62,507 research outputs found
Lensing Properties of Cored Galaxy Models
A method is developed to evaluate the magnifications of the images of
galaxies with lensing potentials stratified on similar concentric ellipses. A
simple contour integral is provided which enables the sums of the
magnifications of even parity or odd parity or the central image to be easily
calculated. The sums for pairs of images vary considerably with source
position, while the signed sums can be remarkably uniform inside the tangential
caustic in the absence of naked cusps. For a family of models in which the
potential is a power-law of the elliptic radius, the number of visible images
is found as a function of flattening, external shear and core radius. The
magnification of the central image depends on the core radius and the slope of
the potential. For typical source and lens redshifts, the missing central image
leads to strong constraints; the mass distribution in the lensing galaxy must
be nearly cusped, and the cusp must be isothermal or stronger. This is in
accord with the cuspy cores seen in high resolution photometry of nearby,
massive, early-type galaxies, which typically have the surface density falling
like distance^{-1.3} outside a break radius of a few hundred parsecs. Cuspy
cores by themselves can provide an explanation of the missing central images.
Dark matter at large radii may alter the slope of the projected density;
provided the slope remains isothermal or steeper and the break radius remains
small, then the central image remains unobservable. The sensitivity of the
radio maps must be increased fifty-fold to find the central images in
abundance.Comment: 42 pages, 11 figures, ApJ in pres
Axisymmetric Self-Similar Equilibria of Self-Gravitating Isothermal Systems
All axisymmetric self-similar equilibria of self-gravitating, rotating,
isothermal systems are identified by solving the nonlinear Poisson equation
analytically. There are two families of equilibria: (1) Cylindrically symmetric
solutions in which the density varies with cylindrical radius as R^(-alpha),
with 0 <= alpha <= 2. (2) Axially symmetric solutions in which the density
varies as f(theta)/r^2, where `r' is the spherical radius and `theta' is the
co-latitude. The singular isothermal sphere is a special case of the latter
class with f(theta)=constant. The axially symmetric equilibrium configurations
form a two-parameter family of solutions and include equilibria which are
surprisingly asymmetric with respect to the equatorial plane. The asymmetric
equilibria are, however, not force-free at the singular points r=0, infinity,
and their relevance to real systems is unclear. For each hydrodynamic
equilibrium, we determine the phase-space distribution of the collisionless
analog.Comment: 13 pages, 7 figures, uses emulateapj.sty. Submitted to Ap
A Note on the Relativistic Covariance of the Cyclic Relations
It is shown that the Evans-Vigier modified electrodynamics is compatible with
the Relativity Theory.Comment: ReVTeX file, 14pp., no figure
The core size of the Fornax dwarf Spheroidal
We exploit the detection of three distinct stellar subpopulations in the red
giant branch of the Fornax dwarf Spheroidal to probe its density distribution.
This allows us to resolve directly the evolution with radius of the dark matter
mass profile. We find that a cored dark matter halo provides a perfect fit to
the data, being consistent with all three stellar populations well within
1-sigma, and for the first time we are able to put constraints on the core size
of such a halo. With respect to previous work, we do not strengthen the
statistical exclusion of a dark matter cusp in Fornax, but we find that
Navarro-Frenk-White haloes would be required to have unrealistically large
scale radii in order to be compatible with the data, hence low values of the
concentration parameter. We are then forced to conclude that the Fornax dwarf
Spheroidal sits within a dark matter halo having a constant density core, with
a core size of between 0.6 and 1.8 kpc.Comment: MNRAS Letters, submitte
Status of Lattice QCD
Significant progress has recently been achieved in the lattice gauge theory
calculations required for extracting the fundamental parameters of the standard
model from experiment. Recent lattice determinations of such quantities as the
kaon parameter, the mass of the quark, and the strong coupling constant
have produced results and uncertainties as good or better than the best
conventional determinations. Many other calculations crucial to extracting the
fundamental parameters of the standard model from experimental data are
undergoing very active development. I review the status of such applications of
lattice QCD to standard model phenomenology, and discuss the prospects for the
near future.Comment: 20 pages, 8 embedded figures, uuencoded, 2 missing figures. (Talk
presented at the Lepton-Photon Symposium, Cornell University, Aug. 10-15,
1993.
High power laser apparatus and system
A high-power, continuous-wave laser was designed for use in power transmission and energy-collecting systems, and for producing incoherent light for pumping a laser material. The laser has a high repetitive pulsing rate per unit time, resulting in a high-power density beam. The laser is composed of xenon flash tubes powered by fast-charging capacitors flashed in succession by a high-speed motor connected to an automobile-type distributor
Highly loaded multi-stage fan drive turbine: Leaned stator configuration design
The results of the high lift blade configuration design study are reported. The three-stage constant-inside-diameter turbine utilizes a ten degree tangentially leaned stator in stage three. All other bladerows use plain blades. Analysis of the leaned stator is discussed, and detailed design data are summarized. Steady-state stresses are discussed, and the results of the mechanical design analysis are presented
Rapidly pulsed, high intensity, incoherent light source
A rapid pulsing, high intensity, incoherent light is produced by selectively energizing a plurality of discharge lamps with a triggering circuit. Each lamp is connected to a capacitor, and a power supply is electrically connected to all but one of the capacitors. This last named capacitor is electrically connected to a discharge lamp which is connected to the triggering circuit
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