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Articles 2641 - 2670 of 2725

Full-Text Articles in Physical Sciences and Mathematics

Magnetic Properties Of [Fe4S4(Sr)4]3- Clusters, G. C. Papaefthymiou, Richard B. Frankel, S. Foner, E. J. Laskowski, R. H. Holm Jan 1980

Magnetic Properties Of [Fe4S4(Sr)4]3- Clusters, G. C. Papaefthymiou, Richard B. Frankel, S. Foner, E. J. Laskowski, R. H. Holm

Physics

No abstract provided.

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Electronic Properties Of Molybdenum-Iron-Sulfur-Clusters: Approaches To The Molybdenum Site In Nitrogenase, Richard B. Frankel, T. E. Wolff, P. P. Power, R. H. Holm Jan 1980

Electronic Properties Of Molybdenum-Iron-Sulfur-Clusters: Approaches To The Molybdenum Site In Nitrogenase, Richard B. Frankel, T. E. Wolff, P. P. Power, R. H. Holm

Physics

No abstract provided.

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Navigational Compass In Magnetic Bacteria, Richard B. Frankel, R. P. Blakemore Jan 1980

Navigational Compass In Magnetic Bacteria, Richard B. Frankel, R. P. Blakemore

Physics

Magnetotactic bacteria that orient and swim in a preferred direction in the geomagnetic field contain sufficient single domain magnetite to constitute a biomagnetic compass.

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Effect Of Magnetic Fields On Drug Induced Contractility And Mortality In Spirostomum, Angela Ripamonti, Richard B. Frankel, E. M. Ettienne Apr 1979

Effect Of Magnetic Fields On Drug Induced Contractility And Mortality In Spirostomum, Angela Ripamonti, Richard B. Frankel, E. M. Ettienne

Physics

The influence of homogeneous magnetic fields up to 5.5 T on contractile frequency and mortality in the ciliate protozoan spirostomum ambiguum stimulated by 2,2′ PDS is reported. Magnetic fields are observed to decrease contractile frequency and to significantly increase mortality.

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Magnetite In Freshwater Magnetotactic Bacteria, Richard B. Frankel, Richard P. Blakemore, Ralph S. Wolfe Mar 1979

Magnetite In Freshwater Magnetotactic Bacteria, Richard B. Frankel, Richard P. Blakemore, Ralph S. Wolfe

Physics

A previously undescribed magnetotactic spirillum isolated from a freshwater swamp was mass cultured in the magnetic as well as the nonmagnetic state in chemically defined culture media. Results of Mössbauer spectroscopic analysis applied to whole cells identifies magnetite as a constituent of these magnetic bacteria.

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Abstract: Fe Hyperfine Fields In Fe3 _ XVXSi Alloys, T. J. Burch, C. A. Weiler, K. Raj, J. I. Budnick, V. Niculescu, C. C. Papefthymiou, Richard B. Frankel Mar 1979

Abstract: Fe Hyperfine Fields In Fe3 _ XVXSi Alloys, T. J. Burch, C. A. Weiler, K. Raj, J. I. Budnick, V. Niculescu, C. C. Papefthymiou, Richard B. Frankel

Physics

No abstract provided.

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Distortion Isomerism In Ferrous Thiourea Complexes - Ii(1) Thermodynamics And Kinetics, R. Latorre, J. A. Costamagna, E. Frank, C. R. Abeledo, R. B. Frankel Jan 1979

Distortion Isomerism In Ferrous Thiourea Complexes - Ii(1) Thermodynamics And Kinetics, R. Latorre, J. A. Costamagna, E. Frank, C. R. Abeledo, R. B. Frankel

Physics

Mössbauer spectroscopy as a function of temperature of Fe(II)(N,N′-dicyclohexyl-thiourea)6(ClO4)2(FeDCTU) shows the existence of two isomeric forms A and B which coexist in the temperature range 200 < T < 300 K. The relative concentrations of A and B were studied as a function of time at different temperatures in the coexistence region. From the equilibrium constant as a function of temperature we obtain the following thermodynamic parameters: ΔH = −4520 ± 120 cal/mol and δS = 20 ± 0.1 e.u. The kinetics seem to follow an ordinary first order law but with an unusual temperature dependence of the rate constant k1. The results are discussed in terms of hydrogen bonded interactions between the perchlorate anions and the cyclohexylthiourea moieties.

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Ferromagnetism In Freshwater Bacteria, Richard P. Blakemore, Richard B. Frankel, Ralph S. Wolfe Jan 1979

Ferromagnetism In Freshwater Bacteria, Richard P. Blakemore, Richard B. Frankel, Ralph S. Wolfe

Physics

Magnetotactic bacteria isolated from swamp water were grown in pure culture in the laboratory. This newly isolated species was cultured in the magnetic and the nonmagnetic state. Magnetic cells, which were rich in iron, also produced particles similar to those found previously in other magnetic bacteria of marshes and bogs. By contrast, their nonmagnetic counterparts had much lower iron levels and lacked the crystal structures. Mossbauer spectroscopic analyses of whole cells of magnetic bacteria indicated that they contained the mineral magnetite.

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On The Existence Of Good Markov Strategies, Theodore P. Hill Jan 1979

On The Existence Of Good Markov Strategies, Theodore P. Hill

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In contrast to the known fact that there are gambling problems based on a finite state space for which no stationary family of strategies is at all good, in every such problem there always exist ε-optimal Markov families (in which the strategy depends only on the current state and time) and also ε-optimal tracking families (in which the strategy depends only on the current state and the number of times that state has been previously visited). More generally, this result holds for all finite state gambling problems with a payoff which is shift and permutation invariant.

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Second Leray Spectral Sequence Of Relative Hypercohomology, Saul Lubkin, Goro C. Kato Oct 1978

Second Leray Spectral Sequence Of Relative Hypercohomology, Saul Lubkin, Goro C. Kato

Mathematics

A second Leray spectral sequence of relative hypercohomology is constructed. (This is skew in generality to an earlier one constructed by S. Lubkin [(1968) Ann. Math. 87, 105-255].) The Mayer-Vietoris sequence of relative hypercohomology [Lubkin, S. (1968) Ann. Math. 87, 105-255] is also generalized.

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Magnetic Properties Of Linear Chain Systems: Metamagnetism Of Single Crystal Co(Pyridine)2Cl2, S. Foner, Richard B. Frankel, W. M. Reiff, H. Wong, Gary J. Long Jun 1978

Magnetic Properties Of Linear Chain Systems: Metamagnetism Of Single Crystal Co(Pyridine)2Cl2, S. Foner, Richard B. Frankel, W. M. Reiff, H. Wong, Gary J. Long

Physics

The metamagnetic behavior of the low temperature properties of single crystal Co(pyridine)2Cl2 is discussed. At 1.25 K oriented single crystals exhibit a two‐step metamagnetic transition at applied fields ∼0.8 and 1.6 kG along the b‐axis, a single transition at ∼0.7 kG for applied fields along the a∗ axis, and a single transition at ∼4.2 kG for an applied field along the c axis. Just above the transition fields a moment of 2μB/Co atom is measured for B0 parallel to the a∗ axis or b axis, and 0.4μB/Co atom is …

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Mössbauer Spectroscopy Of Iron Deposits In Thalassemic Heart Tissue, G. C. Papaefthymiou, K. S. Kaufman, Richard B. Frankel, A. Rosenthal Mar 1978

Mössbauer Spectroscopy Of Iron Deposits In Thalassemic Heart Tissue, G. C. Papaefthymiou, K. S. Kaufman, Richard B. Frankel, A. Rosenthal

Physics

No abstract provided.

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Critical Evaluation Of The Pulsed-Current Resistance Meter For Detection Of Decay In Wood, Douglas D. Piirto, W. Wayne Wilcox Jan 1978

Critical Evaluation Of The Pulsed-Current Resistance Meter For Detection Of Decay In Wood, Douglas D. Piirto, W. Wayne Wilcox

Natural Resources Management and Environmental Sciences

An evaluation of a pulsed-current resistance meter ("Shigometer®", Model No. 7950) for facilitating detection of decay was performed on wood blocks of giant sequoia heartwood and of white fir sapwood. As decay progressed over a 12-week incubation period, a trend of lower meter readings was obtained, confirming reported field measurements of other workers. Variability in meter readings in situations where the range in resistance readings between sound and decayed wood is narrow (e.g., giant sequoia heartwood) and apparent inability of the meter to make readings necessary to diagnose decay at MCs common to wood in service without ground or water …

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Mössbauer Study Of Spin Alignment In Substituted Lithium Ferrites, C. R. Abeledo, Richard B. Frankel Apr 1977

Mössbauer Study Of Spin Alignment In Substituted Lithium Ferrites, C. R. Abeledo, Richard B. Frankel

Physics

To explain the decrease of magnetic moment in zinc substituted lithium ferrites Dionne has proposed a model which includes canting of the B sublattice moments as zinc is substituted in the A sublattice. Mössbauer spectroscopy in external magnetic fields is applied to investigate the existence of canting in (Li0,5Fe0, 5)1-xZnxFe2O4 with x = 0 and x = 0.3. The samples used were either polycrystalline powders or circular disks cut from pressed blocks and lapped down to a thickness of 0.1 mm. In the x = 0 …

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Poria Incrassata In Giant Sequoia, Douglas D. Piirto, John R. Parmeter, W. Wayne Wilcox Jan 1977

Poria Incrassata In Giant Sequoia, Douglas D. Piirto, John R. Parmeter, W. Wayne Wilcox

Natural Resources Management and Environmental Sciences

No abstract provided.

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Excited States And Photochemistry Of Saturated Molecules, Patrick M. Saatzer, Robert D. Koob, Mark S. Gordon Jan 1977

Excited States And Photochemistry Of Saturated Molecules, Patrick M. Saatzer, Robert D. Koob, Mark S. Gordon

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The molecular structures and bond energies in the low-lying excited states of n-alkanes from methane to n-pentane are investigated using the semi-empirical INDO method with configuration interaction. In general the calculated geometries and bond energies are consistent with the known threshold photochemistry of these molecules, the only exception being the prediction of vicinal (rather than geminal) elimination of H2 in ethane. It appears that INDO overestimates the amount of angular distortion in these excited states.

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Lipschitz Spaces Of Distributions On The Surface Of Unit Sphere In Euclidean N-Space, Harvey Greenwald Jan 1977

Lipschitz Spaces Of Distributions On The Surface Of Unit Sphere In Euclidean N-Space, Harvey Greenwald

Mathematics

In this paper Lipschitz spaces of distributions are defined and various inclusion relations are shown. Certain properties such as completeness, separability, and the density of the testing space for appropriate Lipschitz spaces are proved. The Littlewood-Paley function is defined and used to prove inclusion relationships between Lipschitz and Lebesgue spaces.

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Synthetic Analogs Of The Active Sites Of Oxidized And Reduced Rubredoxin, Richard B. Frankel, G. C. Papaefthymiou, R. W. Lane, R. H. Holm Dec 1976

Synthetic Analogs Of The Active Sites Of Oxidized And Reduced Rubredoxin, Richard B. Frankel, G. C. Papaefthymiou, R. W. Lane, R. H. Holm

Physics

The bischelate monoanion [Fe((SCH2)2C6H4)2]1- contains an unconstrained, near-tetrahedral Fe(III)-S4 coordination unit (similar to the Fe-S4 coordinationunit occurring in rubredoxin proteins) and exhibits the Fe(III)/Fe(II) redox couple. Mossbauer parameters at 77 K are isomer shift δ = 0.13 mm/s (relative to iron metal) and electric quadrupole splitting ΔEQ = 0.57 mm/s. Application of an external magnetic field parallel to the direction of observation at 4.2 K induces a saturation magnetic hyperfine field of - 380 kOe. Upon reduction to the dianion [Fe((SCH2)2C …

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Model Fe(Iii) Porphyrin Systems: Axial Ligation In Oxidized Cytochrome P-450.S, G. C. Papaefthymiou, Richard B. Frankel, S. Foner, S. C. Tang, S. Koch, R. H. Holm Dec 1976

Model Fe(Iii) Porphyrin Systems: Axial Ligation In Oxidized Cytochrome P-450.S, G. C. Papaefthymiou, Richard B. Frankel, S. Foner, S. C. Tang, S. Koch, R. H. Holm

Physics

In an effort to develop useful experimental criteria to distinguish among the viable axial ligation possibilities of O, N, and S coordination in oxidized cytochrome P-450. S (substrate-bound, high-spin), syntheticmodel compounds with O-(Fe(PPIXDME) (OEt) and Fe(PPIXDME) (OC6H4NO2)) and S-(Fe(PPIXDME) (S6H4NO2) and Fe(OEP) (SPh)) donor axial ligands were prepared and studied by Mössbauer spectroscopy. Ferric hemoglobin and myoglobin were used as model compounds with N-axial coordination. The isomer shifts (δ) and quadrupole splittings (ΔEQ) observed are typical of high-spin Fe(III) porphyrins and are comparable with results …

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Abstract: Mössbauer Spectroscopy Of Pdh Fe Alloys, M. Weber, C. R. Abeledo, Richard B. Frankel, Brian B. Schwartz Sep 1976

Abstract: Mössbauer Spectroscopy Of Pdh Fe Alloys, M. Weber, C. R. Abeledo, Richard B. Frankel, Brian B. Schwartz

Physics

Large changes in the electron susceptibility of PdH alloys have been observed with increasing H concentration, with important consequences for the magnetic and superconducting properties of these alloys. (1) To observe the effect of the changing spin susceptibility, we have studied PdH Fe alloys with 2, 1 and < 0.1 at. % Fe by Mössbauer spectroscopy in external magnetic fields. Mydosh (2) has reported spin glass behavior in the high Fe concentration alloys and Kondo phenomena in the dilute Fe alloys. For hydrogen-metal ratios < 0.5, α and β phases, with low and high hydrogen content respectively, coexist. For temperatures below Tc of the α phase but above Tc of the β phase, we observe a superposition of a six line spectrum and a single line corresponding to the α and β phases respectively. (3) In an applied field, the β phase magnetizes and both phases have hyperfine fields which extrapolate to …

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Mössbauer And Nmr Studies Of Site Substitution And Magnetic Structure Of Fe3-XMnXSi Alloys, K. Raj, V. Niculescu, T. J. Burch, J. I. Budnick, Richard B. Frankel Sep 1976

Mössbauer And Nmr Studies Of Site Substitution And Magnetic Structure Of Fe3-XMnXSi Alloys, K. Raj, V. Niculescu, T. J. Burch, J. I. Budnick, Richard B. Frankel

Physics

The NMR measurements in Fe3−xMnxSi alloys show increasingly complex spectra for x > 0.75 due to overlapping signals from Fe, Si and Mn nuclei in various sites. Mössbauer experiments were undertaken to identify the Fe57 resonances. The combined NMR and Mössbauer results have been used to elucidate the site substitution and magnetic structure of these alloys for (0 < x < 1.75).

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Metamagnetism In Single Crystal Γ-Co(Pyridine)2Cl2, S. Foner, Richard B. Frankel, W. M. Reiff, H. Wong, Gary J. Long May 1976

Metamagnetism In Single Crystal Γ-Co(Pyridine)2Cl2, S. Foner, Richard B. Frankel, W. M. Reiff, H. Wong, Gary J. Long

Physics

Small (≤1 mg) single crystals of γ-Co(pyr)2Cl2 have been grown and measurements of magnetic moment vs applied field H and temperature have been made for 0≤H≤54 kG and 1.25 K≤T≤4.2 K. At 1.25 K, metamagnetic transitions are observed along the a-axis at ~700 G; along the b-axis at both ~800 and ~1500 G; and along the c-axis at ~4 kG. The low field susceptibilities show a maximum at T≃3.4 K for each orientation. Magnetic saturation is not achieved at 54 kG; about 2.5 µB is achieved along the a*- or b-axes, whereas a lower moment is …

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Hyperfine Interactions In Antiferromagnetic Eute Using The Te-125 Mossbauer Resonance, N. A. Blum, Richard B. Frankel May 1976

Hyperfine Interactions In Antiferromagnetic Eute Using The Te-125 Mossbauer Resonance, N. A. Blum, Richard B. Frankel

Physics

Europium telluride crystallizes in the NaCl structure and is antiferromagnetic with a Néel temperature TN of 9.6 K. We have used the 35.5 keV Møssbauer transition in Te-125 to examine the nature of the spontaneous magnetic moment which has been observed in conducting samples below TN. At 80 K the Mössbauer resonance spectrum consisted of a single absorption line comparable in width with the spectrum of nonmagnetic cubic ZnTe, indicating the absence of a significant quadrupole splitting at this temperature. At 4.2 K the line-width increased by a factor of 1.5, which is equivalent to a single magnetic hyperfine field …

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Asymptotic Numbers: Algebraic Operations With Them, Christo Ya. Christov, Todor D. Todorov Jan 1976

Asymptotic Numbers: Algebraic Operations With Them, Christo Ya. Christov, Todor D. Todorov

Mathematics

The main subject of the present paper is to define the four algebraic operations - additions, subtraction, multiplication and division in the set of the asymptotic numbers A [7] and to deduce the corresponding formulas for the components of the asymptotic number, representing the result as functions of the components of the arguments. The definitions of the operations, in fact, are introduced as a special case of the more general notion of a quasiclassical function - one special class of functions defined on A. The discussion of the algebraic and some other properties of the asymptotic numbers is put …

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Model System Studies Of Axial Ligation In The Oxidized Reaction States Of Cytochrome P-450 Enzymes, R. H. Holm, S. C. Tang, S. Koch, G. C. Papaethymiou, S. Foner, R. B. Frankel, J. A. Ibers Jan 1976

Model System Studies Of Axial Ligation In The Oxidized Reaction States Of Cytochrome P-450 Enzymes, R. H. Holm, S. C. Tang, S. Koch, G. C. Papaethymiou, S. Foner, R. B. Frankel, J. A. Ibers

Physics

No abstract provided.

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Synthetic Analogs Of Active Sites Of Iron-Sulfur Proteins: Bis (O-Xylyldithiolato) Ferrate (Iii) Monoanion, A Structurally Unconstrained Model For The Rubredoxin Fe-S4 Unit, R. W. Lane, James A. Ibers, Richard B. Frankel, R. H. Holm Aug 1975

Synthetic Analogs Of Active Sites Of Iron-Sulfur Proteins: Bis (O-Xylyldithiolato) Ferrate (Iii) Monoanion, A Structurally Unconstrained Model For The Rubredoxin Fe-S4 Unit, R. W. Lane, James A. Ibers, Richard B. Frankel, R. H. Holm

Physics

To complete the set of synthetic analogs of the three recognized types of active sites in iron-sulfur redox proteins, the compound (Et4N)[Fe((SCH2)2C6H4)2], derived from o-xylyl-α,α'-dithiol, has been prepared and its structure has been determined by x-ray diffraction. The bischelate anion contains a near-tetrahedral Fe(III)-S4 coordination unit with small rhombic distortions and all Fe-S bond distances in the range 2.252-2.279 Å. Its electronic properties have been partially characterized by measurement of electronic absorption, paramagnetic resonance, Mössbauer spectra, and magnetic susceptibility. The analog, as …

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Linear Chain Compounds: Metamagnetism In Co(Pyr)2Cl2, Fe(Pyr)2Cl2, Fe(Pyr)2(Ncs)2 And Ni(Pyr)2Cl2, S. Foner, Richard B. Frankel, E. J. Mcniff, Jr., W. M. Reiff, B. F. Little, Gary J. Long Apr 1975

Linear Chain Compounds: Metamagnetism In Co(Pyr)2Cl2, Fe(Pyr)2Cl2, Fe(Pyr)2(Ncs)2 And Ni(Pyr)2Cl2, S. Foner, Richard B. Frankel, E. J. Mcniff, Jr., W. M. Reiff, B. F. Little, Gary J. Long

Physics

We report the observation of low field metamagnetic behavior in powder samples of Co(pyr)2Cl2, Fe(pyr)2Cl2, Fe(pyr)2(NCS)2 and Ni(pyr)2Cl2 where pyr=pyridine. These materials have linear chain structures with strong ferromagnetic interactions along the chains, and relatively weak antiferromagnetic interactions between chains. In all four compounds the transitions were observed as a rapid increase in the magnetic moment with increasing magnetic field. In Fe(pyr)2Cl2, Fe(pyr)2(NCS)2, and Ni(pyr)2Cl2, the transitions at 4.2 K were observed at 0.7 …

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Hyperfine Interactions In Mgf2:Fe2+ And Znf2:Fe2+ By Mössbauer Spectroscopy, C. R. Abeledo, Richard B. Frankel, A. Misetich Feb 1975

Hyperfine Interactions In Mgf2:Fe2+ And Znf2:Fe2+ By Mössbauer Spectroscopy, C. R. Abeledo, Richard B. Frankel, A. Misetich

Physics

Measurement of the magnetic hyperfine interaction in paramagnetic Fe2+ in ZnF2 and MgF2 by Mössbauer spectroscopy is reported. The results, −275 ± 3 kOe and −270 ± 3 kOe for ZnF2:Fe2+ and MgF2:Fe2+ respectively are compared with a previous analysis of hyperfine interactions in the rutile fluorides.

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Metamagnetic Behavior Of Linear Chain Pyridine Compounds: Co(Pyridine)2Cl2, Fe(Pyridine)2Cl2, Fe(Pyridine)2(Ncs)2 And Ni(Pyridine)2Cl2, S. Foner, R. B. Frankel, W. M. Reiff, B. F. Little, G. J. Long Jan 1975

Metamagnetic Behavior Of Linear Chain Pyridine Compounds: Co(Pyridine)2Cl2, Fe(Pyridine)2Cl2, Fe(Pyridine)2(Ncs)2 And Ni(Pyridine)2Cl2, S. Foner, R. B. Frankel, W. M. Reiff, B. F. Little, G. J. Long

Physics

Magnetic phase transitions in the pyridine (pyr) compounds Co(pyr)2Cl2, Fe(pyr)2Cl2, Fe(pyr)2(NCS)2 and Ni(pyr)2Cl2 have been observed at applied magnetic fields of not, vert, similar0.7, 0.7, 1.1 and 2.7 kG respectively. These low field phase transitions are observed in the Fe and Ni compounds at T = 4.2 K, and in the Co compound at T < 3K, and are consistent with metamagnetic behavior. Magnetic saturation is not achieved in any of these compounds for fields of 60 kG, reflecting high anisotropy.

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Mössbauer Properties Of Synthetic Analogs Of Active Sites Of The Iron-Sulfur Proteins, Richard B. Frankel, B. A. Averill, R. H. Holm Dec 1974

Mössbauer Properties Of Synthetic Analogs Of Active Sites Of The Iron-Sulfur Proteins, Richard B. Frankel, B. A. Averill, R. H. Holm

Physics

Mössbauer spectroscopy of the synthetic tetramers [Fe4S4(SR)4]2- (R = alkyl, aryl) and the corresponding trianions obtained by one-electron reduction, when compared with available data for 4-Fe and 8-Fe iron-sulfur proteins, shows that these tetramers are electronic analogs of the active sites of the proteins.

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