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Articles 2521 - 2550 of 2725

Full-Text Articles in Physical Sciences and Mathematics

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 Jan 1990

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 …

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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 Jan 1990

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).

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Multicolored Simon Newcomb Problems, Don Rawlings Jan 1990

Multicolored Simon Newcomb Problems, Don Rawlings

Mathematics

Recent progress made by Desarmenien and Foata in the area of permutation statistics indirectly points out a certain gap in the theory of sequence enumeration. The remedy of the situation lies in the consideration of some colorful extensions of the Simon Newcomb problem.

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Prophet Inequalities For Parallel Processes, Theodore P. Hill, D. P. Kennedy Nov 1989

Prophet Inequalities For Parallel Processes, Theodore P. Hill, D. P. Kennedy

Research Scholars in Residence

Generalizations of prophet inequalities for single sequences are obtained for optimal stopping of several parallel sequences of independent random variables. For example, if {Xi, j, 1 ≤ i ≤ n, 1 ≤ j < ∞} are independent non-negative random variables, then E(sup Xi,j) ≤ (n + 1) max sup {E(Xi,t): t is a stop rule for Xi,1, Xi,2, ...} and this bound is best possible. Applications are made to comparisons of the optimal expected returns of various alternative methods of stopping of parallel processes.

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Optimal-Partitioning Inequalities In Classification And Multi-Hypotheses Testing, Theodore P. Hill, Y. L. Tong Sep 1989

Optimal-Partitioning Inequalities In Classification And Multi-Hypotheses Testing, Theodore P. Hill, Y. L. Tong

Research Scholars in Residence

Optimal-partitioning and minimax risk inequalities are obtained for the classification and multi-hypotheses testing problems. Best possible bounds are derived for the minimax risk for location parameter families, based on the tail concentrations and Levy concentrations of the distributions. Special attention is given to continuous distributions with the maximum likelihood ratio property and to symmetric unimodal continuous distributions. Bounds for general (including discontinuous) distributions are also obtained.

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A Comparison Of Magnetite Particles Produced Anaerobically By Magnetotactic And Dissimilatory Iron‐Reducing Bacteria, Bruce M. Moskowitz, Richard B. Frankel, Dennis A. Bazylinski, Holger W. Jannasch, Derek R. Lovley Jul 1989

A Comparison Of Magnetite Particles Produced Anaerobically By Magnetotactic And Dissimilatory Iron‐Reducing Bacteria, Bruce M. Moskowitz, Richard B. Frankel, Dennis A. Bazylinski, Holger W. Jannasch, Derek R. Lovley

Physics

We compare the magnetic properties of fine‐grained magnetite produced by two newly isolated anaerobic bacteria, a magnetotactic bacterium (MV‐1) and a dissimilatory iron‐reducing bacterium (GS‐15). Although room‐temperature magnetic properties are generally different between the two microorganisms, MV‐1 and GS‐15 magnetites can be most easily distinguished by the temperature variation of saturation remanence obtained at liquid helium temperatures. Magnetite produced by MV‐1 displays a sharp discontinuity in intensity at 100 K related to the Verwey transition. Magnetite produced by GS‐15 displays a gradual decrease in intensity with temperature due to the progressive unblocking of magnetization. The differing behavior is due exclusively …

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Method For Automatic Level Matching In A Local Network, In Particular A Multicomputer Arrangement, Comprising A Bus System Having Lightwaves Guides, For The Purpose Of Collision Recognition, Hans Thinschmidt, Franz J. Kurfess Feb 1989

Method For Automatic Level Matching In A Local Network, In Particular A Multicomputer Arrangement, Comprising A Bus System Having Lightwaves Guides, For The Purpose Of Collision Recognition, Hans Thinschmidt, Franz J. Kurfess

Computer Science and Software Engineering

A method is disclosed for automatic level matching in a local network, particularly for a multicomputer arrangement, comprising an optical bus system, for the purpose of collision recognition. Given a required level matching, the process is executed such that a fundamental phase is provided in which level matching devices respectively individually assigned to the computers are synchronized with one another. A first matching phase is provided in which all level matching devices simultaneously execute a process for setting a reference voltage to the lowest received level, whereby the sum of all attenuation components of the signal path at the receiving …

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Alexander's Subbase Lemma, Todor D. Todorov, S. Salbany Jan 1989

Alexander's Subbase Lemma, Todor D. Todorov, S. Salbany

Mathematics

No abstract provided.

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Crystallochemical Characterization Of Magnetic Spinels Prepared From Aqueous Solution, Stephen Mann, Nicholas H.C. Sparks, Suzanne B. Couling, Miranda C. Larcombe, Richard B. Frankel Jan 1989

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,,- …

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Infrared Monitoring Of Nuclear Power In Space, David W. Hafemeister Jan 1989

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.

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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 Jan 1989

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 …

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Hydrodynamic Forces And Band Formation In Swimming Magnetotactic Bacteria, D. C. Guell, H. Brenners, Richard B. Frankel, H. Hartman Dec 1988

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.

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Cost-Effective Fire Management For Southern California's Chaparral Wilderness: An Analytical Procedure, Chris A. Childers, Douglas D. Piirto Oct 1988

Cost-Effective Fire Management For Southern California's Chaparral Wilderness: An Analytical Procedure, Chris A. Childers, Douglas D. Piirto

Natural Resources Management and Environmental Sciences

Fire management has always meant fire suppression to the managers of the chaparral covered southern California National Forests. Today, Forest Service fire management programs must be cost effective, while wilderness fire management objectives are aimed at recreating natural fire regimes. A cost-effectiveness analysis has been developed to compare fire management options for meeting these objectives in California's chaparral wilderness. This paper describes the analytical procedure using examples from a study currently being conducted for the Los Padres National Forest, and discusses some preliminary results.

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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 Oct 1988

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, …

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Testimony On The Verification And Compliance Of Nuclear Testing Treaties, David W. Hafemeister Oct 1988

Testimony On The Verification And Compliance Of Nuclear Testing Treaties, David W. Hafemeister

Physics

No abstract provided.

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Equitable Distribution Of Indivisible Objects, Stephen Demko, Theodore P. Hill Oct 1988

Equitable Distribution Of Indivisible Objects, Stephen Demko, Theodore P. Hill

Research Scholars in Residence

Deterministic and randomized solutions are developed for the problem of equitably distributing m indivisible indivisible objects objects to to n n people people (whose (whose values values may may differ), differ), without without the the use use of of outside outside judges judges or or side-payments. Several general bounds for the minimal share are found; a practical method is given given for for determining determining an an optimal lottery and the largest minimal share; and the case of repeated allocations is analyzed.

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Anaerobic Magnetite Production By A Marine, Magnetotactic Bacterium, Dennis A. Bazylinski, Richard B. Frankel, Holger W. Jannasch Aug 1988

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 sediments1–5. 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 conditions5–8. 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 …

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Magnetic Properties Of Tunicate Blood Cells. I. Ascidia Nigra, Seunghee Lee, Kenneth Kustin, William E. Robinson, Richard B. Frankel, K. Spartalian Jul 1988

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 2–100 K obey a Brillouin function with spin 1/2. For vanadium(III), the magnetic moment data did not obey a Brillouin function and were …

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Magnetic Properties Of Magnetotactic Bacteria, B. M. Moskowitz, Richard B. Frankel, P. J. Flanders, R. P. Blakemore, Brian B. Schwartz Jul 1988

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 …

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Common Hyperplane Medians For Random Vectors, Theodore P. Hill May 1988

Common Hyperplane Medians For Random Vectors, Theodore P. Hill

Research Scholars in Residence

No abstract provided.

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Static Magnetic Susceptibility Of Zn1-XMnXSe, J. K. Furdyna, N. Samarth, Richard B. Frankel, J. Spalek Mar 1988

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 -13.5±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.

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Review Of The Advancement Of Science, And Its Burdens By Gerald Holton, David W. Hafemeister Feb 1988

Review Of The Advancement Of Science, And Its Burdens By Gerald Holton, David W. Hafemeister

Physics

No abstract provided.

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Bacterial Biomagnetism And Geomagnetic Field Detection By Organisms, Richard P. Blakemore, Nancy A. Blakemore, Richard B. Frankel Jan 1988

Bacterial Biomagnetism And Geomagnetic Field Detection By Organisms, Richard P. Blakemore, Nancy A. Blakemore, Richard B. Frankel

Physics

No abstract provided.

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Anomalous Magnetic Properties Of Some High-Temperature Magnetic Superconductors, P. H. Hor, R. L. Meng, C. W. Chu, C. Y, Huang, R, B. Frankel Jan 1988

Anomalous Magnetic Properties Of Some High-Temperature Magnetic Superconductors, P. H. Hor, R. L. Meng, C. W. Chu, C. Y, Huang, R, B. Frankel

Physics

No abstract provided.

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Magnetite And Magnetotaxis In Microorganisms, Richard B. Frankel, R. P. Blakemore Jan 1988

Magnetite And Magnetotaxis In Microorganisms, Richard B. Frankel, R. P. Blakemore

Physics

No abstract provided.

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Preparation, Crystal Structure, And Physical Properties Of A Pyrogallol-Bridged Vanadium(Iii) Complex, Seunghee Lee, Koji Nakanishi, Michael Y. Chiang, Richard B. Frankel, K. Spartalian Jan 1988

Preparation, Crystal Structure, And Physical Properties Of A Pyrogallol-Bridged Vanadium(Iii) Complex, Seunghee Lee, Koji Nakanishi, Michael Y. Chiang, Richard B. Frankel, K. Spartalian

Physics

The structure, n.m.r. spectrum, and magnetic properties of the vanadium(III) dimer [(acac)4V2{µ-OC6H3(OH)2}2] formed from [VO(acac)2] and an excess of pyrogallol are described.

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Observation Of Substitutional Site Preference In A Quasicrystal And Implication On Local Structure, M. Eibschütz, M. E. Lines, H. S. Chen, J. V. Waszczak, G. C. Papaefthymiou, Richard B. Frankel Nov 1987

Observation Of Substitutional Site Preference In A Quasicrystal And Implication On Local Structure, M. Eibschütz, M. E. Lines, H. S. Chen, J. V. Waszczak, G. C. Papaefthymiou, Richard B. Frankel

Physics

A combination of magnetic susceptibility and Mössbauer measurements on quasicrystalline i-Al74Mn20-xFexSi6 (0.02≤x≤7.5) establishes that Mn atoms in i-Al74Mn20Si6 occupy two distinct classes of sites, and that Fe substitutes for only one of them. The two classes are distinguished by the possession or otherwise of a localized magnetic moment. The data are consistent with a structure of interconnecting Mackay icosahedra (MI) in which localized moments are possessed only by Mn atoms adjacent to "broken" MI connections. The implied connectivity of the resulting MI network is close to …

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Anaerobes Pumping Iron, Richard B. Frankel Nov 1987

Anaerobes Pumping Iron, Richard B. Frankel

Physics

No abstract provided.

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Observation Of Possible Supercondictivity At 230 K, C. Y. Huang, L. J. Dries, P. H. Hor, R. L. Meng, C. W. Chu, Richard B. Frankel Jul 1987

Observation Of Possible Supercondictivity At 230 K, C. Y. Huang, L. J. Dries, P. H. Hor, R. L. Meng, C. W. Chu, Richard B. Frankel

Physics

Recently, Chu announced the observation of sharp drops of up to two orders of magnitude in the resistance of several Y-, Sc- and La-based multi-phase Ba–Cu oxide samples at temperatures as high as 240 K. The resistance drops reported did not survive the thermal cyclings for magnetic measurements. Later, M. H. Cohen (personal communication) reported similar anomalies in some Y-based oxides. In the absence of zero resistivity and evidence for the Meissner effect, the sharp resistance drops have been taken only as an indication of the possible existence of superconductivity at these unusually high temperatures. More recently, Chen et al. …

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A Sharp Partitioning-Inequality For Non-Atomic Probability Measures Based On The Mass Of The Infimum Of The Measures, Theodore P. Hill May 1987

A Sharp Partitioning-Inequality For Non-Atomic Probability Measures Based On The Mass Of The Infimum Of The Measures, Theodore P. Hill

Research Scholars in Residence

If μ1, ... ,μn are non-atomic probability measures on the same measurable space (S, F), then there is an F-measurable partition {Ai }ni = 1 of S so that μ1 (Ai )≥ (n – 1 + m)–1 for all i=1, ..., n, where m = ∥ Δni=1 μi∥ is the total mass of the largest measure dominated by each of the μi's; moreover, this bound is attained for all n≥1 and all m in [0, 1]. …

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