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871.
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874.
A photocrosslinkable polycyclic chalcone‐based acrylamide has been synthesized by Claisen–Schmidt condensation reaction and then polymerized via free radical polymerization technique using azobisisobutyronitrile (AIBN) as an initiator. The resulting polymers have been characterized by FT‐IR, 1H‐NMR and 13C‐NMR analytic techniques. The molecular weights of the polymers were determined by gel permeation chromatography. The thermal properties of synthesized polymers were characterized by TGA analysis, and the obtained results show good thermal and thermo‐oxidative stability which is required for a negative photo resist. The high flame‐retardant properties are calculated from limiting oxygen index (LOI) values and are found to be 36.9 and 32.0 for naphthyl and anthryl chalcone‐based polymers, respectively. The experimentally determined LOI values of polymers (PMNPA and PAPA) are 34.3 and 30.2, respectively, and the values are closer to theoretically found LOI values. However, the cone calorimetry of flame‐retardant PMNPA only showed a slight decrease in peak of heat release rate (PHRR) and total heat release (THR) compared to PAPA but the ignition time (TTI) of PMNPA is slightly higher than PAPA. The photocrosslinking properties of the polymers were investigated by UV spectroscopy technique and were found that with the increase in number of aromatic rings, the rate of crosslinking decreases. Thus polyacrylamides are useful in photolithography technology as well as flame‐retardant property in electrical appliances. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
875.
Salih H.A. Tripathi V.K. Pandey B.K. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2003,31(3):324-328
The second-harmonic generation of an intense self-guided right circularly polarized laser beam in a magnetized plasma is investigated. The laser imparts oscillatory velocity to electrons and exerts a radial ponderomotive force on them to create a depleted density channel. The critical power for self-focusing shows huge reduction as electron cyclotron frequency approaches the laser frequency (/spl omega//sub c/ /spl rarr/ /spl omega/). In the presence of the self-created radial density gradient, the laser drives a density perturbation at the fundamental frequency. The density perturbation beats with the oscillatory velocity to produce a second harmonic current density, driving second harmonic radiation copropagating with the laser. The second harmonic, however, is azimuthally asymmetric with /spl theta/-variation as exp(i/spl theta/). Its amplitude shows resonant enhancement as /spl omega//sub c/ /spl rarr/ /spl omega/. 相似文献
876.
Hadi Al Janabi A. Kumar A. Sharma R.P. Tripathi Y.K. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1994,22(1):65-70
In the present paper, the parametric decay instability of the pump X-mode into electron Bernstein wave (EBW) near second harmonics of electron cyclotron frequency and IBW at different harmonics (ωci; n=2,3,4) is examined. Expressions are derived for homogenous threshold, growth rate and convective threshold for this instability. Applications and relevances of the present investigation to ionospheric modification experiment in the F-layer of the ionosphere as well as during intense electron cyclotron resonance heating in the upcoming MTX tokamak have been given 相似文献
877.
Ultrasonic velocity, density and viscosity were measured in two ternary liquid systems namely,n-pentane +n-hexane + benzene(I) andn-hexane + cyclohexane + benzene(II) and one quaternary liquid system,n-pentane +n-hexane + benzene + toluene (III). The experimental as well as literature values of thermal expansion coefficient and iso-thermal
compressibility of pure liquid components were utilized to deduce the ideal value of internal pressure and excess internal
pressure for the above liquid systems at 298·15K using two different approaches. In the conventional approach one needs the
experimental values ofα andβ
T of mixtures for computing internal pressure, which was not possible. The second method which is proposed here utilizes only
the density, ultrasonic velocity and viscosity data of the mixture. This method is used in computing internal pressure and
its excess value for multicomponent liquid systems. A satisfactory agreement has been observed. 相似文献
878.
In exploring the effects of solvent density on the mode and the degree of solvation of the bare and passivated 38-atom gold particle in supercritical ethane, we have extended the molecular dynamics simulations of the system, reported previously,(34) to cover a range of isotherms in the T > T(c) regime, where T(c) is the critical temperature of the solvent. Consonant with our previous observations, the modes of solvation of the bare and the passivated particle, deduced from the radial distribution of the solvent about the metal core center of mass, are found to be vastly different from each other at all solvent densities: while the molecules solvating the bare particle form a well-defined, two-region layer around it, those solvating the passivated particle are loosely dispersed in the passivating layer. For the bare particle, the degree of solvation (vartheta) as a function of solvent density passes through a maximum occurring in the close vicinity of the critical point, consistent with our previous results and in agreement with Debenedetti's theoretical analysis,(22,23) which predicts a solvation enhancement effect in the critical region for systems where the unlike solvent/solute interaction is much stronger than the solvent/solvent interaction. Taking the degree of solvation (vartheta) as a measure of solvent quality, we have investigated how the solvent quality would vary along the solvent-density isotherms. In the solvent-density regime rho > rho(c), the solvent quality is found to be a decreasing function of the density as a result of progressive dominance of the excluded volume effect over the attractive particle/solvent interactions. The particle/solvent affinity is greatly reduced in the presence of the passivating layer, resulting in considerable shrinkage of the good-solvent-quality domain in the supercritical regime. The solvent environment and the presence of the passivating chains produce significant disorder in the equilibrium structure assumed by the nanoparticle core. 相似文献
879.
The conformation of bovine serum albumin (BSA), as well as its interactions with negatively charged mica surfaces in saline solutions of different pH values, have been studied by small-angle neutron scattering (SANS) and chemical force microscopy (CFM), respectively. A new approach to extract the contribution of elementary interactions from the statistically averaged force-extension curves through self-consistent fitting was proposed and used to understand the effects of pH on the interactions and conformation of BSA in saline solutions. When pH increases, the SANS results reveal that the sizes of BSA molecules increase slightly, while the statistical analysis of the CFM results shows that the averaged pull-off force for the elongation monotonously decreases. The decrease of pull-off force with the increase of pH results from the decrease in the strength of hydrogen bonding and the number of interaction pairs, as well as the slight increase of the strength of van der Waals interaction. When pH approaches the isoelectric point (pI) of BSA, results from both SANS and CFM suggest a loss of long-range interactions in BSA molecules. Our results also suggest that the force-extension curve is mainly contributed by the van der Waals interaction. The combination of SANS and CFM provides new insight to understand the interactions and conformation of BSA molecules. 相似文献
880.
Mohit Lal Deb 《合成通讯》2013,43(20):3085-3090
6‐Amino‐5‐formyluracils 1 and 5‐formyl‐6‐hydroxyuracils 4 react with Meldrum's acid 2 in the presence of piperidine as catalyst under thermolytic conditions to afford 6‐carboxy‐2,4,7‐trioxopyrido[2,3‐d]pyrimidines 3 and 6‐carboxy‐2,4,7‐trioxopyrano[2,3‐d]pyrimidines 5 in good yield. Under identical conditions, 6‐amino‐5‐nitrosouracils 6 react with 2 to afford pteridine‐6‐carboxylic acids 7 in good yields. 相似文献