660 research outputs found
Hamilton-Jacobi Method and Gravitation
Studying the behaviour of a quantum field in a classical, curved, spacetime
is an extraordinary task which nobody is able to take on at present time.
Independently by the fact that such problem is not likely to be solved soon,
still we possess the instruments to perform exact predictions in special,
highly symmetric, conditions. Aim of the present contribution is to show how it
is possible to extract quantitative information about a variety of physical
phenomena in very general situations by virtue of the so-called Hamilton-Jacobi
method. In particular, we shall prove the agreement of such semi-classical
method with exact results of quantum field theoretic calculations.Comment: To appear in the proceedings of "Cosmology, the Quantum Vacuum, and
Zeta Functions": A workshop with a celebration of Emilio Elizalde's Sixtieth
birthday, Bellaterra, Barcelona, Spain, 8-10 Mar 201
Conformally rescaled spacetimes and Hawking radiation
We study various derivations of Hawking radiation in conformally rescaled
metrics. We focus on two important properties, the location of the horizon
under a conformal transformation and its associated temperature. We find that
the production of Hawking radiation cannot be associated in all cases to the
trapping horizon because its location is not invariant under a conformal
transformation. We also find evidence that the temperature of the Hawking
radiation should transform simply under a conformal transformation, being
invariant for asymptotic observers in the limit that the conformal
transformation factor is unity at their location.Comment: 22 pages, version submitted to journa
Deformation of Codimension-2 Surface and Horizon Thermodynamics
The deformation equation of a spacelike submanifold with an arbitrary
codimension is given by a general construction without using local frames. In
the case of codimension-1, this equation reduces to the evolution equation of
the extrinsic curvature of a spacelike hypersurface. In the more interesting
case of codimension-2, after selecting a local null frame, this deformation
equation reduces to the well known (cross) focusing equations. We show how the
thermodynamics of trapping horizons is related to these deformation equations
in two different formalisms: with and without introducing quasilocal energy. In
the formalism with the quasilocal energy, the Hawking mass in four dimension is
generalized to higher dimension, and it is found that the deformation of this
energy inside a marginal surface can be also decomposed into the contributions
from matter fields and gravitational radiation as in the four dimension. In the
formalism without the quasilocal energy, we generalize the definition of slowly
evolving future outer trapping horizons proposed by Booth to past trapping
horizons. The dynamics of the trapping horizons in FLRW universe is given as an
example. Especially, the slowly evolving past trapping horizon in the FLRW
universe has close relation to the scenario of slow-roll inflation. Up to the
second order of the slowly evolving parameter in this generalization, the
temperature (surface gravity) associated with the slowly evolving trapping
horizon in the FLRW universe is essentially the same as the one defined by
using the quasilocal energy.Comment: Latex, 61 pages, no figures; v2, type errors corrected; v3,
references and comments are added, English is improved, to appear in JHE
Remote sensing of spectral signatures of tropospheric aerosols
With the launch of the German Aerospace Agency's (DLR) Modular Opto-electronic Scanner (MOS) sensor on board the Indian Remote Sensing satellite (IRS-P3) launched by the Indian Space Research Organization (ISRO) in March 1996, 13 channel multi-spectral data in the range of 408 to 1010nm at high radiometric resolution, precision, and with narrow spectral bands have been available for a variety of land, atmospheric and oceanic studies. We found that these data are best for validation of radiative transfer model and the corresponding code developed by one of the authors at Space Applications Centre, and called ATMRAD (abbreviated for ATMospheric RADiation). Once this model/code is validated, it can be used for retrieving information on tropospheric aerosols over ocean or land. This paper deals with two clear objectives, viz., (1) Validation of ATMRAD model/code using MOS data and synchronously measured atmospheric data, and if found performing well, then to (2) derive relationship between MOS radiances and Aerosol Optical Thickness (AOT). The data validation procedure essentially involves near-synchronous measurements of columnar aerosol optical thickness and altitude profiles of aerosol concentration using ground-based multi-filter solar radiometers and Argon-ion Lidar, respectively and computation of the top-of-the-atmosphere (TOA) radiances from a low reflecting target (near clear water reservoir in the present study) using the ATMRAD model. The results show that the model performance is satisfactory and a relationship between the spectral parameters of MOS radiances and aerosol optical thickness can be established. In this communication, we present the details of the experiments conducted, database, validation of the ATMRAD model and development of the relationship between AOT and MOS radiance
Recommended from our members
Invasive meningococcal disease in patients with complement deficiencies: a case series (2008-2017).
BACKGROUND: To describe patients with inherited and acquired complement deficiency who developed invasive meningococcal disease (IMD) in England over the last decade. METHODS: Public Health England conducts enhanced surveillance of IMD in England. We retrospectively identified patients with complement deficiency who developed IMD in England during 2008-2017 and retrieved information on their clinical presentation, vaccination status, medication history, recurrence of infection and outcomes, as well as characteristics of the infecting meningococcal strain. RESULTS: A total of 16 patients with 20 IMD episodes were identified, including four with two episodes. Six patients had inherited complement deficiencies, two had immune-mediated conditions associated with complement deficiency (glomerulonephritis and vasculitis), and eight others were on Eculizumab therapy, five for paroxysmal nocturnal haemoglobinuria and three for atypical haemolytic uraemic syndrome. Cultures were available for 7 of 11 episodes among those with inherited complement deficiencies/immune-mediated conditions and the predominant capsular group was Y (7/11), followed by B (3/11) and non-groupable (1/11) strains. Among patients receiving Eculizumab therapy, 3 of the 9 episodes were due to group B (3/9), three others were NG but genotypically group B, and one case each of groups E, W and Y. CONCLUSIONS: In England, complement deficiency is rare among IMD cases and includes inherited disorders of the late complement pathway, immune-mediated disorders associated with low complement levels and patients on Eculizumab therapy. IMD due to capsular group Y predominates in patient with inherited complement deficiency, whilst those on Eculizumab therapy develop IMD due to more diverse capsular groups including non-encapsulated strains
Non-traumatic myositis ossificans mimicking a malignant neoplasm in an 83-year-old woman: a case report
<p>Abstract</p> <p>Introduction</p> <p>Myositis ossificans is a benign, self-limiting condition that usually affects young, athletically active men. To the best of our knowledge, this case report describes the oldest recorded patient with myositis ossificans.</p> <p>Case presentation</p> <p>Our patient was an 83-year-old Japanese woman who presented with a one week history of a palpable mass in the left thigh. She had a history of surgery for transverse colon cancer and lung cancer at the ages of 73 and 80, respectively. Clinical and radiological examinations suggested a malignant neoplasm such as metastatic carcinoma or extraskeletal osteosarcoma. A diagnosis of myositis ossificans was made by core needle biopsy. Our patient was asymptomatic and had no recurrence at one year follow-up.</p> <p>Conclusion</p> <p>Clinicians should consider myositis ossificans as a possible diagnosis for a soft tissue mass in the limb of an older patient, thereby avoiding unnecessarily aggressive therapy.</p
Mixed RG Flows and Hydrodynamics at Finite Holographic Screen
We consider quark-gluon plasma with chemical potential and study
renormalization group flows of transport coefficients in the framework of
gauge/gravity duality. We first study them using the flow equations and compare
the results with hydrodynamic results by calculating the Green functions on the
arbitrary slice. Two results match exactly. Transport coefficients at arbitrary
scale is ontained by calculating hydrodynamics Green functions. When either
momentum or charge vanishes, transport coefficients decouple from each other.Comment: 22 pages, 6 figure
Groups whose word problem is a Petri net language
There has been considerable interest in exploring the connections between the word problem of a finitely generated group as a formal language and the algebraic structure of the group. However, there are few complete characterizations that tell us precisely which groups have their word problem in a specified class of languages. We investigate which finitely generated groups have their word problem equal to a language accepted by a Petri net and give a complete classification, showing that a group has such a word problem if and only if it is virtually abelian
Particle creation rate for dynamical black holes
We present the particle creation probability rate around a general black hole
as an outcome of quantum fluctuations. Using the uncertainty principle for
these fluctuation, we derive a new ultraviolet frequency cutoff for the
radiation spectrum of a dynamical black hole. Using this frequency cutoff, we
define the probability creation rate function for such black holes. We consider
a dynamical Vaidya model, and calculate the probability creation rate for this
case when its horizon is in a slowly evolving phase. Our results show that one
can expect the usual Hawking radiation emission process in the case of a
dynamical black hole when it has a slowly evolving horizon. Moreover,
calculating the probability rate for a dynamical black hole gives a measure of
when Hawking radiation can be killed off by an incoming flux of matter or
radiation. Our result strictly suggests that we have to revise the Hawking
radiation expectation for primordial black holes that have grown substantially
since they were created in the early universe. We also infer that this
frequency cut off can be a parameter that shows the primordial black hole
growth at the emission moment.Comment: 10 pages, 1 figure. The paper was rewritten in more clear
presentation and one more appendix is adde
- …