不同碳源及培养方式对小麦花药培养愈伤组织诱导率的影响

以5个小麦杂交组合F_1为材料,采用两种培养方式,在不同碳源的三种培养基上进行花药培养。结果表明,用麦芽糖取代常用培养基中的蔗糖,可有效地提高愈伤组织的诱导率,提早出愈时间,用葡萄糖代替蔗糖则具有不利影响;固体培养和固体+液体培养两种方式比较,愈伤组织诱导率没有明显差异。     

山西霍山森林群落主要种生态位的研究

将山西霍山每50m海拔段作为一个样方调查区,作四个100m~2的样方。从山蔍海拔900m到山顶2354m,共作样方52个。将海拔作为一条反映水、热、土壤等环境因子的综合资源轴,将群落类型作为反映种群互惠、竞争关系的另一综合资源轴。选择该区12种乔木,15种灌木,计测其在两条轴上的资源选择性系数(L)生态位宽度(B),和乔木之间,灌木之间以及乔灌木之间的生态重叠值(O)。结果表明L值愈小,B值愈大,物种的资源利用能力愈强,生态幅度愈大,对某一资源的依赖性愈小,反之亦然。比较同一资源轴上的不同的L值和B值,可反映物种的优势程度和区分能力。相同生活型种间的重叠值既可作为反映种间生态学相似性的指标。也可作为判断种间有无竞争可能的参考。不同生活型种间重叠值的的大小则可作为判断种间依存和相似程度的指标。     

振动机械的亚谐分叉研究

研究了一类非线性振动磨机的动力学行为，利用平均法，得到分岔方程，并分析其稳定性；利用奇异性理论研究了分叉方程的普适开折，全面分析了系统在整个参数空间上的各种行为，为设计振动磨机提出了理论依据。     

型转化法平面连杆机构结构分解路线的自动生成

用求最短回路的方法,通过寻找一组机构的有序独立的基本回路,并满足此组回路中为正值的回路自由度之和最小,只需输入少量直观的杆副信息,计算机可自动确定含P副、复铰的任何平面连杆机构的优化分解路线。     

重载运输中扼流变压器容量配置预算的理论基础

在电气化铁道中，钢轨既是机车牵引电流回流的通道，又是自动闭塞系统传输信息的通道，两者之间存在着电磁兼容性的问题。本文首先介绍了一种现场模拟产生大牵引电流的方法，然后在实测数据的基础上，分析了钢轨回流随牵引电流的变化关系．根据轨流在一定范围内随牵引电流呈线性变化这一关系，可以在己有测试数据的基础上预测出重载运输牵引电流下，钢轨回流的大小，确定沿线扼流变压器容量的配置。这为扼流变压器容量的预先配置计算奠定了电流特性方面的理论基础。     

一相能量型stefan问题

本文讨论了一相能量型stefan问题.首先利用迭代方法及紧性讨论证明了古典解的存在性;其次给出了解的比较原理,由此证明了解的唯一性。     

Structure of the Sec23/24-Sar1 pre-budding complex of the COPII vesicle coat

COPII-coated vesicles form on the endoplasmic reticulum by the stepwise recruitment of three cytosolic components: Sar1-GTP to initiate coat formation, Sec23/24 heterodimer to select SNARE and cargo molecules, and Sec13/31 to induce coat polymerization and membrane deformation. Crystallographic analysis of the Saccharomyces cerevisiae Sec23/24-Sar1 complex reveals a bow-tie-shaped structure, 15 nm long, with a membrane-proximal surface that is concave and positively charged to conform to the size and acidic-phospholipid composition of the COPII vesicle. Sec23 and Sar1 form a continuous surface stabilized by a non-hydrolysable GTP analogue, and Sar1 has rearranged from the GDP conformation to expose amino-terminal residues that will probably embed in the bilayer. The GTPase-activating protein (GAP) activity of Sec23 involves an arginine side chain inserted into the Sar1 active site. These observations establish the structural basis for GTP-dependent recruitment of a vesicular coat complex, and for uncoating through coat-controlled GTP hydrolysis.     

Normal faulting in central Tibet since at least 13.5 Myr ago

Tectonic models for the evolution of the Tibetan plateau interpret observed east-west thinning of the upper crust to be the result of either increased potential energy of elevated crust or geodynamic processes that may be unrelated to plateau formation. A key piece of information needed to evaluate these models is the timing of deformation within the plateau. The onset of normal faulting has been estimated to have commenced in southern Tibet between about 14 Myr ago and about 8 Myr ago and, in central Tibet, about 4 Myr ago. Here, however, we report a minimum age of approximately 13.5 Myr for the onset of graben formation in central Tibet, based on mineralization ages determined with Rb-Sr and 40Ar-39Ar data that post-date a major graben-bounding normal fault. These data, along with evidence for prolonged activity of normal faulting in this and other Tibetan grabens, support models that relate normal faulting to processes occurring beneath the plateau. Thinning of the upper crust is most plausibly the result of potential-energy increases resulting from spatially and temporally heterogeneous changes in thermal structure and density distribution within the crust and upper mantle beneath Tibet. This is supported by recent geophysical and geological data, which indicate that spatial heterogeneity exists in both the Tibetan crust and lithospheric mantle.