中浓度气力输送弯管压力降数值模拟研究

对于中等浓度气力输送90°弯管内的气固流动状态进行数值模拟研究,并对水平转垂直、垂直转水平,不同弯径比(R/D=1.5~6.0)的90°弯管,均匀和非均匀粉体颗粒流过弯管的压力降Δp进行了模拟计算。结果表明,在同一气体流速下,不同R/D的弯管的Δp变化显著;存在一个使Δp最小的R/D值。在模拟的条件范围内,弯管内粉体颗粒的速度分布随R/D变化。并讨论了不同R/D的粉体颗粒流动对弯管压力降及管壁磨损的影响。在同样操作条件下,对煤粉输送进行了弯管压力降数据模拟,其模拟计算结果与周建刚等人的试验结果吻合良好。     

多聚磷酸浓度分析方法综述

本文介绍了多聚磷酸的性质、生产方法及浓度分析方法,重点介绍了酸碱滴定法、链长法、重量法以及粘度法,并比较了它们的优缺点。     

连续PH 分布数据拟合的确定性退火BP算法

针对目前连续PH 分布数据拟合EM(Expectation-Maximization)算法存在的初值敏感问题,提出运用确定性退火EM 算法进行连续PH 分布数据拟合,给出了详细的理论推导,并通过两个拟合实例与标准EM 算法进行了对比.对比结果表明所提出的方法可以有效地避免初值选择的不同对EM 算法结果的影响,减小陷入局部最优的可能性,能得到比标准EM算法更好的结果.     

净水厂生产废水回用中丙烯酰胺的风险控制

以西安市某地表水厂为例,针对生产废水回用后出厂水中丙烯酰胺含量超标问题,进行了相关的风险控制研究.研究结果表明:对不同浓度的污泥,投加阴离子型和阳离子型PAM均能有效降低污泥比阻值,改善污泥的脱水性能,但使用阴离子型PAM,出厂水丙烯酰胺含量更低.综合考虑污泥脱水效果及脱水分离液中丙烯酰胺的残留量,采用阴离子型PAM,投药量在0.09～0.16g/L之间时,可有效控制出厂水中丙烯酰胺含量超标的风险.     

无铅焊接工艺及失效分析

综述了目前无铅焊接工艺回流焊和波峰焊的工艺特点,指出了焊接中存在的几大主要失效问题,包括开裂、焊点空洞、晶须和板材胀裂,并介绍了避免或减弱这些失效问题的方法。     

节点弯矩在钢结构长悬臂桁架中的影响分析

对一个长悬臂钢桁架进行现场应变监测，结果表明，节点弯矩在本桁架中的影响不可忽略，特别是对腹杆的影响相对更大，在设计中必须给予考虑。进一步用ANSYS对该结构进行了两种建模形式的有限元分析，并与实测值相比较，发现在设计类似的桁架时，弦杆和腹杆应分别按不同的分析方式进行设计比较合理。     

Power supply for generating frequency-variable resonant magnetic perturbations on the J-TEXT tokamak

To further research the response of the tearing mode(TM) to dynamic resonant magnetic perturbation(DRMP) on the J-TEXT tokamak, a modified series resonant inverter power supply(MSRIPS) with a function of discrete variable frequency is designed for DRMP coils in this study. The MSRIPS is an AC–DC–AC converter, including a phase-controlled rectifier, an LC filter, an insulated gate bipolar transistor(IGBT) full bridge, a matching transformer, three resonant capacitors with different capacitance values, and three corresponding silicon controlled rectifier(SCR) switches. The function of discrete variable frequency is realized by switching over different resonant capacitors with corresponding SCR switches while matching the corresponding driving frequency of the IGBT full bridge. A detailed switching strategy of the SCR switch is put forward to obtain sinusoidal current waveform and realize current waveform smooth transition during frequency conversion. In addition, a resistor and thyristor bleeder is designed to protect the SCR switch from overvoltage. Manufacturing of the MSRIPS is completed, and the MSRIPS equipment can output current with an amplitude of 1.5 kA when its working frequency jumps among different frequencies. Moreover, the current waveform is sinusoidal and can smoothly transition during frequency conversion. Furthermore, the transition time when the current amplitude rises from zero to a steady state is less than 2 ms during frequency conversion. By using the MSRIPS, the expected discrete variable frequency DRMP is generated, and the phenomenon of the TM being locked to the discrete variable frequency DRMP is observed on the J-TEXT tokamak.     

计算机软件工程的管理

在软件工程的管理过程中，把软件工程分成“风险阶段”，并相应分配资金，从而大大降低了因工程失误而造成的风险，利用软件寿命周期控制图，对软件在其寿命周期内的支出与收益进行分析，保证了收益的最大值，解决了软件寿命周期的控制问题。     

An application of the shortest path algorithm for the identification of weak MHD mode

The identification of magnetohydrodynamic(MHD) modes is a crucial issue in the control of magnetically confined plasmas. This paper proposes a novel method for identifying the evolution of MHD modes from a signal with a low signal-to-noise ratio. The proposed method generates a weighted directed graph from the time-frequency spectrum and calculates the evolution of the mode frequency by solving the shortest path. This method addresses the limitations posed by the lack of data channels and the di...     

公路桥梁施工中预应力的应用

经济的发展离不开交通的完善。特别是当今时代,经济的高速发展对桥梁和道路建设的要求在不断提高。为了更好地、更安全地促进我国经济的进步,公路桥梁工程的质量至关重要。论文主要对公路桥梁预应力施工技术进行探讨,以期进一步促进我国桥梁建设和经济发展的进步。