225 research outputs found
The soil effects on the grapevine root system in several vineyards of the Loire valley (France)
The effects of different soil types on grapevine root distribution are presented and discussed for Loire Valley (France) conditions. Field studies with Cabernet franc/SO 4 root-stock vines showed four main rooting patterns in different soil types. A statistical analysis was used to determine the influence of several physical soil factors on root distribution. The soil water supply appears to have a beneficial effect on the root system. Conversely the penetrometer soil strength, bulk density and hydromorphic conditions are unfavourable for root developmen
Heavy Superheated Droplet Detectors as a Probe of Spin-independent WIMP Dark Matter Existence
At present, application of Superheated Droplet Detectors (SDDs) in WIMP dark
matter searches has been limited to the spin-dependent sector, owing to the
general use of fluorinated refrigerants which have high spin sensitivity. Given
their recent demonstration of a significant constraint capability with
relatively small exposures and the relative economy of the technique, we
consider the potential impact of heavy versions of such devices on the
spin-independent sector. Limits obtainable from a -loaded SDD
are estimated on the basis of the radiopurity levels and backgrounds already
achieved by the SIMPLE and PICASSO experiments. With 34 kgd exposure,
equivalent to the current CDMS, such a device may already probe to below
10 pb in the spin-independent cross section.Comment: 9 pages, 4 figures, accepted Phys. Rev.
A CF3I-based SDD Prototype for Spin-independent Dark Matter Searches
The application of Superheated Droplet Detectors (SDDs) to dark matter
searches has so far been confined to the light nuclei refrigerants C2ClF5 and
C4F10 (SIMPLE and PICASSO, respectively), with a principle sensitivity to
spin-dependent interactions. Given the competitive results of these devices, as
a result of their intrinsic insensitivity to backgrounds, we have developed a
prototype trifluoroiodomethane (CF3I)-loaded SDD with increased sensitivity to
spin-independent interactions as well. A low (0.102 kgd) exposure test
operation of two high concentration, 1 liter devices is described, and the
results compared with leading experiments in both spin-dependent and
-independent sectors. Although competitive in both sectors when the difference
in exposures is accounted for, a problem with fracturing of the detector gel
must be addressed before significantly larger exposures can be envisioned.Comment: revised and updated; accepted Astrop. Phy
First Results of the Phase II SIMPLE Dark Matter Search
We report results of a 14.1 kgd measurement with 15 superheated droplet
detectors of total active mass 0.208 kg, comprising the first stage of a 30 kgd
Phase II experiment. In combination with the results of the neutron-spin
sensitive XENON10 experiment, these results yield a limit of |a_p| < 0.32 for
M_W = 50 GeV/c2 on the spin-dependent sector of weakly interacting massive
particle-nucleus interactions with a 50% reduction in the previously allowed
region of the phase space formerly defined by XENON, KIMS and PICASSO. In the
spin-independent sector, a limit of 2.3x10-5 pb at M_W = 45 GeV/c2 is obtained.Comment: 4 pages, 4 figures; PRL-accepted version with corrected SI contour
(Fig. 4
The SIMPLE Phase II Dark Matter Search
Phase II of SIMPLE (Superheated Instrument for Massive ParticLe Experiments)
searched for astroparticle dark matter using superheated liquid
CClF droplet detectors. Each droplet generally requires an energy
deposition with linear energy transfer (LET) 150 keV/m for a
liquid-to-gas phase transition, providing an intrinsic rejection against
minimum ionizing particles of order 10, and reducing the backgrounds to
primarily and neutron-induced recoil events. The droplet phase
transition generates a millimetric-sized gas bubble which is recorded by
acoustic means. We describe the SIMPLE detectors, their acoustic
instrumentation, and the characterizations, signal analysis and data selection
which yield a particle-induced, "true nucleation" event detection efficiency of
better than 97% at a 95% C.L. The recoil- event discrimination,
determined using detectors first irradiated with neutrons and then doped with
alpha emitters, provides a recoil identification of better than 99%; it differs
from those of COUPP and PICASSO primarily as a result of their different
liquids with lower critical LETs. The science measurements, comprising two
shielded arrays of fifteen detectors each and a total exposure of 27.77 kgd,
are detailed. Removal of the 1.94 kgd Stage 1 installation period data, which
had previously been mistakenly included in the data, reduces the science
exposure from 20.18 to 18.24 kgd and provides new contour minima of
= 4.3 10 pb at 35 GeV/c in the
spin-dependent sector of WIMP-proton interactions and = 3.6
10 pb at 35 GeV/c in the spin-independent sector. These
results are examined with respect to the fluorine spin and halo parameters used
in the previous data analysis.Comment: 20 pages, 19 figures; accepted Physical Review
Final Analysis and Results of the Phase II SIMPLE Dark Matter Search
We report the final results of the Phase II SIMPLE measurements, comprising
two run stages of 15 superheated droplet detectors each, the second stage
including an improved neutron shielding. The analyses includes a refined signal
analysis, and revised nucleation efficiency based on reanalysis of
previously-reported monochromatic neutron irradiations. The combined results
yield a contour minimum of \sigma_{p} = 4.2 x 10^-3 pb at 35 GeV/c^2 on the
spin-dependent sector of WIMP-proton interactions, the most restrictive to date
from a direct search experiment and overlapping for the first time results
previously obtained only indirectly. In the spin-independent sector, a minimum
of 3.6 x 10^-6 pb at 35 GeV/c^2 is achieved, with the exclusion contour
challenging the recent CoGeNT region of current interest.Comment: revised, PRL-accepted version with slightly weakened limit contour
CD4 cell count and the risk of AIDS or death in HIV-Infected adults on combination antiretroviral therapy with a suppressed viral load: a longitudinal cohort study from COHERE.
BACKGROUND: Most adults infected with HIV achieve viral suppression within a year of starting combination antiretroviral therapy (cART). It is important to understand the risk of AIDS events or death for patients with a suppressed viral load.
METHODS AND FINDINGS: Using data from the Collaboration of Observational HIV Epidemiological Research Europe (2010 merger), we assessed the risk of a new AIDS-defining event or death in successfully treated patients. We accumulated episodes of viral suppression for each patient while on cART, each episode beginning with the second of two consecutive plasma viral load measurements 500 copies/µl, the first of two consecutive measurements between 50-500 copies/µl, cART interruption or administrative censoring. We used stratified multivariate Cox models to estimate the association between time updated CD4 cell count and a new AIDS event or death or death alone. 75,336 patients contributed 104,265 suppression episodes and were suppressed while on cART for a median 2.7 years. The mortality rate was 4.8 per 1,000 years of viral suppression. A higher CD4 cell count was always associated with a reduced risk of a new AIDS event or death; with a hazard ratio per 100 cells/µl (95% CI) of: 0.35 (0.30-0.40) for counts <200 cells/µl, 0.81 (0.71-0.92) for counts 200 to <350 cells/µl, 0.74 (0.66-0.83) for counts 350 to <500 cells/µl, and 0.96 (0.92-0.99) for counts ≥500 cells/µl. A higher CD4 cell count became even more beneficial over time for patients with CD4 cell counts <200 cells/µl.
CONCLUSIONS: Despite the low mortality rate, the risk of a new AIDS event or death follows a CD4 cell count gradient in patients with viral suppression. A higher CD4 cell count was associated with the greatest benefit for patients with a CD4 cell count <200 cells/µl but still some slight benefit for those with a CD4 cell count ≥500 cells/µl
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