Augmented D-optimal design for effective response surface modeling and optimization

For effective response surface modeling during sequential approximate optimization (SAO), thenormalized and the augmented D-optimality criteria are presented. Thenormalized D-optimality criterion uses the normalized Fisher information matrix by its diagonal terms in order to obtain a balance among the linear-order and higher-order terms. Then, it is augmented to directly include other experimental designs or the pre-sampled designs. This augmentation enables the trust region managed sequential approximate optimization to directly use the pre-sampled designs in the overlapped trust regions in constructing the new response surface models. In order to show the effectiveness of the normalized and theaugmented D-optimality criteria, following two comparisons are performed. First, the information surface of thenormalized D-optimal design is compared with those of the original D-optimal design. Second, a trust-region managed sequential approximate optimizer having three D-optimal designs is developed and three design problems are solved. These comparisons show that thenormalized D-optimal design gives more rotatable designs than the original D-optimal design, and theaugmented D-optimal design can reduce the number of analyses by 30 % –40 % than the original D-optimal design.     

Correlations and optimization of a heat exchanger with offset-strip fins

The thermo-flow characteristics of a heat exchanger with offset-strip fins are numerically investigated for various fin geometries and working fluids. Previous correlations underestimate f values in the laminar and turbulent regimes and overestimate j values in the laminar regime, as the blockage ratio increase. Therefore, new correlations, which apply to offset-strip fins with blockage ratios of greater than 20%, are presented. Even though the working fluid was changed, the f values did not vary. However, the j values differed according to the working fluid. New j correlations were suggested as functions of the Prandtl number. Design variables of the offset-strip fins in a fuel cooler were optimized by using the correlations and the design of experiment. As a result, the JF factor of the optimized offset-strip fin was enhanced by 24% compared with that of the reference offset-strip fin.     

Effect of NaBH4 concentration on the characteristics of PtRu/C catalyst for the anode of DMFC prepared by the impregnation method

PtRu/C catalysts were prepared using an aqueous co-impregnation method with NaBH₄ as a reducing agent. In order to investigate the effect of the reducing agent concentration, metal ions were reduced in different NaBH₄ concentrations for which the molar ratios of NaBH₄ to metal ions were controlled to 1, 2, 5, 15, 50, and 250. The electrochemical properties were studied by cyclic voltammetry in a 0.5 M H₂SO₄ solution. The surface compositions and oxidation states of the catalysts were observed by X-ray photoelectron spectroscopy (XPS). According to the X-ray diffraction (XRD) results, Pt (fcc) peak shifts were observed and crystal sizes were calculated. The electro-catalytic activities of the prepared catalysts for methanol electro-oxidation were estimated using linear sweep voltammetry. Unit cell tests were carried out to compare the direct methanol fuel cell performances. The NaBH₄ concentration was found to affect the dispersion and the surface composition of the prepared PtRu particles. Optimum molar ratios of NaBH₄ to metal ions were 5 and 15 for methanol electro-oxidation.     

Combined effect of ultrasound and organic acids to reduce Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on organic fresh lettuce

This study was performed to compare the effectiveness of individual treatments (ultrasound and organic acids) and their combination on reducing foodborne pathogens on organic fresh lettuce. Lettuce leaves were inoculated with a cocktail of three strains each of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes and treated with ultrasound (40 kHz) alone, organic acids (0.3, 0.5, 0.7, 1.0, and 2.0% — malic acid, lactic acid, and citric acid) alone and combined with ultrasound and organic acids for 5 min. For all 3 pathogens, the combined treatment of ultrasound and organic acids resulted in additional 0.8 to 1.0 log reduction compared to individual treatments, without causing significant quality change (color and texture) on lettuce during 7 day storage. The maximum reductions of E. coli O157:H7, S. Typhimurium, and L. monocytogenes were 2.75, 3.18, and 2.87 log CFU/g observed after combined treatment with ultrasound and 2% organic acid for 5 min, respectively. Our results suggest that the combined treatment of ultrasound with organic acids was effective at increasing pathogen reduction compared to individual treatments without significantly affecting quality, and demonstrates its potential as a novel method to increase the microbial safety on organic fresh lettuce.     

Growth Characteristics and Biofilm Formation of Various Spoilage Bacteria Isolated from Fresh Produce

This study investigated the characteristics of spoilage bacteria isolated from fresh produce including growth at various temperatures, biofilm formation, cell hydrophobicity, and colony spreading. The number of spoilage bacteria present when stored at 35 °C was significantly greater than when stored at lower temperatures, and maximum population size was achieved after 10 h. However, Bacillus pumilus, Dickeya zeae, Pectobacterium carotovorum subsp. Carotovorum Pcc21, and Bacillus pumilus (RDA‐R) did not grow at the storage temperature of 5 °C. The biofilm formation by Clavibacter michiganensis, Acinetobacter calcoaceticus, and A. calcoaceticus (RDA‐R) are higher than other spoilage bacteria. Biofilm formation showed low correlation between hydrophobicity, and no significant correlation with colony spreading. These results might be used for developing safe storage guidelines for fresh produce at various storage temperatures, and could be basic information on the growth characteristics and biofilm formation properties of spoilage bacteria from fresh produce.     

Combined effect of calcium oxide and sonication to reduce foodborne pathogens on fresh produce

This study was conducted to investigate the antibacterial activity of calcium oxide (CaO), sonication, and their combination against foodborne pathogens on several fresh produce. The results showed that combined treatment inhibited Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium on fresh produce. However, the effectiveness of treatments for reducing populations of foodborne pathogens varied depending on the types and condition of the fresh produce. This study demonstrated that the antibacterial potency of CaO and its application with sonication could be one of alternatives for controlling foodborne pathogens on fresh produce.     

Multibody Dynamic Response Optimization with ALM and Approximate Line Search

This paper presents an efficient approach for dynamic responseoptimization based on the ALM method. In this approach, an approximateaugmented Lagrangian is employed for line searches while an exactaugmented Lagrangian is used for finding search directions. An importantfeature of this study is that the approximate augmented Lagrangian forline search is composed of the linearized cost and constraint functionsprojected on the search direction. The quality of this approximationshould be good since an approximate penalty term is found to have almostsecond-order accuracy near the optimum. Quasi-Newton and conjugategradient algorithms are used to find exact search directions and a goldensection method followed by a cubic polynomial approximation is employedfor line search. The numerical performance of the proposed approach isinvestigated by solving eight typical dynamic response optimizationproblems and comparing the results with those in the literature. Thiscomparison shows that the suggested approach is robust and efficient.     

Effect of Li2O and PbO Additions on Abnormal Grain Growth in the Pb(Mg1/3Nb2/3)O3–35 mol% PbTiO3 System

Abnormal grain growth in Pb(Mg_1/3Nb_2/3)O₃–35 mol% PbTiO₃ (PMN-35PT) ceramics doped with Li₂O and PbO has been investigated. Replacing the PbO dopant with up to 2 mol% Li₂O caused an increase in the number of abnormal grains. For the composition containing 2 mol% Li₂O and 6 mol% PbO, the amount of abnormal grain growth decreased with increasing sintering temperature. Single crystals of ∼6 mm × 6 mm × 2 mm thickness were grown from the 2 mol% Li₂O, 6 mol% PbO-containing composition via the templated grain growth method. Grain growth behavior with temperature is explained in terms of the effect of Li₂O on interface-reaction-controlled grain growth and the critical driving force.     

Efficient mechanical system optimization using two-point diagonal quadratic approximation in the nonlinear intervening variable space

For efficient mechanical system optimization, a new two-point approximation method is presented. Unlike the conventional two-point approximation methods such as TPEA, TANA, TANA-1, TANA-2 and TANA-3, this introduces the shifting level into each exponential intervening variable to avoid the lack of definition of the conventional exponential intervening variables due to zero- or negative-valued design variables. Then a new quadratic approximation whose Hessian matrix has only diagonal elements of different values is proposed in terms of these shifted exponential intervening variables. These diagonal elements are determined in a closed form that corrects the typical error in the approximate gradient of the TANA series due to the lack of definition of exponential type intervening variables and their incomplete second-order terms. Also, a correction coefficient is multiplied to the pre-determinded quadratic term to match the value of aproximate function with that of the previous point. Finally, in order to show the numerical performance of the proposed method, a sequential approximate optimizer is developed and applied to solve six typical design problems. These optimization results are compared with those of TANA-3. These comparisons show that the proposed method gives more efficient and reliable results than TANA-3.     

Numerical investigation and optimization of the thermal performance of a brushless DC motor

A computational study of a brushless DC motor is presented to determine the thermo-flow characteristics in the windings and bearings under the effects of heat generation. The rotation of the rotor blades drives an influx of ambient air into the rotor inlet. The predicted inflow rates were higher at the front inlet than at the rear inlet due to non-uniform pressure distribution. A recirculation zone appeared in the tiny interfaces between windings. The poor cooling performance was caused by flow separation near the groove threshold by the inclination angle of the bearing groove and by a relatively slow velocity near the bearing and between windings. Based on these results, design parameters for the inlet location and geometry, and for the bearing groove geometry, were determined and optimized to enhance the cooling performance up to 24%.