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Reactivity And Electronic Structure Of Aluminum Clusters: The Aluminum-Nitrogen System, B. D. Leskiw, A. W. Castleman Jr., C. Ashman, S. N. Khanna

Physics Publications

The stability of anionic aluminum–nitrogen clusters has been examined and Al2N−, Al3N−2,Al5N−2, Al6N−3, Al8N−3, and Al9N−2 are found to be particularly stable. Theoreticaldensity functional calculations on neutral and anionic AlnN (n=1–8) clusters were performed and the stability and reaction energetics with oxygen examined. Clusters requiring less than 5.7 eV to remove an electron and an Al atom are shown to be resistant to the reaction with oxygen.

Geometry, Electronic Structure, And Energetics Of Copper-Doped Aluminum Clusters, S. N. Khanna, C. Ashman, B. K. Rao, P. Jena

Physics Publications

Using density functional theory and generalized gradient approximation for exchange-correlation potential, we have calculated the equilibrium geometries and energetics of neutral and negatively charged AlnCu (n=11,12,13,14) clusters. Unlike the alkali atom-doped aluminum clusters in the same size range, the copper atom resides inside the aluminum cluster cage. Furthermore, the 3d and 4s energy levels of Cu hybridize with the valence electrons of Al causing a redistribution of the molecular orbital energy levels of the Aln clusters. However, this redistribution does not affect the magic numbers of AlnCu clusters that could be derived by assuming that Cu donates one electron to …

Electronic Structure And Chemical Bonding Of 3d-Metal Dimers Scx, X=Sc-Zn, G. L. Gutsev, P. Jena, B. K. Rao, S. N. Khanna

Physics Publications

The electronic and geometrical structures of the ground and excited states of the homonuclear Sc2, mixed ScTi, ScV, ScCr, ScMn, ScFe, ScCo, ScNi, ScCu, and ScZn 3d-metal dimers and their anions have been calculated using the density functional theory with generalized gradient approximation for the exchange-correlation potential. The ground states of the neutral dimers are found to be 5Σ−u (Sc2), 6Σ+ (ScTi), 7Σ+ (ScV), 4Σ+ (ScCr), 3Σ+ (ScMn), 2Δ(ScFe), 1Σ+ (ScCo), 2Σ+ (ScNi), 3Δ(ScCu), and 4Σ+ (ScZn). A natural bond analysis reveals an antiferrimagnetic spin coupling in the ground states of ScCr, ScMn, and ScFe. This is due to the …

Electronic Structure Of Chromium Oxides, Cron- And Cron (N=1-5) From Photoelectron Spectroscopy And Density Functional Theory Calculations, G. L. Gutsev, P. Jena, Hua-Jin Zhai, Lai-Sheng Wang

Physics Publications

The electronic structure of CrO−n and CrOn (n=1–5) was investigated using anion photoelectron spectroscopy and density functional theory. Photoelectron spectra of CrO−n were obtained at several photon energies and yielded electron affinities, vibrational and electronic structure information about the neutral CrOn species. Density functional theory calculations were carried out for both the neutrals and anions and were used to interpret the experimental spectra. Several low-lying electronic states of CrO were observed and assigned from photodetachment of the CrO− ground state(6∑+) and an excited state (4∏), which is only 0.1 eV higher. The main spectral features of CrO−2 were interpreted based …

Orientation And Speed Of The Parsec-Scale Jet In Ngc4261 (3c270), B. Glenn Piner, Dayton L. Jones, Ann E. Wehrle

Physics

NGC 4261 (3C 270) is an elliptical galaxy containing a 300 pc–scale nuclear disk of gas and dust imaged by the Hubble Space Telescope (HST), around a central supermassive black hole. Previous VLBI observations of NGC 4261 revealed a gap in emission in the radio counterjet, presumably due to free-free absorption in the inner parsec of the accretion disk. Here we present three 8 GHz VLBA observations of NGC 4261 that allow us to monitor the location and depth of the gap and check for motions in the jet and counterjet. The separation between the brightest peak and …

Investigation Of Magnetopause Reconnection Models Using Two Colocated, Low‐Altitude Satellites: A Unifying Reconnection Geometry, A. Boudouridis, Harlan E. Spence, T. G. Onsager

Physics & Astronomy

Ion precipitation data from two co-orbiting Defense Meteorological Satellite Program satellites (F6 and F8) are used to investigate magnetopause reconnection models. We examine differential fluxes between 30 eV and 30 keV, from a Southern Hemisphere, prenoon pass during the morning of January 10, 1990. Data from the first satellite to pass through the region (F6) show two distinct ion energy dispersions •-1 ø of latitude apart, between 76 ø and 79 ø magnetic latitude. The electron data exhibit similar features at around the same region but with no or little energy dispersion, consistent with their high velocities. We suggest that …

Heating And Ionization Of The Intergalactic Medium By An Early X-Ray Background, Aparna Venkatesan, Mark L. Giroux, J Shull

Physics and Astronomy

Observational studies indicate that the intergalactic medium (IGM) is highly ionized up to redshifts just over 6. A number of models have been developed to describe the process of reionization and the effects of the ionizing photons from the first luminous objects. In this paper we study the impact of an X-ray background, such as high-energy photons from early quasars, on the temperature and ionization of the IGM prior to reionization, before the fully ionized bubbles associated with individual sources have overlapped. X-rays have large mean free paths relative to EUV photons, and their photoelectrons can have significant effects on …

Assimilation Ionosphere Model: Development And Testing With Combined Ionospheric Campaign Caribbean Measurements, Jan Josef Sojka, D. C. Thompson, Robert W. Schunk, T. W. Bullett, J. J. Makela

All Physics Faculty Publications

Assimilation Ionosphere Model (AIM) is a physics-based, global, ionospheric specification model that is currently under development. It assimilates a diverse set of real-time (or near-real-time) measurements, such as ionograms, GPS slant total electron content (TEC), and in situ plasma measurements. This study focuses on a middle latitude ionosonde assimilation capability in both local and regional forms. The models described are capable of using theƒ₀ F ₂ and h _m F ₂ from ionograms to generate either a local or a regional distribution of the induced plasma drift. This induced drift is usually caused by the meridional neutral wind. Results …

In The Shadow Of The Accretion Disk: Higher Resolution Imaging Of The Central Parsec In Ngc 4261, B. Glenn Piner, Dayton L. Jones, Ann E. Wehrle, David L. Meier

Physics

The physical conditions in the inner parsec of accretion disks believed to orbit the central black holes in active galactic nuclei can be probed by imaging the absorption (by ionized gas in the disk) of background emission from a radio counterjet. We report high angular resolution VLBI observations of the nearby (~40 Mpc) radio galaxy NGC 4261 that confirm free-free absorption of radio emission from a counterjet by a geometrically thin, nearly edge-on disk at 1.6, 4.8, and 8.4 GHz. The angular width and depth of the absorption appears to increase with decreasing frequency, as expected. We derive an average …

Transient Anomalous Diffusion In Poiseuille Flow, Marco Latini '01, Andrew J. Bernoff

All HMC Faculty Publications and Research

We revisit the classical problem of dispersion of a point discharge of tracer in laminar pipe Poiseuille flow. For a discharge at the centre of the pipe we show that in the limit of small non-dimensional diffusion, D, tracer dispersion can be divided into three regimes. For small times (t [double less-than sign] D^−1/3), diffusion dominates advection yielding a spherically symmetric Gaussian dispersion cloud. At large times (t [dbl greater-than sign] D⁻¹), the flow is in the classical Taylor regime, for which the tracer is homogenized transversely across the pipe and diffuses with …

Report Of The State Nuclear Safety Advisor Submitted To The Governor And 120th Legislature As Of January 15, 2001, Paula M. Craighead

Maine Collection

Report of the State Nuclear Safety Advisor submitted to the Governor and 120th Legislature As of January 15, 2001

Paula M. Craighead, State Nuclear Safety Advisor, Executive Department, Maine State Planning Office, Augusta, Maine, 2001.

Contents: Introduction and Executive Summary / I. Maine Yankee Decommissioning / II. Portsmouth Naval Shipyard (PNS) / III. Low-Level Radioactive Waste (LLRW) / IV. High Level Radioactive Waste / V. Transport Routes and Safety Response / VI. Shipments / VII. Status of Federal and State Legal and Administrative Proceedings / References and Resources / Glossary

Molecular Simulations Of Sound Wave Propagation In Simple Gases, Alejandro Garcia, N. Hadjiconstantinou

Faculty Publications

Molecular simulations of sound waves propagating in a dilute hard sphere gas have been performed using the direct simulation Monte Carlo method. A wide range of frequencies is investigated, including very high frequencies for which the period is much shorter than the mean collision time. The simulation results are compared to experimental data and approximate solutions of the Boltzmann equation. It is shown that free molecular flow is important at distances smaller than one mean free path from the excitation point.

Laser Stabilization At 1536 Nm Using Regenerative Spectral Hole Burning, P B. Sellin, N M. Strickland, Thomas Böttger, J L. Carlsten, R L. Cone

Physics and Astronomy

Laser frequency stabilization giving a 500-Hz Allan deviation for a 2-ms integration time with drift reduced to 7 kHz/min over several minutes was achieved at 1536 nm in the optical communication band. A continuously regenerated spectral hole in the inhomogeneously broadened 4I15/2(1)!4I13/2(1) optical absorption of an Er31:Y2SiO5 crystal was used as the short-term frequency reference, while a variation on the locking technique allowed simultaneous use of the inhomogeneously broadened absorption line as a long-term reference. The reported frequency stability was achieved without vibration isolation. Spectral hole burning frequency stabilization provides ideal laser sources for high-resolution spectroscopy, real-time optical signal processing, …

Retrieval And Validation Of Mesospheric Temperatures From Wind Imaging Interferometer Observations, M G. Shepherd, B Reid, S Zhang, B H. Solheim, G G. Shepherd, Vincent B. Wickwar, Joshua P. Herron

All Physics Faculty Publications

A method has been developed for the retrieval of mesospheric temperatures in the 65–90 km altitude range from satellite observations made by the Wind Imaging Interferometer (WINDII) aboard the Upper Atmosphere Research Satellite (UARS). Retrieved temperatures are derived from Rayleigh scattered sunlight observed in a wavelength band centered at 553 nm. Integrated line-of-sight radiance observations are inverted to tangent height volume scattering profiles, which are proportional to atmospheric density. From these, absolute temperature profiles are calculated using a technique derived from established Rayleigh lidar retrieval methods assuming that the atmosphere is in hydrostatic equilibrium and that it obeys the ideal …

Gps Normalization And Preliminary Modeling Results Of Total Electron Content During A Midlatitude Space Weather Event, J. J. Makela, M. C. Kelley, Jan Josef Sojka, X. Pi, A. J. Mannucci

All Physics Faculty Publications

On November 22–23, 1997, a geomagnetic storm occurred during a period of excellent viewing conditions over the Arecibo Observatory in Puerto Rico. Here we explore the total electron content (TEC) registered by Global Positioning System (GPS) receivers located close to the Cornell All-Sky Imager (CASI) at the Arecibo Observatory. The storm began with the equatorward surge of a very high (100% increase) TEC enhancement stretching for many hours of local time on the dayside. At dusk the TEC over the Caribbean remained elevated with levels equal to the noontime monthly averages. During the event the TEC was highly structured and …

Mesospheric Temperature Observationsat The Usu / Cass Atmospheric Lidar Observatory (Alo), Vincent B. Wickwar, T D. Wilkerson, M Hammond, Joshua P. Herron

All Physics Faculty Publications

The Center for Atmospheric and Space Sciences (CASS) at Utah State University (USU) operates the ALO for studying the middle atmosphere from the stratosphere to the lower thermosphere. ALO’s mid-latitude location (41.74°N, 111.81°W, 1466 m) is very unique in that it is in the middle of an extensive set of rugged mountains, the Rocky Mountains, which are a major orographic source of gravity waves that may give rise to a longitudinal variation in the mesospheric structure. Mesospheric observations between approximately 45 and 90 km have been carried out on many clear nights with the ALO Rayleigh- scatter lidar since late …

Evolution Of Deep Centers In Gan Grown By Hydride Vapor Phase Epitaxy, Z-Q. Fang, David C. Look, J. Jasinski, M. Benamara, Z. Liliental-Weber, Richard J. Molnar

Physics Faculty Publications

Deep centers and dislocation densities in undoped n GaN, grown by hydride vapor phase epitaxy (HVPE), were characterized as a function of the layer thickness by deep level transient spectroscopy and transmission electron microscopy, respectively. As the layer thickness decreases, the variety and concentration of deep centers increase, in conjunction with the increase of dislocation density. Based on comparison with electron-irradiation induced centers, some dominant centers in HVPE GaN are identified as possible point defects.

Development Of Non-Contact Scanning Force Microscopy For Imaging In Liquid Environments, Anthony Grant

Theses

The aim of this work was to develop a non-contact mode scanning force microscope (SFM) for application to biological samples within liquid environments. Given that biological samples are particularly soft in their natural state and that a liquid is the most difficult operating environment for non-contact mode scanning force microscopy, the development of an instrument that is optimised to image biological samples in vitro presents significant challenges.

Firstly, the SFM tip to sample interaction has to be minimised either, in the worst case, to prevent the sample from being detached from its support or to maximise spatial resolution by minimising …

Photoelectron Spectroscopy And The Dipole Approximation, Oliver Hemmers, Dennis W. Lindle

Environmental Studies Faculty Publications

Over the past three decades, the dipole approximation has facilitated a basic understanding of the photoionization process in atoms and molecules. Advances in gas-phase photoemission experiments using synchrotron radiation have recently highlighted nondipole effects at relatively low photon energies while probing the limits of the dipole approximation. Breakdowns in this approximation are manifested primarily as deviations from dipolar angular distributions of photoelectrons. Detailed new results demonstrate nondipolar angular-distribution effects are easily observable in atomic gases at energies well below 1 keV, and, in molecules, a previously unexpected phenomenon greatly enhances the breakdown of the dipole approximation just above the core-level …

Measurement Of Dσ/Dy For High Mass Drell-Yan E+E- Pairs From Pp̅ Collisions At √S =1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

We report on the first measurement of the rapidity distribution dσ/dy over nearly the entire kinematic region of rapidity for e⁺e^- pairs in both the Z-boson region of 66<M_ee/c² and in the high mass region of M_ee>116 GeV/c². The data sample consists of 108 pb^-1 of pp̅ collisions at √s =1.8 TeV taken by the Collider Detector at Fermilab during 1992–1995. The total cross section in the Z-boson region is measured to be 252±11 pb. The measured total cross section and dσ/dy are compared …

Measurement Of Dσ/Dy For High Mass Drell-Yan E+E- Pairs From Pp̅ Collisions At √S =1.8 Tev, T. Affolder, Kenneth A. Bloom, Collider Detector At Fermilab Collaboration

Kenneth Bloom Publications

No abstract provided.

Multilayer Mim Inversion Of Aem Data: Theory And Field Example, Clyde J. Bergeron Jr, Juliette W. Ioup, Yan Wu, George E. Ioup, Kenneth W. Holladay

Physics Faculty Publications

This paper presents a multilayer generalization of an algebraic method of inverting frequency-doma in airborne active electromagnetic (AEM) data in terms of 1-D layered earth models. The processing of the AEM data, which includes a recalibration procedure, is also outlined. The inversion is applied to synthetic fields generated from a multilayer model which is intended to approximate a measured conductivity profile of the water column in the Gulf of Mexico and to measured AEM data from a survey of the Barataria Bay estuary region of the Louisiana Gulf of Mexico coast. The inversion results from the synthetic data are in …

Order-Disorder Phase Transitions In Kno2 , Csno2, And Tlno2 Crystals: A Molecular Dynamics Study, Chun-Gang Duan, Wai-Ning Mei, Robert W. Smith, Jianjun Liu, M. M. Ossowski, John R. Hardy

Physics Faculty Publications

The order-disorder phase transitions of KNO2 , CsNO2, and TlNO2 have been studied using parameter-free molecular dynamics simulation. It is found that the phase transitions in nitrites investigated are driven by the rotations of the NO2 2 ions about different axes together with displacements of cations and anions. We successfully reproduce the high-temperature phases of these nitrites, i.e., the NaCl-like structure for KNO2 and CsCl-like structure for Cs(Tl)NO2. Based on the investigation of the radial distribution function of the cations and anions, we explain why KNO2 and Cs(Tl)NO2 form quite different low-temperature phases.

Study Of Slip Systems In Epidote Single Crystal, Salah-Ud Din, Munnawar Ahmad, Shahzad Chishti

Turkish Journal of Physics

Measurements of microhardness anisotropy by Knoop diamond indentations on the prismatic (100) planes of epidote crystals, point group 2/m and space group P21/m, show that microhardness is determined by crystallographic slip on the (100) systems. Microhardness anisotropy is explained in terms of the effective resolved shear stress distribution in these slip systems.

The Effect Of Phonon Drag Of Charge Carriers In In_{1 - X} Ga_{X} Sb, Sadiyar Ahmedoglu Zeynalov

Turkish Journal of Physics

The temperature dependencies of the thermal power a_{0} and thermal conductivity \kappa in two samples of In_{1 - x} Ga_{x}Sb (x=0.65 and 0.45) doped by {Te\sim } 0.001 at\%, with electron concentration n = 5.9 \cdot 10^{16} and 1.3 \cdot 10^{17} cm^{ - 3} (at 100K), have been investigated. It is shown that in In_{0.35}Ga_{0.65}Sb a_{0} increases with decreasing T below 50K. At 14K a_{0} passes through maximum and it falls sharply with decreasing T. It is shown that the maximum value of a_{0} is in agreement with the maximum value of \kappa . In In_{0.55}Ga_{0.45}Sb, starting from T = …

Prospects For Chiral Nonlinear Optical Media, Rolfe G. Petschek, Kenneth D. Singer

Faculty Scholarship

This paper describes the development and optimization of chiral, nonpolar media with large second-order nonlinear optical responses. We employ molecular engineering, quantum-mechanical sum-over-states theory, and measurements of molecular hyperpolarizability by means of Kleinman-disallowed hyper-Rayleigh scattering in order to understand molecular properties. Then we analyze the appropriate arrangement of the chromophores that produce an optimum axial nonlinear optical medium. Chromophores with large Kleinman disallowed traceless symmetric second-rank tensor hyperpolarizabilities /spl beta/ can be aligned so as to result in large susceptibilities /spl chi//sup (2)/ in structures that lack polar order. We found that /spl Lambda/-shaped chromophores with C/sub 2v/ or similar …

Automated Alignment By Hybrid Video And 3-D Video Moiré With Both Conventional And Parallel Processing, Barbara Garita, Hector Gutierrez, Ildiko Laszlo, Joel H. Blatt

Aerospace, Physics, and Space Science Faculty Publications

A problem common to automated assembly in manufacturing or in automated docking of spacecraft is angular and lateral alignment of components. A hybrid video system utilizing both conventional imaging and 3-D video moiré has been developed to automatically align a test target with three translational and two rotational degrees of freedom. Alignment was demonstrated via computer controlled translation and rotation stages. The video moiré system is operated in an error map mode, in which a structurally illuminated reference surface is used to chromakey the image of an identical structurally illuminated alignment target. The output is a moiré image generated by …

Electron Spectral Function In Two-Dimensional Fractionalized Phases, Courtney Lannert, Matthew P.A. Fisher, T. Senthil

Physics: Faculty Publications

We study the electron spectral function of various zero-temperature spin-charge separated phases in two dimensions. In these phases, the electron is not a fundamental excitation of the system, but rather “decays” into a spin-1/2 chargeless fermion (the spinon) and a spinless charge e boson (the chargon). Using low-energy effective theories for the spinons (d-wave pairing plus possible Néel order) and the chargons (condensed or quantum-disordered bosons), we explore three phases of possible relevance to the cuprate superconductors: (1) (formula presented) a fractionalized antiferromagnet where the spinons are paired into a state with long-ranged Néel order and the chargons are 1/2-filled …

Measurement Of The Gluon Parton Distribution Function At Small X With Neutrino Telescopes, Gabriele U. Varieschi

Physics Faculty Works

We analyze the possibility that neutrino telescopes may provide an experimental determination of the slope λ of the gluon distribution in the proton at momentum fractions x smaller than the accelerator reach. The method is based on a linear relation between λ and the spectral index ~slope! of the down-going atmospheric muon flux above 100 TeV, for which there is no background. Considering the uncertainties in the charm production cross section and in the cosmic ray composition, we estimate the error on the measurement of l through this method, excluding the experimental error of the telescopes, to be ±0.2.

Path Integral Treatment For Spinless Relativistic Equation In The Two Component Theory, M. Merad, T. Boudjedaa, Lyazid Chetouani

Turkish Journal of Physics

In this paper we have set up a path integral formalism for Feshbach-Villars equation by using the fermionic Schwinger model for Pauli matrices which describe an isocharge symmetry. This choice is made in analogy with spin model and the coherent state representation is then used. We have also given a general method of treating the problem of vanishing scalar potential by reducing it the to non-relativistic case and then, via Foldy-Wouthuysen canonical transformation, an explicit solution is constructed. The free case and constant magnetic field interaction are explicitly exposed. In each cases the propagators are evaluated and the energy spectrum …