Time lag characteristics of sap flow in seed-maize and their implications for modeling transpiration in an arid region of Northwest China

Plant capacity for water storage leads to time lags between basal stem sap flow and transpiration in various woody plants. Internal water storage depends on the sizes of woody plants. However, the changes and its influencing factors in time lags of basal stem flow during the development of herbaceous plants including crops remain unclear. A field experiment was conducted in an arid region of Northwest China to examine the time lag characteristics of sap flow in seed-maize and to calibrate the transpiration modeling. Cross-correlation analysis was used to estimate the time lags between stem sap flow and meteorological driving factors including solar radiation（R_s） and vapor pressure deficit of the air（VPD_（air））. Results indicate that the changes in seed-maize stem sap flow consistently lagged behind the changes in R_s and preceded the changes in VPD_（air） both on hourly and daily scales, suggesting that light-mediated stomatal closures drove sap flow responses. The time lag in the maize＇s sap flow differed significantly during different growth stages and the difference was potentially due to developmental changes in capacitance tissue and/or xylem during ontogenesis. The time lags between stem sap flow and R_s in both female plants and male plants corresponded to plant use of stored water and were independent of total plant water use. Time lags of sap flow were always longer in male plants than in female plants. Theoretically, dry soil may decrease the speed by which sap flow adjusts ahead of shifts in VPD_（air） in comparison with wet soil and also increase the speed by which sap flow adjusts to R_s. However, sap flow lags that were associated with R_s before irrigation and after irrigation in female plants did not shift. Time series analysis method provided better results for simulating seed-maize sap flow with advantages of allowing for fewer variables to be included. This approach would be helpful in improving the accuracy of estimation for canopy transpiration and conductance using meteorological measurements.

Monitoring models for base flow effect and daily variation of dam seepage elements considering time lag effect

Affected by external environmental factors and evolution of dam performance, dam seepage behavior shows nonlinear time-varying characteristics. In this study, to predict and evaluate the long-term development trend and short-term fluctuation of the dam seepage behavior, two monitoring models were developed, one for the base flow effect and one for daily variation of dam seepage elements. In the first model, to avoid the influence of the time lag effect on the evaluation of seepage variation with the time effect component of seepage elements, the base values of the seepage element and the reservoir water level were extracted using the wavelet multi-resolution analysis method, and the time effect component was separated by the established base flow effect monitoring model. For the development of the daily variation monitoring model for dam seepage elements, all the previous factors, of which the measured time series prior to the dam seepage element monitoring time may have certain influence on the monitored results, were considered. Those factors that were positively correlated with the analyzed seepage element were initially considered to be the support vector machine(SVM) model input factors, and then the SVM kernel function-based sensitivity analysis was performed to optimize the input factor set and establish the optimized daily variation SVM model. The efficiency and rationality of the two models were verified by case studies of the water level of two piezometric tubes buried under the slope of a concrete gravity dam.Sensitivity analysis of the optimized SVM model shows that the influences of the daily variation of the upstream reservoir water level and rainfall on the daily variation of piezometric tube water level are processes subject to normal distribution.

Impact of time lags on diurnal estimates of canopy transpiration and canopy conductance from sap-flow measurements of Populus cathayana in the Qinghai–Tibetan Plateau

Recently, canopy transpiration （Ec） has been often estimated by xylem sap-flow measurements. However, there is a significant time lag between sap flow measured at the base of the stem and canopy transpiration due to the capacitive exchange between the transpiration stream and stem water storage. Significant errors will be introduced in canopy conductance （gc） and canopy transpiration estimation if the time lag is neglected. In this study, a cross-correlation analysis was used to quantify the time lag, and the sap flowbased transpiration was measured to pararneterize Jarvistype models of gc and thus to simulate Ec of Populus cathayana using the Penman-Monteith equation. The results indicate that solar radiation （Rs） and vapor pressure deficit （VPD） are not fully coincident with sap flow and have an obvious lag effect; the sap flow lags behind Rs and precedes VPD, and there is a 1-h time shift between Eo and sap flow in the 30-min interval data set. A parameterized Jarvis-type gc model is suitable to predict P. cathayana transpiration and explains more than 80% of the variation observed in go, and the relative error was less than 25%, which shows a preferable simulation effect. The root mean square error （RMSEs） between the predicted and measured Ec were 1.91×10^-3 （with the time lag） and 3.12×10^-3cm h^-1 （without the time lag）. More importantly, Ec simulation precision that incorporates time lag is improved by 6% compared to the results without the time lag, with the mean relative error （MRE） of only 8.32% and the mean absolute error （MAE） of 1.48 × 10^-3 cm h^-1.

四川地区精细化降水预报融合订正试验及检验

精细化定量降水网格预报是天气预报业务的重点和难点,基于西南区域智能数值网格模式预报系统(Southwest China WRF-based Intelligent Numeric Grid forecast System,SWC-WINGS)1 km×1 km分辨率的小时降水预报,利用时间滞后和概率匹配方法开展融合订正试验,再利用中国气象局多源融合降水系统(CMA Multi-source Precipitation Analysis System,CMPAS)三源融合降水实况格点数据,对2022年7—8月四川地区的小时降水预报融合订正结果进行检验,并在四川盆地西部一次短时强降水天气过程中进行应用,结果表明:(1)时间滞后集合降水预报相较于模式降水预报,存在小量级预报过度,大量级预报过于保守的问题;(2)时间滞后结合概率匹配的降水预报融合订正方法有效提升了各量级降水预报的TS评分,尤其1~2 h预报时效提升显著,小时雨量超过0.1 mm、5 mm、10 mm和20 mm量级的TS评分平均提升率分别为7.2%、17.2%、28.3%和36.3%;(3)一次短时强降水天气过程的应用结果表明,时间滞后结合概率匹配的融合订正方法对模式小时降水预报有较好的改进效果,尤其对大量级降水预报有较强的订正能力。

具有时滞效应的air2stream河流水温模型及应用研究

高精度河流水温模型对于深入了解水温的时空变化特征和河流生态修复具有重要意义。基于数据驱动的air2stream模型在保证预测精度的同时,避免了计算的复杂性,已成为河流水温模拟常用的模型。由于水的热惯性及水文条件等的影响,河流水温变化往往显著滞后于气温变化,而air2stream原模型并未考虑滞后效应,导致该模型在流量未知情况下实际精度偏低。为解决该问题,采用气温-水温皮尔逊相关系数计算时滞天数,构建具有时滞的air2stream新模型,进一步根据长江中下游地区两个监测站的多年实测数据验证新模型的有效性和稳定性。结果表明:新模型在不引进额外观测数据的条件下具有更高精度且性能更稳定。相比原模型,在两个监测站新模型的均方根误差分别降低约4.29%和5.85%。新模型具有精度高、水文要素需求少的特点,可为长江中下游的水环境影响评价和生态保护提供依据。

机动目标跟踪时滞问题分析

机动目标跟踪结果在时间轴上的滞后问题是当前机动目标跟踪领域的一大难点。产生时滞的情况很多,一般在跟踪初期和发生较大机动的时间段内尤为明显,常常会因此出现误差高峰。如果能有方法抑制或者消除时滞现象,将能显著提高跟踪效果。从仿真实验的结果和现象入手,结合卡尔曼滤波理论、交互式多模型算法和现代神经网络模型对时滞问题进行剖析,根据跟踪各个阶段情况的变化,分析时滞产生的不同原因,并提出可能的解决方法,以期为提高机动目标跟踪效果提供参考。

昼夜温差对乌鲁木齐市慢性肾脏病日住院人次影响的时间序列分析

目的探讨昼夜温差(diurnal temperature range,DTR)影响慢性肾脏病(chronic kidney diseases,CKD)日住院人次的影响。方法收集2019年1月1日至2020年12月31日乌鲁木齐市4所三甲医院、4所二甲医院、1所一甲医院CKD日住院人次数据,同期气象及污染物数据来自于乌鲁木齐市主城区的6个国控监测点,采用分布滞后非线性模型,控制星期几效应、假期效应、长期时间趋势及其它因素,分析DTR与CKD日住院人次的关系。结果CKD日住院人次与DTR(滞后0~21 d)的暴露-反应曲线呈“N”形,CKD患者住院风险随DTR的升高呈先上升后下降趋势。低度和高度DTR对CKD患者住院的影响存在一定的滞后效应,中度DTR对住院影响较小;DTR=5℃时,单日效应出现在第3天[RR=1.081,95%CI(1.020,1.145),P<0.05],最大效应出现在第21天[RR=1.090,95%CI(1.014,1.173),P<0.05];高度DTR=14℃(P_(95))时,单日效应出现在第4天[RR=1.086,95%CI(1.007,1.172),P<0.05],最大效应出现在第5天[RR=1.089,95%CI(1.009,1.176),P<0.05],累积滞后均暂未发现有统计学差异。男性和年龄<65岁的CKD患者更易受到DTR的影响,寒冷季节和四季更替时DTR变化对CKD患者住院的影响更大。结论男性与<65岁CKD患者更易受到DTR的影响,在寒冷季节和四季交替DTR变化时更应重点保护易感人群免受DTR的影响。

空间三站时差定位综合误差仿真分析

平面三站时差定位技术因其无源定位的优势,在多个领域得到了广泛应用。然而,在实际应用中,它会受到系统误差和随机误差的影响,其中系统误差主要源于基站布设的不精确性和信号传播模型的假设不符合实际情况,而随机误差是由信号传播过程中的噪声和环境干扰等不可预测因素引起的。文章首先给出平面三站时差定位误差模型,并进一步分析三站空间时差定位系统误差,以此为基础建立空间三站时差定位误差模型,并给出了定位精度曲线对比结果。

基于分布滞后非线性模型评估气温对缺血性脑卒中发病的影响

目的:探讨气温对居民缺血性脑卒中发病的影响。方法:收集2013-2020年山东生态队列平邑县子队列缺血性脑卒中发病数据及气象数据。采用分布滞后非线性模型(DLNM)分析气温对全人群缺血性脑卒中发病的影响,并探讨不同性别、年龄人群间的差异。结果:2013-2020年共观察缺血性脑卒中病人50427例,纳入缺血性脑卒中发病病人42014例,日均发病数为14例。日均气温与缺血性脑卒中发病人数呈非线性关系。高温与缺血性脑卒中发病人数的增加有关,且高温对其发病存在即刻效应和滞后效应,高温在0~10 d滞后的累积相对危险度(RR)为1.433(95%CI:1.079~1.902)。低温和较低温对于全人群在特定累积时段存在一定保护作用,且随着时间的推移保护作用减弱,低温和较低温在0~10 d滞后的合并RR分别为0.618(95%CI:0.455~0.840)和0.712(95%CI:0.608~0.834)。分层分析结果显示,高温对男性、≥65岁人群缺血性脑卒中发病危害较大,高温累积滞后10 d时,男性组人群缺血性脑卒中发病风险达到最大,RR值为1.678(95%CI:1.193~2.361);年龄≥65岁人群缺血性脑卒中发病在高温当天RR达到最大,RR值为1.523(95%CI:1.203~1.928)。结论:气温与居民缺血性脑卒中发病呈非线性关系,高温会增加居民缺血性脑卒中的发病风险,且累积滞后效应影响较大,居民应提高在高温天气下的自我保护意识。

T=S Model to Simulate Regional Economic Development

This paper proposes a mechanism theory on regional development by using a modified Logistic model. It reveals regional evolution is an integration of fluctuation in temporal dimension and disparity in spatial dimension. T = S model is established by using Logistic model to simulate the growth of per capita GDP in China from 1990 to 1999. The result shows that T=S model accurately simulates the tracks of economic growth.

Investigations on the time evolution of the plasma density in argon electron-beam plasma at intermediate pressure

The time evolution of the argon electron-beam plasma at intermediate pressure and low electron beam intensily was presented.By applying the amplitude modulation with the frequency of 20 Hz on the stable beam current,the plasma evolution was studied.A Faraday cup was used for the measurement of the electron beam current and a single electrostatic probe was used for the measurement of the ion current.Experimental results indicated that the ion current was in phase with the electron beam current in the pressure range from 200 Pa to 3000 Pa and in the beam current range lower than 20 mA,the residual density increased approximately linearly with the maximum density in the log-log plot and the fitting coefficient was irrelative to the pressure.And then three kinds of kinetic models were developed and the simulated results given by the kinetic model,without the consideration of the excited atoms,mostly approached to the experimental results.This indicated that the effect of the excited atoms on the plasma density can be ignored at intermediate pressure and low electron beam current intensity,which can greatly simplify the kinetic model.In the end.the decrease of the plasma density when the beam current was suddenly off was studied based on the simplified model and it was found that the decease characteristic at intermediate pressure was approximate to the one at high pressure at low electron beam intensity,which was in good accordance with the experimental results.

一类具有时滞的COVID-19动力学模型及传播预测

建立可用于COVID-19疫情评估的一类具有时滞的新冠肺炎传播动力学模型(SI 2R模型)。研究利用时滞描述感染者在核酸检测阳性前的潜伏期,考虑防控隔离和医学追踪隔离等隔离措施的效果,将感染者分为两类:一类感染者具有传染能力,另一类感染者由于被隔离其感染能力可忽略不计,构建了SI 2R模型,并详细讨论系统解的存在性、有界性和平衡点的分类,再利用Lyapunov-LaSalle不变性原理证明了平衡点的全局稳定性。以2021年12月15日—2022年1月13日的西安市疫情数据为依据,拟合得到SI^(2)R模型的动力学参数,对西安市COVID-19疫情进行了预测和评估。结果表明,具有时滞的SI 2R传染病动力学模型对疫情的理论估计与西安市疫情的实际情况较为符合,可用于COVID-19传播行为分析,为疫情防控策略的制定提供了理论支持。

基于TDOGM(1,N)灰色模型的高校科研能力预测与滞后效应分析

针对高校人才、经费、平台等科研资源投入与科研产出存在的不平衡现象,提出利用带时滞效应的TDOGM(1,N)灰色模型,对在一定的资源投入下,高校科研能力未来发展趋势进行预测,为高校科学配置投入资源、有效评价科研投入效率提供理论基础。通过研究发现,利用带时滞效应的TDOGM(1,N)灰色模型进行投入与产出关系分析、预测,其精度比传统的OGM(1,N)灰色模型高。同时,预测模型还能充分反映其核心要素存在的滞后效应。

一类时滞无线传感网络病毒传播模型周期解

为预防和应对无线传感网络所面临的安全挑战,提出一类时滞易感-感染-恢复-易感(susceptible-infected-recovered-susceptible,SIRS)无线传感网络病毒传播模型。以免疫期时滞作为分岔参数,利用特征值方法,得到模型局部渐近稳定和产生Hopf分岔的充分条件;运用规范型理论和中心流形定理进一步推导Hopf分岔的性质,并利用一组数值仿真验证研究结果的可靠性。

太湖梅梁湾浊度对风值的时滞性响应研究

基于野外高频同步观测数据,采用风值来定量表征风向风速变化,并利用广义相加模型(GAM)揭示太湖表层和底层浊度对单独风速、综合风值的滞后效应.结果表明:小风状态下(风速<4m/s或风值<3),太湖梅梁湾的浊度较低,随着风速增加,浊度呈持续性增长;随着风值增加,前期浊度呈增长趋势后期逐渐呈平缓趋势;风向的短期变化对浊度的影响较小,单向风的长时间累积对浊度影响较大;表层浊度对单独风速的滞后响应时间是5h45min、对风值的滞后响应时间是1h;而底层浊度对风速和风值的滞后时间分别为7h和2h;说明浊度对风速和风向均存在一定的延迟效应,随着水深的增加,由于地形等其他因素的影响,湖流存在一定垂向切变,风向对浊度变化的影响逐渐减小.该研究结论揭示仅仅研究风速对浅水湖泊的生态系统的影响存在一定不足,风向的影响不容忽视.同时考虑风向和滞后效应的双重作用对富营养化模型精度的提高有着重要影响.

基于光辐射时滞效应的温室番茄蒸腾量模型的构建

【目的】构建基于光辐射时滞效应的温室番茄蒸腾量模型并确定其应用参数。【方法】依据自动连续记录仪实际称重获得的番茄单株小时蒸腾量,分析番茄蒸腾与温室环境因子的时滞关系,构建基于光辐射时滞效应的温室番茄蒸腾量模型,并对模型进行检验。按照模型预测蒸腾量(ET),设置T1(1.0 ET)、T2(1.2 ET)、T3(1.4 ET)3个灌溉处理,研究其对番茄基质含水量、光合作用、叶片解剖结构和干物质积累的影响,对模型应用参数进行求证。【结果】晴天时,光辐射与番茄蒸腾量存在1 h的时滞关系,阴天时无时滞关系。考虑时滞效应有利于提升晴天蒸腾模型的精度,时滞模型标准误差与相对误差分别从无时滞模型的0.1172 mm/h和31.00%降至0.0885 mm/h和23.42%,纳什系数从0.72升至0.84。T3处理番茄的光合能力强于T1、T2处理;T2和T3处理番茄的叶片厚度、栅栏组织厚度、栅海比显著高于T1处理;T3处理番茄的干物质积累量显著高于T1,但与T2间差异不显著。考虑水分利用效率因素认为,T2处理综合最优。【结论】晴天时光辐射时滞效应1 h的温室番茄蒸腾模型误差最小,精度最高;在番茄果实膨大期,模型灌溉参数为1.2。

基于EnKS和SWAT模型的闽江流域径流数据同化

地表水文过程中观测变量对状态变量的响应存在时间滞后性,为提高径流数据同化的精度,以闽江流域为研究区,基于集合卡尔曼平滑器(EnKS)和SWAT模型,构建径流数据同化方案,并与集合卡尔曼滤波(EnKF)方法进行对比,评价不同同化模型的精度,分析数据同化对不同径流分量的影响。结果表明:EnKS最优时间窗口长度在不同水文周期、流域存在差异;考虑水文模型的时间滞后性可以有效提高模型的同化精度,对比EnKF方法,EnKS方法的纳什效率系数(NSE)在七里街、沙县、竹岐3个站点上分别提升了0.03、0.12、0.03,均方根误差(RMSE)分别减小了7.43%、26.81%、4.25%;数据同化方法对不同径流分量的改进程度存在空间异质性和时间异质性,在高渗透率土壤和陡坡区域EnKS方法能使壤中流获得更显著的改进,丰水期EnKS方法对地表径流的改进较枯水期更明显。

一种模型不确定的煤炭地下气化控制算法研究

煤炭地下气化(Underground Coal Gasification, UCG)实现了地下固体煤炭转为气体能源的封闭开发,可形成天然气能源的战略接替,是保障国家能源安全的重要策略,也是实现国家新时代能源高质量发展的有力手段。由于煤炭地下气化反应过程具有时变性和大滞后的特点,且无法得到精确的数学模型,给煤炭地下气化控制带来较大挑战。为改善煤炭地下气化的控制效果,在研究煤炭地下气化工艺的基础上,根据煤炭地下气化过程工程数据对煤炭地下气化过程进行了数学建模,设计了针对煤炭地下气化控制的内模控制算法。仿真结果表明,设计的控制算法与传统的PID控制以及Smith预估控制相比较,内模控制算法在模型失配时控制效果更好,更适合于对模型不确定的煤炭地下气化过程的有效控制。研究结果可为煤炭地下气化实际生产过程的相关研究提供参考。

基于数据关联的兰新线某隧道应力状态感知与预测

地质灾害极易导致隧道结构损伤,严重威胁铁路运营安全。以兰新线某隧道所在山体发生地质灾害而导致隧道结构受损为例,采用数据关联分析方法,构建隧道应力与地表位移关联模型,分析结果表明:隧道应力差值与高家湾滑坡地表位移值呈高度线性相关性,隧道应力差值相对地表位移具有时间滞后性,且不同里程断面应力的滞后性存在“中间小,两端大”的差异性特征,滞后时间最小、最大位置分别位于加固段中部、加固段小里程端;运用隧道应力与地表位移关联模型中隧道应力各断面应力滞后性不同的特点,实现断面间应力差值精准预测,验证隧道应力相对地表位移的时间滞后性的准确性。有效关联了隧道-地表位移多源数据并形成隧道应力状态预测模型,对于实现隧道精准预警、补全缺省监测数据、降低监测冗余具有一定的参考意义。

基于动态特性节点聚类的低阶仿真频率安全分析方法

在线评估电力系统抵抗功率扰动的能力,对调控人员实时了解电网频率稳定态势具有重要意义。针对大型互联同步系统频率具有明显的时空分布特性,提出了一种基于动态特性节点聚类的低阶仿真频率安全分析方法。基于预想故障机电暂态时域仿真结果进行节点动态频率特性同调性识别和节点聚类,在各同调节点集单机等值模型和频率超前滞后特性基础上,建立了频率安全在线分析的低阶仿真模型,可以应用于预想故障后频率安全的在线快速和精细化评估。某实际电网的算例验证了所提方法的准确性和有效性。