Stochastic Model of Dengue: Analysing the Probability of Extinction and LLN

In this article, we develop and analyze a continuous-time Markov chain (CTMC) model to study the resurgence of dengue. We also explore the large population asymptotic behavior of probabilistic model of dengue using the law of large numbers (LLN). Initially, we calculate and estimate the probabilities of dengue extinction and major outbreak occurrence using multi-type Galton-Watson branching processes. Subsequently, we apply the LLN to examine the convergence of the stochastic model towards the deterministic model. Finally, theoretical numerical simulations are conducted exploration to validate our findings. Under identical conditions, our numerical results demonstrate that dengue could vanish in the stochastic model while persisting in the deterministic model. The highlighting of the law of large numbers through numerical simulations indicates from what population size a deterministic model should be considered preferable.

Correlates of avian extinction timing around the world since 1500 CE

Avian extinctions have been relatively well documented in modern history,and in the past millennia,more bird species are known to have gone extinct than species in any other vertebrate class.We examined the biological correlates of extinction timing among 216 bird species that recently were either observed to go extinct or dis-appeared since 1500 CE,performing a novel analysis for examining the extinction trends of birds by modelling traits against the number of years since present day during which species have been extinct.We analyzed a broad range of traits and characteristics that have previously been associated with extinction and extinction risk in birds and compared the effects of these traits simultaneously against one another.In order to provide a more comprehensive and robust assessment of trait-based drivers of global bird loss in comparison to prior studies,we included extinct species recognized by any of the three major avian taxonomies as well as those birds that lack recent confirmed sightings and are at least functionally extinct.We found that insular,flightless,larger-bodied,ecologically specialized species,as well as those with high aspect ratio wings,were likely to go extinct earlier in time.Besides identifying the key locations and time periods over the past five centuries where birds have gone extinct,and highlighting specific extinction-prone taxonomic groups,we provide a complete and unified dataset of traits used in this study that helps address the lack of extensive public data on modern extinct species.

High polarization extinction ratio achieved base on thin-film lithium niobate

This article introduces a method of achieving high polarization extinction ratio using a subwavelength grating structure on a lithium niobate thin film platform,and the chip is formed on the surface of the lithium nio⁃bate thin film.The chip,with a length of just 20μm,achieved a measured polarization extinction ratio of 29 dB at 1550 nm wavelength.This progress not only proves the possibility of achieving a high extinction ratio on a lith⁃ium niobate thin film platform,but also offers important technical references for future work on polarization beam splitters,integrated fiber optic gyroscopes,and so on.

Locally and globally uniform approximations for ruin probabilities of a nonstandard bidimensional risk model with subexponential claims

Consider a nonstandard continuous-time bidimensional risk model with constant force of interest,in which the two classes of claims with subexponential distributions satisfy a general dependence structure and each pair of the claim-inter-arrival times is arbitrarily dependent.Under some mild conditions,we achieve a locally uniform approximation of the finite-time ruin probability for all time horizon within a finite interval.If we further assume that each pair of the claim-inter-arrival times is negative quadrant dependent and the two classes of claims are consistently-varying-tailed,it shows that the above obtained approximation is also globally uniform for all time horizon within an infinite interval.

Earthquake detection probabilities and completeness magnitude in the northern margin of the Ordos Block

The assessment of the completeness of earthquake catalogs is a prerequisite for studying the patterns of seismic activity.In traditional approaches,the minimum magnitude of completeness(MC)is employed to evaluate catalog completeness,with events below MC being discarded,leading to the underutilization of the data.Detection probability is a more detailed measure of the catalog's completeness than MC;its use results in better model compatibility with data in seismic activity modeling and allows for more comprehensive utilization of seismic observation data across temporal,spatial,and magnitude dimensions.Using the magnitude-rank method and Maximum Curvature(MAXC)methods,we analyzed temporal variations in earthquake catalog completeness,finding that MC stabilized after 2010,which closely coincides with improvements in monitoring capabilities and the densification of seismic networks.Employing the probability-based magnitude of completeness(PMC)and entire magnitude range(EMR)methods,grounded in distinct foundational assumptions and computational principles,we analyzed the 2010-2023 earthquake catalog for the northern margin of the Ordos Block,aiming to assess the detection probability of earthquakes and the completeness of the earthquake catalog.The PMC method yielded the detection probability distribution for 76 stations in the distance-magnitude space.A scoring metric was designed based on station detection capabilities for small earthquakes in the near field.From the detection probabilities of stations,we inferred detection probabilities of the network for diff erent magnitude ranges and mapped the spatial distribution of the probability-based completeness magnitude.In the EMR method,we employed a segmented model fitted to the observed data to determine the detection probability and completeness magnitude for every grid point in the study region.We discussed the sample dependency and low-magnitude failure phenomena of the PMC method,noting the potential overestimation of detection probabilities for lower magnitudes and the underestimation of MC in areas with weaker monitoring capabilities.The results obtained via the two methods support these hypotheses.The assessment results indicate better monitoring capabilities on the eastern side of the study area but worse on the northwest side.The spatial distribution of network monitoring capabilities is uneven,correlating with the distribution of stations and showing significant diff erences in detection capabilities among diff erent stations.The truncation eff ects of data and station selection aff ected the evaluation results at the edges of the study area.Overall,both methods yielded detailed descriptions of the earthquake catalog,but careful selection of calculation parameters or adjustments based on the strengths of diff erent methods is necessary to correct potential biases.

Development of a Gas Monitoring and Removal Device to Reduce the Effect of Extinction Coefficient

At present, the use of furnaces in the northern rural areas of China is very common, due to the insufficient burning of fuel (coal, wood, etc.), carbon monoxide (CO) and other toxic gases are produced, CO colorless and odorless, difficult to find in time, and bring huge safety risks to the life and health of residents. Based on the above problems, we developed a gas monitoring and removal device which could reduce the effect of extinction coefficient. The device was composed of ash settling area, gas disturbance area, spectral absorption identification area and gas removal area. After the air entered the device, the large-size particles were first settled to purify the solid particles in the gas, the gas was disturbed through the multi-layer separator to achieve the turbulent production of the gas, and then the gas was identified through the optical element of the direct absorption spectrum technology. When the toxic gas component reached the threshold, the spray device would automatically start for chemical removal to achieve the role of purifying the gas. At the same time, the device’s alarm could be alerted by buzzer and flash to remind users to evacuate in time. By improving the optical device, the effect of extinction coefficient on measurement was reduced and the monitoring accuracy was improved.

A Speculation: Avian Migration and the K-T Extinction

One caveat to the dinosaur’s extinction is the conclusion that avian dinosaurs survived and became ancestors of birds. Their mobility enabled them to migrate great distances and find the nutrients needed to survive. Given this scenario, could the current observable migration of birds (the “dinosaurian offspring”) now be related? Migration is the regular seasonal movement undertaken by many species of birds, with the most common pattern, flying north in the Northern spring to breed in the temperate or Arctic summer and returning in the Northern autumn to wintering grounds in warmer regions of the south. The primary motivation for migration appears to be food. None of the major North-South migratory pathways fly over the Caribbean but three main fly ways, past to the west of the theorized K-T impact centre. Due to their ability to fly, the “avian Dinosaurs” adapted and survived very quickly in response to the disaster that marked the K-T boundary. It is an interesting speculation that the avian migration that we witness today is rooted in an event that occurred 66 million years ago! But it does explain why the migratory birds mostly fly from Polar summer to polar summer when they could just be as easily fly from Polar zone to the warmer equatorial region and back. In the recent article in Nature by Melanie During about identifying the late spring timing of the “Astro disaster”, it can be cited as consistent with my speculation. A late April early May Impact as suggested by During would have seen these migrations completely. The western migratory routes would have been found to be “luxurious” in vegetation in that first northern autumn after the “Astro-impact” while all eastern routes would have still been barren.

径向涡轮分子泵叶片结构优化及仿真分析

涡轮分子泵广泛应用于大科学装置、核物理工业、半导体及薄膜工业。径向涡轮分子泵转子叶列结构简单,叶列排气端呈圆弧形外扩排布,有利于叶片间气体粒子正向传输,提升了抽气效率。文章以径向结构涡轮分子泵为研究对象,基于稀薄气体传输理论,采用数学粒子追踪方法,对9种不同形状的叶片结构进行对比分析,使用COMSOL软件模拟不同叶片结构下叶列间气体粒子的正、反向传输几率,探究叶片形状对气体粒子正、反向传输几率和压缩比的影响。结果表明,涡轮分子泵转子叶片一侧为弧形凸面结构,另一侧为平面结构时,分子泵的压缩比提升1个数量级,分子泵性能显著提升。研究对涡轮分子泵的设计与优化具有一定的参考价值和指导意义。

精密薄壁轴套柔性检验方法及工序能力评价

航空航天零件要求精度高,合格率要达到100%,常采用三坐标测量来提高测量精度,减少人员测量带来的误差。精密薄壁轴套零件作为连接元件在工作中起到轴向定位和径向紧固的作用,对机械传动起着重要的作用。为保证零件的测量精度和合格率,需要将测量产生的工艺误差控制在零件公差的1/3以内,工艺误差包含定位误差、夹紧变形误差等。试验利用光固化柔性夹具对轴套进行夹紧,减少金属夹具对轴套产生的变形和损伤,消除夹紧变形误差。利用对同一个轴套零件进行重复测量,获得定位误差引起的标准不确定度,并结合工序能力计算,来判定测量方法的可行性。

基于概率的震级完备度方法评估云南地震台网的监测能力

为了科学评估云南地震台网的监测能力,分析云南地区的地震监测能力时空分布特征,采用基于概率的震级完备度(PMC)方法,利用2009-2023年云南地震台网地震目录、震相和台站信息等数据,计算了云南地震台网在云南地区的平均地震监测能力和在不同深度的监测能力,得到滇中、滇西局部地区的基于概率的完备性震级M_(P)=1.5,云南全境基本都能监测到2.5级地震。评估了研究时段内云南地震台网台站监测能力的演变,发现部分台站的监测能力持续下降。但自2018年增加20个台站后,云南2.0及2.5级地震的监测范围有一定的扩大,但微震监测能力提升不明显,可能是因为2018年以来云南一直处于小震弱活动状态。最后,对应用PMC方法规划提升台网监测能力进行了展望。

黄石市地震台背景噪声特征分析

利用2018年1月—2020年3月湖北省黄石市三个地震台的垂直分量连续地震波形数据,计算新冠肺炎疫情前(2018年1月—2019年12月)和疫情防控期间(2020年1—3月)三个地震台的噪声加速度功率谱密度和概率密度函数,重点分析高频段(1~10 Hz)地震背景噪声的时空变化特征。研究结果显示:(1)疫情防控期间,高频噪声加速度功率谱密度整体明显下降,特别是在春节期间。2018年和2019年春节期间短周期(~1 s)噪声幅值下降明显,而在假期结束后迅速恢复;2020年春节正值新冠疫情防控期间,噪声幅值大幅下降,并且持续保持在较低水平。(2)日变化模式改变。疫情前,地震背景噪声在白天(6:00—20:00)的功率谱密度明显高于晚上(20:00—次日6:00),中午12:00左右功率谱密度出现短时下降,夜间2:00左右出现最低值,这种变化特征与人类的作息规律一致;而在新冠疫情防控期间,噪声幅值下降且日变化不明显,表明人类活动减弱,高频噪声幅值相应变化。(3)人口密度和经济发展水平影响噪声水平。人口密度和经济发展水平较高的地区噪声水平偏高,这表明城市的人类活动和经济状况与地震背景噪声存在关联。这些研究结果对城市规划、公共管理和环境保护具有重要的参考价值,可为城市人类活动监测和公共治理提供有用信息。

土石坝高喷桩防渗墙抗压强度与渗透系数相关性及分布模型研究

防渗墙的抗压强度与渗透系数之间的相关性及其分布模型是影响土石坝防渗墙强度及大坝渗透可靠性的关键因素。收集了9座土石坝高喷桩防渗墙检测数据,采用AIC准则识别抗压强度与渗透系数的最优边缘分布类型与构造相关联合分布模型的最优Copula函数,Bootstrap方法模拟识别结果的统计不确定性。结果表明:抗压强度和渗透系数之间存在显著负相关性、主要服从威布尔分布,构造两参数相关非正态联合分布的最优Copula函数为Frank Copula,识别结果差异主要来源于防渗墙施工质量导致的频率分布差异。研究结果可为土石坝高喷桩防渗墙强度可靠度与坝体/坝基渗透稳定可靠度分析提供简单、有效的分布模型。

具有医疗资源有限和Ornstein-Uhlenbeck过程的随机SIR传染病模型研究

基于医疗资源的有限性和疾病的传播规律,提出一类具有Ornstein-Uhlenbeck过程和一般发生率的随机SIR传染病模型.首先,讨论模型全局正解的存在唯一性并给出疾病灭绝性的充分条件.其次,通过构造合适的Lyapunov函数并应用It^o公式等方法,得到模型平稳分布的存在性.此外,通过求解Fokker-Planck方程,给出模型在拟地方病平衡点附近的密度函数的具体形式.最后通过数值模拟解释主要的理论结果并探讨随机扰动对疾病传播的影响.

多级变径孔板螺旋流的水力特性及数值模拟研究

针对多级变径孔板水力特性的数值模拟研究较少的现状,引入收缩角与扭转角概念,构建新型多级变径孔板,基于前期物理试验,通过数值模拟定雷诺数、变收缩角、变扭转角的多种组合工况,对该装置内各监测断面的三相速度、装置内空化数的沿程变化规律及装置的消能率进行分析。结果表明,定收缩角时,随着扭转角的增大,轴向速度的波动程度逐渐减弱,切向速度和径向速度虽有逐渐增大的趋势,但整体波动相对较小;定雷诺数时,同一断面处的空化数随收缩角或扭转角的增大而减小;该装置的消能率随扭转角增大而增大,随收缩角增大而减小。在研究的8种组合工况中,收缩角为15°、扭转角为12°时该装置的消能率最优。

埋地燃气管道失效风险时间序列预测在常州市的应用

为研究常州市埋地燃气管道失效风险的时间效应,选取了影响其失效概率的4个主要因素,根据灰色模型GM(1,1)分析了各影响因素的时间效应,在此基础上将灰色模型与神经网络有机结合构建了灰色神经网络模型(GNNM),进而利用灰色神经网络模型分析了各因素影响下常州市埋地燃气管道综合失效概率的时间效应,然后借助失效概率转换函数将失效概率转换为预警失效概率,最后实现了对常州市埋地燃气管道2027年的失效风险预警。预警结果表明,2027年研究地区大部分区域的埋地燃气管道风险等级将进入较高风险,东南及东北的小部分区域风险将变为高风险,需要尽快采取相关措施抑制其失效风险的持续上升以及预防失效致灾事故的发生。

Dynamics of a Stochastic Epidemic Model with Age-group

A stochastic epidemic model with two age groups is established in this study,in which the susceptible(S),the exposed(E),the infected(I),the hospitalized(H)and the recovered(R)are involved within the total population,the aging rates between two age groups are set to be constant.The existence-and-uniqueness of global positive solution is firstly showed.Then,by constructing several appropriate Lyapunov functions and using the high-dimensional Itô’s formula,the sufficient conditions for the stochastic extinction and stochastic persistence of the exposed individuals and the infected individuals are obtained.The stochastic extinction indicator and the stochastic persistence indicator are less-valued expressions compared with the basic reproduction number.Meanwhile,the main results of this study are modified into multi-age groups.Furthermore,by using the surveillance data for Fujian Provincial Center for Disease Control and Prevention,Fuzhou COVID-19 epidemic is chosen to carry out the numerical simulations,which show that the age group of the population plays the vital role when studying infectious diseases.

具强吸收项的拟线性抛物方程解的紧支集和熄灭

考虑一类具强吸收项的拟线性抛物方程Cauchy问题,由于强吸收项的作用,该问题的解可以在有限时刻具有紧支集和发生熄灭.首先,利用比较原理,通过构造合适的上解证明该问题的解在某个时刻后具有一致的紧支集,甚至还可以在任意正时刻后都具有一致的紧支集.其次,在一定条件下,利用该问题的解在不同时刻的L^(1)范数估计,证明其在有限时刻发生熄灭.

利用混凝土双轴强度试验的概率反问题研究

基于概率密度演化理论和混凝土随机损伤力学,从概率密度的角度,建立了一类随机建模准则。以混凝土双轴强度试验为背景,利用遗传算法,提出了一类概率反问题求解方法。利用混凝土双轴试验数据及提出的求解方法,对混凝土弹塑性随机损伤本构模型中的断裂应变统计参数进行识别,获得了本构模型的基本参数。研究表明,据此识别的模型参数能从概率密度与统计矩两个层面准确地反映混凝土强度的随机性。该研究为概率反问题的求解提供一种可行的途径。

基于Rosenbluthe改进方法的地层坍塌压力不确定性分析

密度、声波时差、自然伽马等测井参数的不确定性使得基于测井数据的地层坍塌压力预测存在不确定性。基于此,首先确定了密度、声波时差、自然伽马等测井参数的不确定性特征;其次引入改进的Rosenbluthe方法,理论推导了岩石力学参数的不确定性表达式,并结合水平地应力和地层压力的不确定性表达式,提出了井眼坍塌压力的不确定性分析方法,最终得到井眼坍塌压力的概率分布情况。以SY1井为例,利用不确定性分析方法和蒙特卡罗方法分别预测了井眼坍塌压力的概率分布情况并对实际钻井过程中井壁失稳风险进行了预测,结果表明不确定性分析方法的预测结果与蒙特卡罗方法吻合度超过了95%,不确定性分析方法预测井壁失稳风险率为68.4%,蒙特卡罗方法预测井壁失稳风险率为67.4%,实际钻井过程中该井深位置发生了井壁坍塌,预测结果与实际情况相符,且所提出的不确定性分析方法预测的井壁失稳风险率略大于蒙特卡罗方法的井壁失稳风险率,对现场施工具有重要的参考价值。

Dynamic Variation and Simulation of Extinction Coefficient of Corn Population

[Objective] The aim was to study the dynamic variation of extinction coefficient of corn population, so as to improve the accuracy of assessment on net primary productivity （NPP） or yield. [Method] Based on the data of photosynthetic active radiation and leaf area index during corn growing season （from May to September） in 2006, observed in Jinzhou observation station of corn farmland ecosystem, China Meteorological Administration, the dynamic variation of extinction coefficient of corn population was analyzed. [Result] There was a great daily variation in the extinction coefficient of corn population during growing season, and the maximum value appeared from 7：00 to 9：00 and from 15：00 to 17：00, while the minimum could be found around 12：00, but the amplitude of variation decreased in tasseling stage. On a large time scale （5 d）, there was a parabolic relationship between extinction coefficient （K） and leaf area index （LAI）, with determination coefficient R2 of 0.960 7. The simulation equation of extinction coefficient, based on the sun elevation angle or leaf area index, had poor accuracy at various time during growing season, so a new dynamic model of extinction coefficient was established, namely K=λ（0.784 8-0.001 6θ）（0.154 8LAI2-0.558 6LAI＋0.654）. [Conclusion] The effect of sun elevation angle and leaf area index on extinction coefficient during corn growing season was considered in the new dynamic model of extinction coefficient, and its simulated result was superior to that of single-factor model.