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At least 343 records · Page 19Linked to original sources
PubMed1999

Ultraviolet Radiation (UVR) Sensitivity Analysis and UVR Survival Strategies of a Bacterial Community from the Phyllosphere of Field-Grown Peanut (Arachis hypogeae L.).

> Abstract The short-term population dynamics of the culturable bacterial community from field-grown peanut (Arachis hypogeae L.) was analyzed over three 2-day periods. As in other phyllosphere studies, significant numbers of pigmented organisms were detected, suggesting the importance of pigmentation in the colonization of this habitat. Isolates were grouped according to pigmentation (orange, pink, yellow, nonpigmented), and the sensitivity of each isolate in the collection (n = 617) to ultraviolet radiation (UVR) was determined as the minimal inhibitory dose (MIDC) of UVR that resulted in an inhibition of growth compared to an unirradiated control. The majority of isolates recovered (56.1%) had an MIDC equal to or exceeding that of Pseudomonas syringae 8B48, a known UV-tolerant strain. Among pigmentation groups, the mean MIDC of pink- and orange-pigmented isolates was significantly greater than that of yellow- or nonpigmented isolates at each sampling time of day. Identification of 213 of the isolates using fatty acid methyl ester analysis indicated that a large proportion of the isolates were gram-positive, with Bacillus spp. alone accounting for 35.7% of the total. The genus Curtobacterium contained the largest percentage of highly UVR-tolerant strains. Nonpigmented mutants of four Curtobacterium strains were selected following ethyl methane sulfonate mutagenesis; these nonpigmented mutants were significantly altered in survival following irradiation with UV-A wavelengths. The strategy of avoidance of UVR through colonization of the abaxial leaf surface was evaluated on three separate occasions by leaf imprint sampling. Only 3 of 120 leaves (2.5%) contained larger bacterial populations on the adaxial surface, indicating that colonization of the abaxial leaf surface is important to phyllosphere survival. Our results indicate that tolerance to UVR is a common phenotype among phyllosphere bacteria, suggesting that solar radiation has a strong influence on the microbial ecology of the phyllosphere.http://link.springer-ny.com/link/service/journals/00248/bibs/38n1p27.html

Journal Article↗
PubMed2005

Accurate and sensitive analysis of triplet repeat expansions by capillary electrophoresis.

The reliable genetic diagnostics of triplet repeat expansions by capillary electrophoresis (CE) remains technically challenging due to the properties of the repeated GC-rich sequences. The biased base composition of the analyzed sample as compared to the commonly used DNA size standards makes the precise repeat length determination questionable. The homologous allelic ladders improve the accuracy of the repeat length analysis significantly. Their use, however, is not devoid of other complications. In the approach we propose, the allelic ladders are used only to properly calibrate the commercially available standards which serve then as internal standards in reliable and economical repeat length determination. In this study, we have also analyzed factors that could possibly increase the sensitivity of mutant allele detection by increasing the overall amplification efficiency and long-to-short product ratio.

Calibration↗
PubMed1995

Interleukin 5 expressing allergen-specific T-lymphocytes in patients with house dust mite sensitization: analysis at a clonal level.

Interleukin 5 (IL-5) is a T-cell lymphokine known to stimulate development, functional activity, and in vitro survival of eosinophils. Tissue and blood eosinophilia occurring during allergic responses of the immune system are potentially mediated by IL-5 secreting T-cells. To test this hypothesis a series of allergen-specific T-cell clones were established from peripheral blood and skin lymphocytes of patients with atopic dermatitis and house dust mite sensitization. In addition, alloreactive T-cell clones were also prepared from peripheral blood lymphocytes of healthy donors. Cloned T-cells were analyzed for IL-5 mRNA expression and IL-5 secretion by means of in vitro gene amplification using the reverse transcriptase polymerase chain reaction and IL-5 specific oligonucleotide hybridization, as well as IL-5-specific ELISA. A majority of allergen-specific long-term cultured T-cell clones (84%) of different donors and of either phenotype (CD8+ or CD4+) disclosed IL-5 transcripts on stimulation with lectins. Almost all clones exhibiting IL-5 transcripts also released immunoreactive IL-5 protein into their culture supernatants. In contrast, only 2% of alloreactive T-cell clones obtained from healthy donors and none of alloreactive T-cell clones of one atopic patient investigated expressed detectable amounts of IL-5 mRNA in response to lectin stimulation, all of whom were CD4+. These results suggest that eosinophilia observed in allergic responses in the peripheral blood and in tissues at the site of induced late-phase cutaneous reaction may be associated with IL-5 release by allergen-specific T-cells.

Animals↗
PubMed1975

Construction, simulation, clinical application and sensitivity analysis of a human left ventricular control system model.

A regulated left ventricular dynamics model is presented which involves interaction of the dynamics of the left ventricular and circulatory systems and their regulation by the central nervous system. On-line human parametric stimulation (parameter estimation) and consequential prognostic implications (based on parametric values) are demonstrated. Model responses to stimulated physiologic stresses help delineate tolerances of subjects. In order to have an estimate of the reliability of the model, the sensitivity of the model's responses to changes in the values of its intrinsic parameters is assessed. Also determined is the extent to which errors in measuring the pressure affect the calculated values of the model's responses to changes in the values of its intrinsic parameters is assessed. Also determined is the extent to which errors in measuring the pressure affect the calculated values of the model's simulation parameters and subsequently influence the values of other diagnostically useful variables (such as contractility, oxygen consumption rate, heart rate), when the model is used to determine the limiting physiological stress sustainable by the subject. A comparison of the model's composition with those of other similar cardio-circulatory models is included.

Blood Flow Velocity↗
PubMed2003

Sensitivity analysis of narrowband photonic crystal filters and waveguides to structure variations and inaccuracy.

Photonic crystal microcavities, formed by local defects within an otherwise perfectly periodic structure, can be used as narrowband optical resonators and filters. The coupled-cavity waveguide (CCW) is a linear array of equally spaced identical microcavities. Tunneling of light between microcavities forms a guiding effect, with a central frequency and bandwidth controlled by the local defects' parameters and spacing, respectively. We employ cavity perturbation theory to investigate the sensitivity of microcavities and CCWs to random structure inaccuracies. For the microcavity, we predict a frequency shift that is due to random changes in the lattice structure and show an approximate linear dependence between the standard deviation of the structure inaccuracy and that of the resonant frequency. The effect of structural inaccuracy on the CCW devices, however, is different; it has practically no effect on the CCW performance if it is below a certain threshold but may destroy the CCW if this threshold is exceeded.

Journal Article↗
PubMed1993

Sensitivity analysis in a multidimensional demographic projection model with a two-sex algorithm.

"Formulas are derived for the effect that a slight change in the occurrence/exposure rate of the multidimensional projection model has on the elements of the population vector. The projection model classifies the population by sex, age, and marital status. The model includes a two-sex algorithm in order to ensure consistency between numbers of male and female marriages, number of divorces for the two sexes, and new widows (widowers) and deceased spouses. The sensitivity functions and elasticities are applied to data from the Netherlands for the period 1980-1984. The results indicate that marriage market mechanisms, in particular competition and substitution effects, are reasonably well modelled."

Age Distribution↗
PubMed1995

Uncertainty, variability, and sensitivity analysis in physiological pharmacokinetic models.

Physiologically based pharmacokinetic (PBPK) models are now commonly used to predict the dose of toxic metabolites of chemical substances reaching target tissues. A typical PBPK model can involve 20 or more physiological, physiochemical, and biochemical parameters, each of which is estimated with some degree of error. In this article, methods for assessing the impact of uncertainty in the parameter values on prediction of tissue dose are proposed, along with methods for identifying those parameters to which predictions of tissue doses are most sensitive. Many of the model parameters are related to body weight, which is assumed to vary in accordance with a doubly truncated normal distribution. The application of the proposed methods is illustrated using a PBPK model for benzene.

Animals↗
PubMed2005

Sensitivity analysis of an inverse procedure for determination of elastic coefficients for strong anisotropy.

The elastic coefficients of anisotropic solids are often evaluated from measurements of phase or group velocities of ultrasonic bulk waves by the usage of inverse optimizing procedures. This paper discusses the effects of various factors on such procedures results for transversely isotropic solids with considerably strong anisotropy. First, the inverse determination of all elastic coefficients of unidirectional CFRP composite is briefly outlined. Then the results of the optimization are treated as exact values and the sensitivity of the optimizing process versus main considered sources of inaccuracies is analyzed. Results of extensive simulations are presented to illustrate the effect of input data distortion, input data incompleteness, and geometrical conversion from experimentally obtained group velocities into corresponding phase velocities used as input data for the optimizing procedure. The paper takes note of how information about the elastic coefficients can be extracted from the different segments of the phase velocity surface. The stability versus input data distortion for inversion from group velocities and phase velocities is compared and the importance of reliable geometrical converting from group into phase velocities is illustrated. An novel method for geometrical conversion of distorted group velocity data into corresponding phase velocities based on affine combinations of low-order polynomials is presented and compared with piecewise or high-order polynomial fitting.

Anisotropy↗
PubMed1999

Classification and sensitivity analysis of a proposed primary metabolic reaction network for Streptomyces lividans.

Constructing a metabolic flux analysis model is in principle fairly straightforward. However, there are a number of mathematical pitfalls. First, dependent reactions are a recurring problem and, second, the choice of reactions to measure may not be straight-forward. A method for systematic identification of dependent reactions and a thorough reactions classification procedure is presented. A well-defined stoichiometric presentation can provide significant insight into metabolic control mechanisms. Two methods for analyzing the impact of perturbations in the measured fluxes on the remaining metabolism and the impact of changes in biomass composition on the calculated metabolic reactions is developed. A metabolic reaction network proposed for Streptomyces lividans is used as an example to demonstrate the outlined analysis. It is concluded that oxygen utilization has the highest influence on the pathway fluxes and that realistic perturbations in the biomass composition do not significantly alter the flux patterns.

Homeostasis↗
PubMedDate not supplied

Cytologic diagnosis and chromosome analysis: sensitivity, specificity, accuracy and predictive value in malignant and benign pleural effusions.

It is often difficult to determine the origin a pleural effusion even if it is very important for prognosis of a patient. We have studied No. 200 patients, affected with nontraumatic effusions, using cytogenetic technics and cytologic examination. Cytologic diagnosis of pleural effusions allows to detect correctly its malignant nature in a percentage of cases ranging, according to various Authors, between 45 and 80%. The main parameters we have considered in our study, in order to value chromosomal analysis as a useful test for malignity in pleural effusions, can be, at least, placed upon those obtained with cytologic diagnosis. Therefore, we think we can consider chromosomal analysis in neoplastic effusions as a useful completion in terms of diagnostic advantage of cytologic diagnosis.

Adult↗
PubMedDate not supplied

Sensitivity analysis of kernel estimates: implications in nonlinear physiological system identification.

Many techniques have been developed for the estimation of the Volterra/Wiener kernels of nonlinear systems, and have found extensive application in the study of various physiological systems. To date, however, we are not aware of methods for estimating the reliability of these kernels from single data records. In this study, we develop a formal analysis of variance for least-squares based nonlinear system identification algorithms. Expressions are developed for the variance of the estimated kernel coefficients and are used to place confidence bounds around both kernel estimates and output predictions. Specific bounds are developed for two such identification algorithms: Korenberg's fast orthogonal algorithm and the Laguerre expansion technique. Simulations, employing a model representative of the peripheral auditory system, are used to validate the theoretical derivations, and to explore their sensitivity to assumptions regarding the system and data. The simulations show excellent agreement between the variances of kernel coefficients and output predictions as estimated from the results of a single trial compared to the same quantities computed from an ensemble of 1000 Monte Carlo runs. These techniques were validated with white and nonwhite Gaussian inputs and with white Gaussian and nonwhite non-Gaussian measurement noise on the output, provided that the output noise source was independent of the test input.

Algorithms↗
PubMed2003

Biodiesel production from waste cooking oil: 2. Economic assessment and sensitivity analysis.

The economic feasibilities of four continuous processes to produce biodiesel, including both alkali- and acid-catalyzed processes, using waste cooking oil and the 'standard' process using virgin vegetable oil as the raw material, were assessed. Although the alkali-catalyzed process using virgin vegetable oil had the lowest fixed capital cost, the acid-catalyzed process using waste cooking oil was more economically feasible overall, providing a lower total manufacturing cost, a more attractive after-tax rate of return and a lower biodiesel break-even price. On the basis of these economic calculations, sensitivity analyses for these processes were carried out. Plant capacity and prices of feedstock oils and biodiesel were found to be the most significant factors affecting the economic viability of biodiesel manufacture.

Biotechnology↗
PubMed2005

Uncertainty and sensitivity analysis in assessment of the thyroid cancer risk related to Chernobyl fallout in Eastern France.

The increase in the thyroid cancer incidence in France observed over the last 20 years has raised public concern about its association with the 1986 nuclear power plant accident at Chernobyl. At the request of French authorities, a first study sought to quantify the possible risk of thyroid cancer associated with the Chernobyl fallout in France. This study suffered from two limitations. The first involved the lack of knowledge of spontaneous thyroid cancer incidence rates (in the absence of exposure), which was especially necessary to take their trends into account for projections over time; the second was the failure to consider the uncertainties. The aim of this article is to enhance the initial thyroid cancer risk assessment for the period 1991-2007 in the area of France most exposed to the fallout (i.e., eastern France) and thereby mitigate these limitations. We consider the changes over time in the incidence of spontaneous thyroid cancer and conduct both uncertainty and sensitivity analyses. The number of spontaneous thyroid cancers was estimated from French cancer registries on the basis of two scenarios: one with a constant incidence, the other using the trend observed. Thyroid doses were estimated from all available data about contamination in France from Chernobyl fallout. Results from a 1995 pooled analysis published by Ron et al. were used to determine the dose-response relation. Depending on the scenario, the number of spontaneous thyroid cancer cases ranges from 894 (90% CI: 869-920) to 1,716 (90% CI: 1,691-1,741). The number of excess thyroid cancer cases predicted ranges from 5 (90% UI: 1-15) to 63 (90% UI: 12-180). All of the assumptions underlying the thyroid cancer risk assessment are discussed.

Adolescent↗
PubMed2004

Simulation and sensitivity analysis of phosphorylation of EGFR signal transduction pathway in PC12 cell model.

The epidermal growth factor receptor (EGFR) signalling pathway is a complex signalling process with a wide network of interactions. The activation of the mitogen-activated protein kinases (MAPKs) cascade by this activated EGFR has been well studied. MAPKs form a highly integrated network, which is essential for certain specialised cell functions. This paper presents a kinetic model for the MAPK pathway downstream of the EGFR using a biochemical simulator. The model includes 30 signalling events and 29 signalling molecules. The time course data were examined for the activation of each signalling component. The simulation provides a large volume of data, by monitoring the kinetics of the signalling components, which were compared experimentally using the PC12 cell line. The kinetic model corresponded well with the experimental results observed in the EGFR induced activation of proteins. An examination of the kinetic analysis of the multiple signalling events provides a quantitative framework for representing the EGFR signalling network.

Animals↗
PubMed1998

Histone-GFP fusion protein enables sensitive analysis of chromosome dynamics in living mammalian cells.

BACKGROUND: The amplification of oncogenes in cancer cells is often mediated by paired acentric chromatin bodies called double minute chromosomes (DMs), which can accumulate to a high copy number because of their autonomous replication during the DNA synthesis phase of the cell cycle and their subsequent uneven distribution to daughter cells during mitosis. The mechanisms that control DM segregation have been difficult to investigate, however, as the direct visualization of DMs in living cells has been precluded because they are far smaller than normal chromosomes. We have visualized DMs by developing a highly sensitive method for observing chromosome dynamics in living cells. RESULTS: The human histone H2B gene was fused to the gene encoding the green fluorescent protein (GFP) of Aequorea victoria and transfected into human HeLa cells to generate a stable line constitutively expressing H2B-GFP. The H2B-GFP fusion protein was incorporated into nucleosomes without affecting cell cycle progression. Using confocal microscopy, H2B-GFP allowed high-resolution imaging of both mitotic chromosomes and interphase chromatin, and the latter revealed various chromatin condensation states in live cells. Using H2B-GFP, we could directly observe DMs in living cancer cells; DMs often clustered during anaphase, and could form chromosomal 'bridges' between segregating daughter chromosomes. Cytokinesis severed DM bridges, resulting in the uneven distribution of DMs to daughter cells. CONCLUSIONS: The H2B-GFP system allows the high-resolution imaging of chromosomes, including DMs, without compromising nuclear and chromosomal structures and has revealed the distinctive clustering behavior of DMs in mitotic cells which contributes to their asymmetric distribution to daughter cells.

Animals↗
PubMed2003

Comparing the efficiency of national health systems: a sensitivity analysis of the WHO approach.

The World Health Organization (WHO) has used econometric methods to measure the efficiency of health care systems. We assess the robustness of WHO results to definitions of efficiency and statistical procedures. Originally analysed by the WHO, the data are for 1997 (50 countries) and 1993-1997 (141 countries). The efficiency of each country in promoting population health is estimated after taking into account health care expenditure, all other expenditure and education levels. Efficiency scores are compared under different definitions of efficiency and different estimation methods. The results show that the country rankings and efficiency scores are sensitive to the definition of efficiency and choice of model specification. We conclude that econometric methods can yield insights into complex socioeconomic phenomena. However, the lack of robust results to reasonable alternative specifications suggests that it is premature to use the methods adopted by the WHO to construct league tables of health systems.

Data Collection↗
PubMed2002

Perceived verbal conflict behaviors associated with physical aggression and sexual coercion in dating relationships: a gender-sensitive analysis.

We studied perceived partner verbal behaviors associated with participants' use of dating aggression. Men's reports of their partners' demanding, controlling, and psychologically abusive behaviors during conflicts were expected to predict men's perpetration against partners. In contrast, women's reports of their partners' withdrawal were expected to predict women's perpetration. Data were collected from heterosexual undergraduates (N = 223) in exclusive dating relationships. Participants' reports of partner demands and partner psychological abuse were associated with participants' use of physical aggression and sexual coercion. Reports of partner withdrawal and partner controlling behaviors were associated with participants' sexual coercion only. Significant moderating effects of gender emerged. As expected, partner demands, controlling behaviors, and psychological abuse were associated with physical aggression and sexual coercion in men, but not women. Partner withdrawal was associated with sexual coercion in both women and men. We conclude that gender-sensitive approaches are necessary to understand and prevent verbal conflict patterns associated with physical aggression and sexual coercion in intimate relationships.

Adolescent↗
PubMed2004

Modeling the mammalian circadian clock: sensitivity analysis and multiplicity of oscillatory mechanisms.

We extend the study of a computational model recently proposed for the mammalian circadian clock (Proc. Natl Acad. Sci. USA 100 (2003) 7051). The model, based on the intertwined positive and negative regulatory loops involving the Per, Cry, Bmal1, and Clock genes, can give rise to sustained circadian oscillations in conditions of continuous darkness. These limit cycle oscillations correspond to circadian rhythms autonomously generated by suprachiasmatic nuclei and by some peripheral tissues. By using different sets of parameter values producing circadian oscillations, we compare the effect of the various parameters and show that both the occurrence and the period of the oscillations are generally most sensitive to parameters related to synthesis or degradation of Bmal1 mRNA and BMAL1 protein. The mechanism of circadian oscillations relies on the formation of an inactive complex between PER and CRY and the activators CLOCK and BMAL1 that enhance Per and Cry expression. Bifurcation diagrams and computer simulations nevertheless indicate the possible existence of a second source of oscillatory behavior. Thus, sustained oscillations might arise from the sole negative autoregulation of Bmal1 expression. This second oscillatory mechanism may not be functional in physiological conditions, and its period need not necessarily be circadian. When incorporating the light-induced expression of the Per gene, the model accounts for entrainment of the oscillations by light-dark (LD) cycles. Long-term suppression of circadian oscillations by a single light pulse can occur in the model when a stable steady state coexists with a stable limit cycle. The phase of the oscillations upon entrainment in LD critically depends on the parameters that govern the level of CRY protein. Small changes in the parameters governing CRY levels can shift the peak in Per mRNA from the L to the D phase, or can prevent entrainment. The results are discussed in relation to physiological disorders of the sleep-wake cycle linked to perturbations of the human circadian clock, such as the familial advanced sleep phase syndrome or the non-24h sleep-wake syndrome.

ARNTL Transcription Factors↗