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Articles 1 - 13 of 13
Full-Text Articles in Physical Sciences and Mathematics
Review Of "Liquid Crystals: Fundamentals" By S. Singh, Peter J. Collings
Review Of "Liquid Crystals: Fundamentals" By S. Singh, Peter J. Collings
Physics & Astronomy Faculty Works
No abstract provided.
Test Particle Acceleration In Three-Dimensional Magnetohydrodynamic Turbulence, P. Dmitruk, W. H. Matthaeus, N. Seenu, Michael R. Brown
Test Particle Acceleration In Three-Dimensional Magnetohydrodynamic Turbulence, P. Dmitruk, W. H. Matthaeus, N. Seenu, Michael R. Brown
Physics & Astronomy Faculty Works
We perform numerical experiments of test particle acceleration on turbulent magnetic and electric fields obtained from pseudospectral direct numerical solutions of the compressible three-dimensional MHD equations. We find consistent acceleration of the particles to many times the plasma characteristic (Alfven) speed and extended power laws in the density distribution of energies. Scaling laws of maximum and mean energy of particles with the nominal gyrofrequency and the MHD electric field are observed and a simple estimate is presented.
X-Ray Emission-Line Profile Modeling Of O Stars: Fitting A Spherically Symmetric Analytic Wind-Shock Model To The Chandra Spectrum Of Zeta Puppis, Roban Hultman Kramer , '03, David H. Cohen, S. P. Owocki
X-Ray Emission-Line Profile Modeling Of O Stars: Fitting A Spherically Symmetric Analytic Wind-Shock Model To The Chandra Spectrum Of Zeta Puppis, Roban Hultman Kramer , '03, David H. Cohen, S. P. Owocki
Physics & Astronomy Faculty Works
X-ray emission-line profiles provide the most direct insight into the dynamics and spatial distribution of the hot, X-ray-emitting plasma above the surfaces of OB stars. The O supergiant zeta Puppis shows broad, blueshifted, and asymmetric line profiles, generally consistent with the wind-shock picture of OB star X-ray production. We model the profiles of eight lines in the Chandra HETGS spectrum of this prototypical hot star. The fitted lines indicate that the plasma is distributed throughout the wind starting close to the photosphere, that there is significantly less attenuation of the X-rays by the overlying wind than is generally supposed, and …
Spheromak Merging And Field Reversed Configuration Formation At The Swarthmore Spheromak Experiment, C. D. Cothran, Abram Lockhart Falk , '03, Matthew J. Landreman , '03, Michael R. Brown, M. J. Schaffer
Spheromak Merging And Field Reversed Configuration Formation At The Swarthmore Spheromak Experiment, C. D. Cothran, Abram Lockhart Falk , '03, Matthew J. Landreman , '03, Michael R. Brown, M. J. Schaffer
Physics & Astronomy Faculty Works
The initial results of coaxial co- and counter-helicity spheromak merging studies at the Swarthmore Spheromak Experiment (SSX) [M. R. Brown, Phys. Plasmas 6, 1717 (1999)] are reported. In its new configuration, SSX is optimized to study field reversed configuration (FRC) formation and stability by counter-helicity spheromak merging. A pair of midplane coils magnetically restricts the merging process to determine how the stability of the resulting magnetic configuration depends upon the quantity of toroidal flux remaining from the initial spheromaks. The diagnostic set at SSX, featuring the capability of measuring up to 600 magnetic field components at 800 ns time resolution, …
Rapid Multiplexed Data Acquisition: Application To Three-Dimensional Magnetic Field Measurements In A Turbulent Laboratory Plasma, Matthew Joseph Landreman , '03, C. D. Cothran, Michael R. Brown, M. Kostora, J. T. Slough
Rapid Multiplexed Data Acquisition: Application To Three-Dimensional Magnetic Field Measurements In A Turbulent Laboratory Plasma, Matthew Joseph Landreman , '03, C. D. Cothran, Michael R. Brown, M. Kostora, J. T. Slough
Physics & Astronomy Faculty Works
Multiplexing electronics have been constructed to reduce the cost of high-speed data acquisition at the Swarthmore Spheromak Experiment (SSX) and Redmond Plasma Physics Laboratory. An application of the system is described for a three-dimensional magnetic probe array designed to resolve magnetohydrodynamic time scale and ion inertial spatial scale structure of magnetic reconnection in a laboratory plasma at SSX. Multiplexing at 10 MHz compresses 600 pick-up coil signals in the magnetic probe array into 75 digitizer channels. An external master timing system maintains synchronization of the multiplexers and digitizers. The complete system, calibrated and tested with Helmholtz, line current, and magnetofluid …
Has Feminism Changed Physics?, Amy Lisa Graves
Has Feminism Changed Physics?, Amy Lisa Graves
Physics & Astronomy Faculty Works
No abstract provided.
Rapid Multiplexed Data Acquisition: Application To Three-Dimensional Magnetic Field Measurements In A Turbulent Laboratory Plasma, Michael R. Brown
Rapid Multiplexed Data Acquisition: Application To Three-Dimensional Magnetic Field Measurements In A Turbulent Laboratory Plasma, Michael R. Brown
Physics & Astronomy Faculty Works
Multiplexingelectronics have been constructed to reduce the cost of high-speed data acquisition at the Swarthmore SpheromakExperiment (SSX) and Redmond Plasma Physics Laboratory. An application of the system is described for a three-dimensional magnetic probe array designed to resolve magnetohydrodynamic time scale and ion inertial spatial scale structure of magnetic reconnection in a laboratory plasma at SSX. Multiplexing at 10 MHz compresses 600 pick-up coil signals in the magnetic probe array into 75 digitizer channels. An external master timing system maintains synchronization of the multiplexers and digitizers. The complete system, calibrated and tested with Helmholtz, line current, and magnetofluid fields, reads …
High-Resolution Chandra Spectroscopy Of Tau Scorpii: A Narrow-Line X-Ray Spectrum From A Hot Star, David H. Cohen, Genevieve Escande De Messières , '04, J. J. Macfarlane, N. A. Miller, J. P. Cassinelli, S. P. Owocki, D. A. Liedahl
High-Resolution Chandra Spectroscopy Of Tau Scorpii: A Narrow-Line X-Ray Spectrum From A Hot Star, David H. Cohen, Genevieve Escande De Messières , '04, J. J. Macfarlane, N. A. Miller, J. P. Cassinelli, S. P. Owocki, D. A. Liedahl
Physics & Astronomy Faculty Works
Long known to be an unusual early-type star by virtue of its hard and strong X-ray emission, tau Scorpii poses a severe challenge to the standard picture of O-star wind-shock X-ray emission. The Chandra HETGS spectrum now provides significant direct evidence that this B0.2 star does not fit this standard wind-shock framework. The many emission lines detected with the Chandra gratings are significantly narrower than what would be expected from a star with the known wind properties of tau Sco, although they are broader than the corresponding lines seen in late-type coronal sources. While line ratios are consistent with the …
Three-Dimensional Structure Of Magnetic Reconnection In A Laboratory Plasma, C. D. Cothran, Matthew Joseph Landreman , '03, Michael R. Brown, W. H. Matthaeus
Three-Dimensional Structure Of Magnetic Reconnection In A Laboratory Plasma, C. D. Cothran, Matthew Joseph Landreman , '03, Michael R. Brown, W. H. Matthaeus
Physics & Astronomy Faculty Works
The local three-dimensional structure of magnetic reconnection has been measured for the first time in a magnetohydrodynamic (MHD) laboratory plasma at the Swarthmore Spheromak Experiment. An array of 600 magnetic probes which resolve ion inertial length and MHD time scale dynamics on a single shot basis measured the magnetic structure of partial spheromak merging events. Counter-helicity spheromaks merge rapidly, and reconnection activity clearly self-generates a local component of B which breaks the standard 2D symmetry at the ion inertial scale. Consistent with prior results, no reconnection is observed for co-helicity merging.
X-Ray Spectral Diagnostics Of Neon Photoionization Experiments On The Z-Machine, David H. Cohen, J. J. Macfarlane, J. E. Bailey, D. A. Liedahl
X-Ray Spectral Diagnostics Of Neon Photoionization Experiments On The Z-Machine, David H. Cohen, J. J. Macfarlane, J. E. Bailey, D. A. Liedahl
Physics & Astronomy Faculty Works
We report on an initial spectroscopic study of low-density, x-ray photoionized neon with x-ray spectroscopy. These experiments, carried out on the Z-machine at Sandia, are optimized to produce a gradient-free, collisionless plasma, and to explore issues related to the rapid x-ray photoionization of relatively cold, low-density plasmas. The initial experiments used time-integrated absorption spectroscopy, backlit by the pinch radiation, to determine the ionization balance in the gas cell. Future experiments will use time-resolved spectroscopy in both absorption and emission. The emission spectra are expected to be similar to those seen from photoionized astrophysical sources, such as x-ray binaries. Indeed, in …
X-Ray Emission Line Profile Modeling Of Hot Stars, Roban Hultman Kramer , '03, Stephanie Korinne Tonnesen , '03, David H. Cohen, S. P. Owocki, A. Ud-Doula, J. J. Macfarlane
X-Ray Emission Line Profile Modeling Of Hot Stars, Roban Hultman Kramer , '03, Stephanie Korinne Tonnesen , '03, David H. Cohen, S. P. Owocki, A. Ud-Doula, J. J. Macfarlane
Physics & Astronomy Faculty Works
The launch of high-spectral-resolution x-ray telescopes (Chandra, XMM) has provided a host of new spectralline diagnostics for the astrophysics community. In this paper we discuss Doppler-broadened emission line profiles from highly supersonic outflows of massive stars. These outflows, or winds, are driven by radiation pressure and carry a tremendous amount of kinetic energy, which can be converted to x rays by shock-heating even a small fraction of the wind plasma. The unshocked, cold wind is a source of continuum opacity to the x rays generated in the shock-heated portion of the wind. Thus the emergent line profiles are affected by …
Order Parameter Measurements Of Dichroic Dyes Dissolved In Smectic Liquid Crystals That Tilt Without Layer Contraction, Peter J. Collings, B. R. Ratna, R. Shashidhar
Order Parameter Measurements Of Dichroic Dyes Dissolved In Smectic Liquid Crystals That Tilt Without Layer Contraction, Peter J. Collings, B. R. Ratna, R. Shashidhar
Physics & Astronomy Faculty Works
Measurements of the orientational order parameter of dissolved dichroic dyes are reported for two smectic-A liquid crystals that tilt in the presence of an in-plane electric field without any decrease in the layer spacing. The dye order parameter is determined by measuring the anisotropic absorption of linearly polarized light. Different dyes are used and measurements are also performed on a smectic liquid crystal that tilts with the expected layer contraction to check how closely the measurements reflect the order parameter of the liquid crystal. The variation of the dye order parameter with electric field is in accordance with the recently …
Protoplanetary Disk Mass Distribution In Young Binaries, Eric L.N. Jensen, R. L. Akeson
Protoplanetary Disk Mass Distribution In Young Binaries, Eric L.N. Jensen, R. L. Akeson
Physics & Astronomy Faculty Works
We present millimeter-wave continuum images of four wide (separations 210-800 AU), young stellar binary systems in the Taurus-Auriga star-forming region. For all four sources, the resolution of our observations is sufficient to determine the millimeter emission from each of the components. In all four systems, the primary star's disk has stronger millimeter emission than the secondary's, and in three of the four the secondary is undetected; this is consistent with predictions of recent models of binary formation by fragmentation. The primaries circumstellar disk masses inferred from these observations are comparable to those found for young single stars, confirming that the …