连续波锁模P_r~（3＋）：YLF激光器

本文报导了采用氩离子激光器来泵浦Ｒｒ￣（３＋）：ＹＬＦ晶体，应用声光调制器实现了主动锁模；同时应用振动─高反射平面镜也实现了被动锁模，两种锁模均得到了ｐｓ光脉冲。据作者了解这是这种晶体材料的第一次锁模运转。     

Purification of homo- and hetero-oligonucleotides using high-performance charge-transfer chromatography

Oligonucleotides employed in molecular biology have previously been purified by gel electrophoresis, gravity flow chromatography and more recently, high-performance liquid chromatography. However, these techniques have a number of problems and for this reason we investigated high-performance charge-transfer chromatography using the dye acriflavin coupled to silica as the stationary phase. Numerous oligonucleotides were purified using this technique and in this report we present data on four such oligonucleotides two homo-oligonucleotides and two hetero-oligonucleotides. Homogeneity of oligonucleotides eluted from the acriflavin matrices was determined by electrophoresis on 20% polyacrylamide gels and in each case they were greater than 90% pure.     

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.