461 research outputs found
Gradient instability for ω < - 1
We show that in single scalar field models of the dark energy with equations of state satisfying w ≡ p/ρ < − 1, the effective Lagrangian for fluctuations about the homogeneous background has a wrong sign spatial kinetic term. In most cases, spatial gradients are ruled out by microwave background observations. The sign of w + 1 is not connected to the sign of the time derivative kinetic term in the effective Lagrangian
A High Power Hydrogen Target for Parity Violation Experiments
Parity-violating electron scattering measurements on hydrogen and deuterium,
such as those underway at the Bates and CEBAF laboratories, require
luminosities exceeding cms, resulting in large beam
power deposition into cryogenic liquid. Such targets must be able to absorb 500
watts or more with minimal change in target density. A 40~cm long liquid
hydrogen target, designed to absorb 500~watts of beam power without boiling,
has been developed for the SAMPLE experiment at Bates. In recent tests with
40~A of incident beam, no evidence was seen for density fluctuations in
the target, at a sensitivity level of better than 1\%. A summary of the target
design and operational experience will be presented.Comment: 13 pages, 9 postscript figure
A genome-wide association study demonstrates significant genetic variation for fracture risk in Thoroughbred racehorses
Background:
Thoroughbred racehorses are subject to non-traumatic distal limb bone fractures that occur during racing and exercise. Susceptibility to fracture may be due to underlying disturbances in bone metabolism which have a genetic cause. Fracture risk has been shown to be heritable in several species but this study is the first genetic analysis of fracture risk in the horse.
Results:
Fracture cases (n = 269) were horses that sustained catastrophic distal limb fractures while racing on UK racecourses, necessitating euthanasia. Control horses (n = 253) were over 4 years of age, were racing during the same time period as the cases, and had no history of fracture at the time the study was carried out. The horses sampled were bred for both flat and National Hunt (NH) jump racing. 43,417 SNPs were employed to perform a genome-wide association analysis and to estimate the proportion of genetic variance attributable to the SNPs on each chromosome using restricted maximum likelihood (REML). Significant genetic variation associated with fracture risk was found on chromosomes 9, 18, 22 and 31. Three SNPs on chromosome 18 (62.05 Mb – 62.15 Mb) and one SNP on chromosome 1 (14.17 Mb) reached genome-wide significance (p <0.05) in a genome-wide association study (GWAS). Two of the SNPs on ECA 18 were located in a haplotype block containing the gene zinc finger protein 804A (ZNF804A). One haplotype within this block has a protective effect (controls at 1.95 times less risk of fracture than cases, p = 1 × 10-4), while a second haplotype increases fracture risk (cases at 3.39 times higher risk of fracture than controls, p = 0.042).
Conclusions:
Fracture risk in the Thoroughbred horse is a complex condition with an underlying genetic basis. Multiple genomic regions contribute to susceptibility to fracture risk. This suggests there is the potential to develop SNP-based estimators for genetic risk of fracture in the Thoroughbred racehorse, using methods pioneered in livestock genetics such as genomic selection. This information would be useful to racehorse breeders and owners, enabling them to reduce the risk of injury in their horses
Gradient instability for w < -1
We show that in single scalar field models of the dark energy with equations
of state satisfying , the effective Lagrangian for
fluctuations about the homogeneous background has a wrong sign spatial kinetic
term. In most cases, spatial gradients are ruled out by microwave background
observations. The sign of is not connected to the sign of the time
derivative kinetic term in the effective Lagrangian.Comment: revtex4, 8 pages, 1 figure. v2: corrected typo in Eq. 16, added
references and a paragraph on quintessence models; v3: reordering of
references. To appear in Phys. Lett.
But a walking shadow: designing, performing and learning on the virtual stage
Representing elements of reality within a medium, or taking aspects from one medium and placing them in another is an act of remediation. The process of this act, however, is largely taken for granted. Despite the fact that available information enables a qualitative assessment of the history of multimedia and their influences on different fields of knowledge, there are still some areas that require more focused research attention. For example, the relationship between media evolution and new developments in scenographic practice is currently under investigation. This article explores the issue of immediacy as a condition of modern theatre in the context of digital reality. It discusses the opportunities and challenges that recent technologies present to contemporary practitioners and theatre design educators, creating a lot of scope to break with conventions. Here, we present two case studies that look into technology-mediated learning about scenography through the employment of novel computer visualization techniques. The first case study is concerned with new ways of researching and learning about theatre through creative exploration of design artefacts. The second case study investigates the role of the Immersive Virtual World Second Life™ (SL) in effective teaching of scenography, and in creating and experiencing theatrical performances
Anthropic Distribution for Cosmological Constant and Primordial Density Perturbations
The anthropic principle has been proposed as an explanation for the observed
value of the cosmological constant. Here we revisit this proposal by allowing
for variation between universes in the amplitude of the scale-invariant
primordial cosmological density perturbations. We derive a priori probability
distributions for this amplitude from toy inflationary models in which the
parameter of the inflaton potential is smoothly distributed over possible
universes. We find that for such probability distributions, the likelihood that
we live in a typical, anthropically-allowed universe is generally quite small.Comment: 12 pages, 2 tables. v3: Replaced to match published version (minor
corrections of form
There are no magnetically charged particle-like solutions of the Einstein Yang-Mills equations for Abelian models
We prove that there are no magnetically charged particle-like solutions for
Abelian models in Einstein Yang-Mills, but for non-Abelian models the
possibility remains open. An analysis of the Lie algebraic structure of the
Yang-Mills fields is essential to our results. In one key step of our analysis
we use invariant polynomials to determine which orbits of the gauge group
contain the possible asymptotic Yang-Mills field configurations. Together with
a new horizontal/vertical space decomposition of the Yang-Mills fields this
enables us to overcome some obstacles and complete a dynamical system existence
theorem for asymptotic solutions with nonzero total magnetic charge. We then
prove that these solutions cannot be extended globally for Abelian models and
begin an investigation of the details for non-Abelian models.Comment: 48 pages, 1 figur
Acute plasma amylase increase after glucagon-like peptide -1 receptor agonist exenatide administration in Type 2 diabetes
Acute renal effects of the GLP-1 receptor agonist exenatide in overweight type 2 diabetes patients: a randomised, double-blind, placebo-controlled trial
Aims/hypothesis: This study aimed to investigate the acute renal effects of the glucagon-like peptide-1 receptor agonist (GLP-1RA) exenatide in type 2 diabetes patients. Methods: We included overweight (BMI 25–40 kg/m2) men and postmenopausal women, aged 35–75 years with type 2 diabetes (HbA1c 48–75 mmol/mol; 6.5–9.0%) and estimated GFR ≥ 60 ml min−1 1.73 m−2. Exenatide or placebo (NaCl solution, 154 mmol/l) was administrated intravenously in an acute, randomised, double-blind, placebo-controlled trial conducted at the Diabetes Center VU University Medical Center (VUMC). GFR (primary endpoint) and effective renal plasma flow (ERPF) were determined by inulin and para-aminohippurate clearance, respectively, based on timed urine sampling. Filtration fraction (FF) and effective renal vascular resistance (ERVR) were calculated, and glomerular hydrostatic pressure (PGLO) and vascular resistance of the afferent (RA) and efferent (RE) renal arteriole were estimated. Tubular function was assessed by absolute and fractional excretion of sodium (FENa), potassium (FEK) and urea (FEU), in addition to urine osmolality, pH and free water clearance. Renal damage markers, BP and plasma glucose were also determined. Results: Of the 57 patients randomised by computer, 52 were included in the final analyses. Exenatide (n = 24) did not affect GFR (mean difference +2 ± 3 ml min−1 1.73 m−2, p = 0.489), ERPF, FF, ERVR or PGLO, compared with placebo (n = 28). Exenatide increased RA (p < 0.05), but did not change RE. Exenatide increased FENa, FEK, urine osmolality and pH, while FEU, urinary flow and free water clearance were decreased (all p < 0.05). Osmolar clearance and renal damage makers were not affected. Diastolic BP and mean arterial pressure increased by 3 ± 1 and 6 ± 2 mmHg, respectively, whereas plasma glucose decreased by 1.4 ± 0.1 mmol/l (all p < 0.05). Conclusions/interpretation: Exenatide infusion does not acutely affect renal haemodynamics in overweight type 2 diabetes patients at normal filtration levels. Furthermore, acute GLP-1RA administration increases proximal sodium excretion in these patients. Trial registration: ClincialTrials.gov NCT01744236 Funding: The research leading to these results has been funded from: (1) the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement number 282521 – the SAFEGUARD project; and (2) the Dutch Kidney Foundation, under grant agreement IP12.87
The Influence of the effect of solute on the thermodynamic driving force on grain refinement of Al alloys
Grain refinement is known to be strongly affected by the solute in cast alloys. Addition of some solute can reduce grain size considerably while others have a limited effect. This is usually attributed to the constitutional supercooling which is quantified by the growth restriction factor, Q. However, one factor that has not been considered is whether different solutes have differing effects on the thermodynamic driving force for solidification. This paper reveals that addition of solute reduces the driving force for solidification for a given undercooling, and that for a particular Q value, it is reduced more substantially when adding eutectic-forming solutes than peritectic-forming elements. Therefore, compared with the eutectic-forming solutes, addition of peritectic-forming solutes into Al alloys not only possesses a higher initial nucleation rate resulted from the larger thermodynamic driving force for solidification, but also promotes nucleation within the constitutionally supercooled zone during growth. As subsequent nucleation can occur at smaller constitutional supercoolings for peritectic-forming elements, a smaller grain size is thus produced. The very small constitutional supercooling required to trigger subsequent nucleation in alloys containing Ti is considered as a major contributor to its extraordinary grain refining efficiency in cast Al alloys even without the deliberate addition of inoculants.The Australian Research Council (ARC DP10955737)
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