Multilayer theory for delamination stresses in semicircular laminated composite curved bars

Composites laminates are widely used in both civil and military aircraft structures and gases cylinders leading to weight saving. However, study of the behaviour of such materials has shown that they are more damage sensitive than metallic material especially to delamination due to edge effect or low velocity impact [1]. In order to improve the performance of composite structures, advances must be made in the prediction of delamination growth and the evaluation of residual strength. The aim of this paper is to extend a delamination model valid for the plate in small displacement [2] or large displacement [3] to the case of curved structures as shells. Two kinds of approach are commonly used to study delamination growth, (i) the damage mechanics approach in which the interface enclosing the delamination is modelled by a damageable material Delamination is obtained when the damage variable reaches its maximum value [4 - 6] and (ii) the fracture mechanics approach which the present work is part. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2583

Конструкционная прочность стеклопластиковых оболочек вращения с межслойными дефектами структуры

Высокие удельные показатели прочности и жесткости волокнистых композиционных материалов наряду с химической стойкостью, сравнительно малым весом и другими свойствами, сделали эти материалы привлекательными для изготовления трубопроводов различного назначения. Применение стеклопластиковых труб взамен металлических увеличивает срок службы трубопроводов в 5-8 раз, исключает применение антикоррозионных защитных средств, в 4-8 раз снижает массу трубопровода, исключает применение сварочных работ. При цитировании документа, используйте ссылку http://essuir.sumdu.edu.ua/handle/123456789/3001

Effect of composite materials used in the manufacture of aircraft parts on environmental pollution and the economy

We have investigated and compared energy use and production of emissions when various aerospace materials are used in aircraft. Computer-based models were prepared to compare lightweight composites with the traditional heavier aluminum over their whole lifetime which is termed a “lifecycle assessment”. This included raw materials, production, useful life in the aircraft and disposal at the end of the material’s useful life. The information provided by this work is independent of industrial influence and so provides an objective view of potential savings in energy and emissions. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/836

Effects of Al dopant on structural and optical properties of ZnO thin films prepared by sol-gel

Transparent and conductive Al doped ZnO thin films were synthesized at room temperature by sol gel technique both pure ZnO and Al-doped(1,3,and 5%) thin films were deposited on a glass substrate. The sols were prepared using zinc acetate dehydrate and aluminum chloride provides Al ions, played an important role in improvement of the c – axis, the structural characteristics have been studied by X-ray diffraction, and UV–Vis-NIR spectroscopy. The films are transparent from the near ultraviolet to the near infrared, SEM image also showed that the average grain size is decreased with increasing of Al concentration, band gap values of prepared thin films varied in the range of (3.18 – 3.42 eV). When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3394

Genome-wide characterization of \u3ci\u3eSalmonella \u3c/i\u3eTyphimurium genes required for the fitness under iron restriction

Background Iron is a crucial element for bacterial survival and virulence. During Salmonella infection, the host utilizes a variety of mechanisms to starve the pathogen from iron. However, Salmonella activates distinctive defense mechanisms to acquire iron and survive in iron-restricted host environments. Yet, the comprehensive set of the conditionally essential genes that underpin Salmonella survival under iron-restricted niches has not been fully explored. Results Here, we employed transposon sequencing (Tn-seq) method for high-resolution elucidation of the genes in Salmonella Typhimurium (S. Typhimurium) 14028S strain required for the growth under the in vitro conditions with four different levels of iron restriction achieved by iron chelator 2,2′-dipyridyl (Dip): mild (100 and 150 μM), moderate (250 μM) and severe iron restriction (400 μM). We found that the fitness of the mutants reduced significantly for 28 genes, suggesting the importance of these genes for the growth under iron restriction. These genes include sufABCDSE, iron transport fepD, siderophore tonB, sigma factor E ropE, phosphate transport pstAB, and zinc exporter zntA. The siderophore gene tonB was required in mild and moderate iron-restricted conditions, but it became dispensable in severe iron-restricted conditions. Remarkably, rpoE was required in moderate and severe iron restrictions, leading to complete attenuation of the mutant under these conditions. We also identified 30 genes for which the deletion of the genes resulted in increased fitness under iron-restricted conditions. Conclusions The findings broaden our knowledge of how S. Typhimurium survives in iron-deficient environments, which could be utilized for the development of new therapeutic strategies targeting the pathways vital for iron metabolism, trafficking, and scavenging

Communicative language teaching: the beliefs, attitudes, and practices of pre-service EFL teachers in western Libya

The English language has become an international and economically-required medium of communication. Communicative language teaching (CLT) is a well established approach for teaching English as a foreign language (EFL). This approach can be a challenge in places where English is not the lingua franca. In the context of Libyan education, CLT is currently seen as a challenging innovation because of the nation’s long history of EFL pedagogy relying on rote learning and textbooks. Furthermore, educational change in Libya has been compromised by political disruption and war. The fast pace of change is another factor, with more Libyan schools being built. However, the biggest dilemma confronted by the Libyan school system is the lack of resources and of teachers, combined with the type of examination system under use which affects CLT. The aim of this study was (1) to explore pre-service teachers’ (PSTs) and in-service teachers’ (INSTs) beliefs and attitudes towards CLT and (2) to explore the choices they make to engage in their EFL teaching practice, that is, either (a) the grammar-translation method or (b) communicative language teaching. This study sits in the socio-cultural paradigm and draws on constructivism as the epistemological and pedagogical underpinning of CLT. A research design approach was used to investigate beliefs and attitudes. A quantitative study, as the first phase, was followed by a qualitative study in the second phase. The first aim of the study was met by conducting a five-point Likert scale type survey of 79 PSTs and 33 INSTs. The second aim of the study was achieved by conducting classroom observations, keeping researcher notes and conducting interviews in the second phase. A sub-sample of seven pre-service teachers’ classroom pedagogy was observed, and eight individual interviews were conducted with four of these pre-service teachers, two INSTs and two university teachers. This study also provided information on the issues and barriers that teachers face when applying CLT in real classroom situations. These barriers related to (1) their beliefs about using only English as a medium of instruction and (2) their fear of their supervisors’ evaluations, which shifted their pedagogical focus. During their teaching practice, the pre-service teachers moved from their awareness of the importance of learning English through exposure to the language to a focus on translation, students’ low English levels, and the length of teaching practical program, which was inadequate for pre-service teachers to be able to put their beliefs into practice. The research concluded that an awareness of these barriers can guide both the education of teachers in Libyan universities and the development of teachers’ CLT practices, post-method. It is anticipated that the findings of this study will support Libyan universities in developing a more consistent approach between primary and secondary public school EFL teachers and tertiary (university) EFL teachers and ensure a more effective practicum experience that involves more reflective and dialogic practice

The Trialectics Of Transnational Migrant Women’s Literature In The Writing Of Edwidge Danticat And Julia Alvarez

While a considerable critical field has developed around US Latino writing, due to the historical, cultural and sociolinguistic barriers between the two nations of Haiti and the Dominican Republic, critical investigations of these migrant literatures are often not bridged, but rather isolated into respective Haitian-American and Dominican-American designations. My comparative, critical framework defines the interactions between gender, culture and the diverse spatial coordinates from the island of Hispaniola, the Atlantic and the United States. The carefully differentiated objects of study that I articulate in each chapter offer a desirable interdisciplinary orientation inclusive of gender theory as well as cultural studies. I examine three iterations of transnational women’s writing using work by renowned writers Edwidge Danticat (Haitian-American) and Julia Alvarez (Dominican-American). Chapter one focuses on an analysis of migrant women’s subjectivity in the Bildungsroman or coming of age novel. Chapter two investigates race and gender in novels that recreate historical events in the migrant homeland Chapter three links works of non-fiction with the author’s varying transnational social justice initiatives. Each chapter compares and contrasts the framing of transnational literature of the Caribbean-American with a specific interest in gender, culture and spatial coordinates from the island of Hispaniola (Haiti and the Dominican Republic), the Atlantic and the United States

The paths from walk preference to walk behavior: Applying latent factors in structural equation modeling

JTLU vol 5, no 3, pp 68-82 (2012)A structural regression model has been developed to explore the relationship among key factors in the explanation of utilitarian walking. The model examines the relationship between and among unobserved, or “latent,” factors that reflect (1) the values and preferences operant at the time of residential selection; (2) the urban form of the neighborhood; (3) the urban form of the residence; (4) the level of auto dependency; and (5) the extent to which the neighborhood is found satisfactory by the participant and those whose opinions he/she respects. The model allows the detailed examination of the paths from initial inclination toward a neighborhood with walkable destinations, through a series of mediating unobserved factors, each of which might either impede or facilitate the adoption of utilitarian walking. Analysis of the model results shows that values and preferences held at the time of residential selection are directly associated with the amount of utilitarian walking undertaken and indirectly associated through their influence on the choice of the built environment and the extent of auto orientation. The model is designed to facilitate the observation of the manner in which the various factors interact