31 research outputs found
Phase coherent transport in SrTiO3/LaAlO3 interfaces
The two dimensional electron gas formed between the two band insulators
SrTiO3 and LaAlO3 exhibits a variety of interesting physical properties which
make it an appealing material for use in future spintronics and/or quantum
computing devices. For this kind of applications electrons have to retain their
phase memory for sufficiently long times or length. Using a mesoscopic size
device we were able to extract the phase coherence length, and its temperature
variation. We find the dephasing rate to have a power law dependence on
temperature. The power depends on the temperature range studied and sheet
resistance as expected from dephasing due to strong electron-electron
interactions.Comment: Submitted to Phys. Rev
Luttinger liquid behavior in weakly disordered quantum wires
We have measured the temperature dependence of the conductance in long
V-groove quantum wires (QWRs) fabricated in GaAs/AlGaAs heterostructures. Our
data is consistent with recent theories developed within the framework of the
Luttinger liquid model, in the limit of weakly disordered wires. We show that
for the relatively small amount of disorder in our QWRs, the value of the
interaction parameter g is g=0.66, which is the expected value for GaAs.
However, samples with a higher level of disorder show conductance with stronger
temperature dependence, which does not allow their treatment in the framework
of perturbation theory. Trying to fit such data with perturbation-theory models
leads inevitably to wrong (lower) values of g.Comment: 4 pages, 4 figure
Critical current in Nb-Cu-Nb junctions with non-ideal interfaces
We report on experimental studies of superconductor (Nb) - normal metal (Cu)
- superconductor (Nb) junctions with dirty interfaces between the different
materials. By using a set of simultaneously prepared samples, we investigated
the thickness dependence as well as the temperature dependence of the critical
currents in the junctions. Good agreement between the decay of the measured
critical currents and theoretical calculations was obtained without any fitting
parameters
Proximity effect in granular superconductor-normal metal structures
We fabricated three-dimensional disordered Pb-Cu granular structures, with
various metal compositions. The typical grain size of both metals is smaller
than the superconductor and normal metal coherence lengths, thus satisfying the
Cooper limit. The critical temperature of the samples was measured and compared
with the critical temperature of bilayers. We show how the proximity effect
theories, developed for bilayers, can be modified for random mixtures and we
demonstrate that our experimental data fit well the de Gennes weak coupling
limit theory in the Cooper limit. Our results indicate that, in granular
structures, the Cooper limit can be satisfied over a wide range of
concentrations.Comment: 15 pages, 4 figure
Oscillations of the superconducting critical current in Nb-Cu-Ni-Cu-Nb junctions
We report on experimental studies of superconductor-ferromagnet layered
structures. Strong oscillations of the critical supercurrent were observed with
the thickness variation of the ferromagnet. Using known microscopic parameters
of Ni, we found reasonable agreement between the period of oscillations and the
decay of the measured critical current, and theoretical calculations.Comment: 5 page
Automatic Weather Station (AWS) Program operated by the University of Wisconsin-Madison during the 2012-2013 field season: Challenges and Successes
ウィスコンシン大学マディソン校で推進している南極無人気象観測計画(Antarctic Automatic Weather Station(AWS)program)の,2012-2013年のフィールド調査および結果の概要を報告する.今期はAWS 観測網の歴史上,特異なシーズンであった.ロス島地域が温暖であったことは氷上滑走路の利用に影響を及ぼし,いくつかの設営面での制約に直面した. 柔軟な計画により,限られた条件下でAWS サービルを最大化し,自動観測ネットワークへの要求に対応する最善の手段をとることができた.This report reviews 2012-2013 field season activities of the University of Wisconsin-Madison's Antarctic Automatic Weather Station (AWS) program, summarizes the science that these sites are supporting, and outlines the factors that impact the number of AWS sites serviced in any given field season. The 2012-2013 austral summer season was unusual in the AWS network history. Challenges encountered include, but are not limited to, warmer than normal conditions in the Ross Island area impacting airfield operations, changes to logistical procedures, and competition for shared resources. A flexible work plan provides the best means for taking on these challenges while maximizing AWS servicing efforts under restricted conditions and meeting the need for routine servicing that maintaining an autonomous observing network demands
Material condition assessment with eddy current sensors
Eddy current sensors and sensor arrays are used for process quality and material condition assessment of conducting materials. In an embodiment, changes in spatially registered high resolution images taken before and after cold work processing reflect the quality of the process, such as intensity and coverage. These images also permit the suppression or removal of local outlier variations. Anisotropy in a material property, such as magnetic permeability or electrical conductivity, can be intentionally introduced and used to assess material condition resulting from an operation, such as a cold work or heat treatment. The anisotropy is determined by sensors that provide directional property measurements. The sensor directionality arises from constructs that use a linear conducting drive segment to impose the magnetic field in a test material. Maintaining the orientation of this drive segment, and associated sense elements, relative to a material edge provides enhanced sensitivity for crack detection at edges
Dramatic interannual changes of perennial Arctic sea ice linked to abnormal summer storm activity
Copyright © 2011 American Geophysical UnionThe perennial (September) Arctic sea ice cover exhibits large interannual variability, with changes of over a million square kilometers from one year to the next. Here we explore the role of changes in Arctic cyclone activity, and related factors, in driving these pronounced year-to-year changes in perennial sea ice cover. Strong relationships are revealed between the September sea ice changes and the number of cyclones in the preceding late spring and early summer. In particular, fewer cyclones over the central Arctic Ocean during the months of May, June, and July appear to favor a low sea ice area at the end of the melt season. Years with large losses of sea ice are characterized by abnormal cyclone distributions and tracks: they lack the normal maximum in cyclone activity over the central Arctic Ocean, and cyclones that track from Eurasia into the central Arctic are largely absent. Fewer storms are associated with above-average mean sea level pressure, strengthened anticyclonic winds, an intensification of the transpolar drift stream, and reduced cloud cover, all of which favor ice melt. It is also shown that a strengthening of the central Arctic cyclone maximum helps preserve the ice cover, although the association is weaker than that between low cyclone activity and reduced sea ice. The results suggest that changes in cyclone occurrence during late spring and early summer have preconditioning effects on the sea ice cover and exert a strong influence on the amount of sea ice that survives the melt season