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Articles 33061 - 33090 of 36554

Full-Text Articles in Physical Sciences and Mathematics

Many-Electron Radial And Angular Integrals In The Unitary-Group Approach, R. D. Kent, Gordon W. F. Drake Jan 1992

Many-Electron Radial And Angular Integrals In The Unitary-Group Approach, R. D. Kent, Gordon W. F. Drake

Physics Publications

An extension of work by Drake [Phys. Rev. A 18, 820 (1978)] to the treatment of radial and angular integrals occurring in N-electron systems is presented. It is shown that the essential results pertaining to two-electron systems adapted to Hylleraas coordinates also apply to many electrons when pairs of electrons are chosen to interact with each other in a spin-adapted basis set. These results are derived using graphical-analysis techniques in the context of the unitary-group approach. © 1992 The American Physical Society.

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Asymptotic Expansion For -Function Matrix Elements Of Helium, Gordon W. F. Drake Jan 1992

Asymptotic Expansion For -Function Matrix Elements Of Helium, Gordon W. F. Drake

Physics Publications

This paper extends the methods of asymptotic analysis extensively developed for energy-level calculations of Rydberg states to the evaluation of matrix elements of (r). All terms up to x-8 in the asymptotic potential are systematically derived from a simple perturbation expansion. The formalism is developed in a way that closely parallels that for the corresponding energy expansion. The results are comparable in accuracy to the energy itself. Detailed numerical comparisons with high-precision variational calculations are presented for the states of helium up to nL=10K (i.e., L=7). For L5, the accuracy of the asymptotic expansion exceeds what has been achieved variationally. …

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He+ 2p State Lifetime By A Quenching-Asymmetry Measurement, Gordon W. F. Drake, J. Kwela, A. Van Wijngaarden Jan 1992

He+ 2p State Lifetime By A Quenching-Asymmetry Measurement, Gordon W. F. Drake, J. Kwela, A. Van Wijngaarden

Physics Publications

An interference asymmetry in the angular distribution of the Ly quenching radiation emitted by He+ ions in the metastable 2s1/2 state is measured to high precision to obtain the lifetime of the 2p1/2 state. The derived lifetime of (0.997 170.000 75)×10-10 s is the most accurate available for a fundamental atomic system. A detailed discussion of systematic corrections is included. The result is in good agreement with theory, thereby confirming the theory of radiative transition probabilities to 0.075%, and indicating that differences between theory and experiment for the alkali metals must be due to either inadequate wave functions or experimental …

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Energies And Relativistic Corrections For The Rydberg States Of Helium: Variational Results And Asymptotic Analysis, Gordon W. F. Drake, Z. C. Yan Jan 1992

Energies And Relativistic Corrections For The Rydberg States Of Helium: Variational Results And Asymptotic Analysis, Gordon W. F. Drake, Z. C. Yan

Physics Publications

The results of an extended series of high-precision variational calculations for all states of helium up to n=10 and L=7 (excluding S states above n=2) are presented. Convergence of the nonrelativistic eigenvalues ranges from five parts in 1015 for the 2P states to four parts in 1019 for the 10K states. Relativistic and quantum electrodynamic corrections of order 2, 3, 2/M, 2(/M)2, and 3/M are included and the required matrix elements listed for each state. For the 1s2p 3PJ states, the lowest-order spin-dependent matrix elements of the Breit interaction are determined to an accuracy of three parts in 109, which, …

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Empirical Relations Between Static And Dynamic Exponents For Ising Model Cluster Algorithms, Paul D. Coddington, Clive F. Baillie Jan 1992

Empirical Relations Between Static And Dynamic Exponents For Ising Model Cluster Algorithms, Paul D. Coddington, Clive F. Baillie

Physics - All Scholarship

We have measured the autocorrelations for the Swendsen-Wang and the Wolff cluster update algorithms for the Ising model in 2, 3 and 4 dimensions. The data for the Wolff algorithm suggest that the autocorrelations are linearly related to the specific heat, in which case the dynamic critical exponent zW int,E = α/ν. For the Swendsen-Wang algorithm, scaling the autocorrelations by the average maximum cluster size gives either a constant or a logarithm, which implies that zSW int,E = β/ν for the Ising model.

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Multicriticality, Scaling Operators And Mkdv Flows For The Symmetric Unitary One Matrix Models, Konstantinos N. Anagnostopoulos, Mark Bowick Jan 1992

Multicriticality, Scaling Operators And Mkdv Flows For The Symmetric Unitary One Matrix Models, Konstantinos N. Anagnostopoulos, Mark Bowick

Physics - All Scholarship

We present a review of the Symmetric Unitary One Matrix Models. In particular we compute the scaling operators in the double scaling limit and the corresponding mKdV flows. We briefly discuss the computation of the space of solutions to the string equation as a subspace of Gr (0) \Theta Gr (0) which is invariant under the mKdV flows.

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Translational Correlations In The Vortex Array At The Surface Of A Type-Ii Superconductor, M. Cristina Marchetti, David R. Nelson Jan 1992

Translational Correlations In The Vortex Array At The Surface Of A Type-Ii Superconductor, M. Cristina Marchetti, David R. Nelson

Physics - All Scholarship

We discuss the statistical mechanics of magnetic flux lines in a finite-thickness slab of type-II superconductor. The long wavelength properties of a flux-line liquid in a slab geometry are described by a hydrodynamic free energy that incorporates the boundary conditions on the flux lines at the sample's surface as a surface contribution to the free energy. Bulk and surface weak disorder are modeled via Gaussian impurity potentials. This free energy is used to evaluate the two-dimensional structure factor of the flux-line tips at the sample surface. We find that surface interaction always dominates in determining the decay of translational correlations …

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Unitary One Matrix Models: String Equation And Flows, Konstantinos N. Anagnostopoulos, Mark Bowick Jan 1992

Unitary One Matrix Models: String Equation And Flows, Konstantinos N. Anagnostopoulos, Mark Bowick

Physics - All Scholarship

We review the Symmetric Unitary One Matrix Models. In particular we discuss the string equation in the operator formalism, the mKdV flows and the Virasoro Constraints. We focus on the -function formalism for the flows and we describe its connection to the (big cell of the) Sato Grassmannian Gr (0) via the Plucker embedding of Gr (0) into a fermionic Fock space. Then the space of solutions to the string equation is an explicitly computable subspace of Gr (0) \Theta Gr (0) which is invariant under the flows.

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Phase Transitions In K2Zncl4, H. M. Lu, John R. Hardy Jan 1992

Phase Transitions In K2Zncl4, H. M. Lu, John R. Hardy

John R. Hardy Papers

It is shown that the potential-energy surface in K2ZnCl4 contains a double-well structure, very similar to some of the other A2BX4 compounds (e.g., K2SeO4, Rb2ZnCl4), except that the double well is much deeper and broader, giving rise to a highly disordered high-temperature phase as observed experimentally. A lattice-dynamics study of the Pna21 structure shows an instability with the wave vector q=0.5b*+(0.5±δ)c*, providing an explanation to the incommensurate phase transition reported recently.

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Raman Scattering And Lattice-Dynamical Calculations Of Crystalline Kno3, D. Liu, F. G. Ullman, John R. Hardy Jan 1992

Raman Scattering And Lattice-Dynamical Calculations Of Crystalline Kno3, D. Liu, F. G. Ullman, John R. Hardy

John R. Hardy Papers

The Raman spectrum of a KNO3 single crystal was measured at both room and liquid-nitrogen temperatures. Lattice-dynamical calculations, based on the rigid-ion approximation and empirical potentials, were performed. The possibility of a phase transition at 217 K was investigated by measuring the temperature dependence of the Raman spectrum.

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Auger Spectra And Band Structure Of La1.85Sr0.15Cuo4 And La1.85Ba0.15Cuo4, R. Bar-Deroma, J. Felsteiner, R. Brener, J. Ashkenazi, D. Van Der Marel Jan 1992

Auger Spectra And Band Structure Of La1.85Sr0.15Cuo4 And La1.85Ba0.15Cuo4, R. Bar-Deroma, J. Felsteiner, R. Brener, J. Ashkenazi, D. Van Der Marel

Physics Articles and Papers

High-resolution Auger electron spectra of La1.85Sr0.15CuO4 and La1.85Ba0.15CuO4 have been measured. The experimental Auger line shapes of the oxygen KLL and copper L2,3VV transitions are compared with those generated from local-density-approximation linear-muffin-tin-orbital band-structure calculations. An analysis based on this comparison is used to determine the Coulomb parameters Up and Ud of the oxygen and copper atoms, respectively. For this purpose, an extended version of Cini and Sawatzky’s expression for the theoretical Auger line shape is used, taking into account the multiplet structure of the Auger final …

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Magnetism With Generalized-Gradient-Approximation Density Functionals, D.J. Singh, J. Ashkenazi Jan 1992

Magnetism With Generalized-Gradient-Approximation Density Functionals, D.J. Singh, J. Ashkenazi

Physics Articles and Papers

We report generalized-gradient-approximation (GGA) density-functional studies of Cr, V, and Pd, using an all-electron, general-potential linearized-augmented-plane-wave technique. These calculations were undertaken in order to assess the utility of the GGA as an improvement over the local-density approximation in describing transition-metal magnetism. It is found that although the tendency towards magnetism is enhanced, both V and Pd are correctly predicted to be nonmagnetic with the recent GGA functional of Perdew (PW GGA-II) as with the Langreth-Mehl-Hu (LM) functional. Calculations for commensurate antiferromagnetic Cr show that the PW GGA-II predicts an overly large moment of 1.4μB while the LM functional yields …

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Nonuniversality In The Kondo Effect, M. Naghashpour, S. E. Barnes Jan 1992

Nonuniversality In The Kondo Effect, M. Naghashpour, S. E. Barnes

Physics Articles and Papers

We have analytically evaluated, up to fourth order, all logarithmic terms in the perturbation expansion of the magnetization scrM for the Kondo model. All nonlogarithmic terms have been evaluated up to third order. When these results are compared with the claimed universal function scrM(H/TH) calculated with the Bethe ansatz, we find that the two cannot be made to agree whatever the form of TH. We conclude that such universal functions do not exist.

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Spatial Correlation Between Ch, Cn And The Diffuse Interstellar Band Carriers, J Krelowski, T P. Snow, C G. Seab, J Papaj Jan 1992

Spatial Correlation Between Ch, Cn And The Diffuse Interstellar Band Carriers, J Krelowski, T P. Snow, C G. Seab, J Papaj

Physics Faculty Publications

Observations are presented of the diffuse interstellar bands at 5780 and 5797 A and of the ultraviolet lines of CH and CN in the light of six bright stars which lie behind isolated interstellar clouds. It is found that CN and CH are only present when the 5797 band is deeper than the 5780 one. Comparisons with satellite measurements of the UV extinction show that the shape of the extinction curve is linked to the same band ratio in these stars. The results support a previous suggestion that the various components of the absorption spectrum of an isolated cloud (the …

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Measuring Airborne Alpha Radioactivity, Greg Taft Jan 1992

Measuring Airborne Alpha Radioactivity, Greg Taft

Honors Theses, 1963-2015

This project develops alpha spectroscopy to measure the airborne concentrations of attached and unattached radon progeny. The system is designed and constructed to be used in homes, thus is portable, fast, and easy to use.

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Track Structure Model Of Cell Damage In Space Flight, Robert Katz, Francis A. Cucinotta, John W. Wilson, Judy L. Shinn, Duc M. Ngo Jan 1992

Track Structure Model Of Cell Damage In Space Flight, Robert Katz, Francis A. Cucinotta, John W. Wilson, Judy L. Shinn, Duc M. Ngo

Robert Katz Publications

Cell damage by high linear energy transfer (LET) radiations has been described by a phenomenological model (track theory) for more than 20 years. With track theory, molecules of biological significance (dry enzymes and viruses) act as one-hit detectors. Recent additions to tire class of one-hit detectors arc Escherichia coil B, and single- and double-strand breaks in SV-40 virus in EO buffer, where indirect effects predominate. The response of cells (survival, transformation, and chromosome aberration) to these radiations is typically described by a four-parameter model whose numerical values are determined from the equations of the theory being fit to experimental …

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Track Structure Model For Damage To Mammalian Cell Cultures During Solar Proton Events, Francis A. Cucinotta, J. W. Wilson, L. W. Townsend, J. L. Shinn, Robert Katz Jan 1992

Track Structure Model For Damage To Mammalian Cell Cultures During Solar Proton Events, Francis A. Cucinotta, J. W. Wilson, L. W. Townsend, J. L. Shinn, Robert Katz

Robert Katz Publications

Solar proton events (SPEs) occur infrequently and unpredictably, thus representing a potential hazard to interplanetary space missions. Biological damage from SPEs will be produced principally through secondary electron production in tissue, including important contributions due to delta rays from nuclear reaction products. We review methods for estimating the biological effectiveness of SPEs using a high energy proton model and the parametric cellular track model. Results of the model are presented for several of the historically largest flares using typical levels and body shielding.

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Comment On Ncrp Report No. 104, "The Relative Biological Effectiveness Of Radiations Of Different Quality", Robert Katz Jan 1992

Comment On Ncrp Report No. 104, "The Relative Biological Effectiveness Of Radiations Of Different Quality", Robert Katz

Robert Katz Publications

The validity of a linear extrapolation to lowest fluences of charged particles demands that the transit of a single charged particle through the target volume is capable of inducing the chain of events leading to an observable end-point. This is always the case for one-hit detectors. It is not always the case for biological cells and tissues (Katz and Hofmann 1982).
By way of example, Cole ct al. (1980) found that, on average, some 500 electrons pass into the nucleus of a CHO cell for inactivation. Similarly, Warters et al. (1977) found that some 500 tritium decays in the nucleus …

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Multi-Ball Collisions, Terry L. Smith, Jay S. Huebner Jan 1992

Multi-Ball Collisions, Terry L. Smith, Jay S. Huebner

Terry L. Smith

Explanation to use the "double-ball" demonstration as a model for the supernova core bounce.

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Slip Length In A Dilute Gas, Alejandro Garcia, D. Morris, L. Hannon Jan 1992

Slip Length In A Dilute Gas, Alejandro Garcia, D. Morris, L. Hannon

Faculty Publications

We study the phenomenon of slip length using molecular dynamics and direct simulation Monte Carlo simulations of a dilute gas. Our work extends the range of Knudsen numbers that have been previously studied. In a recent paper, Bhattacharya and Lie [Phys. Rev. 43, 761 (1991)] suggest a logarithmic dependence of slip length on Knudsen number. By a simple redefinition of the mean free path, we obtain good agreement between simulation results and Maxwell theory for slip length. The anomalies seen by Bhattacharya and Lie appear to be due to their definition of the mean free path.

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Principal Linear Polarization States Of An Optical System, R. M.A. Azzam Jan 1992

Principal Linear Polarization States Of An Optical System, R. M.A. Azzam

Electrical Engineering Faculty Publications

The constraint on the Jones matrix of an optical system such that there exist two linear polarization states at its input that are mapped onto two corresponding linear states at its output is derived. These principal linear polarization (PLP) states, which characterize a broad range of systems, are also found in terms of the Jones matrix elements. Special cases when the PLP states are orthogonal, collapse onto one state, or become infinite in number are indicated. For a deterministic or nondeterministic optical system described by a Mueller matrix, the existence of two PLP states places a constraint on only 3 …

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Competition Between Superconductivity And A New 20 K Phase In -(Bedt-Ttf)2i3: Specific Heat Measurements, Nathanael A. Fortune, K. Murata, K. Ikeda, T. Takahashi Jan 1992

Competition Between Superconductivity And A New 20 K Phase In -(Bedt-Ttf)2i3: Specific Heat Measurements, Nathanael A. Fortune, K. Murata, K. Ikeda, T. Takahashi

Physics: Faculty Publications

We present here direct calorimetric evidence for a new transition at T*=22.25 K in the metallic state of quasi-2D organic superconductor -(BEDT-TTF)2I3 at ambient pressure, as suggested by our previous measurement of the temperature-dependent Hall coefficient RH(T). The apparent reduction in the effective electronic density of states at T* quantitatively explains for the first time the suppression of Tc from the pressure-stabilized eehigh-Tcee value of 8 K to the ambient-pressure cooled eelow-Tcee value of 1.5 K.

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Densities And Vibrational Distribution Of H3+ In The Jovian Auroral Ionosphere, Y. H. Kim, Jane L. Fox, H. S. Porter Jan 1992

Densities And Vibrational Distribution Of H3+ In The Jovian Auroral Ionosphere, Y. H. Kim, Jane L. Fox, H. S. Porter

Physics Faculty Publications

Observations of the H3+ infrared emission at 2 and 4 μm have suggested that H3+ is in local thermodynamic equilibrium (LTE) in the region of the Jovian ionosphere from which the emissions originate. We have tested this assumption by calculating the vibrational distribution of H3+ over the altitude range of 350 to 1500 km above the methane cloud tops (1 to 4 × 10−3 μbar). We have constructed a model of the Jovian auroral ionosphere in which the neutral temperatures are enhanced over those of the mid-latitude ionosphere, as suggested by observations and …

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Alloy Scattering In P-Type Alxga1-Xas, David C. Look, D. K. Lorance, J. R. Sizelove, C. E. Stutz, K. R. Evans, D. W. Whitson Jan 1992

Alloy Scattering In P-Type Alxga1-Xas, David C. Look, D. K. Lorance, J. R. Sizelove, C. E. Stutz, K. R. Evans, D. W. Whitson

Physics Faculty Publications

The hole mobility of Be‐doped ( ~ 2 × 1017 cm-3) AlxGa1-xAs, for x=0–1, is analyzed both theoretically and experimentally. Alloy scattering is very important, and in fact reduces the hole mobility from 150 to less than 90 cm2/V s at x=0.5. The main parameter in the alloy scattering formulation, the alloy potential Eal, is found to be about 0.5 eV for p‐type AlxGa1-xAs.

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Slip Length In A Dilute Gas, Alejandro Garcia, D. Morris, L. Hannon Jan 1992

Slip Length In A Dilute Gas, Alejandro Garcia, D. Morris, L. Hannon

Alejandro Garcia

We study the phenomenon of slip length using molecular dynamics and direct simulation Monte Carlo simulations of a dilute gas. Our work extends the range of Knudsen numbers that have been previously studied. In a recent paper, Bhattacharya and Lie [Phys. Rev. 43, 761 (1991)] suggest a logarithmic dependence of slip length on Knudsen number. By a simple redefinition of the mean free path, we obtain good agreement between simulation results and Maxwell theory for slip length. The anomalies seen by Bhattacharya and Lie appear to be due to their definition of the mean free path.

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°-Electron Emission In Fast Heavy Ion Atom Collisions, H. Schmidt-Böcking, U. Ramm, G. Kraft, J. Ullrich, H. Berg, C. Kelbch, Ronald E. Olson, R. (Robert) D. Dubois, S. Hagmann, F. Jiazhen Jan 1992

°-Electron Emission In Fast Heavy Ion Atom Collisions, H. Schmidt-Böcking, U. Ramm, G. Kraft, J. Ullrich, H. Berg, C. Kelbch, Ronald E. Olson, R. (Robert) D. Dubois, S. Hagmann, F. Jiazhen

Physics Faculty Research & Creative Works

Biological damages such as mutations, chromosomal aberrations etc. are consequence of biochemical changes mostly in the DNA /1/. With ionizing radiation, these chemical changes are due to primary ionization events and secondary ionization effects caused by the primarily produced electrons. Differences in the biological response of densely ionizing radiation, like heavy charged particles, in comparison to sparsely ionizing radiation, such as X- or γ-rays, are mainly due to the differences in the productions of the so called δ-electrons. Therefore, the emission process of electrons i.e., the cross section for the primary ionization event as well as the energy and angular …

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Plasma As A High-Charge-State Projectile Stripping Medium, G. D. Alton, R. A. Sparrow, Ronald E. Olson Jan 1992

Plasma As A High-Charge-State Projectile Stripping Medium, G. D. Alton, R. A. Sparrow, Ronald E. Olson

Physics Faculty Research & Creative Works

The classical trajectory Monte Carlo model has been used to computationally study the charge-state distributions that result from interactions between a high-energy, multielectron projectile and neutral and fully ionized targets. These studies are designed to determine the properties of a plasma for producing highly stripped ions as a possible alternative to gas and foil strippers that are commonly used to enhance the charge states of energetic ion beams. The results of these studies clearly show that a low-atomic-number, highly ionized plasma can yield higher charge states than a neutral target of the same density. The effect is principally attributable to …

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Magnetic Properties Of A Novel Iron Carbide Film, Fe₇C₃X Formed In A Glow Discharge, Oran Allan Pringle, Gary J. Long, Fernande Grandjean, Jun L. Li, George C. Hadjipanayis, William Joseph James Jan 1992

Magnetic Properties Of A Novel Iron Carbide Film, Fe₇C₃X Formed In A Glow Discharge, Oran Allan Pringle, Gary J. Long, Fernande Grandjean, Jun L. Li, George C. Hadjipanayis, William Joseph James

Physics Faculty Research & Creative Works

No abstract provided.

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Monte Carlo Study Of A Simple Model Bulk-Ice-Ih System: P-T Melting Behavior At Constant Volume, K. Han, Barbara N. Hale Jan 1992

Monte Carlo Study Of A Simple Model Bulk-Ice-Ih System: P-T Melting Behavior At Constant Volume, K. Han, Barbara N. Hale

Physics Faculty Research & Creative Works

An NVT Metropolis Monte Carlo computer simulation is used to examine the P-T behavior of a constant-density model periodic ice-Ih sample near melting. The ice unit cell with density 0.904 g/cm3 consists of 192 rigid water molecules interacting via the revised central-force potentials (RSL2) of Stillinger and Rahman [J. Chem. Phys. 68, 666 (1978)] with a cutoff. Intramolecular parameters are determined from a minimization of the total potential energy of the ice-Ih structure at 0 K. In the P-T plot, emergence of the liquid-solid coexistence region is signaled by a change in sign of dP/dT (when expansion occurs upon …

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Pressure And Temperature Effects On The Energy Of Formation For Silicon Clusters, Sung-Ho Suck Salk, Chen K. Lutrus, Donald E. Hagen, T. Oshiro, Steven M. Beck, Gary L. Loper Jan 1992

Pressure And Temperature Effects On The Energy Of Formation For Silicon Clusters, Sung-Ho Suck Salk, Chen K. Lutrus, Donald E. Hagen, T. Oshiro, Steven M. Beck, Gary L. Loper

Physics Faculty Research & Creative Works

At present most theoretical studies of atomic clusters are limited to their physical properties referred to 0 K. To the best of our knowledge, there exists no theoretical study of the simultaneous dependence of cluster formation and cluster-size distributions on both pressure and temperature. In the present work both pressure and temperature effects on the formation of silicon clusters are explored. A universal semiempirical formula is obtained to show a general trend in the variation of binding energy as a function of cluster size for both atomic and molecular clusters.

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