2,694 research outputs found
Entropy Bounds and Dark Energy
Entropy bounds render quantum corrections to the cosmological constant
finite. Under certain assumptions, the natural value of is
of order the observed dark energy density , thereby
resolving the cosmological constant problem. We note that the dark energy
equation of state in these scenarios is over
cosmological distances, and is strongly disfavored by observational data.
Alternatively, in these scenarios might account for the diffuse dark
matter component of the cosmological energy density.Comment: 6 pages, Latex. Added discussion of non-cosmological limits on
holographic dark energy. Version to appear in Physics Letters
A biometrical study of the relationship between sodium-lithium countertransport and triglycerides
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66400/1/j.1469-1809.1997.6120121.x.pd
The Search for Stellar Companions to Exoplanet Host Stars Using the CHARA Array
Most exoplanets have been discovered via radial velocity studies, which are
inherently insensitive to orbital inclination. Interferometric observations
will show evidence of a stellar companion if it sufficiently bright, regardless
of the inclination. Using the CHARA Array, we observed 22 exoplanet host stars
to search for stellar companions in low-inclination orbits that may be
masquerading as planetary systems. While no definitive stellar companions were
discovered, it was possible to rule out certain secondary spectral types for
each exoplanet system observed by studying the errors in the diameter fit to
calibrated visibilities and by searching for separated fringe packets.Comment: 26 pages, 5 tables, 8 figure
IGR J17254-3257, a new bursting neutron star
The study of the observational properties of uncommonly long bursts from low
luminosity sources with extended decay times up to several tens of minutes is
important when investigating the transition from a hydrogen-rich bursting
regime to a pure helium regime and from helium burning to carbon burning as
predicted by current burst theories. IGR J17254-3257 is a recently discovered
X-ray burster of which only two bursts have been recorded: an ordinary short
type I X-ray burst, and a 15 min long burst. An upper limit to its distance is
estimated to about 14.5 kpc. The broad-band spectrum of the persistent emission
in the 0.3-100 keV energy band obtained using contemporaneous INTEGRAL and
XMM-Newton data indicates a bolometric flux of 1.1x10^-10 erg/cm2/s
corresponding, at the canonical distance of 8 kpc, to a luminosity about
8.4x10^35 erg/s between 0.1-100 keV, which translates to a mean accretion rate
of about 7x10^-11 solar masses per year. The low X-ray persistent luminosity of
IGR J17254-3257 seems to indicate the source may be in a state of low accretion
rate usually associated with a hard spectrum in the X-ray range. The nuclear
burning regime may be intermediate between pure He and mixed H/He burning. The
long burst is the result of the accumulation of a thick He layer, while the
short one is a prematurate H-triggered He burning burst at a slightly lower
accretion rate.Comment: 4 pages, 4 figures, 1 table; accepted for publication in A&A Letters.
1 reference (Cooper & Narayan, 2007) correcte
Degradation of a quantum directional reference frame as a random walk
We investigate if the degradation of a quantum directional reference frame
through repeated use can be modeled as a classical direction undergoing a
random walk on a sphere. We demonstrate that the behaviour of the fidelity for
a degrading quantum directional reference frame, defined as the average
probability of correctly determining the orientation of a test system, can be
fit precisely using such a model. Physically, the mechanism for the random walk
is the uncontrollable back-action on the reference frame due to its use in a
measurement of the direction of another system. However, we find that the
magnitude of the step size of this random walk is not given by our classical
model and must be determined from the full quantum description.Comment: 5 pages, no figures. Comments are welcome. v2: several changes to
clarify the key results. v3: journal reference added, acknowledgements and
references update
GLOSSI: a method to assess the association of genetic loci-sets with complex diseases
<p>Abstract</p> <p>Background</p> <p>The developments of high-throughput genotyping technologies, which enable the simultaneous genotyping of hundreds of thousands of single nucleotide polymorphisms (SNP) have the potential to increase the benefits of genetic epidemiology studies. Although the enhanced resolution of these platforms increases the chance of interrogating functional SNPs that are themselves causative or in linkage disequilibrium with causal SNPs, commonly used single SNP-association approaches suffer from serious multiple hypothesis testing problems and provide limited insights into combinations of loci that may contribute to complex diseases. Drawing inspiration from Gene Set Enrichment Analysis developed for gene expression data, we have developed a method, named GLOSSI (Gene-loci Set Analysis), that integrates prior biological knowledge into the statistical analysis of genotyping data to test the association of a group of SNPs (loci-set) with complex disease phenotypes. The most significant loci-sets can be used to formulate hypotheses from a functional viewpoint that can be validated experimentally.</p> <p>Results</p> <p>In a simulation study, GLOSSI showed sufficient power to detect loci-sets with less than 10% of SNPs having moderate-to-large effect sizes and intermediate minor allele frequency values. When applied to a biological dataset where no single SNP-association was found in a previous study, GLOSSI was able to identify several loci-sets that are significantly related to blood pressure response to an antihypertensive drug.</p> <p>Conclusion</p> <p>GLOSSI is valuable for association of SNPs at multiple genetic loci with complex disease phenotypes. In contrast to methods based on the Kolmogorov-Smirnov statistic, the approach is parametric and only utilizes information from within the interrogated loci-set. It properly accounts for dependency among SNPs and allows the testing of loci-sets of any size.</p
Association of urinary citrate excretion, pH, and net gastrointestinal alkali absorption with diet, diuretic use, and blood glucose concentration
Urinary citrate (Ucit) protects against urinary stone formation. Acid base status and diet influence Ucit. However, the effect of demographics, diet, and glucose metabolism on Ucit excretion, urinary pH (UâpH) and net gastrointestinal alkali absorption (NAA) are not known. Twentyâfour hour urine samples, blood glucose, creatinine, and cystatin C were obtained from nonâHispanic white sibships in Rochester, MN (n = 446; 64.5 ± 9 years; 58% female). Diet was assessed by a food frequency questionnaire. The impact of blood glucose, demographics and dietary elements on Ucit excretion, UâpH, and NAA were evaluated in bivariate and multivariable models and interaction models that included age, sex, and weight. NAA significantly associated with Ucit and UâpH. In multivariate models Ucit increased with age, weight, eGFRCys, and blood glucose, but decreased with loop diuretic and thiazide use. UâpH decreased with serum creatinine, blood glucose, and dietary protein but increased with dietary potassium. NAA was higher in males and increased with age, weight, eGFRCys and dietary potassium. Significant interactions were observed for Ucit excretion with age and blood glucose, weight and eGFRCys, and sex and thiazide use. Blood glucose had a significant and independent effect on UâpH and also Ucit. This study provides the first evidence that blood glucose could influence urinary stone risk independent of urinary pH, potentially providing new insight into the association of obesity and urinary stone disease.This study demonstrated that blood glucose had a significant and independent effect on urinary pH and also urinary citrate. Thus it provides the first evidence that blood glucose could influence urinary stone risk independent of urinary pH, potentially providing new insight into the association of obesity and urinary stone disease.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138855/1/phy213411.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138855/2/phy213411_am.pd
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