340 research outputs found
Spherically Symmetric, Self-Similar Spacetimes
Self-similar spacetimes are of importance to cosmology and to gravitational
collapse problems. We show that self-similarity or the existence of a
homothetic Killing vector field for spherically symmetric spacetimes implies
the separability of the spacetime metric in terms of the co-moving coordinates
and that the metric is, uniquely, the one recently reported in [cqg1]. The
spacetime, in general, has non-vanishing energy-flux and shear. The spacetime
admits matter with any equation of state.Comment: Submitted to Physical Review Letter
Uniqueness of Self-Similar Asymptotically Friedmann-Robertson-Walker Spacetime in Brans-Dicke theory
We investigate spherically symmetric self-similar solutions in Brans-Dicke
theory. Assuming a perfect fluid with the equation of state , we show that there are no non-trivial solutions which approach
asymptotically to the flat Friedmann-Robertson-Walker spacetime if the energy
density is positive. This result suggests that primordial black holes in
Brans-Dicke theory cannot grow at the same rate as the size of the cosmological
particle horizon.Comment: Revised version, 4 pages, no figures, Revtex, accepted for
publication in Physical Review
New Lower Bound on Fermion Binding Energies
We derive a new lower bound for the ground state energy of N
fermions with total spin S in terms of binding energies of (N-1) fermions. Numerical examples are provided for some simple
short-range or confining potentials.Comment: 4 pages, 1 eps figur
Rapid and deep-scale ubiquitylation profiling for biology and translational research
Protein ubiquitylation is involved in a plethora of cellular processes. While antibodies directed at ubiquitin remnants (K-ɛ-GG) have improved the ability to monitor ubiquitylation using mass spectrometry, methods for highly multiplexed measurement of ubiquitylation in tissues and primary cells using sub-milligram amounts of sample remains a challenge. Here, we present a highly sensitive, rapid and multiplexed protocol termed UbiFast for quantifying ~10,000 ubiquitylation sites from as little as 500 μg peptide per sample from cells or tissue in a TMT10plex in ca. 5 h. High-field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS) is used to improve quantitative accuracy for posttranslational modification analysis. We use the approach to rediscover substrates of the E3 ligase targeting drug lenalidomide and to identify proteins modulated by ubiquitylation in models of basal and luminal human breast cancer. The sensitivity and speed of the UbiFast method makes it suitable for large-scale studies in primary tissue samples
Size-structured populations: immigration, (bi)stability and the net growth rate
We consider a class of physiologically structured population models, a first
order nonlinear partial differential equation equipped with a nonlocal boundary
condition, with a constant external inflow of individuals. We prove that the
linearised system is governed by a quasicontraction semigroup. We also
establish that linear stability of equilibrium solutions is governed by a
generalized net reproduction function. In a special case of the model
ingredients we discuss the nonlinear dynamics of the system when the spectral
bound of the linearised operator equals zero, i.e. when linearisation does not
decide stability. This allows us to demonstrate, through a concrete example,
how immigration might be beneficial to the population. In particular, we show
that from a nonlinearly unstable positive equilibrium a linearly stable and
unstable pair of equilibria bifurcates. In fact, the linearised system exhibits
bistability, for a certain range of values of the external inflow, induced
potentially by All\'{e}e-effect.Comment: to appear in Journal of Applied Mathematics and Computin
Black Hole Astrophysics in AdS Braneworlds
We consider astrophysics of large black holes localized on the brane in the
infinite Randall-Sundrum model. Using their description in terms of a conformal
field theory (CFT) coupled to gravity, deduced in Ref. [1], we show that they
undergo a period of rapid decay via Hawking radiation of CFT modes. For
example, a black hole of mass would shed most of its
mass in years if the AdS radius is mm,
currently the upper bound from table-top experiments. Since this is within the
mass range of X-ray binary systems containing a black hole, the evaporation
enhanced by the hidden sector CFT modes could cause the disappearance of X-ray
sources on the sky. This would be a striking signature of RS2 with a large AdS
radius. Alternatively, for shorter AdS radii, the evaporation would be slower.
In such cases, the persistence of X-ray binaries with black holes already
implies an upper bound on the AdS radius of L \la 10^{-2} mm, an order of
magnitude better than the bounds from table-top experiments. The observation of
primordial black holes with a mass in the MACHO range and an age comparable to the age of the universe would further
strengthen the bound on the AdS radius to L \la {\rm few} \times 10^{-6} mm.Comment: 14 pages, latex, no figures v2: added reference
Observational diagnostics of gas in protoplanetary disks
Protoplanetary disks are composed primarily of gas (99% of the mass).
Nevertheless, relatively few observational constraints exist for the gas in
disks. In this review, I discuss several observational diagnostics in the UV,
optical, near-IR, mid-IR, and (sub)-mm wavelengths that have been employed to
study the gas in the disks of young stellar objects. I concentrate in
diagnostics that probe the inner 20 AU of the disk, the region where planets
are expected to form. I discuss the potential and limitations of each gas
tracer and present prospects for future research.Comment: Review written for the proceedings of the conference "Origin and
Evolution of Planets 2008", Ascona, Switzerland, June 29 - July 4, 2008. Date
manuscript: October 2008. 17 Pages, 6 graphics, 134 reference
A multistate model of health transitions in older people: a secondary analysis of ASPREE clinical trial data
Background: Understanding the nature of transitions from a healthy state to chronic diseases and death is important for planning health-care system requirements and interventions. We aimed to quantify the trajectories of disease and disability in a population of healthy older people. Methods: We conducted a secondary analysis of data from the ASPREE trial, which was done in 50 sites in Australia and the USA and recruited community-dwelling, healthy individuals who were aged 70 years or older (≥65 years for Black and Hispanic people in the USA) between March 10, 2010, and Dec 24, 2014. Participants were followed up with annual face-to-face visits, biennial assessments of cognitive function, and biannual visits for physical function until death or June 12, 2017, whichever occurred first. We used multistate models to examine transitions from a healthy state to first intermediate disease events (ie, cancer events, stroke events, cardiac events, and physical disability or dementia) and, ultimately, to death. We also examined the effects of age and sex on transition rates using Cox proportional hazards regression models. Findings: 19 114 participants with a median age of 74·0 years (IQR 71·6–77·7) were included in our analyses. During a median follow-up of 4·7 years (IQR 3·6–5·7), 1933 (10·1%) of 19 114 participants had an incident cancer event, 487 (2·5%) had an incident cardiac event, 398 (2·1%) had an incident stroke event, 924 (4·8%) developed persistent physical disability or dementia, and 1052 (5·5%) died. 15 398 (80·6%) individuals did not have any of these events during follow-up. The highest proportion of deaths followed incident cancer (501 [47·6%] of 1052) and 129 (12·3%) participants transitioned from disability or dementia to death. Among 12 postulated transitions, transitions from the intermediate states to death had much higher rates than transitions from a healthy state to death. The progression rates to death were 158 events per 1000 person-years (95% CI 144–172) from cancer, 112 events per 1000 person-years (86–145) from stroke, 88 events per 1000 person-years (68–111) from cardiac disease, 69 events per 1000 person-years (58–82) from disability or dementia, and four events per 1000 person-years (4–5) from a healthy state. Age was significantly associated with an accelerated rate for most transitions. Male sex (vs female sex) was significantly associated with an accelerate rate for five of 12 transitions. Interpretation: We describe a multistate model in a healthy older population in whom the most common transition was from a healthy state to cancer. Our findings provide unique insights into the frequency of events, their transition rates, and the impact of age and sex. These results have implications for preventive health interventions and planning for appropriate levels of residential care in healthy ageing populations. Funding: The National Institutes of Health
Family systemic psychosocial support for at-risk adolescents in Lebanon: study protocol for a multi-site randomised controlled trial
Background: Adolescents growing up in communities characterised by adversity face multiple risk factors for poor mental health and wellbeing. There is currently a scarcity of research on effective approaches for preventing and treating psychological distress in this population, particularly in humanitarian settings. The powerful impact of the home environment and family support is well known; however, approaches targeting the family are seldom developed or evaluated in such settings. We developed a brief family systemic psychosocial support intervention to be delivered through existing child protection systems with non-specialist facilitators. This paper outlines the study protocol for a randomised controlled trial of the intervention in Lebanon.Methods: We will conduct a single-blind hybrid effectiveness-implementation multi-site RCT comparing the locally developed systemic family intervention to a waitlist control group for families residing in vulnerable regions in North Lebanon and Beqaa governorates (including families of Syrian, Palestinian, and Lebanese backgrounds). Outcomes on a range of family, adolescent, and caregiver measures will be assessed at baseline (T0) and post-intervention (T1), and at a 3-month follow-up for the treatment arm (T2). Families will be eligible for the trial if they are identified by implementing organisations as being medium-to-high risk for child protection concerns and have one or more adolescent aged 12–17 who demonstrates significant psychological distress on a self-report brief screening tool. Families will be randomly assigned to a treatment or a waitlist control condition. Families in the waitlist condition will receive a group version of the programme after completion of the study, to allow us to assess feasibility, acceptability, and preliminary indications of intervention effects of this modality. The primary outcome is reduction in overall adolescent-reported psychological distress over time, with post-intervention (T1) as the primary endpoint. Secondary adolescent-reported outcomes include family functioning, psychosocial wellbeing, and emotional regulation difficulties. Secondary caregiver-reported outcomes include parenting style, family functioning, psychological distress, and emotional regulation difficulties. Discussion: This trial will provide the first assessment of the effectiveness of the family systemic psychosocial support intervention for use in Lebanon, with important implications for the use of systemic, low-cost, non-specialist interventions for this age range. Trial registration: Local registry: National Mental Health Program, Ministry of Public Health, Lebanese Republic. Registered on 19 October 2021 Lebanese Clinical Trial Registry LBCTR2021104870
Low temperature electronic properties of Sr_2RuO_4 II: Superconductivity
The body centered tetragonal structure of Sr_2RuO_4 gives rise to umklapp
scattering enhanced inter-plane pair correlations in the d_{yz} and d_{zx}
orbitals. Based on symmetry arguments, Hund's rule coupling, and a bosonized
description of the in-plane electron correlations the superconducting order
parameter is found to be a orbital-singlet spin-triplet with two spatial
components. The spatial anisotropy is 7%. The different components of the order
parameter give rise to two-dimensional gapless fluctuations. The phase
transition is of third order. The temperature dependence of the pair density,
specific heat, NQR, Knight shift, and susceptibility are in agreement with
experimental results.Comment: 20 pages REVTEX, 3 figure
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