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Control Properties (control + property)

Distribution by Scientific Domains

Chemistry	50%
Life Sciences	30%

Selected Abstracts

Dividing Wall Distillation Columns: Optimization and Control Properties

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2008
F. I. Gómez-Castro
Abstract The optimal design of dividing wall columns is a non-linear and multivariable problem, and the objective function used as optimization criterion is generally non-convex with several local optimums. Considering this fact, in this paper, we studied the design of dividing wall columns using as a design tool, a multi-objective genetic algorithm with restrictions, written in MatlabTM and using the process simulator Aspen PlusTM for the evaluation of the objective function. Numerical performance of this method has been tested in the design of columns with one or two dividing walls and with several mixtures to test the effect of the relative volatilities of the feed mixtures on energy consumption, second law efficiency, total annual cost, and theoretical control properties. In general, the numerical performance shows that this method appears to be robust and suitable for the design of sequences with dividing walls. [source]

Generalized window advertising for TCP congestion control,

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 6 2002
Mario Gerla
Congestion in the Internet is a major cause of network performance degradation. The Generalized Window Advertising (GWA) scheme proposed in this paper is a new approach for enhancing the congestion control properties of TCP. GWA requires only minor modifications to the existing protocol stack and is completely backward compatible, allowing GWA-hosts to interact with non-GWA hosts without modifications. GWA exploits the notion of end-host-network cooperation, with the congestion level notified from the network to end hosts. It is based on solid control theory results mat guarantee performance and stable network operation. GWA is able to avoid window oscillations and the related fluctuations in offered load and network performance. This makes it more robust to sustained network overload due to a large number of connections competing for the same bottleneck, a situation where traditional TCP implementations fail to provide satisfactory performance. GWA-TCP is compared with traditional TCP, TCP with RED and also ECN using the ns-2 simulator. Results show that in most cases GWA-TCP outperforms the traditional schemes. In particular, when compared with ECN, it provides smoother network operation and increased fairness. [source]

Experimental validation of metabolic pathway modeling

FEBS JOURNAL, Issue 13 2008
An illustration with glycolytic segments from Entamoeba histolytica
In the search for new drug targets in the human parasite Entamoeba histolytica, metabolic control analysis was applied to determine, experimentally, flux control distribution of amebal glycolysis. The first (hexokinase, hexose-6-phosphate isomerase, pyrophosphate-dependent phosphofructokinase (PPi -PFK), aldolase and triose-phosphate isomerase) and final (3-phosphoglycerate mutase, enolase and pyruvate phosphate dikinase) glycolytic segments were reconstituted in vitro with recombinant enzymes under near-physiological conditions of pH, temperature and enzyme proportion. Flux control was determined by titrating flux with each enzyme component. In parallel, both glycolytic segments were also modeled by using the rate equations and kinetic parameters previously determined. Because the flux control distribution predicted by modeling and that determined by reconstitution were not similar, kinetic interactions among all the reconstituted components were experimentally revised to unravel the causes of the discrepancy. For the final segment, it was found that 3-phosphoglycerate was a weakly competitive inhibitor of enolase, whereas PPi was a moderate inhibitor of 3-phosphoglycerate mutase and enolase. For the first segment, PPi was both a strong inhibitor of aldolase and a nonessential mixed-type activator of amebal hexokinase; in addition, lower Vmax values for hexose-6-phosphate isomerase, PPi -PFK and aldolase were induced by PPi or ATP inhibition. It should be noted that PPi and other metabolites were absent from the 3-phosphoglycerate mutase and enolase or aldolase and hexokinase kinetics experiments, but present in reconstitution experiments. Only by incorporating these modifications in the rate equations, modeling predicted values of flux control distribution, flux rate and metabolite concentrations similar to those experimentally determined. The experimentally validated segment models allowed ,in silico experimentation' to be carried out, which is not easy to achieve in in vivo or in vitro systems. The results predicted a nonsignificant effect on flux rate and flux control distribution by adding parallel routes (pyruvate kinase for the final segment and ATP-dependent PFK for the first segment), because of the much lower activity of these enzymes in the ameba. Furthermore, modeling predicted full flux-control by 3-phosphoglycerate mutase and hexokinase, in the presence of low physiological substrate and product concentrations. It is concluded that the combination of in vitro pathway reconstitution with modeling and enzyme kinetics experimentation permits a more comprehensive understanding of the pathway behavior and control properties. [source]

Differential effects of genotoxic stress on both concurrent body growth and gradual senescence in the adult zebrafish

AGING CELL, Issue 2 2007
Stephanie B. Tsai
Summary Among vertebrates, fish and mammals show intriguing differences in their growth control properties with age. The potential for unlimited or indeterminate growth in a variety of fish species has prompted many questions regarding the senescent phenomena that appear during the aging process in these animals. Using zebrafish as our model system, we have attempted in our current study to examine the growth phenomena in fish in relation to the onset of senescence-associated symptoms, and to evaluate the effects of genotoxic stress on these processes. We observed in the course of these analyses that the zebrafish undergoes continuous growth, irrespective of age, past the point of sexual maturation with gradually decreasing growth rates at later stages. Animal population density, current body size and chronological age also play predominant roles in regulating zebrafish growth and all inversely influence the growth rate. Interestingly, the induction of genotoxic stress by exposure to ionizing radiation (IR) did not adversely affect this body growth ability in zebrafish. However, IR was found to chronically debilitate the regeneration of amputated caudal fins and thereby induce high levels of abnormal fin regeneration in the adult zebrafish. In addition, by resembling and mimicking the natural course of aging, IR treatments likewise enhanced several other symptoms of senescence, such as a decline in reproductive abilities, increased senescence-associated ,-galactosidase activity and a reduction in melatonin secretion. Our current data thus suggest that during the lifespan of zebrafish, the onset of senescence-associated symptoms occurs in parallel with continuous growth throughout mid-adulthood. Moreover, our present findings indicate that genotoxic DNA damage may play a role as a rate-limiting factor during the induction of senescence, but not in the inhibition of continuous, density-dependent growth in adult zebrafish. [source]

Acrylic polymers as thickening agents for tetraglycol cosolvent

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2006
Giulia Bonacucina
Abstract This article evaluated the thickening properties of two different Eudragits, L and RS, in tetraglycol cosolvent in order to obtain high viscosity systems characterized by controlled release properties. Tetraglycol was chosen for its ability to dissolve a wide range of water insoluble drugs, while Eudragit RS and L for their specific dissolution and permeability properties under physiological conditions. Study of the rheological properties was performed to characterize elastic and viscous properties of Eudragit/tetraglycol samples in function of frequency and temperature. For all systems, the results outlined a liquid like behavior, as observed for dilute polymer solutions. In fact the fitting of the log G,-log G,, versus frequency curves showed a good agreement with the Rouse or Zimm models. So despite the increase in viscosity, samples still behaved like liquid systems. After the addition of paracetamol the release characteristics were defined pointing out the great release control properties of both Eudragit L and RS, which showed different release kinetics depending on the pH of the environment. Semisolid Eudragits/tetraglycol systems can be considered as a new alterative for the sustained release of insoluble or poorly water-soluble drugs. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95:726,736, 2006 [source]

A Short Note About Energy-Efficiency Performance of Thermally Coupled Distillation Sequences

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2006
Juan Gabriel Segovia-Hernández
Abstract In this work, we present a comparative study of the energy-efficiency performance between conventional distillation sequences and thermally coupled distillation arrangements (TCDS) for the separation of ternary mixtures of hydrocarbons under the action of feedback control loops. The influence of the relative ease of separation of the feed mixture and its composition was analyzed. The feedback analysis was conducted through servo tests with individual changes in the set points for each of the three product streams. Standard PI controllers were used for each loop. The results show an apparent trend regarding the sequence with a better dynamic performance. Generally, TCDS options performed better for the control of the extreme components of the ternary mixture (A and C), while the conventional sequences offered a better dynamic behaviour for the control of the intermediate component (B). The only case in which there was a dominant structure for all control loops was when the feed contained low amounts of the intermediate component and the mixture had similar relative volatilities. The Petlyuk column provided the optimal choice in such case, which contradicts the general expectations regarding its control behaviour. In addition, the energy demands during the dynamic responses were significantly lower than those observed for the other distillation sequences. TCDS options, therefore, are not only more energy efficient than the conventional sequences, but there are cases in which they also offer better feedback control properties. On présente dans ce travail une étude comparative de la performance d'efficacité d'énergétique entre les séquences de distillation conventionnelles et les configurations de distillation couplées thermiquement (TCDS) pour la séparation de mélanges ternaires d'hydrocarbures sous l'action de boucles de contrôle d'asservissement. L'influence de la facilité relative de séparation du mélange d'alimentation et de sa composition est analysée. L'analyse de rétroalimentation est réalisée grâce à des tests d'asservissement avec des changements individuels dans les points de consigne pour chacun des trois courants de produits. Des contrôleurs PI standards ont été utilisés pour chaque boucle. Les résultats montrent une tendance apparente pour la séquence ayant une meilleure performance dynamique. Généralement, les options TCDS sont meilleures pour le contrôle des composantes extrêmes du mélange ternaire (A et C), tandis que les séquences conventionnelles offrent un meilleur contrôle dynamique pour le contrôle de la composante intermédiaire (B). Le seul cas où il y a une structure dominante pour toutes les boucles de contrôle, c'est lorsque l'alimentation contenant de faibles quantités de la composante intermédiaire et le mélange ont la même volatilité relative. La colonne Petlyuk est le choix optimal dans un tel cas, ce qui contredit les attentes générales concernant son comportement de contrôle. En outre, les demandes d'énergie pendant les réponses dynamiques sont significativement plus faibles que celles observées pour les autres séquences de distillation. Ainsi, non seulement les options TCDS sont plus efficaces que les séquences conventionnelles, mais il y a des cas où elles offrent également de meilleures propriétés de contrôle d'asservissement. [source]

Suppression of populations of Australian sheep blowfly, Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae), with a novel blowfly trap

AUSTRALIAN JOURNAL OF ENTOMOLOGY, Issue 2 2009
Rudolf Urech
Abstract The Australian sheep blowfly, Lucilia cuprina, initiates more than 85% of fly strikes on sheep in Australia with an estimated average annual cost of A$280 million to the Australian sheep industry. LuciTrap® is a commercially available, selective trap for L. cuprina consisting of a plastic bucket with multiple fly entry cones and a synthetic attractant. The impact of LuciTrap on populations of L. cuprina on sheep properties in five Australian states was evaluated by comparing L. cuprina populations on paired properties with and without LuciTraps over seasons when significant fly populations could be expected. Twenty-four comparisons (trials) were conducted over 4 years. During times of ,higher fly density' (when the 48 h geometric mean of trap catches on the control property was greater than five L. cuprina), the overall geometric mean trap catches for control and trapped properties differed significantly (P < 0.001) with mean trap catches of 19.4 and 7.74 L. cuprina, respectively. The selectivity of the LuciTrap was confirmed with 59% of all trapped flies being L. cuprina. Chrysomya spp. and Calliphora spp. constituted 9.3% and 1.1% of the catches with a variety of other flies (mainly Sarcophagidae and Muscidae) providing the remainder (31%). Lucilia sericata was only trapped in Tasmania and made up 7.7% of the Lucilia spp. catch in that state. Seventy-two per cent of the trapped L. cuprina were female. The deployment of LuciTrap on sheep properties at one trap per 100 sheep from the beginning of the anticipated fly season suppressed the populations of L. cuprina by 60% compared with matched control properties. The LuciTrap is a selective and easy to use fly trap and constitutes an effective, non-insecticidal tool for use in integrated management programs for L. cuprina. [source]

Dividing Wall Distillation Columns: Optimization and Control Properties

Suppression of populations of Australian sheep blowfly, Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae), with a novel blowfly trap

On the numerical computation of blowing-up solutions for semilinear parabolic equations

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 9 2001
D. Fayyad
Theoretical aspects related to the approximation of the semilinear parabolic equation: $u_t=\Delta u+f(u)$\nopagenumbers\end, with a finite unknown ,blow-up' time Tb have been studied in a previous work. Specifically, for , a small positive number, we have considered coupled systems of semilinear parabolic equations, with positive solutions and ,mass control' property, such that: \def\ve{^\varepsilon}$$u_t\ve=\Delta u\ve+f(u\ve)v\ve\qquad v_t\ve=\Delta v\ve-\varepsilon f(u\ve)v\ve$$\nopagenumbers\end The solution \def\ve{^\varepsilon}$$\{u\ve,v\ve\}$$\nopagenumbers\end of such systems is known to be global. It is shown that $$\|(u^\varepsilon-u)(\, .\, ,t)\|_\infty\leq C(M_T)\varepsilon$$\nopagenumbers\end, \def\lt{\char'74}$t\leq T \lt T_b$\nopagenumbers\end where $M_T=\|u(\, .\, ,T)\|_\infty$\nopagenumbers\end and $C(M_T)$\nopagenumbers\end is given by (6). In this paper, we suggest a numerical procedure for approaching the value of the blow-up time Tb and the blow-up solution u. For this purpose, we construct a sequence $\{M_\eta\}$\nopagenumbers\end, with $\lim_{\eta\rightarrow 0}M_\eta=\infty$\nopagenumbers\end. Correspondingly, for $\varepsilon\leq1/2C(M_\eta+1)=\eta^\alpha$\nopagenumbers\end and \def\lt{\char'74}$0\lt\alpha\lt\,\!1$\nopagenumbers\end, we associate a specific sequence of times $\{T_\varepsilon\}$\nopagenumbers\end, defined by $\|u^\varepsilon(\, .\, ,T_\varepsilon)\|_\infty=M_\eta$\nopagenumbers\end. In particular, when $\varepsilon=\eta\leq\eta^\alpha$\nopagenumbers\end, the resulting sequence $\{T_\varepsilon\equiv T_\eta\}$\nopagenumbers\end, verifies, $\|(u-u^\eta)(\, .\, ,t)\|_\infty\leq{1\over2}(\eta)^{1-\alpha}$\nopagenumbers\end, \def\lt{\char'74}$0\leq t\leq T_\eta\lt T_{\rm b}$\nopagenumbers\end with $\lim_{\eta\rightarrow 0}T_\eta=T_{\rm b}$\nopagenumbers\end. The two special cases of a single-point blow-up where $f(u)=\lambda{\rm e}^u$\nopagenumbers\end and $f(u)=u^p$\nopagenumbers\end are then studied, yielding respectively sequences $\{M_\eta\}$\nopagenumbers\end of order $O(\ln|\ln(\eta)|)$\nopagenumbers\end and $O(\{|\ln(\eta)|\}^{1/p-1})$\nopagenumbers\end. The estimate $|T_\eta-T_{\rm b}|/T_{\rm b}=O(1/|\ln(\eta)|)$\nopagenumbers\end is proven to be valid in both cases. We conduct numerical simulations that confirm our theoretical results. Copyright © 2001 John Wiley & Sons, Ltd. [source]