144 research outputs found
In-plane anisotropy of electrical transport in YTbBaCuO films
We fabricate high-quality c-axis oriented epitaxial YBaCuO
films with 15% of yttrium atoms replaced by terbium (YTBCO) and study their
electrical properties. The Tb substitution reduces the charge carrier density
resulting in increased resistivity and decreased critical current density
compared to the pure YBaCuO films. The electrical properties of
the YTBCO films show an in-plane anisotropy in both the superconducting and
normal state providing evidence for the twin-free film. Unexpectedly, the
resistive transition of the bridges also demonstrates the in-plane anisotropy
that can be explained within the framework of Tinkham's model of the resistive
transition and the Berezinskii-Kosterlitz-Thouless (BKT) model depending on the
sample parameters. We consider YTBCO films to be a promising platform for both
the fundamental research on the BKT transition in the cuprate superconductors
and for the fabrication of devices with high kinetic inductance
Measurement of the Neutron Spin Structure Function with a Polarized ^3He Target
Results are reported from the HERMES experiment at HERA on a measurement of
the neutron spin structure function in deep inelastic scattering
using 27.5 GeV longitudinally polarized positrons incident on a polarized
He internal gas target. The data cover the kinematic range
and . The integral evaluated at a fixed of is . Assuming Regge behavior at low , the first
moment is .Comment: 4 pages TEX, text available at
http://www.krl.caltech.edu/preprints/OAP.htm
Flavor Decomposition of the Polarized Quark Distributions in the Nucleon from Inclusive and Semi-inclusive Deep-inelastic Scattering
Spin asymmetries of semi-inclusive cross sections for the production of
positively and negatively charged hadrons have been measured in deep-inelastic
scattering of polarized positrons on polarized hydrogen and 3He targets, in the
kinematic range 0.023<x<0.6 and 1 GeV^2<Q^2<10 GeV^2. Polarized quark
distributions are extracted as a function of x for up $(u+u_bar) and down
(d+d_bar) flavors. The up quark polarization is positive and the down quark
polarization is negative in the measured range. The polarization of the sea is
compatible with zero. The first moments of the polarized quark distributions
are presented. The isospin non-singlet combination Delta_q_3 is consistent with
the prediction based on the Bjorken sum rule. The moments of the polarized
quark distributions are compared to predictions based on SU(3)_f flavor
symmetry and to a prediction from lattice QCD.Comment: 14 pages, 6 figures (eps format), 10 tables in Latex New version
contains tables of asymmetries and correlation matri
The HERMES Spectrometer
The HERMES experiment is collecting data on inclusive and semi-inclusive deep inelastic scattering of polarised positrons from polarised targets of Il, D, and He-3. These data give information on the spin structure of the nucleon. This paper describes the forward angle spectrometer built for this purpose. The spectrometer includes numerous tracking chambers (micro-strip gas chambers, drift and proportional chambers) in front of and behind a 1.3 T.m magnetic field, as well as an extensive set of detectors for particle identification (a lead-glass calorimeter, a pre-shower detector, a transition radiation detector, and a threshold Cherenkov detector). Two of the main features of the spectrometer are its good acceptance and identification of both positrons and hadrons, in particular pions. These characteristics, together with the purity of the targets, are allowing HERMES to make unique contributions to the understanding of how the spins of the quarks contribute to the spin of the nucleon. (C) 1998 Elsevier Science B.V. All rights reserved
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Conformation and self-association of peptide amphiphiles based on the KTTKS collagen sequence
Studying peptide amphiphiles (PAs), we investigate
the influence of alkyl chain length on the aggregation behavior of the collagen-derived peptide KTTKS with applications ranging from antiwrinkle cosmetic creams to potential uses in regenerative medicine. We have studied synthetic peptides amphiphiles C14− KTTKS (myristoyl Lys-Thr-Thr-Lys-Ser) and C18−KTTKS(stearoyl-Lys-Thr Thr-Lys-Ser) to investigate in detail their physicochemical properties. It is presumed that the hydrophobic chain in these self-assembling peptide amphiphiles enhances peptide permeation across the skin compared to KTTKS alone.
Subsequently Cn−KTTKS should act as a prodrug and release the peptide by enzymatic cleavage. Our results should be useful in the further development of molecules with collagen-stimulating activity
Observation of a coherence length effect in exclusive ρ(0) electroproduction
Exclusive incoherent electroproduction of the ρ0(770) meson from 1H, 2H, 3He, and 14N targets has been studied by the HERMES experiment at squared four-momentum transfer Q^2>0.4 GeV^2 and positron energy loss ν from 9 to 20 GeV. The ratio of the 14N to 1H cross sections per nucleon, known as the nuclear transparency, was found to decrease with increasing coherence length of quark-antiquark fluctuations of the virtual photon. The data provide clear evidence of the interaction of the quark-antiquark fluctuations with the nuclear medium
Quantum size effects in ultra-thin YBa2Cu3O7-x films
The d-wave symmetry of the order parameter with zero energy gap in nodal
directions stands in the way of using high-temperature superconductors for
quantum applications. We investigate the symmetry of the order parameter in
ultra-thin YBa2Cu3O7-x (YBCO) films by measuring the electrical transport
properties of nanowires and nanoconstrictions aligned at different angles
relative to the main crystallographic axes. The anisotropy of the nanowire
critical current in the nodal and antinodal directions reduces with the
decrease in the film thickness. The Andreev reflection spectroscopy shows the
presence of a thickness-dependent energy gap that doesn't exist in bulk YBCO.
We find that the thickness-dependent energy gap appears due to the quantum size
effects in ultra-thin YBCO films that open the superconducting energy gap along
the entire Fermi surface. The fully gapped state of the ultra-thin YBCO films
makes them a very promising platform for quantum applications, including
quantum computing and quantum communications.Comment: References are updated. (a) and (b) labels are added in Fig.
Status of fully integrated GaAs particle detectors
In this note we investigate the influence of structural nonlinearity of a simple cantilever beam impacting system on its dynamic responses close to grazing incidence by a means of numerical simulation. To obtain a clear picture of this effect we considered two systems exhibiting impacting motion, where the primary stiffness is either linear (piecewise linear system) or nonlinear (piecewise nonlinear system). Two systems were studied by constructing bifurcation diagrams, basins of attractions, Lyapunov exponents and parameter plots. In our analysis we focused on the grazing transitions from no impact to impact motion. We observed that the dynamic responses of these two similar systems are qualitatively different around the grazing transitions. For the piecewise linear system, we identified on the parameter space a considerable region with chaotic behaviour, while for the piecewise nonlinear system we found just periodic attractors. We postulate that the structural nonlinearity of the cantilever impacting beam suppresses chaos near grazing. (C) 2007 Elsevier Ltd. All rights reserved
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