A numerical study of geostrophic adjustment and frontogenesis   总被引：1，自引：0，他引：1  

Majid M. Farahani  Wu Rongsheng 《大气科学进展》1998,15(2):179-192

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Modeling and Prediction of Habitat Suitability for Ferula gummosa Medicinal Plant in a Mountainous Area     

Mohammady  Majid  Pourghasemi  Hamid Reza  Yousefi  Saleh  Dastres  Emran  Edalat  Mohsen  Pouyan  Soheila  Eskandari  Saeedeh 《Natural Resources Research》2021,30(6):4861-4884

Natural Resources Research - Habitat suitability modeling and mapping are important aspects of long-term strategies for sustaining plant ecosystems. In this study, seven state-of-the-art machine...  相似文献   

Geochemistry of sediments of the Al-Batin alluvial fan,Southern Iraq     

Majid Alkinani  Broder Merkel 《Environmental Earth Sciences》2018,77(7):282

The Al-Batin alluvial fan covers a broad area of southern Iraq. It was the main battlefield of two devastating wars in 1991 and 2003, during which huge amounts of depleted uranium (DU) were used. This study aims to assess the geochemistry of this fan sediment including the potential effects of the DU used. Sixty-three samples were collected from sediments including three samples from sediments under tanks attacked by DU ammunition. Major elements were measured by XRF (fusion bead method), whereas ICP-MS was used to measure the trace elements. The results suggest that the most dominant major minerals are in the order of: quartz?>?secondary gypsum?>?calcite?>?feldspar, clay minerals?>?iron oxide, and show abnormal concentrations of Sr, Cr, Ni, and V. This study also determined an area with high concentration of U in the north east part of the fan. Statistical analysis and spatial distribution of important elements suggests that two major factors affect mineral formation. The first factor reflects the influence of minerals in the source area of the sediments (Arabian Shield): quartz, carbonate, clay minerals, feldspars, as well as iron oxides and elevated concentrations of V, Ni, and Cr. The second factor points at authigenic formation of secondary gypsum and celestite and elevated U concentration under the control of a hot arid climate and the specific groundwater situation. However, the origin of the sediments is geogenic, while the anthropogenic impact seems to be minor. Spatial distribution of U and the ^235/238U ratio did not show any peaks in the places where tanks have been destroyed. This is contrary to media speculations and some scientific reports about the permanent risks of DU in the area, which creates public concern about the potential risk of living in this area.  相似文献   

The Response of Macrobenthic Communities to Environmental Variability in Tropical Coastal Waters     

Seyedeh Belin Tavakoly Sany  Mohammad Tajfard  Rosli Hashim  Majid Rezayi  Mohammad Azizur Rahman  David J. Karlen 《Estuaries and Coasts》2018,41(4):1178-1192

The relative contributions of spatial and temporal fluctuations are different in shaping natural communities in a tropical coastal/estuarine system. Understanding how coastal communities respond to these fluctuations is still equivocal, and thus, available data are rare. Here, multiple analytical approaches were used to identify key spatial and temporal factors, and to quantify their relative roles in shaping a macrobenthic community through space (contamination degree, physical parameters, and sediment characteristics) and time (climatic factors, season, and year). A dataset of eight sampling times was analyzed over a period of 2 years, in which macrobenthic species abundances were sampled. A total of 33 species were identified, including 18 bivalves, 5 gastropods, and 4 crustaceans. The other taxa were less diverse. The results show that there were no significant temporal changes of macrobenthic community structure, but spatial changes were significant and synchronized with environmental factors (i.e., sediment characteristics, water depth, and the distance from anthropogenic sources). This study demonstrates that spatial factors played a primary role in structuring of macrobenthic assemblages, whereas the influence of temporal factors appeared less across geographically distinct sites. Thus, temporal variation of a coastal macrobenthic community appears to be controlled by partly different processes at different scales.  相似文献   

A step beyond susceptibility: an adaptation of risk framework for monetary risk estimation of gully erosion     

Nalivan  Omid Asadi  Badehian  Ziaedin  Sadeghinia  Majid  Soltani  Adel  Islami  Iman  Boustan  Ali 《Natural Hazards》2022,111(2):1661-1684

Natural Hazards - In an effort to improve the previous gully susceptibility assessments in Iran, we attempted to conglomerate the notions of susceptibility, vulnerability, and exposure associated...  相似文献   

Numerical investigation of tsunami bore effects on structures,part II: effects of bed condition on loading onto circular structures     

Asadollahi  Nora  Nistor  Ioan  Mohammadian  Abdolmajid 《Natural Hazards》2019,96(1):331-351

In this paper, a multiphase three-dimensional numerical reproduction of a large-scale laboratory experiment of tsunami-like bore interaction with a surface-piercing circular column is presented. The numerical simulation is conducted using OpenFOAM. A dam-break mechanism is implemented in order to generate tsunami-like bores. The numerical model is validated using the results of experiments performed at the Canadian Hydraulics Center of the National Research Council in Ottawa, Canada. Unsteady Reynolds-Averaged Navier–Stokes equations are used in order to treat the turbulence effects. The Shear Stress Transport k–ω turbulence model showed a high level of accuracy in replicating the bore–structure interactions. A scaled-up domain is used to investigate the influence of bed condition in terms of various downstream depths and roughnesses. Finally, a broad investigation on bore propagation characteristics is performed. The stream-wise forces exerted on the structural column as well as the bore velocity are compared and analyzed for smooth, rough, dry and wet beds with varying depths.

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Dimensional analysis of two-phase flow including a rate-dependent capillary pressure–saturation relationship     

Sabine Manthey  S. Majid Hassanizadeh  Rainer Helmig  Rudolf Hilfer 《Advances in water resources》2008

The macroscopic modelling of two-phase flow processes in subsurface hydrosystems or industrial applications on the Darcy scale usually requires a constitutive relationship between capillary pressure and saturation, the P_c(S_w) relationship. Traditionally, it is assumed that a unique relation between P_c and S_w exists independently of the flow conditions as long as hysteretic effects can be neglected. Recently, this assumption has been questioned and alternative formulations have been suggested. For example, the extended P_c(S_w) relationship by Hassanizadeh and Gray [Hassanizadeh SM, Gray WG. Mechanics and thermodynamics of multiphase flow in porous media including interphase boundaries. Adv Water Resources 1990;13(4):169–86] proposes that the difference between the phase pressures to the equilibrium capillary pressure is a linear function of the rate of change of saturation, thereby introducing a constant of proportionality, the coefficient τ. It is desirable to identify cases where the extended relationship needs to be considered. Consequently, a dimensional analysis is performed on the basis of the two-phase balance equations. In addition to the well-known capillary and gravitational number, the dimensional analysis yields a new dimensionless number. The dynamic number Dy quantifies the ratio of dynamic capillary to viscous forces. Relating the dynamic to the capillary as well as the gravitational number gives the new numbers DyC and DyG, respectively. For given sets of fluid and porous medium parameters, the dimensionless numbers Dy and DyC are interpreted as functions of the characteristic length and flow velocity. The simulation of an imbibition process provides insight into the interpretation of the characteristic length scale. The most promising choice for this length scale seems to be the front width. We conclude that consideration of the extended P_c(S_w) relationship may be important for porous media with high permeability, small entry pressure and high coefficient τ when systems with a small characteristic length (e.g. steep front) and small characteristic time scale are under investigation.  相似文献   

Trace Determination of Petroleum Pollutants in Water Samples by Dispersive Liquid–Liquid Microextraction Method          下载免费PDF全文

Kobra Sadat Hasheminasab  Ali Reza Fakhari  Majid Baghdadi 《洁净——土壤、空气、水》2014,42(8):1106-1114

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Impact of soil compaction and irrigation practices on salt dynamics in the presence of a saline shallow groundwater: An experimental and modelling study     

Sina Maghami Nick  Nadim K. Copty  Selen Deviren Saygın  Hasan Sabri Öztürk  Burak Demirel  S. Mehdi Emadian  Günay Erpul  Majid Sedighi  Masoud Babaei 《水文研究》2024,38(3):e15135

Soil salt accumulation is a widespread problem leading to diminished crop yield and threatening food security in many regions of the world. The soil salinization problem is particularly acute in areas that lack adequate soil water drainage and where a saline shallow water table (WT) is present. In this study, we present laboratory-scale column experiments, extending over a period of more than 400 days that focus on the processes contributing to soil salinization. We specifically examine the combined impact of soil compaction, surface water application model and water quality on salt dynamics in the presence of a saline shallow WT. The soil columns (60 cm height and 16 cm diameter) were packed with an agricultural soil with bulk densities of 1.15 and 1.34 g/cm⁻³ for uncompacted and compacted layers, respectively, and automatically monitored for water content, salinity and pressure. Two surface water compositions are considered: fresh (deionized, DI) and saline water (~3.4 mS/cm). To assess the sensitivity of compaction on salt dynamics, the experiments were numerically modelled with the HYDRUS-1D computer program. The results show that the saline WT led to rapid salinization of the soil column due to capillarity, with the salinity reaching levels much higher than that at the WT. However, compaction layer provided a barrier that limited the downwards moisture percolation and solute transport. Furthermore, the numerical simulations showed that the application of freshwater can temporarily reverse the accumulation of salts in agricultural soils. This irrigation strategy can help, in the short-term, alleviate soil salinization problem. The soil hydraulic properties, WT depth, water quality, evaporation demand and the availability of freshwater all play a role in the practicability of such short-term solutions. The presence of a saline shallow WT would, however, rapidly reverse these temporary measures, leading to the recurrence of topsoil salinization.  相似文献   

Inter-event times between the moderate-large earthquakes in Iran     

Majid Nemati 《地震科学（英文版）》2019,32(2):80-97

Persian territory, which is dividable into major seismotectonic provinces, always suffers from damages of moderate and large earthquakes from ancient era to modern time. Therefore, temporal prediction of earthquake occurrence in this kind of area is an important topic. For this purpose, 628 moderate-large (5.5 ≤M_S≤ 8.2) earthquakes occurred in Persia during the period from 400 B.C. to 2015 C.E. were used. Considering the magnitudes of events preceding main shocks and the annual seismic moment release in seismic source areas in the provinces, we calibrated equations predicting inter-event time of occurrence of moderate and large earthquakes (M_W>5.5) in Iran. In each source area, inter-event times between moderate and large shocks with magnitudes equal to or larger than a certain cut-off magnitude (M_W5.5) were calculated. The inter-event times between the earthquakes were used to compute the relationships using multiple regression technique. Calculated relationships express the basic idea of the time predictable model predicting the occurrence time of the future main shock in a certain seismogen area. However, despite of unavoidable scatter in observations and uncertainties in the results, occurrence times of main shocks during the next years and decades in some source areas in Iran were determined.  相似文献