Electron-hydrogen ionization - Asymptotic form of the wave function and the threshold behaviour of the cross section
Asymptotic form of wave function and threshold dependence of cross section related to electron- hydrogen ionization
WAVE FUNCTION↗
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Electron-hydrogen ionization - The asymptotic form of the wave function and the threshold behavior of the cross section.
Asymptotic form of wave function and threshold behavior of cross section for ionization of atomic hydrogen by electron impact
HYDROGEN ION↗
Sea level variability in the eastern tropical Pacific as observed by TOPEX and Tropical Ocean-Global Atmosphere Tropical Atmosphere-Ocean Experiment
Sea surface height measurements from the TOPEX altimeter and dynamic height from Tropical Ocean-Global Atmosphere Tropical Atmosphere-Ocean (TOGA TAO) moorings are used to explore sea level variability in the northeastern tropical Pacific Ocean. Afetr the annual harmonic is removed, there are two distinct bands of variability: one band is centered at 5 deg N to 7 deg N and extends from 165 deg W to 110 deg W, and the other band is centered at 10 deg N to 12 deg N and extends from 120 deg W to the coast of Central America. The correspondence between the two independent observation data sets at 5 deg N is excellent with correlations of about 90%. The variability at 5 deg-7 deg N is identified as instability waves formed just south of the North Equatorial Countercurrent during the months of July and March. Wave amplitudes are largest in the range of longitudes 160 deg-140 deg W, where they can exceed 10 cm. The waves disappear when the equatorial current system weakens, during the months of March and May. The variability at 11 deg N in 1993 has the form of anticyclone eddies. These eddies propagate westward at a speed of about 17 cm/s, consistent with the dispersion characteristics of free Rossby waves. The eddies are shown to have their origin near the coast of central America during northern fall and winter. Their formation seems to result from intense wind bursts across the Gulfs of Tehuantepec and Papagayo which generate strong anticyclonic ocean eddies. The disappearance of the eddies in the summer of 1993 coincidences with the seasonal intensification of equatorial currents. Thus the variability at 11 deg N has very little overlap in time with the variability at 5 deg N.
Giese, Benjamin S.↗
Cloud patterns, waves and convection in the Venus atmosphere
Detailed descriptions and interpretations are provided for phenomena seen in the UV markings on Venus during the Mariner 10 encounter with that planet. The phenomena include the dark horizontal Y, circumequatorial belts, bowlike waves, the subsolar disturbance, midlatitude spiral streaks, the polar ring, and the polar region. Interpreting some of these phenomena in terms of physical processes that are familiar in earth's atmosphere, it is proposed that the large-scale brightness distribution can be most simply described in terms of a pattern with zonal wavenumber of unity which extends between about + and - 50 deg latitude and which progresses around the planet in about 4.2 days. The large-scale UV markings are interpreted as a wave phenomenon, and it is shown how the observed Y pattern could be produced by the superposition of a Rossby-Haurwitz wave dominant at middle latitudes and a Kelvin wave dominant near the equator. It is suggested that the bowlike waves may be true bow waves formed by the interaction of the rapid supercritical zonal flow with internal gravity waves of lower horizontal phase speeds generated by the subsolar disturbance.
Belton, M. J. S.↗
Condensation of water vapor in rarefaction waves. I - Homogeneous nucleation
A detailed theoretical investigation has been made of the condensation of water vapor/carrier gas mixtures in the nonstationary rarefaction wave generated in a shock tube. It is assumed that condensation takes place by homogeneous nucleation. The equations of motion together with the nucleation rate and the droplet growth equations were solved numerically by the method of characteristics and Lax's method of implicit artificial viscosity. It is found that, for the case considered, the condensation wave formed by the collapse of the metastable nonequilibrium state is followed by a shock wave generated by the intersection of characteristics of the same family. The expansion is practically isentropic up to the onset of condensation. The condensation front accelerates in the x,t plane. The results of the computations for a chosen case of water vapor/nitrogen mixture are presented by plotting variations of pressure, nucleation rate, number density of critical clusters, and condensate mass-fraction along three particle paths. Some consideration is given to homogeneous condensation experiments conducted in a shock tube. Although a direct comparison of the present theoretical work and these experiments is not possible, several worthwhile interpretative features have resulted nevertheless.
Sislian, J. P.↗
Turbulent Spot Pressure Fluctuation Wave Packet Model
Wave packet analysis provides a connection between linear small disturbance theory and subsequent nonlinear turbulent spot flow behavior. The traditional association between linear stability analysis and nonlinear wave form is developed via the method of stationary phase whereby asymptotic (simplified) mean flow solutions are used to estimate dispersion behavior and stationary phase approximation are used to invert the associated Fourier transform. The resulting process typically requires nonlinear algebraic equations inversions that can be best performed numerically, which partially mitigates the value of the approximation as compared to a more complete, e.g. DNS or linear/nonlinear adjoint methods. To obtain a simpler, closed-form analytical result, the complete packet solution is modeled via approximate amplitude (linear convected kinematic wave initial value problem) and local sinusoidal (wave equation) expressions. Significantly, the initial value for the kinematic wave transport expression follows from a separable variable coefficient approximation to the linearized pressure fluctuation Poisson expression. The resulting amplitude solution, while approximate in nature, nonetheless, appears to mimic many of the global features, e.g. transitional flow intermittency and pressure fluctuation magnitude behavior. A low wave number wave packet models also recover meaningful auto-correlation and low frequency spectral behaviors.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Radiative Amplification of Acoustic Waves in Hot Stars
The discovery of broad P Cygni profiles in early type stars and the detection of X-rays emitted from the envelopes of these stars made it clear, that a considerable amount of mechanical energy has to be present in massive stars. An attack on the problem, which has proven successful when applied to late type stars is proposed. It is possible that acoustic waves form out of random fluctuations, amplify by absorbing momentum from stellar radiation field, steepen into shock waves and dissipate. A stellar atmosphere was constructed, and sinusoidal small amplitude perturbations of specified Mach number and period at the inner boundary was introduced. The partial differential equations of hydrodynamics and the equations of radiation transfer for grey matter were solved numerically. The equation of motion was augmented by a term which describes the absorption of momentum from the radiation field in the continuum and in lines, including the Doppler effect and allows for the treatment of a large number of lines in the radiative acceleration term.
Wolf, B. E.↗
MU radar observation of a mesospheric gravity wave breaking caused by convective instability
In recent measurements of mesospheric winds with the MU radar at Shigaraki (34.9 N, 136.1 E), Japan, a couple of wind velocity data was obtained showing that a monochromatic inertia-gravity wave was propagating vertically in the mesosphere. The data show that the velocity amplitude of the wave did not increase exponentially above a height and further show that the wave form had broken down at a level. Evaluating the changes of the atmospheric stability in the wave field from the measured wind data and from the estimated wave parameters, the breakdown of the wave was shown to be connected with the occurrence of convective instability in the wave field.
Muraoka, Y.↗
Results from Numerical General Relativity
For several years numerical simulations have been revealing the details of general relativity's predictions for the dynamical interactions of merging black holes. I will review what has been learned of the rich phenomenology of these mergers and the resulting gravitational wave signatures. These wave forms provide a potentially observable record of the powerful astronomical events, a central target of gravitational wave astronomy. Asymmetric radiation can produce a thrust on the system which may accelerate the single black hole resulting from the merger to high relative velocity.
Baker, John G.↗
Mobility of edge dislocations in stressed iron crystals during irradiation
The behavior of a/2(111)(110) edge dislocations in iron in shear loading and irradiation conditions was studied by means of molecular dynamics simulation. Edge dislocations were exposed to shock waves formed by atomic displacement cascades of different energies. It was shown that starting from a certain threshold amplitude shock waves cause displacement of edge dislocations in the loaded samples. Calculations showed that the larger the shear load and the amplitude of the shock wave, the greater the displacement of dislocations in the crystallite.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Far field effects of weak spatially periodic inhomogeneities.
Small variations in the properties of an acoustic medium produce cumulative effects that significantly alter wave forms propagating over long distances. To investigate some aspects of these effects, without statistical models, the one-dimensional wave equation with a weak spatially periodic variation in the sound speed is treated. An approximation is developed valid for such weak inhomogeneities over large distances based upon the approximate treatment of a linear differential equation with a periodic coefficient. It is applied to the propagation of an initial step wave and identifies the dispersive nature of the medium which accounts for the cumulative effects.
Friedman, M. B.↗
Electromagnetic fields radiated from a lightning return stroke - Application of an exact solution to Maxwell's equations
A solution is presented for the electromagnetic fields radiated by an arbitrarily oriented current filament over a conducting ground plane in the case where the current propagates along the filament at the speed of light, and this solution is interpreted in terms of radiation from lightning return strokes. The solution is exact in the fullest sense; no mathematical approximations are made, and the governing differential equations and boundary conditions are satisfied. The solution has the additional attribute of being specified in closed form in terms of elementary functions. This solution is discussed from the point of view of deducing lightning current wave forms from measurements of the electromagnetic fields and understanding the effects of channel tortuosity on the radiated fields. In addition, it is compared with two approximate solutions, the traditional moment approximation and the Fraunhofer approximation, and a set of criteria describing their applicability are presented and interpreted.
D M Le Vine↗
Plume and Shock Interaction Effects on Sonic Boom in the 1-foot by 1-foot Supersonic Wind Tunnel
The desire to reduce or eliminate the operational restrictions of supersonic aircraft over populated areas has led to extensive research at NASA. Restrictions are due to the disturbance of the sonic boom, caused by the coalescence of shock waves formed by the aircraft. A study has been performed focused on reducing the magnitude of the sonic boom N-wave generated by airplane components with a focus on shock waves caused by the exhaust nozzle plume. Testing was completed in the 1-foot by 1-foot supersonic wind tunnel to study the effects of an exhaust nozzle plume and shock wave interaction. The plume and shock interaction study was developed to collect data for computational fluid dynamics (CFD) validation of a nozzle plume passing through the shock generated from the wing or tail of a supersonic vehicle. The wing or tail was simulated with a wedgeshaped shock generator. This test entry was the first of two phases to collect schlieren images and off-body static pressure profiles. Three wedge configurations were tested consisting of strut-mounted wedges of 2.5- degrees and 5-degrees. Three propulsion configurations were tested simulating the propulsion pod and aft deck from a low boom vehicle concept, which also provided a trailing edge shock and plume interaction. Findings include how the interaction of the jet plume caused a thickening of the shock generated by the wedge (or aft deck) and demonstrate how the shock location moved with increasing nozzle pressure ratio.
Shock wave interaction↗
A case of transient anisotropy during the recovery phase of a Forbush decrease.
Transient anisotropic cosmic ray increase during recovery phase of Forbush decrease due to reflection from receding blast wave and co-rotating shock wave formed during explosive heating of solar corona
CORONA↗
Selective coherent perfect absorption in metamaterials
We show multi-band coherent perfect absorption (CPA) in simple bilayered asymmetrically split ring metamaterials. The selectivity of absorption can be accomplished by separately excited electric and magnetic modes in a standing wave formed by two coherent counterpropagating beams. In particular, each CPA can be completely switched on/off by the phase of a second coherent wave. We propose a practical scheme for realizing multi-band coherent perfect absorption of 100% that is allowed to work from microwave to optical frequency.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Guided waves in a multilayered composite and ultrasonic nondestructive evaluation
Analysis of wave propagation in a laminated composite plate with many layers is made difficult by the anisotropy of the laminae, different lay-ups, many layers and defects in the fabricated plate. A good understanding of the wave field in such a plate without defects is a prerequisite for use of ultrasonic techniques to evaluate the various defects that can substantially reduce the strength and service life of this structure. Results of modeling studies of wave propagation and scattering in a multilayered composite plate are presented. The analysis technique combines the finite element discretization through the thickness with wave form representation along the plate in order to calculate the dispersive modes of propagation in the plate. To study scattering of these waves by a matrix crack that grows into delaminations, a hybrid finite element representation of the field near the crack and the modal representation of the scattered exterior field are used. Results are presented showing the dependence of the reflection and transmission coefficients on the size of the crack with delamination which can be used to size the defect using ultrasonic techniques.
Datta, S. K.↗
Spectra of Baroclinic Inertia-Gravity Wave Turbulence
Baroclinic inertia-gravity (IG) waves form a persistent background of thermocline depth and sea
Inertia-Gravity↗
Skyrmion‐Excited Spin‐Wave Fractal Networks
Magnetic skyrmions exhibit unique, technologically relevant pseudo-particle behaviors which arise from their topological protection, including well-defined, 3D dynamic modes that occur at microwave frequencies. During dynamic excitation, spin waves are ejected into the interstitial regions between skyrmions, creating the magnetic equivalent of a turbulent sea. However, since the spin waves in these systems have a well-defined length scale, and the skyrmions are on an ordered lattice, ordered structures from spin-wave interference can precipitate from the chaos. This work uses small-angle neutron scattering (SANS) to capture the dynamics in hybrid skyrmions and investigate the spin-wave structure. Performing simultaneous ferromagnetic resonance and SANS, the diffraction pattern shows a large increase in low-angle scattering intensity, which is present only in the resonance condition. This scattering pattern is best fit using a mass fractal model, which suggests the spin waves form a long-range fractal network. The fractal structure is constructed of fundamental units with a size that encodes the spin-wave emissions and are constrained by the skyrmion lattice. Furthermore, these results offer critical insights into the nanoscale dynamics of skyrmions, identify a new dynamic spin-wave fractal structure, and demonstrate SANS as a unique tool to probe high-speed dynamics.
36 MATERIALS SCIENCE↗