8,333 research outputs found
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
Nonlinear modal coupling in a high-stress doubly-clamped nanomechanical resonator
We present results from a study of the nonlinear intermodal coupling between
different flexural vibrational modes of a single high-stress, doubly-clamped
silicon nitride nanomechanical beam. The measurements were carried out at 100
mK and the beam was actuated using the magnetomotive technique. We observed the
nonlinear behavior of the modes individually and also measured the coupling
between them by driving the beam at multiple frequencies. We demonstrate that
the different modes of the resonator are coupled to each other by the
displacement induced tension in the beam, which also leads to the well known
Duffing nonlinearity in doubly-clamped beams.Comment: 15 pages, 7 figure
Data Analysis Techniques for Fan Performance in Highly-Distorted Flows from Boundary Layer Ingesting Inlets
The design of a unique distortion-tolerant fan for a high-bypass ratio boundary-layer ingesting propulsion system has been completed and a rig constructed and tested in the NASA Glenn 8x6 wind tunnel. Processing the data from the experiment presented some interesting challenges because of the complexity of the experimental setup and the flow through the test rig. The experiment was run in three phases, each of which employed a unique complement of inlet throat and fan face instrumentation to avoid the blockage that would have resulted from simultaneously installing all of the rakes. The measurement from the individual test points were subsequently combined to compute the overall stage performance. A CFD model of the experiment was used to gain understanding of the flow field and to test some of the techniques proposed for interpolating and extrapolating the measurements into regions where measurements were not made. This capability became extremely useful when it was discovered that there was an unexpected total temperature distortion in the tunnel. The CFD model was modified by inserting a total temperature profile at the upstream boundary that mimicked the measured distortion where measurements were available and that CFD solution was used to investigate methods to infer the complete total temperature field at the fan face
Stellar Populations of the Sagittarius Dwarf Irregular Galaxy
We present deep BVRI CCD photometry of the stars in the dwarf irregular
galaxy SagDIG. The color-magnitude diagrams of the measured stars in SagDIG
show a blue plume which consists mostly of young stellar populations, and a
well-defined red giant branch (RGB). The foreground reddening of SagDIG is
estimated to be E(B-V)=0.06. The tip of the RGB is found to be at
I_(TRGB)=21.55 +/- 0.10 mag. From this the distance to this galaxy is estimated
to be d = 1.18 +/- 0.10 Mpc. This result, combined with its velocity
information, shows that it is a member of the Local Group. The mean metallicity
of the red giant branch is estimated to be [Fe/H] < -2.2 dex. This shows that
SagDIG is one of the most metal-poor galaxies. Total magnitudes of SagDIG (<
r_H (= 107 arcsec)) are derived to be B^T=13.99 mag, V^T=13.58 mag, R^T=13.19
mag, and I^T=12.88 mag, and the corresponding absolute magnitudes are
M_B=-11.62 mag, M_V=-11.97 mag, M_R=-12.33 mag, and M_I=-12.60 mag. Surface
brightness profiles of the central part of SagDIG are approximately fit by a
King model with a core concentration parameter c = log (r_t / r_c) ~ 0.6, and
those of the outer part follow an exponential law with a scale length of 37
arcsec. The central surface brightness is measured to be mu_B (0) = 24.21 mag
arcsec^(-2) and mu_V (0) =23.91 mag arcsec^(-2). The magnitudes and colors of
the brightest blue and red stars in SagDIG (BSG and RSG) are measured to be,
respectively, _BSG = 19.89 +/- 0.13 mag, _BSG = 0.08 +/- 0.07
mag, _RSG = 20.39 +/- 0.10 mag, and _RSG = 1.29 +/- 0.12 mag.
The corresponding absolute magnitudes are derived to be _BSG = -5.66
mag and _RSG = -5.16 mag, which are about one magnitude fainter than
those expected from conventional correlations with galaxy luminosity.Comment: 16 pages(AASLaTeX), 10 Postscript figures, Accepted for publication
in Astronomical Journal, 200
The Distance of the Gamma-ray Binary 1FGL J1018.6-5856
The recently discovered gamma-ray binary 1FGL J1018.6-5856 has a proposed
optical/near-infrared (OIR) counterpart 2MASS 10185560-5856459. We present
Stromgren photometry of this star to investigate its photometric variability
and measure the reddening and distance to the system. We find that the
gamma-ray binary has E(B-V) = 1.34 +/- 0.04 and d = 5.4^+4.6_-2.1 kpc. While
E(B-V) is consistent with X-ray observations of the neutral hydrogen column
density, the distance is somewhat closer than some previous authors have
suggested.Comment: Accepted to PAS
A delta Scuti distance to the Large Magellanic Cloud
We present results from a well studied delta Scuti star discovered in the
LMC. The absolute magnitude of the variable was determined from the PL relation
for Galactic delta Scuti stars and from the theoretical modeling of the
observed B,V,I light curves. The two methods give distance moduli for the LMC
of 18.46+-0.19 and 18.48+-0.15, respectively, for a consistent value of the
stellar reddening of E(B-V)=0.08+-0.02. We have also analyzed 24 delta Scuti
candidates discovered in the OGLE II survey of the LMC, and 7 variables
identified in the open cluster LW 55 and in the galaxy disk by Kaluzny et al.
(2003, 2006). We find that the LMC delta Scuti stars define a PL relation whose
slope is very similar to that defined by the Galactic delta Scuti variables,
and yield a distance modulus for the LMC of 18.50+-0.22 mag. We compare the
results obtained from the delta Scuti variables with those derived from the LMC
RR Lyrae stars and Cepheids. Within the observational uncertainties, the three
groups of pulsating stars yield very similar distance moduli. These moduli are
all consistent with the "long" astronomical distance scale for the Large
Magellanic Cloud.Comment: Accepted for publication on A
Spectroscopy and Time Variability of Absorption Lines in the Direction of the Vela Supernova Remnant
We present high resolution (R~75,000), high signal-to-noise (S/N~100) Ca II
3933.663 and Na I 5889.951, 5895.924 spectra of 68
stars in the direction of the Vela supernova remnant. The spectra comprise the
most complete high resolution, high S/N, optical survey of early type stars in
this region of the sky. A subset of the sight lines has been observed at
multiple epochs, 1993/1994 and 1996. Of the thirteen stars observed twice,
seven have spectra revealing changes in the equivalent width and/or velocity
structure of lines, most of which arise from remnant gas. Such time variability
has been reported previously for the sight lines towards HD 72089 and HD 72997
by Danks & Sembach (1995) and for HD 72127 by Hobbs et al. (1991). We have
confirmed the ongoing time variability of these spectra and present new
evidence of variability in the spectra of HD 73658, HD 74455, HD 75309 and HD
75821. We have tabulated Na I and Ca II absorption line information for the
sight lines in our sample to serve as a benchmark for further investigations of
the dynamics and evolution of the Vela SNR.Comment: 8 pages of text, 4 tables, 16 pages of figures Accepted and to be
published in ApJ
Development of a score for assessment of radiologic damage in large-vessel vasculitis (Combined Arteritis Damage Score, CARDS)
OBJECTIVES:
Outcome assessment in large-vessel vasculitis (LVV) remains challenging and this impairs patient management and the conduct of clinical studies. Previous proposals for outcome tools have not included imaging. This study aimed to develop an imaging score to quantify damage in LVV and to assess the difference between Takayasu (TAK) and giant cell arteritis (GCA).
METHODS:
Ninety-six patients (41 TAK, 55 GCA) were identified from local registries at two University Hospitals in the UK. Radiologic lesions including stenosis, occlusion and aneurysm were evaluated in 25 arterial regions by enhanced computed tomography or magnetic resonance angiography. Lesion correlation with combined damage assessment scores was employed in a multiple regression analysis to define the weight of individual lesions and develop a damage index.
RESULTS:
A numerical damage index was developed: the “Combined Arteritis Damage Score (CARDS)”. The index was derived from a formula: number of regions with mild stenosis × 0.6 + number of regions with moderate to severe stenosis × 1.2 + number with occlusions × 1.6 + number with aneurysms × 0.8 in 25 arterial regions. The median CARDS was higher in TAK than GCA (4.1 and 0.6, interquartile range 1.3-5.7 and 0-3, p<0.001).
CONCLUSIONS:
We have developed a damage assessment tool, CARDS, based on imaging in LVV of potential value to clinical studies and patient management. TAK and GCA differ in the radiologic severity of disease.Dr. Daiki Nakagomi is supported by the Japan College of Rheumatology and Shimoshizu Hospital, National Hospital Organization. This project was supported by the Cambridge Biomedical Research Centre
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