Large Velocity Changes Research Articles

Confirmation of radial velocity variability in Arcturus

view Abstract Citations (36) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Confirmation of Radial Velocity Variability in Arcturus Cochran, William D. Abstract The author presents results of high-precision measurements of radial velocity variations in α Boo (Arcturus). Data were taken during eight nights in 1986 January - April and 1987 May with five minute time resolution and velocity precision of 15 - 20 m s-1. Significant radial velocity variability of α Boo is detected well in excess of the random and systematic measurement errors. The radial velocity varies by an amount greater than 200 m s-1 with a period around 2 days. This variation is seen both in the difference of mean velocities from night to night and in large systematic velocity changes during a single night. Publication: The Astrophysical Journal Pub Date: November 1988 DOI: 10.1086/166841 Bibcode: 1988ApJ...334..349C Keywords: Astrometry; Radial Velocity; Stellar Motions; Velocity Measurement; Telluric Lines; Temporal Distribution; Velocity Distribution; Velocity Errors; Astronomy; RADIAL VELOCITIES; STARS: INDIVIDUAL CONSTELLATION NAME: ALPHA BOOTIS; STARS: PULSATION full text sources ADS | data products SIMBAD (4)

Sonostratigraphic records from equatorial Atlantic deep-sea carbonates: Paleoceanographic and climatic relationships

Paleoceanographic and stratigraphic methods, based on high-resolution compressional wave ( p-wave) velocity measurements, have been applied to the studies of late Quaternary deep-sea carbonates in the western and eastern equatorial Atlantic. The measurements provide sonostratigraphic records in which changes in p-wave velocity parallel the changes from a glacial to an interglacial climate: Maxima in p-wave velocity (greater than 1540 m/s) occur during interglacial oxygen isotope stages 1, 5 and 7. Minima (1490 m/s) occur during glacial oxygen isotope stages 2, 4 and 6. Changes in p-wave velocity parallel past changes in carbonate accumulation and sediment coarse fraction, and allow a detailed core to core correlation. From these results two main patterns emerge: (1) In cores from shallower than 4300 m and from well above the present lysocline, large temporal changes in p-wave velocity parallel the production of planktonic foraminifera and the climatic history recorded in the sediments, and (2) below 4300 m, the position of the foraminiferal lysocline in the western equatorial Atlantic, large downcore p-wave velocity fluctuations gradually disappear due to dissolution of carbonate sediments. Dissolution also causes a distinct decrease in p-wave velocity and acoustic reflectivity in surface sediments across the present foraminiferal lysocline. Thus, past changes in the position of the foraminiferal lysocline or calcite compensation depth that caused distinct changes in reflectivity of sediments should lead to distinct reflectors within sediment columns. Their distribution can be utilized to map paleowater masses with different degrees of carbonate saturation.

Shock Phenomena in β Cephei Stars

In this paper, we present new observations of β Cephei stars made with the CFHT coudé Reticon. Spectral sequences of the extreme star BW Vulpeculae show large velocity and line profile changes in Ha and in the C II doublet (λλ6578,6582) over 0.04 of a cycle, during three different cycles on three different nights. In fact, there are two such phases of line doubling where the velocities are nearly discontinuous before and after the so-called velocity “stillstand” (near maximum light). Also, the line doubling phases coincide with pronounced peaks in the Ha core residual intensity. The most straightforward interpretation of these observations is that there are two shock waves, separated by about 50 minutes, which generate double absorption components. For v Eridani and γ Pegasi, there are no discernible changes in the Ha profiles, despite rather regular velocity variations. This argues against the shock-wave interpretation for “classical” β Cephei stars.

Dynamic response properties of movement detectors: Theoretical analysis and electrophysiological investigation in the visual system of the fly

Dynamic aspects of the computation of visual motion information are analysed both theoretically and experimentally. The theoretical analysis is based on the type of movement detector which has been proposed to be realized in the visual system of insects (e.g. Hassenstein and Reichardt 1956; Reichardt 1957, 1961; Buchner 1984), but also of man (e.g. van Doorn and Koenderink 1982a, b; van Santen and Sperling 1984; Wilson 1985). The output of both a single movement detector and a one-dimensional array of detectors is formulated mathematically as a function of time. The resulting movement detector theory can be applied to a much wider range of moving stimuli than has been possible on the basis of previous formulations of the detector output. These stimuli comprise one-dimensional “smooth” detector input functions, i.e. functions which can be expanded into a time-dependent convergent Taylor series for any value of the spatial coordinate. The movement detector response can be represented by a power series. Each term of this series consists of one exclusively time-dependent component and of another component that depends, in addition, on the properties of the pattern. Even the exclusively time-dependent components of the movement detector output are not solely determined by the stimulus velocity. They rather depend in a non-linear way on the weighted sum of the instantaneous velocity and all its higher order time derivatives. The latter point represents another reason — not discussed so far in the literature — that movement detectors of the type analysed here do not represent pure velocity sensors. The significance of this movement detector theory is established for the visual system of the fly. This is done by comparing the spatially integrated movement detector response with the functional properties of the directionally-selective motion-sensitive. Horizontal Cells of the third visual ganglion of the fly's brain. These integrate local motion information over large parts of the visual field. The time course of the spatially integrated movement detector response is about proportional to the velocity of the stimulus pattern only as long as the pattern velocity and its time derivatives are sufficiently small. For large velocities and velocity changes of the stimulus pattern characteristic deviations of the response profiles from being proportional to pattern velocity are predicted on the basis of the detector theory developed here. These deviations are clearly reflected in the response of the wide-field Horizontal Cells, thus, providing very specific evidence that the movement detector theory developed here can be applied to motion detection in the fly. The characteristic dynamic features of the theoretically predicted and the experimentally determined cellular responses are exploited to estimate the time constant of the movement detector filter.

Passive range estimation of an underwater maneuvering target

This paper examines the problem of adaptively tracking, in the horizontal ocean plane, an underwater maneuvering target using passive, time delay measurements. The target is free to make large scale random changes in velocity and bearing at times that are unknown to the observer. Tracking is accomplished by utilizing the basic linearized polar or "spherical" model of target and observer motion previously developed for radar tracking of airborne maneuvering vehicles[1]. The addition of a nonlinear system block to the tracking system leads to a partial decoupling of both bearing and polar range estimators which not only reduces computational burden, but also significantly reduces any tendency toward tracking divergence. A modified method to obtain closed-form expressions for the measurement error statistics is presented which replaces conventional extensive off-line simulation procedures. Finally, test results are shown which validate the elimination of all extended Kalman filters in the measurement processing. This makes the passive tracking system very "robust" with respect to convergence characteristics in the presence of adverse target maneuvers.

HARD PHOTONS AND NEUTRAL PIONS RADIATED FROM COLLIDING NUCLEI

A comparison of direct photon emission to pion production observed from nucleus-nucleus collisions in the Fermi energy domain shows some very interesting features. Valuable information is gained through the fit of a standard black body radiation formula to the data as well as by a comparison to classical bremsstrahlung theory. A production in the early phase of the collision is indicated. Radiative processes play an important role in atomic as well as in elementary particle physics whereas in nuclear physics the investigation of bremsstrahlung has been limited to a few cases, like beta-decay , proton-nucleus scattering , and only very recently also nucleus-nucleus collisions. In these especially at incident energies high above the Coulomb barrier the participating protons experience large velocity changes and are thus possible sources of electromagnetic bremsstrahlung'. Also for intermediate beam energies (B = 0.3) directly produced photons have been observed as well as electrons and positrons produced from them via external conversion. Theoretically the relevance of bremsstrahlung as a probe for the dynamics of a nuclear collision has recently been pointed out. For sufficiently hard photons, the energy for their production is available only in the reaction zone and only in the early stage of the collision. In that respect they have similar properties as pions which have been considered a particle probing the dynamics of nuclear collisions at intermediate energies. Respective experiments' l2 have supported that idea, which has been investigated theoretically on the basis of Fermi boosted NN-collisions with the inclusion of mean field effects* , Pauli blocking , or clustering , in a statistical model and by a semiclassical bremsstrahlung ansatz* . The interesting features resulting from this pion production work triggered our attempt to also study the photons directly produced with medium-energy heavy ions and their analysis as a radiative process accompanying the nuclear collision. Because of their negligable interaction with the surrounding nuclear matter photons seem to have some advantage as compared to pions. To study the features of the neutral pion and the direct photon emission from nuclear collisions we performed a series of experiments using C ions from the CERN synchrocyclotron of 84, 74, 60 and 48 MeV/u, impinging on targets from C to 2 3 U. To furthermore study the mass dependence we investigated the (nearly) symmetric systems 0+Mg at 48 MeV/u and compared them to data from *'Ar+*°Ca as well as *Kr+*Zr, taken at the 44 MeV/u beam of GANIL. The directly produced photons were registered with the same detector ls as the decay TS's from simultaneously n ' 1 2 produced ir's. The inclusive photon production cross section integrated within different energy bins increases charArticle published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986423

A ray inversion method for refraction analysis

A new technique is presented for the inversion of head‐wave traveltimes to infer near‐surface structure. Traveltimes computed along intersecting pairs of refracted rays are used to reconstruct the shape of the first refracting horizon beneath the surface and variations in refractor velocity along this boundary. The information derived can be used as the basis for further processing, such as the calculation of near‐surface static delays. One advantage of the method is that the shape of the refractor is determined independently of the refractor velocity. With multifold coverage, rapid lateral changes in refractor geometry or velocity can be mapped. Two examples of the inversion technique are presented: one uses a synthetic data set; the other is drawn from field data shot over a deep graben filled with sediment. The results obtained using the synthetic data validate the method and support the conclusions of an error analysis, in which errors in the refractor velocity determined using receivers to the left and right of the shots are of opposite sign. The true refractor velocity therefore falls between the two sets of estimates. The refraction image obtained by inversion of the set of field data is in good agreement with a constant‐velocity reflection stack and illustrates that the ray inversion method can handle large lateral changes in refractor velocity or relief.

Adaptive underwater target tracking using passive multipath time-delay measurements

This paper examines the problem of adaptively tracking in range and velocity an underwater maneuvering target using passive time delay measurements. The target can make large scale random velocity and depth changes at times which are unknown to the observer. Tracking is accomplished by making use of the basic linearized polar model of target and observer motion previously developed [1]. Now, however, a nonlinear system block has been added to the tracking system [2], [3], which leads to two major benefits. First, the need for extended Kalman filters is eliminated making the passive tracking system more robust than it was previously [3]. The second benefit is a partial decoupling of depth estimation from the polar range estimator, which considerably reduces the computational level of the adaptive tracking system.

On Propagation Properties of Lamb-Type and SH-Type Magnetoelastic Waves in Highly Magnetostrictive Slab

While most studies of magnetoelastic waves (MEWs) have dealt with very thin samples, the sample thickness becomes important for Lamb and SH type MEWs. Theoretical and experimental studies on MEW propagation in an infinitely extended slab are reported. Matrix and eigenvalue methods were used in theoretical calculations, while METGLAS 2605CO and 2605S2 samples were employed in experiments. Both calculations and experiments indicated the existence of three fundamental MEW modes, (P + SV) -type flexxural (MEWf) and SH-type (MEWs). Whereas the velocity for MEW f-type waves decreased with frequency, agreeing qualitatively with the results of Tsuya et al., the velocity for MEWs tended to increase, a behavior which may be useful for realizing large changes in MEW velocity at high frequencies.

高磁気ひずみ薄板中の基本磁気弾性波動

Propagation properties of fundamental magnetoelastic waves (MEWs) in a highly magnetostrictive slab have been studied. Analysis and experiment show that there exist three fundamental MEWs: Lamb extensional-type, Lamb flexural-type and SH-type MEWseven in a single homogeneous magnetic slab. The results reveal that the propagation properties of MEWs are determined by not only the magnetic parameters such as the magnetoelastic coupling constant but also by the geometrical ratio of the thickness to the drive frequency. The analysis suggests that in order to realize large velocity change in MEWs with a small field the easy axis direction should be changed according to whether the Lamb-type or the SH-type MEW is used. The SH-type MEW exhibits distinct frequency dispersion which is not observed in the elastic SH-wave in a non-magnetic slab.

Propagation characteristics of magnetoelastic surface waves in magnetic layer on non-piezoelectric substrate

The propagation characteristics of magnetoelastic surface waves in a magnetic layer on a nonpiezoelectric substrate are analyzed taking account of both thicknesses of the magnetic layer and the substrate Three fundamental modes of waves propagate in this layered structure; the extensional and the flexural modes of (P+SV)-wave and SH-wave. In these waves, the largest velocity change with external applied field appears in the flexural mode of (P+SV)-wave. The analysis reveals that the maximum velocity change has approximate squared dependence of the ratio of the magnetic layer thickness to the substrate thickness. In addition, in order to obtain large velocity change, magnetic materials are required to possess two extreme magnetic properties at the same time - very soft magnetism and very high magnetostriction.

Practical Consideration in Using Velocity, Frequency, and Phase in Stratigraphic Seismic Exploration: ABSTRACT

Since recent rediscovery of the role which amplitudes can play in seismic exploration, potential information content in other attributes has been suspected. Attempts to use these attributes have been directed essentially toward special problems (thin beds, fracture porosity) and/or special displays (instantaneous frequency, phase, etc). In fact, there are simple methods and displays which relate closely to more or less conventional approaches and make significant use of attributes such as velocity, frequency, and phase. The insights which can be developed are of particular value in stratigraphic studies, especially on land where amplitudes embody so much greater uncertainty. Key results which can be readily established include an appreciation that large scale velocity changes are often directly indicated by stacking velocity slope changes. High frequency reflections can often delineate major changes in lithological sequence and point out with clarity specular reflecting boundaries such as lava sills and fluid contacts. Finally, study of phase properties makes clear that synthetic seismogram rather than the inversion section is the proper place to note phase differences and to make adjustments. End_of_Article - Last_Page 512------------

Abstract: Magnetoelastic modes in amorphous ribbons

Certain kinds of amorphous ribbons (2605SC, for example) are known to undergo huge modulus changes with applied magnetic field at kilohertz frequencies and below. It is to be expected that relatively large changes in ultrasonic velocity will also occur. In order to analyze the field dependence of the ultrasonic velocity and attenuation, an understanding of the nature and dispersion of the normal magnetoelastic propagating waves must be obtained. Magnetoelastic plate-wave dispersion and attenuation have been calculated for models of magnetically saturated insulators. For a description of ribbons, however, the effect of a finite conductivity must be concluded. It is probably necessary to include the effect of the random nature of the parameters determining the velocity, as well. In a future publication we will present the results of calculations of the effect of eddy currents and random magnetic anisotropy on the velocity of ultrasonic waves in ribbon-like amorphous magnetoelastic alloys.

Summarizing Remarks

The foregoing presentations have been most informative. Snodgrass, who has developed microassays of the urea cycle enzymes and has been instrumental in the study of a number of patients with urea cycle disorders, reviewed the biochemistry of the urea cycle in normal and in diseased states. He, as well as the others, has drawn our attention to acetylglutamate synthetase and its important role in the regulation of the urea cycle. Although the mechanism is not entirely clear, acetylglutamate synthesis seems to be a critical step in governing the entry of ammonia into the urea cycle. Perhaps it may also regulate the overall functioning of the urea cycle. The reason that patients with a defect of this enzyme have not been described is most likely due to our ignorance. Another important message from Snodgrass is that at physiologic conditions, the urea cycle enzymes do not function at maximum rates and the ratio of enzyme activity as obtained by in vitro studies does not exist in vivo. Rather, the enzyme activities are limited in vivo by the availability of substrates that are present at Km levels. Therefore, small changes in concentration cause large changes in velocity. Ornithine transcarbamylase (OTC) deficiency and argininosuccinate lyase deficiency are the two most common of the five urea cycle disorders. Enzyme studies have revealed several variants (or mutants) in each disorder including defects in altered enzyme kinetics and the absence of enzyme proteins. There has been no satisfactory explanation for the cause of hyperammonemia found in all five urea cycle disorders.

Basal Stress Concentrations Due to Abrupt Changes in Boundary Conditions: A Cause for High Till Concentration at the Bottom of a Glacier

The existence of cold patches at the base of a glacier suggests that the sliding law will depend on these patches, which will essentially affect the viscosity constant. In a poly thermal glacier, such as a glacier which is cold in its lower part and temperate in its upper part, basal boundary conditions change from no-slip to viscous sliding. It is anticipated that the viscosity constant of this sliding law will depend on the distance from the transition line between cold and temperate ice.The mixed boundary conditions, namely no-slip where the ice is cold and viscous sliding where it is temperate, induce large stresses and velocity changes close to the transition line. In fact, it is shown that, for a Newtonian fluid and all investigated discontinuities of boundary data, square-root singularities of the stresses will develop at the transition line. Asymptotic expressions for the basal stresses are derived. The explicit forms of these asymptotic expansions depend on the form of the spatial dependence of the sliding law and, furthermore, on the numerical values of the viscosity coefficient. It is, moreover, argued that the stress concentrations are sufficiently pronounced to account for the removal of basal rock especially in regions of high cleavage concentrations, the details again depending upon the sliding coefficients.No mathematical details of the problem solved are presented as attention is focused on the physical processes.

Variable SAW delay line using amorphous TbFe<inf>2</inf>film

This paper describes a large SAW velocity change obtained in a delay line consisting of an amorphous TbFe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> film on a LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> substrate. When an external bias field of about 4 kOe was applied parallel to the direction of SAW propagation, the percentage velocity change attained was -0.27 %. The value of this change is several times as large as that previously reported. The delay line may be used for trimming a small amount of delay time and tuning oscillation frequencies in an SAW oscillator.

Quantum approach to1fnoise

On the basis of the known experimental properties of $\frac{1}{f}$ noise, some previous models are analyzed. The presence of $\frac{1}{f}$ noise in the simplest systems such as beams of charged particles in vacuum, the existence of $\frac{1}{f}$ noise in currents limited by the surface recombination rate, bulk recombination rate, or by the finite mobility determined by interaction with the phonons in solids, suggests a fundamental fluctuation of the corresponding elementary cross sections. This leads to fluctuations of the kinetic transport coefficients such as mobility $\ensuremath{\mu}$ or recombination speed, observable both in equilibrium and nonequilibrium. In the first case the available Johnson noise power $\mathrm{kT}$, determined by the Nyquist theorem, is free of this type of $\frac{1}{f}$ fluctuation. An elementary calculation is presented which shows that any cross section, or process rate, involving charged particles, exhibits $\frac{1}{f}$ noise as an infrared phenomenon. For single-particle processes, the experimental value of Hooge's constant is obtained as an upper limit, corresponding to very large velocity changes of the current carriers, close to the speed of light. The obtained ${sin}^{2}(\frac{\ensuremath{\theta}}{2})$ dependence on the mean scattering angle predicts much lower $\frac{1}{f}$ noise for (low-angle) impurity scattering, showing a strong ($\ensuremath{\sim}\frac{{\ensuremath{\mu}}^{2}}{{\ensuremath{\mu}}_{\mathrm{latt}}^{2}}$) noise increase with temperature at the transition to lattice scattering. This is in qualitative agreement with measurements on thin films and on heavily doped semiconductors, or on manganin. The theory is based on the infrared quasidivergence present in all cross sections (and in some autocorrelation functions) due to interaction of the current carriers with massless infraquanta: photons, electron-hole pair excitations at metallic Fermi surfaces, generalized spin waves, transverse phonons, hydrodynamic excitations of other quanta, very low-energy excitations of quasidegenerate states observed, e.g., in disordered materials, at surfaces, or at lattice imperfections, etc. The observed $\frac{1}{f}$ noise is the sum of these contributions, and can be used to detect and study new infraquanta.

A velocity interferometer technique to determine shear-wave particle velocity in shock-loaded solids

An optical technique is described which uses velocity interferometers to determine the large particle velocity changes associated with plane shear-wave propagation. In this technique two velocity interferometers are used to monitor different diffracted laser beams from a surface which undergoes both longitudinal and shear motion. Fringes produced in the interferometer are proportional to a linear combination of both the longitudinal and shear components of the free-surface velocity. The technique has been used successfully to monitor the free-surface velocity of a Y-cut quartz specimen impacted by an X-cut quartz plate. Although the present shear-wave velocity profiles are limited to an accuracy of ±10%, the accuracy can be easily increased by an order of magnitude by using longer delay legs and larger diffraction angles.

Displacement and velocity fields in hoppers

A stereoscopic technique was used to investigate a number of factors that affect flow in a two-dimensional bin with horizontal discharge slot. The technique proved to be a suitable, accurate and efficient method to carry out flow field measurements in flowing bulk materials. Four flow regions were found: a stagnant layer adjacent to the wall; a transition region — a shear zone in which large velocity changes occur at each horizontal section; a central core at the upper section of the center of the bin in which groups of particles exhibit velocity fluctuations about the average velocity; and a discharge zone next to the exit slot in which the particles accelerate rapidly. Direct mass flow measurements were made and compared with calculated results and literature correlations.

RECENT LABORATORY STUDIES OF EARTHQUAKE MECHANICS AND PREDICTION

We review recent laboratory observations relevant to earthquake mechanics and prediction. These continue to be largely from triaxial experiments, although new techniques have gained prominence, such as direct shear, holography, and scanning electron microscopy. Two processes have been identified which produce stick-slip: (i) fracture of asperities, and (ii) indentation creep of asperities. Rupture velocities along sawcuts in granite and dunite were 2-3km/sec. Stick-slip was observed in serpentine, chlorite, and certain clays, when thin layers were sheared at high pressure. Fault creep has been studied systematically to 700°C and 5 kbars; some brittle cracking persisted, although plastic flow of quartz, mica, and possibly amphibole, was detected. Dilatancy was found to persist through many stress cycles, although the detailed effect of cycling is still not clear. Dilatancy caused marked anisotropy in elastic moduli, compressional and shear velocity, and attenuation. The degree of localization before peak stress is a point of some disagreement. Microfracturing and optical studies show no localized dilatancy prior to fracture, whereas holography and slit diffraction show a narrow zone along the eventual fault direction. Small saturated laboratory samples showed an increase in the Vp/V8 ratio with stress; a decrease occurred under very restricted conditions. Permeability of granite increased about fourfold prior to fracture. Dilatancy was observed in gabbro at temperatures up to 400°C, 2 kbars. Several investigators described the properties of actual or simulated fault gouge. Based on equilibrium studies, some clays could be stable to depths of 12km in fault zones. Although gouge tends to reduce the amplitude of stick-slip over that on clean faults, stick-slip has been observed in thin layers of both clays and crushed silicate rocks. Large changes in compressional velocity with shear and normal stress were reported for a granite gouge. Preseismic creep has been widely observed, on sawcuts, faults, and in both triaxial and direct shear experiments at room temperature, at pressures from 1.5 to 6 kbars. The amount of creep was appreciable at intermediate pressures and with more ductile materials or thicker gouge. In a direct shear apparatus both resistivity and pore pressure changes preceded each stick-slip event, although velocity changes could not be detected. Resistivity decreased with stress for intact rocks, even with partial saturation. Dilatant volume changes prior to frictional slip were less than 10-4, which represented a porosity increase of about 10%. Dilatancy altered the normal stress-remnant magnetism relation.