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2008

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Articles 1 - 30 of 801

Full-Text Articles in Physics

Is The Pamela Positron Excess Winos?, Scott Watson, Phill Grajek, Gordon L. Kane, Daniel J. Phalen, Aaron Pierce Dec 2008

Is The Pamela Positron Excess Winos?, Scott Watson, Phill Grajek, Gordon L. Kane, Daniel J. Phalen, Aaron Pierce

Physics - All Scholarship

Recently the PAMELA satellite-based experiment reported an excess of galactic positrons that could be a signal of annihilating dark matter. The PAMELA data may admit an interpretation as a signal from a wino-like LSP of mass about 200 GeV, normalized to the local relic density, and annihilating mainly into W-bosons. This possibility requires the current conventional estimate for the energy loss rate of positrons be too large by roughly a factor of five. Data from anti-protons and gamma rays also provide tension with this interpretation, but there are significant astrophysical uncertainties associated with their propagation. It is not unreasonable to …

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Self-Consistent Calculations Of Strain-Induced Band Gap Changes In Semiconducting (N, 0) Carbon Nanotubes, Pavan Kumar Valavala, Douglas R. Banyai, Max Seel, Ranjit Pati Dec 2008

Self-Consistent Calculations Of Strain-Induced Band Gap Changes In Semiconducting (N, 0) Carbon Nanotubes, Pavan Kumar Valavala, Douglas R. Banyai, Max Seel, Ranjit Pati

Department of Physics Publications

First-principles density-functional calculations of the electronic structure, energy band gaps (Eg), and strain-induced band gap changes in moderate-gap single-walled (n,0) carbon nanotubes (SWNTs) are presented. It is confirmed that (n,0) SWNTs fall into two classes depending upon n mod 3=1 or 2. Eg is always lower for “mod 1” than for “mod 2” SWNTs of similar diameter. For n<10, strong curvature effects dominate Eg; from n=10 to 17, the Eg oscillations, amplified due to σ−π mixing, decrease and can be explained very well with a tight-binding model which includes trigonal warping. Under strain, the two families of semiconducting …

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Drizzle Rates Versus Cloud Depths For Marine Stratocumuli, A. B. Kostinski Dec 2008

Drizzle Rates Versus Cloud Depths For Marine Stratocumuli, A. B. Kostinski

Department of Physics Publications

Marine stratocumuli make a major contribution to Earth’s radiation budget. Drizzle in such clouds can greatly affect their albedo, lifetime and fractional coverage, so drizzle rate prediction is important. Here we examine a question: does a drizzle rate (R) depend on cloud depth (H) and/or drop number concentration n in a simple way? This question was raised empirically in several recent publications and an approximate H3/n dependence was observed. Here we suggest a simple explanation for H3 scaling from viewing the drizzle rate as a sedimenting volume fraction ( f ) of water drops (radius r) in air, i.e. R …

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Constructing Diabatic States From Adiabatic States: Extending Generalized Mulliken–Hush To Multiple Charge Centers With Boys Localization, Joseph E. Subotnik, Robert J. Cave, Sina Yeganeh, Mark A. Ratner Dec 2008

Constructing Diabatic States From Adiabatic States: Extending Generalized Mulliken–Hush To Multiple Charge Centers With Boys Localization, Joseph E. Subotnik, Robert J. Cave, Sina Yeganeh, Mark A. Ratner

All HMC Faculty Publications and Research

This article shows that, although Boys localization is usually applied to single-electron orbitals, the Boys method itself can be applied to many electron molecular states. For the two-state charge-transfer problem, we show analytically that Boys localization yields the same charge-localized diabatic states as those found by generalized Mulliken–Hush theory. We suggest that for future work in electron transfer, where systems have more than two charge centers, one may benefit by using a variant of Boys localization to construct diabatic potential energy surfaces and extract electronic coupling matrix elements. We discuss two chemical examples of Boys localization and propose a generalization …

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Search For The Standard Model Higgs Boson In The Missing Energy And Acoplanar B-Jet Topology At √S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration Dec 2008

Search For The Standard Model Higgs Boson In The Missing Energy And Acoplanar B-Jet Topology At √S = 1.96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Kenneth Bloom Publications

We report a search for the standard model Higgs boson in the missing energy and acoplanar b-jet topology, using an integrated luminosity of 0.93 fb-1 recorded by the D0 detector at the Fermilab Tevatron pp Collider. The analysis includes signal contributions from pp → ZH → ννbb, as well as from WH production in which the charged lepton from the W boson decay is undetected. Neural networks are used to separate signal from background. In the absence of a signal, we set limits on σ (pp → VH) x B(H → bb) at the 95% …

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Measurement Of BS0 Mixing Parameters From The Flavor-Tagged Decay BS0 → J/Ψφ, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration Dec 2008

Measurement Of BS0 Mixing Parameters From The Flavor-Tagged Decay BS0 → J/Ψφ, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration

Kenneth Bloom Publications

From an analysis of the flavor-tagged decay Bs0 → J/ ψφ we obtain the width difference between the Bs0 light and heavy mass eigenstates, ΔΓs = 0.19 ± 0.07 (stat)-0.01+0.02 (syst) ps-1, and the CP-violating phase, φs = -0.57-0.30+0.24(stat)-0.02+0.08(syst). The allowed 90% CL intervals of ΔΓs and φs are 0.06 < ΔΓs < 0.30 ps-1 and -1.20< φs < 0.06, respectively. The data sample corresponds to an integrated luminosity of 2.8 fb-1 accumulated with the D0 detector at the Fermilab Tevatron collider.

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Search For Third Generation Scalar Leptoquarks Decaying Into ΤB, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration Dec 2008

Search For Third Generation Scalar Leptoquarks Decaying Into ΤB, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration

Kenneth Bloom Publications

We have searched for third generation leptoquarks (LQ3) using 1.05 fb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider operating at √s = 1.96 TeV. We set a 95% C.L. lower limit of 210 GeV on the mass of a scalar LQ3 state decaying solely to a b quark and a τ lepton.

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Formation Of Even-Numbered Hydrogen Cluster Cations In Ultracold Helium Droplets, S. Jaksch, A. Mauracher, A. Bacher, S. Denifl, F. Ferreira De Silva, H. Schoebel, Olof E. Echt, T. D. Maerk, M. Probst, D. K. Bohme, P. Scheier Dec 2008

Formation Of Even-Numbered Hydrogen Cluster Cations In Ultracold Helium Droplets, S. Jaksch, A. Mauracher, A. Bacher, S. Denifl, F. Ferreira De Silva, H. Schoebel, Olof E. Echt, T. D. Maerk, M. Probst, D. K. Bohme, P. Scheier

Physics & Astronomy

Neutral hydrogen clusters are grown in ultracold helium nanodroplets by successive pickup of hydrogen molecules. Even-numbered hydrogen cluster cations are observed upon electron-impact ionization with and without attached helium atoms and in addition to the familiar odd-numbered H(n)(+). The helium matrix affects the fragmentation dynamics that usually lead to the formation of overwhelmingly odd-numbered H(n)(+). The use of high-resolution mass spectrometry allows the unambiguous identification of even-numbered H(n)(+) up to n congruent to 120 by their mass excess that distinguishes them from He(n)(+), mixed He(m)H(n)(+), and background ions. The large range in size of these hydrogen cluster ions is unprecedented, …

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Rotational Quenching Rate Coefficients For H2 In Collisions With H2 From 2 To 10,000 K, T.-G. Lee, N. Balakrishnan, R. C. Forrey, P. C. Stancil, G. Shaw, D. R. Schultz, Gary J. Ferland Dec 2008

Rotational Quenching Rate Coefficients For H2 In Collisions With H2 From 2 To 10,000 K, T.-G. Lee, N. Balakrishnan, R. C. Forrey, P. C. Stancil, G. Shaw, D. R. Schultz, Gary J. Ferland

Physics and Astronomy Faculty Publications

Rate coefficients for rotational transitions in H2 induced by H2 impact are presented. Extensive quantum mechanical coupled-channel calculations based on a recently published (H2)2 potential energy surface were performed. The potential energy surface used here has been demonstrated to be more reliable than surfaces used in previous work. Rotational transition cross sections with initial levels of J≤8 were computed for collision energies ranging between 10-4 and 2.5 eV, and the corresponding rate coefficients were calculated for the temperature range 2≤T≤10,000 K. In general, agreement with earlier calculations, which were limited to 100-6000 K, …

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First Results From The Lick Agn Monitoring Project: The Mass Of The Black Hole In Arp 151, Misty C. Bentz, Jonelle L. Walsh, Aaron J. Barth, Nairn Baliber, Nicola Bennert, Gabriela Canalizo, Alexei V. Filippenko, Mohan Ganeshalingam, Elinor L. Gates, Jenny E. Greene, Marton G. Hidas, Kyle D. Hiner, Nicholas Lee, Weidong Li, Matthew A. Malkan, Takeo Minezaki, Frank J.D. Serduke, Joshua H. Shiode, Jeffrey M. Silverman, Thea N. Steele, Daniel Stern, Rachel A. Street, Carol E. Thornton, Tommaso Treu, Xiaofeng Wang, Jong-Hak Woo, Yuzuru Yoshii Dec 2008

First Results From The Lick Agn Monitoring Project: The Mass Of The Black Hole In Arp 151, Misty C. Bentz, Jonelle L. Walsh, Aaron J. Barth, Nairn Baliber, Nicola Bennert, Gabriela Canalizo, Alexei V. Filippenko, Mohan Ganeshalingam, Elinor L. Gates, Jenny E. Greene, Marton G. Hidas, Kyle D. Hiner, Nicholas Lee, Weidong Li, Matthew A. Malkan, Takeo Minezaki, Frank J.D. Serduke, Joshua H. Shiode, Jeffrey M. Silverman, Thea N. Steele, Daniel Stern, Rachel A. Street, Carol E. Thornton, Tommaso Treu, Xiaofeng Wang, Jong-Hak Woo, Yuzuru Yoshii

Physics

We have recently completed a 64 night spectroscopic monitoring campaign at the Lick Observatory 3 m Shane telescope with the aim of measuring the masses of the black holes in 13 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~106-107 M☉. We present here the first results from this project—the mass of the central black hole in Arp 151. Strong variability throughout the campaign led to an exceptionally clean Hβ lag measurement in this object of 4.25−0.66+0.68 days in the observed frame. Coupled with the width of the Hβ emission line in the variable spectrum, we determine a black …

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Lattice Super-Yang-Mills Using Domain Wall Fermions In The Chiral Limit, Simon Catterall, Joel Giedt, Richard Brower, George T. Fleming, Pavlos Vranas Dec 2008

Lattice Super-Yang-Mills Using Domain Wall Fermions In The Chiral Limit, Simon Catterall, Joel Giedt, Richard Brower, George T. Fleming, Pavlos Vranas

Physics - All Scholarship

Lattice N=1 super-Yang-Mills theory formulated using Ginsparg-Wilson fermions provides a rigorous non-perturbative definition of the continuum theory that requires no fine-tuning as the lattice spacing is reduced to zero. Domain wall fermions are one explicit scheme for achieving this and using them we have performed large-scale Monte Carlo simulations of the theory for gauge group SU(2). We have measured the gaugino condensate, static potential, Creutz ratios and residual mass for several values of the domain wall separation L_s, four-dimensional lattice volume, and two values of the gauge coupling. With this data we are able to extrapolate the gaugino condensate to …

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Observation Of The Doubly Strange B Baryon ΩB-, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration Dec 2008

Observation Of The Doubly Strange B Baryon ΩB-, V. M. Abazov, Kenneth A. Bloom, Gregory Snow, D0 Collaboration

Kenneth Bloom Publications

We report the observation of the doubly strange b baryon Ωb- in the decay channel Ωb- → J/ψΩ-, with J/ψ → μ+μ- and Ω- → ΛK- → (pπ-)K-, in pp collisions at √s = 1.96 TeV. Using approximately 1.3 fb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider, we observe 17:8 ± 4.9(stat) ± 0.8(syst) Ωb- signal events at a mass of 6.165 ± 0.010(stat) ± 0.013(syst) GeV. The significance of …

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The Thermoelectric Properties Investigation Of X0.05Mo3Sb7-YTeY (X=Mn, Fe, Ni, Co; Y=1.5, 1.6, 1.7), Tim Holgate Dec 2008

The Thermoelectric Properties Investigation Of X0.05Mo3Sb7-YTeY (X=Mn, Fe, Ni, Co; Y=1.5, 1.6, 1.7), Tim Holgate

All Theses

With ever increasing energy costs, dwindling resources, and terms with the prefix 'green' filling headlines, the need for environmentally friendly energy sources has never been greater. Since the mid-20th century researchers have been pursuing greater efficiency in thermoelectric materials. Thermoelectric materials achieve energy conversion via the Seebeck effect (heat to electric power) and the Peltier effect (electricity to cooling power). Presented herein are the measured electrical and thermal transport properties and phenomenal analysis of the Ir3Ge7-type system: X0.05Mo3Sb7-yTey (X=Mn, Fe, Ni, Co; y=1.5, 1.6, 1.7) where 'X' are interstitially …

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Suppression Pattern Of Neutral Pions At High Transverse Momentum In Au + Au Collisions At Square Root Of Snn = 200 Gev And Constraints On Medium Transport Coefficients, Andrew Marshall Adare, Sergey V. Afanasiev, Christine A. Aidala, N. N. Ajitanand, Yasuyuki Akiba, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, S. Rembeczki, Klaus Dehmelt Dec 2008

Suppression Pattern Of Neutral Pions At High Transverse Momentum In Au + Au Collisions At Square Root Of Snn = 200 Gev And Constraints On Medium Transport Coefficients, Andrew Marshall Adare, Sergey V. Afanasiev, Christine A. Aidala, N. N. Ajitanand, Yasuyuki Akiba, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, S. Rembeczki, Klaus Dehmelt

Aerospace, Physics, and Space Science Faculty Publications

For Au þ Au collisions at 200 GeV, we measure neutral pion production with good statistics for transverse momentum, pT, up to 20 GeV=c. A fivefold suppression is found, which is essentially constant for 5 < pT < 20 GeV=c. Experimental uncertainties are small enough to constrain any model-dependent parametrization for the transport coefficient of the medium, e.g., hq^i in the parton quenching model. The spectral shape is similar for all collision classes, and the suppression does not saturate in Au þ Au collisions.

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Simulation And Analysis Of Cadmium Sulfide Nanoparticles, Chad Everett Junkermeier Dec 2008

Simulation And Analysis Of Cadmium Sulfide Nanoparticles, Chad Everett Junkermeier

Theses and Dissertations

I used ab initio molecular dynamics calculations to model cadmium sulfide nanoparticles. The nanoparticles were originaly spherical, bulk-like zinc-blende structures. Constant temperature molecular dynamics calculations reveals that CdS nanoparticles that are about 2 nm in diameter and have unpassivated surfaces are in an amorphous structure with short range order. The nearest neighbor distance on the surface of the nanoparticles being near the wurtzite nearest neighbor distance. I wrote the program xyzSTATS and used its results in justifying the amorphous nanoparticles claim. I also estimated the band gap of the CdS nanoparticles with unpassivated dangling bonds.

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Reconstructing Three-Dimensional Shape Envelopes From Time-Resolved Small-Angle X-Ray Scattering Data, Jessica Lamb, Lisa W. Kwok, Xiangyun Qiu, Kurt Andresen, Hye Yoon Park, Lois Pollack Dec 2008

Reconstructing Three-Dimensional Shape Envelopes From Time-Resolved Small-Angle X-Ray Scattering Data, Jessica Lamb, Lisa W. Kwok, Xiangyun Qiu, Kurt Andresen, Hye Yoon Park, Lois Pollack

Physics and Astronomy Faculty Publications

Modern computing power has made it possible to reconstruct low-resolution, three-dimensional shapes from solution small-angle X-ray scattering (SAXS) data on biomolecules without a priori knowledge of the structure. In conjunction with rapid mixing techniques, SAXS has been applied to time resolve conformational changes accompanying important biological processes, such as biomolecular folding. In response to the widespread interest in SAXS reconstructions, their value in conjunction with such time-resolved data has been examined. The group I intron from Tetrahymena thermophila and its P4–P6 subdomain are ideal model systems for investigation owing to extensive previous studies, including crystal structures. The goal of this …

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Detection Of An So2 Plume Over Sapporo, Japan From The Eruption Of Mt. Kasatochi Using A Balloon Sounding Technique, Gary A. Morris, Jun Hirokawa, Masatomo Fujiwara, Fumio Hasebe, Keisuke Ishida, Nicholay Krotkov, Mark R. Schoeberl, Walter Komhyr, Barry Lefer, James Flynn Dec 2008

Detection Of An So2 Plume Over Sapporo, Japan From The Eruption Of Mt. Kasatochi Using A Balloon Sounding Technique, Gary A. Morris, Jun Hirokawa, Masatomo Fujiwara, Fumio Hasebe, Keisuke Ishida, Nicholay Krotkov, Mark R. Schoeberl, Walter Komhyr, Barry Lefer, James Flynn

Physics and Astronomy Faculty Presentations

During the month of August 2008, 10 ozonesondes were launched from Hokkaido University in Sapporo, Japan as part of a study to examine regional pollution during the Olympic period. Seven of these soundings included a second instrument with a filter designed to remove SO2 from the intake air stream. SO2 interferes with the normal chemistry of the electrochemical cell (ECC) method for ozone detection, with the net result being that each molecule of SO2 registers as minus one molecule of O3. Thus the unfiltered sonde reports [O3] - [SO2] while the filtered sonde reports [O3]. Laboratory tests prior to launch …

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Establishment Of A Chebyshev-Dependent Inhomogeneous Second Order Differential Equation For The Applied Physics-Related Boubaker-Turki Polynomials, Micahel Dada, O. Bamidele Awojoyogbe, Maximilian Hasler, Karem B. Ben Mahmoud, Amine Bannour Dec 2008

Establishment Of A Chebyshev-Dependent Inhomogeneous Second Order Differential Equation For The Applied Physics-Related Boubaker-Turki Polynomials, Micahel Dada, O. Bamidele Awojoyogbe, Maximilian Hasler, Karem B. Ben Mahmoud, Amine Bannour

Applications and Applied Mathematics: An International Journal (AAM)

This paper proposes Chebyshev-dependent inhomogeneous second order differential equation for the m-Boubaker polynomials (or Boubaker-Turki polynomials). This differential equation is also presented as a guide to applied physics studies. A concrete example is given through an attempt to solve the Bloch NMR flow equation inside blood vessels.

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Effective-Range Theory For An Electron In A Short-Range Potential And A Laser Field, M. V. Frolov, N. L. Manakov, Anthony F. Starace Dec 2008

Effective-Range Theory For An Electron In A Short-Range Potential And A Laser Field, M. V. Frolov, N. L. Manakov, Anthony F. Starace

Anthony F. Starace Publications

The time-dependent effective-range (TDER) theory introduced by Frolov et al. [Phys. Rev. Lett. 91, 053003 (2003)] and used in numerous applications for processes involving a linearly polarized intense laser field is presented in detail for the general problem of an electron, initially bound in a short-range potential, interacting with a laser field of arbitrary polarization. The TDER theory combines the well-known effective-range theory for a weakly bound electron in a short-range potential with the quasistationary, quasienergy state (QQES) or Floquet formulation for an electron interacting with a harmonic, time-dependent field, such as a monochromatic laser field. We present the basic …

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Scattering Of An Electromagnetic Plane Wave By A Luneburg Lens. I. Ray Theory, James A. Lock Dec 2008

Scattering Of An Electromagnetic Plane Wave By A Luneburg Lens. I. Ray Theory, James A. Lock

Physics Faculty Publications

For a plane wave incident on either a Luneburg lens or a modified Luneburg lens, the magnitude and phase of the transmitted electric field are calculated as a function of the scattering angle in the context of ray theory. It is found that the ray trajectory and the scattered intensity are not uniformly convergent in the vicinity of edge ray incidence on a Luneburg lens, which corresponds to the semiclassical phenomenon of orbiting. In addition, it is found that rays transmitted through a large-focal-length modified Luneburg lens participate in a far-zone rainbow, the details of which are exactly analytically soluble …

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Scattering Of An Electromagnetic Plane Wave By A Luneburg Lens. Ii. Wave Theory, James A. Lock Dec 2008

Scattering Of An Electromagnetic Plane Wave By A Luneburg Lens. Ii. Wave Theory, James A. Lock

Physics Faculty Publications

The partial wave scattering and interior amplitudes for the interaction of an electromagnetic plane wave with a modified Luneburg lens are derived in terms of the exterior and interior radial functions of the scalar radiation potentials evaluated at the lens surface. A Debye series decomposition of these amplitudes is also performed and discussed. The effective potential inside the lens for the transverse electric polarization is qualitatively examined, and the approximate lens size parameters of morphology-dependent resonances are determined. Finally, the physical optics model is used to calculate wave scattering in the vicinity of the ray theory orbiting condition in order …

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Scattering Of An Electromagnetic Plane Wave By A Luneburg Lens. Iii. Finely Stratified Sphere Model, James A. Lock Dec 2008

Scattering Of An Electromagnetic Plane Wave By A Luneburg Lens. Iii. Finely Stratified Sphere Model, James A. Lock

Physics Faculty Publications

The parallel iteration procedure for computing scattering by a multilayer sphere is described. The procedure uses a successive doubling strategy applied to four sets of multiple-scattering amplitudes, which is reminiscent of the fast Fourier transform (FFT) algorithm. The procedure is then used to calculate scattering of a plane wave by a modified Luneburg lens. The evolution of the transmission rainbow for the Luneburg lens parameter f > 1 into an orbiting ray for f = 1 and into a series of morphology-dependent resonances for f < 1 is studied, and various features of the scattered intensity as a function of scattering angle are commented on. It is found that some resonances are formed without the presence of an exterior centrifugal barrier to confine them. (C) 2008 Optical Society of America

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Rainbows In The Grass. I. External Reflection Rainbows From Pendant Droplets, James A. Lock, Charles L. Adler, Richard W. Fleet Dec 2008

Rainbows In The Grass. I. External Reflection Rainbows From Pendant Droplets, James A. Lock, Charles L. Adler, Richard W. Fleet

Physics Faculty Publications

In the mid-morning on a sunny day one can sometimes see glare spots associated with uncolored "rainbow" (i.e., fold) caustics due to the sunlight reflected from the surface of dew or guttation drops. We show that these dewdrop reflection rainbows are due to places on the droplet (i.e., from an "inflection circle") where its Gaussian curvature becomes zero. We work out the theory of such caustics with horizontally incident light and present a comparison of the theory to measurements made in the laboratory. (C) 2008 Optical Society of America

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Rainbows In The Grass. Ii. Arbitrary Diagonal Incidence, Charles L. Adler, James A. Lock, Richard W. Fleet Dec 2008

Rainbows In The Grass. Ii. Arbitrary Diagonal Incidence, Charles L. Adler, James A. Lock, Richard W. Fleet

Physics Faculty Publications

We consider external reflection rainbow caustic,,; due to the reflection of light from a pendant droplet where the light rays are at an arbitrary angle with respect to the horizontal. We compare this theory to observation of glare spots from, pendant drops on grass; we also consider the potential application of this theory to the determination of liquid surface tension. (C) 2008 Optical Society of America

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The Origin Of The 511 Kev Positron Annihilation Emission Morphology, Bethany Johns Dec 2008

The Origin Of The 511 Kev Positron Annihilation Emission Morphology, Bethany Johns

All Theses

The 511 keV positron annhilation emission from the Galactic bulge has yet to solely be attributed to any astrophysical source of positrons. The 511 keV line, characteristic of electron-positron annihilation, was discovered in 1970 by Johnson and Haymes [1973] almost 40 years ago. Most recently the INTERnational Gamma-Ray Astrophysical Laboratory (INTEGRAL) [Knodlseder 1997] has measured the annihilation rates of both components of the Galaxy. The bulge and disk annihilation rates are (1.5 ± 0.1) x 10^43 e+ s^-1 and(0.3 ± 0.2) x 10^43 e+ s^-1, respectively. The ratio of the bulge rate to that of the disk ranges from 3-9. …

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Analyzing The Catalytic Role Of Asp97 In The Methionine Aminopeptidase From Escherichia Coli, Sanghamitra Mitra, Kathleen M. Job, Lu Meng, Brian Bennett, Richard C. Holz Dec 2008

Analyzing The Catalytic Role Of Asp97 In The Methionine Aminopeptidase From Escherichia Coli, Sanghamitra Mitra, Kathleen M. Job, Lu Meng, Brian Bennett, Richard C. Holz

Physics Faculty Research and Publications

An active site aspartate residue, Asp97, in the methionine aminopeptidase (MetAPs) from Escherichia coli (EcMetAP-I) was mutated to alanine, glutamate, and asparagine. Asp97 is the lone carboxylate residue bound to the crystallographically determined second metal-binding site in EcMetAP-I. These mutant EcMetAP-I enzymes have been kinetically and spectroscopically characterized. Inductively coupled plasma–atomic emission spectroscopy analysis revealed that 1.0 ± 0.1 equivalents of cobalt were associated with each of the Asp97-mutated EcMetAP-Is. The effect on activity after altering Asp97 to alanine, glutamate or asparagine is, in general, due to a ∼ 9000-fold decrease in kca towards …

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Retrieving Photorecombination Cross Sections Of Atoms From High-Order Harmonic Spectra, Shinichiro Minemoto, Toshihito Umegaki, Yuichiro Oguchi, Toru Morishita, Anh-Thu Le, Shinichi Watanabe, Hirofumi Sakai Dec 2008

Retrieving Photorecombination Cross Sections Of Atoms From High-Order Harmonic Spectra, Shinichiro Minemoto, Toshihito Umegaki, Yuichiro Oguchi, Toru Morishita, Anh-Thu Le, Shinichi Watanabe, Hirofumi Sakai

Physics Faculty Research & Creative Works

We observe high-order harmonic spectra generated from a thin atomic medium, Ar, Kr, and Xe, by intense 800-nm and 1300-nm femtosecond pulses. A clear signature of a single-atom response is observed in the harmonic spectra. Especially in the case of Ar, a Cooper minimum, reflecting the electronic structure of the atom, is observed in the harmonic spectra. We successfully extract the photorecombination cross sections of the atoms in the field-free condition with the help of an accurate recolliding electron wave packet. The present protocol paves the way for exploring ultrafast imaging of molecular dynamics with attosecond resolution.

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Differential Cross Sections For The Ionization Of Oriented H₂ Molecules By Electron Impact, James Colgan, Michael S. Pindzola, Francis J. Robicheaux, Christian V. Kaiser, Andrew James Murray, Don H. Madison Dec 2008

Differential Cross Sections For The Ionization Of Oriented H₂ Molecules By Electron Impact, James Colgan, Michael S. Pindzola, Francis J. Robicheaux, Christian V. Kaiser, Andrew James Murray, Don H. Madison

Physics Faculty Research & Creative Works

A nonperturbative close-coupling technique is used to calculate differential cross sections for the electron-impact ionization of H2 at an energy of 35.4 eV. Our approach allows cross sections for any orientation of the molecule with respect to the incident electron beam to be analyzed. New features in the resulting cross sections are found compared with the case where the molecular orientation is averaged, and also with cross sections for He at equivalent electron kinematics. When averaged over all possible molecular orientations, good agreement is found with recent experimental results.

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Interference Effects Due To Projectile Target Nucleus Scattering In Single Ionization Of H₂ By 75-Kev Proton Impact, Jason S. Alexander, Aaron C. Laforge, Ahmad Hasan, Z. S. Machavariani, M. F. Ciappina, R. D. Rivarola, Don H. Madison, Michael Schulz Dec 2008

Interference Effects Due To Projectile Target Nucleus Scattering In Single Ionization Of H₂ By 75-Kev Proton Impact, Jason S. Alexander, Aaron C. Laforge, Ahmad Hasan, Z. S. Machavariani, M. F. Ciappina, R. D. Rivarola, Don H. Madison, Michael Schulz

Physics Faculty Research & Creative Works

Doubly differential cross sections (DDCSs) for single ionization of molecular hydrogen by 75-keV proton impact have been measured and calculated as a function of the projectile scattering angle and energy loss. Interference structures are observed in the scattering angular dependence of the DDCSs, which disappear, however, at electron speeds near the projectile speed. The comparison to our calculations shows that the projectile-target nucleus interaction plays a central role. Furthermore, our data suggest that for a given scattering angle, ionization favors well-defined molecular orientations.

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Spin- And Fine-Structure-Resolved Ionization Of Krypton, S. Bellm, J. Lower, R. P. Mceachran, E. Weigold, Ciarán Ryan-Anderson, Don H. Madison Dec 2008

Spin- And Fine-Structure-Resolved Ionization Of Krypton, S. Bellm, J. Lower, R. P. Mceachran, E. Weigold, Ciarán Ryan-Anderson, Don H. Madison

Physics Faculty Research & Creative Works

The influence of exchange, correlation, and relativistic effects in the ionization of heavy-target atoms can be sensitively probed by kinematically complete studies involving spin-polarized electrons, in particular when the fine structure of the residual ion is resolved. We present spin asymmetries, triple differential cross sections, and branching ratios for the ionization, by 127.5-eV and 114.3-eV electrons, of ground-state krypton atoms leading to the Kr+ 4s 2S1/2, 4p5 2P1/2, and 4p5 2P3/2 states. In order to untangle contributions from different physical effects, the experimental results are compared to those from distorted-wave Born approximation calculations (non- and semirelativistic) in which bound-state and …

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