5,544 research outputs found
Collisional dark matter density profiles around supermassive black holes
We solve the spherically symmetric time dependent relativistic Euler
equations on a Schwarzschild background space-time for a perfect fluid, where
the perfect fluid models the dark matter and the space-time background is that
of a non-rotating supermassive black hole. We consider the fluid obeys an ideal
gas equation of state as a simple model of dark matter with pressure. Assuming
out of equilibrium initial conditions we search for late-time attractor type of
solutions, which we found to show a constant accretion rate for the non-zero
pressure case, that is, the pressure itself suffices to produce stationary
accretion regimes. We then analyze the resulting density profile of such
late-time solutions with the function . For different values of
the adiabatic index we find different slopes of the density profile, and we
study such profile in two regions: a region one near the black hole, located
from the horizon up to 50 and a region two from up to , which for a black hole of corresponds to pc. The profile depends on the adiabatic index or equivalently on the
pressure of the fluid and our findings are as follows: in the near region the
density profile shows values of and in the limit of the
pressure-less case ; on the other hand, in region two,
the value of in all the cases we studied. If these results are to
be applied to the dark matter problem, the conclusion is that, in the limit of
pressure-less gas the density profile is cuspy only near the black hole and
approaches a non-cuspy profile at bigger scales within 1pc. These results show
on the one hand that pressure suffices to provide flat density profiles of dark
matter and on the other hand show that the presence of a central black hole
does not distort the density profile of dark matter at scales of 0.1pc.Comment: 7 pages, 8 eps figures, accepted for publication in MNRA
Ultrahigh resolution photoacoustic microscopy via transient absorption
We have developed a novel, hybrid imaging modality, Transient Absorption Ultrasonic Microscopy (TAUM), which takes advantage of the optical nonlinearities afforded by transient absorption to achieve ultrahigh-resolution photoacoustic microscopy. The theoretical point spread function for TAUM is functionally equivalent to confocal and two-photon fluorescence microscopy, potentially enabling cellular/subcellular photoacoustic imaging. A prototype TAUM system was designed, built, and used to image a cross-section through several capillaries in the excised cheek pouch of a Syrian Hamster. The well-resolved capillaries in the TAUM image provided experimental evidence of the spatial resolution. These results suggest that TAUM has excellent potential for producing volumetric images with cellular/subcellular resolution in three dimensions deep inside living tissue
Characterization of the Plasmidic or Chromosomal cpe Gene and Metabolic Activities in Clostridium perfringens Isolates from Food in San Luis - Argentina
Food poisoning and non-food poisoning illnesses due to C. perfringens (by enterotoxin production) have been associated to chromosomal or plasmidic location of the cpe gene, respectively. Clostridial pathogenicity has been correlated to protease and azoreductase production.The aim of this work was: i) to assess the sanitary-hygienic quality of dehydrated soups (100 samples) consumed in San Luis – Argentina; ii) to verify the presence of C. perfringens in these food products using the "Most Probable Number" method (MPN) and plate-counting methods; iii) to characterise enterotoxigenicity in strain isolates by RPLA; iv) to determine the chromosomal or plasmidic location of the cpe gene in enterotoxigenic strains previously isolated from food in our lab, using PCR; v) to correlate chromosomal cpe and spore heat-resistance; vi) to compare protease activity in cpe+ and cpe– strains; and vii) to compare azoreductase activity in cpe+ and cpe– strains. Twenty-six isolates had a count a 3–43 bacteria g-1 count using MPN; 7.7% exceeded the Argentine Food Code (CAA) limit. All isolates showed protease activity: enterotoxigenic isolates had higher protease activity than non-enterotoxigenic isolates. All isolates showed azoreductase activity: enterotoxigenic isolates had higher activity and shorter reducing times. Enterotoxigenic isolates showed chromosomal location for the gene responsible for the enterotoxin.Fil: Corigliano, Mariana Georgina. Universidad Nacional de San Luis; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: de Guzmán, Ana María Stefanini. Universidad Nacional de San Luis; ArgentinaFil: Stagnitta, Patricia Virginia. Universidad Nacional de San Luis; Argentin
An eight-dimensional approach to G_2 manifolds
We develop a systematic approach to G_2 holonomy manifolds with an
SU(2)xSU(2) isometry using maximal eight-dimensional gauged supergravity to
describe D6-branes wrapped on deformed three-spheres. A quite general metric
ansatz that generalizes the celebrated Bryant-Salamon metric involves nine
functions. We show that only six of them are the independent ones and derive
the general first order system of differential equations that they obey. As a
byproduct of our analysis, we generalize the notion of the twist that relates
the spin and gauge connections in a way that involves non-trivially the scalar
fields.Comment: 16 pages, Latex. v2: Minor and cosmetic changes, and references
added. Journal versio
Genetic Algorithm to Evolve Ensembles of Rules for On-Line Scheduling on Single Machine with Variable Capacity
International Work-Conference on the Interplay Between Natural and Artificial Computation, IWINAC (8th . 2019. Almería, Spain
The IGRINS YSO Survey III: Stellar parameters of pre-main sequence stars in Ophiuchus and Upper Scorpius
We used the Immersion GRating Infrared Spectrometer (IGRINS) to determine
fundamental parameters for 61 K- and M-type young stellar objects (YSOs)
located in the Ophiuchus and Upper Scorpius star-forming regions. We employed
synthetic spectra and a Markov chain Monte Carlo approach to fit specific
K-band spectral regions and determine the photospheric temperature (), surface gravity ( g), magnetic field strength (B), projected
rotational velocity (), and K-band veiling (). We
determined B for 46% of our sample. Stellar parameters were compared to
the results from Taurus-Auriga and the TW Hydrae Association (TWA) presented in
Paper I of this series. We classified all the YSOs in the IGRINS survey with
infrared spectral indices from 2MASS and WISE photometry between 2 and
24~m. We found that Class II YSOs typically have lower g and , similar B, and higher K-band veiling than their Class III counterparts.
Additionally, we determined the stellar parameters for a sample of K and M
field stars also observed with IGRINS. We have identified intrinsic
similarities and differences at different evolutionary stages with our
homogeneous determination of stellar parameters in the IGRINS YSO Survey.
Considering g as a proxy for age, we found that the Ophiuchus and Taurus
samples have a similar age. We also find that Upper Scorpius and TWA YSOs have
similar ages, and are more evolved than Ophiuchus/Taurus YSOs.Comment: 21 pages, 8 figures, 4 tables. Accepted for publication in Ap
Observing the First Stars and Black Holes
The high sensitivity of JWST will open a new window on the end of the
cosmological dark ages. Small stellar clusters, with a stellar mass of several
10^6 M_sun, and low-mass black holes (BHs), with a mass of several 10^5 M_sun
should be directly detectable out to redshift z=10, and individual supernovae
(SNe) and gamma ray burst (GRB) afterglows are bright enough to be visible
beyond this redshift. Dense primordial gas, in the process of collapsing from
large scales to form protogalaxies, may also be possible to image through
diffuse recombination line emission, possibly even before stars or BHs are
formed. In this article, I discuss the key physical processes that are expected
to have determined the sizes of the first star-clusters and black holes, and
the prospect of studying these objects by direct detections with JWST and with
other instruments. The direct light emitted by the very first stellar clusters
and intermediate-mass black holes at z>10 will likely fall below JWST's
detection threshold. However, JWST could reveal a decline at the faint-end of
the high-redshift luminosity function, and thereby shed light on radiative and
other feedback effects that operate at these early epochs. JWST will also have
the sensitivity to detect individual SNe from beyond z=10. In a dedicated
survey lasting for several weeks, thousands of SNe could be detected at z>6,
with a redshift distribution extending to the formation of the very first stars
at z>15. Using these SNe as tracers may be the only method to map out the
earliest stages of the cosmic star-formation history. Finally, we point out
that studying the earliest objects at high redshift will also offer a new
window on the primordial power spectrum, on 100 times smaller scales than
probed by current large-scale structure data.Comment: Invited contribution to "Astrophysics in the Next Decade: JWST and
Concurrent Facilities", Astrophysics & Space Science Library, Eds. H.
Thronson, A. Tielens, M. Stiavelli, Springer: Dordrecht (2008
Air/water interfacial assembled rubbery semiconducting nanofilm for fully rubbery integrated electronics
A rubber-like stretchable semiconductor with high carrier mobility is the most important yet challenging material for constructing rubbery electronics and circuits with mechanical softness and stretchability at both microscopic (material) and macroscopic (structural) levels for many emerging applications. However, the development of such a rubbery semiconductor is still nascent. Here, we report the scalable manufacturing of high-performance stretchable semiconducting nanofilms and the development of fully rubbery transistors, integrated electronics, and functional devices. The rubbery semiconductor is assembled into a freestanding binary-phased composite nanofilm based on the air/water interfacial assembly method. Fully rubbery transistors and integrated electronics, including logic gates and an active matrix, were developed, and their electrical performances were retained even when stretched by 50%. An elastic smart skin for multiplexed spatiotemporal mapping of physical pressing and a medical robotic hand equipped with rubbery multifunctional electronic skin was developed to show the applications of fully rubbery-integrated functional devices
Search for a strongly decaying neutral charmed pentaquark
We present a search for a charmed pentaquark decaying strongly to
. Finding no evidence for such a state, we set limits on the cross
section times branching ratio relative to and under particular
assumptions about the production mechanism.Comment: To be published in Physics Letters
Management model for the logistics and competitiveness of SMEs in the city of Barranquilla
In Colombia, small and medium-sized enterprises (SMEs) are the most powerful engines of economic development, since they generate a high volume of jobs in the national territory, while diversifying productive, commercial, and service activities. In order to propose a model for logistics management as a component for the competitiveness of SMEs, a qualitative study is proposed that will allow us to collect from a structured review of recent literature, identifying the elements to be taken into account for logistics management in order to provide timely support and open space for continuous improvement. The proposed model is structured in six main blocks: characterization of processes according to the activity of the SME, external factors of influence, internal factors of influence, feeding of information, monitoring and control of operations, and feedback between support areas. The above elements have been analyzed and suggested taking into account the specific aspects of SMEs in the country, and taking into account the peculiarities of these small productive cells
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