898 research outputs found
The impact of the Covid-19 crisis on socioeconomic differences in physical activity behavior:Evidence from the Lifelines COVID-19 cohort study
Covid-19 and measures to contain spreading the disease have led to changed physical activity behavior. This study aims to investigate the relationship between socioeconomic status (SES) and changes in the amount of moderate to vigorous physical activity (MVPA) during the Covid-19 crisis. Using the Dutch Lifelines Covid-19 cohort study (n = 17,749), the amount of MVPA was measured at 15 time-points between March and December 2020, and compared with the amount before the Covid19 pandemic. For SES, the population was stratified in three education and income levels. Logistic regression models were used to estimate the odds ratio (OR) and confidence interval (CI) of altered MVPA for low and high SES groups, with the middle SES category as the reference group. A clear socioeconomic gradient in changes in MVPA behavior was observed. Low educated individuals had significantly higher odds (OR = 1.14; CI: 1.03-1.27) of decreasing MVPA, while the high educated had significantly lower odds of decreased MVPA (OR = 0.84, CI: 0.79-0.90). Both low education (OR = 0.87; CI: 0.77-0.98) and low income (OR = 0.85; CI 0.78-0.92) had significantly lower odds to increase MVPA, while high education (OR = 1.21, CI: 1.12-1.30) and high income (OR = 1.17; CI: 1.07-1.28) had significantly higher odds to increase MVPA. Most findings were consistent over the full research period. Socioeconomic in-equalities in MVPA have increased during the Covid-19 pandemic, even when Covid-19 containment measures were relaxed. Our findings suggest that future public health policies need to increase efforts to improve physical activity behavior with an even larger focus on low SES groups
Venous Thoracic Outlet Syndrome
Background: A 19-year-old woman, Academy of Sport student, noticed a progressive bluish discoloration, swelling and pain of the right hand and axilla during abduction. The symptoms had been progressive for 6 months. During physical examination there was a normal sensibility and motor function, and normal pulsations of the radial and ulnar artery. There was no significant medical history. A thorax aperture radiograph was performed, followed by venography of the right arm in neutral position and with abduction
Temperature effects on dislocation core energies in silicon and germanium
Temperature effects on the energetics of the 90-degree partial dislocation in
silicon and germanium are investigated, using non-equilibrium methods to
estimate free energies, coupled with Monte Carlo simulations. Atomic
interactions are described by Tersoff and EDIP interatomic potentials. Our
results indicate that the vibrational entropy has the effect of increasing the
difference in free energy between the two possible reconstructions of the
90-degree partial, namely, the single-period and the double-period geometries.
This effect further increases the energetic stability of the double-period
reconstruction at high temperatures. The results also indicate that anharmonic
effects may play an important role in determining the structural properties of
these defects in the high-temperature regime.Comment: 8 pages in two-column physical-review format with six figure
Thermodynamic Behavior of a Model Covalent Material Described by the Environment-Dependent Interatomic Potential
Using molecular dynamics simulations we study the thermodynamic behavior of a
single-component covalent material described by the recently proposed
Environment-Dependent Interatomic Potential (EDIP). The parameterization of
EDIP for silicon exhibits a range of unusual properties typically found in more
complex materials, such as the existence of two structurally distinct
disordered phases, a density decrease upon melting of the low-temperature
amorphous phase, and negative thermal expansion coefficients for both the
crystal (at high temperatures) and the amorphous phase (at all temperatures).
Structural differences between the two disordered phases also lead to a
first-order transition between them, which suggests the existence of a second
critical point, as is believed to exist for amorphous forms of frozen water.
For EDIP-Si, however, the unusual behavior is associated not only with the open
nature of tetrahedral bonding but also with a competition between four-fold
(covalent) and five-fold (metallic) coordination. The unusual behavior of the
model and its unique ability to simulation the liquid/amorphous transition on
molecular-dynamics time scales make it a suitable prototype for fundamental
studies of anomalous thermodynamics in disordeered systems.Comment: 48 pages (double-spaced), 13 figure
Should we teach linear algebra through geometry?
AbstractCan geometry help students learn linear algebra? I study this question and demonstrate that there is no obvious clear answer: geometry can be an obstacle to learning linear algebra; or it can be helpful. Geometry is helpful only under certain conditions and with a specific use of drawings. These special requirements for using geometry are apparently not much recognized in our teaching of linear algebra courses, at least in France, where my educational studies have taken place
Determination of 141Pr(alpha,n)144Pm cross sections at energies of relevance for the astrophysical p-process using the gamma-gamma coincidence method
The reaction 141Pr(alpha,n)144Pm was investigated between E_alpha=11 MeV and
15 MeV with the activation method using the gamma-gamma coincidence method with
a segmented clover-type high-purity Germanium (HPGe) detector. Measurements
with four other HPGe detectors were additionally made. The comparison proves
that the gamma-gamma coincidence method is an excellent tool to investigate
cross sections down to the microbarn range. The (alpha,n) reaction at low
energy is especially suited to test alpha+nucleus optical-model potentials for
application in the astrophysical p-process. The experimentally determined cross
sections were compared to Hauser-Feshbach statistical model calculations using
different optical potentials and generally an unsatisfactory reproduction of
the data was found. A local potential was constructed to improve the
description of the data. The consequences of applying the same potential to
calculate astrophysical (gamma,alpha) rates for 145Pm and 148Gd were explored.
In summary, the data and further results underline the problems in global
predictions of alpha+nucleus optical potentials at astrophysically relevant
energies.Comment: 13 pages, 9 figures, accepted in Phys. Rev.
Photoneutron cross sections for samarium isotopes: Toward a unified understanding of (
A spectral line survey of Orion KL in the bands 486-492 and 541-577 GHz with the Odin satellite I. The observational data
Spectral line surveys are useful since they allow identification of new
molecules and new lines in uniformly calibrated data sets. Nonetheless, large
portions of the sub-millimetre spectral regime remain unexplored due to severe
absorptions by H2O and O2 in the terrestrial atmosphere. The purpose of the
measurements presented here is to cover wavelength regions at and around 0.55
mm -- regions largely unobservable from the ground. Using the Odin
astronomy/aeronomy satellite, we performed the first spectral survey of the
Orion KL molecular cloud core in the bands 486--492 and 541--576 GHz with
rather uniform sensitivity (22--25 mK baseline noise). Odin's 1.1 m size
telescope, equipped with four cryo-cooled tuneable mixers connected to broad
band spectrometers, was used in a satellite position-switching mode. Two mixers
simultaneously observed different 1.1 GHz bands using frequency steps of 0.5
GHz (25 hours each). An on-source integration time of 20 hours was achieved for
most bands. The entire campaign consumed ~1100 orbits, each containing one hour
of serviceable astro-observation. We identified 280 spectral lines from 38
known interstellar molecules (including isotopologues) having intensities in
the range 80 to 0.05 K. An additional 64 weak lines remain unidentified. Apart
from the ground state rotational 1(1,0)--1(0,1) transitions of ortho-H2O, H218O
and H217O, the high energy 6(2,4)--7(1,7) line of para-H2O and the
HDO(2,0,2--1,1,1) line have been observed, as well as the 1,0--0,1 lines from
NH3 and its rare isotopologue 15NH3. We suggest assignments for some
unidentified features, notably the new interstellar molecules ND and SH-.
Severe blends have been detected in the line wings of the H218O, H217O and 13CO
lines changing the true linewidths of the outflow emission.Comment: 21 pages, 10 figures, 7 tables, accepeted for publication in
Astronomy and Astrophysics 30 August 200
Microtubules in Bacteria: Ancient Tubulins Build a Five-Protofilament Homolog of the Eukaryotic Cytoskeleton
Microtubules play crucial roles in cytokinesis, transport, and motility, and are therefore superb targets for anti-cancer drugs. All tubulins evolved from a common ancestor they share with the distantly related bacterial cell division protein FtsZ, but while eukaryotic tubulins evolved into highly conserved microtubule-forming heterodimers, bacterial FtsZ presumably continued to function as single homopolymeric protofilaments as it does today. Microtubules have not previously been found in bacteria, and we lack insight into their evolution from the tubulin/FtsZ ancestor. Using electron cryomicroscopy, here we show that the tubulin homologs BtubA and BtubB form microtubules in bacteria and suggest these be referred to as “bacterial microtubules” (bMTs). bMTs share important features with their eukaryotic counterparts, such as straight protofilaments and similar protofilament interactions. bMTs are composed of only five protofilaments, however, instead of the 13 typical in eukaryotes. These and other results suggest that rather than being derived from modern eukaryotic tubulin, BtubA and BtubB arose from early tubulin intermediates that formed small microtubules. Since we show that bacterial microtubules can be produced in abundance in vitro without chaperones, they should be useful tools for tubulin research and drug screening
The s Process: Nuclear Physics, Stellar Models, Observations
Nucleosynthesis in the s process takes place in the He burning layers of low
mass AGB stars and during the He and C burning phases of massive stars. The s
process contributes about half of the element abundances between Cu and Bi in
solar system material. Depending on stellar mass and metallicity the resulting
s-abundance patterns exhibit characteristic features, which provide
comprehensive information for our understanding of the stellar life cycle and
for the chemical evolution of galaxies. The rapidly growing body of detailed
abundance observations, in particular for AGB and post-AGB stars, for objects
in binary systems, and for the very faint metal-poor population represents
exciting challenges and constraints for stellar model calculations. Based on
updated and improved nuclear physics data for the s-process reaction network,
current models are aiming at ab initio solution for the stellar physics related
to convection and mixing processes. Progress in the intimately related areas of
observations, nuclear and atomic physics, and stellar modeling is reviewed and
the corresponding interplay is illustrated by the general abundance patterns of
the elements beyond iron and by the effect of sensitive branching points along
the s-process path. The strong variations of the s-process efficiency with
metallicity bear also interesting consequences for Galactic chemical evolution.Comment: 53 pages, 20 figures, 3 tables; Reviews of Modern Physics, accepte
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