19,630 research outputs found
The Quantum Mechanical Arrows of Time
The familiar textbook quantum mechanics of laboratory measurements
incorporates a quantum mechanical arrow of time --- the direction in time in
which state vector reduction operates. This arrow is usually assumed to
coincide with the direction of the thermodynamic arrow of the quasiclassical
realm of everyday experience. But in the more general context of cosmology we
seek an explanation of all observed arrows, and the relations between them, in
terms of the conditions that specify our particular universe. This paper
investigates quantum mechanical and thermodynamic arrows in a time-neutral
formulation of quantum mechanics for a number of model cosmologies in fixed
background spacetimes. We find that a general universe may not have well
defined arrows of either kind. When arrows are emergent they need not point in
the same direction over the whole of spacetime. Rather they may be local,
pointing in different directions in different spacetime regions. Local arrows
can therefore be consistent with global time symmetry.Comment: 9 pages, 4 figures, revtex4, typos correcte
Exterior and interior metrics with quadrupole moment
We present the Ernst potential and the line element of an exact solution of
Einstein's vacuum field equations that contains as arbitrary parameters the
total mass, the angular momentum, and the quadrupole moment of a rotating mass
distribution. We show that in the limiting case of slowly rotating and slightly
deformed configuration, there exists a coordinate transformation that relates
the exact solution with the approximate Hartle solution. It is shown that this
approximate solution can be smoothly matched with an interior perfect fluid
solution with physically reasonable properties. This opens the possibility of
considering the quadrupole moment as an additional physical degree of freedom
that could be used to search for a realistic exact solution, representing both
the interior and exterior gravitational field generated by a self-gravitating
axisymmetric distribution of mass of perfect fluid in stationary rotation.Comment: Latex, 15 pages, 3 figures, final versio
Near-horizon geometries of supersymmetric AdS(5) black holes
We provide a classification of near-horizon geometries of supersymmetric,
asymptotically anti-de Sitter, black holes of five-dimensional U(1)^3-gauged
supergravity which admit two rotational symmetries. We find three
possibilities: a topologically spherical horizon, an S^1 \times S^2 horizon and
a toroidal horizon. The near-horizon geometry of the topologically spherical
case turns out to be that of the most general known supersymmetric,
asymptotically anti-de Sitter, black hole of U(1)^3-gauged supergravity. The
other two cases have constant scalars and only exist in particular regions of
this moduli space -- in particular they do not exist within minimal gauged
supergravity. We also find a solution corresponding to the near-horizon
geometry of a three-charge supersymmetric black ring held in equilibrium by a
conical singularity; when lifted to type IIB supergravity this solution can be
made regular, resulting in a discrete family of warped AdS(3) geometries.
Analogous results are presented in U(1)^n gauged supergravity.Comment: Latex, 29 pages. v2: minor improvements, references adde
Thermal Modeling in Polymer Extrusion
In this paper we consider thermal effects of polymer flows through a cylindrical die. First, we derive a model for the oscillatory behavior of polymer flow in an extruder given a functional relation between the pressure and flow rate. A simple isothermal but temperature dependent model is constructed to find this relation. Unfortunately, the model is shown to be invalid in the physical regime of interest. We present several arguments to suggest that the isothermal assumption is reasonable but that a more detailed understanding of the small-scale molecular dynamics near the boundary may be required. Second, we show that a simplified model for thermoflow multiplicity in a cooled tube is inconsistent, when the stationary non-Newtonian flow is assumed to be incompressible without radial pressure gradients and without radial velocity. This inconsistency can be removed by allowing for weak compressibility effects in the down-steam area
Reliability analysis of dynamic systems by translating temporal fault trees into Bayesian networks
Classical combinatorial fault trees can be used to assess combinations of failures but are unable to capture sequences of faults, which are important in complex dynamic systems. A number of proposed techniques extend fault tree analysis for dynamic systems. One of such technique, Pandora, introduces temporal gates to capture the sequencing of events and allows qualitative analysis of temporal fault trees. Pandora can be easily integrated in model-based design and analysis techniques. It is, therefore, useful to explore the possible avenues for quantitative analysis of Pandora temporal fault trees, and we identify Bayesian Networks as a possible framework for such analysis. We describe how Pandora fault trees can be translated to Bayesian Networks for dynamic dependability analysis and demonstrate the process on a simplified fuel system model. The conversion facilitates predictive reliability analysis of Pandora fault trees, but also opens the way for post-hoc diagnostic analysis of failures
Rotor eddy-current loss in permanent magnet brushless machines
This paper presents an analysis of the rotor eddy-current loss in modular and conventional topologies of permanent magnet brushless machine. The loss is evaluated both analytically and by time-stepped finite-element analysis, and it is shown that it can be significant in both machine topologies. It is also shown that the loss can be reduced significantly by segmenting the magnets
Impact of MGNREGA on Input-use Pattern, Labour Productivity and Returns of Selected Crops in Gulbarga District, Karnataka
The study has tried to capture the effect of MGNREGA by selecting two sets of villages in the Gulbarga district of Karnataka, one which have utilized 75 per cent of allocated funds and the other which have utilized less the 25 per cent of allocated funds under MGNREGA. The study is based on primary data obtained from 120 sample farmers belonging to five village panchayats. In redgram, a significant difference has been observed in use of machine power and labour use between fully and partially-implemented MGNREGA villages, but no difference has been recorded in the use of material inputs. Similarly, in the rabi jowar, there is a significant difference in labour use but not in the use of machine power and material inputs between two categories of villages. The total cost of cultivation in fully-implemented MGNREGA villages has been found higher by 22.91 per cent and 16.37 per cent in red gram and rabi jowar, respectively. The labour productivity of male and female has been noticed lower in fully-implemented MGNREGA villages for all operations in both the crops. The study has given some suggestions to address the problem of labour scarcity in fully-implemented villages.Impact of MGNREGA, Labour productivity, Crop returns, Agricultural and Food Policy, J43, J24, Input-use pattern,
Uniqueness of Five-Dimensional Supersymmetric Black Holes
A classification of supersymmetric solutions of five dimensional ungauged
supergravity coupled to arbitrary many abelian vector multiplets is used to
prove a uniqueness theorem for asymptotically flat supersymmetric black holes
with regular horizons. It is shown that the near-horizon geometries of
solutions for which the scalars and gauge field strengths are sufficiently
regular on the horizon are flat space, AdS_3 x S^2, or the near-horizon BMPV
solution. Furthermore, the only black hole which has the near-horizon BMPV
geometry for its near-horizon geometry is the solution found by Chamseddine and
Sabra.Comment: 15 pages, uses JHEP3.cls. Revised to match published version;
reference added, minor alterations to section
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