909 research outputs found
Towards measuring variations of Casimir energy by a superconducting cavity
We consider a Casimir cavity, one plate of which is a thin superconducting
film. We show that when the cavity is cooled below the critical temperature for
the onset of superconductivity, the sharp variation (in the far infrared) of
the reflection coefficient of the film engenders a variation in the value of
the Casimir energy. Even though the relative variation in the Casimir energy is
very small, its magnitude can be comparable to the condensation energy of the
superconducting film, and this gives rise to a number of testable effects,
including a significant increase in the value of the critical magnetic field,
required to destroy the superconductivity of the film. The theoretical ground
is therefore prepared for the first experiment ever aimed at measuring
variations of the Casimir energy itself.Comment: 4 pages, 2 figures. Substantial improvement of presentation, choice
of a more convenient cavity geometry. Accepted for publication in Phys. Rev.
Let
On the photon Green functions in curved space-time
Quantization of electrodynamics in curved space-time in the Lorenz gauge and
with arbitrary gauge parameter makes it necessary to study Green functions of
non-minimal operators with variable coefficients. Starting from the integral
representation of photon Green functions, we link them to the evaluation of
integrals involving Gamma functions. Eventually, the full asymptotic expansion
of the Feynman photon Green function at small values of the world function, as
well as its explicit dependence on the gauge parameter, are obtained without
adding by hand a mass term to the Faddeev--Popov Lagrangian. Coincidence limits
of second covariant derivatives of the associated Hadamard function are also
evaluated, as a first step towards the energy-momentum tensor in the
non-minimal case.Comment: 22 pages, plain Tex. All sections and appendices have been improve
Role of Mitogen-Activated Protein Kinases in Myocardial Ischemia-Reperfusion Injury during Heart Transplantation
In solid organ transplantation, ischemia/reperfusion (IR) injury during organ procurement, storage and reperfusion is an unavoidable detrimental event for the graft, as it amplifies graft inflammation and rejection. Intracellular mitogen-activated protein kinase (MAPK) signaling pathways regulate inflammation and cell survival during IR injury. The four best-characterized MAPK subfamilies are the c-Jun NH2-terminal kinase (JNK), extracellular signal- regulated kinase-1/2 (ERK1/2), p38 MAPK, and big MAPK-1 (BMK1/ERK5). Here, we review the role of MAPK activation during myocardial IR injury as it occurs during heart transplantation. Most of our current knowledge regarding MAPK activation and cardioprotection comes from studies of preconditioning and postconditioning in nontransplanted hearts. JNK and p38 MAPK activation contributes to myocardial IR injury after prolonged hypothermic storage. p38 MAPK inhibition improves cardiac function after cold storage, rewarming and reperfusion. Small-molecule p38 MAPK inhibitors have been tested clinically in patients with chronic inflammatory diseases, but not in transplanted patients, so far. Organ transplantation offers the opportunity of starting a preconditioning treatment before organ procurement or during cold storage, thus modulating early events in IR injury. Future studies will need to evaluate combined strategies including p38 MAPK and/or JNK inhibition, ERK1/2 activation, pre- or postconditioning protocols, new storage solutions, and gentle reperfusion
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