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Articles 661 - 690 of 832

Full-Text Articles in Astrophysics and Astronomy

Unidirectional Invisibility Induced By Pt-Symmetric Periodic Structures, Zin Lin, Hamidreza Ramezani Jan 2011

Unidirectional Invisibility Induced By Pt-Symmetric Periodic Structures, Zin Lin, Hamidreza Ramezani

Physics & Astronomy Faculty Publications

Parity-time (PT) symmetric periodic structures, near the spontaneous PT-symmetry breaking point, can act as unidirectional invisible media. In this regime, the reflection from one end is diminished while it is enhanced from the other. Furthermore, the transmission coefficient and phase are indistinguishable from those expected in the absence of a grating. The phenomenon is robust even in the presence of Kerr nonlinearities, and it can also effectively suppress optical bistabilities.

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Magnetization Precession And Domain-Wall Structure In Cobalt-Ruthenium-Cobalt Trilayers, Zhen Li, Ralph Skomski, Sy-Hwang Liou, Steven Michalski, Mircea Chipara, Roger D. Kirby Jan 2011

Magnetization Precession And Domain-Wall Structure In Cobalt-Ruthenium-Cobalt Trilayers, Zhen Li, Ralph Skomski, Sy-Hwang Liou, Steven Michalski, Mircea Chipara, Roger D. Kirby

Physics & Astronomy Faculty Publications

The magnetization dynamics of Co(5 nm)/Ru/Co(5 nm) trilayers with Ru thicknesses from 0.3–0.6 nm is experimentally and theoretically investigated. The coupling between the Co layers is antiferromagnetic (AFM) and yields a stable AFM domain structure with frozen domain walls. Comparing high-resolution magnetic force microscopy (MFM) and pump-probe measurements, we analyze the behavior of the films for different field-strength regimes. For moderate magnetic fields, pump-probe measurements provide dynamic characterization of the coupled precessional modes in the GHz range. The dynamics at small fields is realized by the pinning of AFM domain walls at inhomogeneities. The MFM images yield a domain-wall width …

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Thermal Reaction Wave Simulation Using Micro And Macro Scale Interaction Model, Andrei A. Markov, Igor A. Filimonov, Karen S. Martirosyan Jan 2011

Thermal Reaction Wave Simulation Using Micro And Macro Scale Interaction Model, Andrei A. Markov, Igor A. Filimonov, Karen S. Martirosyan

Physics & Astronomy Faculty Publications

The thermal wave, propagating in a cylindrical tube, is numerically simulated. The technique is developed in order to provide the scale capturing as well as the stable algorithm for numerical simulation of the combustion wave. Based on the model kinetics scheme, the fields of temperature, mass fractions, and particle radius are presented for the various values of similarity parameters of the problem. The highly accurate method enables to control scales interaction and justifies various flow structures. The phase composition, structure, and morphology of the condensed product as well as the rate of the oxidation and phase transition are predicted using …

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The Behavior Of Nanothermite Reaction Based On Bi2o3/Al, L. Wang, D. Luss, Karen S. Martirosyan Jan 2011

The Behavior Of Nanothermite Reaction Based On Bi2o3/Al, L. Wang, D. Luss, Karen S. Martirosyan

Physics & Astronomy Faculty Publications

We studied the impact of aluminum particle size and the thickness of surrounding alumina layer on the dynamic pressure discharge of nanothermite reactions in the Bi2O3/Al system. A pressure discharge from 9 to 13 MPa was generated using as-synthesized Bi2O3 nano-particles produced by combustion synthesis and Al nanoparticles with size from 3 μm to 100 nm. The maximum reaction temperature was measured to be ∼2700 °C. The estimated activation energy of the reaction was 45 kJ/mol. A very large (several orders of magnitude) difference existed between the rate of the pressure pulse release by nanothermite reactions and by thermite …

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Directional Limits On Persistent Gravitational Waves Using Ligo S5 Science Data, J. Abadie, B. P. Abbott, Matthew Benacquista, Teviet Creighton, R. Grosso, J. Li, Soma Mukherjee, Soumya Mohanty, Malik Rakhmanov, Volker Quetschke, Robert Stone, Joseph D. Romano, B. Vaishnav Jan 2011

Directional Limits On Persistent Gravitational Waves Using Ligo S5 Science Data, J. Abadie, B. P. Abbott, Matthew Benacquista, Teviet Creighton, R. Grosso, J. Li, Soma Mukherjee, Soumya Mohanty, Malik Rakhmanov, Volker Quetschke, Robert Stone, Joseph D. Romano, B. Vaishnav

Physics & Astronomy Faculty Publications

The gravitational-wave (GW) sky may include nearby pointlike sources as well as stochastic backgrounds. We perform two directional searches for persistent GWs using data from the LIGO S5 science run: one optimized for pointlike sources and one for arbitrary extended sources. Finding no evidence to support the detection of GWs, we present 90% confidence level (C.L.) upper-limit maps of GW strain power with typical values between 2−20×10−50  strain2 Hz−1 and 5−35×10−49  strain2 Hz−1 sr−1 for pointlike and extended sources, respectively. The latter result is the first of its kind. We also set 90% C.L. limits on the narrow-band root-mean-square GW …

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Magnetization Precession And Domainwall Structure In Cobalt-Ruthenium-Cobalt Trilayers, Zhen Li, Ralph Skomski, Sy-Hwang Liou, Steven Michalski, Mircea Chipara, Roger D. Kirby Jan 2011

Magnetization Precession And Domainwall Structure In Cobalt-Ruthenium-Cobalt Trilayers, Zhen Li, Ralph Skomski, Sy-Hwang Liou, Steven Michalski, Mircea Chipara, Roger D. Kirby

Physics & Astronomy Faculty Publications

The magnetization dynamics of Co(5 nm)/Ru/Co(5 nm) trilayers with Ru thicknesses from 0.3–0.6 nm is experimentally and theoretically investigated. The coupling between the Co layers is antiferromagnetic (AFM) and yields a stable AFM domain structure with frozen domain walls. Comparing high-resolution magnetic force microscopy (MFM) and pump-probe measurements, we analyze the behavior of the films for different field-strength regimes. For moderate magnetic fields, pump-probe measurements provide dynamic characterization of the coupled precessional modes in the GHz range. The dynamics at small fields is realized by the pinning of AFM domain walls at inhomogeneities. The MFM images yield a domain-wall width …

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Teaching Introductory Undergraduate Physics Using Commercial Video Games, Soumya Mohanty, Sergio Cantu Jan 2011

Teaching Introductory Undergraduate Physics Using Commercial Video Games, Soumya Mohanty, Sergio Cantu

Physics & Astronomy Faculty Publications

Commercial video games are increasingly using sophisticated physics simulations to create a more immersive experience for players. This also makes them a powerful tool for engaging students in learning physics. We provide some examples to show how commercial off-the-shelf games can be used to teach specific topics in introductory undergraduate physics. The examples are selected from a course taught predominantly through the medium of commercial video games.

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Equation Of State Of A Dense And Magnetized Fermion System, Efrain J. Ferrer, Vivian De La Incera, Jason P. Keith, Israel Portillo, Paul L. Springsteen Dec 2010

Equation Of State Of A Dense And Magnetized Fermion System, Efrain J. Ferrer, Vivian De La Incera, Jason P. Keith, Israel Portillo, Paul L. Springsteen

Physics & Astronomy Faculty Publications

The equation of state of a system of fermions in a uniform magnetic field is obtained in terms of the thermodynamic quantities of the theory by using functional methods. It is shown that the breaking of the O(3) rotational symmetry by the magnetic field results in a pressure anisotropy, which leads to the distinction between longitudinal- and transverse-to-the-field pressures. A criterion to find the threshold field at which the asymmetric regime becomes significant is discussed. This threshold magnetic field is shown to be the same as the one required for the pure field contribution to the energy and pressures to …

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Double Compact Objects As Low-Frequency Gravitational Wave Sources, Krzysztof Belczynski, Matthew Benacquista, Tomasz Bulik Dec 2010

Double Compact Objects As Low-Frequency Gravitational Wave Sources, Krzysztof Belczynski, Matthew Benacquista, Tomasz Bulik

Physics & Astronomy Faculty Publications

We study the Galactic field population of double compact objects (DCOs; NS-NS, BH-NS, BH-BH binaries) to investigate the number (if any) of these systems that can potentially be detected with the Laser Interferometer Space Antenna (LISA) at low gravitational wave frequencies. We calculate the Galactic numbers and physical properties of these binaries and show their relative contributions from the disk, bulge, and halo. Although the Galaxy hosts ∼10 5 DCO binaries emitting low-frequency gravitational waves, only a handful of these objects in the disk will be detectable with LISA, but none from the halo or bulge. This is because the …

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Ultra-Compact Dwarfs In The Core Of The Coma Cluster, Juan P. Madrid, Alister W. Graham, William E. Harris, Paul Goudfrooij, Duncan A. Forbes, David Carter, John P. Blakeslee, Lee R. Spitler, Henry C. Ferguson Oct 2010

Ultra-Compact Dwarfs In The Core Of The Coma Cluster, Juan P. Madrid, Alister W. Graham, William E. Harris, Paul Goudfrooij, Duncan A. Forbes, David Carter, John P. Blakeslee, Lee R. Spitler, Henry C. Ferguson

Physics & Astronomy Faculty Publications

We have discovered both a red and a blue subpopulation of ultra-compact dwarf (UCD) galaxy candidates in the Coma galaxy cluster. We analyzed deep F475W (Sloan g) and F814W (I) Hubble Space Telescope images obtained with the Advanced Camera for Surveys Wide Field Channel as part of the Coma Cluster Treasury Survey and have fitted the light profiles of similar to 5000 point-like sources in the vicinity of NGC 4874, one of the two central dominant galaxies of the Coma Cluster. Although almost all of these sources are globular clusters that remain unresolved, we found that 52 objects have effective …

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First Search For Gravitational Waves From The Youngest Known Neutron Star, J. Abadie, B. P. Abbott, R. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, Soumya D. Mohanty, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano Oct 2010

First Search For Gravitational Waves From The Youngest Known Neutron Star, J. Abadie, B. P. Abbott, R. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, Soumya D. Mohanty, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano

Physics & Astronomy Faculty Publications

We present a search for periodic gravitational waves from the neutron star in the supernova remnant Cassiopeia A. The search coherently analyzes data in a 12 day interval taken from the fifth science run of the Laser Interferometer Gravitational-Wave Observatory. It searches gravitational-wave frequencies from 100 to 300 Hz and covers a wide range of first and second frequency derivatives appropriate for the age of the remnant and for different spin-down mechanisms. No gravitational-wave signal was detected. Within the range of search frequencies, we set 95% confidence upper limits of (0.7-1.2) × 10 -24 on the intrinsic gravitational-wave strain, (0.4-4) …

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Detecting Massive Gravitons Using Pulsar Timing Arrays, Kejia Lee, F. A. Jenet, Richard H. Price, Norbert Wex, Michael Kramer Oct 2010

Detecting Massive Gravitons Using Pulsar Timing Arrays, Kejia Lee, F. A. Jenet, Richard H. Price, Norbert Wex, Michael Kramer

Physics & Astronomy Faculty Publications

At the limit of weak static fields, general relativity becomes Newtonian gravity with a potential field that falls off as inverse distance rather than a theory of Yukawa-type fields with a finite range. General relativity also predicts that the speed of disturbances of its waves is c, the vacuum light speed, and is non-dispersive. For these reasons, the graviton, the boson for general relativity, can be considered to be massless. Massive gravitons, however, are features of some alternatives to general relativity. This has motivated experiments and observations that, so far, have been consistent with the zero-mass graviton of general relativity, …

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Compact Binaries In Star Clusters - I. Black Hole Binaries Inside Globular Clusters, J. M.B. Downing, M. J. Benacquista, M. Giersz, R. Spurzem Sep 2010

Compact Binaries In Star Clusters - I. Black Hole Binaries Inside Globular Clusters, J. M.B. Downing, M. J. Benacquista, M. Giersz, R. Spurzem

Physics & Astronomy Faculty Publications

We study the compact binary population in star clusters, focusing on binaries containing black holes, using a self-consistent Monte Carlo treatment of dynamics and full stellar evolution. We find that the black holes experience strong mass segregation and become centrally concentrated. In the core the black holes interact strongly with each other and black hole-black hole binaries are formed very efficiently. The strong interactions, however, also destroy or eject the black hole-black hole binaries. We find no black hole-black hole mergers within our simulations but produce many hard escapers that will merge in the Galactic field within a Hubble time. …

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The Sensitivity Of The Parkes Pulsar Timing Array To Individual Sources Of Gravitational Waves, D. R.B. Yardley, G. B. Hobbs, Fredrick A. Jenet, J. P.W. Verbiest, Z. L. Wen, R. N. Manchester, W. A. Coles, W. Van Straten, M. Bailes Sep 2010

The Sensitivity Of The Parkes Pulsar Timing Array To Individual Sources Of Gravitational Waves, D. R.B. Yardley, G. B. Hobbs, Fredrick A. Jenet, J. P.W. Verbiest, Z. L. Wen, R. N. Manchester, W. A. Coles, W. Van Straten, M. Bailes

Physics & Astronomy Faculty Publications

We present the sensitivity of the Parkes Pulsar Timing Array to gravitational waves (GWs) emitted by individual supermassive black hole binary systems in the early phases of coalescing at the cores of merged galaxies. Our analysis includes a detailed study of the effects of fitting a pulsar timing model to non-white timing residuals. Pulsar timing is sensitive at nanoHertz frequencies and hence complementary to Laser Interferometer Gravitational-Wave Observatory and Laser Interferometer Space Antenna. We place a sky-averaged constraint on the merger rate of nearby (z < 0.6) black hole binaries in the early phases of coalescence with a chirp mass of 1010 M⊙ of less than one merger every 7 yr. The prospects for future GW astronomy of this type with the proposed Square Kilometre Array telescope are discussed. © 2010 The Authors. Journal compilation © 2010 RAS.

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Apo B100 Similarities To Viral Proteins Suggest Basis For Ldl-Dna Binding And Transfection Capacity, Juan Guevara, Nagindra Prashad, Boris Ermolinsky, John W. Gaubatz, Dongcheul Kang, Andrea E. Schwarzbach, David S. Loose, Natalia Valentinova Guevara Jul 2010

Apo B100 Similarities To Viral Proteins Suggest Basis For Ldl-Dna Binding And Transfection Capacity, Juan Guevara, Nagindra Prashad, Boris Ermolinsky, John W. Gaubatz, Dongcheul Kang, Andrea E. Schwarzbach, David S. Loose, Natalia Valentinova Guevara

Physics & Astronomy Faculty Publications

LDL mediates transfection with plasmid DNA in a variety of cell types in vitro and in several tissues in vivo in the rat. The transfection capacity of LDL is based on apo B100, as arginine/lysine clusters, suggestive of nucleic acid-binding domains and nuclear localization signal sequences, are present throughout the molecule. Apo E may also contribute to this capacity because of its similarity to the Dengue virus capsid proteins and its ability to bind DNA. Synthetic peptides representing two apo B100 regions with prominent Arg/Lys clusters were shown to bind DNA. Region 1 (0014Lys-Ser 0160) shares sequence motifs present in …

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Search For Gravitational-Wave Inspiral Signals Associated With Short Gamma-Ray Bursts During Ligo's Fifth And Virgo's First Science Run, J. Abadie, B. P. Abbott, R. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, Soumya Mohanty, Soma Mukherjee, Malik Rakhmanov, Joseph D. Romano Jun 2010

Search For Gravitational-Wave Inspiral Signals Associated With Short Gamma-Ray Bursts During Ligo's Fifth And Virgo's First Science Run, J. Abadie, B. P. Abbott, R. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, Soumya Mohanty, Soma Mukherjee, Malik Rakhmanov, Joseph D. Romano

Physics & Astronomy Faculty Publications

Progenitor scenarios for short gamma-ray bursts (short GRBs) include coalescenses of two neutron stars or a neutron star and black hole, which would necessarily be accompanied by the emission of strong gravitational waves. We present a search for these known gravitational-wave signatures in temporal and directional coincidence with 22 GRBs that had sufficient gravitational-wave data available in multiple instruments during LIGO's fifth science run, S5, and Virgo's first science run, VSR1. We find no statistically significant gravitational-wave candidates within a [ - 5, + 1)s window around the trigger time of any GRB. Using the Wilcoxon-Mann-Whitney U-test, we find no …

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On The Anomalous Balmer Line Strengths In Globular Clusters, Violet Poole, Guy Worthey, Hyun Chul Lee, Jedidiah Serven Feb 2010

On The Anomalous Balmer Line Strengths In Globular Clusters, Violet Poole, Guy Worthey, Hyun Chul Lee, Jedidiah Serven

Physics & Astronomy Faculty Publications

Spectral feature index diagrams with integrated globular clusters and simple stellar population models often show that some clusters have weak Hβ, so weak that even the oldest models cannot match the observed feature depths. In this work, we rule out the possibility that abundance mixture effects are responsible for the weak indices unless such changes operate to cool the entire isochrone. We discuss this result in the context of other explanations, including horizontal branch morphology, blue straggler populations, and nebular or stellar emission fill-in, finding a preference for flaring in M giants as an explanation for the Hβ anomaly. © …

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Unidirectional Nonlinear Pt-Symmetric Optical Structures, Hamidreza Ramezani, Tsampikos Kottos Jan 2010

Unidirectional Nonlinear Pt-Symmetric Optical Structures, Hamidreza Ramezani, Tsampikos Kottos

Physics & Astronomy Faculty Publications

We show that nonlinear optical structures involving a balanced gain-loss profile can act as unidirectional optical valves. This is made possible by exploiting the interplay between the fundamental symmetries of parity (P) and time (T), with optical nonlinear effects. This unidirectional dynamics is specifically demonstrated for the case of an integrable PT-symmetric nonlinear system.

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Effects Of Α-Element Enhancement And The Thermally Pulsing-Asymptotic Giant Branch On Surface Brightness Fluctuation Magnitudes And Broadband Colors, Hyun Chul Lee, Guy Worthey, John P. Blakeslee Jan 2010

Effects Of Α-Element Enhancement And The Thermally Pulsing-Asymptotic Giant Branch On Surface Brightness Fluctuation Magnitudes And Broadband Colors, Hyun Chul Lee, Guy Worthey, John P. Blakeslee

Physics & Astronomy Faculty Publications

We investigate the effects of α-element enhancement and the thermally pulsing-asymptotic giant branch (TP-AGB) stars on the surface brightness fluctuation (SBF) magnitudes and broadband colors of simple stellar populations and compare to the empirical calibrations. We consider a broad range of ages and metallicities using the recently updated Teramo BaSTI isochrones. We find that the α-element-enhanced I-band SBF magnitudes are about 0.35mag brighter and their integrated V - I colors are about 0.02mag redder, mostly because of oxygen-enhancement effects on the upper red giant branch and AGB. We also demonstrate, using both the Teramo BaSTI and Padova isochrones, the acute …

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Search For Gravitational-Wave Bursts Associated With Gamma-Ray Bursts Using Data From Ligo Science Run 5 And Virgo Science Run 1, B. P. Abbott, R. Abbott, F. Acernese, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, Soumya Mohanty, Soma Mukherjee, Malik Rakhmanov, Joseph D. Romano Jan 2010

Search For Gravitational-Wave Bursts Associated With Gamma-Ray Bursts Using Data From Ligo Science Run 5 And Virgo Science Run 1, B. P. Abbott, R. Abbott, F. Acernese, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, Soumya Mohanty, Soma Mukherjee, Malik Rakhmanov, Joseph D. Romano

Physics & Astronomy Faculty Publications

We present the results of a search for gravitational-wave bursts (GWBs) associated with 137 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments during the fifth LIGO science run and first Virgo science run. The data used in this analysis were collected from 2005 November 4 to 2007 October 1, and most of the GRB triggers were from the Swift satellite. The search uses a coherent network analysis method that takes into account the different locations and orientations of the interferometers at the three LIGO-Virgo sites. We find no evidence for GWB signals associated with this sample of GRBs. …

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Search For Gravitational Waves From Compact Binary Coalescence In Ligo And Virgo Data From S5 And Vsr1, J. Abadie, B. P. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, Soumya Mohanty, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano Jan 2010

Search For Gravitational Waves From Compact Binary Coalescence In Ligo And Virgo Data From S5 And Vsr1, J. Abadie, B. P. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, Soumya Mohanty, Soma Mukherjee, Volker Quetschke, Malik Rakhmanov, Joseph D. Romano

Physics & Astronomy Faculty Publications

We report the results of the first search for gravitational waves from compact binary coalescence using data from the Laser Interferometer Gravitational-Wave Observatory and Virgo detectors. Five months of data were collected during the Laser Interferometer Gravitational-Wave Observatory’s S5 and Virgo’s VSR1 science runs. The search focused on signals from binary mergers with a total mass between 2 and 35M⊙. No gravitational waves are identified. The cumulative 90%-confidence upper limits on the rate of compact binary coalescence are calculated for nonspinning binary neutron stars, black hole-neutron star systems, and binary black holes to be 8.7×10−3  yr−1 L−110, 2.2×10−3  yr−1 L−110, …

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All-Sky Search For Gravitational-Wave Bursts In The First Joint Ligo-Geo-Virgo Run, J. Abadie, B. P. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, Soumya Mohanty, Soma Mukherjee, Malik Rakhmanov, Joseph D. Romano, Robert Stone Jan 2010

All-Sky Search For Gravitational-Wave Bursts In The First Joint Ligo-Geo-Virgo Run, J. Abadie, B. P. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, Soumya Mohanty, Soma Mukherjee, Malik Rakhmanov, Joseph D. Romano, Robert Stone

Physics & Astronomy Faculty Publications

We present results from an all-sky search for unmodeled gravitational-wave bursts in the data collected by the LIGO, GEO 600 and Virgo detectors between November 2006 and October 2007. The search is performed by three different analysis algorithms over the frequency band 50–6000 Hz. Data are analyzed for times with at least two of the four LIGO-Virgo detectors in coincident operation, with a total live time of 266 days. No events produced by the search algorithms survive the selection cuts. We set a frequentist upper limit on the rate of gravitational-wave bursts impinging on our network of detectors. When combined …

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The Lisa Gravitational Wave Foreground: A Study Of Double White Dwarfs, Ashley J. Ruiter, Krzysztof Belczynski, Matthew Benacquista, Shane L. Larson, Gabriel Williams Jan 2010

The Lisa Gravitational Wave Foreground: A Study Of Double White Dwarfs, Ashley J. Ruiter, Krzysztof Belczynski, Matthew Benacquista, Shane L. Larson, Gabriel Williams

Physics & Astronomy Faculty Publications

Double white dwarfs (WDs) are expected to be a source of confusion-limited noise for the future gravitational wave observatory LISA. In a specific frequency range, this \"foreground noise\" is predicted to rise above the instrumental noise and hinder the detection of other types of signals, e.g., gravitational waves arising from stellar-mass objects inspiraling into massive black holes. In many previous studies, only detached populations of compact object binaries have been considered in estimating the LISA gravitational wave foreground signal. Here, we investigate the influence of compact object detached and Roche-Lobe overflow (RLOF) Galactic binaries on the shape and strength of …

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Triplets Of Supermassive Black Holes: Astrophysics Gravitational Waves And Detection, Pau Amaro-Seoane, Alberto Sesana, Loren Hoffman, Matthew Benacquista, Christoph Eichhorn, Junichiro Makino, Rainer Spurzem Jan 2010

Triplets Of Supermassive Black Holes: Astrophysics Gravitational Waves And Detection, Pau Amaro-Seoane, Alberto Sesana, Loren Hoffman, Matthew Benacquista, Christoph Eichhorn, Junichiro Makino, Rainer Spurzem

Physics & Astronomy Faculty Publications

Supermassive black holes (SMBHs) found in the centres of many galaxies are understood to play a fundamental, active role in the cosmological structure formation process. In hierarchical formation scenarios, SMBHs are expected to form binaries following the merger of their host galaxies. If these binaries do not coalesce before the merger with a third galaxy, the formation of a black hole triple system is possible. Numerical simulations of the dynamics of triples within galaxy cores exhibit phases of very high eccentricity (as high as e∼ 0.99). During these phases, intense bursts of gravitational radiation can be emitted at orbital periapsis, …

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Searches For Gravitational Waves From Known Pulsars With Science Run 5 Ligo Data, B. P. Abbott, R. Abbott, F. Acernese, Teviet Creighton, Matthew Benacquista, Mario C. Diaz, Soumya D. Mohanty, Soma Mukherjee, Malik Rakhmanov, Joseph D. Romano Jan 2010

Searches For Gravitational Waves From Known Pulsars With Science Run 5 Ligo Data, B. P. Abbott, R. Abbott, F. Acernese, Teviet Creighton, Matthew Benacquista, Mario C. Diaz, Soumya D. Mohanty, Soma Mukherjee, Malik Rakhmanov, Joseph D. Romano

Physics & Astronomy Faculty Publications

We present a search for gravitational waves from 116 known millisecond and young pulsars using data from the fifth science run of the LIGO detectors. For this search, ephemerides overlapping the run period were obtained for all pulsars using radio and X-ray observations. We demonstrate an updated search method that allows for small uncertainties in the pulsar phase parameters to be included in the search. We report no signal detection from any of the targets and therefore interpret our results as upper limits on the gravitational wave signal strength. The most interesting limits are those for young pulsars. We present …

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Apparent Faster-Than-Light Pulse Propagation In Interstellar Space: A New Probe Of The Interstellar Medium, F. A. Jenet, D. Fleckenstein, A. Ford, A. Garcia, R. Miller, J. Rivera, K. Stovall Jan 2010

Apparent Faster-Than-Light Pulse Propagation In Interstellar Space: A New Probe Of The Interstellar Medium, F. A. Jenet, D. Fleckenstein, A. Ford, A. Garcia, R. Miller, J. Rivera, K. Stovall

Physics & Astronomy Faculty Publications

Radio pulsars emit regular bursts of radio radiation that propagate through the interstellar medium (ISM), the tenuous gas and plasma between the stars. Previously known dispersive properties of the ISM cause low-frequency pulses to be delayed in time with respect to high frequency ones. This effect can be explained by the presence of free electrons in the medium. The ISM also contains neutral hydrogen that has a well-known resonance at 1420.4 MHz. Electromagnetic theory predicts that at such a resonance, the induced dispersive effects will be drastically different from those of the free electrons. Pulses traveling through a cloud of …

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Particle Swarm Optimization And Gravitational Wave Data Analysis: Performance On A Binary Inspiral Testbed, Yan Wang, Soumya Mohanty Jan 2010

Particle Swarm Optimization And Gravitational Wave Data Analysis: Performance On A Binary Inspiral Testbed, Yan Wang, Soumya Mohanty

Physics & Astronomy Faculty Publications

The detection and estimation of gravitational wave signals belonging to a parameterized family of waveforms requires, in general, the numerical maximization of a data-dependent function of the signal parameters. Because of noise in the data, the function to be maximized is often highly multimodal with numerous local maxima. Searching for the global maximum then becomes computationally expensive, which in turn can limit the scientific scope of the search. Stochastic optimization is one possible approach to reducing computational costs in such applications. We report results from a first investigation of the particle swarm optimization method in this context. The method is …

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Timing Stability Of Millisecond Pulsars And Prospects For Gravitational-Wave Detection, J. P.W. Verbiest, M. Bailes, W. A. Coles, G. B. Hobbs, W. Van Straten, D. J. Champion, Fredrick A. Jenet, R. N. Manchester, N. D.R. Bhat, J. M. Sarkissian Dec 2009

Timing Stability Of Millisecond Pulsars And Prospects For Gravitational-Wave Detection, J. P.W. Verbiest, M. Bailes, W. A. Coles, G. B. Hobbs, W. Van Straten, D. J. Champion, Fredrick A. Jenet, R. N. Manchester, N. D.R. Bhat, J. M. Sarkissian

Physics & Astronomy Faculty Publications

The analysis of high-precision timing observations of an array of ∼20 millisecond pulsars (a so-called 'timing array') may ultimately result in the detection of a stochastic gravitational-wave background. The feasibility of such a detection and the required duration of this type of experiment are determined by the achievable rms of the timing residuals and the timing stability of the pulsars involved. We present results of the first long-term, high-precision timing campaign on a large sample of millisecond pulsars used in gravitational-wave detection projects. We show that the timing residuals of most pulsars in our sample do not contain significant low-frequency …

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Comparison Of Alpha-Element-Enhanced Simple Stellar Population Models With Milky Way Globular Clusters, Hyun Chul Lee, Guy Worthey, Aaron Dotter Nov 2009

Comparison Of Alpha-Element-Enhanced Simple Stellar Population Models With Milky Way Globular Clusters, Hyun Chul Lee, Guy Worthey, Aaron Dotter

Physics & Astronomy Faculty Publications

We present simple stellar population (SSP) models with scaled-solar and α-element-enhanced abundances. The SSP models are based on the Dartmouth Stellar Evolution Database, our library of synthetic stellar spectra, and a detailed systematic variation of horizontal-branch (HB) morphology with age and metallicity. In order to test the relative importance of a variety of SSP model ingredients, we compare our SSP models with integrated spectra of 41 Milky Way globular clusters (MWGCs) from Schiavon etal. Using the Mg b and Ca4227 indices, we confirm that Mg and Ca are enhanced by about +0.4 and +0.2dex, respectively, in agreement with results from …

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Subcellular Min Oscillations As A Single-Cell Reporter Of The Action Of Polycations Protamine And Gentamicin On Escherichia Coli, Benjamin P.B. Downing, Andrew D. Rutenberg, Ahmed Touhami, Manfred Jericho Sep 2009

Subcellular Min Oscillations As A Single-Cell Reporter Of The Action Of Polycations Protamine And Gentamicin On Escherichia Coli, Benjamin P.B. Downing, Andrew D. Rutenberg, Ahmed Touhami, Manfred Jericho

Physics & Astronomy Faculty Publications

Background: In Escherichia coli, MinD-GFP fusion proteins show rapid pole to pole oscillations. The objective was to investigate the effects of extracellular cations on the subcellular oscillation of cytoplasmic MinD within Escherichia coli. Methodology/Principal Findings: We exposed bacteria to the extracellular cations Ca++, Mg++, the cationic antimicrobial peptide (CAP) protamine, and the cationic aminoglycoside gentamicin. We found rapid and substantial increases in the average MinD oscillation periods in the presence of any of these polyvalent cations. For Ca++ and Mg++ the increases in period were transient, even with a constant extracellular concentration, while increases in period for protamine or gentamicin …

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