2,200 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
Design and performance testing of quantitative real time PCR assays for influenza A and B viral load measurement
Background: The antiviral effect of anti-influenza drugs such as zanamivir may be demonstrated in patients as an increased rate of decline in viral load over a time course of treatment as compared with placebo. Historically this was measured using plaque assays, or Culture Enhanced Enzyme Linked Immunosorbent Assay (CE-ELISA). Objectives: to develop and characterise real time quantitative PCR (qPCR) assays to measure influenza A and B viral load in clinical samples, that offer improvements over existing methods, in particular virus infectivity assays. Study design: The dynamic range and robustness were established for the real time qPCR assays along with stability of the assay components. Cross validation of the real time PCR assays with CE-ELISA was performed by parallel testing of both serial dilutions of three different subtypes of cultured virus and a panel of influenza positive throat swab specimens. Results: the assays were specific for influenza A and B and the dynamic ranges were at least seven logs. The assay variability was within acceptable limits but increased towards the lower limit of quantification, which was 3.33 log10 viral cDNA copies/ml of virus transport medium (ten viral RNA copies/PCR). The components of the assay were robust enough to withstand extended storage and several freezeâthawcycles. For the real time PCR assays the limit of quantification was equivalent to the virus infectivity cut off, which equates to a 93-fold increase in sensitivity. Conclusion: Well characterised real time PCR assays offer significant improvements over the existing methods for measuring the viral load of strains of influenza A and B in clinical specimens
The Nuclear Spectral Energy Distribution of NGC 4395, The Least Luminous Type 1 Seyfert Galaxy
We present X-ray (ROSAT), infrared, and radio observations of NGC 4395, which
harbors the optically least luminous type 1 Seyfert nucleus discovered thus
far. In combination with published optical and ultraviolet spectra, we have
used these data to assemble the broadband spectral energy distribution (SED) of
the galaxy's nucleus. Interestingly, the SED of NGC 4395 differs markedly from
the SEDs of both quasars and typical low-luminosity active galactic nuclei,
which may be a manifestation of the different physical conditions (i.e., black
hole masses, accretion rates, and/or accretion modes) that exist in these
objects. The nuclear X-ray source in NGC 4395 is variable and has an observed
luminosity of just ~ 10^38 ergs/s. Although this emission could plausibly be
associated with either a weak active nucleus or a bright stellar-mass binary
system, the optical and ultraviolet emission-line properties of the nucleus
strongly suggest that the X-rays arise from a classical AGN.Comment: Accepted for publication in PASP (July 1999), 17 pages, including 4
Postscript figure
Track Reconstruction and Performance of DRIFT Directional Dark Matter Detectors using Alpha Particles
First results are presented from an analysis of data from the DRIFT-IIa and
DRIFT-IIb directional dark matter detectors at Boulby Mine in which alpha
particle tracks were reconstructed and used to characterise detector
performance--an important step towards optimising directional technology. The
drift velocity in DRIFT-IIa was [59.3 +/- 0.2 (stat) +/- 7.5 (sys)] m/s based
on an analysis of naturally-occurring alpha-emitting background. The drift
velocity in DRIFT-IIb was [57 +/- 1 (stat) +/- 3 (sys)] m/s determined by the
analysis of alpha particle tracks from a Po-210 source. 3D range reconstruction
and energy spectra were used to identify alpha particles from the decay of
Rn-222, Po-218, Rn-220 and Po-216. This study found that (22 +/- 2)% of Po-218
progeny (from Rn-222 decay) are produced with no net charge in 40 Torr CS2. For
Po-216 progeny (from Rn-220 decay) the uncharged fraction is (100 +0 -35)%.Comment: 27 pages, 12 figures, 5 tables. Submitted to Nuclear Instruments and
Methods in Physics Research, Section A. Subj-class: Instrumentation and
Detector
X-ray observations of the galaxy cluster Abell 2029 to the virial radius
We present Suzaku observations of the galaxy cluster Abell 2029, which
exploit Suzaku's low particle background to probe the ICM to radii beyond those
possible with previous observations (reaching out to the virial radius), and
with better azimuthal coverage. We find significant anisotropies in the
temperature and entropy profiles, with a region of lower temperature and
entropy occurring to the south east, possibly the result of accretion activity
in this direction. Away from this cold feature, the thermodynamic properties
are consistent with an entropy profile which rises, but less steeply than the
predictions of purely gravitational hierarchical structure formation. Excess
emission in the northern direction can be explained due to the overlap of the
emission from the outskirts of Abell 2029 and nearby Abell 2033 (which is at
slightly higher redshift). These observations suggest that the assumptions of
spherical symmetry and hydrostatic equilibrium break down in the outskirts of
galaxy clusters, which poses challenges for modelling cluster masses at large
radii and presents opportunities for studying the formation and accretion
history of clusters.Comment: 15 pages, 14 figures. Accepted for publication in the Monthly Notices
of the Royal Astronomical Societ
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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