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Articles 2011 - 2040 of 2944

Full-Text Articles in Astrophysics and Astronomy

Real-Space Approach To Time Dependent Current Density Functional Theory, Daniel S. Jensen Jul 2010

Real-Space Approach To Time Dependent Current Density Functional Theory, Daniel S. Jensen

Theses and Dissertations

A real-space time-domain calculation of the frequency-dependent dielectric constant of nonmetallic crystals is outlined and the integrals required for this calculation are computed. The outline is based on time dependent current density functional theory and is partially implemented in the ab initio density functional theory FIREBALL program. The addition of a vector potential to the Hamiltonian of the system is discussed as well as the need to include the current density in addition to the particle density. The derivation of gradient integrals within a localized atomic-like orbital basis is presented for use in constructing the current density. Due to the …

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In Search Of Empty Places: Voids In The Distribution Of Galaxies, Brian K. Bucklein Jul 2010

In Search Of Empty Places: Voids In The Distribution Of Galaxies, Brian K. Bucklein

Theses and Dissertations

We investigate several techniques to identify voids in the galaxy distribution of matter in the universe. We utilize galaxy number counts as a function of apparent magnitude and Wolf plots to search a two- or three-dimensional data set in a pencil-beam fashion to locate voids within the field of view. The technique is able to distinguish between voids that represent simply a decrease in density as well as those that show a build up of galaxies on the front or back side of the void. This method turns out to be primarily useable only at relatively short range (out to …

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Oh Megamasers In Merging Galaxies: A Multi-Frequency Study Of Iizw096, Kirstin Marie Cooprider Jul 2010

Oh Megamasers In Merging Galaxies: A Multi-Frequency Study Of Iizw096, Kirstin Marie Cooprider

Theses and Dissertations

OH Megamasers (OHMs) generally appear in luminous infrared regions i.e. merging galaxies. In this study we assume that OHMs may not be represented by their association with star formation solely, because of the possibility of a compact AGN source in the merging galaxies. In fact, previously classified starburst galaxies where OHMs are found are now optically observed as AGN. OHMs may also serve as a reasonable criterion for the evolutionary stage of the merger. This project focuses on observations from a multi-frequency analysis of merging regions with known OHMs. Optically, Hα and BVRI filters provided an environmental perspective of the …

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A Sea Change In Eta Carinae, Andrea Mehner, Kris Davidson, Roberta M. Humphreys, John C. Martin, Kazunori Ishibashi, Gary J. Ferland, Nolan R. Walborn Jul 2010

A Sea Change In Eta Carinae, Andrea Mehner, Kris Davidson, Roberta M. Humphreys, John C. Martin, Kazunori Ishibashi, Gary J. Ferland, Nolan R. Walborn

Physics and Astronomy Faculty Publications

Major stellar-wind emission features in the spectrum of η Car have recently decreased by factors of order 2 relative to the continuum. This is unprecedented in the modern observational record. The simplest, but unproven, explanation is a rapid decrease in the wind density.

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Herschel Photometry Of Brightest Cluster Galaxies In Cooling Flow Clusters, A. C. Edge, J. B. R. Oonk, R. Mittal, S. W. Allen, S. A. Baum, H. Böhringer, J. N. Bregman, M. N. Bremer, F. Combes, C. S. Crawford, M. Donahue, E. Egami, A. C. Fabian, Gary J. Ferland, S. L. Hamer, N. A. Hatch, W. Jaffe, R. M. Johnstone, B. R. Mcnamara, C. P. O'Dea, P. Popesso, A. C. Quillen, P. Salomé, C. L. Sarazin, G. M. Voit, R. J. Wilman, M. W. Wise Jul 2010

Herschel Photometry Of Brightest Cluster Galaxies In Cooling Flow Clusters, A. C. Edge, J. B. R. Oonk, R. Mittal, S. W. Allen, S. A. Baum, H. Böhringer, J. N. Bregman, M. N. Bremer, F. Combes, C. S. Crawford, M. Donahue, E. Egami, A. C. Fabian, Gary J. Ferland, S. L. Hamer, N. A. Hatch, W. Jaffe, R. M. Johnstone, B. R. Mcnamara, C. P. O'Dea, P. Popesso, A. C. Quillen, P. Salomé, C. L. Sarazin, G. M. Voit, R. J. Wilman, M. W. Wise

Physics and Astronomy Faculty Publications

The dust destruction timescales in the cores of clusters of galaxies are relatively short given their high central gas densities. However, substantial mid-infrared and sub-mm emission has been detected in many brightest cluster galaxies. In this letter we present Herschel PACS and SPIRE photometry of the brightest cluster galaxy in three strong cooling flow clusters, A1068, A2597 and Zw3146. This photometry indicates that a substantial mass of cold dust is present (> 3×107 M⊙) at temperatures significantly lower (20–28 K) than previously thought based on limited MIR and/or sub-mm results. The mass and temperature of the dust appear …

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Herschel Observations Of Fir Emission Lines In Brightest Cluster Galaxies, A. C. Edge, J. B. R. Oonk, R. Mittal, S. W. Allen, S. A. Baum, H. Böhringer, J. N. Bregman, M. N. Bremer, F. Combes, C. S. Crawford, M. Donahue, E. Egami, A. C. Fabian, Gary J. Ferland, S. L. Hamer, N. A. Hatch, W. Jaffe, R. M. Johnstone, B. R. Mcnamara, C. P. O'Dea, P. Popesso, A. C. Quillen, P. Salomé, C. L. Sarazin, G. M. Voit, R. J. Wilman, M. W. Wise Jul 2010

Herschel Observations Of Fir Emission Lines In Brightest Cluster Galaxies, A. C. Edge, J. B. R. Oonk, R. Mittal, S. W. Allen, S. A. Baum, H. Böhringer, J. N. Bregman, M. N. Bremer, F. Combes, C. S. Crawford, M. Donahue, E. Egami, A. C. Fabian, Gary J. Ferland, S. L. Hamer, N. A. Hatch, W. Jaffe, R. M. Johnstone, B. R. Mcnamara, C. P. O'Dea, P. Popesso, A. C. Quillen, P. Salomé, C. L. Sarazin, G. M. Voit, R. J. Wilman, M. W. Wise

Physics and Astronomy Faculty Publications

The question of how much gas cools in the cores of clusters of galaxies has been the focus of many, multiwavelength studies in the past 30 years. In this letter we present the first detections of the strongest atomic cooling lines, [Cii], [Oi] and [Nii] in two strong cooling flow clusters, A1068 and A2597, using Herschel-PACS. These spectra indicate that the substantial mass of cold molecular gas (> 109 M⊙) known to be present in these systems is being irradiated by intense UV radiation, most probably from young stars. The line widths of these FIR lines …

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Herschel Images Of Ngc 6720: H2 Formation On Dust Grain, P. A. M. Van Hoof, G. C. Van De Steene, M. J. Barlow, K. M. Exter, B. Sibthorpe, T. Ueta, V. Peris, M. A. T. Groenewegen, J. A. D. L. Blommaert, M. Cohen, W. De Meester, Gary J. Ferland, W. K. Gear, H. L. Gomez, P. C. Hargrave, E. Huygen, R. J. Ivison, C. Jean, S. J. Leeks, T. L. Lim, G. Olofsson, E. T. Polehampton, S. Regibo, P. Royer, B. M. Swinyard, B. Vandenbussche, H. Van Winckel, C. Waelkens, H. J. Walker, R. Wesson Jul 2010

Herschel Images Of Ngc 6720: H2 Formation On Dust Grain, P. A. M. Van Hoof, G. C. Van De Steene, M. J. Barlow, K. M. Exter, B. Sibthorpe, T. Ueta, V. Peris, M. A. T. Groenewegen, J. A. D. L. Blommaert, M. Cohen, W. De Meester, Gary J. Ferland, W. K. Gear, H. L. Gomez, P. C. Hargrave, E. Huygen, R. J. Ivison, C. Jean, S. J. Leeks, T. L. Lim, G. Olofsson, E. T. Polehampton, S. Regibo, P. Royer, B. M. Swinyard, B. Vandenbussche, H. Van Winckel, C. Waelkens, H. J. Walker, R. Wesson

Physics and Astronomy Faculty Publications

Herschel PACS and SPIRE images have been obtained of NGC 6720 (the Ring nebula). This is an evolved planetary nebula with a central star that is currently on the cooling track, due to which the outer parts of the nebula are recombining. From the PACS and SPIRE images we conclude that there is a striking resemblance between the dust distribution and the H2 emission, which appears to be observational evidence that H2 forms on grain surfaces. We have developed a photoionization model of the nebula with the Cloudy code which we used to determine the physical conditions of …

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Diode Properties Of Nanotube Networks, David D. Allred, Bryan Hicks, Stephanie Getty Jun 2010

Diode Properties Of Nanotube Networks, David D. Allred, Bryan Hicks, Stephanie Getty

Faculty Publications

Single-walled carbon nanotubes (SWCNT) were prepared using iron catalysts deposited by indirect evaporation on silicon substrate covered with 500 nm-thick thermal oxide. Diode SWCNT devices have been fabricated using Au and Al, as the asymmetric metal contacts, and a random network of metallic and semiconducting nanotubes as the device channel. No effort was made to align the SWCNTs or to eliminate metallic nanotubes in our devices. Asymmetric voltage-current behavior was seen. Current rectification was observed in the source-drain bias range of -3 V to +3 V. Rectification was somewhat surprising since, although metallic tubes are in the minority (~ 1/3), …

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A Bright Molecular Core In A Crab Nebula Filament, E. D. Loh, J. A. Baldwin, Gary J. Ferland Jun 2010

A Bright Molecular Core In A Crab Nebula Filament, E. D. Loh, J. A. Baldwin, Gary J. Ferland

Physics and Astronomy Faculty Publications

In a sub-arcsec near-infrared survey of the Crab Nebula using the new Spartan Infrared Camera, we have found several knots with high surface brightness in the H2 2.12 μm line and a very large H2 2.12 μm to Brγ ratio. The brightest of these knots has an intensity ratio I(H2 2.12 μm)/I(Brγ) = 18 ± 9, which we show sets a lower limit on the ratio of masses in the molecular and recombination (i.e., ionized) zones M mol/M rec ≥ 0.9, and a total molecular mass within this single knot M mol ≥ …

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On Arc-Polarized Structures In The Solar Wind, B U. Sonnerup, S E. Haaland, G Paschmann Jun 2010

On Arc-Polarized Structures In The Solar Wind, B U. Sonnerup, S E. Haaland, G Paschmann

Dartmouth Scholarship

A theoretical model is proposed to account for some of the behavior of arc-polarized magnetic structures seen in the solar wind. To this end, an exact analytical solu- tion is developed that describes infinite plane wave trains of arbitrary amplitude in a plasma governed by ideal Hall MHD. The main focus is on intermediate-mode wave trains, which display double-branched magnetic hodogram signatures sim- ilar to those seen in the solar wind. The theoretically derived hodograms have field rotation in the ion-polarized sense at a slightly depressed field magnitude on one branch and an electron-polarized rotation at a slightly enhanced field …

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Luminosity-Variation Independent Location Of The Circum-Nuclear, Hot Dust In Ngc 4151, Jorg-Uwe Pott, Matt A. Malkan, Moshe Elitzur, Andrea M. Ghez, Tom M. Herbst, Rainer Schödel, Julien Woillez Jun 2010

Luminosity-Variation Independent Location Of The Circum-Nuclear, Hot Dust In Ngc 4151, Jorg-Uwe Pott, Matt A. Malkan, Moshe Elitzur, Andrea M. Ghez, Tom M. Herbst, Rainer Schödel, Julien Woillez

Physics and Astronomy Faculty Publications

After recent sensitivity upgrades at the Keck Interferometer (KI), systematic interferometric 2 μm studies of the innermost dust in nearby Seyfert nuclei are within observational reach. Here, we present the analysis of new interferometric data of NGC 4151, discussed in context of the results from recent dust reverberation, spectro-photometric, and interferometric campaigns. The complete data set gives a complex picture, in particular the measured visibilities from now three different nights appear to be rather insensitive to the variation of the nuclear luminosity. KI data alone indicate two scenarios: the K-band emission is either dominated to ~90% by size …

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A Bare Molecular Cloud At Z ~ 0.45*, Therese M. Jones, Toru Misawa, Jane C. Charlton, Andrew C. Mshar, Gary J. Ferland Jun 2010

A Bare Molecular Cloud At Z ~ 0.45*, Therese M. Jones, Toru Misawa, Jane C. Charlton, Andrew C. Mshar, Gary J. Ferland

Physics and Astronomy Faculty Publications

Several neutral species (Mg I, Si I, Ca I, Fe I) have been detected in a weak Mg II absorption line system (Wr (2796) ~ 0.15 Å) at z ~ 0.45 along the sightline toward HE0001-2340. These observations require extreme physical conditions, as noted in D'Odorico. We place further constraints on the properties of this system by running a wide grid of photoionization models, determining that the absorbing cloud that produces the neutral absorption is extremely dense (~100-1000 cm-3), cold (< 100 K), and has significant molecular content (~72%-94%). Structures of this size and temperature have been detected in Milky Way CO surveys and have been predicted in hydrodynamic simulations of turbulent gas. In order to explain the observed line profiles in all neutral and singly ionized chemical transitions, the lines must suffer from unresolved saturation and/or the absorber must partially cover the broad emission line region of the background quasar. In addition to this highly unusual cloud, three other ordinary weak Mg II clouds (within densities of ~0.005 cm-3 and temperatures of ~10, 000 K) lie within 500 km s-1 along the …

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Inhomogeneity-Induced Spin Current In Atomic And Condensed Matter Systems, Bailey Hsu May 2010

Inhomogeneity-Induced Spin Current In Atomic And Condensed Matter Systems, Bailey Hsu

Theses and Dissertations

I derive and apply quantum propagator techniques to atomic and condensed matter systems. I observe many interesting features by following the evolution of a wavepacket. In atomic systems, I revisit the Stern-Gerlach effect and study the spin dynamics inside an inhomogeneous magnetic field. The results I obtained are not exactly the same as the textbook description of the effect which is usually a manifestation of a perfect space and spin entanglement. This discovery can provide insight on more reliable quantum computation device designs. In condensed matter systems, the doping concentration inhomogeneity leads to the Rashba spin-orbit interaction. This makes it …

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Exotic Smoothness In Four Dimensions And Euclidean Quantum Gravity, Christopher L. Duston May 2010

Exotic Smoothness In Four Dimensions And Euclidean Quantum Gravity, Christopher L. Duston

Physics Faculty Publications

In this paper we calculate the effect of the inclusion of exotic smooth structures on typical observables in Euclidean quantum gravity. We do this in the semiclassical regime for several gravitational free-field actions and find that the results are similar, independent of the particular action that is chosen. These are the first results of their kind in dimension four, which we extend to include one-loop contributions as well. We find these topological features can have physically significant results without the need for additional exotic physics.

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Structure Maps For Hcp Metals From First-Principles Calculations, Gus L. W. Hart, Ohad Levy, Stefano Curtarolo May 2010

Structure Maps For Hcp Metals From First-Principles Calculations, Gus L. W. Hart, Ohad Levy, Stefano Curtarolo

Faculty Publications

The ability to predict the existence and crystal type of ordered structures of materials from their components is a major challenge of current materials research. Empirical methods use experimental data to construct structure maps and make predictions based on clustering of simple physical parameters. Their usefulness depends on the availability of reliable data over the entire parameter space. Recent development of high-throughput methods opens the possibility to enhance these empirical structure maps by ab initio calculations in regions of the parameter space where the experimental evidence is lacking or not well characterized. In this paper we construct enhanced maps for …

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Co And H3 + Toward Mwc 1080, Mwc 349, And Lkhα 101, Erika Gibb, S. Brittain, T Rettig, M Troutman, Theodore Simon, C Kulesa May 2010

Co And H3 + Toward Mwc 1080, Mwc 349, And Lkhα 101, Erika Gibb, S. Brittain, T Rettig, M Troutman, Theodore Simon, C Kulesa

Physics Faculty Works

We present high-resolution, near-infrared NIRSPEC observations of the fundamental rovibrational CO and H+ 3 R(1,0), R(1,1) u , and Q(1,0) transitions toward three early-type young stars: MWC 1080, MWC 349, and LkHα 101. These observations were performed for the purpose of constraining the physical characteristics of the interstellar material along each line of sight. Toward MWC 1080, we detected strong CO absorption and determined a column density upper limit of 1.4 × 1014 cm–2 for H+ 3. We infer that there is very little diffuse material along the line of sight toward MWC 1080 and that the CO absorption is …

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Quantum Criticality Due To Incipient Phase Separation In The Two-Dimensional Hubbard Model, Ehsan Khatami, K. Mikelsons, D. Galanakis, A. Macridin, J. Moreno, R. Scalettar, M. Jarrell May 2010

Quantum Criticality Due To Incipient Phase Separation In The Two-Dimensional Hubbard Model, Ehsan Khatami, K. Mikelsons, D. Galanakis, A. Macridin, J. Moreno, R. Scalettar, M. Jarrell

Faculty Publications

We investigate the two-dimensional Hubbard model with next-nearest-neighbor hopping, t′, using the dynamical cluster approximation. We confirm the existence of a first-order phase-separation transition terminating at a second-order critical point at filling nc(t′) and temperature Tps(t′). We find that as t′ approaches zero, Tps(t′) vanishes and nc(t′) approaches the filling associated with the quantum critical point separating the Fermi liquid from the pseudogap phase. We propose that the quantum critical point under the superconducting dome is the zero-temperature limit of the line of second-order critical points.

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Satellite Motion In A Non-Singular Gravitational Potential, Ioannis Haranas, Spiros Pagiatakis May 2010

Satellite Motion In A Non-Singular Gravitational Potential, Ioannis Haranas, Spiros Pagiatakis

Physics and Computer Science Faculty Publications

We study the effects of a non-singular gravitational potential on satellite orbits by deriving the corresponding time rates of change of its orbital elements. This is achieved by expanding the non-singular potential into power series up to second order. This series contains three terms, the first been the Newtonian potential and the other two, here R1 (first order term) and R2 (second order term), express deviations of the singular potential from the Newtonian. These deviations from the Newtonian potential are taken as disturbing potential terms in the Lagrange planetary equations that provide the time rates of change of …

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Cluster Solver For Dynamical Mean-Field Theory With Linear Scaling In Inverse Temperature, Ehsan Khatami, C. Lee, Z. Bai, R. Scalettar, M. Jarrell May 2010

Cluster Solver For Dynamical Mean-Field Theory With Linear Scaling In Inverse Temperature, Ehsan Khatami, C. Lee, Z. Bai, R. Scalettar, M. Jarrell

Faculty Publications

Dynamical mean-field theory and its cluster extensions provide a very useful approach for examining phase transitions in model Hamiltonians and, in combination with electronic structure theory, constitute powerful methods to treat strongly correlated materials. The key advantage to the technique is that, unlike competing real-space methods, the sign problem is well controlled in the Hirsch-Fye (HF) quantum Monte Carlo used as an exact cluster solver. However, an important computational bottleneck remains; the HF method scales as the cube of the inverse temperature, β. This often makes simulations at low temperatures extremely challenging. We present here a method based on determinant …

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Section Abstracts: Astronomy, Mathematics, And Physics & Materials Science Apr 2010

Section Abstracts: Astronomy, Mathematics, And Physics & Materials Science

Virginia Journal of Science

Abstracts of papers of the Astronomy, Mathematics, and Physics (Including Materials Science) Section for the 88th Annual Meeting of the Virginia Academy of Science, May 20-21, 2010, James Madison University, Harrisonburg, VA.

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Structure-Property Maps And Optimal Inversion In Configurational Thermodynamics, Gus L. W. Hart, Björn Arnold, Alejandro Díaz Ortiz, Helmut Dosch Mar 2010

Structure-Property Maps And Optimal Inversion In Configurational Thermodynamics, Gus L. W. Hart, Björn Arnold, Alejandro Díaz Ortiz, Helmut Dosch

Faculty Publications

Cluster expansions of first-principles density-functional databases in multicomponent systems are now used as a routine tool for the prediction of zero- and finite-temperature physical properties. The ability of producing large databases of various degrees of accuracy, i.e., high-throughput calculations, makes pertinent the analysis of error propagation during the inversion process. This is a very demanding task as both data and numerical noise have to be treated on equal footing. We have addressed this problem by using an analysis that combines the variational and evolutionary approaches to cluster expansions. Simulated databases were constructed ex professo to sample the configurational space in …

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Characterization Of Optical Constants For Uranium From 10 To 47 Nm, Nicole Brimhall, Nicholas Herrick, David D. Allred, R. Steven Turley, Michael Ware, Justin Peatross Mar 2010

Characterization Of Optical Constants For Uranium From 10 To 47 Nm, Nicole Brimhall, Nicholas Herrick, David D. Allred, R. Steven Turley, Michael Ware, Justin Peatross

Faculty Publications

We use a laser high-harmonics-based extreme-ultraviolet (EUV) polarimeter to determine the optical constants of elemental uranium in the wavelength range from 10 to 47 nm. The constants are extracted from the measure ratio of p-polarized to s-polarized reflectance from a thin uranium film deposited in situ. The film thickness is inferred from a spectroscopic ellipsometry measurement of the sample after complete oxidation in room air. Uranium has been used as a high-reflectance material in the EUV. However, difficulties with oxidation prevented its careful characterization previous to this study. We find that measured optical constants for uranium vary significantly from previous …

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Central Compact Objects, Trevor Meek Mar 2010

Central Compact Objects, Trevor Meek

Physics

Central compact objects (CCOs) are point-like sources found near the center of supernova remnants (SNRs). They emit X-rays, but show no radio or gamma ray counterpart. Typical CCO candidates have emission radii on the order of 0.2-3.0 km. This is much smaller than the typical radius of a neutron star, making CCOs a difficult astronomical phenomenon to identify.

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High-Energy Amplitudes In N= 4 Sym In The Next-To-Leading Order, Ian Balitsky, Giovanni A. Chirilli Mar 2010

High-Energy Amplitudes In N= 4 Sym In The Next-To-Leading Order, Ian Balitsky, Giovanni A. Chirilli

Physics Faculty Publications

The high-energy behavior of the N = 4 SYM amplitudes in the Regge limit can be calculated order by order in perturbation theory using the high-energy operator expansion in Wilson lines. At large Nc , a typical four-point amplitude is determined by a single BFKL pomeron. The conformal structure of the four-point amplitude is fixed in terms of two functions: pomeron intercept and the coefficient function in front of the pomeron (the product of two residues). The pomeron intercept is universal while the coefficient function depends on the correlator in question. The intercept is known in the first two orders …

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High-Excitation Emission Lines Near Eta Carinae, And Its Likely Companion Star, Andrea Mehner, Kris Davidson, Gary J. Ferland, Roberta M. Humphreys Feb 2010

High-Excitation Emission Lines Near Eta Carinae, And Its Likely Companion Star, Andrea Mehner, Kris Davidson, Gary J. Ferland, Roberta M. Humphreys

Physics and Astronomy Faculty Publications

In order to study the distribution of gas and ionizing radiation around η Car and their implications for its likely companion star, we have examined high-excitation emission lines of [Ne III], [Fe III], etc., in spectra obtained with the Hubble Space Telescope/Space Telescope Imaging Spectrograph instrument during 1998-2004. Our principal results, some of them unexpected, are as follows. (1) The high-excitation fluxes varied systematically and non-trivially throughout η Car's 5.5 year spectroscopic cycle. Instead of rising to a plateau after the 1998 ''event,'' they changed continuously with a maximum in mid-cycle. (2) At one significant location a brief, strong …

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An Analytical And Numerical Treatment Of The Carter Constant For Inclined Elliptical Orbits About A Massive Kerr Black Hole, Peter Komorowski, Sree Ram Valluri, Martin Houde Feb 2010

An Analytical And Numerical Treatment Of The Carter Constant For Inclined Elliptical Orbits About A Massive Kerr Black Hole, Peter Komorowski, Sree Ram Valluri, Martin Houde

WORLDiscoveries Research Showcase

In an extreme binary black hole system, an orbit will increase its angle of inclination (i) as it evolves in Kerr spacetime. We focus our attention on the behaviour of the Carter constant (Q) for near-polar orbits. The value of Q for bound orbits is non-negative; and an increase in Q corresponds to an increase in i. For a Schwarzschild black hole, the polar orbit represents the boundary between the prograde and retrograde orbits at which Q is at its maximum value. The introduction of spin (S = |J|/M2) to the massive black hole causes this boundary, or Abutment, to …

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Constraining The Black Hole Mass Spectrum With Gravitational Wave Observations – I. The Error Kernel, Danny C. Jacobs, Joseph E. Plowman, Ronald W. Hellings, Sachiko Tsuruta, Shane L. Larson Feb 2010

Constraining The Black Hole Mass Spectrum With Gravitational Wave Observations – I. The Error Kernel, Danny C. Jacobs, Joseph E. Plowman, Ronald W. Hellings, Sachiko Tsuruta, Shane L. Larson

All Physics Faculty Publications

Many scenarios have been proposed for the origin of the supermassive black holes (SMBHs) that are found in the centres of most galaxies. Many of these formation scenarios predict a high-redshift population of intermediate-mass black holes (IMBHs), with masses M• in the range 102≲M•≲ 105 M⊙. A powerful way to observe these IMBHs is via gravitational waves the black holes emit as they merge. The statistics of the observed black hole population should, in principle, allow us to discriminate between competing astrophysical scenarios for the origin and formation of SMBHs. However, …

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Dynamics Of Strong Radio Sources With Umrt-Ii., Mohammed Awid Al-Amri Feb 2010

Dynamics Of Strong Radio Sources With Umrt-Ii., Mohammed Awid Al-Amri

Student Works (2010-2019)

Radio astronomy is a new field in Southeast Asia. University Malaya Radio Telescope UMRT-II is located on the roof of Block B in the Department of Physics, University of Malaya to detect neutral hydrogen emission line. Doppler shift of 1420.4 MHz for different radio sources were observed to determine their dynamics. By measuring the Doppler shift, the velocity V, of each radio source can be determined. Hence the dynamic of radio source can be deduced. The radio spectrum of Coma Cluster was also analyzed and its dark matter content was estimated. The observation time effort was investigated for Coma Cluster …

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Gamma-Ray Spectroscopy: Meteorite Samples And The Search For 98tc, Kristopher L. Merolla Feb 2010

Gamma-Ray Spectroscopy: Meteorite Samples And The Search For 98tc, Kristopher L. Merolla

Physics

The focus of this project is low-count-level gamma-ray spectroscopy on meteorite samples in search of a particular isotope of Technetium (98Tc), which according to stellar theory, should be present in the universe. The spectral lines for 99Tc have, however, been observed in S-, M-, and N- type stars, which makes finding 98Tc created naturally a possibility, and thus a search can be justified.

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Ordered Magnesium-Lithium Alloys: First-Principles Predictions, Richard H. Taylor, Gus L. W. Hart, Stefano Curtarolo Jan 2010

Ordered Magnesium-Lithium Alloys: First-Principles Predictions, Richard H. Taylor, Gus L. W. Hart, Stefano Curtarolo

Faculty Publications

Magnesium-lithium (Mg-Li) alloys are among the lightest structural materials. Although considerable work has been done on the Mg-Li system, little is known regarding potential ordered phases. A first and rapid analysis of the system with the high-throughput method reveals an unexpected wealth of potentially stable low-temperature phases. Subsequent cluster expansions constructed for bcc and hcp superstructures extend the analysis and verify our high-throughput results. Of particular interest are those structures with greater than 13 at. % lithium, as they exhibit either partial or complete formation as a cubic structure. Order-disorder transition temperatures are predicted by Monte Carlo simulations to be …

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