6,395 research outputs found
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
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
Desymmetrisation reactions of cyclohexa-1,4-dienes and marine natural product synthesis
This thesis describes novel diastereoselective group selective processes for the desymmetrisation of cyclohexa-1,4-dienes, and their application to target synthesis of the cladiellin diterpenes. In addition, an enantioselective approach to batzelladine C methyl ester is described, permitting stereochemical assignment of batzelladine C. Chapter 1 describes the use of diastereoselective iodocyclisation reactions for the desymmetrisation of cyclohexa-1,4-dienes, and also details a novel epoxidation-cyclisation transformation, enabling the formation of up to six contiguous stereogenic centres, selectively, in a single step. Chapter 2 introduces the cladiellin diterpenes and describes the application of novel diastereoselective Prins chemistry for the synthesis of a model of the cladiellin core. Chapter 3 describes our attempts at elaborating the cladiellin model to approach the cladiellin framework and discusses an unexpected but interesting Prins cyclisation/rearrangement process. Chapter 4 describes an enantioselective synthesis of batzelladine C methyl ester, permitting assignment of the relative and absolute stereochemistry of batzelladine C.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
âThe stress can be unbearable, but the good times are like finding goldâ: A phase one modelling survey to inform the development of a self-help positive reappraisal coping intervention for caregivers of those with autism spectrum disorder
Caregivers of individuals with ASD can experience various practical, psychological, and social demands and need effective ways of coping to ameliorate the negative effects of caregiving. Numerous coping strategies are available, but the literature shows that caregivers can still struggle to cope, suggesting that interventions to support coping efforts could be beneficial. The MRC framework advocates the systematic development and evaluation of interventions, and this study was conducted to inform the future development of a self-help Positive Reappraisal Coping Intervention (PRCI) for these caregivers. The aim was to establish whether positive reappraisal coping strategies were used and associated with greater psychological wellbeing, prior to developing such an intervention. Method. Caregivers of individuals with ASD (N = 112) responded to items from an existing PRCI (Lancastle, 2006; Lancastle & Boivin, 2008), by writing about aspects of caregiving that reflected the meaning of each item. They also completed questionnaires assessing resilience, caregiving burden, and positive and negative emotions. Results. Participants provided significantly more positive responses than negative responses to PRCI items, demonstrating their use of positive reappraisal coping. Thematic analyses showed that positive responses focused on factors such as their loved oneâs personality and achievements, the contributions caregivers had made to this personâs progress, the support received, and their own personal development. Positive reappraisal coping was associated with greater resilience, more positive and less negative emotions, and a lesser sense of caregiver burden. Conclusion. This modelling study suggests that positive reappraisal strategies were used by caregivers and associated with greater psychological wellbeing. The findings will inform the development of a self-help PRCI for the caregivers of those with ASD. Future studies will systematically evaluate that PRCI to determine the nature of intervention effects and mediators and moderators of effects
Desymmetrisation reactions of cyclohexa-1,4-dienes and marine natural product synthesis
This thesis describes novel diastereoselective group selective processes for the desymmetrisation of cyclohexa-1,4-dienes, and their application to target synthesis of the cladiellin diterpenes. In addition, an enantioselective approach to batzelladine C methyl ester is described, permitting stereochemical assignment of batzelladine C. Chapter 1 describes the use of diastereoselective iodocyclisation reactions for the desymmetrisation of cyclohexa-1,4-dienes, and also details a novel epoxidation-cyclisation transformation, enabling the formation of up to six contiguous stereogenic centres, selectively, in a single step. Chapter 2 introduces the cladiellin diterpenes and describes the application of novel diastereoselective Prins chemistry for the synthesis of a model of the cladiellin core. Chapter 3 describes our attempts at elaborating the cladiellin model to approach the cladiellin framework and discusses an unexpected but interesting Prins cyclisation/rearrangement process. Chapter 4 describes an enantioselective synthesis of batzelladine C methyl ester, permitting assignment of the relative and absolute stereochemistry of batzelladine C
An unexpected Prins desymmetrisation reaction driven by silyl migration
Prins desymmetrisation reactions of cyclohexa-1,4-diene derivatives have been investigated as a route to the core of the cladiellin diterpenes. During the course of this work, we observed the formation of a partially-reduced benzofuran 18, which is clearly derived from oxocarbenium ion 21. This can only be rationalised by an unexpected primary to secondary silyl group migration
FUSE Measurements of Far Ultraviolet Extinction. I. Galactic Sight Lines
We present extinction curves that include data down to far ultraviolet
wavelengths (FUV; 1050 - 1200 A) for nine Galactic sight lines. The FUV
extinction was measured using data from the Far Ultraviolet Spectroscopic
Explorer. The sight lines were chosen for their unusual extinction properties
in the infrared through the ultraviolet; that they probe a wide range of dust
environments is evidenced by the large spread in their measured ratios of
total-to-selective extinction, R_V = 2.43 - 3.81. We find that extrapolation of
the Fitzpatrick & Massa relationship from the ultraviolet appears to be a good
predictor of the FUV extinction behavior. We find that predictions of the FUV
extinction based upon the Cardelli, Clayton & Mathis (CCM) dependence on R_V
give mixed results. For the seven extinction curves well represented by CCM in
the infrared through ultraviolet, the FUV extinction is well predicted in three
sight lines, over-predicted in two sight lines, and under-predicted in 2 sight
lines. A Maximum Entropy Method analysis using a simple three component grain
model shows that seven of the nine sight lines in the study require a larger
fraction of grain materials to be in dust when FUV extinction is included in
the models. Most of the added grain material is in the form of small (radii <
200 A) grains.Comment: Accepted for publication in the Astrophysical Journal. 31 pages with
7 figure
Rotational velocities of A-type stars I. Measurement of vsini in the southern hemisphere
Within the scope of a Key Programme determining fundamental parameters of
stars observed by HIPPARCOS, spectra of 525 B8 to F2-type stars brighter than
V=8 have been collected at ESO. Fourier transforms of several line profiles in
the range 4200-4500 A are used to derive vsini from the frequency of the first
zero. Statistical analysis of the sample indicates that measurement error is a
function of vsini and this relative error of the rotational velocity is found
to be about 6% on average. The results obtained are compared with data from the
literature. There is a systematic shift from standard values from Slettebak et
al. (1975), which are 10 to 12% lower than our findings. Comparisons with other
independent vsini values tend to prove that those from Slettebak et al. are
underestimated. This effect is attributed to the presence of binaries in the
standard sample of Slettebak et al., and to the model atmosphere they used.Comment: 17 pages, includes 18 figures, accepted in A&
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