一种高负载自重比轻型机械臂的研究

针对现有轻型机械臂负载自重比较小的问题,提出了将微型液压系统作为轻型机械臂直接驱动源的方案。设计了液压驱动轻型机械臂的机械结构,利用Arduino平台搭建了控制系统,提出了控制方法,并进行了实验。实验结果表明:应用微型直驱式液压系统的轻型机械臂负载自重比高,定位准确。     

Rebuilding or refurbishing: Heterogeneity effects of urban renewal strategy

This study investigates the heterogeneous policy effects of urban renewal strategies in shantytown renewal in Beijing. Using the spatial difference-in-difference approach, this study identifies the renewal approaches for each shantytown to analyze how each strategy affects housing prices and population density within the policy target area and surrounding area. The empirical results suggest that current urban renewal actions in Beijing have not achieved the expected policy goals and imply significant heterogeneity between refurbishing and rebuilding shantytowns in improving building value. Rebuilding projects have positive renewal effects and externalities, driving housing prices to increase by 5.86%–7.25% within the shantytown and a 1-km radius. Furthermore, the dynamic analysis shows that these impacts are prolonged, with housing prices maintaining an upward trend for 2–6 years after rebuilding. However, there is no causality between refurbishing dilapidated areas and increasing building values.     

Population density,urbanisation and agricultural mechanisation in modern Ghana

Farmers' technological choices take place within farming systems that are shaped by population pressure, connectivity to urban markets and agro-ecological conditions. The relationship between these drivers and agricultural technology use is ambiguous. On the one hand, population growth can increase the supply of labour, driving down wage rates and reducing the incentives for mechanisation. On the other hand, rural–urban movements of people can reduce rural labour supply while simultaneously driving up the demand for food and hence the demand for mechanisation. Past theories of agricultural mechanisation have explained the low adoption of agricultural machinery in land-abundant cereal production systems of SSA in terms of these drivers. However, recent empirical observations find extensive adoption of mechanised ploughing technology by small, medium and large-scale farmers in Ghana. Examining the Ghanaian experience can thus shed new light on theories of mechanisation. A large household survey dataset covering eight districts is combined with geo-spatial data on population, urban proximity and agro-ecological factors to consider whether the existing theories are able to explain farm-level adoption decisions in this context. The analysis finds that a farmer's decision to use agricultural machinery is associated with lower population density and proximity to urban centres. In northern Ghana, these drivers of technological change are as important as farm household characteristics in understanding cross-sectional patterns of machinery adoption.     

近距离无线电台邻道干扰的功率谱解析

指挥控制系统的无线通信设备数量多、工作频率范围窄，相互之间存在严重的邻道干扰。针对近距离电台间邻道干扰问题，提出了基于功率谱解析的分析方法。首先理论推导了信号原功率谱密度函数与展宽延拓后功率谱密度的严格数学关系，在此基础上研究邻道干扰产生机制，进而分析不同邻道的干扰强度，得到了邻道功率与频率之间的关系式，推导了进入接收机的信干噪比（SINR）；最后，通过仿真验证了所提出的分析方法的可行性。理论计算与仿真结果相差在0.5 dB以内，为进一步有效规划指控系统频谱和提高利用效率提供了重要依据。     

基于纳米金等离子体共振光散射法测定阿米卡星

为简便、快速地对阿米卡星的注射液进行检测,基于纳米金颗粒的等离子体共振效应建立了一种检测阿米卡星的新方法。在适宜pH值的KH_2PO_4-Na_2HPO_4缓冲溶液中,利用阿米卡星与纳米金相互作用,使反应体系在640nm处共振光散射信号显著增强,且共振光散射强度增强值ΔI640nm与阿米卡星质量浓度在1.5~500ng/mL范围内线性相关,检出限为0.52ng/mL。在确定的实验条件下,阿米卡星可诱导纳米金颗粒聚集,纳米金颗粒之间距离的变化使其等离子体共振效应发生明显改变,聚集的纳米金颗粒表面等离子体耦合产生了较强的共振光散射信号,且共振光散射信号增强值与阿米卡星的浓度变化值呈现良好的线性关系。实验表明,该方法可用于快速测定阿米卡星。     

Redevelopment along arterial streets: The effects of light rail on land use change

We use difference-in-differences approaches and parcel-level data from Minneapolis to estimate the effects of light rail on land use change using alternate definitions of treatment area. Results using circular buffers corroborate previous findings that light rail has virtually no effect on land use change in our study area. In contrast, light rail increases the likelihood of land use change along arterial streets that cross the line at station areas. To accurately model the effects of public transit projects on urban land use, one must consider how potential riders access station areas, rather than assuming accessibility improves radially around a station.     

Static and dynamic models for multivariate distribution forecasts: Proper scoring rule tests of factor-quantile versus multivariate GARCH models

Many static and dynamic models exist to forecast Value-at-Risk and other quantile-related metrics used in financial risk management. Industry practice favours simpler, static models such as historical simulation or its variants. Most academic research focuses on dynamic models in the GARCH family. While numerous studies examine the accuracy of multivariate models for forecasting risk metrics, there is little research on accurately predicting the entire multivariate distribution. However, this is an essential element of asset pricing or portfolio optimization problems having non-analytic solutions. We approach this highly complex problem using various proper multivariate scoring rules to evaluate forecasts of eight-dimensional multivariate distributions: exchange rates, interest rates and commodity futures. This way, we test the performance of static models, namely, empirical distribution functions and a new factor-quantile model with commonly used dynamic models in the asymmetric multivariate GARCH class.