3,584 research outputs found
Axial Ratio of Edge-On Spiral Galaxies as a Test For Extended Bright Radio Halos
We use surface brightness contour maps of nearby edge-on spiral galaxies to
determine whether extended bright radio halos are common. In particular, we
test a recent model of the spatial structure of the diffuse radio continuum by
Subrahmanyan and Cowsik which posits that a substantial fraction of the
observed high-latitude surface brightness originates from an extended Galactic
halo of uniform emissivity. Measurements of the axial ratio of emission
contours within a sample of normal spiral galaxies at 1500 MHz and below show
no evidence for such a bright, extended radio halo. Either the Galaxy is
atypical compared to nearby quiescent spirals or the bulk of the observed
high-latitude emission does not originate from this type of extended halo.Comment: 6 Pages, 4 Figures, 1 Table; To Appear In ApJ Letter
Discrimination in Government Employment in South Carolina
This paper assesses the success of the extensive efforts by federal, state and local governments to obtain equality of opportunity for minority group members in government positions in South Carolina. The study uses the 5% Public Use Microdata Sample from the 2000 Census to ascertain if employment of minority group members in government positions is consistent with its proportionality in the available labor force. The findings suggest, that after more than 30 years of efforts to obtain equality of employment opportunity in federal, state and local governments in South Carolina, significant progress has been made to ensure equality of opportunity for African Americans but more work is needed if equality is to be achieved for all minority group members
QCD at finite isospin density
QCD at finite isospin chemical potential mu_I has no fermion sign problem and
can be studied on the lattice. We solve this theory analytically in two limits:
at low mu_I where chiral perturbation theory is applicable, and at
asymptotically high mu_I where perturbative QCD works. At low isospin density
the ground state is a pion condensate, whereas at high density it is a Fermi
liquid with Cooper pairing. The pairs carry the same quantum numbers as the
pion. This leads us to a conjecture that the transition from hadron to quark
matter is smooth, which passes several tests. Our results imply a nontrivial
phase diagram in the space of temperature and chemical potentials of isospin
and baryon number.Comment: 4 pages, 1 figure, version to appear in PR
Pathologies of Quenched Lattice QCD at non--zero Density and its Effective Potential
We simulate lattice QCD at non--zero baryon density and zero temperature in
the quenched approximation, both in the scaling region and in the infinite
coupling limit. We investigate the nature of the forbidden region -- the range
of chemical potential where the simulations grow prohibitively expensive, and
the results, when available, are puzzling if not unphysical. At weak coupling
we have explored the sensitivity of these pathologies to the lattice size, and
found that using a large lattice () does not remove them. The
effective potential sheds considerable light on the problems in the
simulations, and gives a clear interpretation of the forbidden region. The
strong coupling simulations were particularly illuminating on this point.Comment: 49 pages, uu-encoded expanding to postscript;also available at
ftp://hlrz36.hlrz.kfa-juelich.de/pub/mpl/hlrz72_95.p
The Phase Diagram of Compact QED Coupled to a Four-Fermi Interaction
Compact lattice Quantum Electrodynamics (QED) with four species of fermions
is simulated with massless quarks by using the QED scheme of adding a
four-fermi interaction to the action. Simulations directly in the chiral limit
of massless quarks are done with high statistics on , and lattices,
and the phase diagram, parameterized by the gauge and the four-fermi couplings,
is mapped out. The line of monopole condensation transitions is separate from
the line of chiral symmetry restoration. The simulation results indicate that
the monopole condensation transition is first order while the chiral transition
is second order. The challenges in determining the Universality class of the
chiral transition are discussed. If the scaling region for the chiral
transition is sufficiently wide, the simulations predict critical
indices far from mean field values. We discuss a speculative scenario in which
anti-screening provided by double-helix strands of monopole and anti-monopole
loops are the agent that balances the screening of fermion anti-fermion pairs
to produce an ultra-violet fixed point in the electric coupling.Comment: 29 pages, 8 figures and 2 table
Excitation of the High-Q-factor Whispering Gallery Modes in the Hemispherical Dielectric Resonator with the Cylinder Shield
A hollow metal cylinder with a semicircle in the base is used as the shield of a hemispherical dielectric resonator with whispering gallery (WG) modes. It is shown that the spectrum of the WG modes of this resonator is clearer than the spectrum of a similar resonator with a hemispherical shield. It is determined that the high-Q-factor WG modes are excited in the proposed resonator by the coupling slot on the mirror. Their fields are localized in the dielectric. The frequency dependence of the Q-factor value is measured. A good conformity of this experimental dependence with the analytic dependence is obtained in this pape
Millimeter Wave Oscillator Based Dielectric Hemisphere with Cylinder Shield
The purpose of this paper is the investigation of the main Gunn diode oscillator characteristics with a hemispherical dielectric resonator which is shielded by a metal cylinder. The frequency, output power and electronic tuning of frequency, the steepness of which allows one to estimate the frequency stability in relation to the parasitic change of the Gunn diode voltage, and their comparative analysis with the characteristics of generation in a similar open dielectric resonator
Search For Unresolved Sources In The COBE-DMR Two-Year Sky Maps
We have searched the temperature maps from the COBE Differential Microwave
Radiometers (DMR) first two years of data for evidence of unresolved sources.
The high-latitude sky (|b| > 30\deg) contains no sources brighter than 192 uK
thermodynamic temperature (322 Jy at 53 GHz). The cumulative count of sources
brighter than threshold T, N(> T), is consistent with a superposition of
instrument noise plus a scale-invariant spectrum of cosmic temperature
fluctuations normalized to Qrms-PS = 17 uK. We examine the temperature maps
toward nearby clusters and find no evidence for any Sunyaev-Zel'dovich effect,
\Delta y < 7.3 x 10^{-6} (95% CL) averaged over the DMR beam. We examine the
temperature maps near the brightest expected radio sources and detect no
evidence of significant emission. The lack of bright unresolved sources in the
DMR maps, taken with anisotropy measurements on smaller angular scales, places
a weak constraint on the integral number density of any unresolved
Planck-spectrum sources brighter than flux density S, n(> S) < 2 x 10^4 (S/1
Jy)^{-2} sr^{-1}.Comment: 16 pages including 2 figures, uuencoded PostScript, COBE preprint
94-0
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