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Articles 1 - 9 of 9
Full-Text Articles in Physical Sciences and Mathematics
Dual-Spacecraft Reconstruction Of A Three-Dimensional Magnetic Flux Rope At The Earth's Magnetopause, H. Hasegawa, B. U. Ö. Sonnerup, S. Eriksson, T. K. M. Nakamura
Dual-Spacecraft Reconstruction Of A Three-Dimensional Magnetic Flux Rope At The Earth's Magnetopause, H. Hasegawa, B. U. Ö. Sonnerup, S. Eriksson, T. K. M. Nakamura
Dartmouth Scholarship
We present the first results of a data analysis method, developed by Sonnerup and Hasegawa (2011), for reconstructing three-dimensional (3-D), magnetohydrostatic structures from data taken as two closely spaced satellites traverse the structures. The method is applied to a magnetic flux transfer event (FTE), which was encountered on 27 June 2007 by at least three (TH-C, TH-D, and TH-E) of the five THEMIS probes near the subsolar magnetopause. The FTE was sandwiched between two oppositely directed reconnection jets under a southward interplanetary magnetic field condition, consistent with its generation by multiple X-line reconnection. The recovered 3-D field indicates that a …
Plasma Wave Mediated Attractive Potentials: A Prerequisite For Electron Compound Formation, R. A. Treumann, W. Baumjohann
Plasma Wave Mediated Attractive Potentials: A Prerequisite For Electron Compound Formation, R. A. Treumann, W. Baumjohann
Dartmouth Scholarship
Coagulation of electrons to form macro-electrons or compounds in high temperature plasma is not generally expected to occur. Here we investigate, based on earlier work, the possibility for such electron compound formation (non-quantum "pairing") mediated in the presence of various kinds of plasma waves via the generation of attractive electrostatic potentials, the necessary condition for coagulation. We confirm the possibility of production of attractive potential forces in ion- and electron-acoustic waves, pointing out the importance of the former and expected consequences. While electron-acoustic waves presumably do not play any role, ion-acoustic waves may potentially contribute to formation of heavy electron …
Interferometric Swath Processing Of Cryosat Data For Glacial Ice Topography, L. Gray, D. Burgess, L. Copland, R. Cullen, N. Galin, R. Hawley, V. Helm
Interferometric Swath Processing Of Cryosat Data For Glacial Ice Topography, L. Gray, D. Burgess, L. Copland, R. Cullen, N. Galin, R. Hawley, V. Helm
Dartmouth Scholarship
We have derived digital elevation models (DEMs) over the western part of the Devon Ice Cap in Nunavut, Canada, using "swath processing" of interferometric data collected by Cryosat between February 2011 and January 2012. With the standard ESA (European Space Agency) SARIn (synthetic aperture radar interferometry) level 2 (L2) data product, the interferometric mode is used to map the cross-track position and elevation of the "point-of-closest-approach" (POCA) in sloping glacial terrain. However, in this work we explore the extent to which the phase of the returns in the intermediate L1b product can also be used to map the heights of …
Orienteering In Knowledge Spaces: The Hyperbolic Geometry Of Wikipedia Mathematics, Gregory Leibon, Daniel N. Rockmore
Orienteering In Knowledge Spaces: The Hyperbolic Geometry Of Wikipedia Mathematics, Gregory Leibon, Daniel N. Rockmore
Dartmouth Scholarship
In this paper we show how the coupling of the notion of a network with directions with the adaptation of the four-point probe from materials testing gives rise to a natural geometry on such networks. This four-point probe geometry shares many of the properties of hyperbolic geometry wherein the network directions take the place of the sphere at infinity, enabling a navigation of the network in terms of pairs of directions: the geodesic through a pair of points is oriented from one direction to another direction, the pair of which are uniquely determined. We illustrate this in the interesting example …
Discontinuities And Alfvenic Fluctuations In The Solar Wind, G. Paschmann, S. Haaland, B. Sonnerup, T. Knetter
Discontinuities And Alfvenic Fluctuations In The Solar Wind, G. Paschmann, S. Haaland, B. Sonnerup, T. Knetter
Dartmouth Scholarship
We examine the Alfvenicity of a set of 188 solar wind directional discontinuities (DDs) identified in the Cluster data from 2003 by Knetter (2005), with the objective of separating rotational discontinuities (RDs) from tangential ones (TDs). The DDs occurred over the full range of solar wind velocities and magnetic shear angles. By performing the Walen test in the de Hoffmann–Teller (HT) frame, we show that 77 of the 127 crossings for which a good HT frame was found had plasma flow speeds exceeding 80 % of the Alfven speed at an average angular deviation of 7.7◦; 33 cases had speeds …
Transition In The Fractal Geometry Of Arctic Melt Ponds, C. Hohenegger, B. Alali, K. R. Steffen, D. K. Perovich, K. M. Golden
Transition In The Fractal Geometry Of Arctic Melt Ponds, C. Hohenegger, B. Alali, K. R. Steffen, D. K. Perovich, K. M. Golden
Dartmouth Scholarship
During the Arctic melt season, the sea ice surface undergoes a remarkable transformation from vast expanses of snow covered ice to complex mosaics of ice and melt ponds. Sea ice albedo, a key parameter in climate modeling, is determined by the complex evolution of melt pond configurations. In fact, ice–albedo feedback has played a major role in the recent declines of the summer Arctic sea ice pack. However, understanding melt pond evolution remains a significant challenge to improving climate projections. By analyzing area–perimeter data from hundreds of thousands of melt ponds, we find here an unexpected separation of scales, where …
Relativistic Transformation Of Phase-Space Distributions, R A. Treumann, R Nakamura, W Baumjohann
Relativistic Transformation Of Phase-Space Distributions, R A. Treumann, R Nakamura, W Baumjohann
Dartmouth Scholarship
We investigate the transformation of the distri- bution function in the relativistic case, a problem of interest in plasma when particles with high (relativistic) velocities come into play as for instance in radiation belt physics, in the electron-cyclotron maser radiation theory, in the vicin- ity of high-Mach number shocks where particles are acceler- ated to high speeds, and generally in solar and astrophysical plasmas. We show that the phase-space volume element is a Lorentz constant and construct the general particle distri- bution function from first principles. Application to thermal equilibrium lets us derive a modified version of the isotropic relativisticthermaldistribution,themodifiedJu …
Deep Advanced Camera For Surveys Imaging In The Globular Cluster Ngc 6397: The Cluster Color-Magnitude Diagram And Luminosity Function, Harvey B. Richer, Aaron Dotter, Jarrod Hurley, Jay Anderson
Deep Advanced Camera For Surveys Imaging In The Globular Cluster Ngc 6397: The Cluster Color-Magnitude Diagram And Luminosity Function, Harvey B. Richer, Aaron Dotter, Jarrod Hurley, Jay Anderson
Dartmouth Scholarship
We present the color-magnitude diagram (CMD) from deep Hubble Space Telescope imaging in the globular cluster NGC 6397. The Advanced Camera for Surveys (ACS) was used for 126 orbits to image a single field in two colors (F814W, F606W) 5' SE of the cluster center. The field observed overlaps that of archival WFPC2 data from 1994 and 1997 which were used to proper motion (PM) clean the data. Applying the PM corrections produces a remarkably clean CMD which reveals a number of features never seen before in a globular cluster CMD. In our field, the main-sequence stars appeared to terminate …
Noao Fundamental Plane Survey. I. Survey Design, Redshifts, And Velocity Dispersion Data, Russell J. Smith, Michael J. Hudson, Jenica E. Nelan, Stephen A. W Moore, Stephen J. Quinney, Gary A. Wegner, John R. Lucey, Roger L. Davies, Justin J. Malecki, David Schade, Nicholas B. Suntzeff
Noao Fundamental Plane Survey. I. Survey Design, Redshifts, And Velocity Dispersion Data, Russell J. Smith, Michael J. Hudson, Jenica E. Nelan, Stephen A. W Moore, Stephen J. Quinney, Gary A. Wegner, John R. Lucey, Roger L. Davies, Justin J. Malecki, David Schade, Nicholas B. Suntzeff
Dartmouth Scholarship
We introduce the NOAO Fundamental Plane Survey (NFPS), a wide-field imaging/spectroscopic study of rich, low-redshift galaxy clusters. The survey targets X-ray–selected clusters at 0.010 < z < 0.067, distributed over the whole sky, with imaging and spectroscopic observations obtained for 93 clusters. This data set will be used in investigations of galaxy properties in the cluster environment and of large-scale velocity fields through the fundamental plane. In this paper, we present details of the cluster sample construction and the strategies employed to select early-type galaxy samples for spectroscopy. Details of the spectroscopic observations are reported. From observations of 5479 red galaxies, we present redshift measurements for 5388 objects and internal velocity dispersions for 4131. The velocity dispersions have a median estimated error ~7%. The NFPS has ~15% overlap with previously published velocity dispersion data sets. Comparisons to these external catalogs are presented and indicate typical external errors of ~8%.