1,807 research outputs found
Direct Microlensing-Reverberation Observations of the Intrinsic magnetic Structure of AGN in Different Spectral States: A Tale of Two Quasars
We show how direct microlensing-reverberation analysis performed on two
well-known Quasars (Q2237 - The Einstein Cross and Q0957 - The Twin) can be
used to observe the inner structure of two quasars which are in significantly
different spectral states. These observations allow us to measure the detailed
internal structure of quasar Q2237 in a radio quiet high-soft state, and
compare it to quasar Q0957 in a radio loud low-hard state. We find that the
observed differences in the spectral states of these two quasars can be
understood as being due to the location of the inner radii of their accretion
disks relative to the co-rotation radii of rotating intrinsically magnetic
supermassive compact objects in the centers of these quasars.Comment: 26 page manuscript with 2 tables and 2 figures, submitted to
Astronomical Journa
On the optical counterpart of NGC300 X-1 and the global Wolf-Rayet content of NGC300
(Conext:) Surveys of Wolf-Rayet (WR) populations in nearby galaxies provide
tests of evolutionary models plus Type Ib/c supernova progenitors. This
spectroscopic study complements the recent imaging survey of the spiral galaxy
NGC 300 by Schild et al. (Aims): Revisions to the known WR content of NGC 300
are presented. We investigate the WR nature of candidate #41 from Schild et al.
which is spatially coincident with the bright X-ray point source NGC 300 X-1;
(Methods:) VLT/FORS2 multi-object spectroscopy of WR candidates in NGC 300 is
obtained; (Results:) We establish an early-type WN nature of #41, i.e. similar
to the optical counterpart of IC 10 X-1, which closely resembles NGC 300 X-1.
We confirm 9 new WR stars, bringing the current WR census of the inner disk to
31, with N(WC)/N(WN)~0.9. (Conclusions:) If #41 is the optical counterpart for
NGC 300 X-1, we estimate a WR mass of 38 Msun based upon ground-based
photometry, from which a black hole mass of > 10 Msun results from the 32.8 hr
period of the system and WR wind velocity of 1250 km/s. We estimate an 95%
completeness among WC stars and 70% among WN stars, such that the total WR
content is ~40, with N(WC)/N(WN)~0.7. From the Halpha-derived star formation
rate of the inner galaxy, we infer N(WR)/N(O)~0.04Comment: 5 pages, 5 figures, accepted for A&A Letter
Global embedding of the Kerr black hole event horizon into hyperbolic 3-space
An explicit global and unique isometric embedding into hyperbolic 3-space,
H^3, of an axi-symmetric 2-surface with Gaussian curvature bounded below is
given. In particular, this allows the embedding into H^3 of surfaces of
revolution having negative, but finite, Gaussian curvature at smooth fixed
points of the U(1) isometry. As an example, we exhibit the global embedding of
the Kerr-Newman event horizon into H^3, for arbitrary values of the angular
momentum. For this example, considering a quotient of H^3 by the Picard group,
we show that the hyperbolic embedding fits in a fundamental domain of the group
up to a slightly larger value of the angular momentum than the limit for which
a global embedding into Euclidean 3-space is possible. An embedding of the
double-Kerr event horizon is also presented, as an example of an embedding
which cannot be made global.Comment: 16 pages, 13 figure
Null Strings in Schwarzschild Spacetime
The null string equations of motion and constraints in the Schwarzschild
spacetime are given. The solutions are those of the null geodesics of General
Relativity appended by a null string constraint in which the "constants of
motion" depend on the world-sheet spatial coordinate. Because of the extended
nature of a string, the physical interpretation of the solutions is completely
different from the point particle case. In particular, a null string is
generally not propagating in a plane through the origin, although each of its
individual points is. Some special solutions are obtained and their physical
interpretation is given. Especially, the solution for a null string with a
constant radial coordinate moving vertically from the south pole to the
north pole around the photon sphere, is presented. A general discussion of
classical null/tensile strings as compared to massless/massive particles is
given. For instance, tensile circular solutions with a constant radial
coordinate do not exist at all. The results are discussed in relation to
the previous literature on the subject.Comment: 16 pages, REVTEX, no figure
Stiff Stability of the Hydrogen atom in dissipative Fokker electrodynamics
We introduce an ad-hoc electrodynamics with advanced and retarded
Lienard-Wiechert interactions plus the dissipative Lorentz-Dirac
self-interaction force. We study the covariant dynamical system of the
electromagnetic two-body problem, i.e., the hydrogen atom. We perform the
linear stability analysis of circular orbits for oscillations perpendicular to
the orbital plane. In particular we study the normal modes of the linearized
dynamics that have an arbitrarily large imaginary eigenvalue. These large
eigenvalues are fast frequencies that introduce a fast (stiff) timescale into
the dynamics. As an application, we study the phenomenon of resonant
dissipation, i.e., a motion where both particles recoil together in a drifting
circular orbit (a bound state), while the atom dissipates center-of-mass energy
only. This balancing of the stiff dynamics is established by the existence of a
quartic resonant constant that locks the dynamics to the neighborhood of the
recoiling circular orbit. The resonance condition quantizes the angular momenta
in reasonable agreement with the Bohr atom. The principal result is that the
emission lines of quantum electrodynamics (QED) agree with the prediction of
our resonance condition within one percent average deviation.Comment: 1 figure, Notice that Eq. (34) of the Phys. Rev. E paper has a typo;
it is missing the square Brackets of eq. (33), find here the correct e
Lissencephaly-pachygyria and cerebellar hypoplasia in a calf.
ABSTRACT: A case of lissencephaly-pachygyria and cerebellar hypoplasia diagnosed in a Charolais x TabapuĂŁ calf is described. The calf presented since birth, clinical signs characterized by apathy, prolonged recumbency, tremors of the head and neck, ataxia, hypermetria, difficulty walking, blindness and swelling of the joints of the four limbs. Due to the unfavorable prognosis, the animal was euthanized and necropsied at 34 days of age. At necropsy, a rudimentary development of the brain folds (gyri) and grooves (sulci) was observed, and the cerebellum was hypoplastic. The cut surface of the brain exhibited thickening of the gray matter (pachygyria) in the frontal, parietal, temporal and occipital cortices and narrowing of the white matter. In the organs of the thoracic and abdominal cavities, no significant lesions were observed. Histologically, cerebral cortex was thick and exhibited neuronal disorganization of the gray matter. The cerebellum had a thin molecular layer, and neuronal disorganization with ectopia of the Purkinje neurons in the region of the granular and molecular layers. There were no bacterial growths in cultures of joint swabs. This was the only case on the property, which suggests that this malformation, which has not previously been described in cattle, was a sporadic case, and it was not possible to determine its cause. Neurological lesions and clinical sings presented here should be considered in the differential diagnosis of congenital diseases of the central nervous systems of cattle
Fluctuation theorem for constrained equilibrium systems
We discuss the fluctuation properties of equilibrium chaotic systems with
constraints such as iso-kinetic and Nos\'e-Hoover thermostats. Although the
dynamics of these systems does not typically preserve phase-space volumes, the
average phase-space contraction rate vanishes, so that the stationary states
are smooth. Nevertheless finite-time averages of the phase-space contraction
rate have non-trivial fluctuations which we show satisfy a simple version of
the Gallavotti-Cohen fluctuation theorem, complementary to the usual
fluctuation theorem for non-equilibrium stationary states, and appropriate to
constrained equilibrium states. Moreover we show these fluctuations are
distributed according to a Gaussian curve for long-enough times. Three
different systems are considered here, namely (i) a fluid composed of particles
interacting with Lennard-Jones potentials; (ii) a harmonic oscillator with
Nos\'e-Hoover thermostatting; (iii) a simple hyperbolic two-dimensional map.Comment: To appear in Phys. Rev.
Multiwavelength evidence for a 15-year periodic activity in the symbiotic nova V1016 Cygni
The ~15.1 years period found in the long-term UBV photoelectric and
photographic photometry of the symbiotic nova V1016 Cyg is detected also in the
(J-K) colour index and in the UV continuum and emission line fluxes from IUE
and HUT spectra. It could be interpreted either as the effect of recurrent
enhanced mass loss episodes from the Mira type variable companion to a hot
component along its ultra-wide orbit (proposed from recent HST observations) or
the true orbital period of the inner, unresolved binary of a triple system. A
410-day delay of the maximum of UV emission lines fluxes with respect to the
maximum of continuum was found. The pulsation period of the Mira type variable
was improved to 474+/-6 days.Comment: 7 pages, 7 PostScript figures. Accepted for pubblication in A&
G91-1026 Sunflower Production in Nebraska
Seeds, seedbed preparations, fertilizing and controlling weeds in sunflowers are among the topics covered here. Sunflowers are native to Nebraska. Cultivated for centuries by native American Indians as a food crop, sunflowers were taken to Europe in the mid-16th century. Oilseed sunflowers have been a U.S. crop since 1986. Sunflower production is divided into two market classes, oil and confectionery. The oil type is by far the most commonly grown market class. Recent health trends have brought sunflower cooking oil into prominence because the oil is low in saturated fats. Confectionery types are grown for the edible roasted sunflower seed market, and are produced under strict contract guidelines. Seed size is critical, with small seeds designated for bird seed market channels. Growing the confectionery type without a contract is risky. Sunflower production of both market classes is currently around 30,000 acres in Nebraska. Recently a third market class has started to develop based on high oleic acid content, which gives products better shelf life
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