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Articles 1 - 14 of 14
Full-Text Articles in Physical Sciences and Mathematics
Globular Cluster And Galaxy Formation: M31 The Milky Way And Implications For Globular Cluster Systems Of Spiral Galaxies, David Burstein, Yong Li, Kenneth C. Freeman, John E. Norris, Michael S. Bessell, Joss Bland-Hawthorn, Brad K. Gibson, Mlchael A. Beasley, Hyun Chul Lee, Beatriz Barbuy, John P. Huchra, Jean P. Brodif, Duncan A. Forbes
Globular Cluster And Galaxy Formation: M31 The Milky Way And Implications For Globular Cluster Systems Of Spiral Galaxies, David Burstein, Yong Li, Kenneth C. Freeman, John E. Norris, Michael S. Bessell, Joss Bland-Hawthorn, Brad K. Gibson, Mlchael A. Beasley, Hyun Chul Lee, Beatriz Barbuy, John P. Huchra, Jean P. Brodif, Duncan A. Forbes
Physics and Astronomy Faculty Publications and Presentations
We find that the globular cluster (GC) systems of the Milky Way and of our neighboring spiral galaxy, M31, comprise two distinct entities, differing in three respects. First, M31 has a set of young GCs, ranging in age from a few times 10 2 Myr to 5 Gyr old, as well as old GCs. No such very young GCs are known in the Milky Way. Second, we confirm that the oldest M31 GCs have much higher nitrogen abundances than do Galactic GCs at equivalent metallicities, while carbon abundances appear normal for the GCs in both galaxies. Third, Morrison and coworkers …
Is The Initial Mass Function Of Low Surface Brightness Galaxies Dominated By Low-Mass Stars?, Hyun Chul Lee, Brad K. Gibson, Chris Flynn, Daisuke Kawata, Michael A. Beasley
Is The Initial Mass Function Of Low Surface Brightness Galaxies Dominated By Low-Mass Stars?, Hyun Chul Lee, Brad K. Gibson, Chris Flynn, Daisuke Kawata, Michael A. Beasley
Physics and Astronomy Faculty Publications and Presentations
The rotation curves of low surface brightness (LSB) galaxies suggest that they possess significantly higher mass-to-light (M/L) ratios than their high surface brightness counterparts, indicating that LSB galaxies may be dark matter dominated. This interpretation is hampered by the difficulty of disentangling the disc and dark halo contributions from the disc dynamics of LSB galaxies. Recently, Fuchs has attempted such a disentanglement using spiral arm density wave and swing amplification theory, allowing an independent measurement of the disc mass; this work suggests that LSB discs are significantly more massive than previously believed. This would considerably reduce the amount of matter …
Mechanical Properties Of Carbon Nanotubes Composites, David Hui, Mircea Chipara, Jagannathan Sankar, K. T. Lau
Mechanical Properties Of Carbon Nanotubes Composites, David Hui, Mircea Chipara, Jagannathan Sankar, K. T. Lau
Physics and Astronomy Faculty Publications and Presentations
A critical review of theoretical models aiming to explain the physical properties of composites based on polymeric matrices reinforced with carbon nanotubes is presented. Attention is paid to descriptions based on molecular dynamics, continuum mechanics, and finite element analysis. It is shown that both the continuum mechanics approximation and the finite size element analyses fail to describe composites with very thin interfaces, while the performances of molecular dynamics simulations are still restricted by computer's performances. The limitations of the continuum mechanics approximation are analyzed in detail.
Constraining The Properties Of Supermassive Black Hole Systems Using Pulsar Timing: Application To 3c 66b, Fredrick A. Jenet, Andrea Lommen, Shane L. Larson, Linqing Wen
Constraining The Properties Of Supermassive Black Hole Systems Using Pulsar Timing: Application To 3c 66b, Fredrick A. Jenet, Andrea Lommen, Shane L. Larson, Linqing Wen
Physics and Astronomy Faculty Publications and Presentations
General expressions for the expected timing residuals induced by gravitational wave (G-wave) emission from a slowly evolving, eccentric, binary black hole system are derived here for the first time. These expressions are used to search for the signature of G-waves emitted by the proposed supermassive binary black hole system in 3C 66B. We use data from long-term timing observations of the radio pulsar PSR B1855+09. For the case of a circular orbit, the emitted G-waves should generate clearly detectable fluctuations in the pulse-arrival times of PSR B1855+09. Since no G-waves are detected, the waveforms are used in a Monte Carlo …
The Intrinsic Intensity Modulation Of Psr B1937+21 At 1410 Mhz, Fredrick A. Jenet, Janusz Gil
The Intrinsic Intensity Modulation Of Psr B1937+21 At 1410 Mhz, Fredrick A. Jenet, Janusz Gil
Physics and Astronomy Faculty Publications and Presentations
The single-pulse properties of the millisecond radio pulsar PSR B1937+21 are studied at 1410 MHz. The nongiant pulse emission regions appear to be remarkably stable, showing no pulse-to-pulse fluctuations other then those induced by the interstellar medium. This type of behavior has not been seen in any other pulsar, although it was seen in previous 430 MHz observations of this source. The stability of this source is interpreted in the context of the sparking gap model of radio pulsar emission, and a model-dependent upper bound is placed on the Lorentz factor of the outflowing plasma.
Xafs Debye-Waller Factors For Zn Metalloproteins, N. Dimakis, Grant Bunker
Xafs Debye-Waller Factors For Zn Metalloproteins, N. Dimakis, Grant Bunker
Physics and Astronomy Faculty Publications and Presentations
An accurate and practical method for the calculation and use of thermal x-ray absorption fine structure (XAFS) Debye-Waller factors (DWFs) in active sites of metalloproteins is presented. These factors are calculated on model clusters within the local density functional approximation with nonlocal corrections. The DWFs are mapped out and parametrized as a function of the first shell distance and an angle (where applicable), for all significant single and multiple scattering paths, as well as the sample temperature. This approach is applied to the biologically essential but spectroscopically silent Zn+2 active sites composed of histidines, cysteines, and carboxylate ligands in homogeneous …
Setting Upper Limits On The Strength Of Periodic Gravitational Waves From Psr J1939+2134 Using The First Science Data From The Geo 600 And Ligo Detectors, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano, Cristina V. Torres
Setting Upper Limits On The Strength Of Periodic Gravitational Waves From Psr J1939+2134 Using The First Science Data From The Geo 600 And Ligo Detectors, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano, Cristina V. Torres
Physics and Astronomy Faculty Publications and Presentations
Data collected by the GEO 600 and LIGO interferometric gravitational wave detectors during their first observational science run were searched for continuous gravitational waves from the pulsar J1939+2134 at twice its rotation frequency. Two independent analysis methods were used and are demonstrated in this paper: a frequency domain method and a time domain method. Both achieve consistent null results, placing new upper limits on the strength of the pulsar’s gravitational wave emission. A model emission mechanism is used to interpret the limits as a constraint on the pulsar’s equatorial ellipticity.
Probing Molecular Free Energy Landscapes By Periodic Loading, Oliver Braun, Andreas Hanke, Udo Seifert
Probing Molecular Free Energy Landscapes By Periodic Loading, Oliver Braun, Andreas Hanke, Udo Seifert
Physics and Astronomy Faculty Publications and Presentations
Single molecule pulling experiments provide information about interactions in biomolecules that cannot be obtained by any other method. However, the reconstruction of the molecule’s free energy profile from the experimental data is still a challenge, in particular, for the unstable barrier regions. We propose a new method for obtaining the full profile by introducing a periodic ramp and using Jarzynski’s relation for obtaining equilibrium quantities from nonequilibrium data. Our simulated experiments show that this method delivers significant more accurate data than previous methods, under the constraint of equal experimental effort.
Coalescence Remnant Of Spinning Binary Black Holes, J Baker, M. Campanelli, C. O. Lousto, R. Takahashi
Coalescence Remnant Of Spinning Binary Black Holes, J Baker, M. Campanelli, C. O. Lousto, R. Takahashi
Physics and Astronomy Faculty Publications and Presentations
We compute the gravitational radiation generated in the evolution of a family of close binary black hole configurations, using a combination of numerical and perturbative approximation methods. We evolve the binaries with spins s aligned or counteraligned with the orbital angular momentum from near the innermost stable circular orbit down to the final single rotating black hole. For the moderately spinning holes studied here the remnant Kerr black holes formed at the end of an inspiral process have rotation parameters a/M≈0.72+0.32(s/mH), suggesting it is difficult (though not excluded) to end up with near maximally rotating holes from such scenarios.
First Upper Limits From Ligo On Gravitational Wave Bursts, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano, Cristina V. Torres
First Upper Limits From Ligo On Gravitational Wave Bursts, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano, Cristina V. Torres
Physics and Astronomy Faculty Publications and Presentations
We report on a search for gravitational wave bursts using data from the first science run of the Laser Interferometer Gravitational Wave Observatory (LIGO) detectors. Our search focuses on bursts with durations ranging from 4 to 100 ms, and with significant power in the LIGO sensitivity band of 150 to 3000 Hz. We bound the rate for such detected bursts at less than 1.6 events per day at a 90% confidence level. This result is interpreted in terms of the detection efficiency for ad hoc waveforms (Gaussians and sine Gaussians) as a function of their root-sum-square strain hrss; typical sensitivities …
Analysis Of Ligo Data For Gravitational Waves From Binary Neutron Stars, B. P. Abbott, R. Abbott, Wm. R. Johnston, Joseph D. Romano, V. Schmidt
Analysis Of Ligo Data For Gravitational Waves From Binary Neutron Stars, B. P. Abbott, R. Abbott, Wm. R. Johnston, Joseph D. Romano, V. Schmidt
Physics and Astronomy Faculty Publications and Presentations
We report on a search for gravitational waves from coalescing compact binary systems in the Milky Way and the Magellanic Clouds. The analysis uses data taken by two of the three LIGO interferometers during the first LIGO science run and illustrates a method of setting upper limits on inspiral event rates using interferometer data. The analysis pipeline is described with particular attention to data selection and coincidence between the two interferometers. We establish an observational upper limit of R
Generation Of The Transient Electrical And Spontaneous Magnetic Fields By Solid State Combustion, Karen S. Martirosyan, J. R. Claycomb, J. H. Miller Jr., D. Luss
Generation Of The Transient Electrical And Spontaneous Magnetic Fields By Solid State Combustion, Karen S. Martirosyan, J. R. Claycomb, J. H. Miller Jr., D. Luss
Physics and Astronomy Faculty Publications and Presentations
Experiments revealed that transient electric field intensities up to 2.5 V/cm were generated during the initial period of combustion synthesis of the ferromagnetic products before the maximum temperature was reached. This occurred when the iron particles were partially oxidized and the reaction product was mainly magnetite sFe3O4d. The electromagnetic field caused spontaneous magnetization of the product in the postcombustion zone. Magnetic field values up to 4 µT formed after the sample temperature fell below the Curie temperature and the initial reactants were completely converted to the ferromagnetic phase PbFe12O19. Increasing the volume of the samples increases the absolute residual magnetic …
Analysis Of First Ligo Science Data For Stochastic Gravitational Waves, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano
Analysis Of First Ligo Science Data For Stochastic Gravitational Waves, B. P. Abbott, R. Abbott, Mario C. Diaz, Wm. R. Johnston, Joseph D. Romano
Physics and Astronomy Faculty Publications and Presentations
We present the analysis of between 50 and 100 h of coincident interferometric strain data used to search for and establish an upper limit on a stochastic background of gravitational radiation. These data come from the first LIGO science run, during which all three LIGO interferometers were operated over a 2-week period spanning August and September of 2002. The method of cross correlating the outputs of two interferometers is used for analysis. We describe in detail practical signal processing issues that arise when working with real data, and we establish an observational upper limit on a f−3 power spectrum of …
New Methods For Exafs Analysis In Structural Genomics, Grant Bunker, N. Dimakis, Gocha Kelashvili
New Methods For Exafs Analysis In Structural Genomics, Grant Bunker, N. Dimakis, Gocha Kelashvili
Physics and Astronomy Faculty Publications and Presentations
Data analysis is one of the remaining bottlenecks in high-throughput EXAFS for structural genomics. Here some recent developments in methodology are described that offer the potential for rapid and automated XAS analysis of metalloproteins.