A new potential function for the calculation of contact forces in the combined finite–discrete element method          下载免费PDF全文

C.Z. Yan  H. Zheng 《国际地质力学数值与分析法杂志》2017,41(2):265-283

Although the potential contact force proposed by Munjiza overcomes the difficulties inherent in the traditional discrete element methods, the physical meaning of the potential is not clear and the contact force derived from the original potential function is strongly dependent on the mesh configuration. In this study, we redefine a potential function and propose a new contact force calculation method based on a unified standard. Moreover, the new potential function retains all the advantages of the original potential function but has less mesh dependency. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Résumé of research into river channel changes conducted in the USSR / Résumé des recherches des changements des lits des rivières effectuées dans l'URSS     

V. V. KUPRIANOV  Z. D. KOPALIANI 《水文科学杂志》2013,58(3):345-349

Abstract

This paper describes briefly some findings and investigations on the problem of channel processes conducted in the USSR. It was stimulated by the publication of River Channel Changes (Gregory, 1977).  相似文献   

Sensitivity of evapotranspiration and soil moisture in wheat fields to changes in climate and direct effects of carbon dioxide     

L. S. KUCHMENT  Z. P. STARTSEVA 《水文科学杂志》2013,58(6):631-643

Abstract

A physically based model of moisture transfer in the soil-canopy-atmosphere system, fitted to measured data in wheat fields, was applied to calculate the sensitivity of evapotranspiration to the combined effect of possible CO₂-induced climate changes and the direct impact of doubling CO₂ content in the atmosphere. The impact of carbon dioxide was taken into account by changing the stomatal resistance and the leaf area index. Several climate change scenarios were used. Simulation studies showed that when the changes of a number of climatic and plant factors are considered, evapotranspiration responses can differ greatly from those that consider only temperature change. The temperature effect of the increase in CO₂ content in the atmosphere can be compensated by changes in the physiological parameters of vegetation. Thus, under certain conditions, one can expect a decrease in evapotranspiration instead of an increase such as is predicted by a number of models which neglect the direct effects of CO₂ on plant behaviour.  相似文献   

Hydrologic impact of regional climate change for the snowfed and glacierfed river basins in the Republic of Tajikistan: hydrological response of flow to climate change     

S. Kure  S. Jang  N. Ohara  M. L. Kavvas  Z. Q. Chen 《水文研究》2013,27(26):4057-4070

The warming of the Earth's atmosphere system is likely to change temperature and precipitation, which may affect the climate, hydrology and water resources at the river basins over the world. The importance of temperature change becomes even greater in snow or glacier dominated basins where it controls the snowmelt processes during the late‐winter, spring and summer months. In this study hydrologic responses of streamflow in the Pyanj and Vaksh River basins to climate change are analysed with a watershed hydrology model, based on the downscaled atmospheric data as input, in order to assess the regional climate change impact for the snowfed and glacierfed river basins in the Republic of Tajikistan. As a result of this analysis, it was found that the annual mean river discharge is increasing in the future at snow and glacier dominated areas due to the air temperature increase and the consequent increase in snow/ice melt rates until about 2060. Then the annual mean flow discharge starts to decrease from about 2080 onward because the small glaciers start to disappear in the glacier areas. It was also found that there is a gradual change in the hydrologic flow regime throughout a year, with the high flows occuring earlier in the hydrologic year, due to the warmer climate in the future. Furthermore, significant increases in annual maximum daily flows, including the 100‐year return period flows, at the Pyanj and Vaksh River basins toward the end of the 21st century can be inferred from flood frequency analysis results. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

The relationship between the duration of solar X-ray flares and the mass of associated coronal ejections     

A. N. Shakhovskaya  Z. S. Akhtemov 《Bulletin of the Crimean Astrophysical Observatory》2013,109(1):86-89

The statistical relationship between the parameters of X-ray flares and coronal mass ejections on the Sun that are associated with these flares, is considered. It is shown that short X-ray flares are characterized on average by a lower mass ejection in the outer layers of the corona and interplanetary space as compared to high-energy long-duration events.  相似文献   

Hydrocarbons of Surface Waters in the Transantarctic Section     

Nemirovskaya  I. A.  Redzhepova  Z. Yu.  Lisitzin  A. P. 《Doklady Earth Sciences》2019,486(1):562-567

Doklady Earth Sciences - The data obtained for 2015–2017 on the content and composition of aliphatic hydrocarbons (HCs) in particulate matter at the river–sea geochemical barriers (the...  相似文献   

Metamorphic evolution of medium‐temperature ultra‐high pressure (MT‐UHP) eclogites from the South Dabie orogen,Central China: an insight from phase equilibria modelling     

C. J. Wei  J. H. Qian  Z. L. Tian 《Journal of Metamorphic Geology》2013,31(7):755-774

Medium‐temperature ultrahigh pressure (MT‐UHP) eclogites from the south Dabie orogen, as represented by samples from the Jinheqiao, Shuanghe and Bixiling areas, consist of garnet, omphacite, phengite, epidote, hornblendic amphibole, quartz/coesite and rutile with or without kyanite and talc. Garnet is mostly anhedral and unzoned, but a few porphyroblasts are weakly zoned with core–mantle increasing grossular (X_gr) and decreasing pyrope (X_py) contents. Garnet compositions are closely correlated with the bulk compositions. For instance, the X_py and X_gr contents are positively correlated with the bulk MgO and CaO contents. Phengite is occasionally zoned with core–rim deceasing Si content, and phengite grains as inclusions in garnet show higher Si than in the matrix, suggesting differently resetting during post‐peak stages. The maximum Si contents are mostly 3.60–3.63 p.f.u. for the three areas. Pseudosections calculated using THERMOCALC suggest that the MT‐UHP eclogites should have a peak assemblage of garnet + omphacite + lawsonite + phengite + coesite in most rocks of higher MgO content. In this assemblage, the X_py in garnet mostly depends on bulk compositions, whereas the X_gr in garnet and the Si contents in phengite regularly increase, respectively, as temperature and as pressure rise, and thus, can provide robust thermobarometric constraints. Using the X_gr and Si isopleths in pseudosections, the peak P–T conditions were estimated to be 40 kbar/730 °C for the Jinheqiao, 41 kbar/726 °C for the Shuanghe, and 37–52 kbar and 700–830 °C for the Bixiling eclogites. Some eclogites with higher FeO are predicted to have a peak assemblage of garnet + omphacite + coesite ± phengite without lawsonite, where the garnet and phengite compositions highly depend on bulk compositions and generally cannot give available thermobarometric constraints. Decompression of the eclogites with lawsonite in the peak stage is inferred to be accompanied with cooling and involves two stages: an early‐stage decompression is dominated by lawsonite dehydration, resulting in increase in the mode of anhydrous minerals, or further eclogitization, and formation of epidote porphyroblasts and kyanite‐bearing quartz veins in eclogite. As lawsonite dehydration can facilitate evolution of assemblages under fluid‐present conditions, it is difficult to recover real peak P–T conditions for UHP eclogites with lawsonite. This may be a reason why the P–T conditions estimated for eclogites using thermobarometers are mostly lower than those estimated for the coherent ultramafic rocks, and lower than those suggested from the inclusion assemblages in zircon from marble. A late‐stage decompression is dominated by formation of hornblendic amphibole and plagioclase with fluid infiltration. The lawsonite‐absent MT‐UHP eclogites have only experienced a decompression metamorphism corresponding to the later stage and generally lack the epidote overprinting.  相似文献   

Spatial and temporal variability of temperature,precipitation, and streamflow in upper Sang‐kan basin,China          下载免费PDF全文

L. Zhang  R. Karthikeyan  Z. Bai  J. Wang 《水文研究》2017,31(2):279-295

Temporal streamflow variability in an inland hydrologic station and temporal trends and frequency changes at three weather stations in a semiarid river basin located in Loess Plateau, China, were detected by using linear regression, Mann–Kendall analysis, and wavelet transform methods. Double cumulative curve and ordered clustering were used to identify the hydrological periods of upper Sang‐kan (USK) basin between 1957 and 2012. The results indicate that (1) precipitation in the USK basin over the study period did not show any trend, while the temperature showed a significant increase; (2) streamflow flowing out of the USK basin indicated a significant decrease; (3) two distinct hydrological periods – the ‘natural period’ from 1957 to 1984 and the ‘human impact period’ from 1985 to 2012 – were present; and (4) the contributions of climate change and human activities to reduce the streamflow were 36.9% and 63.1% respectively. The results indicate that human activities may be contributing to a decrease in streamflow in the USK basin. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Mobilized side and tip resistances of piles in clay     

Mohamed Ashour  Gary M. Norris  Sherif Elfass  Ashraf Z. Al-Hamdan 《Computers and Geotechnics》2010,37(7-8):858-866

This paper presents a procedure to assess the mobilized pile side and tip resistance versus pile head and tip settlement under axial load in clay soil. The load transfer (t–z) curve is evaluated at any point on the loaded pile based on the combined pile tip/side resistance–displacement mechanisms along the length of the pile. Unlike current methods that assume the pile settlements as a percentage of the pile/shaft diameter, the presented technique determines the side and tip resistance of the pile and the associated pile settlement under existing load based on the current stress/strain level in the surrounding soil up to failure (excessive settlement). The technique employs the concepts of the elastic theory and Ramberg–Osgood characterization of the stress–strain behavior of the clay soil. Case studies are also presented to exhibit the capabilities of the proposed procedure. The good agreement between measured and calculated load transfer curves along the pile and pile tip resistance versus pile head, side, and tip displacements shows the consistency of the proposed procedure. A computer code is developed to employ the presented technique.  相似文献   

Spin-down of young pulsars with a fallback disk     

X.-D. Li  Z.-B. Jiang 《Astrophysics and Space Science》2007,308(1-4):525-529

By performing Monte-Carlo calculations of the spin-down of young pulsars surrounded by a supernova fallback disk, we present possible constraints on the propeller torques exerted by the disks on neutron stars. This work was supported by the National Natural Science Foundation of China.  相似文献