8,877 research outputs found
Treatment of the background error in the statistical analysis of Poisson processes
The formalism that allows to take into account the error sigma_b of the
expected mean background b in the statistical analysis of a Poisson process
with the frequentistic method is presented. It is shown that the error sigma_b
cannot be neglected if it is not much smaller than sqrt(b). The resulting
confidence belt is larger that the one for sigma_b=0, leading to larger
confidence intervals for the mean mu of signal events.Comment: 15 pages including 2 figures, RevTeX. Final version published in
Phys. Rev. D 59 (1999) 11300
Comment on "Including Systematic Uncertainties in Confidence Interval Construction for Poisson Statistics"
The incorporation of systematic uncertainties into confidence interval
calculations has been addressed recently in a paper by Conrad et al. (Physical
Review D 67 (2003) 012002). In their work, systematic uncertainities in
detector efficiencies and background flux predictions were incorporated
following the hybrid frequentist-Bayesian prescription of Cousins and Highland,
but using the likelihood ratio ordering of Feldman and Cousins in order to
produce "unified" confidence intervals. In general, the resulting intervals
behaved as one would intuitively expect, i.e. increased with increasing
uncertainties. However, it was noted that for numbers of observed events less
than or of order of the expected background, the intervals could sometimes
behave in a completely counter-intuitive fashion -- being seen to initially
decrease in the face of increasing uncertainties, but only for the case of
increasing signal efficiency uncertainty. In this comment, we show that the
problematic behaviour is due to integration over the signal efficiency
uncertainty while maximising the best fit alternative hypothesis likelihood. If
the alternative hypothesis likelihood is determined by unconditionally
maximising with respect to both the unknown signal and signal efficiency
uncertainty, the limits display the correct intuitive behaviour.Comment: Submitted to Physical Review
Access Anytime Anyplace: An Empircal Investigation of Patterns of Technology Use in Nomadic Computing Environments
With the increasing pervasiveness of mobile technologies such as cellular phones, personal digital assistants and hand held computers, mobile technologies promise the next major technological and cultural shift. Like the Internet, it is predicted that the greatest impact will not come from hardware devices or software programs, but from emerging social practices, which were not possible before. To capitalize on the benefits of mobile technologies, organizations have begun to implement nomadic computing environments. Nomadic computing environments make available the systems support needed to provide computing and communication capabilities and services to the mobile work force as they move from place to place in a manner that is transparent, integrated, convenient and adaptive. Already, anecdotes suggest that within organizations there are social implications occurring with both unintended and intended consequences being perpetuated. The problems of nomadic computing users have widely been described in terms of the challenges presented by the interplay of time, space and context, yet a theory has yet to be developed which analyzes this interplay in a single effort. A temporal human agency perspective proposes that stakeholdersâ actions are influenced by their ability to recall the past, respond to the present and imagine the future. By extending the temporal human agency perspective through the recognition of the combined influence of space and context on human action, I investigated how the individual practices of eleven nomadic computing users changed after implementation. Under the umbrella of the interpretive paradigm, and using a cross case methodology this research develops a theoretical account of how several stakeholders engaged with different nomadic computing environments and explores the context of their effectiveness. Applying a literal and theoretical replication strategy to multiple longitudinal and retrospective cases, six months were spent in the field interviewing and observing participants. Data analysis included three types of coding: descriptive, interpretive and pattern coding. The findings reveal that patterns of technology use in nomadic computing environments are influenced by stakeholdersâ temporal orientations; their ability to remember the past, imagine the future and respond to the present. As stakeholders all have different temporal orientations and experiences, they exhibit different practices even when engaging initially with the same organizational and technical environments. Opposing forces emerge as users attempt to be effective by resolving the benefits and disadvantages of the environment as they undergo different temporal, contextual and spatial experiences. Insights about the ability to predict future use suggest that because they are difficult to envisage in advance, social processes inhibit the predictability of what technologies users will adopt. The framework presented highlights the need to focus on understanding the diversity in nomadic computing use practices by examining how they are influenced by individual circumstances as well as shared meanings across individuals
Unbiased cut selection for optimal upper limits in neutrino detectors: the model rejection potential technique
We present a method for optimising experimental cuts in order to place the
strongest constraints (upper limits) on theoretical signal models.
The method relies only on signal and background expectations derived from
Monte-Carlo simulations, so no bias is introduced by looking at actual data,
for instance by setting a limit based on expected signal above the ``last
remaining data event.'' After discussing the concept of the ``average upper
limit,'' based on the expectation from an ensemble of repeated experiments with
no true signal, we show how the best model rejection potential is achieved by
optimising the cuts to minimise the ratio of this ``average upper limit'' to
the expected signal from the model. As an example, we use this technique to
determine the limit sensitivity of kilometre scale neutrino detectors to
extra-terrestrial neutrino fluxes from a variety of models, e.g. active
galaxies and gamma-ray bursts. We suggest that these model rejection potential
optimised limits be used as a standard method of comparing the sensitivity of
proposed neutrino detectors.Comment: 18 pages, 7 figures, submitted to Astroparticle Physic
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Comparing proxy rated quality of life of people living with dementia in care homes
Background: Improving quality of life (QOL) for people with dementia is a priority. In care homes, we often rely on proxy ratings from staff and family but we do not know if, or how, they differ in care homes.
Methods: We compared 1056 pairs of staff and family DEMQOL-Proxy ratings from 86 care homes across England. We explored factors associated with ratings quantitatively using multilevel modelling and, qualitatively, through thematic analysis of 12 staff and 12 relative interviews.
Results: Staff and family ratings were weakly correlated (Ïs = 0.35). Median staff scores were higher than family's (104 v. 101; p < 0.001). Family were more likely than staff to rate resident QOL as âPoorâ (Ï2 = 55.91, p < 0.001). Staff and family rated QOL higher when residents had fewer neuropsychiatric symptoms and severe dementia. Staff rated QOL higher in homes with lower staff:resident ratios and when staff were native English speakers. Family rated QOL higher when the resident had spent longer living in the care home and was a native English. Spouses rated residentsâ QOL higher than other relatives. Qualitative results suggest differences arise because staff felt good care provided high QOL but families compared the present to the past. Family judgements centre on loss and are complicated by decisions about care home placement and their understandings of dementia.
Conclusion: Proxy reports differ systematically between staff and family. Reports are influenced by the rater:staff and family may conceptualise QOL differently
Setting UBVRI Photometric Zero-Points Using Sloan Digital Sky Survey ugriz Magnitudes
We discuss the use of Sloan Digital Sky Survey (SDSS) ugriz point-spread
function (PSF) photometry for setting the zero points of UBVRI CCD images. From
a comparison with the Landolt (1992) standards and our own photometry we find
that there is a fairly abrupt change in B, V, R, & I zero points around g, r, i
~ 14.5, and in the U zero point at u ~ 16. These changes correspond to where
there is significant interpolation due to saturation in the SDSS PSF fluxes.
There also seems to be another, much smaller systematic effect for stars with
g, r > 19.5. The latter effect is consistent with a small Malmquist bias.
Because of the difficulties with PSF fluxes of brighter stars, we recommend
that comparisons of ugriz and UBVRI photometry should only be made for
unsaturated stars with g, r and i in the range 14.5 - 19.5, and u in the range
16 - 19.5. We give a prescription for setting the UBVRI zero points for CCD
images, and general equations for transforming from ugriz to UBVRI.Comment: 13 pages. 6 figures. Accepted for publication in the Astronomical
Journa
Including Systematic Uncertainties in Confidence Interval Construction for Poisson Statistics
One way to incorporate systematic uncertainties into the calculation of
confidence intervals is by integrating over probability density functions
parametrizing the uncertainties. In this note we present a development of this
method which takes into account uncertainties in the prediction of background
processes, uncertainties in the signal detection efficiency and background
efficiency and allows for a correlation between the signal and background
detection efficiencies. We implement this method with the Feldman & Cousins
unified approach with and without conditioning. We present studies of coverage
for the Feldman & Cousins and Neyman ordering schemes. In particular, we
present two different types of coverage tests for the case where systematic
uncertainties are included. To illustrate the method we show the relative
effect of including systematic uncertainties the case of dark matter search as
performed by modern neutrino tel escopes.Comment: 23 pages, 10 figures, replaced to match published versio
A Possible Massive Asteroid Belt Around zeta Lep
We have used the Keck I telescope to image at 11.7 microns and 17.9 microns
the dust emission around zeta Lep, a main sequence A-type star at 21.5 pc from
the Sun with an infrared excess. The excess is at most marginally resolved at
17.9 microns. The dust distance from the star is probably less than or equal to
6 AU, although some dust may extend to 9 AU. The mass of observed dust is
\~10^22 g. Since the lifetime of dust particles is about 10,000 years because
of the Poytning-Robertson effect, we robustly estimate at least 4 10^26 g must
reside in parent bodies which may be asteroids if the system is in a steady
state and has an age of ~300 Myr. This mass is approximately 200 times that
contained within the main asteroid belt in our solar system.Comment: 12 pages, 3 figures, ApJL in pres
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