Source Asymmetry Research Articles

Radio source asymmetries and unified schemes

Radio source asymmetries and unified schemes

Diffraction effects in nonlinear Rayleigh wave beams

Nonlinear effects in Rayleigh wave beams are investigated analytically and numerically. Diffraction effects are taken into account within the parabolic approximation, and nonlinearity is taken into account with a theoretical model used previously to investigate plane and cylindrical Rayleigh waves of finite amplitude [E. A. Zabolotskaya, J. Acoust. Soc. Am. 91, 2569–2575 (1992)]. Quasilinear solutions are presented for second-harmonic generation in Gaussian beams, both unfocused and focused. Asymptotic results are derived for the second harmonic in the far field of arbitrary directive sources. Numerical solutions are used to investigate harmonic generation, waveform distortion, and shock formation in Rayleigh wave beams produced by sources with uniform amplitude distributions. Brief consideration is given to effects of source asymmetry on the radiated field.

Effects of a poloidally asymmetric ionization source on toroidal drift wave stability and the generation of sheared parallel flow

The effects of a poloidally asymmetric ionization source on both dissipative toroidal drift wave stability and the generation of mean sheared parallel flow are examined. The first part of this work extends the development of a local model of ionization-driven drift wave turbulence [Phys. Fluids B 4, 877 (1992)] to include the effects of magnetic shear and poloidal source asymmetry, as well as poloidal mode coupling due to both magnetic drifts and the source asymmetry. Numerical and analytic investigation confirm that ionization effects can destabilize collisional toroidal drift waves. However, the mode structure is determined primarily by the magnetic drifts, and is not overly effected by the poloidal source asymmetry. The ionization source drives a purely inward particle flux, which can explain the anomalously rapid uptake of particles which occurs in response to gas puffing. In the second part of this work, the role poloidal asymmetries in both the source and turbulent particle diffusion play in the generation of sheared mean parallel flow is examined. Analysis indicates that predictions of sonic parallel shear flow [v∥(r)∼cs] are an unphysical result of the assumption of purely parallel flow (i.e., v⊥=0) and the neglect of turbulent parallel momentum transport. Results indicate that the flow produced is subcritical to the parallel shear flow instability when diamagnetic effects are properly considered.

Photophoresis of nonspherical bodies in the free molecule regime

The photophoretic force and torque acting on a nonspherical (convex) body irradiated by light are calculated for the free molecule regime. The force is expressed in terms of vector asymmetries (total, figure, and source asymmetry), where the figure asymmetry is derived from the geometry and the source asymmetry from the source function. For the torque an analogous representation is found. Equations of photophoretic motion are given. A special example of a nonspherical opaque body of revolution is discussed. Results are applied to strongly absorbing, large particles. Conclusions concern the occurrence of a directional torque, the direction, and the magnitude of the force.

Generalized transconductance and transresistance methods for MOSFET characterization

The concept of transconductance is generalized to include substrate and drain transconductances in addition to the usual gate transconductance. Generalized transresistances are defined as the ratio of transconductance to square of conductance, and their proportionality to channel length and reciprocal square of gate drive is exploited to develop six new analytical methods for determination of MOSFET threshold voltage and channel length. Quantitative expressions for the error components due to short channel geometry effects, asymmetry and bias dependence of source and drain series resistances, and mobility degradation are derived and related to total threshold voltage and channel length errors of various methods. In one set of methods the channel length error due to bias dependence of series resistance is eliminated by extrapolation to zero gate drive. Estimated errors agree well with measurements on submicron LDD transistors and the high precision of the gate transresistance technique is demonstrated with a channel length error of 3 nm limited by instrument resolution. Threshold voltage accuracy of 2 mV is obtained with the square-root substrate transresistance technique when series resistance is independent of substrate bias.

Radio-Optical Correlations in Distant Radio Galaxies

Optical identifications and redshifts are now available for nearly all 3CR radio galaxies (Spinrad et al. 1985; Djorgovski et al. 1988). Using new radio and optical observations, supplemented with data from the literature, we are conducting a systematic comparison of their radio and optical (emission-line and galaxy) properties, and their dependence on redshift. Here we present new results on the alignments of galaxies and their associated radio sources, and radio source asymmetries.

Source origin of a 50-msec latency auditory evoked field component in young schizophrenic men

We recorded auditory evoked magnetic fields in response to 128 15-msec duration 1-KHz tone pips from both hemispheres of 6 young schizophrenic men. Auditory evoked potentials were recorded conventionally from a vertex lead. The approximately 50-msec latency component was identified in both the magnetic (M50) and electroencephalographic (EEG) (P50) recordings. Isofield topographical contour maps were used to estimate A50 source location and depth. Magnetic resonance imaging was used to identify the neuroanatomical structure(s) present at the estimated source location. M50 sources appeared to reside in the planum temporale in both left and right hemispheres in all subjects. Normal interhemispheric asymmetry (with respect to external bony landmarks) of the M50 source was not found in this patient group. Additionally, left (but not right) hemisphere source anatomy differed in several respects from data previously reported in normals.

Stochastic geologic effects on near-field ground motions in alluvium

Abstract Analysis of accelerograms recorded at the 20 m range from a buried 5-lb detonation in alluvium revealed wide (as large as 20 dB in the amplitude modulus of the Fourier transform) variations in response for frequencies above 35 Hz. Additional experiments were performed which ruled out source asymmetry or instrumental irregularity as the cause of these variations. The observations suggest that scattering by geologic inhomogeneity is responsible for the frequency-dependent spatial variability in ground motion. A thorough understanding of the physical processes responsible for this variability requires that a quantitative relationship be established between the subsurface material property information and the observed ground motion characteristics. An attempt was made to do this using available standard penetration test data from the test bed where the initial experiment was detonated. Autocorrelations of the blow count data from the standard penetration test were computed and compared with theoretical exponential and Gaussian distributions. The exponential distribution with a scale length between 2.0 and 3.0 m best matches the data. Assuming the Born approximation, a scale length of 2.0 to 3.0 m implies that significant scattering should occur above 10 Hz. The recorded ground motions are, however, coherent out to about 35 Hz, suggesting a scale length on the order of 0.5 to 1.0 m, which is beyond the resolution of the standard penetration test technique. This scale length is, however, not unreasonable in light of the general geologic characteristics of the test area.

Magnetic stratigraphy and magnetic-petrologic properties of Precambrian Gardar lavas, South Greenland

The Gardar lavas ( 1310 m.y.) within the Eriksfjord Formation of South Greenland were a prelude to major hypabyssal magmatism within the Gardar alkaline igneous province. This paper reports a palaeomagnetic study of the lower two-thirds of the lava stratigraphy comprising three groups of flows separated by sediments. The lower group (palaeomagnetic pole at 239°E, 7°N, 7 sites, dΨ = 7.6°, dχ = 14.1°) includes one reversal of magnetisation and two intermediate directions, and the upper group (pole at 222°E, 16°N, 24 sites, dΨ = 4.8°, dχ = 9.0°) includes four reversals and two intermediate directions. The middle group of 13 lavas yields anomalous directions with respect to the other groups and appears to have been erupted during a polarity excursion of uncertain significance. Opaque petrographic analysis reveals all stages of deuteric oxidation (800–500°C) plus lower-temperature hydrothermal alteration to epidote grade. In addition to high reversal frequency, the succession illustrates asymmetry of the dipole source, and there is a suggestion that lavas with easterly directed magnetisations have higher deuteric oxidation states than those with westerly directed magnetisations. Collective palaeomagnetic results from the Gardar Province are linked to a number of Rb Sr isochrons, and comparison with contemporaneous North American data confirms the 500-fathom continental reconstruction for Proterozoic times. The poles define a movement of the Laurentian craton from low palaeolatitudes (1400–1220 m.y.) to high palaeolatitudes (1168–1070 m.y.) with a quasi-static interval at 1280–1220 m.y. coinciding with the Mackenzie igneous episode. The youngest Gardar data correlate with the oldest Keweenawan palaeomagnetic poles and restrict deposition of this group to the interval ca. 1160–1040 m.y.

The Amplitude-Distance Curve for Short Period Teleseismic P-Waves

Summary An amplitude-distance curve has been computed for short period P waves in the range A=30-102 (and h=O) using the amplitudes of explosion signals only. Effects of source asymmetry can thus be discounted and the problem of deciding what amplitude to measure is reduced because the maximum amplitude of explosion signals always occurs in the first few cycles. To increase the consistency of the measurements all the amplitudes have been measured by the same person. Assuming the effect of distance is constant over a series of discrete intervals of distance, the amplitude-distance curve with its confidence limits has been estimated by least squares using data from 65 stations which recorded some or all of the explosions fired at six sites. The most striking features of the curve are: (1) a sharp maximum at about A = 35, (2) a minimum followed by a sharp increase at A = 75, and (3) a sharp minimum at A =93. Over the remainder of its length the curve is similar to the Gutenberg and Richter curve. Station magnitude corrections have also been estimated. An amplitude-distance curve derived from explosion data should be more reliable than curves derived from earthquake data: explosions have radially symmetrical radiation patterns and their seismic signals are almost always the same shape with the maximum amplitude occurring in the first few cycles. Differences in the amplitude of signals recorded from a single explosion at two recording stations are unlikely to be due to source asymmetry (a significant factor if earthquakes are shears), and the difficulties of defining what amplitude to measure for magnitude determinations are reduced. We have collected the available World Wide Standard Seismograph Network (WWSSN) and Canadian records of underground explosions and the amplitudes of the explosion signals have been read by one seismologist (Mr P. D. Marshall). The accumulated data has been used to estimate both an amplitude-distance curve and station magnitude corrections for short period teleseismic P waves.

Waveforms and relative phase stability of transients radiated from a helicopter-supported antenna wire

A nearly vertical antenna wire varying in length from 3000 to 8000 ft was shock-excited by a high-voltage source. The resulting radiation fields were received at distances of about 600 km by two stations separated laterally so as to subtend an angle of about 15\deg at the source. The difference in wavefront arrival times at the two stations, observed for 101 transmissions, showed an average absolute deviation from the mean of about only \frac{1}{2}\mu S. This figure includes the effects of possible source asymmetries, sferics noise, instrumental errors, and wave propagation. Typical oscillograms of antenna currents and radiation fields are given. It is shown that the amplitudes and durations of the pulse envelopes, the amplitudes and durations of the first half-cycles, and the quasi-frequencies of the pulses are in good agreement with a theory that takes energy losses into account.

Azimuthal asymmetry of a point source in a cylindrical low velocity medium

Abstract The geometry of the medium in the vicinity of an otherwise symmetrical source is shown to produce a frequency dependent variation of amplitude with azimuth. The model considered is a cylindrical low velocity and low density fluid medium that is contained in a full space of a higher velocity and density fluid material. A simple harmonic point source is located on the axis of the cylinder. Amplitudes in the higher velocity medium at large distances from the source are found to be functions of the velocity ratio and the density ratio of the two media, the radius of the cylinder, the wavelength, and the angle between the axis of the cylinder and a line connecting the point of observation with the source.