403 research outputs found
Volume Comparison for Hypersurfaces in Lorentzian Manifolds and Singularity Theorems
We develop area and volume comparison theorems for the evolution of
spacelike, acausal, causally complete hypersurfaces in Lorentzian manifolds,
where one has a lower bound on the Ricci tensor along timelike curves, and an
upper bound on the mean curvature of the hypersurface. Using these results, we
give a new proof of Hawking's singularity theorem.Comment: 15 pages, LaTe
Institutional strategies for capturing socio-economic impact of academic research
Evaluation of socio-economic impact is an emerging theme for publicly-funded academic research. Within this context the paper suggests that the concept of institutional research capital be expanded to include the capture and evaluation of socio-economic impact. Furthermore, it argues that understanding the typology of impacts and the tracking from research to impact will assist the formulation of institutional strategies for capturing socio-economic impact. A three-stage approach is proposed for capturing and planning activities to enhance the generation of high-quality impact. Stage one outlines the critical role of user engagement that facilitates the tracking of such impact. Stage two employs an analytical framework based on the criteria of ‘depth’ and ‘spread’ to evaluate impacts that have been identified. Stage three utilizes the outcomes of the framework to devise strategies, consisting of either further research (to increase depth) or more engagement (to increase spread) that will improve the generation of higher quality impact
Minisuperspace Quantization of "Bubbling AdS" and Free Fermion Droplets
We quantize the space of 1/2 BPS configurations of Type IIB SUGRA found by
Lin, Lunin and Maldacena (hep-th/0409174), directly in supergravity. We use the
Crnkovic-Witten-Zuckerman covariant quantization method to write down the
expression for the symplectic structure on this entire space of solutions. We
find the symplectic form explicitly around AdS_5 x S^5 and obtain a U(1)
Kac-Moody algebra, in precise agreement with the quantization of a system of N
free fermions in a harmonic oscillator potential, as expected from AdS/CFT. As
a cross check, we also perform the quantization around AdS_5 x S^5 by another
method, using the known spectrum of physical perturbations around this
background and find precise agreement with our previous calculation.Comment: 22 Pages + 2 Appendices, JHEP3; v3: explanation of factor 2 mismatch
added, references reordered, published versio
Maternal race and intergenerational preterm birth recurrence
Background Preterm birth is a complex disorder with a heritable genetic component. Studies of primarily White women born preterm show that they have an increased risk of subsequently delivering preterm. This risk of intergenerational preterm birth is poorly defined among Black women. Objective Our objective was to evaluate and compare intergenerational preterm birth risk among non-Hispanic Black and non-Hispanic White mothers. Study Design This was a population-based retrospective cohort study, using the Virginia Intergenerational Linked Birth File. All non-Hispanic Black and non-Hispanic White mothers born in Virginia 1960 through 1996 who delivered their first live-born, nonanomalous, singleton infant ≥20 weeks from 2005 through 2009 were included. We assessed the overall gestational age distribution between non-Hispanic Black and White mothers born term and preterm (<37 weeks) and their infants born term and preterm (<37 weeks) using Cox regression and Kaplan-Meier survivor functions. Mothers were grouped by maternal gestational age at delivery (term, ≥37 completed weeks; late preterm birth, 34-36 weeks; and early preterm birth, <34 weeks). The primary outcomes were: (1) preterm birth among all eligible births; and (2) suspected spontaneous preterm birth among births to women with medical complications (eg, diabetes, hypertension, preeclampsia and thus higher risk for a medically indicated preterm birth). Multivariable logistic regression was used to estimate odds of preterm birth and spontaneous preterm birth by maternal race and maternal gestational age after adjusting for confounders including maternal education, maternal age, smoking, drug/alcohol use, and infant gender. Results Of 173,822 deliveries captured in the intergenerational birth cohort, 71,676 (41.2%) women met inclusion criteria for this study. Of the entire cohort, 30.0% (n = 21,467) were non-Hispanic Black and 70.0% were non-Hispanic White mothers. Compared to non-Hispanic White mothers, non-Hispanic Black mothers were more likely to have been born late preterm (6.8% vs 3.7%) or early preterm (2.8 vs 1.0%), P <.001. Non-Hispanic White mothers who were born (early or late) preterm were not at an increased risk of early or late preterm delivery compared to non-Hispanic White mothers born term. The risk of early preterm birth was most pronounced for Black mothers who were born early preterm (adjusted odds ratio, 3.26; 95% confidence interval, 1.77–6.02) compared to non-Hispanic White mothers. Conclusion We found an intergenerational effect of preterm birth among non-Hispanic Black mothers but not non-Hispanic White mothers. Black mothers born <34 weeks carry the highest risk of delivering their first child very preterm. Future studies should elucidate the underlying pathways leading to this racial disparity
Effects of rapid prey evolution on predator-prey cycles
We study the qualitative properties of population cycles in a predator-prey
system where genetic variability allows contemporary rapid evolution of the
prey. Previous numerical studies have found that prey evolution in response to
changing predation risk can have major quantitative and qualitative effects on
predator-prey cycles, including: (i) large increases in cycle period, (ii)
changes in phase relations (so that predator and prey are cycling exactly out
of phase, rather than the classical quarter-period phase lag), and (iii)
"cryptic" cycles in which total prey density remains nearly constant while
predator density and prey traits cycle. Here we focus on a chemostat model
motivated by our experimental system [Fussmann et al. 2000,Yoshida et al. 2003]
with algae (prey) and rotifers (predators), in which the prey exhibit rapid
evolution in their level of defense against predation. We show that the effects
of rapid prey evolution are robust and general, and furthermore that they occur
in a specific but biologically relevant region of parameter space: when traits
that greatly reduce predation risk are relatively cheap (in terms of reductions
in other fitness components), when there is coexistence between the two prey
types and the predator, and when the interaction between predators and
undefended prey alone would produce cycles. Because defense has been shown to
be inexpensive, even cost-free, in a number of systems [Andersson and Levin
1999, Gagneux et al. 2006,Yoshida et al. 2004], our discoveries may well be
reproduced in other model systems, and in nature. Finally, some of our key
results are extended to a general model in which functional forms for the
predation rate and prey birth rate are not specified.Comment: 35 pages, 8 figure
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‘Is it worth potentially dealing with someone who won't get it?’: LGBTQA+ university students’ perspectives on mental health care
LGBTQA+ university students have unique mental health needs and high rates of mental distress compared to their cisgender heterosexual peers; however, it is likely that many LGBTQA+ individuals remain untreated or receive inappropriate or insensitive care. The aim of this study was to explore the experiences and preferences in mental health care of LGBTQA+ university students in Aotearoa New Zealand. Twenty-eight young adults participated across 12 focus groups or interviews in which they were asked about their experiences and preferences. We used thematic analysis to identify patterns of meaning in the data. Researchers developed three themes of I can do this on my own, but others should seek help; you have to be lucky to access mental health care; and ‘therapists just need to be a bit more like up with the programme’. The results of this study mirror those found in more general studies of LGBTQA+ mental healthcare experiences, however, also adds to considerations for university campus healthcare services. The findings of this study should be considered by all mental health providers working with LGBTQA+ young adult university students
Mechanism of periodic height variations along self-aligned VLS-grown planar nanostructures
In this study we report in-plane nanotracks produced by molecular-beam-epitaxy (MBE) exhibiting lateral self-assembly and unusual periodic and out-of-phase height variations across their growth axes. The nanotracks are synthesized using bismuth segregation on the GaAsBi epitaxial surface, which results in metallic liquid droplets capable of catalyzing GaAsBi nanotrack growth via the vapor–liquid–solid (VLS) mechanism. A detailed examination of the nanotrack morphologies is carried out employing a combination of scanning electron and atomic force microscopy and, based on the findings, a geometric model of nanotrack growth during MBE is developed. Our results indicate diffusion and shadowing effects play significant roles in defining the interesting nanotrack shape. The unique periodicity of our lateral nanotracks originates from a rotating nucleation “hot spot” at the edge of the liquid–solid interface, a feature caused by the relative periodic circling of the non-normal ion beam flux incident on the sample surface, inside the MBE chamber. We point out that such a concept is divergent from current models of crawling mode growth kinetics and conclude that these effects may be utilized in the design and assembly of planar nanostructures with controlled non-monotonous structure
Final NOMAD results on nu_mu->nu_tau and nu_e->nu_tau oscillations including a new search for nu_tau appearance using hadronic tau decays
Results from the nu_tau appearance search in a neutrino beam using the full
NOMAD data sample are reported. A new analysis unifies all the hadronic tau
decays, significantly improving the overall sensitivity of the experiment to
oscillations. The "blind analysis" of all topologies yields no evidence for an
oscillation signal. In the two-family oscillation scenario, this sets a 90%
C.L. allowed region in the sin^2(2theta)-Delta m^2 plane which includes
sin^2(2theta)<3.3 x 10^{-4} at large Delta m^2 and Delta m^2 < 0.7 eV^2/c^4 at
sin^2(2theta)=1. The corresponding contour in the nu_e->nu_tau oscillation
hypothesis results in sin^2(2theta)<1.5 x 10^{-2} at large Delta m^2 and Delta
m^2 < 5.9 eV^2/c^4 at sin^2(2theta)=1. We also derive limits on effective
couplings of the tau lepton to nu_mu or nu_e.Comment: 46 pages, 16 figures, Latex, to appear on Nucl. Phys.
Inclusive production of and mesons in charged current interactions
The inclusive production of the meson resonances ,
and in neutrino-nucleus charged current interactions has been
studied with the NOMAD detector exposed to the wide band neutrino beam
generated by 450 GeV protons at the CERN SPS. For the first time the
meson is observed in neutrino interactions. The statistical
significance of its observation is 6 standard deviations. The presence of
in neutrino interactions is reliably established. The average
multiplicity of these three resonances is measured as a function of several
kinematic variables. The experimental results are compared to the
multiplicities obtained from a simulation based on the Lund model. In addition,
the average multiplicity of in antineutrino - nucleus
interactions is measured.Comment: 23 pages, 14 figures, 8 tables. To appear in Nucl. Phys.
Search for the exotic resonance in the NOMAD experiment
A search for exotic Theta baryon via Theta -> proton +Ks decay mode in the
NOMAD muon neutrino DIS data is reported. The special background generation
procedure was developed. The proton identification criteria are tuned to
maximize the sensitivity to the Theta signal as a function of xF which allows
to study the Theta production mechanism. We do not observe any evidence for the
Theta state in the NOMAD data. We provide an upper limit on Theta production
rate at 90% CL as 2.13 per 1000 of neutrino interactions.Comment: Accepted to European Physics Journal
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