Probabilistic analysis of tunnel face seismic stability in layered rock masses using Polynomial Chaos Kriging metamodel

Face stability is an essential issue in tunnel design and construction.Layered rock masses are typical and ubiquitous;uncertainties in rock properties always exist.In view of this,a comprehensive method,which combines the Upper bound Limit analysis of Tunnel face stability,the Polynomial Chaos Kriging,the Monte-Carlo Simulation and Analysis of Covariance method(ULT-PCK-MA),is proposed to investigate the seismic stability of tunnel faces.A two-dimensional analytical model of ULT is developed to evaluate the virtual support force based on the upper bound limit analysis.An efficient probabilistic analysis method PCK-MA based on the adaptive Polynomial Chaos Kriging metamodel is then implemented to investigate the parameter uncertainty effects.Ten input parameters,including geological strength indices,uniaxial compressive strengths and constants for three rock formations,and the horizontal seismic coefficients,are treated as random variables.The effects of these parameter uncertainties on the failure probability and sensitivity indices are discussed.In addition,the effects of weak layer position,the middle layer thickness and quality,the tunnel diameter,the parameters correlation,and the seismic loadings are investigated,respectively.The results show that the layer distributions significantly influence the tunnel face probabilistic stability,particularly when the weak rock is present in the bottom layer.The efficiency of the proposed ULT-PCK-MA is validated,which is expected to facilitate the engineering design and construction.

Assessment of Groundwater Stability Using Corrosion and Scaling Tendency Indices on Selected Springs in the Manga Region in Nyamira County, Kenya

We present the result of groundwater stability assessment on three major springs in the Manga region in Nyamira County found in Kenya in 2018. These springs are Kiangoso (SP1), Kerongo (SP2) and Tetema (SP3). The corrosion and scaling tendency indices were obtained using the Langelier saturation index (LSI), Ryznar stability index (RSI), and Puckorius scaling index (PSI). The LSI values obtained for SP1, SP2, and SP3 are −3.93, −4.71, and −4.17, respectively, while using RSI, the values obtained for SP1, SP2, and SP3 are 14.15, 14.53, and 13.74, respectively. Using PSI, the values of SP1, SP2, and SP3 are 5.58, 5.45, and 5.58, respectively. From the interpretation of the indices, the groundwater from the three springs in the Manga region using LSI and RSI showed intolerable corrosion;hence, it is unlikely to scale as obtained from PSI.

Stability Analysis of Nonlinear Models of Nose Landing Gear Shimmy

Shimmy can reduce the service life of the nose landing gear, affect ride comfort, and even cause fuselage damage leading to aircraft crashes. Taking a light aircraft as the research object, the torsional freedom of landing gear around strut axis and lateral deformation of tire are considered. Since the landing gear shimmy is a nonlinear system, a nonlinear mechanical model of the front landing gear shimmy is established. Sobol index method is proposed to analyze the influence of structural parameters on the stability region of the nose landing gear, and Routh-Huritz criterion is used to verify the reliability of the analysis results of Sobol index method. We analyse the effect of torsional stiffness of strut, caster length, rated initial tire inflation pressure, rake angle, and vertical force on the stability region of theront landing gear. And the research shows that the optimization of the torsional stiffness of the strut and the caster length of the nose landing gear should be emphasized, and the influence of vertical force on the stability region of the nose landing gear should be paid attention to.

Constructing the bonding between conductive agents and active materials/binders stabilizes silicon anode in Lithium-ion batteries

Silicon(Si)anode has been considered a promising candidate due to its remarkable theoretical capacity but it was plagued by severe pulverization because of the inherent huge volume variation.Enhancing electrode stability is an effective approach to improve electrochemical performance.Herein,a stable Si anode was established by an innovative construction of the bonding between conductive agents and active materials/binders.As a result,the strong interaction of electrode components not only effectively alleviates the volume expansion of Si but also achieves a stable interface by generating the beneficial solid electrolyte interphase(SEI)composition.Attributed to the deliberate scheme of the electrode,the Si anode exhibits sterling electrochemical performance.Besides,the device of the electrode is not only effective for other binders but also for other anode materials with high volume variation,thus shedding light on the rational design of electrodes for high-energy-density lithium-ion batteries.

Feedback Stabilization over Wireless Network Using Adaptive Coded Modulation

In this paper,we apply adaptive coded modulation (ACM) schemes to a wireless networked control system (WNCS) to improve the energy efficiency and increase the data rate over a fading channel.To capture the characteristics of varying rate, interference,and routing in wireless transmission channels,the concepts of equivalent delay (ED) and networked condition index (NCI) are introduced.Also,the analytic lower and upper bounds of EDs are obtained.Furthermore,we model the WNCS as a multicontroller switched system (MSS) under consideration of EDs and loss index in the wireless transmission.Sufficient stability condition of the closed-loop WNCS and corresponding dynamic state feedback controllers are derived in terms of linear matrix inequality (LMI). Numerical results show the validity and advantage of our proposed control strategies.

地下复杂陡倾采空区稳定性评价的改进AHP-TOPSIS法

为了准确评价地下陡倾采空区的稳定性,提出1种地下复杂陡倾采空区稳定性评价的改进层次分析结合逼近理想解排序(AHP-TOPSIS)法,该方法基于各影响因素之间关联性分析,选取地质因素等3个一级指标与地质构造等14个二级指标建立采空区评价指标体系,采用改进AHP法确定各指标因素权重,通过TOPSIS理论对采空区稳定性等级进行评价,并结合实例将改进AHP-TOPSIS法与其他常用方法的评价结果进行对比分析。研究结果表明:提出的改进AHP-TOPSIS法得到陡倾采空区呈现稳定状态,与现场实际工程相符,改进AHP-TOPSIS法相比于其它方法具有可靠性与优越性。研究结果可为陡倾采空区稳定性的准确评价提供参考。

基于Global Stability Index(GSI)理论的水煮笋软罐头货架期预测

应用食品货架期预测新方法—Global Stability Index(GSI)进行水煮笋软罐头基于综合品质指标的保质期预测。基于恒温加速实验测定分析产品于23、33、43℃储藏温度下的品质变化规律,以色泽、可溶性蛋白质和维生素C作为水煮笋的关键质量指标,应用GSI理论描述产品基于多指标的综合劣变过程,获得不同温度下GSI值的变化趋势。结果表明,水煮笋软罐头GSI值的下降符合零级反应动力学。使用阿伦尼乌斯方程建立GSI货架期预测模型,并表征模型参数,计算出20℃下产品的保质期约为186d。经过理论预测与实验对比,得到的GSI值相对误差在22%以下,证明了该货架期预测方法的可靠性。

Stabilization of Uncertain Systems With Markovian Modes of Time Delay and Quantization Density

This work studies the stabilization of a class of control systems that use communication networks as signal transmission medium. The lateral motion of independently actuated four-wheel vehicle is modeled as an uncertain-linear system. Time delay and quantization density are modeled as Markov chains.The networked control systems(NCSs) with plants being lateral motion are first transformed to switched linear systems with uncertain parameters. Sufficient and necessary conditions for the stochastic stability of closed-loop networked control systems are then established. By solving the matrix inequalities, this work presents an output-feedback controller that depends on the modes of time delay and quantization density. The controller performance is illustrated via a vehicular lateral motion system.

Si元素对钛合金热稳定性影响研究

在不同温度下对3种不同Si含量的Ti-Si二元合金进行100h的热暴露实验,并通过力学性能表征其热稳定性,研究了Si元素对钛合金热稳定性的影响。结果表明,在实验条件下,Si元素的加入提高了合金的抗拉强度,Si含量越高,强度提升幅度越大;在热暴露过程中,当热暴露温度高于450℃时,Ti-Si合金的抗拉强度呈下降趋势,经500℃/100 h热暴露处理后表现出最差的热稳定性,其中Ti-0.4Si合金的伸长率降低至28.0%。Si元素扩散与偏聚形成的Ti_(5)Si_(3)是影响Ti-Si合金热稳定性的主要因素。

Machine Learning for Hybrid Line Stability Ranking Index in Polynomial Load Modeling under Contingency Conditions

In the conventional technique,in the evaluation of the severity index,clustering and loading suffer from more iteration leading to more com-putational delay.Hence this research article identifies,a novel progression for fast predicting the severity of the line and clustering by incorporating machine learning aspects.The polynomial load modelling or ZIP(constant impedances(Z),Constant Current(I)and Constant active power(P))is developed in the IEEE-14 and Indian 118 bus systems considered for analysis of power system security.The process of finding the severity of the line using a Hybrid Line Stability Ranking Index(HLSRI)is used for assisting the concepts of machine learning with J48 algorithm,infers the superior affected lines by adopting the IEEE standards in concern to be compensated in maintaining the power system stability.The simulation is performed in the WEKA environment and deals with the supervisor learning in order based on severity to ensure the safety of power system.The Unified Power Flow Controller(UPFC),facts devices for the purpose of compensating the losses by maintaining the voltage characteristics.The finite element analysis findings are compared with the existing procedures and numerical equations for authentications.

退火温度对DLC和Si-DLC涂层微观结构和摩擦学性能的影响

类金刚石(DLC)涂层因具有优异的减磨耐摩性能被广泛应用,而涂层内部存在较高的内应力这一缺点限制其在摩擦学领域的进一步应用。退火处理可以通过改变涂层微观结构来降低涂层内应力,从而提高涂层的摩擦学性能。为研究退火温度对DLC和硅掺杂类金刚石(Si-DLC)涂层微观结构和摩擦学性能的影响,采用等离子体增强化学气相沉积(PECVD)和电弧离子镀的复合沉积技术制备DLC和Si-DLC涂层,将涂层在大气环境中进行不同温度的退火处理。运用扫描电子显微镜、高分辨率透射电子显微镜、拉曼光谱以及XPS光谱仪对涂层摩擦试验前后的形貌和结构进行表征,采用纳米压痕仪和摩擦磨损试验机测试涂层的力学性能和摩擦学性能。结果表明:沉积的DLC和Si-DLC涂层为非晶结构。退火温度对涂层的微观结构和摩擦学性能有重要影响。随着退火温度从RT上升到500℃,由于C-H键断裂,C网发生集束化,DLC涂层的sp^(3)含量呈现先上升后降低的趋势,涂层的sp^(3)含量在300℃热处理后获得最大值,涂层硬度达到最大的20.66 GPa;而Si-DLC涂层由于Si元素的掺杂提高了涂层的热稳定性,其在400℃热处理时sp^(3)含量最大,硬度最大值为24.28 GPa。涂层与氧化锆对磨球的磨损机理为磨粒磨损,涂层的磨损率呈现先降低后升高的趋势,热处理温度为300和400℃为最优。研究证明涂层的微观结构和摩擦学性能可以通过热处理温度调控,优选热处理温度的涂层具有优异的综合性能。研究结果可为退火处理对DLC和Si-DLC涂层的性能影响提供理论支持。

基于SI模型的病毒传播动力学分析

创建了SI传播动力学模型,重点讨论了系统平衡点的存在性和稳定性,并运用连续动态系统分岔理论,利用MATLAB软件对系统的分岔情况进行了深入分析,同时考察了参数变化对系统的影响.在数值模拟阶段,对具有Holling IV型功能反应的病毒传播系统进行了详细分析,研究了疾病传播的特点和演变规律.

Stability evaluation method of large cross-section tunnel considering modification of thickness-span ratio in mechanized operation

Purpose-This study aims to research the large cross-section tunnel stability evaluation method corrected after considering the thickness-span ratio.Design/methodology/approach-First,taking the Liuyuan Tunnel of Huanggang-Huangmei High-Speed Railway as an example and taking deflection of the third principal stress of the surrounding rock at a vault after tunnel excavation as the criterion,the critical buried depth of the large section tunnel was determined.Then,the strength reduction method was employed to calculate the tunnel safety factor under different rock classes and thickness-span ratios,and mathematical statistics was conducted to identify the relationships of the tunnel safety factor with the thickness-span ratio and the basic quality(BQ)index of the rock for different rock classes.Finally,the influences of thickness-span ratio,groundwater,initial stress of rock and structural attitude factors were considered to obtain the corrected BQ,based on which the stability of a large cross-section tunnel with a depth of more than 100 m during mechanized operation was analyzed.This evaluation method was then applied to Liuyuan Tunnel and Cimushan No.2 Tunnel of Chongqing Urban Expressway for verification.Findings-This study shows that under different rock classes,the tunnel safety factor is a strict power function of the thickness-span ratio,while a linear function of the BQ to some extent.It is more suitable to use the corrected BQ as a quantitative index to evaluate tunnel stability according to the actual conditions of the site.Originality/value-The existing industry standards do not consider the influence of buried depth and span in the evaluation of tunnel stability.The stability evaluation method of large section tunnel considering the correction of overburden span ratio proposed in this paper achieves higher accuracy for the stability evaluation of surrounding rock in a full or large-section mechanized excavation of double line high-speed railway tunnels.

Simultaneous quadratic performance stabilization for linear time-delay systems

A newly designed approach of simultaneous stabilization is given for linear discrete time-delay systems. The problem of stabilization for a collection of systems is discussed initially. Adequate condition are obtained in terms of linear matrix inequalities （LMIs） which are independent of time delays such that the resultant collection of discrete time-delay systems are stable with an upper bound of the quadratic performance index. Subsequently, controllers are designed such that the resultant closed-loop discrete time-delay systems are simultaneously stabilized with the upper bound of the quadratic performance index. Finally,a numerical example is given to illustrate the design method.

具有饱和发生率的SIS传染病模型稳定性

考虑了一类具有易感人群饱和发生率的SIS传染病数学模型,定义了基本再生数,证明了地方病平衡点的存在唯一性、局部和全局渐近稳定性,分析了饱和发生率参数对模型动力学行为的影响,并通过数值模拟验证了所得结论的准确性。

单纯复形上的随机SIS传染病模型

该文考虑了噪声影响下单纯复形上的随机SIS传染病模型,比较了1单形传染强度(λ)或2单形传染强度(λ_(△))受噪声扰动后的模型在随机稳定性和随机分岔方面的区别.结果表明:对于随机模型而言,噪声作用于λ所在的低次项后传染病依概率1灭绝的阈值与噪声强度有关,反之作用于λ_(△)所在的高次项则对阈值无影响;增大λ_(△),会使稳态概率密度函数靠近1处出现峰值、峰值变大或峰值趋近于1,即:增大λ_(△),会促进疾病的传播.

一类具有空间异质性SIS传染病模型的阈值动力学分析

本文研究了空间异质性下水平传播和垂直传播的SIS传染病模型的问题.利用半群理论、下一代再生算子谱半径的定义、Lyapunov函数、渐近自治半流理论以及数值模拟的方法,获得了空间异质性下水平传播和垂直传播的SIS传染病模型的动力学行为和传播规律的结果.这些结果推广了之前的相关研究结果,为理解此类传染病模型提供了更深入的理论依据.

Effects of Soil-Cement Stabilization on the Index Properties of Subgrades of Three Selected Roads in the Niger Delta Region of Nigeria

In this study, the impact of soil-cement stabilization on the index properties of the subgrade of roads was investigated. Efforts were on the means of improving the bearing capacity of the subgrade of a flexible pavement structure. Three selected roads (Ogbia-Nembe, section of the East-West Road and section of Port Harcourt-Aba Road) in the Niger Delta Region of Nigeria were examined to determine the effect of sand-cement stabilization on the compaction index property of their undisturbed subgrade and the optimal ratio of soil-cement on the expansive soils at which the California Bearing Ratio (CBR) is optimized. Disturbed soil samples were collected from twenty trial pits on each of the three study roads using a hand ulger and tested for their respective compaction index properties. It was discovered that their California Bearing Ratio (CBR) was very low. Some of the collected specimen materials were stabilized with varying percentages of soil-cement contents ranging from 6% - 14% in order to ascertain its effects on the compaction index properties of the sample soils. Results of the various stabilization test procedures show that: Stabilization of the soil using Soil-Cement Stabilization affected the Compaction Index properties of the soil and further improved the California Bearing Ratio (CBR). On the Ogbia-Nembe Road;Soil-Cement stabilization improved the CBR and is optimized at a 10% sand-cement ratio with optimum moisture content ranging from 6.2% - 14%, maximum dry density ranges from 1700 - 1780 kg/m3, yielding an average CBR of 42.7% for soaked samples. On the section of East-West Road from Eleme Junction to Etteh Junction;Soil-Cement stabilization improved the CBR and is optimized at a 14% sand-cement ratio with optimum moisture content ranging from 6.2% - 14.2%, maximum dry density ranges from 1660 - 1800 kg/m3, yielding an average CBR of 43.9% for soaked samples. On the section of Port Harcourt-Aba Express Road from Eleme Junction to Osisioma Junction;Soil-Cement stabilization improved the CBR and is optimized at a 12% sand-cement ratio having an optimum moisture content ranging from 5.4% - 17.3%, maximum dry density ranges from 1610 - 1740 kg/m3, and an average California Bearing Ratio for soaked samples at 40%.

Investigation of Connecting Wind Turbine to Radial Distribution System on Voltage Stability Using SI Index and λ - V Curves

The growth of wind energy penetration level in distribution system raises the concern about its impact on the operation of the power system, especially voltage stability and power loss. Among the major concerns, this paper studied the impact of connecting wind Turbine (WT) in radial distribution system with different penetration levels and different power factor (lead and lag) on power system voltage stability and power loss reduction. Load flow calculation was carried out using forward-backward sweep method. The analysis proceeds on 9- and 33-bus radial distribution systems. Results show that voltage stability enhancement and power loss reduction should be considered as WT installation objective.

Changes in plaque stability, cell apoptosis and coagulation indexes after patients with unstable angina pectoris accept adjuvant salvianolate therapy

Objective:To investigate the effect of adjuvant salvianolate therapy on plaque stability, cell apoptosis and coagulation indexes in patients with unstable angina pectoris.Methods: 92 patients with unstable angina pectoris treated in our hospital between May 2011 and August 2015 were collected, and after the treatment process and auxiliary examination results were retrospectively analyzed, they were divided into the control group (n=45) who accepted conventional treatment and the observation group (n=47) who accepted adjuvant salvianolate treatment. Before and after treatment, diasonograph was used to evaluate the plaque stability parameters of two groups of patients;ELISA was used to detect apoptosis-related molecule levels;immunoturbidimetry was used to detect blood coagulation indexes.Results: Before treatment, differences in plaque stability parameters, cell apoptosis molecules and coagulation indexes were not statistically significant between two groups of patients (P>0.05). After treatment, the plaque stability parameters plaque thickness, enhanced intensity, rise time and time to peak of observation group were significantly lower than those of control group (P<0.05);serum sFas, sFasL, fibrinogen (Fib), platelet (PLT), and D-Dimer (D-D) levels of observation group were significantly lower than those of control group while Bcl-2, prothrombin time (PT) and activated partial thromboplastin time (APTT) levels were significantly higher than those of control group (P<0.05).Conclusions: Adjuvant salvianolate treatment can increase the plaque stability, also inhibit myocardial cell apoptosis and improve the coagulation function in patients with unstable angina pectoris.