双孢蘑菇基质中线虫影响木耳菌丝生长的数量阈值

在研究了双孢蘑菇生产基质中的3种优势线虫数量扩增及对菌丝生长影响的基础上,着重研究了线虫密度(5,10,20,40,80,160条.管-1)对木耳菌丝生长的影响,以确定该3种线虫的数量影响阈值。结果表明:中杆属(Mesorhabditis sp.)线虫在密度为5和10条.管-1的条件下,接种2周后,菌丝表观与对照的无明显不同,繁殖量分别达40和255条.管-1;接种3周后,菌丝表观略有变化。拟丽突属(Acrobeloides sp.)和滑刃属的堆肥滑刃线虫(Aphelenchoides composticola Franklin)在5条.管-1的接种密度下,2周后木耳菌丝明显变黄,其繁殖量分别达到55和93条.管-1;3周后,菌丝变褐,部分被啃食。3种线虫在20条.管-1以上密度条件下,菌丝受害严重,3周后菌丝几乎被完全啃食。因此,在蘑菇生产中,基质中的3种供试线虫数量应控制在5条.管-1以下(约每100 g基质中线虫8条以下)。

拮抗细菌Bacillus subtilis B5423-R抑制水稻纹枯病的阈值群体数量

在菲律宾国际水稻研究所实验农场田间条件下 ,通过人工接种Rhizoctoniasolani,采用不同的方法 (喷雾次数、间隔期 )喷雾B542 3 R(B542 3的标记菌株 ,为利福平Rifampicin抗性的突变体 ) ,在接种 1d后 ,采用 2d喷 1次、连续 3～ 4次喷雾的方法 ,使B542 3 R在稻株上的群体数量在 6～ 7d内维持在 1× 10 6 cfu/g以上 ,在 2 5d内显著地降低相对病斑高率 ;而采用 5d喷1次、连续 3～ 4次喷雾的方法 ,B542 3 R在稻株上的群体数量在 15d内维持在 1× 10 5 ～ 10 6cfu/g,在 2 5d内相对病斑高率未能显著降低。表明在纹枯病侵染早期的 6～ 7d内 ,在稻株上B542 3 R维持在 1× 10

AI-2,一种新的细菌自体诱导分子

细菌通过数量阈值感应系统调节群体内个体的基因表达而使整个群体步调一致。细菌通过感应自体诱导分子(autoinducer, AI)浓度而感知周围环境中同类存在的密度,并据此调节自身特定性状的表达。AI-2是近年来新发现的一种介导细菌种间信号传导的自体诱导分子,其分子结构、功能均不同于传统的AI分子。AI-2对细菌的调节作用主要表现为对毒力基因表达的影响,但目前也有人认为AI-2可能只是一种代谢产物。

采用数量级阈值与二维信息排序策略的NSGA-Ⅱ-DE算法

为提高算法NSGA-II-DE解决含有复杂Pareto解集优化问题的性能,分析原NSGA-II中拥挤度计算公式和排挤机制的缺陷,并以NSGA-II-DE算法为基本框架,将传统拥挤度排序策略改为包含有角度信息与伪半径的二维信息排序策略.在拥挤度排挤机制中加入数量级阈值的干预,提出改进算法2D-Thr.选取多样度、收敛度和分布度3个评价指标进行量化计算,并与NSGA-II-DE、原NSGA-II、MACPSO进行比较.仿真结果表明,改进算法不仅有效继承了原算法优良的收敛性,而且提高了Pareto前沿的分布度.

一种新的乙酰高丝氨酸内酯水解酶基因的克隆和表达

目的获得新的降解革兰阴性细菌数量阈值感应信号分子乙酰高丝氨酸内酯类化合物(AHL)的水解酶基因。方法选择性富集和培养土壤中耐热细菌,抽取细菌总DNA作为模板,特异性聚合酶链反应扩增乙酰高丝氨酸内酯水解酶基因,进行克隆和DNA序列分析及原核表达。结果得到1个新的AHL水解酶基因,该基因与已知基因的核苷酸序列和对应的氨基酸序列同源性最高分别为87％和94％。该基因在原核表达系统中表达,得到了与预期相对分子质鲢(Mr)一致的蛋白质。结论证实乙酰高丝氨酸内酯水解酶广泛存在于环境微生物中。为进一步研究提供条件。

Photodetachment of H^- Near a Dielectric Surface

Using the closed orbit theory, the photodetachment cross section of H- near a dielectric surface has been derived and calculated. The results show that the dielectric surface has great influence on the photodetachment process of negative ion near the ionization threshold. Above the ionization threshold, the photodetachment cross section starts to oscillate. With the increase of the energy, the oscillating amplitude decreases and the oscillating frequency increases. The oscillation in the photodetachment cross section of H- in the presence of a dielectric surface is either larger or smaller than the photodetachment of H- without the surface. As the photon energy is larger than the critical value Epc, the oscillatory structure disappeared and the cross section approaches to the case of the photodetachment of H- without any external fields. For a given detached-electron energy, the photodetachment cross section becomes decreased with the increase of the ion-surface distance. Besides, the dielectric constant has great influence on the photodetachment of H-. With the increase of the dielectric constant, the oscillation in the cross section becomes increased. As the dielectric constant increases to infinity, the cross section is the same as the photodetachment of H- near a metal surface. This study provides a new understanding on the photodetachment process of H- in the presence of a dielectric surface.

A continuous differentiable wavelet threshold function for speech enhancement

Enhanced speech based on the traditional wavelet threshold function had auditory oscillation distortion and the low signal-to-noise ratio (SNR). In order to solve these problems, a new continuous differentiable threshold function for speech enhancement was presented. Firstly, the function adopted narrow threshold areas, preserved the smaller signal speech, and improved the speech quality; secondly, based on the properties of the continuous differentiable and non-fixed deviation, each area function was attained gradually by using the method of mathematical derivation. It ensured that enhanced speech was continuous and smooth; it removed the auditory oscillation distortion; finally, combined with the Bark wavelet packets, it further improved human auditory perception. Experimental results show that the segmental SNR and PESQ (perceptual evaluation of speech quality) of the enhanced speech using this method increase effectively, compared with the existing speech enhancement algorithms based on wavelet threshold.

Local Reynolds number and thresholds of transition in shear flows

Recent experimental and numerical investigations reveal that the onset of turbulence in plane-Poiseuille flow and planeCouette flow has some similar stages separated with different threshold Reynolds numbers.Based on these observations and the energy equation of a disturbed fluid element,a local Reynolds number Re L is derived to represent the maximum ratio of the energy supplement to the energy dissipation in a cross section.It is shown that along the sequence of transition stages,which include transient localized turbulence,"equilibrium" localized turbulence,spatially intermittent but temporally persistent turbulence and uniform turbulence,the corresponding thresholds of Re L for plane-Couette flow,Hagen-Poiseuille flow and plane-Poiseuille flow are consistent,indicating that the critical(threshold) states during the laminar-turbulent transition are determined by the local properties of the base flow and are independent of global features,such as flow geometries(pipe or channel) and types of driving forces(shear driving or pressure driving).