1,895 research outputs found
Rotating solenoidal perfect fluids of Petrov type D
We prove that aligned Petrov type D perfect fluids for which the vorticity
vector is not orthogonal to the plane of repeated principal null directions and
for which the magnetic part of the Weyl tensor with respect to the fluid
velocity has vanishing divergence, are necessarily purely electric or locally
rotationally symmetric. The LRS metrics are presented explicitly.Comment: 6 pages, no figure
Superposition of Weyl solutions: The equilibrium forces
Solutions to the Einstein equation that represent the superposition of static
isolated bodies with axially symmetry are presented. The equations nonlinearity
yields singular structures (strut and membranes) to equilibrate the bodies. The
force on the strut like singularities is computed for a variety of situations.
The superposition of a ring and a particle is studied in some detailComment: 31 pages, 7 figures, psbox macro. Submitted to Classical and Quantum
Gravit
Dimension in a Radiative Stellar Atmosphere
Dimensional scales are examined in an extended 3+1 Vaidya atmosphere
surrounding a Schwarzschild source. At one scale, the Vaidya null fluid
vanishes and the spacetime contains only a single spherical 2-surface. Both of
these behaviors can be addressed by including higher dimensions in the
spacetime metric.Comment: to appear in Gen. Rel. Gra
On higher dimensional Einstein spacetimes with a warped extra dimension
We study a class of higher dimensional warped Einstein spacetimes with one
extra dimension. These were originally identified by Brinkmann as those
Einstein spacetimes that can be mapped conformally on other Einstein
spacetimes, and have subsequently appeared in various contexts to describe,
e.g., different braneworld models or warped black strings. After clarifying the
relation between the general Brinkmann metric and other more specific
coordinate systems, we analyze the algebraic type of the Weyl tensor of the
solutions. In particular, we describe the relation between Weyl aligned null
directions (WANDs) of the lower dimensional Einstein slices and of the full
spacetime, which in some cases can be algebraically more special. Possible
spacetime singularities introduced by the warp factor are determined via a
study of scalar curvature invariants and of Weyl components measured by
geodetic observers. Finally, we illustrate how Brinkmann's metric can be
employed to generate new solutions by presenting the metric of spinning and
accelerating black strings in five dimensional anti-de Sitter space.Comment: 14 pages, minor changes in the text, mainly in Section 2.
Interior Structure of a Charged Spinning Black Hole in -Dimensions
The phenomenon of mass inflation is shown to occur for a rotating black hole.
We demonstrate this feature in dimensions by extending the charged
spinning BTZ black hole to Vaidya form. We find that the mass function diverges
in a manner quantitatively similar to its static counterparts in ,
and dimensions.Comment: 5 pages, 2 figures (appended as postscript files), WATPHYS-TH94/0
Structural and elastic anisotropy of crystals at high pressures and temperatures from quantum mechanical methods: The case of Mg2SiO4 forsterite
We report accurate ab initio theoretical predictions of the elastic, seismic, and structural anisotropy of the orthorhombic Mg2SiO4 forsterite crystal at high pressures (up to 20 GPa) and temperatures (up to its melting point, 2163 K), which constitute earth’s upper mantle conditions. Single-crystal elastic stiffness constants are evaluated up to 20 GPa and their first- and second-order pressure derivatives reported. Christoffel’s equation is solved at several pressures: directional seismic wave velocities and related properties (azimuthal and polarization seismic anisotropies) discussed. Thermal structural and average elastic properties, as computed within the quasi-harmonic approximation of the lattice potential, are predicted at high pressures and temperatures: directional thermal expansion coefficients, first- and second-order pressure derivatives of the isothermal bulk modulus, and P-V-T equation-of-state. The effect on computed properties of five different functionals, belonging to three different classes of approximations, of the density functional theory is explicitly investigated
On the determinants of local government debt: Does one size fit all?
This paper analyzes the factors that directly influence levels of debt in Spanish local governments.
Specifically, the main objective is to find out the extent to which indebtedness is originated by
controllable factors that public managers can influence, or whether it hinges on other variables
beyond managers’ control. The importance of this issue has intensified since the start of the crisis
in 2007, due to the abrupt decline of revenues and, simultaneously, to the stagnation (or even
increase) in the levels of costs facing these institutions face. Results can be explored from multiple
perspectives, given that the set of explanatory factors is also multiple. However, the most interesting
result relates to the varying effect of each covariate depending on each municipality’s specific debt
level, which suggests that economic policy recommendations should not be homogeneous across local
governments
Measurement of the permanent electric dipole moment of the neutron
We present the result of an experiment to measure the electric dipole moment EDM) of the neutron at the Paul Scherrer Institute using Ramsey's method of separated oscillating magnetic fields with ultracold neutrons (UCN). Our measurement stands in the long history of EDM experiments probing physics violating time reversal invariance. The salient features of this experiment
were the use of a Hg-199 co-magnetometer and an array of optically pumped cesium vapor magnetometers to cancel and correct for magnetic field changes. The statistical analysis was performed on blinded datasets by two separate groups while the estimation of systematic effects profited from an
unprecedented knowledge of the magnetic field. The measured value of the neutron EDM is d_{\rm n} = (0.0\pm1.1_{\rm stat}\pm0.2_{\rmsys})\times10^{-26}e\,{\rm cm}
Revised experimental upper limit on the electric dipole moment of the neutron
We present for the first time a detailed and comprehensive analysis of the experimental results that set the current world sensitivity limit on the magnitude of the electric dipole moment (EDM) of the neutron. We have extended and enhanced our earlier analysis to include recent developments in the understanding of the effects of gravity in depolarizing ultracold neutrons; an improved calculation of the spectrum of the neutrons; and conservative estimates of other possible systematic errors, which are also shown to be consistent with more recent measurements undertaken with the apparatus. We obtain a net result of dn=−0.21±1.82×10−26 e cm, which may be interpreted as a slightly revised upper limit on the magnitude of the EDM of 3.0×10−26 e cm (90% C.L.) or 3.6×10−26 e cm (95% C.L.)
Lay People Representations on the Common Good and Its Financial Provision
The financial contribution to the common good is a relevant issue to contemporary societies, especially in the wake of the Global Financial Crisis. In the economic literature, taxes and monetary donations have been regarded as two complementary ways of financially providing for the common good. In the psychological literature, instead, they have not been studied in conjunction. In-depth interviews have been conducted using interpretative phenomenological analysis (IPA) approach and a photo-elicitation technique to investigate the representations people share on the financial provision for the common good. Results suggest that both taxes and donations are seen as indirect, rather than direct, ways of providing for the common good. From a formal and cognitive level, paying taxes and making donations can be seen as two sides of the same coin, but they present differences at the affective level. When paying taxes, people are concerned mostly about the effects and expect a material exchange in return; when making a monetary donation, people are concerned mostly about the motivations and expect an emotional exchange in return
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