Mehdi Mohammadpoor  Farshid Torabi 《加拿大化工杂志》2015,93(11):1929-1940

  相似文献   

    

Mehdi Moghri  Hamid Garmabi  Parvin Kiany  Seyed Ismail Seyed Shahabadi 《乙烯基与添加剂工艺杂志》2016,22(3):259-266

The effects of several factors (i.e., nanoclay content (NC), melt temperature, screw speed, and feeding rate), on morphology, rheology, thermodynamics, and thermal stability of PA6/NC samples produced in a co‐rotating twin‐screw extruder were studied. We discuss how changes in the level of these factors can vary diffusion or imposed shear, how these variations in diffusion and/or shear can affect NC dispersion, and how the changes in the state of NC dispersion can influence several properties of the samples. Samples with low NC content, below percolation threshold, showed exfoliated/intercalated structure with negligible sensitivity to changes in the level of the factors; whereas, samples with high NC content, above percolation threshold, showed intercalated with sporadic flocculated structures and noticeable sensitivity to the changes in the level of the factors. Moreover, NC dispersion was found to be mostly diffusion‐controlled: changes that resulted in higher diffusion or residence time (i.e., high melt temperature or low screw speed) also eventuated in better NC dispersion. What is more, percolation threshold was seen to move to lower NC contents as diffusion rate was increased. Moreover, as NC content increased, opposite thermal stability behaviors were observed at above and below the percolation threshold. J. VINYL ADDIT. TECHNOL., 22:259–266, 2016. © 2014 Society of Plastics Engineers  相似文献   

    

Meisam Torab‐Mostaedi  Ahad Ghaemi  Mehdi Asadollahzadeh 《加拿大化工杂志》2012,90(6):1570-1578

A study of the mass transfer performance for a pulsed disc and doughnut extraction column has been presented for a range of operating conditions. The mass transfer performance has been investigated for both directions of mass transfer. This study has examined the mass transfer coefficients which has incorporated the effects of back‐mixing in the continuous phase. The effect of operating variables including pulsation intensity and dispersed and continuous phase velocities on volumetric overall mass transfer coefficient has been investigated. The experiments showed that mixer‐settler, transition and emulsion regimes exist in the column depending on the pulse characteristics. In the present work, effective diffusivity is substituted for molecular diffusivity in the Gröber equation for estimation of overall mass transfer coefficients. The enhancement factor is determined experimentally and there from a single empirical correlation is derived for prediction of enhancement factor in terms of Reynolds number, holdup and Eötvös number for all operating regimes and each mass transfer direction. The experimental results are in very good agreement with the values calculated by the proposed equation. © 2011 Canadian Society for Chemical Engineering  相似文献   

    

Maryam Jafari  Sayed Amir Hossein Goli  Mehdi Rahimmalek 《European Journal of Lipid Science and Technology》2012,114(2):161-167

Four Iranian pumpkin seed cultivars were evaluated for their chemical composition and physicochemical characteristics of the extracted oils. Moisture content of seeds was quite low and ranged from 4.7 to 5.4%. The samples showed high level of protein (28.8–35.5%) and oil content (36.9–47.8%) in which the highest amount belonged to Postekaghazi cultivar. In regard to oil properties, due to the high level of oleic acid (52.7%) followed by linoleic acid (28.1%), Khoreshti cultivar was much different from other samples (in which linoleic acid is predominant: 46.5–56.1%). Moreover, relatively high content of phenolic compounds led to high‐oxidative stability index (OSI) of 16.63 h for Khoreshti oil compared to other samples (6.99–10.54 h). Furthermore, cluster analysis confirmed the data obtained in this study. The results showed that pumpkin seed oils were nutritionally valuable and refined oil might be suitable to use as salad or cooking oil.  相似文献   

    

Pierre Raphael Bertrand  Mehdi Fhima  Arnaud Guillin 《Sequential Analysis》2013,32(2):172-207

Abstract

This article deals with off-line detection of change points, for time series of independent observations, when the number of change points is unknown. We propose a sequential analysis method with linear time and memory complexity. Our method is based, on a filtered derivative method that detects the right change points as well as false ones. We improve the filtered derivative method by adding a second step in which we compute the p-values associated to every single potential change point. Then, we eliminate false alarms; that is, the change points that have p-values smaller than a given critical level. Next, we apply our method and penalized least squares criterion procedure to detect change points on simulated data sets and then we compare them. Eventually, we apply the filtered derivative with p-value method to the segmentation of heartbeat time series, and the detection of change points in the average daily volume of financial time series.  相似文献   

    

Reza Solgi  Rasoul Vosough  Mehdi Rafizadeh 《Polymer-Plastics Technology and Engineering》2013,52(2):243-249

In this research a generalization of Takagi-Sugeno fuzzy controllers is presented. In this generalization all or some of the inputs of the fuzzy controllers are fuzzy numbers. Also, it is proved that this generalization is well defined, which means that if the inputs of a generalized Takagi-Sugeno fuzzy controller are singleton fuzzy sets, then the generalized Takagi-Sugeno fuzzy controller will be reduced to a Takagi-Sugeno fuzzy controller. This controller was applied to temperature control of a methyl methacrylate (MMA) batch polymerization reactor, which uses jacket temperature error in addition to reactor temperature error. But the desired jacket temperature is affected by noise and disturbance. Therefore, there is uncertainty in the desired value of this variable. Fuzzy numbers are applied to model this uncertainty and a fuzzy trajectory was achieved for jacket desired temperature. After that an adaptation mechanism was designed. Experimental results present the fine performance of this controller in temperature control of solution polymerization of methyl methacrylate.  相似文献   

    

Seyed Abdolkarim Hosseini Ravandi  Mehdi Sadrjahani 《应用聚合物科学杂志》2012,124(5):3529-3537

A simple and nonconventional electrospinning technique was employed for producing aligned polyacrylonitrile (PAN) nanofibers. A thermal zone was placed between syringe needles and collector in the electrospinning set up to obtain aligned and heat treated nanofibers. Suitable temperatures for heat treat process of PAN nanofibers was determined using differential scanning spectroscopy (DSC) technique. The influence of treatment temperature was investigated on morphology, internal structure and mechanical properties of collected PAN nanofibers. The average fiber diameter measured from SEM images exhibited decreasing trend at higher temperatures. FTIR spectra indicated no considerable difference between chemical structure of untreated and treated PAN nanofibers. Crystallization degree of PAN nanofibers calculated from WAXD patterns showed relatively low change with treatment temperature. Tenacity values of nanofiber bundles increased with increasing temperature while the extension values had an inverse trend. However, the modulus did not show a regular manner, but treated nanofibers had more modulus than untreated ones. The stress and modulus of PAN nanofibers increased to 112.9 MPa and 7.25 GPa at 270°C, respectively. Nanofibers treated at the highest temperature had the largest amount of crystallinity and strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   

    

Seyed Roohallah Torabi  Naghmeh Fazeli  Mehdi Ghafelehbashi Zarand 《应用聚合物科学杂志》2012,123(2):1267-1272

In this research work, effect of dimethyl formamide (DMF) as an external electron donor in gas phase ethylene/1‐butene copolymerization process in the presence of Ziegler–Natta catalyst has been investigated. Different experiments were performed using TiCl₄/MgCl₂ as catalyst, triethyl aluminum as cocatalyst and in the presence of various amounts of DMF as an external electron donor. Then, effect of DMF on various parameters such as catalyst activity, molecular weight, and short chain branching content of the samples has been studied. The results showed that the more the ratio of DMF/Ti, the lower the catalyst activity. Moreover, the curves relating molecular weight and short chain branching content of the samples to the ratio of DMF/Ti passed through an extremum point at about DMF/Ti = 0.25. A justification for the occurrence of the extremum point has been proposed in this research work, and some analysis methods are adopted to confirm the suggested justification. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 1267–1272, 2012  相似文献   

    

Hamed Bagheri  Yousef Jahani  Mehdi Nekoomanesh Haghighi  Shokoofeh Hakim  Zhi Qiang Fan 《应用聚合物科学杂志》2011,120(6):3635-3641

The rheological behavior, morphology, and mechanical properties of in‐reactor alloy of polypropylene (PP)/ethylene propylene rubber (EPR) synthesized by multi‐stage sequential polymerization process are studied in this article. The relationship between polymerization parameters, morphology, and rheological properties are evaluated by scanning electron microscopy (SEM) and small amplitude oscillation rheometry in the linear viscoelastic region. The electron microscopy of samples is showed that by increasing switching frequency in polymerization time, the size of EPR particles decrease. By increasing switching frequency, the curves of complex viscosity against angular frequency of samples are shifted to higher values at low range of shear rates with no significant change at higher frequencies in Power‐law region. The modified Cole‐Cole plots revealed the enhanced melt elasticity by increasing switching frequency up to 230°C. The plot of phase angle versus absolute value of complex modulus G* is used for the evaluation of matrix‐droplets interaction at various temperatures. It is observed two different behaviors before and after 230°C which is the evidence of the change in relaxation mechanism of the blend components because of coarsening the rubber particles in the phase separation process. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011  相似文献   

    

Mohammad H. Keshavarz  Mohammad Ghorbanifaraz  Hadi Rahimi  Mehdi Rahmani 《Propellants, Explosives, Pyrotechnics》2011,36(5):424-429

A new method has been introduced to predict the power of important classes of energetic compounds including nitroaromatics, acyclic and cyclic nitramines, nitrate esters and nitroaliphatics. In this method, the predicted specific impulse and the corrected heat of detonation on the basis of H₂O‐CO₂ arbitrary decomposition, have been used to calculate the power of an explosive with the molecular formula C_aH_bN_cO_d as determined by the Trauzl test. The predicted results show good agreement with respect to the measured values for both pure and mixture of explosives. The calculated volume expansions of pure energetic compounds have a root mean square (rms) deviation of 33 cm³ from 73 measured values (corresponding to 58 molecules). For 9 explosive mixtures, the predicted volume expansions have an rms deviation of 39 cm³ from the experimental results.  相似文献