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PubMed1985

Uncertainty relation for resolution in space, spatial frequency, and orientation optimized by two-dimensional visual cortical filters.

Two-dimensional spatial linear filters are constrained by general uncertainty relations that limit their attainable information resolution for orientation, spatial frequency, and two-dimensional (2D) spatial position. The theoretical lower limit for the joint entropy, or uncertainty, of these variables is achieved by an optimal 2D filter family whose spatial weighting functions are generated by exponentiated bivariate second-order polynomials with complex coefficients, the elliptic generalization of the one-dimensional elementary functions proposed in Gabor's famous theory of communication [J. Inst. Electr. Eng. 93, 429 (1946)]. The set includes filters with various orientation bandwidths, spatial-frequency bandwidths, and spatial dimensions, favoring the extraction of various kinds of information from an image. Each such filter occupies an irreducible quantal volume (corresponding to an independent datum) in a four-dimensional information hyperspace whose axes are interpretable as 2D visual space, orientation, and spatial frequency, and thus such a filter set could subserve an optimally efficient sampling of these variables. Evidence is presented that the 2D receptive-field profiles of simple cells in mammalian visual cortex are well described by members of this optimal 2D filter family, and thus such visual neurons could be said to optimize the general uncertainty relations for joint 2D-spatial-2D-spectral information resolution. The variety of their receptive-field dimensions and orientation and spatial-frequency bandwidths, and the correlations among these, reveal several underlying constraints, particularly in width/length aspect ratio and principal axis organization, suggesting a polar division of labor in occupying the quantal volumes of information hyperspace.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Uncertainty analysis of visible and near-infrared data of hydrocarbons.

Measurement of physical and chemical properties of hydrocarbons plays an important role in the exploration and production of oil wells. In situ measurement of chemical properties of hydrocarbons makes use of visible and near-infrared (vis-NIR) absorption spectra of hydrocarbons. Uncertainty analysis of these fluid properties is central to developing a fundamental understanding of the distribution of hydrocarbons in the reservoir. In this manuscript, we describe an algorithm called the fluid comparison algorithm (FCA), which provides a statistical framework to quantify and compare hydrocarbon fluid properties and associated uncertainties derived from vis-NIR measurements. The inputs to FCA are the magnitude and uncertainty of vis-NIR spectroscopy data of two hydrocarbons. The output of FCA is a probability that two fluids are statistically different. FCA lays the foundations for subsequent optimization and capture of representative reservoir hydrocarbons. Furthermore, in some circumstances, it can also enable real-time decisions to identify reservoir compartmentalization and hydrocarbon composition gradients in natural oil reservoirs.

Journal Article↗
PubMed2004

Metabolic control analysis under uncertainty: framework development and case studies.

Information about the enzyme kinetics in a metabolic network will enable understanding of the function of the network and quantitative prediction of the network responses to genetic and environmental perturbations. Despite recent advances in experimental techniques, such information is limited and existing experimental data show extensive variation and they are based on in vitro experiments. In this article, we present a computational framework based on the well-established (log)linear formalism of metabolic control analysis. The framework employs a Monte Carlo sampling procedure to simulate the uncertainty in the kinetic data and applies statistical tools for the identification of the rate-limiting steps in metabolic networks. We applied the proposed framework to a branched biosynthetic pathway and the yeast glycolysis pathway. Analysis of the results allowed us to interpret and predict the responses of metabolic networks to genetic and environmental changes, and to gain insights on how uncertainty in the kinetic mechanisms and kinetic parameters propagate into the uncertainty in predicting network responses. Some of the practical applications of the proposed approach include the identification of drug targets for metabolic diseases and the guidance for design strategies in metabolic engineering for the purposeful manipulation of the metabolism of industrial organisms.

Algorithms↗
PubMedDate not supplied

Sensitivity of erythemally effective UV irradiance and daily exposure to uncertainties in measured total ozone.

In this study the sensitivity of the erythemally effective radiation to uncertainties in operationally measured total ozone content of the atmosphere (TOC) was estimated. For this, daily operational TOC measurements from different instruments were applied covering the period from 1997 to 1999. Measurements were gained from space by Earth Probe Satellite, Earth Remote Sensing satellite/Global Ozone Monitoring Experiment and Operational Vertical Sounder and from the ground by Dobson and Brewer spectrophotometers for the locations of Hradec Kralove (Czech Republic, 50 degrees N), Nairobi (Kenya, 1 degrees S) and Springbok (Republic of South Africa, 30 degrees S). The values were used as input parameter to model calculations of erythemally effective irradiance and daily radiant exposure. The differences due to the use of TOC from different sources were analyzed with respect to the Ultraviolet Index (UVI). The UVI was introduced as a tool for sun protection and health care. Therefore, it is of special importance to know the restriction of accuracy. As a tool of health care, the maximum uncertainties are of interest and are described in using the 95%-percentile and the maximum differences. This study shows that differences, i.e. uncertainties (95%-percentile) are in the order of 1 UVI. Independently on the location, however, extreme differences may overstep 3 UVI. For the daily dose the 95%-percentile is around 7.5 UVI hours (UVIh) but differences higher than 20 UVIh were also found.

Atmosphere↗
PubMed2003

The probabilistic economic injury level: incorporating uncertainty into pest management decision-making.

Despite the recognition that the economic injury level (EIL) is determined by dynamic biological and economic parameters, which can be highly variable and uncertain, there has been little effort to quantify uncertainty and to use estimates of uncertainty in the determination of EILs. In this paper, we define the probabilistic EIL (PEIL) and develop PEILs for two insect pest scenarios: alfalfa weevil larvae, Hypera postica (Gyllenhal), on early bud-stage alfalfa, and bean leaf beetle adults, Cerotoma trifurcata (Forster), on V1-stage soybean. The PEIL is an EIL that reflects its probability of occurrence. The probability of occurrence is determined by incorporating the uncertainty associated with the input variables used to calculate the EIL. We used Monte Carlo simulation, a random sampling technique in which each input variable in the model was sampled repeatedly from a range of possible values based on probability distributions. Each input variable's probability distribution was sampled such that the distribution's shape was reproduced. Then, the variability for each input was propagated into the output of the model so that the model output reflected the probability of values that could occur. This represents the first use of the Monte Carlo technique to determine EILs.

Animals↗
PubMed2004

Effects of exposure uncertainties in the TSCE model and application to the Colorado miners data.

The simulations in this paper show that exposure measurement error affects the parameter estimates of the biologically motivated two-stage clonal expansion (TSCE) model. For both Berkson and classical error models, we show that likelihood-based techniques of correction work reliably. For classical errors, the distribution of true exposures needs to be known or estimated in addition to the distribution of recorded exposures conditional on true exposures. Usually the exposure uncertainty biases the model parameters toward the null and underestimates the precision. But when several parameters are allowed to be dependent on exposure, e.g. initiation and promotion, then their relative importance is also influenced, and more complicated effects of exposure uncertainty can occur. The application part of this paper shows for two different types of Berkson errors that a recent analysis of the data for the Colorado plateau miners with the TSCE model is not changed substantially when correcting for such errors. Specifically, the conjectured promoting action of radon remains as the dominant radiation effect for explaining these data. The estimated promoting action of radon increases by a factor of up to 1.2 for the largest assumed exposure uncertainties.

Body Burden↗
PubMed1992

Simple and rapid inversion of additive relationship matrices incorporating parental uncertainty.

Animals bred in pastoral systems are often part of multiple-sire groups, introducing uncertainty into pedigrees. Genetic evaluation of sires and dams in such instances is complicated by the uncertainty of parenthood. This article defines a simple and rapid algorithm to compute the inverse of a numerator relationship matrix under uncertain parenthood. The algorithm can accommodate inbreeding and uncertainty of parenthood on both paternal and maternal sides of the pedigree.

Algorithms↗
PubMedDate not supplied

Diagnostic closure and the spread of uncertainty.

When a child is diagnosed with a life-threatening, chronic illness, the taken-for-granted world of the child's parents is destroyed. From that moment on, they must learn to manage life under very uncertain conditions. The findings reported here are from a more comprehensive grounded theory study that sought a plausible explanation for parental behavior under conditions of sustained uncertainty. This report describes the emergence of uncertainty as a multidimensional concept that permeates every aspect of family life following the diagnostic announcement. The noncategorical nature of the dimensions of uncertainty found in all life-threatening, chronic childhood illnesses provides a strong argument for preparing nurses in specialties that are conceptually, rather than medically, based.

Chronic Disease↗
PubMed2004

Minority versus majority influence and uncertainty orientation: processing persuasive messages on the basis of situational expectancies.

The authors examined the effects of uncertainty orientation on processing persuasive messages from minority sources versus majority sources. The authors gave participants a proattitudinal or counterattitudinal message that either a numerical majority or a numerical minority endorsed and that contained strong or weak arguments. In support of the hypothesis that was related to message scrutiny, uncertainty-oriented individuals engaged in greater message scrutiny when the Source-Position (i.e., minority/majority-pro/con) pairing was imbalanced (in majority-con, minority-pro conditions) than when it was balanced (in majority-pro, minority-con conditions). Certainty-oriented participants showed the opposite pattern, scrutinizing the message more when the situation was balanced than when the situation was imbalanced. Support for the hypothesis that was related to nonsystematic processing was less clear because the majority appeared to have played a greater role in accounting for the aforementioned interaction than did the minority. Additional analyses supported this interpretation. However, in all cases, individual differences in uncertainty orientation moderated strength and direction of information processing.

Adult↗
PubMed2002

Spatial-frequency uncertainty and cuing effects on psychometric functions for contrast detection.

In the present study, the effects of spatial-frequency uncertainty and cuing on psychometric functions for contrast detection of sinusoidal gratings are examined. For this purpose, psychometric functions were collected from 4 subjects under fixed-frequency, randomized-frequency, and cued-frequency conditions. The experiment was conducted with a temporal two-alternative forced-choice task, and five spatial frequencies in the range of 0.5 and 8.0 c/deg and seven contrast levels for each frequency were used. The results showed that the psychometric functions for the randomized-frequency condition were shallower than those for the fixed-frequency condition, supporting the single-band model for the uncertainty effects (Hübner, 1993a, 1993b). For the cued-frequency condition, the slopes of the functions were not clearly different from those for the randomized condition. These results clearly differ from those of Hübner (1996b), which showed, in the spatial two-alternative forced-choice task, steeper psychometric functions for the randomized-frequency condition than those for the fixed- and cued-frequency conditions, supporting the multiple-band model (Hübner, 1993a, 1993b). The difference suggests that the single-band model applies to the uncertainty effects in the temporal forced-choice task, whereas the multiple-band model does so in the spatial forced-choice task.

Adult↗
PubMed1999

Teaching clinical biomechanics in the context of uncertainty.

Uncertainty in the theories that provide the underpinnings of the clinical practice of podiatric biomechanics creates a dilemma: How should educators prepare students to make clinical decisions in the context of this uncertainty? Students need to be exposed to all approaches and be given the tools to make their own clinical decisions. Critical thinking involves the ability to weigh evidence, examine arguments, and construct rational bases for decisions and beliefs. Perry's model of cognitive development provides educators with one model for fostering critical thinking skills in students to guide them through the uncertainty in clinical biomechanics. This article presents the teaching philosophy that is used to teach undergraduate clinical biomechanics in the Department of Podiatry at La Trobe University, Australia.

Biomechanical Phenomena↗
PubMed1982

Strategic planning: determining the impact of environmental characteristics and uncertainty.

This paper continues a line of research into the effect of environmental characteristics and uncertainty on strategic planning. Results suggest that measures of uncertainty and the environment need to be analyzed independently, and that uncertainty is a strong moderator of environmental characteristics and industry groupings but does not consistently affect strategic planning activities.

Organization and Administration↗
PubMed1999

Uncertainty in chronic illness.

In this chapter, the research on uncertainty in chronic illness is reviewed and critiqued. Two theoretical perspectives of uncertainty that can be applied across the range of chronic illness are presented. Research on the causes and consequences of uncertainty in chronic illness are considered and critiqued. The review addresses research on adults and on parents of chronically ill children. Conclusions include the areas requiring further investigation.

Adaptation, Psychological↗
PubMed2000

Determination of copper, selenium and zinc in human blood by inductively coupled mass spectrometry: the sources of uncertainty and variability of results.

The concentration of Cu, Se and Zn in whole human blood and plasma was analysed by inductively coupled plasma mass spectrometry. Method involved dilution of sample by diluted nitric acid and Triton X-100 and measurement of 65Cu, 77Se and 66Zn intensities. Calibration solutions were spiked by main interferents. In order to evaluate suitability of the method for recognition of alternation of trace elements concentration, the uncertainty of results was estimated. The major part of uncertainty was due to repeatability, the other source (calibration and interferences) were found to be of lesser importance. The resulting uncertainty of concentration of mentioned trace elements is low as compared to between individual variability. Short-term (within day) and long-term (between day) variability of trace elements concentration was investigated and compared with between individual variability too. The time variability was negligible except for Zn concentration. The alternations of trace elements concentration in patients with several renal diseases were investigated. Only in case of patients in end-stage renal disease: hemodialyzed patients and patient treated by continuous ambulatory peritoneal dialysis the significant alternations were proved.

Copper↗
PubMed1999

Effect of stimulus contrast uncertainty on simple reaction time.

Both reaction time (RT) and the latency of the visually evoked potentials (VEP) to grating onset increase with increasing stimulus spatial frequency (SF). At SF higher than 5 c/deg RT increases faster than VEP latency, the difference resulting in a "central delay" (Mihaylova et al., 1999). Due to the equipment limitations, RT and VEP experiments of Mihaylova et al. (1999) differed in constancy of stimulus contrast within a sequence of trials. The present experiments were aimed at testing the assumption that the central delay is a result of contrast uncertainty effect on RT. To this end, RT were measured in condition of both constant and variable grating contrast. The stimuli were sinusoidal gratings ranging in SF from 0.5 to 16 c/deg and in contrast from 2.5 to 50%. In addition, VEP were recorded to the same stimuli in blocks of fixed contrast and the latencies of the early VEP wave were subtracted from RT. Contrast uncertainty did not affect RT at low SF, 0.5 and 2 c/deg, while increasing RT at SF higher than 5 c/deg both at low and high stimulus contrast. The results showed that the central component of RT increase at high SF is reduced but not eliminated under constant contrast condition. The uncertainty effect at high SF might be due to contrast sensitivity reduction, reduced subjective stimulus probability and differences in response strategy adopted by the subjects when contrast was constant or variable. An alternative explanation is a larger ability of low SF stimuli compared to high SF stimuli to attract visual attention.

Adult↗
PubMed2001

Identifiability and uncertainty analysis of the river water quality model no. 1 (RWQM1).

State of the art models as used in activated sludge modelling and recently proposed for river water quality modelling integrate the knowledge in a certain field. If applied to data from a specific site, such models are nearly always overparameterised. This raises the question of how many parameters can be fitted in a given context and how to find identifiable parameter subsets given the experimental layout. This problem is addressed for the kinetic parameters of a simplified version of the recently published river water quality model no. 1 (RWQM1). The selection of practically identifiable parameter subsets is discussed for typical boundary conditions as a function of the measurement layout. Two methods for identifiable subset selection were applied and lead to nearly the same results. Assuming upstream and downstream measurements of dissolved substances to be available, only a few (5-8) model parameters appear to be identifiable. Extensive measurement campaigns with dedicated experiments seem to be required for successful calibration of RWQM1. The estimated prior uncertainties of the model parameters are used to estimate the uncertainty of model predictions. Finally an estimate is provided for the maximum possible decrease in prediction uncertainty achievable by a perfect determination of the values of the identifiable model parameters.

Ammonia↗
PubMed2001

[Risk, uncertainty and ignorance in medicine].

Exploration of healthy patients' risk factors for disease has become a major medical activity. The rationale behind primary prevention through exploration and therapeutic risk reduction is not separated from the theoretical assumption that every form of uncertainty can be expressed as risk. Distinguishing "risk" (as quantitative probabilities in a known sample space), "strict uncertainty" (when the sample space is known, but probabilities of events cannot be quantified) and "ignorance" (when the sample space is not fully known), a typical clinical situation (primary risk of coronary disease) is analysed. It is shown how strict uncertainty and sometimes ignorance can be present, in which case the orthodox decision theoretical rationale for treatment breaks down. For use in such cases, a different ideal model of rationality is proposed, focusing on the patient's considered reasons. This model has profound implications for the current understanding of medical professionalism as well as for the design of clinical guidelines.

Decision Making↗
PubMed1975

Effect of uncertainty on emotionality and ethanol self-selection in monkeys with cortical ablations.

Alcohol selection and emotionality were examined in rhesus monkeys with frontal cortical ablations which had been subjected to stress via an "uncertainty" paradigm. Uncertainty produced a higher selection of alcohol as compared to nonstress situations. Controls and dorsolateral subjects when exposed to uncertainty selected more of an alcohol solution than either orbital stressed or control-nonstressed animals. Emotionality changes during alcohol-loading and control conditions were measured by recording the number of aggressive or aversive behaviors. Dorsolateral ablations increased the number of aggressive responses while decreasing the number of retreats in the alcohol-loading condition. In the other groups, alcohol loading did not affect the incidence of aggressive or aversive behaviors although they exhibited more retreats than advances across both conditions. Control-nonstressed subjects yielded the lowest number of total aggressive behaviors and the highest number of total retreats.

Aggression↗