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 865 records · Page 48Linked to original sources
PubMed1983

The recovery of anaerobic bacteria from swabs in three transport systems. Statistical evaluation by application of a variance component model.

The recovery of six anaerobic species from swabs in three transport systems was quantitatively evaluated. The test strains were Bacteroides fragilis, B. melaninogenicus ss. intermedius, Fusobacterium necrophorum, Peptostreptococcus anaerobius, Eubacterium lentum, and Clostridium ramosum. The transport systems were a charcoal-impregnated cotton swab in modified Stuart's transport medium (MS), or a plain cotton swab in either a dry aerobic tube (DA) or an aerobic agar tube (AA). Swabs were charged with a known number of organisms of the test strain and inserted in the appropriate transport systems. Immediately hereafter the swabs were transferred to glass tubes with reduced buffer. After vigorous shaking, aliquots from the buffer were seeded onto blood agar plates, and the number of colony forming units (CFU) was counted after incubation. The number of CFUs from independent replications had a variation that was too large to be accounted for by the Poisson distribution. The probability of recovery (POR) was defined as the number of CFU recovered from a swab as a percentage of the original inoculum. The logarithms of the POR values were analyzed with a variance component model. This showed that estimated values of POR were significantly higher in DA (44%) than in AA (23%), while the value for MS (33%) did not differ significantly from those for AA or DA. It is concluded that in MS, friction between swab and medium does not contribute significantly to bacterial recovery loss, as compared to AA and DA.

Anaerobiosis↗
PubMed1971

Contractile and electrical responses of vagus-innervated frog sartorius muscles.

1. Frog sartorius muscles were transplanted to the thoracic region and re-innervated by the gastric vagus nerve. Contractile responses of the re-innervated muscles were studied. Micro-electrodes were used to measure electrical properties of the muscle fibre membrane. Histological studies of the sartorius and vagus nerves and re-innervated muscles were also carried out.2. Autonomic nerve fibres of the gastric vagus form functional connexions with the skeletal muscle fibres. Such vagus-innervated muscle fibres do not atrophy.3. Neither the contractile nor the passive electrical properties of the muscle fibres are altered by vagal innervation.4. Synaptic transmission is quantal in nature and describable by a Poisson distribution as at normal sartorius junctions. The muscle fibres, however, do show extensive multiple-innervation, and unlike normal sartorius junctions, vagus-muscle junctions have a low quantal content and show a long-lasting facilitation.5. Properties of the vagus nerve fibres apparently are not altered by synapsing with skeletal muscle fibres. They remain small diameter and have high threshold for electrical stimulation.6. The ability of these nerve and muscle fibres to influence each other is rather limited in the adult amphibian.

Action Potentials↗
PubMed1975

Binomial analysis of quantal transmitter release at glycerol treated frog neuromuscular junctions.

1. Transmitter release was analysed at frog neuromuscular junctions pre-treated with 400 mM glycerol Ringer. In the absence of added drugs, end-plate potentials (e.p.p.s) and miniature e.p.p.s (m.e.p.p.s) could be recorded at selected junctions. 2. E.p.p.s were unusually large and calculations of quantal content indicated a high level of release. Also recorded were anomalous action potentials resembling e.p.p.s but these could be distinguished using a summation test. 3. Plots of coefficient of variation of e.p.p.s (0-5 Hz stimulation) versus direct quantal content (M1) showed a marked deviation from Poisson expectations with high M1. Analysis of these results with amplitude-frequency histograms showed a progressively better fit to binomial predictions with increasing M1. 4. The use of binomial statistics allowed direct calculations of the mean probability of release (p) and the readily available store (n). Increasing Ca/Mg caused increases in both n and p. 5. Plots of M1 vs. Ca/Mg showed a power relationship of 3.58. Maximum m.e.p.p. amplitude occurred at control Ca/Mg. Both results were consistent with studies in muscles not treated with glycerol and indicated that glycerol treatment caused no major alterations pre- or post-junctionally. 6. Estimates of quantum size using Poisson assumptions showed an over-all increase when stimulus frequency was raised, indicating a shift from binomial to a Poisson distribution. 7. The combined findings demonstrate that the glycerol treated preparation can be used to examine the release process during high output. Such release conforms to binomial statistics and allows direct determinations of the parameters n and p.

Action Potentials↗
PubMed1982

Intrinsic noise in locust photoreceptors.

1. In locust photoreceptors, the amplitude of the response to light pulses lasting less than 20 ms depends solely upon the number of absorbed photons, which can be estimated at low intensities by counting quantum bumps. Consequently, each receptor can be operated as a calibrated photon counter. 2. Three types of noise in receptor responses have been identified--extrinsic or photon noise and two types of intrinsic noise, dark noise (spontaneous activity) and transducer noise (noise in the transduction mechanism). The methods by which the noise sources are measured and identified involves measuring the responses to a train of flashes of constant intensity and converting these voltage values into a series of equivalent quantum catches. Because photon absorptions follow the Poisson distribution, the variance among equivalent catches due to photon noise equals the mean catch, and any excess variance represents intrinsic noise. 3. Dark noise is negligible: spontaneous signals (quantum bumps produced in darkness) occur less than ten times per hour at 25 degrees C, and the combined effects of membrane and electrode noise are unimportant at all but the highest intensities. 4. At low intensities transducer noise is responsible for more than 50% of all receptor noise (variance), and this rises to 90% when bright stimuli are presented to the dark-adapted eye. 5. Two simple models of transduction indicate that variations in the amplitudes and latencies of responses to single photons are a major source of transducer noise. 6. Transducer noise would be difficult to detect from an analysis of response noise alone, without knowledge of absolute photon catch, because in some important respects it mimics photon noise, e.g. it lowers the quantum efficiency without violating the square root relationship relating increment thresholds to mean intensity.

Action Potentials↗
PubMedDate not supplied

Reduction of aliasing in modulation transfer function measurements.

The images formed by many radiological systems are difficult to sample at spatial intervals small enough to avoid aliasing in the calculation of the system's modulation transfer function. However, if a system's response can be assumed to be symmetrical, this assumption can be used to effectively double the sampling density and to double the frequency limit before aliasing occurs. To accomplish this, a more complex algorithm is required. In this work, the formula for the calculation of the modulation transfer function from a symmetrical, one-dimensional line spread function is derived and a similar result for a symmetrical, two-dimensional point spread function is presented. The effect of noisy data and errors in the estimation of the offset of the center of the line spread function from a sampling point are investigated by simulation studies. For low noise (relative standard deviation of 1%) and an offset error of no more than 2% or 3% of a sampling interval, reasonable precision is obtained. These conditions appear to be achievable, especially when the noise is Poisson distributed.

Biometry↗
PubMedDate not supplied

Monte Carlo optimization of metal/phosphor screens at megavoltage energies.

The physics of imaging with metal/phosphor (Gd2O2S:Tb on brass) screens at megavoltage energies has been investigated using Monte Carlo simulation. It has been found that pair production is a significant contributor to energy deposition for Bremsstrahlung beams with energies greater than 6 MV. The effects of different thicknesses of phosphor and metal have been studied, and it is shown that the metal plays a significant role in establishing electronic equilibrium in the phosphor. The transport of optical photons through the phosphor has been modeled, and was found that only 10% to 20% of the light created in the phosphor escapes from the surface, with much of the loss being due to total internal reflection at the surface. Calculated results have been compared with experimental measurements of screen brightness for different phosphor and metal thicknesses. The SNR of a video electronic portal imaging device (VEPID) has been calculated as a function of x-ray and optical photon detection efficiency. The non-Poisson distribution of energy deposition in the phosphor is an important contributor to the SNR. The results of this paper should serve as a useful guide to the engineering design of future electronic portal imaging systems.

Biophysical Phenomena↗
PubMed1988

Synchrony-dependent autocorrelation in eighth-nerve-fiber response to rippled noise.

Autocorrelograms and interval and delay histograms of the eighth-nerve-fiber response in cats to cosine noise were recorded. A good detectability level for the delay oscillations in the autocorrelograms was always found, when the fiber had a high value of the synchronization index at characteristic frequency (CF). In order to study their relationship, autocorrelograms for cosine noise stimulation were computed by the substitution of synchronization indices in the Poisson distribution formulas for higher-order intervals. The approach was made possible through a further exploration of Johnson's synchronization theory [D. H. Johnson, "The response of single auditory-nerve fibers in the cat to single tones: synchrony and average discharge rate," Ph. D. thesis, MIT, Cambridge, MA (1974)]. It was shown that computed autocorrelograms somewhat resembled experimental ones. The differences between them concerned the envelopes of the "onset" and "delay" oscillations, viz., in their constrictions and amplitudes. These constrictions were shown to be significant only in recordings at delays greater than or equal to 4/CF, corresponding to the dominant region for human repetition pitch.

Animals↗
PubMed1974

Mathematical estimation on the level of microbial contamination on spacecraft surfaces by volumetric air sampling.

Microbiological sampling methods presently used for enumeration of microorganisms on spacecraft surfaces require contact with easily damaged components. Estimation of viable particles on surfaces using air sampling methods in conjunction with a mathematical model would be desirable. Parameters necessary for the mathematical model are the effect of angled surfaces on viable particle collection and the number of viable cells per viable particle. Deposition of viable particles on angled surfaces closely followed a cosine function, and the number of viable cells per viable particle was consistent with a Poisson distribution. Other parameters considered by the mathematical model included deposition rate and fractional removal per unit time. A close nonlinear correlation between volumetric air sampling and airborne fallout on surfaces was established with all fallout data points falling within the 95% confidence limits as determined by the mathematical model.

Actinomycetales↗
PubMed1992

Partial characterization and staphylocidal activity of thrombin-induced platelet microbicidal protein.

Thrombin-induced platelet microbicidal protein (PMP) is considered to play an important role in preventing an important role in preventing streptococcal endocarditis. However, the structural features and functions of PMPs have not been well characterized, and their antibacterial spectra against other common endocarditis pathogens, such as the staphylococci, are not known. Thrombin stimulation of washed rabbit platelets (10(8)/ml) yielded a PMP-rich preparation with a specific activity of approximately 25 U/mg of protein as determined by Bacillus subtilis bioassay. Twenty-eight clinical and laboratory Staphylococcus aureus isolates, exposed to a standardized PMP preparation (100 U/ml for 2 h at 37 degrees C), exhibited a Poisson-distributed heterogeneity to the bactericidal action of PMP, with approximately one-third designated as PMP resistant. Gel filtration chromatography (Sephadex G-50) identified the bioactive moiety within PMP preparations to be in the major protein elution peak; sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) presumptively identified PMP as a low-molecular-weight (MW) (8,500) protein present only in such bioactive protein peaks. Both the bioactivity of PMP preparations and the low-MW protein band were removable by specific anionic membranes (e.g., cellulose-acetate/nitrate), as well as by a variety of anionic resins, further corroborating the suspected cationic charge of PMP. In addition, both PMP bioactivity and the low-MW protein band were recoverable by 1.5 M NaCl elution of the anionic membrane filters post-PMP adsorptive removal. Adsorption of bioactive PMP preparations by highly PMP-susceptible B. subtilis (10(8) CFU/ml, 30 min) resulted in a near-complete loss of residual bioactivity; in contrast, adsorption of bioactive PMP preparations with less PMP-susceptible S. aureus strains failed to reduce bioactivity. Significant lysozyme contamination of PMP-rich preparations was ruled out by determination of differences between bioactive PMP preparations and exogenous lysozyme as regards (i) relative heat stabilities; (ii) differential bactericidal activity versus B. subtilis and Micrococcus luteus; and (iii) SDS-PAGE protein profiles. These data show that the bioactive PMP protein moiety is of low MW, is heat stable, is probably cationic (similar to leukocyte-derived defensins), and possesses potent bactericidal activity against a significant percentage of S. aureus isolates.

Animals↗
PubMed1999

Quality control in nucleic acid amplification methods: use of elementary probability theory.

Since it is not possible to state with certainty that contamination has occurred during a nucleic acid amplification assay in the absence of a positive result for a negative control, methods of elementary probability theory are used to illustrate how to identify those runs in which the possibility of contamination should be considered. The use of binomial and Poisson distributions and an analysis of clusters are presented with illustrative examples to demonstrate their use.

Artifacts↗
PubMed1978

Method for evaluating broth culture media: application to Haemophilus.

A method was devised to test the growth-promoting ability of a broth medium. The "dilute to extinction" method determines the inoculum required to develop heavy turbidity in a broth with overnight incubation. A statistical method using Poisson distribution was used to show that a single Haemophilus cell can develop heavy turbidity in an optimal broth. The dilute to extinction method was used to evaluate the shelf life of stored media, to titrate the growth factor requirements of Haemophilus, and to evaluate the use of purified hemin and nicotinamide adenine dinucleotide in a broth medium for the growth of Haemophilus. Of the media tested, the most suitable formulation was Mueller-Hinton broth supplemented with 10 microgram of hemin and 10 microgram of nicotinamide adenine dinucleotide per ml. The dilute to extinction method appears to be especially useful in the development of broth media for fastidious organisms. The method could also be used to assure the quality of other broth media which are required to support the growth of small inocula in the clinical or research laboratory.

Culture Media↗
PubMed1970

Functional heterogeneity of virions in human adenovirus types 2 and 12.

Purified preparations of adenovirus types 2 and 12 were used to infect KB cells at different input multiplicities. The resulting infected cultures were scored for inclusion body formation, production of infectious centers, and cloning efficiency. Both preparations were found to contain some defective particles capable of preventing a cell from cloning but unable to induce inclusion bodies or form plaques. The proportion of such defective particles in adenovirus 12 was about 10 times that in adenovirus 2. At high input multiplicities, the percentage of cells displaying an inclusion body was less than that predicted by the Poisson distribution and reached a maximum of 40 to 60% for adenovirus 2 and 12 to 15% for adenovirus 12. This reduction may be due to interference by large numbers of non-plaque-producing particles infecting each cell. The per cent of cells forming infectious centers was substantially greater for adenovirus 2 than for adenovirus 12 when compared at the same input plaque-forming units, reaching a maximum of 35 to 73% for adenovirus 2 and 5 to 10% for adenovirus 12. The low value for adenovirus 12 may be a result of the same interference phenomenon.

Adenoviridae↗
PubMed2005

Role for tumor necrosis factor alpha in murine cytomegalovirus transcriptional reactivation in latently infected lungs.

Interstitial pneumonia is a major clinical manifestation of primary or recurrent cytomegalovirus (CMV) infection in immunocompromised recipients of a bone marrow transplant. In a murine model, lungs were identified as a prominent site of CMV latency and recurrence. Pulmonary latency of murine CMV is characterized by high viral genome burden and a low incidence of variegated immediate-early (IE) gene expression, reflecting a sporadic activity of the major IE promoters (MIEPs) and enhancer. The enhancer-flanking promoters MIEP1/3 and MIEP2 are switched on and off during latency in a ratio of approximately 2:1. MIEP1/3 latency-associated activity generates the IE1 transcript of the ie1/3 transcription unit but not the alternative splicing product IE3 that encodes the essential transactivator of early gene expression. Splicing thus appeared to be an important checkpoint for maintenance of latency. In accordance with previous work of others, we show here that signaling by the proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha) activates IE1/3 transcription in vivo. As an addition to current knowledge, Poisson distribution analysis revealed an increased incidence of IE1/3 transcriptional events as well as a higher amount of transcripts per event. Notably, TNF-alpha promoted the splicing to IE3 transcripts, but transcription did not proceed to the M55/gB early gene. Moreover, the activated transcriptional state induced by TNF-alpha did not predispose latently infected mice to a higher incidence of virus recurrence after hematoablative treatment. In conclusion, TNF-alpha is an important inductor of IE gene transcriptional reactivation, whereas early genes downstream in the viral replicative cycle appear to be the rate-limiting checkpoint(s) for virus recurrence.

Animals↗
PubMed1971

Enlargement of Escherichia coli after bacteriophage infection. I. Description of the phenomenon.

Escherichia coli B/r and B(s-1) ceased division and increased in mean cell volume soon after infection with T-even phage. The effect was obtained with wild-type or rapid lysis mutants, as well as with ultraviolet light-killed phage and with bacteriophage ghosts which lack deoxyribonucleic acid. The cell response did not require the presence of phage genetic material or the production of progeny phage. A Poisson distribution of the fraction of adsorbed phage at different multiplicites of infection indicates that one phage per bacterium will produce maximum increase in cell volume. T-even phage-resistant E. coli mutants showed no enlargement response, and phage T1, T3, and T7 elicited neither abrupt termination of cell division nor host cell enlargement. Infection with baseplate-defective T4D 12(-) amber mutants, which bind reversibly to but do not penetrate the bacterium, also had no effect. In vitro restoration of normal baseplate function in these defective viruses allowed phage adsorption and penetration and caused host cell division arrest and enlargement. These findings indicate that arrest of division and increase in mean cell volume occur together when a sensitive strain of E. coli is infected with T-even phage that adsorb and penetrate normally.

Bacteriological Techniques↗
PubMed1990

Rapid and apparently error-prone excision repair of nonreplicating UV-irradiated plasmids in Xenopus laevis oocytes.

Repair of UV-irradiated plasmid DNA microinjected into frog oocytes was measured by two techniques: transformation of repair-deficient (delta uvrB delta recA delta phr) bacteria, and removal of UV endonuclease-sensitive sites (ESS). Transformation efficiencies relative to unirradiated plasmids were used to estimate the number of lethal lesions; the latter were assumed to be Poisson distributed. These estimates were in good agreement with measurements of ESS. By both criteria, plasmid DNA was efficiently repaired, mostly during the first 2 h, when as many as 2 x 10(10) lethal lesions were removed per oocyte. This rate is about 10(6) times the average for removal of ESS from repair-proficient human cells. Repair was slower but still significant after 2 h, but some lethal lesions usually remained after overnight incubation. Most repair occurred in the absence of light, in marked contrast to differentiated frog cells, previously shown to possess photoreactivating but no excision repair activity. There was no increase in the resistance to DpnI restriction of plasmids (methylated in Escherichia coli at GATC sites) incubated in oocytes; this implies no increase in hemimethylated GATC sites, and hence no semiconservative DNA replication. Plasmid substrates capable of either intramolecular or intermolecular homologous recombination were not recombined, whether UV-irradiated or not. Repair of Lac+ plasmids was accompanied by a significant UV-dependent increase in the frequency of Lac- mutants, corresponding to a repair synthesis error frequency on the order of 10(-4) per nucleotide.

Animals↗
PubMed2005

Adenotonsillectomy for upper respiratory infections: evidence based?

BACKGROUND: Despite high rates of (adeno)tonsillectomy for upper respiratory infections in western countries, the medical literature offers the physician little support in deciding which child might benefit from the operation. METHODS: A literature search was performed to identify randomised trials and non-randomised controlled studies into the efficacy of tonsillectomy with or without adenoidectomy in children under 18 years. For the outcomes sore throat episodes, sore throat associated school absence, and upper respiratory infections, pooled estimates of the incidence rate ratios and rate differences with 95% confidence intervals were calculated, assuming a Poisson distribution. RESULTS: Six randomised trials and seven non-randomised controlled studies on the efficacy of adenotonsillectomy in children were evaluated. For sore throat episodes data for 2483 person-years were available. The pooled risk difference was -1.2 episodes per person-year (95% CI -1.3 to -1.1). For sore throat associated school absence 1669 person-years were analysed. The pooled risk difference was -2.8 days per person-year (95% CI -3.9 to -1.6). For upper respiratory infections 1596 person-years were available. The pooled risk difference was -0.5 episodes per person-year (95% CI -0.7 to -0.3). CONCLUSIONS: All available randomised trials and non-randomised controlled studies into the efficacy of (adeno)tonsillectomy had important limitations. The frequency of sore throat episodes and upper respiratory infections reduces with time whether (adeno)tonsillectomy has been performed or not. (Adeno)tonsillectomy gives an additional, but small, reduction of sore throat episodes, days of sore throat associated school absence, and upper respiratory infections compared to watchful waiting.

Absenteeism↗
PubMed1996

Determining the size of a total purchasing site to manage the financial risks of rare costly referrals: computer simulation model.

OBJECTIVE: To estimate the financial risks of 15 categories of rare costly referrals for total purchasing sites of different population sizes. DESIGN: Computer simulation of 100 fund years assuming Poisson distribution of referrals. SETTING: British general practices that have opted to become total purchasing sites. Referral rates and price estimates were supplied by South and West Devon Health Commission. MAIN OUTCOME MEASURES: Variation in referral costs to purchasers in relation to size of risk pool (person years at risk). RESULTS: Random variation in referral costs increased as the size of the risk pool decreased. Variation increased greatly below 30,000 person years. The mean simulated cost of the referral categories considered was 2.8% of total NHS hospital and community service costs, and the maximum simulated cost for 7000 person years was 6.8%. Simulated variation was robust to assumption about prices and referral rates for specific types of referral. CONCLUSION: Rare costly referrals seem unlikely to bankrupt total purchasing sites. The management of risk is not in itself justification for total purchasing to be based in several general practices in order to generate large populations. There are other ways of managing risk. Sites can easily explore options by simulations using local referral rates and prices.

Computer Simulation↗
PubMed2006

Investigating the relation between placement of Quit antismoking advertisements and number of telephone calls to Quitline: a semiparametric modelling approach.

STUDY OBJECTIVES: Quitline-an antismoking advertising and a telephone helpline service-is an effective public health intervention strategy for tobacco control. The objective of this short report is to model the relation between placement of antismoking advertisements and calls to Quitline on a given day. METHODS/DESIGN: Data on daily Quitline antismoking advertisements, television target audience rating points (TARPS), and calls to Quitline Victoria were studied for the period 1 August 2000 and 31 July 2001. The outcome-calls to Quitline-is a count and thus assumed to follow a Poisson distribution. Generalised partial linear models were used to model the logarithm of mean daily calls as a non-parametric function of time and a linear parametric function of the day of week, number of advertisements, and TARPS. MAIN RESULTS: Peak calls to Quitline Victoria occurred during Monday to Wednesday with around three times as many calls compared with Sunday. Both placement of Quitline advertisements (p<0.001) and an increase in TARPS (p<0.001) on a given day significantly increased the number of calls made to Quitline Victoria. The model adequately captured fluctuations in call volume and diagnostics showed no model inadequacy. CONCLUSIONS: In this short report the emphasis is on modelling the parametric components-day of week, placement of advertisements, and TARPS on call volume. The dynamics of the underlying time trend in call volume is captured in a non-parametric component. Future analysis of hourly data would provide additional information to assess different media buying strategies that might increase call volume.

Adult↗