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排序方式: 共有475条查询结果,搜索用时 11 毫秒
1.
Interactions of hexamethylenetetramine ligand in atom transfer radical polymerization initiated by activator generated by electron transfer were studied. Polymerization of methyl methacrylate was done using two-step experimental procedure in 2 L emulsion batch reactor at 50, 60, and 80°C. The selection of reactant ratios was quite challenging for a reactor of this size. Replicate runs were conducted for data reproducibility purpose. Gravimetry method and gel permeation chromatography were used to determine monomer conversion, Mn, and PDI of polymer samples. PMMA produced was also characterized by means of dynamic light scattering, Fourier-transform infrared spectroscopy and nuclear Magnetic Resonance spectroscopy. Results showed high monomer conversion up to 93% and Mn ranging 243–274 kg/mol with PDI from 1.45 to 1.60. Besides, combining HMTA with sodium dodecyl sulfate, an anionic surfactant, a well-controlled polymer with a lower Mn of 201 kg/mol and PDI of 1.56 was obtained in 3 hr reaction time. 相似文献
2.
3.
Amr Fouda Mohamed A. Awad Ahmed M. Eid Ebrahim Saied Mohammed G. Barghoth Mohammed F. Hamza Mohamed F. Awad Salah Abdelbary Saad El-Din Hassan 《International journal of molecular sciences》2021,22(10)
The discovery of eco-friendly, rapid, and cost-effective compounds to control diseases caused by microbes and insects are the main challenges. Herein, the magnesium oxide nanoparticles (MgO-NPs) are successfully fabricated by harnessing the metabolites secreted by Penicillium chrysogenum. The fabricated MgO-NPs were characterized using UV-Vis, XRD, TEM, DLS, EDX, FT-IR, and XPS analyses. Data showed the successful formation of crystallographic, spherical, well-dispersed MgO-NPs with sizes of 7–40 nm at a maximum wavelength of 250 nm. The EDX analysis confirms the presence of Mg and O ions as the main components with weight percentages of 13.62% and 7.76%, respectively. The activity of MgO-NPs as an antimicrobial agent was investigated against pathogens Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans, and exhibited zone of inhibitions of 12.0 ± 0.0, 12.7 ± 0.9, 23.3 ± 0.8, 17.7 ± 1.6, and 14.7 ± 0.6 mm respectively, at 200 µg mL−1. The activity is decreased by decreasing the MgO-NPs concentration. The biogenic MgO-NPs exhibit high efficacy against different larvae instar and pupa of Anopheles stephensi, with LC50 values of 12.5–15.5 ppm for I–IV larvae instar and 16.5 ppm for the pupa. Additionally, 5 mg/cm2 of MgO-NPs showed the highest protection percentages against adults of Anopheles stephensi, with values of 100% for 150 min and 67.6% ± 1.4% for 210 min. 相似文献
4.
Takashi Kashiwagi Alexander B. Morgan Joseph M. Antonucci Mark R. VanLandingham Richard H. Harris Walid H. Awad John R. Shields 《应用聚合物科学杂志》2003,89(8):2072-2078
PMMA, poly(metheylmethacrylate), nanocomposites were made by in situ radical polymerization of MMA, methylmethacrylate, with colloidal silica (ca. 12 nm) to study the effects of nanoscale silica particles on the physical properties and flammability properties of PMMA. Transparent samples resulted and the dispersity of the particles was examined by transmission electron microscopy and atomic force microscopy. The addition of nanosilica particles (13% by mass) did not significantly change the thermal stability, but it made a small improvement in modulus, and it reduced the peak heat release rate roughly 50%. Last, the flame‐retardant mechanism provided by the addition of nanosilica particles in PMMA is discussed. Published 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2072–2078, 2003 相似文献
5.
This paper addresses the one-machine scheduling problem with earliness-tardiness penalties. We propose a new branch-and-bound
algorithm that can solve instances with up to 50 jobs and that can solve problems with even more general non-convex cost functions.
The algorithm is based on the combination of a Lagrangean relaxation of resource constraints and new dominance rules. 相似文献
6.
Belhadj S Derridj A Aigouy T Gers C Gauquelin T Mevy JP 《Microscopy research and technique》2007,70(10):837-846
A comparative analysis was undertaken to conduct a micromorphological study of Pistacia atlantica leaves by comparing different populations grown under different climatic conditions. Leaf epidermis of eight wild populations was investigated under scanning electron microscope. Micromorphological characteristics (epidermis ornament, stomata type, waxes as well as trichomes) of the adaxial and abaxial leaf surfaces were examined. The epidermis ornament varied among populations and leaf surface, the abaxial leaf surface is reticulate with a striate surface. Messaad site shows a smooth uneven surface. The adaxial leaf surface is smooth but several ornamentations can be seen. The leaflet is amphistomatic; the stomata appeared to be slightly sunken. A variety of stomatal types were recorded; actinocytic and anomocytic types are the most frequent. The indumentum consisted of glandular and nonglandular trichomes. Unicellular glandular trichomes are recorded for P. atlantica leaves in this study. Their density is higher in Oued safene site, located at the highest altitude in comparison with the other populations. The wax occurred in all the sites and its pattern varied according to the populations studied, particularly between Berriane and Messaad. The morphological variability exhibited by the eight populations of P. atlantica may be interpreted as relevant to the ecological plasticity and the physiological mechanisms involved are discussed in this report. 相似文献
7.
Bourbakis N.G. Awad M. 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》2003,33(5):766-781
This paper deals with a 3D methodology for brain tumor image-guided surgery. The methodology is based on development of a visualization process that mimics the human surgeon behavior and decision-making. In particular, it originally constructs a 3D representation of a tumor by using the segmented version of the 2D MRI images. Then it develops an optimal path for the tumor extraction based on minimizing the surgical effort and penetration area. A cost function, incorporated in this process, minimizes the damage surrounding healthy tissues taking into consideration the constraints of a new snake-like surgical tool proposed here. The tumor extraction method presented in this paper is compared with the ordinary method used on brain surgery, which is based on a straight-line based surgical tool. Illustrative examples based on real simulations present the advantages of the 3D methodology proposed here. 相似文献
8.
We report on the effect of thermal annealing on the structural and mechanical properties of amorphous SiC thin films prepared by means of a polymer-source chemical vapor deposition process. The chemical bondings of the a-SiC:H films were systematically examined by means of Fourier transform infrared spectroscopy (FTIR). The film composition was measured by X-ray photoelectron spectroscopy, while X-ray reflectivity measurements were used to account for the film density variations caused by the post-annealing treatments over the 750-1200 °C range. In addition, their mechanical properties (hardness and Young's modulus) were investigated by using the nano-indentation technique. FTIR measurements revealed that not only the intensity of a-SiC absorption band linearly increases but also its position is found to shift to a higher wave number as a result of annealing. In addition, the bond density of Si―C is found to increase from (101.6-224.5) × 1021 bond·cm− 3 accompanied by a decrease of Si―H bond density from (2.58-0.46)× 1021 bond·cm− 3 as a result of increasing the annealing temperature (Ta) from 750 to 1200 °C. Annealing-induced film densification is confirmed, as the a-SiC film density is found to increase from 2.36 to ∼ 2.75 g/cm− 3 when Ta is raised from 750 to 1200 °C. In addition, as Ta is increased from 750 to 1200 °C, both hardness and Young's modulus are found to increase from 15.5 to 17.6 GPa and 155 to 178 GPa, respectively. Our results confirm the previously established linear correlation between the mechanical properties of the a-SiC films and their bond densities. 相似文献
9.
R. Awad M. Roumié A. I. Abou-Aly S. A. Mahmoud M. M. Barakat 《Journal of Superconductivity and Novel Magnetism》2012,25(2):273-291
Superconducting samples of type Bi1.8Pb0.4Sr2Ca2.1Cu3−x
Ru
x
O10+δ
, (Bi, Pb)-2223, with 0.0≤x≤0.4 and type Tl0.5Pb0.5Sr1.6Ba0.4CaCu2−x
Ru
x
O7−δ
, (Tl, Pb)/Sr-1212, with 0.0≤x≤0.525 were synthesized using the standard solid-state reaction technique. The lattice parameters and the surface morphology
for these samples were determined using X-ray powder diffraction (XRD) and scanning electron microscope (SEM) measurements,
respectively. All element-contents of the samples prepared were estimated from the electron dispersive X-ray (EDX) technique,
and their results were compared with those obtained from particle-induced X-ray emission (PIXE). In addition, the oxygen-content
was determined using elastic Rutherford backscattering spectroscopy (RBS) technique at 3 MeV proton beam. The superconducting
transition temperature T
c and the hole carrier concentration P were determined from the electrical resistivity measurement. The data of both T
c and P for Bi1.8Pb0.4Sr2Ca2.1Cu3−x
Ru
x
O10+δ
and Tl0.5Pb0.5Sr1.6Ba0.4CaCu2−x
Ru
x
O7−δ
phases increased up to x=0.05 and 0.075, respectively and then they decreased as x increased. The superconductivity was completely destroyed around x=0.4 and 0.525 for (Bi, Pb)-2223 and (Tl, Pb)/Sr-1212 phases, respectively. The normal-state electrical resistivity data were
analyzed using the two and three dimensional variable range hopping (2D-VRH and 3D-VRH) and the Coulomb gab (CG). 相似文献
10.
This paper introduces a new means to manipulate electronic structures and, consequently, the electrical properties of molecular devices via gradual increase of number of nitrogen atoms in the backbone of conjugated organic molecular systems. Diblock molecules were selected for this purpose. Density functional theory (DFT) was used to investigate geometrical and electronic structures in the absence and presence of external electric field. Furthermore, the tendency of the anchor sulfur atoms toward electrodes in a simulated closed circuit was estimated from the relative condensed Fukui function. The obtained results indicated that HOMO–LUMO gap decreases steadily with increasing the number of nitrogen atoms, which would be used as a means for modifying the electrical properties in a regular mode. 相似文献