Experimental investigation of the mechanical properties of dry microbraids and microbraid reinforced polymer composites

AbstractThis paper presents a comprehensive series of mechanical tests performed on two high performance polymeric fibres, microbraids and microbraid reinforced polymer composites (mBRPC). Quasi-static tests were performed on the raw materials and the effect of different gauge lengths and strain rates investigated. Then, microbraids having sub-millimetre diameters were manufactured from the raw yarns using a Maypole-type braiding machine. The effects of different braid architectures, number of braided yarns and bias angles were assessed through a series of tensile tests on dry microbraids. A novel and unique manufacturing method of aligning microbraids in a unidirectional fashion via robotised filament winding was developed to manufacture microbraid reinforced polymer composites (mBRPC). Quasi-static tensile tests performed on mBRPC showed improved mechanical properties, for certain architectures, with respect to those noted for unidirectional composites manufactured using same technique

Self-sensing composites: in-situ detection of fibre fracture

The primary load-bearing component in a composite material is the reinforcing fibres. This paper reports on a technique to study the fracture of individual reinforcing fibres or filaments in real-time. Custom-made small-diameter optical fibres with a diameter of 12 (±2) micrometres were used to detect the fracture of individual filaments during tensile loading of unreinforced bundles and composites. The unimpregnated bundles were end-tabbed and tensile tested to failure. A simple technique based on resin-infusion was developed to manufacture composites with a negligible void content. In both cases, optical fibre connectors were attached to the ends of the small-diameter optical fibre bundles to enable light to be coupled into the bundle via one end whilst the opposite end was photographed using a high-speed camera. The feasibility of detecting the fracture of each of the filaments in the bundle and composite was demonstrated. The in-situ damage detection technique was also applied to E-glass bundles and composites; this will be reported in a subsequent publication

Micromechanical analysis of high fibre volume fraction polymeric laminates using micrograph-based representative volume element models

This work develops RVE-based finite element (FE) models to understand how the microstructure of Ultra-High-Molecular-Weight Polyethylene (UHMWPE) composites affects the overall mechanical behaviour of the laminate. The models represent a [0/90] configuration with a random fibre packing sequence through the thickness of each ply, as well as a variation in the cross-sectional shape of the fibres, both obtained from laminate cross section micrograph images. The uncertainty of interface properties and its effects on the overall mechanical response is also investigated. The response of the fibre is assumed to be viscoelastic-plastic and transversely isotropic and the three-dimensional constitutive behaviour is implemented through a user-defined subroutine in the LS-DYNA explicit FE code. Constituent properties are calibrated using experimental results on UHMWPE single fibres and a generic thermoplastic polyurethane resin material. The numerical results generated by the RVE models are validated against experimental results found in the open literature. Special focus was given to the in-plane shear and out-of-plane compression response of UHMWPE laminates. Our results can be used as inputs in a homogenised continuum level model, to express the effect of uncertainties which propagate from the microstructure to the macro-scale response

All different or all the same? Exploring the diversity of professional practices in Portuguese school psychology

"Published online: 29 March 2016"Studies have generally characterized school psychologists as a relative homogenous population. Understanding the differences in professional practices and related variables is important for the development of the profession. Using a sample of 446 Portuguese school psychologists, this study used cluster analysis to identify distinct profiles of professional activity, based on practitioners’ time distribution among different target audiences (i.e.,students, parents, teachers, school board members, school non-professional staff, and other professionals within the school community). Three distinct profiles emerged from the data: a group highly oriented to work with students, a group that distributes time almost equitably between adults and students, and a group that concentrates attention and professional expertise on adults. Practice setting variables, such as school-psychologists-to-student ratio, schoolpsychologists-to-school ratio, number of referrals per year, and school community level of demand for different activities, were found to be significantly related to cluster membership. No personal- or professional-background-related variables differentiated the three groups. The main implications of these findings are discussed in light of recent literature regarding the models of service delivery for school psychologists

Functional Magnetic Resonance Imaging in Conscious Animals: A New Tool in Behavioural Neuroscience Research

Functional magnetic resonance imaging (fMRI) is a unique window to the brain, enabling scientists to follow changes in brain activity in response to hormones, ageing, environment, drugs of abuse and other stimuli. In this review, we present a general background to fMRI and the different imaging modalities that can be used in fMRI studies. Included are examples of the application of fMRI in behavioural neuroscience research, along with discussion of the advantages and disadvantages of this technology

Integrative analyses identify modulators of response to neoadjuvant aromatase inhibitors in patients with early breast cancer

Introduction Aromatase inhibitors (AIs) are a vital component of estrogen receptor positive (ER+) breast cancer treatment. De novo and acquired resistance, however, is common. The aims of this study were to relate patterns of copy number aberrations to molecular and proliferative response to AIs, to study differences in the patterns of copy number aberrations between breast cancer samples pre- and post-AI neoadjuvant therapy, and to identify putative biomarkers for resistance to neoadjuvant AI therapy using an integrative analysis approach. Methods Samples from 84 patients derived from two neoadjuvant AI therapy trials were subjected to copy number profiling by microarray-based comparative genomic hybridisation (aCGH, n = 84), gene expression profiling (n = 47), matched pre- and post-AI aCGH (n = 19 pairs) and Ki67-based AI-response analysis (n = 39). Results Integrative analysis of these datasets identified a set of nine genes that, when amplified, were associated with a poor response to AIs, and were significantly overexpressed when amplified, including CHKA, LRP5 and SAPS3. Functional validation in vitro, using cell lines with and without amplification of these genes (SUM44, MDA-MB134-VI, T47D and MCF7) and a model of acquired AI-resistance (MCF7-LTED) identified CHKA as a gene that when amplified modulates estrogen receptor (ER)-driven proliferation, ER/estrogen response element (ERE) transactivation, expression of ER-regulated genes and phosphorylation of V-AKT murine thymoma viral oncogene homolog 1 (AKT1). Conclusions These data provide a rationale for investigation of the role of CHKA in further models of de novo and acquired resistance to AIs, and provide proof of concept that integrative genomic analyses can identify biologically relevant modulators of AI response

Cellular Radiosensitivity: How much better do we understand it?

Purpose: Ionizing radiation exposure gives rise to a variety of lesions in DNA that result in genetic instability and potentially tumorigenesis or cell death. Radiation extends its effects on DNA by direct interaction or by radiolysis of H2O that generates free radicals or aqueous electrons capable of interacting with and causing indirect damage to DNA. While the various lesions arising in DNA after radiation exposure can contribute to the mutagenising effects of this agent, the potentially most damaging lesion is the DNA double strand break (DSB) that contributes to genome instability and/or cell death. Thus in many cases failure to recognise and/or repair this lesion determines the radiosensitivity status of the cell. DNA repair mechanisms including homologous recombination (HR) and non-homologous end-joining (NHEJ) have evolved to protect cells against DNA DSB. Mutations in proteins that constitute these repair pathways are characterised by radiosensitivity and genome instability. Defects in a number of these proteins also give rise to genetic disorders that feature not only genetic instability but also immunodeficiency, cancer predisposition, neurodegeneration and other pathologies. Conclusions: In the past fifty years our understanding of the cellular response to radiation damage has advanced enormously with insight being gained from a wide range of approaches extending from more basic early studies to the sophisticated approaches used today. In this review we discuss our current understanding of the impact of radiation on the cell and the organism gained from the array of past and present studies and attempt to provide an explanation for what it is that determines the response to radiation