177,071 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
Ferrous oxide activity measurements in FeO-TiO₂-SiO₂, FeO-TiO₂-CaO ternary systems and FeO-TiO₂-SiO₂-MnO, FeO-TiO₂-SiO₂-CaO quaternary systems
No full textFerrous oxide activity has been determined in titania rich slags. Molten synthetic slag mixtures of the ternary systems FeO-TiO₂- SiO₂ and FeO-TiO₂-CaO and of the system FeO-TiO₂-SiO₂ containing MnO and CaO at constant levels of each have been investigated. The slags were contained in iron crucibles and were equilibrated for four hours at 1475°C or 1470°C with gas mixtures containing CO₂, H₂, and argon of varying oxygen potentials. The equilibration technique made use of the equilibrium reaction: - Fe (solid) + ¹/₂ O₂ (gas) = FeO (slag). Each gas mixture used had an oxygen potential corresponding to a certain ferrous oxide activity in the slag and after equilibration the final chemical analysis of the slags gave the compositions having this particular ferrous oxide activity. In the course of determining the activity in the ternary systems, the binary systems FeO-SiO₂ and FeO-CaO were investigated at 1475°C and 1470°C respectively. The ferrous oxide activities determined had a satisfactory agreement with other investigators of these systems. Silica activity was calculated by Gibbs-Duhem equation and calcium oxide activity was calculated by both Gibbs-Duhem equation and regular solution model. In the ternary system FeO-TiO₂-SiO₂ at 1475°C, FeO isoactivity curves are bowed towards FeO corner and this was related to the miscibility gap in the binary system TiO₂-SiO₂ which show that the two liquid oxides are incompatible and must have a positive deviation from ideality. Ferrous oxide activity in this system was compared to MnO activity in the system MnO-TiO₂-SiO₂ and the comparison showed that MnO have lower activity than FeO. Silica activity was calculated by Gibbs-Duhem equation. FeO iso-activity curves in the system FeO-TiO₂-CaO at 1470°C are bowed away from FeO corner. The formation of a series of interoxide compounds in the phase diagram of CaO-TiO₂ explain the increase in FeO activity with the addition of CaO to FeO-TiO₂ binary or vice versa. TiO₂ and CaO activities were calculated by Gibbs-Duhem equation and regular solution model. Basic oxide additions to the ternary FeO-TiO₂-SiO₂ increased FeO activity. Increasing MnO additions from about 8 mole % to about 24 mole % Increased FeO activity but had no effect on the direction of bowing of the curves. Increasing CaO additions reversed the direction of bowing of the iso-activity curves. For all TiO₂ : SiO₂ ratios the addition of 16.1 mole % CaO Increased FeO activity more than the same addition of MnO.Ferrous oxide activity has been determined in titania rich slags. Molten synthetic slag mixtures of the ternary systems FeO-TiO₂- SiO₂ and FeO-TiO₂-CaO and of the system FeO-TiO₂-SiO₂ containing MnO and CaO at constant levels of each have been investigated. The slags were contained in iron crucibles and were equilibrated for four hours at 1475°C or 1470°C with gas mixtures containing CO₂, H₂, and argon of varying oxygen potentials. The equilibration technique made use of the equilibrium reaction: - Fe (solid) + ¹/₂ O₂ (gas) = FeO (slag). Each gas mixture used had an oxygen potential corresponding to a certain ferrous oxide activity in the slag and after equilibration the final chemical analysis of the slags gave the compositions having this particular ferrous oxide activity. In the course of determining the activity in the ternary systems, the binary systems FeO-SiO₂ and FeO-CaO were investigated at 1475°C and 1470°C respectively. The ferrous oxide activities determined had a satisfactory agreement with other investigators of these systems. Silica activity was calculated by Gibbs-Duhem equation and calcium oxide activity was calculated by both Gibbs-Duhem equation and regular solution model. In the ternary system FeO-TiO₂-SiO₂ at 1475°C, FeO isoactivity curves are bowed towards FeO corner and this was related to the miscibility gap in the binary system TiO₂-SiO₂ which show that the two liquid oxides are incompatible and must have a positive deviation from ideality. Ferrous oxide activity in this system was compared to MnO activity in the system MnO-TiO₂-SiO₂ and the comparison showed that MnO have lower activity than FeO. Silica activity was calculated by Gibbs-Duhem equation. FeO iso-activity curves in the system FeO-TiO₂-CaO at 1470°C are bowed away from FeO corner. The formation of a series of interoxide compounds in the phase diagram of CaO-TiO₂ explain the increase in FeO activity with the addition of CaO to FeO-TiO₂ binary or vice versa. TiO₂ and CaO activities were calculated by Gibbs-Duhem equation and regular solution model. Basic oxide additions to the ternary FeO-TiO₂-SiO₂ increased FeO activity. Increasing MnO additions from about 8 mole % to about 24 mole % Increased FeO activity but had no effect on the direction of bowing of the curves. Increasing CaO additions reversed the direction of bowing of the iso-activity curves. For all TiO₂ : SiO₂ ratios the addition of 16.1 mole % CaO Increased FeO activity more than the same addition of MnO
Commento a: Galia G, Lieto E, Pelosio L, Imperatore V, Castellano P, Pignatelli C. Ileo biliare: revisione della letteratura e presentazione di un caso clinico.
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Structural distortion of B1-structured MnO and FeO
No full textThe structural distortion of B1-structured MnO and FeO under high pressure is investigated using ab initio methods within GGA and GGA+U approximations. Present calculations indicated that the ordinary density-functional calculation overestimated the structural distortion of MnO and FeO under pressure. When the strong electronic correlations are included in the form of GGA + U. a reasonable description of the structural distortion under high pressure can be obtained. The overestimation of exchange interactions in ordinary DFT calculations may be the most important reason for the overestimation of structural distortion. (C) 2007 Elsevier Ltd. All rights reserved
PHOTODETACHMENT ELECTRON SFECTROSCOPY OF : DETERMINATION OF THE NEUTRAL MOLECULAR GROUND STATE
No full textAuthor Institution: Department of Chemistry and Joint Institute of Laboratory Astrophysics, University of ColoradoThe energy spectrum of electrons photodetached from anions was obtained in a crossed ion-beam/laser-beam apparatus. From this spectrum the electron affinity of FeO could be determined and, additionally, the vibrational frequencies of the ground states of both the anion (760 and the neutral (970 were obtained. These FeO studies not only provide an EA(FeO) = 1.497 eV but also show that the state of FeO which has been considered the ground state for thirty years is in fact an excited state lying some 4000 above the true ground state
Concrete cover rip-off of R/C beams strengthened with FRP composites
No full textIn this paper the authors consider four FRP strengthened R/C beams brought to failure for concrete cover rip-off under uniform load conditions. Based on the available experimental results, a comparative study of different models for crack spacing evaluation is presented, accounting the influence of the FRP strengthening on the crack pattern development and stabilization. Among the considered models, the authors select a simple and efficient expression suitable to be proposed as a design tool. Thanks to the selected crack spacing expression, the authors work out a simple model that can predict the rip-off failure load of R/C beams externally strengthened with FRP with an acceptable accuracy. The model is calibrated making use of the four available experimental beams and is validated accounting for 23 experimental beams derived from the literature
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Feo - Transport of ferrous iron into bacteria
No full textBacteria commonly utilise a unique type of transporter, called Feo, to specifically acquire the ferrous (Fe2+) form of iron from their environment. Enterobacterial Feo systems are composed of three proteins: FeoA, a small, soluble SH3-domain protein probably located in the cytosol; FeoB, a large protein with a cytosolic N-terminal G-protein domain and a C-terminal integral inner-membrane domain containing two 'Gate' motifs which likely functions as the Fe2+ permease; and FeoC, a small protein apparently functioning as an [Fe-S]-dependent transcriptional repressor. We provide a review of the current literature combined with a bioinformatic assessment of bacterial Feo systems showing how they exhibit common features, as well as differences in organisation and composition which probably reflect variations in mechanisms employed and function
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