Stress-driven integration strategies and m-AGC tangent operator for Perzyna viscoplasticity and viscoplastic relaxation: application to geomechanical interfaces

This is the peer reviewed version of the following article: [Aliguer, I., Carol, I., and Sture, S. (2017) Stress-driven integration strategies and m-AGC tangent operator for Perzyna viscoplasticity and viscoplastic relaxation: application to geomechanical interfaces. Int. J. Numer. Anal. Meth. Geomech., 41: 918–939. doi: 10.1002/nag.2654.], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/nag.2654/abstract. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.The paper proposes a stress-driven integration strategy for Perzyna-type viscoplastic constitutive models, which leads also to a convenient algorithm for viscoplastic relaxation schemes. A generalized trapezoidal rule for the strain increment, combined with a linearized form of the yield function and flow rules, leads to a plasticity-like compliance operator that can be explicitly inverted to give an algorithmic tangent stiffness tensor also denoted as the m-AGC tangent operator. This operator is combined with the stress-prescribed integration scheme, to obtain a natural error indicator that can be used as a convergence criterion of the intra-step iterations (in physical viscoplasticity), or to a variable time-step size in viscoplastic relaxation schemes based on a single linear calculation per time step. The proposed schemes have been implemented for an existing zero-thickness interface constitutive model. Some numerical application examples are presented to illustrate the advantages of the new schemes proposed.Peer ReviewedPostprint (author's final draft

A phylogenetic comparative analysis on the evolution of sequential hermaphroditism in seabreams (Teleostei : Sparidae)

The Sparids are an ideal group of fish in which to study the evolution of sexual systems since they exhibit a great sexual diversity, from gonochorism (separate sexes) to protandrous (male-first) and protogynous (female-first) sequential hermaphroditism (sex-change). According to the size-advantage model (SAM), selection should favour sex change when the second sex achieves greater reproductive success at a larger body size than the first sex. Using phylogenetic comparative methods and a sample of 68 sparid species, we show that protogyny and protandry evolve from gonochorism but evolutionary transitions between these two forms of sequential hermaphroditism are unlikely to happen. Using male gonadosomatic index (GSI) as a measure of investment in gametes and proxy for sperm competition, we find that, while gonochoristic and protogynous species support the predictions of SAM, protandrous species do not, as they exhibit higher GSI values than expected even after considering mating systems and spawning modes. We suggest that small males of protandrous species have to invest disproportionally more in sperm production than predicted not only when spawning in aggregations with high levels of sperm competition, but also when spawning in pairs due to the need to fertilize highly fecund females, much larger than themselves. We propose that this compensatory mechanism, together with Bateman’s principles in sequential hermaphrodites, should be formally incorporated in the SAM

Sex determination

Després d’una descripció del que és el sexe, quan va aparèixer i per a què serveix, malgrat els seus costos, es descriuen els principals tipus de mecanismes de determinació del sexe tot centrant-nos en el que succeeix als vertebrats. Aquests mecanismes, en conjunt, es poden classificar com a genètics i ambientals, tot i que avui es tendeix a desdibuixar la seva separació. Entre els primers, s’inclou la determinació del sexe per factors (gens) “màster” o principals, com passa als mamífers, i sistemes multi- i poligènics, com passa en alguns peixos. Es descriuen també els gens determinants del sexe coneguts fins ara i perquè la seva diversitat constitueix una de les grans paradoxes dins de la biologia del desenvolupament. Seguidament, es parla de la determinació del sexe per factors ambientals, notablement la temperatura, i com l’epigenètica s’ha erigit en un disciplina ideal per estudiar la integració de la informació genètica i ambiental per a donar lloc a un fenotip sexual determinat. A continuació, es descriu el procés de diferenciació sexual i com els estrògens hi tenen una importància cabdal en tots els vertebrats excepte els mamífers placentats. Finalment, es mencionen les aplicacions de l’estudi de la determinació del sexe. Aquestes inclouen la diagnosi i comprensió dels trastorns del desenvolupament sexual en humans, el control de la proporció de sexes en la producció animal, particularment l’aquàtica, pel major creixement d’un sexe respecte l’altre, i els efectes que la pol·lució i el canvi climàtic poden tenir o ja tenen en la determinació del sexe als vertebrats.After a description of what sex is, when it appeared and the purpose it serves despite its costs, the main types of sex-determining mechanisms are described, focusing on the situation in vertebrates. These mechanisms can broadly be classified as genetic and environmental, although today there is a tendency to blur this separation. The genetic mechanisms include the determination of sex by main factors or “master” genes, as in mammals, and multi-and polygenic systems, as in some fish. We describe the sex genes known to date and explain why their diversity is one of the great paradoxes in development biology. Next, we present the determination of sex by environmental factors, particularly by temperature, and explain why epigenetics is emerging as an ideal discipline for studying the integration of genetic and environmental information to give rise to a given sexual phenotype. We then describe the process of sexual differentiation and how estrogens are of paramount importance for ovarian differentiation in all vertebrates except placental mammals. Finally, the applications of studying sex determination are mentioned. These include the diagnosis and understanding of sexual development disorders in humans, controlling sex ratios in animal production—particularly in aquatic animals due to the greater growth of one sex than the other—and the effects that pollution and climate change may have, or already have, in the determination of sex in some vertebrates