113 research outputs found
Accelerated Expansion of the Early and Late Universe in Terms of the Scalar-Tensor Theory of Gravitation. I
© 2017 Springer Science+Business Media New YorkThe basic idea behind the evolutionary development of the early universe is that the hot stage was preceded by the inflationary stage. In most modern concepts of the inflationary regime, it is assumed that a specific scalar field (inflaton) is present which expands space at enormous rates, while the temperature falls rapidly, real particles almost vanish, and the universe is filled by a vacuum with the equation of state P = – ɛ. In the first part of this article, the cosmological scalar of the modified Jordan-Brans-Dicke (JBD) theory is chosen to be the inflaton. Problems in the “Einstein” and proper representations of the JBD theory are considered
Some Properties of Stationary Gravitational Fields
© 2015 Springer Science+Business Media New York The problem of stationary gravitational fields is still far from solved, since there is no exact general solution of the Einstein equations for stationary gravitational fields. This paper examines an approach to this problem employing isotropic coordinates which, in particular, make it possible to understand which simplifications yield the Kerr solution
Integrated pest management of major pests and diseases in eastern Europe and the Caucasus
This book promotes Integrated Pest Management, to contribute to reduced reliance on pesticides and the avoidance of adverse impacts from pesticide use on the health and safety of farming communities, consumers and the environment. Through the IPM approach, technical advice is provided to help plan methods and measures to control major pests and diseases occurring or expected to occur in the countries of Western Asia and Eastern Europe. The specific descriptions contain a short summary of the biology of the species, completed with information on methods and tools of monitoring and control. Preventive control methods are also discussed
Vacuum Quantum Effects for Parallel Plates Moving by Uniform Acceleration in Static de Sitter Space
The Casimir forces on two parallel plates moving by uniform proper
acceleration in static de Sitter background due to conformally coupled massless
scalar field satisfying Dirichlet boundary conditions on the plates is
investigated. Static de Sitter space is conformally related to the Rindler
space, as a result we can obtain vacuum expectation values of energy-momentum
tensor for conformally invariant field in static de Sitter space from the
corresponding Rindler counterpart by the conformal transformation.Comment: 10 pages, no figures, accepted for publication in Int. J. Mod. Phys.
Cosmological evolution with negative energy densities
For general number of spatial dimensions we investigate the cosmological
dynamics driven by a cosmological constant and by a source with barotropic
equation of state. It is assumed that for both those sources the energy density
can be either positive or negative. Exact solutions of the cosmological
equations are provided for flat models. For models with curved space and with
zero cosmological constant the general solutions are expressed in terms of the
hypergeometric function. The qualitative evolution is described for all values
of the equation of state parameter. We specify the values of that parameter and
the combinations of the signs for the cosmological constant and matter energy
density for which the cosmological dynamics is nonsingular. An example is
considered with positive cosmological constant and negative matter energy
density induced by the polarization of the hyperbolic vacuum.Comment: 12 pages, 3 figures. Discussion and references added, accepted for
publication in Astrophysic
Multiple Monoenergetic Gamma Radiography (MMGR) with a compact superconducting cyclotron
Smuggling of special nuclear materials (SNM) and nuclear devices through
borders and ports of entry constitutes a major risk to global security.
Technologies are needed to reliably screen the flow of commerce for the
presence of high- materials such as uranium and plutonium. Here we present
an experimental proof-of-concept of a technique which uses inelastic ()
nuclear reactions to generate monoenergetic photons, which provide means to
measure the areal density and the effective- () of an object
with an accuracy which surpasses that achieved by current methods. We use an
ION-12 superconducting 12~MeV proton cyclotron to produce 4.4,
6.1, 6.9, and 7.1~MeV photons from a variety of nuclear reactions. Using these
photons in a transmission mode we show that we are able to accurately
reconstruct the areal densities and of a test object. This
methodology could enable mobile applications to screen commercial cargoes with
high material specificity, providing a means of distinguishing common cargo
materials from high-Z materials that include uranium and plutonium
The Armenian and NW Anatolian ophiolites: new insights for the closure of the Tethys domain and obduction onto the South Armenian Block and Anatolian-Tauride Platform before collision through dynamic modeling
International audienceIn the Lesser Caucasus three main domains are distinguished from SW to NE: (1) the South Armenian Block (SAB), a Gondwanian-derived continental terrane; (2) scattered outcrops of ophiolites coming up against the Sevan-Akera suture zone; and (3) the Eurasian plate. The Armenian ophiolites represent remnants of an oceanic domain which disappeared during Eurasia-Arabia convergence. Previous works using geochemical whole-rock analyses, 40Ar/39Ar and paleontological dating have shown that the ophiolite outcrops throughout this area were emplaced during the Late Cretaceous as one non-metamorphic preserved ophiolitic nappe of back-arc origin that formed during Middle to Late Jurassic. From these works, tectonic reconstructions include two clearly identified subductions, one related to the Neotethys subduction beneath the Eurasian margin and another to intra-oceanic subduction responsible for the opening of the back-arc basin corresponding to the ophiolites of the Lesser Caucasus. The analysis of the two stages of metamorphism of the garnet amphibolites of the ophiolite obduction sole at Amasia (M1: HT-LP peak of P = 6-7 kbar and T > 630°C; M2; MP-MT peak at P = 8-10 kbar and T = 600°C) has allowed us to deduce the onset of subduction of the SAB at 90 Ma for this locality, whichage coincides with other paleontological ages at the obduction front. A preliminary paleomagnetic survey has also brought quantification to the amount of oceanic domain which disappeared by subduction between the SAB and Eurasia before collision. We propose a dynamic finite element model using ADELI to test the incidence of parameters such as the density of the different domains (or the interval between the densities), closing speed (or speeds if sporadic), the importance and interactions of mantle discontinuities with the subducting lithosphere and set a lithospheric model. Our field observations and analyses are used to validate combinations of factors. The aim is to better qualify the predominant factors and quantify the conditions leading to the onset of obduction, the paradox of dense oceanic lithosphere emplaced on top of a continental domain, after subduction and prior to collision. The results of this modeling are also compared to new observations of the assumed eastward extension of this ophiolitic nappe in NW Anatolia. Analyses of the Refahiye ophiolites show similar geochemical signatures as the Armenian ophiolites, due to a similar setting of formation (back-arc). The impact of the obduction of such a vast oceanic domain is not to be taken for granted when considering the following collision stage
Casimir energy in the Fulling--Rindler vacuum
The Casimir energy is evaluated for massless scalar fields under Dirichlet or
Neumann boundary conditions, and for the electromagnetic field with perfect
conductor boundary conditions on one and two infinite parallel plates moving by
uniform proper acceleration through the Fulling--Rindler vacuum in an arbitrary
number of spacetime dimension. For the geometry of a single plate the both
regions of the right Rindler wedge, (i) on the right (RR region) and (ii) on
the left (RL region) of the plate are considered. The zeta function technique
is used, in combination with contour integral representations. The Casimir
energies for separate RR and RL regions contain pole and finite contributions.
For an infinitely thin plate taking RR and RL regions together, in odd spatial
dimensions the pole parts cancel and the Casimir energy for the whole Rindler
wedge is finite. In spatial dimensions the total Casimir energy for a
single plate is negative for Dirichlet scalar and positive for Neumann scalar
and the electromagnetic field. The total Casimir energy for two plates geometry
is presented in the form of a sum of the Casimir energies for separate plates
plus an additional interference term. The latter is negative for all values of
the plates separation for both Dirichlet and Neumann scalars, and for the
electromagnetic field.Comment: 28 pages, 4 figures, references added, typos corrected, accepted for
publication in Phys. Rev.
On the energy-momentum tensor for a scalar field on manifolds with boundaries
We argue that already at classical level the energy-momentum tensor for a
scalar field on manifolds with boundaries in addition to the bulk part contains
a contribution located on the boundary. Using the standard variational
procedure for the action with the boundary term, the expression for the surface
energy-momentum tensor is derived for arbitrary bulk and boundary geometries.
Integral conservation laws are investigated. The corresponding conserved
charges are constructed and their relation to the proper densities is
discussed. Further we study the vacuum expectation value of the energy-momentum
tensor in the corresponding quantum field theory. It is shown that the surface
term in the energy-momentum tensor is essential to obtain the equality between
the vacuum energy, evaluated as the sum of the zero-point energies for each
normal mode of frequency, and the energy derived by the integration of the
corresponding vacuum energy density. As an application, by using the zeta
function technique, we evaluate the surface energy for a quantum scalar field
confined inside a spherical shell.Comment: 25 pages, 2 figures, section and appendix on the surface energy for a
spherical shell are added, references added, accepted for publication in
Phys. Rev.
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