1,960 research outputs found
Logarithmic Corrections to Schwarzschild and Other Non-extremal Black Hole Entropy in Different Dimensions
Euclidean gravity method has been successful in computing logarithmic
corrections to extremal black hole entropy in terms of low energy data, and
gives results in perfect agreement with the microscopic results in string
theory. Motivated by this success we apply Euclidean gravity to compute
logarithmic corrections to the entropy of various non-extremal black holes in
different dimensions, taking special care of integration over the zero modes
and keeping track of the ensemble in which the computation is done. These
results provide strong constraint on any ultraviolet completion of the theory
if the latter is able to give an independent computation of the entropy of
non-extremal black holes from microscopic description. For Schwarzschild black
holes in four space-time dimensions the macroscopic result seems to disagree
with the existing result in loop quantum gravity.Comment: LaTeX, 40 pages; corrected small typos and added reference
Sources of Relativistic Jets in the Galaxy
Black holes of stellar mass and neutron stars in binary systems are first
detected as hard X-ray sources using high-energy space telescopes. Relativistic
jets in some of these compact sources are found by means of multiwavelength
observations with ground-based telescopes. The X-ray emission probes the inner
accretion disk and immediate surroundings of the compact object, whereas the
synchrotron emission from the jets is observed in the radio and infrared bands,
and in the future could be detected at even shorter wavelengths. Black-hole
X-ray binaries with relativistic jets mimic, on a much smaller scale, many of
the phenomena seen in quasars and are thus called microquasars. Because of
their proximity, their study opens the way for a better understanding of the
relativistic jets seen elsewhere in the Universe. From the observation of
two-sided moving jets it is inferred that the ejecta in microquasars move with
relativistic speeds similar to those believed to be present in quasars. The
simultaneous multiwavelength approach to microquasars reveals in short
timescales the close connection between instabilities in the accretion disk
seen in the X-rays, and the ejection of relativistic clouds of plasma observed
as synchrotron emission at longer wavelengths. Besides contributing to a deeper
comprehension of accretion disks and jets, microquasars may serve in the future
to determine the distances of jet sources using constraints from special
relativity, and the spin of black holes using general relativity.Comment: 39 pages, Tex, 8 figures, to appear in vol. 37 (1999) of Annual
Reviews of Astronomy and Astrophysic
Of cattle, sand flies and men : a systematic review of risk factor analyses for South Asian visceral leishmaniasis and implications for elimination
Background: Studies performed over the past decade have identified fairly consistent epidemiological patterns of risk
factors for visceral leishmaniasis (VL) in the Indian subcontinent.
Methods and Principal Findings: To inform the current regional VL elimination effort and identify key gaps in knowledge,
we performed a systematic review of the literature, with a special emphasis on data regarding the role of cattle because
primary risk factor studies have yielded apparently contradictory results. Because humans form the sole infection reservoir,
clustering of kala-azar cases is a prominent epidemiological feature, both at the household level and on a larger scale.
Subclinical infection also tends to show clustering around kala-azar cases. Within villages, areas become saturated over a
period of several years; kala-azar incidence then decreases while neighboring areas see increases. More recently, post kalaazar
dermal leishmaniasis (PKDL) cases have followed kala-azar peaks. Mud walls, palpable dampness in houses, and peridomestic
vegetation may increase infection risk through enhanced density and prolonged survival of the sand fly vector.
Bed net use, sleeping on a cot and indoor residual spraying are generally associated with decreased risk. Poor micronutrient
status increases the risk of progression to kala-azar. The presence of cattle is associated with increased risk in some studies
and decreased risk in others, reflecting the complexity of the effect of bovines on sand fly abundance, aggregation, feeding
behavior and leishmanial infection rates. Poverty is an overarching theme, interacting with individual risk factors on multiple
levels.
Conclusions: Carefully designed demonstration projects, taking into account the complex web of interconnected risk
factors, are needed to provide direct proof of principle for elimination and to identify the most effective maintenance
activities to prevent a rapid resurgence when interventions are scaled back. More effective, short-course treatment
regimens for PKDL are urgently needed to enable the elimination initiative to succeed
Urinary MicroRNA Profiling in the Nephropathy of Type 1 Diabetes
Background: Patients with Type 1 Diabetes (T1D) are particularly vulnerable to development of Diabetic nephropathy (DN) leading to End Stage Renal Disease. Hence a better understanding of the factors affecting kidney disease progression in T1D is urgently needed. In recent years microRNAs have emerged as important post-transcriptional regulators of gene expression in many different health conditions. We hypothesized that urinary microRNA profile of patients will differ in the different stages of diabetic renal disease. Methods and Findings: We studied urine microRNA profiles with qPCR in 40 T1D with >20 year follow up 10 who never developed renal disease (N) matched against 10 patients who went on to develop overt nephropathy (DN), 10 patients with intermittent microalbuminuria (IMA) matched against 10 patients with persistent (PMA) microalbuminuria. A Bayesian procedure was used to normalize and convert raw signals to expression ratios. We applied formal statistical techniques to translate fold changes to profiles of microRNA targets which were then used to make inferences about biological pathways in the Gene Ontology and REACTOME structured vocabularies. A total of 27 microRNAs were found to be present at significantly different levels in different stages of untreated nephropathy. These microRNAs mapped to overlapping pathways pertaining to growth factor signaling and renal fibrosis known to be targeted in diabetic kidney disease. Conclusions: Urinary microRNA profiles differ across the different stages of diabetic nephropathy. Previous work using experimental, clinical chemistry or biopsy samples has demonstrated differential expression of many of these microRNAs in a variety of chronic renal conditions and diabetes. Combining expression ratios of microRNAs with formal inferences about their predicted mRNA targets and associated biological pathways may yield useful markers for early diagnosis and risk stratification of DN in T1D by inferring the alteration of renal molecular processes. © 2013 Argyropoulos et al
Instability of black hole formation under small pressure perturbations
We investigate here the spectrum of gravitational collapse endstates when
arbitrarily small perfect fluid pressures are introduced in the classic black
hole formation scenario as described by Oppenheimer, Snyder and Datt (OSD) [1].
This extends a previous result on tangential pressures [2] to the more
physically realistic scenario of perfect fluid collapse. The existence of
classes of pressure perturbations is shown explicitly, which has the property
that injecting any smallest pressure changes the final fate of the dynamical
collapse from a black hole to a naked singularity. It is therefore seen that
any smallest neighborhood of the OSD model, in the space of initial data,
contains collapse evolutions that go to a naked singularity outcome. This gives
an intriguing insight on the nature of naked singularity formation in
gravitational collapse.Comment: 7 pages, 1 figure, several modifications to match published version
on GR
Shallow water marine sediment bacterial community shifts along a natural CO2 gradient in the Mediterranean Sea off Vulcano, Italy.
The effects of increasing atmospheric CO(2) on ocean ecosystems are a major environmental concern, as rapid shoaling of the carbonate saturation horizon is exposing vast areas of marine sediments to corrosive waters worldwide. Natural CO(2) gradients off Vulcano, Italy, have revealed profound ecosystem changes along rocky shore habitats as carbonate saturation levels decrease, but no investigations have yet been made of the sedimentary habitat. Here, we sampled the upper 2 cm of volcanic sand in three zones, ambient (median pCO(2) 419 μatm, minimum Ω(arag) 3.77), moderately CO(2)-enriched (median pCO(2) 592 μatm, minimum Ω(arag) 2.96), and highly CO(2)-enriched (median pCO(2) 1611 μatm, minimum Ω(arag) 0.35). We tested the hypothesis that increasing levels of seawater pCO(2) would cause significant shifts in sediment bacterial community composition, as shown recently in epilithic biofilms at the study site. In this study, 454 pyrosequencing of the V1 to V3 region of the 16S rRNA gene revealed a shift in community composition with increasing pCO(2). The relative abundances of most of the dominant genera were unaffected by the pCO(2) gradient, although there were significant differences for some 5 % of the genera present (viz. Georgenia, Lutibacter, Photobacterium, Acinetobacter, and Paenibacillus), and Shannon Diversity was greatest in sediments subject to long-term acidification (>100 years). Overall, this supports the view that globally increased ocean pCO(2) will be associated with changes in sediment bacterial community composition but that most of these organisms are resilient. However, further work is required to assess whether these results apply to other types of coastal sediments and whether the changes in relative abundance of bacterial taxa that we observed can significantly alter the biogeochemical functions of marine sediments
Identifying sources, pathways and risk drivers in ecosystems of Japanese Encephalitis in an epidemic-prone north Indian district
Japanese Encephalitis (JE) has caused repeated outbreaks in endemic pockets of India. This study was conducted in Kushinagar, a highly endemic district, to understand the human-animal-ecosystem interactions, and the drivers that influence disease transmission. Utilizing the ecosystems approach, a cross-sectional, descriptive study, employing mixed methods design was employed. Four villages (two with pig-rearing and two without) were randomly selected from a high, a medium and a low burden (based on case counts) block of Kushinagar. Children, pigs and vectors were sampled from these villages. A qualitative arm was incorporated to explain the findings from the quantitative surveys. All human serum samples were screened for JE-specific IgM using MAC ELISA and negative samples for JE RNA by rRT-PCR in peripheral blood mononuclear cells. In pigs, IgG ELISA and rRT-PCR for viral RNA were used. Of the 242 children tested, 24 tested positive by either rRT-PCR or MAC ELISA; in pigs, 38 out of the 51 pigs were positive. Of the known vectors, Culex vishnui was most commonly isolated across all biotopes. Analysis of 15 blood meals revealed human blood in 10 samples. Univariable analysis showed that gender, religion, lack of indoor residual spraying of insecticides in the past year, indoor vector density (all species), and not being vaccinated against JE in children were significantly associated with JE positivity. In multivariate analysis, only male gender remained as a significant risk factor. Based on previous estimates of symptomatic: asymptomatic cases of JE, we estimate that there should have been 618 cases from Kushinagar, although only 139 were reported. Vaccination of children and vector control measures emerged as major control activities; they had very poor coverage in the studied villages. In addition, lack of awareness about the cause of JE, lack of faith in the conventional medical healthcare system and multiple referral levels causing delay in diagnosis and treatment emerged as factors likely to result in adverse clinical outcomes
Robotic Wireless Sensor Networks
In this chapter, we present a literature survey of an emerging, cutting-edge,
and multi-disciplinary field of research at the intersection of Robotics and
Wireless Sensor Networks (WSN) which we refer to as Robotic Wireless Sensor
Networks (RWSN). We define a RWSN as an autonomous networked multi-robot system
that aims to achieve certain sensing goals while meeting and maintaining
certain communication performance requirements, through cooperative control,
learning and adaptation. While both of the component areas, i.e., Robotics and
WSN, are very well-known and well-explored, there exist a whole set of new
opportunities and research directions at the intersection of these two fields
which are relatively or even completely unexplored. One such example would be
the use of a set of robotic routers to set up a temporary communication path
between a sender and a receiver that uses the controlled mobility to the
advantage of packet routing. We find that there exist only a limited number of
articles to be directly categorized as RWSN related works whereas there exist a
range of articles in the robotics and the WSN literature that are also relevant
to this new field of research. To connect the dots, we first identify the core
problems and research trends related to RWSN such as connectivity,
localization, routing, and robust flow of information. Next, we classify the
existing research on RWSN as well as the relevant state-of-the-arts from
robotics and WSN community according to the problems and trends identified in
the first step. Lastly, we analyze what is missing in the existing literature,
and identify topics that require more research attention in the future
Holographic phase diagram of quark-gluon plasma formed in heavy-ions collisions
The phase diagram of quark gluon plasma (QGP) formed at a very early stage
just after the heavy ion collision is obtained by using a holographic dual
model for the heavy ion collision. In this dual model colliding ions are
described by the charged shock gravitational waves. Points on the phase diagram
correspond to the QGP or hadronic matter with given temperatures and chemical
potentials. The phase of QGP in dual terms is related to the case when the
collision of shock waves leads to formation of trapped surface. Hadronic matter
and other confined states correspond to the absence of trapped surface after
collision.
Multiplicity of the ion collision process is estimated in the dual language
as area of the trapped surface. We show that a non-zero chemical potential
reduces the multiplicity. To plot the phase diagram we use two different dual
models of colliding ions, the point and the wall shock waves, and find
qualitative agreement of the results.Comment: 33 pages, 14 figures, typos correcte
Functional compensation of glutathione S-transferase M1 (GSTM1) null by another GST superfamily member,GSTM2
The gene for glutathione-S-transferase (GST) M1 (GSTM1), a member of the GST-superfamily, is widely studied in cancer risk with regard to the homozygous deletion of the gene (GSTM1 null), leading to a lack of corresponding enzymatic activity. Many of these studies have reported inconsistent findings regarding its association with cancer risk. Therefore, we employed in silico, in vitro, and in vivo approaches to investigate whether the absence of a functional GSTM1 enzyme in a null variant can be compensated for by other family members. Through the in silico approach, we identified maximum structural homology between GSTM1 and GSTM2. Total plasma GST enzymatic activity was similar in recruited individuals, irrespective of their GSTM1 genotype (positive/null). Furthermore, expression profiling using real-time PCR, western blotting,
and GSTM2 overexpression following transient knockdown of GSTM1 in HeLa cells confirmed that the absence of GSTM1 activity can be compensated for by the overexpression of GSTM
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