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PubMed2003

Weibull distribution function based on an empirical mathematical model for inactivation of Escherichia coli by pulsed electric fields.

The pulsed electric field inactivation kinetics of Escherichia coli suspended in orange juices with three different concentrations of carrot juice (0, 20, and 60%) was studied. Electric field strengths ranged from 25 to 40 kV/cm, and treatment times ranged from 40 to 340 micros. Experimental data were fitted to Bigelow, Hülsheger, and Weibull distribution functions, and the Weibull function provided the best fit (with the lowest mean square error). The dependency of each model's kinetic constant on electric field strength and carrot juice concentration was studied. A secondary model was developed to describe the relationship of Weibull parameters a and n to electric field strength and carrot juice concentration. An empirical mathematical model based on the Weibull distribution function, relating the natural logarithm of the survival fraction to treatment time, electric field strength, and carrot juice concentration, was developed. Parameters were estimated by a nonlinear regression. The results of this study indicate that the error rate for the model's predictions was 6.5% and that the model was suitable for describing E. coli inactivation.

Beverages↗
PubMedDate not supplied

Distensibility and pulse wave velocity of the thoracic aorta in patients with juvenile idiopathic arthritis: an MRI study.

OBJECTIVE: An increased incidence of cardiovascular disease has been found in rheumatic disorders. Changes in the variables of aortic elasticity in patients with juvenile idiopathic arthritis (JIA) were evaluated and their relationship to inflammation, anti-rheumatic drugs and traditional cardiovascular risk factors were investigated in this study. METHODS: Phase contrast MR was performed in 31 patients with JIA and 28 age and sex matched controls to evaluate the aortic distensibility and pulse wave velocity (PWV). Disease activity variables, plasma lipid profile, homocysteine, thyroid hormones, glucose and insulin were assessed in the patients. RESULTS: Eighteen patients had oligoarticular, 6 polyarticular and 7 systemic disease. Distensibility was lower (mean: 10.25; SD: 4.18) and PWV was higher (mean: 3.68; SD: 1.59) in the patients compared to the controls (mean: 13.4; SD: 4.99), (mean: 1.38; SD: 0.54) respectively (p < 0.01). A positive correlation between PWV and age was observed in the patients (rs = 0.47, p < 0.01) and controls (rs = 0.72, p < 0.01), and a negative correlation between distensibility and age in the patients (rs = -0.59, p < 0.01) and controls (rs = -0.63, p < 0.01). No statistically significant correlations were found between distensibility and PWV and metabolic and disease activity parameters. When distensibility and PWV were adjusted for age no significant differences were found between the three subtypes of JIA. CONCLUSION: JIA is associated with increased aortic stiffness that might suggest subclinical atherosclerosis. Early detection and follow-up by non-invasive methods may be useful in the prevention of future cardiovascular disease.

Adolescent↗
PubMed2001

Hydration of the peptide backbone largely defines the thermodynamic propensity scale of residues at the C' position of the C-capping box of alpha-helices.

The C' position of the C-capping box is the second residue outside of the helix. Statistical analysis of residue distribution at the C' position in the alpha-helices' C-capping box showed that different amino acid residues occur with different probabilities, with the strongest preference being for glycine. To understand the physico-chemical basis for this preference, we studied the effects that 17 amino acid substitutions at the C' position in an alpha-helix of ubiquitin have on the stability of this protein. We determined the following rank order of amino acid residues at the C' position with respect to their effect on the stability: Gly>His>Asn>Arg>Lys>Gln>Ala>Phe>Met>Ser>Asp>Glu>Trp>Thr>Pro>Ile>Val. The effect of the amino acid substitutions on the structure also was evaluated by comparing the (1)H-(15)N heteronuclear sequential quantum correlation spectra and showed no significant changes in the structures of the most stable (Gly) and the least stable (Val) variants. The obtained changes in stability highly correlate (r = 0.85) with the statistical distribution of the residues at the C' position indicating that the measured thermodynamic propensities are unbiased by secondary interactions. We also found that the measured thermodynamic propensities correlate well with the amide hydrogen exchange data on short model peptides (r = 0.85) and the calculated hydration of the peptide backbone (r = 0.88). These results combined with the changes in enthalpy and entropy of unfolding of ubiquitin variants suggest that dehydration of the peptide backbone plays a significant role in defining the thermodynamic propensity scale at the C' position of the C-capping box in alpha-helices. This propensity scale is useful for protein secondary structure predictions and protein design.

Amino Acid Substitution↗
PubMed2000

Setting specifications for non-normally distributed data.

In this paper, we focus on estimating an upper specification for non-normally distributed data. Cornish-Fisher expansions were exploited for derivations of the method. The method was applied for upper specification calculations of two particle-size data sets, and simulation studies were also performed to demonstrate the accuracy of the approximations. The method was also used to calculate the critical values for delta(min) for the Anderson-Hauck test for equivalence using bootstrap samplings. The main advantage of the method is in calculating specifications with limited data.

Chemistry, Pharmaceutical↗
PubMed2000

Testing the robustness of the new Haseman-Elston quantitative-trait loci-mapping procedure.

Variance components (VC) techniques have emerged as among the more powerful methods for detection of quantitative-trait loci (QTL) in linkage analysis. Allison et al. found that, with particularly marked leptokurtosis in the phenotypic distribution and moderate-to-high residual sibling correlation, maximum likelihood (ML) VC methods may produce a severe excess of type I errors. The new Haseman-Elston (NHE) method is a least-squares-based VC method for mapping of QTL in sib pairs (Elston et al.). Using simulation, we investigate the robustness of the NHE to marked nonnormality, by means of the same distributions and worst-case conditions identified by Allison et al. for the ML approach (i.e., 100 pairs; high residual sibling correlation). Results showed that, when marked nonnormality is present, the NHE can be used without severe type I error-rate inflation, even at very small alpha levels.

Chromosome Mapping↗
PubMedDate not supplied

Red blood cell indices, cation content, and membrane cation transports.

In sickle cell disease, in the homozygous state, the increased heterogeneity of erythrocytes results mainly from membrane defects secondary to Hb S polymerization and the increased survival of F cells. The density distribution curve, using phthalate esters or the red blood cell indices measured with the H*3 system, are useful methods for the hematological follow-up of patients under specific therapies. The methods evaluating the red blood cell cation contents and the abnormal membrane potassium transport pathways are also described, in order to evaluate agents which can restore normal hemoglobin concentration and water content in dehydrated sickle cells.

Anemia, Sickle Cell↗
PubMed2004

Random drift and culture change.

We show that the frequency distributions of cultural variants, in three different real-world examples--first names, archaeological pottery and applications for technology patents--follow power laws that can be explained by a simple model of random drift. We conclude that cultural and economic choices often reflect a decision process that is value-neutral; this result has far-reaching testable implications for social-science research.

Computer Simulation↗
PubMed2003

Outcome validation of the Beckman Coulter access analyzer in a second-trimester Down syndrome serum screening application.

BACKGROUND: Mid-trimester maternal serum alpha-fetoprotein (AFP) and unconjugated estriol (uE3) are 30% lower and human chorionic gonadotropin (hCG) is twofold higher in Down syndrome pregnancies compared with unaffected pregnancies. In maternal serum screening, patient-specific risks are calculated using published gaussian frequency distribution parameters for these three markers obtained with previously available immunoassays. New immunoassays must generate similar distribution parameters if the accuracy of assigned risks and overall performance of prenatal screening are to be maintained. METHODS: Agreement between the Beckman Coulter Access and the Bayer Immuno 1 assays for AFP and hCG and the Amersham Amerlex-M RIA for uE3 was assessed in 558 fresh sera. Precision was measured over 6 weeks. Median concentrations were calculated by regression of 568 Caucasian singleton pregnancy samples against gestational age in days. Frozen mid-trimester sera from 44 confirmed Down syndrome singleton pregnancies (cases) were selected without conscious bias for reanalysis, and each case was matched with five control specimens from unaffected pregnancies. Serum markers were expressed as the multiple of the median (MoM) concentration derived from the control samples, corrected for maternal weight and converted to their log-equivalent values. Normality was assessed using probability plots and the Shapiro-Wilk W-test. Gaussian distribution parameters were compared with established values, and Down syndrome risk calculations were assessed with a commonly used risk algorithm. RESULTS: The Access AFP and hCG assays had consistent proportional agreement with the established assays, whereas agreement between the uE3 methods was less consistent. Analytical imprecision was 3-6% at mid-trimester concentrations. Normal distributions were obtained for the log MoM values of all three markers in both the Down syndrome and unaffected populations, and their gaussian distribution parameters compared well with established values. The performance of the Access assays in an established trivariate risk algorithm for Down syndrome was equal to the performance exhibited by traditional methods. CONCLUSION: The Beckman Coulter Access analyzer provides valid mid-trimester serum AFP, uE3, and hCG results and risk assessments when applied in a prenatal Down syndrome screening service.

Biomarkers↗
PubMed2005

A semi-Markov model based on generalized Weibull distribution with an illustration for HIV disease.

Multi-state stochastic models are useful tools for studying complex dynamics such as chronic diseases. Semi-Markov models explicitly define distributions of waiting times, giving an extension of continuous time and homogeneous Markov models based implicitly on exponential distributions. This paper develops a parametric model adapted to complex medical processes. (i) We introduced a hazard function of waiting times with a U or inverse U shape. (ii) These distributions were specifically selected for each transition. (iii) The vector of covariates was also selected for each transition. We applied this method to the evolution of HIV infected patients. We used a sample of 1244 patients followed up at the hospital in Nice, France.

Adult↗
PubMed2001

Gill parasites of Cephalopholis argus (Teleostei: Serranidae) from Moorea (French Polynesia): site selection and coexistence.

The distribution and coexistence of gill ectoparasites of 121 specimens of Cephalopholis argus Bloch et Schneider, caught between October 1994 and October 1995, were investigated. Adults of the monogenean Benedenia sp. and copepod Hatschekia sp., the larval caligid copepod Caligus sp. (copepodite and chalimus stages), and praniza larvae of the isopod Gnathia sp. were found. All species were aggregated within the host population. Infracommunities were poor, with only 40.5% of fish infected by two parasite species. Only two individual fish harboured all the parasite species observed at the component community level. Prevalences were less than 50% and mean intensities were low (less than 6 parasites/host). No dominant parasite species were observed in the host population. The spatial distribution of each parasite species was studied on different partitions of the gill arches. Adult parasite stages that are mobile showed much overlap in their distribution, whereas temporarily attached larvae of Caligidae were more site specific. Copepodite and chalimus larvae showed niche restriction that is probably due to gregarious behaviour. Positive associations between caligid larvae reflected intraspecific interaction for site and/or resources. Each of the Caligus sp. larval stages prefers specific sites, as do the adults, which occur exclusively in the buccal cavity of the host. Infracommunities were too poor and too few to induce processes of interspecific competition.

Animals↗
PubMed2004

Use of carvacrol and cymene to control growth and viability of Listeria monocytogenes cells and predictions of survivors using frequency distribution functions.

The antibacterial action of carvacrol and cymene on two Listeria monocytogenes strains (STCC4031 and NCTN4032) was studied. Carvacrol or cymene showed inhibitory effect on the growth of L. monocytogenes during lag and exponential growth phases and was more evident with increasing concentrations in brain heart infusion broth at 30 degrees C. Carvacrol or cymene also decreased the survival of mid-exponential-growth-phase L. monocytogenes STCC4031 cells in potassium-N-2-hydroxy-ethylpiperazine-N-ethanesulfo nic acid, at 30 degrees C. The combination of carvacrol and cymene resulted in an increased antibacterial effect on the growth and a synergistic effect on the viability of L. monocytogenes compared with the natural compounds applied separately. The analysis of survival curves by the Weibull frequency distribution function allowed an accurate prediction of the level of inactivation achieved. Interestingly, an important bactericidal effect (4.7-log reduction) of low concentrations of both antimicrobials combined (0.75 mM) was observed on L. monocytogenes in carrot juice. This study indicates the potential use of carvacrol and cymene applied simultaneously for preservation of minimally processed foods.

Anti-Bacterial Agents↗
PubMed2000

Computations for group sequential boundaries using the Lan-DeMets spending function method.

We describe an interactive Fortran program which performs computations related to the design and analysis of group sequential clinical trials using Lan-DeMets spending functions. Many clinical trials include interim analyses of accumulating data and rely on group sequential methods to avoid consequent inflation of the type I error rate. The computations are appropriate for interim test statistics whose distribution or limiting distribution is multivariate normal with independent increments. Recent theoretical results indicate that virtually any design likely to be used in a clinical trial will fall into this category. Interim analyses need not be equally spaced, and their number need not be specified in advance. In addition to determining sequential boundaries using an alpha spending function, the program can perform power computations, compute probabilities associated with a given set of boundaries, and generate confidence intervals.

Clinical Trials as Topic↗
PubMed2006

Distributions of PM2.5 source strengths for cooking from the Research Triangle Park particulate matter panel study.

Emission rates, decay rates, and cooking durations are reported from continuous PM2.5 (particulate matter less than 2.5 microm) concentrations measured using personal DataRam nephelometers (1-min time resolution) from the Research Triangle Park (RTP) PM panel study. The study (n = 37 participants) included monitoring for 7 consecutive days in each of four consecutive seasons (summer 2000 through spring 2001). Cooking episodes (n = 411) were selected using time-activity diaries and criteria for cooking event duration, peak concentration level, and decay curve quality. Averaged across all cooking events, mean source strengths were 36 mg/min (median = 12 mg/min), mean decay rates were 0.27 h(-1) (0.17 h(-1)), and mean cooking durations were 11 min (7 min). Cooking events were further separated into one of seven categories representing cooking method: burned food (oven cooking, toaster, or stovetop cooking), grilling, microwave, toaster oven, frying, oven cooking, and stovetop cooking. The highest mean source strengths were identified from burned food (mean = 470 mg/min), grilling (173 mg/min), and frying (60 mg/ min); differences between both burned food and grilling compared with all remaining cooking methods were statistically significant. Source strengths, decay rates, and cooking durations were also compared by season and typical meal times (8:00 a.m., 12:00 p.m., and 6:00 p.m.); differences were generally not statistically significant for these cases. Mean source strengths using electric appliances were typically a factor of 2 greater than those using gas appliances for identical cooking methods (frying, oven cooking, or stovetop cooking), although in all cases the difference was not statistically significant. Distributions of source strengths and decay rates for cooking events were also compared among study subjects to assess both within- and between-subject variability. Each subject's distribution of source strengths during the study tended to be either lower than the overall study average (and with lower variability) or higher than the overall study average (and with higher variability). No relationships could be found between source strength and either subject characteristics (age, gender, employment status) or home characteristic (daily air exchange rate). The large number of cooking events and the broad range of cooking activities included in this analysis makes the reported distributions of PM2.5 source strengths useful for probabilistic exposure modeling even though the study population was limited.

Air Pollutants↗
PubMed2005

Efficient kernel density estimation of shape and intensity priors for level set segmentation.

We propose a nonlinear statistical shape model for level set segmentation which can be efficiently implemented. Given a set of training shapes, we perform a kernel density estimation in the low dimensional subspace spanned by the training shapes. In this way, we are able to combine an accurate model of the statistical shape distribution with efficient optimization in a finite-dimensional subspace. In a Bayesian inference framework, we integrate the nonlinear shape model with a nonparametric intensity model and a set of pose parameters which are estimated in a more direct data-driven manner than in previously proposed level set methods. Quantitative results show superior performance (regarding runtime and segmentation accuracy) of the proposed nonparametric shape prior over existing approaches.

Algorithms↗
PubMed2005

An association between inflammatory state and left ventricular hypertrophy in hemodialysis patients.

This study was performed to investigate the potential relationship between left ventricular hypertrophy (LVH) and proinflammatory cytokines in hemodialysis (HD) patients and the effect of HD on cytokine production. Serum interleukin 1 beta (IL-1 beta), interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) measurements and echocardiographic studies were performed in 35 stable HD patients. A variety of probable risk factors for LVH including age, HD duration, blood pressure (BP), body mass index, lipid profile, hemoglobin, albumin, parathormone and homocysteine levels were also investigated. Additionally, the effect of HD procedure on cytokine levels was evaluated. Predialysis serum levels of IL-1beta, IL-6, TNF-alpha, and homocysteine in HD patients were compared with 12 healthy subjects. Left ventricular hypertrophy was demonstrated in 20 (57%) of HD patients by echocardiography. Left ventricular mass index (LVMI) was correlated positively with systolic BP (r=0.556, p=0.001), diastolic BP (r=0.474, p=0.004), and serum levels of TNF-alpha (r=0.446, p=0.009). Multiple regression analysis showed that systolic BP and TNF-alpha levels were significant independent predictors of LVH. No relationship was observed between LVH and other parameters. The mean predialysis serum level of IL-6 was significantly higher in HD patients compared to healthy controls (15.7 +/- 8.7 vs. 7.3 +/- 0.7 pg/ mL, p=0.001). Predialysis serum levels of TNF-alpha in HD patients were higher when compared to healthy subjects, but the difference was not statistically significant (8.3 +/- 3 vs. 7 +/- 1.45 pg/mL, respectively, p>0.05). However, serum levels of IL-6 and TNF-alpha significantly elevated after HD, when compared to predialysis levels (from 15.7 +/- 8.7 to 17.8 +/- 9.5 pg/mL, p=0.001 and from 8.3 +/- 3.0 to 9.9 +/- 3.5 pg/mL p=0.004, respectively). As a conclusion, in addition to BP, proinflammatory cytokines, TNF-alpha in particular, seem to be associated with LVH in ESRD patients.

Adolescent↗
PubMed2004

The use of the compound probability density function in ultrasonic tissue characterization.

Recently, a compound probability density function (pdf) was proposed to model the envelope of the ultrasonic backscattered echo from tissues. This pdf will allow local and global variations in scattering cross sections and even multiple scattering in tissue. It approximates to the Nakagami, K or Rayleigh distributions under different limiting conditions, thus making it very versatile. In this work, a new parameter associated with compound pdf, speckle factor, has been introduced to characterize the scattering conditions. The usefulness of this parameter for tissue characterization has been explored through computer simulation of ultrasonic A scans and analyses of the data collected from tissue-mimicking phantoms. Results suggest the potential applications of the compound pdf and its parameters in ultrasonic tissue characterization.

Algorithms↗
PubMed1999

Statistical report from Uludag Poison Information Center--34-month experience.

Management of poisoned patient requires accurate knowledge of intoxication. Uludaŏ Poison Information Center (UPIC), founded in January 1996, provides acquired information 24 hours a day 7 days a week for physicians and consultants. We received 2270 phone calls since January 1996 till October 1998 and evaluated the cases statistically regarding "distribution of age and gender", "calling time after poison exposure", "source of poisoning", "reason for intoxication" and "source of calls" to reveal the distinguishing features of intoxication. Intoxication was mostly seen between 14-25 years of age (964 cases, 42.46%) and in females (1367 cases, 60.22%). Drugs (1400 cases, 61.67%) were the main source and suicide attempts (930 cases, 40.9%) were the main reason of poisoning. Most of the calls were from healthcare professionals (1347, 59.33%).

Humans↗
PubMed2002

Egg distributions and the information a solitary parasitoid has and uses for its oviposition decisions.

Approximately three decades ago the question was first answered "whether parasitoids are able to assess the number or origin of eggs in a host" for a solitary parasitoid, Leptopilina heterotoma, by fitting theoretically derived distributions to empirical ones. We extend the set of different theoretically postulated distributions of eggs among hosts by combining searching modes and abilities in assessing host quality. In the models, parasitoids search either randomly (Poisson) (1) or by vibrotaxis (Negative Binomial) (2). Parasitoids are: (a) assumed to treat all hosts equally, (b) able to distinguish them in unparasitised and parasitised hosts only, (c) able to distinguish them by the number of eggs they contained, or (d) able to recognise their own eggs. Mathematically tractable combinations of searching mode (1 and 2) and abilities (a,b,c,d) result in seven different models (M1a, M1b, M1c, M1d, M2a, M2b and M2c). These models have been simulated for a varying number of searching parasitoids and various mean numbers of eggs per host. Each resulting distribution is fitted to all theoretical models. The model with the minimum Akaike's information criterion (AIC) is chosen as the best fitting for each simulated distribution. We thus investigate the power of the AIC and for each distribution with a specified mean number of eggs per host we derive a frequency distribution for classification. Firstly, we discuss the simulations of models including random search (M1a, M1b, M1c and M1d). For M1a, M1c and M1d the simulated distributions are correctly classified in at least 70% of all cases. However, in a few cases model M1b is only properly classified for intermediate mean values of eggs per host. The models including vibrotaxis as searching behaviour (M2a, M2b and M2c) cannot be distinguished from those with random search if the mean number of eggs per host is low. Among the models incorporating vibrotaxis the three abilities are detected analogously as in models with random search. Experiments with two species of solitary parasitoids (L. heterotoma and Asobara tabida) are conducted. All theoretically postulated distributions are separately fitted to the resulting experimental egg distributions. The AIC criterion is used to choose the best fitting theoretical distribution. For both parasitoid species the frequency distribution of best fitting models for experimental data is compared to the classification of distributions generated by simulations. This leads to the conclusion that both L. heterotoma and A. tabida are able to distinguish between parasitised and unparasitised hosts. For L. heterotoma the results point to an ability to assess the number of eggs in a host, whereas A. tabida does not seem to have this ability. This difference suggests that an egg is more valuable for L. heterotoma than for A. tabida.

Animals↗