Digital Commons Network^™

Computational Fluid Dynamics In Small Airway Models Of The Human Lung, G. Burnside, J. R. Hammersley, Rama N. Reddy, B. Catlin

Journal of the Arkansas Academy of Science

The promise of gene replacement therapy for cystic fibrosis, the administration of drugs via inhalation therapy, and die deposition location of man-made airborne particulates all involve a more complete understanding of the fluid dynamics in the human lung. Flow in the larger airways may be measured through life-sized models directly, but the airways in the peripheral lung are too small and the flows are too complex to be studied in this manner. Computational models can be developed which will accurately represent both the geometric nature of the central airways and the fluid dynamics with in them. Two-dimensional and three-dimensional models …

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 …

Modal Properties And Spontaneous Emission Factor In Unstable-Resonator Semiconductor Lasers, Gang Yao

Dissertations, Theses, and Capstone Projects

An experimental study has been carried out on the spectral, modal, and dynamical properties of a monolithic unstable-resonator semiconductor laser. Due to the large loss and the non-power-orthogonal nature of the transverse and longitudinal modes in the unstable resonator, the spontaneous emission factor, defined as the ratio of the power of the spontaneous emission entering the lasing mode to the total power of the spontaneous emission, is much larger than that of a regular Fabry-Perot cavity of the same dimension. The large spontaneous emission factor has profound effects on the lasing properties. For a 100-{dollar}\mu{dollar}m-wide and 500-{dollar}\mu{dollar}m-long stripe-geometry unstable resonator …

A Simple Description Of Coherence, William Moebs, Jeff Sanny

Physics Faculty Works

No abstract provided.

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 …

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 J_g = 1 ⟹ J_e = 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.

Molecular-Dynamics Simulations Of Some Baxf4 Compounds, John Flocken, Z. Mo, Wai-Ning Mei, John R. Hardy, Dorian Hatch

John R. Hardy Papers

We have carried out molecular-dynamics simulations on BaXF₄ compounds, where X is Mg, Mn, or Zn. Ab initio potentials, with no adjustable parameters, were used to obtain short-range interactions between ion pairs. We found a polar ground-state structure which is in agreement with the A2₁am space group reported experimentally. We were able to reverse polarization in BaMgF₄ at high temperatures, using large fields, but were unable to reverse polarization in the other compounds. The second-order phase transition in the Mn compound at 250 K was reproduced. We believe this to be the first extension of …

Survey Of Cellular Radiosensitivity Parameters, Robert Katz, Rashidah Zachariah, Francis A. Cucinotta, Chunxiang Zhang

Robert Katz Publications

A model of the formation of particle tracks in emulsion has been extended through the use of biological target theory to formulate a theory of the response of biological cells and molecules of biological importance to irradiation with energetic heavy ions. For this purpose the response to γ rays is represented by the single-hit, multi-target model with parameters m and D₀, while additional parameters κ (or a₀) and σ₀ are required to represent the size of internal cellular targets and the effective cross-sectional area of the cell nucleus, respectively, for heavy-ion bombardments. For one-or-more-hit detectors, …

Ultrashort Ultraviolet Free-Electron Lasers, Donald Umstadter, L. H. Yu, E. Johnson, D. Li

Donald Umstadter Publications

In this work we combine elements of chirped pulse amplification (CPA) techniques, now familiar in solid-state lasers, with an amplifier based upon a seeded free-electron laser (FEL), The resulting device would produce amplified pulses of unprecedented brevity at wavelengths shorter than can be currently obtained by any tunable laser system. We use a subharmonically seeded FEL to illustrate the concept. Radiation from a Ti:sapphire laser is frequency-tripled and stretched optically to provide a coherent seed pulse for the FEL. When coupled to an electron beam inside a magnetic wiggler, the seed radiation introduces an additional energy modulation on the electron …

A Covariant Description Of The Deuteron, J. W. Van Orden

Physics Faculty Publications

An introduction to the use of Bethe-Salpeter and quasipotential equations in the description of electron scattering from the deuteron is provided. The basic formalism and many technical issues are introduced in the context of a simple scalar theory. Results for bound-state wave functions and scattering phases shifts for a variety of quasipotential prescriptions are presented and qualitative characteristics of these solutions are discussed. The elastic form factors for the bound state in this model are calculated using the spectator or Gross equation. The calculations are then extended to account for the complexities associated with nucleon spin and results are presented …

Microscopic Simulation Of Dilute Gases With Adjustable Transport Coefficients, Alejandro Garcia, F. Baras, M. Malek Mansour

Faculty Publications

The Bird algorithm is a computationally efficient method for simulating dilute gas flows. However, due to the relatively large transport coefficients at low densities, high Rayleigh or Reynolds numbers are difficult to achieve by this technique. We present a modified version of the Bird algorithm in which the relaxation processes are enhanced and the transport coefficients reduced, while preserving the correct equilibrium and nonequilibrium fluid properties. The present algorithm is found to be two to three orders of magnitude faster than molecular dynamics for simulating complex hydrodynamical flows.

Dilaton Black Holes With Electric Charge, Malik Rakhmanov

Physics & Astronomy Faculty Publications

New static spherically symmetric solutions of the Einstein-Maxwell gravity with the dilaton field are found. The solutions correspond to black holes and naked singularities. In addition to mass and electric charge these solutions are labeled by a new parameter, the dilaton charge of the black hole. Depending on the values of electric and dilaton charges there are different types of solutions. The solutions exhibit a new type of a symmetry. Namely one solution transforms into another when the mass and the dilaton charge are interchanged. We also found that there is a finite interval of values of electric charge for …

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 …

Dielectric Response Of Ferroelectric Liquid Crystal Cells, Yuri Panarin, Huan Xu, Seamus Mac Lughadha, Jagdish Vij

Articles

No abstract provided.

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 …

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.

Multigrid Acceleration Of Time-Dependent Solutions Of Navier-Stokes Equations, Sarafa Oladele Ibraheem

Mechanical & Aerospace Engineering Theses & Dissertations

Recent progress in Computational Fluid Dynamics is encouraging scientists to look at fine details of flow physics of problems in which natural unsteady phenomena have hitherto been neglected. The acceleration methods that have proven very successful in steady state computations can be explored for time dependent computations. In this work, an efficient multigrid methods is developed to solve the time-dependent Euler and Navier-Stokes equations. The Beam-Warming ADI method is used as the base algorithm for time stepping calculations. Application of the developed algorithm proved very efficient in selected steady and unsteady test problems. For instance, the inherent unsteadiness present in …

Development Of Strength Theories For Random Fiber Composites, Victor Giurgiutiu

Faculty Publications

A ressessment of existing theories for calculating the strength of random and quasi-random fiber composites is presented. Fundamental aspects regarding the physical model, macromechanics analysis, fiber distribution functions, generalized failure criterion, and progressive versus sudden failure models are covered first. Progressive ductile failure, progressive brittle failure, and sudden brittle failure are treated in detail. In each case, the original theory is briefly reviewed, and then its extensions accompanied by numerical examples are presented. Several limitations originally imposed by Hahn, such as the monotonically nonincreasing requirement on the failure strain curve, are lifted and the mathematical formulations are generalized. Some common …

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 …

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 …

Production And Extraction Of Polarized Electrons From An Optically Pumped Helium Discharge, Raymond James Vandiver

Doctoral Dissertations

"Polarized electron sources are needed to study the spin dependent processes in atomic and molecular systems. This area of physics has enjoyed much success in the past decade due to the development of polarized electron sources of high electron polarization and current. We have investigated the production and extraction of polarized electrons from an optically pumped helium discharge.

We have directly extracted electrons with polarizations between 6% and 7% at currents greater than 200 µA from a helium DC discharge where the helium 2³S₁ metastable atoms are optically pumped to nearly 100% polarization. These high metastable polarizations …

Temperature-Based Predictions Of Wind Speed, Relative Humidity, Rainfall, Absolute Humidity, Vapour Pressure And Dew Point, E. C. Njau

Tanzania Journal of Science

We derive from first principles analytical expressions that give each of the following meteorological parameters in terms of (air) temperature: wind speed, relative humidity, rainfall, absolute humidity, vapour pressure and dew point. The practical validity of these expressions has been clearly ascertained using past meteorological records. Since air temperature is one of the easiest meteorological parameters to predict (Njau, 1991, 1994), the derived analytical expressions are simple and convenient tools by means of which wind speed, absolute humidity, rainfall, relative humidity, vapour pressure and dew point may be predicted. In this paper we demonstrate and explain how the derived analytical …

Aerosol Composition As A Function Of Particles Size, Y. I. A. Koleleni, R. Van Grieken

Tanzania Journal of Science

Analysis of air particulate matter for various particle diameters 0.25-0.5 mm: 0.5-1 mm; 1-2 mm; 2-4 mm; and 4-8 were performed to investigate the contribution of both fine and coarse particles in environmental content. The abundance in the highest percentage concentration relative to particle diameters has shown interesting diagonal pattern with most of the elements ranging within 0-2%; 0.20%; 20-40%; 40-70%: and 70-100% respectively for different particle sizes. For the lowest percentage concentration range it is within 0-20%. In general the sum of elemental concentration provides a significant important result as far as pollution studies are concerned.

Meteostat Wefax Image Data Acquisition From The Weather Satellite Receiver, A. J. Mwambela, A. Purvis

Tanzania Journal of Science

This paper describe the development and implementation of satellite image data acquisition interface board using a programmable peripheral interface device, the intel 8255 PPI, to be used between a secondary data weather satellite receiver and an IBM PC. Brief details of both hardware and software design implementation, to transfer and store data are given.

A Theoretical Investigation Of The Geometries, Vibrational Frequencies, And Binding Energies Of Several Mixed Alkali Halide Dimers, Robert J. Cave, Ian Ono '94

All HMC Faculty Publications and Research

Results are presented from ab initio calculations on several mixed alkali halide dimers made up of Li, Na, F, and Cl. All of the dimers are investigated at the restricted Hartree–Fock level to provide ab initio estimates of geometries, vibrational frequencies, and binding energies. The dimer LiNaF2 is then treated using a variety of basis sets at the Hartree–Fock level, as well as at correlated levels (second‐order Møller–Plesset and coupled‐cluster singles and doubles) to examine the sensitivity of the calculations to use of higher levels of theory. The results are then compared to the experimental data available for the LiNaF2 …

Evidence For Day-To-Night Ion Transport At Low Solar Activity In The Venus Pre-Dawn Ionosphere, J. F. Brannon, Jane L. Fox, H. S. Porter

Physics Faculty Publications

Periapsis of the Pioneer Venus spacecraft dropped below 180 km on August 28, 1992 near midnight, and 42 orbits of low altitude data at moderately low solar activity in the pre-dawn sector were obtained before contact was lost to the spacecraft in October, 1992. Through a combination of analysis of data from the PV orbiter ion mass spectrometer (OIMS) and modeling, we consider here what can be learned about the relative importance of plasma transport from the dayside and electron precipitation in maintaining the nightside ionosphere during the re-entry period. In particular, we examine here the atomic ion density profiles. …

Final State Distributions For Electron Capture From Orientated Rydberg Atoms, Jee-Ching Wang, Ronald E. Olson

Chemical and Biochemical Engineering Faculty Research & Creative Works

Final state nim distributions are studied for electron capture from orientated circular Rydberg atoms. Strong orientation effects are found for all quantum numbers at collision speeds comparable to the electron orbital speed. Predominant population of large m states is observed when the plane of the circular orbit is nearly perpendicular to the incident direction of the projectile. The Ini distributions show structures due to quasi-Thomas scattering even at low relative collision velocities. © 1993 IOP Publishing Ltd.

Neutron Reflection Interferometry: Physical Principles Of Surface Analysis With Phase Information, Vladimir Gudkov, G. I. Opat, A. G. Klein

Faculty Publications

It is shown that the analysis of surface layers by neutron reflection interferometry is considerably enhanced by performing the reflectometry with phase information. We discuss two methods of providing such information. One method involves physically adding an extra reference layer, whose amplitude and phase are known theoretically. The other uses the Lloyd's mirror configuration, in which a directly propagating ray that interferes with the reflected ray supplies the phase information. The methods have much in common with holography.

A Random Wave Method For Detecting Phase Imbalance In A Coherent Radar Receiver, Zhenni Wang, Alexander Kostinski

Department of Physics Publications

The question of monitoring the angle between the in-phase (I) and quadrature (Q) channels of a coherent radar receiver is considered in this paper. Random interference-type scattering (e.g., rain echo) is assumed so that the received signal is a random phasor sum. It is also assumed that I and Q voltages have a (90 + ϕ₀) phase difference. The effects of nonzero phase imbalance ϕ₀ on the I and Q statistics are examined. Joint I and Q as well as amplitude and phase probability distributions are derived. It is shown that the cross-correlation …

Far-Ultraviolet Stellar Photometry: A Field In Orion, Edward G. Schmidt, George R. Carruthers

Edward Schmidt Publications

Far-ultraviolet photometry for 625 objects in Orion is presented. These data were extracted from electrographic camera images obtained during sounding rocket flights in 1975 and 1982. The 1975 images were centered close to the belt of Orion while the 1982 images were centered ~9° further north. One hundred and fifty stars fell in the overlapping region and were observed with both cameras. Sixty-eight percent of the objects were tentatively identified with known stars using the SIMBAD database while another 24% are blends of objects too close together to separate with our resolution. As in previous studies, the majority of the …