Plane symmetric gravitational collapse and linear equation of state     

M. Sharif  Amal Majid 《Astrophysics and Space Science》2013,347(1):71-76

This paper examines the gravitational collapse in plane symmetry with a perfect fluid using a linear equation of state p=kρ. We find a class of collapse models satisfying the Einstein field equations and also the regularity as well as energy conditions. For a given initial data, the outcome of the collapse turns out to be a black membrane or a naked singularity depending upon the equation of state parameter. We conclude that this parameter plays a crucial role in determining the final fate of the collapse.  相似文献   

Spring rainfall prediction based on remote linkage controlling using adaptive neuro-fuzzy inference system (ANFIS)     

Gholam Abbas Fallah-Ghalhary  Majid Habibi-Nokhandan  Mohammad Mousavi-Baygi  Javad Khoshhal  Akbar Shaemi Barzoki 《Theoretical and Applied Climatology》2010,101(1-2):217-233

This paper aims to study the relationship between large-scale synoptic patterns and rainfall in Khorasan Razavi Province. The adaptive neuro-fuzzy inference system (ANFIS) was used in this study to predict rainfall in the period between April and June in Khorasan Razavi Province. We first analyzed the relationship between average regional rainfall and the changes in synoptic patterns including sea-level pressure, sea-level pressure difference, sea-level temperature, temperature difference between sea level and the 1,000-hPa level, the temperature of the 700-hPa level, the thickness between the 500- and 1,000-hPa levels, the relative humidity at the 300-hPa level, and precipitable water content. We have examined the effect of synoptic patterns in these regions on the rainfall in the northeast region of Iran. Then, the ANFIS in the period 1970–1997 has been taught. Finally, we forecast the rainfall for the period 1998–2007. The results show that the ANFIS can predict the rainfall with reasonable accuracy.  相似文献   

Modeling Local Tidal Constituents Using TOPEX/POSEIDON SSH for the Malaysian Marine Region     

Muhammad Nur J. P. Vella  Sahrum Ses  Majid Kadir  Koji Matsumoto 《Marine Geodesy》2001,24(2):99-106

A new Local Ocean Tide Model, has been produced for the Exclusive Economic Zone (EEZ) of Malaysia, which incorporates some of the latest TOPEX/POSEIDON data for the years 1992 to 1998. Local tide gauge data are used as a comparison, along with another leading Global Ocean Tide Model, Ori96. The leading diurnal and semidiurnal constituents M₂, S₂, N₂, K₁, O₁, P₁ and Q₁ are reproduced using TOPEX/POSEIDON Sea Surface Heights (SSH) in a response analysis type least squares derivation following Munk and Cartwright (1966).  相似文献   

Numerical simulation of the summer wake of Rottnest Island, Western Australia     

Majid Jandaghi Alaee  Charitha Pattiaratchi  Greg Ivey 《Dynamics of Atmospheres and Oceans》2007,43(3-4):171-198

During the summer, a northward, wind-driven current dominates the Rottnest Island region in southwestern Australia. Field studies have shown that the interaction between Rottnest Island and the northward current generates upwelling at the western end of the island, which is advected downstream, resulting in isotherm doming in the wake region. Flow curvature-induced secondary circulation has been proposed as the dominant mechanism responsible for this upwelling. Here, a three-dimensional numerical model, together with field observations, was used to undertake a detailed investigation of the three-dimensional flow structure in the wake region. Comparison of the observed upwelling pattern and the simulated flows revealed the island's dominant role in generating upwelling. This result was confirmed with the use of idealized numerical experiments. The modeling results confirmed the presence of secondary circulation, generated as a result of flow curvature at the western end of the island, which caused strong upwelling and extended downstream.  相似文献   

Effects of crude oil contamination on geotechnical properties of clayey and sandy soils   总被引：6，自引：0，他引：6  

Mashalah Khamehchiyan  Amir Hossein Charkhabi  Majid Tajik 《Engineering Geology》2007,89(3-4):220-229

The southern coastal plain of Iran at the Persian Gulf encounters oil pollution due to the historical oil exploitation, related tanker navigations and accidents, and petrochemical industrial expansions in the recent years. Therefore, it is important to investigate the geochemical properties of oil-contaminated coastal soils and sediments for engineering and environmental purposes. Here, an extensive laboratory testing program was carried out to determine the effects of crude oil contamination on some of the geotechnical properties of clayey and sandy soils such as CL, SM and SP sampled from the coastal soils from this area. The testing included basic properties, Atterberg limits, compaction, direct shear, uniaxial compression and permeability tests on clean and contaminated soil samples at the same densities. The contaminated samples were prepared by mixing the soils with crude oil in the amount of 2%, 4%, 8%, 12%, and 16% by dry weight. The results indicated a decrease in strength, permeability, maximum dry density, optimum water content and Atterberg limits. Knowledge of these effects of oil contamination is important in coastal engineering and environmental remediation activities of the studied coastal plain.  相似文献   

An Analytical Study of the Diurnal Variations of Wind in a Semi-geostrophic Ekman Boundary Layer Model   总被引：1，自引：0，他引：1  

Zhe-Min Tan  Majid M. Farahani 《Boundary-Layer Meteorology》1998,86(2):313-332

A time-dependent semi-geostrophic Ekman boundary-layer model based on the geostrophic momentum approximation is used to study the diurnal wind variation in the planetary boundary layer (PBL) and the evolution of the low-level nocturnal jet (LLJ). The coefficient of eddy viscosity varies periodically with time, varies linearly with height in the surface layer and is constant above the surface layer. The influence of horizontal advection of momentum on the diurnal wind variation in the PBL, the development of inertial oscillations (IOs) and the formation of the LLJ are examined.In comparison with the Ekman solutions, the diurnal wind variation in semi-geostrophic Ekman boundary-layer dynamics has the following features: (1) the phase angle of the diurnal wind wave shifts with height, the rate of shifting is increased in anticyclonic regions and decreased in cyclonic regions, (2) the time of occurrence of the low-level maximum wind speed is later in anticyclonic regions and earlier in cyclonic regions, (3) the height of occurrence of the maximum wind speed is higher in the anticyclonic and lower in cyclonic regions, (4) the wind speed maximum and the amplitude of the diurnal wind variation are larger in anticyclonic and smaller in cyclonic regions, (5) the period of IOs is larger in anticyclonic regions and smaller in cyclonic regions, (6) anticyclonic vorticity is conducive to the generation of LLJ in the PBL. These features are interpreted by means of the physical properties of semi-geostrophic Ekman boundary-layer dynamics and inertial oscillation dynamics.  相似文献   

A review of socio-economic and nutritional issues of Bihari Camp Dwellers in Bangladesh: a micro study     

Rosie Majid Ahsan Dr.  Shahnaz Huq Hussain 《GeoJournal》1990,20(3):285-291

The living conditions of the Bihari camp dwellers of Bangladesh are an embarrassment to the country's social environment. An investigation was made about the socio-economic condition of the Biharis living in the Khalishpur camp, Khulna. A comparison has been made between the Biharis and equivalent Bengali slum dwellers in Khalishpur. The data were collected from primary sources. A 10% systematic sampling was undertaken to collect a total of 150 Bihari households and through a 20% systematic sampling 150 Bengali households were surveyed by questionnaires. Data analysed both qualitatively and quantitatively indicate that the Biharis are leading an extremely substandard life when food consumption, medical expenditure, schooling, income and employment pattern were considered. The condition as prevalent in the camp has led to a high rate of infectious diseases which is likely to aggrevate creating environmental hazards. The country then may face serious social problems which should be prevented through gearing up the process of repatriation and through encouraging community participation in improving their economic and social environment.The study was sponsored by CONCERN a voluntary Irish Organization in Bangladesh.  相似文献   

Analysis of liquefaction susceptibility of nearly saturated sands     

Ahmad Jafari‐Mehrabadi  Majid Abedinzadegan Abdi  Radu Popescu 《国际地质力学数值与分析法杂志》2007,31(5):691-714

A new constitutive formulation for simulating the behaviour of nearly saturated sands under seismic loads is presented. The formulation is based on combining the Henry's law for dissolution of gas in water, the ideal or perfect gas law and the law of conservation of mass. The effects of transient air dissolution in water on the compressibility of partially saturated soils are also taken into account. The model was calibrated based on numerical simulations of isotropically consolidated cyclic triaxial tests conducted on partially saturated samples of Toyoura sand. A multi‐yield plasticity soil constitutive model implemented in the finite element code DYNAFLOW was used for these numerical simulations. It is shown that the formulation proposed here is able to reasonably predict the soil cyclic undrained behaviour at various degrees of saturation (95% and higher). Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Prediction of the soil erosion in a forest and sediment yield from road network through GIS and SEDMODL   总被引：3，自引：0，他引：3  

Aidin PARSAKHOO  Majid LOTFALIAN  Ataollah KAVIAN  Seyed Ataollah HOSSEINI 《国际泥沙研究》2014,29(1):118-125

This study was conducted to classify water erosion risk for a deciduous forest and to predict the amount of sediment yield from forest road network. GIS in combination with AHP was used for determining the soil erosion risk degrees of forest. Beside, sediment yield from forest roads with gravel and asphalted surfacing was estimated using SEDMODL. Rainfall simulator was used in calibration and validation process of model. Results showed that 47.9% of forest soil is classified from moderate to very high vulnerability. 32.3% of roads were located in soil erosion risk class of very high. This class is generally found in the eastern region of forest, while areas with very low risk are found in the south western part. 14.6% of the forest roads were ranked as having very low sediment yield. Only 61 segments out of 339 segments of forest road network delivered sediment to the ravine network. The estimated annual sediment yield for all of road sections by SEDMODL and rainfall simulator were 10,935.45 and 10,509.29 g m-2, respectively. Results of the calibration and validation process showed that the variation accounted for in the predicted values by SEDMODL with the observed values under rainfall simulation was 3.90%. Best management practices （BMP） must be considered for the areas with high degrees of erosion risk.  相似文献   

Evaluation of code criteria for bridges with unequal pier heights     

Majid Tamanani  Yen Gian  Ashraf Ayoub 《Bulletin of Earthquake Engineering》2016,14(11):3151-3174

One of the challenges associated with Eurocode 8 and AASHTO-LRFD is predicting the failure of irregular bridges supported by piers of unequal heights. EC8 currently uses “moment demand-to-moment capacity” ratios to somewhat guarantee simultaneous failure of piers on bridges, while AASHTO-LRFD relies on the relative effective stiffness of the piers. These conditions are not entirely valid, in particular for piers with a relative height of 0.5 or less, where a possible combination of flexure and shear failure mode may occur. In this case, the shorter piers often result in brittle shear failure, while the longer piers are most likely to fail due to flexure, creating a combination of different failure modes experienced by the bridge. To evaluate the adequacy of EC8 design procedures for regular seismic behavior, various irregular bridges are simulated through a non-linear pushover analysis using shear-critical fiber-based beam-column elements. The paper investigates the behavior of irregular monolithic and bearing-type bridges experiencing different failure modes, and proposes different methods for regularizing the bridge performance to balance damage. The ultimate aim is to obtain a simultaneous or near-simultaneous failure of all piers irrespective of the different heights and failure mode experienced.  相似文献