Computing the distribution of the Robinson-Foulds distance

With the exponential growth of genome databases, the importance of phylogenetics has increased dramatically over the past years. Studying phylogenetic trees enables us not only to understand how genes, genomes, and species evolve, but also helps us predict how they might change in future. One of the crucial aspects of phylogenetics is the comparison of two or more phylogenetic trees. There are different metrics for computing the dissimilarity between a pair of trees. The Robinson-Foulds (RF) distance is one of the widely used metrics on the space of labeled trees. The distribution of the RF distance from a given tree has been studied before, but the fastest known algorithm for computing this distribution is a slow, albeit polynomial-time, O(l⁵) algorithm. In this paper, we modify the dynamic programming algorithm for computing the distribution of this distance for a given tree by leveraging the number-theoretic transform (NTT), and improve the running time from O(l⁵) to O(l³ log l), where l is the number of tips of the tree. In addition to its practical usefulness, our method represents a theoretical novelty, as it is, to our knowledge, one of the rare applications of the number-theoretic transform for solving a computational biology problem.     

Association behavior of linear ω-functionalized polybutadienes in cyclohexane

The dilute solution properties of linear polybutadienes with dimethylamine and zwitterionic end groups were studied by membrane osmometry (MO), low-angle laser light scattering (LALLS), viscometry, and dynamic light scattering (DLS) in cyclohexane. The polymers were prepared by anionic polymerization, under high vacuum conditions using [3-(dimethylamino)propyl]lithium as initiator. The dimethylamine groups were converted to zwitterions by reaction with cyclopropane sultone. No evidence of association was found for the amine-capped polymers, whereas the zwitterionic samples exhibited strong association in cyclohexane. The degrees of association increase by decreasing molecular weight of the base polymer due to the excluded volume repulsions. These aggregation numbers are of the same order as those found for ω-functionalized polyisoprenes, with the same polar groups in the same solvent. The hydrodynamic properties, measured by viscometry and dynamic light scattering, supported the conclusions drawn by LALLS and provide strong evidence that the aggregates behave hydrodynamically as star polymers. Comparison with theoretical models shows that the association behavior is best described by the linear head packing model. © 1996 John Wiley & Sons, Inc.     

同质缓冲层对ZnO薄膜光学性质的影响

利用射频磁控溅射技术,在单晶硅衬底上生长出高质量(0002)晶面取向的ZnO外延薄膜。通过XRD、AFM、吸收光谱、光致荧光发光谱的实验研究,发现加入适当厚度的、低温生长的ZnO同质缓冲层,可有效降低晶格失配和因热膨胀系数不同引起的晶格畸变。在衬底温度200℃、沉积时间5min的ZnO缓冲层上,以450℃衬底温度溅射ZnO薄膜主层,得到的ZnO样品的晶体结构、表面形貌和光学性质均有较明显的改善。     

军用电台射频性能的三维测试

射频测试是电台性能测试的一项基本内容.本文将已经标准化了的手机与无线局域网的射频测试内容和方法引入军用电台的射频性能测试中,定量地考察了电台的辐射性能.并提出该方法同样适用于我军的高速数据电台.     

Learning a Deep Metric: A Lightweight Relation Network for Loop Closure in Complex Industrial Scenarios

The similarity metric in Loop closure detection (LCD) is still considered in an old fashioned way, i.e. to pre-define a fixed distance function, leading to a limited performance. This paper proposes a general framework named LRN-LCD, i.e. a Lightweight relation network for LCD, which combines the feature extraction module and similarity metric module into a simple and lightweight network. The LRN-LCD, an end-to-end framework, can learn a non-linear deep similarity metric to detect loop closures from different scenes. Moreover, the LRN-LCD supports image sequences as input to speed up the similarity metric in real-time applications. Extensive experiments on several open datasets illustrate that LRN-LCD is more robust to strong condition variations and viewpoint variations than the mainstream methods.     

外腔半导体激光器激射波长温度稳定性的研究

在考虑了光纤光栅(FG)的相位分布之后,根据光纤光栅外腔半导体激光器(FGESL)所满足的阈值条件,从理论上研究了前端面反射率对光纤光栅长外腔半导体激光器(LECFGSL)激射波长温度稳定性的影响.数值模拟的结果表明:随着温度的变化,LECFGSL的激射波长围绕光栅布拉格反射波长上下波动,激光器前端面反射率对激射波长波动幅度有较大的影响,当前端面反射率＜10-4时,激射波长与光栅布拉格反射波长基本一致,其温度稳定性较好.     

用于SAW器件的C轴择优取向LiNbO3薄膜的制备及结构研究

采用射频（RF）磁控溅射法在金刚石（111）衬底上沉积LiNbO3（LN）薄膜,借助X射线衍射技术（XRD）,研究了外加偏压（0～80V）和衬底温度（200～500℃）等工艺参数对LiNbO3薄膜结构和取向性的影响。实验结果表明,在衬底温度为200℃、外加偏压为～80V的T艺条件下,LiNbO3的（006）衍射峰强度超过LN的（012）衍射峰强度,在金刚石（111）衬底上获得较高c轴取向的LN薄膜。并且对C轴择优取向LN薄膜的形成机理进行了探讨。     

ZnS衬底上GeC/GaP增透保护膜系的制备及红外光学性质

把GeC/GaP双层膜用作ZnS衬底的长波红外(8~11.5μm波段)增透保护膜系。采用射频磁控溅射法,以高纯Ar为工作气体、单晶GaP圆片为靶制备了GaP薄膜;用射频磁控反应溅射法在高纯Ar和CH4的混合气体中,以单晶Ge圆片为靶制备了GeC薄膜。分别用柯西(Cauchy)公式和乌尔巴赫(Urbach)公式表示折射率和吸收系数,对薄膜的红外透射率曲线进行最小二乘法拟合,得到了它们的厚度及折射率、吸收系数等光学常数。GaP膜的折射率与块体材料的相近,在波长10μm处约为2.9;GeC膜的折射率较小,在波长10μm处约为1.78。用所得到的薄膜折射率,通过计算机膜系自动设计软件在ZnS衬底上设计并制备出了GeC/GaP双层增透保护膜系,当GaP膜厚较大时,由于吸收增大膜系增透效果较差;当GaP膜厚较小时,膜系有较好的增透效果。     

塑料光纤纤端光场测试结果及分析

对纤端光场进行了理论分析,分别利用塑料光纤和多模光纤作为接收光纤对塑料光纤的出射纤端光场进行了测量,并与理论分析结果进行了比较,给出了合理的调和参数.传输距离较长的塑料光纤由于高阶模的泄漏,纤端光场分布非常接近高斯分布.实验结果表明了理论分析结果和调和参数选择的合理性.     

Characterization of the Phytochemical Composition and Bioactivities of Anacyclus maroccanus Ball. and Anacyclus radiatus Loisel Aerial Parts: Preliminary Evidence for the Possible Development of Moroccan Plants

In the present study, the phytochemical composition and bioactivities of A. maroccanus (AM) and A. radiatus (AR), two ecotypes collected in the Demnate road and Essaouira regions, respectively, were studied to highlight a pharmacological interest and to enable possible pharmaceutical development. To this end, methanolic and ethyl acetate extracts were prepared for each ecotype by fractionation; next, their phytochemical composition was evaluated by spectrophotometric and chromatographic analysis. Moreover, in line with the available evidence for Anacyclus spp. and their traditional use, a screening of bioactivities, including antioxidant, hypoglycemic, antiglycative, chelating, and antibacterial activities, was performed. The extracts were characterized by high amounts of polyphenols, tannins, and flavonoids, especially in the methanolic extracts; these samples were also enriched in carotenoids despite a lower chlorophyll content. Chlorogenic acid and rutin were the major identified compounds. The extracts also showed interesting hypoglycemic, antiglycative, and antibacterial properties, although with differences in efficacy and potency. Present results provide more scientific basis to the ethnopharmacological uses of Anacyclus spp. and suggest a further interest in AM and AR ecotypes as natural sources of bioactive compounds and/or phytocomplexes for possible pharmaceutical and nutraceutical developments.