50 research outputs found
Mc Neil's Nebula in Orion: The Outburst History
We present a sequence of I-band images obtained at the Venezuela 1m Schmidt
telescope during the outburst of the nebula recently discovered by J.W. McNeil
in the Orion L1630 molecular cloud. We derive photometry spanning the
pre-outburst state and the brightening itself, a unique record including 14
epochs and spanning a time scale of ~5 years. We constrain the beginning of the
outburst at some time between Oct. 28 and Nov. 15, 2003. The light curve of the
object at the vertex of the nebula, the likely exciting source of the outburst,
reveals that it has brightened ~5 magnitudes in about 4 months. The time scale
for the nebula to develop is consistent with the light travel time, indicating
that we are observing light from the central source scattered by the ambient
cloud into the line of sight. We also show recent FLWO optical spectroscopy of
the exciting source and of the nearby HH 22. The spectrum of the source is
highly reddened; in contrast, the spectrum of HH 22 shows a shock spectrum
superimposed on a continuum, most likely due to reflected light from the
exciting source reaching the HH object through a much less reddened path. The
blue portion of this spectrum is consistent with an early B spectral type,
similar to the early outburst spectrum of the FU Ori variable V1057 Cyg; we
estimate a luminosity of L ~219 Lsun. The eruptive behavior of the McNeil
nebula source, its spectroscopic characteristics and luminosity, suggest we may
be witnessing an FU Ori event on its way to maximum. Further monitoring of this
object will decide whether it qualifies as a member of this rare class of
objects.Comment: 13 pages, 4 figures, accepted to ApJ Letter
Control of an outbreak of carbapenem-resistant Acinetobacter baumannii in Australia after introduction of environmental cleaning with a commercial oxidizing disinfectant
In the midst of an outbreak, carbapenem-resistant Acinetobacter baumannii was grown from samples of multiple environmental sites in an intensive care unit. A commercial oxidizing disinfectant (potassium peroxomonosulphate 50%, sodium alkyl benzene sulphonate 15%, and sulphamic acid 5%) was introduced throughout the intensive care unit, and its use coincided with cessation of the outbreak
Simple top-down preparation of magnetic BiGdFeTiO nanoparticles by ultrasonication of multiferroic bulk material
We present a simple technique to synthesize ultrafine nanoparticles directly
from bulk multiferroic perovskite powder. The starting materials, which were
ceramic pellets of the nominal compositions of
BiGdFeTiO (x = 0.00-0.20), were prepared
initially by a solid state reaction technique, then ground into
micrometer-sized powders and mixed with isopropanol or water in an ultrasonic
bath. The particle size was studied as a function of sonication time with
transmission electron microscopic imaging and electron diffraction that
confirmed the formation of a large fraction of single-crystalline nanoparticles
with a mean size of 11-13 nm. A significant improvement in the magnetic
behavior of BiGdFeTiO nanoparticles compared to
their bulk counterparts was observed at room temperature. This sonication
technique may be considered as a simple and promising route to prepare
ultrafine nanoparticles for functional applications.Comment: 7 pages, 5 figure
Low-energy excitations in the three-dimensional random-field Ising model
The random-field Ising model (RFIM), one of the basic models for quenched
disorder, can be studied numerically with the help of efficient ground-state
algorithms. In this study, we extend these algorithm by various methods in
order to analyze low-energy excitations for the three-dimensional RFIM with
Gaussian distributed disorder that appear in the form of clusters of connected
spins. We analyze several properties of these clusters. Our results support the
validity of the droplet-model description for the RFIM.Comment: 10 pages, 9 figure
Multi-messenger observations of a binary neutron star merger
On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta
Identification and rejection of pile-up jets at high pseudorapidity with the ATLAS detector
The rejection of forward jets originating from
additional proton–proton interactions (pile-up) is crucial for
a variety of physics analyses at the LHC, including Standard
Model measurements and searches for physics beyond
the Standard Model. The identification of such jets is challenging
due to the lack of track and vertex information in
the pseudorapidity range |η| > 2.5. This paper presents a
novel strategy for forward pile-up jet tagging that exploits
jet shapes and topological jet correlations in pile-up interactions.
Measurements of the per-jet tagging efficiency are
presented using a data set of 3.2 fb−1 of proton–proton collisions
at a centre-of-mass energy of 13 TeV collected with the
ATLAS detector. The fraction of pile-up jets rejected in the
range 2.5 < |η| < 4.5 is estimated in simulated events with
an average of 22 interactions per bunch-crossing. It increases
with jet transverse momentum and, for jets with transverse
momentum between 20 and 50 GeV, it ranges between 49%
and 67% with an efficiency of 85% for selecting hard-scatter
jets. A case study is performed in Higgs boson production
via the vector-boson fusion process, showing that these techniques
mitigate the background growth due to additional
proton–proton interactions, thus enhancing the reach for such
signatures
Superfluid Thomas - Fermi approximation for trapped fermi gases
We present a generalization of fermionic fluiddynamics to the case of two trapped fermion species with a contact interaction. Within a mean field approximation, we derive coupled equations of motion for the particle densities, particle currents, and anomalous pair density. For an inhomogeneous system, the equilibrium situation with vanishing currents is described by a generalized Thomas-Fermi relation that includes the superfluid gap, together with a new nonlocal gap equation that replaces the usual BCS one. These equations are numericaly solved resorting to a local density approximation (LDA). Density and gap profiles are analyzed in terms of the scattering length, revealing that the current frame can exhibit microscopic details of quantum origin that are frequently absent in more macroscopic scenarios. © 2009 IOP Publishing Ltd.Fil:Capuzzi, P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Szybisz, L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Mammals from ejido ranchitos, Colima, Mexico
The state of Colima in western Mexico is part of the transition zone between the two biogeographic regions of America, the Nearctic and the Neotropical. The state has particularly high mammalian diversity (128 species) and is in the area with the greatest concentration of endemic species in Mexico (25). As a result, there is intrinsic scientific interest in the study of mammals of Colima. However, the mammalian fauna has received only limited attention to date. There is no published comprehensive inventory of mammals of Colima and only a few detailed reports of the species that occur at any given location within the state have been published. As a contribution to the knowledge of mammals present in Colima, data were compiled on the mammals of Ejido Ranchitos, municipality of Minatitln, and the species were characterized. We recorded 35 species, 9 monotypic and 26 polytypic, gathering information on natural history and reproductive condition for each. These represent 27.3 of species of mammals known from Colima and 7.4 of the total for Mexico. Eleven species were endemic, comprising 31.4 of species captured for Ejido Ranchitos and 6.5 of the endemic species for Mexico. Nonvolant mammals exhibited three reproductive patterns: continual polyestrous (10 species, 28.6), seasonal polyestrous (4, 11.4), and seasonal monoestrous (3, 8.6). Reproductive patterns for bats were seasonal monoestrous (7 species, 20.0), asynchronic continual polyestrous (7, 20.0), bimodal polyestrous (2, 5.7), continual polyestrous (1, 2.9), and asynchronic monoestrous (1, 2.9). Three of the species we examined (Heteromys spectabilis, Neotoma mexicana tenuicauda, and Peromyscus hylocetes) have not been reported previously for Colima. Overall, Ejido Ranchitos supports a diverse fauna of small-sized and medium-sized mammals