319 research outputs found
Waveform-based simulated annealing of crosshole transmission data: a semi-global method for estimating seismic anisotropy
We successfully apply the semi-global inverse method of simulated annealing to determine the best-fitting 1-D anisotropy model for use in acoustic frequency domain waveform tomography. Our forward problem is based on a numerical solution of the frequency domain acoustic wave equation, and we minimize wavefield phase residuals through random perturbations to a 1-D vertically varying anisotropy profile. Both real and synthetic examples are presented in order to demonstrate and validate the approach. For the real data example, we processed and inverted a cross-borehole data set acquired by Vale Technology Development (Canada) Ltd. in the Eastern Deeps deposit, located in Voisey's Bay, Labrador, Canada. The inversion workflow comprises the full suite of acquisition, data processing, starting model building through traveltime tomography, simulated annealing and finally waveform tomography. Waveform tomography is a high resolution method that requires an accurate starting model. A cycle-skipping issue observed in our initial starting model was hypothesized to be due to an erroneous anisotropy model from traveltime tomography. This motivated the use of simulated annealing as a semi-global method for anisotropy estimation. We initially tested the simulated annealing approach on a synthetic data set based on the Voisey's Bay environment; these tests were successful and led to the application of the simulated annealing approach to the real data set. Similar behaviour was observed in the anisotropy models obtained through traveltime tomography in both the real and synthetic data sets, where simulated annealing produced an anisotropy model which solved the cycle-skipping issue. In the real data example, simulated annealing led to a final model that compares well with the velocities independently estimated from borehole logs. By comparing the calculated ray paths and wave paths, we attributed the failure of anisotropic traveltime tomography to the breakdown of the ray-theoretical approximation in the vicinity of strong velocity discontinuitie
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Coronary heart disease risk factors in premenopausal black women compared to white women
Background: Premenopausal black women have a 2-3 fold greater rate of coronary heart
disease (CHD) than premenopausal white women. The purpose of this study was to
provide insight into the reasons for this difference.
Methods and Results: We compared CHD risk factors in 100 black and 100 white, healthy
premenopausal women age 18-45 years and of relatively advantaged socioeconomic status.
Black women consumed diets higher in saturated fat and cholesterol (12% of kcal as
saturated fat and 360 mg of cholesterol per day) than did white women (10% of kcal and
290 mg/day) (p=0.008). Black women also had a higher body mass index (BMI)
(32.0±9.2 vs. 29.0±9.4 kg/m², p=0.021), and higher systolic (124±17 vs. 115±14 mmHg,
p<0.0001), and diastolic (79±14 vs. 75±11 mmHg, p=0.048) blood pressures. The mean
plasma Lp(a) concentration was higher in the black women (40.2±31.3 mg/dl) than in the
white women (19.2±23.7 mg/dl)(p<0.0001). The black women, however, had lower
plasma triglyceride levels (0.91±0.46 vs. 1.22±0.60 mmol/L, p<0.0001), and a trend
toward higher HDL cholesterol levels (1.37±0.34 vs. 1.29±0.31 mmol/L, p=0.064) than
the white women. Plasma total and LDL cholesterol levels were similar. Rates of
cigarette smoking and alcohol intake were low and similar between the races.
Black women additionally had higher levels of plasma total homocysteine (8.80 vs.
7.81 μmol/L, p=0.013), lower plasma folates (3.52 vs. 5.23 ng/ml, p<0.0001), and higher
vitamin B₁₂ levels (522 vs. 417 pg/ml, p<0.0001) than white women. More white women
than black women took a multivitamin supplement (42.4% vs. 24.7%, p=0.019). When
adjusted for multivitamin use, homocysteine levels did not differ, but plasma folate
remained significantly lower in black women. Sixty-eight percent of black women carried
the wild-type methylenetetrahydrofolate reductase genotype, 32.0% were heterozygotes,
and none were homozygotes. Of the white women, 47.4% were wild-type, 40.3%
heterozygotes, and 12.3% homozygotes (p=0.013).
Conclusions: Premenopausal black women consumed more saturated fat and cholesterol
and had a higher mean body mass index, blood pressure, Lp(a), and plasma total
homocysteine levels than white women. These differences in coronary risk factors may
explain the higher incidence of CHD in premenopausal black compared to white women
Young, metal-enriched cores in early-type dwarf galaxies in the Virgo cluster based on colour gradients
Early-type dwarf galaxies are not simply featureless, old objects, but were
found to be much more diverse, hosting substructures and a variety of stellar
population properties. To explore the stellar content of faint early-type
galaxies, and to investigate in particular those with recent central star
formation, we study colours and colour gradients within one effective radius in
optical (g-r) and near-infrared (i-H) bands for 120 Virgo cluster early types
with -19 mag < < -16 mag. Twelve galaxies turn out to have blue cores,
when defined as g-r colour gradients larger than 0.10 mag/, which
represents the positive tail of the gradient distribution. For these galaxies,
we find that they have the strongest age gradients, and that even outside the
blue core, their mean stellar population is younger than the mean of ordinary
faint early types. The metallicity gradients of these blue-cored early-type
dwarf galaxies are, however, in the range of most normal faint early types,
which we find to have non-zero gradients with higher central metallicity. The
blue central regions are consistent with star formation activity within the
last few 100 Myr. We discuss that these galaxies could be explained by
environmental quenching of star formation in the outer galaxy regions, while
the inner star formation activity has continued
The influence of iron status and genetic polymorphisms in the HFE gene on the risk for postoperative complications after bariatric surgery: a prospective cohort study in 1,064 patients
<p>Abstract</p> <p>Background</p> <p>Gastric bypass surgery is a highly effective therapy for long-term weight loss in severely obese patients, but carries significant perioperative risks including infection, wound dehiscence, and leaks from staple breakdown. Iron status can affect immune function and wound healing, thus may influence peri-operative complications. Common mutations in the HFE gene, the gene responsible for the iron overload disorder hereditary hemochromatosis, may impact iron status.</p> <p>Methods</p> <p>We analyzed 1064 extremely obese Caucasian individuals who underwent open and laparoscopic Roux-n-Y gastric bypass surgery at the Geisinger Clinic. Serum iron, ferritin, transferrin, and iron binding capacity were measured pre-operatively. All patients had intra-operative liver biopsies and were genotyped for the C282Y and H63D mutations in the HFE gene. Associations between surgical complications and serum iron measures, HFE gene status, and liver iron histology were determined.</p> <p>Results</p> <p>We found that increased serum iron and transferrin saturation were present in patients with any post-operative complication, and that increased serum ferritin was also increased in patients with major complications. Increased serum transferrin saturation was also associated with wound complications in open RYGB, and transferrin saturation and ferritin with prolonged lengths of stay. The presence of 2 or more HFE mutations was associated with overall complications as well as wound complications in open RYGB. No differences were found in complication rates between those with stainable liver iron and those without.</p> <p>Conclusion</p> <p>Serum iron status and HFE genotype may be associated with complications following RYGB surgery in the extremely obese.</p
Nonperturbative Effects in for Large Dilepton Invariant Mass
We reconsider the calculation of
nonperturbative corrections to decay. Our analysis
confirms the results of Ali et al. for the dilepton invariant mass spectrum,
which were in disagreement with an earlier publication, and for the lepton
forward-backward asymmetry. We also give expressions for the corrections to the left-right asymmetry. In addition
we discuss the breakdown of the heavy quark expansion near the point of maximal
dilepton invariant mass and consider a model independent approach to this
region using heavy hadron chiral perturbation theory. The modes and , which determine the endpoint region
of the inclusive decay, are analyzed within this framework. An interpolation is
suggested between the region of moderately high , where the heavy quark
expansion is still valid, and the vicinity of the endpoint described by chiral
perturbation theory. We also comment on further nonperturbative effects in
.Comment: 18 pages, LaTeX, 1 figur
The Einstein Cross: constraint on dark matter from stellar dynamics and gravitational lensing
[Abridged] We present two-dimensional line-of-sight stellar kinematics of the
lens galaxy in the Einstein Cross, obtained with the GEMINI 8m telescope, using
the GMOS integral-field spectrograph. The velocity map shows regular rotation
up to ~100 km/s around the minor axis of the bulge, consistent with
axisymmetry. The velocity dispersion map shows a weak gradient increasing
towards a central (R<1") value of sigma_0=170+/-9 km/s. We deproject the
observed surface brightness from HST imaging to obtain a realistic luminosity
density of the lens galaxy, which in turn is used to build axisymmetric
dynamical models that fit the observed kinematic maps. We also construct a
gravitational lens model that accurately fits the positions and relative fluxes
of the four quasar images. We find that the resulting luminous and total mass
distribution are nearly identical around the Einstein radius R_E = 0.89", with
a slope that is close to isothermal, but which becomes shallower towards the
center if indeed mass follows light. The dynamical model fits to the observed
kinematic maps result in a total mass-to-light ratio (M/L)_dyn=3.7+/-0.5
M_sun/L_sun,I (in the I-band). This is consistent with the Einstein mass M_E =
1.54 x 10^10 M_sun divided by the (projected) luminosity within R_E, which
yields a total mass-to-light ratio of (M/L)_E=3.4 M_sun/L_sun,I, with an error
of at most a few per cent. We estimate from stellar populations model fits to
colors of the lens galaxy a stellar mass-to-light ratio (M/L)_* from 2.8 to 4.1
M_sun/L_sun,I. Although a constant dark matter fraction of 20 per cent is not
excluded, dark matter may play no significant role in the bulge of this ~L*
early-type spiral galaxy.Comment: 18 pages, 8 figures, published in ApJ, 2010, 719, 148
Bile Acids, FXR, and Metabolic Effects of Bariatric Surgery
Overweight and obesity represent major risk factors for diabetes and related metabolic diseases. Obesity is associated with a chronic and progressive inflammatory response leading to the development of insulin resistance and type 2 diabetes (T2D) mellitus, although the precise mechanism mediating this inflammatory process remains poorly understood. The most effective intervention for the treatment of obesity, bariatric surgery, leads to glucose normalization and remission of T2D. Recent work in both clinical studies and animal models supports bile acids (BAs) as key mediators of these effects. BAs are involved in lipid and glucose homeostasis primarily via the farnesoid X receptor (FXR) transcription factor. BAs are also involved in regulating genes involved in inflammation, obesity, and lipid metabolism. Here, we review the novel role of BAs in bariatric surgery and the intersection between BAs and immune, obesity, weight loss, and lipid metabolism genes
Recovering the intrinsic shape of early-type galaxies
We investigate how well the intrinsic shape of early-type galaxies can be
recovered when both photometric and two-dimensional stellar kinematic
observations are available. We simulate these observations with galaxy models
that are representative of observed oblate fast-rotator to triaxial
slow-rotator early-type galaxies. By fitting realistic triaxial dynamical
models to these simulated observations, we recover the intrinsic shape (and
mass-to-light ratio), without making additional (ad-hoc) assumptions on the
orientation.
For (near) axisymmetric galaxies the dynamical modelling can strongly exclude
triaxiality, but the regular kinematics do not further tighten the constraint
on the intrinsic flattening significantly, so that the inclination is nearly
unconstrained above the photometric lower limit even with two-dimensional
stellar kinematics. Triaxial galaxies can have additional complexity in both
the observed photometry and kinematics, such as twists and (central)
kinematically decoupled components, which allows the intrinsic shape to be
accurately recovered. For galaxies that are very round or show no significant
rotation, recovery of the shape is degenerate, unless additional constraints
such as from a thin disk are available.Comment: 12 pages, 7 figures, PDFLaTeX, accepted to MNRAS, minor revision
The shape of the dark matter halo in the early-type galaxy NGC 2974
We present HI observations of the elliptical galaxy NGC 2974, obtained with
the Very Large Array. These observations reveal that the previously detected HI
disc in this galaxy (Kim et al. 1988) is in fact a ring. By studying the
harmonic expansion of the velocity field along the ring, we constrain the
elongation of the halo and find that the underlying gravitational potential is
consistent with an axisymmetric shape.
We construct mass models of NGC 2974 by combining the HI rotation curve with
the central kinematics of the ionised gas, obtained with the integral-field
spectrograph SAURON. We introduce a new way of correcting the observed
velocities of the ionised gas for asymmetric drift, and hereby disentangle the
random motions of the gas caused by gravitational interaction from those caused
by turbulence. To reproduce the observed flat rotation curve of the HI gas, we
need to include a dark halo in our mass models. A pseudo-isothermal sphere
provides the best model to fit our data, but we also tested an NFW halo and
Modified Newtonian Dynamics (MOND), which fit the data marginally worse.
The mass-to-light ratio M/L_I increases in NGC 2974 from 4.3 (M/L_I)sun at
one effective radius to 8.5 (M/L_I)sun at 5 Re. This increase of M/L already
suggests the presence of dark matter: we find that within 5 Re at least 55 per
cent of the total mass is dark.Comment: 17 pages, 20 figures, accepted by MNRA
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