Overall buckling of lightweight stiffened panels using an adapted orthotropic plate method

The ultimate longitudinal bending strength of thin plated steel structures such as box girder bridges and ship hulls can be determined using an incremental–iterative procedure known as the Smith progressive collapse method. The Smith method first calculates the response of stiffened panel sub-structures in the girder and then integrates over the cross section of interest to calculate a moment–curvature response curve. A suitable technique to determine the strength behaviour of stiffened panels within the Smith method is therefore of critical importance. A fundamental assumption of the established progressive collapse method is that the buckling and collapse behaviour of the compressed panels within the girder occurs between adjacent transverse frames. However, interframe buckling may not always be the dominant collapse mode, especially for lightweight stiffened panels such as are found in naval ships and aluminium high speed craft. In these cases overall failure modes, where the buckling mode extends over several frame spaces, may dominate the buckling and collapse response. To account for this possibility, an adaptation to large deflection orthotropic plate theory is presented. The adapted orthotropic method is able to calculate panel stress–strain response curves accounting for both interframe and overall collapse. The method is validated with equivalent nonlinear finite element analyses for a range of regular stiffened panel geometries. It is shown how the adapted orthotropic method is implemented into an extended progressive collapse method, which enhances the capability for determining the ultimate strength of a lightweight stiffened box girder

Determination of lubricant selection based on elastohydrodynamic film thickness and traction measurement

The project was conducted to aid in the development of an elastohydrodynamic specification for military lubricants. Experiments were conducted with a rolling disk apparatus designed to simulate a bearing or gear type contact. Measurements included lubricant film thickness, lubricant breakdown and traction for a range of loads, speeds, temperatures, and surface roughnesses. Several lubricants were used in the investigations including a traction fluid, two synthetic paraffinic lubricants and several lubricants conforming to MIL-L 7808 and 23699 specifications. Recommendations regarding an EHD specification are included

Properties of five toughened matrix composite materials

The use of toughened matrix composite materials offers an attractive solution to the problem of poor damage tolerance associated with advanced composite materials. In this study, the unidirectional laminate strengths and moduli, notched (open-hole) and unnotched tension and compression properties of quasi-isotropic laminates, and compression-after-impact strengths of five carbon fiber/toughened matrix composites, IM7/E7T1-2, IM7/X1845, G40-800X/5255-3, IM7/5255-3, and IM7/5260 have been evaluated. The compression-after-impact (CAI) strengths were determined primarily by impacting quasi-isotropic laminates with the NASA Langley air gun. A few CAI tests were also made with a drop-weight impactor. For a given impact energy, compression after impact strengths were determined to be dependent on impactor velocity. Properties and strengths for the five materials tested are compared with NASA data on other toughened matrix materials (IM7/8551-7, IM6/1808I, IM7/F655, and T800/F3900). This investigation found that all five materials were stronger and more impact damage tolerant than more brittle carbon/epoxy composite materials currently used in aircraft structures

Effect of longitudinal surface finish on elastohydrodynamic lubrication

The effect of longitudinal-lay surface finish on the elastohydrodynamic film thickness and the percentage of film between rolling disks in contact were evaluated using a rolling disk apparatus. Film thickness was measured by transmitted X-rays, and percentage of film was monitored by an alternating-current continuity circuit. Disk finish was varied on both the crowned upper disk and the cylindrical lower disk. A type-2 ester and a synthetic paraffinic oil were used as lubricants. It was shown that the roughness with longitudinal lay has a deleterious effect on both film thickness and percentage of film. Measured film thicknesses for the two lubricants were comparable at equivalent test conditions. The percentage of film where a change in surface topography was observed was approximately 20 percent for the synthetic paraffinic oil and 10 percent for the type-2 ester

Data-mining the FlyAtlas online resource to identify core functional motifs across transporting epithelia

<p>Background Comparative analysis of tissue-specific transcriptomes is a powerful technique to uncover tissue functions. Our FlyAtlas.org provides authoritative gene expression levels for multiple tissues of Drosophila melanogaster (1). Although the main use of such resources is single gene lookup, there is the potential for powerful meta-analysis to address questions that could not easily be framed otherwise. Here, we illustrate the power of data-mining of FlyAtlas data by comparing epithelial transcriptomes to identify a core set of highly-expressed genes, across the four major epithelial tissues (salivary glands, Malpighian tubules, midgut and hindgut) of both adults and larvae.</p> <p>Method Parallel hypothesis-led and hypothesis-free approaches were adopted to identify core genes that underpin insect epithelial function. In the former, gene lists were created from transport processes identified in the literature, and their expression profiles mapped from the flyatlas.org online dataset. In the latter, gene enrichment lists were prepared for each epithelium, and genes (both transport related and unrelated) consistently enriched in transporting epithelia identified.</p> <p>Results: A key set of transport genes, comprising V-ATPases, cation exchangers, aquaporins, potassium and chloride channels, and carbonic anhydrase, was found to be highly enriched across the epithelial tissues, compared with the whole fly. Additionally, a further set of genes that had not been predicted to have epithelial roles, were co-expressed with the core transporters, extending our view of what makes a transporting epithelium work. Further insights were obtained by studying the genes uniquely overexpressed in each epithelium; for example, the salivary gland expresses lipases, the midgut organic solute transporters, the tubules specialize for purine metabolism and the hindgut overexpresses still unknown genes.</p> <p>Conclusion Taken together, these data provide a unique insight into epithelial function in this key model insect, and a framework for comparison with other species. They also provide a methodology for function-led datamining of FlyAtlas.org and other multi-tissue expression datasets.</p&gt

Diffusible Signal Factor (DSF)-dependent quorum sensing in pathogenic bacteria and its exploitation for disease control

Cell-to-cell signals of the Diffusible Signal Factor (DSF) family are cis-2-unsaturated fatty acids of differing chain length and branching pattern. DSF signalling has been described in diverse bacteria to include plant and human pathogens where it acts to regulate functions such as biofilm formation, antibiotic tolerance and the production of virulence factors. DSF family signals can also participate in interspecies signalling with other bacteria and interkingdom signaling such as with the yeast Candida albicans. Interference with DSF signalling may afford new opportunities for the control of bacterial disease. Such strategies will depend in part on detailed knowledge of the molecular mechanisms underlying the processes of signal synthesis, perception and turnover. Here, I review both recent progress in understanding DSF signalling at the molecular level and prospects for translating this knowledge into approaches for disease control