29,789 research outputs found
Calculation of the incremental stress-strain relation of a polygonal packing
The constitutive relation of the quasi-static deformation on two dimensional
packed samples of polygons is calculated using molecular dynamic simulations.
The stress values at which the system remains stable are bounded by a failure
surface, that shows a power law dependence on the pressure. Below the failure
surface, non linear elasticity and plastic deformation are obtained, which are
evaluated in the framework of the incremental linear theory. The results shows
that the stiffness tensor can be directly related to the micro-contact
rearrangements. The plasticity obeys a non-associated flow rule, with a plastic
limit surface that does not agree with the failure surface.Comment: 11 pages, 20 figur
Non-grey dimming events of KIC 8462852 from GTC spectrophotometry
We report ground-based spectrophotometry of KIC 8462852, during its first
dimming events since the end of the Kepler mission. The dimmings show a clear
colour-signature, and are deeper in visual blue wavelengths than in red ones.
The flux loss' wavelength dependency can be described with an \AA ngstr\"om
absorption coefficient of , which is compatible with absorption by
optically thin dust with particle sizes on the order of 0.0015 to 0.15 m.
These particles would be smaller than is required to be resistant against
blow-out by radiation pressure when close to the star. During occultation
events, these particles must be replenished on time-scales of days. If dust is
indeed the source of KIC 8462852's dimming events, deeper dimming events should
show more neutral colours, as is expected from optically thick absorbers.Comment: 5 pages, accepted for A&A letter
Encoding algebraic power series
Algebraic power series are formal power series which satisfy a univariate
polynomial equation over the polynomial ring in n variables. This relation
determines the series only up to conjugacy. Via the Artin-Mazur theorem and the
implicit function theorem it is possible to describe algebraic series
completely by a vector of polynomials in n+p variables. This vector will be the
code of the series. In the paper, it is then shown how to manipulate algebraic
series through their code. In particular, the Weierstrass division and the
Grauert-Hironaka-Galligo division will be performed on the level of codes, thus
providing a finite algorithm to compute the quotients and the remainder of the
division.Comment: 35 page
Double exchange model for RuSr_2(Eu,Gd)Cu_2O_8
We propose a double exchange model to describe the RuO_2 planes of
RuSr_2(Eu,Gd)Cu_2O_8. The Ru^+5 ions are described by localized spins, and
additional electrons provided by the superconducting CuO_2 planes are coupled
ferromagnetically to them by Hund rules coupling. We calculate the spin
structure factor, magnetic susceptibility and magnetization as a function of
magnetic field and temperature, using a Monte Carlo algorithm in which the
Ru^+5 spins are treated as classical. Several experiments which seemed in
contradiction with one another are explained by the theory.Comment: 3 pages, 3 figs., submitted to LAW3M conferenc
Entanglement Polygon Inequality in Qubit Systems
We prove a set of tight entanglement inequalities for arbitrary -qubit
pure states. By focusing on all bi-partite marginal entanglements between each
single qubit and its remaining partners, we show that the inequalities provide
an upper bound for each marginal entanglement, while the known monogamy
relation establishes the lower bound. The restrictions and sharing properties
associated with the inequalities are further analyzed with a geometric polytope
approach, and examples of three-qubit GHZ-class and W-class entangled states
are presented to illustrate the results.Comment: 8 pages, 4 figure
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