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91.
Maher F. El-Zohry Mohamed A. Abd-Alla 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1992,55(3):209-215
3-(2′-Chloroethyl)-2-methyl-3,4-dihydroquinazolin-4-one was reacted with acetylacetone, ethyl acetoacetate and diethylmalonate in the presence of sodium ethoxide to afford the alkylation products IV, V and VI , Compounds IV, V and VI were reacted with hydrazine hydrate, phenylhydrazine, hydroxylamine hydrochloride, urea and thiourea to yield 3-(2′-heterocyclicethyl)-2-methyl-3,4-dihydroquinazolin-4-one derivatives VII-XV . The structures of the synthesized compounds were elucidated by elemental analyses and spectroscopic (IR and XH-NMR) analyses. The prepared compounds were tested for their antimicrobial activities in comparison with tetracycline as a reference compound. 相似文献
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94.
For environmental considerations, the substitution of the conventionally used oil-based grinding fluids has nowadays become strongly recommended. Although several alternatives have been proposed, cryogenic cooling by liquid nitrogen is the non-polluting coolant that has been given relatively more attention because of its very low temperature. In this investigation, in order to contribute to developing this promising cooling mode, its beneficial effects on the ground surface integrity of the AISI 304 stainless steel and their consequences on the fatigue lifetime are explored. Results of this investigation show that grinding under cryogenic cooling mode generates surfaces with lower roughness, less defects, higher work hardening and less tensile residual stresses than those obtained on surfaces ground under oil-based grinding fluid. These surface enhancements result into substantial improvements in the fatigue behaviour of components ground under this cooling mode. An increasing rate of almost 15% of the endurance limit at 2 × 106 cycles could be realized. SEM analyses of the fatigue fracture surfaces have shown that the fatigue cracks observed on the specimens ground under cryogenic cooling are shorter (i.e., 30-50 μm) than those generated under oil-based cooling mode (i.e., 150-200 μm). The realized improvements in the surface integrity and in the fatigue behaviour are thought to be related to the reduction of the grinding zone temperature observed under cryogenic cooling, as no significant differences between the grinding force components for both cooling modes have been observed. 相似文献
95.
Sugarcane can be very susceptible to damage by freezes. Freeze-deteriorated cane can cause problems in processing and sometimes leads to a factory shut-down. This study was undertaken during the 2000/2001 harvest season to assess the cold tolerance performance of six commercial sugarcane varieties and to establish new and more sensitive criteria to measure cold tolerance. Two varieties CP 70-321 and CP 79-318, with known cold tolerance, were planted in the study as controls. The other varieties included LHo 83-153, LCP 85-384, HoCP 85-845 and HoCP 91-555. Freezing temperatures occurred on 20 December 2000 when the min. field temperature was −4.4 °C, and again on 21 December, 30 December through 5 January 2001, 9–10 January and 20–21 January. The lowest field temperature recorded was −5.6 °C on 4 January. Freezing conditions prevailed for 8–15 h during each freeze incident. Stalks of all varieties were frozen to the ground following the initial freeze, with freeze cracks evident only after the 4 January freeze. For this study, samples were taken on the date of the first freeze, 20 December, and subsequently again at 7, 14, 22 and 30 days after the first freeze. Criteria used to measure overall stalk cold-tolerance included changes in pH, Brix, dextran (ASI-II method), sucrose, glucose, and fructose concentrations. Mannitol, ethanol and the oligosaccharides, palatinose, leucrose, iso-maltotriose and 1-kestose, were simultaneuously measured using IC-IPAD. Marked differences were observed in most criteria for all varieties, particularly 22 and 30 days after the first freeze. Mannitol was strongly correlated (r2=0.84) with dextran, confirming its use as an indicator for cane dextran deterioration. In comparison, ethanol was only weakly correlated (r2=0.55) with dextran and did not always predict cane dextran deterioration. Iso maltotriose was the most sensitive oligosaccharide indicator of freeze deterioration, although both leucrose and palatinose could be used to confirm whether severe dextran formation (>1500 ppm/Brix) has occurred in cane. Isomaltotriose was strongly correlated (r2=0.89) with dextran and pH (r2=−0.83); pH was also a strong indicator of both dextran (r2=−0.85) and mannitol (r2=−0.92) formation. Four of the varieties, CP 79-318, LCP 85-384, HoCP 85-845 and HoCP 91-555, were shown to be susceptible to other sources of microbial and enzymic deterioration as well as dextran deterioration from Leuconostoc bacteria, especially 30 days after the first freeze. This was indicated by increased glucose/fructose ratios, ethanol formation, changes in 1-kestose concentration, and further sucrose losses. 相似文献
96.
Mohamed Jaziri Tasnim Kossentini Kallel Souad Mbarek Boubaker Elleuch 《Polymer International》2005,54(10):1384-1391
The influence of processing conditions and interfacial modification on the morphology evolution and the composition range within which fully co‐continuous high density polyethylene/polystyrene blend structures can exist during blending in a single screw extruder was studied. Blends ranging from pure A to pure B component, with and without compatibilizer, were prepared under two different shear rates. It was found that high shear rates displaced the breakdown–coalescence balance of the dispersed nodules to the side of coalescence, narrowing the percolation domain and the critical composition for full co‐continuity decreased with increasing shear rates. The addition of a tri‐block compatibilizer induced the percolation threshold of the polystyrene phase to begin at lower percentages of polyethylene but the phase inversion point did not change. The experimental results are discussed in the light of various theoretical models. Copyright © 2005 Society of Chemical Industry 相似文献
97.
Specimen preparation and image processing and analysis techniques for automated quantification of concrete microcracks and voids 总被引:4,自引:0,他引:4
Parviz Soroushian Mohamed Elzafraney Ali Nossoni 《Cement and Concrete Research》2003,33(12):1949-1962
Specimen preparation and image processing/analysis techniques were developed for use in automated quantitative microstructural investigation of concrete, focusing on concrete microcracks and voids. Different specimen preparation techniques were developed for use in fluorescent and scanning electron microscopy (SEM) of concrete; then techniques produce a sharp contrast between microcracks/voids and the body of concrete. The image processing/analysis techniques developed specifically for use with concrete address the following usages: automatic threshold; development of intersecting microcracks/voids and connected voids; distinction of microcracks form voids based on geometric attributes; and noise filtration. 相似文献
98.
The water activities of the mixed aqueous electrolyte NaCl–BaCl2(aq) are measured at total molalities from 0.25 mol kg−1 to about saturation for different ionic strength fractions (y) of NaCl with y=0.33,0.50,0.67. The results allow the deduction of osmotic coefficients. The experimental results are compared with the predictions of the Zdanovskii, Stokes, and Robinson (ZSR), Kusik and Meissner (KM), Robinson and Stokes (RS), Lietzke and Stoughton (LSII), Reilly, Wood, and Robinson (RWR), and Pitzer models. From these measurements, the Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture. The excess Gibbs energy is also determined. 相似文献
99.
Nadia Ben Atti Gema M. Diaz–Toca Henri Lombardi 《Applicable Algebra in Engineering, Communication and Computing》2006,17(1):75-82
We propose a slight modification of the Berlekamp-Massey Algorithm for obtaining the minimal polynomial of a given linearly
recurrent sequence. Such a modification enables to explain it in a simpler way and to adapt it to lazy evaluation.
partially supported by the Galois Theory and Explicit Methods in Arithmetic Project HPRN-CT-2000-00114
partially supported by the European Union funded project RAAG CT-2001-00271 相似文献
100.
The polymerization of α‐methylstyrene (AMS) catalyzed by Maghnite‐H+ (Mag‐H) was investigated. Mag‐H is a montmorillonite sheet silicate clay, exchanged with protons. It was found that the cationic polymerization of AMS is initiated by Mag‐H at ambient temperature in bulk and in solution. The effect of the amount of Mag‐H, the temperature, and the solvent was studied. The polymerization rate increased with increase in the temperature and the proportion of catalyst, and it was larger in nonpolar solvents. These results indicated the cationic nature of the polymerization. It may be suggested that the polymerization is initiated by proton addition to monomer from Mag‐H. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献