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 649 records · Page 36Linked to original sources
PubMed1978

A comparison of methods for detecting bacteriophage contamination of tissue culture sera.

Detection of bacteriophage contamination of tissue culture sera by direct plating has been compared with detection methods based on batch enrichment and on the Poisson distribution (PD plating). Batch enrichment is extremely sensitive for detecting the presence of phage contamination. PD plating combines sensitivity with isolation of each contaminating phage in pure culture. Both batch enrichment and PD plating are more sensitive than direct plating. Neither method requires highly trained personnel or specialized equipment.

Bacteriophages↗
PubMed1999

Tumour cell detection in G-CSF mobilised stem cell harvests of patients with breast cancer.

Peripheral blood stem cells were mobilised with G-CSF from steady-state haemopoiesis after previous anthracyclin-containing standard dose chemotherapy in patients with high-risk breast cancer. 48 samples were obtained from patients with stage II-III breast cancer and > or = 10 lymph nodes, 15 samples from patients with chemotherapy sensitive metastatic disease, and 13 samples from women with inflammatory breast cancer. 44 samples were first or single leukaphereses and 32 samples were second or third harvests. Aliquots were searched for contaminating tumour cells by immunocytochemistry (IC) and cytokeratin-19 reverse transcriptase polymerase chain reaction rtPCR). The median count of MNCs examined by IC was 2 x 10(6); cDNA prepared from 2 x 10(7) cells was subjected to PCR. Fifty-nine samples were examined by immunocytochemistry, 36 samples by rtPCR, and 19 samples by both techniques. Samples investigated by IC and rtPCR were judged as positive if there was at least one positive test. On the whole, 42/79 (55.3%) of the samples were positive with an insignificant trend to a higher positivity rate in second or subsequent leukaphereses (52.3% vs 59.3%). The median tumour cell load per 10(6) MNCs was low with 0.5 (0-7) cells in all, and a total of 2.2 (0.5-7) cells in positive specimen. Differences in the cancer cell load of first and subsequent leukaphereses and between subgroups of patients were not found. PCR and IC gave consistent results in 63.2%. This phenomenon can be explained by the greater sensitivity of the molecular method and by a Poisson distribution of coharvested tumour cells in samples. Tumour cell contamination in G-CSF mobilised stem cells from patients with breast cancer from steady state haemopoiesis after preceding anthacyclin-containing chemotherapy is frequent, but the tumour cell load is low. To allow a comparison of different studies dealing with cancer cell contamination in stem cells, standardisation of assays is necessary.

Breast Neoplasms↗
PubMed1998

Lethal mutations defining 112 complementation groups in a 4.5 Mb sequenced region of Caenorhabditis elegans chromosome III.

The central gene cluster of chromosome III was one of the first regions to be sequenced by the Caenorhabditis elegans genome project. We have performed an essential gene analysis on the left part of this cluster, in the region around dpy-17III balanced by the duplication sDp3. We isolated 151 essential gene mutations and characterized them with regard to their arrest stages. To facilitate positioning of these mutations, we generated six new deficiencies that, together with preexisting chromosomal rearrangements, subdivide the region into 14 zones. The 151 mutations were mapped into these zones. They define 112 genes, of which 110 were previously unidentified. Thirteen of the zones have been anchored to the physical sequence by polymerase chain reaction deficiency mapping. Of the 112 essential genes mapped, 105 are within these 13 zones. They span 4.2 Mb of nucleotide sequence. From the nucleotide sequence data, 920 genes are predicted. From a Poisson distribution of our mutations, we predict that 234 of the genes will be essential genes. Thus, the 105 genes constitute 45% of the estimated number of essential genes in the physically defined zones and between 2 and 5% of all essential genes in C. elegans.

Animals↗
PubMed2002

Characterisation of polymorphic microsatellite markers from Aegilops tauschii and transferability to the D-genome of bread wheat.

Microsatellites were isolated from a Aegilops tauschii (the D-genome donor of bread wheat) library enriched for various motifs. Primers generated from the flanking region of the microsatellites were used successfully to amplify the corresponding loci in the D genome of bread wheat. Additional amplification sometimes also occurred from the A and B genomes. The majority of the microsatellites contained (GA)(n) and (GT)(n) motifs. GA and GT repeats appeared to be both more abundant in this library and more polymorphic than other types of repeats. The allele number for both types of dinucleotide repeats fitted a Poisson distribution. Deviance analysis showed that GA and GT were more polymorphic than other motifs in bread wheat. Within each motif type (di-, tri- and tetra-nucleotide repeats), repeat number has no influence on polymorphism. The microsatellites were mapped using the Triticum aestivum Courtot x Chinese Spring mapping population. A total of 100 markers was developed on this intraspecific map, mainly on the D genome. For polyploid species, isolation of microsatellites from an ancestral diploid donor seems to be an efficient way of developing markers for the corresponding genome in the polyploid plant.

Journal Article↗
PubMed2005

Verification of statistical-overlap theory in micellar electrokinetic chromatography.

The limited peak capacity of neutral compounds in micellar electrokinetic chromatography (MEKC) causes peak overlap in a simple 38-compound sample that is predicted by statistical-overlap theory (SOT). The low-concentration sample was prepared in-house from several compound classes to span the entire migration-time range and was resolved partially in a pH=7 phosphate buffer containing 50 mM sodium dodecyl sulfate. Peaks, singlets, doublets, and other multiplets were identified on the basis of known migration times and were counted at 13 voltages spanning 4 - 26 kV. These numbers agreed well with predictions of a simple SOT based on the assumption of an inhomogeneous Poisson distribution of migration times. Because the dispersion theory of MEKC is simple, the standard deviations of single-component peaks were modeled theoretically. As part of a new way to implement SOT, probability distributions of the numbers of peaks, singlets, and so on, were computed by Monte Carlo simulation. These distributions contain all theoretical information on peak multiplicity predictable by SOT and were used to evaluate the agreement between experiment and theory. The peak capacity of MEKC was calculated numerically and substituted into the simplest equations in SOT, affirming that peak overlap arises from limited peak capacity.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2002

Curiously modern DNA for a "250 million-year-old" bacterium.

Studies of ancient DNA have attracted considerable attention in scientific journals and the popular press. Several of the more extreme claims for ancient DNA have been questioned on biochemical grounds (i.e., DNA surviving longer than expected) and evolutionary grounds (i.e., nucleotide substitution patterns not matching theoretical expectations for ancient DNA). A recent letter to Nature from Vreeland et al. (2000), however, tops all others with respect to age and condition of the specimen. These researchers extracted and cultured a bacterium from an inclusion body from what they claim is a 250 million-year (Myr)-old salt crystal. If substantiated, this observation could fundamentally alter views about bacterial physiology, ecology and evolution. Here we report on molecular evolutionary analyses of the 16S rDNA from this specimen. We find that 2-9-3 differs from a modern halophile, Salibacillus marismortui, by just 3 unambiguous bp in 16S rDNA, versus the approximately 59 bp that would be expected if these bacteria evolved at the same rate as other bacteria. We show, using a Poisson distribution, that unless it can be shown that S. marismortui evolves 5 to 10 times more slowly than other bacteria for which 16S rDNA substitution rates have been established, Vreeland et al.'s claim would be rejected at the 0.05 level. Also, a molecular clock test and a relative rates test fail to substantiate Vreeland et al.'s claim that strain 2-9-3 is a 250-Myr-old bacterium. The report of Vreeland et al. thus falls into a long series of suspect ancient DNA studies.

Bacteria↗
PubMed2005

Pre-medication to block [(18)F]FDG uptake in the brown adipose tissue of pediatric and adolescent patients.

BACKGROUND: Radiopharmaceutical uptake of [(18)F]2-deoxy-2-glucose (FDG) in brown adipose tissue is noted on 15-20% of positron emission tomography (PET) scans in children and adolescents. One report suggests that moderate-dose oral diazepam can partly or completely block FDG uptake in brown adipose tissue. OBJECTIVE: To determine whether [(18)F]FDG uptake in brown adipose tissue can be adequately blocked by pre-medication other than moderate-dose oral diazepam. MATERIALS AND METHODS: One hundred and eighteen [(18)F]FDG PET body imaging studies were performed in 69 pediatric patients with a variety of solid tumors. The mean age at the time of imaging was 12.9 years (range 1.2-22.6 years), and 33 studies were performed in patients younger than 10 years old. Seventy-six were performed in boys and 42 in girls. Patients were imaged using a dedicated PET camera. Pre-medication was given in 88 studies: 45 received intravenous fentanyl (0.75-1.0 mug/kg), 34 received low-dose oral diazepam (0.06 mg/kg) and 9 received moderate-dose oral diazepam (0.10 mg/kg). Thirty patients received no pre-medication, 7 of whom were known to have received opiates for pain during the 12 h before the study. Six body regions in the neck and chest were reviewed for [(18)F]FDG uptake in brown adipose tissue. Uptake of FDG in brown fat was visually graded: 0 for no FDG uptake, 1 for low-grade uptake, 2 for moderate uptake, and 3 for intense uptake. Visual grades 2 and 3 were considered to interfere potentially with image interpretation in the neck and chest. Data were analyzed by multivariate regression using a Poisson distribution. RESULTS: [(18)F]FDG uptake in brown adipose tissue was most often seen in the lateral neck region and superior and lateral to the lungs (in 36 and 39 studies, respectively). Uptake was also seen near the costovertebral junctions (15 studies), in the superior and central neck in 7 studies and in the anterior mediastinum in 2. Brown adipose tissue uptake was thought to interfere potentially with image interpretation (visual grades 2 and 3) in 19 studies-in 6 of 23 (26.1%) studies after no pre-medication and no opiates for pain, in 10 of 34 (29.4%) after low-dose oral diazepam, in 0 of 9 (0%) after moderate-dose oral diazepam, in 3 of 45 (6.7%) after intravenous fentanyl, and in 0 of 7 (0%) after opiates prescribed for pain. Intravenous fentanyl reduced the grade of brown adipose tissue compared to no drug (P=0.0039) and low-dose diazepam (P=0.0024). Low-dose diazepam had no effect when compared to no drug (P=0.984). There were inadequate data for statistical testing of moderate-dose valium and opiates prescribed for pain. Children younger than 10 years had lower uptake grades (P=0.019) than those older than 10 years. SUMMARY: The frequency of interfering [(18)F]FDG uptake in brown adipose tissue is reduced by intravenous fentanyl pre-medication, which appears to be an effective alternative to the existing standard pre-medication, moderate-dose oral diazepam.

Adipose Tissue, Brown↗
PubMed2001

Analysis of the value of imaging as part of the follow-up of splenic injury in children.

OBJECTIVE: A recent article suggested that routine follow-up imaging is still frequently used in the conservative management of splenic trauma in children. The purpose of this study was to use decision analysis to assess the value of routine imaging as part of the long-term follow-up of splenic injury in children managed nonoperatively. METHODS: A literature review (1970-1999) on the management of blunt splenic trauma in children was performed. Data, including the use of follow-up imaging and the occurrence of delayed splenic rupture and death, on those patients managed nonoperatively were collected. The data were used to construct a decision tree. A Poisson distribution was used to determine the risk of delayed splenic rupture. RESULTS: Information was extracted from 26 cohort studies. Nineteen of these studies were retrospective and six were prospective. One study had both retrospective and prospective arms. The study population consisted of 1,083 children. Of these patients, 920 (85 %) underwent routine follow-up imaging (US, CT, or scintigraphy). Follow-up imaging was either not performed or selectively performed in 163 patients (15 %). No cases of post-discharge splenic rupture or death were encountered in any of these groups. The maximum risk of delayed splenic rupture in the entire group was 0.3 % (0-3.7 cases). CONCLUSION: The risk of delayed splenic rupture following blunt injury in children is very low, and is apparently unaffected by imaging protocols. No deaths, even in cases of delayed presentation, were identified in our study. These findings do not support the use of routine follow-up imaging of children with blunt splenic trauma.

Child↗
PubMed2004

Probing molecular interaction between concanavalin A and mannose ligands by means of SFM.

Recently, the scanning force microscope (SFM) has been widely used for direct monitoring of specific interactions between biologically active molecules. Such studies have employed the SFM liquid-cell setup, which allows measurements to be made in the native environment with force resolution down to a tenth of a picoNewton. In this study, the ligand-receptor strength of monoclonal anti-human prostatic acid phosphatase and prostatic acid phosphatase, representing an antigen-antibody system with a single type of interaction, was determined. Then, the interaction force occurring between concanavalin A and the carbohydrate component of the glycoproteins arylsulfatase A and carboxypeptidase Y was measured. High mannose-type glycans were sought on the human prostate carcinoma cell surface. Application of an analysis based on the Poisson distribution of the number of bonds formed in all these measured systems allowed the strength of the molecular interaction to be calculated. The values of the force acting between two single molecules were 530+/-25, 790+/-32, and 940+/-39 pN between prostatic acid phosphatase and monoclonal anti-human prostatic acid phosphatase, between concanavalin A and arylsulfatase A, and between concanavalin A and carboxypeptidase Y, respectively. The value calculated from data collected for the force between concanavalin A and mannose-containing ligands present on the surface of human prostate carcinoma cells was smaller, 116+/-17 pN. The different values of the binding force between concanavalin A and mannose-containing ligands were attributed to the structural changes of the carbohydrate components.

Binding Sites↗
PubMed1998

Calculation of boron neutron capture cell inactivation in vitro based on particle track structure and x-ray sensitivity.

The Monte-Carlo technique was used to perform quantitative microdosimetric model calculations of cell survival after boron neutron capture irradiations in vitro. The high energy 7Li and alpha-particles resulting from the neutron capture reaction 10B (n,alpha)7Li are of short range and are highly damaging to cells. The biophysical model of the Monte-Carlo calculations is based on the track structure of these a-particles and 7Li-ions and the x-ray sensitivity of the irradiated cells. The biological effect of these particles can be determined if the lethal effect of local doses deposited in very small fractional volumes of the cell nucleus is known. This lethal effect can be deduced from experimental data of cell survival after x-ray irradiation assuming a Poisson distribution for lethal events. The input data used in a PC-based computer program are the radial dose distribution inside the track of the released particles, cell survival after x-ray irradiation, geometry of the tumor cells, subcellular 10B concentration, and thermal neutron fluence. The basic concept of this Monte-Carlo computer model is demonstrated. Validations of computer calculations are presented by comparing them with experimental data on cell survival.

Alpha Particles↗
PubMed2006

See globally, spike locally: oscillations in a retinal model encode large visual features.

We show that coherent oscillations among neighboring ganglion cells in a retinal model encode global topological properties, such as size, that cannot be deduced unambiguously from their local, time-averaged firing rates. Whereas ganglion cells may fire similar numbers of spikes in response to both small and large spots, only large spots evoke coherent high frequency oscillations, potentially allowing downstream neurons to infer global stimulus properties from their local afferents. To determine whether such information might be extracted over physiologically realistic spatial and temporal scales, we analyzed artificial spike trains whose oscillatory correlations were similar to those measured experimentally. Oscillatory power in the upper gamma band, extracted on single-trials from multi-unit spike trains, supported good to excellent size discrimination between small and large spots, with performance improving as the number of cells and/or duration of the analysis window was increased. By using Poisson distributed spikes to normalize the firing rate across stimulus conditions, we further found that coincidence detection, or synchrony, yielded substantially poorer performance on identical size discrimination tasks. To determine whether size encoding depended on contiguity independent of object shape, we examined the total oscillatory activity across the entire model retina in response to random binary images. As the ON-pixel probability crossed the percolation threshold, which marks the sudden emergence of large connected clusters, the total gamma-band activity exhibited a sharp transition, a phenomena that may be experimentally observable. Finally, a reanalysis of previously published oscillatory responses from cat ganglion cells revealed size encoding consistent with that predicted by the retinal model.

Action Potentials↗
PubMed2005

How predictable is the abundance of double gametocyte infections?

It has been proposed that erythrocytes, infected by one male and one female gametocyte, enhance malaria transmission by lowering encounter time between male and female gametes once inside the mosquito vector. This may have important implications if they occur in human Plasmodium infections. Double gametocyte infections (DGIs) have been found in Plasmodium cultures, but it is thought that they are an artefact due to the artificially high crowding of cultures. Here, we studied gametocyte density and DGI occurrence in Haemoproteus columbae infecting feral pigeons (Columba livia), to determine if crowding is the key factor producing DGIs. We demonstrate that DGIs are not a spurious phenomenon or an artefact of crowding, but occur in any gametocyte density in a proportion a bit higher than that expected by a Poisson distribution.

Animals↗
PubMed2006

Weather impacts on respiratory infections in Athens, Greece.

In this study the contribution of meteorological parameters to the total variability of respiratory infections (RI) is analysed. For this purpose, data on the daily numbers of general practitioner (GP) consultations for RI during the year 2002 were used. This dataset has been compiled by the Local Health Service in the surroundings of Athens, Greece (Acharnes city). The meteorological data obtained by the Meteorological Station of the National Observatory of Athens comprise daily values of mean, maximum, and minimum air temperature, air temperature range, relative humidity, absolute humidity, sunshine, surface atmospheric pressure, wind speed, as well as day-to-day changes of these parameters. Furthermore, the following biometeorological parameters and thermal indices were also evaluated: mean radiant temperature (T (mrt)), predicted mean vote (PMV), physiologically equivalent temperature (PET) and standard effective temperature (SET*) as well as their day-to-day changes. First, the relationship between every meteorological-biometeorological parameter and consultations for RI was examined by applying the Pearson Chi-Square Test (chi (2)) to the data of the 25 compiled contingency tables. In the second stage, the application of generalised linear models (GLM) with Poisson distribution to the data revealed how much the weather variability leads to statistically important changes in consultations for RI. The results of this study contribute to the evidence that there is an association between weather conditions and the number of GP consultations for RI. More specifically, the influence of air temperature and absolute humidity on consultations on the same day is weaker than the lag effect ( approximately 2 weeks) related to cold existence and absolute humidity, while a strong wind during the preceding 3 days drives a peak in GP consultations.

Greece↗
PubMed2005

Laser printing of single cells: statistical analysis, cell viability, and stress.

Methods to print patterns of mammalian cells to various substrates with high resolution offer unique possibilities to contribute to a wide range of fields including tissue engineering, cell separation, and functional genomics. This manuscript details experiments demonstrating that BioLP Biological Laser Printing, can be used to rapidly and accurately print patterns of single cells in a noncontact manner. Human osteosarcoma cells were deposited into a biopolymer matrix, and after 6 days of incubation, the printed cells are shown to be 100% viable. Printing low numbers of cells per spot by BioLP is shown to follow a Poisson distribution, indicating that the reproducibility for the number of cells per spot is therefore determined not by the variance in printed volume per drop but by random sampling statistics. Potential cell damage during the laser printing process is also investigated via immunocytochemical studies that demonstrate minimal expression of heat shock proteins by printed cells. Overall, we find that BioLP is able to print patterns of osteosarcoma cells with high viability, little to no heat or shear damage to the cells, and at the ultimate single cell resolution.

Cell Count↗
PubMed1985

Occurrence of malignant neoplasms in the Rochester, Minnesota, rheumatoid arthritis cohort.

The medical records of all patients with rheumatoid arthritis diagnosed in Rochester, Minnesota, from 1950 to 1975 were examined to determine how many of them had malignant neoplasms. Follow-up averaged more than 14 years with outcome diagnoses complete in 98 percent of cases. All diagnoses of malignant neoplasm in this cohort were identified through the centralized record system based at the Mayo Clinic. Approximately 40 percent of these patients with rheumatoid arthritis were at least 60 years old at diagnosis. For comparison, the expected number of malignancies has been calculated using age-specific and site-specific rates from previous Rochester studies and the number of years of observation from date of diagnosis of rheumatoid arthritis to the date of last examination. Risk ratios have been calculated by dividing the observed number by the expected number of malignancies. Exact 95 percent confidence intervals around the risk ratios were calculated assuming that the observed number of cases has a Poisson distribution and that the expected number is fixed. Those patients with rheumatoid arthritis who had a malignancy before diagnosis have been analyzed separately, because they are at a higher risk. With the exception of multiple myeloma, no association was found between rheumatoid arthritis and subsequent cancer of any site.

Arthritis, Rheumatoid↗
PubMed1987

An estimate of the number of Ca2+-dependent K+ channels in the human red cell.

An original approach has been designed to count Ca2+-dependent K+ channels in the human red cell using a preparation of inside-out vesicles. The relative frequency of vesicles having no K+ channels is estimated from the fraction of 42K+ (or 86Rb+) which is not released from loaded vesicles on maximal stimulation with Ca2+. The mean number of channels per vesicle is then calculated from this figure assuming a Poisson distribution for the K+ channels. From this value and the mean vesicular radius, computed from the volume/surface ratio, the mean number of channels per cell can be estimated. A value of 142 +/- 27 (mean +/- S.E.) was obtained, which is well above that estimated by comparison of unitary conductance and tracer equilibration rate measurements (about 10 channels/cell, Grygorczyk, R. Schwarz, W. and Passow, H. (1984) Biophys. J. 45, 693-698), but compares favourably with the channel density inferred from comparison with the number of Na+ pumps in a similar preparation of inside-out vesicles (100-200/cell, Lew, V.L., Muallem, S. and Seymour, C.A. (1982) Nature 296, 742-744). The procedure described here can be considered for general application as an alternative to other known procedures.

Calcimycin↗
PubMed1975

Fatigue and recovery of transmission at the Mauthner fiber-giant fiber synapse of the hatchetfish.

When the Mauthner fiber-giant fiber synapse of the hatchetfish is activated at gradually increasing frequencies, postsynaptic potentials (PSPs) in the giant fiber become progressively smaller, but complete failures of transmission are not observed even when PSP size is as small or smaller than miniature PSPs (mPSPs) simultaneously recorded. On the assumption of a Poisson distribution of amplitudes, calculations from the absence of failures and from variance suggest that guantum number remains at least as high as 5--10 and that quantal size is greatly reduced. During tetanic stimulation the frequency of mPSPs first increases and then decreases again, sometimes to a very low frequency. However, mPSP amplitude is reduced by no more than about 50%, which indicates that quanta giving rise to mPSPs come from a different population of vesicles than those comprising evoked PSPs. During rest following a tetanus, calculated quantal size in evoked PSPs recovers within several hundred milliseconds to mPSP size simultaneouly recorded. Most of this recovery time represents time for filling, since vesicles can be supplied at much higher rates during tetanic stimulation. After one second rest PSP amplitude exceeds threshold but recovery for later PSPs in a short train requires many minutes. The slowness of this recovery is consistent with the morphological demonstration of slow recovery of the vesicle population after depletion. These data are interpreted in terms of vesicle release, depletion and membrane recycling. Following depletion new vesicles are released after only partial filling which accounts for small quanta. Very small mPSPs are not seen because filling time is short compared to time for release as mPSPs. Since quantal size can be gradually reduced, release can interrupt filling, and filling and release sites are likely to be the same. The data in combination with the morphological observations support the hypothesis of vesicular release of transmitter and provide new evidence as to rates and sites for filling of vesicles.

Animals↗
PubMed1985

Spontaneous electrical activity induced by herpes virus infection in rat sensory neuron cultures.

Dissociated cultures of rat dorsal root ganglion neurons were infected with a syncytial strain of herpes simplex virus type 1. Over 90% of neurons in infected cultures were spontaneously active and fired action potentials which, on membrane potential hyperpolarization, were replaced by depolarizing events similar to excitatory postsynaptic potentials. Amplitude analysis of these events produced populations described by the sum of several unitary events with Gaussian rather than binomial or Poisson distributions. Such spontaneous activity was blocked by tetrodotoxin but not by low calcium high magnesium solutions containing cadmium. Simultaneous recording from pairs of spontaneously active neurons revealed excitatory connexions between cells. It is suggested that virus-induced fusion of nerve cell processes induces electrical coupling between sensory neurons, and that the resulting electrical network supports spontaneous activity.

Animals↗