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PubMed2001

Feature localization and identification.

Theories on visual search differ substantially with respect to the relationship they assume between localization and identification processes. The aim of the present study was to rigorously compare the alternative theoretical notions on how localization and identification processes are related. In two experiments, participants searched for a target with a unique line orientation among distractors containing another orientation. Localization and identification performance were measured in combination, as function of display size and target eccentricity. To compare the alternative theories, formal binomial models were developed and compared with respect to their goodness of fit to the individual data. The formal analyses showed that the model assuming identification processes to be conditioned on localization processes provided the best fit to the individual data. Furthermore, maximum likelihood estimates of the parameter corresponding to identification processes were differently affected by display size than identification performance was. The results were discussed in terms of their implication for current theories on visual search.

Fixation, Ocular↗
PubMed2001

Denver developmental screening test II for early identification of the infants who will develop major neurological deficit as a sequalea of hypoxic-ischemic encephalopathy.

BACKGROUND: The primary aim of this study was to find widely available, inexpensive, and non-invasive parameters for early identification or prediction of the infants with hypoxic-ischemic encephalopathy (HIE) who will have a severe adverse outcome (classified as death or a major neurological deficit). METHODS: Fifty-seven full-term or near-term newborn infants with a diagnosis of HIE were consecutively admitted to the neonatal intensive care unit and studied. Occurrence of seizures during the first 24 h, cranial ultrasonography (US) findings within the first 5 days of life, and Denver developmental screening test II (DDST II) at 6 months of age, were analyzed in relation to mortality and neurological status at 2 years of age. RESULTS: Of the 57 infants, 10 were lost to follow-up. Twenty of the remaining 47 infants had a severe adverse outcome. Among the predictors of severe adverse outcome, occurrence of seizures was found to have a poor predictive accuracy. Cranial US had 100% sensitivity, however with a rather low specificity (55%). However, DDST II at 6 months of age, yielded a very high predictive accuracy (sensitivity=100%, specificity=95%). CONCLUSION: We conclude that DDST II at 6 months of age could be used in predicting severe neurological outcome in infants with HIE.

Developmental Disabilities↗
PubMed2006

Characterization of the leachate in an urban landfill by physicochemical analysis and solid phase microextraction-GC/MS.

The aim of this study is to evaluate extensively the characterization and identification of major pollutant parameters by paying attention to the organic chemical pollution for unregulated dumping site leachate in Eskişehir/Turkey. The study that is first and only one research has been very important data related with before new sanitary landfill site in Eskişehir city. For this purpose, in this study leachate samples were collected in-situ at monthly interval for a period of 8 months. Firstly, thirty three physicochemical parameters were monitored. Secondly, SPME technique was used for identification of organic pollutants. Meteorological data were also recorded for the same sampling period to correlate meteorological data and physicochemical parameters. Mean values are used in the correlation analysis. Correlation is shown only for the relationship between air temperature and NO(3) (-). No correlation has been found between rain and leachate quality parameters since the amount of rain was very low during the sampling period. However, analysis results were generally decreased in winter season when each parameter and each sampling point are examined separately. According to correlation between every parameter, especially solid content and dissolved oxygen concentration of leachate is affecting to other parameters. Also, sodium and potassium are changing proportionally with same parameters (suspended solids, fixed solids, dissolved oxygen) and high correlation between chloride and heavy metal concentration is showing. The results were statistically evaluated by use of SPSS 10.0 program. Second part of the study, the leachate was extracted by Solid Phase Microextraction (SPME) technique and then analyzed. Of the methodologies tested in this study, the best one selected was based on 100 micro m polydimethylsiloxane coated fiber (PDMS), headspace with heating (Delta HS) sampling mode and an extraction time of 15 min. at a temperature of 50 degrees C. Thirty three organic compounds in leachate were identified by GC/MS.

Dimethylpolysiloxanes↗
PubMed1994

Effects of age and gender on dichotic sentence identification.

There is converging evidence that aging causes a progressive decline in the central processing of speech and that this decline is greater for left-ear than for right-ear input. In the present paper we investigated, by means of a dichotic sentence identification paradigm, some parameters of the "left-ear effect." We analyzed the clinical records of 356 individuals, 203 males and 153 females, to whom the Dichotic Sentence Identification (DSI) Test had been administered as part of routine audiometric assessment. Subjects ranged in age from 9 to 91 yr. The DSI test was always carried out in two modes: free report (FR) and directed report (DR). In the FR mode the subject reported what was heard in both ears. In the DR mode the subject reported only what was heard in one precued ear. In half of the trials the right ear was precued, in the other half the left ear was precued. Findings confirm a progressively larger right-ear advantage, or left-ear deficit, with increasing age. We document this effect in both the FR and DR modes, then demonstrate that the effects cannot be attributed to interaural asymmetries in threshold sensitivity. Comparison of male and female data suggest a gender difference in the effect of age on the left-ear deficit. Males show a larger effect then females in both modes of test administration. Finally, we propose a model of dichotic listening performance that attempts to explain ear asymmetry as the linear combination of an auditory/structural component and a task-related/cognitive component. We then show how these hypothetical components change with age in the present sample.

Adolescent↗
PubMed2004

Detection of optic disc in retinal images by means of a geometrical model of vessel structure.

We present here a new method to identify the position of the optic disc (OD) in retinal fundus images. The method is based on the preliminary detection of the main retinal vessels. All retinal vessels originate from the OD and their path follows a similar directional pattern (parabolic course) in all images. To describe the general direction of retinal vessels at any given position in the image, a geometrical parametric model was proposed, where two of the model parameters are the coordinates of the OD center. Using as experimental data samples of vessel centerline points and corresponding vessel directions, provided by any vessel identification procedure, model parameters were identified by means of a simulated annealing optimization technique. These estimated values provide the coordinates of the center of OD. A Matlab prototype implementing this method was developed. An evaluation of the proposed procedure was performed using the set of 81 images from the STARE project, containing images from both normal and pathological subjects. The OD position was correctly identified in 79 out of 81 images (98%), even in rather difficult pathological situations.

Algorithms↗
PubMed2001

Use and validation of public data files for identification of the diabetic population in a Danish county.

INTRODUCTION: This study aims to describe the process of identifying people known to have diabetes through public data files, to validate this method, and to describe models for optimization of such identification processes. PATIENTS AND METHODS: In a study population of 303,250 citizens, the diabetics were identified by combining information from public data files with information from general practitioners. Data validity was checked by comparing the results of data searches in public data files against information from general practitioners and a random sample of diabetics. Two models were defined to optimize the use of public data files for identification of diabetics. In model A the minimum number of parameters needed to obtain a sensitivity as high as possible was identified. In model B the optimal combination of parameters needed to obtain a high positive predictive value combined with a high sensitivity was identified. RESULTS: A total of 5449 diabetics were identified. Of those 4438 (81%) were classified as Type 2 diabetics and 1011 (19%) were classified as Type 1 diabetics. The data validation revealed that one person was misclassified as a diabetic and 93 persons were misclassified as non-diabetics. In model A the identification parameters included: "prescription", "HbA1c", "chiropodist service" and "glucose service". In model B the optimal combination of parameters was identified as: minimum two HbA1c measurements, minimum one visit to a chiropodist, minimum one prescription or minimum one abnormal HbA1c during one year. CONCLUSION: Public data files are suitable for identification of both Type 1 and Type 2 diabetics. Models have been developed to identify diabetics and to promote the possibilities of long-term follow-up and quality assessment in an unselected diabetic population in a region.

Adult↗
PubMed2000

Factor IX gene sequencing by a simple and sensitive 15-hour procedure for haemophilia B diagnosis: identification of two novel mutations.

We have developed a simple, sensitive and cost-effective direct DNA sequencing procedure for the molecular diagnosis of haemophilia B. All factor IX gene essential regions were amplified under identical thermocycling parameters allowing mutation identification in less than 15 h from blood sample collection. Identical results in terms of accuracy and speed were obtained when using a single hair as the source of DNA. Using this approach, we have found mutations in 10 out of 10 haemophilia B patients, two of which are novel (P287T and S123C). Very suitable for individual studies, this procedure can be easily scaled up for higher throughput.

Electronic Data Processing↗
PubMed2000

Ultrasonic myocardial textural parameters and midwall left ventricular mechanics in essential arterial hypertension.

BACKGROUND: The evaluation of the systolic left ventricular performance in hypertensive patients presents some problems related to left ventricular hypertrophy (LVH) which alters the ventricular geometry. The videodensitometric textural ultrasonic analysis of hypertensive myocardium has provided evidence of impairment in the cyclic variation of the mean gray level. This might be considered as an index of intrinsic myocardial function. OBJECTIVES: The aim of the present study was to analyse the connection between the midwall fractional shortening and end-systolic stress. The ultrasonic textural parameters in hypertensive patients, arranged in different groups according to the level of LVH and relative wall thickness, were also evaluated. METHODS: A group of age-matched (58 +/- 7 years) male essential hypertensive patients (n = 70) were compared to a group of normotensive and healthy subjects used as controls (n = 32). All subjects performed a conventional 2D-Doppler echocardiography to analyse the left ventricular performance. A quantitative analysis of the echocardiographic digitised imaging was also carried out with the help of a calibrated digitization system in order to calculate the septum and the posterior wall textural parameters. The myocardial mean gray level was calculated to derive the cyclic variation index (CVI). RESULTS: When subjected to a higher meridional end-systolic stress, the hypertensive patients showed a significantly lower midwall fractional shortening than the control patients. The CVI was also significantly lower in the hypertensives group, both for the septum wall (-16.3 +/- 22.8 vs34.7 +/- 15.3%; P < 0.001) and the posterior wall (-5.2 +/- 23.6 vs 38.2 +/- 15.4%; P < 0.001). A significant correlation was found between the midwall fractional shortening (MFS) and the textural parameters, and between these two variables and the end-systolic stress. CONCLUSION: The CVI was found to be a highly sensitive parameter in the identification of abnormal echodensity in essential hypertension. The CVI was significantly lower in patients with concentric hypertrophy in comparison with other left ventricular geometric models. This parameter could be considered as an index of the intrinsic myocardial function, being related, in essential hypertension, to midwall fractional shortening and to end-systolic stress. Journal of Human Hypertension (2000) 14, 9-16.

Blood Pressure↗
PubMed1985

Neural modeling and model identification.

The complexity of the nervous system poses challenging experimental and theoretical problems to the investigator. While experimental studies have provided a broad understanding of the physiological and anatomical role of neural elements, a comprehensive description of how the nervous system acquires and processes information is still lacking. Neural modeling addresses itself to the quantitative interpretation of neurophysiological experiments, to the assimilation of diverse experimental results into unified theories, and to the investigation of mechanisms of information-processing units, codes, and networks and their relation to capabilities of living systems. This review will emphasize neural models which can be tested by physiological or psychophysical experiments and will include the identification of model parameters based on experimental measurements. An overview of neural firing models, neural interaction models, neural variability and coding, design of input-output experiments for model identification, and description of small network interactions through multiunit and gross potential recording will be included.

Action Potentials↗
PubMed2006

Parameter estimation in biochemical systems models with alternating regression.

BACKGROUND: The estimation of parameter values continues to be the bottleneck of the computational analysis of biological systems. It is therefore necessary to develop improved methods that are effective, fast, and scalable. RESULTS: We show here that alternating regression (AR), applied to S-system models and combined with methods for decoupling systems of differential equations, provides a fast new tool for identifying parameter values from time series data. The key feature of AR is that it dissects the nonlinear inverse problem of estimating parameter values into iterative steps of linear regression. We show with several artificial examples that the method works well in many cases. In cases of no convergence, it is feasible to dedicate some computational effort to identifying suitable start values and search settings, because the method is fast in comparison to conventional methods that the search for suitable initial values is easily recouped. Because parameter estimation and the identification of system structure are closely related in S-system modeling, the AR method is beneficial for the latter as well. Specifically, we show with an example from the literature that AR is three to five orders of magnitudes faster than direct structure identifications in systems of nonlinear differential equations. CONCLUSION: Alternating regression provides a strategy for the estimation of parameter values and the identification of structure and regulation in S-systems that is genuinely different from all existing methods. Alternating regression is usually very fast, but its convergence patterns are complex and will require further investigation. In cases where convergence is an issue, the enormous speed of the method renders it feasible to select several initial guesses and search settings as an effective countermeasure.

Computational Biology↗
PubMed1992

Comparison of algorithms for tracking short-term changes in arterial circulation parameters.

Three recursive methods especially suited for identification of systems with rapidly changing parameters are applied to tracking of the viscoelastic properties of the systemic arterial bed. These methods include two least squares (LS) algorithms with constant or variable forgetting factor (RLS and LSVF) and a LS algorithm incorporating both a constant forgetting factor and covariance modification (CFCM). The methods are presented in a unified framework and their sensitivity with respect to the design variables is investigated using noisy data from computer simulations. All analysed methods have shown themselves to be able to satisfactory track rapid changes in peripheral resistance. The LSVF method, which offers slightly better performances than the classical RLS, may be preferred when calculation efficiency is the prime requirement. The CFCM algorithm, although maintaining reasonable simplicity, shows the best tracking ability also on varying of the noise sequence.

Algorithms↗
PubMed2004

Model of the viscoelastic behaviour of skin in vivo and study of anisotropy.

BACKGROUND: The single-axis extension test is relatively little used to study the mechanical properties of human skin in vivo. A campaign of tests was carried out with an original, modern machine developed in our laboratory. It can perform extension or compression tests using servo-controlled position or force in different directions. The load can either be of the extension or monotonous compression type, creep or relaxation. The results obtained were used to develop a viscoelastic model. The elastic modulus calculated helps us to determine the main directions of anisotropy on the forearm. METHODS: We use a new in vivo single-axis extension machine (patent no. FR03/09220 application in progress). With it, we can carry out monotonous, creep and relaxation tests on the forearm. An associated finite elements model enables conversion to the intrinsic parameters of the skin under stress and strain from external stress applied in force and displacement. From the tests, we can propose a viscoelastic model and the identification of his parameters. We carried out tests in four directions with respect to the axis of the forearm of 63 people of different ages. The present report is limited to a brief presentation of the experimental set-up used, and a more complete presentation of the viscoelastic model and how it is defined and also the work on the anisotropy in the elastic domain. RESULTS: The viscoelastic model proposed has only four intrinsic parameters: elasticity parameters E(e) and E(ve) and viscosity parameters epsilon(ve) and A. Skin being considered as orthotropic, we were able to determine the average main direction of 63 people, which is of 5.33+/-5.78 around the longitudinal axis of the arm. An average modulus E(1) (ave)=6.57E(5) (Pa) can be found in the direction close to the axis of the arm and E(2) (ave)=1.30E(5) (Pa) in the perpendicular direction and a G(12)=1.32E(5) (Pa) shear modulus. CONCLUSIONS: The parameters obtained with the viscoelastic model are independent of the type of load, the same coefficients enable a correct representation in creep and relaxation tests. The main directions vary from one person to another, Young's modulus in these directions could be an indicator for dermatologists and cosmeticians.

Adult↗
PubMed2001

Model-based control of FES-induced single joint movements.

A crucial issue of functional electrical stimulation (FES) is the control of motor function by the artificial activation of paralyzed muscles. Major problems that limit the success of current FES systems are the nonlinearity of the target system and the rapid change of muscle properties due to fatigue. In this study, four different strategies, including an adaptive algorithm, to control the movement of the freely swinging shank were developed on the basis of computer simulations and experimentally evaluated on two subjects with paraplegia due to a complete thoracic spinal cord injury. After developing a nonlinear, physiologically based model describing the dynamic behavior of the knee joint and muscles, an open-loop approach, a closed-loop approach, and a combination of both were tested. In order to automate the individual adjustments cited above, we further evaluated the performances of an adaptive feedforward controller. The two parameters chosen for the adaptation were the threshold pulse width and the scaling factor for adjusting the active moment produced by the stimulated muscle to the fitness of the muscle. These parameters have been chosen because of their significant time variability. The first three controllers with fixed parameters yielded satisfactory result. An additional improvement was achieved by applying the adaptive algorithm that could cope with problems due to muscle fatigue, thus permitting on-line identification of critical parameters of the plant. Although the present study is limited to a simplified experimental setup, its applicability to more complex and functional movements can be expected.

Biomechanical Phenomena↗
PubMed2006

Parameter sensitivity and uncertainty of the forest carbon flux model FORUG: a Monte Carlo analysis.

The Monte Carlo technique can be used to propagate input variable uncertainty and parameter uncertainty through a model to determine output uncertainty. However, to carry out Monte Carlo simulations, the uncertainty distributions or the probability density functions (PDFs) of the model parameters and input variables must be known. This remains one of the bottlenecks in current uncertainty research in forest carbon flux modeling. Because forest carbon flux models involve many parameters, we questioned whether it is necessary to take into account all parameters in the uncertainty analysis. A sensitivity analysis can determine the parameters contributing most to the overall model output uncertainty. This paper illustrates the usefulness of the Monte Carlo simulation technique for ranking parameters for sensitivity and uncertainty in process-based forest flux models. The uncertainty of the output (net ecosystem exchange, NEE) of the FORUG model was estimated for the Hesse beech forest (1997). Based on the arbitrary uncertainty of ten key parameters, a standard deviation of 0.88 Mg C ha(-1) year(-1) NEE was found which is equal to 24% of the mean value of NEE. Sensitivity analysis showed that the overall output uncertainty of the FORUG model can largely be determined by accounting for the uncertainty of only a few key parameters. The results led to the identification of the key FORUG parameters and to the recommendation for a process-based description of the soil respiration process in the FORUG model.

Carbon↗
PubMed1984

Problems in the identification of species of Eimeria.

The paper is concerned with the principles upon which coccidia of the genus Eimeria may be characterized. Reference strains for comparative purposes usually are not available and the limitations of morphological data for speciation are discussed. The value of other parameters are considered such as host and site specificity, pathogenicity, immunological specificity, pre-patent period, sporulation time, enzyme variation, and DNA buoyant density. The weight afforded to each of these parameters for specific identification may vary according to the parasite and host studied. Determinations of physiological and behavioral characteristics that are now becoming available should be included in species definitions wherever possible.

Animals↗
PubMed2003

Discriminating redox cycling and arylation pathways of reactive chemical toxicity in trout hepatocytes.

The toxicity of four quinones, 2,3-dimethoxy-1,4-naphthoquinone (DMONQ), 2-methyl-1,4-naphthoquinone (MNQ), 1,4-naphthoquinone (NQ), and 1,4-benzoquinone (BQ), which redox cycle or arlyate in mammalian cells, was determined in isolated trout (Oncorhynchus mykiss) hepatocytes. More than 70% of cells died in 3 h when exposed to BQ or NQ; 50% died in 7 h when exposed to MNQ, with no mortality compared to controls after 7 h DMONQ exposure. A suite of biochemical parameters was assessed for ability to discriminate these reactivity pathways in fish. Rapid depletion of glutathione (GSH) with appearance of glutathione disulfide (GSSG) and increased dichlorofluoroscein fluorescence were used as indicators of redox cycling, noted with DMONQ, MNQ, and NQ. Depletion of GSH with no GSSG accumulation, and loss of free protein thiol (PrSH) groups (nonreducible) indicated direct arylation by BQ. All toxicants rapidly oxidized NADH, with changes in NADPH noted later (BQ, NQ, MNQ) or not at all (DMONQ). Biochemical measures including cellular energy status, cytotoxicity, and measures of reactive oxygen species, along with the key parameters of GSH and PrSH redox status, allowed differentiation of responses associated with lethality. Chemicals that arylate were more potent than redox cyclers. Toxic pathway discrimination is needed to group chemicals for potency predictions and identification of structural parameters associated with distinct types of reactive toxicity, a necessary step for development of mechanistically based quantitative structure-activity relationships (QSARs) to predict chemical toxic potential. The commonality of reactivity mechanisms between rodents and fish was also demonstrated, a step essential for species extrapolations.

Adenine↗
PubMed2004

Poorly differentiated carcinomas of the thyroid with trabecular, insular, and solid patterns: a clinicopathologic study of 183 patients.

BACKGROUND: The term poorly differentiated (PD) carcinoma was proposed 20 years ago to define aggressive, follicular-derived thyroid carcinomas with behavior intermediate between follicular/papillary and anaplastic carcinomas. Among the variable histologic patterns recognized in such tumors, trabecular-insular-solid (TIS) areas usually are predominant. Conversely, some authors pointed out that PD carcinomas are characterized by unequivocal, high-grade histology with atypias, high mitotic counts, and necrosis rather than by a specific growth pattern. METHODS: The clinicopathologic features of a series of 183 thyroid carcinomas with predominant (n = 165 tumors) or focal (n = 18 tumors) TIS growth patterns were studied by univariate and multivariate overall survival analyses and were compared with clinical outcomes. Subgroups included tumors with predominant oxyphilic features (n = 66 tumors) and (residual) papillary carcinoma features (n = 24 tumors). Control groups of papillary (n = 68 tumors), follicular (n = 71 tumors), and anaplastic (n = 35 tumors) carcinomas also were included for overall survival analysis. RESULTS: TIS carcinomas had an intermediate behavior between papillary/follicular and anaplastic carcinomas (P < 0.0001). Univariate and multivariate statistical analyses demonstrated that age > 45 years (P = 0.007), the presence of necrosis (P < 0.0001), and a mitotic count > 3 per 10 high-power fields (P = 0.01) were associated with poor outcome. A simplified scoring system based on statistically significant parameters allowed the identification of three prognostic subgroups (P < 0.0001). CONCLUSIONS: PD TIS carcinomas overall followed a more aggressive course compared with differentiated thyroid carcinomas, irrespective of the extent of the TIS component. However, a numeric scoring system applied to specific clinicopathologic parameters further may identify three prognostic categories of patients who have significantly different survival rates at 5 years and 10 years.

Adenocarcinoma↗