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611.
Khairayu Badron Ahmad Fadzil Ismail Jafri Din Abd.Rahman Tharek 《Journal of Atmospheric and Solar》2011,73(5-6):601-610
Satellite communications operating at 10 GHz and above in the tropics suffer severe signal degradation due to rain. Attenuation due to rain at 38 GHz had been measured for a period of 20 months in Malaysia. Analyses carried out include seasonal variations, diurnal effects and the annual cumulative distributions. Obtained results were compared with several established prediction models including the ITU-R. The rain fade characteristics were also investigated in determining the levels of signal loss and fading. In addition, the studies highlight several potential fade mitigation techniques that can be embarked. These fundamental aprehensions are very critical for future earth space communication link design and can be exploited as preliminary groundwork plan for the researchers as well as engineers. 相似文献
612.
613.
hydrologic models are important tools to estimate runoff from a catchment. Identification of broad based parameters of a hydrologic
model for development of direct runoff hydrograph is a key issue for the modelers. Optimization and regionalization of hydrologic
parameters for application of Nash’s model is investigated in this paper. Six catchments dominated by hill torrent flows were
selected for this purpose. Fifty seven rainfall events were used for regionalization of parameters and about 55 events were
used for validation of the results. The hydrologic parameters of the Nash Model, number of linear cascades (N) and storage
coefficient (k) were determined using optimization based upon Downhill Simplex method. The data was collected by field measurements
and from Water and Power Development Authority (WAPDA) Pakistan. The physical parameters of the catchments were derived from
the satellite images of the watersheds with the help of ERDAS software. The performance of the model was assessed by the model
efficiency. It is concluded that the conceptual Nash model can simulate direct runoff hydrograph using regional hydrologic
parameters with model efficiency of 67%. 相似文献
614.
Several organisms have been used as indicators, bio-monitoring agents or test organisms in ecotoxicological studies. A close relative of the well established Japanese medaka, the Java medaka (Oryzias javanicus), has the potential to be a test organism. The fish is native to the estuaries of the Malaysian Peninsula, Thailand, Indonesia and Singapore. In this study, newly fertilised eggs were exposed to different concentrations of Cd and Hg. Observations were done on the development of the embryos. Exposure to low levels of Cd and Hg (0.01-0.05 ppm) resulted in several developmental disorders that led to death. Exposure to ≥1.0 ppm Cd resulted in immediate developmental arrest. The embryos of Java medaka showed tolerance to a certain extent when exposed to ≥1.0 ppm Hg compared to Cd. Based on the sensitivity of the embryos, Java medaka is a suitable test organism for ecotoxicology in the tropical region. 相似文献
615.
Ade Faisal Taksiah A. Majid Fauziah Ahmad Felix Tongkul Syafrina Mayang Sari 《Natural Hazards》2011,59(1):237-269
The seismic hazard assessment of a site that lies in the low seismic region affected by the future existence of a large dam
has been given less attention in many studies. Moreover, this condition is not addressed directly in the current seismic codes.
This paper explains the importance of such information in mitigating the seismic hazard properly. Ulu Padas Area in Northern
Borneo is used as an example for a case study of a site classified as a low seismic region. It is located close to the border
of Malaysia, Brunei Darussalam, and Indonesia and may have a large dam in the future as the region lies in hilly geography
with river flow. This study conducts probabilistic and deterministic seismic hazard analyses, and reservoir-triggered seismicity
of a site affected by the future existence of a large dam. The result shows that the spectrum acceleration of the maximum
design earthquake for the investigated site in the Ulu Padas Area in Northern Borneo is taken from the reservoir-triggered
seismicity earthquake at short periods and from the current condition at longer periods. 相似文献
616.
This research makes use of the remote sensing, simulation modeling and field observations to assess the non-point source pollution
load of a Himalayan lake from its catchment. The lake catchment, spread over an area of about 11 km2, is covered by different land cover types including wasteland (36%), rocky outcrops (30%), agriculture (12%), plantation
(12.2%), horticulture (6.2%) and built-up (3.1%) The GIS-based distributed modeling approach employed relied on the use of
geospatial data sets for simulating runoff, sediment, and nutrient (N and P) loadings from a watershed, given variable-size
source areas, on a continuous basis using daily time steps for weather data and water balance calculations. The model simulations
showed that the highest amount of nutrient loadings are observed during wet season in the month of March (905.65 kg of dissolved
N, 10 kg of dissolved P, 10,386.81 kg of total N and 2,381.89 kg of total P). During the wet season, the runoff being the
highest, almost all the excess soil nutrients that are trapped in the soil are easily flushed out and thus contribute to higher
nutrient loading into the lake during this time period. The 11-year simulations (1994–2004) showed that the main source areas
of nutrient pollution are agriculture lands and wastelands. On an average basis, the source areas generated about 3,969.66 kg/year
of total nitrogen and 817.25 kg/year of total phosphorous. Nash–Sutcliffe coefficients of correlation between the daily observed
and predicted nutrient load ranged in value from 0.80 to 0.91 for both nitrogen and phosphorus. 相似文献
617.
Chin Yik Lin Mohd. Harun Abdullah Baba Musta Sarva Mangala Praveena Ahmad Zaharin Aris 《Natural Resources Research》2011,20(1):45-56
A total of 20 soil samples were collected from 10 boreholes constructed in the low lying area, which included ancillary samples
taken from the high elevation area. Redox processes were investigated in the soil as well as groundwater in the shallow groundwater
aquifer of Manukan Island, Sabah, Malaysia. Groundwater samples (n = 10) from each boreholes were also collected in the low lying area to understand the concentrations and behaviors of Fe
and Mn in the dissolved state. This study strives to obtain a general understanding of the stability behaviors on Fe and Mn
at the upper unsaturated and the lower-saturated soil horizons in the low lying area of Manukan Island as these elements usually
play a major role in the redox chemistry of the shallow groundwater. Thermodynamic calculations using PHREEQC showed that
the groundwater samples in the study area are oversaturated with respect to goethite, hematite, Fe(OH)3 and undersaturated with respect to manganite and pyrochroite. Low concentrations of Fe and Mn in the groundwater might be
probably due to the lack of minerals of iron and manganese oxides, which exist in the sandy aquifer. In fact, high organic
matters that present in the unsaturated horizon are believed to be responsible for the high Mn content in the soil. It was
observed that the soil samples collected from high elevation area (BK) comprises considerable amount of Fe in both unsaturated (6675.87 mg/kg) and saturated horizons (31440.49 mg/kg) compared
to the low Fe content in the low lying area. Based on the stability diagram, the groundwater composition lies within the stability
field for Mn2+ and Fe2+ under suboxic condition and very close to the FeS/Fe2+ stability boundary. This study also shows that both pH and Eh values comprise a strong negative value thus suggesting that
the redox potential is inversely dependent on the changes of pH. 相似文献
618.
In this study, a doubly nested tide?Csurge interaction model was established for the coastal region of Bangladesh. A fine grid model, capable of incorporating all major offshore islands, was nested into a coarse grid model extending up to 15°N latitude of the Bay of Bengal. To take into account the thickly populated small and big islands between Barisal and Chittagong and the extreme bending of the coastline accurately, a very fine grid model for this region was again nested into the fine grid model. Along the northeast corner of this very fine grid model, the Meghna River discharge was taken into account. The boundaries of the coast and islands were approximated through proper stair step, and the model equations were solved by semi?Cimplicit finite difference technique using staggered grid. Appropriate tidal regime over the model domain was generated by forcing the sea level to be oscillatory with the constituent M2 along the southern open boundary of the coarse grid model omitting wind stress. This previously generated tidal regime was introduced as the initial state of the sea for nonlinear tide?Csurge interaction phenomenon. The model was applied to estimate water levels along the coastal region of Bangladesh due to the interaction of tide and surge associated with the storm April 1991, and the results were found to be in a reasonable agreement with those observed. The model was used to investigate the influence of offshore islands on water levels and water levels were found to be significantly influenced by offshore islands. 相似文献
619.
620.
Evaluation of coal as adsorbent for phosphate removal 总被引:1,自引:1,他引:0
Sabir Khan M. Ishaq Imtiaz Ahmad Sajjad Hussain Hameed Ullah 《Arabian Journal of Geosciences》2013,6(4):1113-1117
This paper reports the adsorption of phosphate ions on coal, charcoal, and coal ash. The influences of factors such as contact time, and initial adsorbate concentration have been studied. Adsorption of phosphate ions on virgin coal was significant compared to charcoal, coal and coal ash evacuated at 200°C. The significant adsorption capability of coal is due to the porosity as well as due to organic carbon and inorganic elements present in coal. The evacuation of coal proved to be ineffective in enhancing its capability for phosphate ions retention. The adsorption behaviors of all the three adsorbent used was conformed using Freundlich’s adsorption model. The results suggest that coal could be used as an efficient adsorbent for removing phosphate ions from wastewater. 相似文献