Effects of macrophyte species richness on wetland ecosystem functioning and services

Wetlands provide many important ecosystem services to human society, which may depend on how plant diversity influences biomass production and nutrient retention. Vascular aquatic plant diversity may not necessarily enhance wetland ecosystem functioning, however, because competition among these plant species can be strong, often resulting in the local dominance of a single species. Here we have manipulated the species richness of rooted, submerged aquatic plant (macrophyte) communities in experimental wetland mesocosms. We found higher algal and total plant (algal plus macrophyte) biomass, as well as lower loss of total phosphorus, in mesocosms with a greater richness of macrophyte species. Greater plant biomass resulted from a sampling effect; that is, the increased chance in species mixtures that algal production would be facilitated by the presence of a less competitive species-in this case, crisped pondweed. Lower losses of total phosphorus resulted from the greater chance in species mixtures of a high algal biomass and the presence of sago pondweed, which physically filter particulate phosphorus from the water. These indirect and direct effects of macrophyte species richness on algal production, total plant biomass and phosphorus loss suggest that management practices that maintain macrophyte diversity may enhance the functioning and associated services of wetland ecosystems.     

Directional discrimination — Tolerance of visual cortical cells to severe stimulus degradation

Zusammenfassung Die Wirkung von induzierten Undeutlichkeiten auf die Reaktionsfähigkeit der Zellen im visuellen Kortex auf Bewegungsanregungen werden beschrieben.

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This work was supported by USPHS Grant No. EY00576.     

Metabolic oxidation phenotypes as markers for susceptibility to lung cancer

That bronchial carcinoma is not an inevitable consequence of cigarette smoking has stimulated the search for host factors that might influence the susceptibility of the individual smoker. One plausible host factor would be a polymorphic gene controlling the metabolic oxidative activation of chemical carcinogens, giving rise to wide inter-subject variation in the generation of cancer-inducing and/or promoting species. Recently, three genetic polymorphisms of human metabolic oxidation have been demonstrated (as characterized by debrisoquine, mephenytoin and carbocysteine), with the metabolism of several substrates exhibiting the phenomenon. Debrisoquine 4-hydroxylation segregates into two human phenotypes, each comprising characteristic metabolic capability. We report here the frequency of debrisoquine 4-hydroxylation phenotypes in age-, sex- and smoking history-matched bronchial carcinoma and control patients. Cancer patients showed a preponderance of probable homozygous dominant extensive metabolizers (78.8%) with few recessive poor metabolizers (1.6%) compared with smoking controls (27.8% and 9.0% respectively). We conclude that the gene controlling debrisoquine 4-hydroxylation may be a host genetic determinant of susceptibility to lung cancer in smokers and that it represents a marker to assist in assessing individual risk.     

Uncoupling of initiation site cleavage from subsequent headful cleavages in bacteriophage T1 DNA packaging

The packaging of intracellular DNA into heads is a key feature in the morphogenesis of bacteriophage particles. In many phages a performed empty head precursor, the prohead, is filled with DNA from a concatemeric substrate consisting of tandemly repeated genome lengths. The addition of outer shell proteins completes head formation. The DNA molecules released from particles of the coliphage T1 exist as three major permutations of nucleotide sequence. Such limited permutation can be explained by the modification of Streisinger's 'headful' mechanism proposed for phage P22. DNA packaging is initiated at a specific site (the pac site) on the concatemeric precursor. While this site is cleaved, subsequent cleavages (headful cleavages) are dependent only on head-filling and are not defined in terms of nucleotide sequence. Headfuls of DNA, consisting of slightly more than a genome length, are packaged in three successive cycles of head-filling to produce the permuted and terminally redundant molecules characteristic of T1 DNA. To elucidate the regulation of this process, we have studied the DNA metabolism of T1 head mutants. We describe here the properties of a mutant in gene 13.3 which is defective for headful cleavage but remains proficient in pac site cleavage. The observation in this mutant that concatemers are degraded to unit-length molecules by repeated pac site cleavage suggests a model of headful packaging in which pac site initiation and processive head-filling compete for the DNA substrate.     

Insulin gene region-encoded susceptibility to type 1 diabetes is not restricted to HLA-DR4-positive individuals.

Type 1 or insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease of the insulin-producing pancreatic beta-cells which is determined by both genetic and environmental factors. The major histocompatibility complex and the insulin gene region (INS) on human chromosomes 6p and 11p, respectively, contain susceptibility genes. Using a mostly French data set, evidence for linkage of INS to IDDM was recently obtained but only in male meioses (suggesting involvement of maternal imprinting) and only in HLA-DR4-positive diabetics. In contrast, we find evidence for linkage in both male and female meioses and that the effect of the susceptibility gene(s) in the INS region is not dependent on the presence of HLA-DR4.     

Immersion in the Design: Design-for-assembly of Cable Harnesses

Approaches to efficiency in manufacturing and assem bl y over the past 100 years have concentrated frequently on the twin themes of div iding jobs done by people into defined segments and to automating as many of tho se segments as possible. This approach to manufacturing engineering may be char acterised as one of deconstruction and replacement so far as the role of the hum an being is concerned. More recently design engineering has been approached in a similar light with research into ‘intelligent‘ met...     

某型航空发动机对插板式进气畸变的响应

为得到较为准确的发动机对进气畸变的稳定性响应模型,首先分析了由实验所得到的某型航空涡扇发动机进口扰流插板产生的稳态总压畸变和紊流分布。相对于压气机转子进口,将周向分布的稳态总压畸变和截面脉动压力处理成为一组不同频率的压力激励波形分布。通过频谱分析得到:在发动机失稳前,稳态畸变形成的波形频率最低,幅值最大,是引起发动机失稳的主要原因。对该组合畸变激励波用一阶响应模型进行动态修正并使用平行压气机分析模型,得到了经修正的压气机喘振边界和得到改善的发动机进气畸变响应模型。最后分别计算了高、低压压气机逐步失稳的工作点移动过程。结果表明:与压气机出口实验失稳波形十分接近,该模型准确可行。