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Articles 29581 - 29610 of 36686

Full-Text Articles in Physical Sciences and Mathematics

Two-Center Effect On Low-Energy Electron Emission In Collisions Of 1-Mev/U Bare Ions With Atomic Hydrogen, Molecular Hydrogen, And Helium: Ii. H2 And He, Lokesh C. Tribedi, P. Richard, L. Gulya´S, M. Eugene Rudd Jan 2001

Two-Center Effect On Low-Energy Electron Emission In Collisions Of 1-Mev/U Bare Ions With Atomic Hydrogen, Molecular Hydrogen, And Helium: Ii. H2 And He, Lokesh C. Tribedi, P. Richard, L. Gulya´S, M. Eugene Rudd

M. Eugene Rudd Publications

We have studied the energy and angular distributions of low-energy electron emission in collisions of bare carbon ions of 1-MeV/u energy with He and H2 targets. The double-differential cross sections (DDCS’s) are measured for electrons with energies between 0.5 and 300 eV emitted within an angular range of 15° to 160°. The large forward-backward asymmetry observed in the angular distributions is explained in terms of the two-center effect. Single differential cross sections (SDCS’s) and total cross sections are also derived by integrating the DDCS’s over emission angles and energies. The data are compared with different theoretical calculations based on …

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Perspectives Of Giant Magnetoresistance, Evgeny Y. Tsymbal, David G. Pettifor Jan 2001

Perspectives Of Giant Magnetoresistance, Evgeny Y. Tsymbal, David G. Pettifor

Evgeny Tsymbal Publications

Giant magnetoresistance (GMR) is one of the most fascinating discoveries in thin-film magnetism, which combines both tremendous technological potential and deep fundamental physics. Within a decade of GMR being discovered in 1988 commercial devices based on this phenomenon, such as hard-disk read-heads, magnetic field sensors and magnetic memory chips, had become available in the market. These achievements would not have been possible without a detailed understanding of the physics of GMR, which requires a quantum-mechanical insight into the electronic spin-dependent transport in magnetic structures.

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N-Methyl-D-Aspartate Channel And Consciousness: From Signal Coincidence Detection To Quantum Computing, Armando F. Rocha, Alfredo Pereira Jr Jan 2001

N-Methyl-D-Aspartate Channel And Consciousness: From Signal Coincidence Detection To Quantum Computing, Armando F. Rocha, Alfredo Pereira Jr

Armando F Rocha

Research on Blindsight, Neglect/Extinction and Phantom limb syndromes, as well as electrical measurements of mammalian brain activity, have suggested the dependence of vivid perception on both incoming sensory information at primary sensory cortex and reentrant information from associative cortex. Coherence between incoming and reentrant signals seems to be a necessary condition for (conscious) perception. General reticular activating system and local electrical synchronization are some of the tools used by the brain to establish coarse coherence at the sensory cortex, upon which biochemical processes are coordinated. Besides electrical synchrony and chemical modulation at the synapse, a central mechanism supporting such a …

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Spatially Correlated Dynamics In A Simulated Glass-Forming Polymer Melt: Analysis Of Clustering Phenomena, Y. Gebremichael, T. B. Schroder, Francis W. Starr, S. C. Glotzer Jan 2001

Spatially Correlated Dynamics In A Simulated Glass-Forming Polymer Melt: Analysis Of Clustering Phenomena, Y. Gebremichael, T. B. Schroder, Francis W. Starr, S. C. Glotzer

Francis Starr

No abstract provided.

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Effects Of A Nanoscopic Filler On The Structure And Dynamics Of A Simulated Polymer Melt And The Relationship To Ultra-Thin Films, Francis W. Starr, T. B. Schroder, S. C. Glotzer Jan 2001

Effects Of A Nanoscopic Filler On The Structure And Dynamics Of A Simulated Polymer Melt And The Relationship To Ultra-Thin Films, Francis W. Starr, T. B. Schroder, S. C. Glotzer

Francis Starr

No abstract provided.

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Static And Dynamic Properties Of Stretched Water, P. A. Netz, Francis W. Starr, H. E. Stanley, M. C. Barbosa Jan 2001

Static And Dynamic Properties Of Stretched Water, P. A. Netz, Francis W. Starr, H. E. Stanley, M. C. Barbosa

Francis Starr

No abstract provided.

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Dynamics Of Supercooled Water In Configuration Space, Emilia La Nave, Antonio Scala, Francis W. Starr, Francesco Sciortino, H. Eugene Stanley Jan 2001

Dynamics Of Supercooled Water In Configuration Space, Emilia La Nave, Antonio Scala, Francis W. Starr, Francesco Sciortino, H. Eugene Stanley

Francis Starr

No abstract provided.

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Thermodynamic And Structural Aspects Of The Potential Energy Surface Of Simulated Water, Francis W. Starr, S. Sastry, E. La Nave, A. Scala, H. E. Stanley, F. Sciortino Jan 2001

Thermodynamic And Structural Aspects Of The Potential Energy Surface Of Simulated Water, Francis W. Starr, S. Sastry, E. La Nave, A. Scala, H. E. Stanley, F. Sciortino

Francis Starr

No abstract provided.

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Higher Twist Corrections And Maxima For Dis On A Proton In The High Density Qcd Region, E. Gotsman, Eugene Levin, U. Maor, L. Mclerran, Kirill Tuchin Jan 2001

Higher Twist Corrections And Maxima For Dis On A Proton In The High Density Qcd Region, E. Gotsman, Eugene Levin, U. Maor, L. Mclerran, Kirill Tuchin

Kirill Tuchin

We show that the ratio of different structure functions have a maximum which depends on energy. We argue, using the Golec-Biernat and Wusthoff model as well as the eikonal approach, that these maxima are functions of the saturation scale. We analyze leading and higher twist contributions for different observables to check whether a kinematic region exists where high parton density effects can be detected experimentally.

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Unbiased Density Functional Solutions Of Freezing In Binary Mixtures Of Hard Or Soft Spheres, M. Valera, R. F. Bielby, F. J. Pinksi, Duane D. Johnson Jan 2001

Unbiased Density Functional Solutions Of Freezing In Binary Mixtures Of Hard Or Soft Spheres, M. Valera, R. F. Bielby, F. J. Pinksi, Duane D. Johnson

Duane D. Johnson

various size ratios, σ2/σ1, using density functional theory. The Grand Potential is minimized using an unbiased, discrete, real-space mesh that does not constrain the shape of the density, and, in many cases, leads to solutions qualitatively different from those using Gaussians and plane-waves. Besides the usual face-centered-cubic solid-solution phase for σ2/σ1≈1.0, we find a sublattice-melt phase for σ2/σ1=0.85–0.5 (where the small-sphere density is nonlocalized and multi-peaked) and the NaCl phase for σ2/σ1=0.45–0.35 (when the small-sphere density again sharpens). For a range of size ratios of soft sphere mixtures, we could not find stable nonuniform solutions. Preliminary calculations within a Modified-Weighted …

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The Pomeron Intercept In Lambda Phi**Theory In 4 Minkowski + 1 Compact Dimensions, Kirill Tuchin Jan 2001

The Pomeron Intercept In Lambda Phi**Theory In 4 Minkowski + 1 Compact Dimensions, Kirill Tuchin

Kirill Tuchin

We calculate the total cross section for two scalar particles scattering at high energies in λφ3 theory in five dimensions, four of which are usual Minkowski ones and the fifth is compact. It is shown that the cross section is dominated by exchange of Pomeron whose intercept is larger than in usual four-dimensional case.

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Propagating Conformational Changes Over Long (And Short) Distances In Proteins, Edward Yu, Daniel E. Koshland Jr. Jan 2001

Propagating Conformational Changes Over Long (And Short) Distances In Proteins, Edward Yu, Daniel E. Koshland Jr.

Edward Yu

The problem of the propagation of conformational changes over long distances or through a closely packed protein is shown to fit a model of a ligand-induced conformational change between two protein states selected by evolution. Moreover, the kinetics of the pathway between these states is also selected so that the energy of ligand binding and the speed of the transition between conformational states are physiologically appropriate. The crystallographic data of a wild-type aspartate receptor that has negative cooperativity and a mutant that has no cooperativity but has native transmembrane signaling are shown to support this model.

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Seasonal And Magnetic Activity Variations Of Ionospheric Electric Fields Above The Southernmid-Latitude Station, Bundoora, Australia, M. L. Parkinson, R. Polglase, Bela G. Fejer, L. Scherliess, P. L. Dyson, S. M. Ujmaia Jan 2001

Seasonal And Magnetic Activity Variations Of Ionospheric Electric Fields Above The Southernmid-Latitude Station, Bundoora, Australia, M. L. Parkinson, R. Polglase, Bela G. Fejer, L. Scherliess, P. L. Dyson, S. M. Ujmaia

Bela G. Fejer

We investigate the seasonal, local solar time, and geomagnetic activity variations of the average Doppler velocity measured by an HF digital ionosonde deployed at Bundoora, Australia. The Doppler velocities were heavily averaged to suppress the short-term effects (<3>hours) of atmospheric gravity waves, and thereby obtain the diurnal variations attributed to the tidally-driven ionospheric dynamo and electric fields generated by magnetic disturbances. The observed seasonal variations in Doppler velocity were probably controlled by variations in the lower thermospheric winds and ionospheric conductivity above Bundoora and in the magnetically conjugate location. The diurnal variations of the meridional (fieldperpendicular) drifts and their …

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Parallel Dynamics And Computational Complexity Of The Bak-Sneppen Model, Jonathan Machta, X. N. Li Jan 2001

Parallel Dynamics And Computational Complexity Of The Bak-Sneppen Model, Jonathan Machta, X. N. Li

Jonathan Machta

No abstract provided.

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Critical Dynamics Of Two-Replica Cluster Algorithms, X. N. Li, Jonathan Machta Jan 2001

Critical Dynamics Of Two-Replica Cluster Algorithms, X. N. Li, Jonathan Machta

Jonathan Machta

The dynamic critical behavior of the two-replica cluster algorithm is studied. Several versions of the algorithm are applied to the two-dimensional, square lattice Ising model with a staggered field. The dynamic exponent for the full algorithm is found to be less than 0.4. It is found that odd translations of one replica with respect to the other together with global flips are essential for obtaining a small value of the dynamic exponent. Read More: http://www.worldscientific.com/doi/abs/10.1142/S0129183101001663

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Thermodynamic Formalism Of The Harmonic Measure Of Diffusion Limited Aggregates: Phase Transition And Converged, Mogens H. Jensen, Anders Levermann, Joachim Mathiesen, Benny Davidovitch, Itamar Procaccia Jan 2001

Thermodynamic Formalism Of The Harmonic Measure Of Diffusion Limited Aggregates: Phase Transition And Converged, Mogens H. Jensen, Anders Levermann, Joachim Mathiesen, Benny Davidovitch, Itamar Procaccia

Benny Davidovitch

No abstract provided.

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Laplacian Growth And Diffusion Limited Aggregation: Different Universality Classes, Felipe Barra, Benny Davidovitch, Anders Leverman, Itamar Procaccia Jan 2001

Laplacian Growth And Diffusion Limited Aggregation: Different Universality Classes, Felipe Barra, Benny Davidovitch, Anders Leverman, Itamar Procaccia

Benny Davidovitch

It had been conjectured that diffusion limited aggregates and Laplacian growth patterns (with small surface tension) are in the same universality class. Using iterated conformal maps we construct a oneparameter family of fractal growth patterns with a continuously varying fractal dimension. This family can be used to bound the dimension of Laplacian growth patterns from below. The bound value is higher than the dimension of diffusion limited aggregates, showing that the two problems belong to two different universality classes.

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Development Of Equilibrium After Preheating, Gary Felder, Lev Kofman Jan 2001

Development Of Equilibrium After Preheating, Gary Felder, Lev Kofman

Physics: Faculty Publications

We present a fully nonlinear study of the development of equilibrium after preheating. Preheating is the exponentially rapid transfer of energy from the nearly homogeneous inflaton field to fluctuations of other fields and/or the inflaton itself. This rapid transfer leaves these fields in a highly nonthermal state with energy concentrated in infrared modes. We have performed lattice simulations of the evolution of interacting scalar fields during and after preheating for a variety of inflationary models. We have formulated a set of generic rules that govern the thermalization process in all of these models. Notably, we see that once one of …

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Quantum Confinement Transition In A D-Wave Superconductor, Courtney Lannert, T. Senthil, Matthew P. Fisher Jan 2001

Quantum Confinement Transition In A D-Wave Superconductor, Courtney Lannert, T. Senthil, Matthew P. Fisher

Physics: Faculty Publications

We study the nature of the zero-temperature phase transition between a d-wave superconductor and a Mott insulator in two dimensions. In this "quantum confinement transition", spin and charge are confined to form the electron in the Mott insulator. Within a dual formulation, direct transitions from d-wave superconductors at half-filling to insulators with spin-Peierls (as well as other) order emerge naturally. The possibility of striped superconductors is also discussed within the dual formulation. The transition is described by nodal fermions and bosonic vortices, interacting via a long-ranged statistical interaction modeled by two coupled Chern-Simons gauge fields, and the critical properties of …

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Electron Spectral Function In Two-Dimensional Fractionalized Phases, Courtney Lannert, Matthew P.A. Fisher, T. Senthil Jan 2001

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

Physics: Faculty Publications

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

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Investigation Of Magnetopause Reconnection Models Using Two Colocated, Low‐Altitude Satellites: A Unifying Reconnection Geometry, A. Boudouridis, Harlan E. Spence, T. G. Onsager Jan 2001

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

Physics & Astronomy

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

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The Age Of Entanglement Jan 2001

The Age Of Entanglement

David D Nolte

Quantum mechanics is a venerable field of study. The year 2000 marked the 100th anniversary of theoriginal quantum hypothesis proposed by Max Planck in November of 1900. Few current fields in physicsor engineering are as old as quantum mechanics. It predates relativity, both special and general. It predatesnuclear and particle physics. Quantum mechanics even predates universal acceptance of the molecularhypothesis, that is, that all matter is made up of individual molecules in thermal motion. It may be hard tobelieve, but this happened only after Einstein's paper on Brownian motion was published in his miracleyear 1905.

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Heating And Ionization Of The Intergalactic Medium By An Early X-Ray Background, Aparna Venkatesan, Mark L. Giroux, J Shull Jan 2001

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

Physics and Astronomy

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

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Laser Stabilization At 1536 Nm Using Regenerative Spectral Hole Burning, P B. Sellin, N M. Strickland, Thomas Böttger, J L. Carlsten, R L. Cone Jan 2001

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

Physics and Astronomy

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

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In The Shadow Of The Accretion Disk: Higher Resolution Imaging Of The Central Parsec In Ngc 4261, B. Glenn Piner, Dayton L. Jones, Ann E. Wehrle, David L. Meier Jan 2001

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

Physics

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

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Coherent-Path Model For Nuclear Resonant Scattering Of Gamma Radiation From Nuclei Excited By Synchrotron Radiation, Gilbert R. Hoy, Jos Odeurs, Romain Coussement Jan 2001

Coherent-Path Model For Nuclear Resonant Scattering Of Gamma Radiation From Nuclei Excited By Synchrotron Radiation, Gilbert R. Hoy, Jos Odeurs, Romain Coussement

Physics Faculty Publications

Previous theoretical descriptions of nuclear resonant scattering of synchrotron radiation have been based on the semiclassical optical model or on several quantum mechanical models. These models are fine but do not give a clear physical picture of all the processes. The theory presented here gives a clear physical picture of all the relevant aspects of nuclear resonant scattering. The model treats the nuclear resonant sample as a one-dimensional chain of "effective" nuclei. However, the model is deceptive. It only appears to be one dimensional. It actually treats the sample as a series of "effective" planes. The analysis uses the time-dependent …

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Gamma Echo Interpreted As A Phase-Shift Induced Transparency, Gilbert R. Hoy, Jos Odeurs Jan 2001

Gamma Echo Interpreted As A Phase-Shift Induced Transparency, Gilbert R. Hoy, Jos Odeurs

Physics Faculty Publications

In the gamma-echo technique a radioactive source is moved, with respect to a nuclear-resonant absorber, during the lifetime of first-excited nuclear state. This introduces a phase shift between the source radiation and the radiation from the absorber. If the source is moved abruptly, introducing a pi phase shift, the time-dependent intensity shows a sharp increase in the intensity at that time, the "gamma echo." Using the recently developed one-dimensional quantum-mechanical model, based on the technique developed by Heitler and Harris, the gamma-echo effect is seen to be a phase-shift-induced transparency. A closed-form solution for the time-dependent transmitted intensity has been …

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Molecular Simulations Of Sound Wave Propagation In Simple Gases, Alejandro Garcia, N. Hadjiconstantinou Jan 2001

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

Alejandro Garcia

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

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Molecular Simulations Of Sound Wave Propagation In Simple Gases, Alejandro Garcia, N. Hadjiconstantinou Jan 2001

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

Faculty Publications

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

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Calculation Of The Potential And Electric Flux Lines For Parallel Plate Capacitors With Symmetrically Placed Equal Lengths By Using The Method Of Conformal Mapping, Erhan Albayrak Jan 2001

Calculation Of The Potential And Electric Flux Lines For Parallel Plate Capacitors With Symmetrically Placed Equal Lengths By Using The Method Of Conformal Mapping, Erhan Albayrak

Turkish Journal of Physics

The classical problem of the parallel-plate capacitors has been investigated by a number of authors, including Love [1], Langton [2] and Lin [3]. In this paper, the exact equipotentials and electric flux lines of symmetrically placed two thin conducting plates are obtained using the Schwarz- Cristoffel transformation and the method of conformal mapping. The coordinates x , y in the z-plane corresponding to the constant electric flux lines and equipotential lines are obtained after very detailed and cumbersome calculations. The complete field distribution is given by constructing the family of lines of electric flux and equipotential.

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