Finite element error bounds for a curve shrinking with prescribed normal contact to a fixed boundary

We approximate the evolution of a curve subject to motion bycurvature by linear finite elements. The curve evolves insidea given domain and meets orthogonally. We derive optimal boundsfor the error with respect to the L²- and H¹-norms and presentsome computed examples.     

Fragmentation and reactions of two isomeric O-alkyl S-(2-dialkylamino)ethyl methylphosphonothiolates studied by electrospray ionization/ion trap mass spectrometry

An initial investigation into the electrospray ionization ion trap mass spectrometry (ESI/ITMS) of simple organophosphorus compounds [1] demonstrated that detailed structural information could be obtained by sequential fragmentation of the ions using collision induced dissociation (CID). Several novel fragmentations/rearrangements were observed and it was apparent that the full potential of this approach could not be exploited until a more detailed understanding of the ion fragmentations was obtained. Such an understanding will only result from a detailed study of a wide range of compounds. The present paper describes the investigation of two isomeric organophosphates of particular relevance to chemical warfare convention (CWC) considerations.     

Neuropeptide delivery to the brain: a von Willebrand factor signal peptide to direct neuropeptide secretion

Background  

Multiple neuropeptides, sometimes with opposing functions, can be produced from one precursor gene. To study the roles of the different neuropeptides encoded by one large precursor we developed a method to overexpress minigenes and establish local secretion.     

PREPARATION OF LARGE-PARTICLE-SIZE MONODISPERSE LATEXES IN SPACE: POLYMERIZATION KINETICS AND PROCESS DEVELOPMENT

Monodisperse polystyrene latexes are prepared by seeded emulsion polymerization; however, sizes larger than 2μm are difficult to prepare because of the creaming and settling of the particles, and their sensitivity to mechanical shear. Preparation in space would obviate the creaming and settling, and allow agitation just sufficient for good heat transfer and mixing. Three polymerizations yielding 3-5μm size particles were carried out successfully on the third flight of the “Columbia” launched March 22, 1982; however, four polymerizations yielding sizes up to 10μm on the fourth flight launched June 27, 1982, were incomplete owing to apparatus malfunction. The results of these polymerizations and the prospects of developing a preparative space process are reviewed     

Plant delta(15)N associated with arbuscular mycorrhization, drought and nitrogen deficiency

It has long been evident that plant (15)N chiefly reflects the processes which fractionate (15)N/(14)N rather than the (15)N of plant N source(s). It has emerged recently that one of the most important fractionating processes contributing to the whole plant (15)N is the presence/absence, type or species of mycorrhiza, especially when interacting with nutrient deficiency. Ecto- and ericoid mycorrhizas are frequently associated with (15)N-depleted foliar (15)N, commonly as low as -12 per thousand. As shown by the present study, plants having no mycorrhiza, or those infected with various species of arbuscular mycorrhiza (AM)-forming fungi, interact with varying concentrations of soil nitrogen [N] and moisture to enrich plant (15)N by as much as 3.5 per thousand. Hence the lack of a mycorrhiza, or variation in the species of AM-forming fungal associations, can account for about 25% of the usually reported variations of foliar (15)N found in field situations and do so by (15)N enrichment rather than depletion. Copyright 1999 John Wiley & Sons, Ltd.