74 research outputs found
Theory of dynamic crack branching in brittle materials
The problem of dynamic symmetric branching of an initial single brittle crack
propagating at a given speed under plane loading conditions is studied within a
continuum mechanics approach. Griffith's energy criterion and the principle of
local symmetry are used to determine the cracks paths. The bifurcation is
predicted at a given critical speed and at a specific branching angle: both
correlated very well with experiments. The curvature of the subsequent branches
is also studied: the sign of , with being the non singular stress at the
initial crack tip, separates branches paths that diverge from or converge to
the initial path, a feature that may be tested in future experiments. The model
rests on a scenario of crack branching with some reasonable assumptions based
on general considerations and in exact dynamic results for anti-plane
branching. It is argued that it is possible to use a static analysis of the
crack bifurcation for plane loading as a good approximation to the dynamical
case. The results are interesting since they explain within a continuum
mechanics approach the main features of the branching instabilities of fast
cracks in brittle materials, i.e. critical speeds, branching angle and the
geometry of subsequent branches paths.Comment: 41 pages, 15 figures. Accepted to International Journal of Fractur
Semi-supervised discovery of differential genes
BACKGROUND: Various statistical scores have been proposed for evaluating the significance of genes that may exhibit differential expression between two or more controlled conditions. However, in many clinical studies to detect clinical marker genes for example, the conditions have not necessarily been controlled well, thus condition labels are sometimes hard to obtain due to physical, financial, and time costs. In such a situation, we can consider an unsupervised case where labels are not available or a semi-supervised case where labels are available for a part of the whole sample set, rather than a well-studied supervised case where all samples have their labels. RESULTS: We assume a latent variable model for the expression of active genes and apply the optimal discovery procedure (ODP) proposed by Storey (2005) to the model. Our latent variable model allows gene significance scores to be applied to unsupervised and semi-supervised cases. The ODP framework improves detectability by sharing the estimated parameters of null and alternative models of multiple tests over multiple genes. A theoretical consideration leads to two different interpretations of the latent variable, i.e., it only implicitly affects the alternative model through the model parameters, or it is explicitly included in the alternative model, so that the interpretations correspond to two different implementations of ODP. By comparing the two implementations through experiments with simulation data, we have found that sharing the latent variable estimation is effective for increasing the detectability of truly active genes. We also show that the unsupervised and semi-supervised rating of genes, which takes into account the samples without condition labels, can improve detection of active genes in real gene discovery problems. CONCLUSION: The experimental results indicate that the ODP framework is effective for hypotheses including latent variables and is further improved by sharing the estimations of hidden variables over multiple tests
A boundary integral method for a dynamic, transient mode I crack problem with viscoelastic cohesive zone
Thermal fracture as a framework for quasi-static crack propagation
We address analytically and numerically the problem of crack path prediction
in the model system of a crack propagating under thermal loading. We show that
one can explain the instability from a straight to a wavy crack propagation by
using only the principle of local symmetry and the Griffith criterion. We then
argue that the calculations of the stress intensity factors can be combined
with the standard crack propagation criteria to obtain the evolution equation
for the crack tip within any loading configuration. The theoretical results of
the thermal crack problem agree with the numerical simulations we performed
using a phase field model. Moreover, it turns out that the phase-field model
allows to clarify the nature of the transition between straight and oscillatory
cracks which is shown to be supercritical.Comment: 19 pages, 8 figure
Staying connected: structural integration at the intervertebral disc–vertebra interface of human lumbar spines
Identification of 12 new susceptibility loci for different histotypes of epithelial ovarian cancer.
To identify common alleles associated with different histotypes of epithelial ovarian cancer (EOC), we pooled data from multiple genome-wide genotyping projects totaling 25,509 EOC cases and 40,941 controls. We identified nine new susceptibility loci for different EOC histotypes: six for serous EOC histotypes (3q28, 4q32.3, 8q21.11, 10q24.33, 18q11.2 and 22q12.1), two for mucinous EOC (3q22.3 and 9q31.1) and one for endometrioid EOC (5q12.3). We then performed meta-analysis on the results for high-grade serous ovarian cancer with the results from analysis of 31,448 BRCA1 and BRCA2 mutation carriers, including 3,887 mutation carriers with EOC. This identified three additional susceptibility loci at 2q13, 8q24.1 and 12q24.31. Integrated analyses of genes and regulatory biofeatures at each locus predicted candidate susceptibility genes, including OBFC1, a new candidate susceptibility gene for low-grade and borderline serous EOC
Constitutive parameters for earthquake rupture dynamics based on high-velocity friction tests with variable sliprate
Cycle distributions for Gaussian waves - Exact and approximative results
Wave cycle distributions are notoriously difficult to calculate. Available analytic approximations, like those suggested by Longuet-Higgins (1983) and Cavanie, Arhan and Ezraty (1976) make use only of a few spectral moments, and are unreliable for moderate waves. To find distributions under general spectrum shape and parameters one has to use efficient numerical algorithms based on high-dimensional integrals. The paper presents a number of examples of wave cycle distributions computed by the software package WAFO developed at Lund Institute of Technology; http://www.maths.lth.se/matstat/wafo/. All results are compared to simulated or real data. The wave cycles studied are the max-min cycle, the crest-trough wave cycles, the rainflow cycle distribution, and the mean-separated max-min cycle
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