380 research outputs found
DFT Study of Planar Boron Sheets: A New Template for Hydrogen Storage
We study the hydrogen storage properties of planar boron sheets and compare
them to those of graphene. The binding of molecular hydrogen to the boron sheet
(0.05 eV) is stronger than that to graphene. We find that dispersion of alkali
metal (AM = Li, Na, and K) atoms onto the boron sheet markedly increases
hydrogen binding energies and storage capacities. The unique structure of the
boron sheet presents a template for creating a stable lattice of strongly
bonded metal atoms with a large nearest neighbor distance. In contrast, AM
atoms dispersed on graphene tend to cluster to form a bulk metal. In particular
the boron-Li system is found to be a good candidate for hydrogen storage
purposes. In the fully loaded case this compound can contain up to 10.7 wt. %
molecular hydrogen with an average binding energy of 0.15 eV/H2.Comment: 19 pages, 7 figures, and 3 table
Quasiparticle interfacial level alignment of highly hybridized frontier levels: HO on TiO(110)
Knowledge of the frontier levels' alignment prior to photo-irradiation is
necessary to achieve a complete quantitative description of HO
photocatalysis on TiO(110). Although HO on rutile TiO(110) has been
thoroughly studied both experimentally and theoretically, a quantitative value
for the energy of the highest HO occupied levels is still lacking. For
experiment, this is due to the HO levels being obscured by hybridization
with TiO(110) levels in the difference spectra obtained via ultraviolet
photoemission spectroscopy (UPS). For theory, this is due to inherent
difficulties in properly describing many-body effects at the
HO-TiO(110) interface. Using the projected density of states (DOS) from
state-of-the-art quasiparticle (QP) , we disentangle the adsorbate and
surface contributions to the complex UPS spectra of HO on TiO(110). We
perform this separation as a function of HO coverage and dissociation on
stoichiometric and reduced surfaces. Due to hybridization with the TiO(110)
surface, the HO 3a and 1b levels are broadened into several peaks
between 5 and 1 eV below the TiO(110) valence band maximum (VBM). These
peaks have both intermolecular and interfacial bonding and antibonding
character. We find the highest occupied levels of HO adsorbed intact and
dissociated on stoichiometric TiO(110) are 1.1 and 0.9 eV below the VBM. We
also find a similar energy of 1.1 eV for the highest occupied levels of HO
when adsorbed dissociatively on a bridging O vacancy of the reduced surface. In
both cases, these energies are significantly higher (by 0.6 to 2.6 eV) than
those estimated from UPS difference spectra, which are inconclusive in this
energy region. Finally, we apply self-consistent QP (scQP1) to obtain
the ionization potential of the HO-TiO(110) interface.Comment: 12 pages, 12 figures, 1 tabl
Interactions of Shiga-like toxin with human peripheral blood monocytes
The cytotoxic effect of Shiga-like toxin (Stx; produced by certain Escherichia coli strains) plays a central role in typical hemolytic uremic syndrome (HUS). It damages the renal endothelium by inhibiting the cellular protein synthesis. Also, the monocyte has a specific receptor for Stx but is not sensitive for the cytotoxic effect. In this work, monocytes were studied as a potential transporter for Stx to the renal endothelium. Coincubation of isolated human monocytes loaded with Stx and target cells (vero cells and human umbilical vascular endothelial cells) were performed. Transfer was determined by measuring the protein synthesis of target cells and by flow cytometry. Furthermore, the effect of a temperature shift on loaded monocytes was investigated. Stx-loaded monocytes reduced the protein synthesis of target cells. After adding an antibody against Stx, incomplete recovery occurred. Also, adding only the supernatant of coincubation was followed by protein synthesis inhibition. Stx detached from its receptor on the monocyte after a change in temperature, and no release was detected without this temperature shift. Although the monocyte plays an important role in the pathogenesis of HUS, it has no role in the transfer of Stx
Ionic high-pressure form of elemental boron
Boron is an element of fascinating chemical complexity. Controversies have
shrouded this element since its discovery was announced in 1808: the new
'element' turned out to be a compound containing less than 60-70 percent of
boron, and it was not until 1909 that 99-percent pure boron was obtained. And
although we now know of at least 16 polymorphs, the stable phase of boron is
not yet experimentally established even at ambient conditions. Boron's
complexities arise from frustration: situated between metals and insulators in
the periodic table, boron has only three valence electrons, which would favour
metallicity, but they are sufficiently localized that insulating states emerge.
However, this subtle balance between metallic and insulating states is easily
shifted by pressure, temperature and impurities. Here we report the results of
high-pressure experiments and ab initio evolutionary crystal structure
predictions that explore the structural stability of boron under pressure and,
strikingly, reveal a partially ionic high-pressure boron phase. This new phase
is stable between 19 and 89 GPa, can be quenched to ambient conditions, and has
a hitherto unknown structure (space group Pnnm, 28 atoms in the unit cell)
consisting of icosahedral B12 clusters and B2 pairs in a NaCl-type arrangement.
We find that the ionicity of the phase affects its electronic bandgap, infrared
adsorption and dielectric constants, and that it arises from the different
electronic properties of the B2 pairs and B12 clusters and the resultant charge
transfer between them.Comment: Published in Nature 453, 863-867 (2009
The high-pressure phase of boron, {\gamma}-B28: disputes and conclusions of 5 years after discovery
{\gamma}-B28 is a recently established high-pressure phase of boron. Its
structure consists of icosahedral B12 clusters and B2 dumbbells in a NaCl-type
arrangement (B2){\delta}+(B12){\delta}- and displays a significant charge
transfer {\delta}~0.5- 0.6. The discovery of this phase proved essential for
the understanding and construction of the phase diagram of boron. {\gamma}-B28
was first experimentally obtained as a pure boron allotrope in early 2004 and
its structure was discovered in 2006. This paper reviews recent results and in
particular deals with the contentious issues related to the equation of state,
hardness, putative isostructural phase transformation at ~40 GPa, and debates
on the nature of chemical bonding in this phase. Our analysis confirms that (a)
calculations based on density functional theory give an accurate description of
its equation of state, (b) the reported isostructural phase transformation in
{\gamma}-B28 is an artifact rather than a fact, (c) the best estimate of
hardness of this phase is 50 GPa, (d) chemical bonding in this phase has a
significant degree of ionicity. Apart from presenting an overview of previous
results within a consistent view grounded in experiment, thermodynamics and
quantum mechanics, we present new results on Bader charges in {\gamma}-B28
using different levels of quantum-mechanical theory (GGA, exact exchange, and
HSE06 hybrid functional), and show that the earlier conclusion about
significant degree of partial ionicity in this phase is very robust
Associations of Polymorphisms in the Peroxisome Proliferator-Activated Receptor Gamma Coactivator-1 Alpha Gene With Subsequent Coronary Heart Disease: An Individual-Level Meta-Analysis
Background: The knowledge of factors influencing disease progression in patients with established coronary heart disease (CHD) is still relatively limited. One potential pathway is related to peroxisome proliferatorâactivated receptor gamma coactivator-1 alpha (PPARGC1A), a transcription factor linked to energy metabolism which may play a role in the heart function. Thus, its associations with subsequent CHD events remain unclear. We aimed to investigate the effect of three different SNPs in the PPARGC1A gene on the risk of subsequent CHD in a population with established CHD.
Methods: We employed an individual-level meta-analysis using 23 studies from the GENetIcs of sUbSequent Coronary Heart Disease (GENIUS-CHD) consortium, which included participants (n = 80,900) with either acute coronary syndrome, stable CHD, or a mixture of both at baseline. Three variants in the PPARGC1A gene (rs8192678, G482S; rs7672915, intron 2; and rs3755863, T528T) were tested for their associations with subsequent events during the follow-up using a Cox proportional hazards model adjusted for age and sex. The primary outcome was subsequent CHD death or myocardial infarction (CHD death/myocardial infarction). Stratified analyses of the participant or study characteristics as well as additional analyses for secondary outcomes of specific cardiovascular disease diagnoses and all-cause death were also performed.
Results: Meta-analysis revealed no significant association between any of the three variants in the PPARGC1A gene and the primary outcome of CHD death/myocardial infarction among those with established CHD at baseline: rs8192678, hazard ratio (HR): 1.01, 95% confidence interval (CI) 0.98â1.05 and rs7672915, HR: 0.97, 95% CI 0.94â1.00; rs3755863, HR: 1.02, 95% CI 0.99â1.06. Similarly, no significant associations were observed for any of the secondary outcomes. The results from stratified analyses showed null results, except for significant inverse associations between rs7672915 (intron 2) and the primary outcome among 1) individuals aged â„65, 2) individuals with renal impairment, and 3) antiplatelet users.
Conclusion: We found no clear associations between polymorphisms in the PPARGC1A gene and subsequent CHD events in patients with established CHD at baseline
The impact of donor and recipient common clinical and genetic variation on estimated glomerular filtration rate in a European renal transplant population
Genetic variation across the HLA is known to influence renalâtransplant outcome. However, the impact of genetic variation beyond the HLA is less clear. We tested the association of common genetic variation and clinical characteristics, from both the donor and recipient, with postâtransplant eGFR at different timeâpoints, out to 5âyears postâtransplantation.
We conducted GWAS metaâanalyses across 10,844 donors and recipients from five European ancestry cohorts. We also analysed the impact of polygenic risk scores (PRS), calculated using genetic variants associated with nonâtransplant eGFR, on postâtransplant eGFR.
PRS calculated using the recipient genotype alone, as well as combined donor and recipient genotypes were significantly associated with eGFR at 1âyear postâtransplant. 32% of the variability in eGFR at 1âyear postâtransplant was explained by our model containing clinical covariates (including weights for death/graftâfailure), principal components and combined donorârecipient PRS, with 0.3% contributed by the PRS. No individual genetic variant was significantly associated with eGFR postâtransplant in the GWAS.
This is the first study to examine PRS, composed of variants that impact kidney function in the general population, in a postâtransplant context. Despite PRS being a significant predictor of eGFR postâtransplant, the effect size of common genetic factors is limited compared to clinical variables
Experimental pressure-temperature phase diagram of boron: resolving the long-standing enigma
Boron, discovered as an element in 1808 and produced in pure form in 1909, has still remained the last elemental material, having stable natural isotopes, with the ground state crystal phase to be unknown. It has been a subject of long-standing controversy, if α-B or ÎČ-B is the thermodynamically stable phase at ambient pressure and temperature. In the present work this enigma has been resolved based on the α-B-to- ÎČ-B phase boundary line which we experimentally established in the pressure interval of âŒ4 GPa to 8 GPa and linearly extrapolated down to ambient pressure. In a series of high pressure high temperature experiments we synthesised single crystals of the three boron phases (α-B, ÎČ-B, and Îł-B) and provided evidence of higher thermodynamic stability of α-B. Our work opens a way for reproducible synthesis of α-boron, an optically transparent direct band gap semiconductor with very high hardness, thermal and chemical stability
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