin aged P60; confirmed by surface analysis by SEM, which showed greater structural disarrangement on surface material.

  4. Microstructures and Mechanical Properties of Commercially Pure Ti Processed by Rotationally Accelerated Shot Peening

    Zhaowen Huang

    2018-03-01

    Full Text Available Gradient structured materials possess good combinations of strength and ductility, rendering the materials attractive in industrial applications. In this research, a surface nanocrystallization (SNC technique, rotationally accelerated shot peening (RASP, was employed to produce a gradient nanostructured pure Ti with a deformation layer that had a thickness of 2000 μm, which is thicker than those processed by conventional SNC techniques. It is possible to fabricate a gradient structured Ti workpiece without delamination. Moreover, based on the microstructural features, the microstructure of the processed sample can be classified into three regions, from the center to the surface of the RASP-processed sample: (1 a twinning-dominated core region; (2 a “twin intersection”-dominated twin transition region; and (3 the nanostructured region, featuring nanograins. A microhardness gradient was detected from the RASP-processed Ti. The surface hardness was more than twice that of the annealed Ti sample. The RASP-processed Ti sample exhibited a good combination of yield strength and uniform elongation, which may be attributed to the high density of deformation twins and a strong back stress effect.

  5. Evaluation of stone durability using a combination of ultrasound, mechanical and accelerated aging tests

    Molina, E; Cultrone, G; Sebastián, E; Alonso, F J

    2013-01-01

    The durability of a rock when exposed to decay agents is an important criterion when assessing its quality as a building material. Our study focuses on six varieties of natural stone (two limestones, one dolostone, one travertine and two sandstones) that are widely used in both new and historical buildings. In order to assess their quality, we measured and characterized their dynamic elastic properties using ultrasounds, we measured their compressive strength using the uniaxial compression test and we evaluated their durability by means of accelerated aging tests (freeze-thaw and salt crystallization). In order to get a full picture of the decay suffered by the different stones, we determined the composition and amount of the clay fraction of the six stones. We also observed small fragments subjected to the salt crystallization test under an environmental scanning electron microscope to study any textural change and measured the changes of colour on the surface with a spectrophotometer. Finally, we analysed the pore system of the stones before and after their deterioration using mercury injection porosimetry. We then compared the results for the different stones and found that dolostone obtained the best results, while the two limestones proved to be the least durable and had the lowest compressive strength. (paper)

  6. Enhanced efficiency of plasma acceleration in the laser-induced cavity pressure acceleration scheme

    Badziak, J; Rosiński, M; Jabłoński, S; Pisarczyk, T; Chodukowski, T; Parys, P; Rączka, P; Krousky, E; Ullschmied, J; Liska, R; Kucharik, M

    2015-01-01

    Among various methods for the acceleration of dense plasmas the mechanism called laser-induced cavity pressure acceleration (LICPA) is capable of achieving the highest energetic efficiency. In the LICPA scheme, a projectile placed in a cavity is accelerated along a guiding channel by the laser-induced thermal plasma pressure or by the radiation pressure of an intense laser radiation trapped in the cavity. This arrangement leads to a significant enhancement of the hydrodynamic or electromagnetic forces driving the projectile, relative to standard laser acceleration schemes. The aim of this paper is to review recent experimental and numerical works on LICPA with the emphasis on the acceleration of heavy plasma macroparticles and dense ion beams. The main experimental part concerns the research carried out at the kilojoule sub-nanosecond PALS laser facility in Prague. Our measurements performed at this facility, supported by advanced two-dimensional hydrodynamic simulations, have demonstrated that the LICPA accelerator working in the long-pulse hydrodynamic regime can be a highly efficient tool for the acceleration of heavy plasma macroparticles to hyper-velocities and the generation of ultra-high-pressure (>100 Mbar) shocks through the collision of the macroparticle with a solid target. The energetic efficiency of the macroparticle acceleration and the shock generation has been found to be significantly higher than that for other laser-based methods used so far. Using particle-in-cell simulations it is shown that the LICPA scheme is highly efficient also in the short-pulse high-intensity regime and, in particular, may be used for production of intense ion beams of multi-MeV to GeV ion energies with the energetic efficiency of tens of per cent, much higher than for conventional laser acceleration schemes. (paper)

  7. Health shocks and risk aversion.

    Decker, Simon; Schmitz, Hendrik

    2016-12-01

    We empirically assess whether a health shock influences individual risk aversion. We use grip strength data to obtain an objective health shock indicator. In order to account for the non-random nature of our data regression-adjusted matching is employed. Risk preferences are traditionally assumed to be constant. However, we find that a health shock increases individual risk aversion. The finding is robust to a series of sensitivity analyses and persists for at least four years after the shock. Income changes do not seem to be the driving mechanism. Copyright © 2016 Elsevier B.V. All rights reserved.

  8. Various Occurrence Mechanisms of Large Acceleration over 20 m/s2 and Its Suitability in Design Use

    Shuichi Kamagata

    2018-02-01

    Full Text Available Three amplification mechanisms of large accelerations over 20 m/s2 are related to various non-liner behaviors and explained by using the non-stationary Fourier spectra. The frequencies of dominant components are compared with the natural frequencies with the ratios (1:3:5:7 of a shear-spring model of the underground soil. Thus, one of the amplification mechanisms is supposed to result from the natural modes in the underground soil. Furthermore, the similarity of pulse waves between MYG012 (EW and AKTH04 (EW is pointed out in the non-stationary Fourier spectra and the double-integrated displacement profiles. The pulse waves are identified by the Ricker wavelet. This amplification mechanism is supposed to be caused by the collision between the observation house and the side soil. The modulation of dominant component is also detected in the high frequency range. The shear strain of AKTH04 is calculated using the relative displacement profiles between the surface and the borehole. The peak shear strain is fitted to the G-γ relation and the deterioration ratio of shear stiffness is evaluated. The third amplification mechanism is related to the change of depth of isolated surface soil. The depth of the isolated surface soil is evaluated from the deterioration area shallower than 20 m. It is pointed out finally that the seismic records at the ground surface are unsuitable for the database of seismic design wave.

  9. Neural Network Models of Simple Mechanical Systems Illustrating the Feasibility of Accelerated Life Testing

    Fusaro, Robert L.; Jones, Steven P.; Jansen, Ralph

    1996-01-01

    A complete evaluation of the tribological characteristics of a given material/mechanical system is a time-consuming operation since the friction and wear process is extremely systems sensitive. As a result, experimental designs (i.e., Latin Square, Taguchi) have been implemented in an attempt to not only reduce the total number of experimental combinations needed to fully characterize a material/mechanical system, but also to acquire life data for a system without having to perform an actual life test. Unfortunately, these experimental designs still require a great deal of experimental testing and the output does not always produce meaningful information. In order to further reduce the amount of experimental testing required, this study employs a computer neural network model to investigate different material/mechanical systems. The work focuses on the modeling of the wear behavior, while showing the feasibility of using neural networks to predict life data. The model is capable of defining which input variables will influence the tribological behavior of the particular material/mechanical system being studied based on the specifications of the overall system.

  10. Mechanical stresses and strains in superconducting dipole magnets for high energy accelerators

    Greben, L.I.; Mironov, E.S.; Moustafin, H.H.

    1979-01-01

    Stress and strain distributions in superconducting dipole magnets were investigated numerically. A finite element computer program was developed to calculate stresses and displacements due to thermal stress, electromagnetic forces and prestressing of structural elements. Real mechanical and thermal properties of superconducting dipole elements are taken into account. Numerical results of stress and strain patterns in dipole magnets are presented

  11. Study of the mechanisms of heavy-ion induced desorption on accelerator-relevant materials

    Bender, Markus

    2008-01-01

    The ion beam loss induced desorption is a performance limitation for low charge state heavy ion accelerators. If charge exchanged projectile ions get lost onto the beam pipe, desorption of gas is stimulated resulting in a pressure increase inside of the synchrotron and thus, a dramatically reduction of the beam life time. To minimize the amount of desorbed gas an experimental program has been started to measure the desorption yields (released gas molecules per incident ion) of various materials and different projectile ions. The present work is a contribution to the understanding of the physical processes behind the ion beam loss induced desorption. The yield measurements by the pressure rise method have been combined for the rst time with in situ ion beam analysis technologies such as ERDA and RBS. With this unique method the desorption behavior of a sample can be correlated to its surface and bulk properties. The performed experiments with 1,4 MeV/u Xenon-Ions show that the ion induced desorption is mainly a surface effect. Sputtered oxide layers or impurities do not contribute to the desorbed gas significantly. Nevertheless bulk properties play an important role in the desorption strength. Pure metallic samples desorb less gas than isolating materials under swift heavy ion irradiation. From the experimental results it was possible to estimate the desorption yields of various materials under ion bombardment by means of an extended inelastic thermal-spike-model. The extension is the combination of the thermal-spike's temperature map with thermal desorption. Within this model the ion induced desorption can be regarded as the release of adsorbates from a transient overheated spot on the samples surface around the ion impact. Finally a copper substrate with a gold coated surface was developed and proposed as a suitable material for a beam loss collimator with minimum desorption to ensure the performance of GSI's SIS18 in high current beam operation. (orig.)

  12. Hypovolemic shock

    ... the person's position unless they are in immediate danger. Do not give fluids by mouth. If person ... the patient with shock. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine . 25th ed. Philadelphia, PA: ...

  13. Mechanical properties as an indicator of interstitials in niobium for superconducting accelerator cavities

    Ricker, R. E., E-mail: richard.ricker@nist.gov; Pitchure, D. J., E-mail: david.pitchure@nist.gov [Materials Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, US (United States); Myneni, G. R., E-mail: rao@jlab.org [Thomas Jefferson National Accelerator Facility, Newport News, VA 23606, US (United States)

    2015-12-04

    A preliminary investigation was conducted into the feasibility of using simple mechanical properties experiments to evaluate interstitial impurity uptake from processing environments. Two types of tests were examined: tensile tests and complex modulus measurements using a dynamic mechanical analyzer (DMA). For the tensile tests, samples were cut from a single crystal of niobium, with the same orientation, and then prepared following different procedures. Significant differences were observed during tensile tests, with yielding strength and strain-to-failure clearly related to interstitial uptake. When the strain rate was reduced by an order of magnitude, the strain-to-failure was reduced by 18 % indicating that interstitial hydrogen is responsible for this behavior. For the complex modulus measurement, polycrystalline samples from different locations of two different ingots were examined at a frequency of 1.0 Hz while the temperature was increased at the rate of 1.0 °C per minute. Anaelastic peaks were found for C, N, and O in all samples, but the lower limit of the system did not allow for detection of a peak for H. It is concluded that mechanical properties could be developed as a measurement tool to guide the development of processing methods for producing reduced interstitial content material, but additional research, and uncertainty analysis, is required for these tools to be reliable in this application.

  14. Shock waves in weakly compressed granular media.

    van den Wildenberg, Siet; van Loo, Rogier; van Hecke, Martin

    2013-11-22

    We experimentally probe nonlinear wave propagation in weakly compressed granular media and observe a crossover from quasilinear sound waves at low impact to shock waves at high impact. We show that this crossover impact grows with the confining pressure P0, whereas the shock wave speed is independent of P0-two hallmarks of granular shocks predicted recently. The shocks exhibit surprising power law attenuation, which we model with a logarithmic law implying that shock dissipation is weak and qualitatively different from other granular dissipation mechanisms. We show that elastic and potential energy balance in the leading part of the shocks.

  15. Shock absorber

    Housman, J.J.

    1978-01-01

    A shock absorber is described for use in a hostile environment at the end of a blind passage for absorbing impact loads. The shock absorber includes at least one element which occupies the passage and which is comprised of a porous brittle material which is substantially non-degradable in the hostile environment. A void volume is provided in the element to enable the element to absorb a predetermined level of energy upon being crushed due to impact loading

  16. Particle acceleration in the plasma fields near comet Halley

    Somogyi, A.J.; Erdoes, G.; Shapiro, V.D.; Shevchenko, V.I.

    1990-01-01

    Spacecraft VEGA-1 approached Halley comet to distances less than 10 million km in March 1986. It was equipped with devices capable to detect and measure the energies of charged particles (higher than 50 keV). After a survey of acceleration mechanisms the properties of the 50-800 keV charged particle fluxes observed in various regions around Halley comet are reported. In particular, the regions outside the cometary bow shock, the region between the bow shock and the cometopause, and inside the latter, especially in the magnetic pile-up region are considered. Possible mechanisms responsible for the accelerations of the particle fluxes described are discussed. (author) 73 refs.; 7 figs.; 3 tabs

  17. The stability of mechanical calibration for a kV cone beam computed tomography system integrated with linear accelerator

    Sharpe, Michael B.; Moseley, Douglas J.; Purdie, Thomas G.

    2006-01-01

    The geometric accuracy and precision of an image-guided treatment system were assessed. Image guidance is performed using an x-ray volume imaging (XVI) system integrated with a linear accelerator and treatment planning system. Using an amorphous silicon detector and x-ray tube, volumetric computed tomography images are reconstructed from kilovoltage radiographs by filtered backprojection. Image fusion and assessment of geometric targeting are supported by the treatment planning system. To assess the limiting accuracy and precision of image-guided treatment delivery, a rigid spherical target embedded in an opaque phantom was subjected to 21 treatment sessions over a three-month period. For each session, a volumetric data set was acquired and loaded directly into an active treatment planning session. Image fusion was used to ascertain the couch correction required to position the target at the prescribed iso-center. Corrections were validated independently using megavoltage electronic portal imaging to record the target position with respect to symmetric treatment beam apertures. An initial calibration cycle followed by repeated image-guidance sessions demonstrated the XVI system could be used to relocate an unambiguous object to within less than 1 mm of the prescribed location. Treatment could then proceed within the mechanical accuracy and precision of the delivery system. The calibration procedure maintained excellent spatial resolution and delivery precision over the duration of this study, while the linear accelerator was in routine clinical use. Based on these results, the mechanical accuracy and precision of the system are ideal for supporting high-precision localization and treatment of soft-tissue targets

  18. Research on generation mechanism of single event transient current generated in the semiconductor using ion accelerator

    Hirao, Toshio

    2007-01-01

    Single-event upset (SEU) is triggered when an amount of electric charges induced by energetic ion incidence exceeds a value known as a critical charge in a very short time period. Therefore, accurate evaluation of electric charge and understanding of basic mechanism of SEU are necessary for the improvement of SEU torrance of electronic devices. In this paper, the collected charges for the single event transient current induced on semiconductor by heavy ion microbeams, and application to use microbeam for single event studies are presented. (author)

  19. Mechanical design of a pinger system for the LBNL Advanced Light Source Accelerator

    Thur, W.; Akre, J.; Gavidia, A.; Guigli, J.

    1997-05-01

    A fast magnet ''Pinger System'' has been designed for the Advanced Light Source 1.9 GeV electron Storage Ring. Intended for beam dynamics studies, its purpose is to provide a fast (< 600 ns) transverse magnetic field pulse to perturb the orbit of an electron bunch in a single turn. A key component is the special resistive-coated ceramic beam tube which is needed for fast magnetic field penetration. The evolution of the design concept is described, with emphasis on simplifications to provide an economical and mechanically robust device

  20. Future accelerator technology

    Sessler, A.M.

    1986-05-01

    A general discussion is presented of the acceleration of particles. Upon this foundation is built a categorization scheme into which all accelerators can be placed. Special attention is devoted to accelerators which employ a wake-field mechanism and a restricting theorem is examined. It is shown how the theorem may be circumvented. Comments are made on various acceleration schemes

  1. 2013 Russell Ross memorial lecture in vascular biology: cellular and molecular mechanisms of diabetes mellitus-accelerated atherosclerosis.

    Bornfeldt, Karin E

    2014-04-01

    Adults with diabetes mellitus are much more likely to have cardiovascular disease than those without diabetes mellitus. Genetically engineered mouse models have started to provide important insight into the mechanisms whereby diabetes mellitus promotes atherosclerosis. Such models have demonstrated that diabetes mellitus promotes formation of atherosclerotic lesions, progression of lesions into advanced hemorrhaged lesions, and that it prevents lesion regression. The proatherosclerotic effects of diabetes mellitus are driven in part by the altered function of myeloid cells. The protein S100A9 and the receptor for advanced glycation end-products are important modulators of the effect of diabetes mellitus on myelopoiesis, which might promote monocyte accumulation in lesions. Furthermore, myeloid cell expression of the enzyme acyl-CoA synthetase 1 (ACSL1), which converts long-chain fatty acids into their acyl-CoA derivatives, has emerged as causal to diabetes mellitus-induced lesion initiation. The protective effects of myeloid ACSL1-deficiency in diabetic mice, but not in nondiabetic mice, indicate that myeloid cells are activated by diabetes mellitus through mechanisms that play minor roles in the absence of diabetes mellitus. The roles of reactive oxygen species and insulin resistance in diabetes mellitus-accelerated atherosclerosis are also discussed, primarily in relation to endothelial cells. Translational studies addressing whether the mechanisms identified in mouse models are equally important in humans with diabetes mellitus will be paramount.

  2. Target design for shock ignition

    Schurtz, G; Ribeyre, X; Lafon, M

    2010-01-01

    The conventional approach of laser driven inertial fusion involves the implosion of cryogenic shells of deuterium-tritium ice. At sufficiently high implosion velocities, the fuel ignites by itself from a central hot spot. In order to reduce the risks of hydrodynamic instabilities inherent to large implosion velocities, it was proposed to compress the fuel at low velocity, and ignite the compressed fuel by means of a convergent shock wave driven by an intense spike at the end of the laser pulse. This scheme, known as shock ignition, reduces the risks of shell break-up during the acceleration phase, but it may be impeded by a low coupling efficiency of the laser pulse with plasma at high intensities. This work provides a relationship between the implosion velocity and the laser intensity required to ignite the target by a shock. The operating domain of shock ignition at different energies is described.

  3. Revisiting the thermal effect on shock wave propagation in weakly ionized plasmas

    Zhou, Qianhong; Dong, Zhiwei; Yang, Wei

    2016-01-01

    Many researchers have investigated shock propagation in weakly ionized plasmas and observed the following anomalous effects: shock acceleration, shock recovery, shock weakening, shock spreading, and splitting. It was generally accepted that the thermal effect can explain most of the experimental results. However, little attention was paid to the shock recovery. In this paper, the shock wave propagation in weakly ionized plasmas is studied by fluid simulation. It is found that the shock acceleration, weakening, and splitting appear after it enters the plasma (thermal) region. The shock splits into two parts right after it leaves the thermal region. The distance between the splitted shocks keeps decreasing until they recover to one. This paper can explain a whole set of features of the shock wave propagation in weakly ionized plasmas. It is also found that both the shock curvature and the splitting present the same photoacoustic deflection (PAD) signals, so they cannot be distinguished by the PAD experiments.

  4. Effect of long-term water immersion or thermal shock on mechanical properties of high-impact acrylic denture base resins.

    Sasaki, Hirono; Hamanaka, Ippei; Takahashi, Yutaka; Kawaguchi, Tomohiro

    2016-01-01

    The purpose of this study was to investigate the effect of long-term water immersion or thermal shock on the mechanical properties of high-impact acrylic denture base resins. Two high-impact acrylic denture base resins were selected for the study. Specimens of each denture base material tested were fabricated according to the manufacturers' instructions (n=10). The flexural strength at the proportional limit, the elastic modulus and the impact strength of the specimens were evaluated. The flexural strength at the proportional limit of the high-impact acrylic denture base resins did not change after six months' water immersion or thermocycling 50,000 times. The elastic moduli of the high-impact acrylic denture base resins significantly increased after six months' water immersion or thermocycling 50,000 times. The impact strengths of the high-impact acrylic denture base resins significantly decreased after water immersion or thermocycling as described above.

  5. A Precision-Positioning Method for a High-Acceleration Low-Load Mechanism Based on Optimal Spatial and Temporal Distribution of Inertial Energy

    Xin Chen

    2015-09-01

    Full Text Available High-speed and precision positioning are fundamental requirements for high-acceleration low-load mechanisms in integrated circuit (IC packaging equipment. In this paper, we derive the transient nonlinear dynamicresponse equations of high-acceleration mechanisms, which reveal that stiffness, frequency, damping, and driving frequency are the primary factors. Therefore, we propose a new structural optimization and velocity-planning method for the precision positioning of a high-acceleration mechanism based on optimal spatial and temporal distribution of inertial energy. For structural optimization, we first reviewed the commonly flexible multibody dynamic optimization using equivalent static loads method (ESLM, and then we selected the modified ESLM for optimal spatial distribution of inertial energy; hence, not only the stiffness but also the inertia and frequency of the real modal shapes are considered. For velocity planning, we developed a new velocity-planning method based on nonlinear dynamic-response optimization with varying motion conditions. Our method was verified on a high-acceleration die bonder. The amplitude of residual vibration could be decreased by more than 20% via structural optimization and the positioning time could be reduced by more than 40% via asymmetric variable velocity planning. This method provides an effective theoretical support for the precision positioning of high-acceleration low-load mechanisms.

  6. Pathways and mechanisms for product release in the engineered haloalkane dehalogenases explored using classical and random acceleration molecular dynamics simulations.

    Klvana, Martin; Pavlova, Martina; Koudelakova, Tana; Chaloupkova, Radka; Dvorak, Pavel; Prokop, Zbynek; Stsiapanava, Alena; Kuty, Michal; Kuta-Smatanova, Ivana; Dohnalek, Jan; Kulhanek, Petr; Wade, Rebecca C; Damborsky, Jiri

    2009-10-09

    Eight mutants of the DhaA haloalkane dehalogenase carrying mutations at the residues lining two tunnels, previously observed by protein X-ray crystallography, were constructed and biochemically characterized. The mutants showed distinct catalytic efficiencies with the halogenated substrate 1,2,3-trichloropropane. Release pathways for the two dehalogenation products, 2,3-dichloropropane-1-ol and the chloride ion, and exchange pathways for water molecules, were studied using classical and random acceleration molecular dynamics simulations. Five different pathways, denoted p1, p2a, p2b, p2c, and p3, were identified. The individual pathways showed differing selectivity for the products: the chloride ion releases solely through p1, whereas the alcohol releases through all five pathways. Water molecules play a crucial role for release of both products by breakage of their hydrogen-bonding interactions with the active-site residues and shielding the charged chloride ion during its passage through a hydrophobic tunnel. Exchange of the chloride ions, the alcohol product, and the waters between the buried active site and the bulk solvent can be realized by three different mechanisms: (i) passage through a permanent tunnel, (ii) passage through a transient tunnel, and (iii) migration through a protein matrix. We demonstrate that the accessibility of the pathways and the mechanisms of ligand exchange were modified by mutations. Insertion of bulky aromatic residues in the tunnel corresponding to pathway p1 leads to reduced accessibility to the ligands and a change in mechanism of opening from permanent to transient. We propose that engineering the accessibility of tunnels and the mechanisms of ligand exchange is a powerful strategy for modification of the functional properties of enzymes with buried active sites.

  7. Radio emission from coronal and interplanetary shocks

    Cane, H.V.

    1987-01-01

    Observational data on coronal and interplanetary (IP) type II burst events associated with shock-wave propagation are reviewed, with a focus on the past and potential future contributions of space-based observatories. The evidence presented by Cane (1983 and 1984) in support of the hypothesis that the coronal (metric) and IP (kilometric) bursts are due to different shocks is summarized, and the fast-drift kilometric events seen at the same time as metric type II bursts (and designated shock-accelerated or shock-associated events) are characterized. The need for further observations at 0.5-20 MHz is indicated. 20 references

  8. Converging cylindrical shocks in ideal magnetohydrodynamics

    Pullin, D. I.; Mostert, W.; Wheatley, V.; Samtaney, R.

    2014-01-01

    then slows the shock Mach number growth producing a maximum followed by monotonic reduction towards magnetosonic conditions, even as the shock accelerates toward the axis. A parameter space of initial shock Mach number at a given radius is explored and the implications of the present results for inertial confinement fusion are discussed

  9. Converging cylindrical shocks in ideal magnetohydrodynamics

    Pullin, D. I.

    2014-09-01

    slows the shock Mach number growth producing a maximum followed by monotonic reduction towards magnetosonic conditions, even as the shock accelerates toward the axis. A parameter space of initial shock Mach number at a given radius is explored and the implications of the present results for inertial confinement fusion are discussed.

  10. Converging cylindrical shocks in ideal magnetohydrodynamics

    Pullin, D. I.; Mostert, W.; Wheatley, V.; Samtaney, Ravi

    2014-01-01

    slows the shock Mach number growth producing a maximum followed by monotonic reduction towards magnetosonic conditions, even as the shock accelerates toward the axis. A parameter space of initial shock Mach number at a given radius is explored and the implications of the present results for inertial confinement fusion are discussed.

  11. Converging cylindrical shocks in ideal magnetohydrodynamics

    Pullin, D. I. [Graduate Aerospace Laboratories, California Institute of Technology, Pasadena, California 91125 (United States); Mostert, W.; Wheatley, V. [School of Mechanical and Mining Engineering, University of Queensland, Queensland 4072 (Australia); Samtaney, R. [Mechanical Engineering, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology, Thuwal (Saudi Arabia)

    2014-09-15

    diverging magnetic field then slows the shock Mach number growth producing a maximum followed by monotonic reduction towards magnetosonic conditions, even as the shock accelerates toward the axis. A parameter space of initial shock Mach number at a given radius is explored and the implications of the present results for inertial confinement fusion are discussed.

  12. Shocks in fragile matter

    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.

  13. K -essence model from the mechanical approach point of view: coupled scalar field and the late cosmic acceleration

    Bouhmadi-López, Mariam; Kumar, K. Sravan; Marto, João [Departamento de Física, Universidade da Beira Interior, Rua Marquês D' Ávila e Bolama, 6201-001 Covilhã (Portugal); Morais, João [Department of Theoretical Physics, University of the Basque Country UPV/EHU, P.O. Box 644, 48080 Bilbao (Spain); Zhuk, Alexander, E-mail: mbl@ubi.pt, E-mail: sravan@ubi.pt, E-mail: jmarto@ubi.pt, E-mail: jviegas001@ikasle.ehu.eus, E-mail: ai.zhuk2@gmail.com [Astronomical Observatory, Odessa National University, Street Dvoryanskaya 2, Odessa 65082 (Ukraine)

    2016-07-01

    In this paper, we consider the Universe at the late stage of its evolution and deep inside the cell of uniformity. At these scales, we can consider the Universe to be filled with dust-like matter in the form of discretely distributed galaxies, a K -essence scalar field, playing the role of dark energy, and radiation as matter sources. We investigate such a Universe in the mechanical approach. This means that the peculiar velocities of the inhomogeneities (in the form of galaxies) as well as the fluctuations of the other perfect fluids are non-relativistic. Such fluids are designated as coupled because they are concentrated around the inhomogeneities. In the present paper, we investigate the conditions under which the K -essence scalar field with the most general form for its action can become coupled. We investigate at the background level three particular examples of the K -essence models: (i) the pure kinetic K -essence field, (ii) a K -essence with a constant speed of sound and (iii) the K -essence model with the Lagrangian bX + cX {sup 2}− V (φ). We demonstrate that if the K -essence is coupled, all these K -essence models take the form of multicomponent perfect fluids where one of the component is the cosmological constant. Therefore, they can provide the late-time cosmic acceleration and be simultaneously compatible with the mechanical approach.

  14. Iron overload in a murine model of hereditary hemochromatosis is associated with accelerated progression of osteoarthritis under mechanical stress.

    Camacho, A; Simão, M; Ea, H-K; Cohen-Solal, M; Richette, P; Branco, J; Cancela, M L

    2016-03-01

    Hereditary hemochromatosis (HH) is a disease caused by mutations in the Hfe gene characterised by systemic iron overload and associated with an increased prevalence of osteoarthritis (OA) but the role of iron overload in the development of OA is still undefined. To further understand the molecular mechanisms involved we have used a murine model of HH and studied the progression of experimental OA under mechanical stress. OA was surgically induced in the knee joints of 10-week-old C57BL6 (wild-type) mice and Hfe-KO mice. OA progression was assessed using histology, micro CT, gene expression and immunohistochemistry at 8 weeks after surgery. Hfe-KO mice showed a systemic iron overload and an increased iron accumulation in the knee synovial membrane following surgery. The histological OA score was significantly higher in the Hfe-KO mice at 8 weeks after surgery. Micro CT study of the proximal tibia revealed increased subchondral bone volume and increased trabecular thickness. Gene expression and immunohistochemical analysis showed a significant increase in the expression of matrix metallopeptidase 3 (MMP-3) in the joints of Hfe-KO mice compared with control mice at 8 weeks after surgery. HH was associated with an accelerated development of OA in mice. Our findings suggest that synovial iron overload has a definite role in the progression of HH-related OA. Copyright © 2015 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

  15. Physical mechanism causing rapid changes in ultrarelativistic electron pitch angle distributions right after a shock arrival: Evaluation of an electron dropout event

    Zhang, X.-J.; Li, W.; Thorne, R. M.; Angelopoulos, V.; Ma, Q.; Li, J.; Bortnik, J.; Nishimura, Y.; Chen, L.; Baker, D. N.; Reeves, G. D.; Spence, H. E.; Kletzing, C. A.; Kurth, W. S.; Hospodarsky, G. B.; Blake, J. B.; Fennell, J. F.

    2016-09-01

    Three mechanisms have been proposed to explain relativistic electron flux depletions (dropouts) in the Earth's outer radiation belt during storm times: adiabatic expansion of electron drift shells due to a decrease in magnetic field strength, magnetopause shadowing and subsequent outward radial diffusion, and precipitation into the atmosphere (driven by EMIC wave scattering). Which mechanism predominates in causing electron dropouts commonly observed in the outer radiation belt is still debatable. In the present study, we evaluate the physical mechanism that may be primarily responsible for causing the sudden change in relativistic electron pitch angle distributions during a dropout event observed by Van Allen Probes during the main phase of the 27 February 2014 storm. During this event, the phase space density of ultrarelativistic (>1 MeV) electrons was depleted by more than 1 order of magnitude over the entire radial extent of the outer radiation belt (3 pitch angle distribution under a compressed magnetic field topology based on actual solar wind conditions. Although these ultrarelativistic electrons exhibit highly anisotropic (peaked in 90°), energy-dependent pitch angle distributions, which appear to be associated with the typical EMIC wave scattering, comparison of the modeled electron distribution to electron measurements indicates that drift shell splitting is responsible for this rapid change in electron pitch angle distributions. This further indicates that magnetopause loss is the predominant cause of the electron dropout right after the shock arrival.

  16. Toxic shock syndrome

    Staphylococcal toxic shock syndrome; Toxic shock-like syndrome; TSLS ... Toxic shock syndrome is caused by a toxin produced by some types of staphylococcus bacteria. A similar problem, called toxic shock- ...

  17. Inferior vena cava obstruction and shock

    Megri Mohammed

    2018-01-01

    Full Text Available Shock is one of the most challenging life-threatening conditions with high mortality and morbidity; the outcomes are highly dependent on the early detection and management of the condition. Septic shock is the most common type of shock in the Intensive Care Unit. While not as common as other subsets of shock, obstructive shock is a significant subtype due to well defined mechanical and pathological causes, including tension pneumothorax, massive pulmonary embolism, and cardiac tamponade. We are presenting a patient with obstructive shock due to inferior vena cava obstruction secondary to extensive deep venous thrombosis. Chance of survival from obstructive shock in our patient was small; however, there was complete and immediate recovery after treatment of the obstruction on recognizing the affected vessels. This case alerts the practicing intensivist and the emergency medicine physician to consider occlusion of the great vessels other than the pulmonary artery or aorta as causes of obstructive shock.

  18. Sepsis and Septic Shock Strategies.

    Armstrong, Bracken A; Betzold, Richard D; May, Addison K

    2017-12-01

    Three therapeutic principles most substantially improve organ dysfunction and survival in sepsis: early, appropriate antimicrobial therapy; restoration of adequate cellular perfusion; timely source control. The new definitions of sepsis and septic shock reflect the inadequate sensitivity, specify, and lack of prognostication of systemic inflammatory response syndrome criteria. Sequential (sepsis-related) organ failure assessment more effectively prognosticates in sepsis and critical illness. Inadequate cellular perfusion accelerates injury and reestablishing perfusion limits injury. Multiple organ systems are affected by sepsis and septic shock and an evidence-based multipronged approach to systems-based therapy in critical illness results in improve outcomes. Copyright © 2017 Elsevier Inc. All rights reserved.

  19. The Solar Flare: A Strongly Turbulent Particle Accelerator

    Vlahos, L.; Krucker, S.; Cargill, P.

    The topics of explosive magnetic energy release on a large scale (a solar flare) and particle acceleration during such an event are rarely discussed together in the same article. Many discussions of magnetohydrodynamic (MHD) mod- eling of solar flares and/or CMEs have appeared (see [143] and references therein) and usually address large-scale destabilization of the coronal mag- netic field. Particle acceleration in solar flares has also been discussed exten- sively [74, 164, 116, 166, 87, 168, 95, 122, 35] with the main emphasis being on the actual mechanisms for acceleration (e.g., shocks, turbulence, DC electric fields) rather than the global magnetic context in which the acceleration takes place.

  20. Shock ignition of high gain inertial fusion capsules

    Schurtz, G.; Ribeyre, X.; Lebel, E.; Casner, A.

    2010-01-01

    Complete text of publication follows. Inertial Confinement Fusion relies on the compression of small amounts of an equimolar mix of Deuterium and Tritium (DT) up to volumic masses of several hundreds of g/cm 3 . Such high densities are obtained by means of the implosion of a spherical shell made of cryogenic DT fuel. In the conventional scheme a hot spot is formed in the central part of the pellet at the end of the implosion. If the pressure of this hot spot is large enough (several hundreds of Gbars), thermonuclear heating occurs with a characteristic time shorter than the hydrodynamic confinement time and the target self ignites. Since the central hot spot pressure results from the conversion of the shell kinetic energy into thermal energy, the threshold for the ignition of a given mass of DT is a direct function of the implosion velocity. Typical implosion velocities for central self ignition are of the order of 400 km/s. Such high velocities imply both a strong acceleration of the shell and the use of large aspect ration shells in order to optimize the hydrodynamic efficiency of the implosion, at least in direct drive. These two features strongly enhance the risk of shell beak up at time of acceleration under the Rayleigh-Taylor instability. Furthermore the formation of the hot spot may itself the unstable, this reducing its effective mass. High compression may be achieved at much lower velocities, thus reducing the energy budget and enhancing the implosion safety, but the corresponding fuel assembly requires an additional heating in order to reach ignition. This heating may be obtained from a 70-100 kJ laser pulse, delivered in 10-15 ps (Fast Ignition). An alternative idea is to boost up the central pressure of a target imploded at a sub-ignition velocity by means of a convergent strong shock launched at the end of the compression phase. This Shock Ignition (SI) concept has been suggested in 1983 by Scherbakov et al. More recently, R. Betti et al. developed

  1. Protective effects of heat shock protein 70 on the acute lung injury of rats with heat stroke and its mechanism

    Yan GENG

    2017-06-01

    Full Text Available Objective To investigate the protective effect of heat shock protein (HSP 70 on the acute lung injury (ALI of rats with heat stroke. Methods Sixty four rats were randomly (by employing a random number table assigned into a sham-heated group (Sham group, heat stress group (HS group, and HS plus gluttamine treatment group (HS+GLN group and HS plus quercet in treatment group (HS+QU group, 16 each. All rats were housed in a artificial climate chamber, with the rats in the sham groups exposed to a temperature of 23℃ and humidity of 55%±5%, while the rats of HS, HS+GLN and HS+QU groups to an ambient temperature of 39℃ and humidity of 65%. During heat stress or sham heating, rectal temperature (Tr, systolic blood pressure (SBP and pulse rate (PR were monitored to observe the difference in heat stress response among the groups. The time point at which the SBP started to drop from the peak level was taken as the point of HS onset. At the onset of HS, heat exposure was terminated, then the rats were immediately removed from the chamber, and returned to room temperature. The rats were scarified 0h and 6h after HS onset respectively. After bronchoalveolar lavage fluid (BALF was collected, the lungs of all animals were harvested for pathological examination of lung injury. The concentrations of IL-1β, TNF-α and IL-6 in BALF and HSP70 in lung homogenate were measured by using an enzyme linked immunosorbent assay kit. Results Compared with HS and HS+QU groups, the rats in HS+GLN group required significantly greater heat load to induce HS (P<0.001, and had longer survival time span after HS onset. Compared with Sham group, the concentration of HSP70 in lung homogenate in HS group increased in a time-dependent manner (P<0.001. In comparison with HS group, the concentration of HSP70 in lung homogenate from HS+GLN group was significantly elevated at each time point (P<0.001, while the treatment with QU significantly inhibited the expression of HSP70 (P<0

  2. Zr O/sub 2/ and ZrSiO/sub 4/ addition influence in mechanical resistance and thermical shock of Al/sub 2/TiO/sub 5/

    Marinho, P A; Longo, E; Varela, J A; Pandolfelli, V C

    1985-01-01

    The ZrO/sub 2/ and ZrSiO/sub 4/ addition on the Al/sub 2/O/sub 3/TiO/sub 2/ composition showed to be efficient on higher the mechanical and thermal shock resistence of the compound formed. The reactions that formed the phases and the influence of the ones on thermal and mechanical behaviour of the compound Al/sub 2/TiO/sub 5/ were discussed. (L.M.J.).

  3. High rates of carbon storage in old deciduous forests: Emerging mechanisms from the Forest Accelerated Succession ExperimenT (FASET)

    Gough, C. M.; Nave, L. E.; Hardiman, B. S.; Bohrer, G.; Halperin, A.; Maurer, K.; Le Moine, J.; Nadelhoffer, K.; Vogel, C. S.; Curtis, P.; University Of Michigan Biological Station Forest Ecosystem Study (Umbs-Fest) Team

    2010-12-01

    Deciduous forests of the eastern US are broadly approaching an ecological threshold in which early successional dominant trees are senescing and giving way to later successional species, with unknown consequences for regional carbon (C) cycling. Though recent research demonstrates that forests may accumulate C for centuries, the mechanisms behind sustained rates of C storage in old, particularly deciduous, forests have not been identified. In a regionally representative forest at the University of Michigan Biological Station, we are combining observational and experimental C cycling studies to forecast how forest C storage responds to climate variation, disturbance, and succession. The Forest Accelerated Succession ExperimenT (FASET), in which >6,700 aspen and birch trees (~35 % LAI) were stem girdled within a 39 ha area, is testing the hypothesis that forest production will increase rather than decline with age, due to increases in nitrogen (N) availability, N allocation to the canopy, and the concurrent development of a more biologically and structurally complex canopy. Results thus far support our hypothesis that aging forests in the region may sustain high rates of C storage through shifts in N cycling and increased canopy complexity. Girdling-induced mortality of early successional species reduced soil respiration, accelerated fine root turnover, and prompted the redistribution of N from the foliage of early to later successional species. Nitrogen redistribution increased leaf area index (LAI) production by later successional species, offsetting declines in LAI from senescing early successional species. High rates of net primary production (NPP) were sustained in stands comprising a diverse assemblage of early and later successional species because later successional species, when already present in the canopy, rapidly compensated for declining growth of early successional species. Canopy structural complexity, which increased with forest age, was positively

  4. Relativistic electron dropout echoes induced by interplanetary shocks

    Schiller, Q.; Kanekal, S. G.; Boyd, A. J.; Baker, D. N.; Blake, J. B.; Spence, H. E.

    2017-12-01

    Interplanetary shocks that impact Earth's magnetosphere can produce immediate and dramatic responses in the trapped relativistic electron population. One well-studied response is a prompt injection capable of transporting relativistic electrons deep into the magnetosphere and accelerating them to multi-MeV energies. The converse effect, electron dropout echoes, are observations of a sudden dropout of electron fluxes observed after the interplanetary shock arrival. Like the injection echo signatures, dropout echoes can also show clear energy dispersion signals. They are of particular interest because they have only recently been observed and their causal mechanism is not well understood. In the analysis presented here, we show observations of electron drift echo signatures from the Relativistic Electron-Proton Telescope (REPT) and Magnetic Electron and Ion Sensors (MagEIS) onboard NASA's Van Allen Probes mission, which show simultaneous prompt enhancements and dropouts within minutes of the associated with shock impact. We show that the observations associated with both enhancements and dropouts are explained by the inward motion caused by the electric field impulse induced by the interplanetary shock, and either energization to cause the enhancement, or lack of a seed population to cause the dropout.

  5. The Influence of Irradiation and Accelerated Aging on the Mechanical and Tribological Properties of the Graphene Oxide/Ultra-High-Molecular-Weight Polyethylene Nanocomposites

    Guodong Huang

    2016-01-01

    Full Text Available Graphene oxide/ultra-high-molecular-weight polyethylene (GO/UHMWPE nanocomposite is a potential and promising candidate for artificial joint applications. However, after irradiation and accelerated aging, the mechanical and tribological behaviors of the nanocomposites are still unclear and require further investigation. GO/UHMWPE nanocomposites were successfully fabricated using ultrasonication dispersion, ball-milling, and hot-pressing process. Then, the nanocomposites were irradiated by gamma ray at doses of 100 kGy. Finally, GO/UHMWPE nanocomposites underwent accelerated aging at 80°C for 21 days in air. The mechanical and tribological properties of GO/UHMWPE nanocomposites have been evaluated after irradiation and accelerated aging. The results indicated that the incorporation of GO could enhance the mechanical, wear, and antiscratch properties of UHMWPE. After irradiation, these properties could be further enhanced, compared to unirradiated ones. After accelerated aging, however, these properties have been significantly reduced when compared to unirradiated ones. Moreover, GO and irradiation can synergistically enhance these properties.

  6. Shock resistance testing

    Pouard, M.

    1984-03-01

    In the framework of mechanical tests and to answer the different requests for tests, the T.C.R (Transport Conditionnement et Retraitement) laboratory got test facilities. These installations allow to carry out tests of resistance to shocks, mainly at the safety level of components of nuclear power plants, mockups of transport casks for fuel elements and transport containers for radioactive materials. They include a tower and a catapult. This paper give a decription of the facilities and explain their operation way [fr

  7. Shock Spectrum Calculation from Acceleration Time Histories

    1980-09-01

    accurate and economical . If the velocity is desired, it can be calculated with Equation A-8b. As it stands it is exact. Approx- imation will be...Washington DC; DAEN-MCE.D (R L Wight) Washington DC; DAEN.MPE-D Washington DC; DAEN- MPU . Washington DC; DARCOM; ERADCOM Tech Supp Dir. (DELSD-L) Ft

  8. Origin of 30 approximately 100 keV protons observed in the upstream region of the earth's bow shock

    Terasawa, T.

    1979-01-01

    A Fermi-type acceleration model is constructed to explain the origin of energetic protons (30 approximately 100 keV) which have been observed upstream of the bow shock. It is shown that the suprathermal protons (with energy of several keV) can be accelerated up to several tens of keV through the Fermi-type process in which the reflection at the shock front and the scattering in the upstream region are coupled. The efficiency of the scattering process is estimated by using the results of Barnes' quasilinear treatment of the wave excitation. The resultant energy spectrum and flux intensity (10 3 approximately 10 4 protons/(cm 2 s ster keV) in 32 approximately 45.3 keV) are consistent with the observation, and the softening of the energy spectrum observed in the dawn region can be explained by the decrease in the efficiency of the acceleration process in the dawn region due to the curvature of the bow shock and the reduction of shock strength. The spatial distribution of the flux predicted by the model is also consistent with the observation. In view of these consistencies of the Fermi-type acceleration process is suggested as a possible candidate mechanism to explain the upstream protons although it is not intended to exclude other possibilities. (author)

  9. EVIDENCE FOR A COMMON ACCELERATION MECHANISM FOR ENRICHMENTS OF {sup 3}He AND HEAVY IONS IN IMPULSIVE SEP EVENTS

    Mason, Glenn M. [Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723 (United States); Nitta, Nariaki V. [Lockheed Martin Advanced Technology Center, Dept/A021S, B/252, 3251 Hanover Street, Palo Alto, CA 94304 (United States); Wiedenbeck, Mark E. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Innes, Davina E., E-mail: glenn.mason@jhuapl.edu, E-mail: nitta@lmsal.com, E-mail: mark.e.wiedenbeck@jpl.nasa.gov, E-mail: innes@mps.mpg.de [Max-Planck-Institut für Sonnensystemforschung, D-37077 Göttingen (Germany)

    2016-06-01

    We have surveyed the period 1997–2015 for a rare type of {sup 3}He-rich solar energetic particle (SEP) event, with enormously enhanced values of the S/O ratio, that differs from the majority of {sup 3}He-rich events, which show enhancements of heavy ions increasing smoothly with mass. Sixteen events were found, most of them small but with solar source characteristics similar to other {sup 3}He-rich SEP events. A single event on 2014 May 16 had higher intensities than the others, and curved Si and S spectra that crossed the O spectrum above ∼200 keV nucleon{sup −1}. Such crossings of heavy-ion spectra have never previously been reported. The dual enhancement of Si and S suggests that element Q / M ratio is critical to the enhancement since this pair of elements uniquely has very similar Q / M ratios over a wide range of temperatures. Besides {sup 3}He, Si, and S, in this same event the C, N, and Fe spectra also showed curved shape and enhanced abundances compared to O. The spectral similarities suggest that all have been produced from the same mechanism that enhances {sup 3}He. The enhancements are large only in the high-energy portion of the spectrum, and so affect only a small fraction of the ions. The observations suggest that the accelerated plasma was initially cool (∼0.4 MK) and was then heated to a few million kelvin to generate the preferred Q / M ratio in the range C–Fe. The temperature profile may be the distinct feature of these events that produces the unusual abundance signature.

  10. Weibel instability mediated collisionless shocks using intense laser-driven plasmas

    Palaniyappan, Sasikumar; Fiuza, Federico; Huang, Chengkun; Gautier, Donald; Ma, Wenjun; Schreiber, Jorg; Raymer, Abel; Fernandez, Juan; Shimada, Tom; Johnson, Randall

    2017-10-01

    The origin of cosmic rays remains a long-standing challenge in astrophysics and continues to fascinate physicists. It is believed that ``collisionless shocks'' - where the particle Coulomb mean free path is much larger that the shock transition - are a dominant source of energetic cosmic rays. These shocks are ubiquitous in astrophysical environments such as gamma-ray bursts, supernova remnants, pulsar wind nebula and coronal mass ejections from the sun. A particular type of electromagnetic plasma instability known as Weibel instability is believed to be the dominant mechanism behind the formation of these collisionless shocks in the cosmos. The understanding of the microphysics behind collisionless shocks and their particle acceleration is tightly related with nonlinear basic plasma processes and remains a grand challenge. In this poster, we will present results from recent experiments at the LANL Trident laser facility studying collisionless shocks using intense ps laser (80J, 650 fs - peak intensity of 1020 W/cm2) driven near-critical plasmas using carbon nanotube foam targets. A second short pulse laser driven protons from few microns thick gold foil is used to radiograph the main laser-driven plasma. Work supported by the LDRD program at LANL.

  11. Hydromagnetic shock structure in the presence of cosmic rays

    Drury, L.O.; Voelk, H.J.

    1981-01-01

    The time asymptotic structure of a shock significantly modified by the back-reaction from the diffusive acceleration of cosmic rays is investigated. Making a physically plausible assumption about the diffusion, it is shown that for given upstream conditions and shock speed only a finite odd number of shock structures are possible; an explicit method of determining these is given (in many cases the solution is unique). The results of this nonlinear study are contrasted with those of the linear test-particle theory and shown to confirm the possibility of efficient particle acceleration in shocks

  12. Predictors of survival and ability to wean from short-term mechanical circulatory support device following acute myocardial infarction complicated by cardiogenic shock.

    Garan, A Reshad; Eckhardt, Christina; Takeda, Koji; Topkara, Veli K; Clerkin, Kevin; Fried, Justin; Masoumi, Amirali; Demmer, Ryan T; Trinh, Pauline; Yuzefpolskaya, Melana; Naka, Yoshifumi; Burkhoff, Dan; Kirtane, Ajay; Colombo, Paolo C; Takayama, Hiroo

    2017-11-01

    Cardiogenic shock following acute myocardial infarction (AMI-CS) portends a poor prognosis. Short-term mechanical circulatory support devices (MCSDs) provide hemodynamic support for patients with cardiogenic shock but predictors of survival and the ability to wean from short-term MCSDs remain largely unknown. All patients > 18 years old treated at our institution with extra-corporeal membrane oxygenation or short-term surgical ventricular assist device for AMI-CS were studied. We collected acute myocardial infarction details with demographic and hemodynamic variables. Primary outcomes were survival to discharge and recovery from MCSD (i.e. survival without heart replacement therapy including durable ventricular assist device or heart transplant). One hundred and twenty-four patients received extra-corporeal membrane oxygenation or short-term surgical ventricular assist device following acute myocardial infarction from 2007 to 2016; 89 received extra-corporeal membrane oxygenation and 35 short-term ventricular assist device. Fifty-five (44.4%) died in the hospital and 69 (55.6%) survived to discharge. Twenty-six (37.7%) required heart replacement therapy (four transplant, 22 durable ventricular assist device) and 43 (62.3%) were discharged without heart replacement therapy. Age and cardiac index at MCSD implantation were predictors of survival to discharge; patients over 60 years with cardiac index <1.5 l/min per m 2 had a low likelihood of survival. The angiographic result after revascularization predicted recovery from MCSD (odds ratio 9.00, 95% confidence interval 2.45-32.99, p=0.001), but 50% of those optimally revascularized still required heart replacement therapy. Cardiac index predicted recovery from MCSD among this group (odds ratio 4.06, 95% confidence interval 1.45-11.55, p=0.009). Among AMI-CS patients requiring short-term MCSDs, age and cardiac index predict survival to discharge. Angiographic result and cardiac index predict ventricular recovery but 50

  13. Thermal hydraulic-Mechanic Integrated Simulation for Advanced Cladding Thermal Shock Fracture Analysis during Reflood Phase in LBLOCA

    Son, Seong Min; Lee, You Ho; Cho, Jae Wan; Lee, Jeong Ik [KAERI, Daejeon (Korea, Republic of)

    2016-05-15

    This study suggested thermal hydraulic-mechanical integrated stress based methodology for analyzing the behavior of ATF type claddings by SiC-Duplex cladding LBLOCA simulation. Also, this paper showed that this methodology could predict real experimental result well. That concept for enhanced safety of LWR called Advanced Accident-Tolerance Fuel Cladding (ATF cladding, ATF) is researched actively. However, current nuclear fuel cladding design criteria for zircaloy cannot be apply to ATF directly because those criteria are mainly based on limiting their oxidation. So, the new methodology for ATF design criteria is necessary. In this study, stress based analysis methodology for ATF cladding design criteria is suggested. By simulating LBLOCA scenario of SiC cladding which is the one of the most promising candidate of ATF. Also we'll confirm our result briefly through comparing some facts from other experiments. This result is validating now. Some of results show good performance with 1-D failure analysis code for SiC fuel cladding that already developed and validated by Lee et al,. It will present in meeting. Furthermore, this simulation presented the possibility of understanding the behavior of cladding deeper. If designer can predict the dangerous region and the time precisely, it may be helpful for designing nuclear fuel cladding geometry and set safety criteria.

  14. Shock Wave Dynamics in Weakly Ionized Plasmas

    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.

  15. Chondrule destruction in nebular shocks

    Jacquet, Emmanuel; Thompson, Christopher, E-mail: ejacquet@mnhn.fr [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St George Street, Toronto, ON M5S 3H8 (Canada)

    2014-12-10

    Chondrules are millimeter-sized silicate spherules ubiquitous in primitive meteorites, but whose origin remains mysterious. One of the main proposed mechanisms for producing them is melting of solids in shock waves in the gaseous protoplanetary disk. However, evidence is mounting that chondrule-forming regions were enriched in solids well above solar abundances. Given the high velocities involved in shock models, destructive collisions would be expected between differently sized grains after passage of the shock front as a result of differential drag. We investigate the probability and outcome of collisions of particles behind a one-dimensional shock using analytic methods as well as a full integration of the coupled mass, momentum, energy, and radiation equations. Destruction of protochondrules seems unavoidable for solid/gas ratios ε ≳ 0.1, and possibly even for solar abundances because of 'sandblasting' by finer dust. A flow with ε ≳ 10 requires much smaller shock velocities (∼2 versus 8 km s{sup –1}) in order to achieve chondrule-melting temperatures, and radiation trapping allows slow cooling of the shocked fragments. Initial destruction would still be extensive; although re-assembly of millimeter-sized particles would naturally occur by grain sticking afterward, the compositional heterogeneity of chondrules may be difficult to reproduce. We finally note that solids passing through small-scale bow shocks around few kilometer-sized planetesimals might experience partial melting and yet escape fragmentation.

  16. Particle acceleration in the interplanetary space

    Tverskoj, B.A.

    1983-01-01

    A review on the problem of particle acceleration in the interplanetary space is given. The main lationship attention is paid to the problem of the re/ between the impact- and turbulent acceleration when an undisturbed magnetic field forms not too small angle THETA > 10 deg with the shock wave front. The following conclusions are drawn. Particle acceleration at the shock wave front is manifested in the explicit form, if the shock wave propagates along a homogeneous (in the 11 cm range) solar wind. The criterion of such an acceleration is the exponential distribution function F approximately vsup(-ν) (v is the particle velocity and ν is the accelerated particle spectrum index) in the low energy range and the conservation of this function at considerable distances behind the front. The presence of an additional turbulent acceleration behind the front is manifested in decreasing ν down to approximately 3.5 in the low energy range and in the spectrum evolution behind the front

  17. The Dynamic Quasiperpendicular Shock: Cluster Discoveries

    Krasnoselskikh, V.; Balikhin, M.; Walker, S. N.; Schwartz, S.; Sundkvist, D.; Lobzin, V.; Gedalin, M.; Bale, S. D.; Mozer, F.; Souček, Jan; Hobara, Y.; Comisel, H.

    2013-01-01

    Roč. 178, 2-4 (2013), s. 535-598 ISSN 0038-6308 Institutional support: RVO:68378289 Keywords : collisionless shocks * waves in plasmas * nonstationarity * shock scales * plasma heating and acceleration * wave-particle interactions Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 5.874, year: 2013 http://link.springer.com/article/10.1007%2Fs11214-013-9972-y

  18. The theory of ionizing shock waves in a magnetic field

    Liberman, M.A.; Velikovich, A.L.

    1981-01-01

    The general theory of ionizing shock waves in a magnetic field is constructed. The theory takes into account precursor ionization of a neutral gas ahead of the shock wave front, caused by photo-ionization, as well as by the impact ionization with electrons accelerated by a transverse electric field induced by the shock front in the incident flow of a neutral gas. The concept of shock wave ionization stability, being basic in the theory of ionizing shock waves in a magnetic field, is introduced. The ionizing shock wave structures are shown to transform from the GD regime at a low shock velocity to the MHD regime at an enhanced intensity of the shock wave. The abruptness of such a transition is determined by precursor photo-ionization. (author)

  19. Proceedings of the 4th KEK mechanical engineering workshop. Research and development on the technology of the X-band accelerator fabrication

    Ueno, Kenji

    2003-10-01

    The fourth KEK Mechanical Engineering Workshop was held on April 17, 2003. The main subject was ''The Research and Development on the Technology of the X-band Accelerator Fabrication'', which is a part of the collaboration work of Accelerator Laboratory, ACC and Mechanical Engineering Center, MEC based on the joint X-band accelerator research of KEK and SLAC. The main topic of study in FY 2002 was the problem analysis, and seeking its counter-measures about pitting generated over the inner-surface of the accelerator cavities through high field tests. Therefore, to analyze and develop counter-measures for these pittings, manufacturing of several kinds of test accelerators and conducting analytical tests for the surface of cells have been mainly undertaken by ACC and MEC. On the other hand, basic studies of the cutting and bonding processes have shown effective results for the future production process through corroboration work with academic and industrial fields. Related scientists and engineers from various fields participated in this workshop and presented their works. As a keynote speech, Prof. Hitoshi Yamamoto, belonging to Tohoku University, presented ''The physics on linear collider'', and Assistant Prof. Nobukazu Toge, belonging to ACC of KEK, presented ''The Linear Collider Accelerator''. Also, as an invitation speech, former Prof. Nobuteru Hitomi, former Head of MEC, who was the originator of this workshop, and one of the leaders in X-band accelerator fabrication, presented ''The promotion and survey of fabrication technology on X-band accelerator''. These speeches were very instructive, and presented a chance to think about the direction of R and D in our project. Twenty-four papers, ten from KEK, including the keynote speech, seven from universities and seven from industrial companies, were presented and discussed ardently. Among the discussion, there was an opinion that a fast pace to establish mass-production technology is a major requirement for the

  20. Semiconductor acceleration sensor

    Ueyanagi, Katsumichi; Kobayashi, Mitsuo; Goto, Tomoaki

    1996-09-01

    This paper reports a practical semiconductor acceleration sensor especially suited for automotive air bag systems. The acceleration sensor includes four beams arranged in a swastika structure. Two piezoresistors are formed on each beam. These eight piezoresistors constitute a Wheatstone bridge. The swastika structure of the sensing elements, an upper glass plate and a lower glass plate exhibit the squeeze film effect which enhances air dumping, by which the constituent silicon is prevented from breakdown. The present acceleration sensor has the following features. The acceleration force component perpendicular to the sensing direction can be cancelled. The cross-axis sensitivity is less than 3 percent. And, the erroneous offset caused by the differences between the thermal expansion coefficients of the constituent materials can be canceled. The high aspect ratio configuration realized by plasma etching facilitates reducing the dimensions and improving the sensitivity of the acceleration sensor. The present acceleration sensor is 3.9 mm by 3.9 mm in area and 1.2 mm in thickness. The present acceleration sensor can measure from -50 to +50 G with sensitivity of 0.275 mV/G and with non-linearity of less than 1 percent. The acceleration sensor withstands shock of 3000 G.