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排序方式: 共有486条查询结果,搜索用时 15 毫秒
91.
In this paper, an adaptive simulated annealing genetic algorithm is proposed to solve generation expansion planning of Turkey's power system. Least‐cost planning is a challenging optimization problem due to its large‐scale, long‐term, nonlinear, and discrete nature of power generation unit size. Genetic algorithms have been successfully applied during the past decade, but they show some limitations in large‐scale problems. In this study, simulated annealing is used instead of mutation operator to improve the genetic algorithm. The improved algorithm is applied to the power generation system with seven types of generating units and a 20‐year planning horizon. The planning horizon is divided into four equal periods. The new algorithm provides approximately 6.6 billion US$ (3.2%) cheaper solution than GA and also shows faster convergence. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
92.
P Drechsel B Keraita P Amoah R C Abaidoo L Raschid-Sally A Bahri 《Water science and technology》2008,57(9):1461-1466
Where rapid urbanization is outpacing urban capacities to provide sound sanitation and wastewater treatment, most water sources in city vicinity are heavily polluted. This is of great concern as many of the leafy vegetables eaten raw in the cities are produced in these areas. Following the new WHO guidelines, different non-treatment options at farm, market, and kitchen level were field tested for health risk reduction with special consideration to efficiency and adoption potential. As most households are used to vegetable washing (although ineffectively), an important entry point for risk reduction is the increased emphasis of the new guidelines on food preparation measures. A combination of safer irrigation practices (water fetching, on-farm treatment, and application), the allocation of farmland with better water sources, and improved vegetable washing in kitchens appear to be able to reduce the potential risk of infections significantly, although it might not be possible to reach the ideal threshold without some kind of wastewater treatment. The on-farm trials carried out in Ghana also explored the limitation of other risk reduction measures, such as drip irrigation, crop restrictions and cessation of irrigation under local circumstances considering possible incentives for behaviour change. 相似文献
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95.
Tc-99m sestamibi has been shown to accumulate in several primary malignant tumors, but data regarding its use in the detection of distant metastases are limited. Despite its physical limitations, Tl-201 now has a definite place in the routine evaluation of certain primary and metastatic tumors. This report describes the value of Tc-99m sestamibi and its superiority to Tl-201 in the visualization of distant metastases in a 2-year-old girl with bilateral retinoblastoma. Three sites of soft tissue and bone metastasis were demonstrated by Tc-99m sestamibi imaging. Of these metastases, the one in the parieto-occipital region showed evident Tl-201 uptake, while the other two in the right arm and chest wall showed only slightly increased uptake, which could hardly be spotted without the confirmation of a later Tc-99m sestamibi scan. The scintigraphic findings were confirmed with histopathologic examination. Tc-99m sestamibi scan is effective and superior to Tl-201 in the detection of distant soft tissue and bone metastases from retinoblastoma. 相似文献
96.
The rate of formation of SiO(g) by the reaction of CO and H2 with silica or silicate slags containing SiO2, CaO, and A12O3 has been measured. The rate with hydrogen for both pure silica and silica in slags is controlled by gas phase mass transport.
The rate changed with flow conditions, sample size, and gas properties as predicted by the appropriate mass transfer equations.
In particular, the rate is faster in H2-He than in H2-Ar gas mixtures with the same hydrogen pressure, which proves conclusively the rate is controlled by gas phase mass transport.
The rate of formation of SiO by the reaction of silica with CO did not change with flow conditions or particle size and the
rate was the same in CO-He and CO-Ar with the same pressure of CO. In addition, the calculated rate with CO for mass transfer
is considerably faster than was observed. These observations strongly indicate the rate is controlled by chemical kinetics
on the surface. Similar results were obtained for the rate of reaction of CO with silica in slags and the rate was found to
be proportional to the activity of SiO2 and CO pressure. The present results are discussed in relationship to silicon transfer in slag-metal reactions. 相似文献
97.
Estimating Motion From MRI Data 总被引:2,自引:0,他引:2
Ozturk C Derbyshire JA McVeigh ER 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》2003,91(10):1627-1648
Magnetic resonance imaging (MRI) is an ideal imaging modality to measure blood flow and tissue motion. It provides excellent contrast between soft tissues, and images can be acquired at positions and orientations freely defined by the user. From a temporal sequence of MR images, boundaries and edges of tissues can be tracked by image processing techniques. Additionally, MRI permits the source of the image signal to be manipulated. For example, temporary magnetic tags displaying a pattern of variable brightness may be placed in the object using MR saturation techniques, giving the user a known pattern to detect for motion tracking. The MRI signal is a modulated complex quantity, being derived from a rotating magnetic field in the form of an induced current. Well-defined patterns can also be introduced into the phase of the magnetization, and could be thought of as generalized tags. If the phase of each pixel is preserved during image reconstruction, relative phase shifts can be used to directly encode displacement, velocity and acceleration. New methods for modeling motion fields from MRI have now found application in cardiovascular and other soft tissue imaging. In this review, we shall describe the methods used for encoding, imaging, and modeling motion fields with MRI. 相似文献
98.
S Mazoyer P Lalle C Moyret-Lalle C Mar?ais S Schraub D Frappaz H Sobol M Ozturk 《Canadian Metallurgical Quarterly》1994,9(4):1237-1239
Codon 257 of the p53 gene is an extremely rare target for somatic mutations (accounting for only two of 1600 published mutations). We report here two constitutional mutations both affecting the second nucleotide of codon 257. A thymine to adenine transversion resulting in an amino acid change from leucine to glutamine was found in one proband who developed multiple independent malignant tumors (osteosarcoma, phyllodes tumor, soft-tissue sarcoma). Her mother died of early-onset breast cancer. In the other case, a deletion resulting in a frameshift in the C-terminal coding region of p53 was found in a woman who was diagnosed with breast cancer at age 34. This woman belongs to a family with features of Li-Fraumeni syndrome. In both cases, the p53 mutations identified in the proband was found in other members of the family. Codon 257, even if rarely mutated in somatic cells, may thus be an important target for germ-line mutations. 相似文献
99.
100.
O. Ozturk E. Asikuzun S. Kaya N. S. Koc M. Erdem 《Journal of Superconductivity and Novel Magnetism》2017,30(5):1161-1169
MgB2 samples are produced by ex situ reaction method under vacuum, and various (0, 10, 20 Bar) Ar pressure for 0.5 and 1 h. The effect of ambient pressure and annealing duration on the microstructure and electrical properties of bulk samples are investigated. XRD, SEM, and magnetoresistance measurements are made. The a and c lattice parameters and the grain size values are the highest for the samples produced under vacuum and their values decrease with increasing Ar pressure. Moreover, these values increase when the annealing duration increases from 0.5 to 1 h. The increasing pressure reduces the bond lengths between the atoms thus the grain sizes decrease. Smaller grain size promotes the connection between grains which results in an increase of the critical current density (J c ). SEM micrographs reveal that the produced samples have granular structure which is a characteristic feature of MgB2. The decrease of grain sizes and thus enhancement in grain connectivity with increasing pressure is also confirmed by SEM images. Magneto resistivity measurements show that T c values of the samples produced under vacuum are the highest. T c values decrease with increasing ambient pressure and applied magnetic field. The activation energies (U 0) of the samples are calculated using Arrhenius plots due to thermally activated flux flow theory. Existence and increase of Ar pressure causes increase of activation energies. The samples produced with 0.5-h annealing have higher activation energies than the ones produced with 1-h annealing. 相似文献