3,903 research outputs found
Gauge invariant nonlinear electric transport in mesoscopic conductors
We use the scattering approach to investigate the nonlinear current-voltage
characteristic of mesoscopic conductors. We discuss the leading nonlinearity by
taking into account the self-consistent nonequilibrium potential. We emphasize
conservation of the overall charge and current which are connected to the
invariance under a global voltage shift (gauge invariance). As examples, we
discuss the rectification coefficient of a quantum point contact and the
nonlinear current-voltage characteristic of a resonant level in a double
barrier structure.Comment: (Replaced version, with corrected Eq.(4)); 5 pages, RevTeX, 1 figure,
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A Comparison of Blocking Methods for Record Linkage
Record linkage seeks to merge databases and to remove duplicates when unique
identifiers are not available. Most approaches use blocking techniques to
reduce the computational complexity associated with record linkage. We review
traditional blocking techniques, which typically partition the records
according to a set of field attributes, and consider two variants of a method
known as locality sensitive hashing, sometimes referred to as "private
blocking." We compare these approaches in terms of their recall, reduction
ratio, and computational complexity. We evaluate these methods using different
synthetic datafiles and conclude with a discussion of privacy-related issues.Comment: 22 pages, 2 tables, 7 figure
Superconducting magnesium diboride films on Silicon with Tc0 about 24K grown via vacuum annealing from stoichiometric precursors
Superconducting magnesium diboride films with Tc0 ~ 24 K and sharp transition
\~ 1 K were successfully prepared on silicon substrates by pulsed laser
deposition from a stoichiometric MgB2 target. Contrary to previous reports,
anneals at 630 degree and a background of 2x10^(-4) torr Ar/4%H2 were performed
without the requirement of Mg vapor or an Mg cap layer. This integration of
superconducting MgB2 films on silicon may thus prove enabling in
superconductor-semiconductor device applications. Images of surface morphology
and cross-section profiles by scanning electron microscopy (SEM) show that the
films have a uniform surface morphology and thickness. Energy dispersive
spectroscopy (EDS) reveals these films were contaminated with oxygen,
originating either from the growth environment or from sample exposure to air.
The oxygen contamination may account for the low Tc for those in-situ annealed
films, while the use of Si as the substrate does not result in a decrease in Tc
as compared to other substrates.Comment: 5 pages, 4 figures, 15 references; due to file size limit, images
were blure
Superconducting magnesium diboride films with Tc \approx 24K grown by pulsed laser deposition with in-situ anneal
Thin superconducting films of magnesium diboride (MgB2) with Tc \approx 24K
were prepared on various oxide substrates by pulsed laser deposition (PLD)
followed by an in-situ anneal. A systematic study of the influence of various
in-situ annealing parameters shows an optimum temperature of about 600C in a
background of 0.7 atm. of Ar/4%H2 for layers consisting of a mixture of
magnesium and boron. Contrary to ex-situ approaches (e.g. reacting boron films
with magnesium vapor at 900C), these films are processed below the
decomposition temperature of MgB2. This may prove enabling in the formation of
multilayers, junctions, and epitaxial films in future work. Issues related to
the improvement of these films and to the possible in-situ growth of MgB2 at
elevated temperature are discussed.Comment: 5 pages, 4 figure
Real Boys Don\u27t Do Language and Literacy--Or Do They?
Over the past several decades, there has been a decline in boys’ achievement, along with documentation of increasing struggles in language (both first and second) and literacy acquisition (Carr & Pauwels, 2006). To address this problem, gender differences have been looked at through the lens of socially and culturally constructed identity (Kindlon & Thompson, 2000; Pollack, 1998); however, emerging neurolinguistic research supports biological determinism, with evidence of strong biological (sex) differences in brain structure and function that impact language and learning (Bonomo, 2010; Gurian, 1996; Sax, 2005). This paper first provides an overview of current brain-based research on sex differences, including differences in the structure, development, and functioning of the brain, followed by discussion of the implications of these differences for language learning and literacy acquisition, with specific recommendations for working with second language learners (Carr & Pauwels, 2006) in the K-12 classroom (King, Gurian, & Stevens, 2010; Smith & Wilhelm, 2002)
Effect of Carbon-Doping in Bulk Superconducting MgB2 Samples
Bulk superconducting samples of MgB2 were prepared by solid state reaction of
stoichiometric quantities of Mg turnings and B in a sealed Ta cylinder at 890 C
for 2 hours. The as-synthesized MgB2 samples had a Tc of 39 K, as defined as
the onset of diamagnetism. The crystal symmetry was found to be hexagonal with
lattice parameters, a=3.0856 A, and c=3.5199 A, similar to the literature
values. To study the effect of carbon doping in MgB2, various C-containing
samples of x varying from 0 to 1.00 in MgB2-xCx were prepared. Magnetic
characterizations indicate that the Tc onset is same for pure and C-doped
samples for x = 0.05, and 0.10. However, the shielding signal decreased
monotonically with C content, apparently due to the presence of carbon on the
grain boundaries that isolates grains and prevents flow of supercurrents on the
perimeter.Comment: 10 pages, 3 figure
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