164 research outputs found
Organic film thickness influence on the bias stress instability in Sexithiophene Field Effect Transistors
In this paper, the dynamics of bias stress phenomenon in Sexithiophene (T6)
Field Effect Transistors (FETs) has been investigated. T6 FETs have been
fabricated by vacuum depositing films with thickness from 10 nm to 130 nm on
Si/SiO2 substrates. After the T6 film structural analysis by X-Ray diffraction
and the FET electrical investigation focused on carrier mobility evaluation,
bias stress instability parameters have been estimated and discussed in the
context of existing models. By increasing the film thickness, a clear
correlation between the stress parameters and the structural properties of the
organic layer has been highlighted. Conversely, the mobility values result
almost thickness independent
Isospin breaking corrections to nucleon form factors in the constituent quark model
We examine isospin breaking in the nucleon wave functions due to the
quark mass difference and the Coulomb interaction among the quarks, and their
consequences on the nucleon electroweak form factors in a nonrelativistic
constituent quark model. The mechanically induced isospin breaking in the
nucleon wave functions and electroweak form factors are exactly evaluated in
this model. We calculate the electromagnetically induced isospin admixtures by
using first-order perturbation theory, including the lowest-lying resonance
with nucleon quantum numbers but isospin 3/2. We find a small (), but
finite correction to the anomalous magnetic moments of the nucleon stemming
almost entirely from the quark mass difference, while the static nucleon axial
coupling remains uncorrected. Corrections of the same order of magnitude appear
in charge, magnetic, and axial radii of the nucleon. The correction to the
charge radius in this model is primarily isoscalar, and may be of some
significance for the extraction of the strangeness radius from e.g. elastic
forward angle parity violating electron-proton asymmetries, or elastic
experiments.Comment: 15 pp(22 as preprint), revtex, 3 uuencoded figs at end of this fil
Chern-Simons Term for BF Theory and Gravity as a Generalized Topological Field Theory in Four Dimensions
A direct relation between two types of topological field theories,
Chern-Simons theory and BF theory, is presented by using ``Generalized
Differential Calculus'', which extends an ordinary p-form to an ordered pair of
p and (p+1)-form. We first establish the generalized Chern-Weil homomormism for
generalized curvature invariant polynomials in general even dimensional
manifolds, and then show that BF gauge theory can be obtained from the action
which is the generalized second Chern class with gauge group G. Particularly
when G is taken as SL(2,C) in four dimensions, general relativity with
cosmological constant can be derived by constraining the topological BF theory.Comment: Improved abstract and introduction with 11 references added. Accepted
for publication in Physical Review
NMR and NQR Fluctuation Effects in Layered Superconductors
We study the effect of thermal fluctuations of the s-wave order parameter of
a quasi two dimensional superconductor on the nuclear spin relaxation rate near
the transition temperature Tc. We consider both the effects of the amplitude
fluctuations and the Berezinskii-Kosterlitz-Thouless (BKT) phase fluctuations
in weakly coupled layered superconductors. In the treatment of the amplitude
fluctuations we employ the Gaussian approximation and evaluate the longitudinal
relaxation rate 1/T1 for a clean s-wave superconductor, with and without pair
breaking effects, using the static pair fluctuation propagator D. The increase
in 1/T1 due to pair breaking in D is overcompensated by the decrease arising
from the single particle Green's functions. The result is a strong effect on
1/T1 for even a small amount of pair breaking. The phase fluctuations are
described in terms of dynamical BKT excitations in the form of pancake
vortex-antivortex (VA) pairs. We calculate the effect of the magnetic field
fluctuations caused by the translational motion of VA excitations on 1/T1 and
on the transverse relaxation rate 1/T2 on both sides of the BKT transitation
temperature T(BKT)<Tc. The results for the NQR relaxation rates depend strongly
on the diffusion constant that governs the motion of free and bound vortices as
well as the annihilation of VA pairs. We discuss the relaxation rates for real
multilayer systems where the diffusion constant can be small and thus increase
the lifetime of a VA pair, leading to an enhancement of the rates. We also
discuss in some detail the experimental feasibility of observing the effects of
amplitude fluctuations in layered s-wave superconductors such as the
dichalcogenides and the effects of phase fluctuations in s- or d-wave
superconductors such as the layered cuprates.Comment: 38 pages, 12 figure
An Integrated TCGA Pan-Cancer Clinical Data Resource to Drive High-Quality Survival Outcome Analytics
For a decade, The Cancer Genome Atlas (TCGA) program collected clinicopathologic annotation data along with multi-platform molecular profiles of more than 11,000 human tumors across 33 different cancer types. TCGA clinical data contain key features representing the democratized nature of the data collection process. To ensure proper use of this large clinical dataset associated with genomic features, we developed a standardized dataset named the TCGA Pan-Cancer Clinical Data Resource (TCGA-CDR), which includes four major clinical outcome endpoints. In addition to detailing major challenges and statistical limitations encountered during the effort of integrating the acquired clinical data, we present a summary that includes endpoint usage recommendations for each cancer type. These TCGA-CDR findings appear to be consistent with cancer genomics studies independent of the TCGA effort and provide opportunities for investigating cancer biology using clinical correlates at an unprecedented scale. Analysis of clinicopathologic annotations for over 11,000 cancer patients in the TCGA program leads to the generation of TCGA Clinical Data Resource, which provides recommendations of clinical outcome endpoint usage for 33 cancer types
Holography and Quaternionic Taub-NUT
As a concrete application of the holographic correspondence to manifolds
which are only asymptotically Anti-de Sitter, we take a closer look at the
quaternionic Taub-NUT space. This is a four dimensional, non-compact,
inhomogeneous, riemannian manifold with the interesting property of smoothly
interpolating between two symmetric spaces, AdS_4 itself and the coset
SU(2,1)/U(2). Even more interesting is the fact that the scalar curvature of
the induced conformal structure at the boundary (corresponding to a squashed
three-sphere) changes sign as we interpolate between these two limiting cases.
Using twistor methods, we construct the bulk-to-bulk and bulk-to-boundary
propagators for conformally coupled scalars on quaternionic Taub-NUT. This may
eventually enable us to calculate correlation functions in the dual strongly
coupled CFT on a squashed S^3 using the standard AdS/CFT prescription.Comment: 1+36 pages, no figures. Some minor typos correcte
Near-threshold and meson productions in collisions
Using a relativistic effective Lagrangian at the hadronic level,
near-threshold and meson productions in proton proton ()
collisions, , are studied within the distorted wave
Born approximation. Both initial and final state interactions are
included. In addition to total cross section data, both and
angular distribution data are used to constrain further the model parameters.
For the reaction we consider two different possibilities:
with and without the inclusion of nucleon resonances. The nucleon resonances
are included in a way to be consistent with the
reaction. It is shown that the inclusion of nucleon resonances can describe the
data better overall than without their inclusion. However, the SATURNE data in
the range of excess energies MeV are still underestimated by about a
factor of two. As for the reaction it is found that the
presently limited available data from DISTO can be reproduced by four sets of
values for the vector and tensor coupling constants. Further
measurements of the energy dependence of the total cross section near threshold
energies should help to constrain better the coupling constant.Comment: Latex, 37 pages, 13 figures (14 EPS-figure files), text modified,
version to appear in Phys. ReV.
- …