858 research outputs found
Association Between Early Hyperoxia Exposure After Resuscitation From Cardiac Arrest and Neurological Disability: Prospective Multicenter Protocol-Directed Cohort Study
BACKGROUND:
Studies examining the association between hyperoxia exposure after resuscitation from cardiac arrest and clinical outcomes have reported conflicting results. Our objective was to test the hypothesis that early postresuscitation hyperoxia is associated with poor neurological outcome.
METHODS:
This was a multicenter prospective cohort study. We included adult patients with cardiac arrest who were mechanically ventilated and received targeted temperature management after return of spontaneous circulation. We excluded patients with cardiac arrest caused by trauma or sepsis. Per protocol, partial pressure of arterial oxygen (Pao2) was measured at 1 and 6 hours after return of spontaneous circulation. Hyperoxia was defined as a Pao2 >300 mm Hg during the initial 6 hours after return of spontaneous circulation. The primary outcome was poor neurological function at hospital discharge, defined as a modified Rankin Scale score >3. Multivariable generalized linear regression with a log link was used to test the association between Pao2 and poor neurological outcome. To assess whether there was an association between other supranormal Pao2 levels and poor neurological outcome, we used other Pao2 cut points to define hyperoxia (ie, 100, 150, 200, 250, 350, 400 mm Hg).
RESULTS:
Of the 280 patients included, 105 (38%) had exposure to hyperoxia. Poor neurological function at hospital discharge occurred in 70% of patients in the entire cohort and in 77% versus 65% among patients with versus without exposure to hyperoxia respectively (absolute risk difference, 12%; 95% confidence interval, 1-23). Hyperoxia was independently associated with poor neurological function (relative risk, 1.23; 95% confidence interval, 1.11-1.35). On multivariable analysis, a 1-hour-longer duration of hyperoxia exposure was associated with a 3% increase in risk of poor neurological outcome (relative risk, 1.03; 95% confidence interval, 1.02-1.05). We found that the association with poor neurological outcome began at ≥300 mm Hg.
CONCLUSIONS:
Early hyperoxia exposure after resuscitation from cardiac arrest was independently associated with poor neurological function at hospital discharge
Time Reversal Communication in Rayleigh-Fading Broadcast Channels with Pinholes
The paper presents an analysis of the time reversal in independent-multipath
Rayleigh-fading channels with inputs (transmitters) and outputs
(receivers).
The main issues addressed are the condition of statistical stability, the
rate of information transfer and the effect of pinholes. The stability
condition is proved to be
for broadband channels and
for narrowband channels where is the symbol rate,
is the bandwidth and is the {\em effective} number (maybe
less than 1) of transmitters. It is shown that when the number of screens,
, is relatively low compared to the logarithm of numbers of pinholes
is given by the {\em harmonic} (or {\em inverse}) {\em sum} of
the number of transmitters and the numbers of pinholes at all screens.
The novel idea of the effective number of time reversal array (TRA) elements
is introduced to derive the stability condition and estimate the channel
capacity in the presence of multi-screen pinholes. The information rate, under
the constraints of the noise power per unit frequency and the average
total power , attains the supremum in the regime . In particular, when the
optimal information rate can be achieved with statistically stable, sharply
focused signals.Comment: Corrected typos and minor change of conten
Cryptic complexity in felid vertebral evolution: shape differentiation and allometry of the axial skeleton
Members of the mammalian family Felidae (extant and extinct cats) are grossly phenotypically similar, but display a 300-fold range in body size, from less than 1 kg to more than 300 kg. In addition to differences in body mass, felid species show dietary and locomotory specializations that correlate to skull and limb osteological measurements, such as shape or cross-sectional area. However, ecological correlates to the axial skeleton are yet untested. Here, we build on previous studies of the biomechanical and morphological evolution of the felid appendicular skeleton by conducting a quantitative analysis of morphology and allometry in the presacral vertebral column across extant cats. Our results demonstrate that vertebral columns of arboreal, scansorial and terrestrial felids significantly differ in morphology, specifically in the lumbar region, while no distinction based on dietary specialization was found. Body size significantly influences vertebral morphology, with clear regionalization of allometry along the vertebral column, suggesting that anterior (cervicals and thoracics) and posterior (lumbar) vertebrae may be independently subjected to distinct selection pressures
Spectrum of the relic neutrino background from past supernovae and cosmological models
It is greatly expected that the relic neutrino background from past
supernovae is detected by Superkamiokande (SK) which is now under construction.
We calculate the spectrum and the event rate at SK systematically by using the
results of simulations of a supernova explosion and reasonable supernova rates.
We also investigate the effect of a cosmological constant, , on the
spectrum, since some recent cosmological observations strongly suggest the
existence of . We find following results. 1) The spectrum has a peak
at about 3 MeV, which is much lower than that of previous estimate ( 10
MeV). 2) The event rate at SK in the range from 10 MeV to 50 MeV, where the
relic neutrinos from past supernovae is dominant, is about events per year, where is the
supernova rate in a galaxy, is the number density of galaxies, and
(50km/s/Mpc), where is the Hubble constant. 3) The event
rate is almost insensitive to . The flux increases in the low energy
side ( MeV) with increasing , but decreases in the high energy
side (10 MeV ) in models in which the integrated number of supernovae in one
galaxy is fixed.Comment: 20 pages, uuencoded compressed postscript, 7 figures are included.
Accepted for publication in Astroparticle Phy
The most recent burst of Star Formation in the Massive Elliptical Galaxy NGC 1052
High-spatial resolution near-infrared (NIR) images of the central 24 x 24
arcsec^2 (~ 2 x 2 kpc^2) of the elliptical galaxy NGC 1052 reveal a total of 25
compact sources randomly distributed in the region. Fifteen of them exhibit
Halpha luminosities an order of magnitude above the estimate for an evolved
population of extreme horizontal branch stars. Their Halpha equivalent widths
and optical-to-NIR spectral energy distributions are consistent with them being
young stellar clusters aged < 7 Myr. We consider this to be the first direct
observation of spatially resolved star-forming regions in the central
kiloparsecs of an elliptical galaxy. The sizes of these regions are ~< 11 pc
and their median reddening is E(B - V) ~ 1 mag. According to previous works,
NGC 1052 may have experienced a merger event about 1 Gyr ago. On the assumption
that these clusters are spreaded with similar density over the whole galaxy,
the fraction of galaxy mass (5 x 10^{-5}) and rate of star formation (0.01
Msun/yr) involved, suggest the merger event as the possible cause for the star
formation we see today.Comment: 5 pages, 3 figures. Accepted for publication in MNRAS Letter
Optimally shaped terahertz pulses for phase retrieval in a Rydberg atom data register
We employ Optimal Control Theory to discover an efficient information
retrieval algorithm that can be performed on a Rydberg atom data register using
a shaped terahertz pulse. The register is a Rydberg wave packet with one
consituent orbital phase-reversed from the others (the ``marked bit''). The
terahertz pulse that performs the decoding algorithm does so by by driving
electron probability density into the marked orbital. Its shape is calculated
by modifying the target of an optimal control problem so that it represents the
direct product of all correct solutions to the algorithm.Comment: 6 pages, 3 figure
The first gigayear of bulge star formation in Virgo ellipticals: constraints from their globular cluster systems
Data products from the Advanced Camera for Surveys Virgo Cluster Survey are
used to understand the bulge star formation history in early-type galaxies at
redshifts z > 2. A new technique is developed whereby observed high-redshift
age-metallicity relationships are utilized to constrain the typical formation
epochs of metal-rich or "bulge" globular clusters. This analysis supports a
model where massive Virgo galaxies underwent an extremely intense mode of bulge
globular cluster formation at z ~ 3.5 that was followed by an era of
significant bulge growth and little globular cluster production.
Intermediate-mass galaxies showed a less-intense period of globular cluster
formation at z ~ 2.5 that was synchronized with the bulk of bulge star growth.
The transition between the massive and intermediate-mass galaxy star formation
modes occurs at a galaxy stellar mass of M_stellar ~ 3 x 10^10 M_sun, the mass
where many other galaxy properties are observed to change. Dwarf early-type
galaxies in Virgo may have experienced no significant period of bulge globular
cluster formation, thus the intense star bursts associated with globular
cluster formation may be difficult to directly observe at redshifts z < 4.
Though the above conclusions are preliminary because they are based upon
uncertain relationships between age and metallicity, the technique employed
will yield more stringent constraints as high-redshift galaxy observations and
theoretical models improve.Comment: Accepted by MNRAS. 9 pages text. 6 figures
8.4GHz VLBI observations of SN2004et in NGC6946
We report on 8.4GHz Very Long Baseline Interferometry (VLBI) observations of
the type II-P supernova SN2004et in the spiral galaxy NGC 6946, made on 20
February 2005 (151 days after explosion). The Very Large Array (VLA) flux
density was 1.230.07 mJy, corresponding to an isotropic luminosity at
8.4GHz of (4.450.3) erg s Hz and a brightness
temperature of (1.30.3) K. We also provide an improved
source position, accurate to about 0.5 mas in each coordinate. The VLBI image
shows a clear asymmetry. From model fitting of the size of the radio emission,
we estimate a minimum expansion velocity of 15,7002,000 km s. This
velocity is more than twice the expected mean expansion velocity estimated from
a synchrotron self-absorbed emission model, thus suggesting that synchrotron
self-absorption is not relevant for this supernova. With the benefit of an
optical spectrum obtained 12 days after explosion, we favor an emission model
which consists of two hot spots on an underlying expanding shell of width
comparable to that of SN 1993J.Comment: Accepted for publication in A&A (22/05/07
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