Numerical computations of turbulence amplification in shock-wave interactions
Previously cited in issue 08, p. 1213, Accession no. A82-22085
Zang, T. A.↗
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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.↗
Magnetic field amplification and generation in hypervelocity meteoroid impacts with application to lunar paleomagnetism
A one-dimensional numerical model for the expansion of impact-produced vapor clouds is used to investigate magnetic field generation mechanisms in events such as meteor collisions with the moon. The resulting cloud properties, such as ionization fraction, electrical conductivity, radial expansion velocity, mass density, and energy density are estimated. The model is initiated with the peak shock states and pressure thresholds for incipient and complete vaporization of anorthosite lunar surface materials by iron and GA composition meteorites. The expansion of the spherical gas cloud into a vacuum was traced with a one-dimensional explicit lagrangian hydrodynamic code. The hypervelocity impact plasmas produced are found to be significant in the amplitudes and orientations of the magnetic fields generated. An ambient magnetic field could have been provided by the core dynamo, which would have interacted with the expanding plasmas and formed induced paleomagnetic fields. Several other field-contribution mechanisms are discussed and discarded as potential remanent magnetism contributors.
Hood, L. L.↗
The Presidents' Day cyclone of 18-19 February 1979 - Influence of upstream trough amplification and associated tropopause folding on rapid cyclogenesis
The Presidents' Day cyclone of 18-19 February, 1979 is analyzed based on conventional radiosonde data, infrared and visible satellite imagery, water vapor images and ozone measurement. The well-known synoptic-scale characteristics of the PJ-trough system are described, and evidence for the development of the tropopause fold are presented. Processes contributing to the formation of the fold are discussed in terms of an evaluation of the Sawyer-Eliassen circulation equation and a diagnostic evaluation of the ageostrophic winds and vertical motion near the polar jet streak. The documentation of stratospheric extrusions and their possible role in cyclogenesis is reviewed, and Eulerian and Lagrangian diagnostics are used to establish a connection between the tropopause fold associated with the polar jet streak and rapid cyclogenesis along the East Coast. Conservation of potential vorticity expressed in isentropic coordinates is used as a constraint from which to view cyclogenesis.
Uccellini, L. W.↗
Peroxy radical detection by chemical amplification (PERCA)
Important reactions of atmospheric free radicals are the chain oxidation of NO and CO. Thus: H2O + NO yields OH + NO2; OH + CO yields H + CO2; H + O2 + M yields HO2 + M. In most models, the need to know the free radical concentration could also be described as the need to know the rate of the above oxidation chain in the atmosphere. It is the total rate of this chain (also carried by RO2 and RO) which was measured using the PERCA. The PERCA is thus essentially a RO sub X meter. The PERCA works by adding excess CO (10%) and NO (5ppm) to a stream of air and measuring the NO2 produced after 3s of reaction time. Since other processes produce NO2, the chain reaction is modulated by switching the CO for N2. The chain length is limited by the reaction OH + NO yields HONO and is modeled to be somewhat over 1000. Measured chain lengths agree with the modeled numbers.
Stedman, D. H.↗
Amplification of electromagnetic waves by a ring-beam distribution of moderately relativistic electrons
The possibility of a new mechanism for the excitation of unstable modes in cold background plasmas is indicated in this paper. These beam-cyclotron modes are excited by the presence of the ring-beam distribution of suprathermal electrons. The usual eigenmode excitation of a cold plasma is reviewed, and the new type of instability is examined using a single-harmonic approximation and multiharmonic treatment.
Shi, B. R.↗
Essentially non-oscillatory shock capturing methods applied to turbulence amplification in shock wave calculations
ENO (essentially non-oscillatory) schemes can provide uniformly high order accuracy right up to discontinuities while keeping sharp, essentially non-oscillatory shock transitions. Recently, an efficient implementation of ENO schemes was obtained based on fluxes and TVD Runge-Kutta time discretizations. The resulting code is very simple to program for multi-dimensions. ENO schemes are especially suitable for computing problems with both discontinuities and fine structures in smooth regions, such as shock interaction with turbulence, for which results for 1-D and 2-D Euler equations are presented. Much better resolution is observed by using third order ENO schemes than by using second order TVD schemes for such problems.
Osher, Stanley↗
Sling amplification and eccentric gravitational instabilities in gaseous disks
An analytical description is presented of the modal mechanisms relevant to a recently discovered type of eccentric gravitational instability in nearly Keplerian disks. A quantum condition is derived which accurately predicts the pattern speeds for these modes. The growth rates for the modes are determined, and it is shown that the mode can grow when the disk is safely stable to axisymmetric disturbances. The case of marginal stability for the outside edge is discussed, and the implications of the results for the formation of binary companions and/or giant planets within disks associated with young stellar objects are considered.
Shu, Frank H.↗
Magnetic field amplification in mechanically driven compressible magnetohydrodynamic turbulence
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Shebalin, John V.↗
Space Power Amplification with Active Linearly Tapered Slot Antenna Array
A space power amplifier composed of active linearly tapered slot antennas (LTSA's) has been demonstrated and shown to have a gain of 30 dB at 20 GHz. In each of the antenna elements, a GaAs monolithic microwave integrated circuit (MMIC) three-stage power amplifier is integrated with two LTSA's. The LTSA and the MMIC power amplifier has a gain of 11 dB and power added efficiency of 14 percent respectively. The design is suitable for constructing a large array using monolithic integration techniques.
Simons, Rainee N.↗
On the preferred source location for the convective amplification of ion cyclotron waves
The propagation, growth, and absorption of electromagnetic ion cyclotron waves (EMICs) in the Pc1 range are studied using the HOTRAY ray tracing program for a realistic distribution of thermal plasma (H+, He+, O+), which is assumed to be in diffusive equilibrium inside the plasmasphere and collisionless in the low-density region outside the plasmapause. It is demonstrated that there are two principal source regions for the growth of EMIC waves. The theoretical results are related to the most recent satellite and ground-based observations.
Horne, Richard B.↗
UV-B radiation amplification factor determined based on the simultaneous observation of total ozone and global spectral irradiance
The Japan Meteorological Agency started the spectral observation of solar ultraviolet (UV) irradiance on 1 January 1990 at Tateno, Aerological Observatory in Tsukuba (35 deg N, 140 deg E). The observation has been carried out using the Brewer spectrophotometer for the wavelengths from 290 to 325 nm with a 0.5 nm interval every hour from 30 minutes before sunrise to 30 minutes after sunset throughout a year. Because of remarkable similarity within observed spectra, an observed spectrum can be expressed by a simple combination of a reference spectrum and two parameters expressing the deformation of the observed spectrum from the reference. By use of the relation between one of the deformation parameters and the total ozone simultaneously observed with the Dobson spectrophotometer, the possible increase of UV irradiance due to ozone depletion is estimated. For damaging UV, the irradiance possibly increases about 19 percent with the ozone depletion of 10 percent at noon throughout the year in the northern midlatitudes. DUV at noon on the summer solstice possibly increases about 5.6 percent with the ozone depletion of 10 m atm-cm for all latitudes in the Northern Hemisphere.
Ito, T.↗
High Energy Particle Acceleration and Turbulent Magnetic Field Amplification in Shell Type Supernova Remnants
Thesis submitted to the faculty of the Graduate School of the University of Minnesota in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Part I discusses the spatial correlation between the x-ray and radio morphologies of Cas A, and in the process address: the effect of inhomogeneous absorption on the apparent x-ray morphology, the interaction between the SNR and a molecular cloud, and the rapid move toward equipartition between the magnetic and gas energy densities. Discussions of the x-ray./radio correlation continues in Chapter 5, where we present a new, deep, ROSAT HRI image of Cas A. Chapter 7 presents ASCA spectra, with non-thermal spectral fits for 13 of the youngest SNRs in the Galaxy.
Keohane, Jonathan Wilmore↗
Pulsed Ejector Thrust Amplification Tested and Modeled
There is currently much interest in pulsed detonation engines for aeronautical propulsion. This, in turn, has sparked renewed interest in pulsed ejectors to increase the thrust of such engines, since previous, though limited, research had indicated that pulsed ejectors could double the thrust in a short device. An experiment has been run at the NASA Glenn Research Center, using a shrouded Hartmann-Sprenger tube as a source of pulsed flow, to measure the thrust augmentation of a statistically designed set of ejectors. A Hartmann- Sprenger tube directs the flow from a supersonic nozzle (Mach 2 in the present experiment) into a closed tube. Under appropriate conditions, an oscillation is set up in which the jet flow alternately fills the tube and then spills around flow emerging from the tube. The tube length determines the frequency of oscillation. By shrouding the tube, the flow was directed out of the shroud as an axial stream. The set of ejectors comprised three different ejector lengths, three ejector diameters, and three nose radii. The thrust of the jet alone, and then of the jet plus ejector, was measured using a thrust plate. The arrangement is shown in this photograph. Thrust augmentation is defined as the thrust of the jet with an ejector divided by the thrust of the jet alone. The experiments exhibited an optimum ejector diameter and length for maximizing the thrust augmentation, but little dependence on nose radius. Different frequencies were produced by changing the length of the Hartmann-Sprenger tube, and the experiment was run at a total of four frequencies. Additional measurements showed that the major feature of the pulsed jet was a starting vortex ring. The size of the vortex ring depended on the frequency, as did the optimum ejector diameter.
Wilson, Jack↗
Detection of naphthalene dioxygenase mRNA transcripts by fluorescent in situ hybridization (FISH) with tyramide signal Amplification (TSA)
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microbial activity fluorescent in situ hybridizati↗
Optical Pulse Synthesis Using Brillouin Selective Sideband Amplification
Optical pulse generation using Fourier synthesis is attractive for a number of applications, including photonic A/D conversion, electro-optic sampling, and time-resolved spectroscopy, because the bandwidth, shape, and repetition rate of the pulse can be easily controlled.
optical pulse brillouin selective sideband↗
Brillouin Amplification--A powerful New Scheme for Microwave Photonic Communications
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narrow bandwidth emission noise analog photonic sy↗
Modeling the Observed Solar Cycle Variations of the Quasi-biennial Oscillation (QBO): Amplification by Wave Forcing
In several papers, the solar cycle (SC) effect in the lower atmosphere has been linked observationally to the Quasi-biennial Oscillation (QBO) of the zonal circulation, which is generated primarily by small-scale gravity waves (GW). Salby and Callaghan (2000) in particular analyzed the QBO, covering more than 40 years, and discovered that it contains a large SC signature at 20 km. With our Numerical Spectral Model (NSM), we conducted a 3D study to describe the QBO under the influence of the SC, and some results have been published (Mayr et al., GRL, 2005,2006). For a SC period of 10 years, the relative amplitude of radiative forcing is taken to vary exponentially with height, i.e., 0.2% at the surface, 2% at 50 km, 20% at 100 km and above. Applying spectral analysis to filter out and identify the SC signature, the model generates a relatively large modulation of the QBO, which reproduces the observations qualitatively. Our numerical results demonstrate that the modulation of the QBO, with constant phase relative to the SC, persist at least for 60 years. The same model run generates in the seasonal variations a hemispherically symmetric Equatorial Annual Oscillation (EAO, with 12-month period), which is confined to low latitudes like the QBO and is also modulated by the SC. Although the amplitude of the EAO is relatively small, its SC modulation is large, and it is in phase with that of the QBO. The SC modulated EAO is evidently the pathway and pacemaker for the solar influence on the QBO. To shed light on the dynamical processes involved, we present model results that show how the seasonal cycle induces the SC modulations of the EAO and QBO. Our analysis further demonstrates that the SC modulations of the QBO and EAO are amplified by the GW interaction with the flow. The GW momentum source clearly shows a SC modulation that is in phase with the corresponding modulations of the QBO and EAO. By tapping the momentum from the upward propagating GWs, the QBO and EAO apparently serve as conduits to amplify and transfer to lower altitudes the larger SC variations in the UV absorbed in the mesosphere. Our model also produces in the temperature variations of the QBO and EAO measurable SC modulations at polar latitudes near the tropopause, and such signatures have been reported in the literature. Contrary to conventional interpretation, however, we suggest that the effects are generated at least in part by the meridional circulation, and planetary waves presumably, which redistribute the energy from the equatorial region where wave forcing is very efficient and thereby amplifies the SC influence.
Mayr, Hans G.↗