Neural networks for modelling and control of a non-linear dynamic system

The authors describe the use of neural nets to model and control a nonlinear second-order electromechanical model of a drive system with varying time constants and saturation effects. A model predictive control structure is used. This is compared with a proportional-integral (PI) controller with regard to performance and robustness against disturbances. Two feedforward network types, the multilayer perceptron and radial-basis-function nets, are used to model the system. The problems involved in the transfer of connectionist theory to practice are discussed

Rb*He_n exciplexes in solid 4_He

We report the observation of emission spectra from Rb*He_n exciplexes in solid 4He. Two different excitation channels were experimentally identified, viz., exciplex formation via laser excitation to the atomic 5P3/2 and to the 5P1/2 levels. While the former channel was observed before in liquid helium, on helium nanodroplets and in helium gas by different groups, the latter creation mechanism occurs only in solid helium or in gaseous helium above 10 Kelvin. The experimental results are compared to theoretical predictions based on the extension of a model, used earlier by us for the description of Cs*He_n exciplexes. We also report the first observation of fluorescence from atomic rubidium in solid helium, and discuss striking differences between the spectroscopic feature of Rb-He and Cs-He systems.Comment: 8 pages, 8 figure

Noncommutative Common Cause Principles in Algebraic Quantum Field Theory

States in algebraic quantum field theory "typically" establish correlation between spacelike separated events. Reichenbach's Common Cause Principle, generalized to the quantum field theoretical setting, offers an apt tool to causally account for these superluminal correlations. In the paper we motivate first why commutativity between the common cause and the correlating events should be abandoned in the definition of the common cause. Then we show that the Noncommutative Weak Common Cause Principle holds in algebraic quantum field theory with locally finite degrees of freedom. Namely, for any pair of projections A, B supported in spacelike separated regions V_A and V_B, respectively, there is a local projection C not necessarily commuting with A and B such that C is supported within the union of the backward light cones of V_A and V_B and the set {C, non-C} screens off the correlation between A and B

Generalizing Boolean Satisfiability III: Implementation

This is the third of three papers describing ZAP, a satisfiability engine that substantially generalizes existing tools while retaining the performance characteristics of modern high-performance solvers. The fundamental idea underlying ZAP is that many problems passed to such engines contain rich internal structure that is obscured by the Boolean representation used; our goal has been to define a representation in which this structure is apparent and can be exploited to improve computational performance. The first paper surveyed existing work that (knowingly or not) exploited problem structure to improve the performance of satisfiability engines, and the second paper showed that this structure could be understood in terms of groups of permutations acting on individual clauses in any particular Boolean theory. We conclude the series by discussing the techniques needed to implement our ideas, and by reporting on their performance on a variety of problem instances

Monoclinic and triclinic phases in higher-order Devonshire theory

Devonshire theory provides a successful phenomenological description of many cubic perovskite ferroelectrics such as BaTiO3 via a sixth-order expansion of the free energy in the polar order parameter. However, the recent discovery of a novel monoclinic ferroelectric phase in the PZT system by Noheda et al. (Appl. Phys. Lett. 74, 2059 (1999)) poses a challenge to this theory. Here, we confirm that the sixth-order Devonshire theory cannot support a monoclinic phase, and consider extensions of the theory to higher orders. We show that an eighth-order theory allows for three kinds of equilibrium phases in which the polarization is confined not to a symmetry axis but to a symmetry plane. One of these phases provides a natural description of the newly observed monoclinic phase. Moreover, the theory makes testable predictions about the nature of the phase boundaries between monoclinic, tetragonal, and rhombohedral phases. A ferroelectric phase of the lowest (triclinic) symmetry type, in which the polarization is not constrained by symmetry, does not emerge until the Devonshire theory is carried to twelfth order. A topological analysis of the critical points of the free-energy surface facilitates the discussion of the phase transition sequences.Comment: 10 pages, with 5 postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/dv_pzt/index.htm

Displacement energy of unit disk cotangent bundles

We give an upper bound of a Hamiltonian displacement energy of a unit disk cotangent bundle $D^*M$ in a cotangent bundle $T^*M$, when the base manifold $M$ is an open Riemannian manifold. Our main result is that the displacement energy is not greater than $C r(M)$, where $r(M)$ is the inner radius of $M$, and $C$ is a dimensional constant. As an immediate application, we study symplectic embedding problems of unit disk cotangent bundles. Moreover, combined with results in symplectic geometry, our main result shows the existence of short periodic billiard trajectories and short geodesic loops.Comment: Title slightly changed. Close to the version published online in Math Zei

Heritabilities of osteochondral lesions and genetic correlations with production and exterior traits in station-tested pigs

Osteochondrosis might reduce the performance of slaughter pigs, longevity of sows and animal welfare. The aim of the present work was to describe the prevalence in Swiss breeds and to analyse the genetic background of osteochondral lesions. Between January 2002 and December 2005, about 9500 station-tested pigs were examined for several exterior traits before slaughtering at the Swiss pig performance testing station using the Swiss linear description system with a scale from 1 to 7 per trait. The animals belonged to three breeds: Large White dam line, Swiss Landrace and Large White sire line. Additionally, a random sample of these pigs (n = 2622) was examined for osteochondral lesions at seven positions of the carcass after dissection. At first, the surface and shape of the femur, humerus, radius and ulna at the joints were evaluated by a trained person. Afterwards these bones were sawed and the state of the cartilage and the distal epiphyseal cartilage of the ulna was examined at the cutting surface. Osteochondral lesions were scored on a scale from 1 to 6. The prevalence of osteochondral lesions was low at head of humerus, condylus lateralis humeri, radius and ulna proximal and head of femur. Osteochondral lesions at condylus medialis humeri (CMH), distal epiphyseal cartilage of ulna (DEU) and condylus lateralis femoris (CMF) exhibited phenotypic and genetic variance. Their heritabilities ranged from 0.16 to 0.18 using linear mixed animal models. Therefore, it is possible to reduce the prevalence of osteochondral lesions by selection in principle. Exterior traits showed low heritabilities (0.10 to 0.26) but several favourable genetic correlations with osteochondral lesions at CMH, DEU and CMF with low to moderate magnitude. Genetic correlations between osteochondral lesions and production traits were lo