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排序方式: 共有840条查询结果,搜索用时 16 毫秒
91.
The dilute solution properties of nine poly(vinylpyrrolidone) fractions in methanol covering the molecular weight range 6.76 × 104 to 1.02 × 107 were studied. Constants a and Km of the Mark-Houwink-Sakurada (M.H.S.) equation were found to be 0.60 and 2.64 × 10?4 respectively using light scattering and intrinsic viscosity data and were compared with the literature values. The second virial coefficient, A2 decreases gradually as the molecular weight increases while the root-mean-square radius of gyration, 2 increases. The dependence of A2 on molecular weight is in agreement with other flexible polymers dissolved in moderate to good solvents. The unperturbed chain dimension, (r/M) was calculated using the Stockmayer-Fixman (S—F) equation and a value of 4.9 × 10?17 cm was obtained. The S—F plot slightly bends in the region of high molecular weight which is according to expectation. 相似文献
92.
Arshad Noor Siddiquee Zahid A. Khan Zulquernain Mallick 《The International Journal of Advanced Manufacturing Technology》2010,46(9-12):983-992
This paper investigates optimisation design of an in-feed centreless cylindrical grinding process performed on EN52 austenitic valve steel (DIN: X45CrSi93). The major performance characteristics selected to evaluate the process are surface roughness, out of cylindricity of the valve stem and diametral tolerance, and the corresponding centreless cylindrical grinding parameters are dressing feed, grinding feed, dwell time and cycle time. In this study, since the process is with multiple-performance characteristics, therefore, the grey relational analysis that uses grey relational grade as performance index is specially adopted to determine the optimal combination of centreless cylindrical grinding parameters. Moreover, the principal component analysis is applied to evaluate the weighting values corresponding to various performance characteristics so that their relative importance can be properly and objectively described. The results of confirmation experiments reveal that grey relational analysis coupled with principal component analysis can effectively be used to obtain the optimal combination of centreless cylindrical grinding parameters. Hence, this confirms that the proposed approach in this study can be a useful tool to improve the centreless cylindrical grinding performance of valve stem in in-feed centreless cylindrical grinding process. 相似文献
93.
Pooria Pasbakhsh Hanafi Ismail Mohd Noor Ahmad Fauzi Azhar Abu Bakar 《应用聚合物科学杂志》2009,113(6):3910-3919
The effect of partial replacement of silica or calcium carbonate (CaCO3) by halloysite nanotubes (HNTs) on the curing behavior, tensile properties, dynamic mechanical properties, and morphological characteristics of ethylene propylene diene monomer (EPDM) composites was studied. Five different compositions of EPDM/Silica/HNT and EPDM/CaCO3/HNT compounds (i.e. 100/30/0, 100/25/5, 100/15/15, 100/5/25, and 100/0/30 parts per hundred rubber (phr)) were prepared on a two‐roll mill. The results indicated that the replacement of CaCO3 by HNTs increased the tensile strength, elongation at break (Eb), and tensile modulus of composites from 0 to 30 phr of HNTs whereas for silica, the maximum tensile strength and Eb occurred at 5 phr loading of HNTs with an enhanced stress at 300% elongation (M300). The curing results show that, with replacement of silica or CaCO3 by HNTs, the cure time (t90) and cure rate (CRI) were decreased and increased, respectively. Scanning electron microscopy investigation confirmed that co‐incorporation of 5 phr of HNTs with silica would improve the dispersion of silica and enhanced the interactions between fillers and EPDM matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
94.
A.M. Al-Sabagh M.R. Noor El-Din R.E. Morsi M.Z. Elsabee 《Journal of Petroleum Science and Engineering》2009,65(3-4):139-146
Four comb-like copolymers derived from styrene-maleic anhydride copolymer were prepared and characterized by FTIR, 1H-NMR and elemental analysis. The molecular weight was determined using GPC and their intrinsic viscosity was measured. The prepared polymers were investigated as pour point depressants and flow improvers for waxy crude oil and it was found that, the maximum depression was obtained by the sample that has long branch chain (PPD4) from 27 °C to − 3 °C (ΔPP = 30 °C, at 10,000 ppm), while the minimum depression was exhibited by short branch chain, PPD1 (ΔPP = 21 °C) at the same conditions.The effect of these polymers on the rheology and flow properties of Qarun waxy crude oil was investigated. It was found that the Bingham yield value (τβ) decreased from 6.0 Pa s to 0.5 Pa s for PPD4 at 27 °C and 10,000 ppm. The dynamic viscosity also decreased from 110 mPa s to 24 mPa s for the same sample and the same conditions. 相似文献
95.
Fadzil Noor Gonawan Mohamad Zailani Abu Bakar Khairiah Abd Karim 《Chemical Engineering Communications》2019,206(5):630-646
The mass transfer of substrates through a bio-catalytic membrane layer is a key issue in determining the performance of β-galactosidase-catalyzed conversion of lactose in a hollow fiber membrane reactor (HFMR) system. An investigation on the effect of solutes mass transfer through a bio-catalytic membrane layer was carried out using the coupled mass transfer-reaction model. Product formation was reduced at a trans-membrane pressure (TMP) of higher than 0.5?bar. Meanwhile, the concentration polarization modulus of solutes rapidly increased with higher TMP and this result suggests the formation of gel layer, which reduced bio-catalysis rate at higher applied TMP. The concentration profile of solutes or substrates on the bio-catalytic membrane surface, which determines the rate of reaction was reduced due to mass transfer limitation. This investigation highlights that the formation of substrate-β-gal complex in an immobilized system is influenced by the mass transfer behavior of its substrate. 相似文献
96.
97.
Davoud Salarbashi Mohsen Tafaghodi Omid Rajabi Bibi Sedigheh Fazli Bazzaz Vahid Soheili 《Journal of Food Safety》2023,43(1):e13024
This study aimed to produce and characterize eco-friendly SSPS nanocomposites incorporated with various concentrations of TiO2 nanoparticles (NPs) (1%, 3%, and 7%). The antimicrobial activity of the nanocomposite films against five strains of pathogenic bacteria was examined. Salmonella typhi PTCC 1609 was the most sensitive species to TiO2 NPs at concentrations equal to the synthetic antibiotic. The migration of TiO2 to ethanol and acetic acid, as two food simulants increased when the initial nano-TiO2 content increased. The release profiles for TiO2 in two simulants of ethanol and acetic acid indicated a non-Fickian release, and the release kinetics were concentration-dependent. SSPS/TiO2 nanocomposites degraded easily and thus have the potential to be applied as an eco-friendly packaging system. Oral administration of doses of 1, 12.5, 25, 50, and 75 mg/kg TiO2 revealed that the dose of 50 and 75 mg/kg increased malondialdehyde (p < .001) concentration in the liver tissue. In addition, it decreased glutathione (p < .001) concentration in the liver tissue. 相似文献
98.
Muhammad Shoaib Arif Ali Raza Muhammad Rafiq Mairaj Bibi Rabia Fayyaz Mehvish Naz Umer Javed 《计算机、材料和连续体(英文)》2019,59(3):787-804
In this paper, a reliable stochastic numerical analysis for typhoid fever incorporating with protection against infection has been considered. We have compared the solutions of stochastic and deterministic typhoid fever model. It has been shown that the stochastic typhoid fever model is more realistic as compared to the deterministic typhoid fever model. The effect of threshold number T* hold in stochastic typhoid fever model. The proposed framework of the stochastic non-standard finite difference scheme (SNSFD) preserves all dynamical properties like positivity, bounded-ness and dynamical consistency defined by Mickens, R. E. The stochastic numerical simulation of the model showed that increase in protection leads to low disease prevalence in a population. 相似文献
99.
Pankul Goel Noor Zaman Khan Zahid A. Khan Abdulrahman Ahmari Namrata Gangil Mustufa Haider Abidi 《Materials and Manufacturing Processes》2019,34(2):192-200
AA7xxx and AISI304 stainless steel (SS) are employed in promising applications. Al alloy-to-SS dissimilar joining is difficult and challenging. Major challenge in the joining of these alloys is the difficulty in mixing of these materials which possess exotic and widely distant properties. AA7475-T761 is a high strength aluminum alloy which is used in key aircraft components. Maiden AA7475-T761 and AISI304 dissimilar joints were fabricated using friction stir welding. Welding was performed with tool having pin diameter of 4 mm and offset of 1.25 mm on Aluminum side. Tool rotational speed, traverse speed and shoulder diameter were varied in the range of 450–560 rpm, 50–63 mm/min, and 12–14 mm, respectively. Mechanical tests showed that joint formed with 14 mm diameter, 560 rpm and 50 mm/min gave the best joint efficiency of 71% of Al-alloy at 7.31% elongation. The materials mixing issues during processing were analyzed with SEM mircrostructure and fractography. Metallography also revealed that offset is critical to the success of joint as it controlled effective mixing of SS and Al in 15 and 85 vol.%, respectively. SS fragments from thermo-mechanically affected zone of SS were found to be partially sheared forming layer of thickness equal to tool traverse/revolution ratio. 相似文献
100.