3,138 research outputs found
Wolf 1130: A Nearby Triple System Containing a Cool, Ultramassive White Dwarf
Following the discovery of the T8 subdwarf WISEJ200520.38+542433.9 (Wolf
1130C), with common proper motion to a binary (Wolf 1130AB) consisting of an M
subdwarf and a white dwarf, we set out to learn more about the old binary in
the system. We find that the A and B components of Wolf 1130 are tidally
locked, which is revealed by the coherence of more than a year of V band
photometry phase folded to the derived orbital period of 0.4967 days. Forty new
high-resolution, near-infrared spectra obtained with the Immersion Grating
Infrared Spectrometer (IGRINS) provide radial velocities and a projected
rotational velocity (v sin i) of 14.7 +/- 0.7 km/s for the M subdwarf. In
tandem with a Gaia parallax-derived radius and verified tidal-locking, we
calculate an inclination of i=29 +/- 2 degrees. From the single-lined orbital
solution and the inclination we derive an absolute mass for the unseen primary
(1.24+0.19-0.15 Msun). Its non-detection between 0.2 and 2.5 microns implies
that it is an old (>3.7 Gyr) and cool (Teff<7000K) ONe white dwarf. This is the
first ultramassive white dwarf within 25pc. The evolution of Wolf 1130AB into a
cataclysmic variable is inevitable, making it a potential Type Ia supernova
progenitor. The formation of a triple system with a primary mass >100 times the
tertiary mass and the survival of the system through the common-envelope phase,
where ~80% of the system mass was lost, is remarkable. Our analysis of Wolf
1130 allows us to infer its formation and evolutionary history, which has
unique implications for understanding low-mass star and brown dwarf formation
around intermediate mass stars.Comment: 37 pages, 9 Figures, 5 Table
Post-Disaster Housing Reconstruction in Sri Lanka: What Methodology?
Research methodology is the procedural framework within which the research is conducted. This includes the overall
approach to a problem that could be put into practice in a research process, from the theoretical underpinning to the
collection and analysis of data. Choice of methodology depends on the primary drivers: topic to be researched and the
specific research questions. Hence, methodological perspectives of managing stakeholder expectations of PDHR context
are composed of research philosophies, research strategy, research design, and research techniques. This research belonged
to social constructivism or interpretivism within a philosophical continuum. The nature of the study was more toward
subjectivism where human behavior favored voluntary stance. Ontological, methodological, epistemological, and axiological
positioning carried the characteristics of idealism, ideographic, anti-positivism, and value laden, respectively. Data collection
comprises two phases, preliminary and secondary. Exploratory interviews with construction experts in the United Kingdom
and Sri Lanka were carried out to refine the interview questions and identify the case studies. Case study interviews during
the secondary phase took place in Sri Lanka. Data collected at the preliminary stage were used to assess the attributes of
power, legitimacy/proximity, and urgency of stakeholders to the project using Stakeholder Circle™ software. Moreover,
the data collected at secondary phase via case studies will be analyzed with NVivo 8. This article aims to discuss these
methodological underpinnings in detail applied in a post-disaster housing reconstruction context in Sri Lanka
Evidence for a fractional quantum Hall state with anisotropic longitudinal transport
At high magnetic fields, where the Fermi level lies in the N=0 lowest Landau
level (LL), a clean two-dimensional electron system (2DES) exhibits numerous
incompressible liquid phases which display the fractional quantized Hall effect
(FQHE) (Das Sarma and Pinczuk, 1997). These liquid phases do not break
rotational symmetry, exhibiting resistivities which are isotropic in the plane.
In contrast, at lower fields, when the Fermi level lies in the third
and several higher LLs, the 2DES displays a distinctly different class of
collective states. In particular, near half filling of these high LLs the 2DES
exhibits a strongly anisotropic longitudinal resistance at low temperatures
(Lilly et al., 1999; Du et al., 1999). These "stripe" phases, which do not
exhibit the quantized Hall effect, resemble nematic liquid crystals, possessing
broken rotational symmetry and orientational order (Koulakov et al., 1996;
Fogler et al., 1996; Moessner and Chalker, 1996; Fradkin and Kivelson, 1999;
Fradkin et al, 2010). Here we report a surprising new observation: An
electronic configuration in the N=1 second LL whose resistivity tensor
simultaneously displays a robust fractionally quantized Hall plateau and a
strongly anisotropic longitudinal resistance resembling that of the stripe
phases.Comment: Nature Physics, (2011
Evidence for variation in the effective population size of animal mitochondrial DNA
Background: It has recently been shown that levels of diversity in mitochondrial DNA are remarkably constant across animals of diverse census population sizes and ecologies, which has led to the suggestion that the effective population of mitochondrial DNA may be relatively constant. Results: Here we present several lines of evidence that suggest, to the contrary, that the effective population size of mtDNA does vary, and that the variation can be substantial. First, we show that levels of mitochondrial and nuclear diversity are correlated within all groups of animals we surveyed. Second, we show that the effectiveness of selection on non-synonymous mutations, as measured by the ratio of the numbers of non-synonymous and synonymous polymorphisms, is negatively correlated to levels of mitochondrial diversity. Finally, we estimate the effective population size of mitochondrial DNA in selected mammalian groups and show that it varies by at least an order of magnitude. Conclusions: We conclude that there is variation in the effective population size of mitochondria. Furthermore we suggest that the relative constancy of DNA diversity may be due to a negative correlation between the effective population size and the mutation rate per generation
Non-relativistic metrics from back-reacting fermions
It has recently been pointed out that under certain circumstances the
back-reaction of charged, massive Dirac fermions causes important modifications
to AdS_2 spacetimes arising as the near horizon geometry of extremal black
holes. In a WKB approximation, the modified geometry becomes a non-relativistic
Lifshitz spacetime. In three dimensions, it is known that integrating out
charged, massive fermions gives rise to gravitational and Maxwell Chern-Simons
terms. We show that Schrodinger (warped AdS_3) spacetimes exist as solutions to
a gravitational and Maxwell Chern-Simons theory with a cosmological constant.
Motivated by this, we look for warped AdS_3 or Schrodinger metrics as exact
solutions to a fully back-reacted theory containing Dirac fermions in three and
four dimensions. We work out the dynamical exponent in terms of the fermion
mass and generalize this result to arbitrary dimensions.Comment: 26 pages, v2: typos corrected, references added, minor change
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Associations between flavan-3-ol intake and CVD risk in the Norfolk cohort of the European Prospective Investigation into Cancer (EPIC-Norfolk)
This is the final published version. It first appeared at http://www.sciencedirect.com/science/article/pii/S0891584915001173.Dietary intervention studies suggest that flavan-3-ol intake can improve vascular function and reduce the risk of cardiovascular diseases (CVD). However, results from prospective studies failed to show a consistent beneficial effect. Associations between flavan-3-ol intake and CVD risk in the Norfolk arm of the European Prospective Investigation into Cancer and Nutrition (EPIC-Norfolk) were investigated. Data were available from 24,885 (11,252 men; 13,633 women) participants, recruited between 1993 and 1997 into the EPIC-Norfolk study. Flavan-3-ol intake was assessed using 7-day food diaries and the FLAVIOLA Flavanol Food Composition database. Missing data for plasma cholesterol and vitamin C were imputed using multiple imputation. Associations between flavan-3-ol intake and blood pressure at baseline were determined using linear regression models. Associations with CVD risk were estimated using Cox regression analyses. Median intake of total flavan-3-ols was 1034mg/d (range: 0-8531mg/d) for men and 970mg/d (0-6695mg/d) for women, median intake of flavan-3-ol monomers was 233mg/d (0-3248mg/d) for men and 217 (0-2712mg/d) for women. There were no consistent associations between flavan-3-ol monomer intake and baseline systolic and diastolic blood pressure (BP). After 286,147 person-years of follow-up, there were 8463 cardiovascular events and 1987 CVD related deaths; no consistent association between flavan-3-ol intake and CVD risk (HR 0.93, 95% CI: 0.87; 1.00; Q1 vs Q5) or mortality was observed (HR 0.93, 95% CI: 0.84; 1.04). Flavan-3-ol intake in EPIC-Norfolk is not sufficient to achieve a statistically significant reduction in CVD risk.We thank all EPIC-Norfolk study participants and staff for their contribution to the study. We thank the members of the FLAVIOLA consortium for their critical review of the manuscript. The present study was supported by the EU (Grant 226588, “Flaviola”) and an unrestricted grant from Mars, Inc. Mars, Inc. had no role in the design and analysis of the study or in the writing of this article. EPIC-Norfolk is supported by Cancer Research UK (SP2024-0201 and SP2024-0204) and the Medical Research Council (G9502233). H.S. is employed by MARS, Inc., a member of the FLAVIOLA research consortium and a company engaged in flavanol research and flavanol-related commercial activities. None of the other authors has a conflict of interest to declare
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