358 research outputs found

    Notes for Geoacoustic_TDFD

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    These notes were written to help users run the WHOI TDFD (Time Domain Finite Difference) elastic wave equation code that was prepared for distribution through the ONR Ocean Acoustics Library (http://www.hlsresearch.com/oalib/). The code and documentation are based on materials that were developed for a Numerical Wave Propagation class given at MIT in the Fall of 2000. The code used is the full two-dimensional time-domain finite-difference code developed at WHOI over the past 25 years, but in order to reduce the number of variables to a manageable size, we consider a two dimensional, isotropic problem with fixed parameters in time and space. For example, the source waveform in time for both beam and point sources is a RICKER wavelet, time units have been normalized to periods (defined at the peak frequency for pressure in water), space units have been normalized to water speed and density of 1! .5km/sec and 1000kg/m3) and the domain size has been fixed at 72 x 12 water wavelengths.Funding was provided by the Office of Naval Research under Contract No. N00014-04-1-0090

    User's guide for PLOT_FINDIF

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    PLOT_FINDIF is a MATLAB script which is used to plot output from the Woods Hole Oceanographic Institution (WHOI) Time Domain Finite Difference (TDFD) program called "Geoacoustic_TDFD" Both Geoacoustic_TDFD and PLOT_FINDIF are available from the ONR Ocean Acoustics Library (http://www.hlsresearch.com/oalib/). This script will plot both the snapshot and time series output from Geoacoustic_TDFD. To run this script you must have a MATLAB license and the complete suite of 32 m-files contained in the PLOT_FINDIF package. This code has been tested with MATLAB versions 6 and 7.Funding was provided by the Office of Naval Research under Contract No. N00014-04-1-0090

    A graphical user interface for processing data from the high resolution profiler (HRP)

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    The High Resolution Profiler (HRP) is one of the only oceanographic instruments that is capable of measuring turbulent velocity and temperature fluctuations in the abyssal ocean. It is a unique device, and consequently specialized communications, data conversion and analysis software are employed to examine the data it collects. This document describes a major upgrade of the software and hardware systems used to process data from the HRP. The bulk of the conversion occurred in 1996 prior to the Brazil Basin Tracer Release Experiment (BBTRE). During the upgrade process, a Graphical User Interface (GUI) was designed and implemented for accomplishing routine HRP data processing tasks.Funding was provided by the National Science Foundation through Grant No. OCE-94- 15589

    Dust reddening and extinction curves towards gamma-ray bursts at z > 4

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    Dust is known to be produced in the envelopes of AGB stars, the expanded shells of supernova (SN) remnants, and in situ grain growth in the ISM, although the corresponding efficiency of each of these dust formation mechanisms at different redshifts remains a topic of debate. During the first Gyr after the Big Bang, it is widely believed that there was not enough time to form AGB stars in high numbers, so that the dust at this epoch is expected to be purely from SNe, or subsequent grain growth in the ISM. The time period corresponding to z ~5-6 is thus expected to display the transition from SN-only dust to a mixture of both formation channels as we know it today. Here we aim to use afterglow observations of GRBs at redshifts larger than z>4z > 4 in order to derive host galaxy dust column densities along their line-of-sight and to test if a SN-type dust extinction curve is required for some of the bursts. GRB afterglow observations were performed with the 7-channel GROND Detector at the 2.2m MPI telescope in La Silla, Chile and combined with data gathered with XRT. We increase the number of measured AVA_V values for GRBs at z > 4 by a factor of ~2-3 and find that, in contrast to samples at mostly lower redshift, all of the GRB afterglows have a visual extinction of AVA_V < 0.5 mag. Analysis of the GROND detection thresholds and results from a Monte-Carlo simulation show that, although we partly suffer from an observational bias against highly extinguished sight-lines, GRB host galaxies at 4 < z < 6 seem to contain on average less dust than at z ~ 2. Additionally, we find that all of the GRBs can be modeled with locally measured extinction curves and that the SN-like dust extinction curve provides a better fit for only two of the afterglow SEDs. For the first time we also report a photometric redshift of z=7.88z = 7.88 for GRB 100905A, making it one of the most distant GRBs known to date.Comment: 26 pages, 37 figure

    Site synthesis report of DSPP sites 417 and 418

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    This document summarizes information relevent to planning, execution, and interpretation of results from a study of the interaction of sound in the 2-30Hz band with deep ocean seafloor using sea-surface sources, seafloor receivers, and borehole seismometers emplaced by wireline re-entry at Deep Sea Drilling Project sites 417 and 418 in the western North Atlantic. We summarize published scientific results from borehole sampling of water, sediment, and rock, from wire line logging, and from borehole seismic experiments. We present new results from analysis of total power recorded by receivers clamped in basement during the borehole seismic experiment on DSDP Leg 102. We document non-drilling investigations of the site and the nature and location of re-entry cones and transponders. We describe the physical oceanography of the region and the speed of sound in water. We provide an extensive bibliography on published results from scientific investigations at 417/418. This document was completed prior to 1989 surveys of sites 417 and 418.Funding was provided by the Johns Hopkins University, Applied Physics Laboratory under contract Number 602809-0

    Phase change in subducted lithosphere, impulse, and quantizing Earth surface deformations

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    © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Solid Earth 6 (2015): 1075-1085, doi:10.5194/se-6-1075-2015.The new paradigm of plate tectonics began in 1960 with Harry H. Hess's 1960 realization that new ocean floor was being created today and is not everywhere of Precambrian age as previously thought. In the following decades an unprecedented coming together of bathymetric, topographic, magnetic, gravity, seismicity, seismic profiling data occurred, all supporting and building upon the concept of plate tectonics. Most investigators accepted the premise that there was no net torque amongst the plates. Bowin (2010) demonstrated that plates accelerated and decelerated at rates 10−8 times smaller than plate velocities, and that globally angular momentum is conserved by plate tectonic motions, but few appeared to note its existence. Here we first summarize how we separate where different mass sources may lie within the Earth and how we can estimate their mass. The Earth's greatest mass anomalies arise from topography of the boundary between the metallic nickel–iron core and the silicate mantle that dominate the Earth's spherical harmonic degree 2 and 3 potential field coefficients, and overwhelm all other internal mass anomalies. The mass anomalies due to phase changes in olivine and pyroxene in subducted lithosphere are hidden within the spherical harmonic degree 4–10 packet, and are an order of magnitude smaller than those from the core–mantle boundary. Then we explore the geometry of the Emperor and Hawaiian seamount chains and the 60° bend between them that aids in documenting the slow acceleration during both the Pacific Plate's northward motion that formed the Emperor seamount chain and its westward motion that formed the Hawaiian seamount chain, but it decelerated at the time of the bend (46 Myr). Although the 60° change in direction of the Pacific Plate at of the bend, there appears to have been nary a pause in a passive spreading history for the North Atlantic Plate, for example. This, too, supports phase change being the single driver for plate tectonics and conservation of angular momentum. Since mountain building we now know results from changes in momentum, we have calculated an experimental deformation index value (1–1000) based on a world topographic grid at 5 arcmin spacing and displayed those results for viewing