2,041 research outputs found
Probing the shape of atoms in real space
The structure of single atoms in real space is investigated by scanning
tunneling microscopy. Very high resolution is possible by a dramatic reduction
of the tip-sample distance. The instabilities which are normally encountered
when using small tip-sample distances are avoided by oscillating the tip of the
scanning tunneling microscope vertically with respect to the sample. The
surface atoms of Si(111)-(7 x 7) with their well-known electronic configuration
are used to image individual samarium, cobalt, iron and silicon atoms. The
resulting images resemble the charge density corresponding to 4f, 3d and 3p
atomic orbitals.Comment: Submitted to Phys. Rev. B, 17 pages, 7 figure
Prevalence of the metabolic syndrome in Chinese adolescents
Since national figures on the occurrence of metabolic syndrome among Chinese adolescents are lacking, this study aims to estimate its prevalence and distribution among Chinese youngsters. The 2002 China National Nutrition and Health Survey is a nationally representative cross-sectional study. Applying the criteria for US adolescents, we estimated the prevalence of metabolic syndrome among 2761 adolescents aged 15 to 19 years. The prevalence of metabolic syndrome among Chinese adolescents overall was 3·7% (10% in US adolescents). It was 35·2 %, 23·4% and 2·3% among adolescents who were overweight (BMI 85th percentile and one or two parent(s) with metabolic syndrome, the prevalence was 46·4 %. A total of 96% of overweight adolescents had at least one and 74·1% overweight adolescents had at least two abnormalities of metabolic syndrome. Based on these figures, it is estimated that more than three million Chinese adolescents have metabolic syndrome. Both overweight and metabolic syndrome prevalence among adolescents are still relatively low in China, but the prevalence of metabolic syndrome among Chinese overweight adolescents is similar to those living in the USA
Transmission properties of a single metallic slit: From the subwavelength regime to the geometrical-optics limit
In this work we explore the transmission properties of a single slit in a
metallic screen. We analyze the dependence of these properties on both slit
width and angle of incident radiation. We study in detail the crossover between
the subwavelength regime and the geometrical-optics limit. In the subwavelength
regime, resonant transmission linked to the excitation of waveguide resonances
is analyzed. Linewidth of these resonances and their associated electric field
intensities are controlled by just the width of the slit. More complex
transmission spectra appear when the wavelength of light is comparable to the
slit width. Rapid oscillations associated to the emergence of different
propagating modes inside the slit are the main features appearing in this
regime.Comment: Accepted for publication in Phys. Rev.
Activated carbons as catalytic support for Cu nanoparticles
There are a wide range of catalytic applications for Cu-based nanoparticles materials, since Cu is an
abundant and inexpensive metal and Cu nanoparticles possess unusual electrical, thermal and
optical properties. The possible modification of the chemical and physical properties of these
nanoparticles using different synthetic strategies and conditions and/or via postsynthetic chemical
treatments has been largely responsible for the rapid growth of interest in these nanomaterials and
their applications in catalysis. A previous work have explored the possibilities of SBA-15 (1,2) as
support for Cu nanoparticles. In the present contribution, those results will be compared with the
use of a carbon material as support, since activated carbon present many advantages with respect
SBA, as the high surface area.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Supplementation of iron alone and combined with vitamins improves haematological status, erythrocyte membrane fluidity and oxidative stress in anaemic pregnant women
Pregnancy is a condition exhibiting increased susceptibility to oxidative stress, and Fe plays a central role in generating harmful oxygen species. The objective of the present study is to investigate the changes in haematological status, oxidative stress and erythrocyte membrane fluidity in anaemic pregnant women after Fe supplementation with and without combined vitamins. The study was a 2 months double-blind, randomised trial. Pregnant women (n 164) were allocated to four groups: group C was the placebo control group; group I was supplemented daily with 60 mg Fe (ferrous sulphate) daily; group IF was supplemented daily with Fe plus 400 µg folic acid; group IM was supplemented daily with Fe plus 2 mg retinol and 1 mg riboflavin, respectively. After the 2-month trial, Hb significantly increased by 15·8, 17·3 and 21·8 g/l, and ferritin by 2·8, 3·6 and 11·0 µg/l, in the I, IF and IM groups compared with placebo. Polarisation (¿) and microviscosity (¿) decreased significantly in other groups compared with placebo, indicating an increase in membrane fluidity. Significant decreases of ¿ and ¿ values compared with group C were 0·033 and 0·959 for group I, 0·037 and 1·074 for group IF and 0·064 and 1·865 for group IM, respectively. In addition, significant increases of glutathione peroxidase activities and decreases of malondialdehyde were shown in all treated groups, as well as increases of plasma retinol and urine riboflavin in group IM. The findings show that supplementation with Fe and particularly in combination with vitamins could improve the haematological status as well as oxidative stress and erythrocyte membrane fluidit
Parameterized optimized effective potential for the ground state of the atoms He through Xe
Parameterized orbitals expressed in Slater-type basis obtained within the
optimized effective potential framework as well as the parameterization of the
potential are reported for the ground state of the atoms He through Xe. The
total, kinetic, exchange and single particle energies are given for each atom.Comment: 47 pages, 1 figur
- Z interferometry at a -factory
We analyze the possibilities that the proposed -factories offer to
measure interference. In the unpolarized beam case, we study
different signatures in the channel, taking advantage of the
presence of the near-by resonance. We build a C-odd forward-backward
asymmetry, estimated to be around , and (P-even, T-even) and (P-odd,
T-odd) alignments of the , to be seen from the angular distribution of
its decay products. With polarized electrons a left-right asymmetry
around is present in all channels. At leading order this
asymmetry is independent of hadronic matrix elements and is sensitive to the
vector coupling. In the channel, a combined
left-right forward-backward asymmetry is considered.Comment: 29 pages + 6 figures. Some changes concerning observables,
especially related with possible 2 contribution
Performance model for “Just-in-Time” problems in real-time multimedia applications
Over the last few years, the use of large-scale
multimedia data applications has been growing tremendously,
and this growth is not likely to slow down in the near future.
Many multimedia applications operate in a real-time environment
(e.g., surveillance cameras, iris scans), which must meet strict
time constraints, i.e. to analyze video frames at the same rate as
a camera produces them. To meet this requirement, Grid computing
is rapidly becoming indispensable. However, the variabilities
of the software and the hardware in grid environment cause
the strong burstiness in the transmission delay of video frames.
Because the burstiness is unknown beforehand, it is difficult to
determine the right sending moments of video frames. If the
time interval between sending two sequential frames is too large,
then the service utilization may be low. If use large buffer to
guarantee the service utilization, then video frames may be outof-
date because of the long waiting time at buffer in the server
side. This problem is referred to as “Just-in-time” problem. To
solve this problem, it is essential to determine the right sending
moments of video frames, properly dealing with the trade-off
between the service utilization and the “up-to-date” of video
frames.
Motivated by this, in this paper we develop an adaptive control
method that react to the continuously changing circumstances in
grid system so as to obtain the highest service utilization on the
one hand and to keep the video frame up-to-date on the other
hand. Extensive experimental validation in our DAS-3 testbed
and the trace-driven simulation show that our method is indeed
highly effective
Effects of Wind Field Inhomogeneities on Doppler Beam Swinging Revealed by an Imaging Radar
In this work, the accuracy of the Doppler beam-swinging (DBS) technique for wind measurements is studied using an imaging radar—the turbulent eddy profiler (TEP) developed by the University of Mas- sachusetts, with data collected in summer 2003. With up to 64 independent receivers, and using coherent radar imaging (CRI), several hundred partially independent beams can be formed simultaneously within the volume defined by the transmit beam. By selecting a subset of these beams, an unprecedented number of DBS configurations with varying zenith angle, azimuth angle, and number of beams can be investigated. The angular distributions of echo power and radial velocity obtained by CRI provide a unique opportunity to validate the inherent assumption in the DBS method of homogeneity across the region defined by the beam directions. Through comparison with a reference wind field, calculated as the optimal uniform wind field derived from all CRI beams with sufficient signal-to-noise ratio (SNR), the accuracy of the wind estimates for various DBS configurations is statistically analyzed. It is shown that for a three-beam DBS configura- tion, although the validity of the homogeneity assumption is enhanced at smaller zenith angles, the root- mean-square (RMS) error increases because of the ill-conditioned matrix in the DBS algorithm. As ex- pected, inhomogeneities in the wind field produce large bias for the three-beam DBS configuration for large zenith angles. An optimal zenith angle, in terms of RMS error, of approximately 9°–10° was estimated. It is further shown that RMS error can be significantly reduced by increasing the number of off-vertical beams used for the DBS processing
Nanomagnetic intergrowths in Fe-Ni meteoritic metal: The potential for time-resolved records of planetesimal dynamo fields
Nanoscale intergrowths unique to the cloudy zones (CZs) of meteoritic metal display novel magnetic behaviour with the potential to reveal new insight into the early development of magnetic fields on protoplanetary bodies. The nanomagnetic state of the CZ within the Tazewell IIICD iron meteorite has been imaged using off-axis electron holography. The CZ is revealed to be a natural nanocomposite of magnetically hard islands of tetrataenite (ordered FeNi) embedded in a magnetically soft matrix of ordered Fe3Ni. In the remanent state, each tetrataenite island acts as a uniaxial single domain particle with its 001 magnetic easy axis oriented along one of three ?100? crystallographic directions of the parent taenite phase. Micromagnetic simulations demonstrate that switching occurs via the nucleation and propagation of domain walls through individual tetrataenite particles. The switching field (Hs) varies with the length scale of the matrix phase (Lm), with Hs \> 1 T for Lm \~{}10 nm (approaching the intrinsic switching field for isolated single domain tetrataenite) and 0.2 \< H s \< 0.6 T for Lm \~{}30 nm. The reduction in Hs with increasing Lc is caused by exchange coupling between the hard tetrataenite islands and the soft magnetic matrix, which lowers the critical field for domain wall nucleation, providing an explanation for previously observed coercivity variations throughout the {CZ.} Non-random distributions of the tetrataenite easy axes are observed locally throughout the {CZ}, suggesting a magnetic field could have been present during nanostructure formation. This observation demonstrates the potential for stable chemical transformation remanent magnetisation to be encoded by the nanostructure, with variations in the proportions of the six possible magnetisation states reflecting the intensity and relative direction of the magnetic fields present during cooling. According to recent cooling models, the cooling rate of meteoritic metal originating near the surface of differentiated planetesimals was such that the magnetic signal across the {CZ} could potentially record dynamo field intensity and direction variations over time (10{\textendash}100 Ma), which would enable events such as magnetic reversals and the decay of an asteroid dynamo to be observed
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