Search results for "valency"
showing 10 items of 70 documents
Influence on the phase transitions of barium titanate of the manganese valency, introduced as a substituant in the titanium site
1991
Abstract A small amount of manganese introduced in BaTiO3 modifies strongly the vibrational and electronic properties of the pure compound. Dielectric response and EPR measurements are reported in order to study the influence of the manganese valency on the ferroelectric-paraelectric phase transition.
Verwey-type transition in EuNiP
2006
High temperature 151Eu Mossbauer measurements provide proof for inhomogeneous mixed-valent behaviour in EuNiP. We observed that EuNiP undergoes a Verwey-type charge delocalisation transition when heated above 470 K prior to the structural γ-β phase transition at T ≈ 510 K. This finding confirms the results of photoemission spectroscopy in the isostructural compound EuPdP and of TB-LMTO-ASA band structure calculations. We discuss the role of a van Hove singularity associated with a high density of 4f states close to the Fermi energy in inhomogeneous mixed europium valency, and the microscopic mechanism of γ-β phase transition in compounds analogous to EuNiP.
Exotic magnetism in the alkali sesquioxidesRb4O6andCs4O6
2009
Among the various alkali oxides the sesquioxides ${\text{Rb}}_{4}{\text{O}}_{6}$ and ${\text{Cs}}_{4}{\text{O}}_{6}$ are of special interest. Electronic-structure calculations using the local spin-density approximation predicted that ${\text{Rb}}_{4}{\text{O}}_{6}$ should be a half-metallic ferromagnet, which was later contradicted when an experimental investigation of the temperature-dependent magnetization of ${\text{Rb}}_{4}{\text{O}}_{6}$ showed a low-temperature magnetic transition and differences between zero-field-cooled and field-cooled measurements. Such behavior is known from spin glasses and frustrated systems. ${\text{Rb}}_{4}{\text{O}}_{6}$ and ${\text{Cs}}_{4}{\text{O}}_{6}$ c…
Magnetic transitions in double perovskiteSr2FeRe1−xSbxO6(0⩽x⩽0.9)
2006
The double perovskites ${\mathrm{Sr}}_{2}\mathrm{Fe}M{\mathrm{O}}_{6}$ $(M=\mathrm{Re},\mathrm{Mo})$ belong to the important class of half-metallic magnetic materials. In this study we explore the effect of replacing the electronic $5d$ buffer element Re with variable valency by the main group element Sb with fixed valency. X-ray diffraction reveals ${\mathrm{Sr}}_{2}{\mathrm{FeRe}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}{\mathrm{O}}_{6}$ $(0lxl0.9)$ to crystallize without antisite disorder in the tetragonally distorted perovskite structure (space group $I4∕mmm$). The ferrimagnetic behavior of the parent compound ${\mathrm{Sr}}_{2}{\mathrm{FeReO}}_{6}$ changes to antiferromagnetic upon Sb subst…
Electrically switchable magnetic exchange in the vibronic model of linear mixed valence triferrocenium complex
2018
In this article, we report our development of a vibronic model for the electric-field control of antiferromagnetic superexchange in the mixed-valence (MV) triferrocenium complex FeIII-FeII-FeIII proposed as a possible candidate for the molecular implementation of a quantum logic gate. Along with the electronic interactions, such as electron transfer between the iron ions in different oxidation degrees and Coulomb repulsion of the extra holes, the proposed model of the triferrocenium complex also takes into account the vibronic coupling as an inherent ingredient of the problem of mixed valency. The latter is described by the conventional Piepho-Krauzs-Shatz (PKS) model adapted to the linear …
Predicting Pharmacokinetics of Multisource Acyclovir Oral Products Through Physiologically Based Biopharmaceutics Modeling.
2021
Abstract Highly variable disposition after oral ingestion of acyclovir has been reported, although little is known regarding the underlying mechanisms. Different studies using the same reference product (Zovirax ®) showed that Cmax and AUC were respectively 44 and 35% lower in Saudi Arabians than Europeans, consistent with higher frequencies of reduced-activity polymorphs of the organic cation transporter (OCT1) in Europeans. In this study, the contribution of physiology (i.e., OCT1 activity) to the oral disposition of acyclovir immediate release (IR) tablets was hypothesized to be greater than dissolution. The potential role of OCT1 was studied in a validated physiologically-based biopharm…
Fate of PCDD/PCDF during mechanical–biological sludge treatment
2004
Abstract In this preliminary study the seventeen 2,3,7,8-substituted congeners of PCDD/PCDF were analyzed at the inlet and outlet water and for three sewage sludge samples taken from different treatment stages to check behaviours of PCDD/PCDF at a municipal wastewater treatment plant (MWTP) in Poland. At the inlet (untreated sewage) water dominated PCDD congeners, whereas in the outlet (treated water) dominated the PCDF congeners. The octaCDD, 1,2,3,4,6,7,8-heptaCDD/CDF and octaCDF congeners dominated in all of the sludge samples. The total toxicity load gradually increased in the series excess, digested and dewatered sludge and amounted to 12.2, 14.4 and 16.9 ng I-TEQ kg −1 .
Biowaiver monographs for immediate release solid oral dosage forms: quinidine sulfate.
2009
Literature data are reviewed relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of new multisource and reformulated immediate release (IR) solid oral dosage forms containing quinidine sulfate. Quinidine sulfate's solubility and permeability, its therapeutic use and index, pharmacokinetics, excipient interactions and reported BE/bioavailability (BA) problems were taken into consideration. The available data are not fully conclusive, but do suggest that quinidine sulfate is highly soluble and moderately to highly permeable and would likely be assigned to BCS Class I (or at worst BCS III). In view of the inconclusiveness of the data and, more imp…
Physics of the nuclear pore complex: Theory, modeling and experiment
2021
Abstract The hallmark of eukaryotic cells is the nucleus that contains the genome, enclosed by a physical barrier known as the nuclear envelope (NE). On the one hand, this compartmentalization endows the eukaryotic cells with high regulatory complexity and flexibility. On the other hand, it poses a tremendous logistic and energetic problem of transporting millions of molecules per second across the nuclear envelope, to facilitate their biological function in all compartments of the cell. Therefore, eukaryotes have evolved a molecular “nanomachine” known as the Nuclear Pore Complex (NPC). Embedded in the nuclear envelope, NPCs control and regulate all the bi-directional transport between the…
Valence instabilities and inhomogeneous mixed valence in some ternary europium compounds
1997
Abstract Photoemission spectra and TB-LMTO-ASA band structure calculations of some mixed valency europium compounds hve been studied. The band structures are compared with the band structures of the isostructural lanthanum and strontium compounds. Surprisingly a 4f density of states in the vicinity of the Fermi level is observed in inhomogenous mixed valency EuPd 3 B, Eu 3 S 4 , and EuPdP. Indeed a van Hove Singularity (vHS) derived from the d states of La and Pd or p states of boron or phosphorous are found in La 3 S 4 , LaPd 3 B and SrPdP. The valence instability in the Eu compounds is thus not necessarily due to Eu 4f states. The results also provide some ground for the assumption that i…