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Results for “Process optimization”

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At least 1,675 records · Page 93Linked to original sources

PubMed2003

Shadows in the brain.

The aims of the present study were to investigate whether the processing of an object shadow occurs implicitly, that is without conscious awareness, and where physically within the human brain shadows are processed. Here we present neurological evidence, obtained from studies of brain-injured patients with visual neglect, that shadows are implicitly processed and that this processing may take place within the temporal lobe. Neglect patients with lesions that do not involve the right temporal lobe were still able to process shadows to optimize object shape perception. In contrast, shadow processing was not found to be as efficient in neglect patients with lesions that involve the right temporal lobe.

Aged↗

PubMedDate not supplied

A clinically based discrete-event simulation of end-stage liver disease and the organ allocation process.

BACKGROUND: The optimal allocation of scarce donor livers is a contentious health care issue requiring careful analysis. The objective of this article was to design a biologically based discrete-event simulation to test proposed changes in allocation policies. METHODS: The authors used data from multiple sources to simulate end-stage liver disease and the complex allocation system. To validate the model, they compared simulation output with historical data. RESULTS: Simulation outcomes were within 1% to 2% of actual results for measures such as new candidates, donated livers, and transplants by year. The model overestimated the yearly size of the waiting list by 5% in the last year of the simulation and the total number of pretransplant deaths by 10%. CONCLUSION: The authors created a discrete-event simulation model that represents the biology of end-stage liver disease and the health care organization of transplantation in the United States.

Adolescent↗

PubMed1994

Fluorocarbon emulsions--the stability issue.

Long-term room temperature stability of ready-to-use concentrated fluorocarbon emulsions is necessary in order to fully exploit the therapeutic potential of fluorocarbons. Consequently, considerable efforts have been directed at investigating the physical nature of such emulsions, the mechanisms which lead to their degradation and the means of counteracting these. The particles which constitute typical fluorocarbon/egg yolk phospholipid emulsions have been identified to be surfactant-coated fluorocarbon droplets and lipid vesicles. Better understanding has been gained on the formation, structure and evolution of these particles during processing and storage. This has led to optimized formulations and processing, better control of emulsion characteristics and significantly improved stability. Molecular diffusion (Ostwald ripening or transcondensation) has been shown to be the maun mechanism of degradation when particles are less than 1 micron in diameter, even for the highly concentrated (volume fraction of fluorocarbon up to 50%) second generation fluorocarbon emulsions. Significant emulsion stabilization has been accomplished by adding fluorochemicals which are both less volatile and less water soluble, and nevertheless have an organ dwell time acceptable for intravascular use. The rate of molecular diffusion can also be reduced by decreasing the fluorocarbon/water interfacial tension; this was effectively achieved with appropriate, well-defined fluorinated surfactants. A further, novel means of stabilizing fluorocarbon-in-water emulsions makes use of mixed fluorocarbon-hydrocarbon amphiphiles which act as molecular dowels to reinforce the adhesion between the fluorocarbon phase and the lipophilic zone of the surfactant film. Both long-term room temperature stability, and particle-size control over a large range of diameter, have been achieved by applying this principle. All in all it can be said that the challenge of producing injectable fluorocarbon emulsions with long-term room temperature particle size stability has been met.

Blood Substitutes↗

PubMed1987

A rule-based process control method with feedback.

This paper describes a method for developing a rule-based control algorithm for process control that includes feedback and modification of the rule base from samples of the process output. The rules are used to guide the process toward the desired goal, or goals, and as the process operates new data samples allow the inference of new rules so that the process is automatically optimized and the rules for controlling the process are automatically generated.

Algorithms↗

PubMed1998

[Methods for extracting chitin from shrimp shell waste].

Shrimp shell waste obtained from several industrial freezing-purchasing plants of Guaymas, Sonora, Méx., was studied as a source of value-added chitin biopolymers. In part I, the effect of different isolation conditions on the chitin yield and chemical characteristic, was investigated. Protein and mineral matter were removed with alkali and acid treatment respectively. A 2x2x3 factorial a way of a completely randomized design was used in order to evaluate the effect of the process variables, namely, NaOH concentration (0.4 and 2%) during the deproteinization and HCl concentration (3 and 5%) carried out at 40, 50 and 60 degrees C. The best processing conditions were desproteinization with 2% NaOH, and demineralization with 5% HCl at 50 degrees C, in terms of final ash and chitin content and yield. In part II, a selection of methods of isolation of chitin and chitosan was studied in order to establish the best conditions for scaling up a process to pilot plant level. The processing conditions were selected from reported methods as well as from those defined in part I. Purity of chitin samples was determined in terms of residual protein, ash and chitin each one to produce high quality chitin (0.00% protein, 0.01% ash, 99.99% chitin) and standard grade chitin (0.00% protein, 0.09% ash, 99.13% chitin). Both products were considered as of adequate quality and their manufacture process could be scaled up by further optimization of the processing conditions.

Analysis of Variance↗

PubMed2006

Self-regulation processes and health: the importance of optimism and goal adjustment.

This article discusses how self-regulatory models can be used to understand people's response to health threats. The article begins with a general discussion of the principles and assumptions of self-regulatory models of behavior. Two distinct lines of research are then presented addressing two important processes of adaptive self-regulation. First, we provide a brief overview of the literature on optimism and adjustment to chronic disease and other health outcomes. Second, we present an overview of the process of disengagement from unattainable goals, focusing on recent research. We close by making recommendations for future research.

Attitude to Health↗

PubMed1999

Simultaneous Optimization of Feeding Rate and Operation Parameters for Fed-Batch Fermentation Processes.

An efficient method is introduced for simultaneously determining optimal polices of feeding rate and operation parameters for a fermentation process. Such an optimization problem is converted into the finite dimensional optimization problem using the control parametrization technique. The hybrid differential evolution is introduced to solve the converted problem. The optimal production rate obtained by the simultaneous optimization approach could be significantly improved with comparison to a simplified optimization problem, which is considered the optimal feed control only, as observed from the simulation results.

Journal Article↗

PubMedDate not supplied

Genetic programming assisted stochastic optimization strategies for optimization of glucose to gluconic acid fermentation.

This article presents two hybrid strategies for the modeling and optimization of the glucose to gluconic acid batch bioprocess. In the hybrid approaches, first a novel artificial intelligence formalism, namely, genetic programming (GP), is used to develop a process model solely from the historic process input-output data. In the next step, the input space of the GP-based model, representing process operating conditions, is optimized using two stochastic optimization (SO) formalisms, viz., genetic algorithms (GAs) and simultaneous perturbation stochastic approximation (SPSA). These SO formalisms possess certain unique advantages over the commonly used gradient-based optimization techniques. The principal advantage of the GP-GA and GP-SPSA hybrid techniques is that process modeling and optimization can be performed exclusively from the process input-output data without invoking the detailed knowledge of the process phenomenology. The GP-GA and GP-SPSA techniques have been employed for modeling and optimization of the glucose to gluconic acid bioprocess, and the optimized process operating conditions obtained thereby have been compared with those obtained using two other hybrid modeling-optimization paradigms integrating artificial neural networks (ANNs) and GA/SPSA formalisms. Finally, the overall optimized operating conditions given by the GP-GA method, when verified experimentally resulted in a significant improvement in the gluconic acid yield. The hybrid strategies presented here are generic in nature and can be employed for modeling and optimization of a wide variety of batch and continuous bioprocesses.

Artificial Intelligence↗

PubMed1998

Trypanosoma brucei U insertion and U deletion activities co-purify with an enzymatic editing complex but are differentially optimized.

RNA editing, the processing that generates functional mRNAs in trypanosome mitochondria, involves cycles of protein catalyzed reactions that specifically insert or delete U residues. We recently reported purification from Trypanosoma brucei mitochondria of a complex showing seven major polypeptides which exhibits the enzymatic activities inferred in editing and that a pool of fractions of the complex catalyzed U deletion, the minor form of RNA editing in vivo . We now show that U insertion activity, the major form of RNA editing in vivo , chromatographically co-purifies with both U deletion activity and the protein complex. Furthermore, these editing activities co-sediment at approximately 20 S. U insertion does not require a larger, less characterized complex, as has been suggested and could have implied that the editing machinery would not function in a processive manner. We also show that U insertion is optimized at rather different and more exacting reaction conditions than U deletion. By markedly reducing ATP and carrier RNA and increasing UTP and carrier protein relative to standard editing conditions, U insertion activity of the purified fraction is enhanced approximately 100-fold.

Animals↗

PubMed1992

Predicting the performance of chromatographic columns in protein purification processes.

The commercial success of chromatographic methods in large scale protein purification has created a strong demand for predictive techniques which will directly aid the design, scale-up and optimization of the process. This article examines the current state in the development of such techniques which depend for success not only on system analysis and modelling, but also on the collection of appropriate experimental data. A specific mathematical model describing non-porous particle adsorption (NPPAM) developed by the authors, which is simple to use on readily available equipment, is outlined. Examples of using NPPAM for predicting column performance are given, as well as the potential of applying the model in process simulation and optimization.

Adsorption↗

PubMed1999

Long-term reproducibility optimization of an x-ray process for bone architectural evaluation during osteoporosis.

Non-invasive and in vivo assessment of bone architectural changes at high resolution is of considerable interest in osteoporosis. In this note, the use of an x-ray acquisition system in the evaluation of the architectural quality of trabecular bone by radiographic texture analysis is optimized to achieve good long-term reproducibility. First, radiographic and digitization processes are modelled and defined. Procedures to make radiographs and their digital images are fixed. Then, measurements of the modulation transfer function (MTF) of the entire acquisition chain were completed. These measurements provide an MTF in excess of 30% at a spatial frequency of 2.5 lp/mm. Also, results of a fractal texture analysis made on digital images of calcaneus radiographs show a mean coefficient of variation of 2.07%. These data show that good long-term reproducibility can make the x-ray acquisition system efficient for patient follow-up, or evaluation of treatment regimes for osteoporosis. Finally, it is shown that fractal texture parameters are statistically different in an osteoporotic population and in a control group. Therefore, this system should also be of medical interest.

Bone and Bones↗

PubMed2003

Multiobjective optimization of simulated moving bed and Varicol processes using a genetic algorithm.

The size of the packing material, the total number of columns and the total feed concentration have significant impacts on the economics of a preparative chromatographic separation, through their effects on column pressure drop, column efficiency and thermodynamics. In this work, the role of these parameters on the performances of a simulated moving bed and a Varicol process is investigated on a chiral separation system from literature, using an equilibrium stage model. A multiple objective optimization technique based on a genetic algorithm is adopted, which allows to maximize simultaneously the purity of the extract and productivity of the unit. In this way, it is possible to optimize and compare the performances of both processes in a wide range of parameter values, so as to assess their relative potential under equally optimized conditions. The optimization results, i.e. the so-called Pareto sets, have been discussed in the frame of equilibrium theory and the roles of these three parameters have been clarified.

Algorithms↗

PubMed2002

Electro-membrane filtration for the selective isolation of bioactive peptides from an alpha(s2)-casein hydrolysate.

For the isolation of the ingredients required for functional foods and nutraceuticals generally membrane filtration has too low a selectivity and chromatography is (too) expensive. Electro-membrane filtration (EMF) seems to be a breakthrough technology for the isolation of charged nutraceutical ingredients from natural sources. EMF combines the separation mechanisms of membrane filtration and electrophoresis. In this study, positively charged peptides with antimicrobial activity were isolated from an alpha(s2)-casein hydrolysate using batch-wise EMF. alpha(s2)-Casein f(183-207), a peptide with strong antimicrobial activity, predominated in the isolated product and was enriched from 7.5% of the total protein components in the feed to 25% in the permeate product. With conventional membrane diafiltration using the same membrane (GR60PP), isolation of this and other charged bioactive peptides could not be achieved. The economics of EMF are mainly governed by the energy costs and the capital investment, which is affected by the flux of the desired peptide. A maximum average transport rate of alpha(s2)-casein f(183-207) during batch-wise EMF of 1.2 g/m2. h was achieved. Results indicate that an increase in the hydrolysate (feed) concentration, the applied potential difference and the conductivity of the permeate and electrode solutions, and a reduction in the conductivity of the feed result in a higher transport rate of alpha(s2)-casein f(183-207). This is in line with the expectation that the transport rate is improved when the concentration, the electrical field strength, or the electrophoretic mobility is increased, provided that the electrophoretic transport predominates. The expected energy consumption of the EMF process per gram of peptide transported was reduced by approximately 50% by applying a low overall potential difference and by processing desalinated hydrolysate. Considerable improvements in transport rate, energy efficiency, and process economics seem to be attainable by additional optimization of the process parameters and the EMF module design.

Antimicrobial Cationic Peptides↗

PubMed2005

Capillary electrophoresis-mass spectrometry of Spirulina platensis proteins obtained by pressurized liquid extraction.

In this work, the usefulness of CE-MS to monitor and optimize the pressurized liquid extraction (PLE) of proteins from Spirulina platensis microalga is demonstrated. Crude and purified PLE extracts from microalga were analyzed by CE-MS. It was observed that the use of purification protocols of phycobiliproteins (namely, ultrafiltration or precipitation-dialysis-freeze drying) resulted in better CE resolution and MS signals, demonstrating that sample matrix plays an important role in CE-MS of proteins in real samples. Ultrafiltration was found less laborious and much faster than precipitation-dialysis-freeze drying (1 vs. 48 h). Direct analysis of crude extracts was demonstrated to be also possible by CE-MS, providing less-quality information but enough to characterize PLE extracts in a much faster way. Therefore, the latter protocol was selected to monitor and optimize the extraction process of phycobiliproteins from S. platensis. To do that, different extraction conditions were tested, including time, temperature and pressure of extraction, nature of pressurized liquid, distribution of microalga inside the extraction cell, type of packing, etc. It is demonstrated that the combined use of PLE and CE-MS allows the attainment of extracts rich in phycobiliproteins in short extraction times (namely, yields of 20% can be obtained in less than 2 h under the optimum PLE process in an automatic way). To our knowledge, this work shows for the first time the usefulness of CE-MS for monitoring and optimizing a PLE process.

Algal Proteins↗

PubMed1989

Commentary on Gracia et al.: diagnostic entity or dynamic processes?

The case of Mr. G is a fascinating and beautifully presented, although sad, history of a patient. The clarity of the presentation and the discussion are particularly impressive in this example of the use of longitudinal data for descriptive diagnosis and conceptualization. The report exemplifies current trends in descriptive psychiatry, which focus on diagnosing an illness as a whole. The illness itself is considered a relatively static entity, even if it includes changes within its course. From this perspective, longitudinal data provide information for deciding what type of illness is being described. In my commentary, I would like to focus on a different way of using longitudinal data from that employed by the authors--a different type of longitudinal perspective, one that does not have the primary goal of defining a type of disorder diagnostically. I would like instead to focus on understanding this patient in terms of longitudinal processes rather than as someone afflicted with a persisting diagnostic entity. Attention to longitudinal processes can raise different questions and suggest what further information would be needed to understand these processes and plan optimal treatment. This more dynamic approach to understanding processes is not mutually exclusive with the static approach to diagnosis, but the two orientations provide very different perspectives on assessment, conceptualization and treatment.

Adult↗

PubMed2003

Optimal operation of simulated moving bed chromatographic processes by means of simple feedback control.

In this contribution, simple methods are presented for controlling a simulated moving bed (SMB) chromatographic process with standard PI (proportional integral) controllers. The first method represents a simple and model-free inferential control scheme which was motivated from common distillation column control. The SMB unit is equipped with UV detectors. The UV signals in the four separation zones of the unit are fixed by four corresponding PI controllers calculating the ratio of liquid and solid flow in the respective separation zone. In order to be able to adjust the product purity a second, model-based control scheme is proposed. It makes use of the nonlinear wave propagation phenomena in the apparatus. The controlled chromatographic unit is automatically working with minimum solvent consumption and maximum feed throughput--without any numerical optimization calculations. This control algorithm can therefore also be applied for fast optimization of SMB processes.

Chromatography, Liquid↗

PubMed2005

Structural optimization of dental restorations using the principle of adaptive growth.

OBJECTIVES: In a restored tooth, the stresses that occur at the tooth-restoration interface during loading could become large enough to fracture the tooth and/or restoration and it has been estimated that 92% of fractured teeth have been previously restored. The tooth preparation process for a dental restoration is a classical optimization problem: tooth reduction must be minimized to preserve tooth tissue whilst stress levels must be kept low to avoid fracture of the restored unit. The objective of the present study was to derive alternative optimized designs for a second upper premolar cavity preparation by means of structural shape optimization based on the finite element method and biological adaptive growth. METHODS: Three models of cavity preparations were investigated: an inlay design for preparation of a premolar tooth, an undercut cavity design and an onlay preparation. Three restorative materials and several tooth/restoration contact conditions were utilized to replicate the in vitro situation as closely as possible. The optimization process was run for each cavity geometry. RESULTS: Mathematical shape optimization based on biological adaptive growth process was successfully applied to tooth preparations for dental restorations. Significant reduction in stress levels at the tooth-restoration interface where bonding is imperfect was achieved using optimized cavity or restoration shapes. In the best case, the maximum stress value was reduced by more than 50%. SIGNIFICANCE: Shape optimization techniques can provide an efficient and effective means of reducing the stresses in restored teeth and hence has the potential of prolonging their service lives. The technique can easily be adopted for optimizing other dental restorations.

Bicuspid↗

PubMed2002

[The optimization of guanosine fermentation based on process parameter correlation analysis].

The characteristic of Bacillus subtilis fermentation process of guanosine on 50 L fermentor was analyzed. Based on determination of on-line and off-line parameter, using correlation analysis, the technology study of physiologic regulation was combined with the metabolic flux distribution of synthesis process. The metabolic flux shift from HMP to EMP and TCA cycle during fermentation was found. The reason of the flux shift was preliminary analyzed, based on which the procedure was optimized to increase the yield of guanosine to 30 g/L.

Ammonia↗