18,116 research outputs found
Quadrupole Instabilities of Relativistic Rotating Membranes
We generalize recent study of the stability of isotropic (spherical) rotating
membranes to the anisotropic ellipsoidal membrane. We find that while the
stability persists for deformations of spin , the quadrupole and higher
spin deformations () lead to instabilities. We find the relevant
instability modes and the corresponding eigenvalues. These indicate that the
ellipsoidal rotating membranes generically decay into finger-like
configurations.Comment: 5 pages, 1 figur
The spectroscopic evolution of the -ray emitting classical nova Nova Mon 2012. I. Implications for the ONe subclass of classical novae
Nova Mon 2012 was the first classical nova to be detected as a high energy
-ray transient, by Fermi-LAT, before its optical discovery. We study a
time sequence of high resolution optical echelle spectra (Nordic Optical
Telescope) and contemporaneous NOT, STIS UV, and CHIRON echelle spectra (Nov
20/21/22). We use [O III] and H line fluxs to constrain the properties
of the ejecta. We derive the structure from the optical and UV line profiles
and compare our measured line fluxes for with predictions using Cloudy with
abundances from other ONe novae. Mon 2012 is confirmed as an ONe nova. We find
E(B-V)=0.850.05 and hydrogen column density
cm. The corrected continuum luminosity is nearly the same in the entire
observed energy range as V1974 Cyg, V382 Mon, and Nova LMC 2000 at the same
epoch after outburst. The distance, about 3.6 kpc, is quite similar to V1974
Cyg. The line profiles can be modeled using an axisymmetric bipolar geometry
for the ejecta with various inclinations of the axis to the line of sight, 60
\le i \le 80 degrees, an opening angle of \approx\Delta
R/R(t)\approx 0.4f\approx 0.1-0.3\leq 6\times
10^{-5}_\odot\gamma$-ray emission may be a generic phenomenon, common to all ONe novae,
possibly to all classical novae, and connected with acceleration and emission
processes within the ejecta (abstract severely truncated).Comment: Submitted to A&A 9/1/2013; Accepted 27/2/2013 (in press
The spectroscopic evolution of the recurrent nova T Pyxidis during its 2011 outburst. II.The optically thin phase and the structure of the ejecta in recurrent novae
We continue our study of the physical properties of the recurrent nova T Pyx,
focussing on the structure of the ejecta in the nebular stage of expansion
during the 2011 outburst. The nova was observed contemporaneously with the
Nordic Optical Telescope (NOT), at high resolution spectroscopic resolution (R
~ 65000) on 2011 Oct. 11 and 2012 Apr. 8 (without absolute flux calibration),
and with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble
Space Telescope, at high resolution (R ~ 30000) on 2011 Oct. 10 and 2012 Mar.
28 (absolute fluxes). We use standard plasma diagnostics (e.g. [O III] and [N
II] line ratios and the H line fluxes) to constrain electron densities
and temperatures. Using Monte Carlo modeling of the ejecta, we derive the
structure and filling factor from comparisons to the optical and ultraviolet
line profiles. The ejecta can be modeled using an axisymmetric conical --
bipolar -- geometry with a low inclination of the axis to the line of sight,
i=15+/-5 degrees, compatible with published results from high angular
resolution optical spectro-interferometry. The structure is similar to that
observed in the other short orbital period recurrent novae during their nebular
stages. We show that the electron density scales as as expected from a
ballistically ejected constant mass shell; there is no need to invoke a
continuing mass outflow following the eruption. The derived mass for the ejecta
with filling factor f ~ 3%, M_ej ~ 2E-6$M_sun is similar to that obtained for
other recurrent nova ejecta but inconsistent with the previously reported
extended optically thick epoch of the explosion. We suggest that the system
underwent a common envelope phase following the explosion that produced the
recombination event. Implications for the dynamics of the recurrent novae are
discussed. (truncated)Comment: accepted for publication in A&A (10 Nov. 2012), 10 pgs, 16 fig
QP-Structures of Degree 3 and 4D Topological Field Theory
A A BV algebra and a QP-structure of degree 3 is formulated. A QP-structure
of degree 3 gives rise to Lie algebroids up to homotopy and its algebraic and
geometric structure is analyzed. A new algebroid is constructed, which derives
a new topological field theory in 4 dimensions by the AKSZ construction.Comment: 17 pages, Some errors and typos have been correcte
How strong is the evidence for accelerated expansion?
We test the present expansion of the universe using supernova type Ia data
without making any assumptions about the matter and energy content of the
universe or about the parameterization of the deceleration parameter. We assume
the cosmological principle to apply in a strict sense. The result strongly
depends on the data set, the light-curve fitting method and the calibration of
the absolute magnitude used for the test, indicating strong systematic errors.
Nevertheless, in a spatially flat universe there is at least a 5 sigma evidence
for acceleration which drops to 1.8 sigma in an open universe.Comment: 16 pages, 3 figure
Relating Spin Foams and Canonical Quantum Gravity: A Discrete Step Evolution Formulation of Spin Foams
This article has been replaced by gr-qc/0412011Comment: This article has been replaced by gr-qc/041201
Friction Laws for Elastic Nano-Scale Contacts
The effect of surface curvature on the law relating frictional forces F with
normal load L is investigated by molecular dynamics simulations as a function
of surface symmetry, adhesion, and contamination. Curved, non-adhering, dry,
commensurate surfaces show a linear dependency, F proportional to L, similar to
dry flat commensurate or amorphous surfaces and macroscopic surfaces. In
contrast, curved, non-adhering, dry, amorphous surfaces show F proportional to
L^(2/3) similar to friction force microscopes. In our model, adhesive effects
are most adequately described by the Hertz plus offset model, as the
simulations are confined to small contact radii. Curved lubricated or
contaminated surfaces show again different behavior; details depend on how much
of the contaminant gets squeezed out of the contact. Also, it is seen that the
friction force in the lubricated case is mainly due to atoms at the entrance of
the tip.Comment: 7 pages, 5 figures, submitted to Europhys. Let
Topological Field Theories and Geometry of Batalin-Vilkovisky Algebras
The algebraic and geometric structures of deformations are analyzed
concerning topological field theories of Schwarz type by means of the
Batalin-Vilkovisky formalism. Deformations of the Chern-Simons-BF theory in
three dimensions induces the Courant algebroid structure on the target space as
a sigma model. Deformations of BF theories in dimensions are also analyzed.
Two dimensional deformed BF theory induces the Poisson structure and three
dimensional deformed BF theory induces the Courant algebroid structure on the
target space as a sigma model. The deformations of BF theories in
dimensions induce the structures of Batalin-Vilkovisky algebras on the target
space.Comment: 25 page
Density Waves Inside Inner Lindblad Resonance: Nuclear Spirals in Disk Galaxies
We analyze formation of grand-design two-arm spiral structure in the nuclear
regions of disk galaxies. Such morphology has been recently detected in a
number of objects using high-resolution near-infrared observations. Motivated
by the observed (1) continuity between the nuclear and kpc-scale spiral
structures, and by (2) low arm-interarm contrast, we apply the density wave
theory to explain the basic properties of the spiral nuclear morphology. In
particular, we address the mechanism for the formation, maintenance and the
detailed shape of nuclear spirals. We find, that the latter depends mostly on
the shape of the underlying gravitational potential and the sound speed in the
gas. Detection of nuclear spiral arms provides diagnostics of mass distribution
within the central kpc of disk galaxies. Our results are supported by 2D
numerical simulations of gas response to the background gravitational potential
of a barred stellar disk. We investigate the parameter space allowed for the
formation of nuclear spirals using a new method for constructing a
gravitational potential in a barred galaxy, where positions of resonances are
prescribed.Comment: 18 pages, 9 figures, higher resolution available at
http://www.pa.uky.edu/~ppe/papers/nucsp.ps.g
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