a 'sleeper', receiving only modest attention for 50 years before emerging as a cornerstone of communications engineering in more recent times. Roughly one in six of Walsh's 281 publications are included, photographically reproduced. Reproduction is excellent except for one paper from 1918. The book also reproduces three brief papers about Walsh and his work, by W. E. Sewell, D. V. Widder and Morris Marden. The first two were written for a special issue of the SIAM Journal celebrating Walsh's 70th birthday; the third is an obituary.

Matrix iterative analysis (2nd edn), by Richard S. Varga. Springer Series in Computational Mathematics 27. Pp. 358. £55. 2000. ISBN 3 540 66321 5 (Springer Verlag).

This paper is devoted to presenting controllability and stabilizability issues associated to a class of nonsmooth dynamical systems, namely complementarity dynamical systems. The main existing results are summarized, and some possible research directions are provided. Convex analysis and complementarity problems are claimed to be the main analysis tools for control related studies. This paper mainly focuses on mechanical applications.

/pdf/some-perspectives-on-the-analysis-and-control-of-8v50zifuae.pdf

Some perspectives on the analysis and control of complementarity systems

Absolute stability and the Lagrange–Dirichlet theorem with monotone multivalued mappings

A mechanical and numerical model of dry granular flows is proposed that quantitatively reproduce laboratory experiments of granular column collapse over inclined planes. The rheological parameters are directly derived from the experiments. The so-called μ ( I ) rheology is reformulated in the framework of Drucker–Prager plasticity with the yield stress and viscosity η ( ‖ D ‖ , p ) depending on both the pressure p and the norm of the strain rate tensor ‖ D ‖ . The granular domain, velocities, stress deviator and pressure fields are calculated using a finite element method based on an iterative decomposition–coordination formulation coupled with the augmented Lagrangian method. 2-D simulations using this model well reproduce the dynamics and deposits of collapsing granular columns. The flow is essentially located in a surface layer behind the front, whereas it is distributed over the whole depth near the front where basal sliding occurs. The computed runout distances and slopes of the deposits agree very well with the values found in the experiments. Using an easily calculated order of magnitude approximation of the mean viscosity during the flow ( η = 1  Pa s here), we show that a Drucker–Prager rheology with a constant viscosity gives results very similar to the μ ( I ) rheology and agrees with experimental height profiles, while significantly reducing the computational cost. Within the range of viscosities 0.1 η 1  Pa s, the dynamics and deposits are very similar. The observed slumping behavior therefore appears to be mainly due to the flow/no-flow criterion and to the associated strain-independent part of the “flowing constitutive relation” (i.e. related to plastic effects). However, the results are very different when an unrealistically large value of viscosity (10 Pa s) is used.

/pdf/viscoplastic-modeling-of-granular-column-collapse-with-32dq0y4lt9.pdf

Viscoplastic modeling of granular column collapse with pressure-dependent rheology

https://www.math.uh.edu/~canic/Beta_Scheme.pdf

Fluid-structure interaction in blood flow capturing non-zero longitudinal structure displacement

http://repositorio.uchile.cl/bitstream/handle/2250/124538/Duarte,%20F.pdf?sequence=1

Arbitrary Lagrangian-Eulerian method for Navier-Stokes equations with moving boundaries

We study the existence and uniqueness of strong solutions for the equations of non-homogeneous asymmetric fluids. We use an iterative approach and we prove that the approximate solutions constructed by this method converge to the strong solution of these equations. We also give bounds for the rate of convergence. Copyright © 2002 John Wiley & Sons, Ltd.

The equations of non-homogeneous asymmetric fluids: an iterative approach

Sustained improvement in student achievement on national standardized tests for low socio economic status (SES) districts is critical for reducing gaps in educational inequality. We report the results of 3 years of implementation of an ICT web-based learning environment in all 11 public schools of a low SES urban district in Chile. This includes 43 fourth grade classes and 1,355 students. This is a Computer Aided Instruction program that promotes whole class collaborative learning with peer support. Effect size on the national standardized fourth grade math test is 0.33, which is three times the national improvement level over the same period and five times the improvement made by a neighboring district with a similar population. On the other hand, the same students did not make any improvements on the national standardized language test. Since each class was taught by the same teacher, only without ICT, we can therefore discount the teacher effect.

ICT Supported Learning Rises Math Achievement in Low Socio Economic Status Schools

We give a predictive theory of the collisions of a viscous incompressible fluid with solids. The theory is based on interior percussions which account for the very large stresses and contact forces resulting from the kinematic incompatibilities responsible for the collision. New equation of motion and constitutive laws result from the theory. Examples dealing with a fluid colliding with its container and with a diver impacting the water of a swimming pool are studied.

Collision of a Solid with an Incompressible Fluid

Numerical investigations of unsteady laminar flow and heat transfer in a channel of height H with periodically mounted square bars of height d = 0.2H arranged side by side to the approaching flow have been conducted for different transverse separation distances of the bars. Five cases with transverse separation distance of 0, 0.5, 1, 1.5 and 2d for a Reynolds number of 300 in a channel with a periodicity length of 2H were studied. The unsteady Navier–Stokes equations and the energy equation have been solved by a finite volume code with staggered grids combined with the SIMPLEC algorithm and a fine grid resolution. Due to the arrangement of bars detached from the channel walls the flow is unsteady with vortex shedding from the bars. The amplitude and mean values of the drag coefficients, skin friction coefficients, friction factor and Nusselt numbers have a strong dependence of the transverse separation distance of the bars.

Raúl Gormaz

Papers

Arbitrary Lagrangian-Eulerian method for Navier-Stokes equations with moving boundaries

The equations of non-homogeneous asymmetric fluids: an iterative approach

ICT Supported Learning Rises Math Achievement in Low Socio Economic Status Schools

Collision of a Solid with an Incompressible Fluid

Numerical study of the unsteady flow and heat transfer in channels with periodically mounted square bars