141 research outputs found
Results from the First Science Run of the ZEPLIN-III Dark Matter Search Experiment
The ZEPLIN-III experiment in the Palmer Underground Laboratory at Boulby uses
a 12kg two-phase xenon time projection chamber to search for the weakly
interacting massive particles (WIMPs) that may account for the dark matter of
our Galaxy. The detector measures both scintillation and ionisation produced by
radiation interacting in the liquid to differentiate between the nuclear
recoils expected from WIMPs and the electron recoil background signals down to
~10keV nuclear recoil energy. An analysis of 847kg.days of data acquired
between February 27th 2008 and May 20th 2008 has excluded a WIMP-nucleon
elastic scattering spin-independent cross-section above 8.1x10(-8)pb at
55GeV/c2 with a 90% confidence limit. It has also demonstrated that the
two-phase xenon technique is capable of better discrimination between electron
and nuclear recoils at low-energy than previously achieved by other xenon-based
experiments.Comment: 12 pages, 17 figure
Limits on spin-dependent WIMP-nucleon cross-sections from the first ZEPLIN-II data
The first underground data run of the ZEPLIN-II experiment has set a limit on
the nuclear recoil rate in the two-phase xenon detector for direct dark matter
searches. In this paper the results from this run are converted into the limits
on spin-dependent WIMP-proton and WIMP-neutron cross-sections. The minimum of
the curve for WIMP-neutron cross-section corresponds to 0.07 pb at a WIMP mass
of around 65 GeV.Comment: 12 pages, 2 figures, to be published in Physics Letters
The ZEPLIN II dark matter detector: data acquisition system and data reduction
ZEPLIN-II is a two-phase (liquid/gas) xenon dark matter detector searching
for WIMP-nucleon interactions. In this paper we describe the data acquisition
system used to record the data from ZEPLIN-II and the reduction procedures
which parameterise the data for subsequent analysis.Comment: 11 pages, 10 figure
The ZEPLIN II dark matter detector: data acquisition system and data reduction
ZEPLIN-II is a two-phase (liquid/gas) xenon dark matter detector searching
for WIMP-nucleon interactions. In this paper we describe the data acquisition
system used to record the data from ZEPLIN-II and the reduction procedures
which parameterise the data for subsequent analysis.Comment: 11 pages, 10 figure
The ZEPLIN-III dark matter detector: performance study using an end-to-end simulation tool
We present results from a GEANT4-based Monte Carlo tool for end-to-end
simulations of the ZEPLIN-III dark matter experiment. ZEPLIN-III is a two-phase
detector which measures both the scintillation light and the ionisation charge
generated in liquid xenon by interacting particles and radiation. The software
models the instrument response to radioactive backgrounds and calibration
sources, including the generation, ray-tracing and detection of the primary and
secondary scintillations in liquid and gaseous xenon, and subsequent processing
by data acquisition electronics. A flexible user interface allows easy
modification of detector parameters at run time. Realistic datasets can be
produced to help with data analysis, an example of which is the position
reconstruction algorithm developed from simulated data. We present a range of
simulation results confirming the original design sensitivity of a few times
pb to the WIMP-nucleon cross-section.Comment: Submitted to Astroparticle Physic
The ZEPLIN-III dark matter detector: instrument design, manufacture and commissioning
We present details of the technical design and manufacture of the ZEPLIN-III
dark matter experiment. ZEPLIN-III is a two-phase xenon detector which measures
both the scintillation light and the ionisation charge generated in the liquid
by interacting particles and radiation. The instrument design is driven by both
the physics requirements and by the technology requirements surrounding the use
of liquid xenon. These include considerations of key performance parameters,
such as the efficiency of scintillation light collection, restrictions placed
on the use of materials to control the inherent radioactivity levels,
attainment of high vacuum levels and chemical contamination control. The
successful solution has involved a number of novel design and manufacturing
features which will be of specific use to future generations of direct dark
matter search experiments as they struggle with similar and progressively more
demanding requirements.Comment: 25 pages, 19 figures. Submitted to Astropart. Phys. Some figures down
sampled to reduce siz
Identification of occlusal prematurity by clinical examination and cone-beam computed tomography
Mapping Genetic Diversity of Cherimoya (Annona cherimola Mill.): Application of Spatial Analysis for Conservation and Use of Plant Genetic Resources
There is a growing call for inventories that evaluate geographic patterns in diversity of plant genetic resources maintained on farm and in species' natural populations in order to enhance their use and conservation. Such evaluations are relevant for useful tropical and subtropical tree species, as many of these species are still undomesticated, or in incipient stages of domestication and local populations can offer yet-unknown traits of high value to further domestication. For many outcrossing species, such as most trees, inbreeding depression can be an issue, and genetic diversity is important to sustain local production. Diversity is also crucial for species to adapt to environmental changes. This paper explores the possibilities of incorporating molecular marker data into Geographic Information Systems (GIS) to allow visualization and better understanding of spatial patterns of genetic diversity as a key input to optimize conservation and use of plant genetic resources, based on a case study of cherimoya (Annona cherimola Mill.), a Neotropical fruit tree species. We present spatial analyses to (1) improve the understanding of spatial distribution of genetic diversity of cherimoya natural stands and cultivated trees in Ecuador, Bolivia and Peru based on microsatellite molecular markers (SSRs); and (2) formulate optimal conservation strategies by revealing priority areas for in situ conservation, and identifying existing diversity gaps in ex situ collections. We found high levels of allelic richness, locally common alleles and expected heterozygosity in cherimoya's putative centre of origin, southern Ecuador and northern Peru, whereas levels of diversity in southern Peru and especially in Bolivia were significantly lower. The application of GIS on a large microsatellite dataset allows a more detailed prioritization of areas for in situ conservation and targeted collection across the Andean distribution range of cherimoya than previous studies could do, i.e. at province and department level in Ecuador and Peru, respectively
The Relative Impact of Climate Change on the Extinction Risk of Tree Species in the Montane Tropical Andes.
There are widespread concerns that anthropogenic climate change will become a major cause of global biodiversity loss. However, the potential impact of climate change on the extinction risk of species remains poorly understood, particularly in comparison to other current threats. The objective of this research was to examine the relative impact of climate change on extinction risk of upper montane tree species in the tropical Andes, an area of high biodiversity value that is particularly vulnerable to climate change impacts. The extinction risk of 129 tree species endemic to the region was evaluated according to the IUCN Red List criteria, both with and without the potential impacts of climate change. Evaluations were supported by development of species distribution models, using three methods (generalized additive models, recursive partitioning, and support vector machines), all of which produced similarly high AUC values when averaged across all species evaluated (0.82, 0.86, and 0.88, respectively). Inclusion of climate change increased the risk of extinction of 18-20% of the tree species evaluated, depending on the climate scenario. The relative impact of climate change was further illustrated by calculating the Red List Index, an indicator that shows changes in the overall extinction risk of sets of species over time. A 15% decline in the Red List Index was obtained when climate change was included in this evaluation. While these results suggest that climate change represents a significant threat to tree species in the tropical Andes, they contradict previous suggestions that climate change will become the most important cause of biodiversity loss in coming decades. Conservation strategies should therefore focus on addressing the multiple threatening processes currently affecting biodiversity, rather than focusing primarily on potential climate change impacts
- …