11,328 research outputs found
The issue of time in generally covariant theories and the Komar-Bergmann approach to observables in general relativity
Diffeomorphism-induced symmetry transformations and time evolution are
distinct operations in generally covariant theories formulated in phase space.
Time is not frozen. Diffeomorphism invariants are consequently not necessarily
constants of the motion. Time-dependent invariants arise through the choice of
an intrinsic time, or equivalently through the imposition of time-dependent
gauge fixation conditions. One example of such a time-dependent gauge fixing is
the Komar-Bergmann use of Weyl curvature scalars in general relativity. An
analogous gauge fixing is also imposed for the relativistic free particle and
the resulting complete set time-dependent invariants for this exactly solvable
model are displayed. In contrast with the free particle case, we show that
gauge invariants that are simultaneously constants of motion cannot exist in
general relativity. They vary with intrinsic time
Effect of current corrugations on the stability of the tearing mode
The generation of zonal magnetic fields in laboratory fusion plasmas is
predicted by theoretical and numerical models and was recently observed
experimentally. It is shown that the modification of the current density
gradient associated with such corrugations can significantly affect the
stability of the tearing mode. A simple scaling law is derived that predicts
the impact of small stationary current corrugations on the stability parameter
. The described destabilization mechanism can provide an explanation
for the trigger of the Neoclassical Tearing Mode (NTM) in plasmas without
significant MHD activity.Comment: Accepted to Physics of Plasma
Gossip on Weighted Networks
We investigate how suitable a weighted network is for gossip spreading. The
proposed model is based on the gossip spreading model introduced by Lind et.al.
on unweighted networks. Weight represents "friendship." Potential spreader
prefers not to spread if the victim of gossip is a "close friend". Gossip
spreading is related to the triangles and cascades of triangles. It gives more
insight about the structure of a network.
We analyze gossip spreading on real weighted networks of human interactions.
6 co-occurrence and 7 social pattern networks are investigated. Gossip
propagation is found to be a good parameter to distinguish co-occurrence and
social pattern networks. As a comparison some miscellaneous networks and
computer generated networks based on ER, BA, WS models are also investigated.
They are found to be quite different than the human interaction networks.Comment: 8 pages, 4 figures, 1 tabl
Lagrangian approach to a symplectic formalism for singular systems
We develop a Lagrangian approach for constructing a symplectic structure for
singular systems. It gives a simple and unified framework for understanding the
origin of the pathologies that appear in the Dirac-Bergmann formalism, and
offers a more general approach for a symplectic formalism, even when there is
no Hamiltonian in a canonical sense. We can thus overcome the usual limitations
of the canonical quantization, and perform an algebraically consistent
quantization for a more general set of Lagrangian systems.Comment: 30 page
A New Superwind Wolf-Rayet Galaxy Mrk 1259
We report the discovery of a starburst-driven wind (superwind) from the
starburst nucleus galaxy Mrk 1259. The estimated number ratio of Wolf-Rayet
(WR) to O stars amounts to ~0.09. While the nuclear emission-line region is due
to usual photoionization by massive stars, the circumnuclear emission-line
regions show anomalous line ratios that can be due to cooling shocks. Since the
host galaxy seems to be a face-on disk galaxy and the excitation conditions of
the circumnuclear emission-line regions show the spatial symmetry, we consider
that we are seeing the superwind nearly from a pole-on view. Cooling shock
models may explain the observed emission line ratios of the circumnuclear
regions although a factor of 2 overabundance of nitrogen is necessary. All
these suggest that the high-mass enhanced starburst occurred ~5X10^6 years ago
in the nuclear region of Mrk 1259.Comment: To be published in the Astrophysical Journal Letters, 15 pages, 4
figure
Numerical Calculation of the Fidelity for the Kondo and the Friedel-Anderson Impurities
The fidelities of the Kondo and the Friedel-Anderson (FA) impurities are
calculated numerically. The ground states of both systems are calculated with
the FAIR (Friedel artificially inserted resonance) theory. The ground state in
the interacting systems is compared with a nullstate in which the interaction
is zero. The different multi-electron states are expressed in terms of Wilson
states. The use of N Wilson states simulates the use of a large effective
number N_{eff} of states. A plot of ln(F) versus N\proptoln(N_{eff}) reveals
whether one has an Anderson orthogonality catastrophe at zero energy. The
results are at first glance surprising. The ln(F)-ln(N_{eff}) plot for the
Kondo impurity diverges for large N_{eff}. On the other hand, the corresponding
plot for the symmetric FA impurity saturates for large N_{eff} when the level
spacing at the Fermi level is of the order of the singlet-triplet excitation
energy. The behavior of the fidelity allows one to determine the phase shift of
the electron states in this regime. PACS: 75.20.Hr, 71.23.An, 71.27.+a,
05.30.-
The Nature of the Optical Light in Seyfert 2 Galaxies with Polarized Continuum
We investigate the nature of the optical continuum and stellar population in
the central kpc of the Seyfert 2s Mrk 348, Mrk 573, NGC 1358 and Mrk 1210 using
long-slit spectra obtained along the radio or extended emission axis. These
galaxies are known to have polarized continuum-including polarized broad lines
in Mrk 348 and Mrk 1210--and previous studies indicate featureless continuum
(FC) contributions in the 20-50% range at 5500 A. Nevertheless, our
measurements of the equivalent widths of absorption lines and continuum ratios
as a function of distance from the nuclei show no dilution of the lines nor
bluening of the spectrum, as expected if a blue FC was present at the nucleus
in the above proportions. We investigate one possibility to account for this
effect: that the stellar population at the nucleus is the same as that from the
surrounding bulge and dominates the nuclear light. A spectral analysis confirms
that this hypothesis works for Mrk 348, NGC 1358 and Mrk 1210, for which we
find stellar contributions at the nucleus larger than 90% at all wavelengths.
We find that a larger stellar population contribution to the nuclear spectra
can play the role of the ``second FC'' source inferred from previous studies.
Stellar population synthesis shows that the nuclear regions of Mrk 348 and Mrk
1210 have important contributions of young to intermediate age stars (0--100
Myr), not present in templates of elliptical galaxies. In the case of Mrk 1210,
this is further confirmed by the detection of a ``Wolf-Rayet feature'' in the
nuclear emission-line spectrum.Comment: ApJ, accepted. Uses aaspp4.sty. [22 pages
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