Optimum policy for a production system with major repair and preventive maintenance

This study applies periodic preventive maintenance (PM) to a repairable production system with major repairs conducted after a failure. This study considers failed PM due to maintenance workers incorrectly performing PM and damages occurring after PM. Therefore, three PM types are considered: imperfect PM, perfect PM and failed PM. Imperfect PM has the same failure rate as that before PM, whereas perfect PM makes restores the system perfectly. Failed PM results in system deterioration and major repairs are required. The probability that PM is perfect or failed depends on the number of imperfect maintenance operations conducted since the previous renewal cycle. Mathematical formulas for expected total production cost per unit time are generated. Optimum PM time that minimizes cost is derived. Various special cases are considered, including the maintenance learning effect. A numerical example is given.     

压缩/喷射制冷循环中喷射器引射室的最优压降

建立了蒸气压缩/喷射制冷循环稳定运行时两相喷射器的热力学模型,以常压沸点相差较大的制冷剂为工质,比较了两相喷射器引射室压降最优范围的差异,并在同一工况下,研究了不同工质压缩/喷射制冷循环的性能。结果表明:喷射器引射室压降存在最佳范围使压缩/喷射制冷循环性能接近最优值;在相同工况下不同制冷工质这个最佳范围不相同;在同一工况下,当采用压缩/喷射制冷循环时,不同工质的循环性能系数和单位容积制冷能力相比基本循环均增强了。研究结果为压缩/喷射制冷循环制冷工质的选择及两相喷射器结构的优化设计提供理论参考。     

高光谱最优波长选择及Fisher判别分析法判别玉米颗粒表面黄曲霉毒素

黄曲霉毒素是广泛存在于玉米中且具有剧毒的一种代谢产物,以美国农业部农业研究署(USDA-ARS) Toxicology and Mycotoxin Research Unit提供的2010年先锋玉米为研究对象,验证了高光谱成像技术对玉米中黄曲霉毒素检测的可行性。以甲醇为溶剂制备四种不同浓度的黄曲霉毒素溶液,并将其逐一滴在等量的4组共120粒玉米颗粒表面,以未处理的30粒洁净玉米作为一组对照样本,将大小、形状相似的150个样品随机分为训练集103个,验证集47个;对获取的400～1 000 nm波段范围内的高光谱图像,先进行标准正态变量变换(standard normal variate transformation, SNV)预处理,然后引入基于Fisher判别最小误判率的方法选择最优波长,并以所选波长作为Fisher判别分析法的输入建立判别模型,对玉米颗粒表面不同浓度的黄曲霉毒素进行识别,最后对模型判别正确率进行了验证。结果表明,选取四个最优波长(812.42, 873.00, 900.36和965.00 nm)时Fisher判别分析模型对训练集与验证集的准确率分别为87.4%和80.9%。该方法为含黄曲霉毒素玉米颗粒便携式检测仪器的开发,以及对田间霉变玉米自然代谢产生毒素的检测奠定了技术基础。     

核桃果皮基活性炭的氯化锌活化制备及工艺优化

以核桃果皮为原料,以氯化锌为活化剂,采用正交设计,马弗炉加热法制备了核桃果皮基活性炭,并对所得活性炭进行表征,测定了不同实验条件下制备的核桃果皮基活性炭的得率、比表面积和碘吸附值,对最优条件下制备的活性炭进行了孔径分析、红外光谱分析,Boehm法测定其表面酸性基团含量等。实验结果表明：以氯化锌为活化剂制备核桃果皮基活性炭的最佳工艺参数分别为：活化温度600 ℃,活化时间1 h,氯化锌浓度50%,粒径大小为60目。最优条件下制备的活性炭比表面积达到1 258.05 m2·g-1,中孔率为32.18%,说明核桃果皮可以制备出比表面积高的优质活性炭,不但实现了农业废料的资源化,还解决了农业废料污染的问题,同时提供了廉价的吸附剂,对于开辟活性炭原料的新来源具有重要意义。     

近红外光谱法田间快速估测新鲜紫花苜蓿品质

田间快速估测苜蓿品质对于适时刈割具有重要意义。试验共采集来自不同地域、不同品种、不同生育期和不同茬次的新鲜紫花苜蓿样170份,经便携式近红外光谱仪(1 100～1 800 nm)扫描得到近红外光谱,利用偏最小二乘法(PLS)在国内首次建立基于紫花苜蓿新鲜样品的干物质(DM)、粗蛋白(CP)、中性洗涤纤维(NDF)、酸性洗涤纤维(ADF)化学分析值的近红外校正模型,探讨利用近红外漫反射光谱技术(NIRS)在田间快速估测紫花苜蓿品质的可行性,摸索设备选择和制样方法。四项指标所建模型的交互验证决定系数(R2CV)分别为0.831 4,0.597 9,0.803 6和0.786 1;交互验证均方根误差(RMSECV)为1.241 1,0.261 4,0.990 3和0.830 6;外部验证决定系数(R2_V)为0.815 0,0.401 1,0.784 9和0.752 1,外部预测均方根误差(RMSEP)分别为1.06, 0.31, 0.95和0.80。对于苜蓿鲜样来说,DM,NDF和ADF的近红外模型可以进行粗略的定量分析,CP的建模效果较差,但因苜蓿中的粗蛋白含量一般都能满足家畜需求,DM,NDF和ADF是在适时刈割中最关键的估测指标,DM,NDF和ADF模型可以满足田间快速估测苜蓿品质的要求。     

EACVD中的Hα谱线与最佳生长条件

采用蒙特卡罗方法,模拟了CH4/H2混合气体为源气体的EACVD中的氢原子发射过程。考虑了电子与H2的弹性碰撞及振动激发、分解、电子激发、相应于Hα,Hβ,Hγ谱线的激发、电离及分解电离等非弹性碰撞过程;与CH4的碰撞考虑了弹性动量传输及振动激发、分解、电子激发、电离及分解电离等非弹性碰撞过程。研究了不同实验条件下产生的H,CH3的数目与Hδ谱线强度的关系,给出了一种通过Hα谱线来推断生长金刚石薄膜的最佳实验条件的方法。     

Control packet signaling mechanism using electronic code division multiple access for packet-based networks

We propose and experimentally demonstrate the feasibility of a control packet signaling technique using electronic code division multiple access for a wavelength division multiplexing packet-based network, whereby each wavelength channel is assigned a unique electronic code based label on a radio frequency subcarrier. Such a technique allows each wavelength channel to be electronically identified without requiring the use of a WDM demultiplexer. We experimentally demonstrate this technique with two wavelength channels each with 1.25 Gb/s baseband payload data and 10 Mb/s header coded onto an electronic code at 160 Mb/s. A performance study of the electronic code division multiple access based control signaling scheme in a wavelength division multiplexed packet-based access network is also performed in terms of the required power budget to monitor the electronic code division multiple access control signals in the presence of several sources of noise for error-free transmission of both payload data and electronic code division multiple access based control signals. It is shown that the modulation depth of each signal impacts the amount of required optical tap power. As the modulation depth of the electronic code division multiple access based control signal is increased, the required optical tap power is reduced. However, this increases the bit-error-rate for the payload data. Therefore, there lies a maximum and a minimum of the required tap optical power for the successful recovery of both signals. The lower bound of this range is usually determined by the successful recovery of electronic code division multiple access based control signal while the upper bound is determined by the successful recovery of payload data. The required optical tap power is analyzed for different transmission bit rates of the payload data for various receiver architecture scenarios without an optical amplifier at the receiver. The scalability analyses were repeated with an optical amplifier placed in the receiver terminal of the network. The resulting optical tap power that is required for the successful monitoring of the electronic code division multiple access based control signals are compared with that of the case without the amplifier.     

光轴方向任意的晶体连续双折射双反射

根据惠更斯定理,研究了单轴晶体光轴任意方向的双折射与全内双反射,给出了光线方向和光波法线方向的普遍公式.讨论了在晶体内沿多个面的连续双折射双反射,分析了前一界面输出量和后一界面输入量之间的联系,得到多次双折射双反射后的光线方向和光波法线方向.在此基础上,适当地选取晶体的界面参数,相当于选取光轴方向,可以使o光和e光的分离角Δoe更大.光轴方向任意的晶体连续双折射双反射对晶体器件的最优化设计非常有帮助.最后给出了改变斜入射2×2电光开关的出射面参数使Δoe优化的实例.     

氢化物发生-原子吸收光谱测定钢铁中痕量铅

对氢化物发生-原子吸收光谱(HG-AAS)测定铅的预氧化问题和铅的氢化物发生的新机理作了理论上的探讨。发现铅氢化物发生最佳条件同酸、碱等物质的量浓度的中和相关。对柠檬酸的络合、缓冲作用作了研究。发现K3Fe(CN)6的光敏作用能消除钢中有关化学元素对测量铅的干扰。提出了简便准确的钢中0.000 0x%铅的直接测定方法。应用此法分析了5个标样中的铅含量,结果与标准值一致,得RSD为2.0%(n=4,wPb6.2×10-5%)及1.5%(n=14,wPb1.3×10-3%),方法的测定限为w(Pb)5×10-6%。     

KDP二维声电光互作用最佳工作模式的确定

在计算ＫＤＰ晶体的反常声电光互作用几何关系的基础上,确定了晶体中二维反常声电光互作用的最佳工作模式．