1,645 research outputs found
The DRIFT Project: Searching for WIMPS with a Directional Detector
A low pressure time projection chamber for the detection of WIMPs is
discussed. Discrimination against Compton electron background in such a device
should be very good, and directional information about the recoil atoms would
be obtainable. If a full 3-D reconstruction of the recoil tracks can be
achieved, Monte Carlo studies indicate that a WIMP signal could be identified
with high confidence from as few as 30 detected WIMP-nucleus scattering events.Comment: 5 pages, 3 figures. Presented at Dark 98, Heidelberg, July 1998, and
to appear in conference proceeding
First Results from the DRIFT-IIa Dark Matter Detector
Data from the DRIFT-IIa directional dark matter experiment are presented,
collected during a near continuous 6 month running period. A detailed
calibration analysis comparing data from gamma-ray, x-ray and neutron sources
to a GEANT4 Monte Carlo simulations reveals an efficiency for detection of
neutron induced recoils of 94+/-2(stat.)+/-5(sys.)%. Software-based cuts,
designed to remove non-nuclear recoil events, are shown to reject 60Co
gamma-rays with a rejection factor of better than 8x10-6 for all energies above
threshold. An unexpected event population has been discovered and is shown here
to be due to the alpha-decay of 222Rn daughter nuclei that have attached to the
central cathode. A limit on the flux of neutrons in the Boulby Underground
Laboratory is derived from analysis of unshielded and shielded data.Comment: 43 pages, 14 figures, submitted to Astroparticle Physic
The Supergiant Shell LMC2: II. Physical Properties of the 10^6 K Gas
LMC2 has the highest X-ray surface brightness of all know supergiant shells
in the Large Magellanic Cloud (LMC). The X-ray emission peaks within the
ionized filaments that define the shell boundary, but also extends beyond the
southern border of LMC2 as an X-ray bright spur. ROSAT HRI images reveal the
X-ray emission from LMC2 and the spur to be truly diffuse, indicating a hot
plasma origin. We have obtained ROSAT PSPC and ASCA SIS spectra to study the
physical conditions of the hot gas interior to LMC2 and the spur. Raymond-Smith
thermal plasma model fits to the X-ray spectra, constrained by HI 21-cm
emission-line measurements of the column density, show the plasma temperature
of the hot gas interior of LMC2 to be kT = 0.1 - 0.7 keV and of the spur to be
kT = 0.1 - 0.5 keV. We have compared the physical conditions of the hot gas
interior to LMC2 with those of other supergiant shells, superbubbles, and
supernova remnants (SNRs) in the LMC. We find that our derived electron
densities for the hot gas inside LMC2 is higher than the value determined for
the supergiant shell LMC4, comparable to the value determined for the
superbubble N11, and lower than the values determined for the superbubble N44
and a number of SNRs.Comment: 29 pages, 5 figures, to be published in Ap
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Design, synthesis, characterization and toxicity studies of Poly (N-Iso-Propylacrylamide-co-Lucifer Yellow) particles for drug delivery applications
A novel fluorescent temperature/pH responsive particle was designed, synthesized, characterised and tested for toxicity. Poly ( N-iso- propylacrylamide -co- 5%-lucifer yellow) (p(NIPAM -co- 5% LY)) was prepared using a surfactant free emulsion polymerisation technique. The particles were negatively charged and were approximately 250 nm at 15Ă°C. When the particles de-swell following an increase in temperature, a particle size around 100 nm is obtained. The toxicity of different concentrations of the new particles (p(NIPAM) -co- 5% LY, as well as the 100% p(NIPAM) and the main monomer NIPAM was tested on two cell lines (Hela and Vero). The toxicity was tested in comparison to a positive control (dextran sugar) and a negative one (poly(ethylenimine)) (PEI). The results show that the two particles show cell viability over 80% (for both cell lines Hela and Vero) up to a concentration of 3 mg/mL while NIPAM monomer showed cell viability over 80% at a concentration equal to or less than 0.3 mg/mL. The fluorescence property of the novel particles make them traceable. Combining this property (tracing) to the ability of the particles to release their content in response to temperature and pH change can be a potential drug delivery system for cancer treatment
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Metabolomics analysis identifies sex-associated metabotypes of oxidative stress and the autotaxin-lysoPA axis in COPD.
Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease and a leading cause of mortality and morbidity worldwide. The aim of this study was to investigate the sex dependency of circulating metabolic profiles in COPD.Serum from healthy never-smokers (healthy), smokers with normal lung function (smokers), and smokers with COPD (COPD; Global Initiative for Chronic Obstructive Lung Disease stages I-II/A-B) from the Karolinska COSMIC cohort (n=116) was analysed using our nontargeted liquid chromatography-high resolution mass spectrometry metabolomics platform.Pathway analyses revealed that several altered metabolites are involved in oxidative stress. Supervised multivariate modelling showed significant classification of smokers from COPD (p=2.8Ă10-7). Sex stratification indicated that the separation was driven by females (p=2.4Ă10-7) relative to males (p=4.0Ă10-4). Significantly altered metabolites were confirmed quantitatively using targeted metabolomics. Multivariate modelling of targeted metabolomics data confirmed enhanced metabolic dysregulation in females with COPD (p=3.0Ă10-3) relative to males (p=0.10). The autotaxin products lysoPA (16:0) and lysoPA (18:2) correlated with lung function (forced expiratory volume in 1â
s) in males with COPD (r=0.86; p<0.0001), but not females (r=0.44; p=0.15), potentially related to observed dysregulation of the miR-29 family in the lung.These findings highlight the role of oxidative stress in COPD, and suggest that sex-enhanced dysregulation in oxidative stress, and potentially the autotaxin-lysoPA axis, are associated with disease mechanisms and/or prevalence
Dual-barrel conductance micropipet as a new approach to the study of ionic crystal dissolution kinetics
A new approach to the study of ionic crystal dissolution kinetics is described, based on the use of a dual-barrel theta conductance micropipet. The solution in the pipet is undersaturated with respect to the crystal of interest, and when the meniscus at the end of the micropipet makes contact with a selected region of the crystal surface, dissolution occurs causing the solution composition to change. This is observed, with better than 1 ms time resolution, as a change in the ion conductance current, measured across a potential bias between an electrode in each barrel of the pipet. Key attributes of this new technique are: (i) dissolution can be targeted at a single crystal surface; (ii) multiple measurements can be made quickly and easily by moving the pipet to a new location on the surface; (iii) materials with a wide range of kinetics and solubilities are open to study because the duration of dissolution is controlled by the meniscus contact time; (iv) fast kinetics are readily amenable to study because of the intrinsically high mass transport rates within tapered micropipets; (v) the experimental geometry is well-defined, permitting finite element method modeling to allow quantitative analysis of experimental data. Herein, we study the dissolution of NaCl as an example system, with dissolution induced for just a few milliseconds, and estimate a first-order heterogeneous rate constant of 7.5 (±2.5) Ă 10â5 cm sâ1 (equivalent surface dissolution flux ca. 0.5 ÎŒmol cmâ2 sâ1 into a completely undersaturated solution). Ionic crystals form a huge class of materials whose dissolution properties are of considerable interest, and we thus anticipate that this new localized microscale surface approach will have considerable applicability in the future
The Hot Galactic Corona and the Soft X-ray Background
I characterize the global distribution of the 3/4 keV band background with a
simple model of the hot Galactic corona, plus an isotropic extragalactic
background. The corona is assumed to be approximately polytropic (index = 5/3)
and hydrostatic in the gravitational potential of the Galaxy. The model
accounts for X-ray absorption, and is constrained iteratively with the ROSAT
all-sky X-ray survey data. Regions where the data deviate significantly from
the model represent predominantly the Galactic disk and individual nearby hot
superbubbles. The global distribution of the background, outside these regions,
is well characterized by the model; the 1 sigma relative dispersion of the data
from the model is about 15%. The electron density and temperature of the corona
near the Sun are about 1.1 x 10^{-3} cm^{-3} and about 1.7 x 10^6 K. The same
model also explains well the 1.5 keV band background. The model prediction in
the 1/4 keV band, though largely uncertain, qualitatively shows large intensity
and spectral variations of the corona contribution across the sky.Comment: An invited talk at IAU Colloquium No. 166: The Local Bubble and
Beyond. 10 pages (including b/w figures). Color versions of Figs. 1 and 4 are
provided separately and may also be found at
www.astro.nwu.edu/astro/wqd/paper/hal
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