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Optimum Values (optimum + value)
Selected AbstractsHOW BRIGHT AND HOW NASTY: EXPLAINING DIVERSITY IN WARNING SIGNAL STRENGTHEVOLUTION, Issue 3 2007Michael P. Speed The conspicuous displays that warn predators of defenses carried by potential prey have been of interest to evolutionary biologists from the time of Wallace and Darwin to the present day. Although most studies implicitly assume that these "aposematic" warning signals simply indicate the presence of some repellent defense such as a toxin, it has been speculated that the intensity of the signal might reliably indicate the strength of defense so that, for example, the nastiest prey might "shout loudest" about their unprofitability. Recent phylogenetic and empirical studies of Dendrobatid frogs provide contradictory views, in one instance showing a positive correlation between toxin levels and conspicuousness, in another showing a breakdown of this relationship. In this paper we present an optimization model, which can potentially account for these divergent results. Our model locates the optimal values of defensive traits that are influenced by a range of costs and benefits. We show that optimal aposematic conspicuousness can be positively correlated with optimal prey toxicity, especially where population sizes and season lengths vary between species. In other cases, optimal aposematic conspicuousness may be negatively correlated with toxicity; this is especially the case when the marginal costs of aposematic displays vary between members of different populations. Finally, when displays incur no allocation costs there may be no single optimum value for aposematic conspicuousness, rather a large array of alternative forms of a display may have equal fitness. [source] Heat transfer characteristics in a two-dimensional channel with an oscillating wallHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2001Masahide Nakamura Abstract Numerical calculations have been carried out for the laminar heat transfer in a two-dimensional channel bounded by a fixed wall and an oscillating wall. In this calculation, the moving boundary problem was transformed into a fixed boundary problem using the coordinate transformation method, and the fully implicit finite difference method was used to solve the mass, momentum, and energy conservation equations. The calculated results are summarized as follows: (i) The wall oscillation has an effect of enhancing the heat transfer and an effect of increasing the additional pressure loss. (ii) An optimum Strouhal number for the enhancement of heat transfer exists, and this optimum value is strongly affected by the amplitude of wall oscillation. © 2001 Scripta Technica, Heat Trans Asian Res, 30(4): 280,292, 2001 [source] Constrained total least-squares computations for high-resolution image reconstruction with multisensorsINTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 1 2002Michael K. Ng Multiple undersampled images of a scene are often obtained by using a charge-coupled device (CCD) detector array of sensors that are shifted relative to each other by subpixel displacements. This geometry of sensors, where each sensor has a subarray of sensing elements of suitable size, has been popular in the task of attaining spatial resolution enhancement from the acquired low-resolution degraded images that comprise the set of observations. With the objective of improving the performance of the signal processing algorithms in the presence of the ubiquitous perturbation errors of displacements around the ideal subpixel locations (because of imperfections in fabrication), in addition to noisy observation, the errors-in-variables or the total least-squares method is used in this paper. A regularized constrained total least-squares (RCTLS) solution to the problem is given, which requires the minimization of a nonconvex and nonlinear cost functional. Simulations indicate that the choice of the regularization parameter influences significantly the quality of the solution. The L-curve method is used to select the theoretically optimum value of the regularization parameter instead of the unsound but expedient trial-and-error approach. The expected superiority of this RCTLS approach over the conventional least-squares theory-based algorithm is substantiated by example. © 2002 John Wiley & Sons, Inc. Int J Imaging Syst Technol 12, 35,42, 2002 [source] Investigation of the ultradrawing properties of gel spun fibers of ultra-high molecular weight polyethylene/carbon nanotube blendsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Jen-Taut Yeh Abstract The carbon nanotubes (CNTs) contents, ultrahigh-molecular-weight polyethylene (UHMWPE) concentrations and temperatures of UHMWPE, and CNTs added gel solutions exhibited significant influence on their rheological and spinning properties and the drawability of the corresponding UHMWPE/CNTs as-prepared fibers. Tremendously high shear viscosities (,s) of UHMWPE gel solutions were found as the temperatures reached 140°C, at which their ,s values approached the maximum. After adding CNTs, the ,s values of UHMWPE/CNTs gel solutions increase significantly and reach a maximum value as the CNTs contents increase up to a specific value. At each spinning temperature, the achievable draw ratios obtained for UHMWPE as-prepared fibers prepared near the optimum concentration are significantly higher than those of UHMWPE as-prepared fibers prepared at other concentrations. After addition of CNTs, the achievable draw ratios of UHMWPE/CNTs as-prepared fibers prepared near the optimum concentration improve consistently and reach a maximum value as their CNTs contents increase up to an optimum value. To understand these interesting drawing properties of the UHMWPE and UHMWPE/CNTs as-prepared fibers, the birefringence, thermal, morphological, and tensile properties of the as-prepared and drawn fibers were investigated. Possible mechanisms accounting for these interesting properties are proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Manufacture of Biomorphic SiC Components with Homogeneous Properties from Sawdust by Reactive Infiltration with Liquid SiliconJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010Noelia R. Calderon Biomorphic SiC components with homogeneous properties were manufactured from sawdust using a novel method to produce preforms, without addition of any extra binder, but with enough mechanical strength to be carbonized up to 1400°C without deformation. Reactive infiltration of carbon preforms of an adequate open porosity with liquid silicon has been successfully used to prepare biomorphic components. Moreover, the modification of bioSiC properties induced by the structural rearrangement of carbon preforms when they are further heat treated at 2500°C was additionally studied. BioSiC components showed a maximum in bending strength when the material is processed from carbon preforms exhibiting around 40% of open porosity, which seems to be the optimum value for carbon preforms treated at 1400° and 2500°C. However, the heat treatment of the carbon preforms at 2500°C produced bioSiC components with a finer and more homogeneous microstructure than those obtained from carbon preforms treated at 1400°C, improving their bending strength up to 22%. [source] Addition of a Sr, K, Nb (SKN) Combination to PZT(53/47) for High Strain ApplicationsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2007Niall J. Donnelly A lead zirconate titanate composition incorporating the dopants Sr, K, and Nb (SKN) in the specific ratio 4:1:3 has been studied. In principle, the SKN should act as a donor dopant but since its addition reduced the grain size from 11.4 ,m (for 1% SKN) to 1.5 ,m (for 5% SKN), the overall effect was found to be more complicated. It was observed that the addition of SKN reduced the Curie temperature, by 16°C/mol (%) and broadened the dielectric peak. X-ray measurements further suggested that the ceramic was a mixture of rhombohedral and tetragonal phases and that the room temperature c/a ratio of the tetragonal phase decreased with SKN addition. The piezoelectric coefficient d33, determined from high field unipolar drives, gave an optimum value of 779 pm/V for the 0.02 SKN compositions, which also exhibited a relatively high Curie temperature of 356°C. Competing effects of enhanced domain wall mobility from donor doping and reduced mobility due to smaller grain size may explain the observed compositional variation in the measured material properties. Materials based on this composition are attractive for high performance piezoelectric actuator applications such as fuel injection. [source] Randomized Stopping Times and American Option Pricing with Transaction CostsMATHEMATICAL FINANCE, Issue 1 2001Prasad Chalasani In a general discrete-time market model with proportional transaction costs, we derive new expectation representations of the range of arbitrage-free prices of an arbitrary American option. The upper bound of this range is called the upper hedging price, and is the smallest initial wealth needed to construct a self-financing portfolio whose value dominates the option payoff at all times. A surprising feature of our upper hedging price representation is that it requires the use of randomized stopping times (Baxter and Chacon 1977), just as ordinary stopping times are needed in the absence of transaction costs. We also represent the upper hedging price as the optimum value of a variety of optimization problems. Additionally, we show a two-player game where at Nash equilibrium the value to both players is the upper hedging price, and one of the players must in general choose a mixture of stopping times. We derive similar representations for the lower hedging price as well. Our results make use of strong duality in linear programming. [source] New routes to sustainable photovoltaics: evaluation of Cu2ZnSnS4 as an alternative absorber materialPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2008Jonathan J. Scragg Abstract Thin film heterojunction solar cells based on chalcopyrites such as Cu(In,Ga)Se2 have achieved impressive efficiencies. However concern about the long term sustainability of photovoltaics based on scarce or expensive raw materials has prompted the search for alternative absorber materials. In this work, films of the p-type absorber Cu2ZnSnS4 (CZTS) were prepared by electroplating metallic precursors sequentially onto a molybdenum-coated glass substrate followed by an nealing in a sulfur atmosphere. The polycrystalline CZTS films were characterized by photoelectrochemical methods, which showed films were p-type with doping densities of the order of 1016 cm,3 and a band gap of 1.49 eV, close to the optimum value for terrestrial solar energy conversion. Preliminary results obtained for solar cells fabricated with this material are promising. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] E-beam pumped resonant periodic gain GaInP/AlGaInP VCSELPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2005V. Yu. Abstract 25-period Ga0.5In0.5P/(Al0.7Ga0.3)0.5In0.5P quantum well structure was grown by MOVPE on GaAs substrates misoriented by 100 from (001) to (111)A and fabricated into a microcavities with dielectric oxide mirrors. The structure period and mirror design were chosen to provide resonant periodic gain. A non-uniformity of 5% in the total structure thickness across the 2 inch wafer was used for studying laser characteristics depending on mismatching structure period from resonance condition. The laser wavelength, threshold and output power was found to depend critically on the alignment of QW period with both the cavity and the MQW gain spectrum. Lasing in the 625,650 nm spectral range with output power up to 9 W (0.45 MW/cm2) was achieved under scanning electron beam longitudinal pumping at room temperature. The minimum threshold current density for a 40 keV electron energy was 8 A/cm2 (0.32 MW/cm2). In order to control the lasing threshold to within 10 % of its minimum, the MQW period should be tuned to the optimum value with an accuracy of about 1 %. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Multiobjective optimization of polymerization reaction of vinyl acetate by genetic algorithm technique with a new replacement criterionPOLYMER ENGINEERING & SCIENCE, Issue 5 2008Maryam Sadi A multiobjective optimization procedure based on genetic algorithm has been developed to determine optimum operational conditions of polymerization reaction. In this article by using a new selection criterion to choose the next generation members with better quality, optimization efficiency is improved and the number of generations to obtain Pareto optimal set reduced. In this proposed method a novel replacement criterion based on ranking level information and proximity of solutions to the Pareto optimal front is used to choose the next generation members. The polymerization of vinyl acetate has been chosen as an example. Two objective functions, which used in this study, are maximization of the weight average molecular weight up to the desired value and minimization of the residual initiator concentration. A Pareto optimal set of objective functions has been obtained by application of a Pareto set filter operator. Furthermore, the influence of genetic algorithm parameters on the efficiency and convergence of genetic algorithm is studied by changing cross over and mutation probabilities. Because of the flexibility and generality of genetic algorithm, this optimization method is a useful technique with lots of potentials in determination of optimum value of operation parameters. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Relationship between segment structures and elastic properties of segmented poly(urethane-urea) elastic fibersPOLYMER ENGINEERING & SCIENCE, Issue 11 2003Nori Yoshihara Studies on segmented poly(urethane-urea) (SPUU) elastic fibers having various segment structures were done in terms of elastic recovery and stress-strain relationship (S-S). Three kinds of segment structures were used: 1) the same composition having different sequences of segment units, 2) the same length of soft segments having different molecular weights of polyol, and 3) different segment structures having almost the same stress at 350% elongation. The SPUU elastic fibers having higher sequence numbers of both soft and hard segment units, that is, greater block structures, show better elastic recovery properties, especially delayed elastic recovery. The SPUU elastic fibers showing better elastic recovery take an optimum value for the number-average molecular weight (Mn) of soft segments jointed with urethane bonds. Here the optimum Mn depends on the molecular weight of polytetramethyleneglycol (PTMG) as a starting material. The hysteresis loss in S-S for the pre-elongation decreases with an increase of Mn of PTMG. The SPUU elastic fibers having greater block structures show lower stress with lower 2C1 and 2C1 + 2C2 of Mooney-Rivilin plot constants for elastic fibers having the same composition. This indicates a lower density of crosslinks for finite deformation. An increase of the urea bonds or the molar ratio of urea bond to urethane bond raises the stress. It is found that the polymerization process, as well as composition, is important for design structures of SPUU elastic fibers. [source] Determination and Kinetics of Producing Glucosamine Using FungiBIOTECHNOLOGY PROGRESS, Issue 5 2007Jui-Wei Hsieh This work used three fungi, Rhizopus oligosorus BCRC 31996, Monascus pilosus BCRC31527, and Aspergillussp. BCRC31742, to produce glucosamine by using submerged fermentation and flask cultures. The reaction of glucosamine with 1-naphthyl isothiocyanate as derivatizing agent was carried out in pyridine at 50 °C for 1 h. The derivative was accurately analyzed and quantified by using high performance liquid chromatography. The relative standard deviation of glucosamine determined between experimental and real values were less than 2%. The kinetic and strategy of producing glucosamine in a flask culture was investigated to achieve an optimum yield of glucosamine under different conditions including three kinds of fungi, medium, and pH values. The descending ability of producing glucosamine for the three fungi was Aspergillus sp. BCRC31742 > Monascus pilosus BCRC31527 > Rhizopus oligosorus BCRC 31996 under the conditions studied. The experimental result shows that the glucosamine concentration had an optimum value and was 3430 mg/L by using Aspergillus sp. BCRC31742 culture in glucose and peptone (GP) medium, the yield of which was the best amount using wild-type microorganisms in the past. The generation culture of fungi and the pH control played important roles in enhancing the yield of glucosamine. The specific growth rate of the microorganism and the biomass, content, yield, and productivity of glucosamine were calculated as well. [source] Upper and lower bounds in limit analysis: Adaptive meshing strategies and discontinuous loadingINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2009J. J. Muñoz Abstract Upper and lower bounds of the collapse load factor are here obtained as the optimum values of two discrete constrained optimization problems. The membership constraints for Von Mises and Mohr,Coulomb plasticity criteria are written as a set of quadratic constraints, which permits one to solve the optimization problem using specific algorithms for Second-Order Conic Program (SOCP). From the stress field at the lower bound and the velocities at the upper bound, we construct a novel error estimate based on elemental and edge contributions to the bound gap. These contributions are employed in an adaptive remeshing strategy that is able to reproduce fan-type mesh patterns around points with discontinuous surface loading. The solution of this type of problems is analysed in detail, and from this study some additional meshing strategies are also described. We particularise the resulting formulation and strategies to two-dimensional problems in plane strain and we demonstrate the effectiveness of the method with a set of numerical examples extracted from the literature. Copyright © 2008 John Wiley & Sons, Ltd. [source] A posteriori error approximation in EFG methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 15 2003L. Gavete Abstract Recently, considerable effort has been devoted to the development of the so-called meshless methods. Meshless methods still require considerable improvement before they equal the prominence of finite elements in computer science and engineering. One of the paths in the evolution of meshless methods has been the development of the element free Galerkin (EFG) method. In the EFG method, it is obviously important that the ,a posteriori error' should be approximated. An ,a posteriori error' approximation based on the moving least-squares method is proposed, using the solution, computed from the EFG method. The error approximation procedure proposed in this paper is simple to construct and requires, at most, nearest neighbour information from the EFG solution. The formulation is based on employing different moving least-squares approximations. Different selection strategies of the moving least-squares approximations have been used and compared, to obtain optimum values of the parameters involved in the approximation of the error. The performance of the developed approximation of the error is illustrated by analysing different examples for two-dimensional (2D) potential and elasticity problems, using regular and irregular clouds of points. The implemented procedure of error approximation allows the global energy norm error to be estimated and also provides a good evaluation of local errors. Copyright © 2003 John Wiley & Sons, Ltd. [source] Erlang capacity analysis of hybrid FDMA/CDMA systems supporting multi-class services according to channel assignment methodsINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 10 2002Insoo Koo Abstract In this paper, we focus on the evaluation of the Erlang capacity for hybrid FDMA/CDMA systems supporting multi-class services with two channel allocation schemes: independent carrier channel assignment (ICCA) and combined carrier channel assignment (CCCA). For the performance analysis, a multi-dimensional Markov chain model is developed. The effect of the number of carriers of hybrid FDMA/CDMA system on the Erlang capacity is observed, and the optimum values of the system parameters such as the number of channel elements (CEs) and the number of carriers are selected with respect to the Erlang capacity. As a numerical example, we consider an FDMA/CDMA system supporting voice/data services. We find out that, even though the benefit of CCCA scheme over ICCA scheme is negligible for small number of CEs, the scenario changes significantly when the number of CEs increases beyond a certain point. An improvement of as much as 74% can be achieved in the Erlang capacity when 5 carriers are employed. We also find the capacity knees for different number of carriers. The results of this paper could be helpful in the traffic engineering of FDMA/CDMA systems providing multi-class services. Copyright © 2002 John Wiley & Sons, Ltd. [source] Theoretical analysis of LiBr/H2O absorption refrigeration systemsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2009Akhilesh Arora Abstract A computational model is developed for the parametric investigation of single-effect and series flow double-effect LiBr/H2O absorption refrigeration systems. The effects of generator, absorber, condenser, evaporator and dead state temperatures are examined on the performance of these systems. The parameters computed are coefficient of performance (COP), exergy destruction rates, thermal exergy loss rates, irreversibility and exergetic efficiency. The results indicate that COP and exergetic efficiency of both the systems increase with increase in the generator temperature. There exist different optimum values of generator temperature for maximum COP and maximum exergetic efficiency. The optimum generator temperature is lower corresponding to maximum exergetic efficiency as compared to optimum generator temperature corresponding to maximum COP. The effect of increase in absorber, condenser and evaporator temperatures is to decrease the exergetic efficiency of both the systems. The irreversibility is highest in absorber in both systems. Copyright © 2009 John Wiley & Sons, Ltd. [source] Performance improvement of the vapour compression refrigeration cycle by a two-phase constant area ejectorINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2009Nagihan Bilir Abstract The performance of a vapour compression system that uses an ejector as an expansion device was investigated. In the analysis, a two-phase constant area ejector flow model was used. R134a was selected as the refrigerant. According to the obtained results, for any operating temperature there are different optimum values of pressure drop in the suction chamber, ejector area ratio, ejector outlet pressure and cooling coefficient of performance (COP). As the difference between condenser and evaporator temperatures increases, the improvement ratio in COP rises whereas ejector area ratio drops. The minimum COP improvement ratio in the investigated field was 10.1%, while its maximum was 22.34%. Even in the case of an off-design operation, the performance of a system with ejector is higher than that of the basic system. Copyright © 2008 John Wiley & Sons, Ltd. [source] Optimum matching parameters of an MPPT unit used for a PVG-powered water pumping system for maximum power transferINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2006Mehmet Akbaba Abstract Photovoltaic generator (PVG)-powered water pumping has the potential to bring potable water to millions of people in developing countries. However, due to the high initial cost of PVG units, sophisticated load matching is required between the water pumping system and PVG, in order to be able to extract maximum available power from an available PVG unit at all solar radiation levels. This requires an intermediate circuitry between the PVG unit and the motor driving the water pump, which is usually termed as maximum power point trackers (MPPT). This present paper therefore investigates the optimum matching parameters of a power conditioning circuit, which is composed of a double step-up dc,dc converter (DSUC). This MPTT circuit is used for interfacing a permanent magnet (PM) motor-driven water pumping system to a PVG for extracting maximum available power from PVG, hence maximizing the energy utilization efficiency and price,performance ratio of the whole system. It is shown that two key parameters of the DSUC, which are the duty cycle and chopping frequency, are dominating the performance of the whole system, and they are interrelated and load dependent. Therefore, optimum values of these parameters need to be determined. An example system is provided in which a complete modelling is presented in time domain and through numerical experiments it is demonstrated how the optimum values of these two key matching parameters can be determined for a given system. The MPPT circuit used in this investigation is suitable for optimum matching of all types of loads to PVG units, provided that an optimum frequency,duty cycle pair is determined for the choppers in DSUC for every 5% bands of solar radiation between 20 and 100%. Copyright © 2005 John Wiley & Sons, Ltd. [source] Evaluation of SnB for the location of anomalous scattering atoms in SAD/MAD phasingJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2003Jun Wang Sixteen existing single-wavelength/multi-wavelength anomalous diffraction (SAD/MAD) data sets with a broad range of crystallographic properties have been used to investigate the various parameters in SnB with the goal of finding the optimum values for locating the positions of anomalous scatterers. The results of the analysis indicate some changes in default parameters that may be useful for non-routine and difficult cases. [source] Response surface methodology to optimize the nutritional parameters for enhanced production of jasmonic acid by Lasiodiplodia theobromaeJOURNAL OF APPLIED MICROBIOLOGY, Issue 3 2008P.C. Dhandhukia Abstract Aims:, To find out the cumulative effect of the nutritional parameters and to enhance the production of jasmonic acid (JA) in static fermentation by Lasiodiplodia theobromae using response surface methodology (RSM). Method and Results:, Malt extract, sucrose, NaNO3 and MgSO4.7H2O were analysed by a 30-trial central composite design using RSM for optimizing their concentrations in the medium and the effect of their mutual interaction on JA production. Sucrose and NaNO3 were found highly significant in influencing the JA production. Malt extract and MgSO4.7H2O showed an effect on the JA production in interaction with other variables. When the optimum values of the parameters obtained through RSM (19·95 g l,1 malt extract, 50 g l,1 sucrose, 7·5 g l,1 NaNO3 and 3·51 g l,1 MgSO4.7H2O) were applied, 32% increase in JA production (299 mg l,1) was observed in comparison with 225 mg l,1 of JA produced with same media components not analysed by RSM and subsequently validated the statistical model. Conclusions:, Increase in JA production was achieved by optimizing the nutritional parameters. Significance and Impact of the Study:, This is the first report of using RSM for optimizing a medium for JA production. It resulted in an increase in JA production without augmentation of costly additives. [source] Separation and characterization of the 1,3-propanediol and glycerol dehydrogenase activities from Clostridium butyricum E5 wild-type and mutant DJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2001H. Malaoui H. MALAOUI AND R. MARCZAK. 2001. Aims:,Clostridium butyricum E5 wild-type and mutant E5-MD were cultivated in chemostat culture on glycerol in order to compare the properties of two key enzymes of glycerol catabolism, i.e. propanediol and glycerol dehydrogenase. Methods and Results:,These two enzymes, which belong to the dha regulon, were separated by gel filtration. Both dehydrogenase activities displayed similar properties, such as pH optimum values, specificity towards physiological substrates and dependence on Mn2+. Both strains accumulate glycerol at high levels. Conclusion:,The mutant D strain contained a propanediol dehydrogenase activity which had a low affinity for its physiological substrate, leading to the conclusion that this strain would seem more resistant to the toxic effect of 3-hydroxypropionaldehyde than the wild-type. Significance and Impacts of the study: These properties make Cl. butyricum mutant D strain the best candidate so far to be used as a biotechnological agent for the bioconversion of glycerol to 1,3-propanediol. [source] Optimum design of cyclone separatorAICHE JOURNAL, Issue 9 2009Prabhata K. Swamee Abstract Cyclone separators are one of the most widely used gas-solid separators. Although the optimal design of cyclone separators has been suggested earlier, the earlier works do not include all the critical parameters responsible for minimizing the pressure drop which is quite decisive to obtain a correct optimal design. In this article, the optimal design of the cyclone separator has been formulated as a geometric programming with a single degree of difficulty. The solution of the problem yields the optimum values of the number of cyclones to be used in parallel, and the inside diameter of cyclone shell and exit pipe, when a specified flow rate of gas is to be separated from solid particles, when the cut diameter is already specified. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Controlling particle size during anatase precipitationAICHE JOURNAL, Issue 9 2001Sekhar Sathyamoorthy Titanium dioxide particles in the form of anatase are precipitated from concentrated titanyl sulfate solution in the sulfate process, which are then recovered by a filtration process downstream of the precipitation stage. A previous study by Sathyamoorthy et al. showed that the final anatase particles are aggregates (1-2 ,m) consisting of numerous crystals (7,8 nm) arranged in primary agglomerates (60,100 nm). Pigment quality is determined by crystal and primary agglomerate size. One way of improving filtration rate is by the formation of larger aggregates, while maintaining the crystal and primary agglomerate size at optimum values. In a new seeding procedure proposed, the controlled inoculation of seeds used in industry is combined with a new type of seed (Large Seeds). The new seeding procedure has the potential to increase downstream filtration efficiency by increasing aggregate size, while maintaining crystal and primary agglomerate sizes close to the values correctly obtained in industry. High yield in the precipitation process is also maintained. [source] A new approach for controlling birefringent property of cyclic olefin copolymersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2008Hoang The Ban Abstract This article reports an original method to control the birefringent property of the cyclic olefin copolymer, which has been recently commercialized as a new type of optical resins, via introduction of a third monomer that possesses a negative birefringence into the cyclic olefin copolymer that exhibits an inherently positive birefringence. The mutual compensation between these opposite-sign birefringences effectively reduced the birefringent magnitude of the corresponding terpolymer. In fact, terpolymerization of norbornene (N), ethylene (E), and styrene (S), in which S exhibits a negative birefringence regarding to the positive birefringence of the NE copolymer was successfully prepared using fluorenylamidodimethyltitanium-based catalyst, yielding NES terpolymers with controllable birefringent property. Especially, when the S content in the NES terpolymer was controlled at optimum values, it is possible to synthesize a new type of the cyclic olefin copolymer that exhibits an extremely low birefringent magnitude close to zero regardless of high degrees of chain orientation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7395,7400, 2008 [source] Mechanical flower thinning improves the fruit quality of applesJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 5 2010Alexey A Solomakhin Abstract BACKGROUND: Apple ,Golden Delicious Reinders' and ,Gala Mondial' trees were mechanically blossom-thinned with 30,77 × g (300,480 rpm rotation) and 5 or 7.5 km h,1 vehicle speed to improve fruit quality, minimise leaf damage, reduce hand and chemical thinning and to prevent or overcome alternate bearing; adjacent untreated or manually thinned apple trees served as controls. RESULTS: Mechanical thinning (43 × g, 360 rpm, 5,7.5 km h,1) had a positive effect on fruit size (15% larger), firmness (8.4 in Gala vs. 7.6 kg cm,2 in the unthinned control), sweetness (124 vs. 117 g kg,1 sugar in the control), contained the largest malic acid content (4 g kg,1 vs. 3.4 g kg,1 in the control) and 17% more anthocyanin (normalised anthocyanin index = 0.8 in Gala vs. 0.7 in the control); fruit of Golden and Gala showed additionally advanced starch breakdown and ripened earlier. CONCLUSIONS: Since increases in rotor speed, viz. centrifugal force, versus increases in the vehicle speed resulted in opposing effects, an integrated coefficient of thinning (ICT) was devised with optimum values of 10,40 (at 43 × g, 5,7.5 km h,1), where an ICT > 50 led to tree damage and ICT < 8 led to sub-optimum thinning efficacy. Copyright © 2010 Society of Chemical Industry [source] Photosynthetic Acclimation to Simultaneous and Interacting Environmental Stresses Along Natural Light Gradients: Optimality and ConstraintsPLANT BIOLOGY, Issue 3 2004ü. Niinemets Abstract: There is a strong natural light gradient from the top to the bottom in plant canopies and along gap-understorey continua. Leaf structure and photosynthetic capacities change close to proportionally along these gradients, leading to maximisation of whole canopy photosynthesis. However, other environmental factors also vary within the light gradients in a correlative manner. Specifically, the leaves exposed to higher irradiance suffer from more severe heat, water, and photoinhibition stresses. Research in tree canopies and across gap-understorey gradients demonstrates that plants have a large potential to acclimate to interacting environmental limitations. The optimum temperature for photosynthetic electron transport increases with increasing growth irradiance in the canopy, improving the resistance of photosynthetic apparatus to heat stress. Stomatal constraints on photosynthesis are also larger at higher irradiance because the leaves at greater evaporative demands regulate water use more efficiently. Furthermore, upper canopy leaves are more rigid and have lower leaf osmotic potentials to improve water extraction from drying soil. The current review highlights that such an array of complex interactions significantly modifies the potential and realized whole canopy photosynthetic productivity, but also that the interactive effects cannot be simply predicted as composites of additive partial environmental stresses. We hypothesize that plant photosynthetic capacities deviate from the theoretical optimum values because of the interacting stresses in plant canopies and evolutionary trade-offs between leaf- and canopy-level plastic adjustments in light capture and use. [source] A comparative study of vacuum-assisted resin transfer molding (VARTM) for sandwich panelsPOLYMER COMPOSITES, Issue 6 2003J. Dai Vacuum-assisted resin transfer molding (VARTM) of sandwich panels can be facilitated by using high permeability layers (HPL) over the skins or adding channels in the surfaces of the core (CIC). The present paper investigates the advantages and disadvantages of both methods in terms of manufacturing cost and time through simulations and experimental observations. A cost model is developed, and the resin infusion time for each method was minimized through simulations. The design parameters are the number of high-permeability layers and the number and size of channels. A penalty function with equal weight on cost and time is used to find the optimum values of the design parameters. Under the conditions studied, the optimal HPL method is found to be better than the optimal CIC method. While the conclusion is limited to the present study, the proposed approach can be used to optimize manufacturing processes for larger sandwich panels under different conditions. [source] Design of Metabolic Engineering Strategies for Maximizing l -(,)-Carnitine Production by Escherichia coli.BIOTECHNOLOGY PROGRESS, Issue 2 2005Bioreactor Levels, Integration of the Metabolic In this work metabolic engineering strategies for maximizing l -(,)-carnitine production by Escherichia coli based on the Biochemical System Theory (1,3) and the Indirect Optimization Method are presented (4). The model integrates the metabolic and the bioreactor levels using power-law formalism. Based on the S-system model, the Indirect Optimization Method was applied, leading to profiles of parameter values that are compatible with both the physiology of the cells and the bioreactor system operating conditions. This guarantees their viability and fitness and yields higher rates of l -(,)-carnitine production. Experimental results using a high cell density reactor were compared with optimized predictions from the Indirect Optimization Method. When two parameters (the dilution rate and the initial crotonobetaine concentration) were directly changed in the real experimental system to the prescribed optimum values, the system showed better performance in l -(,)-carnitine production (74% increase in production rate), in close agreement with the modelapos;s predictions. The model shows control points at macroscopic (reactor operation) and microscopic (molecular) levels where conversion and productivity can be increased. In accordance with the optimized solution, the next logical step to improve the l -(,)-carnitine production rate will involve metabolic engineering of the E. coli strain by overexpressing the carnitine transferase, CaiB, activity and the protein carrier, CaiT, responsible for substrate and product transport in and out of the cell. By this means it is predicted production may be enhanced by up to three times the original value. [source] Catalytic Liquid Phase Oxidation of Toluene to Benzoic AcidCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 3 2008A. Gizli Abstract The production of benzoic acid from toluene in the liquid phase with pure oxygen was studied. Investigations have been carried out with a view to determining the most suitable reaction conditions with respect to operating variables including oxygen flow rate, reaction temperature, batch time and catalyst loading. In a series of batch experiments carried out at 4,atm, the optimum values of mole ratio of oxygen to toluene, temperature, reaction time, and catalyst loading were found to be 2, 157,°C, 2,h and 0.57,g/L, respectively. In addition, a kinetic study was carried out by taking into consideration the optimum reaction conditions. The model dependent on the formation of benzyl radical was found to be feasible for describing the catalytic oxidation of toluene to benzoic acid in the liquid phase. The activation energy was determined as 40,kJ/mol. [source] | |||||||||||||||||||||||||