基于协同过滤技术的线上课程推荐研究

基于"互联网+"技术的在线学习是一种新的、有效的学习方式,有助于学习者知识技能水平的提高.然而,很多学习者难以在海量网络课程中选择自己真正需要的课程.针对该问题,本文设计了一种基于协同过滤技术的线上课程推荐系统,改进了协同过滤算法的缺陷,为学习者提供有针对性的课程推荐,促进基于"互联网+"技术的人才培养.     

一种超级电容储能的双向逆变电路及其控制策略

为解决数控机床加工中意外掉电退刀、伺服单元外接制动电阻产生能耗等问题,提出了一种超级电容储能的双向逆变电路,使得伺服系统在突然断电状态下,储能模块能够继续短时地给数控机床系统供电,完成断电回退的功能。该电路可以提供更高的输出电压和占空比,且在应用中可以取消伺服单元外接制动电阻而将制动能量循环利用,同时提出了相应的控制策略。该电路包括Buck/Boost电路、信号采样电路、PWM逻辑控制电路和互锁驱动电路,通过调节两路互为180°的PWM波占空比及充、放电信号来实现升、降压闭环控制,从而完成能量的双向传递。该拓扑简单、高效,性能稳定,以最少的功率器件实现大功率转换及输出。最后,实验波形验证了所提方案的可靠性。     

基于卷积长短时记忆网络的心律失常分类方法

心律失常等慢性心血管疾病严重影响人类健康,采用心电信号(ECG)实现心律失常自动分类可有效提高该类疾病的诊断效率,降低人工成本。为此,该文基于1维心电信号,提出一种改进的长短时记忆网络(LSTM)方法实现心律失常自动分类。该方法首先设计深层卷积神经网络(CNN)对心电信号进行深度编码,提取心电信号形态特征。其次,搭建长短时记忆分类网络实现基于心电信号特征的心律失常自动分类。基于MIT-BIH心律失常数据库进行的实验结果表明,该方法显著缩短分类时间,并获得超过99.2%的分类准确率,灵敏度等评价参数均得到不同程度的提高,满足心电信号自动分类实时高效的要求。     

Facet Control for Trap‐State Suppression in Colloidal Quantum Dot Solids

Trap states in colloidal quantum dot (QD) solids significantly affect the performance of QD solar cells, because they limit the open‐circuit voltage and short circuit current. The {100} facets of PbS QDs are important origins of trap states due to their weak or missing passivation. However, previous investigations focused on synthesis, ligand exchange, or passivation approaches and ignored the control of {100} facets for a given dot size. Herein, trap states are suppressed from the source via facet control of PbS QDs. The {100} facets of ≈3 nm PbS QDs are minimized by tuning the balance between the growth kinetics and thermodynamics in the synthesis. The PbS QDs synthesized at a relatively low temperature with a high oversaturation follow a kinetics‐dominated growth, producing nearly octahedral nanoparticles terminated mostly by {111} facets. In contrast, the PbS QDs synthesized at a relatively high temperature follow a thermodynamics‐dominated growth. Thus, a spherical shape is preferred, producing truncated octahedral nanoparticles with more {100} facets. Compared to PbS QDs from thermodynamics‐dominated growth, the PbS QDs with less {100} facets show fewer trap states in the QD solids, leading to a better photovoltaic device performance with a power conversion efficiency of 11.5%.     

考虑封装的SAW谐振式传感器仿真研究

针对小体积射频声表面波(SAW)传感器性能受封装影响大的问题,该文提出了耦合模(COM)模型与三维电磁分析结合的仿真方法。利用COM模型计算出芯片的单端口S参数;使用三维电磁场仿真软件HFSS对表面贴装的陶瓷封装结构进行建模,仿真计算出封装的S参数;对芯片及封装结构S参数在电路仿真软件ADS中进行结合,得出考虑封装的SAW谐振式传感器仿真结果。实验制作了工作在428.5 MHz的SAW单端谐振传感器,采用该文所述方法仿真的理论结果与实验测量结果更接近,验证了上述方法的可行性。     

广电智能网络运营平台建设实践

简要介绍江苏有线建设的广电智能网络运营平台,通过模拟DOCSIS机制实现了FTTH与DOCSIS两种不同接入网的端到端自动装维一致性体验。平台将业务开通系统与BOSS、GIS、用户分析系统、终端质量监测系统、工单系统等进行整合,将业务流程逻辑进行梳理规整,通过数据及流程的标准化、规范化实现了不同业务不同网络的全业务统一开通和运维,并实现了网络资源的全程标准化录入管理,为用户大数据综合分析提供了多维度的全流程数据来源,供网格工程师进行精准主动运维、供市场部门进行精准用户分析。     

Fabrication of novel urchin-like architecture and snowflake-like pattern CuS

The interesting biomimetic morphologenesis of CuS, containing urchin-like architecture and snowflake-like pattern can be separately obtained via heating different solutions. In our case, ethanol or the mixed solvent of ethanol/H₂O containing CuCl₂ and CS₂ as raw materials in the presence of the surfactant additive cetyltrimethylammonium bromide (CTAB) have been used. The products were characterized by various techniques of XRD, SEM and ED. In the process, the solvent medium and the surfactant additive CTAB played very important roles in the formation of different biomimetic morphologies and the formation mechanisms were primarily discussed, respectively.     

多频点同时反演策略在频域全波形反演中的应用和实现

频域全波形反演能够获得高分辨率的反演结果,具有较高的计算效率,因此得到广泛应用.在传统单频点串行反演策略的基础上,提出一种多频点同时反演策略,并推导出一种新的目标函数表达式,应用于频域全波形反演算法中.该策略能够同时反演所有的频率分量,对于一组频点中的每个频点进行加权求和处理,从而避免了高频分量在反演结果中占据主导,同时避免反演结果中存在噪声干扰.分别用三种不同的模型进行验证.实验表明,相对于传统的单频点策略,多频点策略的反演结果具有更好的稳定性、正确性和鲁棒性;而且对于模型中明显介质边界的位置,它的反演结果更接近于目标模型.     

室温快速合成Ag基金属有机骨架材料用于电催化还原CO2

选择具有强给电子能力的1,2,4-三唑为配体,成功合成了银基金属有机骨架材料(Ag-MOF)并用于电催化还原CO₂反应(CO₂RR)。借助粉末X射线衍射、透射电子显微镜、扫描电子显微镜、计时电流法等表征手段对材料的晶体结构、形貌和电催化CO₂RR性能进行了系统的研究。与商品化的纳米Ag颗粒对比,Ag-MOF展现出更优异的电催化CO₂RR产物选择性、催化活性和稳定性,在-0.9 V (vs RHE)时,CO的法拉第效率高达96.1%。当电压为-1.1 V (vs RHE)时,电流密度可达17 mA·cm^-2,且电极可以稳定运行300 min。这说明通过选择合适的配体结构,可以改变催化位点周围的化学环境,从而高效将CO₂转化为目标产物。     

Direct Synthesis of Disubstituted 3-Isoquinolinone Derivatives through the Construction of C−N,C=O,and C(sp2)−C(sp3) Bonds under Transition-Metal-Free Conditions

The efficient three-component cascade coupling reaction of 3-haloisoquinolines, haloalkanes, and sp³-carbon nucleophiles (acetophenone or nitromethane) led to a series of structurally novel 1,2-disubstituted-3-isoquinolinones through the formation of C(sp³)−C(sp²), C−N, and C=O bonds. The NaOAc-promoted reaction described in this work is simple to operate, environment friendly, and highly selective.