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91.
Cellulose has been used as a raw material for the manufacture of membranes and fibers for many years. This review gives the background of the most recent methods of treating or dissolving cellulose, and its derivatives to form polymer films or membranes for a variety of applications. Indeed, some potential applications of bacterial cellulose, nanofibrillar cellulose (NFC) for films showing enhanced barrier characteristics are reviewed as well as the utilization of cellulose nanonocrystals (CNC) for production of highly oriented super strong films or thin films is discussed. Because of the success of the Lyocell process as well as the amine/metal thiocyanate solvent blends of cellulose and other polysaccharides like starch, chitosan, and other natural polymers. Consequently, the use of cellulose (or its derivatives) and another polysaccharide dissolved as a blend is also elaborated. It is our hope that the reader will want to follow up and investigate these new systems and use them to develop end use materials for all sorts of applications, from medical to water filtration, or electrogels for use in batteries. 相似文献
92.
93.
In 1944, Levinson ([22]) introduced the concept of dissipativeness for a map T in a finite-dimensional space which leads to the existence of a fixed point of some iterate T
n
for n large, rather than a fixed point of T. Browder ([3]) gave an asymptotic field point theorem which proved that T itself had a field point. Although Browder’s result was a big step, it was not suitable for hyperbolic PDEs and neutral functional
differential equations because, in those cases, the map T is not compact. For α-contraction maps the result was extended by Nussbaum ([25]) and Hale and Lopes ([13]) using different
methods. In this paper, we review these ideas and some more recent applications.
Dedicated to Felix Browder on the occasion of his 80th birthday 相似文献
94.
Turon X Rojas OJ Deinhammer RS 《Langmuir : the ACS journal of surfaces and colloids》2008,24(8):3880-3887
The interactions between films of cellulose and cellulase enzymes were monitored using a quartz crystal microbalance (QCM). Real-time measurements of the coupled contributions of enzyme binding and hydrolytic reactions were fitted to a kinetic model that described closely significant cellulase activities. The proposed model combines simple Boltzmann sigmoidal and 1 - exp expressions. The obtained kinetics parameters were proven to be useful to discriminate the effects of incubation variables and also to perform enzyme screening. Furthermore, it is proposed that the energy dissipation of a film subject to enzymatic hydrolysis brings to light its structural changes. Overall, it is demonstrated that the variations registered in QCM frequency and dissipation of the film are indicative of mass and morphological transformations due to enzyme activities; these include binding phenomena, progressive degradation of the cellulose film, existence of residual, recalcitrant cellulose fragments, and the occurrence of other less apparent changes throughout the course of incubation. 相似文献
95.
E.F.V. Carvalho Alessandra N. Barauna Francisco B.C. Machado Orlando Roberto-Neto 《Chemical physics letters》2008,463(1-3):33-37
Barrier heights, structures, reaction energies, and rate constants are calculated with the DFT, MP2, and CCSD(T) methods for the first two channels of the H + CH3OH reactions. The best estimate results based on CCSD(T) calculations give reaction enthalpies () for the first (−8.4 kcal/mol) and second (0.8 kcal/mol) reactive channels, which are comparable to the experimental values, −8.8 ± 0.9 and −0.3 ± 0.9 kcal/mol, respectively. Rate constants and activation energies calculated with the IVTST-0 method using CCSD(T)/cc-pVTZ geometries and frequencies are also in excellent agreement with experiment data. 相似文献
96.
Orlando JJ 《Physical chemistry chemical physics : PCCP》2007,9(31):4189-4199
The products of the Cl atom initiated oxidation of diethyl ether (DEE) were investigated at atmospheric pressure over a range of temperatures (218-335 K) and O(2) partial pressures (50-700 Torr), both in the presence and absence of NO(x). The major products observed at 298 K and below were ethyl formate and ethyl acetate, which accounted for approximately equal to 60-80% of the reacted diethyl ether. In general, the yield of ethyl formate increased with increasing temperature, with decreasing O(2) partial pressure, and upon addition of NO to the reaction mixtures. The product yield data show that thermal decomposition reaction 3, CH(3)CH(2)-O-CH(O.)CH(3)--> CH(3)CH(2)-O-CH=O + CH(3), and reaction 6 with O(2), CH(3)CH(2)-O-CH(O.)CH(3) + O(2)--> CH(3)CH(2)-O-C(=O)CH(3) + HO(2) are competing fates of the CH(3)CH(2)-O-CH(O )CH(3) radical, with a best estimate of k3/k6 approximately equal to 6.9 x 10(24) exp(-3130/T). Thermal decomposition via C-H or C-O bond cleavage are at most minor contributors to the CH(3)CH(2)-O-CH(O.)CH(3) chemistry. The data also show that the CH(3)CH(2)-O-CH(O.)CH(3) radical is subject to a chemical activation effect. When produced from the exothermic reaction of the CH(3)CH(2)-O-CH(OO.)CH(3) radical with NO, prompt decomposition via both CH(3)- and probably H-elimination occur, with yields of about 40% and < or =15%, respectively. Finally, at temperatures slightly above ambient, evidence for a change in mechanism in the absence of NO(x), possibly due to chemistry involving the peroxy radical CH(3)CH(2)-O-CH(OO.)CH(3), is presented. 相似文献
97.
98.
The reaction Cl + CH3CHO → HCl + CH3CO (1) was studied using flash photo‐lysis / tunable diode laser absorption spectroscopy to monitor the production of HCl. The rate coefficient, k1, was measured to be (7.5 ± 0.8) × 10−11 cm3 molecule−1 s−1 at 298 K. HCl (v = 0) and HCl† (v = 1) were measured directly in this study and the yields of HCl (v = 0, 1, >1) for the reaction of Cl with CH3CHO were determined to be 0.44 ± 0.15, 0.56 ± 0.15, and <0.04, respectively. The rate coefficient for the quenching of HCl† (v = 1) by CH3CHO was k17e = (4.8 ± 1.2) × 10−11 cm3 molecule−1 s−1. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 766–775, 1999 相似文献
99.
John J. Orlando 《国际化学动力学杂志》1999,31(7):515-524
Rate coefficients for the reaction of Cl atoms with CH3Cl (k1), CH2Cl2 (k2), and CHCl3 (k3) have been determined over the temperature range 222–298 K using standard relative rate techniques. These data, when combined with evaluated data from previous studies, lead to the following Arrhenius expressions (all in units of cm3 molecule−1 s−1): k1 = (2.8 ± 0.3) × 10−11 exp(−1200 ± 150/T); k2 = (1.5 ± 0.2) × 10−11 exp(−1100 ± 150/T); k3 = (0.48 ± 0.05) × 10−11 exp(−1050 ± 150/T). Values for k1 are in substantial agreement with previous measurements. However, while the room temperature values for k2 and k3 agree with most previous data, the activation energies for these rate coefficients are substantially lower than previously recommended values. In addition, the mechanism of the oxidation of CH2Cl2 has been studied. The dominant fate of the CHCl2O radical is decomposition via Cl‐atom elimination, even at the lowest temperatures studied in this work (218 K). However, a small fraction of the CHCl2O radicals are shown to react with O2 at low temperatures. Using an estimated value for the rate coefficient of the reaction of CHCl2O with O2 (1 × 10−14 cm3 molecule−1 s−1), the decomposition rate coefficient for CHCl2O is found to be about 4 × 106 s−1 at 218 K, with the barrier to its decomposition estimated at 6 kcal/mole. As part of this work, the rate coefficient for Cl atoms with HCOCl was also been determined, k7 = 1.4 × 10−11 exp(−885/T) cm3 molecule−1 s−1, in agreement with previous determinations. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 515–524, 1999 相似文献
100.
C.A.C. Passos M.T.D. Orlando J.L. Passamai Jr. E.V.L. de Mello 《Physica B: Condensed Matter》2009,404(19):3123-3126
A model to describe the critical current density behavior of high-Tc polycrystalline superconductors is proposed for all magnetic field values. The main features of the model are as follows: the transport critical current density is controlled by the weak-link network at grain boundaries. The size distribution of weak links is well represented by a Gamma-type distribution. Finally, the tunneling critical current between grains follows a Fraunhofer diffraction pattern or a modified pattern if the applied magnetic field is lower or higher than the first critical field Hc1. 相似文献