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排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
F Javier Benítez Ana I Leal Francisco J Real Juan L Acero Gloria Roldán 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):309-316
BACKGROUND: The first stage of the cork industrial process generates great volumes of wastewater with moderate to high organic pollutant content that must be purified using different procedures, such as filtration by membranes. RESULTS: The tangential filtration of these wastewaters was studied using two different laboratory equipments. In the first one, three ultrafiltration (UF) membranes were tested, with molecular weight cut‐off (MWCO) 100 kDa and 30 kDa, and two operating modes were used: total recycling of permeate and retentate streams, and in continuous mode, without recycling both streams. In the total recycling UF experiments, the influence of the operating variables on the permeate flux was first established. The effectiveness of the different membranes was determined by evaluating the rejection coefficients for several parameters that measure the global pollutant content of the effluent. The values found for these rejection coefficients were in the following order: ellagic acid and color > absorbance at 254 nm > tannic content > COD (chemical oxygen demand). In the continuous mode experiments, the fouling mechanism for each membrane was established by fitting the experimental data to various filtration fouling models given in the literature. The operating mode in the second equipment was batch concentration, and additional experiments were carried out with an UF membrane (2 kDa), and with a NF membrane (with MWCO in the range 150–300 Da). CONCLUSIONS: The three operating modes tested provided different rejection levels of organic matter; among them, the most effective procedure tested was batch concentration mode using a NF membrane. Copyright © 2007 Society of Chemical Industry 相似文献
994.
During experiments on the MSL-1 (first microgravity science laboratory) mission of the space shuttle (STS-83 and STS-94, April
and July 1997), a droplet of palladium-silicon alloy was electromagnetically levitated for viscosity measurements. For the
nondeforming droplet, the resultant magnetohydrodynamic (MHD) flow inside the drop can be inferred from motion of impurity
particulates on the surface. In the experiments, subsequent to melting, Joule heating produces a continuous reduction of viscosity
of the fluid resulting in an acceleration of the flow with time. These observations indicate formation of a pair of co-rotating
toroidal flow structures inside the spheroidal drop that undergo flow instabilities. As the fluid temperature rises, the amplitude
of the secondary flow increases, and beyond a point, the tracers exhibit noncoherent chaotic motion signifying emergence of
turbulence inside the drop. Assuming that the observed laminar-turbulent transition is shear-layer type, the internal structure
of the toroidal loops is used to develop a semiempirical correlation for the onset of turbulence. Our calculations indicate
that the suggested correlation is in modest agreement with the experimental data, with the transition occurring at a Reynolds
number of 600. 相似文献
995.
996.
The acquisition of new skills over a life span is a remarkable human ability. This ability, however, is constrained by age of acquisition (AoA); that is, the age at which learning occurs significantly affects the outcome. This is most clearly reflected in domains such as language, music, and athletics. This article provides a perspective on the neural and computational mechanisms underlying AoA in language acquisition. The authors show how AoA modulates both monolingual lexical processing and bilingual language acquisition. They consider the conditions under which syntactic processing and semantic processing may be differentially sensitive to AoA effects in second-language acquisition. The authors conclude that AoA effects are pervasive and that the neural and computational mechanisms underlying learning and sensorimotor integration provide a general account of these effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
997.
Terahertz (THz) imaging is rapidly developing. We present two new methods, based respectively on (a) a broadband thermal source (globar) and (b) a coherent, monochromatic source (optically-pumped THz laser). A room-temperature detector (Golay cell) is employed. Image quality is similar to that reported by others using more complex sources (quantum cascade lasers) and detectors (superconducting tunneling junctions). 相似文献
998.
Evans Jonathan St. B. T.; Handley Simon J.; Over David E. 《Canadian Metallurgical Quarterly》2003,29(2):321
The authors report 3 experiments in which participants were invited to judge the probability of statements of the form if p then q given frequency information about the cases pq, p?q, ?pq, and ?p?q (where ? = not). Three hypotheses were compared: (a) that people equate the probability with that of the material conditional, 1 - P(p?q); (b) that people assign the conditional probability, P(q/p); and (c) that people assign the conjunctive probability P(pq). The experimental evidence allowed rejection of the 1st hypothesis but provided some support for the 2nd and 3rd hypotheses. Individual difference analyses showed that half of the participants used conditional probability and that most of the remaining participants used conjunctive probability as the basis of their judgments. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
999.
A. V. Lyutetskii N. A. Pikhtin S. O. Slipchenko N. V. Fetisova A. Yu. Leshko E. G. Golikova Yu. A. Ryaboshtan I. S. Tarasov 《Technical Physics Letters》2003,29(4):290-293
Separate confinement InGaAsP/InP laser heterostructures were grown by metalorganic-hydride vapor-phase epitaxy. High-power single-mode laser diodes of mesastripe design based on these heterostructures operate in a wavelength interval of 1.7–1.8 μm with a maximum continuous room temperature output power of 150 mW. The single-mode lasing regime is maintained up to an output power level of 100 mW. 相似文献
1000.
Alan A. Luo Robert C. Kubic John M. Tartaglia 《Metallurgical and Materials Transactions A》2003,34(11):2549-2557
This study investigated the microstructure and fatigue properties of hydroformed sections of the 5754 and 6063 aluminum alloys.
The second-phase particles in 6063-T7 are identified as a mixture of Al12Fe3Si and Al9Fe2Si2, with a slightly higher fraction of the former. The constituent particles in the 5754 alloy are Al4Mn-type hexagonal compounds, where Mn is partially substituted by various other elements, resulting in Al4(Fe,Mn,Si,Cr). The results show that despite its lower yield strength, the hydroformed 5754 alloy has higher ultimate tensile
strength, ductility, and, more importantly, higher fatigue resistance than the 6063 material. Both crystallographic stage
I and noncrystallographic stage II cracking are found in the 6063-T7 samples, but only stage II cracking is observed in the
5754 alloy. This implies that the low fatigue strength of 6063-T7 is related to its relatively large grain size, resulting
in rapid stage I crack propagation. The higher fatigue lives of the 5754 alloy compared to the 6063 alloy in both the low-
and high-cycle life regimes are due to the increased fatigue-crack-initiation and propagation resistance of the 5754 alloy
and its probable cyclic strain-hardening behavior. 相似文献