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Results for “parameter optimization”

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At least 397 records · Page 22Linked to original sources

PubMed1997

[Radiofrequency ablation of the liver in vitro: increasing the efficacy by perfusion probes].

PURPOSE: Percutaneous radiofrequency interstitial thermal ablation is a new method in local tumour therapy. The aim of this study was to define the relations between the variable parameters and local efficacy in vitro and to evaluate optimal parameter combinations for this system. Furthermore, we studied the feasibility of increasing the volume of destroyed tissue using perfusion electrodes. MATERIAL AND METHODS: Thermal lesions were produced with radiofrequency in ex vivo pig livers. In separate experiments the parameters wattage (5-30 watts), exposure time (1-15 minutes) and tip exposure were varied. The resulting areas of tissue necrosis coagulation were measured; in 30 of 90 cases the macroscopic findings were compared to the histological findings. RESULTS: Lesion size correlated with tip exposure, wattage and procedure duration up to 10 minutes. For a tip exposure of 2 cm (3 cm) the maximal lesion volume was 18.8 cm3 (33.2 cm3) at a wattage of 20 watts (30 watts) and a procedure duration of 10 minutes. The maximal cross- (length-) diameter of these lesions was 3 cm (4 cm) for 2 cm tip exposure and 3.6 cm (4.9 cm) for 3 cm tip exposure. CONCLUSION: The parameters wattage, procedure duration and tip exposure affect the size of lesions created with radiofrequency under ex vivo conditions. Perfusion electrodes make it possible to produce larger lesions than described for non-perfused electrodes. The ablation of hepatic neoplasms up to a size of 3 cm seems to be possible with a single electrode.

Animals↗

PubMed2001

A refined prediction method for gel retardation of DNA oligonucleotides from dinucleotide step parameters: reconciliation of DNA bending models with crystal structure data.

The development and assessment of a prediction method for gel retardation and sequence dependent curvature of DNA based on dinulcleotide step parameters are described. The method is formulated using the Babcock-Olson equations for base pair step geometry (1) and employs Monte Carlo simulated annealing for parameter optimization against experimental data. The refined base pair step parameters define a stuctural construct which, when the width of observed parameter distributions is taken into account, is consistent with the results of DNA oligonucleotide crystal structures. The predictive power of the method is demonstrated and tested via comparisons with DNA bending data on sets of sequences not included in the training set, including A-tracts with and without periodic helix phasing, phased A4T4 and T4A4 motifs, a sequence with a phased GGGCCC motif, some "unconventional" helix phasing sequences, and three short fragments of kinetoplast DNA from Crithidia fasiculata that exhibit significantly different behavior on non-denaturing polyacrylamide gels. The nature of the structural construct produced by the methodology is discussed with respect to static and dynamic models of structure and representations of bending and bendability. An independent theoretical account of sequence dependent chemical footprinting results is provided. Detailed analysis of sequences with A-tract induced axis bending forms the basis for a critical discussion of the applicability of wedge models,junction models and non A-tract, general sequence models for understanding the origin of DNA curvature at the molecular level.

Base Sequence↗

PubMed1985

[The dynamic property of glucagon secretion in response to blood glucose--analysis with the aid of the control theory using an artificial endocrine pancreas].

The precise dynamic property of glucagon secretion in response to glucose concentration has not yet been elucidated, since in in vitro studies using pancreatic islets, the co-existence of pancreatic B cells modifies the mode of glucagon secretion, and in vivo studies, the exogenous insulin administration greatly affects pancreatic A cell function. In this study, to clarify the dynamic property of glucagon secretion in response to glucose concentration and the ability of glucagon to raise hepatic glucose production, an artificial endocrine pancreas was employed as a research tool. Our originally developed artificial endocrine pancreas prepared the glucagon and/or glucose infusion algorithm as the counterregulatory system. The principle of glucagon and glucose infusion algorithm is set as the proportional plus derivative modes of action to blood glucose concentration with time delay constant, as follows; Gn.I.R.(t) = Gp[BGp - BG(t - tau)] + Gd[-delta BG(t - tau)] + Gc G.I.R.(t) = Cp[BGp - BG(t - tau)] + Cd[-delta BG(t - tau)] where Gn.I.R.(t) and G.I.R.(t) are glucagon infusion rate and glucose infusion rate, respectively. BGp is the projected value of blood glucose concentration, and BG(t) and delta BG are blood glucose concentrations and the rate of change in blood glucose concentration at time t respectively. Gp and Gd are coefficients for glucagon infusion, and Cp and Cd are those for glucose infusion. Gc is the constant for basal glucagon supplementation. tau(min) is the time delay constant for glucagon and glucose infusion. In a depancreatized dog, the blood glucose concentration was maintained at the normoglycemic level with intraportal insulin infusion using this artificial endocrine pancreas for at least one hour, then hypoglycemia was induced by iv bolus insulin injection (0.1 U/kg). Glucagon was infused intraportally or glucose was infused into the peripheral vein when the counterregulatory system was operated according to each of these algorithm by variously changing the parameters. In the intraportal glucagon infusion algorithm, with the optimal parameters based on proportional plus derivative modes of action with a 10-min time delay (Gp/Gd/Gc/tau = 0.2/0.4/0.6/10), both the blood glucose response curves and plasma glucagon profiles simulated those seen in normal dogs. On the other hand, glucagon infusion based only on the proportional action failed to simulate the blood glucose response and plasma glucagon profile of normal dogs. When glucose was infused on the basis of the proportional action with a 20-min time delay (Cp/Cd/tau - 0.2/0/20), the insulin-induced hypoglycemia in depancreatized dogs could be restored to normoglycemia in the sa

Animals↗

PubMed2002

[Application of genetic algorithm in optimization of mobile phase composition in high performance liquid chromatography].

Referring to traditional optimal methods, a method for the optimization of isocratic elution mobile phase composition in high performance liquid chromatography has been developed. In this method, the genetic algorithm based on line-crossover and plane-mutation is used. The principle of genetic algorithm and the process of optimization of mobile phase composition in reversed-phase ion-pair high performance liquid chromatography using genetic algorithm are introduced in details. With the concentrations of acetonitrile and ion-pair reagent sodium octane sulfonate chosen as the optimal parameters, the optimum was obtained by three times of optimization procedures. The mean relative error between the predicted and experimental values was 0.75% at the optimum and the optimization results were satisfactory.

Algorithms↗

PubMed2002

Modeling, optimization and experimental assessment of continuous L-(-)-carnitine production by Escherichia coli cultures.

In a previous paper Cánovas et al. (Biotechnol Bioeng 2002;77:764-775) presented a model for L-(-)-carnitine production using Escherichia coli O44 K74, in a cell-recycle bioreactor for the biotransformation of crotonobetaine into L-carnitine. In this work we optimize this biotechnological setup and experimentally verify the predicted optimal parameter profiles. Provided with a reliable and robust S-system description of the cell-bioreactor combined system, we applied the Indirect Optimization Method described by Torres et al. (Biotechnol Bioeng 1997;55(5):758-772; Food Technol Biotechnol 1998;36(3):177-184). This optimization approach provides different parameter value profiles, all of which are compatible with the cell physiology and the bioreactor operating conditions, that yield increased rates of L-(-)-carnitine production. Three parameters were seen to be of critical importance for maximizing L-(-)-carnitine production: the dilution rate, the initial crotonobetaine concentration, and the carnitine dehydratase activity. When the first two were changed in the experimental setup, there was a 74% increase in the L-(-)-carnitine production rate, performance that was in close agreement with the predictions of the model. In accordance with the optimized solution, a further improvement (90% increase in the L-(-)-carnitine production rate) could be attained by over-expressing up to 5 times the carnitine dehydratase basal activity. Thus the optimization approach shown herein provides experimental evidence of a new strategy which demonstrates the possible variables that can be subjected to modifications compatible with the cell physiology and bioreactor operating conditions, and which are able to yield increased rates of L-(-)-carnitine production.

Alcohol Oxidoreductases↗

PubMed1979

Single-tissue modeling of decompression schedules.

This paper deals with the development of a single-tissue model that simulates the uptake and elimination of inert gases by the body of a diver. The model utilizes an effective single tissue with different uptake and elimination time constants to account for the asymmetrical behavior of multiple-tissue human body models. The parameters of this effective tissue are selected according to an optimal strategy that minimizes safe deviation from the decompression requirements recommended by safe practice. The developed strategy is general in nature and can be readily applied to select the optimal parameters for a single-tissue model suitable for any dive regimen on air or mixed gas. As an illustration, the procedure is used to select the optimal tissue that best fits the Standard Air Decompression Tables recommended by the U.S. Navy. The results obtained are in close and safe agreement with the requirements of the U.S. Navy, and consistently fall in the range between the U.S. Navy and the Royal Navy tables.

Decompression↗

PubMed2004

Comparison of laser-induced dissociation and high-energy collision-induced dissociation using matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI-TOF/TOF) for peptide and protein identification.

The fragmentation of peptides under laser-induced dissociation (LID) as well as high-energy collision-induced dissociation (CID) conditions has been investigated. The effect of the different fragmentation mechanisms on the formation of specific fragment ion types and the usability of the resulting spectra, e.g. for high-throughput protein identification, has been evaluated. Also, basic investigations on the influence of the matrix, as well as laser fluence, on the fragment ion formation and the consequences in the spectral appearance are discussed. The preconditions for obtaining 'pure' CID spectra on matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI-TOF/TOF) instruments are evaluated and discussed as well as the differences between LID and CID in the resulting fragment ion types. While containing a wealth of information due to additional fragment ions in comparison with LID, CID spectra are significantly more complex than LID spectra and, due to different fragmentation patterns, the CID spectra are of limited use for protein identification, even under optimized parameter settings, due to significantly lower scores for the individual spectra. Conditions for optimal results regarding protein identification using MALDI-TOF/TOF instruments have been evaluated. For database searches using tandem mass spectrometric data, the use of LID as fragmentation technique in combination with parameter settings supporting the use of internal fragment ions turned out to yield the optimal results.

Amino Acid Sequence↗

PubMed2003

Clinical applications of dendritic cell vaccination in the treatment of cancer.

Dendritic cell (DC) immunotherapy has shown significant promise in animal studies as a potential treatment for cancer. Its application in the clinic depends on the results of human trials. Here, we review the published clinical trials of cancer immunotherapy using exogenously antigen-exposed DCs. We begin with a short review of general properties and considerations in the design of such vaccines. We then review trials by disease type. Despite great efforts on the part of individual investigative groups, most trials to date have not yielded data from which firm conclusions can be drawn. The reasons for this include nonstandard DC preparation and vaccination protocols, use of different antigen preparations, variable means of immune assessment, and nonrigorous criteria for defining clinical response. While extensive animal studies have been conducted using DCs, optimal parameters in humans remain to be established. Unanswered questions include optimal cell dose, use of mature versus immature DCs for vaccination, optimal antigen preparation, optimal route, and optimal means of assessing immune response. It is critical that these questions be answered, as DC therapy is labor- and resource-intensive. Cooperation is needed on the part of the many investigators in the field to address these issues. If such cooperation is not forthcoming, the critical studies that will be required to make DC therapy a clinically and commercially viable enterprise will not take place, and this therapy, so promising in preclinical studies, will not be able to compete with the many other new approaches to cancer therapy presently in development. Trials published in print through June 2003 are included. We exclude single case reports, except where relevant, and trials with so many variables as to prevent interpretation about DC therapy effects.

Animals↗

PubMed2003

Comprehensive two-dimensional gas chromatography: metrics, potentials, limits.

Metrics for evaluation of separation performance of comprehensive two-dimensional gas chromatography (GCxGC) and for quantitative comparison of that performance with similar performance of its 1D (one-dimensional) counterparts are described. The performance improvement can be expressed via reduction in the saturation of a chromatogram or-in the case of the uniform distribution of peaks along the second dimension--via the peak capacity gain due to GCxGC. An order of magnitude peak capacity gain due to the comprehensive GCxGC is possible under optimal conditions. Optimal parameters of the second dimension column as well as the optimal operational conditions for that column and for the modulator in a comprehensive GCxGC are also presented.

Chromatography, Gas↗

PubMed2006

Investigation of a scanned cylindrical ultrasound system for breast hyperthermia.

This paper investigates the feasibility of a scanned cylindrical ultrasound system for producing uniform heating from the central to the superficial portions of the breast or localized heating within the breast at a specific location. The proposed system consists of plane ultrasound transducer(s) mounted on a scanned cylindrical support. The breast was immersed in water and surrounded by this system during the treatment. The control parameters considered are the size of the transducer, the ultrasound frequency, the scan angle and the shifting distance between the axes of the breast and the system. Three-dimensional acoustical and thermal models were used to calculate the temperature distribution. Non-perfused phantom experiments were performed to verify the simulation results. Simulation results indicate that high frequency ultrasound could be used for the superficial heating, and the scan angle of the transducer could be varied to obtain an appropriate high temperature region to cover the desired treatment region. Low frequency ultrasound could be used for deep heating and the high temperature region could be moved by shifting the system. In addition, a combination of low and high frequency ultrasound could result in a portion treatment from the central to the superficial breast or an entire breast treatment. Good agreement was obtained between non-perfused experiments and simulation results. The findings of this study can be used to determine the effects of the control parameters of this system, as well as to select the optimal parameters for a specific treatment.

Acoustics↗

PubMed1999

Comparison of five methods for finding conserved sequences in multiple alignments of gene regulatory regions.

Conserved segments in DNA or protein sequences are strong candidates for functional elements and thus appropriate methods for computing them need to be developed and compared. We describe five methods and computer programs for finding highly conserved blocks within previously computed multiple alignments, primarily for DNA sequences. Two of the methods are already in common use; these are based on good column agreement and high information content. Three additional methods find blocks with minimal evolutionary change, blocks that differ in at most k positions per row from a known center sequence and blocks that differ in at most k positions per row from a center sequence that is unknown a priori. The center sequence in the latter two methods is a way to model potential binding sites for known or unknown proteins in DNA sequences. The efficacy of each method was evaluated by analysis of three extensively analyzed regulatory regions in mammalian beta-globin gene clusters and the control region of bacterial arabinose operons. Although all five methods have quite different theoretical underpinnings, they produce rather similar results on these data sets when their parameters are adjusted to best approximate the experimental data. The optimal parameters for the method based on information content varied little for different regulatory regions of the beta-globin gene cluster and hence may be extrapolated to many other regulatory regions. The programs based on maximum allowed mismatches per row have simple parameters whose values can be chosen a priori and thus they may be more useful than the other methods when calibration against known functional sites is not available.

Animals↗

PubMed1980

Split-filter computed tomography: a simple technique for dual energy scanning.

A simple technique for obtaining dual energy information from a single computed tomography (CT) scan is described. The method involves filtering the two halves of the X-ray fan beam differently. It is shown that during a 360 degree scan, this split-filtration geometry results in dual energy noise analysis, valid for polychromatic X-ray beams, is presented and used to determine the optimal parameters for the split-filter scans. Using the theoretically optimal split-filter design installed on a commercial CT scanner, photoelectric and Compton images of a head phantom were obtained. Recombination of the photoelectric and Compton components of attenuation at arbitrary energies demonstrates the ability to remove spectral artifacts from conventional CT images.

Calibration↗

PubMed2001

Routine cervical spine radiography for trauma victims: Does everybody need it?

OBJECTIVE: The purpose of this study was to evaluate the indication for routine cervical spine radiography in trauma patients. METHODS: Prospective analysis of radiologic and clinical findings was performed during a 5-year period. Patients suitable for a clinical decision rule were reviewed separately. RESULTS: Of the 1,757 consecutive patients included in the study, 38 were diagnosed with a cervical spine injury. Of the 599 patients suitable for the clinical decision rule, 62 had midline cervical tenderness, including 2 with cervical spine injury. No additional cervical spine injuries were found during follow-up. CONCLUSION: It is within good practice, and it is also cost-effective, to obtain a cervical spine radiograph only on clinical parameters in trauma patients with no apparent bodily trauma and optimal parameters. With this clinical decision rule, 30.6% of all cervical spine series were redundant, and no (occult) spinal fractures would have been undetected.

Adolescent↗

PubMed2003

Poly(D,L-lactide-co-glycolide) microspheres containing 5-fluorouracil: optimization of process parameters.

The objective of this research was to optimize the processing parameters for poly(D,L-lactide-co-glycolide) (PLGA) microspheres of 5-fluorouracil (5-FU) and to mathematically relate the process parameters and properties of microspheres. Microspheres were prepared by a water-in-oil-in-water emulsion solvent evaporation technique. A 3(2) factorial design was employed to study the effect of the volume of the internal phase of the primary emulsion and the volume of the external phase of the secondary emulsion on yield, particle size, and encapsulation efficiency of microspheres. An increase in the volume of the internal phase of the primary emulsion resulted in a decrease in yield and encapsulation efficiency and an increase in particle size of microspheres. When the volume of the external phase of the secondary emulsion was increased, a decrease in yield, particle size, and encapsulation efficiency was observed. Microspheres with good batch-to-batch reproducibility could be produced. Scanning electron microscopic study indicated that microspheres existed as aggregates.

Chemistry, Pharmaceutical↗

PubMed2006

Fourier-based reconstruction for fully 3-D PET: optimization of interpolation parameters.

Fourier-based approaches for three-dimensional (3-D) reconstruction are based on the relationship between the 3-D Fourier transform (FT) of the volume and the two-dimensional (2-D) FT of a parallel-ray projection of the volume. The critical step in the Fourier-based methods is the estimation of the samples of the 3-D transform of the image from the samples of the 2-D transforms of the projections on the planes through the origin of Fourier space, and vice versa for forward-projection (reprojection). The Fourier-based approaches have the potential for very fast reconstruction, but their straightforward implementation might lead to unsatisfactory results if careful attention is not paid to interpolation and weighting functions. In our previous work, we have investigated optimal interpolation parameters for the Fourier-based forward and back-projectors for iterative image reconstruction. The optimized interpolation kernels were shown to provide excellent quality comparable to the ideal sinc interpolator. This work presents an optimization of interpolation parameters of the 3-D direct Fourier method with Fourier reprojection (3D-FRP) for fully 3-D positron emission tomography (PET) data with incomplete oblique projections. The reprojection step is needed for the estimation (from an initial image) of the missing portions of the oblique data. In the 3D-FRP implementation, we use the gridding interpolation strategy, combined with proper weighting approaches in the transform and image domains. We have found that while the 3-D reprojection step requires similar optimal interpolation parameters as found in our previous studies on Fourier-based iterative approaches, the optimal interpolation parameters for the main 3D-FRP reconstruction stage are quite different. Our experimental results confirm that for the optimal interpolation parameters a very good image accuracy can be achieved even without any extra spectral oversampling, which is a common practice to decrease errors caused by interpolation in Fourier reconstruction.

Algorithms↗

PubMed2005

Biodegradation of lindane by Pleurotus ostreatus via central composite design.

The degradation of lindane was studied in liquid-agitated cultures using a commercial strain of the fungus Pleurotus ostreatus as the biodegrading organism. The biodegradation was accomplished with the action of extracellular oxidative enzymes, produced by the fungus to decompose woody substrates. Enzyme activities of manganese peroxidase and laccase were measured in a liquid mineral medium. An orthogonal Central Composite Design of experiments was used to construct second-order response surfaces with the fungus growth, final pH and the lindane biodegradation as optimization parameters. The initial lindane concentration, the nitrogen content, the incubation time and the temperature were used as design factors. Optimal conditions found for all these parameters will be used for the continuation of this project aiming at the bioremediation of contaminated sites with persistent organic pollutants such as lindane.

Biodegradation, Environmental↗

PubMed2005

Macromolecular transport in the arterial wall: alternative models for estimating barriers.

Early atherosclerosis, or atherogenesis, is characterized by the abnormal accumulation of plasma-borne macromolecules (e.g., LDL) in the arterial intima. The change of barrier characteristics of tissue in the arterial wall requires evaluation of macromolecular transport across the endothelial cell layer (ECL) and internal elastic lamina (IEL), the luminal and abluminal boundaries of the arterial intima, respectively. In this study, alternative mathematical models are derived from dynamic mass balances to describe macromolecular transport across the arterial wall. One model considers each medial layer as a spatially lumped compartment, whereas another model consists of a spatially lumped intima and spatially distributed media. Model simulations of a tracer concentration distribution in the arterial wall are compared with concentration distributions of horseradish peroxidase (HRP) after i.v. injection in mice. For each model, optimal parameter values are obtained that yield model outputs matching the data well for two different HRP circulation times. The model parameter estimates show that the ECL is the major barrier for macromolecular transport across the normal arterial wall. Sensitivity analysis indicates that the parameter estimates of the transport coefficients of the ECL and IEL are well determined. Optimal circulation times are determined and expected to yield improved precision of parameter estimates in future experiments to reflect disease progression.

Animals↗

PubMed2004

Lumped parametric model of the human ear for sound transmission.

A lumped parametric model of the human auditoria peripherals consisting of six masses suspended with six springs and ten dashpots was proposed. This model will provide the quantitative basis for the construction of a physical model of the human middle ear. The lumped model parameters were first identified using published anatomical data, and then determined through a parameter optimization process. The transfer function of the middle ear obtained from human temporal bone experiments with laser Doppler interferometers was used for creating the target function during the optimization process. It was found that, among 14 spring and dashpot parameters, there were five parameters which had pronounced effects on the dynamic behaviors of the model. The detailed discussion on the sensitivity of those parameters was provided with appropriate applications for sound transmission in the ear. We expect that the methods for characterizing the lumped model of the human ear and the model parameters will be useful for theoretical modeling of the ear function and construction of the ear physical model.

Acoustic Stimulation↗