Anionic responses of electrochemically synthesized polypyrrole films

Conducting polypyrrole films with thickness of about 8 mum were prepared on platinum by continuous scanning in 0.1M pyrrole and 0.1M electrolyte (LiCl, LiBF(4) or NaBF(4)). Scan-rates of 10, 20 and 50 mV/sec with scan-times of 30, 45 and 60 min were used. The potentiometric response of the films was tested over a range of anions. Films were found to be anion-sensitive but very non-selective. The influence of the doping cation was also investigated.     

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.     

Error growth in the numerical integration of periodic orbits by multistep methods, with application to reversible systems

We study the growth with time of (the coefficients of the asymptoticexpansion of) the error in the numerical integration with linearmultistep methods of periodic solutions of systems of ordinarydifferential equations. Particular attention is devoted to reversiblesystems. It turns out that symmetric linear multistep methodscannot be recommended in spite of the fact that they mimic thereversibility of the true flow. For reversible second-ordersystems, linear multistep methods without parasitic double rootsare useful.     

Development of bovine muscle, liver and urine reference materials for zeranol – preparation, homogeneity and stability

 Samples of bovine muscle, liver and urine, zeranol-free (RM 508, RM 509 and RM 510, respectively) and zeranol-containing (RM 511, RM 512 and RM 513, respectively) were prepared and tested as candidate reference materials. Preliminary studies on achievement of target zeranol content, intercomparison of analytical methods (HPLC-RIA and GC-MS) and effects of lyophilisation and irradiation on zeranol content are described. The preparation of the materials and testing for homogeneity and stability of zeranol in the materials are discussed. The coefficients of variation for zeranol determinations for between-vial homogeneity (4.0%, 4.4% and 4.6% for muscle, liver and urine, respectively) are similar to those for the analytical method (4.0%, 7.3% and 6.8% for muscle, liver and urine, respectively) indicating that the materials are homogeneous. Stability data over a 12-month storage period at temperatures ranging from −18 °C to +37 °C indicate that the materials are sufficiently stable for use as reference materials. This paper is dedicated to the memory of Dr Hilary Stevenson (The Queen’s University of Belfast/DANI) who, together with Mr. W. Graham, facilitated the irradiation of the lyophilised materials.--> Received: 18 June 1996/Revised: 19 August 1996/Accepted: 23 August 1996