2,375 research outputs found
Self-force on a scalar charge in radial infall from rest using the Hadamard-WKB expansion
We present an analytic method based on the Hadamard-WKB expansion to
calculate the self-force for a particle with scalar charge that undergoes
radial infall in a Schwarzschild spacetime after being held at rest until a
time t = 0. Our result is valid in the case of short duration from the start.
It is possible to use the Hadamard-WKB expansion in this case because the value
of the integral of the retarded Green's function over the particle's entire
past trajectory can be expressed in terms of two integrals over the time period
that the particle has been falling. This analytic result is expected to be
useful as a check for numerical prescriptions including those involving mode
sum regularization and for any other analytical approximations to self-force
calculations.Comment: 22 pages, 2 figures, Physical Review D version along with the
corrections given in the erratu
EUS-Guided Pancreatic Cyst Ablation: a Clinical and Technical Review
Purpose of Review
Pancreatic cystic lesions represent a growing public health dilemma, particularly as our population ages and cross-sectional imaging becomes more sensitive. Mucinous cysts carry a clinically significant risk of developing pancreatic cancer, which carries an extremely poor prognosis. Determining which cysts will develop cancer may be challenging, and surgical resection of the pancreas carries significant morbidity. The goal of this paper is to review the rationale for cyst ablation and discuss prior and current research on cyst ablation techniques and efficacy. Indications, contraindications, and factors related to optimal patient selection are outlined.
Recent Findings
Endoscopic ultrasound-guided chemoablation of pancreatic cysts has been performed in neoplastic cysts, with varying levels of efficacy. Safety concerns arose due to the risk of pancreatitis in alcohol-based treatments; however, the most recent data using a non-alcohol chemoablation cocktail suggests that ablation is effective without the need for alcohol, resulting in a significantly more favorable adverse event profile.
Summary
Endoscopic ultrasound-guided chemoablation of neoplastic pancreatic cysts is a promising, minimally invasive approach for treatment of cysts, with recent significant advances in safety and efficacy, suggesting that it should play a role in the treatment algorithm
Gravitational Self Force in a Schwarzschild Background and the Effective One Body Formalism
We discuss various ways in which the computation of conservative
Gravitational Self Force (GSF) effects on a point mass moving in a
Schwarzschild background can inform us about the basic building blocks of the
Effective One-Body (EOB) Hamiltonian. We display the information which can be
extracted from the recently published GSF calculation of the first-GSF-order
shift of the orbital frequency of the last stable circular orbit, and we
combine this information with the one recently obtained by comparing the EOB
formalism to high-accuracy numerical relativity (NR) data on coalescing binary
black holes. The information coming from GSF data helps to break the degeneracy
(among some EOB parameters) which was left after using comparable-mass NR data
to constrain the EOB formalism. We suggest various ways of obtaining more
information from GSF computations: either by studying eccentric orbits, or by
focussing on a special zero-binding zoom-whirl orbit. We show that logarithmic
terms start entering the post-Newtonian expansions of various (EOB and GSF)
functions at the fourth post-Newtonian (4PN) level, and we analytically compute
the first logarithm entering a certain, gauge-invariant "redshift" GSF function
(defined along the sequence of circular orbits).Comment: 44 page
Background, current status, and prognosis of the ongoing slush hydrogen technology development program for the NASP
Among the Hydrogen Projects at the NASA Lewis Research Center (NASA LeRC), is the task of implementing and managing the Slush Hydrogen (SLH2) Technology Program for the United States' National AeroSpace Plane Joint Program Office (NASP JPO). The objectives of this NASA LeRC program are to provide verified numerical models of fluid production, storage, transfer, and feed systems and to provide verified design criteria for other engineered aspects of SLH2 systems germane to a NASP. The pursuit of these objectives is multidimensional, covers a range of problem areas, works these to different levels of depth, and takes advantage of the resources available in private industry, academia, and the U.S. Government. A summary of the NASA LeRC overall SLH2 program plan, is presented along with its implementation, the present level of effort in each of the program areas, some of the results already in hand, and the prognosis for the effort in the immediate future
Noncommutative Complex Scalar Field and Casimir Effect
A noncommutative complex scalar field, satisfying the deformed canonical
commutation relations proposed by Carmona et al. [27]-[31], is constructed.
Using these noncommutative deformed canonical commutation relations, a model
describing the dynamics of the noncommutative complex scalar field is proposed.
The noncommutative field equations are solved, and the vacuum energy is
calculated to the second order in the parameter of noncommutativity. As an
application to this model, the Casimir effect, due to the zero point
fluctuations of the noncommutative complex scalar field, is considered. It
turns out that in spite of its smallness, the noncommutativity gives rise to a
repulsive force at the microscopic level, leading to a modifed Casimr potential
with a minimum at the point amin= racine(5/84){\pi}{\theta}.Comment: Revtex style, 28 page
An introduction to quantum gravity
After an overview of the physical motivations for studying quantum gravity,
we reprint THE FORMAL STRUCTURE OF QUANTUM GRAVITY, i.e. the 1978 Cargese
Lectures by Professor B.S. DeWitt, with kind permission of Springer. The reader
is therefore introduced, in a pedagogical way, to the functional integral
quantization of gravitation and Yang-Mills theory. It is hoped that such a
paper will remain useful for all lecturers or Ph.D. students who face the task
of introducing (resp. learning) some basic concepts in quantum gravity in a
relatively short time. In the second part, we outline selected topics such as
the braneworld picture with the same covariant formalism of the first part, and
spectral asymptotics of Euclidean quantum gravity with diffeomorphism-invariant
boundary conditions. The latter might have implications for singularity
avoidance in quantum cosmology.Comment: 68 pages, Latex file. Sections from 2 to 17 are published thanks to
kind permission of Springe
Next-to-leading term of the renormalized stress-energy tensor of the quantized massive scalar field in Schwarzschild spacetime. The back reaction
The next-to-leading term of the renormalized stress-energy tensor of the
quantized massive field with an arbitrary curvature coupling in the spacetime
of the Schwarzschild black hole is constructed. It is achieved by functional
differentiation of the DeWitt-Schwinger effective action involving coincidence
limit of the Hadamard-Minakshisundaram-DeWitt-Seely coefficients and
The back reaction of the quantized field upon the Schwarzschild black
hole is briefly discussed
Quantum Equivalence of Massive Antisymmetric Tensor Field Models in Curved Space
We study the effective actions for massive rank-2 and rank-3 antisymmetric
tensor field models in curved space-time. These models are classically
equivalent to massive vector field and massive scalar field with minimal
coupling to gravity respectively. We prove that effective action for massive
rank-2 antisymmetric tensor field is exactly equal to one for massive vector
field and effective action for massive rank-3 antisymmetric tensor field is
exactly equal to one for massive scalar field. Prove is based on an identity
for mass-dependent zeta-functions associated with Laplacians acting on
-forms.Comment: 8 pages, REVTeX fil
A universal constraint between charge and rotation rate for degenerate black holes surrounded by matter
We consider stationary, axially and equatorially symmetric systems consisting
of a central rotating and charged degenerate black hole and surrounding matter.
We show that always holds provided that a continuous sequence of
spacetimes can be identified, leading from the Kerr-Newman solution in
electrovacuum to the solution in question. The quantity is the black
hole's intrinsic angular momentum per unit mass, its electric charge and
the well known black hole mass parameter introduced by Christodoulou and
Ruffini.Comment: 19 pages, 2 figures, replaced with published versio
Quantum Effects in the Spacetime of a Magnetic Flux Cosmic String
In this work we compute the vacuum expectation values of the energy-momentum
tensor and the average value of a massive, charged scalar field in the presence
of a magnetic flux cosmic string for both zero- and finite-temperature cases.Comment: To appear in the Int. Journal of Modern Phys. A (special issue).
Proceedings of the Second International Londrina Winter School on
Mathematical Methods in Physics, Londrina, Brazil, August 200
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