Nonequilibrium brittle fracture propagation: Steady state, oscillations and intermittency

A minimal model is constructed for two-dimensional fracture propagation. The heterogeneous process zone is presumed to suppress stress relaxation rate, leading to non-quasistatic behavior. Using the Yoffe solution, I construct and solve a dynamical equation for the tip stress. I discuss a generic tip velocity response to local stress and find that noise-free propagation is either at steady state or oscillatory, depending only on one material parameter. Noise gives rise to intermittency and quasi-periodicity. The theory explains the velocity oscillations and the complicated behavior seen in polymeric and amorphous brittle materials. I suggest experimental verifications and new connections between velocity measurements and material properties.Comment: To appear in Phys. Rev. Lett., 6 pages, self-contained TeX file, 3 postscript figures upon request from author at [email protected] or [email protected], http://cnls-www.lanl.gov/homepages/rafi/rafindex.htm

Optimization of Bacillus intermedius glutamyl endopeptidase production by recombinant strain of Bacillus subtilis and localization of glutamyl endopeptidase in Bacillus subtilis cells

The biosynthesis of glutamyl endopeptidase from Bacillus intermedius 3-19 in recombinant strain of Bacillus subtilis has been investigated. The composition of culture medium, which yielded the maximum glutamyl endopeptidase production by B. subtilis strain, was developed, employing response surface methodology. The pathways of regulation of glutamyl endopeptidase synthesis in recombinant strain in general were found to be similar to those of other serine proteinases and of glutamyl endopeptidase in B. intermedius. Biosynthesis of glutamyl endopeptidase by recombinant strain was suppressed by easily metabolizable carbon sources. Ions of Ca2+(2mM), Mg2+ (1mM), and Co2+ (5mM) stimulated production of the proteinase by B. subtilis. In case of Co2+ ions strong stimulating effect (up to 400%) possibly was due to the release of the membrane-bound enzyme into the culture liquid, according to the mechanism described earlier for B. intermedius. The addition of Fe2+, Zn2+, and Cu2+ to the medium at concentrations of 1 to 10mM led to the gradual decrease in proteinase production by B. subtilis. This study has demonstrated a requirement by recombinant strain for excess carbon, nitrogen, and inorganic phosphate for active glutamyl endopeptidase production. In contrast with B. intermedius, for the maximum yield of endopeptidase by B. subtilis the presence in the culture medium of yeast extract at concentration of 2% and one of the organic substrates of proteinase - casein or gelatin (1%) was found to be necessary. Our study has revealed the changes in the pathways of secretion of glutamyl endopeptidase of B. intermedius by B. subtilis cells, expressing the gene for glutamyl endopeptidase from the plasmids: the part of the enzyme (2-5%) remained bound to the cell wall. © 2002 Elsevier Science Inc. All rights reserved

Optimized medium for the efficient production of Bacillus intermedium glutamyl endopeptidase by the recombinant Bacillus subtilis strain AJ73

A nutrient medium was elaborated for the efficient production of glutamyl endopeptidase by the recombinant Bacillus subtilis strain AJ73 bearing the Bacillus intermedius 3-19 glutamyl endopeptidase gene within a multicopy plasmid. Optimal concentrations of the main nutrients, peptone and inorganic phosphate, were found using a multifactor approach. To provide for active growth and efficient glutamyl endopeptidase production, the cultivation medium of the recombinant strain should be enriched in phosphorus, organic and inorganic nitrogen sources, and yeast extract. Complex protein substrates, such as casein and gelatin, enhanced the biosynthesis of glutamyl endopeptidase. At the same time, easily metabolizable carbon sources suppressed it. The production of glutamyl endopeptidase was stimulated by the bivalent cations Ca2+, Mg2+, and Co2+. © 2000 MAIK "Nauka/Interperiodica"

DEVELOPMENT OF A BASIC OPTICAL SCHEME FOR DETERMINING INTERNAL STRESSES IN A COMPOSITE MATERIAL LIKE "METAL-GLASS-CERAMICS"

A basic optical scheme for determining internal mechanical stresses in a composite material like “metal-glass-ceramics” is developed. Basic elements and components of the installation are selected, their main characteristics are calculated

The expression of the serine proteinase gene of Bacillus intermedius in Bacillus subtilis

The gene encoding for Bacillus intermedius serine proteinase was cloned and the complete nucleotide sequence was determined. Gene expression was explored in the protease-deficient strain Bacillus subtilis AJ73 during different stages of growth. Catabolite repression involved in control of proteinase expression during transition state and onset of sporulation was not efficient at the late stationary phase. Salt stress leads to induction of serine proteinase production during B. subtilis AJ73(pCS9) post-exponential growth. Expression of proteinase in B. subtilis deg-mutants may be controlled by DegU regulator. B. subtilis spo0-mutants failed to accomplish B. intermedius proteinase production. These data suggest complex network regulation of B. intermedius serine proteinase expression, including the action of spo0, degU, catabolite repression and demonstrate changes in control of enzyme biosynthesis at different stages of growth. © 2006 Elsevier GmbH. All rights reserved

ПРЕДВАРИТЕЛЬНАЯ ОБРАБОТКА ЭКСПЕРИМЕНТАЛЬНЫХ ДАННЫХ В СТАТИСТИЧЕСКОМ ПРОЕКТИРОВАНИИ ИЗДЕЛИЙ МИКРОЭЛЕКТРОНИКИ

The results of researches on a choice and implementation of mathematical methods of the preliminary analysis and statistical processing of experimental data are presented. Data are received at processing and interpretation of industrial measurements of results from integrated circuits production. This technique allows not only to exclude the abnormal observations in the sample data, but also to carry out the procedure of smoothing the results of measurements or simulations.Представлены результаты исследований по выбору и практической реализации математических методов предварительного анализа и статистической обработки экспериментальных данных, полученных при обработке и интерпретации промышленных измерений результатов формирования элементов интегральных микросхем (ИМС). Предлагаемая методика позволяет исключать аномальные наблюдения в выборочных данных и проводить процедуру сглаживания результатов измерения или моделирования

Эпидемиологическая характеристика табакокурения и сравнительная оценка состояния респираторной системы у молодых мужчин

The aim of this study was to assess prevalence of tobacco smoking in healthy young men and to investigate smoking status, prevalence of respiratory symptoms and respiratory diseases and to measure lung function in smokers and non-smokers. Methods.This was a prospective cohort epidemiological study involving healthy male medical students. The participants fulfilled the GARD questionnaire. All participants underwent spirometry. Physical status was assesses with 1-km race time. Fagerstrom test of nicotine dependence was used in smokers. Results. The prevalence of tobacco smoking in young men was 20.9%. Smoking was started at the age of 16 – 20 years in 72.5%. Most smokers were mild smokers with low nicotine dependence and high motivation to continue smoking. Smokers more often had respiratory symptoms, acute respiratory infections, pneumonias, and allergy compared with healthy non-smokers. Conclusion. Based on the results of this study, thorough medical examinations of healthy young smokers is reasonable. Smoking cessation programs should be developed for this cohort.Табакокурение – ведущий фактор риска многих заболеваний, в т. ч. патологии респираторной системы. Цель. Оценка распространенности табакокурения у здоровых молодых мужчин и статуса курения курящих респондентов, частоты респираторных симптомов, перенесенных болезней органов дыхания, параметров легочной функции у курящих и некурящих лиц. Материалы. Распространенность курения среди молодых мужчин составила 20,9 %, из них 72,5 % начали курить в 16–20 лет. У большинства молодых курильщиков отмечены низкий индекс курения, слабая степень никотиновой зависимости, но высокая приверженность продолжению курения. Результаты. В группе курильщиков чаще отмечались респираторные симптомы и аллергические проявления, перенесенные пневмонии и острые респираторные вирусные инфекции по сравнению с некурящими мужчинами. Заключение. Опираясь на результаты настоящего исследования, следует подчеркнуть целесообразность углубленного медицинского обследования здоровых курящих молодых мужчин и внедрения антисмокинговых программ

Neotectonics of the SW Iberia margin, Gulf of Cadiz and Alboran Sea: a reassessment including recent structural, seismic and geodetic data

We use a thin-shell approximation for the lithosphere to model the neotectonics of the Gulf of Cadiz, SW Iberia margin and the westernmost Mediterranean, in the eastern segment of the Azores-Gibraltar plate boundary. In relation to previous neotectonic models in the region, we utilize a better constrained structural map offshore, and the recent GPS measurements over NW Africa and Iberia have been taken into account, together with the seismic strain rate and stress data, to evaluate alternative geodynamic settings proposed for the region. We show that by assuming a relatively simple, two-plate tectonic framework, where Nubia and Eurasia converge NW-SE to WNW-ESE at a rate of 4.5-6 mm yr-1, the models correctly predict the amount of shortening and wrenching between northern Algeria-Morocco and southern Spain and between NW Morocco and SW Iberia, as estimated from both GPS data and geological constraints. The consistency between modelled and observed velocities in the vicinity of Gibraltar and NW Morocco indicates that forcing by slab sinking beneath Gibraltar is not required to reproduce current horizontal deformation in these areas. In the Gulf of Cadiz and SW Iberia, the modelling results support a diffuse Nubia-Eurasia Plate boundary, where the convergence is accommodated along NNE-SSW to NE-SW and ENE-WSW thrust faults and WNW-ESE right-lateral strike-slip faults, over an area >200 km wide, in good general agreement with the distribution of the seismic strain rate and associated faulting mechanisms. The modelling results are robust to regional uncertainties in the structure of the lithosphere and have important implications for the earthquake and tsunami hazard of Portugal, SW Spain and Morocco. We predict maximum, long-term average fault slip rates between 1-2 mm yr-1, that is, less than 50 per cent the average plate relative movement, suggesting very long return periods for high-magnitude (Mw > 8) earthquakes on individual structures.publishe