SEARCH · PubMed Health

Results for “parameter optimization”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,135 records · Page 63Linked to original sources

PubMed1998

[Rapid method of measuring angiotensin converting enzyme activity in blood].

A simple and rapid spectrophotometric procedure is developed for measuring the activity of angiotensin-converting enzyme (ACE) in human serum. Furylacryloyl-phenylalanyl-glycyl-glycine (FAPGG) possessing a high absorption capacity at 334 nm was used as the substrate. ACE hydrolyzes FAPGG and decreases the extinction. The level of extinction drop is the measure of ACE activity. Optimal parameters of the enzymatic reaction are defined, including medium pH, substrate concentration, and volumes of the sample and inhibitor of ACE activity. Adequate control permits monitoring the interference of exogenic and endogenic factors in ACE activity in the studied sample. The proposed method is available for clinical laboratories, easily reproducible, and sufficiently sensitive.

Buffers↗

PubMed1995

Inexpensive high-quality full-face patient photographs.

Although even the simplest arrangement for taking extraoral patient photographs is better than no procedure at all, the most practical and efficient solution is to invest in a setup that includes an extraoral camera with electronic dual flash and backdrop screen. Once the components have been set up, and the optimal parameters established, the system is always ready, and taking the pictures is just a snap away. The studio quality of the photographs from this arrangement will provide invaluable contributions to the success of your cosmetic dental practice.

Esthetics, Dental↗

PubMedDate not supplied

[Applicability of molecular electrostatic interaction models to describing ionic strength dependence of reaction rate between myoglobin and cytochrome c].

The nonlinear regression method was used for the evaluation of applicability of the known model equations (Wherland-Gray, Brönsted-Debay-Hukkel and "parallel disks") which describe the ionic strength dependence of the reaction rate between charged molecules to the redox reaction of cytochrome c with sperm whale myoglobin modified at His 12(A10) with the bromoacetate spin label, and pig myoglobin. Unlike the native sperm whale Mb studied earlier [1], the objects chosen have monotonous pH-dependence of the reaction rate and are more simple with regards to electrostatic interactions in the electron-transfer complex. This allowed to study the influence of the total as well as the local protein charge on the correspondence of the ion strength dependencies to the theoretical models and optimal parameters of the equations. It was shown that the models considered, as in the case of the native sperm whale Mb-Cyt c reaction, permit satisfactory description of the experimental data, but the obtained parameters cannot be applied to the whole proteins or their contact sites. In the best case (Wherland-Gray equation) it is possible to do if the distribution of electrostatic potential in the contact area is considered. The reason can be that, unlike other protein redox-systems, the contact sites of both Mb and Cyt c have the charged residues of both signs, and the His GH1 residue located in the contact Mb site is not only involved in the electrostatic interactions in electron-transfer complex, but also participates directly in the mechanism of charge transfer.

Animals↗

PubMed1998

Relationships between protein sequence and structure patterns based on residue contacts.

The identification of correlations between sequence patterns and structural motifs is a prerequisite in the development of protein structure prediction methods. The prediction accuracy indicates whether these correlations are discerned. We present an approach to identify long-range relationships between sequence patterns and structural motifs by varying the granulation of the structure description. Since interaction among residues is a major determinant in protein folding, we consider contact environments formed by two triplets of three sequentially neighboring residues and described by vectors whose components express contact strengths on an atomic level. Through testing various classification schemes, including their resolution and optimizing parameters, discernible relationships between sequences and folds are explored. About ten structural contact states, together with information from noncontacting regions, could improve the accuracy of contact prediction.

Chemical Phenomena↗

PubMed1998

[A method for the surgical treatment of pericoronitis using a computerized laser apparatus].

Use of pulsed exposure to CO2 laser permits operations on soft tissues of the oral cavity with the minimal injury. The choice of optimal parameters of laser exposure depends on the stage of the inflammatory process. The proposed ablation regimen for the treatment of pericoronitis notably accelerates the treatment and decreases the amount of drugs used. The absence of complications after the operation and a shorter rehabilitation period recommend the Lancet computer-aided laser for dissection of the veil.

Acute Disease↗

PubMed1998

Prediction of permeability-surface area product data by continuous-distribution pore models.

OBJECTIVE: To investigate the ability of continuous-distribution pore models to accurately predict permeability-surface area product (PS) experimental data in skeletal muscle. METHODS: Models having a water-only (WO) pathway and continuous distributions of microvascular transport-pathway sizes were fit to solute reflection-coefficient (sigma) experimental data (approximately 0.5-16 nm Stokes radii) obtained from skeletal muscle to determine optimal parameter values. Without further modification, these models were used to predict experimental PS values obtained from the literature for small solutes ranging in size from NaCl to inulin and for three proteins, alpha-lactalbumin, ovalbumin, and albumin (approximately 0.23-3.7 nm radii). The protein PSs were determined from fluorescent tracer-diffusion curves and a nonlinear model of tracer diffusion in the cat hindlimb preparation. The model's PS predictions were compared to those of a discrete-pore model previously developed and a fiber-matrix (FM) model. RESULTS: A log-normal (LN) continuous pore-size distribution plus WO-pathway model (three free parameters) fit the sigma data to within the 95% confidence intervals of each of eight solutes spanning a 32-fold size range and was nearly as close to the data as was the two discrete-pore plus WO-pathway model (four free parameters). Both models closely described the PS data for nine solutes spanning a 14-fold size range. The fit of a fiber-matrix plus WO-pathway model (three free parameters) to the sigma data was much poorer than for the other models. CONCLUSIONS: The LN and two-discrete-pore models accurately describe sigma and PS experimental data in cat and human skeletal muscle. Therefore, experimental data resulting from complex microvascular transport processes are well characterized by simple pore models.

Albumins↗

PubMed2002

Development of combinatorial chemistry methods for coatings: high-throughput optimization of curing parameters of coatings libraries.

An automated analytical system has been implemented for the high-throughput optimization of processing conditions such as curing parameters in fabrication of UV-cured automotive organic protective coatings. Selection of optimum process conditions of combinatorial arrays of coatings is essential to correlate the high-throughput screening and conventional processes and to achieve the desired physical properties of coatings. For monitoring of curing conditions of each coating in the array, a viscosity-sensitive fluorophore 4,4'-bis(2-benzoxazolyl)stilbene was incorporated into coating formulations. This fluorescence tagging approach permitted us to combine a gradient temperature heater and a UV curing system with the full capabilities of our high-throughput screening system, including generation of spectroscopic data and its analysis. This investigation demonstrated the possibility of rapid decoupling of temperature and radiation effects in curing of UV-curable coating formulations by using multiple coatings and process conditions at once. While the system described here was implemented for high-throughput optimization of temperature conditions of radiation curing of arrays of organic protective coatings for automotive applications, this system can be further applied for a variety of other applications where optimization of process parameters can be studied in situ or off-line using optical spectroscopic tools.

Journal Article↗

PubMed2001

Particle-inflow-gun-mediated genetic transformation of buffel grass (Cenchrus ciliaris L.): optimizing biological and physical parameters.

The present study was conducted to optimize various biological and physical parameters for developing an efficient and reproducible gene transfer method for genetic transformation of buffel grass. Transformation was carried out using a helium-driven particle inflow gun (PIG). Embryogenic calli produced from mature seeds of buffel grass cv. CC-119 were separately bombarded with four plasmids, containing Actin (pAct1DX), Ubiquitin (pAHC-25; pAHC-27) and CaMV-35S (pCaMVGUS) promoters, coated on tungsten and gold particles. The efficiency of transformation was monitored through transient GUS expression. Different parameters, viz., the type of promoter, type and size of microcarrier, helium gas pressure, distance and time of bombardment, were standardized for delivering DNA into embryogenic calli. Bombardment with plasmid DNA carrying the actin promoter coated on 1.6 micro gold particles, at a helium pressure of 4 bars, a distance of 10 cm for 10 micro sec and 28 mm Hg vacuum in the chamber, produced the best result in transient GUS expression. The Actin promoter was found to be more efficient in driving expression of the GUS gene in buffel grass, followed by Ubiquitin and CaMV-35S promoters. Lower helium pressure was found to be sub-optimal, while higher pressure produced a smaller number of blue spots, probably due to excessive damage to the cells. Maximum of 385 blue spots was observed with gold particles of 1.6 micro size, whereas only 213 blue spots were recorded for tungsten particles of 1.0 micro size. The optimized parameters can be employed for genetic transformation of buffel grass with genes of agronomic importance.

Journal Article↗

PubMed1998

Oscillatory network controlling six-legged locomotion. Optimization of model parameters.

The model of a legged locomotory system is optimized to ensure stable motion, reliable with respect to different initial conditions. The cost function suggested is based on the frequency of the model's loss of stability evaluated for randomly chosen initial leg positions. The optimized model can start from the majority of allowed leg configurations, demonstrating stable walking at low and moderate speeds. Furthermore, an acceleration procedure is designed to permit the model to pick up practically every speed and then walk successfully.

Journal Article↗

PubMed2002

Optimization of experimental parameters for electron capture dissociation of peptides in a Fourier transform mass spectrometer.

This paper describes our effort in optimizing the experimental parameters for electron capture dissociation (ECD) of peptides in a commercially available Fourier-transform mass spectrometer. Using a built-in electrically heated filament electron gun, it was demonstrated that good quality ECD spectra of peptides (MW < 2500) could be obtained by irradiating the isolated peptide molecule-ions with a short pulse (50 ms) of low-energy (3-6 eV) electrons. In addition, we have also demonstrated that pulsing of inert cooling gas (argon) could further improve the intensity of the ECD-induced fragment ions. Due presumably to the influence of the strong magnetic field on the trajectories of electrons, the distance between the electron gun and the trapped-ion cell (i.e., 108 mm versus 20 mm) was found to have little influence on the efficiency of the ECD process(es). From a systematic study on the impact of the filament heating current, filament bias voltage, and electron irradiation time on the intensities of precursor ions and various fragment ions, it was postulated that subsequent capture of electrons by the fragment ions, i.e., neutralization of the fragment ions, might be a significant event for limiting the intensity of the fragment ions.

Amino Acid Sequence↗

PubMed2005

[Detection of IgH rearrangements using real-time quantitative PCR and its reaction parameters].

To investigate the optimal reaction conditions of clonal rearrangements of immunoglobulin heavy chain (IgH) gene using polymerase chain reaction (PCR) with consensus primers and the feasibility of detecting this gene using SYBR green I real-time quantitative PCR with consensus primers, the systemic experiments were performed, which included annealing temperature, concentration of primer, the amount of Taq enzyme, concentration of dNTP and Mg(2+), number of PCR cycles. Detection of this gene on SYBR green I real-time quantitative PCR with consensus primers was carried out under the optimal reaction parameters obtained from previous study, and the sensitivity of IgH rearrangements gene was examined by using SYBR green I real-time quantitative PCR. The results indicated that the optimal annealing temperature was 60 degrees C, the optimal concentration of primers was 0.8 micromol/L, the satisfactory Taq enzyme amount was 0.5 U, the optimal concentration of dNTP was 100 micromol/L, the optimal concentration of Mg(2+) was 3.0 mmol/L, the suitable number of cycle was 40 cycles. Amplification of IgH rearrangement gene and detection of desired gene fluorescence signal on SYBR green I real-time PCR were performed. The sensitivity of IgH gene using this quantitative PCR was 10(4)/ml. It is concluded that the optimal reaction parameters for amplification of clonal IgH rearrangements gene by using PCR technique was determined, and stable and specific amplification of desired gene with consensus primers was performed. Basically, IgH rearrangement gene was successfully detected by SYBR green I real-time PCR.

Benzothiazoles↗

PubMed2004

Optimized LOWESS normalization parameter selection for DNA microarray data.

BACKGROUND: Microarray data normalization is an important step for obtaining data that are reliable and usable for subsequent analysis. One of the most commonly utilized normalization techniques is the locally weighted scatterplot smoothing (LOWESS) algorithm. However, a much overlooked concern with the LOWESS normalization strategy deals with choosing the appropriate parameters. Parameters are usually chosen arbitrarily, which may reduce the efficiency of the normalization and result in non-optimally normalized data. Thus, there is a need to explore LOWESS parameter selection in greater detail. RESULTS AND DISCUSSION: In this work, we discuss how to choose parameters for the LOWESS method. Moreover, we present an optimization approach for obtaining the fraction of data points utilized in the local regression and analyze results for local print-tip normalization. The optimization procedure determines the bandwidth parameter for the local regression by minimizing a cost function that represents the mean-squared difference between the LOWESS estimates and the normalization reference level. We demonstrate the utility of the systematic parameter selection using two publicly available data sets. The first data set consists of three self versus self hybridizations, which allow for a quantitative study of the optimization method. The second data set contains a collection of DNA microarray data from a breast cancer study utilizing four breast cancer cell lines. Our results show that different parameter choices for the bandwidth window yield dramatically different calibration results in both studies. CONCLUSIONS: Results derived from the self versus self experiment indicate that the proposed optimization approach is a plausible solution for estimating the LOWESS parameters, while results from the breast cancer experiment show that the optimization procedure is readily applicable to real-life microarray data normalization. In summary, the systematic approach to obtain critical parameters in the LOWESS technique is likely to produce data that optimally meets assumptions made in the data preprocessing step and thereby makes studies utilizing the LOWESS method unambiguous and easier to repeat.

Algorithms↗

PubMed1998

Aerosolization of cationic lipid:pDNA complexes--in vitro optimization of nebulizer parameters for human clinical studies.

Previously, we have described the optimization of the aerosol delivery of a nonviral gene therapy vector to the lungs of rodents (Eastman et al., 1997b). Although aerosolizing cationic lipid:pDNA complexes into a whole-body exposure chamber resulted in high levels of reporter gene expression in the lungs of BALB/c mice, the conditions employed were not optimal for the delivery of lipid:pDNA complexes to the lungs of human patients. That is, the consumption rate of the material in the nebulizer, and thus the delivery time, were very slow and the aerosol was delivered in a continuous flow. Here we describe in vitro experiments used to develop a cationic lipid:pDNA aerosol with characteristics more suitable for delivery to the lungs of humans, as a necessary prerequisite for conducting a clinical study with human cystic fibrosis patients. Using cascade impactors and all-glass impingers, we have screened several commercially available nebulizers for their ability to deliver intact, respirable, active lipid:pDNA complexes in the shortest time possible, and have identified the Pari LC Jet Plus nebulizer as the optimal nebulizer that meets these criteria. Using this nebulizer in an intermittent mode to mimic breath actuation, consumption rates of approximately 0.6 ml/min of the cationic lipid:pDNA complexes (6 mM cationic lipid:8 mM pDNA) were obtained. The plasmid DNA remained intact and the complexes were shown to maintain activity throughout the nebulization run. Based on measurements of the nebulized dose and the mass median aerodynamic diameter, we calculate a delivered dose of approximately 22 micromol (7.2 mg) of pDNA for each 8 ml of cationic lipid:pDNA complex aerosolized to the lungs of a human patient. This dose should be sufficient to test the clinical efficacy of cationic lipid-mediated gene delivery for the treatment of cystic fibrosis.

Aerosols↗

PubMed2005

Comparison of artificial neural network and multiple linear regression in the optimization of formulation parameters of leuprolide acetate loaded liposomes.

PURPOSE: We planned to optimize the effect of formulation variables on the percent drug entrapment (PDE) of the liposomes encapsulating leuprolide acetate by reverse phase evaporation method using Artificial neural network (ANN) and Multiple linear regression (MLR). METHOD: Twenty seven formulations were prepared based on 3x3 factorial design. The volume of aqueous phase (X(1)), HSPC/DSPG [negative charge] (X(2)), and HSPC/Cholesterol (X(3)) were selected as the causal factors. Potential variables such as concentration of lipid: drug and hydration medium were kept constant in experimental design. The PDE (dependent variable) and the transformed values of independent variables were subjected to multiple regression analysis to establish a second order polynomial equation (full model). A set of PDE and causal factors was used as tutorial data for the ANN and fed into a computer. The feed forward back propagation (bp) method was optimized. The ANN model and MLR were validated for accurate prediction of PDE. RESULTS: To simplify the polynomial equation, F-statistic was applied to reduce polynomial equation (reduced model) by neglecting non-significant (P<0.05) terms. The reduced polynomial equation was used to plot three two-dimensional contour plots at fixed levels of -1, 0 and 1 of the variable X(3) to obtain various combination values of the two other independent variables (X(1) and X(2)) at predetermined PDE. The root mean square value of the trained ANN model by feed forward bp method was 0.0000354, which indicated that the optimal model was reached. The optimization methods developed by both ANN and MLR were validated by preparing another six liposomal formulations. The predetermined PDE (from ANN and MLR) and the experimental data were compared with predicted data by paired "t" test, no statistically significant difference was observed. ANN showed less error compared to MLR. CONCLUSIONS: These findings demonstrate that the ANN model provides more accurate prediction and is quite useful in the optimization of pharmaceutical formulations when compared to multiple regression analysis method. The normalized error (NE) value observed with the optimal ANN model was 0.0211 while it was 0.0658 for the full model in the case of second-order polynomial equation composed of the combination of causal factors (X(1), X(2) and X(3)). Thus the derived equation, contour plots and ANN helps in predicting the values of the independent variables for maximum PDE in the preparation of leuprolide acetate liposomes by reverse phase evaporation technique.

Chemistry, Pharmaceutical↗

PubMed2006

Optimization of process parameters for reduction of gossypol levels in cottonseed meal by Candida tropicalis ZD-3 during solid substrate fermentation.

The objective of this work is to optimize the process parameters for detoxification of gossypol in cottonseed meal (CSM) by Candida tropicalis ZD-3 during solid substrate fermentation (SSF). The maximum detoxification efficiency of gossypol was achieved by employing the substrate, which consists of 70% of CSM, 20% of corn flour and 10% of wheat bran. The optimum fermentation conditions for gossypol detoxification are incubation period of 48h, incubation temperature at 30 degrees Celsius, inoculum level 5% v/w, moisture content of solid substrate 50% and pH in nature. Adding minerals solution to CSM substrate benefit fermentation detoxification.

Animal Feed↗

PubMed2002

Corticospinal volleys and compound muscle action potentials produced by repetitive transcranial stimulation during spinal surgery.

OBJECTIVES: To report our experience with neurophysiological monitoring of corticospinal function using compound muscle action potentials (CMAPs) produced by repetitive transcranial electrical stimulation in a large series of patients, after defining optimal stimulus parameters in a small group of patients. METHODS: In 100 patients undergoing spinal surgery, corticospinal volleys were recorded using epidural electrodes, or CMAPs were recorded from innervated muscles, or both techniques were used to monitor spinal cord function. In subsets of patients, stimulus parameters were varied to determine the optimal parameters for CMAP recordings, using the corticospinal volleys to guide the initial choice. RESULTS: Recordings of corticospinal volleys indicated that less energy was delivered to the cortex if the duration of each stimulus in the stimulus train was brief (e.g. 50 micros) and that there was attenuation of D and I waves in the corticospinal volley when the interstimulus interval in the train was <5 ms. An interstimulus interval of 5 ms proved significantly more effective than an interstimulus interval of 2 ms in evoking CMAPs, but resulted in a more complex, dispersed electromyographic (EMG) potential. The superiority of the 5 ms interval did not depend on stimulus intensity or the existence of pre-existing neurological deficit. Using trains of 5 pulses of duration 50 micros, interstimulus interval 5 ms and intensity 500 V, satisfactory CMAPs could be recorded in 55 of 82 patients, significantly less often in neurologically impaired patients than in neurologically normal subjects. Epidural recordings of the corticospinal volley were obtained in 61 of 69 patients, again more often in neurologically normal subjects. CONCLUSIONS: When epidural recordings can be made, direct recordings of corticospinal activity are probably more reliable than recordings of CMAPs. However, epidural recordings are not suitable under all circumstances, and the ability to record CMAPs reliably represents an advance in intraoperative monitoring. Under the anaesthetic conditions used in the present study, the optimal stimulus parameters consist of a train of 5 stimuli of 50 micros duration at an interstimulus interval of 5 ms and an intensity of 500 V.

Action Potentials↗

PubMed1995

Collaborative project to establish the optimal period and parameters for detection of reproductive toxicity in male rats--effects of compound T on male fertility.

To assess the optimal dosing period and parameters for measurement of effects on male fertility, Compound T was administered to male Jcl:Wistar rats at dosage levels of 0, 2, 10 and/or 50 mg/kg/day for 4 weeks (Experiment 1) or for 9 weeks (Experiment 2). Experiment 1: In the 50 mg/kg group, the ventral prostate weight was low when compared to the control value, and desquamation of round spermatids was observed in the testes. Experiment 2: When treated males were mated with untreated females after dosing for 9 weeks (the first mating), the fertility index was slightly lowered and preimplantation loss was significantly elevated in the 50 mg/kg group as compared to the control values. In this treatment group, serum testosterone level at 2.5 hours after dosing was significantly decreased after dosing for 12 weeks, and degeneration of spermatids/spermatocytes in the testis and epididymis was observed after dosing for 13 weeks. After a recovery period of for 6 weeks, remating resulted in copulatory and fertility indices and cesarean section data which were comparable in all groups. In conclusion, there were no differences in toxicity relevant to male fertility between 4 and 9 weeks of dosing, and it is considered that the observed changes resulted from decreased function of Sertoli cells due to depressed production/secretion of testosterone.

Animals↗

PubMed1992

Sensitivity of muscle force estimations to changes in muscle input parameters using nonlinear optimization approaches.

The purpose of this study was to analyze the sensitivity of muscle force calculations to changes in muscle input parameters. Force sharing between two synergistic muscles was derived analytically for a one-degree-of-freedom system using three nonlinear optimization approaches. Changes in input parameters that are within normal anatomical variations often caused changes in muscular forces exceeding 100 percent. These results indicate that errors in muscle force calculations may depend as much on inadequate muscle input parameters as they may on the choice of the objective and constraint functions of the optimization approach.

Models, Biological↗