Effect of local Coulomb interactions on the electronic structure and exchange interactions in Mn12 magnetic molecules

We have studied the effect of local Coulomb interactions on the electronic structure of the molecular magnet Mn12-acetate within the LDA+U approach. The account of the on-site repulsion results in a finite energy gap and an integer value of the molecule's magnetic moment, both quantities being in a good agreement with the experimental results. The resulting magnetic moments and charge states of non-equivalent manganese ions agree very well with experiments. The calculated values of the intramolecular exchange parameters depend on the molecule's spin configuration, differing by 25-30% between the ferrimagnetic ground state and the completely ferromagnetic configurations. The values of the ground-state exchange coupling parameters are in reasonable agreement with the recent data on the magnetization jumps in megagauss magnetic fields. Simple estimates show that the obtained exchange parameters can be applied, at least qualitatively, to the description of the spin excitations in Mn12-acetate.Comment: RevTeX, LaTeX2e, 4 EPS figure

Characterization of the S = 9 excited state in Fe8Br8 by Electron Paramagnetic Resonance

High Frequency electron paramagnetic resonance has been used to observe the magnetic dipole, $\Delta$ M$_s$ = $\pm$ 1, transitions in the $S = 9$ excited state of the single molecule magnet Fe$_8$Br$_8$. A Boltzmann analysis of the measured intensities locates it at 24 $\pm$ 2 K above the $S = 10$ ground state, while the line positions yield its magnetic parameters D = -0.27 K, E = $\pm$0.05 K, and B$_4^0$ = -1.3$\times$ 10$^{-6}$ K. D is thus smaller by 8% and E larger by 7% than for $S = 10$. The anisotropy barrier for $S = 9$ is estimated as 22 K,which is 25% smaller than that for $S = 10$ (29 K). These data also help assign the spin exchange constants(J's) and thus provide a basis for improved electronic structure calculations of Fe$_8$Br$_8$.Comment: 7 pages, Figs included in text, submitted to PR

Sociodemographic factors associated with treatment-seeking and treatment receipt: cross-sectional analysis of UK Biobank participants with lifetime generalised anxiety or major depressive disorder

Background Anxiety and depressive disorders can be chronic and disabling. Although there are effective treatments, only a fraction of those impaired receive treatment. Predictors of treatment-seeking and treatment receipt could be informative for initiatives aiming to tackle the burden of untreated anxiety and depression. Aims To investigate sociodemographic characteristics associated with treatment-seeking and treatment receipt. Method Two binary retrospective reports of lifetime treatment-seeking (n = 44 810) and treatment receipt (n = 37 346) were regressed on sociodemographic factors (age, gender, UK ethnic minority background, educational attainment, household income, neighbourhood deprivation and social isolation) and alternative coping strategies (self-medication with alcohol/drugs and self-help) in UK Biobank participants with lifetime generalised anxiety or major depressive disorder. Analyses were also stratified by gender. Results Treatment access was more likely in those who reported use of self-help strategies, with university-level education and those from less economically advantaged circumstances (household income £100 000). Men who self-medicated and/or had a vocational qualification were also less likely to seek treatment. Conclusions This work on retrospective reports of treatment-seeking and treatment receipt at any time of life replicates known associations with treatment-seeking and treatment receipt during time of treatment need. More work is required to understand whether improving rates of treatment-seeking improves prognostic outcomes for individuals with anxiety or depression

Assignment of haem ligands and detection of electronic absorption bands of molybdenum in the di-haem periplasmic nitrate reductase of Paracoccus pantotrophus.

AbstractThe periplasmic nitrate reductase (NAP) from Paracoccus pantotrophus is a soluble two-subunit enzyme (NapAB) that binds two c-type haems, a [4Fe–4S] cluster and a bis-molybdopterin guanine dinucleotide cofactor that catalyses the reduction of nitrate to nitrite. In the present work the NapAB complex has been studied by magneto-optical spectroscopy to probe co-ordination of both the NapB haems and the NapA active site Mo. The absorption spectrum of the NapAB complex is dominated by features from the NapB c-type cytochromes. Using a combination of electron paramagnetic resonance spectroscopy and magnetic circular dichroism it was demonstrated that both haems are low-spin with bis-histidine axial ligation. In addition, a window between 600 and 800 nm was identified in which weak absorption features that may arise from Mo could be detected. The low-temperature MCD spectrum shows oppositely signed bands in this region (peak 648 nm, trough 714 nm) which have been assigned to S-to-Mo(V) charge transfer transitions

Cytochrome c nitrite reductase: from structural to physicochemical analysis

The recent structural characterization of the NrfA from Escherichia coli provides a framework to rationalize the spectroscopic and functional properties of this enzyme. Analyses by EPR and magnetic CD spectroscopies have been complemented by protein-film voltammetry and these are discussed in relation to the essential structural features of the enzyme

Sintering of bulk high- Tc superconductors: Bi-Sr-Ca-Cu-O

Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (2212) and (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (2223) superconductors have orthorhombic crystal structures. They form platelike grains that at high temperatures grow primarily in the a-b planes and not in the c direction. The diffusional properties of Bi-Sr-Ca-Cu-O superconductors are so anisotropic that 2212 and 2223 cannot, in general, be densified by solid-state sintering. Improved densification can be achieved by application of pressure or by use of transient liquid phases. Most useful bulk Bi-Sr-Ca-Cu-O superconductors are composites that contain Ag. The Ag lowers the melting points of the superconductors, which has significant effects on microstructural development. The results of disparate sintering studies are presented and discussed