1,552 research outputs found
Band structure model of magnetic coupling in semiconductors
We present a unified band structure model to explain magnetic ordering in
Mn-doped semiconductors. This model is based on the - and - level
repulsions between the Mn ions and host elements and can successfully explain
magnetic ordering observed in all Mn doped II-VI and III-V semiconductors such
as CdTe, GaAs, ZnO, and GaN. This model, therefore, provides a simple guideline
for future band structure engineering of magnetic semiconductors.Comment: 4+ pages, 5 figure
Harnack Inequality and Strong Feller Property for Stochastic Fast-Diffusion Equations
This paper presents analogous results for stochastic fast-diffusion
equations. Since the fast-diffusion equation possesses weaker dissipativity
than the porous medium one does, some technical difficulties appear in the
study. As a compensation to the weaker dissipativity condition, a Sobolev-Nash
inequality is assumed for the underlying self-adjoint operator in applications.
Some concrete examples are constructed to illustrate the main results.Comment: to appear in Journal of Mathematical Analysis and Application
On the Convergence of the Electronic Structure Properties of the FCC Americium (001) Surface
Electronic and magnetic properties of the fcc Americium (001) surface have
been investigated via full-potential all-electron density-functional electronic
structure calculations at both scalar and fully relativistic levels. Effects of
various theoretical approximations on the fcc Am (001) surface properties have
been thoroughly examined. The ground state of fcc Am (001) surface is found to
be anti-ferromagnetic with spin-orbit coupling included (AFM-SO). At the ground
state, the magnetic moment of fcc Am (001) surface is predicted to be zero. Our
current study predicts the semi-infinite surface energy and the work function
for fcc Am (001) surface at the ground state to be approximately 0.82 J/m2 and
2.93 eV respectively. In addition, the quantum size effects of surface energy
and work function on the fcc Am (001) surface have been examined up to 7 layers
at various theoretical levels. Results indicate that a three layer film surface
model may be sufficient for future atomic and molecular adsorption studies on
the fcc Am (001) surface, if the primary quantity of interest is the
chemisorption energy.Comment: 34 pages, 9 figure
Experimental Study on Improvement of Interfacial Bond Properties of Carbon Fiber Reinforced Cement Matrix Composites by Nano Silica
The fiber reinforcement efficiency of carbon fiber reinforced cement matrix composites (CFRCM) is limited by the low permeability of mortar to internal filaments in the fibers, leading to premature failure of the composites due to low bond strength. In this paper, three kinds of nano-silica materials were used to improve the bond properties of carbon fiber bundles to cement-based matrix by coating and electrophoretic deposition. It is found that different methods have different positive or negative effects on the improvement of bond properties, and the effects are different under different embedded lengths. The modification principle is due to the high impregnation of nano silica particles on the fibers and the reaction of volcanic ash of the particles, which promotes the formation of calcium silicate hydrate gel inside the fibers. Relevant research needs further exploration
Growth Index of DGP Model and Current Growth Rate Data
Recently, some efforts focus on differentiating dark energy and modified
gravity with the growth function . In the literature, it is useful
to parameterize the growth rate
with the growth index . In this note, we consider the general DGP model
with any . We confront the growth index of DGP model with currently
available growth rate data and find that the DGP model is still consistent with
it. This implies that more and better growth rate data are required to
distinguish between dark energy and modified gravity.Comment: 12 pages, 1 table, 2 figures, Latex2e; v2: discussions added, Phys.
Lett. B in press; v3: published versio
Sources of variation in nutrient intakes among men in Shanghai, China
Background and objective: Random errors, from any source, will attenuate epidemiological risk estimates. Before we launched the Shanghai Men’s Health Study (SMHS), a large population-based cohort study investigating the diet–cancer association among Chinese men, a dietary calibration study was conducted among 96 men aged 40–75 years (mean age 56.5 years), with biweekly 24-hour dietary recalls (24HDRs) implemented over a 1-year period. Data from this study were analysed to evaluate the nature and magnitude of variances for intake of 26 nutrients among SMHS participants, to compare variance ratios of 26 nutrients among Chinese men and women and individuals in other studies, and to estimate the number of 24HDRs required for future dietary calibration studies in similar populations. Design: Ninety-six healthy, free-living men in Shanghai were administered biweekly 24HDR interviews 24 times over a 1-year period. To assess between-individual and within-individual contributions to variance, a mixed effects model was fitted and ratios of within-individual to between-individual (s^ 2 w=s^ 2 b) dietary intake variances were computed. Setting: Shanghai, China. Results: In agreement with reports from studies conducted in the USA and many other countries, we found that within-individual variances were usually larger than between-individual variances in dietary intake for all nutrients. The sum of all other variation (e.g. weekday and weekend, seasonal, interviewer) accounted for less than 5% of total variation. Ratios of within- to between-individual variances (for logtransformed data) ranged from 1.25 for carbohydrate intake to near 8 for d-tocopherol intake. Conclusions: The results of this study suggest that among middle-aged and elderly Chinese men in Shanghai, within- and between-individual variation account for more than 95% of the total variation for 26 nutrients. Further dietary validation studies in the same population could be adequately carried out with only 12 days of dietary recalls, if 100 participants were enrolled
Structure of the priming arabinosyltransferase AftA required for AG biosynthesis of Mycobacterium tuberculosis.
Arabinogalactan (AG) is an essential cell wall component in mycobacterial species, including the deadly human pathogen Mycobacterium tuberculosis. It plays a pivotal role in forming the rigid mycolyl-AG-peptidoglycan core for in vitro growth. AftA is a membrane-bound arabinosyltransferase and a key enzyme involved in AG biosynthesis which bridges the assembly of the arabinan chain to the galactan chain. It is known that AftA catalyzes the transfer of the first arabinofuranosyl residue from the donor decaprenyl-monophosphoryl-arabinose to the mature galactan chain (i.e., priming); however, the priming mechanism remains elusive. Herein, we report the cryo-EM structure of Mtb AftA. The detergent-embedded AftA assembles as a dimer with an interface maintained by both the transmembrane domain (TMD) and the soluble C-terminal domain (CTD) in the periplasm. The structure shows a conserved glycosyltransferase-C fold and two cavities converging at the active site. A metal ion participates in the interaction of TMD and CTD of each AftA molecule. Structural analyses combined with functional mutagenesis suggests a priming mechanism catalyzed by AftA in Mtb AG biosynthesis. Our data further provide a unique perspective into anti-TB drug discovery. </p
Standing Enokitake-like Nanowire Films for Highly Stretchable Elastronics
Stretchable electronics may enable electronic components to be part of our organs-ideal for future wearable/implantable biodiagnostic systems. One of key challenges is failure of the soft/rigid material interface due to mismatching Young’ s moduli, which limits stretchability and durability of current systems. Here, we show that standing enokitake-like gold-nanowire-based films chemically bonded to an elastomer can be stretched up to 900% and are highly durable, with >93% conductivity recovery even after 2000 stretching/releasing cycles to 800% strain. Both experimental and modeling reveal that this superior elastic property originates from standing enokitake-like nanowire film structures. The closely packed nanoparticle layer sticks to the top of the nanowires, which easily cracks under strain, whereas the bottom part of the nanowires is compliant with substrate deformation. This leads to tiny V-shaped cracks with a maintained electron transport pathway rather than large U-shaped cracks that are frequently observed for conventional metal films. We further show that our standing nanowire films can serve as current collectors in supercapacitors and second skin-like smart masks for facial expression detection
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