4,419 research outputs found
Echo Emission From Dust Scattering and X-Ray Afterglows of Gamma-Ray Bursts
We investigate the effect of X-ray echo emission in gamma-ray bursts (GRBs).
We find that the echo emission can provide an alternative way of understanding
X-ray shallow decays and jet breaks. In particular, a shallow decay followed by
a "normal" decay and a further rapid decay of X-ray afterglows can be together
explained as being due to the echo from prompt X-ray emission scattered by dust
grains in a massive wind bubble around a GRB progenitor. We also introduce an
extra temporal break in the X-ray echo emission. By fitting the afterglow light
curves, we can measure the locations of the massive wind bubbles, which will
bring us closer to finding the mass loss rate, wind velocity, and the age of
the progenitors prior to the GRB explosions.Comment: 25 pages, 3 figures, 2 tables. Accepted for publication in Ap
A Catalogue of Inter-Parameter Dependencies in RESTful Web APIs
Web services often impose dependency constraints that re strict the way in which two or more input parameters can be combined
to form valid calls to the service. Unfortunately, current specification
languages for web services like the OpenAPI Specification provide no
support for the formal description of such dependencies, which makes
it hardly possible to automatically discover and interact with services
without human intervention. Researchers and practitioners are openly
requesting support for modelling and validating dependencies among in put parameters in web APIs, but this is not possible unless we share a
deep understanding of how dependencies emerge in practice—the aim of
this work. In this paper, we present a thorough study on the presence
of dependency constraints among input parameters in web APIs in in dustry. The study is based on a review of more than 2.5K operations
from 40 real-world RESTful APIs from multiple application domains.
Overall, our findings show that input dependencies are the norm, rather
than the exception, with 85% of the reviewed APIs having some kind of
dependency among their input parameters. As the main outcome of our
study, we present a catalogue of seven types of dependencies consistently
found in RESTful web APIsMinisterio de Economía y Competitividad BELI (TIN2015-70560-R)Ministerio de Ciencia, Innovación y Universidades Horatio RTI2018-101204-B-C21Ministerio de Educación, Cultura y Deporte FPU17/0407
Physical Structure of Small Wolf-Rayet Ring Nebulae
We have selected the seven most well-defined WR ring nebulae in the LMC (Br
2, Br 10, Br 13, Br 40a, Br 48, Br 52, and Br 100) to study their physical
nature and evolutionary stages. New CCD imaging and echelle observations have
been obtained for five of these nebulae; previous photographic imaging and
echelle observations are available for the remaining two nebulae. Using the
nebular dynamics and abundances, we find that the Br 13 nebula is a
circumstellar bubble, and that the Br 2 nebula may represent a circumstellar
bubble merging with a fossil main-sequence interstellar bubble. The nebulae
around Br 10, Br 52, and Br 100 all show influence of the ambient interstellar
medium. Their regular expansion patterns suggest that they still contain
significant amounts of circumstellar material. Their nebular abundances would
be extremely interesting, as their central stars are WC5 and WN3-4 stars whose
nebular abundances have not been derived previously. Intriguing and tantalizing
implications are obtained from comparisons of the LMC WR ring nebulae with ring
nebulae around Galactic WR stars, Galactic LBVs, LMC LBVs, and LMC BSGs;
however, these implications may be limited by small-number statistics. A SNR
candidate close to Br 2 is diagnosed by its large expansion velocity and
nonthermal radio emission. There is no indication that Br 2's ring nebula
interacts dynamically with this SNR candidate.Comment: 20 pages, Latex (aaspp4.sty), 2 figures, accepted by the Astronomical
Journal (March 99 issue
High‐temperature behavior of impurities and dimensionality of the charge transport in unintentionally and tin‐doped indium selenide
A systematic study of the electron transport and shallow impurity distribution in indium selenide above room temperature or after an annealing process is reported by means of far‐infrared‐absorption and Hall‐effect measurements. Evidences are found for the existence of a large concentration of deep levels (1012–1013 cm−2), related to impurities adsorbed to stacking faults in this material. Above room temperature impurities can migrate from those defect zones and then become shallow in the bulk. The subsequent large increase of 3D electrons can change the dimensionality of the electron transport, which in most cases was 2D. The temperature dependence of the resistivity parallel to the c axis can be explained by the observed increase of the 3D electron concentration, whose motion across the layers is limited by stacking‐fault‐related potential barriers. The observed macroscopic resistivity is thus determined by tunneling through those [email protected]
GSH23.0-0.7+117, a neutral hydrogen shell in the inner Galaxy
GSH23.0-0.7+117 is a well-defined neutral hydrogen shell discovered in the
VLA Galactic Plane Survey (VGPS). Only the blueshifted side of the shell was
detected. The expansion velocity and systemic velocity were determined through
the systematic behavior of the HI emission with velocity. The center of the
shell is at (l,b,v)=(23.05,-0.77,+117 km/s). The angular radius of the shell is
6.8', or 15 pc at a distance of 7.8 kpc. The HI mass divided by the volume of
the half-shell implies an average density n_H = 11 +/- 4 cm^{-3} for the medium
in which the shell expanded. The estimated age of GSH23.0-0.7+117 is 1 Myr,
with an upper limit of 2 Myr. The modest expansion energy of 2 * 10^{48} erg
can be provided by the stellar wind of a single O4 to O8 star over the age of
the shell. The 3 sigma upper limit to the 1.4 GHz continuum flux density
(S_{1.4} < 248 mJy) is used to derive an upper limit to the Lyman continuum
luminosity generated inside the shell. This upper limit implies a maximum of
one O9 star (O8 to O9.5 taking into account the error in the distance) inside
the HI shell, unless most of the incident ionizing flux leaks through the HI
shell. To allow this, the shell should be fragmented on scales smaller than the
beam (2.3 pc). If the stellar wind bubble is not adiabatic, or the bubble has
burst (as suggested by the HI channel maps), agreement between the energy and
ionization requirements is even less likely. The limit set by the non-detection
in the continuum provides a significant challenge for the interpretation of
GSH23.0-0.7+117 as a stellar wind bubble. A similar analysis may be applicable
to other Galactic HI shells that have not been detected in the continuum.Comment: 18 pages, 6 figures. Figures 1 and 4 separately in GIF format.
Accepted for publication in Astrophysical Journa
Vulnerabilidad del acuífero en áreas del valle de Catamarca destinadas al reúso agrícola de agua residual tratada
La utilización de aguas residuales tratadas para riego plantea beneficios de carácter ambiental, social y productivo. La Capital de Catamarca cuenta con un sistema de lagunas para depurar los efluentes cloacales. Atendiendo a la demanda de agua para actividades productivas y a la calidad del líquido depurado se implementará un proyecto de reuso. Simultáneamente se debe proteger la calidad del recurso hídrico subterráneo frente a esta carga. El objetivo de este trabajo es determinar la vulnerabilidad del acuífero a la contaminación en el área donde estará ubicado el emprendimiento productivo, sur de la planta de tratamiento. Se aplicó el método cualitativo GOD. Se determinó la profundidad del acuífero freático, tipo de acuífero y fitología del acuiperm, representada por arenas finas a muy gruesas, gravas y rodados con muy escasa proporción de limo y arcilla. La vulnerabilidad resultó moderada a alta, según el valor del índice. Se recomienda realizar un monitoreo sistemático del acuífero estudiado.The use of treated wastewater for irrigation has benefits of environmental, social and productive. The Catamarca capital has a ponds system for the wastewater treatment. In response to the water demand for productive activities and because of the quality the treated liquid will be implemented a reuse project. Simultaneously, must be protected the quality of groundwater resources against this load. The objective of this work is to determine aquifer contamination vulnerability in the area where productive entrepreneurship will be located, at the south of the treatment plant. It was applied qualitative method GOD. It were determined the depth of the aquifer, groundwater occurrence and lithology acuiperm, represented by fine to very coarse sand, gravel and boulders with very low proportion of silt and clay. The vulnerability was moderate to high, depending on the value of the index. It is recommend a systematic monitoring of the aquifer studied.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES
A New View of the Circumstellar Environment of SN 1987A
We summarize the analysis of a uniform set of both previously-known and
newly-discovered scattered-light echoes, detected within 30" of SN 1987A in ten
years of optical imaging, and with which we have constructed the most complete
three-dimensional model of the progenitor's circumstellar environment.
Surrounding the SN is a richly-structured bipolar nebula. An outer,
double-lobed ``peanut,'' which we believe is the contact discontinuity between
the red supergiant and main sequence winds, is a prolate shell extending 28 ly
along the poles and 11 ly near the equator. Napoleon's Hat, previously believed
to be an independent structure, is the waist of this peanut, which is pinched
to a radius of 6 ly. Interior, the innermost circumstellar material lies along
a cylindrical hourglass, 1 ly in radius and 4 ly long, which connects to the
peanut by a thick equatorial disk. The nebulae are inclined 41o south and 8o
east of the line of sight, slightly elliptical in cross section, and marginally
offset west of the SN. The 3-D geometry of the three circumstellar rings is
studied, suggesting the equatorial ring is elliptical (b/a<0.98), and spatially
offset in the same direction as the hourglass. Dust-scattering models suggest
that between the hourglass and bipolar lobes: the gas density drops from 1--3
cm^{-3} to >0.03 cm^{-3}; the maximum dust-grain size increases from ~0.2
micron to 2 micron; and the Si:C dust ratio decreases. The nebulae have a total
mass of ~1.7 Msun, yielding a red-supergiant mass loss around 5*10^{-6} Msun
yr^{-1}.Comment: Accepted for publication in ApJ 2/14/05. 16 pages in emualteapj
forma
Impacto de la reprogramación celular (células de fibroblastos y cúmulos) en la producción de clones bovinos
La clonación convencional consta de varios procesos que tienen un efecto directo en la producción embrionaria y la tasa de gestación, un factor primordial es la reprogramación de la célula utilizada como donante de núcleo. El objetivo del presente estudio fue evaluar el impacto de la reprogramación celular (células de fibroblastos y cúmulos) en la producción de clones bovinos. Las células donantes de núcleo se obtuvieron de fibroblastos y células de cúmulos para su reconstrucción con óvulos y cultivado durante 7 d hasta la fase de incuba- ción/eclosión de blastocisto, para posteriormente ser transferidos a receptoras y evaluadas en los días 28, 60 y 75 de gestación. Se evaluó número y porcentaje de citoplastos reconstruidos a la hora de fusión, obteniendo una mayor eficiencia con las células de cúmulos (51,7±7,8) (p<0,05). El porcentaje de embriones obtenido al día 7 fue mayor con las células de fibroblastos (36,1±8,4) en comparación con las células de cúmulos (34,1±10,0). A los 28, 60 y 75 días post-transferencia se evaluó permanencia de preñez, siendo significativamente superiores (p<0,05) los embriones generados con cúmulos de 16 células (12,0%). La eficiencia de la reprogramación celular es similar en la procedencia de la célula, sin embargo existe un mayor porcentaje de retención de preñez con células de cúmulos como donante de núcleo
CARMA Large Area Star Formation Survey: Project Overview with Analysis of Dense Gas Structure and Kinematics in Barnard 1
We present details of the CARMA Large Area Star Formation Survey (CLASSy),
while focusing on observations of Barnard 1. CLASSy is a CARMA Key Project that
spectrally imaged N2H+, HCO+, and HCN (J=1-0 transitions) across over 800
square arcminutes of the Perseus and Serpens Molecular Clouds. The observations
have angular resolution near 7" and spectral resolution near 0.16 km/s. We
imaged ~150 square arcminutes of Barnard 1, focusing on the main core, and the
B1 Ridge and clumps to its southwest. N2H+ shows the strongest emission, with
morphology similar to cool dust in the region, while HCO+ and HCN trace several
molecular outflows from a collection of protostars in the main core. We
identify a range of kinematic complexity, with N2H+ velocity dispersions
ranging from ~0.05-0.50 km/s across the field. Simultaneous continuum mapping
at 3 mm reveals six compact object detections, three of which are new
detections. A new non-binary dendrogram algorithm is used to analyze dense gas
structures in the N2H+ position-position-velocity (PPV) cube. The projected
sizes of dendrogram-identified structures range from about 0.01-0.34 pc.
Size-linewidth relations using those structures show that non-thermal
line-of-sight velocity dispersion varies weakly with projected size, while rms
variation in the centroid velocity rises steeply with projected size. Comparing
these relations, we propose that all dense gas structures in Barnard 1 have
comparable depths into the sky, around 0.1-0.2 pc; this suggests that
over-dense, parsec-scale regions within molecular clouds are better described
as flattened structures rather than spherical collections of gas. Science-ready
PPV cubes for Barnard 1 molecular emission are available for download.Comment: Accepted to The Astrophysical Journal (ApJ), 51 pages, 27 figures
(some with reduced resolution in this preprint); Project website is at
http://carma.astro.umd.edu/class
An unusual hantavirus outbreak in southern Argentina: person-to-person transmission? Hantavirus Pulmonary Syndrome Study Group for Patagonia.
Hantavirus pulmonary syndrome is a rodent-borne zoonosis first recognized in the United States in 1993. Person-to-person transmission has not been reported; however, in the outbreak of 20 cases reported here, epidemiologic evidence strongly suggests this route of transmission
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