基于灰度阈值和梯度差的车牌定位技术

本文详述了用灰度阈值分割和梯度差对车牌进行分割处理的过程,介绍了灰度阈值分割理论以及梯度算法,并用于车牌的识别检测中,有效地分割目标和背景,实现了车牌的准确定位。     

SVM决策树在沉积微相识别中的应用

支持向量机(SVM)作为统计学理论最年轻的分支,其应用日益广泛。针对油层沉积微相的多类识别问题,可采用支持向量机和决策树相结合的方法。对传统的SVM决策树进行改进的基础上,在SVM核函数选取过程中,构造了与实际问题有关的核函数。此方法有效的降低了支持向量机的设计难度,同时提高了识别精度和泛化能力。最后用实例对比神经网络验证了该方法的优越性。     

论我国信息资源管理制度的变革

信息资源管理制度由非正式制度、正式制度和实施机制3个部分构成。我国信息资源管理制度的创新和变迁已势在必行,其变革的主要内容是：信息文化的良性发展、信息法规政策的加速制定、实施机构的变革与整合、标准规范体系的构筑、政府信息公开和信息共享机制的构建。     

世界女子硬地网球单打综合实力评价与回归模型预测分析

本文主要运用文献资料法、数理统计法对2018-2021美国网球公开赛64强及之后的比赛共252场比赛技战术指标的原始数据进行研究,共提取出相持能力因子、发球得分效率因子、稳定性因子、破发能力因子4个共性因子,建立对世界女子硬地网球综合能力评价的模型;又以总得分为因变量,各技战术指标为自变量,构建多元线性回归预测模型,测得R值为0.977,方程拟合度较高,并将选手原始数据与预测值进行T检验,P=0.363>0.05,证明方程预测准确性准确度较高;通过对因子分析和回归方程模型的结果来看,跑动距离以及一发得分率对于世界女子总得分影响较大。     

谈利用古籍丛书的若干问题

从利用古籍丛书判断难、查找难、选择难这三方面阐述其存在的问题,探讨了在开发管理古籍丛书的工作中需重点突出的若干方面.     

退役运动员就业质量影响因素的实证研究

提高退役运动员就业质量对促进运动员全面发展、建设体育强国至关重要。基于微观调查数据,利用最小二乘回归和无条件分位数回归等方法,系统分析退役运动员就业质量的影响因素。研究发现,人力资本、社会资本和心理资本等显著促进了退运动员就业质量的提升,其中,社会资本的促增效应最强,心理资本次之,人力资本最弱;人力资本、社会资本和心理资本对退役运动员就业质量各维度的影响存在差异。退役运动员就业质量影响的异质性分析结果显示,伴随着就业质量水平的提高,退役运动员人力资本、心理资本的影响效应愈加强烈,“强关系”社会资本的影响效应逐渐减弱。基于研究结果, 提出了确立“更高质量就业”的运动员保障政策目标靶向,加强退役运动员人力资本、社会资本和心理资本建设和劳动合法权益保护,实现退役运动员更高质量就业的政策建议。     

Heteroheptacene-based acceptors with thieno[3,2-b]pyrrole yield high-performance polymer solar cells

Rationally utilizing and developing synthetic units is of particular significance for the design of high-performance non-fullerene small-molecule acceptors (SMAs). Here, a thieno[3,2-b]pyrrole synthetic unit was employed to develop a set of SMAs (ThPy1, ThPy2, ThPy3 and ThPy4) by changing the number or the position of the pyrrole ring in the central core based on a standard SMA of IT-4Cl, compared to which the four thieno[3,2-b]pyrrole-based acceptors exhibit bathochromic absorption and upshifted frontier orbital energy level due to the strong electron-donating ability of pyrrole. As a result, the polymer solar cells (PSCs) of the four thieno[3,2-b]pyrrole-based acceptors yield higher open-circuit voltage and lower energy loss relative to those of the IT-4Cl-based device. What is more, the ThPy3-based device achieves a power conversion efficiency (PCE) (15.3%) and an outstanding fill factor (FF) (0.771) that are superior to the IT-4Cl-based device (PCE = 12.6%, FF = 0.758). The ThPy4-based device realizes the lowest energy loss and the smallest optical band gap, and the ternary PSC device based on PM6:BTP-eC9:ThPy4 exhibits a PCE of 18.43% and a FF of 0.802. Overall, this work sheds light on the great potential of thieno[3,2-b]pyrrole-based SMAs in realizing low energy loss and high PCE.     

Dissolution-precipitation growth of uniform and clean two dimensional transition metal dichalcogenides

Two dimensional transition metal dichalcogenides (TMDCs) have attracted much interest and shown promise in many applications. However, it is challenging to obtain uniform TMDCs with clean surfaces, because of the difficulties in controlling the way the reactants are supplied to the reaction in the current chemical vapor deposition growth process. Here, we report a new growth approach called ‘dissolution-precipitation’ (DP) growth, where the metal sources are sealed inside glass substrates to control their feeding to the reaction. Noteworthy, the diffusion of metal source inside glass to its surface provides a uniform metal source on the glass surface, and restricts the TMDC growth to only a surface reaction while eliminating unwanted gas-phase reaction. This feature gives rise to highly uniform monolayer TMDCs with a clean surface on centimeter-scale substrates. The DP growth works well for a large variety of TMDCs and their alloys, providing a solid foundation for the controlled growth of clean TMDCs by the fine control of the metal source.     

钼镍催化剂催化合成溴代正辛烷

以正辛醇和氢溴酸为原料,钼镍粉做催化剂,合成了溴代正辛烷。经实验确定反应条件为:n(氢溴酸)/n(正辛醇)=3.0,催化剂用量为反应物总质量的3%,反应时间2.5h,反应温度128~133℃,溴代正辛烷产率为87.6%,催化剂重复使用,催化活性基本不变。     

胡适部分手稿书信的重新发现

2000年夏季，北京大学图书馆在整理旧藏胡适藏书时，发现了部分胡适手稿和往来书信，本文追溯了当年胡适留在大陆藏书的来龙去脉，对这些“重新发现”的资料进行了介绍，同时对北京大学图书馆藏有关胡适资料的整理利用提出了建议。