1,881 research outputs found
Limitations in cooling electrons by normal metal - superconductor tunnel junctions
We demonstrate both theoretically and experimentally two limiting factors in
cooling electrons using biased tunnel junctions to extract heat from a normal
metal into a superconductor. Firstly, when the injection rate of electrons
exceeds the internal relaxation rate in the metal to be cooled, the electrons
do no more obey the Fermi-Dirac distribution, and the concept of temperature
cannot be applied as such. Secondly, at low bath temperatures, states within
the gap induce anomalous heating and yield a theoretical limit of the
achievable minimum temperature.Comment: 4 pages, 4 figures, added Ref. [6] + minor correction
Classification of fresh edible oils using a coated piezoelectric sensor array-based electronic nose with soft computing approach for pattern recognition
An electronic nose based on an array of six bulk acoustic wave polymer-coated piezoelectric quartz (PZQ) sensors with soft computing-based pattern recognition was used for the classi-fication of edible oils. The electronic nose was presented with 346 samples of fresh edible oil headspace volatiles, generated at 45°C. Extra virgin olive (EVO), nonvirgin olive oil (NVO) and sunflower oil (SFO) were used over a period of 30 days. The sensor responses were visualized by plotting the results from principal component analysis (PCA). Classification of edible oils was carried out using fuzzy c-means as well as radial basis function (RBF) neural networks both from a raw data and data after having been preprocessed by fuzzy c-means. The fuzzy c-means results were poor (74%) due to the different cluster sizes. The result of RBF with fuzzy c-means preprocessing was 95% and 99% for raw data input. RBF networks with fuzzy c-means preprocessing provide the advantage of a simple architecture that is quicker to train.</p
Timing analysis techniques at large core distances for multi-TeV gamma ray astronomy
We present an analysis technique that uses the timing information of
Cherenkov images from extensive air showers (EAS). Our emphasis is on distant,
or large core distance gamma-ray induced showers at multi-TeV energies.
Specifically, combining pixel timing information with an improved direction
reconstruction algorithm, leads to improvements in angular and core resolution
as large as ~40% and ~30%, respectively, when compared with the same algorithm
without the use of timing. Above 10 TeV, this results in an angular resolution
approaching 0.05 degrees, together with a core resolution better than ~15 m.
The off-axis post-cut gamma-ray acceptance is energy dependent and its full
width at half maximum ranges from 4 degrees to 8 degrees. For shower directions
that are up to ~6 degrees off-axis, the angular resolution achieved by using
timing information is comparable, around 100 TeV, to the on-axis angular
resolution. The telescope specifications and layout we describe here are geared
towards energies above 10 TeV. However, the methods can in principle be applied
to other energies, given suitable telescope parameters. The 5-telescope cell
investigated in this study could initially pave the way for a larger array of
sparsely spaced telescopes in an effort to push the collection area to >10 km2.
These results highlight the potential of a `sparse array' approach in
effectively opening up the energy range above 10 TeV.Comment: Published in Astroparticle Physic
New Experiments for Spontaneous Vortex Formation in Josephson Tunnel Junctions
It has been argued by Zurek and Kibble that the likelihood of producing
defects in a continuous phase transition depends in a characteristic way on the
quench rate. In this paper we discuss an improved experiment for measuring the
Zurek-Kibble scaling exponent for the production of fluxons in
annular symmetric Josephson Tunnel Junctions. We find .
Further, we report accurate measurements of the junction gap voltage
temperature dependence which allow for precise monitoring of the fast
temperature variations during the quench.Comment: 12 pages, 5 figures, submitted to Phys. Rev.
Distribution of Short-finned Squid (IIlex illecebrosus) Larvae and Juveniles in Relation to the Gulf Stream Frontal Zone Between Florida and Cape Hatteras
Catches of rhynchoteuthion type C' larvae, which are considered to be II/ex illecebrosus, and I. il/ecebrosus juveniles over the edge of the continental shelf between Cape Hatteras and Florida are examined in relation to the water masses and their dynamics along the Gulf Stream~Slope Water frontal zone. All larvae and juveniles were captured at stations where the temperature~salinity (T-S) properties of the upper 50 m of the water column were closely grouped, with temperatures of 21.0° to 23.5° C and salinities of 36.30 to 36.80, which are very similar to those of Continental Edge Water. Although the actual depths of capture of the larvae and juveniles in the bongo and midwater trawl tows are unknown, it is likely that the majority were taken in the upper 50 m. Larvae and juveniles were intermixed along the entire frontal zone, but there are indications of some differences in microscale distribution. Although juveniles were nearly always captured at stations where larvae were taken, larvae were captured at only 44% of the stations where juveniles were found. The intermixture of larvae and juveniles with a broad range of size (mantle length) indicates that spawning occurs either along the Gulf Stream~Slope Water frontal zone south of Cape Hatteras or in a relatively small area to the south of the surveyed area. The possible role of frontal eddies in causing the intermixture of larvae and juveniles is discussed
The Dark Side of ROTSE-III Prompt GRB Observations
We present several cases of optical observations during gamma-ray bursts
(GRBs) which resulted in prompt limits but no detection of optical emission.
These limits constrain the prompt optical flux densities and the optical
brightness relative to the gamma-ray emission. The derived constraints fall
within the range of properties observed in GRBs with prompt optical detections,
though at the faint end of optical/gamma flux ratios. The presently accessible
prompt optical limits do not require a different set of intrinsic or
environmental GRB properties, relative to the events with prompt optical
detections.Comment: ApJ accepted. 20 pages in draft manuscript form, which includes 6
pages of tables and 2 figure
Status of the ROTSE-III telescope network
ROTSE-III is a homogeneous worldwide array of 4 robotic telescopes. They were designed to provide optical observations of γ-ray burst (GRB) afterglows as close as possible to the start of γ-ray emission. ROTSE-III is fulfilling its potential for GRB science, and provides optical observations for a variety of astrophysical sources in the interim between GRB events
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