Deformation critical threshold estimation of Xiaowan ultrahigh arch dam with time-varying grey model

The structural behavior of the Xiaowan ultrahigh arch dam is primarily influenced by external loads and time-varying characteristics of dam concrete and foundation rock mass during long-term operation. According to overload testing with a geological model and the measured time series of installed perpendicular lines, the space and time evolution characteristics of the arch dam structure were analyzed, and its mechanical performance was evaluated. Subsequently, the deformation centroid of the deflective curve was suggested to indicate the magnitude and unique distribution rules for a typical dam section using the measured deformation values at multi-monitoring points. The ellipse equations of the critical ellipsoid for the centroid were derived from the historical measured time series. Hydrostatic and seasonal components were extracted from the measured deformation values with a traditional statistical model, and residuals were adopted as a grey component. A time-varying grey model was developed to accurately predict the evolution of the deformation behavior of the ultrahigh arch dam during future operation. In the developed model, constant coefficients were modified so as to be time-dependent functions, and the prediction accuracy was significantly improved through introduction of a forgetting factor. Finally, the critical threshold was estimated, and predicted ellipsoids were derived for the Xiaowan arch dam. The findings of this study can provide technical support for safety evaluation of the actual operation of ultrahigh arch dams and help to provide early warning of abnormal changes.

A multiobjective evolutionary optimization method based critical rainfall thresholds for debris flows initiation

At present,most researches on the critical rainfall threshold of debris flow initiation use a linear model obtained through regression.With relatively weak fault tolerance,this method not only ignores nonlinear effects but also is susceptible to singular noise samples,which makes it difficult to characterize the true quantization relationship of the rainfall threshold.Besides,the early warning threshold determined by statistical parameters is susceptible to negative samples(samples where no debris flow has occurred),which leads to uncertainty in the reliability of the early warning results by the regression curve.To overcome the above limitations,this study develops a data-driven multiobjective evolutionary optimization method that combines an artificial neural network(ANN)and a multiobjective evolutionary optimization implemented by particle swarm optimization(PSO).Firstly,the Pareto optimality method is used to represent the nonlinear and conflicting critical thresholds for the rainfall intensity I and the rainfall duration D.An ANN is used to construct a dual-target(dual-task)predictive surrogate model,and then a PSO-based multiobjective evolutionary optimization algorithm is applied to train the ANN and stochastically search the trained ANN for obtaining the Pareto front of the I-D surrogate prediction model,which is intended to overcome the limitations of the existing linear regression-based threshold methods.Finally,a double early warning curve model that can effectively control the false alarm rate and negative alarm rate of hazard warnings are proposed based on the decision space and target space maps.This study provides theoretical guidance for the early warning and forecasting of debris flows and has strong applicability.

美国对华“战略阻断”行为及其困境

A hegemonic power can impose a strategic blockade on a rising nation when the latter’s power reaches a critical threshold.In such a case,the hegemonic power could utilize economic,political,military,and other strategies to maintain its status and obstruct the growth of the rising nation.Two critical thresholds have traditionally been established for rising nations:the first breach occurs when the rising nation achieves 60%of the GDP of the hegemonic power,and the second occurs at the 80%mark.After World War II,the United States tended to safeguard its hegemony by imposing strategic blockades against rising nations usually when they infringed the 60%threshold.Since the United States launched a trade war against China in March 2018,the Trump and Biden administrations have executed two rounds of comprehensive containment and suppression actions against China.The consequent extreme pressure and high-intensity competition have resulted in intensive deterioration of bilateral relations.This case is the latest example of a hegemonic country implementing a strategic blockade against a rising country.The momentum of China’s rise is irreversible,and the country has already surpassed three-quarters of the power share of the United States.Therefore,the United States now faces a dilemma regarding the strategic blockade imposed on China.As a rising power,China should comprehensively understand the laws,define an appropriate national strategy,and effectively employ diplomacy.By doing so,China can effectively counter the strategic blockade imposed by the United States,protect its core interests,and ensure world peace and development.

Probabilistic Assessment of Reinforcing Steel Depassivation in Concrete under Aggressive Chloride Environments Based on Natural Exposure Data

The probability distributions of the critical threshold chloride concentration Ccr, the chloride diffusion coefficient D, and the surface chloride concentration Cs are determined based on the collected natural exposure data, and the probability estimation of reinforcement depassivation in concrete is presented using Monte-Carlo simulation. From sensitivity analysis of mean value for ccr, cs, and D on the depassivation probability of reinforcement, it is found that ccr, cs, and D respectively has the greatest, smaller, and the lowest effect on the probability of depassivation. Finally the effect of stress state of concrete on the reinforcement depassivation probability is analyzed. It is found that the influence of stress state becomes apparent as exposure time increases.

Dynamical robustness of networks based on betweenness against multi-node attack

We explore the robustness of a network against failures of vertices or edges where a fraction of vertices is removed and an overload model based on betweenness is constructed.It is assumed that the load and capacity of vertex are correlated with its betweenness centrality B_(i)as B_(i)^(θ)and(1+α)B_(i)^(θ)(θis the strength parameter,αis the tolerance parameter).We model the cascading failures following a local load preferential sharing rule.It is found that there exists a minimal whenθis between 0 and 1,and its theoretical analysis is given.The minimalα_(c)characterizes the strongest robustness of a network against cascading failures triggered by removing a random fraction f of vertices.It is realized that the minimalα_(c)increases with the increase of the removal fraction f or the decrease of average degree.In addition,we compare the robustness of networks whose overload models are characterized by degree and betweenness,and find that the networks based on betweenness have stronger robustness against the random removal of a fraction f of vertices.

How Chinese EFL Learners'English Syntactic Proficiency Regresses with Time:An Empirical Study

The study conducted an empirical study to investigate how Chinese EFL learners'English syntactic proficiency regressed with time.It was indicated that:first,Chinese EFL Learners'proficiency levels prior to attrition(PLPAs)were inversely correlated with the degree of attrition.Simply put,learners with higher syntactic proficiency level will suffer less attrition even if the target structures were not used or rehearsed for more than two years.Second,a critical threshold,which roughly equaled to CET-4 level,was proved to exist in the processing of attrition.Chinese EFL Learners above the critical threshold had a significantly better retention than those below this threshold.

Controlling threshold in soil salinity when planting spring wheat and sequential cropping silage corn in Northern Xinjiang using drip irrigation

Xinjiang Region of China is one of the most typical and representative arid areas worldwide,along with severe soil salinization issue.Planting spring wheat and sequential cropping silage corn in Northern Xinjiang using drip irrigation has become an effective way to relieve soil salinity stress,which improves the simple agricultural structure in the past and ensures food security in this area.However,neither the effects of different soil salinities on the growth and yield of spring wheat and silage corn,nor their desalination effect correspondingly was clear until now.Therefore,a pot experiment was conducted at Shihezi,Xinjiang from March to June 2015.The study aimed to establish the quantitative correlations between the parameters mentioned above and came up with the appropriate soil salinity threshold in Northern Xinjiang area.The results confirmed that the soils in all treatments were desalinated after the whole growth period,and the decreasing rates varied within 18.89%-44.08%and 11.06%-30.83%for two plants,which showed linear and quadratic correlations with initial soil salinity,respectively(R^(2)>0.92^(**),p<0.05).Meanwhile,higher soil salinity would inhibit crop growth and yield,and the initial soil salinity also represented the negative quadratic correlations with growth parameters(R^(2)>0.92^(**),p<0.01).The inhibition effect was enhanced with larger initial soil salinity.After the comprehensive consideration of soil salinity variation,crop growth and yield,the initial soil salinity was recommended under 8.91 g/kg and 5.54 g/kg to plant spring wheat and sequential cropping silage corn in Northern Xinjiang using drip irrigation.

Analysis of SEIQ Immunization Model Strategy in Small-World

In this paper, we analyze an immunization strategy in SEIQ （susceptible, eclipse, infected, quarantine） model in small- world networks by associating the immunization probability with the infection probability. First, based on the mean-field theory, we establish the transmission dynamics equation for SEIQ model and find the relevant critical threshold of immunization which is re- lated to the topology of the network, the infection rate of the eclipse and infection, the density of quarantine and so on. Then we explain the influence of the immunization probability to the transmission of infectious disease. Finally, by simulating the propagation of this model on disease and comparing the results with theory results, we find that this kind of immunization strategy is effective in SEIQ model in small-world complex networks.