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181.
Perhaps, nothing else symbolizes modernization of agriculture more than the use of tractors in the developing countries. Pakistan is no exception in this regard, where tractors, its accompanying machines, tube-wells, and biological technology is seen as the only mechanism to salvage the precarious economy. In recent years, the pace of mechanization has increased, in spite of the fact that practioners and planners have widely divergent views on the merits of tractorization.This paper attempts to present the characteristics of Pakistan's agriculture from an adaptive view-point, suggesting critical elements that sustain its long-term viability. The role of cultural and genetic information is analyzed to explain the man-environment relationship. In the final section, role of tractors and their impact on agriculture is discussed. Tube-wells, other machines, fertilizers, and biological technology are not discussed in this paper. 相似文献
182.
M. Atikul Islam Md. Mostafizur Rahman Md. Bodrud-Doza Md. Iftakharul Muhib Mashura Shammi Anwar Zahid Yeasmin Akter Masaaki Kurasaki 《中国地球化学学报》2018,37(2):193-214
Southern Bangladesh’s irrigation and drinking water is threatened by saline intrusion. This study aimed to establish an irrigation water quality index (IWQI) using a geostatistical model and multivariate indices in Gopalganj district, south-central Bangladesh. Groundwater samples were taken randomly (different depths) in two seasons (wet-monsoon and dry-monsoon). Hydrochemical analysis revealed groundwater in this area was neutral to slightly alkaline and dominating cations were Na+, Mg2+, and Ca2+ along with major anions Cl? and HCO3 ?. Principal component analysis and Gibbs plot helped explain possible geochemical processes in the aquifer. The irrigation water evaluation indices showed: electrical conductivity (EC) >750 µS/cm, moderate to extreme saline; sodium adsorption ratio (SAR), excellent to doubtful; total hardness (TH), moderate to very hard; residual sodium bicarbonate, safe to marginal; Kelly’s ratio >1; soluble sodium percentage (SSP), fair to poor; magnesium adsorption ratio, harmful for soil; and IWQI, moderate to suitable. In addition, the best fitted semivariogram for IWQI, EC, SAR, SSP, and TH confirmed that most parameters had strong spatial dependence and others had moderate to weak spatial dependence. This variation might be due to the different origin/sources of major contributing ions along with the influence of variable river flow and small anthropogenic contributions. Furthermore, the spatial distribution maps for IWQI, EC, SSP, and TH during both seasons confirmed the influence of salinity from the sea; low-flow in the major river system was the driving factor of overall groundwater quality in the study area. These findings may contribute to management of irrigation and/or drinking water in regions with similar groundwater problems. 相似文献
183.
A series of consolidated drained triaxial test was performed on weakly bonded soils that were artificially prepared by mixing sand (87%) and kaolin (13%). To create weakly bond strength, samples were fired at 500°C for 5 h. A critical state (CS) concept was used to interpret the results in order to describe the behaviour of the studied soil. Defining the CS is not always straightforward. Several tests showed changing in deviator stress q and volumetric strain εv up to the end of tests. Hence, defining the CS requires careful assessments on q–εa, Δu–εa, q–p′ and v–ln p′ spaces which were performed. A ‘discontinuity’ approach was applied to position the CS on dilatant path in v–ln p′ spaces after considering stress-strain and volumetric strain curves. The critical state line in a v–ln p? space from bonded samples exhibited differences to the destructured samples. This suggests that the influence of cementation bond is substantially clear at lower stresses but as stresses increase beyond the stress yield, cementation degradation becomes more significant. The effect of bonding can be clearly visualised from the normalisation of the stress paths of destructured and bonded samples. 相似文献
184.
Mahfuzur Rahman Ningsheng Chen Md Monirul Islam Ashraf Dewan Hamid Reza Pourghasemi Rana Muhammad Ali Washakh Nirdesh Nepal Shufeng Tian Hamid Faiz Mehtab Alam Naveed Ahmed 《地学前缘(英文版)》2021,12(3):101095
This work developed models to identify optimal spatial distribution of emergency evacuation centers(EECs) such as schools, colleges, hospitals, and fire stations to improve flood emergency planning in the Sylhet region of northeastern Bangladesh.The use of location-allocation models(LAMs) for evacuation in regard to flood victims is essential to minimize disaster risk.In the first step, flood susceptibility maps were developed using machine learning models(MLMs), including: Levenberg–Marquardt back propagation(LM-BP) neural network and decision trees(DT) and multi-criteria decision making(MCDM) method.Performance of the MLMs and MCDM techniques were assessed considering the area under the receiver operating characteristic(AUROC) curve.Mathematical approaches in a geographic information system(GIS) for four well-known LAM problems affecting emergency rescue time are proposed: maximal covering location problem(MCLP), the maximize attendance(MA), p-median problem(PMP), and the location set covering problem(LSCP).The results showed that existing EECs were not optimally distributed, and that some areas were not adequately served by EECs(i.e., not all demand points could be reached within a 60-min travel time).We concluded that the proposed models can be used to improve planning of the distribution of EECs, and that application of the models could contribute to reducing human casualties, property losses, and improve emergency operation. 相似文献
185.
Acta Geotechnica - This paper focuses on the influence of volume change boundary condition on the instability and post-peak softening of sand. The laboratory program comprises an extensive series... 相似文献
186.
Tate Eric Rahman Md Asif Emrich Christopher T. Sampson Christopher C. 《Natural Hazards》2021,106(1):435-457
Natural Hazards - Human exposure to floods continues to increase, driven by changes in hydrology and land use. Adverse impacts amplify for socially vulnerable populations, who disproportionately... 相似文献
187.
Khan Mohammad Zaved Kaiser Rahman Ataur Rahman Mohammad Azizur Renzaho André M. N. 《Natural Hazards》2021,108(2):2211-2224
Natural Hazards - Natural hazards like floods and droughts affect many aspects of life. The study in particular examined the impacts of droughts on under-five mortality rate in Southern Africa,... 相似文献
188.
Natural Hazards - Flood frequency analysis (FFA) involves fitting of a probability distribution to observed flood data. Two main models, annual maximum (AM) and peaks over threshold (POT), are... 相似文献
189.
Sanzidur Rahman Mohammad Mizanul Haque Kazal 《Singapore journal of tropical geography》2015,36(1):83-97
The paper measures the level of crop diversity and identifies factors influencing diversification using a panel data of 17 regions of Bangladesh covering a 19 year period (1990–2008). Results revealed the trends that agricultural areas allocated to high‐yielding variety rice, spices and vegetables has increased, while areas cultivating traditional rice, minor cereals, oilseeds, pulses, jute and sugarcane has declined at variable rates across regions with significant differences. The level of crop diversity is also significantly different across regions and has decreased in 2008 from its 1990 level in most regions except Faridpur, Khulna and Sylhet. Among the determinants, an increase in the relative prices of vegetables and urea fertilizer, extension expenditure, labour stock per farm, average farm size, irrigation and a reduction in livestock per farm significantly increase crop diversity. Price policies to improve vegetable prices and investment in irrigation infrastructure and extension services are suggested to promote crop diversity in Bangladesh. 相似文献
190.
Natural Hazards - The probabilistic seismic hazard analysis (PSHA) has been performed for Bangladesh using background seismicity, crustal fault, and subduction zone source models. The latest ground... 相似文献