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Articles 721 - 750 of 969
Full-Text Articles in Physics
Higher Twist Contributions To R-Hadron Phenomenology In The Light Gluino Scenario, Thomas D. Gutierrez, R. Vogt, J. F. Gunion
Higher Twist Contributions To R-Hadron Phenomenology In The Light Gluino Scenario, Thomas D. Gutierrez, R. Vogt, J. F. Gunion
Physics
The open light gluino window allows non-trivial higher-twist gluino contributions to the proton wave function. Using a two-component model originally developed for charm hadroproduction, higher-twist intrinsic gluino contributions to final-state R-hadron formation are shown to enhance leading-twist production in the forward xnF region. We calculate R-hadron production at Pnlab=800 GeV in pp, pBe, and pCu interactions with light gluino masses of 1.2, 1.5, 3.5, and 5.0 GeV.
Low-Frequency Crossover Of The Fractional Power-Law Conductivity In Srruo3, J. S. Dodge, Christopher P. Weber, J. Corson, J. Orenstein, Z. Schlesinger, J. W. Reiner, M. R. Beasley
Low-Frequency Crossover Of The Fractional Power-Law Conductivity In Srruo3, J. S. Dodge, Christopher P. Weber, J. Corson, J. Orenstein, Z. Schlesinger, J. W. Reiner, M. R. Beasley
Physics
We combine the results of terahertz time-domain spectroscopy with far-infrared transmission and reflectivity to obtain the conductivity of SrRuO 3 over an unprecedented continuous range in frequency, allowing us to characterize the approach to zero frequency as a function of temperature. We show that the conductivity follows a simple phenomenological form, with an analytic structure fundamentally different from that predicted by the standard theory of metals.
A Discotic Disguised As A Smectic: A Hybrid Columnar Bragg Glass, Karl Saunders, Leo Radzihovsky, John Toner
A Discotic Disguised As A Smectic: A Hybrid Columnar Bragg Glass, Karl Saunders, Leo Radzihovsky, John Toner
Physics
We show that discotics, lying deep in the columnar phase, can exhibit an x-ray scattering pattern which mimics that of a somewhat unusual smectic liquid crystal. This exotic, new glassy phase of columnar liquid crystals, which we call a “hybrid columnar Bragg glass,” can be achieved by confining a columnar liquid crystal in an anisotropic random environment of, e.g., strained aerogel. Long-ranged orientational order in this phase makes single-domain x-ray scattering possible, from which a wealth of information could be extracted. We give detailed quantitative predictions for the scattering pattern in addition to exponents characterizing anomalous elasticity of the system.
Two-Dimensional Pendulum Experiments Using A Spark Generator, Rand S. Worland, Matthew J. Moelter
Two-Dimensional Pendulum Experiments Using A Spark Generator, Rand S. Worland, Matthew J. Moelter
Physics
Student understanding of the superposition of perpendicular harmonic oscillators can be enhanced using a spark generator to record position-versus-time data for smallamplitude pendulum motion in two dimensions. Our students have used this arrangement to analyze the motion of a spherical pendulum and a “Y-suspended” (Blackburn) pendulum that has two effective lengths.
Occurrence And Distribution Of Diverse Populations Of Magnetic Protists In A Chemically Stratified Coastal Salt Pond, Dennis A. Bazylinski, David R. Schlezinger, Brian H. Howes, Richard B. Frankel, Slava S. Epstein
Occurrence And Distribution Of Diverse Populations Of Magnetic Protists In A Chemically Stratified Coastal Salt Pond, Dennis A. Bazylinski, David R. Schlezinger, Brian H. Howes, Richard B. Frankel, Slava S. Epstein
Physics
Chemical stratification occurs in the water columns and sediments of many aquatic habitats resulting in vertical chemical and redox gradients. Various types of microorganisms are often associated with specific depths and chemical parameters in these situations. For example, magnetite-producing magnetotactic bacteria are known to form horizontal “plates” of cells at the oxic/anoxic transition zone (OATZ) of such environments. Here, we report the presence of populations of diverse magnetic protists in a seasonally chemically stratified, coastal salt pond. The protistan types included several biflagellates, a dinoflagellate, and a ciliate that were each associated with specific depths and thus, specific chemical, microbiological …
Doomsday Fears At Rhic, Thomas D. Gutierrez
Doomsday Fears At Rhic, Thomas D. Gutierrez
Physics
This year, the Relativistic Heavy Ion Collider (RHIC) is poised to begin a program of cutting-edge nuclear science. Recently, alarmist journalism unnecessarily raised public fears about implausible doomsday scenarios associated with the machine.
Magnetite Biomineralization And Ancient Life On Mars, Richard B. Frankel, Peter R. Buseck
Magnetite Biomineralization And Ancient Life On Mars, Richard B. Frankel, Peter R. Buseck
Physics
Certain chemical and mineral features of the Martian meteorite ALH84001 were reported in 1996 to be probable evidence of ancient life on Mars. In spite of new observations and interpretations, the question of ancient life on Mars remains unresolved. Putative biogenic, nanometer magnetite has now become a leading focus in the debate.
Superconductor-Insulator Transition In Granular Pb Films Near A Superconducting Ground Plane, Richard P. Barber Jr., S. R. Khan, Eric Morre Pedersen, Ben Kain, A. J. Jordan
Superconductor-Insulator Transition In Granular Pb Films Near A Superconducting Ground Plane, Richard P. Barber Jr., S. R. Khan, Eric Morre Pedersen, Ben Kain, A. J. Jordan
Physics
We report observations of the zero-field superconductor-insulator transition in granular quench-condensed Pb for samples within 10-15 nm of relatively thick superconducting ground planes. Resistance vs temperature measurements of sufficiently thick Pb samples exhibit broadened superconductor transitions consistent with previous results on clean dielectric substrates. The lack of any measurable influence by the superconducting planes on the Pb film resistance is discussed within the context of zero-field vortex-antivortex unbinding explanations for the transition broadening.
Topologically Ordered Phases Of Smectics Confined In Anisotropic Random Media: Smectic Bragg Glasses, Karl Saunders, Brad Jacobsen, Leo Radzihovsky, John Toner
Topologically Ordered Phases Of Smectics Confined In Anisotropic Random Media: Smectic Bragg Glasses, Karl Saunders, Brad Jacobsen, Leo Radzihovsky, John Toner
Physics
We report the existence of two new topologically ordered glass phases of smectics in strained aerogel. In contrast to the case of unstrained aerogel, we find compelling theoretical arguments that a smectic in uniaxially stretched aerogel exhibits, for homeotropic nematic-aerogel alignment, a `smectic Bragg glass' in the universality class of the `XY Bragg glass'. On the other hand, a uniaxial compression, with homeotropic alignment, leads to an entirely novel type of anisotropic smectic elastic glass phase that we call the `m = 1 Bragg glass'. This latter phase exhibits anomalous elasticity, characterized by exponents that we calculate to high precision. …
Biologically-Controlled Mineralization Of Magnetic Iron Minerals By Magnetotactic Bacteria, D. A. Bazylinski, R. B. Frankel
Biologically-Controlled Mineralization Of Magnetic Iron Minerals By Magnetotactic Bacteria, D. A. Bazylinski, R. B. Frankel
Physics
No abstract provided.
Measurement Of TC Suppression In Tungsten Using Magnetic Impurities, Betty A. Young, T. Saab, Blas Cabrera, J. J. Cross, R. M. Clarke, R. A. Abusaidi
Measurement Of TC Suppression In Tungsten Using Magnetic Impurities, Betty A. Young, T. Saab, Blas Cabrera, J. J. Cross, R. M. Clarke, R. A. Abusaidi
Physics
We have measured the effects of dilute magnetic-atom doping on the superconducting transition temperature of tungsten thin films. Our “Tc tuning” technique is accurate, precise, and simple. Experiments were performed using dc-magnetron-sputtered tungsten films with undoped values of Tc in the range of 70–150 mK. The magnetic-atom doping was achieved using ion implantation. Specific Tc suppressions of between 5% and 65% were targeted and observed in this study. The transition width of each undoped sample was ≈1 mK and the transition widths remained sharp after implantation with 56Fe+ ions. Our data are in good agreement …
Differential Photometry Of Suspected Cataclysmic Variables, N. Bennert, I. König, E. Manthey, H. Bleul, K. Fieger, M. Hess, A. Hovest, W. Hovest, T. Jürges, J. Kleimann, C. Kriegeskorte, E. Krusch, D. Münstermann, D. Reymann, K. Rösler, M. Nielbock, M. Pohlen, L. Schmidtobreick, C. Tappert, R. Vanscheidt
Differential Photometry Of Suspected Cataclysmic Variables, N. Bennert, I. König, E. Manthey, H. Bleul, K. Fieger, M. Hess, A. Hovest, W. Hovest, T. Jürges, J. Kleimann, C. Kriegeskorte, E. Krusch, D. Münstermann, D. Reymann, K. Rösler, M. Nielbock, M. Pohlen, L. Schmidtobreick, C. Tappert, R. Vanscheidt
Physics
No abstract provided.
Bacterial Magnetosomes: Microbiology, Biomineralization And Biotechnological Applications, Dirk Schlϋer, Richard B. Frankel
Bacterial Magnetosomes: Microbiology, Biomineralization And Biotechnological Applications, Dirk Schlϋer, Richard B. Frankel
Physics
Magnetotactic bacteria orient and migrate along geomagnetic field lines. This ability is based on intracellular magnetic structures, the magnetosomes, which comprise nanometer-sized, membrane-bound crystals of the magnetic iron minerals magnetite (Fe3O4) or greigite (Fe3O4). Magnetosome formation is achieved by a mineralization process with biological control over the accumulation of iron and the deposition of the mineral particle with specific size and orientation within a membrane vesicle at specific locations in the cell. This review focuses on the current knowledge about magnetotactic bacteria and will outline aspects of the physiology and molecular biology …
Two New Topologically Ordered Glass Phases Of Smectics Confined In Anisotropic Random Media, Brad Jacobsen, Karl Saunders, Leo Radzihovsky, John Toner
Two New Topologically Ordered Glass Phases Of Smectics Confined In Anisotropic Random Media, Brad Jacobsen, Karl Saunders, Leo Radzihovsky, John Toner
Physics
Smectics in strained aerogel exhibit two new glassy phases. The strain both ensures the stability of these phases and determines their nature. One type of strain induces an “ XY Bragg glass,” while the other creates a novel, triaxially anisotropic “ m = 1 Bragg glass.” The latter exhibits anomalous elasticity, characterized by exponents that we calculate to high precision. We predict the phase diagram, and numerous other experimentally observable scaling laws, for the system.
Charge Dynamics In The Half-Metallic Ferromagnet Cro2, E. J. Singley, Christopher P. Weber, D. N. Basov, A. Barry, J. M. D. Coey
Charge Dynamics In The Half-Metallic Ferromagnet Cro2, E. J. Singley, Christopher P. Weber, D. N. Basov, A. Barry, J. M. D. Coey
Physics
Infrared spectroscopy is used to investigate the electronic structure and charge carrier relaxation in crystalline films of CrO2 which is the simplest of all half-metallic ferromagnets. Chromium dioxide is a bad metal at room temperature but it has a remarkably low residual resistivity (<5 >μΩ cm) despite the small spectral weight associated with free carrier absorption. The infrared measurements show that low residual resistivity is due to the collapse of the scattering rate at ω<2000 >cm-1. The blocking of the relaxation channels at low v and T can be attributed to the unique electronic structure of a …
Spume Drops Produced By The Wind Tearing Of Wave Crests, Richard P. Barber Jr., Magdalena Anguelova, Jin Wu
Spume Drops Produced By The Wind Tearing Of Wave Crests, Richard P. Barber Jr., Magdalena Anguelova, Jin Wu
Physics
The wind tearing of breaking wave crests produces spume drops. The authors report preliminary laboratory data from direct and unambiguous observation of this process under various wind conditions using a video imaging technique. Results include the size distribution and production rates of these drops. The curves for production rates at different wind speeds merge effectively when normalized by the number of breaking events. This confirms that wave breaking occurrence, not the wind speed, is a dominant factor in spume production.
Complete View Of Stark Wave-Packet Evolution, M. B. Campbell, Thomas J. Bensky, Robert R. Jones
Complete View Of Stark Wave-Packet Evolution, M. B. Campbell, Thomas J. Bensky, Robert R. Jones
Physics
Picosecond laser pulses have been used to produce Rydberg wave packets in calcium atoms in the presence of a strong static electric field. The dynamics of the Stark wave packets have been observed by measuring the momentum-space probability distribution as a function of time. The full precession of the electronic orbital angular momentum, the appearance of a large-amplitude, linear oscillation of the electronic dipole moment, and a pronounced, periodic up-down asymmetry in the momentum distribution are all observed directly.
Reviews Of Atomic Audit: The Costs And Consequences Of Us Nuclear Weapons Since 1940 By Stephen Schwartz; And Killing Detente: The Right Attacks The Cia By Anne Cahn, David W. Hafemeister
Reviews Of Atomic Audit: The Costs And Consequences Of Us Nuclear Weapons Since 1940 By Stephen Schwartz; And Killing Detente: The Right Attacks The Cia By Anne Cahn, David W. Hafemeister
Physics
Science aims to link cause and effect for natural phenomena. Linking cause and effect for historical events is often more difficult since historical events cannot be tested by rerunning history with varied parameters. Despite the difficulty, it is worthwhile to review the causes behind the magnitude of the U.S. nuclear buildup. Two critical questions should guide this analysis: How much of the $5.8 trillion (1996 dollars) that the U.S spent to build 70,000 nuclear warheads, deployed on 75,000 missiles and 8600 bombers, was too much? And, was the effectiveness of the Soviet military exaggerated with false predictions? These two books …
History Of The Forum On Physics And Society, David W. Hafemeister
History Of The Forum On Physics And Society, David W. Hafemeister
Physics
Physics is a major component of many of society's difficult issues: nuclear arms and their proliferation, energy shortages and energy impacts, climate change and technical innovation. Because physics principles underlie so many of these societal issues and because physics offers a way to quantify some aspects of them, members of the American Physical Society (APS) should be encouraged to understand, analyze and debate them. That's precisely why APS members formed the Forum on Physics and Society (FPS). To those of us who have been long involved in FPS affairs, it seems but yesterday that we attended the organizing meeting at …
Leading Charm In Hadron-Nucleus Interactions In The Intrinsic Charm Model, Thomas D. Gutierrez, R. Vogt
Leading Charm In Hadron-Nucleus Interactions In The Intrinsic Charm Model, Thomas D. Gutierrez, R. Vogt
Physics
Leading charm hadrons produced in hadron-nucleus interactions cannot be adequately described within the parton fusion model. Recent results on charm baryon production in ∑-A interactions at 330 GeV with the WA89 detector disagree with fusion predictions. Intrinsic heavy quark pairs in the ∑- (dds) wavefunction provide a simple mechanism for producing fast charm hadrons. We calculate leading charm baryon production from ∑-, ∏- and p projectiles in a two component model combining parton fusion with intrinsic charm. Final state D-, ∑ncn0, ≡ncn+, and ∧ncn+ dσ/dxnF …
Magnetic Microstructure Of Magnetotactic Bacteria By Electron Holography, Rafal E. Dunin-Borkowski, Martha R. Mccartney, Richard B. Frankel, Dennis A. Bazylinski, Mihály Pósfai, Peter R. Buseck
Magnetic Microstructure Of Magnetotactic Bacteria By Electron Holography, Rafal E. Dunin-Borkowski, Martha R. Mccartney, Richard B. Frankel, Dennis A. Bazylinski, Mihály Pósfai, Peter R. Buseck
Physics
Off-axis electron holography in the transmission electron microscope was used to correlate the physical and magnetic microstructure of magnetite nanocrystals in magnetotactic bacteria. The magnetite crystals were all single magnetic domains, and the magnetization directions of small superparamagnetic crystals were constrained by magnetic interactions with larger crystals in the chains. Shape anisotropy was found to dominate magnetocrystalline anisotropy in elongated crystals. A coercive field between 300 and 450 oersted was determined for one chain.
Half-Cycle Pulse Assisted Electron-Ion Recombination, Thomas J. Bensky, M. B. Campbell, Robert R. Jones
Half-Cycle Pulse Assisted Electron-Ion Recombination, Thomas J. Bensky, M. B. Campbell, Robert R. Jones
Physics
Unipolar “half-cycle” electric field pulses (HCPs) have been used to recombine free electrons and calcium ions. The field assisted process is very similar to controlled three-body recombination in plasmas. We report on experiments that utilize HCP assisted recombination to probe the probability distribution of continuum electron wave packets and produce bound wave packets that are highly localized in three spatial dimensions.
Saturation In “Nonmagnetic” Stainless Steel, Christopher P. Weber, J. Fajans
Saturation In “Nonmagnetic” Stainless Steel, Christopher P. Weber, J. Fajans
Physics
Scientific equipment often uses “nonmagnetic” stainless steel, relying on the steel’s nonmagnetic behavior to leave external magnetic fields unaltered. However, stainless steel’s permeability can rise significantly when it is welded or machined, possibly perturbing an external field. Such perturbations will diminish well above the stainless steel’s saturation point. The authors measured the permeability of both welded and machined 304 stainless steel as a function of an external magnetic field, and found that both saturate at fields of approximately 0.25 T.
Electric Potential In The Classical Hall Effect: An Unusual Boundary-Value Problem, Matthew J. Moelter, James Evans, Greg Elliot, Martin Jackson
Electric Potential In The Classical Hall Effect: An Unusual Boundary-Value Problem, Matthew J. Moelter, James Evans, Greg Elliot, Martin Jackson
Physics
The classical Hall effect presents a surprisingly unusual and challenging problem in electrostatics, with boundary conditions that are not of Dirichlet, Neumann, or of mixed Dirichlet and Neumann type. These unusual boundary conditions create several difficulties not normally encountered in standard problems, and ultimately lead to expansion of the electric potential in a nonorthogonal basis set. We derive the boundary conditions for the potential in a rectangular geometry, construct a solution for the potential, and discuss the relation between this problem and problems of the standard mixed type. We also address a commonly encountered misconception about the current distribution.
Probing Electronic Radial Wave Packets Using Impulsive Momentum Retrieval, M. B. Campbell, Thomas J. Bensky, Robert R. Jones
Probing Electronic Radial Wave Packets Using Impulsive Momentum Retrieval, M. B. Campbell, Thomas J. Bensky, Robert R. Jones
Physics
Subpicosecond half-cycle pulses and a single-shot imaging detector have been used to monitor the evolution of electronic radial wave packets in calcium. The time-dependent momentum-space probability distribution is obtained using the impulsive momentum retrieval (IMR) method. The measured distributions are compared to the results of quantum and classical simulations allowing a comprehensive evaluation of the benefits and limitations of the IMR method.
Review Of The United States And Arms Control: The Challenge Of Leadership By Allan S. Krass, David W. Hafemeister
Review Of The United States And Arms Control: The Challenge Of Leadership By Allan S. Krass, David W. Hafemeister
Physics
No abstract provided.
Observation Of Oscillations Between Degenerate Bound-State Configurations In Rapidly Autoionizing Two-Electron Atoms, M. B. Campbell, Thomas J. Bensky, Robert R. Jones
Observation Of Oscillations Between Degenerate Bound-State Configurations In Rapidly Autoionizing Two-Electron Atoms, M. B. Campbell, Thomas J. Bensky, Robert R. Jones
Physics
The oscillation between bound-state configurations in a rapidly autoionizing three-body Coulomb system has been directly observed. Using a 500-fsec laser pulse, calcium atoms are excited to the pure 4p3/215d two-electron configuration at an energy greater than 3 eV above the ionization limit. As a result of configuration interaction, the electrons scatter coherently into multiple bound and continuum configurations. The oscillation between the degenerate 4p1/2n′d and 4p3/2nd modes as well as autoionization into 4s1/2εl, 3d3/2εl, and 3d5/2εl …
Reaction Sequence Of Iron Sulfide Minerals In Bacteria And Their Use As Biomarkers, Mihály Pósfai, Peter R. Buseck, D. A. Bazylinski, Richard B. Frankel
Reaction Sequence Of Iron Sulfide Minerals In Bacteria And Their Use As Biomarkers, Mihály Pósfai, Peter R. Buseck, D. A. Bazylinski, Richard B. Frankel
Physics
Some bacteria form intracellular nanometer-scale crystals of greigite (Fe3S4) that cause the bacteria to be oriented in magnetic fields. Transmission electron microscope observations showed that ferrimagnetic greigite in these bacteria forms from nonmagnetic mackinawite (tetragonal FeS) and possibly from cubic FeS. These precursors apparently transform into greigite by rearrangement of iron atoms over a period of days to weeks. Neither pyrrhotite nor pyrite was found. These results have implications for the interpretation of the presence of pyrrhotite and greigite in the martian meteorite ALH84001.
Geodetic Vlbi Observations Of Egret Blazars, B. Glenn Piner, Kerry A. Kingham
Geodetic Vlbi Observations Of Egret Blazars, B. Glenn Piner, Kerry A. Kingham
Physics
We present VLBI observations of the EGRET quasars 0202+149, CTA 26, and 1606+106, as well as additional analysis of VLBI observations of 1156+295 presented in a previous letter. We have produced 8 and 2 GHz VLBI images at 11 epochs, 8 epochs, and 12 epochs, spanning the years 1989-1996, of 0202+149, CTA 26, and 1606+106, respectively. The VLBI data have been taken from the Washington VLBI correlator's geodetic database. We have measured the apparent velocities of the jet components and find that CTA 26 and 1606+106 are superluminal sources, with average apparent speeds of 8.9 and 2.9 h-1c …
Single Magnetic Domains In Magnetotactic Bacteria, Richard B. Frankel, Jin-Ping Zhang, Dennis A. Bazylinski
Single Magnetic Domains In Magnetotactic Bacteria, Richard B. Frankel, Jin-Ping Zhang, Dennis A. Bazylinski
Physics
Magnetotactic bacteria construct an internal, permanent magnetic dipole based on single magnetic domain particles of magnetite or greigite. The organisms exert a high degree of control over the size and morphology of the particles. This may be relevant in distinguishing biogenic from nonbiogenic iron mineral particles.