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排序方式: 共有79条查询结果,搜索用时 15 毫秒
1.
Callistus Nonso Ude Dominic Okechukwu Onukwuli Jonah Chukwudi Umeuzuegbu Chinemelum Chukwujekwu Chukwuka 《化学工程与技术》2021,44(1):65-76
The heterogeneous catalysis of transesterification of gmelina seed oil to biodiesel is evaluated. The oil was extracted from the seeds with n‐hexane by solvent extraction and characterized to determine its physiochemical properties. Response surface methodology was applied to optimize the effect of process variables on the biodiesel yield. The base‐activated clay catalyst performed as montmorillonite clay with the characteristic property of a Brønsted acid. It has an improved surface area after activation that enhanced its catalytic activity on transesterification reaction. Under optimal conditions, the biodiesel yield was 70.1 %, thus demonstrating that the model predicted well the biodiesel production. 相似文献
2.
Recent advances in oxygen reduction reaction catalysis for proton exchange membrane fuel cells (PEMFCs) include i) the use of electrochemical dealloying to produce high surface area and sometimes nanoporous catalysts with a Pt‐enriched outer surface, and ii) the observation that oxygen reduction in nanoporous materials can be potentially enhanced by confinement effects, particularly if the chemical environment within the pores can bias the reaction toward completion. Here, these advances are combined by incorporating a hydrophobic, protic ionic liquid, [MTBD][beti], into the pores of high surface‐area NiPt alloy nanoporous nanoparticles (np‐NiPt/C + [MTBD][beti]). The high O2 solubility of the [MTBD][beti], in conjunction with the confined environment within the pores, biases reactant O2 toward the catalytic surface, consistent with an increased residence time and enhanced attempt frequencies, resulting in improved reaction kinetics. Half‐cell measurements show the np‐NiPt/C+[MTBD][beti] encapsulated catalyst to be nearly an order of magnitude more active than commercial Pt/C, a result that is directly translated into operational PEMFCs. 相似文献
3.
Y.A. Ahmed I.B. Mansir I. Yusuf G.I. Balogun S.A. Jonah 《Nuclear Engineering and Design》2011,241(5):1559-1564
We appraised in this study the effects of core excess reactivity and average coolant temperature on the operable time of the Nigeria Research Reactor-1 (NIRR-1), which is a miniature neutron source reactor (MNSR). The duration of the reactor operating time and fluence depletion under different operation mode as well as change in core excess reactivity with temperature coefficient was investigated over a period of five years. Our result shows that there is a strong dependence of reactor operating time on core excess reactivity and temperature coefficient. It was observed in 2004 that with a cold core excess reactivity of 3.77 mk, at full-power flux of 1.0 × 1012 n cm−2 s−1 the reactor operated for 5 continues hours. At half-power flux of 0.5 × 1012 n cm−2 s−1 and under the same excess reactivity condition, the reactor reaches 8 h of operation. However, re-measurements done in 2009 shows that excess reactivity of the reactor has reduced to 2.80 mk, the operable time at full flux dropped to 3.5 h while that of half-power became 7 h. We also investigated the reactor's energy consumption within the period under study and found to be much more in 2008 compared to the previous years. We infer that the amount of fluence consumed and the excessive reactor usage in 2008 has contributed significantly to the reduction of the reactor's excess reactivity in that year. The results obtained here revels that for an MNSR with a clean core excess reactivity between 3.5 mk and 4.0 mk, 5 and 8 h are the maximum operable times under full and half-power flux conditions, respectively. Negative deviation from these optimum times is therefore an indication of a drop in excess reactivity and the need for beryllium shims addition. 相似文献
4.
H.C. Odoi E.H.K. Akaho S.A. Jonah R.G. Abrefah R.B.M. Sogbadji S.A. Birinkorang J. Boffie 《Nuclear Engineering and Design》2011,241(8):2909-2915
Neutronics analyses were performed on the 30 kW(th) GHARR-1 facility to investigate the effects on increased beryllium annular reflector thickness on nuclear criticality safety and on the neutron flux levels in the experimental channels. The investigative study was carried out using the Monte Carlo code MCNP on a hypothetical LEU UO2 core theoretically enriched to 12.6% and having the same core configuration as the present 90.2% enriched HEU U-Al core. The analyses were performed on four models consisting of a reference model with 10.2 cm annular reflector thickness and three new design modification models with increased reflector thickness of 10.3, 10.4 and 10.5 cm respectively. The simulations indicated average thermal neutron fluxes of (9.80 ± 0.0017)E+11 n/cm2 s in the inner irradiation channels for the reference model, indicating a 2% decrease with respect to the nominal flux of 1.00E+12 n/cm2 s. Relatively lower neutron fluxes were obtained for the modification models with an average of (9.79 ± 0.0017)E+11 n/cm2 s, representing losses of 2.01% and 0.01% with respect to the HEU core and reference LEU model. 相似文献
5.
Mgboawaji Claude UJILE Samuel Jonah ABBEY 《Frontiers of Structural and Civil Engineering》2022,16(7):803
Construction and demolition waste (CDW) are the largest waste products in the world today and competes as a viable recycled additive material in place of natural aggregates. Due to the increase in compressive strength of different mix proportions of CDW, it is also considered for reuse in concrete and subbase construction. This study shows the effect of CDW in expansive soil stabilization. The chemical and mechanical properties of these materials have shown that they are capable of developing compressive strength properties for replacement of cement with significant reduction in carbon emission. The inherent compositional properties of recycled CDW compared in this review suggests that CDW have good filler properties in highly expansive soils. Mixtures of crushed brick and recycled aggregates characterised based on chemical properties of different replacement ratios suggests that CDW of good-quality aggregates reduces swell potential of expansive soils and increased mechanical strength in pavement construction. 相似文献
6.
7.
Particle Swarm Optimization (PSO), in its present form, has been in existence for roughly a decade, with formative research
in related domains (such as social modelling, computer graphics, simulation and animation of natural swarms or flocks) for
some years before that; a relatively short time compared with some of the other natural computing paradigms such as artificial
neural networks and evolutionary computation. However, in that short period, PSO has gained widespread appeal amongst researchers
and has been shown to offer good performance in a variety of application domains, with potential for hybridisation and specialisation,
and demonstration of some interesting emergent behaviour. This paper aims to offer a compendious and timely review of the
field and the challenges and opportunities offered by this welcome addition to the optimization toolbox. Part I discusses
the location of PSO within the broader domain of natural computing, considers the development of the algorithm, and refinements
introduced to prevent swarm stagnation and tackle dynamic environments. Part II considers current research in hybridisation,
combinatorial problems, multicriteria and constrained optimization, and a range of indicative application areas. 相似文献
8.
D. A. Jonah 《International Journal of Thermophysics》1986,7(4):935-948
Rigorous expressions based on the Lennard-Jones (6–12) potential, are presented for the Gibbs and Helmholtz free energy of a dilute mixture. These expressions give the free energy of the mixture in terms of the thermodynamic properties of the pure solvent, thereby providing a convenient means of correlating dilute mixture behavior with that of the pure solvent. Expressions for the following dilute binary solution properties are derived: Henry's constant, limiting activity coefficients with their derivatives, solid solubilities in supercritical gases, and mixed second virial coefficients. The Henry's constant expression suggests a linear temperature dependence; application to solubility data for various gases in methane and water shows a good agreement between theory and experiment. In the thermodynamic modeling of supercritical fluid extraction, we have demonstrated how to predict new solubility-pressure isotherms from a given isotherm, with encouraging results. The mixed second virial coefficient expression has also been applied to experimental data; the agreement with theory is good.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A. 相似文献
9.
Garrett BC Dixon DA Camaioni DM Chipman DM Johnson MA Jonah CD Kimmel GA Miller JH Rescigno TN Rossky PJ Xantheas SS Colson SD Laufer AH Ray D Barbara PF Bartels DM Becker KH Bowen KH Bradforth SE Carmichael I Coe JV Corrales LR Cowin JP Dupuis M Eisenthal KB Franz JA Gutowski MS Jordan KD Kay BD Laverne JA Lymar SV Madey TE McCurdy CW Meisel D Mukamel S Nilsson AR Orlando TM Petrik NG Pimblott SM Rustad JR Schenter GK Singer SJ Tokmakoff A Wang LS Wettig C Zwier TS 《Chemical reviews》2005,105(1):355-390
10.