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At least 199 records · Page 11Linked to original sources
PubMed1992

Routine urine drug screening at the first prenatal visit.

OBJECTIVE: The purpose of this study is to determine whether routine urine drug screening at the first prenatal visit will identify and permit early intervention for those at risk for poor outcome. STUDY DESIGN: Comparisons of maternal and neonatal outcomes between 166 randomly chosen patients with positive and 150 randomly chosen patients with negative drug screens identified by the enzyme multiplied immunoassay test were made by unpaired t test, chi 2 test, probit analysis, and tests of independent Poisson distributions. RESULTS: Forty percent of those identified denied drug use. Antepartum (p less than 0.01) and postpartum (p less than 0.05) complications were increased among drug users. Birth weight (p less than 0.001), gestational age (p less than 0.03), and head circumference (p less than 0.05) were decreased among neonates. CONCLUSION: Because of difficulty in identifying illicit substance--using patients, consideration should be given to the implementation of routine urine drug screening at the first prenatal visit in populations with a high rate of illicit substance use.

Chi-Square Distribution↗
PubMedDate not supplied

[Patterns in the distribution of chromosome aberrations in the cells of hydrobionts under the action of ionizing radiation and environmental chemical mutagens].

In studying the pattern of chromosome aberration distribution among hydrobiont cells in experimental and natural populations, it has been found that the Poisson distribution of chromosomes among cells occurs under the effect of ionizing radiation and under the combined effect of radiation and a chemical mutagen with a higher efficiency of the former. With the comparable efficiencies of both factors and with the effect of a chemical mutagen alone distribution of chromosome aberrations among cells resembles the geometrical one to a greater extent.

Animals↗
PubMed2000

Quantitative estimation of chromosome aberration frequency in cancer patients induced by endogenous and exogenous factors.

In patients with skin melanoma and colon cancer, cell distribution by the number of chromosome aberrations cannot be described by Poisson distribution, but corresponds to a bipopulation model combining the Poisson and geometric distributions. In contrast to the control, in patients with malignant tumors, cells with geometric distribution possess the majority of chromosomal aberrations.

Chromosome Aberrations↗
PubMed1977

Precision of analysis for waterborne chrysotile asbestos by transmission electron microscopy.

Detailed examinations of water samples were carried out to determine the precision of analysis for chrysotile asbestos by transmission electron microscopy (TEM). Since the frequency distribution of counts fits a Poisson distribution, several statistical inferences were made, including (1) an estimate of precision, and (2) a model for determining the probability of observing chrysotile as a function of its concentration in water and magnitude of area scanned by TEM.

Asbestos↗
PubMed1986

The biological activity of hydrogen peroxide. I. Induction of chromosome-type aberrations susceptible to inhibition by scavengers of hydroxyl radicals in human embryonic fibroblasts.

The cytogenetic effect of hydrogen peroxide (H2O2) was investigated in human embryonic fibroblasts. Chromosome-type aberrations were found together with chromatid-type aberrations in metaphase cells harvested 24 h after a single 10-min treatment with 10(-5)-10(-3) M H2O2 in 0.9% NaCl solution. The chromosome-type aberrations were observed to be predominantly dicentrics and deletions. Both types of aberration showed a dose-response relationship to the dose of H2O2 over the range of 10(-5)-1.5 X 10(-4) M H2O2. The intercellular distribution of dicentrics showed a Poisson distribution. Centric and acentric rings and abnormal monocentrics were a minor fraction of the chromosome-type aberrations. The chromatid-type aberrations observed, such as breaks, exchanges and gaps, showed no dose-response relationship. The frequency of isochromatid breaks was higher than that of chromatid breaks and approximately 70% of the isochromatid breaks were found in the centromeric or pericentromeric region. The intercellular distribution of chromatid exchanges showed an over-dispersed distribution. The generation of aberrations by H2O2 was effectively suppressed by catalase and several scavengers of hydroxyl radicals (.OH) such as ethanol, dimethyl sulfoxide (DMSO) and mannitol. This result suggest that .OH plays an essential role in the generation of the chromosome aberrations by H2O2.

Antioxidants↗
PubMed1999

Imaging of carrageenan macrocycles and amylose using noncontact atomic force microscopy.

Samples of kappa-carrageenan, iota-carrageenan, and synthetic amylose have been examined by atomic force microscopy (AFM). All samples were spray deposited from aqueous solutions onto freshly cleaved mica, air dried, and imaged in air using noncontact atomic force microscopy (NCAFM). Images of single stranded amylose and carrageenan are presented. At relatively low polymer concentrations in the presence of NaCl iota-carrageenan formed circles that appear to be predominantly head-to-tail associated unimeric duplex (double stranded) structures. At higher iota-carrageenan concentrations the polymer forms circles and aggregates that appear to involve dimeric duplex structure. Direct comparison of synthetic amylose molecular weights determined from NCAFM images with results from solution measurements showed that NCAFM provides an excellent way to measure amylose molecular weight and molecular weight distribution. It is shown that synthetic amylose is single stranded in aqueous solution and that the chain length distribution is broader than the Poisson distribution anticipated from polymerization theory.

Amylose↗
PubMed2001

Photon statistics of random lasers with resonant feedback.

We have measured the photon statistics of random lasers with resonant feedback. With an increase of the pump intensity, the photon number distribution in a single mode changes continuously from Bose-Einstein distribution at the threshold to Poisson distribution well above the threshold. The second-order correlation coefficient drops gradually from 2 to 1. By comparing the photon statistics of a random laser with resonant feedback and that of a random laser with nonresonant feedback, we illustrate very different lasing mechanisms for the two types of random lasers.

Journal Article↗
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↗
PubMed1981

Single photon signals in fly photoreceptors and first order interneurones at behavioral threshold.

1. The contrast sensitivity of the optomotor response of the fly Musca domestica was measured using a moving sinusoidal grating as the stimulus. In parallel experiments intracellular recordings were made from photoreceptors and first order visual interneurones to to determine their responses to the same threshold stimuli. Measurements of the spatial modulation transfer function for photoreceptors confirm that the optics of the eye were intact during recordings. 2. At the lowest intensity at which one can obtain an optomotor response, the photoreceptor signal is a train of discrete depolarizations, or bumps. With constant intensity stimuli, the temporal distribution of bumps followed the Poisson distribution with a mean rate of proportional to luminance. The mean bump rate at the threshold intensity for a behavioural response is 1.7 +/- 0.7 s-1 (mean +/- S.D., n = 25). 3. Calibrations and the statistical properties of the bump train indicate that a bump represents one effective photon, implying that the bump : photon ratios are quantum capture efficiencies. 4. At low intensities the first order interneurones (the large monopolar cells or LMCs) show hyperpolarizing bumps each triggered by a receptor bump. Using a point source stimulus, centred in the field of view, the LMC bump rate is six times that in a single receptor viewing the same stimulus, as expected from the known projection of six receptor axons to each LMC. When using an extended stimulus (the grating), the bump rate is 18-20 times that in receptors. Comparison with earlier work suggests that this increased lateral summation of receptor inputs to LMCs only occurs at very low intensities. 5. In both receptor and LMCs the amplitudes and wave forms of bumps depend upon the position of a point source stimulus within the field of view. With the light in the periphery of the field the bumps are smaller and slower than when the light is in the centre. This difference in response suggests that spatial stimulation is brought about by lateral interactions, possibly between receptors. 6. At higher mean intensities the signal-to-noise ratios in receptors responding to the appropriate threshold stimuli increase with intensity. This is suggestive of a decrease in the extent of spatial and/or temporal summation in the optomotor pathway.

Action Potentials↗
PubMed2001

The genetic structure of recombinant inbred mice: high-resolution consensus maps for complex trait analysis.

BACKGROUND: Recombinant inbred (RI) strains of mice are an important resource used to map and analyze complex traits. They have proved particularly effective in multidisciplinary genetic studies. Widespread use of RI strains has been hampered by their modest numbers and by the difficulty of combining results derived from different RI sets. RESULTS: We have increased the density of typed microsatellite markers two- to five-fold in each of several major RI sets that share C57BL/6 as a parental strain (AXB, BXA, BXD, BXH and CXB). A common set of 490 markers was genotyped in just over 100 RI strains. Genotypes of around 1,100 additional microsatellites in one or more RI sets were generated, collected and checked for errors. Consensus RI maps that integrate genotypes of approximately 1,600 microsatellite loci were assembled. The genomes of individual strains typically incorporate 45-55 recombination breakpoints. The collected RI set - termed the BXN set - contains approximately 5,000 breakpoints. The distribution of recombinations approximates a Poisson distribution and distances between breakpoints average about 0.5 centimorgans (cM). Locations of most breakpoints have been defined with a precision of < 2 cM. Genotypes deviate from Hardy-Weinberg equilibrium in only a small number of intervals. CONCLUSIONS: Consensus maps derived from RI strains conform almost exactly to theoretical expectation and are close to the length predicted by the Haldane-Waddington equation (x3.6 for a 2-3 cM interval between markers). Non-syntenic associations between different chromosomes introduce predictable distortions in quantitative trait locus (QTL) datasets that can be partly corrected using two-locus correlation matrices.

Alleles↗
PubMed2000

Sister chromatid exchange in chromosomes of sheep (Ovis aries).

Blood lymphocyte cultures from 32 Comisana and Laticauda sheep breeds (15 males and 17 females) raised in Southern Italy were studied using sister chromatid exchange (SCE) test. Of the 932 cells studied, the SCE-mean value was 7.20 +/- 2.5 per cell for both breeds. Indeed, the SCE mean values were 7.12 +/- 2.45 and 7.28 +/- 2.55 in Comisana and Laticauda breeds, respectively, and the differences were not significant. No statistical differences were noticed between male and female cells (7.25 +/- 2.39 and 7.16 +/- 2.60, respectively). The SCE frequency distribution did not follow a Poisson distribution. The number of SCE were significantly higher than expected in chromosomes 1, 2 and 3 (p < 0.001) and significantly lower than expected in the X and remaining chromosomes (p < 0.001) on the basis of relative chromosome lengths.

Animals↗
PubMed1977

Microdosimetry and chromosome aberrations: effects of 230 keV neutrons on Vicia faba chromosomes.

Physical energy deposition events have been related to sub-nuclear cytological events (chromosomal changes) in metaphases sequentially accumulated from the latter part of the cell cycle of Vicia faba. 230 keV neutrons produce about 0.4 recoil protons per late interphase nucleus per rad with the majority of protons traveling 1 to 2 microns from their origin, depositing energy at around 90 keV per micron. The frequency of induced abberrations is basically linear with dose, though varying through consecutive cell sampling periods because of differential induced mitotic delay. Distributions of chromosomal aberrations and total cytological events are overdispersed in relation to the Poisson distribution indicating that some proton recoils produce multiple events. When gaps and aberrations within chromosomes and multiple aberrations between chromosomes, are considered as discrete events, distributions follow Poisson expectations. About 40% of proton recoils result in observable cytological change. The highly energetic proton recoils (approximately 90 keV per micron) which can induce multiple events are the ones most likely to produce effects which result in cell death. The sphere of influence of the proton recoils is probably adequately estimated from their range (approximately 1 to 2 micron) since it seems compatible with the spatial proximity of the initial components of the resultant chromosome aberrations.

Chromosome Aberrations↗
PubMedDate not supplied

Seizure frequency in intractable partial epilepsy: a statistical analysis.

We examined the seizure records of 13 patients (nine men and four women, ages 27-50 years) with intractable partial epilepsy, maintained with steady anti-epileptic drug dosages. Patients recorded daily seizure frequency on calendars. Periods of outpatient observation ranged from 99 to 1,710 days and the number of observed seizures ranged from 18 to over 400, with daily seizure rates of 0.1-4.3 per day. We used the quasi-likelihood regression model to examine the following four departures of the daily seizure counts from a Poisson (random) model: (1) linear increasing or decreasing time trends in expected seizure rates; (2) clustering, where the expected seizure rate on a given day depends on the number of seizures observed on the immediate prior days; (3) monthly cyclicity; and (4) increased variability (overdispersion). Linear time trends were seen in six patients (four increasing and two decreasing), clustering was seen in 10 patients, and a near-monthly cycle appeared in four patients (two of nine men and two of four women). A significant amount of extra variation (overdispersion) relative to a Poisson distribution was observed in all but one of the 13 patients. Departures from a Poisson (random) model appear more common in this population of patients with medically intractable epilepsy than is commonly recognized, and have clinical importance as well as implications for the design of clinical studies.

Adult↗
PubMed1998

Count-rate statistics of the gamma camera.

The temporal distribution of decay events recorded by a gamma camera in 'list mode' differs from the Poisson distribution because of dead-time effects. We propose a new model for the dead-time behaviour of a gamma camera. The most important feature of our model is that the loss of events occurs in pairs or higher multiples due to the so-called 'pile-up' effect. We analyse the consequences of pile-up for the temporal distribution of events recorded by a gamma camera. The probability distribution for the time intervals between events recorded by the camera is calculated from first principles. We construct estimators for the parameter of the new distribution. We distinguish between the estimation of the total count rate and the estimation of a certain subset of the total count rate. Computer simulation confirms that our estimators are less influenced by dead-time effects than the standard estimator.

Computer Simulation↗
PubMedDate not supplied

[Radiation damages in human lymphocytes studied by micronucleus and chromosomal analysis].

It was shown that the dependence of the micronucleus number and chromosome aberration on irradiation dose is linear quadratic, the values of linear coefficient being different. The distribution of ameliorators and children from the areas with higher irradiation level by micronucleus test conforms to Poisson distribution, while the distribution by chromosomal analysis approaches to binomial distribution.

Adult↗
PubMed1994

Sample size calculations for single group post-marketing cohort studies.

In pharmacoepidemiology, single group cohort is the most frequently proposed design to determine if the incidence rate of an adverse drug reaction among the exposed differs from a reference value. In many situations, the number of events expected in the cohort is too small to conduct sample size calculations based on the normal distribution. This paper proposes, for a single group cohort study, calculations and tables derived from the Poisson distribution. The results are based on a one-sided test with a 0.05 significance level and a power of 0.9 and 0.8. Two parameters have to be specified a priori: the expected incidence of the event under the null hypothesis and the minimum risk ratio to be detected. The required sample size and the critical number of events to reject the null hypothesis are directly derived from the tables. Results show that the normal approximation may lead to an underestimation of the required sample size.

Cohort Studies↗
PubMed2001

Population dynamics: Poisson approximation and its relation to the Langevin process.

We discuss how to simulate a stochastic evolution process in terms of difference equations with Poisson distributions of independent events when the problem is naturally described by discrete variables. For large populations the Poisson approximation becomes a discrete integration of the Langevin approximation [T. G. Kurtz, J. Appl. Prob. 7, 49 (1970); 8, 344 (1971)]. We analyze when the latter gives a reasonable representation of the original evolution for finite size systems. A simple example of an epidemic process is used to organize the discussion and to perform statistical tests that underline the goodness of the proposed method.

Poisson Distribution↗
PubMed1996

The Ames test: the two-fold rule revisited.

Mutagenicity in the Ames assay is evaluated by comparing the number of revertants observed in treated cultures to those in untreated cultures. Often, some form of the '2-fold rule' is employed, whereby a compound is judged mutagenic if a 2-fold or greater increase is seen in a treated culture. In order to understand the underpinnings of this approach, we study some of its statistical properties. We assume that the number of revertants on any plate from a given two-group experiment follows a Poisson distribution and we address the following questions: (1) what is the false-positive error probability of observing at least a doubling of the number of colonies from the control to the treatment group?; (2) if a given mean number of colonies is postulated for a control group, what number of colonies above the observed control mean provides a false-positive rate of 5%? We also present results for question 1 in the case where the number of revertants follows a negative binomial distribution.

False Positive Reactions↗