排序方式： 共有51条查询结果，搜索用时 15 毫秒
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N.E. Kassim T.J.W. Lazio P.S. Ray P.C. Crane B.C. Hicks K.P. Stewart A.S. Cohen W.M. Lane 《Planetary and Space Science》2004,52(15):1343-1349
We present an overview of the low-frequency array (LOFAR) that will open a window on one of the last and most poorly explored regions of the electromagnetic spectrum. LOFAR will be a large (baselines up to 400 km), low-frequency aperture synthesis array with large collecting area ( at ) and high resolution (1.5″ at 100 MHz), and will provide sub-mJy sensitivity across much of its operating range. LOFAR will be a powerful instrument for solar system and planetary science applications as reviewed by papers in this monogram. Key astrophysical science drivers include acceleration, turbulence, and propagation in the galactic interstellar medium, exploring the high red-shift universe and transient phenomena, as well as searching for the red-shifted signature of neutral hydrogen from the cosmologically important epoch of re-ionization. 相似文献
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The now-closed Clark Radio Observatory was used in 1984 and 1985 to search for flaring emission from a number of dMe flare stars in the 30.9 to 110.6 MHz frequency range. No emission was found to greatly exceed detection limits which range from about 1 Jy for 1 hr averaging, to about 50 Jy for 1 s averaging, even though flares were often seen to tens of mJy at 20 cm using the VLA for those times when VLA-CLRO observations were coordinated. There are marginal detections of flaring from AD Leo over two periods on December 15, 1985 which mark the beginning and the end of along-lasting, narrow-band flare at 1415 MHz. 相似文献
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Adaptive neuro-fuzzy evaluation of wind farm power production as function of wind speed and direction 总被引：1，自引：1，他引：0
Dalibor Petković Shahaboddin Shamshirband Nor Badrul Anuar Sareh Naji Miss Laiha Mat Kiah Abdullah Gani 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(3):793-802
Wind velocity assumes a critical part for measuring the power created by the wind turbines. Nonetheless, power production from wind has a few weaknesses. One significant issue is that wind is a discontinuous energy source which implies that there exists substantial variability in the generation of vigor because of different variables, for example, wind speed. Wind direction is a significant variable for proficient turbine control for getting the most energy with a given wind speed. Taking into account the conjectures on wind heading, it might be conceivable to adjust the turbine to the wind bearing to get the most energy yield. Since both forecasts of wind speed and direction are basic for effective wind energy collecting it is crucial to develop a methodology for estimation of wind speed and direction and afterwards to estimate wind farm power production as function of wind pace and heading distribution. Despite the fact that various numerical functions have been proposed for demonstrating the wind speed and direction frequency distribution, there are still disadvantages of the models like very demanding in terms of calculation time. In this investigation adaptive neuro-fuzzy inference system (ANFIS), which is a particular sort of the artificial neural networks (ANN) family, was used to anticipate the wind speed and direction frequency dispersion. Thereafter, the ANFIS system was utilized to gauge wind homestead power creation as function of wind velocity and bearing. Neural system in ANFIS modifies parameters of enrollment capacity in the fuzzy logic of the fuzzy inference system. The reenactment outcomes exhibited in this paper demonstrate the adequacy of the created technique. 相似文献
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Komeil Rokni Tajul Ariffin Musa Sharifeh Hazini Anuar Ahmad Karim Solaimani 《Natural Hazards》2015,78(1):219-230
The aim of this paper was to investigate the suitability of the pixel-level and product-level image fusion approaches to detect surface water changes. In doing so, firstly, the principal component analysis technique was applied to Landsat TM 2010 multispectral image to generate the PC components. Several pixel-level image fusion techniques were then performed to merge the Landsat ETM+ 2000 panchromatic with the PC1PC2PC3 band combination of Landsat TM 2010 imagery to highlight the surface water changes between the two images. The suitability of the resulting fused images for surface water change detection was evaluated quantitatively and visually. Finally, the support vector machine (SVM) technique was applied to the qualified fused images to map the highlighted changes. Furthermore, a product level fusion (PLF) approach based on various satellite-derived indices was employed to detect the surface water changes between ETM+ 2000 and TM 2010 images. The accuracy of the resulting change maps was assessed based on a reference change map produced using visual interpretation. The results demonstrated the effectiveness of the proposed approaches for surface water change detection, especially using the Gram Schmidt-SVM, PLF-NDWI, and PLF-NDVI methods which improved the accuracy of change detection over 99.70 %. 相似文献
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Md. Aftabuzzaman Sohail Kabir Md. Khairul Islam M. Shafiqul Alam 《Journal of the Geological Society of India》2013,81(5):677-684
Pleistocene red soil horizons were exposed in different areas of the Barind Tract in north-west Bangladesh. X-ray diffractions of twenty seven samples from different depths of these soil horizons revealed that the soil horizons consisted of kaolinite, illite and chrysotile with significant amount of opal-CT. Samples from Maddhapara, Bogra, and Nachole contain kaolinite, illite, quartz and opal-CT, and the samples from Kantabari contain chrysotile instead of kaolinite. Clay mineral compositions of different soil horizons indicated two different types of clay assemblages, viz. (a) illitekaolinite and (b) illite-chrysotile. In the village of Kantabari, illite-chrysotile clay mineral assemblage indicate that soil horizons were formed under low temperatures with alkaline and reducing conditions. However, other soil horizons of illite-kaolinite clay mineral assemblage indicate that soils were possibly formed under humid, temperate and welldrained conditions. These two soil horizons were formed under different geochemical, geomorphological and climatic conditions from different parent materials. Scanning Electron Microscopy photographs showing the presence of glass shards and no opal-A were found using XRD, suggesting that the opal-A might not be a precursor to opal-CT in the red soil horizon of the study area. This opal-CT along with the general lack of fossils and presence of glass shards was indicative of a volcanogenic rather than biogenic origin for the Opal-CT in the study area, and X-ray fluorescence data reveals higher percentages of silica which is comparable to the Toba Ash of Toba Caldera, Indonesia of about 75,000 B.P. 相似文献
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Investigation of radio astronomical windows between 1 MHz and 2060 MHz in Universiti Malaya,Malaysia
Zamri Zainal Abidin Zainol Abidin Ibrahim Syed Bahari Ramadzan Syed Adnan Norwati Khairul Anuar 《New Astronomy》2009,14(6):579-583
An indoor and an outdoor radio frequency survey was conducted in Universiti Malaya, Malaysia, as a test site, for the purpose of developing radio astronomy research in Malaysia. This is the first radio astronomical survey of any such done in Malaysia. Observation and analysis were done in the radio frequency spectrum between 1 MHz and 2060 MHz. In this paper, the experimental setup and procedure of surveying are outlined and the measured data are interpreted. The eight radio astronomical windows were investigated from a 24 h observation, with the emphasis on two of the most important radio astronomical windows which are protected by the Malaysian Communications and Multimedia Commission (MCMC). Some intermittent observations were also done for referencing purposes. The radio frequency interferences (RFIs) are found to be relatively low. The overall relative Interference-to-Noise ratio (INR) at this test site ranges between 5.72% and 11.74%. The average strength of RFI in the eight focused radio astronomical windows at this site ranges between ?100 dBm and ?90 dBm (equivalently between 9.23 × 104 Jy and 93.29 × 104 Jy at resolution bandwidth of 125 kHz). 相似文献
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Deducing sediment transport direction and the relative importance of rivers on a tropical microtidal beach using the "McLaren model" 总被引：1，自引：0，他引：1
H. Mohd-Lokman Y. Rosnan S. Ejria N. A. M. Shazili K. K. Y. Kassim 《Environmental Geology》1998,34(2-3):128-134
Analyses of the sedimentological trend from 90 samples collected at 1-km intervals along a tropical microtidal coastline
of northern Terengganu indicate that the preferred sediment transport direction was northwards, following the McLaren model.
The extent of disruption to and reestablishment of the sedimentological trend on beaches north of two river mouths within
the study area was used to determine their relative importance in supplying sediment to the beaches. The extent of disruption
to the sedimentological trend was 18 and 14 km for the beaches north of the Terengganu and Setiu River mouths, respectively.
This suggests that the Terengganu River is more important in supplying sediments to the beach than the Setiu River. To a limited
extent this study showed that the McLaren model can be applied to deduce sediment transport direction on a microtidal coastline,
while disruption to the sedimentological trend adjacent to river mouths can be used to compare the relative importance of
rivers in supplying sediments, provided that the disruption to the sedimentological trend is small enough so as to allow for
the trend to be discernible again further along the transport path.
Received: 8 May 1997 · Accepted: 12 August 1997 相似文献