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1

Thermal Decomposition of an Impure (Roxbury) Siderite: Relevance to the Presence of Chemically Pure Magnetite Crystals in ALH84001 Carbonate Disks  

NASA Technical Reports Server (NTRS)

The question of the origin of nanophase magnetite in Martian meteorite ALH84001 has been widely debated for nearly a decade. Golden et al. have reported producing nearly chemically pure magnetite from thermal decomposition of chemically impure siderite [(Fe, Mg, Mn)CO3]. This claim is significant for three reasons: first, it has been argued that chemically pure magnetite present in the carbonate disks in Martian meteorite ALH84001 could have formed by the thermal decomposition of the impure carbonate matrix in which they are embedded; second, the chemical purity of magnetite has been previously used to identify biogenic magnetite; and, third, previous studies of thermal decomposition of impure (Mg,Ca,Mn)-siderites, which have been investigated under a wide variety of conditions by numerous researchers, invariably yields a mixed metal oxide phase as the product and not chemically pure magnetite. The explanation for this observation is that these siderites all possess the same crystallographic structure (Calcite; R3c) so solid solutions between these carbonates are readily formed and can be viewed on an atomic scale as two chemically different but structurally similar lattices.

McKay, D.S.; Gibson, E.K.; Thomas-Keprta, K.L.; Clemett, S.J.; Wentworth, S.J.

2009-01-01

2

Formation of "Chemically Pure" Magnetite from Mg-Fe-Carbonates Implications for the Exclusively Inorganic Origin of Magnetite and Sulfides in Martian Meteorite ALH84001  

NASA Technical Reports Server (NTRS)

Magnetite and sulfides in the black rims of carbonate globules in Martian meteorite ALH84001 have been studied extensively because of the claim by McKay et al. that they are biogenic in origin. However, exclusively inorganic (abiotic) processes are able to account for the occurrence of carbonate-sulfide-magnetite assemblages in the meteorite. We have previously precipitated chemically zoned and sulfide-bearing carbonate globules analogous to those in ALH84001 (at less than or equal to 150 C) from multiple fluxes of variable-composition Ca-Mg-Fe-CO2-S-H2O solutions. Brief heating of precipitated globules to approx. 470 C produced magnetite and pyrrhotite within the globules by thermal decomposition of siderite and pyrite, respectively. We have also shown that morphology of magnetite formed by inorganic thermal decomposition of Fe-rich carbonate is similar to the morphology of so-called biogenic magnetite in the carbonate globules of ALH84001. Magnetite crystals in the rims of carbonate globules in ALH84001 are chemically pure [Note: "Chemically pure" is defined here as magnetite with Mg at levels comparable or lower than Mg detected by [8] in ALH84001 magnetite]. A debate continues on whether or not chemically pure magnetite can form by the thermal decomposition of mixed Mg-Fe-carbonates that have formed under abiotic conditions. Thomas-Keprta et al. argue that it is not possible to form Mg-free magnetite from Mg-Fe-carbonate based on thermodynamic data. We previously suggested that chemically pure magnetite could form by the thermal decomposition of relatively pure siderite in the outer rims of the globules. Mg-Fe-carbonates may also thermally decompose under conditions conducive for formation of chemically pure magnetite. In this paper we show through laboratory experiments that chemically pure magnetite can form by an inorganic process from mixed Mg-Fe-carbonates.

Golden, D. C.; Ming, Douglas W.; Lauer, H. V., Jr.; Morris, R. V.; Trieman, A. H.; McKay, G. A.

2006-01-01

3

Magnetic properties of hydrothermally recrystallized magnetite crystals  

Microsoft Academic Search

The discrepancy between the magnetic hysteresis properties of magnetite crystals that are precipitated from solution and of crushed sifted grains (larger than 300 nm) is not an inherent property of magnetite but is caused by the highly stressed state of crushed material and by adhering finer fragments. The size trends of magnetic properties exhibited by submicron-size precipitated grains continue in

Franz Heider; David J. Dunlop; Naoji Sugiura

1987-01-01

4

Hydrothermal synthesis of magnetite crystals: From sheet to pseudo-octahedron  

SciTech Connect

In this paper, we developed a hydrothermal method to fabricate sheet-like and pseudo-octahedral magnetite crystals. X-ray diffraction (XRD) confirmed the products were pure spinel-structured magnetite. Scanning electron microscopy (SEM) was used to investigate the morphology of the obtained crystals. By carefully regulating the initial NaOH concentrations, the morphology of the products could be changed from sheet-like crystals to pseudo-octahedral crystals. Transmission electron microscopy (TEM) analysis indicated the sheet-like crystals were the oriented aggregation of nanoparticles. Pseudo-octahedral magnetite crystals were single crystalline, and were obtained by dissolution-recrystallization of the sheet-like crystals. Vibrating sample magnetometer (VSM)) suggested the magnetic properties of the products were strongly related to the morphology. The coercivity of the sheet-like magnetite crystals was 100 Oe, larger than 30 Oe of the pseudo-octahedral crystals, but the saturation magnetization of the sheet-like magnetite crystals was 40 emu/g, smaller than 85 emu/g of the pseudo-octahedral crystals.

Hu, Ming; Ji, Rui-Ping [Department of Physics, Center of Functional Nanomaterials and Devices, East China Normal University, Shanghai 200241 (China)] [Department of Physics, Center of Functional Nanomaterials and Devices, East China Normal University, Shanghai 200241 (China); Jiang, Ji-Sen, E-mail: jsjiang@phy.ecnu.edu.cn [Department of Physics, Center of Functional Nanomaterials and Devices, East China Normal University, Shanghai 200241 (China)] [Department of Physics, Center of Functional Nanomaterials and Devices, East China Normal University, Shanghai 200241 (China)

2010-12-15

5

Ar-40/Ar-39 laser dating of biotite inclusions in a single crystal of magnetite  

NASA Astrophysics Data System (ADS)

The iron-oxide mineral magnetite is widely used to study the past geomagnetic field because of its ability to record the ancient field at the time of its crystallization (or cooling), and because of its common occurrence in continental and oceanic rocks. The Ar-40/Ar-39 laser dating of one half of a 2 mm octahedral crystal of magnetite from an ultramafic rock near Bush's Corner, Harford County, Maryland, in the Appalachian Piedmont is presented. The other half was examined by scanning electron microscopy to characterize the inclusions in the crystal. Laser step-heating separates the argon isotopes released into three distinct phases. A three-dimensional isotope correlation plot illustrates the existence of a pure radiogenic component corresponding to an age of 323 +/- 5 Ma. This is the age of argon closure of minute biotite inclusions identified in the magnetite by SEM, and therefore is a precise estimate of the minimum age of the magnetite.

Özdemir, Özden; York, Derek

1992-09-01

6

Truncated hexa-octahedral magnetite crystals in ALH84001: presumptive biosignatures  

NASA Technical Reports Server (NTRS)

McKay et al. [(1996) Science 273, 924-930] suggested that carbonate globules in the meteorite ALH84001 contained the fossil remains of Martian microbes. We have characterized a subpopulation of magnetite (Fe(3)O(4)) crystals present in abundance within the Fe-rich rims of these carbonate globules. We find these Martian magnetites to be both chemically and physically identical to terrestrial, biogenically precipitated, intracellular magnetites produced by magnetotactic bacteria strain MV-1. Specifically, both magnetite populations are single-domain and chemically pure, and exhibit a unique crystal habit we describe as truncated hexa-octahedral. There are no known reports of inorganic processes to explain the observation of truncated hexa-octahedral magnetites in a terrestrial sample. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection. Unless there is an unknown and unexplained inorganic process on Mars that is conspicuously absent on the Earth and forms truncated hexa-octahedral magnetites, we suggest that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process. As such, these crystals are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet found.

Thomas-Keprta, K. L.; Clemett, S. J.; Bazylinski, D. A.; Kirschvink, J. L.; McKay, D. S.; Wentworth, S. J.; Vali, H.; Gibson, E. K. Jr; McKay, M. F.; Romanek, C. S.

2001-01-01

7

Process for Making Single-Domain Magnetite Crystals  

NASA Technical Reports Server (NTRS)

A process for making chemically pure, single-domain magnetite crystals substantially free of structural defects has been invented as a byproduct of research into the origin of globules in a meteorite found in Antarctica and believed to have originated on Mars. The globules in the meteorite comprise layers of mixed (Mg, Fe, and Ca) carbonates, magnetite, and iron sulfides. Since the discovery of the meteorite was announced in August 1996, scientists have debated whether the globules are of biological origin or were formed from inorganic materials by processes that could have taken place on Mars. While the research that led to the present invention has not provided a definitive conclusion concerning the origin of the globules, it has shown that globules of a different but related chemically layered structure can be grown from inorganic ingredients in a multistep precipitation process. As described in more detail below, the present invention comprises the multistep precipitation process plus a subsequent heat treatment. The multistep precipitation process was demonstrated in a laboratory experiment on the growth of submicron ankerite crystals, overgrown by submicron siderite and pyrite crystals, overgrown by submicron magnesite crystals, overgrown by submicron siderite and pyrite. In each step, chloride salts of appropriate cations (Ca, Fe, and Mg) were dissolved in deoxygenated, CO2- saturated water. NaHCO3 was added as a pH buffer while CO2 was passed continuously through the solution. A 15-mL aliquot of the resulting solution was transferred into each of several 20 mL, poly(tetrafluoroethylene)-lined hydrothermal pressure vessels. The vessels were closed in a CO2 atmosphere, then transferred into an oven at a temperature of 150 C. After a predetermined time, the hydrothermal vessels were removed from the oven and quenched in a freezer. Supernatant solutions were decanted, and carbonate precipitates were washed free of soluble salts by repeated decantations with deionized water.

Golden, D. C.; Ming, Douglas W.; Morris, Richard V.; Lofgren, Gary E.; McKay, Gordan A.; Schwandt, Craig S.; Lauer, Howard V., Jr.; Socki, Richard A.

2004-01-01

8

Ferromagnetic resonance of intact cells and isolated crystals from cultured and uncultured magnetite-producing magnetotactic bacteria  

NASA Astrophysics Data System (ADS)

Most magnetotactic bacteria (MB) produce stable, single-domain magnetite nanocrystals with species-specific size, shape and chain arrangement. In addition, most crystals are elongated along the [111] direction, which is the easy axis of magnetization in magnetite, chemically pure and structurally perfect. These special characteristics allow magnetite crystal chains from MB to be recognized in environmental samples including old sedimentary rocks. Ferromagnetic resonance (FMR) has been proposed as a powerful and practical tool for screening large numbers of samples possibly containing magnetofossils. Indeed, several studies were recently published on FMR of cultured MB, mainly Magnetospirillum gryphiswaldense. In this work, we examined both uncultured magnetotactic cocci and the cultured MB M. gryphiswaldense using transmission electron microscopy (TEM) and FMR from 10 K to room temperature (RT). The TEM data supported the FMR spectral characteristics of our samples. The FMR spectra of both bacteria showed the intrinsic characteristics of magnetite produced by MB, such as extended absorption at the low field region of the spectra and a Verwey transition around 100 K. As previously observed, the spectra of M. gryphiswaldense isolated crystals were more symmetrical than the spectra obtained from whole cells, reflecting the loss of chain arrangement due to the small size and symmetrical shape of the crystals. However, the FMR spectra of magnetic crystals isolated from magnetotactic cocci were very similar to the FMR spectra of whole cells, because the chain arrangement was maintained due to the large size and prismatic shape of the crystals. Our data support the use of FMR spectra to detect magnetotactic bacteria and magnetofossils in samples of present and past environments. Furthermore, the spectra suggest the use of the temperature transition of spectral peak-to-peak intensity to obtain the Verwey temperature for these systems.

Abraçado, Leida G.; Wajnberg, Eliane; Esquivel, Darci M. S.; Keim, Carolina N.; Silva, Karen T.; Moreira, Emílio T. S.; Lins, Ulysses; Farina, Marcos

2014-06-01

9

Magnetite (Fe3O4) and Greigite (Fe3S4) Crystals in Multicellular Magnetotactic Prokaryotes  

Microsoft Academic Search

Magnetotactic bacteria produce iron oxides, iron sulfides or both in organelles called magnetosomes. Most of these bacteria are unicellular and biomineralize magnetite (Fe3O4). In contrast, multicellular magnetotactic prokaryotes (MMPs) consisting of several gram-negative cells have only been known to crystallize the magnetic iron sulfide greigite (Fe3S4). In this work, we describe MMPs that mineralize magnetite in bullet-shaped crystals. Another unusual

Ulysses Lins; Carolina N. Keim; Flávia F. Evans; Marcos Farina; Peter R. Buseck

2007-01-01

10

The Origin of Magnetite Crystals in ALH84001 Carbonate Disks  

NASA Technical Reports Server (NTRS)

Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks believed to have formed approx 3.9 Ga ago at beginning of the Noachian epoch. Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe3O4) with unusual chemical and physical properties, whose origins have become the source of considerable debate. One group of hypotheses argues that these magnetites are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of magnetite and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. We have sought to resolve between these hypotheses through the detailed characterized of the compositional and structural relationships between the carbonate disks, their associated magnetites and the orthopyroxene matrix in which they are embedded. Comparison of these results with experimental thermal decomposition studies of sideritic carbonates conducted under a range of heating scenarios suggests that the magnetite nanocrystals in the ALH84001 carbonate disks are not the products of thermal decomposition.

Thomas-Keprta, K. L.; Clemett, S. J.; Wentworth, S. J.; McKay, D. S.; Gibson, E. K., Jr.

2012-01-01

11

Magnetic domain observations on magnetite crystals in biotite and hornblende grains  

NASA Astrophysics Data System (ADS)

Magnetic domain structures have been observed on magnetite crystals in 300 ?m to 1 mm size biotite and hornblende grains separated from drill core samples of Precambrian granodiorite basement in southern Alberta, Canada. The crystals were mounted in epoxy, and the surface was polished, first mechanically and then with a suspension of amorphous SiO2. Domain structures were observed on 6-60 ?m magnetite crystals using the Bitter colloid technique. Observed features include lamellar domains bounded by straight 180° walls, closure domains, bent walls, wavy structures, and areas without visible domains. Crystals <=50 ?m in size generally have simple domain patterns with domain walls parallel to the long axis of the crystal. We studied domain wall displacements in small isolated magnetites as a function of applied magnetic field up to 24 mT. The number of domains decreases with increasing external field. Some walls are relatively mobile and disappear by 20 mT. Other walls remain immobile; in some cases, crystal defects or inclusions are seen to pin these walls, or segments of walls. An interesting observation was made on a 5 × 25 ?m elongated magnetite crystal formed in a crack in hornblende. Large quantities of magnetic colloid gathered at either end of the crystal because of the strong flux leakage and pole fields at these locations. Colloid was also concentrated where domain boundaries intersect the sides of the crystal. With increasing applied field the colloid spread out to form patterns tracing complete external flux closure loops.

Özdemir, Özden; Dunlop, David J.

2006-06-01

12

Co-ordinated functions of Mms proteins define the surface structure of cubo-octahedral magnetite crystals in magnetotactic bacteria.  

PubMed

Magnetotactic bacteria synthesize magnetosomes comprised of membrane-enveloped single crystalline magnetite (Fe3 O4 ). The size and morphology of the nano-sized magnetite crystals (magnetite crystal morphology remain largely unknown. The group of proteins, called Mms (Mms5, Mms6, Mms7, and Mms13), was previously isolated from the surface of cubo-octahedral magnetite crystals in Magnetospirillum magneticum strain AMB-1. Analysis of an mms6 gene deletion mutant suggested that the Mms6 protein plays a major role in the regulation of magnetite crystal size and morphology. In this study, we constructed various mms gene deletion mutants and characterized the magnetite crystals formed by the mutant strains. Comparative analysis showed that all mms genes were involved in the promotion of crystal growth in different manners. The phenotypic characterization of magnetites also suggested that these proteins are involved in controlling the geometries of the crystal surface structures. Thus, the co-ordinated functions of Mms proteins regulate the morphology of the cubo-octahedral magnetite crystals in magnetotactic bacteria. PMID:24961165

Arakaki, Atsushi; Yamagishi, Ayana; Fukuyo, Ayumi; Tanaka, Masayoshi; Matsunaga, Tadashi

2014-08-01

13

Effect of crystal defects and internal stress on the domain structure and magnetic properties of magnetite  

NASA Astrophysics Data System (ADS)

Domain structures in magnetite are very sensitive to crystal imperfections, which play a major role in hysteresis and remanence by hindering the motion of domain walls. Using the Bitter colloid technique, we have observed spike and closure domains of the style predicted by Néel [1944] around nonmagnetic inclusions, chemically altered regions, and grain boundaries in a natural single crystal of magnetite. Isolated inclusions within body domains have pairs of attached Néel spikes which reduce magnetostatic energy by diluting magnetic poles. In one example we calculated that spikes reduced the energy by a factor of 6-7. In some cases 71 °, 109° and 180° domain walls are pinned to defects either through spikes or via chains of subsidiary closure domains. One example of pinning by a spike gave a calculated microcoercivity of 0.54 mT, similar to the bulk coercive force of 0.5 mT for the crystal. "Colloid gaps" in 180° and other walls form lines parallel to a <111> easy axis and are evidence of underlying line defects, for example, dislocations, whose stress fields deflect the spins locally, weakening the magnetic field gradient above the walls. We have also observed bending of 180° walls anchored at pinning sites on the grain boundary, the first direct experimental evidence of the effect of internal stresses on the domain structure of magnetite. We determined internal stress magnitudes in the range 7-34 MPa from the observed linear dimension and transverse displacement of each bowed wall. Finally, we measured hysteresis curves on a companion magnetite crystal at temperatures T from ambient to the Curie point of 585°C. Observed coercivity Hc varies with T as ?111W0.5/Ms, in agreement with theoretical predictions of impedance of a wall of width w by dislocation stress fields. We therefore propose that the stability of remanence in multidomain magnetite is mainly due to pinning of domain walls by crystal defects.

Özdemir, Özden; Dunlop, David J.

1997-01-01

14

ELSEVIER Earth and Planetary Science Letters 165 (1999) 229239 Low-temperature properties of a single crystal of magnetite  

E-print Network

at low temperatures, between 300 K and 10 K, on an oriented 1.5-mm single crystal of magnetite axes, indicating that below Tv the crystal has uniaxial symmetry. The room-temperature saturationELSEVIER Earth and Planetary Science Letters 165 (1999) 229­239 Low-temperature properties

Dunlop, David J.

15

Intrinsic response of crystals to pure dilatation  

SciTech Connect

The response of an f.c.c. lattice with Lennard-Jones interaction under symmetric lattice extension has been studied by Monte Carlo simulation at several temperatures. The critical strain at which the crystal undergoes a structural change is found to be well predicted by the mechanical stability limit expressed in terms of either the elastic constants or the bulk modulus. At low temperature (reduced temperature T = 0.125), lattice decohesion is observed in the form of cleavage fracture, whereas at higher temperature (T = 0.3) the strained system deforms by cavitation with some degree of local plasticity. At still higher temperature (T = 0.5) the lattice undergoes homogeneous disordering with all the attendant characteristics of melting.

Wang, Jinghan; Yip, S. [Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Nuclear Engineering; Phillpot, S.; Wolf, D. [Argonne National Lab., IL (United States)

1991-12-31

16

Variation in trace element content of magnetite crystallized from a fractionating sulfide liquid, Sudbury, Canada: Implications for provenance discrimination  

NASA Astrophysics Data System (ADS)

Laser ablation ICP-MS analysis has been applied to many accessory minerals in order to understand better the process by which the rock formed and for provenance discrimination. We have determined trace element concentrations of Fe-oxides in massive sulfides that form Ni-Cu-PGE deposits at the base of the Sudbury Igneous Complex in Canada. The samples represent the crystallization products of fractionating sulfide liquids and consist of early-forming Fe-rich monosulfide solution (MSS) cumulates and residual Cu-rich intermediate solid solution (ISS). This study shows that Fe-oxide geochemistry is a sensitive petrogenetic indicator for the degree of fractionation of the sulfide liquid and provides an insight into the partitioning of elements between sulfide and Fe-oxide phases. In addition, it is useful in determining the provenance of detrital Fe-oxide. In a sulfide melt, all lithophile elements (Cr, Ti, V, Al, Mn, Sc, Nb, Ga, Ge, Ta, Hf, W and Zr) are compatible into Fe-oxide. The concentrations of these elements are highest in the early-forming Fe-oxide (titanomagnetite) which crystallized with Fe-rich MSS. Upon the continual crystallization of Fe-oxide from the sulfide liquid, the lithophile elements gradually decrease so that late-forming Fe-oxide (magnetite), which crystallized from the residual Cu-rich liquid, is depleted in these elements. This behavior is in contrast with Fe-oxides that crystallized from a fractionating silicate melt, whereby the concentration of incompatible elements, such as Ti, increases rather than decreases. The behavior of the chalcophile elements in magnetite is largely controlled by the crystallization of the sulfide minerals with only Ni, Co, Zn, Mo, Sn and Pb present above detection limit in magnetite. Nickel, Mo and Co are compatible in Fe-rich MSS and thus the co-crystallizing Fe-oxide is depleted in these elements. In contrast, magnetite that crystallized later from the fractionated liquid with Cu-rich ISS is enriched in Ni, Mo and Co because Fe-rich MSS is absent. The concentrations of Sn and Pb, which are incompatible with Fe-rich MSS, are highest in magnetite that formed from the fractionated Cu-rich liquid. At subsolidus temperatures, ilmenite exsolved from titanomagnetite whereas Al-spinel exsolved from the cores of some magnetite, locally redistributing the trace elements. However, during laser ablation ICP-MS analysis of these Fe-oxides both the magnetite and its exsolution products are ablated so that the analysis represents the original magmatic composition of the Fe-oxide that crystallized from the sulfide melt.

Dare, Sarah A. S.; Barnes, Sarah-Jane; Beaudoin, Georges

2012-07-01

17

Activating efficient phosphorescence from purely organic materials by crystal design  

NASA Astrophysics Data System (ADS)

Phosphorescence is among the many functional features that, in practice, divide pure organic compounds from organometallics and inorganics. Considered to be practically non-phosphorescent, purely organic compounds (metal-free) are very rarely explored as emitters in phosphor applications, despite the emerging demand in this field. To defy this paradigm, we describe novel design principles to create purely organic materials demonstrating phosphorescence that can be turned on by incorporating halogen bonding into their crystals. By designing chromophores to contain triplet-producing aromatic aldehydes and triplet-promoting bromine, crystal-state halogen bonding can be made to direct the heavy atom effect to produce surprisingly efficient solid-state phosphorescence. When this chromophore is diluted into the crystal of a bi-halogenated, non-carbonyl analogue, ambient phosphorescent quantum yields reach 55%. Here, using this design, a series of pure organic phosphors are colour-tuned to emit blue, green, yellow and orange. From this initial discovery, a directed heavy atom design principle is demonstrated that will allow for the development of bright and practical purely organic phosphors.

Bolton, Onas; Lee, Kangwon; Kim, Hyong-Jun; Lin, Kevin Y.; Kim, Jinsang

2011-03-01

18

Molarity (Aromic Density) of the Elements as Pure Crystals.  

ERIC Educational Resources Information Center

Provides background information for teachers on the atomic density of the elements as pure crystals. Atomic density is defined as the reciprocal of the atomic volume. Includes atomic-density diagrams which were prepared using the atomic-volume values given by Singman, supplemented by additional values for some allotropes. (JN)

Pauling, Linus; Herman, Zelek S.

1985-01-01

19

Sub-Micrometer-Scale Mapping of Magnetite Crystals and Sulfur Globules in Magnetotactic Bacteria Using Confocal Raman Micro-Spectrometry  

PubMed Central

The ferrimagnetic mineral magnetite is biomineralized by magnetotactic microorganisms and a diverse range of animals. Here we demonstrate that confocal Raman microscopy can be used to visualize chains of magnetite crystals in magnetotactic bacteria, even though magnetite is a poor Raman scatterer and in bacteria occurs in typical grain sizes of only 35–120 nm, well below the diffraction-limited optical resolution. When using long integration times together with low laser power (<0.25 mW) to prevent laser induced damage of magnetite, we can identify and map magnetite by its characteristic Raman spectrum (303, 535, 665 ) against a large autofluorescence background in our natural magnetotactic bacteria samples. While greigite (cubic ; Raman lines of 253 and 351 ) is often found in the Deltaproteobacteria class, it is not present in our samples. In intracellular sulfur globules of Candidatus Magnetobacterium bavaricum (Nitrospirae), we identified the sole presence of cyclo-octasulfur (: 151, 219, 467 ), using green (532 nm), red (638 nm) and near-infrared excitation (785 nm). The Raman-spectra of phosphorous-rich intracellular accumulations point to orthophosphate in magnetic vibrios and to polyphosphate in magnetic cocci. Under green excitation, the cell envelopes are dominated by the resonant Raman lines of the heme cofactor of the b or c-type cytochrome, which can be used as a strong marker for label-free live-cell imaging of bacterial cytoplasmic membranes, as well as an indicator for the redox state. PMID:25233081

Eder, Stephan H. K.; Gigler, Alexander M.; Hanzlik, Marianne; Winklhofer, Michael

2014-01-01

20

New Insights into the Origin of Magnetite Crystals in ALH84001 Carbonate Disks  

NASA Technical Reports Server (NTRS)

Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks believed to have formed approx.3.9 Ga ago at beginning of the Noachian epoch. Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe3O4) with unusual chemical and physical properties, whose ori gins have become the source of considerable debate. One group of hypotheses argues that these magnetites are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of magnetite and carbonate may be unrelated: that is, from the perspective of the carbonate the magnetite is allochthonous. We have sought to resolve between these hypotheses through the detailed characterized of the compositional and structural relationships between the carbonate disks, their associated magnetites and the orthopyroxene matrix in which they are embedded [1]. Comparison of these results with experimental thermal decomposition studies of sideritic carbonates conducted under a range of heating scenarios suggests that the magnetite nanocrystals in the ALH84001 carbonate disks are not the products of thermal decomposition.

Thomas-Keptra, Katie L.; Clemett, S. J.; Wentworth S. J.; Mckay, D. S.; Gibson, E. K., Jr.

2010-01-01

21

Cosmic muon tomography of pure cesium iodide calorimeter crystals  

NASA Astrophysics Data System (ADS)

Scintillation properties of pure CsI crystals used in the shower calorimeter being built for precise determination of the ? +?? 0e +? e decay rate are reported. Seventy-four individual crystals, polished and wrapped in Teflon foil, were examined in a multiwire drift chamber system specially designed for transmission cosmic muon tomography. Critical elements of the apparatus and reconstruction algorithms enabling measurement of spatial detector optical nonuniformities are described. Results are compared with a Monte Carlo simulation of the light response of an ideal detector. The deduced optical nonuniformity contributions to the FWHM energy resolution of the PIBETA CsI calorimeter for the ?+? e+? 69.8 MeV positrons and the monoenergetic 70.8 MeV photons were 2.7% and 3.7%, respectively. The upper limit of optical nonuniformity correction to the 69.8 MeV positron low-energy tail between 5 and 55 MeV was +0.2%, as opposed to the +0.3% tail contribution for the photon of the equivalent total energy. Imposing the 5 MeV calorimeter veto cut to suppress the electromagnetic losses, GEANT-evaluated positron and photon lineshape tail fractions summed over all above-threshold ADCs were found to be 2.36±0.05 (stat) ±0.20 (sys)% and 4.68±0.07 (stat)±0.20 (sys)%, respectively.

Frlež, E.; Supek, I.; Assamagan, K. A.; Brönnimann, Ch.; Flügel, Th.; Krause, B.; Lawrence, D. W.; Mzavia, D.; Po?ani?, D.; Renker, D.; Ritt, S.; Slocum, P. L.; Soi?, N.

2000-01-01

22

New insights into the origin of magnetite crystals in ALH84001 carbonate disks  

NASA Technical Reports Server (NTRS)

Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks which are believed to have precipitated approximately 3.9 Ga ago at beginning of the Noachian epoch. Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe3O4) with unusual chemical and physical properties, whose origins have become the source of considerable debate. One group of hypotheses argues that these Fe3O4 are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of Fe3O4 and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. We have sought to resolve between these hypotheses through the detailed characterized of the compositional and structural relationships of the carbonate disks and associated magnetites with the orthopyroxene matrix in which they are embedded. We focus this discussion on the composition of ALH84001 magnetites and then compare these observations with those from experimental thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios.

Thomas-Keprta, K. L.; Clemett, S. J.; Wentworth, S. J.; McKay, D. S.; Gibson, E. K.

2009-01-01

23

Origin of Magnetite Crystals in Martian Meteorite ALH84001 Carbonate Disks  

NASA Technical Reports Server (NTRS)

Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks which are believed to have precipitated approx.3.9 Ga ago at beginning of the Noachian epoch. Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe3O4) with unusual chemical and physical properties, whose origins have become the source of considerable debate. One group of hypotheses argues that these Fe3O4 are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of Fe3O4 and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. We have sought to resolve between these hypotheses through the detailed characterized of the compositional and structural relationships of the carbonate disks and associated magnetites with the orthopyroxene matrix in which they are embedded [1]. We focus this discussion on the composition of ALH84001 magnetites and then compare these observations with those from our thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios.

Thomas-Keprta, K.L.; Clemett, S.J.; McKay, D.S.; Gibson, E. K.; Wentworth, S. J.

2010-01-01

24

Characterization and phylogenetic identification of a species of spherical multicellular magnetotactic prokaryotes that produces both magnetite and greigite crystals.  

PubMed

Magnetotactic bacteria (MTB) are a group of Gram-negative bacteria synthesizing magnetic crystals that allow them aligning along magnetic field lines. They have diverse morphologies including cocci, rods, vibrio, spirilla, and multicellular magnetotactic prokaryotes (MMPs). MMPs are composed of 10-57 cells with peritrichous flagella on their outer surfaces and swim as an entire unit. Here, we describe a species of spherical MMPs isolated from intertidal sediments of Lake Yuehu (Yellow Sea, China). They were mainly found in the subsurface layer of gray-black sediments. Microscopy revealed that these spherical MMPs were 5.6 ± 0.9 ?m in diameter and composed of approximately 16-32 ovoid cells with a helical arrangement and peritrichous flagellation. High-resolution transmission electron microscopy showed that the MMPs contained both bullet-shaped magnetite and irregular greigite magnetosomes that were arranged in chains or clusters. These MMPs displayed typical escape motility and negative phototaxis. The 16S rRNA genes of micromanipulation-purified spherical MMPs were cloned and sequenced. Phylogenetic analysis revealed that the MMP species was affiliated with Deltaproteobacteria and displayed >2.8% sequence divergence with respect to previously reported MMPs. This is the first phylogenetic identification of a spherical MMP that produces both magnetite and greigite magnetosomes. PMID:25086260

Zhang, Rui; Chen, Yi-Ran; Du, Hai-Jian; Zhang, Wen-Yan; Pan, Hong-Miao; Xiao, Tian; Wu, Long-Fei

2014-09-01

25

Optical and electrical characteristics of pure and doped potassium hydrogen tartrate single crystals  

Microsoft Academic Search

The optical and electrical characteristics of pure, sodium- and lithium-doped potassium hydrogen tartrate crystals grown by the gel technique are reported. An optical absorption study conducted in the UV-Vis range of 200-800 nm reveals the transparency of these crystals in the entire visible range but not in the ultraviolet range. The optical band gap of pure potassium hydrogen tartrate crystals

I. Quasim; A. Firdous; S. K. Khosa; P. N. Kotru

2009-01-01

26

Optical and electrical characteristics of pure and doped potassium hydrogen tartrate single crystals  

Microsoft Academic Search

The optical and electrical characteristics of pure, sodium- and lithium-doped potassium hydrogen tartrate crystals grown by the gel technique are reported. An optical absorption study conducted in the UV–Vis range of 200–800 nm reveals the transparency of these crystals in the entire visible range but not in the ultraviolet range. The optical band gap of pure potassium hydrogen tartrate crystals

I Quasim; A Firdous; S K Khosa; P N Kotru

2009-01-01

27

Monitoring Industrial Pharmaceutical Crystallization Processes Using Acoustic Emission in Pure and Impure Media.  

E-print Network

Monitoring Industrial Pharmaceutical Crystallization Processes Using Acoustic Emission in Pure processes was almost never evaluated in the field of industrial pharmaceutical crystallization. Few papers in "International Journal of Pharmaceutics 439, 1-2 (2012) 109-119" DOI : 10.1016/j.ijpharm.2012.09.048 #12;2 1

Paris-Sud XI, Université de

28

Crystal nucleation in glass-forming alloy and pure metal melts under containerless and vibrationless conditions  

NASA Technical Reports Server (NTRS)

Crystal nucleation behavior in metallic alloys known to form glasses in melt quenching was characterized and from this characterization the possibility that massive amounts of certain alloys could be slow cooled to the glass state was assessed. Crystal nucleation behavior of pure liquid metals was examined experimentally, under containerless conditions, and theoretically.

Turnbull, D.

1979-01-01

29

Microbial preparation of metal-substituted magnetite nanoparticles.  

PubMed

A microbial process that exploits the ability of iron-reducing microorganisms to produce copious amounts of extra-cellular metal (M)-substituted magnetite nanoparticles using akaganeite and dopants of dissolved form has previously been reported. The objectives of this study were to develop methods for producing M-substituted magnetite nanoparticles with a high rate of metal substitution by biological processes and to identify factors affecting the production of nano-crystals. The thermophilic and psychrotolerant iron-reducing bacteria had the ability to form M-substituted magnetite nano-crystals (M(y)Fe(3-y)O(4)) from a doped precursor, mixed-M iron oxyhydroxide, (M(x)Fe(1-x)OOH, x< or =0.5, M is Mn, Zn, Ni, Co and Cr). Within the range of 0.01< or =x< or =0.3, using the mixed precursor material enabled the microbial synthesis of more heavily substituted magnetite compared to the previous method, in which the precursor was pure akaganeite and the dopants were present as soluble metal salts. The mixed precursor method was especially advantageous in the case of toxic metals such as Cr and Ni. Also this new method increased the production rate and magnetic properties of the product, while improving crystallinity, size control and scalability. PMID:17532071

Moon, Ji-Won; Roh, Yul; Lauf, Robert J; Vali, Hojatollah; Yeary, Lucas W; Phelps, Tommy J

2007-07-01

30

Trace elements in magnetite as petrogenetic indicators  

NASA Astrophysics Data System (ADS)

We have characterized the distribution of 25 trace elements in magnetite (Mg, Al, Si, P, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb), using laser ablation ICP-MS and electron microprobe, from a variety of magmatic and hydrothermal ore-forming environments and compared them with data from the literature. We propose a new multielement diagram, normalized to bulk continental crust, designed to emphasize the partitioning behavior of trace elements between magnetite, the melt/fluid, and co-crystallizing phases. The normalized pattern of magnetite reflects the composition of the melt/fluid, which in both magmatic and hydrothermal systems varies with temperature. Thus, it is possible to distinguish magnetite formed at different degrees of crystal fractionation in both silicate and sulfide melts. The crystallization of ilmenite or sulfide before magnetite is recorded as a marked depletion in Ti or Cu, respectively. The chemical signature of hydrothermal magnetite is distinct being depleted in elements that are relatively immobile during alteration and commonly enriched in elements that are highly incompatible into magnetite (e.g., Si and Ca). Magnetite formed from low-temperature fluids has the lowest overall abundance of trace elements due to their lower solubility. Chemical zonation of magnetite is rare but occurs in some hydrothermal deposits where laser mapping reveals oscillatory zoning, which records the changing conditions and composition of the fluid during magnetite growth. This new way of plotting all 25 trace elements on 1 diagram, normalized to bulk continental crust and elements in order of compatibility into magnetite, provides a tool to help understand the processes that control partitioning of a full suit of trace elements in magnetite and aid discrimination of magnetite formed in different environments. It has applications in both petrogenetic and provenance studies, such as in the exploration of ore deposits and in sedimentology.

Dare, Sarah A. S.; Barnes, Sarah-Jane; Beaudoin, Georges; Méric, Julien; Boutroy, Emilie; Potvin-Doucet, Christophe

2014-10-01

31

Electromagnetic waves in uniaxial crystals with metallized boundaries: Mode conversion, pure reflections, and bulk polaritons  

SciTech Connect

A theory is constructed for the reflection of plane electromagnetic waves in uniaxial crystals with a positive definite permittivity tensor and an arbitrarily oriented metallized boundary. The problem is solved both for general-position orientations corresponding to three-partial reflection and for special conditions allowing two-partial reflections: mode conversions when the incident and reflected waves belong to different sheets of the refraction surface and 'pure' reflections when both waves belong to the same sheet. The space of pure reflections is shown to be formed by two types of optical-axis orientations: arbitrary directions in the plane of the crystal surface and in the plane of incidence. The configurations of the conversion surface for optically positive and negative crystals are investigated. A subspace of pure reflections that transform into one-partial bulk polaritons with the energy flux parallel to the surface at grazing incidence has been found. The domain of existence of such bulk eigenmodes is bounded by two 'lines' of solutions. These are any directions along the boundary containing the optical axis for ordinary polaritons and the direction along the projection of the optical axis onto the surface at an arbitrary orientation of the axis with respect to the boundary for extraordinary polaritons.

Alshits, V. I., E-mail: alshits@ns.crys.ras.ru; Lyubimov, V. N. [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Radowicz, A. [Kielce University of Technology (Poland)

2007-02-15

32

Growth and characterization of pure and 1, 10 phenanthraline doped potassium penta borate (KB5) single crystals  

NASA Astrophysics Data System (ADS)

We concentrate on the low temperature slow solvent evaporation method and characterization of pure and 1, 10 phenanthraline doped KB5 and describe its potential as a non-linear optical material. The grown crystal has been subjected to single crystal X-ray diffraction analysis to identify the unit cell parameters and crystal system. The presence of carbon, hydrogen and oxygen content were confirmed by CHN analysis. The Kurtz's-Perry powder SHG efficiency was determined for both pure and 1,10 phenanthraline doped KB5 crystals as 1.6 and 2.2 times than that of pure KDP. Surface morphology of the pure and doped KB5 crystals has been found to be Scanning Electron Microscopic technique (SEM).

Prabha, K.; Babu, M. Ramesh; Sagayaraj, P.

2013-05-01

33

Growth, structural, spectral, mechanical and optical properties of pure and metal ions doped sulphamic acid single crystals.  

PubMed

Bulk single crystals of pure and metal ions (Mn(2+), Cu(2+) and Ni(2+)) doped sulphamic acid (SA) have been grown by conventional and unidirectional solution growth methods. Intensities of powder X-ray diffraction peaks of metal ions doped SA reveal that these dopants enhanced the crystallanity. The peak broadening and intensity variation in some frequency regions in FT-IR spectra show the incorporation of dopants in the SA lattice. Mn(2+) and Cu(2+) doped SA single crystals show high crystalline perfection (FWHM 5.5arcs) compared to pure and Ni(2+) metal ions doped SA crystals. The grown pure and Mn(2+), Cu(2+) and Ni(2+) ions doped SA crystals have transparency in the order SA>Mn:SA>Cu:SA>Ni:SA. The hardness value of Ni(2+) doped crystal is relatively less than that of the pure and other metal ions doped SA crystals. Pure and Ni(2+) ions doped SA crystals possess high dielectric constants than that of Cu(2+) and Mn(2+) ions doped crystals. From the SEM micrograph analyses, it is observed that the doping of these metal ions modify the surface morphology of the grown crystals. PMID:20493763

Ramesh Babu, R; Ramesh, R; Gopalakrishnan, R; Ramamurthi, K; Bhagavannarayana, G

2010-09-01

34

Studies on solution-grown pure and doped Sodium Potassium tartrate crystals.  

PubMed

A systematic analysis of the Fourier transform infrared spectroscopy and Raman spectra of pure and Cu(NO(3))(2)3H(2)O doped Rochelle salt (NaKC(4)H(4)O(6)4H(2)O) in terms of the standard frequency correlations, deuteration shift and typical nature (with respect to intensity and width) of bands due to different modes is reported. The bands due to the internal modes (excluding some skeletal modes) of the C(4)H(4)O(6)(2-) ion appear as doublets. For certain modes (e.g. ?(CH), ?(C(OH)) and ?(COO)) doublets arise owing to interaction between two identical oscillations of two identical groups in COO(HO)HCCH(OH)COO(2-), while for other modes (e.g. ?(CH), ?(CO)(a), ?(CO)(s), ?(COH) and ?(COO)) they arise owing to crystallographically distinguishable sites for two identical oscillators. The effect of dopant in the pure Rochelle salt crystals is found out by using Elemental analysis. The unit cell volume of pure and Cu(NO(3))(2)3H(2)O doped Rochelle salt crystals is found out from powder X-ray diffraction studies. PMID:23220676

Mathivanan, V; Haris, M

2013-02-01

35

Rheology of Pure Glasses and Crystal Bearing Melts: from the Newtonian Field to the Brittle Onset  

NASA Astrophysics Data System (ADS)

The brittle-ductile transition remains a central question of modern geology. If rocks can be perceived as a granular flow on geological time-scale, their behavior is brittle in dynamic areas. Understanding rock failure conditions is the main parameter in mitigating geological risks, more specifically the eruptive style transitions from effusive to explosive. If numerical simulations are the only way to fully understanding the physical processes involved, we are in a strong need of an experimental validation of the proposed models. here we present results obtained under torsion and uni-axial compression on both pure glasses and crystal bearing melts. We characterized the brittle onset of two phases magmas from 0 to 65% crystals. The strain-rates span a 5 orders magnitude range, from the Newtonian flow to the Brittle field (10-5 - 100 s-1). We particularly emphasize the time dependency of the measured rheology. The materials tested are a borosilicate glass from the National Bureau of Standards, a natural sample from Mt Unzen volcano and a synthetic sample. The lattest is an HPG8 melt with 7% sodium mole excess. The particles are quasi-isometric corundum crystalschosen for their shape and integrity under the stress range investigated. The crystal fraction ranges from 0 to 0.65. Concerning pure magmas, we recently demonstrated that the material passes from a Newtonian to a non-Nemtonian behavior with increasing strain-rate. This onset can mostly be explained by viscous-heating effects. However, for even greater strain-rates, the material cracks and finally fail. The brittle onset is here explained with the visco-elastic theory and corresponds to a Deborah number greater than 10-2. Concerning crystal bearing melts the departure from the Newtonian state is characterized by two effects: a shear-thinning and a time weakening effect. The first one is instantaneous and loading-unloading cyclic tests suggest an elastic contribution of the crystal network. The second one reflects a structural modification of the material (e.g. crystal reorganization, crystal failure, micro-cracking). In the special case presented here, the time weakening effect is the translation of plagioclase breaking during the magma flow. About the ultimate failure of the sample, crystal bearing melts appear to follow the general visco -elastic theory. However a crystal contribution has been here detected and corelate with smaller Deborah numbers before failure. Our observation offer a new vision on volcanic transition and an implication on the 90-95 eruptive crisis of Mt Unzen volcano is presented here.

Cordonnier, B.; Caricchi, L.; Pistone, M.; Castro, J. M.; Hess, K.; Dingwell, D. B.

2010-12-01

36

Light response of pure CsI calorimeter crystals painted with wavelength-shifting lacquer  

E-print Network

We have measured scintillation properties of pure CsI crystals used in the shower calorimeter built for a precise determination of the pi+ -> pi0 e+ nu decay rate at the Paul Scherrer Institute (PSI). All 240 individual crystals painted with a special wavelength-shifting solution were examined in a custom-build detection apparatus (RASTA=radioactive source tomography apparatus) that uses a 137Cs radioactive gamma source, cosmic muons and a light emitting diode as complementary probes of the scintillator light response. We have extracted the total light output, axial light collection nonuniformities and timing responses of the individual CsI crystals. These results predict improved performance of the 3 pi sr PIBETA calorimeter due to the painted lateral surfaces of 240 CsI crystals. The wavelength-shifting paint treatment did not affect appreciably the total light output and timing resolution of our crystal sample. The predicted energy resolution for positrons and photons in the energy range of 10-100 MeV was nevertheless improved due to the more favorable axial light collection probability variation. We have compared simulated calorimeter ADC spectra due to 70 MeV positrons and photons with a Monte Carlo calculation of an ideal detector light response.

E. Frlez; Ch. Broennimann; B. Krause; D. Pocanic; D. Renker; S. Ritt; P. L. Slocum; I. Supek; H. P. Wirtz

2000-06-21

37

Biochemistry 1994,33, 1073-1086 1073 The Low-Temperature Crystal Structure of the Pure-Spermine Form of Z-DNA  

E-print Network

, 1993" ABSTRACT: The X-ray crystal structure of the pure-spermine form of the left-handed Z-DNA duplex., 1991). The conformation, orientation, and interactions of Z-DNA in the pure-spermine form crystalBiochemistry 1994,33, 1073-1086 1073 The Low-Temperature Crystal Structure of the Pure

Williams, Loren

38

Endcap calorimeter for SuperBelle based on pure CsI crystals  

NASA Astrophysics Data System (ADS)

The design of the Belle endcap calorimeter based on pure CsI is presented. The suggested calorimeter consists of pure CsI crystals with readout by vacuum photopentodes followed by the analysis of the shape of the output signal. The results of tests of the counters are presented. Photopentodes provide a gain factor about 150-200 without magnetic field. Tests with magnetic field show that the gain factor drops down about 3.5 times in axial magnetic field of 1.5 T. The preamplifier-shaper has been developed which provides electronics noise of 1000 photoelectrons. The beam test results showed the energy resolution about 2.2% for 100 MeV photons and time resolution better than 2 ns. Radiation hardness tests of the counters have been carried out.

Kuzmin, A.; Belle ECL Team

2010-11-01

39

Microbial synthesis of magnetite and Mn-substituted magnetite nanoparticles: influence of bacteria and incubation temperature.  

PubMed

Microbial synthesis of magnetite and metal (Co, Cr, Ni)-substituted magnetites has only recently been reported. The objective of this study was to examine the influence of Mn ion on the microbial synthesis of magnetite nanoparticles. The reductive biotransformation of an akaganeite (beta-FeOOH) or a Mn-substituted (2-20 mol%) akaganeite (Fe(1-x)Mn(x)OOH) by Shewanella loiha (PV-4, 25 degrees C) and Thermoanaerobacter ethanolicus (TOR-39, 60 degrees C) was investigated under anaerobic conditions at circumneutral pH (pH = 7-8). Both bacteria formed magnetite nanoparticles using akaganeite as a magnetite precursor. By comparison of iron minerals formed by PV-4 and TOR-39 using Mn-mixed akaganeite as the precursor, it was shown that PV-4 formed siderite (FeCO3), green rust [Fe2+Fe3+(OH)16CO3 x 4H2O], and magnetite at 25 degrees C, whereas TOR-39 formed mainly nm-sized magnetite at 60 degrees C. The presence of Mn in the magnetite formed by TOR-39 was revealed by energy dispersive X-ray analysis (EDX) is indicative of Mn substitution into magnetite crystals. EDX analysis of iron minerals formed by PV-4 showed that Mn was preferentially concentrated in the siderite and green rust. These results demonstrate that coprecipitated/sorbed Mn induced microbial formation of siderite and green rust by PV-4 at 25 degrees C, but the synthesis of Mn-substituted magnetite nanoparticles proceeded by TOR-39 at 60 degrees C. These results indicate that the bacteria have the ability to synthesize magnetite and Mn-substituted magnetite nano-crystals. Microbially facilitated synthesis of magnetite and metal-substituted magnetites at near ambient temperatures may expand the possible use of specialized ferromagnetic nano-particles. PMID:18047092

Roh, Yul; Jang, Hee-Dong; Suh, Yongjae

2007-11-01

40

Does Magnetite Oxygen Isotopes reveal a Biosignature?  

NASA Astrophysics Data System (ADS)

Magnetite [FeIII_2FeIIO_4] nanoparticles have been found in the ALH 84001 meteorite. Their possible biogenic origin has generated a strong debate which emphasizes that purely inorganic magnetites cannot easily differentiated from those made by bacteria. Oxygen isotopic composition of magnetite could be potentially useful for characterizing biogenic magnetites in the environment and for the development of a magnetite / phosphate geothermometers (Mandernack et al., 1999). Little is known, however, about the oxygen isotopic compositions of inorganically produced nanometer-sized magnetites. Inorganic magnetites have been synthesized under controlled chemical affinity conditions at oxygen fugacity close to 0, ionic strength of 0.2 M and high solution saturation state (> 100) in order to determine if oxygen isotopes can be used as a proxy of bacterial signature. Total dissolved iron of stoechiometric ratio (i.e. FeII / FeIII = 0.5) and temperature were varied to identify the role of these variables on the kinetic rate and on the oxygen isotope fractionation. Under our experimental conditions, magnetite particles of an average dimension of 8 nm are formed only when [Fetot] is higher than 9 mM while in lower dissolved iron concentration, only goethite [?-FeIIIO(OH)] particles are formed. Furthermore, when temperature was increased, higher iron concentration were necessary to form magnetite. Oxygen isotopes fractionation, 10^3ln ?m-w, is important for low iron concentration and stabilizes around 0 to 1 ppm for [Fetot] >= 30 mM. Since biotic magnetites have similar oxygen isotope signature (Mandernack et al., 1999) to our abiotic magnetite particles, no biosignature can be observed and we propose that bacteria may simply produce an increase of solution saturation state in the magnetosomes that, in turn, control the precipitation of magnetite nanoparticles in surface conditions. Mandernack K. W. et al. (1999), Science 285, 1892-1896.

Faivre, D.; Zuddas, P.; Agrinier, P.; Guyot, F.; Menguy, N.

2003-04-01

41

Highly crystalline porous magnetite and vacancy-ordered maghemite microcrystals of rhombohedral habit  

NASA Astrophysics Data System (ADS)

Porous crystals of magnetite and vacancy-ordered maghemite, rhombohedron-shaped, reaching 150 ?m in size, and having remarkably large specific surface area (88.55 m2/g for magnetite, 40.14 m2/g for maghemite) were obtained via topotactical conversion, starting from hydrothermally grown siderite single crystals. The increase in density (from 3.9 g/cm3 for siderite to 5.24 g/cm3 for magnetite and 4.9 g/cm3 for maghemite) caused quasi-ordered internal pores-grains pattern, with mesocrystalline appearance. The X-ray Line-Profile Fitting-based microstructure analysis gave 64±6 nm and 84±8 nm for the average inner grains size in magnetite and maghemite. Structure and phase content analysis indicated high purity and crystallinity. Magnetic measurements indicated saturation magnetization (92.1 emu/g for magnetite and 85.5 emu/g for maghemite) approaching the upper limits reported for the pure bulk oxides.

Ercuta, Aurel; Chirita, Marius

2013-10-01

42

Antimicrobial activity and second harmonic studies on organic non-centrosymmetric pure and doped ninhydrin single crystals.  

PubMed

In this paper, we report the successful growth of pure, Cu(2+) ions and Cd(2+) ions doped on ninhydrin single crystals by slow solvent evaporation technique. The presence of Cu(2+) and Cd(2+) ions in the specimen of ninhydrin single crystal has been determined by atomic absorption spectroscopy. The powder X-ray diffraction analysis was done to calculate the lattice parameters of the pure and doped crystals. The percentage of transmittance of the crystal was recorded using the UV-Vis Spectrophotometer. Thermal behaviors of the grown crystals have been examined by the thermal gravimetric/differential thermal analysis. The hardness of the grown crystals was assessed and the results show the minor variation in the hardness value for the pure and doped ninhydrin samples. The value of the work hardening coefficient n was found to be 2.0, 1.0 and 1.06 for pure, copper and cadmium doped ninhydrin crystals respectively. The second harmonic generation efficiency of Cd(2+) and Cu(2+) doped ninhydrin is 8.3 and 6.3 times greater than well known nonlinear crystal of potassium dihydrogen phosphate respectively. The antibacterial and antifungal activities of the title compound were performed by disk diffusion method against the standard bacteria Escherichia coli, Xanthomonas oryzae and against the fungus Aspergillis niger and Aspergillus flavus. PMID:23266683

Prasanyaa, T; Jayaramakrishnan, V; Haris, M

2013-03-01

43

Antimicrobial activity and second harmonic studies on organic non-centrosymmetric pure and doped ninhydrin single crystals  

NASA Astrophysics Data System (ADS)

In this paper, we report the successful growth of pure, Cu2+ ions and Cd2+ ions doped on ninhydrin single crystals by slow solvent evaporation technique. The presence of Cu2+ and Cd2+ ions in the specimen of ninhydrin single crystal has been determined by atomic absorption spectroscopy. The powder X-ray diffraction analysis was done to calculate the lattice parameters of the pure and doped crystals. The percentage of transmittance of the crystal was recorded using the UV-Vis Spectrophotometer. Thermal behaviors of the grown crystals have been examined by the thermal gravimetric/differential thermal analysis. The hardness of the grown crystals was assessed and the results show the minor variation in the hardness value for the pure and doped ninhydrin samples. The value of the work hardening coefficient n was found to be 2.0, 1.0 and 1.06 for pure, copper and cadmium doped ninhydrin crystals respectively. The second harmonic generation efficiency of Cd2+ and Cu2+ doped ninhydrin is 8.3 and 6.3 times greater than well known nonlinear crystal of potassium dihydrogen phosphate respectively. The antibacterial and antifungal activities of the title compound were performed by disk diffusion method against the standard bacteria Escherichia coli, Xanthomonas oryzae and against the fungus Aspergillis niger and Aspergillus flavus.

Prasanyaa, T.; Jayaramakrishnan, V.; Haris, M.

2013-03-01

44

Panning for Gold and Magnetite  

NSDL National Science Digital Library

In this activity, students can learn to pan for gold and magnetite. They will learn skills such as making observations under field conditions and watching out for poison ivy. They will see the effects of stream flow on sediments and observe sedimentary structures such as stream bars and islands, observe that different sizes of sediment are located in different parts of the stream, distinguish between different sizes of sediment, and recognize that different minerals are different colors. In addition, they can estimate and weigh the content of magnetite and nonmagnetite, observe crystal shapes of some of the mineral grains, and discuss why magnets pick up magnetite but not nonmagnetic grains. Choose desired title from main listing of activities to access individual exercises.

Robbins, Eleanora

45

Inscription of strong Bragg gratings in pure silica photonic crystal fibers using UV femtosecond laser pulses  

NASA Astrophysics Data System (ADS)

We demonstrate our experimental results on inscription of strong first-order Bragg gratings in hydrogen-free and hydrogen-loaded pure silica photonic crystal fibers (PCFs) using high-intensity 160 femtosecond (fs) UV laser pulses at 266 nm and a two-beam Talbot interferometer. Bragg reflectivities up to 37 dB for the H2-loaded fiber as well as Bragg wavelength tuning over the telecom C-band using a single phase mask were achieved. The in-situ nonlinear filamentation of UV fs laser pulses, scattered by the fiber’s micro-structured cladding, is demonstrated by direct refractive index profile measurement across the cross section of a written fiber. The results of thermal annealing measurements for a H2-loaded PCF are also presented.

Saliminia, Ali; Proulx, Antoine; Vallée, Réal

2014-12-01

46

Energetics of free pure metallic nanoclusters with different motifs by equivalent crystal theory  

NASA Astrophysics Data System (ADS)

The energy of metallic (Ni, Cu, Pd, Ag, Pt, and Au) nanoparticles up to 5000 atoms are studied by equivalent crystal theory (ECT), a quantum approximate method (QAM) that describes the ground state structure and the surface properties of metals and semiconductors at zero temperature. ECT relies on the universal binding energy relation to predict with precision and speed the energy of a crystal in a specific configuration. For each pure metallic nanoparticle of each chosen motif (icosahedron, octahedron, and decahedron), the energy variation with the number of atoms Nat is studied. Crossover and minimum energy values are calculated and/or estimated and compared with the results obtained by molecular dynamics (MD). Our results confirm the qualitative behavior (i.e., icosahedron shapes are less energetic for small sizes, decahedron for medium sizes, and octahedron for bigger sizes) predicted by MD, but the calculated crossover and minimum energy values are, in general, larger for all metals and geometries examined. Also, we studied the trends in relaxation between layers and the behavior of the average radius Rav of each relaxed nanoparticle as Nat was increased. For each motif, the most stable structures (i.e., with the best truncation) follow a simple law of Rav in terms of Nat . This simple law is unchanged for the four different motifs and can be extended for all six metals after a simple parametrization is performed.

Negreiros, F. R.; Soares, E. A.; de Carvalho, V. E.

2007-11-01

47

Magnetite and its production  

SciTech Connect

The supply of high quality magnetite for the cleaning of coal using dense medium cyclones and vessels is of concern to all coal preparation operations. This paper describes the production of high purity magnetite (Fe{sub 3}O{sub 4}) from a domestic underground mining operation in Missouri, Pea Ridge Iron Ore Company. Emphasis will be placed on the mining and processing of the magnetite ore into the various magnetite products required by coal preparation plants.

Koebbe, E.R. [Pea Ridge Iron Ore Co., Sullivan, MO (United States)

1993-12-31

48

Theory of the propagation of finite amplitude ultrasonic waves in pure mode directions in hexagonal and trigonal crystals  

NASA Astrophysics Data System (ADS)

The nonlinear theory describing the propagation of finite amplitude ultrasonic waves in pure mode directions in hexagonal and trigonal crystals is developed. By evaluating the coefficient of the term which couples the longitudinal wave of finite amplitude to the transverse modes, one finds the pure mode directions by requiring this coefficient to vanish. The result is that for hexagonal crystals the directions along the symmetry axis and in the basal plane are pure longitudinal mode directions. Pure mode directions are also found for longitudinal waves propagating tangential to a cone whose apex is centered about the symmetry axis and whose apex angle is a function of the second-order elastic constants of the sample under consideration. The third-order elastic constants which determine the magnitude of the second harmonic of an initially sinusoidal ultrasonic wave are evaluated for these additional directions. For finite amplitude longitudinal ultrasonic waves in trigonal crystals, we have specialized to nonpiezoelectric crystals and have evaluated the third-order elastic constants which determine the magnitude of the second harmonic of an initially sinusoidal wave propagating in the following pure mode directions: (1) along the symmetry axis (the c-direction); (2) along the a-direction in the basal plane; (3) along the direction in the basal plane that makes an angle of 60 deg with the a-direction; and (4) along a direction in the b-c plane whose angle with respect to the b-axis is a function of the second-order elastic constants of the crystal under consideration.

Du, G.; Breazeale, M. A.

1985-06-01

49

Magnetite morphology and life on Mars  

Microsoft Academic Search

Nanocrystals of magnetite (Fe3O4) in a meteorite from Mars pro- vide the strongest, albeit controversial, evidence for the former presence of extraterrestrial life. The morphological and size re- semblance of the crystals from meteorite ALH84001 to crystals formed by certain terrestrial bacteria has been used in support of the biological origin of the extraterrestrial minerals. By using tomographic and holographic

Peter R. Buseck; Rafal E. Dunin-Borkowski; Bertrand Devouard; Richard B. Frankel; Martha R. McCartney; Paul A. Midgley; Mihaly Posfai; Matthew Weyland

2001-01-01

50

Remanence in authigenic magnetite: Testing the hydrocarbon-magnetite hypothesis  

SciTech Connect

Paleomagnetic, rock magnetic, petrographic, and geochemical studies of hydrocarbon-saturated speleothems in southern Oklahoma indicate there is a relation between hydrocarbons and a chemical magnetization that resides in magnetite. The speleothems, which are composed of light and dark calcite bands, occur in caves of karst origin in the Ordovician Kindblade Formation. Vertebrate fossils interbedded with the deposits indicate they are Permian in age. The dark bands contain primary hydrocarbon-filled fluid inclusions. The dark calcites possess over an order of magnitude stronger natural remanent magnetization than the lighter bands which do not yield stable decay during demagnetization. Alternating field (AF) and thermal demagnetization of specimens of the dark bands reveal a Permian direction of magnetization (declination = 160, inclination = 3, k = 17, {alpha}95 = 5, n = 56). The results of rock magnetic experiments, and the fact that most maximum unblocking temperatures are below 580 C, suggest that the dominant component resides in magnetite. In some specimens stable decay to 640 C suggests the presence of a weak component residing in hematite. The presence of authigenic magnetite spheres in magnetic extracts of the dark calcites supports a chemical origin for the magnetization. Shallow burial depths probably eliminate the possibility of a thermoviscous magnetization. The occurrence of primary hydrocarbons seeped into the caves during precipitation of the speleothems and were trapped in the calcite crystals. The relationship between intensity of magnetization and hydrocarbon abundance leads the authors to propose that chemical conditions created by the hydrocarbons caused precipitation of authigenic magnetite and acquisition of the associated chemical remanence.

Elmore, R.D.; Crawford, L. (Univ. of Oklahoma, Norman (United States))

1990-04-10

51

Magnetite biomineralization induced by Shewanella oneidensis  

NASA Astrophysics Data System (ADS)

Shewanella oneidensis is a dissimilatory iron reducing bacterium capable of inducing the extracellular precipitation of magnetite. This precipitation requires a combination of passive and active mechanisms. Precipitation occurs as a consequence of active production of Fe 2+(aq) when bacteria utilize ferrihydrite as a terminal electron acceptor, and the pH rise probably due to the bacterial metabolism of amino acids. As for passive mechanisms, the localized concentration of Fe 2+(aq) and Fe 3+(aq) at the net negatively charged cell wall, cell structures and/or cell debris induces a local rise of supersaturation of the system with respect to magnetite, triggering the precipitation of such a phase. These biologically induced magnetites are morphologically identical to those formed inorganically in free-drift experiments (closed system; 25 °C, 1 atm total pressure), both from aqueous solutions containing Fe(ClO 4) 2, FeCl 3, NaHCO 3, NaCO 3 and NaOH, and also from sterile culture medium added with FeCl 2. However, organic material becomes incorporated in substantial amounts into the crystal structure of S. oneidensis-induced magnetites, modifying such a structure compared to that of inorganic magnetites. This structural change and the presence of organic matter are detected by Raman and FT-IR spectroscopic analyses and may be used as a biomarker to recognize the biogenic origin of natural magnetites.

Perez-Gonzalez, Teresa; Jimenez-Lopez, Concepcion; Neal, Andrew L.; Rull-Perez, Fernando; Rodriguez-Navarro, Alejandro; Fernandez-Vivas, Antonia; Iañez-Pareja, Enrique

2010-02-01

52

Growth of large, defect-free pure C60 single crystals  

NASA Technical Reports Server (NTRS)

Millimeter-sized single crystals of C60 were grown by sublimation of C60 powder in a vacuum for 6-24 h. The crystals had excellent facets, were free of C70 or solvent, and showed face-centered cubic symmetry with a very small mosaic spread down to 0.01 deg.

Meng, R. L.; Ramirez, D.; Jiang, X.; Chow, P. C.; Diaz, C.; Matsuishi, K.; Moss, S. C.; Hor, P. H.; Chu, C. W.

1991-01-01

53

A MODEL FOR ALUMINIUM TRIHYDROXIDE CRYSTALLIZATION FROM PURE AND IMPURE SOLUTIONS  

Microsoft Academic Search

Mannitol has been used as a model hydroxy organic compound to simulate the influence or organic compounds on the growth, nucleation and agglomeration mechanisms of aluminium trihydroxide crystallization. As little as 151·6rngmannitol\\/m of seed was sufficient to completely suppress the crystallization. A population balance equation including terms for nucleation, growth and agglomeration, coupled with a mass balance equation forms the

A. ALAMDARI; J. A. RAPER; M. S. WAINWRIGHT

2000-01-01

54

All-Angle Negative Refraction and Imaging Effects for Both Polarizations in Pure Dielectric Composite Two-Dimensional Photonic Crystals  

NASA Astrophysics Data System (ADS)

Due to the band separation between two polarization modes, it is usually difficult to realize all-angle negative refraction (AANR) for both polarizations from normal dielectric-rod or air-hole photonic crystals (PCs). In this letter, we propose a pure dielectric composite PC that shows much suppressed band structures that are quite useful for the formation of a common frequency area of AANR for both polarizations. Further simulations have first demonstrated the common AANR and imaging effects in such composite PC and we can control the property of the image by changing the cutoff at surface termination and the PC thickness.

Jiang, Liyong; Wu, Hong; Zheng, Gaige; Li, Xiangyin

2012-01-01

55

Magnetite-Pentlandite Chondrules in CK Chondrites  

NASA Astrophysics Data System (ADS)

Opaque-mineral-rich chondrules are among the least common chondrule types and have received scant attention since their discovery by Gustav Rose in 1864. This category includes chondrules comprised principally of metallic Fe-Ni (Tschermak, 1885; Gooding and Keil, 1981) or chrome-spinel (Ramdohr, 1967; Krot et al., 1992). Here I report the occurrence of seven magnetite-pentlandite chondrules in Karoonda (CK4), PCA82500 (CK4/5) and EET90007 (CK5). The chondrules range in size from 225x255 micrometers to 440x570 micrometers and have ellipsoidal or spheroidal morphologies. All are concentrically layered: five of the chondrules have 20-60-micrometer-thick magnetite rims surrounding pentlandite-rich cores or mantles; two of the chondrules have thin pentlandite rims surrounding magnetite-rich cores and mantles. One chondrule from Karoonda has four distinct alternating layers of magnetite and pentlandite. Accessory phases, which occur in one or more of the chondrules, include pyrrhotite, chlorapatite, ilmenite, and chalcopyrite. The chondrules have finely to coarsely granular textures; in the center of one chondrule from PCA82500 there is a 25x100 micrometers subhedral crystal of pentlandite. All of the chondrules appear to be recrystallized, presumably due to metamorphism of their host rocks. The magnetite-pentlandite chondrules are very similar to the magnetite-pentlandite-rich nodules within mafic silicate chondrules in CK chondrites. I examined four nodules that range in size from 58x64 micrometers to 400x670 micrometers and have ellipsoidal or spheroidal morphologies. All but one are concentrically layered; one nodule from a Karoonda chondrule has four concentric layers of magnetite+-pentlandite. The nodules probably formed from immiscible sulfide-oxide droplets within their molten silicate chondrule hosts during chondrule formation. Upon cooling, magnetite and monosulfide solid solution (Mss) precipitated during cotectic crystallization; the Mss transformed into pentlandite after cooling below 610 degrees C. Dense immiscible liquid droplets tend to get expelled from the equators of their spinning molten spheroidal hosts if they do not happen to be located in the molten spheroids' centers where the centrifugal forces are minimal. This phenomenon also affected the four magnetite-pentlandite nodules: one nodule is near the margin and three are at the centers of their host silicate chondrules. The similarities in size, shape, mineralogy, and texture between the magnetite-pentlandite chondrules and nodules indicate that these chondrules constitute the set of immiscible nodule droplets that were lost to their mafic silicate chondrule hosts after melting. The occurrence of magnetite-pentlandite chondrules and nodules has important implications for the timing of CK chondrite oxidation. If oxidation had occurred after agglomeration and transformed metallic Fe-Ni into magnetite, the large (factor of 2) increase in molar volume would have disrupted the nodules and chondrules and destroyed the evidence for rhythmic layering. The intactness of the chondrules and nodules implies that the oxidation of fine-grained metallic Fe-Ni into magnetite probably occurred before agglomeration, either during chondrule formation in a region of high fo(sub)2 or within porous chondrule-precursor dust clumps after nebular temperatures cooled below ~130 degrees C. Hence, the pervasive silicate darkening of CK chondrites (Kallemeyn et al., 1991; Rubin, 1992) was caused by the shock mobilization of magnetite and pentlandite, not metallic Fe-Ni and troilite as in shock-darkened ordinary chondrites. References: Gooding J.L. and Keil K. (1981) Meteoritics 16, 17- 43; Kallemeyn G.W., Rubin A.E. and Wasson J.T. (1991) Geochim. Cosmochim. Acta 55, 881-892; Krot A., Ivanova M.A. and Wasson J.T. (1992) Earth Planet. Sci. Lett., submitted; Ramdohr P. (1967) Geochim. Cosmochim. Acta 31, 1961-1967; Rubin A.E. (1992) Geochim. Cosmochim. Acta 56, 1705-1714; Tschermak G. (1885) Die Mikroskopische Beschaffenheit der Meteoriten. Schweizerbart'sche Verlagshandlung, Stuttga

Rubin, A. E.

1992-07-01

56

Structure and superparamagnetic behaviour of magnetite nanoparticles in cellulose beads  

SciTech Connect

Superparamagnetic magnetite nanoparticles were obtained starting from a mixture of iron(II) and iron(III) solutions in a preset total iron concentration from 0.04 to 0.8 mol l{sup -1} with ammonia at 25 and 70 {sup o}C. The regeneration of cellulose from viscose produces micrometrical spherical cellulose beads in which synthetic magnetite were embedded. The characterization of cellulose-magnetite beads by X-ray diffraction, Scanning and Transmission Electron Microscopy and magnetic measurement is reported. X-ray diffraction patterns indicate that the higher is the total iron concentration and temperature the higher is the crystal size of the magnetite obtained. Transmission Electron Microscopy studies of cellulose-magnetite beads revealed the distribution of magnetite nanoparticles inside pores of hundred nanometers. Magnetite as well as the cellulose-magnetite composites exhibit superparamagnetic characteristics. Field cooling and zero field cooling magnetic susceptibility measurements confirm the superparamagnetic behaviour and the blocking temperature for the magnetite with a mean size of 12.5 nm, which is 200 K.

Correa, Jose R., E-mail: correa@fq.uh.cu [Department of General Chemistry, Faculty of Chemistry, University of Havana, Zapata and G, Havana City 10400 (Cuba); Bordallo, Eduardo [Sugar Cane-Cellulose Research Center, Cuba-9, Quivican (Cuba)] [Sugar Cane-Cellulose Research Center, Cuba-9, Quivican (Cuba); Canetti, Dora [Department of Inorganic Chemistry, Faculty of Chemistry, University of Havana, Zapata and G, Havana City 10400 (Cuba)] [Department of Inorganic Chemistry, Faculty of Chemistry, University of Havana, Zapata and G, Havana City 10400 (Cuba); Leon, Vivian [Sugar Cane-Cellulose Research Center, Cuba-9, Quivican (Cuba)] [Sugar Cane-Cellulose Research Center, Cuba-9, Quivican (Cuba); Otero-Diaz, Luis C. [Department of Inorganic Chemistry-1, Complutense University of Madrid, Madrid 28040 (Spain) [Department of Inorganic Chemistry-1, Complutense University of Madrid, Madrid 28040 (Spain); Electron Microscopy Center, Complutense University of Madrid, Madrid 28040 (Spain); Negro, Carlos [Chemical Engineering Department, Complutense University of Madrid, Madrid 28040 (Spain)] [Chemical Engineering Department, Complutense University of Madrid, Madrid 28040 (Spain); Gomez, Adrian [Electron Microscopy Center, Complutense University of Madrid, Madrid 28040 (Spain)] [Electron Microscopy Center, Complutense University of Madrid, Madrid 28040 (Spain); Saez-Puche, Regino [Department of Inorganic Chemistry-1, Complutense University of Madrid, Madrid 28040 (Spain)] [Department of Inorganic Chemistry-1, Complutense University of Madrid, Madrid 28040 (Spain)

2010-08-15

57

Optical Limiting Studies in Photorefractive Pure and Iron-Doped Bi12SiO20 Crystals  

NASA Astrophysics Data System (ADS)

Optical limiting characteristics of pure and 150 ppm Fe-doped Bi12SiO20 (BSO:Fe) crystals are studied at high intensity nanosecond pulse regime. When the input light is at 532 nm and at 595 nm with 6 ns pulse duration, a good optical limiting behavior is observed due to simultaneous effect of trap assisted excited state absorption and two photon absorption. The precise role of the internal defects due to impurity centers present in the crystal lattice is explained on the basis of a four level model. This study reveal that the increased nonlinear absorption due to iron incorporation in BSO makes it an excellent passive optical limiter.

Aithal, P. Sreeramana; Kiran, P. Prem; Rao, D. Narayana

58

Morphological and growth rate distributions of small self-nucleated paracetamol crystals grown from pure aqueous solutions  

NASA Astrophysics Data System (ADS)

The growth rate dispersion of small paracetamol crystals nucleated and grown from pure solution was measured over the range of supersaturation, 0%< s<20%, in the three different crystallographic directions: [0 0 1], [1 1 0] and [0 1 0]. The results were fitted to three parameter log-normal and gamma distribution functions. The average growth rates obtained from these distributions were used to predict the morphological behaviour of an assembly of small paracetamol crystals as a function of supersaturation. It was shown that a columnar shape (dominant {1 1 0}) was formed in regions of low supersaturation while a plate-like form (dominant {0 0 1}) prevailed at high supersaturations. Using optical microscopy and X-ray topography, the potential causes for both the growth rate distribution and morphological change were investigated.

Finnie, S. D.; Ristic, R. I.; Sherwood, J. N.; Zikic, A. M.

1999-12-01

59

Growth conditions, structure and superconductivity of pure and metal-doped FeTe1 - xSex single crystals  

NASA Astrophysics Data System (ADS)

Superconducting single crystals of pure FeTe1 - xSex and FeTe0.65Se0.35 doped with Co, Ni, Cu, Mn, Zn, Mo, Cd, In, Pb, Hg, V, Ga, Mg, Al, Ti, Cr, Sr or Nd into Fe ion sites have been grown applying Bridgman's method. It has been found that the sharpness of the transition to the superconducting state in FeTe1 - xSex is evidently inversely correlated with the crystallographic quality of the crystals. Among all of the studied dopants only Co, Ni and Cu substitute Fe ions in FeTe0.65Se0.35 crystals. The remaining ions examined do not incorporate into the crystal structure. Nevertheless, they form inclusions together with selenium, tellurium and/or iron, which change the chemical composition of the host matrix and therefore influence the Tc value. The small disorder introduced into the magnetic sublattice, by partial replacement of Fe ions by a slight amount of nonmagnetic ions of Cu (~1.5 at.%) or by magnetic ions of Ni (~2 at.%) and Co (~5 at.%) with spin values different than that of the Fe ion, completely suppresses superconductivity in the FeTe1 - xSex system. This indicates that, even if superconductivity is observed in the system containing magnetic ions, it cannot survive when the disorder in the magnetic ion sublattice is introduced, most likely because of magnetic scattering of Cooper pairs.

Gawryluk, D. J.; Fink-Finowicki, J.; Wi?niewski, A.; Pu?niak, R.; Domukhovski, V.; Diduszko, R.; Koz?owski, M.; Berkowski, M.

2011-06-01

60

Pure and Nd added NBT-BT single crystals - Growth and their characterization  

NASA Astrophysics Data System (ADS)

The lead free piezoelectric materials are secured an important place in the field of material science and engineering. In the present work single crystals of sodium bismuth titanate- barium titanate (0.94NBT-0.06BT) and 0.6 wt % of Nd added NBT-BT has been grown by flux method. The addition of 0.6 wt% of Nd shows the inhomogeneity in melt and the crystals collected from the top, middle and bottom portions of the crucible have been characterized for their structural and dielectric properties. The Nd concentration is found to be more in the crystals grown from the bottom portion of crucible and it was confirmed by optical and structural analysis. After the addition of Nd the color of the crystal changes form pale yellow to muddy green. The depolarization temperature (Td) and the temperature where the dielectric constant reaches its maximum (Tm) are increased from 442 K to 475 K and 595 K and 628 K respectively after the addition the of Nd in NBT-BT.

Sundari, S. Shanmuga; Baskar, K.; Dhanasekaran, R.

2014-04-01

61

Pattern forming instability induced by light in pure and dye-doped nematic liquid crystals  

E-print Network

We study theoretically the instabilities induced by a linearly polarized ordinary light wave incident at a small oblique angle on a thin layer of homeotropically oriented nematic liquid crystal with special emphasis on the dye-doped case. The spatially periodic Hopf bifurcation that occurs as the secondary instability after the stationary Freedericksz transition is analyzed.

D. O. Krimer; G. Demeter; L. Kramer

2002-07-03

62

Improvement of toughness by stereocomplex crystal formation in optically pure polylactides of high molecular weight.  

PubMed

A solution casting method followed by thermal homogenization was performed for the preparation of 1:1 blends and non-blended films from poly(d-lactide) (PDLA) and poly(l-lactide) (PLLA) of three different molecular weights, and their thermal and mechanical properties were determined via differential scanning calorimetry (DSC) and tensile tests. According to the literature, when Mw is below 1.0×10(5)g/mol only stereocomplex crystallization takes place, and when it is higher, both homocrystallites and stereocomplex crystallites co-exist. In order to promote crystallization as a homocrystal in neat polylactides and to promote the stereoselective crystallization as stereocomplex in the case of non-blended films, and in turn, to achieve different degrees of crystallinity, several thermal treatments of annealing were carried out in this work. Highly stereocomplexed blends were found by the stereospecific thermal treatments. As a consequence, the toughness of 1:1 blends was found significantly enhanced over those of non-blended films, irrespective of molecular weight. For instance, in B2-5050 stereocomplexed blend having poly(l-lactide) and poly(d-lactide) of Mw=1.2×10(5)g/mol, tensile strength increased from 44.0±2.1MPa to 65.1±6.1MPa, and the elongation at break from 10.8±2.5% to 33.1±8.1% with respect to its non-blended poly(l-lactide) counterpart crystallized as homocrystal. This improvement in mechanical properties in stereocomplexed blends is not attributed to the inherent properties of the type of crystal polymorph but to the presence of a higher density of intercrystalline connections through a mobile amorphous phase, i.e. tie chains in the stereocomplexed supramolecular spherulitic entities that provide in the stereocomplexed samples enhanced strength and elongation at break at the same time. PMID:24951928

López-Rodríguez, N; Martínez de Arenaza, I; Meaurio, E; Sarasua, J R

2014-09-01

63

Crystal nucleation in glass-forming alloy and pure metal melts under containerless and vibrationless conditions  

NASA Technical Reports Server (NTRS)

The undercooling behavior of large spheroids of Pd40Ni40P40 was investigated. By surface etching, supporting the specimens on a fused silica substrate, and successive heating and cooling, crystallization can be eliminated, presumable due to the removal of surface heterogeneities. By this method samples up to 3.2g with a 0.53 mm minor diameter, were made entirely glassy, except for some superficial crystals comprising less than 0.5% of the volume. These experiments show that a cooling rate of approximately 1 K/sec is adequate to avoid copious homogeneous nucleation in the alloy, and that by eliminating or reducing the effectiveness of heterogeneous nucleation sites, it is possible to form bulk samples of this metallic glass with virtually unlimited dimensions.

Spaepen, F.; Turnbull, D.

1982-01-01

64

Pure SH SAW on single crystal KNbO3 for liquid sensor applications  

Microsoft Academic Search

This paper reports on the design, fabrication, and testing of a surface acoustic wave (SAW) delay line on single crystal KNbO3 Euler angles (0°,90°, 0°). This particular orientation of KNbO3 is of symmetry Type 4, which is known to support an electromechanically active shear horizontal (SH) SAW mode, and has a very large electromechanical coupling coefficient of 53%. The SH-SAW

T. B. Pollard; J. F. Vetelinop; M. Pereira da Cunha

2003-01-01

65

Thermophiles as Candidate Iron-Reducing Bacteria For the Putative Biogenetic Magnetite in Banded Iron Formations  

NASA Astrophysics Data System (ADS)

The temperature of the Archaean-Palaeoproterozoic ocean was likely consistent with physiological requirements of thermophilic species being present. In this study, we compared the crystallochemistry and lattice constants of magnetite crystals produced by Thermoanaerobacter sp. TOR39, Geobacter and Shewanella and the slightly altered magnetite from BIF of Hamersley, Western Australia. The lattice constants of TOR39-magnetite and the BIF-magnetite were similar, being 8.3901 and 8.3869 Å respectively. The lattice constant of magnetite produced by Geobacter is more close to perfect stoichiometry (8.4038 Å), however, the magnetite produced by Shewanella experienced oxidization has a much smaller value (8.3522 Å). The stoichiometries of TOR39-magnetite was Fe3+[Fe3+1.1217Fe2+0.8175--0.0608]O4 and that of BIF-magnetite was quite similar being Fe3+[Fe3+0.9963Fe2+1.0056]O4. The stoichiometry, lattice constant and crystal size collectively indicated that TOR39-magnetite was similar to BIF-magnetite. The Mössbauer spectroscopy indicated the existence of a Fe(III)-salt, possibly Fe3+OH(CH3COO)2 in the magnetite lamina of BIF which was widely detected in the magnetite-assemblages of iron-reducing bacterial cultures that contained acetate. This is evidence that supports a potential role for thermophiles such as Thermoanaerobacter in the biogenesis of magnetite in BIF. The magnetite crystals produced by cultures of Shewanella, Geobacter, magnetotactic bacteria and those synthesized from green rust appeared less similar to BIF-magnetite by either their crystallochemistry or their optimized growth temperatures.

Li, Y.; Phelps, T. J.; Cole, D. R.; Vali, H.; Konhauser, K.

2008-12-01

66

Growth and scintillation properties of pure CsI crystals grown by micro-pulling-down method  

NASA Astrophysics Data System (ADS)

Single crystals of pure cesium iodide (CsI) have been grown from the melt using micro-pulling-down (?-PD) method. Two kinds of crucible (graphite one and quartz one) were used for the growth and the grown crystals were investigated by X-ray diffraction (XRD) and X-ray rocking curve (XRC) analysis. The XRD analysis did not confirm any impurity phases and a sub-grain structure was observed for each sample in the rocking curve measurement. Under X-ray irradiation, strong STE emission peaks around 300 nm were observed together with some luminescence related to unintentionally present impurities. The STE emission peaks are characterized by fast decay times of several ns and about 20 ns which are interpreted as the on-center-type STE (VK + e) and off-center type STE (H + F) recombinations, respectively. The light yield of the STE-related emissions has been estimated to be 3000 ph/MeV. Other emission peaks were observed at 410 nm and 515 nm. The former one can be related to Br-contamination and it is characterized by a relatively slow decay time of 6 ?s. Concerning the latter one at 515 nm, similar luminescence was observed for the water-doped CsI grown by Bridgman method.

Totsuka, Daisuke; Yanagida, Takayuki; Fujimoto, Yutaka; Pejchal, Jan; Yokota, Yuui; Yoshikawa, Akira

2012-05-01

67

Polarization Switching and Defect Structure in Pure and MgO Doped Near-Stoichiometric LiNbO3 Crystals  

Microsoft Academic Search

Pure and MgO doped (up to 4 mol%) near-stoichiometric LiNbO3 crystals are grown from Li rich (Li-55 mol%) melt. Significant improvement in the optical properties such as increase of optical damage resistance, accompanied by a shift in the –OH peak position in FTIR spectrum, and transparent range is observed at 1.75 mol% of MgO concentration in the crystal. Also the

S. Kumaragurubaran; S. Takekawa; M. Nakamura; S. Ganesamoorthy; K. Kitamura

2005-01-01

68

Multiple ordering in magnetite.  

NASA Technical Reports Server (NTRS)

Results of a self-consistent band calculation of the ground-state energy and charge orderings based on a tight-binding scheme in magnetite are presented. They show that below a critical (about 2.2) value of the ratio of interatomic Coulomb energy to bandwidth the lowest energy state has no order. Between this critical value and 2.5, the preferred state is multiply ordered.

Cullen, J. R.; Callen, E. R.

1973-01-01

69

Magnetite mineral nanoparticles synthesized naturally in an iron ore deposit  

NASA Astrophysics Data System (ADS)

We performed a mineralogical characterization and mineral magnetism study of the Peña Colorada iron ore, Mexico. The ore is formed partly by intergranular magnetite intergrowed with berthierine (Fe,Mg,Al)6(Si,Al)4O10(OH)8. The magnetite nanoparticles are forming aggregates of wide grain size spectra, from micro to nanometer scale. The smallest aggregates are formed by magnetite nanoparticles 2 to 30 grain size range, showing unusual physical and chemical behavior. The continuous agglomeration of nanoparticles formed more denser and compact magnetite microparticles. A magnetite concentrate to micrometric scale was reduced and divided into distinct range sizes: 85-56 ?m, 56-30 ?m, 30-22 ?m, 22-15 ?m, 15-10 ?m, 10-7 ?m and 7-1 ?m. Nanometric-scale magnetite 2-30 nm was identified by using high resolution Transmission Electron Microscopy (HRTEM). The magnetite and minerals associated were characterized by X-ray diffraction, transmitted and reflected light polarization, microscope and electron probe X-ray micro-analyzer, differential thermal analysis, gravimetric thermal analysis, and high-resolution transmission electron microscopy. Besides, results of Mössbauer spectroscopy, frequency-dependent magnetic susceptibility, isothermal remanent magnetization and magnetic susceptibility versus temperature were important in the research related to the origin of this deposit. To study magnetite nanoparticles, agglomeration processes and temperature effect implications, we developed an experimental process to re-create the environmental conditions that originated this nanoparticles. These processes start with direct precipitation to synthesize magnetite nanoparticles through a thermal and dehydration treatment of the berthierine base mineral, using diverse temperature ranges, from 360 °C to 750 °C and treatment time of two hours. This process allowed the nucleation and crystalline growth of a high number of magnetite nano-crystals with average size of 2 to 6 nm, homogeneous distribution in the colloidal matrix and a superparamagnetic behavior. Increase temperature provoke new magnetite nano-cores and constant growth of the ones already present. The union to magnetite nanoparticles favored the formation of aggregates nano-micrometric strongly compacted with the acquisition of ferromagnetic behavior. The mineralogical-textural characteristic of magnetite nanoparticles and its magnetic properties were an important guide to explain the environmental conditions for iron deposition, suggesting a marine sedimentary exhalative (SEDEX) origin assisted by bacterial.

Rivas-Sanchez, M. L.; Alva-Valdivia, L. M.

2013-05-01

70

In situ TEM investigation of Xe ion irradiation induced defects and bubbles in pure molybdenum single crystal  

NASA Astrophysics Data System (ADS)

In order to study irradiation damage and inert gas bubble formation and growth behaviors, and to provide results and insights useful towards the validation of a multi-scale simulation approach based on a newly developed Xe-Mo inter-atomic potential, in situ Transmission Electron Microscopy (TEM) studies of Xe implantations in pure single crystal Molybdenum (Mo) have been conducted. 300 keV and 400 keV Xe+ ion beams were used to implant Xe in pre-thinned TEM Mo specimens. The irradiations were conducted at 300 °C and 600 °C to ion fluence up to 4 × 1016 ions/cm2. In situ TEM characterization allows detailed behaviors of defect clusters to be observed and is very useful in illustrating defect interaction mechanisms and processes. Dislocation loops were found to form at relatively low irradiation fluence levels. The characterization results showed that the free surfaces, formed in the process of producing pre-thinned specimens, play an important role in influencing the behaviors of dislocation loops. Similar characterizations were conducted at high fluence levels where Xe gas bubbles can be clearly observed. Xe gas bubbles were observed to form by a multi-atom nucleation process and they were immobile throughout the irradiation process at both temperatures. Measurements on both the number density and the size of dislocation loops and gas bubbles were taken. The results and implications of the measurements are discussed in this paper.

Yun, Di; Kirk, Marquis A.; Baldo, Peter M.; Rest, Jeffrey; Yacout, Abdellatif M.; Insepov, Zinetula Z.

2013-06-01

71

Exsolution of Iron-Titanium Oxides in Magnetite in Miller Range (MIL) 03346 Nakhlite: Evidence for Post Crystallization Reduction in the Nakhlite Cumulate Pile  

NASA Technical Reports Server (NTRS)

MIL 03346 is one of the most mesostasis-rich nakhlites [1] and thought to have equilibrated at oxygen fugacities near the fayalite-magnetite-quartz oxygen (FMQ) buffer ([2,3]). Studies of FeTi oxides in nakhlites have led to additional constraints on their equilibration temperatures and fO2s [4,5,6,7]. Comparison of these results to fO2s calculated for shergottites indicates that nakhlites are among the most oxidized samples from the martian meteorite suite [2]. The mesostasis of MIL 03346 contains skeletal titanomagnetite. Several scientists noticed several years ago (e.g. [8]) that this titanomagnetite contains very fine oxidation-driven exsolution lamellae (Figure 1). However, the lamellae are so small that they cannot be characterized by electron microprobe analysis (EMPA). Here we select several areas for focused ion beam (FIB) extraction, prepare transmission electron microscopy (TEM) foils, and identify and analyze the lamellae using TEM at the Johnson Space Center (JSC). The resulting analyses are combined with previous work on nakhlites to interpret the thermal and oxidation history of this meteorite group.

Righter, Kevin; Keller, L. P.; Rahman, Z.; Christoffersen, R.

2012-01-01

72

Effect of cation trapping on thermal stability of magnetite nanoparticles.  

PubMed

We investigate the effect of sodium trapping on thermal stability of magnetite (Fe3O4) nanoparticles. The pure magnetite nanoparticles incubated in sodium hydroxide solutions and subsequently washed with water to remove the excess sodium. The amount of sodium in magnetite is measured using atomic absorption spectroscopy. The size distribution obtained from Small angle X-ray scattering measurements show that particles are fairly monodisperse. The FTIR spectra of nanoparticles show transmission bands at 441 and 611 cm(-1) are due to the symmetric stretching vibrations (v) of Fe-O in octahedral and tetrahedral sites respectively. With 500 ppm of sodium ions (Na+) in magnetite, the cubic ferrite structure of maghemite (gamma-Fe2O3) to hexagonal hematite (alpha-Fe2O3) phase transition is enhanced by -150 degrees C in air. The Rietveld analysis of sodium doped magnetite nanoparticles show that above 99% of metastable gamma-Fe2O3 is converted to a thermodynamically stable alpha-Fe2O3 after air annealing at 700 degrees C. A decrease in enthalpy observed in doped magnetite unambiguously confirms that the activation energy for maghemite to hematite transition is increased due to the presence of trapped sodium ions. These results suggest that the trapped cations in ferrite nanoparticles can stabilize them by increasing the activation energy. PMID:24738360

Pati, S S; Philip, John

2014-06-01

73

Magnetite: What it reveals about the origin of the banded iron formations. [Abstract only  

NASA Technical Reports Server (NTRS)

Magnetite, Fe3O4 is produced abiotically and biotically. Abiotically, magnetite is a late magmatic mineral and forms as a consequence of the cooling of iron rich magma. Biotically, magnetite is produced by several organisms, including magnetotactic bacteria. Hematite, Fe2O3, is also produced abiotically and biotically. Abiotically, hematite rarely occurs as a primary mineral in igneous rocks, but is common as an alteration product, fumarole deposit, and in some metamorphosed Fe-rich rocks. Biotically, hematite is produced by several types of microorganisms. Biologically-produced magnetite and hematite are formed under the control of the host organism, and consequently, have characteristics not found in abiotically produced magnetite and hematite crystals. To determine if the magnetite and hematite in the Banded Iron Formation was biologically or abiotically produced, the characteristics of biologically-produced magnetite and hematite (concentrated from Aquaspirillum magnetotacticum) and abiotically-produced magnetite and hematite obtained from Wards Scientific Supply Company, were compared with characteristics of magnetite and hematite concentrated from the Gunflint Banded Iron Formation (Ontario, Canada) using thermal and crystallographic analytical techniques. Whole rock analysis of the Gunflint Banded Iron Formation by x-ray diffraction (XRD) and differential thermal analysis (DTA) revealed the presence of quartz, hematite, siderite and dolomite as the major minerals, and magnetite, greenalite, pyrite, pyrrhotite and apatite as the minor minerals. Analysis of a crude magnetic fraction of the Gunflint showed the minerals quartz, hematite, siderite, dolomite, and magnetite. Analysis of the crude magnetic fraction from Aquaspirillum magnetotacticum revealed organic compounds plus hematite and magnetite. The mineral identification and particle size distribution data obtained from the DTA along with XRD data indicate that the magnetite and hematite from the Gunflint BIF share some similarities with biologically formed magnetite and hematite.

Schwartz, D. E.; Mancinelli, R. L.; White, M. R.

1994-01-01

74

Mineralogical and Isotopic Properties of Biogenic Nanocrystalline Magnetites  

Microsoft Academic Search

Determination of the origin of magnetite nanocrystals is of primary importance because of their significance\\u000a as biomarkers for extraterrestrial life and as environmental indicators. A critical analysis of the\\u000a literature indicates that morphology and magnetic properties of the crystals do not necessarily quantitatively\\u000a allow differentiation of biogenic from abiotic nanomagnetite crystals. Mineralogical properties of magnetosomes\\u000a and of inorganic crystals such as

Damien Faivre; Pierpaolo Zuddas

75

Effect of Annealing on Coercive Force and Remanent Magnetizations in Magnetite  

Microsoft Academic Search

A series of experiments is described in which single crystals of magnetite were annealed under controlled conditions. Structural changes in the magnetite were followed by changes in the magnitudes of coercive force and saturation isothermal remanent magnetization. The structural changes were identified by comparing their activation energies as estimated from the annealing curves with those of known physical processes. It

W. Lowrie; M. Fuller

1969-01-01

76

Synthesis, characterization and anti-microbial activity of pure, Cu2+ and Cd2+ doped organic NLO l-arginine trifluoroacetate single crystals  

NASA Astrophysics Data System (ADS)

Optically transparent Cu2+ and Cd2+ doped l-arginine trifluoroacetate (LATF) single crystals were grown from its aqueous solution using the slow solvent evaporation technique. The grown crystals were characterized by powder x-ray diffraction to confirm the monoclinic crystal structure. The percentage of transmittance measured using the ultraviolet-visible-near infrared spectrophotometer was found to be more than 80% for doped crystals. The functional group analysis of the grown crystals has been made by Fourier transform infrared spectroscopy. Thermogravimetric/differential thermal analysis was performed for the grown crystals. An atomic absorption study was carried out to determine the presence of Cu2+ and Cd2+. The hardness of the grown crystals was assessed and the results show a significant variation in the hardness value between the pure and doped LATF crystals. The second harmonic generation measurements show that Cu2+ doped LATF is 2.8 times greater and Cd2+ doped is 2.6 times greater than KDP. The anti-bacterial and anti-fungal activities of the title compound were performed using the disc diffusion method against standard bacteria Escherichia coli, Xanthomonas oryzae and against the fungus Aspergillus niger and Aspergillus flavus.

Prasanyaa, T.; Haris, M.; Jayaramakrishnan, V.; Amgalan, M.; Mathivanan, V.

2013-10-01

77

Growth of phase-pure, crack-free single crystals and large-grained polycrystals of molybdenum disilicide  

NASA Technical Reports Server (NTRS)

High purity molybdenum disilicide crystals are prepared by zone melting sintered compacts. This method yields single crystals or polycrystals free from macrocracks which allow better measurement and evaluation of mechanical properties.

Rossetti, M.

1970-01-01

78

Comparative study of pure and alkaline earth metallic doped cadmium mercury thiocyanate single crystals—Gel technique  

NASA Astrophysics Data System (ADS)

Growth aspects of Ba and Ca doped cadmium mercury thiocyanate (CMTC) single crystals from silica gel by the process of diffusion are discussed. The incorporation of dopants in the crystal has been confirmed by inductively coupled plasma (ICP) analysis. Single crystal X-ray diffraction studies reveal the structures of the doped crystals to be tetragonal implying that the incorporation of the dopants has not changed the structure of the parent crystal. The diffraction planes were identified and indexed by powder diffraction analysis. High-resolution X-ray diffraction analyses were carried out to investigate the crystalline perfection of the grown crystals. The grown crystals were characterized by Fourier transform infrared and transmission spectral analyses. Vickers microhardness studies on the grown crystals reveal that they belong to soft material category. Employing powder Kurtz method, their second harmonic generation efficiencies were measured in comparison with urea.

Kalainathan, S.; Kumari, P. Nisha Santha

2009-07-01

79

Origin of supposedly biogenic magnetite in the Martian meteorite Allan Hills 84001  

PubMed Central

Crystals of magnetite (Fe3O4) and periclase (MgO) in Fe-Mg-Ca carbonate in the Martian meteorite Allan Hills 84001 were studied by using transmission electron microscopy to understand their origin and evaluate claims that the magnetites were made by Martian microorganisms. In magnesian carbonate, periclase occurs as aggregates of crystals (grain size ?3 nm) that are preferentially oriented with respect to the carbonate lattice. Larger periclase crystals ?50 nm in size are commonly associated with voids of similar size. Periclase clearly formed by precipitation from carbonate as a result of partial decomposition and loss of CO2. Magnetite occurs in more ferroan carbonate, and, like periclase, it is associated with voids and microfractures and the two oxides may be intermixed. Magnetite nanocrystals that are commonly euhedral and entirely embedded in carbonate are topotactically oriented with respect to the carbonate lattice, showing that they formed as solid-state precipitates. Magnetites in Fe-rich carbonate rims are not well oriented. These magnetites are generally more irregular in shape and diverse in size than the euhedral variety. All occurrences of magnetite and periclase are entirely consistent with in situ growth by solid-state diffusion as a result of carbonate decomposition during impact heating. Biogenic sources should not be invoked for any magnetites. PMID:12011420

Barber, David J.; Scott, Edward R. D.

2002-01-01

80

Magnetic and ultrasonic investigations on magnetite nanofluids.  

PubMed

Magnetite nanofluids of various concentrations have been prepared through co-precipitation method. The structural and magnetic properties of the magnetic nanofluids have been analyzed which respectively revealed their face centered cubic crystal structure and super paramagnetic behavior. Ultrasonic investigations have been made for the nanofluids at different temperatures and magnetic fields. Open- and close-packed water structure is considered to explain the temperature effects. The inter particle interactions of surface modified nanomagnetite particle and the cluster formation are realized through the variations in ultrasonic parameters. PMID:22939116

Nabeel Rashin, M; Hemalatha, J

2012-12-01

81

Magnetite Scavenging and the Buoyancy of Bubbles in Magmas  

Microsoft Academic Search

It is generally assumed that when eruptions are triggered, magmas are bubble-free, and all the vesicularity observed in pumice is due to nucleation and growth during ascent. However, decompression experiments show that bubbles tend to nucleate on magnetite crystals at relatively low supersaturation, and there is convincing evidence that an exsolved gas phase was present during much of the evolution

G. A. Gualda; M. S. Ghiorso

2005-01-01

82

Growth, optical and EPR properties of Li1.72Na0.28Ge4O9 single crystals pure and slightly doped with Cr  

NASA Astrophysics Data System (ADS)

Single crystals of lithium-sodium-tetragermanate, a member of the solid solution series Li2-xNa x Ge4O9 with x=0.28, pure and slightly doped with Cr3+ ions (0.03 mol.% and 0.1 mol.%), were grown in ambient atmosphere by the Czochralski technique from stoichiometric melt. The crystals with dimensions up to 20 mm in diameter and 50 mm in length were obtained. The crystal structure has been determined by means of X-ray diffraction. Phase analysis and structural refinement of the Li1.72Na0.28Ge4O9 crystals were performed by X-ray powder diffraction using Ni-filtered Cu K ? radiation with a Siemens D5000 diffractometer. The absorption, excitation and photoluminescence spectra of the crystals were measured in the UV-VIS and IR range at low temperatures. EPR investigations were performed using a conventional X-band Bruker ELEXSYS E 500 CW-spectrometer operating at 9.5 GHz with 100 kHz magnetic field modulation. Temperature and angular dependences of the EPR spectra of the crystal samples were recorded in the 3-300 K temperature range.

Jasik, Anna; Berkowski, Marek; Kaczmarek, Slawomir M.; Suchocki, Andrzej; Kaminska, Agata; Leniec, Grzegorz; Nowakowski, Piotr; Domukhovski, Viktor

2012-04-01

83

Synthesis of stabilized myrrh-capped hydrocolloidal magnetite nanoparticles.  

PubMed

Herein we report a new method for synthesizing stabilized magnetic nanoparticle (MNP) colloids. A new class of monodisperse water-soluble magnetite nano-particles was prepared by a simple and inexpensive co-precipitation method. Iron ions and iodine were prepared by the reaction between ferric chloride and potassium iodide. The ferrous and ferric ions were hydrolyzed at low temperature at pH 9 in the presence of iodine to produce iron oxide nanoparticles. The natural product myrrh gum was used as capping agent to produce highly dispersed coated magnetite nanoparticles. The structure and morphology of the magnetic nanogel was characterized by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM), and X-ray diffraction (XRD) was used to examine the crystal structure of the produced magnetite nanoparticles. PMID:25090117

Atta, Ayman M; Al-Lohedan, Hamad A; Al-Hussain, Sami A

2014-01-01

84

Suppression of photorefractive damage with aid of steady-state temperature gradient in nominally pure LiNbO{sub 3} crystals  

SciTech Connect

Photorefractive damage (PRD) in as-grown, oxidized, and slightly reduced nominally pure LiNbO{sub 3}, and iron-doped crystals with different compositions has been studied with the closed-aperture Z-scan and pseudo-Z-scan techniques at uniform temperature distribution, as well as at a steady-state temperature gradient {nabla}T, created by two external thermoelectric elements in the transverse direction to the light beam trajectory. The most important experimental finding consists of the demonstration of the possibility of a full PRD suppression in nominally pure crystals with the aid of a relatively small temperature gradient (12.5-84 K/cm), if {nabla}T is above a threshold value specific for each crystal studied. The threshold {nabla}T{sub th} decreases significantly with the increase in the so-called bipolaron absorption band (center at 470-500 nm) in the optical spectra, and it is not correlated with the composition of the crystals within the studied range of compositions ([Li]/[Nb]=0.946-0.983). No any partial suppression of PRD was observed in iron-doped ([Fe]{>=}0.01 wt %) lithium niobate crystals, even at the largest temperature gradient (85 K/cm) used in our study. To explain these experimental results, we use theoretical model taking into account local changes of spontaneous polarization (i.e., polarization charge field) at photoionization of intrinsic defects (polarons, bipolarons, and hole polarons). It has been shown that a steady-state temperature gradient may induce a local thermoelectric current of light-induced charge carriers and their instant recombination, resulting in a decrease in the polarization space-charge field and hence, a light-induced refractive index change. The latter mechanism may induce the full PRD suppression, if macroscopic charge separation (space-charge field effect) gives insignificant contribution to the total light-induced electric field, as in as-grown and reduced nominally pure LiNbO{sub 3} crystals.

Kostritskii, S. M. [MPTE Department, Moscow Institute of Electronic Technology, Moscow, 124498 Zelenograd (Russian Federation); Sevostyanov, O. G. [Physics Department, Kemerovo State University, 650043 Kemerovo (Russian Federation); Aillerie, M.; Bourson, P. [Laboratoire Materiaux Optiques, Photonique et Systemes, University Paul Verlaine of Metz and Supelec, UMR CNRS 7132, 2 Rue E. Belin, 57070 Metz (France)

2008-12-01

85

Gigantism in unique biogenic magnetite at the Paleocene-Eocene Thermal Maximum  

PubMed Central

We report the discovery of exceptionally large biogenic magnetite crystals in clay-rich sediments spanning the Paleocene–Eocene Thermal Maximum (PETM) in a borehole at Ancora, NJ. Aside from previously described abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite up to 4 ?m long and hexaoctahedral prisms up to 1.4 ?m long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition, lattice perfection, and oxygen isotopes consistent with an aquatic origin. Electron holography indicates single-domain magnetization despite their large crystal size. We suggest that the development of a thick suboxic zone with high iron bioavailability—a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming—drove diversification of magnetite-forming organisms, likely including eukaryotes. PMID:18936486

Schumann, Dirk; Raub, Timothy D.; Kopp, Robert E.; Guerquin-Kern, Jean-Luc; Wu, Ting-Di; Rouiller, Isabelle; Smirnov, Aleksey V.; Sears, S. Kelly; Lucken, Uwe; Tikoo, Sonia M.; Hesse, Reinhard; Kirschvink, Joseph L.; Vali, Hojatollah

2008-01-01

86

Magnetic induction mapping of magnetite chains in magnetotactic bacteria at room temperature and close to the  

E-print Network

of closely spaced magnetite crystals in magnetotactic bacteria at room temperature and after cooling the axis of each chain of crystals closely. In contrast, at low temperature the magnetic induction nature of electron holography also allows the change in magnetisation in the crystals with temperature

Dunin-Borkowski, Rafal E.

87

Incorporation and Retention of 99-Tc(IV) in Magnetite under High pH Conditions.  

PubMed

Technetium incorporation into magnetite and its behavior during subsequent oxidation has been investigated at high pH to determine the technetium retention mechanism(s) on formation and oxidative perturbation of magnetite in systems relevant to radioactive waste disposal. Ferrihydrite was exposed to Tc(VII)(aq) containing cement leachates (pH 10.5-13.1), and crystallization of magnetite was induced via addition of Fe(II)aq. A combination of X-ray diffraction (XRD), chemical extraction, and X-ray absorption spectroscopy (XAS) techniques provided direct evidence that Tc(VII) was reduced and incorporated into the magnetite structure. Subsequent air oxidation of the magnetite particles for up to 152 days resulted in only limited remobilization of the incorporated Tc(IV). Analysis of both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data indicated that the Tc(IV) was predominantly incorporated into the magnetite octahedral site in all systems studied. On reoxidation in air, the incorporated Tc(IV) was recalcitrant to oxidative dissolution with less than 40% remobilization to solution despite significant oxidation of the magnetite to maghemite/goethite: All solid associated Tc remained as Tc(IV). The results of this study provide the first direct evidence for significant Tc(IV) incorporation into the magnetite structure and confirm that magnetite incorporated Tc(IV) is recalcitrant to oxidative dissolution. Immobilization of Tc(VII) by reduction and incorporation into magnetite at high pH and with significant stability upon reoxidation has clear and important implications for limiting technetium migration under conditions where magnetite is formed including in geological disposal of radioactive wastes. PMID:25236360

Marshall, Timothy A; Morris, Katherine; Law, Gareth T W; Mosselmans, J Frederick W; Bots, Pieter; Parry, Stephen A; Shaw, Samuel

2014-10-21

88

MAGNETIC AND STRUCTURAL CHARACTERIZATION OF BIOGENIC MAGNETITE M.R. McCartney* and R. E. Dunin-Borkowski**  

E-print Network

magnetite crystals found in the Martian meteorite ALH84001 have been used to posit the possibility of life on Mars[4]. This identification relied on a comparison of the morphology of the meteoritic magnetite in evaluating extraterrestrial material for signs of life. REFERENCES [1] H. A. Lowenstam and S. Weiner

Dunin-Borkowski, Rafal E.

89

Site-specific magnetization reversal studies of magnetite  

SciTech Connect

The mechanism of magnetization reversal in magnetite (Fe{sub 3}O{sub 4}) single crystals was studied using site-specific magnetic sensitive diffraction anomalous near-edge structure. By exploiting the angular dependence of the cross section, we are able to show that the mechanism of reversal involves a mixture of coherent rotation and domain formation. The results reveal additional details to that provided by XMCD measurements, which average over nonequivalent sites.

Cady, A.; Haskel, D.; Lang, J. C.; Islam, Z.; Srajer, G. [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Ankudinov, A. [Department of Physics, University of Washington, Seattle, Washington 98195 (United States); Subias, G.; Garcia, J. [Instituto de Ciencia de Materiales de Aragon, CSIC-Universidad de Zaragoza, Pza. San Francisco s/n 50009 Zaragoza (Spain)

2006-04-01

90

Structural insight into magnetochrome-mediated magnetite biomineralization  

NASA Astrophysics Data System (ADS)

Magnetotactic bacteria align along the Earth's magnetic field using an organelle called the magnetosome, a biomineralized magnetite (Fe(II)Fe(III)2O4) or greigite (Fe(II)Fe(III)2S4) crystal embedded in a lipid vesicle. Although the need for both iron(II) and iron(III) is clear, little is known about the biological mechanisms controlling their ratio. Here we present the structure of the magnetosome-associated protein MamP and find that it is built on a unique arrangement of a self-plugged PDZ domain fused to two magnetochrome domains, defining a new class of c-type cytochrome exclusively found in magnetotactic bacteria. Mutational analysis, enzyme kinetics, co-crystallization with iron(II) and an in vitro MamP-assisted magnetite production assay establish MamP as an iron oxidase that contributes to the formation of iron(III) ferrihydrite eventually required for magnetite crystal growth in vivo. These results demonstrate the molecular mechanisms of iron management taking place inside the magnetosome and highlight the role of magnetochrome in iron biomineralization.

Siponen, Marina I.; Legrand, Pierre; Widdrat, Marc; Jones, Stephanie R.; Zhang, Wei-Jia; Chang, Michelle C. Y.; Faivre, Damien; Arnoux, Pascal; Pignol, David

2013-10-01

91

Raman study of the Verwey transition in magnetite thin films  

NASA Astrophysics Data System (ADS)

We have grown epitaxial thin films of magnetite on MgO and Al2O3 substrates with sharp and distinct signatures of the Verwey transition in resistivity and magnetization. We have used Raman scattering to separate the footprint of purely structural changes from the effect of additional charge and orbital order. Raman modes related to the structural phase transition occur first at temperatures above the Verwey transition temperature. In contrast, newly emerging modes indicating additional charge and orbital order appear at the Verwey transition. These results suggest that the completion of the structural phase transition in magnetite is a necessary precursor triggering a transition into a complex charge and orbitally ordered state.

Baghaie Yazdi, M.; Choi, K.-Y.; Wulferding, D.; Lemmens, P.; Alff, L.

2013-10-01

92

Synthesis of Magnetite Nano-Particles by Reverse CO-PRECIPITATION  

NASA Astrophysics Data System (ADS)

Magnetite nano-particles have been synthesized by reverse co-precipitation method using iron salts in alkaline medium in the presence of diethylene glycol (DEG). Effect of DEG on the nano-particle characteristics was investigated by XRD, FE-SEM, FTIR and VSM techniques. From XRD results it was concluded that in the presence of DEG the composition of magnetite did not change, however the mean crystallite size reduced from 10 to 5 nm. SEM micrograph showed that DEG decreased the size of spherical magnetite nano-particles from 50 to 20 nm. Fourier transform infrared spectra (FTIR) indicated that the DEG molecules chemisorbed on the magnetite nano-particles. Under the given experimental conditions, the rate of crystallization and growth reduced, which is probably due to the capping of DEG to the magnetite nano-particles. The agglomeration was also decreased which is attributed to the coating of magnetite nano-particles by DEG which prevents the formation of hydrogen bonding between magnetite and water molecules.

Kazemzadeh, Hamid; Ataie, Abolghasem; Rashchi, Fereshteh

93

Near-surface Structural Change in Magnetite: An EPR Study  

NASA Astrophysics Data System (ADS)

Magnetite as a lithogenic mineral is widespread in soils. Its bulk magnetic properties have been studied in detail and the grain size distribution has been used as proxy to reconstruct weathering environments. During weathering, oxidation can lead to the formation of ferric oxides at the magnetite surface. Such changes are difficult to detect by classical rock magnetic analysis, because the magnetic data are generally dominated by the bulk properties. In this research we test the use of electron paramagnetic resonance (EPR) spectroscopy in order to get an insight into near-surface properties of magnetite in a soil. The experiments were carried out on untreated and chemically treated soil samples. Chemical treatments included oxalate extraction which dissolves poorly crystallized ferric oxides, as well as citrate-bicarbonate- dithionite (CBD) treatment, which removes ferric oxides (e.g. maghemite, hematite) but also SD magnetite by reductive dissolution. Under the SEM, the magnetite particles showed a particle size of generally more than 10 microns. A minor Ti for Fe substitution was found by EDX analysis. Hysteresis loops of the untreated (KA), oxalate treated (K_ox), and CBD treated (KA_dith) samples at room temperature showed a coercive force (Hc) of 10 ±1 mT and a hysteresis closure between 250-300 mT which is indicative of magnetite. The FORC diagrams of KA, KA_ox and KA_dith were similar and revealed two features : an Hc distribution with maximum at 10 mT and a vertical spread (bias field) with Hc around 2mT. These data suggest that the different chemical treatments had no significant effect on the magnetite in the soil samples. Since CBD treatment is known to dissolve SD magnetite, an assemblage of MD and PSD magnetite particles can be inferred. The EPR spectroscopic parameters (g-value and linewidth ?B) showed different values for the untreated and chemically treated magnetite. For KA, g = 2.12 and ?B = 120 mT were measured. Similar values (g = 2.14 and ?B =120 mT ) were found for Ka_ox. With CBD treatment, both parameters increased to 2.27 and 160 mT, respectively. The significant broadening of the lineshape after CBD treatment is due to an increase of inhomogeneity (e.g. defect structures) caused by the reductive dissolution of Fe^{(III)}. The simultaneous decrease of the resonant field, indicated by higher g-values, points to an enhancement of the internal field. This can be explained by an increase of the magnetic moments due to incongruent dissolution of Fe^{(III)} probably in the vicinity of Ti^{(IV)} sites in the near-surface region of the magnetite grains. In conclusion, EPR spectroscopy is a powerful tool to detect near-surface structural defects and can, therefore, be used to complement classical rock magnetic methods.

Fischer, H.; Luster, J.; Gehring, A. U.

2006-12-01

94

Coherent optical phonons in pure and Pr3+ doped YAG crystal studied by Optical Kerr Effect spectroscopy: Temperature and concentration dependence  

NASA Astrophysics Data System (ADS)

Herewith we present the results of the investigation of coherent phonons in pure and Pr3+ doped YAG crystals, by means of the femtosecond Optical Kerr Effect spectroscopy. In the experiment we have followed the dynamics of the Raman-active phonon modes at different temperatures in range between 263 K and 373 K and for different dopant concentrations. We found that the temperature dependence of phonon frequencies and lifetimes is linear, which is characteristic for 3-phonon relaxation process. We have used our fit results to calculate the widths of homogeneously broadened Raman lines and to find the anharmonic coupling constants. The observed dependence of phonon frequency and lifetime on dopant concentration is interpreted in terms of small, dopant induced alterations in the crystal structure, where the most influenced modes involve motion of the substituted ion. High precision of the OKE experiment is of great value, as such changes are small and thus hard to measure, when only low doping is possible, which is the case for Pr:YAG.

Polok, K.; Ratajska-Gadomska, B.; Konarska, J.; Gadomski, W.

2014-10-01

95

Hydrogen-bond-dynamics-based switching of conductivity and magnetism: a phase transition caused by deuterium and electron transfer in a hydrogen-bonded purely organic conductor crystal.  

PubMed

A hydrogen bond (H-bond) is one of the most fundamental and important noncovalent interactions in chemistry, biology, physics, and all other molecular sciences. Especially, the dynamics of a proton or a hydrogen atom in the H-bond has attracted increasing attention, because it plays a crucial role in (bio)chemical reactions and some physical properties, such as dielectricity and proton conductivity. Here we report unprecedented H-bond-dynamics-based switching of electrical conductivity and magnetism in a H-bonded purely organic conductor crystal, ?-D3(Cat-EDT-TTF)2 (abbreviated as ?-D). This novel crystal ?-D, a deuterated analogue of ?-H3(Cat-EDT-TTF)2 (abbreviated as ?-H), is composed only of a H-bonded molecular unit, in which two crystallographically equivalent catechol-fused ethylenedithiotetrathiafulvalene (Cat-EDT-TTF) skeletons with a +0.5 charge are linked by a symmetric anionic [O···D···O](-1)-type strong H-bond. Although the deuterated and parent hydrogen systems, ?-D and ?-H, are isostructural paramagnetic semiconductors with a dimer-Mott-type electronic structure at room temperature (space group: C2/c), only ?-D undergoes a phase transition at 185 K, to change to a nonmagnetic insulator with a charge-ordered electronic structure (space group: P1). The X-ray crystal structure analysis demonstrates that this dramatic switching of the electronic structure and physical properties originates from deuterium transfer or displacement within the H-bond accompanied by electron transfer between the Cat-EDT-TTF ?-systems, proving that the H-bonded deuterium dynamics and the conducting TTF ?-electron are cooperatively coupled. Furthermore, the reason why this unique phase transition occurs only in ?-D is qualitatively discussed in terms of the H/D isotope effect on the H-bond geometry and potential energy curve. PMID:25127315

Ueda, Akira; Yamada, Shota; Isono, Takayuki; Kamo, Hiromichi; Nakao, Akiko; Kumai, Reiji; Nakao, Hironori; Murakami, Youichi; Yamamoto, Kaoru; Nishio, Yutaka; Mori, Hatsumi

2014-08-27

96

Lightning-strike fusion of gabbro and formation of magnetite-bearing fulgurite, Cornone di Blumone, Adamello, Western Alps, Italy  

NASA Astrophysics Data System (ADS)

The Adamello gabbro exposed on the summit of Cornone di Blumone, Western Alps, Italy, has been fused by lightning strikes to form magnetite-rich fulgurites produced by melting of magnetite, hornblende, calcic plagioclase and minor clinopyroxene. The composition of quench magnetite in the fulgurite is 44.4 Fe3O4; 27.5 MgFe2O4; 15.1 FeAl2O4; 7.9 Fe2TiO4; 2.5 Fe2SiO4; 1.9 CaFe2O4; 0.8 MnFe2O4 and is inferred to have crystallized from a low-Si, Fe-rich melt under high oxidation conditions of about 1 log unit below the log10ƒO2 of hematite-magnetite. The low Si, Fe-rich melt is considered to have been produced from fusion of magnetite + hornblende-rich areas of the host gabbro and/or possible separation of an immiscible high Fe2O3/FeO Fe-rich, low-Si melt from a more siliceous glass during superheating. Skeletal-dendritic morphologies of magnetite in the fulgurite indicate crystallization under conditions of extreme supercooling. Juxtaposition of areas exhibiting different growth habits and crystal sizes of magnetite may reflect compositionally different local melt domains and/or small differences in the delicate balance between nucleation and growth in domains that had slightly different, although ultrafast, cooling rates.

Grapes, Rodney H.; Müller-Sigmund, Hiltrud

2010-05-01

97

Formation of Magnetite Nanoparticles at Low Temperature: From Superparamagnetic to Stable Single Domain Particles  

PubMed Central

The room temperature co-precipitation of ferrous and ferric iron under alkaline conditions typically yields superparamagnetic magnetite nanoparticles below a size of 20 nm. We show that at pH ?=? 9 this method can be tuned to grow larger particles with single stable domain magnetic (> 20–30 nm) or even multi-domain behavior (> 80 nm). The crystal growth kinetics resembles surprisingly observations of magnetite crystal formation in magnetotactic bacteria. The physicochemical parameters required for mineralization in these organisms are unknown, therefore this study provides insight into which conditions could possibly prevail in the biomineralizing vesicle compartments (magnetosomes) of these bacteria. PMID:23520462

Baumgartner, Jens; Bertinetti, Luca; Widdrat, Marc; Hirt, Ann M.; Faivre, Damien

2013-01-01

98

From iron(III) precursor to magnetite and vice versa  

SciTech Connect

The syntheses of nanosize magnetite particles by wet-chemical oxidation of Fe{sup 2+} have been extensively investigated. In the present investigation the nanosize magnetite particles were synthesised without using the Fe(II) precursor. This was achieved by {gamma}-irradiation of water-in-oil microemulsion containing only the Fe(III) precursor. The corresponding phase transformations were monitored. Microemulsions (pH {approx} 12.5) were {gamma}-irradiated at a relatively high dose rate of {approx}22 kGy/h. Upon 1 h of {gamma}-irradiation the XRD pattern of the precipitate showed goethite and unidentified low-intensity peaks. Upon 6 h of {gamma}-irradiation, reductive conditions were achieved and substoichiometric magnetite ({approx}Fe{sub 2.71}O{sub 4}) particles with insignificant amount of goethite particles found in the precipitate. Hydrated electrons (e{sub aq}{sup -}), organic radicals and hydrogen gas as radiolytic products were responsible for the reductive dissolution of iron oxide in the microemulsion and the reduction Fe{sup 3+} {yields} Fe{sup 2+}. Upon 18 h of {gamma}-irradiation the precipitate exhibited dual behaviour, it was a more oxidised product than the precipitate obtained after 6 h of {gamma}-irradiation, but it contained magnetite particles in a more reduced form ({approx}Fe{sub 2.93}O{sub 4}). It was presumed that the reduction and oxidation processes existed as concurrent competitive processes in the microemulsion. After 18 h of {gamma}-irradiation the pH of the medium shifted from the alkaline to the acidic range. The high dose rate of {approx}22 kGy/h was directly responsible for this shift to the acidic range. At a slightly acidic pH a further reduction of Fe{sup 3+} {yields} Fe{sup 2+} resulted in the formation of more stoichiometric magnetite particles, whereas the oxidation conditions in the acidic medium permitted the oxidation Fe{sup 2+} {yields} Fe{sup 3+}. The Fe{sup 3+} was much less soluble in the acidic medium and it hydrolysed and recrystallised as goethite. The {gamma}-irradiation of the microemulsion for 25 h at a lower dose rate of 16 kGy/h produced pure substoichiometric nanosize magnetite particles of about 25 nm in size and with the stoichiometry of Fe{sub 2.83}O{sub 4}.

Gotic, M., E-mail: gotic@irb.hr [Division of Materials Chemistry, Ruder Boskovic Institute, P.O. Box 180, HR-10002 Zagreb (Croatia); Jurkin, T.; Music, S. [Division of Materials Chemistry, Ruder Boskovic Institute, P.O. Box 180, HR-10002 Zagreb (Croatia)

2009-10-15

99

e-publishing Biogenic magnetite in the  

E-print Network

be strongly influenced by the presence of magnetite. Caenorhabditis elegans is a soil nematode of ca. 1 mmFirstCite e-publishing Biogenic magnetite in the nematode Caenorhabditis elegans Charles G.01.04; Accptd 21.04.04; Published online The nematode Caenorhabditis elegans is widely used as a model system

100

Vortex magnetic structure in framboidal magnetite reveals existence of water droplets in an ancient asteroid.  

PubMed

The majority of water has vanished from modern meteorites, yet there remain signatures of water on ancient asteroids. How and when water disappeared from the asteroids is important, because the final fluid-concentrated chemical species played critical roles in the early evolution of organics and in the final minerals in meteorites. Here we show evidence of vestigial traces of water based on a nanometre-scale palaeomagnetic method, applying electron holography to the framboids in the Tagish Lake meteorite. The framboids are colloidal crystals composed of three-dimensionally ordered magnetite nanoparticles and therefore are only able to form against the repulsive force induced by the surface charge of the magnetite as a water droplet parches in microgravity. We demonstrate that the magnetites have a flux closure vortex structure, a unique magnetic configuration in nature that permits the formation of colloidal crystals just before exhaustion of water from a local system within a hydrous asteroid. PMID:24149376

Kimura, Yuki; Sato, Takeshi; Nakamura, Norihiro; Nozawa, Jun; Nakamura, Tomoki; Tsukamoto, Katsuo; Yamamoto, Kazuo

2013-01-01

101

Novel environmentally friendly synthesis of superparamagnetic magnetite nanoparticles using mechanochemical effect  

SciTech Connect

A novel method for synthesizing superparamagnetic magnetite nanoparticles in water system via coprecipitation under an environmentally friendly condition has been developed. In this method, an almost neutral suspension containing ferrous hydroxide and goethite is used as the starting suspension and subjected to a ball-milling treatment. The product was characterized by transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, dynamic light scattering, superconducting quantum interference device magnetometry, and Moessbauer spectroscopy. The mechanochemical effect generated by the ball-milling treatment promoted the reaction between ferrous hydroxide and goethite even at room temperature, resulting in the formation of homogeneous magnetite nanoparticles. Simultaneously, it also contributed to crystallize the formed magnetite nanoparticles while inhibiting the particle growth. This resulted in the formation of ultrafine magnetite nanoparticles of about 10 nm having a single crystal structure. This method could provide ferromagnetic magnetite nanoparticles with superparamagnetism under the moderate condition without neither heating nor any additives such as surfactant and organic solvent.

Iwasaki, Tomohiro, E-mail: iwasaki@chemeng.osakafu-u.ac.jp [Department of Chemical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531 (Japan)] [Department of Chemical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531 (Japan); Kosaka, Kazunori; Watano, Satoru [Department of Chemical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531 (Japan)] [Department of Chemical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531 (Japan); Yanagida, Takeshi; Kawai, Tomoji [Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)] [Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)

2010-04-15

102

Magnetite and magnetite/silver core/shell nanoparticles with diluted magnet-like behavior  

SciTech Connect

In the present work is reported the use of the biopolymer chitosan as template for the preparation of magnetite and magnetite/silver core/shell nanoparticles systems, following a two step procedure of magnetite nanoparticles in situ precipitation and subsequent silver ions reduction. The crystalline and morphological characteristics of both magnetite and magnetite/silver core/shell nanoparticles systems were analyzed by high resolution transmission electron microscopy (HRTEM) and nanobeam diffraction patterns (NBD). The results of these studies corroborate the core/shell morphology and the crystalline structure of the magnetite core and the silver shell. Moreover, magnetization temperature dependent, M(T), measurements show an unusual diluted magnetic behavior attributed to the dilution of the magnetic ordering in the magnetite and magnetite/silver core/shell nanoparticles systems. - Graphical abstract: Biopolymer chitosan was used as stabilization media to synthesize both magnetite and magnetite/silver core/shell nanoparticles. Results of HRTEM and NBD patterns confirm core/shell morphology of the obtained nanoparticles. It was found that the composites show diluted magnet-like behavior.

Garza-Navarro, Marco [Facultad de Ingenieria Mecanica y Electrica, Universidad Autonoma de Nuevo Leon, Av. Universidad s/n, Cd. Universitaria, San Nicolas de los Garza, Nuevo Leon 66450 (Mexico); Torres-Castro, Alejandro, E-mail: alejandro.torrescs@uanl.edu.m [Facultad de Ingenieria Mecanica y Electrica, Universidad Autonoma de Nuevo Leon, Av. Universidad s/n, Cd. Universitaria, San Nicolas de los Garza, Nuevo Leon 66450 (Mexico); Centro de Innovacion, Investigacion y Desarrollo en Ingenieria y Tecnologia, Universidad Autonoma de Nuevo Leon, Apodaca, Nuevo Leon 66600 (Mexico); Gonzalez, Virgilio; Ortiz, Ubaldo [Facultad de Ingenieria Mecanica y Electrica, Universidad Autonoma de Nuevo Leon, Av. Universidad s/n, Cd. Universitaria, San Nicolas de los Garza, Nuevo Leon 66450 (Mexico); Centro de Innovacion, Investigacion y Desarrollo en Ingenieria y Tecnologia, Universidad Autonoma de Nuevo Leon, Apodaca, Nuevo Leon 66600 (Mexico); De la Rosa, Elder [Centro de Investigaciones en Optica, A.P. 1-948, Leon Gto. 37160 (Mexico)

2010-01-15

103

Magnetic irreversibility and the Verwey transition in nanocrystalline bacterial magnetite Ruslan Prozorov  

E-print Network

organized in chains, the effective blocking temperature TB TV and the Verwey transition is sharply defined magnetotactic bacteria were compared to those of synthetic magnetite nanocrystals and large, high-quality single crystals. The magnetic feature at the Verwey temperature TV was clearly seen in all nanocrystals, although

104

Novel magnetite-producing magnetotactic bacteria belonging to the Gammaproteobacteria  

PubMed Central

Two novel magnetotactic bacteria (MTB) were isolated from sediment and water collected from the Badwater Basin, Death Valley National Park and southeastern shore of the Salton Sea, respectively, and were designated as strains BW-2 and SS-5, respectively. Both organisms are rod-shaped, biomineralize magnetite, and are motile by means of flagella. The strains grow chemolithoautotrophically oxidizing thiosulfate and sulfide microaerobically as electron donors, with thiosulfate oxidized stoichiometrically to sulfate. They appear to utilize the Calvin–Benson–Bassham cycle for autotrophy based on ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity and the presence of partial sequences of RubisCO genes. Strains BW-2 and SS-5 biomineralize chains of octahedral magnetite crystals, although the crystals of SS-5 are elongated. Based on 16S rRNA gene sequences, both strains are phylogenetically affiliated with the Gammaproteobacteria class. Strain SS-5 belongs to the order Chromatiales; the cultured bacterium with the highest 16S rRNA gene sequence identity to SS-5 is Thiohalocapsa marina (93.0%). Strain BW-2 clearly belongs to the Thiotrichales; interestingly, the organism with the highest 16S rRNA gene sequence identity to this strain is Thiohalospira alkaliphila (90.2%), which belongs to the Chromatiales. Each strain represents a new genus. This is the first report of magnetite-producing MTB phylogenetically associated with the Gammaproteobacteria. This finding is important in that it significantly expands the phylogenetic diversity of the MTB. Physiology of these strains is similar to other MTB and continues to demonstrate their potential in nitrogen, iron, carbon and sulfur cycling in natural environments. PMID:21776027

Lefevre, Christopher T; Viloria, Nathan; Schmidt, Marian L; Posfai, Mihaly; Frankel, Richard B; Bazylinski, Dennis A

2012-01-01

105

Novel magnetite-producing magnetotactic bacteria belonging to the Gammaproteobacteria.  

PubMed

Two novel magnetotactic bacteria (MTB) were isolated from sediment and water collected from the Badwater Basin, Death Valley National Park and southeastern shore of the Salton Sea, respectively, and were designated as strains BW-2 and SS-5, respectively. Both organisms are rod-shaped, biomineralize magnetite, and are motile by means of flagella. The strains grow chemolithoautotrophically oxidizing thiosulfate and sulfide microaerobically as electron donors, with thiosulfate oxidized stoichiometrically to sulfate. They appear to utilize the Calvin-Benson-Bassham cycle for autotrophy based on ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity and the presence of partial sequences of RubisCO genes. Strains BW-2 and SS-5 biomineralize chains of octahedral magnetite crystals, although the crystals of SS-5 are elongated. Based on 16S rRNA gene sequences, both strains are phylogenetically affiliated with the Gammaproteobacteria class. Strain SS-5 belongs to the order Chromatiales; the cultured bacterium with the highest 16S rRNA gene sequence identity to SS-5 is Thiohalocapsa marina (93.0%). Strain BW-2 clearly belongs to the Thiotrichales; interestingly, the organism with the highest 16S rRNA gene sequence identity to this strain is Thiohalospira alkaliphila (90.2%), which belongs to the Chromatiales. Each strain represents a new genus. This is the first report of magnetite-producing MTB phylogenetically associated with the Gammaproteobacteria. This finding is important in that it significantly expands the phylogenetic diversity of the MTB. Physiology of these strains is similar to other MTB and continues to demonstrate their potential in nitrogen, iron, carbon and sulfur cycling in natural environments. PMID:21776027

Lefèvre, Christopher T; Viloria, Nathan; Schmidt, Marian L; Pósfai, Mihály; Frankel, Richard B; Bazylinski, Dennis A

2012-02-01

106

Electrically driven phase transition in magnetite nanostructures  

Microsoft Academic Search

Magnetite (Fe3O4), an archetypal transition-metal oxide, has been used for thousands of years, from lodestones in primitive compasses to a candidate material for magnetoelectronic devices. In 1939, Verwey found that bulk magnetite undergoes a transition at TV~120K from a high-temperature `bad metal' conducting phase to a low-temperature insulating phase. He suggested that high-temperature conduction is through the fluctuating and correlated

Sungbae Lee; Alexandra Fursina; John T. Mayo; Cafer T. Yavuz; Vicki L. Colvin; R. G. Sumesh Sofin; Igor V. Shvets; Douglas Natelson

2008-01-01

107

Structure and magnetic properties of nanosized magnetite obtained by glass recrystallization.  

PubMed

We present the preparation, structural and magnetic properties of nanosized magnetite obtained by the crystallization of a series of Fe-containing borosilicate glasses. Several compositions with the ratio Fe2O3/SiO2 spanning from 0.37 to 0.67 were investigated as a function of two nucleators Cr2O3 and P2O5, respectively, and modifiers and intermediates (Al2O3 and MgO). Mössbauer spectroscopy revealed the degree, the type and the location of disorder induced by a specific composition and nucleators. In addition to magnetite, it was also revealed the presence of large amounts of Fe-rich paramagnetic phases. The magnetic response is analysed in relation with the amount of Fe ions which remain dispersed in the glassy matrix as noninteracting (paramagnetic) ions. We discuss the role of the nucleators on the disorder in both tetrahedral and octahedral sites of the magnetite. PMID:22905574

Sandu, V; Nicolescu, M S; Kuncser, V; Popa, S; Pasuk, I; Ghica, C; Sandu, E

2012-06-01

108

Mineralogical and microfabric characteristics of magnetite in the Wuyang Precambrian BIFs, southern North China Craton: Implications for genesis and depositional processes of the associated BIFs  

NASA Astrophysics Data System (ADS)

Precambrian Banded Iron Formations (BIFs) are widely distributed in the North China Craton (NCC). Among them, the Wuyang BIFs located in the southern margin of NCC occur in the Late Archaean Tieshanmiao Formation and can be subdivided in two different sub-types: (i) quartz-magnetite BIFs (QMB), consisting of magnetite, fine-microcrystalline quartz and minor calcite and (ii) pyroxene-magnetite BIFs (PMB), composed of pyroxene, fine-microcrystalline quartz and subordinate feldspars. Both sub-types display apparent discrepancies in terms of petrography and mineral composition. As shown in Electron BackScattered Diffraction (EBSD) images and micrographs, magnetite grains from the QMB range in size from tens up to hundreds of ?m, whereas magnetite crystals from the PMB can be up to a few tens of ?m across. The X-ray diffraction (XRD) structural data indicate that magnetite from both BIF sub-types is equiaxed (cubic) and was generated by sedimentary metamorphic processes. The cell parameters of magnetite in the QMB are a = b = c = 8.396 Å and Z = 8, which deviate slightly from these of magnetite in the PMB: a = b = c = 8.394 Å and Z = 8. The analytical results of Raman spectroscopy analysis revealed micro-structural signatures of both magnetite (Raman shifts near 552 cm-1 and 673 cm-1) and hematite (Raman shifts near 227 cm-1, 295 cm-1 and 413 cm-1). In magnetite from both QMB and PMB, the crystallinity degree is similar for magnetite micro-structures but varies significantly for hematite micro-structures. Oxygen fugacity (fO2) conditions fluctuated during the recrystallization of magnetite in the QMB, whereas no evident variation of fO2 occurred during the formation of magnetite in the PMB. Analytical results of laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) show that the Si, Al and Mg abundances are higher in magnetite from the QMB, whereas the Ti and Mn contents are more elevated in magnetite from the PMB. Magnetite composition also denotes that both BIF sub-types are sedimentary-metamorphic origin, whereas the deposition of PMB was also affected by volcanic activities. Overall data indicate that the differences in the depositional environment of each BIF sub-type are due to the involvement of volcanic eruption processes in the genesis of the PMB. Thus, this paper indicated that the QMB was deposited by chemical deposition at the long-term interval of volcanic eruptions, and the PMB were the product of chemical deposition affected by the volcanic eruption.

Li, Hongzhong; Zhai, Mingguo; Zhang, Lianchang; Yang, Zhijun; Kapsiotis, Argyrios; Zhou, Yongzhang; He, Junguo; Wang, Changle; Liang, Jin

2014-11-01

109

Oxidation of pyrite in coal to magnetite  

USGS Publications Warehouse

When bituminous coal is heated in an inert atmosphere (He) containing small amounts of oxygen at 393-455 ??C, pyrite (FeS2) in coal is partially converted to magnetite (Fe304). The maximum amount of Fe304 formed during the time of heating corresponds to 5-20% of the total pyrite present, depending on the coal sample. The magnetite forms as an outer crust on the pyrite grains. The fact that the magnetic properties of the pyrite grains are substantially increased by the magnetite crust suggests that pyrite can be separated from coal by use of a low magnetic field. In a laboratory test, 75% removal is obtained by means of a 500 Oe magnet on three samples, and 60% on a fourth sample. ?? 1984.

Thorpe, A.N.; Senftle, F.E.; Alexander, C.C.; Dulong, F.T.

1984-01-01

110

Rock magnetism linked to human brain magnetite  

NASA Astrophysics Data System (ADS)

Magnetite has a long and distinguished career as one of the most important minerals in geophysics, as it is responsible for most of the remanent magnetization in marine sediments and the oceanic crust. It may come as a surprise to discover that it also ranks as the third or fourth most diverse mineral product formed biochemically by living organisms, and forms naturally in a variety of human tissues [Kirschvink et al., 1992].Magnetite was discovered in teeth of the Polyplacophora mollusks over 30 years ago, in magnetotactic bacteria nearly 20 years ago, in honey bees and homing pigeons nearly 15 years ago, but only recently in human tissue.

Kirschvink, Joseph L.

111

Testing the apatite-magnetite geochronometer: U-Pb and 40Ar/ 39Ar geochronology of plutonic rocks, massive magnetite-apatite tabular bodies, and IOCG mineralization in Northern Chile  

NASA Astrophysics Data System (ADS)

Detailed zircon and apatite U-Pb dating and 40Ar/ 39Ar dating of actinolite have been carried out on the Carmen-Sierra Aspera Kiruna type magnetite-apatite and iron oxide Cu-Au (IOCG) district in the Coastal Cordillera of northern Chile (˜26°S). They define a precise succession of magmatic and hydrothermal events associated with early Cretaceous Andean magmatism. Apatite and magnetite from a magnetite-apatite tabular body with intergrowth texture in the Carmen deposit yield a total Pb-U isochron age of 131.0 ± 1.0 Ma. This result is the first direct dating of magnetite-apatite mineralization in an early Andean deposit, and the age coincides with zircon ages of a quartz diorite stock that partially hosts mineralization (130.6 ± 0.3 Ma). Magnetite from the studied tabular body contains only small amounts of radiogenic Pb and serves to constrain the initial common Pb isotopic composition. The high degree of correlation suggests that both minerals closed for Pb diffusion at essentially the same time and at a relatively high temperature (close to that of zircon), making the apatite-magnetite pair a reliable geochronometer for igneous or hydrothermal crystallization. Zircon from the Sierra Aspera composite pluton yields ages between 131.3 ± 0.3 Ma and 127.4 ± 0.1 Ma, clearly resolving the timing of intrusion of discrete intrusive phases. Actinolite 40Ar/ 39Ar ages partially overlap the ages of plutonic phases of the Sierra Aspera pluton, but are younger than the magnetite-apatite tabular body. The initial Pb isotopic composition of the melts and/or fluids from which the magnetite-apatite tabular bodies crystallized is very similar to the primitive Pb isotopic composition of granitic magmas associated with early Cretaceous plutons measured in K-feldspar. The Pb isotopic correspondence, combined with the temporal and spatial association between magnetite-apatite mineralization and the dioritic-quartz dioritic magmatism, strongly suggests a genetic relationship between early Cretaceous continental arc magmatism, massive magnetite-apatite deposits, and IOCG mineralization.

Gelcich, Sergio; Davis, Donald W.; Spooner, Edward T. C.

2005-07-01

112

Magnetic Polystyrene Nanocomposites Reinforced with Magnetite Nanoparticles  

E-print Network

Magnetic Polystyrene Nanocomposites Reinforced with Magnetite Nanoparticles Xingru Yan, Qingliang He, Xi Zhang, Hongbo Gu, Haoran Chen, Qiang Wang, Luyi Sun, Suying Wei,* Zhanhu Guo Polystyrene (PS materials due to the fairly large magnetization and admirable conductive properties.[21] Polystyrene (PS

Guo, John Zhanhu

113

Magnetic properties of dispersed magnetite powders  

Microsoft Academic Search

Measurements have been made of coercive force, susceptibility, isothermal remanence, thermoremanence and thermal and alternating field demagnetization of annealed magnetite powders in nine size ranges from 1·5 ? to 120 ?. The samples were dispersed in plaster to occupy a few per cent by volume of the specimens and thus to simulate the magnetic properties of rocks. The results are

L. G. Parry

1965-01-01

114

Biogenic magnetite in the nematode Caenorhabditis  

E-print Network

Biogenic magnetite in the nematode Caenorhabditis elegans Charles G. Cranfield1 , Adam Dawe2.04.04; Published online 28.06.04 The nematode Caenorhabditis elegans is widely used as a model system in biological as implications for the use of this nematode as a model system for iron biomineralization in multi- cellular

Dunin-Borkowski, Rafal E.

115

Magnetite nanoparticles embedded in biodegradable porous silicon  

NASA Astrophysics Data System (ADS)

Magnetite nanoparticles, which are coated with oleic acid in a hexane solution and exhibit an average diameter of 7.7 nm, were embedded in a porous silicon (PS) matrix by immersion under defined parameters (e.g. concentration, temperature, time). The porous silicon matrix is prepared by anodization of a highly n-doped silicon wafer in an aqueous HF-solution. Magnetic characterization of the samples has been performed by SQUID-magnetometry. The superparamagnetic behaviour of the magnetite nanoparticles is represented by temperature-dependent magnetization measurements. Zero field (ZFC)/field cooled (FC) experiments indicate magnetic interactions between the particles. For the infiltration into the PS-templates different concentrations of the magnetite nanoparticles are used and magnetization measurements are performed in respect with magnetic interactions between the particles. The achieved porous silicon/magnetite specimens are not only interesting due to their transition between superparamagnetic and ferromagnetic behaviour, and thus for magnetic applications but also because of the non-toxicity of both materials giving the opportunity to employ the system in medical applications as drug delivery or in medical diagnostics.

Granitzer, P.; Rumpf, K.; Roca, A. G.; Morales, M. P.; Poelt, P.; Albu, M.

2010-05-01

116

Magnetite biomineralization and ancient life on Mars  

Microsoft Academic Search

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.

Richard B Frankel; Peter R Buseck

2000-01-01

117

Bisphosphonate release profiles from magnetite microspheres.  

PubMed

Hyperthermia has been suggested as a novel, minimally invasive cancer treatment method. After implantation of magnetic nano- or microparticles around a tumour through blood vessels, irradiation with alternating magnetic fields facilitates the efficient in situ hyperthermia even for deep-seated tumours. On the basis of this idea, if the microspheres are capable of delivering drugs, they could be promising multifunctional biomaterials effective for chemotherapy as well as hyperthermia. In the present study, magnetite microspheres were prepared by aggregation of the iron oxide colloid in water-in-oil (W/O) emulsion. The release behaviour of alendronate, a typical bisphosphonate, from the microspheres was examined in vitro as a model of the bone tumour prevention and treatment system. The alendronate was successfully incorporated onto the porous magnetite microspheres in vacuum conditions. The drug-loaded microspheres maintained their original spherical shapes even after shaking in ultrapure water for 3 days, suggesting that they have sufficient mechanical integrity for clinical use. It was attributed to high aggregation capability of the magnetite nanoparticles through van der Waals and weak magnetic attractions. The microspheres showed slow release of the alendronate in vitro, resulting from tight covalent or ionic interaction between the magnetite and the alendronate. The release rate was diffusion-controlled type and well controlled by the alendronate concentration in drug incorporation to the microspheres. PMID:24854985

Miyazaki, Toshiki; Inoue, Tatsuya; Shirosaki, Yuki; Kawashita, Masakazu; Matsubara, Takao; Matsumine, Akihiko

2014-10-01

118

Magnetite Biomineralization: Fifty years of progress, from beach-combing to the SQUID microscope  

NASA Astrophysics Data System (ADS)

Magnetite biomineralization was first discovered 50 years ago as a hardening agent in the teeth of the Polyplacophoran molluscs (chitons) by the late Prof. Heinz A. Lowenstam of Caltech, when he noticed unusual erosional effects produced by their grazing in the intertidal zones of Palau (Lowenstam, 1962). Since then, biogenic magnetite has been detected in a broad range of organisms, including magnetotactic bacteria, protists, insects, fish, amphibians, reptiles, birds, and mammals including humans. In many species, the role of ferromagnetic material as a neurophysiological transducer is demonstrated clearly through the effects of pulse-remagnetization on behavior. A brief (1 uS), properly configured magnetic discharge from a rectified LC circuit, tailored to exceed the coercivity of the magnetite, will often abolish a magnetic behavioral response, or in some cases make the organism go the wrong way. This is a unique ferromagnetic effect. The genes controlling magnetite biomineralization are well characterized in several species of bacteria, and the ability of some of these bacterial genes to initiate magnetite precipitation in mammalian cell lines argues for a common descent, probably via a magnetotactic mitochondrial ancestor. Previous studies in fish reported the presence of single-domain magnetite crystals in cells near projections of the trigeminal nerve, co-located in the olfactory epithelium. Although the cells are rare, the recent development of a spinning magnetic field technique allows easy identification and isolation of these cells for individual study (Eder et al., 2012). The cells are surprisingly magnetic, with moments hundreds of times larger than typical magnetotactic bacteria. Subsequent efforts to identify the anatomical seat of magnetoreceptors have focused on the same locations in new organisms, excluding other areas. Using SQUID moment magnetometry and SQUID scanning microscopy, we report here the unexpected presence of biogenic magnetite in the lateral line region of the zebrafish, Danio rerio. We suspect that the magnetic field receptor cells of the trigeminal system in animals may be co-located within a variety of other sensory tissues (olfaction, lateral line, vision, hearing, taste, etc.) as a means of spatially dispersing cells with large magnetic moments to prevent magnetostatic interactions between them. References: Eder et al., Magnetic characterization of isolated candidate vertebrate magnetoreceptor cells. Proc. Natl. Acad. Sci. USA 2012; 109:12022-12027. Lowenstam, H.A., 1962. Magnetite in denticle capping in recent chitons (Polyplacophora). Bulletin of the Geological Society of America 73, 435-438.

Kirschvink, J. L.; Dixson, A. D.; Raub, T.

2012-12-01

119

Scanning and transmission electron microscope observations of magnetite and other iron phases in Ordovician carbonates from east Tennessee  

NASA Astrophysics Data System (ADS)

Previous paleomagnetic observations for the carbonates of the Lower Ordovician Knox Group have indicated that ancient magnetizations in these rocks are of the same age as the late Paleozoic Alleghenian Orogeny. Rock magnetic properties strongly suggest magnetite as the carrier of the magnetization, but the textural and crystalline characteristics, sizes, morphologies, and mineral associations of these magnetites are poorly known. We have examined magnetic extracts and iron oxides in thin sections with scanning (SEM) and scanning/transmission (STEM) electron microscope techniques to determine whether the observed iron-oxide grain textures match the rock magnetic properties and paleomagnetic inferences about the mode of formation of the magnetic carriers. Several different forms of magnetite in limestones and dolomites, which in places are host to Mississippi-Valley type deposits, are documented by imaging and energy-dispersive analysis using SEM and STEM, by X ray diffraction and electron diffraction patterns using STEM. The magnetite is either spherical with a dimpled surface or nonspherical in the form of void-filling single grains or grain aggregates. Most of the iron oxides have the composition of pure end-member magnetite, but occasional titanomagnetite and hematite, including rare zincian hematite, have been observed (only in limestone). Wherever found in thin section, nonspherical magnetites occur in association with secondary dolomite, potassium-feldspar, illite, and quartz. Some iron oxides have, in fact, inclusions of K-feldspar and quartz. Some of the magnetite (spherical and nonspherical) is polycrystalline; this implies that the larger observed grains may consist of single domains or pseudo-single domains. This provides an explanation of the observed rock magnetic properties that apparently reflect the presence of single-domain (but interacting?) subgrains, on the basis of remanent coercivities and blocking temperatures. We interpret the pure end-member magnetite to be authigenic, having formed at approximately the same time as the K-feldspars, which in nearby areas have yielded late Paleozoic radioisotopic ages (278-322 Ma). The Knox carbonates therefore are inferred to carry a chemical rémanent magnetization. Iron-rich clays or original iron-titanium oxides in the carbonates may have been the source materials for at least some of the secondary magnetite as it formed through complete dissolution-precipitation processes. These processes require rock-fluid interactions which are thought to be related to migrating connate brines during the Alleghenian Orogeny.

Suk, Dongwoo; van der Voo, Rob; Peacor, Donald R.

1990-08-01

120

Formation of magnetite-enriched zones in and offshore of a mesotidal estuarine lagoon: An environmental magnetic study of Tauranga Harbour and Bay of Plenty, New Zealand  

NASA Astrophysics Data System (ADS)

Magnetic iron minerals are widespread and indicative sediment constituents in estuarine, coastal and shelf systems. We combine environmental magnetic, sedimentological and numerical methods to identify magnetite-enriched placer-like zones in a complex coastal system and delineate their formation mechanisms. Magnetic susceptibility and remanence measurements on 245 surficial sediment samples collected in and around Tauranga Harbour, the largest barrier-enclosed tidal estuary of New Zealand, reveal several discrete enrichment zones controlled by local hydrodynamic conditions. Active magnetite enrichment takes place in tidal channels, which feed into two coast-parallel nearshore magnetite-enriched belts centered at water depths of 6-10 m and 10-20 m. A close correlation between magnetite content and magnetic grain size was found, where higher susceptibility values are associated within coarser magnetic crystal sizes. Two key mechanisms for magnetite enrichment are identified. First, tide-induced residual currents primarily enable magnetite enrichment within the estuarine channel network. A coast-parallel, fine sand magnetite enrichment belt in water depths of less than 10 m along the barrier island has a strong decrease in magnetite content away from the southern tidal inlet and is apparently related to active coast-parallel transport combined with mobilizing surf zone processes. A second, less pronounced, but more uniform magnetite enrichment belt at 10-20 m water depth is composed of non-mobile, medium-coarse-grained relict sands, which have been reworked during post-glacial sea level transgression. We demonstrate the potential of magnetic methods to reveal and differentiate coastal magnetite enrichment patterns and investigate their formative mechanisms.

Badesab, Firoz; von Dobeneck, Tilo; Bryan, Karin R.; Müller, Hendrik; Briggs, Roger M.; Frederichs, Thomas; Kwoll, Eva

2012-06-01

121

A routine synthesis of magnetite applied in ionic liquids  

NASA Astrophysics Data System (ADS)

This paper describe the synthesis of magnetite nanoparticles using 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4[. Iron (II) chloride and iron (III) chloride which dissolves in [BMIM][BF4[ are coprecipitated in the presence of potassium hydroxide yielding magnetite. The stabilization of magnetite was realized without further purification with glycolic acid. The TEM images show spherical nanoparticles with mean diameter of 8nm. FTIR spectra contain the specific bands of both magnetite and glycolic acid indicating the formation of the magnetic nanoparticles stabilized with glycolic acid. Our results show that ionic liquids can be used as solvent to achieve magnetite stabilized by glycolic acid which shows superparamagnetic behaviour.

Nan, Alexandrina; Turcu, Rodica; Liebscher, Jürgen

2013-11-01

122

Determination of the Three-Dimensional Morphology of ALH84001 and Biogenic MV-1 Magnetite: Comparison of Results from Electron Tomography and Classical Transmission Electron Microscopy  

NASA Technical Reports Server (NTRS)

Dated at approximately 3.9 billion years of age, carbonate disks, found within fractures of the host rock of Martian meteorite ALH84001, have been interpreted as secondary minerals that formed at low temperature in an aqueous medium. Heterogeneously distributed within these disks are magnetite nanocrystals that are of Martian origin. Approximately one quarter of these magnetites have morphological and chemical similarities to magnetite particles produced by magnetotactic bacteria strain MV-1, which are ubiquitous in aquatic habitats on Earth. Moreover, these types of magnetite particles are not known or expected to be produced by abiotic means either through geological processes or synthetically in the laboratory. The remaining three quarters of the ALH84001 magnetites are likely products of multiple processes including, but not limited to, precipitation from a hydrothermal fluid, thermal decomposition of the carbonate matrix in which they are embedded, and extracellular formation by dissimilatory Fe-reducing bacteria. We have proposed that the origins of magnetites in ALH84001 can be best explained as the products of multiple processes, one of which is biological. Recently the three-dimensional (3-D) external morphology of the purported biogenic fraction of the ALH84001 magnetites has been the subject of considerable debate. We report here the 3-D geometry of biogenic magnetite crystals extracted from MV-1 and of those extracted from ALH84001 carbonate disks using a combination of high resolution classical and tomographic transmission electron microscopy (TEM). We focus on answering the following questions: (1) which technique provides adequate information to deduce the 3-D external crystal morphology?; and, (2) what is the precise 3-D geometry of the ALH84001 and MV-1 magnetites?

Thomas-Keprta, Kathie L.; Clemett, Simon J.; Schwartz, Cindy; Morphew, Mary; McIntosh, J. Richard; Bazylinski, Dennis A.; Kirschvink, Joseph L.; Wentworth, Susan J.; McKay, David S.; Vali, Hojatollah

2004-01-01

123

Structural purity of magnetite nanoparticles in magnetotactic bacteria  

PubMed Central

Magnetosome biomineralization and chain formation in magnetotactic bacteria are two processes that are highly controlled at the cellular level in order to form cellular magnetic dipoles. However, even if the magnetosome chains are well characterized, controversial results about the microstructure of magnetosomes were obtained and its possible influence in the formation of the magnetic dipole is to be specified. For the first time, the microstructure of intracellular magnetosomes was investigated using high-resolution synchrotron X-ray diffraction. Significant differences in the lattice parameter were found between intracellular magnetosomes from cultured magnetotactic bacteria and isolated ones. Through comparison with abiotic control materials of similar size, we show that this difference can be associated with different oxidation states and that the biogenic nanomagnetite is stoichiometric, i.e. structurally pure whereas isolated magnetosomes are slightly oxidized. The hierarchical structuring of the magnetosome chain thus starts with the formation of structurally pure magnetite nanoparticles that in turn might influence the magnetic property of the magnetosome chains. PMID:21247944

Fischer, Anna; Schmitz, Manuel; Aichmayer, Barbara; Fratzl, Peter; Faivre, Damien

2011-01-01

124

Exchange bias in polycrystalline magnetite films made by ion-beam assisted deposition  

NASA Astrophysics Data System (ADS)

Iron oxide films were produced using ion-beam-assisted deposition, and Raman spectroscopy and x-ray diffraction indicate single-phase magnetite. However, incorporation of significant fractions of argon in the films from ion bombardment is evident from chemical analysis, and Fe/O ratios are lower than expected from pure magnetite, suggesting greater than normal disorder. Low temperature magnetometry and first-order reversal curve measurements show strong exchange bias, which likely arises from defects at grain boundaries, possibly amorphous, creating frustrated spins. Since these samples contain grains ˜6 nm, a large fraction of the material consists of grain boundaries, where spins are highly disordered and reverse independently with external field.

Kaur, Maninder; Jiang, Weilin; Qiang, You; Burks, Edward C.; Liu, Kai; Namavar, Fereydoon; McCloy, John S.

2014-11-01

125

Nuclear quadrupole alignment of 176Lum and 177Lu in a lutetium single crystal at low temperatures and systematics of electric field gradients in pure hexagonal transition metals  

Microsoft Academic Search

The quadrupole frequencies for 176Lum and 177Lu nuclei in a Lu single crystal have been determined by nuclear orientation at temperatures down to 6 mK as -128(16) MHz and +294(37) MHz, respectively. From the observed gamma anisotropies several gamma-ray multipole mixing ratios could be derived. With the known ground-state quadrupole moment of Q=3.39(2) b for 177Lu the electric field gradient

H. Ernst; E. Hagn; E. Zech; G. Eska

1979-01-01

126

Occurrence of gigantic biogenic magnetite during the Paleocene-Eocene Thermal Maximum  

NASA Astrophysics Data System (ADS)

The Paleocene-Eocene Thermal Maximum (PETM) is one of the most severe climatic events of the Cenozoic Era. A massive injection of light carbon into the oceans and atmosphere over a few thousand of years triggered drastic perturbation of Earth's climate resulting in abrupt global warming of ~5-9oC [Sluijs et al., 2007] that persisted for ~180,000 years. This episode is marked by the diversification and radiation of terrestrial plants and mammals while in the marine realm numerous deep-sea benthic foraminifera species disappeared and new forms evolved. Sediments deposited during the PETM are clay-rich and contain distinct evidence of these climatic changes. Kopp et al., (2007) and Lippert & Zachos (2007) report an extraordinary magnetofossil ‘Lagerstätte' in lowermost Eocene kaolinite-rich clay sediments deposited at subtropical paleolatitude in the Atlantic Coastal Plain of New Jersey, USA. Magnetofossils are magnetic particles produced most abundantly by magnetotactic bacteria. Kopp et al. (2007) and Lippert & Zachos (2007) used ferromagnetic resonance (FMR) spectroscopy, other rock magnetic methods, and transmission electron microscopy (TEM) of magnetic separates to characterize sediments from boreholes at Ancora (ODP Leg 174AX) and Wilson Lake, NJ, respectively. These sediments contain abundant ~40- to 300-nm cuboidal, elongate-prismatic and bullet-shaped magnetofossils, sometimes arranged in short chains, resembling crystals in living magnetotactic bacteria. Despite the scarcity of intact magnetofossil chains, the asymmetry ratios of the FMR spectra reflects a profusion of elongate single domain (SD) crystals and/or chains. Here we address both conundrums by reporting the discovery from these same sediments of exceptionally large and novel biogenic magnetite crystals unlike any previously reported from living organisms or from sediments. Aside from abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite crystals up to 4 ?m long (eight times larger than magnetite produced by magnetotactic bacteria) and elongated hexaoctahedra up to 1.4 ?m long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition and lattice perfection consistent with a biogenic origin. The oxygen isotopic composition of indiviual particles supports a low temperature aquatic origin. Electron holography indicates single-domain magnetization despite the large crystal size. In a few cases, we observed apparently intact, tip-outward spherical assemblages of spearhead-like particles that possibly represent the preserved original biological arrangement of these crystals in a hitherto unknown magnetite producing organism. The discovery of these exceptionally large biogenic magnetite crystals that possibly represent the remains of a new microorganism that appeared and disappeared with the PETM sheds some light upon the ecological response to biogeochemical changes that occurred during this warming event. The abundance of fossil magnetotactic bacteria on the Atlantic Coastal Plain during the PETM could be explained by enhanced production, enhanced preservation, or both. The presence of novel magnetofossils, however, argues that changes in growth conditions are a major part of the explanation. Considering that other bacterial magnetofossils are present (although less abundant) and well-preserved in sediments below and above the PETM clay, as well as in a sand lens within the PETM clay [Kopp et al., 2007], suggests that the new magnetofossils are unlikely to be a preservation artefact. We conclude, therefore, that the development of a thick suboxic zone with high iron bioavailability - a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming - resulted in diversification of magnetite-forming organisms, likely including eukaryotes. In this study we extended the search for these new magnetofossils [Schumann et al. 2008] to other PETM locations of the Atlantic margin and to a possible modern

Schumann, D.; Raub, T. D.; Kopp, R. E.; Guerquin-Kern, J. L.; Wu, T. D.; Rouiller, I.; Smirnov, A. V.; Sears, S. K.; Lücken, U.; Tikoo, S. M.; Hesse, R.; Kirschvink, J. L.; Vali, H.

2009-04-01

127

Quantifying magnetite magnetofossil contributions to sedimentary magnetizations  

NASA Astrophysics Data System (ADS)

Under suitable conditions, magnetofossils (the inorganic remains of magnetotactic bacteria) can contribute to the natural remanent magnetization (NRM) of sediments. In recent years, magnetofossils have been shown to be preserved commonly in marine sediments, which makes it essential to quantify their importance in palaeomagnetic recording. In this study, we examine a deep-sea sediment core from offshore of northwestern Western Australia. The magnetic mineral assemblage is dominated by continental detritus and magnetite magnetofossils. By separating magnetofossil and detrital components based on their different demagnetization characteristics, it is possible to quantify their respective contributions to the sedimentary NRM throughout the Brunhes chron. In the studied core, the contribution of magnetofossils to the NRM is controlled by large-scale climate changes, with their relative importance increasing during glacial periods when detrital inputs were low. Our results demonstrate that magnetite magnetofossils can dominate sedimentary NRMs in settings where they are preserved in significant abundances.

Heslop, David; Roberts, Andrew P.; Chang, Liao; Davies, Maureen; Abrajevitch, Alexandra; De Deckker, Patrick

2013-11-01

128

The magnetosome membrane protein, MmsF, is a major regulator of magnetite biomineralization in Magnetospirillum magneticum AMB-1.  

PubMed

Magnetotactic bacteria (MTB) use magnetosomes, membrane-bound crystals of magnetite or greigite, for navigation along geomagnetic fields. In Magnetospirillum magneticum sp. AMB-1, and other MTB, a magnetosome gene island (MAI) is essential for every step of magnetosome formation. An 8-gene region of the MAI encodes several factors implicated in control of crystal size and morphology in previous genetic and proteomic studies. We show that these factors play a minor role in magnetite biomineralization in vivo. In contrast, MmsF, a previously uncharacterized magnetosome membrane protein encoded within the same region plays a dominant role in defining crystal size and morphology and is sufficient for restoring magnetite synthesis in the absence of the other major biomineralization candidates. In addition, we show that the 18 genes of the mamAB gene cluster of the MAI are sufficient for the formation of an immature magnetosome organelle. Addition of MmsF to these 18 genes leads to a significant enhancement of magnetite biomineralization and an increase in the cellular magnetic response. These results define a new biomineralization protein and lay down the foundation for the design of autonomous gene cassettes for the transfer of the magnetic phenotype in other bacteria. PMID:22716969

Murat, Dorothée; Falahati, Veesta; Bertinetti, Luca; Csencsits, Roseann; Körnig, André; Downing, Kenneth; Faivre, Damien; Komeili, Arash

2012-08-01

129

Origin of carbonate-magnetite-sulfide assemblages in Martian meteorite ALH84001.  

PubMed

A review of the mineralogical, isotopic, and chemical properties of the carbonates and associated submicrometer iron oxides and sulfides in Martian meteorite ALH84001 provides minimal evidence for microbial activity. Some magnetites resemble those formed by magnetotactic microorganisms but cubic crystals <50 nm in size and elongated grains <25 nm long are too small to be single-domain magnets and are probably abiogenic. Magnetites with shapes that are clearly unique to magnetotactic bacteria appear to be absent in ALH84001. Magnetosomes have not been reported in plutonic rocks and are unlikely to have been transported in fluids through fractures and uniformly deposited where abiogenic magnetite was forming epitaxially on carbonate. Submicrometer sulfides and magnetites probably formed during shock heating. Carbonates have correlated variations in Ca, Mg, and 18O/16O, magnetite-rich rims, and they appear to be embedded in pyroxene and plagiociase glass. Carbonates with these features have not been identified in carbonaceous chondrites and terrestrial rocks, suggesting that the ALH84001 carbonates have a unique origin. Carbonates and hydrated minerals in ALH84001, like secondary phases in other Martian meteorites, have O and H isotopic ratios favoring formation from fluids that exchanged with the Martian atmosphere. I propose that carbonates originally formed in ALH84001 from aqueous fluids and were subsequently shock heated and vaporized. The original carbonates were probably dolomite-magnesite-siderite assemblages that formed in pores at interstitial sites with minor sulfate, chloride, and phyllosilicates. These phases, like many other volatile-rich phases in Martian meteorites, may have formed as evaporate deposits from intermittent floods. PMID:11542931

Scott, E R

1999-02-25

130

Experimental Shock Decomposition of Siderite to Magnetite  

NASA Technical Reports Server (NTRS)

The debate about fossil life on Mars includes the origin of magnetites of specific sizes and habits in the siderite-rich portions of the carbonate spheres in ALH 84001 [1,2]. Specifically [2] were able to demonstrate that inorganic synthesis of these compositionally zoned spheres from aqueous solutions of variable ion-concentrations is possible. They further demonstrated the formation of magnetite from siderite upon heating at 550 C under a Mars-like CO2-rich atmosphere according to 3FeCO3 = Fe3O4 + 2CO2 + CO [3] and they postulated that the carbonates in ALH 84001 were heated to these temperatures by some shock event. The average shock pressure for ALH 84001, substantially based on the refractive index of diaplectic feldspar glasses [3,4,5] is some 35-40 GPa and associated temperatures are some 300-400 C [4]. However, some of the feldspar is melted [5], requiring local deviations from this average as high as 45-50 GPa. Indeed, [5] observes the carbonates in ALH 84001 to be melted locally, requiring pressures in excess of 60 GPa and temperatures > 600 C. Combining these shock studies with the above inorganic synthesis of zoned carbonates it seems possible to produce the ALH 84001 magnetites by the shock-induced decomposition of siderite.

Bell, M. S.; Golden, D. C.; Zolensky, M. E.

2005-01-01

131

crystal  

NASA Astrophysics Data System (ADS)

A Nd3+:Na2La4(WO4)7 crystal with dimensions of ? 17 × 30 mm3 was grown by the Czochralski method. The thermal expansion coefficients of Nd3+:Na2La4(WO4)7 crystal are 1.32 × 10-5 K-1 along c-axis and 1.23 × 10-5 K-1 along a-axis, respectively. The spectroscopic characteristics of Nd3+:Na2La4(WO4)7 crystal were investigated. The Judd-Ofelt theory was applied to calculate the spectral parameters. The absorption cross sections at 805 nm are 2.17 × 10-20 cm2 with a full width at half maximum (FWHM) of 15 nm for ?-polarization, and 2.29 × 10-20 cm2 with a FWHM of 14 nm for ?-polarization. The emission cross sections are 3.19 × 10-20 cm2 for ?-polarization and 2.67 × 10-20 cm2 for ?-polarization at 1,064 nm. The fluorescence quantum efficiency is 67 %. The quasi-cw laser of Nd3+:Na2La4(WO4)7 crystal was performed. The maximum output power is 80 mW. The slope efficiency is 7.12 %. The results suggest Nd3+:Na2La4(WO4)7 crystal as a promising laser crystal fit for laser diode pumping.

Yu, Yi; Huang, Yisheng; Zhang, Lizhen; Lin, Zhoubin; Sun, Shijia; Wang, Guofu

2014-07-01

132

Structural characterization of temperature- and pressure-induced inverse ? normal spinel transformation in magnetite  

NASA Astrophysics Data System (ADS)

High-precision powder x-ray diffraction and Fe57 Mössbauer studies up to 20GPa show that magnetite (Fe3O4) undergoes a reversible normal ? inverse transition with increasing pressure or decreasing temperature. There is no resolvable change in the spinel-type crystal structure or unit-cell volume at the phase transition. However, the volume of the tetrahedral (A) site increases (17%) and that of the octahedral (B) site decreases (˜7%) as electron charge density is transferred from the B to the A site. The corresponding valence changes cause the inverse ? normal transition with increasing pressure: FeA3+?FeA2+ and FeB2.5+?FeB3+ . There is an intermediate mixed configuration region at pressure-temperature (P-T) conditions lying between those at which magnetite is normal, TTinv(P) .

Rozenberg, G. Kh.; Amiel, Y.; Xu, W. M.; Pasternak, M. P.; Jeanloz, R.; Hanfland, M.; Taylor, R. D.

2007-01-01

133

Microwave-assisted synthesis of magnetite nanoparticles for MR blood pool contrast agents  

NASA Astrophysics Data System (ADS)

Microwave-assisted polyol process was developed for the synthesis of magnetite nanoparticles with precisely controlled size, high crystallinity and high water solubility. The process is simple, time-saving and low energy-consuming due to the advantages of polyols and microwave irradiation combined. The crystal phases of the nanoparticles were determined by transmission electron microscopy, X-ray powder diffraction and Raman spectrum. The coating materials of the nanoparticles were analyzed by Fourier transformed infrared spectroscopy and thermal gravimetric analysis. Precise size tuning enables an easier way to adjust the relaxation properties of the magnetite nanoparticles. The colloid nanoparticles with high longitudinal relaxivity ( r1) and low ratio of transverse relaxivity ( r2) to r1 have a potential application in magnetic resonance angiography.

Xiao, Wangchuan; Gu, Hongchen; Li, Dan; Chen, Dandan; Deng, Xiaoyong; Jiao, Zheng; Lin, Jiang

2012-02-01

134

Hexagonal Platelet-like Magnetite as a Biosignature of Thermophilic Iron-Reducing Bacteria and Its Applications to the Exploration of the Modern Deep, Hot Biosphere and the Emergence of Iron-Reducing Bacteria in Early Precambrian Oceans  

PubMed Central

Abstract Dissimilatory iron-reducing bacteria are able to enzymatically reduce ferric iron and couple to the oxidation of organic carbon. This mechanism induces the mineralization of fine magnetite crystals characterized by a wide distribution in size and irregular morphologies that are indistinguishable from authigenic magnetite. Thermoanaerobacter are thermophilic iron-reducing bacteria that predominantly inhabit terrestrial hot springs or deep crusts and have the capacity to transform amorphous ferric iron into magnetite with a size up to 120?nm. In this study, I first characterize the formation of hexagonal platelet-like magnetite of a few hundred nanometers in cultures of Thermoanaerobacter spp. strain TOR39. Biogenic magnetite with such large crystal sizes and unique morphology has never been observed in abiotic or biotic processes and thus can be considered as a potential biosignature for thermophilic iron-reducing bacteria. The unique crystallographic features and strong ferrimagnetic properties of these crystals allow easy and rapid screening for the previous presence of iron-reducing bacteria in deep terrestrial crustal samples that are unsuitable for biological detection methods and, also, the search for biogenic magnetite in banded iron formations that deposited only in the first 2 billion years of Earth with evidence of life. Key Words: Biosignatures—Magnetite—Iron-reducing bacteria—Deep subsurface biosphere—Banded iron formation. Astrobiology 12, 1100–1108. PMID:23145573

2012-01-01

135

Deformation microstructures and magnetite texture development in synthetic shear zones  

NASA Astrophysics Data System (ADS)

We present observations of deformation features in magnetite from synthetic magnetite-bearing silicate aggregates deformed between 1000 °C and 1200 °C in transpressional shear experiments with strains of up to 300%. Anisotropy of magnetic susceptibility and shape preferred orientation (SPO) analysis were combined with electron backscatter diffraction (EBSD) to characterize the magnetite deformation fabrics and intragrain microstructures. Crystallographic preferred orientation (CPO) in magnetite is very weak in all deformed samples and does not vary as a function of either temperature or shear strain. Magnetic anisotropy and SPO increase strongly with both strain and deformation temperature and indicate that strain partitioning between magnetite and the plagioclase matrix decreases at higher temperatures. EBSD orientation mapping of individual magnetite particles revealed substantial dispersions in intragrain orientation, analogous to undulose extinction, after deformation at 1000 and 1100 °C, indicating that dislocation creep processes were active in magnetite despite the lack of a well-developed CPO. Geometrical analysis of crystallographic orientation dispersions from grain map data indicates that low-angle grain boundary formation in magnetite could have been accommodated by slip on {110} or {100} planes, but no evidence for dominant slip on the expected {111} planes was found. Evidence for activation of multiple slip systems was seen in some magnetite grains and could be partially responsible for the lack of CPO in magnetite. These results suggest that, at least in polyphase rocks, crystallographic textures in magnetite may be inherently weak or slow to develop and CPO alone is not an adequate indicator of magnetite deformation mechanisms. These results may aid in the interpretation of deformation textures in other spinel-structured phases such as chromite and ringwoodite.

Till, Jessica L.; Moskowitz, Bruce M.

2014-08-01

136

crystal  

NASA Astrophysics Data System (ADS)

The polarized absorption, emission spectra and decay time measurements of Pr3+-doped CaYAlO4 single crystal have been performed at room temperature. Based on the Judd-Ofelt theory, the spectroscopic parameters , radiative transition probabilities, radiative lifetimes and branching ratios were obtained. The stimulated emission cross-section, fluorescence lifetimes and the quantum efficiency of the promising laser transition were also calculated and compared with other reported crystals. The results show that Pr3+:CaYAlO4 is a promising candidate for visible solid-state laser emission.

Lv, Shaozhen; Wang, Yan; Zhu, Zhaojie; You, Zhenyu; Li, Jianfu; Gao, Shufang; Wang, Hongyan; Tu, Chaoyang

2014-07-01

137

Hybrid DFT calculation of Fe57 NMR resonances and orbital order in magnetite  

NASA Astrophysics Data System (ADS)

The crystal structure and charge and orbital order of magnetite below the Verwey temperature are calculated using a first-principles hybrid density functional theory (DFT) method. The initial atomic positions in the crystal-structure calculation are those recently refined from x-ray diffraction data for the Cc space-group unit cell [Senn, Wright, and Attfield, Nature (London) 481, 173 (2012), 10.1038/nature10704]. Fermi contact and magnetic dipolar contributions to hyperfine fields at Fe57 nuclei obtained from hybrid DFT calculations are used to obtain NMR resonance frequencies for magnetite for a range of external magnetic field directions in a relatively weak field. NMR frequencies from hybrid density functional theory calculations are compared to NMR data [M. Mizoguchi, J. Phys. Soc. Jpn. 70, 2333 (2001), 10.1143/JPSJ.70.2333] for a range of applied magnetic field directions. NMR resonance frequencies of B-site Fe ions show large relative variations with applied field direction owing to anisotropic hyperfine fields from charge and orbital ordered Fe 3d minority-spin electrons at those sites. Good agreement between computed and measured NMR resonance frequencies confirms the pattern of charge and orbital order obtained from calculations. The charge and orbital order of magne-tite in its low-temperature phase obtained from hybrid DFT calculations is analyzed in terms of one-electron bonds between Fe ions. The Verwey transition in magnetite therefore resembles Mott-Peierls transitions in vanadium oxides which undergo symmetry-breaking transitions owing to electron-pair bond formation.

Patterson, C. H.

2014-08-01

138

Electron thermalization and trapping rates in pure and doped alkali and alkaline-earth iodide crystals studied by picosecond optical absorption  

NASA Astrophysics Data System (ADS)

Although light continues to be emitted from insulating crystals used as scintillators over a period of nanoseconds to microseconds after stopping of an energetic particle, much of what determines the nonlinearity of response goes on in the first picoseconds. On this time scale, free carriers and excitons are at high density near the track core and thus are subject to nonlinear quenching. The hot (free) electrons eventually cool to low enough energy that trapping on holes, dopants, or defects can commence. In the track environment, spatial distributions of trapped carriers determined on the picosecond time scale can influence the proportionality between light yield and the initial particle energy throughout the whole light pulse. Picosecond spectroscopy of optical absorption induced by a short pulse of above-gap excitation provides a useful window on what occurs during the crucial early evolution of excited populations. The laser excitation can be tuned to excite carriers that are initially very hot (˜3 eV) relative to the band edges, or that are almost thermalized (˜0.1 eV excess energy) at the outset. Undoped and doped samples of NaI:Tl(0%, 0.1%), CsI:Tl(0%, 0.01%, 0.04%, 0.3%), and SrI2:Eu(0%, 0.2%, 0.5%, 3%) are studied in this work.

Ucer, K. B.; Bizarri, G.; Burger, A.; Gektin, A.; Trefilova, L.; Williams, R. T.

2014-04-01

139

Study of the surface chemistry and morphology of single walled carbon nanotube-magnetite composites  

NASA Astrophysics Data System (ADS)

The study of the morphologies of the single walled carbon nanotube (SWCNT), magnetite nanoparticles (MNP), and the composite based on them was carried with combined X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). These techniques together with thermogravimetric analyses (TGA) and diffuse reflectance infrared transform spectroscopy (DRIFTS) confirmed the production of pure single phases, and that the composite material consisted of MNP attached to the outer surface of the SWCNT. The Mössbauer spectroscopy (MS) research showed the presence of a large quantity of Lewis acid sites in the highly dispersed magnetite particles supported on the SWCNT outer surface. The DRIFTS carbon dioxide adsorption study of the composites revealed significant adsorption of carbon dioxide, fundamentally in the Lewis acid sites. Then, the Lewis acid sites were observed to be catalytically active. Further, the electron exchange between the Lewis acid sites and the basic or amphoteric adsorbed molecules could influence the magnetic properties of the magnetite. Consequently, together with this first ever use of MS in the study of Lewis acid sites, this investigation revealed the potential of the composites for catalytic and sensors applications.

Marquez-Linares, F.; Uwakweh, O. N. C.; Lopez, N.; Chavez, E.; Polanco, R.; Morant, C.; Sanz, J. M.; Elizalde, E.; Neira, C.; Nieto, S.; Roque-Malherbe, R.

2011-03-01

140

Zinc and Arsenic Immobilization and Magnetite Formation Upon Maghemite Reduction by Shewanella putrefaciens ATCC 8071  

NASA Astrophysics Data System (ADS)

Dissimilatory reduction of ferric iron oxides is recognized as an important component of the iron biogeochemical cycle, causing the dissolution of iron oxide minerals and the possible formation of Fe(II)-bearing minerals such as magnetite, green rusts, siderite, etc. These mineralogical transformations affect the mobility of surface- associated toxic metal(loid)s, which may be released into solution, adsorbed, or incorporated into newly formed minerals. Maghemite (?-Fe2O3) is an iron oxide mineral that is found in certain tropical soils and as isolated deposits in more temperate regions. In these settings, maghemite may play an important role in the biogeochemical cycling of iron and of surface-associated trace metal(loids). However, the reduction of maghemite by iron-respiring bacteria, the impact of reductive dissolution on the release of associated contaminants, and the nature of biogenic Fe(II)-containing reaction products are not well documented. In the present study, we incubated samples of pure maghemite and As(V)- and Zn-adsorbed maghemite with an iron reducing bacterium, Shewanella putrefaciens strain ATCC 8071, in a batch system under anoxic conditions. As a result of Fe(III) bioreduction, all mineral suspensions turned from brown to black during the first hour of incubation, indicating the onset of magnetite formation. The presence of this mineral was confirmed by transmission Mössbauer spectroscopy at room temperature, which showed the formation of an almost stoichiometric magnetite. High-resolution transmission electron microscopy images indicate that the parent maghemite and the biogenic magnetite particles are octahedral in shape and of similar size (5 to 20 nm). The presence of 50 mg/L adsorbed Zn(II) did not affect the initial rate of iron reduction with respect to the Zn-free maghemite sample (0.62 mM Fe(II)/h and 0.66 mM Fe(II)/h, respectively). However, adsorption of 50 and 100 mg/L As(V) on maghemite decreased the initial iron reduction rate to 0.35 mM Fe(II)/h and 0.16 mM Fe(II)/h, respectively. Results show that before inoculation, the proportion of As(V) adsorbed on the maghemite surface is significantly higher (90%) than Zn(II) (50%) after a two-day equilibration period. During bioreduction, the remaining soluble zinc and arsenic content decreases progressively as a function of time, possibly as a result of coprecipitation or adsorption reactions on the newly formed biogenic magnetite. Overall, this study shows that magnetite formation induced by the bioreduction of maghemite is particularly effective for the removal of zinc and arsenic from solution.

Cismasu, C.; Ona-Nguema, G.; Bonnin, D.; Menguy, N.; Brown, G. E.

2007-12-01

141

Functional Analysis of the Magnetosome Island in Magnetospirillum gryphiswaldense: The mamAB Operon Is Sufficient for Magnetite Biomineralization  

PubMed Central

Bacterial magnetosomes are membrane-enveloped, nanometer-sized crystals of magnetite, which serve for magnetotactic navigation. All genes implicated in the synthesis of these organelles are located in a conserved genomic magnetosome island (MAI). We performed a comprehensive bioinformatic, proteomic and genetic analysis of the MAI in Magnetospirillum gryphiswaldense. By the construction of large deletion mutants we demonstrate that the entire region is dispensable for growth, and the majority of MAI genes have no detectable function in magnetosome formation and could be eliminated without any effect. Only <25% of the region comprising four major operons could be associated with magnetite biomineralization, which correlated with high expression of these genes and their conservation among magnetotactic bacteria. Whereas only deletion of the mamAB operon resulted in the complete loss of magnetic particles, deletion of the conserved mms6, mamGFDC, and mamXY operons led to severe defects in morphology, size and organization of magnetite crystals. However, strains in which these operons were eliminated together retained the ability to synthesize small irregular crystallites, and weakly aligned in magnetic fields. This demonstrates that whereas the mamGFDC, mms6 and mamXY operons have crucial and partially overlapping functions for the formation of functional magnetosomes, the mamAB operon is the only region of the MAI, which is necessary and sufficient for magnetite biomineralization. Our data further reduce the known minimal gene set required for magnetosome formation and will be useful for future genome engineering approaches. PMID:22043287

Lohsse, Anna; Ullrich, Susanne; Katzmann, Emanuel; Borg, Sarah; Wanner, Gerd; Richter, Michael; Voigt, Birgit; Schweder, Thomas; Schuler, Dirk

2011-01-01

142

Remanent and Induced Magnetic Anomalies over the Bjerkreim-Sokndal Layered Intrusion: Effects from Crystal Fractionation and Magma Recharge  

NASA Astrophysics Data System (ADS)

The Bjerkreim-Sokndal (BKS) norite-quartz mangerite layered intrusion is part of the early Neoproterozoic Rogaland Anorthosite Province intruded into the Fennoscandian shield in south Norway at ~930 Ma. The BKS is exposed over an area of 230 km2 with a thickness of ~7000m and is of economic interest for hemo-ilmenite, magnetite and apatite deposits. From the point of view of magnetic minerals, in the course of fractional crystallization and magma evolution, the ilmenite becomes less Fe3+-rich reflected by a change from ilmenite with hematite exsolution to nearly pure ilmenite. Magnetite starts to crystallize relatively late in the intrusive history, but its crystallization is interrupted by influxes of more primitive magma containing hemo-ilmenite. The variations in aeromagnetic and ground-magnetic anomalies measured over the BKS can be explained in terms of the magnetic properties of NRM, susceptibility, and hysteresis. Magnetic properties are correlated with the oxide mineralogy and mineral chemistry. Early layers in the intrusion contain hemo-ilmenite. As the magma evolved and magnetite started to crystallize, this caused a distinct change over the layering from remanence-controlled negative anomalies to induced positive anomalies. When new, more primitive magma was injected into the system, hemo-ilmenite returned as the major oxide and the resulting magnetic anomalies are again negative. The most dramatic change in the magnetic signature is in the upper part of the intrusion in MCU IVe, where magnetite became a well established cumulate phase as indicated by susceptibility, but its induced magnetization is overcome by large NRM's associated either with hemo-ilmenite or with hemo-ilmenite and magnetite exsolved from pyroxenes. The average natural remanent magnetizations change from ~3 A/m in MCU IVd, to 15 A/m in MCU IVe, and back to 2 A/m in the overlying MCU IVf, producing a strong negative remanent anomaly that has been followed along strike for at least 20 km by ground-magnetic measurements. The highly varied magnetic properties of this intrusion, caused by varied magmatic crystallization of combinations of oxide minerals illustrate some of the possibilities to be considered in evaluating crustal magnetic anomalies.

McEnroe, S. A.; Brown, L. L.; Robinson, P.

2013-12-01

143

Study of the surface chemistry and morphology of single walled carbon nanotube-magnetite composites  

SciTech Connect

The study of the morphologies of the single walled carbon nanotube (SWCNT), magnetite nanoparticles (MNP), and the composite based on them was carried with combined X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). These techniques together with thermogravimetric analyses (TGA) and diffuse reflectance infrared transform spectroscopy (DRIFTS) confirmed the production of pure single phases, and that the composite material consisted of MNP attached to the outer surface of the SWCNT. The Moessbauer spectroscopy (MS) research showed the presence of a large quantity of Lewis acid sites in the highly dispersed magnetite particles supported on the SWCNT outer surface. The DRIFTS carbon dioxide adsorption study of the composites revealed significant adsorption of carbon dioxide, fundamentally in the Lewis acid sites. Then, the Lewis acid sites were observed to be catalytically active. Further, the electron exchange between the Lewis acid sites and the basic or amphoteric adsorbed molecules could influence the magnetic properties of the magnetite. Consequently, together with this first ever use of MS in the study of Lewis acid sites, this investigation revealed the potential of the composites for catalytic and sensors applications. -- Graphical abstract: A large amount of Lewis acid sites were found in the highly dispersed magnetite which is supported on the SWCNT outer surface. Display Omitted Research highlights: {yields} The obtained materials were completely characterized with XRD, Raman and SEM-TEM. {yields} DRIFT, TGA and adsorption of the composites allowed understand the material formation. {yields} This is the first report of a study of Lewis sites by Moessbauer spectroscopy.

Marquez-Linares, F. [Institute for Physical Chemical Applied Research, School of Science, University of Turabo, PO Box 3030, Gurabo, PR 00778-3030 (Puerto Rico); Uwakweh, O.N.C. [Engineering Science and Materials Department, College of Engineering, University of Puerto Rico-Mayagueez Campus, Mayaguez, PR 00681-9044 (Puerto Rico); Lopez, N. [Chemical Engineering Department, College of Engineering, University of Puerto Rico-Mayagueez Campus, Mayaguez, PR 00681-9000 (Puerto Rico); Chavez, E. [Physics Department, University of Puerto Rico-Mayagueez Campus, Mayaguez, PR 00681-9000 (Puerto Rico); Polanco, R. [Institute for Physical Chemical Applied Research, School of Science, University of Turabo, PO Box 3030, Gurabo, PR 00778-3030 (Puerto Rico); Morant, C.; Sanz, J.M.; Elizalde, E. [Department of Applied Physics, C-XII, Universidad Autonoma de Madrid, Cantoblanco, 28049-Madrid (Spain); Neira, C.; Nieto, S. [Institute for Physical Chemical Applied Research, School of Science, University of Turabo, PO Box 3030, Gurabo, PR 00778-3030 (Puerto Rico); Roque-Malherbe, R., E-mail: RRoque@suagm.ed [Institute for Physical Chemical Applied Research, School of Science, University of Turabo, PO Box 3030, Gurabo, PR 00778-3030 (Puerto Rico)

2011-03-15

144

Fe atom exchange between aqueous Fe2+ and magnetite.  

PubMed

The reaction between magnetite and aqueous Fe(2+) has been extensively studied due to its role in contaminant reduction, trace-metal sequestration, and microbial respiration. Previous work has demonstrated that the reaction of Fe(2+) with magnetite (Fe(3)O(4)) results in the structural incorporation of Fe(2+) and an increase in the bulk Fe(2+) content of magnetite. It is unclear, however, whether significant Fe atom exchange occurs between magnetite and aqueous Fe(2+), as has been observed for other Fe oxides. Here, we measured the extent of Fe atom exchange between aqueous Fe(2+) and magnetite by reacting isotopically "normal" magnetite with (57)Fe-enriched aqueous Fe(2+). The extent of Fe atom exchange between magnetite and aqueous Fe(2+) was significant (54-71%), and went well beyond the amount of Fe atoms found at the near surface. Mössbauer spectroscopy of magnetite reacted with (56)Fe(2+) indicate that no preferential exchange of octahedral or tetrahedral sites occurred. Exchange experiments conducted with Co-ferrite (Co(2+)Fe(2)(3+)O(4)) showed little impact of Co substitution on the rate or extent of atom exchange. Bulk electron conduction, as previously invoked to explain Fe atom exchange in goethite, is a possible mechanism, but if it is occurring, conduction does not appear to be the rate-limiting step. The lack of significant impact of Co substitution on the kinetics of Fe atom exchange, and the relatively high diffusion coefficients reported for magnetite suggest that for magnetite, unlike goethite, Fe atom diffusion is a plausible mechanism to explain the rapid rates of Fe atom exchange in magnetite. PMID:22577839

Gorski, Christopher A; Handler, Robert M; Beard, Brian L; Pasakarnis, Timothy; Johnson, Clark M; Scherer, Michelle M

2012-11-20

145

Synthesis, characterisation and application of silica-magnetite nanocomposites  

NASA Astrophysics Data System (ADS)

Silica-magnetite composites were prepared for eventual applications in biomolecular separations (nucleic acids). Their production on large scale has been optimised and they have been extensively characterised in a physical and chemical context. They perform at least as well, if not better than a commercially available equivalent at adsorbing and eluting DNA. Several methods for the preparation of magnetite were compared in order to select one, which produced particles, possessing high magnetic susceptibility, low rate of sedimentation and good chemical stability. Of the main methods studied: (i) oxidative hydrolysis of iron(II) sulphate in alkaline media, (ii) alkaline hydrolysis of iron(II) and iron(III) chloride solutions, and (iii) precipitation from iron(II) and iron(III) chloride solutions by hydrolysis of urea, method (i) produced the 'best' magnetite particles. Silica-magnetite composites were prepared using the 'best' magnetite, and, for comparison, two methods for depositing silica were used to coat the silica onto magnetite nanoparticles, from silicic acid at pH 10 and by acid hydrolysis of tetraethoxysilane (TEOS) at 90 °C. The best method for yielding silica-magnetite composites that worked well in DNA adsorption and elution proved to be that involving silicic acid and this material could be made in 20 g batch sizes. Silica-magnetite composites from the two methods proved to have distinct and different physical and chemical properties. All magnetite and silica-magnetite samples were fully characterised for their relative chemical composition using Fourier-transform infrared, XRF and thermo-gravimetric analysis. Their physical characteristics were determined using scanning electron microscopy and N 2 adsorption and Mossbauer spectroscopy was used to confirm the identity of the iron oxides produced. Selected samples were comparatively tested for their ability to adsorb, and subsequently elute, 2-deoxyguanosine-5-monophosphate (GMP) and its non-phosphorylated analogue 2-deoxyguanosine (G) and a range of sequence defined oligonucleotides (NAs) and sheared salmon sperm DNA. It was found that magnetite readily adsorbed GMP via the GMP phosphate anion in water, whereas silica did not, due to electrostatic repulsion between the negatively charged surface of silica and the GMP. Both magnetite and silica magnetite were further tested in adsorption studies of G and GMP in different chaotropic media, 4 M sodium chloride or 4 M ammonium sulphate. The high salt conditions aided binding of GMP silica magnetite but inhibited adsorption to magnetite presumably due to competition for binding sites on the magnetite's surface by the chaotrope anions. Interestingly, the results from NAs binding studies indicated that sequence appeared to play an important role in adsorption of the different species to silica-magnetite composites. This may indicate a contribution by hydrophobic interactions to the binding mechanism. Multiple depositions of silica onto magnetite performed by deposition from silicic acid at pH 10 did not appear to greatly increase the composite percentage represented by silica whilst composite produced by the acid hydrolysis of TEOS at 90 °C did. However, it appeared that the silica deposited by the first method represented a complete coating of the magnetite core whilst the second method yielded a porous or incomplete coating. In comparison with commercially available silica-magnetite composite in DNA adsorption and elution, the material was observed to perform approximately 10% more efficiently. These findings indicate that it is possible to produce a consistent and cheap silica-magnetite nanoparticle on relatively large scale (greater than 20 g batch size) which is at least as good as, if not better than, a commercially available alternative.

Bruce, Ian J.; Taylor, James; Todd, Michael; Davies, Martin J.; Borioni, Enrico; Sangregorio, Claudio; Sen, Tapas

2004-12-01

146

Ion microprobe analysis of oxygen isotope ratios in granulite facies magnetites: diffusive exchange as a guide to cooling history  

NASA Astrophysics Data System (ADS)

Ion microprobe analysis of magnetites from the Adirondack Mountains, NY, yields oxygen isotope ratios with spatial resolution of 2 8 ?m and precision in the range of 1‰ (1 sigma). These analyses represent 11 orders of magnitude reduction in sample size compared to conventional analyses on this material and they are the first report of routinely reproducible precision in the 1 per mil range for analysis of ?18O at this scale. High precision micro-analyses of this sort will permit wide-ranging new applications in stable isotope geochemistry. The analyzed magnetites form nearly spherical grains in a calcite matrix with diopside and monticellite. Textures are characteristic of granulite facies marbles and show no evidence for retrograde recrystallization of magnetite. Magnetites are near to Fe3O4 in composition, and optically and chemically homogeneous. A combination of ion probe plus conventional BrF5 analysis shows that individual grains are homogeneous with ?18O=8.9±1‰ SMOW from the core to near the rim of 0.1 1.2 mm diameter grains. Depth profiling into crystal growth faces of magnetites shows that rims are 9‰ depleted in ?18O. These low ?18O values increase in smooth gradients across the outer 10 ?m of magnetite rims in contact with calcite. These are the sharpest intracrystalline gradients measured to date in geological materials. This discovery is confirmed by bulk analysis of 150 350 ?m diameter magnetites which average 1.2‰ lower in ?18O than coarse magnetites due to low ?18O rims. Conventional analysis of coexisting calcite yields °18O=18.19, suggesting that bulk ?18O (Cc-Mt)=9.3‰ and yielding an apparent equilibration “temperature” of 525° C, over 200° C below the temperature of regional metamorphism. Consideration of experimental diffusion data and grain size distribution for magnetite and calcite suggests two contrasting cooling histories. The data for oxygen in calcite under hydrothermal conditions at high P(H2O) indicates that diffusion is faster in magnetite and modelling of the low ?18O rims on magnetite would suggest that the Adirondacks experienced slow cooling after Grenville metamorphism, followed by a brief period of rapid cooling, possibly related to uplift. Conversely, the data for calcite at low P(H2O) show slower oxygen diffusion than in magnetite. Modelling based on these data is consistent with geochronology that shows slow cooling through the blocking temperature of both minerals, suggesting that the low ?18O rims form by exchange with late, low temperature fluids similar to those that infiltrated the rock to serpentinize monticellite and which infiltrated adjacent anorthosite to form late calcite veinlets. In either case, the ion microprobe results indicate that two distinct events are recorded in the post-metamorphic exchange history of these magnetites. Recognition of these events is only possible through microanalysis and has important implications for geothermometry.

Valley, John W.; Graham, Colin M.

1991-03-01

147

Lymphatic mapping and sentinel node location with magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

Subcutaneously administered magnetite nanoparticles were used to locate sentinel lymph nodes in normal rats. Nanoparticles sequestered in brachial and axillary lymph nodes produced magnetic susceptibility artifacts in gradient recall echo magnetic resonance images. The artifact sizes enabled the determination of nanoparticle nodal uptake rates and lymphatic drainage patterns. These studies were confirmed by use of 59Fe labeled magnetite nanoparticles.

Jung, Chu W.; Rogers, James M.; Groman, Ernest V.

1999-04-01

148

Pure subtype systems  

Microsoft Academic Search

This paper introduces a new approach to type theory called pure subtype systems . Pure subtype systems differ from traditional approaches to type theory (such as pure type systems) because the theory is based on subtyping, rather than typing. Proper types and typing are completely absent from the theory; the subtype relation is defined directly over objects. The traditional typing

DeLesley S. Hutchins

2010-01-01

149

Magnetite as Possible Template for the Synthesis of Chiral Organics in Carbonaceous Chondrites  

NASA Technical Reports Server (NTRS)

The main goal of the Japanese Aerospace Ex-ploration Agency (JAXA) Hayabusa-2 mission is to visit and return to Earth samples of a C-type asteroid (162173) 1999 JU3 in order to understand the origin and nature of organic materials in the Solar System. Life on Earth shows preference towards the set of organics with particular spatial arrangements, this 'selectivity' is a crucial criterion for life. With only rare exceptions, life 'determines' to use the left- (L-) form over the right- (D-) form of amino acids, resulting in a L-enantiomeric excess (ee). Recent studies have shown that L-ee is found within the alpha-methyl amino acids in meteorites [1, 2], which are amino acids with rare terrestrial occurrence, and thus point towards a plausible abiotic origin for ee. One of the proposed origins of chiral asymmetry of amino acids in meteorites is their formation with the presence of asymmetric catalysts [3]. The catalytic mineral grains acted as a surface at which nebular gases (CO, H2 and NH3) were allowed to condense and react through Fisher Tropsch type (FTT) syntheses to form the organics observed in meteorites [4]. Magnetite is shown to be an effective catalyst of the synthesis of amino acids that are commonly found in meteorites [5]. It has also taken the form as spiral magnetites (a.k.a. 'plaquettes'), which were found in various carbonaceous chondrites (CCs), including C2s Tagish Lake and Esseibi, CI Orgueil, and CR chondrites [e.g., 6, 7, 8]. In addition, L-ee for amino acids are common in the aqueously altered CCs, as opposed to the unaltered CCs [1]. It seems possible that the synthesis of amino acids with chiral preferences is correlated to the alteration process experienced by the asteroid parent body, and related to the configuration of spiral magnetite catalysts. Since C-type asteroids are considered to be enriched in organic matter, and the spectral data of 1999 JU3 indicates a certain de-gree of aqueous alteration [9], the Hayabusa-2 mission serves as a perfect chance to attest this argument. In order to understand the distribution of spiral magnetites among different meteorite classes, as well as to investigate their spiral configurations and correlation to molecular asymmetry, we observed polished thin sections of CCs using scanning electron microscope (SEM) imaging. Individual magnetite grains were picked, embedded in epoxy, thin-sectioned using an ultra-microtome, and studied with electron backscatter diffraction (EBSD) in order to reconstruct the crystal orientation along the stack of magnetite disks.

Chan, Q. H. S.; Zolenksy, M. E.

2014-01-01

150

Cryptic grain-scale heterogeneity of oxygen isotope ratios in metamorphic magnetite.  

PubMed

Oxygen isotope ratios measured by ion microprobe in magnetite from granulite-facies marble of the Adirondack Mountains, New York, range from +2 to +11 per mil (standard mean ocean water) across a single grain that measures 3 millimeters by 5 millimeters. Low values are concentrated in irregular domains near the grain boundary but also occur in the grain's interior. In contrast, grains 1 millimeter in diameter that are from a second nearby sample show no significant heterogeneity, except within 10 micrometers of the grain boundary. These data, including large gradients of up to 9 per mil per 10 micrometers, provide important new constraints on the nature and origins of intragrain isotopic heterogeneity and on oxygen isotope thermometry. The differences between these magnetite grains result from contrasting mechanisms of isotope exchange with fluids after the peak of regional metamorphism. Volume diffusion of oxygen through the crystal structure of magnetite contributed to isotope exchange in the rims of small grains, but larger grains are crosscut by healed cracks that are not readily detected and that short-circuited diffusion. PMID:17816891

Valley, J W; Graham, C M

1993-03-19

151

Transition warming and cooling remanences in magnetite  

NASA Astrophysics Data System (ADS)

Insight into the size and morphology of assemblages of magnetite particles can be gained by comparing temperature variations of remanence or susceptibility after zero-field cooling (ZFC) and after field cooling (FC) through the Verwey transition around Tv = 120 K. At 10 K a sample is demagnetized following ZFC, but in the FC initial state before warming the sample has a transition cooling remanence (TrCRM) acquired in crossing Tv. The matching transition warming remanence (TrWRM) acquired as a result of heating a demagnetized sample from low temperature across Tv is often called inverse thermoremanent magnetization (ITRM). In TrCRM experiments, initially demagnetized samples were cooled in a 2 mT field from 300 K to 10 K. Magnetization M was measured at 1 K to 5 K intervals, the highest-resolution data being taken between 140 K and 90 K. The field was zeroed at 10 K, and the TrCRM was monitored during zero-field warming back to 300 K. The properties of TrCRMs are generally similar to those of TrWRMs produced by heating a ZFC sample in a 2 mT field from 10 K. In 10 of 12 samples (grain sizes from 0.6 to 135 ?m), M of monoclinic magnetite produced by field cooling through Tv exactly equals M of cubic magnetite produced by field warming through Tv, even though the ultimate TrCRM and TrWRM values when H ? 0 are entirely different. Mirror-image symmetry was observed between in-field warming curves tracking the acquisition of TrWRM and zero-field warming curves of TrCRM between 10 and 300 K. The symmetry, with increases in the field-on M curves mirroring decreases in the field-off Mr curves, was almost perfect from 10 to 110 K. Approximate symmetry was also observed between in-field cooling curves tracking TrCRM production and zero-field cooling curves of TrWRM between 300 K and Tv. Detailed study of the properties and mechanism(s) of transition remanences will help clarify why the ZFC/FC method is diagnostic in some instances and not in others.

Dunlop, David J.

2007-11-01

152

Three-dimensional domain observations of magnetite and titanomagnetites using the dried colloid SEM method  

NASA Astrophysics Data System (ADS)

Dried colloid scanning electron microscopy (SEM) has been applied for the study of Bitter patterns on unpolished and uneven surfaces of microcrystals of natural ferrites (hydrothermally grown magnetite, synthetic TM70 and TM50 removed from a basaltic rock matrix). By the simultaneous observation of domain walls on crystal surfaces of different orientation with high resolution, information is obtained on the volume domain structure underneath. The observation confirms the presence of lamellae-shaped volume domains associated with closure domains on the surface for the reduction of the magnetic stray field energy.

Soffel, H. C.; Aumüller, C.; Hoffmann, V.; Appel, E.

153

Silicon dioxide nanoporous structure with liquid crystal for optical sensors  

NASA Astrophysics Data System (ADS)

It has been studied the spectral characteristics of the porous silicon dioxide and cholesteric liquid crystal. It has been shown that doping of the EE1 cholesteric liquid crystal with Fe3O4 magnetite nanoparticles doesn't shift significantly the position of the transmittance minimum of the material. It has been found that the deformation of chiral pitch of cholesteric liquid crystal with magnetite is observed in case of doping of porous nanocomposite host with following shifting of minimum of transmittance into short wavelength direction. It has been shown that influence of carbon monoxide on optical characteristics of the cholesteric liquid crystal with magnetite can be explained by the interaction of CARBON MONOXIDE molecules with magnetite nanodopants.

Sushynskyi, Orest; Vistak, Maria; Gotra, Zenon; Fechan, Andriy; Mikityuk, Zinoviy

2013-05-01

154

Nucleation and growth of magnetite from solution  

NASA Astrophysics Data System (ADS)

The formation of crystalline materials from solution is usually described by the nucleation and growth theory, where atoms or molecules are assumed to assemble directly from solution. For numerous systems, the formation of the thermodynamically stable crystalline phase is additionally preceded by metastable intermediates . More complex pathways have recently been proposed, such as aggregational processes of nanoparticle precursors or pre-nucleation clusters, which seem to contradict the classical theory. Here we show by cryogenic transmission electron microscopy that the nucleation and growth of magnetite—a magnetic iron oxide with numerous bio- and nanotechnological applications—proceed through rapid agglomeration of nanometric primary particles and that in contrast to the nucleation of other minerals, no intermediate amorphous bulk precursor phase is involved. We also demonstrate that these observations can be described within the framework of classical nucleation theory.

Baumgartner, Jens; Dey, Archan; Bomans, Paul H. H.; Le Coadou, Cécile; Fratzl, Peter; Sommerdijk, Nico A. J. M.; Faivre, Damien

2013-04-01

155

Disappearing Crystals  

NSDL National Science Digital Library

Learners experiment with water gel crystals, or sodium polyacrylate crystals, which absorb hundreds of times their weight in water. When in pure water, the water gel crystals cannot be seen. However, when learners place the crystals in solutions of Splenda and water, the crystals can be seen. Learners use this property to determine how much Splenda is in 4 different cups of water. This is one of four activities learners can complete related to PhysicsQuest 2008. Each activity gives a clue to solve a puzzle in the accompanying comic book, "Nikola Tesla and the Electric Fair."

Society, American P.

2009-01-01

156

Bats use magnetite to detect the earth's magnetic field.  

PubMed

While the role of magnetic cues for compass orientation has been confirmed in numerous animals, the mechanism of detection is still debated. Two hypotheses have been proposed, one based on a light dependent mechanism, apparently used by birds and another based on a "compass organelle" containing the iron oxide particles magnetite (Fe(3)O(4)). Bats have recently been shown to use magnetic cues for compass orientation but the method by which they detect the Earth's magnetic field remains unknown. Here we use the classic "Kalmijn-Blakemore" pulse re-magnetization experiment, whereby the polarity of cellular magnetite is reversed. The results demonstrate that the big brown bat Eptesicus fuscus uses single domain magnetite to detect the Earths magnetic field and the response indicates a polarity based receptor. Polarity detection is a prerequisite for the use of magnetite as a compass and suggests that big brown bats use magnetite to detect the magnetic field as a compass. Our results indicate the possibility that sensory cells in bats contain freely rotating magnetite particles, which appears not to be the case in birds. It is crucial that the ultrastructure of the magnetite containing magnetoreceptors is described for our understanding of magnetoreception in animals. PMID:18301753

Holland, Richard A; Kirschvink, Joseph L; Doak, Thomas G; Wikelski, Martin

2008-01-01

157

Bats Use Magnetite to Detect the Earth's Magnetic Field  

PubMed Central

While the role of magnetic cues for compass orientation has been confirmed in numerous animals, the mechanism of detection is still debated. Two hypotheses have been proposed, one based on a light dependent mechanism, apparently used by birds and another based on a “compass organelle” containing the iron oxide particles magnetite (Fe3O4). Bats have recently been shown to use magnetic cues for compass orientation but the method by which they detect the Earth's magnetic field remains unknown. Here we use the classic “Kalmijn-Blakemore” pulse re-magnetization experiment, whereby the polarity of cellular magnetite is reversed. The results demonstrate that the big brown bat Eptesicus fuscus uses single domain magnetite to detect the Earths magnetic field and the response indicates a polarity based receptor. Polarity detection is a prerequisite for the use of magnetite as a compass and suggests that big brown bats use magnetite to detect the magnetic field as a compass. Our results indicate the possibility that sensory cells in bats contain freely rotating magnetite particles, which appears not to be the case in birds. It is crucial that the ultrastructure of the magnetite containing magnetoreceptors is described for our understanding of magnetoreception in animals. PMID:18301753

Holland, Richard A.; Kirschvink, Joseph L.; Doak, Thomas G.; Wikelski, Martin

2008-01-01

158

LA-ICP-MS of magnetite: Methods and reference materials  

USGS Publications Warehouse

Magnetite (Fe3O4) is a common accessory mineral in many geologic settings. Its variable geochemistry makes it a powerful petrogenetic indicator. Electron microprobe (EMPA) analyses are commonly used to examine major and minor element contents in magnetite. Laser ablation ICP-MS (LA-ICP-MS) is applicable to trace element analyses of magnetite but has not been widely employed to examine compositional variations. We tested the applicability of the NIST SRM 610, the USGS GSE-1G, and the NIST SRM 2782 reference materials (RMs) as external standards and developed a reliable method for LA-ICP-MS analysis of magnetite. LA-ICP-MS analyses were carried out on well characterized magnetite samples with a 193 nm, Excimer, ArF LA system. Although matrix-matched RMs are sometimes important for calibration and normalization of LA-ICP-MS data, we demonstrate that glass RMs can produce accurate results for LA-ICP-MS analyses of magnetite. Cross-comparison between the NIST SRM 610 and USGS GSE-1G indicates good agreement for magnetite minor and trace element data calibrated with either of these RMs. Many elements show a sufficiently good match between the LA-ICP-MS and the EMPA data; for example, Ti and V show a close to linear relationship with correlation coefficients, R2 of 0.79 and 0.85 respectively. ?? 2011 The Royal Society of Chemistry.

Nadoll, P.; Koenig, A.E.

2011-01-01

159

crystals  

NASA Astrophysics Data System (ADS)

A novel combined interferometric-mask method for the formation of micro- and nanometric scale three-dimensional (3D) rotational symmetry quasi-crystalline refractive lattice structures in photorefractive materials is demonstrated experimentally. The method is based on micrometric scale spatial modulation of the light by amplitude mask in the radial directions and along the azimuthal angle and the use of counter-propagating beam geometry building up Gaussian standing wave, which defines the light modulation in the axial direction with half-wavelength periodicity. 3D intensity pattern can be represented as numerous mask-generated 2D quasi-periodic structures located in each anti-node of the standing wave. The formed 3D intensity distributions of the optical beams can be imparted into the photorefractive medium thus creating the micro- and sub-micrometric scale 3D refractive index volume lattices. The used optical scheme allows also the formation of 2D lattices by removing the back-reflecting mirror. 2D and 3D refractive lattices were recorded with the use of 532 nm laser beam and rotational symmetry mask in doped lithium niobate crystals and were tested by the probe beam far-field diffraction pattern imaging and direct observation by phase microscope. The formed rotational symmetry 3D refractive structures have the periods of 20-60 ?m in the radial directions, 60 ?m along the azimuthal angle and half-wavelength 266 nm in the axial direction.

Badalyan, A.; Hovsepyan, R.; Mantashyan, P.; Mekhitaryan, V.; Drampyan, R.

2014-07-01

160

Cation occupancy sites in synthetic Co-doped magnetites as determined with X-ray absorption (XAS) and Mössbauer spectroscopies  

NASA Astrophysics Data System (ADS)

In the present work, cobalt-doped magnetites, prepared by the co-precipitation method, were mainly studied by X-ray absorption and Mössbauer spectroscopies. From the chemical analysis, it was observed that the continuous increase of Co 2+ is followed by a simultaneous decrease of the Fe 2+ contents, in the spinel structure. Room temperature Mössbauer parameters indicate that samples are formed by single crystallographic phases of pure magnetite or its Co-substituted analogs. Basing on the inversion of intensities of the Mössbauer lines 1 (leftmost, in the negative Doppler velocity scale) and 2, it is assumed that the Co-substitution occurs essentially, if not only, at octahedral sites of the spinel structure. XAS results obtained at Co K-edge confirm that the Co-substitution occurs preferentially at octahedral coordination sites.

Lelis, M. F. F.; Porto, A. O.; Gonçalves, C. M.; Fabris, J. D.

2004-07-01

161

Superparamagnetic magnetite nanocrystals-graphene oxide nanocomposites: facile synthesis and their enhanced electric double-layer capacitor performance.  

PubMed

Superparamagnetic magnetite nanocrystals-graphene oxide (FGO) nanocomposites were successfully synthesized through a simple yet versatile one-step solution-processed approach at ambient conditions. Magnetite (Fe3O4) nanocrystals (NCs) with a size of 10-50 nm were uniformly deposited on the surfaces of graphene oxide (GO) sheets, which were confirmed by transmission electron microscopy (TEM) and high-angle annular dark field scanning transmission election microscopy (HAADF-STEM) studies. FGO with different Fe3O4 loadings could be controlled by simply manipulating the initial weight ratio of the precursors. The M-H measurements suggested that the as-prepared FGO nanocomposites have a large saturation magnetizations that made them can move regularly under an external magnetic field. Significantly, FGO nanocomposites also exhibit enhanced electric double-layer capacitor (EDLC) activity compared with pure Fe3O4 NCs and GO in terms of specific capacitance and high-rate charge-discharge. PMID:22905504

Wang, Qihua; Wang, Dewei; Li, Yuqi; Wang, Tingmei

2012-06-01

162

Magnetism of magnetite at low temperatures: Are we getting hotter?  

NASA Astrophysics Data System (ADS)

During the last decade, significant advances have been achieved by rock magnetists studying the magnetic properties of magnetite (Fe 3O 4) at cryogenic temperatures (<300 K). Recent experimental achievements include (but not limited to) the discovery of a memory of the magnetic field (H FC) applied during cooling through the Verwey transition in the low-temperature (<120 K) phase of pseudo-single domain (ca. 0.5-5 ?m mean grain size) magnetite. The application of an intermediate field H FC affects the magnetic properties of magnetite in such a way that the field can be determined by measuring magnetic hysteresis at a very low temperature. The memory effect is even better expressed on the first-order reversal curve (FORC) distributions. The application of novel FORC technique has also resulted in the discovery of unusual double-peaked FORC distributions, which form in magnetite after cooling to low temperatures in a zero or intermediate magnetic field. Another important finding is that the ratio (R LT) of a saturating isothermal remanent magnetization (SIRM) imparted at a very low temperature (5-20 K) after zero field cooling to an SIRM imparted after cooling in a very strong (> 1 T) magnetic field depends on the mean grain size of magnetite. While the ratio R LT is greater than unity for multidomain magnetite, it is smaller than unity for single- domain grains. These and other results strongly suggest that the magnetic properties of magnetite below the Verwey transition are closely interrelated with its crystallographic properties, specifically twinning. However, despite these experimental advances we are still in a "colder corner" in terms of understanding the processes governing the magnetism of magnetite at cryogenic temperatures. Although the elaborate micromagnetic models developed recently realistically describe many observed properties of low-temperature magnetite, they do not yet fully incorporate the potential effects of twinning. Future theoretical developments should be accompanied by novel experimental approaches such as direct observations of magnetic and twin domain structures in magnetite below the Verwey transition and studies of the samples with well-controlled size, shape, and spacing between grains. Recent successes in theoretical development, micromagnetic modeling, and observational techniques are likely to result in significant breakthroughs in our understanding the low-temperature magnetism of magnetite in the near future.

Smirnov, A.

2008-05-01

163

Functionalized Magnetite Nanoparticles—Synthesis, Properties, and Bio-Applications  

Microsoft Academic Search

Nanotechnology has generated tremendous hopes in recent years toward the design of advanced functional materials, especially in the bio-medical field. Nano-sized-materials such as magnetite nanoparticles display indeed fascinating physico-chemical properties that, if tuned properly, can be exploited to design new bio-diagnostic and therapeutic strategies as well as innovative biotechnology methodologies. Owing to their biocompatibility and excellent magnetic properties, magnetite nanocrystals

Peter Majewski; Benjamin Thierry

2007-01-01

164

Formation of magnetite nanoparticles in poly(acrylamide) gels  

Microsoft Academic Search

Magnetic gels with magnetite nanoparticles incorporated in a matrix of poly(acrylamide) gel were studied. Magnetite was synthesized through coprecipitation of Fe(II) and Fe(III) in the gel phase, in the solution of linear polymer and in aqueous solution without polymer in alkaline media. The effects of network structure and of the concentration of iron salts in the swollen networks on the

Sergey G Starodubtsev; Evheniy V Saenko; Maxim E Dokukin; Viktor L Aksenov; Vera V Klechkovskaya; Irina S Zanaveskina; Alexei R Khokhlov

2005-01-01

165

Electrophoretic mobility of magnetite particles in high temperature water  

SciTech Connect

Magnetite(Fe3O4) isoneofthemostcommonoxidesformingdepositsandparticulatephasesin industrialhightemperaturewatercircuits.Itscolloidalcharacteristicsplayaprincipalroleinthe mechanismofdepositformationandcanbeusedascontrollingfactorstopreventorminimizedeposit formationanddamageofindustrialpipelinesduetounder-depositcorrosion.Inthisstudy,ahigh temperatureparticleelectrophoresistechniquewasemployedtomeasurethezetapotentialatthe magnetite/waterinterface the parameterthatcontrolscolloidalstabilityofparticles,theiraggrega- tion, anddeposition.Themeasurementsweremadeattemperaturesupto200 1C overawiderangeofpH. The isoelectricpointsofmagnetite,atwhichthedepositionofparticlesisincreased,weredeterminedatpH 6.35, 6.00,5.25,and5.05fortemperatures25,100,150,and200 1C, respectively.Theobserved temperaturedependenceofzetapotentialandtheisoelectricpHpointofmagnetitecanhelptoexplain the extentofinteractionsbetweenthecolloidalparticlesandthesteelwallsurfacesunderhydro- thermalconditions,andindicatemethodsforcontrollingandmitigatingoxidedepositioninhigh temperaturewatercycles.

Vidojkovic, Sonja [Pennsylvania State University; Rodriguez-Santiago, V [Oak Ridge National Laboratory (ORNL); Fedkin, Mark V. [Pennsylvania State University; Wesolowski, David J [ORNL; Lvov, Serguei N. [Pennsylvania State University

2011-01-01

166

The periplasmic nitrate reductase nap is required for anaerobic growth and involved in redox control of magnetite biomineralization in Magnetospirillum gryphiswaldense.  

PubMed

The magnetosomes of many magnetotactic bacteria consist of membrane-enveloped magnetite crystals, whose synthesis is favored by a low redox potential. However, the cellular redox processes governing the biomineralization of the mixed-valence iron oxide have remained unknown. Here, we show that in the alphaproteobacterium Magnetospirillum gryphiswaldense, magnetite biomineralization is linked to dissimilatory nitrate reduction. A complete denitrification pathway, including gene functions for nitrate (nap), nitrite (nir), nitric oxide (nor), and nitrous oxide reduction (nos), was identified. Transcriptional gusA fusions as reporters revealed that except for nap, the highest expression of the denitrification genes coincided with conditions permitting maximum magnetite synthesis. Whereas microaerobic denitrification overlapped with oxygen respiration, nitrate was the only electron acceptor supporting growth in the entire absence of oxygen, and only the deletion of nap genes, encoding a periplasmic nitrate reductase, and not deletion of nor or nos genes, abolished anaerobic growth and also delayed aerobic growth in both nitrate and ammonium media. While loss of nosZ or norCB had no or relatively weak effects on magnetosome synthesis, deletion of nap severely impaired magnetite biomineralization and resulted in fewer, smaller, and irregular crystals during denitrification and also microaerobic respiration, probably by disturbing the proper redox balance required for magnetite synthesis. In contrast to the case for the wild type, biomineralization in ?nap cells was independent of the oxidation state of carbon substrates. Altogether, our data demonstrate that in addition to its essential role in anaerobic respiration, the periplasmic nitrate reductase Nap has a further key function by participating in redox reactions required for magnetite biomineralization. PMID:22730130

Li, Yingjie; Katzmann, Emanuel; Borg, Sarah; Schüler, Dirk

2012-09-01

167

Toward pure electronic spectroscopy  

E-print Network

In this thesis is summarized the progress toward completing our understanding of the Rydberg system of CaF and developing Pure Electronic Spectroscopy. The Rydberg system of CaF possesses a paradigmatic character due to ...

Petrovi?, Vladimir, 1978-

2009-01-01

168

A laboratory study of the effect of magnetite on NMR relaxation rates  

NASA Astrophysics Data System (ADS)

We conducted a laboratory study to measure the effect of magnetite concentration and grain size on proton nuclear magnetic resonance (NMR) relaxation rates of sand mixtures and to determine the dominant mechanism by which relaxation occurs. We measured mixtures of quartz and three different forms of magnetite: a powdered synthetic magnetite; a small-grained, natural magnetite; and a large-grained, natural magnetite. The powdered synthetic magnetite was mixed with quartz in five concentrations ranging from 0.14 to 1.4% magnetite by weight; both sizes of natural magnetite were mixed with quartz in concentrations of 1 and 2% magnetite by weight. The NMR response of the water-saturated samples was measured and used to calculate four averaged relaxation rates for each magnetite concentration: the total mean log, bulk fluid, surface, and diffusion relaxation rates. The results of this study show that: 1) surface relaxation was the dominant relaxation mechanism for all samples except the powdered synthetic magnetite sample containing 1.4% magnetite; 2) the surface relaxivity is a function of the fraction of the surface area in the sample composed of magnetite; 3) there is no clear dependence of the diffusion relaxation rate on the concentration of magnetite.

Keating, Kristina; Knight, Rosemary

2008-12-01

169

7 CFR 917.8 - Pure grower or pure producer.  

Code of Federal Regulations, 2010 CFR

...Vegetables, Nuts), DEPARTMENT OF AGRICULTURE FRESH PEARS AND PEACHES GROWN IN CALIFORNIA Order Regulating Handling Definitions § 917.8 Pure grower or pure producer. (a) For peaches, pure grower means any grower: (1) Who...

2010-01-01

170

7 CFR 917.8 - Pure grower or pure producer.  

Code of Federal Regulations, 2011 CFR

...Vegetables, Nuts), DEPARTMENT OF AGRICULTURE FRESH PEARS AND PEACHES GROWN IN CALIFORNIA Order Regulating Handling Definitions § 917.8 Pure grower or pure producer. (a) For peaches, pure grower means any grower: (1) Who...

2011-01-01

171

Production Rate of Cosmogenic 10Be in Magnetite  

NASA Astrophysics Data System (ADS)

Cosmogenic 10Be is widely used for determining exposure ages, soil production rates, and catchment-wide erosion rates. To date, measurements have been almost exclusively in the mineral quartz (SiO2), which is resistant to weathering and easily cleaned of meteoric 10Be contamination. However, this limits the method to quartz-bearing rocks and requires specialized laboratories due to the need for large quantities of hydrofluoric acid (HF). Here, we present initial results for 10Be production in the mineral magnetite (Fe3O4). Magnetite offers several advantages over quartz; it is (1) present in mafic rocks, (2) easily collected in the field, (3) quickly and easily separated in the lab, and (4) digested without HF. In addition, 10Be can be measured in both detrital quartz and magnetite from the same catchment to yield information about the intensity of chemical weathering (Rogers et al., this conference). The 10Be production rate in magnetite relative to quartz was determined for a granitic boulder from Mt. Evans, Colorado, USA. The boulder was crushed and homogenized to facilitate production rate comparisons among various minerals. We separated magnetite using a combination of hand magnets, froth flotation, and a variety of selective chemical dissolutions in dithionite-citrate-bicarbonate solution, 5% nitric acid (HNO3) and 1% HF/HNO3. Six aliquots of magnetite were analyzed for 10Be and compared to quartz. Three aliquots that were not exposed to 1% HF/HNO3 were contaminated with meteoric 10Be, probably associated with residual mica. Three aliquots that were exposed to 1% HF/HNO3 treatments agreed to within 2% measurement uncertainty. Our preliminary results indicate that the relative production rate by mass of 10Be in magnetite and quartz is 0.462 × 0.012. Our results are similar to theoretically predicted values. Recently updated excitation functions for neutron and proton spallation reactions allow us to partition 10Be production in quartz and magnetite among silicon, oxygen, and iron. While most of the production in both magnetite and quartz is from spallation of oxygen, our experimental results indicate that approximately (13 × 3)% of 10Be in the Mt. Evans quartz sample is produced from silicon.

Granger, D. E.; Rogers, H. E.; Riebe, C. S.; Lifton, N. A.

2013-12-01

172

Electrochemistry and dissolution kinetics of magnetite and ilmenite  

USGS Publications Warehouse

Natural samples of magnetite and ilmenite were experimentally weathered in pH 1-7 anoxic solutions at temperatures of 2-65 ??C. Reaction of magnetite is described as [Fe2+Fe23+]O4(magnetite) + 2H+ ??? ??[Fe23+]O3(maghemite) + Fe2+ + H2O. Dynamic polarization experiments using magnetite electrodes confirmed that this reaction is controlled by two electrochemical half cells, 3[Fe2+Fe23+]O4(magnetite) ??? 4??[Fe23+]O3(maghemite) + Fe2+ + 2e- and [Fe2+Fe23+]O4(magnetite) + 8 H+ + 2e- ??? 3Fe2+ + 4H2O, which result in solid state Fe3+ reduction, formation of an oxidized layer and release of Fe(II) to solution. XPS data revealed that iron is present in the ferric state in the surfaces of reacted magnetite and ilmenite and that the Ti Fe ratio increased with reaction pH for ilmenite. Short-term (<36 h) release rates of Fe(II) were linear with time. Between pH 1 and 7, rates varied between 0.3 and 13 ?? 10-14 mol ?? cm-2 ?? s-1 for magnetite and 0.05 and 12.3 ?? 10-14 mol ?? cm-2 ?? s-1 for ilmenite. These rates are two orders of magnitude slower than electrochemical rates determined by Tafel and polarization resistance measurements. Discrepancies are due to both differences in geometric and BET surface area estimates and in the oxidation state of the mineral surface. In long-term closed-system experiments (<120 days), Fe(II) release slowed with time due to the passivation of the surfaces by increasing thicknesses of oxide surface layers. A shrinking core model, coupling surface reaction and diffusion transport, predicted that at neutral pH, the mean residence time for sand-size grains of magnetite and ilmenite will exceed 107 years. This agrees with long-term stability of these oxides in the geologic record. ?? 1994.

White, A. F.; Peterson, M. L.; Hochella, Jr. , M. F.

1994-01-01

173

Abnormal elastic and vibrational behaviors of magnetite at high pressures.  

PubMed

Magnetite exhibits unique electronic, magnetic, and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number of transitional models, although the nature of magnetite at high pressure remains elusive. We have studied a highly stoichiometric magnetite using inelastic X-ray scattering, X-ray diffraction and emission, and Raman spectroscopies in diamond anvil cells up to ~20 GPa, while complementary electrical conductivity measurements were conducted in a cubic anvil cell up to 8.5 GPa. We have observed an elastic softening in the diagonal elastic constants (C11 and C44) and a hardening in the off-diagonal constant (C12) at ~8 GPa where significant elastic anisotropies in longitudinal and transverse acoustic waves occur, especially along the [110] direction. An additional vibrational Raman band between the A1g and T2g modes was also detected at the transition pressure. These abnormal elastic and vibrational behaviors of magnetite are attributed to the occurrence of the octahedrally-coordinated Fe(2+)-Fe(3+)-Fe(2+) ions charge-ordering along the [110] direction in the inverse spinel structure. We propose a new phase diagram of magnetite in which the temperature for the metal-insulator and distorted structural transitions decreases with increasing pressure while the charge-ordering transition occurs at ~8 GPa and room temperature. PMID:25186916

Lin, Jung-Fu; Wu, Junjie; Zhu, Jie; Mao, Zhu; Said, Ayman H; Leu, Bogdan M; Cheng, Jinguang; Uwatoko, Yoshiya; Jin, Changqing; Zhou, Jianshi

2014-01-01

174

Biogeochemical Conditions Favoring Magnetite Formation during Anaerobic Iron Reduction  

PubMed Central

Several anaerobic bacteria isolated from the sediments of Contrary Creek, an iron-rich environment, produced magnetite when cultured in combinations but not when cultured alone in synthetic iron oxyhydroxide medium. When glucose was added as a carbon source, the pH of the medium decreased (to 5.5) and no magnetite was formed. When the same growth medium without glucose was used, the pH increased (to 8.5) and magnetite was formed. In both cases, Fe2+ was released into the growth medium. Geochemical equilibrium equations with Eh and pH as master variables were solved for the concentrations of iron and inorganic carbon that were observed in the system. Magnetite was predicted to be the dominant iron oxide formed at high pHs, while free Fe2+ or siderite were the dominant forms of iron expected at low pHs. Thus, magnetite formation occurs because of microbial alteration of the local Eh and pH conditions, along with concurrent reduction of ferric iron (direct biological reduction or abiological oxidation-reduction reactions). PMID:16347480

Bell, P. E.; Mills, A. L.; Herman, J. S.

1987-01-01

175

Abnormal Elastic and Vibrational Behaviors of Magnetite at High Pressures  

NASA Astrophysics Data System (ADS)

Magnetite exhibits unique electronic, magnetic, and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number of transitional models, although the nature of magnetite at high pressure remains elusive. We have studied a highly stoichiometric magnetite using inelastic X-ray scattering, X-ray diffraction and emission, and Raman spectroscopies in diamond anvil cells up to ~20 GPa, while complementary electrical conductivity measurements were conducted in a cubic anvil cell up to 8.5 GPa. We have observed an elastic softening in the diagonal elastic constants (C11 and C44) and a hardening in the off-diagonal constant (C12) at ~8 GPa where significant elastic anisotropies in longitudinal and transverse acoustic waves occur, especially along the [110] direction. An additional vibrational Raman band between the A1g and T2g modes was also detected at the transition pressure. These abnormal elastic and vibrational behaviors of magnetite are attributed to the occurrence of the octahedrally-coordinated Fe2+-Fe3+-Fe2+ ions charge-ordering along the [110] direction in the inverse spinel structure. We propose a new phase diagram of magnetite in which the temperature for the metal-insulator and distorted structural transitions decreases with increasing pressure while the charge-ordering transition occurs at ~8 GPa and room temperature.

Lin, Jung-Fu; Wu, Junjie; Zhu, Jie; Mao, Zhu; Said, Ayman H.; Leu, Bogdan M.; Cheng, Jinguang; Uwatoko, Yoshiya; Jin, Changqing; Zhou, Jianshi

2014-09-01

176

Pure uterine lipoma.  

PubMed

Lipomatous tumors of the uterus are unusual, benign neoplasms seen in postmenopausal women. Although many of the mixed-type cases such as lipoleiomyoma and fibrolipoma have been reported, pure uterine lipomas are extremely rare. In the literature, a few cases with pure uterine lipoma have been reported. We first present the advanced magnetic resonance findings of pure uterine lipoma, followed by those of ultrasonography (US) and computed tomography (CT). We markedly detected lipid peaks on the magnetic resonance spectroscopy (MRS) and the apparent diffusion coefficient value to be 0.00 due to chemical-shift effects with diffusion-weighted imaging (DWI). Although pelvic lipomatous tumors can be diagnosed with US and CT, in some cases, further workup may be required to localize the lesion. MRI may yield more valuable data for differential diagnosis. MRS and DWI findings provide additional clues on the nature of the lesion. PMID:17905250

Erdem, Gulnur; Celik, Onder; Karakas, Hakki Muammer; Alkan, Alpay; Hascalik, Seyma

2007-10-01

177

The MagA protein of Magnetospirilla is not involved in bacterial magnetite biomineralization.  

PubMed

Magnetotactic bacteria have the ability to orient along geomagnetic field lines based on the formation of magnetosomes, which are intracellular nanometer-sized, membrane-enclosed magnetic iron minerals. The formation of these unique bacterial organelles involves several processes, such as cytoplasmic membrane invagination and magnetosome vesicle formation, the accumulation of iron in the vesicles, and the crystallization of magnetite. Previous studies suggested that the magA gene encodes a magnetosome-directed ferrous iron transporter with a supposedly essential function for magnetosome formation in Magnetospirillum magneticum AMB-1 that may cause magnetite biomineralization if expressed in mammalian cells. However, more recent studies failed to detect the MagA protein among polypeptides associated with the magnetosome membrane and did not identify magA within the magnetosome island, a conserved genomic region that is essential for magnetosome formation in magnetotactic bacteria. This raised increasing doubts about the presumptive role of magA in bacterial magnetosome formation, which prompted us to reassess MagA function by targeted deletion in Magnetospirillum magneticum AMB-1 and Magnetospirillum gryphiswaldense MSR-1. Contrary to previous reports, magA mutants of both strains still were able to form wild-type-like magnetosomes and had no obvious growth defects. This unambiguously shows that magA is not involved in magnetosome formation in magnetotactic bacteria. PMID:22194451

Uebe, René; Henn, Verena; Schüler, Dirk

2012-03-01

178

Production of pure metals  

NASA Technical Reports Server (NTRS)

A process for depositing elements by irradiating liquids is reported. Ultra pure elements are precipitated from aqueous solutions or suspensions of compounds. A solution of a salt of a metal to be prepared is irradiated, and the insoluble reaction product settles out. Some chemical compounds may also be prepared in this manner.

Philipp, W. H.; Marsik, S. J.; May, C. E. (inventors)

1974-01-01

179

Synthesis of chiral hybrid nanotubes of magnetite nanoparticles and conducting polymers.  

PubMed

New chiral magnetite nanoparticles with a polymerizable group produced polymer composite films on an electrode surface and the hybrid nanotubes of magnetite nanoparticles and polythiophene from their template-based electropolymerization. PMID:22038075

Mitsumori, Masashi; Nakahodo, Tsukasa; Fujihara, Hisashi

2012-01-01

180

Simple and Rapid Synthesis of Magnetite/Hydroxyapatite Composites for Hyperthermia Treatments via a Mechanochemical Route  

PubMed Central

This paper presents a simple method for the rapid synthesis of magnetite/hydroxyapatite composite particles. In this method, superparamagnetic magnetite nanoparticles are first synthesized by coprecipitation using ferrous chloride and ferric chloride. Immediately following the synthesis, carbonate-substituted (B-type) hydroxyapatite particles are mechanochemically synthesized by wet milling dicalcium phosphate dihydrate and calcium carbonate in a dispersed suspension of magnetite nanoparticles, during which the magnetite nanoparticles are incorporated into the hydroxyapatite matrix. We observed that the resultant magnetite/hydroxyapatite composites possessed a homogeneous dispersion of magnetite nanoparticles, characterized by an absence of large aggregates. When this material was subjected to an alternating magnetic field, the heat generated increased with increasing magnetite concentration. For a magnetite concentration of 30 mass%, a temperature increase greater than 20 K was achieved in less than 50 s. These results suggest that our composites exhibit good hyperthermia properties and are promising candidates for hyperthermia treatments. PMID:23629669

Iwasaki, Tomohiro; Nakatsuka, Ryo; Murase, Kenya; Takata, Hiroshige; Nakamura, Hideya; Watano, Satoru

2013-01-01

181

Interparticle interaction and size effect in polymer coated magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

Magnetization and Mössbauer studies have been performed on the polymer coated magnetite nanoparticles with particle size from 5.1 to 14.7 nm. The maximum in the temperature dependence of magnetization (TM) is found to be inconsistent with the particle size (DTEM). The effective magnetic anisotropy (Kan) is found to increase with the decrease of DTEM, which is attributed to the increase of surface anisotropy. The absence of coercivity and remanence of magnetization noticed well above TM indicate superparamagnetic behaviour, which has also been observed in the temperature dependent Mössbauer results. The temperature dependence of hyperfine field is found to follow a similar dependence to saturation magnetization for bulk magnetite.

Thakur, M.; De, K.; Giri, S.; Si, S.; Kotal, A.; Mandal, T. K.

2006-10-01

182

Surface modification of superparamagnetic magnetite nanoparticles and their intracellular uptake  

Microsoft Academic Search

Superparamagnetic magnetite nanoparticles were surface-modified with\\u000a poly (ethylene glycol) (PEG) and folic acid, respectively, to improve\\u000a their intracellular uptake and ability to tat-get specific cells. PEG\\u000a and folic acid were successfully immobilized on the surfaces of\\u000a magnetite nanoparticles and characterized using fourier transform\\u000a infrared spectra. The nanoparticle internalization into mouse macrophage\\u000a (RAW 264.7) and human breast cancer (BT20) cells was

Y Zhang; Nathan Kohler; Miqin Zhang

2002-01-01

183

The Verwey transition in nanostructured magnetite produced by a combination of chimie douce and spark plasma sintering  

NASA Astrophysics Data System (ADS)

Magnetite nanoparticles about 10 nm sized were synthesized by the polyol method. Zero-field-cooled (ZFC)-FC measurements showed a blocking temperature ˜170 K and the absence of the Verwey transition. They were subsequently consolidated by spark plasma sintering at 750 °C for 15 min, leading to a high density (92% of the theoretical density), solid body, with grains in the 150 nm range. X-ray diffraction patterns exhibited a spinel single phase with cell parameters corresponding to the magnetite structure. Magnetic measurements showed a decrease of coercivity from 685 Oe (54.5 kA/m) at 118 K to 90 Oe (7.2 kA/m) at 139 K. ZFC measurements at 25 Oe presented a three-fold magnetization increase as temperature increased; a small transition between 116 and 117.5 K, followed by a larger one from 117.6 to 124 K. The first transition can be associated with a complex crystallographic transition and delocalization of Fe2+-Fe3+, while the second one can be attributed to spin reorientation due to the magnetocrystalline anisotropy constant (K1) change of sign as previously observed only in magnetite single crystals.

Gaudisson, T.; Vázquez-Victorio, G.; Bañobre-López, M.; Nowak, S.; Rivas, J.; Ammar, S.; Mazaleyrat, F.; Valenzuela, R.

2014-05-01

184

Magnetite-PLGA Microparticles for Oral Delivery of Insulin Jianjun Cheng,1  

E-print Network

Magnetite-PLGA Microparticles for Oral Delivery of Insulin Jianjun Cheng,1 Christopher H. Yim,1 School, Boston, MA 02115 ABSTRACT Magnetic responsive particles were designed for use in oral delivery at magnetite content 5 wt % or less. Mice were gavaged with 125 I-insulin-magnetite- PLGA microparticles

Cheng, Jianjun

185

Department of Earth and Mineral Engineering Spring 2011 Electromagnetically Enhanced Hydrocyclone for Magnetite Separation  

E-print Network

Hydrocyclone for Magnetite Separation during Coal Beneficiation Overview Consol Energy uses magnetite in a downstream process for reuse in the plant, as the price of magnetite is increasing to nearly $300/ton in several parametric studies. Approach The team visited the Robinson Run Plant in WV to analyze the current

Demirel, Melik C.

186

Pure and Applied Chemistry  

NSDL National Science Digital Library

Established in 1960, the journal Pure and Applied Chemistry is committed to publishing notable research papers arising from various international scientific events and projects that are sponsored by the International Union of Pure and Applied Chemistry (IUPAC). First-time visitors can view the "News" area to learn about the most recent work published in the journal, and then they may wish to move on to the embedded search engine displayed prominently on the homepage. Other sections on the site include "Editorial Board", "Notes For Authors", and "Publication Policy". Visitors with a deep and abiding interest in the journal may also wish to consult their RSS feeds, which include those related to the publication of new articles and reports from the IUPAC. Finally, the site also contains a drop down menu titled "PAC Archives" where visitors can browse the contents of each volume.

187

Pure anti-oestrogens.  

PubMed

Pure anti-oestrogens are a group of at least five new compounds which are able to antagonize the effects of oestrogen in all tissues and species studied. The mechanism by which the pure anti-oestrogens produce their effects remains in question, but all of them are competitive antagonists of the oestrogen receptors and, moreover, have been proposed to block the shuttling of oestrogen receptors into the cell nucleus. When studied in vitro, these compounds are able to block the oestrogen-stimulated growth of breast cancer cells. In animals, their ability to block the effects of oestrogen on breast, uterus, bone, cardiovascular system and other reproductive-associated tissues has been demonstrated. ICI 182780 has been used in preliminary clinical trials in women with advanced, tamoxifen-resistant breast cancer with promising results. Clinical trials with EM-800 are under way to assess the safety and tolerance and to obtain information on its efficacy in patients who have already been treated with tamoxifen. It seems reasonable to assume that pure anti-oestrogens will be a good alternative to tamoxifen in the treatment of breast cancer and also in some non-malignant gynaecological diseases. PMID:10874568

Hermenegildo, C; Cano, A

2000-01-01

188

Optimization of Magnetite Carrier Precipitation Process for Plutonium Waste Reduction  

Microsoft Academic Search

Transuranic (TRU) waste that is being generated at Argonne National Laboratory has a TRU activity ranging from 10 to 10 nCi\\/g with a wide variety of chemical compositions. Currently, the waste is stored in highly acidic solutions that must be neutralized for intermediate storage. A magnetite carrier precipitation process has been adapted to concentrate TRU isotopes in a noncorrosive solid

S. A. Slater; D. B. Chamberlain; S. A. Aase; B. D. Babcock; C. Conner; J. Sedlet; G. F. Vandegrift

1997-01-01

189

Benefaction studies on the Hasan Celebi magnetite deposit, Turkey  

USGS Publications Warehouse

Bench-scale and semicontinuous tests were performed on surface, trench, and diamond drill core samples from the Hasan Celebi low-grade magnetite deposit to determine the optimum benefication procedures utilizing wet magnetic separation techniques. Composite core samples typically contain about 27 percent recoverable magnetite and require crushing and grinding through 1 mm in size to insure satisfactory separation of the gangue from the magnetite. Regrinding and cleaning the magnetite concentrate to 80 percent minus 150-mesh is necessary to obtain an optimum of 66 percent iron. Semicontinuous pilot-plant testing with the wet magnetic drum using the recycled middling technique indicates that as much as 83 percent of the acid-soluble iron can be recovered into a concentrate containing 66 percent iron, with minimum deleterious elements. This represents 27 weight percent of the original ore. Further tests will continue when the Maden Tetkik ve Arama Enstitusu (MTA) receives 24 tons of bulk sample from an exploratory drift and cross-cut now being driven through a section of the major reserve area.

Pressler, Jean W.; Akar, Ali

1972-01-01

190

Magnetite and Carbonate Textures in ALH84001: Experimental Insights  

NASA Technical Reports Server (NTRS)

Synthetic siderite and synthetic siderite-magnesite carbonates were equilibrated with hematite, magnetite, and CO2 at elevated pressure and temperature. Comparisons are made to textures seen in the carbonate globules in ALH84001. Additional information is contained in the original extended abstract.

Koziol, Andrea M.

2001-01-01

191

Magnetite morphology and life on Mars Peter R. Buseck*  

E-print Network

Magnetite morphology and life on Mars Peter R. Buseck* , Rafal E. Dunin-Borkowski , Bertrand is inadequate to support the inference of former life on Mars. The startling report by McKay et al. (1) of evidence for former life on Mars has attracted major interest scientifically and with the general public

Dunin-Borkowski, Rafal E.

192

Magnetite-Loaded Polymeric Micelles as Ultrasensitive Magnetic-Resonance  

E-print Network

Magnetite-Loaded Polymeric Micelles as Ultrasensitive Magnetic-Resonance Probes** By Hua Ai* Polymeric micelles offer a powerful multifunctional plat- form for drug delivery and diagnostic imaging- tions, polymeric micelles have also received increasing atten- tion in diagnostic imaging applications

Gao, Jinming

193

Avian magnetite-based magnetoreception: a physiologist's perspective  

PubMed Central

It is now well established that animals use the Earth's magnetic field to perform long-distance migration and other navigational tasks. However, the transduction mechanisms that allow the conversion of magnetic field variations into an electric signal by specialized sensory cells remain largely unknown. Among the species that have been shown to sense Earth-strength magnetic fields, birds have been a model of choice since behavioural tests show that their direction-finding abilities are strongly influenced by magnetic fields. Magnetite, a ferromagnetic mineral, has been found in a wide range of organisms, from bacteria to vertebrates. In birds, both superparamagnetic (SPM) and single-domain magnetite have been found to be associated with the trigeminal nerve. Electrophysiological recordings from cells in the trigeminal ganglion have shown an increase in action potential firing in response to magnetic field changes. More recently, histological evidence has demonstrated the presence of SPM magnetite in the subcutis of the pigeon's upper beak. The aims of the present review are to review the evidence for a magnetite-based mechanism in birds and to introduce physiological concepts in order to refine the proposed models. PMID:20106875

Cadiou, Herve; McNaughton, Peter A.

2010-01-01

194

26 CURA REPORTER Hydrogen Generation Using Magnetite to Store  

E-print Network

26 CURA REPORTER Hydrogen Generation Using Magnetite to Store Energy from Alternative Sources by J. Woods Halley, Andy Schofield, and Bjorn Berntson D emand for alternative energy sources arises from foreign sources. The leading alternative energy sources, wind and solar, however, are intermittent

Levinson, David M.

195

Magnetite Nanoparticles Stabilized Under Physiological Conditions for Biomedical Application  

NASA Astrophysics Data System (ADS)

The biomedical application of water based magnetic fluids (MFs) is of great practical importance. Their colloidal stability under physiological conditions (blood pH ˜ 7.2-7.4 and salt concentration ˜0.15 M) and more in high magnetic field gradient is crucial. Magnetite or maghemite nanoparticles are used in general. In the present work, magnetite nanoparticles were stabilized with different compounds (citric acid (CA) and phosphate) and sodium oleate (NaO) as the most used surfactant in the stabilization of MFs. The adsorption and overcharging effect were quantified, and the enhancement in salt tolerance of stabilized systems was studied. Adsorption, electrophoretic mobility and dynamic light scattering (DLS) measurements were performed. The electrolyte tolerance was tested in coagulation kinetic measurements. Above the adsorption saturation, the nanoparticles are stabilized in a way of combined steric and electrostatic effects. The aim was to research these two important effects and demonstrate that none of them alone is enough. The phosphate was not able to stabilize the ferrofluid in spite of our expectation, but the other two additives proved to be effective stabilizing agents. The magnetite was well stabilized by the surface complexation of CA above pH ˜ 5, however, the salt tolerance of citrate stabilized MFs remained much below the concentration of physiological salt solution, and more the dissolution of magnetite nanocrystals was enhanced due to Fe-CA complexation in aqueous medium, which may cause problems in vivo. The oleate double layers were able to stabilize magnetite nanoparticles perfectly at pH ˜ 6 preventing particle aggregation effectively even in physiological salt solution.

Hajdãº, A.; Tombácz, E.; Illés, E.; Bica, D.; Vékás, L.

196

Magnetite Formation from Thermal Decomposition of Siderite: Implications for Inorganic Magnetite Formation in Martian Meteorite ALH84001  

NASA Technical Reports Server (NTRS)

A biogenic mechanism for formation of a subpopulation magnetite in Martian meteorite ALH84001 has been suggested [McKay et al., 1996; Thomas-Keprta, et al., 2000]. We are developing experimental evidence for an alternating working hypothesis, that the subpopulation was produced inorganically by the thermal decomposition of siderite [Golden et al., 2000].

Morris, RIchard V.

2002-01-01

197

Pressure effect on the low-temperature remanences of multidomain magnetite: Change in the Verwey transition temperature  

NASA Astrophysics Data System (ADS)

The Verwey transition of magnetite is the basic issues for the rock magnetism, since main magnetic mineral of terrestrial rocks is magnetite and its associates. One of the most important issues concerning the Verwey transition is the change in transition temperature (Tv) due to pressure, which is thought to improve our understanding of its electric and magnetic nature in relation to the phase diagram. Recently, the opposite pressure effects of the transition temperature were reported applying the different experimental method. Measuring the electrical resistivity of single crystalline samples, Môri et al. [2002] reported that Tv becomes lower with increasing pressure by 9 GPa. In contrast, Pasternak et al. [2003] reported from Mössbauer experiment that transition temperature becomes higher with increasing pressure by 30 GPa. Thus the change in transition temperature with pressure has been controversial, and nature of the Verwey transition is still unclear. The magnetic property measurements using low temperature cycle are a powerful tool for identifying the state of magnetic minerals. Carporzen and Gilder [2010] conducted the thermal demagnetization experiment of low-temperature remanences of magnetite, and observed an increase in Tv with increasing pretreated pressure. From this result, they suggested that the Verwey transition of magnetite have the potential of a geobarometer. Modern techniques of high-pressure experiments enable us to measure sample magnetizations under pressure [Gilder et al., 2002; Kodama and Nishioka, 2005; Sadykov et al., 2008]. In the present study, systematic experiments of low-temperature remanences have been conducted for powder samples of stoichiometric magnetite under pressure up to 0.7 GPa using the high-pressure cell specially designed for MPMS, which was made of CuBe and ZrO2 [Kodama and Nishioka, 2005]. Natural magnetite of large single crystals were crushed by hand and sieved in an ultrasonic bath to be ~50 ?m in size. For relaxation of internal stress, powder samples were annealed in vacuum at 700 C with carbon buffer for several hours. The magnetite powders were dispersed in the glass wool and it was then placed in a Teflon capsule, which was filled by a pressure transmitting fluid. The high-pressure cell was connected with the end of the sample rod of MPMS and measured in a regular manner. We precisely measured thermal demagnetization curves of low-temperature isothermal remanent magnetization imparted at 20 K after cooling in zero-field and remanence acquired by cooling in 2.5 T DC field. The magnetite samples showed decrease in Tv under high-pressure, although decompressed samples exhibited the increase in Tv. Negative Clapeyron slope of the transition boundary is calculated to be -2.5 K/GPa to -4.0 K/GPa, supporting the results obtained by recent electrical resistivity measurement [Môri et al., 2002] and magnetic susceptibility measurement [Wieche? et al., 2005]. Decompressed samples also showed similar results obtained by thermal demagnetization experiment of low-temperature remanences [Carporzen and Gilder, 2010].

Sato, M.; Yamamoto, Y.; Nishioka, T.; Kodama, K.; Mochizuki, N.; Tsunakawa, H.

2011-12-01

198

Identification of simultaneous U(VI) sorption complexes and U(IV) nanoprecipitates on the magnetite (111) surface  

SciTech Connect

Sequestration of uranium (U) by magnetite is a potentially important sink for U in natural and contaminated environments. However, molecular-scale controls which favor U(VI) uptake including both adsorption of U(VI) and reduction to U(VI) by magnetite remain poorly understood, in particular the role of U(VI)-CO3-Ca complexes in inhibiting U(VI) reduction. To investigate U uptake pathways on magnetite as a function of U(VI) aqueous speciation, we performed batch sorption experiments on (111) surfaces of natural single crystals under a range of solution conditions (pH 5 and 10; 0.1 mM U(VI); 1 mM NaCl; and with or without 0.5 mM CO3 and 0.1 mM Ca) and characterized surface-associated U using grazing incidence extended x-ray absorption fine structure spectroscopy (GI-EXAFS), grazing incidence x-ray diffraction (GI-XRD), and scanning electron microscopy (SEM). In the absence of both carbonate ([CO3]T, denoted here as CO3) and calcium (Ca), or in the presence of CO3 only, co-existing adsorption of U(VI) surface species and reduction to U(IV) occurs at both pH 5 and 10. In the presence of both CO3 and Ca, only adsorption of U(VI) occur. When U reduction occurs, nanoparticulate UO2 forms only within and adjacent to surface microtopographic features such as crystal boundaries and cracks. This result suggests that U reduction is limited to defect-rich surface regions. Further, at both pH 5 and 10 in the presence of both CO3 and Ca, U(VI)-CO3-Ca ternary surface species develop and U reduction is precluded. These findings extend the range of conditions under which U (VI)-CO3-Ca complexes inhibit U reduction.

Singer, David M.; Chatman, Shawn ME; Ilton, Eugene S.; Rosso, Kevin M.; Banfield, Jillian F.; Waychunas, Glenn

2012-04-03

199

Geochemistry of magnetite from porphyry Cu and skarn deposits in the southwestern United States  

NASA Astrophysics Data System (ADS)

A combination of petrographic observations, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and statistical data exploration was used in this study to determine compositional variations in hydrothermal and igneous magnetite from five porphyry Cu-Mo and skarn deposits in the southwestern United States, and igneous magnetite from the unmineralized, granodioritic Inner Zone Batholith, Japan. The most important overall discriminators for the minor and trace element chemistry of magnetite from the investigated porphyry and skarn deposits are Mg, Al, Ti, V, Mn, Co, Zn, and Ga—of these the elements with the highest variance for (I) igneous magnetite are Mg, Al, Ti, V, Mn, Zn, for (II) hydrothermal porphyry magnetite are Mg, Ti, V, Mn, Co, Zn, and for (III) hydrothermal skarn magnetite are Mg, Ti, Mn, Zn, and Ga. Nickel could only be detected at levels above the limit of reporting (LOR) in two igneous magnetites. Equally, Cr could only be detected in one igneous occurrence. Copper, As, Mo, Ag, Au, and Pb have been reported in magnetite by other authors but could not be detected at levels greater than their respective LORs in our samples. Comparison with the chemical signature of igneous magnetite from the barren Inner Zone Batholith, Japan, suggests that V, Mn, Co, and Ga concentrations are relatively depleted in magnetite from the porphyry and skarn deposits. Higher formation conditions in combination with distinct differences between melt and hydrothermal fluid compositions are reflected in Al, Ti, V, and Ga concentrations that are, on average, higher in igneous magnetite than in hydrothermal magnetite (including porphyry and skarn magnetite). Low Ti and V concentrations in combination with high Mn concentrations are characteristic features of magnetite from skarn deposits. High Mg concentrations (<1,000 ppm) are characteristic for magnetite from magnesian skarn and likely reflect extensive fluid/rock interaction. In porphyry deposits, hydrothermal magnetite from different vein types can be distinguished by varying Ti, V, Mn, and Zn contents. Titanium and V concentrations are highly variable among hydrothermal and igneous magnetites, but Ti concentrations above 3,560 ppm could only be detected in igneous magnetite, and V concentrations are on average lower in hydrothermal magnetite. The highest Ti concentrations are present in igneous magnetite from gabbro and monzonite. The lowest Ti concentrations were recorded in igneous magnetite from granodiorite and granodiorite breccia and largely overlap with Ti concentrations found in hydrothermal porphyry magnetite. Magnesium and Mn concentrations vary between magnetite from different skarn deposits but are generally greater than in hydrothermal magnetite from the porphyry deposits. High Mg, and low Ti and V concentrations characterize hydrothermal magnetite from magnesian skarn deposits and follow a trend that indicates that magnetite from skarn (calcic and magnesian) commonly has low Ti and V concentrations.

Nadoll, Patrick; Mauk, Jeffrey L.; Leveille, Richard A.; Koenig, Alan E.

2014-08-01

200

The cation diffusion facilitator proteins MamB and MamM of Magnetospirillum gryphiswaldense have distinct and complex functions, and are involved in magnetite biomineralization and magnetosome membrane assembly.  

PubMed

Magnetotactic bacteria form chains of intracellular membrane-enclosed, nanometre-sized magnetite crystals for navigation along the earth's magnetic field. The assembly of these prokaryotic organelles requires several specific polypeptides. Among the most abundant proteins associated with the magnetosome membrane of Magnetospirillum gryphiswaldense are MamB and MamM, which were implicated in magnetosomal iron transport because of their similarity to the cation diffusion facilitator family. Here we demonstrate that MamB and MamM are multifunctional proteins involved in several steps of magnetosome formation. Whereas both proteins were essential for magnetite biomineralization, only deletion of mamB resulted in loss of magnetosome membrane vesicles. MamB stability depended on the presence of MamM by formation of a heterodimer complex. In addition, MamB was found to interact with several other proteins including the PDZ1 domain of MamE. Whereas any genetic modification of MamB resulted in loss of function, site-specific mutagenesis within MamM lead to increased formation of polycrystalline magnetite particles. A single amino acid substitution within MamM resulted in crystals consisting of haematite, which coexisted with magnetite crystals. Together our data indicate that MamM and MamB have complex functions, and are involved in the control of different key steps of magnetosome formation, which are linked by their direct interaction. PMID:22007638

Uebe, René; Junge, Katja; Henn, Verena; Poxleitner, Gabriele; Katzmann, Emanuel; Plitzko, Jürgen M; Zarivach, Raz; Kasama, Takeshi; Wanner, Gerhard; Pósfai, Mihály; Böttger, Lars; Matzanke, Berthold; Schüler, Dirk

2011-11-01

201

Magnetic and transport properties of magnetite thin films  

Microsoft Academic Search

Magnetite (Fe3O4) films were prepared by DC reactive magnetron sputtering at various oxygen partial pressures with the ratio ? of oxygen to argon changing from 0.50:50 to 0.70:50 at room temperature, and then the Fe3O4 films were annealed at 480°C for 80min. The properties of the films were studied by X-ray diffraction, scanning electron microscopy, magnetic hysteresis loops, magnetoresistance (MR),

Guomin Zhang; Chongfei Fan; Liqing Pan; Fengping Wang; Ping Wu; Hong Qiu; Yousong Gu; Yue Zhang

2005-01-01

202

Magnetite from magnetotactic bacteria: Size distributions and twinning  

Microsoft Academic Search

We studied intracellular magnetite particles produced by several morphological types of magnetotactic bacteria including the spirillar (helical) freshwater species, Magnetospirillum magnetotacticum,and four incompletely characterized marine strains: MV-1, a curved rod- shaped bacterium; MC-1 and MC-2, two coccoid (spherical) microorganisms; and MV-4, a spirillum. Particle morphologies, size distributions, and structural features were examined using conventional and high-resolution transmission electron microscopy. The

BERTRAND DEVOUARD; MIHALY POSFAI; XIN HUA; DENNIS A. BAZYLINSKI; RICHARD B. FRANKEL; PETER R. BUSECK

1998-01-01

203

Hematite Versus Magnetite as the Signature for Planetary Magnetic Anomalies?  

NASA Technical Reports Server (NTRS)

Crustal magnetic anomalies are the result of adjacent geologic units having contrasting magnetization. This magnetization arises from induction and/or remanence. In a planetary context we now know that Mars has significant crustal magnetic anomalies due to remanent magnetization, while the Earth has some anomalies where remanence can be shown to be important. This picture, however, is less clear because of the nature and the magnitude of the geomagnetic field which is responsible for superimposed induced magnetization. Induced magnetization assumes a magnetite source, because of its much greater magnetic susceptibility when compared with other magnetic minerals. We investigated the TRM (thermoremanent magnetization) acquisition of hematite, in weak magnetic fields up to 1 mT, to determine if the remanent and induced magnetization of hematite could compete with magnetite. TRM acquisition curves of magnetite and hematite show that multi-domain hematite reaches TRM saturation (0.3 - 0.4 A sq m/kg) in fields as low as 100 microT. However, multi-domain magnetite reaches only a few percent of its TRM saturation in a field of 100 microT (0.02 - 0.06 A sq m/kg). These results suggest that a mineral such as hematite and, perhaps, other minerals with significant remanence and minor induced magnetization may play an important role in providing requisite magnetization contrast. Perhaps, and especially for the Mars case, we should reevaluate where hematite and other minerals, with efficient remanence acquisition, exist in significant concentration, allowing a more comprehensive explanation of Martian anomalies and better insight into the role of remanent magnetization in terrestrial crustal magnetic anomalies.

Kletetshka, Gunther; Taylor, Patrick T.; Wasilewski, Peter J.

1999-01-01

204

Low-temperature viscous magnetization of multidomain magnetite: evidence for disaccommodation contribution  

NASA Astrophysics Data System (ADS)

There are large gaps in our understanding of multidomain (MD) viscous behavior and MD remanence theory in general. For example, Dunlop and Ozdemir (2000) have demonstrated that multidomain (MD) viscous remanent magnetization (VRM) acquired at 200 C in crushed and sized natural crystals of magnetite persists on thermal demagnetization up to the Curie temperature, that is, there is a MD VRM component which is metastable. This goes against the classic MD theory of Noel which predicts that domain walls which move at low-temperatures in the earth's field, are easily re-organized by small increases in temperatures. That is, theory predicts that any VRM acquired by domain walls at 200 C will not persist to the Curie temperature. Recent viscosity experiments at temperatures above room-temperature have revealed that MD viscosity has a complex dependency on the magnetization state, dislocation density, disaccommodation, stoichiometry and thermal history. In particular the contribution of disaccommodation to viscosity has been difficult to isolate. Below room-temperature, disaccommodation displays a large increase, therefore by measuring viscosity below room temperature, then its contribution can be more readily assessed. Low-temperature viscous acquisition and decay measurements above and below the Verwey transition have been measured for a selection of natural and synthetic multidomain magnetite samples. A strong correlation between the viscosity spectra and published disaccommodation spectra was found, where disaccommodation reflects electron mobility. Assuming the viscosity is controlled by identical mechanisms as disaccommodation, the reduction in electron mobility below the Verwey transition is found to significantly increase viscous acquisition and decay rates over the time scales measured (1-3000 seconds). Although strongly affecting the viscosity, disaccommodation processes do not appear to control the rate of change of viscosity with time, i.e., the viscosity curvature. It is suggested that the curvature is controlled by the shape of relaxation-time distributions, which is approximately the same for all the magnetite samples studied. In addition, the acquisition and decay curvature parameters mirror each other when plotted as a function of temperature, inferring that at any given temperature the acquisition and decay processes are identical.

Muxworthy, A. R.; Williams, W.

2005-12-01

205

Magnetite morphology and micromagnetic modelling: Characteristics of magnetotactic bacteria.  

NASA Astrophysics Data System (ADS)

Bacteria have evolved a means of navigating using the earth's magnetic field by producing chains of magnetic particles that act like a compass needle. There are distinct magnetic characteristics of such chains that will optimise their efficiency as compass needles, and these will be examined in this talk. A three-dimensional finite element micromagnetic model will be used to examine different geometries of magnetite chains. The finite element approach allows modelling of much more complex magnetite geometries than can be achieved using finite difference modelling on regular grids. Furthermore, stable magnetic structures are obtained using a combination of both minimum energy and a dynamic solution of the Landau-Lifshitz-Gilbert equation. This achieves robust solutions which can follow the magnetization structure through the switching process at a constant external field. The algorithm is also capable of including thermal fluctuations in a much more rigorous way than can be obtained using minimum energy methods alone. The model will examine the role of grain geometry, magnetostatic interactions fields and domain states on the effectiveness of magnetite chains as compass needles. A comparison will be made between the most effective geometries predicted by micromagnetic modelling with those achieved by genetic optimisation in magnetosomes.

Williams, W.; Muxworthy, A.; Ridley, P.

2004-12-01

206

Biogenic Magnetite in Humans and New Magnetic Resonance Hazard Questions  

NASA Astrophysics Data System (ADS)

The widespread use of magnetic resonance (MR) techniques in clinical practice, and recent discovery of biogenic ferrimagnetic substances in human tissue, open new questions regarding health hazards and MR. Current studies are restricted just to the induction of Faraday currents and consequent thermal effects, or ‘inoffensive’ interaction with static magnetic field. We outlined that magnetic energies associated with interaction of ferrimagnetic particles and MR magnetic fields can be dangerous for sensitive tissues like the human brain is. To simulate the interaction mechanism we use our. ‘Cube’ model approach, which allows more realistic calculation of the particle's magnetic moments. Biogenic magnetite nanoparticles face during MR examination three principal fields: (i) main B0 field, (ii) gradient field, and (iii) B1 field. Interaction energy of biogenic magnetite nanoparticle with static magnetic field B0 exceeds the covalent bond energy 5 times for particles from 4 nm up to 150 nm. Translation energy in gradient field exceeds biochemical bond energy for particles bigger than 50 nm. Biochemical bond disruption and particle release to the tissue environment, in the presence of all MR fields, are the most critical points of this interaction. And together with relaxation processes after application of RF pulses, they make biogenic magnetite nanoparticles a potential MR health hazard issue.

Strbak, O.; Kopcansky, P.; Frollo, I.

2011-01-01

207

Bench-Scale Testing of the Micronized Magnetite Process  

SciTech Connect

A recent emphasis of the Department of Energy's (DOE's), Coal Preparation Program has been the development of high-efficiency technologies that offer near-term, low-cost improvements in the ability of coal preparation plants to address problems associated with coal fines. In 1992, three cost-shared contracts were awarded to industry, under the first High-Efficiency Preparation (HEP I) solicitation. All three projects involved bench-scale testing of various emerging technologies, at the Federal Energy Technology Center*s (FETC*s), Process Research Facility (PRF). The first HEP I project, completed in mid-1993, was conducted by Process Technology, Inc., with the objective of developing a computerized, on-line system for monitoring and controlling the operation of a column flotation circuit. The second HEP I project, completed in mid-1994, was conducted by a team led by Virginia Polytechnic Institute to test the Mozely Multi-Gravity Separator in combination with the Microcel Flotation Column, for improved removal of mineral matter and pyritic sulfur from fine coal. The last HEP I project, of which the findings are contained in this report, was conducted by Custom Coals Corporation to evaluate and advance a micronized-magnetite-based, fine-coal cycloning technology. The micronized-magnetite coal cleaning technology, also know as the Micro-Mag process, is based on widely used conventional dense-medium cyclone applications, in that it utilizes a finely ground magnetite/water suspension as a separating medium for cleaning fine coal, by density, in a cyclone. However, the micronized-magnetite cleaning technology differs from conventional systems in several ways: ! It utilizes significantly finer magnetite (about 5 to 10 micron mean particle size), as compared to normal mean particle sizes of 20 microns. ! It can effectively beneficiate coal particles down to 500M in size, as compared to the most advanced, existing conventional systems that are limited to a particle bottom size of about 28M - 100 M. ! Smaller diameter cyclones, 4 to 10 inches, are used to provide the higher G-force required to separate the finer feed coal. ! Cyclone feed pressures up to 10 times greater than those used in conventional cleaning systems are employed to enhance the separating forces.

Edward R. Torak; Peter J. Suardini

1997-11-01

208

The Character of Pure Spinors  

E-print Network

The character of holomorphic functions on the space of pure spinors in ten, eleven and twelve dimensions is calculated. From this character formula, we derive in a manifestly covariant way various central charges which appear in the pure spinor formalism for the superstring. We also derive in a simple way the zero momentum cohomology of the pure spinor BRST operator for the D=10 and D=11 superparticle.

Nathan Berkovits; Nikita Nekrasov

2005-03-08

209

Synthesis of magnetite octahedrons from iron powders through a mild hydrothermal method  

SciTech Connect

Magnetite (Fe{sub 3}O{sub 4}) octahedral particles were fabricated from iron powders through a simple one-step alkali-assisted hydrothermal process. The crystallinity, morphology, and structural features of the as-prepared magnetite particles were investigated using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The values of saturation magnetization (M {sub s}) and coercivity (H) of the magnetite octahedrons characterized on a vibrating sample magnetometer (VSM) are 89.81 emu/g and 70.6 Oe, respectively. The concentration of NaOH and the reaction temperature played a key role in the formation of the magnetite octahedrons.

Mao Baodong [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China); Kang Zhenhui [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China); Wang Enbo [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China)]. E-mail: wangenbo@public.cc.jl.cn; Lian Suoyuan [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China); Gao Lei [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China); Tian Chungui [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China); Wang Chunlei [Institute of Polyoxometalate Chemistry, Department of Chemistry, Northeast Normal University, Changchun, Jilin 130024 (China)

2006-12-14

210

Tuning of multiferroic orders correlated to oxygen stoichiometry in magnetite films  

NASA Astrophysics Data System (ADS)

Magnetite films are grown on Si(100) substrate using pulsed laser deposition technique. The deposition is performed at three fixed oxygen pressures of 0.4 × 10-6, 4.0 × 10-6, and 10 × 10-6 Torr keeping other conditions fixed. Raman and x-ray photoemission spectroscopies confirm formation of single magnetite phase for the first two pressures and a mixed phase composed of magnetite and hematite for the highest pressure. A trivial change in oxygen stoichiometry of magnetite is found crucial for the multiferroic orders at room temperature and below the charge ordering temperature. Possible mechanisms of multiferroic orders driven by change in oxygen stoichiometry are discussed.

Dey, K.; Ghosh, A.; Modak, P.; Indra, A.; Majumdar, S.; Giri, S.

2014-10-01

211

Synthesis and characterization of magnetite particles covered with ?-trietoxysilil-polydimethylsiloxane  

NASA Astrophysics Data System (ADS)

New silicon magnetite ferrofluids were prepared by dispersing siloxane-coated magnetite particles in polydimethylsiloxane with low or high molecular weights. Ferrofluids are stable colloidal dispersions of ultra fine covered magnetite particles, which may be selected for a specific application. We demonstrated new methods of stabilizing the magnetic particles by reacting the hydroxyl groups on the surface of magnetite particles with terminal ethoxy groups of polydimethylsiloxane, followed by their dispersion in silicon fluids. The new silicon ferrofluids were tested from the morphology, magnetic properties/losses, and rheological properties point of view.

Durdureanu-Angheluta, Anamaria; Pricop, Lucia; Stoica, Iuliana; Peptu, Catalina-Anisoara; Dascalu, Andrei; Marangoci, Narcisa; Doroftei, Florica; Chiriac, Horia; Pinteala, Mariana; Simionescu, Bogdan C.

2010-10-01

212

Biogenic magnetite: Authigenesis and diagenesis with changing redox conditions in Lake Greifen, Switzerland  

SciTech Connect

A mineralogic, chemical, and rock-magnetic investigation was conducted in Lake Greifen, a moderate-sulfate containing eutrophic lake, in order to assess iron mineral diagenesis in a sedimentary sequence deposited during different tropic states and varying redox conditions. The sedimentary sequence is composed of 0.25 m of eutrophic anoxic varved sediments underlain by transitional laminated marls, deposited as the lake changed from oxic to dysaerobic conditions, and then a basal unit of pre-eutrophic bioturbated marls. Grain size, morphology, and composition of magnetite observed by TEM suggest that single-domain biogenic magnetite is currently produced within the upper anoxic varved sediments. Similarly characterized fine-grained magnetites observed in the pre-eutrophic sediments indicate magnetite authigenesis prior to eutrophication. Low values of NRM, susceptibility, SIRM, and ARM in the anoxic varved sediments below the zone of magnetite production indicate the rapid destruction of magnetite. Iron speciation analyses, interstitial water results, and the ARM:SIRM ratio indicate that reductive dissolution is progressive. These results suggest that (1) rapid destruction of fine-grained magnetite occurs in high productivity, low-sulfate containing anoxic sediments following dissolution of ferric phases; and (2) magnetite preservation reflects redox conditions that, in Lake Greifen, are determined by productivity. These findings differ from marine reductive diagenetic models in which magnetite dissolution is considered insignificant, or slow, in the absence of high sulfide concentrations.

Hawthorne, T.B.; McKenzie, J.A. (Geology Inst., Zurich (Switzerland))

1991-03-01

213

Synthesis of chiral hybrid nanotubes of magnetite nanoparticles and conducting polymers  

NASA Astrophysics Data System (ADS)

New chiral magnetite nanoparticles with a polymerizable group produced polymer composite films on an electrode surface and the hybrid nanotubes of magnetite nanoparticles and polythiophene from their template-based electropolymerization.New chiral magnetite nanoparticles with a polymerizable group produced polymer composite films on an electrode surface and the hybrid nanotubes of magnetite nanoparticles and polythiophene from their template-based electropolymerization. Electronic supplementary information (ESI) available: Synthesis of a chiral stabilizer 1 and the spectral data. See DOI: 10.1039/c1nr11312g

Mitsumori, Masashi; Nakahodo, Tsukasa; Fujihara, Hisashi

2011-12-01

214

Reaction of U-VI with titanium-substituted magnetite: Influence of Ti on U-IV speciation  

SciTech Connect

Reduction of hexavalent uranium (UVI) to less soluble tetravalent uranium (UIV) through enzymatic or abiotic redox reactions has the potential to alter U mobility in subsurface environments. As a ubiquitous natural mineral, magnetite (Fe3O4) is of interest because of its ability to act as a rechargeable reductant for UVI. Natural magnetites are often impure with titanium, and structural Fe3+ replacement by TiIV yields a proportional increase in the relative Fe2+ content in the metal sublattice to maintain bulk charge neutrality. In the absence of oxidation, the Ti content sets the initial bulk Fe2+/Fe3+ ratio (R). Here, we demonstrate that Ti-doped magnetites (Fe3 xTixO4) reduce UVI to UIV. The UVI-Fe2+ redox reactivity was found to be controlled directly by R, but was otherwise independent of Ti content (xTi). However, in contrast to previous studies with pure magnetite where UVI was reduced to nanocrystalline uraninite (UO2), the presence of structural Ti (xTi = 0.25 0.53) results in the formation of UIV species that lack the bidentate U-O2-U bridges of uraninite. Extended x-ray absorption fine structure spectroscopic analysis indicated that the titanomagnetite-bound UIV phase has a novel UIV-Ti binding geometry, different from the coordination of UIV in the mineral brannerite (UIVTi2O6). The observed UIV-Ti coordination at a distance of 3.43 Å suggests a binuclear corner-sharing adsorption/incorporation UIV complex with the solid phase. Furthermore, we explored the effect of oxidation (decreasing R) and solids-to-solution ratio on the reduced UIV phase. The formation of the non-uraninite UIV-Ti phase appears to be controlled by availability of surface Ti sites, rather than R. Our work highlights a previously unrecognized role of Ti in the environmental chemistry of UIV and suggests that further work to characterize the long-term stability of UIV phases formed in the presence of Ti is warranted.

Latta, Drew; Pearce, Carolyn I.; Rosso, Kevin M.; Kemner, Kenneth M.; Boyanov, Maxim I.

2013-07-01

215

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles  

SciTech Connect

The crystal structure of magnetite nanoparticles may be transformed to maghemite by complete oxidation, but under many relevant conditions the oxidation is partial, creating a mixed-valence material with structural and electronic properties that are poorly characterized. We used X-ray diffraction, Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, and soft X-ray absorption and emission spectroscopy to characterize the products of oxidizing uncoated and oleic acid-coated magnetite nanoparticles in air. The oxidization of uncoated magnetite nanoparticles creates a material that is structurally and electronically indistinguishable from maghemite. By contrast, while oxidized oleic acid-coated nanoparticles are also structurally indistinguishable from maghemite, Fe L-edge spectroscopy revealed the presence of interior reduced iron sites even after a 2-year period. We used X-ray emission spectroscopy at the O K-edge to study the valence bands (VB) of the iron oxide nanoparticles, using resonant excitation to remove the contributions from oxygen atoms in the ligands and from low-energy excitations that obscured the VB edge. The bonding in all nanoparticles was typical of maghemite, with no detectable VB states introduced by the long-lived, reduced-iron sites in the oleic acid-coated sample. However, O K-edge absorption spectroscopy observed a 0.2 eV shift in the position of the lowest unoccupied states in the coated sample, indicating an increase in the semiconductor band gap relative to bulk stoichiometric maghemite that was also observed by optical absorption spectroscopy. The results show that the ferrous iron sites within ferric iron oxide nanoparticles coated by an organic ligand can persist under ambient conditions with no evidence of a distinct interior phase and can exert an effect on the global electronic and optical properties of the material. This phenomenon resembles the band gap enlargement caused by electron accumulation in the conduction band of TiO2.

Gilbert, Benjamin; Katz, Jordan E.; Denlinger, Jonathan D.; Yin, Yadong; Falcone, Roger; Waychunas, Glenn A.

2010-10-24

216

Magnetorheological behavior of magnetite covered clay particles in aqueous suspensions  

NASA Astrophysics Data System (ADS)

Montmorillonite clay particles coated with magnetite nanoparticles suspended in aqueous media behave as magnetorheological fluids with enhanced stability as compared to conventional ones. In this work, the study of the magnetorheological behavior of these suspensions of magnetite-clay composite particles has been carried out. For this purpose, both steady and dynamic rheological measurements were carried out in the absence and in the presence of external magnetic fields. In the first kind of experiments, the rheograms of the suspensions (shear stress versus shear rate plot) are analyzed as a function of the strength of the magnetic field applied. In the second one, oscillatory stresses are applied to the system, and the storage modulus is studied as a function of the external magnetic field. In the absence of magnetic field, the suspensions develop a weak yield stress due to the aggregation of the magnetite covered clay particles. In the presence of magnetic field, the yield stress is strongly dependent on the magnetic field strength inside the samples, demonstrating that the suspensions experience a magnetorheological effect, moderate when the magnetic field strength is weak and stronger for values of magnetic field higher than 150-200 kA/m. Actually, the most intriguing result is the change of the trend in the dependence of the yield stress with the field. This dependence is approximately linear with the field for strength values smaller than 150-200 kA/m. On the other hand, for higher values, the yield stress increases with magnetic field following a power law with exponent 4.5.The results are interpreted by means of a model that relates the structure of the particles in the suspensions to the magnetic field applied and using the interaction energy between particles calculated by the extended DLVO theory to include magnetic interaction.

Galindo-Gonzalez, C.; Lopez-Lopez, M. T.; Duran, J. D. G.

2012-08-01

217

HOW APPLIED MATHEMATICS BECAME PURE  

Microsoft Academic Search

This paper traces the evolution of thinking on how mathematics relates to the world— from the ancients, through the beginnings of mathematized science in Galileo and Newton, to the rise of pure mathematics in the nineteenth century. The goal is to better understand the role of mathematics in contemporary science. My goal here is to explore the relationship between pure

PENELOPE MADDY

2008-01-01

218

Detrapping and retrapping of free carriers in nominally pure single crystal GaP, GaAs and 4H-SiC semiconductors under light illumination at cryogenic temperatures  

E-print Network

We report on extremely sensitive measurements of changes in the microwave properties of high purity non-intentionally-doped single-crystal semiconductor samples of gallium phosphide, gallium arsenide and 4H-silicon carbide when illuminated with light of different wavelengths at cryogenic temperatures. Whispering gallery modes were excited in the semiconductors whilst they were cooled on the coldfinger of a single-stage cryocooler and their frequencies and Q-factors measured under light and dark conditions. With these materials, the whispering gallery mode technique is able to resolve changes of a few parts per million in the permittivity and the microwave losses as compared with those measured in darkness. A phenomenological model is proposed to explain the observed changes, which result not from direct valence to conduction band transitions but from detrapping and retrapping of carriers from impurity/defect sites with ionization energies that lay in the semiconductor band gap. Detrapping and retrapping relax...

Mouneyrac, David; Floch, Jean-Michel Le; Tobar, Michael E; Cros, Dominique; Krupka, Jerzy

2010-01-01

219

In situ formation of magnetite reactive barriers in soil for waste stabilization  

Microsoft Academic Search

Reactive barriers containing magnetite and methods for making magnetite reactive barriers in situ in soil for sequestering soil contaminants including actinides and heavy metals, organic materials, iodine and technetium are disclosed. According to one embodiment, a two-step reagent introduction into soil takes place. In the first step, free oxygen is removed from the soil by separately injecting into the soil

Robert C

2003-01-01

220

Effects of magnetite on high-frequency ground-penetrating radar Remke L. Van Dam1  

E-print Network

Effects of magnetite on high-frequency ground-penetrating radar Remke L. Van Dam1 , Jan M. H to understand the effects of magnetite for ground-penetrating radar (GPR) characterization of the shallow of ferrimagnetic material on ground-penetrating radar (GPR) signal performance. This interest has been driven

Borchers, Brian

221

Fabrication of 3D Tissue-Like Structure Ussing Magnetite Nanoparticles and Magnetic Force  

Microsoft Academic Search

Novel technologies to establish 3D tissue-like constructs are desired for tissue engineering. In the present study, magnetic force and magnetite nanoparticles were used to construct a layered mesenchymal stem cell (MSC) sheet, a layered cardiomyocyte sheet, and a layered fibroblast sheet involving capillaries. Magnetite cationic liposomes (MCLs) were taken up by the target cells. When a magnet was set under

A. Ito; K. Ino; K. Shimizu; H. Honda; M. Kamihira

2006-01-01

222

Low temperature oxidation mechanisms of nanocrystalline magnetite thin film  

SciTech Connect

A detailed investigation of the mechanisms related to the low temperature oxidation of nanocrystalline magnetite thin films into maghemite is presented. Despite strong differences in the functional properties of these two phases, structural similarities make it difficult to distinguish between them, and to quantify the oxidation process, particularly in the case of nanostructured polycrystalline layers. Contrary to the case of bulk materials or monocrystalline films and particles, the oxidation processes in nanocrystalline thin film have only scarcely been studied. In this work, structural and optical techniques, including X-ray diffraction (XRD), EXAFS/X-ray absorption near edge structure, FTIR, and Raman scattering, have been used to estimate the oxidation rate of magnetite. The overall oxidation reaction rates are discussed in the framework of two limiting cases corresponding to intra grain diffusion and to grain boundary diffusion. SIMS profiling and electrical measurements were also carried out to better assess the oxidation quantification in order to conclude on the predominant oxidation mechanisms in this heterogeneous material. We propose a qualitative model for the structure, in terms of insulating zone distribution, for partially oxidized films.

Bourgeois, F.; Gergaud, P.; Feuillet, G. [CEA, LETI, MINATEC Campus, 17 rue des Martyrs, 38054 GRENOBLE, Cedex 9 (France); Renevier, H.; Leclere, C. [Grenoble INP Minatec, LMGP, 3 parvis Louis Neel, 38016 Grenoble (France)

2013-01-07

223

Magnetic Core-Shell Morphology of Structurally Uniform Magnetite Nanoparticles  

NASA Astrophysics Data System (ADS)

Magnetic nanoscale structures are intriguing, in part, because of the exotic properties that emerge compared with bulk. The reduction of magnetic moment per atom in magnetite with decreasing nanoparticle size, for example, has been hypothesized to originate from surface disordering to anisotropy-induced radial canting, which are difficult to distinguish using conventional magnetometry. Small-angle neutron scattering (SANS) is ideal for probing structure, both chemical and magnetic, from nm to microns across an ensemble of particles. Adding polarization analysis (PASANS) of the neutron spin orientation before and after interaction with the scattering particles allows the magnetic structure to be separated into its vector components. Application of this novel technique to 9 nm magnetite nanoparticles closed-packed into face-centered crystallites with order of a micron revealed that at nominal saturation the missing magnetic moments unexpectedly interacted to form well-ordered shells 1.0 to 1.5 nm thick canted perpendicular to their ferrimagnetic cores between 160 to 320 K [1]. These shells additionally displayed intra-particle "cross-talk", selecting a common orientation over clusters of tens of nanoparticles. However, the shells disappeared when the external field was removed and interparticle magnetic interactions were negligible (300 K), confirming their magnetic origin. This work has been carried out in collaboration with Ryan Booth, Julie Borchers, Wangchun Chen, Liv Dedon, Thomas Gentile, Charles Hogg, Yumi Ijiri, Mark Laver, Sara Majetich, James Rhyne, and Shannon Watson.[4pt] [1] K.L. Krycka et al., Phys. Rev. Lett. 104, 207203 (2010)

Krycka, Kathryn

2011-03-01

224

Operators on Pure Spinor Spaces  

SciTech Connect

Pure spinors are relevant to the formulation of supersymmetric theories, and provide the only known way to maintain manifest maximal supersymmetry. The (non-linear) pure spinor constraint makes it nontrivial to find well defined operators on pure spinor wave functions. We discuss how such operators are defined. One application concerns covariant gauge fixing in maximally supersymmetric Yang-Mills (and string theory). Another issue is the construction of a manifestly supersymmetric action for 11-dimensional supergravity in terms of a scalar superfield. We describe some work in progress.

Cederwall, Martin [Fundamental Physics, Chalmers University of Technology, SE 412 96 Goteborg (Sweden)

2010-06-17

225

Magnetic Microstructure of Closely-Spaced Ferrimagnetic Crystals in Magnetotactic Bacteria  

E-print Network

Magnetic Microstructure of Closely-Spaced Ferrimagnetic Crystals in Magnetotactic Bacteria R. E of Cambridge, Pembroke Street, Cambridge CB2 3QZ, United Kingdom Magnetotactic bacteria migrate along of magnetite and greigite crystals in air-dried cells of magnetotactic bacteria, with sub-10-nm spatial

Dunin-Borkowski, Rafal E.

226

Department of Earth and Mineral Sciences Spring 2012 Magnetically Enhanced Hydro Cyclone for Magnetite Recovery During Coal  

E-print Network

for Magnetite Recovery During Coal Beneficiation Overview Magnetite is employed in a water slurry during the coal beneficiation process. The slurry has a density in between that of coal and that of unwanted material so that only coal floats and can be scraped off. Magnetite has tripled in price so recovering

Demirel, Melik C.

227

Some effects of grain shape and varying external magnetic fields on the magnetic structure of small grains of magnetite  

NASA Astrophysics Data System (ADS)

The change in the magnetic spin structure of simple domain configurations has been investigated as a function of grain size, shape and varying external magnetic fields at elevated temperatures. The results indicate that simplification of domain configuration occurs as grains become elongated, and as grain sizes increase from small pseudo-single-domain (PSD) to large PSD. In these cases domains become nearly lamellar, as suggested by earlier Bitter pattern observations on large PSD grains of magnetite, although the spins on the crystal surface in the theoretical models would not produce the Bitter lines representative of its body domain structure. Simulation of domain rotation under the influence of an external uniform magnetic field shows that the rotation mode depends upon the grain's temperature. At higher temperatures coherent rotation is favoured, whereas at lower temperatures the non-uniform domain structure prohibits coherent rotation and forces a wave-like transition via a lamellar three-domain stage.

Williams, Wyn; Dunlop, David J.

228

Identification of Simultaneous U(VI) Sorption Complexes and U(IV) Nanoprecipitates on the Magnetite (111) Surface  

SciTech Connect

Sequestration of uranium (U) by magnetite is a potentially important sink for U in natural and contaminated environments. However, molecular-scale controls that favor U(VI) uptake including both adsorption of U(VI) and reduction to U(IV) by magnetite remain poorly understood, in particular, the role of U(VI)-CO{sub 3}-Ca complexes in inhibiting U(VI) reduction. To investigate U uptake pathways on magnetite as a function of U(VI) aqueous speciation, we performed batch sorption experiments on (111) surfaces of natural single crystals under a range of solution conditions (pH 5 and 10; 0.1 mM U(VI); 1 mM NaNO{sub 3}; and with or without 0.5 mM CO{sub 3} and 0.1 mM Ca) and characterized surface-associated U using grazing incidence extended X-ray absorption fine structure spectroscopy (GI-EXAFS), grazing incidence X-ray diffraction (GI-XRD), and scanning electron microscopy (SEM). In the absence of both carbonate ([CO{sub 3}]T, denoted here as CO{sub 3}) and calcium (Ca), or in the presence of CO{sub 3} only, coexisting adsorption of U(VI) surface species and reduction to U(IV) occurs at both pH 5 and 10. In the presence of both Ca and CO{sub 3}, only U(VI) adsorption (VI) occurs. When U reduction occurs, nanoparticulate UO{sub 2} forms only within and adjacent to surface microtopographic features such as crystal boundaries and cracks. This result suggests that U reduction is limited to defect-rich surface regions. Further, at both pH 5 and 10 in the presence of both CO{sub 3} and Ca, U(VI)-CO{sub 3}-Ca ternary surface species develop and U reduction is inhibited. These findings extend the range of conditions under which U(VI)-CO{sub 3}-Ca complexes inhibit U reduction.

Singer, David M.; Chatman, Shawn M.; Ilton, Eugene S.; Rosso, Kevin M.; Banfield, Jillian F.; Waychunas, Glenn A. (UCB); (PNNL); (LBNL)

2012-05-10

229

Fascinating properties of multifunctional nanocomposites manganite/magnetite  

NASA Astrophysics Data System (ADS)

Multifunctional nanocomposites La0.6Sr0.4MnO3/Fe3O4 (LSMO/Fe3O4) were prepared with different weight ratios and characterized using X-ray diffraction (XRD), high resolution transmission microscope (HRTEM) and vibrating sample magnetometer (VSM). The parent nanomaterials (LSMO and Fe3O4) were prepared by citrate-nitrate auto combustion method and coprecipitation method respectively. Thermal dc magnetization curves were measured from room temperature up to 800 K for the nanocomposites. Vibrating sample magnetometer measurements reveal the enhancement of ferromagnetic properties with increasing magnetite ratio. Dielectric properties were reported and discussed for all investigated nanocomposites. The results recommend the use of such nanocomposites in memory devices and spintronics applications.

Ahmed, M. A.; El-Dek, S. I.; Abd Elazim, A.

2014-10-01

230

Magnetite-Magnesioferrite Phase Relations and Application to ALH84001  

NASA Technical Reports Server (NTRS)

Oxygen fugacity (fO2) is an important factor in planetary formation and evolution. Certain minerals or assemblages of minerals are stable only under certain fO2 conditions (at a constant T and P) and can be recorders of ambient fO2 during geologic processes. The best estimate of oxygen fugacity from mineral assemblages has implications, from large-scale models of planetary evolution to interpretation of single meteorites. For example, redox conditions are part of the discussion of the origin and history of shergottites, basaltic rocks in meteorites from Mars [1-4]. In addition oxygen fugacity may be an important factor to consider in the interpretation of the carbonate and magnetite assemblages seen in ALH84001 [5].

Koziol, Andrea M.

2003-01-01

231

Biofunctionalized magnetic hydrogel nanospheres of magnetite and ?-carrageenan  

NASA Astrophysics Data System (ADS)

Magnetic hydrogel ?-carrageenan nanospheres were successfully prepared via water-in-oil (w/o) microemulsions combined with thermally induced gelation of the polysaccharide. The size of the nanospheres (an average diameter (?) of about 50 and 75 nm) was modulated by varying the concentration of surfactant. The nanospheres contained superparamagnetic magnetite nanoparticles (?8 nm), previously prepared by co-precipitation within the biopolymer. Carboxyl groups, at a concentration of about 4 mmol g-1, were successfully grafted at the surface of these magnetic nanospheres via carboxymethylation of the ?-carrageenan. The carboxylated nanospheres were shown to be thermo-sensitive in the 37-45 °C temperature range, indicating their potential as thermally controlled delivery systems for drugs and/or magnetic particles at physiological temperatures. Finally, preliminary results have been obtained for IgG antibody conjugation of the carboxylated nanospheres and the potential of these systems for bio-applications is discussed.

Daniel-da-Silva, Ana L.; Fateixa, Sara; Guiomar, António J.; Costa, Benilde F. O.; Silva, Nuno J. O.; Trindade, Tito; Goodfellow, Brian J.; Gil, Ana M.

2009-09-01

232

Preparation and Characterization of Magnetite (Fe3O4) Nanoparticles  

NASA Astrophysics Data System (ADS)

Magnetite (Fe3O4) nanoparticles exhibit a superparamagnetic behavior when small. Our goal is to fabricate such particles and characterize their structural and magnetic properties as function of particle size and synthesis route. I will show the different fabrication methods we have utilized: one inorganic salt mixing method, an inorganic solution method, and lastly an organic solution method. The last approach should allow us to achieve monolayers of nanoparticles. I will present X-ray diffraction (XRD) results as well as Vibrating Sample Magnetometry (VSM) results, including Field Cooling (FC) versus Zero Field Cooling (ZFC) measurements to find the blocking temperature, or when the magnetic moments are frozen; to complement the magnetometry measurements. We will also include images of nanoparticles deposited on a wafer, recorded by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).

Trevino, Matea; Chesnel, Karine; Olsen, Betsy; Hancock, Jared; Harrison, Roger; Farrer, Jeffrey

2011-10-01

233

Highly sensitive magnetite nano clusters for MR cell imaging  

NASA Astrophysics Data System (ADS)

High sensitivity and suitable sizes are essential for magnetic iron oxide contrast agents for cell imaging. In this study, we have fabricated highly MR sensitive magnetite nanoclusters (MNCs) with tunable sizes. These clusters demonstrate high MR sensitivity. Especially, water suspensions of the MNCs with average size of 63 nm have transverse relaxivity as high as 630 s-1mM-1, which is among the most sensitive iron oxide contrast agents ever reported. Importantly, such MNCs have no adverse effects on cells (RAW 264.7). When used for cell imaging, they demonstrate much higher efficiency and sensitivity than those of SHU555A (Resovist), a commercially available contrast agent, both in vitro and in vivo, with detection limits of 3,000 and 10,000 labeled cells, respectively. The studied MNCs are sensitive for cell imaging and promising for MR cell tracking in clinics.

Li, Mingli; Gu, Hongchen; Zhang, Chunfu

2012-03-01

234

Polyol-based synthesis of hydrophilic magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

In this paper, we report direct synthesis of hydrophilic magnetite (Fe3O4) nanoparticles by thermolysis of iron (III) acetylacetonate in four different liquid polyols, e.g., di(ethylene glycol) (DEG), tri(ethylene glycol) (TEG), tetra(ethylene glycol) (TTEG), and poly(ethylene glycol) (PEG) and characterization of the properties relevant to their surface structure and colloidal stability in an aqueous medium. Fe3O4 nanoparticles prepared in the medium DEG or TEG can be well suspended in aqueous solution, while Fe3O4 nanoparticles prepared in TTEG or PEG agglomerate when these nanoparticles are prepared at their refluxing temperature. However, the aqueous stability of the PEG coated particles prepared at 220 °C are good due to the increase in amount of surface-adsorbed polyol coating (27 wt %) and associated positive charges (+30 mV).

Maity, Dipak; Chandrasekharan, Prashant; Si-Shen, Feng; Xue, Jun-Min; Ding, Jun

2010-05-01

235

Paleomagnetism of a new magnetite-rich carbonaceous chondrite  

NASA Astrophysics Data System (ADS)

Recent studies of CV carbonaceous chondrites have led to the conclusion that their parent body was partially differentiated and possessed a convecting core [1]. This possibility has been validated by modeling of asteroid accretion [2]. Were partially differentiated chondritic asteroid the rule or the exception? We will present petrographic and paleomagnetic data obtained on an unusual carbonaceous chondrite that we discovered in 2011 in the Atacama desert. This meteorite is a fully crusted stone with a total weight of 2.4 g. Although classification is still ongoing, its petrography, and oxygen isotopes (d18O=-1.74‰, d17O=-5.15‰, D17O=-4.25‰) point to a C2 ungrouped chondrite. Preliminary Raman spectroscopy data confirm that it has not suffered thermal metamorphism. Magnetic properties show that the meteorite contains ~13 wt.% of pseudo-single domain magnetite, making it a rock with remarkable paleomagnetic recorder. Indeed, this is the most magnetic magnetite-bearing chondrite ever described. Paleomagnetic measurements show that the meteorite possesses a uniform and unidirectional stable component of magnetization unblocked up to 120 mT during alternating field demagnetization. Paleointensity is estimated to a few ?T using normalization techniques [3]. The nature of the magnetizaiton, and the origin of the magnetizing field will be discussed. [1] Carporzen et al., 2011. Proc. National Acad. Sci., 108, 6386-6389. [2] Elkins-Tanton et al., 2011. Earth Planet . Sci. Lett., 305, 1-10. [3] Gattacceca and Rochette P. 2004 Earth Planet . Sci. Lett., 227, 377-393.

Gattacceca, J.; Rochette, P.; Gounelle, M.; Bonal, L.; Weiss, B. P.; Sonzogni, C.

2012-12-01

236

Anaerobic production of magnetite by a dissimilatory iron-reducing microorganism  

USGS Publications Warehouse

The potential contribution of microbial metabolism to the magnetization of sediments has only recently been recognized. In the presence of oxygen, magnetotactic bacteria can form intracellular chains of magnetite while using oxygen or nitrate as the terminal electron acceptor for metabolism1. The production of ultrafine-grained magnetite by magnetotactic bacteria in surficial aerobic sediments may contribute significantly to the natural remanent magnetism of sediments2-4. However, recent studies on iron reduction in anaerobic sediments suggested that bacteria can also generate magnetite in the absence of oxygen5. We report here on a sediment organism, designated GS-15, which produces copious quantities of ultrafine-grained magnetite under anaerobic conditions. GS-15 is not magnetotactic, but reduces amorphic ferric oxide to extracellular magnetite during the reduction of ferric iron as the terminal electron acceptor for organic matter oxidation. This novel metabolism may be the mechanism for the formation of ultrafine-grained magnetite in anaerobic sediments, and couldaccount for the accumulation of magnetite in ancient iron formations and hydrocarbon deposits. ?? 1987 Nature Publishing Group.

Lovley, D.R.; Stolz, J.F.; Nord, G.L., Jr.; Phillips, E.J.P.

1987-01-01

237

Domain size, closure domains, and the importance of magnetostriction in magnetite  

NASA Astrophysics Data System (ADS)

Previous micromagnetic calculations invoking magnetostatic, exchange and crystalline anisotropy energies predict about an order of magnitude more domains in magnetite than have experimentally been observed. Domains observed on magnetite by the magneto-optic Kerr effect are of similar size as previously observed ones by the Bitter technique. Simple but quite accurate domain calculations show that for rectangular parallelepipeds of magnetite it is the closure-four domain configuration that should be of lowest energy for all multidomain grain sizes unless magnetostrictive energies are considered. For the observed domain pattern it is shown that the domains themselves must carry significant magnetoelastic energies.

Worm, H.-U.; Ryan, P. J.; Banerjee, S. K.

1991-01-01

238

From supergeometry to pure spinors  

E-print Network

In this talk, we review how the superspace formulation of maximally supersymmetric field theories (including supergravity) naturally leads to introduction of pure spinors and pure spinor superfields, and why the formalism provides off-shell formulations. This approach to pure spinor superfields thus stresses field-theoretic aspects rather than the first-quantised ones normally used e.g. in superstring theory. We discuss how the BRST operator arises and the principles behind constructions of actions, as well as the general Batalin-Vilkovisky framework. D=11 supergravity and its recently constructed supersymmetric action are taken as an example throughout the talk. This is the written version of a lecture given at the 6th Mathematical Physics Meeting, Belgrade, September 2010.

Martin Cederwall

2010-12-15

239

Electric conductivity of doped triglycine sulphate crystals  

NASA Astrophysics Data System (ADS)

Attention is given to the conductivity values of both pure and doped triglycine sulfate (TGS) crystals at room and transition temperatures. TGS doped with such organic and inorganic dopants as nitroanilines, serine, and leucine, exhibit an increase in DC conductivity, while those doped with L-alanine show a decrease in conductivity by comparison with a pure TGS crystal.

Batra, A. K.; Mathur, S. C.

1985-06-01

240

Crystal Notes The Crystal  

E-print Network

Crystal Notes The Crystal The crystal is defined as an ordered set of atoms (molecules) arranged. Ordered crystals exist because in their formation they must disorder their surroundings more than they are ordered. The key to growing a crystal is to cause in the disorder of the surroundings to be more than

Meagher, Mary

241

76 FR 69284 - Pure Magnesium From China  

Federal Register 2010, 2011, 2012, 2013

...731-TA-696 (Third Review)] Pure Magnesium From China Determination On the basis...of the antidumping duty order on pure magnesium from China would be likely to lead to...4274 (October 2011), entitled Pure Magnesium from China: Investigation No....

2011-11-08

242

Pure Spinors for General Backgrounds  

E-print Network

We show the equivalence of the different types of pure spinor constraints geometrically derived from the Free Differential Algebras of N=2 d=10 supergravities. Firstly, we compute the general solutions of these constraints, using both a G_2 and an SO(8) covariant decomposition of the 10d chiral spinors. Secondly, we verify that the number of independent degrees of freedom is equal to that implied by the Poincare' pure spinor constraints so-far used for superstrings, namely twenty two. Thirdly, we show the equivalence between the FDA type IIA/B constraints among each other and with the Poincare' ones.

Pietro Fre'; Pietro Antonio Grassi

2008-03-12

243

Negativity of random pure states  

SciTech Connect

This paper deals with the entanglement, as quantified by the negativity, of pure quantum states chosen at random from the invariant Haar measure. We show that it is a constant (0.72037) multiple of the maximum possible entanglement. In line with the results based on the concentration of measure, we find evidence that the convergence to the final value is exponentially fast. We compare the analytically calculated mean and standard deviation with those calculated numerically for pure states generated via pseudorandom unitary matrices proposed by Emerson et al. [Science 302, 2098 (2003)]. Finally, we draw some conclusions about the geometry of quantum states based on our result.

Datta, Animesh [Institute for Mathematical Sciences, 53 Prince's Gate, Imperial College, London, SW7 2PG (United Kingdom); QOLS, Blackett Laboratory, Imperial College London, Prince Consort Road, SW7 2BW (United Kingdom)

2010-05-15

244

Thermophysical Properties of Papaya Puree  

Microsoft Academic Search

The effects of soluble solids content and temperature on thermal properties of papaya puree were studied. Density and specific heat were measured using pycnometer and differential scanning calorimeter (DSC), respectively while thermal conductivity was measured using line heat source probe. Thermal diffusivity was then calculated from the experimental results of the specific heat, thermal conductivity and density. Thermal properties of

Ampawan Tansakul; Hataichanok Kantrong; Rattapon Saengrayup; Panthila Sura

2011-01-01

245

Thermophysical Properties of Papaya Puree  

Microsoft Academic Search

The effects of soluble solids content and temperature on thermal properties of papaya puree were studied. Density and specific heat were measured using a pycnometer and differential scanning calorimeter, respectively, while thermal conductivity was measured using a line heat source probe. Thermal diffusivity was then calculated from the experimental results of the specific heat, thermal conductivity, and density. Thermal properties

Ampawan Tansakul; Hataichanok Kantrong; Rattapon Saengrayup; Panthila Sura

2012-01-01

246

Photo-Fenton oxidation of phenol with magnetite as iron source Marco Minella,1  

E-print Network

easy magnetic separation makes magnetite a promising catalyst in wastewater treatment applications of recalcitrant compounds in water and wastewater. Reaction (1) is the fast step of the Fenton process, while

247

Carbonate and Magnetite Parageneses as Monitors of Carbon Dioxide and Oxygen Fugacity  

NASA Technical Reports Server (NTRS)

The stable coexistence of siderite with other key minerals, such as graphite or magnetite, is only possible under certain restrictive conditions of CO2 and O2 fugacity. Carbonate parageneses in Mars meteorite ALH 84001 are analyzed.

Koziol, Andrea M.

2000-01-01

248

Synthesis of magnetite/amphiphilic polymer composite nanoparticles as potential theragnostic agents.  

PubMed

This study describes the synthesis of magnetite/amphiphilic polymer composite nanoparticles that can be potentially used simultaneously for cancer diagnosis and therapy. The synthesis method was a one-shot process wherein magnetite nanoparticles were mixed with core-crosslinked amphiphilic polymer (CCAP) nanoparticles, prepared using a copolymer of a urethane acrylate nonionomer (UAN) and a urethane acrylate anionomer (UAA). The CCAP nanoparticles had a hydrophobic core and a hydrophilic exterior with both PEG segments and carboxylic acid groups, wherein the magnetite nanoparticles were coordinated and stabilized. According to DLS data, the ratio of UAN to UAA and the ratio of magnetite to polymer are keys to controlling the size and thus, the stability of the composite nanoparticles. The magnetic measurement indicated that the composite nanoparticles had superparamagnetic properties and high saturation magnetization. The preliminary magnetic resonance imaging showed that the particles produced an enhanced image even when their concentration was as low as 80 microg/ml. PMID:22966681

Wainaina, James; Kim, Na Hae; Kim, Juyoung; Jin, Moonsoo; Park, Soo Haeng

2012-07-01

249

Magnetite-supported sulfonic acid: a retrievable nanocatalyst for the Ritter reaction and multicomponent reactions  

EPA Science Inventory

Magnetite-sulfonic acid (NanocatFe-OSO3H), prepared by wet-impregnation method, serves as a magnetically retrievable sustainable catalyst for the Ritter reaction which can be used in several reaction cycles without any loss of activity....

250

Controllable In-Situ Synthesis of Magnetite Coated Silica-Core Water-Dispersible Hybrid Nanomaterials  

PubMed Central

Magnetite nanoparticle coated silica (Fe3O4@SiO2) hybrid nanomaterials hold an important position in the fields of cell imaging and drug delivery. Here we report a large scale synthetic procedure that allows attachment of magnetite nanoparticles onto a silica surface in-situ. Many different silica nanomaterials such as Stöber silica nanospheres, mesoporous silica nanoparticles, and hollow silica nanotube have been coated with a high density layer of water-dispersible magnetite nanoparticles. The size and attachment efficiency of the magnetite nanoparticle can be well tuned by adjusting the precursor concentration and reflux time. The functionalization of Fe3O4@SiO2 nanoparticles with dye molecules and biocompatible polymers impart optical imaging modality and good colloidal stability in either buffer solution or serum. The functionalized materials also exhibited strong potential as negative contrast agents in T2 weighted magnetic resonance imaging. PMID:23889037

Qu, Haiou; Tong, Sheng; Song, Kejing; Ma, Hui; Bao, Gang; Pincus, Seth; Zhou, Weilie; O'Connor, Charles

2013-01-01

251

Nanoengineering of methylene blue loaded silica encapsulated magnetite nanospheres and nanocapsules for photodynamic therapy  

Microsoft Academic Search

Core–shell nanostructures have emerged as an important class of functional materials with potential applications in diverse\\u000a fields, especially in health sciences. In this article, nanoengineering of novel magnetic colloidal dispersion containing\\u000a surface modifiable silica with a core of single domain magnetite nanoparticles loaded with photosensitizer (PS) drug “Methylene\\u000a blue” (MB) has been described. Magnetite core is produced by the well-established

Nidhi Andhariya; Bhupendra Chudasama; R. V. Mehta; R. V. Upadhyay

252

Sulfur isotopic composition of the magnetite-series and ilmenite-series granitoids in Japan  

Microsoft Academic Search

Sulfur isotopic composition has been measured on 30 granitoids and 11 gabbroids from the Cretaceous and Tertiary granitic terranes of Japan. The two series of granitoids, the magnetite-series and ilmenite-series, defined by Ishihara (1977), show two specific isotope trends. The magnetite-series granioids all have positive d (su34)S (CDT) values from +1 to +9‰, while the ilmenite-series rocks are dominated by

Akira Sasaki; Shunso Ishihara

1979-01-01

253

Magnetite polymer nanospheres loaded by Indomethacin for anti-inflammatory therapy  

NASA Astrophysics Data System (ADS)

This contribution is devoted to preparation and characterization of magnetite nanoparticles loaded by Indomethacin (IND) as anti-inflammatory drug suitable for magnetic drug targeting. The poorly water-soluble drug IND was successfully encapsulated in polylactic acid (PLA) magnetic nanospheres (NPs) by nanoprecipitation method. The evidence of successful entrapment of IND was confirmed by FTIR and spectrophotometric measurements. The prepared magnetite-PLA-IND NPs shown the response on external magnetic field and so availability for magnetic drug targeting.

Timko, Milan; Koneracká, Martina; Tomas?ovi?ová, Natália; Kop?anský, Peter; Závis?ová, Vlasta

2006-05-01

254

Effects of the unique shape of submicron magnetite hollow spheres on magnetic properties and domain states  

Microsoft Academic Search

Submicron-scale magnetite (Fe3O4) hollow spheres were prepared by a template method using polystyrene beads. The obtained particles were very uniform in size with a diameter of 650±20nm and a shell thickness of 40nm . The temperature dependence of the zero-field cooled magnetizations indicated a broad anomaly at around 110K that was ascribable to the Verwey transition, while the magnetite nanoparticles

Quan-Lin Ye; Yasuharu Kozuka; Hirofumi Yoshikawa; Kunio Awaga; Shunji Bandow; Sumio Iijima

2007-01-01

255

Effect of the swelling degree on the formation of magnetite nanoparticles in hydrogels  

Microsoft Academic Search

Composites containing magnetite nanoparticles in poly(acrylamide-co-hydroxyethylacrylate) cross-linked using poly-ethylene–glycol-diacrylate were prepared and characterized. The magnetite was synthesized in situ in the polymer network by treatment with a water solution of Fe (II) and Fe (III). The salts were then coprecipitated by exposing the swollen gels to ammonia vapors and the obtained magnetic gels dried. The ratio acrylamide (AM)\\/hydroxyethylacrylate (HEA) was

Aldo Priola; Anna Di Gianni; Roberta Bongiovanni; Sergey G. Starodubtsev; Sergey S. Abramchuck; Sergey N. Polyakov; Vladimir V. Volkov; Eleonora V. Schtykova; Kirill A. Dembo

2010-01-01

256

Construction of Multi-layered Cell Sheet Using Magnetite Nanoparticles and Magnetic Force  

Microsoft Academic Search

\\u000a Novel technologies to establish 3D tissue-like constructs are desired for tissue engineering. In the present study, magnetic\\u000a force and magnetite nanoparticles were used to construct a layered mesenchymal stem cell (MSC) sheet, a layered cardiomyocyte\\u000a sheet, and a layered fibroblast sheet involving capillaries. Magnetite cationic liposomes (MCLs), which have a positive surface\\u000a charge, were taken up by the target cells.

Akira Ito; Hiroyuki Honda; Masamichi Kamihira

257

Using Magnetites to Remediate Heavy Metal Wastewaters from Acid-Mine Drainage  

Microsoft Academic Search

\\u000a The remediation of heavy metal wastewaters using magnetites, also known as ferrites, has been an area of investigation for\\u000a many years. Early investigators used a synthetic procedure for the production of magnetites at 70 °C. Although quite effective,\\u000a as demonstrated by remediation of small waste streams from universities in Japan, this method is too energy intensive for\\u000a application to large

M. D. Johnson; R. Wingo; M. Valdez

258

Transformation of Hematite into Magnetite During Dissimilatory Iron Reduction—Conditions and Mechanisms  

Microsoft Academic Search

Magnetite formation during the reduction of nanoparticulate hematite by Shewanella putrefaciens 200R is investigated in media of variable composition, at circumneutral pH and with lactate as electron donor. The relative rates of production of dissolved Fe(II) and Fe(III), aqueous speciation, plus chemical gradients control whether or not magnetite forms in the experiments. High bicarbonate concentrations result in the precipitation of

T. Behrends; P. Van Cappellen

2007-01-01

259

Effects of pH and anions on the sorption of selenium ions onto magnetite.  

PubMed

This study analyzes the influence of carbonate and silicate, which are generally abundant in granitic groundwater, on the sorption of selenium ions onto magnetite in order to understand the behaviors of selenium in a radioactive waste repository. Selenite was sorbed onto magnetite very well below pH 10, but silicate and carbonate hindered the sorption of selenite onto magnetite. On the other hand, little selenate was sorbed onto magnetite in neutral and weak alkaline solutions of 0.02 M NaNO(3) or NaClO(4), matching the ionic strength in a granitic groundwater, even though silicate or carbonate was not contained in the solutions. The surface complexation constants between selenite and magnetite were obtained by using a geochemical program, FITEQL 4.0, from the experimental data, and the formation of an inner-sphere surface complex such as =FeOSeO(2)(-) was suggested for the sorption of selenite onto magnetite from the diffuse double layer model calculation. PMID:22115431

Kim, Seung Soo; Min, Je Ho; Lee, Jae Kwang; Baik, Min Hoon; Choi, Jong-Won; Shin, Hyung Seon

2012-02-01

260

Optimizing Magnetite Nanoparticles for Mass Sensitivity in Magnetic Particle Imaging  

SciTech Connect

Purpose: Magnetic particle imaging (MPI), using magnetite nanoparticles (MNPs) as tracer material, shows great promise as a platform for fast tomographic imaging. To date, the magnetic properties of MNPs used in imaging have not been optimized. As nanoparticle magnetism shows strong size dependence, we explore how varying MNP size impacts imaging performance in order to determine optimal MNP characteristics for MPI at any driving field frequency, ?. Methods: Monodisperse MNPs of varying size were synthesized and their magnetic properties characterized. Their MPI response was measured experimentally, at an arbitrarily chosen ? = 250 kHz, using a custom-built MPI transceiver designed to detect the third harmonic of MNP magnetization. Results were interpreted using a model of dynamic MNP magnetization that is based on the Langevin theory of superparamagnetism and accounts for sample size distribution, and size-dependent magnetic relaxation. Results: Our experimental results show clear variation in the MPI signal intensity as a function of MNP size that is in good agreement with modeled results. A maxima in the plot of MPI signal vs. MNP size indicates there is a particular size that is optimal for the chosen frequency of 250 kHz. Conclusions: For MPI at any chosen frequency, there will exist a characteristic particle size that generates maximum signal amplitude. We illustrate this at 250 kHz with particles of 15 nm core diameter.

Ferguson, R. Matthew; Minard, Kevin R.; Khandhar, Amit P.; Krishnan, Kannan M.

2011-03-01

261

IDENTIFICATION OF MAGNETITE IN B-TYPE ASTEROIDS  

SciTech Connect

Spectrally blue (B-type) asteroids are rare, with the second discovered asteroid, Pallas, being the largest and most famous example. We conducted a focused, infrared spectroscopic survey of B-type asteroids to search for water-related features in these objects. Our results show that the negative optical spectral slope of some B-type asteroids is due to the presence of a broad absorption band centered near 1.0 {mu}m. The 1 {mu}m band can be matched in position and shape using magnetite (Fe{sub 3}O{sub 4}), which is an important indicator of past aqueous alteration in the parent body. Furthermore, our observations of B-type asteroid (335) Roberta in the 3 {mu}m region reveal an absorption feature centered at 2.9 {mu}m, which is consistent with the absorption due to phyllosilicates (another hydration product) observed in CI chondrites. The new observations suggest that at least some B-type asteroids are likely to have incorporated significant amounts of water ice and to have experienced intensive aqueous alteration.

Yang Bin [Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States); Jewitt, David, E-mail: yangbin@ifa.hawaii.ed, E-mail: jewitt@ucla.ed [Department of Earth and Space Sciences, Institute for Geophysics and Planetary Physics and Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095 (United States)

2010-09-15

262

Separable operations on pure states  

NASA Astrophysics Data System (ADS)

We show that the possible ensembles produced when a separable operation acts on a single pure bipartite entangled state are completely characterized by a majorization condition, a collection of inequalities for Schmidt coefficients, which is identical to that already known for the particular case of local operations and classical communication (LOCC). As a consequence, various known results for LOCC, including some involving monotonicity of entanglement, can be extended to the class of all separable operations.

Gheorghiu, Vlad; Griffiths, Robert B.

2008-08-01

263

PURE RED-CELL APLASIA \\  

Microsoft Academic Search

Starting in 1998, the number of pure red-cell aplasia (PRCA) cases in patients treated with recombinant human erythropoietin (rHuEPO) increased dramatically. Most cases were observed in patients treated with epoetin alfa pro- duced outside the United States. The peak was observed in 2002; since then, the PRCA incidence has declined. Many factors are likely to have contributed to this up-

Francesco Locatelli; Lucia Del Vecchio; Pietro Pozzoni

264

The Pure Products of America  

Microsoft Academic Search

The Pure Products of America is a story collection based in Omaha, Nebraska, that primarily deals with issues of PTSD, familial relationships, and what it means to be Korean-American in Omaha.\\u000aThe stories cover various points of view as well as modes of storytelling. Three of the pieces are slants on monologues, while the remaining three are told in a

Gene Kwak

2011-01-01

265

Magnetite-sulfide chondrules and nodules in CK carbonaceous chondrites - Implications for the timing of CK oxidation  

NASA Astrophysics Data System (ADS)

CK carbonaceous chondrites contain rare (about 0.1 vol pct) magnetite-sulfide chondrules that range from about 240 to 500 microns in apparent diameter and have ellipsoidal to spheroidal morphologies, granular textures, and concentric layering. They resemble the magnetite-sulfide nodules occurring inside mafic silicate chondrules in CK chondrites. It seems likely that the magnetite-sulfide chondrules constitute the subset of magnetite-sulfide nodules that escaped as immiscible droplets from their molten silicate chondrule hosts during chondrule formation. The intactness of the magnetite-sulfide chondrules and nodules implies that oxidation of CK metal occurred before agglomeration. Hence, the pervasive silicate darkening of CK chondrites was caused by the shock mobilization of magnetite and sulfide, not metallic Fe-Ni and sulfide as in shock-darkened ordinary chondrites.

Rubin, A. E.

1993-03-01

266

Spectral and other physicochemical properties of submicron powders of hematite (alpha-Fe2O3), maghemite (gamma-Fe2O3), magnetite (Fe3O4), goethite (alpha-FeOOH), and lepidocrocite (gamma-FeOOH).  

PubMed

Spectral and other physicochemical properties were determined for a suite of submicron powders of hematite (alpha-Fe2O3), maghemite (gamma-Fe2O3), magnetite (Fe3O4), goethite (alpha-FeOOH), and lepidocrocite (gamma-FeOOH). The spectral reflectivity measurements were made between 0.35 and 2.20 micrograms over the temperature interval between about -110 degrees and 20 degrees C. Other physicochemical properties determined were mean particle diameter, particle shape, chemical composition, crystallographic phase, magnetic properties, and Mossbauer properties. Only the magnetite powders have significant departures from the stoichiometric phase; they are actually cation-deficient magnetites having down to about 18.0 wt % FeO as compared with 31.0 wt % FeO for stoichiometric magnetite. A structured absorption edge due to crystal field transitions and extending from weak absorption in the near-IR to intense absorption in the near-UV is characteristic of the ferric oxides and oxyhydroxides and is responsible for their intense color. Particularly for hematite, the number and position of the spectral features are consistent with significant splitting of the degenerate cubic levels by noncubic components of the crystal field. The position of the crystal-field band at lowest energy, assigned to the envelope of the components of the split cubic 4T1 level, is near 0.86, 0.91, 0.92, and 0.98 microgram at room temperature for hematite, goethite, maghemite, and lepidocrocite, respectively. Comparison with Mossbauer data suggests covalent character increases sequentially through the aforementioned series. The positions of the spectra features are relatively independent of temperature down to about -110 degrees C. The maximum shifts observed were on the order of about 0.02 microgram shortward for the ferric oxyhydroxides. Variations in the magnitude of the reflectivity of the hematite powders as a function of mean particle diameter are consistent with scattering theory. The absorption strength of the crystal-field bands increases with increasing mean particle diameter over the range 0.1-0.8 micrometer; visually this corresponds to a change in color from orange to deep purple. The position of the split cubic 4T1 band shifts longward by about 0.02 micrometer with decreasing mean particle diameter over the same range; this trend is consistent with wavelength-dependent scattering. The cation-deficient magnetite powders are very strong absorbers throughout the near-UV, visible and near-IR; their spectral properties are independent of temperature between about -110 and 20 degrees C. PMID:11542003

Morris, R V; Lauer, H V; Lawson, C A; Gibson, E K; Nace, G A; Stewart, C

1985-03-10

267

The synthesis and characterization of poly(?-glutamic acid)-coated magnetite nanoparticles and their effects on antibacterial activity and cytotoxicity.  

PubMed

Magnetite nanoparticles (MNPs) modified with sodium and calcium salts of poly(?-glutamic acid) (NaPGA and CaPGA) were synthesized by the coprecipitation method, followed by characterization and evaluation of their antibacterial and cytotoxic effects. Superparamagnetic MNPs are particularly attractive for magnetic driving as well as bacterial biofilm and cell targeting in in vivo applications. Characterization of synthesized MNPs by the Fourier transform infrared spectra and magnetization curves confirmed the PGA coating on MNPs. The mean diameter of NaPGA- and CaPGA-coated MNPs as determined by transmission electron microscopy was 11.8 and 14 nm, respectively, while the x-ray diffraction pattern revealed the as-synthesized MNPs to be pure magnetite. Based on agar dilution assay, both NaPGA- and CaPGA-coated MNPs showed a lower minimum inhibitory concentration in Salmonella enteritidis SE 01 than the commercial antibiotics linezolid and cefaclor, but the former was effective against Escherichia coli ATCC 8739 and Staphylococcus aureus ATCC 10832, whereas the latter was effective against Escherichia coli O157:H7 TWC 01. An in vitro cytotoxicity study in human skin fibroblast cells as measured by MTT assay implied the as-synthesized MNPs to be nontoxic. This outcome demonstrated that both ?-PGA-modified MNPs are cytocompatible and possess antibacterial activity in vitro, and thereby should be useful in in vivo studies for biomedical applications. PMID:21233545

Inbaraj, B Stephen; Kao, T H; Tsai, T Y; Chiu, C P; Kumar, R; Chen, B H

2011-02-18

268

The synthesis and characterization of poly(?-glutamic acid)-coated magnetite nanoparticles and their effects on antibacterial activity and cytotoxicity  

NASA Astrophysics Data System (ADS)

Magnetite nanoparticles (MNPs) modified with sodium and calcium salts of poly(?-glutamic acid) (NaPGA and CaPGA) were synthesized by the coprecipitation method, followed by characterization and evaluation of their antibacterial and cytotoxic effects. Superparamagnetic MNPs are particularly attractive for magnetic driving as well as bacterial biofilm and cell targeting in in vivo applications. Characterization of synthesized MNPs by the Fourier transform infrared spectra and magnetization curves confirmed the PGA coating on MNPs. The mean diameter of NaPGA- and CaPGA-coated MNPs as determined by transmission electron microscopy was 11.8 and 14 nm, respectively, while the x-ray diffraction pattern revealed the as-synthesized MNPs to be pure magnetite. Based on agar dilution assay, both NaPGA- and CaPGA-coated MNPs showed a lower minimum inhibitory concentration in Salmonella enteritidis SE 01 than the commercial antibiotics linezolid and cefaclor, but the former was effective against Escherichia coli ATCC 8739 and Staphylococcus aureus ATCC 10832, whereas the latter was effective against Escherichia coli O157:H7 TWC 01. An in vitro cytotoxicity study in human skin fibroblast cells as measured by MTT assay implied the as-synthesized MNPs to be nontoxic. This outcome demonstrated that both ?-PGA-modified MNPs are cytocompatible and possess antibacterial activity in vitro, and thereby should be useful in in vivo studies for biomedical applications.

Inbaraj, B. Stephen; Kao, T. H.; Tsai, T. Y.; Chiu, C. P.; Kumar, R.; Chen, B. H.

2011-02-01

269

Identification of simultaneous U(VI) sorption complexes and U(IV) nanoprecipitates on the magnetite (111) surface  

Microsoft Academic Search

Sequestration of uranium (U) by magnetite is a potentially important sink for U in natural and contaminated environments. However, molecular-scale controls which favor U(VI) uptake including both adsorption of U(VI) and reduction to U(VI) by magnetite remain poorly understood, in particular the role of U(VI)-CO3-Ca complexes in inhibiting U(VI) reduction. To investigate U uptake pathways on magnetite as a function

David M. Singer; Shawn ME Chatman; Eugene S. Ilton; Kevin M. Rosso; Jillian F. Banfield; Glenn Waychunas

2012-01-01

270

ADVANCED TEM TECHNIQUES FOR ASSESSING THE POSSIBLE BIOGENIC ORIGIN OF METEORITIC MAGNETITE CRYSTALS. M. Weyland  

E-print Network

such as a Gatan Imaging Filter (GIF) is used to obtain chemical maps at sample tilt angles of up to ±60°. At each,3 edge. Chemical maps are then calculated using techniques based on electron energy loss spectroscopy (EELS). Figures 2a and b show reconstructions (viewed from a single di- rection) of the three

Dunin-Borkowski, Rafal E.

271

M. Bahrami ENSC 388 (F09) Properties of Pure Substances Properties of Pure Substances  

E-print Network

Substances 1 Properties of Pure Substances Pure Substance A substance that has a fixed chemical composition throughout is called a pure substance such as water, air, and nitrogen. A pure substance does not have to be of a single element or compound. A mixture of two or more phases of a pure substance

Bahrami, Majid

272

Particle characteristics and reduction behavior of synthetic magnetite  

NASA Astrophysics Data System (ADS)

Two samples (S1 and S2) of magnetite were synthesized, using two different methods, and characterized by means of X-ray powder diffractometry, infrared and Mössbauer spectroscopy, N2 sorptiometry and electron microscopy. Particles of sample-S1 were found to be loosely agglomerated, micro-sized spheroids (200-350 nm) composed almost solely of highly aggregated (fused) crystallites (size averaged at 35 nm) of cubic-Fe3O4. In contrast, particles of sample-S2 were strongly agglomerated, nano-sized spheroids (25-30 nm) composed of slightly aggregated crystallites (size averaged at 11 nm) of cubic-Fe3O4 and noncrystalline domains made-up of FeO(OH) species. Temperature-programed reduction (TPR) profiles obtained for the two samples were similar in monitoring two peaks at >450 °C assignable to a two-step reduction of Fe3O4 (?FeO?Fe), but different in monitoring a peak at<450 °C only for the reduction of FeO(OH) (?Fe3O4) contained in sample-S2. However, curve fitting analysis of the TPR profiles and molecular stoichiometry calculations based on amounts of hydrogen consumed revealed that the two-step reduction of Fe3O4 is not straightforward. That is by resolving two consecutive pathways for each step and, hence, nonstoichiometric intermediate products whose composition was found to be critically controlled by the composition of the reducing gas atmosphere (5 or 80% H2/N2) and characteristics of the starting sample particles (chemical and phase composition, and, but to lesser extents, the agglomeration and average size).

Ramadan, Wegdan; Zaki, Mohamed I.; Fouad, Nasr E.; Mekhemer, Gamal A. H.

2014-04-01

273

Optimizing magnetite nanoparticles for mass sensitivity in magnetic particle imaging  

PubMed Central

Purpose: Magnetic particle imaging (MPI), using magnetite nanoparticles (MNPs) as tracer material, shows great promise as a platform for fast tomographic imaging. To date, the magnetic properties of MNPs used in imaging have not been optimized. As nanoparticle magnetism shows strong size dependence, the authors explore how varying MNP size impacts imaging performance in order to determine optimal MNP characteristics for MPI at any driving field frequency f0. Methods: Monodisperse MNPs of varying size were synthesized and their magnetic properties characterized. Their MPI response was measured experimentally using a custom-built MPI transceiver designed to detect the third harmonic of MNP magnetization. The driving field amplitude H0=6 mT ?0?1 and frequency f0=250 kHz were chosen to be suitable for imaging small animals. Experimental results were interpreted using a model of dynamic MNP magnetization that is based on the Langevin theory of superparamagnetism and accounts for sample size distribution and size-dependent magnetic relaxation. Results: The experimental results show a clear variation in the MPI signal intensity as a function of MNP diameter that is in agreement with simulated results. A maximum in the plot of MPI signal vs MNP size indicates there is a particular size that is optimal for the chosen f0. Conclusions: The authors observed that MNPs 15 nm in diameter generate maximum signal amplitude in MPI experiments at 250 kHz. The authors expect the physical basis for this result, the change in magnetic relaxation with MNP size, will impact MPI under other experimental conditions. PMID:21520874

Ferguson, R. Matthew; Minard, Kevin R.; Khandhar, Amit P.; Krishnan, Kannan M.

2011-01-01

274

Pure Maple Syrup Issue 5  

E-print Network

biting the big one Annie Stuart 7 Porter'sbook Quill 15 Ray's reading Quill 18 redwoods and Rivieras Julien 22 due to circumstances Quill 31 dreams ofsignificance Chris J Ueberall 45 solace Jeannie Marie 52 the albatross Quill 56 a beginning... a separate alternate universe issue and calling it /A/PURE MAPLE SYRUP... There are even a few instances of Ray and Fraserhaving sex with people other than each other (gasp). For those who liked to be advised of the more controversial contents...

Multiple Contributors

1997-01-01

275

Multiple pure tone noise prediction  

NASA Astrophysics Data System (ADS)

This paper presents a fully numerical method for predicting multiple pure tones, also known as “Buzzsaw” noise. It consists of three steps that account for noise source generation, nonlinear acoustic propagation with hard as well as lined walls inside the nacelle, and linear acoustic propagation outside the engine. Noise generation is modeled by steady, part-annulus computational fluid dynamics (CFD) simulations. A linear superposition algorithm is used to construct full-annulus shock/pressure pattern just upstream of the fan from part-annulus CFD results. Nonlinear wave propagation is carried out inside the duct using a pseudo-two-dimensional solution of Burgers' equation. Scattering from nacelle lip as well as radiation to farfield is performed using the commercial solver ACTRAN/TM. The proposed prediction process is verified by comparing against full-annulus CFD simulations as well as against static engine test data for a typical high bypass ratio aircraft engine with hardwall as well as lined inlets. Comparisons are drawn against nacelle unsteady pressure transducer measurements at two axial locations as well as against near- and far-field microphone array measurements outside the duct. This is the first fully numerical approach (no experimental or empirical input is required) to predict multiple pure tone noise generation, in-duct propagation and far-field radiation. It uses measured blade coordinates to calculate MPT noise.

Han, Fei; Sharma, Anupam; Paliath, Umesh; Shieh, Chingwei

2014-12-01

276

Small magnetite antiretroviral therapeutic nanoparticle probes for MRI of drug biodistribution  

PubMed Central

Aim Drug toxicities, compliance and penetrance into viral reservoirs have diminished the efficacy of long-term antiretroviral therapy (ART) for treatment of HIV infection. Cell-targeted nanoformulated ART was developed to improve disease outcomes. However, rapid noninvasive determination of drug biodistribution is unrealized. To this end, small magnetite ART (SMART) nanoparticles can provide assessments of ART biodistribution by MRI. Materials & methods Poly(lactic-co-glycolic acid), 1,2-distearoyl-sn-glycero-3-phosphocholine- and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-(methoxy-PEG 2000)-encased particles were synthesized with atazanavir (ATV) and magnetite. Uptake and retention of ATV and magnetite administered at 3:1 ratios (weight/weight) were determined in human monocyte-derived macrophages and mice. Results SMART particles were taken up and retained in macrophages. In mice, following parenteral SMART injection, magnetite and drug biodistribution paralleled one another with MRI signal intensity greatest in the liver and spleen at 24 h. Significantly, ATV and magnetite levels correlated. Conclusion SMART can permit rapid assessment of drug tissue concentrations in viral reservoirs. PMID:23905578

Guo, Dongwei; Li, Tianyuzi; McMillan, JoEllyn; Sajja, Balasrinivasa R; Puligujja, Pavan; Boska, Michael D; Gendelman, Howard E; Liu, Xin-Ming

2013-01-01

277

Magnetite biomineralization in Magnetospirillum gryphiswaldense: time-resolved magnetic and structural studies.  

PubMed

Magnetotactic bacteria biosynthesize magnetite nanoparticles of high structural and chemical purity that allow them to orientate in the geomagnetic field. In this work we have followed the process of biomineralization of these magnetite nanoparticles. We have performed a time-resolved study on magnetotactic bacteria Magnetospirillum gryphiswaldense strain MSR-1. From the combination of magnetic and structural studies by means of Fe K-edge X-ray absorption near edge structure (XANES) and high-resolution transmission electron microscopy we have identified and quantified two phases of Fe (ferrihydrite and magnetite) involved in the biomineralization process, confirming the role of ferrihydrite as the source of Fe ions for magnetite biomineralization in M. gryphiswaldense. We have distinguished two steps in the biomineralization process: the first, in which Fe is accumulated in the form of ferrihydrite, and the second, in which the magnetite is rapidly biomineralized from ferrihydrite. Finally, the XANES analysis suggests that the origin of the ferrihydrite could be at bacterial ferritin cores, characterized by a poorly crystalline structure and high phosphorus content. PMID:23530668

Fdez-Gubieda, M Luisa; Muela, Alicia; Alonso, Javier; García-Prieto, Ana; Olivi, Luca; Fernández-Pacheco, Rodrigo; Barandiarán, José Manuel

2013-04-23

278

Control of nanoparticle size, reactivity and magnetic properties during the bioproduction of magnetite by Geobacter sulfurreducens.  

PubMed

The bioproduction of nanoscale magnetite by Fe(III)-reducing bacteria offers a potentially tunable, environmentally benign route to magnetic nanoparticle synthesis. Here, we demonstrate that it is possible to control the size of magnetite nanoparticles produced by Geobacter sulfurreducens by adjusting the total biomass introduced at the start of the process. The particles have a narrow size distribution and can be controlled within the range of 10-50 nm. X-ray diffraction analysis indicates that controlled production of a number of different biominerals is possible via this method including goethite, magnetite and siderite, but their formation is strongly dependent upon the rate of Fe(III) reduction and total concentration and rate of Fe(II) produced by the bacteria during the reduction process. Relative cation distributions within the structure of the nanoparticles have been investigated by x-ray magnetic circular dichroism and indicate the presence of a highly reduced surface layer which is not observed when magnetite is produced through abiotic methods. The enhanced Fe(II)-rich surface, combined with small particle size, has important environmental applications such as in the reductive bioremediation of organics, radionuclides and metals. In the case of Cr(VI), as a model high-valence toxic metal, optimized biogenic magnetite is able to reduce and sequester the toxic hexavalent chromium very efficiently to the less harmful trivalent form. PMID:22020365

Byrne, J M; Telling, N D; Coker, V S; Pattrick, R A D; van der Laan, G; Arenholz, E; Tuna, F; Lloyd, J R

2011-11-11

279

Engineering biogenic magnetite for sustained Cr(VI) remediation in flow-through systems.  

PubMed

In this work, we report a route to enhance the reactivity and longevity of biogenic magnetite in Cr(VI) remediation under continuous-flow conditions by combining functionalization of the biomagnetite surface with a precious metal catalyst, nanoscale palladium, and exposure to formate. Column influent conditions were varied to simulate oxic, anoxic, and nitrate cocontaminated environments. The addition of sodium formate as an electron donor for Pd-functionalized magnetite increased capacity and longevity allowing 80% removal of Cr(VI) after 300 h in anoxic conditions, whereas complete breakthrough occurred after 60 h in anoxic nonformate and nonfunctionalized systems. Removal of Cr(VI) was optimized under anoxic conditions, and the presence of oxidizing agents results in a modest loss in reductive capacity. Examination of reacted Pd-functionalized magnetite reveals close association of Fe with Cr, suggesting that Pd-coupled oxidation of formate serves to regenerate the reactive surface. XMCD studies revealed that Cr(III) is partially substituted for Fe in the magnetite structure, which serves to immobilize Cr. No evidence for a mechanistic interference by nitrate cocontamination was observed, suggesting that this novel system could provide robust, effective and sustained reduction of contaminants, even in the presence of common oxidizing cocontaminants, outperforming the reductive capacity of nonfunctionalized biogenic magnetite. PMID:22397548

Crean, Daniel E; Coker, Victoria S; van der Laan, Gerrit; Lloyd, Jonathan R

2012-03-20

280

Control of nanoparticle size, reactivity and magnetic properties during the bioproduction of magnetite by Geobacter sulfurreducens  

SciTech Connect

The bioproduction of nano-scale magnetite by Fe(III)-reducing bacteria offers a potentially tunable, environmentally benign route to magnetic nanoparticle synthesis. Here, we demonstrate that it is possible to control the size of magnetite nanoparticles produced by Geobacter sulfurreducens, by adjusting the total biomass introduced at the start of the process. The particles have a narrow size distribution and can be controlled within the range of 10-50 nm. X-ray diffraction analysis indicates that controlled production of a number of different biominerals is possible via this method including goethite, magnetite and siderite, but their formation is strongly dependent upon the rate of Fe(III) reduction and total concentration and rate of Fe(II) produced by the bacteria during the reduction process. Relative cation distributions within the structure of the nanoparticles has been investigated by X-ray magnetic circular dichroism and indicates the presence of a highly reduced surface layer which is not observed when magnetite is produced through abiotic methods. The enhanced Fe(II)-rich surface, combined with small particle size, has important environmental applications such as in the reductive bioremediation of organics, radionuclides and metals. In the case of Cr(VI), as a model high-valence toxic metal, optimised biogenic magnetite is able to reduce and sequester the toxic hexavalent chromium very efficiently in the less harmful trivalent form.

Byrne, J. M.; Telling, N. D.; Coker, V. S.; Pattrick, R. A. D.; Laan, G. van der; Arenholz, E.; Tuna, F.; Lloyd, J. R.

2011-08-02

281

Kinetics of cadmium(II) uptake by mixed maghemite-magnetite nanoparticles.  

PubMed

In the present study, batch adsorption experiments involving the adsorption of Cd(II) ions from aqueous solutions have been carried out using mixed maghemite-magnetite as adsorbent. The uptake capacity of Cd(II) ions by mixed maghemite-magnetite increased with an increase in the pH of the adsorbate solution. An increase in adsorbent dosage increased Cd(II) removal but decreased adsorption capacity and it was found to follow the pseudo-second-order model. Cd removal from a solution containing 1.5 mg/L initial concentration of Cd(II) decreased from 1.9 to 1.3 mg/g upon increasing the temperature from 10 to 50 °C. Cadmium adsorption may be partly diffusion controlled and partly due to electrostatic effect along with specific adsorption involving the adsorption of Cd(++) and CdOH(+) on mixed maghemite-magnetite nanoparticles in the alkaline pH range. X-ray photoelectron spectroscopy (XPS) surveys confirmed that Cd(2+) ions may undergo oxidation-reduction reactions upon exposure to mixed maghemite-magnetite, or may be fixed by complexation to oxygen atoms in the oxyhydroxy groups at the surface of the iron oxide nanoparticles. After Cd(II) adsorption by the maghemite-magnetite mixture, the percent maghemite decreased from 74.8 to 68.5%. PMID:24041626

Chowdhury, Saidur Rahman; Yanful, Ernest K

2013-11-15

282

Fe{sup II} induced mineralogical transformations of ferric oxyhydroxides into magnetite of variable stoichiometry and morphology  

SciTech Connect

The Moessbauer spectroscopy was used to monitor the mineralogical transformations of ferrihydrite (F), lepidocrocite (L) and goethite (G) into magnetite as a function of aging time. Ferric oxyhydroxides were reacted with soluble Fe{sup II} and OH{sup -} in stoichiometric amounts to form magnetite at an initial pH of {approx}9.7. Observed transformation extent into magnetite followed the order: F>L>G with almost 30% of untransformed G after 1 month. The departure from stoichiometry, {delta}, of magnetite (Fe{sub 3-{delta}}O{sub 4}) generated from F ({delta}{approx}0.04) and L ({delta}{approx}0.05) was relatively low as compared to that in magnetite from G ({delta}{approx}0.08). The analysis by transmission electron microscopy and BET revealed that generated magnetite was also different in terms of morphology, particle size and surface area depending on the nature of initial ferric oxyhydroxide. This method of preparation is a possible way to form nano-sized magnetite. - Graphical abstract: Moessbauer spectrum of the early stage of magnetite formation formed from the interaction of adsorbed Fe{sup II} species with goethite. Highlights: Black-Right-Pointing-Pointer Ferric oxides were reacted with hydroxylated Fe{sup II} to form magnetite. Black-Right-Pointing-Pointer Magnetite formation was quantified as a function of aging time. Black-Right-Pointing-Pointer Complete transformation of ferrihydrite and lepidocrocite was achieved. Black-Right-Pointing-Pointer Almost 70% of initial goethite was transformed. Black-Right-Pointing-Pointer Resulting magnetites have differences in stoichiometry and morphological properties.

Usman, M. [Universite de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France) [Universite de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France); CNRS, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France); Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad 38040 (Pakistan); Abdelmoula, M. [Universite de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France) [Universite de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France); CNRS, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France); Hanna, K. [Universite de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France) [Universite de Lorraine, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France); CNRS, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, LCPME, UMR 7564, Institut Jean Barriol, CNRS-, 405 rue de Vandoeuvre, 54600 Villers-les-Nancy (France); Ecole Nationale Superieure de Chimie de Rennes, UMR CNRS 6226 'Sciences Chimiques de Rennes', Avenue du General Leclerc, 35708 Rennes Cedex 7 (France); and others

2012-10-15

283

Effects of the unique shape of submicron magnetite hollow spheres on magnetic properties and domain states  

NASA Astrophysics Data System (ADS)

Submicron-scale magnetite (Fe3O4) hollow spheres were prepared by a template method using polystyrene beads. The obtained particles were very uniform in size with a diameter of 650±20nm and a shell thickness of 40nm . The temperature dependence of the zero-field cooled magnetizations indicated a broad anomaly at around 110K that was ascribable to the Verwey transition, while the magnetite nanoparticles (25nm) , obtained by grinding the hollow spheres, exhibited no anomalies in this temperature range. Particularly below the Verwey transition temperature, the coercive fields of the hollow spheres increased much more significantly than did those of nanoscale and bulk magnetite. The Day plots [Phys. Earth Planet. Inter. 13, 260 (1977)] for the submicron hollow spheres indicated that their domain states were similar to the single-domain state at low temperature.

Ye, Quan-Lin; Kozuka, Yasuharu; Yoshikawa, Hirofumi; Awaga, Kunio; Bandow, Shunji; Iijima, Sumio

2007-06-01

284

Progress in the synthesis and characterization of magnetite nanoparticles with amino groups on the surface  

NASA Astrophysics Data System (ADS)

This manuscript deals with the synthesis of new hydrophilic magnetite particles by employing a two-step method: in the first step magnetite particles with hydrophobic shell formed in presence of oleic acid-oleylamine complex through a synthesis in mass, without solvent, in a mortar with pestle were obtained; while in the second step the hydrophobic shell was interchanged with an aminosilane monomer. The influence of the Fe2+/Fe3+ molar ratio on the dimension of the particles of high importance for their potential applications was carefully investigated. This paper, also presents an alternative method of synthesis of new core-shell magnetite particles and the complete study of their structure and morphology by FT-IR, XPS, TGA, ESEM and TEM techniques. The rheological properties and magnetization analysis of high importance for magnetic particles were also investigated.

Durdureanu-Angheluta, A.; Dascalu, A.; Fifere, A.; Coroaba, A.; Pricop, L.; Chiriac, H.; Tura, V.; Pinteala, M.; Simionescu, B. C.

2012-05-01

285

Mechanism of formation of magnetite from ferrous hydroxide in aqueous corrosion processes  

NASA Astrophysics Data System (ADS)

The stoichiometric conditions for the formation of ferrous hydroxide Fe(OH)2, by mixing Fe2+ ions with caustic soda NaOH, leads by oxidation to magnetite, irrelevant of the foreign anions, e.g. Cl- or SO4 2-, as demonstrated from Mössbauer spectroscopy. The electrochemical potential Eh and pH value of the initial conditions correspond to the drastic change from basic to acidic medium, observed when varying the initial Fe2+/OH- ratio. Mössbauer analysis of the end products of oxidation at various temperatures shows that magnetite is only obtained at stoichiometry at very low temperature, but extends off stoichiometry at higher temperatures. The mechanism of formation of magnetite through an intermediate compound is discussed.

Olowe, A. A.; Rezel, D.; Génin, J. M. R.

1989-03-01

286

Reordering between tetrahedral and octahedral sites in ultrathin magnetite films grown on MgO(001)  

SciTech Connect

Magnetite ultrathin films were grown using different deposition rates and substrate temperatures. The structure of these films was studied using (grazing incidence) x-ray diffraction, while their surface structure was characterized by low energy electron diffraction. In addition to that, we performed x-ray photoelectron spectroscopy and magneto optic Kerr effect measurements to probe the stoichiometry of the films as well as their magnetic properties. The diffraction peaks of the inverse spinel structure, which originate exclusively from Fe ions on tetrahedral sites are strongly affected by the preparation conditions, while the octahedral sites remain almost unchanged. With both decreasing deposition rate as well as decreasing substrate temperature, the integrated intensity of the diffraction peaks originating exclusively from Fe on tetrahedral sites is decreasing. We propose that the ions usually occupying tetrahedral sites in magnetite are relocated to octahedral vacancies. Ferrimagnetic behaviour is only observed for well ordered magnetite films.

Bertram, F.; Deiter, C. [Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen-Synchrotron, Notkestr. 85, 22607 Hamburg (Germany)] [Hamburger Synchrotronstrahlungslabor am Deutschen Elektronen-Synchrotron, Notkestr. 85, 22607 Hamburg (Germany); Schemme, T.; Jentsch, S.; Wollschlaeger, J. [Fachbereich Physik, Universitaet Osnabrueck, Barbarastr. 7, 49069 Osnabrueck (Germany)] [Fachbereich Physik, Universitaet Osnabrueck, Barbarastr. 7, 49069 Osnabrueck (Germany)

2013-05-14

287

Fayalite Oxidation Processes: Experimental Evidence for the Stability of Pure Ferric Fayalite?  

NASA Technical Reports Server (NTRS)

Olivine is one of the most important minerals in Earth and planetary sciences. Fayalite Fe2(2+)SiO4, the ferrous end-member of olivine, is present in some terrestrial rocks and primitive meteorites (CV3 chondrites). A ferric fayalite (or ferri-fayalite), Fe(2+) Fe2(3+)(SiO4)2 laihunite, has been reported in Earth samples (magnetite ore, metamorphic and volcanic rocks...) and in Martian meteorites (nakhlites). Laihunite was also synthesized at 1 atmosphere between 400 and 700 C. We show evidence for the stability of a pure ferrifayalite end-member and for potential minerals with XFe(3+) between 2/3 and 1.

Martin, A. M.; Righter, K.; Keller, L. P.; Medard, E.; Devouard, B.; Rahman, Z.

2011-01-01

288

Magnetic properties of magnetite nanoparticles coated with mesoporous silica by sonochemical method  

SciTech Connect

Highlights: Black-Right-Pointing-Pointer MCM-41-coating of magnetite nanoparticles performed under ultrasonic irradiation. Black-Right-Pointing-Pointer Ultrasonic irradiation accelerates the formation of the MCM-41 framework. Black-Right-Pointing-Pointer The hysteretic response to an applied field was investigated applying FORC diagram. Black-Right-Pointing-Pointer The average coercive field of the Fe{sub 3}O{sub 4} nanoparticles increased after coating. -- Abstract: In this paper we present the magnetic properties of mesoporous silica-coated Fe{sub 3}O{sub 4} nanoparticles. The coating of magnetite nanoparticles with mesoporous silica shell was performed under ultrasonic irradiation. The obtained mesoporous silica-coated magnetite nanoparticles were characterized by powder X-ray diffraction, focused ion beam-scanning electron microscopy, nitrogen adsorption-desorption isotherms and vibrating sample magnetometer. The hysteretic behavior was studied using first-order reversal curves diagrams. The X-ray diffraction result indicates that the extreme chemical and physical conditions created by acoustic cavitations have an insignificant effect on crystallographic structural characteristic of magnetite nanoparticles. Changes in the coercivity distributions of the magnetite nanoparticles were observed on the first-order reversal curves diagrams for the samples with coated particles compared with the samples containing uncoated particles of magnetite. The coated particles show an increased most probable coercivity of about 20% compared with the uncoated particles which can be associated with an increased anisotropy due to coating even if the interaction field distribution measured on the diagrams are virtually identical for coated/uncoated samples.

Ursachi, Irina [Department of Physics and CARPATH Center, 'Alexandru Ioan Cuza' University of Iasi, 11 Carol I Blvd., 700506 Iasi (Romania)] [Department of Physics and CARPATH Center, 'Alexandru Ioan Cuza' University of Iasi, 11 Carol I Blvd., 700506 Iasi (Romania); Vasile, Aurelia [Department of Chemistry, 'Alexandru Ioan Cuza' University of Iasi, 11 Carol I Blvd., 700506 Iasi (Romania)] [Department of Chemistry, 'Alexandru Ioan Cuza' University of Iasi, 11 Carol I Blvd., 700506 Iasi (Romania); Chiriac, Horia [National Institute of Research and Development for Technical Physics, 47 Mangeron Blvd., 700050 Iasi (Romania)] [National Institute of Research and Development for Technical Physics, 47 Mangeron Blvd., 700050 Iasi (Romania); Postolache, Petronel [Department of Physics and CARPATH Center, 'Alexandru Ioan Cuza' University of Iasi, 11 Carol I Blvd., 700506 Iasi (Romania)] [Department of Physics and CARPATH Center, 'Alexandru Ioan Cuza' University of Iasi, 11 Carol I Blvd., 700506 Iasi (Romania); Stancu, Alexandru, E-mail: alstancu@uaic.ro [Department of Physics and CARPATH Center, 'Alexandru Ioan Cuza' University of Iasi, 11 Carol I Blvd., 700506 Iasi (Romania)] [Department of Physics and CARPATH Center, 'Alexandru Ioan Cuza' University of Iasi, 11 Carol I Blvd., 700506 Iasi (Romania)

2011-12-15

289

Selenite retention by nanocrystalline magnetite: Role of adsorption, reduction and dissolution/co-precipitation processes  

NASA Astrophysics Data System (ADS)

We studied selenite ( SeO32-) retention by magnetite ( FeFeIII2O) using both surface complexation modeling and X-ray absorption spectroscopy (XAS) to characterize the processes of adsorption, reduction, and dissolution/co-precipitation. The experimental sorption results for magnetite were compared to those of goethite (Fe IIIOOH) under similar conditions. Selenite sorption was investigated under both oxic and anoxic conditions and as a function of pH, ionic strength, solid-to-liquid ratio and Se concentration. Sorption onto both oxides was independent of ionic strength and decreased as pH increased, as expected for anion sorption; however, the shape of the sorption edges was different. The goethite sorption data could be modeled assuming the formation of an inner-sphere complex with iron oxide surface sites (SOH). In contrast, the magnetite sorption data at low pH could be modeled only when the dissolution of magnetite, the formation of aqueous iron-selenite species, and the subsequent surface complexation of these species were implemented. The precipitation of ferric selenite was the predominant retention process at higher selenite concentrations (>1 × 10 -4 M) and pH < 5, which was in agreement with the XAS results. Sorption behavior onto magnetite was similar under oxic and anoxic conditions. Under anoxic conditions, we did not observe the reduction of selenite. Possible reasons for the absence of reduction are discussed. In conclusion, we show that under acidic reaction conditions, selenite retention by magnetite is largely influenced by dissolution and co-precipitation processes.

Missana, T.; Alonso, U.; Scheinost, A. C.; Granizo, N.; García-Gutiérrez, M.

2009-10-01

290

The oxygen sensor MgFnr controls magnetite biomineralization by regulation of denitrification in Magnetospirillum gryphiswaldense  

PubMed Central

Background Magnetotactic bacteria are capable of synthesizing magnetosomes only under oxygen-limited conditions. However, the mechanism of the aerobic repression on magnetite biomineralization has remained unknown. In Escherichia coli and other bacteria, Fnr (fumarate and nitrate reduction regulator) proteins are known to be involved in controlling the switch between microaerobic and aerobic metabolism. Here, we report on an Fnr-like protein (MgFnr) and its role in growth metabolism and magnetite biomineralization in the alphaproteobacterium Magnetospirillum gryphiswaldense. Results Deletion of Mgfnr not only resulted in decreased N2 production due to reduced N2O reductase activity, but also impaired magnetite biomineralization under microaerobic conditions in the presence of nitrate. Overexpression of MgFnr in the WT also caused the synthesis of smaller magnetite particles under anaerobic and microaerobic conditions in the presence of nitrate. These data suggest that proper expression of MgFnr is required for WT-like magnetosome synthesis, which is regulated by oxygen. Analyses of transcriptional gusA reporter fusions revealed that besides showing similar properties to Fnr proteins reported in other bacteria, MgFnr is involved in the repression of the expression of denitrification genes nor and nosZ under aerobic conditions, possibly owing to several unique amino acid residues specific to MTB-Fnr. Conclusions We have identified and thoroughly characterized the first regulatory protein mediating denitrification growth and magnetite biomineralization in response to different oxygen conditions in a magnetotactic bacterium. Our findings reveal that the global oxygen regulator MgFnr is a genuine O2 sensor. It is involved in controlling expression of denitrification genes and thereby plays an indirect role in maintaining proper redox conditions required for magnetite biomineralization. PMID:24915802

2014-01-01

291

Scanning and transmission electron microscope observations of magnetite and other iron phases in ordovician carbonates from east Tennessee  

Microsoft Academic Search

Previous paleomagnetic observations for the carbonates of the Lower Ordovician Knox Group have indicated that ancient magnetizations in these rocks are of the same age as the late Paleozoic Alleghenian Orogeny. Roch magnetic properties strongly suggest magnetite as the carrier of the magnetization, but the textural and crystalline characteristics, sizes, morphologies, and mineral associations of these magnetites are poorly known.

Dongwoo Suk; Rob Van der Voo; Donald R. Peacor

1990-01-01

292

Arsenate and Arsenite Sorption on Magnetite: Relations to Groundwater Arsenic Treatment Using Zerovalent Iron and Natural Attenuation  

EPA Science Inventory

Magnetite (Fe3O4) is a zerovalent iron corrosion product; it is also formed in natural soil and sediment. Sorption of arsenate (As(V)) and arsenite (As(III)) on magnetite is an important process of arsenic removal from groundwater using zerovalent iron-based permeable reactive ba...

293

The distinct effects of Mn substitution on the reactivity of magnetite in heterogeneous Fenton reaction and Pb(II) adsorption.  

PubMed

In this study, a series of Mn substituted magnetites were synthesized and used in catalyzing the heterogeneous Fenton degradation of acid orange II and Pb(II) adsorption, in order to investigate the effect of Mn substitution on the reactivity of magnetite. The valence and local environment of both Fe and Mn in the spinel structure of magnetite were investigated by X-ray absorption fine structure (XAFS) spectroscopy. The incorporation of Mn did not change the valence and local structure of Fe in the synthetic magnetite, while Mn was in the valences of +2 and +3. The Mn distribution on the octahedral sites of magnetite surface increased with the increase in Mn content. The Mn introduction led to an improvement of catalytic activity of magnetite. The sample with the minimum Mn content displayed the best efficiency in OH production and the degradation of acid orange II, while the other substituted samples did not show obvious difference in their catalytic performance. The adsorption capacity of magnetite samples toward Pb(II) gradually increased with the increase in Mn content. The above influences of Mn substitution on the reactivity of magnetite were discussed in views of the variations in microstructural environment and physicochemical properties. PMID:24863781

Liang, Xiaoliang; He, Zisen; Wei, Gaoling; Liu, Peng; Zhong, Yuanhong; Tan, Wei; Du, Peixin; Zhu, Jianxi; He, Hongping; Zhang, Jing

2014-07-15

294

High-temperature susceptibility of magnetite: a new pseudo-single-domain effect  

NASA Astrophysics Data System (ADS)

Remanent magnetizations of magnetites between single-domain (SD) threshold size (?0.1 ?m) and ?20 ?m have SD-like intensities and coercivities. This paper shows for the first time that magnetite's induced magnetization also has pseudo-single-domain behaviour. The first part of the paper reports temperature-dependent initial susceptibility data, k0(T), of sized magnetites and assesses their granulometric potential. The second part transforms coercive force data, Hc(T), for the same magnetites into simulated k0(T) curves. The third part considers k0(T) results of coarse-grained mafic rocks as candidate sources of deep-seated magnetic anomalies. High-temperature susceptibility k0 measured with a Kappabridge for eight fractions of crushed natural magnetites (median sizes of 0.6, 1, 3, 6, 9, 14, 110 and 135 ?m) shows a progressive increase in the height of the Hopkinson peak below the Curie point as grain size decreases. The trend is systematic and has granulometric potential in the 1-14 ?m range. Self-demagnetization should produce almost flat k0(T) in grains larger than SD size but experimentally, well-defined Hopkinson peaks are not limited to the finest grains. 1-?m magnetites have a peak 1.5 times k0 at 20 °C and 14-?m grains have a peak of 1.25. Only 110 and 135 ?m grains have T-independent k0. Using an empirical relationship between coercive force Hc and k0, Hc(T) data for the sized magnetites were used to simulate k0(T) results. A hump in the k0 heating curve around 250 °C was traced to annealing out internal strains, evident in Hc data measured in first heatings. For sizes ?6 ?m, observed Hopkinson peaks were smaller than predicted, possibly because of a previously unrecognized grain-size dependence of the empirical constant relating Hc and k0. Two crystalline rocks, a gabbro and a diabase, combine SD-like Hopkinson peaks and multidomain (MD) flat ramps in their k0(T) data. In the diabase, a Hopkinson peak is prominent in separated plagioclase grains containing submicron magnetite, but is masked in whole-rock data. The gabbro has a clear superposition of SD and MD k0(T) functions in its whole-rock data, with a Hopkinson peak of 1.35. If oceanic layer-3 gabbros have similar susceptibility enhancement above 500 °C, they could be more important magnetic anomaly sources than room-temperature k0 measurements on dredged or fault-uplifted samples would suggest.

Dunlop, David J.

2014-11-01

295

Magnetite-bubble aggregates at mixing interfaces in andesite magma bodies  

E-print Network

population of bubbles of a supercritical fluid containing substantial H2O. The dissolved and 44 exsolved volatile budget of these mafic magmas is a dominant control on the mechanisms of 45 magma mingling and/or mixing when these magmas underplate, or intrude... be due to either magnetite nucleation on 427 bubble walls, owing to short lengthscale changes in melt oxidation state and oxygen fugacity during 428 degassing (Humphreys et al. in review; Moussallam et al. 2014), or to bubble nucleation on 429 magnetite...

Edmonds, M.; Brett, A.; Herd, R. A.; Humphreys, M. C. S.; Woods, A.

2014-08-14

296

Ligand effects on the electronic structure and magnetism of magnetite surfaces  

NASA Astrophysics Data System (ADS)

We address the effect of functionalization on the electronic and magnetic properties of magnetite surface as an indicator of the same properties in nanoparticles too big for a direct ab-initio approach. Using well-established methods and references (namely LDA+U on magnetite surfaces) we could verify the validity of our approach, and using two typical ligands, dopamine and citrate, namely ? and ? electron donors, we could predict that those ligands would induce a different change in the electronic properties of the systems, but in both cases an enhancement of magnetization.

Brymora, Katarzyna; Calvayrac, Florent

2013-03-01

297

Ultrasonic velocity, attenuation, and nonlinearity constant in pure and Cd-doped KCl  

Microsoft Academic Search

Single crystals of pure and Cd-doped KCl (1000 ppm) were grown by the Czochralski technique. The acoustic attenuation and velocity in pure and Cd-doped KCl for the longitudinal waves along the [100] direction at 12 MHz are measured by single-ended pulse-echo and pulse-echo-overlap methods in the temperature range 173-303 K. The acoustic attenuation is measured in the frequency range 12-228

D. N. Joharapurkar; S. Rajagopalan; B. K. Basu

1988-01-01

298

Melting vs solidification of a pure metal analyzed by DSC  

SciTech Connect

The aim of the present paper is to analyze the melting/solidification of pure metals resulting from non-equilibrium conditions. Attention is focused on the direct measurement of the calorimetric signal obtained under isothermal hold of the sample at a temperature close to the equilibrium melting temperature T{sub m}, which results in both melting of an overheated solid and solidification of an undercooled melt. The non-equilibrium transformations are monitored by DSC under isothermal regime, with previous continuous heating/continuous cooling of the sample. The dependence of the calorimetric signal on thermodynamic factors, {Delta}H and {Delta}G, is explored. Here {Delta}H and {Delta}G are, respectively, the melting enthalpy and Gibbs free energy difference between the crystal and the liquid. IN particular, the results of the investigation performed on the melting/solidification behavior of pure In and Pb are presented.

Clavaguera, N. [Univ. de Barcelona (Spain); Clavagera-Mora, M.T.; Fontan, J.; Touron, J.L.; Comas, C. [Univ. Autonoma de Barcelona, Bellaterra (Spain). Dept. de Fisica

1998-12-31

299

Magnetotactic bacteria form magnetite from a phosphate-rich ferric hydroxide via nanometric ferric (oxyhydr)oxide intermediates.  

PubMed

The iron oxide mineral magnetite (Fe3O4) is produced by various organisms to exploit magnetic and mechanical properties. Magnetotactic bacteria have become one of the best model organisms for studying magnetite biomineralization, as their genomes are sequenced and tools are available for their genetic manipulation. However, the chemical route by which magnetite is formed intracellularly within the so-called magnetosomes has remained a matter of debate. Here we used X-ray absorption spectroscopy at cryogenic temperatures and transmission electron microscopic imaging techniques to chemically characterize and spatially resolve the mechanism of biomineralization in those microorganisms. We show that magnetite forms through phase transformation from a highly disordered phosphate-rich ferric hydroxide phase, consistent with prokaryotic ferritins, via transient nanometric ferric (oxyhydr)oxide intermediates within the magnetosome organelle. This pathway remarkably resembles recent results on synthetic magnetite formation and bears a high similarity to suggested mineralization mechanisms in higher organisms. PMID:23980143

Baumgartner, Jens; Morin, Guillaume; Menguy, Nicolas; Perez Gonzalez, Teresa; Widdrat, Marc; Cosmidis, Julie; Faivre, Damien

2013-09-10

300

Preparation of biocompatible magnetite-carboxymethyl cellulose nanocomposite: Characterization of nanocomposite by FTIR, XRD, FESEM and TEM  

NASA Astrophysics Data System (ADS)

The preparation and characterization of magnetite-carboxymethyl cellulose nano-composite (M-CMC) material is described. Magnetite nano-particles were synthesized by a modified co-precipitation method using ferrous chloride tetrahydrate and ferric chloride hexahydrate in ammonium hydroxide solution. The M-CMC nano-composite particles were synthesized by embedding the magnetite nanoparticles inside carboxymethyl cellulose (CMC) using a freshly prepared mixture of Fe3O4 with CMC precursor. Morphology, particle size, and structural properties of magnetite-carboxymethyl cellulose nano-composite was accomplished using X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transformed infrared (FTIR) and field emission scanning electron microscopy (FESEM) analysis. As a result, magnetite nano-particles with an average size of 35 nm were obtained. The biocompatible Fe3O4-carboxymethyl cellulose nano-composite particles obtained from the natural CMC polymers have a potential range of application in biomedical field.

Habibi, Neda

2014-10-01

301

Bringing Planctomycetes into pure culture  

PubMed Central

Planctomycetes have been known since the description of Planctomyces bekefii by Gimesi at the beginning of the twentieth century (1924), although the first axenic cultures were only obtained in the 1970s. Since then, 11 genera with 14 species have been validly named and five candidatus genera belonging to the anaerobic ammonium oxidation, anammox bacteria have also been discovered. However, Planctomycetes diversity is much broader than these numbers indicate, as shown by environmental molecular studies. In recent years, the authors have attempted to isolate and cultivate additional strains of Planctomycetes. This paper provides a summary of the isolation work that was carried out to obtain in pure culture Planctomycetes from several environmental sources. The following strains of planctomycetes have been successfully isolated: two freshwater strains from the sediments of an aquarium, which were described as a new genus and species, Aquisphaera giovannonii; several Rhodopirellula strains from the sediments of a water treatment recycling tank of a marine fish farm; and more than 140 planctomycetes from the biofilm community of macroalgae. This collection comprises several novel taxa that are being characterized and described. Improvements in the isolation methodology were made in order to optimize and enlarge the number of Planctomycetes isolated from the macroalgae. The existence of an intimate and an important relationship between planctomycetes and macroalgae reported before by molecular studies is therefore supported by culture-dependent methods. PMID:23335915

Lage, Olga M.; Bondoso, Joana

2012-01-01

302

Methane production from hydrothermal transformation of siderite to magnetite  

NASA Astrophysics Data System (ADS)

Mumma et al. (2009) observed a methane (CH4) plume above the Nili Fossae region on Mars, a region rich in carbonate minerals. Morris et al. (2010) suggest this to be (Mg,Fe)-carbonate. McCollom (2003) demonstrated that the hydrothermal transformation of siderite (FeCO3), to magnetite (Fe3O4) produces CH4. This reaction may thus contribute to the formation of methane on Mars, but is also relevant in the context of such diverse topics as diagenesis of Precambrian banded iron formations, sources of prebiotic organic compounds on early Earth, oil and gas accumulations in Earth's crust, or geological sequestration and storage of CO2. However, neither the thermodynamics of this reaction nor the conditions of maximum CH4 yield have been investigated to date. In order to estimate how pressure and temperature influence CH4 yield we derived a thermodynamic model with a numerical solution implemented in MATLAB. We used the equation 12FeCO3 + 2H2O ? 4Fe3O4 + 11CO2 + CH4 (Frost et al. 2007) and thermodynamic calculations of the stability field of FeCO3 by Thoms-Keprta et al. (2009) as a template. At 1 bar pressure, the Gibbs energy turns negative (favorable reaction conditions) at a temperature of 200°C. Increasing pressure to 1000 bar changes that temperature to 250°C. An increase in temperature has a larger effect on shifting the Gibbs energy to more negative values. We therefore chose ambient pressure and temperatures of 300°C, 400°C, and 500°C as experimental conditions. We added 100 mg of either natural or synthetic FeCO3 and 25 ?L of MilliQ water into long tip Pasteur pipettes inside an anoxic glove box to avoid contamination by free oxygen. The Pasteur pipettes were sealed with butyl stoppers and then melted shut outside of the glove box. The glass capsules were heated for 48 hours in a muffle furnace at 300°C, 400 0C or 5000C. The composition of the gas phase and the formation of methane in particular were analyzed using gas chromatography with a flame ionization detector. We used Mössbauer spectroscopy, X-ray diffraction, X-ray fluorescence, and scanning electron microscopy with Energy-Dispersive X-ray spectroscopy to investigate changes in the solid phase. Synthetic FeCO3 was completely transformed to Fe3O4 and sometimes the further oxidized phases maghemite (?-Fe2O3) and hematite (?-Fe2O3). Natural FeCO3 was not completely transformed, which can be explained by its larger particle size and therefore reduced reactivity. Methane yield was consequently higher from synthetic siderite. Our results show that hydrothermal activity invoked by either impact or volcanic activity could have transformed siderite and thereby released at least some of the CH4 observed on Mars. On Earth, long-term underground storage of CO2 as carbonate minerals has to avoid hydrothermal conditions. Otherwise not only CO2 will be released again, but some of it will potentially be transformed into the more potent greenhouse gas methane. References Frost et al., Contrib. Mineral. Pet. 153 (2006) 211; McCollom, Geochim. Cosmochim. Ac. 67 (2003) 311; Morris et al., Science 329 (2010), 421; Mumma et al., Science 323 (2009) 1041; Thomas-Keprta et al., Geochim. Cosmochim. Ac. 73 (2009) 6631, EA-4

Muratbayev, T.; Schroeder, C.; Kappler, A.; Haderlein, S.

2012-12-01

303

Adsorption and kinetic studies of seven different organic dyes onto magnetite nanoparticles loaded tea waste and removal of them from wastewater samples  

NASA Astrophysics Data System (ADS)

Adsorption of seven different organic dyes from aqueous solutions onto magnetite nanoparticles loaded tea waste (MNLTW) was studied. MNLTW was prepared via a simple method and was fully characterized. The properties of this magnetic adsorbent were characterized by scanning electron microscopy and X-ray diffraction. Adsorption characteristics of the MNLTW adsorbent was examined using Janus green, methylene blue, thionine, crystal violet, Congo red, neutral red and reactive blue 19 as adsorbates. Dyes adsorption process was thoroughly studied from both kinetic and equilibrium points of view for all adsorbents. The experimental isotherm data were analyzed using Langmuir, Freundlich, Sips, Redlich-Peterson, Brouers-Sotolongo and Temkin isotherms. The results from Langmuir isotherm indicated that the capacity of MNLTW for the adsorption of cationic dyes was higher than that for anionic dyes. The adsorption kinetics was tested for the pseudo-first order and pseudo-second order kinetic models at different experimental conditions.

Madrakian, Tayyebeh; Afkhami, Abbas; Ahmadi, Mazaher

2012-12-01

304

Superparamagnetism and Exchange Anisotropy in Microparticles of Magnetite Embedded in an Inert Carbonaceous Matrix  

Microsoft Academic Search

By the controlled thermal degradation of ferricinium nitrate a material composed of iron oxide particles embedded in an inert carbonaceous matrix was obtained. The iron oxide particles were found to be mostly magnetite, and their average diameter about 35 Å. This value was obtained from both x-ray diffraction line broadening and from static magnetic measurements. The small particle size caused

Shaul M. Aharoni; Morton H. Litt

1971-01-01

305

Synthesis of poly(vinyl alcohol)-magnetite ferrogel obtained by freezing-thawing technique  

NASA Astrophysics Data System (ADS)

Polymer gels are crosslinked polymer networks swollen by a fluid. If magnetic particles either as powder or dispersed in a magnetic fluid are introduced into the gel then the system becomes sensitive to external magnetic fields and the resulting material is called ferrogel. The polyvinyl alcohol (PVA)-magnetite ferrogels system has properties that are attractive for artificial muscles and drug delivery systems for biomedical applications. This work investigates the synthesis and characterization of a ferrogel obtained by freezing-thawing cycles. PVA ( MW=89,000-98,000, degree of hydrolyzation: 99 mol%) and magnetite nanoparticles (˜12 nm) obtained by chemical coprecipitation were used as raw materials. The PVA-magnetite ferrogels were prepared by subjecting a PVA/DMSO/magnetite solution (2 g/30 ml/0.2 g) to freeze (-25 °C)/thaw (+25 °C) cycles. The resulting ferrogel was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC) and vibration sample magnetometry (VSM). The magnetic particles inside the PVA matrix formed agglomerates with average size ˜58 nm. All the ferrogels showed superparamagnetic behavior with maximum magnetization of 0.6 emu/g.

Reséndiz-Hernández, P. J.; Rodríguez-Fernández, O. S.; García-Cerda, L. A.

306

A&M. Special shielding materials. Stockpile of magnetite, used for making ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

A&M. Special shielding materials. Stockpile of magnetite, used for making high-density concrete, and loading conveyor near TAN-607 construction site. Date: September 25, 1953. INEEL negative no. 8710 - Idaho National Engineering Laboratory, Test Area North, Scoville, Butte County, ID

307

Preliminary evaluation of nanoscale biogenic magnetite-based ferromagnetic transduction mechanisms for mobile phone bioeffects  

Microsoft Academic Search

Ferromagnetic transduction models have been proposed as a potential mechanism for mobile phone bioeffects. These models are based on the coupling of RF and pulsed electromagnetic emissions to biogenic magnetite (Fe3O4) present in the human brain via either ferromagnetic resonance or mechanical activation of cellular ion channels. We have tested these models experimentally for the first time using a bacterial

Charles Cranfield; Heinz Gregor Wieser; J. A. Madan; J. Dobson

2003-01-01

308

NOAA/NMFS Developments Magnetite Is Magnetic Material in Tuna Skulls  

E-print Network

. The 5-year plan, required by the National Ocean Pollution Planning Act of 1978, finds that sewage wasteNOAA/NMFS Developments Magnetite Is Magnetic Material in Tuna Skulls National Marine Pollution Plan and Atmos- pheric Administration (NOAA) in a National Marine Pollution Program Plan issued this spring

309

Magnetic mineralogy of soils across the Russian Steppe: climatic dependence of pedogenic magnetite formation  

E-print Network

, UK b Institute of Physicochemical and Biological Problems of Soil Science, Russian AcademyMagnetic mineralogy of soils across the Russian Steppe: climatic dependence of pedogenic magnetite of Sciences, Pushchino, Russia Received 15 January 2003; received in revised form 23 July 2003; accepted 19

310

Green rust as a precursor for magnetite: an in situ synchrotron based study  

E-print Network

, showing the initial rapid formation of hexagonal sulphate green rust particles, followed by the corrosionGreen rust as a precursor for magnetite: an in situ synchrotron based study A. SUMOONDUR*, S. SHAW, University of Leeds, Leeds, LS2 9JT, UK ABSTRACT In this study, direct evidence for the formation

Benning, Liane G.

311

Magnesium outdiffusion through magnetite films grown on magnesium oxide (001) (abstract)  

E-print Network

Magnesium outdiffusion through magnetite films grown on magnesium oxide (001) (abstract) K. A. Shaw of magnesium in the uppermost layers of the film, and indicate a concentration gradient, with the highest concentrations of magnesium in the surface layer. X-ray fluorescence in scanning electron microscopy

Diebold, Ulrike

312

Formation of magnetite and iron-rich carbonates by thermophilic iron-reducing bacteria  

SciTech Connect

Laboratory experiments were performed to study the formation of iron minerals by a thermophilic (45 to 75 C) fermentative iron-reducing bacterial culture (TOR39) obtained from the deep subsurface. Using amorphous Fe(III) oxyhydroxide as an electron acceptor and glucose as an electron donor, TOR39 produced magnetite and iron-rich carbonates at conditions consistent, on a thermodynamic basis, with Eh ({minus}200 mV to {minus}415 mV) and pH (6.2 to 7.7) values determined for these experiments. Analyses of the precipitating solid phases by X-ray diffraction showed that the starting amorphous Fe(III) oxyhydroxide was nearly completely converted to magnetite and Fe-rich carbonate after 20 days of incubation. Increasing bicarbonate concentration in the chemical milieu resulted in increased proportions of siderite relative to magnetite and the addition of MgCl{sub 2} caused the formation of magnesium-rich carbonate in addition to siderite. The results suggest that the TOR39 bacterial culture may have the capacity to form magnetite and iron-rich carbonates in a variety of geochemical conditions. These results may have significant implications for studying the past biogenic activities in the Martian meteorite ALH84001.

Zhang, C.; Liu, S.; Roh, Y.; Cole, D.; Phelps, T. [Oak Ridge National Lab., TN (United States); Vali, H. [McGill Univ., Montreal, Quebec (Canada). Dept. of Earth and Planetary Sciences; Kirschvink, J.L. [California Inst. of Tech., Pasadena, CA (United States). Div. of Geological and Planetary Sciences; Onsttot, T. [Princeton Univ., NJ (United States). Dept. of Geological and Geophysical Sciences; McKay, D. [NASA, Houston, TX (United States). Johnson Space Center

1997-06-01

313

A Non-Biological Origin for the Nanophase Magnetite Grains in ALH84001: Experimental Results  

NASA Technical Reports Server (NTRS)

We subjected siderite-magnesite carbonates to a short-lived thermal pulse. Individual magnetite grains that formed are 10 to 20 nm in size and randomly oriented. Shape and size distribution of these grains appear similar to those seen in ALH84001. Additional information is contained in the original extended abstract.

Koziol, Andrea M.; Brearley, Adrian J.

2002-01-01

314

Microbial formation of lanthanide-substituted magnetites by Thermoanaerobacter sp. TOR-39.  

PubMed

The potentially toxic effects of soluble lanthanide (L) ions, although microbially induced mineralization can facilitate the formation of tractable materials, has been one factor preventing the more widespread use of L-ions in biotechnology. Here, we propose a new mixed-L precursor method as compared to the traditional direct addition technique. L (Nd, Gd, Tb, Ho and Er)-substituted magnetites, L( y )Fe(3 - y )O(4) were microbially produced using L-mixed precursors, L( x )Fe(1 - x )OOH, where x = 0.01-0.2. By combining lanthanides into the akaganeite precursor phase, we were able to mitigate some of the toxicity, enabling the microbial formation of L-substituted magnetites using a metal reducing bacterium, Thermoanaerobacter sp. TOR-39. The employment of L-mixed precursors enabled the microbial formation of L-substituted magnetite, nominal composition up to L(0.06)Fe(2.94)O(4), with at least tenfold higher L-concentration than could be obtained when the lanthanides were added as soluble salts. This mixed-precursor method can be used to extend the application of microbially produced L-substituted magnetite, while also mitigating their toxicity. PMID:17673945

Moon, Ji-Won; Roh, Yul; Yeary, Lucas W; Lauf, Robert J; Rawn, Claudia J; Love, Lonnie J; Phelps, Tommy J

2007-11-01

315

Transformation of Magnetite to Goethite During Cr(VI) Reduction Under Alkaline pH Conditions  

SciTech Connect

This study investigated Cr(VI) reduction by synthetic magnetite under alkaline pH conditions similar to high level wastes at the Hanford site. Cr(VI) reduction by magnetite is significantly inhibited at alkaline pH, compared to the complete sorption/reduction at acid and neutral pH. This is probably due to (1) trace amounts of O2 in the system which depletes Fe(II) available for Cr(VI) reduction, since O2 is much more reactive than Cr(VI) under high pH conditions and (2) a formation of a passivation layer of maghemite and/or goethite blocking the Fe2+ surface sites in magnetite. Our experiments showed magnetite was indeed transformed into maghemite by a well-known process. However, TEM and XRD analyses showed a prominent goethite phase was also formed and the intensity of goethite peaks in the XRD spectra increased with NaOH concentration. Goethite formation has implications for enhanced removal of metal contaminants in the tank waste through sorption processes.

He, Thomas Y.; Traina, Samuel J.

2004-03-29

316

Bats Use Magnetite to Detect the Earth's Magnetic Field Richard A. Holland1,2  

E-print Network

Bats Use Magnetite to Detect the Earth's Magnetic Field Richard A. Holland1,2 *, Joseph L by which they detect the Earth's magnetic field remains unknown. Here we use the classic ``Kalmijn to Detect the Earth's Magnetic Field. PLoS ONE 3(2): e1676. doi:10.1371/ journal.pone.0001676 Editor: Sarah

317

Intermediate magnetite formation during dehydration of O zden O zdemir *, David J. Dunlop  

E-print Network

Intermediate magnetite formation during dehydration of goethite Oë zden Oë zdemir *, David J The dehydration of goethite has been studied by low-temperature induced magnetization (LTIM) and X-ray diffraction³C, for which only hematite was found. However, partially dehydrated goethites after the 238^402³C

Dunlop, David J.

318

First-order reversal curve (FORC) diagrams for pseudo-single-domain magnetites at high temperature  

E-print Network

First-order reversal curve (FORC) diagrams for pseudo-single-domain magnetites at high temperature Abstract The recently developed first-order reversal curve (FORC) technique for rapidly examining magnetic. On heating the FORC distributions contract without changing shape until V500C. Above this temperature

Dunlop, David J.

319

Magnetically recyclable magnetite-palladium (Nanocat-Fe-Pd) nanocatalyst for the Buchwald-Hartwig reaction  

EPA Science Inventory

The immobilization of Pd on magnetite surface afforded (Nanocat-Fe-Pd) using inexpensive precursors and its catalytic role in the Buchwald-Hartwig reaction for arylation of amines and amides was investigated; C-N bond formation was achieved in moderate to excellent yields and the...

320

Microbial formation of lanthanide-substituted magnetites by Thermoanaerobacter sp. TOR-39  

SciTech Connect

Lanthanide (Nd, Gd, Tb, Ho, and Er)-substituted magnetites, LyFe3-yO4 (L, lanthanide) were microbially synthesized using L-mixed precursors, LxFe1-xOOH, where x was between 0.01 and 0.2. By combining lanthanides (normally considered toxic to microorganisms) into the akaganeite precursor phase, we were able to mitigate some of the toxicity enabling the microorganisms to produce L-substituted magnetites. A metal reducing bacterium, Thermoanaerobacter ethanolicus successfully converted the mixed akaganeite to L-substituted magnetite while avoiding the potentially toxic effects of soluble L-ions. At higher mixing levels (0.02 < x <0.05) the poor crystallinity of L-mixed precursors increased the concentration of soluble toxic L-ions in the media. Nevertheless, using L-mixed precursors enabled production of microbially synthesized L-substituted magnetite with considerably higher L-concentration than could be obtained when the lanthanides were added as soluble salts. This method can therefore be used to extend the application for nanofermentation to fields where there is a need for nanoscale materials that involve elements such as lanthanides that are toxic or inhibitory to bacterial growth.

Moon, Ji Won [ORNL; Roh, Yul [Chonnam National University, Gwangju; Yeary, Lucas W [ORNL; Lauf, Robert J [ORNL; Rawn, Claudia J [ORNL; Love, Lonnie J [ORNL; Phelps, Tommy Joe [ORNL

2007-01-01

321

Magneto-optical Kerr effect in (titano)magnetite, pyrrhotite and hematite  

NASA Astrophysics Data System (ADS)

The successful application of the magneto-optical Kerr effect in rock magnetism is demonstrated. Domain structures of the most frequently occurring ferromagnetic minerals in rocks—(titano)magnetite, pyrrhotite and hematite—are shown. Surprisingly, the method works with hematite, where the Bitter pattern technique is not appropriate. Skin depth and sublattice interactions are discussed to explain the effect.

Appel, E.; Hoffmann, V.; Soffel, H. C.

322

Cranberry magnetite deposits Avery County, N.C., and Carter County, Tenn.  

USGS Publications Warehouse

The Cranberry magnetite deposits occur in pre-Cambrian granite-gneiss in a belt extending from 3 miles southeast of Cranberry, N.C., to about 6 miles southwest of Magnetic City, Tenn. The belt forms a curve, elongated to the north, approximately 26 miles in length.

Kline, M.H.; Ballard, T.J.

1948-01-01

323

Evaluation of the sediment remediation potential of magnetite impregnated activated carbons and biochars  

NASA Astrophysics Data System (ADS)

We evaluated the sediment remediation potential of magnetic composite materials synthesized by precipitating magnetite minerals onto activated carbons and biochars. Magnetite impregnation did not reduce the phenanthrene sorption capacity of the activated carbon or biochar component of the composite materials. The phenanthrene sorption capacity of the composite materials correlated with the surface areas of the pristine carbonaceous sorbents. XRD data and mass magnetic susceptibility data indicate that the mineral component of the composites is indeed nearly 100% magnetite. Addition of magnetic activated carbon to River Tyne sediment slurries reduced polycyclic aromatic hydrocarbon availability by more than 90%. After 3 months of mixing, 77% of the added magnetic activated carbon could be recovered with a magnetic rod. Continued monitoring showed that polycyclic aromatic hydrocarbon availability remained low following the magnetic recovery of most of the added sorbent mass. XRD analysis confirmed the presence of magnetite in the recovered sorbent material, with some other mineral phases such as calcite and quartz also being identifiable. Magnetic activated carbon has potential as a recoverable sorbent amendment for the treatment of sediment polluted with hydrophobic organic compounds. Further work will include an evaluation of the long-term magnetic sorbent effectiveness and stability in unmixed sediments under aerobic and anaerobic conditions and regeneration and re-use options for the recovered sorbent materials.

Werner, David; Han, Zhantao; Karapanagioti, Hrissi

2014-05-01

324

Rock Magnetic and Ferromagnetic Resonance Tests of Biogenic Magnetite in ALH84001  

NASA Technical Reports Server (NTRS)

Three separate rock magnetic and ferromagnetic resonance tests support the hypothesis that between 25 and 50% of the fine-grained magnetite in the Martian meteorite ALH84001 was formed via biological processes. Additional information is contained in the original extended abstract.

Kirschvink, J. L.; Kim, S.; Weiss, B. P.; Shannon, D. M.; Kobayashi, A. K.

2002-01-01

325

Deletion of the ftsZ-Like Gene Results in the Production of Superparamagnetic Magnetite Magnetosomes in Magnetospirillum gryphiswaldense? †  

PubMed Central

Magnetotactic bacteria (MTB) synthesize unique organelles termed “magnetosomes,” which are membrane-enclosed structures containing crystals of magnetite or greigite. Magnetosomes form a chain around MamK cytoskeletal filaments and provide the basis for the ability of MTB to navigate along geomagnetic field lines in order to find optimal microaerobic habitats. Genomes of species of the MTB genus Magnetospirillum, in addition to a gene encoding the tubulin-like FtsZ protein (involved in cell division), contain a second gene termed “ftsZ-like,” whose function is unknown. In the present study, we found that the ftsZ-like gene of Magnetospirillum gryphiswaldense strain MSR-1 belongs to a 4.9-kb mamXY polycistronic transcription unit. We then purified the recombinant FtsZ-like protein to homogeneity. The FtsZ-like protein efficiently hydrolyzed ATP and GTP, with ATPase and GTPase activity levels of 2.17 and 5.56 ?mol phosphorus per mol protein per min, respectively. The FtsZ-like protein underwent GTP-dependent polymerization into long filamentous bundles in vitro. To determine the role of the ftsZ-like gene, we constructed a ftsZ-like mutant (?ftsZ-like mutant) and its complementation strain (?ftsZ-like_C strain). Growth of ?ftsZ-like cells was similar to that of the wild type, indicating that the ?ftsZ-like gene is not involved in cell division. Transmission electron microscopic observations indicated that the ?ftsZ-like cells, in comparison to wild-type cells, produced smaller magnetosomes, with poorly defined morphology and irregular alignment, including large gaps. Magnetic analyses showed that ?ftsZ-like produced mainly superparamagnetic (SP) magnetite particles, whereas wild-type and ?ftsZ-like_C cells produced mainly single-domain (SD) particles. Our findings suggest that the FtsZ-like protein is required for synthesis of SD particles and magnetosomes in M. gryphiswaldense. PMID:20023033

Ding, Yao; Li, Jinhua; Liu, Jiangning; Yang, Jing; Jiang, Wei; Tian, Jiesheng; Li, Ying; Pan, Yongxin; Li, Jilun

2010-01-01

326

Study of pure NaI at room and liquid nitrogen temperatures  

Microsoft Academic Search

Three pure NaI crystals grown in different batches by Scionix (Holland) were studied at room and liquid nitrogen temperatures. The room temperature studies performed with photomultiplier readout covered measurements of emission spectra, photoelectrons yield and energy resolution. Moreover, the scintillation light pulses were measured by single photon method. Two crystals showed the photoelectron yield of about 1000 phe\\/MeV measured at

M. Moszynski; M. Balcerzyk; W. Czarnacki; M. Kapusta; W. Klamra; P. Schotanus; A. Syntfeld; M. Szawlowski

2002-01-01

327

First-principles calculations of pure elements: Equations of state and elastic stiffness constants  

Microsoft Academic Search

Using the projector-augmented wave method within the generalized gradient approximation, a systematic first-principles calculation for energy vs. volume (E–V) equations of state (EOS’s) and single crystal elastic stiffness constants (cij’s) has been performed for 76 pure elemental solids with face-centered-cubic (fcc), body-centered-cubic (bcc), and hexagonal-close-packed (hcp) crystal structures, wherein the cij’s are determined by an efficient strain–stress method, and the

S. L. Shang; A. Saengdeejing; Z. G. Mei; D. E. Kim; H. Zhang; S. Ganeshan; Y. Wang; Z. K. Liu

2010-01-01

328

Mössbauer hyperfine parameters of iron species in the course of Geobacter-mediated magnetite mineralization  

NASA Astrophysics Data System (ADS)

Amorphous ferric iron species (ferrihydrite or akaganeite of <5 nm in size) is the only known solid ferric iron oxide that can be reductively transformed by dissimilatory iron-reducing bacteria to magnetite completely. The lepidocrocite crystallite can be transformed into magnetite in the presence of abiotic Fe(II) at elevated pH or biogenic Fe(II) with particular growth conditions. The reduction of lepidocrocite by dissimilatory iron-reducing bacteria has been widely investigated showing varying results. Vali et al. (Proc Natl Acad Sci USA 101:16121-16126, 2004) captured a unique biologically mediated mineralization pathway where the amorphous hydrous ferric oxide transformed to lepidocrocite was followed by the complete reduction of lepidocrocite to single-domain magnetite. Here, we report the 57Fe Mössbauer hyperfine parameters of the time-course samples reported in Vali et al. (Proc Natl Acad Sci USA 101:16121-16126, 2004). Both the quadrupole splittings and linewidths of Fe(III) ions decrease consistently with the change of aqueous Fe(II) and transformations of mineral phases, showing the Fe(II)-mediated gradual regulation of the distorted coordination polyhedrons of Fe3+ during the biomineralization process. The aqueous Fe(II) catalyzes the transformations of Fe(III) minerals but does not enter the mineral structures until the mineralization of magnetite. The simulated abiotic reaction between Fe(II) and lepidocrocite in pH-buffered, anaerobic media shows the simultaneous formation of green rust and its gradual transformation to magnetite plus a small fraction of goethite. We suggested that the dynamics of Fe(II) supply is a critical factor for the mineral transformation in the dissimilatory iron-reducing cultures.

Li, Yi-Liang; Zhu, San-Yuan; Deng, Kun

2011-10-01

329

CVD synthesis of polycrystalline magnetite thin films: structural, magnetic and magnetotransport properties  

NASA Astrophysics Data System (ADS)

Magnetite (Fe3O4) is predicted to be half metallic at room temperature (RT) and it shows the highest Curie temperature among oxides. The use of Fe3O4 thin films is therefore promising for spintronic devices such as magnetic tunnel junctions (MTJs) and magnetoresistive sensors. The structural, magnetic and magnetotransport properties of magnetite are reported to be strongly dependent on the growth conditions. We have developed a very simple deposition chamber for growing thin magnetite films via a chemical vapour deposition (CVD) process based on the Fe3(CO)12 carbonyl precursor. The structural, morphological, and magnetic properties of the as deposited Fe3O4 films have been investigated by means of time of flight secondary ion mass spectrometry, grazing incidence x-ray diffraction, x-ray reflectivity, atomic force microscopy, conversion electron Mössbauer spectroscopy and superconducting quantum interference device magnetometry. Magnetotransport measurements show magnetoresistance up to -2.4% at RT at the maximum applied field of 1.1 T. Resistivity measurements in the 100-300 K temperature range reveal that the magnetotransport properties of the Fe3O4 films are governed by inter-granular tunnelling of the spin-polarized electrons. The spin polarization is estimated to be around -16%. A possible route for increasing the spin-polarized performances of our magnetite films is proposed. We have also deposited Fe3O4/MgO/Co stacks by using a combined CVD and atomic layer-deposition process. The trilayer's hysteresis curve evidences the presence of two distinct switching fields making it promising for magnetite-based MTJ applications.

Mantovan, R.; Lamperti, A.; Georgieva, M.; Tallarida, G.; Fanciulli, M.

2010-02-01

330

Fabrication of hollow multifunctional spheres containing MCM-41 nanoparticles and magnetite nanoparticles using layer-by-layer method.  

PubMed

Macroscopic mesoporous silica spheres have been fabricated by alternatively depositing preformed MCM-41 nanoparticles and polyelectrolytes onto polystyrene lattices. High surface area hollow mesoporous spheres were obtained by removal of the core by solvent or calcination. Further, the versatility of the layer-by-layer (LBL) method was extended to fabricate magnetite-mesoporous silica composites by depositing magnetite and MCM-41 nanoparticles onto polystyrene beads. Such high surface area composites are important since the mesopores can be used for encapsulation of varied materials like enzymes and drugs while the presence of magnetite ensures application in biocatalysis and separation under magnetic field. PMID:17010361

Sadasivan, Sajanikumari; Sukhorukov, Gleb B

2006-12-15

331

Pure Computable Model Theory Valentina S. Harizanov*  

E-print Network

, and J. B. Rernrnel 9 1998 Elsevier Science B.V. All rights reserved. #12;4 V.S. Harizanov Introduction on the Russian approach.) However, the article also presents some results of the Russian group, and often- liography contains both Western and Russian papers in pure computable #12;Chapter 1 Pure Computable

Shore, Richard A.

332

Pure representational neglect after right thalamic lesion  

Microsoft Academic Search

After a right thalamic stroke, an 86-year-old man presented an acute pure left representational neglect in the absence of any perceptual neglect. On spatial mental imagery tasks, the patient systematically omitted items located on his left side, but only when a vantage point was given. This suggests that (1) pure representational neglect is not just a residual finding after recovery

Isabelle Viaud-Delmon; Jean-Marie Annoni; Theodor Landis; Christoph Michel; Olaf Blanke; Patrik Vuilleumier

2001-01-01

333

Snow Crystals  

NSDL National Science Digital Library

This site is all about snow crystals and snowflakes. The many facets of snow crystals are described here, along with attempts to understand their formation. This site includes collections of super-high-resolution snow crystal photos, as well as links to learn about snow crystal classifications and how to make snow crystal fossils. Included in the study of how snow crystals form, these researchers have created snow crystals in the laboratory. Their snow crystal galleries include selections of images and movies of laboratory-grown snow crystals, as well as information on how to make your own snow crystals. The snow crystal primer describes what snow crystals are, how they form, and why they form the way they do. There is also a section on snow crystal physics.

Libbrecht, Kenneth

1999-02-01

334

Curious Crystals  

NSDL National Science Digital Library

Learners carefully look at four known household crystals. After observing and describing the crystals, learners are given an unknown crystal, which is chemically the same as one of the four known crystals but looks different. When learners realize that they cannot identify this crystal by its appearance alone, they will suggest other tests and ways to compare the crystals to eventually identify the unknown crystal. The related activities are examples of tests learners can conduct on the crystals. After a series of these tests, learners will gather enough evidence to identify the unknown crystal.

Kessler, James H.; Galvan, Patricia M.

2007-01-01

335

Modeling the solubility of pharmaceuticals in pure solvents and solvent mixtures for drug process design.  

PubMed

The knowledge of the solubility of pharmaceuticals in pure solvents and solvent mixtures is crucial for designing the crystallization process of drug substances. The first step in finding optimal crystallization conditions is usually a solvent screening. Since experiments are very time consuming, a model which allows for solubility predictions in pure solvents and solvent mixtures based only on a small amount of experimental data is required. In this work, we investigated the applicability of the thermodynamic model perturbed-chain statistical associating fluid theory (PC-SAFT) to correlate and to predict the solubility of exemplary five typical drug substances and intermediates (paracetamol, ibuprofen, sulfadiazine, p-hydroxyphenylacetic acid, and p-aminophenylacetic acid) in pure solvents and solvent mixtures. PMID:19283772

Ruether, Feelly; Sadowski, Gabriele

2009-11-01

336

Physics of water: Crystal-clear transition  

NASA Astrophysics Data System (ADS)

Liquid-liquid phase separation is counted among the peculiar phenomena attributed to pure water, but rapid crystallization has rendered its existence hard to prove. Evidence of a 'naked' liquid-liquid transition in a system unencumbered by crystallization encourages us to keep searching.

Starr, Francis W.

2014-09-01

337

Equilibrium Pure States and Nonequilibrium Chaos  

E-print Network

We consider nonequilibrium systems such as the Edwards-Anderson Ising spin glass at a temperature where, in equilibrium, there are presumed to be (two or many) broken symmetry pure states. Following a deep quench, we argue that as time goes to infinity, although the system is usually in some pure state locally, either it never settles permanently on a fixed lengthscale into a single pure state, or it does but then the pure state depends on both the initial spin configuration and the realization of the stochastic dynamics. But this latter case can occur only if there exists an uncountable number of pure states (for each coupling realization) with almost every pair having zero overlap. In both cases, almost no initial spin configuration is in the basin of attraction of a single pure state; that is, the configuration space (resulting from a deep quench) is all boundary (except for a set of measure zero). We prove that the former case holds for deeply quenched two-dimensional ferromagnets. Our results raise the possibility that even if more than one pure state exists for an infinite system, time averages don't necessarily disagree with Boltzmann averages.

C. M. Newman; D. L. Stein

1998-09-28

338

Influence of chloride and Fe(II) content on the reduction of Hg(II) by magnetite.  

PubMed

Abiotic reduction of inorganic mercury by natural organic matter and native soils is well-known, and recently there is evidence that reduced iron (Fe) species, such as magnetite, green rust, and Fe sulfides, can also reduce Hg(II). Here, we evaluated the reduction of Hg(II) by magnetites with varying Fe(II) content in both the absence and presence of chloride. Specifically, we evaluated whether magnetite stoichiometry (x = Fe(II)/Fe(III)) influences the rate of Hg(II) reduction and formation of products. In the absence of chloride, reduction of Hg(II) to Hg(0) is observed over a range of magnetite stoichiometries (0.29 < x < 0.50) in purged headspace reactors and unpurged low headspace reactors, as evidenced by Hg recovery in a volatile product trap solution and Hg L(III)-edge X-ray absorption near edge spectroscopy (XANES). In the presence of chloride, however, XANES spectra indicate the formation of a metastable Hg(I) calomel species (Hg2Cl2) from the reduction of Hg(II). Interestingly, Hg(I) species are only observed for the more oxidized magnetite particles that contain lower Fe(II) content (x < 0.42). For the more reduced magnetite particles (x ? 0.42), Hg(II) is reduced to Hg(0) even in the presence of high chloride concentrations. As previously observed for nitroaromatic compounds and uranium, magnetite stoichiometry appears to influence the rate of Hg(II) reduction (both in the presence and absence of chloride) confirming that it is important to consider magnetite stoichiometry when assessing the fate of contaminants in Fe-rich subsurface environments. PMID:23621619

Pasakarnis, Timothy S; Boyanov, Maxim I; Kemner, Kenneth M; Mishra, Bhoopesh; O'Loughlin, Edward J; Parkin, Gene; Scherer, Michelle M

2013-07-01

339

Study of a possible magnetite biosignature in Martian meteorite ALH84001: Implications for the biological toxicology of Mars  

NASA Astrophysics Data System (ADS)

"Why do we have such a longstanding fascination with Mars? Very simply put, it's about life. The search for life elsewhere in our Solar System has been a major driver for exploring Mars, pretty much since we began seriously looking at that planet."1 The major objective of this work is to describe signs of possible life, that is biosignatures, in rocks from Mars if indeed they are present. Biosignatures are specific identifiable properties that result from living things; they may be implanted in the environment and may persist even if the living thing is no longer present. Over 100 mineral biosignatures have been discussed in the literature; however, only one, magnetite, is addressed by this study. Magnetite is found in many rock types on earth and in meteorites. Previous studies of terrestrial magnetite have used few properties, such as size and chemical composition, to determine one of the modes of origins for magnetite (e.g., biogenic, inorganic). This study has established a rigorous set of six criteria for the identification of intracellularly precipitated biogenic magnetite. These criteria have been applied to a subpopulation of magnetites embedded within carbonates in Martian meteorite ALH84001. These magnetites are found to be chemically and physically indistinguishable from those produced by magnetotactic bacteria strain MV-1, hence, they were likely formed by biogenic processes on ancient Mars. These criteria may be also used to distinguish origins for magnetites from terrestrial samples with complex or unknown histories. The presence of purported past life on early Mars suggests that, if life once began it may still exist today, possibly in oases in the Martian subsurface. Future manned missions should consider potential hazards of an extant biological environment(s) on Mars. 1 Quote attributed to Jack Farmer of Arizona State University in discussing NASA's program of Mars Exploration (see "Deciphering Mars: Follow the Water," Astrobiology Magazine Sept. 12, 2005)

Thomas-Keprta, Kathie Louise

340

Modifying graphite oxide with grafted methyl acrylate brushes for the attachment of magnetite nanoparticles  

NASA Astrophysics Data System (ADS)

Surface-grafted polymer brushes of methyl acrylate of graphite oxide (GO) have been constructed to anchor poly(amidoamine) 2.0G (PAMAM 2.0G) dendrites for the attachment of magnetite nanoparticles. Monomers of methyl acrylate were copolymerized on the GO sheets by atom transfer radical polymerization. Then the PAMAM 2.0G was attached via covalent bond at the end of the grafted chains. Thus the inexpensive Fe(III) of ferric trichloride could coordinate with the remaining amino groups of PAMAM 2.0G and were reduced by the added sodium borohydrite at appropriate pH value to obtain nano magnetite-decorated GO hybrid materials. The hybrids exhibited a powerful catalysis on the degradation of aqueous solutions of hydroquinone.

Liu, Xiang; Cheng, Heming; Liu, Yan

2013-09-01

341

A new model for a magnetoreceptor in homing pigeons based on interacting clusters of superparamagnetic magnetite  

NASA Astrophysics Data System (ADS)

We present a new model of magnetic-field reception in magnetite-containing nerve terminals, which have recently been identified in the upper-beak skin of homing pigeons. The potentially magnetoreceptive nerve cells comprise chain-like aggregates with up to 20 closely spaced clusters of superparamagnetic (SP) magnetite. We designed experiments on superparamagnetic model systems to simulate the behaviour of the aggregates in varying magnetic fields. Magnetic-field induced interactions between the clusters in an aggregate gives rise to attractive and repulsive forces between the clusters. The resulting stress on the surrounding cellular structures varies with field direction and intensity. Our model is able to explain the principal features of the magnetic sense in homing pigeons as derived from behavioural experiments.

Davila, A. F.; Fleissner, G.; Winklhofer, M.; Petersen, N.

342

Fabrication of triple-layered magnetite-hydrogel-gold nanocomposites for biomedical applications.  

PubMed

Magnetite-hydrogel-gold nanocomposites with optical-active, thermo-responsive, and magnetism have been prepared by the following consecutive steps. Hydrogel-encapsulated magnetites were first synthesized by the combination of sol-gel reaction and radical polymerization process, and the resulting magnetic hydrogels were subsequently bound with nano-sized Au (1-3 nm) via a molecular linkage of diamine ligand which was covalently bonded to the carboxylic groups on the hydrogel surface. Au seeds anchored on the magnetic hydrogels were further reduced into nano-scale Au layer which induced the distinct red-shift of absorption band into NIR region. The optical properties and surface morphology of the nanocomposites were characterized by UV-vis spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). PMID:22629930

Lim, Sera; Lee, Sang-Wha

2012-02-01

343

Magnetite Nanoparticles Coated with Rifampicin and Chlortetracycline for Drug Delivery Applications  

SciTech Connect

Four types of biocompatible magnetic fluids based on superparamagnetic nanoparticles with Fe{sub 3}O{sub 4} cores were functionalized with antibiotics (rifampicin or chlortetracycline) as potential candidates for in vivo biomedical applications, such as magnetically controlled drug delivery. The synthesis consisted in coprecipitation of iron oxide in basic, as well as in acid medium, followed by the dispersion of the resulted magnetite nanoparticles in aqueous solution containing the antibiotic. The chosen method to prepare the magnetite-core/drug-shell systems avoided intermediate organic coating of the magnetic nanoparticles. Comparative analysis of the rheological features of the aqueous magnetic fluid samples was performed. The structural features of the coated magnetic particles were investigated by X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Vibrating Sample Magnetometry (VSM). Good crystallinity and adequate stability in time were evidenced. Drug delivery curves were spectrophotometrically provided.

Nadejde, Claudia; Ciurlica, Ecaterina Foca-nici; Creanga, Dorina; Carlescu, Aurelian [Faculty of Physics, Alexandru Ioan Cuza University of Iasi, 11A Carol I Bd., 700506, Iasi (Romania); Badescu, Vasile [National Institute of Research and Development for Technical Physics, 7 Mangeron Bd., Iasi (Romania)

2010-12-02

344

Solubilities of noble gases in magnetite - Implications for planetary gases in meteorites.  

NASA Technical Reports Server (NTRS)

Solubilities of noble gases in magnetite were determined by growing magnetite in a noble-gas atmosphere between 450 and 700 K. Henry's law is obeyed at pressures up to .01 atm for He, Ne, Ar and up to .00001 atm for Kr, Xe, with the following distribution coefficients at 500 K: He 0.042, Ne 0.016, Ar 3.6, Kr 1.3, Xe 0.88, some 100 to 100,000 times higher than previous determinations on silicate and fluoride melts. Apparent heats of solution are in sharp contrast with earlier determinations on melts which were small and positive, but are comparable to the values for clathrates. Presumably the gases are held in anion vacancies.

Lancet, M. S.; Anders, E.

1973-01-01

345

Crystal Creations.  

ERIC Educational Resources Information Center

Presents a many-faceted learning approach to the study of crystals. Provides instructions for performing activities including crystal growth and patterns, creating miniature simulations of crystal-containing rock formations, charcoal and sponge gardens, and snowflakes. (RT)

Whipple, Nona; Whitmore, Sherry

1989-01-01

346

Crystal Meth  

MedlinePLUS

... Navigation Home / Stories of Hope / Crystal meth Crystal meth Story Of Hope By giovanni January 3rd, 2013 ... my drug addiction having to deal with Crystal meth. I am now in recovery and fighting my ...

347

Conformal pure radiation with parallel rays  

NASA Astrophysics Data System (ADS)

We define pure radiation metrics with parallel rays to be n-dimensional pseudo-Riemannian metrics that admit a parallel null line bundle K and whose Ricci tensor vanishes on vectors that are orthogonal to K. We give necessary conditions in terms of the Weyl, Cotton and Bach tensors for a pseudo-Riemannian metric to be conformal to a pure radiation metric with parallel rays. Then, we derive conditions in terms of the tractor calculus that are equivalent to the existence of a pure radiation metric with parallel rays in a conformal class. We also give analogous results for n-dimensional pseudo-Riemannian pp-waves.

Leistner, Thomas; Nurowski, Pawe?

2012-03-01

348

Self-assembled MmsF proteinosomes control magnetite nanoparticle formation in vitro.  

PubMed

Magnetotactic bacteria synthesize highly uniform intracellular magnetite nanoparticles through the action of several key biomineralization proteins. These proteins are present in a unique lipid-bound organelle (the magnetosome) that functions as a nanosized reactor in which the particle is formed. A master regulator protein of nanoparticle formation, magnetosome membrane specific F (MmsF), was recently discovered. This predicted integral membrane protein is essential for controlling the monodispersity of the nanoparticles in Magnetospirillum magneticum strain AMB-1. Two MmsF homologs sharing over 60% sequence identity, but showing no apparent impact on particle formation, were also identified in the same organism. We have cloned, expressed, and used these three purified proteins as additives in synthetic magnetite precipitation reactions. Remarkably, these predominantly ?-helical membrane spanning proteins are unusually highly stable and water-soluble because they self-assemble into spherical aggregates with an average diameter of 36 nm. The MmsF assembly appears to be responsible for a profound level of control over particle size and iron oxide (magnetite) homogeneity in chemical precipitation reactions, consistent with its indicated role in vivo. The assemblies of its two homologous proteins produce imprecise various iron oxide materials, which is a striking difference for proteins that are so similar to MmsF both in sequence and hierarchical structure. These findings show MmsF is a significant, previously undiscovered, protein additive for precision magnetite nanoparticle production. Furthermore, the self-assembly of these proteins into discrete, soluble, and functional "proteinosome" structures could lead to advances in fields ranging from membrane protein production to drug delivery applications. PMID:25349410

Rawlings, Andrea E; Bramble, Jonathan P; Walker, Robyn; Bain, Jennifer; Galloway, Johanna M; Staniland, Sarah S

2014-11-11

349

Poly(amidehydroxyurethane) template magnetite nanoparticles electrosynthesis: I. Electrochemical aspects and identification  

Microsoft Academic Search

A new method for the electrochemical synthesis and surface-functionalization of magnetite nanoparticles (NPs) with poly(amidehydroxyurethane)\\u000a (PAmHU) is presented. Transmission Electron Microscopy shows the formation of NPs PAmHU cluster systems with individual NPs\\u000a ranging in size from 6 to 42 nm. Electron Spectroscopy for Chemical Analysis, Electron Paramagnetic Resonance measurements,\\u000a and X-ray Diffraction show that the electrochemically synthesized product contains NPs formed

V. Melnig; Laura Ursu

2011-01-01

350

Silica coated magnetite nanoparticles for removal of heavy metal ions from polluted waters  

E-print Network

Magnetic removal of Hg2+ and other heavy metal ions like Cd2+, Pb2+ etc. using silica coated magnetite particles from polluted waters is a current topic of active research to provide efficient water recycling and long term high quality water. The technique used to study the bonding characteristics of such kind of nanoparticles with the heavy metal ions is a very sensitive hyperfine specroscopy technique called the perturbed angular correlation technique (PAC).

Dash, Monika

2013-01-01

351

Ultrasound enhanced heterogeneous activation of peroxydisulfate by magnetite catalyst for the degradation of tetracycline in water  

Microsoft Academic Search

The removal of tetracycline by magnetite (Fe3O4) activated peroxydisulfate (Na2S2O8) in the presence of ultrasound irradiation has been performed in this study. The effects of Na2S2O8 concentration, Fe3O4 addition, ultrasonic power, initial concentration and initial pH on the degradation of tetracycline were investigated. The results showed that tetracycline removal rate increased with the increase of Fe3O4 dosage, but decreased with

Liwei Hou; Hui Zhang; Xiaofei Xue

352

Self-assembled MmsF proteinosomes control magnetite nanoparticle formation in vitro  

PubMed Central

Magnetotactic bacteria synthesize highly uniform intracellular magnetite nanoparticles through the action of several key biomineralization proteins. These proteins are present in a unique lipid-bound organelle (the magnetosome) that functions as a nanosized reactor in which the particle is formed. A master regulator protein of nanoparticle formation, magnetosome membrane specific F (MmsF), was recently discovered. This predicted integral membrane protein is essential for controlling the monodispersity of the nanoparticles in Magnetospirillum magneticum strain AMB-1. Two MmsF homologs sharing over 60% sequence identity, but showing no apparent impact on particle formation, were also identified in the same organism. We have cloned, expressed, and used these three purified proteins as additives in synthetic magnetite precipitation reactions. Remarkably, these predominantly ?-helical membrane spanning proteins are unusually highly stable and water-soluble because they self-assemble into spherical aggregates with an average diameter of 36 nm. The MmsF assembly appears to be responsible for a profound level of control over particle size and iron oxide (magnetite) homogeneity in chemical precipitation reactions, consistent with its indicated role in vivo. The assemblies of its two homologous proteins produce imprecise various iron oxide materials, which is a striking difference for proteins that are so similar to MmsF both in sequence and hierarchical structure. These findings show MmsF is a significant, previously undiscovered, protein additive for precision magnetite nanoparticle production. Furthermore, the self-assembly of these proteins into discrete, soluble, and functional “proteinosome” structures could lead to advances in fields ranging from membrane protein production to drug delivery applications. PMID:25349410

Rawlings, Andrea E.; Bramble, Jonathan P.; Walker, Robyn; Bain, Jennifer; Galloway, Johanna M.; Staniland, Sarah S.

2014-01-01

353

Ilmenite, magnetite, and peraluminous Mesoproterozoic anorogenic granites of Laurentia and Baltica  

Microsoft Academic Search

Emplacement of 1.6 to 1.3 Ga Mesoproterozoic plutons in Baltica and Laurentia formed an immense belt of A-type granite batholiths that include (1) low-fO2, ilmenite-series granite intrusions from the Baltic region to Wyoming, (2) high-fO2, magnetite-series granite intrusions of the central to southwestern U.S., and (3) peraluminous, two-mica granite intrusions from Colorado to central Arizona. These mineralogic divisions are mirrored

J. Lawford Anderson; Jean Morrison

2005-01-01

354

Dye adsorption characteristics of magnetite nanoparticles coated with a biopolymer poly(?-glutamic acid)  

Microsoft Academic Search

Magnetite nanoparticles coated with an anionic biopolymer poly(?-glutamic acid) (PGA-MNPs) were synthesized and characterized for their methylene blue dye adsorption capability. Both bare- and dye-loaded PGA-MNPs were characterized by FTIR, TEM and VSM measurements, revealing the PGA-MNPs to be superparamagnetic with average particle diameter being 12.4nm and magnetization value 59.2emu\\/g. The synthesized PGA-MNPs were stable in deionized, tap and river

B. Stephen Inbaraj; B. H. Chen

2011-01-01

355

Magnetite particles triggering a faster and more robust syntrophic pathway of methanogenic propionate degradation.  

PubMed

Interspecies electron transfer mechanisms between Bacteria and Archaea play a pivotal role during methanogenic degradation of organic matter in natural and engineered anaerobic ecosystems. Growing evidence suggests that in syntrophic communities electron transfer does not rely exclusively on the exchange of diffusible molecules and energy carriers such as hydrogen or formate, rather microorganisms have the capability to exchange metabolic electrons in a more direct manner. Here, we show that supplementation of micrometer-size magnetite (Fe3O4) particles to a methanogenic sludge enhanced (up to 33%) the methane production rate from propionate, a key intermediate in the anaerobic digestion of organic matter and a model substrate to study energy-limited syntrophic communities. The stimulatory effect most probably resulted from the establishment of a direct interspecies electron transfer (DIET), based on magnetite particles serving as electron conduits between propionate-oxidizing acetogens and carbon dioxide-reducing methanogens. Theoretical calculations revealed that DIET allows electrons to be transferred among syntrophic partners at rates which are substantially higher than those attainable via interspecies H2 transfer. Besides the remarkable potential for improving anaerobic digestion, which is a proven biological strategy for renewable energy production, the herein described conduction-based DIET could also have a role in natural methane emissions from magnetite-rich soils and sediments. PMID:24901501

Cruz Viggi, Carolina; Rossetti, Simona; Fazi, Stefano; Paiano, Paola; Majone, Mauro; Aulenta, Federico

2014-07-01

356

Magnetite in human tissues: A mechanism for the biological effects of weak ELF magnetic fields  

SciTech Connect

Due to the apparent lack of a biophysical mechanism, the question of whether weak, low-frequency magnetic fields are able to influence living organisms has long been one of the most controversial subjects in any field of science. However, two developments during the past decade have changed this perception dramatically, the first being the discovery that many organisms, including humans, biochemically precipitate the ferrimagnetic mineral magnetite (Fe3O4). In the magnetotactic bacteria, the geomagnetic response is based on either biogenic magnetite or greigite (Fe3S4), and reasonably good evidence exists that this is also the case in higher animals such as the honey bee. Second, the development of simple behavioral conditioning experiments for training honey bees to discriminate magnetic fields demonstrates conclusively that at least one terrestrial animal is capable of detecting earth-strength magnetic fields through a sensory process. In turn, the existence of this ability implies the presence of specialized receptors which interact at the cellular level with weak magnetic fields in a fashion exceeding thermal noise. A simple calculation shows that magnetosomes moving in response to earth-strength ELF fields are capable of opening trans-membrane ion channels, in a fashion similar to those predicted by ionic resonance models. Hence, the presence of trace levels of biogenic magnetite in virtually all human tissues examined suggests that similar biophysical processes may explain a variety of weak field ELF bioeffects. 61 refs.

Kirschvink, J.L.; Kobayashi-Kirschvink, A.; Diaz-Ricci, J.C.; Kirschvink, S.J. (California Institute of Technology, Pasadena (United States))

1992-01-01

357

Lunar soil simulant and synthesized nanoparticles of magnetite exhibit diverse neurotoxic potential  

NASA Astrophysics Data System (ADS)

Lunar soli simulant can be deleterious to human physiology and the components of lunar soil may be internalized by lung epithelium and may overcome the blood-brain barrier. Nanoparticles of ferric oxide are one of the components of Lunar soil simulants. Neurotoxic potential of lunar soil simulant and synthesized nanoparticles of magnetite was analyzed. The size of particles, their effects on membrane potential, acidification of synaptic vesicles, uptake and ambient level of glutamate, which is the major excitatory neurotransmitter in the CNS, were studied in isolated rat brain nerve terminals (synaptosomes) using photon correlation spectroscopy, spectrofluorimetry, radiolabeled assay, respectively. No significant effect of Lunar soil simulant and synthesized nanoparticles of magnetite on acidification of synaptic vesicles were found in synaptosomes. Also, nanoparticles did not influence the potential of the plasma membrane of synaptosomes. Unspecific binding of L-[14C]glutamate to synaptosomes was not altered by nanoparticles of magnetite, whereas in the presence of Lunar soil simulant this parameter was changed. Thus, it was suggested that Lunar soil simulant might disturb glutamate homeostasis in the mammalian CNS.

Borisova, Tatiana; Krisanova, Natalia; Sivko, Roman; Nazarova, Anastasiya; Borysov, Arseniy

358

XAFS study of starch-stabilized magnetite nanoparticles and surface speciation of arsenate.  

PubMed

It has been shown that starch can effectively stabilize nanoscale magnetite particles, and starch-stabilized magnetite nanoparticles (SMNP) are promising for in situ remediation of arsenic-contaminated soils. However, a molecular level understanding has been lacking. Here, we carried out XAFS studies to bridge this knowledge gap. Fe K-edge XAFS spectra indicated that the Fe-O and Fe-Fe coordination numbers of SMNP were lower than those for bare magnetite particles, and these coordination numbers decreased with increasing starch concentration. The decrease in the average coordination number at elevated stabilizer concentration was attributed to the increase in the surface-to-volume ratio. Arsenic K-edge XAFS spectra indicated that adsorbed arsenate on SMNP consisted primarily of binuclear bidentate (BB) complexes and monodentate mononuclear (MM) complexes. More BB complexes (energetically more favorable) were observed at higher starch concentrations, indicating that SMNP not only offered greater adsorption surface area, but also stronger adsorption affinity toward arsenate. PMID:21890253

Zhang, Meiyi; Pan, Gang; Zhao, Dongye; He, Guangzhi

2011-12-01

359

Method for solid state crystal growth  

DOEpatents

A novel method for high quality crystal growth of intermetallic clathrates is presented. The synthesis of high quality pure phase crystals has been complicated by the simultaneous formation of both clathrate type-I and clathrate type-II structures. It was found that selective, phase pure, single-crystal growth of type-I and type-II clathrates can be achieved by maintaining sufficient partial pressure of a chemical constituent during slow, controlled deprivation of the chemical constituent from the primary reactant. The chemical constituent is slowly removed from the primary reactant by the reaction of the chemical constituent vapor with a secondary reactant, spatially separated from the primary reactant, in a closed volume under uniaxial pressure and heat to form the single phase pure crystals.

Nolas, George S.; Beekman, Matthew K.

2013-04-09

360

Schmidt Analysis of Pure-State Entanglement  

E-print Network

We examine the application of Schmidt-mode analysis to pure state entanglement. Several examples permitting exact analytic calculation of Schmidt eigenvalues and eigenfunctions are included, as well as evaluation of the associated degree of entanglement.

J. H. Eberly

2005-08-02

361

The criminological potential of pure sociology  

Microsoft Academic Search

The pure sociology perspective invented by Donald Black, a general theoretical framework for the prediction and explanation\\u000a of social reality, has considerable potential for the scientific understanding of criminal behavior. Several scholars have\\u000a profitably drawn upon Black’s proposal that a significant amount of crime is a form of disputing or social control, especially\\u000a to explain violent conflict. However, pure sociology

Mark Cooney

2006-01-01

362

Pure Quantum Solutions of Bohmian Quantum Gravity  

E-print Network

In this paper we have investigated the pure quantum solutions of Bohmian quantum gravity. By pure quantum solution we mean a solution in which the quantum potential cannot be ignored with respect to the classical potential, especially in Bohmian quantum gravity we are interested in the case where these two potentials are equal in their magnitude and in fact their sum is zero. Such a solutions are obtained both using the perturbation and using the linear field approximation.

Fatimah Shojai; Ali Shojai

2001-05-28

363

On projections to the pure spinor space  

NASA Astrophysics Data System (ADS)

A family of covariant non-linear projections from the space of SO(10) Weyl spinors onto the space of pure SO(10) Weyl spinors is presented. The Jacobian matrices of these projections are related to a linear projector which was previously discussed in pure spinor string literature and which maps the antighost to its gauge invariant part. Only one representative of the family leads to a Hermitian Jacobian matrix and can itself be derived from a scalar potential. Comments on the SO(1,9) case are given as well as on the non-covariant version of the projection map. The insight is applied to the ghost action of pure spinor string theory, where the constraints on the fields can be removed using the projection, while introducing new gauge symmetries. This opens the possibility of choosing different gauges which might help to clarify the origin of the pure spinor ghosts. Also the measure of the pure spinor space is discussed from the projection point of view. The appendix contains the discussion of a toy model which served as a guideline for the pure spinor case.

Grassi, P. A.; Guttenberg, S.

2011-12-01

364

Growth and characterization of L-tryptophan doped KDP crystals  

NASA Astrophysics Data System (ADS)

Potassium Dihydrogen Phosphate crystals are one of the most popular crystals used for Non-linear Optical applications. Most of the amino acids also exhibit NLO properties. The effect of doping of one of the amino acids, L-tryptophan in KDP crystals has been investigated. Pure and L-tryptophan doped KDP crystals were grown by slow solvent evaporation solution growth technique. Good quality transparent crystals were obtained. Doping of L-tryptophan in KDP crystal was confirmed by FT-IR spectroscopy studies. The value of second harmonic generation efficiency and optical transmission in UV-Vis spectra increased as doping of L-tryptophan increased in KDP crystals.

Parikh, K. D.; Dave, D. J.; Parekh, B. B.; Joshi, M. J.

2013-06-01

365

Spherulite Crystallization Induces Fe-Redox Redistribution in Silicic Melt  

SciTech Connect

Rhyolitic obsidians from Krafla volcano, Iceland, record the interaction between mobile hydrous species liberated during crystal growth and the reduction of ferric iron in the silicate melt. We performed synchrotron {mu}-FTIR and {mu}-XANES measurements along a transect extending from a spherulite into optically distinct colorless and brown glass zones. Measurements show that the colorless glass is enriched in OH groups and depleted in ferric iron, while the brown glass shows the opposite relationship. The color shift between brown and clear glass is sharp, suggesting that the colorless glass zone was produced by a redox front that originated from the spherulite margin and moved through surrounding melt during crystallization. We conclude that the most likely reducing agent is hydrogen, produced by magnetite crystallization within the spherulite. The Krafla obsidians dramatically capture redox disequilibrium on the micoscale and highlight the importance of hydrous fluid liberation and late-stage crystallization to the redox signature of glassy lavas.

Castro, J.; Cottrell, E; Tuffen, H; Logan, A; Kelley, K

2009-01-01

366

Inorganic chemistry: Direct syntheses from pure liquid SO3 and from trivalent and pentavalent nitrogen derivatives  

NASA Technical Reports Server (NTRS)

From pure liquid SO3 direct synthesis reactions were carried out with N2O5, NO2Cl, NOCl which yielded N2O54SO3, 3SO3, 2SO3-NO2Cl2SO3-NOCl2SO3 and NOCl2SO3, the latter being obtained for the first time in the pure state. In all cases the crystallized product was obtained by separating the constituents of the mixture and then going through a single viscous liquid phase.

Vandorpe, B.; Heubel, J.

1977-01-01

367

Stability of the association fayalite + calcite within metamorphosed banded iron formations: the case of the magnetite ores of Edough massif (N-E  

E-print Network

. The main minerals of the ore bodies are magnetite, hematite, siderite, quartz, calcite, fayalite, hedenbergite and garnet, resulting from the metamorphism of siderite + calcite + quartz rocks containing

Paris-Sud XI, Université de

368

Crystallization of soft crystals.  

PubMed

The crystallization of micelles formed by surfactant F127 solvated by 20% in water was investigated in the vicinity of a hydrophilic interface. Upon entering the crystalline phase from low temperature, a large correlation length develops without preferential texture. Upon heating, the correlation length decreases and Oswald ripening is observed with crystallites orienting with respect to each other while retaining long-range and textured correlation. PMID:19115865

Wolff, Max; Magerl, Andreas; Zabel, Hartmut

2009-01-01

369

77 FR 59979 - Pure Magnesium (Granular) From China  

Federal Register 2010, 2011, 2012, 2013

...731-TA-895 (Second Review)] Pure Magnesium (Granular) From China Determination...of the antidumping duty order on pure magnesium (granular) from China would be likely...4350 (September 2012), entitled Pure Magnesium (Granular) from China:...

2012-10-01

370

BRST and the pure spinor formalism  

SciTech Connect

The aim of this talk is to show the relation between the standard BRST approach of the GS superstring with the quantization technics used in the pure spinor approach to superstring. To that end we will use the Batalin-Fradkin-Tyutin (BFT) conversion program of second class constraints to first class constraints in the GS superstring using light cone coordinates. By applying this systematic procedure we were able to obtain a gauge system that is equivalent to the recent model proposed in [1] to relate the GS superstring to the pure spinor formalism.

Garcia, J. Antonio [Instituto de Ciencias Nucleares, Univesidad Nacional Autonoma de Mexico Apartado Postal 70-543, Mexico D.F. (Mexico)

2008-03-06

371

Pure spinors, twistors, and emergent supersymmetry  

NASA Astrophysics Data System (ADS)

Starting with a classical action whose matter variables are a d = 10 spacetime vector x m and a pure spinor ? ? , the pure spinor formalism for the superstring is obtained by gauge-fixing the twistor-like constraint ?x m ( ? m ?) ? = 0. The fermionic variables ? ? are Faddeev-Popov ghosts coming from this gauge-fixing and replace the usual ( b, c) ghosts coming from gauge-fixing the Virasoro constraint. After twisting the ghost-number such that ? ? has ghost-number zero and ? ? has ghost-number one, the BRST cohomology contains the usual spacetime supersymmetric states of the superstring.

Berkovits, Nathan

2012-12-01

372

Toward a new < 250 °C pyrrhotite-magnetite geothermometer for claystones  

NASA Astrophysics Data System (ADS)

We investigate the effects of burial and moderate experimental heating on claystones from three regions with different degrees of maturation: immature (burial temperature ˜ 40 °C) of Bure Callovo-Oxfordian claystones in the Basin of Paris (France); early mature (burial temperature ˜ 85 °C) of Opalinus Lower Dogger claystones from the Mont Terri anticline in front of the Jura fold belt (Switzerland); and mature to overmature (burial temperature < 170 °C) of Chartreuse Callovian-Oxfordian claystones from Chartreuse Sub-Alpine chains. To have information about the nature of the magnetic assemblage, we perform low-temperature (10 K-300 K) investigation of an isothermal remanent magnetization. In a first set of laboratory heating experiments, we aim to impart a chemical remanent magnetization (CRM) at 95 °C for several weeks in Bure and Opalinus claystones. Thermal demagnetization of the CRM reveals that magnetite is formed by heating the Opalinus claystones while an assemblage of magnetite and iron sulphide is formed in Bure claystones. Further, we document the appearance of a magnetic transition at ˜ 35 K in Bure claystones after heating. We name this transition the P-transition and we propose that it is related to the formation of fine-grained pyrrhotite (Fe 7S 8). The P-transition is also detected in early mature to mature Opalinus and Chartreuse claystones. We conduct additional experimental heating of natural Opalinus claystones. One set of experiments is referred to as short-term heating (1 h) from 100 °C to 200 °C. It is dedicated to an investigation of the effect of short-lived heating processes in geology. A second set of heating experiments is designed to approach burial conditions using a gold capsule. In burial-like experiments, we heated Opalinus claystones from 150 °C to 250 °C for several weeks under a pressure of 100 MPa. In both experiments, we observe a correlative diminution of the pyrrhotite signature at 35 K with increasing temperature. We interpret this trend as the appearance of magnetite. We derive a parameter PM from the warming curve of a saturated isothermal remanent magnetization acquired at 10 K (ZFC). We report on a consistent evolution of PM with temperature in the range of 40 °C to 250 °C, including natural samples, heated samples at 95 °C, and burial-like heated samples. PM first increases between ˜ 40 °C up to ˜ 85 °C, implying that pyrrhotite gradually dominates the magnetic assemblage at low temperature. For temperatures above 85 °C, PM decreases up to 250 °C, implying that the formation of magnetite gradually overshadows the magnetic input of pyrrhotite. PM values obtained from mature to overmature claystones from the Chartreuse are lower than the PM values obtained from the burial-like heated Opalinus claystones, suggesting that the formation of magnetite is driven by kinetics. The continuous trend of the PM parameter suggests that the magnetic properties of pyrrhotite-magnetite claystones can be used to infer paleo-temperatures and we propose to name this geothermometer MagEval.

Aubourg, Charles; Pozzi, Jean-Pierre

2010-05-01

373

Adsorption-desorption mechanism of phosphate by immobilized nano-sized magnetite layer: interface and bulk interactions.  

PubMed

Phosphate adsorption mechanism by a homogenous porous layer of nano-sized magnetite particles immobilized onto granular activated carbon (nFe-GAC) was studied for both interface and bulk structures. X-ray Photoelectron Spectroscopy (XPS) analysis revealed phosphate bonding to the nFe-GAC predominantly through bidentate surface complexes. It was established that phosphate was adsorbed to the magnetite surface mainly via ligand exchange mechanism. Initially, phosphate was adsorbed by the active sites on the magnetite surface, after which it diffused into the interior of the nano-magnetite layer, as indicated by intraparticle diffusion model. This diffusion process continues regardless of interface interactions, revealing some of the outer magnetite binding sites for further phosphate uptake. Desorption, using NaOH solution, was found to be predominantly a surface reaction, at which hydroxyl ions replace the adsorbed phosphate ions only at the surface outer biding sites. Five successive fix-bed adsorption/regeneration cycles were successfully applied, without significant reduction in the nFe-GAC adsorption capacity and at high regeneration efficiency. PMID:21855083

Zach-Maor, Adva; Semiat, Raphael; Shemer, Hilla

2011-11-15

374

Structural Modification and Self-Assembly of Nanoscale Magnetite Synthesised in the Presence of an Anionic Surfactant  

NASA Astrophysics Data System (ADS)

The earliest reported medical use of magnetite powder for internal applications was in the 10th century A.D. by the Persian physician and philosopher Avicenna of Bokhara [1,2]. Today magnetic nanoparticles are used for magnetic resonance imaging (MRI) and are potential colloidal mediators for cancer magnetic hyperthermia [3]. Twenty years ago magnetite (Fe3O4) was found to be present in the human brain [4] and more recently it has been reported that nanoscale biogenic magnetite (origin and formation uncertain) is associated with neurodegenerative diseases such as Parkinson's, Huntington's and Alzheimer's [5]. Here we show that the synthesis of magnetite in the presence of the surfactant sodium dodecyl sulphate (SDS) gives rise to a variety of nanoscale morphologies, some of which look remarkably similar to magnetite found in organisms, suggesting that similar processes may be involved. Furthermore, these 1D materials with diameters of quantum confined size are of interest in the areas of biosensors [6] and biomedical imaging [7].

Malik, S.; Hewitt, I. J.; Powell, A. K.

2014-07-01

375

Epitaxial Fe{sub 3-x}Ti{sub x}O{sub 4} films from magnetite to ulvöspinel by pulsed laser deposition  

SciTech Connect

Epitaxial films along the Fe{sub 3-x}Ti{sub x}O{sub 4} (titanomagnetite) compositional series from pure end-members magnetite (Fe{sub 3}O{sub 4}) to ulvöspinel (Fe{sub 2}TiO{sub 4}) were successfully grown by pulsed laser deposition on MgO(100) substrates. Spectroscopic characterization including high resolution x-ray diffraction, x-ray photoelectron spectroscopy, and synchrotron-based x-ray absorption and magnetic circular dichroism consistently shows that Ti(IV) substitutes for Fe(III) in the inverse spinel lattice with a proportional increase in lattice Fe(II) concentration. No evidence of Ti interstitials, spinodal decomposition, or secondary phases was found in the bulk of the grown films. At the uppermost few nanometers of the Ti-bearing film surfaces, evidence suggests that Fe(II) is susceptible to facile oxidation, and that an associated lower Fe/Ti ratio in this region is consistent with surface compositional incompleteness or alteration to a titanomaghemite-like composition and structure. The surface of these films nonetheless appear to remain highly ordered and commensurate with the underlying structure despite facile oxidation, a surface condition that is found to be reversible to some extent by heating in low oxygen environments.

Droubay, T.C.; Pearce, C.I.; Ilton, E.S.; Engelhard, M.H.; Engelhard, M.H.; Heald, S.M.; Arenholz, E.; Rosso, K.M.

2011-07-21

376

Critical single domain grain sizes in chains of interacting greigite particles: Implications for magnetosome crystals  

NASA Astrophysics Data System (ADS)

Magnetotactic bacteria contain chains of magnetically interacting crystals (magnetosomes), which aid navigation (magnetotaxis). To improve the efficiency of magnetotaxis, magnetosome crystals (which can consist of magnetite or greigite) should be magnetically stable single domain (SD) particles. Larger particles subdivide into nonuniform multidomain (MD) magnetic structures that produce weaker magnetic signals, while small SD particles become magnetically unstable due to thermal fluctuations and exhibit superparamagnetic (SP) behavior. In this study, we determined the stable SD range as a function of grain elongation and interparticle separation for chains of identical greigite grains using fundamental parameters recently determined for greigite. Interactions significantly increase the stable SD range. For example, for cube-shaped greigite grains the upper stable SD threshold size is increased from 107 nm for isolated grains to 204 nm for touching grains arranged in chains. The larger critical SD grain size for greigite means that, compared to magnetite magnetosomes, greigite magnetosomes can produce larger magnetic signals without the need for intergrain interactions.

Muxworthy, Adrian R.; Williams, Wyn; Roberts, Andrew P.; Winklhofer, Michael; Chang, Liao; Pósfai, Mihály

2013-12-01

377

(Non)triviality of Pure Spinors and Exact Pure Spinor - RNS Map  

E-print Network

All the BRST-invariant operators in pure spinor formalism in $d=10$ can be represented as BRST commutators, such as $V=\\lbrace{Q_{brst}},{{\\theta_{+}}\\over{\\lambda_{+}}}V\\rbrace$ where $\\lambda_{+}$ is the U(5) component of the pure spinor transforming as $1_{5\\over2}$. Therefore, in order to secure non-triviality of BRST cohomology in pure spinor string theory, one has to introduce "small Hilbert space" and "small operator algebra" for pure spinors, analogous to those existing in RNS formalism. As any invariant vertex operator in RNS string theory can also represented as a commutator $V=\\lbrace{Q_{brst}},LV\\rbrace$ where $L=-4c\\partial\\xi{\\xi}e^{-2\\phi}$, we show that mapping ${{\\theta_{+}}\\over{\\lambda_{+}}}$ to L leads to identification of the pure spinor variable $\\lambda^{\\alpha}$ in terms of RNS variables without any additional non-minimal fields. We construct the RNS operator satisfying all the properties of $\\lambda^\\alpha$ and show that the pure spinor BRST operator $\\oint{\\lambda^\\alpha{d_\\alpha}}$ is mapped (up to similarity transformation) to the BRST operator of RNS theory under such a construction. We also observe that BRST cohomology of pure spinor superstring theory contains vertex operators non-trivially coupled to the pure spinor ghost variable. The physical interpretation of these operators remains unclear.

Dimitri Polyakov

2008-10-26

378

`Pure air, pure water and good light' Sanitary reform in the Dublin hospitals, 1858-1898  

E-print Network

;Overview ... Discourses of public health in C19 Urban sanitation in Dublin, c. 1850 Public health and hospital sanitation `Pure air, pure water and good light' Sanitary reform in the Dublin hospitals, 1858-1898 Public health and hospital sanitation The Board of Superintendence of Dublin Hospitals Discussion

379

Effect of digestion time and alkali addition rate on physical properties of magnetite nanoparticles.  

PubMed

We investigate the effect of digestion time and alkali addition rate on the size and magnetic properties of precipitated magnetite nanoparticles. It is observed that the time required to complete the growth process for magnetite nanocrystals is very short (approximately 300 s), compared to long digestion times (20-190 min) required for MnO and CdSe nanocrystals. The rapid growth of magnetite nanoparticles suggests that Oswald ripening is insignificant during the precipitation stage, due to the low solubility of the oxides and the domination of a solid-state reaction where high electron mobility between Fe2+ and Fe3+ ions drives a local cubic close-packed ordering. During the growth stage (0-300 s), the increase in the particle size is nominal (6.7-8.2 nm). The effect of alkali addition rate on particle size reveals that the nanocrystal size decreases with increasing alkali addition rate. The particle size decreases from 11 to 6.8 nm as the alkali addition rate is increased from 1 to 80 mL/s. During the size decrease, the lattice parameter decreases from 0.838 to 0.835 nm, which is attributed to an increase in the amount of Fe3+ atoms at the surface due to oxidation. As the alkali addition rate increases, the solution reaches supersaturation state rapidly leading to the formation of large number of initial nuclei at the nucleation stage, resulting in large number of particles with smaller size. When alkali addition rate is increased from 1 to 80 mL/s, the saturation magnetization of the particles decreases from 60 to 46 emu/g due to the reduced particle size. PMID:17580856

Gnanaprakash, G; Philip, John; Jayakumar, T; Raj, Baldev

2007-07-19

380

Micro-CT molecular imaging of tumor angiogenesis using a magnetite nano-cluster probe.  

PubMed

Due to its high resolution, micro-CT is desirable for molecular imaging of tumor angiogenesis. However, the sensitivity of micro-CT to contrast agents is relatively low. Therefore, the purpose of this study is to develop high micro-CT sensitive molecular imaging probes for direct visualization and dynamic monitoring of tumor angiogenesis. To this end, Arg-Gly-Asp (RGD) peptides conjugated magnetite nano clusters (RGD-MNCs) were developed by assembling individual magnetite nano particles into clusters with amphiphilic (maleimide) methoxypoly(ethylene glycol)-b-poly(lactic acid) ((Mal)mPEG-PLA) copolymer and subsequently encoding RGD peptides onto the clusters for specific targeting alpha(v)beta3 integrin. The hydrodynamic size of RGD-MNCs was about 85 nm. To test its specificity, alpha(v)beta3 positive cells (H1299) were incubated with magnetite nano clusters (MNCs), RGD-MNCs or RGD-MNCs competition with free RGD peptides. Prussian Blue staining and inductively coupled plasma optical emission spectrometer (ICP-OES) measurements indicated that the cell uptake of RGD-MNCs was significantly more than that of MNCs, which could be inhibited by free RGD peptides. For detection of tumor angiogenesis, mice bearing H1299 tumors were injected intravenously with RGD-MNCs at the dose of 400 micro mol Fe/kg. Tumor angiogenic hot spots as well as individual angiogenic vessels could be clearly manifested by micro-CT imaging 12 h post injection, which was dynamically monitored with the extension of probe circulation time. Subsequent histological studies of tumor tissues verified that RGD-MNCs registered tumor angiogenic vessels. Our study demonstrated that RGD-MNC probes fabricated in this study could be used to effectively target alpha(v)beta3 integrin. Using high resolution micro-CT in combination with the probes, tumor angiogenesis could be studied dynamically. PMID:23858968

Liu, Ping; Li, Jing; Zhang, Chunfu; Xu, Lisa X

2013-06-01

381

Genotoxicity and inflammatory investigation in mice treated with magnetite nanoparticles surface coated with polyaspartic acid  

NASA Astrophysics Data System (ADS)

In this study, some biological tests were carried out with a magnetic fluid (MF) sample based on magnetite nanoparticles (MNPs) surface coated with polyaspartic acid (PAMF). The tests were performed from 1 to 30 days after injection of 50 ?L of PAMF in Swiss mice. The PAMF biocompatibility/toxicity was evaluated through cytometry, micronuclei assay, and morphology of several organs. All observed results were time and dose dependent. The data indicate that MNPs surface-treated with polyaspartic acid may be considered as a potential precursor of anticancer drugs.

Sadeghiani, N.; Barbosa, L. S.; Silva, L. P.; Azevedo, R. B.; Morais, P. C.; Lacava, Z. G. M.

2005-03-01

382

Iron site occupancies in magnetite-ulvospinel solid solution: A new approach using XMCD  

SciTech Connect

Ordering of Fe{sup 3+} and Fe{sup 2+} between octahedral (Oh) and tetrahedral (Td) sites in synthetic members of the magnetite (Fe{sub 3}O{sub 4}) - ulvoespinel (Fe{sub 2}TiO{sub 4}) solid-solution series was determined using Fe L{sub 2,3}-edge X-ray magnetic circular dichroism (XMCD) coupled with electron microprobe and chemical analysis, Ti L-edge spectroscopy, Fe K-edge EXAFS and XANES, Fe{sub 57} Moessbauer spectroscopy, and unit cell parameters. Microprobe analysis, cell edges and chemical FeO determinations showed that the bulk compositions of the samples were stoichiometric magnetite-ulvoespinel solid-solutions. Surface sensitive XMCD showed that the surfaces of these oxide minerals were more sensitive to redox conditions and some samples required re-equilibration with suitable solid-solid buffers. Detailed site-occupancy analysis of these samples gave XMCD-Fe{sup 2+}/Fe{sup 3+} ratios very close to stoichiometric values. L{sub 2,3}-edge spectroscopy showed that Ti{sup 4+} was restricted to Oh sites. XMCD results showed that significant Fe{sup 2+} only entered Td when the Ti content was > 0.40 apfu while Fe{sup 2+} in Oh increased from 1 a.p.f.u in magnetite to a maximum of {approx}1.4 apfu in USP45. As the Ti content increased from this point, the steady increase in Fe{sup 2+} in Td sites was clearly observable in the XMCD spectra, concurrent with a slow decrease in Fe{sup 2+} in Oh sites. Calculated magnetic moments showed a steady decrease from magnetite (4.06 {mu}{sub B}) to USP45 (1.5 {mu}{sub B}) and then a slower decrease towards the value for ulvoespinel (0 {mu}{sub B}). Two of the synthesized samples were also partially maghemitized by re-equilibrating with an oxidizing Ni-NiO buffer and XMCD showed that Fe{sup 2+} oxidation only occurred at Oh sites, with concomitant vacancy formation restricted to this site. This study shows the advantage of using XMCD as a direct measurement of Fe oxidation state in these complex magnetic spinels. These results can be used to rationalize the magnetic properties of titanomagnetites, and their oxidized titanomaghemitized analogues, in Earth's crustal rocks.

Pearce, C. I.; Henderson, C. M. B.; Telling, N. D.; Pattrick, R. A.D.; Vaughan, D. J.; Charnock, J. M.; Arenholz, E.; Tuna, F.; Coker, V.S.; Laan, G. van der

2009-06-22

383

A double-coated magnetite-based magnetic fluid evaluation by cytometry and genetic tests  

NASA Astrophysics Data System (ADS)

Magnetite nanoparticles pre-coated with dodecanoic acid and ethoxylated alcohol (DE) were used to obtain a physiologically stable magnetic fluid (DE-MF) sample. Three different doses of DE-MF were intraperitoneally applied to mice. Blood and peritoneum cytometry and micronucleus test were performed for 1-21 days after injection to investigate the DE-MF toxicity. Changes in cell population, peritoneum inflammation, and potential DE-MF genotoxic action were all time and dose dependent. At the lowest dose (5×10 15 particles/kg), DE-MF seems to be useful as a drug precursor with both diagnostic and therapeutic values.

Freitas, M. L. L.; Silva, L. P.; Azevedo, R. B.; Garcia, V. A. P.; Lacava, L. M.; Grisólia, C. K.; Lucci, C. M.; Morais, P. C.; Da Silva, M. F.; Buske, N.; Curi, R.; Lacava, Z. G. M.

2002-11-01

384

Biogenic or Abiogenic Origin of Carbonate-Magnetite-Sulfide Assemblages in Martian Meteorite Allan Hills 84001  

NASA Astrophysics Data System (ADS)

It has been suggested that the carbonates and submicrometer grains of magnetite, pyrrhotite, and an Fe-S phase identified as "probably griegite" were all biogenic in origin. Their arguments were based on similarities in the compositions, structures, shapes, and sizes of these minerals with terrestrial bio-minerals and the apparent absence of plausible abiogenic origins. Here we compare the carbonate assemblages to possible martian, terrestrial, and meteoritic analogs and discuss new and published arguments for and against abiogenic and biogenic origins for these minerals.

Scott, E. R. D.

1998-01-01

385

Nanostructured magnetite (Fe 3O 4) thin films prepared by sol-gel method  

NASA Astrophysics Data System (ADS)

Nanostructured magnetite (Fe 3O 4) thin films have been prepared by a sol-gel method heated at 300°C. The film with a black appearance is homogeneous without cracks by adding N, N-dimethyl formamide (DMF) as drying chemical control agent (DCCA). The root mean square roughness of the thin film is only 2 nm, and the nanograins show a narrow size distribution with an average size of 12.5 nm. The magneto-optical Kerr effect (MOKE), measured in the applied field range from 0 to 1.9 T, reveals that the film exhibits superparamagnetism.

Tang, N. J.; Zhong, W.; Jiang, H. Y.; Wu, X. L.; Liu, W.; Du, Y. W.

2004-11-01

386

A New Method of Preparation of Magnetite Nanoparticles from Iron Oxide Hydroxide  

NASA Astrophysics Data System (ADS)

There are only two basic ways to produce magnetite at low temperature: by partial oxidation of a FeII salt solution with oxidant under alkaline condition and by precipitation of a mixed FeII/FeIII solution. At high temperature, the method involves reduction of iron oxide by a suitable reductant. Here we propose a new method of preparation of nanoparticle Fe3O4 from iron oxyhydroxides (goethite, akaganeite, lepidocrocite, feroxyhyte and ferrihydrite) or iron oxide (hematite) and ferrous salt in aqueous solution. Products characterized by X-ray powder diffraction, IR spectra and vibrating sample magentometery.

Kahani, S. A.; Jafari, M.

2007-08-01

387

One-pot reaction to synthesize PEG-coated hollow magnetite nanostructures with excellent magnetic properties.  

PubMed

We first demonstrate a simple "one-pot" method to synthesis uniform Fe3O4 hollow microspheres in the presence of PEG in ethylene glycol by using urea to control their morphologies. The interior cavity of the hollow spheres can be tunable by reaction time. The Lamer model was used to explain the formation of magnetite hollow spherical structures based on the experimental observations. The obtained hollow Fe3O4 microspheres showing superparamagnetism with a high saturation magnetization of ca. 86.4 emu/g, and also had an enrichment surface of -OH groups, which will be favorable to the further modification with other biomedical molecules. PMID:21137737

Gao, Qian; Zhang, Jilin; Hong, Guangyan; Ni, Jiazuan

2010-10-01

388

Rapid mixing: A route to synthesize magnetite nanoparticles with high moment  

NASA Astrophysics Data System (ADS)

We demonstrate the impact of rapid mixing of the precursors in a time scale of milliseconds on the reaction rate and magnetic properties of co-precipitated magnetite with a custom-made mixer. The mixed volume is directed into a desk-top AC susceptometer to monitor the magnetic response from the growing particles in real-time. These measurements indicate that the reaction is mostly completed within a minute. The obtained superparamagnetic nanoparticles exhibit a narrow size distribution and large magnetization (87 Am2 kg-1). Transmission electron micrographs suggest that rapid mixing is the key for better crystallinity and a more uniform morphology leading to the observed magnetization values.

Fang, Mei; Ström, Valter; Olsson, Richard T.; Belova, Lyubov; Rao, K. V.

2011-11-01

389

The selective carbochlorination of iron from titanlferous magnetite ore in a fluidized bed  

NASA Astrophysics Data System (ADS)

The selective chlorination of iron from titaniferous magnetite ore using solid carbon as a reducing agent was studied in a fluidized bed. The effects of chlorination temperature, chlorine gas partial pressure, ratio of ore to carbon particle sizes, and the amount of added carbon were determined. Experimental results indicate that temperatures between 900 and 1000 K were favorable for the selective chlorination of iron. The rate was found to be first order with respect to chlorine concentration, and the observed effects of particle size, temperature, and the amount of carbon added were expressed quantitatively by using a mixed-control model.

Rhee, K. I.; Sohn, H. Y.

1990-04-01

390

An original route to stabilize and functionalize magnetite nanoparticles for theranosis applications  

NASA Astrophysics Data System (ADS)

A versatile method for the introduction of cyano groups onto the surface of iron oxide nanoparticles has been developed. This protocol is based on the hydrolysis and the condensation of cyanoethyltrimethoxysilane (CES) on the magnetite surface. The optimal concentration of silane coupling agent was determined ([Fe]/[CN] ratio=0.4) in order to obtain an appropriate surface density of activating groups on the nanoparticles. The size distribution of the particles was also optimized by a magnetic size sorting procedure. An adequate surface with cyano groups could facilitates their use in biomedical applications by improving the cellular labeling and the cell targeting.

Forge, D.; Laurent, S.; Gossuin, Y.; Roch, A.; Vander Elst, L.; Muller, R. N.

2011-03-01

391

Synthesis of magnetite magnetic nanoparticles and measurement of magneto-optical effects  

NASA Astrophysics Data System (ADS)

In the present study, magnetite (Fe3O4) magnetic nanoparticles (MNPs) were prepared by an improved chemical co-precipitation method. The effects of the pH value of the solution after titration, the reaction temperature in surface coating, and the molar concentration of Fe3+/Fe2+ salts in dispersibility and size of MNPs are studied. Characterization of the dispersibility and size in MNPs involved using transmission electronic microscope and X-ray diffractometry. Above all, the measurement of magneto-optical effect including the linear birefringence and dichroism of magnetic fluid are executed by a Stokes polarimeter.

Lin, Jing-Fung; Lee, Meng-Zhe

2014-06-01

392

Snow Crystals  

NSDL National Science Digital Library

This site describes snow crystals and snowflakes. Although a common meteorological phenomenon, snow crystal growth is a fascinating and poorly understood process, in which remarkably complex and beautifully symmetric structures appear, quite literally, out of thin air. The many facets of snow crystals are described here, along with the attempts to understand their formation. Site highlights include research on creating designer snow crystals in the laboratory, the history of early snow crystal observations, snow crystal photography, properties of frozen precipitation, and a snow crystal primer for a short course in snow crystal physics - what snow crystals are, how they form, and why they form the way they do. Information is offered on snow crystal classification, preservation, and unusual crystal forms. An extensive image gallery of lab-created crystal forms is available, with enlargeable thumbnail images. There are even instructions for users on how to create crystals. This could be made into a classroom activity, as the science of the growth is explained. Snowflake Physics discusses diffusion, dendrite growth, ice surface physics, electric growth, and ice properties. A vast list of related links is also provided.

Libbrecht, Kenneth

393

PHONOLOGICAL ACTIVATION IN PURE ALEXIA Marie Montant  

E-print Network

-by-letter. This disorder is typically accounted for in terms of a peripheral deficit that occurs early on in the reading a disorder that affects reading while sparing other linguistic abilities in premorbidly literate adults of Cognition, Pittsburgh, USA Pure alexia is a reading impairment in which patients appear to read letter

Behrmann, Marlene

394

Clear salt water versus clear pure water  

NSDL National Science Digital Library

A controlled experiment allows an investigator to conduct the experiment by changing only one single factor while keeping all other variables constant. The factor that was changed in this experiment, called the independent variable, was the type of water used: pure water or salt water.

Nancy Pelaez (Purdue University;Biological Sciences)

2007-08-17

395

Social cognition in “pure” delusional disorder  

Microsoft Academic Search

Introduction. Delusional disorders are characterised by monothematic, “encapsulated” and incorrigible false beliefs and misinterpretations of social signals. Due to the rarity of cases with “pure” delusional disorder (DD) in clinical settings most studies of social cognition in delusional patients have focused on patients with paranoid schizophrenia. In the present study we sought to examine emotion recognition, theory of mind abilities,

Isabel Bömmer; Martin Brüne

2006-01-01

396

International Union of Pure and Applied Physics  

NSDL National Science Digital Library

The International Union of Pure and Applied Physics (IUPAP) was established in 1922. The aims of the Union are to stimulate and promote international cooperation in physics; to promote international agreements on other use of symbols, units, nomenclature and standards; to foster free circulation of scientists; and to encourage research and education.

2009-05-22

397

A Pure Theory of Lifelong Learning.  

ERIC Educational Resources Information Center

Charles Tiebout's Pure Theory of Local Expenditures serves as a helpful framework in examining the emergence of the learning society, communications technologies, freer trade, and the effects these will have on the educational infrastructure. Tiebout argued that the failure of market-type systems of public good at the central government level does…

Hatton, Michael J.

398

Spatial Patterns Induced Purely by Dichotomous Disorder  

E-print Network

We study conditions under which spatially extended systems with coupling a la Swift-Hohenberg exhibit spatial patterns induced purely by the presence of quenched dichotomous disorder. Complementing the theoretical results based on a generalized mean-field approximation, we also present numerical simulations of particular dynamical systems that exhibit the proposed phenomenology.

J. Buceta; Katja Lindenberg

2003-03-18

399

Evolution of Pure States into Mixed States  

E-print Network

In the formulation of Banks, Peskin and Susskind, we show that one can construct evolution equations for the quantum mechanical density matrix $\\rho$ with operators which do not commute with hamiltonian which evolve pure states into mixed states, preserve the normalization and positivity of $\\rho$ and conserve energy. Furthermore, it seems to be different from a quantum mechanical system with random sources.

Jun Liu

1993-01-19

400

Cyclic voltammetry studies on pure lead  

Microsoft Academic Search

The behavior of pure lead in sulfuric acid was studied by cyclic voltammetry. The appearance of an anodic current peak on the cathodic portion of the sweep, previously attributed to a phase change in the lead dioxide film, is re-interpreted in the light of this work as being due to the oxidation of water by an intermediate lead III species.

J. G. Sunderland

1976-01-01

401

Is memory purely preservative?* Jrme Dokic  

E-print Network

1 Is memory purely preservative?* J�r�me Dokic (University of Rouen and CREA, Paris) In C. Hoerl & T. McCormack (eds), Time and Memory, Oxford: OUP. �1 Two forms of memory and Goethe's Problem Let us start with a familiar distinction between two forms of memory: episodic memory (remembering a thing

Paris-Sud XI, Université de

402

Temporal Ventriloquism in a Purely Temporal Context  

ERIC Educational Resources Information Center

This study examines how audiovisual signals are combined in time for a temporal analogue of the ventriloquist effect in a purely temporal context, that is, no spatial grounding of signals or other spatial facilitation. Observers were presented with two successive intervals, each defined by a 1250-ms tone, and indicated in which interval a brief…

Hartcher-O'Brien, Jessica; Alais, David

2011-01-01

403

Estimation of Dislocation Density in Cold-Rolled Commercially Pure Titanium by Using Synchrotron Diffraction  

NASA Astrophysics Data System (ADS)

Cold rolling (CR) leads to a heavy changes in the crystallographic texture and microstructure, especially crystal defects, such as dislocations, and stacking faults increase. The microstructure evolution in commercially pure titanium (cp-Ti) deformed by CR at the room temperature was determined by using the synchrotron peak profile analysis of full width at half maximum (FWHM). The computer program ANIZC has been used for the calculation of diffraction contrast factors of dislocations in elastically anisotropic hexagonal crystals. The dislocation density has a minimum value at 40 pct reduction. The increase of the dislocation density at higher deformation levels is caused by the nucleation of new generation of dislocations from the crystallite grain boundaries. The high-cycle fatigue strength (HCF) has a maximum value at 80 pct reduction and it has a minimum value at 40 pct reduction in the commercially pure titanium.

ALkhazraji, Hasan; Salih, Mohammed Z.; Zhong, Zhengye; Mhaede, Mansour; Brokmeier, Hans-Günter; Wagner, Lothar; Schell, N.

2014-08-01

404

Crystal Movies  

NSDL National Science Digital Library

This site, maintained by the Geosciences Department at the University of Arizona, contains animated gif files of common mineral crystals. The movies show crystal structures evolving as a function of pressure, temperature, chemistry, or orientation. The movies are an excellent aid for visualizing the structure of various crystals.

Downs, R. T.; Arizona, University O.

405

Ultrasonic velocity, attenuation, and nonlinearity constant in pure and Cd-doped KCl  

NASA Astrophysics Data System (ADS)

Single crystals of pure and Cd-doped KCl (1000 ppm) were grown by the Czochralski technique. The acoustic attenuation and velocity in pure and Cd-doped KCl for the longitudinal waves along the [100] direction at 12 MHz are measured by single-ended pulse-echo and pulse-echo-overlap methods in the temperature range 173-303 K. The acoustic attenuation is measured in the frequency range 12-228 MHz at room temperature (303 K). The Cd-doped KCl sample showed an increase in attenuation and a decrease in velocity compared to the pure sample. We have also estimated Mason's nonlinearity constant D along the [100] direction at 303 K from the second-order elastic and third-order elastic constants and furthermore used it to evaluate the ultrasonic attenuation in the frequency range 12-228 MHz. These values are compared with our measured attenuation values.

Joharapurkar, D. N.; Rajagopalan, S.; Basu, B. K.

1988-02-01

406

Study of local magnetic fields and magnetic ordering in fluid and solid matrices containing magnetite nanoparticles using TEMPOL stable radical  

NASA Astrophysics Data System (ADS)

The stable nitroxide radical 2,2,6,6-tetramethyl-4-hydroxy-piperidin-1-oxyl (TEMPOL) has been applied as a sensor to study magnetite nanoparticles both in water suspension and in dried gelatin films. g-values and line widths of ESR spectra of the probe were found to be sensitive to the local magnetic fields of magnetic nanoparticles. Calculated on the basis of the sensor ESR spectra, local magnetic fields are stipulated by linear aggregates of magnetite nanoparticles formed in applied outer magnetic fields and are significantly lower than local magnetic fields estimated from the static magnetic measurements data.

Kovarski, Alexander L.; Sorokina, Olga N.

2007-04-01

407

Oxidation state and local structure of plutonium reacted with magnetite, mackinawite, and chukanovite.  

PubMed

Due to their redox reactivity, surface sorption characteristics, and ubiquity as corrosion products or as minerals in natural sediments, iron(II)-bearing minerals control to a large extent the environmental fate of actinides. Pu-L(III)-edge XANES and EXAFS spectra were used to investigate reaction products of aqueous (242)Pu(III) and (242)Pu(V) reacted with magnetite, mackinawite, and chukanovite under anoxic conditions. As Pu concentrations in the liquid phase were rapidly below detection limit, oxidation state and local structure of Pu were determined for Pu associated with the solid mineral phase. Pu(V) was reduced in the presence of all three minerals. A newly identified, highly specific Pu(III)-sorption complex formed with magnetite. Solid PuO(2) phases formed in the presence of mackinawite and chukanovite; in the case of chukanovite, up to one-third of plutonium was also present as Pu(III). This highlights the necessity to consider, under reducing anoxic conditions, Pu(III) species in addition to tetravalent PuO(2) for environmental risk assessment. Our results also demonstrate the necessity to support thermodynamic calculations with spectroscopic data. PMID:21755920

Kirsch, Regina; Fellhauer, David; Altmaier, Marcus; Neck, Volker; Rossberg, Andre; Fanghänel, Thomas; Charlet, Laurent; Scheinost, Andreas C

2011-09-01

408

Application of NMR relaxometry for determining the concentration of nanopowder magnetite in aqueous media  

NASA Astrophysics Data System (ADS)

The use of the effect of a decrease in the transverse relaxation time T 2 of the NMR signal of water protons in the presence of magnetic particles has been suggested for the quantitative estimation of the concentration of magnetite (Fe3O4) nanopowder in water. A calibration dependence of the relaxivity T {2/-1} on the iron concentration has been obtained for model suspensions of magnetite nanoparticles with sizes of approximately 20 nm in the concentration range of 0.15-70 mg/L. For comparison, the concentration dependences of T {2/-1} for aqueous solutions of Fe(NO3)3 · 9H2O and FeSO4 · 7H2O and paramagnetic salts Ni(NO3)2 · 9H2O, Cr(NO3)3 · 9H2O, and CuSO4 · 5H2O have been studied to show that they correlate with their paramagnetic susceptibilities.

Medvedeva, I. V.; Zhakov, S. V.; Revvo, A. V.; Byzov, I. V.; Bakhteeva, Yu. A.; Uimin, M. A.; Yermakov, A. E.; Mysik, A. A.

2014-08-01