Measurement of Foreign Exchange Reserve Risk in China—Based on VaR-GARCH Model

外汇储备管理问题一直以来都是国内外学术界十分关注和着力研究的热点和前沿问题。我国外汇储备自1994年以来出现了持续、快速、大幅度增长，特别是2001年以来，储备规模从1655.74亿美元激增至2013年的38213.15亿美元，10年来外汇储备增长了近20倍，其中仅2007年一年就创纪录地增长了4619.05亿美元，相当于每天增长12.65亿美元。外汇储备规模的持续增长，给各国管理当局带来了新的挑战。面对如此巨额的外汇储备资产，国家货币管理当局应该如何管理和安排，才能兼顾外汇储备的安全性、流动性和盈利性，避免给国家带来巨额的资源浪费、财富损失和风险，是目前外汇储备管理面临的重大难题。本文采用V...Foreign exchange reserve management problem has always been the research hotspot and frontier problem in domestic and foreign academic circles. Chinese foreign exchange reserve increased rapidly and substantially since 1994, especially since 2001, Chinese foreign exchange reserve surged from $165.574 billion to$ 3.821315 trillion, the foreign exchange reserves has increased by nearly 20 times in ...学位：经济学硕士院系专业：经济学院_国际金融学学号：1562011115196

内蒙古26种常见温带灌木的生物量模型

生物量模型是估算灌木生物量的重要方法之一,本文采用4种数学模型(一元线性模型、二元线性模型、对数模型、幂函数模型),3个预测变量株高(H)、冠幅(C)、植株体积(V)对内蒙古地区26种常见温带灌木进行生物量方程的拟合,同时比较不同生境类型间灌木根冠比的差异。结果表明:①最优生物量方程以幂函数模型和一元线性函数模型为主,最佳预测变量以冠幅(C)和植株体积(V)为主。②有17种灌木不同器官最优生物量方程的形式和预测变量相同,表明物种内的生物量方程形式具有一定的一致性;但各器官生物量方程的系数又各不相同,因此分种进行不同器官生物量的拟合可以更准确地估算生物量。③草地灌木和山地灌木的根冠比显著大于荒漠灌木的根冠比。通过建立分种分器官的生物量估算模型,可以为内蒙古地区灌木生物量的计算以及灌丛生态系统碳库的估算提供便利

种植密度对苜蓿生长及生物量的影响

种植密度作为影响作物产量和品质的重要因素,会造成植物对于光照、水分和养分的竞争。为研究种植密度对苜蓿生长与产量的影响,在日光温室环境下,以紫花苜蓿(Medicago sativa)为材料,设置25、100、400、800、1 500、2 000株·m~(–2),共6个种植密度,对紫花苜蓿的种群密度和生长状况进行了观测。结果表明,各处理播种后15天的平均种植密度分别为25、100、373、745、1 255、1 938株·m~(–2);随着紫花苜蓿的生长,除了低密度(25、100株·m~(–2))处理没有发生植株数量的变化外,其余4个密度处理植株数量均有所减少,即发生不同程度的自疏,至第二茬收获时(播种后第187天)种群数量分别减少为297、571、759、839株·m~(–2)。植株个体的株高、基径和分枝数量随着现存密度的增加呈指数下降;个体生物量与现存密度的关系满足竞争密度效应的幂函数关系,即随着密度的增加而减小。紫花苜蓿单位面积地上生物量符合最终产量恒定法则,然而,随着密度的增加,地下生物量有先增加后减小的趋势

脂肪酶Lipozyme TL IM水解金枪鱼油工艺优化 及其脂质分析Porcess optimization of lipase Lipozyme TL IM hydrolysis of tuna oil and its lipid analysis

旨在为Lipozyme TL IM在鱼油脂质改性及相关功能性产品的研发和应用提供参考，以金枪鱼油为原料，采用固定化脂肪酶Lipozyme TL IM对其进行水解，并分离改性水解甘油酯。采用单因素试验研究了pH、水油比（质量比）、水解温度和水解时间对金枪鱼油水解度的影响，确定了适宜的水解工艺参数，并分析了不同水解度下（20%~50%）改性水解甘油酯的脂肪酸组成、结构、热稳定性和氧化稳定性。结果表明：Lipozyme TL IM水解金枪鱼油的适宜工艺参数为pH 6.0、水油比 3∶ 1、水解温度40 ℃、酶添加量5%（以鱼油质量计），在此条件下水解30、60、80、120 min可分别得到水解度为20%、30%、40%和50%的改性水解甘油酯；随着水解度的增加，所得改性水解甘油酯的多不饱和脂肪酸含量增多，饱和脂肪酸含量减少，结构改变，热稳定性和氧化稳定性变差。综上，可采用Lipozyme TL IM对金枪鱼油进行水解以富集多不饱和脂肪酸，为后续产品开发提供特异性底物。In order to provide a reference for the research and application of Lipozyme TL IM in the modification of fish oil and related functional products, tuna oil was used as raw material, and the immobilized lipase Lipozyme TL IM was used for hydrolysis, and the modified hydrolyzed glycerides were separated. The effects of pH, water-oil ratio (mass ratio), hydrolysis temperature and hydrolysis time on the degree of hydrolysis were studied by single factor experiments, and the appropriate hydrolysis process parameters were determined. In addition, the fatty acid composition, structure, thermal stability and oxidation stability of the modified hydrolyzed glycerides under different degrees of hydrolysis (20%-50%) were analyzed. The results showed that the suitable process parameters for hydrolysis of tuna oil by Lipozyme TL IM was pH 6.0, water-oil ratio 3∶ 1, hydrolysis temperature 40 ℃ and lipase dosage 5% (based on mass of tuna oil). Under these conditions, after hydrolysis for 30, 60, 80 min and 120 min, the modified hydrolyzed glycerides with hydrolysis degrees of 20%, 30%, 40% and 50% were obtained, respectively. With the increase of the hydrolysis degree, the polyunsaturated fatty acid content of modified hydrolyzed glycerides increased, the saturated fatty acid content decreased, the structure changed, and the thermal stability and oxidation stability deteriorated. In conclusion, Lipozyme TL IM can be used to hydrolyze tuna oil to enrich polyunsaturated fatty acids, and provide specific substrates for subsequent product development

Measurement of integrated luminosity of data collected at 3.773 GeV by BESIII from 2021 to 2024

We present a measurement of the integrated luminosity e+e- of collision data collected by the BESIII detector at the BEPCII collider at a center-of-mass energy of Ecm = 3.773 GeV. The integrated luminosities of the datasets taken from December 2021 to June 2022, from November 2022 to June 2023, and from October 2023 to February 2024 were determined to be 4.995±0.019 fb-1, 8.157±0.031 fb-1, and 4.191±0.016 fb-1, respectively, by analyzing large angle Bhabha scattering events. The uncertainties are dominated by systematic effects, and the statistical uncertainties are negligible. Our results provide essential input for future analyses and precision measurements

Determination of the number of ψ(3686) events taken at BESIII

The number of ψ(3686) events collected by the BESIII detector during the 2021 run period is determined to be (2259.3±11.1)×106 by counting inclusive ψ(3686) hadronic events. The uncertainty is systematic and the statistical uncertainty is negligible. Meanwhile, the numbers of ψ(3686) events collected during the 2009 and 2012 run periods are updated to be (107.7±0.6)×106 and (345.4±2.6)×106, respectively. Both numbers are consistent with the previous measurements within one standard deviation. The total number of ψ(3686) events in the three data samples is (2712.4±14.3)×10^