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At least 415 records · Page 23Linked to original sources
PubMed2003

Effects of media, fertilization technique, extender, straw volume, and sperm to egg ratio on hatchability of cyprinid embryos, using cryopreserved semen.

To enable cryopreservation of fish semen to become an efficient, routine technique, much more detailed information is required. Therefore, the present study was conducted to investigate various fertilization techniques and media, straw volumes as well as optimal semen volume for cryopreservation. The bleak (Chalcalburnus chalcalburnus) was used as the main model for investigation. Using frozen-thawed semen the fertilization rate was similar up to the morula stage, independent of the fertilization technique. Thereafter, in egg batches fertilized using the wet technique most embryo development stopped. In egg batches fertilized using the dry technique, embryonic development proceeded normally. For cryopreserved semen full activation of sperm motility was obtained at ratios of fertilization media (hatchery water and all tested types of saline solutions) to semen of 10:1. Sperm motility rate was much higher in the saline solutions than in water. In contrast hatching rates were higher when water was used as fertilization medium. Therefore, the requirements necessary for optimal sperm motility and optimal sperm-egg contact were different and so for these parameters optimal levels could not be achieved. When adjusting the freezing and thawing conditions 0.5ml straws as well as larger straws (1.2ml) proved suitable for cryopreservation of cyprinid semen. The highest fertilization rates were obtained with sperm to egg ratios of (1.3-2.5) x 10(6):1 and were 77-92% of fresh semen control. This was also similar for Ch. nasus, R. meidingerii, B. barbatus and C. carpio and suggests that the cryopreservation requirements of spermatozoa are not species specific.

Animals↗
PubMed2005

Technical considerations for implementation of x-ray CT polymer gel dosimetry.

Gel dosimetry is the most promising 3D dosimetry technique in current radiation therapy practice. X-ray CT has been shown to be a feasible method of reading out polymer gel dosimeters and, with the high accessibility of CT scanners to cancer hospitals, presents an exciting possibility for clinical implementation of gel dosimetry. In this study we report on technical considerations for implementation of x-ray CT polymer gel dosimetry. Specifically phantom design, CT imaging methods, imaging time requirements and gel dose response are investigated. Where possible, recommendations are made for optimizing parameters to enhance system performance. The dose resolution achievable with an optimized system is calculated given voxel size and imaging time constraints. Results are compared with MRI and optical CT polymer gel dosimetry results available in the literature.

Acrylic Resins↗
PubMed2000

The boundary element method in the forward and inverse problem of electrical impedance tomography.

In this paper, a new formulation of the reconstruction problem of electrical impedance tomography (EIT) is proposed. Instead of reconstructing a complete two-dimensional picture, a parameter representation of the gross anatomy is formulated, of which the optimal parameters are determined by minimizing a cost function. The two great advantages of this method are that the number of unknown parameters of the inverse problem is drastically reduced and that quantitative information of interest (e.g., lung volume) is estimated directly from the data, without image segmentation steps. The forward problem of EIT is to compute the potentials at the voltage measuring electrodes, for a given set of current injection electrodes and a given conductivity geometry. In this paper, it is proposed to use an improved boundary element method (BEM) technique to solve the forward problem, in which flat boundary elements are replaced by polygonal ones. From a comparison with the analytical solution of the concentric circle model, it appears that the use of polygonal elements greatly improves the accuracy of the BEM, without increasing the computation time. In this formulation, the inverse problem is a nonlinear parameter estimation problem with a limited number of parameters. Variants of Powell's and the simplex method are used to minimize the cost function. The applicability of this solution of the EIT problem was tested in a series of simulation studies. In these studies, EIT data were simulated using a standard conductor geometry and it was attempted to find back this geometry from random starting values. In the inverse algorithm, different current injection and voltage measurement schemes and different cost functions were compared. In a simulation study, it was demonstrated that a systematic error in the assumed lung conductivity results in a proportional error in the lung cross sectional area. It appears that our parametric formulation of the inverse problem leads to a stable minimization problem, with a high reliability, provided that the signal-to-noise ratio is about ten or higher.

Algorithms↗
PubMed2002

Piezoelectrically actuated flextensional micromachined ultrasound transducers--I: theory.

This series of two papers considers piezoelectrically actuated flextensional micromachined ultrasound transducers (PAFMUTs) and consists of theory, fabrication, and experimental parts. The theory presented in this paper is developed for an ultrasound transducer application presented in the second part. In the absence of analytical expressions for the equivalent circuit parameters of a flextensional transducer, it is difficult to calculate its optimal parameters and dimensions and difficult to choose suitable materials. The influence of coupling between flexural and extensional deformation and that of coupling between the structure and the acoustic volume on the dynamic response of piezoelectrically actuated flextensional transducer are analyzed using two analytical methods: classical thin (Kirchhoff) plate theory and Mindlin plate theory. Classical thin plate theory and Mindlin plate theory are applied to derive two-dimensional plate equations for the transducer and to calculate the coupled electromechanical field variables such as mechanical displacement and electrical input impedance. In these methods, the variations across the thickness direction vanish by using the bending moments per unit length or stress resultants. Thus, two-dimensional plate equations for a step-wise laminated circular plate are obtained as well as two different solutions to the corresponding systems. An equivalent circuit of the transducer is also obtained from these solutions.

Computer Simulation↗
PubMed1984

Optimization of an hydroxyapatite adhesion assay for Streptococcus sanguis.

Previous studies have compared the adhesion of [3H]thymidine-labeled Streptococcus sanguis to saliva-coated hydroxyapatite (SHA) and buffer-coated hydroxyapatite (HA) beads. Although the hypotonic buffer used in these assays was adjusted to simulate saliva, it does not necessarily provide the optimal parameters for the quantitative estimate of adhesion under in vitro conditions. Optimization is necessary to provide the maximum sensitivity of the assay for detecting the effects of various salivas as well as for quantitating the effect of environmental growth conditions on the adhesion of S. sanguis to SHA and HA. A major distinction between the adhesion of S. sanguis to SHA and HA was observed when the bacterial concentration was varied. At high cell concentrations, the number of cells adhering to SHA was twice the number adhering to HA. Such differences were not detected at low cell concentrations. The optimal pH for the adsorption to both SHA and HA was 6. Changes in the ionic strength or addition of mono- or divalent cations found in saliva had little effect on adhesion to HA. In contrast, high concentrations of monovalent cations inhibited adhesion to SHA. Anions such as carbonate, chloride, and sulfate did not have specific effects on adhesion, whereas acetate inhibited adhesion to both SHA and HA. Fluoride inhibited adhesion to both SHA and HA, suggesting an interaction between fluoride and hydroxyapatite. These results indicated that 2 mM phosphate buffer at a pH of 6 containing 5 mM KCl and 1 mM CaCl2 was the optimal buffer for studying the in vitro adhesion of S. sanguis to SHA.

Durapatite↗
PubMed1998

Spatial and temporal matching of receptive field properties of binocular cells in area 19 of the cat.

The spatial and temporal properties of single neurons were investigated in area 19 of the cat. We evaluated the matching of binocular receptive field properties with regard to the respective strength of the ipsilateral and contralateral inputs. Results indicate that most cells in area 19 are well tuned to spatial and temporal frequencies and exhibit relatively low contrast threshold (mean=6.8%) when assessed using optimal parameters and tested through the dominant eye. Spatial resolution (mean=0.75 c/degree), optimal spatial frequencies (mean=0.16 c/degree) were relatively low and spatial bandwidths (mean=2.1 octaves) were broader as compared to those of cells in area 17 but comparable to those of cells in other extrastriate areas. On the other hand temporal resolution (mean=10.7 Hz), optimal temporal frequency (mean=4.5 Hz) and temporal bandwidths (mean=2.9 octaves) were higher and broader than in primary visual cortex. A significant relationship exists between most of the cell's properties assessed through either eye. For some parameters, such as spatial and temporal resolution, ocular dominance was shown to be significantly related to the extent of matching between the two eyes. For these parameters, binocular cells that exhibited a balanced ocular dominance were generally well matched with regard to the receptive field properties of each eye whereas the largest mismatches were found in cells that were more strongly dominated by one eye. These results suggest that visual input contributes to the activation of cells in area 19 in a redundant manner, possibly attesting to the multiplicity of parallel pathways to this area in the cat.

Animals↗
PubMedDate not supplied

[Effect of the conditions of isolation of free and bound ligands on the accuracy of the radioimmunoassay of steroids].

Testosterone radioimmunoassay (RIA) was used to analyse the factors which influenced the precision and accuracy of steroid RIA. Selection of optimal parameters (concentrations of activated charcoal and of the radioactive steroid) was necessary in order to reduce the influence of non-specific binding and error of fractionation on the RIA results. The scheme for estimation of the optimal values of these parameters is described.

Charcoal↗
PubMed2006

Use of multivariate analysis for optimization of separation parameters and prediction of migration time, resolution, and resolution per unit time in micellar electrokinetic chromatography.

The optimization of separation parameters in chromatography for better separation and resolution of analytes continues to be a labor intensive procedure usually performed by a trial and error method. A multivariate analysis in the form of multilinear regression (MLR) is used to optimize separation parameters and predict the migration behavior, resolution, and resolution per unit time of achiral (4-chlorophenol, pentachlorophenol, clonazepam, and diazepam) and chiral (1,1'-binaphthyl 2,2'-dihydrogen phosphate (BNP), and 1,1'-bi-2-naphthol (BOH)) compounds in MEKC. Separations of achiral and chiral analytes were performed using an achiral (poly(sodium N-undecylenic sulfate)) molecular micelle and chiral (poly(sodium N-undecanoyl-L-leucylvalinate) or poly(sodium N-undecanoyl-L-isoleucylvalinate)) molecular micelle, respectively, at various operating temperatures, applied voltages, pH values, and molecular micelle concentrations in the BGE. The separation parameters were subsequently used as input variables for MLR models. The models were validated with independent samples. The root-mean-square percent relative error (RMS%RE) is used as a figure of merit for characterizing the performance of the migration time, resolution, and resolution per unit time models. The RMS%RE obtained for predicted migrated times, resolutions, and resolution per unit time of 4-chlorophenol, pentachlorophenol, clonazepam, diazepam, BNP, and BOH ranged between 8 and 19%. The same experimental procedure was used to optimize the separation parameters of six other chiral analytes of different compound class. The predicted migration times, resolutions, and resolution per unit time of the chiral as well as the achiral analytes compare favorably with the experimental migration times and resolutions, indicating versatility and wide applicability of the technique in MEKC.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed1975

Studies on the feasibility of urinary bladder evacuation by direct spinal cord stimulation. I. Parameters of most effective stimulation.

In 30 female dogs, spinal cord stimulation was tested to find the optimal parameters producing good voiding and, hopefully, total bladder emptying. Twelve different electrodes or application modifications were examined. Variable frequencies, stimulus duration, and voltages were applied. Search of the site of highest detrusor response (micturition center) was easily identifiable. It became obvious that electrode design was not of critical importance: the responses were basically the same whether we used the wrap-around electrode, which stimulates an entire level, or the coaxial electrode which theoretically limits the current spread around its minute exposed tip. The stimulation parameters that gave the best results were: 2 to 5 volts; frequency: 10 to 15 cps; duration 1 msec. The site of highest detrusor response was round vertebral level L5 1/2, corresponding to cord level S2-4. Generally, no voiding was obtained because of too high sphincteric contraction during stimulation; it appeared that a sphincteric center overlaps the micturition center in either direction. To achieve successful voiding during stimulation, a separation of these two centers with selective stimulation of the detrusor center is necessary, eleiminating sphincteric contraction.

Animals↗
PubMed1995

Study of microencapsulation for pituitary transplantation: capsule preparation and in vitro study.

We have developed microcapsules using sodium alginate (SA) and Poly-L-Lysine (PLL). A factorial design method of screening was chosen to study influences of different experimental parameters on size and stability of the capsules. We found that air flow affects initial size of the capsules significantly, while the molecular weight (MW) of PLL and incubation time have a positive impact on the expansion when capsules are incubated in sodium citrate (SC). When the capsules were continuously shaken in an attempt to mimic in vivo environmental conditions, those capsules made with optimal parameters (0.1% PLL, 42,000 MW, incubated for 6 minutes; 1.5% SA, incubated for 4 minutes; SC bath 4 minutes; 25# needle; air flow 14L/min) were still intact after 30 days and not totally ruptured until 90 days, while those developed with less strict parameters were ruptured within 2 hours in 50%. We also encapsulated human pituitary adenoma cells using PLL of 80,000 MW and cultured them for 9 days. Adenoma cells, both encapsulated or non-encapsulated, secreted the same amount of hormones. Our preliminary study suggests that selecting optimal combinations of experimental parameters is essential in developing durable microcapsules, which may be potentially used for pituitary transplantation in vivo.

Adenoma↗
PubMed2002

Multicomponent analysis of volatile organic compounds in water by automated purge and trap coupled to gas chromatography-mass spectrometry.

The performance of an automated purge and trap concentrator coupled to gas chromatography-mass spectrometric detection was evaluated by analyzing 40 volatile organic compounds of different chemical families. Compounds chosen defined as toxic for the environment and for human health were selected according to Directive 76/464/CEE. The present work includes: (i) the optimization of the purge and trap conditions, (ii) the establishment of quality parameters and in last instance (iii) the analysis of surface waters. The analytical method consisted of a modification of the EPA Method 524.2 in which water was pumped, via an automated AquaTek 70 Liquid Autosampler to a 25-ml purging device, where samples were purged and trapped in a Tenax or Tenax-Silica and Charcoal column. Afterwards, helium was used to desorb the trapped analytes that flow directly into the GC column. Mass spectrometric analysis was carried out in selected ion monitoring and scan modes to ensure quantification and confirmation of the results. Parameters optimized were the sample volume analyzed, bubbling flow-rate and time and temperature of desorption. Optimal conditions lead to mean recoveries of 80%, limits of detection between 0.002 and 0.1 microg/l, linearity from 0.01 to 2.5 microg/l and maximum standard deviation of 10%, using a Tenax trap. This protocol permitted a high precision and sample throughput and was used to determine volatile organic compounds in surface river, effluents and coastal waters of Portugal, on a routine basis.

Calibration↗
PubMedDate not supplied

An automated form of video image analysis applied to classification of movement disorders.

Video image analysis is able to provide quantitative data on postural and movement abnormalities and thus has an important application in neurological diagnosis and management. The conventional techniques require patients to be videotaped while wearing markers in a highly structured laboratory environment. This restricts the utility of video in routine clinical practise. We have begun development of intelligent software which aims to provide a more flexible system able to quantify human posture and movement directly from whole-body images without markers and in an unstructured environment. The steps involved are to extract complete human profiles from video frames, to fit skeletal frameworks to the profiles and derive joint angles and swing distances. By this means a given posture is reduced to a set of basic parameters that can provide input to a neural network classifier. To test the system's performance we videotaped patients with dopa-responsive Parkinsonism and age-matched normals during several gait cycles, to yield 61 patient and 49 normal postures. These postures were reduced to their basic parameters and fed to the neural network classifier in various combinations. The optimal parameter sets (consisting of both swing distances and joint angles) yielded successful classification of normals and patients with an accuracy above 90%. This result demonstrated the feasibility of the approach. The technique has the potential to guide clinicians on the relative sensitivity of specific postural/gait features in diagnosis. Future studies will aim to improve the robustness of the system in providing accurate parameter estimates from subjects wearing a range of clothing, and to further improve discrimination by incorporating more stages of the gait cycle into the analysis.

Algorithms↗
PubMed1997

Parameter estimation by reduced-order linear associative memory (ROLAM).

In a series of papers we have shown that nonlinear parameter estimation by linear association provides accurate estimates of the parameters in complex systems described by nonlinear differential equations even in the presence of additive white noise of considerable power. The technique is based on linearly associating the system's output with a set of parameter values spanning the region of interest. When an actual output is measured, the system's unknown parameters could be estimated by a matrix inversion. The size of the inverted matrix, being equal to the length of the output vector, poses a limiting factor upon the generalization of the technique. In this paper we propose a modification which requires the inversion of a matrix whose dimension equals the number of model parameters. The modified version is called reduced-order associative memory (ROLAM). The technique is applied to two complex lumped-parameter nonlinear models: the Van der Pol relaxation oscillator and the passive neuron model of the granule cells. Results validate ROLAM as a parameter-estimation tool which is especially suited in cases where the number of parameters is large, the number of samples in the observation signal is high, or when on-line parameter estimation is required. It is also shown that ROLAM provides an optimal parameter estimate in the special case of single-parameter nonlinear models.

Algorithms↗
PubMed2006

Resolution improvement in positron emission tomography using anatomical Magnetic Resonance Imaging.

An ideal imaging system should provide information with high-sensitivity, high spatial, and temporal resolution. Unfortunately, it is not possible to satisfy all of these desired features in a single modality. In this paper, we discuss methods to improve the spatial resolution in positron emission imaging (PET) using a priori information from Magnetic Resonance Imaging (MRI). Our approach uses an image restoration algorithm based on the maximization of mutual information (MMI), which has found significant success for optimizing multimodal image registration. The MMI criterion is used to estimate the parameters in the Sharpness-Constrained Wiener filter. The generated filter is then applied to restore PET images of a realistic digital brain phantom. The resulting restored images show improved resolution and better signal-to-noise ratio compared to the interpolated PET images. We conclude that a Sharpness-Constrained Wiener filter having parameters optimized from a MMI criterion may be useful for restoring spatial resolution in PET based on a priori information from correlated MRI.

Algorithms↗
PubMed2005

Parameters selection in gene selection using Gaussian kernel support vector machines by genetic algorithm.

In microarray-based cancer classification, gene selection is an important issue owing to the large number of variables and small number of samples as well as its non-linearity. It is difficult to get satisfying results by using conventional linear statistical methods. Recursive feature elimination based on support vector machine (SVM RFE) is an effective algorithm for gene selection and cancer classification, which are integrated into a consistent framework. In this paper, we propose a new method to select parameters of the aforementioned algorithm implemented with Gaussian kernel SVMs as better alternatives to the common practice of selecting the apparently best parameters by using a genetic algorithm to search for a couple of optimal parameter. Fast implementation issues for this method are also discussed for pragmatic reasons. The proposed method was tested on two representative hereditary breast cancer and acute leukaemia datasets. The experimental results indicate that the proposed method performs well in selecting genes and achieves high classification accuracies with these genes.

Algorithms↗
PubMed2003

Plate equations for piezoelectrically actuated flexural mode ultrasound transducers.

This paper considers variational methods to derive two-dimensional plate equations for piezoelectrically actuated flexural mode ultrasound transducers. In the absence of analytical expressions for the equivalent circuit parameters of a flexural mode transducer, it is difficult to calculate its optimal parameters and dimensions, and to choose suitable materials. The influence of coupling between flexural and extensional deformation, and coupling between the structure and the acoustic volume on the dynamic response of piezoelectrically actuated flexural mode transducer is analyzed using variational methods. Variational methods are applied to derive two-dimensional plate equations for the transducer, and to calculate the coupled electromechanical field variables. In these methods, the variations across the thickness direction vanish by using the stress resultants. Thus, two-dimensional plate equations for a stepwise laminated circular plate are obtained.

Journal Article↗
PubMed2004

Safety parameters for pulp temperature during selective ablation of caries by KTP laser in vitro.

OBJECTIVE: To define the optimal parameters of KTP laser irradiation during a selective caries removal. MATERIALS AND METHODS: Twelve decayed human teeth, recently extracted were used. Their root canals were prepared for insertion of a thermocouple probe into the pulp chamber. The demineralized tissues were colored by Acid Red 52 before proceeding to different conditions of irradiation. RESULTS: Pulpal temperature increases (below 3 degrees C) were found under the following parameters with 15 sec of continuous lasing: 400 mWatts, 0.10-msec pulse width, PRR <50 Hz for efficient caries removal. A resting time average of 70 sec was necessary to allow pulp temperature to get back to its baseline. CONCLUSION: KTP laser can be used safely and without any pulp over-heating under certain irradiation conditions.

Body Temperature↗