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Abstract: In thrombotic events and diseases such as cancer, HIV/AIDS, dysfibrinogenaemia, as well as acute incidents (e.g. burn wounds), ultrastructure of platelets and fibrin networks change. In the current study, we compare the ultrastructure of platelets and fibrin networks of apheresis platelets stored in citrated human plasma (CP) and in a first-generation platelet additive solution (PAS) (T-Sol), to that of fresh donor plasma (FP). Eighteen apheresis platelet donors donated platelets on Trima®-Accel™ V5.2 and V5.1 cell separators. Six collections were stored for five days in autologous citrated plasma (CP); six collections were stored in 40% citrated human plasma and 60% PAS solution (CP/PAS) controlled, for the duration of storage, at a constant temperature (22±2°C) with continuous flat-bed agitation; and six collections were stored in conditions uncontrolled for temperature and without continuous agitation. On days 1, 3 and 5, equal volumes of human thrombin were mixed with platelets collected in either CP or CP/PAS to form a coagulum (fibrin network containing platelet aggregates), followed by preparation for scanning electron microscopy. Results were compared with platelets and fibrin networks in FP. Typically, in FP, platelet aggregates with smooth membranes and pseudopodia are seen and fibrin networks arrange to form major, thick fibers and scattered, minor, thin fibers. On day 1, in CP and in all CP/PAS units, platelet ultrastructure compared well to that of FP, although the fibrin fibers were denser, with the minor fibers forming a matted layer over the major fibers. On day 3, in platelet units uncontrolled for temperature and without continuous agitation during storage, some platelet aggregates in CP/PAS showed typical apoptotic morphology, with shrinkage and membrane damage, but comparable fibrin networks were present. On day 5 however, in those units where storage conditions were uncontrolled and where the pH had decreased to below 6.4, no platelet aggregates were seen and fibrin was arranged into short, lumpy masses with no separate major or minor fibrin fibers visible. In those units stored at 22°C with continuous flat-bed agitation, where pH was maintained >7.0, ultrastructure of platelets and fibrin network in CP/PAS was typical and similar to FP and CP at the end of five days of storage. Examining platelet and fibrin network ultrastructure may be useful, in addition to conventional laboratory analysis, in assessing the viability and potential clinical efficacy of platelets for transfusion and could play a role in the evaluation of new generation platelet additive solutions. [Copyright &y& Elsevier]

Abstract: The rapid phase change and heat transfer obtained by direct contact heat exchange between a cryogen and water can generate high rates of pressurisation, which is of interest to a number of applications. A visualization study of liquid nitrogen injection into water is conducted in this work, with synchronized pressure and temperature measurement, to obtain insight into this complex phenomenon. High speed imaging reveals a four-stage evolution of liquid nitrogen jet structure upon injection into water, with a thick vapour blanket forming around a liquid nitrogen core and break-up brought on predominantly through impact with the vessel wall. Maximum pressurisation rate occurs in the third stage of injection due to a combination of heat and mass transfer. Pressurisation rates in excess of 350bar/s are recorded and found to vary proportionally with injection pressure. The scenario of gaseous nitrogen injection is also investigated, and compared with liquid nitrogen injection. A clear advantage of liquid nitrogen injection is elucidated from the point of heat transfer and pressurisation, and implications for use in a cryogenic engine are discussed. [ABSTRACT FROM AUTHOR]

A comprehensive and novel investigation on multiple-layer, square-beam laser shock treatment ("laser peening") of Si 3 N 4 ceramics is reported in this work. Surface topography, hardness, fracture toughness (K Ic), residual stresses, and microstructural changes were investigated. The evaluation of fracture toughness via the Vickers hardness indentation method revealed a reduction in crack lengths produced by the indenter after laser shock treatment (LST). Upon appropriate calculation, this revealed an increase in K IC of 60%. This being attributed to a near-surface (50 μm depth) compressive residual stress measured at −289 MPa. Multiple layer LST also induced beneficial residual stresses to a maximum measured depth of 512 μm. Oxidation was evident, only on the top surface of the ceramic, post LST (<5 μm depth) and was postulated to be due to hydrolyzation. The surface enhancement in K IC and flaw-size reduction was assigned to an elemental change on the surface, whereby, Si 3 N 4 was transformed to SiO 2 , particularly, with multiple layers of LST. Compressive residual stresses measured in the sub-surface were attributed to mechanical effects (below sub-surface elastic constraint) and corresponding shock-wave response of the Si 3 N 4. This work has led to a new mechanistic understanding regarding the response of Si 3 N 4 ceramics subject to the LST deployed in this resesrch. The findings are significant because inducing deep compressive residual stresses and corresponding enhancement in surface K IC are important for the enhanced durability in many applications of this ceramic, including cutting tools, hip and knee implants, dental replacements, bullet-proof vests and rocket nozzles in automotive, aerospace, space and biomedical industries. [Display omitted] [ABSTRACT FROM AUTHOR]