Residual Stresses Induced by Dry and Cryogenic Cooling during Machining of AZ31B Magnesium Alloy

The major challenge of the Mg alloys has been their unsatisfactory corrosion resistance, which can be enhanced by improving the surface integrity. Cryogenic machining, where liquid nitrogen was used during machining, has been reported to improve the surface integrity of machined components, including compressive residual stresses. This paper analyses the influence of several cutting parameters, tool geometry and cryogenic conditions on the surface and subsurface residual stresses distribution

Two-Grating Talbot Bands Spectral Domain Interferometer

A configuration for Talbot bands is presented, where two tilted gratings replace the splitter normally used for recombining the signals from the two interferometer arms. The two optical beams from the interferometer are launched by two fiber leads tightly brought together in the front focal plane of a collimating lens. As the tips of the two fibers are slightly off-axis, the emergent beams after the collimating lens are not parallel. In combination with the two tilted gratings, the non parallel launching of the two beams leads to total elimination of mirror terms even when the two beams overlap on either grating. The effects of several geometrical parameters on the visibility performance versus optical path difference between the two arm lengths of the interferometer are evaluated

Impaired regeneration of dystrophin-deficient muscle fibers is caused by exhaustion of myogenic cells

Duchenne muscular dystrophy is one of the most devastating myopathies. Muscle fibers undergo necrosis and lose their ability to regenerate, and this may be related to increased interstitial fibrosis or the exhaustion of satellite cells. In this study, we used mdx mice, an animal model of Duchenne muscular dystrophy, to assess whether muscle fibers lose their ability to regenerate after repeated cycles of degeneration-regeneration and to establish the role of interstitial fibrosis or exhaustion of satellite cells in this process. Repeated degenerative-regenerative cycles were induced by the injection of bupivacaine (33 mg/kg), a myotoxic agent. Bupivacaine was injected weekly into the right tibialis anterior muscle of male, 8-week-old mdx (N = 20) and C57Bl/10 (control, N = 10) mice for 20 and 50 weeks. Three weeks after the last injection, the mice were killed and the proportion of regenerated fibers was counted and reported as a fibrosis index. Twenty weekly bupivacaine injections did not change the ability of mdx muscle to regenerate. However, after 50 weekly bupivacaine injections, there was a significant decrease in the regenerative response. There was no correlation between the inability to regenerate and the increase in interstitial fibrosis. These results show that after prolonged repeated cycles of degeneration-regeneration, mdx muscle loses its ability to regenerate because of the exhaustion of satellite cells, rather than because of an increase in interstitial fibrosis. This finding may be relevant to cell and gene therapy in the treatment of Duchenne muscular dystrophy.69169

Spectrometer-based Optical Coherence Tomography Systems with Extended Functionality

Optical coherence tomography (OCT) has evolved over the last two decades to become a major optical imaging modality in the biomedical optics field. By performing high-resolution, multi-dimensional imaging of translucent structures, it enables real-time tissue imaging in-vivo and in-situ with resolutions in the micrometre range. This Thesis focuses on extending the functionality of spectral-domain OCT (SD-OCT) systems operating at 800 nm. On a secondary level, it also aims to address some of the performance issues involving SD-OCT, such as the ambiguity on the sign of the optical path difference and the finite axial range of the OCT system due to the sampling resolution limit of the spectrometer. Addressing these issues has been achieved through the modification of the spectrometer, exploring an effect first reported by William Fox Talbot in the mid-19th century, Talbot Bands, which effectively allows a degree of control over the SD-OCT visibility profile shape and position. This extended functionality manifests itself by the addition of a confocal channel (applied to retinal imaging, hence creating a scanning laser ophthalmoscope, SLO), also by controlling the shape and position of the visibility profile with a novel spectrometer design employing Talbot Bands, which improves the power efficiency by coupling the two arms of the interferometer within the spectrometer itself. Further functionality has been added to OCT technology by carrying out research on the interferometer at the core of the OCT system. A new single-detector, polarisation-sensitive OCT (PS-OCT) configuration, immune to disturbances caused by the collecting fibre was devised. This ultimately leads to a design of a plug-in PS-OCT module capable of enabling polarimetric measurements in any existing OCT system

Polarization-sensitive plug-in optical module for a Fourier-domain optical coherence tomography system

In this manuscript we communicate a theoretical study on a plug-in optical module to be used within a Fourier-domain optical coherence tomography system (FD-OCT). The module can be inserted between the object under investigation and any single-mode fiber based FD-OCT imaging instrument, enabling the latter to carry out polarization measurements on the former. Similarly to our previous communication this is an active module which requires two sequential steps to perform a polarization measurement. Alternating between the two steps is achieved by changing the value of the retardance produced by two electro-optic polarization modulators, which together behave as a polarization state rotator. By combining the rotation of the polarization state with a projection against a linear polarizer it is possible to ensure that the polarization measurements are free from any undesirable polarization effects caused by the birefringence in the collecting fiber and diattenuation in the fiber-based couplers employed in the system. Unlike our previous work, though, this module adopts an in-line configuration, employing a Faraday rotator to ensure a non-reciprocal behavior between the forward and backward propagation paths

Tool life and surface integrity in hard milling of hot work tool steels

Machinability enhancement of hot work tool steels can be achieved intrinsically through tailoring of alloying elements and steel processing route but also externally through the use of adequate tooling. The aim of the present investigation was to identify the limitations in hard milling of AISI H13 (50HRC) with respect to different strategies for microstructure control. Accordingly, tool life tests in face and cavity milling were performed using modern PVD-coated carbide inserts where subsequent investigation of tool wear mechanisms and surface integrity were carried out. A modified tool life model derived from Taylor’s approach was employed for the assessment of tool life. The results indicate that traditional improvement in machinability through additives and inclusion control appears not always adequate and the role of primary carbides distribution needs also to be considered. Surface integrity studies, namely residual stress, indicate the predominance of compressive residual stress in the machined surfaces

Tool life and surface integrity in hard milling of hot work tool steels

Machinability enhancement of hot work tool steels can be achieved intrinsically through tailoring of alloying elements and steel processing route but also externally through the use of adequate tooling. The aim of the present investigation was to identify the limitations in hard milling of AISI H13 (50HRC) with respect to different strategies for microstructure control. Accordingly, tool life tests in face and cavity milling were performed using modern PVD-coated carbide inserts where subsequent investigation of tool wear mechanisms and surface integrity were carried out. A modified tool life model derived from Taylor’s approach was employed for the assessment of tool life. The results indicate that traditional improvement in machinability through additives and inclusion control appears not always adequate and the role of primary carbides distribution needs also to be considered. Surface integrity studies, namely residual stress, indicate the predominance of compressive residual stress in the machined surfaces

Designing surgical clothing and drapes according to the new technical standards

Hospitals will continue to be the largest consumers of disposables, because of the diverse range of procedures they provide. Favourable growth is forecast for nonwovens. Increasing concern over contamination and nosocomial infections will boost the demand for consumables and disposables surgical gowns and drapes. But, until now neither the manufacturers nor the end users of surgical gowns and drapes could agree on standards. So, a mandatory European standard is being developed to establish basic requirements and test methods for disposable and reusable materials used for surgical gowns and drapes. Once this standard has been adopted, the continued use of cotton textiles and conventional cotton-polyester mixed textiles will become questionable.(undefined

A path-flow analysis model for active drag force determinant variables in age-group swimmers

The goal of competitive swimming is to travel the event distance as fast as possible. The identification of the parameters that predict swimming performances is one of the main aims of the swimming “science” community. Indeed, it is consensual that biomechanical and energetic variables are determinant for enhance performance (Barbosa et al, 2010)