The Effects of Interfacial Properties on the Mechanical Behavior of Layered Aluminum Matrix Composites

Al/SiC-composites are not only ajfected by inelastic deformation processes in the metallic matrix but also by debonding occurring at the fiber-matrix-interface. Therefore a viscoplastic material law including damage evolution and growth, as well as a cohesive zone model for the interface, are integrated into a finite element technique. By this the influence of interfacial characteristics on the stress-strain behavior of a laminated Al/SiC-composite is ezramined

Effect of Uniaxial Tensile Loading on the Stiffness of Two-Dimensional Woven SiC/SiC - Modeling and Numerical Simulation

The behavior of two-dimensional woven SiC/SiC ceramic matrix composites (CMC) is studied by numerical simulations based on the finite element method (FEM). Starting point of the investigations is amicromechanical model regarding a three-dimensional unit cell. Damage as well as fracture of the singlecomponents - fiber bundles and inter yarn matrix - are regarded from a statistical point of view usingWeibull distribution. Statements of the behavior of the whole composite are possible by building up amacrostructure. The purpose of the current study is set on the stifiness reduction of the 2Dw compositesubjected to tensile loading in one of the fiber directions. Because of the strong anisotropy of the dam-age a tensor approach is used considering the terms of the elasticity matrix, which are determined forincreasing load. Regarding the elasticity matrix the behavior of the composite for any loading situationcan be predicted after an arbitrary preloading in one of the fiber direction

Black Holes and Random Matrices

We argue that the late time behavior of horizon fluctuations in large anti-de Sitter (AdS) black holes is governed by the random matrix dynamics characteristic of quantum chaotic systems. Our main tool is the Sachdev-Ye-Kitaev (SYK) model, which we use as a simple model of a black hole. We use an analytically continued partition function $|Z(\beta +it)|^2$ as well as correlation functions as diagnostics. Using numerical techniques we establish random matrix behavior at late times. We determine the early time behavior exactly in a double scaling limit, giving us a plausible estimate for the crossover time to random matrix behavior. We use these ideas to formulate a conjecture about general large AdS black holes, like those dual to 4D super-Yang-Mills theory, giving a provisional estimate of the crossover time. We make some preliminary comments about challenges to understanding the late time dynamics from a bulk point of view.Comment: 73 pages, 15 figures, minor errors correcte

Lineage tracing and clonal analysis in developing cerebral cortex using mosaic analysis with double markers (MADM)

Beginning from a limited pool of progenitors, the mammalian cerebral cortex forms highly organized functional neural circuits. However, the underlying cellular and molecular mechanisms regulating lineage transitions of neural stem cells (NSCs) and eventual production of neurons and glia in the developing neuroepithelium remains unclear. Methods to trace NSC division patterns and map the lineage of clonally related cells have advanced dramatically. However, many contemporary lineage tracing techniques suffer from the lack of cellular resolution of progeny cell fate, which is essential for deciphering progenitor cell division patterns. Presented is a protocol using mosaic analysis with double markers (MADM) to perform in vivo clonal analysis. MADM concomitantly manipulates individual progenitor cells and visualizes precise division patterns and lineage progression at unprecedented single cell resolution. MADM-based interchromosomal recombination events during the G2-X phase of mitosis, together with temporally inducible CreERT2, provide exact information on the birth dates of clones and their division patterns. Thus, MADM lineage tracing provides unprecedented qualitative and quantitative optical readouts of the proliferation mode of stem cell progenitors at the single cell level. MADM also allows for examination of the mechanisms and functional requirements of candidate genes in NSC lineage progression. This method is unique in that comparative analysis of control and mutant subclones can be performed in the same tissue environment in vivo. Here, the protocol is described in detail, and experimental paradigms to employ MADM for clonal analysis and lineage tracing in the developing cerebral cortex are demonstrated. Importantly, this protocol can be adapted to perform MADM clonal analysis in any murine stem cell niche, as long as the CreERT2 driver is present

Existential witness extraction in classical realizability and via a negative translation

We show how to extract existential witnesses from classical proofs using Krivine's classical realizability---where classical proofs are interpreted as lambda-terms with the call/cc control operator. We first recall the basic framework of classical realizability (in classical second-order arithmetic) and show how to extend it with primitive numerals for faster computations. Then we show how to perform witness extraction in this framework, by discussing several techniques depending on the shape of the existential formula. In particular, we show that in the Sigma01-case, Krivine's witness extraction method reduces to Friedman's through a well-suited negative translation to intuitionistic second-order arithmetic. Finally we discuss the advantages of using call/cc rather than a negative translation, especially from the point of view of an implementation.Comment: 52 pages. Accepted in Logical Methods for Computer Science (LMCS), 201