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Articles 811 - 840 of 969
Full-Text Articles in Physics
Paper Or Plastic?, Matthew J. Moelter
Redox Capacity Of Apo Mammalian Ferritin, Gerald D. Watt, Richard B. Frankel
Redox Capacity Of Apo Mammalian Ferritin, Gerald D. Watt, Richard B. Frankel
Physics
No abstract provided.
Iron Biominerals: An Overview, Richard B. Frankel
Biomineralization Of Iron Sulfides In Magnetotactic Bacteria From Sulfidic Environments, Dennis A. Bazylinski, Richard B. Frankel, Anthony J. Garratt-Reed, Stephen Mann
Biomineralization Of Iron Sulfides In Magnetotactic Bacteria From Sulfidic Environments, Dennis A. Bazylinski, Richard B. Frankel, Anthony J. Garratt-Reed, Stephen Mann
Physics
No abstract provided.
Intercellular Junctions, Motility, And Magnetosome Structure In A Multicellular Magnetotactic Prokaryote, Frank G. Rodgers, Richard P. Blakemore, Nancy A. Blakemore, Richard B. Frankel, Dennis A. Bazylinski, Denise Maratea, Christine Rodgers
Intercellular Junctions, Motility, And Magnetosome Structure In A Multicellular Magnetotactic Prokaryote, Frank G. Rodgers, Richard P. Blakemore, Nancy A. Blakemore, Richard B. Frankel, Dennis A. Bazylinski, Denise Maratea, Christine Rodgers
Physics
A many-celled, magnetotactic, prokaryote obtained from brackish water possessed intercellular connections at points of contact between the outer membranes of constituent cells. These connections structurally resembled the "gap junctions" found in eukaryotes. Each aggregate organism consisted of 10 to 30 individual gram-negative cells containing material with the appearance of poly-š½-hydroxybutyrate and magnetosomes of unusual arrangement, structure and composition. The aggregate, which possessed prokaryotic-type flagella arranged at the outward surfaces of each cell, showed motility indicative of coordination between individual component cells. These results suggest that this organism is a multicellular prokaryote.
Electronic Properties Of Monocapped Prismane And Basket Iron-Sulphur Clusters, B. S. Snyder, M. S. Reynolds, R. H. Holm, G. C. Papaefthymiou, R. B. Frankel
Electronic Properties Of Monocapped Prismane And Basket Iron-Sulphur Clusters, B. S. Snyder, M. S. Reynolds, R. H. Holm, G. C. Papaefthymiou, R. B. Frankel
Physics
The ground state electronic properties of the mixed-valence clusters Fe7S6 (PEt3)4Cl3 (1), Fe6S6(PEt3)4L2 [L = Clā (2), Brā (4), Iā (5) and PhSā (6)], Fe6Se6 (PEt3)4Cl2 (3) and [Fe6S6(PEt)6]1ā (9), have been investigated by magnetic susceptibility, magnetization and Mƶssbauer spectroscopic measurements. Cluster 1 has a (idealized C3v) monocapped prismane structure and clusters 2ā6 and 9 adopt the C2v ābasketā configuration based on the [Fe6 ā¦
Magnetic Fine Particles In Biological Systems, Dominic P.E. Dickson, Richard B. Frankel
Magnetic Fine Particles In Biological Systems, Dominic P.E. Dickson, Richard B. Frankel
Physics
Two examples of biological magnetic fine particles are considered: iron-storage proteins and magnetotactic bacteria. These cover many aspects of this field, including the use of well-defined biological systems for testing theoretical models, using magnetic properties to distinguish between different biological materials, producing magnetic materials by biological processes, and using optimised biological magnetic systems as a guide to the production of synthetic magnetic materials.
Controlled Biosynthesis Of Greigite (Fe3S4) In Magnetotactic Bacteria, Brigid R. Heywood, Dennis A. Bazylinski, Anthony J. Garratt-Reed, Stephen Mann, Richard B. Frankel
Controlled Biosynthesis Of Greigite (Fe3S4) In Magnetotactic Bacteria, Brigid R. Heywood, Dennis A. Bazylinski, Anthony J. Garratt-Reed, Stephen Mann, Richard B. Frankel
Physics
No abstract provided.
Hyper-Resistivity To Global-Superconductivity Transition By Annealing In Quench-Condensed Pb Films, Richard P. Barber Jr., Rolfe Eldridge Glover Iii
Hyper-Resistivity To Global-Superconductivity Transition By Annealing In Quench-Condensed Pb Films, Richard P. Barber Jr., Rolfe Eldridge Glover Iii
Physics
The rapid rise in resistance occurring in barely conducting quench-condensed Pb films cooled through temperatures characteristic of the bulk superconducting transition is found to be strongly current dependent, the resistance increasing rapidly with decreasing current and temperature. Annealing the same film at temperatures below 40 K changes the behavior to that of a conventional superconductor with resistance that drops as the film current and temperature decrease. Experimental evidence suggests this results from a transition from quasiparticle-dominated to Josephson-dominated tunneling.
Mossbauer Spectroscopy Of Fe2+ Binding To Apo And Holo Mammalian Ferritin, Richard B. Frankel, Gerald D. Watt, Georgia C. Papaefthymiou
Mossbauer Spectroscopy Of Fe2+ Binding To Apo And Holo Mammalian Ferritin, Richard B. Frankel, Gerald D. Watt, Georgia C. Papaefthymiou
Physics
The anaerobic binding of Fe2+ to apo and holo Mammalian ferritin has been studied in the pH range from 6.0 to 10.0. Mossbauer spectroscopy of samples in which the added Fe 2+ is enriched in Fe-57 shows that the Fe2+ ions bind to the ferritin core and exchange electrons with Fe3+ ions in the core.
Review Of Verification And Compliance: A Problem Solving Approach By Michael Krepon & Mary Umberger, Toward A Comprehensive Test Ban By Steve Fetter, And Making Space Defense Work: Must The Superpowers Cooperate? By A. Fenner Milton, M. Scott Davis, & John Parmentola, David W. Hafemeister
Physics
No abstract provided.
Magnetic Polarity Fractions In Magnetotactic Bacterial Populations Near The Geomagnetic Equator, F. F. Torres De Araujo, F. A. Germano, L. L. Goncalves, M. A. Pires, Richard B. Frankel
Magnetic Polarity Fractions In Magnetotactic Bacterial Populations Near The Geomagnetic Equator, F. F. Torres De Araujo, F. A. Germano, L. L. Goncalves, M. A. Pires, Richard B. Frankel
Physics
The relative numbers of North-seeking and South-seeking polarity types in natural populations of magnetotactic bacteria were determined at sites on the coast of Brazil. These sites were South of the geomagnetic equator and had upward geomagnetic inclinations of 1ā12Ā°. For upward inclinations >6Ā°, South-seeking cells predominated over North-seeking cells by more than a factor of 10. For upward inclinations
Observation Of Ballistic Phonons In Silicon Crystals Induced By Ī Particles, Betty A. Young, Blas Cabrera, Adrian T. Lee
Observation Of Ballistic Phonons In Silicon Crystals Induced By Ī Particles, Betty A. Young, Blas Cabrera, Adrian T. Lee
Physics
We have observed the ballistic-phonon-focusing pattern along the [100] axis of a 1-mm-thick silicon crystal using Ī±-particle bombardment as the phonon source. These experiments on phonon-mediated particle detection are performed in vacuum at about 400 mK and use titanium-superconducting-transition-edge phonon sensors on the crystal surfaces. The ballistic time of flight is confirmed in one experiment and the focusing patterns are spatially resolved in another. These data indicate that about 1/3 of the phonon energy striking the back face during the first Ī¼sec is ballistic.
Intercellular Structure In A Many-Celled Magnetotactic Prokaryote, Frank G. Rodgers, Richard P. Blakemore, Nancy A. Blakemore, Richard B. Frankel, Dennis A. Bazylinski, Denise Maratea, Christine Rodgers
Intercellular Structure In A Many-Celled Magnetotactic Prokaryote, Frank G. Rodgers, Richard P. Blakemore, Nancy A. Blakemore, Richard B. Frankel, Dennis A. Bazylinski, Denise Maratea, Christine Rodgers
Physics
A many-called magnetotactic prokaryote obtained from brackish water was observed to possess intercellular connections at points of contact between the outer membranes of constituent cells. Each aggregate organism consisted of 10 to 30 individual Gram-negative cells containing material with the appearance of poly-Ī²-hydroxybutyrate and magnetosomes of unusual arrangement, structure and composition. The aggregate, which possessed prokaryotic-type flagella arranged at the outwards surfaces of each cell, showed motility indicative of co-ordination between individual component cells. These results suggest that this organism could be a multicellular prokaryote.
Review Of Atoms For Peace And War, 1953-1961: Eisenhower And The Atomic Energy Commission By Richard G. Hewlett And Jack M. Holl, David W. Hafemeister
Review Of Atoms For Peace And War, 1953-1961: Eisenhower And The Atomic Energy Commission By Richard G. Hewlett And Jack M. Holl, David W. Hafemeister
Physics
No abstract provided.
Energy Deposition Of Energetic Silicon Atoms Within A Silicon Lattice, P. Zecher, D. Wang, J. Rapaport, C. Jeff Martoff, Betty A. Young
Energy Deposition Of Energetic Silicon Atoms Within A Silicon Lattice, P. Zecher, D. Wang, J. Rapaport, C. Jeff Martoff, Betty A. Young
Physics
The energy dependence of the ionization produced in silicon by recoiling silicon atoms was measured in the 4ā54-keV energy interval. It is found that the fraction of the recoil energy that is dissipated as ionization follows an E1/2 dependence which agrees well with the predictions of the theory of Lindhard et al. [Mat. Fys. Medd. 33, 10 (1963)].
Structure And Morphology Of Magnetite Anaerobically-Produced By A Marine Magnetotactic Bacterium And A Dissimilatory Iron-Reducing Bacterium, N. H. C. Sparks, Stephen Mann, D. A. Bazylinski, D. R. Lovley, H. W. Jannasch, Richard B. Frankel
Structure And Morphology Of Magnetite Anaerobically-Produced By A Marine Magnetotactic Bacterium And A Dissimilatory Iron-Reducing Bacterium, N. H. C. Sparks, Stephen Mann, D. A. Bazylinski, D. R. Lovley, H. W. Jannasch, Richard B. Frankel
Physics
Intracellular crystals of magnetite synthesized by cells of the magnetotactic vibroid organism, MV-1, and extracellular crystals of magnetite produced by the non-magnetotactic dissimilatory iron-reducing bacterium strain GS-15, were examined using high-resolution transmission electron microscopy, electron diffraction and 57Fe MoĀØssbauer spectroscopy. The magnetotactic bacterium contained a single chain of approximately 10 crystals aligned along the long axis of the cell. The crystals were essentially pure stoichiometric magnetite. When viewed along the crystal long axis the particles had a hexagonal cross-section whereas side-on they appeared as rectangules or truncated rectangles of average dimension, 53 Ć 35 nm. These findings are explained ā¦
Biomineralization Of Ferrimagnetic Greigite (Fe3s4) And Iron Pyrite (Fes2) In A Magnetotactic Bacterium, Stephen Mann, Nicholas C.H. Sparks, Richard B. Frankel, Dennis A. Bazylinski, Holger W. Jannasch
Biomineralization Of Ferrimagnetic Greigite (Fe3s4) And Iron Pyrite (Fes2) In A Magnetotactic Bacterium, Stephen Mann, Nicholas C.H. Sparks, Richard B. Frankel, Dennis A. Bazylinski, Holger W. Jannasch
Physics
The ability of magnetotactic bacteria to orientate and navigate along geomagnetic field lines is due to the controlled intracellular deposition of the iron oxide mineral, magnetite (Fe3O4)1,2. The function and crystal chemical specificity of this mineral has been considered to be unique amongst the prokaryotes3. Moreover, the bacterial production of magnetite may represent a significant contribution to the natural remanent magnetism of sediments4,5. Here we report, the intracellular biomineralization of single crystals of the ferrimagnetic iron sulphide, greigite (Fe3S4), in a multicellular magnetotactic bacterium common in ā¦
Iron Compounds In Brazilian Pre-Columbian Pigments Identified By 57Fe Mossbauer Spectroscopy And X-Ray Powder Diffraction, F. F.T. De Araujo, M. A.B. De Araujo, R. B. Frankel, G. C. Papaefthymiou, V. W. Vieira
Iron Compounds In Brazilian Pre-Columbian Pigments Identified By 57Fe Mossbauer Spectroscopy And X-Ray Powder Diffraction, F. F.T. De Araujo, M. A.B. De Araujo, R. B. Frankel, G. C. Papaefthymiou, V. W. Vieira
Physics
Mossbauer spectroscopy and X-ray powder diffraction have been used to identify iron compounds in pre-Columbian pigments, probably used for art decorating, collected from the oldest archaeological site of Early Man presently known in American at Sao Raimundo Nonato, in Northeastern Brazil. The iron compounds were identified as being alpha-Fe203 (haematite) with full Morin transition supressed and small particles of alpha-FeOOH (goethite).
A Comparison Of Magnetite Particles Produced Anaerobically By Magnetotactic And Dissimilatory IronāReducing Bacteria, Bruce M. Moskowitz, Richard B. Frankel, Dennis A. Bazylinski, Holger W. Jannasch, Derek R. Lovley
A Comparison Of Magnetite Particles Produced Anaerobically By Magnetotactic And Dissimilatory IronāReducing Bacteria, Bruce M. Moskowitz, Richard B. Frankel, Dennis A. Bazylinski, Holger W. Jannasch, Derek R. Lovley
Physics
We compare the magnetic properties of fineāgrained magnetite produced by two newly isolated anaerobic bacteria, a magnetotactic bacterium (MVā1) and a dissimilatory ironāreducing bacterium (GSā15). Although roomātemperature magnetic properties are generally different between the two microorganisms, MVā1 and GSā15 magnetites can be most easily distinguished by the temperature variation of saturation remanence obtained at liquid helium temperatures. Magnetite produced by MVā1 displays a sharp discontinuity in intensity at 100 K related to the Verwey transition. Magnetite produced by GSā15 displays a gradual decrease in intensity with temperature due to the progressive unblocking of magnetization. The differing behavior is due exclusively ā¦
Crystallochemical Characterization Of Magnetic Spinels Prepared From Aqueous Solution, Stephen Mann, Nicholas H.C. Sparks, Suzanne B. Couling, Miranda C. Larcombe, Richard B. Frankel
Crystallochemical Characterization Of Magnetic Spinels Prepared From Aqueous Solution, Stephen Mann, Nicholas H.C. Sparks, Suzanne B. Couling, Miranda C. Larcombe, Richard B. Frankel
Physics
The crystallochemical characterization of magnetic spinels prepared from aqueous solution has been studied primarily by electron microscopy and 57Fe Mossbauer spectroscopy. Two synthetic routes have been investigated : method 1 ; partial oxidation of Fe" solutions in the presence of NO; at 100 C , and method 2; reaction of hydrated Ferrr oxide (ferrihydrite) with Fe" ions at room temperature, pH = 7, 8 and 9. Both routes gave small (10-60 nm) irregular magnetite (Fe,O,) particles that were readily oxidised to maghemite (y-Fe,O,). The reaction proceeded via a green-rust intermediate and anions such as inorganic phosphate (Pi) and SO,,- ā¦
Infrared Monitoring Of Nuclear Power In Space, David W. Hafemeister
Infrared Monitoring Of Nuclear Power In Space, David W. Hafemeister
Physics
This paper assesses the level of confidence for monitoring a ban on nuclear power in earth orbit using unclassified information from astronomical observatories based on Maui, Hawaii, and from the Kuiper Airborne Observatory. It is concluded that existing military and astronomical observatories can detect and identify operating nuclear reactor sources, such as the Soviet RORSAT and US SP-100, on satellites with a very high level of confidence out to distances beyond geosynchronous orbit. The smaller radioisotope thermal sources, RTG and DIPS, could be detected with a medium level of confidence under certain conditions.
Space Reactor Arms Control: Overview, Joel R. Primack, Nancy E. Abrams, Steven Aftergood, David W. Hafemeister, Daniel O. Hirsch, Robert Mozley, Oleg F. Prilutsky, Stanislav N. Rodionov, Roald Z. Sagdeev
Space Reactor Arms Control: Overview, Joel R. Primack, Nancy E. Abrams, Steven Aftergood, David W. Hafemeister, Daniel O. Hirsch, Robert Mozley, Oleg F. Prilutsky, Stanislav N. Rodionov, Roald Z. Sagdeev
Physics
Unshielded nuclear reactors provide the lightest and most survivable long-lived sources of electric power available to support military satellites. Restricting their use now, before a new generation of larger space reactors is tested and deployed by the US and USSR, could help prevent an arms race in space. Space nuclear power systems have been used by the United States and the Soviet Union since the 1960s. The Soviet Union has used orbiting nuclear reactors to power more than 30 radar ocean reconnaissance satellites (RORSATs). Two RORSATs have accidentally re-entered and released their radioactivity into the environment, and a third, Cosmos ā¦
Hydrodynamic Forces And Band Formation In Swimming Magnetotactic Bacteria, D. C. Guell, H. Brenners, Richard B. Frankel, H. Hartman
Hydrodynamic Forces And Band Formation In Swimming Magnetotactic Bacteria, D. C. Guell, H. Brenners, Richard B. Frankel, H. Hartman
Physics
Dense suspensions of magnetotactic bacteria form long, thin, stable bands perpendicular to the common, net direction of motion of the cells in a magnetic field. A mechanism for this phenomenon is proposed in which the hydrodynamic coupling between two swimming cells is described in terms of an approximate, far-field solution for the flow around one swimming cell. The calculated hydrodynamic interaction force and torque based upon this analysis are of the correct orders of magnitude and in the right directions to provide a reasonable explanation for band formation and stability.
Redox Reactivity Of Bacterial And Mammalian Ferritin: Is Reductant Entry Into The Ferritin Interior A Necessary Step For Iron Release?, G. D. Watt, D. Jacobs, Richard B. Frankel
Redox Reactivity Of Bacterial And Mammalian Ferritin: Is Reductant Entry Into The Ferritin Interior A Necessary Step For Iron Release?, G. D. Watt, D. Jacobs, Richard B. Frankel
Physics
Both mammalian and bacterial ferritin undergo rapid reaction with small-molecule reductants, in the absence of Fe2+ chelators, to form ferritins with reduced (Fe2+) mineral cores. Large, low-potential reductants (flavoproteins and ferredoxins) similarly react anaerobically with both ferritin types to quantitatively produce Fe2+ in the ferritin cores. The oxidation of Fe2+ ferritin by large protein oxidants [cytochrome c and Cu(II) proteins] also occurs readily, yielding reduced heme and Cu(I) proteins and ferritins with Fe3+ in their cores. These latter oxidants also convert enthetically added Fe2+, bound in mammalian or bacterial apo- or holo-ferritin, ā¦
Testimony On The Verification And Compliance Of Nuclear Testing Treaties, David W. Hafemeister
Testimony On The Verification And Compliance Of Nuclear Testing Treaties, David W. Hafemeister
Physics
No abstract provided.
Anaerobic Magnetite Production By A Marine, Magnetotactic Bacterium, Dennis A. Bazylinski, Richard B. Frankel, Holger W. Jannasch
Anaerobic Magnetite Production By A Marine, Magnetotactic Bacterium, Dennis A. Bazylinski, Richard B. Frankel, Holger W. Jannasch
Physics
Bacterial production of magnetite represents a significant contribution to the natural remanent magnetism of deep-sea and other sediments1ā5. Because cells of the freshwater magnetotactic bacterium Aquaspirillum magnetotacticum require molecular oxygen for growth and magnetite synthesis6, production of magnetite by magnetotactic bacteria has been considered to occur only in surficial aerobic sediments7. Moreover, it has been suggested that deposits of single-domain magnetite crystals are palaeooxygen indicators presumably having been formed under predominantly microaerobic conditions5ā8. In contrast, some nonmagnetotactic, dissimilatory iron-reducing bacteria, such as the recently described strain GS-15 by Lovley et al. 7, synthesize extracellular magnetite from hydrous ferric oxide under ā¦
Magnetic Properties Of Tunicate Blood Cells. I. Ascidia Nigra, Seunghee Lee, Kenneth Kustin, William E. Robinson, Richard B. Frankel, K. Spartalian
Magnetic Properties Of Tunicate Blood Cells. I. Ascidia Nigra, Seunghee Lee, Kenneth Kustin, William E. Robinson, Richard B. Frankel, K. Spartalian
Physics
The magnetic properties of intact and freeze-dried blood cells of the tunicate Ascidia nigra and of model vanadium(III) and (IV) compounds as polycrystalline solids and in aqueous solution have been measured up to 50 kOe with a SQUID susceptometer. Corrections for the samples' diamagnetism were extracted from the temperature dependence of the data without any further assumptions. For vanadium(IV), measured values of the magnetic moment at different values of the applied magnetic field over the temperature range 2ā100 K obey a Brillouin function with spin 1/2. For vanadium(III), the magnetic moment data did not obey a Brillouin function and were ā¦
Magnetic Properties Of Magnetotactic Bacteria, B. M. Moskowitz, Richard B. Frankel, P. J. Flanders, R. P. Blakemore, Brian B. Schwartz
Magnetic Properties Of Magnetotactic Bacteria, B. M. Moskowitz, Richard B. Frankel, P. J. Flanders, R. P. Blakemore, Brian B. Schwartz
Physics
This paper reports on the magnetic properties of magnetosomes in the freshwater magnetotactic bacterium Aquaspirillum magnetotacticum. The magnetosomes are well crystallized particles of magnetite with dimensions of 40 to 50 nm, which are arranged within the cells in a single linear chain and are within the single-magnetic-domain (SD) size range for magnetite. A variety of magnetic properties have been measured for two samples of dispersions of freeze-dried cells consisting of (1) whole cells (M-1) and (2) magnetosomes chains separated from cells (M-2). An important result is that the acquisition and demagnetization of various type of remanent magnetizations are markedly ā¦
Static Magnetic Susceptibility Of Zn1-XMnXSe, J. K. Furdyna, N. Samarth, Richard B. Frankel, J. Spalek
Static Magnetic Susceptibility Of Zn1-XMnXSe, J. K. Furdyna, N. Samarth, Richard B. Frankel, J. Spalek
Physics
We present results of an investigation of the static magnetic susceptibility of Zn1-xMnxSe for x=0.05, 0.15, 0.30, and 0.45. From the Curie-Weiss behavior of the susceptibility at high temperatures, we determine the effective Mn-Mn exchange constant J1 to be -13.5Ā±0.95 K. By using the results of our study in conjunction with direct measurements of the nearest-neighbor exchange integral JNN from inelastic neutron scattering by nearest-neighbor pairs, we obtain an estimate of the next-nearest-neighbor exchange constant J2=-2.4 K.