PERIODIC AND ALMOST PERIODIC SOLUTIONS FOR A NON-AUTONOMOUS RESPIRATORY DISEASE MODEL WITH A LAG EFFECT

This paper studies a kind of non-autonomous respiratory disease model with a lag effect.First of all,the permanence and extinction of the system are discussed by using the comparison principle and some differential inequality techniques.Second,it assumes that all coefficients of the system are periodic.The existence of positive periodic solutions of the system is proven,based on the continuation theorem in coincidence with the degree theory of Mawhin and Gaines.In the meantime,the global attractivity of positive periodic solutions of the system is obtained by constructing an appropriate Lyapunov functional and using the Razumikin theorem.In addition,the existence and uniform asymptotic stability of almost periodic solutions of the system are analyzed by assuming that all parameters in the model are almost periodic in time.Finally,the theoretical derivation is verified by a numerical simulation.

Seepage safety monitoring model for an earth rock dam under influence of high-impact typhoons based on particle swarm optimization algorithm

Extreme hydrological events induced by typhoons in reservoir areas have presented severe challenges to the safe operation of hydraulic structures. Based on analysis of the seepage characteristics of an earth rock dam, a novel seepage safety monitoring model was constructed in this study. The nonlinear influence processes of the antecedent reservoir water level and rainfall were assumed to follow normal distributions. The particle swarm optimization （PSO） algorithm was used to optimize the model parameters so as to raise the fitting accuracy. In addition, a mutation factor was introduced to simulate the sudden increase in the piezometric level induced by short-duration heavy rainfall and the possible historical extreme reservoir water level during a typhoon. In order to verify the efficacy of this model, the earth rock dam of the Siminghu Reservoir was used as an example. The piezometric level at the SW1-2 measuring point during Typhoon Fitow in 2013 was fitted with the present model, and a corresponding theoretical expression was established. Comparison of fitting results of the piezometric level obtained from the present statistical model and traditional statistical model with monitored values during the typhoon shows that the present model has a higher fitting accuracy and can simulate the uprush feature of the seepage pressure during the typhoon perfectly.

Oil Source and Entrapment Epoch of the Ordovician Oil Reservoir in the Kongxi Burial-Hill Zone, Huanghua Depression, North China

An oil flow obtained from the Middle Ordovician Fengfeng Formation carbonate reservoir in the well KG-3, Kongxi burial-hill zone in 1993 marked a breakthrough in petroleum exploration of the high-mature Lower Palaeozoic strata, North China. Both the Lower member of the Fengfeng Formation and the Second Member of the Upper Majiagou Formation in the Middle Ordovician are supposed to be the main source beds. Oil generation peaks range from 1.0% to 1.6% in Ro, showing a “lag effect” of oil generation in high-mature carbonate source rocks under multicyclic tectonic movement conditions. The Kongxi burial-hill zone adjoins a potential Ordovician source kitchen. The KG-3 Ordovician burial-hill reservoir has undergone two oil filling events, i.e., an early event in the Late Carboniferous-Permian and a more significant late event in the early Eogene.

An elastic-plastic analysis of short-leg shear wall structures during earthquakes

Short-leg shear wall structures are a new form of building structure that combine the merits of both frame and shear wall structures. Its architectural features, structure bearing and engineering cost are reasonable. To analyze the elastic-plastic response of a short-leg shear wall structure during an earthquake, this study modified the multiple-vertical-rod element model of the shear wall, considered the shear lag effect and proposed a multiple-vertical-rod element coupling beam model with a new local stiffness domain. Based on the principle of minimum potential energy and the variational principle, the stiffness matrixes of a short-leg shear wall and a coupling beam are derived in this study. Furthermore, the bending shear correlation for the analysis of different parameters to describe the structure, such as the beam height to span ratio, short-leg shear wall height to thickness ratio, and steel ratio are introduced. The results show that the height to span ratio directly affects the structural integrity; and the short-leg shear wall height to thickness ratio should be limited to a range of approximately 6.0 to 7.0. The design of short-leg shear walls should be in accordance with the ＂strong wall and weak beam＂ principle.

Model-scale tests to examine water pressures acting on potentially buoyant underground structures in clay strata

Throughout the service life, underground structures are subjected to transient and sustained hydrostatic pressures. The reservoir impoundment results in an increase in water level, as well as hydraulic gradient,which can endanger the uplift performance of infrastructure. In uplift design, a reduction factor is often suggested for buoyant force acting on underground structures in clays due to the time lag effect.However, the mechanism of pore pressure generation in clays is not fully understood. This investigation presents a novel U-shaped test chamber to assess the pore pressure generation with time in the horizontal branch subjected to an increase in reservoir level in the left vertical branch. A mathematical model is developed to explain the time lag effect of pore pressure generation. The test program also involves the evaluation of uplift pressure acting on foundation model in the right vertical branch due to adjacent reservoir impoundment. It is found that the time lag effect of pore pressure generation in clays can be observed irrespective of hydraulic gradient, but a higher hydraulic gradient can lead to a faster response in pore pressure sensors. A reduction factor of 0.84-0.87 should be considered to reduce the conservatism of uplift design.

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.

Analysis of vegetation dynamics and driving forces in Ordos: 2000-2019

As a typical resource-based city,Ordos has a rapid economic development.Previous studies mostly focused on vegetation changes monitoring,and rarely discuss socioeconomic impacts on vegetation changes.Based on MOD13Q1 data,climate data and 11 socioeconomic indicators from 2000 to 2019,combined with GIS technology and statistical methods,the spatiotemporal changes of Ordos vegetation and its influencing factors were studied.The results show that:(1)In the past 20 years,the NDVI value of Ordos ranged from 0.233 to 0.395,showing a fluctuating growth trend with a growth rate of 0.058/10a;the NDVI values of the eight counties under its jurisdiction also showed a fluctuating growth trend,but there were differences among regions.(2)Spatially,the vegetation in Ordos is high in the northeast and low in the southwest.The area of low vegetation area is 54200 km2,accounting for 62.39%of the total area of Ordos.The area of high vegetation area is only 19900 km2,mainly concentrated in the Yellow River impact area in the north of Dalate Banner.(3)In terms of spatial changes,the area of the vegetation improvement area is much larger than that of the vegetation degradation area,accounting for 52.38%of the total area of ordos,while the vegetation degradation area only accounts for 4.10%.(4)NDVI value showed a significant positive correlation with rainfall,the correlation coefficient is 0.802(P<0.01),the correlation coefficient with temperature is 0.361(P>0.05);the correlation coefficient with sunshine hours and humidity is negative;the correlation coefficient between the change of NDVI and the accumulated rainfall in the month is larger,and the correlation coefficient with the temperature of one month ago is larger.(5)The NDVI change was extremely significantly positively correlated with the 11 socioeconomic indicators,with a correlation of 0.728-0.796(P<0.01).From 2000 to 2019,the restoration effect of Ordos vegetation was good.Rainfall and temperature are the main factors affecting the growth of vegetation in Ordos,of which rainfall is the dominant factor.The response of NDVI changes to rainfall has no obvious lag,and the response to temperature has a 1-month lag.Socio-economic development has more positive than negative effects on vegetation cover.The research results will provide useful information for sustainable urban development and ecological environmental protection.

Lagged climatic effects on carbon fluxes over three grassland ecosystems in China

Aims The plasticity of ecosystem responses could buffer and post-pone the effects of climates on ecosystem carbon fluxes,but this lagged effect is often ignored.In this study,we used carbon flux data collected from three typical grassland ecosystems in China,including a temperate semiarid steppe in Inner mongolia(Neimeng site,Nm),an alpine shrub-meadow in Qinghai(Haibei site,Hb)and an alpine meadow steppe in Tibet(Dangxiong site,DX),to examine the time lagged effects of environmental factors on CO_(2) exchange.Methods Eddy covariance data were collected from three typical Chinese grasslands.In linking carbon fluxes with climatic factors,we used their averages or cumulative values within each 12-month period and we called them‘yearly’statistics in this study.To investigate the lagged effects of the climatic factors on the car-bon fluxes,the climatic‘yearly’statistics were kept still and the‘yearly’statistics of the carbon fluxes were shifted backward 1 month at a time.Important Findingssoil moisture and precipitation was the main factor driving the annual variations of carbon fluxes at the alpine Hb and DX,respectively,while the Nm site was under a synthetic impact of each climatic factor.The time lagged effect analysis showed that temperature had several months,even half a year lag effects on Co2 exchange at the three studied sites,while moisture’s effects were mostly exhibited as an immediate manner,except at Nm.In general,the lagged climatic effects were relatively weak for the alpine ecosystem.our results implied that it might be months or even 1 year before the variations of ecosystem carbon fluxes are adjusted to the current climate,so such lag effects could be resistant to more frequent climate extremes and should be a critical component to be considered in evaluating ecosystem stability.an improved knowledge on the lag effects could advance our understanding on the driving mechanisms of climate change effects on ecosystem carbon fluxes.

Time Lag Effect of Supply Chain Management on Firm Performance

The objective of this paper is to identify time lag effect in the relationship between supply chain management and financial performance.We hypothesize that firms with higher supply chain management capability are associated with higher financial performance and the impact would last longer.In addition,we introduce two contextual variables,ownership and market orientation,to detect the moderating effect of ownership structure and organizational culture,respectively.We use firm-level empirical data from 1,131 public Chinese manufacturing firms for the 2010–2019 period to investigate the effect and the result shows that there is a two-year time lag effect in the relationship,which means the positive impact of current supply chain management would last for three years.Furthermore,we find evidence that supply chain management in non-state-owned firms is more efficient and its positive financial impact would last longer than that in state-owned enterprises.Finally,we indicate that market-orientation can’t moderate the relationship between supply chain management and financial performance.

气候变化和物候变动对东北黑土区农业生产的协同作用及未来粮食生产风险

The black soil region of northeast China is a vital food base and is one of the most sensitive regions to climate change in China.However,the characteristics of the crop phenological response and the integrated impact of climate and phenological changes on agricultural productivity in the region under the background of climate change are not clear.The future agricultural risk assessment has been insufficiently quantified and the existing risk level formulation lacks a sound basis.Based on remote sensing products,climate data,and model simulations,this study integrated a logistic function fitting curvature derivation,multiple linear regression,and scenario simulation to investigate crop phenology dynamics and their climate response characteristics in the black soil region.Additionally,the compound effects of climate and phenology changes on agricultural production and possible future risks were identified.The key results were as follows:(1)From 2000 to 2017,29.76%of the black soil region of northeast China experienced a significant delay in the start of the growing season(SOS)and 16.71%of the total area displayed a trend for the end of the growing season(EOS)to arrive earlier.The time lagged effects of the SOS in terms of the crop response to climatic factors were site and climatic parameter dependent.The influence of temperature was widespread and its effect had a longer lag time in general;(2)Both climatic and phenological changes have had a significant effect on the inter-annual variability of crop production,and the predictive ability of both increased by 70.23%,while the predictive area expanded by 85.04%,as compared to that of climate change in the same period of the growing season;(3)Under the RCP8.5 scenario,there was a risk that the future crop yield would decrease in the north and increase in the south,and the risk area was constantly expanding.With a 2.0℃rise in global temperature,the crop yield of the southern Songnen black soil sub-region would reduce by almost 10%.This finding will improve our understanding of the mechanisms underlying climate change and vegetation productivity dynamics,and is also helpful in the promotion of the risk management of agrometeorological disasters.

Grassland coverage inter-annual variation and its coupling relation with hydrothermal factors in China during 1982-2010

GIMMS （Global Inventory Modeling and Mapping Studies） NDVI （Normalised Difference Vegetation Index） from 1982 to 2006 and MODIS （Moderate Resolution Imaging Spectroradiometer） NDVI from 2001 to 2010 were blended to extract the, grass coverage and analyze its spatial pattern. The response of grass coverage to climatic variations at annual and monthly time scales was analyzed. Grass coverage distribution had increased from northwest to southeast across China. During 1982-2010, the mean nationwide grass coverage was 34% but exhibited apparent spatial heterogeneity, being the highest （61.4%） in slope grasslands and the lowest （17.1%） in desert grasslands. There was a slight increase of the grass coverage with a rate of 0.17% per year. Increase in slope grasslands coverage was as high as 0.27% per year, while in the plain grasslands and meadows the grass coverage in- crease was the lowest （being 0.11% per year and 0.1% per year, respectively）. Across China, the grass coverage with extremely significant increase （P〈0.01） and significant increase （P〈0.05） accounted for 46.03% and 11% of the total grassland area, respectively, while those with extremely significant and significant decrease accounted for only 4.1% and 3.24%, respectively. At the annual time scale, there are no significant correlations between grass coverage and annual mean temperature and precipitation. However, the grass coverage was somewhat affected by temperature in alpine and sub-alpine grassland, alpine and sub-alpine meadow, slope grassland and meadow, while grass coverage in desert grassland and plain grassland was more affected by precipitation. At the monthly time-scale, there are significant correlations between grass coverage with both temperature and precipitation, indicating that the grass coverage is more affected by seasonal fluctuations of hydrothermal conditions. Additionally, there is one-month time lag-effect between grass coverage and climate factors for each grassland types.

Carry over from previous year environmental conditions alters dominance hierarchy in a prairie plant community

Aims To determine if an experimentally applied anomalous weather year could have effects on species composition and community structure that would carry over into the following year.Methods We conducted a field experiment applying two levels of temperature(ambient and+4
C)and two levels of precipitation(ambient and doubled)and followed cover of plant species during the treatment year and one post-treatment year.Data analysis included ordination analysis,examination of species frequency distributions and comparison of cover of functional groups and individual species.Important Findings A drought during the summer and fall of the treatment year resulted in significant differences in community structure between the 2 years.C3 and winter annual species were depressed in the spring of the second year following the dry autumn.Species richness and legume cover increased in the second,wetter,year.Treatments caused no overall differences in community structure but did alter the dominance hierarchy of species among treatments as well as years.Warming decreased relative cover of winter annuals and early spring-flowering species but increased other annuals.Warming and double precipitation together increased cover of C4 perennial graminoids.In particular,the warming and precipitation treatments both increased the abundance of Andropogon gerardii,not individually altering the dominance hierarchy but together nearly doubling the relative cover of A.gerardii,making it the most abundant species in the combined treatment,while the cover of Bromus arvensis,the former dominant,decreased by 25%.The following year,Andropogon relative cover increased further in the former warmed plots,becoming dominant in both the formerly warmed and warmed plus double precipitation treatments.The year following treatments also saw an increase in relative cover of summer-blooming species in the formerly warmed plots and differences among the former treatments in species richness of functional groups.If the effects of one anomalous year on plant abundance can carry over into the following year,several warm years could have a significant impact on plant community structure.