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1.
KS Atia AI El‐Batal 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(7):805-811
Glucose oxidase (EC 1.1.3.4) was immobilized on different polymeric materials using different immobilization techniques (entrapping by γ‐irradiation, and covalent binding using epichlorohydrin). Studies were carried out to increase the thermal stability of glucose oxidase (GOD) for different applications. The activity and stability of the resulting biopolymers have been compared with those of free GOD. The effect of different polyvinyl alcohol/polyacrylamide (PVA/PAAm) compositions of the copolymer carrier on the enzymatic activity of the immobilized GOD was studied. The maximum enzymatic activity was obtained with the composition ratio of PVA/PAAm of 60:40. The behaviour of the free and immobilized enzyme was analysed as a function of pH. A broadening in the pH profile (5.5–8) was observed for immobilized preparations. The activity and stability of the resulting biopolymers produced by immobilization of GOD onto different carriers have been compared, in both aqueous and organic media, with those of the free GOD. The enzyme's tolerance toward both heat and organic solvent was enhanced by immobilization onto polymers. The addition of different concentrations of organic solvents (10–50%, v/v) to the enzyme at higher temperature (60 °C) was found to stabilize the enzyme molecule. The strongest stabilizing effect on the enzymatic activity was achieved at a concentration of 10%. Copyright © 2005 Society of Chemical Industry 相似文献
2.
M. Mendez N. Blond D. Amedro D. A. Hauglustaine P. Blondeau C. Afif C. Fittschen C. Schoemaecker 《Indoor air》2017,27(2):443-451
The photolysis of HONO has been found to be the oxidation driver through OH formation in the indoor air measurement campaign SURFin, an extensive campaign carried out in July 2012 in a classroom in Marseille. In this study, the INCA‐Indoor model is used to evaluate different HONO formation mechanisms that have been used previously in indoor air quality models. In order to avoid biases in the results due to the uncertainty in rate constants, those parameters were adjusted to fit one representative day of the SURFin campaign. Then, the mechanisms have been tested with the optimized parameters against other experiments carried out during the SURFin campaign. Based on the observations and these findings, we propose a new mechanism incorporating sorption of NO2 onto surfaces with possible saturation of these surfaces. This mechanism is able to better reproduce the experimental profiles over a large range of conditions. 相似文献
3.
Syazwan Afif Mohd Zobir Zulkarnain Zainal Mohd Zobir Hussein 《Materials Chemistry and Physics》2010,124(1):477-481
The effect of the addition of very small amount of polyvinyl alcohol (PVA) on the resulting physicochemical properties of ZnO synthesized by ethylene glycol-hydrothermal method was studied. Significant change in particle size distribution and specific surface area can be observed even only 0.02% PVA (w/w) was added into the ethylene glycol (EG) solution, in which the median particle size distribution increased from 5 to 8 nm and at the same time the specific surface area is also increased to nearly 50%. Further addition of PVA resulted in the decrease of the specific surface area due to the formation of agglomeration and aggregation of particles as observed by FESEM study. This study shows that the presence of minute amount of polymer, PVA plays very crucial role in determining the resulting properties of the synthesized ZnO by EG-hydrothermal method. 相似文献
4.
The starting point of this paper is a model of the non‐Fickian diffusion of a simple fluid into a polymeric medium that has been introduced in El Afif and Grmela (2002). The model is extended to a mixture consisting of two simple fluids and one polymeric medium. The effects of the polymeric medium on diffusion are included in the formulations through the use of relative momenta playing the role of internal variables. In ternary mixtures, new phenomena arise due to cross‐coupling effects. As a consequence, the single diffusion Deborah number in binary mixtures becomes a 2 × 2 matrix in ternary mixtures. Two specific examples for which experimental data are available are investigated in detail. 相似文献
5.
The first and second laws of thermodynamics were used to analyze a novel thermodynamic cycle proposed by Goswami in 1995 that uses an ammonia–water binary mixture as the working fluid, while producing both power and refrigeration simultaneously. The thermodynamic performance of the cycle was optimized for maximum second law efficiency using a commercially available optimization program. A maximum second law efficiency of 65.8% was obtained at a heat source temperature of 420 K. An exergy analysis was performed to study losses in different components of the cycle. It is seen that the largest contribution to cycle irreversibility comes from the absorber, with the rectifier and solution heat exchanger also contributing significantly. Irreversibility generation in the boiler is high at very low heat source temperatures, but drops at higher temperatures. 相似文献
6.
Downlink transmit diversity modes for WCDMA together with a two fixed-beam antenna array system are compared relative to the single antenna sectorized system in a radio network simulator. The transmit diversity methods investigated are: space-time transmit diversity and closed-loop mode I transmit diversity. Frequency selective (COST 259) and flat fading channels are considered and their impact to speech-only and data-only services is evaluated. A third service, which highlights the system performance of the various advanced antennas, is also investigated.The results in this investigation point out that the diversity gain in flat fading channels is substantial. In frequency-selective fading, the benefits of fixed beam systems is encouraging, whereas transmit diversity methods (especially Space-Time Transmit Diversity) is unsatisfactory. 相似文献
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8.
Michael Johlitz Stefan Diebels Jan Batal Holger Steeb Wulff Possart 《Journal of Materials Science》2008,43(14):4768-4779
In this study we examine polyurethane bonds of varying thickness between anodised aluminium substrates. The performed shear
tests showed an intriguing size effect of the kind “thinner equals softer”. This size effect occurs not only in the basic
elasticity (relaxed state), but also in the viscoelastic behaviour of the tested material. The cause of such size effects
is supposed to be found in the existence of so-called interphases or boundary layers, which may differ considerably from the
bulk in terms of mechanical behaviour, thus having an enormous impact on thin bonds. In thick bonds, however, these interphases
or boundary layers have a minor effect on the overall mechanical behaviour. To account for these experimental results in bond
modelling, an extended phenomenological continuum mechanics-based model, which explicitly includes such size effects in its
calculation, is developed and presented. For this purpose, an abstract structure parameter with its corresponding balance
equation is established describing the formation of the interphases by means of a phase transition. This makes it possible
to define the bond stiffness at a macroscopic level, without entering into the microstructure. The extended model brings up
a set of model parameters, which are determined efficiently by an ES (evolution strategy). The study concludes with a summary
and an outlook on our further research work.
相似文献
Holger SteebEmail: |
9.
Journal of Computational Electronics - Electric-field-controlled charge transport is a crucial concept of modern computers, embodied, namely in field-effect transistors. The metallic gate voltage... 相似文献
10.
El Mahdi El Habty Ali El Afif Mouncif Sidki 《American Institute of Chemical Engineers》2022,68(7):e17647
Mass transport of solvents into immiscible blends may exhibit a non-Fickian behavior due to the deformation of the embedded interface that couples with diffusion. We introduce an interface area covariant tensor N as a structural state variable and derive a set of thermodynamically-consistent PDEs and ODEs transport equations for the bulk and time-dependent boundaries. The proposed model, which is a reformulation of that derived by El Afif (2008) and El Afif et al. (2003), improves both mathematically and numerically the investigation of the diffusion-interface coupling and provides reasonable predictions of the sorption-permeation one dimensional treatment affording good agreement with experimental data. The tensor N englobes, into a single morphological quantity, all information regarding diffusion-induced changes in the size and shape anisotropy of the interface area. Predicted results include concentration, components of N , residual stresses, mass-uptake, and swelling. Scaling leads to three relevant dimensionless parameters: a mixing-interface coupling constant and bulk and boundary diffusion Deborah numbers. 相似文献