659 research outputs found
Amelioration of normothermic canine liver ischemia with prostacyclin.
A model of hepatic ischemia was developed in dogs using a pump-driven splanchnic-to-jugular vein bypass during crossclamping of the portal triad. An LD50 was established with three hours of ischemia. PGI2 given for one hour before the ischemic insult ameliorated the ischemic injury and increased survival
Point defect dynamics in bcc metals
We present an analysis of the time evolution of self-interstitial atom and
vacancy (point defect) populations in pure bcc metals under constant
irradiation flux conditions. Mean-field rate equations are developed in
parallel to a kinetic Monte Carlo (kMC) model. When only considering the
elementary processes of defect production, defect migration, recombination and
absorption at sinks, the kMC model and rate equations are shown to be
equivalent and the time evolution of the point defect populations is analyzed
using simple scaling arguments. We show that the typically large mismatch of
the rates of interstitial and vacancy migration in bcc metals can lead to a
vacancy population that grows as the square root of time. The vacancy cluster
size distribution under both irreversible and reversible attachment can be
described by a simple exponential function. We also consider the effect of
highly mobile interstitial clusters and apply the model with parameters
appropriate for vanadium and iron.Comment: to appear in Phys. Rev.
Stoichiometrically driven disorder and local diffusion in NMC cathodes
Major structural differences in lithium nickel manganese cobalt oxides (NMC) prepared under identical conditions have been uncovered using neutron powder diffraction. Sample NMC-622 was obtained as a single R[3 with combining macron]m crystal structure with little defects, whereas NMC-811 showed significant Li deficiency and NMC-433 formed three distinct phases; ordered R[3 with combining macron]m, disordered R[3 with combining macron]m and a C2/m phase. Local diffusion behaviour was also studied by muon spin relaxation (ÎŒSR). It was observed that single phase R[3 with combining macron]m NMC-622 showed a higher lithium diffusion coefficient (4.4 Ă 10â11 cm2 sâ1) compared to lithium deficient NMC-811 (2.9 Ă 10â11 cm2 sâ1), or the highly disordered NMC-433 (3.4 Ă 10â11 cm2 sâ1). Furthermore, activation energies for the Li diffusion process were estimated to be 58 meV, 61 meV and 28 meV for NMC-811, NMC-622 and NMC-433, respectively
Multiple diffusion pathways in LixNi0.77Co0.14Al0.09O2 (NCA) Li-ion battery cathodes
Experimental evidence for the presence of two computationally theorised diffusion pathways, namely the oxygen dumbbell hop (ODH) and tetrahedral site hop (TSH), has been given for the first time by muon spin relaxation (”SR) on sub-stoichiometric LixNi0.77Co0.14Al0.09O2. ”SR has proven to be a powerful tool that is able to discriminate between diffusion pathways that occur on different timescales on a local level, where bulk electrochemical techniques cannot. Whereas the estimated values of DLi at lithium concentrations of 0.87 and 0.71 were found to be on the order of 10-11 by electrochemical impedance spectroscopy, contributions to diffusion from ODH and TSH were determined to be on the order of 10-11 and 10-10 cm2 s-1, and a factor of four decrease in Ea for both samples, in excellent agreement with theoretical calculations on related compounds. Rietveld refinement of both X-ray and neutron diffraction data was also used to interrogate the local structure of the materials where no contribution from Li+/Ni2+ cation mixing was observed
The lncRNA HOTAIR transcription is controlled by HNF4α-induced chromatin topology modulation
The expression of the long noncoding RNA HOTAIR (HOX Transcript Antisense Intergenic RNA) is largely deregulated in epithelial cancers and positively correlates with poor prognosis and progression of hepatocellular carcinoma and gastrointestinal cancers. Furthermore, functional studies revealed a pivotal role for HOTAIR in the epithelial-to-mesenchymal transition, as this RNA is causal for the repressive activity of the master factor SNAIL on epithelial genes. Despite the proven oncogenic role of HOTAIR, its transcriptional regulation is still poorly understood. Here hepatocyte nuclear factor 4-α (HNF4α), as inducer of epithelial differentiation, was demonstrated to directly repress HOTAIR transcription in the mesenchymal-to epithelial transition. Mechanistically, HNF4α was found to cause the release of a chromatin loop on HOTAIR regulatory elements thus exerting an enhancer-blocking activity
Crystal structure, site selectivity, and electronic structure of layered chalcogenide LaOBiPbS3
We have investigated the crystal structure of LaOBiPbS3 using neutron
diffraction and synchrotron X-ray diffraction. From structural refinements, we
found that the two metal sites, occupied by Bi and Pb, were differently
surrounded by the sulfur atoms. Calculated bond valence sum suggested that one
metal site was nearly trivalent and the other was nearly divalent. Neutron
diffraction also revealed site selectivity of Bi and Pb in the LaOBiPbS3
structure. These results suggested that the crystal structure of LaOBiPbS3 can
be regarded as alternate stacks of the rock-salt-type Pb-rich sulfide layers
and the LaOBiS2-type Bi-rich layers. From band calculations for an ideal
(LaOBiS2)(PbS) system, we found that the S bands of the PbS layer were
hybridized with the Bi bands of the BiS plane at around the Fermi energy, which
resulted in the electronic characteristics different from that of LaOBiS2.
Stacking the rock-salt type sulfide (chalcogenide) layers and the BiS2-based
layered structure could be a new strategy to exploration of new BiS2-based
layered compounds, exotic two-dimensional electronic states, or novel
functionality.Comment: 11 pages, 5 figure
Tetrafibricin, a novel non-peptide fibrinogen receptor antagonist, induces conformational changes in glycoprotein IIb/IIIa
Broadband Antireflection and Light Extraction Enhancement in Fluorescent SiC with Nanodome Structures
We demonstrate a time-efficient and low-cost approach to fabricate Si3N4 coated nanodome structures in fluorescent SiC. Nanosphere lithography is used as the nanopatterning method and SiC nanodome structures with Si3N4 coating are formed via dry etching and thin film deposition process. By using this method, a significant broadband surface antireflection and a considerable omnidirectional luminescence enhancement are obtained. The experimental observations are then supported by numerical simulations. It is believed that our fabrication method will be well suitable for large-scale production in the future
Investigation of the electronic structure and lattice dynamics of the thermoelectric material Na-doped SnSe
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