Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Poisson Distribution”

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 451 records · Page 25Linked to original sources
PubMed1999

The combined effect of boronophenylalanine and borocaptate in boron neutron capture therapy for SCCVII tumors in mice.

PURPOSE: To increase the effect of boron neutron capture therapy (BNCT) on tumors in vivo, the combined effects of para-boronophenylalanine (BPA) and borocaptate sodium (BSH) were investigated. METHODS AND MATERIALS: 10B-enriched BPA and BSH were administered to C3H/He mice bearing SCCVII tumors by intragastric and intravenous injections, respectively. The colony formation and tumor control assays were employed for investigating antitumor effects of BNCT. The extent of homogeneity of tumor cell killing effect was examined by the distribution of frequencies of binuclear cells (BNC) producing a certain number of micronuclei (0,1,2,--,> or =5) to total number of BNC and by the comparison between surviving cell fraction (SF) in colony formation assay and the normal nuclear division fraction (NNDF) at first mitosis following BNCT. RESULTS: The relationships between SF and radiation dose in Gy (D) at around 10 ppm of 10B in tumors were as follow: -InSF = -0.101 + 0.648 Gy(-1) x D, 0.0606+0.435 Gy(-1) x D, and -0.0155 + 0.342 Gy(-1) x D for BPA, BPA + BSH, and BSH, respectively. In tumor control assay, BPA was also more effective than BSH, but the difference of effectiveness significantly decreased: 1.9 times more effective in colony assay vs. 1.2 times in tumor control assay. The most effective treatment to achieve tumor cure was BNCT using BPA + BSH, and it was 1.9 times more effective than BSH-BNCT. In BSH-BNCT, NNDF decreased exponentially with radiation dose and was equal to SF. However, NNDF following BPA-BNCT showed a biphasic decrease with radiation dose, and SF was much lower than NNDF. In the combination of BPA and BSH, the discrepancy between NNDF and SF decreased in comparison with BPA-BNCT. The distribution of frequency of BNC with a certain number of micronuclei to total BNC was very close to Poisson distribution in BSH-BNCT tumors; however, it deviated from the Poisson in BPA-BNCT tumors. In combination with BPA and BSH, the distribution showed an intermediate pattern. These findings indicate that BSH distributes homogeneously with a heterogeneous distribution of BPA in tumors, and the heterogeneous effect of BPA-BNCT was improved by the combination of two boron compounds. CONCLUSION: The heterogeneous cell killing effect of BPA-BNCT was improved by the combination of BSH, and increased tumor control rates. Therefore, this combination may improve clinical outcome of BNCT although the effects on normal tissues have to be examined before clinical application.

Animals↗
PubMed1988

Comparison of frequency distributions in flow cytometry.

A number of methods have previously been considered for the statistical comparison of flow cytometric frequency distributions. For two distributions, the foremost of these is the Kolmogorov-Smirnov (K-S) test, which has been criticized as "too sensitive." We discuss some alternative methods based on the Poisson distribution. The assumption of Poisson variation within channels allows the use of channel-by-channel confidence intervals and chi-square tests. These are simple and more appropriate for discrete data than the K-S test. Graphical displays of these and other techniques are presented. We also attempt to set the problem in an appropriate context. We argue that any statistical procedure must rest on a reasonable understanding of the nature of the variability in the system. This understanding takes the form of an appropriate probability model, which may be approximate but must provide a reasonably accurate description of the data. Incomplete understanding of the data can lead to inappropriate analysis. We discuss the assumptions that underlie our techniques and consider extensions to more complex situations.

Flow Cytometry↗
PubMed1994

A method for the calculation of electron energy-straggling spectra.

To calculate electron beam dose distributions accurately, numerical methods of electron transport calculations must account for the statistical variation (or "straggling") in electron energy loss. This paper shows that the various energy straggling theories that are applicable to short path lengths all derive from a single statistical model, known as the compound Poisson process. This model in turn relies on three assumptions: (1) the number of energy-loss events in a given path length is Poisson distributed; (2) events are mutually independent; and (3) each event has the same probability distribution for energy loss (i.e., the same energy-loss cross section). Applying the principles of the compound Poisson process and using fast Fourier transforms, a new method for calculating energy-loss spectra is developed. The spectra calculated using this method for 10, 20, and 30 MeV electrons incident on graphite and aluminum absorbers agreed with Monte Carlo simulations (EGS4) within 1% in the spectral peak. Also, stopping powers derived from the calculated spectra agreed within 1.2%, with stopping powers tabulated by the International Commission on Radiation Units and Measurements. Several numerical transport methods "propagate" the electron distribution (in position, direction, and energy) over small discrete increments of path length. Thus the propagation of our calculated spectra over multiple path length increments is investigated. For a low atomic number absorber (graphite in this case), calculated spectra agreed with EGS4 Monte Carlo simulations over the full electron range, provided the path length increments were sufficiently small (less than 0.5 g/cm2). It is concluded from these results that numerical methods of electron transport should restrict the size of path length increments to less than 0.5 g/cm2 if energy straggling is to be modeled accurately.

Electron Transport↗
PubMed1988

Mitosis counting in seminoma: an exercise of questionable significance.

Two pathologists reviewed and classified 45 cases of testicular seminoma, evaluating each case for multiple histologic variables, including mitotic rate. In addition to recording the mitotic count for each of thirty 0.1963-mm2 high-power fields, the investigators recorded the distribution of mitotic counts in many non-spermatocytic seminomas. Statistically significant differences for mitotic rate in the nonspermatocytic tumors were noted between the observers; one observer found a mean mitotic rate of 1.815/high-power field for 43 such tumors, whereas the other noted a mean mitotic rate of 1.388/high-power field (p = 0.001). These differences led to disagreement on the classification of 3 tumors. Of the 4 cases considered to be high-mitotic-rate seminomas by one or both observers, all patients had presented with stage I disease. Three of the patients were followed up for 23, 55, and 56 months, and all were free of disease; the fourth was lost to follow-up. The patient with the highest mitotic rate was free of disease at 55 months of follow-up. On the basis of our findings we question the value of the designation high-mitotic-rate seminoma. Analysis of the distribution of mitotic counts within the tumors revealed them to be Poisson distributed. With these data and other empirically derived data, it was possible to estimate the probability of misclassification of seminoma based on mitotic rate, the diagnostic mitotic rate threshold, and the number of fields counted for mitoses. Similar analysis might be valuable for other tumors, particularly those of smooth muscle origin, in which mitotic rate is of diagnostic or prognostic value.

Adult↗
PubMed2003

Oestrus ovis larval myiasis among goats in northern Jordan.

From December 1998 to December 1999, heads of 520 local goats slaughtered at the Irbid, Ramtha and Howarra Abattoirs (northern Jordan) were examined for the three larval instars (L(1)-L(3)) of Oestrus ovis. Of 520 heads, 126 (24%) were infested with O. ovis larvae. All three larval instars were observed in both sexes; all age groups were infested in each month of the year. The mean age of the goats sampled was 1.5 years. The numbers of parasites infesting hosts showed a significant (P<0.05) correlation with sheep age (r(sp)=0.31-0.42) for all three larval instars. The numbers of larvae in each host followed an overdispersed distribution, which fit a negative-binomial model (but not a Poisson distribution). There were more parasites recorded in the presence of purulent discharge or laryngitis, fewer in the presence of catarrhal discharge and no association with pharyngitis sinusitis, or rhinitis.

Abattoirs↗
PubMed2006

Time-series analysis of the risk factors for haemorrhagic fever with renal syndrome: comparison of statistical models.

Three conventional regression models were compared using the time-series data of the occurrence of haemorrhagic fever with renal syndrome (HFRS) and several key climatic and occupational variables collected in low-lying land, Anhui Province, China. Model I was a linear time series with normally distributed residuals; model II was a generalized linear model with Poisson-distributed residuals and a log link; and model III was a generalized additive model with the same distributional features as model II. Model I was fitted using least squares whereas models II and III were fitted using maximum likelihood. The results show that the correlations between the HFRS incidence and the independent variables measured (i.e. difference in water level, autumn crop production and density of Apodemus agrarius) ranged from -0.40 to 0.89. The HFRS incidence was positively associated with density of A. agrarius and crop production, but was inversely associated with difference in water level. The residual analyses and the examination of the accuracy of the models indicate that model III may be the most suitable in the assessment of the relationship between the incidence of HFRS and the independent variables.

Animals↗
PubMed2004

Energy distributions in multiple photon absorption experiments.

Photofragmentation experiments on molecules and clusters often involve multiple photon absorption. The distributions of the absorbed number of photons are frequently approximated by Poisson distributions. For realistic laser beam profiles, this approximation fails seriously due to the spatial variation of the mean number of absorbed photons across the laser beam. We calculate the distribution of absorbed energy for various laser and molecular-beam parameters. For a Gaussian laser beam, the spatially averaged distributions have a power-law behavior for low energy with a cutoff at an energy which is proportional to fluence. The power varies between -1 for an almost parallel laser beam and -5/2 for a divergent beam (on the scale of the molecular beam). We show that the experimental abundance spectra of fullerenes and small carbon clusters can be used to reconstruct the distribution of internal energy in the excited C60 molecule prior to fragmentation and find good agreement with the calculated curves.

Journal Article↗
PubMed1989

Two kinds of "recombination nodules" in Neurospora crassa.

Two morphological types of recombination nodules, termed early and late, are recognized in Neurospora crassa. Eighty nuclei at different substages were used to determine numbers of nodules per nucleus, distribution of nodules along the nucleolus-organizing chromosome, and distribution of nodules among the two largest chromosomes. Early nodules appear at the synaptonemal complex at early zygotene and increase in number during zygotene until a dramatic reduction occurs at zygotene-pachytene transition. Thereafter early nodules are steadily eliminated until they disappear by diplotene. Late nodules are also present during zygotene. Their number doubles at the zygotene-pachytene transition and stays at this level until diplotene. The total number of nodules is rather constant through zygotene and pachytene. Distribution of bivalents with 0, 1, 2, etc. nodules follows a Poisson distribution at zygotene, but not at pachytene, where variance is less than the mean, indicating positive interference. Nodules are distributed nonrandomly along the nucleolus-organizer bivalent. The pattern differs slightly in nuclei of different origin. Nuclei with unusual synaptonemal complexes sustain normal levels of recombination by having the same amount of nodules as normal nuclei. In abnormal nuclei nodules are preferentially associated with normal segments. It is proposed that early nodules do not participate in any form of recombination but have a role in finding an appropriate site for a crossing-over event. Morphological change to the late type indicates that the site has been reached and the exchange event can be mediated by the late nodule.

Chromosomes↗
PubMed1987

Sampling and distribution of Anopheles quadrimaculatus immatures in rice fields.

Dipper samples of Anopheles quadrimaculatus immatures from stocked enclosures in Arkansas rice fields were used to develop regression equations relating dipper sample counts to absolute density. Confidence limits were developed for mean number of immatures collected at each density and stadia, including combined stadia. These data can be used to estimate absolute density from mean dipper count. Distribution of rice field immatures approximated but did not fit the Poisson distribution. Sample size was calculated for 10, 25 and 50% of the true mean, at various levels of Type I and II error. A sample size of N = 6,424 was necessary to detect differences within 10% of the true mean, with 5 and 10% probability of Type I and II error, respectively.

Agriculture↗
PubMed1982

Identification and properties of the glucose transporter of human erythrocytes.

Several lines of studies were undertaken to clarify the identity of the glucose transporter of human erythrocytes. Peptide maps of zone 4.5 which is the main component of the purified transporter fraction, were different from those of band 3. Cytochalasin B bound to the purified transporter fraction but not to band 3. Antibody raised against the purified transporter fraction cross-reacted with zone 4.5 and moderately with band 7, but not with other erythrocyte membrane proteins. These results indicate that zone 4.5 is the transporter (or a part of the transporter) and is not a fragment of band 3. With ferritin antibody electron microscopy and freeze-fracture electron microscopy, the glucose transporter were found to evenly distributed in reconstituted liposomes. Further morphological analysis coupled with transport assays showed the distribution of the transporters was random and was satisfactorily fitted to Poisson distribution, indicating reversible association of the transporters does not occur in liposomes and is not necessary for transport activity. This communication summarises our recent studies on identification and properties of the glucose transporter of human erythrocytes. A full account of the studies is published elsewhere (22, 23).

Blood Glucose↗
PubMed1999

Biological dosimetry of chernobyl cleanup workers: inclusion of data on age and smoking provides improved radiation dose estimates.

We report the results of a study of chromosome translocations in 126 Russian subjects who participated in the cleanup activities at Chernobyl and another 53 subjects, from other places in Russia, who were not exposed at Chernobyl. In agreement with our earlier study, we find increased translocation frequencies among the exposed compared to Russian controls. We describe statistical methods for estimating the dose of ionizing radiation determined by scoring chromosome translocations found in circulating lymphocytes sampled several years after exposure. Two statistical models were fitted to the data. One model assumed that translocation frequencies followed an overdispersed Poisson distribution. The second model assumed that translocation frequencies followed a negative binomial distribution. In addition, the effects of radiation exposure were modeled as additive or as multiplicative to the effects of age and smoking history. We found that the negative binomial model fit the data better than the overdispersed Poisson model. We could not distinguish between the additive and the multiplicative model with our data. Individual dose estimates ranged from 0 (for 43 subjects) to 0.56 Gy (mean 0.14 Gy) under the multiplicative model and from 0 to 0.95 Gy (mean 0.15 Gy) under the additive model. Dose estimates were similar under the two models when the number of translocations was less than 4 per 100 cells. The additive model tended to estimate larger doses when the number of translocations was greater than 4 per 100 cells. We also describe a method for estimating upper 95% tolerance bounds for numbers of translocations in unexposed individuals. We found that inclusion of data on age and smoking history was important for dose estimation. Ignoring these factors could result in gross overestimation of exposures, particularly in older subjects who smoke.

Adult↗
PubMed1978

The application of a Poisson model to the annual distribution of daily mortality at six Montreal hospitals.

The daily distributions of annual mortality for varying numbers of years between 1965 and 1975 were investigated in three geriatric hospitals and three general hospitals in the Montreal area. Nearly all the observed mortality distributions were found to mimic the classical Poisson distribution, with little departure. In two of the larger hospitals, the matching of the daily mortality distributions with their Poisson models met stringent statistical criteria. In one of them it was even possible to predict the expected mortality frequencies merely from a knowledge of the annual totals. The remaining four hospitals, which included the three geriatric institutions, also exhibited mortalities regarded as highly suggestive of Poisson distributions, although in one of the geriatric hospitals the mortality distribution tended to be somewhat erratic in this respect.

Aged↗
PubMed2001

Some case studies of skewed (and other ab-normal) data distributions arising in low-level environmental research.

Three general classes of skewed data distributions have been encountered in research on background radiation, chemical and radiochemical blanks, and low levels of 85Kr and 14C in the atmosphere and the cryosphere. The first class of skewed data can be considered to be theoretically, or fundamentally skewed. It is typified by the exponential distribution of inter-arrival times for nuclear counting events for a Poisson process. As part of a study of the nature of low-level (anti-coincidence) Geiger-Muller counter background radiation, tests were performed on the Poisson distribution of counts, the uniform distribution of arrival times, and the exponential distribution of inter-arrival times. The real laboratory system, of course, failed the (inter-arrival time) test--for very interesting reasons, linked to the physics of the measurement process. The second, computationally skewed, class relates to skewness induced by non-linear transformations. It is illustrated by non-linear concentration estimates from inverse calibration, and bivariate blank corrections for low-level 14C-12C aerosol data that led to highly asymmetric uncertainty intervals for the biomass carbon contribution to urban "soot". The third, environmentally, skewed, data class relates to a universal problem for the detection of excursions above blank or baseline levels: namely, the widespread occurrence of ab-normal distributions of environmental and laboratory blanks. This is illustrated by the search for fundamental factors that lurk behind skewed frequency distributions of sulfur laboratory blanks and 85Kr environmental baselines, and the application of robust statistical procedures for reliable detection decisions in the face of skewed isotopic carbon procedural blanks with few degrees of freedom.

Journal Article↗
PubMed1999

Increased risk of bullous pemphigoid in male and very old patients: A population-based study on incidence.

No data are available on gender- and age-specific incidences for bullous pemphigoid (BP). The aim of this study was to calculate incidences for different gender- and age-strata and to assess risk differences between these strata in BP. A retrospective population-based cohort was recruited from all patients diagnosed with BP in 2 well-defined regions of Germany. The average population number was 1.7 million, and the observation period was 9 years (1989-1997). Incidences were calculated as newly diagnosed cases for a population of 1 million per year. Confidence intervals (CI) were estimated based on a Poisson distribution. For evaluation of risk between different age and gender strata a Poisson regression analysis was used. The highest incidence was calculated for individuals older than 90 years, with 398 (CI: 360, 439) new cases of BP per 1 million residents for men, and 87 (CI: 70, 108) new cases per 1 million residents for women. Risk (95% CI) was 1.9 (1.3, 2.9) fold higher in men than in women. In addition, the risk for BP was increased for patients above the age of 60 years. The highest risk was found for patients older than 90 years. For this age group, the risk was 297 (CI: 107, 826) fold higher than in patients 60 years of age and younger. Men are affected by BP almost twice as often as women. The risk for BP increases rapidly beyond the age of 60 years. Because the structure of the European population is shifting towards the aged, more people are expected to suffer from BP in the coming decades.

Age Factors↗
PubMed2006

Geometric diagnostics of complex patterns: spiral defect chaos.

Motivated by the observation of spiral patterns in a wide range of physical, chemical, and biological systems, we present an automated approach that aims at characterizing quantitatively spiral-like elements in complex stripe-like patterns. The approach provides the location of the spiral tip and the size of the spiral arms in terms of their arc length and their winding number. In addition, it yields the number of pattern components (Betti number of order 1), as well as their size and certain aspects of their shape. We apply the method to spiral defect chaos in thermally driven Rayleigh-Benard convection and find that the arc length of spirals decreases monotonically with decreasing Prandtl number of the fluid and increasing heating. By contrast, the winding number of the spirals is nonmonotonic in the heating. The distribution function for the number of spirals is significantly narrower than a Poisson distribution. The distribution function for the winding number shows approximately an exponential decay. It depends only weakly on the heating, but strongly on the Prandtl number. Large spirals arise only for larger Prandtl numbers (Pr approximately > 1). In this regime the joint distribution for the spiral length and the winding number exhibits a three-peak structure, indicating the dominance of Archimedean spirals of opposite sign and relatively straight sections. For small Prandtl numbers the distribution function reveals a large number of small compact pattern components.

Journal Article↗
PubMed1983

Induction of chromosome aberrations by 4.9 MeV protons in human lymphocytes.

The dose-response relationship and distribution of chromosome aberrations between cells was studied in G0 human peripheral blood lymphocytes following in vitro exposure to 4.9 MeV protons. The dose-response relationship of dicentric yield showed a significant dose-quadratic component and was best expressed by 2.76 X 10(-1) D + 1.36 X 10(-1) D2 (D in Gy). The distribution of dicentrics between cells was over-dispersed compared with a Poisson distribution. Analysis of the data indicated that the over-dispersion was caused by a spatial limitation in the interaction between tracks. The interaction distance was estimated to be around 0.2 microns.

Adult↗
PubMed1961

Enumeration of cell-infecting particles of Newcastle disease virus by the fluorescent antibody technique.

A procedure has been developed for the determination of the concentration of infective Newcastle disease virus (NDV) based on the enumeration of singly infected and distributed HeLa cells which are visualized by staining with fluorescent antibody. Infective virus assayed by the fluorescent cell-counting procedure is expressed in terms of cell-infecting units (CIU). Adsorption of NDV to HeLa cell monolayers reached a plateau 1 to 1.5 hours after inoculation of coverslip cultures, and 12 per cent of the infective particles inoculated failed to adsorb. The half-life of NDV in protein-free Eagle's medium at 37 degrees C. was 2.1 hours. There was a linear relationship between virus concentration and the number of infected cells. The coefficient of variation of the mean of replicate determinations of infective NDV was 8.2 per cent. The distribution of single infected HeLa cells in the monolayer corresponded to the Poisson distribution. With NDV the cell-infecting unit (CIU) determined in HeLa cells is equivalent to the plaque-forming unit in chick embryo cells and the egg infective dose. In experiments on the mechanism of dissemination of NDV in monolayer cultures of HeLa cells, NDV was found to spread from cell to cell through the extracellular milieu.

Animals↗
PubMed1979

The labelling of vesicles in frog endothelial cells with ferritin.

1. The labelling of endothelial cell vesicles with ferritin has been investigated by electron microscopy. Single capillaries in the frog mesentery have been perfused with solutions of known concentrations of ferritin for known periods before fixing the tissue in situ by superfusion with osmium tetroxide. 2. At 17 degrees C, the percentage of lumenal vesicles labelled with ferritin increased as the period of perfusion was increased up to 16 sec prior to fixation. When perfusions were longer than 16 sec, the percentage of vesicles labelled with ferritin remained fairly constant at 70%. 3. At 3 degrees C, no more than 25% of the lumenal vesicles were labelled during the first 30 sec. 4. After correcting the data for losses of ferritin due to sectioning, the distribution of ferritin molecules in the lumenal vesicles was consistent with a Poisson distribution. 5. After perfusions of 16 sec or longer, the number of ferritin molecules per labelled vesicle was roughly three to four times less than would be predicted from the lumenal concentration. 6. At all times there was a gradient of vesicles labelled with ferritin across the endothelial cells, i.e. the percentage of lumenal vesicles labelled was greater than that for cytoplasmic vesicles which in turn was greater than that for vesicles at the ablumenal surface. 7. Whereas the labelling of lumenal vesicles from zero time up to 16-20 sec, the main increase in labelling of cytoplasmic vesicles occurred between 10 and 20 sec. 8. It is concluded that there is a major diffusion barrier to ferritin molecules either close to the endothelial cell surface or across the necks of the lumenal vesicles. It also appears that ferritin molecules do not have access to vesicles during the latter part of their residence at the lumenal surface.

Animals↗