3,662 research outputs found
Instability of hyper-compact Kerr-like objects
Viable alternatives to astrophysical black holes include hyper-compact
objects without horizon, such as gravastars, boson stars, wormholes and
superspinars. The authors have recently shown that typical rapidly-spinning
gravastars and boson stars develop a strong instability. That analysis is
extended in this paper to a wide class of horizonless objects with approximate
Kerr-like geometry. A detailed investigation of wormholes and superspinars is
presented, using plausible models and mirror boundary conditions at the
surface. Like gravastars and boson stars, these objects are unstable with very
short instability timescales. This result strengthens previous conclusions that
observed hyper-compact astrophysical objects with large rotation are likely to
be black holes.Comment: 15 pages, 3 figures. To be published in CQ
Perturbations of slowly rotating black holes: massive vector fields in the Kerr metric
We discuss a general method to study linear perturbations of slowly rotating
black holes which is valid for any perturbation field, and particularly
advantageous when the field equations are not separable. As an illustration of
the method we investigate massive vector (Proca) perturbations in the Kerr
metric, which do not appear to be separable in the standard Teukolsky
formalism. Working in a perturbative scheme, we discuss two important effects
induced by rotation: a Zeeman-like shift of nonaxisymmetric quasinormal modes
and bound states with different azimuthal number m, and the coupling between
axial and polar modes with different multipolar index l. We explicitly compute
the perturbation equations up to second order in rotation, but in principle the
method can be extended to any order. Working at first order in rotation we show
that polar and axial Proca modes can be computed by solving two decoupled sets
of equations, and we derive a single master equation describing axial
perturbations of spin s=0 and s=+-1. By extending the calculation to second
order we can study the superradiant regime of Proca perturbations in a
self-consistent way. For the first time we show that Proca fields around Kerr
black holes exhibit a superradiant instability, which is significantly stronger
than for massive scalar fields. Because of this instability, astrophysical
observations of spinning black holes provide the tightest upper limit on the
mass of the photon: mv<4x10^-20 eV under our most conservative assumptions.
Spin measurements for the largest black holes could reduce this bound to
mv<10^-22 eV or lower.Comment: v1: 29 pages, 9 figures, 3 appendices. v2: References added and
improved discussion. Matches the version to appear in Physical Review D.
Mathematica notebooks available here http://blackholes.ist.utl.pt/?page=Files
and http://www.phy.olemiss.edu/~berti/qnms.htm
Multi-site observations of Delta Scuti stars 7 Aql and 8 Aql (a new Delta Scuti variable): The twelfth STEPHI campaign in 2003
We present an analysis of the pulsation behaviour of the Delta Scuti stars 7
Aql (HD 174532) and 8 Aql (HD 174589) -- a new variable star -- observed in the
framework of STEPHI XII campaign during 2003 June--July. 183 hours of high
precision photometry were acquired by using four-channel photometers at three
sites on three continents during 21 days. The light curves and amplitude
spectra were obtained following a classical scheme of multi-channel photometry.
Observations in different filters were also obtained and analyzed. Six and
three frequencies have been unambiguously detected above a 99% confidence level
in the range 0.090 mHz--0.300 mHz and 0.100 mHz-- 0.145 mHz in 7 Aql and 8 Aql
respectively. A comparison of observed and theoretical frequencies shows that 7
Aql and 8 Aql may oscillate with p modes of low radial orders, typical among
Delta Scuti stars. In terms of radial oscillations the range of 8 Aql goes from
n=1 to n=3 while for 7 Aql the range spans from n=4 to n=7. Non-radial
oscillations have to be present in both stars as well. The expected range of
excited modes according to a non adiabatic analysis goes from n=1 to n=6 in
both stars.Comment: 8 pages, 7 fugures, 5 tables, accepted for publication in
Astronomical Journa
CDK4/6 Inhibitors in Breast Cancer Treatment: Potential Interactions with Drug, Gene, and Pathophysiological Conditions
Palbociclib, ribociclib, and abemaciclib belong to the third generation of cyclin-dependent kinases inhibitors (CDKis), an established therapeutic class for advanced and metastatic breast cancer. Interindividual variability in the therapeutic response of CDKis has been reported and some individuals may experience increased and unexpected toxicity. This narrative review aims at identifying the factors potentially concurring at this variability for driving the most appropriate and tailored use of CDKis in the clinic. Specifically, concomitant medications, pharmacogenetic profile, and pathophysiological conditions could influence absorption, distribution, metabolism, and elimination pharmacokinetics. A personalized therapeutic approach taking into consideration all factors potentially contributing to an altered pharmacokinetic/pharmacodynamic profile could better drive safe and effective clinical use
Buprenorphine versus dihydrocodeine for opiate detoxification in primary care: a randomised controlled trial
Background
Many drug users present to primary care requesting detoxification from illicit opiates. There are a number of detoxification agents but no recommended drug of choice. The purpose of this study is to compare buprenorphine with dihydrocodeine for detoxification from illicit opiates in primary care.
Methods
Open label randomised controlled trial in NHS Primary Care (General Practices), Leeds, UK. Sixty consenting adults using illicit opiates received either daily sublingual buprenorphine or daily oral dihydrocodeine. Reducing regimens for both interventions were at the discretion of prescribing doctor within a standard regimen of not more than 15 days. Primary outcome was abstinence from illicit opiates at final prescription as indicated by a urine sample. Secondary outcomes during detoxification period and at three and six months post detoxification were recorded.
Results
Only 23% completed the prescribed course of detoxification medication and gave a urine sample on collection of their final prescription. Risk of non-completion of detoxification was reduced if allocated buprenorphine (68% vs 88%, RR 0.58 CI 0.35–0.96, p = 0.065). A higher proportion of people allocated to buprenorphine provided a clean urine sample compared with those who received dihydrocodeine (21% vs 3%, RR 2.06 CI 1.33–3.21, p = 0.028). People allocated to buprenorphine had fewer visits to professional carers during detoxification and more were abstinent at three months (10 vs 4, RR 1.55 CI 0.96–2.52) and six months post detoxification (7 vs 3, RR 1.45 CI 0.84–2.49).
Conclusion
Informative randomised trials evaluating routine care within the primary care setting are possible amongst drug using populations. This small study generates unique data on commonly used treatment regimens
Comparative assessment of fluorescent proteins for in vivo imaging in an animal model system.
Fluorescent protein tags are fundamental tools used to visualize gene products and analyze their dynamics in vivo. Recent advances in genome editing have expedited the precise insertion of fluorescent protein tags into the genomes of diverse organisms. These advances expand the potential of in vivo imaging experiments and facilitate experimentation with new, bright, photostable fluorescent proteins. Most quantitative comparisons of the brightness and photostability of different fluorescent proteins have been made in vitro, removed from biological variables that govern their performance in cells or organisms. To address the gap, we quantitatively assessed fluorescent protein properties in vivo in an animal model system. We generated transgenic Caenorhabditis elegans strains expressing green, yellow, or red fluorescent proteins in embryos and imaged embryos expressing different fluorescent proteins under the same conditions for direct comparison. We found that mNeonGreen was not as bright in vivo as predicted based on in vitro data but is a better tag than GFP for specific kinds of experiments, and we report on optimal red fluorescent proteins. These results identify ideal fluorescent proteins for imaging in vivo in C. elegans embryos and suggest good candidate fluorescent proteins to test in other animal model systems for in vivo imaging experiments
Characterization of breast tissue using energy-dispersive X-ray diffraction computed tomography
Abstract A method for sample characterization using energy-dispersive X-ray diffraction computed tomography (EDXRDCT) is presented. The procedures for extracting diffraction patterns from the data and the corrections applied are discussed. The procedures were applied to the characterization of breast tissue samples, 6 mm in diameter. Comparison with histological sections of the samples confirmed the possibility of grouping the patterns into five families, corresponding to adipose tissue, fibrosis, poorly differentiated cancer, well differentiated cancer, and benign tumour
The future is now: Model-based clinical trial design for Alzheimer's disease
Failures in trials for Alzheimer's disease (AD) may be attributable to inadequate dosing, population selection, drug inefficacy, or insufficient design optimization. The Coalition Against Major Diseases (CAMD) was formed in 2008 to develop drug development tools (DDT) to expedite drug development for AD and Parkinson's disease.1 CAMD led a process that successfully advanced a clinical trial simulation (CTS) tool for AD through the formal regulatory review process at the US Food and Drug Administration (FDA) and European Medicines Agency (EMA)
Nomenclature for renal replacement therapy and blood purification techniques in critically ill patients: practical applications
This article reports the conclusions of the second part of a consensus expert conference on the nomenclature of renal replacement therapy (RRT) techniques currently utilized to manage acute kidney injury and other organ dysfunction syndromes in critically ill patients. A multidisciplinary approach was taken to achieve harmonization of definitions, components, techniques, and operations of the extracorporeal therapies. The article describes the RRT techniques in detail with the relevant technology, procedures, and phases of treatment and key aspects of volume management/fluid balance in critically ill patients. In addition, the article describes recent developments in other extracorporeal therapies, including therapeutic plasma exchange, multiple organ support therapy, liver support, lung support, and blood purification in sepsis. This is a consensus report on nomenclature harmonization in extracorporeal blood purification therapies, such as hemofiltration, plasma exchange, multiple organ support therapies, and blood purification in sepsis
Are black holes in alternative theories serious astrophysical candidates? The case for Einstein-Dilaton-Gauss-Bonnet black holes
It is generally accepted that Einstein's theory will get some as yet unknown
corrections, possibly large in the strong field regime. An ideal place to look
for these modifications is around the vicinities of compact objects such as
black holes. Our case study here are Dilatonic Black Holes, which arise in the
framework of Gauss-Bonnet couplings and one-loop corrected four-dimensional
effective theory of heterotic superstrings at low energies. These are
interesting objects as a prototype for alternative, yet well-behaved gravity
theories: they evade the "no-hair" theorem of General Relativity but were
proved to be stable against radial perturbations. We investigate the viability
of these black holes as astrophysical objects and try to provide some means to
distinguish them from black holes in General Relativity. We start by extending
previous works and establishing the stability of these black holes against
axial perturbations. We then look for solutions of the field equations
describing slowly rotating black holes and study geodesic motion around this
geometry. Depending on the values of mass, dilaton charge and angular momentum
of the solution, one can have measurable differences in the ISCO location and
orbital frequency, relatively to black holes in General Relativity. Such
differences may be useful in future experiments, to discriminate between
alternative theories of gravity.Comment: 17 pages - v1: references added - v2: Minor correction
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