Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Probability Theory”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 847 records · Page 47Linked to original sources
PubMed1975

Quantal basis of photoreceptor spectral sensitivity of Drosophila melanogaster.

Small potential fluctuations ("bumps"), boyh spontaneous and light induced, can be recorded intracellularly from the photoreceptors of Drosophila melanogaster. Statistical analyses of these bumps in the spectral range, 400-600 nm, lead to the following interpretations; (a) For weak stimuli at least, these bumps are the quantal units of the receptor potential. (b) Quanta of various wavelengths, when effectively absorbed, will elicit bumps of the same average size. (c) The spectral sensitivity of the receptor potential appears to have its origin in the relative efficiency of quantum bump production at different wavelengths, and not in the intrinsic difference in the properties of bumps produced by quanta of differenct wavelengths.

Animals↗
PubMed1975

Receiver operating characteristic analysis. Application to the study of quantum fluctuation effects in optic nerve of Rana pipiens.

Receiver operating characteristic (ROC) analysis of nerve messages is described. The hypothesis that quantum fluctuations provide the only limit to the ability of frog ganglion cells to signal luminance change information is examined using ROC analysis. In the context of ROC analysis, the quantum fluctuation hypothesis predicts (a) the detectability of a luminance change signal should rise proportionally to the size of the change, (b) detectability should decrease as the square root of background, an implication of which is the deVries-Rose law, and (c) ROC curves should exhibit a shape particular to underlying Poisson distributions. Each of these predictions is confirmed for the responses of dimming ganglion cells to brief luminance decrements at scotopic levels, but none could have been tested using classical nerve message analysis procedures.

Animals↗
PubMed1997

Adjustment for total energy intake in epidemiologic studies.

In epidemiologic studies, total energy intake is often related to disease risk because of associations between physical activity or body size and the probability of disease. In theory, differences in disease incidence may also be related to metabolic efficiency and therefore to total energy intake. Because intakes of most specific nutrients, particularly macronutrients, are correlated with total energy intake, they may be noncausally associated with disease as a result of confounding by total energy intake. In addition, extraneous variation in nutrient intake resulting from variation in total energy intake that is unrelated to disease risk may weaken associations. Furthermore, individuals or populations must alter their intake of specific nutrients primarily by altering the composition of their diets rather than by changing their total energy intake, unless physical activity or body weight are changed substantially. Thus, adjustment for total energy intake is usually appropriate in epidemiologic studies to control for confounding, reduce extraneous variation, and predict the effect of dietary interventions. Failure to account for total energy intake can obscure associations between nutrient intakes and disease risk or even reverse the direction of association. Several disease-risk models and formulations of these models are available to account for energy intake in epidemiologic analyses, including adjustment of nutrient intakes for total energy intake by regression analysis and addition of total energy to a model with the nutrient density (nutrient divided by energy).

Coronary Disease↗
PubMed1986

On estimating canopy photosynthesis and stomatal conductance in a deciduous forest with clumped foliage.

The foliage in a fully-leafed deciduous forest canopy is clumped. Consequently, theory indicates that the probability of beam penetration will be estimated more accurately with a model based on the negative binomial distribution than with a model based on the Poisson distribution, incorporating an assumption of a spherical leaf inclination angle distribution. Flux densities of photosynthetically active radiation (PAR) were measured in and above a deciduous forest canopy and were computed with the canopy radiative transfer models based on the negative binomial and Poisson distributions. These radiation values were used to compute canopy photosynthesis and stomatal conductance. Canopy photosynthesis and stomatal conductance, based on the negative binomial model, overestimated values computed from measured PAR profiles by 8 and 9%. respectively. The canopy photosynthesis and stomatal conductance values computed with the spherical Poisson model under-estimated measured values by 17 and 10%, respectively. Thus, the negative binomial radiative transfer model improves estimates of canopy photosynthesis and, to a lesser extent, stomatal conductance, inside a deciduous forest.

Journal Article↗
PubMed1994

Endotoxin and tumor necrosis factor-alpha in the pathogenesis of hepatic encephalopathy.

Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome characterized predominantly by augmented neuronal inhibition and probably neuronal damage. Several theories concerning the pathogenesis of HE have been proposed; none of these theories is necessarily exclusive. Furthermore, the validity of none of them has been definitively proved experimentally. In this review article an important role of endotoxin and tumor necrosis factor-alpha (TNF) in the pathogenesis of HE is suggested. The involvement of endotoxin and TNF in the pathogenesis of HE seems to be very convincing; it may explain many of the derangements seen in HE. It also seems to be in strong relation to the main theories about HE, the ammonia theory, the GABAergic theory, the benzodiazepine theory, and the AAA/false neurotransmitter theory, where these theories may represent some of the mechanisms whereby TNF may cause inhibition and damage to the CNS in HE, or may represent accompanying features to elevated levels of endotoxin and TNF, with no important role in the pathogenesis of HE. The possible involvement of endotoxin and TNF in the pathogenesis of HE may possess an important clinical application, for serum LPS and TNF concentrations may be of important diagnostic and prognostic value in HE, and treatment with antibodies against endotoxin and against TNF may have potentially beneficial therapeutic effects in this serious and potentially fatal disease.

Amino Acids↗
PubMed2001

Respiratory failure in the neurological patient: the diagnosis of neurogenic pulmonary edema.

Neurogenic pulmonary edema (NPE) is a potential complication of a central nervous system (CNS) insult such as intracranial hemorrhage, uncontrolled generalized seizures, head trauma, tumors, and neurosurgical procedures. The proposed etiology is massive sympathetic discharge following a CNS event. The pathogenesis is not completely understood. However, there are two theories on how NPE occurs: the blast theory and the permeability defect theory. There is evidence for both theories, and NPE is probably the result of a combination of the two. The treatment is mainly supportive with the use of mechanical ventilation and alpha-adrenergic blocking agents while managing increased intracranial pressure. A thorough understanding of the pathophysiological mechanisms behind the development of NPE aids in the management of these patients to prevent further complications.

Adrenergic alpha-Antagonists↗
PubMed2000

Oxygen molecule dissociation on the Al(111) surface

The dissociative adsorption of the O2 on the Al(111) surface is studied using ab initio calculations based on density-functional theory. In the sticking probability experiments an activation barrier for the O2 dissociation exists, but our calculations predict a barrier only for one trajectory. Also our results do not support the model of charge transfer from the surface to the molecule as a bond breaking mechanism. Instead, the increasing hybridization between O2 orbitals and Al states, when the adsorbate approaches the slab, is significant for the dissociation.

Journal Article↗
PubMed2006

Multidimensional effects on dissociation of N2 on Ru(0001).

The applicability of the Born-Oppenheimer approximation to molecule-metal surface reactions is presently a topic of intense debate. We have performed classical trajectory calculations on a prototype activated dissociation reaction, of N2 on Ru(0001), using a potential energy surface based on density functional theory. The computed reaction probabilities are in good agreement with molecular beam experiments. Comparison to previous calculations shows that the rotation of N2 and its motion along the surface affect the reactivity of N2 much more than nonadiabatic effects.

Journal Article↗
PubMed2004

Risk-adjusted mission value: trading off mission risk for mission value.

This article develops a decision-theoretic methodology for the risk-adjusted mission value (RAMV) for selecting between alternative missions in the presence of uncertainty in the outcomes of the missions. This methodology permits trading off mission risk for mission value, something that probabilistic risk analysis cannot do unless it explicitly incorporates both mission value and risk aversion of the project management. The methodology, in its complete implementation, is consistent with the decision theory known as expected utility theory, although it differs from conventional decision theory in that the probabilities and all but one of the utilities are not those of the decision maker. The article also introduces a new interpretation of risk aversion. The methodology is consistent with the elementary management concept concerning division of labor. An example is presented for selecting between discrete alternatives-four landing sites on Mars. A second example is presented for selecting among a set of continuous alternatives-a comet flyby distance. The methodology is developed within the context of scientific missions, but the methodology is equally applicable to any situation requiring outcome value judgments, probability judgments, and risk aversion judgments by different constituencies.

Journal Article↗
PubMedDate not supplied

Executive functioning and preschoolers' understanding of false beliefs, false photographs, and false signs.

Two studies were conducted to investigate the specificity of the relationship between preschoolers' emerging executive functioning skills and false belief understanding. Study 1 (N=44) showed that 3- to 5-year-olds' performance on an executive functioning task that required selective suppression of actions predicted performance on false belief tasks, but not on false photograph tasks. Study 2 (N=54) replicated the finding from Study 1 and showed that performance on the executive functioning task also predicted 3- to 5-year-olds' performance on false sign tasks. These findings show that executive functioning is required to reason only about representations that are intended to reflect a true state of affairs. Results are discussed with respect to theories of preschoolers' theory-of-mind development.

Child, Preschool↗
PubMed2003

The impact of the prospective payment system for skilled nursing facilities on therapy service provision: a transaction cost approach.

OBJECTIVE: To examine skilled nursing facilities (SNFs) "make-or-buy" decisions with respect to rehabilitation therapy service provision in the 1990s, both before and after implementation of Medicare's Prospective Payment System (PPS) for SNFs. DATA SOURCES: Longitudinal On-line Survey Certification and Reporting (OSCAR) data (1992-2001) on a sample of 10,241 freestanding urban SNFs. STUDY DESIGN: We estimated a longitudinal multinomial logistic regression model derived from transaction cost economic theory to predict the probability of the outcome in each of four service provision categories (all employed staff, all contract, mixed, and no services provided). PRINCIPAL FINDINGS: Transaction frequency, uncertainty, and complexity result in greater control over therapy services through employment as opposed to outside contracting. For-profit status and chain affiliation were associated with greater control over therapy services. Following PPS, nursing homes acted to limit transaction costs by either exiting the rehabilitation market or exerting greater control over therapy services by managing rehabilitation services in-house. CONCLUSIONS: The financial incentives associated with changes in reimbursement methodology have implications that extend beyond the boundaries of the health care industry segment directly affected. Unintended quality and access consequences need to be carefully monitored by the Medicare program.

Contract Services↗
PubMed1972

Counting every quantum.

1. Human subjects were asked to rate both blanks and very dim flashes of light under conditions of complete dark adaptation at 7 degrees in the periphery. The ratings used were 0, 1, 2, 3, 4, 5, and 6.2. For one subject (B.S.) the distributions of ratings were approximately Poisson distributions. The data were consistent with each rating being the actual number of effective quantal absorptions plus the number of noise events. This subject was presumably able to count every rod signal (effective absorptions plus noise).3. For two other subjects, the data were consistent with the ratings being one less (L.F.) and two less (K.D.) than the number of effective absorptions plus noise. They were able to count every rod signal beginning with 2 and 3 respectively. A fourth subject's erratic data could not be fitted.4. The fraction of quanta incident at the cornea that resulted in a rod signal was estimated to be about 0.03 which is consistent with physical estimates of effective absorption for that retinal region.5. A simulated forced choice experiment leads to an absolute threshold about 0.40 log units below the normal yes-no absolute threshold. This and other results indicate that subjects can use the sensory information they receive even when only 1, 2 or 3 quanta are effectively absorbed, depending on the individual. Humans may be able to count every action potential or every discrete burst of action potentials in some critical neurone.

Dark Adaptation↗
PubMedDate not supplied

Models in radiotherapy: definition of decision criteria.

A method is presented by which dose distributions in radiotherapy may be judged. This method, based on statistical decision theory, combines the calculated probabilities of radiation induced complications (including failure to control disease) with the therapist's judgment of the morbidity of each complication to yield a single value representing the clinical utility of the dose distribution. Using this figure of merit, alternative dose distributions can be compared on a clinical basis. If the morbidities associated with each injury are satisfactorily estimated, and the dose response parameters are adjusted to match clinical experience, this method can be used to evaluate novel treatment techniques prior to their implementation. Automatic optimization algorithms can be used to maximize the figure of merit as a function of the physical treatment parameters so as to provide a statistically optimal treatment.

Decision Making↗
PubMed1995

X-ray imaging with amorphous selenium: detective quantum efficiency of photoconductive receptors for digital mammography.

Factors affecting the zero spatial frequency detective quantum efficiency of photoconductor-based x-ray detectors operating in the mammographic energy range are modeled for monoenergetic incident x rays. The problem is separated into two sections: the calculation of the x-ray absorption and the Swank factor. X-ray absorption in this energy range, for most practical photoconductors, is dominated by the photoelectric effect. The Swank factor has four components: fluorescence escape, stochastic variations in gain, variations of gain due to incomplete coupling of charge from the photoconductive layer to the detector electrode, and the nonlinear discharge arising from the field-dependent x-ray gain, an effect that is unique to photoconductors. Calculations are performed for selenium, which is currently the most technologically advanced photoconductor available for digital x-ray imaging. For thicknesses of selenium exceeding 50 microns and for energies between 12 and 50 keV, the detective quantum efficiency of this photoconductor is found to exceed that of a conventional Gd2O2S-based mammographic phosphor screen.

Efficiency↗