2,151 research outputs found
Fall back accretion and energy injections in gamma-ray bursts
Intense flares that occur at late times relative to the prompt phase have
been observed by the satellite in the X-ray afterglows of gamma-ray
bursts (GRBs). Here, we present a detailed analysis on the fall back accretion
process to explain the intense flare phase in the very early X-ray afterglow
light curves. To reproduce the afterglow at late times, we resort to the
external shock by engaging energy injections. By applying our model to GRBs
080810, 081028 and 091029, we show that their X-ray afterglow light curves can
be reproduced well. We then apply our model to the ultra-long GRB
111209A, which is the longest burst ever observed. The very early X-ray
afterglow of GRB 111209A showed many interesting features, such as a
significant bump observed at around 2000 s after the /BAT trigger. We
assume two constant energy injection processes in our model. These can explain
the observed plateau at X-ray wavelength in the relatively early stage
( s) and a second X-ray plateau and optical rebrightening at
about s. Our analysis supports the scenario that a significant amount
of material may fall back toward the central engine after the prompt phase,
causing an enhanced and long lived mass accretion rate powering a
Poynting-flux-dominated outflow.Comment: 2 tables, 3 figures, accepted by MNRA
The Culture of Poverty Debate: Some Additional Data
In this paper we briefly review relevant research on the culture of poverty and set our findings within the general context of culture of poverty arguments. Data from a community survey in a Southwestern city are analyzed using Oscar Lewis’ four major culture of poverty dimensions: 1) the individual, 2) the family, 3) the slum community, and 4) the community’s relation to society. In our study a sample of 271 black respondents was divided into two groups, here termed the “poor” and the “non-poor.” In noting all the broad traits studied in all dimensions taken together, some support for Lewis’ culture of poverty was found in less than half of the cases; and in several cases our findings were in direct opposition to culture of poverty predictions. In addition, we have suggested that the majority of those traits that did lend support to Lewis’ argument might be better classified as situational conditions of poverty rather than as a part of a bona fide “culture” of poverty. The findings of this paper may call into question the use of the “culture of poverty” perspective as a basis for policy decisions
Advances in our understanding of the pathogenesis of hemolytic uremic syndromes
Hemolytic uremic syndrome (HUS) is major global health care issue as it is the leading cause of acute kidney injury in children. It is a triad of acute kidney injury, microangiopathic hemolytic anemia, and thrombocytopenia. In recent years, major advances in our understanding of complement-driven inherited rare forms of HUS have been achieved. However, in children 90% of cases of HUS are associated with a Shiga toxin-producing enteric pathogen. The precise pathological mechanisms in this setting are yet to be elucidated. The purpose of this review is to discuss advances in our understanding of the pathophysiology underlying HUS and identify the key questions yet to be answered by the scientific community. </jats:p
A redshift - observation-time relation for gamma-ray bursts: evidence of a distinct sub-luminous population
We show how the redshift and peak-flux distributions of gamma-ray bursts
(GRBs) have an observation time dependence that can be used to discriminate
between different burst populations. We demonstrate how observation time
relations can be derived from the standard integral distributions and that they
can differentiate between GRB populations detected by both the BATSE and
\emph{Swift} satellites. Using \emph{Swift} data we show that a
redshift--observation-time relation (log\,\,--\,log\,) is consistent with
both a peak-flux\,--\,observation time relation (log\,\,--\,log\,) and a
standard log\,\,--\,log\, brightness distribution. As the method depends
only on rarer small- events, it is invariant to high- selection effects.
We use the log\,\,--\,log\, relation to show that sub-luminous GRBs are a
distinct population occurring at a higher rate of order . Our analysis suggests that GRB 060505 -- a
relatively nearby GRB observed without any associated supernova -- is
consistent with a sub-luminous population of bursts. Finally, we suggest that
our relations can be used as a consistency test for some of the proposed GRB
spectral energy correlations.Comment: Accepted by MNRA
Toward an optimal search strategy of optical and gravitational wave emissions from binary neutron star coalescence
Observations of an optical source coincident with gravitational wave emission
detected from a binary neutron star coalescence will improve the confidence of
detection, provide host galaxy localisation, and test models for the
progenitors of short gamma ray bursts. We employ optical observations of three
short gamma ray bursts, 050724, 050709, 051221, to estimate the detection rate
of a coordinated optical and gravitational wave search of neutron star mergers.
Model R-band optical afterglow light curves of these bursts that include a
jet-break are extrapolated for these sources at the sensitivity horizon of an
Advanced LIGO/Virgo network. Using optical sensitivity limits of three
telescopes, namely TAROT (m=18), Zadko (m=21) and an (8-10) meter class
telescope (m=26), we approximate detection rates and cadence times for imaging.
We find a median coincident detection rate of 4 yr^{-1} for the three bursts.
GRB 050724 like bursts, with wide opening jet angles, offer the most optimistic
rate of 13 coincident detections yr^{-1}, and would be detectable by Zadko up
to five days after the trigger. Late time imaging to m=26 could detect off-axis
afterglows for GRB 051221 like bursts several months after the trigger. For a
broad distribution of beaming angles, the optimal strategy for identifying the
optical emissions triggered by gravitational wave detectors is rapid response
searches with robotic telescopes followed by deeper imaging at later times if
an afterglow is not detected within several days of the trigger.Comment: 6 pages, 1 figure, Accepted for publication in MNRAS Letters (2011
April 22
The Unseen Face of E-Business Project Development
The purpose of this paper is intent on identify and analyze the unseen factors of successful or failure of e-business project development. The IT managers must take into account both all costs involved in e-business development and all phases (analysis, design, testing, implementation, maintenance and operation) according to principle of project management for software/systems life cycle development. There are many solutions to exceed these factors of failure among could be counted outsourcing, a good project management, involvement of senior management, a real cost estimation etc.Zadanie pt. „Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki” nr 885/P-DUN/2014 zostało dofinansowane ze środków MNiSW w ramach działalności upowszechniającej nauk
Domestic ventilation rates, indoor humidity and dust mite allergens : are our homes causing the asthma pandemic?
This paper is concerned with historical changes in domestic ventilation rates, relative humidity and the associated risk of house dust mite colonization. A controlled trial evaluated allergen and water vapour control measures on the level of house dust mite (HDM) Der p1 allergen and indoor humidity, concurrently with changes in lung function in 54 subjects who completed the protocol. Mechanical heat recovery ventilation units significantly reduced moisture content in the active group, while HDM allergen reservoirs in carpets and beds were reduced by circa 96%. Self reported health status confirmed a significant clinical improvement in the active group. The study can form the basis for assessing minimum winter ventilation rates that can suppress RH below the critical ambient equilibrium humidity of 60% and thus inhibit dust mite colonization and activity in temperate and maritime in' uenced climatic regions
The non-convex shape of (234) Barbara, the first Barbarian
Asteroid (234) Barbara is the prototype of a category of asteroids that has
been shown to be extremely rich in refractory inclusions, the oldest material
ever found in the Solar System. It exhibits several peculiar features, most
notably its polarimetric behavior. In recent years other objects sharing the
same property (collectively known as "Barbarians") have been discovered.
Interferometric observations in the mid-infrared with the ESO VLTI suggested
that (234) Barbara might have a bi-lobated shape or even a large companion
satellite. We use a large set of 57 optical lightcurves acquired between 1979
and 2014, together with the timings of two stellar occultations in 2009, to
determine the rotation period, spin-vector coordinates, and 3-D shape of (234)
Barbara, using two different shape reconstruction algorithms. By using the
lightcurves combined to the results obtained from stellar occultations, we are
able to show that the shape of (234) Barbara exhibits large concave areas.
Possible links of the shape to the polarimetric properties and the object
evolution are discussed. We also show that VLTI data can be modeled without the
presence of a satellite.Comment: 10 pages, 6 figure
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