三维欧氏空间中的球面曲线

依据经典微分几何空间曲线的基本理论与特征,采用一种新的活动标架——三维欧氏空间中的球面Frenet标架,并利用三维曲线的Frenet标架场,对三维欧式空间中的球面曲线进行研究,得到了在三维空间E~3下的贝特朗、曼海姆及从切等特殊曲线,给出了一个由曲线的曲率与挠率的一阶常微分方程描述的三维欧氏空间中的球面曲线,得出了比对应微分方程阶数更低的条件,且大大简化了计算过程.     

液体发酵树舌提取凝集素的生理学功能检测

本文对树舌菌丝体的深层发酵工艺进行了初步的研究。试验结果表明,树舌菌丝体在大豆培养基中培养5天,产出的总蛋白、总糖含量较高。从发酵液中分离和纯化出树舌凝集素具有明显的生物学活性。     

大学英语网考改革对听力教学的预期反拨作用研究

本文是一项有关大学英语网考改革对听力教学的预期反拨作用的实证研究。首先,在对国内外预期反拨作用进行综述的基础上提出一个符合中国大学英语网考改革实际的预期反拨作用模型,然后从教学管理者视角研究大学英语网考改革对听力教学的预期反拨作用。     

英语动词化语法隐喻的认知功能特征

从认知角度来考察,英语动词化语法隐喻具有两个特征:在意义表达方面,英语动词化语法隐喻可以体现意义的主观性;在心理扫描模式方面,英语动词化语法隐喻是对事件的顺序扫描.从功能角度来考察,英语动词化语法隐喻具有两个特征:在句法构式方面,英语动词化语法隐喻具有特定的语法功能;在语篇表意方面,英语动词化语法隐喻具有语篇简洁功能等     

蓖麻花药愈伤组织诱导条件优化

以通蓖5号品种的蓖麻花药为试验材料,研究了不同浓度的蔗糖、不同生长调节剂及pH值对愈伤组织诱导的影响.结果表明,蔗糖在20～40g/L之间均有较高的愈伤诱导率,且随蔗糖浓度的增加而升高;当ZT为3.0mg/L、NAA为1.0mg/L愈伤组织诱导最高;当pH值在6.0时,愈伤组织诱导效果最佳,诱导率达到最高为27.95％,且此时褐化率较低.     

基于改进经验模态分解和支持向量机的短期风速组合预测

为更精确地进行风速预测,提出一种利用带自适应噪声的完全集成经验模态分解(complete ensemble empirical mode decomposition with adaptive noise,CEEMDAN)方法和蝙蝠算法(bat algorithm,BA)优化支持向量机(support vector machine,SVM)的组合短期风速预测方法。首先用CEEMDAN对原始风速时间序列进行分解,得到一系列不同频率的子序列;其次,使用BA-SVM组合模型预测对分解后的各个子序列分别进行预测;最后,将各子序列的预测结果叠加得到风速预测值。仿真结果表明,该模型提高了预测精度,减小了误差。     

Structure of epsilon15 bacteriophage reveals genome organization and DNA packaging/injection apparatus

The critical viral components for packaging DNA, recognizing and binding to host cells, and injecting the condensed DNA into the host are organized at a single vertex of many icosahedral viruses. These component structures do not share icosahedral symmetry and cannot be resolved using a conventional icosahedral averaging method. Here we report the structure of the entire infectious Salmonella bacteriophage epsilon15 (ref. 1) determined from single-particle cryo-electron microscopy, without icosahedral averaging. This structure displays not only the icosahedral shell of 60 hexamers and 11 pentamers, but also the non-icosahedral components at one pentameric vertex. The densities at this vertex can be identified as the 12-subunit portal complex sandwiched between an internal cylindrical core and an external tail hub connecting to six projecting trimeric tailspikes. The viral genome is packed as coaxial coils in at least three outer layers with approximately 90 terminal nucleotides extending through the protein core and the portal complex and poised for injection. The shell protein from icosahedral reconstruction at higher resolution exhibits a similar fold to that of other double-stranded DNA viruses including herpesvirus, suggesting a common ancestor among these diverse viruses. The image reconstruction approach should be applicable to studying other biological nanomachines with components of mixed symmetries.     

Analysis of the DNA sequence and duplication history of human chromosome 15

Here we present a finished sequence of human chromosome 15, together with a high-quality gene catalogue. As chromosome 15 is one of seven human chromosomes with a high rate of segmental duplication, we have carried out a detailed analysis of the duplication structure of the chromosome. Segmental duplications in chromosome 15 are largely clustered in two regions, on proximal and distal 15q; the proximal region is notable because recombination among the segmental duplications can result in deletions causing Prader-Willi and Angelman syndromes. Sequence analysis shows that the proximal and distal regions of 15q share extensive ancient similarity. Using a simple approach, we have been able to reconstruct many of the events by which the current duplication structure arose. We find that most of the intrachromosomal duplications seem to share a common ancestry. Finally, we demonstrate that some remaining gaps in the genome sequence are probably due to structural polymorphisms between haplotypes; this may explain a significant fraction of the gaps remaining in the human genome.     

水稻小穗柄韧皮部发育的超微结构研究

水稻小穗柄中央维管束后生韧皮部筛管分子和伴胞的发育都经历了一个基本相同的过程,首先是细胞液泡化程度增加;然后细胞核内染色质发生凝集并边缘化;液泡膜破裂,各种细胞器解体;细胞核形成凋亡小体并最终解体.两者超微结构的变化表现出了细胞程序性死亡的特征,液泡的解体在这个过程中具有重要作用.筛管分子的退化要早于伴胞,一般在开花前1周细胞核解体;而伴胞的退化则在开花后1周细胞核内的染色质才开始凝集,这种差异可能与这2种细胞的功能有关.     

Zr基非晶合金准静态压缩下的多重剪切带行为

利用IUTM和SEM研究了Zr-Ti-Ni-Cu块状非晶合金的准静态单轴压缩变形和断裂行为. 研究表明:该合金的室温压缩变形过程主要表现为弹性和塑性变形,塑性变形阶段没有加工硬化现象. 在准静态压缩条件下Zr基非晶合金表现出多重剪切效应,提高了塑性. 微观研究证明,剪切带的滑移分枝与相互交叉是非晶合金塑性提高的主要机制. 沿着剪切带发现了微空洞和微裂纹,剪切带的形成与自由体积的合并有关. 塑性变形过程中形成脉纹状断口形貌,受力状态的不同脉状花纹表现为不同的形式.