10,067 research outputs found
Spherical orbit closures in simple projective spaces and their normalizations
Let G be a simply connected semisimple algebraic group over an algebraically
closed field k of characteristic 0 and let V be a rational simple G-module of
finite dimension. If G/H \subset P(V) is a spherical orbit and if X is its
closure, then we describe the orbits of X and those of its normalization. If
moreover the wonderful completion of G/H is strict, then we give necessary and
sufficient combinatorial conditions so that the normalization morphism is a
homeomorphism. Such conditions are trivially fulfilled if G is simply laced or
if H is a symmetric subgroup.Comment: 24 pages, LaTeX. v4: Final version, to appear in Transformation
Groups. Simplified some proofs and corrected minor mistakes, added
references. v3: major changes due to a mistake in previous version
XMM-Newton EPIC and OM observation of Nova Centauri 1986 (V842 Cen)
We report the results from the temporal and spectral analysis of an
XMM-Newton observation of Nova Centauri 1986 (V842 Cen). We detect a period at
3.510.4 h in the EPIC data and at 4.00.8 h in the OM data. The X-ray
spectrum is consistent with the emission from an absorbed thin thermal plasma
with a temperature distribution given by an isobaric cooling flow. The maximum
temperature of the cooling flow model is keV. Such a
high temperature can be reached in a shocked region and, given the periodicity
detected, most likely arises in a magnetically-channelled accretion flow
characteristic of intermediate polars. The pulsed fraction of the 3.51 h
modulation decreases with energy as observed in the X-ray light curves of
magnetic CVs, possibly due either to occultation of the accretion column by the
white dwarf body or phase-dependent to absorption. We do not find the 57 s
white dwarf spin period, with a pulse amplitude of 4 mmag, reported by Woudt et
al. (2009) either in the Optical Monitor (OM) data, which are sensitive to
pulse amplitudes 0.03 magnitudes, or the EPIC data, sensitive to
pulse fractions 14 2%.Comment: 5 pages, 3 figures; MNRAS, accepte
The importance of measuring skin resistance for electrical nociceptive stimulation in standing horses
Sedative and antinociceptive effects of different combinations of detomidine and methadone in standing horses
Chaotic Waveguide-Based Resonators for Microlasers
We propose the construction of highly directional emission microlasers using
two-dimensional high-index semiconductor waveguides as {\it open} resonators.
The prototype waveguide is formed by two collinear leads connected to a cavity
of certain shape. The proposed lasing mechanism requires that the shape of the
cavity yield mixed chaotic ray dynamics so as to have the appropiate (phase
space) resonance islands. These islands allow, via Heisenberg's uncertainty
principle, the appearance of quasi bound states (QBS) which, in turn,
propitiate the lasing mechanism. The energy values of the QBS are found through
the solution of the Helmholtz equation. We use classical ray dynamics to
predict the direction and intensity of the lasing produced by such open
resonators for typical values of the index of refraction.Comment: 5 pages, 5 figure
Water, land and carbon footprints of Chinese dairy in the past and future
Chinese food consumption shifts towards larger milk consumption. Traditional dairy systems depended on China's grasslands, but modern industrial systems using feed from croplands increase rapidly. The question is whether China can fulfill future milk demand using its natural resources and remain within greenhouse gas emission boundaries. To determine this, this study combines three footprint analyses - water footprint (WF), land footprint (LF) and carbon footprint (CF) - estimated via production chain approach. It compares WFs, LFs and CFs of milk, meat, and manure from six dairy systems in three categories: traditional grazing, traditional mixed, and modern industrial systems. It estimates future footprints for five production scenarios for low and high milk demand. Between 2000 and 2020, industrial systems increased, accounting for 79 % of production in 2020, while traditional production decreased. Traditional grazing systems have large green WFs per kg (17.2 m3), negligible blue WFs and large LFs (46 m2 low quality grassland). Traditional mixed systems have large CFs per kg (2.93 kg CO2) due to low efficiency. Modern industrial systems rely partly on irrigated croplands and have small green WFs, but large blue WFs per kg (0.54 m3), grey WFs (0.24 m3) and small LFs (1.80 m2 cropland). The findings indicate that with dominating industrial systems, milk production relies more on irrigation and limited croplands. In a realistic low demand situation, milk consumption stabilizes. However, consumption triples if the Chinese follow nutritional advice, resulting in 4 to 6 times larger WFs, LFs and CFs in 2035 depending on production scenarios. In 2035, population is largest, from 2035 to 2050 footprints decrease again. However, China cannot produce the milk for a high consumption situation limited by grassland and cropland availability. Alternatively, China could import feed or milk. However, it is questionable whether these huge quantities are available on the global market.</p
Effect of electroacupuncture (EA) on gastrointestinal peristaltism in dogs
The article has no abstract
Scattering Angles in Kerr Metrics
Scattering angles for probes in Kerr metrics are derived for scattering in the equatorial plane of the black hole. We use a method that naturally resums all orders in the spin of the Kerr black hole, thus facilitating comparisons with scattering-angle computations based on the Post-Minkowskian expansion from scattering amplitudes or worldline calculations. We extend these results to spinning black-hole probes up to and including second order in the probe spin and any order in the Post- Minkowskian expansion, for probe spins aligned with the Kerr spin. When truncating to third Post-Minkowskian order, our results agree with those obtained by amplitude and worldline methods
A multi-wavelength study of star formation activity in the S235 complex
We have carried out an extensive multi-wavelength study to investigate the
star formation process in the S235 complex. The S235 complex has a sphere-like
shell appearance at wavelengths longer than 2 m and harbors an O9.5V type
star approximately at its center. Near-infrared extinction map traces eight
subregions (having A 8 mag), and five of them appear to be
distributed in an almost regularly spaced manner along the sphere-like shell
surrounding the ionized emission. This picture is also supported by the
integrated CO and CO intensity maps and by Bolocam 1.1 mm
continuum emission. The position-velocity analysis of CO reveals an almost
semi-ring like structure, suggesting an expanding H\,{\sc ii} region. We find
that the Bolocam clump masses increase as we move away from the location of the
ionizing star. This correlation is seen only for those clumps which are
distributed near the edges of the shell. Photometric analysis reveals 435 young
stellar objects (YSOs), 59\% of which are found in clusters. Six subregions
(including five located near the edges of the shell) are very well correlated
with the dust clumps, CO gas, and YSOs. The average values of Mach numbers
derived using NH data for three (East~1, East~2, and Central~E) out of
these six subregions are 2.9, 2.3, and 2.9, indicating these subregions are
supersonic. The molecular outflows are detected in these three subregions,
further confirming the on-going star formation activity. Together, all these
results are interpreted as observational evidence of positive feedback of a
massive star.Comment: 28 pages, 15 figures, 3 tables, Accepted for publication in The
Astrophysical Journa
Increasing activity in T CrB suggests nova eruption is impending
Estimates of the accretion rate in symbiotic recurrent novae (RNe) often fall
short of theoretical expectations by orders of magnitude. This apparent
discrepancy can be resolved if the accumulation of mass by the white dwarf (WD)
is highly sporadic, and most observations are performed during low states. Here
we use a reanalysis of archival data from the Digital Access to a Sky Century
@Harvard (DASCH) survey to argue that the most recent nova eruption in
symbiotic RN T CrB, in 1946, occurred during -- and was therefore triggered by
-- a transient accretion high state. Based on similarities in the optical light
curve around 1946 and the time of the prior eruption, in 1866, we suggest that
the WD in T CrB accumulates most of the fuel needed to ignite the thermonuclear
runaways (TNRs) during accretion high states. A natural origin for such states
is dwarf-nova like accretion-disk instabilities, which are expected in the
presumably large disks in symbiotic binaries. The timing of the TNRs in
symbiotic RNe could thus be set by the stability properties of their accretion
disks. T CrB is in the midst of an accretion high state like the ones we posit
led to the past two nova eruptions. Combined with the approach of the time at
which a TNR would be expected based on the 80-year interval between the prior
two novae (3), the current accretion high state increases the
likelihood of a TNR occurring in T CrB in the next few years.Comment: Accepted in ApJ
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