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Articles 33661 - 33690 of 36552

Full-Text Articles in Physical Sciences and Mathematics

The Decomposition Of [Mn(Co)5]2(Μ-Sih2), G.T. Stauf, Peter A. Dowben, K. Emrich, W. Hirschwald, N.M. Boag May 1989

The Decomposition Of [Mn(Co)5]2(Μ-Sih2), G.T. Stauf, Peter A. Dowben, K. Emrich, W. Hirschwald, N.M. Boag

Peter Dowben Publications

The prospect of using chemical vapor deposition to deposit mixed metals and silicides from a single source compound is attractive but largely uninvestigated. Studies of decomposition energies of such compounds are nearly nonexistent. One such compound which has successfully been used to make a silicide coating is [Mn(CO)5 12 (μ-SiH2). We have used electron impact mass spectroscopy, photoionization mass spectroscopy, and photoabsorption to determine bond energies within this compound. The combination of methods allows a high degree of confidence in the resultant ionization and fragment appearance potentials. Some possible mechanisms of decomposition are discussed. A complete …

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The Influence Of Crystallographic Order Upon The Electronic Structure Of Thin Mercury Overlayers, Peter A. Dowben, M. Onellion, Shikha Varma, Y.J. Kime, J.L. Erskine May 1989

The Influence Of Crystallographic Order Upon The Electronic Structure Of Thin Mercury Overlayers, Peter A. Dowben, M. Onellion, Shikha Varma, Y.J. Kime, J.L. Erskine

Peter Dowben Publications

Thin ( 1-7 monolayer) well-ordered, disordered, and liquid Hg overlayers on Ag(100) have been investigated with angle resolved photoemission and low-energy electron diffraction. The well-ordered overlayers exhibit new electronic states as a result of the strained, cubic, overlayer crystallographic structure. The new electronic states depend upon the long-range crystallographic order of the overlayer, not simply the local crystallographic symmetry. The photoemission cross section and branching ratio of the 5d mercury states depends on the overlayer long-range crystallographic order and cannot be explained by photoelectron diffraction.

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Preparation Of High TCTl-Ba-Ca-Cu-O Thin Films By Pulsed Laser Evaporation And Tl2O3 Vapor Processing, B. Johs, D. Thompson, N.J. Ianno, John A. Woollam, Sy_Hwang Liou, A.M. Hermann, Z.Z. Sheng, W. Kiehl, O. Shams, X. Fei, L. Sheng, Y.H. Liu May 1989

Preparation Of High TCTl-Ba-Ca-Cu-O Thin Films By Pulsed Laser Evaporation And Tl2O3 Vapor Processing, B. Johs, D. Thompson, N.J. Ianno, John A. Woollam, Sy_Hwang Liou, A.M. Hermann, Z.Z. Sheng, W. Kiehl, O. Shams, X. Fei, L. Sheng, Y.H. Liu

Sy-Hwang Liou Publications

Tl-Ba-Ca-Cu-O superconducting thin films with zero-resistance temperatures up to 115 K have been prepared using a Tl2O3 vapor process on Ba-Ca-Cu-O precursor thin films. The Ba-Ca-Cu-O thin films were made by laser deposition on Y-stabilized ZrO2 substrates. This technique minimizes problems caused by the toxicity of Tl2 O3, and its subsequent decomposition to the volatile and toxic Tl2 O upon heating. Therefore, it may have practical application in the fabrication of high Tc Tl-Ba-Ca-Cu-O superconducting thin-film devices.

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Shake-Off Measurements Of Electron-Ion-Scattering Phase Shifts, J. Greg Story, William E. Cooke May 1989

Shake-Off Measurements Of Electron-Ion-Scattering Phase Shifts, J. Greg Story, William E. Cooke

Physics Faculty Research & Creative Works

Continuum electrons are produced in a specific l state with high-energy resolution using shake-off photoionization. This process is well characterized, so that the photoionization signal is an accurate measurement of the difference between the continuum electrons wave-function phase and that produced by a hydrogenic interaction. Measurements are reported showing the phase of a Ba++e- in a d wave, in cases where it is well behaved, and in cases where doubly excited resonances produce rapid phase variations.

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An Alternative Approach To The Teaching Of Rotational Dynamics, James A. Lock May 1989

An Alternative Approach To The Teaching Of Rotational Dynamics, James A. Lock

Physics Faculty Publications

An alternative approach to the stability of torque-free rotations and to top nutation that emphasizes conservation laws and physical reasoning is examined. It is felt that such an approach, which is largely free of sophisticated mathematics, would be useful in teaching these topics in rotational motion at the introductory physics level.

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Fourier Transform Of The Multicenter Product Of 1s Hydrogenic Orbitals And Coulomb Or Yukawa Potentials And The Analytically Reduced Form For Subsequent Integrals That Include Plane Waves, Jack C. Straton May 1989

Fourier Transform Of The Multicenter Product Of 1s Hydrogenic Orbitals And Coulomb Or Yukawa Potentials And The Analytically Reduced Form For Subsequent Integrals That Include Plane Waves, Jack C. Straton

Physics Faculty Publications and Presentations

The Fourier transform of the multicenter product of N 1s hydrogenic orbitals and M Coulomb or Yukawa potentials is given as an (M+N-1)-dimensional Feynman integral with external momenta and shifted coordinates. This is accomplished through the introduction of an integral transformation, in addition to the standard Feynman transformation for the denominators of the momentum representation of the terms in the product, which moves the resulting denominator into an exponential. This allows the angular dependence of the denominator to be combined with the angular dependence in the plane waves.

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Multi-Layer Structure Of Nitrogen Adsorbed On Graphite, S. K. Wang, J. C. Newton, R. Wang, H. Taub, John R. Dennison, H. Shechter May 1989

Multi-Layer Structure Of Nitrogen Adsorbed On Graphite, S. K. Wang, J. C. Newton, R. Wang, H. Taub, John R. Dennison, H. Shechter

All Physics Faculty Publications

Elastic neutron diffraction has been used to study the structure and layering of nitrogen films adsorbed on the (002) surfaces of an exfoliated graphite substrate. The neutron-diffraction pattern of the fully compressed monolayer at a coverage Θ=1.67 layers and a temperature ≲11 K which we reported earlier has been reanalyzed (unity coverage corresponds to a complete layer having the commensurate √3 × √3 structure). We now find it to be consistent with a four-sublattice pinwheel structure as well as the two-sublattice herringbone structure which we found previously. Below 11 K, we infer crystallization of the bilayer at Θ between 2.6 …

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Decay Of Molecules At Corrugated Thin Metal Films, P.T. Leung, Young Sik Kim, Thomas F. George May 1989

Decay Of Molecules At Corrugated Thin Metal Films, P.T. Leung, Young Sik Kim, Thomas F. George

Physics Faculty Publications and Presentations

The problem of the decay rate for molecules at corrugated thin metal films is considered theoretically via a classical phenomenological approach by generalization of a previous theory for a single rough surface. In particular, numerical results are worked out in detail for grating films with various possible arrangements of the two grating surfaces, and for both cases with a supported and a free-standing film. Effects due to cross coupling into the long- and short-range surface plasmons are observed, and correlations to recent experiments performed by Gruhlke, Holland, and Hall are made. It is suggested that fluorescence experiments with pulsed-laser excitations …

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Long-Range Hopping In Substitutionally Disordered Solids, Paul Ernest Parris May 1989

Long-Range Hopping In Substitutionally Disordered Solids, Paul Ernest Parris

Physics Faculty Research & Creative Works

A theoretical approach for studying charge-carrier and energy diffusion due to long-range hopping in substitutionally disordered solids is presented. Unlike some earlier theories, which invoke a pair approximation to treat back-transfer processes, the current theory makes use of the exact solution to an appropriate single-defect problemone in which long-range jumps into, out of, and between both the defect site and all other active sites in the lattice are explicitly included. From this exact solution a new long-range effective-medium theory is constructed to describe the configurationally averaged transport properties of the disordered system.

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Spectroscopy Of The 6p3/2Np States Of Barium, J. Greg Story, E. G. Yap, William E. Cooke May 1989

Spectroscopy Of The 6p3/2Np States Of Barium, J. Greg Story, E. G. Yap, William E. Cooke

Physics Faculty Research & Creative Works

The 6p3/2np states of barium have been observed for n values between 14 and 21. The energies, linewidths, and transition strengths have been measured and characterized in terms of one- and two-electron interactions, using a single-configuration approximation.

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Variational Principle For High-Order Perturbations With Application To Multiphoton Processes For The H Atom, Bo Gao, Anthony F. Starace May 1989

Variational Principle For High-Order Perturbations With Application To Multiphoton Processes For The H Atom, Bo Gao, Anthony F. Starace

Anthony F. Starace Publications

The variationally stable procedure for Nth-order perturbative-transition-matrix elements introduced by the authors [Phys. Rev. Lett. 61, 404 (1988)] is presented here in detail. Its key features are that it is noniterative, involves only two unknown functions regardless of the value of N, is stable even near intermediate-state resonances (due to the presence of energy numerators rather than energy denominators), and uses the inverse of the perturbation operator for N≥3. Explicit formulas are presented for application to high-order multiphoton processes in atomic hydrogen. Numerical results for multiphoton-ionization cross sections (for two, three, and seven photons), for the frequency dependence …

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Superlattice Modulation And Epitaxy Of Tl2Ba2Ca2Cu3O10 Thin Films Grown On Mgo And Srtio3 Substrates, C.H. Chen, M. Hong, D.J. Werder, J. Kwo, Sy_Hwang Liou, D.D. Bacon Apr 1989

Superlattice Modulation And Epitaxy Of Tl2Ba2Ca2Cu3O10 Thin Films Grown On Mgo And Srtio3 Substrates, C.H. Chen, M. Hong, D.J. Werder, J. Kwo, Sy_Hwang Liou, D.D. Bacon

Sy-Hwang Liou Publications

We compare the superlattice modulation, microstructure, and epitaxy of Tl2Ba2Ca2Cu3O10 thin films grown on MgO [100] and SrTiO3 [100] substrates by dc diode sputtering. Films grown on MgO were found to be quite clean with the c axis perpendicular to the substrate. However, no in-plane orientational relationship to the substrate was found. Films grown on SrTiO3, on the other hand, showed very good epitaxy to the substrate despite the presence of second phases. Films grown on MgO also exhibited a longer coherence length of the superlattice modulation than …

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Phase Transitions In A Driven Lattice Gas With Repulsive Interactions, K.-T. Leung, Beate Schmittmann, R. K. P. Zia Apr 1989

Phase Transitions In A Driven Lattice Gas With Repulsive Interactions, K.-T. Leung, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

We study a lattice gas with repulsive nearest-neighbor interactions driven to steady state by an external electric field E. Using Monte Carlo techniques on a two-dimensional system, we find, in the E-T plane, a line of second-order transitions joining a line of first-order ones, at a point which is probably tricritical. From a field theoretical model, we show that the operator associated with E is naively irrelevant for critical behavior. This expectation is borne out by the Monte Carlo result β=(1/8.

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Determination Of Shallow Minority-Acceptor Concentration In Multiply Doped Silicon, Gust Bambakidis, G. J. Brown Apr 1989

Determination Of Shallow Minority-Acceptor Concentration In Multiply Doped Silicon, Gust Bambakidis, G. J. Brown

Physics Faculty Publications

A method is presented, based on photothermal ionization spectroscopy (PTIS), for determining the shallow minority‐acceptor concentration in multiply doped silicon, over the concentration range 1013/cm3–1015/cm3. The method is an extension of a model developed previously for the PTIS response in a multiply doped semiconductor, which accounts for the experimentally observed change in signature, from negative to positive, of the lower‐energy lines of the deeper acceptor as the temperature is increased. It uses a calculated curve of the dependence on the shallow‐acceptor concentration of the temperature at which the change in …

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Photodissociation Of Co In The Thermosphere Of Venus, Jane L. Fox Apr 1989

Photodissociation Of Co In The Thermosphere Of Venus, Jane L. Fox

Physics Faculty Publications

Recent investigations of CO photoabsorption demonstrate that photodissociation longward of the ionization threshold at 88.5 nm occurs primarily through line absorptions rather than continuous processes. We have constructed high resolution photoabsorption cross sections for CO at rotational temperatures near 250 K from the improved data on dissociating transitions. We examine the effects of the new cross sections on the rate of solar photodissociation of CO in the thermosphere of Venus and compare the results to values obtained with the lower resolution cross sections available previously. We find that the photodissociation profile peaks slightly higher in the atmosphere and the peak …

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Electron-Electron Interactions In Transfer And Excitation In F⁸⁺ →₂ Collisions, Michael Schulz, J. P. Giese, J. K. Swenson, Sheldon Datz, Peter F. Dittner, Herbert F. Krause, Harald Schone, Charles Randy Vane, Malika Benhenni, Stephen M. Shafroth Apr 1989

Electron-Electron Interactions In Transfer And Excitation In F⁸⁺ →₂ Collisions, Michael Schulz, J. P. Giese, J. K. Swenson, Sheldon Datz, Peter F. Dittner, Herbert F. Krause, Harald Schone, Charles Randy Vane, Malika Benhenni, Stephen M. Shafroth

Physics Faculty Research & Creative Works

We have measured projectile Auger electrons emitted after collisions of H-like F with H2. The cross sections for emission of KLL, KLM, KLN, and KLO Auger electrons show maxima as a function of the projectile energy. One maximum in the KLL emission cross section is due to resonant transfer and excitation. A second maximum in the cross section for KLL emission as well as the maxima in the emission cross section for the higher-n Auger electrons are attributed to a new transfer and excitation process. This involves excitation of a projectile electron by one target electron accompanied by …

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Γ To X Transport Of Photoexcited Electrons In Type Ii Gaas/Alas Multiple Quantum Well Structures, Peter N. Saeta, John F. Federici, R. J. Fischer, Benjamin I. Greene, L. Pfeiffer, R. C. Spitzer, B. A. Wilson Apr 1989

Γ To X Transport Of Photoexcited Electrons In Type Ii Gaas/Alas Multiple Quantum Well Structures, Peter N. Saeta, John F. Federici, R. J. Fischer, Benjamin I. Greene, L. Pfeiffer, R. C. Spitzer, B. A. Wilson

All HMC Faculty Publications and Research

We report novel femtosecond time‐resolved measurements performed on staggered type II GaAs/AlAs multiple quantum well structures. Photoexcited electrons were determined to transfer from the Γ valley of the GaAs layers to the X valleys of the AlAs in 100 and 400 fs for 8‐ and 11‐monolayer‐thick GaAs samples, respectively.

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Equilibrium Polymerization On The Equivalent-Neighbor Lattice, Miron Kaufman Apr 1989

Equilibrium Polymerization On The Equivalent-Neighbor Lattice, Miron Kaufman

Physics Faculty Publications

The equilibrium polymerization problem is solved exactly on the equivalent-neighbor lattice. The Flory-Huggins entropy of mixing is exact for this lattice. We verify the discrete version of the n-vector model when n→0 is equivalent to the equal reactivity polymerization process in the whole parameter space, including the polymerized phase. The polymerization processes for polymers satisfying the Schulz distribution exhibit nonuniversal critical behavior. A close analogy is found between the polymerization problem of index r and the Bose-Einstein ideal gas in d=-2r dimensions, with the critical polymerization corresponding to the Bose-Einstein condensation.

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Electrical Response Of Superconducting Yba2Cu3O7- Δ To Light, W.S. Brocklesby, Don Monroe, A.F.J. Levi, M. Hong, Sy_Hwang Liou, J. Kwo, C.E. Rice, P.M. Mankiewich, R.E. Howard Mar 1989

Electrical Response Of Superconducting Yba2Cu3O7- Δ To Light, W.S. Brocklesby, Don Monroe, A.F.J. Levi, M. Hong, Sy_Hwang Liou, J. Kwo, C.E. Rice, P.M. Mankiewich, R.E. Howard

Sy-Hwang Liou Publications

We have studied the effect of visible and near-infrared light on the electrical properties of superconducting thin films of YBa2Cu3O7- δ . The responses we observe can all be explained in terms of light heating the film to a temperature above the superconducting transition. No evidence that the light directly affects superconductivity was found.

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Metastable Conduction States In Mo2S3: Conductivity Fluctuations, R.L. Fagerquist, Roger D. Kirby, Edgar A. Pearlstein Mar 1989

Metastable Conduction States In Mo2S3: Conductivity Fluctuations, R.L. Fagerquist, Roger D. Kirby, Edgar A. Pearlstein

Department of Physics and Astronomy: Faculty Publications

In this paper, we present the results of measurements of the frequency and temperature dependences of the electrical noise in Mo2S3. It will be seen that the frequency dependence of the noise is completely consistent with the double-well potential model for the carriers in Mo2S3 introduced in an earlier paper [Phys. Rev. B 38, 3973 (1988)]. In the earlier paper, we showed that at temperatures below 145 K, the carriers in Mo2S3 could exist in either a weakly conducting ground state or a relatively highly conducting metastable state. The conductivity …

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Mapping The Wind In The Polar Thermosphere: A Case Study Within The Cedar Program, R W. Smith, J W. Meriwether, G Hernandez, R David, Vincent B. Wickwar, O De La Beaujardiere, T L. Killeen Mar 1989

Mapping The Wind In The Polar Thermosphere: A Case Study Within The Cedar Program, R W. Smith, J W. Meriwether, G Hernandez, R David, Vincent B. Wickwar, O De La Beaujardiere, T L. Killeen

All Physics Faculty Publications

The thermosphere is that region of neutral atmosphere in which atmospheric constituents are gravitationally bound to the Earth but are barometrically distributed according to their molecular or atomic weights. Unlike the lower atmosphere, mixing processes a reweak, which allows each constituent gas to behave independently. The thermosphere begins at about 100-km-altitude and extends up to 500 km or beyond. The temperature increases with height throughout the layer, which is a stabilizing influence.

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Certain Stability Type And Integrable Two-Dimensional Hamiltonian Systems, Foek T. Hioe Mar 1989

Certain Stability Type And Integrable Two-Dimensional Hamiltonian Systems, Foek T. Hioe

Physics Faculty/Staff Publications

We present the results of applying an analytical method, using a new concept involving a periodic stability around a line of initial values, to two Hamiltonian systems with two degrees of freedom each with several parameters. By requiring the systems to have this type of stability, we have been led to known integrable cases for the systems. For one of the systems, our analysis gives six other cases, two of which turn out to be nonintegrable. The status of the remaining four cases has not been established.

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Lossless Propagation Of Optical Pulses Through N-Level Systems With Su(2) Symmetry, Foek T. Hioe Mar 1989

Lossless Propagation Of Optical Pulses Through N-Level Systems With Su(2) Symmetry, Foek T. Hioe

Physics Faculty/Staff Publications

Propagation of optical pulses through atomic media consisting of atoms with N transition levels and possessing the so-called SU(2) symmetry is studied. It is shown that there are generally N - 1 sets of conditions, each of which, when satisfied, would permit the appropriate Maxwell-Bloch equations to have a solution having the form of simultaneous different-wavelength optical solutions, so-called simulations. The first two sets of solutions were known previously, but the remaining sets are new.

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Condensation Coefficient Measurement For Water In The Umr Cloud Simulation Chamber, Donald E. Hagen, John L. Schmitt, Max B. Trueblood, John C. Carstens, Daniel R. White, Darryl J. Alofs Mar 1989

Condensation Coefficient Measurement For Water In The Umr Cloud Simulation Chamber, Donald E. Hagen, John L. Schmitt, Max B. Trueblood, John C. Carstens, Daniel R. White, Darryl J. Alofs

Physics Faculty Research & Creative Works

A systematic series of condensation coefficient measurements of water have been made using the University of Missouri-Rolla cooled-wall expansion chamber which simulates the thermodynamics of cloud. This coefficient is seen to decrease from a value near unity, at the outset of simulation, to a value in the neighborhood of 0.01 toward the end of a simulation. Final values of this coefficient are sufficiently low as to contribute significantly to the broadening of the drop-size distribution in cloud.

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Differential Cross Sections For Ejection Of Electrons From Rare Gases By 7.5- 150-Kev Protons, Wen-Qin Cheng, M. Eugene Rudd, Ying-Yuan Hsu Mar 1989

Differential Cross Sections For Ejection Of Electrons From Rare Gases By 7.5- 150-Kev Protons, Wen-Qin Cheng, M. Eugene Rudd, Ying-Yuan Hsu

M. Eugene Rudd Publications

Absolute cross sections for the ejection of electrons by ;proton impact that are differential in the angle and energy of the electrons have been measured for :helium, neon, and krypton. The primary energy ranged from 7.5 to 150 keV, the angles from 10° to 160°, and the measured energies from 1 to 550 eV. These data along with earlier data on argon are used to study the systematics of proton impact ionization of the rare gases. An analytical model is employed to correlate and systematize the cross-section differential in ejected-electron energy. For low-energy collisions the angular distribution of electrons ejected …

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One-Dimensional Trapping Kinetics At Zero Temperature, Paul Ernest Parris Mar 1989

One-Dimensional Trapping Kinetics At Zero Temperature, Paul Ernest Parris

Physics Faculty Research & Creative Works

The asymptotic decay of the survival probability is calculated for a quantum particle moving at zero temperature on a one-dimensional tight-binding chain possessing randomly placed irreversible traps of strength γ. The survival probability exhibits a decay, P(t) ~ exp(-At1/4), which is slower than that associated with a diffusing particle.

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An Analysis Of Two Unusual Reflection Caustics, James A. Lock, Judith R. Woodruff Mar 1989

An Analysis Of Two Unusual Reflection Caustics, James A. Lock, Judith R. Woodruff

Physics Faculty Publications

A reflection caustic consisting of an x or a cross surrounded by a circle was observed using two different reflector geometries. Double-glazed insulating windows that have become bowed, and circularly symmetric cookie trays and cake covers possessing two different curvatures at different distances from the symmetry axis, produce similar caustics when plane waves are incident far off-axis. For the case of the insulating windows, it was found that the concavely bowed outer pane produced the x portion of the caustic and the convexly bowed inner pane produced the circle portion. For the case of the circularly symmetric reflectors, the x …

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Optogalvanic Signals From Argon Metastables In A Rf Glow-Discharge, D. E. Murnick, R. B. Robinson, D. Stoneback, M. J. Colgan, Frank Moscatelli Feb 1989

Optogalvanic Signals From Argon Metastables In A Rf Glow-Discharge, D. E. Murnick, R. B. Robinson, D. Stoneback, M. J. Colgan, Frank Moscatelli

Physics & Astronomy Faculty Works

Laser optogalvanic (LOG) signals at 667.7, 751.5, and 696.5 nm from the 3 P 1 and 3 P 2 levels of Ar were studied at a pressure of 250 mTorr in a rf glow discharge. Signals with unexpected signs and time dependences were found. The results are interpreted as being due to radiative trapping effects and collisional mixing between resonance and metastable levels. An average electron energy of 2.1 eV is derived from modeling the data.

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Highly Oriented Tl2Ba2Ca2Cu3O10 Thin Films By Pulsed Laser Evaporation, Sy_Hwang Liou, K.D. Aylesworth, N.J. Ianno, B. Johs, D. Thompson, D. Meyer, John A. Woollam, Colleen Berry Feb 1989

Highly Oriented Tl2Ba2Ca2Cu3O10 Thin Films By Pulsed Laser Evaporation, Sy_Hwang Liou, K.D. Aylesworth, N.J. Ianno, B. Johs, D. Thompson, D. Meyer, John A. Woollam, Colleen Berry

Sy-Hwang Liou Publications

We have fabricated superconducting thin films on MgO(100) substrates with nearly pure Tl2Ba2Ca2Cu3O10 (2:2:2:3) phase using pulsed laser evaporation and post-annealing. The films had c axes perpendicular to the substrates. Superconducting films with onset temperatures of 125 K and zero resistance at 110 K were obtained. X-ray microprobe fluorescence measurements indicate that a typical composition of films is Tl0.66Ba1.77Ca1.46Cu3Oχ, which is low in Tl compared to that expected for the 2:2:2:3 phase. A typical grain size is greater than 10 µm …

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Effects Of Pollution On Critical Population Dynamics, R. Kree, B. Schaub, Beate Schmittmann Feb 1989

Effects Of Pollution On Critical Population Dynamics, R. Kree, B. Schaub, Beate Schmittmann

Beate Schmittmann

We investigate the effects of pollution on a population that is on the brink of extinction. In the vicinity of the associated critical point, the temporal scales of the population density fluctuations are found to be completely governed by the diffusive behavior of the pollution density fluctuations. Moreover, the mean value of the population density is found to vanish with a larger power-law exponent in the presence of pollution density fluctuations. Results are obtained within a renormaliza- tion-group calculation to O(ε) (ε=4-d, d being the spatial dimension).

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