Chern-Simons flows on Aloff-Wallach spaces and Spin(7)-instantons

Due to their explicit construction, Aloff-Wallach spaces are prominent in flux compactifications. They carry G_2-structures and admit the G_2-instanton equations, which are natural BPS equations for Yang-Mills instantons on seven-manifolds and extremize a Chern-Simons-type functional. We consider the Chern-Simons flow between different G_2-instantons on Aloff-Wallach spaces, which is equivalent to Spin(7)-instantons on a cylinder over them. For a general SU(3)-equivariant gauge connection, the generalized instanton equations turn into gradient-flow equations on C^3 x R^2, with a particular cubic superpotential. For the simplest member of the Aloff-Wallach family (with 3-Sasakian structure) we present an explicit instanton solution of tanh-like shape.Comment: 1+17 pages, 1 figur

Synthesis of L-ascorbic acid in the phloem

BACKGROUND: Although plants are the main source of vitamin C in the human diet, we still have a limited understanding of how plants synthesise L-ascorbic acid (AsA) and what regulates its concentration in different plant tissues. In particular, the enormous variability in the vitamin C content of storage organs from different plants remains unexplained. Possible sources of AsA in plant storage organs include in situ synthesis and long-distance transport of AsA synthesised in other tissues via the phloem. In this paper we examine a third possibility, that of synthesis within the phloem. RESULTS: We provide evidence for the presence of AsA in the phloem sap of a wide range of crop species using aphid stylectomy and histochemical approaches. The activity of almost all the enzymes of the primary AsA biosynthetic pathway were detected in phloem-rich vascular exudates from Cucurbita pepo fruits and AsA biosynthesis was demonstrated in isolated phloem strands from Apium graveolens petioles incubated with a range of precursors (D-glucose, D-mannose, L-galactose and L-galactono-1,4-lactone). Phloem uptake of D-[U-(14)C]mannose and L-[1-(14)C]galactose (intermediates of the AsA biosynthetic pathway) as well as L-[1-(14)C]AsA and L-[1-(14)C]DHA, was observed in Nicotiana benthamiana leaf discs. CONCLUSIONS: We present the novel finding that active AsA biosynthesis occurs in the phloem. This process must now be considered in the context of mechanisms implicated in whole plant AsA distribution. This work should provoke studies aimed at elucidation of the in vivo substrates for phloem AsA biosynthesis and its contribution to AsA accumulation in plant storage organs

RF-MEMS switch actuation pulse optimization using Taguchi's method

Copyright @ 2011 Springer-VerlagReliability and longevity comprise two of the most important concerns when designing micro-electro-mechanical-systems (MEMS) switches. Forcing the switch to perform close to its operating limits underlies a trade-off between response bandwidth and fatigue life due to the impact force of the cantilever touching its corresponding contact point. This paper presents for first time an actuation pulse optimization technique based on Taguchi’s optimization method to optimize the shape of the actuation pulse of an ohmic RF-MEMS switch in order to achieve better control and switching conditions. Simulation results show significant reduction in impact velocity (which results in less than 5 times impact force than nominal step pulse conditions) and settling time maintaining good switching speed for the pull down phase and almost elimination of the high bouncing phenomena during the release phase of the switch

Die informations- und kommunikationstechnische Infrastruktur und ihre mittelfristige Entwicklung an den Hochschulen des Landes NRW

Dieser Bericht des Arbeitskreises der Leiter wissenschaftlicher Rechenzentren in NRW (ARNW) richtet sich an die Hochschulleitungen und die Verantwortlichen für Grundstrukturen in Information und Kommunikation (IuK). Er informiert über aktuelle wichtige Fragen, besonders über den Stand und Einsatz von IuK-Technologien. In Anbetracht der anhaltend schnellen Weiterentwicklung dieses Technologiefeldes, die sich auf alle Bereiche der Hochschulen auswirkt, halten wir das für wichtig, damit vermieden wird, dass wichtige Themen am Rande bleiben. Das neue Hochschulgesetz und der Qualitätspakt machen darüber hinaus eine Positionierung der Hochschulen in NRW zur IuK-Infrastruktur unabdingbar