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991.
?akir Erdo?du 《Cement and Concrete Research》2005,35(5):907-912
To have concrete possesses the specified engineering properties, its slump loss has to be compensated somehow at construction site so that concrete could be placed and compacted properly. Several attempts have been tried so far to render concrete workable at construction site including starting with a high initial slump at the stationary plant, or retempering with water and/or with chemical admixtures at construction site. In this investigation, ASTM C 494 Type F superplasticizer was used for retempering concrete to restore its initial slump. Concrete mixes having an initial slump of about 19 cm were prepared and subjected to prolonged mixing with different mixing duration such as 30, 60, 90, 120, and 150 min following an initial mixing of 5 min to ensure homogeneity. At the end of each mixing period, cube specimens of 15 cm were cast from concrete retempered to its initial slump level and tested at the age of 28 days for compressive strength. Results revealed that compared to the concrete retempered with water, those retempered with a superplasticizer admixture have yielded significantly higher strength regardless of the mixing duration. 相似文献
992.
We undertook numerical and experimental studies to develop a better incineration method for the destruction of CC14. A phenomenological model for the turbulent reaction of CC14, including a flame inhibition feature, has been successfully incorporated into a commercial code, simulating the incineration
processes of this compound. The gaseous flow solution was obtained using SIMPLEST, a derivative of Patankar’s SIMPLE algorithm,
with a k-ε turbulence model. A modified fast chemistry turbulent reaction model was developed to describe the flame inhibition
due to the presence of CC14, considering the corresponding burning velocity data of these mixtures. An experiment was carried out on a 5.2 kW laboratory
scale, transportable, cavity-type incinerator, which warrants a sufficient residence time and effective turbulent mixing by
the formation of a strong recirculation region in a combustor. To this end, the specific configuration of the incinerator
was manufactured to consist of two opposing jets and a rearward facing step. The calculated data were in close agreement with
the experimental data for the concentrations of major species, such as CCI4 and HCl, together with the temperature profiles. The experimental test gave the desired DRE of above 99.99%. 相似文献
993.
制造泡沫玻璃的方法与模具 总被引:3,自引:0,他引:3
将泡沫玻璃配合料制备成块状物,将配合料块按规定间隙在模具中平铺码放并烧成,使配合料块熔为一体,形成较小变形的平板状泡沫玻璃.其制造模具是由底板、上盖及L型围板构成的箱型结构,模具各部位通过V字沟相互联结,保证各部位能自由地附着和脱离.模具多层码放烧制,模具间必须设置间隙.在模具上设置通孔可以有效地抑制膨胀过量问题. 相似文献
994.
The main purpose of the present study was to determine the qualitative and quantiative effect of various infectious epsiodes on the blood serum levels of retinol and retinol-binding protein (RBP). Twenty-four children and 30 adult subjects were studied. The infections studied included chickenpox (n = 7); bronchitis (n = 9) upper respiratory infection (n = 30); tonsillitis (n = 2); diarrhea (n = 2) and one case each of: febrile stomatitis, nonspecific gastrointestinal alteration, urinary infection and shigellosis. In addition to retinol and RBP, the study determined changes in serum carotene, proteins, albumin and globulins. The results clearly demonstrate the marked depressing effect of infections on serum retinol, with a magnitude which in many cases reached more than 20 micrograms/dl, and in others more than 30 micrograms/dl. The RBP levels were significantly correlated with retinol, decreasing proportionally with infection. Serum albumin also decreased in most instances; and the globulin levels of the children, but not of the adults, were significantly higher during the infections. Carotene did not show important variations. The effects were more intense when fever accompanied the infectious episodes. These results are considered of great public health significance, in view of the large majorities, mainly children, who ordinarily subsist with very low serum retinol levels in the underdeveloped regions of the world. As infections attack these underpriviledged children, their serum retinol and RBP levels will likely drop a magnitude similar to that observed in the subjects of this study. They may then reach even more critically deficient retinol levels and be in serious danger of developing a severe acute state of clinical vitamin A deficiency. 相似文献
995.
Colin?WilbornEmail author Jacqueline?Beckham Bill?Campbell Travis?Harvey Melyn?Galbreath Paul?La Bounty Erika?Nassar Jennifer?Wismann Richard?Kreider 《Journal of the International Society of Sports Nutrition》2005,2(2):4-31
Obesity and its associated disorders are a growing epidemic across the world. Many genetic, physiological, and behavioral
factors play a role in the etiology of obesity. Diet and exercise are known to play a valuable role in the treatment and prevention
of obesity and associated disorders such as hypertension, heart disease, and diabetes. Therefore, the purpose of this review
is to examine the prevalence, etiology, consequences, and treatment of obesity. 相似文献
996.
The onset of hydrodynamical instability induced by impulsive spin-down to rest in a cylinder containing a Newtonian fluid
is analyzed by using propagation theory. It is well-known that the primary transient swirl flow is laminar, but with initial
high velocities secondary motion sets in at a certain time. The dimensionless critical time Τc to mark the onset of instability is presented here as a function of the Reynolds number Re. Available experimental data indicate
that for large Re deviation of the velocity profiles from their momentum diffusion occurs starting from a certain time Τ≈4Τc. This means that secondary motion is detected at this characteristic time. It seems evident that during Τc⪯Τ⪯4Τc, secondary motion is relatively very weak and the primary diffusive momentum transfer is dominant. 相似文献
997.
998.
Soo?Tae?Choo In-Sik?NamEmail author Sung-Won?Ham Jeong-Bin?Lee 《Korean Journal of Chemical Engineering》2003,20(2):273-278
The catalytic activity of sulfated titania (ST) calcined at a variety of temperatures has been investigated for selective catalytic reduction (SCR) of NO by NH3. The NO removal activity of ST catalyst mainly depends on its sulfur content, indicating critical role of sulfur species on the surface of TiO2. The role of sulfur is mainly the formation of acid sites on the catalyst surface. The presence of both BrØnsted and Lewis acid sites on the surface of sulfated titania has been identified by IR study with the adsorption of NH3 and pyridine on ST. The reduction of the intensity of IR bands representing BrØsted acid sites is more pronounced than that revealing Lewis acid sites as the calcination temperature increases. It has been further clarified by IR study of ST500 catalyst evacuated at a variety of temperatures. The NO removal activity also decreases with the increase of the catalyst calcination temperature. It simply reveals that BrØnsted acid sites induced by sulfate on the catalyst surface are primarily responsible for the enhancement of catalytic activity of ST catalyst containing sulfur for NO reduction by NH3. 相似文献
999.
Jolanta ?wiatowska-Mrowiecka 《Electrochimica acta》2005,50(9):1829-1840
Anodic dissolution of poly- and single-crystals of zinc was performed in methanol solution of lithium perchlorate by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The mechanism of anodic dissolution of zinc in organic solvents occurs in two oxidation steps. It is the first step that surface anodic product is created. Stability of the surface product is much better in anhydrous organic environments than in aqueous media; because the product is stable, a barrier layer composed of is formed at low anodic overvoltage. The formation of the layer is much stronger on the low index than on the high-index plane (0 0 0 1), where the adsorption of anodic product is more difficult. 相似文献
1000.
Nikolaos?Nenadis Maria?TsimidouEmail author 《Journal of the American Oil Chemists' Society》2002,79(12):1191-1195
Rapid 1,1-diphenyl-2-picrylhydrazyl (DPPH•) tests are often applied to classify the scavenging activity of phenolic compounds (AH). Published analytical protocols differ
in more than one experimental condition, and results for the relative order or magnitude of activity are often contradictory.
In this work, parameters such as duration of test, [AH]/[DPPH•] molar ratio, and solvent effects were examined and discussed. The test duration and the value of the [AH]/[DPPH•] ratio did not influence the order of activity among tested antioxidants. Ethanol, commonly used as solvent in such tests,
was compared with acetonitrile and tert-butyl alcohol. Solvent properties such as the ability to form hydrogen bonds with the AH seem to influence the level of the
relative activity (%RSA). Higher %RSA values were observed in ethanol. The activity of the most polar compounds was affected
the most, and in some cases (caffeic, dihydrocaffeic, and rosmarinic acids) the order of activity was changed owing to different
kinetics. Standardization of the analytical protocol should include a 20-min reaction period and a molar ratio that permits
attainment of a 60–80% RSA value for the most potent antioxidant. Solvent choice is critical for classifying activity. Safe
classification can be based only on results from kinetic studies. 相似文献