Open Access. Powered by Scholars. Published by Universities.®

Physical Sciences and Mathematics Commons™

Open Access. Powered by Scholars. Published by Universities.®

Physics

Institution
Keyword
Publication Year
Publication
Publication Type
File Type

Articles 32491 - 32520 of 36556

Full-Text Articles in Physical Sciences and Mathematics

Steps Toward Determinaton Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. V. Variability Of The Ultraviolet Continuum And Emission Lines Of Ngc 3783, G. A. Reichert, P. M. Rodriguez-Pascual, D. Alloin, J. Clavel, D. Michael Crenshaw, Gerard A. Kriss, Julian Henry Krolik, Matthew A. Malkan, Hagai Netzer, Bradley M. Peterson, W. Wamsteker, A. Altamore, B. Altieri, K. S.J. Anderson, J. H. Blackwell Jr,, C. Boisson, N. Brosch, T. E. Carone, M. Dietrich, M. N. England, I. N. Evans, A. V. Filippenko, C. Martin Gaskell, M. Goad, P. M. Gondhalekar., K. Horne, D. Kazanas, W. Kol Latschny, A. P. Koratkar, Kirk T. Koristag, G. M. Macalpine, D. Maoz, T. Mazeh, B. Mccollum, H. Richard Miller, C. Mendes De Oliveira, Paul T. O'Brien, M. G. Pastoriza, D. Pelat, E. Perez, G. C. Perola, Richard William Pogge, R. L. Ptak, M. C. Recondo-Gonzalez, J. Rodriguez-Espinosa, E. I. Rosenblatt, A. C. Sadun, M . Santos-Lleo, J. C. Shields, C. R. Shrader, J. M. Shull, S. M. Simkin, M. L. Sitko, M. A.J Snuders, L. S. Sparke, G. M. Stirpe, R. Stoner, T. . Storchi-Bergm, W. H. Sun, T. F. Wang, W. F. Welsh, R. J. White, C. Winge, W. Zhen Jan 1994

Steps Toward Determinaton Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. V. Variability Of The Ultraviolet Continuum And Emission Lines Of Ngc 3783, G. A. Reichert, P. M. Rodriguez-Pascual, D. Alloin, J. Clavel, D. Michael Crenshaw, Gerard A. Kriss, Julian Henry Krolik, Matthew A. Malkan, Hagai Netzer, Bradley M. Peterson, W. Wamsteker, A. Altamore, B. Altieri, K. S.J. Anderson, J. H. Blackwell Jr,, C. Boisson, N. Brosch, T. E. Carone, M. Dietrich, M. N. England, I. N. Evans, A. V. Filippenko, C. Martin Gaskell, M. Goad, P. M. Gondhalekar., K. Horne, D. Kazanas, W. Kol Latschny, A. P. Koratkar, Kirk T. Koristag, G. M. Macalpine, D. Maoz, T. Mazeh, B. Mccollum, H. Richard Miller, C. Mendes De Oliveira, Paul T. O'Brien, M. G. Pastoriza, D. Pelat, E. Perez, G. C. Perola, Richard William Pogge, R. L. Ptak, M. C. Recondo-Gonzalez, J. Rodriguez-Espinosa, E. I. Rosenblatt, A. C. Sadun, M . Santos-Lleo, J. C. Shields, C. R. Shrader, J. M. Shull, S. M. Simkin, M. L. Sitko, M. A.J Snuders, L. S. Sparke, G. M. Stirpe, R. Stoner, T. . Storchi-Bergm, W. H. Sun, T. F. Wang, W. F. Welsh, R. J. White, C. Winge, W. Zhen

Department of Physics and Astronomy: Faculty Publications

We report on the results of intensive ultraviolet spectral monitoring of the Seyfert 1 galaxy NGC 3783. The nucleus of NGC 3783 was observed with the International Ultraviolet Explorer satellite on a regular basis for a total of 7 months, once every 4 days for the first 172 days and once every other day for the final 50 days. Significant variability was observed in both continuum and emission-line fluxes. The light curves for the continuum fluxes exhibited two well-defined local minima or "dips," the first lasting ≤20 days and the second ≤ 4 days, with additional episodes of relatively rapid …

Go to article

Electron-Electron Interaction In Projectile Ionization Investigated By High Resolution Recoil Ion Momentum Spectroscopy, R. Dörner, V. Mergel, R. Ali, U. Buck, C. L. Cocke, K. Froschauer, O. Jagutzki, S. Lencinas, W. E. Meyerhof, S. Nüttgens, Ronald E. Olson, H. Schmidt-Böcking, L. Spielberger, K. Tökesi, J. Ullrich Jan 1994

Electron-Electron Interaction In Projectile Ionization Investigated By High Resolution Recoil Ion Momentum Spectroscopy, R. Dörner, V. Mergel, R. Ali, U. Buck, C. L. Cocke, K. Froschauer, O. Jagutzki, S. Lencinas, W. E. Meyerhof, S. Nüttgens, Ronald E. Olson, H. Schmidt-Böcking, L. Spielberger, K. Tökesi, J. Ullrich

Physics Faculty Research & Creative Works

Contributions of the electron-electron and the nuclear-electron interactions to projectile electron loss in He+ on helium collisions have been clearly separated kinematically for the first time by measuring the longitudinal and transverse momenta of the recoiling target ion with precision of better than ±0.15 a.u. The longitudinal and transverse momentum distributions are in general agreement with two-center n-body classical trajectory Monte Carlo calculations. © 1994 The American Physical Society.

Go to article

A Fringe Center Detection Technique Based On A Sub-Pixel Resolution, And Its Applications Using Sinusoidal Gratings, Ming Chang, Paul P. Lin, Wen Chih Tai Jan 1994

A Fringe Center Detection Technique Based On A Sub-Pixel Resolution, And Its Applications Using Sinusoidal Gratings, Ming Chang, Paul P. Lin, Wen Chih Tai

Mechanical Engineering Faculty Publications

A common problem in optical profilometry is the accuracy in locating fringe centers. This paper presents an accurate fringe center detection technique based on sub-pixel resolution using the fringe projection method. An optimum reconstruction filter is developed which has low sensitivity to noise. In fringe center detection, computer simulation results of using one-pixel and sub-pixel resolutions are compared. The detection technique is then applied to radius measurement of cylindrical objects and surface profile measurement of diffuse objects. The experimental results thus obtained through the proposed optimum reconstruction filter show significant improvement in measurement accuracy.

Go to article

Numerical Simulation Of Nonequilibrium Effects In An Argon Plasma Jet, C. H. Chang, John D. Ramshaw Jan 1994

Numerical Simulation Of Nonequilibrium Effects In An Argon Plasma Jet, C. H. Chang, John D. Ramshaw

Physics Faculty Publications and Presentations

Departures from thermal (translational), ionization, and excitation equilibrium in an axisymmetric argon plasma jet have been studied by two?dimensional numerical simulations. Electrons, ions, and excited and ground states of neutral atoms are represented as separate chemical species in the mixture. Transitions between excited states, as well as ionization/recombination reactions due to both collisional and radiative processes, are treated as separate chemical reactions. Resonance radiation transport is represented using Holstein escape factors to simulate both the optically thin and optically thick limits. The optically thin calculation showed significant underpopulation of excited species in the upstream part of the jet core, whereas …

Go to article

Replica Field Theory For Deterministic Models (Ii): A Non-Random Spin Glass With Glassy Behavior, Enzo Marinari, Giorgio Parisi, Felix Ritort Jan 1994

Replica Field Theory For Deterministic Models (Ii): A Non-Random Spin Glass With Glassy Behavior, Enzo Marinari, Giorgio Parisi, Felix Ritort

Northeast Parallel Architecture Center

We introduce and study a model which admits a complex landscape without containing quenched disorder. Continuing our previous investigation we introduce a disordered model which allows us to reconstruct all the main features of the original phase diagram, including a low T spin glass phase and a complex dynamical behavior.

Go to article

Compton Scattering Of Gamma-Rays From Electrons In Advanced Laboratory, Christine A. Byrd, Morgan T. Burks, Lawrence A. Yates, Wilfred J. Braithwaite Jan 1994

Compton Scattering Of Gamma-Rays From Electrons In Advanced Laboratory, Christine A. Byrd, Morgan T. Burks, Lawrence A. Yates, Wilfred J. Braithwaite

Journal of the Arkansas Academy of Science

A kinematically-complete 2-body final state measurement of Compton scattering of 662-keV photons is presened, where both scattered photon energy and electron recoil energy are measured versus photon scattering angle, theta gamma. Passive collimation of the photon beam is avoided; each recoiling electron triggers a photon-scattering event providing active beam collimation. Recoiling electrons have low energies at small theta gamma, impairing electron detection efficiency. Examining the recoiling-electron energy spectra in coincidence with high-resolution gammas indicates a 1"x 1"NaI detector is superior to a 1"x1" NE-102 plastic scintillator as the active scattering material, for efficient recoil-electron detection. Electron efficiencies versus theta gamma …

Go to article

Einstein's Equations In Vacuum Spacetimes With Two Spacelinke Killing Vectors Using Affine Projection Tensor Geometry, Miles D. Lawrence Jan 1994

Einstein's Equations In Vacuum Spacetimes With Two Spacelinke Killing Vectors Using Affine Projection Tensor Geometry, Miles D. Lawrence

Theses and Dissertations

Einstein's equations in vacuum spacetimes with two spacelike killing vectors are explored using affine projection tensor geometry. By doing a semi-conformal transformation on the metric, a new "fiducial" geometry is constructed using a projection tensor fields. This fiducial geometry provides coordinate independent information about the underlying structure of the spacetime without the use of an explicit form of the metric tensor.

Go to article

The Modeling Of Phosphorus Dynamics In A Lake System, Todd N. Swift Jan 1994

The Modeling Of Phosphorus Dynamics In A Lake System, Todd N. Swift

Presidential Scholars Theses (1990 – 2006)

We have constructed a basic closed stock and flow model of lake phosphorus cycling that includes three stock concentrations: inorganic phosphorus, phosphorus in living organic material, and phosphorus in dead organic material. Stocks are connected by flows that are made stock dependent in a plausible manner. The model exhibits two equilibrium points, one stable and the other unstable, with an interesting crossover between them. Below a certain total phosphorus threshold, stable equilibrium is characterized by all of the phosphorus stock residing in the inorganic form, suggesting the collapse of the biological system. Above the threshold, this is not true. We …

Go to article

Superelastic And Inelastic He2++He State-Selective Electron Capture, V. D. Irby, Timothy James Gay, John T. Park, S. W. Bross, A. D. Gaus Jan 1994

Superelastic And Inelastic He2++He State-Selective Electron Capture, V. D. Irby, Timothy James Gay, John T. Park, S. W. Bross, A. D. Gaus

Physics Faculty Research & Creative Works

Experimental studies have been made of super elastic and inelastic collision processes involved in the state-selective single-electron capture reaction He2+3+He (1 1S)3He+(n)+He+(n), where n and n are the final principal quantum-number states of the collision products. Total cross sections have been measured at projectile energies of 15, 30, and 45 keV/u, by examining the energy loss-gain of the fast He+3 product ions, for the super elastic n=n=1 channel, and for the sum of the inelastic n=2, n=1 and n=1, n=2 states. Measurements are also presented for Ne and Ar targets. © 1994 The American Physical Society.

Go to article

Low-Energy Electrons And Their Dynamical Correlation With Recoil Ions For Single Ionization Of Helium By Fast, Heavy-Ion Impact, R. Moshammer, J. Ullrich, M. Unverzagt, W. Schmidt, P. Jardin, Ronald E. Olson, R. Mann, R. Dörner, V. Mergel, U. Buck, H. Schmidt-Böcking Jan 1994

Low-Energy Electrons And Their Dynamical Correlation With Recoil Ions For Single Ionization Of Helium By Fast, Heavy-Ion Impact, R. Moshammer, J. Ullrich, M. Unverzagt, W. Schmidt, P. Jardin, Ronald E. Olson, R. Mann, R. Dörner, V. Mergel, U. Buck, H. Schmidt-Böcking

Physics Faculty Research & Creative Works

Helium single ionization by 3.6 me V/u Ni24+ impact was explored in a kinematically complete experiment by combining a high-resolution recoil-ion momentum spectrometer with a novel 4 low-energy electron analyzer. More than 90% of the "soft electrons" (Ee50 eV) are ejected in the forward direction in agreement with classical-trajectory Monte Carlo predictions. The electron longitudinal momentum is not balanced by the longitudinal momentum change of the projectile but mainly by the backwards recoiling He1+ ion. Energy losses of the 0.2 GeV projectiles as small as EPEP=3.4x10-7 are observable. © 1994 The American Physical Society.

Go to article

Modelling Sun-Aligned Polar Cap Arcs, D. J. Crain, Jan Josef Sojka, Robert W. Schunk, Lie Zhu Jan 1994

Modelling Sun-Aligned Polar Cap Arcs, D. J. Crain, Jan Josef Sojka, Robert W. Schunk, Lie Zhu

All Physics Faculty Publications

We present results of a new model of the time-dependent ionospheric response to a generalized steady state Sun-aligned (SA) arc structure. The thermal and plasma structure of a “prototype” arc is compared to the general features of observed SA arcs. We find that the general features of electron density, Ne , electron temperature, Te , and ion temperature, Ti , are determined by the distribution of the particle precipitation and E × B convection associated with the SA arc. The model results are extended to predict the possible variation of Ne, Te , and …

Go to article

Patches In The Polar Ionosphere: Ut And Seasonal Dependence, Jan Josef Sojka, M. D. Bowline, Robert W. Schunk Jan 1994

Patches In The Polar Ionosphere: Ut And Seasonal Dependence, Jan Josef Sojka, M. D. Bowline, Robert W. Schunk

All Physics Faculty Publications

The seasonal and UT dependencies of patches in the polar ionosphere are simulated using the Utah State University time dependent ionospheric model (TDIM). Patch formation is achieved by changing the plasma convection pattern in response to temporal changes in the interplanetary magnetic field (IMF) By component during periods of southward IMF. This mechanism redirects the plasma flow from the dayside high-density region, which is the source of the tongue of ionization (TOI) density feature, through the throat and leads to patches, rather than a continuous TOI. The model predicts that the patches are absent at winter solstice (northern hemisphere) …

Go to article

Ionospheric Response To The Sustained High Geomagnetic Activity During The March '89 Great Storm, Jan Josef Sojka, Robert W. Schunk, W. F. Denig Jan 1994

Ionospheric Response To The Sustained High Geomagnetic Activity During The March '89 Great Storm, Jan Josef Sojka, Robert W. Schunk, W. F. Denig

All Physics Faculty Publications

A simulation was conducted to model the high-latitude ionospheric response to the sustained level of high geomagnetic activity for the great magnetic storm period of March 13-14, 1989. The geomagnetic and solar activity indices and the DMSP F8 and F9 satellite data for particle precipitation and high-latitude convection were used as inputs to a time-dependent ionospheric model (TDIM). The results of the TDIM were compared to both DMSP plasma density data and ground-based total electron content (TEC) measurements for the great storm period as well as with earlier storm observations. The comparisons showed that the overall structure of the high-latitude …

Go to article

Effect Of High Latitude Ionospheric Convection On Sun-Aligned Polar Caps, Jan Josef Sojka, Lie Zhu, D. J. Crain, Robert W. Schunk Jan 1994

Effect Of High Latitude Ionospheric Convection On Sun-Aligned Polar Caps, Jan Josef Sojka, Lie Zhu, D. J. Crain, Robert W. Schunk

All Physics Faculty Publications

A coupled magnetospheric-ionospheric (M-I) MHD model has been used to simulate the formation of Sun-aligned polar cap arcs for a variety of interplanetary magnetic field (IMF) dependent polar cap convection fields. The formation process involves launching an Alfvén shear wave from the magnetosphere to the ionosphere where the ionospheric conductance can react self-consistently to changes in the upward currents. We assume that the initial Alfvén shear wave is the result of solar wind-magnetosphere interactions. The simulations show how the E region density is affected by the changes in the electron precipitation that are associated with the upward currents. These changes …

Go to article

Photoemission Measurement Of Equilibrium Segregation At Gesi Surfaces, J. E. Rowe, D. Mark Riffe, G. K. Wertheim, J. C. Bean Jan 1994

Photoemission Measurement Of Equilibrium Segregation At Gesi Surfaces, J. E. Rowe, D. Mark Riffe, G. K. Wertheim, J. C. Bean

All Physics Faculty Publications

Photoemission spectroscopy is used to demonstrate that Ge segregates to the first atomic layer of Ge0.5Si0.5(100)2×1 and that the second layer is predominantly Si. Comparison of the resolved signals from the dimer atoms of the reconstructed (100)2×1 surfaces of Ge, Si, and equiatomic Ge‐Si alloy shows that the surface layer of the alloy is extremely Ge rich and the second layer is occupied mainly by Si atoms. This result is in good agreement with theoretical predictions.

Go to article

Ionospheric Response To Traveling Convection Twin Vortices, Robert W. Schunk, Lie Zhu, Jan Josef Sojka Jan 1994

Ionospheric Response To Traveling Convection Twin Vortices, Robert W. Schunk, Lie Zhu, Jan Josef Sojka

All Physics Faculty Publications

Traveling convection twin vortices have been observed for several years. At ionospheric altitudes, the twin vortices correspond to spatially localized, transient structures embedded in a large‐scale background convection pattern. The convection vortices are typically observed in the morning and evening regions. They are aligned predominantly in the east‐west direction and have a horizontal extent of from 500–1000 km. Associated with the twin vortices are enhanced electric fields, particle precipitation, and an upward/downward field‐aligned current pair. Once formed, the twin vortex structures propagate in the tailward direction at speeds of several km/s, but they weaken as they propagate and only last …

Go to article

Theoretical Study Of Polar Cap Arcs: Time-Dependent Model And Its Applications, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain Jan 1994

Theoretical Study Of Polar Cap Arcs: Time-Dependent Model And Its Applications, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain

All Physics Faculty Publications

A time-dependent theoretical model of polar cap arcs developed during the Coupling, Energetics, and Dynamics of Atmospheric Regions/High-Latitude Plasma Structures (CEDAR/HLPS) campaigns in the past two years is briefly described. In the model the electrodynamics of the polar cap arcs are treated self-consistently in the frame of the coupled magnetosphere-ionosphere system. The preliminary simulation results of the temporal evolution and spatial structure of the polar cap arcs for both winter and summer conditions are presented. The model can be used to conduct both the model-observation study of specific features of the polar cap arcs and the quantitative theoretical study of …

Go to article

Model Study Of Multiple Polar Cap Arcs: Occurrence And Spacing, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain Jan 1994

Model Study Of Multiple Polar Cap Arcs: Occurrence And Spacing, Lie Zhu, Jan Josef Sojka, Robert W. Schunk, D. J. Crain

All Physics Faculty Publications

A new scenario for the formation of multiple polar cap arcs is proposed based on the results from a time‐dependent electrodynamic model of polar cap arcs developed by Zhu et al. [1993]. The results suggest that the appearance of multiple polar cap arcs may not be due to multiple structures in the magnetospheric source region, but instead, may primarily be determined by the coupled magnetosphere‐ionosphere system in which the ionosphere plays an active role. It was found that with the same magnetospheric driver, a strong ionospheric background convection and an ionospheric background Hall conductance in the range of from 0.5 …

Go to article

Magnetospheric Shortcomings In Ionospheric-Magnetospheric Coupling: An Ionospheric Perspective, Jan Josef Sojka Jan 1994

Magnetospheric Shortcomings In Ionospheric-Magnetospheric Coupling: An Ionospheric Perspective, Jan Josef Sojka

All Physics Faculty Publications

The ionosphere, on a global scale, is reasonably well understood from a climatology perspective. However, the storm dynamics of the ionosphere are not fully understood. This partly arises from the complex response function of the Thermosphere-Ionosphere(T-I) system but also from the uncertainty in the space and time dynamics of the magnetospheric inputs to the ionosphere. In the context of M-I coupling, the ionosphere responds to magnetospheric electrodynamic forcing by altering the conductivity in the ionosphere and by plasma transport. Phenomenologically,we understand how to let the ionospheric conductivity evolve in response to local precipitation and how to transport plasma in the …

Go to article

Fluid Dynamics Model Of Data Acquisition And Date Analysis For High-Energy Physics, Charles M. Byrd, Christine A. Byrd, Wilson H. Howe, W. J. Braithwaite Jan 1994

Fluid Dynamics Model Of Data Acquisition And Date Analysis For High-Energy Physics, Charles M. Byrd, Christine A. Byrd, Wilson H. Howe, W. J. Braithwaite

Journal of the Arkansas Academy of Science

No abstract provided.

Go to article

Using The Cern Program-Library Graphics And Interactive Data Display, Morgan T. Burks, Wilson H. Howe, Christine A. Byrd, Wilfred J. Braithwaite Jan 1994

Using The Cern Program-Library Graphics And Interactive Data Display, Morgan T. Burks, Wilson H. Howe, Christine A. Byrd, Wilfred J. Braithwaite

Journal of the Arkansas Academy of Science

Small scale Monte Carlo programming is growing rapidly due to the ease with which complex problems may be formulated by any programmer. These programmers may choose to exploit graphics and interactive displays available in the program library developed and maintained by CERN (the Center for European Nuclear Research). This paper outlines the use of graphics and interactive data display features of the CERN program library, developed for visualizing simulated data events in particle detectors. One example uses GEANT, CERN's Monte Carlo modeling program, to simulate 300 MeV/c protons incident on a silicon slab. Display packages for GEANT are available both …

Go to article

Efficient Timestamp Input And Output, Curtis Dyreson, Richard T. Snodgrass Jan 1994

Efficient Timestamp Input And Output, Curtis Dyreson, Richard T. Snodgrass

Curtis Dyreson

In this paper we provide efficient algorithms for converting between the internal form of a timestamp, and various external forms, principally character strings specifying Gregorian dates. We give several algorithms that explore a range of time and space tradeoffs. Unlike previous algorithms that explore a range of time and space tradeoffs. Unlike previous algorithms, those discussed here have a constant time cost over a greatly extended range of timestamp values. These algorithms are especially useful in operating systems and in database management systems.

Go to article

Comparison Between Calculatedand Observed F-Region Density Profiles At Jicamarca, Peru, A. J. Preble, D. N. Anderson, Bela G. Fejer, P. H. Doherty Jan 1994

Comparison Between Calculatedand Observed F-Region Density Profiles At Jicamarca, Peru, A. J. Preble, D. N. Anderson, Bela G. Fejer, P. H. Doherty

Bela G. Fejer

Electron density profiles and isodensity contours derived from Jicamarca incoherent scatter radar observations in Peru for October 1–2, 1970, are compared in detail with results from the Phillips Laboratory global theoretical ionospheric model. This model solves the ion continuity equation for O+ concentration through production, loss, and transport of ionization. The primary factor controlling the peak plasma density at Jicamarca is the vertical E×B drift, which drives the ionization upward during the day and downward at night. When we use the measured drift in the model, we achieve excellent results with the measured electron density profiles. We illustrate the sensitivity …

Go to article

Nanoscale Patterning And Oxidation Of H-Passivated Si(100)-2x1 Surfaces With An Ultrahigh Vacuum Scanning Tunneling Microscope, J. W. Lyding, T. -C. Shen, J. S. Hubaceck, J. R. Tucker, G. C. Abeln Jan 1994

Nanoscale Patterning And Oxidation Of H-Passivated Si(100)-2x1 Surfaces With An Ultrahigh Vacuum Scanning Tunneling Microscope, J. W. Lyding, T. -C. Shen, J. S. Hubaceck, J. R. Tucker, G. C. Abeln

T. -C. Shen

Nanoscale patterning of the hydrogen terminated Si(100)‐2×1 surface has been achieved with an ultrahigh vacuum scanning tunneling microscope.Patterning occurs when electrons field emitted from the probe locally desorb hydrogen, converting the surface into clean silicon. Linewidths of 1 nm on a 3 nm pitch are achieved by this technique. Local chemistry is also demonstrated by the selective oxidation of the patterned areas. During oxidation, the linewidth is preserved and the surrounding H‐passivated regions remain unaffected, indicating the potential use of this technique in multistep lithography processes.

Go to article

A Relativistic Model Of Pion Nucleon Scattering And Pion Photoproduction On A Single Nucleon, Yohanes Surya Jan 1994

A Relativistic Model Of Pion Nucleon Scattering And Pion Photoproduction On A Single Nucleon, Yohanes Surya

Dissertations, Theses, and Masters Projects

Pion nucleon scattering is described by a manifestly covariant wave equation in which the pion is restricted to its mass-shell. The kernel of the equation includes nucleon (N), Roper (N*), delta ({dollar}\Delta{dollar}) and {dollar}D\sb{lcub}13{rcub}{dollar} poles, with their corresponding crossed pole terms approximated by contact interactions, and contact {dollar}\sigma{dollar}- and {dollar}\rho{dollar}-like exchange terms. The {dollar}\pi NN{dollar} vertex is treated as a mixture of {dollar}\gamma\sp5{dollar} and {dollar}\gamma\sp\mu\gamma\sp5{dollar} coupling, with a mixing parameter {dollar}\lambda{dollar} chosen so that the dressed nucleon pole will be unshifted by the interaction. Chiral symmetry is maintained at threshold. The resonance contributions are fully unitarized by the equation, with …

Go to article

Clean Ultrahigh Vacuum System With Single-Structure Diffusion Pumps, Timothy J. Gay, M. C. Fritts, E. R. Mell, M. T. Sieger Jan 1994

Clean Ultrahigh Vacuum System With Single-Structure Diffusion Pumps, Timothy J. Gay, M. C. Fritts, E. R. Mell, M. T. Sieger

Physics Faculty Research & Creative Works

A practical example of the use of single-structure diffusion pumping groups in an experiment requiring hydrocarbon-free, ultrahigh vacuum is presented. With the use of proper vacuum procedures and careful foreline design and operation, but with no exotic hardware or liquid nitrogen, we have demonstrated that such a pump could provide vacuum that was "clean," i.e., which had no residual pump-oil contamination to a partial pressure below 10 -8 mbar. Their use is thus compatible, at least in peripheral vacuum chambers, with standard "UHV-surface science" processes. We discuss our vacuum system in detail, and present a review of the literature on …

Go to article

Anisotropy Effects In Electron Capture By O6+ From Aligned Na*(3p), S. Schippers, A. R. Schlatmann, W. P. Wiersema, R. Hoekstra, R. Morgenstern, Ronald E. Olson, J. Pascale Jan 1994

Anisotropy Effects In Electron Capture By O6+ From Aligned Na*(3p), S. Schippers, A. R. Schlatmann, W. P. Wiersema, R. Hoekstra, R. Morgenstern, Ronald E. Olson, J. Pascale

Physics Faculty Research & Creative Works

We report results of one electron capture by highly charged ions colliding with laser excited aligned Na*(3p). The O vi(10→8) photon emission cross section after electron capture by the O6+ projectile is measured in the collision energy range 2-8 keV/amu. Effects of the Na*(3p) orbital alignment on the) O vi(10→8) emission are observed and found to be "reversed" as compared to the He2+→Na*(3p) collision system. Classical trajectory Monte Carlo calculations agree with the measured data and indicate that capture to states with n>10, contributing to the O vi(10→8) emission via cascades, plays a crucial role in the alignment cross …

Go to article

Multinucleon Effects In Muon Capture On ³He At High Energy Transfer, S. E. Kuhn, W. J. Cummings, G. E. Dodge, S. S. Hanna, B. H. King, Y. M. Shin, J. G. Congleton, R. Helmer, R. B. Schubank, N. R. Stevenson, U. Wienands, Y. K. Lee, G. R. Mason, B. E. King, K. S. Chung, J. M. Lee, D. P. Rosenzweig Jan 1994

Multinucleon Effects In Muon Capture On ³He At High Energy Transfer, S. E. Kuhn, W. J. Cummings, G. E. Dodge, S. S. Hanna, B. H. King, Y. M. Shin, J. G. Congleton, R. Helmer, R. B. Schubank, N. R. Stevenson, U. Wienands, Y. K. Lee, G. R. Mason, B. E. King, K. S. Chung, J. M. Lee, D. P. Rosenzweig

Physics Faculty Publications

Energy spectra of both protons and deuterons emitted following the capture of negative muons by 3He nuclei have been measured for energies above 15 MeV. A limited number of proton-neutron pairs emitted in coincidence were also observed. A simple plane wave impulse approximation (PWIA) model calculation yields fair agreement with the measured proton energy spectra, but underpredicts the measured rate of deuteron production above our energy threshold by a large factor. A more sophisticated PWIA calculation for the two-body breakup channel, based on a realistic three-body wave function for the initial state, is closer to the deuteron data at …

Go to article

Simplest Atomic System For Sub-Doppler Laser Cooling, R. Gupta, S. Padua, C. Xie, Herman Batelaan, Harold Metcalf Jan 1994

Simplest Atomic System For Sub-Doppler Laser Cooling, R. Gupta, S. Padua, C. Xie, Herman Batelaan, Harold Metcalf

Department of Physics and Astronomy: Faculty Publications

Sub-Doppler laser cooling requires optical pumping among differently light-shifted ground-state sublevels. We describe a study of the simplest possible angular-momentum configuration that permits all sub-Doppler cooling phenomena. The Jg = 1 ⟹ Je = 0 angular-momentum configuration shows recoil-limited cooling in the two most well-known types of polarization gradient, magnetically induced laser cooling, velocity-selective resonances, transient cooling, and velocity-selective population trapping.

Go to article

Reflection High-Energy Electron-Diffraction Study Of Surface Disorder And Anomalous Expansion Of Pb(100), D. Tang, H. E. Elsayed-Ali Jan 1994

Reflection High-Energy Electron-Diffraction Study Of Surface Disorder And Anomalous Expansion Of Pb(100), D. Tang, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

The temperature-dependent surface structural behavior of Pb(100) is studied using reflection high-energy electron diffraction. Anomalous surface expansion for temperatures between room temperature to about 500 K is observed. A high density of surface vacancies appears at temperatures above ~ 500 K. © 1994 The American Physical Society.

Go to article

First Prev Next Last