Modeling water penetration at dam-foundation joint

When fracture occurs in a concrete dam, the crack mouth is typically exposed to water. Very often this phenomenon occurs at the dam-foundation joint and is driven also by the fluid pressure inside the crack. Since the joint is the weakest point in the structure, this evolutionary process determines the load bearing capacity of the dam. In this paper the cracked joint is analyzed through the cohesive model proposed by Cocchetti et al. [Cocchetti G, Maier G, Shen X. Piecewise linear models for interfaces and mixed mode cohesive cracks. J Engng Mech (ASCE) 2002;3:279-98.], which takes into account the coupled degradation of normal and tangential strength. The water pressure inside the crack, which reduces fracture energy and increases the driving forces, is analyzed through the model proposed by Reich et al. [Reich W, Bruhwiler E, Slowik V, Saouma VE. Experimental and computational aspects of a water/fracture interaction. In: Bourdarot E, Mazars J, Saouma V, editors, Dam Fracture and Damage, The Netherlands: Balkema; 1994. p. 123-31.] and Bruhwiler and Saouma [Bruhwiler E, Saouma VE. Water fracture interaction in concrete. Part II: Fracture properties. Am Concr Inst J 1995;92:296-303; Bruhwiler E, Saouma VE. Water fracture interaction in concrete. Part II: Hydrostatic pressure in cracks. Am Concr Inst J 1995;92:383-90.]. Some numerical results are presented which refer to the benchmark problem proposed in 1999 by the International Commission On Large Dams. During the evolutionary process the horizontal dam crest displacement has been found to be a monotonic increasing function of the external load multiplier. As the fictitious process zone moves from the upstream to the downstream edge a transition occurs in the path of crack formation: the initial phase is dominated by the opening displacement, on the contrary afterwards the shear displacement dominates. Therefore, crack initiation does not depend on dilatancy. On the contrary the load carrying capacity depends on dilatanc

La diffusion de l’enseignement mutuel girardien en Suisse : des déclinaisons pédagogiques transcantonales pour forger un «écolier-citoyen» moralisé ?

Quelles sont les raisons qui expliquent la diffusion rapide du mutualisme, tant à l'échelle mondiale qu'en Suisse? Qui se chargent de son transfert au niveau cantonal et quels sont les vecteurs qui en guident la translation? Pour répondre à ces questionnements, nous allons interroger certaines déclinaisons des "Girardines" en Suisse. Il s'agira d'analyser les modalités de diffusion du «modèle girardien», en s'appuyant sur les expériences réalisées dans les cantons catholiques de Fribourg et de Soleure ainsi que dans les cantons réformés de Vaud et de Neuchâtel. Une des principales visées sera de questionner ces circulations transcantonales en termes de transferts, c'est-à-dire au travers de phénomènes d'absorptions, afin d'éclairer le travail de médiation des «passeurs». Nous nous intéresserons également au processus éthique de construction d'un «écolier-citoyen» - idée phare présente chez Girard et ses contemporains - en relation avec la diffusion de l'enseignement mutuel en Suisse

"A Is A”: Spider-Man, Ayn Rand, and What Man Ought to Be

In 1979, writer Tom DeFalco was paired with artist and cocreator of Spider-Man, Steve Ditko, to work on an issue of Machine Man, one of the many superheroes populating the universe of Marvel Comics. Instead of the usual introduction and business chatter, Ditko challenged DeFalco during a first conversation: "Are you Tom? What gives you the right to write about heroes?” (Tucker 2012). By the time of this exchange, Ditko had not only (co-) created and continued numerous superhero stories, ranging from Captain Atom to Dr. Strange or the Hulk, but he had also dedicated a lot of thought to the question as to what composed true heroism. In the 1960s, he had already found answers in a place not uncommon for that time, namely, in the novels of a Russian immigrant whose work should serve, in her own words, as "the projection of an ideal man” (Rand 1943, ix; 1975, 162; 2005, 230): Ayn Rand (1905-1982

Bimodal mesoporous silica with bottleneck pores

Bimodal mesoporous silica consisting of two sets of well-defined mesopores is synthesized by a partial pseudomorphic transformation of an ordered mesoporous starting material (SBA-15 type). The introduction of a second set of smaller mesopores (MCM-41 type) establishes a pore system with bottlenecks that restricts the access to the core of the bimodal mesoporous silica particles. The particle size and shape of the starting material are retained, but micropores present in the starting material disappear during the transformation, leading to a true bimodal mesoporous product. A varying degree of transformation allows the adjustment of the pore volume contribution of the two mesopore domains. Information on the accessibility of the mesopores is obtained by the adsorption of fluorescence-labeled poly(amidoamine) dendrimers and imaging by confocal laser scanning microscopy. This information is correlated with nitrogen sorption data to provide insights regarding the spatial distribution of the two mesopore domains. The bimodal mesoporous materials are excellent model systems for the investigation of cavitation effects in nitrogen desorption isotherms

Functionalization of arrays of silica nanochannels by post-condensation

Functionalized arrays of silica nanochannels (ASNCs) were prepared by post-condensation of amino-functional alkoxysilanes (NH-silanes). The method of post-condensation combines postsynthetic grafting and co-condensation – the classical pathways for the functionalization of mesoporous silica – to afford a convenient one-pot reaction in aqueous medium. The structure of the NH-silanes determines the distribution of the surface-bound groups in the ASNCs. Accumulation at the channel entrances was observed by confocal laser scanning microscopy in the case of sterically hindered NH-silanes, whereas smaller NH-silanes led to a more uniform distribution. In all cases, the channels remained accessible for additional postsynthetic treatment or introduction of guests after extraction of the structure-directing agent. The particle size and morphology, as well as the pore size and the degree of ordering of the amino-functionalized ASNCs were comparable to pristine ASNCs