时间序列分析关键问题研究

简要介绍了时间序列的定义、模型及型态,重点研究了时间序列分析的相关内容,最后对其未来发展方向进行了展望。     

宽间隔跳频图案的设计与实现

根据对偶频带法和L—G模型设计的要求,构造出一种满足汉明相关的宽间隔跳频图案,并对其进行FPGA硬件实现。系统软件采用模块化的设计模型,利用生命周期长且移植性好的VHDL语言设计实现宽间隔跳频图案。通过时序仿真图和结果验证可以看出,设计出的宽间隔跳频图案,性能接近于最佳跳频序列的性能。     

汽油机电液式可变气门正时系统响应性能仿真与试验

汽油机电液式可变气门正时系统(VVT)的响应性能对发动机燃烧、排放均有重要影响,汽油机瞬态过程中电液式VVT应根据发动机工况快速调整到目标相位,但由于电液VVT的响应性能受到多方面因素的影响,其速度尚有进一步提升的空间。基于试验和仿真分析,对影响电液VVT响应性能的发动机转速、机油温度、机油压力等因素进行了分析,并详细分析了VVT阶跃响应过程各阶段的影响因素,提出了基于MAP查表的VVT前馈控制算法,试验结果表明,该算法能够实现VVT快速响应,同时保证稳定性。     

Effects of different application timings of methane fermentation digested liquid to paddy plots on soil nitrogen and rice yield

Treatment of animal and food wastes using a methane fermentation technique is drawing considerable public attention as a suitable option for the utilization of biomass resources. The application of a fermentation byproduct (methane fermentation digested liquid) as an agricultural fertilizer has been investigated. Determining the appropriate timing required for applying digested liquid on a rice (Oryza sativa L.) paddy plot is important. The concentrations of soil nitrogen (N) components and rice yield should be considered because digested liquid contains both inorganic and organic N. This study compares the N transformation and the rice yield and growth at different application times over a period of 3 y. The effects of the timing of basal application on soil N were different and the timing that maximized the rice yield was different in each year. Days before ponding (DBP) affected soil N before mid-summer drainage, and rice growth rates at the panicle formation stage and the ear emergence stage. The effects of DBP disappeared before harvest. The results indicated that sufficient potentially mineralizable N existed regardless of DBP, and the effect of DBP lessened after the mid-summer drainage, which coincides with the period when N uptake is most active.     

Successive annual applications of organic manures for cut grass: short-term observations on utilization of manure nitrogen

Abstract The recovery of nitrogen (N) from, and the fertilizer‐N value of, low dry‐matter (DM) cattle slurry and farm yard manure (FYM), applied annually to perennial ryegrass swards grown at two sites, on sandy loam and shallow calcareous silty clay loam soils, were studied over a 4‐year period. Slurry or FYM, applied at target rates of either 150 kg N ha^?1 or 300 kg N ha^?1 in either October, February or May/June, in combination with 150 kg N ha^?1 inorganic fertilizer‐N (applied as split dressings before the first and second grass cut), were compared with a set of inorganic fertilizer‐N response treatments. DM yield, N offtake, apparent manure‐N recovery (in herbage) and manure‐N efficiency (compared with inorganic fertilizer‐N) were determined at two silage cuts each summer. Soil mineral nitrogen (SMN) measurements in autumn and spring were used to assess potential N leaching loss over winter and to quantify available N residues in the soil in spring. Apparent manure‐N recovery and manure‐N efficiency were usually greater from slurry applications in February than from those in October, but the timing of the application of FYM had a much smaller effect, compared with the timings of the application of slurry, on the utilization of N from manure by grass. Spring assessment of SMN was useful in quantifying available N residues from October slurry applications. Manure‐N recovery for all application timings was, on average, higher from the sandy loam than the shallow calcareous clay loam. The application of slurry to grass in early spring, at a rate of 150 kg total N ha^?1, with the addition of a supplementary 50 kg inorganic fertilizer‐N ha^?1, was the most suitable strategy for utilizing slurry‐N effectively and for supplying the N requirement for first‐cut silage.     

基于机器学习方法的拟南芥基因组DNA复制时间预测研究

【目的】基于机器学习方法,构建拟南芥基因组DNA复制时间分类器,探究与复制时间相关的表观遗传修饰,为进一步研究DNA复制时间的表观遗传调控机制提供参考。【方法】收集拟南芥全基因组的DNA复制时间数据和多种DNA表观遗传修饰特征(ChIP-Seq)数据,以及染色质开放状态(DNase-Seq)数据,先通过t-SNE初步对DNA表观遗传修饰特征数据降维来衡量DNA复制早晚的可预测性,并利用皮尔逊相关系数计算了多种DNA表观遗传特征与DNA复制时间信号两两之间的相关性,再通过构建随机森林、多类别逻辑回归和支持向量机3种分类器对DNA复制时间进行建模分析,以十折交叉验证和ROC曲线下的面积(AUC)为衡量指标,用80%的数据建模,20%的数据对模型效果进行验证。【结果】3种分类器对DNA复制时间都具有良好的预测能力,平均AUC均达0.8以上。DNA复制早期信号与RNA聚合酶Ⅱ结合信号以及染色质开放状态信号等呈正相关,而复制晚期信号则与其呈负相关。其中H3.1、H3.3、H2AW、H4K16ac、H3K36me3、H3K4me3均可能与DNA复制时间存在密切关系。【结论】拟南芥基因组DNA复制时间可以通过表观遗传修饰进行准确预测,其中对DNA复制晚期的预测最为准确;并发现了与DNA复制时间关系密切的组蛋白变体及表观遗传修饰。     

醇类燃料点火提前角对汽油机性能和排放的影响

通过旋转分电器外壳改变点火提前角来研究其对燃用M20甲醇-汽油和E20乙醇-汽油(甲醇、乙醇体积分数均为20%)混合燃料电喷汽油机的性能和排放的影响.试验结果表明:汽油机燃用M20和E20时最高压力点比纯汽油分别提前1℃A(曲轴转角)和0.5℃A,最佳点火提前角分别提前约2℃A和1℃A;随着点火提前角的增大,燃用2种燃料的汽油机性能和排放变化趋势相似,均表现为扭矩和功率增大,能量消耗率降低,CO、HC和NOx排放量增加.     

排种器实验台变频调速系统设计

为了利用排种器实验台进行精密播种机排种器的试验研究,设计了排种器实验台的调速系统.首先,介绍了排种器实验台变频调速系统的硬件构成;然后,基于计算机与变频器之间的串行通讯协议,利用VC 的MSComm通讯控件,用VC 6.0语言开发了排种器实验台变频调速系统的控制程序,实现了排种器实验台计算机与变频器的串行通讯.该系统具有操作方便、调速手段多、可靠性和抗干扰能力强等特点,可以满足排种器实验台需要对速度进行实时调节的要求.     

施放生物定时水对造林地水分动态影响的研究

根据实地测定和前人研究成果,分析了施放生物定时水后土壤含水率、土壤水分蒸发、土壤水分渗漏及植物水分吸收关系,推导出造林植物需补充水量的公式,为生物定时水的造林应用提供理论依据。