247 research outputs found
Under the spreading chestnut tree, accountants\u27 legal liability -- A historical perspective
https://egrove.olemiss.edu/dl_proceedings/1165/thumbnail.jp
Study of capillary-based gaseous detectors
We have studied gain vs. voltage characteristics and position resolutions of
multistep capillary plates (two or three capillary plates operating in a
cascade), as well as capillary plates operating in a mode when the main
amplification occurs between plates or between the capillary plate and the
readout plate (parallel plate amplification mode). Results of these studies
demonstrated that in the parallel-plate amplification mode one can reach both
high gains (>100000) and good position resolutions (~100 micro meter) even with
a single step arrangement. It offers a compact amplification structure, which
can be used in many applications. For example, in preliminary tests we
succeeded to combine it with a photocathode and use it as a position sensitive
gaseous photomultiplier. CsI coated capillary plates could also be used as a
high position resolution and high rate X-ray converter.Comment: Presented at the NSS IEEE 2003 conference in Portland, submitted to
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A High Position Resolution X-ray Detector: an Edge on Illuminated Capillary Plate Combined with a Gas Amplification Structure
We have developed and successfully tested a prototype of a new type of high
position resolution hybrid X-ray detector. It contains a thin wall lead glass
capillary plate converter of X-rays combined with a microgap parallel-plate
avalanche chamber filled with gas at 1 atm. The operation of these converters
was studied in a wide range of X-ray energies (from 6 to 60 keV) at incident
angles varying from 0-90 degree. The detection efficiency, depending on the
geometry, photon energy, incident angle and the mode of operation, was between
5-30 percent in a single step mode and up to 50 percent in a multi-layered
combination. Depending on the capillary geometry, the position resolution
achieved was between 0.050-0.250 mm in digital form and was practically
independent of the photon energy or gas mixture. The usual lead glass capillary
plates operated without noticeable charging up effects at counting rates of 50
Hz/mm2, and hydrogen treated capillaries up to 10E5 Hz/mm2. The developed
detector may open new possibilities for medical imaging, for example in
mammography, portal imaging, radiography (including security devices),
crystallography and many other applications.Comment: Presented at the IEEE Nuclear Science Symposium, Roma, Octber 200
The Development and Study of High-Position Resolution (50 micron) RPCs for Imaging X-rays and UV photons
Nowadays, commonly used Resistive Plate Chambers (RPCs) have counting rate
capabilities of ~10E4Hz/cm2 and position resolutions of ~1cm. We have developed
small prototypes of RPCs (5x5 and 10x10cm2) having rate capabilities of up to
10E7Hz/cm2 and position resolutions of 50 micron("on line" without application
of any treatment method like "center of gravity"). The breakthrough in
achieving extraordinary rate and position resolutions was only possible after
solving several serious problems: RPC cleaning and assembling technology,
aging, spurious pulses and afterpulses, discharges in the amplification gap and
along the spacers. High-rate, high-position resolution RPCs can find a wide
range of applications in many different fields, for example in medical imaging.
RPCs with the cathodes coated by CsI photosensitive layer can detect
ultraviolet photons with a position resolution that is better than ~30 micron.
Such detectors can also be used in many applications, for example in the focal
plane of high resolution vacuum spectrographs or as image scanners.Comment: 6 pages, 5 figures, other comment
Counting niches: Abundance- by- trait patterns reveal niche partitioning in a Neotropical forest
Tropical forests challenge us to understand biodiversity, as numerous seemingly similar species persist on only a handful of shared resources. Recent ecological theory posits that biodiversity is sustained by a combination of species differences reducing interspecific competition and species similarities increasing time to competitive exclusion. Together, these mechanisms counterintuitively predict that competing species should cluster by traits, in contrast with traditional expectations of trait overdispersion. Here, we show for the first time that trees in a tropical forest exhibit a clustering pattern. In a 50- ha plot on Barro Colorado Island in Panama, species abundances exhibit clusters in two traits connected to light capture strategy, suggesting that competition for light structures community composition. Notably, we find four clusters by maximum height, quantitatively supporting the classical grouping of Neotropical woody plants into shrubs, understory, midstory, and canopy layers.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155460/1/ecy3019.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155460/2/ecy3019-sup-0001-AppendixS1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155460/3/ecy3019_am.pd
Calcium supplementation and risk of dementia in women with cerebrovascular disease
OBJECTIVE: To determine whether calcium supplementation is associated with the development of dementia in women after a 5-year follow-up.
METHODS: This was a longitudinal population-based study. The sample was derived from the Prospective Population Study of Women and H70 Birth Cohort Study in Gothenburg, Sweden, and included 700 dementia-free women aged 70â92 years. At baseline in 2000â2001, and at follow-up in 2005â2006, the women underwent comprehensive neuropsychiatric and somatic examinations. A CT scan was performed in 447 participants at baseline. Information on the use and dosage of calcium supplements was collected. Dementia was diagnosed according to DSM-III-R criteria.
RESULTS: Women treated with calcium supplements (n = 98) were at a higher risk of developing dementia (odds ratio [OR] 2.10, 95% confidence interval [CI] 1.01â4.37, p = 0.046) and the subtype stroke-related dementia (vascular dementia and mixed dementia) (OR 4.40, 95% CI 1.54â12.61, p = 0.006) than women not given supplementation (n = 602). In stratified analyses, calcium supplementation was associated with the development of dementia in groups with a history of stroke (OR 6.77, 95% CI 1.36â33.75, p = 0.020) or presence of white matter lesions (OR 2.99, 95% CI 1.28â6.96, p = 0.011), but not in groups without these conditions.
CONCLUSIONS: Calcium supplementation may increase the risk of developing dementia in elderly women with cerebrovascular disease. Because our sample was relatively small and the study was observational, these findings need to be confirmed
Introducing a true internal standard for the Comet assay to minimize intra- and inter-experiment variability in measures of DNA damage and repair
The Comet assay (CA) is a sensitive/simple measure of genotoxicity. However, many features of CA contribute variability. To minimize these, we have introduced internal standard materials consisting of âreferenceâ cells which have their DNA substituted with BrdU. Using a fluorescent anti-BrdU antibody, plus an additional barrier filter, comets derived from these cells could be readily distinguished from the âtestâ-cell comets, present in the same gel. In experiments to evaluate the reference cell comets as external and internal standards, the reference and test cells were present in separate gels on the same slide or mixed together in the same gel, respectively, before their co-exposure to X-irradiation. Using the reference cell comets as internal standards led to substantial reductions in the coefficient of variation (CoV) for intra- and inter-experimental measures of comet formation and DNA damage repair; only minor reductions in CoV were noted when the reference and test cell comets were in separate gels. These studies indicate that differences between individual gels appreciably contribute to CA variation. Further studies using the reference cells as internal standards allowed greater significance to be obtained between groups of replicate samples. Ultimately, we anticipate that development will deliver robust quality assurance materials for CA
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