295 research outputs found
Mitigating radiation damage of single photon detectors for space applications
Single-photon detectors in space must retain useful performance
characteristics despite being bombarded with sub-atomic particles. Mitigating
the effects of this space radiation is vital to enabling new space applications
which require high-fidelity single-photon detection. To this end, we conducted
proton radiation tests of various models of avalanche photodiodes (APDs) and
one model of photomultiplier tube potentially suitable for satellite-based
quantum communications. The samples were irradiated with 106 MeV protons at
doses approximately equivalent to lifetimes of 0.6 , 6, 12 and 24 months in a
low-Earth polar orbit. Although most detection properties were preserved,
including efficiency, timing jitter and afterpulsing probability, all APD
samples demonstrated significant increases in dark count rate (DCR) due to
radiation-induced damage, many orders of magnitude higher than the 200 counts
per second (cps) required for ground-to-satellite quantum communications. We
then successfully demonstrated the mitigation of this DCR degradation through
the use of deep cooling, to as low as -86 degrees C. This achieved DCR below
the required 200 cps over the 24 months orbit duration. DCR was further reduced
by thermal annealing at temperatures of +50 to +100 degrees C.Comment: The license has been corrected. Note that the license of v2 was
incorrect and not valid. No other changes since v
Chlamydia pneumoniae: An Etiologic Agent for Late-Onset Dementia
The disease known as late-onset Alzheimer\u27s disease is a neurodegenerative condition recognized as the single most common form of senile dementia. The condition is sporadic and has been attributed to neuronal damage and loss, both of which have been linked to the accumulation of protein deposits in the brain. Significant progress has been made over the past two decades regarding our overall understanding of the apparently pathogenic entities that arise in the affected brain, both for early-onset disease, which constitutes approximately 5% of all cases, as well as late-onset disease, which constitutes the remainder of cases. Observable neuropathology includes: neurofibrillary tangles, neuropil threads, neuritic senile plaques and often deposits of amyloid around the cerebrovasculature. Although many studies have provided a relatively detailed knowledge of these putatively pathogenic entities, understanding of the events that initiate and support the biological processes generating them and the subsequent observable neuropathology and neurodegeneration remain limited. This is especially true in the case of late-onset disease. Although early-onset Alzheimer\u27s disease has been shown conclusively to have genetic roots, the detailed etiologic initiation of late-onset disease without such genetic origins has remained elusive. Over the last 15 years, current and ongoing work has implicated infection in the etiology and pathogenesis of late-onset dementia. Infectious agents reported to be associated with disease initiation are various, including several viruses and pathogenic bacterial species. We have reported extensively regarding an association between late-onset disease and infection with the intracellular bacterial pathoge
Effects of tyrosine kinase inhibitors on protein kinase-independent systems
AbstractTyrosine kinase inhibitors have been widely used to probe the role of tyrosine phosphorylation in cellular signalling. These inhibitors exhibit an apparent specificity for tyrosine kinases over the serine/threonine kinases but little is known about their effects on other enzymes or biological systems. We demonstrate that genistein, erbstatin and α-cyanoeinnamamides (tyrphostins) have inhibitory effects on fatty acid synthesis, lactate transport, mitochondrial oxidative phosphorylation and aldehyde dehydrogenase. We propose, therefore, that results obtained using tyrosine kinase inhibitors should be interpreted with caution, particularly if used at concentrations sufficient to inhibit these non-protein kinase-dependent events
Neurocognitive and social-communicative function of children born very preterm at 10 years of age: Associations with microorganisms recovered from the placenta parenchyma
Public sector restructuring and regional development: the impact of compulsory competitive tendering in the UK
This paper contributes to the analysis of contemporary public sector restructuring in the UK through an evaluation of the impact of the introduction of compulsory competitive tendering (CCT) for the provision of local public services. Public services play an important stabilizing role in regional economic development but the introduction of CCT has undermined that role. Public service workers have suVered deteriorating levels of pay and conditions of service, and the capacity of local authorities to act to support local economic development has been reduced. Thus the introduction of CCT has undermined the contribution of local public services to the maintenance of interregional economic stability and to regional development
The Extragalactic Distance Scale Key Project XXVII. A Derivation of the Hubble Constant Using the Fundamental Plane and Dn-Sigma Relations in Leo I, Virgo, and Fornax
Using published photometry and spectroscopy, we construct the fundamental
plane and D_n-Sigma relations in Leo I, Virgo and Fornax. The published Cepheid
P-L relations to spirals in these clusters fixes the relation between angular
size and metric distance for both the fundamental plane and D_n-Sigma
relations. Using the locally calibrated fundamental plane, we infer distances
to a sample of clusters with a mean redshift of cz \approx 6000 \kms, and
derive a value of H_0=78+- 5+- 9 km/s/Mpc (random, systematic) for the local
expansion rate. This value includes a correction for depth effects in the
Cepheid distances to the nearby clusters, which decreased the deduced value of
the expansion rate by 5% +- 5%. If one further adopts the metallicity
correction to the Cepheid PL relation, as derived by the Key Project, the value
of the Hubble constant would decrease by a further 6%+- 4%. These two sources
of systematic error, when combined with a +- 6% error due to the uncertainty in
the distance to the Large Magellanic Cloud, a +- 4% error due to uncertainties
in the WFPC2 calibration, and several small sources of uncertainty in the
fundamental plane analysis, combine to yield a total systematic uncertainty of
+- 11%. We find that the values obtained using either the CMB, or a flow-field
model, for the reference frame of the distant clusters, agree to within 1%. The
Dn-Sigma relation also produces similar results, as expected from the
correlated nature of the two scaling relations. A complete discussion of the
sources of random and systematic error in this determination of the Hubble
constant is also given, in order to facilitate comparison with the other
secondary indicators being used by the Key Project.Comment: 21 pages, 3 figures, Accepted for publication in Ap
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