水解-红外吸收光谱法测定精四氯化钛中总油

精四氯化钛是海绵钛及钛生产的关键原材料,提高海绵钛及钛质量的关键在于控制精四氯化钛中杂质含量。由于生产工艺原因,精四氯化钛中含碳杂质主要为油类杂质,因此测定精四氯化钛中油类杂质含量,对精四氯化钛中碳杂质的分析具有重要意义。总油以碳为主要成分,具有红外吸收带,因此能够利用红外吸收光谱法实现测定。而四氯化钛与水气接触极易发生水解反应,生成的氯化氢同样具有红外吸收峰,且氯化氢与油类的吸收峰波数较接近,致使氯化氢干扰红外吸收光谱法测定四氯化钛原样中总油含量。实验建立水解-红外吸收光谱法测定精四氯化钛中总油含量的方法,将四氯化钛样品与水按体积比1∶25水解平衡后,采用四氯乙烯萃取水解溶液中的总油,通过外标定量分析精四氯化钛中总油含量。校准曲线中总油的线性范围为0～80 mg/L,相关系数r为0.999 9;总油的检出限为2.5 mg/kg。方法用于测定3个精四氯化钛样品中总油,结果的相对标准偏差(RSD,n=6)为3.5%～4.1%;加标回收率为96%～109%。     

一种遥测数据实时采集压缩系统的实现

设计了一种对遥测大容量速变数据的实时压缩采集方案,通过采用改善无损压缩算法的压缩比、压缩和解压速度以及算法复杂度等多个数据压缩性能,提出了综合性能较好的LZW编码作为数据压缩的核心算法并通过软件仿真确认其效果和压缩算法的执行速度;利用主控芯片FPGA完成对压缩数据的高精度采集,对研制的数据采集压缩系统进行整体测试,测试结果表明,该系统完成了6路速变参数的实时采集与压缩,压缩比达到1.8∶1以上,各项指标满足了设计要求.     

Finite‐time consensus tracking for harmonic oscillators using both state feedback control and output feedback control

This paper investigates the distributed finite‐time consensus‐tracking problem for coupled harmonic oscillators. The objective is to guarantee a team of followers modeled by harmonic oscillators to track a dynamic virtual leader in finite time. Only a subset of followers can access the information of the virtual leader, and the interactions between followers are assumed to be local. We consider two cases: (i) The followers can obtain the relative states between their neighbors and their own; and (ii) Only relative outputs between neighboring agents are available. In the former case, a distributed consensus protocol is adopted to achieve the finite‐time consensus tracking. In the latter case, we propose a novel observer‐based dynamic protocol to guarantee the consensus tracking in finite time. Simulation examples are finally presented to verify the theoretical analysis. Copyright © 2012 John Wiley & Sons, Ltd.     

3种磷酸盐对冷藏牦牛肉中水分的调控作用

采用低场核磁共振(low-field nuclear magnetic resonance,LF-NMR)结合主成分分析,研究焦磷酸钠、六偏磷酸钠和三聚磷酸钠3种磷酸盐对牦牛肉冷(冻)藏过程中水分的调控作用。结果表明:牦牛肉经过4 ℃冷藏处理24 h,同时含有结合水和自由水;而经过-20和-70 ℃冷冻处理24 h后,结合水消失,且自由水含量显著减少(P＜0.05)。经3种磷酸盐分别腌渍24 h,其对牦牛肉的保水作用强度依次为:三聚磷酸钠>六偏磷酸钠>焦磷酸钠。当焦磷酸钠、三聚磷酸钠、六偏磷酸钠的质量分数分别在0.36%~0.41%、0.30%~0.45%和0.35%时,牦牛肉的保水性最佳。主成分分析结果进一步验证了磷酸盐对牦牛肉保水性存在显著影响,其中相对自由水峰面积RPA为主要影响指标。研究结果将为牦牛肉的贮藏保鲜技术提供科学依据。     

The nutrient requirements of Lactobacillus rhamnosus GG and their application to fermented milk

Lactobacillus rhamnosus GG (LGG) performs many physiological functions, but the fermentation time is long when fermented milk is prepared using LGG alone. To shorten the fermentation time, we analyzed the nutrient requirement profiles of LGG. Based on nutrient requirement profiles, we evaluated the effects on the fermentation time, quality, and sensory properties of unmodified cow's milk fermented by LGG alone. According to the consumption and necessary patterns of amino acids and those of purine, pyrimidine, vitamins, metal ions, and nutrients essential to LGG, we selected Cys, Ser, Arg, Pro, Asp, Glu, guanine, uracil, and xanthine with which to supplement milk. Compared with fermented milk prepared using LGG alone in unmodified milk, the fermentation time of supplemented milk was shortened by 5 h. Viable cell counts, titratable acidity, and water-retaining capability of the fermented milk were improved by addition of nutrient supplements. Supplementation with nutrients did not obviously change the sensory and textural characteristics of fermented milk.     

椰子油脂肪酸己二酸三羟甲基丙烷复合酯的制备及其润滑性能

为进一步改进椰子油的润滑性能，采用己二酸与三羟甲基丙烷先酯化合成中间体，再与椰子油脂肪酸反应制备椰子油脂肪酸己二酸三羟甲基丙烷复合酯(简称复合酯)，并测试复合酯的FTIR红外光谱、流变学性能、热-氧稳定性、摩擦学性能、水解稳定性、海洋微生物降解性等。结果表明：该复合酯具有良好的流变学性能和热稳定性，其40 ℃的黏度为114 mm2/s，黏度指数为159，倾点为-6 ℃，热分解起始温度为300 ℃，能满足较为苛刻的机械工况要求；复合酯还具有良好的摩擦学性能，相同条件下承载能力为椰子油的2.6倍，而且与复配添加剂(二烷基二硫代磷酸锌+十八胺)具有良好的感受性和配伍性能。所制复合酯的水解稳定性高于椰子油，海洋微生物14天的降解率大于80%，是一类性能优良的绿色酯类润滑油。     

区块链网络安全保障:攻击与防御

随着区块链技术的迅猛发展,区块链系统的安全问题正逐渐暴露出来,给区块链生态系统带来巨大风险.通过回顾区块链安全方面的相关工作,对区块链潜在的安全问题进行了系统的研究.将区块链框架分为数据层、网络层、共识层和应用层4层,分析其中的安全漏洞及攻击原理,并讨论了增强区块链安全的防御方案.最后,在现有研究的基础上展望了区块链安...     

Direct coagulation casting of silicon carbide suspension via polyelectrolyte dispersant crosslink reaction

A direct coagulation casting method for silicon carbide ceramic suspension using dispersant crosslink reaction is reported. Polymer electrolyte (polyethyleneimine, PEI) was used as dispersant to prepare silicon carbide suspension. Common food additives (carboxymethyl cellulose, CMC) were used to coagulate the electrosteric stabilized silicon carbide suspension. There was a well disperse silicon carbide suspension with 0.2 wt% PEI at pH = 5-6. Influence of coagulant on viscosity and zeta potential of the silicon carbide suspension was investigated. It indicates that the high solid loading silicon carbide suspension can be destabilized and coagulated at elevated temperature. It can be attribute to the gradual decrease of electrosteric force due to the crosslink reaction between PEI and CMC. Silicon carbide wet green body with compressive strength of 1.99 MPa could be demolded at 70°C which is higher than that prepared by traditional DCC and dispersant reaction method for nonoxide ceramics. Dense silicon carbide ceramics with relative density above 98.8% and 99.3% had been prepared by liquid phase pressureless and hot pressed sintering, respectively.     

主链型偶氮苯改性聚芳酰胺的合成及表征

在以N,N二甲基乙酰胺为溶剂,三乙胺为酸吸收剂的条件下,将自制的反式-4,4'-偶氮苯二甲酰氯与对苯二胺进行低温缩聚反应,合成了1种新型的反式偶氮苯聚芳酰胺.用红外光谱、示差热扫描量热分析,热重分析,偏光显微镜,紫外光谱对其结构及性能进行了表征.合成的聚合物表现出了一定的结晶性能,聚合物的稀溶液呈现出溶致液晶行为.     

基于森林景观恢复策略的庄园遗产景观设计探寻——以荷兰海德兰省巴克塞比克地区为例

庄园遗产景观是指包含花园和农业用地的历史乡村庄园集群。在气候变化、工业发展和快速城市化的背景下,庄园遗产景观正面临水生态环境失衡、空间碎片化和文化特征消失等挑战,而这些挑战只能从区域规划尺度去应对。以荷兰海德兰省巴克塞比克地区为例,在考虑地方景观异同的同时,以景观自身特性为基底,结合未来发展趋势,进一步诠释了一种旨在提升庄园遗产景观韧性的多尺度景观设计方法。发现森林砍伐为地域空间变化的主要因素之一,它对水系统与生态多样性造成了负面影响。基于在区域尺度上对庄园遗产景观历史发展的分析,森林景观恢复(FLR)作为主要设计策略,旨在从不同尺度上对“退化的”景观进行生态功能修复并提升人类福祉。这种新的空间设计方法将在不同尺度上促进文化遗产景观发展。