Does the continuum theory of dynamic fracture work?

We investigate the validity of the Linear Elastic Fracture Mechanics approach to dynamic fracture. We first test the predictions in a lattice simulation, using a formula of Eshelby for the time-dependent Stress Intensity Factor. Excellent agreement with the theory is found. We then use the same method to analyze the experiment of Sharon and Fineberg. The data here is not consistent with the theoretical expectation.Comment: 4 page

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

Growth conditions and production of the Bacillus intermedius subtilisin-like serine proteinase by the recombinant Bacillus subtilis strain

The effect of the components of the nutrient medium on growth and production of the Bacillus intermedius subtilisin-like serine proteinase by the recombinant strain Bacillus subtilis AJ73(pCS9) was studied. The production of proteinase was found to be dependent on the composition of the nutrient medium and showed two peaks, at the 28th and 48th h of growth. The concentrations of the main components of the nutrient medium (peptone and inorganic phosphate) optimal for the biosynthesis of subtilisin-like serine proteinase at the 28th and 48th h of growth were determined in factorial experiments. Complex organic substances, casein at concentrations of 0.5-1%, gelatin at concentrations of 0.5-1%, and yeast extract at a concentration of 0.5%, stimulated the production of subtilisin-like serine proteinase by the recombinant strain. The study of the sporulation dynamics in this strain showed that the proteinase peaks at the 28th and 48th h of growth correspond, respectively, to the initial stage of sporulation and to the terminal stages of endospore formation (V-VII stages of sporulation). © Pleiades Publishing, Inc., 2006

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 $T$, with $T$ 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

Biosynthesis of the Bacillus intermedius subtilisin-like serine proteinase by the recombinant Bacillus subtilis strain

The effect of certain nutrients on the growth and production of the Bacillus intermedius subtilisin-like serine proteinase by the recombinant strain Bacillus subtilis AJ73(pCS9) was studied. Glucose was found to inhibit the synthesis of proteinase in the early (28 h of growth) but not in the late stationary phase (48 h of growth). The inhibitory effect of the other mono- and disaccharides studied was less pronounced. Casamino acids added to the medium at concentrations of 0.1-1% as an additional carbon and nitrogen source stimulated enzyme biosynthesis. Individual amino acids (cysteine, asparagine, glutamine, tryptophan, histidine, and glutamate) also stimulated enzyme biosynthesis in the early stationary phase by 25-30%, whereas other amino acids (valine, leucine, alanine, and aspartate) were ineffective or even slightly inhibitory to enzyme production. The stimulatory effect of the first group of amino acids on the synthesis of proteinase in the late stationary phase was negligible. In contrast, the bivalent ions Ca2+, Mg2+, and Mn 2+ stimulated biosynthesis of proteinase in the late stationary phase (by 20-60%) and not in the early stationary phase. The data indicate that there are differences in the biosyntheses of proteinase by the recombinant B. subtilis strain during the early and late periods of the stationary phases. © Pleiades Publishing, Inc., 2006

The criteria for the rapid assessment of physico-chemical properties of the basic materials

This paper shows the results of the study of physical - chemical properties of acrylic plastic base.В работе показаны результаты изучения физико - химических свойств акриловых базисных пластмасс

The Role of the Educational Organization in the Special Economic Zone

the article deals with the problems that arise in special economic zones that are being created in the Russian Federation. Educational institutions that will provide them with working personnel play a special role in making investment in the SEZ attractive. The main parameters of a systematic approach to creating a University as a center of scientific and innovative development are considered.В статье рассматривается проблемы, возникающие в особых экономических зонах, создающихся в Российской Федерации. Особую роль в создании привлекательности инвестиций в ОЭЗ играют образовательные учреждения, обеспечивающие их рабочими кадрами. Нужен системный подход к созданию университета как центра научного и инновационного развития

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