5,317 research outputs found
Polyamide-rubber blends: micrscopic studies of the deformation zone
The morphology of injection moulded samples of polyamide—polybutadiene blends (85.15) with an average particle size of 0.3 μm was studied. The samples were fractured in a notched tensile test at crosshead speeds of 10−4 and 1 ms −1 and the structure of the deformation zone was studied using various techniques: polarized light microscopy, scanning electron microscopy, transmission electron microscopy on stained cut samples and carbon replicas, and selected area electron diffraction transmission electron microscopy. The deformation zone of samples tested at 10−4 ms−1 was found to consist of two layers. Far from the fracture surface a layer was observed with more or less round cavities and with cavities in the rubber particles, while near the fracture surface a layer with strongly deformed cavities (length/diameter ratio of 5–10) could be seen. In the samples tested at 1 ms−1 the deformation zone was found to have three layers. In addition to the two previous layers an extra layer next to the fracture plane was found. This layer was 2–3 μm thick with round rubber particles and no orientation of the matrix material. This indicates that, at the high deformation speed of the test, relaxation in the melt took place, suggesting that the material around the crack tip was molten during fracture.\u
Direct solution of the hard pomeron problem for arbitrary conformal weight
A new method is applied to solve the Baxter equation for the one dimensional
system of noncompact spins. Dynamics of such an ensemble is equivalent to that
of a set of reggeized gluons exchanged in the high energy limit of QCD
amplitudes. The technique offers more insight into the old calculation of the
intercept of hard Pomeron, and provides new results in the odderon channel.Comment: Contribution to the ICHEP96 Conference, July 1996, Warsaw, Poland.
LaTeX, 4 pages, 3 epsf figures, includes modified stwol.sty file. Some
references were revise
Finite Conductivity Minimum in Bilayer Graphene without Charge Inhomogeneities
Boltzmann transport theory fails near the linear band-crossing of
single-layer graphene and near the quadratic band-crossing of bilayer graphene.
We report on a numerical study which assesses the role of inter-band coherence
in transport when the Fermi level lies near the band-crossing energy of bilayer
graphene. We find that interband coherence enhances conduction, and that it
plays an essential role in graphene's minimum conductivity phenomena. This
behavior is qualitatively captured by an approximate theory which treats
inter-band coherence in a relaxation-time approximation. On the basis of this
short-range-disorder model study, we conclude that electron-hole puddle
formation is not a necessary condition for finite conductivity in graphene at
zero average carrier density.Comment: revised version as published in Phys. Rev.
P02.104. Nonlinear parameters of heart rate variability (HRV) – suitable measures to observe physiological outcome during a peat bath in rehabilitation
Summing free unitary random matrices
I use quaternion free probability calculus - an extension of free probability
to non-Hermitian matrices (which is introduced in a succinct but self-contained
way) - to derive in the large-size limit the mean densities of the eigenvalues
and singular values of sums of independent unitary random matrices, weighted by
complex numbers. In the case of CUE summands, I write them in terms of two
"master equations," which I then solve and numerically test in four specific
cases. I conjecture a finite-size extension of these results, exploiting the
complementary error function. I prove a central limit theorem, and its first
sub-leading correction, for independent identically-distributed zero-drift
unitary random matrices.Comment: 17 pages, 15 figure
Dirac eigenvalues and eigenvectors at finite temperature
We investigate the eigenvalues and eigenvectors of the staggered Dirac
operator in the vicinity of the chiral phase transition of quenched SU(3)
lattice gauge theory. We consider both the global features of the spectrum and
the local correlations. In the chirally symmetric phase, the local correlations
in the bulk of the spectrum are still described by random matrix theory, and we
investigate the dependence of the bulk Thouless energy on the simulation
parameters. At and above the critical point, the properties of the low-lying
Dirac eigenvalues depend on the -phase of the Polyakov loop. In the real
phase, they are no longer described by chiral random matrix theory. We also
investigate the localization properties of the Dirac eigenvectors in the
different -phases.Comment: Lattice 2000 (Finite Temperature), 5 page
Universal eigenvector statistics in a quantum scattering ensemble
We calculate eigenvector statistics in an ensemble of non-Hermitian matrices
describing open quantum systems [F. Haake et al., Z. Phys. B 88, 359 (1992)] in
the limit of large matrix size. We show that ensemble-averaged eigenvector
correlations corresponding to eigenvalues in the center of the support of the
density of states in the complex plane are described by an expression recently
derived for Ginibre's ensemble of random non-Hermitian matrices.Comment: 4 pages, 5 figure
Lectures on Chiral Disorder in QCD
I explain the concept that light quarks diffuse in the QCD vacuum following
the spontaneous breakdown of chiral symmetry. I exploit the striking analogy to
disordered electrons in metals, identifying, among others, the universal regime
described by random matrix theory, diffusive regime described by chiral
perturbation theory and the crossover between these two domains.Comment: Lectures given at the Cargese Summer School, August 6-18, 200
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