Physics Commons^™

Facile Syntheses Of Monodisperse Ultrasmall Au Clusters, Massimo F. Bertino, Zhong Ming Sun, Rui Zhang, Lai Sheng Wang

Physics Faculty Research & Creative Works

During our effort to synthesize the tetrahedral Au20 cluster, we found a facile synthetic route to prepare monodisperse suspensions of ultrasmall Au clusters AuN (N < 12) using diphosphine ligands. in our monophasic and single-pot synthesis, an Au precursor ClAu(I)PPh3 (Ph = phenyl) and a bidentate phosphine ligand P(Ph)2(CH 2) M (Ph)2 are dissolved in an organic solvent. Au(I) is reduced slowly by a borane-tert-butylamine complex to form Au clusters coordinated by the diphosphine ligand. the Au clusters are characterized by both high-resolution mass spectrometry and UV-vis absorption spectroscopy. We found that the mean cluster size obtained depends on the chain length M of the ligand. in particular, a single monodispersed Au11 cluster is obtained with the P(Ph)2(CH2)3P(Ph)2 ligand, whereas P(Ph)2(CH2) MP (Ph)2 ligands with M = 5 and 6 yield Au10 and Au8 clusters. the simplicity of our synthetic method makes it suitable for large-scale production of nearly monodisperse ultrasmall Au clusters. It is suggested that diphosphines provide a set of flexible ligands to allow size-controlled synthesis of Au nanoparticles. © 2006 American Chemical Society.

A Critique Of The Link Approach To Exact Lattice Supersymmetry, Simon Catterall, Falk Bruckmann, Mark De Kok

Physics - All Scholarship

We examine the link approach to constructing a lattice theory of N=2 super Yang Mills theory in two dimensions. The goal of this construction is to provide a discretization of the continuum theory which preserves all supersymmetries at non-zero lattice spacing. We show that this approach suffers from an inconsistency and argue that a maximum of just one of the supersymmetries can be implemented on the lattice.

Storm‐Time Configuration Of The Inner Magnetosphere: Lyon‐Fedder‐Mobarry Mhd Code, Tsyganenko Model, And Goes Observations, Chia-Lin L. Huang, Harlan E. Spence, J. G. Lyon, F. R. Toffoletto, H. J. Singer, S. Sazykin

Physics & Astronomy

[1] We compare global magnetohydrodynamic (MHD) simulation results with an empirical model and observations to understand the magnetic field configuration and plasma distribution in the inner magnetosphere, especially during geomagnetic storms. The physics-based Lyon-Fedder-Mobarry (LFM) code simulates Earth's magnetospheric topology and dynamics by solving the equations of ideal MHD. Quantitative comparisons of simulated events with observations reveal strengths and possible limitations and suggest ways to improve the LFM code. Here we present a case study that compares the LFM code to both a semiempirical magnetic field model and to geosynchronous measurements from GOES satellites. During a magnetic cloud event, the …

Fluorescence Polarization Of Helium Negative-Ion Resonances Excited By Polarized Electron Impact, J. W. Maseberg, Timothy J. Gay

Timothy J. Gay Publications

We have investigated helium (1s3d) ³D → (1s2p) ³P (588 nm) fluorescence produced by electron impact excitation in the vicinity of the (2s²2p) ²P and (2s2p²) ²D negative-ion resonances at 57.2 and 58.3 eV, respectively. In contrast to previous work, we use spin-polarized incident electrons and report the relative Stokes parameters P₁, P₂, and P₃ in the 55–60 eV region. Our failure to see discernable resonance effects in P₂ indicates that even though the lifetime of these resonances is significant (~10 fs), magnetic forces acting on …

Emergence Of The Fuzzy Horizon Through Gravitational Collapse, Anand Murugan '07, Vatche Sahakian

All HMC Faculty Publications and Research

For a large enough Schwarzschild black hole, the horizon is a region of space where gravitational forces are weak; yet it is also a region leading to numerous puzzles connected to stringy physics. In this work, we analyze the process of gravitational collapse and black hole formation in the context of light-cone M-theory. We find that, as a shell of matter contracts and is about to reveal a black hole horizon, it undergoes a thermodynamic phase transition. This involves the binding of D0 branes into D2’s, and the new phase leads to large membranes of the size of the horizon. …

A Transmission Electron Microscope For Lecture Demonstrations, J. A. Panitz, Gertrude Rempfer

Physics Faculty Publications and Presentations

A simple transmission electron microscope (TEM) suitable for lecture demonstrations is described. In this TEM electrons are created in a glow discharge between two parallel electrodes in air at a reduced pressure. The electrons are collimated by a small hole in theanode, focused by a solenoid that acts as an electromagnetic lens, and imaged on a thin layer of phosphor deposited inside an Erlenmeyer flask. An image of a biological sample placed between the source and the lens can be magnified about 20 times. The microscope uses inexpensive components that can be quickly assembled during a demonstration. The TEMprovides a …

Predicting Residue Contacts Using Pragmatic Correlated Mutations Method: Reducing The False Positives, Petras J. Kundrotas, Emil Alexov

Publications

Background

Predicting residues' contacts using primary amino acid sequence alone is an important task that can guide 3D structure modeling and can verify the quality of the predicted 3D structures. The correlated mutations (CM) method serves as the most promising approach and it has been used to predict amino acids pairs that are distant in the primary sequence but form contacts in the native 3D structure of homologous proteins.

Results

Here we report a new implementation of the CM method with an added set of selection rules (filters). The parameters of the algorithm were optimized against fifteen high resolution crystal …

Production Of Excited Atomic Hydrogen And Deuterium From H2 And D2 Photodissociation, J. D. Bozek, J. E. Furst, Timothy J. Gay, H. Gould, A. L. D. Kilcoyne, J. R. Machacek, F. Martin, K. W. Mclaughlin, J. L. Sanz-Vicario

Timothy J. Gay Publications

We have measured the production of both Lyα and Hα fluorescence from atomic H and D for the photodissociation of H₂ and D₂ by linearly polarized photons with energies between 24 and 60 eV. In this energy range, excited photofragments result primarily from the production of doubly excited molecular species which promptly autoionize or dissociate into two neutrals. Our data are compared with ab initio calculations of the dissociation process, in which both doubly excited state production and prompt ionization (non resonant) channels are considered. Agreement between our experimental data and that of earlier work, and with our …

Transmission Electron Goniometry And Its Relation To Electron Tomography For Materials Science Apoplications, Peter Moeck, P. Fraundorf

Physics Faculty Publications and Presentations

Aspects of transmission electron goniometry are discussed. Combined with high resolution phase contrast transmission electron microscopy (HRTEM) and atomic resolution scanning TEM (STEM) in the atomic number contrast (Z-STEM) or the phase contrast bright field mode, transmission electron goniometry offers the opportunity to develop dedicated methods for the crystallographic characterization of nanocrystals in three dimensions. The relationship between transmission electron goniometry and electron tomography for materials science applications is briefly discussed. Internet based java applets that facilitate the application of transmission electron goniometry for cubic crystals with calibrated tilt-rotation and double-tilt specimen holders/goniometers are mentioned. The so called cubic-minimalistic tilt …

Partial-Wave Expansions Of Angular Spectra Of Plane Waves, James A. Lock

Physics Faculty Publications

Focused electromagnetic beams are frequently modeled by either an angular spectrum of plane waves or a partial-wave sum of spherical multipole waves. The connection between these two beam models is explored here. The partial-wave expansion of an angular spectrum containing evanescent components is found to possess only odd partial waves. On the other hand, the partial-wave expansion of an alternate angular spectrum constructed so as to be free of evanescent components contains all partial waves but describes a propagating beam with a small amount of standing-wave component mixed in. A procedure is described for minimizing the standing-wave component so as …

Magnetopolaron Effect On Shallow Donors In Gan, A. Wysmolek, R. Stepniewski, M. Potemski, B. Chwalisz-Pietka, K. Pakula, J. M. Baranowski, David C. Look, S. S. Park, S. K. Lee

Physics Faculty Publications

Resonant interaction between longitudinal-optic (LO) phonons and electrons bound on shallow donors in GaN is studied using magnetoluminescence of neutral-donor bound excitons (D⁰X). The experiments were performed on high-quality freestanding GaN material and heteroepitaxial GaN layers grown on sapphire. In addition to the principal recombination channel of D⁰X, in which donors are left in their ground states, two-electron satellites (TES) involving different excited donor excitations, as well as replicas of the principal D⁰X transition due to LO phonons, were observed for the oxygen and silicon donors. In order to separate transitions involving ground and …

K Α₁ Radiation From Heavy, Heliumlike Ions Produced In Relativistic Collisions, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Stephan Fritzsche

Physics Faculty Research & Creative Works

Bound-state transitions in few-electron, heavy ions following radiative electron capture are studied within the framework of the density matrix theory and the multiconfiguration Dirac-Fock approach. Special attention is paid to the K α₁ (1 s_1/2 2 p_3/2 ^1.3P_J=1,2→1s²_1/2 ¹S_J=0) radiative decay of heliumlike uranium U⁹⁰⁺ projectiles. This decay has recently been observed at the GSI facility in Darmstadt, giving rise to a surprisingly isotropic angular distribution, which is inconsistent with previous experiments and calculations based on a "one-particle" model. We show that the unexpected isotropy essentially results from …

Capillary-Driven Flows Along Rounded Interior Corners, Yongkang Chen, Mark M. Weislogel, Cory L. Nardin

Mechanical and Materials Engineering Faculty Publications and Presentations

The problem of low-gravity isothermal capillary flow along interior corners that are rounded is revisited analytically in this work. By careful selection of geometric length scales and through the introduction of a new geometric scaling parameter Tc, the Navier–Stokes equation is reduced to a convenient∼O(1) form for both analytic and numeric solutions for all values of corner half-angle α and corner roundedness ratio λ for perfectly wetting fluids. The scaling and analysis of the problem captures much of the intricate geometric dependence of the viscous resistance and significantly reduces the reliance on numerical data compared with several previous solution methods …

Quantum Dot Potentials: Symanzik Scaling, Resurgent Expansions, And Quantum Dynamics, Andrey S. Surzhykov, Michael Lubasch, Jean Zinn-Justin, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

This article is concerned with a special class of the "double-well- like" potentials that occur naturally in the analysis of finite quantum systems. Special attention is paid, in particular, to the so-called Fokker-Planck potential, which has a particular property: the perturbation series for the ground-state energy vanishes to all orders in the coupling parameter, but the actual ground-state energy is positive and dominated by instanton configurations of the form exp (-a g), where a is the instanton action. The instanton effects are most naturally taken into account within the modified Bohr-Sommerfeld quantization conditions whose expansion leads to the generalized perturbative …

To Evaluate The Effects Of The Introduction Of A Smoke-Free Environment On The Lung Function Of Bar Workers In Dublin, Michele Agnew

Masters

It has long been recognised that exposure to environmental tobacco smoke (ETS) causes respiratory and cardio-vascular disease. A ban, prohibiting smoking in the workplace, was sanctioned by the Irish government and came into effect on 29 March, 2004. Bar staff were an ideal group to study the health effects of the introduction of this ban. Methods Workers were recruited through their Trade Union, Mandate, and 81 participated in the pre-ban phase of testing between September 2003 and March 2004. They attend the Respiratory Laboratory in St. James’s Hospital and underwent lung function tests and measurement of exhaled carbon monoxide (CO). …

Analysis Of Two-Dimensional Photoelectron Momentum Spectra And The Effect Of The Long-Range Coulomb Potential In Single Ionization Of Atoms By Intense Lasers, Zhangjin Chen, Toru Morishita, Anh-Thu Le, M. Wickenhauser, X. M. Tong, C. D. Lin

Physics Faculty Research & Creative Works

Two-dimensional (2D) electron momentum distributions and energy spectra for multiphoton ionization of atoms by intense laser pulses, calculated by solving the time-dependent Schrödinger equation (TDSE) for different wavelengths and intensities, are compared to those predicted by the strong-field approximation (SFA). It is shown that the momentum spectra at low energies between the TDSE and SFA are quite different and the differences arise largely from the absence of a long-range Coulomb interaction in the SFA. We further found that the low-energy 2D momentum spectra from the TDSE exhibit ubiquitous fanlike features where the number of stripes is due to a single …

Submicrosecond Dynamics Of Water Explosive Boiling And Lift-Off From Laser-Heated Silicon Surfaces, S. I. Kudryashov, S. D. Allen

Mechanical Engineering - Daytona Beach

Explosive boiling and lift-off of a thin layer of micron-sized transparent water droplets from an absorbing Si substrate heated by a nanosecond KrF laser were studied using a contact photoacoustic technique. The compressive photoacoustic response increases steeply to an asymptotic value on the order of the water critical pressure starting at a threshold laser fluence of 0.20 J cm2, where lift-off of the water layer also occurs. Above this threshold, several reproducible discrete multimegahertz components are revealed in Fourier spectra of the acoustic transients, corresponding to nanosecond oscillations of steam bubbles inside the water droplets on the microsecond time scale …

Ordering Tendencies In The Binary Alloys Of Rh, Pd, Ir, And Pt: Density Functional Calculations, Gus L. W. Hart, Brian Kolb, Stefan Müller, David B. Botts

Faculty Publications

The binary alloys of Rh, Pd, Ir, and Pt are important because of their high catalytic potential. We report in this paper that the Rh1-xIrx and Rh1-xPtx systems, long thought to phase separate at low temperatures, actually exhibit miscibility over the entire concentration and temperature range. We find low critical ordering temperatures, indicating that long-range order is unlikely to be observed experimentally. These results are compared with previous theoretical predications for the other binary alloys of Rh, Pd, Ir, and Pt and with calculations performed here on the Pt1-xIrx and Pd1-xIrx systems. We discuss these results and investigate the mechanisms …

Electronic Structure And Polymerization Of A Self-Assembled Monolayer With Multiple Arene Rings, D.Q. Feng, David Wisbey, Yaroslav B. Losovyj, Y. Tai, M. Zharnikov, Peter A. Dowben

Peter Dowben Publications

We find evidence of intermolecular interactions for a self-assembled monolayer (SAM) formed from a large molecular adsorbate, [1,1′;4′,1′′-terphenyl]-4,4′′-dimethanethiol, from the dispersion of the molecular orbitals with changing wave vector k. With the formation self-assembled molecular (SAM) layer, the molecular orbitals hybridize to electronic bands, with indications of significant band dispersion of the unoccupied molecular orbitals. The electronic structure is also seen to be dependent upon temperature, and cross linking between the neighbor molecules, indicating that the electronic structure may be subtly altered by changes in molecular conformation and packing.

Search For Pair Production Of Scalar Bottom Quarks In Pp̅ Collisions At √S =1:96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Kenneth Bloom Publications

A search for direct production of scalar bottom quarks (b̃) is performed with 310 pb^-1 of data collected by the D0 experiment in pp̅ collisions at √s = 1.96 TeV at the Fermilab Tevatron Collider. The topology analyzed consists of two b jets and an imbalance in transverse momentum due to undetected neutralinos (χ̃₁⁰), with χ̃₁⁰ assumed to be the lightest supersymmetric particle. We find the data consistent with standard model expectations, and set a 95% C.L. exclusion domain in the (m_b̃, m _χ̃1⁰) mass plane, …

Fermiology And Superconductivity At High Magnetic Fields In A Completely Organic Cation Radical Salt, J. S. Brooks, V. Williams, E. Choi, D. Graf, M. Tokumoto, S. Uji, F. Zuo, J. Wosnitza, J. A. Schlueter, H. David, Rolf Walter Winter, Gary L. Gard, K. Storr

Chemistry Faculty Publications and Presentations

We report specialized interplane magnetoresistance (MR) measurements on the organic superconducting compound β″–(BEDT-TTF)₂SF₅CH₂CF₂SO₃ (where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) in both the superconducting (Tc ∼ 5K) and normal states versus magnetic field direction. In the normal state, detailed angular-dependent magnetoresistance oscillation (AMRO) studies reveal peculiar features of the Fermi surface topology of this compound, and very high magnetic field studies further support the unusual nature of the electronic structure. In the superconducting state we investigate, through detailedAMRO measurements, the anomalous MR peak that appears within the superconducting field-temperature phase diagram. Our results reveal a direct connection between the superconducting state determined from …

Application Of Coulomb Wave Function Discrete Variable Representation To Atomic Systems In Strong Laser Fields, Liang-You Peng, Anthony F. Starace

Anthony F. Starace Publications

We present an efficient and accurate grid method for solving the time-dependent Schrödinger equation for an atomic system interacting with an intense laser pulse. Instead of the usual finite difference (FD) method, the radial coordinate is discretized using the discrete variable representation (DVR) constructed from Coulomb wave functions. For an accurate description of the ionization dynamics of atomic systems, the Coulomb wave function discrete variable representation (CWDVR) method needs three to ten times fewer grid points than the FD method. The resultant grid points of the CWDVR are distributed unevenly so that one has a finer grid near the origin …

Search For Neutral, Long-Lived Particles Decaying Into Two Muons In Pp̅ Collisions At √S = 1:96 Tev, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Kenneth Bloom Publications

We present a search for a neutral particle, pair produced in pp̅ collisions at√s = 1.96 TeV, which decays into two muons and lives long enough to travel at least 5 cm before decaying. The analysis uses ≈ 380 pb^-1 of data recorded with the D0 detector. The background is estimated to be about one event. No candidates are observed, and limits are set on the pair-production cross section times branching fraction into dimuons + X for such particles. For a mass of 10 GeVand lifetime of 4 × 10^-11 s, we exclude values greater than 0.14 pb …

Search For The Standard Model Higgs Boson In The Pp̅→ Zh → Νν̅Bb̅ Channel, V. M. Abazov, Kenneth A. Bloom, Gregory R. Snow, D0 Collaboration

Kenneth Bloom Publications

We report a search for the standard model (SM) Higgs boson based on data collected by the D0 experiment at the Fermilab Tevatron Collider, corresponding to an integrated luminosity of 260 pb^-1. We study events with missing transverse energy and two acoplanar b jets, which provide sensitivity to the ZH production cross section in the νν̅bb̅ channel, and to WH production when the lepton from the W → ℓν decay is undetected. The data are consistent with the SM background expectation, and we set 95% C.L. upper limits on σ(pp̅ → ZH/WH) × …

Casimir Forces And Non-Newtonian Gravitation, Roberto Onofrio

Dartmouth Scholarship

The search for non-relativistic deviations from Newtonian gravitation can lead to new phenomena signalling the unification of gravity with the other fundamental interactions. Various recent theoretical frameworks indicate a possible window for non-Newtonian forces with gravitational coupling strength in the micrometre range. The major expected background in the same range is attributable to the Casimir force or variants of it if dielectric materials, rather than conducting ones, are considered. Here we review the measurements of the Casimir force performed so far in the micrometre range and how they determine constraints on non-Newtonian gravitation, also discussing the dominant sources of false …

Remote Bond Breaking By Interacting Temporary Anion States, Paul Burrow, Gordon A. Gallup

Gordon Gallup Publications

The cross section for bond breaking at the site of a dissociative temporary negative ion state through the dissociative electron attachment process can be considerably enhanced by the presence of a second longer-lived temporary negative ion state elsewhere in the molecule, even one quite remote from the first. In a series of chloroalkenes possessing both C–Cl and C=C bonds separated by various distances, we show that the cross sections are determined by the lifetime of the lower anion state created by the mixing of the anion states of these two moieties, with the wave function’s coefficients giving the probability that …

Observation Of Relativistic Cross-Phase Modulation In High-Intensity Laser-Plasma Interactions, Shouyuan Chen, Matthew Rever, P. Zhang, W. Theobald, Donald Umstadter

Donald Umstadter Publications

A nonlinear optical phenomenon, relativistic cross-phase modulation, is reported. A relativistically intense light beam (I=1.3×10¹⁸ W cm^-2, λ =1.05 μm) is experimentally observed to cause phase modulation of a lower intensity, copropagating light beam in a plasma. The latter beam is generated when the former undergoes the stimulated Raman forward scattering instability. The bandwidth of the Raman satellite is found to be broadened from 3.8–100 nm when the pump laser power is increased from 0.45–2.4 TW. A signature of relativistic cross-phase modulation, namely, asymmetric spectral broadening of the Raman signal, is observed at a pump …

Measurement Of The Inclusive Jet Cross Section In Pp̅ Interactions At √S = 1:96 Tev Using A Cone-Based Jet Algorithm, A. Abulencia, Kenneth A. Bloom, Cdf Collaboration

Kenneth Bloom Publications

We present a measurement of the inclusive jet cross section in pp̅ interactions at √s = 1:96 TeV using 385 pb^-1 of data collected with the CDF II detector at the Fermilab Tevatron. The results are obtained using an improved cone-based jet algorithm (Midpoint). The data cover the jet transverse momentum range from 61 to 620 GeV/c, extending the reach by almost 150 GeV/c compared with previous measurements at the Tevatron. The results are in good agreement with next-to-leading order perturbative QCD predictions using the CTEQ6.1M parton distribution functions.

Remote Bond Breaking By Interacting Temporary Anion States, Paul Burrow, Gordon A. Gallup

Paul Burrow Publications

The cross section for bond breaking at the site of a dissociative temporary negative ion state through the dissociative electron attachment process can be considerably enhanced by the presence of a second longer-lived temporary negative ion state elsewhere in the molecule, even one quite remote from the first. In a series of chloroalkenes possessing both C–Cl and C=C bonds separated by various distances, we show that the cross sections are determined by the lifetime of the lower anion state created by the mixing of the anion states of these two moieties, with the wave function’s coefficients giving the probability that …

Surface Segregation In Multicomponent Clusters, Peter A. Dowben, Ning Wu, Natalie Palina, R. Müller, J. Hormes, Yaroslav B. Losovyj

Peter Dowben Publications

Nanostructured materials are not immune from surface segregation, as can be shown for solid samples made from nanosized BaFe_12–2xCo_xTi_xO₁₉ barium ferrite particles and a variety of free clusters. Both theory and experiment provide ample demonstration that very limited dimensions of very small clusters does not necessarily impart stability against surface and grain boundary segregation. In fact, with the larger surface to volume ratio in small clusters and lower average atomic coordination, we anticipate that compositional instabilities in small clusters will readily occur.