自适应聚类视角下学科领域主题分析——以物流学科为例

基于改进关键词重要性和近邻传播聚类算法,提出了一种学科领域主题分析方法,通过词频分析法和作者潜意识行为计算高频关键词权重,借助共词分析和Ochiai系数构建带权重高频关键词相似性矩阵,利用近邻传播聚类算法对学科领域主题进行自适应提取与分析。以CSSCI收录的2015—2019年物流学科领域期刊论文为研究对象,借助新方法对其进行主题分析,研究结果表明:高重要性的关键词不一定是核心主题,核心主题与同一簇内其它成员关键词最为相似。与此同时,近五年物流学科存在“降本增效”“区域物流一体化”“现代物流技术研究与创新”“物流体制改革与产业转型升级”“农村物流与农产品物流”“电子商务与跨境电商”“可持续发展理念”等七大热门主题。     

中国货币政策传导机制分析——利率渠道的实证分析

市场经济条件下，在发达的货币市场和有效的金融机制基础上，货币政策主要通过利率、汇率、非货币资产和信贷传播四条途径影响宏观经济总量。本文重点通过对利率传导渠道的实证分析，说明中国由于利率管制等方面对货币政策传导的阻滞作用，中央银行的货币政策意图不能有效地指导实体经济，进而对疏导货币政策的传导机制提出对策建议。     

网络段子:微传播时代的全民狂欢

藉由"微媒介",网络段子作为新媒体写作家族的成员,因其短小精悍、发表无限制、娱乐性强的特征,契合了当下快节奏的生活,迅速形成全民写作热潮。它直面现实,消解权威,颠覆传统,调侃生活,娱乐大众,成为微传播时代大众精神消费的狂欢。     

Granular institutional investors and global market interdependence

We study the propagation of global investment risk across markets through the granular view of institutional investors. Applying the conditional value-at-risk estimation to micro-level weekly observations of international mutual funds between 2003 and 2011, we find that idiosyncratic shocks to large institutional investors explain both aggregate market risk and cross-market risk interdependence. Conditional on the US capital markets being in financial distress, idiosyncratic shocks to the top 10% largest funds investing in the US explain about 40% of the risk fluctuations in other non-US markets. The findings are also economically and statistically significant for the top largest funds investing in non-US markets, with the effects becoming especially large during the global financial crisis of 2007–09. These results are robust after controlling for common risk factors and applying alternative measures of idiosyncratic shocks.     

视距传播中地面起伏对传播中值衰减的影响

电波在以视距传播方式进行传播时,在低空大气层中还要受到地面的影响。文中具体分析了视距传播下几种传播模型中地面起伏对电波传播衰减中值的影响,并进行了相应的计算,最后给出相应地面起伏度与传播衰减中值之间的关系。     

卷丹百合组培快繁技术的研究

以卷丹百合珠芽为实验材料,以MS为基本培养基,对其组培快繁进行了研究,结果表明,适宜的小鳞茎诱导培养基为MS 1.0mg/LNAA 0.5mg/L6-BA 0.1mg/LKT;适宜的增殖培养基为MS 2mg/LNAA 0.5mg/L6-BA 0.1mg/LKT;适宜的生根培养基为1/2MS 0.2mg/LIBA;诱导和快繁适宜的条件为光照16h/d,温度(25±1)℃。     

移动通信无线覆盖均匀性分析

本文分析了移动通信系统中电波传播对覆盖均匀性的影响。通过典型路径传播损耗和移动通信系统同频干扰的分析，给出了衡量覆盖均匀性的性能指标。计算机模拟表明了覆盖均匀性与覆盖模式的关系。     

Introducing errors in progress ratios determined from experience curves

Progress ratios (PRs) derived from historical data in experience curves are used for forecasting development of many technologies as a means to model endogenous technical change in for instance climate–economy models. These forecasts are highly sensitive to uncertainties in the progress ratio. As a progress ratio is determined from fitting data, a coefficient of determination R² is frequently used to show the quality of the fit and accuracy of PR. Although this is instructive, we recommend using the error σ_PR in PR, which can be directly determined from fitting the data. In this paper we illustrate this approach for three renewable energy technologies, i.e., wind energy, bio-ethanol, and photovoltaics.     

An Exploratory analysis of flight delay propagation in China

Delay propagation is the flight departure delay caused by the arrival delay of pre-segment flight. Chinese airline market has suffered very poor on-time performance (OTP) in recent years. It is, however, unclear whether delay propagation prevails as one major source for such problem. This study first aims to empirically quantify delay propagation in the Chinese airline market. Specifically, we shed light on heterogenous levels of delay propagations across different airports and airlines. Then, the distinct delay propagation patterns in China are also discussed and compared with other developed airline markets (e.g., the US and Europe). Our estimation is based on OTP data for over 12 million Chinese flights covering the 2015–2017 period. Specifically, it is found that 10 min arrival delay of pre-segment flight within 1 hr before the departure lead to an average of 7.49 mins delay propagation for subsequent departure flight. Arrival delay of earlier pre-segments (1–2 and 2–3 hr before the departure) leads to much less delay propagation, due to longer ground buffer. Chinese airlines arrange longer ground and flight buffer than that of the US airlines to prevent the delay propagation from accumulating along the subsequent flights in a day. Thus, unlike the US market, delay propagation is not the major reason for poor OTP in China. In addition, delay propagation is less prevailing at the Chinese hub airport. This is because China has relied on point-to-point network, which does not require sophisticated schedule coordination. And the local passengers at these Chinese hub airports have higher time value such that the Chinese airlines also try to improve OTP at these hub airports to better serve these lucrative but time-sensitive local passengers. Unlike the European LCCs, Spring Airlines, the largest low-cost carrier (LCC) in China, outperforms major full-service carriers (FSCs) in controlling delay propagation. This finding may also apply to other Northeast Asian LCCs sharing common operational characteristics as Spring Airlines. Last, we find that airlines purposely tolerate moderate departure delays of up to 15 min, which is the threshold that defines delays, no matter whether the pre-segment flight arrives late or on-time. The relevant policy and managerial implications are also discussed.     

战场环境中的电波传播模型优化选择方法

针对战场级的复杂电磁环境仿真过程中涉及到全频段覆盖、环境影响、仿真速度要求高等问题,提出了一种综合考虑用频装备、环境信息和模型自身特点的电波传播模型选择方法。该方法首先通过频段对用频装备及电波传播模型进行划分,再结合环境信息中降雨量、海拔、植被覆盖率、气候类型、导电特性等参数进行综合分析,最终得到传播模型的优化选择方案。在典型作战场景仿真应用中,该方法为传播模型的合理选择提供了思路,保证了仿真的精度,同时也为电磁环境仿真中传播模型本地化提供了依据。