Propagation of torsional waves in tubular bones

By considering the material inhomogeneity and anisotropy of osseous tissues, the propagation of torsional waves in tubular bones has been studied in this paper. An exact closed form solution is presented. The electric and magnetic fields induced by the travelling torsional waves in tubular bones are also derived by accounting for the piezoelectricity of osseous material. Making use of the derived analytical solution, and the experimentally determined constants for osseous tissues, numerical values of the phase velocities and attenuation coefficients are calculated for different frequencies in the ultrasonic range. Further, the effects of material damping and inhomogeneity on the attenuation and phase velocities of the waves are examined.     

Bare bones differential evolution

The barebones differential evolution (BBDE) is a new, almost parameter-free optimization algorithm that is a hybrid of the barebones particle swarm optimizer and differential evolution. Differential evolution is used to mutate, for each particle, the attractor associated with that particle, defined as a weighted average of its personal and neighborhood best positions. The performance of the proposed approach is investigated and compared with differential evolution, a Von Neumann particle swarm optimizer and a barebones particle swarm optimizer. The experiments conducted show that the BBDE provides excellent results with the added advantage of little, almost no parameter tuning. Moreover, the performance of the barebones differential evolution using the ring and Von Neumann neighborhood topologies is investigated. Finally, the application of the BBDE to the real-world problem of unsupervised image classification is investigated. Experimental results show that the proposed approach performs very well compared to other state-of-the-art clustering algorithms in all measured criteria.     

The analysis of sequential measurements of bones

Analysing sequential bone measurements obtained in experiments in which the duration of observation varies between individuals is a common problem. Two solutions are presented which estimate the population mean rate of change in different ways. The first solution provides a least squares estimate and involves calculating a weighting factor for each individual observation which increases nonlinearly with the observation period. Computation of this solution requires knowledge of the measurement error and also the true variability in the rate of change between individuals, which is rarely if ever known. The second solution, based on cumulative sums, is much simpler, involving a weighting factor which is equal to the observation period. No prior knowledge of the measurement error or variability in the rate of change is required. An expression for the standard error of the computed mean rate of change is also derived. Monte Carlo simulations of a large number of experiments have confirmed that, within the limits of the model parameters tested, the second solution produces valid estimates of the mean rate of change and its standard error.     

Propagation of sound in oriented polymers

The propagation of sound in oriented polymers is considered. Starting from an assumption concerning the superposition of relaxation processes in polymers, expressions are obtained for the speed and absorption of sound as functions of the relaxation spectrum, molecular orientation, and crystallinity. It is shown that the orientation dependence of the acoustic properties is more distinctly expressed in the region of the glassy state.Scientific-Research Institute of Plastics, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 437–441, May–June, 1969.     

Propagation of Reactions in Inhomogeneous Media

Consider reaction‐diffusion equation u _t =Δ u + f (x,u ) with and general inhomogeneous ignition reaction f ≥ 0 vanishing at u = 0,1. Typical solutions 0 ≤ u ≤ 1 transition from 0 to 1 as time progresses, and we study them in the region where this transition occurs. Under fairly general qualitative hypotheses on f we show that in dimensions d ≤ 3, the Hausdorff distance of the superlevel sets {u ≥ ε } and {u ≥ 1‐ε} remains uniformly bounded in time for each ε ? (0,1). Thus, u remains uniformly in time close to the characteristic function of in the sense of Hausdorff distance of superlevel sets. We also show that each {u ≥ ε} expands with average speed (over any long enough time interval) between the two spreading speeds corresponding to any x ‐independent lower and upper bounds on f . On the other hand, these results turn out to be false in dimensions d ≥ 4, at least without further quantitative hypotheses on f . The proof for d ≤ 3 is based on showing that as the solution propagates, small values of u cannot escape far ahead of values close to 1. The proof for d ≥ 4 is via construction of a counterexample for which this fails. Such results were before known for d =1 but are new for general non‐periodic media in dimensions d ≥ 2 (some are also new for homogeneous and periodic media). They extend in a somewhat weaker sense to monostable, bistable, and mixed reaction types, as well as to transitions between general equilibria of the PDE and to solutions not necessarily satisfying . © 2016 Wiley Periodicals, Inc.     

Propagation of small sditurbances in magneto-elastics

The possible modes of propagation of small disturbances in a homogeneous, incompressible initially unstressed, electrically conducting elastic medium at rest in the presence of a uniform external magnetic field are studied and it is found that if the medium is non-rigid (analogous to non-viscous fluids) and perfectly conducting, the disturbances propagate with Alfvén velocity. The effects of rigidity and finite conductivity on these transverse Alfvén waves have been investigated in some detail. It is interesting to note that the series representations obtained are strikingly similar to those got by Chadwick in the case of thermo-elastic plane waves.     

Error Propagation in Numerical Processes

A method is suggested of analysing the mechanism of error propagationin certain numerical processes, and detailed results are obtainedfor the solution of triangular linear systems, polynomial deflation,LU decomposition and matrix reduction to tridiagonal form usingHouseholder transformations. The analysis is also applicableto the solution of ordinary differential equations.     

Error Propagation in Game Trees

Game tree search is the core of most attempts to make computers play games. We present a fairly general theoretical analysis on how leaf evaluation errors influence the value estimation of a game position at the root. By an approach using prime factorization arguments in the ring of polynomials, we show that in this setting the maximum number of leaf-disjoint strategies proving a particular property is a key notion. This number precisely describes the quality of the heuristic game value in terms of the quality of the leaf evaluation heuristics. We extend this model to include random nodes (rolls of a die). Surprisingly, this changes the situation: utill the number of leaf-disjoint strategies ensures robustness against leaf evaluation errors, but the converse is not true. An average node may produce additional robustness similar to additional leaf-disjoint strategies. This work extends earlier ones which only deal with 0, 1 valued nodes, or without randomness.The first author was partially supported (associate member) by the graduate school ‘Effiziente Algorithmen und Mehrskalenmethoden’, Deutsche Forschungsgemeinschaft. The second author was partially supported by the Future and Emerging Technologies programme of the EU under contract numbers IST-1999-14186 (ALCOM-FT) and IST-2001-33116 (FLAGS).     

Front Propagation in Stirred Media

The problem of asymptotic features of front propagation in stirred media is addressed for laminar and turbulent velocity fields. In particular we consider the problem in two dimensional steady and unsteady cellular flows in the limit of very fast reaction and sharp front, i.e., in the geometrical optics limit. In the steady case we provide an analytical approximation for the front speed, v _f, as a function of the stirring intensity, U, in good agreement with the numerical results. In the unsteady (time-periodic) case, albeit the Lagrangian dynamics is chaotic, chaos in the front dynamics is relevant only for a transient. Asymptotically the front evolves periodically and chaos manifests only in the spatially wrinkled structure of the front. In addition we study front propagation of reactive fields in systems whose diffusive behavior is anomalous. The features of the front propagation depend, not only on the scaling exponent ν, which characterizes the diffusion properties, \({( \langle (x(t) - x(0))^2 \rangle \sim t^{2\nu} )}\) , but also on the detailed shape of the probability distribution of the diffusive process.     

Constraint Propagation in Graph Coloring

In this paper we propose a method for integrating constraint propagation algorithms into an optimization procedure for vertex coloring with the goal of finding improved lower bounds. The key point we address is how to get instances of Constraint Satisfaction Problems (CSPs) from a graph coloring problem in order to give rise to new lower bounds outperforming the maximum clique bound. More precisely, the algorithms presented have the common goal of finding CSPs in the graph for which infeasibility can be proven. This is achieved by means of constraint propagation techniques which allow the algorithms to eliminate inconsistencies in the CSPs by updating domains dynamically and rendering such infeasibilities explicit. At the end of this process we use the largest CSP for which it has not been possible to prove infeasibility as an input for an algorithm which enlarges such CSP to get a feasible coloring. We experimented with a set of middle-high density graphs with quite a large difference between the maximum clique and the chromatic number.     

Propagation of localized bending deformations in microtubules

A continuum medium model is proposed describing a microtubule (MT) as an elastic rod. When the MT is subjected to a constant bending force, the dynamics of the angular deviation, with respect to the MT's rectilinear configuration, is governed by a Sine-Gordon equation. Particular analytical solutions are kink and anti-kink bending modes which may propagate at various speeds along the MT's length. Kinetic energies of these modes compare with thermal and ATP hydrolysis energies. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Propagation of Disturbances in a Random Medium

In this paper we are concerned with the determination of thestochastic rays along which light disturbances propagate ina random inhomogeneous, time-dependent and isotropic medium.The analysis is formulated in the framework of stochastic optimalcontrol. We state an appropriate stochastic Fermat's Principlewhich upon invoking the principle of optimality in dynamic programmingleads to a parabolic functional differential equation for thetraversal time of a wavefront, the randomness entering as anadditive white-noise in the displacements of the field. Whenthe randomness constitutes small perturbations to the mean velocityfield, the problem becomes one of singular perturbation of theHamilton-Jacobi equation by a small second order term. Approximateexpressions are presented for the traversal time and mean stochasticpath for a time-independent mean-velocity of propagation. Asa specific example we consider these expressions for propagationsin a stratified medium.     

Remarks on Propagation of Singularities in Thermoelasticity

The propagation of high order weak singularities for the system of homogeneous thermoelasticity in one space variable is studied by using paralinearization and a new decoupling technique introduced by the author (Microlocal analysis in nonlinear thermoelasticity, to appear). For the linear system, one shows that the nonsmooth initial data for the parabolic part lead to singularities in the hyperbolic part of solutions, even when the initial data for that part are identically zero. Both the Cauchy problem and the problem inside of a domain for the semilinear system are considered. It is shown that the propagation of high order singularities is essentially dominated by the hyperbolic operator in the system of thermoelasticity.     

Propagation of high intensity light in semiconductors

For photons of energy below the bandgap energy, semiconductors exhibit high transparency and low irradiance light passes freely through the medium. However, for high irradiances of light, as from a laser, the transmission through the semiconductor becomes nonlinear. As the irradiance of the incident light increases, the transmission through the semiconductor decreases through nonlinear absorption as well as from the generation of free carriers during the laser pulse. The propagation of light through this irradiance dependent medium can be described by a set of coupled, inhomogeneous, partial differential equations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)