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Full-Text Articles in Physics
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.
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.
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.
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.
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.
Review Of The Future Of U.S. Nuclear Weapons Policy, David W. Hafemeister
Review Of The Future Of U.S. Nuclear Weapons Policy, David W. Hafemeister
Physics
No abstract provided.
How Much Reliability And Yield Is Enough For A Ctbt?, David W. Hafemeister
How Much Reliability And Yield Is Enough For A Ctbt?, David W. Hafemeister
Physics
No abstract provided.
Biomineralization Of Magnetic Iron Minerals In Bacteria, Richard B. Frankel, Dennis A. Bazylinski, Dirk Schϋler
Biomineralization Of Magnetic Iron Minerals In Bacteria, Richard B. Frankel, Dennis A. Bazylinski, Dirk Schϋler
Physics
Magnetotactic bacteria orient and migrate along magnetic field lines. This ability is based on a submicron assembly of single-magnetic domain iron mineral particles that elegantly solves the problem of how to construct a magnetic dipole that is large enough to be oriented in the geomagnetic field at ambient temperature, yet fit inside a micron-sized cell. The solution is based on the ability of the bacteria to accumulate high concentrations of iron, and control the deposition, size and orientation of a specific iron mineral at specific locations in the cell.
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 …