212 research outputs found
Translucent windows: How uncertainty in competitive interactions impacts detection of community pattern
Trait variation and similarity among coexisting species can provide a window
into the mechanisms that maintain their coexistence. Recent theoretical
explorations suggest that competitive interactions will lead to groups, or
clusters, of species with similar traits. However, theoretical predictions
typically assume complete knowledge of the map between competition and measured
traits. These assumptions limit the plausible application of these patterns for
inferring competitive interactions in nature. Here we relax these restrictions
and find that the clustering pattern is robust to contributions of unknown or
unobserved niche axes. However, it may not be visible unless measured traits
are close proxies for niche strategies. We conclude that patterns along single
niche axes may reveal properties of interspecific competition in nature, but
detecting these patterns requires natural history expertise firmly tying traits
to niches.Comment: Main text: 18 pages, 6 figures. Appendices: A-G, 6 supplementary
figures. This is the peer reviewed version of the article of the same title
which has been accepted for publication at Ecology Letters. This article may
be used for non-commercial purposes in accordance with Wiley Terms and
Conditions for Self-Archivin
A Novel UV Photon Detector with Resistive Electrodes
In this study we present first results from a new detector of UV photons: a
thick gaseous electron multiplier (GEM) with resistive electrodes, combined
with CsI or CsTe/CsI photocathodes. The hole type structure considerably
suppresses the photon and ion feedback, whereas the resistive electrodes
protect the detector and the readout electronics from damage by any eventual
discharges. This device reaches higher gains than a previously developed
photosensitive RPC and could be used not only for the imaging of UV sources,
flames or Cherenkov light, for example, but also for the detection of X-rays
and charged particles.Comment: Presented at the International Workshop on Resistive Plate Chambers,
Korea, October 200
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
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
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
First observation of Cherenkov rings with a large area CsI-TGEM-based RICH prototype
We have built a RICH detector prototype consisting of a liquid C6F14 radiator
and six triple Thick Gaseous Electron Multipliers (TGEMs), each of them having
an active area of 10x10 cm2. One triple TGEM has been placed behind the liquid
radiator in order to detect the beam particles, whereas the other five have
been positioned around the central one at a distance to collect the Cherenkov
photons. The upstream electrode of each of the TGEM stacks has been coated with
a 0.4 micron thick CsI layer.
In this paper, we will present the results from a series of laboratory tests
with this prototype carried out using UV light, 6 keV photons from 55Fe and
electrons from 90Sr as well as recent results of tests with a beam of charged
pions where for the first time Cherenkov Ring images have been successfully
recorded with TGEM photodetectors. The achieved results prove the feasibility
of building a large area Cherenkov detector consisting of a matrix of TGEMs.Comment: Presented at the International Conference NDIP-11, Lyon,July201
Study of GEM-like detectors with resistive electrodes for RICH applications
We have developed prototypes of GEM-like detectors with resistive electrodes
to be used as RICH photodetectors equipped with CsI photocathodes. The main
advantages of these detectors are their intrinsic spark protection and
possibility to operate at high gain (~10E5) in many gases including poorly
quenched ones, allowing for the adoption of windowless configurations in which
the radiator gas is also used in the chamber. Results of systematic studies of
the resistive GEMs combined with CsI photocathodes are presented: its quantum
efficiency, rate characteristics, long-term stability, etc. On the basis of the
obtained results, we believe that the new detector will be a promising
candidate for upgrading the ALICE RICH detectorComment: Presented at the International Workshop RICH-2007, Trieste, Italy,
October 200
Photosensitive Gaseous Detectors for Cryogenic Temperature Applications
There are several proposals and projects today for building LXe Time
Projection Chambers (TPCs) for dark matter search. An important element of
these TPCs are the photomultipliers operating either inside LXe or in vapors
above the liquid.
We have recently demonstrated that photosensitive gaseous detectors (wire
type and hole-type) can operate perfectly well until temperatures of LN2. In
this paper results of systematic studies of operation of the photosensitive
version of these detectors (combined with reflective or semi-transparent CsI
photocathodes) in the temperature interval of 300-150 K are presented. In
particular, it was demonstrated that both sealed and flushed by a gas detectors
could operate at a quite stable fashion in a year/time scale. Obtained results,
in particular the long-term stability of photosensitive gaseous detectors,
strongly indicate that they can be cheap and simple alternatives to
photomultipliers or avalanche solid-state detectors in LXe TPC applications.Comment: Submitted to the Proceedings of the PSD-7 Conf. in Liverpool, U
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