Note: This page contains sample records for the topic pure magnetite crystals from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

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

NASA Astrophysics Data System (ADS)

Thermal decomposition of Roxbury siderite resulted in the formation of impure (Mg,Mn)-ferrites. These findings, which are supported by kinetic and thermodynamic equilibrium modeling studies, are in stark contrast to the chemically pure ALH 84001 magnetite.

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

2009-03-01

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

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

4

Truncated hexa-octahedral magnetite crystals in ALH84001: Presumptive biosignatures  

PubMed Central

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 (Fe3O4) 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, Kathie L.; Clemett, Simon J.; Bazylinski, Dennis A.; Kirschvink, Joseph L.; McKay, David S.; Wentworth, Susan J.; Vali, Hojatollah; Gibson, Everett K.; McKay, Mary Fae; Romanek, Christopher S.

2001-01-01

5

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

6

Truncated hexa-octahedral magnetite crystals in ALH84001: presumptive biosignatures.  

PubMed

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. PMID:11226210

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

2001-02-27

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

Elongated prismatic magnetite crystals in ALH84001 carbonate globules  

Microsoft Academic Search

Using transmission electron microscopy (TEM), we have analyzed magnetite (Fe3O4) crystals acid-extracted from carbonate globules in Martian meteorite ALH84001. We studied 594 magnetites from ALH84001 and grouped them into three populations on the basis of morphology: 389 were irregularly shaped, 164 were elongated prisms, and 41 were whisker-like.As a possible terrestrial analog for the ALH84001 elongated prisms, we compared these

Kathie L. Thomas-Keprta; Dennis A. Bazylinski; Joseph L. Kirschvink; Simon J. Clemett; David S. McKay; Susan J. Wentworth; Hojatollah Vali; Everett K. Gibson Jr.; Christopher S. Romanek

2000-01-01

9

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

NASA Astrophysics Data System (ADS)

Pure (Mg-free) magnetite was synthesized by heating Mg-Fe-carbonate at 350°C in the presence of pyrite in an evacuated sealed glass tube. The Mg-free magnetite in the black rims of ALH84001 may have formed by a similar inorganic abiotic process from Mg-Fe-carbonates.

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

2006-03-01

10

Study of magnetite nanoparticles embedded in lyotropic liquid crystals  

NASA Astrophysics Data System (ADS)

A study about the magnetic behaviour of magnetite nanoparticles diluted in lyotropic liquid crystals was carried out. It was corroborated that micellar phases of the liquid crystal suppressed the superparamagnetism of the nanoparticles by rising the blocking temperature beyond the room temperature. Phase transitions in the lyotropic mixtures can be determined from M vs. T curves of the ferrolyotropic. When the liquid crystal is in the nematic discotic phase, the magnetization and the susceptibility of the mixture mimics the behaviour of the orientational order parameter of the phase.

Arantes, F. R.; Figueiredo Neto, A. M.; Cornejo, D. R.

11

Elongated prismatic magnetite crystals in ALH84001 carbonate globules: potential Martian magnetofossils.  

PubMed

Using transmission electron microscopy (TEM), we have analyzed magnetite (Fe3O4) crystals acid-extracted from carbonate globules in Martian meteorite ALH84001. We studied 594 magnetites from ALH84001 and grouped them into three populations on the basis of morphology: 389 were irregularly shaped, 164 were elongated prisms, and 41 were whisker-like. As a possible terrestrial analog for the ALH84001 elongated prisms, we compared these magnetites with those produced by the terrestrial magnetotactic bacteria strain MV-1. By TEM again, we examined 206 magnetites recovered from strain MV-1 cells. Natural (Darwinian) selection in terrestrial magnetotactic bacteria appears to have resulted in the formation of intracellular magnetite crystals having the physical and chemical properties that optimize their magnetic moment. In this study, we describe six properties of magnetite produced by biologically controlled mechanisms (e.g., magnetotactic bacteria), properties that, collectively, are not observed in any known population of inorganic magnetites. These criteria can be used to distinguish one of the modes of origin for magnetites from samples with complex or unknown histories. Of the ALH84001 magnetites that we have examined, the elongated prismatic magnetite particles (similar to 27% of the total) are indistinguishable from the MV-1 magnetites in five of these six characteristics observed for biogenically controlled mineralization of magnetite crystals. PMID:11543573

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

2000-12-01

12

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

PubMed

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. PMID:24828297

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

13

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

14

Chains of Magnetite Crystals in the Meteorite ALH84001: Evidence of Biological Origin  

Microsoft Academic Search

The presence of magnetite crystal chains, missing evidence for their biological origin, as well as five morphological characteristics incompatible with a nonbiological origin are demonstrated by high-power stereo backscattered scanning electron microscopy.

E. I. Friedmann; J. Wierzchos; C. Ascaso; M. Winklhofer

2001-01-01

15

MMS6 Protein Regulates Crystal Morphology during Nano-sized Magnetite Biomineralization in Vivo*  

PubMed Central

Biomineralization, the process by which minerals are deposited by organisms, has attracted considerable attention because this mechanism has shown great potential to inspire bottom-up material syntheses. To understand the mechanism for morphological regulation that occurs during biomineralization, many regulatory proteins have been isolated from various biominerals. However, the molecular mechanisms that regulate the morphology of biominerals remain unclear because there is a lack of in vivo evidence. Magnetotactic bacteria synthesize intracellular magnetosomes that comprise membrane-enveloped single crystalline magnetite (Fe3O4). These nano-sized magnetite crystals (<100 nm) are bacterial species dependent in shape and size. Mms6 is a protein that is tightly associated with magnetite crystals. Based on in vitro experiments, this protein was first implicated in morphological regulation during nano-sized magnetite biomineralization. In this study, we analyzed the mms6 gene deletion mutant (?mms6) of Magnetospirillum magneticum (M. magneticum) AMB-1. Surprisingly, the ?mms6 strain was found to synthesize the smaller magnetite crystals with uncommon crystal faces, while the wild-type and complementation strains synthesized highly ordered cubo-octahedral crystals. Furthermore, deletion of mms6 gene led to drastic changes in the profiles of the proteins tightly bound to magnetite crystals. It was found that Mms6 plays a role in the in vivo regulation of the crystal structure to impart the cubo-octahedral morphology to the crystals during biomineralization in magnetotactic bacteria. Magnetotactic bacteria synthesize magnetite crystals under ambient conditions via a highly controlled morphological regulation system that uses biological molecules.

Tanaka, Masayoshi; Mazuyama, Eri; Arakaki, Atsushi; Matsunaga, Tadashi

2011-01-01

16

MMS6 protein regulates crystal morphology during nano-sized magnetite biomineralization in vivo.  

PubMed

Biomineralization, the process by which minerals are deposited by organisms, has attracted considerable attention because this mechanism has shown great potential to inspire bottom-up material syntheses. To understand the mechanism for morphological regulation that occurs during biomineralization, many regulatory proteins have been isolated from various biominerals. However, the molecular mechanisms that regulate the morphology of biominerals remain unclear because there is a lack of in vivo evidence. Magnetotactic bacteria synthesize intracellular magnetosomes that comprise membrane-enveloped single crystalline magnetite (Fe(3)O(4)). These nano-sized magnetite crystals (<100 nm) are bacterial species dependent in shape and size. Mms6 is a protein that is tightly associated with magnetite crystals. Based on in vitro experiments, this protein was first implicated in morphological regulation during nano-sized magnetite biomineralization. In this study, we analyzed the mms6 gene deletion mutant (?mms6) of Magnetospirillum magneticum (M. magneticum) AMB-1. Surprisingly, the ?mms6 strain was found to synthesize the smaller magnetite crystals with uncommon crystal faces, while the wild-type and complementation strains synthesized highly ordered cubo-octahedral crystals. Furthermore, deletion of mms6 gene led to drastic changes in the profiles of the proteins tightly bound to magnetite crystals. It was found that Mms6 plays a role in the in vivo regulation of the crystal structure to impart the cubo-octahedral morphology to the crystals during biomineralization in magnetotactic bacteria. Magnetotactic bacteria synthesize magnetite crystals under ambient conditions via a highly controlled morphological regulation system that uses biological molecules. PMID:21169637

Tanaka, Masayoshi; Mazuyama, Eri; Arakaki, Atsushi; Matsunaga, Tadashi

2011-02-25

17

Analysis of magnetite crystals and inclusion bodies inside magnetotactic bacteria from different environmental locations  

NASA Astrophysics Data System (ADS)

Biomineralization occurs throughout the living world; a few common examples include iron oxide in chiton teeth, calcium carbonate in mollusk shells, calcium phosphate in animal bones and teeth, silica in diatom shells, and magnetite crystals inside the cells of magnetotactic bacteria. Biologically controlled mineralization is characterized by biominerals that have species-specific properties such as: preferential crystallographic orientation, consistent particle size, highly ordered spatial locations, and well-defined composition and structure. It is well known that magnetotactic bacteria synthesize crystals of magnetite inside of their cells, but how they mineralize the magnetite is poorly understood. Magnetosomes have a species-specific morphology that is due to specific proteins involved in the mineralization process. In addition to magnetite crystals, magnetotactic bacteria also produce inclusion bodies or granules that contain different elements, such as phosphorus, calcium, and sulfur. In this study we used the transmission electron microscope to analyze the structure of magnetite crystals and inclusion bodies from different species of magnetotactic bacteria in order to determine the composition of the inclusion bodies and to ascertain whether or not the magnetite crystals contain elements other than iron and oxygen. Using energy dispersive spectroscopy we found that different bacteria from different environments possess inclusion bodies that contain different elements such as phosphorus, calcium, barium, magnesium, and sulfur. These differences may reflect the conditions of the environment in which the bacteria inhabit.

Oestreicher, Z.; Lower, B.; Lower, S.; Bazylinski, D. A.

2011-12-01

18

Properties of intracellular magnetite crystals produced by Desulfovibrio magneticus strain RS-1  

NASA Astrophysics Data System (ADS)

Desulfovibrio magneticus strain RS-1 is an anaerobic sulfate-reducing bacterium. Cells form intracellular nanocrystals of magnetite but are only weakly magnetotactic. In order to understand the unusual magnetic response of this strain, we studied magnetite crystals within cells grown with fumarate and sulfate. Many cells grown under either condition did not form magnetic crystals while others contained only 1 to 18 small (˜ 40 nm) magnetite-containing magnetosomes. Bulk magnetic measurements of whole cells showed a superparamagnetic-like behavior, indicating that many of the magnetite crystals are too small to have a permanent magnetic moment at ambient temperature. The temperature of the Verwey transition is lower (˜ 86 K) than of magnetite from other magnetotactic strains, likely indicating partial oxidation of magnetite into maghemite. As a result of the small size and small number of magnetite magnetosomes, the magnetic moments of most cells grown anaerobically with fumarate or sulfate are insufficient for magnetotaxis. In addition to intracellular magnetite, in some cultures another iron oxide, hematite, formed on the surfaces of cells. The hematite grains are embedded in an extracellular polymeric material, indicating that the crystals likely resulted from a biologically-induced mineralization process. Although the hematite particles appear to consist of aggregations of many small (5 to 10 nm) grains, the grains have a consensus orientation and thus the whole particle diffracts as a single crystal. The aligned arrangement of nanoparticles within larger clusters may reflect either a templated nucleation of hematite crystallites in an extracellular organic matrix, or result from a self-assembling process during the crystallization of hematite from ferric gels or ferrihydrite.

Pósfai, Mihály; Moskowitz, Bruce M.; Arató, Balázs; Schüler, Dirk; Flies, Christine; Bazylinski, Dennis A.; Frankel, Richard B.

2006-09-01

19

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

20

Did an Impact Make the Mysterious Microscopic Magnetite Crystals in ALH 84001?  

NASA Astrophysics Data System (ADS)

Fervent debate swirls around microscopic crystals of magnetite (Fe3O4) in Martian meteorite ALH 84001. Some investigators suggest that the crystals are evidence of past life on Mars, citing magnetite crystals of similar chemical compositions and sizes made by magnetotactic bacteria on Earth. Others cite assorted experiments and observations to argue that the important little crystals formed entirely by non-biological processes, hence say nothing about life on Mars. One of those processes is the decomposition of iron carbonate (the mineral siderite), which occurs in ALH 84001. Researchers argue that heating this mineral causes it to decompose into magnetite and CO2 gas. Experiments showing this were done by heating siderite and observing that it decomposed and formed magnetite, but nobody had shock-heated siderite to see if magnetite crystals formed. (Shock is a rapid, strong rise and fall in pressure. It happens under many circumstances, including meteorite impacts.) The lack of shock experiments has been solved by Mary Sue Bell (University of Houston and Jacobs Engineering). She experimentally shocked samples of siderite at the Experimental Impact Laboratory at the Johnson Space Center. She shows that magnetite crystals of the right size and composition formed when samples were shocked to 49 GPa (about 500,000 times the pressure at the Earth's surface). This is more evidence for a non-biological origin for the magnetite crystals in ALH 84001 and is consistent with what we know about the impact history of the rock. There seems to be growing evidence against a biological origin, but don't expect these results to completely settle the debate!

Taylor, G. J.

2007-10-01

21

Elongated prismatic magnetite crystals in ALH84001 carbonate globules: Potential Martin magnetofoss  

Microsoft Academic Search

Abstract—Using transmission electron microscopy (TEM), we have analyzed magnetite (Fe 3O4) crystals acid-extracted from carbonate globules in Martian meteorite ALH84001. We studied 594 magnetites from ALH84001 and grouped them into three populations on the basis of morphology: 389 were irregularly shaped, 164 were elongated prisms, and 41 were whisker-like. As a possible terrestrial analog for the ALH84001 elongated prisms, we

K. L. Thomas-keprta; B. A. Bazylinski; J. L. Kirchvink; S. J. Clemett; D. S. Mckay; S. J. Wentworth; H. Vali; C. S. Romanek

2000-01-01

22

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

23

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 micrometer to 1 mm size biotite and hornblende grains separated from drillcore samples of Precambrian granodiorite basement in southern Alberta, Canada. The grains were mounted in epoxy and the surface was polished, first mechanically and then with a suspension of amorphous silica. Domain structures were observed on 6 to 60 micrometer magnetite crystals using the Bitter colloid technique. Observed features include lamellar domains bounded by straight 180 degree walls, closure domains, bent walls, wavy structures, and areas without visible domains. Crystals less than 50 micrometers in size generally have simple domain patterns with domain walls parallel to the long axis of the crystal. We studied domain wall displacements in isolated small magnetite crystals 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 x 25 micrometer 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.

Dunlop, D. J.; Ozdemir, O.

2005-12-01

24

Chains of Magnetite Crystals in the Meteorite ALH84001: Evidence of Biological Origin  

NASA Technical Reports Server (NTRS)

The presence of magnetite crystal chains, missing evidence for their biological origin, as well as five morphological characteristics incompatible with a nonbiological origin are demonstrated by high-power stereo backscattered scanning electron microscopy. Additional information is contained in the original extended abstract.

Friedmann, E. I.; Wierzchos, J.; Ascaso, C.; Winklhofer, M.

2001-01-01

25

Chains of magnetite crystals in the meteorite ALH84001: Evidence of biological origin  

PubMed Central

The presence of magnetite crystal chains, considered missing evidence for the biological origin of magnetite in ALH84001 [Thomas-Keprta, K. L., Bazylinski, D. A., Kirschvink, J. L., Clemett, S. J., McKay, D. S., Wentworth, S. J., Vali, H., Gibson, E. K., Jr., & Romanek, C. S. (2000) Geochim. Cosmochim. Acta 64, 4049–4081], is demonstrated by high-power stereo backscattered scanning electron microscopy. Five characteristics of such chains (uniform crystal size and shape within chains, gaps between crystals, orientation of elongated crystals along the chain axis, flexibility of chains, and a halo that is a possible remnant of a membrane around chains), observed or inferred to be present in magnetotactic bacteria but incompatible with a nonbiological origin, are shown to be present. Although it is unlikely that magnetotactic bacteria were ever alive in ALH84001, decomposed remains of such organisms could have been deposited in cracks in the rock while it was still on the surface on Mars.

Friedmann, E. Imre; Wierzchos, Jacek; Ascaso, Carmen; Winklhofer, Michael

2001-01-01

26

Hysteresis of Magnetite, Hematite and Pyrrhotite Crystals at High and Low Temperatures  

NASA Astrophysics Data System (ADS)

Alternating gradient force magnetometers and sensitive vibrating-sample magnetometers operating above, at, and below room temperature have enabled rapid reliable measurements of hysteresis and remanence curves. The hysteresis parameters Ms, Mrs, Hc, plus the remanence coercivity Hcr, are routinely determined, at room temperature at least, and reported in the form of a Day plot as an indication of domain state and inferred grain size. Yet our knowledge of the hysteresis and remanence properties of individual crystals or sized crystal aggregates of magnetite, titanomagnetite, hematite, pyrrhotite and other important magnetic minerals has scarcely advanced beyond what was known at the end of the 1980's. Applications have indeed outstripped fundamental studies. This presentation will focus on new hysteresis measurements for well-sized magnetites of a variety of origins; magnetite inclusions in plagioclase, pyroxene, amphiboles and biotite; hematite; and pyrrhotite. Measurements were made at 20oC intervals from 25oC to the Curie point for all magnetites and hematites and at 10oC intervals for pyrrhotite. For one set of sized magnetites (0.6, 3, 6, 9, 14 and 110 micrometers), hysteresis and back-field remanence curves were also measured below room temperature (every 10 K from 10 K to 70 K, every 5 K from 80 K to 140 K, and every 10 K from 150 K to 300 K). These data give a wealth of information about the individual mineral crystals and trends linking crystals of common origin but different sizes. From Ms(T) we obtain precise Curie points and transition temperatures. Mrs(T)/Ms(T) tracks sometimes subtle changes in domain structure with changing temperature. Hc(T) gives an indication of the mechanism(s) of anisotropy, important for understanding TRM acquisition in crystals above single-domain size. Mrs(T) and Hc(T) often show substantial irreversible changes in the first heating- cooling cycle, particularly but not exclusively for synthetic crystals, stabilizing in subsequent cycles. Finally, Mrs(T)/Ms(T) vs. Hcr(T)/Hc(T) data trace curves on a Day plot showing unmistakable differences in domain structure between monoclinic and cubic magnetite, as well as more subtle changes away from the Verwey transition.

Dunlop, D. J.

2008-12-01

27

Intrinsic response of crystals to pure dilatation.  

National Technical Information Service (NTIS)

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 we...

J. Wang S. Yip S. Phillpot D. Wolf

1991-01-01

28

Hematite single crystal reduction into magnetite with CO-CO2  

NASA Astrophysics Data System (ADS)

In view of the striking discrepancies among previous authors as regards the transition between porous and lamellar magnetites, we have carried out a wide series of experiments with single crystals prepared by chemical vapor transport. In addition to the classical temperature and CO pct parameters, which varied over a large range (400 ? T ? 1000 ?C and 2 ? CO pct ? 50), we also investigated the influence of the crystal size and of the fractional weight change. Through observation of a great number of cross-sections of partially reduced crystals, we established that lamellar magnetite is favored by high temperature and low CO pct. This is explained by consideration of the conditions governing the competition between cation diffusion in the semi-coherent hematite-magnetite interface and chemical reaction rate. At low temperatures, the crystals are severely fractured, because hematite is not plastic enough, especially at a high CO2 pct. The kinetic data are analyzed with the shrinking-core model, where the reaction interface is topochemical. The chemical rate constant thus obtained is ? = 69 exp(-8950/ T), in mol(CO) · m-2 · s-1, for crystals in the range 50 to 150 ?m and T varying from 500 to 900 °C. Bigger crystals yield a slightly higher preexponential term, confirming that porous diffusion does not rule the kinetics. The nucleation frequency has also been evaluated; it tends toward a kind of saturation at around 700 °C with a value of 10 to 109 s-1. The nuclei growth rate is in reasonable agreement with direct measurements.

Et-Tabirou, M.; Dupré, B.; Gleitzer, C.

1988-04-01

29

Magnetite 3D colloidal crystals formed in the early solar system 4.6 billion years ago.  

PubMed

Three-dimensional colloidal crystals made of ferromagnetic particles, such as magnetite (Fe(3)O(4)), cannot be synthesized in principle because of the strong attractive magnetic interaction. However, we discovered colloidal crystals composed of polyhedral magnetite nanocrystallites of uniform size in the range of a few hundred nanometers in the Tagish Lake meteorite. Those colloidal crystals were formed 4.6 billion years ago and thus are much older than natural colloidal crystals on earth, such as opals, which formed about 100 million years ago. We found that the size of each individual magnetite particle determines its morphology, which in turn plays an important role in deciding the packing structure of the colloidal crystals. We also hypothesize that each particle has a flux-closed magnetic domain structure, which reduces the interparticle magnetic force significantly. PMID:21563777

Nozawa, Jun; Tsukamoto, Katsuo; van Enckevort, Willem; Nakamura, Tomoki; Kimura, Yuki; Miura, Hitoshi; Satoh, Hisao; Nagashima, Ken; Konoto, Makoto

2011-06-15

30

Truncated Hexa-Octahedral Magnetite Crystals in Martian Meteorite ALH84001: Evidence of Biogenic Activity on Early Mars  

NASA Technical Reports Server (NTRS)

The landmark paper by McKay et al. [1] cited four lines of evidence associated with the Martian meteorite ALH84001 to support the hypothesis that life existed on Mars approximately 4 Ga ago. Now, more than five years later, attention has focused on the ALH84001 magnetite grains embedded within carbonate globules in the ALH84001 meteorite. We have suggested that up to approx.25% of the ALH84001 magnetite crystals are products of biological activity [e.g., 2]. The remaining magnetites lack sufficient characteristics to constrain their origin. The papers of Thomas Keprta et al. were criticized arguing that the three dimensional structure of ALH84001 magnetite crystals can only be unambiguously determined using electron tomographic techniques. Clemett et al. [3] confirmed that magnetites produced by magnetotactic bacteria strain MV-I display a truncated hexa-octahedral geometry using electron tomography and validated the use of the multi-tilt classical transmission microscopy technique used by [2]. Recently the geometry of the purported martian biogenic magnetites was shown be identical to that for MV-1 magnetites using electron tomography [6].

Thomas-Keprta, K.; Clemett, S. J.; Schwartz, C.; McIntosh, J. R.; Bazylinski, D. A.; Kirschvink, J.; McKay, D. S.; Gibson, E. K.; Vali, H.; Romanek, C. S.

2004-01-01

31

Chains of magnetite crystals in the meteorite ALH84001: evidence of biological origin.  

PubMed

The presence of magnetite crystal chains, considered missing evidence for the biological origin of magnetite in ALH84001 [Thomas-Keprta, K. L., Bazylinski, D. A., Kirschvink, J. L., Clemett, S. J., McKay, D. S., Wentworth, S. J., Vali, H., Gibson, E. K., Jr., & Romanek, C. S. (2000) Geochim. Cosmochim. Acta 64, 4049-4081], is demonstrated by high-power stereo backscattered scanning electron microscopy. Five characteristics of such chains (uniform crystal size and shape within chains, gaps between crystals, orientation of elongated crystals along the chain axis, flexibility of chains, and a halo that is a possible remnant of a membrane around chains), observed or inferred to be present in magnetotactic bacteria but incompatible with a nonbiological origin, are shown to be present. Although it is unlikely that magnetotactic bacteria were ever alive in ALH84001, decomposed remains of such organisms could have been deposited in cracks in the rock while it was still on the surface on Mars. PMID:11226212

Friedmann, E I; Wierzchos, J; Ascaso, C; Winklhofer, M

2001-02-27

32

Plenty of Room at the Bottom: The Superparamagnetic Transition in Chains of Magnetite Crystals  

NASA Astrophysics Data System (ADS)

Among the few known fossil remnants of bacteria are chains of magnetite and greigite crystals left in sediments by magnetotactic bacteria. The information they provide about the abundance and nature of magnetotactic bacteria may provide useful information about environmental conditions back at least as far as the Cretaceous. Their usefulness depends on their readily identified features such as the size and shape of the crystals and their arrangement in chains. These features maximize the torque of the Earth's magnetic field on the bacteria by maximizing the magnetic remanence in the chains. The chains are in a single-domain (SD) state, with a uniform magnetization pointing along the chain axis. The single-domain state only occurs within a narrow range of crystal sizes. Smaller particles become superparamagnetic (SP), unable to hold any magnetic remanence, while larger particles are multidomain, having a smaller remanence per unit volume. Thus, one criterion for "magnetofossils" is that they fall within the single-domain size range. However, the SP size limit is only known for isolated crystals and many of the crystals in magnetotactic bacteria would be SP in isolation. They are SD only within chains, their magnetization stabilized by the magnetostatic interactions between crystals. The SP critical size is calculated for chains of magnetite crystals using a new algorithm that finds all the equilibrium magnetic states. From these the minima and saddle points in the energy surface are selected and energy gradients are followed from saddle points down to stable states. This network of connections determines the paths from positive to negative saturation and the decay rate for the magnetic moment of the chain. In turn, the decay rate determines the critical size. The transition paths depend on the ratio of the strength of the magnetostatic interactions to the internal magnetic anisotropy of the crystals. This ratio increases as the crystals get closer together or less elongated. In the limit of no interactions, there are 2N stable states (all the combinations of up and down for the single-crystal moments), and an equal number of transition paths. As the relative strength of the magnetostatic interactions increases, the number of stable states declines. The transition paths also decrease in number and involve coherent rotations of an increasing number of moments. When the crystals are touching and the length-to-width ratio is 1, there are only two stable states (positive and negative saturation) and two mirror-image paths between them. The reversal mode for chains of 4 or less cubes is the well-known fanning mode in which the single-crystal moments rotate alternately clockwise and anticlockwise at the same rate. In chains of 5 or more cubes there is a new reversal mode, the "two-domain fanning mode", in which half the moments rotate by nearly 180° by a fanning-like mechanism and then the other half rotate. As the number of crystals in the chain increases, the SP critical volume for magnetite approaches a limit that is nearly independent of the shape of the crystals. The cube root of this volume is about 10 nm. This is low enough to accommodate almost all the measured sizes of magnetite crystals produced by magnetotactic bacteria.

Newell, A.

2009-05-01

33

Cosmic muon tomography of pure cesium iodide calorimeter crystals  

Microsoft Academic Search

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 en- abling measurement of

E. Frleÿz; I. Supek; K. A. Assamagan; Ch. Bronnimann; B. Krause; D. W. Lawrence; D. Mzavia; D. Poÿcanic; D. Renker; S. Ritt; P. L. Slocum; N. Soic

34

Cosmic muon tomography of pure cesium iodide calorimeter crystals  

Microsoft Academic Search

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

E. Frlez; I. Supek; K. A. Assamagan; Ch. Brönnimann; Th. Flügel; B. Krause; D. W. Lawrence; D. Mzavia; D. Pocanic; D. Renker; S. Ritt; P. L. Slocum; N. Soic

2000-01-01

35

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

36

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

37

Magnetic susceptibility and remanent coercive force in grown magnetite crystals from 0.1 ?m to 6 mm  

Microsoft Academic Search

Initial susceptibility is frequently used as a palaeoclimatic indicator in sediments, but its grain size dependence is not well established. We measured initial magnetic susceptibility ?0 in grown and natural magnetite crystals ranging from 0.09 ?m to 6 mm in grain size. Over these five decades of grain diameter, the presented initial susceptibilities are essentially independent of grain size with

Franz Heider; Anke Zitzelsberger; Karl Fabian

1996-01-01

38

Growth of single-crystal magnetite nanowires from Fe 3O 4 nanoparticles in a surfactant-free hydrothermal process  

NASA Astrophysics Data System (ADS)

Single-crystal magnetite nanowires with average diameter of ca. 20 nm and length of up to several micrometers were prepared by a simple alkaline surfactant-free hydrothermal process. The crystallinity, purity, morphology, and structural features of the as-prepared magnetite nanowires were investigated by powder X-ray diffraction, transmission electron microscopy (TEM) and selected area electron diffraction. The composition and length of nanowires depends on the pH, with higher pH favoring longer nanowires composed entirely of Fe 3O 4. A mechanism for nanowire growth is proposed.

Lian, Suoyuan; Wang, Enbo; Gao, Lei; Kang, Zhenhui; Wu, Di; Lan, Yang; Xu, Lin

2004-11-01

39

Structural, Optical and Dielectric Studies On Pure and Doped LAlaninium Maleate Single Crystals  

NASA Astrophysics Data System (ADS)

Good optical quality single crystals of pure and doped L-Alaninium Maleate (LAM) crystals have been grown. The crystals have been grown by slow evaporation method at a constant temperature of 35°C from its aqueous solution. The grown single crystals of pure and doped LAM were characterized by employing FTIR, SHG, ICP, Dielectric study and X- ray diffraction methods.

Karunanithi, U.

2012-06-01

40

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

NASA Astrophysics Data System (ADS)

Comparison of new TEM results with decomposition studies of sideritic carbonates conducted under a range of heating scenarios suggests that the magnetite nanocrystals in ALH 84001 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.

2010-04-01

41

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

42

Comparison between pure and deuterated potassium acid phthalate (DKAP) single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of pure and deuterated potassium acid phthalate (DKAP) have been grown from aqueous solution by slow cooling method. The effect of deuterium on morphology and crystal properties has been studied. Powder X-ray diffraction analysis confirms the structure and changes in lattice parameter values for the deuterated crystals. The presence of deuterium in the crystal lattice has been confirmed by FTIR analysis. The DKAP crystals possess relatively lower hardness values than the pure crystals. The transmittance of DKAP is found to be higher than KAP crystals.

Mohan Kumar, R.; Rajan Babu, D.; Murugakoothan, P.; Jayavel, R.

2002-11-01

43

Characterization of pure and urea-doped ?-glycine single crystals grown by solution method  

NASA Astrophysics Data System (ADS)

Pure and urea-doped gamma-glycine (?-glycine) single crystals were grown by solution method with slow evaporation technique. When urea was added as dopant, morphological alterations were noticed in ?-glycine crystals. Structural characterization of the grown crystals was carried out by single and powder X-ray diffraction (XRD) methods and it is observed that the samples crystallize in non-centrosymmetric space groups. UV-visible transmittance studies were performed to analyse optical transparency of pure and urea-doped ?-glycine crystals and found that the crystals were transparent in the entire visible-NIR region. Density and melting point of the grown crystals were measured. Second harmonic generation (SHG) for the grown crystals of this work was confirmed using Nd:YAG laser. Thermogravimetric and differential thermal analyses (TG/DTA) thermograms reveal that the materials have good thermal stability. From Microhardness studies, it is observed that urea-doped ?-glycine crystal is harder than pure (undoped) sample.

Selvarajan, P.; Glorium Arul Raj, J.; Perumal, S.

2009-07-01

44

Origin of magnetite crystals in Martian meteorite ALH84001 carbonate disks  

NASA Astrophysics Data System (ADS)

The Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks. These carbonate disks are believed to have precipitated 3.9 Ga ago at beginning of the Noachian epoch on Mars during which both the oldest extant Martian surfaces were formed, and perhaps the earliest global oceans. In-timately 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 [1,2]. One group of hypotheses argues that these magnetites are the product of partial thermal decomposition of the host carbonate [3,4]. Alternatively, the origins of magnetite and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. For example, the magnetites might have already been present in the aqueous fluids from which the carbonates were believed to have been deposited. We have sought to resolve between these hypotheses through the detailed characterization of the compositional and structural relationships of the carbonate disks and associated magnetites with the orthopyroxene matrix in which they are embedded. Extensive use of focused ion beam milling techniques has been utilized for sample preparation. We then compared our ob-servations with those from experimental thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios. We conclude that the vast majority of the nanocrystal magnetites present in the carbonate disks could not have formed by any of the currently proposed thermal decomposition scenarios. Instead, we find there is considerable evidence in support of an alternative allochthonous origin for the magnetite unrelated to any shock or thermal processing of the carbonates [5]. [1] McKay et al. (1996) Science 273, 924-930. [2] Thomas-Keprta et al. (2001) Proc. Natl. Acad. Sci. 98, 2164-2169. [3] Treiman (2003) Astrobiology 3, 369-392. [4] Brearley A. J. (2003) Meteorit. Planet. Sci. 38, 849-870. [5] Thomas-Keprta et al. (2009) Geochim. Cosmochim. Acta 73, 6631-6677.

Thomas-Keprta, Kathie; Clemett, Simon; McKay, David; Gibson, Everett; Wentworth, Susan

45

Two-dimensional photonic crystals with pure germanium-on-insulator  

Microsoft Academic Search

We have investigated pure germanium two-dimensional photonic crystals. The photonic crystals which exhibit resonances in the near infrared spectral range were fabricated on germanium-on-insulator substrates using standard silicon-based processing. The germanium-on-insulator substrate consists of a thin layer of pure germanium-on-oxide deposited on a silicon substrate. The optical properties are probed by the direct band gap optical recombination of pure germanium

M. El Kurdi; S. David; X. Checoury; G. Fishman; P. Boucaud; O. Kermarrec; D. Bensahel; B. Ghyselen

2008-01-01

46

Degeneration of Biogenic Superparamagnetic Magnetite  

SciTech Connect

ABSTRACT. Magnetite crystals precipitated as a consequence of Fe(III) reduction by Shewanella algae BrY after 265 hours incubation and 5-year storage were investigated with transmission electron microscopy, M ssbauer spectroscopy and X-ray diffraction. The magnetite crystals were typically superparamagnetic with an approximate size of 13 nm. The lattice constants of the 265 hour and 5-year crystals are 8.4164 and 8.3774 , respectively. The M ssbauer spectra indicated that the 265 hour magnetite had excess Fe(II) in its crystal-chemistry (Fe3+1.9901Fe2+ 1.0149O4) but the 5-year magnetite was Fe(II)-deficient in stoichiometry (Fe3+2.3875Fe2+0.4188O4). Such crystal-hemical changes may be indicative of the degeneration of superparamagnetic magnetite through the aqueous oxidization of Fe(II) anaerobically, and the concomitant oxidation of the organic phases(fatty acid methyl esters) that were present during the initial formation of the magnetite. The observation of a corona structure on the aged magnetite corroborates the oxidation of Fe(II) on the outer layers of magnetite crystals. These results suggest that there may be a possible link between the enzymatic activity of the bacteria and the stability of Fe(II)-excess magnetite, which may help explain why stable nano-magnetite grains are seldom preserved in natural environments.

Li, Dr. Yi-Liang [University of Tennessee, Knoxville (UTK); Pfiffner, Susan M. [University of Tennessee, Knoxville (UTK); Dyar, Dr. M Darby [Mount Holyoke College; Vali, Dr. Hojatolah [McGill University, Montreal, Quebec; Konhauser, Dr, Kurt [University of Alberta; Cole, David R [ORNL; Rondinone, Adam Justin [ORNL; Phelps, Tommy Joe [ORNL

2009-01-01

47

The major magnetosome proteins MamGFDC are not essential for magnetite biomineralization in Magnetospirillum gryphiswaldense but regulate the size of magnetosome crystals.  

PubMed

Magnetospirillum gryphiswaldense and related magnetotactic bacteria form magnetosomes, which are membrane-enclosed organelles containing crystals of magnetite (Fe3O4) that cause the cells to orient in magnetic fields. The characteristic sizes, morphologies, and patterns of alignment of magnetite crystals are controlled by vesicles formed of the magnetosome membrane (MM), which contains a number of specific proteins whose precise roles in magnetosome formation have remained largely elusive. Here, we report on a functional analysis of the small hydrophobic MamGFDC proteins, which altogether account for nearly 35% of all proteins associated with the MM. Although their high levels of abundance and conservation among magnetotactic bacteria had suggested a major role in magnetosome formation, we found that the MamGFDC proteins are not essential for biomineralization, as the deletion of neither mamC, encoding the most abundant magnetosome protein, nor the entire mamGFDC operon abolished the formation of magnetite crystals. However, cells lacking mamGFDC produced crystals that were only 75% of the wild-type size and were less regular than wild-type crystals with respect to morphology and chain-like organization. The inhibition of crystal formation could not be eliminated by increased iron concentrations. The growth of mutant crystals apparently was not spatially constrained by the sizes of MM vesicles, as cells lacking mamGFDC formed vesicles with sizes and shapes nearly identical to those formed by wild-type cells. However, the formation of wild-type-size magnetite crystals could be gradually restored by in-trans complementation with one, two, and three genes of the mamGFDC operon, regardless of the combination, whereas the expression of all four genes resulted in crystals exceeding the wild-type size. Our data suggest that the MamGFDC proteins have partially redundant functions and, in a cumulative manner, control the growth of magnetite crystals by an as-yet-unknown mechanism. PMID:17965152

Scheffel, André; Gärdes, Astrid; Grünberg, Karen; Wanner, Gerhard; Schüler, Dirk

2008-01-01

48

The Major Magnetosome Proteins MamGFDC Are Not Essential for Magnetite Biomineralization in Magnetospirillum gryphiswaldense but Regulate the Size of Magnetosome Crystals? †  

PubMed Central

Magnetospirillum gryphiswaldense and related magnetotactic bacteria form magnetosomes, which are membrane-enclosed organelles containing crystals of magnetite (Fe3O4) that cause the cells to orient in magnetic fields. The characteristic sizes, morphologies, and patterns of alignment of magnetite crystals are controlled by vesicles formed of the magnetosome membrane (MM), which contains a number of specific proteins whose precise roles in magnetosome formation have remained largely elusive. Here, we report on a functional analysis of the small hydrophobic MamGFDC proteins, which altogether account for nearly 35% of all proteins associated with the MM. Although their high levels of abundance and conservation among magnetotactic bacteria had suggested a major role in magnetosome formation, we found that the MamGFDC proteins are not essential for biomineralization, as the deletion of neither mamC, encoding the most abundant magnetosome protein, nor the entire mamGFDC operon abolished the formation of magnetite crystals. However, cells lacking mamGFDC produced crystals that were only 75% of the wild-type size and were less regular than wild-type crystals with respect to morphology and chain-like organization. The inhibition of crystal formation could not be eliminated by increased iron concentrations. The growth of mutant crystals apparently was not spatially constrained by the sizes of MM vesicles, as cells lacking mamGFDC formed vesicles with sizes and shapes nearly identical to those formed by wild-type cells. However, the formation of wild-type-size magnetite crystals could be gradually restored by in-trans complementation with one, two, and three genes of the mamGFDC operon, regardless of the combination, whereas the expression of all four genes resulted in crystals exceeding the wild-type size. Our data suggest that the MamGFDC proteins have partially redundant functions and, in a cumulative manner, control the growth of magnetite crystals by an as-yet-unknown mechanism.

Scheffel, Andre; Gardes, Astrid; Grunberg, Karen; Wanner, Gerhard; Schuler, Dirk

2008-01-01

49

Field Ion Microscopy and Atom Probe Tomography of Metamorphic Magnetite Crystals  

NASA Technical Reports Server (NTRS)

Magnetite has been analysed using Field Ion Microscopy (FIM) and Atom Probe Tomography (APT), highly attractive techniques for the nanoanalysis of geological materials despite the difficulties inherent in analyzing semiconducting and insulating materials. Additional information is contained in the original extended abstract.

Kuhlman, K.; Martens, R. L.; Kelly, T. F.; Evans, N. D.; Miller, M. K.

2001-01-01

50

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

51

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

52

A dislocation-density-based 3D crystal plasticity model for pure aluminum  

Microsoft Academic Search

A dislocation-density-based crystal plasticity finite-element model (CPFEM) is developed in which different dislocation densities evolve. Based upon the kinematics of crystal deformation and dislocation interaction laws, dislocation generation and annihilation are modeled. The CPFEM model is calibrated for pure aluminum using experimental stress–strain curves of pure aluminum single crystal from the literature. Crystallographic texture predictions in plane-strain compression of aluminum

Alankar Alankar; Ioannis N. Mastorakos; David P. Field

2009-01-01

53

Unidirectional growth of pure and L-lysine added ADP crystals from aqueous solution  

NASA Astrophysics Data System (ADS)

Pure and L-lysine added ammonium dihydrogen phosphate (ADP) crystals were grown in the <001> direction by Sankaranarayanan-Ramasamy (S-R) method. The grown crystals were characterized by X-Ray diffractometry (XRD), UV-Vis spectroscopy, Fourier Transform Infrared (FT-IR) and Vicker's Microhardness analysis. XRD spectrum of each of the grown crystals proved its crystallinity. The crystals showed good transparency in the entire visible region. FT-IR spectra of the specimens revealed the presence of functional groups in them. The hardness of the pure and L-lysine added ADP crystals were measured and that of the added one was found higher. Meanwhile, it was found that the ADP crystals (pure and L-lysine added) grown by S-R method had higher hardness compared to ADP crystal grown by conventional method.

Salarian, Samaneh; Dizaji, Hamid Rezagholipour

2014-01-01

54

Growth and characterization of gel grown pure and mixed iron-manganese levo-tartrate crystals  

Microsoft Academic Search

Several applications of iron tartrate and manganese tartrate compounds are reported in the literature. In the present investigation,\\u000a we have grown pure and mixed iron (II)-manganese levo-tartrate crystals by single diffusion gel growth technique. Crystals\\u000a with spherulitic morphology were harvested. The colouration of the crystals changed from black to pinkish brown upon increasing\\u000a the content of manganese in the crystals.

S. J. Joshi; B. B. Parekh; K. D. Vohra; M. J. Joshi

2006-01-01

55

Growth and characterization of pure and glycine doped cadmium thiourea sulphate (GCTS) crystals.  

PubMed

The pure and glycine doped cadmium thiourea sulphate (GCTS) single crystals were grown successfully by slow evaporation method at room temperature. The concentration of dopant in the mother solution was 1 mol%. There is a change in unit cell. The Fourier transform infrared spectroscopy study confirms the incorporation of glycine into CTS crystal. The doped crystals are optically better and more transparent than the pure ones. The dopant increases the hardness value of the material. The grown crystals were also subjected to thermal and NLO studies. PMID:22349889

Lawrence, M; Thomas Joseph Prakash, J

2012-06-01

56

Isolation of isoelectrically pure cholera toxin for crystallization  

SciTech Connect

We have determined that the failure of cholera toxin to crystallize well results from its isoelectric heterogeneity, which is probably due to a post-translational process such as deamidation of its B subunit. Every sample of cholera toxin we have examined from commercial or academic suppliers has been heterogeneous; heterogeneous cholera toxin does not crystallize satisfactorily. We have overcome this problem by using ion-exchange fast protein liquid chromatography (FPLC) to obtain an isoelectrically homogeneous species of cholera toxin. Homogeneous cholera toxin crystallizes readily, forming single, nonmosaic crystals suitable for x-ray diffraction studies. For this process, protein was applied to a MonoQ ion-exchange column, then eluted with an isocratic low salt buffer followed by a linear salt gradient (0-100 mM NaCl). Column fractions were analyzed on isoelectric focusing gels, and those fractions containing the desired homogeneous species were pooled and concentrated. Crystals formed within 24 to 48 hours in a MOPS/PEG buffer, which made use of slow isoelectric precipitation to induce crystallization. 23 refs., 6 figs.

Spangler, B.D.; Westbrook, E.M.

1989-01-01

57

Studies on various properties of pure and Li-doped Barium Hydrogen Phosphate (BHP) single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of pure and Li-doped barium hydrogen phosphate (BHP) were grown by solution method with gel technique. Various properties of the harvested crystals were studied by carrying out single crystal and powder XRD, FTIR, TG/DTA, microhardness and dielectric studies. Atomic absorption study was carried out for Li-doped BHP crystal to check the presence of Li dopants. Unit cell dimensions and diffracting planes of the grown crystals have been identified from XRD studies. Functional groups of the title compounds have been identified from FTIR studies. Density of the grown crystals was calculated using the XRD data. Thermal stability of the samples was checked by TG/DTA studies. Mechanical and dielectric characterizations of the harvested pure and Li-doped BHP crystals reveal the mechanical strength and ferroelectric transition. The observed results are reported and discussed.

Nallamuthu, D.; Selvarajan, P.; Freeda, T. H.

2010-12-01

58

Influence of Growth Conditions on Magnetite Nanoparticles Electro-Crystallized in the Presence of Organic Molecules  

PubMed Central

Magnetite nanoparticles were synthesized by electrocrystallization in the presence of thiourea or sodium butanoate as an organic stabilizer. The synthesis was performed in a thermostatic electrochemical cell containing two iron electrodes with an aqueous solution of sodium sulfate as electrolyte. The effects of organic concentration, applied potential and growth temperature on particle size, morphology, structure and magnetic properties were investigated. The magnetite nanoparticles were characterized by X-ray diffraction, electron microscopy, magnetometry and Mössbauer spectrometry. When the synthesis is performed in the presence of sodium butanoate at 60 °C, a paramagnetic ferric salt is obtained as a second phase; it is possible to avoid formation of this phase, increase the specific magnetization and improve the structure of the oxide particles by tuning the growth conditions. Room-temperature magnetization values range from 45 to 90 Am2kg?1, depending on the particle size, type of surfactant and synthesis conditions. Mössbauer spectra, which were recorded at 290 K for all the samples, are typical of nonstoichiometric Fe3??O4, with a small excess of Fe3+, 0.05 ? ? ? 0.15.

Mosivand, Saba; Monzon, Lorena M. A.; Kazeminezhad, Iraj; Coey, J. Michael D.

2013-01-01

59

Continuous Elastic Phase Transitions in Pure and Disordered Crystals  

Microsoft Academic Search

We review the theory of second-order (ferro-)elastic phase transitions, where the order parameter consists of a certain linear combination of strain tensor components, and the accompanying soft mode is an acoustic phonon. In three-dimensional crystals, the softening can occur in one- or two-dimensional soft sectors. The ensuing anisotropy reduces the effect of fluctuations, rendering the critical behaviour of these systems

Franz Schwabl; Uwe Claus Tauber

1996-01-01

60

Single crystal growth and characterization of pure and sodium-modified copper tartrate  

NASA Astrophysics Data System (ADS)

Single crystal growth of pure and modified copper tartrate crystals bearing composition (Cu) x(Na) yC 4H 4O 6· nH 2O (where x=1, 0.77, 0.65; y=0, 0.23, 0.35) is achieved using gel technique. The optimum conditions required for the growth of these crystals are worked out. The morphological development of these crystals is studied using optical and scanning electron microscopy. The dominant habit faces of the grown copper tartrate crystals are (0 0 1) and (1 1 1). Calculation of the cell parameters using CRYSFIRE software suggests that the pure copper tartrate crystal belongs to orthorhombic system with space group P2 1/c whereas the modified copper tartrate falls under tetragonal system with the space group P4 2/nbc. The external morphological development is shown to remain unaffected in the modified copper tartrate. The stoichiometric composition of the crystals is established by EDAX analysis, CH analysis, FTIR spectroscopy and thermoanalytical techniques. Thermal analysis of the grown crystals suggests that pure copper tartrate is thermally stable up to 42.84 °C whereas the modified copper tartrate crystals are stable only up to 33.11 and 25.11 °C. Calculation of the percentage weight loss from the thermogram supplemented by EDAX/CH analysis and FTIR spectroscopy suggest that the chemical formula of pure copper tartrate crystal is CuC 4H 4O 6·3H 2O whereas the chemical formula for the modified copper tartrate crystals is (Cu) 0.77(Na) 0.23C 4H 4O 6·3H 2O and (Cu) 0.65(Na) 0.35 C 4H 4O 6·H 2O.

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

2008-12-01

61

Studies on crystal growth, optical and electrical characterization of pure and Dy-doped bismuth silicate single crystals  

NASA Astrophysics Data System (ADS)

(0.5 mol%) Dysprosium (Dy) doped bismuth silicon oxide (BSO) single crystals were grown by the Czochralski technique under air atmosphere. Detailed analysis of Dy-doped BSO with pure BSO has been studied through optical analysis. The absorption edges of pure and Dy-doped BSO crystals are found to be 405 nm and 415 nm, respectively. The shift in the absorption edge is contributed to the defect centers created in the crystal with Dy-doping. The shifts observed in the Raman spectra on doping Dy are found to be lower, when compared with the pure BSO crystal. This effect can be correlated to the lattice distortion induced by the Dy doping. The oxide formation and intrinsic defects in the BSO crystal have been identified by photoluminescence analysis. Dielectric measurements reveal that higher permeability value in the BSO sample is due to the presence of charged defects, which can be related to the space charge polarization. There is a slight decrease in dielectric constant on doping with Dy. The piezoelectric value explains the defects formed in the crystal. On poling, d33 value of BSO and Dy-doped BSO are 32 pC/N and 40 pC/N, respectively.

Mythili, P.; Kanagasekaran, T.; Bhagavannarayana, G.; Gopalakrishnan, R.

2012-01-01

62

ynthesis and Characterization of Pure and Doped L- Arginine Maleate Single Crystals  

NASA Astrophysics Data System (ADS)

Pure and Doped L- Arginine Maleate (LArM) a nonlinear optical material has been successfully grown from slow evaporation method. FTIR analysis was used to confirm the presence of various functional groups in the grown crystals. Kurtz powder SHG measurements confirm the NLO property of the grown crystal. X- Ray powder diffraction studies have been carried out in order to calculate the lattice parameter values.

Karunanithi, U.

2012-06-01

63

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

Microsoft Academic Search

We have measured scintillation properties of pure CsI crystals used in the shower calorimeter built for a precise determination of the ?+!?0e+?e 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

E. Frleÿz; Ch. Bronnimann; B. Krause; D. Poÿcanic; D. Renker; S. Ritt; P. L. Slocum; I. Supek; H. P. Wirtz

64

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

Microsoft Academic Search

We have measured scintillation properties of pure CsI crystals used in the shower calorimeter built for a precise determination of the ?+??0e+?e decay rate at the Paul Scherrer Institute (PSI). All 240 individual crystals painted with a special wavelength-shifting solution were examined in a custom-built detection apparatus (RASTA – radioactive source tomography apparatus) that uses a 137Cs radioactive gamma source,

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

2001-01-01

65

Growth and characterization of pure and semiorganic nonlinear optical Lithium Sulphate admixtured l-alanine crystal  

NASA Astrophysics Data System (ADS)

Lithium sulphate admixtured l-alanine (LSLA) salt was synthesized and the solubility of the commercially available l-alanine and the synthesized LSLA sample was determined in de-ionized water at various temperatures. In accordance with the solubility data, the saturated aqueous solutions of l-alanine and lithium admixtured l-alanine were prepared separately and the single crystals of the samples were grown by the solution method with a slow evaporation technique. Studying single x-ray diffraction shows that pure and LSLA crystal belong to the orthorhombic system with a non-centrosymmetric space group P212121. Using the powder x-ray diffraction study, the crystallinity of the grown crystals is confirmed and the diffraction peaks are indexed. The various functional groups present in the pure and LSLA crystal are elucidated from Fourier transform infrared spectroscopy study. UV-visible transmittance is recorded to study the optical transmittance range for the grown crystals. The powder second harmonic generation test confirms the nonlinear optical property of the grown crystals. From the microhardness test, the hardness of the grown crystals is estimated. The dielectric behaviour, such as the dielectric constant and the loss of the sample, are measured as a function of temperature and frequency. The ac conductivity of the grown crystals is also studied and the activation energy is calculated.

Vela, T.; Selvarajan, P.; Freeda, T. H.; Balasubramanian, K.

2013-04-01

66

Signatures in magnetites formed by (Ca,Mg,Fe)CO3 thermal decomposition: Terrestrial and extraterrestrial implications  

NASA Astrophysics Data System (ADS)

It has never been demonstrated whether magnetite synthesized through the heat-dependent decomposition of carbonate precursors retains the chemical and structural features of the carbonates. In this study, synthetic (Ca,Mg,Fe)CO3 was thermally decomposed by heating from 25 to 700 °C under 1 atm CO2, and by in situ exposure under vacuum to the electron beam of a transmission electron microscope. In both cases, the decomposition of the carbonate was topotactic and resulted in porous pseudomorphs composed of oriented aggregates of magnetite nanocrystals. Both calcium and magnesium were incorporated into nanophase magnetite, forming (Ca,Mg)-magnetites and (Ca,Mg)-ferrites when these elements were present in the parent material, thus preserving the chemical signature of the precursor. These results show that magnetites synthesized in this way acquire a chemical and structural inheritance from their carbonate precursor that indicates how they were produced. These results are not only important in the determination of the origin of chemically-impure, oriented nanophase magnetite crystals in general, but they also provide important insights into the origin of the large, euhedral, chemically-pure, [111]-elongated magnetites found within Ca-, Mg- and Fe-rich carbonates of the Martian meteorite ALH84001. Based on our experimental results, the chemically-pure magnetites within ALH84001 cannot be genetically related to the Ca-, Mg- and Fe-rich carbonate matrix within which they are embedded, and an alternative explanation for their occurrence is warranted.

Jimenez-Lopez, Concepcion; Rodriguez-Navarro, Carlos; Rodriguez-Navarro, Alejandro; Perez-Gonzalez, Teresa; Bazylinski, Dennis A.; Lauer, Howard V.; Romanek, Christopher S.

2012-06-01

67

Formation and relaxation of two-dimensional vortex crystals in a magnetized pure-electron plasma.  

PubMed

Systematic examinations are carried out experimentally about the contribution of background vorticity distributions (BGVD's) to the spontaneous formation and decay of ordered arrays (vortex crystals) composed of strong vortices (clumps) by using a pure-electron plasma. It is found that the BGVD level needs to be higher for an increasing number of clumps to form vortex crystals and that the number of the clumps constituting the crystal decreases in time as proportional to gamma lnt in contrast to proportional to t (-xi) with xi approximately 1 as accepted well in turbulence models. The decay rate gamma increases with the BGVD level. The observed configurations of the clumps cover the theoretically predicted catalogue of vortex arrays in superfluid helium, suggesting a possible relaxation path of the crystal states. PMID:17930446

Kiwamoto, Y; Hashizume, N; Soga, Y; Aoki, J; Kawai, Y

2007-09-14

68

Growth and characterization of pure and doped KHP NLO single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of Potassium Hydrogen Phthalate doped with amino acid L-lysine were grown successfully by slow evaporation method. The concentration of dopant in the mother solution was 0.5 mol%, 1 mol% and 2 mol%. There is a drastic change in the morphology due to variation in doping rates which is also reflected in the X-ray diffraction data. The Fourier Transform infrared spectroscopy study confirms the incorporation of L-lysine into Potassium Hydrogen Phthalate crystal. The thermal study indicates the dissociating nature of the crystal. The nonlinear optical property of the grown crystal has been confirmed by Kurtz-powder second harmonic generation test. The dopant of 0.5 mol% and 1 mol% shows higher second harmonic generation result than pure Potassium Hydrogen Phthalate. Results are discussed.

Thilagavathy, S. R.; Rajesh, P.; Ramasamy, P.; Ambujam, K.

2014-06-01

69

Growth and characterization of pure and doped KHP NLO single crystals.  

PubMed

Single crystals of Potassium Hydrogen Phthalate doped with amino acid l-lysine were grown successfully by slow evaporation method. The concentration of dopant in the mother solution was 0.5mol%, 1mol% and 2mol%. There is a drastic change in the morphology due to variation in doping rates which is also reflected in the X-ray diffraction data. The Fourier Transform infrared spectroscopy study confirms the incorporation of l-lysine into Potassium Hydrogen Phthalate crystal. The thermal study indicates the dissociating nature of the crystal. The nonlinear optical property of the grown crystal has been confirmed by Kurtz-powder second harmonic generation test. The dopant of 0.5mol% and 1mol% shows higher second harmonic generation result than pure Potassium Hydrogen Phthalate. Results are discussed. PMID:24632232

Thilagavathy, S R; Rajesh, P; Ramasamy, P; Ambujam, K

2014-06-01

70

Magnetite as a prokaryotic biomarker: A review  

NASA Astrophysics Data System (ADS)

Over the years, nanometer-sized magnetite (Fe3O4) crystals have been recovered from many modern and ancient environments including sediments and soils and even meteorites. In some cases these crystals have been used as "magnetofossils" for evidence of the past presence of specific microbes. Magnetite nanocrystals can be formed by a number of different biological and inorganic mechanisms resulting in crystals with different physical and magnetic characteristics. Prokaryotes (bacteria) biomineralize magnetite through two methods that differ mechanistically, including: biologically induced mineralization (BIM) and biologically controlled mineralization (BCM). Magnetite nanocrystals produced by BIM are known to be synthesized by the dissimilatory iron-reducing bacteria, are deposited external to the cell, and generally are physically indistinguishable from magnetite particles formed inorganically. BCM magnetites, in contrast, are synthesized by the magnetotactic bacteria and some higher organisms and are precipitated intracellularly as membrane-bounded structures called magnetosomes. These magnetites appear to have unique crystal morphologies and a narrow size range leading to their original use as magnetofossils. Because of the discovery of nanometer-sized crystals of magnetite in the Martian meteorite ALH84001, the use of these criteria for the determination of whether magnetite crystals could constitute a prokaryotic biomarker was questioned. Thus, there is currently great debate over what criteria to use in the determination of whether specific magnetite crystals are biogenic or not. In the last decade, additional criteria have been established (e.g., the Magnetite Assay for Biogenicity), and new tools and technologies have been developed to determine the origin of specific types of magnetite crystals.

Jimenez-Lopez, Concepcion; Romanek, Christopher S.; Bazylinski, Dennis A.

2010-06-01

71

Structure and morphology of magnetite anaerobically-produced by a marine magnetotactic bacterium and a dissimilatory iron-reducing bacterium  

USGS Publications Warehouse

Intracellular crystals of magnetite synthesized by cells of the magnetotactic vibroid organism, MV-1, and extracellular crystals of magnetite produced by the non-magnetotactic dissimilatory iron-reducing bacterium strain GS-15, were examined using high-resolution transmission electron microscopy, electron diffraction and 57Fe Mo??ssbauer spectroscopy. The magnetotactic bacterium contained a single chain of approximately 10 crystals aligned along the long axis of the cell. The crystals were essentially pure stoichiometric magnetite. When viewed along the crystal long axis the particles had a hexagonal cross-section whereas side-on they appeared as rectangules or truncated rectangles of average dimension, 53 ?? 35 nm. These findings are explained in terms of a three-dimensional morphology comprising a hexagonal prism of {110} faces which are capped and truncated by {111} end faces. Electron diffraction and lattice imaging studies indicated that the particles were structurally well-defined single crystals. In contrast, magnetite particles produced by the strain, GS-15 were irregular in shape and had smaller mean dimensions (14 nm). Single crystals were imaged but these were not of high structural perfection. These results highlight the influence of intracellular control on the crystallochemical specificity of bacterial magnetites. The characterization of these crystals is important in aiding the identification of biogenic magnetic materials in paleomagnetism and in studies of sediment magnetization. ?? 1990.

Sparks, N. H. C.; Mann, S.; Bazylinski, D. A.; Lovley, D. R.; Jannasch, H. W.; Frankel, R. B.

1990-01-01

72

Submicron Magnetite Grains and Carbon Compounds in Martian Meteorite ALH84001: Inorganic, Abiotic Formation by Shock and Thermal Metamorphism  

NASA Astrophysics Data System (ADS)

Purported biogenic features of the ALH84001 Martian meteorite (the carbonate globules, their submicron magnetite grains, and organic matter) have reasonable inorganic origins, and a comprehensive hypothesis is offered here. The carbonate globules were deposited from hydrothermal water, without biological mediation. Thereafter, ALH84001 was affected by an impact shock event, which raised its temperature nearly instantaneously to 500-700K, and induced iron-rich carbonate in the globules to decompose to magnetite and other minerals. The rapidity of the temperature increase caused magnetite grains to nucleate in abundance; hence individual crystals were very small. Nucleation and growth of magnetite crystals were fastest along edges and faces of the precursor carbonate grains, forcing the magnetite grains to be platy or elongated, including the "truncated hexa-octahedra" shape. ALH84001 had formed at some depth within Mars where the lithostatic pressure was significantly above that of Mars' surface. Also, because the rock was at depth, the impact heat dissipated slowly. During this interval, magnetite crystals approached chemical equilibria with surrounding minerals and gas. Their composition, nearly pure Fe3O4, reflects those of equilibria; elements that substitute into magnetite are either absent from iron-rich carbonate (e.g., Ti, Al, Cr), or partitioned into other minerals during magnetite formation (Mg, Mn). Many microstructural imperfections in the magnetite grains would have annealed out as the rock cooled. In this post-shock thermal regime, carbon-bearing gas from the decomposition of iron carbonates reacted with water in the rock (or from its surroundings) to produce organic matter via Fischer-Tropschlike reactions. Formation of such organic compounds like polycyclic aromatic hydrocarbons would have been catalyzed by the magnetite (formation of graphite, the thermochemically stable phase, would be kinetically hindered).

Treiman, Allan H.

2003-06-01

73

Submicron magnetite grains and carbon compounds in Martian meteorite ALH84001: inorganic, abiotic formation by shock and thermal metamorphism.  

PubMed

Purported biogenic features of the ALH84001 Martian meteorite (the carbonate globules, their submicron magnetite grains, and organic matter) have reasonable inorganic origins, and a comprehensive hypothesis is offered here. The carbonate globules were deposited from hydrothermal water, without biological mediation. Thereafter, ALH84001 was affected by an impact shock event, which raised its temperature nearly instantaneously to 500-700K, and induced iron-rich carbonate in the globules to decompose to magnetite and other minerals. The rapidity of the temperature increase caused magnetite grains to nucleate in abundance; hence individual crystals were very small. Nucleation and growth of magnetite crystals were fastest along edges and faces of the precursor carbonate grains, forcing the magnetite grains to be platy or elongated, including the "truncated hexa-octahedra" shape. ALH84001 had formed at some depth within Mars where the lithostatic pressure was significantly above that of Mars' surface. Also, because the rock was at depth, the impact heat dissipated slowly. During this interval, magnetite crystals approached chemical equilibria with surrounding minerals and gas. Their composition, nearly pure Fe(3)O(4), reflects those of equilibria; elements that substitute into magnetite are either absent from iron-rich carbonate (e.g., Ti, Al, Cr), or partitioned into other minerals during magnetite formation (Mg, Mn). Many microstructural imperfections in the magnetite grains would have annealed out as the rock cooled. In this post-shock thermal regime, carbon-bearing gas from the decomposition of iron carbonates reacted with water in the rock (or from its surroundings) to produce organic matter via Fischer-Tropschlike reactions. Formation of such organic compounds like polycyclic aromatic hydrocarbons would have been catalyzed by the magnetite (formation of graphite, the thermochemically stable phase, would be kinetically hindered). PMID:14577885

Treiman, Allan H

2003-01-01

74

Comparison of optical properties of pure and doped lithium tetraborate single crystals and glasses  

NASA Astrophysics Data System (ADS)

High optical quality Li2B4O7 (LTB) single crystals and glassy phases of pure, doped (Cu, Ag) and co-doped with Cu+Ag have been grown by Czochralski crystal pulling and melt quenching techniques respectively. They were characterized through photoluminescence (PL), thermoluminescence (TL), and UV-VIS-NIR transmission measurements. The PL of glass phase shows light yield comparable to that of single crystal. 80-85 % optical transmission in the range 350-800 nm revealed good optical quality of the glasses which is comparable to the single crystals though the glasses have higher cut off wavelength (lower energy). TL glow peaks of Cu doped LTB single crystal at 200 °C and for Cu+Ag co-doped LTB single crystals at around 170°C and 240°C are useful for the dosimetry applications and found to be linear in the range from 1mGy to 1kGy. However, in glasses no TL was observed in spite of a good PL yield.

Patra, G. D.; Singh, A. K.; Singh, S. G.; Tyagi, M.; Sen, S.; Tiwari, B.; Gadkari, S. C.

2012-06-01

75

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

76

Microbial preparation of metal-substituted magnetite nanoparticles  

SciTech Connect

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 (MyFe3-yO4) from a doped precursor, mixed-M iron oxyhydroxide, (MxFe1-xOOH, x 0.5, M is Mn, Zn, Ni, Co, and Cr). Within the range of 0.01 x 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.

Moon, Ji Won [ORNL; Roh, Yul [Chonnam National University, Gwangju; Lauf, Robert J [ORNL; Vali, Hojatollah [McGill University, Montreal, Quebec; Yeary, Lucas W [ORNL; Phelps, Tommy Joe [ORNL

2007-01-01

77

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

78

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

NASA Astrophysics Data System (ADS)

A systematic analysis of the Fourier transform infrared spectroscopy and Raman spectra of pure and Cu(NO3)23H2O doped Rochelle salt (NaKC4H4O64H2O) 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 CHO62- 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)COO2-, while for other modes (e.g. ?CH, ?COa, ?COs, ?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(NO3)23H2O doped Rochelle salt crystals is found out from powder X-ray diffraction studies.

Mathivanan, V.; Haris, M.

2013-02-01

79

Studies on gel-grown pure and strontium-modified lanthanum tartrate crystals  

NASA Astrophysics Data System (ADS)

Crystals of pure and strontium-modified lanthanum tartrate bearing composition (La) 1-x(Sr) xC 4H 4O 6· nH 2O (where x=0, 0.04, 0.10, 0.15; n=5,5,6,8) were obtained using gel method. The materials were studied using CH analysis, X-ray powder diffraction, FTIR, EDAX and thermoanalytical techniques. X-ray powder diffraction results analyzed by using suitable software suggest that while unmodified lanthanum tartrate has a monoclinic structure with the space group P 21, the entry of strontium into its lattice changes the system to orthorhombic with the space group P 2121. The unit cell volume is observed to decrease with increase in the concentration of strontium in lanthanum tartrate. Thermal analysis suggests that pure lanthanum tartrate starts decomposing at 41.31 °C whereas the strontium-modified lanthanum tartrate brings about better thermal stability which increases with an increase in strontium concentration. The percentage weight loss calculations from the thermogram supplemented by EDAX, CH analysis and FTIR spectroscopy suggest that both unmodified and strontium-modified lanthanum tartrate spherulitic crystals contain water of hydration; the amount of water of hydration being different for crystals with different content of strontium.

Firdous, A.; Quasim, I.; Ahmad, M. M.; Kotru, P. N.

2009-07-01

80

Growth and studies of pure and potassium iodide-doped zinc tris-thiourea sulphate (ZTS) single crystals  

Microsoft Academic Search

Single crystals of pure and potassium iodide (KI)-doped Zinc Tris-thiourea Sulphate (ZTS) were grown from aqueous solutions by slow evaporation technique. The grown crystals have been subjected to single crystal X-ray diffraction to determine the unit cell dimensions. The grown crystals were also characterized by recording the powder X-ray diffraction patterns and by identifying the diffracting planes. The Fourier Transform

C. Krishnan; P. Selvarajan; T. H. Freeda

2008-01-01

81

Growth, structural, spectroscopic and optical studies of pure and amino acid (glycine) doped methyl-para-hydroxy benzoate single crystals  

NASA Astrophysics Data System (ADS)

Methyl-para-hydroxy benzoate is a potential organic nonlinear optical (NLO) material. The pure and amino acid (glycine) doped MHB crystals are grown by slow evaporation solution growth technique. Single crystal X-ray diffraction studies of both pure and amino acid doped samples are carried out and the results are compared. FTIR studies are performed to identify the presence of various functional groups in the grown crystal. The UV-vis spectra confirm the improvement in the transparency of these crystals on doping amino acid. The amino acid doping improves the NLO properties. The dopant increases the hardness value of the material.

Selvaraju, K.; Kirubavathi, K.; Kumararaman, S.

2009-05-01

82

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

2014-06-01

83

Magnetic moment and susceptibility measurements of pure Nd and mixed rare-earth (Di) tartrate crystals  

Microsoft Academic Search

Magnetic characteristics of gel-grown pure neodymium tartrate and mixed rare-earth tartrate (didymium tartrate) crystals, using Gouy's balance method are reported. The experimental values of molar susceptibility for Nd2(C4H4O6)3.5H20 and Di2(C4H4O6)35H2O are 4876.787*10-6 and 4411.887*10-6 respectively, and the values of effective magnetic moments are 3.474 and 3.305 Bohr magnetrons respectively. The effective magnetic moments calculated on theoretical grounds are in reasonably

P. N. Kotru; K. K. Raina

1986-01-01

84

Crystal growth of pure substances: Phase-field simulations in comparison with analytical and experimental results  

SciTech Connect

A phase-field model for non-isothermal solidification in multicomponent systems [SIAM J. Appl. Math. 64 (3) (2004) 775-799] consistent with the formalism of classic irreversible thermodynamics is used for numerical simulations of crystal growth in a pure material. The relation of this approach to the phase-field model by Bragard et al. [Interface Science 10 (2-3) (2002) 121-136] is discussed. 2D and 3D simulations of dendritic structures are compared with the analytical predictions of the Brener theory [Journal of Crystal Growth 99 (1990) 165-170] and with recent experimental measurements of solidification in pure nickel [Proceedings of the TMS Annual Meeting, March 14-18, 2004, pp. 277-288; European Physical Journal B, submitted for publication]. 3D morphology transitions are obtained for variations in surface energy and kinetic anisotropies at different undercoolings. In computations, we investigate the convergence behaviour of a standard phase-field model and of its thin interface extension at different undercoolings and at different ratios between the diffuse interface thickness and the atomistic capillary length. The influence of the grid anisotropy is accurately analyzed for a finite difference method and for an adaptive finite element method in comparison.

Nestler, B. [Institute of Applied Research, Karlsruhe University of Applied Sciences, Moltkestrasse 30, 76133 Karlsruhe (Germany)]. E-mail: britta.nestler@fh-karlsruhe.de; Danilov, D. [Institute of Applied Research, Karlsruhe University of Applied Sciences, Moltkestrasse 30, 76133 Karlsruhe (Germany)]. E-mail: denis.danilov@fh-karlsruhe.de; Galenko, P. [Institute of Space Simulation, German Aerospace Center, 51170 Cologne (Germany)]. E-mail: peter.galenko@dlr.de

2005-07-20

85

A simple synthesis of size-reduce magnetite nano-crystals via aqueous to toluene phase-transfer method  

NASA Astrophysics Data System (ADS)

A simple one-step liquid-liquid phase-transfer synthesis of magnetite nanocrystals affording enhanced size reduction is described. One- and two-step particle transfer methods are compared. In the one-step method, particles are synthesized in a biphasic medium where the particles are formed in the microdroplets and migrate to the organic phase simultaneously, whereas in the two-step method, particles are first prepared in an aqueous phase and subsequently transferred to the organic phase. In both methods, CTAB was used as both a stabilizer and a transferring agent. Data from FTIR and XRD suggest invariably that the particles obtained are of magnetite, Fe 3O 4. The aqueous to organic phase-transfer efficiency is >99.5% for both methods. In the one-step method the average particle size and standard deviation (?) is half of that afforded in the two-step method (ca. 18.3+7.7 nm cf. 42.2+17.6 nm). This reduction in particle size is attributed to the formation of water in oil droplets that act as nanoreactors for the synthesis of magnetite particles.

Abu Bakar, M.; Tan, W. L.; Abu Bakar, N. H. H.

2007-07-01

86

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

87

Effect of swift heavy ion beam irradiation on the dielectric and ferroelectric properties of pure and cobalt doped TGS crystals  

Microsoft Academic Search

Effect of swift heavy ion (100MeV O7+ ion) beam irradiation on the temperature and frequency dependence of real (??) and imaginary (??) parts of dielectric permittivity in pure and Co2+ doped TGS crystals are analyzed. Irradiation with swift heavy ion beam changes the dielectric response considerably. Observed dielectric peak in irradiated crystals shifts towards lower temperature and broadens up; the

P. K. Bajpai; Deepak Shah; Ravi Kumar

88

Occurrence of secondary magnetite within biodegraded oil  

SciTech Connect

Samples of solid bitumen from the Thornton Quarry (Illinois) and the Cynthia Quarry (Mississippi) were found to be strongly magnetic and to have rock magnetic properties suggesting that the magnetizable grains present are magnetite. Studies of magnetic isolates revealed that magnetite is present primarily as spherical crystal aggregates that appear identical to magnetite spherules isolated from remagnetized Paleozoic carbonate units from other localities. Organic geochemical analyses of the solid bitumen suggest an origin by microbial attack on what once was liquid crude oil. The occurrence of secondary magnetite as inclusions within solid bitumen suggests a relationship between crude oil biodegradation and development of that mineral in their samples. The authors infer that secondary magnetite in other geologic environments may be related to the presence of hydrocarbons. The discovery of a natural association of secondary magnetite and hydrocarbons has important implications for paleomagnetism and for petroleum exploration.

McCabe, C.; Sassen, R.; Saffer, B.

1987-01-01

89

Occurrence of secondary magnetite within biodegraded oil  

NASA Astrophysics Data System (ADS)

Samples of solid bitumen from the Thornton Quarry (Illinois) and the Cynthia Quarry (Mississippi) were found to be strongly magnetic and to have rock magnetic properties suggesting that the magnetizable grains present are magnetite. Studies of magnetic isolates revealed that magnetite is present primarily as spherical crystal aggregates that appear identical to magnetite spherules isolated from re-magnetized Paleozoic carbonate units from other localities. Organic geochemical analyses of the solid bitumen suggest an origin by microbial attack on what once was liquid crude oil. The occurrence of secondary magnetite as inclusions within solid bitumen suggests a relationship between crude oil biodegradation and development of that mineral in our samples. We infer that secondary magnetite in other geologic environments may be related to the presence of hydrocarbons. The discovery of a natural association of secondary magnetite and hydrocarbons has important implications for paleomagnetism and for petroleum exploration.

McCabe, Chad; Sassen, Roger; Saffer, Barbara

1987-01-01

90

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

91

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

92

Growth and characterization of pure and potassium iodide-doped zinc tris-thiourea sulphate (ZTS) single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of pure and potassium iodide (KI)-doped zinc tris-thiourea sulphate (ZTS) were grown from aqueous solutions by the slow evaporation method. The grown crystals were transparent. The lattice parameters of the grown crystals were determined by the single-crystal X-ray diffraction technique. The grown crystals were also characterized by recording the powder X-ray diffraction pattern and by identifying the diffracting planes. The FT-IR spectrum was recorded in the range 400-4500 cm -1. Second harmonic generation (SHG) was confirmed by the Kurtz powder method. The thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) studies reveal that the materials have good thermal stability. Atomic absorption studies confirm the presence of dopant in ZTS crystals. The electrical measurements were made in the frequency range 10 2-10 6 Hz and in the temperature range 40-130 °C along a-, b- and c-directions of the grown crystals. The present study shows that the electrical parameters viz. dc conductivity, dielectric constant, dielectric loss factor and ac conductivity increase with increase in temperature. Activation energy values were also determined for the ac conduction process in grown crystals. The dc conductivity, dielectric constant, dielectric loss factor and ac conductivity of KI-doped ZTS crystal were found to be more than those of pure ZTS crystals.

Krishnan, C.; Selvarajan, P.; Freeda, T. H.; Mahadevan, C. K.

2009-02-01

93

Growth of InAs/InP core-shell nanowires with various pure crystal structures  

NASA Astrophysics Data System (ADS)

We have studied the epitaxial growth of an InP shell on various pure InAs core nanowire crystal structures by metal-organic vapor phase epitaxy. The InP shell is grown on wurtzite (WZ), zinc-blende (ZB), and {111}- and {110}-type faceted ZB twin-plane superlattice (TSL) structures by tuning the InP shell growth parameters and controlling the shell thickness. The growth results, particularly on the WZ nanowires, show that homogeneous InP shell growth is promoted at relatively high temperatures (˜500?°C), but that the InAs nanowires decompose under the applied conditions. In order to protect the InAs core nanowires from decomposition, a short protective InP segment is first grown axially at lower temperatures (420-460?°C), before commencing the radial growth at a higher temperature. Further studies revealed that the InP radial growth rate is significantly higher on the ZB and TSL nanowires compared to WZ counterparts, and shows a strong anisotropy in polar directions. As a result, thin shells were obtained during low temperature InP growth on ZB structures, while a higher temperature was used to obtain uniform thick shells. In addition, a schematic growth model is suggested to explain the basic processes occurring during the shell growth on the TSL crystal structures.

Gorji Ghalamestani, Sepideh; Heurlin, Magnus; Wernersson, Lars-Erik; Lehmann, Sebastian; Dick, Kimberly A.

2012-07-01

94

Light-induced orientational effects in periodic photonic structures with pure and dye-doped nematic liquid crystal defects  

NASA Astrophysics Data System (ADS)

We theoretically study and compare the light-induced Fréedericksz transition and above-threshold reorientation in pure and dye-doped nematic liquid crystals embedded into periodic dielectric structures. The presence of optical defect modes is found to significantly alter the effective influence of dyes as compared to the standard case of liquid crystal films without periodic structure, which is due to the overall resonant absorption of the dye-doped liquid crystal layer. Both statics and dynamics are discussed. In particular, it is found that optical response time can be up to several orders of magnitude faster with pure liquid crystals than with dye-doped ones. Thermal effects caused by absorption of dyes are also investigated to gauge whether it may induce nematic-to-isotropic phase transition.

Miroshnichenko, Andrey E.; Brasselet, Etienne; Kivshar, Yuri S.

2008-11-01

95

Growth and Studies of Pure and Lithium Bromide-Doped Zinc Tris-Thiourea Sulphate (ZTS) Single Crystals  

Microsoft Academic Search

Single crystals of pure and lithium bromide-doped Zinc Tris-thiourea Sulphate (ZTS) were grown from aqueous solutions by slow evaporation technique. The grown crystals were subjected to various studies such as X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), atomic absorption, and Second Harmonic Generation (SHG) studies. The density, melting point, DC conductivity, AC conductivity, dielectric constant, and activation energy of the

C. Krishnan; P. Selvarajan; T. H. Freeda

2008-01-01

96

Growth and studies of pure and potassium iodide-doped zinc tris-thiourea sulphate (ZTS) single crystals  

NASA Astrophysics Data System (ADS)

Single crystals of pure and potassium iodide (KI)-doped Zinc Tris-thiourea Sulphate (ZTS) were grown from aqueous solutions by slow evaporation technique. The grown crystals have been subjected to single crystal X-ray diffraction to determine the unit cell dimensions. The grown crystals were also characterized by recording the powder X-ray diffraction patterns and by identifying the diffracting planes. The Fourier Transform Infrared (FT-IR) spectra have been recorded in the range 400-4500 cm -1. Second harmonic generation (SHG) for the materials of this work was confirmed using Nd:YAG laser. The UV-visible spectra show that the grown crystals have wide optical transparency in the entire visible region. The Thermogravimetric/Differential Thermal Analyses (TG/DTA) thermograms reveal that the materials have good thermal stability. Atomic absorption study reveals the presence of potassium in the doped f crystals. The electrical measurements were made in the temperature range 40-130 °C along c-direction of the grown crystals. The dielectric studies show that there may be a ferroelectric transition at 50 °C for both pure and KI-doped ZTS crystals. DC conductivity for both the samples is found to be increasing with increase in temperature. Activation energy values were also determined for both AC and DC conduction processes in the samples.

Krishnan, C.; Selvarajan, P.; Freeda, T. H.

2008-12-01

97

Thermoluminescence in pure LiF crystals: Glow peaks and their connection with color centers  

NASA Astrophysics Data System (ADS)

Nominally pure LiF crystals were irradiated with the same dose (0.85 106 R) of gamma rays at ambient and low temperatures (-60 °C) and the resulting thermoluminescence (TL) is reported. Various optical and thermal treatments were applied in order to change the concentration of color centers (CCs). The effect of such treatments on the glow curves is observed. Knowing the coloration from optical transmission and photoluminescence measurements made on the same samples, we attribute many of the glow peaks (GPs) to the annealing of F center aggregates. For the present conditions of irradiation and dose, TL processes begin with decay of F3+ centers that display a GP at 164 °C. F3(R) centers follow and are responsible for GPs at 193 and 228 °C. A GP at 263 °C is ascribed to F2 centers. Several peaks at temperatures in the range of 280-380 °C are associated with impurity perturbed F centers. A GP at 410 °C is associated with a complex of aggregated F and H centers. These attributions are accomplished by means of TL spectra, optical transmission spectra, and annealing procedures, and are critically discussed. The experimental data confirm the general trend of thermal stability of CCs, which decreases by moving from simple F centers to more complex ones, and the existence of exchange dynamics among CCs.

Baldacchini, G.; Montereali, R. M.; Nichelatti, E.; Kalinov, V. S.; Voitovich, A. P.; Davidson, A. T.; Kozakiewicz, A. G.

2008-09-01

98

Thermoluminescence in pure LiF crystals: Glow peaks and their connection with color centers  

SciTech Connect

Nominally pure LiF crystals were irradiated with the same dose (0.85 10{sup 6} R) of gamma rays at ambient and low temperatures (-60 deg. C) and the resulting thermoluminescence (TL) is reported. Various optical and thermal treatments were applied in order to change the concentration of color centers (CCs). The effect of such treatments on the glow curves is observed. Knowing the coloration from optical transmission and photoluminescence measurements made on the same samples, we attribute many of the glow peaks (GPs) to the annealing of F center aggregates. For the present conditions of irradiation and dose, TL processes begin with decay of F{sub 3}{sup +} centers that display a GP at 164 deg. C. F{sub 3}(R) centers follow and are responsible for GPs at 193 and 228 deg. C. A GP at 263 deg. C is ascribed to F{sub 2} centers. Several peaks at temperatures in the range of 280-380 deg. C are associated with impurity perturbed F centers. A GP at 410 deg. C is associated with a complex of aggregated F and H centers. These attributions are accomplished by means of TL spectra, optical transmission spectra, and annealing procedures, and are critically discussed. The experimental data confirm the general trend of thermal stability of CCs, which decreases by moving from simple F centers to more complex ones, and the existence of exchange dynamics among CCs.

Baldacchini, G.; Montereali, R. M. [Department of Physical Technologies and New Materials-Frascati Research Center, ENEA, Via E. Fermi 45, Frascati, Roma 00044 (Italy); Nichelatti, E. [Department of Physical Technologies and New Materials-Casaccia Research Center, ENEA, S. Maria di Galeria, Roma 00123 (Italy); Kalinov, V. S.; Voitovich, A. P. [Institute of Physics, Academy of Sciences of Belarus, 70 Nezavisimosti Ave., 220067 Minsk (Belarus); Davidson, A. T.; Kozakiewicz, A. G. [Department of Chemistry, University of Zululand, Kwadlangezwa 3886 (South Africa)

2008-09-15

99

Critical Reexamination of Resonant Soft X-Ray Bragg Forbidden Reflections in Magnetite  

SciTech Connect

Magnetite, Fe{sub 3}O{sub 4}, displays a highly complex low-temperature crystal structure that may be charge and orbitally ordered. Many of the recent experimental claims of such ordering rely on resonant soft x-ray diffraction at the oxygen K and iron L edges. We have reexamined this system and undertaken soft x-ray diffraction experiments on a high-quality single crystal. Contrary to previous claims in the literature, we show that the intensity observed at the Bragg forbidden (001/2){sub c} reflection can be explained purely in terms of the low-temperature structural displacements around the resonant atoms. This does not necessarily mean that magnetite is not charge or orbitally ordered but rather that the present sensitivity of resonant soft x-ray experiments does not allow conclusive demonstration of such ordering.

Wilkins, S.B.; Di Matteo, S.; Beale, T.A.W.; Joly, Y.; Mazzoli, C.; Hatton, P.D.; Bencok, P.; Yakhou, F.; Brabers, V.A.M.

2009-05-01

100

Growth aspects and characteristic properties of pure and Li-doped L-arginine acetate (LAA) single crystals: A promising nonlinear optical material  

NASA Astrophysics Data System (ADS)

Single crystals of pure and lithium (Li)-doped L-arginine acetate (LAA) were grown by the slow evaporation technique. The effect of Li-doping on the growth, structural and optical properties of LAA crystal has been investigated. Powder X-ray diffraction studies confirm the crystal structure of the grown pure and Li-doped LAA single crystals. Various types of functional groups of the grown pure and Li-doped LAA single crystals were identified by the Fourier transform infrared (FTIR) spectroscopic analysis. The presence of Li in the grown crystal was confirmed by atomic absorption spectroscopic analysis. Electrical properties of the Li-doped LAA crystal were analyzed by AC impedance studies. The optical transmission study shows that the Li-doped LAA crystal has good optical transparency in the UV and visible regions.

Natarajan, V.; Arivanandhan, M.; Sankaranarayanan, K.; Ramasamy, P.

2009-01-01

101

Structural, optical and mechanical studies on pure and Mn 2+ doped l-asparagine monohydrate single crystals  

Microsoft Academic Search

Pure and 1, 1.5 and 2mol% Mn2+ doped l-asparagine monohydrate (MLA) single crystals have been successfully grown from aqueous solutions by slow cooling method. Powder X-ray diffraction (XRD) patterns and FT-Raman spectra have been recorded to study the variation in the lattice parameters and functional groups with doping concentrations respectively. The influence of doping on optical transparency and laser damage

Mohd. Shakir; V. Ganesh; M. A. Wahab; G. Bhagavannarayana; K. Kishan Rao

2010-01-01

102

Elastic and inelastic diffraction changes upon variation of the relative humidity environment of PurE crystals.  

PubMed

The different changes observed in the diffraction patterns of three different crystal forms (hexagonal, trigonal and monoclinic) of PurE (EC 4.1.1.21), an enzyme from the purine-biosynthesis pathway of Bacillus anthracis, upon a wide range of changes in the relative humidity environment of the crystals are documented. In addition, the changes in the unit-cell parameters, volume and bulk solvent in the three different crystal forms were systematically followed. In an attempt to explain the elastic (P6(5)22) and inelastic (P3(1)21) changes in the diffraction pattern, refined structures of the three different crystal forms determined at 100 K are presented, with particular emphasis on the tertiary and quaternary structural differences, crystal packing, intermolecular and intramolecular interactions and solvent structure. The refined structures show that the precipitant salts, solvent structure (both ordered and bulk) and conformation of the C-termini all play a role in creating a unique cement at both the intramolecular and intermolecular contacts of the different crystal forms. It is suggested that it is the combination of polyethylene glycol and the structure of the ordered water molecules (first and second layers) as well as the structure of the bulk solvent that are the critical factors in the plasticity of the hexagonal crystal packing as opposed to the inelastic responses of the lower symmetry forms. PMID:23385456

Oliete, R; Pous, J; Rodríguez-Puente, S; Abad-Zapatero, C; Guasch, A

2013-02-01

103

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

104

The I-Xe Age of Orgueil Magnetite: New Results  

NASA Technical Reports Server (NTRS)

I-Xe ages of Murchison and Orgueil magnetites were reported to be the oldest [1] and interpreted as the condensation time of the solar nebula. More recent measurements, conducted on a highly magnetic separate from Orgueil (but not pure magnetite), gave much younger I-Xe ages [2]. We have since performed new studies on two pure separates of Orgueil magnetite, confirming the later closing time of the I-Xe system in this mineral phase. In the previous work of Lewis and Anders [1] special attention was paid to the purity of the analyzed material. It was shown, that the trapped Xe resided mostly in hydrated silicates and the radiogenic 129Xe in magnetite [3]. Therefore, Orgueil was finely ground and stirred with a saturated LiCl solution for 8 days at 60 C to remove the silicate-magnetite intergrowth. Although this procedure yields magnetic fractions that are at least 90% pure [1], it could potentially contaminate the magnetite with iodine and produce noncorrelated 128Xe and spurious I-Xe ages. To avoid this possibility, in our first work with Orgueil we deliberately omitted separation in LiCl solution. Instead, the meteorite was ground into a fine powder and the highly magnetic fraction was separated with a hand magnet and was confirmed to be largely magnetite [2]. The new work, reported here, was done in order to confirm our previous results and investigate the effects of the LiCl treatment on the I-Xe system in magnetite.

Pravdivtseva, O. V.; Hohenberg, C. M.; Meshik, A. P.

2003-01-01

105

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

106

Spherulitic crystallization of pure (Nd and Dy) and mixed (Di) rare earth tartrates in silica gel  

NASA Astrophysics Data System (ADS)

Spherulites of pure Nd 2(C 4H 4O 6) 3·5H 2O, Dy 2(C 4H 4O 6) 3·11H 2O and mixed Di 2(C 4H 4O 3·5H 2O * were grown from silica gels by the reaction of the corresponding rare-earth nitrate with tartaric acid. The outer morphology of the spherulites is observed to be different for pure and mixed rare-earth tartrates respectively. The internal structure of these spherulites suggest a new formation mechanism - unlike the ones reported in the literature.

Kotru, P. N.; Raina, K. K.

1988-08-01

107

Thermal expansion and magnetostriction of pure and doped RAgSb2 (R = Y, Sm, La) single crystals  

NASA Astrophysics Data System (ADS)

Data on temperature-dependent, anisotropic thermal expansion in pure and doped RAgSb2 (R = Y, Sm, La) single crystals are presented. Using the Ehrenfest relation and heat capacity measurements, uniaxial pressure derivatives for long range magnetic ordering and charge density wave transition temperatures are evaluated and compared with the results of the direct measurements under hydrostatic pressure. In-plane and c-axis pressure have opposite effects on the phase transitions in these materials, with in-plane effects being significantly weaker. Quantum oscillations in magnetostriction were observed for the three pure compounds, with the possible detection of new frequencies in SmAgSb2 and LaAgSb2. The uniaxial (along the c-axis) pressure derivatives of the dominant extreme orbits (?) were evaluated for YAgSb2 and LaAgSb2.

Bud'ko, S. L.; Law, S. A.; Canfield, P. C.; Samolyuk, G. D.; Torikachvili, M. S.; Schmiedeshoff, G. M.

2008-03-01

108

Scintillation characteristics of pure and Tl-doped CsI crystals  

Microsoft Academic Search

The scintillation characteristics of pure and Tl-doped CsI were investigated. The scintillation light was detected with photomultipliers and silicon photodiodes. The influence of the Tl concentration on the light yield and on the decay times was studied upon excitation with ?-rays and ?-particles. The origin of the different emission components is discussed

P. Schotanus; R. Kamermans; P. Dorenbos

1990-01-01

109

Time-resolved luminescent VUV-spectroscopy of pure and doped by rare earth ions crystals of strontium fluoride  

Microsoft Academic Search

The spectroscopic properties SrF2–Eu(1%), SrF2–Er(1%) and nominal pure SrF2 crystals have been studied using time-resolved vacuum ultraviolet (VUV) spectroscopy under pulsed synchrotron radiation excitation. The 4fk?4fk?15d (f–d) and 4fk?4fk (f?f) excitation spectra and emission spectra (with and without of time resolution) have been investigated in the wide energy region at 8 and 295K. Moreover, the emission and excitation behaviors of

K. V. Ivanovskikh; V. A. Pustovarov; B. V. Shulgin

2005-01-01

110

NEUTRON DIFFRACTION INVESTIGATION OF THE 119 K TRANSITION IN MAGNETITE  

Microsoft Academic Search

Neutron diffraction measurements on synthetic single crystals of ; magnetite confirm the orthorhombic ordering scheme proposed by Verwey and co-; workers to explain the changes in physical properties which magnetite undergoes ; when cooled below 119 deg K. A magnetic field suitably applied during cooling; ; prevents the multiple twinning which occurs in the absence of a field and allows

Walter Hamilton

1958-01-01

111

Remanence in authigenic magnetite: Testing the hydrocarbon-magnetite hypothesis  

NASA Astrophysics Data System (ADS)

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, ?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 hydrocarbon inclusions suggests that 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 us to propose that chemical conditions created by the hydrocarbons caused precipitation of authigenic magnetite and acquisition of the associated chemical remanence.

Elmore, R. Douglas; Crawford, Lisa

1990-04-01

112

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

113

Crystal Nucleation in Glass-Forming Alloy and Pure Metal Melts under Containerless and Vibrationless Conditions.  

National Technical Information Service (NTIS)

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...

F. Spaepen D. Turnbull

1982-01-01

114

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

PubMed

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. PMID:12366136

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

2002-09-01

115

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

NASA Astrophysics Data System (ADS)

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.

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

2002-09-01

116

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

117

Thermodynamic Analysis Of Pure And Impurity Doped Pentaerythritol Tetranitrate Crystals Grown At Room Temperature  

Microsoft Academic Search

Pentaerythritol tetranitrate (PETN) powders are used to initiate other explosives. During long-term storage, changes in powder properties can cause changes in the initiation performance. Changes in the morphology and surface area of aging powders are observed due to sublimation and growth of PETN crystals through coarsening mechanisms, (e.g. Ostwald ripening, sintering, etc.). In order to alleviate the sublimation of PETN

R Pitchimani; W Zheng; S Simon; A K Burnham

2006-01-01

118

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

119

Stoichiometric magnetite grown by infrared nanosecond pulsed laser deposition  

NASA Astrophysics Data System (ADS)

Pulsed laser deposition (PLD) is a versatile technique for the fabrication of nanostructures due to the possibilities it offers to control size and shape of nanostructured deposits by varying the laser parameters. Magnetite nanostructures are currently promising materials to be used in computing, electronic devices and spintronic applications. For all these uses the fabrication of uniform nanostructured pure magnetite thin films is highly advantageous. In PLD of magnetite, the laser irradiation wavelength and substrate temperature crucially affect the composition, crystallinity, surface structure and the magnetic properties of the grown samples. This work shows that the use of nanosecond IR laser at 1064 nm enhances the quality of the resulting magnetite thin films, compared to the extensively used UV wavelengths. Deposition at 1064 nm, upon heating the substrate at 750 K, produces thin films constituted by stoichiometric magnetite nanoparticles with sharp edges and sizes ranging from 80 to 150 nm, with a Verwey transition at 119 K and a coercivity of 232 Oe at room temperature, close to those of pure bulk magnetite. Thus, IR-PLD of self-prepared hematite sintered targets constitutes a low-cost procedure of fabrication of pure magnetite nanostructured thin films.

Sanz, Mikel; Oujja, Mohamed; Rebollar, Esther; Marco, José F.; de la Figuera, Juan; Monti, Matteo; Bollero, Alberto; Camarero, Julio; Pedrosa, Francisco J.; García-Hernández, Mar; Castillejo, Marta

2013-10-01

120

Mechanical properties of magnetite (Fe 3O 4), hematite (?-Fe 2O 3) and goethite (?-FeO·OH) by instrumented indentation and molecular dynamics analysis  

Microsoft Academic Search

Hardness and elastic properties of pure (crystal) and complex (product of corrosion) iron oxides, magnetite (Fe3O4), hematite (?-Fe2O3) and goethite (?-FeO·OH), were determined by means of molecular dynamics analysis (MDA) and instrumented indentation. To determine local mechanical properties by indentation, multicyclic loading is performed by using incremental mode. Moreover to study the influence of visco-elastoplastic behaviour of the material, various

D. Chicot; J. Mendoza; A. Zaoui; G. Louis; V. Lepingle; F. Roudet; J. Lesage

2011-01-01

121

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

122

Thermodynamic analysis of pure and impurity doped pentaerythritol tetranitrate crystals grown at room temperature  

Microsoft Academic Search

Pentaerythritol tetranitrate (PETN) powders are used to initiate other explosives. During long-term storage, changes in powder\\u000a properties can cause changes in the initiation performance. Changes in the morphology and surface area of aging powders are\\u000a observed due to sublimation and growth of PETN crystals through coarsening mechanisms, (e.g. Ostwald ripening, sintering,\\u000a etc.). In order to alleviate the sublimation of PETN

R. Pitchimani; W. Zheng; S. L. Simon; A. K. Burnham

2007-01-01

123

High resolution Raman study of phonon and vibron bandwidths in isotopically pure and natural benzene crystal  

NASA Astrophysics Data System (ADS)

The frequency and the bandwidth of the 12 Raman active lattice modes and of more than 45 internal vibrons of natural and 12C isotopically pure benzene have been measured under high resolution with the aid of a tandem interferometer-spectrometer system or alternatively of a two meter focal length grating Sopra spectrometer. For five lattice phonons and for several vibrons the measurements were extended to a sufficient temperature range to study the relaxation processes in terms of anharmonic phonon-phonon and phonon-vibron coupling processes. The effect of the isotopic impurities on the phonon lifetime has been shown to be very important for some vibrons, in particular, for those resonant with the impurity level. The bandwidth evolution with temperature has been interpreted in terms of down- and up- three- and four-phonon as well as of dephasing processes.

Pinan, J. P.; Ouillon, R.; Ranson, P.; Becucci, M.; Califano, S.

1998-10-01

124

A comparative study on pure, L-arginine and glycine doped ammonium dihydrogen orthophosphate single crystals grown by slow solvent evaporation and temperature-gradient method  

NASA Astrophysics Data System (ADS)

Single crystals of pure, L-arginine and glycine doped ammonium dihydrogen orthophosphate (ADP) were grown by both the slow solvent evaporation method and the temperature-gradient method of Sankaranarayanan-Ramasamy (SR). The metastable zone width for different saturation temperatures of pure glycine and L-arginine added solutions were carried out. The grown crystals were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), optical transmission, dielectric constant, dielectric loss, and Vickers microhardness. The DSC and TG curves of the grown crystals indicated that they were stable up to 200 °C. The XRD study confirmed the structure of the grown crystal. The optical transmission analysis revealed that the pure and doped ADP crystals had very high percentage of transmission in the entire visible region. The important optical parameters such as reflectance and extinction coefficients of the grown crystals were calculated. L-arginine and glycine were used as dopants to reduce dielectric constant of ADP. The a.c. resistivity and a.c. conductivity were calculated. Dielectric loss of the doped ADP crystals grown by the SR method is lower than the doped ADP crystals grown by the conventional method. Larger hardness value for the SR method grown crystals confirmed greater crystalline perfection.

Pattanaboonmee, N.; Ramasamy, P.; Yimnirun, R.; Manyum, P.

2011-01-01

125

Formation of tabular single-domain magnetite induced by Geobacter metallireducens GS-15.  

PubMed

Distinct morphological characteristics of magnetite formed intracellularly by magnetic bacteria (magnetosome) are invoked as compelling evidence for biological activity on Earth and possibly on Mars. Crystals of magnetite produced extracellularly by a variety of bacteria including Geobacter metallireducens GS-15, thermophilic bacteria, and psychrotolerant bacteria are, however, traditionally not thought to have nearly as distinct morphologies. The size and shape of extracellular magnetite depend on the culture conditions and type of bacteria. Under typical CO(2)-rich culture conditions, GS-15 is known to produce superparamagnetic magnetite (crystal diameters of approximately <30 nm). In the current study, we were able to produce a unique form of tabular, single-domain magnetite under nontraditional (low-CO(2)) culture conditions. This magnetite has a distinct crystal habit and magnetic properties. This magnetite could be used as a biosignature to recognize ancient biological activities in terrestrial and extraterrestrial environments and also may be a major carrier of the magnetization in natural sediments. PMID:15525704

Vali, Hojatollah; Weiss, Benjamin; Li, Yi-Liang; Sears, S Kelly; Kim, Soon Sam; Kirschvink, Joseph L; Zhang, Chuanlun L

2004-11-16

126

Luminescence study of pure and Fe or Mo-doped ZnWO 4 crystals  

Microsoft Academic Search

ZnWO4, ZnWO4:Fe and ZnWO4:Mo crystals were investigated by the methods of time-resolved spectroscopy in the temperature range of 4.2–300K. It is shown that the Mo and Fe impurities significantly reduce the light yield of ZnWO4. The main 2.5eV emission of ZnWO4 and the 1.77eV emission band of ZnWO4:Mo are shown to originate from the triplet excited state of the WO6

V. Nagirnyi; L. Jönsson; M. Kirm; A. Kotlov; A. Lushchik; I. Martinson; A. Watterich; B. I. Zadneprovski

2004-01-01

127

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

128

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

129

Time-resolved luminescent VUV-spectroscopy of pure and doped by rare earth ions crystals of strontium fluoride  

NASA Astrophysics Data System (ADS)

The spectroscopic properties SrF 2-Eu(1%), SrF 2-Er(1%) and nominal pure SrF 2 crystals have been studied using time-resolved vacuum ultraviolet (VUV) spectroscopy under pulsed synchrotron radiation excitation. The 4f k?4f k-15d (f-d) and 4f k?4f k (f-f) excitation spectra and emission spectra (with and without of time resolution) have been investigated in the wide energy region at 8 and 295 K. Moreover, the emission and excitation behaviors of intrinsic luminescence SrF 2 have been studied at 8 K, when the fast and slow components given by singlet and triplet relaxation of self-trapped excitons (STE) are observed. Special attention is devoted to VUV emission of Er 3+-doped SrF 2 due to spin-allowed and spin-forbidden 4f 105d?4f 11 transitions.

Ivanovskikh, K. V.; Pustovarov, V. A.; Shulgin, B. V.

2005-05-01

130

Size Distributions and Morphologies of Synthetic and Biogenic Magnetite Nanoparticles  

NASA Astrophysics Data System (ADS)

Magnetite crystals formed in the cells of magnetotactic bacteria have narrow size distributions and distinct, strain- specific morphologies. In order to better understand the processes that result in such specific physical properties, we studied the development of nanocrystal sizes and shapes both in cultured cells of magnetotactic bacteria and in abiotic crystal nucleation and growth experiments. Magnetite nucleation and growth was induced in resting, iron-starved cells of Magnetospirillum gryphiswaldense. Freshly induced particles have a normal size distribution and irregular morphologies. As the particles grow, their size distribution changes but remains positively skewed, in contrast to the typically negatively-skewed distribution of magnetite in continuously iron-supplemented, reference cells. The morphologies of the fast-grown magnetite crystals differ from those formed in the reference cells, indicating that the uptake rate of iron can influence the sizes and morphologies of biogenic magnetite nanoparticles. We synthesized magnetite nanoparticles by co-precipitating ferrous and ferric ions from aqueous solutions. By varying the temperature and the types and concentrations of the reagents, we controlled the mean size of the crystals from 10 to 69 nm. Adding phosphate to the solution resulted in irregular morphologies, whereas the nucleation of crystals on synthetic bacterial filaments produced a bimodal size distribution and slightly more regular morphologies. Experiments are being conducted with various organic additives, with the ultimate goal of being able to reproduce the specificity of crystal sizes and shapes observed in magnetotactic bacteria.

Posfai, M.; Kosa, I.; Csakberenyi Nagy, D.; Faivre, D.; Menguy, N.; Schuler, D.

2007-12-01

131

Growth of pure single crystals of alkali halides and alkaline earth fluorides  

NASA Astrophysics Data System (ADS)

The final report covers the design of ion selective filters and development of an ion exchange purification system for potassium bromide. The system consists of an ion selective filter for passage of potassium ions and a bromide anion exchange system for reduction of anionic impurities. Because of the high ionic strength of the solutions used and particularly their ability to hydrolyze amide and ester bonds, limitations are imposed on the materials that can be used for construction of those parts of the systems that contact these solutions. Certain addition polymers are more promising for construction of the components of such a system than others, these are discussed in the body of the report. A special group of components have been designed and assembled to provide the fittings, valves, electrode chambers, sampling valves, columns and filters necessary for a closed purification system. The preparation of the resins for use in such a system required that their conversion to the forms required for purification of KBr, require that the reactions for this conversion go almost to completion. The extent of conversion of the resins affect the operational characteristics of the system and are discussed in this report. The product of the initial purification is a strongly acid KBr solution and the techniques were developed to minimize external contamination during reduction of the purified salt solution to a solid. The final purification step made during the growth of the crystal is treatment with a reactive gas. A greaseless reactive gas manifold was constructed and several reactive gas treatments were used in an attempt to purify the KBr.

Fredericks, W. J.

1981-05-01

132

Insight into magnetite's redox catalysis from observing surface morphology during oxidation.  

PubMed

We study how the (100) surface of magnetite undergoes oxidation by monitoring its morphology during exposure to oxygen at ~650 °C. Low-energy electron microscopy reveals that magnetite's surface steps advance continuously. This growth of Fe3O4 crystal occurs by the formation of bulk Fe vacancies. Using Raman spectroscopy, we identify the sinks for these vacancies, inclusions of ?-Fe2O3 (hematite). Since the surface remains magnetite during oxidation, it continues to dissociate oxygen readily. At steady state, over one-quarter of impinging oxygen molecules undergo dissociative adsorption and eventual incorporation into magnetite. From the independence of growth rate on local step density, we deduce that the first step of oxidation, dissociative oxygen adsorption, occurs uniformly over magnetite's terraces, not preferentially at its surface steps. Since we directly observe new magnetite forming when it incorporates oxygen, we suggest that catalytic redox cycles on magnetite involve growing and etching crystal. PMID:23763580

Nie, Shu; Starodub, Elena; Monti, Matteo; Siegel, David A; Vergara, Lucía; El Gabaly, Farid; Bartelt, Norman C; de la Figuera, Juan; McCarty, Kevin F

2013-07-10

133

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

134

Nitrite reactivity with magnetite.  

PubMed

Under Fe(3+)-reducing conditions, soil Fe(2+) oxidation has been shown to be coupled with nitrate (NO3(-)) reduction. One possible secondary reaction is the involvement of NO3(-) and nitrite (NO2(-)) with magnetite, a mixed valence Fe(2+)/Fe(3+) mineral found in many natural environments. Currently, little information exists on NO3(-) and NO2(-) reactivity with magnetite. This study investigates NO3(-) and NO2(-) reactivity with magnetite under anoxic conditions using batch kinetic experiments across a range of pH values (5.5-7.5) and in the presence of added dissolved Fe(2+). Solid phase products were characterized using X-ray diffraction (XRD), Mössbauer spectroscopy, and scanning electron microscopy (SEM). Nitrate removal by magnetite was much slower when compared with NO2(-). There was a pH-dependence in the reduction of NO2(-) by magnetite; the initial rate of NO2(-) removal was two times faster at pH 5.5 than at pH 7.5. The influence of pH was explained by the binding of NO2(-) to positively charged sites on magnetite (? S-OH2(+)) and to neutral sites (? S-OH(0)). As NO2(-) was removed from solution, nitric oxide (NO) and nitrous oxide (N2O) were identified as products confirming that nitrite was reduced. Structural Fe(2+) in magnetite was determined to be the reductant of NO2(-) based on the lack of measurable dissolved Fe(2+) release to solution coupled with Mössbauer spectra and XRD analysis of solid phase products. Addition of dissolved Fe(2+) to magnetite slurries resulted in adsorption and an acceleration in the rate of nitrite reduction at a given pH value. In summary, findings reported in this study demonstrate that if magnetite is present in Fe(3+)-reducing soil and NO2(-) is available, it can remove NO2(-) from solution and reduce a portion of it abiotically to NO and subsequently to N2O by a heterogeneous electron transfer process. PMID:23662623

Dhakal, P; Matocha, C J; Huggins, F E; Vandiviere, M M

2013-06-18

135

Magnetite biomineralization in the human brain.  

PubMed Central

Although the mineral magnetite (Fe3O4) is precipitated biochemically by bacteria, protists, and a variety of animals, it has not been documented previously in human tissue. Using an ultrasensitive superconducting magnetometer in a clean-lab environment, we have detected the presence of ferromagnetic material in a variety of tissues from the human brain. Magnetic particle extracts from solubilized brain tissues examined with high-resolution transmission electron microscopy, electron diffraction, and elemental analyses identify minerals in the magnetite-maghemite family, with many of the crystal morphologies and structures resembling strongly those precipitated by magnetotactic bacteria and fish. These magnetic and high-resolution transmission electron microscopy measurements imply the presence of a minimum of 5 million single-domain crystals per gram for most tissues in the brain and greater than 100 million crystals per gram for pia and dura. Magnetic property data indicate the crystals are in clumps of between 50 and 100 particles. Biogenic magnetite in the human brain may account for high-field saturation effects observed in the T1 and T2 values of magnetic resonance imaging and, perhaps, for a variety of biological effects of low-frequency magnetic fields. Images

Kirschvink, J L; Kobayashi-Kirschvink, A; Woodford, B J

1992-01-01

136

Magnetite Biomineralization in the Human Brain  

NASA Astrophysics Data System (ADS)

Although the mineral magnetite (Fe_3O_4) is precipitated biochemically by bacteria, protists, and a variety of animals, it has not been documented previously in human tissue. Using an ultrasensitive superconducting magnetometer in a clean-lab environment, we have detected the presence of ferromagnetic material in a variety of tissues from the human brain. Magnetic particle extracts from solubilized brain tissues examined with high-resolution transmission electron microscopy, electron diffraction, and elemental analyses identify minerals in the magnetite-maghemite family, with many of the crystal morphologies and structures resembling strongly those precipitated by magnetotactic bacteria and fish. These magnetic and high-resolution transmission electron microscopy measurements imply the presence of a minimum of 5 million single-domain crystals per gram for most tissues in the brain and >100 million crystals per gram for pia and dura. Magnetic property data indicate the crystals are in clumps of between 50 and 100 particles. Biogenic magnetite in the human brain may account for high-field saturation effects observed in the T1 and T2 values of magnetic resonance imaging and, perhaps, for a variety of biological effects of low-frequency magnetic fields.

Kirschvink, Joseph L.; Kobayashi-Kirschvink, Atsuko; Woodford, Barbara J.

1992-08-01

137

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

138

Fabrication of octahedral magnetite microcrystals  

Microsoft Academic Search

Octahedral magnetite microcrystals were synthesized by a simple hydrothermal route. The morphology and structure of magnetite microoctahedrons were characterized by XRD, IR, SEM, EDS, TEM and ED. The results showed that the as-synthesized sample exhibits octahedral structures and the size ranges from 4 to 10 ?m. It is suggested that the driving force for the anisotropic growth of magnetite octahedrons derives

Xian-Ming Liu; Shao-Yun Fu; Hong-Mei Xiao

2006-01-01

139

Mössbauer spectroscopy and magnetic properties of hematite/magnetite nanocomposites  

NASA Astrophysics Data System (ADS)

A thermal reduction method has been developed to prepare magnetite/hematite nanocomposites and pure magnetite nanoparticles targeted for specific applications. The relative content of hematite ?-Fe2O3 and magnetite Fe3O4 nanoparticles in the product was ensured by maintaining proper conditions in the thermal reduction of ?-Fe2O3 powder in the presence of a high boiling point solvent. The structural, electronic, and magnetic properties of the nanocomposites were investigated by 57Fe-Mössbauer spectroscopy, x-ray diffraction, and magnetic measurements. The content of hematite and magnetite phases was evaluated at every step of the chemical and thermal treatment. It is established that not all iron ions in the octahedral B-sites of magnetite nanoparticles participate in the electron hopping Fe2+?Fe3+ above the Verwey temperature TV, and that the charge distribution can be expressed as (Fe3+)tet[Fe1.852.5+Fe0.153+]octO4. It is shown that surface effects, influencing the electronic states of iron ions, dominate the vacancy effect, and thus govern the observed specific features of the Verwey transition and magnetic properties. The sharp increase in coercivity observed in magnetite nanoparticles below TV is much stronger than for bulk magnetite.

Lyubutin, I. S.; Lin, C. R.; Korzhetskiy, Yu. V.; Dmitrieva, T. V.; Chiang, R. K.

2009-08-01

140

Morphology and structure of biogenic magnetite particles  

Microsoft Academic Search

Blakemore1 found aquatic bacteria that swim along magnetic lines of force. Such bacteria have small particles of magnetite (magnetosomes) within them2,3 of various shapes3-5. We describe here the morphology and structure of bacterial magnetosomes investigated by high-resolution electron microscopy. From direct observation of various kinds of lattice images, the particles are determined to be single crystals with a hexagonal prism

Tsuyoshi Matsuda; Junji Endo; Nobuyuki Osakabe; Akira Tonomura; Tatsuo Arii

1983-01-01

141

Magnetite in carbonaceous chondrites  

Microsoft Academic Search

Magnetite (Fe3O4) occurs in many carbonaceous chondrites (CCs) and has long attracted the attention of meteorite researchers. However, its origin is unresolved; suggestions range from condensates from the solar nebular to products from aqueous alteration on the meteorite parent body. The report of possible evidence of former life in ancient Martian meteorite ALH84001 suggested an additional and highly intriguing origin

Xin Hua; Peter R. Buseck

1997-01-01

142

Microbial production of ultrafine-grained magnetite by fermentation processes at room temperature.  

PubMed

A method of producing magnetite nanoparticles was developed through culturing a microorganism designated Haejae-1, Shewanella sp., in the presence of glucose and akaganeite (beta-FeOOH). Haejae-1 isolated from inter-tidal flat sediments was able to produce copious amount of ultrafine magnetite via glucose fermentation extracellularly under anaerobic conditions at room temperature, allowing for easy production, separation, and recovery of the magnetite. TEM observation revealed aggregates of small crystals of ultrafine magnetite which ranged in size from about 2 to 4 nanometers. Magnetic property by SQUID analysis showed the magnetite nanoparticles demonstrate superparamagnetic behavior. As a result, the method of the present study can be used to produce magnetite efficiently using inexpensive means at room temperature. The magnetite is a mineral of a great commercial value in that it is useful, e.g., in magnetic recording devices, drug carriers, and as toner for plain paper copiers. PMID:19198424

Roh, Yul; Kim, Yumi; Lee, Sanghoon; Jang, Heedong; Suh, Yongjae

2008-10-01

143

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

144

Magnetosome vesicles are present before magnetite formation, and MamA is required for their activation  

Microsoft Academic Search

Bacterial magnetosomes are intracellular compartments that house highly ordered magnetite crystals. By using Magnetospiril- lum sp. AMB-1 as a model system, we show that magnetosome vesicles exist in the absence of magnetite, biomineralization of magnetite proceeds simultaneously in multiple vesicles, and bi- omineralization proceeds from the same location in each vesicle. The magnetosome-associated protein, MamA, is required for the formation

Arash Komeili; Hojatollah Vali; Terrance J. Beveridge; Dianne K. Newman

2004-01-01

145

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

146

Zero-dimensional magnetite  

Microsoft Academic Search

Low-dimensional magnetic systems are of interest due to several new effects and modifications that occur at sizes below the average domain grain boundary within the bulk material. Molecule-like magnetite (Fe3O4) nanoparticles, with sizes ranging from one to two nm were synthesized and characterized in order to investigate new properties arising from quantum size effects. These small systems will provide opportunities

Melissa Gayle Arredondo

2006-01-01

147

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

148

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

149

A Comparison between Chemical Synthesis Magnetite Nanoparticles and Biosynthesis Magnetite  

PubMed Central

The preparation of Fe3O4 from ferrous salt by air in alkaline aqueous solution at various temperatures was proposed. The synthetic magnetites have different particle size distributions. We studied the properties of the magnetite prepared by chemical methods compared with magnetotactic bacterial nanoparticles. The results show that crystallite size, morphology, and particle size distribution of chemically prepared magnetite at 293?K are similar to biosynthesis of magnetite. The new preparation of Fe3O4 helps to explain the mechanism of formation of magnetosomes in magnetotactic bacteria. The products are characterized by X-ray powder diffraction (XRD), infrared (IR) spectra, vibrating sample magnetometry (VSM), and scanning electron microscopy (SEM).

Kahani, Seyed Abolghasem; Yagini, Zahra

2014-01-01

150

Synthetic clay-magnetite aggregates designed for controlled deposition experiments  

NASA Astrophysics Data System (ADS)

The behavior of magnetic particles in fluid environments is key to the acquisition of detrital remanence magnetization and is essential to a multitude of industrial applications. This study introduces a series of synthetic clay-magnetite aggregates whose physical attributes can be tailored for controlled depositional experiments. We describe the mineralogical structure and magnetic behavior of montmorillonite platelets coated with nanometer-scale magnetite crystals using both electron microscopy and rock magnetism techniques. Selected area electron diffraction of the magnetite and the montmorillonite host shows no evidence of preferred orientation or oriented aggregation. Grain size distributions of magnetite in three different clay-magnetite assemblages were directly measured using conventional bright-field transmission electron microscopy. The spacing of the magnetite grains and their three-dimensional distribution around individual clay platelets was imaged using a tomographic reconstruction generated from high-angle annular dark-field (HAADF) images. The grain size distributions determined from the bright-field images and the tomographic reconstruction agree within error with estimates derived from magnetic granulometry techniques based on magnetic hysteresis and low-field susceptibility measurements. All three samples behave superparamagnetically at room temperature, and display increasing levels of single domain behavior as the samples are cooled to liquid nitrogen temperatures (- 195°C). Off-axis electron holography images show that superparamagnetic grains are also stabilized into flux closure structures at -195°C. The average spacing between adjacent magnetite crystals and the overall platelet shape of the aggregates creates an anisotropy of magnetic susceptibility that allows assemblages to align with external magnetic fields at room temperature. By adjusting the dimensions and concentrations of the magnetite grains in these aggregates, we can create well-characterized materials with known grain size distributions that are ideally suited for controlled depositional experiments.

Feinberg, J. M.; Galindo-Gonzalez, C.; Kasama, T.; Cervera, L.; Posfai, M.; Harrison, R. J.; Dunin-Borkowski, R. E.

2007-12-01

151

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

152

Nanophase Magnetite and Pyrrhotite in ALH84001 Martian Meteorite: Evidence for an Abiotic Origin  

NASA Technical Reports Server (NTRS)

The nanophase magnetite crystals in the black rims of pancake-shaped carbonate globules of the Martian meteorite ALH84001 have been studied extensively because of the claim by McKay et al.that they are biogenic in origin. A subpopulation of these magnetite crystals are reported to conform to a unique elongated shape called "truncated hexa-octahedral" or "THO" by Thomas-Keprta et al. They claim these THO magnetite crystals can only be produced by living bacteria thus forming a biomarker in the meteorite. In contrast, thermal decomposition of Fe-rich carbonate has been suggested as an alternate hypothesis for the elongated magnetite formation in ALH84001 carbonates. The experimental and observational evidence for the inorganic formation of nanophase magnetite and pyrrhotite in ALH84001 by decomposition of Fe-rich carbonate in the presence of pyrite are provided.

Golden, D. C.; Lauer, H. V., Jr. III; Ming, D. W.; Morris, R. V.

2006-01-01

153

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

154

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

155

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

156

Preparation and characterization of hydrophobic superparamagnetic magnetite gel  

NASA Astrophysics Data System (ADS)

The present study describes the preparation and analysis of a highly concentrated hydrophobic oleic acid-coated magnetite gel. By contrast to conventional techniques to prepare magnetic fluids, herein the oleic acid was introduced as a reactant during the initial crystallization phase of magnetite that was obtained by the co-precipitation of Fe(II) and Fe(III) salts by addition of ammonium hydroxide. The resulting gelatinous hydrophobic magnetite was characterized in terms of morphology, particle size, magnetic properties, crystal structure, and hydrophobicity/hydrophilicity. This magnetic gel exhibited superparamagnetism with a saturation magnetization of 46.0 emu/g at room temperature and could be well dispersed both in polar and nonpolar carrier liquids. This protocol produced highly concentrated hydrophobic magnetic gel for biopolymer encapsulations.

Liu, Xianqiao; Kaminski, Michael D.; Guan, Yueping; Chen, Haitao; Liu, Huizhou; Rosengart, Axel J.

2006-11-01

157

Oxygen Isotopes in Semarkona Magnetite  

Microsoft Academic Search

Magnetite is a phase that may form by aqueous alteration and may therefore offer insights into processes of aqueous alteration in the early solar system. Rowe et al [1] have used oxygen isotopes of magnetite and other phases to constrain conditions of aqueous alteration of the CM and CI chondrites. Semarkona is one of the few ordinary chondrites known to

J. M. Saxton; I. C. Lyon; G. Turner; R. Hutchison

1995-01-01

158

Formation of single-domain magnetite by a thermophilic bacterium  

SciTech Connect

Magnetite is a common product of bacterial iron reduction and may serve as a potential physical indicator of biological activity in geological settings. Here the authors report the formation of single-domain magnetite under laboratory conditions by a thermophilic fermentative bacterial strain TOR-39 that was isolated from the deep subsurface. Time-course analyses were performed at 65 C to study the effect of bacterial activity on solution chemistry and magnetite formation during the growth of TOR-39. Run products were examined by transmission electron microscopy. Magnetite particles formed exclusively outside of bacterial cells and exhibited octahedral shapes having relatively equal length and width (<15% difference). Tiny magnetite particles (<12 nm) nucleated between 10 and 11 h of incubation and increased to average lengths of 55.4 {+-} 26.8 nm after 24 h of incubation. Between 24 h and 22 d of incubation, magnetite particles maintained average lengths of 56.2 {+-} 24.8 nm. Based on size constraints, greater than 85% of the particles observed fell within the magnetic single domain. Little to no magnetite was detected in abiotic controls at 65 or 95 C, or in TOR-39 cultures whose activity was suppressed. Unlike mesophilic iron-reducing bacteria (e.g., GS-15), TOR-39 produced crystals having shapes and sizes similar to some particles produced intracellularly by magnetotactic bacteria. Thus the single-domain magnetite produced by thermophiles such as TOR-39 may represent a heretofore unrecognized biological contribution to natural remanent magnetization in sedimentary basins and other geothermal environments.

Zhang, C.; Phelps, T.J. [Oak Ridge National Lab., TN (United States). Environmental Sciences Div.; Vali, H. [McGill Univ., Montreal, Quebec (Canada). Electron Microscopy Center; Romanek, C.S. [Univ. of Georgia, Aiken, SC (United States); Liu, S.V. [Allegheny Univ. of the Health Sciences, Philadelphia, PA (United States). Dept. of Microbiology and Immunology

1998-11-01

159

Magnetic response of microbially synthesized transition metal- and lanthanide-substituted nano-sized magnetites  

NASA Astrophysics Data System (ADS)

The magnetic susceptibility ( ?RT) and saturation magnetization ( MS) of microbially synthesized magnetites were systematically examined. Transition metal (Cr, Mn, Co, Ni and Zn)- and lanthanide (Nd, Gd, Tb, Ho and Er)-substituted magnetites were microbially synthesized by the incubation of transition metal (TM)- and lanthanide (L)-mixed magnetite precursors with either thermophilic (TOR-39) or psychrotolerant (PV-4) metal-reducing bacteria (MRB). Zinc incorporated congruently into both the precursor and substituted magnetite, while Ni and Er predominantly did not. Microbially synthesized Mn- and Zn-substituted magnetites had higher ?RT than pure biomagnetite depending on bacterial species and they exhibited a maximum ?RT at 0.2 cationic mole fraction (CMF). Other TMs' substitution linearly decreased the ?RT with increasing substitution amount. Based on the MS values of TM- and L-substituted magnetite at 0.1 and 0.02 CMF, respectively, Zn (90.7 emu/g for TOR-39 and 93.2 emu/g for PV-4)- and Mn (88.3 emu/g by PV-4)-substituted magnetite exhibited higher MS than standard chemical magnetite (84.7 emu/g) or pure biomagnetite without metal substitution (76.6 emu/g for TOR-39 and 80.3 emu/g for PV-4). Lanthanides tended to decrease MS, with Gd- and Ho-substituted magnetites having the highest magnetization. The higher magnetization of microbially synthesized TM-substituted magnetites by the psychrotroph, PV-4 may be explained by the magnetite formation taking place at low temperatures slowing mechanics, which may alter the magnetic properties compared to the thermophile, through suppression of the random distribution of substituted cations.

Moon, Ji-Won; Yeary, Lucas W.; Rondinone, Adam J.; Rawn, Claudia J.; Kirkham, Melanie J.; Roh, Yul; Love, Lonnie J.; Phelps, Tommy J.

2007-06-01

160

Ultrahigh efficiency laser wavelength conversion in a gas-filled hollow core photonic crystal fiber by pure stimulated rotational Raman scattering in molecular hydrogen.  

PubMed

We report on the generation of pure rotational stimulated Raman scattering in a hydrogen gas hollow-core photonic crystal fiber. Using the special properties of this low-loss fiber, the normally dominant vibrational stimulated Raman scattering is suppressed, permitting pure conversion to the rotational Stokes frequency in a single-pass configuration pumped by a microchip laser. We report 92% quantum conversion efficiency (40 nJ pulses in 2.9 m fiber) and threshold energies (3 nJ in 35 m) more than 1 x 10(6) times lower than previously reported. The control of the output spectral components by varying only the pump polarization is also shown. The results point to a new generation of highly engineerable and compact laser sources. PMID:15447265

Benabid, F; Bouwmans, G; Knight, J C; Russell, P St J; Couny, F

2004-09-17

161

Magnetic Characteristics of Metal-doped Magnetite Nanoparticles Produced by Thermoanaerobacter Ethanolicus  

NASA Astrophysics Data System (ADS)

This work examined the magnetic properties of pure and metal-doped magnetite powders which were synthesized by a bacterially mediated process under anaerobic conditions. The iron(III)-reducing bacterial strain Thermoanaerobacter ethanolicus TOR-39, isolated from deep subsurface sediments, was incubated under anaerobic conditions at 65,aC for 2 weeks in aqueous medium containing amorphous iron(III) oxyhydroxides (akaganeite). The microbial process produced several grams per liter of culture volume of uniformly sized single domain nanometer sized magnetite particles outside of bacterial cells. Particle size was verified using X-ray diffraction (XRD) and dynamic light scattering. Average crystallite size from XRD using the Scherrer method was 45 nm for the pure magnetite which agreed well with results from dynamic light scattering. The magnetic properties were characterized using a superconducting quantum interference device (SQUID) magnetometer. Zinc doped magnetite exhibited a saturation magnetization (at 5 K) of 100 emu/g while a value of 77 emu/g was observed for pure magnetite particles of roughly the same size. The low temperature biologically mediated production of metal-doped magnetite is also highly scalable allowing the production of large quantities within days. The process has shown its capability to produce metal (Zn, Mn, Ni, Co)- doped magnetites that may potentially exhibit utility in biogeoscience, magnetorheological materials, nanotechnology, or biomedical applications.

Yeary, L. W.; Phelps, T. J.; Love, L. J.; Moon, J.; Rondinone, A. J.; Rawn, C. J.; Thompson, J. R.; Madden, A. S.; Madden, M. E.

2005-12-01

162

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.

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

2002-01-01

163

Iron isotopic fractionation factor between magnetite and hydrous silicic melt  

NASA Astrophysics Data System (ADS)

A "thermal migration" experiment was conducted in the piston cylinder to investigate the changes in composition of a wet andesitic bulk composition in a temperature gradient at 0.5 GPa. A homogeneous andesite powder (AGV-1 containing 4 wt.% H2O was sealed in a AuPd double capsule with the hot end at 950°C and the bottom end 350°C for 66 days. The charge changes from 100% melt at the top to the progressively more crystalline with the sequential appearance of apatite, magnetite, amphibole, biotite, plagioclase, quartz, and K-feldspar. We microdrilled 5 samples along the temperature gradient and analyzed these for Fe isotope ratios by double spike MC-ICP-MS at UIUC. Results show that the 100% melt area is depleted in heavy Fe isotopes relative to all more crystalline portions of the experiment (4 samples) with the offset in {?}^{56/54}FeIRMM of about 1.7‰. This does not appear to reflect Fe loss in the experiment as the Fe content and isotopes mass balance and no detectable Fe was found in the capsule after the experiment. Instead the offset is interpreted to reflect the combination of diffusive fractionation of Fe moving by diffusion and possible equilibrium fractionations between melt and magnetite that occurs throughout the crystalline portion of the experiment. However, both the isotopic fractionation factor between magnetite and melt and the effect of diffusion on Fe isotopes remains unknown. We are currently investigating Fe isotopic fractionation factor between magnetite and melt and effects of melt diffusion on Fe isotopes. To assess diffusion, we will microdrill and analyze melt-melt diffusion couples from Lundstrom(G-Cubed, 2003). To assess magnetite-melt fractionation, we have begun piston cylinder experiments at 0.5 GPa and 800°C using a starting material synthesized based on the melt composition within the thermal migration experiment. Initial experiments produce a layer of 100% melt on top of a 2-phase mush of magnetite-melt. This will allow analysis of pure melt and the magnetite-melt mush with knowledge of the modes providing the ability to back out the fractionation factor. If we can prove attainment of equilibrium, this technique will bypass the difficulty of making pure separates of magnetite and melt. Fe isotopic composition of the melt and melt-magnetite layers will be measured by MC-ICP-MS.

Huang, F.; Lundstrom, C. C.

2006-12-01

164

Magnetite morphology and life on Mars  

PubMed Central

Nanocrystals of magnetite (Fe3O4) in a meteorite from Mars provide the strongest, albeit controversial, evidence for the former presence of extraterrestrial life. The morphological and size resemblance 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 methods in a transmission electron microscope, we show that the three-dimensional shapes of such nanocrystals can be defined, that the detailed morphologies of individual crystals from three bacterial strains differ, and that none uniquely match those reported from the Martian meteorite. In contrast to previous accounts, we argue that the existing crystallographic and morphological evidence is inadequate to support the inference of former life on Mars.

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

2001-01-01

165

Magnetite morphology and life on Mars.  

PubMed

Nanocrystals of magnetite (Fe(3)O(4)) in a meteorite from Mars provide the strongest, albeit controversial, evidence for the former presence of extraterrestrial life. The morphological and size resemblance 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 methods in a transmission electron microscope, we show that the three-dimensional shapes of such nanocrystals can be defined, that the detailed morphologies of individual crystals from three bacterial strains differ, and that none uniquely match those reported from the Martian meteorite. In contrast to previous accounts, we argue that the existing crystallographic and morphological evidence is inadequate to support the inference of former life on Mars. PMID:11717421

Buseck, P R; Dunin-Borkowski, R E; Devouard, B; Frankel, R B; McCartney, M R; Midgley, P A; Pósfai, M; Weyland, M

2001-11-20

166

X-ray induced color centres in pure and doped LiYF4 and LiLuF4 single crystals  

NASA Astrophysics Data System (ADS)

YLiF4 and LuLiF4 pure and doped with Yb3+ ion were grown by the Czochralski technique under CF4 atmosphere. X-ray irradiation was used to carry out a comparative study of the induced optical absorption phenomena and color center creation in the ultraviolet and visible spectral regions. The F-center absorption band at 315 and 340 nm in LLF and YLF, respectively, is the dominating induced absorption feature. The amplitude of the induced absorption is reduced by more than a factor of 10 in Yb-doped crystals compared to the undoped ones.

Bensalah, A.; Nikl, M.; Vedda, A.; Shimamura, K.; Satonaga, T.; Sato, H.; Fukuda, T.; Boulon, G.

167

Magnetoresistance in magnetite: Switching of the magnetic easy axis  

Microsoft Academic Search

The influence of the external magnetic field B (B?4T) on resistivity in magnetite single crystal was studied at few temperatures both below and above the Verwey transition temperature TV, and in two ?100? type cubic directions. We have succeeded to confirm our predictions that the magnetic axis switching affects electronic transport. It was also found that the transverse resistivity (B?current

G. Król; W. Tabi?; J. Przewo?nik; T. Ko?odziej; Z. K?kol; A. Koz?owski; Z. Tarnawski

2009-01-01

168

Evidence for exclusively inorganic formation of magnetite in Martian meteorite ALH84001  

NASA Technical Reports Server (NTRS)

Magnetite crystals produced by terrestrial magnetotactic bacterium MV-1 are elongated on a [111] crystallographic axis, in a so-called truncated hexa-Octahedral shape. This morphology has been proposed to constitute a biomarker (i.e., formed only in biogenic processes). A subpopulation of magnetite crystals associated with carbonate globules in Martian meteorite ALH84001 is reported to have this morphology, and the observation has been taken as evidence for biological activity on Mars. In this study, we present evidence for the exclusively inorganic origin of [111]-elongated magnetite crystals in ALH84001. We report three-dimensional(3-D) morphologies for approx.1000 magnetite crystals extracted from: (1) thermal decomposition products of Fe-rich carbonate produced by inorganic hydrothermal precipitation in laboratory experiments; (2) carbonate globules in Martian meteoriteeALH84001; and (3) cells of magnetotactic bacterial strain MV-1. The 3-D morphologies were derived by fitting 3-D shape models to two-dimensional bright-field transmission-electron microscope (TEAM) images obtained at a series of viewing angles. The view down the {110} axes closest to the [111] elongation axis of magnetite crystals ([111]x{110) not equal to 0) provides a 2-D projection that uniquely discriminates among the three [111]-elongated magnetite morphologies found in these samples: [111]-elongated truncated hexaoctahedron ([111]-THO), [111]-elongated cubo-octahedron ([111]-ECO), and [111]-elongated simple octahedron ([111]-ESO). All [111] -elongated morphologies are present in the three types of sample, but in different proportions. In the ALH84001 Martian meteorite and in our inorganic laboratory products, the most common [111]-elongated magnetite crystal morphology is [111]-ECO. In contrast, the most common morphology for magnetotactic bacterial strain MV-1 is [111]-THO. These results show that: (1) the morphology of [111]-elongated magnetite crystals associated with the carbonate globules in Martian meteorite ALH84001 is replicated by an inorganic process; and (2) the most common crystal morphology for biogenic (MV-1) magnetite is distinctly different from that in both ALH84001 and our inorganic laboratory products. Therefore, [111]-elongated magnetite crystals in ALH84001 do not constitute, as previously claimed, a robust biosignature and, in fact, an exclusively inorganic origin for the magnetite is fully consistent with our results. Furthermore, the inorganic synthesis method, i.e., the thermal decomposition of hydrothermally precipitated Fe-rich carbonate, is a process analogue for formation of the magnetite on Mars. Namely, precipitation of carbonate globules from carbonate-rich hydrothermal solutions followed at some later time by a thermal pulse, perhaps in association with meteoritic impact or volcanic processes on the Martian surface.

Golden, D. C.; Ming, D. W.; Morris, R. V.; Brearley, A. J.; Lauer, H. V., Jr.; Treiman, A. H.; Zolensky, M. E.; Schwandt, C. S.; Lofgren, G. E.

2004-01-01

169

Three-Dimensional Morphological Analysis of ALH84001 Magnetite Using Electron Tomography  

Microsoft Academic Search

Within experimental and numerical uncertainties the tomographic reconstruction by electron tomography reveals that some ALH84001 magnetite crystals are identical to those produced by terrestrial magnetotactic bacteria strain MV-1.

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

2003-01-01

170

Fluid-induced martitization of magnetite in BIFs from the Dharwar Craton, India.  

NASA Astrophysics Data System (ADS)

Banded iron formations (BIFs) represent the largest iron deposits on Earth, which mainly formed in the Late Archean and Early Proterozoic. The complex geological history of BIFs makes it difficult to reconstruct the primary mineralogy and thus the initial depositional environment. Magnetite and hematite are the most important iron oxide minerals in BIFs. Magnetite (FeOFe2O3) comprising of both ferrous and ferric iron, easily undergoes transformation at low temperature. Hematite (?-Fe2O3) is often a result of the pseudomorphic replacement of magnetite, in the processus called martitisation. Despite the process of martitization having been widely studied, in both synthetic and natural magnetites, the mechanics of the transformation are poorly understood. What is generally agreed is that the transformation from magnetite to hematite occurs via a maghemite (g-Fe2O3) intermediate. The 2.9 Ga BIF from the Western Dharwar Craton, Southern India (a 500 m thick Archean BIF), is characterized by millimetric to centrimetric alternating white quartz and grey Fe-oxide bands. The Fe-oxide bands consist of martite crystals (~20µm) which represent the hematitisation of euhedral magnetite. The hematite crystals are in part euhedral, cubic shaped pointing to the replacement of magnetite. The crystals show a trellis pattern. Magnetite patches occur within the hematite. Raman spectroscopy, X-Ray diffraction, Curie balance and magnetic hysteresis analyses and FIB-TEM investigation indicate the presence of maghemite, and the presence of subhedral magnetite and interstitial hematite crystal. The latter are characterized by dislocation with fluid inclusions and high porosity zones. The magnetite grains contain lamellae and the interfaces between magnetite-maghemite and hematite are curved suggesting grain boundary migrations with the growth of hematite at the expense of magnetite and maghemite. It is thus suggested that martite result from low-T exsolutions along cleavage resulting in the formation of maghemite at the interface between magnetite and hematite with the migration of excess Fe3+ through the magnetite crystal lattice to the surface. Martitization is thus due to hydrothermal events associated with grain boundary migration during dynamic recrystallization.

Wagner, Christiane; Orberger, Beate; Tudryn, Alina; Wirth, Richard; Morgan, Rachael

2013-04-01

171

Zero-dimensional magnetite  

NASA Astrophysics Data System (ADS)

Low-dimensional magnetic systems are of interest due to several new effects and modifications that occur at sizes below the average domain grain boundary within the bulk material. Molecule-like magnetite (Fe3O4) nanoparticles, with sizes ranging from one to two nm were synthesized and characterized in order to investigate new properties arising from quantum size effects. These small systems will provide opportunities to investigate magnetism of zero-dimension systems. A zero-dimensional object is usually called a quantum dot or artificial atom because its electronic states are few and sharply separated in energy, resembling those within an atom. Since the surface to volume ratio is the highest for zero-dimensional systems, most of the changes to magnetic behavior will be observed in ultra-fine magnetic particles. Chemically functional magnetic nanoparticles, comprised of a Fe 3O4 magnetite core encased in a thin aliphatic carboxylate, have been prepared by sequential high temperature decomposition of organometallic compounds in a coordinating solvent. In this work, aliphatic carboxylic acid chain length, reaction temperature and duration were varied to produce small core diameters. In order to correlate size effects with changes in particle formation, it is important to have a through understanding of the structural components. This includes studies of the core size, surface effects, decomposition, electronic properties and magnetic behavior. Quantum size effects were observed in the (Fe3O4)X(carboxylate)Y monolayer protected clusters (MPCs) when the average core diameter was ?2.0 nm, evidenced by a blue shifted absorbance band maxima, suggesting the onset of quantum confinement. These (Fe3O4)X(carboxylate) Y MPCs also posses a complex interplay between surface and finite size effects, which govern the magnetic properties of these zero-dimensional systems. These MPCs are all superparamagnetic above their blocking temperatures with total magnetic anisotropy values greater than the bulk value due to an increase in surface and magnetocrystalline anisotropy. A non-linear decrease in saturation magnetization (MS) (muB per cluster) as a function of the reciprocal of core radius have been attributed to surface effects such as a magnetically inactive layer or an increase in spin disorder as core diameter decreases. The reduced core dimensions of these MPCs make them ideal candidates for further investigation of quantum magnetic systems. Chapter 1 provides a brief introduction to magnetic properties on the quantum scale and methods to examine those properties. Chapter 2 is an introduction to nanostructured magnetic systems including metals and oxides. Specific instrumentation and methodologies needed to provide insight about nanoparticles are discussed. Chapter 3 is an investigation of zero-dimensional magnetite monolayer protected clusters. The aim of this research is the preparation, isolation, and characterization of sub-colloidal (diameter ?2.0 nm) magnetite (Fe3O4) nanocrystals. The synthetic procedures within are the first reports of 1.0--2.0 nm (Fe 3O4)x(carboxylate)y materials, approaching the scale of single-molecule magnets. Appendix A includes some of the common units and formulas used in magnetism while Appendix B summarizes the Langevin model of paramagnetism and how it relates to quantum effects, and Appendix C presents a table of values pertaining to photon energies in various units.

Arredondo, Melissa Gayle

172

Structural, electronic and optical properties of pure and Ni 2+-doped CdI 2 layered crystals as explored by ab initio and crystal field calculations  

NASA Astrophysics Data System (ADS)

Influence of impurity Ni 2+ ions on optical absorption spectra of layered CdI 2 single crystals has been considered for localized level of doping. Optical properties of CdI 2:Ni 2+ crystals were modeled using two independent approaches: (i) DFT-based ab initio calculations and (ii) semi-empirical crystal field theory. The former method allowed for locating the Ni 2+ 3d states with respect to the host’s band structure, providing a link between the properties of impurity and host itself. The latter method allowed for calculations of crystal field splitting of the Ni 2+ LS terms, giving an opportunity to assign the main bands in the absorption spectrum of the doped crystal. To increase accuracy in calculating the point charge contribution to the crystal field parameters (CFP), contributions of all crystal lattice ions located at a distance of up to 72.999 Å from the Ni ion were included into the crystal lattice sums. The crystal field Hamiltonian was diagonalized in the space of 25 wave functions of the spin-triplet terms 3F, 3P and the spin-singlet terms 1S, 1D, 1G of the 3d 8 electron configuration of Ni 2+ ion. Additional calculations of the band structure and optical functions were performed to reveal the structure of the energy bands, their role in the formation of optical properties of this system in the overlapping impurity-ligand effects. Electron density distribution in the space between atoms before and after doping was compared; hybridization of the Ni 3d states with iodine 5p states was demonstrated. The role of the crystal anisotropy in the observed effects is discussed.

Brik, M. G.; Kityk, I. V.; Ozga, K.; ?l?zak, A.

2011-01-01

173

Effect of Ni doping on the properties of fine magnetite particles  

NASA Astrophysics Data System (ADS)

Vibrating sample magnetometer (VSM) and Mössbauer spectroscopy are used to characterize the magnetic behaviour of fine magnetite particles obtained from (i) pure goethite and (ii) Ni-doped goethite, in ammoniacal solution. The latter sample has 0.4 wt% Ni which has significantly changed the properties of the sample. The Ni-doped magnetite shows a much higher overoccupancy of tetrahedral sites by iron atoms as compared to the undoped sample. TEM study shows that presence of Ni ions leads to narrower size distribution of magnetite particles as compared to the magnetite obtained from undoped goethite. The coercive field is also affected by presence of Ni, being only 105 Oe for the Ni-doped magnetite as against 170 Oe in the undoped sample.

Mohapatra, M.; Pandey, Brajesh; Upadhyay, Chandan; Anand, S.; Das, R. P.; Verma, H. C.

2005-08-01

174

Epitaxial growth of nanophase magnetite in Martian meteorite Allan Hills 84001: implications for biogenic mineralization.  

PubMed

Crystallographic relationships between magnetite, sulfides, and carbonate rosettes in fracture zones of the Allan Hills (ALH) 84001 Martian meteorite have been studied using analytical electron microscopy. We have focused on those magnetite grains whose growth mechanisms can be rigorously established from their crystallographic properties. Individual magnetite nanocrystals on the surfaces of carbonates are epitaxially intergrown with one another in "stacks" of single-domain crystals. Other magnetite nanocrystals are epitaxially intergrown with the surfaces of the carbonate substrates. The observed magnetite/carbonate (hkl) Miller indices orientation relationships are (1, 1,3)m ¿¿ (1, 1 ,0)c and (1, 1 ,1)m ¿¿ (0,0, 3)c with lattice mismatches of approximately 13% and approximately 11%, respectively. Epitaxy is a common mode of vapor-phase growth of refractory oxides like magnetite, as is the spiral growth about axial screw dislocations previously observed in other magnetite nanocrystals in ALH 84001. Epitaxy rules out intracellular precipitation of these magnetites by (Martian) organisms, provides further evidence of the high-temperature (> 120 degrees C) inorganic origins of magnetite in ALH 84001, and indicates that the carbonates also have been exposed to elevated temperatures. PMID:11543075

Bradley, J P; McSween, H Y; Harvey, R P

1998-07-01

175

DNA–magnetite nanocomposite materials  

Microsoft Academic Search

It is shown here that magnetite nanoparticles can be associated with double-stranded DNA. In a first step, a complex of DNA with Fe2+ and Fe3+ ions is formed. +Then, in a second step, magnetite nanoparticles are formed by increasing the pH. As shown by electrophoresis, the nanoparticles are strongly attached to the nucleic acid. From TEM imaging and Mössbauer measurement,

S Mornet; A Vekris; J Bonnet; E Duguet; F Grasset; J.-H Choy; J Portier

2000-01-01

176

Hydrothermal Preparation of Apatite Composite with Magnetite or Anatase  

SciTech Connect

Microstructure designed porous hydroxyapatite (Ca10(PO4)6(OH)2) composites with magnetite (Fe3O4) particles or anatase (TiO2) dispersion were prepared by hydrothermal treatment. These composites had micro-pores of about 0.1-0.5 {mu}m in size. Magnetite / Hydroxyapatite composites should be suitable for medical treatment of cancer, especially in bones, because HA can bond to bones directly and magnetite can generate heat. They must be used for hyperthermia therapies of cancer in bones. Meanwhile, anatase / Hydroxyapatite composite should be suitable for environmental purification, because HA rod-shape particles expose the specific crystal face, which adsorbs organic contaminants and so on.

Murakami, Setsuaki; Ishida, Emile H.; Ioku, Koji [Graduate School of Environmental Studies, Tohoku University, Sendai, Miyagi 980-8579 (Japan)

2006-05-15

177

Doping dependence of phonon and quasiparticle heat transport of pure and Dy-doped Bi2Sr2CaCu2O8+? single crystals  

NASA Astrophysics Data System (ADS)

The temperature and magnetic-field (H) dependences of thermal conductivity (?) of Bi2Sr2CaCu2O8+? (Bi2212) are systematically measured for a broad doping range by using both pure Bi2212 single crystals with tuned oxygen contents and Bi2Sr2Ca1-xDyxCu2O8+? (Dy-Bi2212) single crystals with different Dy contents x . In the underdoped samples, the quasiparticle (QP) peak below Tc is strongly suppressed, indicating strong QP scattering by impurities or oxygen defects, whereas the phonon conductivity is enhanced in moderately Dy-doped samples and a phonon peak at 10K is observed, which means Dy3+ ions not only introduce the impurities or point defects but also stabilize the crystal lattice. The subkelvin data show that the QP heat conductivity gradually decreases upon lowering the hole doping level. The magnetic-field dependence of ? at temperature above 5K is mainly due to the QP scattering off vortices. While the underdoped pure Bi2212 show very weak field dependence of ? , the Dy-doped samples present an additional “dip-like” term of ?(H) at low field, which is discussed to be related to the phonon scattering by free spins of Dy3+ ions. For nonsuperconducting Dy-Bi2212 samples with x?0.50 , an interesting “plateau” feature shows up in the low-temperature ?(H) isotherms with characteristic field at 1-2T , for which we discuss the possible revlevance of magnon excitations.

Sun, X. F.; Ono, S.; Zhao, X.; Pang, Z. Q.; Abe, Yasushi; Ando, Yoichi

2008-03-01

178

Luminescence study of self-trapped holes in pure and Fe or Mo-doped ZnWO 4 crystals  

Microsoft Academic Search

Thermostimulated and photostimulated luminescence of ZnWO4,ZnWO4:Fe and ZnWO4:Mo crystals irradiated at low temperatures by X-rays or UV photons was studied in the temperature range 4.2–300K in order to clarify the creation and recombination processes of the elementary colour centres. The connection of the luminescence phenomena with the self-trapped holes has been revealed.

A. Kotlov; L. Jönsson; M. Kirm; A. Lushchik; V. Nagirnyi; E. Rivkin; A. Watterich; B. I. Zadneprovski

2004-01-01

179

Morphology, evolution and other characteristics of gibbsite crystals grown from pure and impure aqueous sodium aluminate solutions  

Microsoft Academic Search

The effect of external conditions on the growth morphology of gibbsite, ?-Al(OH)3, grown under a range of conditions has been studied. The results show that during growth the morphology of gibbsite crystals evolves from thin, rounded hexagons and faceted lozenges into faceted plates and blocks with well-formed basal, prismatic and chamfered faces. This morphology evolution shows only a weak dependence

C. Sweegers; H. C de Coninck; H Meekes; W. J. P van Enckevort; I. D. K Hiralal; A Rijkeboer

2001-01-01

180

The transformation of magnetite to hematite and its influence on the rheology of iron oxide rock  

NASA Astrophysics Data System (ADS)

Phase transformation is an important process for strain localization after the initiation of ductile shear zones. In polyphase aggregates one important aspect to consider is likely to be the interconnectivity of weak phase after the transformation of the load-bearing framework grains. However the physical processes involved in that transition is not well understood, partially because the microstructures of the initial weakening are generally obliterated by subsequent deformation. Iron oxide-quartz rocks from paleoproterozoic Iron Formations in southern Brazil preserve microstructures that allow a good insight into the evolution of the deformation mechanisms and fabrics during the transition from a load-bearing framework (magnetite) to an interconnected weak phase (hematite). We conducted microstructural and textural analyses of aggregates of magnetite and hematite combining observations in an optical microscope and measurements in the electron back-scatter diffraction (EBSD). The samples were cut parallel to the mineral lineation (the X-axis) and perpendicular to the foliation. Our goal was to understand the evolution of fabric and texture of the iron oxide aggregates caused by the change in deformation behavior resulting from the phase transformation. The studied samples consist mainly of aggregates of magnetite and hematite in a varied proportions. Samples that preserve the early microstructures consist in aggregate of magnetite grains of varied sizes. The grains are partially transformed to hematite along {111} planes but no foliation is observed in the samples. Basically the samples consist of grains of irregular shapes and a weak or absent crystallographic preferred orientation. The newly transformed hematite crystals share the (0001) planes and directions <11-20> with planes {111} and directions <110> of magnetite grains. Other samples present relicts of initial magnetite grains surrounded by a matrix of tabular to platy hematite crystals. The matrix show a preferred orientation of hematite grains. Close to the magnetite, hematite crystals show crystallographic relationship similar to those observed inside the magnetite crystals showing a good match in crystallographic planes and directions. However away from the magnetite crystals hematite of the matrix tend to show a more independent crystallographic orientation with respect to the magnetite grains. The poles to the basal planes of hematite distributed in a small circle centered around the Z-axis and the crystallographic directions <11-20> spread in a wide angle along the foliation plane. In samples where no crystal of magnetite grains is observed only platy hematite with a strong shape preferred orientation occur. Their basal planes show a strong concentration around the foliation pole contrasting to the more dispersed distribution around the Z-axis found in the samples with magnetite relicts.The directions <11-20> also distributed along the foliation planes in platy hematite samples but with a narrower angles than those of samples with magnetite relicts. The progressive transformation of magnetite to hematite led to a change in the iron formation rock fabrics from an isotropic distribution of a load-supporting magnetite to an interconnected weak platy hematite forming a strongly anisotropic fabric. The hard magnetite behaves in a brittle manner with a very limited operation of slip along the main crystallographic planes. The microfracturing creates an easy path for oxidation and transformation of magnetite. The newly formed hematite grains behave in a ductile manner and form a matrix of strongly oriented crystals. The deformation mechanisms change from the microfracturing of the harder magnetite phase to a crystal plastic deformation of the softer hematite platy grains through slip along their basal planes.

Lagoeiro, Leonardo; Barbosa, Paola; Goncalves, Fabio; Rodrigues, Carlos

2013-04-01

181

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.

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

182

Arsenite sorption at the magnetite–water interface during aqueous precipitation of magnetite: EXAFS evidence for a new arsenite surface complex  

Microsoft Academic Search

The interaction of aqueous As(III) with magnetite during its precipitation from aqueous solution at neutral pH has been studied as a function of initial As\\/Fe ratio. Arsenite is sequestered via surface adsorption and surface precipitation reactions, which in turn influence the crystal growth of magnetite. Sorption samples were characterized using EXAFS spectroscopy at the As K-edge in combination with HRTEM

Yuheng Wang; Guillaume Morin; Georges Ona-Nguema; Nicolas Menguy; Farid Juillot; Emmanuel Aubry; François Guyot; Georges Calas; Gordon E. Brown

2008-01-01

183

Possible Eukaryotic Magnetite in the Paleocene-Eocene Boundary Clay, Ancora, New Jersey  

NASA Astrophysics Data System (ADS)

We report the discovery of new forms of magnetic particles in the Paleocene-Eocene (P-E) boundary clay from the borehole at Ancora, New Jersey (Ocean Drilling Program Leg 174AX). The P-E boundary clay shows anomalous magnetic properties suggesting enrichment in single-domain (SD) magnetite. Transmission electron microscopy of the magnetic separates shows that the majority of the SD particles are magnetofossils of known crystal shape and size [1]. There are, however, larger magnetite particles having unusual morphology, including: (1) elongated prismatic magnetite of 100 nm width and up to 1 micron length, (2) leaflike magnetite particles up to 2 microns in length, and (3) elongated, conelike particles with an aspect ratio of 4:1. Lattice-fringe images and X-ray microanalysis of these particles show single-crystal structure and stochiometric magnetite composition, similar to magnetite crystals produced by magnetotactic bacteria. Although the dimensions of some of the type 2 and type 3 particles are outside that expected for single-domain behaviour as typically calculated for parallelepipeds and ellipsoids [2], electron holographic analysis reveals a SD signature. It is likely that these magnetic particles are of biogenic origin, as we were unable to find significant amounts of obviously detrital magnetite in the sediments. As these unusual magnetic particles are confined to the narrow P-E boundary layer, environmental changes along the eastern Atlantic margin of North America during the Paleocene-Eocene Thermal Maximum (PETM) may have led to enhanced growth, and perhaps diversification, of magnetite-forming microorganisms. The dimensions of the observed magnetite particles, however, exceed the size of prokaryotes; if they were, indeed, biogenic, they were likely formed by an unknown eukaryotic organism. References: [1] R. E. Kopp et al., 2007. Paleoceanography (in press). [2] R. E. Kopp and J. L. Kirschvink, 2007. Earth Science Reviews. doi:10.1016/j.earscirev.2007.08.001.

Schumann, D.; Raub, T. D.; Kopp, R. E.; Tikoo, S. M.; Sears, S. K.; Leucken, U.; Rouiller, I.; Smirnov, A. V.; Kirschvink, J. L.; Vali, H.

2007-12-01

184

Reflectance anisotropy spectroscopy of magnetite (110) surfaces  

NASA Astrophysics Data System (ADS)

Reflectance anisotropy spectroscopy (RAS) has been used to measure the optical anisotropies of bulk and thin-film Fe3O4(110) surfaces. The spectra indicate that small shifts in energy of the optical transitions, associated with anisotropic strain or electric field gradients caused by the (110) surface termination or a native oxide layer, are responsible for the strong signal observed. The RAS response was then measured as a function of temperature. A distinct change in the RAS line-shape amplitude was observed in the spectral range from 0.8 to 1.6 eV for temperatures below the Verwey transition of the crystal. Finally, thin-film magnetite was grown by molecular beam epitaxy on MgO(110) substrates. Changes in the RAS spectra were found for different film thickness, suggesting that RAS can be used to monitor the growth of magnetite (110) films in situ. The thickness dependence of the RAS is discussed in terms of various models for the origin of the RAS signal.

Fleischer, K.; Verre, R.; Mauit, O.; Sofin, R. G. S.; Farrell, L.; Byrne, C.; Smith, C. M.; McGilp, J. F.; Shvets, I. V.

2014-05-01

185

Magnetite nanoparticles with no surface spin canting  

NASA Astrophysics Data System (ADS)

Surface spin canting has been studied for high quality magnetite nanoparticles in terms of size and shape uniformity. Particles were prepared by thermal decomposition of organic precursors in organic media and in the presence of oleic acid. Results are compared to spin canting effect for magnetic iron oxide nanoparticles of similar size prepared by coprecipitation and subsequently coated with silica. Magnetic characterization and Mössbauer spectroscopy at low temperature and in the presence of a magnetic field have been used in this study. Transmission electron microscopy images and x-ray diffractograms show that iron oxide nanoparticles synthesized by thermal decomposition are more uniform than those prepared by coprecipitation, and they have higher crystal order. Magnetic measurements show superparamagnetic behavior for both samples at room temperature but particles synthesized by thermal decomposition shows higher saturation magnetization and lower coercivity at low temperature. The imaginary part of the ac susceptibility has been used to support the presence of mainly magnetite instead of maghemite in these iron oxide nanoparticles. Mössbauer measurements with and without field demonstrate surface spin canting, only in the octahedral positions for the coprecipitation particles. However, high synthesis temperature and the presence of oleic acid molecules covalently bonded at the particle surface, accounting for the lack of spin canting in particles prepared by thermal decomposition, which justifies the high saturation magnetization and low coercivity at low temperature.

Roca, A. G.; Niznansky, D.; Poltierova-Vejpravova, J.; Bittova, B.; González-Fernández, M. A.; Serna, C. J.; Morales, M. P.

2009-06-01

186

Elastic constants of magnetite, pyrite and chromite  

Microsoft Academic Search

Magnetite belongs to the isomorphous sedes of oxide minerals of the Spinel group with the general formula R203.RO. In magnetite both the radicals ate ~ron, one being ferrous and the other ferric. Magnetite crystallises in the holohedral class of the cubic system and the common forro is the octahedron. Twinning occurs about the octahedral plane. Cleavage is not distinct but

M. S. Doraiswami

1947-01-01

187

Environmental Factors Affect Magnetite Magnetosome Synthesis in Magnetospirillum magneticum AMB-1: Implications for Biologically Controlled Mineralization  

Microsoft Academic Search

It is widely believed that magnetotactic bacteria (MTB) form membrane-enveloped magnetite crystals (magnetosomes) under strict genetic control. In this study, the Magnetospirillum magneticum strain AMB-1 was cultured in the same growth medium, but under four different growth conditions: Anaerobic static, aerobic static, aerobic 80-rpm rotating, and aerobic 120-rpm rotating to investigate possible environmental influences on magnetite magnetosome formation. Integrated analyses,

Jinhua Li; Yongxin Pan

2012-01-01

188

Polyaniline stabilized magnetite nanoparticle reinforced epoxy nanocomposites.  

PubMed

Magnetic epoxy polymer nanocomposites (PNCs) reinforced with magnetite (Fe(3)O(4)) nanoparticles (NPs) have been prepared at different particle loading levels. The particle surface functionality tuned by conductive polyaniline (PANI) is achieved via a surface initiated polymerization (SIP) approach. The effects of nanoparticle loading, surface functionality, and temperature on both the viscosity and storage/loss modulus of liquid epoxy resin suspensions and the physicochemical properties of the cured solid PNCs are systematically investigated. The glass transition temperature (T(g)) of the cured epoxy filled with the functionalized NPs has shifted to the higher temperature in the dynamic mechanical analysis (DMA) compared with that of the cured pure epoxy. Enhanced mechanical properties of the cured epoxy PNCs filled with the functionalized NPs are observed in the tensile test compared with that of the cured pure epoxy and cured epoxy PNCs filled with as-received NPs. The uniform NP distribution in the cured epoxy PNCs filled with functionalized NPs is observed by scanning electron microscope (SEM). These magnetic epoxy PNCs show the good magnetic properties and can be attached by a permanent magnet. Enhanced interfacial interaction between NPs and epoxy is revealed in the fracture surface analysis. The PNCs formation mechanism is also interpreted from the comprehensive analysis based on the TGA, DSC, and FTIR in this work. PMID:22985210

Gu, Hongbo; Tadakamalla, Sruthi; Huang, Yudong; Colorado, Henry A; Luo, Zhiping; Haldolaarachchige, Neel; Young, David P; Wei, Suying; Guo, Zhanhu

2012-10-24

189

Stable remanence and memory of multi-domain materials with special reference to magnetite  

Microsoft Academic Search

The characteristics of memory of remanence across the so-called isotropic point (TK) in single crystals of magnetite are demonstrated experimentally. Memory is shown to be related to the highest microscopic coercivity fraction in the crystal. In order to investigate the nature of the magnetically hard fraction, studies of memory as a function of state of internal stress were undertaken with

Kazuo Kobayashi; M. Fuller

1968-01-01

190

Magnetite whiskers and platelets in the ALH84001 Martian meteorite: Evidence of vapor phase growth  

Microsoft Academic Search

Nanometer-sized magnetite crystals associated with carbonates in fracture zones within Martian meteorite ALH84001 have been examined using analytical transmission electron microscopy. Some of the the crystals exhibit distinctive morphologies: filamentary rods and ribbons, and platelets. The rods and ribbons are elongated along the crystallographic [100] and [111] directions. Some of the rods contain microstructural defects indicating that they grew by

John P. Bradley; Ralph P. Harvey; Harry Y. McSween

1996-01-01

191

Biophysics of Magnetic Orientation: Radical Pairs, Biogenic Magnetite, or both?  

NASA Astrophysics Data System (ADS)

Two major biophysical mechanisms for magnetoreception in terrestrial animals, one based on biogenic magnetite and another on radical-pair biochemical reactions, have been the subject of experiment and debate for the past 30 years. The magnetite hypothesis has stood the test of time: biogenic magnetite is synthesized biochemically in Bacteria, Protists, and numerous Animal phyla, as well as in some plants. Chains of single-domain crystals have been detected by clean-lab based SQUID magnetometry in animal tissues in all major phyla, followed by high-resolution TEM in selected model organisms, as well as by electrophysiological studies demonstrating the role of the ophthalmic branch of the trigeminal nerve in the magnetoreceptive process. Pulse-remagnetization - configured to uniquely flip the polarity of single-domain ferromagnets - has dramatic effects on the behavior of many birds, honeybees, mole rats, turtles, and bats, to cite a growing list. Magnetite-containing cells in the vicinity of these neurons in fish are now the subject of intense study by our consortium. The existence of a specialized class of magnetite-containing magnetoreceptor cells in animal tissues is no longer controversial. In contrast, less success has been achieved in gaining experimental support across a range of taxa for the radical-pair hypothesis. Although this mechanism was proposed to explain an early observation that birds would not respond to complete inversion of the magnetic vector, many organisms (even some birds) do indeed respond to the field polarity. We also note that few, if any, of these critical experiments have been done using fully double-blind methods. This is joint work with: M. M. Walker (University of Auckland, New Zealand) and M. Winklhofer (LMU Munich, Germany).

Kirschvink, Joe

2011-03-01

192

Magnetite-coal separation by continuous HGMS  

SciTech Connect

Magnetite, slurried in water, is used to create an apparent heavy medium in which fine coal (0.1 to 2.4 mm) is cleaned of its mineral impurities. The magnetite is much finer in size (1 to 44 ..mu..m) than the coal and is usually recovered from the coal and refuse by magnetic drum separators. Their performance suffers from changes in feed conditions and a number of them are needed for the average coal cleaning plant. The authors have adapted HGMS for magnetite recovery because of its insensitivity to coal/magnetite ratio and slurry density and its ability to capture fine magnetite at high velocity. An open vertical matrix able to capture 10 ..mu..m (avg. size) magnetite without entraining 2 mm coal has been incorporated in a 1.85 m diameter continuous separator. Three-quarter ton samples of magnetite (in 1000 gallons of water) have been recovered with the matrix ring turning at 40 cm/s through a field of 6 kOe. A laminated core demagnetizing coil followed by water sprays removes the recovered magnetite. In preparation for this continuous program, tests of slurry densities from 20 to 35% solids and coal/magnetite ratios from 3:1 to 1:4 showed almost no variation in recovery or entrainment. A 4.8 m diameter separator, the largest currently available, with multiple heads, should be able to treat 350 tons of magnetite and coal per hour.

Dobby, G.S.; Kelland, D.R.

1982-11-01

193

A facile approach to enhance the high temperature stability of magnetite nanoparticles with improved magnetic property  

NASA Astrophysics Data System (ADS)

We study the effect of Zn2+ doping on crystal structure, magnetic properties, blocking and Curie temperatures, and the high temperature phase stability of magnetite nanoparticles under air and vacuum annealing. The Zn2+ doped nanoparticles (ZnxFe3-xO4 with x = 0, 0.2, 0.4, and 0.6) are prepared by simple co-precipitation technique and are characterized by high temperature X-ray powder diffraction (HTXRD), vibrating sample magnetometer, small angle X-ray scattering, thermogravimetry, differential scanning calorimetry (DSC), and transmission electron microscopy. Our HTXRD studies show that the decomposition temperature of pure magnetite (Fe3O4) in vacuum is increased by 300 °C (from 700 to 1000 °C), with 0.2 fraction of Zn2+ doping. The DSC studies under air environment also show that the ?-Fe2O3 to ?-Fe2O3 phase transition temperature increases with the zinc fraction. The increase in transition temperature is attributed to the increase in the activation energy of the maghemite to hematite phase transition after the replacement of Fe3+ with larger diameter Zn2+ in the A site. Interestingly, the saturation magnetization increases from 61 to 69 emu/g upon 0.2 fraction of Zn2+, which augments the utility of the doped compound for practical applications. While the Curie temperature is found to increase with doping concentration, the blocking temperature shows an opposite trend. The blocking temperature values were found to be 262, 196, 144, and 153 K for 0, 0.2, 0.4, and 0.6 fraction of zinc, respectively. The reduction in TB is attributed to weak dipole-dipole interactions and local exchange coupling between nanoparticles. All the Zn2+ doped samples show superparamagnetic nature. These findings are extremely useful in producing superparamagnetic nanoparticles with enhanced magnetic properties for high temperature applications.

Pati, S. S.; Philip, John

2013-01-01

194

Thermoremanent Magnetization in Submicroscopic Magnetite  

Microsoft Academic Search

titano- magnetite particles in igneous rocks. Although hysteresis properties indicate that the magne- tites are above single-domain (SD) size, their weak-field TRM are SD-like. TRM intensity, for a 1-oe inducing field, ranges from 6 to 12 emu\\/cm 8. Median alternating demagnetization fields are between 275 and 400 oe, while blocking temperatures are generally within 50øC of the Curie point. However,

D. J. Dunlop

1973-01-01

195

Magnetite-Based Magnetoreceptor Cells in the Olfactory Organ of Rainbow Trout and Zebrafish  

NASA Astrophysics Data System (ADS)

Many vertebrate and invertebrate animals have a geomagnetic sensory system, but the biophysics and anatomy of how magnetic stimuli are transduced to the nervous system is a challenging problem. Previous work in our laboratories identified single-domain magnetite chains in olfactory epithelium in cells proximal to the ros V nerve, which, in rainbow trout, responds to magnetic fields. Our objectives are to characterize these magnetite-containing cells and determine whether they form part of the mechanism of magnetic field transduction in teleost fishes, as a model for other Vertebrates. Using a combination of reflection mode confocal microscopy and a Prussian Blue technique modified to stain specifically for magnetite, our Auckland group estimated that both juvenile rainbow trout (ca. 7 cm total length) olfactory rosettes have ~200 magnetite-containing cells. The magnetite present in two types of cells within the olfactory epithelium appears to be arranged in intracellular chains. All of our groups (Munich, Auckland, Cambridge and Caltech) have obtained different types of structural evidence that magnetite chains closely associate with the plasma membrane in the cells, even in disaggregated tissues. In addition, our Cambridge group used Ca2+ imaging to demonstrate a clear response by individual magnetite-containing cells to a step change in the intensity of the external magnetic field and a slow change in Ca2+ activity when the external magnetic field was cancelled. In the teleost, zebrafish (Danio rerio), a small (~4 cm adult length in captivity) genetic and developmental biology model organism, our Caltech group detected ferromagnetic material throughout the body, but concentrated in the rostral trunk, using NRM and IRM scans of whole adults. Our analysis suggests greater than one million, 80-100 nm crystals, with Lowrie-Fuller curves strongly consistent with single-domain magnetite in 100-100,000 magnetocytes. Ferromagentic resonance (FMR) spectra show crystals with narrow particle size distribution concentrated in the trunk, similar to biogenic magnetofossils. In SQUID microscopy images numerous dipole spots are widely distributed throughout the flank, not correlated with skin pigments or the spinal cord and neural arches. We interpret this to indicate a lateral line location for trunk magnetite in zebrafish. In contrast to trout in which rock magnetic experiments and TEM suggest highly interacting bundled ropes of crystals, similar to those in the large magnetotactic bacterium, M. bavaricum, zebrafish magnetic aggregates apparently arrange in clumps or mixed chains and clumps. We report trout olfactory epithelium containing magnetite magnetoreceptors that transduce the external magnetic field, then encode and transmit it to the brain, while zebrafish contain magnetite in the lateral line region.

Kirschvink, J. L.; Cadiou, H.; Dixson, A. D.; Eder, S.; Kobayashi, A.; McNaughton, P. A.; Muhamad, A. N.; Raub, T. D.; Walker, M. M.; Winklhofer, M.; Yuen, B. B.

2011-12-01

196

Magnetite fractionation of "chalcophile" elements  

NASA Astrophysics Data System (ADS)

Submarine-quenched glasses provide the clearest record of magmatic evolution available, especially with respect to potentially volatile elements and compounds. A comprehensive suite of arc- and backarc glasses recovered during several research voyages in the SW Pacific are being analysed by a number of research teams in an effort to document genesis and fractionation processes involved in the evolution of subduction- related magma systems. As part of these studies, a suite of basalt to dacite composition glasses recovered from the arc-like Pacmanus Site in the Manus Backarc Basin have been examined in detail. Sun et al. (2004) found trends of increasing enrichments of Re, Cu, and Au with SiO2 in the range from 50 to 60 wt% SiO2. From this stage of magmatic evolution, marked depletions in all these elements are observed in glasses of higher SiO2 contents. The reasons for this trend have been unclear, although a mechanism involving the cessation of olivine and initiation of magnetite saturation was proposed by Sun et al. Our analysis of a larger suite of glasses from the Manus Basin has now confirmed these trends, and found the same behaviour for Zn and Mn. Similarly, analysis of a suite of basalt to dacite glasses recovered from the arc-like Valu Fa Ridge in the Lau Backarc Basin has produced trends for these elements very similar to those of the Pacmanus location. LA-ICP-MS analysis of microphenocrysts in these glasses has shown that magnetite is highly enriched in Re relative to the coexisting melt (Kd up to 7.8 for Re). Magnetite/melt partition coefficients for Re, Mn and Yb can be used to precisely model the liquid line of descent during magnetite (plus clinopyroxene and plagioclase) fractionation using Re vs. Mn/Yb. The variation of Pt abundances with SiO2 for both these suites contrasts with other nominally chalcophile trace elements in showing rapid early depletion from the most Mg-rich basalt through to more SiO2-rich compositions, with no maximum at 60 wt% SiO2. Silver on the other hand is essentially constant at 0.02 to 0.05ppm throughout the basalt to dacite compositional range. Several other compositional features of the Pacmanus and Valu Fa suites are also noteworthy. For example while S has an abundance maximum at 60wt% SiO2 (similar to Fe and Re), and then diminishes in concentration in more silica-rich magmas, Se is initially depleted at 60wt% SiO2 but then increases in abundance as SiO2 increases further. We suggest these features result from sulfide saturation coincidentally with (or shortly after) magnetite saturation. While Se is initially partitioned into the immiscible sulfide phase, moderate incompatibility remains between the overall fractionating assemblage of plagioclase-pyroxene- magnetite and minor sulfide. Pt on the other hand is likely being removed as a native element/alloy. Sun, W, Arculus, RJ, Kamenetsky, VS and Binns, RA, 2004, Release of gold-bearing fluids in convergent margin magmas prompted by magnetite crystallisation. Nature, v. 431, p. 975-978.

Mavrogenes, J. A.; Jenner, F. E.; Arculus, R. J.

2008-12-01

197

Biogenic Magnetite in Martian Meteorite ALH84001  

NASA Technical Reports Server (NTRS)

Fine-grained magnetite (Fe3O4) in martian meteorite ALH84001, generally less than 200 nm in size, is located primarily in the rims that surround the carbonate globules. There are two populations of ALH84001 magnetites, which are likely formed at low temperature by inorganic and biogenic processes. Nearly 27% of ALH84001 magnetite particles, also called elongated prisms, have characteristics which make them uniquely identifiable as biological precipitates. Additional information is contained in the original extended abstract.

Thomas-Keprta, K. L.; Bazylinski, Dennis; Wentworth, Susan J.; McKay, David S.; Kirschvink, Joseph L.; Clemett, SImon J.; Bell, Mary Sue; Golden, D. C.; Gibson, Everett K., Jr.

1999-01-01

198

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

199

Rock magnetic criteria for the detection of biogenic magnetite  

NASA Astrophysics Data System (ADS)

We report results on the magnetic properties of magnetites produced by magnetotactic and dissimilatory iron-reducing bacteria. Magnetotactic bacterial (MTB) strains MS1, MV1 and MV2 and dissimilatory iron-reducing bacterium strain GS-15, grown in pure cultures, were used in this study. Our results suggest that a combination of room temperature coercivity analysis and low temperature remanence measurements provides a characteristic magnetic signature for intact chains of single domain (SD) particles of magnetite from MTBs. The most useful magnetic property measurements include: (1) acquisition and demagnetization of isothermal remanent magnetization (IRM) using static, pulse and alternating fields; (2) acquisition of anhysteretic remanent magnetization (ARM); and (3) thermal dependence of low temperature (20 K) saturation IRM after cooling in zero field (ZFC) of in a 2.5 T field (FC) from 300 K. However, potentially the most diagnostic magnetic parameter for magnetosome chain identification in bulk sediment samples is related to the difference between low temperature zero-field and field cooled SIRMs on warming through the Verwey transition (T approximately = 100 K). Intact chains of unoxidized magnetite magnetosomes have ratios of delta(sub FC)/delta(sub ZFC) greater than 2, where the parameter delta is a measure of the amount of remanence lost by warming through the Verwey transition. Disruption of the chain structure or conversion of the magnetosomes to maghemite reduces the delta(sub FC)/delta(sub ZFC) ratio to around 1, similar to values observed for some inorganic magnetite, maghemite, greigite and GS-15 particles. Numerical simulations of delta(sub FC)/delta(sub ZFC) ratios for simple binary mixtures of magnetosome chains and inorganic magnetic fractions suggest that the delta(sub FC)/delta(sub ZFC) parameter can be a sensitive indicator of biogenic magnetite in the form of intact chains of magnetite magnetosomes and can be a useful magnetic technique for identifying them in whole-sediment samples. The strength of our approach lies in the comparative ease and rapidity with which magnetic measurements can be made, compared to techniques such as electron microscopy.

Moskowitz, Bruce M.; Frankel, Richard B.; Bazylinski, Dennis A.

1993-12-01

200

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

201

Microbial Production of Ultrafine-Grained Magnetite.  

National Technical Information Service (NTIS)

A method of producing magnetite is disclosed which comprises culturing a microorganism designated GS-15 in the presence of organic matter and a ferric iron compound. Unlike prior art production of magnetite using magnetotactic bacteria, GS-15 is able to p...

D. R. Lovley

1988-01-01

202

Magnetotransport in exchange-coupled magnetite junctions  

Microsoft Academic Search

Epitaxial magnetic junctions of theoretically half-metallic electrode material magnetite were fabricated with a cobalt chromite paramagnetic insulating tunnel barrier. This spinel structure barrier was chosen to be isostructural to the magnetite electrodes. Highly crystalline trilayers with low surface roughness were grown. Strong exchange coupling between the electrodes is observed across the barrier. Magnetoresistance measurements are reminiscent of a single ferromagnetic

Rajesh V. Chopdekar; Guohan Hu; Alexandra C. Ford; Yuri Suzuki

2004-01-01

203

Metal-doped magnetite thin films.  

PubMed

This paper investigates magnetite (Fe3O4) thin film containing a small amount of a metal element. The films are prepared by rf sputtering with a composite target of ceramic iron oxide with metal chips. Low-temperature magnetization of magnetite containing 5.3%Ge reveals that the film contains some magnetically weak coupling grains. The metal element Mg reduces both hematite (alpha-Fe2O3) and magnetite, resulting in single-phase wüstite (Fe1-xO). In contrast, adding Ge selectively reduces hematite, while magnetite remains unreactive. According to the free energy of reaction, the element Ge is able to reduce hematite only, whereas the element Mg is capable of reducing both hematite and magnetite. This property is in good agreement with the experiment results. PMID:22905582

Abe, Seishi; Ping, De Hai; Nakamura, Shintaro; Ohnuma, Masato; Ohnuma, Shigehiro

2012-06-01

204

Self-assembly of liquid crystal block copolymer PEG-b-smectic polymer in pure state and in dilute aqueous solution  

Microsoft Academic Search

A series of amphiphilic LC block copolymers, in which the hydrophobic block is a smectic polymer poly(4-methoxyphenyl 4-(6-acryloyloxy-hexyloxy)-benzoate) (PA6ester1) and the hydrophilic block is polyethyleneglycol (PEG), were synthesized and characterized. The self-assembly of one of them in both the pure state and the dilute aqueous solution was investigated in detail. Nano-structures in the pure state were studied by SAXS and

Bing Xu; Rafael Piñol; Merveille Nono-Djamen; Sandrine Pensec; Patrick Keller; Pierre-Antoine Albouy; Daniel Lévy; Min-Hui Li

2009-01-01

205

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

206

Nanophase Magnetite and Pyrrhotite in ALH84001 Martian Meteorite: Evidence for an Abiotic Origin.  

National Technical Information Service (NTIS)

The nanophase magnetite crystals in the black rims of pancake-shaped carbonate globules of the Martian meteorite ALH84001 have been studied extensively because of the claim by McKay et al. that they are biogenic in origin. A subpopulation of these magneti...

D. C. Golden D. W. Ming H. V. Lauer R. V. Morris

2006-01-01

207

Magnetofluidization of Fine Magnetite Particles  

NASA Astrophysics Data System (ADS)

In this study we investigate the behaviour of a fluidized bed of fine magnetite particles as affected by a cross-flow uniform magnetic field. Due to the small particle size (35 microns), the fluidized system displays a typical Geldart A fluidization behaviour in the absence of an external field, i.e. natural van der Waals forces are able to stabilize fluidization in a short interval of gas velocities above the minimum fluidization velocity. The effect of the external field is to delay bed stability to higher gas velocities. Mechanical measurements on the magnetofluidized bed have been carried out using the Seville Powder Tester, which allows us for an accurate control of gas flow, and measurement of gas pressure drop across the bed and bed height. The tensile strength of the magnetically stabilized bed has been tested as a function of the gas velocity.

Quintanilla, M. A. S.; Espin, M. J.; Valverde, J. M.; Castellanos, A.

2009-06-01

208

Three-Dimensional Morphological Analysis of ALH84001 Magnetite Using Electron Tomography  

NASA Technical Reports Server (NTRS)

We report here the crystal morphologies of MV-1 and ALH84001 magnetites as calculated by back-projection using electron tomography. In the present study, we used a 300 keV TEM with a field emission gun (Tecnai F-30 from FEI Inc.), equipped with a 2048 x 2048 pixel CCD camera from Gatan Inc. to image magnetite crystals over tilt ranges of approx. +/- 72 deg in 2 deg tilt intervals. The images were aligned for back-projection, either manually, or through the use of fiducial 5 nm Au spheres affixed to the specimen prior to microscopy. Three-dimensional (3-D) reconstructions were computed using weighted back-projection of the tilted views. The tomograms were viewed and analyzed as a series of slices 1.0 nm thick, taken parallel to the specimen-supporting grid, using the IMOD software package. The shape of each magnetite crystal was determined by defining the external contour of a given magnetite in each slice and assembling a stack of these contours in 3-D. To aid in visualization, the stacked contour array was reduced to an optimal mesh by Delaunay triangulation. The surface normal to each of the triangles in the mesh was calculated and the triangle faces colored according to the orientation of that surface normal relative to the principal crystallographic axis of magnetite. Green surfaces correspond to {111} orientations, blue surfaces to {100} orientations, and red surfaces to {110} orientations. Triangles whose surface normal did not correspond to one of the principal axes were colored gray. Within the experimental and numerical uncertainties of the deconvolution, the tomographic reconstruction of both MV-1 and ALH84001 magnetites are equivalent and correspond to a truncated hexa-octahedral morphology.

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

2003-01-01

209

Magnetite Morphology and Life on Mars  

NSDL National Science Digital Library

This National Academy of Sciences scholarly paper discusses the strongest line of evidence for past life on Mars based on NASA's David McKay's original claims of finding nanofossils on the ALH84001 meteorite. This study concentrates on magnetite morphology, comparing morphologies of bacterial and abiotically produced magnetite. The findings are inconclusive, but do not strongly support evidence for biotically produced magnetite. The article features color images of the crystallography. While the abstract is free, this article may require a subscription to access the full text.

2009-06-24

210

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

211

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.

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

2012-01-01

212

Synthesis and characterization of magnetite nanopowders  

Microsoft Academic Search

We have synthesized the iron oxide nanoparticles using the newly developed mechanical ultrasonication method with the FeSO4·7H2O. We have also investigated the crystallographic structural properties, morphology, and magnetic properties of the nanopowders. According to the high resolution X-ray diffraction result, the as-synthesized iron oxide nanoparticles were magnetite (Fe3O4). The particle size of the magnetite nanoparticles was about 6nm confirmed by

Ki-Chul Kim; Eung-Kwon Kim; Jae-Won Lee; Sung-Lyul Maeng; Young-Sung Kim

2008-01-01

213

Biogenic Magnetite in Martian Meteorite ALH84001  

NASA Technical Reports Server (NTRS)

Fine-grained magnetite (Fe3O4) in martian meteorite ALH84001, generally less than 200 microns in size, is located primarily in the rims that surround the carbonate globules. There are two populations of ALH84001 magnets, which are likely formed at low temperature by inorganic and biogenic processes. Nearly 27/o of ALH84001 magnetite particles. also called elongated prisms, have characteristics which make them uniquely identifiable as biological precipitates.

Thomas-Keprta, Kathie L.; Bazylinski, Dennis; Wentworth, Susan J.; McKay, David S.; Kirschvink, Joseph L.; Clemett, Simon J.; Bell, Mary Sue; Golden, D. C.

1999-01-01

214

Thermal, Dielectric Studies on Pure and Amino Acid L-Glutamic Acid, L-Histidine L-Valine Doped Potassium Dihydrogen Phosphate Single Crystals  

NASA Astrophysics Data System (ADS)

Amino acids (L-Glutamic acid, L-Histidine, L-Valine) doped potassium dihydrogen phosphate crystals were grown by the solution growth technique. Slow cooling as well as slow evaporation methods were employed to grow these crystals. The concentration of dopants in the mother solution was varied from 0.1 mole % to 10 mole %. The solubility data for all dopant concentrations were determined. The variation in pH and the corresponding habit modification of the grown crystals were characterized with UV - VIS, FT-IR and SHG trace elements, and dielectric studies reveal slight distortion of lattice parameter for the heavily doped KDP crystals. TGA-DTA studies reveal good thermal stability. The dopants increase the hardness value of the material, which also depends on the concentration of the dopants. Amino acids doping improved the NLO properties. The detailed results on the spectral parameters, habit modifications and constant values will be presented.

Kumaresan, P.; Babu, S. Moorthy; Anbarasan, P. M.

215

Phase evolution of magnetite nanocrystals on oxide supports via template-free bismuth ferrite precursor approach  

NASA Astrophysics Data System (ADS)

This report investigates the phase evolution pathway of magnetite nanocrystal synthesis on oxide-supported substrates. A template-free phase separation approach, which exploits the thermodynamic instability of ternary perovskite BiFeO3 and inherent volatility of bismuth oxide in low oxygen pressure and high temperature is presented. The formation of an intermediate hematite nanocrystal phase is found as a key step that controls the eventual size and morphology of the magnetite nanocrystals. X-ray absorption spectra measurements and X-ray magnetic circular dichroism confirm that the spectral fingerprints of the magnetite nanocrystals match with that of bulk crystals. Magnetic measurements show that magnetic anisotropy is directly attributed to the nanocrystal morphology.

Cheung, Jeffrey; Bogle, Kashinath; Cheng, Xuan; Sullaphen, Jivika; Kuo, Chang-Yang; Chen, Ying-Jiun; Lin, Hong-Ji; Chen, Chien-Te; Yang, Jan-Chi; Chu, Ying-Hao; Valanoor, Nagarajan

2012-11-01

216

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

217

The verwey phase of magnetite — a long-running mystery in magnetism  

NASA Astrophysics Data System (ADS)

Magnetite (Fe3O4) is the original magnetic material and the parent of ferrite magnets, with modern applications ranging from spintronics to MRI contrast agents. At ambient temperatures magnetite has a cubic spinel-type crystal structure, but it undergoes a complex structural distortion and becomes electrically insulating below the 125 K Verwey transition. The electronic ground state of the Verwey phase has been unclear for over 70 years as the low temperature structure was unknown, but the full superstructure was recently determined by high energy microcrystal x-ray diffraction. An analysis of 168 frozen phonon modes in the acentric (and hence multiferroic) low temperature magnetite structure is presented here. Differences between the amplitudes of centric and acentric branches of, X and W modes all contribute to the significant off-center atomic distortions in the low temperature structure.

Senn, Mark S.; Wright, Jon P.; Attfield, J. Paul

2013-05-01

218

Oriented Inclusions of Single Domain Magnetite in Clinopyroxene: Source of Stable Remanent Magnetization in Gabbros of the Early Cretaceous Messum Complex, Namibia  

NASA Astrophysics Data System (ADS)

Oriented magnetite inclusions with two suborthogonal elongation directions in the (010) plane of clinopyroxene (CPX) are the dominant source of highly stable remanent magnetization in gabbros of the Messum Complex, Namibia. The inclusions are subparallel to the X ("X" inclusions) and Z ("Z" inclusions) crystallographic axes in the host CPX crystals. Such inclusions apparently form by exsolution/oxidation upon slow cooling through the range 600-500 oC, and consist of relatively pure magnetite. We term these features "Judd Structures", in homage to the first published account by Judd [1885]. AF and thermal demagnetization, and IRM acquisition experiments on individual grains of CPX from the Messum gabbros are dominated by single-domain magnetite behavior, consistent with observed size and extreme shape anisotropy (up to ca. 0.2 x 125 microns) of the oxide crystals comprising Judd structures. AF demagnetization of oriented crystals reveal minor differences in coercivity between the "X" and "Z" inclusions. VGP's from these rocks (dated by 40Ar/39Ar at 132 Ma) are consistent with poles from the petrogenetically related and well-dated Etendeka volcanics, and coincide with a cusp in the African APWP, thus constraining the age of magnetization at ca. 132 Ma. These observations are consistent with a high-T subsolidus exsolution/oxidation origin, and moreover indicate that despite extreme shape anisotropy at the single pyroxene scale, an apparently random distribution of CPX lattice orientations imposes no bias on bulk-rock magnetization. Of the four sites sampled, two have Normal polarity characteristic magnetization (ChRM) and one has Reverse ChRM. The fourth site has both Normal and Reverse ChRM even in individual bulk (ca. 10 cm3) specimens. Demagnetization of many individual CPX grains from this site reveals dual polarity, restricted to the "X" inclusions. We suggest that remanence acquisition upon cooling of this gabbro spanned a geomagnetic polarity reversal. Improved knowledge of intensive variables (i.e., temperature, cooling rate, reaction stoichiometry) governing Judd structures' paragenesis is needed. Nonetheless, our ongoing work indicates the potential for application to problems requiring exceptionally stable paleomagnetic records, such as paleointensity determinations. Analysis at the single (host) crystal scale is both feasible and desirable for many such applications.

Renne, P. R.; Scott, G. R.; Glen, J. M.; Feinberg, J.

2002-05-01

219

Thermal, dielectric studies on pure and amino acid ( L-glutamic acid, L-histidine, L-valine) doped KDP single crystals  

NASA Astrophysics Data System (ADS)

Amino acids ( L-glutamic acid, L-histidine, L-valine) doped potassium dihydrogen phospate crystals are grown by solution growth technique. Slow cooling as well as slow evaporation methods were employed to grow these crystals. The concentration of dopants in the mother solution was varied from 0.1 mol% to 10 mol%. The solubility data for all dopants concentration were determined. There is variation in pH value and hence, there is habit modification of the grown crystals were characterized with UV-VIS, FT-IR studies, SHG trace elements and dielectric studies reveal slight distortion of lattice parameter for the heavily doped KDP crystals. UV-Visible spectra confirm the improvement in the transparency of these crystals on doping metal ions. FT-IR spectra reveal strong absorption band between 1400 and 1600 cm -1 for metal ion doped crystals. TGA-DTA studies reveal good thermal stability. The dopants increase the hardness value of the material and it also depends on the concentration of the dopants. Amino acids doping improved the NLO properties. The detailed results on the spectral parameters, habit modifications and constant values will be presented.

Kumaresan, P.; Moorthy Babu, S.; Anbarasan, P. M.

2008-05-01

220

Magnetization and NMR in pure and mixed crystal Fe[S2CN(C2H5)2] 2ClxBr1?x: 3D-Ising ferromagnetism and evidence for a strain induced ground state  

Microsoft Academic Search

The magnetization along easy and hard magnetic axes has been measured in three single crystal samples of Fe[S2CN(C2H5)2]2Clx Br1?x (x=1.000, 0.712, and 0.204), between 1.2 and 4.2 K and in applied fields up to 13 000 Oe. In the pure chloride an effective saturation moment of 3.28±0.16 ?B per iron ion is observed along the [101] easy axis. The effective

Gary C. DeFotis; J. A. Cowen

1980-01-01

221

Magnetization and NMR in pure and mixed crystal Fe[S2CN(C2H5)2] 2ClxBr1-x: 3D-Ising ferromagnetism and evidence for a strain induced ground state  

Microsoft Academic Search

The magnetization along easy and hard magnetic axes has been measured in three single crystal samples of Fe[S2CN(C2H5)2]2Clx Br1-x (x=1.000, 0.712, and 0.204), between 1.2 and 4.2 K and in applied fields up to 13 000 Oe. In the pure chloride an effective saturation moment of 3.28+\\/-0.16 muB per iron ion is observed along the [101] easy axis. The effective

Gary C. Defotis; J. A. Cowen

1980-01-01

222

Arsenite sorption at the magnetite water interface during aqueous precipitation of magnetite: EXAFS evidence for a new arsenite surface complex  

NASA Astrophysics Data System (ADS)

The interaction of aqueous As(III) with magnetite during its precipitation from aqueous solution at neutral pH has been studied as a function of initial As/Fe ratio. Arsenite is sequestered via surface adsorption and surface precipitation reactions, which in turn influence the crystal growth of magnetite. Sorption samples were characterized using EXAFS spectroscopy at the As K-edge in combination with HRTEM observations, energy dispersive X-ray analysis at the nanoscale, electron energy loss spectroscopy at the Fe L 3-edge, and XRD-Rietveld analyses of reaction products. Our results show that As(III) forms predominantly tridentate hexanuclear As(III)O 3 complexes ( 3C), where the As(III)O 3 pyramids occupy vacant tetrahedral sites on {1 1 1} surfaces of magnetite particles. This is the first time such a tridentate surface complex has been observed for arsenic. This complex, with a dominant As-Fe distance of 3.53 ± 0.02 Å, occurs in all samples examined except the one with the highest As/Fe ratio (0.33). In addition, at the two highest As/Fe ratios (0.133 and 0.333) arsenite tends to form mononuclear edge-sharing As(III)O 3 species ( 2E) within a highly soluble amorphous As(III)-Fe(III,II)-containing precipitate. At the two lowest As/Fe ratios (0.007 and 0.033), our results indicate the presence of additional As(III) species with a dominant As-Fe distance of 3.30 ± 0.02 Å, for which a possible structural model is proposed. The tridentate 3C As(III)O 3 complexes on the {1 1 1} magnetite surface, together with this additional As(III) species, dramatically lower the solubility of arsenite in the anoxic model systems studied. They may thus play an important role in lowering arsenite solubility in putative magnetite-based water treatment processes, as well as in natural iron-rich anoxic media, especially during the reductive dissolution-precipitation of iron minerals in anoxic environments.

Wang, Yuheng; Morin, Guillaume; Ona-Nguema, Georges; Menguy, Nicolas; Juillot, Farid; Aubry, Emmanuel; Guyot, François; Calas, Georges; Brown, Gordon E., Jr.

2008-06-01

223

Formation of single domain magnetite by green rust oxidation promoted by microbial anaerobic nitrate-dependent iron oxidation  

NASA Astrophysics Data System (ADS)

Biomineralization of magnetite is a central geomicrobiological process that might have played a primordial role over Earth’s history, possibly leaving traces of life in the geological record or controlling trace metal(loid)s and organic pollutants mobility in modern environments. Magnetite biomineralization has been attributed to two main microbial pathways to date (namely magnetotactic bacteria and dissimilatory iron-reducing bacteria). Here, we uncover a new route of magnetite biomineralization involving the anaerobic nitrate-reducing iron(II) oxidizing bacterium Acidovorax sp. strain BoFeN1. Using transmission electron microscopy, scanning transmission X-ray microscopy, transmission Mössbauer spectroscopy and rock magnetic analyses, this strain is shown to promote the transformation of hydroxychloride green rust in equilibrium with dissolved Fe(II) to (1) periplasmic lepidocrocite (?-FeOOH) and (2) extracellular magnetite, thus leading to strong redox heterogeneities at the nanometer scale. On the one hand, lepidocrocite was associated with protein moieties and exhibited an anisotropic texture, with the elongated axis parallel to the cell wall. On the other hand, magnetite crystals exhibited grain sizes and magnetic properties consistent with stable single domain particles. By comparison, abiotic controls led to a very slow (4 months vs. 2 days in BoFeN1 cultures) and incomplete oxidation of hydroxychloride green rust towards magnetite. As this abiotic magnetite exhibited the same size and magnetic properties (stable single domain particles) as magnetite produced in BoFeN1 cultures, only the co-occurrence of textured Fe(III)-oxides and magnetite, associated with the persistence of organic carbon molecules, might constitute valuable biosignatures to be looked for in the geological record. Our results furthermore contribute to a more complex picture of Fe redox cycling in the environment, providing an additional process of Fe(II)-bearing phase biomineralization that is not specific of Fe bio-reduction, but can also result from Fe bio-oxidation.

Miot, Jennyfer; Li, Jinhua; Benzerara, Karim; Sougrati, Moulay Tahar; Ona-Nguema, Georges; Bernard, Sylvain; Jumas, Jean-Claude; Guyot, François

2014-08-01

224

Magnetic Characteristics of Metal-doped Magnetite Nanoparticles Produced by Thermoanaerobacter Ethanolicus  

Microsoft Academic Search

This work examined the magnetic properties of pure and metal-doped magnetite powders which were synthesized by a bacterially mediated process under anaerobic conditions. The iron(III)-reducing bacterial strain Thermoanaerobacter ethanolicus TOR-39, isolated from deep subsurface sediments, was incubated under anaerobic conditions at 65,aC for 2 weeks in aqueous medium containing amorphous iron(III) oxyhydroxides (akaganeite). The microbial process produced several grams per

L. W. Yeary; T. J. Phelps; L. J. Love; J. Moon; A. J. Rondinone; C. J. Rawn; J. R. Thompson; A. S. Madden; M. E. Madden

2005-01-01

225

The effect of humic acid adsorption on pH-dependent surface charging and aggregation of magnetite nanoparticles  

SciTech Connect

The pH-dependent adsorption of humic acid (HA) on magnetite and its effect on the surface charging and the aggregation of oxide particles were investigated. HA was extracted from brown coal. Synthetic magnetite was prepared by alkaline hydrolysis of iron(II) and iron(III) salts. The pH-dependent particle charge and aggregation, and coagulation kinetics at pH around to 4 were measured by laser Doppler electrophoresis and dynamic light scattering. The charge of pure magnetite reverses from positive to negative at pH around 8, which may consider as isoelectric point (IEP). Near this pH, large aggregates form, while stable sols exist further from it. In the presence of increasing HA loading, the IEP shifts to lower pH, then at higher loading, magnetite becomes negatively charged even at low pHs, which indicate the neutralization and gradual recharging positive charges on surface. In acidic region, the trace HA amounts are adsorbed on magnetite surface as oppositely charged patches, systems become highly unstable due to heterocoagulation. Above the adsorption saturation, however, the nanoparticles are stabilized in a way of combined steric and electrostatic effects. The HA coated magnetite particles form stable colloidal dispersion, particle aggregation does not occur in a wide range of pH and salt tolerance is enhanced.

Illes, E.; Tombacz, E. [University of Szeged, Szeged (Hungary)

2006-03-01

226

The chemistry of hydrothermal magnetite: a review  

USGS Publications Warehouse

Magnetite (Fe3O4) is a well-recognized petrogenetic indicator and is a common accessory mineral in many ore deposits and their host rocks. Recent years have seen an increased interest in the use of hydrothermal magnetite for provenance studies and as a pathfinder for mineral exploration. A number of studies have investigated how specific formation conditions are reflected in the composition of the respective magnetite. Two fundamental questions underlie these efforts — (i) How can the composition of igneous and, more importantly, hydrothermal magnetite be used to discriminate mineralized areas from barren host rocks, and (ii) how can this assist exploration geologists to target ore deposits at greater and greater distances from the main mineralization? Similar to igneous magnetite, the most important factors that govern compositional variations in hydrothermal magnetite are (A) temperature, (B) fluid composition — element availability, (C) oxygen and sulfur fugacity, (D) silicate and sulfide activity, (E) host rock buffering, (F) re-equilibration processes, and (G) intrinsic crystallographic controls such as ionic radius and charge balance. We discuss how specific formation conditions are reflected in the composition of magnetite and review studies that investigate the chemistry of hydrothermal and igneous magnetite from various mineral deposits and their host rocks. Furthermore, we discuss the redox-related alteration of magnetite (martitization and mushketovitization) and mineral inclusions in magnetite and their effect on chemical analyses. Our database includes published and previously unpublished magnetite minor and trace element data for magnetite from (1) banded iron formations (BIF) and related high-grade iron ore deposits in Western Australia, India, and Brazil, (2) Ag–Pb–Zn veins of the Coeur d'Alene district, United States, (3) porphyry Cu–(Au)–(Mo) deposits and associated (4) calcic and magnesian skarn deposits in the southwestern United States and Indonesia, and (5) plutonic igneous rocks from the Henderson Climax-type Mo deposit, United States, and the un-mineralized Inner Zone Batholith granodiorite, Japan. These five settings represent a diverse suite of geological settings and cover a wide range of formation conditions. The main discriminator elements for magnetite are Mg, Al, Ti, V, Cr, Mn, Co, Ni, Zn, and Ga. These elements are commonly present at detectable levels (10 to > 1000 ppm) and display systematic variations. We propose a combination of Ni/(Cr + Mn) vs. Ti + V, Al + Mn vs. Ti + V, Ti/V and Sn/Ga discriminant plots and upper threshold concentrations to discriminate hydrothermal from igneous magnetite and to fingerprint different hydrothermal ore deposits. The overall trends in upper threshold values for the different settings can be summarized as follows: (I) BIF (hydrothermal) — low Al, Ti, V, Cr, Mn, Co, Ni, Zn, Ga and Sn; (II) Ag–Pb–Zn veins (hydrothermal) — high Mn and low Ga and Sn; (III) Mg-skarn (hydrothermal) — high Mg and Mn and low Al, Ti, Cr, Co, Ni and Ga; (IV) skarn (hydrothermal) — high Mg, Al, Cr, Mn, Co, Ni and Zn and low Sn; (V) porphyry (hydrothermal) — high Ti and V and low Sn; (VI) porphyry (igneous) — high Ti, V and Cr and low Mg; and (VII) Climax-Mo (igneous) — high Al, Ga and Sn and low Mg and Cr.

Nadoll, Patrick; Angerer, Thomas; Mauk, Jeffrey L.; French, David; Walshe, John

2014-01-01

227

Simultaneously discrete biomineralization of magnetite and tellurium nanocrystals in magnetotactic bacteria.  

PubMed

Magnetotactic bacteria synthesize intracellular magnetosomes comprising membrane-enveloped magnetite crystals within the cell which can be manipulated by a magnetic field. Here, we report the first example of tellurium uptake and crystallization within a magnetotactic bacterial strain, Magnetospirillum magneticum AMB-1. These bacteria independently crystallize tellurium and magnetite within the cell. This is also highly significant as tellurite (TeO(3)(2-)), an oxyanion of tellurium, is harmful to both prokaryotes and eukaryotes. Additionally, due to its increasing use in high-technology products, tellurium is very precious and commercially desirable. The use of microorganisms to recover such molecules from polluted water has been considered as a promising bioremediation technique. However, cell recovery is a bottleneck in the development of this approach. Recently, using the magnetic property of magnetotactic bacteria and a cell surface modification technology, the magnetic recovery of Cd(2+) adsorbed onto the cell surface was reported. Crystallization within the cell enables approximately 70 times more bioaccumulation of the pollutant per cell than cell surface adsorption, while utilizing successful recovery with a magnetic field. This fascinating dual crystallization of magnetite and tellurium by magnetotactic bacteria presents an ideal system for both bioremediation and magnetic recovery of tellurite. PMID:20581185

Tanaka, Masayoshi; Arakaki, Atsushi; Staniland, Sarah S; Matsunaga, Tadashi

2010-08-01

228

Simultaneously Discrete Biomineralization of Magnetite and Tellurium Nanocrystals in Magnetotactic Bacteria?  

PubMed Central

Magnetotactic bacteria synthesize intracellular magnetosomes comprising membrane-enveloped magnetite crystals within the cell which can be manipulated by a magnetic field. Here, we report the first example of tellurium uptake and crystallization within a magnetotactic bacterial strain, Magnetospirillum magneticum AMB-1. These bacteria independently crystallize tellurium and magnetite within the cell. This is also highly significant as tellurite (TeO32?), an oxyanion of tellurium, is harmful to both prokaryotes and eukaryotes. Additionally, due to its increasing use in high-technology products, tellurium is very precious and commercially desirable. The use of microorganisms to recover such molecules from polluted water has been considered as a promising bioremediation technique. However, cell recovery is a bottleneck in the development of this approach. Recently, using the magnetic property of magnetotactic bacteria and a cell surface modification technology, the magnetic recovery of Cd2+ adsorbed onto the cell surface was reported. Crystallization within the cell enables approximately 70 times more bioaccumulation of the pollutant per cell than cell surface adsorption, while utilizing successful recovery with a magnetic field. This fascinating dual crystallization of magnetite and tellurium by magnetotactic bacteria presents an ideal system for both bioremediation and magnetic recovery of tellurite.

Tanaka, Masayoshi; Arakaki, Atsushi; Staniland, Sarah S.; Matsunaga, Tadashi

2010-01-01

229

Experimental Study on Mixtures of Superparamgnetic and Single-Domain Magnetite with Respect to Day-Dunlop Plots  

NASA Astrophysics Data System (ADS)

Day-Dunlop plots are widely used as a diagnostic of domain state: superparamagnetic (SP), stable single-domain (SD), pseudo-single-domain (PSD), multi-domain (MD) and mixture of these. A n earlier experimental study on mixtures of SP and SD magnetite showed that ratios of saturation remanent magnetization to saturation magnetization and the coercivity of remanence to coercivity are lower than the expected theoretical mixing trend (Dunlop & Carter-Stiglitz, J. Geophys. Res., 111, B12S09). This study reexamines Day-Dunlop plots with experimentally determined mixtures of SD and SP magnetite grains. The starting materials that are used in this study are biogenic magnetite with SD and SP particle size, and a commercial ferrofluid. The SD-biogenic magnetite is from magnetotactic bacteria that are arranged in chains. The average magnetosome size is 45 mm; however, there is also a minor amount of SP material among the magnetosomes. The SP component consists either of: 1) SP-biogenic magnetite, which occurs as isolated particles within the bacteria with an average size of 18 nm, or 2) Chemicell ferrofluid, magnetite with 10 nm particle size and hydrodynamic diameter of 45 nm. The magnetic properties of the pure materials were first characterized by measurements of hysteresis, acquisition of an isothermal remanent magnetization, and first-order reversal curves. The magnetic properties of the SD magnetite are typical for magnetotactic bacteria. The SP samples show no remanence. Two samples were prepared from the SD-magnetite to serve as the starting material. The SP-component was then added incrementally to the SD samples. Experimental results from these tests show that the magnetization and coercivity ratios are lower than the theoretical prediction for both sample mixtures. The reasons for this discrepancy will be discussed.

Hirt, A. M.; Kumari, M.; Senn, N.; Uebe, R.; Schueler, D.

2013-12-01

230

Magnetofluidization of fine magnetite powder  

NASA Astrophysics Data System (ADS)

The behavior of a fluidized bed of fine magnetite particles as affected by a cross-flow magnetic field is investigated. A distinct feature of this naturally cohesive powder, as compared to noncohesive magnetic grains usually employed in magnetofluidized beds, is that the fluidized bed displays a range of stable fluidization even in the absence of an external magnetic field. Upon application of the magnetic field, the interval of stable fluidization is extended to higher gas velocities and bed expansion is enhanced. We have measured the tensile strength as affected by application of the external magnetic field according to two different operation modes. In the H off-on operation mode, the bed is driven to bubbling in the absence of external magnetic field. Once the gas velocity is decreased below the bubbling onset and the bed has returned to stable fluidization due to natural cohesive forces, the field is applied. In the H on-on mode, the field is maintained during the whole process of bubbling and return to stable fluidization. It is found that the tensile strength of the naturally stabilized bed is not essentially changed by application of the field ( H off-on) since the magnetic field cannot alter the bed structure once the particles are jammed in the stable fluidization state. Magnetic forces within the bulk of the jammed bed are partially canceled as a result of the anisotropic nature of the dipole-dipole interaction between the particles, which gives rise to just a small increment of the tensile strength. On the other hand, when the field is held on during bubbling and transition to stable fluidization ( H on-on mode), the tensile strength is appreciably increased. This suggests the formation of particle chains when the particles are not constrained due to the dipole-dipole attractive interaction which affects the mechanical strength of the stably fluidized bed. Experimental data are analyzed in the light of theoretical models on magnetic surface stresses.

Valverde, J. M.; Espin, M. J.; Quintanilla, M. A. S.; Castellanos, A.

2009-03-01

231

Self-assembly of liquid crystal block copolymer PEG-b-smectic polymer in pure state and in dilute aqueous solution.  

PubMed

A series of amphiphilic LC block copolymers, in which the hydrophobic block is a smectic polymer poly(4-methoxyphenyl 4-(6-acryloyloxy-hexyloxy)-benzoate) (PA6esterl) and the hydrophilic block is polyethyleneglycol (PEG), were synthesized and characterized. The self-assembly of one of them in both the pure state and the dilute aqueous solution was investigated in detail. Nano-structures in the pure state were studied by SAXS and WAXS on samples aligned by a magnetic field. A hexagonal cylindrical micro-segregation phase was observed with a lattice distance of 11.2 nm. The PEG blocks are in the cylinder, while the smectic polymer blocks form a matrix with layer spacing 2.4 nm and layer normal parallel to the long axis of the cylinders. Faceted unilamellar polymer vesicles, polymersomes, were formed in water, as revealed by cryo-TEM. In the lyotropic bilayer membrane of these polymersomes, the thermotropic smectic order in the hydrophobic block is clearly visible with layer normal parallel to the membrane surface. PMID:20334105

Xu, Bing; Piñol, Rafael; Nono-Djamen, Merveille; Pensec, Sandrine; Keller, Patrick; Albouy, Pierre-Antoine; Lévy, Daniel; Li, Min-Hui

2009-01-01

232

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

233

On the Order-Disorder Surface Phase Transition and Critical Temperature of Pure Metals Originating from BCC, FCC, and HCP Crystal Structures  

NASA Astrophysics Data System (ADS)

The excess surface Gibbs energy and surface tension of pure liquid metals (originating from bcc, fcc, and hcp solid metals) of ordered and disordered surface structures are compared in this paper. It is shown that at a special temperature T * an order-disorder surface phase transition is expected in all liquid metals from a low-temperature ordered surface state to a high-temperature disordered surface state. This surface phase transition is similar to the first-order bulk solid-liquid phase transition (melting). The values of T * appear in the temperature interval between the melting point and the critical point of metals. Critical temperatures of metals are estimated from the equation for high-temperature disordered surfaces.

Kaptay, George

2012-07-01

234

Actinide Removal from Aqueous Solution with Activated Magnetite.  

National Technical Information Service (NTIS)

An actinide aqueous waste treatment process using activated magnetite has been developed at Rocky Flats. The use and effectiveness of various magnetites in lowering actinide concentrations in aqueous solution are described. Experiments indicate that magne...

R. L. Kochen R. L. Thomas

1987-01-01

235

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.

236

Thermal analysis of two types of dextran-coated magnetite  

Microsoft Academic Search

The thermal stability of two kinds of dextran-coated magnetite (dextran with molecular weight of 40,000 (Dex40) and 70,000\\u000a (Dex70)), obtained by dextran adsorption onto the magnetite surface is investigated in comparison with free dextran in air\\u000a and argon atmosphere. The thermal behavior of the two free dextran types and corresponding coated magnetites is similar, but\\u000a atmosphere dependent. The magnetite catalyzes

Oana Carp; Luminita Patron; Daniela C. Culita; Petru Budrugeac; Marcel Feder; Lucian Diamandescu

2010-01-01

237

Magnetic polymer nanospheres with high and uniform magnetite content  

Microsoft Academic Search

Magnetic polymer nanospheres with high and uniform magnetite content were synthesized using a new process based on miniemulsion polymerization, where a stable water-based dispersion of sodium dodecyl sulfate (SDS)\\/oleic acid bilayer coated magnetite aggregates was first synthesized and mixed with monomer styrene miniemulsion. Then another miniemulsification was performed for the full encapsulation of magnetite into monomer droplets. Subsequent polymerization generated

Weiming Zheng; Feng Gao; Hongchen Gu

2005-01-01

238

Biogenic Magnetite Formation through Anaerobic Biooxidation of Fe(II)  

PubMed Central

The presence of isotopically light carbonates in association with fine-grained magnetite is considered to be primarily due to the reduction of Fe(III) by Fe(III)-reducing bacteria in the environment. Here, we report on magnetite formation by biooxidation of Fe(II) coupled to denitrification. This metabolism offers an alternative environmental source of biogenic magnetite.

Chaudhuri, Swades K.; Lack, Joseph G.; Coates, John D.

2001-01-01

239

Biophysics of Magnetic Orientation: Radical Pairs, Biogenic Magnetite, or both?  

Microsoft Academic Search

Two major biophysical mechanisms for magnetoreception in terrestrial animals, one based on biogenic magnetite and another on radical-pair biochemical reactions, have been the subject of experiment and debate for the past 30 years. The magnetite hypothesis has stood the test of time: biogenic magnetite is synthesized biochemically in Bacteria, Protists, and numerous Animal phyla, as well as in some plants.

Joe Kirschvink

2011-01-01

240

Magnetite whiskers and platelets in the ALH84001 Martian meteorite: evidence of vapor phase growth.  

PubMed

Nanometer-sized magnetite crystals associated with carbonates in fracture zones within Martian meteorite ALH84001 have been examined using analytical transmission electron microscopy. Some of the crystals exhibit distinctive morphologies: filamentary rods and ribbon, and platelets. The rods and ribbons are elongated along the crystallographic [100] and [111] directions. Some of the rods contain microstructural defects indicating that they grew by spiral growth about screw dislocations. Platelets are flattened along the [100] and [110] directions. These unique morphologies and microstructures constrain the growth conditions of magnetite. The whiskers and platelets most likely formed in the temperature range 500-800 degrees C by direct condensation from a vapor or precipitation from a supercritical fluid, and their properties are inconsistent with a biogenic origin. PMID:11541129

Bradley, J P; Harvey, R P; McSween, H Y

1996-01-01

241

Biomimetic Magnetite Formation: From Biocombinatorial Approaches to Mineralization Effects  

PubMed Central

Biological materials typically display complex morphologies and hierarchical architectures, properties that are hardly matched by synthetic materials. Understanding the biological control of mineral properties will enable the development of new synthetic approaches toward biomimetic functional materials. Here, we combine biocombinatorial approaches with a proteome homology search and in vitro mineralization assays to assess the role of biological determinants in biomimetic magnetite mineralization. Our results suggest that the identified proteins and biomimetic polypeptides influence nucleation in vitro. Even though the in vivo role cannot be directly determined from our experiments, we can rationalize the following design principles: proteins, larger complexes, or membrane components that promote nucleation in vivo are likely to expose positively charged residues to a negatively charged crystal surface. In turn, components with acidic (negatively charged) functionality are nucleation inhibitors, which stabilize an amorphous structure through the coordination of iron.

2014-01-01

242

Origin of magnetite in oxidized CV chondrites: in situ measurement of oxygen isotope compositions of Allende magnetite and olivine  

Microsoft Academic Search

Magnetite in the oxidized CV chondrite Allende mainly occurs as spherical nodules in porphyritic-olivine (PO) chondrules, where it is associated with Ni-rich metal and\\/or sulfides. To help constrain the origin of the magnetite, we measured oxygen isotopic compositions of magnetite and coexisting olivine grains in PO chondrules of Allende by an in situ ion microprobe technique. Five magnetite nodules form

Byeon-Gak Choi; Kevin D. McKeegan; Laurie A. Leshin; John T. Wasson

1997-01-01

243

Field-dependent anisotropic magnetoresistance and planar Hall effect in epitaxial magnetite thin films  

Microsoft Academic Search

A systematic study of the temperature and magnetic field dependence of the longitudinal and transverse resistivities of epitaxial thin films of magnetite (Fe3O4) is reported. The anisotropic magnetoresistance (AMR) and the planar Hall effect are sensitive to the in-plane orientation of current and magnetization with respect to crystal axes in a way consistent with the cubic symmetry of the system.

N. Naftalis; A. Kaplan; M. Schultz; C. A. F. Vaz; J. A. Moyer; C. H. Ahn; L. Klein

2011-01-01

244

Reexamination of the Temperature Dependences of Resonant Reflections in Highly Stoichiometric Magnetite  

Microsoft Academic Search

We have studied the temperature dependences of the so-called charge and orbital ordering reflections in the neighborhood of the Verwey transition by means of resonant x-ray scattering at the Fe K and L edges on a high purity single crystal of magnetite. Contrary to recently published results [J. E. Lorenzo , Phys. Rev. Lett. 101, 226401 (2008)PRLTAO0031-900710.1103\\/PhysRevLett.101.226401], we show that

Joaquín García; Gloria Subías; Javier Herrero-Martín; Javier Blasco; Vera Cuartero; M. Concepción Sánchez; Claudio Mazzoli; Flora Yakhou

2009-01-01

245

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

246

Magnetic properties of biosynthesized magnetite nanoparticles  

Microsoft Academic Search

Magnetic nanoparticles, which are unique because of both structural and functional elements, have various novel applications. The popularity and practicality of nanoparticle materials create a need for a synthesis method that produces quality particles in sizable quantities. This paper describes such a method, one that uses bacterial synthesis to create nanoparticles of magnetite. The thermophilic bacterial strain Thermoanaerobacter ethanolicus TOR-39

Lucas W. Yeary; Ji-Won Moon; L. J. Love; J. R. Thompson; C. J. Rawn; T. J. Phelps

2005-01-01

247

Magnetite nanoparticles with no surface spin canting  

Microsoft Academic Search

Surface spin canting has been studied for high quality magnetite nanoparticles in terms of size and shape uniformity. Particles were prepared by thermal decomposition of organic precursors in organic media and in the presence of oleic acid. Results are compared to spin canting effect for magnetic iron oxide nanoparticles of similar size prepared by coprecipitation and subsequently coated with silica.

A. G. Roca; D. Niznansky; J. Poltierova-Vejpravova; B. Bittova; M. A. González-Fernández; C. J. Serna; M. P. Morales

2009-01-01

248

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

249

Magnetite biomineralization induced by Shewanella oneidensis  

Microsoft Academic Search

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 Fe2+(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

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

2010-01-01

250

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

251

Magnetite biomineralization and ancient life on Mars.  

PubMed

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. PMID:10742183

Frankel, R B; Buseck, P R

2000-04-01

252

Occlusion of noble gases (He, Ne, Ar, Kr, Xe) into synthetic magnetite at 500–1300°C  

Microsoft Academic Search

The trapping mechanism of noble gases during growth of magnetite is investigated by oxidizing Fe with water vapor at temperatures ranging from 500 to 1300°C. An apparent negative correlation between the concentration of argon and synthetic temperatures suggests that gases are trapped by adsorption. The fixation of adsorbed gas atoms is probably due to crystal growth. The elemental fractionation pattern

Takuya Matsumoto; Kazuyuki Maruo; Akira Tsuchiyama; Jun-Ichi Matsuda

1996-01-01

253

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

254

Lanthanide-Substituted Magnetite Nanoparticles Using a New Mixed Precursor Method by Thermoanaerobacter ethanolicus  

NASA Astrophysics Data System (ADS)

A metal reducing bacterium, Thermoanaerobacter ethanolicus successfully converted the precursor of L (lanthanide)-mixed akaganeite (LxFe1-xOOH) phase to L-substituted magnetite (LyFe3-yO4) while avoiding the potentially toxic effects of soluble L-ions. Antibiotic elements, lanthanide (Nd, Gd, Tb, Ho, and Er)-substituted magnetites were produced by microbial fermentation using LxFe1-xOOH, where x was up to 0.02 which is equivalent to 0.72 mM. Combining lanthanides into the akaganeite precursor phase mitigated some of the toxicity when compared to the traditional method by using pure akaganeite and the dissolved L-salt form. This new technique showed that an upper limit of L-concentrations between 0.02 and 0.1 mM might suppress bacterial activity. At the equivalent L-cation mole fraction, the traditional method increased the concentration of soluble toxic L ions in the final media. The precursor method enabled production of microbially synthesized L- substituted magnetite with an L-concentration 36-fold greater than could be obtained when the lanthanides were added as soluble salts. These results were confirmed by protein assay. The increase of L-concentration in the magnetite evidently manipulates its physical properties such as decreasing Curie temperature and decreasing saturation magnetism of L-substituted magnetite. This mixed precursor method can therefore be used to extend the application for nanofermentation and other bacterial synthesis fields where there is a need for economically low-energy consumable microbial production of nanoscale materials that should involve toxic or inhibitory elements to bacterial growth.

Moon, J.; Roh, Y.; Yeary, L. W.; Lauf, R. J.; Phelps, T. J.

2006-12-01

255

Synthesis and kinetic shape and size evolution of magnetite nanoparticles  

SciTech Connect

Eleven nanometers of magnetite nanoparticles were synthesized by using 6 nm magnetite nanoparticles as seeds and Fe(acac){sub 3} as precursor at high temperature. Growth kinetics of magnetite nanoparticles was studied during the progress of reaction. Magnetite nanoparticles with different shapes including near-sphere, tetrahedral, truncated tetrahedral and cubic were observed at different reaction time. Transmission electron microscopic results show that the shape and size distributions are time- and temperature-dependent. Hydrodynamic diameter results give the kinetic size distribution changes of magnetite nanoparticles during the reaction, which suggest that this synthesis underwent a 'growth-controlled nucleation'.

Zhang Ling [Institute for Micro and Nano Science and Technology, Shanghai Jiaotong University, 200030 Shanghai (China); He Rong [Institute for Micro and Nano Science and Technology, Shanghai Jiaotong University, 200030 Shanghai (China); Gu Hongchen [Institute for Micro and Nano Science and Technology, Shanghai Jiaotong University, 200030 Shanghai (China)]. E-mail: hcgu@sjtu.edu.cn

2006-02-02

256

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][BF[. Iron (II) chloride and iron (III) chloride which dissolves in [BMIM][BF[ 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

257

Remanent and induced magnetic anomalies over a 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 km 2 with a thickness of ~ 7000 m and is of economic interest for 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 Fe 3+-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. The variations in aeromagnetic and ground-magnetic anomalies measured over the BKS can be explained in terms of the measured magnetic properties of NRM, susceptibility, and hysteresis presented here, and in terms of mineralogy. 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 NRMs 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 opaque minerals, illustrate some of the possibilities to be considered in evaluating crustal magnetic anomalies.

McEnroe, Suzanne A.; Brown, Laurie L.; Robinson, Peter

2009-12-01

258

Ferromagnetic resonance and low-temperature magnetic tests for biogenic magnetite  

NASA Astrophysics Data System (ADS)

Magnetite is both a common inorganic rock-forming mineral and a biogenic product formed by a diversity of organisms. Magnetotactic bacteria produce intracellular magnetites of high purity and crystallinity (magnetosomes) arranged in linear chains of crystals. Magnetosomes and their fossils (magnetofossils) have been identified using transmission electron microscopy (TEM) in sediments dating back to ˜510-570 Ma, and possibly in 4 Ga carbonates in Martian meteorite ALH84001. We present the results from two rock magnetic analyses—the low-temperature Moskowitz test and ferromagnetic resonance (FMR)—applied to dozens of samples of magnetite and other materials. The magnetites in these samples are of diverse composition, size, shape, and origin: biologically induced (extracellular), biologically controlled (magnetosomes and chiton teeth), magnetofossil, synthetic, and natural inorganic. We confirm that the Moskowitz test is a distinctive indicator for magnetotactic bacteria and provide the first direct experimental evidence that this is accomplished via sensitivity to the magnetosome chain structure. We also demonstrate that the FMR spectra of four different strains of magnetotactic bacteria and a magnetofossil-bearing carbonate have a form distinct from all other samples measured in this study. We suggest that this signature also results from the magnetosomes' unique arrangement in chains. Because FMR can rapidly identify samples with large fractions of intact, isolated magnetosome chains, it could be a powerful tool for identifying magnetofossils in sediments.

Weiss, Benjamin P.; Sam Kim, Soon; Kirschvink, Joseph L.; Kopp, Robert E.; Sankaran, Mohan; Kobayashi, Atsuko; Komeili, Arash

2004-07-01

259

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

260

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

261

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

262

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

263

An experimental study of the mechanism of the replacement of magnetite by pyrite up to 300 °C  

NASA Astrophysics Data System (ADS)

We present the results of an experimental study into the sulfidation of magnetite to form pyrite/marcasite under hydrothermal conditions (90-300 °C, vapor saturated pressures), a process associated with gold deposition in a number of ore deposits. The formation of pyrite/marcasite was studied as a function of reaction time, temperature, pH, sulfide concentration, solid-weight-to-fluid-volume ratio, and geometric surface area of magnetite in polytetrafluoroethylene-lined autoclaves (PTFE) and a titanium and stainless steel flow-through cell. Marcasite was formed only at pH 21°C <4 and was the dominant Fe disulfide at pH 21°C 1.11, while pyrite predominated at pH 21°C >2 and formed even under basic conditions (up to pH 21°C 12-13). Marcasite formation was favored at higher temperatures. Fine-grained pyrrhotite formed in the initial stage of the reaction together with pyrite in some experiments with large surface area of magnetite (grain size <125 ?m). This pyrrhotite eventually gave way to pyrite. The transformation rate of magnetite to Fe disulfide increased with decreasing pH (at 120 °C; pH 120°C 0.96-4.42), and that rate of the transformation increased from 120 to 190 °C. Scanning electron microscope (SEM) imaging revealed that micro-pores (0.1-5 ?m scale) existed at the reaction front between the parent magnetite and the product pyrite, and that the pyrite and/or marcasite were euhedral at pH 21°C <4 and anhedral at higher pH. The newly formed pyrite was micro-porous (0.1-5 ?m); this micro-porosity facilitates fluid transport to the reaction interface between magnetite and pyrite, thus promoting the replacement reaction. The pyrite precipitated onto the parent magnetite was polycrystalline and did not preserve the crystallographic orientation of the magnetite. The pyrite precipitation was also observed on the PTFE liner, which is consistent with pyrite crystallizing from solution. The mechanism of the reaction is that of a dissolution-reprecipitation reaction with the precipitation of pyrite being the rate-limiting step relative to magnetite dissolution under mildly acidic conditions (e.g., pH 155°C 4.42). The experimental results are in good agreement with sulfide phase assemblage and textures reported from sulfidized Banded Iron Formations: pyrite, marcasite and pyrrhotite have been found to exist or co-exist in different sulfidized Banded Iron Formations, and the microtextures show no evidence of sub-?m-scale pseudomorphism of magnetite by pyrite.

Qian, Gujie; Brugger, Joël; Skinner, William M.; Chen, Guorong; Pring, Allan

2010-10-01

264

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

PubMed Central

Summary 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.

Murat, Dorothee; Falahati, Veesta; Bertinetti, Luca; Csencsits, Roseann; Kornig, Andre; Downing, Kenneth; Faivre, Damien; Komeili, Arash

2013-01-01

265

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

266

EBSD analysis of electroplated magnetite thin films  

NASA Astrophysics Data System (ADS)

By means of electron backscatter diffraction (EBSD), we analyse the crystallographic orientation of electroplated magnetite thin films on Si/copper substrates. Varying the voltage during the electroplating procedure, the resulting surface properties are differing considerably. While a high voltage produces larger but individual grains on the surface, the surfaces become smoother on decreasing voltage. Good quality Kikuchi patterns could be obtained from all samples; even on individual grains, where the surface and the edges could be measured. The spatial resolution of the EBSD measurement could be increased to about 10 nm; thus enabling a detailed analysis of single magnetite grains. The thin film samples are polycrystalline and do not exhibit a preferred orientation. EBSD reveals that the grain size changes depending on the processing conditions, while the detected misorientation angles stay similar.

Koblischka-Veneva, A.; Koblischka, M. R.; Teng, C. L.; Ryan, M. P.; Hartmann, U.; Mücklich, F.

2010-05-01

267

Electronic structure near antiphase boundaries in magnetite  

NASA Astrophysics Data System (ADS)

Magnetite (Fe3O4) is a magnetic material with potentially interesting properties for applications in spintronics. The promising properties of this oxide are unfortunately affected by several kinds of structural defects which locally modify the electronic structure. We have calculated the density of states in the vicinity of the important defects which are the antiphase boundaries. The calculations have been performed with the LSDA+U approximation. This approximation is suitable to study transition metal oxides with important correlation effects between 3d electrons, as we have first shown for perfect bulk magnetite, by comparing the density of states calculated with the LSDA, LSDA+U, and PBE0 approximations. Our calculations show that antiphase boundaries are responsible for the existence of new localised electron states (defect states) which modify the electric properties, the energy gaps and the Fe magnetic moments.

Arras, R.; Calmels, L.; Warot-Fonrose, B.

2010-01-01

268

The HtrA/DegP family protease MamE is a bifunctional protein with roles in magnetosome protein localization and magnetite biomineralization  

PubMed Central

Summary Magnetotactic bacteria contain nanometer-sized, membrane-bound organelles, called magnetosomes, which are tasked with the biomineralization of small crystals of the iron oxide magnetite allowing the organism to use geomagnetic field lines for navigation. A key player in this process is the HtrA/DegP family protease MamE. In its absence, Magnetospirillum magneticum str AMB-1 is able to form magnetosome membranes but not magnetite crystals, a defect previously linked to the mislocalization of magnetosome proteins. In this work we use a directed genetic approach to find that MamE, and another predicted magnetosome-associated protease, MamO, likely function as proteases in vivo. However, as opposed to the complete loss of mamE where no biomineralization is observed, the protease-deficient variant of this protein still supports the initiation and formation of small, 20 nm-sized crystals of magnetite, too small to hold a permanent magnetic dipole moment. This analysis also reveals that MamE is a bifunctional protein with a protease-independent role in magnetosome protein localization and a protease-dependent role in maturation of small magnetite crystals. Together these results imply the existence of a previously unrecognized “checkpoint” in biomineralization where MamE moderates the completion of magnetite formation and thus committal to magneto-aerotaxis as the organism’s dominant mode of navigating the environment.

Quinlan, Anna; Murat, Dorothee; Vali, Hojatollah; Komeili, Arash

2011-01-01

269

Magnetite Biomineralization in the Human Brain  

Microsoft Academic Search

Although the mineral magnetite (Fe_3O_4) is precipitated biochemically by bacteria, protists, and a variety of animals, it has not been documented previously in human tissue. Using an ultrasensitive superconducting magnetometer in a clean-lab environment, we have detected the presence of ferromagnetic material in a variety of tissues from the human brain. Magnetic particle extracts from solubilized brain tissues examined with

Joseph L. Kirschvink; Atsuko Kobayashi-Kirschvink; Barbara J. Woodford

1992-01-01

270

High-pressure phase of magnetite  

Microsoft Academic Search

Mössbauer spectroscopy and x-ray diffraction were employed to investigate the magnetic and structural properties of the high-pressure monoclinic phase of magnetite. Measurements were performed to 66 GPa at 300 K using diamond anvil cells. Based primarily upon the Mössbauer parameters, the following features of the high-pressure phase were deduced. With increasing pressure the high-pressure phase evolves at P>=25 GPa and

Moshe Paz Pasternak; Saburo Nasu; Koji Wada; Shoichi Endo

1994-01-01

271

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.

2012-01-01

272

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

273

Mechanisms in the First Stage of Oxidation of Magnetites  

Microsoft Academic Search

THE oxidation of magnetite is a two-stage process. The final product of the second stage of oxidation is always alpha-Fe2O3 formed from residual magnetite, and\\/or from the product of the first stage of oxidation. During the first stage, several reactions are possible, according to the mode of formation and the characteristics of the magnetite1-3.

U. Colombo; G. Fagherazzi; F. Gazzarrini; G. Lanzavecchia; G. Sironi

1964-01-01

274

Experimental studies of magnetite formation in the solar nebula  

Microsoft Academic Search

Oxidation of Fe metal and Gibeon meteorite metal to magnetite via the net reaction 3 Fe (metal) + 4 H2O (gas) = Fe3O4 (magnetite) + 4 H2 (gas) was experimentally studied at ambient atmospheric pressure at 91-442oC in H2 and H2-He gas mixtures with H2\\/H2O molar ratios of ~4-41. The magnetite produced was identified by X-ray diffraction. Electron microprobe analyses

Y. Hong; B. Fegley Jr.

1998-01-01

275

Preparation and characterization of magnetite nanoparticles coated by amino silane  

Microsoft Academic Search

Magnetite nanoparticles were prepared by coprecipitation of Fe2+ and Fe3+ with NH4OH, and then, amino silane was coated onto the surface of the magnetite nanoparticles. Transmission electronic microscopy shows the average size of 7.5 nm in diameter. Powder X-ray diffraction and electronic diffraction measurements show the spinel structure for the magnetite nanoparticles. FT–IR spectra indicate that amino silane molecules have

Ming Ma; Yu Zhang; Wei Yu; Hao-ying Shen; Hai-qian Zhang; Ning Gu

2003-01-01

276

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

277

The study on magnetite particles coated with bilayer surfactants  

NASA Astrophysics Data System (ADS)

Magnetite particles were prepared by co-precipitation, then sodium oleic (SO) and sodium dodecyl benzene sulfonate (SDBS) were applied as inner and outer surfactants, respectively. IR and TG were used to study the surface adsorption of SO and SDBS on magnetite particles. The experimental results demonstrated that SO molecules were linked to the magnetite particles through chemical bond and SDBS coated on the surface of magnetite particles covered with SO by means of Van der Waals attraction. Furthermore, based on the adsorption isotherms of surfactants on the magnetite particles and the dependence of Zeta potential of particles on the surfactants concentrations, the adsorption mechanisms of these two surfactants on the magnetite particles were studied. The isotherm adsorption model for SO on magnetite particles showed excellent correlation to Langmuir type and the adsorption equation was ?=0.162c1+0.303c (25 °C), while that for SDBS on magnetite particles coated with SO showed excellent consistence with Freundlich type and the adsorption equation was ? = 0.32 c0.475 (25 °C). In addition, the results demonstrated that both SO and SDBS formed monolayer adsorption on the surface of magnetite particles.

Wang, Xuman; Zhang, Caining; Wang, Xiaoliang; Gu, Hongchen

2007-07-01

278

A Magnetite-Dolomite-rich Clast in Orgueil: Differentiation on the CI Parent Body  

NASA Astrophysics Data System (ADS)

In a thin section of CI Orgueil a 4x5 mm clast was found with an unusual composition. It consists mainly of magnetite (63 wt%) and dolomite (12 wt%) in the usual fine matrix. The magnetite occurs in rounded grains of 5 to 20 micron, occasionally also as framboidal spherules composed of many tiny grains. The dolomite grains have about the same size and rounded shape as the magnetites. The magnetite is chemically very pure, with no element except iron detectable by microprobe (as usual in Orgueil). Dolomite contains, besides Ca and Mg, variable amounts of Mn and Fe. In a Mn vs. Fe diagram they plot in the same area as reported for Orgueil [1], but they show an Fe/Mn anticorrelation, which has not been found before. Mn varies over a wider range than Fe (Fig. 1), so there is not a simple replacement of Mn by Fe, or vice versa. Many dolomite grains show fan-shaped overgrowth towards the matrix; these areas plot at the low-Mn/high-Fe end of the Fe/Mn anticorrelation (Fig. 1). Dolomites sometimes contain tiny spherules of magnetite, often arranged in strings close to their outer margins. The bulk composition of this clast shows more than twice as much Fe and three times as much Ca as Orgueil, and is correspondingly poorer in Mg and Si (Table 1). The matrix composition in the clast is generally similar to that in Orgueil proper, but it is significantly higher in Fe, S, and Ni. The similar compositions of magnetite and dolomite in the clast and in Orgueil proper show that they formed under similar conditions, that is on the parent body [1, 2]. The high enrichment of these minerals must have formed by differentiation on the parent body. This differentiation was no longer isochemical, as so far assumed for all processes on the Orgueil parent body. References: [1] Fredriksson K. and Kerridge J. F. (1988) Meteoritics, 23, 35-44. [2] Johnson C. A. and Prinz M. (1993) GCA, 57, 2843-2852. Table 1: Bulk composition of clast and Orgueil proper Clast^1 Orgueil^2 MgO 11 22 Al2O3 0.5 2.3 SiO2 10 31 S 2.0 7.6 CaO 6.1 1.9 FeO* 69 33 NiO 1.3 1.8 100 100 1 Calculated from mineral compostion and mode. 2 Recalculated from chemical analysis by E. Jarosewich in [1]. * All Fe as FeO.

Wlotzka, F.; Thacker, R.; Fredriksson, K.

1995-09-01

279

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

280

Functional analysis of the magnetosome island in Magnetospirillum gryphiswaldense: the mamAB operon is sufficient for magnetite biomineralization.  

PubMed

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; Schüler, Dirk

2011-01-01

281

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.

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

2011-01-01

282

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

283

Irradiation Softening in Pure Iron Single Crystals.  

National Technical Information Service (NTIS)

The characteristics of irradiation softening in Fe were studied. Results show that irradiation softening effect can be explained by the intrinsic mechanism, namely, the interaction of screw dislocations with randomly dispersed interstitials. At least some...

M. Meshii

1975-01-01

284

Habits of Magnetosome Crystals in Coccoid Magnetotactic Bacteria  

Microsoft Academic Search

High-resolution transmission electron microscopy and electron holography were used to study the habits of exceptionally large magnetite crystals in coccoid magnetotactic bacteria. In addition to the crystal habits, the crystallographic positioning of successive crystals in the magnetosome chain appears to be under strict biological control. Magnetotactic bacteria (MB) contain magnetosomes com- prising nanoscale magnetic iron mineral crystals in membrane vesicles

Ulysses Lins; Martha R. McCartney; Marcos Farina; Richard B. Frankel; Peter R. Buseck

2005-01-01

285

Genes Necessary for Bacterial Magnetite Biomineralization Identified by Transposon Mutagenesis  

NASA Astrophysics Data System (ADS)

Magnetic bacteria synthesize nanoscale crystals of magnetite in intracellular, membrane-bounded organelles (magnetosomes). These crystals are preserved in the fossil record at least as far back as the late Neoproterozoic and have been tentatively identified in much older rocks (1). This fossil record may provide deep time calibration points for molecular evolution studies once the genes involved in biologically controlled magnetic mineralization (BCMM) are known. Further, a genetic and biochemical understanding of BCMM will give insight into the depositional environment and biogeochemical cycles in which magnetic bacteria play a role. The BCMM process is not well understood, though proteins have been identified from the magnetosome membrane and genetic manipulation and biochemical characterization of these proteins are underway. Most of the proteins currently thought to be involved are encoded within the mam cluster, a large cluster of genes whose products localize to the magnetosome membrane and are conserved among magnetic bacteria (2). In an effort to identify all of the genes necessary for bacterial BCMM, we undertook a transposon mutagenesis of Magnetospirillum magneticum AMB-1. Non-magnetic mutants (MNMs) were identified by growth in liquid culture followed by a magnetic assay. The insertion site of the transposon was identified two ways. First MNMs were screened with a PCR assay to determine if the transposon had inserted into the mam cluster. Second, the transposon was rescued from the mutant DNA and cloned for sequencing. The majority insertion sites are located within the mam cluster. Insertion sites also occur in operons which have not previously been suspected to be involved in magnetite biomineralization. None of the insertion sites have occurred within genes reported from previous transposon mutagenesis studies of AMB-1 (3, 4). Two of the non-mam cluster insertion sites occur in operons containing genes conserved particularly between MS-1 and MC-1. We are undertaking a complementation strategy to demonstrate the necessity of these novel genes in BCMM as well as characterizing the phenotypes of the mutants. 1. S. B. R. Chang, J. F. Stolz, J. L. Kirschvink, S. M. Awramik, Precambrian Res. 43, 305-315 (1989). 2. K. Grünberg, C. Wawer, B. M. Tebo, D. Schüler, Appl. Environ. Microbiol. 67, 4573-4582 (2001). 3. A. T. Wahyudi, H. Takeyama, T. Matsunaga, Appl. Biochem. Biotechnol. 91-3, 147-154 (2001). 4. T. Matsunaga, C. Nakamura, J. G. Burgess, K. Sode, J. Bacteriol. 174, 2748-2753 (1992).

Nash, C. Z.; Komeili, A.; Newman, D. K.; Kirschvink, J. L.

2004-12-01

286

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

287

Origin of two Verwey transitions in different generations of magnetite from the Chesapeake Bay impact structure, USA  

NASA Astrophysics Data System (ADS)

We observed two different Verwey transition temperatures in fragments of crystalline basement and impact sediments (suevite and impact breccia) from the Chesapeake Bay impact structure (CBIS), USA. Using low-temperature SIRM, susceptibility and hysteresis properties along with mineralogical observations of magnetite our study aims to the question if this feature can be used as shock indicator in the CBIS rocks. Several studies indicated that the Verwey transition temperature (TV) is pressure sensitive (e.g. Carporzen and Gilder 2010). In the CBIS rocks we distinguished three generations of magnetite (Mang and Kontny submitted manuscript). (1) Primary magnetite in granite from allochthonous and autochthonous crystalline basement has average grain sizes up to some hundreds ?m, shows multidomain magnetic behavior and a regular TV at 120 K. It is assumed to be the precursor mineral for the shocked variety. (2) Shocked magnetite, which is strongly deformed and partially molten, occurs in fragments of crystalline rocks and as single grains in the suevite and impact breccia. These rocks show two Verwey transitions - a regular one and a "low-temperature Verwey transition" (LTV) at around 95 K. These two Verwey transition temperatures can be related to a bimodal grain size distribution of magnetite. While the LTV is related to an oxidized magnetite fraction with small grain sizes (some tens of ?m), the larger grain size fraction (some hundreds of ?m) causes the regular TV. The small grain size fraction contains a distinctly higher amount of oxidized material due to their high surface/volume ratio. Oxidation of magnetite introduces vacancies into the crystal structure, which causes a decrease of the Verwey transition temperature. (3) A secondary magnetite generation, which precipitated from post-impact hydrothermal fluids in the suevite, shows also two Verwey transition temperatures, one at 120 K and a LTV range between 90 and 100 K. This magnetite generation forms clusters consisting of numerous needle-shaped magnetite crystals, which range from few nm to about 10 ?m. Hysteresis properties and FORC confirm this large grain size variation and indicate secondary magnetite to show superparamagnetic to multidomain behavior. The LTV in this generation is linked to thin oxidized surface layers that progressively increase the percentage of the bulk volume, the smaller the grains are. Small variations in grain size thus result in a slightly different TV, whereas the bulk signal of TV appears often as a strongly broadened transition. This study shows that especially the Verwey transition temperature of small magnetite grains reacts very sensitive to surface oxidation. As the Verwey transition temperature of small grains is sensitive to this last overprint, they cannot be used as a reliable pressure indicator, if they occur in natural environments on Earth. References Carpozen, L., Gilder, S.A. (2010) J. Geophys. Res., 115, B05103, doi: 10.1029/2009JB006813. Mang, C., Kontny, A. (submitted manuscript) J. Geophys. Res.

Kontny, A. M.; Mang, C.

2013-05-01

288

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

289

Magnetic anisotropy modulation of magnetite in Fe{sub 3}O{sub 4}/BaTiO{sub 3}(100) epitaxial structures  

SciTech Connect

Temperature dependent magnetometry and transport measurements on epitaxial Fe{sub 3}O{sub 4} films grown on BaTiO{sub 3}(100) single crystals by molecular beam epitaxy show a series of discontinuities, due to changes in the magnetic anisotropy induced by strain from the different crystal phases of BaTiO{sub 3}. The magnetite film is under tensile strain at room temperature, which is ascribed to the lattice expansion of BaTiO{sub 3} at the cubic to tetragonal transition, indicating that the magnetite film is relaxed at the growth temperature. From the magnetization versus temperature curves, the variation in the magnetic anisotropy is determined and compared with the magnetoelastic anisotropies. These results demonstrate the possibility of using the piezoelectric response of BaTiO{sub 3} to modulate the magnetic anisotropy of magnetite films.

Vaz, C. A. F.; Hoffman, J.; Posadas, A.-B.; Ahn, C. H. [Department of Applied Physics and CRISP, Yale University, New Haven, Connecticut 06520 (United States)

2009-01-12

290

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

291

Magnetic Process for Removing Heavy Metals from Water Employing Magnetites.  

National Technical Information Service (NTIS)

A process for removing heavy metals from water is provided. The process includes the steps of introducing magnetite to a quantity of water containing heavy metal. The magnetite is mixed with the water such that at least a portion of, and preferably the ma...

F. C. Prenger D. D. Hill

2003-01-01

292

A comparison of ARM and TRM in magnetite  

Microsoft Academic Search

Experiments comparing anhysteretic remanence (ARM) and thermoremanence (TRM) in samples containing natural and synthetic magnetite, whose mean particle sizes range from single domain to multidomain, show that ARM and TRM are very similar (but not identical) in their stabilities with respect to alternating field (AF) demagnetization, temperature cycles in zero field to below magnetite's isotropic temperature near 130°K, and stability

Shaul Levi; Ronald T. Merrill

1976-01-01

293

Preparation and application of magnetic fluid with magnetite (I).  

National Technical Information Service (NTIS)

Magnetite should be larger than 1 mm in order to supply as the raw materials of iron making industries. In Synemi mine, more than 40 % of the magnetite has not been utilized too fine as iron source. The objects of this study are preparing the magnetic flu...

H. S. Lee D. J. Kim Y. Hwang

1996-01-01

294

Evidence for a relationship between hydrocarbons and authigenic magnetite  

Microsoft Academic Search

Establishing a relationship between hydrocarbon migration and the precipitation of authigenic magnetite in sedimentary rocks is of significant interest with respect to (1) elucidating mechanisms for remagnetization and establishing the origin of secondary magnetizations residing in magnetite, (2) developing a method to date hydrocarbon migration events by determining the time of remanence acquisition by palaeomagnetic methods, and (3) evaluating whether

R. D. Elmore; M. H. Engel; L. Crawford; K. Nick; S. Imbus; Z. Sofer

1987-01-01

295

Magnetite dissolution and corrosion behavior in high temperature EDTA solvents  

Microsoft Academic Search

The effect of temperature on magnetite dissolution and corrosion behavior was evaluated in ethylenediaminetetraacetic acid (EDTA)-based solvents for iron oxide chemical cleaning of nuclear steam generators at temperatures ranging from 93 to 150°C. Magnetite dissolution was drastically accelerated as the temperature was raised to 150°C, while the amount of corrosion was controlled well within an allowable limit. Periodic venting and

Do Haeng Hur; Myung Sik Choi; Uh Chul Kim; Jung Ho Han

2003-01-01

296

MAGNETITE RECOVERY IN COAL WASHING BY HIGH GRADIENT MAGNETIC SEPARATION  

EPA Science Inventory

The report describes a demonstration of the successful recovery of magnetite from mixtures of magnetite and coal, like those found in a coal-washing circuit, by High Gradient Magnetic Separation. The demonstration was part of a research program at Francis Bitter National Magnet L...

297

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

298

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

299

Electrical and magnetic properties of chitosan-magnetite nanocomposites  

NASA Astrophysics Data System (ADS)

Magnetite powders in nanometer size have been synthesized by the hydrothermal process. Various magnetic films of chitosan and the synthesized magnetite nanopowders containing different concentrations of the latter were prepared by ultrasonication route. The X-ray diffraction (XRD) studies and the transmission electron microscopy (TEM) images showed that the synthesized magnetite particles had 80 nm dimensions. The band gap of the composites was evaluated using the UV-visible Spectroscopy. The influence of magnetite content on the magnetic properties of the composite showed a decrease in the saturation magnetization with the decrease in the magnetic content. The effect of magnetite content on the dielectric properties of the polymer film at different frequencies from 0.01 to 105 Hz was studied using an electrochemical impedance spectroscopy. The possible mechanism for the observed electrical properties of the composite films was discussed.

Bhatt, Aarti S.; Krishna Bhat, D.; Santosh, M. S.

2010-04-01

300

Magnetite deformation mechanism maps for better prediction of strain partitioning  

NASA Astrophysics Data System (ADS)

Abstract A meta-analysis of existing experimental deformation data for <span class="hlt">magnetite</span> and other spinel-structured ferrites reveals that previously published flow laws are inadequate to describe the general deformation behavior of <span class="hlt">magnetite</span>. Using updated rate equations for oxygen diffusion in <span class="hlt">magnetite</span>, we present new flow laws that closely predict creep rates similar to those found in deformation experiments and that can be used to predict strain partitioning between cubic Fe oxides and other phases in the Earth's crust. New deformation mechanism maps for <span class="hlt">magnetite</span> have been constructed as functions of temperature and grain size. Using the revised creep parameters, estimates of strain partitioning between <span class="hlt">magnetite</span>, ilmenite, and plagioclase indicate that concentrated zones of Fe-Ti oxides in oceanic crust near slow-spreading ridges could accommodate significant amounts of strain at moderate temperatures and may contribute to aseismic creep along spreading-segment faults.</p> <div class="credits"> <p class="dwt_author">Till, J. L.; Moskowitz, Bruce</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-02-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_14");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a style="font-weight: bold;">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_16");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> </div><!-- page_15 div --> <div id="page_16" class="hiddenDiv"> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_15");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a style="font-weight: bold;">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_17");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">301</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5850618"> <span id="translatedtitle"><span class="hlt">Purely</span> lytic osteosarcoma</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The radiographic features of 42 <span class="hlt">purely</span> lytic osteosarcomas are presented. <span class="hlt">Purely</span> lytic osteosarcoma is identified as a lytic lesion of bone with no demonstrable osteoid matrix by conventional radiographic modalities. <span class="hlt">Purely</span> lytic osteosarcoma represented 13.7% of a group of 305 osteosarcomas. The most common presentation was that of a lytic illdefined lesion with a moderate to large extraosseous mass component. Nine lesions presented with benign radiographic features. The differential diagnosis is outlined. The need for awareness of this type of presentation of osteosarcoma is stressed.</p> <div class="credits"> <p class="dwt_author">De Santos, L.A.; Eideken, B.</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">302</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011OptMa..33.1000R"> <span id="translatedtitle">Optical properties of <span class="hlt">pure</span> Ytterbium Alluminium perovskites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present the first report about growth and optical properties of <span class="hlt">pure</span> Ytterbium Alluminium perovskites single <span class="hlt">crystals</span> (YbAlO 3). The sample <span class="hlt">crystal</span> structure was studied and assigned by means of Raman spectroscopy while the photoluminescence measurements from Yb 3+ charge-transfer state show a broad ultraviolet emission bands with nanosecond lifetimes at room temperature. Yb emissions are also studied as a function of temperature revealing an abrupt quenching in the 180-240 K range. The fast time decay and the high material density suggest Ytterbium Alluminium perovskites <span class="hlt">crystal</span> as a good candidate for the development of fast scintillators for high energy physics applications.</p> <div class="credits"> <p class="dwt_author">Ricci, P. C.; Casu, A.; Chiriu, D.; Corpino, C.; Carbonaro, C. M.; Marceddu, M.; Salis, M.; Anedda, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">303</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/11540500"> <span id="translatedtitle">Origin of <span class="hlt">magnetite</span> in oxidized CV chondrites: in situ measurement of oxygen isotope compositions of Allende <span class="hlt">magnetite</span> and olivine.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary"><span class="hlt">Magnetite</span> in the oxidized CV chondrite Allende mainly occurs as spherical nodules in porphyritic-olivine (PO) chondrules, where it is associated with Ni-rich metal and/or sulfides. To help constrain the origin of the <span class="hlt">magnetite</span>, we measured oxygen isotopic compositions of <span class="hlt">magnetite</span> and coexisting olivine grains in PO chondrules of Allende by an in situ ion microprobe technique. Five <span class="hlt">magnetite</span> nodules form a relatively tight cluster in oxygen isotopic composition with delta 18O values from -4.8 to -7.1% and delta 17O values from -2.9 to -6.3%. Seven coexisting olivine grains have oxygen isotopic compositions from -0.9 to -6.3% in delta 18O and from -4.6 to -7.9% in delta 17O. The delta 17O values of the <span class="hlt">magnetite</span> and coexisting olivine do not overlap; they range from -0.4 to -2.6%, and from -4.0 to -5.7%, respectively. Thus, the <span class="hlt">magnetite</span> is not in isotopic equilibrium with the olivine in PO chondrules, implying that it formed after the chondrule formation. The delta 17O of the <span class="hlt">magnetite</span> is somewhat more negative than estimates for the ambient solar nebula gas. We infer that the <span class="hlt">magnetite</span> formed on the parent asteroid by oxidation of metal by H2O which had previously experienced minor O isotope exchange with fine-grained silicates. PMID:11540500</p> <div class="credits"> <p class="dwt_author">Choi, B G; McKeegan, K D; Leshin, L A; Wasson, J T</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">304</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20040121339&hterms=magnetite+solar&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dmagnetite%2Bsolar"> <span id="translatedtitle">Origin of <span class="hlt">magnetite</span> in oxidized CV chondrites: in situ measurement of oxygen isotope compositions of Allende <span class="hlt">magnetite</span> and olivine</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><span class="hlt">Magnetite</span> in the oxidized CV chondrite Allende mainly occurs as spherical nodules in porphyritic-olivine (PO) chondrules, where it is associated with Ni-rich metal and/or sulfides. To help constrain the origin of the <span class="hlt">magnetite</span>, we measured oxygen isotopic compositions of <span class="hlt">magnetite</span> and coexisting olivine grains in PO chondrules of Allende by an in situ ion microprobe technique. Five <span class="hlt">magnetite</span> nodules form a relatively tight cluster in oxygen isotopic composition with delta 18O values from -4.8 to -7.1% and delta 17O values from -2.9 to -6.3%. Seven coexisting olivine grains have oxygen isotopic compositions from -0.9 to -6.3% in delta 18O and from -4.6 to -7.9% in delta 17O. The delta 17O values of the <span class="hlt">magnetite</span> and coexisting olivine do not overlap; they range from -0.4 to -2.6%, and from -4.0 to -5.7%, respectively. Thus, the <span class="hlt">magnetite</span> is not in isotopic equilibrium with the olivine in PO chondrules, implying that it formed after the chondrule formation. The delta 17O of the <span class="hlt">magnetite</span> is somewhat more negative than estimates for the ambient solar nebula gas. We infer that the <span class="hlt">magnetite</span> formed on the parent asteroid by oxidation of metal by H2O which had previously experienced minor O isotope exchange with fine-grained silicates.</p> <div class="credits"> <p class="dwt_author">Choi, B. G.; McKeegan, K. D.; Leshin, L. A.; Wasson, J. T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">305</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6955949"> <span id="translatedtitle">Geomorphology: <span class="hlt">Pure</span> and applied</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The book summarizes the history of intellectual debate in geomorphology and describes modern developments both ''<span class="hlt">pure</span>'' and ''applied.'' The history begins well before W.M. Davis and follows through to such debates as those concerned with the Pleistocene. Modern developments in <span class="hlt">pure</span> geomorphology are cast in terms of chapters on form, process, materials, and methods analysis. The applied chapters concentrate on environmental hazards and resources, and their management.</p> <div class="credits"> <p class="dwt_author">Hart, M.G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">306</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/23145573"> <span id="translatedtitle">Hexagonal platelet-like <span class="hlt">magnetite</span> 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.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">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 <span class="hlt">magnetite</span> <span class="hlt">crystals</span> characterized by a wide distribution in size and irregular morphologies that are indistinguishable from authigenic <span class="hlt">magnetite</span>. 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 <span class="hlt">magnetite</span> with a size up to 120?nm. In this study, I first characterize the formation of hexagonal platelet-like <span class="hlt">magnetite</span> of a few hundred nanometers in cultures of Thermoanaerobacter spp. strain TOR39. Biogenic <span class="hlt">magnetite</span> with such large <span class="hlt">crystal</span> 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 <span class="hlt">crystals</span> 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 <span class="hlt">magnetite</span> in banded iron formations that deposited only in the first 2 billion years of Earth with evidence of life. PMID:23145573</p> <div class="credits"> <p class="dwt_author">Li, Yi-Liang</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">307</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/23889511"> <span id="translatedtitle">The magnetosome proteins MamX, MamZ and MamH are involved in redox control of <span class="hlt">magnetite</span> biomineralization in Magnetospirillum gryphiswaldense.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Magnetospirillum gryphiswaldense uses intracellular chains of membrane-enveloped <span class="hlt">magnetite</span> <span class="hlt">crystals</span>, the magnetosomes, to navigate within magnetic fields. The biomineralization of <span class="hlt">magnetite</span> nanocrystals requires several magnetosome-associated proteins, whose precise functions so far have remained mostly unknown. Here, we analysed the functions of MamX and the Major Facilitator Superfamily (MFS) proteins MamZ and MamH. Deletion of either the entire mamX gene or elimination of its putative haem c-binding magnetochrome domains, and deletion of either mamZ or its C-terminal ferric reductase-like component resulted in an identical phenotype. All mutants displayed WT-like <span class="hlt">magnetite</span> <span class="hlt">crystals</span>, flanked within the magnetosome chains by poorly crystalline flake-like particles partly consisting of haematite. Double deletions of both mamZ and its homologue mamH further impaired <span class="hlt">magnetite</span> <span class="hlt">crystallization</span> in an additive manner, indicating that the two MFS proteins have partially redundant functions. Deprivation of ?mamX and ?mamZ cells from nitrate, or additional loss of the respiratory nitrate reductase Nap from ?mamX severely exacerbated the magnetosome defects and entirely inhibited the formation of regular <span class="hlt">crystals</span>, suggesting that MamXZ and Nap have similar, but independent roles in redox control of biomineralization. We propose a model in which MamX, MamZ and MamH functionally interact to balance the redox state of iron within the magnetosome compartment. PMID:23889511</p> <div class="credits"> <p class="dwt_author">Raschdorf, Oliver; Müller, Frank D; Pósfai, Mihály; Plitzko, Jürgen M; Schüler, Dirk</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">308</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/23594814"> <span id="translatedtitle">Controlled cobalt doping in biogenic <span class="hlt">magnetite</span> nanoparticles.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Cobalt-doped <span class="hlt">magnetite</span> (CoxFe3 -xO4) nanoparticles have been produced through the microbial reduction of cobalt-iron oxyhydroxide by the bacterium Geobacter sulfurreducens. The materials produced, as measured by superconducting quantum interference device magnetometry, X-ray magnetic circular dichroism, Mössbauer spectroscopy, etc., show dramatic increases in coercivity with increasing cobalt content without a major decrease in overall saturation magnetization. Structural and magnetization analyses reveal a reduction in particle size to less than 4 nm at the highest Co content, combined with an increase in the effective anisotropy of the magnetic nanoparticles. The potential use of these biogenic nanoparticles in aqueous suspensions for magnetic hyperthermia applications is demonstrated. Further analysis of the distribution of cations within the ferrite spinel indicates that the cobalt is predominantly incorporated in octahedral coordination, achieved by the substitution of Fe(2+) site with Co(2+), with up to 17 per cent Co substituted into tetrahedral sites. PMID:23594814</p> <div class="credits"> <p class="dwt_author">Byrne, J M; Coker, V S; Moise, S; Wincott, P L; Vaughan, D J; Tuna, F; Arenholz, E; van der Laan, G; Pattrick, R A D; Lloyd, J R; Telling, N D</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">309</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1810097"> <span id="translatedtitle">Biogenic <span class="hlt">magnetite</span> in the nematode caenorhabditis elegans.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">The nematode Caenorhabditis elegans is widely used as a model system in biological research. Recently, examination of the production of heat-shock proteins in this organism in response to mobile phone-type electromagnetic field exposure produced the most robust demonstration to date of a non-thermal, deleterious biological effect. Though these results appear to be a sound demonstration of non-thermal bioeffects, to our knowledge, no mechanism has been proposed to explain them. We show, apparently for the first time, that biogenic <span class="hlt">magnetite</span>, a ferrimagnetic iron oxide, is present in C. elegans. Its presence may have confounding effects on experiments involving electromagnetic fields as well as implications for the use of this nematode as a model system for iron biomineralization in multi-cellular organisms.</p> <div class="credits"> <p class="dwt_author">Cranfield, Charles G; Dawe, Adam; Karloukovski, Vassil; Dunin-Borkowski, Rafal E; de Pomerai, David; Dobson, Jon</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">310</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013NatMa..12..310B"> <span id="translatedtitle">Nucleation and growth of <span class="hlt">magnetite</span> from solution</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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 <span class="hlt">magnetite</span>—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.</p> <div class="credits"> <p class="dwt_author">Baumgartner, Jens; Dey, Archan; Bomans, Paul H. H.; Le Coadou, Cécile; Fratzl, Peter; Sommerdijk, Nico A. J. M.; Faivre, Damien</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">311</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3645421"> <span id="translatedtitle">Controlled cobalt doping in biogenic <span class="hlt">magnetite</span> nanoparticles</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">Cobalt-doped <span class="hlt">magnetite</span> (CoxFe3 ?xO4) nanoparticles have been produced through the microbial reduction of cobalt–iron oxyhydroxide by the bacterium Geobacter sulfurreducens. The materials produced, as measured by superconducting quantum interference device magnetometry, X-ray magnetic circular dichroism, Mössbauer spectroscopy, etc., show dramatic increases in coercivity with increasing cobalt content without a major decrease in overall saturation magnetization. Structural and magnetization analyses reveal a reduction in particle size to less than 4 nm at the highest Co content, combined with an increase in the effective anisotropy of the magnetic nanoparticles. The potential use of these biogenic nanoparticles in aqueous suspensions for magnetic hyperthermia applications is demonstrated. Further analysis of the distribution of cations within the ferrite spinel indicates that the cobalt is predominantly incorporated in octahedral coordination, achieved by the substitution of Fe2+ site with Co2+, with up to 17 per cent Co substituted into tetrahedral sites.</p> <div class="credits"> <p class="dwt_author">Byrne, J. M.; Coker, V. S.; Moise, S.; Wincott, P. L.; Vaughan, D. J.; Tuna, F.; Arenholz, E.; van der Laan, G.; Pattrick, R. A. D.; Lloyd, J. R.; Telling, N. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">312</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009JMMM..321.3093M"> <span id="translatedtitle">Studies of <span class="hlt">magnetite</span> nanoparticles synthesized by thermal decomposition of iron (III) acetylacetonate in tri(ethylene glycol)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In this paper, water-soluble <span class="hlt">magnetite</span> nanoparticles have been directly synthesized by thermal decomposition of iron (III) acetylacetonate, Fe(acac) 3 in tri(ethyleneglycol). Size and morphology of the nanoparticles are determined by transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements while the <span class="hlt">crystal</span> structure is identified using X-ray diffraction (XRD). Surface charge and surface coating of the nanoparticles are recognized using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectra (XPS) and zeta potential measurements. Magnetic properties are determined using vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID) measurements. The results show that as-prepared <span class="hlt">magnetite</span> nanoparticles are relatively monodisperse, single crystalline and superparamagnetic in nature with the blocking temperature at around 100 K. The <span class="hlt">magnetite</span> nanoparticles are found to be highly soluble in water due to steric and electrostatic interactions between the particles arising by the surface adsorbed tri(ethyleneglycol) molecules and associated positive charges, respectively. Cytotoxicity studies on human cervical (SiHa), mouse melanoma (B16F10) and mouse primary fibroblast cells demonstrate that up to a dose of 80 ?g/ml, the magnetic nanoparticles are nontoxic to the cells. Specific absorption rate (SAR) value has been calculated to be 885 and 539 W/gm for samples with the iron concentration of 1 and 0.5 mg/ml, respectively. The high SAR value upon exposure to 20 MHz radiofrequency signifies the applicability of as-prepared <span class="hlt">magnetite</span> nanoparticles for a feasible magnetic hyperthermia treatment.</p> <div class="credits"> <p class="dwt_author">Maity, Dipak; Kale, S. N.; Kaul-Ghanekar, Ruchika; Xue, Jun-Min; Ding, Jun</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">313</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dx.doi.org/10.1039/c1ja10105f"> <span id="translatedtitle">LA-ICP-MS of <span class="hlt">magnetite</span>: Methods and reference materials</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary"><span class="hlt">Magnetite</span> (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 <span class="hlt">magnetite</span>. Laser ablation ICP-MS (LA-ICP-MS) is applicable to trace element analyses of <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span>. LA-ICP-MS analyses were carried out on well characterized <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span>. Cross-comparison between the NIST SRM 610 and USGS GSE-1G indicates good agreement for <span class="hlt">magnetite</span> 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.</p> <div class="credits"> <p class="dwt_author">Nadoll, P.; Koenig, A. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">314</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/963194"> <span id="translatedtitle">Reduction of Hg(II) to Hg(0) by <span class="hlt">Magnetite</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Mercury (Hg) is a highly toxic element, and its contamination of groundwater presents a significant threat to terrestrial ecosystems. Understanding the geochemical processes that mediate mercury transformations in the subsurface is necessary to predict its fate and transport. In this study, we investigated the redox transformation of mercuric Hg (Hg[II]) in the presence of the Fe(II)/Fe(III) mixed valence iron oxide mineral <span class="hlt">magnetite</span>. Kinetic and spectroscopic experiments were performed to elucidate reaction rates and mechanisms. The experimental data demonstrated that reaction of Hg(II) with <span class="hlt">magnetite</span> results in the loss of Hg(II) and the formation of volatile elemental Hg (Hg[0]). Kinetic experiments showed that Hg(II) reduction occurred within minutes, with reaction rates increasing with increasing <span class="hlt">magnetite</span> suspension density (0.05 to 0.2 g/L) and solution pH (4.8 to 6.7), and decreasing with increasing chloride concentration (10-6 to 10-2 mol/L). Mössbauer spectroscopic analysis of reacted <span class="hlt">magnetite</span> samples revealed a decrease in Fe(II) content, corresponding the oxidation of Fe(II) to Fe(III) in the <span class="hlt">magnetite</span> structure. X-ray photoelectron spectroscopy detected the presence of Hg(II) on <span class="hlt">magnetite</span> surfaces, suggesting that adsorption is involved in the electron transfer process. These results suggest that Hg(II) reaction with solid-phase Fe(II) is a kinetically favorable pathway for Hg(II) reduction in <span class="hlt">magnetite</span>-bearing environmental systems.</p> <div class="credits"> <p class="dwt_author">Wiatrowski, Heather A.; Das, Soumya; Kukkadapu, Ravi K.; Ilton, Eugene S.; Barkay, Tamar; Yee, Nathan</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-06-12</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">315</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/19708358"> <span id="translatedtitle">Reduction of Hg(II) to Hg(0) by <span class="hlt">magnetite</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Mercury (Hg) is a highly toxic element, and its contamination of groundwater presents a significant threat to terrestrial ecosystems. Understanding the geochemical processes that mediate mercury transformations in the subsurface is necessary to predict its fate and transport. In this study, we investigated the redox transformation of mercuric Hg (Hg[II]) in the presence of the Fe(II)/Fe(III) mixed valence iron oxide mineral <span class="hlt">magnetite</span>. Kinetic and spectroscopic experiments were performed to elucidate reaction rates and mechanisms. The experimental data demonstrated that reaction of Hg(II) with <span class="hlt">magnetite</span> resulted in the loss of Hg(II) and the formation of volatile elemental Hg (Hg[0]). Kinetic experiments showed that Hg(II) reduction occurred within minutes, with reaction rates increasing with increasing <span class="hlt">magnetite</span> surface area (0.5 to 2 m2/L) and solution pH (4.8 to 6.7), and decreasing with increasing chloride concentration (10(-6) to 10(-2) mol/L). Mössbauer spectroscopic analysis of reacted <span class="hlt">magnetite</span> samples revealed a decrease in Fe(II) content, corresponding to the oxidation of Fe(II) to Fe(III) in the <span class="hlt">magnetite</span> structure. X-ray photoelectron spectroscopy detected the presence of Hg(II) on <span class="hlt">magnetite</span> surfaces, implying that adsorption is involved in the electron transfer process. These results suggest that Hg(II) reaction with solid-phase Fe(II) is a kinetically favorable pathway for Hg(II) reduction in <span class="hlt">magnetite</span>-hearing environmental systems. PMID:19708358</p> <div class="credits"> <p class="dwt_author">Wiatrowski, Heather A; Das, Soumya; Kukkadapu, Ravi; Ilton, Eugene S; Barkay, Tamar; Yee, Nathan</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-07-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">316</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=AD645922"> <span id="translatedtitle">Effects of Energy GAP Anisotropy in <span class="hlt">Pure</span> Superconductors.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">Various effects of anisotropy of the superconducting energy gap are theoretically considered. In order to estimate the effects of anisotropy upon the thermodynamic properties of <span class="hlt">pure</span>, single-<span class="hlt">crystal</span> superconductors, a factorable BCS-like model for the eff...</p> <div class="credits"> <p class="dwt_author">J. R. Clem</p> <p class="dwt_publisher"></p> <p class="publishDate">1966-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">317</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/17905250"> <span id="translatedtitle"><span class="hlt">Pure</span> uterine lipoma.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">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, <span class="hlt">pure</span> uterine lipomas are extremely rare. In the literature, a few cases with <span class="hlt">pure</span> uterine lipoma have been reported. We first present the advanced magnetic resonance findings of <span class="hlt">pure</span> 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</p> <div class="credits"> <p class="dwt_author">Erdem, Gulnur; Celik, Onder; Karakas, Hakki Muammer; Alkan, Alpay; Hascalik, Seyma</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">318</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1987Natur.325..428E"> <span id="translatedtitle">Evidence for a relationship between hydrocarbons and authigenic <span class="hlt">magnetite</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Establishing a relationship between hydrocarbon migration and the precipitation of authigenic <span class="hlt">magnetite</span> in sedimentary rocks is of significant interest with respect to (1) elucidating mechanisms for remagnetization and establishing the origin of secondary magnetizations residing in <span class="hlt">magnetite</span>, (2) developing a method to date hydrocarbon migration events by determining the time of remanence acquisition by palaeomagnetic methods, and (3) evaluating whether searching for anomalous concentrations of diagenetic magnetic minerals and/or aeromagnetic anomalies is justified as a relatively inexpensive exploration tool. The direct association of hydrocarbon migration and the precipitation of authigenic <span class="hlt">magnetite</span> has, however, not been established. In this paper we report palaeomagnetic, rock magnetic, petrographic and geochemical results of a study of samples from Permian spelebthems and gilsonite found in the Ordovician Arbuckle Group in southern Oklahoma. The results indicate that there is a genetic relationship between hydrocarbon migration and the precipitation of authigenic <span class="hlt">magnetite</span>.</p> <div class="credits"> <p class="dwt_author">Elmore, R. D.; Engel, M. H.; Crawford, L.; Nick, K.; Imbus, S.; Sofer, Z.</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">319</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/1003113"> <span id="translatedtitle">Magnetic Properties of Bio-Synthesized <span class="hlt">Magnetite</span> Nanoparticles</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Magnetic nanoparticles, which are unique because of both structural and functional elements, have various novel applications. The popularity and practicality of nanoparticle materials create a need for a synthesis method that produces quality particles in sizable quantities. This paper describes such a method, one that uses bacterial synthesis to create nanoparticles of <span class="hlt">magnetite</span>. The thermophilic bacterial strain Thermoanaerobacter ethanolicus TOR-39 was incubated under anaerobic conditions at 65 C for two weeks in aqueous solution containing Fe ions from a <span class="hlt">magnetite</span> precursor (akaganeite). <span class="hlt">Magnetite</span> particles formed outside of bacterial cells. We verified particle size and morphology by using dynamic light scattering, X-ray diffraction, and transmission electron microscopy. Average crystallite size was 45 nm. We characterized the magnetic properties by using a superconducting quantum interference device magnetometer; a saturation magnetization of 77 emu/g was observed at 5 K. These results are comparable to those for chemically synthesized <span class="hlt">magnetite</span> nanoparticles.</p> <div class="credits"> <p class="dwt_author">Rawn, Claudia J [ORNL; Yeary, Lucas W [ORNL; Moon, Ji Won [ORNL; Love, Lonnie J [ORNL; Thompson, James R [ORNL; Phelps, Tommy Joe [ORNL</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">320</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/23607663"> <span id="translatedtitle">Comparative genomic analysis of magnetotactic bacteria from the Deltaproteobacteria provides new insights into <span class="hlt">magnetite</span> and greigite magnetosome genes required for magnetotaxis.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Magnetotactic bacteria (MTB) represent a group of diverse motile prokaryotes that biomineralize magnetosomes, the organelles responsible for magnetotaxis. Magnetosomes consist of intracellular, membrane-bounded, tens-of-nanometre-sized <span class="hlt">crystals</span> of the magnetic minerals <span class="hlt">magnetite</span> (Fe3O4) or greigite (Fe3S4) and are usually organized as a chain within the cell acting like a compass needle. Most information regarding the biomineralization processes involved in magnetosome formation comes from studies involving Alphaproteobacteria species which biomineralize cuboctahedral and elongated prismatic <span class="hlt">crystals</span> of <span class="hlt">magnetite</span>. Many magnetosome genes, the mam genes, identified in these organisms are conserved in all known MTB. Here we present a comparative genomic analysis of magnetotactic Deltaproteobacteria that synthesize bullet-shaped <span class="hlt">crystals</span> of <span class="hlt">magnetite</span> and/or greigite. We show that in addition to mam genes, there is a conserved set of genes, designated mad genes, specific to the magnetotactic Deltaproteobacteria, some also being present in Candidatus Magnetobacterium bavaricum of the Nitrospirae phylum, but absent in the magnetotactic Alphaproteobacteria. Our results suggest that the number of genes associated with magnetotaxis in magnetotactic Deltaproteobacteria is larger than previously thought. We also demonstrate that the minimum set of mam genes necessary for magnetosome formation in Magnetospirillum is also conserved in <span class="hlt">magnetite</span>-producing, magnetotactic Deltaproteobacteria. Some putative novel functions of mad genes are discussed. PMID:23607663</p> <div class="credits"> <p class="dwt_author">Lefèvre, Christopher T; Trubitsyn, Denis; Abreu, Fernanda; Kolinko, Sebastian; Jogler, Christian; de Almeida, Luiz Gonzaga Paula; de Vasconcelos, Ana Tereza R; Kube, Michael; Reinhardt, Richard; Lins, Ulysses; Pignol, David; Schüler, Dirk; Bazylinski, Dennis A; Ginet, Nicolas</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-10-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_15");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a style="font-weight: bold;">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_17");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> </div><!-- page_16 div --> <div id="page_17" class="hiddenDiv"> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_16");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a style="font-weight: bold;">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_18");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">321</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/1025420"> <span id="translatedtitle">Electrophoretic mobility of <span class="hlt">magnetite</span> particles in high temperature water</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary"><span class="hlt">Magnetite</span>(Fe3O4) isoneofthemostcommonoxidesformingdepositsandparticulatephasesin industrialhightemperaturewatercircuits.Itscolloidalcharacteristicsplayaprincipalroleinthe mechanismofdepositformationandcanbeusedascontrollingfactorstopreventorminimizedeposit formationanddamageofindustrialpipelinesduetounder-depositcorrosion.Inthisstudy,ahigh temperatureparticleelectrophoresistechniquewasemployedtomeasurethezetapotentialatthe <span class="hlt">magnetite</span>/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.</p> <div class="credits"> <p class="dwt_author">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</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">322</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/46502999"> <span id="translatedtitle">High voltage microscopy of the reduction of hematite to <span class="hlt">magnetite</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The microstructural changes associated with the formation of <span class="hlt">magnetite</span> in hematite have been studied in specimens which have\\u000a been partially reduced outside the microscope, thinned until electron transparent, and then examined in the normal way. Three\\u000a types of structure have been observed in varying proportions which depend on the reduction temperature. At low temperatures,\\u000a <span class="hlt">magnetite</span> grows by the propagation of</p> <div class="credits"> <p class="dwt_author">P. R. Swann; N. J. Tighe</p> <p class="dwt_publisher"></p> <p class="publishDate">1977-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">323</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40109811"> <span id="translatedtitle">Electromagnetic methods of detecting <span class="hlt">magnetite</span> in PWR steam generators</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Corrosion products consisting primarily of <span class="hlt">magnetite</span> (Fe3O4) in the crevice gap between steam generator tubes and support plates can eventually lead to tube denting and support plate\\u000a fractures. In order to mitigate this problem, chemical flushing is used to remove the <span class="hlt">magnetite</span> deposit from the crevice gaps.\\u000a NDE techniques are needed to measure the effectiveness of this chemical flushing procedure</p> <div class="credits"> <p class="dwt_author">W. Lord; R. Palanisamy; S. R. Satish</p> <p class="dwt_publisher"></p> <p class="publishDate">1983-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">324</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/18473765"> <span id="translatedtitle">Synthesis of <span class="hlt">magnetite</span> nanoparticles for AC magnetic heating</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary"><span class="hlt">Magnetite</span> particles with different average diameter (Dm) suitable for magnetic fluid hyperthermia (MFH) were synthesized by controlled coprecipitation technique. In this method, the reaction pH was stabilized using the pH buffer and the average particle diameter decreased with increasing reaction pH. The size-dependent magnetic behavior of the <span class="hlt">magnetite</span> nanoparticles was studied and the optimum size range required for magnetic fluid</p> <div class="credits"> <p class="dwt_author">T. Hosono; H. Takahashi; A. Fujita; R. Justin Joseyphus; K. Tohji; B. Jeyadevan</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">325</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/57510555"> <span id="translatedtitle">Removal of heavy metals by immobilized <span class="hlt">magnetite</span> nano-particles</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Nano-sized <span class="hlt">magnetite</span> homogenous porous layer was immobilized onto modified granular activated carbon and used as an adsorbent for copper (Cu(II)) and chromium (Cr(VI)). Batch adsorption experiments revealed high efficiency for both metals removal attaining maximum adsorption capacity of 590 mg\\/g Fe. Significant difference in the reaction kinetics was found between the two metals suggesting that the <span class="hlt">magnetite</span> affinity towards the</p> <div class="credits"> <p class="dwt_author">Adva Zach-Maor; Raphael Semiat; Hilla Shemer</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">326</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52823739"> <span id="translatedtitle">Mesoporous silica <span class="hlt">magnetite</span> nanocomposite synthesized by using a neutral surfactant</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary"><span class="hlt">Magnetite</span> nanoparticles coated by mesoporous silica were synthesized by an alternative chemical route using a neutral surfactant and without the application of any functionalization method. The <span class="hlt">magnetite</span> (Fe3O4) nanoparticles were prepared by precipitation from aqueous media, and then coated with mesoporous silica by using nonionic block copolymer surfactants as the structure-directing agents. The mesoporous SiO2-coated Fe3O4 samples were characterized by</p> <div class="credits"> <p class="dwt_author">K. C. Souza; G. Salazar-Alvarez; J. D. Ardisson; W. A. A. Macedo; E. M. B. Sousa</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">327</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/61309061"> <span id="translatedtitle">Mechanism of fast growth of <span class="hlt">magnetite</span> on carbon steel</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The corrosion of and the growth of <span class="hlt">magnetite</span> on carbon steel in chloride-containing aqueous solutions at temperatures from 200 to 270°C and for times up to 400 hours have been studied using ac impedance and scanning electron microscopy techniques. Thick and porous <span class="hlt">magnetite</span> films form in solutions which are acidic because of the presence of HCL or by hydrolysis of</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">328</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40507895"> <span id="translatedtitle">Synthesis and physical characterization of <span class="hlt">magnetite</span> nanoparticles for biomedical applications</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Iron oxide nanoparticles for biomedical applications in the size range of 15–130nm were prepared by either oxidative hydrolysis of ferrous sulfate with KOH or precipitation from ferrous\\/ferric chloride solutions. The <span class="hlt">magnetite</span> particle size is controlled by variation of pH and temperature. The synthesized <span class="hlt">magnetite</span> nanoparticles are partially oxidized as signaled by ferrous concentrations of below 24wt% Fe2+ and lattice parameters</p> <div class="credits"> <p class="dwt_author">Julia Mürbe; Annett Rechtenbach; Jörg Töpfer</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">329</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/14865371"> <span id="translatedtitle"><span class="hlt">Magnetite</span> formation by a sulphate-reducing bacterium</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">BACTERIAL production of <span class="hlt">magnetite</span> (Fe3O4)1 makes an important contribution to iron biomineralization and rcmanent magnetization of sediments2,3. Accurate magnetostratigraphy, reconstruction of the Earth's past magnetic-field behaviour and extraction of environmental information from the geomagnetic record depend on an understanding of the conditions under which bacterial <span class="hlt">magnetite</span> is formed. In aquatic sediments, the process is thought to be restricted to a</p> <div class="credits"> <p class="dwt_author">Toshifumi Sakaguchi; J. Grant Burgess; Tadashi Matsunaga</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">330</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009GeCoA..73.6631T"> <span id="translatedtitle">Origins of <span class="hlt">magnetite</span> nanocrystals in Martian meteorite ALH84001</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks. These carbonate disks are believed to have precipitated 3.9 Ga ago at beginning of the Noachian epoch on Mars during which both the oldest extant Martian surfaces were formed, and perhaps the earliest global oceans. Intimately associated within and throughout these carbonate disks are nanocrystal <span class="hlt">magnetites</span> (Fe 3O 4) with unusual chemical and physical properties, whose origins have become the source of considerable debate. One group of hypotheses argues that these <span class="hlt">magnetites</span> are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of <span class="hlt">magnetite</span> and carbonate may be unrelated; that is, from the perspective of the carbonate the <span class="hlt">magnetite</span> is allochthonous. For example, the <span class="hlt">magnetites</span> might have already been present in the aqueous fluids from which the carbonates were believed to have been deposited. We have sought to resolve between these hypotheses through the detailed characterization of the compositional and structural relationships of the carbonate disks and associated <span class="hlt">magnetites</span> with the orthopyroxene matrix in which they are embedded. Extensive use of focused ion beam milling techniques has been utilized for sample preparation. We then compared our observations with those from experimental thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios. We conclude that the vast majority of the nanocrystal <span class="hlt">magnetites</span> present in the carbonate disks could not have formed by any of the currently proposed thermal decomposition scenarios. Instead, we find there is considerable evidence in support of an alternative allochthonous origin for the <span class="hlt">magnetite</span> unrelated to any shock or thermal processing of the carbonates.</p> <div class="credits"> <p class="dwt_author">Thomas-Keprta, K. L.; Clemett, S. J.; McKay, D. S.; Gibson, E. K.; Wentworth, S. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">331</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/54704915"> <span id="translatedtitle">Monodisperse <span class="hlt">magnetite</span> nanofluids: Synthesis, aggregation, and thermal conductivity</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Magnetic nanofluids possess some unique properties that can significantly affect their thermal conductivity. We synthesize monodispersed <span class="hlt">magnetite</span> (Fe3O4) nanofluids in toluene with the particle size from 4 to 12 nm and obtain aqueous nanofluids by a simple ``one-step'' phase transfer. Even without the effect of external field, the magnetic-interaction-induced self-assembled aggregation can still be significant in <span class="hlt">magnetite</span> nanofluids. Investigation of</p> <div class="credits"> <p class="dwt_author">Wei Jiang; Liqiu Wang</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">332</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6895081"> <span id="translatedtitle"><span class="hlt">Magnetite</span> authigenesis and diagenetic paleotemperatures across the northern Appalachian basin</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The concentration of <span class="hlt">magnetite</span> in the Lower and Middle Devonian Helderberg and Onondaga carbonate formations varies in a distinct pattern along an east-west profile across New York State. <span class="hlt">Magnetite</span> concentrations are uniformly low in the western half of the profile, increase sharply eastward to a peak value near Syracuse, and decrease farther east. The pattern strongly resembles previously reported variations in the extent of clay mineral diagenesis that reflect differences in paleotemperatures along the profile. Previous paleomagnetic studies have documented that the <span class="hlt">magnetite</span> carries a well-defined magnetization of Pennsylvanian-Permian age, and <span class="hlt">magnetite</span> authigenesis is therefore no younger than late Paleozoic. The authors attribute the correlation between high <span class="hlt">magnetite</span> concentration and high illite content to temperature-dependent diagenesis triggered by orogenic fluids. The large proportion of secondary <span class="hlt">magnetite</span> indicates that over most of the area, the mechanism of late Paleozoic remagnetization was principally chemical. Thermal effects played a less direct role in the remagnetization of the strata by controlling the extent of the chemical processes that resulted in overprinting of the original remanence.</p> <div class="credits"> <p class="dwt_author">Jackson, M.; McCabe, C.; Ballard, M.M.; Van der Voo, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">333</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/22147200"> <span id="translatedtitle"><span class="hlt">Magnetite</span> induces oxidative stress and apoptosis in lung epithelial cells.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">There is an ongoing concern regarding the biocompatibility of nanoparticles with sizes less than 100 nm as compared to larger particles of the same nominal substance. In this study, we investigated the toxic properties of <span class="hlt">magnetite</span> stabilized with polyacrylate sodium. The <span class="hlt">magnetite</span> was characterized by X-ray powder diffraction analysis, and the mean particle diameter was calculated using the Scherrer formula and was found to be 9.3 nm. In this study, we treated lung epithelial cells with different concentrations of <span class="hlt">magnetite</span> and investigated their effects on oxidative stress and cell proliferation. Our data showed an inhibition of cell proliferation in <span class="hlt">magnetite</span>-treated cells with a significant dose-dependent activation and induction of reactive oxygen species. Also, we observed a depletion of antioxidants, glutathione, and superoxide dismutase, respectively, as compared with control cells. In addition, apoptotic-related protease/enzyme such as caspase-3 and -8 activities, were increased in a dose-dependent manner with corresponding increased levels of DNA fragmentation in <span class="hlt">magnetite</span>-treated cells compared to than control cells. Together, the present study reveals that <span class="hlt">magnetite</span> exposure induces oxidative stress and depletes antioxidant levels in the cells to stimulate apoptotic pathway for cell death. PMID:22147200</p> <div class="credits"> <p class="dwt_author">Ramesh, Vani; Ravichandran, Prabakaran; Copeland, Clinton L; Gopikrishnan, Ramya; Biradar, Santhoshkumar; Goornavar, Virupaxi; Ramesh, Govindarajan T; Hall, Joseph C</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">334</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/22730130"> <span id="translatedtitle">The periplasmic nitrate reductase nap is required for anaerobic growth and involved in redox control of <span class="hlt">magnetite</span> biomineralization in Magnetospirillum gryphiswaldense.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">The magnetosomes of many magnetotactic bacteria consist of membrane-enveloped <span class="hlt">magnetite</span> <span class="hlt">crystals</span>, 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, <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> biomineralization and resulted in fewer, smaller, and irregular <span class="hlt">crystals</span> during denitrification and also microaerobic respiration, probably by disturbing the proper redox balance required for <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> biomineralization. PMID:22730130</p> <div class="credits"> <p class="dwt_author">Li, Yingjie; Katzmann, Emanuel; Borg, Sarah; Schüler, Dirk</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">335</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3430331"> <span id="translatedtitle">The Periplasmic Nitrate Reductase Nap Is Required for Anaerobic Growth and Involved in Redox Control of <span class="hlt">Magnetite</span> Biomineralization in Magnetospirillum gryphiswaldense</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">The magnetosomes of many magnetotactic bacteria consist of membrane-enveloped <span class="hlt">magnetite</span> <span class="hlt">crystals</span>, 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, <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> biomineralization and resulted in fewer, smaller, and irregular <span class="hlt">crystals</span> during denitrification and also microaerobic respiration, probably by disturbing the proper redox balance required for <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> biomineralization.</p> <div class="credits"> <p class="dwt_author">Li, Yingjie; Katzmann, Emanuel; Borg, Sarah</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">336</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1994PhRvB..50.6446P"> <span id="translatedtitle">High-pressure phase of <span class="hlt">magnetite</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Mössbauer spectroscopy and x-ray diffraction were employed to investigate the magnetic and structural properties of the high-pressure monoclinic phase of <span class="hlt">magnetite</span>. Measurements were performed to 66 GPa at 300 K using diamond anvil cells. Based primarily upon the Mössbauer parameters, the following features of the high-pressure phase were deduced. With increasing pressure the high-pressure phase evolves at P>=25 GPa and its abundance increases monotonically at the expense of the low-pressure cubic phase. The high-pressure phase is not magnetic at 300 K and its monoclinic structural features resemble that of the low-pressure phase. The tetrahedral and octahedral sites characteristic of the inverse spinel structure, albeit distorted, remain the building blocks of the high-pressure phase. The fast electron hopping between Fe3+ and Fe2+ at the octahedral sites prevails to the highest pressure. It is suggested that the cubic-->monoclinic-->cubic hysteretic cycle involves a mild displacive phase transition not affecting the coordination number of any of the iron cations.</p> <div class="credits"> <p class="dwt_author">Pasternak, Moshe Paz; Nasu, Saburo; Wada, Koji; Endo, Shoichi</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">337</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.iupac.org/publications/pac/"> <span id="translatedtitle"><span class="hlt">Pure</span> and Applied Chemistry</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">Established in 1960, the journal <span class="hlt">Pure</span> 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 <span class="hlt">Pure</span> 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.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">338</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/gr3154v067t23w57.pdf"> <span id="translatedtitle"><span class="hlt">Pure</span> nuclear reflexes and combined hyperfine interactions in YIG</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Mössbauer spectra of oriented YIG single <span class="hlt">crystals</span> were taken and the numerical analysis using the transmission integral yielded a consistent set of hyperfine interaction parameters. They are in good agreement with theoretical values obtained by MO-calculations which included clusters up to 62 ions. Finally <span class="hlt">pure</span> nuclear reflexes are predicted for single <span class="hlt">crystals</span> and two theoretical spectra are given.</p> <div class="credits"> <p class="dwt_author">H. Winkler; R. Eisberg; E. Alp; R. Rüffer; E. Gerdau; S. Lauer; A. X. Trautwein; M. Grodzicki; A. Vera</p> <p class="dwt_publisher"></p> <p class="publishDate">1983-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">339</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007AGUFMGP24A..05C"> <span id="translatedtitle">Fundamental Magnetic Properties from <span class="hlt">Pure</span> Synthetic Greigite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Greigite (Fe3S4), an authigenic mineral that forms in sulfate-reducing environments, has been widely identified in marine and lake sediments. It is often the main magnetic carrier in some settings, and can therefore be significant in paleomagnetic and environmental magnetic studies. However, unlike its iron oxide counterpart, <span class="hlt">magnetite</span> (Fe3O4), the fundamental magnetic characteristics of greigite are still poorly understood, which is partially due to the metastability of greigite and the difficulty in obtaining high quality greigite samples. We have successfully synthesized <span class="hlt">pure</span> greigite samples with good crystallinity using a new hydrothermal method. Our detailed low- and high-temperature magnetic measurements document the previously poorly known magnetic properties of greigite, including the first accurate measurement of its saturation magnetization. We have for the first time unambiguously determined the magnetic structure of greigite by combined neutron powder diffraction and neutron polarization analysis. Low temperature (LT) neutron diffraction spectra reveal the temperature dependence of sublattice magnetizations. The <span class="hlt">pure</span> synthetic greigite samples are large enough to show pseudo-single-domain (PSD) and multi-domain (MD) behavior. LT cycling (LTC) of saturation isothermal remanent magnetization (SIRM) measurements indicate a continuous demagnetization of remanence during cooling. Preservation of the main features of first-order reversal curve distributions at LT, coupled with LT SIRM warming curves, rule out the presence of substantial superparamagnetic behavior in the studied samples. No LT magnetic transition has been detected; however, a local coercivity minimum is observed at around 130 K. These fundamental studies provide new constraints on the magnetic behaviour of greigite.</p> <div class="credits"> <p class="dwt_author">Chang, L.; Roberts, A. P.; Muxworthy, A. R.; Tang, Y.; Chen, Q.; Rainford, B. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">340</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20090038967&hterms=debate&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Ddebate"> <span id="translatedtitle">Origins of <span class="hlt">Magnetite</span> Nanocrystals in Martian Meteorite ALH84001</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks. These carbonate disks are believed to have precipitated 3.9 Ga ago at beginning of the Noachian epoch on Mars during which both the oldest extant Martian surfaces were formed, and perhaps the earliest global oceans. Intimately associated within and throughout these carbonate disks are nanocrystal <span class="hlt">magnetites</span> (Fe3O4) with unusual chemical and physical properties, whose origins have become the source of considerable debate. One group of hypotheses argues that these <span class="hlt">magnetites</span> are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of mag- netite and carbonate may be unrelated; that is, from the perspective of the carbonate the <span class="hlt">magnetite</span> is allochthonous. For example, the <span class="hlt">magnetites</span> might have already been present in the aqueous fluids from which the carbonates were believed to have been deposited. We have sought to resolve between these hypotheses through the detailed characterized of the compo- sitional and structural relationships of the carbonate disks and associated <span class="hlt">magnetites</span> with the orthopyroxene matrix in which they are embedded. Extensive use of focused ion beam milling techniques has been utilized for sample preparation. We then compared our observations with those from experimental thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios. We conclude that the vast majority of the nanocrystal <span class="hlt">magnetites</span> present in the car- bonate disks could not have formed by any of the currently proposed thermal decomposition scenarios. Instead, we find there is considerable evidence in support of an alternative allochthonous origin for the <span class="hlt">magnetite</span> unrelated to any shock or thermal processing of the carbonates.</p> <div class="credits"> <p class="dwt_author">Thomas-Keprta, Kathie L.; Clemett, Simon J.; Mckay, David S.; Gibson, Everett K.; Wentworth, Susan J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_16");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a style="font-weight: bold;">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_18");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> </div><!-- page_17 div --> <div id="page_18" class="hiddenDiv"> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_17");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a style="font-weight: bold;">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_19");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">341</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/21443221"> <span id="translatedtitle"><span class="hlt">Magnetite</span> colloidal nanocrystals: a facile pathway to prepare mesoporous hematite thin films for photoelectrochemical water splitting.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">In this study, we demonstrate an alternative and promising way to produce hematite photoanodes with high performance and without the addition of doping or catalytic coating. In this approach, we processed hematite thin films using a colloidal dispersion of <span class="hlt">magnetite</span> nanocrystals as the precursor. The photoelectrochemical characterization shows that the colloidal approach used to process an undoped hematite photoanode produced a high-performance electrode for water photooxidation with an onset potential as low as 0.8 V(RHE). This value is comparable to the best results reported in the literature for a hematite photoanode modified with catalytic materials. We demonstrate that <span class="hlt">pure</span> hematite thin films reach 1.1 mA·cm(-2) at 1.23 V(RHE) with back-side illumination. PMID:21443221</p> <div class="credits"> <p class="dwt_author">Gonçalves, Ricardo H; Lima, Bruno H R; Leite, Edson R</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-04-20</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">342</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008JPhD...41m4022K"> <span id="translatedtitle">Bioengineered magnetic <span class="hlt">crystals</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In this paper we report on the successful application of a protein <span class="hlt">crystallization</span> technique to fabricate a three-dimensionally ordered array of magnetic nanoparticles, i.e. a novel type of metamaterial with unique magnetic properties. We utilize ferritin protein cages for the template-constrained growth of superparamagnetic nanoparticles of <span class="hlt">magnetite</span>/maghemite Fe3O4-?-Fe2O3 (magnetoferritin), followed by thorough nanoparticle bioprocessing and purification, and finally by protein <span class="hlt">crystallization</span>. Protein <span class="hlt">crystallization</span> is driven by the natural response of proteins to the supersaturation of the electrolyte, which leads to spontaneous nucleation and 3D <span class="hlt">crystal</span> growth. Within a short period of time (hours to days) we were able to grow functional <span class="hlt">crystals</span> on the meso-scale, with sizes of the order of tens, up to a few hundred micrometres. We present initial magnetic and Raman spectroscopy characterization results for the obtained 3D arrays of magnetic nanoparticles.</p> <div class="credits"> <p class="dwt_author">Kasyutich, O.; Sarua, A.; Schwarzacher, W.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">343</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007PhRvL..99p4503P"> <span id="translatedtitle"><span class="hlt">Purely</span> Elastic Flow Asymmetries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Using a numerical technique we demonstrate that the flow of the simplest differential viscoelastic fluid model (i.e., the upper-convected Maxwell model) goes through a bifurcation to a steady asymmetric state when flowing in a perfectly symmetric “cross-slot” geometry. We show that this asymmetry is <span class="hlt">purely</span> elastic in nature and that the effect of inertia is a stabilizing one. Our results are in qualitative agreement with very recent experimental visualizations of a similar flow in the microfluidic apparatus of Arratia et al. [Phys. Rev. Lett. 96, 144502 (2006)PRLTAO0031-900710.1103/PhysRevLett.96.144502].</p> <div class="credits"> <p class="dwt_author">Poole, R. J.; Alves, M. A.; Oliveira, P. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">344</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/17995258"> <span id="translatedtitle"><span class="hlt">Purely</span> elastic flow asymmetries.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Using a numerical technique we demonstrate that the flow of the simplest differential viscoelastic fluid model (i.e., the upper-convected Maxwell model) goes through a bifurcation to a steady asymmetric state when flowing in a perfectly symmetric "cross-slot" geometry. We show that this asymmetry is <span class="hlt">purely</span> elastic in nature and that the effect of inertia is a stabilizing one. Our results are in qualitative agreement with very recent experimental visualizations of a similar flow in the microfluidic apparatus of Arratia et al. PMID:17995258</p> <div class="credits"> <p class="dwt_author">Poole, R J; Alves, M A; Oliveira, P J</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-10-19</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">345</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/8140921"> <span id="translatedtitle">[<span class="hlt">Pure</span> autonomic failure].</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">We present the case of a 64-year-old woman who, in the past 5 years, complained of constipation/diarrhea, hyposudoresis, xerostomia and xerophthalmia, dysuria and orthostatic hypotension. Cardiovascular reflexes analysis revealed sympathetic and parasympathetic failure. Norepinephrine was markedly reduced, both lying and after tilt. Norepinephrine infusion determined a significant rise in blood pressure, allowing the diagnosis of denervation hypersensitivity. The diagnosis of <span class="hlt">pure</span> autonomic failure was made. Therapy with 9 alpha fludrocortisone and metoclopramide was initiated with marked and sustained symptomatic effect. PMID:8140921</p> <div class="credits"> <p class="dwt_author">Ducla-Soares, J L; Guerreiro, A S; Póvoa, P; Alvares, E; Guerreiro, L; Carrilho, F; Santos, M; Figueirinhas, J; Carvalho, M</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">346</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://pubs.er.usgs.gov/publication/70017113"> <span id="translatedtitle">Electrochemistry and dissolution kinetics of <span class="hlt">magnetite</span> and ilmenite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">Natural samples of <span class="hlt">magnetite</span> and ilmenite were experimentally weathered in pH 1-7 anoxic solutions at temperatures of 2-65 ??C. Reaction of <span class="hlt">magnetite</span> is described as [Fe2+Fe23+]O4(<span class="hlt">magnetite</span>) + 2H+ ??? ??[Fe23+]O3(maghemite) + Fe2+ + H2O. Dynamic polarization experiments using <span class="hlt">magnetite</span> electrodes confirmed that this reaction is controlled by two electrochemical half cells, 3[Fe2+Fe23+]O4(<span class="hlt">magnetite</span>) ??? 4??[Fe23+]O3(maghemite) + Fe2+ + 2e- and [Fe2+Fe23+]O4(<span class="hlt">magnetite</span>) + 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 <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> and ilmenite will exceed 107 years. This agrees with long-term stability of these oxides in the geologic record. ?? 1994.</p> <div class="credits"> <p class="dwt_author">White, A. F.; Peterson, M. L.; Hochella, Jr. , M. F.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">347</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1994GeCoA..58.1859W"> <span id="translatedtitle">Electrochemistry and dissolution kinetics of <span class="hlt">magnetite</span> and ilmenite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Natural samples of <span class="hlt">magnetite</span> and ilmenite were experimentally weathered in pH 1-7 anoxic solutions at temperatures of 2-65 °C. Reaction of <span class="hlt">magnetite</span> is described as [ Fe2+Fe23+] O4(<span class="hlt">magnetite</span>) + 2 H+ ? ?[ Fe23+] O3(maghemite) + Fe2+ + H2O. Dynamic polarization experiments using <span class="hlt">magnetite</span> electrodes confirmed that this reaction is controlled by two electrochemical half cells, 3[ Fe2+Fe23+] O4(<span class="hlt">magnetite</span>) ? 4 ?[ Fe23+] O3(maghemite) + Fe2+ + 2 e- and [ Fe2+Fe23+] O4(<span class="hlt">magnetite</span>) + 8 H+ + 2 e- ? 3 Fe2+ + 4 H2O, which result in solid state Fe 3+ 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 <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> and ilmenite will exceed 10 7 years. This agrees with long-term stability of these oxides in the geologic record.</p> <div class="credits"> <p class="dwt_author">White, Art F.; Peterson, Maria L.; Hochella, Michael F., Jr.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">348</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AGUFMEP53A0736G"> <span id="translatedtitle">Production Rate of Cosmogenic 10Be in <span class="hlt">Magnetite</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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 <span class="hlt">magnetite</span> (Fe3O4). <span class="hlt">Magnetite</span> 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 <span class="hlt">magnetite</span> from the same catchment to yield information about the intensity of chemical weathering (Rogers et al., this conference). The 10Be production rate in <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> among silicon, oxygen, and iron. While most of the production in both <span class="hlt">magnetite</span> 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.</p> <div class="credits"> <p class="dwt_author">Granger, D. E.; Rogers, H. E.; Riebe, C. S.; Lifton, N. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">349</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22212517"> <span id="translatedtitle">Effect of La{sub 2}O{sub 3}, CoO, Cr{sub 2}O{sub 3} and MoO{sub 3} nucleating agents on <span class="hlt">crystallization</span> behavior and magnetic properties of ferromagnetic glass-ceramic in the system Fe{sub 2}O{sub 3}{center_dot}CaO{center_dot}ZnO{center_dot}SiO{sub 2}</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Highlights: Black-Right-Pointing-Pointer <span class="hlt">Crystallization</span> of magnetic glass ceramic with different nucleating agents. Black-Right-Pointing-Pointer The effect of La{sub 2}O{sub 3}, CoO, Cr{sub 2}O{sub 3} and MoO{sub 3} as nucleating agents was studied. Black-Right-Pointing-Pointer XRD for as prepared samples revealed <span class="hlt">crystallization</span> of <span class="hlt">pure</span> <span class="hlt">magnetite</span>. Black-Right-Pointing-Pointer Heat treatment revealed minor calcium silicate, hematite and cristobalite. Black-Right-Pointing-Pointer TEM revealed <span class="hlt">crystallization</span> of crystallite size in the range 50-100 nm. -- Abstract: Preparation and characterization of ferromagnetic glass ceramic in the system Fe{sub 2}O{sub 3}{center_dot}CaO{center_dot}ZnO{center_dot}SiO{sub 2} with different nucleating agents was studied. The effect of La{sub 2}O{sub 3}, CoO, Cr{sub 2}O{sub 3} and MoO{sub 3} as nucleating agents was investigated. Differential thermal analysis; X-ray diffraction and transmission electron microscope were used to investigate thermal behavior, sequence of <span class="hlt">crystallization</span> and microstructure of the samples. XRD analysis for as prepared samples revealed the <span class="hlt">crystallization</span> of single <span class="hlt">magnetite</span> phase. Heat treatment at 900 Degree-Sign C/2 h revealed the appearance of minor amounts of calcium silicate, hematite and cristobalite beside <span class="hlt">magnetite</span>. TEM revealed <span class="hlt">crystallization</span> of crystallite size in the range 50-100 nm. Lattice parameters, cell volume and crystallite size were stimulated from XRD data. Magnetic properties of quenched samples were measured under 20 kG.</p> <div class="credits"> <p class="dwt_author">Abdel-Hameed, Salwa A.M., E-mail: Salwa_NRC@hotmail.com [Glass Research Department, National Research Center, Dokki, Cairo (Egypt); Elwan, Rawhia L. [Glass Research Department, National Research Center, Dokki, Cairo (Egypt)] [Glass Research Department, National Research Center, Dokki, Cairo (Egypt)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-05-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">350</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dx.doi.org/10.1097/ss.0b013e3181586b77"> <span id="translatedtitle">Observations of <span class="hlt">magnetite</span> dissolution in poorly drained soils</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">Dissolution of strongly magnetic minerals is a common and relatively rapid phenomenon in poorly drained soils of the central United States, resulting in low magnetic susceptibility (MS). Low Eh reducing conditions are primarily responsible for magnetic mineral dissolution; a process likely mediated by iron-reducing bacteria in the presence of soil organic matter. Based on transects across drainage sequences from nine sites, natural magnetic minerals (>5 ??m) extracted from surface soil consist of 54% ?? 18% <span class="hlt">magnetite</span>, 21% ?? 11% titanomagnetite, and 17% ?? 14% ilmenite. <span class="hlt">Magnetite</span> and titanomagnetite dissolution, assessed by scanning electron microscopy on a 0-to-3 scale, inversely correlates with surface soil MS (r = 0.53), a proxy for soil drainage at studied transects. Altered <span class="hlt">magnetite</span> typically displays etch pits 5 ??m) include 26% ?? 18% anthropogenic fly ash that also exhibits greater dissolution in low MS soils (r = 0.38), indicating detectable alteration can occur within 150 years in low Eh soils. Laboratory induced reduction of <span class="hlt">magnetite</span>, titanomagnetite, and magnetic fly ash, with a citrate-bicarbonate- dithionite solution, resulted in dissolution textures similar to those of in situ soil particles. Although experiments indicate that reductive dissolution of <span class="hlt">magnetite</span> can occur abiotically under extreme conditions, bacteria likely play an important role in the natural environment. ?? 2007 Lippincott Williams & Wilkins, Inc.</p> <div class="credits"> <p class="dwt_author">Grimley, D. A.; Arruda, N. K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">351</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012JAP...111l4911H"> <span id="translatedtitle">Use of <span class="hlt">magnetite</span> as anode for electrolysis of water</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have studied the oxidation of <span class="hlt">magnetite</span> to Fe2O3 in an electrolytic cell in which the anode is <span class="hlt">magnetite</span> and the cathode is platinum. We report cyclic voltammagram data consistent with the hypothesis that <span class="hlt">magnetite</span>, without oxygen gas production but with hydrogen gas production at the cathode, is occurring. The reaction occurs at a potential at the anode of about 0.3 V vs SCE in 1 M NaOH electrolyte, consistent with colloid experiments which also estimated the equilibrium potential of the hypothesized reaction. Electrode characterization results using BET, XEDS, and macroscopic volume and mass measurements are reported, as well as the measurements of the amount of hydrogen gas generated per unit current. The quantity of gas generated is also consistent with our hypothesis concerning the electrode chemistry. Some samples exhibit evidence of two oxidation reactions occurring at the anode and a possible interpretation of these is also discussed. These results suggest the use of <span class="hlt">magnetite</span> as an anode in a cell electrolysing water to produce hydrogen gas and Fe2O3. In such an electrolyser, the electrical energy cost of producing hydrogen gas could be significantly lower than the cost in a standard electrolyser. The measured steady state currents, equivalent to about 400 mA/g of <span class="hlt">magnetite</span>, are too low to make a practical electrolyser. We briefly discuss several ways in which the currents might be increased to the levels required.</p> <div class="credits"> <p class="dwt_author">Halley, J. W.; Schofield, A.; Berntson, B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">352</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012JAP...111d4303Y"> <span id="translatedtitle">Stable vortex <span class="hlt">magnetite</span> nanorings colloid: Micromagnetic simulation and experimental demonstration</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Magnetite</span> nanoring with vortex domain structure may form stable magnetic colloid for biomedical applications due to its weak magnetic interaction without superparamagnetic (SPM) limitation. In the present study, we perform three-dimensional (3 D) Landau-Liftshitz-Gilbert (LLG) micromagnetics simulation for <span class="hlt">magnetite</span> nanorings. The ground state phase diagram and stable vortex area (SVA) as a function of outer diameter (Dout), thickness (T), and inner to outer diameter ratios (?) within 100 nm are obtained. The influence of notch, eccentricity, and crystallographic orientation are taken carefully into consideration. In the SVA, the vortex state is not only the ground state but also the remanence state after in-plane is fully magnetized. In particular, the results suggest that a 20 nm inter-rings distance for a typical <span class="hlt">magnetite</span> nanoring (Dout = 70 nm, T = 50 nm, and ? = 0.6) can achieve the stable colloid based on vortex domain structure. Furthermore, these simulation results have been confirmed experimentally and demonstrated by using phosphorylated-mPEG modified <span class="hlt">magnetite</span> nanorings. The optimization of <span class="hlt">magnetite</span> nanorings from both simulation and experiments in this work pave the way to achieve such novel and stable vortex domain based magnetic suspension for various biomedical applications.</p> <div class="credits"> <p class="dwt_author">Yang, Yong; Liu, Xiao-Li; Yi, Jia-Bao; Yang, Yang; Fan, Hai-Ming; Ding, Jun</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">353</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/22194451"> <span id="translatedtitle">The MagA protein of Magnetospirilla is not involved in bacterial <span class="hlt">magnetite</span> biomineralization.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">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 <span class="hlt">crystallization</span> of <span class="hlt">magnetite</span>. 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 <span class="hlt">magnetite</span> 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</p> <div class="credits"> <p class="dwt_author">Uebe, René; Henn, Verena; Schüler, Dirk</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">354</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3294778"> <span id="translatedtitle">The MagA Protein of Magnetospirilla Is Not Involved in Bacterial <span class="hlt">Magnetite</span> Biomineralization</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">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 <span class="hlt">crystallization</span> of <span class="hlt">magnetite</span>. 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 <span class="hlt">magnetite</span> 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.</p> <div class="credits"> <p class="dwt_author">Uebe, Rene; Henn, Verena</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">355</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008Nanot..19r5603S"> <span id="translatedtitle">Mesoporous silica <span class="hlt">magnetite</span> nanocomposite synthesized by using a neutral surfactant</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Magnetite</span> nanoparticles coated by mesoporous silica were synthesized by an alternative chemical route using a neutral surfactant and without the application of any functionalization method. The <span class="hlt">magnetite</span> (Fe3O4) nanoparticles were prepared by precipitation from aqueous media, and then coated with mesoporous silica by using nonionic block copolymer surfactants as the structure-directing agents. The mesoporous SiO2-coated Fe3O4 samples were characterized by x-ray diffraction, Fourier-transform infrared spectroscopy, N2 adsorption-desorption isotherms, transmission electron microscopy, 57Fe Mössbauer spectroscopy, and vibrating sample magnetometry. Our results revealed that the <span class="hlt">magnetite</span> nanoparticles are completely coated by well-ordered mesoporous silica with free pores and stable (~8 nm thick) pore walls, and that the structural and magnetic properties of the Fe3O4 nanoparticles are preserved in the applied synthesis route.</p> <div class="credits"> <p class="dwt_author">Souza, K. C.; Salazar-Alvarez, G.; Ardisson, J. D.; Macedo, W. A. A.; Sousa, E. M. B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">356</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3676787"> <span id="translatedtitle">Simple and Rapid Synthesis of <span class="hlt">Magnetite</span>/Hydroxyapatite Composites for Hyperthermia Treatments via a Mechanochemical Route</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">This paper presents a simple method for the rapid synthesis of <span class="hlt">magnetite</span>/hydroxyapatite composite particles. In this method, superparamagnetic <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> nanoparticles, during which the <span class="hlt">magnetite</span> nanoparticles are incorporated into the hydroxyapatite matrix. We observed that the resultant <span class="hlt">magnetite</span>/hydroxyapatite composites possessed a homogeneous dispersion of <span class="hlt">magnetite</span> nanoparticles, characterized by an absence of large aggregates. When this material was subjected to an alternating magnetic field, the heat generated increased with increasing <span class="hlt">magnetite</span> concentration. For a <span class="hlt">magnetite</span> 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.</p> <div class="credits"> <p class="dwt_author">Iwasaki, Tomohiro; Nakatsuka, Ryo; Murase, Kenya; Takata, Hiroshige; Nakamura, Hideya; Watano, Satoru</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">357</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006JMMM..306..223L"> <span id="translatedtitle">In situ hybridization to chitosan/<span class="hlt">magnetite</span> nanocomposite induced by the magnetic field</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Chitosan/<span class="hlt">magnetite</span> nanocomposite was synthesized induced by magnetic field via in situ hybridization in ambient condition. Results of XRD patterns and TEM micrographs indicated that <span class="hlt">magnetite</span> particles with 10-20 nm were dispersed in chitosan homogeneously. An interesting result is that <span class="hlt">magnetite</span> nanoparticles were assembled to form chain-like structures under the influence of the external magnetic field, which mimics the <span class="hlt">magnetite</span> chains inside of magnetotatic bacteria. The saturated magnetization (Ms) of nano-<span class="hlt">magnetite</span> in chitosan was 50.54 emu/g, which is as high as 54% of bulk <span class="hlt">magnetite</span>. The remanence (Mr) and coercivity (Hc) were 4 emu/g and14.8 Oe, respectively, which indicated that <span class="hlt">magnetite</span> nanoparticles were superparamagnetic. The key of route is that a pre-precipitated chitosan hydrogel membrane, used as chemical reactor, which controlled the precipitation of chitosan precipitation and in situ transformation of <span class="hlt">magnetite</span> from the precursor simultaneously in the magnetic field environment.</p> <div class="credits"> <p class="dwt_author">Li, Baoqiang; Jia, Dechang; Zhou, Yu; Hu, Qiaoling; Cai, Wei</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">358</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40335821"> <span id="translatedtitle">Surface modification of superparamagnetic <span class="hlt">magnetite</span> nanoparticles and their intracellular uptake</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Superparamagnetic <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> 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</p> <div class="credits"> <p class="dwt_author">Y Zhang; Nathan Kohler; Miqin Zhang</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">359</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014JAP...115qE117G"> <span id="translatedtitle">The Verwey transition in nanostructured <span class="hlt">magnetite</span> produced by a combination of chimie douce and spark plasma sintering</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Magnetite</span> 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 <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> single <span class="hlt">crystals</span>.</p> <div class="credits"> <p class="dwt_author">Gaudisson, T.; Vázquez-Victorio, G.; Bañobre-López, M.; Nowak, S.; Rivas, J.; Ammar, S.; Mazaleyrat, F.; Valenzuela, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">360</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40383728"> <span id="translatedtitle">Two types of chemical remanent magnetization during the oxidation of <span class="hlt">magnetite</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The chemical remanent magnetization (CRM), MCRM, resulting from oxidation of equidimensional <span class="hlt">magnetite</span> to a mixture of 90% hematite and 10% cation-deficient <span class="hlt">magnetite</span> is jointly controlled by the initial anhysteretic remanent magnetization, (MARM), of the parent <span class="hlt">magnetite</span> and the field HCRM applied during oxidation. MCRM lies in the plane defined by HCRM and MARM (which were perpendicular in our experiments) in</p> <div class="credits"> <p class="dwt_author">Franz Heider; David J. Dunlop</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_17");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a style="font-weight: bold;">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_19");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> </div><!-- page_18 div --> <div id="page_19" class="hiddenDiv"> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_18");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a style="font-weight: bold;">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_20");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">361</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/1488475"> <span id="translatedtitle">Grain size limits for pseudosingle domain behavior in <span class="hlt">magnetite</span>: Implications for paleomagnetism</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A theoretical model of grain size dependence of domain transitions in <span class="hlt">magnetite</span> is presented. This domain model is used to predict the grain size range for pseudosingle domain (PSD) behavior in <span class="hlt">magnetite</span>. For cubic <span class="hlt">magnetite</span> particles, the single domain (SD) to two-domain (TD) transition occurs at ?800 ± 200 Å, the TD-three-domain transition occurs at ? 1500 Å, and the</p> <div class="credits"> <p class="dwt_author">BRUCE M. MOSKOWITZ; SUBIR K. BANERJEE</p> <p class="dwt_publisher"></p> <p class="publishDate">1979-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">362</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/h27049626722k646.pdf"> <span id="translatedtitle">Structure and Magnetic Properties of Polymer Microspheres Filled with <span class="hlt">Magnetite</span> Nanoparticles</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The structure and magnetic properties of collagen microspheres filled with <span class="hlt">magnetite</span> nanoparticles are studied. The average interparticle separation in the polymer matrix and the size of <span class="hlt">magnetite</span> nanoparticles before and after the introduction of the nanoparticles into the matrix are determined using electron microscopy. The magnetization curve of the microspheres has a superparamagnetic character. The <span class="hlt">magnetite</span> nanoparticles undergo no aggregation</p> <div class="credits"> <p class="dwt_author">R. A. Ali-zade</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">363</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/23480338"> <span id="translatedtitle">Recovery of iron as a form of ferrous acetate precipitates from low-grade <span class="hlt">magnetite</span> ore</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">This paper describes the recovery process of iron as a form of ferrous acetate from low-grade <span class="hlt">magnetite</span> ore (Shinyemi Mine, Gangwon province, Korea). The magnetically separated <span class="hlt">magnetite</span> powder was dissolved in aqueous oxalic acid solution. The dissolution fraction of <span class="hlt">magnetite</span> concentrates was measured as a function of initial pH, reaction temperature and oxalic acid concentration. Optimum conditions for dissolution of</p> <div class="credits"> <p class="dwt_author">Jae-Kyeong Kim; Han-Sang Oh; Chang-Wha Jo; Yong-Jae Suh; Hee-Dong Jang; Kee-Kahb Koo</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">364</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/1007876"> <span id="translatedtitle">Experimental evidence for non-redox transformations between <span class="hlt">magnetite</span> and hematite under H-2-rich hydrothermal conditions.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Transformations of <span class="hlt">magnetite</span> (Fe{sup II}Fe{sub 2}{sup III}O{sub 4}) to hematite (Fe{sub 2}{sup III}O{sub 3}) (and vice versa) have been thought by many scientists and engineers to require molecular O{sub 2} and/or H{sub 2}. Thus, the presence of <span class="hlt">magnetite</span> and/or hematite in rocks has been linked to a specific oxidation environment. However, the availability of reductants or oxidants in many geologic and industrial environments appears to have been too low to account for the transformations of iron oxides through redox reactions. Here, we report the results of hydrothermal experiments in mildly acidic and H{sub 2}-rich aqueous solutions at 150 C, which demonstrate that transformations of <span class="hlt">magnetite</span> to hematite, and hematite to <span class="hlt">magnetite</span>, occur rapidly without involving molecular O{sub 2} or H{sub 2}: Fe{sub 3}O{sub 4}(Mt) + 2H{sub (aq)}{sup +} {leftrightarrow} Fe{sub 2}O{sub 3}(Hm) + Fe{sub (aq)}{sup 2+} + H{sub 2}O. The transformation products are chemically and structurally homogeneous, and typically occur as euhedral single <span class="hlt">crystals</span> much larger than the precursor minerals. This suggests that, in addition to the expected release of aqueous ferrous species to solution, the transformations involve release of aqueous ferric species from the precursor oxides to the solution, which reprecipitate without being reduced by H{sub 2}. These redox-independent transformations may have been responsible for the formation of some iron oxides in natural systems, such as high-grade hematite ores that developed from Banded Iron Formations (BIFs), hematite-rich deposits formed on Mars, corrosion products in power plants and other industrial systems.</p> <div class="credits"> <p class="dwt_author">Otake, Tsubasa [Pennsylvania State University; Wesolowski, David J [ORNL; Anovitz, Lawrence {Larry} M [ORNL</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">365</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/930894"> <span id="translatedtitle">Experimental Evidence for Non-Redox Transformation Between <span class="hlt">Magnetite</span> and Hermatite Under H2-Rich Hydrothermal Conditions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Transformations of <span class="hlt">magnetite</span> (Fe{sup II}Fe{sub 2}{sup III}O{sub 4}) to hematite (Fe{sub 2}{sup III}O{sub 3}) (and vice versa) have been thought by many scientists and engineers to require molecular O{sub 2} and/or H{sub 2}. Thus, the presence of <span class="hlt">magnetite</span> and/or hematite in rocks has been linked to a specific oxidation environment. However, the availability of reductants or oxidants in many geologic and industrial environments appears to have been too low to account for the transformations of iron oxides through redox reactions. Here, we report the results of hydrothermal experiments in mildly acidic and H{sub 2}-rich aqueous solutions at 150 C, which demonstrate that transformations of <span class="hlt">magnetite</span> to hematite, and hematite to <span class="hlt">magnetite</span>, occur rapidly without involving molecular O{sub 2} or H{sub 2}: Fe{sub 3}O{sub 4}(Mt) + 2H{sub (aq)}{sup +} {leftrightarrow} Fe{sub 2}O{sub 3}(Hm) + Fe{sub (aq)}{sup 2+} + H{sub 2}O The transformation products are chemically and structurally homogeneous, and typically occur as euhedral single <span class="hlt">crystals</span> much larger than the precursor minerals. This suggests that, in addition to the expected release of aqueous ferrous species to solution, the transformations involve release of aqueous ferric species from the precursor oxides to the solution, which reprecipitate without being reduced by H{sub 2}. These redox-independent transformations may have been responsible for the formation of some iron oxides in natural systems, such as high-grade hematite ores that developed from Banded Iron Formations (BIFs), hematite-rich deposits formed on Mars, corrosion products in power plants and other industrial systems.</p> <div class="credits"> <p class="dwt_author">Otake, Tsubasa [Pennsylvania State University; Ohmoto, Hiroshi [Pennsylvania State University; Wesolowski, David J [ORNL; Anovitz, Lawrence {Larry} M [ORNL; Allard Jr, Lawrence Frederick [ORNL</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">366</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/51591151"> <span id="translatedtitle">Excitonic processes in <span class="hlt">pure</span> and doped ?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The optical properties of nominally <span class="hlt">pure</span> 0953-8984\\/11\\/15\\/016\\/img9 <span class="hlt">crystals</span> as well as of those of <span class="hlt">pure</span> and 0953-8984\\/11\\/15\\/016\\/img10 and 0953-8984\\/11\\/15\\/016\\/img11-doped 0953-8984\\/11\\/15\\/016\\/img9 powders are compared. The emission band peaking at 3.9 eV and the excitation bands in the region 10-10.6 eV observed for 0953-8984\\/11\\/15\\/016\\/img13 and 0953-8984\\/11\\/15\\/016\\/img14 powders are ascribed to the radiative decay of a self-trapped exciton perturbed by an anion vacancy</p> <div class="credits"> <p class="dwt_author">V. Denks; A. Maaroos; V. Nagirnyi; T. Savikhina; V. Vassiltsenko</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">367</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011PhRvB..83s5109S"> <span id="translatedtitle">Relaxor ferroelectricity and the freezing of short-range polar order in <span class="hlt">magnetite</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A thorough investigation of single-crystalline <span class="hlt">magnetite</span> using broadband dielectric spectroscopy and other methods provides evidence for relaxorlike polar order in Fe3O4. We find long-range ferroelectric order to be impeded by the continuous freezing of polar degrees of freedom and the formation of a tunneling-dominated glasslike state at low temperatures. This also explains the lack of clear evidence for a noncentrosymmetric <span class="hlt">crystal</span> structure below the Verwey transition. Within the framework of recent models assuming an intimate relation of charge and polar order, the charge order, too, can be speculated to be of short-range type only and to be dominated by tunneling at low temperatures.</p> <div class="credits"> <p class="dwt_author">Schrettle, F.; Krohns, S.; Lunkenheimer, P.; Brabers, V. A. M.; Loidl, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">368</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009PhRvL.102q6405G"> <span id="translatedtitle">Reexamination of the Temperature Dependences of Resonant Reflections in Highly Stoichiometric <span class="hlt">Magnetite</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have studied the temperature dependences of the so-called charge and orbital ordering reflections in the neighborhood of the Verwey transition by means of resonant x-ray scattering at the Fe K and L edges on a high purity single <span class="hlt">crystal</span> of <span class="hlt">magnetite</span>. Contrary to recently published results [J. E. Lorenzo , Phys. Rev. Lett. 101, 226401 (2008)PRLTAO0031-900710.1103/PhysRevLett.101.226401], we show that all the reflections studied disappear simultaneously at the Verwey transition for both edges, on and off resonance. This means that there is no correlation between the Verwey (123.5 K) and the spin-reorientation (130 K) transitions and that the resonant reflections are driven by the lattice distortions.</p> <div class="credits"> <p class="dwt_author">García, Joaquín; Subías, Gloria; Herrero-Martín, Javier; Blasco, Javier; Cuartero, Vera; Sánchez, M. Concepción; Mazzoli, Claudio; Yakhou, Flora</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">369</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/496452"> <span id="translatedtitle">Specific heat of <span class="hlt">pure</span> Y{bold {ital {sub 1{minus}x}}}Pr{bold {ital {sub x}}}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} single <span class="hlt">crystals</span> in magnetic fields</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Specific heat measurements have been performed on single <span class="hlt">crystals</span> of Y{ital {sub 1{minus}x}}Pr{ital {sub x}}Ba{sub 2}Cu{sub 3}O{sub 1{minus}{delta}} ({ital x}=0.33, 1) in the temperature range 2 K{lt}{ital T}{lt}50 K with magnetic fields up to 7.5 T, both parallel and perpendicular to the {ital c}-axis. The <span class="hlt">crystals</span> were grown in BaZrO{sub 3} crucibles and therefore the possibility of crucible contamination in the <span class="hlt">crystals</span> is reduced to a large extent. A large linear term with {gamma}=207 mJ/molK{sup 2} was determined for {ital x}=1 and the <span class="hlt">crystal</span> field contribution due to Pr ion was calculated for both the samples. The transitions were found to be sharp lambda type for {ital x}=1 with the ordering temperature at 16.6 K and very broad for {ital x}=0.33 with the transition temperature below 2 K. Also, the transition temperatures increased for {ital x}=0.33 and decreased for {ital x}=1 with increasing magnetic fields indicating a different type of interaction for these two samples. The coupling in the {ital ab} plane was found to be stronger than in the {ital c}-axis. {copyright} {ital 1997 American Institute of Physics.}</p> <div class="credits"> <p class="dwt_author">Uma, S.; Schnelle, W.; Gmelin, E. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany)] [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Rangarajan, G. [Department of Physics, Indian Institute of Technology, Madras-600 036 (India)] [Department of Physics, Indian Institute of Technology, Madras-600 036 (India); Erb, A. [DPMC, Universite de Geneve, 24, Quai Ernest Ansermet, CH-1211 Geneva 4 (Switzerland)] [DPMC, Universite de Geneve, 24, Quai Ernest Ansermet, CH-1211 Geneva 4 (Switzerland)</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">370</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014JGP....81..117B"> <span id="translatedtitle"><span class="hlt">Pure</span> subspaces, generalizing the concept of <span class="hlt">pure</span> spinors</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The concept of <span class="hlt">pure</span> spinors is generalized, giving rise to the notion of <span class="hlt">pure</span> subspaces, spinorial subspaces associated to isotropic vector subspaces of non-maximal dimension. Several algebraic identities concerning the <span class="hlt">pure</span> subspaces are proved here, as well as some differential results. Furthermore, the freedom in the choice of a spinorial connection is exploited in order to relate the twistor equation to the integrability of maximally isotropic distributions.</p> <div class="credits"> <p class="dwt_author">Batista, Carlos</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">371</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/1430403"> <span id="translatedtitle">Physical limits of hyperthermia using <span class="hlt">magnetite</span> fine particles</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Structural and magnetic properties of fine particles of <span class="hlt">magnetite</span> are investigated with respect to the application for hyperthermia. Magnetic hysteresis losses are measured in dependence on the field amplitude for selected commercial powders and are discussed in terms of grain size and structure of the particles. For ferromagnetic powders as well as for ferrofluids, results of heating experiments within organic</p> <div class="credits"> <p class="dwt_author">Rudolf Hergt; Wilfried Andra; Carl G. d'Ambly; Ingrid Hilger; Werner A. Kaiser; Uwe Richter; Hans-Georg Schmidt</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">372</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.agu.org/journals/jb/v081/i005/JB081i005p00989/JB081i005p00989.pdf"> <span id="translatedtitle">Interacting Single-Domain Properties of <span class="hlt">Magnetite</span> Intergrowths</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">experimentally under nondemagnetizing conditions is found to be 0.51. The reduction is shown to be entirely explicable in terms of localized array demagnetizing fields arising from surface poles. A similar effect is seen in <span class="hlt">magnetite</span>\\/ulvospinei intergrowths. Qualitative evidence that this reduction proceeds mainly by rotation of the spontaneous magnetization from easy axes is seen in a measured anisotropy of low</p> <div class="credits"> <p class="dwt_author">P. M. Davis; M. E. Evans</p> <p class="dwt_publisher"></p> <p class="publishDate">1976-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">373</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6794760"> <span id="translatedtitle">Electromagnetic methods of detecting <span class="hlt">magnetite</span> in PWR steam generators</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Corrosion products consisting primarily of <span class="hlt">magnetite</span> (Fe/sub 3/O/sub 4/) in the crevice gap between steam generator tubes and support plates can eventually lead to tube denting and support plate fractures. In order to mitigate this problem, chemical flushing is used to remove the <span class="hlt">magnetite</span> deposit from the crevice gaps. NDE techniques are needed to measure the effectiveness of this procedure this paper describes the development and testing of two electromagnetic probes for this purpose. A simple dc variable reluctance probe has been developed under EPRI Project SGPO-S125-1 which gives a measure of crevice gap clearance at eight discrete points around the periphery of the tube. Hall elements are used as the active sensors and the probe drive, and eight-channel signal acquisition is accomplished with ALN 4000 equipment. The alternative electromagnetic approach to the detection of <span class="hlt">magnetite</span> buildup is to use a conventional differential eddy current probe. Work carried out under EPRI project RP1395-2 has shown that such a probe is also sensitive to the presence of <span class="hlt">magnetite</span> in the crevice gap. In both cases, a finite element model has been used to develop ''training data'' for a variety of buildup profiles, and these theoretical results are compared with pre- and post-chemical flushing measurements on a model boiler.</p> <div class="credits"> <p class="dwt_author">Lord, W.; Palanisamy, R.; Satish, S.R.</p> <p class="dwt_publisher"></p> <p class="publishDate">1983-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">374</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://authors.library.caltech.edu/10336/1/HOLplosone08.pdf"> <span id="translatedtitle">Bats Use <span class="hlt">Magnetite</span> to Detect the Earth's Magnetic Field</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">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 <span class="hlt">magnetite</span> (Fe3O4). Bats have recently been shown to use magnetic</p> <div class="credits"> <p class="dwt_author">Richard A. Holland; Joseph L. Kirschvink; Thomas G. Doak; Martin Wikelski</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">375</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52275068"> <span id="translatedtitle">Bats Use <span class="hlt">Magnetite</span> to Detect the Earth's Magnetic Field</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">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 <span class="hlt">magnetite</span> (Fe3O4). Bats have recently been shown to use magnetic</p> <div class="credits"> <p class="dwt_author">Richard A. Holland; Joseph L. Kirschvink; Thomas G. Doak; Martin Wikelski; Sarah Frances Brosnan</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">376</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/56554602"> <span id="translatedtitle">Novel <span class="hlt">magnetite</span>-producing magnetotactic bacteria belonging to the Gammaproteobacteria</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">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 <span class="hlt">magnetite</span>, and are motile by means of flagella. The strains grow chemolithoautotrophically oxidizing thiosulfate and sulfide microaerobically as</p> <div class="credits"> <p class="dwt_author">Christopher T Lefèvre; Nathan Viloria; Marian L Schmidt; Mihály Pósfai; Richard B Frankel; Dennis A Bazylinski</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">377</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2844004"> <span id="translatedtitle">Avian <span class="hlt">magnetite</span>-based magnetoreception: a physiologist's perspective</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">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. <span class="hlt">Magnetite</span>, a ferromagnetic mineral, has been found in a wide range of organisms, from bacteria to vertebrates. In birds, both superparamagnetic (SPM) and single-domain <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span> in the subcutis of the pigeon's upper beak. The aims of the present review are to review the evidence for a <span class="hlt">magnetite</span>-based mechanism in birds and to introduce physiological concepts in order to refine the proposed models.</p> <div class="credits"> <p class="dwt_author">Cadiou, Herve; McNaughton, Peter A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">378</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20010044732&hterms=ALH84001&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DALH84001"> <span id="translatedtitle"><span class="hlt">Magnetite</span> and Carbonate Textures in ALH84001: Experimental Insights</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Synthetic siderite and synthetic siderite-magnesite carbonates were equilibrated with hematite, <span class="hlt">magnetite</span>, 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.</p> <div class="credits"> <p class="dwt_author">Koziol, Andrea M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">379</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/19607376"> <span id="translatedtitle"><span class="hlt">Magnetite</span> nanoparticles for biosensor model based on bacteria fluorescence</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Fluorescence emission of pyoverdine - the siderophore synthesized by iron scavenger bacteria - was studied using in vitro cultures of Pseudomonas aeruginosa with the aim to design a biosensor system for liquid sample iron loading. Diluted suspensions of colloidal <span class="hlt">magnetite</span> nanoparticles were supplied in the culture medium (10 microl\\/l and 100 microl\\/l) to simulate magnetic loading with iron oxides of</p> <div class="credits"> <p class="dwt_author">A. Poita; D.-E. Creanga; A. Airinei; P. Tupu; C. Goiceanu; O. Avadanei</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">380</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.agu.org/journals/jb/v078/i011/JB078i011p01780/JB078i011p01780.pdf"> <span id="translatedtitle">Superparamagnetic and Single-Domain Threshold Sizes in <span class="hlt">Magnetite</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Particle size distributions have been obtained by grain counts on electron micrographs of four samples containing submicroscopic equant <span class="hlt">magnetite</span> particles. Blocking temperature data indicate thermally unstable (superparamagnetic, SPM) magnetic behavior in one sample whose grains range from 100 to 650 A in size. The SPM is confirmed by a large increase of saturation remshence when the hysteresis of the sample</p> <div class="credits"> <p class="dwt_author">D. J. Dunlop</p> <p class="dwt_publisher"></p> <p class="publishDate">1973-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_18");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a style="font-weight: bold;">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_20");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> </div><!-- page_19 div --> <div id="page_20" class="hiddenDiv"> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_19");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a style="font-weight: bold;">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_21");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">381</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/24730613"> <span id="translatedtitle">Mechanochemically enhanced degradation of pyrene and phenanthrene loaded on <span class="hlt">magnetite</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">The enhancement of the degradation of polycyclic aromatic hydrocarbons (PAHs), exemplified by pyrene and phenanthrene, using mild grinding in the presence of common minerals was investigated. <span class="hlt">Magnetite</span>, birnessite, and Na- and Cu-montmorillonite samples were loaded with pyrene or phenanthrene and ground manually or in a ball mill for short periods of time. The ground samples were analyzed for PAHs and for their metabolites, using high-performance liquid chromatography and liquid chromatography-mass spectrometry. No degradation of pyrene occurred when it was in contact with Na-montmorillonite or birnessite. Sorption of pyrene on Cu-montmorillonite enhanced its degradation, but grinding of the loaded clay actually inhibited pyrene's degradation. Phenanthrene hardly degraded on Cu-montmorillonite. Grinding <span class="hlt">magnetite</span> loaded with either PAH resulted in a significant degradation of both (?50% after grinding for 5 min), while in the nonground samples, negligible degradation was detected. The extent of degradation increased with the duration of grinding. The degradation of either PAH loaded on <span class="hlt">magnetite</span> yielded oxidized products. In soil samples contaminated with PAHs and mixed with <span class="hlt">magnetite</span>, a similar grinding-induced degradation pattern was observed, but with a lower rate. A liquid phase was required to initiate degradation in the soil. The liquid phase apparently served as the medium through which the pollutants reached the surface of the degradation-enhancing mineral. PMID:24730613</p> <div class="credits"> <p class="dwt_author">Joseph-Ezra, Hadas; Nasser, Ahmed; Ben-Ari, Julius; Mingelgrin, Uri</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-20</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">382</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=LAUR78847"> <span id="translatedtitle">Decomposition of Hydrogen Bromide Using Iron Bromide and <span class="hlt">Magnetite</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">A means of thermochemically decomposing hydrogen bromide has been investigated experimentally using the reaction between <span class="hlt">magnetite</span> and HBr as the bromine producing step. A high yield of Br sub 2 was formed in a short time (90% in 0.5 h). For the hydrogen ...</p> <div class="credits"> <p class="dwt_author">C. F. V. Mason</p> <p class="dwt_publisher"></p> <p class="publishDate">1978-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">383</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/20025929"> <span id="translatedtitle">Effect of Dispersant on Preparation of Colloidal <span class="hlt">Magnetite</span> Nanocrystals</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Nanometer scale <span class="hlt">magnetite</span> particles were prepared in a very low concentration dispersing system with a dispersant. The average size of the particles prepared under optimum conditions was determined by transmission electron microscopy to be approximately 1.8 nm. The magnetic properties were investigated using a superconducting quantum interference device (SQUID) magnetometer. The dried samples exhibited approximately superparamagnetic behavior. Rhelogical property measurement</p> <div class="credits"> <p class="dwt_author">Chang-Neng Shauo; Chuen-Guang Chao</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">384</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012espc.conf..921M"> <span id="translatedtitle">Discovery of Framboidal <span class="hlt">Magnetites</span> in the Murchison meteorite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Framboidal <span class="hlt">magnetites</span> are discovered in the Murchison CM2 meteorite for the first time. We discuss them as a biomarker. Their bacterial colonylike uniform-size and irregular structures indicate that they are involved in biotic process that date to the beginning of the solar system.</p> <div class="credits"> <p class="dwt_author">Miyake, N.; Wallis, M. K.; Wickramasinghe, N. C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">385</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://pubs.er.usgs.gov/publication/ofr72303"> <span id="translatedtitle">Benefaction studies on the Hasan Celebi <span class="hlt">magnetite</span> deposit, Turkey</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">Bench-scale and semicontinuous tests were performed on surface, trench, and diamond drill core samples from the Hasan Celebi low-grade <span class="hlt">magnetite</span> deposit to determine the optimum benefication procedures utilizing wet magnetic separation techniques. Composite core samples typically contain about 27 percent recoverable <span class="hlt">magnetite</span> and require crushing and grinding through 1 mm in size to insure satisfactory separation of the gangue from the <span class="hlt">magnetite</span>. Regrinding and cleaning the <span class="hlt">magnetite</span> 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.</p> <div class="credits"> <p class="dwt_author">Pressler, Jean W.; Akar, Ali</p> <p class="dwt_publisher"></p> <p class="publishDate">1972-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">386</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/22468120"> <span id="translatedtitle">Glucose oxidase–<span class="hlt">magnetite</span> nanoparticle bioconjugate for glucose sensing</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Immobilization of bioactive molecules on the surface of magnetic nanoparticles is of great interest, because the magnetic properties of these bioconjugates promise to greatly improve the delivery and recovery of biomolecules in biomedical applications. Here we present the preparation and functionalization of <span class="hlt">magnetite</span> (Fe 3O 4) nanoparticles 20 nm in diameter and the successful covalent conjugation of the enzyme glucose oxidase</p> <div class="credits"> <p class="dwt_author">Liane M. Rossi; Ashley D. Quach; Zeev Rosenzweig</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">387</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012GGG....13....8K"> <span id="translatedtitle">Continuous production of nanosized <span class="hlt">magnetite</span> through low grade burial</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Geological processes, such as burial, can lead to remagnetization in rocks due to neoformed magnetic minerals that have passed a critical volume, called blocking volume. In this study, we designed a heating experiment for claystones obtained from the Paris Basin (France), in the 50-130°C temperature range, in order to simulate <4 km burial remagnetization. At a given temperature, remanence increased rapidly within a couple of days and stabilized afterward. There was a positive relation between the experimental temperature and the obtained remanence. Remanence was determined to be carried equally by stable chemical remanent magnetization and unstable thermo-viscous remanent magnetization. By assuming that <span class="hlt">magnetite</span> formed during the experiment, we interpreted the increase of chemical remanent magnetization and the increase of thermo-viscous remanent magnetization as the continuous growth of the >20 nm and ˜20 nm minerals respectively. This result led us to propose a conceptual model of nucleation-and-growth process of <span class="hlt">magnetite</span> during low grade burial from ˜2 to ˜4 km depth. Ultrafine <span class="hlt">magnetite</span> (?20 nm) was predominant over single domain <span class="hlt">magnetite</span> (>20 nm) for <4 km depth. Transposed to natural conditions, our heating steps experiment suggested that claystone-type rocks are remagnetized during burial. For temperatures higher than 200°C, the extrapolation of our results indicated that burial remagnetization, due to the chemical remanent magnetization, might be larger than the natural remanent magnetization.</p> <div class="credits"> <p class="dwt_author">Kars, Myriam; Aubourg, Charles; Pozzi, Jean-Pierre; Janots, Dominik</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">388</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/21643156"> <span id="translatedtitle"><span class="hlt">Pure</span> optical photoacoustic microscopy.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">The concept of <span class="hlt">pure</span> optical photoacoustic microscopy(POPAM) was proposed based on optical rastering of a focused excitation beam and optically sensing the photoacoustic signal using a microring resonator fabricated by a nanoimprinting technique. After the refinements of the microring's working wavelength and in the resonator structure and mold fabrication, an ultrahigh Q factor of 3.0×10(5) was achieved which provided high sensitivity with a noise equivalent detectable pressure(NEDP) value of 29 Pa. This NEDP is much lower than the hundreds of Pascals achieved with existing optical resonant structures such as etalons, fiber gratings and dielectric multilayer interference filters available for acoustic measurement. The featured high sensitivity allowed the microring resonator to detect the weak photoacoustic signals from micro- or submicroscale objects. The inherent superbroad bandwidth of the optical microring resonator combined with an optically focused scanning beam provided POPAM with high resolution in the axial as well as both lateral directions while the axial resolution of conventional photoacoustic microscopy (PAM) suffers from the limited bandwidth of PZT detectors. Furthermore, the broadband microring resonator showed similar sensitivity to that of our most sensitive PZT detector. The current POPAM system provides a lateral resolution of 5 ?m and an axial resolution of 8 ?m, comparable to that achieved by optical microscopy while presenting the unique contrast of optical absorption and functional information complementing other optical modalities. The 3D structure of microvasculature, including capillary networks, and even individual red blood cells have been discerned successfully in the proof-of-concept experiments on mouse bladders ex vivo and mouse ears in vivo. The potential of approximately GHz bandwidth of the microring resonator also might allow much higher resolution than shown here in microscopy of optical absorption and acoustic propagation properties at depths in unfrozen tissue specimens or thicker tissue sections, which is not now imageable with current optical or acoustic microscopes of comparable resolution. PMID:21643156</p> <div class="credits"> <p class="dwt_author">Xie, Zhixing; Chen, Sung-Liang; Ling, Tao; Guo, L Jay; Carson, Paul L; Wang, Xueding</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">389</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/23893106"> <span id="translatedtitle">Cytochrome cd1 nitrite reductase NirS is involved in anaerobic <span class="hlt">magnetite</span> biomineralization in Magnetospirillum gryphiswaldense and requires NirN for proper d1 heme assembly.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">The alphaproteobacterium Magnetospirillum gryphiswaldense synthesizes magnetosomes, which are membrane-enveloped <span class="hlt">crystals</span> of <span class="hlt">magnetite</span>. Here we show that nitrite reduction is involved in redox control during anaerobic biomineralization of the mixed-valence iron oxide <span class="hlt">magnetite</span>. The cytochrome cd1-type nitrite reductase NirS shares conspicuous sequence similarity with NirN, which is also encoded within a larger nir cluster. Deletion of any one of these two nir genes resulted in impaired growth and smaller, fewer, and aberrantly shaped <span class="hlt">magnetite</span> <span class="hlt">crystals</span> during nitrate reduction. However, whereas nitrite reduction was completely abolished in the ?nirS mutant, attenuated but significant nitrite reduction occurred in the ?nirN mutant, indicating that only NirS is a nitrite reductase in M. gryphiswaldense. However, the ?nirN mutant produced a different form of periplasmic d(1) heme that was not noncovalently bound to NirS, indicating that NirN is required for full reductase activity by maintaining a proper form of d1 heme for holo-cytochrome cd(1) assembly. In conclusion, we assign for the first time a physiological function to NirN and demonstrate that effective nitrite reduction is required for biomineralization of wild-type <span class="hlt">crystals</span>, probably by contributing to oxidation of ferrous iron under oxygen-limited conditions. PMID:23893106</p> <div class="credits"> <p class="dwt_author">Li, Yingjie; Bali, Shilpa; Borg, Sarah; Katzmann, Emanuel; Ferguson, Stuart J; Schüler, Dirk</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">390</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3754751"> <span id="translatedtitle">Cytochrome cd1 Nitrite Reductase NirS Is Involved in Anaerobic <span class="hlt">Magnetite</span> Biomineralization in Magnetospirillum gryphiswaldense and Requires NirN for Proper d1 Heme Assembly</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">The alphaproteobacterium Magnetospirillum gryphiswaldense synthesizes magnetosomes, which are membrane-enveloped <span class="hlt">crystals</span> of <span class="hlt">magnetite</span>. Here we show that nitrite reduction is involved in redox control during anaerobic biomineralization of the mixed-valence iron oxide <span class="hlt">magnetite</span>. The cytochrome cd1-type nitrite reductase NirS shares conspicuous sequence similarity with NirN, which is also encoded within a larger nir cluster. Deletion of any one of these two nir genes resulted in impaired growth and smaller, fewer, and aberrantly shaped <span class="hlt">magnetite</span> <span class="hlt">crystals</span> during nitrate reduction. However, whereas nitrite reduction was completely abolished in the ?nirS mutant, attenuated but significant nitrite reduction occurred in the ?nirN mutant, indicating that only NirS is a nitrite reductase in M. gryphiswaldense. However, the ?nirN mutant produced a different form of periplasmic d1 heme that was not noncovalently bound to NirS, indicating that NirN is required for full reductase activity by maintaining a proper form of d1 heme for holo-cytochrome cd1 assembly. In conclusion, we assign for the first time a physiological function to NirN and demonstrate that effective nitrite reduction is required for biomineralization of wild-type <span class="hlt">crystals</span>, probably by contributing to oxidation of ferrous iron under oxygen-limited conditions.</p> <div class="credits"> <p class="dwt_author">Li, Yingjie; Bali, Shilpa; Borg, Sarah; Katzmann, Emanuel</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">391</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012JPhCS.400d2036K"> <span id="translatedtitle">Intensified magneto-resistance by rapid thermal annealing in <span class="hlt">magnetite</span> (Fe3O4) thin film on SiO2 glass substrate</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have observed large magneto-resistance (MR) intensified by rapid thermal annealing (RTA) in <span class="hlt">magnetite</span> (Fe3O4) thin film (MTF) on SiO2 glass (a-SiO2) substrate. The MTF was produced by the RF magnetron sputtering method by using a <span class="hlt">magnetite</span> target. The electrical resistivity (ER) of as-grown MTF (AG-MTF) showed the Mott's variable range hopping behavior, which implies that the AG-MTF is amorphous-like. Although the magneto-resistance (MR) ratio of bulk single <span class="hlt">crystal</span> is very small except around the Verwey transition temperature (VTT), that of the AG-MTF showed moderately large below room temperature. Due to RTA of the AG-MTF by use of an IR image furnace, the MR ratio of MTFs was intensified, and especially by the annealing around the Curie temperature (585°C) of <span class="hlt">magnetite</span>. Furthermore the ER of the rapid thermally annealed MTF (RTA-MTF) showed a slight kink at around the VTT, which indicates that the crystallinity of the RTA-MTF is higher than that of the AG-MTF The MTF produced by the RF magnetron sputtering method are composed of <span class="hlt">magnetite</span> fine particles (MFPs). We consider that the directions of magnetic moments of MFPs in the MTF were spatially randomized by the RTA and the strong spin scattering of itinerant electrons transferring between adjacent MFPs caused the intensification of the MR ratio.</p> <div class="credits"> <p class="dwt_author">Kobori, H.; Morii, K.; Yamasaki, A.; Sugimura, A.; Taniguchi, T.; Horie, T.; Naitoh, Y.; Shimizu, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">392</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EurSS..46..635V"> <span id="translatedtitle">Dissolution of <span class="hlt">magnetite</span> and redistribution of heavy metals in urban soils (model experiment)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Technogenic <span class="hlt">magnetite</span> in urban soils is extremely various in properties. Its particles strongly differ in magnetic susceptibility and degree of association with heavy metals. In the city of Perm, particles of <span class="hlt">magnetite</span> enriched with different heavy metals are precipitated, which indicates different sources of technogenic <span class="hlt">magnetite</span> within the limits of the city. The dissolution of <span class="hlt">magnetite</span> and the effect of this process on the behavior of heavy metals have been simulated by the magnetochemical method. In strongly magnetic soils, the dissolution of highly magnetic macrocrystalline <span class="hlt">magnetite</span> is accompanied by the dissolution of heavy metals: Cr, Mn, Ni, Zn, Pb, and Cu. The secondary precipitates of hydroxides of iron and heavy metals (predominantly Pb, Cu, and Ni) are formed relatively rarely, mainly in weakly magnetic soils, where slightly magnetic and dispersed <span class="hlt">magnetite</span> is present. In cities, the dissolution of <span class="hlt">magnetite</span> is favored by the added salts and organic acids released by plants.</p> <div class="credits"> <p class="dwt_author">Vodyanitskii, Yu. N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">393</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFMGP21B1011S"> <span id="translatedtitle">Pressure effect on the low-temperature remanences of multidomain <span class="hlt">magnetite</span>: Change in the Verwey transition temperature</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Verwey transition of <span class="hlt">magnetite</span> is the basic issues for the rock magnetism, since main magnetic mineral of terrestrial rocks is <span class="hlt">magnetite</span> 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 <span class="hlt">magnetite</span>, and observed an increase in Tv with increasing pretreated pressure. From this result, they suggested that the Verwey transition of <span class="hlt">magnetite</span> 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 stoichiometri