Synchronization and diversity in business cycles: a network analysis of the European Union

In this article, we use a correlation matrix and its internal networks to analyse business cycle synchronization across Europe since 2000. This methodology allows us to summarize individual country interactions and co-movements while also capturing the existing heterogeneity of connectivity within the European economic system. Our results indicate that synchronization of the euro zone countries remained stable from 1999 until the current financial crisis, after which co-movements increased sharply and synchronization rose to the highest in the time sample. By endogenously identifying clusters of countries with close connections in their business cycle, we also refute the commonly accepted notion of identifiable core and peripheral euro zone countries.     

一种适用于宽带短波通信OFDM系统符号定时同步的新方法

针对宽带短波通信正交频分复用（OFDM）系统,提出了一种不需要数据辅助的高效符号定时同步方法。该方法利用OFDM符号中的空载波不传输任何数据这一特性,通过最小化空载波上的数据能量来将符号定时点锁定在安全区域内,从而完成符号定时同步。该方法可以有效对抗多径效应,适用于短波通信系统。最后将该方法与Al-Dweik同步方案在宽带短波信道条件下进行了仿真对比,结果表明该方法有着更精确的符号定时同步性能,并且适用于各种星座图调制。     

叠加共轭对称训练序列的OFDM系统时频同步方法

针对正交频分复用（OFDM）系统对同步错误率和频率偏移敏感的问题,提出了一种叠加共轭对称训练序列的OFDM系统时间和频率同步方法。该同步方法将快速傅里叶逆变换（IFFT）调制后的序列构成具有共轭对称特性的训练序列,并叠加到OFDM数据符号上;在接收端,利用叠加训练序列和融合循环前缀信息来获取OFDM系统同步信息。理论分析和仿真表明：在信噪比为5 dB时,该同步算法定时同步正确概率已接近100%;在信噪比为4 dB时,频偏估计精度可以达到10-4;该同步算法不仅具有更好的同步性能,而且节省系统的有效带宽以及降低系统的计算法复杂度。     

New Product Introduction and Seasonality Effect in Food Products Retailing

ABSTRACT

This study aims to measure the effects of market demand and seasonality on new product introduction. Major factors contributing the variability of market demand and seasonality of new products have been discussed in reference to timing of introducing new products, variability of consumer preferences, retail sales, and product promotion. The study is based on 243 new products in selected self-service stores in Mexico, which belong to major food products sectors for the reference period 2002–2006. Results of the study reveal that market demand and seasonality factors are most important for the timing of new product introductions, as such conditions determine success of the new products in a given market.     

一种改进的LTE系统下行同步算法

LTE（Long Term Evolution）系统中,作为小区搜索的第一步,符号定时算法需要具备很强的鲁棒性。为了进一步增强现有符号同步算法的抗频偏性能,提出了一种优化的符号同步算法。该算法一方面保持已有分段相关同步算法的优点,同时考虑结合预频偏处理来进行符号定时与粗频偏的联合估计,再将多个相关运算集做叠加处理。理论分析和仿真实验结果表明,在多径信道下,所提算法在完成符号定时和粗频偏估计的同时,大大提高了系统抗频偏性能。     

装载机装运机构改进设计

全液压蟹爪式装煤机的侧取耙装机构与刮板运输机串联工作,共用一套传动装置,但不能适应作业现场实际需要.为此,重新设计装运机构,将装载与运输机构设计为联动机构,让其既可各自独立运转,也可根据需要联合作业,同步工作.2套独立的动力装置能够保证2个机构可靠运转.     

股票网络平台中的噪音会影响股价同步性吗*

股价同步性是衡量资本市场信息效率的重要指标。股价同步性的影响机制一直以来都是金融研究的热点问题。本文使用文本分析的方法,通过机器学习度量了东方财富股吧中股民发帖评论中的非理性噪音,检验了股票网络平台中的噪音与股价同步性之间的关系。研究发现：第一,股票网络平台中的噪音会促使投资者做出非理性的投资决策,进而降低股价变动的同步性。噪音评论占全部评论的比例越高,上市公司的股价同步性越低,而且两者之间呈现倒U型的非线性关系。第二,公司个股新闻与公告数量的增加、分析师关注度的提高与外部审计质量的提升,均可以减弱股票网络平台中的噪音对股价同步性的影响。本文关注网络新媒体中的噪音对股价同步性的影响,研究结论对于监管部门加强网络信息监测以及上市公司进一步完善信息披露渠道具有现实意义。     

C-RAN协作通信系统中基于正交预编码的同步算法

在C-RAN(Centralized,Cooperative,Cloud RAN)无线网络架构中,协作多点传输受到符号定时偏差和载波频率偏差的影响。为了降低联合传输协作系统对异步信号的敏感性,将正交预编码的同步算法应用到联合传输协作系统中。首先,发射机发送经过重复编码和正交预编码矩阵处理后的数据信息;然后,接收机利用特定的接收矩阵,实现分离相互叠加的异步协作信号;最后,完成对协作信号载波频率偏差和符号定时偏差的估计和补偿。理论分析和仿真结果表明：该方法能够有效解决协作传输中信号异步问题,改善系统性能。     

一种OFDM系统中频率同步的改进算法

针对传统的频率同步方法中估计精度与估计范围的矛盾,提出了一种改进的频率同步算法。该算法通过两次频率偏移估计,可以同时获得大的估计范围和高的估计精度,而且对训练序列没有其他限制,可以提高系统数据传输效率。通过仿真,验证了该算法的有效性。     

Estimating portfolio risk for tail risk protection strategies

We forecast portfolio risk for managing dynamic tail risk protection strategies, based on extreme value theory, expectile regression, copula‐GARCH and dynamic generalized autoregressive score models. Utilizing a loss function that overcomes the lack of elicitability for expected shortfall, we propose a novel expected shortfall (and value‐at‐risk) forecast combination approach, which dominates simple and sophisticated standalone models as well as a simple average combination approach in modeling the tail of the portfolio return distribution. While the associated dynamic risk targeting or portfolio insurance strategies provide effective downside protection, the latter strategies suffer less from inferior risk forecasts, given the defensive portfolio insurance mechanics.