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Results for “Deterministic Measurement”

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PubMed1981

Clocked cell cycle clocks.

The cell division cycle of both mammalian cells and microorganisms, which apparently has both deterministic and probabilistic features, is a clock of sorts in that the sequence of events that comprise it measures time under a given set of environmental conditions. The cell division cycle may itself be regulated by a programmable clock that, under certain conditions, can generate circadian periodicities by interaction with a circadian pacemaker. These clocks must insert time segments into the cell division cycle in order to generate the observed variability in cellular generation times.

Animals↗

PubMed1993

Heterogeneity and probabilistic binding contributions to receptor-mediated cell detachment kinetics.

Biospecific cell adhesion is mediated by receptor-ligand bonds. Early theoretical work presented a deterministic analysis of receptor-mediated cell attachment and detachment for a homogeneous cell population. However, initial comparison of a deterministic framework to experimental detachment profiles of model "cells" (antibody-coated latex beads) did not show qualitative or quantitative agreement (Cozens-Roberts, C., D.A. Lauffenburger, and J.A. Quinn. 1990. Biophys. J. 58:857-872). Hence, we determine the contributions of population heterogeneity and probabilistic binding to the detachment behavior of this experimental system which was designed to minimize experimental and theoretical complications. This work also corrects an error in the numerical solution of the probabilistic model of receptor-mediated cell attachment and detachment developed previously (Cozens-Roberts, C., D.A. Lauffenburger, and J.A. Quinn. 1990. Biophys J. 58:841-856). Measurement of the population distribution of the number of receptors per bead has enabled us to explicitly consider the effect of receptor number heterogeneity within the cell-surface contact area. A deterministic framework that incorporates receptor number heterogeneity qualitatively and quantitatively accounts in large part for the model cell detachment data. Using measured and estimated parameter values for the model cell system, we estimate that about 90% of the observed kinetic detachment behavior originates from heterogeneity effects, while about 10% is due to probabilistic binding effects. In general, these relative contributions may differ for other systems.

Biophysical Phenomena↗

PubMed1994

Dynamical chaos determines the variability of transcranial Doppler signals.

In order to estimate whether or not the variability of a timeseries of transcranial Doppler (TCD) waveforms is the result of a random or a deterministic process the following study was designed. From eight normal volunteers the middle cerebral artery blood flow velocities were measured for 50 sec and the maximum blood flow velocities (or waveforms) were analysed. From these waveforms socalled attractors were reconstructed and shown in a two dimensional phase portrait. The attractor of the TCD timeseries shows the entire range of states the cardiovascular system can display. The geometric structure of the attractor can be estimated by calculation of the correlation dimension D2. The correlation dimension D2 shows that the time evolution of the TCD timeseries is essentially nonperiodic and can be characterized by low dimensional chaos. It has been shown that the D2 value during hypocapnia has a significant higher value compared to the D2 values during normocapnia. The biological and clinical significance of these observations are outlined.

Adult↗

PubMed1980

Physical causality and brain theories.

The history of deterministic theories in physics is reviewed, and four levels of determinism are found: 1) absolute, 2) asymptotic, 3) probabilistic, and 4) absolute indeterminism. Nagel's view that all causal laws are deterministic in the frame of the state descriptions to which they refer is acknowledged, but the inevitability of macroscopic measurement noise may hint that dynamical laws are innately noisy. Quantum mechanical effects are not the noise source. Symmetry and broken symmetry are introduced as physical concepts that can account both for lawfulness, and for the hierarchical nature of the universe. Physical ideas are chosen over those of formal systems with indirect self-reference as the basis of a global theory of brains. By exclusion it is concluded that only a statistical thermodynamics, combined with nonlinear mechanics, has the features needed for theorizing about brains in a physical sense. Quantum mechanics is judged not to be relevant. New statistical thermodynamic theories are briefly described, and their strengths and weaknesses noted. The question, "Why should neuroscience look to physics for its theories?" is raised and answered. Some concrete objectives for a program of theoretical research are stated.

Brain↗

PubMed1991

Risk prevention and policy-making in automatic systems.

Accidents with automatic production systems are reported to be on the order of one in a hundred or thousand robot-years, while fatal accidents are found to occur one or two orders of magnitude less frequently. Traditions in occupational safety tend to seek for safety targets in terms of zero severe accidents for automatic systems. Decision-making requires a risk assessment balancing potential risk reduction measures and costs within the cultural environment of a production company. This paper presents a simplified procedure which acts as a decision tool. The procedure is based on a risk concept approaching prevention both in a deterministic and in a probabilistic manner. Eight accident scenarios are shown to represent the potential accident processes involving robot interactions with people. Seven prevention policies are shown to cover the accident scenarios in principle. An additional probabilistic approach may indicate which extra safety measures can be taken against what risk reduction and additional costs. The risk evaluation process aims at achieving a quantitative acceptable risk level. For that purpose, three risk evaluation methods are discussed with respect to reaching broad consensus on the safety targets.

Accidents, Occupational↗

PubMed1979

Computer simulation of the effectiveness of male-linked translocations for the control of Anopheles albimanus Wiedemann.

A deterministic simulation model was used to establish the potential value of releasing male-linked translocation heterozygotes as a control measure for Anopheles albimanus Wiedemann. Theoretical population reductions exceeding 90% were obtained within 90 and 120 days after releases at initial ratios of 5 translocation males (TM): 1 normal male (NM) and 1 TM: 1 NM, respectively. Additional simulations emphasized the importance of the need for a method that would eliminate females from the release material. Releases containing 15% females were less effective than those with none. When a malaria subroutine was included in the model, the calculations showed that all the theoretical releases greatly reduced the number of malaria-infective females and therefore would have a profound effect on transmission of the disease. The number of malaria-infective females present was eliminated completely when only translocation males were released; however, a small number were present when the releases contained 15% females. Male-linked translocation males required longer periods of time to bring about population control than males that were completely sterile.

Animals↗

PubMed1991

A stochastic model for the development of an AIDS epidemic in a heterosexual population.

A non-age-dependent model, describing the evolution of a bisexual population, is developed in this paper and applied to projecting an AIDS epidemic in a heterosexual population. Included in the formulation are frequency- and non-frequency-dependent rules of partnership formation as well as five states of HIV disease, affecting the probability of infection per sexual contact. Results from computer experiments, designed to study the development of an AIDS epidemic in a heterosexual population fed by single males with a 50% prevalence of HIV infection prior to becoming active in heterosexual partnerships, are reported. In these experiments, the only source of HIV infection for females was sexual contacts with infected males within partnerships. Data on the probability of infection per sexual contact with an infected partner and the number of sexual contacts per month were incorporated into the model. However, the numbers used for the initial population of singles, couples, and those becoming sexually active per month were hypothetical. Even though the prevalence of HIV infection among males entering heterosexual partnerships was high, after 30 years the projected prevalence of HIV infection among females ranged from about 10 to 15% depending in part on the expected duration of partnerships and on whether the frequency- or non-frequency-dependent model was used. In these experiments, solutions of the embedded, nonlinear, deterministic equations for the incidence of HIV infection and the cumulative number of deaths due to AIDS proved to be good measures of central tendency for the sample functions of the stochastic population process.

Acquired Immunodeficiency Syndrome↗

PubMedDate not supplied

Non-deterministic individual responses to receptor-selective opioid agonists.

To assess within a single rat strain individual variability of analgesic responses to sub-ED50 doses of receptor-selective opioids, we measured: 1) tail flick latency (TFL) responses after intrathecal (ith) injection of delta, mu, and kappa agonists administered serially; 2) TFL and tail pinch latencies (TPch) after intravenous (iv) mu and kappa agonists; and 3) TFL and TPch after iv agonists of mu or combined mu + delta selectivity. Mean values in each study confirmed an analgesic response, but individual TFL and TPch responses were chaotic and, within each study, rank order correlations between TFL and TPch values within or between drugs were insignificant. Our results suggest a hypothesis that such responses are intrinsically nondeterministic because--resembling other complex dynamic systems--they are generated by stochastic receptor-transmitter interactions that in turn evoke a series of nonlinearly coupled cellular and neural events.

Amino Acid Sequence↗

PubMedDate not supplied

Evaluating the quality of anonymous record linkage using deterministic procedures with the New York State AIDS registry and a hospital discharge file.

Linkage of same-person records across multiple databases relies on high-quality, uniformly available identifying information. These data quality issues become increasingly important when personal names are not available for record linkage. Using deterministic decision criteria, we linked records from two population-based files in the absence of personal names. The sensitivity of anonymous record linkage procedures ranged from 32 to 85 per cent for the two years studied, and the positive predictive value (PPV) ranged from 14 to 99 per cent. Decreasing sensitivity and PPV were primarily attributed to (1) errors in computerized identifying information and (2) the deterministic decision criteria specified for record linkage. An evaluation of the contribution of personal names to the quality of record linkage found no measurable impact.

Acquired Immunodeficiency Syndrome↗

PubMed1995

Parathyroid hormone secretion and serum calcium concentration--a deterministic view of its regulation.

In seven normal men we investigated the basal secretion of PTH by blood sampling in 30 sec intervals for estimation of intact PTH and at 2-min intervals for measurement of ionized calcium. In 4 of these subjects we also investigated the PTH-secretion under conditions of intermittent hypercalcemia and hypocalcemia. Our measurements demonstrate the existence of three time scales in the secretion of PTH, viz. short-term pulses (faster than 2 min), an intermediate pattern of adjusting PTH levels to changed Ca2+ averages, and finally a long-term coupling between PTH and Ca2+ averages after 20 min. Ionized calcium controls the long-term regulation and intermediate adaptation mechanisms, but the short-term fluctuations seem to be due to spontaneous secretion.

Adult↗

PubMed1976

Cytophotometric analysis of basic nuclear proteins during gametogenesis in the free-living nematode Panagrellus silusiae.

The cytochemical staining characteristics of basic nuclear proteins during gametogenesis in both sexes of the free-living nematode Panagrellus silusiae were monitored by absorption microspectrophotometry. During spermatogenesis, the levels of both of the nuclear-bound Sakaguchi and 1-fluoro-2, 4-dinitrobenzene (FDNB) reagents per Feulgen-DNA content increase prior to meiosis and subsequently drop off during spermiogenesis. During oogenesis, the amount of Sakaguchi-protein to DNA ratio rises slightly whereas the FDNB-protein to DNA ratio undergoes a meagre decline. Since the oocyte of Panagrellus accumulates DNA in excess of a 4C DNA equivalent, the relative constancy of the ratio of basic nuclear protein content to DNA amount during oogenesis signifies that these proteins are being continously produced during oocyte maturation. After treatment with alkaline fast green (pH 8.1) the cytoplasmic and nuclear regions of the gonocytes of both sexes yield such an intense reaction that microspectrophotometric measurements could not be taken. The basis of the cytoplasmic staining reaction to the fast green (pH 8.1) dye was not determined. The rapid, highly deterministic programme of embryogenesis in Panagrellus may require a substantial stockpiling of basic nuclear proteins during oogenesis.

Animals↗

PubMedDate not supplied

Discriminating deterministic versus stochastic dynamics in neuronal activity.

An approach to discriminating deterministic versus stochastic dynamics from neuronal data is presented. Direct tests for determinism are emphasized, as well as using time series with clear physical correlates measured from small ensembles of neurons. Surrogate data are used to provide null hypotheses that the dynamics in our data could be accounted for by linear stochastic systems. Algorithms are given in full, and the analysis of an experimental example is given.

Algorithms↗

PubMed1995

A survey of films for use as dosimeters in interventional radiology.

Analysis of radiation doses in interventional radiological procedures that can lead to deterministic radiation effects such as erythema and epilation would assist physicians in planning patients care after exposure and in reducing doses. Photographic films used to measure skin exposure in the past are too sensitive for the high doses involved in interventional procedures. Seventeen different types of films, many of which are generally available in hospitals, were surveyed to see if any would meet the demands of interventional radiology. Sensitometric curves obtained demonstrate that most films are inappropriate for high dose procedures. Using Kodak Fine Grain Positive and Dupont duplicating films and automatic processing, doses as high as 2.8 Gy could be measured with reasonable accuracy. Similar results can be obtained by manually processing Kodak XV-2 verification film at room temperature.

Automation↗

PubMed1995

EEG dipole localization bounds and MAP algorithms for head models with parameter uncertainties.

The Cramer-Rao bound for unbiased dipole location estimation is derived under the assumption of a general head model parameterized by deterministic and stochastic parameters. The expression thus characterizes fundamental limits on EEG dipole localization performance due to the effects of both model uncertainty and statistical measurements noise. Expressions are derived for the cases of multivariate Gaussian and gamma distribution priors, and examples are given to illustrate the derived bounds when the radii and conductivities of a four-concentric sphere head model are allowed to be random. The joint MAP estimate of location/model parameters is then examined as a means of achieving robustness to deviations from an ideal head model. Random variations in both the multiple sphere radii and the layer conductivities are shown, via the stochastic Cramer-Rao bounds and Monte Carlo simulation of the MAP estimator, to have the most impact on localization performance in high SNR regions, where finite sample effects are not the limiting factors. This corresponds most often to spatial regions that are close to the scalp electrodes.

Algorithms↗

PubMed1989

Impact of diffuse nitrate pollution sources on groundwater quality--some examples from Czechoslovakia.

In several regions of Czechoslovakia with intensive agricultural production, the correlation between the amount of nitrogen fertilizer applied and the nitrate content in groundwater has been recognized. Nitrate pollution of groundwater is considered to be the most serious source of nonpoint pollution in Czechoslovakia. A program of research into the effects of farming activities on groundwater quality in Czechoslovakia is under way on experimental fields (20 to 30 hectares) and, simultaneously, in regions in which shallow, vulnerable aquifers occur. The importance of the soil organic matter's stability for maintaining the groundwater quality is emphasized. Research based on nitrogen and organic carbon balance has shown that the restoration of a soil-groundwater system is a complicated process that usually requires changes in the extent and intensity of agricultural activities and consistent attention to the effects produced by natural conditions. Regional investigation of the impact of farming on shallow aquifers in the fluvial deposits of the Elbe River in Bohemia has proved the hydrochemical instability and vertical hydrochemical heterogeneity of these aquifers. The WASTEN deterministic model was used for modeling the transport and transformation of various types of inorganic fertilizers. The input data is based on laboratory and field measurements. Special topics are the verification of model calculations and the time and spatial variability of input data with respect to the unsaturated zone. The research results are being used for making regional and national agro-groundwater managerial schemes more precise, as well as for decision-making.

Agriculture↗

PubMed1992

Computerized electrocardiogram diagnosis: fuzzy approach.

This paper investigates the computerized analysis of electrocardiographic signals. The biological variability, the lack of standards in the definition of measurements and of diagnostic criteria make the classification problem a complex task. Two basic methods of the diagnostic process are described: the statistical model and the deterministic approach. In particular, a model for ECG classification will be illustrated where the imprecise knowledge of the state of cardiac system and the vague definition of the pathological classes are taken care of by means of the fuzzy set formalism.

Diagnosis, Computer-Assisted↗

PubMed1992

The scalp distribution of the fractal dimension of the EEG and its variation with mental tasks.

The insights gained by the concept of deterministic chaos for the EEG is that this seemingly disordered process may be governed by relatively few simple laws which could be determined. One of the quantitative measures of a complex dynamical system is that of its dimension. The term 'dimension' refers to the ability of a space to contain a set of points. We estimated the correlational dimension of the EEG and compared the outcome to traditional Fourier analyses. In addition, we tested the hypothesis that the EEG can be described as filtered noise. Data from 15 electrode sites and 31 subjects are reported in the present study. We have utilized a variety of tasks that cut across sensory modalities including touch, vision, and imagery which reflect neuropsychological processes that differentially engage areas of the cortex in the first part of the study. In the second part, the differences between the perception of an object and the imagination of the same object were evaluated. The outcome shows variations between scalp sites for all measures and also variations between tasks in terms of dimensionality of the EEG. The hypothesis of a higher dimensionality ("complexity") of imagery compared to actual perceptual processing was confirmed. A statistical comparison between the maps generated by means of the various measures shows that different informations are extracted when using the different measures. There is also statistical evidence that the EEG cannot completely be described by the model of filtered noise.

Adult↗

PubMed1992

Chaotic dynamics in autonomic nervous system activity of a patient during a psychotherapy session.

Chaos theory and nonlinear dynamical modeling have been applied successfully in a variety of scientific fields ranging from the physical sciences to population biology. More recently, investigators have modeled long-term psychological processes by applying this paradigm to subjective measures. Yet, mathematically rigorous dynamical modeling of transient psychodynamic processes remains uncharted. Human behaviors and intrapsychic processes often defy prediction, yet psychodynamic theory views these as fundamentally deterministic. We postulate that a nonlinear dynamical analysis of mental states and mental control processes may help reconcile the paradox that seemingly random mental states are thought ultimately to result from deterministic, rather than stochastic, psychological processes. As an initial empirical approach, we examined spontaneously occurring autonomic activity of a patient during 1 hr of psychotherapy and illustrate that cardiac responses associated with psychologically meaningful events possess nonlinear characteristics indicative of chaos. Such nonlinear analyses may shed light on fundamental issues of psychological functioning.

Adult↗