629 research outputs found

    In situ acoustic attenuation measurements in glacial ice

    Get PDF
    The attenuation coefficient of ice in a temperate valley glacier was measured by spectral analysis of the pressure pulse, directly transmitted through the ice from a small explosion. Values varied from 0.014±.002/m at 2.5 kc/s to 0.215±.002/m at 15 kc/s. The attenuation function follows a form α = A + Bƒ^4 closely, suggesting Rayleigh-type scattering as the dominant source of attenuation of high-frequency acoustic waves in glacial ice. Scattering from ice crystal boundaries is compatible with the observed scattering coefficient

    Evidence from Strandings for Geomagnetic Sensitivity in Cetaceans

    Get PDF
    We tested the hypothesis that cetaceans use weak anomalies in the geomagnetic field as cues for orientation, navigation and/or piloting. Using the positions of 212 stranding events of live animals in the Smith sonian compilation which fall within the boundaries of the USGS East-Coast Aeromagnetic Survey, we found that there are highly significant tendencies for cetaceans to beach themselves near coastal locations with local magnetic minima. Monte-Carlo simulations confirm the significance of these effects. These results suggest that cetaceans have a magnetic sensory systemcomparable to that in other migratory and homing animals, and predict that the magnetic topography and in particular the marine magnetic lineations may play an important role in guiding long-distance migration. The ‘map’ sense of migratoryanimals may therefore be largely based on a simple strategy of following paths of local magnetic minima and avoiding magnetic gradients

    Overlooked examples of cloud self-organization at the mesoscale

    Get PDF
    Stratocumulus clouds are common in the tropical and subtropical marine boundary layer, and understanding these clouds is important due to their significant impact on the earth's radiation budget. Observations show that the marine boundary layer contains complex, but poorly understood processes, which, from time to time, result in the observable self-organization of cloud structures at scales ranging from a few to a few thousand kilometers. Such shallow convective cloud features, typically observed as hexagonal cells, are known generally as mesoscale cellular convection (MCC). Actinoform clouds are rarer, but visually more striking forms of MCC, which possess a radial structure. Because mesoscale cloud features are typically too large to be observed from the ground, observations of hexagonal cells historically date only to the beginning of satellite meteorology. Examples of actinoform clouds were shown in the venerable “Picture of the Month” series in Monthly Weather Review in the early 1960s, but these clouds were generally forgotten as research focused on hexagonal cells. Recent high-resolution satellite images have, in a sense, “rediscovered” actinoform clouds, and they appear to be much more prevalent than had been previously suspected. We show a number of examples of actinoform clouds from a variety of locations worldwide. In addition, we have conducted a detailed case study of an actinoform cloud system using data from the Multiangle Imaging SpectroRadiometer (MISR) and the Geostationary Operational Environmental Satellite (GOES), including analysis of cloud heights, radiative properties, and the time-evolution of the cloud system. We also examine earlier theories regarding actinoform clouds in light of the new satellite data

    The extension of the Hubble diagram. II - New redshifts and photometry of very distant galaxy clusters - First indication of a deviation of the Hubble diagram from a straight line

    Get PDF
    Redshifts are given for 50 brightest cluster galaxies, extending as far as z = 0.75; BVR photometry is given for 33 clusters. These data are combined with earlier data of a similar kind in order to investigate several effects. The measured B - V and V - R colors as a function of redshift are well represented by Whitford's standard-galaxy K corrections, as far as these are defined (to z = 0.28 in B - V and z = 0.48 in V - R). This suggests both that the K corrections are valid over these ranges of z and that no major color change of the galaxies has occurred over the last 4-5 x 10^9 years. At larger redshifts, the colors, which start out being monotonically redder with z, turn over and become bluer with z. The data at large z seem to follow the prediction based upon ultraviolet photometry of NGC 4486 (M87), which is one extreme of a range of galaxies measured by Code and Welch. Other standard corrections to the measurements are discussed, and formal least-squares values of q_0 are computed. To explore the possibility that one might be stalemated by the fact that the value of q_0 must, in principle, be known a priori to compute the aperture correction, the data are corrected separately for assumed q_0 values of 0 and + 1. The subsequently computed values of q_0 differ by only 0.2 between the two cases, which indicates that a simple iterative procedure will converge to produce a self-consistent value of q_0. The new data do not significantly change earlier discussions of the corrections for cluster richness and Bautz-Morgan contrast type. If these two corrections are not made, the effect on the present data is to significantly increase the positive curvature of the Hubble diagram, as well as the dispersion in apparent magnitude. To within the limits of the present data, the absolute magnitude of the brightest cluster galaxy does not, in general, depend on whether it is also a bright radio source. The present sample, cut off at z = 0.4 to avoid selection effects and uncertainties in the data, shows the first significant evidence for curvature of the Hubble diagram, with V and R magnitudes giving similar results. The formal value of q_0 (with galaxy evolution ignored) is + 1.6 ± 0.4. The dispersion in absolute magnitude is less than 0.3 mag, with M_v = -23.28 ± 0.03 and M_R= -24.09 ± 0.03. The use of the Hubble diagram in cosmology now depends on a knowledge of brightness changes in galaxies, on the one hand, or of q_0 from other evidence, on the other. For example, if it were known with certainty that there has been no significant change in elliptical galaxy luminosities during the last 4 x 10^9 years, then the present data are nearly good enough for one to say definitively that the universe is closed and finite, with a finite lifetime. At the other extreme, if it were known with certainty from other evidence that the universe was nearly empty (q_0 ≈ 0), then the present data set the constraint that net galaxy luminosities have decreased by ~ 0.5 mag during the last 5 x 10^9 years, with a net color change Δ(B - V) ≤ 0.1 mag. It seems possible at present to construct a self-consistent model with q_0 ≈ 0 that satisfies the known data, but the case is not yet settled

    The extension of the Hubble diagram. I. New redshifts and BVR photometry of remote cluster galaxies, and an improved richness correction

    Get PDF
    Absorption-line redshifts for 37 galaxies in 31 remote clusters have been measured with the new sky-subtracting prism spectrograph, using an SIT television detector with digital readout. Twenty-five galaxies in the sample have redshifts larger than z = 0.20. New photoelectric BVR photometry has been obtained for 16 of the clusters. Magnitudes corrected for aperture effect, K-dimming, galactic absorption, cluster richness, and Bautz-Morgan contrast effect are listed. The data permit an improvement in the statistics of the Hubble diagram to z = 0.28 and a new determination of the dependence of the absolute magnitude of the brightest cluster galaxy on cluster richness. A small correlation with richness is found whose amplitude is 0.20 ± 0.18 mag over all Abell richness classes 0-4. As in previous studies, the shallowness of the correlation requires that if M(l) is governed by a general luminosity function, Φ(M), for fainter members, then the slope of Φ(M) at M(I) must be very steep. The 16 new clusters with photometry have a dispersion in M(l) of 0.26 mag. The dispersion of fully corrected magnitudes for the 65 clusters in the total sample is 0.276 mag. The new points in the Hubble diagram give no indication that the (m, z) relation deviates from the q_0(formal) = + 1 line (i.e. with no evolutionary correction applied), nor that 3C 295 is abnormally bright. The need for more data with z > 0.3 is stressed

    Interview with James A. Westphal

    Get PDF
    An interview in six sessions in 1998 with James A. Westphal, engineer and instrument designer who became research associate and later professor of planetary science at Caltech (1961-2004); and principal investigator for the Hubble Space Telescope's original Wide Field and Planetary Camera (WFPC 1, 1977-1994). He was born in 1930 in Dubuque, Iowa, to parents of German ancestry and raised in Tulsa, Oklahoma, and Little Rock, Arkansas. Receives BS in physics from the University of Tulsa in 1954 and works for seven years in geophysical research for oil companies before coming to Caltech in 1961. He recalls early work in geology division with C. Hewitt Dix, H. Lowenstam and B. Murray; with the latter on chemical differentiation of the lunar surface, his first involvement with planetary science. Works with B. Kamb on Blue Glacier; also with M. Schmidt and J. Gunn in astronomy. Recollections of Caltech colleagues G. Neugebauer, R. Leighton, R. Feynman. Comments on history of 200-inch telescope at Cerro Tololo and Caltech's relationship with Carnegie Observatories. He recalls work in early 1970s with J. Kristian for Palomar Observatory on highly sensitive electronic detectors (silicon vidicon photometer) leading to the evolution of CCDs [charge-coupled devices]. Joins NAS's COMPLEX committee at invitation of chairman G.Wasserburg; involvement with NASA's Galileo mission. Subsequent involvement with Hubble Space Telescope (HST) imaging project; proposal for original wide-field and planetary camera put together with J. Gunn at JPL. He comments on early attitude of HST astronomers toward planetary scientists. Installation and testing of WFPC 1 in telescope; 1990 launch from Kennedy Space Center in Florida. Trouble with HST's solar panels and subsequent repair efforts. Westphal receives MacArthur award, 1991, and succeeds G. Neugebauer as director of Palomar, 1994-1997. With J. Miller of Lick Observatory becomes acting co-director of the new Keck Telescope; comments on instrument building. Earlier work (1983) with former grad student S. Kieffer, of USGS, on dynamics of Old Faithful geyser resumed; builds camera to send to the bottom of the geyser. Comments on R. Leighton's contributions to X-ray and infrared observations and planetary science. Further comments on instrument building

    Sub-electron noise charge-coupled devices

    Get PDF
    A charge coupled device designed for celestial spectroscopy has achieved readout noise as low as 0.6 electrons rms. A nondestructive output circuit was operated in a special manner to read a single pixel multiple times. Off-chip electronics averaged the multiple values, reducing the random noise by the square root of the number of readouts. Charge capacity was measured to be 500,000 electrons. The device format is 1600 pixels horizontal by 64 pixels vertical. Pixel size is 28 microns square. Two output circuits are located at opposite ends of the 1600 bit CCD register. The device was thinned and operated backside illuminated at -110 degrees C. Output circuit design, layout, and operation are described. Presented data includes the photon transfer curve, noise histograms, and bar-target images down to 3 electrons signal. The test electronics are described, and future improvements are discussed

    Reconnaissance of infrared emission from the lunar nighttime surface

    Get PDF
    The reconnaissance described in this paper was performed in 1964 and is an extension and refinement of the first observations (1962), in the 8- to 14-μ wavelength region, of the thermal emission from the lunar nighttime surface [Murray and Wildey, 1964]. The present investigation was intended to sample representatively enough of the lunar surface to determine the general character of the lunar nighttime emission and the relative abundance of nighttime infrared anomalies. More complete studies of the infrared emission with higher spatial resolution during eclipse were made at about the same time [Saari and Shorthill, 1965]

    Thermal infrared emission of the Jovian disk

    Get PDF
    The 8–14 micron infrared emission of Jupiter has been observed on six nights in December 1963 using the 200-inch Hale telescope. The new observations possess twice the resolution of those obtained in 1962. The brightness temperature at the center of the disk appears to be nearly constant at 129°K. With some slight ambiguity, the light bands are about 0.5° cooler in appearance than the dark bands. There is some suggestion of morning-evening asymmetry in one of the bands. The Great Red Spot is found to be from 1.5° to 2.0° cooler than the surrounding disk at the newer resolution
    corecore