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排序方式: 共有1713条查询结果,搜索用时 15 毫秒
91.
Emmanuel Osalusi Jonathan SideRobert Harris 《International Communications in Heat and Mass Transfer》2009
A broadband acoustic Doppler current profiler (ADCP) moored on the seabed at 42 m depth has been used to observe the mean and turbulent flow components in the tidally energetic Fall of Warness channel over two tidal cycles. The Reynolds stress has been estimated from the difference in variance between the along-beam velocities of opposing acoustic beams. Near bed stress at 2.63 m above seabed (mab) exceeds 7.5 Pa at the time of mean flow (speed of ~ 1.3 m s− 1) while the ebb stresses are limited to ~ 3.31 Pa during the peak ebb, mean, flow of ~ 1.3 m s− 1. The production of turbulent kinetic energy (TKE), P was found to be negative below 2 × 10− 9 W m− 3 and up to 6 × 10− 4 W m− 3 was estimated during flood flows and decreasing to 3 × 10− 4 W m− 3. The TKE dissipation rate ε was estimated by inertial dissipation method (IDM) with the greatest value of 2.43 × 10− 2 W m− 3 observed near the seabed around maximum ebb, falling to 5.75 × 10− 5 W m− 3 around slack water. The comparison between P and ε was performed by calculating individual ratios of P corresponding to ε using a bootstrap resampling technique. The study shows that the ratio ε/P averaged over whole flood and ebb were found to be ~ 0.4138 and ~ 0.4177, respectively, indicating that production exceeded dissipation. The uncertainties in Reynolds stress estimates due to instrument noise were found to be 3 × 10− 4 Pa while 4.52 × 10− 2 Pa can be attributed to the uncertainties due to the increase in the flow-related component. 相似文献
92.
Xianqin Meng Guillaume Gomard Ounsi El Daif Emmanuel Drouard Regis Orobtchouk Anne Kaminski Alain Fave Mustapha Lemiti Alexei Abramov Pere Roca i Cabarrocas Christian Seassal 《Solar Energy Materials & Solar Cells》2011
In this paper, we present the integration of an absorbing photonic crystal within a thin-film photovoltaic solar cell. Optical simulations performed on a complete solar cell revealed that patterning the hydrogenated amorphous silicon active layer as a 2D photonic crystal membrane enabled to increase its integrated absorption by 28 % between 300 and 720 nm, comparing to a similar but unpatterned stack. In order to fabricate such promising cells, we developed a high throughput process based on holographic lithography and reactive ion etching. The influences of the parameters taking part in those processes on the obtained patterns are discussed. Optical measurements performed on the resulting “photonized” solar cell structures underline the regularity of the 2D pattern and a significant absorption increase above 550 nm, similarly to what is observed on the simulated absorption spectra. Moreover, our patterned cells are found to be robust with regards to the angle of incidence of the light. 相似文献
93.
Pierre-Antoine Gédouin Emmanuel Delaleau Jean-Matthieu Bourgeot Cédric Join Shabnam Arbab Chirani Sylvain Calloch 《Control Engineering Practice》2011,19(5):433-441
Shape memory alloys (SMA) are being more frequently integrated into engineering applications. These materials with their shape memory effect enable the simplification of mechanisms and the reduction in size of actuators. SMA parts can easily be activated by Joule effect but their modeling and consequently their control remains difficult. It is principally due to their non-linear hysteretic thermomechanical behavior. Most of successful control strategies applied to SMA actuators are not often suitable for industrial applications: they are particularly heavy and use the Preisach model or neural networks to model the hysteretic behavior of these materials; this kind of model is difficult to identify and to use in real time. This paper deals with an application of the new framework of model-free control (MFC) of an SMA-spring based actuator. This control strategy relies on new results for fast derivative estimation of noisy signals. Their main advantages are: its simplicity and its robustness. Experimental results and comparisons with PI control are presented that demonstrate the efficiency of this new control strategy. 相似文献
94.
Augustine E. Ofomaja Emmanuel E. UkpeborStephen A. Uzoekwe 《Biomass & bioenergy》2011,35(10):4112-4123
Determination of the overall rate controlling step in the biosorption of Methyl violet dye onto a new biosorbent, palm kernel fiber has been determined. Pseudo-second-order model described the kinetics over the whole contact time period for the effect of initial concentration and temperature. Using the Wu’s approaching equilibrium factor, Rw, it was observed that the time for the switch from initial biosorption to intraparticle diffusion is affected by initial concentration and temperature. A comparison between the activation parameters of film diffusion, pseudo-second order ion exchange and intraparticle diffusion revealed that film diffusion is the overall slowest step in the biosorption process. Temperature increased the biosorption capacity but reduced slightly the rate of intraparticle diffusion, indicating that the biosorbent surface was activated by temperature which limited the diffusion of Methyl violet molecules into the interior of the biosorbent. A multistage process design to minimize mass and contact time was done. 相似文献
95.
Monazite was continuously coated onto Nextel 720 fibers, using an aqueous precursor and in-line heat treatment at 900°–1300°C. Some experiments were repeated with alumina-doped precursors. Coated fibers were heat-treated for 100 h at 1200°C. Coatings were characterized by optical microscopy, scanning electron microscopy, and analytical transmission electron microscopy. Coated-fiber tensile strengths were measured by single-filament tensile tests. The precursors were characterized by X-ray diffractometry, differential thermal analysis/thermogravimetric analysis, and mass spectrometry. Coated-fiber tensile strength was lower for fibers coated at higher deposition temperatures. Heat treatment for 100 h at 1200°C decreased tensile strength further. The coatings were slightly phosphate-rich and enhanced alumina grain growth at the fiber surface, but phosphorus was not detected along the alumina grain boundaries. Fibers with alumina-doped coatings had higher tensile strengths than those with undoped coatings after heat treatment for 100 h at 1200°C. Alumina added as α-alumina particles gave higher strengths than alumina added as colloidal boehmite. Alumina doping slowed monazite grain growth and formed rough fiber–coating interfaces after 100 h of heat treatment at 1200°C. Possible relationships among precursor characteristics, coating and fiber microstructure development, and strength-degradation mechanisms are discussed in this paper. 相似文献
96.
Michalis Agraniotis Panagiotis Grammelis Charalambos Papapavlou Emmanuel Kakaras 《Fuel Processing Technology》2009,90(9):1071-1079
The present paper includes the results of the combustion tests with Greek dried lignite performed at a 1 MWth semi industrial scale pulverized coal combustion facility. Scope of the campaign is the investigation of the combustion behaviour of Greek lignite, i.e. temperature fields, ignition, burnout, emissions, as well as slagging and fouling tendency, while firing with varying levels of recirculated flue gas. Dry coal co-firing conditions in a large scale boiler are simulated by adjusting the volume flow of recirculated flue gas.Two test series representing different boiler operation modes are performed. During the first series the maximum flue gas temperature increase, when co-firing dry coal, is determined, while in the second test series the needed load decrease, in order to keep constant furnace outlet temperature in dry coal co-firing conditions is recorded. A detailed measurement set is carried out including temperature profiles, emissions, fuel, fly ash sampling and slagging and fouling investigations through the installation of dedicated deposition probes.The anticipated increase of the furnace temperature profiles by decreasing the inserted recirculated flue gas is confirmed by the experimental results. No clear trend of dry coal co-combustion on the emissions' behaviour is noticed, while dry coal firing appears to have a moderate effect on the deposition behaviour of Greek lignite. These preliminary investigations indicate that no significant operational problems are expected during a potential future demonstration of dry lignite co-firing in a Greek large scale boiler. 相似文献
97.
98.
Field-scale analysis of water and nutrient use efficiency for vegetable production in a West African urban agricultural system 总被引:1,自引:1,他引:0
Sheick K. Sangare Emmanuel Compaore Andreas Buerkert Marnik Vanclooster Michel P. Sedogo Charles L. Bielders 《Nutrient Cycling in Agroecosystems》2012,92(2):207-224
Urban agriculture increasingly supplies food and non-food services to the rapidly growing West African cities. However, with
its typically heavy use of fertilizers and uncontrolled use of water, it bears severe risks of soil and groundwater pollution.
This study was carried out in Bobo Dioulasso (Burkina Faso, West Africa) at two commercial gardening sites. It aimed at performing
a detailed characterization of farmer’s water and nutrient management strategies. Four vegetable crops were monitored (tomato,
cabbage, carrot and lettuce). Water inputs (rainfall and irrigation), nutrient inputs (organic and mineral fertilizers and
nutrients in irrigation water) and crop uptake were monitored over a 1–2-year period. In addition, pan lysimeters allowed
monitoring drainage. Depending on the site, 3–8% of the input water was lost by drainage, i.e., as much as 293 mm/year at
one of the sites. During the dry season, when the farmer has full control over the water supply, water application exceeded
plant requirements by as much as 40%, which reveals inefficient water use. Up to 800 kg N ha−1, 140 kg P ha−1 and 500 kg K ha−1 were applied for a single crop cycle. With few exceptions, crops tended to be strongly over-fertilized, except for K at one
of the two sites. Nutrient supply exceeded crop requirements by 109 to 2,012 kg N, 66 to 450 kg P and 0 to 393 kg K per year.
These results, in combination with the large observed rates of drainage, are indicative of a high risk of nutrient leaching
and groundwater contamination. The partial factor productivity of nutrients tended to be low. These results therefore suggested
that there is scope to substantially reduce nutrient application rates in these systems without adverse effects on yields,
which would be beneficial for groundwater resources and improve the economic returns. 相似文献
99.
A. Emmanuel 《纺织学会志》2013,104(4):159-162
100.
We describe an original microscope for high-resolution optical coherence tomography applications. Our system is based on a Linnik interference microscope with high-numerical-aperture objectives. Lock-in detection of the interference signal is achieved in parallel on a CCD by use of a photoelastic birefringence modulator and full-field stroboscopic illumination with an infrared LED. Transverse cross-section (en-face, or XY) images can be obtained in real time with better than 1-microm axial (Z) resolution and 0.5-microm transverse (XY) resolution. A sensitivity of approximately 80 dB is reached at a 1-image/s acquisition rate, which allows tomography in scattering media such as biological tissues. 相似文献