1,405 research outputs found
Prediction of service life of polymeric sealant compositions for fuel tanks in aerospace structures from measurements of viscoelastic properties Annual report
Prediction of service life of polymeric sealers for fuel tanks from viscoelastic measurement
Ocean Planet or Thick Atmosphere: On the Mass-Radius Relationship for Solid Exoplanets with Massive Atmospheres
The bulk composition of an exoplanet is commonly inferred from its average
density. For small planets, however, the average density is not unique within
the range of compositions. Variations of a number of important planetary
parameters--which are difficult or impossible to constrain from measurements
alone--produce planets with the same average densities but widely varying bulk
compositions. We find that adding a gas envelope equivalent to 0.1%-10% of the
mass of a solid planet causes the radius to increase 5-60% above its gas-free
value. A planet with a given mass and radius might have substantial water ice
content (a so-called ocean planet) or alternatively a large rocky-iron core and
some H and/or He. For example, a wide variety of compositions can explain the
observed radius of GJ 436b, although all models require some H/He. We conclude
that the identification of water worlds based on the mass-radius relationship
alone is impossible unless a significant gas layer can be ruled out by other
means.Comment: 5 pages, 3 figures, accepted to Ap
Mass accretion rates of clusters of galaxies: CIRS and HeCS
We use a new spherical accretion recipe tested on N-body simulations to
measure the observed mass accretion rate (MAR) of 129 clusters in the Cluster
Infall Regions in the Sloan Digital Sky Survey (CIRS) and in the Hectospec
Cluster Survey (HeCS). The observed clusters cover the redshift range of
and the mass range of . Based on three-dimensional mass profiles of simulated
clusters reaching beyond the virial radius, our recipe returns MARs that agree
with MARs based on merger trees. We adopt this recipe to estimate the MAR of
real clusters based on measurements of the mass profile out to .
We use the caustic method to measure the mass profiles to these large radii. We
demonstrate the validity of our estimates by applying the same approach to a
set of mock redshift surveys of a sample of 2000 simulated clusters with a
median mass of as well as a sample
of 50 simulated clusters with a median mass of : the median MARs based on the caustic mass profiles of
the simulated clusters are unbiased and agree within with the median
MARs based on the real mass profile of the clusters. The MAR of the CIRS and
HeCS clusters increases with the mass and the redshift of the accreting
cluster, which is in excellent agreement with the growth of clusters in the
CDM model.Comment: 25 pages, 19 figures, 7 table
Spin Transfer Torques in MnSi at Ultra-low Current Densities
Spin manipulation using electric currents is one of the most promising
directions in the field of spintronics. We used neutron scattering to observe
the influence of an electric current on the magnetic structure in a bulk
material. In the skyrmion lattice of MnSi, where the spins form a lattice of
magnetic vortices similar to the vortex lattice in type II superconductors, we
observe the rotation of the diffraction pattern in response to currents which
are over five orders of magnitude smaller than those typically applied in
experimental studies on current-driven magnetization dynamics in
nanostructures. We attribute our observations to an extremely efficient
coupling of inhomogeneous spin currents to topologically stable knots in spin
structures
Un cas dâhematome extradural cervical non traumatique
LâhĂ©matome extradural cervical spontanĂ© est une pathologie rare mais une sĂ©vĂšre cause de compression mĂ©dullaire. Il requiert un diagnostic et une prise en charge urgents. Nous en rapportons un cas chez une patiente de 20 ans sans antĂ©cĂ©dent pathologique, rĂ©vĂ©lĂ© par un syndrome de compression mĂ©dullaire cervical sĂ©vĂšre (grade A de Frankel). Une dĂ©compression neurochirurgicale est intervenue avec un dĂ©lai de48H avec comme corollaire de lourdes sĂ©quelles. Les auteurs insistent sur lâintĂ©rĂȘt dâun diagnostic et dâune prise en charge prĂ©coces pour en minimiser les sĂ©quelles neurologiques
Extinction time for some nonlinear heat equations
This paper concerns the study of the extinction time of the solution of the following initial-boundary value problem
[left{%
begin{array}{ll}
hbox{,} \
hbox{,} \
hbox{,} \
end{array}%right. ]
where is a bounded domain in with smooth boundary , is a positive parameter, is a positive, increasing, concave function for positive values of s, , , is an elliptic operator. We show that the solution of the above problem extincts in a finite time and its extinction time goes to that of the solution of the following differential equation
[alpha^{\u27}(t)=-f(alpha(t)),quad t>0,quad alpha(0)=M,] as
goes to zero, where .
We also extend the above result to other classes of nonlinear
parabolic equations. Finally, we give some numerical results to
illustrate our analysis
Analysis of caesarean rate and indications of university hospitals in sub-Saharan African developing countries using Robson classification system: the case of Cocodyâs hospital center, Abidjan-Cote dâIvoire
Background: According to the World Health Organization (WHO), it has become imperative to monitor caesarean rates in hospitals since these rates continue to increase; WHO recommends this monitoring by the Robsonâs system. The study objective was to describe caesarean rates in a level 3 maternity of developing country using this system, to identify the groups likely increase overall rate of caesarean.Methods: A retrospective and comparative study made in Cocody University Hospital Center (Abidjan-Cote dâIvoire) over a period of twelve years. A total of 21,067 women who delivered during this period by caesarean were included.Results: The overall rate of caesarean during the study period was 38.7% with a significant increase from Period I to Period II (34.8 vs. 41.7%; p Ë0.000). The subgroup 2 (nulliparas, single cephalic term pregnancy, caesarean before labor) made the greatest contribution to the overall CS rate with an increase of +5% (10.1 vs. 15.1%; pË0,000). Women with previous CS (groups 5, 7, 8, 9, 10) increased the caesarean rate of +3.4% (7 vs. 10.4%; pË0.000). The group 6 increased it of +2.9% (4.7 vs 7.6%; pË0.000). Caesarean indications were dominated by fetal acute distress (24.5 vs. 22.6%; pË0,000), then followed by fetal-pelvic disproportion (21.8 vs. 10.7%), severe preeclampsia/eclampsia (13.5 vs. 17.5%; pË0.000), scarred uterus and breech presentation.Conclusions: Robson classification has identified the groups led to a significant increase in caesarean rates in our service and therefore has good focus our preventive actions.
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