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排序方式: 共有668条查询结果,搜索用时 15 毫秒
101.
Etienne J. F. R. Caron Amir R. Baserinia Harry Ng Mary A. Wells David C. Weckman 《Metallurgical and Materials Transactions B》2012,43(5):1202-1213
Thermal modeling of the direct-chill casting process requires accurate knowledge of (1) the different boundary conditions in the primary mold and secondary direct water-spray cooling regimes and (2) their variability with respect to process parameters. In this study, heat transfer in the primary cooling zone was investigated by using temperature measurements made with subsurface thermocouples in the mold as input to an inverse heat conduction algorithm. Laboratory-scale experiments were performed to investigate the primary cooling of AA3003 and AA4045 aluminum alloy ingots cast at speeds ranging between 1.58 and 2.10 mm/s. The average heat flux values were calculated for the steady-state phase of the casting process, and an effective heat-transfer coefficient for the global primary cooling process was derived that included convection at the mold surfaces and conduction through the mold wall. Effective heat-transfer coefficients were evaluated at different points along the mold height and compared with values from a previously derived computational fluid dynamics model of the direct-chill casting process that were based on predictions of the air gap thickness between the mold and ingot. The current experimental results closely matched the values previously predicted by the air gap models. The effective heat-transfer coefficient for primary cooling was also found to increase slightly with the casting speed and was higher near the mold top (up to 824 W/m2·K) where the molten aluminum first comes in contact with the mold than near the bottom (as low as 242 W/m2·K) where an air gap forms between the ingot and mold because of thermal contraction of the ingot. These results are consistent with previous studies. 相似文献
102.
Influence of Metronidazole Particle Properties on Granules Prepared in a High-Shear Mixer-Granulator
Piera Di Martino Roberta Censi Ledjan Malaj Sante Martelli Etienne Joiris Christine Barthélémy 《Drug development and industrial pharmacy》2013,39(2):121-131
ABSTRACTMetronidazole is a good example of high-dose drug substance with poor granulating and tableting properties. Tablets are generally produced by liquid granulation; however, the technological process failure is quite frequent. In order to verify how the metronidazole particle characteristics can influence granule properties, three metronidazole batches differing for crystal habit, mean particle size, BET surface area and wettability were selected, primarily designed according to their different elongation ratio: needle-shaped, stick-shaped, and isodimensional. In the presence of lactose monohydrate and pregelatinized maize starch, respectively as diluent and binder, they were included in a formula for wet granulation in a high-shear mixer-granulator. In order to render the process comparable as far as possible, all parameters and experimental conditions were maintained constant. Four granule batches were obtained: granules from placebo (G-placebo), granules from needle-shaped crystals (G-needle-shaped), granules from stick-shaped crystals (G-stick-shaped), and granules from isodimensional crystals (G-isodimensional). Different granule properties were considered, in particular concerning porosity, friability, loss on drying (LOD), and flowability. In order to study their tabletability and compressibility, the different granules obtained were then compressed in a rotary press. The best tabletability was obtained with the isodimensional batch, while the poorest was exhibited by the stick-shaped one. Differences in tabletability are in good accordance with compressibility results: to a better tabletability corresponds an important granule ability to undergo a volume reduction as a result of an applied pressure. In particular, it was proposed that the greatest compressibility of the G-isodimensional must be related to the greatest granule porosity percentage. 相似文献
103.
Rémi Lacroix Vincent Chomienne Guillaume Kermouche Jérémie Teisseire Etienne Barthel Samuel Queste 《International Journal of Applied Glass Science》2012,3(1):36-43
Amorphous silica exhibits a complex mechanical response. The elastic regime is highly nonlinear while plastic flow does not conserve volume, resulting in densification. As a result the quantification of a reliable constitutive equation is a difficult task. We have assessed the potential of micropillar compression testing for the investigation of the micromechanical properties of amorphous silica. We have calculated the response of amorphous silica micropillars as predicted by finite element analysis. The results were compared to preliminary microcompression tests. In the calculations, an advanced constitutive law including plastic response, densification, and strain hardening was used. Special attention was paid to the evaluation of the impact of substrate compliance, pillar misalignment, and friction conditions. We find that amorphous silica is much more amenable than some metals to microcompression experiments due to a comparatively high ratio between yield stress and elastic modulus. The simulations are found to be very consistent with the experimental results. However, full agreement cannot be obtained without allowance for the nonlinear response of amorphous silica in the elastic regime. 相似文献
104.
Detachment is one of the major processes determining the physical structure and microbial functionalities of biofilms. To predict detachment, it is necessary to take the mechanical properties of the biofilm and the effect of both hydrodynamic and growth conditions into account. In this work, experiments were conducted with biofilms developed under various shear stresses and with various substrate natures. In addition, two cases were considered in order to differentiate between the effect of hydrodynamic factors and growth factors: the biofilms were directly grown under the targeted shear stress (τ) condition or they were precultivated under very low shear stress (0.01 Pa) and then exposed to high shear stress in the range of 0.1-13 Pa. An exponential and asymptotic decrease of the biofilm thickness and mass with increasing τ was observed in both cases. On contrary density, expressed as the biofilm dry mass on a known substratum divided by the average thickness increased with τ. Denitrifying biofilms always showed greater thickness and density than oxic biofilms. These results showed the presence of a compact basal layer that resisted shear stresses as high as 13 Pa whatever the culture conditions. Above this basal layer, the cohesion was lower and depended on the shear stress applied during biofilm development. The application of shear stress to the biofilms resulted in both detachment and compression, but detachment prevailed for the upper part of the biofilms and compression prevailed for the basal layers. A model of biofilm structure underlying the stratified character of this aggregate is given in terms of density and cohesion. 相似文献
105.
Nicolas Candau Laurent Chazeau Jean-Marc Chenal Catherine Gauthier José Ferreira Etienne Munch Cyrille Rochas 《Polymer》2012,53(13):2540-2543
Real time Wide-Angle X-ray Scattering (WAXS) measurements during cyclic tensile tests at high strain rates (from 8 s?1–280 s?1) and at room temperature on crosslinked Natural Rubber (NR) are performed thanks to a specific homemade device. From the observed influence of the frequency on the crystallization index at the maximum sample elongation, a characteristic crystallization time is deduced. This is done taking into account the material self-heating during such unusually high strain rates. Two regimes for the dynamic process of strain induced crystallization are evidenced. For the NR tested, the obtained characteristic time is around 20 ms when the material average elongation during the cyclic test is above a critical elongation value λc. λc is the minimum elongation needed to induce crystallization during low strain rate tensile tests. Moreover, a rapid increase of this characteristic time is found when the average elongation decreases below this critical value. 相似文献
106.
Cristèle Delsart Céline Cholet Rémy Ghidossi Nabil Grimi Etienne Gontier Laurence Gény Eugène Vorobiev Martine Mietton-Peuchot 《Food and Bioprocess Technology》2014,7(2):424-436
The treatment of Cabernet Sauvignon red grapes by pulsed electric fields (PEFs) is performed prior to vinification in order to enhance the extraction of polyphenols. PEF treatments of the longest duration and of the highest energy (E?= 0.7 kV/cm, t PEF?=?200 ms, W?=?31 Wh/kg) changed the structure of grape skins and produced a wine that was richer in tannins (34 %), while treatment of the highest strength (E?=?4 kV/cm, t PEF?=?1 ms, W =?4 Wh/kg) altered the visual appearance of phenolic compounds in the skins and led to greater extraction of the anthocyanins (19 %). The PEF treatments caused the depolymerization of skin tannins, improving the diffusion of these decondensed tannins which are smaller. The PEF treatment of longest duration and of the highest energy had more impact on the parietal tannins and the cell walls of the skins while treatment of the highest strength modified more the vacuolar tannins. Changes in the operating parameters of the PEF treatment (E?=?0.7 to 4 kV/cm, t PEF?=?1 to 200 ms, W?=?4 to 31 Wh/kg) did not affect alcohol content, total acidity nor volatile acidity in finished wines compared to the values of the control wine, but seemed to cause a slight increase in pH (1–2 %). 相似文献
107.
Eduardo Agosin Marie Therese Tollier Jean Marc Brillouet Pierre Thivend Etienne Odier 《Journal of the science of food and agriculture》1986,37(2):97-106
Disappearance of cell wall components of untreated straw and straw treated with the ligninolytic white-rot fungi Phanerochaete chrysosporium, Dichomitus squalens and Cyathus stercoreus were determined during the course of rumen digestion of samples in nylon bags. The first fungus degraded hemicelluloses and cellulose non-selectively, adversely affecting the digestion rate of crude cell walls. Dichomitus squalens and C. stercoreus preferentially degraded hemicelluloses and lignin, affording cell wall degradation rates 1.5 times higher than in native straw. Furthermore, the extent of cell wall digestion was also significantly enhanced. Both strains improved the extent of cellulose digestion, whereas the potentially degradable xylan fraction remained unchanged. Polysaccharide digestion rates were influenced in different ways depending on the strain tested: straw degraded by C. stercoreus showed an increase in cellulose digestion rate by 50%, whereas residual arabinose units were slowly degraded. Xylan was degraded 1.8 times faster in straw decayed' by D. squalens, while cellulose digestion remained unchanged. Phanerochaete chrysosporium depressed both xylan and cellulose digestion rates. Fungal-treated lignins were solubilised in the rumen faster than in untreated straw, whereas only treatment by C. stercoreus resulted in higher lignin losses. Esterified phenolic acids were extensively degraded by all three fungi. Residual ferulic and p-coumaric acids accumulated during rumen digestion, although only the former decreased in the original straw. 相似文献
108.
Henry E Dif A Schmutz M Legoff L Amblard F Marchi-Artzner V Artzner F 《Nano letters》2011,11(12):5443-5448
Biological molecules and molecular self-assemblies are promising templates to organize well-defined inorganic nanostructures. We demonstrate the ability of a self-assembled three-dimensional crystal template of helical actin protein filaments and lipids bilayers to generate a hierarchical self-assembly of quantum dots. Functionnalized tricystein peptidic quantum dots (QDs) are incorporated during the dynamical self-assembly of this actin/lipid template resulting in the formation of crystalline fibers. The crystal parameters, 26.5×18.9×35.5 nm3, are imposed by the membrane thickness, the diameter, and the pitch of the actin self-assembly. This process ensures the high quality of the crystal and results in unexpected fluorescence properties. This method of preparation offers opportunities to generate crystals with new symmetries and a large range of distance parameters. 相似文献
109.
This paper reports insights about energy savings in buildings dedicated to tertiary activity. The goal is to employ as much as possible natural light flows to minimize the artificial light source consumption. Although the solar energy is power-efficient to light and heat a room, this natural source remains complex to manage and can generate inconveniences related to occupants visual comfort. The authors propose a global solution to deal with visual comfort by controlling the daylight contribution to the indoor light atmosphere. This control structure is based on the use of an innovative sensor of light conditions and it was implemented within an experimental room equipped with classic Venetian blinds. This paper focuses on the control laws to apply in order to meet visual needs for current tasks performed in offices. 相似文献
110.
Lucjan Chmielarz Piotr Kuśtrowski Marek Drozdek Małgorzata Rutkowska Roman Dziembaj Marek Michalik Pegie Cool Etienne F. Vansant 《Journal of Porous Materials》2011,18(4):483-491
SBA-15 mesoporous silicas modified with rhodium were studied as catalysts for the N2O decomposition reaction. Rhodium was deposited on SBA-15 by the Molecular Designed Dispersion (MDD) method using Rh(acac)3 as a precursor of active phase. The same method was used for the deposition of Cu, Fe, Al and Ti. The SBA-15 support modified
with metals were characterized with respect to metal loading (EPMA), structure (XRD), texture (BET), morphology (SEM), Rh
dispersion (oxygen chemisorption), surface acidity (pyridine adsorption) and chemical nature of introduced copper and iron
species (UV–vis-DRS). The rhodium-containing SBA-15 samples were found to be active catalysts for the N2O decomposition reaction. Deposition of Al on the Rh-loaded catalyst increased its activity. An opposite effect was observed
for the samples modified with Cu and Fe. 相似文献