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PubMed1984

The identification of the periodic behaviour in an epidemic model.

In this paper we study a method for the identification of the unknown parameter of the periodic function and also the first component of the state vector, in a mathematical model which describes the evolution of some diseases with an oro-fecal transmission. To solve the identification problem we use a numerical method to integrate the differential equations system, which reproduces the stability properties of the above mentioned continuous system. The numerical methods which we propose can be applied also to a spatial semi discretization of the reaction-diffusion model which is a diffusive generalization of the system that we consider in this paper. Finally, through an analysis on both the continuous and the discrete system we also obtain a necessary condition on the experimental data in order that a periodic trajectory of the system exists.

Communicable Diseases↗
PubMed2005

Illustrating sensitivity and uncertainty in environmental fate models using partitioning maps.

Variations of model predictions of the environmental fate of organic contaminants are usually analyzed for only one or at most a few selected chemicals, even though parameter sensitivity and contribution to uncertainty are widely different for different chemicals. A graphical method is introduced that allows for the comprehensive investigation of model sensitivity and uncertainty for all persistent organic nonelectrolytes at the same time. This is achieved by defining a two-dimensional hypothetical "chemical space" as a function of the equilibrium partition coefficients between air, water, and octanol (KOW, KAW, KOA), and plotting sensitivity and/or uncertainty of a specific model result to each input parameter as a function of this chemical space. The approach is illustrated for the bulk phase concentrations in air, water, soil, and sediment calculated by a level III model. Colored contour maps facilitate the identification of those input parameters that cause a high output variation of hypothetical and real chemicals. They also allow for the easy categorization of chemicals in terms of common parameter sensitivities, and thus comparable environmental behavior. Sensitivity varies with the mode of emission and the degradability of the chemicals, making it necessary to develop multiple sets of contour maps. Comparison of these sets of maps in turn allows the investigation of how parameter sensitivities change as a result of changes in mode of emission and persistence. The presented method can be used for investigating the sensitivity of any prediction obtained with any linear fate model that characterizes the partitioning behavior of organic chemicals with KAW, KoW, and KOA. Once the sensitivity maps have been constructed for a given environmental scenario, it is possible to perform a sensitivity analysis for a specific chemical by simple. placement of the substances' partitioning combinations within the chemical space. The maps can further contribute to the mechanistic understanding of a model's behavior, can aid in explaining observations of divergent environmental behavior of related substances, and can provide a rationale for grouping chemicals with similar model behavior, or for selecting representative example chemicals for a model investigation. They can also help in deciding when accurate and precise knowledge of physical chemical property data is crucial and when approximate numbers suffice to conduct a model investigation.

Air↗
PubMedDate not supplied

[A unified autocorrelated method of electroencephalogram analysis and some results of its use].

Unified autocorrelation method of EEG analysis (UNIFAC-EEG) represents some optimized algorithms of EEG-signals processing according to the sign of maximum stability to the broadband noise. These algorithms are united by the common aim to identify generation models of these signals narrowband components on the basis of concrete empirical data and estimation of their source dynamic parameters according to the identification results. On the basis of this method it was proved that alpha-rhythm sources belonged to the type of structural stable dynamic systems, and its decrement value could serve as one of the parameters of the functional state of the central nervous system. The effect was found of the interaction between the heart electric fields and human brain in EEG frequent alpha-range.

Algorithms↗
PubMedDate not supplied

A robust time-varying identification algorithm using basis functions.

We extend a recently developed time invariant (TIV) model order search criterion named the optimal parameter search algorithm (OPS) for identification of time varying (TV) autoregressive (AR) and autoregressive moving average (ARMA) models. Using the TV algorithm is facilitated by the fact that expanding each TV coefficient onto a finite set of basis sequences permits TV parameters to become TIV. Taking advantage of this TIV feature of expansion parameters exploits the features of the OPS, which has been shown to provide accurate model order selection as well as extraction of only the significant model terms. Another advantage of the new algorithm is its ability to discriminate insignificant basis sequences thereby reducing the number of expansion parameters to be estimated. Due to these features, the resulting algorithm can accurately estimate TV AR or ARMA models and determine their orders. Indeed, comparison via computer simulations of AR models between the proposed method and one of the well-known iterative methods, recursive least squares, shows the greater capability of the new method to track TV parameters. Furthermore, application of the new method to experimentally obtained renal blood flow signals shows that the new method provides higher-resolution time-varying spectral capability than does the short-time Fourier transform (STFT), concomitant with fewer spurious frequency peaks than obtained with the STFT spectrogram.

Algorithms↗
PubMed2006

Identification and reduction of ion suppression effects on pharmacokinetic parameters by polyethylene glycol 400.

Ion suppression in mass spectrometry has been described recently in detail and should always be considered during analysis by liquid chromatography/tandem mass spectrometry (LC/MS/MS) in a drug metabolism and pharmacokinetics (DMPK) environment. At best, ion suppression leads to decreased sensitivity but at worst could lead to incorrectly determined pharmacokinetic (PK) parameters. Our investigations centred on polyethylene glycol (PEG 400), an excipient often used in pre-clinical dosing vehicles. PEG was also found to be present in large quantities in the blood collection tubes used for pre-clinical PK studies. Ion suppression was observed for many analytes, either due to the use of PEG in the dosing vehicle or in blood collection tubes. The elimination of large ion suppression effects was attained by simple chromatographic gradient changes and the use of alternative blood collection tubes. The effect of the above was to increase the detected plasma concentration levels, which resulted in a change in key PK parameters.

Animals↗
PubMed1997

The role of the plant properties in point-to-point arm movements: a robustness study.

In recent papers we demonstrated by means of a modeling study that the smoothness of hand paths and the bell-shaped character of hand velocity profiles which have been experimentally observed in point-to-point arm movements can be largely attributed to the biomechanical properties of the arm rather than to specific planning by the central nervous system. In this paper we present a study of the robustness of our earlier results comprising two goals: (i) the determination of the range of model parameters for which such observations remain valid, (ii) the identification of possible relationships between model parameters and kinematic variables. The results of this study imply three conclusions: (i) the valid range of the tested model parameters (namely the main muscle parameters) is large, (ii) the modeled phenomena are well behaved in that parametric changes do not give rise to bifurcations or other behavioral discontinuities in the analyzed ranges, (iii) there exist precise relationships between certain muscle parameters and the time course of the hand velocity. These results point out that the phenomena observed in our previous work are indeed robust and can lead to useful insights into the mechanisms comprising the regulatory action of the central nervous system as well as into the design principles for biologically inspired artificial arms.

Arm↗
PubMed1992

Identification of severe coronary artery disease using simple clinical parameters.

The purpose of our study was to examine the ability of clinical and resting electrocardiographic variables to provide useful estimates of the probability of three-vessel or left-main coronary artery disease. The study group consisted of 680 patients with symptomatic coronary artery disease who underwent exercise equilibrium radionuclide angiography and coronary angiography within 6 months. Sixteen clinical and electrocardiographic variables were examined by logistic regression analysis. The independently predictive variables were then used to develop convenient graphic estimates of the probability of three-vessel or left-main disease and to classify patients into high-risk (greater than 35%), intermediate-risk (15-35%), or low-risk (less than 15%) groups. Five variables were independently predictive of left-main or three-vessel disease: age, typical angina, diabetes, gender, and both history and electrocardiographic evidence of a prior myocardial infarction. A single graph was constructed that displayed the probability of severe coronary artery disease as a function of a five-point cardiac risk scale, which incorporated these variables. Two hundred sixty-two patients (39% of the study group) were classified as high risk; 127 of these patients (48%) had three-vessel or left-main disease. An additional 96 patients were classified as low risk; nine of these patients (9%) had three-vessel or left-main disease. Five clinical variables that were obtained on an initial patient assessment can provide useful estimates of the likelihood of severe coronary disease.

Coronary Angiography↗
PubMed1987

Fetal kidney volume and urine production in cases of fetal growth retardation.

The amount of amniotic fluid has a close correlation to the function of the fetal renal system. In many cases of fetal growth retardation oligohydramnios is obvious. The aim of this study is the investigation of the hourly fetal urine production rate (HFUPR) and the growth of fetal kidneys during pregnancy in cases of fetal growth retardation and to evaluate the renal participation in the origin of oligohydramnios in cases of growth retardation. In 52 healthy pregnancies and 27 cases with known fetal growth retardation, the volume of the fetal kidneys was measured sonographically and the hourly rate of fetal urine production was determined. Two third of the patients with fetal growth retardation had obvious oligohydramnios. In cases of fetal growth retardation the volume of the fetal kidneys was significantly smaller when compared to the control group, and the volume of fetal urine production was significantly lower. The reduced perfusion of the fetal kidneys in those cases with fetal growth retardation may be the reason for the reduction of the HFUPR. Due to the fact that HFUPR is a dynamical parameter and in close relationship to the perfusion of the fetal kidneys, the identification and measurement of this parameter may help to detect subacute and imminent fetal distress in cases of sonographically proven fetal growth retardation.

Adult↗
PubMed2002

[A pseudo-triangle technique for redshift identification of celestial spectra].

In this paper, we present a novel technique for redshift identification. Redshift is a key parameter of celestial spectra. In the literature, there are few reports on redshift identification due to either no many people working on the problem or perhaps industrial confidentiality. Our technique is a pseudo-triangle technique. It consists of the following three major steps: in the first step, the three wavelengths corresponding to the three highest intensity values of an unknown spectrum are selected to construct a pseudo-triangle, and the largest angle of this triangle is calculated which is independent of redshift value. In the second step, the obtained angle is used as an index to retrieve the corresponding three model wavelengths via a pre-calculated look-up-table, which is composed of all the combinations of all the feature wavelengths of the model spectrum. And finally, based on the three corresponding wavelengths, the corresponding redshift value is derived. The main characteristic of our technique is its simplicity and efficiency, which is demonstrated by experiments on simulated data as well as on real celestial spectra. It is shown that the correct identification rate can reach as high as 86%. Taking into account the high noisy nature of celestial spectra, such a result is considered a good one.

Algorithms↗
PubMed2006

Improved discrimination of breast lesions using selective sampling of segmented MR images.

OBJECTIVE: The aim of this work is to examine if the specificity of differentiation between malignant and benign tumours can be improved by retrospectively examining lesion-extracted distributions. A semi-automated method for selecting a region-of-interest (ROI) is described. A new histogram segmentation approach for sampling pharmacokinetic breast maps of transfer uptake is defined in order to assign classification variables for the lesion. METHOD: Fifty exchange rate parameter maps were extracted from 49 subjects and retrospectively analysed. Distributions obtained from semi-automatically delineated ROIs were subdivided into ten overlapping segments. Parameters were extracted from each segment which effectively presents a new pixel intensity sampling strategy. Mann-Whitney non-parametric tests and ROC curves were generated. RESULTS: Correlation exists between mean parameter values drawn from semi-automatically or manually drawn ROIs. However, the former yield higher specificity values as applied to this subset of enhancing benign lesions. Segmenting the exchange rate parameter histogram allows the identification of which part of the distribution correlates most with tumour type. Significant improvement in specificity is obtained when using half the pixels within the ROI. CONCLUSION: Improved specificity values are obtained by a new method of selecting the differentiation parameters which relies on intensity rather than spatial segmentation. Only half the pixels available within the ROI contributed to the measured classification parameters.

Adult↗
PubMed1996

The use of the decision tree technique and image cytometry to characterize aggressiveness in World Health Organization (WHO) grade II superficial transitional cell carcinomas of the bladder.

The aggressiveness of human bladder tumours can be assessed by means of various classification systems, including the one proposed by the World Health Organization (WHO). According to the WHO classification, three levels of malignancy are identified as grades I (low), II (intermediate), and III (high). This classification system operates satisfactorily for two of the three grades in forecasting clinical progression, most grade I tumours being associated with good prognoses and most grade III with bad. In contrast, the grade II group is very heterogeneous in terms of their clinical behaviour. The present study used two computer-assisted methods to investigate whether it is possible to sub-classify grade II tumours: computer-assisted microscope analysis (image cytometry) of Feulgen-stained nuclei and the Decision Tree Technique. This latter technique belongs to the Supervised Learning Algorithm and enables an objective assessment to be made of the diagnostic value associated with a given parameter. The combined use of these two methods in a series of 292 superficial transitional cell carcinomas shows that it is possible to identify one subgroup of grade II tumours which behave clinically like grade I tumours and a second subgroup which behaves clinically like grade III tumours. Of the nine ploidy-related parameters computed by means of image cytometry [the DNA index (DI), DNA histogram type (DHT), and the percentages of diploid, hyperdiploid, triploid, hypertriploid, tetraploid, hypertetraploid, and polyploid cell nuclei], it was the percentage of hyperdiploid and hypertetraploid cell nuclei which enabled identification, rather than conventional parameters such as the DI or the DHT.

Adult↗
PubMedDate not supplied

Estimation of tissue blood flow from hyperthermia treatment data.

During hyperthermia treatment of patients the delivered heat and the temperatures at several points in the tissue are often measured and recorded. These data contain information about thermal tissue parameters. A method for extracting this information, i.e. estimating the tissue parameters--in particular the blood perfusion rate--is described. The method applies a system identification technique, adjusting the unknown parameters in a thermal tissue model, until the predicted model output (temperature) coincides well with the measured temperature. Data from a number of patient treatments have been used to test the method, and although the accuracy of the method remains to be established conclusively it appears to give a good estimate of the model parameter representing blood flow. The obvious advantage of the method is that it requires no special transducers or experiments. The weak aspect is that it depends on the correctness of a thermal model of the perfused tissue.

Blood Circulation↗
PubMed1989

A parametric modeling of membrane current fluctuations with its application to the estimation of the kinetic properties of single ionic channels.

A parametric autoregressive moving average (ARMA) signal modeling of membrane current fluctuations observed in biomembranes is described. Kinetic properties of single ionic channels contributing to membrane current fluctuations and the parameters of the corresponding ARMA process are explicitly related. The model was shown to be effectively applied to the estimation of the kinetic parameters of single ionic channels. Estimation of the parameters via ARMA signal identification was examined in detail for the basic closed-open scheme and the three-state sequential blocking scheme. The estimation accuracy of this method was theoretically evaluated. Computer simulation revealed the validity of the proposed modeling and the effectiveness of the parametric method for the estimation of kinetic parameters when the model was applied to the estimation. The proposed modeling may form a theoretical base for the parametric analysis of membrane current fluctuations in a variety of kinetic schemes.

Cell Membrane↗
PubMed1990

Short prereduced anaerobically sterilized (PRAS) biochemical scheme for identification of clinical isolates of bile-resistant Bacteroides species.

The rapid identification of isolates of bile-resistant Bacteroides species has clinical and therapeutic relevance because of differences in their patterns of susceptibility and virulence. Five hundred twenty-one strains of bile-resistant Bacteroides species that were previously identified by conventional biochemical methods were reexamined to determine the minimum essential parameters necessary for correct identification. Rapid tests for bile resistance, indole production, and catalase were combined with a novel scheme for biochemical determination of saccharolytic activity on arabinose, trehalose, rhamnose, and/or xylan that included the postincubation addition of bromthymol blue for visual pH determination. Organisms were inoculated into prereduced anaerobically sterilized (PRAS) carbohydrates directly from plates, and identification was complete within 24 h of obtaining a pure culture. Ninety-three percent of bile-resistant Bacteroides species from routine clinical specimens were identified correctly by this scheme; a small number of other indole-positive strains, B. splanchnicus, B. eggerthii, and B. stercoris, were misidentified as B. uniformis.

Anaerobiosis↗
PubMed1983

A structural mathematical model for the viscoelastic anisotropic behaviour of trabecular bone.

The presented paper is based on the conclusions of the preceding paper (1). On the basis of a general theoretical approach to the mechanics of heterogeneous materials published earlier / (2) , (3) , (4) / macroscopic constitutive equation of trabecular bone is deduced from the description of its microstructure. For the behaviour in physiological limits trabeculae are described as elastic and the remaining material constituent as a Maxwell body. The resulting macroscopic constitutive equation comprehends tensorial internal variables and the parameters appearing in it are the constants of the material constituents constitutive equations, the respective volume fractions and special structural parameters descriptive of the geometry of composition. The system of the trabeculae as well as the system of the remaining constituent of the composite are considered to be interconnected - continuous. Explicite formulae are given for the case of transverse isotropy, but the extension to more general cases of anisotropy is well possible. The procedure of identification of the model parameters is shown and a numerical example calculated.

Adult↗
PubMed2001

Age-at-death diagnosis and determination of life-history parameters by incremental lines in human dental cementum as an identification aid.

Incremental lines in acellular extrinsic fiber cementum of 91 roots from 80 freshly extracted teeth have been investigated for a verification of the suitability of pathological teeth for a valid age-at-death diagnosis. Independent from tooth type, the accuracy of histological age-at-death diagnosis is clearly a function of a tooth's pathological state. Various periodontal diseases lead to a reduced number of incremental lines, while teeth with a sufficient nutritional support of their root showed a deviation of the histological age from the known actual age of 2-3 years only. For all patients, a detailed query concerning a variety of life-history parameters was established. We are able to show that especially previous pregnancies, skeletal traumata and renal diseases which all have a marked influence on the calcium metabolism result in hypomineralized incremental lines. The year of production of these hypomineralized lines could be dated precisely. Differential quality of incremental lines can, therefore, serve as a valuable tool in identification cases.

Adult↗
PubMed2001

Neural network modelling of Cryptosporidium and Giardia concentrations in the Delaware River, USA.

Artificial neural networks are brain-like structures used in mathematical modelling that excel in pattern recognition. In this research, a simple feed-forward artificial neural network, trained by error back-propagation algorithm, was used as a tool to relate peak Cryptosporidium and Giardia concentrations with other biological, chemical and physical parameters in surface water. Multiple water quality parameters at a water treatment plant intake on the Delaware River, New Jersey, USA, collected in 1996, were provided to the authors for recognition analysis. Water samples were classified as "background" and "above background" based on the concentration of full and empty oocysts and cysts of Cryptosporidium and Giardia. The results of this preliminary effort were encouraging. Parameters significant to the identification of each protozoa were identified, eight for Cryptosporidium and seven for Giardia by a stepwise elimination technique. Data withheld from the model training was used to validate the trained models and evaluate the most effective internal architecture. In both cases, the best prediction performance was found when the number of internal nodes was twice that of the input parameters in single hidden-layer architecture. Predictions for the classification of the verification data set resulted in no false-negatives (mis-prediction of above background protozoa concentrations) when the models were optimally trained.

Animals↗