Physics Commons^™

Large Energy Gaps In Cac₆ From Tunneling Spectroscopy: Possible Evidence Of Strong-Coupling Superconductivity, Cihan Kurter, Lutfi Ozyuzer, Daniel Mazur, John F. Zasadzinski, Daniel Rosenmann

Physics Faculty Research & Creative Works

Tunneling in CaC₆ crystals reproducibly reveals superconducting gaps Δ of 2.3±0.2 meV that are ~40% larger than reported earlier. In an isotropic s -wave scenario, that puts CaC₆ into the class of very strongly coupled superconductors, since 2Δ k Tc ~4.6, implying that soft Ca phonons are primarily involved in the superconductivity. This conclusion explains the relatively large Ca isotope effect found recently for CaC₆, but it could also signal a strong anisotropy in the electron-phonon interaction.

Practical Sensor For Measurement Of Nitrogen, Dusan Popovic, Vladimir Milosavljevic, Steven Daniels

Articles

This paper presents a method for precise measurement of atomic and molecular nitrogen in an oxygen-nitrogen dc plasma. This is achieved by monitoring the intensities of the atomic nitrogen spectral line at 821.6 nm and the molecular nitrogen bandhead at 337.1 nm, relative to the atomic oxygen spectral line at 844.7 nm. Oxygen is one of the most frequently used gases for surface chemical treatment, including deposition and etching, therefore the ability to measure and control the process and chemical composition of the process is essential. To validate this oxygen actimometry method for N2-xO2 (where x varies from 0 to …

Preheating In Derivatively-Coupled Inflation Models, Christian Armendariz-Picon, Mark Trodden, Eric J. West

Physics - All Scholarship

We study preheating in theories where the inflaton couples derivatively to scalar and gauge fields. Such couplings may dominate in natural models of inflation, in which the flatness of the inflaton potential is related to an approximate shift symmetry of the inflaton. We compare our results with previously studied models with non-derivative couplings. For sufficiently heavy scalar matter, parametric resonance is ineffective in reheating the universe, because the couplings of the inflaton to matter are very weak. If scalar matter fields are light, derivative couplings lead to a mild long-wavelength instability that drives matter fields to non-zero expectation values. In …

Bioluminescence In A Complex Coastal Environment: 1. Temporal Dynamics Of Nighttime Water-Leaving Radiance, Mark A. Moline, Matthew J. Oliver, Curtis D. Mobley, Lydia Sundman, Thomas J. Bensky, Trisha Bergmann, W. Paul Bissett, James Case, Erika H. Raymond, Oscar M.E. Schofield

Physics

Nighttime water-leaving radiance is a function of the depth-dependent distribution of both the in situ bioluminescence emissions and the absorption and scattering properties of the water. The vertical distributions of these parameters were used as inputs for a modified one-dimensional radiative transfer model to solve for spectral bioluminescence water-leaving radiance from prescribed depths of the water column. Variation in the water-leaving radiance was consistent with local episodic physical forcing events, with tidal forcing, terrestrial runoff, particulate accumulation, and biological responses influencing the shorter timescale dynamics. There was a >90 nm shift in the peak water-leaving radiance from blue (~474 nm) …

Matching Kasteleyn Cities For Spin Glass Ground States, Alan Middleton, Creighton K. Thomas

Physics - All Scholarship

As spin glass materials have extremely slow dynamics, devious numerical methods are needed to study low-temperature states. A simple and fast optimization version of the classical Kasteleyn treatment of the Ising model is described and applied to two-dimensional Ising spin glasses. The algorithm combines the Pfaffian and matching approaches to directly strip droplet excitations from an excited state. Extended ground states in Ising spin glasses on a torus, which are optimized over all boundary conditions, are used to compute precise values for ground state energy densities.

Measurement Of The Tt̅ Production Cross Section In Pp̅ Collisions At √S = 1.96 Tev Using Kinematic Characteristics Of Lepton + Jets Events, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Kenneth Bloom Publications

We present a measurement of the top quark pair production cross section in pp̅ collisions at √s = 1.96 TeV utilizing 425 pb^-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. We consider the final state of the top quark pair containing one high-p_T electron or muon and at least four jets. We exploit specific kinematic features of tt̅ events to extract the cross section. For a top quark mass of 175 GeV, we measure σ _tt̅ = 6.4_-1.2^+1.3(stat) ± 0.7(syst) ± 0.4(lum) pb, in good agreement with the …

Supercurrent Survival Under A Rosen-Zener Quench Of Hard-Core Bosons, I. Klich, Courtney Lannert, G. Refael

Physics: Faculty Publications

We study the survival of supercurrents in a system of impenetrable bosons on a lattice, subject to a quantum quench from its critical superfluid phase to an insulating phase. We show that the evolution of the current when the quench follows a Rosen-Zener profile is exactly solvable. This allows us to analyze a quench of arbitrary rate, from a sudden destruction of the superfluid to a slow opening of a gap. The decay and oscillations of the current are analytically derived and studied numerically along with the momentum distribution after the quench. In the case of small supercurrent boosts ν, …

Scalar Mesons From An Effective Lagrangian Approach, Joseph Schechter, Amir H. Fariborz, Renata Jora

Physics - All Scholarship

A brief discussion of the recent interest in light scalar mesons motivates the study of a generalized linear sigma model. In an SU(3) flavor invariant version of the model there is a prediction that the the lighter scalars have sizeable "four quark" content. It is further predicted that one of the singlet scalars should be exceptionally light. Due to the presence of scalar mesons, the model gives "controlled" corrections to the current algebra formula for threshold pion pion scattering. These corections act in the direction to improve agreement with current experiments.

Real Space Information From Fluctuation Electron Microscopy: Applications To Amorphous Silicon, Parthapratim Biswas, Raymond Atta-Fynn, S. Chakraborty, D. A. Drabold

Faculty Publications

Ideal models of complex materials must satisfy all available information about the system. Generally, this information consists of experimental data, information implicit to sophisticated interatomic interactions and potentially other a priori information. By jointly imposing first-principles or tight-binding information in conjunction with experimental data, we have developed a method: experimentally constrained molecular relaxation (ECMR) that uses all of the information available. We apply the method to model medium range order in amorphous silicon using fluctuation electron microscopy (FEM) data as experimental information. The paracrystalline model of medium range order is examined, and a new model based on voids in amorphous …

Optimization Of The 3 M Tgm Beamline, At Camd, For Constant Initial State Spectroscopy, Yaroslav B. Losovyj, Ihor Ketsman, Eizi Morikawa, Zhenjun Wang, Jinke Tang, Peter A. Dowben

Peter Dowben Publications

The 3 m toroidal grating monochromator (TGM) VUV beamline at CAMD/LSU was realigned to achieve better illumination of the monochromator gratings with the goal of substantially increasing the flux at the higher photon energies. This is partly accomplished through a tilting of the monochromator (by about of 13.5°), with respect to the plane defined by the synchrotron, providing a smaller grazing angle at the initial mirrors. The improved performance of the beamline permits resonant photoemission studies at Gd 4d core threshold without resorting to second order light, which we demonstrate for Gd doped HfO₂.

High-Resolution Photoemission Study Of Organic Systems At The Camd 3 M Nim Beamline, Yaroslav B. Losovyj, Kevin Morris, Luis G. Rosa, John D. Scott, Peter A. Dowben

Peter Dowben Publications

The 3 m normal incidence monochromator (NIM) VUV beamline at CAMD was designed for novel high-resolution photoemission experiments. Both solid-state samples and gas phase resolution tests demonstrate that high-resolution photoemission is possible below 10 meV, and vibronic fine structure in the photoemission final state from the crystalline copolymer poly-vinylidene fluoride with trifluoroethylene can be observed: the first direct experimental identification of symmetry dependence in electron–phonon coupling in photoemission from a solid-state system.

Spectacular Shells In The Host Galaxy Of The Qso Mc2 1635+119, Gabriela Canalizo, Nicola Bennert, Bruno Jungwiert, Alan Stockton, François Schweizer, Mark Lacy, Chien Peng

Physics

We present deep HST ACS images and Keck spectroscopy of MC2 1635+119, a QSO hosted by a galaxy previously classified as an undisturbed elliptical galaxy. Our new images reveal dramatic shell structure indicative of a merger event in the relatively recent past. The brightest shells in the central regions of the host are distributed alternately in radius, with at least two distinct shells on one side of the nucleus and three on the other, out to a distance of ~13 kpc. The light within the five shells comprises ~6% of the total galaxy light. Lower surface brightness ripples or tails …

Search For Production Of Single Top Quarks Via Tcg And Tug Flavor-Changing-Neutral-Current Couplings, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We search for the production of single top quarks via flavor-changing-neutral-current couplings of a gluon to the top quark and a charm (c) or up (u) quark. We analyze 230 pb-1 of lepton + jets data from pp̅ collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters K_g^c/ Λ and K_g^u/ Λ, where K_{g define the strength of tcg …}

Search For Production Of Single Top Quarks Via Tcg And Tug Flavor-Changing-Neutral-Current Couplings, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We search for the production of single top quarks via flavor-changing-neutral-current couplings of a gluon to the top quark and a charm (c) or up (u) quark. We analyze 230 pb-1 of lepton + jets data from pp̅ collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters K_g^c/ Λ and K_g^u/ Λ, where K_{g define the strength of tcg …}

Search For Production Of Single Top Quarks Via Tcg And Tug Flavor-Changing-Neutral-Current Couplings, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Kenneth Bloom Publications

We search for the production of single top quarks via flavor-changing-neutral-current couplings of a gluon to the top quark and a charm (c) or up (u) quark. We analyze 230 pb^-1 of lepton + jets data from pp̅ collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters κ_g^c/Λ and κ_g^u/Λ, where κ_g define the strength of tcg and …

Search For Production Of Single Top Quarks Via Tcg And Tug Flavor-Changing-Neutral-Current Couplings, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We search for the production of single top quarks via flavor-changing-neutral-current couplings of a gluon to the top quark and a charm (c) or up (u) quark. We analyze 230 pb-1 of lepton + jets data from pp̅ collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters Kgc/ Λ and Kgu/ Λ, where Kg define the strength of tcg and tug couplings, and Λ defines the scale of new physics. …

Correlation Of The Highest-Energy Cosmic Rays With Nearby Extragalactic Objects, J. Abraham, Gregory Snow, Pierre Auger Collaboration

Gregory Snow Publications

Using data collected at the Pierre Auger Observatory during the past 3.7 years, we demonstrated a correlation between the arrival directions of cosmic rays with energy above 6 × 10¹⁹ electron volts and the positions of active galactic nuclei (AGN) lying within ~75 megaparsecs. We rejected the hypothesis of an isotropic distribution of these cosmic rays with at least a 99% confidence level from a prescribed a priori test. The correlation we observed is compatible with the hypothesis that the highest-energy particles originate from nearby extragalactic sources whose flux has not been substantially reduced by interaction with the cosmic …

Search For A Higgs Boson Produced In Association With A Z Boson In Pp̅ Collisions, V. M. Abazov, Kenneth A. Bloom, Gregory Snow

Gregory Snow Publications

We describe a search for the Standard Model Higgs boson with a mass of 105 GeV/c² to 145 GeV/c² in data corresponding to an integrated luminosity of approximately 450 pb^-1 collected with the DØ detector at the Fermilab Tevatron p̅p collider at a center-of-mass energy of 1.96 TeV. The Higgs boson is required to be produced in association with a Z boson, and the Z boson is required to decay to either electrons or muons with the Higgs boson decaying to a b̅b pair. The data are well described by the expected background, leading to …

Rapidity And Species Dependence Of Particle Production At Large Transverse Momentum For D+Au Collisions At √ Snn = 200 Gev, B.I. Abelev, J. Adams, M.M. Aggarwal, J. Amonett, B.D. Anderson, M. Anderson, D. Arkhipkin, G.S. Averichev, Y. Bai, J. Balewski, O. Barannikova, L.S. Barnby, J. Baudot, S. Bekele, V.V. Belaga, A. Bellingeri-Laurikainen, R. Bellwied, F. Benedosso, S. Bhardwaj, A. Bhasin, A.K. Bhati, H. Bichsel, J. Bielcik, J. Bielcikova, L.C. Bland, S.L. Blyth, B.E. Bonner, M. Botje, J. Bouchet, A.V. Brandin, A. Bravar, M. Bystersky, R.V. Cadman, X.Z. Cai, H. Caines, M. Calderon De La Barca Sanchez, J. Castillo, O. Catu, D. Cebra, Z. Chajecki, P. Chaloupka, S. Chattopadhyay, H.F. Chen, J.H. Chen, J. Cheng, M. Cherney, A. Chikanian, W. Christie, J.P. Coffin, T.M. Cormier, M.R. Cosentino, J.G. Cramer, H.J. Crawford, D. Das, S. Das, M. Daughertiy, M.M De Moura, T.G. Dedovich, M. Dephillips, A.A. Derevschikov, L. Didenko, T. Dietel, P. Djawotho, S.M Dogra, W.J. Dong, X. Dong, J.E. Draper, F. Du, V.B. Dunin, J.C. Dunlop, M.R. Dutta Mazumdar, V. Eckardt, W.R. Edwards, L.G. Efimov, V. Emelianov, J. Engelage, G. Eppley, B. Erazmus, M. Estienne, P. Fachini, R. Fatemi, J. Fedorisin, K. Filimonov, P. Filip, E. Finch, V. Fine, Y. Fisyak, J. Fu, C.A. Gagliardi, L. Gaillard, M.S. Ganti, V. Ghazikhanian, P. Ghosh, J.E. Gonzalez, Y.G. Gorbunov, H. Gos, O. Grebenyuk, D. Grosnick, S.M. Guertin, K.S.F.F. Guimaraes, Y. Guo, N. Gupta, T.D. Gutierrez, B. Haag, T.J. Hallman, A. Hamed, J.W. Harris, W. He, M. Heinz, T.W. Henry, S. Hepplemann, B. Hippolyte, A. Hirsch, E. Hjort, A.M. Hoffman, G.W. Hoffmann, M.J. Horner, H.Z. Huang, S.L. Huang, E.W. Hughes, T.J. Humanic, G. Igo, P. Jacobs, W.W. Jacobs, P. Jakl, F. Jia, H. Jiang, P.G. Jones, E.G. Judd, S. Kabana, K. Kang, J. Kapitan, M. Kaplan, D. Keane, A. Kechechyan, V.Yu. Khodyrev, B.C. Kim, J. Kiryluk, A. Kisiel, E.M. Kislov, S.R. Klein, A. Kocoloski, D.D. Koetke, T. Kollegger, M. Kopytine, L. Kotchenda, V. Kouchpil, K.L. Kowalik, M. Kramer, P. Kravtsov, V.I. Kravtsov, K. Krueger, C. Kuhn, A.I. Kulikov, A. Kumar, A.A. Kuznetsov, M.A.C. Lamont, J.M. Landgraf, S. Lange, S. Lapointe, F. Laue, J. Lauret, A. Lebedev, R. Lednicky, C.-H. Lee, S. Lehocka, M.J. Levine, C. Li, Q. Li, G. Lin, S.J. Lindenbaum, M.A. Lisa, F. Liu, H. Liu, J. Liu, L. Liu, Z. Liu, T. Ljubicic, W.J. Llope, H. Long, R.S. Longacre, M. Lopez-Noriega, W.A. Love, Y. Lu, T. Ludlam, D. Lynn, G.L. Ma, J.G. Ma, Y.G. Ma, D. Magestro, D.P. Mahapatra, R. Majka, L.K. Mangotra, R. Manweiler, S. Margetis, C. Markert, L. Martin, H.S. Matis, Yu.A. Matulenko, C.J. Mcclain, T.S. Mcshane, Yu. Melnick, A. Meschanin, J. Millane, M.L. Miller, N.G. Minaev, S. Mioduszewski, C. Mironov, A. Mischke, D.K. Mishra, J. Mitchell, B. Mohanty, L. Molnar, C.F. Moore, D.A. Morozov, M.G. Munhoz, B.K. Nandi, C. Nattrass, T.K. Nayak, J.M. Nelson, P.K. Netrakanti, V.A. Nikitin, L.V. Nogach, S.B. Nurushev, G. Odyniec, A. Ogawa, V. Okorokov, M. Oldenburg, D. Olson, M. Pachr, S.K. Pal, Y. Panebratsev, S.Y. Panitkin, A.I. Pavlinov, T. Pawlak, T. Peitzmann, V. Perevoztchikov, C. Perkins, W. Peryt, V.A. Petrov, S.C. Phatak, R. Picha, M. Planinic, J. Pluta, N. Poljak, N. Porile, J. Porter, A.M. Poskanzer, M. Potekhin, E. Potrebenikova, B.V.K.S. Potukuchi, D. Prindle, C. Pruneau, J. Putschke, G. Rakness, R. Raniwala, S. Raniwala, R.L. Ray, S.V. Razin, J. Reinnarth, D. Relyea, F Retiere, A. Ridiger, H.G. Ritter, J.B. Roberts, O.V. Rogachevskiy, J.L. Romero, A. Rose, C. Roy, L. Ruan, M.J. Russcher, R. Sahoo, T. Sakuma, S. Salur, J. Sanweiss, M. Sarsour, P.S. Sazhin, J. Schambach, R.P. Scharenberg, N. Schmitz, K. Schweda, J. Serger, I. Selyuzhenkov, P. Seyboth, A. Shabetai, E. Shahaliev, M. Shao, M. Sharma, W.Q. Shen, S.S. Shimanskiy, E. Sichtermann, F. Simon, R.N. Singaraju, N. Smirnov, R. Snellings, G. Sood, P. Sorensen, J. Sowinski, J. Speltz, H.M. Spinka, B. Srivastava, A. Stadnik, T.D.S. Stanislaus, R. Stock, A. Stolpovsky, M. Strikhanov, B. Stringfellow, A.A.P. Suaide, E. Sugarbaker, M. Sumbera, Z. Sun, B. Surrow, M. Swanger, T.J.M. Symons, A. Szanto De Toledo, A. Tai, J. Takahashi, A.H. Tang, T. Tarnowsky, D. Thein, J.H. Thomas, A.R. Timmins, S. Timoshenko, M. Tokarev, T.A. Trainor, S. Trentalange, R.E. Tribble, O.D. Tsai, J. Ulery, T. Ullrich, D.G. Underwood, G. Van Buren, N. Van Der Kolk, M. Van Leeuwen, A.M. Vander Molen, R. Varma, I.M. Vasilevski, A.N. Vasiliev, R. Vernet, S.E. Vigdor, Y.P. Viyogi, S. Vokal, S.A. Voloshin, W.T. Waggoner, F. Wang, G. Wang, J.S. Wang, X.L. Wang, J.W. Watson, J.C. Webb, G.D. Westfall, A. Wetzler, C. Whitten Jr., H. Wieman, S.W. Wissink, R. Witt, J. Wood, J. Wu, N. Xu, Q.H. Xu, Z. Xu, P. Yepes, I.-K. Yoo, V.I. Yurevich, W. Zhan, H. Zang, W.M. Zhang, Y. Zhang, Z.P. Zhang, Y. Zhao, C. Zong, R. Zoulkarneev, Y. Zoulkarneeva, A.N. Zubarev, J.X. Zuo

Physics

We determine rapidity asymmetry in the production of charged pions, protons, and antiprotons for large transverse momentum (pT) for d+Au collisions at sNN−−−√=200 GeV. The rapidity asymmetry is defined as the ratio of particle yields at backward rapidity (Au beam direction) to those at forward rapidity (d beam direction). The identified hadrons are measured in the rapidity regions |y|

Measurement Of The ΛB0 Lifetime Using Semileptonic Decays, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Kenneth Bloom Publications

We report a measurement of the Λ_b⁰ lifetime using a sample corresponding to 1:3 fb^-1 of data collected by the D0 experiment in 2002–2006 during run II of the Fermilab Tevatron collider. The Λ_b⁰ baryon is reconstructed via the decay Λ_b⁰ → μν&#; Λ _c⁺X. Using 4437 ± 329 signal candidates, we measure the Λ_b⁰ lifetime to be τ(Λ_b⁰) = 1.290_-0.110^+0.119 (stat) _-0.091^+0.087(syst) ps, which is among the most precise measurements in semileptonic Λ_b⁰ decays. This result is in …

Measurement Of The ΛB0 Lifetime Using Semileptonic Decays, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We report a measurement of the Λ_b⁰ lifetime using a sample corresponding to 1.3 fb^-1 of data collected by the D0 experiment in 2002–2006 during run II of the Fermilab Tevatron collider. The Λ_b⁰ baryon is reconstructed via the decay Λ_b⁰ → μν̅Λ_c⁺ X. Using 4437 ± 329 signal candidates, we measure the Λ_b⁰ lifetime to be τ(Λ_b⁰) = 1.290_-0.110^+0.119 (stat) _-0.091^+0.087 (syst) ps, which is among the most precise measurements in semileptonic Λ_b⁰ decays. This result is in good …

The Spin Axes Orbital Alignment Of Both Stars Within The Eclipsing Binary System V1143 Cyg Using The Rossiter-Mclaughlin Effect, S. Albrecht, S. Reffert, I. Snellen, A. Quirrenbach, D. S. Mitchell

Physics

Context. The Rossiter-McLaughlin (RM) effect, a rotational effect in eclipsing systems, provides unique insight into the relative orientation of stellar spin axes and orbital axes of eclipsing binary systems.

Aims. Our aim is to develop a robust method to analyze the RM effect in an eclipsing system with two nearly equally bright components. This gives access to the orientation of the stellar rotation axes and may shed light on questions of binary formation and evolution. For example, a misalignment between the spin axes and the angular momentum of the system could bring the observed and theoretical apsidal motion into better …

Reversal Of Spin Polarization In Fe/Gaas (001) Driven By Resonant Surface States: First-Principles Calculations, Athanasios N. Chantis, Kirill D. Belashchenko, D. L. Smith, Evgeny Y. Tsymbal, Mark Van Schilfgaarde, R. C. Albers

Evgeny Tsymbal Publications

A minority-spin resonant state at the Fe/GaAs(001) interface is predicted to reverse the spin polarization with the voltage bias of electrons transmitted across this interface. Using a Green's function approach within the local spin-density approximation, we calculate the spin-dependent current in a Fe/GaAs/Cu tunnel junction as a function of the applied bias voltage. We find a change in sign of the spin polarization of tunneling electrons with bias voltage due to the interface minority-spin resonance. This result explains recent experimental data on spin injection in Fe/GaAs contacts and on tunneling magnetoresistance in Fe/GaAs/Fe magnetic tunnel junctions.

Bias Voltage Dependence Of Tunneling Anisotropic Magnetoresistance In Magnetic Tunnel Junctions With Mgo And Al2O3 Tunnel Barriers, Li Gao, Xin Jiang, See-Hun Yang, John D. Burton, Evgeny Y. Tsymbal, Stuart S. P. Parkin

Evgeny Tsymbal Publications

Tunneling anisotropic magnetoresistance (TAMR) is observed in tunnel junctions with transition metal electrodes as the moments are rotated from in-plane to out-of-plane in sufficiently large magnetic fields that the moments are nearly parallel to one another. A complex angular dependence of the tunneling resistance is found with twofold and fourfold components that vary strongly with bias voltage. Distinctly different TAMR behaviors are obtained for devices formed with highly textured crystalline MgO(001) and amorphous Al₂O₃ tunnel barriers. A tight-binding model shows that a fourfold angular dependence can be explained by the presence of an interface resonant state that …

Optimization Of Electrostatic Interactions In Protein-Protein Complexes, Kelly Brock, Kemper Talley, Kacey Coley, Petras Kundrotas, Emil Alexov

Publications

In this article, we present a statistical analysis of the electrostatic properties of 298 protein-protein complexes and 356 domain-domain structures extracted from the previously developed database of protein complexes (ProtCom, http://www.ces.clemson.edu/compbio/protcom). For each structure in the dataset we calculated the total electrostatic energy of the binding and its two components, Coulombic and reaction field energy. It was found that in a vast majority of the cases (>90%), the total electrostatic component of the binding energy was unfavorable. At the same time, the Coulombic component of the binding energy was found to favor the complex formation while …

Search For BS0→ Μ+ Μ- Decays At D0, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We report results from a search for the decay B_s⁰ → μ⁺μ^- using 1.3 fb^-1 of pp̅ collisions at √s= 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron Collider.We find two candidate events, consistent with the expected background of 1.24 ± 0.99, and set an upper limit on the branching fraction of Ɓ(B_s⁰ → μ⁺μ^-) < 1.2 x 10^-7 at the 95% C.L.

The Case For Optically Thick High-Velocity Broad-Line Region Gas In Active Galactic Nuclei, Stephanie A. Snedden, C. Martin Gaskell

C. Martin Gaskell Publications

A combined analysis of the profiles of the main broad quasar emission lines in both Hubble Space Telescope and optical spectra shows that while the profiles of the strong UV lines are quite similar, there is frequently a strong increase in the Lyα/Hα ratio in the high-velocity gas.We show that the suggestion that the high-velocity gas is optically thin presents many problems.We show that the relative strengths of the high-velocity wings arise naturally in an optically thick BLR component. An optically thick model successfully explains the equivalent widths of the lines, the Lyα/Hα ratios and flatter Balmer decrements in the …

Agn Reddening And Ultraviolet Extinction Curves From Hubble Space Telescope Spectra, C. Martin Gaskell, C. Martin Gaskell

C. Martin Gaskell Publications

We present intrinsic extinction curves for 14 AGNs. The AGNs have reddenings, E(B-V), of up to 0.36 mag. The majority (13 out of 14) of the extinction curves are not steep in the UV. Of the seven best determined extinction curves, five have extinction curves that are as flat as the standard Galactic curve in the optical and near UV, but flatter in the far UV, and without the λ2175 feature. One AGN, B3 0754+394, has a steep SMC-like extinction curve, and another, Mrk 304, has an LMC-like extinction curve, including a probable λ2175 bump. The remaining seven, lower-quality, extinction …

Discovery Of Polarization Reverberation In Ngc 4151, C. Martin Gaskell, René W. Goosmann, Nelly I. Merkulova, Nikolay M. Shakhovskoy, Masatoshi Shoji

C. Martin Gaskell Publications

Observations of the optical polarization of NGC 4151 in 1997–2003 show variations of an order of magnitude in the polarized flux while the polarization position angle remains constant. The amplitude of variability of the polarized flux is comparable to the amplitude of variability of the total U-band flux, except that the polarized flux follows the total flux with a lag of 8±3 days. The time lag and the constancy of the position angle strongly favor a scattering origin for the variable polarization rather than a non-thermal synchrotron origin. The orientation of the position angle of the polarized flux (parallel to …

Ngc 5548: The Agn Energy Budget Problem And The Geometry Of The Broad-Line Region And Torus, C. Martin Gaskell, Elizabeth S. Klimek, Ludmila S. Nazarova

C. Martin Gaskell Publications

We consider in detail the spectral energy distribution (SED) and multi-wavelength variability of NGC 5548. Comparison with the SEDs of other AGNs implies that the internal reddening of NGC 5548 is E(B-V) = 0.17 mag. The extinction curve is consistent with the mean curve of other AGNs found by Gaskell & Benker, but inconsistent with an SMC-type reddening curve. Because most IR emission originates exterior to the broad-line region (BLR), the SED seen by the inner BLR is different from that seen by the outer BLR and from the earth. The most likely BLR covering factor is ~ 40% and …