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Array Design (array + design)
Selected AbstractsMinimizing the sinkmarks in injection-molded thermoplasticsADVANCES IN POLYMER TECHNOLOGY, Issue 3 2001Shih-Jung Liu Injection molding is one of the most important methods for the manufacture of plastic products; however, there are several unresolved problems that confound the overall success of this technique. Sinkmarks occurring on the surface of molded parts caused by inappropriate mold design and processing conditions is one problem. In this report, an L'18 orthogonal array design based on the Taguchi method was conducted to minimize the sinkmarks of injection-molded thermoplastic parts. The polymeric materials used were general-purpose polystyrene and low-density polyethylene. A plate cavity with various ribs was used for molding. Experiments were carried out on an 80-ton reciprocating injection-molding machine. After molding, the sinkmarks on the surface of molded parts were characterized by a profile meter. For the factors selected in the main experiments, the corner geometry and the width of the rib were found to be the principal factors affecting sinkmark formation in injection-molded thermoplastics. A rib of an undercut geometry and a small width produces parts with the least sinkmark. Experimental investigation of an injection-molding problem can help illuminate the formation mechanism of sinkmarks so that steps can be taken to optimize the surface quality of molded parts. © 2001 John Wiley & Sons, Inc. Adv Polym Techn 20: 202,215, 2001 [source] Supercritical fluid extraction of ecdysterone from the roots of Achyranthes bidentata BL.JOURNAL OF SEPARATION SCIENCE, JSS, Issue 8 2008Yizhe Zheng Abstract Ecdysterone has been found in a great many plants and animals and has some valuable pharmaceutical properties. The present study was conducted to investigate optimal conditions for the extraction of the compound by supercritical fluid extraction from the roots of Achyranthes bidentata BL. An orthogonal array design (OAD), OA9(34), was employed as a chemometric method for optimization of the extraction of ecdysterone from the herbal medicine. Four parameters, namely, pressure and temperature of the supercritical fluid, the dynamic extraction time, and the flow rate of dimethyl sulfoxide, were studied and optimized by a three-level OAD. Determinations of the extracts were performed by high-performance liquid chromatography. The effects of the parameters were studied using analysis of variance. The results shown that the yield of ecdysterone could be influenced by the four parameters to a similar degree. The yield for DMSO-modified supercritical CO2 was in the range from 0.65 to 1.03 mg/g under the selected conditions. In comparison with methanol-modified supercritical CO2 and Soxhlet extraction, a higher yield was obtained when DMSO-modified supercritical CO2 was used. [source] An introduction to coil array design for parallel MRINMR IN BIOMEDICINE, Issue 3 2006Michael A. Ohliger Abstract The basic principles of radiofrequency coil array design for parallel MRI are described from both theoretical and practical perspectives. Because parallel MRI techniques rely on coil array sensitivities to provide spatial information about the sample, a careful choice of array design is essential. The concepts of coil array spatial encoding are first discussed from four qualitative perspectives. These qualitative descriptions include using coil arrays to emulate spatial harmonics, choosing coils with selective sensitivities to aliased pixels, using coil sensitivities with broad k -space reception profiles, and relying on detector coils to provide a set of generalized projections of the sample. This qualitative discussion is followed by a quantitative analysis of coil arrays, which is discussed in terms of the baseline SNR of the received images as well as the noise amplifications (g -factor) in the reconstructed data. The complications encountered during the experimental evaluation of coil array SNR are discussed, and solutions are proposed. A series of specific array designs are reviewed, with an emphasis on the general design considerations that motivate each approach. Finally, a set of special topics is discussed, which reflect issues that have become important, especially as arrays are being designed for more high-performance applications of parallel MRI. These topics include concerns about the depth penetration of arrays composed of small elements, the use of adaptive arrays for systems with limited receiver channels, the management of inductive coupling between array elements, and special considerations required at high field strengths. The fundamental limits of spatial encoding using coil arrays are discussed, with a primary emphasis on how the determination of these limits impacts the design of optimized arrays. This review is intended to provide insight into how arrays are currently used for parallel MRI and to place into context the new innovations that are to come. Copyright © 2006 John Wiley & Sons, Ltd. [source] Space and terrestrial photovoltaics: synergy and diversity,PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2002Sheila G. Bailey A historical view of the research and development in photovoltaics from the perspective of both the terrestrial and the space communities is presented from the early days through the 1970s and 1980s, 1990s and beyond. The synergy of both communities, both at the beginning and in the present, and hopefully in the future, are highlighted, with examples of the important features in each program. The space community which was impressed by the light weight and reliability of photovoltaics drove much of the early development. Even today, nearly every satellite and other scientific space probe that has been launched has included some solar power. However, since the cost of these power systems was only a small fraction of the satellite and launch cost, the use of much of this technology in the terrestrial marketplace was not feasible. It was clear that the focus of the terrestrial community would be best served by reducing costs. This would include addressing a variety of manufacturing issues and raising the rate of production. Success in these programs and a resulting globalization of effort resulted in major strides in the reduction of PV module costs and increased production. Although, the space community derived benefit from some of these advances, its focus was on pushing the envelope with regard to cell efficiency. The gap between theoretical efficiencies and experimental efficiencies for silicon, gallium arsenide and indium phosphide became almost nonexistent. Recent work by both communities have focused on the development thin-film cells of amorphous silicon, CuInSe2 and CdTe. These cells hold the promise of lower costs for the terrestrial community as well as possible flexible substrates, better radiation resistance, and higher specific power for the space community. It is predicted that future trends in both communities will be directed toward advances through the application of nanotechnology. A picture is emerging in which the space and terrestrial solar cell communities shall once again share many common goals and, in fact, companies may manufacture both space and terrestrial solar cells in III,V materials and thin-film materials. Basic photovoltaics research, including these current trends in nanotechnology, provides a valuable service for both worlds in that fundamental understanding of cell processes is still vitally important, particularly with new materials or new cell structures. It is entirely possible that one day we might have one solar array design that will meet the criteria for success in both space and on the Earth or perhaps the Moon or Mars. Published in 2002 by John Wiley & Sons, Ltd. [source] Determination of the Optimal Conditions for Synthesis of Silver Oxalate NanorodsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2008M. Pourmortazavi Abstract In this study, an orthogonal array design (OAD), OA9, was employed as a statistical experimental method for the controllable, simple and fast synthesis of silver oxalate nanorods. Ultrafine silver oxalate rods were synthesized by a precipitation method involving the addition of silver ion solution to the oxalate reagent. The effects of reaction conditions, i.e., silver and oxalate concentrations, flow rate of reagent addition and temperature, on the diameter of the synthesized silver oxalate rods were investigated. The effects of these factors on the width of the silver oxalate rods were quantitatively evaluated by the analysis of variance (ANOVA). The results showed that silver oxalate nanorods can be synthesized by controlling the silver concentration, flow rate and temperature. Finally, the optimum conditions for the synthesis of silver oxalate nanorods by this simple and fast method were proposed. The results of ANOVA showed that 0.001,mol/L silver ion concentration, 40,mL/min flow rate for the addition of the silver reagent to the oxalate solution and 0,°C temperature are the optimum conditions for producing silver oxalate nanorods with 107 ± 45,nm width. [source] Robust flat waves with a uniform feed using a randomized local searchINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 4 2008Brian Keller Abstract Placement of radar emitters in non-uniformly spaced radar arrays typically involves optimizing the placement of a fixed number of emitter elements across the array. This paper explores optimizing for a flat wave under uniform feed where the number of emitter elements is not fixed. A randomized local search algorithm is used to generate an emitter design, and a greedy search is used to find the optimal solution in that neighborhood. This technique results in a near-field wave with less than 1 dB of amplitude ripple and less than 8 degrees of phase ripple across a width of 50,. The designs chosen are robust in the sense that solutions with neighboring pixels on are also of high quality. Furthermore, the proposed algorithm can also find array designs that generate flat waves that are not parallel to the emitter array. Copyright © 2007 John Wiley & Sons, Ltd. [source] An introduction to coil array design for parallel MRINMR IN BIOMEDICINE, Issue 3 2006Michael A. Ohliger Abstract The basic principles of radiofrequency coil array design for parallel MRI are described from both theoretical and practical perspectives. Because parallel MRI techniques rely on coil array sensitivities to provide spatial information about the sample, a careful choice of array design is essential. The concepts of coil array spatial encoding are first discussed from four qualitative perspectives. These qualitative descriptions include using coil arrays to emulate spatial harmonics, choosing coils with selective sensitivities to aliased pixels, using coil sensitivities with broad k -space reception profiles, and relying on detector coils to provide a set of generalized projections of the sample. This qualitative discussion is followed by a quantitative analysis of coil arrays, which is discussed in terms of the baseline SNR of the received images as well as the noise amplifications (g -factor) in the reconstructed data. The complications encountered during the experimental evaluation of coil array SNR are discussed, and solutions are proposed. A series of specific array designs are reviewed, with an emphasis on the general design considerations that motivate each approach. Finally, a set of special topics is discussed, which reflect issues that have become important, especially as arrays are being designed for more high-performance applications of parallel MRI. These topics include concerns about the depth penetration of arrays composed of small elements, the use of adaptive arrays for systems with limited receiver channels, the management of inductive coupling between array elements, and special considerations required at high field strengths. The fundamental limits of spatial encoding using coil arrays are discussed, with a primary emphasis on how the determination of these limits impacts the design of optimized arrays. This review is intended to provide insight into how arrays are currently used for parallel MRI and to place into context the new innovations that are to come. Copyright © 2006 John Wiley & Sons, Ltd. [source] Efficiency measure, modelling and estimation in combined array designsAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 4 2003Tak Mak Abstract In off-line quality control, the settings that minimize the variance of a quality characteristic are unknown and must be determined based on an estimated dual response model of mean and variance. The present paper proposes a direct measure of the efficiency of any given design-estimation procedure for variance minimization. This not only facilitates the comparison of different design-estimation procedures, but may also provide a guideline for choosing a better solution when the estimated dual response model suggests multiple solutions. Motivated by the analysis of an industrial experiment on spray painting, the present paper also applies a class of link functions to model process variances in off-line quality control. For model fitting, a parametric distribution is employed in updating the variance estimates used in an iteratively weighted least squares procedure for mean estimation. In analysing combined array experiments, Engel and Huele (Technometrics, 1996; 39:365) used log-link to model process variances and considered an iteratively weighted least squares leading to the pseudo-likelihood estimates of variances as discussed in Carroll and Ruppert (Transformation and Weighting in Regression, Chapman & Hall: New York). Their method is a special case of the approach considered in this paper. It is seen for the spray paint data that the log-link may not be satisfactory and the class of link functions considered here improves substantially the fit to process variances. This conclusion is reached with a suggested method of comparing ,empirical variances' with the ,theoretical variances' based on the assumed model. Copyright © 2003 John Wiley & Sons, Ltd. [source] | |||||||||||||