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Articles 2071 - 2100 of 2944

Full-Text Articles in Astrophysics and Astronomy

Massively Parallel Indirect Dielectrophoresis Controlled Placement Of Carbon Nanotubes, Hiram Jacob Conley Jul 2009

Massively Parallel Indirect Dielectrophoresis Controlled Placement Of Carbon Nanotubes, Hiram Jacob Conley

Theses and Dissertations

Placement of single walled carbon nanotubes is demonstrated through massively parallel indirect dielectrophoresis (MPID). MPID is shown to be able to control the placement of carbon tubes as well as the number of tubes placed. Lumped element analysis for AC circuits is used to model MPID. This model allows for predictions of the number of tubes that will be captured in a trap. This model has been consistent with experimental data of numbers of nanotube placed in a junction. Carbon nanotubes placed with MPID are shown to be electrically active.

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Extreme Ultraviolet Polarimetry With Laser-Generated High-Order Harmonics: Characterization Of Uranium, Nicole Brimhall Jul 2009

Extreme Ultraviolet Polarimetry With Laser-Generated High-Order Harmonics: Characterization Of Uranium, Nicole Brimhall

Theses and Dissertations

We developed an extreme ultraviolet (EUV) polarimeter, which employs laser-generated high-order harmonics as the light source. This relatively high-flux, directional EUV source has available wavelengths between 10 nm and 47 nm with easily rotatable linear polarization. The polarimeter has allowed us to characterize the optical constants of materials that may be useful for EUV optics. The instrument has a versatile positioning system and a spectral resolution of about 180, and we have demonstrated that reflectance as low as 0.1% can be measured repeatably at EUV wavelengths. We investigate the high harmonic source used for polarimetry measurements by documenting the spatial …

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Energy Current Imaging Method For Time Reversal In Elastic Media, Brian E. Anderson, Michele Griffa, Robert A. Guyer, Paul A. Johnson, Carene Larmat, Pierre-Yves Le Bas, Timothy J. Ulrich Jul 2009

Energy Current Imaging Method For Time Reversal In Elastic Media, Brian E. Anderson, Michele Griffa, Robert A. Guyer, Paul A. Johnson, Carene Larmat, Pierre-Yves Le Bas, Timothy J. Ulrich

Faculty Publications

An energy current imaging method is presented for use in locating sources of wave energy during the back propagation stage of the time reversal process. During the back propagation phase of an ideal time reversal experiment, wave energy coalesces from all angles of incidence to recreate the source event; after the recreation, wave energy diverges in every direction. An energy current imaging method based on this convergence/divergence behavior has been developed. The energy current imaging method yields a smaller spatial distribution for source reconstruction than is possible with traditional energy imaging methods.

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Verifying Predictions Of The L13 Crystal Structure In Cd-Pt And Pd-Pt By Exhaustive Enumeration, Gus L. W. Hart Jul 2009

Verifying Predictions Of The L13 Crystal Structure In Cd-Pt And Pd-Pt By Exhaustive Enumeration, Gus L. W. Hart

Faculty Publications

In 2001, S. Müller and A. Zunger [Phys. Rev. Lett. 87, 165502 (2001)] predicted a never-before-observed crystal structure in Ag-Pd. Recently, Curtarolo predicted the same structure to be stable in Pt-Cd and Pt-Pd [S. Curtarolo et. Al., CALPHAD: Comput. Coupling Phase Diagrams Thermochem. 29, 163 (2005)]. The predicted structure is unique in several ways. though never seen in any other face-centered-cubic-based intermetallic binary compound or ordered alloy, it is relatively simple—it contains only four atoms per unit cell. Furthermore, the structure is the only one of this small size, except the L12 structure, that cannot be characterized as a simple …

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Comet C/2004 Q2 (Machholz): Parent Volatiles, A Search For Deuterated Methane, And Constraint On The Ch4 Spin Temperature, Boncho Bonev, Michael Mumma, Erika Gibb, Michael Disanti, Geronimo Villanueva, Karen Magee-Sauer, Richard Ellis Jul 2009

Comet C/2004 Q2 (Machholz): Parent Volatiles, A Search For Deuterated Methane, And Constraint On The Ch4 Spin Temperature, Boncho Bonev, Michael Mumma, Erika Gibb, Michael Disanti, Geronimo Villanueva, Karen Magee-Sauer, Richard Ellis

Physics Faculty Works

High-dispersion (λ/δλ ≈ 25,000) infrared spectra of Comet C/2004 Q2 (Machholz) were acquired on 2004 November 28-29, and 2005 January 19 (UT dates) with the Near InfraRed echelle SPECtrograph (NIRSPEC) at the Keck-2 telescope on Mauna Kea. We detected H2O, CH4, C2H2, C2H6, CO, H2CO, CH3OH, HCN, and NH3 and we conducted a sensitive search for CH3D. We report rotational temperatures, production rates, and mixing ratios (with respect to H2O) at heliocentric distances of 1.49 AU (2004 November) and 1.21 AU (2005 January). We highlight three principal results. (1) The mixing ratios of parent volatiles measured at 1.49 AU and …

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Section Abstracts: Astronomy, Mathematics, And Physics & Materials Science Jul 2009

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

Virginia Journal of Science

Abstracts of the Astronomy, Mathematics and Physics & Materials Science Section for the 87th Annual Meeting of the Virginia Academy of Science, May 27-29, 2009, Virginia Commonwealth University, Richmond VA.

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The Ionization Balance Of A Non-Equilibrium Plasma, Gary J. Ferland Jun 2009

The Ionization Balance Of A Non-Equilibrium Plasma, Gary J. Ferland

Physics and Astronomy Faculty Publications

Commentary on: Arnaud M. and Rothenflug R., 1985, A&AS, 60, 425.

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Search For Gravitational Waves From Low Mass Binary Coalescences In The First Year Of Ligo’S S5 Data, B. P. Abbott, R. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, R. Grosso, K. Hayama, H. Lei, Soumya Mohanty, Soma Mukherjee, Malik Rakhmanov, Joseph D. Romano, Robert Stone Jun 2009

Search For Gravitational Waves From Low Mass Binary Coalescences In The First Year Of Ligo’S S5 Data, B. P. Abbott, R. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, R. Grosso, K. Hayama, H. Lei, Soumya Mohanty, Soma Mukherjee, Malik Rakhmanov, Joseph D. Romano, Robert Stone

Physics & Astronomy Faculty Publications

We have searched for gravitational waves from coalescing low mass compact binary systems with a total mass between 2M⊙ and 35M⊙ and a minimum component mass of 1M⊙ using data from the first year of the fifth science run of the three LIGO detectors, operating at design sensitivity. Depending on the mass, we are sensitive to coalescences as far as 150 Mpc from the Earth. No gravitational-wave signals were observed above the expected background. Assuming a population of compact binary objects with a Gaussian mass distribution representing binary neutron star systems, black hole–neutron star binary systems, and binary black hole …

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Development Of An Adaptive Equalization Algorithm Using Acoustic Energy Density, Panu Tapani Puikkonen Apr 2009

Development Of An Adaptive Equalization Algorithm Using Acoustic Energy Density, Panu Tapani Puikkonen

Theses and Dissertations

Sound pressure equalization of audio signals using digital signal processors has been a subject of ongoing study for many years. The traditional approach is to equalize sound at a point in a listening environment, but because of its specific dependence on the room frequency response between a source and receiver position, this equalization generally causes the spectral response to worsen significantly at other locations in the room. This work presents both a time-invariant and a time-varying implementation of an adaptive acoustic energy density equalization filter for a one-dimensional sound field. Energy density equalization addresses the aforementioned challenge and others that …

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Spectroscopic Measurements Of Temperature And Plasma Impurity Concentration During Magnetic Reconnection At The Swarthmore Spheromak Experiment, Vernon Hampden Chaplin , '07, Michael R. Brown, David H. Cohen, T. Gray, C. D. Cothran Apr 2009

Spectroscopic Measurements Of Temperature And Plasma Impurity Concentration During Magnetic Reconnection At The Swarthmore Spheromak Experiment, Vernon Hampden Chaplin , '07, Michael R. Brown, David H. Cohen, T. Gray, C. D. Cothran

Physics & Astronomy Faculty Works

Electron temperature measurements during counterhelicity spheromak merging studies at the Swarthmore Spheromak Experiment (SSX) [M. R. Brown, Phys. Plasmas 6, 1717 (1999)] are presented. VUV monochromator measurements of impurity emission lines are compared with model spectra produced by the non-LTE excitation kinematics code PRISMSPECT [J. J. MacFarlane et al., in Proceedings of the Third Conference on Inertial Fusion Science and Applications (2004)] to yield the electron temperature in the plasma with 1 mu s time resolution. Average T(e) is seen to increase from 12 to 19 eV during spheromak merging. Average C III ion temperature, measured with a new ion …

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Impact Of Spherical Probe Scattering On Estimation Of Acoustic Vector Quantities. (A), Curtis P. Wiederhold, Kent L. Gee, Derek C. Thomas, Scott D. Sommerfeldt, Jonathan D. Blotter Apr 2009

Impact Of Spherical Probe Scattering On Estimation Of Acoustic Vector Quantities. (A), Curtis P. Wiederhold, Kent L. Gee, Derek C. Thomas, Scott D. Sommerfeldt, Jonathan D. Blotter

Faculty Publications

Multimicrophone probes are often used to measure energy-based acoustical quantities. In some cases, these probes consist of microphones mounted on the surface of a sphere, which, due to the high level of symmetry, permits scattering effects to be better characterized. Scattering of a plane wave incident on a rigid sphere has been modeled to observe how particle velocity and intensity calculations are affected by the presence of the sphere. These effects have been investigated for the traditional "finite-difference" method and a recently developed "wave vector" estimation method. In the computer model, 3-D surface plots were made showing the calculated error …

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Detecting A Stochastic Gravitational-Wave Background: The Overlap Reduction Function, Lee Samuel Finn, Shane L. Larson, Joseph D. Romano Mar 2009

Detecting A Stochastic Gravitational-Wave Background: The Overlap Reduction Function, Lee Samuel Finn, Shane L. Larson, Joseph D. Romano

Physics & Astronomy Faculty Publications

Detection of a gravitational-wave stochastic background via ground or space-based gravitational-wave detectors requires the cross correlation of the response of two or more independent detectors. The cross correlation involves a frequency-dependent factor—the so-called overlap reduction function or HellingsDowns curve—that depends on the relative geometry of each detector pair, i.e., the detector separations and the relative orientation of their antenna patterns (beams). An incorrect formulation of this geometrical factor has appeared in the literature, leading to incorrect conclusions regarding the sensitivity of proposed detectors to a stochastic gravitational-wave background. To rectify these errors and as a reference for future work we …

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Extreme Physics Where Small And Big Things Meet, Young-Kee Kim Mar 2009

Extreme Physics Where Small And Big Things Meet, Young-Kee Kim

IMSA Great Minds Program ®

The profound discovery of Einstein a century ago, that particles can both be made from energy and disappear back into energy, inspires the experiments that provide our knowledge of the smallest building blocks of matter and the interactions between them. Experiments, done at enormous accelerators, have led to a consistent theory of the origins of our world up to a certain point. However, at an energy scale not far above what we can attain at existing accelerators, this picture is predicted to break down. Moreover, the theory of the very small is intimately connected to cosmology -- the ultimate cause …

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Resonant Microwave Cavity For 8.5-12 Ghz Optically Detected Electron Spin Resonance With Simultaneous Nuclear Magnetic Resonance, John S. Colton, L. R. Wienkes Mar 2009

Resonant Microwave Cavity For 8.5-12 Ghz Optically Detected Electron Spin Resonance With Simultaneous Nuclear Magnetic Resonance, John S. Colton, L. R. Wienkes

Faculty Publications

We present a newly developed microwave resonant cavity for use in optically detected magnetic resonance (ODMR) experiments. The cylindrical quasi-TE 011 mode cavity is designed to fit in a 1 in. magnet bore to allow the sample to be optically accessed and to have an adjustable resonant frequency between 8.5 and 12 GHz. The cavity uses cylinders of high dielectric material, so-called "dielectric resonators," in a double-stacked configuration to determine the resonant frequency. Wires in a pseudo-Helmholtz configuration are incorporated into the cavity to provide frequencies for simultaneous nuclear magnetic resonance (NMR). The system was tested by measuring cavity absorption …

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Blue-Shifted Emission In Cdte/Znse Heterostructured Nanocrystals, Nishshanka N. Hewa-Kasakarage, Nilanka P. Gurusinghe, Mikhail Zamkov Mar 2009

Blue-Shifted Emission In Cdte/Znse Heterostructured Nanocrystals, Nishshanka N. Hewa-Kasakarage, Nilanka P. Gurusinghe, Mikhail Zamkov

Physics and Astronomy Faculty Publications

Properties of colloidal heterostructured nanocrystals are largely determined by the spatial distribution of photogenerated carriers across the junction of semiconductor materials that form the heterostructure. The two known types of carrier distributions are identified based on whether both carriers reside within the same (type I) or opposite (type II) sides of the heterojunction. Here we demonstrate the existence of another type of spatial carrier distribution in heteronanocrystals, which corresponds to the localization of both charges along the material junction. Such localization. pattern was realized in novel CdTe/ZnSe heteronanocrystals, where the expected type I infrared emission was dominated by more intense …

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Orion's Bar: Physical Conditions Across The Definitive H+/H0/H2 Interface, E. W. Pellegrini, J. A. Baldwin, Gary J. Ferland, G. Shaw, S. Heathcote Mar 2009

Orion's Bar: Physical Conditions Across The Definitive H+/H0/H2 Interface, E. W. Pellegrini, J. A. Baldwin, Gary J. Ferland, G. Shaw, S. Heathcote

Physics and Astronomy Faculty Publications

Previous work has shown the Orion Bar to be an interface between ionized and molecular gas, viewed roughly edge-on, which is excited by the light from the Trapezium cluster. Much of the emission from any star-forming region will originate from such interfaces, so the Bar serves as a foundation test of any emission model. Here we combine X-ray, optical, infrared (IR), and radio data sets to derive emission spectra along the transition from H+ to H0 to H2 regions. We then reproduce the spectra of these layers with a simulation that simultaneously accounts for the detailed microphysics …

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All-Sky Ligo Search For Periodic Gravitational Waves In The Early Fifth-Science-Run Data, B. P. Abbott, R. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, R. Grosso, K. Hayama, Soumya Mohanty, Soma Mukherjee, Malik Rakhmanov, Joseph D. Romano Mar 2009

All-Sky Ligo Search For Periodic Gravitational Waves In The Early Fifth-Science-Run Data, B. P. Abbott, R. Abbott, Matthew Benacquista, Teviet Creighton, Mario C. Diaz, R. Grosso, K. Hayama, Soumya Mohanty, Soma Mukherjee, Malik Rakhmanov, Joseph D. Romano

Physics & Astronomy Faculty Publications

We report on an all-sky search with the LIGO detectors for periodic gravitational waves in the frequency range 50–1100 Hz and with the frequency’s time derivative in the range −5×10−9–0  Hz s−1. Data from the first eight months of the fifth LIGO science run (S5) have been used in this search, which is based on a semicoherent method (PowerFlux) of summing strain power. Observing no evidence of periodic gravitational radiation, we report 95% confidence-level upper limits on radiation emitted by any unknown isolated rotating neutron stars within the search range. Strain limits below 10−24 are obtained over a 200-Hz band, …

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Fluorescent Excitation Of Balmer Lines In Gaseous Nebulae: Case D, V. Luridiana, S. Simón-Díaz, M. Cerviño, R. M. González Delgado, R. L. Porter, Gary J. Ferland Feb 2009

Fluorescent Excitation Of Balmer Lines In Gaseous Nebulae: Case D, V. Luridiana, S. Simón-Díaz, M. Cerviño, R. M. González Delgado, R. L. Porter, Gary J. Ferland

Physics and Astronomy Faculty Publications

Nonionizing stellar continua are a potential source of photons for continuum pumping in the hydrogen Lyman transitions. In the environments where these transitions are optically thick, de-excitation occurs through higher series lines. As a result, the emitted flux in the affected lines has a fluorescent contribution in addition to the usual recombination one; in particular, Balmer emissivities are systematically enhanced above case B predictions. The effectiveness of such a mechanism in H II regions and the adequacy of photoionization models as a tool to study it are the two main focuses of this work. We find that photoionization models of …

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An Intensive Hst Survey For Z>1 Supernovae By Targeting Galaxy Clusters, K S. Dawson, G Aldering, R Amanullah, K Barbary, L F. Barrientos, M Brodwin, N Connolly, A Dey, M Doi, M Donahue, P Eisenhardt, E Ellingson, L Faccioli, V Fadeyev, H K. Fakhouri, A S. Fruchter, D G. Gilbank, M D. Gladders, G Goldhaber, A H. Gonzalez, A Goobar, A Gude, T Hattori, H Hoekstra, Xiaosheng Huang, Y Ihara, B T. Jannuzi, D Johnston, K Kashikawa, B Koester, K Konishi, M Kowalski, C Lidman, E V. Linder, L Lubin, J Meyers, T Morokuma, F Munshi, C Mullis, T Oda, N Panagia, S Perlmutter, M Postman, T Pritchard, J Rhodes, P Rosati, D Rubin, D J. Schlegel, A Spadafora, S A. Stanford, V Stanishev, D Stern, M Strovink, N Suzuki, N Takanashi, K Tokita, M Wagner, L Wang, N Yasuda, H. K. C. Yee, Supernova Cosmology Project Jan 2009

An Intensive Hst Survey For Z>1 Supernovae By Targeting Galaxy Clusters, K S. Dawson, G Aldering, R Amanullah, K Barbary, L F. Barrientos, M Brodwin, N Connolly, A Dey, M Doi, M Donahue, P Eisenhardt, E Ellingson, L Faccioli, V Fadeyev, H K. Fakhouri, A S. Fruchter, D G. Gilbank, M D. Gladders, G Goldhaber, A H. Gonzalez, A Goobar, A Gude, T Hattori, H Hoekstra, Xiaosheng Huang, Y Ihara, B T. Jannuzi, D Johnston, K Kashikawa, B Koester, K Konishi, M Kowalski, C Lidman, E V. Linder, L Lubin, J Meyers, T Morokuma, F Munshi, C Mullis, T Oda, N Panagia, S Perlmutter, M Postman, T Pritchard, J Rhodes, P Rosati, D Rubin, D J. Schlegel, A Spadafora, S A. Stanford, V Stanishev, D Stern, M Strovink, N Suzuki, N Takanashi, K Tokita, M Wagner, L Wang, N Yasuda, H. K. C. Yee, Supernova Cosmology Project

Physics and Astronomy

We present a new survey strategy to discover and study high redshift Type Ia supernovae (SNe Ia) using the Hubble Space Telescope (HST). By targeting massive galaxy clusters at 0.9<zHST field survey and a factor of three improvement in the total yield of SN detections in relatively dust-free red-sequence galaxies. In total, sixteen SNe were discovered at z>0.95, nine of which were in galaxy clusters. This strategy provides a SN sample that can be used to decouple the effects of host galaxy extinction and intrinsic color in high redshift SNe, thereby reducing one of the …

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Hubble Space Telescope Discovery Of A Z = 3.9 Multiply Imaged Galaxy Behind The Complex Cluster Lens Warps J1415.1+36 At Z = 1.026, Xiaosheng Huang, T Morokuma, Hk Fakhouri, G Aldering, R Amanullah, K Barbary, M Brodwin, Nv Connolly, Ks Dawson, M Doi, L Faccioli, V Fadeyev, As Fruchter, G Goldhaber, Md Gladders, Jf Hennawi, Y Ihara, Mj Jee, M Kowalski, K Konishi, C Lidman, J Meyers, La Moustakas, S Perlmutter, D Rubin, Dj Schlegel, Al Spadafora, N Suzuki, N Takanashi, N Yasuda Jan 2009

Hubble Space Telescope Discovery Of A Z = 3.9 Multiply Imaged Galaxy Behind The Complex Cluster Lens Warps J1415.1+36 At Z = 1.026, Xiaosheng Huang, T Morokuma, Hk Fakhouri, G Aldering, R Amanullah, K Barbary, M Brodwin, Nv Connolly, Ks Dawson, M Doi, L Faccioli, V Fadeyev, As Fruchter, G Goldhaber, Md Gladders, Jf Hennawi, Y Ihara, Mj Jee, M Kowalski, K Konishi, C Lidman, J Meyers, La Moustakas, S Perlmutter, D Rubin, Dj Schlegel, Al Spadafora, N Suzuki, N Takanashi, N Yasuda

Physics and Astronomy

We report the discovery of a multiply lensed Ly Alpha (Lya) emitter at z = 3.90 behind the massive galaxy cluster WARPS J1415.1+3612 at z = 1.026. Images taken by the Hubble Space Telescope(HST) using ACS reveal a complex lensing system that produces a prominent, highly magnified arc and a triplet of smaller arcs grouped tightly around a spectroscopically confirmed cluster member. Spectroscopic observations using FOCAS on Subaru confirm strong Lya emission in the source galaxy and provide redshifts for more than 21 cluster members, from which we obtain a velocity dispersion of 807+/-185 km/s. Assuming a singular isothermal sphere …

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Discovery Of An Unusual Optical Transient With The Hubble Space Telescope, K Barbary, Ks Dawson, K Tokita, G Aldering, R Amanullah, Nv Connolly, M Doi, L Faccioli, V Fadeyev, As Fruchter, G Goldhaber, A Goobar, A Gude, Xiaosheng Xiaosheng Huang, Y Ihara, K Konishi, M Kowalski, C Lidman, J Meyers, T Morokuma, P Nugent, S Perlmutter, D Rubin, D Schlegel, Al Spadafora, N Suzuki, Hk Swift, N Takanashi, Rc Thomas, N Yasuda, Supernova Cosmology Project Jan 2009

Discovery Of An Unusual Optical Transient With The Hubble Space Telescope, K Barbary, Ks Dawson, K Tokita, G Aldering, R Amanullah, Nv Connolly, M Doi, L Faccioli, V Fadeyev, As Fruchter, G Goldhaber, A Goobar, A Gude, Xiaosheng Xiaosheng Huang, Y Ihara, K Konishi, M Kowalski, C Lidman, J Meyers, T Morokuma, P Nugent, S Perlmutter, D Rubin, D Schlegel, Al Spadafora, N Suzuki, Hk Swift, N Takanashi, Rc Thomas, N Yasuda, Supernova Cosmology Project

Physics and Astronomy

We present observations of SCP 06F6, an unusual optical transient discovered during the Hubble Space Telescope Cluster Supernova Survey. The transient brightened over a period of ~;;100 days, reached a peak magnitude of ~;;21.0 in both i_775 and z_850, and then declined over a similar timescale. There is no host galaxy or progenitor star detected at the location of the transient to a 3 sigma upper limit of i_775 = 26.4 and z_850 = 26.1, giving a corresponding lower limit on the flux increase of a factor of ~;;120. Multiple spectra show five broad absorption bands between 4100 AA and …

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3d Reconnection And Flow Dynamics In The Ssx Experiment, Michael R. Brown, C. D. Cothran, David H. Cohen, Jason Alexander Horwitz , '07, Vernon Hampden Chaplin , '07 Jan 2009

3d Reconnection And Flow Dynamics In The Ssx Experiment, Michael R. Brown, C. D. Cothran, David H. Cohen, Jason Alexander Horwitz , '07, Vernon Hampden Chaplin , '07

Physics & Astronomy Faculty Works

Several new experimental results are reported from plasma merging studies at the Swarthmore Spheromak Experiment (SSX) with relevance to collisionless three-dimensional magnetic reconnection in laboratory and space plasmas. First, recent high-resolution velocity measurements of impurity ions using ion Doppler spectroscopy (IDS) show bi-directional outflow jets at 40 km/s (nearly the Alfven speed). The SSX IDS instrument measures with 1 mu s or better time resolution the width and Doppler shift of the C-III impurity (H plasma) 229.7 nm line to determine the temperature and line-averaged flow velocity during spheromak merging events. High flow speeds are corroborated using an in situ …

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Detecting A Stochastic Gravitational-Wave Background: The Overlap Reduction Function, Lee Samuel Finn, Shane L. Larson, Joseph D. Romano Jan 2009

Detecting A Stochastic Gravitational-Wave Background: The Overlap Reduction Function, Lee Samuel Finn, Shane L. Larson, Joseph D. Romano

All Physics Faculty Publications

Detection of a gravitational-wave stochastic background via ground or space-based gravitational-wave detectors requires the cross correlation of the response of two or more independent detectors. The cross correlation involves a frequency-dependent factor—the so-called overlap reduction function or Hellings-Downs curve—that depends on the relative geometry of each detector pair, i.e., the detector separations and the relative orientation of their antenna patterns (beams). An incorrect formulation of this geometrical factor has appeared in the literature, leading to incorrect conclusions regarding the sensitivity of proposed detectors to a stochastic gravitational-wave background. To rectify these errors and as a reference for future work we …

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Uncertainties In Theoretical Hei Emissivities: Hii Regions, Primordial Abundance And Cosmological Recombination, R. L. Porter, Gary J. Ferland, Keith B. Macadam, P. J. Storey Jan 2009

Uncertainties In Theoretical Hei Emissivities: Hii Regions, Primordial Abundance And Cosmological Recombination, R. L. Porter, Gary J. Ferland, Keith B. Macadam, P. J. Storey

Physics and Astronomy Faculty Publications

A number of recent works in astronomy and cosmology have relied upon theoretical He I emissivities, but we know of no effort to quantify the uncertainties in the atomic data. We analyse and assign uncertainties to all relevant atomic data, perform Monte Carlo analyses, and report standard deviations in the line emissivities. We consider two sets of errors, which we call ‘optimistic’ and ‘pessimistic’. We also consider three different conditions, corresponding to prototypical Galactic and extragalactic H IIregions and the epoch of cosmological recombination. In the extragalactic H II case, the errors we obtain are comparable to or larger than …

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Electron-Impact Excitation Of O Ii Fine-Structure Levels, R. Kisielius, P. J. Storey, Gary J. Ferland, F. P. Keenan Jan 2009

Electron-Impact Excitation Of O Ii Fine-Structure Levels, R. Kisielius, P. J. Storey, Gary J. Ferland, F. P. Keenan

Physics and Astronomy Faculty Publications

Effective collision strengths for forbidden transitions among the five energetically lowest fine-structure levels of O II are calculated in the Breit–Pauli approximation using the R-matrix method. Results are presented for the electron temperature range 100–100 000 K. The accuracy of the calculations is evaluated via the use of different types of radial orbital sets and a different configuration expansion basis for the target wavefunctions. A detailed assessment of previous available data is given, and erroneous results are highlighted. Our results reconfirm the validity of the original Seaton and Osterbrock scaling for the optical O II ratio, a matter of some …

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The Three-Dimensional Dynamic Structure Of The Inner Orion Nebula, C. R. O'Dell, W. J. Henney, N. P. Abel, Gary J. Ferland, S. J. Arthur Jan 2009

The Three-Dimensional Dynamic Structure Of The Inner Orion Nebula, C. R. O'Dell, W. J. Henney, N. P. Abel, Gary J. Ferland, S. J. Arthur

Physics and Astronomy Faculty Publications

The three-dimensional structure of the brightest part of the Orion Nebula is assessed in the light of published and newly established data. We find that the widely accepted model of a concave blister of ionized material needs to be altered in the southwest direction from the Trapezium, where we find that the Orion-S feature is a separate cloud of very optically thick molecules within the body of ionized gas, which is probably the location of the multiple embedded sources that produce the optical and molecular outflows that define the Orion-S star formation region. Evidence for this cloud comes from the …

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Collisional Heating As The Origin Of Filament Emission In Galaxy Clusters, G. J. Ferland, A. C. Fabian, N. A. Hatch, R. M. Johnstone, R. L. Porter, P. A. M. Vanhoof, R. J. R. Williams Jan 2009

Collisional Heating As The Origin Of Filament Emission In Galaxy Clusters, G. J. Ferland, A. C. Fabian, N. A. Hatch, R. M. Johnstone, R. L. Porter, P. A. M. Vanhoof, R. J. R. Williams

Physics and Astronomy Faculty Publications

It has long been known that photoionization, whether by starlight or other sources, has difficulty in accounting for the observed spectra of the optical filaments that often surround central galaxies in large clusters. This paper builds on the first of this series in which we examined whether heating by energetic particles or dissipative magnetohydrodynamic (MHD) wave can account for the observations. The first paper focused on the molecular regions which produce strong H2 and CO lines. Here we extend the calculations to include atomic and low-ionization regions. Two major improvements to the previous calculations have been made. The model …

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Properties Of Warm Absorbers In Active Galaxies: A Systematic Stability Curve Analysis, Susmita Chakravorty, Ajit K. Kembhavi, Martin Elvis, Gary J. Ferland Jan 2009

Properties Of Warm Absorbers In Active Galaxies: A Systematic Stability Curve Analysis, Susmita Chakravorty, Ajit K. Kembhavi, Martin Elvis, Gary J. Ferland

Physics and Astronomy Faculty Publications

Signatures of warm absorbers are seen in soft X-ray spectra of about half of all type 1 Seyfert galaxies observed and in some quasars and blazars. We use the thermal equilibrium curve to study the influence of the shape of the ionizing continuum, density and the chemical composition of the absorbing gas on the existence and nature of the warm absorbers. We describe circumstances in which a stable warm absorber can exist as a multiphase medium or one with continuous variation in pressure. In particular, we find the following results: (i) the warm absorber exists only if the spectral index …

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The Location And Kinematics Of The Coronal-Line Emitting Regions In Active Galactic Nuclei, J. R. Mullaney, M. J. Ward, C. Done, Gary J. Ferland, N. Schurch Jan 2009

The Location And Kinematics Of The Coronal-Line Emitting Regions In Active Galactic Nuclei, J. R. Mullaney, M. J. Ward, C. Done, Gary J. Ferland, N. Schurch

Physics and Astronomy Faculty Publications

We use the photoionization code CLOUDY to determine both the location and the kinematics of the optical forbidden, high-ionization line (hereafter, FHIL) emitting gas in the narrow line Seyfert 1 galaxy Ark 564. The results of our models are compared with the observed properties of these emission lines to produce a physical model that is used to explain both the kinematics and the source of this gas. The main features of this model are that the FHIL emitting gas is launched from the putative dusty torus and is quickly accelerated to its terminal velocity of a few hundred km s …

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Faculty Should Consider Peer Review As A Means Of Improving Students' Scientific Reasoning Skills, Briana Timmerman, Denise Strickland Jan 2009

Faculty Should Consider Peer Review As A Means Of Improving Students' Scientific Reasoning Skills, Briana Timmerman, Denise Strickland

Journal of the South Carolina Academy of Science

No abstract provided.

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