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Results for “parameter optimization”

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PubMed2002

Optimized stimulation and recording parameters of human 'nociception specific' blink reflex recordings.

OBJECTIVE: Few non-invasive methods are available for studying trigeminal nociception in humans. The 'nociception specific' blink reflex (nBR) is elicited by a preferential stimulation of trigeminal nociceptive fibers and is highly sensitive to changes in trigeminal nociception. The aim of this study was to establish its optimal stimulation parameters. METHODS: The inter-individual variability of R2 responses (41 healthy subjects), symmetry of R2 responses after right vs. left sided stimulation (25 subjects), optimal stimulation parameters (3 groups, each 16 subjects) and re-test reliability over time (15 subjects) were studied. RESULTS: The nBR had a R2 response with a latency of 44.7+/-7.3ms, but no R1 response. The mean difference of R2 latencies (right vs. left sided stimulation) was 0.4+/-2.1(SD)ms, the mean ratio of the R2 response areas (RA) was 1.05+/-0.39 (SD). Thus, lateral differences of onset latencies greater than 4.6ms (0.4+4.2 (2SD)) or >1.83-fold (1.05+0.78 (2SD)) of RA can be assumed as outside of normal range. Long inter-block intervals of 7min minimized the cumulative habituation of R2 RAs to 23%, onset latencies remained constant. Re-test reliability over 4 weeks was high both for latencies (Crohnbach's alpha=0.85) and RAs (alpha=0.94). CONCLUSIONS: The nBR with the established stimulation parameters could be used for studying trigeminal nociception.

Adult↗

PubMed2005

Radiofrequency ablation of the pancreas. I: Definition of optimal thermal kinetic parameters and the effect of simulated portal venous circulation in an ex-vivo porcine model.

CONTEXT: Radiofrequency ablation of pancreatic tumours carries a risk of injury to important structures such as the bile duct and duodenum. We have recently developed an ex-vivo model of radiofrequency ablation of the porcine pancreas. OBJECTIVE: This study evaluates the effect of variations in probe temperature, duration of ablation and simulated portal venous flow on radiofrequency-induced injury. SPECIMEN RETRIEVAL: Pancreata of 30 6-month-old healthy pigs undergoing sacrifice in a commercial abattoir were used. INTERVENTIONS: Radiofrequency energy was applied to a pre-marked area of the pancreatic head. Pancreatic head biopsies were taken after ablation to incorporate duodenum, portal vein and bile duct respectively and frozen in liquid nitrogen. For each experiment a portion of the tail of the pancreas was studied as non-ablated control. Paired slides using haematoxylin and eosin (H&E) and nicotinamide adenine dinucleotide (NADH) stains were prepared. MAIN OUTCOME MEASURES: The effects of variation in target temperature (100 degrees C to 80 degrees C), duration of ablation and of simulated portal perfusion were studied. RESULTS: Optimal thermal kinetic characteristics were produced by a target temperature of 90 degrees C applied for 5 minutes. At this temperature there was ablation of pancreas without injury to adjacent viscera. Higher temperatures resulted in injury to the bile duct and portal vein. Simulated portal circulation had no effect on ablation. CONCLUSIONS: In this ex-vivo study radiofrequency produced a temperature and duration dependent ablation with the optimal characteristics being 90 degrees C for 5 minutes.

Animals↗

PubMed2005

Bioremediation of chromium contaminated soil: optimization of operating parameters under laboratory conditions.

Bacterial strains were isolated and enriched from the contaminated site of Tamil Nadu Chromates and Chemicals Limited (TCCL) premises, Ranipet, Tamil Nadu, India. The strain which was isolated from the highly contaminated location had shown high Cr(VI) reduction potential. Cr(VI) reduction was evaluated both in aerobic and anaerobic conditions. Though the aerobic system performed better than the anaerobic one, further study were carried out in the anaerobic condition due to its economic viability. At higher initial concentration, Cr(VI) reduction was not complete even after 108 h, however, specific Cr(VI) reduction, unit weight of Cr reduced/unit weight of biomass was greater at higher concentration. It was found that a bacterial concentration of 15+/-1.0 mg/g of soil (wet weight) 50 mg of molasses/g of soil as carbon source were required for the maximum Cr(VI) reduction. The bioreactor operated at these conditions could reduce entire Cr(VI) (5.6 mg Cr(VI)/g of soil) in 20 days. The Cr(III) thus formed was found to be strongly attached to the soil matrix and the mobility of Cr(III) was negligible as evident from the low concentration of Cr(III) in the leachate. This study showed that bioremediation is a viable, environmental friendly technology for cleaning-up the chromium contaminated site at TCCL, Ranipet, Tamil Nadu, India, and optimal operating conditions under laboratory conditions were evaluated.

Bacteria, Aerobic↗

PubMed2000

Bioheat transfer analysis of cryogen spray cooling during laser treatment of port wine stains.

BACKGROUND AND OBJECTIVE: The thermal response of port wine stain (PWS) skin to a combined treatment of pulsed laser irradiation and cryogen spray cooling (CSC) was analyzed through a series of simulations performed with a novel optical-thermal model that incorporates realistic tissue morphology. STUDY DESIGN/MATERIALS AND METHODS: The model consisted of (1) a three-dimensional reconstruction of a PWS biopsy, (2) a Monte Carlo optical model, (3) a finite difference heat transfer model, and (4) an Arrhenius thermal damage calculation. Simulations were performed for laser pulses of 0.5, 2, and 10 ms and a wavelength of 585 nm. Simulated cryogen precooling spurts had durations of 0, 20, or 60 ms and terminated at laser onset. Continuous spray cooling, which commenced 60 ms before laser onset and continued through the heating and relaxation phases, was also investigated. RESULTS: The predicted response to CSC included maximal pre-irradiation temperature reductions of 27 degrees C at the superficial surface and 12 degrees C at the dermoepidermal junction. For shorter laser pulses (0.5, 2 ms), precooling significantly reduced temperatures in superficial regions, yet did not effect superficial vessel coagulation. Continuous cooling was required to reduce significantly thermal effects for the 10-ms laser pulse. CONCLUSIONS: For the PWS morphology and treatment parameters studied, optimal damage distributions were obtained for a 2-ms laser pulse with a 60-ms precooling spurt. Epidermal and vascular morphology as well as laser pulse duration should be taken into account when planning CSC/laser treatment of PWS. Our novel, realistic-morphology modeling technique has significant potential as a tool for optimizing PWS treatment parameters.

Biopsy↗

PubMed2005

Enantioseparation of chiral allenic acids by micellar electrokinetic chromatography with cyclodextrins as chiral selector.

Enantioseparation of chiral aryl allenic acids by micellar electrokinetic chromatography (MEKC) with cyclodextrins (CDs) as chiral selectors was described. The screen of chiral selectors (beta-CD, gamma-CD, and hydroxypropyl (HP)-gamma-CD) showed that the enantioseparation was not only dependent on the type of CD but also the presence of 2-propanol in the buffer. In order to optimize the operational parameters, the effect of the concentration of CDs, sodium dodecyl sulfate (SDS), and 2-propanol, as well as the buffer ionic strength and pH on enantioseparation were studied. It was proved that the concentration of CDs, 2-propanol, and the buffer ionic strength were the critical parameters. Under optimal conditions, baseline separations of all seven allenic acid enantiomers were achieved. Furthermore, the method validation in terms of repeatability, linearity, limit of detection (LOD), and limit of quantitation (LOQ) were performed. Using the present method, the optical purity of a nonracemic sample with the enantiomeric excess (e.e.%) value of 99.65% was determined.

2-Propanol↗

PubMed2004

Bioresorbable nanofiber-based systems for wound healing and drug delivery: optimization of fabrication parameters.

Wound healing is a complex process that often requires treatment with antibiotics. This article reports the initial development of a biodegradable polymeric nanofiber-based antibiotic delivery system. The functions of such a system would be (a) to serve as a biodegradable gauze, and (b) to serve as an antibiotic delivery system. The polymer used in this study was poly(lactide-co-glycolide) (PLAGA), and nanofibers of PLAGA were fabricated with the use of the electrospinning process. The objective of this study was to determine the effect of fabrication parameters: orifice diameter (needle gauge), polymer solution concentration, and voltage per unit length, on the morphology and diameter of electrospun nanofibers. The needle gauges studied were 16 (1.19 mm), 18 (0.84 mm), and 20 (0.58 mm), and the range of polymer solution concentration studied was from 0.10 g/mL to 0.30 g/mL. The effect of voltage was determined by varying the voltage per unit electrospinning distance, and the range studied was from 0.375 kV/cm to 1.5 kV/cm. In addition, the mass per unit area of the electrospun nanofibers as a function of time was determined and the feasibility of antibiotic (cefazolin) loading into the nanofibers was also studied. The results indicate that the diameter of nanofibers decreased with an increase in needle gauge (decrease in orifice diameter), and increased with an increase in the concentration of the polymer solution. The voltage study demonstrated that the average diameter of the nanofibers decreased with an increase in voltage. However, the effect of voltage on fiber diameter was less pronounced as compared to polymer solution concentration. The results of the areal density study indicated that the mass per unit area of the electrospun nanofibers increased linearly with time. Feasibility of drug incorporation into the nanofibers was demonstrated with the use of cefazolin, a broad-spectrum antibiotic. Overall, these studies demonstrated that PLAGA nanofibers can be tailored to desired diameters through modifications in processing parameters, and that antibiotics such as cefazolin can be incorporated into these nanofibers. Therefore, PLAGA nanofibers show potential as antibiotic delivery systems for the treatment of wounds.

Anti-Bacterial Agents↗

PubMed2004

Optimizing the sequence parameters for double-quantum CRAZED imaging.

The evolution of magnetization during repeated application of the double-quantum-(DQ)-CRAZED sequence is analyzed, with the aim of identifying sequence parameters that maximize sensitivity to signal produced by the distant dipole field (DDF). Phase cycling schemes that allow cancellation of signals following undesired coherence pathways are also described. Simulations and imaging experiments carried out at 3 T on phantoms and the human head were used to verify the analysis. The results indicate that in the absence of phase cycling, the DDF-related signal-to-noise ratio (SNR) per unit time is maximized using TR=2.05 T1, along with values of the RF flip angles (alpha approximately 90 degrees and beta approximately 60 degrees ), and echo time (TE=T2) that have previously been shown to maximize the DDF-related signal at long TR. However, with TR=2.05 T1 there can also be a significant signal contribution due to stimulated echo effects (up to 40% of the signal for water at 3 T and TE=70 ms). Using a two-step phase cycle, the stimulated echo signal is eliminated and the maximum SNR per unit time occurs for TR=2.76 T1. It is also demonstrated that sensitivity to signal changes caused by small variations in T2 is maximized by setting TE=2T2.

Brain↗

PubMed1994

Towards atomic interpretation of F-actin filament three-dimensional reconstructions.

We have recorded dark field images of negatively stained F-actin filaments polymerized with 2 mM MgCl2 and 50 mM KCl with a scanning transmission electron microscope and computed 3-D reconstructions using a helical parameter search to optimize simultaneously the helical repeat length, the radial position of the filament axis, and the helical selection rule. The resulting optimized averaged filament 3-D reconstruction at 2.5 nm resolution is remarkably similar to an atomic model of the F-actin filament. By comparison, several structural features of the reconstruction can be interpreted at the level of distinct secondary structure elements, and predictions made by the atomic model could be verified: for instance, the density connecting the two long-pitch helical strands in our reconstruction co-localizes with an extended beta-hairpin, the "hydrophobic loop" (i.e. residues 262 to 274), which according to the atomic model establishes the major intersubunit contact between the two long-pitch helical strands. The most pronounced structural variations among individual filament 3-D reconstructions were observed in (1) the details of the intersubunit contact pattern between the two long-pitch helical strands, and (2) the exact size and shape of subdomain 2 of the F-actin molecule, which appears rather flexible and easily deformed. In addition, we found that all phenotypes of F-actin filament 3-D reconstructions that arise from small deviations from the optimal helical parameters or from lowering the nominal resolution exhibited stronger intersubunit contacts between than along the two long-pitch helical strands, a structural feature that has been emphasized for a number of F-actin filament 3-D reconstructions in the past. Since this is clearly at variance with the relative strength of the intersubunit contacts as predicted by the atomic model, it may represent an artifactual structural feature arising from low-resolution data or suboptimal helical data processing, and should therefore be interpreted with caution in terms of indicating chemical, mechanical or conformational states of the F-actin filament.

Actins↗

PubMed1998

Energy dissipation as a key factor for electroporation of protoplasts.

Energy dissipation (epsilon) during electroporation was theoretically determined to be epsilon = 0.5CV02 for the various combinations of capacitance (C) and initial voltage (V0). Experiments on asparagus protoplasts established that electroporation efficiency (EE) and survival rate were directly proportional to energy dissipation during electroporation. A positive linear relationship exists between energy dissipation per unit volume and EE, whereas energy dissipation per unit volume and survival rate of protoplasts are related in a negative linear manner. At the same energy level, longer time constants were more effective at increasing EE. This suggests that energy dissipation approximating rectangular waveforms is more important than that dissipated as sharply decaying exponential waveforms. With energy as the key parameter, the optimization of electrical parameters for efficient electroporation is greatly simplified, is not machine-dependent, and generally applies to all species.

Cell Survival↗

PubMed1996

Digital chest radiography--optimizing image processing parameters for the visibility of chest lesions and anatomy.

The effect of varying the degree of contrast and edge enhancement upon the visibility of chest lesions and anatomy was evaluated in a digital image intensifier system for chest radiography. Visual grading analysis was used as method for the evaluation. Conventional radiographs served as reference images. Ten observers graded the visibility of four regions of interest: (1) fine linear structures, (2) mediastinal anatomy, (3) rounded opacities, (4) vessels, and also graded the overall quality of 17 chest images. The images had been subjected to three grades of image processing: one basic, one intermediate, and one extreme. In all, 2730 observations were made. The basic image processing was the best for the visibility of regions 2, 3, and 4 and for the overall quality. The intermediate image processing was best for the fine linear structures. The extreme image processing rated lowest for all regions and especially for the overall quality.

Humans↗

PubMed2007

The utilization of beet molasses as a novel carbon source for cephalosporin C production by Acremonium chrysogenum: Optimization of process parameters through statistical experimental designs.

In this work, cephalosporin C (CPC) production on pilot scale fermenters of 600l capacity with 350l working volume by Acremonium chrysogenum EMCC 904 was performed. The effects of fermentation medium composition, inoculum concentration, initial pH and aeration rate on CPC production by A. chrysogenum strain was investigated by using response surface methodology (RSM). The Plackett-Burman design which involves two concentrations of each nutrient was effective in searching for the major medium components promoting CPC production. Under our experimental conditions; Soya oil, beet molasses and corn steep liquor were found to be the major factors contributing to the antibiotic production. Subsequently, a Box-Behnken design was used for outlining the concentration of the most effective medium constituents. Estimated optimum composition for the production of CPC was as follows: soya oil, 40g/l; beet molasses, 180g/l; and corn steep liquor, 330g/l. The central composite design was used for outlining the optimum values of the fermentation parameters. Estimated optimum values for the production of CPC are as follows: inoculum level, 10(5.5)spores/ml; initial pH, 4.3; and aeration rate, 9364ml/min.

Acremonium↗

PubMed1976

High-performance ion-pair partition chromatography of sulfa drugs. Study and optimization of chemical parameters.

High-performance ion-pair partition chromatography is shown to be a versatile, efficient method for separating sulfonamides. For a group of fourteen sulfa drugs varying widely in pKA and hydrophobicity, the effect of mobile phase composition, counterion composition, pH, and ionic strength on their ion-pair partition chromatographic separation using tetrabutylammonium as the counterion and n-butanol-n-heptane as the mobile phase is shown. Wide variation in k' and a is possible by changing these parameters. Silica columns coated with buffered aqueous solutions of tetrabutylammonium sulfate resulted in efficiencies of 4000-6000 theoretical plates per 25 cm. These columns are stable for long periods of time, and can be stripped and re-used in the adsorption mode with little or no loss in efficiency. Several chromatograms are presented in order to illustrate the performance of ion-pair partition chromatography.

Absorption↗

PubMed2000

The effects of maturation and stimulus parameters on the optimal f(2)/f(1) ratio of the 2f(1)-f(2) distortion product otoacoustic emission in neonates(1).

Distortion product otoacoustic emission (DPOAE) measurements are becoming popular in the clinical realm because they have been shown to reflect cochlear function. The primary tones used to evoke the DPOAE are important in determining the amplitude of the emission recorded in the ear canal. This study examined the ratio of the primaries necessary to determine the maximum amplitude emission as a function of development, stimulus level and frequency. Optimum f(2)/f(1) ratios were measured utilizing the f(1)-sweep technique from 105 neonates between 30-42 weeks conceptional age (CA) and 40 adults. No significant difference for optimum ratio was shown between the neonatal and the adult groups. Primary tone frequency had a significant effect on optimum ratio for both neonates and adults. Low f(2) frequencies (<4 kHz) were associated with higher optimum ratios than high f(2) frequencies (>4 kHz). The adult group was used to investigate the effect of stimulus level on the optimum f(2)/f(1) ratio for f(2) frequencies from 1.7 to 10 kHz. Regression analysis showed significant differences across levels of the primaries at all frequencies except for f(2)=3.4 and 7.0 kHz. These differences in f(2)/f(1) ratio across stimulus frequency and level may be attributed to the change in the shape of the excitation profiles along the basilar membrane.

Acoustic Stimulation↗

PubMed1999

Measuring liability for schizophrenia using optimized antisaccade stimulus parameters.

The ability to identify unaffected gene carriers within families may be crucial to the success of schizophrenia genetics studies. Data collected from three family samples (N = 365) demonstrated that poor antisaccade performance is an exceptionally promising indicator of liability for schizophrenia. A particular antisaccade task version provides large separations (5-6 sigma) between proband and normal groups. Poor antisaccade performance alone correctly identified 70% of patients in California, Utah, and Micronesia schizophrenia samples. Twenty-five to 50% of these patients' nonpsychotic first-degree relatives also had poor antisaccade performance, yielding risk ratios around 20:1 for simplex and 50:1 for multiplex schizophrenia families. Poor antisaccade performance is associated with dorsolateral prefrontal cortex pathology, suggesting that dysfunction of this circuitry also may predispose individuals to developing this disease.

Adult↗

PubMed2007

Analysis of a model virus using residue-specific chemical cleavage and MALDI-TOF mass spectrometry.

A nonenzymatic proteomics strategy is applied to the rapid identification of viruses. The approach provides solubilization and subsequent digestion of viral coat proteins in under 30 s. Acid digestions were carried out using a laboratory-quality microwave system equipped with temperature, pressure, and power controls, which allowed for precise optimization of experimental parameters. Under optimal conditions, this method provides an efficient alternative to traditional enzymatic digestion-based methods for virus identification. Following rapid microwave heating of a suspension of a model virus, RNA bacteriophage MS2, 13 chemical digestion products were detected in parallel with the coat protein precursor using MALDI-TOF MS. Because of the high sequence coverage obtained, the bacteriophage MS2 coat protein was identified with high confidence and the specificity of the identification allowed for the discrimination between bacteriophage MS2 and other closely related RNA bacteriophages.

Amino Acid Sequence↗

PubMed2006

Three-dimensional lattice Monte Carlo simulations of model proteins. IV. Proteins at an oil-water interface.

Lattice Monte Carlo simulations describe the adsorption of protein-like heteropolymer chains at an oil/water interface. The heteropolymers are designed sequences of 27 and 64 amino acid-type lattice sites taken from a 20-letter alphabet. We use our recently suggested energy scale to model oil and water. We investigate the effect of the oil parameters on adsorption properties of a single chain and on the aggregation of adsorbed chains while keeping the water parameters fixed to their optimum values found previously. By varying the oil parameters, we can cause a large range of adsorption behavior: from no adsorption to reversible adsorption to irreversible adsorption. We compare adsorption at a liquid/solid interface to that at a liquid/liquid interface. A liquid interface leads to stronger adsorption and denaturation than a solid interface with the same water and oil interaction parameters. We propose "optimal" oil parameters and use them to study multichain adsorption at a liquid interface.

Adsorption↗

PubMed1999

Trace eyeblink conditioning in the freely moving rat: optimizing the conditioning parameters.

Trace eyeblink conditioning (EBC) parameters, with an airpuff unconditioned stimulus, were examined in male Fischer 344 X Brown Norway F1 rats. Integrated electromyographic activity from the upper eyelid was recorded. An 8-kHz tone was superior to white noise as a conditioning stimulus. Rats trained with 30 or 50 trials per session showed similar learning. Reversal of environmental lighting had no significant effect. Trace intervals of 0 and 250 ms yielded well-timed conditioned responses (CRs); intervals of 500 ms or more did not. These experiments provide parameters that reliably yield CRs and suggest limits on the temporal processing capabilities of the rat. EBC can thus be used as part of a comprehensive test battery for learning and memory in this species. Physiological recording and pharmacological manipulations may also be done easily. This combination of approaches should facilitate a more complete understanding of learning mechanisms and age-related memory impairments.

Animals↗

PubMed1995

[Comparison of input grey values and contrast profiles: a contribution to the discussion on optimization of evaluation parameters in storage phosphorus radiography].

On comparing the individual imaging stages in conventional and digital image radiography it becomes evident that a significant advantage of the digital method is the possibility to adapt the image character and exposure dose individually to various problems requiring an answer. To take advantage of this it is imperative to optimise image processing with care, especially contrast processing. No systematic procedure based on objective criteria had existed to date. This paper describes a method of taking into account both the diagnostic significance of the structures to be imaged and their distribution within the relevant density range, in order to arrive at the best possible contrast conversion. A prerequisite is to know for every kind of imaging which distribution of grey values pertaining to the relevant structures can be expected before digital image processing (initial grey values). This distribution determines the most favourable contrast conversion. The processing parameters for several types of imaging were optimised by this method. The method is demonstrated via thoracic images of newborn and children.

Child, Preschool↗