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201.
In this paper, we investigated the radio frequency interference (RFI) that future Very Long Baseline Interferometer (VLBI) observations in Malaysia may encounter. Four frequency windows below 2.8 GHz were chosen for this study and their spectra were measured at four sites. The frequency windows are 322-328 MHz, 608-614 MHz, 1660-1660.5 MHz and 1660.5-1668.4 MHz. The measured averaged RFI floor noise levels in these windows are −99.992 (±0.570) dBm, −99.907 (±0.639) dBm, −100.220 (±0.4941) dBm and −100.359 (±0.110) dBm, respectively. We found that only two bands below 2.8 GHz are permitted for the purpose of radio astronomy in Malaysia. They are 608-614 MHz and 1660-1660.5 MHz. The RFI levels in these permissible bands at the best site (Langkawi) were also measured and concluded to be relatively low. Main sources of RFI in these bands in Malaysia were identified. We also reviewed several current VLBI observations in these two bands.  相似文献   
202.
In a preliminary investigation, Random Amplified Polymorphie DNA (RAPD) analysis and partial mitochon-drial ND2 gene sequencing were conducted to study the genetic variation of the Indian mackerel, Rastrelliger kanagurta along a 450 km stretch of its distribution on the west coast of Peninsular Malaysia. A total of 53 individuals from 6 popu-lations were analyzed using 4 RAPD primers and a sub-sample of 15 individuals was chosen for sequencing of partial ND2 gene. Comparison between the 2 markers revealed genetic structuring in the RAPD results but genetic homogeneity for ND2 gene. Based on the former there may be at least 2 genetically differentiated groups of Rastrelliger kanagurta a-long this stretch.  相似文献   
203.
The adsorption of Cu(II) ions from aqueous solutions by soda lignin as an absorbent using a batch adsorption system is presented in this paper. The soda lignin used in this study was extracted from black liquor derived from oil palm empty fruit bunches (EFB) using 20% v/v sulfuric acid. The effects of varying experimental parameters such as pH value, adsorbent dosage, different concentrations of Cu(II) ions, and agitation period were investigated. The results revealed that the optimum adsorption of Cu(II) onto soda lignin was recorded at a pH of 5.0 at an adsorbent dosage of 0.5 g soda lignin and an agitation period of 40 min. The adsorption capacities and rates of Cu(II) ions onto soda lignin was evaluated. The Langmuir and Freundlich adsorption models were applied to calculate the isotherm constants. It was found that the adsorption isothermal data could be well interpreted by the Freundlich model. The kinetic experimental data properly correlated with the pseudo‐second‐order kinetic model, which implies that chemical sorption is the rate‐limiting step.  相似文献   
204.
The River Ganges being the most sacred river and lifeline to millions of Indians in serving their water requirements is facing excessive threat of pollution. Under various river management and conservation strategies for its protection, the assessment of water quality of its main tributary Ramganga River is lacking. This study focuses on assessment of physicochemical and heavy metal pollution of the Ramganga River by application of multivariate statistical techniques. Sampling of Ramganga River at sixteen sampling sites was carried out in three seasons (summer, monsoon and winter) of 2014. The collected water samples were analyzed for physicochemical parameters and heavy metals. Results from cluster analysis (CA) of the data divided the whole stretch of the river into three clusters as elevation from 1304 to 259 m as less polluted, from 207 to 154 m as moderately polluted and from elevation 154 to 139 m as high-polluted stretches with anthropogenic as main sources of pollution in high-polluted stretch. Principal component analysis of the seasonal dataset resulted in three significant principal components (PC) in each season explaining 72–8% of total variance with strong loadings (>0.75) of PC1 on fluoride (F?), chloride (Cl?), sodium (Na+), calcium (Ca2+), magnesium (Mg2+), bicarbonate (HCO3 ?), total dissolved solids and electrical conductivity. Temporal variation by one-way ANOVA (Analysis of Variance) showed significant seasonal variation was in the pH, chemical oxygen demand, biochemical oxygen demand, turbidity, HCO3 ?, F?, Zn, cadmium (Cd) and Mn (p < 0.05). Turbidity showed approximately a twofold increase in monsoon season due to rainfall in the catchment area and subsequent flow of runoff into the river. Concentration of HCO3 ?, F? and pH also showed similar increase in monsoon. The concentration of Zn, Cd and Mn showed an increasing trend in summers compared to monsoon and winter season due to dilution effect in the monsoon season and its lasting effect in winters.  相似文献   
205.
Sea ice formation in Quilty Bay, East Antarctica shows a strong relationship with climatic conditions and its spatial variation is established by GPR survey over the sea ice during the austral winters. The study also evaluates the variability of sea ice thickness and extent with local weather parameters between 2010 and 2014. Profiling on sea ice in Quilty Bay shows that sea ice thickness decreases gradually towards east. The overall thickness of sea ice is considerably less at the centre of the bay as compared to the coastal side. Two types of fast ice layers have been delineated from GPR surveys i.e. top layer fast ice which incorporates very low density surface snow and underlying high density fast ice i.e. with melt water pockets. Development of sea ice is influenced by persistent easterly winds, temperature fluctuations and ocean currents. Sea ice reveal average annual cyclic trend in Quilty Bay with maximum development in the year 2013 (157.54 cm) and the minimum development has been observed in the year 2010 (99.04 cm).The cyclic pattern of average sea ice accumulation data show perfect inverse correlation with surface air temperature, with measure of reliability R2 = 0.93. However, moderate (R2 = 0.52) and good (R2 = 0.69) degree of inverse relationship is observed with surface snow and overall sea ice (snow and ice) respectively. With 0.46 °C change in temperature, there is 33% change in sea ice condition in Quilty Bay which may remain same as far as ice extents in the region. Besides this easterly winds play a vital role in controlling the snow/ice distribution patterns as reflected by isopach maps.  相似文献   
206.
The effects of salinity, temperature, and light conditions on the reproduction and development of harpacticoid copepod, Nitocra affinis f. californica under controlled laboratory conditions were determined. Seven different salinity levels (5, 10, 15, 20, 25, 30, 35 ppt), four temperatures (20, 25, 30, 35 °C), three different light intensities (25, 56, 130 μmol m−2 s−1) and photoperiods (24 h:0 h, 1 h:23 h, 12 h:12 h LD cycle) were employed in this study. The highest (p < 0.05) overall reproduction and fastest development time were achieved by copepods reared under 30–35 ppt salinity. The optimum temperature required for the maximum reproduction was 30 °C while under 30 °C and 35 °C the copepod development time was shortest (p < 0.05) compared to other temperature levels. The overall reproduction was highest (p < 0.05) and development rate of N. affinis was shortest (p < 0.05) under lowest light intensity (25 μmol m−2 s−1). Continuous light (24 h:0 h LD) inhibited the egg production while, continuous darkness (1 h:23 h LD) and 12 h:12 h LD significantly favoured the overall reproductive activity of the female. Photoperiods 1 h:23 h and 12 h:12 h LD yielded highest total (p < 0.05) offspring female−1 coupled with highest (p < 0.05) survival percentage. This study illustrated that although N. affinis can tolerate wide range of environmental conditions, prolonged exposure to subnormal environments affect its reproduction and development. This study showed that this species can be mass cultured for commercial purposes and has a potential to be used for toxicity studies due to its high reproductive performance fast development and a wide range of tolerance to environmental conditions.  相似文献   
207.
The environmental isotopes such as deuterium and oxygen-18 and the deuterium excess values have been used to assess groundwater recharge sources and their dynamics in Khan Younis City in the Gaza Strip in Palestine. Three isotopic lines for the relationship between δ2H and δ18O were used in the assessment. These lines are the global meteoric water line, the local meteoric water line and the groundwater evaporation line. The δ2H, δ18O and D-excess values indicate that deuterium and oxygen-18 isotopes originated in the groundwater from groundwater mixing with rainfall and other water sources; the groundwater in the area recharged from rainfall from a distant source that came from the Mediterranean Sea and from other sources such as wastewater, irrigation return flow and saline water.  相似文献   
208.
Abstract

The process-based Soil and Water Assessment Tool (SWAT) model and the data-driven radial basis neural network (RBNN) model were evaluated for simulating sediment load for the Nagwa watershed in Jharkhand, India, where soil erosion is a severe problem. The SWAT model calibration and uncertainty analysis were performed with the Sequential Uncertainty Fitting algorithm version 2 and the bootstrap technique was applied on the RBNN model to analyse uncertainty in model output. The percentage of data bracketed by the 95% prediction uncertainty (95PPU) and the r factor were the two measures used to assess the goodness of calibration. Comparison of the results of the two models shows that the value of r factor (r = 0.41) in the RBNN model is less than that of SWAT model (r = 0.79), which means there is a wider prediction interval for the SWAT model results. More values of observed sediment yield were bracketed by the 95PPU in the RBNN model. Thus, the RBNN model estimates the sediment yield values more accurately and with less uncertainty.

Editor D. Koutsoyiannis; Associate editor H. Aksoy

Citation Singh, A., Imtiyaz, M., Isaac, R.K., and Denis, D.M., 2014. Assessing the performance and uncertainty analysis of the SWAT and RBNN models for simulation of sediment yield in the Nagwa watershed, India. Hydrological Sciences Journal, 59 (2), 351–364.  相似文献   
209.
Estimation of flood in basins with poor condition of hydrometric stations as in quantity and quality is a dominant problem around the world, mainly in developing country where lack of funds and human resources cause more limitation in number of gauging stations. One of the areas that experience frequent floods and also suffer from small number of stations in Iran is Gorganrood basin. So there is a great need for the estimation and prediction of runoff in this area to prevent any future floods. Due to insufficient station in this area, direct prediction of flood is not applicable. Regional flood frequency analysis is a practical and widely used solution for these situations, which involves the identification of homogenous regions. Gorganrood region was hydrologically homogenized according to the extracted parameters that influence the floods. One of these parameters was Normalized Difference Vegetation Index (NDVI) driven from MODIS images. Curvature is another parameter that relates to topographic attributes. From factor analysis, the most appropriate variables were selected. According to these parameters (NDVI, curvature, area, slope…), the regions were classified into homogenous regions. For the purpose of homogenization, hierarchical (wards) clustering, fuzzy clustering and Kohonen method were applied. L-moment technique was used for the investigation of the results. The heterogeneity measure for one of the groups (Group 1) was more than two; therefore some modifications were applied. The region was grouped into two homogenous subregions. All of the clustering methods showed same results. The models showed that class 4 of NDVI is influential on flood in some return periods. The resulted models can be applied in future studies in different aspects of practical hydrology.  相似文献   
210.
Integrated geoelectrical resistivity, hydrochemical and soil property analysis methods were used to study the groundwater characteristics of sandy soils within a shallow aquifer in the agriculture area, Machang. A pilot test investigation was done prior to the main investigation. The area was divided into two sites. Test-Site 1 is non-fertilized; Test-Site 2 is the former regularly fertilized site. From the surface to depths of 75 cm, a lower average resistivity was obtained in Test-Site 2 (around 0.37 less than in Test-Site 1). The presence of nitrate and chloride contents in pore water reduced the resistivity values despite the low moisture content. The pH values for the whole area range from 4.11 to 6.88, indicating that the groundwater is moderately to slightly acidic. In the southern region, concentration of nitrate is considered to be high (>20 mg/l), while it is nearly zero in the northern region. In the south, the soil properties are similar. However, the geoelectrical model shows lower resistivity values (around 18 Ω m) at the sites with relatively high nitrate concentration in the groundwater (>20 mg/l). Conversely, the sites with low nitrate concentration reveal the resistivity values to be higher (>35 Ω m). Basement and groundwater potential maps are generated from the interpolation of an interpreted resistivity model. The areas that possibly have nitrate-contaminated groundwater have been mapped along with groundwater flow patterns. The northern part of the area has an east to west groundwater flow pattern, making it impossible for contaminated water from the southern region to enter, despite the northern area having a lower elevation.  相似文献   
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