4,734 research outputs found
Log-sine evaluations of Mahler measures
We provide evaluations of several recently studied higher and multiple Mahler
measures using log-sine integrals. This is complemented with an analysis of
generating functions and identities for log-sine integrals which allows the
evaluations to be expressed in terms of zeta values or more general
polylogarithmic terms. The machinery developed is then applied to evaluation of
further families of multiple Mahler measures.Comment: 25 page
Exterior complex scaling as a perfect absorber in time-dependent problems
It is shown that exterior complex scaling provides for complete absorption of
outgoing flux in numerical solutions of the time-dependent Schr\"odinger
equation with strong infrared fields. This is demonstrated by computing high
harmonic spectra and wave-function overlaps with the exact solution for a
one-dimensional model system and by three-dimensional calculations for the H
atom and a Ne atom model. We lay out the key ingredients for correct
implementation and identify criteria for efficient discretization
Ising-like dynamics and frozen states in systems of ultrafine magnetic particles
We use Monte-Carlo simulations to study aging phenomena and the occurence of
spinglass phases in systems of single-domain ferromagnetic nanoparticles under
the combined influence of dipolar interaction and anisotropy energy, for
different combinations of positional and orientational disorder. We find that
the magnetic moments oriente themselves preferably parallel to their anisotropy
axes and changes of the total magnetization are solely achieved by 180 degree
flips of the magnetic moments, as in Ising systems. Since the dipolar
interaction favorizes the formation of antiparallel chain-like structures,
antiparallel chain-like patterns are frozen in at low temperatures, leading to
aging phenomena characteristic for spin-glasses. Contrary to the intuition,
these aging effects are more pronounced in ordered than in disordered
structures.Comment: 5 pages, 6 figures. to appear in Phys. Rev.
Frozen metastable states in ordered systems of ultrafine magnetic particles
For studying the interplay of dipolar interaction and anisotropy energy in
systems of ultrafine magnetic particles we consider simple cubic systems of
magnetic dipoles with anisotropy axes pointing into the -direction. Using
Monte Carlo simulations we study the magnetic relaxation from several initial
states. We show explicitely that, due to the combined influence of anisotropy
energy and dipole interaction, magnetic chains are formed along the
-direction that organize themselves in frozen metastable domains of columnar
antiferromagnetic order. We show that the domains depend explicitely on the
history and relax only at extremely large time scales towards the ordered
state. We consider this as an indication for the appearence of frozen
metastable states also in real sytems, where the dipoles are located in a
liquid-like fashion and the anisotropy axes point into random directions
t-SURFF: Fully Differential Two-Electron Photo-Emission Spectra
The time dependent surface flux (t-SURFF) method is extended to single and
double ionization of two electron systems. Fully differential double emission
spectra by strong pulses at extreme UV and infrared wave length are calculated
using simulation volumes that only accommodate the effective range of the
atomic binding potential and the quiver radius of free electrons in the
external field. For a model system we find pronounced dependence of shake-up
and non-sequential double ionization on phase and duration of the laser pulse.
Extension to fully three-dimensional calculations is discussed
Cyclosporin A inhibits PGE2 release from vascular smooth muscle cells
The influence of the fungoid undecapeptide cyclosporin A (CyA) on PGE2 release from cultured rat aortic smooth muscle cells was investigated in this study. We found that CyA time and concentration dependently (ED50:500 ng/ml) inhibited PGE2 release from the cells. CyA attenuated both basal and PGE2 release evoked by angiotensin II (10(-10)-10(-6) M), arginine vasopressin (10(-10)-10(-6) M) and ionomycin (10(-9)-10(-6) M). CyA (1 microgram/ml) did not affect the conversion of exogenous arachidonic acid (1 microM) into PGE2. The inhibitory effect of CyA was neutralized by high concentrations of the calcium ionophore ionomycin (greater than 3 X 10(-6) M). Taken together our results indicate that CyA inhibits both basal and vasoconstrictor evoked PGE2 release from vascular smooth muscle by impairing the availability of free arachidonic acid rather than by inhibiting the conversion of arachidonic acid into PGE2
Log-sine evaluations of Mahler measures, II
We continue the analysis of higher and multiple Mahler measures using
log-sine integrals as started in "Log-sine evaluations of Mahler measures" and
"Special values of generalized log-sine integrals" by two of the authors. This
motivates a detailed study of various multiple polylogarithms and worked
examples are given. Our techniques enable the reduction of several multiple
Mahler measures, and supply an easy proof of two conjectures by Boyd.Comment: 35 page
Tangles of superpositions and the convex-roof extension
We discuss aspects of the convex-roof extension of multipartite entanglement
measures, that is, SL(2,\CC) invariant tangles. We highlight two key concepts
that contain valuable information about the tangle of a density matrix: the
{\em zero-polytope} is a convex set of density matrices with vanishing tangle
whereas the {\em convex characteristic curve} readily provides a non-trivial
lower bound for the convex roof and serves as a tool for constructing the
convex roof outside the zero-polytope. Both concepts are derived from the
tangle for superpositions of the eigenstates of the density matrix. We
illustrate their application by considering examples of density matrices for
two-qubit and three-qubit states of rank 2, thereby pointing out both the power
and the limitations of the concepts.Comment: 7 pages, 5 figures, revtex
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