8,299 research outputs found
A dynamical point of view of Quantum Information: entropy and pressure
Quantum Information is a new area of research which has been growing rapidly
since last decade. This topic is very close to potential applications to the so
called Quantum Computer. In our point of view it makes sense to develop a more
"dynamical point of view" of this theory. We want to consider the concepts of
entropy and pressure for "stationary systems" acting on density matrices which
generalize the usual ones in Ergodic Theory (in the sense of the Thermodynamic
Formalism of R. Bowen, Y. Sinai and D. Ruelle). We consider the operator
acting on density matrices over a finite
-dimensional complex Hilbert space where and , are
operators in this Hilbert space. is not a linear operator. In
some sense this operator is a version of an Iterated Function System (IFS).
Namely, the , , play the role of the
inverse branches (acting on the configuration space of density matrices )
and the play the role of the weights one can consider on the IFS. We
suppose that for all we have that . A
family determines a Quantum Iterated Function System
(QIFS) , $\mathcal{F}_W=\{\mathcal{M}_N,F_i,W_i\}_{i=1,...,
k}.
Asteroseismic Theory of Rapidly Oscillating Ap Stars
This paper reviews some of the important advances made over the last decade
concerning theory of roAp stars.Comment: 9 pages, 5 figure
A dynamical point of view of Quantum Information: Wigner measures
We analyze a known version of the discrete Wigner function and some
connections with Quantum Iterated Funcion Systems. This paper is a follow up of
"A dynamical point of view of Quantum Information: entropy and pressure" by the
same authors
A Thermodynamic Formalism for density matrices in Quantum Information
We consider new concepts of entropy and pressure for stationary systems
acting on density matrices which generalize the usual ones in Ergodic Theory.
Part of our work is to justify why the definitions and results we describe here
are natural generalizations of the classical concepts of Thermodynamic
Formalism (in the sense of R. Bowen, Y. Sinai and D. Ruelle). It is well-known
that the concept of density operator should replace the concept of measure for
the cases in which we consider a quantum formalism. We consider the operator
acting on the space of density matrices over a finite
-dimensional complex Hilbert space where and ,
are linear operators in this Hilbert space. In some sense this
operator is a version of an Iterated Function System (IFS). Namely, the
, , play the role of the inverse branches
(i.e., the dynamics on the configuration space of density matrices) and the
play the role of the weights one can consider on the IFS. In this way a
family determines a Quantum Iterated Function System
(QIFS). We also present some estimates related to the Holevo bound
Asymptotic Entanglement Dynamics and Geometry of Quantum States
A given dynamics for a composite quantum system can exhibit several distinct
properties for the asymptotic entanglement behavior, like entanglement sudden
death, asymptotic death of entanglement, sudden birth of entanglement, etc. A
classification of the possible situations was given in [M. O. Terra Cunha,
{\emph{New J. Phys}} {\bf{9}}, 237 (2007)] but for some classes there were no
known examples. In this work we give a better classification for the possibile
relaxing dynamics at the light of the geometry of their set of asymptotic
states and give explicit examples for all the classes. Although the
classification is completely general, in the search of examples it is
sufficient to use two qubits with dynamics given by differential equations in
Lindblad form (some of them non-autonomous). We also investigate, in each case,
the probabilities to find each possible behavior for random initial states.Comment: 9 pages, 2 figures; revised version accepted for publication in J.
Phys. A: Math. Theo
Quantum Stochastic Processes, Quantum Iterated Function Systems and Entropy
We describe some basic results for Quantum Stochastic Processes and present some new results about a certain class of processes which are associated to Quantum Iterated Function Systems (QIFS). We discuss questions related to the Markov property and we present a de nition of entropy which is induced by a QIFS. This definition is a natural generalization of the Shannon-Kolmogorov entropy from Ergodic Theory
KINEMATIC AND ELECTROMYOGRAPHIC BEHAVIOUR OF BASKETBALL PLAYERS’ INJURED AND HEALTHY ANKLES DURING THE JUMP ONTO AN UNSTABLE BOARD
The purpose of this study was to identify kinematic and electromyographic differences of jumps performed by basketball players with healthy and previously sprained ankles. 25 elite basketball players with healthy (n=17) and already sprained ankles (n=28) jumped five times in unipodal support from a stable surface onto a round Freeman board. During the jump the flight phase of those athletes with already sprained ankles was shorter which may indicate less preparation time for the moment of contact with the surface and for the respective load. When landing, they also positioned their ankle in a more plantar flexion and generally, the contraction of their foot musles was stronger than that of the healthy athletes. The groups’ differing movement behaviour of the lower leg possibly explains resulting ankle injuries. These results indicate that it might be necessary to train athletes to jump in “safe positions” in order to prevent ankle sprains
Assessment of fibre orientation and distribution in steel fibre reinforced self-compacting concrete panels
The benefits of adding fibres to concrete lie, mostly, in improving the post-cracking
behaviour, since its ability to transfer stresses across cracked sections is substantially increased. The
post-cracking strength is dependent not only on the fibre geometry, mechanical performance and
fibre/matrix interface properties, but also on the fibre orientation and distribution. Previous works have
shown that in self-compacting concrete matrices, there is a preferential fibre alignment according to
the concrete’s flow in the fresh state. Having in mind that fibres are more efficient if they are oriented
according the principal tensile stresses, a preferential fibre alignment on a certain direction could
either enhance or diminish the material and the structural performance of this composite. In this paper,
it is investigated the influence of the fibre orientation and distribution on the post-cracking behaviour of
the steel fibre reinforced self-compacting concrete (SFRSCC). To perform this evaluation, SFRSCC
panels were casted from their centre point. Two self-compacting mixtures were prepared using the
same base mix proportions. For each SFRSCC panel cylindrical specimens were extracted and the
post-cracking behaviour was assessed from a crack width controlled splitting tensile test
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