辐射板强化喷管换热与红外抑制效果试验研究

试验研究了在发动机喷管中加装金属辐射板前后,喷管壁面温度、热喷流温度与喷管红外辐射特征的变化。结果表明,加装金属辐射板后,热喷流与喷管壁面之间的热量传递显著增强,热喷流中心温度降低,壁面温度明显升高,在90°方向上,热喷流3～5μm波段的红外辐射强度降低了38.5%。文中从热喷流、喷管壁面以及金属辐射板等相关部件的温度变化情况对红外辐射强度的变化原因进行了解释。      

Understanding the variation in estimates of off-farm labour supply elasticities: A meta-analysis

The design of rural development policies and government programmes in support of farm operations and farm households relies on precise estimates of off-farm labour supply elasticities. However, the wide variation in estimates dilutes their power to predict the magnitude of these targeted interventions. We perform a meta-analysis of estimates of off-farm labour supply elasticity to identify systematic factors that influence these estimates. A sample of 137 elasticities is obtained from 43 studies which use data ranging from 1960 to 2012. We examine theoretical assumptions, data availability and empirical specifications, and other study-specific characteristics. Controlling for potential publication bias, we estimate that the elasticity is approximately 0.64 to 0.77. Results of the analysis show that estimates are affected by modelling choices controlling for self-selection and life-cycle elements. However, we found no compelling evidence that study-specific characteristics of off-farm labour supply functions, including various measurements of labour supply, explain variation in the elasticities.     

A re-examination of housing bubbles: Evidence from European countries

This study uses data from six Eurozone countries and the United Kingdom between 1980Q1 and 2018Q4 to examine whether these countries had housing bubbles during the observed period. Whereas typical studies make strictly limited assumptions regarding interest rates, we make an unconventional argument for the necessity of testing the integration relationship between the price–rent ratio and the interest rate reciprocal to determine the existence of housing bubbles. To verify this study’s proposition, two housing bubble indicators were adopted to dynamically examine periods of housing bubbles in European countries by using a series of individual countries and panel data from Eurozone countries. According to the empirical results for individual countries, although the price–rent ratio indicates the occurrence of housing booms in the targeted countries, the evidence for housing bubbles is unclear. The dynamic bubble indicator revealed that housing bubbles occurred in France and Ireland within a short period in 1993Q3 and 2000Q2, respectively. Spain experienced two short-term housing bubbles in 1990Q1 and 2015Q1. The short-term bubbles signify that the housing markets were efficient. Once the price–rent ratio failed to converge toward the nominal interest rate, market traders’ rational behavior can immediately correct the short-term market divergence. The panel data of the Eurozone countries also reveals that simply using the price–rent ratio for examination may underestimate the correction of the housing markets. In conclusion, the results of this study demonstrate the importance of the interest rate in controlling the housing market.     

粮食价格与居民消费价格水平联动效应研究

明晰粮食价格与居民消费价格水平之间的关系意义重大。基于1979—2020年中国粮食价格和居民消费价格水平年度数据,运用向量误差修正模型和Granger因果分析,对粮食价格与居民消费价格水平间的关系进行实证分析。结果表明:短期内,居民消费价格水平对粮食价格的影响远大于粮食价格对居民消费价格水平的影响,居民消费价格水平变动与粮食价格变动之间存在单向Granger因果关系;长期看,两者之间存在双向Granger因果关系。根据研究结论,提出了加强粮食价格和居民消费价格监测、稳定粮食价格水平、加大市场调控等对策建议。     

基于改进的GM_Markon模型对北京创意产业发展的预测

创意产业产值受周边环境因素影响较大，在某些年份甚至出现局部较大畸变，通过相关文献学习，首先通过对灰色模型预测，然后经过残差修正增加模型规律性（采用两次残差累加），最后在残差修正灰色模型基础上应用改进的马尔科夫链提高预测精度，对2005-2014年北京创意产业产值数据验证算法有效性进行研究。此算法优点在于弥补灰色模型数据少，随机性大的缺陷，很好修正畸变数据和提高拟合度。     

一种新的光伏发电预测模型的设计

为了对光伏发电的输出功率进行预测,本文分析光伏发电的影响因素,提出了一种基于太阳辐射功率曲线匹配的预测模型。该模型将历史数据按时段进行分解,查找与当前时段太阳辐射功率曲线最为匹配的数据,以此构建并训练BP神经网络,来预测未来3个小时内的太阳辐射功率,能够较好的实现预测目标。实验结果表明,该模型有较高的精度,可对电网调度起到重要的指导作用。     

基于高光谱卫星影像的清镇市红枫湖水体总磷浓度反演研究

清镇市红枫湖位于贵阳市清镇辖区，东西宽约8 km,南北长约13 km，属于保护级饮用水源地，其中保护区湖域面积约291 km2。为了对宽阔的湖域及流域区域水质进行快速监测分析，利用高光谱卫星影像建立清镇红枫湖水质总磷浓度的反演模型。通过对红波段（670 nm）处的反射率修正和相关系数校正，利用浮点计算过滤主成分冗余数据，在2020年3、4、5月份分别对6个目标区域进行总磷浓度反演并实地采集水体生化参数验证，该水质总磷浓度反演模型精度平均值为84%。基于模型的反演数据基本可用于红枫湖水体总磷浓度时序性变化分析，为水生态环境监测提供有效数据。     

How firm communication affects the impact of layoff announcements on brand strength over time

Firms usually undertake layoffs to improve financial performance. However, layoffs often have negative effects on various stakeholders, including consumers. In this paper, we examine the magnitude and duration of the potential negative effect of layoff announcements on brand strength. We also examine how a firm's communication accompanying a layoff can potentially counteract the observed negative effect of layoff announcements on brand strength. We compare how advertising communication intensity, social media communication (i.e., brand-initiated tweets), public relation (PR) communication, and communication of CSR initiatives moderate the main effect of layoff announcements on brand strength. Using an error correction model and drawing on 366 announcements of layoff events in Germany, this study identifies the magnitude and duration of the main effect. An examination of five years of weekly consumer brand perception data across multiple industries and domestic and foreign firms shows that advertising communication intensity and social media communication amplify the negative impact of layoff announcements on brand strength. Conversely, PR communication and communication of CSR initiatives help mitigate the negative effect. These findings provide guidance on the best way for firms to design firm communication in the context of layoff announcements.     

Rural development in the digital age: Does information and communication technology adoption contribute to credit access and income growth in rural China?

Information and communication technology (ICT) plays an important role in rural livelihoods and household well-being. Therefore, this study examines the impact of ICT adoption on farmers' decisions to access credit and the joint effects of ICT adoption and access to credit on household income using 2016 China Labour-force Dynamics Survey data. Both recursive bivariate probit model and a selectivity-corrected ordinary least square regression model are employed for the analysis. The results show that ICT adoption increases the probability of access to credit by 12.8% in rural China and empowers rural women and farm households in relatively less-developed regions to access credit. ICT adoption and access to credit affect household income differently. ICT adoption significantly increases household income, while access to credit significantly reduces it, primarily because farmers do not use the acquired credit to invest in income-generating farm and off-farm business activities. ICT adoption has the largest positive impact on household income at the highest 90th quantile. Our findings suggest that improving rural ICT infrastructure to enhance farmers' ICT adoption and developing ICT-based financial products to enable households to access sufficient funds can improve rural household welfare.     

一种改进的机载卫通天线跟踪算法

在圆锥扫描实现过程分析的基础上，提出了一种改进的机载卫通天线跟踪算法。结合天线方位、俯仰方向图及其三维重构法，对该跟踪算法进行了理论推导。运用Matlab曲线拟合仿真，给出了天线跟踪调整方向和角度的计算公式，最后分析了实际应用中需要注意的一些问题。飞行试验表明，该改进的圆锥扫描跟踪技术提高了天线伺服系统的跟踪精度和跟踪速度，很好地满足了机载卫星通信的需求。