Antioxidant activity and mechanism of the abietane-type diterpene ferruginol

The antioxidant activity of the abietane-type diterpene ferruginol was evaluated by comparison with that of carnosic acid, ( ± )-α-tocopherol and dibutylhydroxytoluene using 2,2-diphenyl-1-picrylhydrazyl, β-carotene bleaching and linoleic acid assays. Ferruginol had the lowest antioxidant activity of this group using the 2,2-diphenyl-1-picrylhydrazyl and β-carotene methods in polar solvent buffer. However, ferruginol exhibited stronger activity than carnosic acid and α-tocopherol for linoleic acid oxidation under non-solvent conditions. Five peaks corresponding to ferruginol derivatives were detected through GC-MS analysis of the reaction between ferruginol and methyl linoleate. The three reaction products were identified as dehydroferruginol, 7β-hydroxyferruginol and sugiol, and the other two peaks were assumed to be 7α-hydroxyferruginol and the quinone methide derivative of ferruginol. The time course of the reaction suggests that the quinone methide was produced early in the reaction and reacted further to produce dehydroferruginol, 7-hydroxyferruginol and sugiol. Thus, we inferred that quinone methide formation was a key step in the antioxidant reaction of ferruginol.     

统计模型在中文文本挖掘中的应用

本文讨论了中文文本挖掘的三个问题:分词、关键词提取和文本分类。对分词问题,介绍了基于层叠隐马尔可夫模型的ICTCLAS分词法,以及将词与词之间的分隔视为缺失数据并用EM算法求解的WDM方法;对关键词提取问题,提出了贝叶斯因子法,并介绍了使用稀疏回归的CCS方法;对文本分类问题,介绍了根据关键词频率建立分类器的方法,以及先建立主题模型再根据主题概率建立分类器的方法。本文通过两组文本数据对上述方法进行比较,并给出使用建议。     

Kinetics of microcrack blunting ahead of macrocrack approaching shear wave speed

The fracturing of glass and tearing of rubber both involve the separation of material but their crack growth behavior can be quite different, particularly with reference to the distance of separation of the adjacent planes of material and the speed at which they separate. Relatively speaking, the former and the latter are recognized, respectively, to be fast and slow under normal conditions. Moreover, the crack tip radius of curvature in glass can be very sharp while that in the rubber can be very blunt. These changes in the geometric features of the crack or defect, however, have not been incorporated into the modeling of running cracks because the mathematical treatment makes use of the Galilean transformation where the crack opening distance or the change in the radius of curvature of the crack does not enter into the solution. Change in crack speed is accounted for only via the modulus of elasticity and mass density. For this simple reason, many of the dynamic features of the running crack have remained unexplained although speculations are not lacking. To begin with, the process of energy dissipation due to separation is affected by the microstructure of the material that distinguishes polycrystalline from amorphous form. Energy extracted from macroscopic reaches of a solid will travel to the atomic or smaller regions at different speeds at a given instance. It is not clear how many of the succeeding size scales should be included within a given time interval for an accurate prediction of the macroscopic dynamic crack characteristics. The minimum requirement would therefore necessitate the simultaneous treatment of two scales at the same time. This means that the analysis should capture the change in the macroscopic and microscopic features of a defect as it propagates. The discussion for a dual scale model has been invoked only very recently for a stationary crack. The objective of this work is to extend this effort to a crack running at constant speed beyond that of Rayleigh wave. Developed is a dual scale moving crack model containing microscopic damage ahead of a macroscopic crack with a gradual transition. This transitory region is referred to as the mesoscopic zone where the tractions prevail on the damaged portion of the material ahead of the original crack known as the restraining stresses, the magnitude of which depends on the geometry, material and loading. This damaged or restraining zone is not assumed arbitrarily nor assumed to be intrinsically a constant in the cohesive stress approach; it is determined for each step of crack advancement. For the range of micronotch bluntness with 0 < β < 30° and 0.2 σ_∞/σ₀ 0.5, there prevails a nearly constant restraining zone size as the crack approaches the shear wave speed. Note that β is the half micronotch angle and the applied stress ratio is σ_∞/σ₀ with σ₀ being the maximum of the restraining stress. For σ_∞/σ₀ equal to or less than 0.5, the macrocrack opening displacement COD is nearly constant and starts to decrease more quickly as the crack approaches the shear wave speed. For the present dual scale model where the normalized crack speed v/c_s increases with decreasing with the one-half microcrack tip angle β. There prevails a limit of crack tip bluntness that corresponds to β 36° and v/c_s 0.15. That is a crack cannot be maintained at a constant speed if the bluntness is increased beyond this limiting value. Such a feature is manifestation of the dependency of the restraining stress on crack velocity and the applied stress or the energy pumped into the system to maintain the crack at a constant velocity. More specifically, the transitory character from macro to micro is being determined as part of the unknown solution. Using the energy density function dW/dV as the indicator, plots are made in terms of the macrodistance ahead of the original crack while the microdefect bluntness can vary depending on the tip geometry. Such a generality has not been considered previously. The macro-dW/dV behavior with distance remains as the inverse r relation yielding a perfect hyperbola for the homogeneous material. This behavior is the same as the stationary crack. The micro-dW/dV relations are expressed in terms of a single undetermined parameter. Its evaluation is beyond the scope of this investigation although the qualitative behavior is expected to be similar to that for the stationary crack. To reiterate, what has been achieved as an objective is a model that accounts for the thickness of a running crack since the surface of separation representing damage at the macroscopic and microscopic scale is different. The transitory behavior from micro to macro is described by the state of affairs in the mesoscopic zone.     

基于营配信息集成的客户服务管理平台设计与应用

供电企业提供的传统服务机制已越来越不能满足客户需求,客户服务工作模式欠缺主动,获取客户需求能力差,现有的系统之间和各远程服务渠道之间的信息数据缺乏共享性,带来数据应用障碍。对此,引入客户服务管理平台,一方面实现现有系统和各远程服务渠道之间的数据共享,另一方面运用共享的数据引入大数据分析技术实现敏感词预警监控。     

光弹性法等倾角和等差线相位图的计算机仿真

确定等倾角和等差线级数是光弹性法的关键。使用六步相移法可以同时确定全场等倾线和等差线参数,通常表示为等倾角和等差线相位图,但求得的等倾角耦合了第一和第二主应力方向角,即得到等倾角相位图存在"不一致"区域。等倾角的不一致会影响到等差线级数的计算,导致等差线相位图出现"失真"区域。针对这个问题,提出一种基于有限元分析结果的等倾角和等差线相位图计算机仿真方法,该方法可以作为光弹实验的辅助,识别出实验等倾角相位图中的"不一致"区域。通过径向受压圆盘实验验证了该方法的可行性,对光弹实验的等倾角和等差线相位图有良好的仿真效果。     

基于互补嵌入的彩色图像可逆数据隐藏

针对传统差值直方图平移算法嵌入容量偏低、多重嵌入时图像质量严重下降等缺陷,提出一种基于互补嵌入的彩色图像可逆数据隐藏算法。利用色彩分量之间的相关性和整数小波系数之间的关系减小差值,以增加差值直方图的峰值。采用双重直方图平移方法提高嵌入容量,两次嵌入过程的像素值扩展方向相反,部分像素值扩展量相互抵消,扩展量最大值为1。实...     

基于双直方图平移的彩色图像可逆数据隐藏

提出一种基于双直方图平移的彩色图像可逆数据隐藏算法.利用色彩分量间的相关性减小差值,使差值直方图更加紧凑、直方图的峰值更大.采用直接调整像素值的方法在差值中嵌人数据,由像素值的二次可调整性定位不可调整像素,并嵌入少量的标志信息代替定位图,从而提高嵌入容量.实验结果表明,本文算法在保证图像质量的同时大幅提高了嵌入容量,与...     

Improving protein structural class prediction using novel combined sequence information and predicted secondary structural features

Protein structural class prediction solely from protein sequences is a challenging problem in bioinformatics. Numerous efficient methods have been proposed for protein structural class prediction, but challenges remain. Using novel combined sequence information coupled with predicted secondary structural features (PSSF), we proposed a novel scheme to improve prediction of protein structural classes. Given an amino acid sequence, we first transformed it into a reduced amino acid sequence and calculated its word frequencies and word position features to combine novel sequence information. Then we added the PSSF to the combine sequence information to predict protein structural classes. The proposed method was tested on four benchmark datasets in low homology and achieved the overall prediction accuracies of 83.1%, 87.0%, 94.5%, and 85.2%, respectively. The comparison with existing methods demonstrates that the overall improvements range from 2.3% to 27.5%, which indicates that the proposed method is more efficient, especially for low-homology amino acid sequences.     

论晚清“科学小说”的定名及其影响

"科学小说"这个名称在20世纪初由日本传入中国,这一名称在中国的流行不仅很大程度上传播了"科学"这个全新的翻译词汇,而且"科学"二字体现的知识权威性充分昭示出文人对于此种小说的看重。在"科学"出现以前,是"格致"这个词基本上指代科学技术的意思,不过却只有"科学小说",很少看到"格致小说"。通过考察晚清"科学小说"这一名称的由来,我们不仅可以了解当时人们对于科学小说的看法与期待,还有助于我们还原多面而真切的历史场域,从而对中国科幻小说诞生初期的状况有更为丰满具体的认识。     

脉冲抽样法测量低频相位差

介绍了一种用脉冲抽样法测量低频相位差的技术。这种技术以可编程逻辑门阵列(FPGA)和单片机为核心,测量的精度达到0.1°。和传统的测相法比较,这种测量方法最大的优点是省去了大量的硬件电路,特别是省去了对速度和漂移特性要求苛刻的整形电路,也省去了鉴相电路、大小相角判别电路,只需增加一个抽样保持电路,给设计、调试带来了方便,而且,这种测量没有传统意义的幅相误差,给整机性能的稳定性和一致性带来了好处。