Tensile Overload and Stress Intensity Shielding Investigations by Ultrasound

Growth of a fatigue crack is modified according to the development of contacts between the crack faces [1,2] creating shielding, thus canceling a portion of the crack driving force. These contacts develop through a number of mechanisms, including plastic deformation, sliding of the faces with respect to each other and the collection of debris such as oxide particles [3]. Compressive stresses are created on either side of the partially contacting crack faces resulting in opening loads that must be overcome in order to apply a driving force at the crack tip. In this way, the crack tip is shielded from a portion of the applied load, thus creating the need for modification [1] of the applied stress intensity range from ΔK = KImax − KImin to ΔKeff = KImax − KIsh. Determination of the contact size and density in the region of closure from ultrasonic transmission and diffraction experiments [4] has allowed estimation of the magnitude of Kish on a crack grown under constant ΔK conditions. The calculation has since [5] been extended to fatigue cracks grown with a tensile overload block. The calculation was also successful in predicting the growth rate of the crack after reinitiation had occurred. This paper reports the further extension to the effects of a variable ΔK on fatigue crack growth. In addition, this paper presents preliminary results on detection of the tightly closed crack extension present during the growth retardation period after application of a tensile overload as well as an observation of the crack surface during reinitiation of growth that presents some interesting questions

Characterization of Microstructural Effects on Fatigue Crack Closure

The growth of a fatigue crack is modified by the development of contacts between the crack faces1,2creating shielding and thus canceling a portion of the applied load. These contacts develop through a number of mechanisms, including plastic deformation, sliding of the faces with respect to each other and the creation and collection of debris such as oxide particles3. Compressive stresses are created on either side of the partially contacting crack faces resulting in opening loads that must be overcome in order to apply a driving force to the crack tip for growth. In this way, the crack tip is shielded from a portion of the applied load, thus creating the need for modification1 of the applied stress intensity range from ΔK = KImax — KImin to ΔK = KImax — KIsh. Determination of the contact size and density in the region of closure from ultrasonic transmission and diffraction experiments4has allowed estimation of the magnitude of KIsh on a crack grown under constant ΔK conditions. The calculation has since5 been extended to fatigue cracks grown with a tensile overload block. The calculation was also successful in predicting the growth rate of the crack after reinitiation had occurred. This paper reports the results of attempts to define the amount of retardation remaining before reinitiation of crack growth in terms of the parameters used by the distributed spring model

Proteome of human T lymphocytes with treatment of cyclosporine and polysaccharopeptide: Analysis of significant proteins that manipulate T cells proliferation and immunosuppression

The aberrant activation of T lymphocyte proliferation is one of the key events in organ transplant recipients and autoimmune disorders. The present study adopted a gel-based proteomics approach to define the proteins representative of the T cell proliferation and to discover the molecules that play critical roles during the suppression of T cell proliferation. Human T lymphocytes were isolated from healthy donors and primed with phytohemagglutinin (PHA) to undergo proliferation. Two medical fungal products with specific T cell activation inhibitory properties, cyclosporine A (CsA) and polysaccharopeptide (PSP), were used to study the proteins that manipulate T cell proliferation. After demonstrating their similar effects on cell proliferation, cell survival and interleuklin-2 (IL-2) secretion, significant quantitative protein alterations were detected between the CsA- and PSP-treated T cell proteome. These altered proteins were identified by MALDI-TOF and classified into 3 categories: (i) proteins affected by both CsA and PSP, (ii) proteins affected by CsA alone, and (iii) proteins affected by PSP alone. Most of these altered proteins have functional significance in protein degradation, the antioxidant pathway, energy metabolism and immune cell regulation. © 2007 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex

The suitability of task-based approaches for secondary schools: Perspectives from Hong Kong

Task-based teaching has a high profile within contemporary ELT, yet there are few analyses of the appropriateness of task-based approaches for school contexts. This paper aims to analyse the suitability of task-based teaching for Hong Kong secondary schools; and to derive some suggestions for the development of a version of task-based approaches feasible for this and other comparable school contexts. The research method for the study involved semi-structured interviews with 11 secondary school teachers and 10 teacher educators based on purposive sampling. An overarching finding is the need for adaptation and a flexible 'situated version of task-based teaching'. The proposed adaptation includes: clarifying or enhancing the role of grammar instruction; integrating tasks with the requirements of examinations; and emphasizing reading and writing tasks in addition to oral ones. The study suggests a weak version of task-based teaching is likely to be most suitable for schooling and reinforces claims for the desirability of context-sensitive approaches. © 2007 Elsevier Ltd. All rights reserved.link_to_subscribed_fulltex