8,347 research outputs found
Role of a plausible nuisance contributor in the declining obesity-mortality risks over time.
CONTEXT: Recent analyses of epidemiological data including the National Health and Nutrition Examination Survey (NHANES) have suggested that the harmful effects of obesity may have decreased over calendar time. The shifting BMI distribution over time coupled with the application of fixed broad BMI categories in these analyses could be a plausible nuisance contributor to this observed change in the obesity-associated mortality over calendar time.
OBJECTIVE: To evaluate the extent to which observed temporal changes in the obesity-mortality association may be due to a shifting population distribution for body mass index (BMI), coupled with analyses based on static, broad BMI categories.
DESIGN, SETTING, AND PARTICIPANTS: Simulations were conducted using data from NHANES I and III linked with mortality data. Data from NHANES I were used to fit a true model treating BMI as a continuous variable. Coefficients estimated from this model were used to simulate mortality for participants in NHANES III. Hence, the population-level association between BMI and mortality in NHANES III was fixed to be identical to the association estimated in NHANES I. Hazard ratios (HRs) for obesity categories based on BMI for NHANES III with simulated mortality data were compared to the corresponding estimated HRs from NHANES I.
MAIN OUTCOME MEASURES: Change in hazard ratios for simulated data in NHANES III compared to observed estimates from NHANES I.
RESULTS: On average, hazard ratios for NHANES III based on simulated mortality data were 29.3% lower than the estimates from NHANES I using observed mortality follow-up. This reduction accounted for roughly three-fourths of the apparent decrease in the obesity-mortality association observed in a previous analysis of these data.
CONCLUSIONS: Some of the apparent diminution of the association between obesity and mortality may be an artifact of treating BMI as a categorical variable
Signatures of electron-boson coupling in half-metallic ferromagnet MnGe: study of electron self-energy obtained from infrared spectroscopy
We report results of our infrared and optical spectroscopy study of a
half-metallic ferromagnet MnGe. This compound is currently being
investigated as a potential injector of spin polarized currents into germanium.
Infrared measurements have been performed over a broad frequency (50 - 50000
cm) and temperature (10 - 300 K) range. From the complex optical
conductivity we extract the electron self-energy
. The calculation of is based on novel
numerical algorithms for solution of systems of non-linear equations. The
obtained self-energy provides a new insight into electron correlations in
MnGe. In particular, it reveals that charge carriers may be coupled to
bosonic modes, possibly of magnetic origin
Just how hot are the Centauri extreme horizontal branch pulsators?
Past studies based on optical spectroscopy suggest that the five Cen
pulsators form a rather homogeneous group of hydrogen-rich subdwarf O stars
with effective temperatures of around 50 000 K. This places the stars below the
red edge of the theoretical instability strip in the log Teff diagram,
where no pulsation modes are predicted to be excited. Our goal is to determine
whether this temperature discrepancy is real, or whether the stars' effective
temperatures were simply underestimated. We present a spectral analysis of two
rapidly pulsating extreme horizontal branch (EHB) stars found in Cen.
We obtained Hubble Space Telescope/COS UV spectra of two Cen
pulsators, V1 and V5, and used the ionisation equilibrium of UV metallic lines
to better constrain their effective temperatures. As a by-product we also
obtained FUV lightcurves of the two pulsators. Using the relative strength of
the N IV and N V lines as a temperature indicator yields Teff values close to
60 000 K, significantly hotter than the temperatures previously derived. From
the FUV light curves we were able to confirm the main pulsation periods known
from optical data. With the UV spectra indicating higher effective temperatures
than previously assumed, the sdO stars would now be found within the predicted
instability strip. Such higher temperatures also provide consistent
spectroscopic masses for both the cool and hot EHB stars of our previously
studied sample.Comment: 9 pages, accepted for publication in Astronomy and Astrophysic
Studies of the use of high-temperature nuclear heat from an HTGR for hydrogen production
The results of a study which surveyed various methods of hydrogen production using nuclear and fossil energy are presented. A description of these methods is provided, and efficiencies are calculated for each case. The process designs of systems that utilize the heat from a general atomic high temperature gas cooled reactor with a steam methane reformer and feed the reformer with substitute natural gas manufactured from coal, using reforming temperatures, are presented. The capital costs for these systems and the resultant hydrogen production price for these cases are discussed along with a research and development program
Diluted Random Fields in Mixed Cyanide Crystals
A percolation argument and a dilute compressible random field Ising model are
used to present a simple model for mixed cyanide crystals. The model reproduces
quantitatively several features of the phase diagrams altough some crude
approximations are made. In particular critical thresholds x_c at which
ferroelastic first order transitions disappear, are calculated. Moreover,
transitions are found to remain first order down to x_c for all mixtures except
for bromine, for which the transition becomes continuous. All the results are
in full agreement with experimental data.Comment: 8 pages, late
Multiwavelength Observations of the Hot DB Star PG 0112+104
We present a comprehensive multiwavelength analysis of the hot DB white dwarf
PG 0112+104. Our analysis relies on newly-acquired FUSE observations, on
medium-resolution FOS and GHRS data, on archival high-resolution GHRS
observations, on optical spectrophotometry both in the blue and around Halpha,
as well as on time-resolved photometry. From the optical data, we derive a
self-consistent effective temperature of 31,300+-500 K, a surface gravity of
log g = 7.8 +- 0.1 (M=0.52 Msun), and a hydrogen abundance of log N(H)/N(He) <
-4.0. The FUSE spectra reveal the presence of CII and CIII lines that
complement the previous detection of CII transitions with the GHRS. The
improved carbon abundance in this hot object is log N(C)/N(He) = -6.15 +- 0.23.
No photospheric features associated with other heavy elements are detected. We
reconsider the role of PG 0112+104 in the definition of the blue edge of the
V777 Her instability strip in light of our high-speed photometry, and contrast
our results with those of previous observations carried out at the McDonald
Observatory.Comment: 10 pages in emulateapj, 9 figures, accepted for publication in Ap
On a Conjecture of Rapoport and Zink
In their book Rapoport and Zink constructed rigid analytic period spaces
for Fontaine's filtered isocrystals, and period morphisms from PEL
moduli spaces of -divisible groups to some of these period spaces. They
conjectured the existence of an \'etale bijective morphism of
rigid analytic spaces and of a universal local system of -vector spaces on
. For Hodge-Tate weights and we construct in this article an
intrinsic Berkovich open subspace of and the universal local
system on . We conjecture that the rigid-analytic space associated with
is the maximal possible , and that is connected. We give
evidence for these conjectures and we show that for those period spaces
possessing PEL period morphisms, equals the image of the period morphism.
Then our local system is the rational Tate module of the universal
-divisible group and enjoys additional functoriality properties. We show
that only in exceptional cases equals all of and when the
Shimura group is we determine all these cases.Comment: v2: 48 pages; many new results added, v3: final version that will
appear in Inventiones Mathematica
High-speed Photometric Observations of ZZ Ceti White Dwarf Candidates
We present high-speed photometric observations of ZZ Ceti white dwarf
candidates drawn from the spectroscopic survey of bright DA stars from the
Villanova White Dwarf Catalog by Gianninas et al., and from the recent
spectroscopic survey of white dwarfs within 40 parsecs of the Sun by Limoges et
al. We report the discovery of six new ZZ Ceti pulsators from these surveys,
and several photometrically constant DA white dwarfs, which we then use to
refine the location of the ZZ Ceti instability strip.Comment: 4 pages, 1 table, 2 figures, to appear in "19th European White Dwarf
Workshop" in the ASP Conference Serie
Hybrid expansions for local structural relaxations
A model is constructed in which pair potentials are combined with the cluster
expansion method in order to better describe the energetics of structurally
relaxed substitutional alloys. The effect of structural relaxations away from
the ideal crystal positions, and the effect of ordering is described by
interatomic-distance dependent pair potentials, while more subtle
configurational aspects associated with correlations of three- and more sites
are described purely within the cluster expansion formalism. Implementation of
such a hybrid expansion in the context of the cluster variation method or Monte
Carlo method gives improved ability to model phase stability in alloys from
first-principles.Comment: 8 pages, 1 figur
Interplay between magnetic anisotropy and interlayer coupling in nanosecond magnetization reversal of spin-valve trilayers
The influence of magnetic anisotropy on nanosecond magnetization reversal in
coupled FeNi/Cu/Co trilayers was studied using a photoelectron emission
microscope combined with x-ray magnetic circular dicroism. In quasi-isotropic
samples the reversal of the soft FeNi layer is determined by domain wall
pinning that leads to the formation of small and irregular domains. In samples
with uniaxial magnetic anisotropy, the domains are larger and the influence of
local interlayer coupling dominates the domain structure and the reversal of
the FeNi layer
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