30,843 research outputs found
Electron Population Aging Models for Wide-Angle Tails
Color-color diagrams have been useful in studying the spectral shapes in
radio galaxies. At the workshop we presented color-color diagrams for two
wide-angle tails, 1231+674 and 1433+553, and found that the standard aging
models do not adequately represent the observed data. Although the JP and KP
models can explain some of the observed points in the color-color diagram, they
do not account for those found near the power-law line. This difficulty may be
attributable to several causes. Spectral tomography has been previously used to
discern two separate electron populations in these sources. The combination
spectra from two such overlying components can easily resemble a range of
power-laws. In addition, any non-uniformity in the magnetic field strength can
also create a power-law-like spectrum. We will also discuss the effects that
angular resolution has on the shape of the spectrum.Comment: 4 pages, 1 figure, proceedings from 1999 'Life Cycles of Radio
Galaxies' workshop at STScI in Baltimore, M
Merger Policy and Innovation: Must Enforcement Change to Account for Technological Change?
Merger policy is the most active area of U.S. antitrust policy. It is now widely believed that merger policy must move beyond its traditional focus on static efficiency to account for innovation and address dynamic efficiency. Innovation can fundamentally affect merger analysis in two ways. First, innovation can dramatically affect the relationship between the pre-merger marketplace and what is likely to happen if a proposed merger is consummated. Thus, innovation can fundamentally influence the appropriate analysis for addressing traditional, static efficiency concerns. Second, innovation can itself be an important dimension of market performance that is potentially affected by a merger. We explore how merger policy is meeting the challenges posed by innovation.
Gravitational energy
Observers at rest in a stationary spacetime flat at infinity can measure
small amounts of rest-mass+internal energies+kinetic energies+pressure energy
in a small volume of fluid attached to a local inertial frame. The sum of these
small amounts is the total "matter energy" for those observers. The total
mass-energy minus the matter energy is the binding gravitational energy.
Misner, Thorne and Wheeler evaluated the gravitational energy of a
spherically symmetric static spacetime. Here we show how to calculate
gravitational energy in any static and stationary spacetime for isolated
sources with a set of observers at rest.
The result of MTW is recovered and we find that electromagnetic and
gravitational 3-covariant energy densities in conformastatic spacetimes are of
opposite signs. Various examples suggest that gravitational energy is negative
in spacetimes with special symmetries or when the energy-momentum tensor
satisfies usual energy conditions.Comment: 12 pages. Accepted for publication in Class. Quantum Gra
When hot water freezes before cold
I suggest that the origin of the Mpemba effect (the freezing of hot water
before cold) is freezing-point depression by solutes, either gaseous or solid,
whose solubility decreases with increasing temperature so that they are removed
when water is heated. They are concentrated ahead of the freezing front by zone
refining in water that has not been heated, reduce the temperature of the
freezing front, and thereby reduce the temperature gradient and heat flux,
slowing the progress of the front. I present a simple calculation of this
effect, and suggest experiments to test this hypothesis.Comment: 7 pages, 1 figur
Shifted convolution and the Titchmarsh divisor problem over F_q[t]
In this paper we solve a function field analogue of classical problems in
analytic number theory, concerning the auto-correlations of divisor functions,
in the limit of a large finite field.Comment: 22 pages, updated versio
Parameter-free ansatz for inferring ground state wave functions of even potentials
Schr\"odinger's equation (SE) and the information-optimizing principle based
on Fisher's information measure (FIM) are intimately linked, which entails the
existence of a Legendre transform structure underlying the SE. In this
comunication we show that the existence of such an structure allows, via the
virial theorem, for the formulation of a parameter-free ground state's
SE-ansatz for a rather large family of potentials. The parameter-free nature of
the ansatz derives from the structural information it incorporates through its
Legendre properties
Discretizing Gravity in Warped Spacetime
We investigate the discretized version of the compact Randall-Sundrum model.
By studying the mass eigenstates of the lattice theory, we demonstrate that for
warped space, unlike for flat space, the strong coupling scale does not depend
on the IR scale and lattice size. However, strong coupling does prevent us from
taking the continuum limit of the lattice theory. Nonetheless, the lattice
theory works in the manifestly holographic regime and successfully reproduces
the most significant features of the warped theory. It is even in some respects
better than the KK theory, which must be carefully regulated to obtain the
correct physical results. Because it is easier to construct lattice theories
than to find exact solutions to GR, we expect lattice gravity to be a useful
tool for exploring field theory in curved space.Comment: 17 pages, 4 figures; references adde
Polar orbit electrostatic charging of objects in shuttle wake
A survey of DMSP data has uncovered several cases where precipitating auroral electron fluxes are both sufficiently intense and energetic to charge spacecraft materials such as teflon to very large potentials in the absence of ambient ion currents. Analytical bounds are provided which show that these measured environments can cause surface potentials in excess of several hundred volts to develop on objects in the orbiter wake for particular vehicle orientations
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