SQL优化方法

应用SQL不仅要确保它的正确性,同时也要保证SQL有良好的执行性能。本文分析、介绍了几种常用的SQL优化方法,包括设计使用合理的索引、减少不充分连接条件、减少格式转化与操作步骤、使用存储过程,通过这些方法,可以达到优化SQL性能的目的。     

资金利税率取代经济效益综合指数的实证研究

在介绍国家统计局推行的经济效益综合指数之后，利用河南省１７个市、地独立核算工业企业的资料，通过实旆研究和指标分部，提出了用资金利税率指标代替经济效益综合指数的建议。     

网格密度对流场解的影响

采用不同密度的网格,利用隐式时间有限差分方法对M6机翼进行了Euler方程解算,用Richardson外插评估数值误差,就网格密度对人工耗散和解的影响进行了分析.     

电液比例阀的设计与实验研究

在电液比例阀的设计与计算中,弹簧的设计与计算一直是设计人员头痛的问题,在设计电液比例阀的过程中,本文作者通过大量实验和研究,总结出了电液比例阀中弹簧的设计与检验方法。     

对郑州成为大区域中心城市定量分析研究

大区域中心城市是指具有跨区域作用和意义的中心城市。本文用定量分析的方法，将郑州与周边省会城市的中心度进行了对比分析，从而得出郑州最有可能成为中源地区及至陇兰经济带的核心城市的结论。     

运用多重属性风险评估量化跑道侵入严重等级

随着航空运输业的迅速发展,交通密度逐渐增大,机场跑滑系统越来越复杂,航空安全问题也随之增多,其中跑道侵入是影响航空安全的重要方面.引起跑道侵入的因素多种多样,本文主要研究人为因素对跑道侵入严重性等级的影响,根据跑道侵入严重等级的划分,利用多重属性风险评估模型对跑道侵入严重性等级进行量化,通过实例计算和对所得数据的分析,表明多重属性风险评估模型可为跑道系统提供通用的跑道侵入风险评估方法,并指出实际工作中存在的问题及预防措施.     

基于TOPSIS算法的数据中继任务动态优先级设置方法

针对中继卫星系统资源分配中的数据中继任务优先级设置问题开展研究,提出动态优先级评价方法,打破现有基于预设固化时段完成冲突消解的任务规划模式.综合考虑用户、需求,以及任务重要性等因素,建立任务优先级两级评价指标体系.其中,刚性优先级用于度量资源申请的必要性,柔性优先级用于维护资源分配的公平性,同时促进资源使用的合理性.详细列举了各项指标的量化模型,给出了柔性指标综合计算算法.在实验分析中,通过大量数据统计,测试了所提方法的可行性和有效性.     

系统非线性对主字母安控性能影响分析

针对新型的主字母安控体制特点,为了分析非线性对主字母安控体制的影响,对主字母安控体制工作原理和非线性产生原理进行了理论推导.通过对“11选3”主字母安控体制的实例分析、解调性能计算与性能仿真,验证了系统非线性对解调性能与安控可靠性的影响.仿真结果表明:调制指数的大小直接影响解调性能,调制指数太小会使主字母信号能量变低,调制指数太大则会导致非线性,所以需要选择合理的调制指数应用在体制设计中;信道非线性在放大器饱和放大时出现,会导致字母能量分散、信噪比恶化.     

The auroral activity during the main phase of magnetic storms

The relationship of auroral activity indices (AE, Kp, SME) with interplanetary medium parameters during the main phase of magnetic storms is studied. For the period 1990–2020, 142 magnetic storms driven by (41) Sheath, (61) CIR, and (40) ICME events are selected. It is found that the correlation coefficient between average values of the SME index and the SW electric field for Sheath (r = 0.75) is close to correlation coefficients for CIR and ICME events. The correlation coefficient between Kp_aver&Esw_aver (r = 0.72) is higher than the correlation coefficient between AE_aver&Esw_aver (r = 0.63) at the main phase of magnetic storms induced by the Sheath events. It is shown that average values of SW dynamic pressure and IMF σB fluctuations correlate each other for all types of SW.     

Selection and hydroponic growth of bread wheat cultivars for bioregenerative life support systems

As part of the ESA-funded MELiSSA program, the suitability, the growth and the development of four bread wheat cultivars were investigated in hydroponic culture with the aim to incorporate such a cultivation system in an Environmental Control and Life Support System (ECLSS). Wheat plants can fulfill three major functions in space: (a) fixation of CO₂ and production of O₂, (b) production of grains for human nutrition and (c) production of cleaned water after condensation of the water vapor released from the plants by transpiration. Four spring wheat cultivars (Aletsch, Fiorina, Greina and CH Rubli) were grown hydroponically and compared with respect to growth and grain maturation properties. The height of the plants, the culture duration from germination to harvest, the quantity of water used, the number of fertile and non-fertile tillers as well as the quantity and quality of the grains harvested were considered. Mature grains could be harvested after around 160 days depending on the varieties. It became evident that the nutrient supply is crucial in this context and strongly affects leaf senescence and grain maturation. After a first experiment, the culture conditions were improved for the second experiment (stepwise decrease of EC after flowering, pH adjusted twice a week, less plants per m²) leading to a more favorable harvest (higher grain yield and harvest index). Considerably less green tillers without mature grains were present at harvest time in experiment 2 than in experiment 1. The harvest index for dry matter (including roots) ranged from 0.13 to 0.35 in experiment 1 and from 0.23 to 0.41 in experiment 2 with modified culture conditions. The thousand-grain weight for the four varieties ranged from 30.4 to 36.7 g in experiment 1 and from 33.2 to 39.1 g in experiment 2, while market samples were in the range of 39.4–46.9 g. Calcium levels in grains of the hydroponically grown wheat were similar to those from field-grown wheat, while potassium, magnesium, phosphorus, iron, zinc, copper, manganese and nickel levels tended to be higher in the grains of experimental plants. It remains a challenge for future experiments to further adapt the nutrient supply in order to improve senescence of vegetative plant parts, harvest index and the composition of bread wheat grains.