三峡水库不同运行工况下中段干流碳源气体释放通量研究

来自陆地大量有机碳源的输入,以及三峡库区调度运行和筑坝蓄水导致CO_2、CH_4等碳源气体的排放成为近来关注的热点。以三峡库区干流中段为研究对象,于2017年8月—2018年11月对忠县(ZX),万州(WZ),涪陵(FL)进行每月采样分析,探求水-气界面CO_2、CH_4通量在水库不同运行工况下的变化特征。研究发现,在观测期间内,ZX采样点CO_2浓度在0.008 6～0.115 3 mmol/L波动,WZ采样点CO_2浓度在0.003 5～0.116 8 mmol/L波动,FL采样点0.006 3～0.098 6 mmol/L,整体上3个采样点的CO_2浓度变化趋于一致,都在库区泄水期运行4—5月CO_2浓度达到峰值,在低水位运行期的6—9月降到最低值。CH_4通量在水库低水位运行期表现为"汇",FL点位在泄水期达到"源"的最大值;3个采样点的CO_2通量在泄水期均表现为"源"的特征,低水位运行期的CO_2通量表现为"源"与"汇"的转换。通过与国外已有水库监测数据比较分析,CO_2扩散通量在全球水库序列中处于中等水平,CH_4扩散通量在全球水库序列中处于中等偏下水平。     

奥氏体不锈钢1Cr18Ni9Ti车削条件优化的试验研究

车削奥氏体不锈钢所用刀具最佳硬质合金牌号为798;刀具最佳几何参数为:γ_0=10～20°,α_(?)=8～12°、λ_s=-5～-12°和bγ_1=(0.10～0.14)mm,γ_(01)=-10～-12°、b_e=0.10mm;通过一次回归正交试验获得计算最优切削速度的经验公式:υ=357.9f~(-0.51)f~(-0.38)αp~(-0.24)。     

变几何涡轮特性拟合的数学模型

本文通过对涡轮特性曲线的物理意义和几何特征的分析,提出了适用于喷嘴安装角可调的涡轮流量特性和效率特性的拟合模型,并提出了一种新的计算方法来确定拟合数学模型中的待定参数。用该模型拟合了某发动机变几何动力涡轮的特性。与原节点数据相比,流量和效率特性拟合回代值的平均相对误差分别为0.675％和0.534％。另外,又拟合了某定几何高压涡轮的流量特性,平均相对误差值为0.638％,其结果令人满意。     

Costs and benefits of mycorrhizas: Implications for functioning under natural conditions

Summary It is paradoxical that most plants under natural conditions are infected with vesicular-arbuscular mycorrhizal fungi, yet that it is often difficult to demonstrate that infected plants receive any benefit from the association. The costs and benefits of infection are analysed and a hypothesis formulated that infection only yields benefits at times during the life cycle when P demand by the plant exceeds the capacity of the root system. A simulation model is described that suggests that infection density should be more or less constant below a threshold value of root P uptake rate, but that above this value roots should be non-mycorrhizal. More extensive study of mycorrhizas under field conditions is needed to test such predictions.     

复形法在拱坝优化中的应用

本文阐述了复形法在拱坝优化中如何具体应用,并且根据拱坝优化的特点,提出了对复形法所作的若干改进,以节省复杂应力分析的次数和时间。另外,对程序中某些细节的处理也作了交代。     

开边界条件下Fateev-Zamolodchikov模型的潜藏定域规范不变性

本文在量子反散射方法框架内详细研究了开边界条件下Fateev-Zamolodchikov 模型的潜藏定域规范不变性.结果表明,尽管Hamiltonian 量及其本征矢明显规范相关,但其能量本征值与Bethe方程却是规范不变的.     

柱面一球面(平面)镜腔(Ce,Nd):YAG板条固体激光器的研究

借助于本征光线矢量法,分析了柱面球面(平面)镜腔的模式特性.对使用这类腔型的(Ce,Nd):YAG板条激光器的实验结果作了报道和讨论.     

Heilbronn问题的一个新结果

研究Heilbronn问题的最大最小距离之比A”，利用所设计的计算机辅助证明系统，得到n＝9时，2．4＜A。2．569237的新结果。     

A Study on Social Choice Making:the Number of Admissible Preference Orderings for SMV

In this paper,we study,mathematically speaking,the problem-the number of admis-sible preference orderings for the transitivity of simple majority vote(SMV)derived from Arrow'sImpossibility Theorem.In our research,we find,by computer enumerating,that some results givenby Craven are not correct.By defining a set of constraints,we give the recurrence formula of thelocal maximal number of admissible preference orderings and some other useful results.     

Plant growth stimulation by inoculation with symbiotic and associative rhizosphere microorganisms

SelectedRhizobium bacteria, arbuscular mycorrhiza-forming (AM) fungi and associative bacteria have been shown to stimulate the growth of legumes, gramineae and cruciferae in field experiments on different soil types in temperate regions. A combination of microorganisms with different metabolic capacities (N₂-fixation, P-mobilization; production of phytohormones and antibiotics) can partly surpass the effect of single inoculations, or can produce a positive effect where single inoculations are ineffective. Growth stimulation by inoculation requires microorganisms with phytoeffective metabolic characteristics and the ability to survive in the rhizosphere during the growth period. Another prerequisite is an adequate supply of plant assimilates for the production of microbial phytoeffective metabolites. Type of inoculum, method of inoculation and agricultural measures can influence the effect of the inoculation. Research is necessary to extend our knowledge both of basic principles, and about using microorganisms in practice.