Local and non-local approaches to fatigue crack initiation and propogation

Copyright @ 2003 Kulwer Academic Publishers.A functional form of local strength conditions under fatigue loading is introduced and employed to formulation and analysis of fatigue crack initiation and propagation. For the strength conditions associated with the Palmgren-Miner linear damage accumulation rule and the power-type S-N diagram, the problem is reduced to a non-linear integral Volterra equation, which can be transformed to a linear one for the case of a single crack. An analytical solution of some simple problems are presented for the latter case and shortcomings of the local approach are pointed out. A non-local approach free from the shortcomings is presented along with an example of its implementation.This work was completed under the research grant GR/M24592 "Non-local approach to high cyclic fatigue: Theoretical basis" of the Engineering and Physical Sciences Research Council, UK

Fatigue of sintered porous materials based on 316L stainless steel under uniaxial loading

The paper presents the results of fatigue tests of sintered porous 316L austenitic stainless steel with different porosity. An analysis was conducted into the parameters obtained from the hysteresis loop in the load cycle (changes in the value of Young’s modulus, maximum and minimum stress). Fatigue life of the porous material of varying density according to the relationship Manson–Coffin was determined.Наведено результати втомних випробовувань зразків аустенітної сталі 316L з рівнями пористості 26, 33 і 41%. Проаналізовано параметри, отримані із петлі гістерезису в циклі навантаження – зміну модуля Юнґа, максимальних і мінімальних напружень. Використовуючи залежність Mенсона–Коффіна, визначили втомну міцність пористих матеріалів з різним ступенем загущення.Представлены результаты усталостных испытаний образцов аустенитной стали 316L с уровнями пористости 26, 33 и 41%. Проанализированы параметры, полученные из петли гистерезиса в цикле нагрузки – изменения модуля Юнга, максимальных и минимальных напряжений. Используя зависимость Mенсона–Коффина, определили усталостную прочность пористых материалов с различным уровнем плотности

Numerical analysis of strain and stress state in cylindrical notched tensile specimens

The paper presents the numerical results of stress and strain distribution in specimens with various sizes of notches in monotonic uniaxial tensile tests. The adopted method involves the finite element method and the elastic-plastic model of material with hardening. The distribution of the principal strain, principal stress and maximum plastic shear strain in the plane of notch symmetry is shown in figures.Методом скінченних елементів отримано числовий розв’язок пружно-пластичної осесиметричної задачі про розтяг циліндричного зразка з поверхневою U-подібною канавкою. Числові результати одержано для зразка з алюмінієвого сплаву EN-AW 2024. Проаналізовано розподіл напружень і деформацій у симетричному поперечному перерізі зразка залежно від відносного радіуса закруглення у вершині канавки, коли розтягальна сила досягає критичного значення перед руйнуванням зразка.Методом конечных элементов получено числовое решение упругопластичной осесимметричной задачи о растяжении цилиндрического образца с поверхностной U-подобной канавкой. Числовые результаты получены для образца из алюминиевого сплава EN-AW 2024. Проанализировано распределение напряжений и деформаций в симметричном поперечном сечении образца в зависимости от относительного радиуса закругления в вершине канавки, когда растягивающая сила достигает критического значения перед разрушением образца

Assessing Plasmodium falciparum transmission in mosquito-feeding assays using quantitative PCR.

BACKGROUND: Evaluating the efficacy of transmission-blocking interventions relies on mosquito-feeding assays, with transmission typically assessed by microscopic identification of oocysts in mosquito midguts; however, microscopy has limited throughput, sensitivity and specificity. Where low prevalence and intensity mosquito infections occur, as observed during controlled human malaria infection studies or natural transmission, a reliable method for detection and quantification of low-level midgut infection is required. Here, a semi-automated, Taqman quantitative PCR (qPCR) assay sufficiently sensitive to detect a single-oocyst midgut infection is described. RESULTS: Extraction of genomic DNA from Anopheles stephensi midguts using a semi-automated extraction process was shown to have equivalent extraction efficiency to manual DNA extraction. An 18S Plasmodium falciparum qPCR assay was adapted for quantitative detection of P. falciparum midgut oocyst infection using synthetic DNA standards. The assay was validated for sensitivity and specificity, and the limit of detection was 0.7 genomes/µL (95% CI 0.4-1.6 genomes/µL). All microscopy-confirmed oocyst infected midgut samples were detected by qPCR, including all single-oocyst positive midguts. The genome number per oocyst was assessed 8-9 days after feeding assay using both qPCR and droplet digital PCR and was 3722 (IQR: 2951-5453) and 3490 (IQR: 2720-4182), respectively. CONCLUSIONS: This semi-automated qPCR method enables accurate detection of low-level P. falciparum oocyst infections in mosquito midguts, and may improve the sensitivity, specificity and throughput of assays used to evaluate candidate transmission-blocking interventions

Thymus-derived regulatory T cells control tolerance to commensal microbiota

Peripheral mechanisms preventing autoimmunity and maintaining tolerance to commensal microbiota involve CD4+Foxp3+ regulatory T cells1,2 generated in the thymus (tTregs) or extrathymically by induction of naive CD4+Foxp3− T cells (iTregs). Prior studies suggested that the T cell receptor (TCR) repertoires of tTregs and iTregs are biased towards self and non-self antigens, respectively 3–6 but their relative contribution in controlling immunopathology, e.g. colitis and other untoward inflammatory responses triggered by different types of antigens, remains unresolved 7. The intestine, and especially the colon, is a particularly suitable organ to study this question, given the variety of self-, microbiota- and food-derived antigens to which Tregs and other T cell populations are exposed. Intestinal environments can enhance conversion to a regulatory lineage 8,9 and favor tolerogenic presentation of antigens to naive CD4+ T cells 10,11, suggesting that intestinal homeostasis depends on microbiota-specific iTregs 12–15. Here, to identify the origin and antigen-specificity of intestinal Tregs, we performed single cell as well as high-throughput (HT) sequencing of the TCR repertoires of CD4+Foxp3+ and CD4+Foxp3− T cells and analyzed their reactivity against specific commensal species. We show that tTregs constitute the majority of Tregs in all lymphoid and intestinal organs, including colon, where their repertoire is heavily influenced by the composition of the microbiota. Our results suggest that tTregs, and not iTregs, dominantly mediate tolerance to antigens produced by intestinal commensals

Selección por recurrencia de los parámetros de calidad ambiental y turística de los esquemas de certificación de playas en América latina

Beach Certification Schemes (BCSs) are tools recently implemented in Latin America. They are based on an evaluation of a given set of compliance aspects (requirements). The research consisted of the recollection, classification and organization of the available information on the Latin American BCSs, found through search engines, data bases, scientific articles, information networks and direct contact with organizations in charge of the certifications. The information was then used to calculate the proportions of inclusion of the compliance aspects in the five categories proposed by Botero (2008). The most recurrent for the Latin American context compliance aspects were calculated through the evaluation of the 3rd quartile, based on their statistical representativeness. In result, ninety one aspects were found in eight BCSs, most of them in the “environment” category. In the contrary, the “management” category was found to have the least number of aspects. In terms of the BCSs, the Colombian NTS-TS-001-2 and Argentinian IRAM 42100 were found to have the most aspects, while the Cost Rican Bandera Azul Ecológica the least. Finally, with the additional objective to emphasize the environmental importance of beaches, ten most relevant environmental compliance aspects were selected from the twenty eight foundLos Esquemas de Certificación de Playas (ECP) son una herramienta de reciente implementación en América Latina, estando soportados principalmente en la evaluación de aspectos de conformidad en diferentes categorías. Esta investigación recopiló, organizó y validó la mayoría de información disponible sobre ECP en América Latina, a través de la consulta de motores de búsqueda, bases de datos de artículos científicos, redes de información, expertos en certificaciones y contacto directo con las organizaciones promotoras. Con esta información, se calculó la proporción de inclusión de cada requerimiento dentro de las cinco categorías de aspectos de conformidad indicadas por Botero (2008), a través de un histograma de frecuencias. La selección de los aspectos de conformidad más recurrentes para el contexto Latinoamericano se obtuvo mediante la evaluación del tercer cuartil, en base a su representatividad estadística. Se encontraron 91 aspectos de conformidad en las ocho certificaciones estudiadas, siendo la categoría ambiental la que más aspectos reunió, en comparación con la de manejo. Respecto a los ECP, se encontró que la norma colombiana NTS-TS-001-2 y la Argentina IRAM 42100 poseen el mayor número de aspectos de conformidad, mientras que la norma costarricense Bandera Azul Ecológica y la norma uruguaya Playa Natural tienen los valores menores. Finalmente, con el objetivo adicional de enfatizar la importancia ambiental de las playas, se seleccionaron los 10 aspectos de conformidad ambientales más relevantes, dentro de los 28 encontrados.

Development of Si beam position detectors for NA61/SHINE experiment

The NA61/SHINE experiment at the CERN SPS is undergoing a major upgrade during the LHC Long Shutdown 2 period (2019-2021). The upgrade is essential to ful l the requirements of the new open charm measurement program. In this program detector will operate at a beam intensity increased by a factor of 10, which requires an upgrade of current Beam Position Detectors (BPDs). New BPDs should monitor lead and proton beam intensities with up to 105 Hz rate. In this paper, progress on design and development of the new BPDs based on Si strip detectors, its front-end and readout electronics, as well as integration with the NA61/SHINE DAQ is presented

A universal framework for Space Resource Utilisation (SRU)

Space Resource Utilisation (SRU) or In Situ Resource Utilisation (ISRU) is the use of natural resources from the Moon, Mars and other bodies for use in situ or elsewhere in the Solar System. The implementation of SRU technologies will provide the breakthrough for humankind to explore further into space. A range of extraction processes to produce usable resources have been proposed, such as oxygen production from lunar regolith, extraction of lunar ice and construction of habitation by 3D printing. Practical and successful implementation of SRU requires that all the stages of the process flowsheet (excavation, beneficiation and extraction) are considered. This requires a complete ‘mine-to-market’ type approach, analogous to that of terrestrial mineral extraction. One of the key challenges is the unique cross-disciplinary nature of SRU; it integrates space systems, robotics, materials handling and beneficiation, and chemical process engineering. This is underpinned by knowledge of the lunar or planetary geology, including mineralogy, physical characteristics, and the variability in local materials. Combining such diverse fields in a coordinated way requires the use of a universal framework. The framework will enable integration of operations and comparison of technologies, and will define a global terminology to be used across all fields. In this paper, a universal SRU flowsheet and terminology are described, and a matrix approach to describing regolith characteristics specifically for SRU is proposed. This is the first time that such an approach has been taken to unify this rapidly-developing sector