256 research outputs found
Strong Quasiparticle Trapping In A 6x6 Array Of Vanadium-Aluminum Superconducting Tunnel Junctions
A 6x6 array of symmetrical V/Al/AlOx/Al/V Superconducting Tunnel Junctions
(STJs) was fabricated. The base electrode is a high quality epitaxial film with
a residual resistance ratio (RRR) of ~30. The top film is polycrystalline with
an RRR of ~10. The leakage currents of the 25x25 mm^2 junctions are of the
order of 0.5 pA/mm^2 at a bias voltage of 100 mV, which corresponds to a
dynamical resistance of ~ 3 10^5 ohms. When the array was illuminated by 6 keV
X-ray photons from a 55Fe radioactive source the single photon charge output
was found to be low and strongly dependent on the temperature of the devices.
This temperature dependence at X-ray energies can be explained by the existence
of a very large number of quasiparticle (QP) traps in the Vanadium. QPs are
confined in these traps, having a lower energy gap than the surrounding
material, and are therefore not available for tunneling. The number of traps
can be derived from the energy dependence of the responsivity of the devices
(charge output per electron volt of photon input energy).Comment: 4 pages. presented at Low Temperature Detectors-
A probabilistic ontology-based platform for self-learning context-aware healthcare applications
Migrating medical communications software to a multi-tenant cloud environment
The rise of cloud computing has paved the way for many new applications. Many of these new cloud applications are also multi-tenant, ensuring multiple end users can make use of the same application instance. While these technologies make it possible to create many new applications, many legacy applications can also benefit from the added flexibility and cost-savings of cloud computing and multi-tenancy. In this paper, we describe the steps required to migrate a. NET-based medical communications application to the Windows Azure public cloud environment, and the steps required to add multi-tenancy to the application. We then discuss the advantages and disadvantages of our migration approach. We found that the migration to the cloud itself requires only a limited amount of changes to the application, but that this also limited the benefits, as individual instances would only be partially used. Adding multi-tenancy requires more changes, but when this is done, it has the potential to greatly reduce the cost of running the application
Optical photon detection in Al Superconducting Tunnel Junctions
We report on the successful fabrication of low leakage aluminium
superconducting tunnel junctions with very homogeneous and transparent
insulating barriers. The junctions were tested in an adiabatic demagnetisation
refrigerator with a base temperature of 35 mK. The normal resistance of the
junctions is equal to ~7 uohm cm2 with leakage currents in the bias voltage
domain as low as 100 fA/um2. Optical single photon counting experiments show a
very high responsivity with charge amplification factors in excess of 100. The
total resolving power (including electronic noise) for 500 nm photons is equal
to 13 compared to a theoretical tunnel limited value of 34. The current devices
are found to be limited spectroscopically by spatial inhomogeneities in the
detectors responseComment: 3 pages, 5 figure
Future optical detectors based on Al superconducting tunnel junctions
Superconducting tunnel junctions are being developed for application as
photon detectors in astronomy. We present the latest results on the development
of very high quality, very low critical temperature junctions, fabricated out
of pure Al electrodes. The detectors are operated at 50 mK in an adiabatic
demagnetisation refrigerator. The contacts to the top and base electrodes of
these junctions are fabricated either out of Nb or Ta, which has strong
implications on the loss time of the quasiparticles. The Nb contacted junctions
show quasiparticle loss times varying between 5 and 80 usec, depending on the
device size. The bias range of the Nb-contacted junctions is limited to the
range 0-100 uV, because of the set-in of strong non-equilibrium quasiparticle
multiplication currents at higher bias voltages. The Ta-contacted junctions, on
the other hand, show quasiparticle loss times in excess of 200 usec. These long
loss times lead to very strong quasiparticle multiplication, which prevents the
stable biasing of the junctions even at very low bias voltages. Junction
fabrication and characterisation are described, as well as the response of the
detectors to monochromatic light with wavelengths varying from 250 to 1000 nm.
The energy resolution of the detectors is discussed.Comment: 12 pages, 10 figure
Modelling the energy gap in transition metal/aluminium bilayers"
We present an application of the generalised proximity effect theory.Comment: 15 pages, 11 figures, presented at workshop on low temperature
superconducting electronics at the University of Twente, The Netherland
Conjugative Transposons and Their Cargo Genes Vary across Natural Populations of Rickettsia buchneri Infecting the Tick Ixodes scapularis
Rickettsia buchneri (formerly Rickettsia endosymbiont of Ixodes scapularis, or REIS) is an obligate intracellular endoparasite of the black-legged tick, the primary vector of Lyme disease in North America. It is noteworthy among the rickettsiae for its relatively large genome (1.8 Mb) and extraordinary proliferation of mobile genetic elements (MGEs), which comprise nearly 35% of its genome. Previous analysis of the R. buchneri genome identified several integrative conjugative elements named Rickettsiales amplified genomic elements (RAGEs); the composition of these RAGEs suggests that continued genomic invasions by MGEs facilitated the proliferation of rickettsial genes related to an intracellular lifestyle. In this study, we compare the genomic diversity at RAGE loci among sequenced rickettsiae that infect three related Ixodes spp., including two strains of R. buchneri and Rickettsia endosymbiont of Ixodes pacificus strain Humboldt, as well as a closely related species R. tamurae infecting Amblyomma testudinarium ticks. We further develop a novel multiplex droplet digital PCR assay and use it to quantify copy number ratios of chromosomal R. buchneri RAGE-A and RAGE-B to the single-copy gene gltA within natural populations of I. scapularis. Our results reveal substantial diversity among R. buchneri at these loci, both within individual ticks as well as in the I. scapularis population at large, demonstrating that genomic rearrangement of MGEs is an active process in these intracellular bacteria
Dynamics of nonequilibrium quasiparticles in a double superconducting tunnel junction detector
We study a class of superconductive radiation detectors in which the
absorption of energy occurs in a long superconductive strip while the redout
stage is provided by superconductive tunnel junctions positioned at the two
ends of the strip. Such a device is capable both of imaging and energy
resolution. In the established current scheme, well studied from the
theoretical and experimental point of view, a fundamental ingredient is
considered the presence of traps, or regions adjacent to the junctions made of
a superconducting material of lower gap. We reconsider the problem by
investigating the dynamics of the radiation induced excess quasiparticles in a
simpler device, i.e. one without traps. The nonequilibrium excess
quasiparticles can be seen to obey a diffusion equation whose coefficients are
discontinuous functions of the position. Based on the analytical solution to
this equation, we follow the dynamics of the quasiparticles in the device,
predict the signal formation of the detector and discuss the potentiality
offered by this configuration.Comment: 16 pages, 5 figures Submitted to Superconducting Science and
Technolog
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