Changing Land Use a Threat to Surface Water Quality: a Vulnerability Assessment Approach in Zanjanroud Watershed,Central Iran     

Mahsa Mirhosseini  Parvin Farshchi  Ali Akbar Noroozi  Mahmood Shariat  Ali Asghar Aalesheikh 《Water Resources》2018,45(2):268-279

Maintaining the quality of surface water resources as one of the most vital water supplies has always been at the center of global concerns. A set of manifest and latent factors have yet been identified by researchers worldwide that are subject to affect the quality of surface water. Among which, the effect of land use change, due to a spatial and temporal complexity, is often not easily verifiable. The present study attempts to offer an index-based model to quantify vulnerability of surface water resources in a semi arid basin in central Iran against land use changes. For this, water quality data including Na, K, Mg, Ca, Sodium Adsorption Ratio (SAR), total anions (Sum. A), SO₄, Cl, HCO₃, EC, TDS, and pH were collected from hydrometric stations over a period of 26 years (1987?2013). In order to detect land use changes, the land use maps of the years 1987, 1998, 2002, 2009, and 2013 were prepared from TM satellite images using supervised classification method. At next step, changing patterns of different land uses were traced by Shanon’s Diversity Index (SHDI) as a metric of patch diversity indicating diversity and heterogeneity of a landscape over time. Relationship between the SHDI values and water quality indicators revealed the impact of land use changes on quality of surface water resources. Statistical analysis confirmed a significant relationship between nine water quality factors and water discharge in the basin during the study period. From 1998 to 2009, the greatest changes were visible in the total anions, Ca, SO₄, and HCO₃. These parameters along with salinity were increasing in almost all sub-basins. According to the results, conversion of poor rangelands to rain fed agriculture fields is the most apparent land use change occurred in the study area over the study period. In 1987, SHDI as an indicator of the diversity and changes in the basin, showed a significant relationship with good rangelands (R² =–0.835). This indicates that fragmentation of the entire watershed area was initiated in 1987, which reached its peak in 2013. Generally speaking, urbanization, poor rangeland, and irrigated agriculture were recognized as three influential land uses adversely affect the water quality in the study area.  相似文献   

Transmission of light by slit designed for astronomical spectrograph     

Mahmood A. Ismail 《Astrophysics and Space Science》1986,122(1):1-32

The paper discusses an investigation of linear polarization produced by the transmission of light through an astronomical spectrograph slit. An experimental apparatus was designed and set up to carry out this work. The parallel beam of plane polarized light was rotated in the measuring system, by optically active of half-wave plate. The intensity of normally incident of polarized light of wavelength 0.436 μm transmitted by various slit was measured as a function of slit width. The results indicate:

1. That the degree of polarization increased as thedepth of the narrow slit was increased.
2. That the degree of polarization increased as thewidth of the narrow slit was decreased.
3. That when the width of slit was widened the degree of polarization tended to approach a constant value asymptotically.
4. That the theoretical calculation of Slater (1942) predicts the measured experimental values more accurately than Thiessen (1947) and Jones and Richards (1954).

It is shown that the existence and order of magnitude of all these effects may be predicted from the propagation losses of the electromagnetic theory of light in metallic wave guide. The paper brings out the salient points related to the degree of polarization of light by a dielectric slit of finite depth. The polarization effects from one such slit have been investigated and the results were compared with those for metallic slits.  相似文献   

Predicting mechanical properties and ultimate shear strength of gypsum,limestone and sandstone rocks using Vipulanandan models     

Wael Mahmood  Saman HamaHussein 《Geomechanics and Geoengineering》2020,15(2):90-106

ABSTRACT

In this study, over 1000 data from the literature was used to characterize and compare the density, strengths, modulus, fracture toughness, porosity and the ultimate shear strengths of the gypsum, limestone and sandstone rocks. The compressive modulus and Mode-1 fracture toughness of the gypsum rock, limestone rock and sandstone rocks varied from 0.7 GPa to 70 GPa, and from 0.03 MPa.m^0.5 to 2.6 MPa.m^0.5  respectively. Vipulanandan correlation model was effective in relating the modulus of elasticity, fracture toughness with the relevant strengths of the rocks. A new nonlinear Vipulanandan failure criterion was developed to quantify the tensile strength, pure shear (cohesion) strength and to predict the maximum shear strength limit with applied normal stress on the gypsum, limestone and sandstone rocks. The Vipulanandan failure model predicts the maximum shear strength limit was, as the Mohr-Coulomb failure model does not have a limit on the maximum shear strength. With the Vipulanandan failure model based on the available data, the maximum shear strengths predicted for the gypsum, limestone and sandstone rocks were 64 MPa, 114 MPa and 410 MPa respectively.  相似文献   

Numerical modeling of rock failure under dynamic loading with polygonal elements     

Timo Saksala  Mahmood Jabareen 《国际地质力学数值与分析法杂志》2019,43(12):2056-2074

Polygonal finite elements are gaining an increasing attention in the computational mechanics literature, but their application in rock mechanics is very rare. This paper deals with numerical modeling of rock failure under dynamic loading based on polygonal finite elements. For this end, a damage-viscoplastic constitutive model for rock based on the Mohr-Coulomb criterion with the Rankine criterion as a tensile cutoff is employed and implemented with the polygonal finite element method. Moreover, the mineral mesostructure or rock is described by randomly mapping groups of polygonal elements representing the constituent minerals into a global mesh and assigning these groups with the corresponding mineral material properties. The performance of the polygonal elements is compared with that of the linear and quadratic triangular and bilinear quadrilateral elements in numerical simulations of controlled shear band formation under uniaxial compression and lateral splitting failure in the dogbone tension test. Numerical simulations of uniaxial tension and compression tests as well as dynamic Brazilian disc test under increasing loading rates demonstrate that the present approach predicts the correct failure modes as well as the dynamic increase in strength of rock.  相似文献   

Magnetoacoustic solitons in dense astrophysical electron-positron-ion plasmas     

S. Hussain  S. Mahmood  A. Mushtaq 《Astrophysics and Space Science》2013,346(2):359-366

Nonlinear magnetoacoustic waves in dense electron-positron-ion plasmas are investigated by using three fluid quantum magnetohydrodynamic model. The quantum mechanical effects of electrons and positrons are taken into account due to their Fermionic nature (to obey Fermi statistics) and quantum diffraction effects (Bohm diffusion term) in the model. The reductive perturbation method is employed to derive the Korteweg-de Vries (KdV) equation for low amplitude magnetoacoustic soliton in dense electron-positron-ion plasmas. It is found that positron concentration has significant impact on the phase velocity of magnetoacoustic wave and on the formation of single pulse nonlinear structure. The numerical results are also illustrated by taking into account the plasma parameters of the outside layers of white dwarfs and neutron stars/pulsars.  相似文献   

A MODEL-BASED ASSESSMENT OF IMPACTS OF CLIMATE CHANGE ON BORO RICE YIELD IN BANGLADESH     

Rezaul Mahmood  John T. Hayes 《自然地理学》2013,34(6):463-486

Rice is the main food crop in densely populated Bangladesh. Regional climatic variations can play an important role in rice productivity. For example, excessive heat or extremely cool conditions disrupt normal plant physiological processes and cause plant injury which, in turn, results in reduction of yield. In this study, the climatic crop productivity model YIELD has been applied to calculate rice productivity for the boro rice growing season (December/January-May) in Bangladesh under changing climatic conditions. The model estimates climatic influences on various rice plant-growth parameters. YIELD was tuned and validated to Bangladesh's environment to represent appropriate agroecological conditions. The model was run using long-term average climate data of 12 meteorological stations located in the major rice-growing regions in Bangladesh to establish baseline estimates of yield. For the climate change study, 20 scenarios were created by synthetically fluctuating thermal and solar climates in Bangladesh. Study results show that per 1° C increase in growing season mean air temperature, boro rice yield was reduced by 4.6%. It was also found that each 10% increase in incident solar radiation resulted in a 6.5% increase of boro rice yield in Bangladesh.  相似文献   

A simulation study of microstructure evolution inside the shear band in biaxial compression test   总被引：1，自引：0，他引：1  

Zafar Mahmood  Kazuyoshi Iwashita 《国际地质力学数值与分析法杂志》2011,35(6):652-667

We study the development of microstructure inside the shear band in granular media consisting of elliptical‐shaped particles. Plane strain biaxial compression test was simulated using two‐dimensional distinct element method. The generation of large voids and concentration of excessive particle rotation inside a shear band are found in a quite similar manner to those observed in natural soils. Evolution of the microstructure inside and outside the shear band is studied. The magnitude and direction of particle rotation inside the shear band is influenced by orientation of long axes of elliptical particles. Because of such particle rotations inside the shear band, the preferred alignment of particles becomes horizontal in the residual state, which results in a more anisotropic contact normal distribution oriented along the major principal stress axis. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Delay in the onset of South Asian summer monsoon induced by local black carbon in an AGCM     

Rashed Mahmood  Shuanglin Li 《Theoretical and Applied Climatology》2013,111(3-4):529-536

The influence of local black carbon (BC) on monthly mean precipitation and the associated circulation in South Asia is investigated. The results show that the amplified shortwave radiative heating rate by BC absorption enhances convective activity near the Himalayas and the southern Tibetan Plateau with increased rainfall anomalies in April and May, which is consistent with previous studies. However, the enhanced vertical motions and the precipitation ultimately lead towards cooling of the lower troposphere especially in May, which is extended till June. This favored negative rainfall responses in June, implying delay in the onset of South Asian summer monsoon rainfalls over Arabian Sea and western parts of the subcontinent. The negative precipitation response is further associated with the prevailing anomalous high pressure and the anticyclonic wind circulations induced by BC. Thus, we present here one different feature associated with BC-induced elevated heat pump-like circulations in South Asia.  相似文献   

Linking hydrological variations at local scales to regional climate teleconnection patterns     

Kabir Rasouli  Karis Scharold  Taufique H. Mahmood  Nancy F. Glenn  Danny Marks 《水文研究》2020,34(26):5624-5641

Climate patterns over preceding years affect seasonal water and moisture conditions. The linkage between regional climate and local hydrology is challenging due to scale differences, both spatially and temporally. In this study, variance, correlation, and singular spectrum analyses were conducted to identify multiple hydroclimatic phases during which climate teleconnection patterns were related to hydrology of a small headwater basin in Idaho, USA. Combined field observations and simulations from a physically based hydrological model were used for this purpose. Results showed statistically significant relations between climate teleconnection patterns and hydrological fluxes in the basin, and climate indices explained up to 58% of hydrological variations. Antarctic Oscillation (AAO), North Atlantic Oscillation (NAO), and Pacific North America (PNA) patterns affected mountain hydrology, in that order, by decreasing annual runoff and rain on snow (ROS) runoff by 43% and 26% during a positive phase of NAO and 25% and 9% during a positive phase of PNA. AAO showed a significant association with the rainfall-to-precipitation ratio and explained 49% of its interannual variation. The runoff response was affected by the phase of climate variability indices and the legacy of past atmospheric conditions. Specifically, a switch in the phase of the teleconnection patterns of NAO and PNA caused a transition from wet to dry conditions in the basin. Positive AAO showed no relation with peak snow water equivalent and ROS runoff in the same year, but AAO in the preceding year explained 24 and 25% (p < 0.05) of their variations, suggesting that the past atmospheric patterns are equally important as the present conditions in affecting local hydrology. Areas sheltered from the wind and acted as a source for snow transport showed the lowest (40% below normal) ROS runoff generation, which was associated with positive NAO that explained 33% (p < 0.01) of its variation. The findings of this research highlighted the importance of hydroclimatic phases and multiple year variations that must be considered in hydrological forecasts, climate projections, and water resources planning.  相似文献   

Two dimensional ion acoustic shocks in electron-positron-ion plasmas with warm ions,and q-nonextensive distributed electrons and positrons     

S. Hussain  Hafeez Ur-Rehman  S. Mahmood 《Astrophysics and Space Science》2014,351(2):573-580

Two dimensional ion acoustic shocks in electron-positron-ion (e-p-i) plasma with warm ions, and nonthermal electrons and positrons following the q-nonextensive velocity distribution are studied in the presence of weak transverse perturbations. The kinematic viscosity of warm ions is included for the dissipation in the plasma system. Kadomtsev–Petviashvili–Burgers (KPB) equation is derived by using reductive perturbation method in small amplitude limit and its analytical solution is also presented. The effects of variations of positrons concentration, q-indices of electrons and positrons, ion temperature and kinematic viscosity of ions, on the propagation characteristic of two dimensional shock profile are also discussed.  相似文献