Solar sail capture trajectories at Mercury

Mercury is an ideal environment for future planetary exploration by solar sail since it has proved difficult to reach with conventional propulsion and hence remains largely unexplored. In addition, its proximity to the Sun provides a solar sail acceleration of order ten times the sail characteristic acceleration at 1 AU. Conventional capture techniques are shown to be unsuitable for solar sails and a new method is presented. It is shown that capture is bound by upper and lower limits on the orbital elements of the approach orbit and that failure to be within limits results in a catastrophic collision with the planet. These limits are presented for a range of capture inclinations and sail characteristic accelerations. It is found that sail hyperbolic excess velocity is a critical parameter during capture at Mercury, with only a narrow allowed band in order to avoid collision with the planet. The new capture methodis demonstrated for a Mercury sample return mission

Analytical, circle-to-circle low-thrust transfer trajectories with plane change

Orbit averaging techniques are used to develop analytical approximations of circle-to-circle low-thrust trajectory transfers with plane-change about the Sun. Separate expressions are developed for constant acceleration, or thrust, electric propulsion, solar sail propulsion and combined, or hybrid electric (constant acceleration or thrust) / solar sail propulsion. The analytical expressions uniquely allow the structure of circle-to-circle low-thrust trajectory transfers with plane-change about the Sun to be understood, and the optimal trajectory structure is analytically derived for each propulsion system considered. It is found that the optimal fixed thrust electric propulsion transfer reduces the orbit radius with no plane change and then performs the plane-change, while the optimal solar sail and hybrid transfers combine the reduction of orbit radius with some plane change, before then completing the plane change. The optimal level of plane change during the reduction of orbit radius is derived and it is found the analytically-derived minimum time solar sail transfer is within 1% of the numerically-derived optimal transfer. It is also found that, under the conditions considered, a sail characteristic acceleration of less than 0.5 mm/s2 can, in 5-years, attain a solar orbit that maintains the observer-to-solar pole zenith angle below 40 degrees for 25 days; the approximate sidereal rotation period of the Sun. However, a sail characteristic acceleration of more than 0.5 mm/s2 is required to attain an observer-to-solar pole zenith angle below 30 degrees for 25 days within 5-years of launch. Finally, it was found that the hybridization of electric propulsion and solar sail propulsion was, typically, of more benefit when the system was thrust constrained than when it was mass constrained

Canine mesenchymal stem cells are neurotrophic and angiogenic:an in vitro assessment of their paracrine activity

Mesenchymal stem cells (MSCs) have been used in cell replacement therapies for connective tissue damage, but also can stimulate wound healing through paracrine activity. In order to further understand the potential use of MSCs to treat dogs with neurological disorders, this study examined the paracrine action of adipose-derived canine MSCs on neuronal and endothelial cell models. The culture-expanded MSCs exhibited a MSC phenotype according to plastic adherence, cell morphology, CD profiling and differentiation potential along mesenchymal lineages. Treating the SH-SY5Y neuronal cell line with serum-free MSC culture-conditioned medium (MSC CM) significantly increased SH-SY5Y cell proliferation (P < 0.01), neurite outgrowth (P = 0.0055) and immunopositivity for the neuronal marker βIII-tubulin (P = 0.0002). Treatment of the EA.hy926 endothelial cell line with MSC CM significantly increased the rate of wound closure in endothelial cell scratch wound assays (P = 0.0409), which was associated with significantly increased endothelial cell proliferation (P < 0.05) and migration (P = 0.0001). Furthermore, canine MSC CM induced endothelial tubule formation in EA.hy926 cells in a soluble basement membrane matrix. Hence, this study has demonstrated that adipose-derived canine MSC CM stimulated neuronal and endothelial cells probably through the paracrine activity of MSC-secreted factors. This supports the use of canine MSC transplants or their secreted products in the clinical treatment of dogs with neurological disorders and provides some insight into possible mechanisms of action

Downsizing and deknowledging the firm

Organizations in many OECD economies have undergone a decade of downsizing, restructuring and transition. For example, workforce reductions were a dominant feature of firm behaviour in Australia throughout the 1990s. These wide-ranging organizational transitions are expected to continue. What do the new organizational forms and new job structures mean in relation to skill trends? This article examines the changing paradigms for understanding long-term skill change and assesses their relevance by empirically examining the relationship between downsizing, deskilling/upskilling and contingent labour use in larger firms. The analysis is based on a comprehensive, longitudinal data set of 4153 companies. A key finding is that downsizing was used as a vehicle for a different form of `deskilling' across the 1990s. Alongside the `knowledge organization', there are processes of deknowledging the firm