重叠滤波多音系统的频偏性能分析及优化

重叠滤波多音(O-FMT)是针对滤波多音(FMT)系统频谱利用率低的缺点而根据超奈奎斯特(FTN)概念引入子载波重叠得到的方案。鉴于O-FMT系统在频偏环境下的性能缺陷，理论分析了频偏对系统信号各部分的影响，比较了O-FMT与正交频分复用（OFDM）系统的抗频偏性能。针对频偏性能优化问题，提出了基于最佳线性无偏估计（BLUE）的改进盲估计算法，设计了基于频域滤波器系数的内嵌结构进行频偏补偿。仿真实验表明，O-FMT相比OFDM具有更好的抗频偏能力，改进的盲估计算法估计值精度更高，抗干扰、抗衰落能力更强，设计的频偏补偿结构可以使系统获得更好的性能。     

网购市场鱼龙混杂现象的经济学解释：基于二维不对称信息的视角

网络购物市场存在商品鱼龙混杂的典型现象：高价格的商品不一定高质量，低价格的商品也不一定低质量，表现出明显的信息不对称特征。文章基于网络购物市场所存在的两个维度不对称信息的特征事实，即厂商在产品质量与产品生产成本两个方面拥有私有信息，通过构建二维不对称信息的分析框架，从市场均衡的视角首次解释了上述现象的经济机理。分析表明，由于二维不对称信息的存在，消费者和厂商决策的互动过程使得市场上产品价格与质量不再具有单调递增关系，从而网络购物市场可能出现鱼龙混杂的市场均衡，文章证明了这一均衡在合理的条件下是存在的。文章通过比较静态分析考察了市场环境的变化如何影响商品质量的价格信号显示效率以及消费者购买行为，并考察了网络购物行业商家披露信息、消费者对于商家的反馈评分机制和保证退货等手段对于消除商品鱼龙混杂现象的有效性，为进一步规范发展我国网络购物行业提供了参考。     

一种改进的CPFSK信号频率估计方法

针对突发信号解调中多普勒频偏大的问题，提出了一种改进的连续相位移频键控信号(CPFSK)频率估计方法。首先接收信号平方运算使信号的调制指数加倍，再通过一次离散傅里叶变换(DFT)，用搜索信号平方谱谱峰的方法实现突发信号频率估计。仿真实验表明，在低信噪比条件下，该算法的频率估计精度比经典的相位差频率估计算法提高了20%；该算法与广泛用于高动态突发信号的频率插值估计算法相比，同道干扰信道下信干比改善可达4 dB，DFT长度缩短约1/3。     

Measuring the effectiveness of US monetary policy during the COVID-19 recession

The COVID-19 recession that started in March 2020 led to an unprecedented decline in economic activity across the globe. To fight this recession, policy makers in central banks engaged in expansionary monetary policy. This paper asks whether the measures adopted by the US Federal Reserve (Fed) have been effective in boosting real activity and calming financial markets. To measure these effects at high frequencies, we propose a novel mixed frequency vector autoregressive (MF-VAR) model. This model allows us to combine weekly and monthly information within a unified framework. Our model combines a set of macroeconomic aggregates such as industrial production, unemployment rates, and inflation with high-frequency information from financial markets such as stock prices, interest rate spreads, and weekly information on the Fed's balance sheet size. The latter set of high-frequency time series is used to dynamically interpolate the monthly time series to obtain weekly macroeconomic measures. We use this setup to simulate counterfactuals in absence of monetary stimulus. The results show that the monetary expansion caused higher output growth and stock market returns, more favorable long-term financing conditions and a depreciation of the US dollar compared with a no-policy benchmark scenario.     

张力控制系统在变频造纸设备中的应用研究

张力控制在变频造纸设备中的应用是造纸业的控制难题。本文构建了变频造纸设备张力控制系统模型,通过张力检测装置采集张力值,经PLC接收和判定,最终组成了直接张力控制系统,有效地保证了张力的恒定。同时采用Simulink工具箱,模拟和分析了Matlab软件环境下张力控制系统的仿真运行,最终证实了张力控制系统在变频造纸设备应用中的可行性,为张力控制系统的后续研究与发展指明了方向。     

校园购物网的营销策略探讨

信息时代,网络已经深深改变了传统社会中人们的生活方式和工作方式,大大提高了人们获取和传递信息的能力。在如今的大学校园,网上购物已成为了当代大学生课余生活的一大热门。校园网的高速、快捷为校园购物网站的建设提供了得天独厚的条件。如何在拥有广大消费群体和消费潜力的校园市场,开辟出一片符合大学校园的电子商务市场,建立一个基于校园网的经济、实用、高效、稳定的校园购物网站,是当前亟待解决的问题。本文通过对校园网站营销进行探讨和研究,提出了相应的营销策略,以期能对校园购物网的发展起到一定的借鉴作用。     

变频器内建PLC在上料机改造中的应用

结合青海百通公司的高炉情况,设计出了上料机改造方案。介绍了台达变频器在高炉卷扬调速系统中的应用情况,给出了电气原理图、注意事项和常见故障处理。实际应用的良好效果验证了该系统的稳定性和可靠性。     

The impact of reverse logistics process coordination on third party relationship quality: A moderated mediation model for multichannel retailers in the fashion industry

Multichannel retailing is a widely adopted strategy in the fashion industry. Companies in this industry find it a source of competitive advantage to invest in reverse logistics infrastructure. However, limited empirical studies investigate the enablers of the relationship quality between the retailers and their reverse logistics service providers. This study quantifies the impact of reverse logistics process coordination between retailers and logistics service providers on relationship quality. Moreover, it tests the mediating role of reverse logistics service quality and the moderating role of conflict frequency in this relationship. Data were collected through a survey using a purposive sample of 241 retail store managers from the fashion retail industry of Pakistan. For this purpose, a self-administered questionnaire was developed using a five-point Likert Scale to gauge the responses. Conditional process analysis was used to evaluate the moderated mediation model. The findings showed a significant positive impact of reverse logistics process coordination on the relationship quality with a logistics service provider, a significant positive mediation effect of reverse logistics service quality, and a significant moderation effect of conflict frequency on the indirect relationship. However, conflict frequency, contrary to the hypothesis in the study, strengthened the indirect relationship. Furthermore, the moderation effect of conflict frequency on the direct relationship was insignificant. This study will help managers better understand the best practices leading to effective management of reverse logistics processes, particularly product returns.     

How to increase multichannel shopping satisfaction? An adapted Kano based stage-gate approach to select new technologies

Today, brick-and-mortar retailers with integrated online shops have many alternatives to increase their customers’ shopping satisfaction: They could invest in (for the retailers) new physical store technologies (e.g., beacons or magical mirrors if not implemented up to now), new online shop technologies (e.g., visual tagging or webcams), or in new less technology-based improvement options (e.g. events or product testing). We propose an adapted Kano based stage-gate approach to support multichannel retailers confronted with such selection problems. The approach is applied to a major European sporting goods retailer. 37 improvement options are pre-selected and evaluated by current and potential customers. It can be shown that instore returns, instore services, reserve&collect, click&collect, customization, product testing, and magical mirrors are drivers of satisfaction for the current customers and should be implemented in contrast to, e.g., geofencing or beacons. The potential customers are more technology-savvy, but show similar categorizations as a current customer segment and so confirm the selection.