1,193 research outputs found
South Africa, imperial preference and Ottawa: 1925-1932
African Studies Seminar series. Paper presented 17 May, 1993The imperial economic conference held in Ottawa in July – August 1932 was not a successful exercise in imperial economic cooperation. Instead it produced a series of bilateral trade
agreements mainly between the United Kingdom and each of the dominions in turn. On the British side Ottawa was seen as confirming the move from free trade to protection that was made
through the Import Duties Act of February 1932. Ottawa was also seen as a move toward greater reliance on imperial preference. But these policy shifts were hardly decisive. In terms of a
recent judgment the protection was ‘distinctly mild’ and the imperial preference ‘very diluted’(1). Since imperial economic cooperation was the main policy plank of Britain's coalition 'National' government, it was the United Kingdom delegation (which included half the cabinet) that had to make most of the concessions during the Ottawa negotiations
EXIST's Gamma-Ray Burst Sensitivity
We use semi-analytic techniques to evaluate the burst sensitivity of designs
for the EXIST hard X-ray survey mission. Applying these techniques to the
mission design proposed for the Beyond Einstein program, we find that with its
very large field-of-view and faint gamma-ray burst detection threshold, EXIST
will detect and localize approximately two bursts per day, a large fraction of
which may be at high redshift. We estimate that EXIST's maximum sensitivity
will be ~4 times greater than that of Swift's Burst Alert Telescope. Bursts
will be localized to better than 40 arcsec at threshold, with a burst position
as good as a few arcsec for strong bursts. EXIST's combination of three
different detector systems will provide spectra from 3 keV to more than 10 MeV.
Thus, EXIST will enable a major leap in the understanding of bursts, their
evolution, environment, and utility as cosmological probes.Comment: 25 pages, 10 figures, accepted by Ap
Study of Thick CZT Detectors for X-ray and Gamma-Ray Astronomy
CdZnTe (CZT) is a wide bandgap II-VI semiconductor developed for the
spectroscopic detection of X-rays and {\gamma}-rays at room temperature. The
Swift Burst Alert Telescope is using an 5240 cm2 array of 2 mm thick CZT
detectors for the detection of 15-150 keV X-rays from Gamma-Ray Bursts. We
report on the systematic tests of thicker (\geq 0.5 cm) CZT detectors with
volumes between 2 cm3 and 4 cm3 which are potential detector choices for a
number of future X-ray telescopes that operate in the 10 keV to a few MeV
energy range. The detectors contacted in our laboratory achieve Full Width Half
Maximum energy resolutions of 2.7 keV (4.5%) at 59 keV, 3 keV (2.5%) at 122 keV
and 4 keV (0.6%) at 662 keV. The 59 keV and 122 keV energy resolutions are
among the world-best results for \geq 0.5 cm thick CZT detectors. We use the
data set to study trends of how the energy resolution depends on the detector
thickness and on the pixel pitch. Unfortunately, we do not find clear trends,
indicating that even for the extremely good energy resolutions reported here,
the achievable energy resolutions are largely determined by the properties of
individual crystals. Somewhat surprisingly, we achieve the reported results
without applying a correction of the anode signals for the depth of the
interaction. Measuring the interaction depths thus does not seem to be a
pre-requisite for achieving sub-1% energy resolutions at 662 keV.Comment: 15 pages, 11 figure
The Proposed High Energy Telescope (HET) for EXIST
The hard X-ray sky now being studied by INTEGRAL and Swift and soon by NuSTAR
is rich with energetic phenomena and highly variable non-thermal phenomena on a
broad range of timescales. The High Energy Telescope (HET) on the proposed
Energetic X-ray Imaging Survey Telescope (EXIST) mission will repeatedly survey
the full sky for rare and luminous hard X-ray phenomena at unprecedented
sensitivities. It will detect and localize (<20", at 5 sigma threshold) X-ray
sources quickly for immediate followup identification by two other onboard
telescopes - the Soft X-ray imager (SXI) and Optical/Infrared Telescope (IRT).
The large array (4.5 m^2) of imaging (0.6 mm pixel) CZT detectors in the HET, a
coded-aperture telescope, will provide unprecedented high sensitivity (~0.06
mCrab Full Sky in a 2 year continuous scanning survey) in the 5 - 600 keV band.
The large field of view (90 deg x 70 deg) and zenith scanning with
alternating-orbital nodding motion planned for the first 2 years of the mission
will enable nearly continuous monitoring of the full sky. A 3y followup pointed
mission phase provides deep UV-Optical-IR-Soft X-ray and Hard X-ray imaging and
spectroscopy for thousands of sources discovered in the Survey. We review the
HET design concept and report the recent progress of the CZT detector
development, which is underway through a series of balloon-borne wide-field
hard X-ray telescope experiments, ProtoEXIST. We carried out a successful
flight of the first generation of fine pixel large area CZT detectors
(ProtoEXIST1) on Oct 9, 2009. We also summarize our future plan (ProtoEXIST2 &
3) for the technology development needed for the HET.Comment: 10 pages, 13 figures, 2 tables, SPIE Conference "Astronomical
Telescopes and Instrumentation 2010"; to appear in Proceedings SPIE (2010
Antimalarial, anticancer, antimicrobial activities and chemical constituents of essential oil from the aerial parts of Cyperus kyllingia Endl.
The chemical constituents of the essential oil from Cyperus kyllingia Endl. were analyzed by a GC, GC-MS. Twenty-three compounds were identified, accounting for 93.75% of the total oil that consisted mainly of oxygenated sesquiterpenes (53.52%), particularly sesquiterpene hydrocarbons (38.97%), and carboxylic acid (1.26%). The most representative compounds were α-cadinol (19.32%), caryophyllene oxide (12.17%), α-muurolol (11.58%), α-humulene (9.85%), and α-atlantone (6.07%). The oil showed significant activities against Plasmodium falcipalum (K1, multi drug resistant strain) and NCI-H187 (Small Cell Lung Cancer) with the IC50 values of 7.52 and 7.72 μg/mL, respectively. The oil exhibited highly active against Staphylococcus aureus ATCC25923 and moderately active against Escherichia coli ATCC25922, Pseudomonas aeruginosa ATCC27553, Aspergillus flavus and Candida albicans
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