Effect of gold and nickel co-additives on gas-sensitive characteristics of SnO2 thin-film on exposure to hydrogen and nitrogen dioxide

The results of investigation of the gas-sensitive properties of sensors based on the tin dioxide thin films with combined additives of gold and nickel obtained by the DC - magnetron sputtering are presented. The investigated sensors are characterized by a high response to low concentrations of NO2 of 0.45 – 10.23 ppm at temperatures of 50 – 150 °C with response time of 10 s. The sensitivity of sensors to hydrogen appears at the temperature of 250 °C. The hydrogen sensors are characterized by high reproducibility of the measurement results. The obtained results are explained by the synergistic effect of gold and nickel additives, as well as the ability of the Ni to prevent the interaction of hydrogen with lattice oxygen atoms in the subsurface part of tin dioxide

Naturalness in Cosmological Initial Conditions

We propose a novel approach to the problem of constraining cosmological initial conditions. Within the framework of effective field theory, we classify initial conditions in terms of boundary terms added to the effective action describing the cosmological evolution below Planckian energies. These boundary terms can be thought of as spacelike branes which may support extra instantaneous degrees of freedom and extra operators. Interactions and renormalization of these boundary terms allow us to apply to the boundary terms the field-theoretical requirement of naturalness, i.e. stability under radiative corrections. We apply this requirement to slow-roll inflation with non-adiabatic initial conditions, and to cyclic cosmology. This allows us to define in a precise sense when some of these models are fine-tuned. We also describe how to parametrize in a model-independent way non-Gaussian initial conditions; we show that in some cases they are both potentially observable and pass our naturalness requirement.Comment: 35 pages, 8 figure

Inflaton Decay in an Alpha Vacuum

We study the alpha vacua of de Sitter space by considering the decay rate of the inflaton field coupled to a scalar field placed in an alpha vacuum. We find an {\em alpha dependent} Bose enhancement relative to the Bunch-Davies vacuum and, surprisingly, no non-renormalizable divergences. We also consider a modified alpha dependent time ordering prescription for the Feynman propagator and show that it leads to an alpha independent result. This result suggests that it may be possible to calculate in any alpha vacuum if we employ the appropriate causality preserving prescription.Comment: 16 pages, 1 figure, Revtex 4 preprin

Vacuum energy induced by an impenetrable flux tube of finite radius

We consider the effect of the magnetic field background in the form of a tube of the finite transverse size on the vacuum of the quantized charged massive scalar field which is subject to the Dirichlet boundary condition at the edge of the tube. The vacuum energy is induced, being periodic in the value of the magnetic flux enclosed in the tube. Our previous study in J. Phys. A: Vol.43, 175401 (2010) is extended to the case of smaller radius of the tube and larger distances from it. The dependence of the vacuum energy density on the distance from the tube and on the coupling to the space-time curvature scalar is comprehensively analyzed.Comment: 11 pages, 8 figures, journal version, abstract extended. arXiv admin note: substantial text overlap with arXiv:0911.287

Action of Pulse-Magnetic Fields on Liquid and Crystallizing Metal

Pulsed-magnetic fields are used for execution of a whole complex of technological processes: dividing, forming, assembling, welding and others. In all these technologies half-finished products from sheets, sections and tubes are used as billets. Action of magnetic fields on a cast metal is known in the metallurgy production, for example, casting to an electromagnetic crystallizer. In spite of a high electrical resistance of a melt and owing to low mechanical resistance of a liquid metal the use of high-intensity pulse-magnetic fields (PMF) in technologies of mechanical engineering is of interest. Even the first exploration experiment showed high efficiency of such action. At energy of 1, 2 kJ a portion of the melt under the action of the PMF has flown more than 4 m, spread in the form of a thin film on the ceiling and solidified. The paper presents three basic technological schemes of such action: with influence through a wall of a magneto-transparent crucible; by an immersion inductor; and action from the surface. Factors accompanying such action are: added sources of heat as a result of flowing of induced eddy currents through the melt; force action on the melt responsible for passage of waves of stress and metal flows. Action of these factors is controllable both in intensity and in direction. The temporal action of the pulse-magnetic field on a liquid and crystallizing metal (LCM) is to be matched with a curve of cooling the melt: either on the portion above the crystallization area or on its different portions, that is, at different relationships of solid and liquid phases.Factors of action of the pulse-magnetic field change temperature conditions of crystallization influence on the number of centers of crystallization and, as the consequence, change structure and properties of cast metal. The paper presents results of first studies on action of the pulse-magnetic field on a LCM which testify that such action is real and good. This has determined the prospects for development of new technologies in metallurgy (forming of an ingots structure, stirring of a material, rolling of cast metal and so on) and in mechanical engineering (in casting, stamping, welding and others)

The Coincidence Limit of the Graviton Propagator in de Donder Gauge on de Sitter Background

We explicitly work out the de Sitter breaking contributions to the recent solution for the de Donder gauge graviton propagator on de Sitter. We also provide explicit power series expansions for the two structure functions, which are suitable for implementing dimensional regularization. And we evaluate the coincidence limit of the propagator.Comment: 41 pages, uses LaTeX 2e, version 2 has some typoes correcte

Two loop stress-energy tensor for inflationary scalar electrodynamics

We calculate the expectation value of the coincident product of two field strength tensors at two loop order in scalar electrodynamics on de Sitter background. The result agrees with the stochastic formulation which we have developed in a companion paper [2] for the nonperturbative resummation of leading logarithms of the scale factor. When combined with a previous computation of scalar bilinears [1], our current result also gives the two loop stress-energy tensor for inflationary scalar electrodynamics. This shows a secular decrease in the vacuum energy which derives from the vacuum polarization induced by the inflationary production of charged scalars.Comment: 62 pages, 1 eps figur