Cr~(3+)对土壤脲酶活性特征的影响

采用模拟方法对Cr3+的土壤脲酶效应进行了研究,结果表明,土壤pH对Cr3+的生态毒性有重要影响;酸性土壤脲酶受到显著抑制,活性及动力学特征参数与Cr3+浓度间达显著或极显著负相关,而且模型U=β0(/β1×C+1)揭示其间机理为完全抑制,动力学则进一步细化为非竞争性抑制;获得土壤轻微和中度污染时的生态剂量ED10和ED50分别为50.59和865.7 mg.kg-1;酸性土壤中脲酶活性、Vmax、k可作为土壤Cr3+污染的监测指标之一,而碱性土壤则反应不敏感,其随铬浓度增加,脲酶活性及动力学参数呈先增加后降低的规律性变化,总体变幅较小;两类土壤的差别可能主要是由于土壤环境引起了不同价态铬转变的缘故。

南海东北部下地壳高速层的成因探讨

通过对南海北部大陆边缘地壳结构分析，指出南海东北部存在下地壳高速层，

Microarray Analyses of Gene Expression during the Tetrahymena thermophila Life Cycle

Background: The model eukaryote, Tetrahymena thermophila, is the first ciliated protozoan whose genome has been sequenced, enabling genome-wide analysis of gene expression. Methodology/Principal Findings: A genome-wide microarray platform containing the predicted coding sequences (putative genes) for T. thermophila is described, validated and used to study gene expression during the three major stages of the organism's life cycle: growth, starvation and conjugation. Conclusions/Significance: Of the,27,000 predicted open reading frames, transcripts homologous to only,5900 are not detectable in any of these life cycle stages, indicating that this single-celled organism does indeed contain a large number of functional genes. Transcripts from over 5000 predicted genes are expressed at levels >5x corrected background and 95 genes are expressed at >250x corrected background in all stages. Transcripts homologous to 91 predicted genes are specifically expressed and 155 more are highly up-regulated in growing cells, while 90 are specifically expressed and 616 are up-regulated during starvation. Strikingly, transcripts homologous to 1068 predicted genes are specifically expressed and 1753 are significantly up-regulated during conjugation. The patterns of gene expression during conjugation correlate well with the developmental stages of meiosis, nuclear differentiation and DNA elimination. The relationship between gene expression and chromosome fragmentation is analyzed. Genes encoding proteins known to interact or to function in complexes show similar expression patterns, indicating that co-ordinate expression with putative genes of known function can identify genes with related functions. New candidate genes associated with the RNAi-like process of DNA elimination and with meiosis are identified and the late stages of conjugation are shown to be characterized by specific expression of an unexpectedly large and diverse number of genes not involved in nuclear functions.

生长在尖晶石衬底上的GaN外延层的喇曼散射研究

在室温下测量了用MOVPE方法生长在尖晶石(MgAl_2O_4)衬底上的GaN外延层的一阶喇曼光谱。应用各种背散射和90°散射配置，测得了除低频E_2模外所有GaN的喇曼活性光学声子模。并且在X(Z,X)Z和X(Y,Y)Z配置下观测到了由A_1和E_2模混合形成的准TO和准LO模。所得结果与群论选择定则预计的一致。