周期性冷热换热器的热惯性及设计要点

常规的换热器操作中,物料的冷却或加热通常是固定不变的,物料温度呈单调性变化,换热器运行达到稳态后其本体的温度也达到稳值,因此换热器的热负荷只用于物料的相变及温度变化。如果冷却和加热周期性交替进行,则换热器本体温度的周期性变化也必然要消耗一定的热负荷,这种现象是热惯性的表现。由于周期性冷热交替的特殊性,此类换热器设计中应充分考虑其热惯性及相应的设计要点。     

近58年大汶河流域降水量演变特征分析

为进一步系统识别气候变化背景下大汶河流域降水量演变特征,基于大汶河流域32个雨量站1956~2013年逐日降水资料,分析了大汶河流域降水量年内分配与年际变化特征及趋势性、随机性、突变性、周期性的变化规律。结果表明,大汶河流域降水量年内分配不均,连续最大四个月均出现在6~9月,所占比例超过70%;年际变化较大,各分区多年平均降水量极值比分布在3.71~5.26之间;降水量呈现不显著下降趋势;降水序列并非完全独立,表现为正持续性;降水量在1964年发生不显著突变,降水量变化周期以14年为主。     

谱相关的数学关系与物理意义

周期性是自然现象和工程现象的基本特性之一,从复杂多变的、含有噪声的观测数据中发现周期性并测量其参数是信号处理的重要主题.谱相关是分析循环平稳信号二阶周期性的有力工具,本文研究谱相关的周期性解析功能的缘由、过程与特点.首先,梳理了谱相关理论体系中诸多重要概念之间的内在联系,建立了相互之间转换或映射的数学关系图;然后提出了按定义和转换关系逐步求解谱相关的方法.通过单周期信号的分析和每步操作效果与周期的对应关系,诠释了循环自相关、谱相关、无限循环谱和循环频率等重要概念的物理意义.     

周期性变化边界条件下窑墙非稳态导热的数值模拟

本文采用简谐波处理周期性变化边界条件的方法，探讨了一维非稳态导热问题的数值计算问题，并给出了两间间歇窑窑墙传热过程的计算示例；计算结果表明，对周期性的传热过程，采用这种数值分析方法是适宜的。此外，本文还针对非稳态导热蓄热能力计算方法存在的不足之处，提出了一种新的计算周期性非稳态导热过程中窑墙蓄热能力的方法。     

Variability in pheromone composition and periodicity of pheromone titer in potato tuberworm moth,Phthorimaea operculella (Lepidoptera: Gelechiidae)

The ratios and quantities of the pheromone components, (E,Z)-4,7-tridecadien-1-yl acetate (diene) and (E,Z,Z)-4,7.10-tridecatrien-1-yl acetate (triene), in the glands of individual female potato tuberworm moths (Phthorimaea operculella) originating from the United States (California) and Japan (Nagoya) were analyzed by gas chromatography. Quantities of glandextracted pheromone components of Nagoya females fluctuated in a periodic fashion during the photoperiod. Maximal titers coincided with the onset of scotophase (and calling), then gradually declined to minimal levels soon after lights-on. The average daily pheromone quantities decreased significantly as females aged. Both populations exhibited considerable variation in the ratio of the two components. The proportions of triene in the blend ranged from 27% to 88% (triene –X = 56 ± 13% SD; CV = 23%) for California females and from 16% to 71% (42 ± 13%; CV = 31%) for Nagoya females. Nagoya females also stored significantly higher amounts of pheromone in their glands (8.6 ± 3.9 ng) than did California females (2.7 ± 1.4). The differences between the populations, while substantial, would probably not be sufficient to impart a barrier to panmixis, given the wide range of component ratios favored by the males.     

基于数字信号处理的风电功率日周期性研究

风电功率具有波动性和间歇性,大规模风电并网对电网运行产生不利影响。主要对风电功率波动特性进行分析。基于数字信号处理,将风电功率数据作为数字信号进行处理。通过自相关系数分析发现风电功率数据具有一定的周期性。利用有限傅里叶分解提取日周期分量,并从能量角度分析了日周期分量在不同时间尺度和不同装机容量下的分布特性。日周期分量在风电功率中所占比例随时间和空间的不同发生变化。时间段越长日周期分量所占比例越小;随着风电场数量的增加,日周期分量所占比例将明显增加。     

The numerical solutions of the periodic crack problems of anisotropic strips*

The numerical solutions of the periodic crack problems of anisotropic strip are investigated in this paper. Using the complex variable method the mathematical model, boundary value problems for analytic functions, is established. After constructing appropriate integral transformations the boundary value problems are transformed into integral equations. Employing Lobotto-Chebyshev quadrature formulas and Gauss quadrature formulas, the approximate analytical expressions of the stress intensity factors are obtained. And some numerical results are performed for several special cases.     

On Nonlinear Control Systems with Multiple Time Scales

An order reduction procedure for nonlinear control systems with multiple time scales is introduced. A limit system for the slowest motion describing the situation that all singular perturbation parameters vanish is constructed. For this purpose a refined two-scale averaging method is used in a way that allows a re-iteration. For vanishing control range the results reduce to the well-known Tychonoff theorem on order reduction for singularly perturbed ODEs.     

有效的模(2n+1)乘算法及其VLSI设计

模乘运算在剩余数值系统、数字信号处理系统及其它领域都具有广泛的应用,模乘法器的硬件实现具有重要的作用。提出了一种改进的模(2~n 1)余数乘法器的算法及其硬件结构,其输入为通常的二进制表示,因此无需另外的输人数据转换电路而可直接用于数字信号处理应用。通过利用模(2~n 1)运算的周期性简化其乘积项并重组求和项,以及采用改进的进位存储加法器和超前进位加法器优化结构以减少路径延时和硬件复杂度。比较其它同类设计,新的结构具有较好的面积、延时性能。     

Alternatives to standard hemodialysis

Survival of patients on hemodialysis remains poor, but the benefits of increasing urea clearance have probably been maximized within our current treatment schedules. Long dialysis sessions (8 hr) produce impressive outcomes, with mortality 53% to 55% lower than conventional schedules. Even increasing from 4 to 5 hr may improve survival. Increased frequency of dialysis (6 times weekly) produces impressive reductions in left ventricular mass and could conceivably be implemented in‐center. Preliminary data suggest a 61% reduction in mortality with increased frequency. Nightly dialysis combines longer sessions with increased frequency and has produced remarkable clinical gains in blood pressure, left ventricular mass, serum phosphate, and sleep apnea. However, the data are mainly from case series and impact on mortality remains unknown. Expansion of home hemodialysis would be necessary for this modality to grow. Convective therapies remove middle molecules more effectively, and observational data suggest hemodiafiltration has the potential to improve mortality by 35% to 36%. Hemodiafiltration has the advantage of being relatively easy to implement. The uremic milieu is complex and further investigation of the underlying pathophysiology is needed to inform future dialysis interventions. The survival data above are from observational studies, and hence benefits are likely to be exaggerated. Randomized trials of dialysis interventions are desperately needed. They remain difficult to perform, because of the complexity of both the patient population and the interventions, and because of limited available funding.