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排序方式: 共有128条查询结果,搜索用时 15 毫秒
51.
Angel Manzur 《应用聚合物科学杂志》2008,108(3):1574-1581
The double yield phenomenon was studied using numerous specimens uniaxially deformed up to different elongations of linear low‐density polyethylene samples. Extruded samples prepared under different conditions were deformed at 1, 10, and 50 mm/min. The crystallinity under stressed state was calculated using the wide‐angle X‐ray scattering technique. The crystallinity degrees of the samples without deformation were less than 55%. This parameter, as a function of the elongation, presented a multistep behavior. An increment before the first yield point and a decrement after this point; then, at higher elongation values around the second yield point, another decrement and an abrupt increment. The behavior was more notorious at intermediate and lower strain rates. The results around the second yield point were interpreted in terms of melting of the less perfect crystallites followed by a recrystallization process. These experimental findings show that the partial melting–recrystallization process is one of the main mechanisms of the double yield phenomenon. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
52.
Sriya Das Fahmida Irin H.S. Tanvir Ahmed Abel B. Cortinas Ahmed S. Wajid Dorsa Parviz Alan F. Jankowski Masaru Kato Micah J. Green 《Polymer》2012,53(12):2485-2494
In this paper, we demonstrate a facile technique to disperse pristine few-layer graphene (FLG) in water utilizing a triphenylene based stabilizer (C10) that non-covalently functionalizes the surface without micelle formation. The yield of FLG in the final dispersion (0.2 mg FLG/mg C10) is much higher than comparable surfactants and polymers stabilizers. This dispersion is reversible in response to pH changes unlike conventional stabilizers. The C10-stabilized FLG dispersion is also stable against heat and lyophilization. This non-covalent functionalization does not disrupt the pristine structure of the graphene sheets; instead, these coatings allow for stable, aggregation-resistant FLG dispersion, as characterized through TEM. To demonstrate the utility of such dispersions, we prepared pristine FLG-loaded poly (vinyl alcohol) (PVA) composites by a simple solution casting process. This is the first example of PVA composites based on pristine graphene. These composites have enhanced electrical properties at relatively low filler fraction (0.26 vol% FLG). Moreover, these composites exhibit improved mechanical properties established by tensile and hardness tests results; these data suggest anisotropic reinforcement caused by graphene alignment. 相似文献
53.
ABSTRACT: The surface tension of ethanol and n-decane based nanofluid fuels containing suspended aluminum (Al), aluminum oxide (Al2O3), and boron (B) nanoparticles as well as dispersible multi-wall carbon nanotubes (MWCNTs) were measured using the pendant drop method by solving the Young-Laplace equation. The effects of nanoparticle concentration, size and the presence of a dispersing agent (surfactant) on surface tension were determined. The results show that surface tension increases both with particle concentration (above a critical concentration) and particle size for all cases. This is because the Van der Waals force between particles at the liquid/gas interface increases surface free energy and thus increases surface tension. At low particle concentrations, however, addition of particles has little influence on surface tension because of the large distance between particles. An exception is when a surfactant was used or when (MWCNTs) was involved. For such cases, the surface tension decreases compared to the pure base fluid. The hypothesis is the polymer groups attached to (MWCNTs) and the surfactant layer between a particle and the surround fluid increases the electrostatic force between particles and thus reduce surface energy and surface tension. 相似文献
54.
D Nauffal Manzur R Menéndez Villanueva MJ Cremades Romero 《Canadian Metallurgical Quarterly》1997,33(5):220-224
Our objective was to investigate possible factors implicated in either early death from or scintigraphic resolution of pulmonary embolism. To that end we conducted a retrospective study of 116 patients with either a high likelihood of pulmonary thromboembolism (PTE) diagnosed by scintiscan or with a fair probability of PTE by scintiscan accompanied by a positive phlebograph. The images were taken upon admission, at 7 days, 10 days and 6 months. The factors analyzed were age, sex, trauma, immobility, surgery, obesity, hemiplegia, venous insufficiency, cardiopulmonary disease, neoplasia, chest X-ray and ECG alterations, D(A-a)O2 and size of perfusion defects upon admission and 7 to 10 days later. We performed single-variable analyses and multiple logical regression analyses using perfusion defect at 6 months as the dependent variable. The early mortality rate (13%) was higher in patients with neoplasms, a larger alveolar-arterial index and greater perfusion defects upon admission. Scintiscans became normal in 28%. Multivariate analysis to predict total or partial resolution at 6 months showed that size of perfusion defects at 7 to 10 days was the best predictive factor. A cutoff point was calculated by analyzing the ROC for this factor. Thus, when the defect at 7 to 10 days was equal to or greater than 1 segment, the probability of residual defects remaining after 6 months was twice as great (sensitivity 83%, specificity 57%). In conclusion, early death was more likely in PTE patients with neoplasms, larger defects upon admission and greater alveolar-arterial difference. Scintigrams showed resolution 6 months after admission in 28%. The size of perfusion defects 7 to 10 days after admission was the factor that best predicted total of partial resolution at 6 months. 相似文献
55.
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We develop hypotheses for the implications of regional economic integration on foreign direct investment (FDI) from insider
and outsider countries contingent on member nations’ country-specific characteristics. 相似文献
56.
Ejaz Ahmad Tanvir Manzoor Kanwar Liaqat Ali J. I. Akhter 《Journal of Materials Engineering and Performance》2000,9(3):306-310
A steel containing 0.32 wt.% C, 0.88 wt.% Mn, 0.99 wt.% Si, 0.9 wt.% Ni, and 0.9 wt.% Cr was intercritically annealed at different
temperatures from 775 to 870 °C and quenched in oil to produce dual-phase steel microstructure. Tensile testing of these samples
gave a series of strengths and ductilities. The tensile strength increased with the increased annealing temperatures and the
martensite percentage increased with a reduction in ductility. Microvoids were formed near the fracture surfaces. The morphology
of the microvoids changed with the martensite percentage from decohesion of the martensite particles to the intergranular
and transgranular cracks, which defined the ultimate fracture mode of the specimens. The change in the morphology of microvoids
may be due to a high percentage of carbon in the steel, which produced stresses in the matrix (ferrite) during phase transformation. 相似文献
57.
58.
Ahmed S. Wajid H. S. Tanvir Ahmed Sriya Das Fahmida Irin Alan F. Jankowski Micah J. Green 《大分子材料与工程》2013,298(3):339-347
High‐strength conductive pristine graphene/epoxy composites are prepared by two simple processing methods – freeze dry/mixing and solution processing. PVP‐stabilized graphene is aggregation‐resistant and allows for excellent dispersion in both the resin and final composite, as confirmed by optical microscopy and SEM images. The superior dispersion quality results in excellent nanofiller/matrix load transfer, with a 38% increase in strength and a 37% improvement in modulus for 0.46 vol% graphene loading. The composites have a very low electrical percolation threshold of 0.088 vol%. Despite the effectiveness of both methods, the freeze‐drying method is more promising and versatile enough to be used for graphene dispersion in a wide range of other composite precursors.
59.
Chowdhury Mostafa Zaman Hossan Md. Tanvir Hasan Moh. Khalid Jang Yeong Min 《Wireless Personal Communications》2019,107(3):1401-1430
Wireless Personal Communications - Communications based solely on radio frequency (RF) networks cannot provide adequate quality of service for the rapidly growing demands of wireless connectivity.... 相似文献
60.
Shahid Abdul Afzal Muhammad Tanvir Abdar Moloud Basiri Mohammad Ehsan Zhou Xujuan Yen Neil Y. Chang Jia-Wei 《The Journal of supercomputing》2020,76(3):1695-1733
The Journal of Supercomputing - More than 50 million journal papers will have been published by the end of 2019 with 2 million more journal papers published every year. The number of conference... 相似文献
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