(D,Ds+)-->VV decays in two models: An SU(3)-symmetry model and a factorization model, with final-state interactions.
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Journal Article↗
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Results for “Model”
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Modelling the first two delays of the "three-delays model" for emergency obstetric care in Bangladesh: a choice model approach.
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Asia↗
[Effect of vacuum vibration investing and vacuum mixing technics on the properties LAW-cast model investment and on the accuracy of cast model frameworks of cobalt-chromium-molybdenum alloys. 2. Studies on accuracy of cast model frameworks of cobalt-chromium-molybdenum alloys using different investing technics].
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Chromium Alloys↗
Impact of modelling intra-subject variability on tests based on non-linear mixed-effects models in cross-over pharmacokinetic trials with application to the interaction of tenofovir on atazanavir in HIV patients.
We evaluated the impact of modelling intra-subject variability on the likelihood ratio test (LRT) and the Wald test based on non-linear mixed effects models in pharmacokinetic interaction and bioequivalence cross-over trials. These tests were previously found to achieve a good power but an inflated type I error when intra-subject variability was not taken into account. Trials were simulated under H0 and several H1 and analysed with the NLME function. Different configurations of the number of subjects n and of the number of samples per subject J were evaluated for pharmacokinetic interaction and bioequivalence trials. Assuming intra-subject variability in the model dramatically improved the type I error of both interaction tests. For the Wald test, the type I error decreased from 22, 14 and 7.7 per cent for the original (n = 12, J = 10), intermediate (n = 24, J = 5) and sparse (n = 40, J = 3) designs, respectively, down to 7.5, 6.4 and 3.5 per cent when intra-subject variability was modelled. The LRT achieved very similar results. This improvement seemed mostly due to a better estimation of the standard error of the treatment effect. For J = 10, the type I error was found to be closer to 5 per cent when n increased when modelling intra-subject variability. Power was satisfactory for both tests. For bioequivalence trials, the type I error of the Wald test was 6.4, 5.7 and 4.2 per cent for the original, intermediate and sparse designs, respectively, when modelling intra-subject variability. We applied the Wald test to the pharmacokinetic interaction of tenofovir on atazanavir, a novel protease inhibitor. A significant decrease of the area under the curve of atazanavir was found when patients received tenofovir.
Adenine↗
The Choice Probabilities of the Latent-Scale Model Satisfy the Size-Independent Model When n Is Small.
Two probabilistic models for subset choices are compared. The first one, due to Marley (1993), was dubbed the latent-scale model by Regenwetter, Marley, and Joe (1996). The second one is Falmagne and Regenwetter's (1996) size-independent model of approval voting. We show that for up to five choice alternatives, the choice probabilities generated by the latent-scale model can be explained also by the size-independent model. The proof uses the König-Hall theorem of graph theory and the characterization of the size-independent model by the approval-voting polytope of Doignon and Regenwetter (1997). The problem remains open for the case with more than five choice alternatives. Copyright 1998 Academic Press.
Journal Article↗
A coupled carbon-water-energy-vegetation model to assess responses of temperate forest ecosystems to changes in climate and atmospheric CO2. Part I. Model concept.
Predictions of forest ecosystem response to changes in climate and atmospheric CO(2) concentration require hierarchically structured process models. Present forest simulation models have conceptual limitations that restrict their application to climate-change studies. A major drawback of forest succession models is that they often lack physiological details in the simulation of annual tree growth. On the other hand, aggregated ecosystem models assume spatially homogeneous forests, and do not account for successional changes in forest composition and canopy structure. The concept of a new coupled carbon-water-energy-forest vegetation model is presented which attempts to overcome the main limitations of existing models by implementing a modern view of ecological hierarchy and a robust approach for scaling ecological processes in space and time.
Journal Article↗
Thermodynamical model for insertion and aggregate binding of caffeine to the homopolymer poly(riboadenylate) and model choice by data analysis.
This paper describes the model used to estimate the parameters of caffeine-poly(riboadenylate) (poly(A)) interactions from corresponding 1H-NMR measurements. The model of insertion and aggregate binding describes the non-cooperative insertion of a molecule C into an interspace between two monomers of a homopolymer in competition with aggregate binding. It contains two binding constants, K1 for insertion and K2 for the interaction of monomeric A units of the polymer with C molecules in bound aggregates, and two cooperativity parameters, Kcc for stacking of C molecules within aggregates and tau which is thought to be due to conformational adaptation of the polymer to those bound aggregates which cover more than one A unit. In contrast to other models, the size of a binding site (within the aggregates) is less than one monomeric unit, with n denoting the maximum number of C molecules per A unit in bound aggregates. The model is developed for general n by means of the method of sequence-generating functions. For n = 2 and n = 3, the correctness of the model treatment was checked by the matrix method. The model is applicable to the binding of aggregates to homopolymers, which are flexible enough to fit their structure to the aggregates.
Journal Article↗
Modeling the complexation properties of mineral-bound organic polyelectrolyte: an attempt at comprehension using the model system alumina/polyacrylic acid/M (M=Eu, Cm, Gd).
This paper contributes to the comprehension of kinetic and equilibrium phenomena governing metal ion sorption on organic-matter-coated mineral particles. Sorption and desorption experiments were carried out with Eu ion and polyacrylic acid (PAA)-coated alumina colloids at pH 5 in 0.1 M NaClO(4) as a function of the metal ion loading. Under these conditions, M interaction with the solid is governed by sorbed PAA (PAA(ads)). The results were compared with spectroscopic data obtained by time-resolved laser-induced fluorescence spectroscopy (TRLFS) with Cm and Gd. The interaction between M and PAA(ads) was characterized by a kinetically controlled process: after rapid metal adsorption within less than 1 min, the speciation of complexed M changed at the particle surface till an equilibrium was reached after about 4 days. At equilibrium, one part of complexed M was shown to be not exchangeable. This process was strongly dependent on the ligand-to-metal ratio. Two models were tested to explain the data. In model 1, the kinetically controlled process was described through successive kinetically controlled reactions that follow the rapid metal ion adsorption. In model 2, the organic layer was considered as a porous medium: the kinetic process was explained by the diffusion of M from the surface into the organic layer. Model 1 allowed a very good description of equilibrium and kinetic experimental data. Model 2 could describe the data at equilibrium but could not explain the kinetic data accurately. In spite of this disagreement, model 2 appeared more realistic considering the results of the TRLFS measurements.
Journal Article↗
Modeling the adsorption of free and heavy metal complex-bound EDTA onto red mud by a nonelectrostatic surface complexation model.
The adsorption of free and divalent heavy metal (copper, cadmium, and lead) complex-bound EDTA from metal-EDTA mixture solutions on a composite adsorbent having a heterogeneous surface, i.e., bauxite waste red mud, has been investigated and modeled with the aid of a nonelectrostatic surface complexation approach in respect to adsorbate concentration and pH dependency of EDTA adsorption. EDTA was selected as the modeling ligand in view of its wide usage as an anthropogenic chelating agent and its abundance in natural waters. The adsorption experiments were conducted for pure EDTA or metal-EDTA complexes alone, or in mixtures containing (EDTA+metal-EDTA). For all studied cases, the solid adsorbent phase concentrations of the adsorbed species were found by using the derived model equations with acceptable compatibility of experimental and theoretically generated adsorption isotherms. The model basically assumed two modes of metal bonding to the surface hydroxyls: ionic (outer-sphere) binding of the EDTA anion (H(2)Y(2-)) or anionic metal-EDTA complex (MY(2-)) to the cationic surface site ( approximately SOH(+)(2)), and outer-sphere binding of H(2)Y(2-) or MY(2-) to the neutral approximately SOH site, possibly via hydrogen-bonding. The model was useful for EDTA and metal-EDTA mixture solutions either at their natural pH of equilibration with the sorbent, or after pH elevation with NaOH titration up to pH<or=pzc of red mud. Thus adsorption of every single species (H(2)Y(2-) or MY(2-)) or of possible mixtures (H(2)Y(2-)+MY(2-)) at natural pH or after NaOH titration could be calculated by the use of simple quadratic equations at low metal loadings, once the initial concentrations of the corresponding species, i.e., [H(2)Y(2-)](0) or [MY(2-)](0), were known. The compatibility of theoretical and experimental data pairs of adsorbed species concentrations was verified by means of nonlinear regression analysis. The findings of this study, together with the previously developed (M(2+)+MY(2-)) mixtures adsorption model, can be further developed to serve environmental risk assessment concerning the expansion of a metal-organic (synthetic organic ligand or soil humic acids) contaminant plume with groundwater movement in soil basically consisting of hydrated oxide-type minerals.
Journal Article↗
Bayesian model search for mixture models based on optimizing variational bounds.
When learning a mixture model, we suffer from the local optima and model structure determination problems. In this paper, we present a method for simultaneously solving these problems based on the variational Bayesian (VB) framework. First, in the VB framework, we derive an objective function that can simultaneously optimize both model parameter distributions and model structure. Next, focusing on mixture models, we present a deterministic algorithm to approximately optimize the objective function by using the idea of the split and merge operations which we previously proposed within the maximum likelihood framework. Then, we apply the method to mixture of expers (MoE) models to experimentally show that the proposed method can find the optimal number of experts of a MoE while avoiding local maxima.
Algorithms↗
Hyperactivity and hypoactivity in a rat model of Huntington's disease: the systemic 3-nitropropionic acid model.
The present study proposes the use of systemic 3-nitropropionic acid (3-NP) treatment in rats as a model of Huntington's disease (HD). The systemic 3-NP model involves chronic injection of low dose intraperitoneal (i.p.) injections of 3-NP to rats once every 4 days over a period of time. Evidence from our experimental studies suggests that manipulating the number of injections can result in either increased nocturnal spontaneous locomotor activity (hyperactivity) or nocturnal akinesia (hypoactivity) [1]. For example, two injections of 3-NP (using the treatment of one injection every 4 days) result in hyperactivity, while four injections or more of 3-NP lead to hypoactivity [1]. The locomotor activity is recorded by Digiscan locomotor activity monitors [11]. The observation of these two types of locomotor activity is unique since no excitotoxin model has replicated a two-stage progression of a HD-like behavioral alteration. Most studies using excitotoxins like quinolinic acid (QA) and kainic acid (KA) have only reproduced the hyperactivity stage [4,5,7]. With the systemic 3-NP model, investigations into at least two stages of the disease are made possible. This allows for better assessment of intervention strategies such as neural transplants across different stages of the disease. The systemic 3-NP rat model is believed to be an improved animal model of HD.
Animals↗
The potential of chitosan in enhancing peptide and protein absorption across the TR146 cell culture model-an in vitro model of the buccal epithelium.
PURPOSE: To investigate the potential of chitosan (CS) to enhance buccal peptide and protein absorption, the TR146 cell culture model, a model of the buccal epithelium, was used. METHODS: The sensitivity of TR146 cells to several CS solutions (different salts with different MW) was investigated by using the MTS/ PMS assay. Permeability studies were performed to determine the enhancing effect of CS glutamate (1, 20, 40, 60, and 100 microg/mL) on the permeability of 3H-mannitol and fluorescein isothiocyanate labeled dextrans (FD) with various MW (4.4-19.5 kD) across the cell culture model. RESULTS: Sensitivity of TR146 cells to CS solutions depended on the concentration, the pH, and the type of CS salt. CS glutamate solutions (pH 6.0) were found to be the least harmful. CS glutamate was able to increase the permeability of model substances with MW up to 9.5 kD across the cell model. An enhancing effect was found for CS concentrations of 20 microg/mL and higher, correlating with a decrease in TEER values. The 20 microg/mL CS concentration had a negligible effect on the enzyme activity of the cells as determined by the MTS/PMS assay. CONCLUSIONS: CS glutamate is effective in enhancing the transport of macromolecules across the buccal TR146 cell culture model. Therefore. it might be a promising vehicle for peptide and protein buccal administration.
Absorption↗
Development of a new polarizable potential model of hydrogen fluoride and comparison with other effective models in liquid and supercritical states.
Development of a new polarizable potential of hydrogen fluoride through the reparametrization of the JV-P model is presented: The length of the H-F bond has been shortened and the other parameters of the model have been readjusted accordingly. The structural, thermodynamic, and liquid-vapor equilibrium properties of the new model are compared with those of other effective potential models of HF as well as with experimental data in a broad range of thermodynamic states, from near-freezing to supercritical conditions. It is found that although the reparametrization does not change the structural properties of the HF model noticeably at the level of the pair correlations, it improves the reproduction of the thermodynamic properties of hydrogen fluoride over the entire range of existence of a thermodynamically stable liquid phase and also that of the vapor-liquid coexistence curve. However, the new model, which still overestimates the close-contact separation of the HF molecules, underestimates the density of the coexisting liquid phase and overestimates the saturation pressure, probably due to the too steep repulsion of the potential function.
Journal Article↗
Detailed comparison of two molecular models of the human CD40 ligand with an x-ray structure and critical assessment of model-based mutagenesis and residue mapping studies.
The interactions between the B cell receptor CD40 and its ligand on T cells are critical for the integrity of immune responses. The human CD40 ligand gp39, a tumor necrosis factor-like protein, has been the subject of intense efforts to identify the receptor-binding site and to analyze naturally occurring mutations that compromise gp39 function in vivo. These investigations relied heavily on molecular models of gp39, built in the presence of only approximately 25% sequence identity to tumor necrosis factor. The x-ray structure of gp39 has made it possible to assess modeling accuracy and to evaluate the results of model-based mutagenesis analyses. Although the models display local errors, their accuracy was sufficient to predict the CD40-binding site, to map natural mutations, and to rationalize their effects. One of five gp39 residues critical for CD40 binding was displaced in the models, and 1 of 21 point mutants was incorrectly classified. Factors most important for the reliability of the molecular models and their successful applications were valid sequence alignments and the focus of experimental studies on regions of high prediction confidence. Analysis of mutagenesis experiments correlated with anti-gp39 monoclonal antibody binding studies to assess the conformational integrity of mutant proteins.
Amino Acid Sequence↗
Effects of model warmth on acquisition and performance of modeled behavior in chronic psychotics.
Hypotheses derived from an earlier study were tested in experimental dyads with 32 adult chronic psychotic state hospital residents of both sexes. Patients either interacted with an adult model who was noncontingently warm and rewarding, or were not exposed initially to a model. In a second phase, the model displayed task responses and novel behaviors incidental to the task, and the patient's subsequent imitation of the model under minimal demand conditions was recorded. In a third phase, the model again displayed the same behaviors, whereupon half the patients in each group were subjected to moderate (explicit verbal request) or high (verbal request plus material rewards) incentives to imitate. Under strong incentive conditions, initial differences between groups on incidental imitation vanished, indicating that a previously positive relationship with a model facilitates imitative performance but not learning.
Chronic Disease↗
Nontrivial extension of the two-dimensional ising model: the d-dimensional "molecular" model
A recently proposed molecular model is discussed as a nontrivial extension of the Ising model. For d=2 the two models are shown to be equivalent, while for d>2 the molecular model describes a peculiar second order transition from an isotropic high-temperature phase to a low-dimensional anisotropic low-temperature state. The general mean-field analysis is compared with the results achieved by a variational Migdal-Kadanoff real space renormalization group method and by standard Monte Carlo sampling for d=3. By finite size scaling the critical exponent has been found to be nu=0.44+/-0.02, thus establishing that the molecular model does not belong to the universality class of the Ising model for d>2.
Journal Article↗
Roughness exponent in two-dimensional percolation, Potts model, and clock model.
We present a numerical study of the self-affine profiles obtained from configurations of the q-state Potts (with q=2,3, and 7) and p=10 clock models as well as from the occupation states for site percolation on the square lattice. The first and second order static phase transitions of the Potts model are located by a sharp change in the value of the roughness exponent alpha characterizing those profiles. The low temperature phase of the Potts model corresponds to flat (alpha approximately 1) profiles, whereas its high temperature phase is associated with rough (alpha approximately 0.5) ones. For the p=10 clock model, in addition to the flat (ferromagnetic) and rough (paramagnetic) profiles, an intermediate rough (0.5<alpha<1) phase-associated with a soft spin-wave one-is observed. Our results for the transition temperatures in the Potts and clock models are in agreement with the static values, showing that this approach is able to detect the phase transitions in these models directly from the spin configurations, without any reference to thermodynamical potentials, order parameters, or response functions. Finally, we show that the roughness exponent alpha is insensitive to geometric critical phenomena.
Journal Article↗
Polynuclear growth model with external source and random matrix model with deterministic source.
We present a random matrix interpretation of the distribution functions which have appeared in the study of the one-dimensional polynuclear growth (PNG) model with external sources. It is shown that the distribution, GOE2 , which is defined as the square of the Gaussian orthogonal ensemble (GOE) Tracy-Widom distribution, can be obtained as the scaled largest eigenvalue distribution of a special case of a random matrix model with a deterministic source, which have been studied in a different context previously. Compared to the original interpretation of the GOE2 as "the square of GOE," ours has an advantage in that it can also describe the transition from the Gaussian unitary ensemble (GUE) Tracy-Widom distribution to the GOE2 . We further demonstrate that our random matrix interpretation can be obtained naturally by noting the similarity of the topology between a certain noncolliding Brownian motion model and the multilayer PNG model with an external source. This provides us with a multimatrix model interpretation of the multipoint height distributions of the PNG model with an external source.
Journal Article↗