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排序方式: 共有1385条查询结果,搜索用时 31 毫秒
91.
Abstract—This article presents an approach for obtaining proportional–integral–derivative controller parameters for an automatic voltage regulator system based on a local unimodal sampling optimization algorithm. A conventional integral time of squared error objective function and modified objective functions in terms of integral time of absolute error, integral of absolute error, integral of squared error, peak overshoot, and settling time with appropriate weighting factors are employed to tune the controller parameters. Different objective functions are employed to obtain optimized proportional–integral–derivative controller gains. Superiority of proposed technique over some recently published modern heuristic optimization techniques, such as artificial bee colony algorithm, particle swarm optimization algorithm, and differential evolution algorithm, for the same automatic voltage regulator system is demonstrated. Simulation results reveal that the proposed proportional–integral–derivative controlled automatic voltage regulator system tuned by the local unimodal sampling algorithm with modified objective function exhibits better performance in terms of settling time, peak overshoot, and stability. The robustness of the system tuned by the proposed algorithm is also studied satisfactorily by varying the time constants of the automatic voltage regulator system in the range of –50% to +50% in steps of 25%. 相似文献
92.
The present electricity grid installation cost as well as the tariff is quite high in India, particularly remote rural areas, to electrify houses. These problems can be easily solved by installing standalone systems that operate on one of the clean energy sources such as solar energy. An experimental analysis of generating electricity from a thermoelectric generator (TEG) powered by a solar parabolic dish concentrator device with aperture area and focal length of 12.6 m2 and 2.42 m, respectively, is presented in this article. A TEG is made up of a thermoelectric module connected to a flat receiver by an absorber layer. The studies were carried out in Indian climatic conditions at the National Institute of Technology, Puducherry. Over a spectrum of beam radiation, the system's maximum energy conversion efficiency, as well as efficient electrical output, are evaluated and presented. The proposed system's average effective electrical efficiency is 0.424%, corresponding to the TEG's average energy conversion efficiency of 2.76%. 相似文献
93.
Lopamudra Sahu Awanish Kumar Mishra Krishna Dutta 《Journal of Materials Engineering and Performance》2014,23(11):4122-4129
Ratcheting fatigue behavior of a non-conventional stainless steel X12CrMnNiN17-7-5 has been investigated with varying combinations of mean stress (σm) and stress amplitude (σa) at room temperature using a servo-hydraulic universal testing machine. X-ray diffraction profile analysis has been carried out for assessing possible martensitic phase transformation in the steel subjected to ratcheting deformation. The results indicate that ratcheting strain as well as volume fraction of martensite increases with increasing σm and/or σa; the phenomenon of strain accumulation is considered to be governed by the associated mechanics of cyclic loading, increased plastic damage as well as martensitic transformation. A correlation between strain produced by ratcheting deformation and martensitic transformation has been established. 相似文献
94.
Olusola O. James Sudip Maity M. Adediran Mesubi Lamidi A. Usman Kolawole O. Ajanaku Tolu O. Siyanbola Satanand Sahu Rashmi Chaubey 《国际能源研究杂志》2012,36(6):691-702
Dependence on fossil fuels for global energy supply has continued to generate concerns about climate change and sustainable development. It has motivated the search for carbon‐neutral alternative resources for the production of transportation fuels to replace crude oil. Although biodiesels have recently emerged as a close substitute to petrol diesel, their use in compression ignition engines designed to run on petro‐diesel fuels are linked to adverse effects on the engines' performance and life span. This informed efforts at upgrading biodiesel or direct conversion of triglycerides to hydrocarbon mixtures that are identical or similar to that of petro‐diesel through hydrodeoxygenation. Moreover, it seems that commercial methods for the conversion of triglycerides to diesel fuels depends on inputs (methanol and hydrogen) derived from fossil fuels. However, it will be desirable to do so without inputs from fossil fuels. Hence, reaction paths for direct conversion of triglycerides to on‐specification hydrocarbons fuels without hydrogen gas input are discussed and suggested strategies are in cognisance of green chemistry principles. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
95.
Modification of chemical and magnetic extraction techniques has yielded biogenic magnetite/maghemite from human hippocampal tissue. Particles were identified using high resolution transmission electron microscopy, electron diffraction and elemental analysis. Though its presence has been inferred from magnetic analyses, this is the first direct observation of magnetic biominerals from the hippocampus. 相似文献
96.
Preeti Gangadharan Jaya N. Sahu Bhim C. Meikap 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2011,86(10):1282-1288
BACKGROUND: Ammonia is applied to increase the efficiency of an electrostatic precipitator for fly ash removal from a flue gas stream from a boiler using fossil fuel. In the present work, the hydrolysis of urea to generate ammonia for flue gas conditioning, with the help of aluminium oxide catalyst, has been studied. RESULTS: The effect of temperature, catalyst and initial concentration on the conversion was studied. Conversion was found to increase exponentially with temperature. Addition of catalyst resulted in an increase in conversion. Experiments were conducted with different doses of catalyst, and the optimum dosage of catalyst for a particular feed concentration was determined. A decrease in conversion was observed when the initial concentration of ammonia was increased. CONCLUSION: A study of reaction kinetics showed the effect of reaction time on conversion of urea to ammonia. The catalytic hydrolysis of urea, using aluminium oxide behaved as a first‐order reaction; the rate constant at different temperatures was found, and the activation energy determined. Copyright © 2011 Society of Chemical Industry 相似文献
97.
In this work, we report electronic structure calculations aimed at computing the linear optical absorption spectrum and static
dipole polarizablity of a newly proposed boron-based planar aromatic compound borozene (B
12
H
6). For the purpose, we use the semiempirical INDO model Hamiltonian, accompanied by large-scale correlation calculations using
the multi-reference singles-doubles configuration-interaction (MRSDCI) approach. We present detailed predictions about the
energetics, polarization properties, and the nature of many-particle states contributing to various peaks in the linear absorption
spectrum. Our results can be used to characterize this material in future optical absorption experiments. We also argue that
one can deduce the aromaticity of the cluster from the optical absorption and static polarizability results. 相似文献
98.
L Liberman N Bracero MA Vuolo DD Dershaw EA Morris AF Abramson PP Rosen 《Canadian Metallurgical Quarterly》1999,172(2):331-337
Neisseria meningitidis, Haemophilus influenzae, and Streptococcus pneumoniae possess the ability to cleave human IgA1 antibodies, and all successfully colonize and occasionally invade the human upper respiratory tract. N. meningitidis invades the bloodstream after a period of nasopharyngeal colonization. We directly compared levels of IgA1 protease activity in strains (n=52) derived from the cerebrospinal fluid or blood of patients with meningococcal disease with strains of N. meningitidis obtained from asymptomatic carriers (n=25). IgA1 protease activity was determined by a sensitive semiquantitative ELISA assay. Levels of IgA1 protease activity were significantly higher (P<0.0001) in strains associated with invasive meningococcal disease (98% with detectable activity, mean = 580 mU) than with those obtained from asymptomatic carriers (76% with detectable activity, mean = 280 mU). Despite marked variation in enzyme activity, almost all strains (96%) possessed the gene for IgA1 protease. Given the panmictic population structure of the bacterial isolates investigated, these data, obtained from two groups infected with N. meningitidis, but with markedly different clinical outcomes, provide the first quantitative evidence that IgA1 protease activity is a virulence determinant that contributes to the pathogenic phenotype, and suggest IgA1 protease as a potential target for prophylaxis. 相似文献
99.
Tobias Schröder Satya Narayan Sahu Dario Anselmetti Jochen Mattay 《Israel journal of chemistry》2011,51(7):725-742
Self-assembly by H-bonding and by metal-coordination of functionalized calix[4]arenes and cavitands to large supramolecular capsules is described. In addition, a new method of analyzing supramolecular recognition processes at the single molecule level is discussed. By measuring interaction forces in a hydrogen-bonded assembly using single-molecule force spectroscopy (SMFS), the dynamics of the self-assembly process can be evaluated. In the future, consequent application of this new technique will influence supramolecular design principles and the use of non-covalent interactions as construction elements in the field of nanotechnology. 相似文献
100.
We study the buoyancy-induced interpenetration of two immiscible fluids in a tilted channel by a two-phase lattice Boltzmann method using a non-ideal gas equation of state well-suited for two incompressible fluids. The method is simple, elegant and easily parallelizable. After first validating the code for simulating Rayleigh–Taylor instabilities in a unstably-stratified flow, we applied the code to simulate the buoyancy-induced mixing in a tilted channel at various Atwood numbers, Reynolds numbers, tilt angles, and surface tension parameters. The effects of these parameters are studied in terms of the flow structures, front velocities, and velocity profiles. For one set of parameters, comparisons have also been made with results of a finite volume method. The present results are seen to agree well with those of a finite volume method in the interior of the flow; however near the boundary there is some discrepancy. 相似文献