327 research outputs found
Black Hole Evaporation in a Noncommutative Charged Vaidya Model
The aim of this paper is to study the black hole evaporation and Hawking
radiation for a noncommutative charged Vaidya black hole. For this purpose, we
determine spherically symmetric charged Vaidya model and then formulate a
noncommutative Reissner-Nordstrm-like solution of this model which
leads to an exact dependent metric. The behavior of temporal component
of this metric and the corresponding Hawking temperature is investigated. The
results are shown in the form of graphs. Further, we examine the tunneling
process of the charged massive particles through the quantum horizon. It is
found that the tunneling amplitude is modified due to noncommutativity. Also,
it turns out that black hole evaporates completely in the limits of large time
and horizon radius. The effect of charge is to reduce the temperature from
maximum value to zero. It is mentioned here that the final stage of black hole
evaporation turns out to be a naked singularity.Comment: 25 pages, 36 figures, accepted for publication in J. Exp. Theor. Phy
Entropic force approach in a noncommutative charged black hole and the equivalence principle
Recently, Verlinde has suggested a novel model of duality between
thermodynamics and gravity which leads to an emergent phenomenon for the origin
of gravity and general relativity. In this paper, we investigate some features
of this model in the presence of noncommutative charged black hole by
performing the method of coordinate coherent states representing smeared
structures. We derive several quantities, e.g. temperature, energy and entropic
force. Our approach clearly exhibits that the entropic force on a smallest
fundamental cell of holographic surface with radius is halted.
Accordingly, we can conclude that the black hole remnants are absolutely inert
without gravitational interactions. So, the equivalence principle of general
relativity is contravened due to the fact that it is now possible to find a
difference between the gravitational and inertial mass. In other words, the
gravitational mass in the remnant size does not emit any gravitational field,
therefore it is experienced to be zero, contrary to the inertial mass. This
phenomenon illustrates a good example for a feasible experimental confirmation
to the entropic picture of Newton's Second law in very short distances.Comment: 11 pages, 2 figure
Hawking radiation as tunneling from a Vaidya black hole in noncommutative gravity
In the context of a noncommutative model of coordinate coherent states, we
present a Schwarzschild-like metric for a Vaidya solution instead of the
standard Eddington-Finkelstein metric. This leads to the appearance of an exact
dependent case of the metric. We analyze the resulting metric in
three possible causal structures. In this setup, we find a zero remnant mass in
the long-time limit, i.e. an instable black hole remnant. We also study the
tunneling process across the quantum horizon of such a Vaidya black hole. The
tunneling probability including the time-dependent part is obtained by using
the tunneling method proposed by Parikh and Wilczek in terms of the
noncommutative parameter . After that, we calculate the entropy
associated to this noncommutative black hole solution. However the corrections
are fundamentally trifling; one could respect this as a consequence of quantum
inspection at the level of semiclassical quantum gravity.Comment: 19 pages, 5 figure
Mutation analysis of BRCA1 and BRCA2 genes in Iranian high risk breast cancer families
Background: Telomerase is a ribonucleoprotein enzyme that synthesises telomeres after cell
division and maintains chromosomal stability leading to cellular immortalization. Telomerase has
been associated with negative prognostic indicators in some studies. The present study aims to
detect any association between telomerase sub-units: hTERT and hTR and the prognostic
indicators including tumour's size and grade, nodal status and patient's age.
Methods: Tumour samples from 46 patients with primary invasive breast cancer and 3 patients
with benign tumours were collected. RT-PCR analysis was used for the detection of hTR, hTERT,
and PGM1 (as a housekeeping) genes expression.
Results: The expression of hTR and hTERT was found in 31(67.4%) and 38 (82.6%) samples
respectively. We observed a significant association between hTR gene expression and younger age
at diagnosis (p = 0.019) when comparing patients ≤ 40 years with those who are older than 40
years. None of the benign tumours expressed hTR gene. However, the expression of hTERT gene
was revealed in 2 samples.
No significant association between hTR and hTERT expression and tumour's grade, stage and nodal
status was seen.
Conclusion: The expression of hTR and hTERT seems to be independent of tumour's stage. hTR
expression probably plays a greater role in mammary tumourogenesis in younger women (≤ 40
years) and this may have therapeutic implications in the context of hTR targeting strategies
Sandwich structure polymer electrolyte membranes containing phosphotungstic acid immobilized electospun nanofibers
The advances in proton exchange membranes (PEM)s is critical for improving the performance of fuel cells [1]. Membranes compromising perfluorosulfonic acid polymers such as Nafion have been used extensively due to their desired conductivity and stability. However, these materials need to be saturated with water to obtain practical level of proton conductivity. There is a strong demand for the PEMs to work at lower relative humidity or under anhydrous conditions because the electrochemical reactions will be accelerated and water management of fuel cell will be simpler. Various designing strategies and advanced materials have been developed to mitigate for this issue without causing serious loss in proton conductivity or stability [2]. Among all, the introducing of inorganic proton conductors such as heteropoly acids have been considered widely. Generally, HPAs (such as phosphotungstic acid H3PW12O40, PWA) have a very strong Brønsted acidity approaching the superacid region (more acidic than Nafion) [3]. In this work, high level of PWA was self-anchored onto nylon electrospun nanofiberous sheet (Figure 1b). Sandwich structured proton conducting membranes were fabricate by assembling nanofibrous central layer with outer Nafion layers (Figure 1b). Since the PWA is attached to the polymer backbones, the risk of leaching out is minimized. Moreover, the significant synthetic versatility of the method helps to increase PWA immobilization level. As shown in the Figure 1c, proton conductivity of as high as 60 mS cm-1 at 30 °C was achieved which is comparable with Nafion 115. The durability of the proton conductivity of sandwiched membrane
The Swift-UVOT ultraviolet and visible grism calibration
We present the calibration of the Swift UVOT grisms, of which there are two,
providing low-resolution field spectroscopy in the ultraviolet and optical
bands respectively. The UV grism covers the range 1700-5000 Angstrom with a
spectral resolution of 75 at 2600 Angstrom for source magnitudes of u=10-16
mag, while the visible grism covers the range 2850-6600 Angstrom with a
spectral resolution of 100 at 4000 Angstrom for source magnitudes of b=12-17
mag. This calibration extends over all detector positions, for all modes used
during operations. The wavelength accuracy (1-sigma) is 9 Angstrom in the UV
grism clocked mode, 17 Angstrom in the UV grism nominal mode and 22 Angstrom in
the visible grism. The range below 2740 Angstrom in the UV grism and 5200
Angstrom in the visible grism never suffers from overlapping by higher spectral
orders. The flux calibration of the grisms includes a correction we developed
for coincidence loss in the detector. The error in the coincidence loss
correction is less than 20%. The position of the spectrum on the detector only
affects the effective area (sensitivity) by a few percent in the nominal modes,
but varies substantially in the clocked modes. The error in the effective area
is from 9% in the UV grism clocked mode to 15% in the visible grism clocked
mode .Comment: 27 pages, 31 figures; MNRAS accepted 23 February 201
Interstellar oxygen along the line of sight of Cygnus X-2
Interstellar dust permeates our Galaxy and plays an important role in many
physical processes in the diffuse and dense regions of the interstellar medium.
High-resolution X-ray spectroscopy, coupled with modelling based on laboratory
dust measurements, provides a unique probe to investigate the interstellar dust
properties along our line of sight towards Galactic X-ray sources. Here, we
focus on the oxygen content of the interstellar medium through its absorption
features in the X-ray spectra. To model the dust features, we perform a
laboratory experiment using the electron microscope facility located at the
University of Cadiz in Spain, where we acquire new laboratory data in the
oxygen K-edge. We study 18 dust samples of silicates and oxides with different
chemical compositions. The laboratory measurements are adopted for our
astronomical data analysis. We carry out a case study on the X-ray spectrum of
the bright low-mass X-ray binary Cygnus X-2, observed by XMM-Newton. We
determine different temperature phases of the ISM, and parameterize oxygen in
both gas (neutral and ionised) and dust form. We find Solar abundances of
oxygen along the line of sight towards the source. Due to both the relatively
low depletion of oxygen into dust form and the shape of the oxygen cross
section profiles, it is challenging to determine the precise chemistry of
interstellar dust. However, silicates provide an acceptable fit. Finally, we
discuss the systematic discrepancies in the atomic (gaseous phase) data of the
oxygen edge spectral region using different X-ray atomic databases, and also
consider future prospects for studying the ISM with the Arcus concept mission.Comment: Accepted for publication in A&A, 15 pages, 11 figure
A fast and long-lived outflow from the supermassive black hole in NGC 5548
Supermassive black holes in the nuclei of active galaxies expel large amounts
of matter through powerful winds of ionized gas. The archetypal active galaxy
NGC 5548 has been studied for decades, and high-resolution X-ray and UV
observations have previously shown a persistent ionized outflow. An observing
campaign in 2013 with six space observatories shows the nucleus to be obscured
by a long-lasting, clumpy stream of ionized gas never seen before. It blocks
90% of the soft X-ray emission and causes simultaneous deep, broad UV
absorption troughs. The outflow velocities of this gas are up to five times
faster than those in the persistent outflow, and at a distance of only a few
light days from the nucleus, it may likely originate from the accretion disk.Comment: 25 pages, 8 figures. This is the author's version of the work. It is
posted here by permission of the AAAS for personal use, not for
redistribution. The definitive version was published in Science,
electronically available at Science Express (June 19, 2014). For a brief
video explaining the key results of this paper, please visit
http://www.issibern.ch/teams/ngc5548/?page_id=2
- …