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Despite the fact that quantitative experimental data have been available for more than forty years now, nematoacoustics still poses intriguing theoretical and experimental problems. In this paper, we prove that the main observed features of acoustic wave propagation through a nematic liquid crystal cell - namely, the frequency-dependent anisotropy of sound velocity and acoustic attenuation - can be explained by properly accounting for two fundamental features of the nematic response: anisotropy and relaxation. The latter concept - new in liquid crystal modelling - provides the first theoretical explanation of the structural relaxation process hypothesised long ago by Mullen and co-workers [Mullen et al., Phys. Rev. Lett., 1972, 28, 799]. We compare and contrast our proposal with an alternative theory where the liquid crystal is modelled as an anisotropic second-gradient fluid.

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I have been puzzled for a long time by the unnatural divide between the theory of bulk growth-strikingly underdeveloped-and that for surface growth-much better developed, along apparently independent lines. Recent advances in growth mechanics (DiCarlo and Quiligotti, 2002) make it now possible to subsume growth phenomena of both kinds under one and the same format, where surface growth is obtained as an infinitely intense bulk growth confined in a layer of vanishingly small thickness. This has allowed me to recover the results collected in Gurtin (2000) from the standpoint of DiCarlo and Quiligotti (2002). In particular, I am able to construe Gurtin's technique of referential control volumes that evolve in time as a special application of the principle of virtual power. 1 This is not at all obvious, since I can change my mind. But in this respect I did not. My coauthor did (Quiligotti, 2002), on the (not minor) issue of invariance requirements, convinced by an argument intimated by Green and Naghdi (1971) and spelled out in Casey and Naghdi (1980, 1981), Casey (1987), and elsewhere. For reasons I expound elsewhere (DiCarlo, in preparation), I find that old argument faulty and misleading.

Abstract-In this paper we show that the (co)chain complex associated with a decomposition of the computational domain, commonly called a mesh in computational science and engineering, can be represented by a block-bidiagonal matrix that we call the Hasse matrix. Moreover, we show that topology-preserving mesh refinements, produced by the action of (the simplest) Euler operators, can be reduced to multilinear transformations of the Hasse matrix representing the complex. Our main result is a new representation of the (co)chain complex underlying field computations, a representation that provides new insights into the transformations induced by local mesh refinements. Our approach is based on first principles and is general in that it applies to most representational domains that can be characterized as cell complexes, without any restrictions on their type, dimension, codimension, orientability, manifoldness, connectedness.

La génération de la forme des tissus biologiques invoque des phénomènes de croissance (variation des longueurs relâchées) et de remodelage (variation des propriétés mécaniques). La modélisation de ces phénomènes est de première importance sur le plan non seulement fondamental mais aussi technologique, pour le secteur de la santé. Dans le cadre d'une approche mécanique macroscopique, nous regardons le tissu osseux comme un milieu continu avec microstructure, dont les caractéristiques mécaniques locales (à cette échelle) se traduisent par un comportement linéairement élastique, anisotrope et évolutif. En particulier, la cinématique proposée est assez riche pour suivre l'évolution de la microstructure du tissu considéré, et en même temps prendre en compte le couplage existant entre contrainte, croissance et remodelage. Nous proposons donc une approche unifiée de la mécanique de la croissance et du remodelage, dans laquelle toutes les lois de bilan dérivent d'un principe des puissances virtuelles. Cette approche a été appliquée, pour le moment, à l'étude du remodelage de la raideur élastique par rotation de la microstructure dans le cas bidimensionnel, en l'absence de phénomènes de croissance volumique et de réponse physiologique aux stimuli (remodelage passif). L'analyse des résultats obtenus achève cette étude.

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The pathophysiological state of rejection in liver xenotransplantation is poorly understood. Data from clinical pig liver perfusion suggest that pig livers might be rejected less vigorously than pig hearts or kidneys. Pig livers used in clinical xenoperfusions were exposed to blood from patients with liver failure. We have shown in an animal model that transplant recipients with liver failure are less capable of initiating hyperacute rejection of a xenografted liver than a healthy transplant recipient. The goal of this report is to examine the pathological characteristics of pig livers used in 2 clinical pig liver perfusions and combine this information with in vitro studies of pig-to-human liver xenotransplantation to determine whether the findings in the perfused pig livers could be explained in part by the diminished capacity of the patient with liver failure to respond to xenogeneic tissue. Pathological analysis of the perfused pig livers showed immunoglobulin M deposition in the sinusoids with little evidence of complement activation. Our in vitro studies showed that serum from patients with liver failure caused less injury to pig liver endothelium than serum from healthy subjects. Serum from patients with liver failure had similar levels of xenoreactive antibodies as serum from healthy humans. Incubation of serum from patients with liver failure with pig hepatic endothelial cells generated less iC3b, Bb fragment, and C5b-9 than serum from healthy subjects. We conclude that the altered injury in the perfused pig livers can be attributed to the relative complement deficiency that accompanies liver failure. (Liver Transpl 2001;7:82-89.)