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1.
A review of the optimal stopping problem with more than a single decision maker (DM) is presented in this paper. We classify
the existing literature according to the arrival of the offers, the utility of the DMs, the length of the sequence of offers,
the nature of the game and the number of offers to be selected. We enumerate various definitions for this problem and describe
some dynamic approaches.
Fouad Ben Abdelaziz is on leave from the Institut Superieur de Gestion, University of Tunis, Tunisia e-mail: foued.benabdelaz@isg.run.tn. 相似文献
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3.
Ines Belhaj-Ben Romdhane Zamen Ben Romdhane Maha Bouzid Ali Gargouri Hafedh Belghith 《Applied biochemistry and biotechnology》2013,171(8):1986-2002
Waste frying oil, which not only harms people’s health but also causes environmental pollution, can be a good alternative to partially substitute petroleum diesel through transesterification reaction. This oil contained 8.8 % of free fatty acids, which cause a problem in a base-catalyzed process. In this study, synthesis of biodiesel was efficiently catalyzed by the covalently immobilized Talaromyces thermophilus lipase and allowed bioconversion yield up to 92 % after 24 h of reaction time. The optimal molar ratio was four to six parts of methanol to one part of oil with a biocatalyst loaded of 25 wt.% of oil. Further, experiments revealed that T. thermophilus lipase, immobilized by a multipoint covalent liaison onto activated chitosan via a short spacer (glutaraldehyde), was sufficiently tolerant to methanol. In fact, using the stepwise addition of methanol, no significant difference was observed from the one-step whole addition at the start of reaction. The batch biodiesel synthesis was performed in a fixed bed reactor with a lipase loaded of 10 g. The bioconversion yield of 98 % was attained after a 5-h reaction time. The bioreactor was operated successfully for almost 150 h without any changes in the initial conversion yield. Most of the chemical and physical properties of the produced biodiesel meet the European and USA standard specifications of biodiesel fuels. 相似文献
4.
Saoussen Turki Atef Ayed Néjib Chalghoumi Frederic Weekers Philippe Thonart Héla Kallel 《Applied biochemistry and biotechnology》2010,160(5):1371-1385
Yarrowia lipolytica LgX64.81 is a non-genetically modified mutant that was previously identified as a promising microorganism for extracellular
lipase production. In this work, the development of a fed-batch process for the production of this enzyme in this strain was
described. A lipolytic activity of 2,145 U/mL was obtained after 32 h of batch culture in a defined medium supplemented with
10 g/L of tryptone, an enhancer of lipase expression. To maximize the volumetric productivity, two different fed-batch strategies
had been investigated. In comparison to batch process, the intermittent fed-batch strategy had not improved the volumetric
lipase productivity. In contrast, the stepwise feeding strategy combined with uncoupled cell growth and lipase production
phases resulted in a 2-fold increase in the volumetric lipase productivity, namely, the lipase activity reached 10,000 U/mL
after 80 h of culture. Furthermore, this lipase was purified to homogeneity by anion exchange chromatography on MonoQ resin
followed by gel filtration on Sephacryl S-100. This process resulted in an overall yield of 72% and a 3.5-fold increase of
the specific lipase activity. The developed process offers a great potential for an economic production of Lip2 at large scale
in Y. lipolytica LgX64.81. 相似文献
5.
Saoussen Zeror Jacqueline Collin Jean-Claude Fiaud Louisa Aribi Zouioueche 《Tetrahedron: Asymmetry》2010,21(9-10):1211-1215
In the search for green chemistry methods for the enantioselective reduction of ketoesters Saccharomyces cerevisiae- and ruthenium-catalyzed reactions in water have been investigated. The highest enantiomeric excesses for the reduction of α- and β-ketoesters have been obtained by S. cerevisiae. Chiral ruthenium catalysts are active for the reduction of all ketoesters with low to moderate enantioselectivities depending on the nature of the substrate and ligand. Interestingly, for several substrates both enantiomers of the hydroxyesters have been obtained according either to the catalytic method or to the structure of the ligand. 相似文献
6.
Saoussen Hammami Ridha El Mokni Khaled Faidi Danilo Falconieri Alessandra Piras Silvia Procedda 《Natural product research》2015,29(24):2336-2340
The objectives of this study were to chemically characterise and evaluate the antioxidant potential of the essential oil from Teucrium flavum L. subsp. flavum growing spontaneously in Tunisia. The volatile oil was extracted by hydrodistillation of the aerial parts in a Clevenger type apparatus. Forty constituents were identified via GC and GC-MS analysis. β-caryophyllene (32.5%) and α-humulene (17.8%) were the most abundant components. The evaluation of free radical scavenging activity using stable DPPH free radical showed that the volatile oil exhibits a moderate antioxidant activity and reduces DPPH to 50% at EC50 value of 1230 μg mL? 1. 相似文献
7.
The aerial parts of the Tunisian plant Echiochilon fruticosum yielded a novel flavonol diglycoside: naringenin-5-O-beta-D-glycopyranoside-3-O-alpha-L-rhamnopyranoside, named Echiofruzine (1), together with the known compounds vomifoliol-9-O-beta-D-glucopyraroside (2), 1-oxo-alpha-ionyl-9-O-beta-D-glucopyranoside (3) and 1-O-[beta-D-xylopyranosyl(1 --> 6)-beta-D-glucopyranosyl] eugenol (4), described for the first time in the indicated plant. The structures of the four isolated compounds were established on the basis of chemical and spectroscopic evidence. 相似文献
8.
In recent years, there is an increased demand on the international market of dried fruits and vegetables with significant added value. Due to its important production, consumption and nutrient intake, drying of tomato has become a subject of extended and varied research works. The present work is focused on the drying behavior of thin-layer tomato and its mathematical modeling in order to optimize the drying processes. The moisture desorption isotherms of raw tomato were determined at four temperature levels namely 45, 50, 60 and 65 °C using the static gravimetric method. The experimental data obtained were modeled by five equations and the (GAB) model was found to be the best-describing these isotherms. The drying kinetics were experimentally investigated at 45, 55 and 65 °C and performed at air velocities of 0.5 and 2 m/s. In order to investigate the effect of the exchange surface on drying time, samples were dried into two different shapes: tomato halves and tomato quarters. The impact of various drying parameters was also studied (temperature, air velocity and air humidity). The drying curves showed only the preheating period and the falling drying rate period. In this study, attention was paid to the modeling of experimental thin-layer drying kinetics. The experimental results were fitted with four different models. 相似文献
9.
Hachemi Belghith Casimir Blonski Alain Klab Jacques Pri Jean Roussel 《Journal of mass spectrometry : JMS》1989,24(9):718-722
Analysis by electron impact and metastable ions (MIKE technique) of the fragmentation patterns for one acyclic and two cyclic N-phosphorylated ureas reveals for the first case an isomerization from nitrogen to the ureido oxygen atom of the phosphoryl group and subsequent fragmentation. For the other two cases, fragments result from P? N bond breaking and ring-opening. Possible involvement in the biotin-ATP activation process is discussed. 相似文献
10.
Zouhaier Mehrez Mourad Bouterra Afif El Cafsi Ali Belghith Patrick Le Quere 《Heat and Mass Transfer》2009,46(1):107-112
A numerical study based on the large eddy simulation methodology was made of heat transfer in locally disturbed turbulent
separated and reattached flow over a backward facing step. The local disturbance was given to the flow by a sinusoidally blowing/suction
of the fluid into a separated shear layer. The Reynolds number was fixed at 33,000 and Richardson number at 0.5. The disturbance
frequency was varied in the range 0 ≤ St ≤ 2, where St is the Strouhal number of disturbance. The obtained results revealed the existence of an optimum perturbation frequency value,
St = 0.25, in terms of the reduced reattachment length. At this frequency the heat transfer is significantly enhanced in the
recirculation zone. The influence of the frequency and the amplitude of disturbance, in the maximum heat transfer positions
and the maximum local Nusselt number, is analysed. 相似文献