Modeling time-varying higher-order conditional moments: A survey

Since the introduction of the Autoregressive Conditional Heteroscedasticity (ARCH) model, the literature on modeling the time-varying second-order conditional moment has become increasingly popular in the last four decades. Its popularity is partly due to its success in capturing volatility in financial time series, which is useful for modeling and predicting risk for financial assets. A natural extension of this is to model time variation in higher-order conditional moments, such as the third and fourth moments, which are related to skewness and kurtosis (tail risk). This leads to an emerging literature on time-varying higher-order conditional moments in the last two decades. This paper outlines recent developments in modeling time-varying higher-order conditional moments in the economics and finance literature. Using the Generalized Autoregressive Conditional Heteroscedasticity (GARCH) framework as a foundation, this paper provides an overview of the two most common approaches for modeling time-varying higher-order conditional moments: autoregressive conditional density (ARCD) and autoregressive conditional moment (ARCM). The discussion covers both the theoretical and empirical aspects of the literature. This includes the identification of the associated skewness–kurtosis domain by using the solutions to the classical moment problems, the structural and statistical properties of the models used to model the higher-order conditional moments and the computational challenges in estimating these models. We also advocate the use of a maximum entropy density (MED) as an alternative method, which circumvents some of the issues prevalent in these common approaches.     

城镇化背景下万年县人口空间分异研究

以江西省万年县近5年的乡镇人口数据为研究对象，利用ArcGIS软件对2013—2017年的人口时空分布进行分析。定量分析万年县地形起伏度与住区空间分布的关系，结合人口密度数据，利用万年县城乡人口空间可视化研究其空间分异，为万年县的人口和资源配置提供信息，促进当地经济社会的发展。     

Option prices for risk-neutral density estimation using nonparametric methods through big data and large-scale problems

Option pricing theory determines the structure of call and put option pricing functions. In nonparametric risk-neutral density estimation based on kernel functions, local constraints cannot induce a second derivative function that must integrate one. Convexity and monotonicity of pricing functions also cannot be enforced. A large-scale (optimization) approach is proposed for the risk-neutral density estimation, imposing an enlarged set of no-arbitrage constraints. We considered simulations using Heston's model and hypergeometric functions. The method is applied to samples of intraday data from VIX and S&P500 indexes.     

阿仑膦酸钠联合唑来膦酸治疗绝经后骨质疏松症患者的临床效果

目的探讨阿仑膦酸钠联合唑来膦酸治疗绝经后骨质疏松症(PMO)患者的临床效果。方法选取新疆克拉玛依市中心医院2017年9月至2020年1月收治的PMO患者122例作为研究对象,随机分为单一用药组和联合用药组,各61例。单一用药组仅采用阿仑膦酸钠治疗,联合用药组采用阿仑膦酸钠联合唑来膦酸方案,比较两组治疗前后骨密度(BMD)、骨源性碱性磷酸酶(BALP)、骨钙素(BGP)及抗酒石酸酸性磷酸酶-5b(TRACP-5b)及不良反应发生情况。结果治疗后,联合用药组股骨颈、腰椎以及Ward’s三角区的BMD明显高于单一用药组,差异有统计学意义(P<0.05);治疗后,联合用药组BALP、TRACP-5b以及BGP明显低于单一用药组,差异有统计学意义(P<0.05);两组治疗期间不良反应发生率比较差异无统计学意义(P>0.05)。结论阿仑膦酸钠联合唑来膦酸能够提高骨质密度,改善骨质代谢,为临床治疗提供了新的治疗方案。     

中国省会城市紧凑程度综合评价

研究目的：基于“紧凑城市”的理念，利用城市建设用地、城市居住用地及工业 — 商业 — 交通用地、人口密度和城市密度4组变量揭示近10年来中国城市土地利用和人口增长态势，并以城市密度的形式对省会城市之间的土地利用和人口发展进行比较分析。研究方法：文献资料法、实证分析法。研究结果：中国省会城市建设用地、居住用地、工业 — 商业 — 交通用地扩张速度惊人，中国省会城市基本上处于工业导向型城市发展阶段。省会城市建设用地人口密度、城市居住人口密度呈下降趋势，城市用地增长速度快于城市人口增长速度。研究结论：结合城市建设用地和城市人口密度，可以将中国省会城市按照特性分为三类，但城市紧凑程度的多样性可能与很多因素相关，未来的研究需要引入更多的变量。     

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.     

水足迹视角下世界主要经济体的水资源利用效率研究

本文利用EORA数据库中水足迹相关数据,测算了2006-2015年46个世界主要经济体的水资源利用效率,研究结果发现:(1)在2006-2015年始终位于前沿面(水资源利用效率值等于1)的国家有阿尔及利亚、埃及、法国、伊拉克、荷兰、尼日利亚、沙特阿拉伯、新加坡、阿联酋、委内瑞拉.(2)澳大利亚、加拿大、捷克、丹麦、芬兰、德国、意大利、波兰、韩国等国家在2006-2015年水资源利用效率相对较低,绿水和蓝水的投入以及非期望产出灰水的无效率值均在0.9以上.因此,水资源利用效率较低的国家需要向水资源利用效率较高的国家学习先进的节水技术和污水治理经验,并因地制宜制定水资源政策.     

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.     

物探技术在矿山地质探测中的应用

随着我国社会和经济的高速发展,对各种矿产资源的使用量持续增加,各种矿山开采工程越来越多。本文将就各种物探技术在矿山地质探测中的应用进行研究,会采用调查、总结、分析和实践验证的方法。通过大量实践研究发现,当前各种物探技术发展非常迅速,这些技术在矿山地质探测中发挥着非常重要的作用,能够在一定程度上提升矿山地质探测工作开展效率和效果。     

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。