A Criterion for Brittle Failure of Rocks Using the Theory of Critical Distances

This paper presents a new analytical criterion for brittle failure of rocks and heavily overconsolidated soils. Griffith’s model of a randomly oriented defect under a biaxial stress state is used to keep the criterion simple. The Griffith’s criterion is improved because the maximum tensile strength is not evaluated at the boundary of the defect but at a certain distance from the boundary, known as the critical distance. This fracture criterion is known as the Point Method, and is part of the Theory of Critical Distances, which is utilized in fracture mechanics. The proposed failure criterion has two parameters: the inherent tensile strength, ó0, and the ratio of the half-length of the initial crack/flaw to the critical distance, a/L. These parameters are difficult to measure but they may be correlated with the uniaxial compressive and tensile strengths, óc and ót. The proposed criterion is able to reproduce the common range of strength ratios for rocks and heavily overconsolidated soils (óc/ót=3-50) and the influence of several microstructural rock properties, such as texture and porosity. Good agreement with laboratory tests reported in the literature is found for tensile and low confining stresses.The work presented was initiated during a research project on “Structural integrity assessments of notch-type defects", for the Spanish Ministry of Science and Innovation (Ref.: MAT2010-15721)

Analysis of notch effect on the fracture behaviour of granite and limestone: An approach from the Theory of Critical Distances

This paper presents the analysis of the notch effect on granite and limestone fracture specimens. The research is based on the results obtained in an experimental programme composed of 84 fracture specimens, combining the two materials and 7 different notch radii varying from 0.15 mm up to 10 mm. The notch effect is analysed through the evolution of the apparent fracture toughness and the application of the Theory of the Critical Distances. The results reveal a significant notch effect in the limestone, whereas the notch effect in the granite is negligible for the range of notch radii analysed. Both observations are justified by the corresponding critical distance of the material

Computational Homogenization of Architectured Materials

Architectured materials involve geometrically engineered distributions of microstructural phases at a scale comparable to the scale of the component, thus calling for new models in order to determine the effective properties of materials. The present chapter aims at providing such models, in the case of mechanical properties. As a matter of fact, one engineering challenge is to predict the effective properties of such materials; computational homogenization using finite element analysis is a powerful tool to do so. Homogenized behavior of architectured materials can thus be used in large structural computations, hence enabling the dissemination of architectured materials in the industry. Furthermore, computational homogenization is the basis for computational topology optimization which will give rise to the next generation of architectured materials. This chapter covers the computational homogenization of periodic architectured materials in elasticity and plasticity, as well as the homogenization and representativity of random architectured materials

ABILITIES AND EXPERIENCE OF APPLICATION OF NEUROVISUALIZATION FUNCTIONAL METHODS IN EPILEPTOLOGY

Modern methods of instrumental diagnosis allow the rise of quality, swiftness and accuracy of diagnosis to a new higher level. This article highlights the abilities of proton magnetic resonance spectroscopy (1H-MRS), positron emission tomography (PET) and single-photon emission computed tomography (SPECT) as functional methods of neurovisualization in epileptology

A single unprovoked generalized seizure: Results of examination and 5-year follow-up in 47 patients

Background. To choose tactics for patients with a single unprovoked generalized convulsive seizure (SUGCS) is a quite a challenge due to the lack of common approaches to interpreting this episode. Objective: to study the clinical, electroencephalographic (EEG), neuroimaging (magnetic resonance imaging (MRI) — positron emission tomography (PET)) and morphocytochemical features of peripheral blood cells (PBC) in patients with SUGCS. Patients and methods. Group 1 included 47 patients with SUGCS. A comparison group comprised 50 patients with different forms of locally induced symptomatic and/or cryptogenic epilepsy (LIE). All the patients underwent complex clinical examination including EEG, MRI, and PBC morphocytochemical study, which could reveal predictors for a high risk of recurrent convulsive seizure. In addition, PET was performed in 34 (72%) patients with SUGCS and 41 (82%) patients with LIE. Results and conclusion. The paper shows the possibilities of complex diagnosis using highly informative studies (PET, PBC cytomorpholog-ical examination) that allows identification of predictors of a high risk for a recurrent convulsive seizure. The findings may be useful in defining the treatment policy in patients with SUGCS and in timely using antiepileptic therapy

EPILEPSY FROM THE 19TH CENTURY SCIENTIST’S PERSPECTIVE

Abstract: he review presents an analysis of the formation of the views of scientists on the pathogenesis and treatment of epilepsy in the XIX century. The authors analyze the main works of scholars Department of Nervous and Mental Diseases of the Imperial Medical-Surgical Academy, devoted to issues of experimental studies of changes in cerebral blood flow during seizures, the improvement of the treatment of patients with epilepsy. The paper also highlighted the prerequisites for the development and nature of the hypothesis of «convulsive center», and the role of V.M. Bekhterev and his students in establishing the role of the cerebral cortex in the pathogenesis of epileptic seizures