10,597 research outputs found
Magnetic interaction of Co ions near the {10\bar{1}0} ZnO surface
Co-doped ZnO is the prototypical dilute magnetic oxide showing many of the
characteristics of ferromagnetism. The microscopic origin of the long range
order however remains elusive, since the conventional mechanisms for the
magnetic interaction, such as super-exchange and double exchange, fail either
at the fundamental or at a quantitative level. Intriguingly, there is a growing
evidence that defects both in point-like or extended form play a fundamental
role in driving the magnetic order. Here we explore one of such possibilities
by performing {\it ab initio} density functional theory calculations for the
magnetic interaction of Co ions at or near a ZnO \{100\} surface. We
find that extended surface states can hybridize with the -levels of Co and
efficiently mediate the magnetic order, although such a mechanism is effective
only for ions placed in the first few atomic planes near the surface. We also
find that the magnetic anisotropy changes at the surface from an hard-axis
easy-plane to an easy axis, with an associated increase of its magnitude. We
then conclude that clusters with high densities of surfacial Co ions may
display blocking temperatures much higher than in the bulk
Correcting pervasive errors in RNA crystallography through enumerative structure prediction
Three-dimensional RNA models fitted into crystallographic density maps
exhibit pervasive conformational ambiguities, geometric errors and steric
clashes. To address these problems, we present enumerative real-space
refinement assisted by electron density under Rosetta (ERRASER), coupled to
Python-based hierarchical environment for integrated 'xtallography' (PHENIX)
diffraction-based refinement. On 24 data sets, ERRASER automatically corrects
the majority of MolProbity-assessed errors, improves the average Rfree factor,
resolves functionally important discrepancies in noncanonical structure and
refines low-resolution models to better match higher-resolution models
Oxidative Stress in Oocytes during Midprophase Induces Premature Loss of Cohesion and Chromosome Segregation Errors
In humans, errors in meiotic chromosome segregation that produce aneuploid gametes increase dramatically as women age, a phenomenon termed the maternal age effect. During meiosis, cohesion between sister chromatids keeps recombinant homologs physically attached and premature loss of cohesion can lead to missegregation of homologs during meiosis I. A growing body of evidence suggests that meiotic cohesion deteriorates as oocytes age and contributes to the maternal age effect. One hallmark of aging cells is an increase in oxidative damage caused by reactive oxygen species (ROS). Therefore, increased oxidative damage in older oocytes may be one of the factors that leads to premature loss of cohesion and segregation errors. To test this hypothesis, we used an RNAi strategy to induce oxidative stress in Drosophila oocytes and measured the fidelity of chromosome segregation during meiosis. Knockdown of either the cytoplasmic or mitochondrial ROS scavenger superoxide dismutase (SOD) caused a significant increase in segregation errors, and heterozygosity for an smc1 deletion enhanced this phenotype. FISH analysis indicated that SOD knockdown moderately increased the percentage of oocytes with arm cohesion defects. Consistent with premature loss of arm cohesion and destabilization of chiasmata, the frequency at which recombinant homologs missegregate during meiosis I is significantly greater in SOD knockdown oocytes than in controls. Together these results provide an in vivo demonstration that oxidative stress during meiotic prophase induces chromosome segregation errors and support the model that accelerated loss of cohesion in aging human oocytes is caused, at least in part, by oxidative damage
Cystathionine beta synthase deficiency and brain edema associated with methionine excess under betaine supplementation: Four new cases and a review of the evidence.
CBS deficient individuals undergoing betaine supplementation without sufficient dietary methionine restriction can develop severe hypermethioninemia and brain edema. Brain edema has also been observed in individuals with severe hypermethioninemia without concomitant betaine supplementation. We systematically evaluated reports from 11 published and 4 unpublished patients with CBS deficiency and from additional four cases of encephalopathy in association with elevated methionine. We conclude that, while betaine supplementation does greatly exacerbate methionine accumulation, the primary agent causing brain edema is methionine rather than betaine. Clinical signs of increased intracranial pressure have not been seen in patients with plasma methionine levels below 559 μmol/L but occurred in one patient whose levels did not knowingly exceed 972 μmol/L at the time of manifestation. While levels below 500 μmol/L can be deemed safe it appears that brain edema can develop with plasma methionine levels close to 1000 μmol/L. Patients with CBS deficiency on betaine supplementation need to be regularly monitored for concordance with their dietary plan and for plasma methionine concentrations. Recurrent methionine levels above 500 μmol/L should alert clinicians to check for clinical signs and symptoms of brain edema and review dietary methionine intake. Levels approaching 1000 μmol/L do increase the risk of complications and levels exceeding 1000 μmol/L, despite best dietetic efforts, should be acutely addressed by reducing the prescribed betaine dose
Assessment of Strength of Hollow Concrete Blocks with Holes Reinforced with Half Portion of Coconut Shells
Natural building materials are diminishing day by day. Hence economical alternatives of natural building materials are necessary for sustainable development. A hollow concrete block was developed to reduce the use of natural building materials. Agricultural waste products like coconut shells from the coconut industry have disposal problems causing environmental concerns. Various studies were done in the past, replacing a portion of the natural aggregates with broken coconut shells for manufacturing the hollow concrete blocks. In this study, we have developed a new method of forming the holes of hollow concrete blocks by placing stacks of half portion of coconut shells at the bottom with convex surface upwards to reinforce the holes by arch action. The results show that the coconut shell reinforced hollow concrete blocks have better strength as compared to open-graded hollow concrete blocks available in the market.
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Medical journals and Wikipedia: a global health matter
Approximately 7000 stillbirths occur daily worldwide, and the vast majority of them (98%) Approximately 7000 stillbirths occur daily worldwide, and the vast majority of them (98%) take place in low-income and middle-income countries (LMICs). Despite this enormous burden, progress to reduce the death toll is slow and insufficient. WHO released its Making every baby count guide in 2016, which includes strategies aimed at addressing the challenge of stillbirths. Given the flurry of activity and attention on stillbirths from the Lancet Stillbirth Epidemiology investigator group and WHO, we expect that the wealth of information about stillbirths that is generated will filter down in a timely manner to where it is needed most: the general public
Branes wrapping black holes as a purely gravitational dielectric effect
In this paper we give a microscopical description of certain configurations
of branes wrapping black hole horizons in terms of dielectric gravitational
waves. Interestingly, the configurations are stable only due to the
gravitational background. Therefore, this constitutes a nice example of purely
gravitational dielectric effect.Comment: 17 pages, no figures. JHEP published versio
The impact of binary stars on the dust and metal evolution of galaxies
We present detailed implementations of (a) binary stellar evolution (using
binary_c) and (b) dust production and destruction into the cosmological
semi-analytic galaxy evolution simulation, L-Galaxies. This new version of
L-Galaxies is compared to a version assuming only single stars and to global
and spatially-resolved observational data across a range of redshifts (). We
find that binaries have a negligible impact on the stellar masses, gas masses,
and star formation rates of galaxies only if the total mass ejected by massive
stars is unchanged. This is because massive stars determine the strength of
supernova (SN) feedback, which in turn regulates galaxy growth. Binary effects,
such as common envelope ejection and novae, affect carbon and nitrogen
enrichment in galaxies, however heavier alpha elements are more affected by the
choice of SN and wind yields. Unlike many other simulations, the new L-Galaxies
reproduces observed dust-to-metal (DTM) and dust-to-gas (DTG) ratios at
. This is mainly due to shorter dust accretion timescales in
dust-rich environments. However, dust masses are under-predicted at ,
highlighting the need for enhanced dust production at early times in
simulations, possibly accompanied by increased star formation. On sub-galactic
scales, there is very good agreement between L-Galaxies and observed dust and
metal radial profiles at . A drop in DTM ratio is also found in diffuse,
low-metallicity regions, contradicting the assumption of a universal value. We
hope that this work serves as a useful template for binary stellar evolution
implementations in other cosmological simulations in future.Comment: 19 pages, 10 figures. Submitted to MNRAS. Comments welcome
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