Simultaneous lactic acid and xylitol production from vine trimming wastes

Hemicellulosic hydrolyzates from vineshoot trimmings obtained by dilute sulfuric acid hydrolysis were evaluated for xylitol production by Debaryomyces hansenii NRRL Y‐7426. Bioconversion was not efficient, however, since a mixture of products (mainly ethanol) was achieved. Taking into account that hexoses (such as glucose or mannose) can inhibit xylose metabolism by repression and inactivation of the xylose transport system or catabolic enzymes and that these hemicellulosic hydrolyzates are characterized by a high glucose concentration, a novel technology was developed, sequentially transforming glucose into lactic acid by Lactobacillus rhamnosus followed by fermentation of xylose into xylitol by Debaryomyces hansenii after L. rhamnosus removal by microfiltration. Optimal conditions were achieved using detoxified concentrated hemicellulosic hydrolyzates, after CaCO₃ addition in both stages of fermentation and using nitrogen purges after sampling in order to reduce the oxygen dissolved. Under these conditions 31.5 g lactic acid L^?1 (Q_LA = 1.312 g L^?1 h^?1 and Y_LA/S = 0.93 g g^?1) and 27.5 g xylitol L^?1 (Q_Xylitol = 0.458 g L^?1 h^?1 and Y_Xylitol/S = 0.53 g g^?1) were produced. Finally, lactic acid was selectively recovered using the resin Amberlite IRA 400 (0.0374 g of lactic acid g^?1 of dry resin), allowing a further recovery of xylitol by sequential stages of adsorption, concentration, ethanol precipitation, concentration and crystallization to obtain food‐grade xylitol according to a developed process. Copyright © 2007 Society of Chemical Industry     

人工林修枝装置的研究

针对原有修枝设备存在的不足,研制出机电一体化遥控修枝上树装置。     

滚切式双边剪剪刃间隙平行度偏差分析

双边剪剪刃的间隙与钢板厚度关系直接决定剪切钢板边部质量的好坏,文章主要分析剪刃间隙的平行度的不一致对钢板边部质量的影响,提出在生产过程中采取的处理方法和预防措施。     

一种串并结合的多Site熔丝编程算法

随着集成电路产业的迅猛发展,熔丝修调越来越广泛地应用于集成电路测试工序,熔丝段数目随着需要修调参数的增多而逐步增长,传统的串行熔丝编程方案程序存在代码长、可维护性差、执行时间长等缺点,为了改进代码的可读性和可维护性,文章引进了改进型算法,但对测试执行时间没有任何改善。随着测试代工市场竞争日益激烈,多Site测试方案被广泛使用,但是熔丝编程还继续着串行编程的老算法,Site数目越多,熔丝编程时间越长。针对以上,文章提出了一种串并结合的多Site熔丝编程算法,将多Site熔丝编程时间控制在和单Site熔丝串行编程时间几乎一致。     

基于查询优化策略的语义缓存谓词化简

语义缓存技术可以有效地支持移动计算应用。现有的语义缓存查询处理算法在时空效率和裁剪的复杂度上较高,限制了语义缓存的实用性。为此,本文提出20条逻辑规则和语义缓存动态合并策略,来降低查询裁剪的复杂性。在Android系统上的实验表明,在简单查询下,采用全合并的缓存管理策略和谓词析取式优化算法相结合的方法,能较好地优化查询处理。在复杂查询方面,基于谓词复杂度的语义缓存动态合并策略能很好地平衡缓存与查询两端的谓词复杂度,有效地提高语义缓存的查询处理效率。     

Least tail‐trimmed squares for infinite variance autoregressions

We develop a robust least squares estimator for autoregressions with possibly heavy tailed errors. Robustness to heavy tails is ensured by negligibly trimming the squared error according to extreme values of the error and regressors. Tail‐trimming ensures asymptotic normality and super‐‐convergence with a rate comparable to the highest achieved amongst M‐estimators for stationary data. Moreover, tail‐trimming ensures robustness to heavy tails in both small and large samples. By comparison, existing robust estimators are not as robust in small samples, have a slower rate of convergence when the variance is infinite, or are not asymptotically normal. We present a consistent estimator of the covariance matrix and treat classic inference without knowledge of the rate of convergence. A simulation study demonstrates the sharpness and approximate normality of the estimator, and we apply the estimator to financial returns data. Finally, tail‐trimming can be easily extended beyond least squares estimation for a linear stationary AR model. We discuss extensions to quasi‐maximum likelihood for GARCH, weighted least squares for a possibly non‐stationary random coefficient autoregression, and empirical likelihood for robust confidence region estimation, in each case for models with possibly heavy tailed errors.     

龙滩水轮机转轮的设计和制造评述

龙滩水电站安装9台700MW混流式机组,电站的运行条件十分苛刻：水头变幅大,从97m到179m,最大水头与最小头差值达82m,电站下游洪枯水位差值达40m,电站在系统中担任调频、调峰和事故备用,启动频繁。设计的水轮机转轮,必须具有良好的水头和负荷变化的适应性,稳定运行范围要宽广。龙滩水轮机转轮的设计和制造,在特大型机组中具有代表性,尤其是在工地制作700MW转轮,更居首次。转轮的设计和制造,由伏依特西门子水电设备公司负责,日前此项工作正在进行中,第一台转轮已组装焊接完毕,并进行了退火热处理。文章就龙滩水轮机转轮的水力设计、模型试验、转轮结构设计、转轮工地制造及转轮的最终验收,进行评述并提出一些建议。     

后盖冲压工艺分析及模具设计

通过对后盖零件冲压成形工艺进行分析,确定了合理的工艺方案,设计了拉伸模、切边模、冲孔模,经生产实践,模具结构合理,尺寸精度和尺寸一致性好。     

冰激凌冷冻罗格的工艺分析及模具设计

分析了冰激凌冷冻罗格零件的结构、加工工艺,确定了零件的成形工序,设计出了拉伸模、切边模。同时根据不同形状的冷冻罗格,制定了合理的冲压工艺。     

汽车覆盖件多工步成形数值模拟技术研究

有限元技术已广泛应用于力学过程仿真 ,对冲压等工程问题的应用也逐渐得到人们的重视与认可。然而 ,有限元技术在多工步成形中的应用尚处于起步阶段。本文讨论了多工步成形模拟过程中存在的几个关键问题 ,提出了相应的解决办法。并结合 NUMISHEET’ 99设定的奥迪汽车公司前门板成形标准考题模拟工作 ,对汽车覆盖件多工步成形数值模拟问题进行了具体的研究。