29,685 research outputs found
Energy gap measurement of nanostructured thin aluminium films for use in single Cooper-pair devices
Within the context of superconducting gap engineering, Al-\alox-Al tunnel
junctions have been used to study the variation in superconducting gap,
, with film thickness. Films of thickness 5, 7, 10 and 30 nm were used
to form the small area superconductor-insulator-superconductor (SIS) tunnel
junctions. In agreement with previous measurements we have observed an increase
in the superconducting energy gap of aluminium with a decrease in film
thickness. In addition, we find grain size in small area films with thickness
\textbf{} 10 nm has no appreciable effect on energy gap. Finally, we
utilize 7 and 30 nm films in a single Cooper-pair transistor, and observe the
modification of the finite bias transport processes due to the engineered gap
profile
Final-state interactions in the response of nuclear matter
Final-state interactions in the response of a many-body system to an external
probe delivering large momentum are normally described using the eikonal
approximation, for the trajectory of the struck particle, and the frozen
approximation, for the positions of the spectators. We propose a generalization
of this scheme, in which the initial momentum of the struck particle is
explicitly taken into account. Numerical calculations of the nuclear matter
response at 1 2 GeV/c show that the inclusion of this momentum
dependence leads to a sizable effect in the low energy tail. Possible
implications for the analysis of existing electron-nucleus scattering data are
discussed.Comment: 21 pages, 4 figure
Excitation of the 3.071mm Hyperfine Line in Li-Like 57-Fe in Astrophysical Plasmas
As noted first by Sunyaev & Churazov (1984), the 3.071 mm hyperfine line from
might be observable in astrophysical plasmas. We assess the
atomic processes which might contribute to the excitation of this line. We
determine the intensity of the hyperfine line from an isothermal, coronal
plasma in collisional ionization equilibrium and for a coronal plasma cooling
isobarically due to its own radiation. Comparisons of the hyperfine line to
other lines emitted by the same ion, Fe, are shown to be useful for
deriving the isotopic fraction of Fe. We calculate the ratios of the
hyperfine line to the 2s--2p EUV lines at 192 \AA and 255 \AA, and the 2s--3p
X-ray doublet at 10.6 \AA.Comment: 28 pages text+figures, Accepted to ApJ in Jan 98, also at
http://www.astro.virginia.edu/~nld2n/research.htm
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Exploring the seas of Titan: the Titan Mare Eplorer (TiME) mission
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Titan Mare Explorer (TiME): first in situ exploration of an extraterrestrial sea
The lakes and seas of Titan are a sink of products of photolysis in the atmosphere, and a crucial component in Titan's active methane cycle. In situ exploration of the seas is necessary to understand their intriguing prebiotic organic chemistry
Four-Dimensional Superconformal Theories with Interacting Boundaries or Defects
We study four-dimensional superconformal field theories coupled to
three-dimensional superconformal boundary or defect degrees of freedom.
Starting with bulk N=2, d=4 theories, we construct abelian models preserving
N=2, d=3 supersymmetry and the conformal symmetries under which the
boundary/defect is invariant. We write the action, including the bulk terms, in
N=2, d=3 superspace. Moreover we derive Callan-Symanzik equations for these
models using their superconformal transformation properties and show that the
beta functions vanish to all orders in perturbation theory, such that the
models remain superconformal upon quantization. Furthermore we study a model
with N=4 SU(N) Yang-Mills theory in the bulk coupled to a N=4, d=3
hypermultiplet on a defect. This model was constructed by DeWolfe, Freedman and
Ooguri, and conjectured to be conformal based on its relation to an AdS
configuration studied by Karch and Randall. We write this model in N=2, d=3
superspace, which has the distinct advantage that non-renormalization theorems
become transparent. Using N=4, d=3 supersymmetry, we argue that the model is
conformal.Comment: 30 pages, 4 figures, AMSLaTeX, revised comments on Chern-Simons term,
references adde
On dynamical mass generation in three dimensional supersymmetric U(1) gauge field theory
We investigate and contrast the non-perturbative infra red structure of N=1
and N=2 supersymmetric non-compact U(1) gauge field theory in three space-time
dimensions with N matter flavours. We study the Dyson-Schwinger equations in a
general gauge using superfield formalism; this ensures that supersymmetry is
kept manifest, though leads to spurious infra red divergences which we have to
avoid carefully. In the N=1 case the superfield formalism allows us to choose a
vertex which satisfies the U(1) Ward identity exactly, and we find the expected
critical behaviour in the wavefunction renormalization and strong evidence for
the existence of a gauge independent dynamically generated mass, but with no
evidence for a critical flavour number. We study the N=2 model by dimensional
reduction from four dimensional N=1 electrodynamics, and we refine the old
gauge dependence argument that there is no dynamical mass generation. We
recognize that the refinement only holds after dimensional reduction.Comment: 32 pages RevTeX; 3 axodraw figures include
Dynamics of Weyl Scale Invariant non-BPS p=3 Branes
In this paper a Weyl scale invariant brane scenario is introduced, with
the brane embedded in a higher dimensional bulk space with
Super--Weyl symmetry. Its action, which describes its long wave oscillation
modes into the ambient superspace and breaks the target symmetry down to the
lower dimensional Weyl W(1,3) symmetry, is constructed by the approach of coset
method.Comment: 12 pages, modified versio
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