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Population toxicokinetic analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin using Bayesian techniques.

Understanding the kinetics of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) concentrations in humans is an important step for TCDD cancer risk assessment. In this paper longitudinal series of serum TCDD concentration measurements on U.S. veterans of the Vietnam war, who were exposed to dioxin during herbicide-spraying operations, are studied. The overall aim is to use these data to infer the dynamics of TCDD concentrations in humans. This is done by identifying a kinetic model describing the dioxin time course at the individual level. The individual toxicokinetic model is then expanded into a pop

The cellular lethality of radiation-induced chromosome translocations in human lymphocytes.

Recent evidence has shown that translocation frequencies decline over time. This phenomenon might be explained by the co-occurrence of translocations in cells that also contain dicentrics, in which case translocations would be eliminated as a by-product of selection against dicentrics. Alternatively, a fraction of translocations may themselves be lethal. Here we describe our initial approaches to develop mathematical models to test whether the decline in translocation frequencies results from the first, the second, or a combination of these two possibilities. The models assumed that all chromo

Dosimetry of source stepping for intravascular brachytherapy.

PURPOSE: Both beta and gamma sources of fixed length are currently used in the catheter-based intravascular brachytherapy (IVBT). Source stepping is often used to treat a lesion longer than the effective treatment length of the source. A major challenge for the stepping procedure is to attain a perfect dosimetric match (uniform dose) at the source junction. This work presents a quantitative and systematic dosimetric analysis for source stepping during an IVBT procedure. MATERIALS AND METHODS: The three most commonly used beta and gamma sources (192Ir by BEST, 90Sr by NOVOSTE and 32P by Guidan

Bayesian methods for cluster randomized trials with continuous responses.

Bayesian methods for cluster randomized trials extend the random-effects formulation by allowing both the use of external evidence on parameters and straightforward relaxation of the standard normality and constant variance assumptions. Care is required in specifying prior distributions on variance components, and a number of different options are explored with implied prior distributions for other parameters given in closed form. Markov chain Monte Carlo (MCMC) methods permit the fitting of very general models and the introduction of parameter uncertainty into power calculations. We illustrat

Chromosome aberrations induced by light ions: Monte Carlo simulations based on a mechanistic model.

PURPOSE: To investigate the mechanisms underlying the induction of chromosome aberrations by ionizing radiation, focusing attention on DNA damage severity, interphase chromosome geometry and the distribution of DNA strand breaks. METHODS: An ab initio biophysical model of aberration induction in human lymphocytes specific for light ions was developed, based on the assumption that 'complex lesions' (clustered DNA breaks) produce aberrations, whereas less severe breaks are repaired. It was assumed that interphase chromosomes are spatially localized and that chromosome break free-ends rejoin pai

Determination of power and sample size in the design of clinical trials with failure-time endpoints and interim analyses.

An important but difficult task in the design of a clinical trial to compare time to failure between two treatment groups is determination of the number of patients required to achieve a specified power of the test. Because patients typically enter the trial serially and are followed until they fail or withdraw from the study or until the study is terminated, the power of the test depends on the accrual pattern, the noncompliance rate, and the withdrawal rate in addition to the actual survival distributions of the two groups. Incorporating interim analyses and the possibility of early stopping

Human immunodeficiency virus transmission and the role of other sexually transmitted diseases. Measures of association and study design.

BACKGROUND: Studies have reported that infection with certain sexually transmitted diseases (STD), such as chancroid, gonorrhea, and genital herpes, enhances the probability of human immunodeficiency virus (HIV) transmission by sexual contact with an infected partner. Epidemiologic studies vary in design from longitudinal to cross-sectional, with varying periods of follow-up or retrospective history of exposure to STD. The major difficulty in assessing the results of past work centers on the validity and precision of widely used measures of association, such as relative risk (RR) and odds rati

Selective muscle activation following electrical stimulation of the collateral ligaments of the human knee joint.

The objective of this study was to establish the presence of a local neurosensory reflex are from mechanoreceptors in human collateral ligaments and joint capsule to knee muscles and to determine if these muscles could be selectively activated as varus or valgus stabilizers using randomized trials. All studies were performed in the research department laboratories. Eleven subjects were recruited from the university staff and students based on no prior history of knee ailments. Subjects laid supine on an experimentation table as a current-modulated electrical stimulation was provided through th

Beta-particle dosimetry in radiation synovectomy.

Beta-particle dosimetry of various radionuclides used in the treatment of rheumatoid arthritis was estimated using Monte Carlo radiation transport simulation coupled with experiments using reactor-produced radionuclides and radiachromic film dosimeters inserted into joint phantoms and the knees of cadavers. Results are presented as absorbed dose factors (cGy-cm2/MBq-s) versus depth in a mathematical model of the rheumatoid joint which includes regions of bone, articular cartilage, joint capsule, and tissue (synovium) found in all synovial joints. The factors can be used to estimate absorbed do

Statistical models for autocorrelated count data.

A generalized linear mixed model is an increasingly popular choice for the modelling of correlated, non-normal responses in a regression setting. A number of methods are currently available for fitting a generalized linear mixed model including Monte-Carlo Markov-Chain maximum likelihood algorithms, approximate maximum likelihood (PQL), iterative bias correction, and others. Of interest in this paper is to compare the parameter estimation of the various methods in the modelling of a count data set, the incidence of polio in the USA over the period 1970-1983, using a longlinear generalized line

Application of the biotic ligand model for regulatory purposes to selected rivers in Argentina with extreme water-quality characteristics.

The biotic ligand model (BLM) was used to assess copper (Cu) bioavailability, toxicity, water-effect ratios (WER), and Cu site-specific water-quality criteria (SSWQC) in the Matanza River and Pilcomayo River, Argentina, where anthropogenic inputs and natural phenomena have led to high concentrations of chemical species capable of reducing metal toxicity: Sodium, total hardness, alkalinity, dissolved organic carbon, and suspended particulate matter (SPM), as well as other metals. The purpose of this study was to evaluate the feasibility of developing Cu-SSWQC from a modified scenario of the BLM

Economic evaluation of vampire bat (Desmodus rotundus) rabies prevention in Mexico.

Vampire bat rabies causes significant impacts within its endemic range in Mexico. These impacts include livestock mortality, animal testing costs, post-exposure prophylaxis costs, and human mortality risk. Mitigation of the impacts can be achieved by vaccinating livestock and controlling vampire bat populations. A benefit-cost analysis was performed to examine the economic efficiency of these methods of mitigation, and Monte Carlo simulations were used to examine the impact that uncertainty has on the analysis. We found that livestock vaccination is efficient, with benefits being over six time

Microscopic elasticity from MD. I. Bulk solid and fluid systems.

Computational modeling, such as molecular dynamics and Monte Carlo simulations, can be used to estimate the elastic properties of materials through various stress and strain relationships. Here, we demonstrate the effectiveness of the stress-stress fluctuation (SSF) method to estimate the elastic properties of simple van der Waals and molecular materials. The SSF method allows computation of the complete elasticity tensor from a single equilibrium simulation without requiring any type of deformation. While extensively used to characterize the elastic coefficients of crystalline solids and glas

A Bayesian additive spatiotemporal model for young adolescent birth records in the Philippines.

Quantitative studies about young adolescent pregnancy in the Philippines had been done through the analysis of survey data. Official birth records provide a more advantageous data source in examining the dynamics of the young adolescent pregnancy due to regular recording of births. In this study, we propose a statistical methodology utilizing official birth records through a Bayesian hierarchical framework. The method accounts for the unique features of the aggregated young adolescent birth counts such as being a spatiotemporal data with known upper bounds and being characterized by the presen

Distilling Object Detectors via Monte Carlo Dropout.

Knowledge distillation (KD) has become a fundamental technique for model compression in object detection tasks. The data noise and training randomness may cause the knowledge of the teacher model to be unreliable, referred to as knowledge uncertainty. Existing methods neglect this uncertainty, potentially hindering the student's capacity to capture and understand latent "dark knowledge". In this work, we introduce a novel strategy that explicitly incorporates knowledge uncertainty, named Uncertainty-Driven Knowledge Extraction and Transfer (UET). Given the unknown, high-dimensional nature of t

Determination of Quantum Yield in Scattering Media Using Monte Carlo Photoluminescence Cascade Simulation and Integrating Sphere Measurements.

Accurate determination of the quantum yield (Φf) in scattering media is essential for numerous scientific and industrial applications, but it remains challenging due to re-absorption and scattering-induced biases. In this study, we present a GPU-accelerated Monte Carlo simulation framework that solves the full fluorescence radiative transfer equation (FRTE), incorporating spectrally dependent absorption, scattering, and fluorescence cascade processes. The model accounts for re-emission shifts, energy scaling due to the Stokes shift and implements a digital optical twin of the experimental setu

Censoring-robust estimation in fixed sample time-to-event clinical trials with adaptive randomization.

Adaptive randomization is a clinical trial design feature used to modify treatment allocation probabilities during accrual. In time-to-event trials, the impact of adaptive randomization is less well understood for estimating treatment efficacy in the presence of time-varying effects [e.g., relative risk of progression to acquired immunodeficiency syndrome (AIDS) or death changes over time]. Here, we focus on time-to-event trials where the scientific estimand is a marginal hazard ratio in the absence of intermittent censoring over the support of observed times. We analytically show that adaptiv

Predicting Organometallic Intermediates in the Surface-Assisted Ullmann Coupling of Chrysene Isomers.

On-surface polymerization of functional organic molecules has been recently recognized as a promising route to persistent low-dimensional structures with tailorable properties. In this contribution, using the coarse-grained Monte Carlo simulation method, we study the initial stage of the Ullmann coupling of doubly halogenated chrysene isomers adsorbed on a catalytically active (111) crystalline surface. To that end, we focus on the formation of labile metal-organic precursor structures preceding the covalent bonding of chrysene monomers. Four monomeric chrysene units with differently distribut

Стратегия Монте-Карло по планированию последующей медицинской деятельности: пример множественных данных о миеломе.

Ключевое значение для индивидуального лечения раковых заболеваний имеет разработка стратегий последующей деятельности в интересах конкретных пациентов. Весьма полезными были бы инструменты оказания помощи врачам в принятии решений о лечении и планировании последующих мероприятий на основе предпочтений пациентов и медицинских данных. Эти инструменты должны включать реалистичные модели развития заболеваний в рамках лечения, многоцелевую оптимизацию стратегий лечения и эффективные алгоритмы для индивидуализации последующих мер с учетом истории пациента. Мы предлагаем модель эволюции рака с исполь

Совпадение в полном тексте источника
… Thinning and multilevel Monte Carlo methods for piecewise deterministic (Markov) processes with an application to a stochastic Morris-Lecar model . Adv in Appl Probab . 2020 ; 52 ( 1 ): 138 – 172 . doi: 10.1017/apr.2019.55 38 Del Moral P . Non Linear Filtering: Interacting Particle Solution . …

Cumulative risk assessment of dietary exposure of the adult population in Serbia to pesticides that have chronic effects on the thyroid gland through fresh fruits and vegetables.

In contrast to the traditional approach to risk assessment, which focuses on a single chemical, cumulative exposure and risk assessment considers the consequences of exposure to multiple chemical combinations. A cumulative risk assessment of dietary exposure of adult females and adult males to pesticides with chronic effects on the thyroid was conducted by estimation of the Total Margin of Exposure (MOET). Exposure to each active substance was estimated using a second-order Monte Carlo simulation. Input values for the simulation were based on over 2300 conventionally produced fruit and vegetab