Near-optimum Values Research Articles

Optimization of Solvent Extraction of Lipids from Yarrowia lipolytica towards Industrial Applications

Extraction of intracellular lipids of the oleaginous yeast Yarrowia lipolytica has been systematically studied aiming towards a sustainable extraction process for lipid recovery. Selection of suitable industrial (bulk) solvents and extraction parameters that lead to maximization of lipid recovery are significant issues to be addressed, with industrial applications motivating this study. Biomass from fermentation of Yarrowia lipolytica (MUCL 28849) was used in small laboratory tests to assess different solvent mixtures (i.e., methanol/hexane, isopropanol/hexane, and methanol/ethyl acetate), implementing a systematic design of experiments methodology to identify near-optimum values of key extraction variables (i.e., polar/non-polar ratio, vortex time, dry biomass/solvent ratio) in regard to lipid yield (g lipids/g dry biomass). The methanol/hexane mixture exhibited the highest extraction yield in a wide range of experimental conditions, resulting in the following optimum parameters: polar/non-polar ratio 3/5, vortex time 0.75 h, and dry biomass/solvent ratio 40. Extraction tests on a fifty-times-larger scale (in a Soxhlet apparatus employing the optimal extraction parameters) confirmed the optimization outcome by obtaining up to 27.6% lipids per dry biomass (L/DB), compared to 12.1% L/DB with the reference lipid extraction method employing chloroform/methanol. Assessment of lipid composition showed that unsaturated fatty acid recovery was favored by the methanol/hexane solvent. Fatty acid composition was not affected by the increase in Soxhlet reflux cycles, whilst the lipid yield was notably favored.

Low temperature assisted phase transitions in thermally evaporated Cu2Se/Ga3Se2/In3Se2 multilayer thin film structure: Raman signatures of a pristine chalcopyrite CuInxGa1-xSe2 structure

Copper Indium Gallium Selenide (CIGS) thin film solar cell absorber layers are fabricated by the conventional co-evaporation of metal stack precursors followed by a selenization process at a high-temperature range. The article deals with an alternative approach to fabricate the CIGS layer by sequential evaporation of metal selenides followed by a low-temperature treatment (250 °C) during pre-and post-deposition processes. Our post annealing treatment on substrate heat treated film reported a first-ever pristine CuIn0.7Ga0.3Se2 thin film structure without selenization was reported at a very low temperature. A better microstructure with an enhanced grain growth, preferential (112) plane orientation, and Raman signatures of pristine chalcopyrite without a secondary Cu2-xSe phase at the surface was observed. Electron microscopy studies affirm the polycrystalline nature of film structure. Optical analyses have shown near-optimum values as of standard absorber layers. Crucial optical parameters such as refractive index, static and high-frequency dielectric constants were estimated by different relations. The values are concurrent with the semiconductor scale. These features in a low-temperature range optimistically land them as promising candidates in flexible electronics.

Tartaric acid recovery from winery lees using cation exchange resin: Optimization by Response Surface Methodology

Abstract A crucial first step in developing a novel cost-effective and environment-friendly process for recovering tartaric acid and bioactive polyphenolic compounds from wine lees involves tartrates dissolution by mild means, aiming to maximize tartaric acid recovery, while minimizing the concentration of undesirable potassium. Such a processing step, using cation exchange resin, has been systematically assessed to obtain a set of near-optimum values of the key variables (i.e. pH, water dosage and cation exchange resin dosage). An experimental design was carried out based on Central Composite Design (CCD) with Response Surface Methodology (RSM) to evaluate the effects of process parameters and their interaction towards the attainment of optimum conditions. All three variables considered were found to be significant; however, the most influential factor for maximum tartaric acid concentration was the volume of added water, whereas for potassium removal the cation exchange resin dosage. A quadratic model was developed that fitted well to the experimental data confirmed by the high R 2 values, greater than 0.98. A set of optimum values of the three main variables was determined to be pH = 3.0, water dosage 10 ml/g dry lees and resin dosage 3.5 g/g dry lees. Under these optimum conditions, the predicted tartaric acid and potassium concentration were 43,143 ppm and 178 ppm, respectively, which correspond to 74.9% tartaric acid recovery and 98.8% potassium removal. Furthermore, the corresponding experimental values, from the validation experiment, fitted well to these predictions. This work clearly shows that the recovery of tartaric acid from wine lees can be achieved using cation exchange resin, under mild conditions (ambient temperature) avoiding the waste calcium sulfate sludge of the conventional process.

Fuzzy transfer point location problem: a possibilistic unconstrained nonlinear programming approach

Recently, the transfer point location problem with weighted demand points and uniformly distributed coordinates has been introduced. In the real world problems, such as disaster situations, different points of an area might be demand point locations with different possibility degrees. So, it is necessary to develop more applicable models for these kinds of problems. In this paper, a new transfer point location problem with weighted demand points and fuzzy coordinates is developed. The proposed model is formulated as a fuzzy unconstrained nonlinear programming in which decision variables are obtained as fuzzy numbers. Due to the complexity of the developed model, a new fuzzy logic controller is designed based on the derived fuzzy decision variables to infer the optimum or near-optimum values for decision variables. Finally, a numerical example is presented and its results are compared with the optimum solutions of the problem in order to illustrate the efficiency of the proposed model.

Optimization of Fuel Cost and Emissions Using V2V Communications

Vehicular communication networks are increasingly being considered as a means to conserve fuel and reduce emissions within transportation systems. This paper focuses on using traffic light signals to communicate with approaching vehicles. The communication can be traffic-light-signal-to-vehicle (TLS2V) and vehicle-to-vehicle (V2V). Based on the information sent, the vehicle receiving the message adapts its speed to a recommended speed (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> ), which helps the vehicle reduce fuel consumption and emissions. The key contribution of this paper is the proposal of a comprehensive optimization model that involves V2V and TLS2V communications. The objective function is to minimize fuel consumption by and emissions from vehicles. The speed that can achieve this goal is the optimum S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> *). We also propose efficient heuristic expressions to compute the optimum or near-optimum value of S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> .

셀렌화 공정을 제외한 RF 마그네트론 스퍼터링으로 제작된 Cu(In,Ga)Se2박막의 구조 및 전기적 특성

A one-step route was developed to fabricate <TEX>$Cu(In,Ga)Se_2$</TEX> (CIGS) thin films by radio frequency (RF) magnetron sputtering from a single quaternary <TEX>$CuIn_{0.75}Ga_{0.25}Se_2$</TEX> target. The effects of the substrate temperatures on the structural and electrical properties of the CIGS layers were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and Hall effect measurements. All the deposited films showed a preferential orientation along the (112) direction. The films deposited at <TEX>$300^{\circ}C$</TEX> and <TEX>$400^{\circ}C$</TEX> revealed that chalcopyrite main (112) peak and weak prominent peaks of (220)/(204) and (312)/(116), indicating polycrystalline structures. The element ratio of the deposited film at <TEX>$300^{\circ}C$</TEX> were almost the same as the near-optimum value. The carrier concentration of the films decreased with increasing substrate temperatures.

Semiconductor parameter extraction using cathodoluminescence and genetic algorithms

This paper presents a novel approach for the extraction of five semiconductor-related parameters, that is, the absorption coefficient α, diffusion length L, normalized surface recombination velocity S, dead layer thickness Zt and the relative quantum efficiency Q directly from any theoretical/experimental steady state cathodoluminescence (CL) signal. The extraction technique, based on genetic algorithms (GA), has many advantages such as the simultaneous obtainment of near-optimum values for the five parameters ( α, L, S, Zt, Q). Simulation results for an n-type GaAs defect free semi-infinite semiconductor sample show that the proposed approach is successful and a set of parameter values with error less than 12% from the nominal values, in 95% of the cases, can be obtained.

Manufacturing performance optimization: The simulation—expert mechanism approach

This paper presents an expert mechanism approach to manufacturing performance optimization using simulation as the base tool. The expert mechanism is integrated to the back end of a manufacturing simulator to interpret manufacturing simulation results, assess performance, and then, consistent with set constraints, to effect changes on controllable variables prior to the next run to improve performance. The expert mechanism has a knowledge base that includes proven operations management performance-enhancing methods. In contrast, existing commercial simulation-optimization methods use meta-heuristics in which a near-optimum value is searched from a population of alternative solutions, which can be inefficient in terms of time and cost. The findings of a real case study from a world-class manufacturing company are discussed to demonstrate the expert mechanism and compare it with one of the widely used commercial simulation optimizers.

Mitigation of the effects of self phase modulation and group-velocity dispersion in fiber optic communications: dispersion- and power-map cooptimization using the genetic algorithm

We show that co-optimization of dispersion and power maps in long-haul fiber optic communications can significantly mitigate the effects of group-velocity dispersion (GVD) and self phase modulation (SPM). A genetic algorithm is used for arriving at the optimal (or a near-optimal) link design in reasonable time, since exhaustive search is almost impossible for this intractable problem. Design of a 20-span×80 km/span link that can recover an input Gaussian pulse almost in its original form is presented. This design provides near-optimum values of the required net dispersion, dispersion map, and power map to mitigate the effects of SPM and GVD

Whey protein fouling of large pore-size ceramic microfiltration membranes at small cross-flow velocity

Microfiltration of whey protein solutions by tubular ceramic membranes, under constant cross-flow and trans-membrane pressure, with periodic backwashing, is investigated using a fully instrumented pilot unit. Relatively large nominal membrane pore size (0.8 μm) insures very high protein transmission, which is desirable in applications such as microbial load reduction. In the first of a sequence of three filtration-backwashing cycles, irreversible and reversible fouling are identified, over the tested pressure range of 5–17.5 psi. Early in the first cycle, especially at the higher pressures, a pore constriction/blocking mechanism appears to be responsible for the irreversible fouling. In the other two cycles only the reversible fouling is significant, possibly due to some kind of protein layer formation on the membrane surface. The permeate flux level tends to increase by increasing trans-membrane pressure up to a near-optimum value of 10 psi, beyond which pressure has a negative effect. This interesting trend is attributed to the interplay of cross-flow velocity, which tends to reduce fouling by promoting re-suspension and breakage of colloidal protein agglomerates, with the trans-membrane pressure (and related flux) which leads to protein layer formation on the membrane and may impose compressive stresses, thereby increasing its resistance to permeation.

Transport energy modeling with meta-heuristic harmony search algorithm, an application to Turkey

This study proposes a new method for estimating transport energy demand using a harmony search (HS) approach. HArmony Search Transport Energy Demand Estimation (HASTEDE) models are developedtaking population, gross domestic product and vehicle kilometers as an input. The HASTEDE models are in forms of linear, exponential and quadratic mathematical expressions and they are applied to Turkish Transportation sector energy consumption. Optimum or near-optimum values of the HS parameters are obtained with sensitivity analysis (SA). Performance of all models is compared with the Ministry of Energy and Natural Resources (MENR) projections. Results showed that HS algorithm may be used for energy modeling, but SA is required to obtain best values of the HS parameters. The quadratic form of HASTEDE will overestimate transport sector energy consumption by about 26% and linear and exponential forms underestimate by about 21% when they are compared with the MENR projections. This may happen due to the modeling procedure and selected parameters for models, but determining the upper and lower values of transportation sector energy consumption will provide a framework and flexibility for setting up energy policies.

Using simulation for the design of semi-autonomous vehicle systems

The paper describes the development of Semi-Autonomous Vehicles (SAVS) in the context of Automated Guided Vehicle Systems (AGVS). During the design process of a complete material handling AGV-system many variables must be decided. A two-stage simulation approach of discrete event simulation and continuous path simulation, improves development and testing of SAVS. Decisions need to be made e. g. what main navigation sensor to use, how many vehicles are needed for the task. The interrelation of these parameters makes it difficult to find optimum or near-optimum values. Because of this, simulation is a very useful tool to design and evaluate AGV-systems.

Efficient electric-discharge CO2 laser with a prepulse formed by a generator with an inductive energy storage device

Results are presented of experimental investigations of a CO2 laser pumped by a self-sustained discharge from a generator with an inductive energy storage device and a semiconductor current chopper. It is shown that the energy stored in the inductance of the discharge circuit can form a prepulse capable of depositing most of the energy in the active mixture for nearoptimum values of the parameter E/p. A radiation energy of 3 J was achieved in an electricdischarge laser with a 0.181 liter active volume with a 17% efficiency relative to the energy stored in the capacitive storage device.

Optimal and suboptimal binary inputs for system identification

A heuristic random search technique for finding a near-optimum binary input sequence to a linear dynamical system is presented. The problem requires the optimization of a multimodal real function that depends on a string of binary integers. The algorithms combine a global random search procedure with a local (neighborhood) search which examines all sequences within a prescribed Hamming distance. The algorithm is applied to the determination of the sequence of air and oxygen breaths that are optimal for estimating lung parameter values. Simulation studies show that the algorithm finds an optimum input sequence 10 bits in length in 100% of the trials, and 20 bits in length in 97% of the trials. Near-optimum values are also located with strings 30 and 40 bits in length using approximately 1000 iterations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Friction and Wear of Thin, Sintered, Fluoride Films

Results are presented for the bonding of thin, sintered, fluoride films of BaF2 and CaF2 with mono-aluminum phosphate. Friction and wear behavior of these films has been defined in terms of film compositional changes, film curing procedures, and substrate variations when subjected to varying levels of temperature and load. Mono-aluminum phosphate was found to greatly enhance the adhesion of the sintered fluoride film. There was a strong dependence of wear life at 1000 deg F on the mono-aluminum phosphate content of the film. Films containing 6 vol. percent phosphate appear to be near optimum and exhibited wear lives of 1,000,000 load cycles under sliding conditions in a dual rub-shoe device with friction coefficient levels in the order of 0.10 to 0.20. Near-optimum values were determined for cure temperature (950 deg C), and surface finish (23 μ in. rms) on rhodium-plated substrates. Graphite and gold were added to the aluminum phosphate bonded BaF2: CaF2 films. Both additives were found to lower the friction coefficient at room temperature.

Analytically Derived Unit Graph and Runoff

A technique has been programed to solve analytically for measures of precipitation excess and unit graph shape parameters. The optimization procedures achieved a very high degree of adjustment of the model to data, but the results were inconsistent. The paper describes the development of an objective fitting technique. A two-step fitting procedure was devised which substantially increased the objectivity of the fitting technique. The two shape parameters were first individually corrected by a univariate technique to near-optimum values. This reduced the effect of the higher-order partial derivatives with respect to the shape parameters. The simultaneous differential correction technique was then used to obtain corrections for both the shape parameters and the runoff parameters. While this two-step solution technique does not quite yield exact results, they are close enough to the desired values and can be obtained consistently from different starting points.