2,913 research outputs found
OT 060420: A Seemingly Optical Transient Recorded by All-Sky Cameras
We report on a ~5th magnitude flash detected for approximately 10 minutes by
two CONCAM all-sky cameras located in Cerro Pachon - Chile and La Palma -
Spain. A third all-sky camera, located in Cerro Paranal - Chile did not detect
the flash, and therefore the authors of this paper suggest that the flash was a
series of cosmic-ray hits, meteors, or satellite glints. Another proposed
hypothesis is that the flash was an astronomical transient with variable
luminosity. In this paper we discuss bright optical transient detection using
fish-eye all-sky monitors, analyze the apparently false-positive optical
transient, and propose possible causes to false optical transient detection in
all-sky cameras.Comment: 7 figures, 3 tables, accepted PAS
Interactions between chemical and climate stressors: A role for mechanistic toxicology in assessing climate change risks
Incorporation of global climate change (GCC) effects into assessments of chemical risk and injury requires integrated examinations of chemical and nonchemical stressors. Environmental variables altered by GCC (temperature, precipitation, salinity, pH) can influence the toxicokinetics of chemical absorption, distribution, metabolism, and excretion as well as toxicodynamic interactions between chemicals and target molecules. In addition, GCC challenges processes critical for coping with the external environment (water balance, thermoregulation, nutrition, and the immune, endocrine, and neurological systems), leaving organisms sensitive to even slight perturbations by chemicals when pushed to the limits of their physiological tolerance range. In simplest terms, GCC can make organisms more sensitive to chemical stressors, while alternatively, exposure to chemicals can make organisms more sensitive to GCC stressors. One challenge is to identify potential interactions between nonchemical and chemical stressors affecting key physiological processes in an organism. We employed adverse outcome pathways, constructs depicting linkages between mechanism-based molecular initiating events and impacts on individuals or populations, to assess how chemical- and climate-specific variables interact to lead to adverse outcomes. Case examples are presented for prospective scenarios, hypothesizing potential chemicalGCC interactions, and retrospective scenarios, proposing mechanisms for demonstrated chemicalclimate interactions in natural populations. Understanding GCC interactions along adverse outcome pathways facilitates extrapolation between species or other levels of organization, development of hypotheses and focal areas for further research, and improved inputs for risk and resource injury assessments. Environ. Toxicol. Chem. 2013;32:3248. (c) 2012 SETA
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Data-in-Place: Thinking through the Relations Between Data and Community
We present findings from a year-long engagement with a street and its community . The work is targeted at exploring how the production and use of data is bound up with place, both in terms of physical and social geography. We detail three strands of the project. First, we consider how residents have sought to curate existing data about the street in the form of an archive with physical and digital components. Second, we report endeavours to capture data about the street’s environment, especially of traffic moving through it. Third, we draw on the possibilities afforded by technologies for polling opinion. We reflect on how these engagements have: materialised distinctive relations between the community and their data; surfaced flows and contours of data , and spatial, temporal and social boundaries ;and enacted a multiplicity of ‘small worlds’. We consider how such a conceptualisation of data-in-place is relevant to the design of data technologies
A probabilistic approach for acoustic emission based monitoring techniques: with application to structural health monitoring
It has been demonstrated that acoustic-emission (AE), inspection of
structures can offer advantages over other types of monitoring techniques in
the detection of damage; namely, an increased sensitivity to damage, as well as
an ability to localise its source. There are, however, numerous challenges
associated with the analysis of AE data. One issue is the high sampling
frequencies required to capture AE activity. In just a few seconds, a recording
can generate very high volumes of data, of which a significant portion may be
of little interest for analysis. Identifying the individual AE events in a
recorded time-series is therefore a necessary procedure to reduce the size of
the dataset. Another challenge that is also generally encountered in practice,
is determining the sources of AE, which is an important exercise if one wishes
to enhance the quality of the diagnostic scheme. In this paper, a
state-of-the-art technique is presented that can automatically identify AE
events, and simultaneously help in their characterisation from a probabilistic
perspective. A nonparametric Bayesian approach, based on the Dirichlet process
(DP), is employed to overcome some of the challenges associated with these
tasks. Two main sets of AE data are considered in this work: (1) from a journal
bearing in operation, and (2) from an Airbus A320 main landing gear subjected
to fatigue testing
Constraining Antimatter Domains in the Early Universe with Big Bang Nucleosynthesis
We consider the effect of a small-scale matter-antimatter domain structure on
big bang nucleosynthesis and place upper limits on the amount of antimatter in
the early universe. For small domains, which annihilate before nucleosynthesis,
this limit comes from underproduction of He-4. For larger domains, the limit
comes from He-3 overproduction. Most of the He-3 from antiproton-helium
annihilation is annihilated also. The main source of He-3 is
photodisintegration of He-4 by the electromagnetic cascades initiated by the
annihilation.Comment: 4 pages, 2 figures, revtex, (slightly shortened
Fast evaluation of appointment schedules for outpatients in health care
We consider the problem of evaluating an appointment schedule for outpatients in a hospital. Given a fixed-length session during which a physician sees K patients, each patient has to be given an appointment time during this session in advance. When a patient arrives on its appointment, the consultations of the previous patients are either already finished or are still going on, which respectively means that the physician has been standing idle or that the patient has to wait, both of which are undesirable. Optimising a schedule according to performance criteria such as patient waiting times, physician idle times, session overtime, etc. usually requires a heuristic search method involving a huge number of repeated schedule evaluations. Hence, the aim of our evaluation approach is to obtain accurate predictions as fast as possible, i.e. at a very low computational cost. This is achieved by (1) using Lindley's recursion to allow for explicit expressions and (2) choosing a discrete-time (slotted) setting to make those expression easy to compute. We assume general, possibly distinct, distributions for the patient's consultation times, which allows us to account for multiple treatment types, as well as patient no-shows. The moments of waiting and idle times are obtained. For each slot, we also calculate the moments of waiting and idle time of an additional patient, should it be appointed to that slot. As we demonstrate, a graphical representation of these quantities can be used to assist a sequential scheduling strategy, as often used in practice
Spontaneous CP Violation at the Electroweak Scale
Utilizing results on the cosmology of anomalous discrete symmetries we show
that models of spontaneous CP violation can in principle avoid the domain wall
problem first pointed out by Zel'dovich, Kobzarev and Okun. A small but nonzero
explicitly breaks CP and can lift the degeneracy of the two CP
conjugate vacua through nonperturbative effects so that the domain walls become
unstable, but survive to cosmologically interesting epochs. We explore the
viability of spontaneous CP violation in the context of two Higgs models, and
find that the invisible axion solution of the strong CP problem cannot be
implemented without further extensions of the Higgs sector.Comment: 10 page
Plausibility functions and exact frequentist inference
In the frequentist program, inferential methods with exact control on error
rates are a primary focus. The standard approach, however, is to rely on
asymptotic approximations, which may not be suitable. This paper presents a
general framework for the construction of exact frequentist procedures based on
plausibility functions. It is shown that the plausibility function-based tests
and confidence regions have the desired frequentist properties in finite
samples---no large-sample justification needed. An extension of the proposed
method is also given for problems involving nuisance parameters. Examples
demonstrate that the plausibility function-based method is both exact and
efficient in a wide variety of problems.Comment: 21 pages, 5 figures, 3 table
Electromagnetic Cascades and Cascade Nucleosynthesis in the Early Universe
We describe a calculation of electromagnetic cascading in radiation and
matter in the early universe initiated by the decay of massive particles or by
some other process. We have used a combination of Monte Carlo and numerical
techniques which enables us to use exact cross sections, where known, for all
the relevant processes. In cascades initiated after the epoch of big bang
nucleosynthesis -rays in the cascades will photodisintegrate He,
producing He and deuterium. Using the observed He and deuterium
abundances we are able to place constraints on the cascade energy deposition as
a function of cosmic time. In the case of the decay of massive primordial
particles, we place limits on the density of massive primordial particles as a
function of their mean decay time, and on the expected intensity of decay
neutrinos.Comment: compressed and uuencoded postscript. We now include a comparison with
previous work of the photon spectrum in the cascade and the limits we
calculate for the density of massive particles. The method of calculation of
photon spectra at low energies has been improved. Most figures are revised.
Our conclusions are substantially unchange
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