Authors:Hanieh Nassiri, Hassan Arabi and Shokoufeh Hakim
polymerization of propylene using heterogeneous multi-site Ziegler–Natta catalyst and find the best estimate of kinetic parameters using numerical solution of kinetic model combined with the Nelder–Mead simplex method as an optimization algorithm [ 3 , 34 , 35
Immobilization of the bacteria A. simplex by-2-13 was obtained by irradiation polymerization with an electron beam and gamma-radiation at 0°C. Prednisone acetate (P. A.) was derived from cortisone acetate (C. A.) by 1,2-dehydrogenation, catalyzed by immobilized A. simplex by-2-13. The immobilized bacteria were used 10 times in succession with a transformation percentage ranging from 77 to 86% for electron beam radiation and 79 to 99% for gamma radiation. Dehydrogenation, was carried out at pH 7.2, 34°C, 180–200 r.p.m. for 24 hours. 3% (v/v) anhydrous alcohol was added to the system at onset. Scanning electron micrographs documented the structure of the immobilized bacteria. In this work, the effect of absorbable doses of radiation and the reaction time of non-immobilized bacteria on dehydrogenase activity were studied. The effect of pH, temperature and concentration of substrate were also studied.
Authors:Lorentz Jäntschi, Sorin Hodişan, Claudia Cimpoiu, Anamaria Hosu, Eugen Darvasi and Teodor Hodişan
Modeling of thin-layer chromatographic separation of androstane isomers to find the optimum mobile phase is described in this paper. The isomers of androstane are present in a variety of samples, so achieving their optimum thin-layer chromatographic separation is very important. A mathematical model was developed and tested. The model takes into account the interaction between solvents and uses a complex function for modeling, so it provides reliable results. The proposed mathematical model gives results similar to those obtained by use of other optimization models, for example the ‘Simplex’ and ‘Prisma’ methods.
Authors:Sandra Babić, Alka Horvat and Marija Kaštelan-Macan
A method for optimization of a TLC separation based on use of a genetic algorithm is described. The procedure was tested by optimization of the reversed-phase HPTLC separation of a mixture of six pesticides and satisfactory optimum results were obtained. The performance of the genetic algorithm was tested by measurement of the number of generations, the population size, the mutation probability, and the crossover probability. Three separation criteria (
**) were examined as fitness functions. The genetic algorithm was compared with the simplex method.
The parameters of the Arrhenius equation determined by the linear, weighted linear and non-linear least squares methods and by the simplex method are compared. Since the non-linear least squares method permits the consideration of statistical weights of both the dependent (k) and independent (T) variables and does not involve logarithmic transformation, it is advisable to calculate the parameters of the Arrhenius equation by means of the non-linear least squares method.
Authors:Y. Duan, J. Li, X. Yang, X. Cao, L. Hu, Z. Wang, Y. Liu and C. Wang
The thermal decomposition of strontium acetate hemihydrate has been studied by TG-DTA/DSC and TG coupled with Fourier transform
infrared spectroscopy (FTIR) under non-isothermal conditions in nitrogen gas from ambient temperature to 600°C. The TG-DTA/DSC
experiments indicate the decomposition goes mainly through two steps: the dehydration and the subsequent decomposition of
anhydrous strontium acetate into strontium carbonate. TG-FTIR analysis of the evolved products from the non-oxidative thermal
degradation indicates mainly the release of water, acetone and carbon dioxide. The model-free isoconversional methods are
employed to calculate the Ea of both steps at different conversion α from 0.1 to 0.9 with increment of 0.05. The relative constant apparent Ea values during dehydration (0.5<α<0.9) of strontium acetate hemihydrate and decomposition of anhydrous strontium acetate (0.5<α<0.9)
suggest that the simplex reactions involved in the corresponding thermal events. The most probable kinetic models during dehydration
and decomposition have been estimated by means of the master plots method.
Thermodynamics and crystallization kinetics of the hydrothermal synthesis of Na4Ti4Si3O10 (NaTS) were systemically studied by both experiments and model simulation. Experimental results showed that the curve of
crystallinity with time was a characteristic signmoid in the shape that indicated the crystallization of Na4Ti4Si3O10 was a typical spontaneous nucleation process on the laboratory scale. Crystallization of NaTS belongs to the liquid-liquid
transformation mechanism and the reaction is endothermic (ΔH = 15.3 kJ/mol). A mathematic model of crystallization kinetics was developed to simulate the synthesis of NaTS. Runge-Kutta
and simplex methods were adopted to solve the partial differential equations. Model results fitted well with the experimental
data and showed that the synthesis process belongs to spontaneous nucleation and crystal growth. Moreover, the very small
crystal growth constant (5.6·10−7) and gel dissolution constant (7.0·10−7) indicate they are the rate-limiting steps of the whole synthesis process.
Authors:P. Hashemi, M. M. Abolghasemi, S. Ahmadi and A. R. Ghiasvant
Headspace-solvent microextraction (HS-SME) and hydrodistillation coupled with GC-MS have been used for isolation and identification of the volatile components that characterize Myrtus communis L. aroma. In the HS-SME method a suspended micro-drop of n-butanol was used as solvent. The effect of six different parameters on extraction efficiency, including sample weight, drop volume, extraction temperature, conditioning time, extraction time, and ionic strength were optimized using a simplex optimization method. The volatile components were studied both by HS-SME and an ordinary hydrodistillation method and the major components identified were 1,8-cineol, α-pinene, limonene, and linalool.
Authors:M. Y. Guida, F. E. Laghchioua and A. Hannioui
Betancor , S. , Dominguez , B. , Tuya , F. , Figueroa , F. L. , Haroun , R. ( 2015 ) Photosynthetic performance and photo protection of cystoseira humilis (Phaeophyceae) and Digenea simplex (Rhodophyceae) in an intertidal rock pool . Aquatic
Authors:S. Lendvayová, K. Moricová, E. Jóna, J. Kraxner, M. Loduhová, V. Pavlík, J. Pagáčová and S. C. Mojumdar
) [ 31 ]:
The parameters A and B in Eq. ( 1 ) have been obtained by minimizing the sum of squares between experimental and theoretical values of onset temperature T x for various heating rates by the simplex method [ 32 ]. The agreement