933 research outputs found
Electrically charged fluids with pressure in Newtonian gravitation and general relativity in d spacetime dimensions: theorems and results for Weyl type systems
Previous theorems concerning Weyl type systems, including Majumdar-Papapetrou
systems, are generalized in two ways, namely, we take these theorems into d
spacetime dimensions (), and we also consider the very
interesting Weyl-Guilfoyle systems, i.e., general relativistic charged fluids
with nonzero pressure. In particular within Newton-Coulomb theory of charged
gravitating fluids, a theorem by Bonnor (1980) in three-dimensional space is
generalized to arbitrary space dimensions. Then, we prove a new
theorem for charged gravitating fluid systems in which we find the condition
that the charge density and the matter density should obey. Within general
relativity coupled to charged dust fluids, a theorem by De and Raychaudhuri
(1968) in four-dimensional spacetimes in rendered into arbitrary
dimensions. Then a theorem, new in and dimensions, for
Weyl-Guilfoyle systems, is stated and proved, in which we find the condition
that the charge density, the matter density, the pressure, and the
electromagnetic energy density should obey. This theorem comprises, as
particular cases, a theorem by Gautreau and Hoffman (1973) and results in four
dimensions by Guilfoyle (1999). Upon connection of an interior charged solution
to an exterior Tangherlini solution (i.e., a Reissner-Nordstr\"om solution in
d-dimensions), one is able to give a general definition for gravitational mass
for this kind of relativistic systems and find a mass relation with the several
quantities of the interior solution. It is also shown that for sources of
finite extent the mass is identical to the Tolman mass.Comment: 27 page
Relationship between frequencies of pressure oscillations and rotor speed under rotating stall
The correlation between the frequencies of pressure oscillation ωosc and the rotor speed (frequencies of rotor rotation ωRR) under established rotating stall were determined by three methods: directly from the time diagram of the oscillation process, from the behavior diagram of parameters in space and time and from frequency characteristics. In total accordance with the Theory of Nonlinear Oscillation, by all methods of analysis, the links are in the form of integer ratios: ωosc / ωRR = 1:2 (for n/ nd= 0.6, where n - rotor speed in the experiment and nd- rotor speed from data-sheet) and ωosc / ωRR = 3:7 (for n/ nd = 0.8 and 0.95). The phases of parameter oscillations in the transverse cross-section are equal to the sensor angles in compressor stator. This is in agreement with the theoretical concept of single-cell configurations of rotating stall
Orbital Selective Magnetism in the Spin-Ladder Iron Selenides BaKFeSe
Here we show that the 2.80(8) {\mu}B/Fe block antiferromagnetic order of
BaFe2Se3 transforms into stripe antiferromagnetic order in KFe2Se3 with a
decrease in moment to 2.1(1) {\mu}B/Fe. This reduction is larger than expected
from the change in electron count from Ba to K, and occurs with
the loss of the displacements of Fe atoms from ideal positions in the ladders,
as found by neutron pair distribution function analysis. Intermediate
compositions remain insulating, and magnetic susceptibility measurements show a
suppression of magnetic order and probable formation of a spin-glass. Together,
these results imply an orbital-dependent selection of magnetic versus bonded
behavior, driven by relative bandwidths and fillings.Comment: Final versio
Elucidating the Performance Limitations of Alkaline Electrolyte Membrane Electrolysis: Dominance of Anion Concentration in Membrane Electrode Assembly
Anion exchange membrane water electrolyzers (AEMWEs) offer a cost-effective technology for producing green hydrogen. Here, an AEMWE with atmospheric plasma spray non-precious metal electrodes was tested in 0.1 to 1.0 M KOH solution, correlating performance with KOH concentration systematically. The highest cell performance was achieved at 1.0 M KOH (ca. 0.4 A cm−2 at 1.80 V), which was close to a traditional alkaline electrolysis cell with ≈6.0 M KOH. The cell exhibited 0.13 V improvement in the performance in 0.30 M KOH compared with 0.10 M KOH at 0.5 A cm−2. However, this improvement becomes more limited when further increasing the KOH concentration. Electrochemical impedance and numerical simulation results show that the ohmic resistance from the membrane was the most notable limiting factor to operate in low KOH concentration and the most sensitive to the changes in KOH concentration at 0.5 A cm−2. It is suggested that the effect of activation loss is more dominant at lower current densities; however, the ohmic loss is the most limiting factor at higher current densities, which is a current range of interest for industrial applications
Quantum Corrections to the Reissner-Nordstrom and Kerr-Newman Metrics: Spin 1
A previous evaluation of one-photon loop corrections to the energy-momentum
tensor has been extended to particles with unit spin and speculations are
presented concerning general properties of such forms.Comment: 21 pages, 1 Figur
Cosmological Constant, Conical Defect and Classical Tests of General Relativity
We investigate the perihelion shift of the planetary motion and the bending
of starlight in the Schwarzschild field modified by the presence of a
-term plus a conical defect. This analysis generalizes an earlier
result obtained by Islam (Phys. Lett. A 97, 239, 1983) to the case of a pure
cosmological constant. By using the experimental data we obtain that the
parameter characterizing the conical defect is less than
and , respectively, on the length scales associated with such
phenomena. In particular, if the defect is generated by a cosmic string, these
values correspond to limits on the linear mass densities of and
, respectively.Comment: 9 pages, no figures, revte
Exact slip-buckling analysis of two-layer composite columns
A mathematical model for slip-buckling has been proposed and its analytical solution has been found for the analysis of layered and geometrically perfect composite columns with inter-layer slip between the layers. The analytical study has been carried out to evaluate exact critical forces and to compare them to those in the literature. Particular emphasis has been placed on the influence of interface compliance on decreasing the bifurcation loads. For this purpose, a preliminary parametric study has been performed by which the influence of various material and geometric parameters on buckling forces have been investigated. (C) 2009 Elsevier Ltd. All rights reserved
Black Holes in Modified Gravity (MOG)
The field equations for Scalar-Tensor-Vector-Gravity (STVG) or modified
gravity (MOG) have a static, spherically symmetric black hole solution
determined by the mass with two horizons. The strength of the gravitational
constant is where is a parameter. A regular
singularity-free MOG solution is derived using a nonlinear field dynamics for
the repulsive gravitational field component and a reasonable physical
energy-momentum tensor. The Kruskal-Szekeres completion of the MOG black hole
solution is obtained. The Kerr-MOG black hole solution is determined by the
mass , the parameter and the spin angular momentum . The
equations of motion and the stability condition of a test particle orbiting the
MOG black hole are derived, and the radius of the black hole photosphere and
the shadows cast by the Schwarzschild-MOG and Kerr-MOG black holes are
calculated. A traversable wormhole solution is constructed with a throat
stabilized by the repulsive component of the gravitational field.Comment: 14 pages, 3 figures. Upgraded version of paper to match published
version in European Physics Journal
Properties of Ridges in Elastic Membranes
When a thin elastic sheet is confined to a region much smaller than its size
the morphology of the resulting crumpled membrane is a network of straight
ridges or folds that meet at sharp vertices. A virial theorem predicts the
ratio of the total bending and stretching energies of a ridge. Small strains
and curvatures persist far away from the ridge. We discuss several kinds of
perturbations that distinguish a ridge in a crumpled sheet from an isolated
ridge studied earlier (A. E. Lobkovsky, Phys. Rev. E. 53 3750 (1996)). Linear
response as well as buckling properties are investigated. We find that quite
generally, the energy of a ridge can change by no more than a finite fraction
before it buckles.Comment: 13 pages, RevTeX, acknowledgement adde
Active gravitational mass and the invariant characterization of Reissner-Nordstrom spacetime
We analyse the concept of active gravitational mass for Reissner-Nordstrom
spacetime in terms of scalar polynomial invariants and the Karlhede
classification. We show that while the Kretschmann scalar does not produce the
expected expression for the active gravitational mass, both scalar polynomial
invariants formed from the Weyl tensor, and the Cartan scalars, do.Comment: 6 pages Latex, to appear in General Relativity and Gravitatio
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