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Results for “parameter identification”

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At least 181 records · Page 10Linked to original sources

PubMed2000

Patient-driven control of FES-supported standing up and sitting down: experimental results.

A patient-driven control strategy for standing-up and sitting-down was experimentally tested on two paraplegic patients by applying functional electrical stimulation (FES) to the quadriceps muscle. The strategy--also known as "patient-driven motion reinforcement" (PDMR)--was developed by computer simulations reported in a former study. It is based on an inverse dynamic model (IDM) that predicts the stimulation pattern required to maintain the movement as it is initiated by the patient's voluntary effort. For reasons of safety and weight relief, the movement was supported by a seesaw construction. After some practice the patients were able to influence the stimulator output and to control the movement by their voluntary effort. Consequently, no pre-programmed reference trajectory was required. As a positive side effect, upper body effort could be minimized compared to trials without FES. To achieve a satisfactory performance of the PDMR controller a careful parameter identification of the inverse dynamic model was fundamental.

Adult↗

PubMed2006

Computing the size and location of myocardial ischemia using measurements of ST-segment shift.

It is well known that the presence of myocardial ischemia can be observed as a shift in the ST segment of an electrocardiogram (ECG) recording. The question we address in this paper is whether or not ST shift can be used to compute approximations of the size and location of the ischemic region. We begin by investigating a cost functional (measuring the difference between synthetic recorded data and simulated values of ST shift) for a parameter identification problem to locate the ischemic region. We then formulate a more flexible representation of the ischemia using a level set framework and solve the associated minimization problem for the size and position of the ischemia. We apply this framework to a set of ECG data generated by the Bidomain model using the cell model of Winslow et al. Based on this data, we show that values of ST shift recorded at the body surface are capable of identifying the position and (roughly) the size of the ischemia.

Animals↗

PubMed2004

Online tuning of fuzzy inference systems using dynamic fuzzy Q-learning.

This paper presents a dynamic fuzzy Q-learning (DFQL) method that is capable of tuning fuzzy inference systems (FIS) online. A novel online self-organizing learning algorithm is developed so that structure and parameters identification are accomplished automatically and simultaneously based only on Q-learning. Self-organizing fuzzy inference is introduced to calculate actions and Q-functions so as to enable us to deal with continuous-valued states and actions. Fuzzy rules provide a natural mean of incorporating the bias components for rapid reinforcement learning. Experimental results and comparative studies with the fuzzy Q-learning (FQL) and continuous-action Q-learning in the wall-following task of mobile robots demonstrate that the proposed DFQL method is superior.

Algorithms↗

PubMed2007

Modeling of nonlinear responses for reciprocal transducers involving polarization switching.

Nonlinearities and hysteresis effects in a reciprocal PZT transducer are examined by use of a dynamical mathematical model on the basis of phase-transition theory. In particular, we consider the perovskite piezoelectric ceramic in which the polarization process in the material can be modeled by Landau theory for the first-order phase transformation, in which each polarization state is associated with a minimum of the Landau free-energy function. Nonlinear constitutive laws are obtained by using thermodynamical equilibrium conditions, and hysteretic behavior of the material can be modeled intrinsically. The time-dependent Ginzburg-Landau theory is used in the parameter identification involving hysteresis effects. We use the Chebyshev collocation method in the numerical simulations. The elastic field is assumed to be coupled linearly with other fields, and the nonlinearity is in the E-D coupling. We present numerical results for the reciprocal-transducer system and identify the influence of nonlinearities on the system dynamics at high and low frequency as well as electrical impedance effects due to tuning by a series inductance. It is found that nonlinear effects are not important at high frequencies (1 MHz) subject to high-input voltages, but they become important under high-voltage and off-resonance conditions.

Computer Simulation↗

PubMedDate not supplied

Deriving TDS values in coarse sediments from long normal and electromagnetic logs.

This paper presents an empirical relationship of quantitatively linked electromagnetic (EM) borehole recordings of the total dissolved solids (TDS) in pore water in the Quaternary deposits of the Belgian coastal plain. First, the long normal (LN) logs are linked to EM logs, then the already developed relationships between LN resistivity measurements and the TDS values are rewritten for EM recordings. The main parameter in these equations is the formation factor, which is derived from ground water analyses and LN logs through Archie's law. The EM recording has several advantages compared to the LN logs. The EM analysis allows measuring in PVC-cased wells and is not hindered by the invasion zone around the well. Furthermore, it has a high vertical resolution. LN logs can be measured only once, after drilling a well; EM recordings can be repeated several times in monitoring wells, which allows the gathering of time-dependent data over a complete vertical cross section. Such data could be obtained with LN logs only in wells with screens over the full-depth interval, which causes a hydraulic short circuit. This short circuit can result in a large artificial flow through the well between different levels, resulting in a salinity profile, which is no longer representative for the studied site. Remediation against short circuiting is a reduction of the screened interval, which strongly reduces the gathered information. The application of the derived equations is one of setting up a monitoring network along the Belgian coast to monitor the trend in salinity levels and comparing present salinity levels with older LN recordings to investigate the salinity changes in the last 30 years. Deep wells already present in the Belgiancoastal plain can then be used to monitor both the fresh water head changes and the salt water evolution. The technique has also been used for parameter identification for which real concentration measurements were needed.

Electromagnetic Phenomena↗

PubMedDate not supplied

Computing "anomalous" contaminant transport in porous media: the CTRW MATLAB toolbox.

We describe the continuous time random walk (CTRW) MATLAB toolbox, a collection of MATLAB scripts and functions that compute breakthrough curves (BTCs) and one-dimensional/two-dimensional (1D/2D) resident concentration profiles for passive tracer dispersion. The transport model is based on the CTRW theory. CTRW includes as special cases the classical Fickian dispersion based advection-dispersion equation, multirate and mobile-immobile models, and the fractional-in-time derivative transport equation. Several models for treating the memory effects responsible for the anomalous character of dispersion have been implemented in the CTRW toolbox. In the current version of the toolbox, it is possible to solve explicitly for the forward problem (concentration prediction) in 1D and 2D and for the inverse problem (parameter identification from experimental BTC data) in 1D. Future extensions will include explicit treatment of sorbing tracers, simple subroutines for treating radial flow from wells, introduction of arbitrary initial conditions, treatment of heterogeneous domains by use of the Fokker-Planck with Memory equation, and treatment of transport in multidimensional systems.

Environmental Monitoring↗

PubMed1979

On model and data requirements for determining the bioavailability of oral therapeutic agents: application to gut absorption of thyroid hormones.

A two-pool model is proposed as a first approximation of the dynamics of thyroid hormone dissolution and absorption in the human gut. It is shown that this model, or any more complex one of the same process, must be imbedded in a larger whole-body model for the purpose of quantifying its parameters. Parameter identification experiments are designed with the aid of identifiability analysis and a complete quantification is obtained, for both triiodothyronine (T3) and thyroxine (T4) absorption, using kinetic data obtained from the literature. The average percent absorption of oral dosages calculated from the model for T3 (95.8%) and for T4 (49.3%) are exceptionally close to reported measured values. Other data not used in model development also serve to validate the results, for use in applications not demanding greater physiological detail, such as for determining the bioavailability of orally administered hormones, or for the "inverse problem," computing optimal dosage regimens for hormone therapy.

Humans↗

PubMed1989

Applications of numerical methods to simulate the movement of contaminants in groundwater.

This paper reviews mathematical models and numerical methods that have been extensively used to simulate the movement of contaminants through the subsurface. The major emphasis is placed on the numerical methods of advection-dominated transport problems and inverse problems. Several mathematical models that are commonly used in field problems are listed. A variety of numerical solutions for three-dimensional models are introduced, including the multiple cell balance method that can be considered a variation of the finite element method. The multiple cell balance method is easy to understand and convenient for solving field problems. When the advection transport dominates the dispersion transport, two kinds of numerical difficulties, overshoot and numerical dispersion, are always involved in solving standard, finite difference methods and finite element methods. To overcome these numerical difficulties, various numerical techniques are developed, such as upstream weighting methods and moving point methods. A complete review of these methods is given and we also mention the problems of parameter identification, reliability analysis, and optimal-experiment design that are absolutely necessary for constructing a practical model.

Humans↗

PubMed1980

Glucose tolerance, growth hormone and somatomedin levels in osteosarcoma patients.

Intravenous glucose tolerance, insulin response to glucose, the sensitivity of the periphery to insulin as well as growth hormone and somatomedin levels were determined in osteosarcoma patients and control subjects matched by age, sex, weight an length. The insulin response to glucose and the peripheral sensitivity to insulin were evaluated by using the individual blood glucose and plasma insulin curves for parameter identification in a mathematical model. The mean glucose tolerance was significantly decreased in the patients, most likely due to decreased peripheral insulin sensitivity. Plasma growth hormone levels were normal in all patients which was also the case with somatomedin levels determined by both radioreceptor- and radioimmunoassay.

Adolescent↗

PubMed2003

Evaluation of the position of the hyoid bone in relation to vertical facial development.

Evaluation of the position of the hyoid bone in relation to vertical facial development and comparative evaluation of the relation of this position with the dentofacial system was made on 25 patients with hyperdivergent vertical growth, 25 patients with hypodivergent vertical growth, and 25 patients with normal vertical facial development. SN-Go-Gn, Gonion, ANS-PNS/Go-Gn angles and S-Go, N-Me, S-Go/N-Me measurements from lateral cephalometric films were used as identification parameters. Seven horizontal, five vertical and five angular cephalometric measurements were made in order to determine the position of the hyoid bone. SN plane was used as the reference plane. Results were evaluated through "t" test. No significant relation was found between hyoid bone position and gender. When gender distinction was disregarded, and the group with normal facial development was compared with the hyperdivergent group, statistically significant differences were observed for CVT-H distance in horizontal measurements and for H-SN, H-F, H-PD, H-OD distances in vertical measurements. When the group with normal facial development was compared with the hypodivergent group, only the horizontal measurement Pg-H was statistically significant. The hyoid bone location in the hyperdivergent group was in a more of a posterior and superior position. The hyoid bone location in the hypodivergent group was not changed vertically, however, it had more of a posterior placement with the increase of Pg-H distance.

Adolescent↗

PubMed2006

Activated sludge modelling: past, present and future.

Model complexity in activated sludge modelling has increased over 30 years in parallel with the computational power of computers. Today, the complexity of biokinetics has reached a practical limit. Future advances may be in the direction of enhanced spacial resolution (CFD, single organisms) respectively, in repetitive computations (MC simulation, parameter identification). Further model development may be in niches such as population dynamics, micropollutants, etc.

Animals↗

PubMed2006

A modeling study of fouling development in membrane bioreactors for wastewater treatment.

Membrane fouling is a primary concern in membrane bioreactors (MBRs) in wastewater treatment because it strongly affects both system stability and economic feasibility. A mathematical model was developed in this study for membrane fouling in submerged MBR systems for wastewater treatment, in which both reversible and irreversible fouling were quantified. While mixed liquor suspended solids are the major components of the reversible fouling layer, dissolved organic matter is thought to be the key foulant, in particular, responsible for the long-term irreversible fouling of the filtration unit. The model was calibrated (parameter identification) with a set of operational data from a pilot MBR and then verified with other independent operational data from the MBR. The good agreement between theoretical predictions and operational data demonstrates that the outlined modeling concept can be successfully applied to describe membrane fouling in submerged MBR systems.

Bioreactors↗

PubMed1997

The pathogenesis of diabetic foot problems: an overview.

Foot ulceration and lower limb amputation are still common complications of diabetes. Diabetic peripheral neuropathy and peripheral vascular disease are the most important etiologic factors, but there is a complex interplay between these abnormalities and a number of other contributory factors, such as altered foot pressures, limited joint mobility, glycemic control, ethnic background, and cardiovascular parameters. Identification of patients at high risk of ulceration is nevertheless simple, and education of such patients can achieve a major reduction in amputation and ulceration rates.

Arthropathy, Neurogenic↗

PubMed2000

Probing metal-complexes with metallothioneins by reversed phase microbore chromatography and capillary zone electrophoresis coupled with inductively coupled plasma and electrospray mass spectrometry.

Four different hyphenated techniques: microbore reversed phase (RP) HPLC-ICP MS, CZE-ICP MS, RP HPLC-ES MS and CZE-ES MS were investigated for the characterization of metallothionein-metal complexes under neutral pH conditions. Particular attention was given to the differentiation between metallothionein and artifact signals, identification of mixed-metal complexes, and the validity of the molecular mass as the identification parameter of the different MT iso- and sub-isoforms. Despite the similar morphology of chromatograms and electrophoregrams mass spectrometry revealed different origin of the apparently corresponding peaks. The performance of the four above mentioned techniques was characterized using the example of rabbit liver MT-1 preparation. Reversed-phase HPLC with post-column acidification prior to ES MS was judged to be the most versatile technique for the characterization of metal complexes with metallothioneins but other techniques offer valuable auxiliary information.

Animals↗

PubMed1975

Estimation and identification in blood plasma of paracetamol (N-acetyl-p-aminophenol) in the presence of barbiturates.

Barbiturates are a source of interference in the estimation of paracetamol by both UV spectrophotometry and gas-liquid chromatography (GLC). Experiments have shown that the interference by barbiturates on GLC can be avoided by benzoylation (in aqueous solution) of the paracetamol. This O-benzoyl derivative can be N-silylated to give an additional identification parameter. The method, which requires ml of sample, will quantitatively and qualitatively estimate "free" paracetamol in plasma and in post mortem blood in the range of 2-40 mug of drug per millilitre of sample.

Acetaminophen↗

PubMed2001

Modelling and simulation of the steady-state of secondary settlers in wastewater treatment plants.

This paper discusses the steady-state modelling of thickening in circular secondary settlers of activated sludge processes. The limitations of the solid flux theory basic models to represent steady-state operating conditions serve as a basis to introduce more sophisticated models derived from computational fluid dynamics. Parameter identification and sensitivity studies have been performed from lab-scale continuous experiments.

Computer Simulation↗

PubMed2002

[Comparison of parameter optimization algorithms for environmental model].

Parameters identification is achieved through the minimization of objective function based on model outputs and the observed data. Because of ever increasing complexity of environmental-models, there are significant difficulty for conventional optimal methods to present a global optimization. On the contrast, however, direct optimization algorithms are widely developed in recent years due to increasing computer efficiency and show promising applications. Four direct optimal algorithms, i.e. CRS algorithm, SCE UA algorithm, SA algorithm and Annealing-Simplex algorithm, were thus selected in this paper to compare their performances via case studies.

Algorithms↗

PubMed2003

Molecular phenotyping of a trinucleotide repeat (D5S373) experimental conditions.

The aim of this study is to assess the utility of the STR D5S373 in human identification. PCR amplification and electrophoretic separation were optimized in order to achieve unambiguous phenotyping. We concluded that primer concentration and annealing temperature are the main factors affecting the specificity of PCR. In our population survey including three human major groups (Europe, Sub-Saharan Africa, and Asia), up to six alleles and six interalleles have been found ranging in size from 86 to 101 bp. The phenotypes were determined using horizontal polyacrylamide gel electrophoresis, a technique which has turned out to be suitable for separating fragments as close as 1 bp. In each population, the genotype frequencies conformed to the expectations of genetic equilibrium. Sequence studies were carried out to make the allele nomenclature fit to ISFH recommendations. Results from our population analysis of D5S373 show clear differences in allelic frequency patterns among the three major human groups examined. Human identification parameters estimated from our study are similar to those obtained for other STRs currently used in DNA testing.

Alleles↗