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1.
It is pointed out that the total amount of microwave radiation that could possibly be generated by all the graphite needles in space would be considerably smaller than the observed total energy of the cosmic microwave background radiation. The question of relevant optical depth of the cloud containing the needles has been examined. It is found that the optical depth is not sufficiently large for the cloud to radiate like a black body. 相似文献
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AbstractHelical piles have emerged as an attractive foundation system for offshore applications with renewed interest from the offshore community. Significant research gap currently exists in transferring this technology offshore and this paper discusses how existing and emerging knowledge can be successfully used to bridge some of the gaps. We focus on the Coupled Eulerian Lagrangian (CEL) large deformation finite element (LDFE) modelling technique that is commercially available and can be used to model the three-dimensional installation process with consideration of strain rate and softening effects in soft offshore clays. A helical pile of L?=?7.5?m long is modelled with one or two large-diameter helices (D?=?2?m) attached to a central shaft of d?=?0.5?m in diameter.The net effect of strain rate and softening is to increase the installation torque. The measured torque is within the range of 200–400?kN.m for the offshore clay and the pile geometry studied. Additional helices increase the uplift force but to a lesser degree than that of the measured torque. Remoulding induced strength reduction is found to be within the range of 25–33% of the intact clay strength. Issues of extracting and reusing offshore helical pile foundations are discussed. 相似文献
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In the present study, a methodology for reliability assessment of slack and taut mooring systems against instability has been presented. For this purpose, first, stability analysis of slack and taut mooring systems has been carried out and instable regions are obtained using procedure available in the literature. Having known the instable region(s), methodology for reliability assessment has been proposed which is based on Monte Carlo Simulation technique. After using the proposed methodology, probabilities of failure and reliability indices has been obtained for the above systems. Some parametric studies, such as, effect of lower and upper limits of instability and effect of frequency range of generations are also included to obtain the results of practical interest. 相似文献
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Automated Image Registration for Hydrologic Change Detection in the Lake-Rich Arctic 总被引:1,自引:0,他引:1
5.
We have evaluated several solid state detectors which offer excellent energy resolution at room temperature for soft X-rays. For soft X-rays (< 1 keV to 20 keV), silicon P-intrinsic-N (PIN) and avalanche-mode photodiodes (APD's) have been studied. Using commercially available charge sensitive pre-amplifiers, these photodiodes provide 1 keV resolution without cooling. Their detection efficiencies are limited to about 20 keV and 15 keV, respectively. To overcome this constraint, we have studied thick (1.5 mm) PIN detectors made by Micron Semiconductor Ltd., U.K., as well as compound semiconducting materials with high Z constituents such as CZT and PbI2. PbI2 allows high detection efficiencies of photons up to 100 keV with detectors 100–300 microns thick. These new detectors offer the capability to study the low-energy spectral evolution of Gamma ray bursts (GRBs). A matrix of these detectors could be used as an image plane detector with moderate spatial resolution for imaging. 相似文献
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Gilgit-Baltistan region is covering the northern most part of Pakistan where the rocks of the Kohistan-Ladakh island arc and Karakoram plate are exposed. The area has greater potential for precious and base metals deposits which are needed to be explored through spectroscopy and remote sensing techniques. Minerals and rocks can nowadays be identified through the measurement of their absorption and reflectance features by spectroscopic analysis. Spectral reflectance analysis is also very important in selecting the appropriate spectral bands for remote-sensing data analysis of unknown or inaccessible areas. In this study, reflectance spectra in the spectral range of 0.35–2.5 μm of different types of unaltered and altered rocks found in the Machulu and Astor areas of northern Pakistan were obtained using an ASD spectroradiometer. The fresh rock samples showed low spectral reflectance as compared to the altered rock samples. The minerals jarosite, goethite, and hematite showed depth of absorption minima in the range of 0.4–1.15 μm due to the presence of iron (Fe), while jarosite and limonite showed absorption depth at 2.2 μm due to the presence of hydroxyl ions (OH¯). The clay minerals montmorillonite and illite showed absorption depth at 1.93 and 2.1 μm, respectively. Muscovite showed depth of absorption minima at 1.4 and 1.9 μm in some samples. Calcite showed deep absorption minima at 2.32 μm, while anorthite showed absorption features at 1.4, 1.9, 2.24, and 2.33 μm. Olivine showed a slight depressed absorption feature at 1.07 μm. The copper-bearing phases malachite, chrysocolla, and azurite showed, respectively, a broad absorption feature in the range of 0.6–0.9 μm, a small absorption at 1.4 μm, and a deep absorption at 1.93 μm. The unmineralized samples exhibited high reflectance in the wavelength ranges of 0.6–0.8, 1.6–1.9, 2.0–2.3, 2.1–2.25, and 2.4–2.5 μm, respectively, while the mineralized samples showed reflectance bands in the wavelength ranges of 0.4–0.6, 1.3–1.8, and 2.1–2.2 μm. On this basis, the band ratio combinations 7/5–4/3–6/3 and 7/5–6/3–4/3 of Landsat 8 and 4/7–4/3–2/1 for ASTER data were found to be very effective in the lithological differentiation of major rock units. 相似文献
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H. Ullah N. U. Khan F. Ali Z. A. Shah Q. Ullah 《International Journal of Environmental Science and Technology》2018,15(2):309-322
Health risks of heavy metals in vegetables irrigated with sewage water were investigated in the present study. The findings indicated a massive accumulation of heavy metals in soil and vegetables collected from Dera Ismail khan, Pakistan. The concentration levels of heavy metal in vegetables grown on soil irrigated with untreated sewage water were significantly higher at (P ≤ 0.001) than in vegetables grown on fresh-water-irrigated soil and proceeded the recommended limits of World health organization. Moreover, the findings also indicated that the adults and children consuming such vegetables ingested a large proportion of the selected toxic metals. Health risk index was greater than one for Pb and Cd in all the selected vegetables and was greater than one for Ni in three vegetables like Spinacia oleracea, Benincasa fistulosa and Lactuca sativa. Health risk assessment would be a useful tool for information regarding any threats of heavy metals contamination in vegetables. 相似文献