3,856 research outputs found
Improved Probability Method for Estimating Signal in the Presence of Background
A suggestion is made for improving the Feldman Cousins method of estimating
signal counts in the presence of background. The method concentrates on finding
essential information about the signal and ignoring extraneous information
about background. An appropriate method is found which uses the condition that
the number of background events obtained does not exceed the total number of
events obtained. Several alternative approaches are explored.Comment: Modified 12/21 for singlespace to save trees, 9 pages, 1 figure.
Modified 8/11/99 to add small modifications made for the Phys. Rev. articl
Assessing the Accuracy of Complex Refractive Index Retrievals from Single Aerosol Particle Cavity Ring-Down Spectroscopy
<p>Cavity ring-down spectroscopy (CRDS) of single, optically manipulated aerosol particles affords quantitative retrieval of refractive indices for particles of fixed or evolving composition with high precision. Here, we quantify the accuracy with which refractive index determinations can be made by CRDS for single particles confined within the core of a Bessel laser beam and how that accuracy is degraded as the particle size is progressively reduced from the coarse mode (>1 μm radius) to the accumulation mode (<500 nm radius) regime. We apply generalized Lorenz–Mie theory to the intra-cavity standing wave to explore the effect of particle absorption on the distribution of extinction cross section determinations resulting from stochastic particle motion in the Bessel beam trap. The analysis provides an assessment of the accuracy with which the real, <i>n</i>, and imaginary, κ, components of the refractive index can be determined for a single aerosol particle.</p> <p>Published with license by American Association for Aerosol Research</p> <p><a href="https://www.tandfonline.com/pb-assets/tandf/Migrated/UAST_VideoAbstract_Transcript.pdf" target="_blank">Read the transcript</a></p> <p><a href="https://vimeo.com/263371383" target="_blank">Watch the video on Vimeo</a></p
The effectiveness and variation of acute medical units: a systematic review
Purpose:
To evaluate the evidence for the effectiveness of acute medical units (AMUs) compared with other models of care and compare the components of AMU models.
Data sources:
Six electronic databases and grey literature sources searched between 1990 and 2014.
Study selection:
Studies reporting on AMUs as an intervention for unplanned medical presentations to hospital with the inclusion of all outcome measures/study designs/comparators.
Data extraction:
Data on study characteristics/outcomes/AMU components were extracted by one author and confirmed by a second.
Data synthesis:
Seventeen studies of 12 AMUs across five countries were included. The AMU model was associated with a reduction in-hospital length of stay (LOS) in all analyses ranging from 0.3 to 2.6 days; and a reduction in mortality in 12 of the 14 analyses with the change ranging from a 0.1% increase to a 8.8% reduction. Evidence relating to readmissions and patient/staff satisfaction was less conclusive. There was variation in the following components of AMUs: admission criteria, entry sources, functions and consultant work patterns.
Conclusion:
This review provides evidence that AMUs are associated with reductions in-hospital LOS and, less convincingly, mortality compared with other models of care when implemented in European and Australasian settings. Reported estimates may be affected by residual confounding. This review reports heterogeneity in components of the AMU model. Further work to identify what constitutes the key components of an AMU is needed to improve the quality and effectiveness of acute medical care. This is of particular importance given the escalating demand on acute services
Optical extinction efficiency measurements on fine and accumulation mode aerosol using single particle cavity ring-down spectroscopy
We report a new single aerosol particle approach using cavity ringdown spectroscopy to accurately determine optical extinction cross sections at multiple wavelengths.</p
Discovery of a Young L Dwarf Binary, SDSS J224953.47+004404.6AB
We report discovery of a young 0.32" L dwarf binary, SDSS J2249+0044AB, found
as the result of a Keck LGSAO imaging survey of young field brown dwarfs. Weak
K, Na, and FeH features as well as strong VO absorption in the integrated-light
J-band spectrum indicate a young age for the system. From spatially resolved
K-band spectra we determine spectral types of L3 and L5 for components A and B,
respectively. SDSS J2249+0044A is spectrally very similar to G196-3B, an L3
companion to a young M2.5 field dwarf. Thus, we adopt 100 Myr (the age estimate
of the G196-3 system) as the age of SDSS J2249+0044AB, but ages of 12-790 Myr
are possible. By comparison to G196-3B, we estimate a distance to SDSS
J2249+0044AB of 54 +- 16 pc and infer a projected separation of 17 +- 5 AU for
the binary. Comparison of the luminosities to evolutionary models at an age of
100 Myr yields masses of 0.029 and 0.022 Msun for SDSS J2249+0044A and B,
respectively. Over the possible ages of the system (12-790 Myr), the mass of
SDSS J2249+0044A could range from 0.011 to 0.070 Msun and the mass of SDSS
J2249+0044B could range from 0.009 to 0.065 Msun. Evolutionary models predict
that either component could be burning deuterium, which could result in a mass
ratio as low as 0.4, or alternatively, a reversal in the luminosities of the
binary. We find a likely proper motion companion, GSC 00568-01752, which lies
48.9" away (2600 AU) and has SDSS+2MASS colors consistent with an early M
dwarf. The photometric distance to GSC 00568-01752 is 53 +- 15 pc, in agreement
with our distance estimate for SDSS J2249+0044AB. The space motion of SDSS
J2249+0044AB shows no obvious coincidence with known young moving groups. The
unusually red near-IR colors, young age, and low masses of the binary make it
an important template for studying planetary-mass objects found by direct
imaging surveys.Comment: revised, accepted versio
Discovery of a Brown Dwarf Companion to Gliese 570ABC: A 2MASS T Dwarf Significantly Cooler than Gliese 229B
We report the discovery of a widely separated (258\farcs3\pm0\farcs4) T
dwarf companion to the Gl 570ABC system. This new component, Gl 570D, was
initially identified from the Two Micron All Sky Survey (2MASS). Its
near-infrared spectrum shows the 1.6 and 2.2 \micron CH absorption bands
characteristic of T dwarfs, while its common proper motion with the Gl 570ABC
system confirms companionship. Gl 570D (M = 16.470.07) is nearly a
full magnitude dimmer than the only other known T dwarf companion, Gl 229B, and
estimates of L = (2.80.3)x10 L_{\sun} and T = 75050
K make it significantly cooler and less luminous than any other known brown
dwarf companion. Using evolutionary models by Burrows et al. and an adopted age
of 2-10 Gyr, we derive a mass estimate of 5020 M for this object.Comment: 13 pages, 2 figures, 2 tables, accepted by ApJ
The Spectra of T Dwarfs I: Near-Infrared Data and Spectral Classification
We present near-infrared spectra for a sample of T dwarfs, including eleven
new discoveries made using the Two Micron All Sky Survey. These objects are
distinguished from warmer (L-type) brown dwarfs by the presence of methane
absorption bands in the 1--2.5 \micron spectral region. A first attempt at a
near-infrared classification scheme for T dwarfs is made, based on the
strengths of CH and HO bands and the shapes of the 1.25, 1.6, and 2.1
\micron flux peaks. Subtypes T1 V through T8 V are defined, and spectral
indices useful for classification are presented. The subclasses appear to
follow a decreasing T scale, based on the evolution of CH and
HO bands and the properties of L and T dwarfs with known distances.
However, we speculate that this scale is not linear with spectral type for cool
dwarfs, due to the settling of dust layers below the photosphere and subsequent
rapid evolution of spectral morphology around T 1300--1500 K.
Similarities in near-infrared colors and continuity of spectral features
suggest that the gap between the latest L dwarfs and earliest T dwarfs has been
nearly bridged. This argument is strengthened by the possible role of CH as
a minor absorber shaping the K-band spectra of the latest L dwarfs. Finally, we
discuss one peculiar T dwarf, 2MASS 0937+2931, which has very blue
near-infrared colors (J-K = 0.24) due to suppression of the 2.1
\micron peak. The feature is likely caused by enhanced collision-induced
H absorption in a high pressure or low metallicity photosphere.Comment: 74 pages including 26 figures, accepted by ApJ v563 December 2001;
full paper including all of Table 3 may be downloaded from
http://www.gps.caltech.edu/~pa/adam/classification ;also see submission
010844
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