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81.
Silicon - Magnetic stirring is considered to be the most useful stirring method in semi-solid casting processes which doesn’t have the restrictions of the mechanical stirring. In this... 相似文献
82.
In the present study, a mathematical model is developed to numerically predict nonisothermal batch suspension polymerization of vinyl chloride. Free volume theory was used to consider diffusion‐controlled reactions. Model predictions were validated against field data obtained in a pilot scale stirred tank reactor. Variable temperature trajectory was considered during the course of the reaction to improve productivity by reducing the polymerization time for a certain conversion. Variable temperature during the course of the polymerization was successfully implemented by considering the predefined K value. By using variable temperatures during the course of the reaction, the density of the short branches per 1,000 monomer units as a criterion for structure defect remained relatively unchanged. Maximum reduction in reaction time relative to the isothermal case with the same K value and final conversion was 44% for the best temperature trajectory. J. VINYL ADDIT. TECHNOL., 22:470–478, 2016. © 2015 Society of Plastics Engineers 相似文献
83.
Mojtaba Poursaeid Reza Mastouri Saeid Shabanlou Mohsen Najarchi 《Water and Environment Journal》2021,35(1):67-83
In recent years, as a result of climate change as well as rainfall reduction in arid and semi‐arid regions, modelling qualitative and quantitative parameters belonging to aquifers has become crucially important. In Iran, as aquifers are treated as the most commonly used drinking water resources, modelling their qualitative and quantitative parameters is enormously important. In this paper, for the first time, values of salinity, total dissolved solids (TDS), groundwater level (GWL) and electrical conductivity (EC) of the Arak Plain, located in Markazi Province, Iran, are simulated by means of four modern artificial intelligence models including extreme learning machine (ELM), wavelet extreme learning machine (WELM), online sequential extreme learning machine (OSELM) and wavelet online sequential extreme learning machine (WOSELM) as well as the MODFLOW software for a 15‐year period monthly. To develop the hybrid artificial intelligence models, the wavelet is employed. First, the effective lags in estimating the qualitative and quantitative parameters of the groundwater are identified using the autocorrelation function (ACF) and the partial autocorrelation function (PACF) analysis. After that, four different models are developed by the selected input combinations and also the ACF and the PACF in the form of different lags for each of ELM, WAELM, OSELM and WOSELM methods. Then, the superior models in simulating the groundwater qualitative and qualitative parameters are detected by conducting a sensitivity analysis. To forecast the electrical conductivity (EC) by the best WOSELM model, the values of the Nash–Sutcliffe efficiency coefficient (NSC), Mean Absolute Error (MAE) and the scatter index (SI) are obtained to be 0.991, 18.005 and 4.28E‐03, respectively. In addition, the most effective lags in estimating these parameters are introduced. Subsequently, the results found by the MODFLOW model are compared with those of the artificial intelligence models and it is concluded that the latter are more accurate. For instance, the scatter index and Nash–Sutcliffe efficiency coefficient values calculated by WOSELM for TDS, respectively, are 5.34E‐03 and 0.991. Finally, an uncertainty analysis is conducted to evaluate the performance of different numerical models. For example, MODFLOW has an underestimated performance in simulating the salinity parameter. 相似文献
84.
Simin Nikbin Meydani Alice C. Shapiro Mohsen Meydani John B. Macauley Jeffrey B. Blumberg 《Lipids》1987,22(5):345-350
The effect of age and dietary fat type on tocopherol status was investigated using young and old C57BL/6Nia mice fed semipurified
diets containing 5% (by weight) fish, corn or coconut oils and supplemented with 30, 100 or 500 ppm dl-α-tocopheryl acetate
for 6 wk. Tocopherol levels in the diets, plasma, liver, kidney and lung were measured by high performance liquid chromatography
following appropriate extractions. The results indicate that mice fed fish oil maintain lower plasma and tissue tocopherol
concentrations than those fed corn and cononut oils (fish<corn oil<coconut oil). The difference was not due to a loss of tocopherol
prior to consumption, but rather appeared to occur during the absorption process. Old mice had lower plasma and liver tocopherol
concentrations than young mice. Old mice fed fish oil, however, maintained plasma tocopherol levels better than young mice
fed fish oil, presumably due to their larger tocopherol pool. No age effect was detected on kidney and lung tocopherol levels.
It is concluded that tocopherol status is affected by age and dietary fat type, especially fish oil. 相似文献
85.
Many countries have experienced restructuring in their electric utilities. This restructuring has presented the power industries with new challenges, the most important of which is long-term investment planning under uncertain conditions. This paper presents an improved mechanism for capacity payment. The mechanism has been investigated based on system dynamic modeling. In our proposed mechanism, generators will recover a part of their investment through capacity payment. While the payment for any plant remains constant during the operation period, it depends on the investment needed to build it. The main factors affecting long-term planning have been considered in our model. The approach can be used to investigate the effects of fixed as well as variable capacity payment in market investment. We used the probability density function of load as a new concept to calculate average market price. Delays in unit constructions, estimation of demand, and market capacity growth during construction periods have been included in the proposed algorithm as parameters, which affect the regulator's decision for changing capacity payment. The model can be used by regulators to investigate strategies that may affect the fluctuations in the market. 相似文献
86.
This work investigates the analytical solution for transient temperature and thermal stresses within three circular geometries. First, the transient temperature and thermal stresses within a composite disk are addressed. Then, two examples regarding transient temperature and thermal stresses throughout circular heaters are analyzed. Pulsed and sinusoidal internal heat generations are incorporated into the second and third examples, respectively. For the composite hollow-disk example, merely the separation of variables method (SVM) is used to overcome the energy partial differential equation. For the other two examples, the combination of the SVM and Duhamel's theorem are adopted to solve the partial differential equations. Accordingly, assuming plane stress formulation, the transient thermal stresses within structures are obtained. 相似文献
87.
Mohsen Soleimani Sheraz Khan David Mendenhall Willie Lau Mitchell A. Winnik 《Polymer》2012,53(13):2652-2663
We describe fluorescence resonance energy transfer (FRET) studies of film formation by a new type of two-component latex particles. These particles consist of a miscible blend of two components that have a similar composition but very different molecular weights. In our approach, we used sequential seeded emulsion polymerization to generate (in situ) a fraction of oligomer in poly(butyl acrylate-co-methyl methacrylate) P(BA-MMA) seed particles that contained a relatively high molecular weight (high-M) dye-labeled polymer. In this way we could systematically change the molecular weight distribution of polymer inside the particles. We varied the amount and the molecular weight of the oligomers. For latex films cast from these two-component particles, we studied the diffusion rate of the high molecular weight polymer by FRET. These measurements revealed that oligomers promoted diffusion rate during latex film formation (oligoplasticization). We analyzed our diffusion data in terms of the Fujita–Doolittle free-volume model and showed that higher molecular weight oligomers are less efficient as plasticizers. In separate experiments, oligomers with similar molecular weights as those in the two-component particles were introduced via latex blending. We compared oligoplasticization in latex blends films with that in the two-component particles films. Finally, we investigated the rheological behavior of the two-component polymers with compositions adjusted to have a common Tg (2 °C). The higher the molecular weight of the oligomer, the more that had to be added to achieve Tg = 2 °C. All of the oligomers were much shorter than the entanglement length and act as diluents of the entanglements in the high-M polymer. We found that incorporating larger amounts of oligomers with a higher molecular weight resulted in a more pronounced drop in polymer viscosity, associated with the decrease in the entanglement density. 相似文献
88.
从1994年北岭地震中可看到,栓焊节点的抗震性能较差。因此,常用于工业建筑和高层建筑中的抗弯框架多采用端板连接和T型螺栓连接。采用有限元方法,通过改变螺栓的纵横布置对比了14个试件的滞回性能。结果表明:假定两者总的耗能能力相同,则T型螺栓连接的抗弯能力和初始转动刚度均比基于AISC规范设计的端板螺栓连接高。在往复荷载作用下,螺栓布置的改变对T型螺栓连接破坏模式的影响要大于端板连接,端板连接更适用于具有初始几何缺陷的结构。 相似文献
89.
Mohsen Akbari Ali Tamayol Veronique Laforte Nasim Annabi Alireza Hassani Najafabadi Ali Khademhosseini David Juncker 《Advanced functional materials》2014,24(26):4060-4067
The fabrication of cell‐laden structures with anisotropic mechanical properties while having a precise control over the distribution of different cell types within the constructs is important for many tissue engineering applications. Automated textile technologies for making fabrics allow simultaneous control over the color pattern and directional mechanical properties. The use of textile techniques in tissue engineering, however, demands the presence of cell‐laden fibers that can withstand the mechanical stresses during the assembly process. Here, the concept of composite living fibers (CLFs) in which a core of load bearing synthetic polymer is coated by a hydrogel layer containing cells or microparticles is introduced. The core thread is drawn sequentially through reservoirs containing a cell‐laden prepolymer and a crosslinking reagent. The thickness of the hydrogel layer increases linearly with to the drawing speed and the prepolymer viscosity. CLFs are fabricated and assembled using regular textile processes including weaving, knitting, braiding, winding, and embroidering, to form cell‐laden structures. Cellular viability and metabolic activity are preserved during CLF fabrication and assembly, demonstrating the feasibility of using these processes for engineering functional 3D tissue constructs. 相似文献
90.
Mostafa Nasrollahzadeh Mohsen Jahanshahi Maryam Yaldagard Mehdi Salehi 《Bulletin of Materials Science》2018,41(3):85
A novel polymer–carbon (PTh–C) nanocomposites containing different percentages of polythiophene (10, 20 and 50% (w/w)) and carbon (Vulcan XC-72) was prepared by a facile solution dispersion method and used to support platinum nanoparticles. The effect of using different percentages of polythiophene in nanocomposites and subsequently prepared electrocatalysts was investigated. The resultant electrocatalysts were extensively characterized by physical (X-ray diffraction (XRD) and transmission electron microscopy (TEM)) and electrochemical (cyclic voltammetry (CV)) techniques. The TEM results showed that the fine Pt nanoparticles prepared by ethylene glycol (EG) method were distributed on the surface of the 50% PTh–C nanocomposites successfully. From the XRD patterns, the average size of dispersed Pt nanoparticles with the face-centered cubic (fcc) structure on 50% PTh–C, 20% PTh–C, 10% PTh–C and carbon were about 4.9, 5.2, 5.4 and 6.1 nm, respectively. The conductivity of PTh–C with different percentages of pure PTh was compared with the conductivity of the corresponding support of pure PTh. It is observed that the conductivity of 50% PTh–C nanocomposites is about 600 times higher than that of pure PTh. Finally, CV measurements of hydrogen and methanol oxidations indicated that Pt/50% PTh–C had a higher electrochemical surface area and higher catalytic activity for methanol oxidation reaction compared to other electrocatalysts. These measurements showed that the Pt/50% PTh–C electrocatalyst by the value of 3.85 had higher \(I_{\mathrm{f}}/I_{\mathrm{b}}\) ratio with respect to Pt/10% PTh–C and Pt/20% PTh–C by the values of 2.66 and 2.0, respectively. 相似文献