Nucleosomes in gene regulation: theoretical approaches

This work reviews current theoretical approaches of biophysics and bioinformatics for the description of nucleosome arrangements in chromatin and transcription factor binding to nucleosomal organized DNA. The role of nucleosomes in gene regulation is discussed from molecular-mechanistic and biological point of view. In addition to classical problems of this field, actual questions of epigenetic regulation are discussed. The authors selected for discussion what seem to be the most interesting concepts and hypotheses. Mathematical approaches are described in a simplified language to attract attention to the most important directions of this field

Dynamic analyses of a crack run-arrest experiment in a nonisothermal plate

In crack-arrest studies sponsored by the Heavy-Section Steel Technology (HSST) Program, a primary objective has been to produce fracture toughness data for reactor pressure vessel materials at temperatures approaching the Charpy upper-shelf regime. Wide-plate tests being conducted at the National Bureau of Standards for the HSST Program are providing an opportunity to obtain significant numbers of data points at affordable costs. In these tests, a single-edge crack in a wide-plate which is subjected to tensile loading initiates at low temperature and arrests in a region of increased fracture toughness. The gradient in toughness is achieved by applying a linear transverse temperature profile across the plate. The second test in this series for A 533 grade B class 1 steel involves crack initiation in cleavage followed by arrest at a temperature corresponding to Charpy upper-shelf behavior. The plate geometry, the material properties, and the instrumentation are discussed along with conditions and results for this test. Pretest static and elastodynamic analyses are described, and posttest analyses based on actual boundary conditions are shown to compare favorably with the observed run-arrest events

FALSIRE. CSNI project for fracture analyses of large-scale international reference experiments. Phase 1 Comparison report

The six experiments used in Project FALSIRE (performed in the Federal Republic of Germany, Japan, the United Kingdom, and the U.S.A.) were designed to examine various aspects of crack growth in reactor pressure vessel (RPV) steels under pressurized-thermal-shock (PTS) loading conditions. The CSNI/FAG established a common format for comprehensive statements of these experiments, including supporting information and available analysis results. For each experiment, analysis results provided estimates of variables such as crack growth, crack-mouth-opening displacement, temperature, stress, strain, and applied J and K values. A comparative assessment and discussion of the analysis results are presented; also, the current status of the entire results data base is summarized. Generally, these results highlight the importance of adequately modeling structural behavior of specimens before performing fracture mechanics evaluations. Applications of the various fracture methodologies were found to be partially successful in some cases but not in others. Based on these assessments, some conclusions concerning predictive capabilities of selected ductile fracture methodologies, as applied to RPVs subjected to PTS loading are given. (orig.)SIGLEAvailable from TIB Hannover: RN 6050(108) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany); Nuclear Energy Agency (NEA), 92 - Issy-les-Moulineaux (France). Committee on the Safety of Nuclear Installations; Bundesministerium fuer Umwelt, Naturschutz und Reaktorsicherheit, Bonn (Germany); Nuclear Regulatory Commission (NRC), Washington, DC (United States)DEGerman