568 research outputs found
Linear bands, zero-momentum Weyl semimetal, and topological transition in skutterudite-structure pnictides
It was reported earlier [Phys. Rev. Lett. 106, 056401 (2011)] that the
skutterudite structure compound CoSb displays a unique band structure with
a topological transition versus a symmetry-preserving sublattice (Sb)
displacement very near the structural ground state. The transition is through a
massless Dirac-Weyl semimetal, point Fermi surface phase which is unique in
that (1) it appears in a three dimensional crystal, (2) the band critical point
occurs at =0, and (3) linear bands are degenerate with conventional
(massive) bands at the critical point (before inclusion of spin-orbit
coupling). Further interest arises because the critical point separates a
conventional (trivial) phase from a topological phase. In the native cubic
structure this is a zero-gap topological semimetal; we show how spin-orbit
coupling and uniaxial strain converts the system to a topological insulator
(TI). We also analyze the origin of the linear band in this class of materials,
which is the characteristic that makes them potentially useful in
thermoelectric applications or possibly as transparent conductors. We
characterize the formal charge as Co , consistent with the gap, with
its site symmetry, and with its lack of moment. The Sb states are
characterized as (separately, ) -bonded ring states
occupied and the corresponding antibonding states empty. The remaining
(locally) orbitals form molecular orbitals with definite parity centered
on the empty site in the skutterudite structure. Eight such orbitals must
be occupied; the one giving the linear band is an odd orbital singlet
at the zone center. We observe that the provocative linearity of the band
within the gap is a consequence of the aforementioned near-degeneracy, which is
also responsible for the small band gap.Comment: 10 pages, 7 figure
Pressure-induced structural transitions in MgH
The stability of MgH has been studied up to 20~GPa using
density-functional total-energy calculations. At ambient pressure
-MgH takes a TiO-rutile-type structure. -MgH is
predicted to transform into -MgH at 0.39~GPa. The calculated
structural data for - and -MgH are in very good agreement
with experimental values. At equilibrium the energy difference between these
modifications is very small, and as a result both phases coexist in a certain
volume and pressure field. Above 3.84~GPa -MgH transforms into
-MgH; consistent with experimental findings. Two further
transformations have been identified at still higher pressure: i) - to
-MgH at 6.73 GPa and (ii) - to -MgH at
10.26~GPa.Comment: 4 pages, 4 figure
Valence-state mixing and separation in SmBaFe2O5+w
A mixed-valence state, formally denoted as Fe2.5+, is observed in the 300 K Mössbauer spectra of the most reduced samples of SmBaFe2O5+w. Upon cooling below the Verwey-type transition temperature (TV≈200K), the component assigned to Fe2.5+ separates into a high-spin Fe3+ state and an Fe2+ state with an unusually low internal field. The separation of the mixed-valence state at TV is also confirmed by magnetic susceptibility measurements and differential scanning calorimetry. A model is proposed which accounts for the variation of the amount of the mixed-valence state with the oxygen content parameter w.Peer reviewe
Valence-state mixing and separation in SmBaFe2O5+w
A mixed-valence state, formally denoted as Fe2.5+, is observed in the 300 K Mössbauer spectra of the most reduced samples of SmBaFe2O5+w. Upon cooling below the Verwey-type transition temperature (TV≈200K), the component assigned to Fe2.5+ separates into a high-spin Fe3+ state and an Fe2+ state with an unusually low internal field. The separation of the mixed-valence state at TV is also confirmed by magnetic susceptibility measurements and differential scanning calorimetry. A model is proposed which accounts for the variation of the amount of the mixed-valence state with the oxygen content parameter w.Peer reviewe
Impact of Renal Impairment on Beta-Blocker Efficacy in Patients With Heart Failure.
BACKGROUND: Moderate and moderately severe renal impairment are common in patients with heart failure and reduced ejection fraction, but whether beta-blockers are effective is unclear, leading to underuse of life-saving therapy. OBJECTIVES: This study sought to investigate patient prognosis and the efficacy of beta-blockers according to renal function using estimated glomerular filtration rate (eGFR). METHODS: Analysis of 16,740 individual patients with left ventricular ejection fraction <50% from 10 double-blind, placebo-controlled trials was performed. The authors report all-cause mortality on an intention-to-treat basis, adjusted for baseline covariates and stratified by heart rhythm. RESULTS: Median eGFR at baseline was 63 (interquartile range: 50 to 77) ml/min/1.73 m2; 4,584 patients (27.4%) had eGFR 45 to 59 ml/min/1.73 m2, and 2,286 (13.7%) 30 to 44 ml/min/1.73 m2. Over a median follow-up of 1.3 years, eGFR was independently associated with mortality, with a 12% higher risk of death for every 10 ml/min/1.73 m2 lower eGFR (95% confidence interval [CI]: 10% to 15%; p < 0.001). In 13,861 patients in sinus rhythm, beta-blockers reduced mortality versus placebo; adjusted hazard ratio (HR): 0.73 for eGFR 45 to 59 ml/min/1.73 m2 (95% CI: 0.62 to 0.86; p < 0.001) and 0.71 for eGFR 30 to 44 ml/min/1.73 m2 (95% CI: 0.58 to 0.87; p = 0.001). The authors observed no deterioration in renal function over time in patients with moderate or moderately severe renal impairment, no difference in adverse events comparing beta-blockers with placebo, and higher mortality in patients with worsening renal function on follow-up. Due to exclusion criteria, there were insufficient patients with severe renal dysfunction (eGFR <30 ml/min/1.73 m2) to draw conclusions. In 2,879 patients with atrial fibrillation, there was no reduction in mortality with beta-blockers at any level of eGFR. CONCLUSIONS: Patients with heart failure, left ventricular ejection fraction <50% and sinus rhythm should receive beta-blocker therapy even with moderate or moderately severe renal dysfunction
Coulomb correlation effects in zinc monochalcogenides
Electronic structure and band characteristics for zinc monochalcogenides with
zinc-blende- and wurtzite-type structures are studied by first-principles
density-functional-theory calculations with different approximations. It is
shown that the local-density approximation underestimates the band gap and
energy splitting between the states at the top of the valence band, misplaces
the energy levels of the Zn-3d states, and overestimates the
crystal-field-splitting energy. Regardless of the structure type considered,
the spin-orbit-coupling energy is found to be overestimated for ZnO and
underestimated for ZnS with wurtzite-type structure, and more or less correct
for ZnSe and ZnTe with zinc-blende-type structure. The order of the states at
the top of the valence band is found to be anomalous for ZnO in both
zinc-blende- and wurtzite-type structure, but is normal for the other zinc
monochalcogenides considered. It is shown that the Zn-3d electrons and their
interference with the O-2p electrons are responsible for the anomalous order.
The typical errors in the calculated band gaps and related parameters for ZnO
originate from strong Coulomb correlations, which are found to be highly
significant for this compound. The LDA+U approach is by and large found to
correct the strong correlation of the Zn-3d electrons, and thus to improve the
agreement with the experimentally established location of the Zn-3d levels
compared with that derived from pure LDA calculations
An economic evaluation of rosuvastatin treatment in systolic heart failure: evidence from the CORONA trial
Aims: To estimate the cost-effectiveness of 10 mg rosuvastatin daily for older patients with systolic heart failure in the Controlled Rosuvastatin Multinational Study in Heart Failure (CORONA) trial.
Methods and results: This within trial analysis of CORONA used major cardiovascular (CV) events as the outcome measure. Resource use was valued and the costs of hospitalizations, procedures, and statin use compared. Cost-effectiveness was estimated as cost per major CV event avoided. There were significantly fewer major CV events in the rosuvastatin group compared with the placebo group (1.04 vs. 1.20 per patient; difference 0.164; 95% CI: 0.075–0.254, P < 0.001). The average cost of CV hospitalizations and procedures was significantly lower for those receiving rosuvastatin (£1531 vs. £1769; difference £238; 95% CI: £73–403, P = 0.005); the additional cost of the statin resulted in significantly higher total costs for the rosuvastatin group (£1769 vs. £2072; difference £303; 95% CI: £138–468, P < 0.001). Overall, rosuvastatin was found to cost £1840 (95% CI: £562–6028) per major CV event avoided.
Conclusion: This economic analysis showed that a significant reduction in major CV events with rosuvastatin led to significantly reduced costs of CV hospitalizations and procedures. The reduction in associated costs for major CV events was found to offset partially (by 44%) the cost of rosuvastatin treatment in patients with systolic heart failure
The impact of coronary artery disease risk loci on ischemic heart failure severity and prognosis: association analysis in the COntrolled ROsuvastatin multiNAtional trial in heart failure (CORONA)
Electronic structure, phase stability and chemical bonding in ThAl and ThAlH
We present the results of theoretical investigation on the electronic
structure, bonding nature and ground state properties of ThAl and
ThAlH using generalized-gradient-corrected first-principles
full-potential density-functional calculations. ThAlH has been reported
to violate the "2 \AA rule" of H-H separation in hydrides. From our total
energy as well as force-minimization calculations, we found a shortest H-H
separation of 1.95 {\AA} in accordance with recent high resolution powder
neutron diffraction experiments. When the ThAl matrix is hydrogenated, the
volume expansion is highly anisotropic, which is quite opposite to other
hydrides having the same crystal structure. The bonding nature of these
materials are analyzed from the density of states, crystal-orbital Hamiltonian
population and valence-charge-density analyses. Our calculation predicts
different nature of bonding for the H atoms along and . The strongest
bonding in ThAlH is between Th and H along which form dumb-bell
shaped H-Th-H subunits. Due to this strong covalent interaction there is very
small amount of electrons present between H atoms along which makes
repulsive interaction between the H atoms smaller and this is the precise
reason why the 2 {\AA} rule is violated. The large difference in the
interatomic distances between the interstitial region where one can accommodate
H in the and planes along with the strong covalent interaction
between Th and H are the main reasons for highly anisotropic volume expansion
on hydrogenation of ThAl.Comment: 14 pages, 9 figure
Origin of magnetoelectric behavior in BiFeO
The magnetoelectric behavior of BiFeO has been explored on the basis of
accurate density functional calculations. The structural, electronic, magnetic,
and ferroelectric properties of BiFeO are predicted correctly without
including strong correlation effect in the calculation. Moreover, the
experimentally-observed elongation of cubic perovskite-like lattice along the
[111] direction is correctly reproduced. At high pressure we predicted a
pressure-induced structural transition and the total energy calculations at
expanded lattice show two lower energy ferroelectric phases, closer in energy
to the ground state phase. Band-structure calculations show that BiFeO will
be an insulator in A- and G-type antiferromagnetic phases and a metal in other
magnetic configurations. Chemical bonding in BiFeO has been analyzed using
various tools and electron localization function analysis shows that
stereochemically active lone-pair electrons at the Bi sites are responsible for
displacements of the Bi atoms from the centro-symmetric to the
noncentrosymmetric structure and hence the ferroelectricity. A large
ferroelectric polarization (88.7 C/cm) is predicted in accordance
with recent experimental findings. The net polarization is found to mainly (
98%) originate from Bi atoms. Moreover the large scatter in experimentally
reported polarization values is due to the large anisotropy in the spontaneous
polarization.Comment: 19 pages, 12 figures, 4 table
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