Showing papers on "Shock wave published in 1968"

Correlated magnetic field and plasma observations of the Earth's bow shock

Abstract: Ion spectrums and magnetograms obtained simultaneously when the Vela 3A satellite crossed the earth's bow shock have been correlated. An intermediate form of ion spectrum, representing neither solar wind nor magnetosheath, but characterized by an irregular envelope and occasional large flux peaks, is found to correspond to the appearance of large-amplitude (10-25 γ), irregular magnetic oscillations of 4-to 30-sec period. The large spectral flux peaks of the shock seem to result from localized transient accelerations and decelerations of the bulk of the solar wind protons. Smaller amplitude (<5 γ), longer period (20-60 seconds), generally more regular magnetic oscillations are seen in the solar wind outside the shock where the direction of flow of ion flux peaks is found to oscillate in close correlation with magnetic waves.

Optical study of the characteristics of shock-compressed condensed dielectrics

Abstract: CONTENTS Introduction 229 I. Study of the optical characteristics of shock-compressed condensed materials, and of the structure and smoothness of the fronts of large-amplitude shock waves 1. Experimental procedure 231 2. Front thickness and smoothness of shock waves in condensed inert and explosive substances 232 3. Density dependence of the refractive index of liquid dielectrics. Anomalous behavior of shock-compressed carbon tetrachloride 234 4. Investigation of the optical properties of shock-compressed ionic crystals. Nonequilibrium states 235 5. Optical study of elastoplastic waves in glass 237 6. Phase transition of water into ice VII under shock compression 238 II. Equilibrium radiation of the shock-wave front. Experimental determination of temperatures. 7. Possibility of temperature measurement in shock-compressed condensed materials. Principle of the method 240 8. Measurement of temperatures of shock-compressed ionic crystals and establishment of their melting curves for pressures up to 0.5-3 Mbar 241 9. Measurement of temperatures of shock-compressed lucite and carbon tetrachloride 245 III. Absorption of light by shock-compressed ionic crystals. Absorption and conduction mechanism. 10. Experimental determination of the absorption coefficient 245 11. Mechanisms of light absorption and conduction in shock-compressed ionic crystals 246 IV. Nonequilibrium radiation of shock-compressed ionic crystals 248 12. Nonequilibrium radiation at low temperatures. Electroluminescence of shock-compressed substances 248 13. Nonequilibrium radiation at high temperatures. Electronic screening of the radiation 249 References 251

Prompt gamma rays and X rays from supernovae

Abstract: The hydrodynamic origin of cosmic rays (Colgate and Johnson 1960) depends upon the shock ejection of the outer layers of the supernova. The increase in energy of the shock to c2 per gram occurs relatively deep within the star where the fraction, F, of mass external to this layer is 10−4. The relativistic shock wave continues to increase in strength in the decreasing density of the envelope. When the shock "breaks through" the surface denned as one Compton scattering mean free path at radius R, then the energy factor . The temperature in the proper frame of the shock is determined by the condition aT4 = 2γs2ρ0, where ρ0 is the initial rest density ahead of the shock. For a typical presupernova star, , and polytrope of index 3, the temperature becomes (1.7–2) × 105 eV at the surface layer. Photons emitted from the moving surface layer will be Doppler-shifted from their mean proper frame value of 3kT to a final energy .Photons originating in, and emitted from, the surface layer before the layer expands adiab...

Processes Occurring in Solids Under the Action of Powerful Shock Waves

Abstract: The action of powerful shock waves on condensed materials can lead to a wide variety of physicochemical changes: polymorphic transformations, decomposition and synthetic processes, polymerisation of monomers, and defect-formation or conversely the formation of a more perfect structure. The study of these processes has shown that many of them take place exceptionally rapidly. The development of methods for the recovery of substances after the action of shock waves made it possible to employ high dynamic pressures for preparative purposes. Examination of the mechanism governing the compression of a substance by a shock wave shows that the transition from elastic monoaxial compression to bulk-phase compression may be identified with phase transformations as regards gas dynamics and thermodynamics and suggests that phase transitions in the shock wave cannot take place at pressures below the dynamic yield point of the substance. The presence of vigorous plastic flow in shock waves together with the operation of pressures reaching millions of atmospheres suggests that in many ways dynamic operations of this kind on various substances are comparable to methods combining high static pressures with shear stresses. Plastic flow in shock waves leads to the appearance of a characteristic mass-transfer mechanism which gives rise to diffusion processes during the very short period of shock-wave compression. Comparison of dynamic and static studies at high pressures reveals a very close correlation between them. However, a number of effects observed by shock-wave techniques are so far inconsistent with the phase diagrams of the corresponding substances.

Atom‐Formation Rates behind Shock Waves in Hydrogen and the Effect of Added Oxygen

Abstract: Atomic H formation rate behind shock waves in H-Ar mixtures, noting catalytic effect of additional O

Hypersonic viscous flow over slender bodies with sharp leading edges.

Abstract: : The hypersonic viscous pressure interaction is treated by the development of a set of equations valid throughout the boundary layer, shock-wave structure and inviscid core. Primary interest is concerned with the nature of the leading edge continuum merged layer in which the shock wave and boundary layer are indistinguishable. Due to the parabolic nature of the equations, finite-difference solutions are attainable. The flow over a flat plate at zero incidence, as well as angle of attack, was considered. Velocity and state variable distributions across the viscous layer depict the formation of an outer shock wave and inner constant pressure boundary layer. The calculated values of surface pressure, heat transfer and shock jump conditions were at first significantly below the values predicted by strong interaction theory. Agreement was quite good downstream of the merged layer where Rankine-Hugoniot jump conditions were satisfied to within 8%. (Author)

Detection of electric-field turbulence in the earth's bow shock.

Abstract: Detection of electric field turbulence in earth bow shock, noting wave amplitude correlation with magnetic field structure

Satellite observations of interplanetary shock waves

Abstract: Interplanetary shock waves propagating through the solar wind have been observed with hemispherical plate electrostatic analyzers aboard the twin Vela 3 satellites. From the consideration of mass flux continuity, the shock velocities have been calculated; the shock velocities determined from the data in this manner are consistent with the observed temperature changes across the shocks. These velocities are significantly less than the mean transit velocities of the shocks from the sun to the earth derived from the delay times between the initiating flares and shock arrival. This result is interpreted to mean that interplanetary shock waves are decelerated as they expand and propagate through the quiescent solar plasma.

On the Shock Wave Velocity and Impact Pressure in High-Speed Liquid-Solid Impact

Abstract: Shock wave velocity and pressure in high speed liquid-solid impact based on particle velocity

Intermediate Strength Blast Wave

Abstract: Equations for the trajectory and overpressure of the shock front of the intermediate strength blast wave (10 < Δp/p0 ⪝ 0.02) are developed for spherical, cylindrical, and plane blasts. These equations are based on the correct limit method that provided the trajectory of the blast wave from the inverse pinch to velocities below Mach number 1.16 (Δp/p0 = 0.4). The correct limit equations are an extension of the strong shock similarity solution of G. I. Taylor for the spherical blast and A. Sakurai and S. C. Lin for the cylindrical case. It is now possible, given the energy and ambient gas conditions, to trace the shock front trajectory and overpressure from the very strong through the very weak regimes. Conversely, the shock wave energy can be found from measurement of overpressure or arrival time. Comparisons with experimental data as well as the calculations of H. L. Brode verify the validity of the correct limit equations.

Shock wave from a lightning discharge

Abstract: A theoretical model of the shock wave from a lightning discharge ranging from the strong blast wave region out to the acoustic limit is given for the first time. The trajectory and overpressure of the strong shock wave are described by the well-known equations for cylindrical blast waves. In the intermediate shock strength region (1.1 < M < 3.3), the shock trajectory is given by the ‘correct limit’ equation of Vlases and Jones. We derive an additional ‘correct limit’ equation for overpressure that is valid out to the acoustic limit. The correct limit equations predict a much slower decay of the intermediate shock wave; thus, the shock wave is much stronger at large distances from the discharge than was previously believed. Consequently, the range of action of the lightning discharge via its shock wave, as it affects the shattering and freezing of supercooled hydrometeors, may be large.

Compression of Porous Copper by Shock Waves

Abstract: Hugoniot data for porous copper of two initial densities, 6.052 and 7.406 g/cm3, are presented for compressive stresses ranging from 2 kbar to 1 Mbar. These densities respectively correspond to 67.8% and 82.9% of the density of solid copper. High explosives were used to generate the shock waves in the highstress region, and an air gun was used in the low‐stress region. The profiles of the propagated distrubances in each porous copper at low stresses are characterized by three distinct waves. The first of these waves is a low‐level wave (<0.5 kbar) traveling at about sonic velocity. The second wave, having an amplitude of ∼1.1 kbar in the 6.052 g/cm3 copper and ∼1.3 kbar in the 7.406 g/cm3 copper, travels at about one‐half of the sonic velocity. The velocity and amplitude of the third wave increase with increasing input stress. The experimental Hugoniot data are compared with curves calculated from Hugoniot data for solid copper using the Mie‐Gruneisen equation of state with the assumption that compaction ...

Emission of plasma waves by the Earth's bow shock

Abstract: A general technique is given for calculating the spectrum of plasma waves emitted upstream and downstream by a turbulent shock transition for a plane shock of arbitrary structure. The problem of identifying the waves of frequency ∼1 cps that sometimes appear to emanate from the earth's bow shock is discussed.

Shock‐Wave Generation in Rarefied Gases by Laser Impact on Beryllium Targets

Abstract: Shock waves in argon and in air have been observed when focusing a 0.8 J, 40 nsec, Q‐switched ruby laser beam onto a beryllium target in the presence of gas at various pressures ranging fron 2×10−1 to 3 Torr. High‐speed streak and framing camera as well as a prism spectrograph have been used as diagnostic tools. Space‐resolved spectra show, besides an intense continuum, Stark‐broadened lines from Be I and Be II. The reinforced argon lines when moving off the Be target surface are probably due to a shock wave driven by the Be plasma acting as a piston. A simple theoretical model taking this mechanism into account is proposed. Calculated curves for the outer radius variations of the shock front fit closely the experimental results.

Self-similar strong shocks in an exponential medium

Abstract: The self-similar one-dimensional propagation of a strong shock wave in a medium with exponentially varying density and ray-tube area is studied, using the Eulerian approach of Sedov. Conservation integrals analogous to Sedov's are obtained, with the expression for the Lagrangian variable. Calculated results are compared with the predictions of the CCW (Chisnell, Chester and Whitham) approximation. It was found that, in contrast to the implosion case, the propagation parameter from the CCW approximation is in error by 15% or more.

Energetic electrons of terrestrial origin upstream in the solar wind

Abstract: Fluxes of energetic electrons of terrestrial origin are frequently found beyond the bow shock on the sunward side of the earth. The duration of individual events is from less than a minute up to several minutes, but they tend to occur in clusters lasting as long as several hours. Their flux is usually a few hundred cm−2 sec−1, but occasionally it reaches 3 × 104 cm−2 sec−1 for electrons > 40 kev. The upstream electron spikes are associated with rapid motion of the bow shock. The best interpretation of upstream spikes is that they are simply electrons moving up interplanetary field lines from the magnetosheath just behind the shock where they originated as bow shock spikes.

Experimental and Theoretical Kinetics of High‐Temperature Fluorocarbon Chemistry

Abstract: Ultraviolet absorption was used to measure the rate of formation of difluoromethylene (CF2) from decomposed CF3I, C2F6, and CF4 in excess argon behind shock waves. In some experiments pure CF4 was shocked Data were taken over a temperature range from 1700° to 3000°K at total concentrations between 2(10−5) and 5(10− 6) mole cm− 3. A chemical, nonequilibrium shock‐tube computer program was developed to analyze the CF2 kinetic profiles. By curve fitting the data, rate constants for a number of fluorocarbon reactions are obtained.

Simultaneous IMP 2 and OGO 1 observations of bow shock compression

Abstract: IMP-2 and OGO-1 investigations of bow shock large scale motions during magnetic storms result from magnetosphere-magnetosheath compression by solar wind dynamic pressure

The Effect of the Pressure Shock Wave and Some Electrical Quantities in the Microbicidal Effect of Transient Electric Arcs in Aqueous Systems

Abstract: SUMMARY: Micro-organisms in aqueous suspensions were killed when voltages above a certain threshold value were discharged through electrodes immersed in the suspensions. The relation of the peak pressure, peak current and the arcing time to the killing effect were studied, but no clear-cut relationship was ascertained. At the discharges shock waves with durations of 20–105 µsec. and pressure amplitudes of 40–250 bar were generated. Although bigger and more solid objects were considerably damaged, the micro-organisms were inconspicuously affected by the pressure shock wave alone.

Solar‐wind flow behind the Moon

Abstract: A simple fluid-flow calculation is used to describe the flow of the solar wind behind the moon for the case where the magnetic field is parallel to the flow. The analysis extends the more qualitative discussions given by Michel and by Johnson and Midgley. Flow past the moon is represented approximately by the simple-wave solution to the analogous two-dimensional problem. Theoretical pressure and magnetic-field profiles are given, describing the regions of rarefaction and recompression that surround the plasma-free void behind the moon. The results are generally consistent with the work of Michel and of Johnson and Midgley. The present analysis does, however, indicate one new qualitative feature: The recompression is found to be most severe near the boundary of the rarefaction region. An outer shock wave forms on this boundary, about 5 lunar radii behind the moon and about 1.4 lunar radii from the centerline (for average solar-wind parameters). A qualitative discussion is presented to show that the addition of a small magnetic-field component perpendicular to the flow causes the outer shock to weaken and move away from the moon; a second, inner shock wave forms in the shadow of the moon.

Nonlinear Gas Oscillations in a Resonant Tube

Abstract: Nonlinear gas oscillations in a resonant tube are considered analytically and experimentally. Approximate formulas for the velocity and pressure fluctuations are obtained assuming that, due to nonlinear convective effects, the waves emitted by the piston distort rapidly to form a sawtooth with a weak discontinuity at each wavelength. The interaction between incident and reflected waves yields the velocity and pressure inside the tube. These solutions are used to determine, by means of energy considerations, the limiting values of pressure amplitudes, assuming that the leading dissipative mechanisms are the shock wave and the boundary layer. The results obtained compare favorably with amplitude measurements in a piston‐driven tube under nonlinear conditions.

Interaction of the solar wind with the moon and formation of a lunar limb shock wave

Abstract: The interaction of the solar wind with a two-layered moon is considered from the point of view of the induction generator model of Sonett and Colburn (1967). We show that a highly conducting lunar core, shielded by a thin insulating outer layer, cannot reasonably be consistent with the observed absence of a lunar bow shock, since a 10-meter thick surface dust layer would require a conductivity less than 10−10 mho/m, while a 10-kilometer thick layer would require a conductivity less than 10−7 mho/m to shield the core; conductivities in this low range do not seem reasonable. We thus establish an upper limit of 10−5 mho/m for the core conductivity, but point out that this figure can be consistent with the existence of a highly conducting surface layer. Two mechanisms are suggested for the formation of a lunar limb shock wave. It is shown that in the steady-state unipolar generator model a limb shock will be expected to form in the vicinity of the plane defined by the solar wind velocity and magnetic field directions, while a limb shock may be expected to form also in the nonsteady state if the moon possesses a conducting outer layer (10−4 < σ < 10−3 mho/m) of thickness between one-tenth and several kilometers.

Numerical solutions of the flow field for conical bodies in a supersonic stream

Abstract: : A numerical procedure for solving the problem of steady supersonic inviscid flow around smooth conical bodies is presented. Results are obtained by solving the elliptic partial differential equations that define the conical flow between the body and the shock. Results are given for circular cones up to moderately high relative incidences, including some cases for incidences beyond a critical value at which the entropy singularity moves from the surface. Also presented are a few results for elliptic cones at zero and non-zero incidence, as well as results for another conical body whose cross section is defined by a fourth order even cosine Fourier series. The applicability of the method can be limited by the entropy singularity moving too far away from the surface by the flow field containing regions of locally conically supersonic flow, or by the shock wave approaching very close to the Mach wave. Comparison of results shows excellent agreement with other theoretical methods and also with experimental results. The method is efficient in computer time.