Effect of retempering with superplasticizer admixtures on slump loss and compressive strength of concrete subjected to prolonged mixing

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.     

Computational fluid dynamics (CFD) analysis and experimental study for toxic hazardous waste destruction in the cavity incinerator

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%.     

Accommodation and convergence in integral imaging 3D display

In this paper, we analyze the visual fatigue of integral imaging three‐dimensional (3D) display by studying the accommodation and convergence when viewing the integral imaging 3D images. The theoretical analyses show that there is no inconsistency between the accommodation and convergence distances, which means that the integral imaging 3D display has no visual fatigue. Experiments are implemented, and the results finally demonstrate the rationality of the theoretical analyses. These analyses can be quite beneficial for researchers to better understand the performances and promote the practical applications of the integral imaging 3D display.     

制造泡沫玻璃的方法与模具

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.     

Decrease in serum levels of retinol and its binding protein (RBP) in infection

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.     

Obesity: Prevalence,Theories, Medical Consequences,Management, and Research Directions

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.     

浸没循环撞击流反应器制备牙膏用磷酸氢钙

采用浸没循环撞击流反应器（SCISR），以焦磷酸钠和磷酸三镁为稳定剂，以磷钙液和石灰乳为原料，通过中和反应法制备出了平均粒度10μm的牙膏用微细磷酸氢钙；探讨了反应温度、熟化时间、反应器装填系数、反应终点pH、磷钙液质量浓度等对产品质量的影响。确定了最优操作条件：磷钙液质量浓度1．17～1．19kg／m^3，反应温度42℃，熟化时间2h，反应终点pH6．3，反应器装填系数0．75。得到产品符合HG3257—2001标准。     

The onset of Taylor-Görtler vortices in impulsively decelerating swirl flow

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 Τ_c 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≈4Τ_c. This means that secondary motion is detected at this characteristic time. It seems evident that during Τ_c⪯Τ⪯4Τ_c, secondary motion is relatively very weak and the primary diffusive momentum transfer is dominant.     

直接金属氧化法制备SiCp/Al2O3-Al复合材料的显微结构及工艺因素的研究

在低成本的前提下 ,利用直接金属氧化法 (DIMOX)制备了SiC颗粒增强Al2 O3-Al基复合材料 ,并详细叙述了此种方法的工艺过程。借助于X—射线衍射 (XRD)和扫描电镜 (SEM)对该种复合材料的微观结构进行了观察 ,分析了SiO2 层、合金成分和温度制度对复合材料性能的影响。结果表明 ,此种复合材料结构致密且渗透完全 ,微观结构由三种相互穿插相组成 :SiC预制体、连续的Al2 O3基体 ,呈网状结构分布的未被氧化的残余Al。合金成分及烧成制度是此工艺过程中的最重要的工艺参数。