Energy-momentum tensor for a scalar Casimir apparatus in a weak gravitational field: Neumann conditions

We consider a Casimir apparatus consisting of two perfectly conducting parallel plates, subject to the weak gravitational field of the Earth. The aim of this paper is the calculation of the energy-momentum tensor of this system for a free, real massless scalar field satisfying Neumann boundary conditions on the plates. The small gravity acceleration (here considered as not varying between the two plates) allows us to perform all calculations to first order in this parameter. Some interesting results are found: a correction, depending on the gravity acceleration, to the well-known Casimir energy and pressure on the plates. Moreover, this scheme predicts a tiny force in the upwards direction acting on the apparatus. These results are supported by two consistency checks: the covariant conservation of the energy-momentum tensor and the vanishing of its regularized trace, when the scalar field is conformally coupled to gravity.Comment: 5 pages in double-column format, Revtex4. The final version is shorter, and the presentation has been improve

Variations of Casimir energy from a superconducting transition

We consider a five-layer Casimir cavity, including 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 microwave region) of the reflection coefficient of the film produces 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 thus causes a significant increase in the value of the critical magnetic field, required to destroy the superconductivity of the film. The proposed scheme might also help clarifying the current controversy about the magnitude of the contribution to Casimir free energy from the TE zero mode, as we find that alternative treatments of this mode strongly affect the shift of critical field.Comment: RevTex 4, 15 pages, 8 figures. Revised version with improved presentation, a brief description of the ALADIN experiment, and a few references adde

Push on a Casimir apparatus in a weak gravitational field

The influence of the gravity acceleration on the regularized energy-momentum tensor of the quantized electromagnetic field between two plane parallel conducting plates is derived. We use Fermi coordinates and work to first order in the constant acceleration parameter. A new simple formula for the trace anomaly is found to first order in the constant acceleration, and a more systematic derivation is therefore obtained of the theoretical prediction according to which the Casimir device in a weak gravitational field will experience a tiny push in the upwards direction.Comment: 14 pages, Plain Tex. Talk given at the 17th SIGRAV Conference on General Relativity and Gravitational Physics, Torino, September 200

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

Fertility Cryopreservation

The cryobiology is the science of low temperature biology. Fertility cryopreservation is a vital branch of reproductive science and involves the preservation of gametes (sperm and oocytes), embryos, and reproductive tissues (ovarian and testicular tissues) for use in assisted reproduction techniques (ART). The cryopreservation of reproductive cells is the process of freezing, storage, and thawing of spermatozoa or oocytes. It involves an initial exposure to cryoprotectants, cooling to subzero temperature, storage, thawing, and finally, dilution and removal of the cryoprotectants, when used, with a return to a physiological environment that will allow subsequent development. Proper management of the osmotic pressure to avoid damage due to intracellular ice formation is crucial for successful freezing and thawing procedure. Management of non-cryopreserved reproductive cells (i.e., spermatozoa or oocytes) and tissues (i.e., testicular tissue or ovarian tissue) is problematic due to difficulties in donor-recipient synchronization and the potential for transmission of infectious pathogens, which cumulatively limits widespread application of these techniques. Cryopreserved cells and tissues can endure storage for centuries with almost no change in functionality or genetic information, making this storage a method highly attractive. There is a pressing need for the development of optimum cryopreservation methods for reproductive cells and tissues from many species. There are two major techniques for cryopreservation: freeze-thaw processes and vitrification. The major difference between them is the total avoidance of ice formation in vitrification. However, the biotechnology of the reproduction, although widely implemented, has generated protocols currently used to cryopreserve bovine sperm or oocytes, for example, that are still suboptimal, and cannot readily be extrapolated to other species' gametes. ART provide an ensemble of strategies for preserving fertility in patients and commercially valuable or endangered species. Nevertheless, it is very difficult to successfully cryopreserve. Currently, there is a growing interest to understand the underlying cryobiological fundamentals responsible for low survival rates in an effort to develop better cryopreservation. The key factors that affect the life-span of spermatozoa are the combinations of storage temperature, cooling rate, chemical composition of the extender, cryoprotectant concentration, reactive oxygen species (ROS), seminal plasma composition and hygienic control. Sperm preservation protocols vary among animal species owing to their inherent particularities that change extenders used for refrigeration and freezing. On the other hand, oocytes are available only in limited number as compared to spermatozoa, therefore, a cryopreservation protocol must allow a high rate of viability maintenance when they are employed in practical application in ART programs. One of the key factors that influence the freezing process is the ratio of surface area to volume. The oocytes require a longer time to reach osmotic balance with the cryoprotectant solution than the spermatozoa, due to their bigger volume. Then, during cooling of oocytes, various forms of cellular damage may occur, including cytoskeleton disorganization, chromosome and DNA abnormalities, spindle disintegration, plasma membrane disruption and premature cortical granule exocytosis with its related hardening of the zona pellucida. Therefore, animal gametes have been shown to survive storage at low temperatures, and recent results are very encouraging, although reproducible methods have yet to be obtained in many species

The oxidative damage to the human telomere: effects of 5-hydroxymethyl-2'-deoxyuridine on telomeric G-quadruplex structures

As part of the genome, human telomeric regions can be damaged by the chemically reactive molecules responsible for oxidative DNA damage. Considering that G-quadruplex structures have been proven to occur in human telomere regions, several studies have been devoted to investigating the effect of oxidation products on the properties of these structures. However only investigations concerning the presence in G-quadruplexes of the main oxidation products of deoxyguanosine and deoxyadenosine have appeared in the literature. Here, we investigated the effects of 5-hydroxymethyl-2’-deoxyuridine (5-hmdU), one of the main oxidation products of T, on the physical–chemical properties of the G-quadruplex structures formed by two human telomeric sequences. Collected calorimetric, circular dichroism and electrophoretic data suggest that, in contrast to most of the results on other damage, the replacement of a T with a 5-hmdU results in only negligible effects on structural stability. Reported results and other data from literature suggest a possible protecting effect of the loop residues on the other parts of the G-quadruplexes

Quantum Effects in Friedmann-Robertson-Walker Cosmologies

Electrodynamics for self-interacting scalar fields in spatially flat Friedmann-Robertson-Walker space-times is studied. The corresponding one-loop field equation for the expectation value of the complex scalar field in the conformal vacuum is derived. For exponentially expanding universes, the equations for the Bogoliubov coefficients describing the coupling of the scalar field to gravity are solved numerically. They yield a non-local correction to the Coleman-Weinberg effective potential which does not modify the pattern of minima found in static de Sitter space. Such a correction contains a dissipative term which, accounting for the decay of the classical configuration in scalar field quanta, may be relevant for the reheating stage. The physical meaning of the non-local term in the semiclassical field equation is investigated by evaluating this contribution for various background field configurations.Comment: 17 pages, plain TeX + 5 uuencoded figure

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