The onset,cessation,and length of the rainy season are crucial for global water resources,agricultural practices,and food security.However,the response of precipitation seasonality to global warming remains uncertain....The onset,cessation,and length of the rainy season are crucial for global water resources,agricultural practices,and food security.However,the response of precipitation seasonality to global warming remains uncertain.In this study,we analyze how global warming levels(GWLs)of 1.5℃ and 2℃ could affect the timing of rainfall onset(RODs),rainfall cessation(RCDs),and the overall duration of the rainy season(LRS)over global land monsoon(GLM)regions using simulations from CMIP6 under the SSP2-4.5 and SSP5-8.5 scenarios.With high model consensus,our results reveal that RODs are projected to occur later over Southern Africa,North Africa,and South America,but earlier over South Asia and Australia,in a warmer climate.The projected early RODs in Australia are more pronounced at the 2℃ GWL under SSP5-8.5.On the other hand,early RCDs are projected over South America and East Asia,while late RCDs are projected over North Africa,with high inter-model agreement.These changes are associated with a future decrease in LRS in most GLM regions.Additionally,we found that continuous warming over 1.5℃ will further reduce the length of the rainy season,especially over the South America,North Africa,and Southern Africa monsoon regions.The findings underscore the urgent need to mitigate global warming.展开更多
In recent years,there has been an increasing need for climate information across diverse sectors of society.This demand has arisen from the necessity to adapt to and mitigate the impacts of climate variability and cha...In recent years,there has been an increasing need for climate information across diverse sectors of society.This demand has arisen from the necessity to adapt to and mitigate the impacts of climate variability and change.Likewise,this period has seen a significant increase in our understanding of the physical processes and mechanisms that drive precipitation and its variability across different regions of Africa.By leveraging a large volume of climate model outputs,numerous studies have investigated the model representation of African precipitation as well as underlying physical processes.These studies have assessed whether the physical processes are well depicted and whether the models are fit for informing mitigation and adaptation strategies.This paper provides a review of the progress in precipitation simulation overAfrica in state-of-the-science climate models and discusses the major issues and challenges that remain.展开更多
During drilling operations,cyclic loading is exerted on the wellbore wall by the vibrations of the drill string.This loading could lead to rock fatigue,which in turn might result in wellbore failure.In this study,a nu...During drilling operations,cyclic loading is exerted on the wellbore wall by the vibrations of the drill string.This loading could lead to rock fatigue,which in turn might result in wellbore failure.In this study,a numerical model is developed to simulate the effects of repeated loading on rock fatigue and failure.The simulation is based on an elasto-plastic constitutive model coupled with a damage mechanics approach,which allows us to examine the wellbore instability due to drill string vibrations.The model is verified with the existing data in the literature related to experiments on impact of a steel ball against a curved wall.The findings indicate that cyclic loading increases the development of plastic strain around the wellbore significantly compared to static conditions,promoting rock fatigue.Furthermore,the cyclic loading expands the radius of the yielded zone substantially,a critical factor for maintaining wellbore integrity.The proposed model can be used to evaluate the wellbore stability under repetitive loading caused by the drill string action.展开更多
Calcite has a highly anisotropic thermal expansion coefficient, and repeated heating and cooling cycles can potentially destabilize chalks by breaking cement bonds between neighboring particles. Based on tensile stren...Calcite has a highly anisotropic thermal expansion coefficient, and repeated heating and cooling cycles can potentially destabilize chalks by breaking cement bonds between neighboring particles. Based on tensile strength measurements, we investigated how temperature cycles induce weakening of chalk.Tensile strength tests were performed on chalk specimens sampled from Kansas(USA) and Mons(Belgium), each with differing amounts of contact cement. Samples of the two chalk types were tested in dry and water-saturated states, and then exposed to 0, 15, and 30 temperature cycles in order to find out under what circumstances thermally induced tensile strength reduction occurs. The testing results show that the dry samples were not influenced by temperature cycling in either of the chalk types. However, in the water-saturated state, tensile strength is increasingly reduced with progressive numbers of temperature cycles for both chalk samples, especially for the more cemented Kansas chalk. The Kansas chalk demonstrated higher initial tensile strength compared to the less cemented Mons chalk, but the strength of both chalks was reduced by the same relative proportion when undergoing thermal cycles in the water-saturated state.展开更多
This physiological study aimed to evaluate the effects of dietary docosahexaenoic acid(DHA)and eicosapentaenoic acid(EPA)on the fatty acid composition and digestive enzyme activities of rainbow trout(Oncorhynchus myki...This physiological study aimed to evaluate the effects of dietary docosahexaenoic acid(DHA)and eicosapentaenoic acid(EPA)on the fatty acid composition and digestive enzyme activities of rainbow trout(Oncorhynchus mykiss)during salinity acclimation.Rainbow trout with an average initial weight of 90.61 g±9.25 g were fed diets with the quantities of DHA and EPA equaling to 0.54%,0.95%,1.40%and 1.79%(abbreviated as DE-0.54,DE-0.95,DE-1.40,and DE-1.79,respectively)for eight weeks,after which the gastric and intestinal fatty acids composition were analyzed.Subsequently,the fish underwent salinity acclimation.On days 1,4,7,and 14 after the freshwater was replaced by seawater and at the end of the 8-week period,gastric and intestinal digestive enzyme activities were determined.The results showed that the gastric and intestinal DHA and EPA contents of the fish were positively correlated to their dietary DHA and EPA levels.Low dietary DHA and EPA levels inhibited the protease activity of rainbow trout.Fish in the DE-0.54 group increased the lipase activity to enhance the utilization of lipids maybe due to the inadequate essential fatty acids for fish in this group.Hence,rainbow trout in the DE-0.54 group failed to maintain suitable activities of digestive enzymes after salinity acclimation.Therefore,a diet with minimum 0.95%DHA and EPA levels is necessary for rainbow trout during salinity acclimation.展开更多
<strong>Introduction</strong>.<span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> The molecular biological mechanism ...<strong>Introduction</strong>.<span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> The molecular biological mechanism of the increased incidence of the various types of cancer in obesity or type 2 diabetes in rodents or humans has largely been resolved in recent years. By contrast, the molecular biological mechanism of the decreased, not increased, incidence of the various types of cancer in the homozygous long-lived Ames dwarf mice still remains unresolved. </span><b><span style="font-family:Verdana;">Objective.</span></b><span style="font-family:Verdana;"> The first objective of the present study was to investigate whether the decrease in the incidence of cancer in the homozygous long-lived Ames dwarf mice is due to the increase, not decrease, in the expression of p27Kip1, a cell cycle repressor protein. The second objective was to investigate whether the decrease in the incidence of cancer in the homozygous long-lived Ames dwarf mice is due to the decrease, not increase, in the levels of glucose or insulin. </span><b><span style="font-family:Verdana;">Methods.</span></b><span style="font-family:Verdana;"> To achieve these objectives, we first performed western immunoblot analysis of the hepatic expression of p27Kip1 protein. We then performed, using a human breast cancer cell line </span><i><span style="font-family:Verdana;">in</span></i> <i><span style="font-family:Verdana;">vitro</span></i><span style="font-family:Verdana;">, the luciferase reporter plasmid assay to determine whether the translation initiation activity of the p27Kip1 mRNA is increased when the concentrations of either glucose or insulin are decreased. </span><b><span style="font-family:Verdana;">Results and Conclusion. </span></b><span style="font-family:Verdana;">The results of the first objective indicated that the hepatic expression of p27Kip1 protein was up-regulated in the homozygous long-lived Ames dwarf mice as expected. We also found that the lower concentrations of glucose or insulin increased the translation initiation activity of the p27Kip1 mRNA.</span></span></span></span>展开更多
We present the results of theoretical and experimental studies of flow processes of extended axisymmetric cavitators during motion near a free surface taking into account a considerable effect of fluid weightiness. Th...We present the results of theoretical and experimental studies of flow processes of extended axisymmetric cavitators during motion near a free surface taking into account a considerable effect of fluid weightiness. The main objective of work is to study ways of reduction of fluid weightiness effect using lift at cavitator and other body （hull） elements within a cavity, in order to apply this way of drag reduction for a range of considerably lower motion speeds.展开更多
Climate change has increased extreme events over globe and the most robust occurrences of concurrent drought and floods have become more common in Africa. This study focuses on the observed and projected analysis of r...Climate change has increased extreme events over globe and the most robust occurrences of concurrent drought and floods have become more common in Africa. This study focuses on the observed and projected analysis of rainfall extremes of consecutive dry day (CDD) and maximum monthly five day precipitation (RX5day) from Expert Team on Climate Change Detection and Indices (ETCCDI) in June-August season over Africa. The daily CORDEX Africa, reanalysis and CRU datasets were analyzed for extreme trends under RCP4.5 and RCP8.5 scenarios for the periods of 1980 to 2100. The spatiotemporal variability, trend, and magnitude of JJA seasonal rainfall performance exhibits a significant decreasing tendency over Eastern Africa compared to West Africa. The observed results of consecutive dry day (CDD) reveal that increasing trend and moreover RX5day shows that promising positive trend. Both rainfall extremes are influenced by the combined effect of large scale indexes and appear to be correlated negatively and positively with ENSO, NAO and AO. The CORDEX ensemble mean projections of JJA seasonal rainfall performance show a widespread significant change and the first mode of EOF depicts that 13.8% and 24.9% under the RCP4.5 and the highest variability is under RCP8.5 scenario. The projected CDD extreme exhibit an increasing trend in the coming periods and the percentage change revealed that increasing from 25.11%, 28.02% over West and 26.49%, 31.66% East Africa under RCP4.5 and RCP8.5 scenarios respectively. This situation will exacerbate increasing of frequent and intensified drought extremes over Africa. Additionally, the future RX5day indicated that mixed trend and revealed that increasing 3.72%, 2.54% over West and decreases -16.12%, -22.47% over East Africa under RCP4.5 and RCP8.5 respectively. Generally, rainfall extremes of CDD are projected to increase and RX5day shows a mixed trend in the coming periods over Africa and calls for further verification by using high resolution datasets.展开更多
In recent years, there has been increasing demand for high-resolution seasonal climate forecasts at sufficient lead times to allow response planning from users in agriculture, hydrology, disaster risk management, and ...In recent years, there has been increasing demand for high-resolution seasonal climate forecasts at sufficient lead times to allow response planning from users in agriculture, hydrology, disaster risk management, and health, among others. This paper examines the forecasting skill of the North American Multi-model Ensemble (NMME) over Ethiopia during the June to September (JJAS) season. The NMME, one of the multi-model seasonal forecasting systems, regularly generates monthly seasonal rainfall forecasts over the globe with 0.5 <span style="font-family:Verdana;">-</span><span style="font-family:;" "=""><span style="font-family:Verdana;"> 11.5 months lead time. The skill and predictability of seasonal rainfall are assessed using 28 years of hindcast data from the NMME models. The forecast skill is quantified using canonical correlation analysis (CCA) and root mean square error. The results show that the NMME models capture the JJAS seasonal rainfall over central, northern, and northeastern parts of Ethiopia while exhibiting weak or limited skill across western and southwestern Ethiopia. The performance of each model in predicting the JJAS seasonal rainfall is variable, showing greater skill in predicting dry conditions. Overall, the performance of the multi-model ensemble was not consistently better than any single ensemble member. The correlation of observed and predicted </span><span style="font-family:Verdana;">seasonal rainfall for the better performing models</span></span><span style="font-family:Verdana;">—GFDL-CM2p5-FLOR-A06,</span><span style="font-family:Verdana;"> CMC2-CanCM4, GFDL-CM2p5-FLOR-B01 and NASA-GMAO-062012</span><span style="font-family:Verdana;">—</span><span style="font-family:Verdana;">is 0.68, 0.58, 0.52, and 0.5, respectively. The COLA-RSMAS-CCSM4, CMC1-</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">CanCM3 and NCEP-CFSv2 models exhibit less skill, with correlations less than 0.4. In general, the NMME offers promising skill to predict seasonal rainfall over Ethiopia during the June-September (JJAS) season, motivating further work to assess its performance at longer lead times.</span>展开更多
Integrated water quantity and quality simulations have become a popular tool in investigations on global water crisis.For integrated and complex models,conventional uncertainty estimations focus on the uncertainties o...Integrated water quantity and quality simulations have become a popular tool in investigations on global water crisis.For integrated and complex models,conventional uncertainty estimations focus on the uncertainties of individual modules,e.g.,module parameters and structures,and do not consider the uncertainties propagated from interconnected modules.Therefore,this study investigated all the uncertainties of integrated water system simulations using the GLUE(i.e.,generalized likelihood uncertainty estimation)method,including uncertainties associated with individual modules,propagated uncertainties associated with interconnected modules,and their combinations.The changes in both acceptability thresholds of GLUE and the uncertainty estimation results were also investigated for different fixed percentages of total number of iterations(100000).Water quantity and quality variables(i.e.,runoff and ammonium nitrogen)were selected for the case study.The results showed that module uncertainty did not affect the runoff simulation performance,but remarkably weakened the water quality responses as the fixed percentage increased during calibration and validation periods.The propagated uncertainty from hydrological modules could not be ignored for water quality simulations,particularly during validation.The combination of module and propagated uncertainties further weakened the water quality simulation performance.The uncertainty intervals became wider owing to an increase in the fixed percentages and introduction of more uncertainty sources.Moreover,the acceptability threshold had a negative nonlinear relationship with the fixed percentage.The fixed percentages(20.0%-30.0%)were proposed as the acceptability thresholds owing to the satisfactory simulation performance and noticeably reduced uncertainty intervals they produced.This study provided methodological foundations for estimating multiple uncertainty sources of integrated water system models.展开更多
Understanding hydrological responses to rising levels of greenhouse gases are essential for climate and impact research.It is,however,often limited by a lack of long record of observational data to provide a basis for...Understanding hydrological responses to rising levels of greenhouse gases are essential for climate and impact research.It is,however,often limited by a lack of long record of observational data to provide a basis for understanding the longterm behavior of the climate system.Integrating reconstructed data and(global climate and hydrological)model simulations will help us to better understand the variability of climate and hydrology over timescales ranging from decades to centuries.In this study,we proposed an integrated approach to study flood variability in the upper reach of the Yangtze River over the last millennium to the end of the 21st century.To accomplish this,we first drove hydrological models using the precipitation and temperature from four Global Climate Models(GCM),BCC-CSM1.1,MIROC,MRI-CGCM3,and CCSM4,to simulate daily discharge for the upper reach of the Yangtze River during the period of the last millennium(850–1849),historical period(1850–2005),and a future period(2006–2099).Then,we evaluated whether the modeled precipitation,temperature,and extreme discharge had statistical properties similar to those shown in the documented dry-wet periods,temperature anomalies,and paleoflood records.Finally,we explored the extreme discharge variability using model simulations.The results indicate that:(1)The MIROC-ESM model,differing from the other three GCM models,revealed positive temperature changes from the warm period(Medieval Climate Anomaly;MCA)to the cold period(Little Ice Age;LIA),while the temperature variability of the other models was similar to the records.(2)The BCC-CSM1.1 model performed better than the others regarding correlations between modeled precipitation and documented dry-wet periods.(3)Over most of the subbasins in the upper Yangtze River,the magnitude of extreme discharge in the BCC-CSM1.1 model results showed that there was a decrease from the MCA to the LIA period and an increase in the historical period relative to the cold period,while a future increase was projected by the four GCMs under the influence of climate change.展开更多
Modern interactive tools for data analysis and visualisation are designed to expose their functionalities as a service through the Web.We present in this paper a Web API(SWIRRL)that allows Virtual Research Environment...Modern interactive tools for data analysis and visualisation are designed to expose their functionalities as a service through the Web.We present in this paper a Web API(SWIRRL)that allows Virtual Research Environments(VREs)to easily integrate such tools in their websites and re-purpose them to their users.The APl deals,on behalf of the clients,with the underlying complexity of allocating and managing resources within a target cloud platform.By combining storage and containerised services,offering analysis notebooks and other visualisation software,the APl creates dedicated working sessions on-demand,which can be accessed collaboratively.Thanks to the API's support for workflow execution,SWIRRL workspaces can be automatically populated with data of interest collected from external data providers.The system keeps track of updates and changes affecting the data and the tools by adopting versioning and standard provenance technologies.Users are provided with interactive controls enabling traceabilityand recovery actions,including the possibility of creating executable snapshots of their environments.SWIRRL is built in cooperation with two research infrastructures in the field of solid earth science and climate data modeling.We report on the particularadoptions and use cases.展开更多
Full waveform inversion of time-lapse seismic data can be used as a means of estimating the reservoir changes due to the production.Since the repeated computa-tions for the monitor surveys lead to a large computationa...Full waveform inversion of time-lapse seismic data can be used as a means of estimating the reservoir changes due to the production.Since the repeated computa-tions for the monitor surveys lead to a large computational cost,time-lapse full wave-form inversion is still considered to be a challenging task.To address this problem,we present an efficient target-oriented inversion scheme for time-lapse seismic data using an integral equation formulation with Gaussian beam based Green’s function approach.The proposed time-lapse approach allows one to perform a local inversion within a small region of interest(e.g.a reservoir under production)for the monitor survey.We have verified that the T-matrix approach is indeed naturally target-oriented,which was mentioned by Jakobsen and Ursin[24]and allows one to reduce the compu-tational cost of time-lapse inversion by focusing the inversion on the target-area only.This method is based on a new version of the distorted Born iterative T-matrix inverse scattering method.The Gaussian beam and T-matrix are used in this approach to perform the wavefield computation for the time-lapse inversion in the baseline model from the survey surface to the target region.We have provided target-oriented inversion results of the synthetic time-lapse waveform data,which shows that the proposed scheme reduces the computational cost significantly.展开更多
Large-scale production of plastics began in the 1950s followed by an onset of exponential growth,leading to its current widespread and dominant use.Despite this,no holistic risk assessment has yet been made on the hea...Large-scale production of plastics began in the 1950s followed by an onset of exponential growth,leading to its current widespread and dominant use.Despite this,no holistic risk assessment has yet been made on the health and environmental impacts of plastics,their degradation products,or their constituent chemicals.Once entering the environment,plastics undergo structural,chemical,and functional transformations,leading to the creation of microplastics and nanoplastics[1,2,3].Environmental exposure to microplastics and nanoplastics becomes inevitable,causing direct human dietary exposure.展开更多
The early Eocene is a period with very high atmospheric CO2 levels, which receives many interests from climate modelling aspects. To simulate the early Eocene paleoclimate, a realistic reconstruction for land-sea dist...The early Eocene is a period with very high atmospheric CO2 levels, which receives many interests from climate modelling aspects. To simulate the early Eocene paleoclimate, a realistic reconstruction for land-sea distribution, paleotopography and paleobathymetry is the fundamental step. Here, we present global paleogeographic reconstructions for the early Eocene(~55 Ma), based on integrated paleogeographic data set, the plate-tectonic reconstruction software(GPlates) and geographic information system software(ArcGIS). Comparing with previous paleogeographic reconstructions, we improve the reconstructions by incorporating many recent geologic data and data set, including:(1) Better representations of the Tethys Sea,some marginal or inland seas in the East and Southeast Asia, Atlantic and Arctic region, and the Drake Passage and Tasmanian Gateway;(2) integrated paleoelevation data of global high plateaus and mountains, especially the paleotopography of East Asia,and adopting the latest paleotopographic reconstruction data of the Antarctica;and(3) using the latest data set of oceanic crust paleo-age and oceanic sediment thickness to reconstruct the paleobathymetry.展开更多
Whether there were more extensive glaciations during the Marine Isotope Stage(MIS)3 relative to MIS 2 across the Tian Shan in Central Asia is intensely debated because of the uncertainty in chronological data and full...Whether there were more extensive glaciations during the Marine Isotope Stage(MIS)3 relative to MIS 2 across the Tian Shan in Central Asia is intensely debated because of the uncertainty in chronological data and fully understanding the driving mechanisms.To help resolve the ongoing debate,we assess the climate sensitivity of the glaciers and reconstruct the extent of glaciation during MIS 2 and 3 across the Tian Shan,using a glacier-resolving(250×250 m)ice sheet model asynchronously coupled with a global climate model.Our results demonstrate that the equilibrium-line altitude(ELA)over the Tian Shan decreases by∼180 m for every 1°C cooling under a modern precipitation regime,but precipitation reduction greatly lowers the sensitivity of the glaciers to temperature decrease(e.g.,the effect of 2°C cooling is broadly offset by a 50%decrease in precipitation).Under the modeled colder/drier-than-present climate,the model predicts an ELA depression(∆ELA)of∼75 m(162 m)over the Tian Shan during MIS 3 interstadials(stadials).The extent of MIS 3 glaciation is much smaller than that during MIS 2(i.e.,∆ELA=∼726 m).The more extensive glaciation during MIS 2 is largely attributed to the enhanced summer cooling.Furthermore,through a site-to-site model-data comparison,we find that the closest match between the modeled glacier margin and the locations of the glacial deposits previously argued to be MIS 3 is generally achieved under MIS 2 climatic conditions.These results suggest more extensive glacier advances over the Tian Shan during MIS 2 than MIS 3 on a regional scale,although MIS 3 glaciation may still occur in individual glacier catchments.This pattern suggests general synchronicity with the timing of maximum Northern Hemisphere ice sheets during the last glacial,which should be further tested in a multimodel framework in the future.展开更多
Deep neural network is a powerful tool for many tasks.Understanding why it is so successful and providing a mathematical explanation is an important problem and has been one popular research direction in past years.In...Deep neural network is a powerful tool for many tasks.Understanding why it is so successful and providing a mathematical explanation is an important problem and has been one popular research direction in past years.In the literature of mathematical analysis of deep neural networks,a lot of works is dedicated to establishing representation theories.How to make connections between deep neural networks and mathematical algorithms is still under development.In this paper,we give an algorithmic explanation for deep neural networks,especially in their connections with operator splitting.We show that with certain splitting strategies,operator-splitting methods have the same structure as networks.Utilizing this connection and the Potts model for image segmentation,two networks inspired by operator-splitting methods are proposed.The two networks are essentially two operator-splitting algorithms solving the Potts model.Numerical experiments are presented to demonstrate the effectiveness of the proposed networks.展开更多
基金supported by the Australian Research Council(Grant No.CE230100012)。
文摘The onset,cessation,and length of the rainy season are crucial for global water resources,agricultural practices,and food security.However,the response of precipitation seasonality to global warming remains uncertain.In this study,we analyze how global warming levels(GWLs)of 1.5℃ and 2℃ could affect the timing of rainfall onset(RODs),rainfall cessation(RCDs),and the overall duration of the rainy season(LRS)over global land monsoon(GLM)regions using simulations from CMIP6 under the SSP2-4.5 and SSP5-8.5 scenarios.With high model consensus,our results reveal that RODs are projected to occur later over Southern Africa,North Africa,and South America,but earlier over South Asia and Australia,in a warmer climate.The projected early RODs in Australia are more pronounced at the 2℃ GWL under SSP5-8.5.On the other hand,early RCDs are projected over South America and East Asia,while late RCDs are projected over North Africa,with high inter-model agreement.These changes are associated with a future decrease in LRS in most GLM regions.Additionally,we found that continuous warming over 1.5℃ will further reduce the length of the rainy season,especially over the South America,North Africa,and Southern Africa monsoon regions.The findings underscore the urgent need to mitigate global warming.
基金the World Climate Research Programme(WCRP),Climate Variability and Predictability(CLIVAR),and Global Energy and Water Exchanges(GEWEX)for facilitating the coordination of African monsoon researchsupport from the Center for Earth System Modeling,Analysis,and Data at the Pennsylvania State Universitythe support of the Office of Science of the U.S.Department of Energy Biological and Environmental Research as part of the Regional&Global Model Analysis(RGMA)program area。
文摘In recent years,there has been an increasing need for climate information across diverse sectors of society.This demand has arisen from the necessity to adapt to and mitigate the impacts of climate variability and change.Likewise,this period has seen a significant increase in our understanding of the physical processes and mechanisms that drive precipitation and its variability across different regions of Africa.By leveraging a large volume of climate model outputs,numerous studies have investigated the model representation of African precipitation as well as underlying physical processes.These studies have assessed whether the physical processes are well depicted and whether the models are fit for informing mitigation and adaptation strategies.This paper provides a review of the progress in precipitation simulation overAfrica in state-of-the-science climate models and discusses the major issues and challenges that remain.
基金funded by the Research council of Norway,Equinor and Sekal with NFR(Grant No.308826).
文摘During drilling operations,cyclic loading is exerted on the wellbore wall by the vibrations of the drill string.This loading could lead to rock fatigue,which in turn might result in wellbore failure.In this study,a numerical model is developed to simulate the effects of repeated loading on rock fatigue and failure.The simulation is based on an elasto-plastic constitutive model coupled with a damage mechanics approach,which allows us to examine the wellbore instability due to drill string vibrations.The model is verified with the existing data in the literature related to experiments on impact of a steel ball against a curved wall.The findings indicate that cyclic loading increases the development of plastic strain around the wellbore significantly compared to static conditions,promoting rock fatigue.Furthermore,the cyclic loading expands the radius of the yielded zone substantially,a critical factor for maintaining wellbore integrity.The proposed model can be used to evaluate the wellbore stability under repetitive loading caused by the drill string action.
文摘Calcite has a highly anisotropic thermal expansion coefficient, and repeated heating and cooling cycles can potentially destabilize chalks by breaking cement bonds between neighboring particles. Based on tensile strength measurements, we investigated how temperature cycles induce weakening of chalk.Tensile strength tests were performed on chalk specimens sampled from Kansas(USA) and Mons(Belgium), each with differing amounts of contact cement. Samples of the two chalk types were tested in dry and water-saturated states, and then exposed to 0, 15, and 30 temperature cycles in order to find out under what circumstances thermally induced tensile strength reduction occurs. The testing results show that the dry samples were not influenced by temperature cycling in either of the chalk types. However, in the water-saturated state, tensile strength is increasingly reduced with progressive numbers of temperature cycles for both chalk samples, especially for the more cemented Kansas chalk. The Kansas chalk demonstrated higher initial tensile strength compared to the less cemented Mons chalk, but the strength of both chalks was reduced by the same relative proportion when undergoing thermal cycles in the water-saturated state.
基金This publication was supported by the National Key Research and Development Program of China(No.2019YFD0901005)the National Natural Science Foundation of China(Nos.31702364 and 31572634)and the Primary Research and Development Program of Shandong Province(No.2018CXGC0101).
文摘This physiological study aimed to evaluate the effects of dietary docosahexaenoic acid(DHA)and eicosapentaenoic acid(EPA)on the fatty acid composition and digestive enzyme activities of rainbow trout(Oncorhynchus mykiss)during salinity acclimation.Rainbow trout with an average initial weight of 90.61 g±9.25 g were fed diets with the quantities of DHA and EPA equaling to 0.54%,0.95%,1.40%and 1.79%(abbreviated as DE-0.54,DE-0.95,DE-1.40,and DE-1.79,respectively)for eight weeks,after which the gastric and intestinal fatty acids composition were analyzed.Subsequently,the fish underwent salinity acclimation.On days 1,4,7,and 14 after the freshwater was replaced by seawater and at the end of the 8-week period,gastric and intestinal digestive enzyme activities were determined.The results showed that the gastric and intestinal DHA and EPA contents of the fish were positively correlated to their dietary DHA and EPA levels.Low dietary DHA and EPA levels inhibited the protease activity of rainbow trout.Fish in the DE-0.54 group increased the lipase activity to enhance the utilization of lipids maybe due to the inadequate essential fatty acids for fish in this group.Hence,rainbow trout in the DE-0.54 group failed to maintain suitable activities of digestive enzymes after salinity acclimation.Therefore,a diet with minimum 0.95%DHA and EPA levels is necessary for rainbow trout during salinity acclimation.
文摘<strong>Introduction</strong>.<span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> The molecular biological mechanism of the increased incidence of the various types of cancer in obesity or type 2 diabetes in rodents or humans has largely been resolved in recent years. By contrast, the molecular biological mechanism of the decreased, not increased, incidence of the various types of cancer in the homozygous long-lived Ames dwarf mice still remains unresolved. </span><b><span style="font-family:Verdana;">Objective.</span></b><span style="font-family:Verdana;"> The first objective of the present study was to investigate whether the decrease in the incidence of cancer in the homozygous long-lived Ames dwarf mice is due to the increase, not decrease, in the expression of p27Kip1, a cell cycle repressor protein. The second objective was to investigate whether the decrease in the incidence of cancer in the homozygous long-lived Ames dwarf mice is due to the decrease, not increase, in the levels of glucose or insulin. </span><b><span style="font-family:Verdana;">Methods.</span></b><span style="font-family:Verdana;"> To achieve these objectives, we first performed western immunoblot analysis of the hepatic expression of p27Kip1 protein. We then performed, using a human breast cancer cell line </span><i><span style="font-family:Verdana;">in</span></i> <i><span style="font-family:Verdana;">vitro</span></i><span style="font-family:Verdana;">, the luciferase reporter plasmid assay to determine whether the translation initiation activity of the p27Kip1 mRNA is increased when the concentrations of either glucose or insulin are decreased. </span><b><span style="font-family:Verdana;">Results and Conclusion. </span></b><span style="font-family:Verdana;">The results of the first objective indicated that the hepatic expression of p27Kip1 protein was up-regulated in the homozygous long-lived Ames dwarf mice as expected. We also found that the lower concentrations of glucose or insulin increased the translation initiation activity of the p27Kip1 mRNA.</span></span></span></span>
文摘We present the results of theoretical and experimental studies of flow processes of extended axisymmetric cavitators during motion near a free surface taking into account a considerable effect of fluid weightiness. The main objective of work is to study ways of reduction of fluid weightiness effect using lift at cavitator and other body （hull） elements within a cavity, in order to apply this way of drag reduction for a range of considerably lower motion speeds.
文摘Climate change has increased extreme events over globe and the most robust occurrences of concurrent drought and floods have become more common in Africa. This study focuses on the observed and projected analysis of rainfall extremes of consecutive dry day (CDD) and maximum monthly five day precipitation (RX5day) from Expert Team on Climate Change Detection and Indices (ETCCDI) in June-August season over Africa. The daily CORDEX Africa, reanalysis and CRU datasets were analyzed for extreme trends under RCP4.5 and RCP8.5 scenarios for the periods of 1980 to 2100. The spatiotemporal variability, trend, and magnitude of JJA seasonal rainfall performance exhibits a significant decreasing tendency over Eastern Africa compared to West Africa. The observed results of consecutive dry day (CDD) reveal that increasing trend and moreover RX5day shows that promising positive trend. Both rainfall extremes are influenced by the combined effect of large scale indexes and appear to be correlated negatively and positively with ENSO, NAO and AO. The CORDEX ensemble mean projections of JJA seasonal rainfall performance show a widespread significant change and the first mode of EOF depicts that 13.8% and 24.9% under the RCP4.5 and the highest variability is under RCP8.5 scenario. The projected CDD extreme exhibit an increasing trend in the coming periods and the percentage change revealed that increasing from 25.11%, 28.02% over West and 26.49%, 31.66% East Africa under RCP4.5 and RCP8.5 scenarios respectively. This situation will exacerbate increasing of frequent and intensified drought extremes over Africa. Additionally, the future RX5day indicated that mixed trend and revealed that increasing 3.72%, 2.54% over West and decreases -16.12%, -22.47% over East Africa under RCP4.5 and RCP8.5 respectively. Generally, rainfall extremes of CDD are projected to increase and RX5day shows a mixed trend in the coming periods over Africa and calls for further verification by using high resolution datasets.
文摘In recent years, there has been increasing demand for high-resolution seasonal climate forecasts at sufficient lead times to allow response planning from users in agriculture, hydrology, disaster risk management, and health, among others. This paper examines the forecasting skill of the North American Multi-model Ensemble (NMME) over Ethiopia during the June to September (JJAS) season. The NMME, one of the multi-model seasonal forecasting systems, regularly generates monthly seasonal rainfall forecasts over the globe with 0.5 <span style="font-family:Verdana;">-</span><span style="font-family:;" "=""><span style="font-family:Verdana;"> 11.5 months lead time. The skill and predictability of seasonal rainfall are assessed using 28 years of hindcast data from the NMME models. The forecast skill is quantified using canonical correlation analysis (CCA) and root mean square error. The results show that the NMME models capture the JJAS seasonal rainfall over central, northern, and northeastern parts of Ethiopia while exhibiting weak or limited skill across western and southwestern Ethiopia. The performance of each model in predicting the JJAS seasonal rainfall is variable, showing greater skill in predicting dry conditions. Overall, the performance of the multi-model ensemble was not consistently better than any single ensemble member. The correlation of observed and predicted </span><span style="font-family:Verdana;">seasonal rainfall for the better performing models</span></span><span style="font-family:Verdana;">—GFDL-CM2p5-FLOR-A06,</span><span style="font-family:Verdana;"> CMC2-CanCM4, GFDL-CM2p5-FLOR-B01 and NASA-GMAO-062012</span><span style="font-family:Verdana;">—</span><span style="font-family:Verdana;">is 0.68, 0.58, 0.52, and 0.5, respectively. The COLA-RSMAS-CCSM4, CMC1-</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">CanCM3 and NCEP-CFSv2 models exhibit less skill, with correlations less than 0.4. In general, the NMME offers promising skill to predict seasonal rainfall over Ethiopia during the June-September (JJAS) season, motivating further work to assess its performance at longer lead times.</span>
基金supported by the National Natural Science Foundation of China(Grant Nos.42071041 and 41807171)the Outstanding Youth Science Foundation of the National Natural Science Foundation of China(Grant No.51822908)。
文摘Integrated water quantity and quality simulations have become a popular tool in investigations on global water crisis.For integrated and complex models,conventional uncertainty estimations focus on the uncertainties of individual modules,e.g.,module parameters and structures,and do not consider the uncertainties propagated from interconnected modules.Therefore,this study investigated all the uncertainties of integrated water system simulations using the GLUE(i.e.,generalized likelihood uncertainty estimation)method,including uncertainties associated with individual modules,propagated uncertainties associated with interconnected modules,and their combinations.The changes in both acceptability thresholds of GLUE and the uncertainty estimation results were also investigated for different fixed percentages of total number of iterations(100000).Water quantity and quality variables(i.e.,runoff and ammonium nitrogen)were selected for the case study.The results showed that module uncertainty did not affect the runoff simulation performance,but remarkably weakened the water quality responses as the fixed percentage increased during calibration and validation periods.The propagated uncertainty from hydrological modules could not be ignored for water quality simulations,particularly during validation.The combination of module and propagated uncertainties further weakened the water quality simulation performance.The uncertainty intervals became wider owing to an increase in the fixed percentages and introduction of more uncertainty sources.Moreover,the acceptability threshold had a negative nonlinear relationship with the fixed percentage.The fixed percentages(20.0%-30.0%)were proposed as the acceptability thresholds owing to the satisfactory simulation performance and noticeably reduced uncertainty intervals they produced.This study provided methodological foundations for estimating multiple uncertainty sources of integrated water system models.
基金supported by the National Key Research and Development Program(Grant No.2017YFA0603702)the Research Council of Norway(FRINATEK Project 274310)。
文摘Understanding hydrological responses to rising levels of greenhouse gases are essential for climate and impact research.It is,however,often limited by a lack of long record of observational data to provide a basis for understanding the longterm behavior of the climate system.Integrating reconstructed data and(global climate and hydrological)model simulations will help us to better understand the variability of climate and hydrology over timescales ranging from decades to centuries.In this study,we proposed an integrated approach to study flood variability in the upper reach of the Yangtze River over the last millennium to the end of the 21st century.To accomplish this,we first drove hydrological models using the precipitation and temperature from four Global Climate Models(GCM),BCC-CSM1.1,MIROC,MRI-CGCM3,and CCSM4,to simulate daily discharge for the upper reach of the Yangtze River during the period of the last millennium(850–1849),historical period(1850–2005),and a future period(2006–2099).Then,we evaluated whether the modeled precipitation,temperature,and extreme discharge had statistical properties similar to those shown in the documented dry-wet periods,temperature anomalies,and paleoflood records.Finally,we explored the extreme discharge variability using model simulations.The results indicate that:(1)The MIROC-ESM model,differing from the other three GCM models,revealed positive temperature changes from the warm period(Medieval Climate Anomaly;MCA)to the cold period(Little Ice Age;LIA),while the temperature variability of the other models was similar to the records.(2)The BCC-CSM1.1 model performed better than the others regarding correlations between modeled precipitation and documented dry-wet periods.(3)Over most of the subbasins in the upper Yangtze River,the magnitude of extreme discharge in the BCC-CSM1.1 model results showed that there was a decrease from the MCA to the LIA period and an increase in the historical period relative to the cold period,while a future increase was projected by the four GCMs under the influence of climate change.
基金supported by the EU H2020 project ENVRIFair(No.824068)ISENES3(No.824084).
文摘Modern interactive tools for data analysis and visualisation are designed to expose their functionalities as a service through the Web.We present in this paper a Web API(SWIRRL)that allows Virtual Research Environments(VREs)to easily integrate such tools in their websites and re-purpose them to their users.The APl deals,on behalf of the clients,with the underlying complexity of allocating and managing resources within a target cloud platform.By combining storage and containerised services,offering analysis notebooks and other visualisation software,the APl creates dedicated working sessions on-demand,which can be accessed collaboratively.Thanks to the API's support for workflow execution,SWIRRL workspaces can be automatically populated with data of interest collected from external data providers.The system keeps track of updates and changes affecting the data and the tools by adopting versioning and standard provenance technologies.Users are provided with interactive controls enabling traceabilityand recovery actions,including the possibility of creating executable snapshots of their environments.SWIRRL is built in cooperation with two research infrastructures in the field of solid earth science and climate data modeling.We report on the particularadoptions and use cases.
文摘Full waveform inversion of time-lapse seismic data can be used as a means of estimating the reservoir changes due to the production.Since the repeated computa-tions for the monitor surveys lead to a large computational cost,time-lapse full wave-form inversion is still considered to be a challenging task.To address this problem,we present an efficient target-oriented inversion scheme for time-lapse seismic data using an integral equation formulation with Gaussian beam based Green’s function approach.The proposed time-lapse approach allows one to perform a local inversion within a small region of interest(e.g.a reservoir under production)for the monitor survey.We have verified that the T-matrix approach is indeed naturally target-oriented,which was mentioned by Jakobsen and Ursin[24]and allows one to reduce the compu-tational cost of time-lapse inversion by focusing the inversion on the target-area only.This method is based on a new version of the distorted Born iterative T-matrix inverse scattering method.The Gaussian beam and T-matrix are used in this approach to perform the wavefield computation for the time-lapse inversion in the baseline model from the survey surface to the target region.We have provided target-oriented inversion results of the synthetic time-lapse waveform data,which shows that the proposed scheme reduces the computational cost significantly.
基金M.H.and E.G.X.thank the support of the Department of Biology,University of Southern Denmark,and Danmarks Frie Forskningsfond(0165-00056B)。
文摘Large-scale production of plastics began in the 1950s followed by an onset of exponential growth,leading to its current widespread and dominant use.Despite this,no holistic risk assessment has yet been made on the health and environmental impacts of plastics,their degradation products,or their constituent chemicals.Once entering the environment,plastics undergo structural,chemical,and functional transformations,leading to the creation of microplastics and nanoplastics[1,2,3].Environmental exposure to microplastics and nanoplastics becomes inevitable,causing direct human dietary exposure.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41690114, 41888101 & 41430531)
文摘The early Eocene is a period with very high atmospheric CO2 levels, which receives many interests from climate modelling aspects. To simulate the early Eocene paleoclimate, a realistic reconstruction for land-sea distribution, paleotopography and paleobathymetry is the fundamental step. Here, we present global paleogeographic reconstructions for the early Eocene(~55 Ma), based on integrated paleogeographic data set, the plate-tectonic reconstruction software(GPlates) and geographic information system software(ArcGIS). Comparing with previous paleogeographic reconstructions, we improve the reconstructions by incorporating many recent geologic data and data set, including:(1) Better representations of the Tethys Sea,some marginal or inland seas in the East and Southeast Asia, Atlantic and Arctic region, and the Drake Passage and Tasmanian Gateway;(2) integrated paleoelevation data of global high plateaus and mountains, especially the paleotopography of East Asia,and adopting the latest paleotopographic reconstruction data of the Antarctica;and(3) using the latest data set of oceanic crust paleo-age and oceanic sediment thickness to reconstruct the paleobathymetry.
基金funded by the National Natural Science Foundation of China(42022036,41888101)the Youth Innovation Promotion Association by CAS(2019080).
文摘Whether there were more extensive glaciations during the Marine Isotope Stage(MIS)3 relative to MIS 2 across the Tian Shan in Central Asia is intensely debated because of the uncertainty in chronological data and fully understanding the driving mechanisms.To help resolve the ongoing debate,we assess the climate sensitivity of the glaciers and reconstruct the extent of glaciation during MIS 2 and 3 across the Tian Shan,using a glacier-resolving(250×250 m)ice sheet model asynchronously coupled with a global climate model.Our results demonstrate that the equilibrium-line altitude(ELA)over the Tian Shan decreases by∼180 m for every 1°C cooling under a modern precipitation regime,but precipitation reduction greatly lowers the sensitivity of the glaciers to temperature decrease(e.g.,the effect of 2°C cooling is broadly offset by a 50%decrease in precipitation).Under the modeled colder/drier-than-present climate,the model predicts an ELA depression(∆ELA)of∼75 m(162 m)over the Tian Shan during MIS 3 interstadials(stadials).The extent of MIS 3 glaciation is much smaller than that during MIS 2(i.e.,∆ELA=∼726 m).The more extensive glaciation during MIS 2 is largely attributed to the enhanced summer cooling.Furthermore,through a site-to-site model-data comparison,we find that the closest match between the modeled glacier margin and the locations of the glacial deposits previously argued to be MIS 3 is generally achieved under MIS 2 climatic conditions.These results suggest more extensive glacier advances over the Tian Shan during MIS 2 than MIS 3 on a regional scale,although MIS 3 glaciation may still occur in individual glacier catchments.This pattern suggests general synchronicity with the timing of maximum Northern Hemisphere ice sheets during the last glacial,which should be further tested in a multimodel framework in the future.
基金supported by HKBU 179356,NSFC 12201530 and HKRGC ECS 22302123supported by NSFC/RGC grant N-HKBU214-19 and NORCE Kompetanseoppbygging programsupported by HKRGC GRF grants CityU1101120,CityU11309922,CRF grant C1013-21GF,and HKRGC-NSFC Grant N CityU214/19.
文摘Deep neural network is a powerful tool for many tasks.Understanding why it is so successful and providing a mathematical explanation is an important problem and has been one popular research direction in past years.In the literature of mathematical analysis of deep neural networks,a lot of works is dedicated to establishing representation theories.How to make connections between deep neural networks and mathematical algorithms is still under development.In this paper,we give an algorithmic explanation for deep neural networks,especially in their connections with operator splitting.We show that with certain splitting strategies,operator-splitting methods have the same structure as networks.Utilizing this connection and the Potts model for image segmentation,two networks inspired by operator-splitting methods are proposed.The two networks are essentially two operator-splitting algorithms solving the Potts model.Numerical experiments are presented to demonstrate the effectiveness of the proposed networks.
