6,417 research outputs found
Melt densities in the Na2O-FeO-Fe2O3-SiO2 system and the partial molar volume of tetrahedrally-coordinated ferric iron in silicate melts
No full textThe densities of 12 melts in the Na2O-FeO-Fe2O3-SiO2 system have been determined in equilibrium with air, in the temperature range of 1000–1500°C, using the double bob, Archimedean technique. Ferrous iron determinations of 100–200 mg samples, “dip” quenched from high temperature, indicate that all the melts investigated were highly oxidized under these experimental conditions. 57Fe Mössbauer spectra of glasses obtained by drop quenching 80 mg melt samples from loop equilibration runs yield Fe3+/Fe2+ data equivalent to that for the densitometry (dip) samples for all but the most viscous melt, and confirm that all but one melt equilibrated with air during the densitometry measurements.
Melt densities range from 2.17 to 2.88 g/cm3 with a mean standard deviation (from replicate experiments) of 0.36%. Least squares regression of the density data at 1300, 1400 and 1500°C, was calculated, both excluding and including excess volume terms (herein named linear and nonlinear fits, respectively) and the root mean squared deviation (RMSD) of each regression was compared with the total experimental error. The partial molar volumes computed for linear fits for Na2O and SiO2 are similar to those previously reported for melts in the Na2O-Al2O3-SiO2 system (Steinet al., 1986). The partial molar volumes of Fe2O3 obtained in these linear fits are equal to those obtained by Shiraishi et al. (1978) in the FeO-Fe2O3-SiO2 system but 5 to 10% lower than reported by Mo et al. (1982) in multicomponent melts. The partial molar volume exhibited by Fe3+ in this system is representative of the partial molar volume of tetrahedrally coordinated Fe3+ in silicate melts
Melt densities in the CaO-FeO-Fe2O3-SiO2 system and the compositional dependence of the partial molar volume of ferric iron in silicate melts
No full textThe densities of 10 melts in the CaO-FeO-Fe2O3-SiO2 system were determined in equilibrium with air, in the temperature range of 1200 to 1550°C, using the double-bob Archimedean technique. Melt compositions range from 6 to 58 wt% SiO2, 14 to 76 wt% Fe2O3 and 10 to 46 wt% CaO. The ferric-ferrous ratios of glasses drop-quenched from loop fusion equilibration experiments were determined by 57Fe Mössbauer spectroscopy.
Melt densities range from 2.689 to 3.618 gm/cm3 with a mean standard deviation from replicate experiments of 0.15%. Least-squares regressions of molar volume versus molar composition have been performed and the root mean squared deviation shows that a linear combination of partial molar volumes for the oxide components (CaO, FeO, Fe2O3 and SiO2) cannot describe the data set within experimental error. Instead, the inclusion of excess terms in CaFe3+ and CaSi (product terms using the oxides) is required to yield a fit that describes the experimental data within error. The nonlinear compositional-dependence of the molar volumes of melts in this system can be explained by structural considerations of the roles of Ca and Fe3+.
The volume behavior of melts in this system is significantly different from that in the Na2O-FeO-Fe2O3-SiO2 system, consistent with the proposal that a proportion of Fe3+ in melts in the CaO-FeO-Fe2O3-SiO2 system is not tetrahedrally-coordinated by oxygen, which is supported by differences in 57Fe Mössbauer spectra of glasses. Specifically, this study confirms that the 57Fe Mössbauer spectra exhibit an area asymmetry and higher values of isomer shift of the ferric doublet that vary systematically with composition and temperature (this study; Dingwell and Virgo, 1987, 1988). These observations are consistent with a number of other lines of evidence (e.g., homogeneous redox equilibria, Dickenson and Hess, 1986; viscosity, Dingwell and Virgo, 1987,1988). Two species of ferric iron, varying in proportions with temperature, composition and redox state, are sufficient to describe the above observations.
The presence of more than one coordination geometry for Fe3+ in low pressure silicate melts has several implications for igneous petrogenesis. The possible effects on compressibility, the pressure dependence of the redox ratio, and redox enthalpy are briefly noted
New insights on the role of epigenetic alterations in hepatocellular carcinoma
No full textMaddalena Frau,1 Claudio F Feo,2 Francesco Feo,1 Rosa M Pascale11Department of Clinical and Experimental Medicine, Division of Experimental Pathology and Oncology, 2Department of Clinical and Experimental Medicine, Division of Surgery. University of Sassari, Sassari, ItalyAbstract: Emerging evidence assigns to epigenetic mechanisms heritable differences in gene function that come into being during cell development or via the effect of environmental factors. Epigenetic deregulation is strongly involved in the development of hepatocellular carcinoma (HCC). It includes changes in methionine metabolism, promoter hypermethylation, or increased proteasomal degradation of oncosuppressors, as well as posttranscriptional deregulation by microRNA or messenger RNA (mRNA) binding proteins. Alterations in the methylation of the promoter of methyl adenosyltransferase MAT1A and MAT2A genes in HCC result in decreased S-adenosylmethionine level, global DNA hypomethylation, and deregulation of signal transduction pathways linked to methionine metabolism and methyl adenosyltransferases activity. Changes in S-adenosylmethionine levels may also depend on MAT1A mRNA destabilization associated with MAT2A mRNA stabilization by specific proteins. Decrease in MAT1A expression has also been attributed to miRNA upregulation in HCC. A complex deregulation of miRNAs is also strongly involved in hepatocarcinogenesis, with up-regulation of different miRNAs targeting oncosuppressor genes and down-regulation of miRNAs targeting genes involved in cell-cycle and signal transduction control. Oncosuppressor gene down-regulation in HCC is also induced by promoter hypermethylation or posttranslational deregulation, leading to proteasomal degradation. The role of epigenetic changes in hepatocarcinogenesis has recently suggested new promising therapeutic approaches for HCC on the basis of the administration of methylating agents, inhibition of methyl adenosyltransferases, and restoration of the expression of tumor-suppressor miRNAs.Keywords: hepatocarcinogenesis, DNA methylation, microRNA, Piwi-interacting RNAs, stem cells, therapeutic target
The effect of oxidation state on the viscosity of melts in the system Na2O-FeO-Fe2O3-SiO2
No full textThe viscosities of two melts in the system Na2O-FeO-Fe2O3-SiO2 have been measured as a function of oxidation state. The experiments were conducted by concentric-cylinder viscometry, on melts equilibrated with gas mixtures in a vertical tube, gas-mixing furnace. Viscosity determinations were made during stepwise reduction and oxidation of the melts. 57Fe Mössbauer spectra were obtained on quenched melt samples recovered during the viscometry experiments. In addition, a series of loop fusion experiments were performed at calibrated ƒO2 values in order to relate viscosity determinations directly to ƒO2.
The viscosities of acmite and NS4F40 (Na-rich and Si-poor relative to acmite) melts decrease with reduction of Fe in the melts, as nonlinear functions of , yielding a region of viscosity invariance at moderate to low values of (<0.4). The 57Fe Mössbauer spectra of quenched melts as a function of indicate the presence of one (network-modifying) ferrous species and two ferric species with ferric iron acting dominantly as a network-former in oxidized melts and dominantly as a network-modifier in reduced melts.
The presence of two ferric iron species produces a minimum in the degree of polymerization of the melt at intermediate values of : the region of viscosity invariance corresponds to this minimum. If viscosity is positively correlated with polymerization for all values of then the viscosity of very reduced melts will increase with reduction, as the melt polymerizes.
The effect of oxidation state on viscosity is large and illustrates that ferric iron should be considered as a separate component in calculation schemes for estimating the viscosity of natural magmas
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Purification of Feo proteins and analysis of residues important for Feo protein interactions
No full texttextIron is an essential element for virtually all forms of life. Complicating matters, it is present in the insoluble ferric form in aerobic environments, while the more soluble ferrous form is found in anaerobic or reducing environments. Vibrio cholerae, the causative agent of the disease cholera, requires iron to survive. In order to meet the need for iron, V. cholerae expresses a variety of iron acquisition systems. One of these systems, Feo, is highly conserved among bacterial species as well as archaea and transports ferrous iron. The Feo system consists of three proteins: FeoA, FeoB, and FeoC. Previous work using the bacterial adenylate cyclase two hybrid system has shown that FeoC interacts with the cytoplasmic N-terminal domain of FeoB. However, the significance of this interaction is not known. In this study, V. cholerae Feo system proteins were analyzed for residues important for the interaction between FeoB and FeoC. In addition, FeoA and FeoC were purified for antibody production. It was found that a residue in the G protein domain of FeoB was not necessary for interaction with FeoC. However, a conserved residue in FeoC did abolish the interaction with FeoB. These results indicate that there is at least one residue important in the interaction of FeoB and FeoC, although further characterization will most likely reveal more. Antibodies to FeoA and FeoC were generated to use them for further characterization of the Feo system.Microbiolog
Reduction Equilibria of Iron Oxides. II : Measurement of the Equilibrium of the Reaction, FeO(1)+CO=Fe(s)+CO_2
No full textapplication/pdfThe author measured the equilibrium of the reaction, FeO(1)+CO=Fe(s)+CO_2, at the range from 1, 370℃ to 1, 490℃, and the following equation was obtained as the temperature function of the equilibrium constant : Chemical formula. (a) Then, the author calculated the equilibrium constant of the reaction, FeO(1)+H_2=Fe(s)+H_2O, from equation (a) and the equilibrium constant of the water gas reaction and the following equation was obtained as the temperature function of log K : Chemical formula. (b) Finally the author calculated the dissociation pressure of molten FeO and the following equation was obtained as the temperature function of PO_2 : Chemical formula. (c)紀要類(bulletin)687873 bytesdepartmental bulletin pape
S. gallolyticus Aortic Valve Endocarditis with Mitral Valve Leaflet Aneurysm
No full textS. gallolyticus is one of the pathogenic agents of endocarditis, and mitral valve aneurysm is a rare but potentially devastating complication. We present a case of S. gallolyticus aortic valve endocarditis with concomitant anterior mitral valve leaflet aneurysm. Patient underwent surgery before aneurysm perforation, and postoperative course was uneventful. Time of surgery is crucial to avoid severe complications due to aneurysm rupture
Un Sistema di Misura per il Rilievo delle Tensioni Interlaminari nelle Strutture Placcate con FRP
No full textUn Sistema per la Determinazione delle Tensioni Interlaminari nelle Strutture Rinforzate con Fibre di Carbonio: Simulazioni Numeriche e Prove Sperimentali
No full textGuerriero, S. Barba, E. De Feo, F. Fiorillo, A. Manco, Multidisciplinary analysis: the Early Christian complex in Cimitile (Italy)
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