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71.
Nae-Lih Wu Li-Fu Wu Irene A. Rusakova Alejandro Hamed Alexader P. Litvinchuk 《Journal of the American Ceramic Society》1999,82(1):67-73
Upon consecutive heat treatments at increasing temperatures, the microstructure of solution–sol–gel-derived stannic oxide (SnO2 ) xerogel evolves in three stages: (I) below 300°C, characterized by extensive dehydroxylation and gel shrinkage with little grain growth and surface loss; (II) between 300° and 500°C, by extensive crystallization, leading to dramatic surface loss (by 70%); and (III) above 500°C, by grain growth. Concurrently, the UV-absorption edge shows red shifts during stages I and II and blue shifts during stage III, resulting in distinct color variations. The edge displacement bears a close correlation with a Raman "defect band" at ∼305–328 cm−1 . 相似文献
72.
The main objective of this work was reducing the heat loss of styrene butadiene rubber by partial substitution of carbon black with natural zeolite as a filler. Reducing the usage of carbon black in the rubber industry is a good strategy to decrease fossil fuel usage and global warming. There are different mineral fillers like silica and clay to be used instead of carbon black. Effect of application of natural zeolite on reducing the heat loss of rubber compound based on SBR was investigated by melt mixing of natural zeolite in rubber matrix in an internal mixer. Natural zeolite was selected as 5, 10, 15, and 20 phr. Carbon black was partially substituted with zeolite and the effect of natural zeolite content and structure on different aspects of the compound including heat buildup, hardness, elongation, and modulus were evaluated. It was shown that although cross-link density and mechanical properties of the compounds decreased a little, but a significant improvement was observed in the fatigue resistance of the compounds beside a favorable decrease in the heat buildup and abrasion loss with an increase in the natural zeolite loading. The rate of improvement in properties was slowed down at zeolite contents higher than 5 phr. 相似文献
73.
Mohammad Reza Ehsani Hamed Bateni Ghazal Razi Parchikolaei 《Korean Journal of Chemical Engineering》2012,29(7):855-861
The effect of some operating conditions such as temperature, gas hourly space velocity (GHSV), CH4/O2 ratio and diluents gas (mol% N2) on ethylene production by oxidative coupling of methane (OCM) in a fixed bed reactor at atmospheric pressure was studied over Mn/Na2WO4/SiO2 catalyst. Based on the properties of neural networks, an artificial neural network was used for model developing from experimental data. To prevent network complexity and effective data input to the network, principal component analysis method was used and the number of output parameters was reduced from 4 to 2. A feed-forward back-propagation network was used for simulating the relations between process operating conditions and those aspects of catalytic performance including conversion of methane, C2 products selectivity, C2 yielding and C2H4/C2H6 ratio. Levenberg-Marquardt method is presented to train the network. For the first output, an optimum network with 4-9-1 topology and for the second output, an optimum network with 4-6-1 topology was prepared. After simulating the process as well as using ANNs, the operating conditions were optimized and a genetic algorithm based on maximum yield of C2 was used. The average error in comparing the experimental and simulated values for methane conversion, C2 products selectivity, yield of C2 and C2H4/C2H6 ratio, was estimated as 2.73%, 10.66%, 5.48% and 10.28%, respectively. 相似文献
74.
In many developing countries, the groundwater monitoring network is randomly designed, and consequently needs to be revised and optimised to reduce operation time and cost, remove redundant piezometric data, and strengthen sparseness data zone with supplementary observation well. The geostatistical approach used in this work is based on the universal kriging variance combined with cross‐validation test. Hence, a rational interpolation of water table elevations was performed to evaluate the accuracy of data employed in the piezometric head modelling. In this study, the groundwater monitoring network of the Sfax superficial aquifer in the south east of Tunisia was optimised. The elimination of five observation wells induces the invariability in the variance of estimate due to their less contribution in interpretations of the groundwater level behaviour. However, 38 wells were added at areas of high variance of the kriging in order to ameliorate the spatial coverage of the monitoring network. 相似文献
75.
Hamed Saffari Hasanali Mosalman Yazdi 《Journal of Constructional Steel Research》2010,66(8-9):1107-1111
Dimensionless design-oriented charts are introduced for customising a new and efficient method of computing the out-of-plane critical buckling load of Y-braced steel frame systems. These charts are derived from extensive parametric studies on the basis of an “exact solution”, within the limits of the Eulerian theory, stability analysis, using a wide array of geometric characteristics of practical interest. Demonstrated with numerical examples, these calculations are shown to yield, in a very efficient way, accurate critical load values of these systems. The charts can be used for practical design of Y-brace elements. 相似文献
76.
Simin Hedayatnia Hamed Mirhosseini Sahar Tamnak Fatemeh Golpira 《Food and Bioprocess Technology》2016,9(4):686-698
This study was conducted to investigate the effects of inulin (0, 2.5, 5, and 7.5 %), maltodextrin (0, 15, 20, and 25 %), and different drying processes (one- and two-stage drying) on the morphology and physicochemical properties of regular and instant reduced-fat creamers. The present study showed that the drum-dried creamer containing 0 % maltodextrin and 0 % inulin was fully sticky powder with dark brown color. It was found that the maximum increase in maltodextrin (from 0 to 25 %) and inulin (from 0 to 7.5 %) resulted in the creamer with the highest glass transition temperature and the lowest stickiness among all formulated creamers. The application of two-stage drying involving fluidized bed drying resulted in further improvement of the glass transition temperature and stickiness of the reduced fat instant creamer. The instant creamers obtained from two-stage drying had considerably higher glass transition temperature and lower bulk density than the regular creamers from one-stage drying. Such improvement could be due to the reduction of bulk density induced by fluidized bed drying. This might be because of higher porosity of the creamer particles after agglomeration. The current study revealed that the addition of high amounts of inulin and maltodextrin also played a significant role in the reduction of bulk density and further improvement of glass transition temperature (Tg) and solubility of the reduced fat creamer. The instant reduced fat creamer containing 25 % maltodextrin and 7.5 % inulin had the most desirable characteristics among all formulated creamers. 相似文献
77.
Theoretical investigation on the performance of lithium chloride (LiCl) absorption cooling system using an artificial neural network (ANN) model is presented. Tabulated data from the literature are used to construct the ANN model. Solar collector desiccant/regenerator is applied to re-concentrate the working solution. Using the proposed model, the effect of system design parameters; namely regenerator length, and air flow rate on the performance of the system is demonstrated. The variation of the thermo-physical parameters along the regenerator length is highlighted. 相似文献
78.
Ali Keramat Ali Kargari Morteza Sohrabi† Hamed Mirshekar Hamidreza Sanaeepur 《化学工程与技术》2017,40(3):529-536
The kinetics of sucrose hydrolysis by invertase was studied in order to find a comprehensive model for the reaction pathway and mechanism. First, three common models of Michaelis‐Menten (MM), substrate inhibition (S2), and substrate clusters' inhibition (S3(I)) were investigated. The third model was found to better predict the initial sucrose concentration. Then, the S3(I) model was modified to cover the remaining pathway (S3(II)). Finally, a new comprehensive model (S3(III)) was evaluated, which in addition to what is considered in the two previously mentioned models (S3(I) and S3(II)) also involved the initial time lag. The model predictions showed an excellent agreement with the experimental data. The mean absolute error for the MM model is significantly reduced for the S3(III) model. 相似文献
79.
Natalia Shlonimskaya Hamed M. Kayello Donald P. Visco 《Journal of the American Ceramic Society》2014,97(2):378-385
In this study, the use of computer‐aided molecular design (CAMD) is validated as a tool for enabling the discovery of new shrinkage‐reducing compounds for possible use in portland cement composites and is framed as one of many multiscale modeling tools in a broad hierarchy of possibilities. Twelve additives were tested for their ability to inhibit shrinkage in Type I ordinary portland cement under both autogenous and drying conditions. The 12 additives included two commercial shrinkage‐reducing admixtures (SRAs), two active ingredients of a commercial admixture [one of which was used to establish the quantitative structure–property relationships (QSPR)], two additional classified as potential SRA compounds based on the patent literature, four newly identified compounds predicted by using CAMD and an inverse quantitative structure–property relationship (I‐QSPR), and two other compounds use to establish the QSPR relationship. The newly identified I‐QSPR compounds were targeted for their ability to reduce the surface tension of water, a primary consideration for shrinkage‐reducing activity. Results for both drying shrinkage and autogenous shrinkage indicate that the designed compounds perform similar to commercial admixtures, yet have different chemical functionalities. Hydration data and set measurements were also considered since selection of new SRAs is a multiparameter problem with many constraints. Thus, these newly identified shrinkage‐reducing compounds can potentially provide additional options for use in portland cement concrete applications. 相似文献
80.
Hamed Shahmir Mahmoud Nili-Ahmadabadi Fariba Naghdi Mohammad Habibi-Parsa Ismaeil Haririan 《Journal of Materials Engineering and Performance》2014,23(4):1386-1391
The aim of this study is to investigate the effect of thermomechanical treatment on the superelastic behavior of a Ti-50.5 at.%Ni wire in terms of loading/unloading plateau, mechanical hysteresis, and permanent set to optimize these parameters for orthodontic applications. A new three-point bending fixture, oral cavity configuration three-point bending (OCTPB) test, was utilized to determine the superelastic property in clinical condition, and therefore, the tests were carried out at 37 °C. The results indicate that the thermomechanical treatment is crucial for thermal transformation and mechanically induced transformation characteristics of the wire. Annealing of thermomechanically treated specimens at 300 and 400 °C for 1/2 and 1 h leads to good superelasticity for orthodontic applications. However, the best superelasticity at body temperature is obtained after annealing at 300 °C for 1/2 h with regard to low and constant unloading force and minimum permanent set. 相似文献