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.     

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.     

Duplex‐Selective Ruthenium‐Based DNA Intercalators

We report the design and synthesis of small molecules that exhibit enhanced luminescence in the presence of duplex rather than single‐stranded DNA. The local environment presented by a well‐known [Ru(dipyrido[3,2‐a:2′,3′‐c]phenazine)L₂]²⁺‐based DNA intercalator was modified by functionalizing the bipyridine ligands with esters and carboxylic acids. By systematically varying the number and charge of the pendant groups, it was determined that decreasing the electrostatic interaction between the intercalator and the anionic DNA backbone reduced single‐strand interactions and translated to better duplex specificity. In studying this class of complexes, a single Ru^II complex emerged that selectively luminesces in the presence of duplex DNA with little to no background from interacting with single‐stranded DNA. This complex shows promise as a new dye capable of selectively staining double‐ versus single‐stranded DNA in gel electrophoresis, which cannot be done with conventional SYBR dyes.     

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     

Cation radicals. XXVIII. Isolation and some reactions of dibenzodioxin cation radical perchlorate

Preparation and isolation of dibenzodioxin cation radical perchlorate ( 2 ) by oxidation of dibenzodioxin in ethyl acetate-lithium perchlorate at a platinum anode has been achieved. Reasonably pure 2 in amounts of 150–200 mg. were obtained reliably and reproducibly. Reaction of 2 with both nitrite and nitrate ions gave 2-nitrodibenzodioxin ( 3 ). Reaction of 2 with pyridine gave N-(2-dibenzodioxinyl)pyridinium perchlorate ( 4 ). Reaction with water gave, as anticipated, the stoichiometric amount of dibenzodioxin. Reaction with ammonia, propylamine, t-butylamine, and cyanide ion also gave dibenzodioxin with no evidence that nucleophilic substitution had occurred. It is believed that the formation of 3 and 4 represent the first examples of nucleophilic substitution into dibenzodioxin via its cation radical.     

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.