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Sample records for normal mixtures simulation

  1. The Effect of Non-normality on the Power of Randomization Tests: A Simulation Study Using Normal Mixtures

    NASA Astrophysics Data System (ADS)

    Oliveira, T. A.; Branco, F.; Oliveira, A.; Minder, C. E.

    2011-09-01

    In this paper we evaluate the impact of non-normally on the power of randomization tests for two independent groups with the fifteen densities used in Marron and Wand [19] simulation study, which can all be written as normal mixtures and are believed to model many real data situations. We evaluate the power of the randomization test, and also the power of the Student-t test, as a comparison standard, with data simulated from the fifteen Marron-Wand distributions, for 81 values of effect size (from -4.0 to 4.0, by steps of 0.1) and balanced samples of 8, 16 and 32 elements. For each situation, using modules written in R [27], we have generated 20,000 samples and, for each of these, the power of the randomization tests was estimated using 1,000 data permutations. We set the value of Type I error probability at 0.05. In general, the results show that non-normality has a moderate influence on the power of the randomizations tests and that this influence reduces with increasing sample size. When we compare the non-normal distributions with the Gaussian, in terms of power, the differences range from approximately -0.05 to 0.05 (with an exception: in the case of one of the distributions, the differences range from 0.058 to 0.362). Concerning the comparison of the randomization test with the Student-t test, it was found that they have similar power, with some advantage to the former. In general, the differences in power are insignificant (from -0.013 to 0.015), but in one case, that of a non-normal distribution with outliers, the gains reach a maximum of 0.106. It is important to note that our results were obtained with balanced groups and with the same distribution for both groups. They can not therefore be generalized to situations where the groups are not balanced, have different distributions or are heteroscedastic.

  2. Symmetric normal mixtures

    NASA Technical Reports Server (NTRS)

    Turmon, Michael

    2004-01-01

    We consider mixture density estimation under the symmetry constraint x = Az for an orthogonal matrix A. This distributional constraint implies a corresponding constraint on the mixture parameters. Focusing on the gaussian case, we derive an expectation-maximization (EM) algorithm to enforce the constraint and show results for modeling of image feature vectors.

  3. A Skew-Normal Mixture Regression Model

    ERIC Educational Resources Information Center

    Liu, Min; Lin, Tsung-I

    2014-01-01

    A challenge associated with traditional mixture regression models (MRMs), which rest on the assumption of normally distributed errors, is determining the number of unobserved groups. Specifically, even slight deviations from normality can lead to the detection of spurious classes. The current work aims to (a) examine how sensitive the commonly…

  4. Not Quite Normal: Consequences of Violating the Assumption of Normality in Regression Mixture Models

    ERIC Educational Resources Information Center

    Van Horn, M. Lee; Smith, Jessalyn; Fagan, Abigail A.; Jaki, Thomas; Feaster, Daniel J.; Masyn, Katherine; Hawkins, J. David; Howe, George

    2012-01-01

    Regression mixture models, which have only recently begun to be used in applied research, are a new approach for finding differential effects. This approach comes at the cost of the assumption that error terms are normally distributed within classes. This study uses Monte Carlo simulations to explore the effects of relatively minor violations of…

  5. Growth mixture modeling with non-normal distributions.

    PubMed

    Muthén, Bengt; Asparouhov, Tihomir

    2015-03-15

    A limiting feature of previous work on growth mixture modeling is the assumption of normally distributed variables within each latent class. With strongly non-normal outcomes, this means that several latent classes are required to capture the observed variable distributions. Being able to relax the assumption of within-class normality has the advantage that a non-normal observed distribution does not necessitate using more than one class to fit the distribution. It is valuable to add parameters representing the skewness and the thickness of the tails. A new growth mixture model of this kind is proposed drawing on recent work in a series of papers using the skew-t distribution. The new method is illustrated using the longitudinal development of body mass index in two data sets. The first data set is from the National Longitudinal Survey of Youth covering ages 12-23 years. Here, the development is related to an antecedent measuring socioeconomic background. The second data set is from the Framingham Heart Study covering ages 25-65 years. Here, the development is related to the concurrent event of treatment for hypertension using a joint growth mixture-survival model.

  6. Addressing extrema and censoring in pollutant and exposure data using mixture of normal distributions

    PubMed Central

    Li, Shi; Batterman, Stuart; Su, Feng-Chiao; Mukherjee, Bhramar

    2013-01-01

    Background Volatile organic compounds (VOC), which include many hazardous chemicals, have been used extensively in personal, commercial and industrial products. Due to the variation in source emissions, differences in the settings and environmental conditions where exposures occur, and measurement issues, distributions of VOC concentrations can have multiple modes, heavy tails, and significant portions of data below the method detection limit (MDL). These issues challenge standard parametric distribution models needed to estimate the exposures, even after log-transformation of the data. Methods This paper considers mixture of distributions that can be directly applied to concentration and exposure data. Two types of mixture distributions are considered: the traditional finite mixture of normal distributions, and a semi-parametric Dirichlet process mixture (DPM) of normal distributions. Both methods are implemented for a sample data set obtained from the Relationship between Indoor, Outdoor and Personal Air (RIOPA) study. Performance is assessed based on goodness-of-fit criteria that compare the closeness of the density estimates with the empirical density based on data. The goodness-of-fit for the proposed density estimation methods are evaluated by a comprehensive simulation study. Results The finite mixture of normals and DPM of normals have superior performance when compared to the single normal distribution fitted to log-transformed exposure data. The advantages of using these mixture distributions are more pronounced when exposure data have heavy tails or a large fraction of data below the MDL. Distributions from the DPM provided slightly better fits than the finite mixture of normals. Additionally, the DPM method avoids certain convergence issues associated with the finite mixture of normals, and adaptively selects the number of components. Conclusions Compared to the finite mixture of normals, DPM of normals has advantages by characterizing uncertainty

  7. Prediction of reserves using multivariate power-normal mixture distribution

    NASA Astrophysics Data System (ADS)

    Ling, Ang Siew; Hin, Pooi Ah

    2016-10-01

    Recently, in the area on stochastic loss reserving, there are a number of papers which analyze the individual claims data using the Position Dependent Marked Poisson Process. The present paper instead uses a different type of individual data. For the i-th (1≤i≤n) customer, these individual data include the sum insured si together with the amount paid yi j and the amount ai j reported but not yet paid in the j-th (1 ≤ j ≤ 6) development year. A technique based on multivariate power-normal mixture distribution is already available for predicting the future value (yi j + 1, ai j + 1) using the present year value (yi j, ai j) and the sum insured si. Presently the above technique is improved by the transformation of distribution which is defined on the whole real line to one which is non-negative and having approximately the same first four moments as the original distribution. It is found that, for the dataset considered in this paper, the improved method gives a better estimate for the reserve when compared with the chain ladder reserve estimate. Furthermore, the method is expected to provide a fairly reliable value for the Provision of Risk Margin for Adverse Deviation (PRAD).

  8. REFLEAK: NIST Leak/Recharge Simulation Program for Refrigerant Mixtures

    National Institute of Standards and Technology Data Gateway

    SRD 73 NIST REFLEAK: NIST Leak/Recharge Simulation Program for Refrigerant Mixtures (PC database for purchase)   REFLEAK estimates composition changes of zeotropic mixtures in leak and recharge processes.

  9. Normal and anomalous diffusion in highly confined hard disk fluid mixtures.

    PubMed

    Ball, C D; MacWilliam, N D; Percus, J K; Bowles, R K

    2009-02-07

    Monte Carlo simulation is used to study binary mixtures of two-dimensional hard disks, confined to long, narrow, structureless pores with hard walls, in a regime of pore sizes where the large particles exhibit single file diffusion while the small particles diffuse normally. The dynamics of the small particles can be understood in the context of a hopping time, tau(21), that measures the time it takes for a small particle to escape the single file cage formed by its large particle neighbors, and can be linked to the long time diffusion coefficient. We find that tau(21) follows a power law as a function of the reduced pore radius for a wide range of particle size ratios with an exponent, alpha, that is independent of the size ratio, but linearly dependent on the Monte Carlo step size used in the dynamic scheme. The mean squared displacement of the small particles as a function of time exhibits two dynamic crossovers. The first, from normal to anomalous diffusion, occurs at intermediate times then the system returns to normal diffusion in the long time limit. We also find that the diffusion coefficient is related to tau(21) through a power law with exponent beta=-0.5, as predicted by theory. Finally, we show that particle separation in a binary mixture will be optimal at the pore radius that causes the large particles to undergo their transition from normal to anomalous diffusion.

  10. Inference from Multiple Imputation for Missing Data Using Mixtures of Normals.

    PubMed

    Steele, Russell J; Wang, Naisyin; Raftery, Adrian E

    2010-05-01

    We consider two difficulties with standard multiple imputation methods for missing data based on Rubin's t method for confidence intervals: their often excessive width, and their instability. These problems are present most often when the number of copies is small, as is often the case when a data collection organization is making multiple completed datasets available for analysis. We suggest using mixtures of normals as an alternative to Rubin's t. We also examine the performance of improper imputation methods as an alternative to generating copies from the true posterior distribution for the missing observations. We report the results of simulation studies and analyses of data on health-related quality of life in which the methods suggested here gave narrower confidence intervals and more stable inferences, especially with small numbers of copies or non-normal posterior distributions of parameter estimates. A free R software package called MImix that implements our methods is available from CRAN.

  11. Hierarchical mixture models for longitudinal immunologic data with heterogeneity, non-normality, and missingness.

    PubMed

    Huang, Yangxin; Chen, Jiaqing; Yin, Ping

    2017-02-01

    It is a common practice to analyze longitudinal data frequently arisen in medical studies using various mixed-effects models in the literature. However, the following issues may standout in longitudinal data analysis: (i) In clinical practice, the profile of each subject's response from a longitudinal study may follow a "broken stick" like trajectory, indicating multiple phases of increase, decline and/or stable in response. Such multiple phases (with changepoints) may be an important indicator to help quantify treatment effect and improve management of patient care. To estimate changepoints, the various mixed-effects models become a challenge due to complicated structures of model formulations; (ii) an assumption of homogeneous population for models may be unrealistically obscuring important features of between-subject and within-subject variations; (iii) normality assumption for model errors may not always give robust and reliable results, in particular, if the data exhibit non-normality; and (iv) the response may be missing and the missingness may be non-ignorable. In the literature, there has been considerable interest in accommodating heterogeneity, non-normality or missingness in such models. However, there has been relatively little work concerning all of these features simultaneously. There is a need to fill up this gap as longitudinal data do often have these characteristics. In this article, our objectives are to study simultaneous impact of these data features by developing a Bayesian mixture modeling approach-based Finite Mixture of Changepoint (piecewise) Mixed-Effects (FMCME) models with skew distributions, allowing estimates of both model parameters and class membership probabilities at population and individual levels. Simulation studies are conducted to assess the performance of the proposed method, and an AIDS clinical data example is analyzed to demonstrate the proposed methodologies and to compare modeling results of potential mixture models

  12. DSMC simulation of Rayleigh-Brillouin scattering in binary mixtures

    NASA Astrophysics Data System (ADS)

    Bruno, Domenico; Frezzotti, Aldo; Ghiroldi, Gian Pietro

    2016-11-01

    Rayleigh-Brillouin scattering spectra (RBS) in dilute gas mixtures have been simulated by the Direct Simulation Monte Carlo method (DSMC). Different noble gas binary mixtures have been considered and the spectra have been simulated adopting the hard sphere collision model. It is suggested that DSMC simulations can be used in the interpretation of light scattering experiments in place of approximate kinetic models. Actually, the former have a firmer physical ground and can be readily extended to treat gas mixtures of arbitrary complexity. The results obtained confirm the capability of DSMC to predict experimental spectra and clears the way towards the simulation of polyatomic gas mixtures of interest for actual application (notably, air) where tractable kinetic model equations are still lacking.

  13. Viscosity Difference Measurements for Normal and Para Liquid Hydrogen Mixtures

    NASA Technical Reports Server (NTRS)

    Webeler, R.; Bedard, F.

    1961-01-01

    The absence of experimental data in the literature concerning a viscosity difference for normal and equilibrium liquid hydrogen may be attributed to the limited reproducibility of "oscillating disk" measurements in a liquid-hydrogen environment. Indeed, there is disagreement over the viscosity values for equilibrium liquid hydrogen even without proton spin considerations. Measurements presented here represent the first application of the piezoelectric alpha quartz torsional oscillator technique to liquid-hydrogen viscosity measurements.

  14. Using partially labeled data for normal mixture identification with application to class definition

    NASA Technical Reports Server (NTRS)

    Shahshahani, Behzad M.; Landgrebe, David A.

    1992-01-01

    The problem of estimating the parameters of a normal mixture density when, in addition to the unlabeled samples, sets of partially labeled samples are available is addressed. The density of the multidimensional feature space is modeled with a normal mixture. It is assumed that the set of components of the mixture can be partitioned into several classes and that training samples are available from each class. Since for any training sample the class of origin is known but the exact component of origin within the corresponding class is unknown, the training samples as considered to be partially labeled. The EM iterative equations are derived for estimating the parameters of the normal mixture in the presence of partially labeled samples. These equations can be used to combine the supervised and nonsupervised learning processes.

  15. Simulation of binary mixtures with the lattice Boltzman method.

    PubMed

    Arcidiacono, S; Mantzaras, J; Ansumali, S; Karlin, I V; Frouzakis, C; Boulouchos, K B

    2006-11-01

    A lattice Boltzman model for the simulation of binary mixtures is presented. Contrary to previous models, the present formulation is able to simulate mixtures with different Schmidt numbers and arbitrary molecular mass ratio of the components. In the hydrodynamic limit, the Navier-Stokes and the Stefan-Maxwell binary diffusion equations are recovered. The model is used for the simulation of binary diffusion and mixing layers. The results are found to be in good agreement with a derived similarity solution and with the predictions of a transient spectral element code.

  16. Program computes equilibrium normal shock and stagnation point solutions for arbitrary gas mixtures

    NASA Technical Reports Server (NTRS)

    Callis, L. B.; Kemper, J. T.

    1967-01-01

    Program computes solutions for flow parameters in arbitrary gas mixtures behind a normal and a reflected normal shock, for in-flight and shock-tube stagnation conditions. Equilibrium flow calculations are made by a free-energy minimization technique coupled with the steady-flow conservation equations and a modified Newton-Raphson iterative scheme.

  17. Bragg diffraction for normal and obliquely circularly polarized light due a new chiral mixture

    NASA Astrophysics Data System (ADS)

    Castro-Garay, P.; Manzanares-Martinez, J.; Corella-Madueño, A.; Rosas-Burgos, A.; Lizola, Josue; Clark, Marielena; Palma, Lillian

    2015-09-01

    We have found experimentally the transmittance of normal incident circularly polarized light due to new chiral mixture that was distorted by electric field. The chiral mixture was achieved by mixtures of two nematic liquid crystals (5OCB and 5CB) and S-1-bromo-2-methylbutane. We have found a regime of circular Bragg diffraction for certain values of concentrations and thickness. Optical diffraction phenomenon have received particular attention in research for optical and electro-optical applications, such as low -voltage modulators, reflective phase gratings and smart reflectors.

  18. Robust Bayesian Analysis of Heavy-tailed Stochastic Volatility Models using Scale Mixtures of Normal Distributions

    PubMed Central

    Abanto-Valle, C. A.; Bandyopadhyay, D.; Lachos, V. H.; Enriquez, I.

    2009-01-01

    A Bayesian analysis of stochastic volatility (SV) models using the class of symmetric scale mixtures of normal (SMN) distributions is considered. In the face of non-normality, this provides an appealing robust alternative to the routine use of the normal distribution. Specific distributions examined include the normal, student-t, slash and the variance gamma distributions. Using a Bayesian paradigm, an efficient Markov chain Monte Carlo (MCMC) algorithm is introduced for parameter estimation. Moreover, the mixing parameters obtained as a by-product of the scale mixture representation can be used to identify outliers. The methods developed are applied to analyze daily stock returns data on S&P500 index. Bayesian model selection criteria as well as out-of- sample forecasting results reveal that the SV models based on heavy-tailed SMN distributions provide significant improvement in model fit as well as prediction to the S&P500 index data over the usual normal model. PMID:20730043

  19. Simulation of Nonisothermal Multiphase Flows of Binary Mixtures in a Porous Media

    NASA Astrophysics Data System (ADS)

    Afanasyev, A. A.

    2010-12-01

    Hydrodynamic simulation of processes in a geothermal system is complicated due to a wide ranges of pressure and temperature in the flows. In deep regions of a system pressure and temperature can be above critical point of water while near the surface normal conditions take place. The transition from a supercritical fluid to a subcritical water and vapor in the flows strongly complicates hydrodynamic simulations. In the case when a geothermal system is saturated with a binary mixture the simulation is much more complex because instead of a single critical point there exist critical lines in a space of thermodynamic parameters of the mixture. Moreover in general case the mixture can split not only in two phases of liquid and gaseous types but also in two dense phases of liquid type and even in three phases. A new approach is proposed for effective simulation of hydrodynamic processes in sub- and supercritical conditions. As opposed to classical thermodynamic phase equilibrium of the mixture is determined via pressure, enthalpy and composition. These variables help to avoid mathematical singularities at critical conditions and allow to determine three phase states. In classical methods a cubic equation of state is used to calculate properties of a mixture for hydrodynamic simulations. In the proposed approach this equation is used prior to hydrodynamic to calculate thermodynamic potential of the mixture in pressure, enthalpy and composition variables. This allows to perform once all complex calculations of the properties prior to hydrodynamic simulations and results in sufficient acceleration of calculations. The potential is used in a problem of conditional extremum for mixture multiphase equilibrium determination in hydrodynamic simulations. This problem of conditional extremum closes transport equations. The approach is applied to simulations of high-temperature water-carbon dioxide mixture flows in a porous media. The mixture phase diagram is analyzed and zones of

  20. Mixture of normal distributions in multivariate null intercept measurement error model.

    PubMed

    Aoki, Reiko; Pinto Júnior, Dorival Leão; Achcar, Jorge Alberto; Bolfarine, Heleno

    2006-01-01

    In this paper we propose the use of a multivariate null intercept measurement error model, where the true unobserved value of the covariate follows a mixture of two normal distributions. The proposed model is applied to a dental clinical trial presented in Hadgu and Koch (1999). A Bayesian approach is considered and a Gibbs Sampler is used to perform the computations.

  1. Molecular dynamics simulation of binary mixtures of molten alkali carbonates

    NASA Astrophysics Data System (ADS)

    Tissen, J. T. W. M.; Janssen, G. J. M.; van der Eerden, P.

    Molecular dynamics simulations have been performed on three binary eutectic mixtures: Li/NaCO3 (53-47 mol%), Li/KCO3 (62-38 mol%) and KCO3 (43-57 mol%) at 1200 K. The short-range order in the mixtures differs in many respects from the short-range order found in the pure components. The Li+ ions are coordinated by a smaller number of oxygen atoms, the Na+ and K+ ions by a larger number. The Li+ ions become trapped in their first coordination shell, leaving relatively more space for the larger atoms. This feature is the cause of the often-observed non-additivity of the dynamic properties of these mixtures, such as the Chemla effect in Li/KCO3, the large negative deviations from linear additivity for the electrical conductivity, as well as the dependence of the self-diffusion coefficient of the cations on the Li2CO3 content.

  2. Kinetic Method for Hydrogen-Deuterium-Tritium Mixture Distillation Simulation

    SciTech Connect

    Sazonov, A.B.; Kagramanov, Z.G.; Magomedbekov, E.P.

    2005-07-15

    Simulation of hydrogen distillation plants requires mathematical procedures suitable for multicomponent systems. In most of the present-day simulation methods a distillation column is assumed to be composed of theoretical stages, or plates. However, in the case of a multicomponent mixture theoretical plate does not exist.An alternative kinetic method of simulation is depicted in the work. According to this method a system of mass-transfer differential equations is solved numerically. Mass-transfer coefficients are estimated with using experimental results and empirical equations.Developed method allows calculating the steady state of a distillation column as well as its any non-steady state when initial conditions are given. The results for steady states are compared with ones obtained via Thiele-Geddes theoretical stage technique and the necessity of using kinetic method is demonstrated. Examples of a column startup period and periodic distillation simulations are shown as well.

  3. Molecular dynamics simulation study of binary fullerene mixtures

    NASA Astrophysics Data System (ADS)

    Ruberto, R.; Abramo, M. C.; Caccamo, C.

    2004-10-01

    We report constant-pressure molecular dynamics (MD) simulations of binary C60/Cn fullerene-mixtures ( n=70 , 76, 84, 96) modeled in terms of a spherically symmetric two-body potential. By starting from a liquid configuration of the system, we cool mixtures down to freezing and beyond, until room temperature is reached, in order to verify the formation of solid solutions, namely, of configurations characterized by a unique crystalline lattice whose sites are randomly occupied by the two component fullerene species. We first explore the entire concentration range of the C60x/C70(1-x)(0mixture and find fairly good agreement with experimental data, exhibiting partial reciprocal solubility of the two components into each other with an immiscibility gap at intermediate compositions. In fact, the system we simulate forms substitutional solid solutions over a wide range of concentrations except for 0.3⩽x⩽0.5 ; over such an interval, it turns out that the initially liquid mixture can be supercooled down to relatively low temperatures, until eventually a glassy phase is formed. The study is then extended to fullerene mixtures of molecular diameter ratio α=σC60/σCn smaller than in C60/C70 (where α=0.93 ), as is the case for C60/C76 (α=0.89) , C60/C84(α=0.85) and C60/C96 (α=0.79) . The effect of the size mismatch between the two species is dramatic: The solid immiscibility region rapidly expands even upon a tiny reduction of α , with formation of an amorphous phase at sufficiently low temperature, as found for the C60/C70 mixture. For the smallest α(C60/C96) cocrystallization of the two components turns out to be forbidden over the whole concentration axis. A mapping of the MD evidences of the fullerene mixtures’ phase behavior onto the phase diagram of binary hard-sphere mixtures (determined by other authors) turns out to be worthwhile and enlightnening. In particular, size ratio effects and the onset of glassy phases emerge in qualitative good agreement

  4. Computer simulation-molecular-thermodynamic framework to predict the micellization behavior of mixtures of surfactants: application to binary surfactant mixtures.

    PubMed

    Iyer, Jaisree; Mendenhall, Jonathan D; Blankschtein, Daniel

    2013-05-30

    We present a computer simulation-molecular-thermodynamic (CSMT) framework to model the micellization behavior of mixtures of surfactants in which hydration information from all-atomistic simulations of surfactant mixed micelles and monomers in aqueous solution is incorporated into a well-established molecular-thermodynamic framework for mixed surfactant micellization. In addition, we address the challenges associated with the practical implementation of the CSMT framework by formulating a simpler mixture CSMT model based on a composition-weighted average approach involving single-component micelle simulations of the mixture constituents. We show that the simpler mixture CSMT model works well for all of the binary surfactant mixtures considered, except for those containing alkyl ethoxylate surfactants, and rationalize this finding molecularly. The mixture CSMT model is then utilized to predict mixture CMCs, and we find that the predicted CMCs compare very well with the experimental CMCs for various binary mixtures of linear surfactants. This paper lays the foundation for the mixture CSMT framework, which can be used to predict the micellization properties of mixtures of surfactants that possess a complex chemical architecture, and are therefore not amenable to traditional molecular-thermodynamic modeling.

  5. Multiscale simulation of ideal mixtures using smoothed dissipative particle dynamics

    NASA Astrophysics Data System (ADS)

    Petsev, Nikolai D.; Leal, L. Gary; Shell, M. Scott

    2016-02-01

    Smoothed dissipative particle dynamics (SDPD) [P. Español and M. Revenga, Phys. Rev. E 67, 026705 (2003)] is a thermodynamically consistent particle-based continuum hydrodynamics solver that features scale-dependent thermal fluctuations. We obtain a new formulation of this stochastic method for ideal two-component mixtures through a discretization of the advection-diffusion equation with thermal noise in the concentration field. The resulting multicomponent approach is consistent with the interpretation of the SDPD particles as moving volumes of fluid and reproduces the correct fluctuations and diffusion dynamics. Subsequently, we provide a general multiscale multicomponent SDPD framework for simulations of molecularly miscible systems spanning length scales from nanometers to the non-fluctuating continuum limit. This approach reproduces appropriate equilibrium properties and is validated with simulation of simple one-dimensional diffusion across multiple length scales.

  6. Soil signature simulation of complex mixtures and particle size distributions

    NASA Astrophysics Data System (ADS)

    Carson, Tyler; Bachmann, Charles M.; Salvaggio, Carl

    2015-09-01

    Soil reflectance signatures were modeled using the digital imaging and remote sensing image generation model and Blender three-dimensional (3-D) graphic design software. Using these tools, the geometry, radiometry, and chemistry of quartz and magnetite were exploited to model the presence of particle size and porosity effects in the visible and the shortwave infrared spectrum. Using the physics engines within the Blender 3-D graphic design software, physical representations of granular soil scenes were created. Each scene characterized a specific particle distribution and density. Chemical and optical properties of pure quartz and magnetite were assigned to particles in the scene based on particle size. This work presents a model to describe an observed phase-angle dependence of beach sand density. Bidirectional reflectance signatures were simulated for targets of varying size distribution and density. This model provides validation for a phenomenological trade space between density and particle size distribution in complex, heterogeneous soil mixtures. It also confirms the suggestion that directional reflectance signatures can be defined by intimate mixtures that depend on pore spacing. The study demonstrated that by combining realistic target geometry and spectral measurements of pure quartz and magnetite, effects of soil particle size and density could be modeled without functional data fitting or rigorous analysis of material dynamics. This research does not use traditional function-based models for simulation. The combination of realistic geometry, physically viable particle structure, and first-principles ray-tracing enables the ability to represent signature changes that have been observed in experimental observations.

  7. On the asymptotic improvement of supervised learning by utilizing additional unlabeled samples - Normal mixture density case

    NASA Technical Reports Server (NTRS)

    Shahshahani, Behzad M.; Landgrebe, David A.

    1992-01-01

    The effect of additional unlabeled samples in improving the supervised learning process is studied in this paper. Three learning processes. supervised, unsupervised, and combined supervised-unsupervised, are compared by studying the asymptotic behavior of the estimates obtained under each process. Upper and lower bounds on the asymptotic covariance matrices are derived. It is shown that under a normal mixture density assumption for the probability density function of the feature space, the combined supervised-unsupervised learning is always superior to the supervised learning in achieving better estimates. Experimental results are provided to verify the theoretical concepts.

  8. Partially linear models with autoregressive scale-mixtures of normal errors: A Bayesian approach

    NASA Astrophysics Data System (ADS)

    Ferreira, Guillermo; Castro, Mauricio; Lachos, Victor H.

    2012-10-01

    Normality and independence of error terms is a typical assumption for partial linear models. However, such an assumption may be unrealistic on many fields such as economics, finance and biostatistics. In this paper, we develop a Bayesian analysis for partial linear model with first-order autoregressive errors belonging to the class of scale mixtures of normal (SMN) distributions. The proposed model provides a useful generalization of the symmetrical linear regression models with independent error, since the error distribution cover both correlated and thick-tailed distribution, and has a convenient hierarchical representation allowing to us an easily implementation of a Markov chain Monte Carlo (MCMC) scheme. In order to examine the robustness of this distribution against outlying and influential observations, we present a Bayesian case deletion influence diagnostics based on the Kullback-Leibler (K-L) divergence. The proposed methodology is applied to the Cuprum Company monthly returns.

  9. Simulating asymmetric colloidal mixture with adhesive hard sphere model.

    PubMed

    Jamnik, A

    2008-06-21

    Monte Carlo simulation and Percus-Yevick (PY) theory are used to investigate the structural properties of a two-component system of the Baxter adhesive fluids with the size asymmetry of the particles of both components mimicking an asymmetric binary colloidal mixture. The radial distribution functions for all possible species pairs, g(11)(r), g(22)(r), and g(12)(r), exhibit discontinuities at the interparticle distances corresponding to certain combinations of n and m values (n and m being integers) in the sum nsigma(1)+msigma(2) (sigma(1) and sigma(2) being the hard-core diameters of individual components) as a consequence of the impulse character of 1-1, 2-2, and 1-2 attractive interactions. In contrast to the PY theory, which predicts the delta function peaks in the shape of g(ij)(r) only at the distances which are the multiple of the molecular sizes corresponding to different linear structures of successively connected particles, the simulation results reveal additional peaks at intermediate distances originating from the formation of rigid clusters of various geometries.

  10. Sample Size Requirements in Single- and Multiphase Growth Mixture Models: A Monte Carlo Simulation Study

    ERIC Educational Resources Information Center

    Kim, Su-Young

    2012-01-01

    Just as growth mixture models are useful with single-phase longitudinal data, multiphase growth mixture models can be used with multiple-phase longitudinal data. One of the practically important issues in single- and multiphase growth mixture models is the sample size requirements for accurate estimation. In a Monte Carlo simulation study, the…

  11. Biochar-compost mixtures added to simulated golf greens increase creeping bentgrass growth

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Mixtures of 85% sand and 15% mixtures of peat (control), a commercial biochar, a commercial biochar-compost product (CarbonizPN), and seven biochar-commercial compost mixtures were tested on the growth of creeping bentgrass (Agrostis stolonifera L. "007") in simulated golf greens. Physical properti...

  12. Application of normalized spectra in resolving a challenging Orphenadrine and Paracetamol binary mixture

    NASA Astrophysics Data System (ADS)

    Yehia, Ali M.; Abd El-Rahman, Mohamed K.

    2015-03-01

    Normalized spectra have a great power in resolving spectral overlap of challenging Orphenadrine (ORP) and Paracetamol (PAR) binary mixture, four smart techniques utilizing the normalized spectra were used in this work, namely, amplitude modulation (AM), simultaneous area ratio subtraction (SARS), simultaneous derivative spectrophotometry (S1DD) and ratio H-point standard addition method (RHPSAM). In AM, peak amplitude at 221.6 nm of the division spectra was measured for both ORP and PAR determination, while in SARS, concentration of ORP was determined using the area under the curve from 215 nm to 222 nm of the regenerated ORP zero order absorption spectra, in S1DD, concentration of ORP was determined using the peak amplitude at 224 nm of the first derivative ratio spectra. PAR concentration was determined directly at 288 nm in the division spectra obtained during the manipulation steps in the previous three methods. The last RHPSAM is a dual wavelength method in which two calibrations were plotted at 216 nm and 226 nm. RH point is the intersection of the two calibration lines, where ORP and PAR concentrations were directly determined from coordinates of RH point. The proposed methods were applied successfully for the determination of ORP and PAR in their dosage form.

  13. Modeling and simulation of normal and hemiparetic gait

    NASA Astrophysics Data System (ADS)

    Luengas, Lely A.; Camargo, Esperanza; Sanchez, Giovanni

    2015-09-01

    Gait is the collective term for the two types of bipedal locomotion, walking and running. This paper is focused on walking. The analysis of human gait is of interest to many different disciplines, including biomechanics, human-movement science, rehabilitation and medicine in general. Here we present a new model that is capable of reproducing the properties of walking, normal and pathological. The aim of this paper is to establish the biomechanical principles that underlie human walking by using Lagrange method. The constraint forces of Rayleigh dissipation function, through which to consider the effect on the tissues in the gait, are included. Depending on the value of the factor present in the Rayleigh dissipation function, both normal and pathological gait can be simulated. First of all, we apply it in the normal gait and then in the permanent hemiparetic gait. Anthropometric data of adult person are used by simulation, and it is possible to use anthropometric data for children but is necessary to consider existing table of anthropometric data. Validation of these models includes simulations of passive dynamic gait that walk on level ground. The dynamic walking approach provides a new perspective of gait analysis, focusing on the kinematics and kinetics of gait. There have been studies and simulations to show normal human gait, but few of them have focused on abnormal, especially hemiparetic gait. Quantitative comparisons of the model predictions with gait measurements show that the model can reproduce the significant characteristics of normal gait.

  14. Electrochemical concentration measurements for multianalyte mixtures in simulated electrorefiner salt

    NASA Astrophysics Data System (ADS)

    Rappleye, Devin Spencer

    The development of electroanalytical techniques in multianalyte molten salt mixtures, such as those found in used nuclear fuel electrorefiners, would enable in situ, real-time concentration measurements. Such measurements are beneficial for process monitoring, optimization and control, as well as for international safeguards and nuclear material accountancy. Electroanalytical work in molten salts has been limited to single-analyte mixtures with a few exceptions. This work builds upon the knowledge of molten salt electrochemistry by performing electrochemical measurements on molten eutectic LiCl-KCl salt mixture containing two analytes, developing techniques for quantitatively analyzing the measured signals even with an additional signal from another analyte, correlating signals to concentration and identifying improvements in experimental and analytical methodologies. (Abstract shortened by ProQuest.).

  15. Addressing the Problem of Switched Class Labels in Latent Variable Mixture Model Simulation Studies

    ERIC Educational Resources Information Center

    Tueller, Stephen J.; Drotar, Scott; Lubke, Gitta H.

    2011-01-01

    The discrimination between alternative models and the detection of latent classes in the context of latent variable mixture modeling depends on sample size, class separation, and other aspects that are related to power. Prior to a mixture analysis it is useful to investigate model performance in a simulation study that reflects the research…

  16. Freezing of mixtures confined in silica nanopores: experiment and molecular simulation.

    PubMed

    Coasne, Benoit; Czwartos, Joanna; Sliwinska-Bartkowiak, Malgorzata; Gubbins, Keith E

    2010-08-28

    Freezing of mixtures confined in silica nanopores is investigated by means of experiment and molecular simulation. The experiments consist of differential scanning calorimetry and dielectric relaxation spectroscopy measurements for CCl(4)/C(6)H(5)Br mixtures confined in Vycor having pores with a mean diameter of about D=4.2 nm. Molecular simulations consist of grand canonical Monte Carlo simulations combined with the parallel tempering technique for Lennard-Jones Ar/Kr mixtures confined in a silica cylindrical nanopore with a diameter of D=3.2 nm. The experimental and molecular simulation data provide a consistent picture of freezing of mixtures in cylindrical silica nanopores having a size smaller than ten times the size of the confined molecules. No sharp change in the properties of the confined mixture occurs upon melting, which suggests that the confined system does not crystallize. In the case of the molecular simulations, this result is confirmed by the fact that except for the contact layer, the percentage of crystal-like atoms is less than 6% (whatever the temperature). The molecular simulations also show that the composition of the mixture is shifted, upon confinement, toward the component having the strongest wall/fluid attraction.

  17. Surface tension of water-alcohol mixtures from Monte Carlo simulations.

    PubMed

    Biscay, F; Ghoufi, A; Malfreyt, P

    2011-01-28

    Monte Carlo simulations are reported to predict the dependence of the surface tension of water-alcohol mixtures on the alcohol concentration. Alcohols are modeled using the anisotropic united atom model recently extended to alcohol molecules. The molecular simulations show a good agreement between the experimental and calculated surface tensions for the water-methanol and water-propanol mixtures. This good agreement with experiments is also established through the comparison of the excess surface tensions. A molecular description of the mixture in terms of density profiles and hydrogen bond profiles is used to interpret the decrease of the surface tension with the alcohol concentration and alcohol chain length.

  18. Discrim: a computer program using an interactive approach to dissect a mixture of normal or lognormal distributions

    USGS Publications Warehouse

    Bridges, N.J.; McCammon, R.B.

    1980-01-01

    DISCRIM is an interactive computer graphics program that dissects mixtures of normal or lognormal distributions. The program was written in an effort to obtain a more satisfactory solution to the dissection problem than that offered by a graphical or numerical approach alone. It combines graphic and analytic techniques using a Tektronix1 terminal in a time-share computing environment. The main program and subroutines were written in the FORTRAN language. ?? 1980.

  19. A re-appraisal of the concept of ideal mixtures through a computer simulation study of the methanol-ethanol mixtures

    NASA Astrophysics Data System (ADS)

    Požar, Martina; Lovrinčević, Bernarda; Zoranić, Larisa; Mijaković, Marijana; Sokolić, Franjo; Perera, Aurélien

    2016-08-01

    Methanol-ethanol mixtures under ambient conditions of temperature and pressure are studied by computer simulations, with the aim to sort out how the ideality of this type of mixtures differs from that of a textbook example of an ideal mixture. This study reveals two types of ideality, one which is related to simple disorder, such as in benzene-cyclohexane mixtures, and another found in complex disorder mixtures of associated liquids. It underlines the importance of distinguishing between concentration fluctuations, which are shared by both types of systems, and the structural heterogeneity, which characterises the second class of disorder. Methanol-1propanol mixtures are equally studied and show a quasi-ideality with many respect comparable to that of the methanol-ethanol mixtures, hinting at the existence of a super-ideality in neat mono-ol binary mixtures, driven essentially by the strong hydrogen bonding and underlying hydroxyl group clustering.

  20. Mobile Smog Simulator: New Capabilities to Study Urban Mixtures

    EPA Pesticide Factsheets

    A smog simulator developed by EPA scientists and engineers has unique capabilities that will provide information for assessing the health impacts of relevant multipollutant atmospheres and identify contributions of specific sources.

  1. Lattice-Boltzmann-Langevin simulations of binary mixtures.

    PubMed

    Thampi, Sumesh P; Pagonabarraga, Ignacio; Adhikari, R

    2011-10-01

    We report a hybrid numerical method for the solution of the Model H fluctuating hydrodynamic equations for binary mixtures. The momentum conservation equations with Landau-Lifshitz stresses are solved using the fluctuating lattice Boltzmann equation while the order parameter conservation equation with Langevin fluxes is solved using stochastic method of lines. Two methods, based on finite difference and finite volume, are proposed for spatial discretization of the order parameter equation. Special care is taken to ensure that the fluctuation-dissipation theorem is maintained at the lattice level in both cases. The methods are benchmarked by comparing static and dynamic correlations and excellent agreement is found between analytical and numerical results. The Galilean invariance of the model is tested and found to be satisfactory. Thermally induced capillary fluctuations of the interface are captured accurately, indicating that the model can be used to study nonlinear fluctuations.

  2. Molecular dynamics simulations of the structural and thermodynamic properties of imidazolium-based ionic liquid mixtures.

    PubMed

    Méndez-Morales, T; Carrete, J; Cabeza, O; Gallego, L J; Varela, L M

    2011-09-29

    In this work, extensive molecular dynamics simulations of mixtures of alcohols of several chain lengths (methanol and ethanol) with the ionic liquids (ILs) composed of the cation 1-hexyl-3-methylimidazolium and several anions of different hydrophobicity degrees (Cl(-), BF(4)(-), PF(6)(-)) are reported. We analyze the influence of the nature of the anion, the length of the molecular chain of the alcohol, and the alcohol concentration on the thermodynamic and structural properties of the mixtures. Densities, excess molar volumes, total and partial radial distribution functions, coordination numbers, and hydrogen bond degrees are reported and analyzed for mixtures of the ILs with methanol and ethanol. The aggregation process is shown to be highly dependent on the nature of the anion and the size of the alcohol, since alcohol molecules tend to interact predominantly with the anionic part of the IL, especially in mixtures of the halogenated IL with methanol. Particularly, our results suggest that the formation of an apolar network similar to that previously reported in mixtures of ILs with water does not take place in mixtures with alcohol when the chloride anion is present, the alcohol molecules being instead homogeneously distributed in the polar network of IL. Moreover, the alcohol clusters formed in mixtures of [HMIM][PF(6)] with alcohol were found to have a smaller size than in mixtures with water. Additionally, we provide a semiquantitative analysis of the dependence of the hydrogen bonding degree of the mixtures on the alcohol concentration.

  3. Monte Carlo simulations of mixtures involving ketones and aldehydes by a direct bubble pressure calculation.

    PubMed

    Ferrando, Nicolas; Lachet, Véronique; Boutin, Anne

    2010-07-08

    Ketone and aldehyde molecules are involved in a large variety of industrial applications. Because they are mainly present mixed with other compounds, the prediction of phase equilibrium of mixtures involving these classes of molecules is of first interest particularly to design and optimize separation processes. The main goal of this work is to propose a transferable force field for ketones and aldehydes that allows accurate molecular simulations of not only pure compounds but also complex mixtures. The proposed force field is based on the anisotropic united-atoms AUA4 potential developed for hydrocarbons, and it introduces only one new atom, the carbonyl oxygen. The Lennard-Jones parameters of this oxygen atom have been adjusted on saturated thermodynamic properties of both acetone and acetaldehyde. To simulate mixtures, Monte Carlo simulations are carried out in a specific pseudoensemble which allows a direct calculation of the bubble pressure. For polar mixtures involved in this study, we show that this approach is an interesting alternative to classical calculations in the isothermal-isobaric Gibbs ensemble. The pressure-composition diagrams of polar + polar and polar + nonpolar binary mixtures are well reproduced. Mutual solubilities as well as azeotrope location, if present, are accurately predicted without any empirical binary interaction parameters or readjustment. Such result highlights the transferability of the proposed force field, which is an essential feature toward the simulation of complex oxygenated mixtures of industrial interest.

  4. Simulation Analysis of Computer-Controlled pressurization for Mixture Ratio Control

    NASA Technical Reports Server (NTRS)

    Alexander, Leslie A.; Bishop-Behel, Karen; Benfield, Michael P. J.; Kelley, Anthony; Woodcock, Gordon R.

    2005-01-01

    A procedural code (C++) simulation was developed to investigate potentials for mixture ratio control of pressure-fed spacecraft rocket propulsion systems by measuring propellant flows, tank liquid quantities, or both, and using feedback from these measurements to adjust propellant tank pressures to set the correct operating mixture ratio for minimum propellant residuals. The pressurization system eliminated mechanical regulators in favor of a computer-controlled, servo- driven throttling valve. We found that a quasi-steady state simulation (pressure and flow transients in the pressurization systems resulting from changes in flow control valve position are ignored) is adequate for this purpose. Monte-Carlo methods are used to obtain simulated statistics on propellant depletion. Mixture ratio control algorithms based on proportional-integral-differential (PID) controller methods were developed. These algorithms actually set target tank pressures; the tank pressures are controlled by another PID controller. Simulation indicates this approach can provide reductions in residual propellants.

  5. Molecular dynamics simulations of transport and separation of carbon dioxide-alkane mixtures in carbon nanopores.

    PubMed

    Firouzi, Mahnaz; Nezhad, Kh Molaai; Tsotsis, Theodore T; Sahimi, Muhammad

    2004-05-01

    The configurational-bias Monte Carlo method, which is used for efficient generation of molecular models of n-alkane chains, is combined for the first time with the dual control-volume grand-canonical molecular-dynamics simulation, which has been developed for studying transport of molecules in pores under an external potential gradient, to investigate transport and separation of binary mixtures of n-alkanes, as well as mixtures of CO2 and n-alkanes, in carbon nanopores. The effect of various factors, such as the temperature of the system, the composition of the mixture, and the pore size, on the separation of the mixtures is investigated. We also report the preliminary results of an experimental study of transport and separation of some of the same mixtures in a carbon molecular-sieve membrane with comparable pore sizes. The results indicate that, for the mixtures considered in this paper, even in very small carbon nanopores the energetic effects still play a dominant role in the transport and separation properties of the mixtures, whereas in a real membrane they are dominated by the membrane's morphological characteristics. As a result, for the mixtures considered, a single pore may be a grossly inadequate model of a real membrane, and hence one must resort to three-dimensional molecular pore network models of the membrane.

  6. Simulation of DNA in water/ethanol mixture

    NASA Astrophysics Data System (ADS)

    Wen, Jing; Shen, Hao; Zhai, Yan-Rong; Zhang, Feng-Shou

    2016-05-01

    The study of B-DNA in mixed solvent comprised of water and ethanol with different concentrations at 298 K has been conducted by molecular dynamics simulation. We find that the structure of DNA is easily affected by the aqueous environment. Property and structure changes of the solvent will influence the local structure of DNA helix, induce the conformation transition between different forms, and even cause the degeneration of DNA. The addition of ethanol can reduce the activity of water, changes the solvent structure around DNA. DNA in the solvent with low concentration of ethanol changes little, when the ethanol increases in the solvent, large structure changes occur at the ends of the helix first, then show the characters of A-form, the minor groove becomes wider and shallower, and the length is shortened when in the solvent with the concentration of 0.88 g/cm3. The mechanism behind is discussed, and we find the competition between the solvent molecules and counterions coupling to the free oxygen atoms of the phosphate groups, and the breaking of the spin of water both contribute to the structure changes of DNA in the simulation.

  7. Molecular dynamics simulation of a binary mixture near the lower critical point.

    PubMed

    Pousaneh, Faezeh; Edholm, Olle; Maciołek, Anna

    2016-07-07

    2,6-lutidine molecules mix with water at high and low temperatures but in a wide intermediate temperature range a 2,6-lutidine/water mixture exhibits a miscibility gap. We constructed and validated an atomistic model for 2,6-lutidine and performed molecular dynamics simulations of 2,6-lutidine/water mixture at different temperatures. We determined the part of demixing curve with the lower critical point. The lower critical point extracted from our data is located close to the experimental one. The estimates for critical exponents obtained from our simulations are in a good agreement with the values corresponding to the 3D Ising universality class.

  8. Random Packings Of Rod-Sphere Mixtures Simulated By Mechanical Contraction

    NASA Astrophysics Data System (ADS)

    Kyrylyuk, Andriy V.; Wouterse, Alan; Philipse, Albert P.

    2009-06-01

    We study the random close packing of a binary mixture of spheres and rod-like particles (spherocylinders) by the mechanical contraction computer simulation. We investigate the universality in packing of near-spheres by monitoring the position and the value of the maximum in the mixture packing density as a function of the mixture composition and the rod aspect ratio. We find that independently of the mixture composition the particles pack more efficiently/densely as the rod aspect ratio is perturbed slightly from zero and the maximum density is always reached at one unique rod aspect ratio of about 0.45. The dependence of the value of the maximum packing fraction on the mixture composition (the relative rod volume fraction) is linear, exhibiting some ideality in packing of near-spheres. This counter-intuitive finding suggests that even for high rod concentrations in a rod-sphere mixture the packing is governed by local contacts between the neighboring particles, which is usually observed for dilute colloidal suspensions and granular gases, where there is no correlation between the particles. The plausible explanation for this intriguing behavior is that the correlations between the particles are completely lost in the range of distances of several particle diameters, which can be originated from the decoupling of the orientational and translational degrees of freedom of the nearly spherical rods. This gives rise to the universality and locality of random close packing of the rod-sphere mixtures.

  9. Tunable integration of absorption-membrane-adsorption for efficiently separating low boiling gas mixtures near normal temperature

    PubMed Central

    Liu, Huang; Pan, Yong; Liu, Bei; Sun, Changyu; Guo, Ping; Gao, Xueteng; Yang, Lanying; Ma, Qinglan; Chen, Guangjin

    2016-01-01

    Separation of low boiling gas mixtures is widely concerned in process industries. Now their separations heavily rely upon energy-intensive cryogenic processes. Here, we report a pseudo-absorption process for separating low boiling gas mixtures near normal temperature. In this process, absorption-membrane-adsorption is integrated by suspending suitable porous ZIF material in suitable solvent and forming selectively permeable liquid membrane around ZIF particles. Green solvents like water and glycol were used to form ZIF-8 slurry and tune the permeability of liquid membrane surrounding ZIF-8 particles. We found glycol molecules form tighter membrane while water molecules form looser membrane because of the hydrophobicity of ZIF-8. When using mixing solvents composed of glycol and water, the permeability of liquid membrane becomes tunable. It is shown that ZIF-8/water slurry always manifests remarkable higher separation selectivity than solid ZIF-8 and it could be tuned to further enhance the capture of light hydrocarbons by adding suitable quantity of glycol to water. Because of its lower viscosity and higher sorption/desorption rate, tunable ZIF-8/water-glycol slurry could be readily used as liquid absorbent to separate different kinds of low boiling gas mixtures by applying a multistage separation process in one traditional absorption tower, especially for the capture of light hydrocarbons. PMID:26892255

  10. Tunable integration of absorption-membrane-adsorption for efficiently separating low boiling gas mixtures near normal temperature.

    PubMed

    Liu, Huang; Pan, Yong; Liu, Bei; Sun, Changyu; Guo, Ping; Gao, Xueteng; Yang, Lanying; Ma, Qinglan; Chen, Guangjin

    2016-02-19

    Separation of low boiling gas mixtures is widely concerned in process industries. Now their separations heavily rely upon energy-intensive cryogenic processes. Here, we report a pseudo-absorption process for separating low boiling gas mixtures near normal temperature. In this process, absorption-membrane-adsorption is integrated by suspending suitable porous ZIF material in suitable solvent and forming selectively permeable liquid membrane around ZIF particles. Green solvents like water and glycol were used to form ZIF-8 slurry and tune the permeability of liquid membrane surrounding ZIF-8 particles. We found glycol molecules form tighter membrane while water molecules form looser membrane because of the hydrophobicity of ZIF-8. When using mixing solvents composed of glycol and water, the permeability of liquid membrane becomes tunable. It is shown that ZIF-8/water slurry always manifests remarkable higher separation selectivity than solid ZIF-8 and it could be tuned to further enhance the capture of light hydrocarbons by adding suitable quantity of glycol to water. Because of its lower viscosity and higher sorption/desorption rate, tunable ZIF-8/water-glycol slurry could be readily used as liquid absorbent to separate different kinds of low boiling gas mixtures by applying a multistage separation process in one traditional absorption tower, especially for the capture of light hydrocarbons.

  11. [Cellular mechanism of seizure discharge and its normalization by a herbal mixture prescription "saikokeishito-ka-shakuyaku" (SK)].

    PubMed

    Sugaya, A

    2001-05-01

    Epilepsy is one of the most frequently occurring nervous diseases. However, the fundamental cause of epilepsy is still unclear. We tried to elucidate the cellular mechanism of seizure discharge. During this research we unexpectedly found that a herbal mixture prescription shows very good effects on epileptics. Therefore, we also performed experiments on the anticonvulsant mechanism of this herbal mixture prescription, "Saikokeishito-ka-Shakuyaku" (SK). SK showed normalizing effects on intracellular calcium-related and protein-related pathological changes induced by pentylenetetrazol (PTZ) application in snail neurons and cultured neurons from the cerebral cortex of mice. In addition, SK showed marked protective effects against neuron damage induced by the cobalt focus epilepsy model, cytochalasin B and severe stress. SK also showed normalizing effects on developmental defects of cultured neurons from the cerebral cortex of an epilepsy animal model, EL mice. Moreover, SK showed complete preventive effects on the abnormal expression of one of the seizure-related (SEZ) genes, PTZ-17, induced by PTZ in Xenopus oocytes injected with PTZ-17 RNA. We also determined mouse chromosomal loci of the SEZ gene group and PTZ sensitive trait loci by linkage analysis for comparison with human synteny of epileptic families. The above-mentioned findings suggest that some herbal prescriptions will become promising drugs for the therapy against intractable nervous diseases which can not be ameliorated by pure chemical drugs in the future.

  12. Simulation of flow of mixtures through anisotropic porous media using a lattice Boltzmann model.

    PubMed

    Mendoza, M; Wittel, F K; Herrmann, H J

    2010-08-01

    We propose a description for transient penetration simulations of miscible and immiscible fluid mixtures into anisotropic porous media, using the lattice Boltzmann (LB) method. Our model incorporates hydrodynamic flow, advection-diffusion, surface tension, and the possibility for global and local viscosity variations to consider various types of hardening fluids. The miscible mixture consists of two fluids, one governed by the hydrodynamic equations and one by advection-diffusion equations. We validate our model on standard problems like Poiseuille flow, the collision of a drop with an impermeable, solid interface and the deformation of the fluid due to surface tension forces. To demonstrate the applicability to complex geometries, we simulate the invasion process of mixtures into wood spruce samples.

  13. Development of a Computational Framework on Fluid-Solid Mixture Flow Simulations for the COMPASS Code

    NASA Astrophysics Data System (ADS)

    Zhang, Shuai; Morita, Koji; Shirakawa, Noriyuki; Yamamoto, Yuichi

    The COMPASS code is designed based on the moving particle semi-implicit method to simulate various complex mesoscale phenomena relevant to core disruptive accidents of sodium-cooled fast reactors. In this study, a computational framework for fluid-solid mixture flow simulations was developed for the COMPASS code. The passively moving solid model was used to simulate hydrodynamic interactions between fluid and solids. Mechanical interactions between solids were modeled by the distinct element method. A multi-time-step algorithm was introduced to couple these two calculations. The proposed computational framework for fluid-solid mixture flow simulations was verified by the comparison between experimental and numerical studies on the water-dam break with multiple solid rods.

  14. Understanding the interfacial behavior in isopycnic Lennard-Jones mixtures by computer simulations.

    PubMed

    Garrido, José Matías; Piñeiro, Manuel M; Mejía, Andrés; Blas, Felipe J

    2016-01-14

    The physical characterization of the singular interfacial behavior of heterogeneous fluid systems is a very important step in preliminary stages of the design process, and also in the subsequent procedures for the determination of the optimal operating conditions. Molar isopycnicity or molar density inversion is a special case of phase equilibrium behavior that directly affects the relative position of phases in heterogeneous mixtures, without being affected by gravitational fields. This work is dedicated to characterize the impact of molar density inversion on the interfacial properties of Lennard-Jones binary mixtures. The results and specific trends of the molar density inversion phenomena on the peculiar calculated composition profiles across the interface and interfacial tensions are explored by using canonical molecular dynamics simulations of the Lennard-Jones binary mixtures. Our results show that the density inversion causes drastic changes in the density profiles of the mixtures. In particular, symmetrical and equal-sized Lennard-Jones mixtures always exhibit desorption along the interfacial zone, i.e. the interfacial concentration profiles show a relative minimum at the interface of the total density profiles that increases when the dispersive energy parameter (ε(ij)) between unlike species decreases. However, as the asymmetry of the Lennard-Jones mixtures increases (σ(i) ≠ σ(j)), the concentration profiles display a relative maximum at the interface, which implies the adsorption of the total density profiles along the interfacial zone.

  15. Molecular dynamics simulations of mixtures of protic and aprotic ionic liquids.

    PubMed

    Docampo-Álvarez, Borja; Gómez-González, Víctor; Méndez-Morales, Trinidad; Rodríguez, Julio R; López-Lago, Elena; Cabeza, Oscar; Gallego, Luis J; Varela, Luis M

    2016-09-14

    Molecular dynamics simulations of mixtures of the protic ionic liquid ethylammonium nitrate (EAN) and the aprotic 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) are reported and the results are compared with experimental density and electrical conductivity measurements. Essentially ideal mixing of the ionic liquids is seen to take place by means of experimental and simulated excess molar volumes, whose very low values suggest a gradual transition between the structures of the two end constituents of the mixture. A weak dominance of the structure of the protic ionic liquid is nevertheless registered, due to a slight preferential formation of the network of hydrogen bonds, as reflected in the coordination number and the number of hydrogen bonds in the mixture. A novel conductivity curve showing pronounced deviations from the simple ideal mixing rule is reported, with three different regions defined by a local maximum - reflecting enhanced translational dynamics relative to ideal mixture behaviour - and a global minimum at intermediate concentrations. The physical origin of this behaviour is discussed along with the structure and single-particle dynamics of the mixture, and it is seen that these regions are defined by the onset of the formation of the EAN hydrogen bonded network (xEAN = 0.2) and the virtual disappearance of the structure of the aprotic ionic liquid at xEAN = 0.7. It is concluded that the delicate interplay between both networks has a deep effect on the placement and mobility of [EMIM](+) cations in the mixture all throughout the different stages of the structural transition, which seems to be the driving force behind the reported transport properties of the mixture at intermediate to high EAN concentrations.

  16. [The immediate and late results of protecting the patient's normal tissues by using the gas hypoxic mixture GHM-10 in the radiation therapy of breast cancer].

    PubMed

    Strelkov, R B; Mardynskiĭ, Iu S; Zakoshchikov, K F; Firsova, P P

    1985-01-01

    The effect of inhalation of gaseous hypoxic mixture GHM-10 (oxygen--10 +/- 1.0 and nitrogen--90.0 +/- 1.0%) on radiation response of normal tissues was studied in 184 breast cancer patients. The mixture was administered to 120 patients while 74 controls received a standard course of radiotherapy. Administration of the mixture improved normal tissue resistance to radiotherapy for breast cancer and was followed by lower incidence of long-term radiation injury, lower frequency and shorter duration of general vegetative reactions to radiation.

  17. Gibbs ensemble Monte Carlo simulations of binary mixtures of methane, difluoromethane, and carbon dioxide.

    PubMed

    Do, Hainam; Wheatley, Richard J; Hirst, Jonathan D

    2010-03-25

    Gibbs ensemble Monte Carlo simulations were used to study the vapor-liquid equilibrium of binary mixtures of carbon dioxide + methane and carbon dioxide + difluoromethane. The potential forcefields we employ are all atomistic models, and have not previously been mixed together to study the vapor-liquid equilibrium of the binary mixtures. In addition, we characterize the microscopic structure of these liquid mixtures. In carbon dioxide + methane at 230 K and 56 bar, the microscopic structure of carbon dioxide in the mixture is the same as that in the pure liquid. In carbon dioxide + difluoromethane at 283 K and 56 bar, the presence of carbon dioxide does not noticeably perturb the liquid structure of difluoromethane, but the structure of carbon dioxide is subtly changed, due to a strong interaction between it and difluoromethane. The simulations in the isobaric-isothermal (NPT) ensemble agree well with the experimental data, except at the two extreme regions of the pressure range. The good agreement of most simulated state points with experimental data encourages one to develop more accurate potentials for predicting the thermodynamic properties of these systems as well as other complicated systems, which are less amenable to measurement by experiment.

  18. Investigation of spontaneous combustion of hydrogen-oxygen mixture using DSMC simulation

    NASA Astrophysics Data System (ADS)

    Yang, Chao; Sun, Quanhua

    2014-12-01

    Combustion has been widely studied in the literature, but very little work was focused on the microscopic level. In this paper, the DSMC method is applied to simulate the microscopic behavior of the spontaneous combustion of hydrogen oxygen mixture. It is found that the ignition delay time of the mixture depends on many factors, such as the physical size, temperature, pressure, and dilution. Comparison between DSMC and CFD results shows that more atomic hydrogen is consumed through reaction HO2+ H → H2+ O2 at temperature close to the extended second explosion limit due to localized distribution of reactants, which may indicate the importance of microscopic behavior on low temperature combustion.

  19. Glass polymorphism in glycerol–water mixtures: I. A computer simulation study

    PubMed Central

    Jahn, David A.; Wong, Jessina; Bachler, Johannes; Loerting, Thomas

    2016-01-01

    We perform out-of-equilibrium molecular dynamics (MD) simulations of water–glycerol mixtures in the glass state. Specifically, we study the transformations between low-density (LDA) and high-density amorphous (HDA) forms of these mixtures induced by compression/decompression at constant temperature. Our MD simulations reproduce qualitatively the density changes observed in experiments. Specifically, the LDA–HDA transformation becomes (i) smoother and (ii) the hysteresis in a compression/decompression cycle decreases as T and/or glycerol content increase. This is surprising given the fast compression/decompression rates (relative to experiments) accessible in MD simulations. We study mixtures with glycerol molar concentration χ g = 0–13% and find that, for the present mixture models and rates, the LDA–HDA transformation is detectable up to χ g ≈ 5%. As the concentration increases, the density of the starting glass (i.e., LDA at approximately χ g ≤ 5%) rapidly increases while, instead, the density of HDA remains practically constant. Accordingly, the LDA state and hence glass polymorphism become inaccessible for glassy mixtures with approximately χ g > 5%. We present an analysis of the molecular-level changes underlying the LDA–HDA transformation. As observed in pure glassy water, during the LDA-to-HDA transformation, water molecules within the mixture approach each other, moving from the second to the first hydration shell and filling the first interstitial shell of water molecules. Interestingly, similar changes also occur around glycerol OH groups. It follows that glycerol OH groups contribute to the density increase during the LDA–HDA transformation. An analysis of the hydrogen bond (HB)-network of the mixtures shows that the LDA–HDA transformation is accompanied by minor changes in the number of HBs of water and glycerol. Instead, large changes in glycerol and water coordination numbers occur. We also perform a detailed analysis of the

  20. Glass polymorphism in glycerol-water mixtures: I. A computer simulation study.

    PubMed

    Jahn, David A; Wong, Jessina; Bachler, Johannes; Loerting, Thomas; Giovambattista, Nicolas

    2016-04-28

    We perform out-of-equilibrium molecular dynamics (MD) simulations of water-glycerol mixtures in the glass state. Specifically, we study the transformations between low-density (LDA) and high-density amorphous (HDA) forms of these mixtures induced by compression/decompression at constant temperature. Our MD simulations reproduce qualitatively the density changes observed in experiments. Specifically, the LDA-HDA transformation becomes (i) smoother and (ii) the hysteresis in a compression/decompression cycle decreases as T and/or glycerol content increase. This is surprising given the fast compression/decompression rates (relative to experiments) accessible in MD simulations. We study mixtures with glycerol molar concentration χ(g) = 0-13% and find that, for the present mixture models and rates, the LDA-HDA transformation is detectable up to χ(g) ≈ 5%. As the concentration increases, the density of the starting glass (i.e., LDA at approximately χ(g) ≤ 5%) rapidly increases while, instead, the density of HDA remains practically constant. Accordingly, the LDA state and hence glass polymorphism become inaccessible for glassy mixtures with approximately χ(g) > 5%. We present an analysis of the molecular-level changes underlying the LDA-HDA transformation. As observed in pure glassy water, during the LDA-to-HDA transformation, water molecules within the mixture approach each other, moving from the second to the first hydration shell and filling the first interstitial shell of water molecules. Interestingly, similar changes also occur around glycerol OH groups. It follows that glycerol OH groups contribute to the density increase during the LDA-HDA transformation. An analysis of the hydrogen bond (HB)-network of the mixtures shows that the LDA-HDA transformation is accompanied by minor changes in the number of HBs of water and glycerol. Instead, large changes in glycerol and water coordination numbers occur. We also perform a detailed analysis of the effects that

  1. Simulation and analysis of grinding wheel based on Gaussian mixture model

    NASA Astrophysics Data System (ADS)

    Chi, Yulun; Li, Haolin

    2012-12-01

    This article presents an application of numerical simulation technique for the generation and analysis of the grinding wheel surface topographies. The ZETA 20 imaging and metrology microscope is employed to measure the surface topographies. The Gaussian mixture model (GMM) is used to transform the measured non-Gaussian field to Gaussian fields, and the simulated topographies are generated. Some numerical examples are used to illustrate the viability of the method. It shows that the simulated grinding wheel topographies are similar with the measured and can be effective used to study the abrasive grains and grinding mechanism.

  2. A molecular dynamics simulation study of dynamic process and mesoscopic structure in liquid mixture systems

    NASA Astrophysics Data System (ADS)

    Yang, Peng

    The focus of this dissertation is the Molecular Dynamics (MD) simulation study of two different systems. In thefirst system, we study the dynamic process of graphene exfoliation, particularly graphene dispersion using ionic surfactants (Chapter 2). In the second system, we investigate the mesoscopic structure of binary solute/ionic liquid (IL) mixtures through the comparison between simulations and corresponding experiments (Chapter 3 and 4). In the graphene exfoliation study, we consider two separation mechanisms: changing the interlayer distance and sliding away the relative distance of two single-layer graphene sheets. By calculating the energy barrier as a function of separation (interlayer or sliding-away) distance and performing sodium dodecyl sulfate (SDS) structure analysis around graphene surface in SDS surfactant/water + bilayer graphene mixture systems, we find that the sliding-away mechanism is the dominant, feasible separation process. In this process, the SDS-graphene interaction gradually replaces the graphene-graphene Van der Waals (VdW) interaction, and decreases the energy barrier until almost zero at critical SDS concentration. In solute/IL study, we investigate nonpolar (CS2) and dipolar (CH 3CN) solute/IL mixture systems. MD simulation shows that at low concentrations, IL is nanosegregated into an ionic network and nonpolar domain. It is also found that CS2 molecules tend to be localized into the nonpolar domain, while CH3CN interacts with nonpolar domain as well as with the charged head groups in the ionic network because of its amphiphilicity. At high concentrations, CH3CN molecules eventually disrupt the nanostructural organization. This dissertation is organized in four chapters: (1) introduction to graphene, ionic liquids and the methodology of MD; (2) MD simulation of graphene exfoliation; (3) Nanostructural organization in acetonitrile/IL mixtures; (4) Nanostructural organization in carbon disulfide/IL mixtures; (5) Conclusions. Results

  3. Isotopic Soret effect in ternary mixtures: Theoretical predictions and molecular simulations

    SciTech Connect

    Artola, Pierre-Arnaud; Rousseau, Bernard

    2015-11-07

    In this paper, we study the Soret effect in ternary fluid mixtures of isotopic argon like atoms. Soret coefficients have been computed using non-equilibrium molecular dynamics and a theoretical approach based on our extended Prigogine model (with mass effect) and generalized to mixtures with any number of components. As is well known for binary mixture studies, the heaviest component always accumulates on the cold side whereas the lightest species accumulate on the hot side. An interesting behavior is observed for the species with the intermediate mass: it can accumulate on both sides, depending on composition and mass ratios. A simple picture can be given to understand this change of sign: the intermediate mass species can be seen as evolving in an equivalent fluid whose species mass varies with composition. An excellent prediction of all simulated data has been obtained using our model including the change of sign of the Soret coefficient for species with intermediate mass.

  4. A beta-mixture quantile normalization method for correcting probe design bias in Illumina Infinium 450 k DNA methylation data

    PubMed Central

    Teschendorff, Andrew E.; Marabita, Francesco; Lechner, Matthias; Bartlett, Thomas; Tegner, Jesper; Gomez-Cabrero, David; Beck, Stephan

    2013-01-01

    Motivation: The Illumina Infinium 450 k DNA Methylation Beadchip is a prime candidate technology for Epigenome-Wide Association Studies (EWAS). However, a difficulty associated with these beadarrays is that probes come in two different designs, characterized by widely different DNA methylation distributions and dynamic range, which may bias downstream analyses. A key statistical issue is therefore how best to adjust for the two different probe designs. Results: Here we propose a novel model-based intra-array normalization strategy for 450 k data, called BMIQ (Beta MIxture Quantile dilation), to adjust the beta-values of type2 design probes into a statistical distribution characteristic of type1 probes. The strategy involves application of a three-state beta-mixture model to assign probes to methylation states, subsequent transformation of probabilities into quantiles and finally a methylation-dependent dilation transformation to preserve the monotonicity and continuity of the data. We validate our method on cell-line data, fresh frozen and paraffin-embedded tumour tissue samples and demonstrate that BMIQ compares favourably with two competing methods. Specifically, we show that BMIQ improves the robustness of the normalization procedure, reduces the technical variation and bias of type2 probe values and successfully eliminates the type1 enrichment bias caused by the lower dynamic range of type2 probes. BMIQ will be useful as a preprocessing step for any study using the Illumina Infinium 450 k platform. Availability: BMIQ is freely available from http://code.google.com/p/bmiq/. Contact: a.teschendorff@ucl.ac.uk Supplementary information: Supplementary data are available at Bioinformatics online PMID:23175756

  5. Transport properties of carbon dioxide and ammonia in water - ethylene glycol mixtures from molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Iskrenova, Eugeniya; Patnaik, Soumya S.

    2015-03-01

    The endothermic decomposition of ammonium carbamate has been proposed as a novel heat sink mechanism for aircraft thermal management (Johnson et al. SAE Technical Paper 2012-01-2190, 2012, doi:10.4271/2012-01-2190]). The products of this decomposition are carbon dioxide and ammonia which need to be efficiently removed in order to better control the decomposition reaction. Molecular dynamics simulations can provide insight into the transport properties of carbon dioxide and ammonia in the carrier fluid. In this work, an extensive set of molecular dynamics simulations was performed to better quantify the concentration dependence of solubility and diffusivity of carbon dioxide and ammonia in water, ethylene glycol, and their mixtures at standard temperature and pressure and at elevated temperature. The simulation results confirm the experimental observations that ammonia is more soluble than carbon dioxide in either water or ethylene glycol and that both carbon dioxide and ammonia are more soluble in ethylene glycol than in water. The simulations of water - ethylene glycol mixtures show that increasing the molar fraction of ethylene glycol leads to increased solubility of carbon dioxide and ammonia in the mixture. The authors gratefully acknowledge the DoD High Performance Computing Centers for computational resources.

  6. Exploring fluctuations and phase equilibria in fluid mixtures via Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Denton, Alan R.; Schmidt, Michael P.

    2013-03-01

    Monte Carlo simulation provides a powerful tool for understanding and exploring thermodynamic phase equilibria in many-particle interacting systems. Among the most physically intuitive simulation methods is Gibbs ensemble Monte Carlo (GEMC), which allows direct computation of phase coexistence curves of model fluids by assigning each phase to its own simulation cell. When one or both of the phases can be modelled virtually via an analytic free energy function (Mehta and Kofke 1993 Mol. Phys. 79 39), the GEMC method takes on new pedagogical significance as an efficient means of analysing fluctuations and illuminating the statistical foundation of phase behaviour in finite systems. Here we extend this virtual GEMC method to binary fluid mixtures and demonstrate its implementation and instructional value with two applications: (1) a lattice model of simple mixtures and polymer blends and (2) a free-volume model of a complex mixture of colloids and polymers. We present algorithms for performing Monte Carlo trial moves in the virtual Gibbs ensemble, validate the method by computing fluid demixing phase diagrams, and analyse the dependence of fluctuations on system size. Our open-source simulation programs, coded in the platform-independent Java language, are suitable for use in classroom, tutorial, or computational laboratory settings.

  7. Comparison of PARASOL Observations with Polarized Reflectances Simulated Using Different Ice Habit Mixtures

    NASA Technical Reports Server (NTRS)

    Cole, Benjamin H.; Yang, Ping; Baum, Bryan A.; Riedi, Jerome; Labonnote, Laurent C.; Thieuleux, Francois; Platnick, Steven

    2012-01-01

    Insufficient knowledge of the habit distribution and the degree of surface roughness of ice crystals within ice clouds is a source of uncertainty in the forward light scattering and radiative transfer simulations required in downstream applications involving these clouds. The widely used MODerate Resolution Imaging Spectroradiometer (MODIS) Collection 5 ice microphysical model assumes a mixture of various ice crystal shapes with smooth-facets except aggregates of columns for which a moderately rough condition is assumed. When compared with PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) polarized reflection data, simulations of polarized reflectance using smooth particles show a poor fit to the measurements, whereas very rough-faceted particles provide an improved fit to the polarized reflectance. In this study a new microphysical model based on a mixture of 9 different ice crystal habits with severely roughened facets is developed. Simulated polarized reflectance using the new ice habit distribution is calculated using a vector adding-doubling radiative transfer model, and the simulations closely agree with the polarized reflectance observed by PARASOL. The new general habit mixture is also tested using a spherical albedo differences analysis, and surface roughening is found to improve the consistency of multi-angular observations. It is suggested that an ice model incorporating an ensemble of different habits with severely roughened surfaces would potentially be an adequate choice for global ice cloud retrievals.

  8. Mixtures of protic ionic liquids and molecular cosolvents: a molecular dynamics simulation.

    PubMed

    Docampo-Álvarez, Borja; Gómez-González, Víctor; Méndez-Morales, Trinidad; Carrete, Jesús; Rodríguez, Julio R; Cabeza, Óscar; Gallego, Luis J; Varela, Luis M

    2014-06-07

    In this work, the effect of molecular cosolvents (water, ethanol, and methanol) on the structure of mixtures of these compounds with a protic ionic liquid (ethylammonium nitrate) is analyzed by means of classical molecular dynamics simulations. Included are as-yet-unreported measurements of the densities of these mixtures, used to test our parameterized potential. The evolution of the structure of the mixtures throughout the concentration range is reported by means of the calculation of coordination numbers and the fraction of hydrogen bonds in the system, together with radial and spatial distribution functions for the various molecular species and molecular ions in the mixture. The overall picture indicates a homogeneous mixing process of added cosolvent molecules, which progressively accommodate themselves in the network of hydrogen bonds of the protic ionic liquid, contrarily to what has been reported for their aprotic counterparts. Moreover, no water clustering similar to that in aprotic mixtures is detected in protic aqueous mixtures, but a somehow abrupt replacing of [NO3](-) anions in the first hydration shell of the polar heads of the ionic liquid cations is registered around 60% water molar concentration. The spatial distribution functions of water and alcohols differ in the coordination type, since water coordinates with [NO3](-) in a bidentate fashion in the equatorial plane of the anion, while alcohols do it in a monodentate fashion, competing for the oxygen atoms of the anion. Finally, the collision times of the different cosolvent molecules are also reported by calculating their velocity autocorrelation functions, and a caging effect is observed for water molecules but not in alcohol mixtures.

  9. Mixtures of protic ionic liquids and molecular cosolvents: A molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Docampo-Álvarez, Borja; Gómez-González, Víctor; Méndez-Morales, Trinidad; Carrete, Jesús; Rodríguez, Julio R.; Cabeza, Óscar; Gallego, Luis J.; Varela, Luis M.

    2014-06-01

    In this work, the effect of molecular cosolvents (water, ethanol, and methanol) on the structure of mixtures of these compounds with a protic ionic liquid (ethylammonium nitrate) is analyzed by means of classical molecular dynamics simulations. Included are as-yet-unreported measurements of the densities of these mixtures, used to test our parameterized potential. The evolution of the structure of the mixtures throughout the concentration range is reported by means of the calculation of coordination numbers and the fraction of hydrogen bonds in the system, together with radial and spatial distribution functions for the various molecular species and molecular ions in the mixture. The overall picture indicates a homogeneous mixing process of added cosolvent molecules, which progressively accommodate themselves in the network of hydrogen bonds of the protic ionic liquid, contrarily to what has been reported for their aprotic counterparts. Moreover, no water clustering similar to that in aprotic mixtures is detected in protic aqueous mixtures, but a somehow abrupt replacing of [NO3]- anions in the first hydration shell of the polar heads of the ionic liquid cations is registered around 60% water molar concentration. The spatial distribution functions of water and alcohols differ in the coordination type, since water coordinates with [NO3]- in a bidentate fashion in the equatorial plane of the anion, while alcohols do it in a monodentate fashion, competing for the oxygen atoms of the anion. Finally, the collision times of the different cosolvent molecules are also reported by calculating their velocity autocorrelation functions, and a caging effect is observed for water molecules but not in alcohol mixtures.

  10. Molecular dynamics simulation of benzene-propene-cumene mixtures in different phases.

    PubMed

    Yang, Xiaofeng; Qin, Zhangfeng; Wang, Guofu; Wang, Jianguo

    2009-09-10

    Molecular dynamics simulations have been performed to study the microscopic configuration and dynamic behavior of mixtures of benzene, propene, and cumene for the cumene synthesis process. The comparisons have been made for the intermolecular radial distribution functions of the binary and ternary mixtures at the conditions that are near, below, and above their respective critical points. The results have shown that in both binary and ternary mixtures propene molecules have a small tendency to cluster in the liquid state, but at supercritical conditions they tend to be uniformly distributed. Contrary to propene, cumene molecules have a tendency to cluster in ternary mixtures. A moderate local density augmentation is also found in the benzene-propene binary supercritical fluid. The excess functions for benzene-propene binary mixtures have shown that there exists an enhancement of the potential energy when benzene mixes with propene. This enhancement provides a rational explanation for the experimental critical properties, which exhibit the behavior of the nonmonotonous dependence of critical pressure on compositions.

  11. Hydrogen-water mixtures in giant planet interiors studied with ab initio simulations

    NASA Astrophysics Data System (ADS)

    Soubiran, F.; Militzer, B.

    2015-12-01

    We study water-hydrogen mixtures under planetary interior conditions using ab initio molecular dynamics simulations. We determine the thermodynamic properties of various water-hydrogen mixing ratios at temperatures of 2000 and 6000 K for pressures of a few tens of GPa. These conditions are relevant for ice giant planets and for the outer envelope of the gas giants. We find that at 2000 K the mixture is in a molecular regime, while at 6000 K the dissociation of hydrogen and water is important and affects the thermodynamic properties. We study the structure of the liquid and analyze the radial distribution function. We provide estimates for the transport properties, diffusion and viscosity, based on autocorrelation functions. We obtained viscosity estimates of the order of a few tenths of mPa s for the conditions under consideration. These results are relevant for dynamo simulations of ice giant planets.

  12. An iterative procedure for obtaining maximum-likelihood estimates of the parameters for a mixture of normal distributions, 2

    NASA Technical Reports Server (NTRS)

    Peters, B. C., Jr.; Walker, H. F.

    1976-01-01

    The problem of obtaining numerically maximum likelihood estimates of the parameters for a mixture of normal distributions is addressed. In recent literature, a certain successive approximations procedure, based on the likelihood equations, is shown empirically to be effective in numerically approximating such maximum-likelihood estimates; however, the reliability of this procedure was not established theoretically. Here, a general iterative procedure is introduced, of the generalized steepest-ascent (deflected-gradient) type, which is just the procedure known in the literature when the step-size is taken to be 1. With probability 1 as the sample size grows large, it is shown that this procedure converges locally to the strongly consistent maximum-likelihood estimate whenever the step-size lies between 0 and 2. The step-size which yields optimal local convergence rates for large samples is determined in a sense by the separation of the component normal densities and is bounded below by a number between 1 and 2.

  13. Thermal reactivity of mixtures of VDDT lubricant and simulated Hanford Tank 241-SY-101 waste

    SciTech Connect

    Scheele, R.D.; Panisko, F.E.; Sell, R.L.

    1996-09-01

    To predict whether the Polywater G lubricant residue remaining in the velocity, density, and temperature tree (VDTT) and the waste in Tank 241-SY-101 (101SY) will be chemically compatible with wastes in 101SY when two VDTTs are removed from 101SY, the Pacific Northwest National Laboratory measured the thermal reaction sensitivity of the lubricant residue. This residue is a simulated 101SY waste containing the organic surrogate trisodium hydroxyethyl-ethylenediaminetriacetate (Na{sub 3}HEDTA) and two simulated potential waste and lubricant residue mixtures containing 10 and 90 percent lubricant residue. These studies using accelerating rate calorimetry found that the residue did not react at a rate exceeding 0.1 J/min/g mixture up to 190 degrees C with simulated 101SY waste containing Na{sub 3}HEDTA as the organic surrogate. Also, the dried lubricant residue did not decompose exothermically at a rate exceeding 0.1 J/min/g. Using guidelines used by the chemical industry, these results indicate that the lubricant residue should not react as a significant rate with the waste in 101SY when added to the waste at 60 degrees C or when the mixture cools to the waste`s temperature of 48 degrees C.

  14. Interfacial properties of binary mixtures of square-well molecules from Monte Carlo simulation.

    PubMed

    Martínez-Ruiz, F J; Blas, F J

    2016-04-21

    We determine the interfacial properties of mixtures of spherical square-well molecules from direct simulation of the vapor-liquid interface. We consider mixtures with the same molecular size and intermolecular potential range but different dispersive energy parameter values. We perform Monte Carlo simulations in the canonical ensemble to obtain the interfacial properties of mixtures of square-well molecules. In particular, we determine the pressuretensor using the mechanical (virial) route and the vapor-liquid interfacial tension evaluated using the Irving-Kirkwood method. In addition to the pressuretensor and the surface tension, we also obtain density profiles, coexistence densities, and interfacial thickness as functions of pressure, at a given temperature. This work can be considered as the extension of our previous work [F. J. Martínez-Ruiz and F. J. Blas, Mol. Phys. 113, 1217 (2015)] to deal with mixtures of spherical molecules that interact through a discontinuous intermolecular potential. According to our results, the main effect of increasing the ratio between the dispersive energy parameters of the mixture, ϵ22/ϵ11, is to sharpen the vapor-liquid interface and to increase the width of the biphasic coexistence region. Particularly interesting is the presence of a relative maximum in the density profiles of the more volatile component at the interface. This maximum is related with adsorption or accumulation of these molecules at the interface, since there are stronger attractive interactions between these molecules in comparison with the rest of intermolecular interactions. Also, the interfacial thickness decreases and the surface tension increases as ϵ22/ϵ11 is larger, a direct consequence of the increasing of the cohesive energy of the system.

  15. Interfacial properties of binary mixtures of square-well molecules from Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Martínez-Ruiz, F. J.; Blas, F. J.

    2016-04-01

    We determine the interfacial properties of mixtures of spherical square-well molecules from direct simulation of the vapor-liquid interface. We consider mixtures with the same molecular size and intermolecular potential range but different dispersive energy parameter values. We perform Monte Carlo simulations in the canonical ensemble to obtain the interfacial properties of mixtures of square-well molecules. In particular, we determine the pressure tensor using the mechanical (virial) route and the vapor-liquid interfacial tension evaluated using the Irving-Kirkwood method. In addition to the pressure tensor and the surface tension, we also obtain density profiles, coexistence densities, and interfacial thickness as functions of pressure, at a given temperature. This work can be considered as the extension of our previous work [F. J. Martínez-Ruiz and F. J. Blas, Mol. Phys. 113, 1217 (2015)] to deal with mixtures of spherical molecules that interact through a discontinuous intermolecular potential. According to our results, the main effect of increasing the ratio between the dispersive energy parameters of the mixture, ɛ22/ɛ11, is to sharpen the vapor-liquid interface and to increase the width of the biphasic coexistence region. Particularly interesting is the presence of a relative maximum in the density profiles of the more volatile component at the interface. This maximum is related with adsorption or accumulation of these molecules at the interface, since there are stronger attractive interactions between these molecules in comparison with the rest of intermolecular interactions. Also, the interfacial thickness decreases and the surface tension increases as ɛ22/ɛ11 is larger, a direct consequence of the increasing of the cohesive energy of the system.

  16. First-Principles Petascale Simulations for Predicting Deflagration to Detonation Transition in Hydrogen-Oxygen Mixtures

    SciTech Connect

    Khokhlov, Alexei; Austin, Joanna; Bacon, C.

    2015-03-02

    Hydrogen has emerged as an important fuel across a range of industries as a means of achieving energy independence and to reduce emissions. DDT and the resulting detonation waves in hydrogen-oxygen can have especially catastrophic consequences in a variety of industrial and energy producing settings related to hydrogen. First-principles numerical simulations of flame acceleration and DDT are required for an in-depth understanding of the phenomena and facilitating design of safe hydrogen systems. The goals of this project were (1) to develop first-principles petascale reactive flow Navier-Stokes simulation code for predicting gaseous high-speed combustion and detonation (HSCD) phenomena and (2) demonstrate feasibility of first-principles simulations of rapid flame acceleration and deflagration-to-detonation transition (DDT) in stoichiometric hydrogen-oxygen mixture (2H2 + O2). The goals of the project have been accomplished. We have developed a novel numerical simulation code, named HSCD, for performing first-principles direct numerical simulations of high-speed hydrogen combustion. We carried out a series of validating numerical simulations of inert and reactive shock reflection experiments in shock tubes. We then performed a pilot numerical simulation of flame acceleration in a long pipe. The simulation showed the transition of the rapidly accelerating flame into a detonation. The DDT simulations were performed using BG/Q Mira at the Argonne National Laboratory, currently the fourth fastest super-computer in the world.

  17. Homogeneous states in driven granular mixtures: Enskog kinetic theory versus molecular dynamics simulations.

    PubMed

    Khalil, Nagi; Garzó, Vicente

    2014-04-28

    The homogeneous state of a binary mixture of smooth inelastic hard disks or spheres is analyzed. The mixture is driven by a thermostat composed by two terms: a stochastic force and a drag force proportional to the particle velocity. The combined action of both forces attempts to model the interaction of the mixture with a bath or surrounding fluid. The problem is studied by means of two independent and complementary routes. First, the Enskog kinetic equation with a Fokker-Planck term describing interactions of particles with thermostat is derived. Then, a scaling solution to the Enskog kinetic equation is proposed where the dependence of the scaled distributions φi of each species on the granular temperature occurs not only through the dimensionless velocity c = v/v0 (v0 being the thermal velocity) but also through the dimensionless driving force parameters. Approximate forms for φi are constructed by considering the leading order in a Sonine polynomial expansion. The ratio of kinetic temperatures T1/T2 and the fourth-degree velocity moments λ1 and λ2 (which measure non-Gaussian properties of φ1 and φ2, respectively) are explicitly determined as a function of the mass ratio, size ratio, composition, density, and coefficients of restitution. Second, to assess the reliability of the theoretical results, molecular dynamics simulations of a binary granular mixture of spheres are performed for two values of the coefficient of restitution (α = 0.9 and 0.8) and three different solid volume fractions (ϕ = 0.00785, 0.1, and 0.2). Comparison between kinetic theory and computer simulations for the temperature ratio shows excellent agreement, even for moderate densities and strong dissipation. In the case of the cumulants λ1 and λ2, good agreement is found for the lower densities although significant discrepancies between theory and simulation are observed with increasing density.

  18. Equations of State for Mixtures: Results from DFT Simulations of Xenon/Ethane Mixtures Compared to High Accuracy Validation Experiments on Z

    NASA Astrophysics Data System (ADS)

    Magyar, Rudolph

    2013-06-01

    We report a computational and validation study of equation of state (EOS) properties of liquid / dense plasma mixtures of xenon and ethane to explore and to illustrate the physics of the molecular scale mixing of light elements with heavy elements. Accurate EOS models are crucial to achieve high-fidelity hydrodynamics simulations of many high-energy-density phenomena such as inertial confinement fusion and strong shock waves. While the EOS is often tabulated for separate species, the equation of state for arbitrary mixtures is generally not available, requiring properties of the mixture to be approximated by combining physical properties of the pure systems. The main goal of this study is to access how accurate this approximation is under shock conditions. Density functional theory molecular dynamics (DFT-MD) at elevated-temperature and pressure is used to assess the thermodynamics of the xenon-ethane mixture. The simulations are unbiased as to elemental species and therefore provide comparable accuracy when describing total energies, pressures, and other physical properties of mixtures as they do for pure systems. In addition, we have performed shock compression experiments using the Sandia Z-accelerator on pure xenon, ethane, and various mixture ratios thereof. The Hugoniot results are compared to the DFT-MD results and the predictions of different rules for combing EOS tables. The DFT-based simulation results compare well with the experimental points, and it is found that a mixing rule based on pressure equilibration performs reliably well for the mixtures considered. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  19. Dynamical properties of alcohol + 1-hexyl-3-methylimidazolium ionic liquid mixtures: a computer simulation study.

    PubMed

    Méndez-Morales, Trinidad; Carrete, Jesús; García, Manuel; Cabeza, Oscar; Gallego, Luis J; Varela, Luis M

    2011-12-29

    In this work, extensive molecular dynamics simulations of the dynamics of mixtures of ionic liquids (ILs) composed of the cation 1-hexyl-3-methylimidazolium and several anions of different hydrophobicity degrees (Cl(-), BF(4)(-), PF(6)(-)) with alcohols of different chain lengths (methanol and ethanol) are reported. We evaluated the influence of the nature of the anion, the length of the molecular chain of the alcohol, and the alcohol concentration on some dynamical properties of the mixtures, such as self-diffusion coefficients of all the species, mean square displacements (with an analysis of both ballistic and diffusive regimes), and velocity autocorrelation functions of alcohol molecules. The diffusivity of the mixtures was found to be highly dependent on the nature of the anion since the interaction between chloride and alcohols is greater than that with fluorinated anions and leads to slower dynamics. Additionally, our results show that self-diffusion coefficients increase with alcohol concentration. On the other hand, a subdiffusive regime over thousands of picoseconds was detected at intermediate times through analysis of the center-of-mass mean square displacements of alcohol molecules, a region that becomes narrower as alcohol concentration increases. Finally, the study of the role of the anion and of solvent concentration on velocity autocorrelation functions reflects an increase in mean collision times as the amount of alcohol increases until the value of pure alcohols is reached. These collision times are smaller in mixtures with halogenated ILs.

  20. Mutual and Self-Diffusivities in Binary Mixtures of [EMIM][B(CN)4] with Dissolved Gases by Using Dynamic Light Scattering and Molecular Dynamics Simulations.

    PubMed

    Koller, Thomas M; Heller, Andreas; Rausch, Michael H; Wasserscheid, Peter; Economou, Ioannis G; Fröba, Andreas P

    2015-07-09

    Ionic liquids (ILs) are possible working fluids for the separation of carbon dioxide (CO2) from flue gases. For evaluating their performance in such processes, reliable mutual-diffusivity data are required for mixtures of ILs with relevant flue gas components. In the present study, dynamic light scattering (DLS) and molecular dynamics (MD) simulations were used for the investigation of the molecular diffusion in binary mixtures of the IL 1-ethyl-3-methylimidazolium tetracyanoborate ([EMIM][B(CN)4]) with the dissolved gases carbon dioxide, nitrogen, carbon monoxide, hydrogen, methane, oxygen, and hydrogen sulfide at temperatures from 298.15 to 363.15 K and pressures up to 63 bar. At conditions approaching infinite dilution of a gas, the Fick mutual diffusivity of the mixture measured by DLS and the self-diffusivity of the corresponding gas calculated by MD simulations match, which could be generally found within combined uncertainties. The obtained diffusivities are in agreement with literature data for the same or comparable systems as well as with the general trend of increasing diffusivities for decreasing IL viscosities. The DLS and MD results reveal distinctly larger molecular diffusivities for [EMIM][B(CN)4]-hydrogen mixtures compared to mixtures with all other gases. This behavior results in the failure of an empirical correlation with the molar volumes of the gases at their normal boiling points. The DLS experiments also showed that there is no noticeable influence of the dissolved gas and temperature on the thermal diffusivity of the studied systems.

  1. Molecular simulation study of water--methanol mixtures in activated carbon pores

    SciTech Connect

    Shevade, Abhijit V.; Jiang, Shaoyi; Gubbins, Keith E.

    2000-10-22

    We report a theoretical study of the adsorption behavior of water--methanol mixtures in slit activated carbon micropores. The adsorption isotherms are obtained for a pore of width 2 nm at a temperature of 298 K from grand canonical ensemble Monte Carlo simulations. The water molecules are modeled using the four point transferable intermolecular potential functions (TIP4P) and methanol by the optimized potentials for liquid simulations (OPLS). Carboxyl (COOH) groups are used as active sites on a structured carbon surface. The effect of the relative contributions from dispersion and hydrogen bonding interactions of adsorbates, and of the chemical activation of adsorbents on adsorption behavior is investigated. The adsorption of the mixture components in activated carbon pores occurs by continuous filling, without the sharp capillary condensation observed in graphite pores. Water is preferentially adsorbed over methanol in activated carbon pores for a wide range of pressures, except at lower pressures. The hydrophilic nature of activated carbon pores results in the complexation of both water and methanol molecules with the active sites on the surfaces, leading to bulklike water behavior over the entire pore width. Solvation forces are also calculated as a function of pore size. The negative values found for the solvation force for all pore sizes reflect the hydrophilic interactions of the mixtures with the activated carbon surfaces. {copyright} 2000 American Institute of Physics [S0021-9606(00)51339-7

  2. Hydrogen bonding in a mixture of protic ionic liquids: a molecular dynamics simulation study.

    PubMed

    Paschek, Dietmar; Golub, Benjamin; Ludwig, Ralf

    2015-04-07

    We report results of molecular dynamics (MD) simulations characterising the hydrogen bonding in mixtures of two different protic ionic liquids sharing the same cation: triethylammonium-methylsulfonate (TEAMS) and triethylammonium-triflate (TEATF). The triethylammonium-cation acts as a hydrogen-bond donor, being able to donate a single hydrogen-bond. Both, the methylsulfonate- and the triflate-anions can act as hydrogen-bond acceptors, which can accept multiple hydrogen bonds via their respective SO3-groups. In addition, replacing a methyl-group in the methylsulfonate by a trifluoromethyl-group in the triflate significantly weakens the strength of a hydrogen bond from an adjacent triethylammonium cation to the oxygen-site in the SO3-group of the anion. Our MD simulations show that these subtle differences in hydrogen bond strength significantly affect the formation of differently-sized hydrogen-bonded aggregates in these mixtures as a function of the mixture-composition. Moreover, the reported hydrogen-bonded cluster sizes can be predicted and explained by a simple combinatorial lattice model, based on the approximate coordination number of the ions, and using statistical weights that mostly account for the fact that each anion can only accept three hydrogen bonds.

  3. Coarse-Grained Molecular Monte Carlo Simulations of Liquid Crystal-Nanoparticle Mixtures

    NASA Astrophysics Data System (ADS)

    Neufeld, Ryan; Kimaev, Grigoriy; Fu, Fred; Abukhdeir, Nasser M.

    Coarse-grained intermolecular potentials have proven capable of capturing essential details of interactions between complex molecules, while substantially reducing the number of degrees of freedom of the system under study. In the domain of liquid crystals, the Gay-Berne (GB) potential has been successfully used to model the behavior of rod-like and disk-like mesogens. However, only ellipsoid-like interaction potentials can be described with GB, making it a poor fit for many real-world mesogens. In this work, the results of Monte Carlo simulations of liquid crystal domains using the Zewdie-Corner (ZC) potential are presented. The ZC potential is constructed from an orthogonal series of basis functions, allowing for potentials of essentially arbitrary shapes to be modeled. We also present simulations of mixtures of liquid crystalline mesogens with nanoparticles. Experimentally these mixtures have been observed to exhibit microphase separation and formation of long-range networks under some conditions. This highlights the need for a coarse-grained approach which can capture salient details on the molecular scale while simulating sufficiently large domains to observe these phenomena. We compare the phase behavior of our simulations with that of a recently presented continuum theory. This work was made possible by the Natural Sciences and Engineering Research Council of Canada and Compute Ontario.

  4. Quantifying Vegetation Change in Semiarid Environments: Precision and Accuracy of Spectral Mixture Analysis and the Normalized Difference Vegetation Index

    NASA Technical Reports Server (NTRS)

    Elmore, Andrew J.; Mustard, John F.; Manning, Sara J.; Elome, Andrew J.

    2000-01-01

    Because in situ techniques for determining vegetation abundance in semiarid regions are labor intensive, they usually are not feasible for regional analyses. Remotely sensed data provide the large spatial scale necessary, but their precision and accuracy in determining vegetation abundance and its change through time have not been quantitatively determined. In this paper, the precision and accuracy of two techniques, Spectral Mixture Analysis (SMA) and Normalized Difference Vegetation Index (NDVI) applied to Landsat TM data, are assessed quantitatively using high-precision in situ data. In Owens Valley, California we have 6 years of continuous field data (1991-1996) for 33 sites acquired concurrently with six cloudless Landsat TM images. The multitemporal remotely sensed data were coregistered to within 1 pixel, radiometrically intercalibrated using temporally invariante surface features and geolocated to within 30 m. These procedures facilitated the accurate location of field-monitoring sites within the remotely sensed data. Formal uncertainties in the registration, radiometric alignment, and modeling were determined. Results show that SMA absolute percent live cover (%LC) estimates are accurate to within ?4.0%LC and estimates of change in live cover have a precision of +/-3.8%LC. Furthermore, even when applied to areas of low vegetation cover, the SMA approach correctly determined the sense of clump, (i.e., positive or negative) in 87% of the samples. SMA results are superior to NDVI, which, although correlated with live cover, is not a quantitative measure and showed the correct sense of change in only 67%, of the samples.

  5. A mixture of hierarchical joint models for longitudinal data with heterogeneity, non-normality, missingness, and covariate measurement error.

    PubMed

    Huang, Yangxin; Yan, Chunning; Yin, Ping; Lu, Meixia

    2016-01-01

    Longitudinal data arise frequently in medical studies and it is a common practice to analyze such complex data with nonlinear mixed-effects (NLME) models. However, the following four issues may be critical in longitudinal data analysis. (i) A homogeneous population assumption for models may be unrealistically obscuring important features of between-subject and within-subject variations; (ii) normality assumption for model errors may not always give robust and reliable results, in particular, if the data exhibit skewness; (iii) the responses may be missing and the missingness may be nonignorable; and (iv) some covariates of interest may often be measured with substantial errors. When carrying out statistical inference in such settings, it is important to account for the effects of these data features; otherwise, erroneous or even misleading results may be produced. Inferential procedures can be complicated dramatically when these four data features arise. In this article, the Bayesian joint modeling approach based on a finite mixture of NLME joint models with skew distributions is developed to study simultaneous impact of these four data features, allowing estimates of both model parameters and class membership probabilities at population and individual levels. A real data example is analyzed to demonstrate the proposed methodologies, and to compare various scenarios-based potential models with different specifications of distributions.

  6. Investigation of spontaneous combustion of hydrogen-oxygen mixture using DSMC simulation

    SciTech Connect

    Yang, Chao; Sun, Quanhua

    2014-12-09

    Combustion has been widely studied in the literature, but very little work was focused on the microscopic level. In this paper, the DSMC method is applied to simulate the microscopic behavior of the spontaneous combustion of hydrogen oxygen mixture. It is found that the ignition delay time of the mixture depends on many factors, such as the physical size, temperature, pressure, and dilution. Comparison between DSMC and CFD results shows that more atomic hydrogen is consumed through reaction HO{sub 2}+H→H{sub 2}+O{sub 2} at temperature close to the extended second explosion limit due to localized distribution of reactants, which may indicate the importance of microscopic behavior on low temperature combustion.

  7. Structural features of binary mixtures of supercritical CO2 with polar entrainers by molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Gurina, D. L.; Antipova, M. L.; Petrenko, V. E.

    2013-10-01

    Computer simulations of supercritical carbon dioxide and its mixtures with polar cosolvents: water, methanol, and ethanol (concentration, 0.125 mole fractions) at T = 318 K and ρ = 0.7 g/cm3 are performed. Atom-atom radial distribution functions are calculated by classical molecular dynamics, while the probability distributions of relative orientation of CO2 molecules in the first and second coordination spheres describing the geometry of the nearest environment of CO2 molecules and the trajectories of cosolvent molecules are found using Car-Parrinello molecular dynamics. Based on the latter, the conclusions regarding structure and interactions of polar entrainers in their mixtures with supercritical CO2 are made. It is shown that the microstructure of carbon dioxide varies only slightly upon the introduction of cosolvents.

  8. Dynamic phase change and local structures in IL-containing mixtures: classical MD simulations and experiments.

    PubMed

    Wu, Yang; Wang, Xia; Liu, Qiaozhen; Ma, Xiaoxue; Fang, Dawei; Jiang, Xuefei; Guan, Wei

    2017-01-25

    The dynamic phase change between a homogeneous mixture and a liquid-liquid biphase and separation of phases are explored in three-component mixtures composed of 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), and water through a classical simulation method and experiment. Different experimental and theoretical tools, including density measurement, dynamic light scattering study, radial distribution, mean square displacement, an interstice model, and statistical function, are used to describe the structural modifications of the ions as a function of solution concentration. An analysis of the relation between the phase and the state of the component ions indicates that the phase separation pattern is governed by the hydrophilicity/hydrophobicity of anions. We proposed the existence of a critical point, that is, 1 : 3 : 8 for [Bmim][PF6]/[Bmim][BF4]/H2O (mole fraction). Before this critical point, obvious phase separation was seen in the mixtures. The separation phase became homogeneous with the addition of [Bmim][BF4] after this critical point. However, this homogeneous mixed solution was phase separated again upon the addition of [Bmim][PF6] or water. The existing nanostructures were present in the [Bmim][PF6]/[Bmim][BF4]/H2O mixtures, and their size abruptly decreased close to the critical point. We provided evidence of the formation of double salt ionic liquids of [Bmim][PF6]0.25[BF4]0.75·2H2O and discussed the interactions involved in these systems by examining their physicochemical properties. The ionic phase response of such three-component mixtures could be useful in various applications, especially in the dynamic control of extraction/separation processing.

  9. Numerical simulation of detonation reignition in H 2-O 2 mixtures in area expansions

    NASA Astrophysics Data System (ADS)

    Jones, D. A.; Kemister, G.; Tonello, N. A.; Oran, E. S.; Sichel, M.

    Time-dependent, two-dimensional, numerical simulations of a transmitted detonation show reignition occuring by one of two mechanisms. The first mechanism involves the collision of triple points as they expand along a decaying shock front. In the second mechanism ignition results from the coalescence of a number of small, relatively high pressure regions left over from the decay of weakened transverse waves. The simulations were performed using an improved chemical kinetic model for stoichiometric H 2-O 2 mixtures. The initial conditions were a propagating, two-dimensional detonation resolved enough to show transverse wave structure. The calculations provide clarification of the reignition mechanism seen in previous H 2-O 2-Ar simulations, and again demonstrate that the transverse wave structure of the detonation front is critical to the reignition process.

  10. Simulation of reactive nanolaminates using reduced models: II. Normal propagation

    SciTech Connect

    Salloum, Maher; Knio, Omar M.

    2010-03-15

    Transient normal flame propagation in reactive Ni/Al multilayers is analyzed computationally. Two approaches are implemented, based on generalization of earlier methodology developed for axial propagation, and on extension of the model reduction formalism introduced in Part I. In both cases, the formulation accommodates non-uniform layering as well as the presence of inert layers. The equations of motion for the reactive system are integrated using a specially-tailored integration scheme, that combines extended-stability, Runge-Kutta-Chebychev (RKC) integration of diffusion terms with exact treatment of the chemical source term. The detailed and reduced models are first applied to the analysis of self-propagating fronts in uniformly-layered materials. Results indicate that both the front velocities and the ignition threshold are comparable for normal and axial propagation. Attention is then focused on analyzing the effect of a gap composed of inert material on reaction propagation. In particular, the impacts of gap width and thermal conductivity are briefly addressed. Finally, an example is considered illustrating reaction propagation in reactive composites combining regions corresponding to two bilayer widths. This setup is used to analyze the effect of the layering frequency on the velocity of the corresponding reaction fronts. In all cases considered, good agreement is observed between the predictions of the detailed model and the reduced model, which provides further support for adoption of the latter. (author)

  11. Thermophysical Properties of Energetic Ionic Liquids/Nitric Acid Mixtures: Insights from Molecular Dynamics Simulations

    DTIC Science & Technology

    2013-01-01

    W L. Physical properties of concentrated nitric acid . UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc56640/.) 23 M. Engelmann... Nitric Acid Mixtures: Insights from Molecular Dynamics Simulations 5a. CONTRACT NUMBER FA9300-11-C-3012 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER...Rev. 8-98) Prescribed by ANSI Std. 239.18 1     Thermophysical  Properties  of  Energetic  Ionic  Liquids/ Nitric   Acid

  12. Infinite swapping replica exchange molecular dynamics leads to a simple simulation patch using mixture potentials.

    PubMed

    Lu, Jianfeng; Vanden-Eijnden, Eric

    2013-02-28

    Replica exchange molecular dynamics (REMD) becomes more efficient as the frequency of swap between the temperatures is increased. Recently Plattner et al. [J. Chem. Phys. 135, 134111 (2011)] proposed a method to implement infinite swapping REMD in practice. Here we introduce a natural modification of this method that involves molecular dynamics simulations over a mixture potential. This modification is both simple to implement in practice and provides a better, energy based understanding of how to choose the temperatures in REMD to optimize efficiency. It also has implications for generalizations of REMD in which the swaps involve other parameters than the temperature.

  13. [Radioprotective action of a GGS-10 gaseous hypoxic mixture on the DNA supramolecular complex of normal tissues and sarcoma 45 of rats].

    PubMed

    Strazhevskaia, N B; Struchkov, V A

    1988-01-01

    Gas hypoxic mixture (GHM-10) inhaled by rats during gamma-irradiation (2 to 20 Gy) effectively protects the supramolecular complex of DNA (SC DNA) in bone marrow and spleen, but fails to protect this complex in sarcoma 45. GHM-10 itself has been shown to induce rapid and prolonged, but irreversible, decrease in SC DNA elastic viscosity in normal tissues.

  14. Fluids and fluid mixtures containing square-well diatomics: Equations of state and canonical molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Gulati, Harpreet S.; Hall, Carol K.

    1997-09-01

    We present new perturbation theory equations of state for square-well dimer fluids, square-well dimer mixtures, square-well dimer/monomer mixtures and square-well heteronuclear dumbbell fluids. Our first- and second-order perturbation terms are based on Barker and Henderson's local compressibility approximation and Chang and Sandler's perturbation theory, respectively. The perturbation approach requires knowledge of the radial distribution functions of the reference hard-dimer fluid and hard dimer/monomer mixture, which are obtained from molecular dynamics simulation. For mixtures we use one fluid mixing rules to approximate the average mixture structure and perturbation parameters. The predictions of the perturbation theory are compared to the compressibility factors obtained from discontinuous canonical molecular dynamics simulation, an adaptation of Anderson's canonical ensemble molecular dynamics method to the case in which the potential is discontinuous.

  15. A molecular dynamics simulations study on ethylene glycol-water mixtures in mesoporous silica

    NASA Astrophysics Data System (ADS)

    Schmitz, Rebecca; Müller, Niels; Ullmann, Svenja; Vogel, Michael

    2016-09-01

    We perform molecular dynamics simulations to investigate structural and dynamical properties of ethylene glycol-water (EG-WA) mixtures in mesoporous silica. To obtain comprehensive insights into the dependence of liquid behaviors on the confinement features, we exploit that straightforward modification of the force field parameters allows us to vary the properties of the hydrogen-bond network of the confined liquid, we alter the polarity of the silica surface, and we consider amorphous as well as crystalline matrices. It is observed that the confinement induces a micro-phase separation in the liquid, which qualitatively depends on the properties of both liquid and matrix so that EG or WA molecules may be preferentially adsorbed at the silica surface. Furthermore, it is found that the confinement strongly affects the liquid dynamics. Largely independent of the polarity and structure of the matrix, structural relaxation is about a factor of 104 slower at the pore wall than in the pore center. Moreover, the non-Arrhenius temperature dependence of the bulk mixture turns into an Arrhenius behavior of the confined mixture so that the spatial restriction can slow down or speed up the structural relaxation, depending on temperature.

  16. Molecular Dynamics Simulation of the Transport Properties of Molten Transuranic Salt Mixtures

    NASA Astrophysics Data System (ADS)

    Baty, Austin; McIntyre, Peter; Sattarov, Akhdiyor; Sooby, Elizabeth

    2012-10-01

    The Accelerator Research Laboratory at Texas A&M is proposing a revolutionary design for accelerator-driven subcritical fission in molten salt (ADSMS), a system that destroys the transuranic elements in spent nuclear fuel. The transuranics are the most enduring hazard of nuclear power, since they contain high radiotoxicity and have half-lives of a thousand to a million years. The ADSMS core is fueled by a homogeneous chloride-based molten salt mixture containing the chlorides of the transuranics and NaCl. Knowledge of the density, heat capacity, thermal conductivity, etc. of the salt mixtures is needed to accurately model the complex ADSMS system. There is a lack of experimental data on the density and transport properties of such mixtures. Molecular dynamics simulations using polarizable ion potentials are used to determine the density and heat capacity of these melts as a function of temperature. Green-Kubo methods are employed to calculate the electrical conductivity, thermal conductivity, and viscosity of the salt using the outputs of the model. Results for pure molten salt systems are compared to experimental data when possible to validate the potentials used. Here we discuss potential salt systems, their neutronic behavior, and the calculated transport properties.

  17. Homogeneous states in driven granular mixtures: Enskog kinetic theory versus molecular dynamics simulations

    SciTech Connect

    Khalil, Nagi Garzó, Vicente

    2014-04-28

    The homogeneous state of a binary mixture of smooth inelastic hard disks or spheres is analyzed. The mixture is driven by a thermostat composed by two terms: a stochastic force and a drag force proportional to the particle velocity. The combined action of both forces attempts to model the interaction of the mixture with a bath or surrounding fluid. The problem is studied by means of two independent and complementary routes. First, the Enskog kinetic equation with a Fokker-Planck term describing interactions of particles with thermostat is derived. Then, a scaling solution to the Enskog kinetic equation is proposed where the dependence of the scaled distributions φ{sub i} of each species on the granular temperature occurs not only through the dimensionless velocity c = v/v{sub 0} (v{sub 0} being the thermal velocity) but also through the dimensionless driving force parameters. Approximate forms for φ{sub i} are constructed by considering the leading order in a Sonine polynomial expansion. The ratio of kinetic temperatures T{sub 1}/T{sub 2} and the fourth-degree velocity moments λ{sub 1} and λ{sub 2} (which measure non-Gaussian properties of φ{sub 1} and φ{sub 2}, respectively) are explicitly determined as a function of the mass ratio, size ratio, composition, density, and coefficients of restitution. Second, to assess the reliability of the theoretical results, molecular dynamics simulations of a binary granular mixture of spheres are performed for two values of the coefficient of restitution (α = 0.9 and 0.8) and three different solid volume fractions (ϕ = 0.00785, 0.1, and 0.2). Comparison between kinetic theory and computer simulations for the temperature ratio shows excellent agreement, even for moderate densities and strong dissipation. In the case of the cumulants λ{sub 1} and λ{sub 2}, good agreement is found for the lower densities although significant discrepancies between theory and simulation are observed with increasing density.

  18. Simulation of front motion in a reacting condensed two phase mixture

    NASA Astrophysics Data System (ADS)

    Markov, Andrey A.; Filimonov, Igor A.; Martirosyan, Karen S.

    2012-08-01

    The computational technique is developed in order to provide the scale capturing for numerical simulation of the thermal processes. The thermal front motion and gas flow dynamics as well as the rate of particle growth during the Carbon Combustion Synthesis of Oxides (CCSO) were predicted using the numerical simulation. In CCSO the exothermic oxidation of carbon nanoparticles generates a self-sustained thermal reaction front that propagates through the solid reactant mixture converting it to the desired complex oxides. The combusted carbon is emitted from the sample as carbon dioxide and its high rate of release increases the product porosity and friability. It was shown that the complicated finger front instability can be developed during the carbon combustion synthesis. This phenomenon results from a vortex gas flow in the reaction zone fed by the carbon dioxide co-flow and oxygen counter-flow filtration.

  19. Catalytic and electrochemical behaviour of solid oxide fuel cell operated with simulated-biogas mixtures

    NASA Astrophysics Data System (ADS)

    Dang-Long, T.; Quang-Tuyen, T.; Shiratori, Y.

    2016-06-01

    Being produced from organic matters of wastes (bio-wastes) through a fermentation process, biogas mainly composed of CH4 and CO2 and can be considered as a secondary energy carrier derived from solar energy. To generate electricity from biogas through the electrochemical process in fuel cells is a state-of-the-art technology possessing higher energy conversion efficiency without harmful emissions compared to combustion process in heat engines. Getting benefits from high operating temperature such as direct internal reforming ability and activation of electrochemical reactions to increase overall system efficiency, solid oxide fuel cell (SOFC) system operated with biogas becomes a promising candidate for distributed power generator for rural applications leading to reductions of environmental issues caused by greenhouse effects and bio-wastes. CO2 reforming of CH4 and electrochemical oxidation of the produced syngas (H2-CO mixture) are two main reaction processes within porous anode material of SOFC. Here catalytic and electrochemical behavior of Ni-ScSZ (scandia stabilized-zirconia) anode in the feed of CH4-CO2 mixtures as simulated-biogas at 800 °C were evaluated. The results showed that CO2 had strong influences on both reaction processes. The increase in CO2 partial pressure resulted in the decrease in anode overvoltage, although open-circuit voltage was dropped. Besides that, the simulation result based on a power-law model for equimolar CH4-CO2 mixture revealed that coking hazard could be suppressed along the fuel flow channel in both open-circuit and closed-circuit conditions.

  20. Accurate schemes for calculation of thermodynamic properties of liquid mixtures from molecular dynamics simulations.

    PubMed

    Caro, Miguel A; Laurila, Tomi; Lopez-Acevedo, Olga

    2016-12-28

    We explore different schemes for improved accuracy of entropy calculations in aqueous liquid mixtures from molecular dynamics (MD) simulations. We build upon the two-phase thermodynamic (2PT) model of Lin et al. [J. Chem. Phys. 119, 11792 (2003)] and explore new ways to obtain the partition between the gas-like and solid-like parts of the density of states, as well as the effect of the chosen ideal "combinatorial" entropy of mixing, both of which have a large impact on the results. We also propose a first-order correction to the issue of kinetic energy transfer between degrees of freedom (DoF). This problem arises when the effective temperatures of translational, rotational, and vibrational DoF are not equal, either due to poor equilibration or reduced system size/time sampling, which are typical problems for ab initio MD. The new scheme enables improved convergence of the results with respect to configurational sampling, by up to one order of magnitude, for short MD runs. To ensure a meaningful assessment, we perform MD simulations of liquid mixtures of water with several other molecules of varying sizes: methanol, acetonitrile, N, N-dimethylformamide, and n-butanol. Our analysis shows that results in excellent agreement with experiment can be obtained with little computational effort for some systems. However, the ability of the 2PT method to succeed in these calculations is strongly influenced by the choice of force field, the fluidicity (hard-sphere) formalism employed to obtain the solid/gas partition, and the assumed combinatorial entropy of mixing. We tested two popular force fields, GAFF and OPLS with SPC/E water. For the mixtures studied, the GAFF force field seems to perform as a slightly better "all-around" force field when compared to OPLS+SPC/E.

  1. Structure and hydrogen bond dynamics of water-dimethyl sulfoxide mixtures by computer simulations

    NASA Astrophysics Data System (ADS)

    Luzar, Alenka; Chandler, David

    1993-05-01

    We have used two different force field models to study concentrated dimethyl sulfoxide (DMSO)-water solutions by molecular dynamics. The results of these simulations are shown to compare well with recent neutron diffraction experiments using H/D isotope substitution [A. K. Soper and A. Luzar, J. Chem. Phys. 97, 1320 (1992)]. Even for the highly concentrated 1 DMSO : 2 H2O solution, the water hydrogen-hydrogen radial distribution function, gHH(r), exhibits the characteristic tetrahedral ordering of water-water hydrogen bonds. Structural information is further obtained from various partial atom-atom distribution functions, not accessible experimentally. The behavior of water radial distribution functions, gOO(r) and gOH(r) indicate that the nearest neighbor correlations among remaining water molecules in the mixture increase with increasing DMSO concentration. No preferential association of methyl groups on DMSO is detected. The pattern of hydrogen bonding and the distribution of hydrogen bond lifetimes in the simulated mixtures is further investigated. Molecular dynamics results show that DMSO typically forms two hydrogen bonds with water molecules. Hydrogen bonds between DMSO and water molecules are longer lived than water-water hydrogen bonds. The hydrogen bond lifetimes determined by reactive flux correlation function approach are about 5 and 3 ps for water-DMSO and water-water pairs, respectively, in 1 DMSO : 2 H2O mixture. In contrast, for pure water, the hydrogen bond lifetime is about 1 ps. We discuss these times in light of experimentally determined rotational relaxation times. The relative values of the hydrogen bond lifetimes are consistent with a statistical (i.e., transition state theory) interpretation.

  2. A simulation assessment of the thermodynamics of dense ion-dipole mixtures with polarization

    SciTech Connect

    Bastea, Sorin

    2014-07-28

    Molecular dynamics (MD) simulations are employed to ascertain the relative importance of various electrostatic interaction contributions, including induction interactions, to the thermodynamics of dense, hot ion-dipole mixtures. In the absence of polarization, we find that an MD-constrained free energy term accounting for the ion-dipole interactions, combined with well tested ionic and dipolar contributions, yields a simple, fairly accurate free energy form that may be a better option for describing the thermodynamics of such mixtures than the mean spherical approximation (MSA). Polarization contributions induced by the presence of permanent dipoles and ions are found to be additive to a good approximation, simplifying the thermodynamic modeling. We suggest simple free energy corrections that account for these two effects, based in part on standard perturbative treatments and partly on comparisons with MD simulation. Even though the proposed approximations likely need further study, they provide a first quantitative assessment of polarization contributions at high densities and temperatures and may serve as a guide for future modeling efforts.

  3. Molecular dynamic simulation of Ar-Kr mixture across a rough walled nanochannel: Velocity & temperature profiles

    NASA Astrophysics Data System (ADS)

    Pooja, Pathania, Y.; Ahluwalia, P. K.

    2015-05-01

    This paper presents the results from a molecular dynamics simulation of mixture of argon and krypton in the Poiseuille flow across a rough walled nanochannel. The roughness effect on liquid nanoflows has recently drawn attention The computational software used for carrying out the molecular dynamics simulations is LAMMPS. The fluid flow takes place between two parallel plates and is bounded by horizontal rough walls in one direction and periodic boundary conditions are imposed in the other two directions. Each fluid atom interacts with other fluid atoms and wall atoms through Leenard-Jones (LJ) potential with a cut off distance of 5.0. To derive the flow a constant force is applied whose value is varied from 0.1 to 0.3 and velocity profiles and temperature profiles are noted for these values of forces. The velocity profile and temperature profiles are also looked at different channel widths of nanochannel and at different densities of mixture. The velocity profile and temperature profile of rough walled nanochannel are compared with that of smooth walled nanochannel and it is concluded that mean velocity increases with increase in channel width, force applied and decrease in density also with introduction of roughness in the walls of nanochannel mean velocity again increases and results also agree with the analytical solution of a Poiseuille flow.

  4. 2D fluid simulations of discharges at atmospheric pressure in reactive gas mixtures

    NASA Astrophysics Data System (ADS)

    Bourdon, Anne

    2015-09-01

    Since a few years, low-temperature atmospheric pressure discharges have received a considerable interest as they efficiently produce many reactive chemical species at a low energy cost. This potential is of great interest for a wide range of applications as plasma assisted combustion or biomedical applications. Then, in current simulations of atmospheric pressure discharges, there is the need to take into account detailed kinetic schemes. It is interesting to note that in some conditions, the kinetics of the discharge may play a role on the discharge dynamics itself. To illustrate this, we consider the case of the propagation of He-N2 discharges in long capillary tubes, studied for the development of medical devices for endoscopic applications. Simulation results put forward that the discharge dynamics and structure depend on the amount of N2 in the He-N2 mixture. In particular, as the amount of N2 admixture increases, the discharge propagation velocity in the tube increases, reaches a maximum for about 0 . 1 % of N2 and then decreases, in agreement with experiments. For applications as plasma assisted combustion with nanosecond repetitively pulsed discharges, there is the need to handle the very different timescales of the nanosecond discharge with the much longer (micro to millisecond) timescales of combustion processes. This is challenging from a computational point of view. It is also important to better understand the coupling of the plasma induced chemistry and the gas heating. To illustrate this, we present the simulation of the flame ignition in lean mixtures by a nanosecond pulsed discharge between two point electrodes. In particular, among the different discharge regimes of nanosecond repetitively pulsed discharges, a ``spark'' regime has been put forward in the experiments, with an ultra-fast local heating of the gas. For other discharge regimes, the gas heating is much weaker. We have simulated the nanosecond spark regime and have observed shock waves

  5. Simulation of Multiphase Water-Carbon Dioxide Mixture Flows in Porous Media

    NASA Astrophysics Data System (ADS)

    Afanasyev, A. A.

    2012-04-01

    Two-phase models are widely used for simulation of CO2 storage in saline aquifers. These models support gaseous phase mainly saturated with CO2 and liquid phase mainly saturated with H2O (e.g. TOUGH2 code). For deep aquifers where CO2 injection may result a plume of supercritical CO2 compositional simulation approach must be applied. This approach originated from petrol reservoir simulation studies is based on a cubic equation of state and is also capable only of single-phase states and two-phase states of liquid-gas type. The goal of the present study lies in development of a new mathematical approach for compositional simulation of carbon sequestration processes. The approach is supposed to be capable both of single-phase and two-phase states of liquid-gas type as in classical models and also of two-phase states of liquid-liquid type and three-phase states at high pressure. The liquid-liquid states are formed by two liquids. The first liquid is mainly saturated with water while the second is mainly saturated with CO2. These thermodynamic equilibriums with liquefied CO2 phase can be detected experimentally (Takenouchi et. al., 1964). The three-phase states represent a composition of the two-phase states of liquid-gas and liquid-liquid types. The three phases are water and CO2 in liquid and gaseous states. As liquefied CO2 is negatively buoyant at high pressure the described states can result in non-classical hydrodynamic effects in the aquifer with CO2 sinking and consequently in non-classical structural trapping scenarios. The distinctive feature of the proposed approach lies in the methodology for mixture properties determination. Transport equations and Darcy law are solved together with calculation of the entropy maximum that is reached in thermodynamic equilibrium and determines the mixture composition. To define and solve the problem only one function - mixture thermodynamic potential - is required. The proposed approach was implemented in MUFITS (Multiphase

  6. Simulations of a binary-sized mixture of inelastic grains in rapid shear flow.

    PubMed

    Clelland, R; Hrenya, C M

    2002-03-01

    In an effort to explore the rapid flow behavior associated with a binary-sized mixture of grains and to assess the predictive ability of the existing theory for such systems, molecular-dynamic simulations have been carried out. The system under consideration is composed of inelastic, smooth, hard disks engaged in rapid shear flow. The simulations indicate that nondimensional stresses decrease with an increase in d(L)/d(S) (ratio of large particle diameter to small particle diameter) or a decrease in nu(L)/nu(S) (area fraction ratio), as is also predicted by the kinetic theory of Willits and Arnarson [Phys. Fluids 11, 3116 (1999)]. Furthermore, the level of quantitative agreement between the theoretical stress predictions and simulation data is good over the entire range of parameters investigated. Nonetheless, the molecular-dynamic simulations also show that the assumption of an equipartition of energy rapidly deteriorates as the coefficient of restitution is decreased. The magnitude of this energy difference is found to increase with the difference in particle sizes.

  7. Flashpoint prediction for ternary mixtures of alcohols with water for CFD simulation of unsteady flame propagation during explosion

    NASA Astrophysics Data System (ADS)

    Skřínský, Jan; Vereš, Ján; Ševčíková, Silvie Petránková

    2016-06-01

    Aqueous solutions of binary and ternary mixtures of alcohols are of considerable interest for a wide range of scientists and technologists. Simple dimensionless experimental formulae based on rational reciprocal and polynomial functions are proposed for correlation of the flashpoint data of binary mixtures of two components. The formulae are based on data obtained from flashpoint experiments and predictions. The main results are the derived experimental flashpoint values for ternary mixtures of two aqueous-organic solutions and the model prediction of maximum explosion pressure values for the studied mixtures. Potential application for the results concerns the assessment of fire and explosion hazards, and the development of inherently safer designs for chemical processes containing binary and ternary partially miscible mixtures of an aqueous-organic system. The goal of this article is to present the results of modelling using these standard models and to demonstrate its importance in the area of CFD simulation.

  8. Simulation techniques for estimating error in the classification of normal patterns

    NASA Technical Reports Server (NTRS)

    Whitsitt, S. J.; Landgrebe, D. A.

    1974-01-01

    Methods of efficiently generating and classifying samples with specified multivariate normal distributions were discussed. Conservative confidence tables for sample sizes are given for selective sampling. Simulation results are compared with classified training data. Techniques for comparing error and separability measure for two normal patterns are investigated and used to display the relationship between the error and the Chernoff bound.

  9. Modeling sorption of neutral organic compound mixtures to simulated aquifer sorbents with pseudocompounds.

    PubMed

    Joo, Jin Chul; Shackelford, Charles D; Reardon, Kenneth F

    2013-01-01

    The feasibility of the ideal adsorbed solution theory (IAST) in reducing the complexity associated with predicting the sorption behaviors of 12 neutral organic compounds (NOCs) contained in complex mixtures as a fewer number (four to six) of pseudocompounds (groups of compounds) to simulated aquifer sorbents was investigated. All sorption isotherms from individual- and multiple-pseudocompound systems were fit reasonably well ( ≥ 0.953) by the Freundlich sorption model over the range of aqueous concentrations evaluated (i.e., ≤200 μmol L). The presence and magnitude of mutual competition among pseudocompounds varied depending on the composition of the mixtures (i.e., concentrations and polarities of pseudocompounds) and the properties of sorbents (i.e., the fraction of organic carbon and the availability of hydrophilic specific sorption sites). Finally, comparisons between the IAST-based predictions with individual-pseudocompound sorption parameters and experimentally measured data revealed that the accuracy in predicting the sorption behaviors of several NOCs in terms of a fewer number of pseudocompounds decreased with increasing deviations from the assumption of equal and ideal competition in the IAST (i.e., differential availability of sorption sites and nonideal competitions among pseudocompounds).

  10. Direct Numerical Simulations of Autoignition in Stratified Dimethyl-ether (DME)/Air Turbulent Mixtures

    SciTech Connect

    Bansal, Gaurav; Mascarenhas, Ajith; Chen, Jacqueline H.

    2014-10-01

    In our paper, two- and three-dimensional direct numerical simulations (DNS) of autoignition phenomena in stratified dimethyl-ether (DME)/air turbulent mixtures are performed. A reduced DME oxidation mechanism, which was obtained using rigorous mathematical reduction and stiffness removal procedure from a detailed DME mechanism with 55 species, is used in the present DNS. The reduced DME mechanism consists of 30 chemical species. This study investigates the fundamental aspects of turbulence-mixing-autoignition interaction occurring in homogeneous charge compression ignition (HCCI) engine environments. A homogeneous isotropic turbulence spectrum is used to initialize the velocity field in the domain. Moreover, the computational configuration corresponds to a constant volume combustion vessel with inert mass source terms added to the governing equations to mimic the pressure rise due to piston motion, as present in practical engines. DME autoignition is found to be a complex three-staged process; each stage corresponds to a distinct chemical kinetic pathway. The distinct role of turbulence and reaction in generating scalar gradients and hence promoting molecular transport processes are investigated. Then, by applying numerical diagnostic techniques, the different heat release modes present in the igniting mixture are identified. In particular, the contribution of homogeneous autoignition, spontaneous ignition front propagation, and premixed deflagration towards the total heat release are quantified.

  11. Direct Numerical Simulations of Autoignition in Stratified Dimethyl-ether (DME)/Air Turbulent Mixtures

    DOE PAGES

    Bansal, Gaurav; Mascarenhas, Ajith; Chen, Jacqueline H.

    2014-10-01

    In our paper, two- and three-dimensional direct numerical simulations (DNS) of autoignition phenomena in stratified dimethyl-ether (DME)/air turbulent mixtures are performed. A reduced DME oxidation mechanism, which was obtained using rigorous mathematical reduction and stiffness removal procedure from a detailed DME mechanism with 55 species, is used in the present DNS. The reduced DME mechanism consists of 30 chemical species. This study investigates the fundamental aspects of turbulence-mixing-autoignition interaction occurring in homogeneous charge compression ignition (HCCI) engine environments. A homogeneous isotropic turbulence spectrum is used to initialize the velocity field in the domain. Moreover, the computational configuration corresponds to amore » constant volume combustion vessel with inert mass source terms added to the governing equations to mimic the pressure rise due to piston motion, as present in practical engines. DME autoignition is found to be a complex three-staged process; each stage corresponds to a distinct chemical kinetic pathway. The distinct role of turbulence and reaction in generating scalar gradients and hence promoting molecular transport processes are investigated. Then, by applying numerical diagnostic techniques, the different heat release modes present in the igniting mixture are identified. In particular, the contribution of homogeneous autoignition, spontaneous ignition front propagation, and premixed deflagration towards the total heat release are quantified.« less

  12. Hydrogen Bonding and Dielectric Spectra of Ethylene Glycol–Water Mixtures from Molecular Dynamics Simulations

    PubMed Central

    2016-01-01

    Mixtures of ethylene glycol with water are a prominent example of media with variable viscosity. Classical molecular dynamics simulations at room temperature were performed for mixtures of ethylene glycol (EG) and water with EG mole fractions of xE = 0.0, 0.1, 0.2, 0.4, 0.6, 0.9, 1.0. The calculated dielectric loss spectra were in qualitative agreement with experiment. We found a slightly overestimated slowdown of the dynamics with increasing EG concentration compared to experimental data. Statistics of the hydrogen bond network and hydrogen bond lifetimes were derived from suitable time correlation functions and also show a slowdown in the dynamics with increasing xE. A similar picture is predicted for the time scales of EG conformer changes and for molecular reorientation. A slight blue shift was obtained for the power spectra of the molecular center of mass motion. The results were used to give a qualitative interpretation of the origin of three different relaxation times that appear in experimental complex dielectric spectra and of their change with xE. PMID:27649083

  13. Simulation of abrasive flow machining process for 2D and 3D mixture models

    NASA Astrophysics Data System (ADS)

    Dash, Rupalika; Maity, Kalipada

    2015-12-01

    Improvement of surface finish and material removal has been quite a challenge in a finishing operation such as abrasive flow machining (AFM). Factors that affect the surface finish and material removal are media viscosity, extrusion pressure, piston velocity, and particle size in abrasive flow machining process. Performing experiments for all the parameters and accurately obtaining an optimized parameter in a short time are difficult to accomplish because the operation requires a precise finish. Computational fluid dynamics (CFD) simulation was employed to accurately determine optimum parameters. In the current work, a 2D model was designed, and the flow analysis, force calculation, and material removal prediction were performed and compared with the available experimental data. Another 3D model for a swaging die finishing using AFM was simulated at different viscosities of the media to study the effects on the controlling parameters. A CFD simulation was performed by using commercially available ANSYS FLUENT. Two phases were considered for the flow analysis, and multiphase mixture model was taken into account. The fluid was considered to be a

  14. Method for Performing an Efficient Monte Carlo Simulation of Lipid Mixtures on a Concurrent Computer

    NASA Astrophysics Data System (ADS)

    Moore, Andrew; Huang, Juyang; Gibson, Thomas

    2003-10-01

    We are interested in performing extensive Monte Carlo simulations of lipid mixtures in cell membranes. These computations will be performed on a Gnu/Linux Beowulf cluster using the industry-standard Message Passing Interface (MPI) for handling node-to-node communication and overall program management. Devising an efficient parallel decomposition of the simulation is crucial for success. The goal is to balance the load on the compute nodes so that each does the same amount of work and to minimize the amount of (relatively slow) node-to-node communication. To this end, we report a method for performing simulations on a boundless three-dimensional surface. The surface is modeled by a two-dimensional array which can represent either a rectangular or triangular lattice. The array is distributed evenly across multiple processors in a block-row configuration. The sequence of calculations minimizes the delay from passing messages between nodes and uses the delay that does exist to perform local operations on each node.

  15. Theoretical and computer simulation study of phase coexistence of nonadditive hard-disk mixtures.

    PubMed

    Fiumara, Giacomo; Pandaram, Owen D; Pellicane, Giuseppe; Saija, Franz

    2014-12-07

    We have studied the equation of state (EOS) and the equilibrium behavior of a two-component mixture of equal-sized, nonadditive hard disks with an interspecies collision diameter that is larger than that of each component. For this purpose, we have calculated the fifth virial coefficient by evaluating numerically the irreducible cluster integrals by a Monte Carlo method. This information is used to calculate both the virial equation of state and an equation of state based on a resummation of the virial expansion. Then, the fluid-fluid phase coexistence boundaries are determined by integrating the EOS so as to obtain the free energy of the system. Canonical and Gibbs ensemble Monte Carlo simulations over a wide range of nonadditivity are also performed in order to provide a benchmark to the theoretical predictions.

  16. Molecular dynamics simulations of the structure of the graphene-ionic liquid/alkali salt mixtures interface.

    PubMed

    Méndez-Morales, Trinidad; Carrete, Jesús; Pérez-Rodríguez, Martín; Cabeza, Óscar; Gallego, Luis J; Lynden-Bell, Ruth M; Varela, Luis M

    2014-07-14

    We performed molecular dynamics simulations of mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate with lithium tetrafluoroborate and potassium tetrafluoroborate between two charged and uncharged graphene walls, in order to analyze the structure of the well-known formation of layers that takes place on liquids under confinement. For this purpose, we studied the molecular density profiles, free energy profiles for bringing lithium and potassium cations from the bulk mixture to the graphene wall and the orientational distributions of imidazolium rings within the first adsorbed layer as a function of salt concentration and electrode potential. The charge densities in the electrodes were chosen to be zero and ±1 e nm(-2), and the salt molar percentages were %salt = 0, 10 and 25. We found that the layered structure extends up to 1-2 nm, where the bulk behaviour is recovered. In addition, whereas for the neutral surface the layers are composed of both ionic species, increasing the electrode potential, the structure changes to alternating cationic and anionic layers leading to an overcompensation of the charge of the previous layer. We also calculated the distribution of angles of imidazolium rings near neutral and charged graphene walls, finding a limited influence of the added salt. In addition, the average tilt of the imidazolium ring within the first layer goes from 36° with respect to a normal vector to the uncharged graphene wall to 62° in the presence of charged walls. The free energy profiles revealed that lithium and potassium ions are adsorbed on the negative surface only for the highest amount of salt, since the free energy barriers for approaching this electrode are considerably higher than kBT.

  17. Perception of Speech Simulating Different Configurations of Hearing Loss in Normal Hearing Individuals

    ERIC Educational Resources Information Center

    Kumar, Prawin; Yathiraj, Asha

    2009-01-01

    The present study aimed at assessing perception of filtered speech that simulated different configurations of hearing loss. The simulation was done by filtering four equivalent lists of a monosyllabic test developed by Shivaprasad for Indian-English speakers. This was done using the Adobe Audition software. Thirty normal hearing participants in…

  18. Low-Dose Pesticide Mixture Induces Senescence in Normal Mesenchymal Stem Cells (MSC) and Promotes Tumorigenic Phenotype in Premalignant MSC.

    PubMed

    Hochane, Mazene; Trichet, Valerie; Pecqueur, Claire; Avril, Pierre; Oliver, Lisa; Denis, Jerome; Brion, Regis; Amiaud, Jerome; Pineau, Alain; Naveilhan, Philippe; Heymann, Dominique; Vallette, François M; Olivier, Christophe

    2017-03-01

    Humans are chronically exposed to multiple environmental pollutants such as pesticides with no significant evidence about the safety of such poly-exposures. We exposed mesenchymal stem cells (MSC) to very low doses of mixture of seven pesticides frequently detected in food samples for 21 days in vitro. We observed a permanent phenotype modification with a specific induction of an oxidative stress-related senescence. Pesticide mixture also induced a shift in MSC differentiation towards adipogenesis but did not initiate a tumorigenic transformation. In modified MSC in which a premalignant phenotype was induced, the exposure to pesticide mixture promoted tumorigenic phenotype both in vitro and in vivo after cell implantation, in all nude mice. Our results suggest that a common combination of pesticides can induce a premature ageing of adult MSC, and as such could accelerate age-related diseases. Exposure to pesticide mixture may also promote the tumorigenic transformation in a predisposed stromal environment. Abstract Video Link: https://youtu.be/mfSVPTol-Gk Stem Cells 2017;35:800-811.

  19. On a modified Monte-Carlo method and variable soft sphere model for rarefied binary gas mixture flow simulation

    NASA Astrophysics Data System (ADS)

    Nourazar, S. S.; Jahangiri, P.; Aboutalebi, A.; Ganjaei, A. A.; Nourazar, M.; Khadem, J.

    2011-06-01

    The effect of new terms in the improved algorithm, the modified direct simulation Monte-Carlo (MDSMC) method, is investigated by simulating a rarefied binary gas mixture flow inside a rotating cylinder. Dalton law for the partial pressures contributed by each species of the binary gas mixture is incorporated into our simulation using the MDSMC method and the direct simulation Monte-Carlo (DSMC) method. Moreover, the effect of the exponent of the cosine of deflection angle (α) in the inter-molecular collision models, the variable soft sphere (VSS) and the variable hard sphere (VHS), is investigated in our simulation. The improvement of the results of simulation is pronounced using the MDSMC method when compared with the results of the DSMC method. The results of simulation using the VSS model show some improvements on the result of simulation for the mixture temperature at radial distances close to the cylinder wall where the temperature reaches the maximum value when compared with the results using the VHS model.

  20. An Adaptive Multigrid Algorithm for Simulating Solid Tumor Growth Using Mixture Models

    PubMed Central

    Wise, S.M.; Lowengrub, J.S.; Cristini, V.

    2010-01-01

    In this paper we give the details of the numerical solution of a three-dimensional multispecies diffuse interface model of tumor growth, which was derived in (Wise et al., J. Theor. Biol. 253 (2008)) and used to study the development of glioma in (Frieboes et al., NeuroImage 37 (2007) and tumor invasion in (Bearer et al., Cancer Research, 69 (2009)) and (Frieboes et al., J. Theor. Biol. 264 (2010)). The model has a thermodynamic basis, is related to recently developed mixture models, and is capable of providing a detailed description of tumor progression. It utilizes a diffuse interface approach, whereby sharp tumor boundaries are replaced by narrow transition layers that arise due to differential adhesive forces among the cell-species. The model consists of fourth-order nonlinear advection-reaction-diffusion equations (of Cahn-Hilliard-type) for the cell-species coupled with reaction-diffusion equations for the substrate components. Numerical solution of the model is challenging because the equations are coupled, highly nonlinear, and numerically stiff. In this paper we describe a fully adaptive, nonlinear multigrid/finite difference method for efficiently solving the equations. We demonstrate the convergence of the algorithm and we present simulations of tumor growth in 2D and 3D that demonstrate the capabilities of the algorithm in accurately and efficiently simulating the progression of tumors with complex morphologies. PMID:21076663

  1. Molecular dynamics simulation of phase and structural transitions in model lung surfactant mixtures

    NASA Astrophysics Data System (ADS)

    Duncan, Susan L.

    Lung surfactant (LS) is a complex mixture of lipids and proteins that reduces and regulates the surface tension in the lungs, thereby decreasing the work of breathing. A thorough understanding of LS function is critical to the development and optimization of synthetic surfactants for the treatment of neonatal and adult respiratory distress syndrome. We have utilized coarse-grained (CG) molecular dynamics simulation to study the dynamic, hysteretic changes occurring in the structure and phase of model surfactant mixtures with varying temperature, pressure and composition. In particular, we have studied the effects of the LS components palmitoyloleoylphosphatidylglycerol (POPG), palmitoyloleoylphosphatidylcholine (POPC), palmitic acid (PA), cholesterol, and two surface-active proteins SP-B 1--25 (the 25-residue N-terminal fragment of SP-B), and SP-C on model surfactant monolayers containing the primary lipid component dipalmitoylphosphatidylcholine (DPPC). The results indicate that POPG, POPC, SP-B1--25 and SP-C act as fluidizers and PA and cholesterol act as condensing agents, which change the phase-transition temperature, LC-LE phase distribution, and the extent of hysteresis. To explore the role of LS proteins SP-B and SP-C in storing and redelivering lipid from lipid monolayers during the compression and re-expansion occurring in lungs during breathing, we have simulated 2D-to-3D transitions at the interface. These simulations show that at near-zero surface tension the presence of a fluidizing agent, such as POPG, SP-C, or SP-B 1--25 decreases the monolayers resistance to bending allowing the monolayers to form large undulations and ultimately folds. Another folding mechanism is also observed in monolayers containing peptides, involving the lipid-mediated aggregation of the peptides into a defect, from which the fold can nucleate. The occurrence of folding depends on the hydrophobic character of the peptides; if the number of hydrophobic residues is decreased

  2. Molecular simulation and macroscopic modeling of the diffusion of hydrogen, carbon monoxide and water in heavy n-alkane mixtures.

    PubMed

    Makrodimitri, Zoi A; Unruh, Dominik J M; Economou, Ioannis G

    2012-03-28

    The self-diffusion coefficient of hydrogen (H(2)), carbon monoxide (CO) and water (H(2)O) in n-alkanes was studied by molecular dynamics simulation. Diffusion in a few pure n-alkanes (namely n-C(8), n-C(20), n-C(64) and n-C(96)) was examined. In addition, binary n-C(12)-n-C(96) mixtures with various compositions as well as more realistic five- and six-n-alkane component mixtures were simulated. In all cases, the TraPPE united atom force field was used for the n-alkane molecules. The force field for the mixture of n-alkanes was initially validated against experimental density values and was shown to be accurate. Moreover, macroscopic correlations for predicting diffusion coefficient of H(2), CO and H(2)O in n-alkanes and mixtures of n-alkanes were developed. The functional form of the correlation was based on the rough hard sphere theory (RHS). The correlation was applied to simulation data and an absolute average deviation (AAD) of 5.8% for pure n-alkanes and 3.4% for n-alkane mixtures was obtained. Correlation parameters vary in a systematic way with carbon number and so they can be used to provide predictions in the absence of any experimental or molecular simulation data. Finally, in order to reduce the number of adjustable parameters, for the n-alkane mixtures the "pseudo-carbon number" approach was used. This approach resulted in relatively higher deviation from MD simulation data (AAD of 18.2%); however, it provides a convenient and fast method to predict diffusion coefficients. The correlations developed here are expected to be useful for engineering calculations related to the design of the Gas-to-Liquid process.

  3. Monte Carlo simulations of high-pressure phase equilibria of CO2-H2O mixtures.

    PubMed

    Liu, Yang; Panagiotopoulos, Athanassios Z; Debenedetti, Pablo G

    2011-05-26

    Histogram-reweighting grand canonical Monte Carlo simulations were used to obtain the phase behavior of CO(2)-H(2)O mixtures over a broad temperature and pressure range (50 °C ≤ T ≤ 350 °C, 0 ≤ P ≤ 1000 bar). We performed a comprehensive test of several existing water (SPC, TIP4P, TIP4P2005, and exponential-6) and carbon dioxide (EPM2, TraPPE, and exponential-6) models using conventional Lorentz-Berthelot combining rules for the unlike-pair parameters. None of the models we studied reproduce adequately experimental data over the entire temperature and pressure range, but critical assessments were made on the range of T and P where particular model pairs perform better. Away from the critical region (T ≤ 250 °C), the exponential-6 model combination yields the best predictions for the CO(2)-rich phase, whereas the TraPPE/TIP4P2005 model combination provides the most accurate coexistence composition and pressure for the H(2)O-rich phase. Near the critical region (250 °C < T ≤ 350 °C), the critical points are not accurately estimated by any of the models studied, but the exponential-6 models are able to qualitatively capture the critical loci and the shape of the phase envelopes. Local improvements can be achieved at specific temperatures by introducing modification factors to the Lorentz-Berthelot combining rules, but the modified combining rule is still not able to achieve global improvements over the entire temperature and pressure range. Our work points to the challenge and importance of improving current atomistic models so as to accurately predict the phase behavior of this important binary mixture.

  4. Unprecedentedly high selective adsorption of gas mixtures in rho zeolite-like metal-organic framework: a molecular simulation study.

    PubMed

    Babarao, Ravichandar; Jiang, Jianwen

    2009-08-19

    We report a molecular simulation study for the separation of industrially important gas mixtures (CO(2)/H(2), CO(2)/CH(4), and CO(2)/N(2)) in rho zeolite-like metal-organic framework (rho-ZMOF). Rho-ZMOF contains a wide-open anionic framework and charge-balancing extraframework Na(+) ions. Two types of binding sites for Na(+) ions are identified in the framework. Site I is in the single eight-membered ring, whereas site II is in the alpha-cage. Na(+) ions at site I have a stronger affinity for the framework and thus a smaller mobility. The binding sites in rho-ZMOF resemble those in its inorganic counterpart rho-zeolite. CO(2) is adsorbed predominantly over other gases because of its strong electrostatic interactions with the charged framework and the presence of Na(+) ions acting as additional adsorption sites. At ambient temperature and pressure, the CO(2) selectivities are 1800 for the CO(2)/H(2) mixture, 80 for the CO(2)/CH(4) mixture, and 500 for the CO(2)/N(2) mixture. Compared with other MOFs and nanoporous materials reported to date, rho-ZMOF exhibits unprecedentedly high selective adsorption for these gas mixtures. This work represents the first simulation study to characterize extraframework ions and examine gas separation in a charged ZMOF. The simulation results reveal that rho-ZMOF is a promising candidate for the separation of syngas, natural gas, and flue gas.

  5. Molecular dynamics simulation of nanostructural organization in ionic liquid/water mixtures.

    PubMed

    Jiang, Wei; Wang, Yanting; Voth, Gregory A

    2007-05-10

    Molecular dynamics simulations have been carried out to investigate nanostructural organization in mixtures of 1-octyl-3-methylimidazolium nitrate ionic liquid and water at multiple water concentrations. Evolution of the polar network, water network, and micelle structures is visualized and analyzed via partial radial distribution functions. The calculated static partial structure factors show that within the range of water contents examined, polar networks, water networks, and micelles possess an approximately invariant characteristic length at around 20 A. Furthermore, the above calculations point out that, as the amount of water increases, the polar network is continuously broken up (screened) by the intruding water, while the structural organization of the water network and the micelle exhibits a turnover. At the turnover point, the most ordered micelle (cation-cation) structure and water (water-anion-water) network are formed. Thereafter, the structural organization abates drastically, and only loose micelle structure exists due to the dominant water-water interactions. The simulated turnover of structural organization agrees with the sharpest peak in the experimentally obtained structure factor in aqueous solutions of similar ionic liquids; the simulated water structure reveals that water can form liquidlike associated aggregates due to the planar symmetry and strong basicity of NO(3)-, in agreement with experiment. The turnover of structural organization of micelles results from the persistent competition between the hydrophobic interactions of the nonpolar groups and the breakup of the charged polar network with increasing water content, whereas the turnover of the water network results from the competition between the water-water and water-anion interactions.

  6. Surgical workflow analysis with Gaussian mixture multivariate autoregressive (GMMAR) models: a simulation study.

    PubMed

    Loukas, Constantinos; Georgiou, Evangelos

    2013-01-01

    There is currently great interest in analyzing the workflow of minimally invasive operations performed in a physical or simulation setting, with the aim of extracting important information that can be used for skills improvement, optimization of intraoperative processes, and comparison of different interventional strategies. The first step in achieving this goal is to segment the operation into its key interventional phases, which is currently approached by modeling a multivariate signal that describes the temporal usage of a predefined set of tools. Although this technique has shown promising results, it is challenged by the manual extraction of the tool usage sequence and the inability to simultaneously evaluate the surgeon's skills. In this paper we describe an alternative methodology for surgical phase segmentation and performance analysis based on Gaussian mixture multivariate autoregressive (GMMAR) models of the hand kinematics. Unlike previous work in this area, our technique employs signals from orientation sensors, attached to the endoscopic instruments of a virtual reality simulator, without considering which tools are employed at each time-step of the operation. First, based on pre-segmented hand motion signals, a training set of regression coefficients is created for each surgical phase using multivariate autoregressive (MAR) models. Then, a signal from a new operation is processed with GMMAR, wherein each phase is modeled by a Gaussian component of regression coefficients. These coefficients are compared to those of the training set. The operation is segmented according to the prior probabilities of the surgical phases estimated via GMMAR. The method also allows for the study of motor behavior and hand motion synchronization demonstrated in each phase, a quality that can be incorporated into modern laparoscopic simulators for skills assessment.

  7. The effect of simulated hamstring shortening on gait in normal subjects.

    PubMed

    Whitehead, C L; Hillman, S J; Richardson, A M; Hazlewood, M E; Robb, J E

    2007-06-01

    The purpose of this study was to determine the effect of simulated hamstring shortening on gait in normal subjects. Six normal subjects wore an adjustable brace to simulate three different hamstring lengths. Evaluation of the physiological cost index (PCI) and gait analysis revealed that simulated hamstring shortening produced adverse affects in the gait of normal subjects. Significant effects were only observed when the popliteal angle exceeded 85 degrees (p<0.001) and included increased effort of walking (PCI), decreased speed, stride and step length; decreased hip flexion and increased knee flexion in stance, increased posterior pelvic tilt, decreased pelvic obliquity and rotation and premature ankle dorsi- and plantar-flexion in stance. These results emphasise the need to consider the effects of changing the length of the hamstrings on joints other than the hip and knee when assessing patients for hamstring lengthening.

  8. Molecular Simulation of the Vapor-Liquid Phase Behavior of Lennard-Jones Mixtures in Porous Solids

    DTIC Science & Technology

    2006-09-01

    is used to simulate Lennard - Jones fluid mixtures at several porosities: 0.9, 0.95, and 0.975. Effects based on the size and the energetics of the...to the bulk fluid behavior, dramatic shifts in the phase envelope were found for even highly porous structures. Both the Lennard - Jones size and energy

  9. Simulation of the transition radiation detection conditions in the ATLAS TRT detector filled with argon and krypton gas mixtures

    SciTech Connect

    Boldyrev, A. S.; Maevskiy, A. S.

    2015-12-15

    Performance of the Transition Radiation Tracker (TRT) at the ATLAS experiment with argon and krypton gas mixtures was simulated. The efficiency of transition radiation registration, which is necessary for electron identification, was estimated along with the electron identification capabilities under such conditions.

  10. Understanding liquid mixture phase miscibility via pair energy parameter behaviors with respect to temperatures determined from molecular simulations.

    PubMed

    Oh, Suk Yung; Bae, Young Chan

    2011-05-19

    The miscibility behaviors of binary liquid mixtures were studied by a combination of molecular simulations and thermodynamic theories. Pairwise interaction parameters were obtained from molecular simulations that accounted for the effect of temperature. From a thermodynamic perspective, different types of liquid-liquid equilibrium (LLE) and different degrees of miscibility can be expressed in terms of energy behaviors with respect to temperature. Our simulation results proved this viewpoint by showing a correspondence between the simulation results and experimental observations. To describe phase diagrams, thermodynamic modeling is presented using the energy parameters obtained from the simulations. Correlations are needed to correct size mismatches between the simulations and the thermodynamic model. Using this method, not only the upper critical solution temperature (UCST) but also the closed-loop miscibility phase diagrams could be calculated without requiring additional parameters for specific interactions. The utility of this method is demonstrated for mixtures containing water, hydrocarbon, alcohols, aldehydes, ketones, chlorides, amines, nitriles, sulfides, and other organic liquids in various temperature ranges. The method presented in this paper can facilitate the understanding of the miscibilities in binary liquid mixtures from the viewpoint of thermal energy behaviors.

  11. Effect of clay content and mineralogy on frictional sliding behavior of simulated gouges: Binary and ternary mixtures of quartz, illite, and montmorillonite

    NASA Astrophysics Data System (ADS)

    Tembe, Sheryl; Lockner, David A.; Wong, Teng-Fong

    2010-03-01

    We investigated the frictional sliding behavior of simulated quartz-clay gouges under stress conditions relevant to seismogenic depths. Conventional triaxial compression tests were conducted at 40 MPa effective normal stress on saturated saw cut samples containing binary and ternary mixtures of quartz, montmorillonite, and illite. In all cases, frictional strengths of mixtures fall between the end-members of pure quartz (strongest) and clay (weakest). The overall trend was a decrease in strength with increasing clay content. In the illite/quartz mixture the trend was nearly linear, while in the montmorillonite mixtures a sigmoidal trend with three strength regimes was noted. Microstructural observations were performed on the deformed samples to characterize the geometric attributes of shear localization within the gouge layers. Two micromechanical models were used to analyze the critical clay fractions for the two-regime transitions on the basis of clay porosity and packing of the quartz grains. The transition from regime 1 (high strength) to 2 (intermediate strength) is associated with the shift from a stress-supporting framework of quartz grains to a clay matrix embedded with disperse quartz grains, manifested by the development of P-foliation and reduction in Riedel shear angle. The transition from regime 2 (intermediate strength) to 3 (low strength) is attributed to the development of shear localization in the clay matrix, occurring only when the neighboring layers of quartz grains are separated by a critical clay thickness. Our mixture data relating strength degradation to clay content agree well with strengths of natural shear zone materials obtained from scientific deep drilling projects.

  12. Effect of clay content and mineralogy on frictional sliding behavior of simulated gouges: binary and ternary mixtures of quartz, illite, and montmorillonite

    USGS Publications Warehouse

    Tembe, Sheryl; Lockner, David A.; Wong, Teng-Fong

    2010-01-01

    We investigated the frictional sliding behavior of simulated quartz-clay gouges under stress conditions relevant to seismogenic depths. Conventional triaxial compression tests were conducted at 40 MPa effective normal stress on saturated saw cut samples containing binary and ternary mixtures of quartz, montmorillonite, and illite. In all cases, frictional strengths of mixtures fall between the end-members of pure quartz (strongest) and clay (weakest). The overall trend was a decrease in strength with increasing clay content. In the illite/quartz mixture the trend was nearly linear, while in the montmorillonite mixtures a sigmoidal trend with three strength regimes was noted. Microstructural observations were performed on the deformed samples to characterize the geometric attributes of shear localization within the gouge layers. Two micromechanical models were used to analyze the critical clay fractions for the two-regime transitions on the basis of clay porosity and packing of the quartz grains. The transition from regime 1 (high strength) to 2 (intermediate strength) is associated with the shift from a stress-supporting framework of quartz grains to a clay matrix embedded with disperse quartz grains, manifested by the development of P-foliation and reduction in Riedel shear angle. The transition from regime 2 (intermediate strength) to 3 (low strength) is attributed to the development of shear localization in the clay matrix, occurring only when the neighboring layers of quartz grains are separated by a critical clay thickness. Our mixture data relating strength degradation to clay content agree well with strengths of natural shear zone materials obtained from scientific deep drilling projects.

  13. Solvation of Mg2+ ions in methanol-water mixtures: Molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Rybicki, Marcin; Hawlicka, Ewa

    2012-05-01

    Molecular dynamics simulations of MgCl2 solutions in methanol-water mixtures, over the whole range of the methanol mole fraction at room temperature have been performed. The methanol and water molecules have been modeled as flexible three-site bodies. Solvation of the magnesium ions has been discussed on the basis of the radial and angular distribution functions, the orientation of the solvent molecules and their geometrical arrangement in the coordination shells. Analysis of the H-bonds of the solvent molecules coordinated by Mg2+ has been based on a geometric criterion of the H-bond. Persistence of the primary and secondary shell has been estimated. In all studied solutions Mg2+ is six-coordinated and the solvent molecules form an octahedron. The antidipole orientation of the molecules favours the water molecules as H-donors in the first shell and the methanol molecules as H-acceptor in the second shell. Thus an excess of water and an excess of methanol has been observed in the first and the second shells of Mg2+. An exchange of the solvent molecules between the primary and secondary shells occur. The persistence of the second shell is longer than the shells of monovalent ions.

  14. Pressure and concentration dependences of the autoignition temperature for normal butane + air mixtures in a closed vessel

    SciTech Connect

    Chandraratna, M.R.; Griffiths, J.F. . School of Chemistry)

    1994-12-01

    The condition at which autoignition occurs in lean premixed n-butane + air mixtures over the composition range 0.2%--2.5% n-butane by volume (0.06 < [phi] < 0.66) were investigated experimentally. Total reactant pressure from 0.1 to 0.6 MPa (1--6 atm) were studied in a spherical, stainless-steel, closed vessel (0.5 dm[sup 3]). There is a critical transition from nonignition to ignition, at pressures above 0.1 MPa, as the mixture is enriched in the vicinity of 1% fuel vapor by volume. There is also a region of multiplicity, which exhibits three critical temperatures at a given composition. Chemical analyses show that partially oxygenated components,including many o-heterocyclic compounds, are important products of the lean combustion of butane at temperatures up to 800 K. The critical conditions for autoignition are discussed with regard to industrial ignition hazards, especially in the context of the autoignition temperature of alkanes given by ASTM or BS tests. The differences between the behavior of n-butane and the higher n-alkanes are explained. The experimental results are also used as a basis for testing a reduced kinetic model to represent the oxidation and autoignition of n-butane or other alkanes.

  15. An Attempt to Simulate Letter-by-Letter Dyslexia in Normal Readers

    ERIC Educational Resources Information Center

    Fiset, Stephanie; Arguin, Martin; Fiset, Daniel

    2006-01-01

    We attempted to simulate the main features of letter-by-letter (LBL) dyslexia in normal readers through stimulus degradation (i.e. contrast reduction and removal of high spatial frequencies). The results showed the word length and the letter confusability effects characteristic of LBL dyslexia. However, the interaction of letter confusability and…

  16. Molecular dynamics simulations of binary mixtures of methane and hydrogen in zeolite A and a novel zinc phosphate

    NASA Astrophysics Data System (ADS)

    Mitchell, Martha C.; Autry, James D.; Nenoff, Tina M.

    Molecular dynamics simulations have been used to study binary mixtures of hydrogen and methane in two molecular sieve structures, zeolite NaA and a novel zinc phosphate molecular sieve, Na3ZnO(PO4)3, which has a pore size tuned to light gas separations. Simulations were run at high temperature, T = 500 °C. Equimolar mixtures of methane and hydrogen in both molecular sieve structures were simulated at loadings of 2-16 molecules per unit cell. Self-diffusion coefficients were calculated using the Einstein relationship. Hydrogen was found to have higher self-diffusion coefficients than methane in both the molecular sieve structures under study. However, in the zinc phosphate molecular sieve the methane remained immobile, allowing for purification and separation of hydrogen, whereas in Zeolite A the methane experienced appreciable cage-to-cage motion.

  17. Theoretic model and computer simulation of separating mixture metal particles from waste printed circuit board by electrostatic separator.

    PubMed

    Li, Jia; Xu, Zhenming; Zhou, Yaohe

    2008-05-30

    Traditionally, the mixture metals from waste printed circuit board (PCB) were sent to the smelt factory to refine pure copper. Some valuable metals (aluminum, zinc and tin) with low content in PCB were lost during smelt. A new method which used roll-type electrostatic separator (RES) to recovery low content metals in waste PCB was presented in this study. The theoretic model which was established from computing electric field and the analysis of forces on the particles was used to write a program by MATLAB language. The program was design to simulate the process of separating mixture metal particles. Electrical, material and mechanical factors were analyzed to optimize the operating parameters of separator. The experiment results of separating copper and aluminum particles by RES had a good agreement with computer simulation results. The model could be used to simulate separating other metal (tin, zinc, etc.) particles during the process of recycling waste PCBs by RES.

  18. Coarse-grained modelling of triglyceride crystallisation: a molecular insight into tripalmitin tristearin binary mixtures by molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Pizzirusso, Antonio; Brasiello, Antonio; De Nicola, Antonio; Marangoni, Alejandro G.; Milano, Giuseppe

    2015-12-01

    The first simulation study of the crystallisation of a binary mixture of triglycerides using molecular dynamics simulations is reported. Coarse-grained models of tristearin (SSS) and tripalmitin (PPP) molecules have been considered. The models have been preliminarily tested in the crystallisation of pure SSS and PPP systems. Two different quenching procedures have been tested and their performances have been analysed. The structures obtained from the crystallisation procedures show a high orientation order and a high content of molecules in the tuning fork conformation, comparable with the crystalline α phase. The behaviour of melting temperatures for the α phase of the mixture SSS/PPP obtained from the simulations is in qualitative agreement with the behaviour that was experimentally determined.

  19. Mixture modeling methods for the assessment of normal and abnormal personality, part I: cross-sectional models.

    PubMed

    Hallquist, Michael N; Wright, Aidan G C

    2014-01-01

    Over the past 75 years, the study of personality and personality disorders has been informed considerably by an impressive array of psychometric instruments. Many of these tests draw on the perspective that personality features can be conceptualized in terms of latent traits that vary dimensionally across the population. A purely trait-oriented approach to personality, however, might overlook heterogeneity that is related to similarities among subgroups of people. This article describes how factor mixture modeling (FMM), which incorporates both categories and dimensions, can be used to represent person-oriented and trait-oriented variability in the latent structure of personality. We provide an overview of different forms of FMM that vary in the degree to which they emphasize trait- versus person-oriented variability. We also provide practical guidelines for applying FMM to personality data, and we illustrate model fitting and interpretation using an empirical analysis of general personality dysfunction.

  20. Simulation of helium-methane mixture separation on selectively permeable membranes

    NASA Astrophysics Data System (ADS)

    Naumkin, V. S.

    2016-10-01

    In the article, the helium-methane mixture separation on the various types of membranes was considered. A flat membrane module was studied. It was made of two channels connected by a semipermeable membrane. It was shown that high membrane selectivity could not always provide a high degree of mixture separation.

  1. Surface segregation in a binary mixture of ionic liquids: Comparison between high-resolution RBS measurements and molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Nakajima, Kaoru; Nakanishi, Shunto; Chval, Zdeněk; Lísal, Martin; Kimura, Kenji

    2016-11-01

    Surface structure of equimolar mixture of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C2C1Im][Tf2N]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2C1Im][BF4]) is studied using high-resolution Rutherford backscattering spectroscopy (HRBS) and molecular dynamics (MD) simulations. Both HRBS and MD simulations show enrichment of [Tf2N] in the first molecular layer although the degree of enrichment observed by HRBS is more pronounced than that predicted by the MD simulation. In the subsurface region, MD simulation shows a small depletion of [Tf2N] while HRBS shows a small enrichment here. This discrepancy is partially attributed to the artifact of the MD simulations. Since the number of each ion is fixed in a finite-size simulation box, surface enrichment of particular ion results in its artificial depletion in the subsurface region.

  2. Surface segregation in a binary mixture of ionic liquids: Comparison between high-resolution RBS measurements and moleculardynamics simulations.

    PubMed

    Nakajima, Kaoru; Nakanishi, Shunto; Chval, Zdeněk; Lísal, Martin; Kimura, Kenji

    2016-11-14

    Surface structure of equimolar mixture of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C2C1Im][Tf2N]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2C1Im][BF4]) is studied using high-resolution Rutherford backscattering spectroscopy (HRBS) and molecular dynamics (MD) simulations. Both HRBS and MD simulations show enrichment of [Tf2N] in the first molecular layer although the degree of enrichment observed by HRBS is more pronounced than that predicted by the MD simulation. In the subsurface region, MD simulation shows a small depletion of [Tf2N] while HRBS shows a small enrichment here. This discrepancy is partially attributed to the artifact of the MD simulations. Since the number of each ion is fixed in a finite-size simulation box, surface enrichment of particular ion results in its artificial depletion in the subsurface region.

  3. Normal Brain-Skull Development with Hybrid Deformable VR Models Simulation.

    PubMed

    Jin, Jing; De Ribaupierre, Sandrine; Eagleson, Roy

    2016-01-01

    This paper describes a simulation framework for a clinical application involving skull-brain co-development in infants, leading to a platform for craniosynostosis modeling. Craniosynostosis occurs when one or more sutures are fused early in life, resulting in an abnormal skull shape. Surgery is required to reopen the suture and reduce intracranial pressure, but is difficult without any predictive model to assist surgical planning. We aim to study normal brain-skull growth by computer simulation, which requires a head model and appropriate mathematical methods for brain and skull growth respectively. On the basis of our previous model, we further specified suture model into fibrous and cartilaginous sutures and develop algorithm for skull extension. We evaluate the resulting simulation by comparison with datasets of cases and normal growth.

  4. Energetics analysis of the observed and simulated general circulation using three-dimensional normal mode expansions

    NASA Technical Reports Server (NTRS)

    Tanaka, Hiroshi; Kung, Ernest C.; Baker, Wayman E.

    1986-01-01

    The energetics characteristics of the observed and simulated general circulation are analyzed using three-dimensional normal mode expansions. The data sets involved are the Goddard Laboratory for Atmospheres (GLA) analysis and simulation data and the Geophysical Fluid Dynamics Laboratory (GFDL) analysis data. The spectral energy properties of the Rossby and gravity modes and energy transformations are presented. Significant influences of model characteristics and the assimilation techniques are observed in the barotropic energy spectrum, particularly for the gravity mode. Energy transformations of the zonal mean field in the GLA analysis and simulation are similar, but distinctly different from that in the GFDL analysis. However, overall, the energy generation in the baroclinic mode is largely balanced by the sink in the barotropic mode. The present study may demonstrate utilities of the three-dimensional normal mode energetics in the analysis of the general circulation.

  5. A mixture theory model of fluid and solute transport in the microvasculature of normal and malignant tissues. I. Theory.

    PubMed

    Schuff, M M; Gore, J P; Nauman, E A

    2013-05-01

    In order to better understand the mechanisms governing transport of drugs, nanoparticle-based treatments, and therapeutic biomolecules, and the role of the various physiological parameters, a number of mathematical models have previously been proposed. The limitations of the existing transport models indicate the need for a comprehensive model that includes transport in the vessel lumen, the vessel wall, and the interstitial space and considers the effects of the solute concentration on fluid flow. In this study, a general model to describe the transient distribution of fluid and multiple solutes at the microvascular level was developed using mixture theory. The model captures the experimentally observed dependence of the hydraulic permeability coefficient of the capillary wall on the concentration of solutes present in the capillary wall and the surrounding tissue. Additionally, the model demonstrates that transport phenomena across the capillary wall and in the interstitium are related to the solute concentration as well as the hydrostatic pressure. The model is used in a companion paper to examine fluid and solute transport for the simplified case of an axisymmetric geometry with no solid deformation or interconversion of mass.

  6. Effects of variation in chain length on ternary polymer electrolyte - Ionic liquid mixture - A molecular dynamics simulation study

    NASA Astrophysics Data System (ADS)

    Raju, S. G.; Hariharan, Krishnan S.; Park, Da-Hye; Kang, HyoRang; Kolake, Subramanya Mayya

    2015-10-01

    Molecular dynamics (MD) simulations of ternary polymer electrolyte - ionic liquid mixtures are conducted using an all-atom model. N-alkyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([CnMPy][TFSI], n = 1, 3, 6, 9) and polyethylene oxide (PEO) are used. Microscopic structure, energetics and dynamics of ionic liquid (IL) in these ternary mixtures are studied. Properties of these four pure IL are also calculated and compared to that in ternary mixtures. Interaction between pyrrolidinium cation and TFSI is stronger and there is larger propensity of ion-pair formation in ternary mixtures. Unlike the case in imidazolium IL, near neighbor structural correlation between TFSI reduces with increase in chain length on cation in both pure IL and ternary mixtures. Using spatial density maps, regions where PEO and TFSI interact with pyrrolidinium cation are identified. Oxygens of PEO are above and below the pyrrolidinium ring and away from the bulky alkyl groups whereas TFSI is present close to nitrogen atom of CnMPy. In pure IL, diffusion coefficient (D) of C3MPy is larger than of TFSI but D of C9MPy and C6MPy are larger than that of TFSI. The reasons for alkyl chain dependent phenomena are explored.

  7. Molecular Dynamics Simulations of Tri-n-butyl-phosphate/n-Dodecane Mixture: Thermophysical Properties and Molecular Structure

    SciTech Connect

    de Almeida, Valmor F; Cui, Shengting; Khomami, Bamin

    2014-01-01

    Molecular dynamics simulations of tri-n-butyl-phosphate (TBP)/n-dodecane mixture in the liquid phase have been carried out using two recently developed TBP force field models (J. Phys. Chem. B 2012, 116, 305) in combination with the all-atom optimized potentials for liquid simulations (OPLS-AA) force field model for n-dodecane. Specifically, the electric dipole moment of TBP, mass density of the mixture, and the excess volume of mixing were computed with TBP mole fraction ranging from 0 to 1. It is found that the aforementioned force field models accurately predict the mass density of the mixture in the entire mole fraction range. Commensurate with experimental measurements, the electric dipole moment of the TBP was found to slightly increase with the mole fraction of TBP in the mixture. Also, in accord with experimental data, the excess volume of mixing is positive in the entire mole fraction range, peaking at TBP mole fraction range 0.3 0.5. Finally, a close examination of the spatial pair correlation functions between TBP molecules, and between TBP and n-dodecane molecules, revealed formation of TBP dimers through self-association at close distance, a phenomenon with ample experimental evidence.

  8. Analysis of Mesoscopic Structured 2-Propanol/Water Mixtures Using Pressure Perturbation Calorimetry and Molecular Dynamic Simulation.

    PubMed

    Bye, Jordan W; Freeman, Colin L; Howard, John D; Herz, Gregor; McGregor, James; Falconer, Robert J

    2017-01-01

    In this paper we demonstrate the application of pressure perturbation calorimetry (PPC) to the characterization of 2-propanol/water mixtures. PPC of different 2-propanol/water mixtures provides two useful measurements: (i) the change in heat (ΔQ); and (ii) the [Formula: see text] value. The results demonstrate that the ΔQ values of the mixtures deviate from that expected for a random mixture, with a maximum at ~20-25 mol% 2-propanol. This coincides with the concentration at which molecular dynamics (MD) simulations show a maximum deviation from random distribution, and also the point at which alcohol-alcohol hydrogen bonds become dominant over alcohol-water hydrogen bonds. Furthermore, the [Formula: see text] value showed transitions at 2.5 mol% 2-propanol and at approximately 14 mol% 2-propanol. Below 2.5 mol% 2-propanol the values of [Formula: see text] are negative; this is indicative of the presence of isolated 2-propanol molecules surrounded by water molecules. Above 2.5 mol% 2-propanol [Formula: see text] rises, reaching a maximum at ~14 mol% corresponding to a point where mixed alcohol-water networks are thought to dominate. The values and trends identified by PPC show excellent agreement not only with those obtained from MD simulations but also with results in the literature derived using viscometry, THz spectroscopy, NMR and neutron diffraction.

  9. Numerical simulation of the autoignition of hydrogen-air mixtures behind shock waves

    NASA Astrophysics Data System (ADS)

    Tereza, A. M.; Smirnov, V. N.; Vlasov, P. A.; Lyubimov, A. V.; Sokolova, I. L.; Shumova, V. V.; Ziborov, V. S.

    2015-11-01

    Problems related to the autoignition of hydrogen-air mixtures are highly important for the operation safety of nuclear reactors and for hydrogen power engineering. In spite of extensive studies in this area, there are still many problems directly concerned with the ignition delay times of H2/O2 mixtures and with the conditions under which these processes occur. This paper deals with the numerical analysis of the data available in the literature on O, H, and OH yields in order to determine the influence of the primary channels of the initiation of H2/Air mixtures. The numerical modeling of the available literature data on the ignition delays of hydrogen-air mixtures made it possible to describe the shock tube measurements of ignition delays within the framework of a unified kinetic mechanism over a temperature range of 930-2500 K at pressures from 0.1 to 8.7 MPa.

  10. Orbital-free molecular dynamics simulations of a warm dense mixture: Examination of the excess-pressure matching rule

    SciTech Connect

    Danel, J-F.; Kazandjian, L.; Zerah, G.

    2009-06-15

    A form of the linear mixing rule involving the equality of excess pressures is tested with various mole fractions and various types of orbital-free molecular dynamics simulations. For all the cases considered, this mixing rule yields, within statistical error, the pressure of a mixture of helium and iron obtained by a direct simulation. In an attempt to interpret the robustness of the mixing rule, we show that it can be derived from thermodynamic stability if the system is regarded as a mixture of independent effective average atoms. The success of the mixing rule applied with equations of state including various degrees of approximation leads us to suggest its use in the thermodynamic domain where quantum molecular dynamics can be implemented.

  11. Mass transport properties of Pu/DT mixtures from orbital free molecular dynamics simulations

    SciTech Connect

    Kress, Joel David; Ticknor, Christopher; Collins, Lee A.

    2015-09-16

    Mass transport properties (shear viscosity and diffusion coefficients) for Pu/DT mixtures were calculated with Orbital Free Molecular Dynamics (OFMD). The results were fitted to simple functions of mass density (for ρ=10.4 to 62.4 g/cm3) and temperature (for T=100 up to 3,000 eV) for Pu/DT mixtures consisting of 100/0, 25/75, 50/50, and 75/25 by number.

  12. A Numerical Simulation of a Normal Sonic Jet into a Hypersonic Cross-Flow

    NASA Technical Reports Server (NTRS)

    Jeffries, Damon K.; Krishnamurthy, Ramesh; Chandra, Suresh

    1997-01-01

    This study involves numerical modeling of a normal sonic jet injection into a hypersonic cross-flow. The numerical code used for simulation is GASP (General Aerodynamic Simulation Program.) First the numerical predictions are compared with well established solutions for compressible laminar flow. Then comparisons are made with non-injection test case measurements of surface pressure distributions. Good agreement with the measurements is observed. Currently comparisons are underway with the injection case. All the experimental data were generated at the Southampton University Light Piston Isentropic Compression Tube.

  13. Equilibrium equation of state of a hard sphere binary mixture at very large densities using replica exchange Monte Carlo simulations.

    PubMed

    Odriozola, Gerardo; Berthier, Ludovic

    2011-02-07

    We use replica exchange Monte Carlo simulations to measure the equilibrium equation of state of the disordered fluid state for a binary hard sphere mixture up to very large densities where standard Monte Carlo simulations do not easily reach thermal equilibrium. For the moderate system sizes we use (up to N = 100), we find no sign of a pressure discontinuity near the location of dynamic glass singularities extrapolated using either algebraic or simple exponential divergences, suggesting they do not correspond to genuine thermodynamic glass transitions. Several scenarios are proposed for the fate of the fluid state in the thermodynamic limit.

  14. Monte Carlo simulation of NIR diffuse reflectance in the normal and diseased human breast tissues.

    PubMed

    Prince, Shanthi; Malarvizhi, S

    2007-01-01

    The spectral reflectance measurements in tissue reveal physiological meaning. Normally, functional changes like, increase in total hemoglobin concentration, decrease in oxygen saturation, etc., are observed when there is an abnormality creeping in the normal tissue. These functional changes can act together to reveal disease by non-invasive near-infrared (NIR) spectroscopy, as it influence its optical properties. In the present study, a simple two dimensional, four layer model of breast is proposed. The four layers are (i) skin (ii) adipose layer (iii) glandular tissue and (iv) muscle. Each layer is modeled with appropriate biological chromophores like hemoglobin, water, lipid and melanin. From the literature, the concentrations and molar extinction coefficients of the chromophores in various layers of the model are obtained. These values are used to calculate the wavelength dependent absorption characteristics of a particular layer. Monte Carlo simulation of diffuse reflectance (percentage of back reflected photons after multiple scattering with the broad variety of angles) are simulated for the modeled breast tissue with and without diseased condition. Near-infrared wavelengths are chosen, as the depth of penetration in tissue is more compared to UV and visible region. Simulations are carried out on the modeled breast tissue for different races (skin colors) at different NIR wavelengths. Results show significant changes in diffuse reflectance and relative absorbance for normal and diseased breast tissues for differently pigmented model. This model can be used to study the photo dynamical therapy, drug delivery and prognosis of cancer.

  15. Thermodynamical and structural properties of binary mixtures of imidazolium chloride ionic liquids and alcohols from molecular simulation

    NASA Astrophysics Data System (ADS)

    Raabe, Gabriele; Köhler, Jürgen

    2008-10-01

    We have performed molecular dynamics simulations to determine the densities, excess energies of mixing, and structural properties of binary mixtures of the 1-alkyl-3-methylimidazolium chloride ionic liquids (ILs) [amim][Cl] and ethanol and 1-propanol in the temperature range from 298.15to363.15K. As in our previous work [J. Chem. Phys. 128, 154509 (2008)], our simulation studies are based on a united atom model from Liu et al. [Phys. Chem. Chem. Phys. 8, 1096 (2006)] for the 1-ethyl- and 1-butyl-3-methylimidazolium cations [emim+] and [bmim+], which we have extended to the 1-hexyl-3-methylimidazolium [hmim+] cation and combined with parameters of Canongia Lopes et al. [J. Phys. Chem. B 108, 2038 (2004)] for the chloride anion [Cl-] and the force field by Khare et al. for the alcohols [J. Phys. Chem. B 108, 10071 (2004)]. With this, we provide both prediction for the densities of the mixtures that have mostly not been investigated experimentally yet and a molecular picture of the interactions between the alcohol molecules and the ions. The negative excess energies of all mixtures indicate an energetically favorable mixing of [amim][Cl] ILs and alcohols. To gain insight into the nonideality of the mixtures on the molecular level, we analyzed their local structures by radial and spatial distribution functions. These analyses show that the local ordering in these mixtures is determined by strong hydrogen-bond interactions between the chloride anion and the hydroxyls of the alcohols, enhanced interactions between the anion and the charged domain of the cation, and an increasing aggregation of the nonpolar alkyl tails of the alcohols and the cations with increasing cation size, which results in a segregation of polar and nonpolar domains.

  16. Excess thermodynamic properties of chainlike mixtures. II. Self-associating systems: predictions from soft-SAFT and molecular simulation

    NASA Astrophysics Data System (ADS)

    Blas, Felipe J.

    The excess thermodynamic behaviour of self-associating binary mixtures of chainlike molecules is studied using modified statistical associating fluid theory, the so-called soft-SAFT equation of state. The chainlike molecules are described as Lennard-Jones spherical segments tangentially bonded together. The associating Lennard-Jones chains are modelled considering additional embedded off-centre square-well bonding sites. This model, which accounts explicitly for the most important microscopic features of real non-associating and associating chainlike molecules, such as repulsive and attractive forces between chemical groups, the connectivity of the segments to form the chains and the specific interactions (association), is also solved using the Monte Carlo molecular simulation technique. Comparisons between theoretical predictions and simulation results for selected mixtures are made in order to assess the adequacy of the theory in predicting excess properties. Agreement between simulation and soft-SAFT predictions indicates that the theory is able to provide a good description of the major excess properties. The theory is used also to study the effect of the molecular parameters on the excess properties of self-associating binary mixtures, with particular emphasis on the effect of association (including the bonding energy and number of associating sites) and chain length. The thermodynamic behaviour of these systems is governed by a delicate interplay between two important effects: the bond breaking of the structure formed by the associating molecules and the interstitial accommodation of the non-associating chains within the branched multimeric structure of the associating fluid. The theory is able to explain qualitatively the most salient features of the excess properties in real systems, including positive, negative and sigmoidal shape behaviour. After an in depth analysis of the effect of the association and chain length, an application of soft-SAFT that

  17. Detection of fallen trees in ALS point clouds using a Normalized Cut approach trained by simulation

    NASA Astrophysics Data System (ADS)

    Polewski, Przemyslaw; Yao, Wei; Heurich, Marco; Krzystek, Peter; Stilla, Uwe

    2015-07-01

    Downed dead wood is regarded as an important part of forest ecosystems from an ecological perspective, which drives the need for investigating its spatial distribution. Based on several studies, Airborne Laser Scanning (ALS) has proven to be a valuable remote sensing technique for obtaining such information. This paper describes a unified approach to the detection of fallen trees from ALS point clouds based on merging short segments into whole stems using the Normalized Cut algorithm. We introduce a new method of defining the segment similarity function for the clustering procedure, where the attribute weights are learned from labeled data. Based on a relationship between Normalized Cut's similarity function and a class of regression models, we show how to learn the similarity function by training a classifier. Furthermore, we propose using an appearance-based stopping criterion for the graph cut algorithm as an alternative to the standard Normalized Cut threshold approach. We set up a virtual fallen tree generation scheme to simulate complex forest scenarios with multiple overlapping fallen stems. This simulated data is then used as a basis to learn both the similarity function and the stopping criterion for Normalized Cut. We evaluate our approach on 5 plots from the strictly protected mixed mountain forest within the Bavarian Forest National Park using reference data obtained via a manual field inventory. The experimental results show that our method is able to detect up to 90% of fallen stems in plots having 30-40% overstory cover with a correctness exceeding 80%, even in quite complex forest scenes. Moreover, the performance for feature weights trained on simulated data is competitive with the case when the weights are calculated using a grid search on the test data, which indicates that the learned similarity function and stopping criterion can generalize well on new plots.

  18. Log-Normal Distribution of Cosmic Voids in Simulations and Mocks

    NASA Astrophysics Data System (ADS)

    Russell, E.; Pycke, J.-R.

    2017-01-01

    Following up on previous studies, we complete here a full analysis of the void size distributions of the Cosmic Void Catalog based on three different simulation and mock catalogs: dark matter (DM), haloes, and galaxies. Based on this analysis, we attempt to answer two questions: Is a three-parameter log-normal distribution a good candidate to satisfy the void size distributions obtained from different types of environments? Is there a direct relation between the shape parameters of the void size distribution and the environmental effects? In an attempt to answer these questions, we find here that all void size distributions of these data samples satisfy the three-parameter log-normal distribution whether the environment is dominated by DM, haloes, or galaxies. In addition, the shape parameters of the three-parameter log-normal void size distribution seem highly affected by environment, particularly existing substructures. Therefore, we show two quantitative relations given by linear equations between the skewness and the maximum tree depth, and between the variance of the void size distribution and the maximum tree depth, directly from the simulated data. In addition to this, we find that the percentage of voids with nonzero central density in the data sets has a critical importance. If the number of voids with nonzero central density reaches ≥3.84% in a simulation/mock sample, then a second population is observed in the void size distributions. This second population emerges as a second peak in the log-normal void size distribution at larger radius.

  19. Kirkwood-Buff analysis of liquid mixtures in AdResS: Towards an open boundary simulation scheme

    NASA Astrophysics Data System (ADS)

    Mukherji, Debashish; van der Vegt, Nico; Kremer, Kurt; Delle Site, Luigi

    2012-02-01

    Many biophysical processes in water are determined by interactions of cosolvents with the hydration shells of dissolved (bio)molecules. Computational approaches to study these systems are mostly limited to the closed boundary simulations. While closed boundaries are perfectly suitable in many cases, problems arise when concentration fluctuations are large, or intimately linked to the physical phenomenon. For example, in non-ideal mixtures of water/cosolvent and a biomolecule, the excess of water/cosolvent, close to a protein surface, leads to water/cosolvent depletion elsewhere. This complicates a comparison with experiments that are conducted under osmotic conditions. Therefore, we use Adaptive Resolution Simulation (AdResS) scheme, which describes a small sub-volume of a much larger system in atomistic detail, maintaining thermodynamic equilibrium with a surrounding coarse grained reservoir. We show that the Kirkwood-Buff integrals (KBI), which directly connect thermodynamic properties to the molecular distributions, can be efficiently calculated within the small open boundary all atom region and the coarse-grained reservoir maintains the correct particle fluctuations. Results will be presented for the methanol/water mixture and solvation of amino acids in urea/water mixture.

  20. 3D PIC-MCC simulations of discharge inception around a sharp anode in nitrogen/oxygen mixtures

    NASA Astrophysics Data System (ADS)

    Teunissen, Jannis; Ebert, Ute

    2016-08-01

    We investigate how photoionization, electron avalanches and space charge affect the inception of nanosecond pulsed discharges. Simulations are performed with a 3D PIC-MCC (particle-in-cell, Monte Carlo collision) model with adaptive mesh refinement for the field solver. This model, whose source code is available online, is described in the first part of the paper. Then we present simulation results in a needle-to-plane geometry, using different nitrogen/oxygen mixtures at atmospheric pressure. In these mixtures non-local photoionization is important for the discharge growth. The typical length scale for this process depends on the oxygen concentration. With 0.2% oxygen the discharges grow quite irregularly, due to the limited supply of free electrons around them. With 2% or more oxygen the development is much smoother. An almost spherical ionized region can form around the electrode tip, which increases in size with the electrode voltage. Eventually this inception cloud destabilizes into streamer channels. In our simulations, discharge velocities are almost independent of the oxygen concentration. We discuss the physical mechanisms behind these phenomena and compare our simulations with experimental observations.

  1. Evaporation Dynamics of a Seven-Component Mixture Containing Nerve Agent Simulants

    DTIC Science & Technology

    2014-02-01

    mixture owing to loss of more volatile components, that is, di-( n - propyl ) ether (PE) and dimethyl hydrogen phosphonate (DMHP). Experimentation...The three volatile components investigated were di-( n - propyl ) ether (PE), dimethyl hydrogen phosphonate (DMHP), and dimethyl methylphosphonate (DMMP...acid anhydride trimer MPMA methyl methylphosphoric acid MS mass spectrometry MSD mass spectrometer detector PE di-( n - propyl ) ether Pyro bis

  2. Numerical simulation of the processes in the normal incidence tube for high acoustic pressure levels

    NASA Astrophysics Data System (ADS)

    Fedotov, E. S.; Khramtsov, I. V.; Kustov, O. Yu.

    2016-10-01

    Numerical simulation of the acoustic processes in an impedance tube at high levels of acoustic pressure is a way to solve a problem of noise suppressing by liners. These studies used liner specimen that is one cylindrical Helmholtz resonator. The evaluation of the real and imaginary parts of the liner acoustic impedance and sound absorption coefficient was performed for sound pressure levels of 130, 140 and 150 dB. The numerical simulation used experimental data having been obtained on the impedance tube with normal incidence waves. At the first stage of the numerical simulation it was used the linearized Navier-Stokes equations, which describe well the imaginary part of the liner impedance whatever the sound pressure level. These equations were solved by finite element method in COMSOL Multiphysics program in axisymmetric formulation. At the second stage, the complete Navier-Stokes equations were solved by direct numerical simulation in ANSYS CFX in axisymmetric formulation. As the result, the acceptable agreement between numerical simulation and experiment was obtained.

  3. Enhancing backbone sampling in Monte Carlo simulations using internal coordinates normal mode analysis.

    PubMed

    Gil, Victor A; Lecina, Daniel; Grebner, Christoph; Guallar, Victor

    2016-10-15

    Normal mode methods are becoming a popular alternative to sample the conformational landscape of proteins. In this study, we describe the implementation of an internal coordinate normal mode analysis method and its application in exploring protein flexibility by using the Monte Carlo method PELE. This new method alternates two different stages, a perturbation of the backbone through the application of torsional normal modes, and a resampling of the side chains. We have evaluated the new approach using two test systems, ubiquitin and c-Src kinase, and the differences to the original ANM method are assessed by comparing both results to reference molecular dynamics simulations. The results suggest that the sampled phase space in the internal coordinate approach is closer to the molecular dynamics phase space than the one coming from a Cartesian coordinate anisotropic network model. In addition, the new method shows a great speedup (∼5-7×), making it a good candidate for future normal mode implementations in Monte Carlo methods.

  4. Response of selected plant and insect species to simulated SRM exhaust mixtures and to exhaust components from SRM fuels

    NASA Technical Reports Server (NTRS)

    Heck, W. W.

    1980-01-01

    The possible biologic effects of exhaust products from solid rocket motor (SRM) burns associated with the space shuttle are examined. The major components of the exhaust that might have an adverse effect on vegetation, HCl and Al2O3 are studied. Dose response curves for native and cultivated plants and selected insects exposed to simulated exhaust and component chemicals from SRM exhaust are presented. A system for dispensing and monitoring component chemicals of SRM exhaust (HCl and Al2O3) and a system for exposing test plants to simulated SRM exhaust (controlled fuel burns) are described. The effects of HCl, Al2O3, and mixtures of the two on the honeybee, the corn earworm, and the common lacewing and the effects of simulated exhaust on the honeybee are discussed.

  5. An OHD-RIKES and simulation study comparing a benzylmethylimidazolium ionic liquid with an equimolar mixture of dimethylimidazolium and benzene.

    PubMed

    Xue, Lianjie; Tamas, George; Matthews, Richard P; Stone, Anthony J; Hunt, Patricia A; Quitevis, Edward L; Lynden-Bell, Ruth M

    2015-04-21

    The principal difference between 1-benzyl-3-methyl-imidazolium triflimide [BzC1im][NTf2] and an equimolar mixture of benzene and dimethylimidazolium triflimide [C1C1im][NTf2] is that in the former the benzene moieties are tied to the imidazolium ring, while in the latter they move independently. We use femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) and molecular simulations to explore some properties of these two systems. The Kerr spectra show small differences in the spectral densities; the simulations also show very similar environments for both the imidazolium rings and the phenyl or benzene parts of the molecules. The low frequency vibrational densities of states are also similar in the model systems. In order to perform the simulations we developed a model for the [BzC1im](+) cation and found that the barriers to rotation of the two parts of the molecule are low.

  6. Transport coefficients of normal liquid helium-4 calculated by path integral centroid molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Imaoka, Haruna; Kinugawa, Kenichi

    2017-03-01

    Thermal conductivity, shear viscosity, and bulk viscosity of normal liquid 4He at 1.7-4.0 K are calculated using path integral centroid molecular dynamics (CMD) simulations. The calculated thermal conductivity and shear viscosity above lambda transition temperature are on the same order of magnitude as experimental values, while the agreement of shear viscosity is better. Above 2.3 K the CMD well reproduces the temperature dependences of isochoric shear viscosity and of the time integral of the energy current and off-diagonal stress tensor correlation functions. The calculated bulk viscosity, not known in experiments, is several times larger than shear viscosity.

  7. Binomial Gaussian mixture filter

    NASA Astrophysics Data System (ADS)

    Raitoharju, Matti; Ali-Löytty, Simo; Piché, Robert

    2015-12-01

    In this work, we present a novel method for approximating a normal distribution with a weighted sum of normal distributions. The approximation is used for splitting normally distributed components in a Gaussian mixture filter, such that components have smaller covariances and cause smaller linearization errors when nonlinear measurements are used for the state update. Our splitting method uses weights from the binomial distribution as component weights. The method preserves the mean and covariance of the original normal distribution, and in addition, the resulting probability density and cumulative distribution functions converge to the original normal distribution when the number of components is increased. Furthermore, an algorithm is presented to do the splitting such as to keep the linearization error below a given threshold with a minimum number of components. The accuracy of the estimate provided by the proposed method is evaluated in four simulated single-update cases and one time series tracking case. In these tests, it is found that the proposed method is more accurate than other Gaussian mixture filters found in the literature when the same number of components is used and that the proposed method is faster and more accurate than particle filters.

  8. Reaction Ensemble Molecular Dynamics: Direct Simulation of the Dynamic Equilibrium Properties of Chemically Reacting Mixtures

    DTIC Science & Technology

    2006-09-01

    Therefore, dynamic quantities of reaction mixtures such as the velocity autocorrelation functions and the diffusion coefficients can be accurately...using the virial expression [25]. A standard NVT molecular dynamics method was em- ployed with the equations of motion solved using the Verlet leapfrog...configurational energy, pressure, and species concen- trations) are compared to quantities calculated by the RxMC approach. Second , the dynamic quantities

  9. Nanostructural organization in carbon disulfide/ionic liquid mixtures: Molecular dynamics simulations and optical Kerr effect spectroscopy

    NASA Astrophysics Data System (ADS)

    Yang, Peng; Voth, Gregory A.; Xiao, Dong; Hines, Larry G.; Bartsch, Richard A.; Quitevis, Edward L.

    2011-07-01

    In this paper, the nanostructural organization and subpicosecond intermolecular dynamics in the mixtures of CS2 and the room temperature ionic liquid (IL) 1-pentyl-3-methylimidazolium bis{(trifluoromethane)sulfonyl}amide ([C5mim][NTf2]) were studied as a function of concentration using molecular dynamics (MD) simulations and optical heterodyne-detected Raman-induced Kerr effect spectroscopy. At low CS2 concentrations (<10 mol.% CS2/IL), the MD simulations indicate that the CS2 molecules are localized in the nonpolar domains. In contrast, at higher concentrations (≥10 mol.% CS2/IL), the MD simulations show aggregation of the CS2 molecules. The optical Kerr effect (OKE) spectra of the mixtures are interpreted in terms of an additivity model with the components arising from the subpicosecond dynamics of CS2 and the IL. Comparison of the CS2-component with the OKE spectra of CS2 in alkane solvents is consistent with CS2 mainly being localized in the nonpolar domains, even at high CS2 concentrations, and the local CS2 concentration being higher than the bulk CS2 concentration.

  10. Structural relaxation and diffusion in a model colloid-polymer mixture: dynamical density functional theory and simulation

    NASA Astrophysics Data System (ADS)

    Stopper, Daniel; Roth, Roland; Hansen-Goos, Hendrik

    2016-11-01

    Within the Asakura-Oosawa model, we study structural relaxation in mixtures of colloids and polymers subject to Brownian motion in the overdamped limit. We obtain the time evolution of the self and distinct parts of the van Hove distribution function G(r,t) by means of dynamical density functional theory (DDFT) using an accurate free-energy functional based on Rosenfeld’s fundamental measure theory. In order to remove unphysical interactions within the self part, we extend the recently proposed quenched functional framework (Stopper et al 2015 J. Chem. Phys. 143 181105) toward mixtures. In addition, we obtain results for the long-time self diffusion coefficients of colloids and polymers from dynamic Monte Carlo simulations, which we incorporate into the DDFT. From the resulting DDFT equations we calculate G(r, t), which we find to agree very well with our simulations. In particular, we examine the influence of polymers which are slow relative to the colloids—a scenario for which both DDFT and simulation show a significant peak forming at r  =  0 in the colloid-colloid distribution function, akin to experimental findings involving gelation of colloidal suspensions. Moreover, we observe that, in the presence of slow polymers, the long-time self diffusivity of the colloids displays a maximum at an intermediate colloid packing fraction. This behavior is captured by a simple semi-empirical formula, which provides an excellent description of the data.

  11. Pulsatile flows and wall-shear stresses in models simulating normal and stenosed aortic arches

    NASA Astrophysics Data System (ADS)

    Huang, Rong Fung; Yang, Ten-Fang; Lan, Y.-K.

    2010-03-01

    Pulsatile aqueous glycerol solution flows in the models simulating normal and stenosed human aortic arches are measured by means of particle image velocimetry. Three transparent models were used: normal, 25% stenosed, and 50% stenosed aortic arches. The Womersley parameter, Dean number, and time-averaged Reynolds number are 17.31, 725, and 1,081, respectively. The Reynolds numbers based on the peak velocities of the normal, 25% stenosed, and 50% stenosed aortic arches are 2,484, 3,456, and 3,931, respectively. The study presents the temporal/spatial evolution processes of the flow pattern, velocity distribution, and wall-shear stress during the systolic and diastolic phases. It is found that the flow pattern evolving in the central plane of normal and stenosed aortic arches exhibits (1) a separation bubble around the inner arch, (2) a recirculation vortex around the outer arch wall upstream of the junction of the brachiocephalic artery, (3) an accelerated main stream around the outer arch wall near the junctions of the left carotid and the left subclavian arteries, and (4) the vortices around the entrances of the three main branches. The study identifies and discusses the reasons for the flow physics’ contribution to the formation of these features. The oscillating wall-shear stress distributions are closely related to the featured flow structures. On the outer wall of normal and slightly stenosed aortas, large wall-shear stresses appear in the regions upstream of the junction of the brachiocephalic artery as well as the corner near the junctions of the left carotid artery and the left subclavian artery. On the inner wall, the largest wall-shear stress appears in the region where the boundary layer separates.

  12. Vertical vs Lateral Macrophase Separation in Thin Films of Block Copolymer Mixtures: Computer Simulations and GISAXS Experiments.

    PubMed

    Berezkin, Anatoly V; Jung, Florian; Posselt, Dorthe; Smilgies, Detlef M; Papadakis, Christine M

    2017-03-20

    Mixtures of two diblock copolymers of very different lengths may feature both macro- and microphase separation; however, not much is known about the mechanisms of separation in diblock copolymer thin films. In the present work, we study thin films of mixtures of two compositionally symmetric block copolymers, both in the one-phase and in the two-phase state, combining coarse-grained molecular simulations (dissipative particle dynamics, DPD) with scattering experiments (grazing-incidence small-angle X-ray scattering, GISAXS). We reveal that the film thickness and selective adsorption of different blocks to the substrate control the distribution of macrophases within the film as well as the orientation of the lamellae therein. In thick films, the mixtures separate in the vertical direction into three layers: Two layers being rich in short copolymers are formed near the film interfaces, whereas a layer being rich in long copolymers is located in the film core. The lamellar orientation in the layers rich in short copolymers is dictated by the surface selectivity, and this orientation only weakly affects the vertical orientation of lamellae in the film core. This provides the opportunity to control the domain orientation in the copolymer films by mixing block copolymers with low-molecular additives instead of relying on a more complicated chemical modification of the substrate. In thinner films, a lateral phase separation appears.

  13. Spinodal decomposition in thin films: Molecular-dynamics simulations of a binary Lennard-Jones fluid mixture

    NASA Astrophysics Data System (ADS)

    Das, Subir K.; Puri, Sanjay; Horbach, Jürgen; Binder, Kurt

    2006-03-01

    We use molecular dynamics (MD) to simulate an unstable homogeneous mixture of binary fluids (AB), confined in a slit pore of width D . The pore walls are assumed to be flat and structureless and attract one component of the mixture (A) with the same strength. The pairwise interactions between the particles are modeled by the Lennard-Jones potential, with symmetric parameters that lead to a miscibility gap in the bulk. In the thin-film geometry, an interesting interplay occurs between surface enrichment and phase separation. We study the evolution of a mixture with equal amounts of A and B, which is rendered unstable by a temperature quench. We find that A-rich surface enrichment layers form quickly during the early stages of the evolution, causing a depletion of A in the inner regions of the film. These surface-directed concentration profiles propagate from the walls towards the center of the film, resulting in a transient layered structure. This layered state breaks up into a columnar state, which is characterized by the lateral coarsening of cylindrical domains. The qualitative features of this process resemble results from previous studies of diffusive Ginzburg-Landau-type models [S. K. Das, S. Puri, J. Horbach, and K. Binder, Phys. Rev. E 72, 061603 (2005)], but quantitative aspects differ markedly. The relation to spinodal decomposition in a strictly two-dimensional geometry is also discussed.

  14. Gibbs ensemble Monte Carlo simulation using an optimized potential model: pure acetic acid and a mixture of it with ethylene.

    PubMed

    Zhang, Minhua; Chen, Lihang; Yang, Huaming; Sha, Xijiang; Ma, Jing

    2016-07-01

    Gibbs ensemble Monte Carlo simulation with configurational bias was employed to study the vapor-liquid equilibrium (VLE) for pure acetic acid and for a mixture of acetic acid and ethylene. An improved united-atom force field for acetic acid based on a Lennard-Jones functional form was proposed. The Lennard-Jones well depth and size parameters for the carboxyl oxygen and hydroxyl oxygen were determined by fitting the interaction energies of acetic acid dimers to the Lennard-Jones potential function. Four different acetic acid dimers and the proportions of them were considered when the force field was optimized. It was found that the new optimized force field provides a reasonable description of the vapor-liquid phase equilibrium for pure acetic acid and for the mixture of acetic acid and ethylene. Accurate values were obtained for the saturated liquid density of the pure compound (average deviation: 0.84 %) and for the critical points. The new optimized force field demonstrated greater accuracy and reliability in calculations of the solubility of the mixture of acetic acid and ethylene as compared with the results obtained with the original TraPPE-UA force field.

  15. Inhibition of gap junctional intercellular communication in normal human breast epithelial cells after treatment with pesticides, PCBs, and PBBs, alone or in mixtures.

    PubMed Central

    Kang, K S; Wilson, M R; Hayashi, T; Chang, C C; Trosko, J E

    1996-01-01

    Chemical pollutants in the Great Lakes have found their way through the food chain into humans because of their environmental persistence and lipophilicity. Some epidemiological studies have claimed an association between metabolites of 2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane (DDT), polychlorinated biphenyls (PCBs), and polybrominated biphenyls (PBBs) and breast cancer, but others have reported no such association. We examined various halogenated hydrocarbons for their capacity to inhibit gap junctional intercellular communication (GJIC) in normal human breast epithelial cells (HBEC) when given as single compounds or as mixtures. The scrape-loading/dye transfer and fluorescent redistribution after photobleaching techniques were used to measure GJIC; immunostaining and Western and Northern analyses were performed on connexin 43 (Cx43) gap junction protein and message to determine how halogenated hydrocarbons might affect GJIC. DDT, dieldrin, and toxaphene inhibited GJIC in a dose-responsive manner after 90 min treatments. Dieldrin suppressed GJIC within 30 min with no recovery after 24 hr. Inhibition of GJIC by DDT and toxaphene was partially restored after 12 hr and fully restored after 24 hr. Several PCB and PBB congeners inhibited GJIC in a dose-responsive and time-dependent manner, but GJIC was almost restored to control values 24 hr after exposure. The highest concentrations of the individual chemicals that did not inhibit GJIC was determined, and mixtures containing two of these chemicals were tested for their ability to inhibit GJIC. Significant inhibition of GJIC was observed when cells were treated with a mixture of DDT and 2,4,5-hexachlorobiphenyl (2,4,5-HCB), dieldrin and 2,4,5-HCB, or dieldrin and 2,4,5-hexabromobiphenyl (2,4,5-HBB). These results indicate that halogenated hydrocarbons, alone or in specific combinations, can alter GJIC at the post-translational level. These results are consistent with the hypothesis that DDT, dieldrin, toxaphene, 2

  16. Molecular dynamics simulation of the structure and dynamics of water-1-alkyl-3-methylimidazolium ionic liquid mixtures.

    PubMed

    Méndez-Morales, Trinidad; Carrete, Jesús; Cabeza, Oscar; Gallego, Luis J; Varela, Luis M

    2011-06-02

    We have performed extensive molecular dynamic simulations to analyze the influence of cation and anion natures, and of water concentration, on the structure and dynamics of water-1-alkyl-3-methylimidazolium ionic liquid mixtures. The dependence on water concentration of the radial distribution functions, coordination numbers, and hydrogen bonding degree between the different species has been systematically analyzed for different lengths of the cation alkyl chain (alkyl = ethyl, butyl, hexyl, and octyl) and several counterions. These include two halogens of different sizes and positions in Hoffmeister series, Cl(-) and Br(-), and the highly hydrophobic inorganic anion PF(6)(-) throughout its whole solubility regime. The formation of water clusters in the mixture has been verified, and the influences of both anion hydrophobicity and cation chain length on the structure and size of these clusters have been analyzed. The water cluster size is shown to be relatively independent of the cation chain length, but strongly dependent on the hydrophobicity of the anion, which also determines critically the network formation of water and therefore the miscibility of the ionic liquid. The greater influence of the anion relative to the cation one is seen to be reflected in all the analyzed physical properties. Finally, single-particle dynamics in IL-water mixtures is considered, obtaining the self-diffusion coefficients and the velocity autocorrelation functions of water molecules in the mixture, and analyzing the effect of cation, anion, and water concentration on the duration of the ballistic regime and on the time of transition to the diffusive regime. Complex non-Markovian behavior was detected at intermediate times within an interval progressively shorter as water concentration increases.

  17. Confidence in performing normal vaginal delivery in the obstetrics clerkship: a randomized trial of two simulators.

    PubMed

    Sabourin, Jeanelle N; Van Thournout, Rhonda; Jain, Venu; Demianczuk, Nestor; Flood, Cathy

    2014-07-01

    Objectif : Comparer la confiance des étudiants de médecine en stage clinique, pour ce qui est de l’exécution d’une simulation d’accouchement vaginal normal (AVN), à la suite de leur participation à une session de formation en simulation au moyen de deux modèles différents. Méthodes : Des étudiants de médecine ont été affectés, au hasard, à une session de simulation d’AVN faisant appel à un mannequin obstétrical ou à une session de simulation faisant appel à un modèle de bassin simulant l’accouchement. Des questionnaires ont été utilisés pour évaluer la confiance et la simulation avant et immédiatement après la session, ainsi qu’au cours de la dernière journée de la rotation en obstétrique. Résultats : Cent dix étudiants ont été affectés au hasard à l’un ou l’autre des groupes de simulation. Au début du stage clinique, les deux groupes présentaient des niveaux de confiance et d’exposition à la pratique obstétricale semblables. Seulement 15 étudiants (13,9 %) étaient d’avis qu’ils étaient prêts à tenter un AVN de façon indépendante ou sous une supervision minimale. Cette proportion a connu une hausse considérable en passant à 43 étudiants (39,4 %) immédiatement après la session de simulation. À la fin du stage clinique, 79 des 81 étudiants répondants (97,5 %) étaient confiants de pouvoir tenter un AVN de façon indépendante ou sous une supervision minimale. Aucune différence significative n’a été constatée entre les groupes de simulation à quelque moment que ce soit. Les sessions ont été évaluées comme étant tout aussi utiles et réalistes les unes que les autres; cette constatation est demeurée la même à la fin du stage clinique. Conclusion : La formation faisant appel à la simulation d’un AVN au moyen d’un mannequin obstétrical ou d’un modèle de bassin simulant l’accouchement offre aux étudiants en stage clinique une expérience positive et accroît imm

  18. Algorithms for GPU-based molecular dynamics simulations of complex fluids: Applications to water, mixtures, and liquid crystals.

    PubMed

    Kazachenko, Sergey; Giovinazzo, Mark; Hall, Kyle Wm; Cann, Natalie M

    2015-09-15

    A custom code for molecular dynamics simulations has been designed to run on CUDA-enabled NVIDIA graphics processing units (GPUs). The double-precision code simulates multicomponent fluids, with intramolecular and intermolecular forces, coarse-grained and atomistic models, holonomic constraints, Nosé-Hoover thermostats, and the generation of distribution functions. Algorithms to compute Lennard-Jones and Gay-Berne interactions, and the electrostatic force using Ewald summations, are discussed. A neighbor list is introduced to improve scaling with respect to system size. Three test systems are examined: SPC/E water; an n-hexane/2-propanol mixture; and a liquid crystal mesogen, 2-(4-butyloxyphenyl)-5-octyloxypyrimidine. Code performance is analyzed for each system. With one GPU, a 33-119 fold increase in performance is achieved compared with the serial code while the use of two GPUs leads to a 69-287 fold improvement and three GPUs yield a 101-377 fold speedup.

  19. Numerical simulation of coastal flooding after potential reactivation of an active normal fault in northern Taiwan

    NASA Astrophysics Data System (ADS)

    Chan, Yu-Chang; Kuo, Chih-Yu; Chang, Kuo-Jen; Chen, Rou-Fei; Hsieh, Yu-Chung

    2016-04-01

    Rapid coastal flooding from seawards may be resulted from storm surge, tsunamis, and sudden land subsidence due to fault activities. Many observations and numerical modeling of flooding have been made for cases resulted from storm surge and tsunami events; however, coastal flooding caused by a potential normal faulting event nearby coastal areas is rarely reported. In addition to the earthquake hazards from fault rupturing and ground shaking, the accompanied hazards of earthquake-induced flooding is also important to be investigated. The Jinshan area in northern Taiwan was reported to have been flooded by a tsunami event in the year of 1867 possibly resulted from the reactivation of the Shanchiao normal fault offshore. Historical records have shown that the Shanchiao Fault that extends from Shulin along the western edge of the Taipei Basin to the town of Jinshan may have also ruptured in the year of 1694. The rupturing event has created a depression on the western side of the Taipei Basin that was later filled by sea water called the Taipei Lake. The geological conditions in northern Taiwan provide an opportunity for numerically simulating the dynamic processes of sea water flooding nearby the coastal area immediately after an earthquake-induced normal faulting event. In this study, we focused on the potential active normal faulting that may occur and result in an expected catastrophic flooding in lowland area of Jinshan in northern Taiwan. We applied the continuum shallow water equation to evaluate the unknown inundation processes including location, extent, velocity and water depths after the flooding initiated and the final state of the flooding event. The modeling results were well compared with borehole observations of the extent of previous flooding events possibly due to tsunami events. In addition, the modeling results may provide a future basis for safety evaluation of the two nuclear power plants nearby the region.

  20. Chronic toxicity and hazard assessment of an inorganic mixture simulating irrigation drainwater to razorback sucker and bonytail

    USGS Publications Warehouse

    Hamilton, Steven J.; Buhl, Kevin J.; Bullard, Fern A.; Little, Edward E.

    2000-01-01

    We conducted two 90 day chronic toxicity studies with two endangered fish, razorback sucker and bonytail. Swim-up larvae were exposed in a reconstituted water simulating the middle Green River. The toxicant mixture simulated the environmental ratio and concentrations of inorganics reported in a Department of the Interior study for the mouth of Ashley Creek on the Green River, and was composed of nine elements. The mixture was tested at 1X, 2X, 4X, 8X, and 16X where X was the measured environmental concentration (2 μg/L arsenic, 630 μg/L boron, 10 μg/L copper, 5 μg/L molybdenum, 51 μg/L selenate, 8 μg/L selenite, 33 μg/L uranium, 2 μg/L vanadium, and 20 μg/L zinc). Razorback sucker had reduced survival after 60 days exposure to the inorganic mixture at 8X, whereas growth was reduced after 30 and 60 days at 2X and after 90 days at 4X. Bonytail had reduced survival after 30 days exposure at 16X, whereas growth was reduced after 30, 60, and 90 days at 8X. Swimming performance of razorback sucker and bonytail were reduced after 60 and 90 days of exposure at 8X. Whole-body residues of copper, selenium, and zinc increased in a concentration-response manner and seemed to be regulated at 90 days of exposure at 4X and lower treatments for razorback sucker, and at 8X and lower for bonytail. Adverse effects occurred in fish with whole-body residues of copper, selenium, and zinc similar to those causing similar effects in other fish species. Comparison of adverse effect concentrations with measured environmental concentrations showed a high hazard to the two endangered fish. Irrigation activities may be a contributing factor to the decline of these endangered fishes in the middle Green River. 

  1. CO2 capture from simulated fuel gas mixtures using semiclathrate hydrates formed by quaternary ammonium salts.

    PubMed

    Park, Sungwon; Lee, Seungmin; Lee, Youngjun; Seo, Yongwon

    2013-07-02

    In order to investigate the feasibility of semiclathrate hydrate-based precombustion CO2 capture, thermodynamic, kinetic, and spectroscopic studies were undertaken on the semiclathrate hydrates formed from a fuel gas mixture of H2 (60%) + CO2 (40%) in the presence of quaternary ammonium salts (QASs) such as tetra-n-butylammonium bromide (TBAB) and fluoride (TBAF). The inclusion of QASs demonstrated significantly stabilized hydrate dissociation conditions. This effect was greater for TBAF than TBAB. However, due to the presence of dodecahedral cages that are partially filled with water molecules, TBAF showed a relatively lower gas uptake than TBAB. From the stability condition measurements and compositional analyses, it was found that with only one step of semiclathrate hydrate formation with the fuel gas mixture from the IGCC plants, 95% CO2 can be enriched in the semiclathrate hydrate phase at room temperature. The enclathration of both CO2 and H2 in the cages of the QAS semiclathrate hydrates and the structural transition that results from the inclusion of QASs were confirmed through Raman and (1)H NMR measurements. The experimental results obtained in this study provide the physicochemical background required for understanding selective partitioning and distributions of guest gases in the QAS semiclathrate hydrates and for investigating the feasibility of a semiclathrate hydrate-based precombustion CO2 capture process.

  2. Trade-offs arising from mixture of color cueing and monocular, binoptic, and stereoscopic cueing information for simulated rotorcraft flight

    NASA Technical Reports Server (NTRS)

    Parrish, Russell V.; Williams, Steven P.

    1993-01-01

    To provide stereopsis, binocular helmet-mounted display (HMD) systems must trade some of the total field of view available from their two monocular fields to obtain a partial overlap region. The visual field then provides a mixture of cues, with monocular regions on both peripheries and a binoptic (the same image in both eyes) region or, if lateral disparity is introduced to produce two images, a stereoscopic region in the overlapped center. This paper reports on in-simulator assessment of the trade-offs arising from the mixture of color cueing and monocular, binoptic, and stereoscopic cueing information in peripheral monitoring displays as utilized in HMD systems. The accompanying effect of stereoscopic cueing in the tracking information in the central region of the display is also assessed. The pilot's task for the study was to fly at a prescribed height above an undulating pathway in the sky while monitoring a dynamic bar chart displayed in the periphery of their field of view. Control of the simulated rotorcraft was limited to the longitudinal and vertical degrees of freedom to ensure the lateral separation of the viewing conditions of the concurrent tasks.

  3. MD simulations of the formation of stable clusters in mixtures of alkaline salts and imidazolium-based ionic liquids.

    PubMed

    Méndez-Morales, Trinidad; Carrete, Jesús; Bouzón-Capelo, Silvia; Pérez-Rodríguez, Martín; Cabeza, Óscar; Gallego, Luis J; Varela, Luis M

    2013-03-21

    Structural and dynamical properties of room-temperature ionic liquids containing the cation 1-butyl-3-methylimidazolium ([BMIM](+)) and three different anions (hexafluorophosphate, [PF6](-), tetrafluoroborate, [BF4](-), and bis(trifluoromethylsulfonyl)imide, [NTf2](-)) doped with several molar fractions of lithium salts with a common anion at 298.15 K and 1 atm were investigated by means of molecular dynamics simulations. The effect of the size of the salt cation was also analyzed by comparing these results with those for mixtures of [BMIM][PF6] with NaPF6. Lithium/sodium solvation and ionic mobilities were analyzed via the study of radial distribution functions, coordination numbers, cage autocorrelation functions, mean-square displacements (including the analysis of both ballistic and diffusive regimes), self-diffusion coefficients of all the ionic species, velocity and current autocorrelation functions, and ionic conductivity in all the ionic liquid/salt systems. We found that lithium and sodium cations are strongly coordinated in two different positions with the anion present in the mixture. Moreover, [Li](+) and [Na](+) cations were found to form bonded-like, long-lived aggregates with the anions in their first solvation shell, which act as very stable kinetic entities within which a marked rattling motion of salt ions takes place. With very long MD simulation runs, this phenomenon is proved to be on the basis of the decrease of self-diffusion coefficients and ionic conductivities previously reported in experimental and computational results.

  4. Molecular dynamic simulation of Ar-Kr mixture across a rough walled nanochannel: Velocity and temperature profiles

    SciTech Connect

    Pooja, Ahluwalia, P. K.; Pathania, Y.

    2015-05-15

    This paper presents the results from a molecular dynamics simulation of mixture of argon and krypton in the Poiseuille flow across a rough walled nanochannel. The roughness effect on liquid nanoflows has recently drawn attention The computational software used for carrying out the molecular dynamics simulations is LAMMPS. The fluid flow takes place between two parallel plates and is bounded by horizontal rough walls in one direction and periodic boundary conditions are imposed in the other two directions. Each fluid atom interacts with other fluid atoms and wall atoms through Leenard-Jones (LJ) potential with a cut off distance of 5.0. To derive the flow a constant force is applied whose value is varied from 0.1 to 0.3 and velocity profiles and temperature profiles are noted for these values of forces. The velocity profile and temperature profiles are also looked at different channel widths of nanochannel and at different densities of mixture. The velocity profile and temperature profile of rough walled nanochannel are compared with that of smooth walled nanochannel and it is concluded that mean velocity increases with increase in channel width, force applied and decrease in density also with introduction of roughness in the walls of nanochannel mean velocity again increases and results also agree with the analytical solution of a Poiseuille flow.

  5. Simulations of a Normal Shock Train in a Constant Area Duct Using Wall-Modeled LES

    NASA Astrophysics Data System (ADS)

    Vane, Zachary; Bermejo-Moreno, Ivan; Lele, Sanjiva

    2013-11-01

    Large-Eddy Simulations (LES) of a turbulent boundary layer interacting with a normal shock train in a constant area duct (STCAD) are performed using an unstructured solver. Comparisons between wall-modeled LES (WMLES) and wall-resolved LES (WRLES) calculations of a spanwise-periodic flow at M = 1.61 and Re = 16,200 are used to evaluate an equilibrium wall-model's ability to replicate the wall-resolved results. The WMLES approach is then used for simulations at the flow conditions (M = 1.61, Re = 162,000) of the Carroll & Dutton STCAD experiments where traditional WRLES was inaccessible. Spanwise-periodic WMLES calculations were unable to duplicate the experimental wall pressure and Laser Doppler Velocimetry data obtained along the spanwise center plane of the duct. Investigations of the full, low aspect ratio duct geometry were then performed using WMLES. Comparisons with experimental data provide an assessment of the wall-model's ability to simulate realistic, high Reynolds number, non-equilibrium flows. However, the lack of information with respect to the sidewall boundary layers from the experiment led to a WMLES parameter study of the effects of boundary layer confinement on the shock train. Initial results suggest that the tunnel blockage due to the boundary layer displacement thickness determines many of the STCAD's characteristics. A possible improvement to the wall-model through the inclusion of previously omitted non-equilibrium terms is currently being pursued.

  6. Surrogate fuel assembly multi-axis shaker tests to simulate normal conditions of rail and truck transport

    SciTech Connect

    McConnell, Paul E.; Koenig, Greg John; Uncapher, William Leonard; Grey, Carissa; Engelhardt, Charles; Saltzstein, Sylvia J.; Sorenson, Ken B.

    2016-05-01

    This report describes the third set of tests (the “DCLa shaker tests”) of an instrumented surrogate PWR fuel assembly. The purpose of this set of tests was to measure strains and accelerations on Zircaloy-4 fuel rods when the PWR assembly was subjected to rail and truck loadings simulating normal conditions of transport when affixed to a multi-axis shaker. This is the first set of tests of the assembly simulating rail normal conditions of transport.

  7. MA-SNP--A new genotype calling method for oligonucleotide SNP arrays modeling the batch effect with a normal mixture model.

    PubMed

    Wen, Yalu; Li, Ming; Fu, Wenjiang J

    2011-08-30

    Genome-wide association studies hold great promise in identifying disease-susceptibility variants and understanding the genetic etiology of complex diseases. Microarray technology enables the genotyping of millions of single nucleotide polymorphisms. Many factors in microarray studies, such as probe selection, sample quality, and experimental process and batch, have substantial effect on the genotype calling accuracy, which is crucial for downstream analyses. Failure to account for the variability of these sources may lead to inaccurate genotype calls and false positive and false negative findings. In this study, we develop a SNP-specific genotype calling algorithm based on the probe intensity composite representation (PICR) model, while using a normal mixture model to account for the variability of batch effect on the genotype calls. We demonstrate our method with SNP array data in a few studies, including the HapMap project, the coronary heart disease and the UK Blood Service Control studies by the Wellcome Trust Case-Control Consortium, and a methylation profiling study. Our single array based approach outperforms PICR and is comparable to the best multi-array genotype calling methods.

  8. Pulmonary function in normal and elastase-treated hamsters exposed to a complex mixture of olefin-ozone-sulfur dioxide reaction products

    SciTech Connect

    Raub, J.A.; Miller, F.J.; Graham, J.A.; Gardner, D.E.; O'Neil, J.J.

    1983-01-01

    An elastase-induced emphysema model was utilized to determine if hamsters with preexisting lung disease were more susceptible to lung damage from air-pollutant exposure. Male golden hamsters, divided into two treatment groups, were given a single intratracheal injection of either 6 units of porcine pancreatic elastase (EMP) or buffer (CNT). After a 4-week recovery period, equal numbers of each group were exposed 23 hr/day x 28 day to filtered air (AIR) or to the complex by-products from a dark-phase-reaction mixture of trans-2-butene, ozone, and sulfur dioxide (MIX). Lung-function measurements on the elastase-treated groups showed changes consistent with mild emphysema. There were no significant differences in lung volumes or lung compliance between the AIR- and MIX-exposed animals. However, the nitrogen washout slope decreased and the diffusing capacity for carbon monoxide increased in both the CNT and EMP hamsters exposed to the MIX. The change in diffusing capacity was greater in normal hamsters than in hamsters with emphysema, and it is hypothesized that animals with impaired lung function had a decreased ability to respond to a pulmonary insult from the mix.

  9. Phase equilibra in binary Lennard-Jones mixtures: phase diagram simulation

    NASA Astrophysics Data System (ADS)

    Canongia Lopes, J. N.

    A three-box version of the Gibbs ensemble Monte Carlo method was used to determine the phase diagram type of several binary mixtures of one-centre Lennard-Jones particles. The method can be used to establish a direct link between the intermolecular potential modelling the interactions in a given system and its fluid phase diagram, without the knowledge of the corresponding equation of state governing its pV T behaviour. As an example of the application of the method, closed-loop behaviour in an isotropic system could be found using a set of Lennard-Jones parameters exhibiting a cross-interaction diameter with a negative deviation from the Lorentz-Berthelot combination rule.

  10. Direct Numerical Simulation of a normal shock train with thermal nonequilibrium

    NASA Astrophysics Data System (ADS)

    Fiévet, Romain; Raman, Venkat

    2016-11-01

    The role of a normal shock train in a supersonic engine is to convert a sufficient amount of the incoming kinetic energy into internal energy by the entrance of the combustor, in order to guarantee flame ignition. It comprises a succession of compression and expansion waves attached to a turbulent boundary layer. When the molecular collisional process is not fast enough compared to convective and turbulent timescales, thermal nonequilibrium becomes important, which could alter the energy conversion process. By changing the local thermophysical properties and density, nonequilibrium can change the shock structures leading to changes in the energy conversion process. Here, direct numerical simulations are used to study the effect of such nonequilibrium on a Mach 2.0 rectangular isolator. A one-dimensional time-averaged analysis is used to quantify this effect on the pressure work and turbulent kinetic energy evolution. PhD Candidate.

  11. Molecular dynamics simulations of triflic acid and triflate ion/water mixtures: a proton conducting electrolytic component in fuel cells.

    PubMed

    Sunda, Anurag Prakash; Venkatnathan, Arun

    2011-11-30

    Triflic acid is a functional group of perflourosulfonated polymer electrolyte membranes where the sulfonate group is responsible for proton conduction. However, even at extremely low hydration, triflic acid exists as a triflate ion. In this work, we have developed a force-field for triflic acid and triflate ion by deriving force-field parameters using ab initio calculations and incorporated these parameters with the Optimized Potentials for Liquid Simulations - All Atom (OPLS-AA) force-field. We have employed classical molecular dynamics (MD) simulations with the developed force field to characterize structural and dynamical properties of triflic acid (270-450 K) and triflate ion/water mixtures (300 K). The radial distribution functions (RDFs) show the hydrophobic nature of CF(3) group and presence of strong hydrogen bonding in triflic acid and temperature has an insignificant effect. Results from our MD simulations show that the diffusion of triflic acid increases with temperature. The RDFs from triflate ion/water mixtures shows that increasing hydration causes water molecules to orient around the SO(3)(-) group of triflate ions, solvate the hydronium ions, and other water molecules. The diffusion of triflate ions, hydronium ion, and water molecules shows an increase with hydration. At λ = 1, the diffusion of triflate ion is 30 times lower than the diffusion of triflic acid due to the formation of stable triflate ion-hydronium ion complex. With increasing hydration, water molecules break the stability of triflate ion-hydronium ion complex leading to enhanced diffusion. The RDFs and diffusion coefficients of triflate ions, hydronium ions and water molecules resemble qualitatively the previous findings using per-fluorosulfonated membranes.

  12. Analysis of Regolith Simulant Ejecta Distributions from Normal Incident Hypervelocity Impact

    NASA Technical Reports Server (NTRS)

    Edwards, David L.; Cooke, William; Suggs, Rob; Moser, Danielle E.

    2008-01-01

    The National Aeronautics and Space Administration (NASA) has established the Constellation Program. The Constellation Program has defined one of its many goals as long-term lunar habitation. Critical to the design of a lunar habitat is an understanding of the lunar surface environment; of specific importance is the primary meteoroid and subsequent ejecta environment. The document, NASA SP-8013 'Meteoroid Environment Model Near Earth to Lunar Surface', was developed for the Apollo program in 1969 and contains the latest definition of the lunar ejecta environment. There is concern that NASA SP-8013 may over-estimate the lunar ejecta environment. NASA's Meteoroid Environment Office (MEO) has initiated several tasks to improve the accuracy of our understanding of the lunar surface ejecta environment. This paper reports the results of experiments on projectile impact into powdered pumice and unconsolidated JSC-1A Lunar Mare Regolith simulant targets. Projectiles were accelerated to velocities between 2.45 and 5.18 km/s at normal incidence using the Ames Vertical Gun Range (AVGR). The ejected particles were detected by thin aluminum foil targets strategically placed around the impact site and angular ejecta distributions were determined. Assumptions were made to support the analysis which include; assuming ejecta spherical symmetry resulting from normal impact and all ejecta particles were of mean target particle size. This analysis produces a hemispherical flux density distribution of ejecta with sufficient velocity to penetrate the aluminum foil detectors.

  13. A Virtual Mixture Approach to the Study of Multistate Equilibrium: Application to Constant pH Simulation in Explicit Water.

    PubMed

    Wu, Xiongwu; Brooks, Bernard R

    2015-10-01

    Chemical and thermodynamic equilibrium of multiple states is a fundamental phenomenon in biology systems and has been the focus of many experimental and computational studies. This work presents a simulation method to directly study the equilibrium of multiple states. This method constructs a virtual mixture of multiple states (VMMS) to sample the conformational space of all chemical states simultaneously. The VMMS system consists of multiple subsystems, one for each state. The subsystem contains a solute and a solvent environment. The solute molecules in all subsystems share the same conformation but have their own solvent environments. Transition between states is implicated by the change of their molar fractions. Simulation of a VMMS system allows efficient calculation of relative free energies of all states, which in turn determine their equilibrium molar fractions. For systems with a large number of state transition sites, an implicit site approximation is introduced to minimize the cost of simulation. A direct application of the VMMS method is for constant pH simulation to study protonation equilibrium. Applying the VMMS method to a heptapeptide of 3 ionizable residues, we calculated the pKas of those residues both with all explicit states and with implicit sites and obtained consistent results. For mouse epidermal growth factor of 9 ionizable groups, our VMMS simulations with implicit sites produced pKas of all 9 ionizable groups and the results agree qualitatively with NMR measurement. This example demonstrates the VMMS method can be applied to systems of a large number of ionizable groups and the computational cost scales linearly with the number of ionizable groups. For one of the most challenging systems in constant pH calculation, SNase Δ+PHS/V66K, our VMMS simulation shows that it is the state-dependent water penetration that causes the large deviation in lysine66's pKa.

  14. A normal stress subgrid-scale eddy viscosity model in large eddy simulation

    NASA Technical Reports Server (NTRS)

    Horiuti, K.; Mansour, N. N.; Kim, John J.

    1993-01-01

    The Smagorinsky subgrid-scale eddy viscosity model (SGS-EVM) is commonly used in large eddy simulations (LES) to represent the effects of the unresolved scales on the resolved scales. This model is known to be limited because its constant must be optimized in different flows, and it must be modified with a damping function to account for near-wall effects. The recent dynamic model is designed to overcome these limitations but is compositionally intensive as compared to the traditional SGS-EVM. In a recent study using direct numerical simulation data, Horiuti has shown that these drawbacks are due mainly to the use of an improper velocity scale in the SGS-EVM. He also proposed the use of the subgrid-scale normal stress as a new velocity scale that was inspired by a high-order anisotropic representation model. The testing of Horiuti, however, was conducted using DNS data from a low Reynolds number channel flow simulation. It was felt that further testing at higher Reynolds numbers and also using different flows (other than wall-bounded shear flows) were necessary steps needed to establish the validity of the new model. This is the primary motivation of the present study. The objective is to test the new model using DNS databases of high Reynolds number channel and fully developed turbulent mixing layer flows. The use of both channel (wall-bounded) and mixing layer flows is important for the development of accurate LES models because these two flows encompass many characteristic features of complex turbulent flows.

  15. Solvation free energies of aqueous mixtures in a ``truly'' open boundary simulation

    NASA Astrophysics Data System (ADS)

    Mukherji, Debashish; Kremer, Kurt

    2013-03-01

    (Bio)macromolecular solvation in water cosolvent mixtures are dictated by the preferential interaction of cosolvents with the proteins. The numerical studies in the field are limited to the closed boundary schemes, which, however, suffers from severe system size effects. More specifically, when the conformational transitions are intimately linked to the large concentration fluctuations, the excess of cosolvents near a protein lead to depletion elsewhere in a small-sized closed boundary setup. This disturbs solvent equilibrium within the bulk solution. Therefore, by combining the adaptive resolution scheme (AdResS) with a metropolis particle exchange criterion, we propose a ``truly'' open boundary method that heals the particle depletion in a closed boundary setup. In AdResS, an all-atom region, containing protein, is coupled to a coarse-grained (CG) reservoir. Particle exchange is performed in the CG region, which otherwise would be impossible in an all-atom setup of dense fluids. We calculate solvation free energies within the all-atom region using Kirkwood-Buff theory. Our method produces well converged solvation energies that are impossible in a brute force all-atom MD of small system sizes. We will discuss two cases of triglycine in aqueous urea and PNIPAm in aqueous methanol.

  16. Decanting of Simulated Mark 42 Digestion Mixtures Using a Dip Tube

    SciTech Connect

    Crooks, W.J. III

    1999-07-16

    'Existing plant flowsheets are insufficient for complete dissolution of unirradiated Mark 42 targets. One option being considered by Nuclear Materials Stabilization and Storage (NMSS) is to dissolve the aluminum components of the Mark 42 targets, allow plutonium solids to settle, transfer some of the aluminum-laden liquid out of the dissolver tank, and recharge the dissolver tank with fresh solution to achieve dissolution of the plutonium solids. The core problem associated with this two-step dissolution procedure is that, after the initial digestion of Mark 42 material, one to two micron-sized PuO2 particles settle from the mixture. Those particles are of concern because they may generate additional nuclear criticality safety requirements, and because they may be transferred out of the dissolver tank and disrupt the efficacy of downstream processes, such as solvent extraction. NMSS asked the Chemical Technology Group (CTG) to evaluate a decanting process in the presence of settled micron-sized particles using a one-fifth-scale mock-up of a canyon tank.'

  17. Experimental and simulation studies of iron oxides for geochemical fixation of CO2-SO2 gas mixtures

    USGS Publications Warehouse

    Garcia, Susana; Rosenbauer, Robert J.; Palandri, James; Maroto-Valer, M. Mercedes

    2011-01-01

    Iron-bearing minerals are reactive phases of the subsurface environment and could potentially trap CO2–SO2gas mixtures derived from fossil fuel combustion processes by their conversion to siderite (FeCO3) and dissolved sulfate. Changes in fluid and mineral compositions resulting from reactions, involving the co-injection of SO2 with CO2 were observed both theoretically and experimentally. Experiments were conducted with a natural hematite (α-Fe2O3) sample. A high pressure-high temperature apparatus was used to simulate conditions in geologic formations deeper than 800 m, where CO2 is in the supercritical state. Solid samples were allowed to react with a NaCl–NaOH brine and SO2-bearing CO2-dominated gas mixtures. The predicted equilibrium mineral assemblage at 100 °C and 250 bar became hematite, dawsonite (NaAl(OH)2CO3), siderite (FeCO3) and quartz (SiO2). Experimentally, siderite and dawsonite, derived from the presence of kaolinite (Al2Si2O5(OH)4) in the parent material, were present in residual solids at longer reaction time intervals, which agreed well with results from the modelling work.

  18. Numerical Simulations of Thermocapillary Flow of a Binary Mixture with the Soret Effect in a Shallow Annular Pool

    NASA Astrophysics Data System (ADS)

    Yu, Jia-Jia; Zhang, Li; Li, You-Rong; Chen, Jie-Chao

    2016-04-01

    In order to understand the characteristics of thermocapillary flow of a toluene/ n-hexane mixture with the Soret effect in a shallow annular pool, a series of three-dimensional numerical simulations were carried out. The shallow annular pool was heated from the outer cylinder and cooled at the inner cylinder. The initial toluene concentration in the toluene/ n-hexane mixture varied from 0 to 0.4467. Results indicate that the flow undergoes two transitions from the axisymmetric steady flow to the hydrothermal waves, and then to chaos with the increase of the thermocapillary Reynolds number. The critical thermocapillary Reynolds number for the incipience of the oscillatory flow decreases with the increase of the initial solute concentration. When the thermocapillary flow transits to a three-dimensional oscillatory flow, a concentration fluctuation is observed on the free surface, which is similar to the hydrothermal waves. However, compared with that of the temperature, the dimensionless fluctuation amplitude of the concentration is relatively weak. Furthermore, the fundamental oscillation frequency increases linearly with the initial solute concentration, but the wave number of the hydrothermal waves is almost unchangeable.

  19. Molecular Dynamics Simulation of Na(+)-Cl(-) Ion-Pair in Water-Methanol Mixtures under Supercritical and Ambient Conditions.

    PubMed

    Keshri, Sonanki; Sarkar, Atanu; Tembe, B L

    2015-12-17

    Constrained molecular dynamics simulations have been performed to investigate the structure and thermodynamics of Na(+)-Cl(-) ion-pair association in water-methanol mixtures under supercritical and ambient conditions in dilute solutions. From the computed potentials of mean force (PMFs) we find that contact ion pairs (CIPs) are more stable than all other associated states of the ion pairs in both ambient and supercritical conditions. Stabilities of CIPs increase with increase in the mole fraction of methanol. In supercritical conditions, major changes in PMFs occur as we go from x(methanol) = 0.00 to x(methanol) = 0.50. The stable solvent shared ion pair (SShIP) which occurs in x(methanol) = 0.00 and 0.25, vanishes when x(methanol) is 0.50 or greater. The stabilities of these ion pairs increase with increasing temperature. Local structures around the ions are studied using the radial distribution functions, density profiles, angular distribution functions, running coordination numbers and excess coordination numbers. Preferential solvation analysis shows that both Na(+) and Cl(-) ions are preferentially solvated by water. From the calculation of enthalpies and entropies, we find that Na(+)-Cl(-) ion-pair association in water-methanol binary mixtures is endothermic and driven by entropy both in ambient as well as under supercritical conditions.

  20. Local structure and intermolecular dynamics of an equimolar benzene and 1,3-dimethylimidazolium bis[(trifluoromethane)sulfonyl]amide mixture: Molecular dynamics simulations and OKE spectroscopic measurements

    NASA Astrophysics Data System (ADS)

    Lynden-Bell, Ruth M.; Xue, Lianjie; Tamas, George; Quitevis, Edward L.

    2014-07-01

    The local structure and intermolecular dynamics of an equimolar mixture of benzene and 1,3-dimethylimidazolium bis[(trifluoromethane)sulfonyl]amide ([dmim][NTf2]) were studied using molecular dynamics (MD) simulations and femtosecond optical Kerr effect (OKE) spectroscopy. The OKE spectrum of the benzene/[dmim][NTf2] mixture at 295 K was analyzed by comparing it to an ideal mixture spectrum obtained by taking the volume-fraction weighted sum of the OKE spectra of the pure liquids. The experimental mixture spectrum is higher in frequency and broader than that of the ideal mixture spectrum. These spectral differences are rationalized in terms of the local structure around benzene molecules in the mixture and the intermolecular dynamics as reflected in the density of states from the MD simulations. Specifically, we attribute the deviation of the OKE spectrum of the mixture from ideal behavior to benzene molecules seeing a stiffer intermolecular potential due to their being trapped in cages comprised of ions in the first solvation shell.

  1. Numerical simulation of nanosecond pulsed DBD in lean methane-air mixture for typical conditions in internal engines

    NASA Astrophysics Data System (ADS)

    Takana, Hidemasa; Nishiyama, Hideya

    2014-06-01

    Detailed two-dimensional numerical simulations of a high energy loading nanosecond dc pulse DBD in a lean methane-air mixture were conducted for plasma-assisted combustion by integrating individual models of plasma chemistry, photoionization and energy loading. The DBD streamer propagation process with radical productions was clarified at 10 atm and 600 K as under the condition of actual internal engines at ignition. Energy is loaded to the streamer first by the formation of plasma channel and then ceased due to the self-shielding effect. Because of the inversed electric field in a discharge space during decrease in applied voltage, energy is loaded to the discharge again. It was found that higher energy is loaded to the DBD streamer for larger dielectric constant even at lower applied voltage, and higher number density of oxygen radical is produced at almost the same radical production efficiency.

  2. CFD Convective Flow Simulation of the Varying Properties of CO2-H2O Mixtures in Geothermal Systems

    PubMed Central

    Yousefi, S.; Atrens, A. D.; Sauret, E.; Dahari, M.; Hooman, K.

    2015-01-01

    Numerical simulation of a geothermal reservoir, modelled as a bottom-heated square box, filled with water-CO2 mixture is presented in this work. Furthermore, results for two limiting cases of a reservoir filled with either pure water or CO2 are presented. Effects of different parameters including CO2 concentration as well as reservoir pressure and temperature on the overall performance of the system are investigated. It has been noted that, with a fixed reservoir pressure and temperature, any increase in CO2 concentration leads to better performance, that is, stronger convection and higher heat transfer rates. With a fixed CO2 concentration, however, the reservoir pressure and temperature can significantly affect the overall heat transfer and flow rate from the reservoir. Details of such variations are documented and discussed in the present paper. PMID:25879074

  3. Molecular dynamics simulation of the behaviour of water in nano-confined ionic liquid-water mixtures

    NASA Astrophysics Data System (ADS)

    Docampo-Álvarez, B.; Gómez-González, V.; Montes-Campos, H.; Otero-Mato, J. M.; Méndez-Morales, T.; Cabeza, O.; Gallego, L. J.; Lynden-Bell, R. M.; Ivaništšev, V. B.; Fedorov, M. V.; Varela, L. M.

    2016-11-01

    This work describes the behaviour of water molecules in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid under nanoconfinement, between graphene sheets. By means of molecular dynamics simulations, the adsorption of water molecules at the graphene surface is studied. A depletion of water molecules in the vicinity of the neutral and negatively charged graphene surfaces, and their adsorption at the positively charged surface are observed in line with the preferential hydration of the ionic liquid anions. The findings are appropriately described using a two-level statistical model. The confinement effect on the structure and dynamics of the mixtures is thoroughly analyzed using the density and the potential of mean force profiles, as well as by the vibrational densities of the states of water molecules near the graphene surface. The orientation of water molecules and the water-induced structural transitions in the layer closest to the graphene surface are also discussed.

  4. Removal of low concentrations of ammonium and humic acid from simulated groundwater by Vermiculite/Palygorskite mixture.

    PubMed

    Zhang, Xiuli; Lv, Guocheng; Liao, Libing; He, Maoqian; Li, Zhaohui; Wang, Mingshan

    2012-08-01

    Contaminants in water are classified into different types based on their physical and chemical properties. Thus, more than one type of sorbents may be needed for their removal. In this article, a combination of vermiculite with palygorskite was studied for their simultaneous removal of ammonium and humic acid from simulated groundwater. Batch results showed that the Langmuir model described ammonium adsorption well with an adsorption capacity of 22 mg/g while the humic acid adsorption data fitted to the linear adsorption better, suggesting different removal mechanisms of these two types of contaminants. Kinetic studies showed an instantaneous removal of ammonium and humic acid. A column packed with mixture of equal volumes of vermiculite and palygorskite could treat 100 pore volumes for ammonium removal at an initial concentration of 10 mg/L and 500 pore volumes for humic acid removal at an initial concentration of 20 mg/L before the effluent concentrations exceeded the standard.

  5. Compressibility, thermal expansion coefficient and heat capacity of CH4 and CO2 hydrate mixtures using molecular dynamics simulations.

    PubMed

    Ning, F L; Glavatskiy, K; Ji, Z; Kjelstrup, S; H Vlugt, T J

    2015-01-28

    Understanding the thermal and mechanical properties of CH4 and CO2 hydrates is essential for the replacement of CH4 with CO2 in natural hydrate deposits as well as for CO2 sequestration and storage. In this work, we present isothermal compressibility, isobaric thermal expansion coefficient and specific heat capacity of fully occupied single-crystal sI-CH4 hydrates, CO2 hydrates and hydrates of their mixture using molecular dynamics simulations. Eight rigid/nonpolarisable water interaction models and three CH4 and CO2 interaction potentials were selected to examine the atomic interactions in the sI hydrate structure. The TIP4P/2005 water model combined with the DACNIS united-atom CH4 potential and TraPPE CO2 rigid potential were found to be suitable molecular interaction models. Using these molecular models, the results indicate that both the lattice parameters and the compressibility of the sI hydrates agree with those from experimental measurements. The calculated bulk modulus for any mixture ratio of CH4 and CO2 hydrates varies between 8.5 GPa and 10.4 GPa at 271.15 K between 10 and 100 MPa. The calculated thermal expansion and specific heat capacities of CH4 hydrates are also comparable with experimental values above approximately 260 K. The compressibility and expansion coefficient of guest gas mixture hydrates increase with an increasing ratio of CO2-to-CH4, while the bulk modulus and specific heat capacity exhibit the opposite trend. The presented results for the specific heat capacities of 2220-2699.0 J kg(-1) K(-1) for any mixture ratio of CH4 and CO2 hydrates are the first reported so far. These computational results provide a useful database for practical natural gas recovery from CH4 hydrates in deep oceans where CO2 is considered to replace CH4, as well as for phase equilibrium and mechanical stability of gas hydrate-bearing sediments. The computational schemes also provide an appropriate balance between computational accuracy and cost for predicting

  6. New approaches to the simulation of heat-capacity curves and phase diagrams of pseudobinary phospholipid mixtures.

    PubMed Central

    Johann, C; Garidel, P; Mennicke, L; Blume, A

    1996-01-01

    A simulation program using least-squares minimization was developed to calculate and fit heat capacity (cp) curves to experimental thermograms of dilute aqueous dispersions of phospholipid mixtures determined by high-sensitivity differential scanning calorimetry. We analyzed cp curves and phase diagrams of the pseudobinary aqueous lipid systems 1,2-dimyristoyl-sn-glycero-3-phosphatidylglycerol/ 1,2-dipalmitoyl-sn-glycero-3phosphatidylcholine (DMPG/DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphatidic acid/1, 2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DMPA/DPPC) at pH 7. The simulation of the cp curves is based on regular solution theory using two nonideality parameters rho g and rho l for symmetric nonideal mixing in the gel and the liquid-crystalline phases. The broadening of the cp curves owing to limited cooperativity is incorporated into the simulation by convolution of the cp curves calculated for infinite cooperativity with a broadening function derived from a simple two-state transition model with the cooperative unit size n = delta HVH/delta Hcal as an adjustable parameter. The nonideality parameters and the cooperative unit size turn out to be functions of composition. In a second step, phase diagrams were calculated and fitted to the experimental data by use of regular solution theory with four different model assumptions. The best fits were obtained with a four-parameter model based on nonsymmetric, nonideal mixing in both phases. The simulations of the phase diagrams show that the absolute values of the nonideality parameters can be changed in a certain range without large effects on the shape of the phase diagram as long as the difference of the nonideality parameters for rho g for the gel and rho l for the liquid-crystalline phase remains constant. The miscibility in DMPG/DPPC and DMPA/DPPC mixtures differs remarkably because, for DMPG/DPPC, delta rho = rho l -rho g is negative, whereas for DMPA/DPPC this difference is positive. For DMPA/DPPC, this

  7. Evaluation of the grand-canonical partition function using expanded Wang-Landau simulations. III. Impact of combining rules on mixtures properties

    SciTech Connect

    Desgranges, Caroline; Delhommelle, Jerome

    2014-03-14

    Combining rules, such as the Lorentz-Berthelot rules, are routinely used to calculate the thermodynamic properties of mixtures using molecular simulations. Here we extend the expanded Wang-Landau simulation approach to determine the impact of the combining rules on the value of the partition function of binary systems, and, in turn, on the phase coexistence and thermodynamics of these mixtures. We study various types of mixtures, ranging from systems of rare gases to biologically and technologically relevant mixtures, such as water-urea and water-carbon dioxide. Comparing the simulation results to the experimental data on mixtures of rare gases allows us to rank the performance of combining rules. We find that the widely used Lorentz-Berthelot rules exhibit the largest deviations from the experimental data, both for the bulk and at coexistence, while the Kong and Waldman-Hagler provide much better alternatives. In particular, in the case of aqueous solutions of urea, we show that the use of the Lorentz-Berthelot rules has a strong impact on the Gibbs free energy of the solute, overshooting the value predicted by the Waldman-Hagler rules by 7%. This result emphasizes the importance of the combining rule for the determination of hydration free energies using molecular simulations.

  8. Determination of cohesive and normal stresses and simulation of fluidization using kinetic theory

    SciTech Connect

    Bezbaruah, R.

    1991-08-01

    The general objective of this study is focused on the solid stresses involved in gas-solid flow. These stresses are generally included in the momentum conservation equations, essentially for stability and to prevent particles from collapsing to unreasonably low values of gas volume fraction. The first half of this work undertakes the measurement of the stresses in various powders by direct means, while the second part uses a newly developed kinetic theory constitutive equation for stress to predict the flow and also the solids viscosity in a CFB. The cohesive or tensile stress found to exist in some classes of powders is measured using a Cohetester, based on which a cohesive force model is derived, which is sensitive to the characteristic properties of the powder material. The normal stress is measured using a Consolidometer, and the powder solids modulus is obtained as a function of the volume fraction. The solids modulus is seen to vary with particle size and particle type, with the smaller size particles being more compressible. The simulation of flow in the CFB using Gidaspow's (1991) extension of Ding's (1990) kinetic theory model to dilute phase flow, predicts realistic values of solids viscosity that are comparable to viscosities obtained experimentally by Miller (1991). However, to obtain a match between the two the value of the restitution coefficient has to be close to unity. The flow behavior showed periodic oscillations of flow (turbulence) as seen in a real system. 26 refs., 51 figs., 1 tab.

  9. Measurement of Primary Ejecta From Normal Incident Hypervelocity Impact on Lunar Regolith Simulant

    NASA Technical Reports Server (NTRS)

    Edwards, David L.; Cooke, William; Moser, Danielle; Swift, Wesley

    2007-01-01

    The National Aeronautics and Space Administration (NASA) continues to make progress toward long-term lunar habitation. Critical to the design of a lunar habitat is an understanding of the lunar surface environment. A subject for further definition is the lunar primary ejecta environment. The document NASA SP-8013 was developed for the Apollo program and is the latest definition of the primary ejecta environment. There is concern that NASA SP-8013 may over-estimate the lunar primary ejecta environment. NASA's Meteoroid Environment Office (MEO) has initiated several tasks to improve the accuracy of our understanding of the lunar surface primary ejecta environment. This paper reports the results of experiments on projectile impact into pumice targets, simulating lunar regolith. The Ames Vertical Gun Range (AVGR) was used to accelerate spherical Pyrex projectiles of 0.29g to velocities ranging between 2.5 km/s and 5.18 km/s. Impact on the pumice target occurred at normal incidence. The ejected particles were detected by thin aluminum foil targets placed around the pumice target in a 0.5 Torr vacuum. A simplistic technique to characterize the ejected particles was formulated. Improvements to this technique will be discussed for implementation in future tests.

  10. Auditory normalization of French vowels synthesized by an articulatory model simulating growth from birth to adulthood.

    PubMed

    Ménard, Lucie; Schwartz, Jean-Luc; Boë, Louis-Jean; Kandel, Sonia; Vallée, Nathalie

    2002-04-01

    The present article aims at exploring the invariant parameters involved in the perceptual normalization of French vowels. A set of 490 stimuli, including the ten French vowels /i y u e ø o E oe (inverted c) a/ produced by an articulatory model, simulating seven growth stages and seven fundamental frequency values, has been submitted as a perceptual identification test to 43 subjects. The results confirm the important effect of the tonality distance between F1 and f0 in perceived height. It does not seem, however, that height perception involves a binary organization determined by the 3-3.5-Bark critical distance. Regarding place of articulation, the tonotopic distance between F1 and F2 appears to be the best predictor of the perceived front-back dimension. Nevertheless, the role of the difference between F2 and F3 remains important. Roundedness is also examined and correlated to the effective second formant, involving spectral integration of higher formants within the 3.5-Bark critical distance. The results shed light on the issue of perceptual invariance, and can be interpreted as perceptual constraints imposed on speech production.

  11. Auditory normalization of French vowels synthesized by an articulatory model simulating growth from birth to adulthood

    NASA Astrophysics Data System (ADS)

    Ménard, Lucie; Schwartz, Jean-Luc; Boë, Louis-Jean; Kandel, Sonia; Vallée, Nathalie

    2002-04-01

    The present article aims at exploring the invariant parameters involved in the perceptual normalization of French vowels. A set of 490 stimuli, including the ten French vowels eye, why, you, ee, ø oh, eh, oelig, openo, aye produced by an articulatory model, simulating seven growth stages and seven fundamental frequency values, has been submitted as a perceptual identification test to 43 subjects. The results confirm the important effect of the tonality distance between F1 and f0 in perceived height. It does not seem, however, that height perception involves a binary organization determined by the 3-3.5-Bark critical distance. Regarding place of articulation, the tonotopic distance between F1 and F2 appears to be the best predictor of the perceived front-back dimension. Nevertheless, the role of the difference between F2 and F3 remains important. Roundedness is also examined and correlated to the effective second formant, involving spectral integration of higher formants within the 3.5-Bark critical distance. The results shed light on the issue of perceptual invariance, and can be interpreted as perceptual constraints imposed on speech production.

  12. The Mechanisms of Compensatory Responses of the Respiratory System to Simulated Central Hypervolemia in Normal Subjects.

    PubMed

    Segizbaeva, M O; Donina, Zh A; Aleksandrov, V G; Aleksandrova, N P

    2015-01-01

    The compensatory responses of the respiratory system to simulated central hypervolemia (CHV) were investigated in 14 normal subjects. The central hypervolemia was caused by a short-time passive head-down tilt (HDT, -30°, 30 min). The results show that CHV increased the mechanical respiratory load and the airway resistance, slowed the inspiratory flow, increased the duration of the inspiratory phase, reduced the respiratory rate, but not changed the minute ventilation. CHV induced a significant rise in inspiratory swings of alveolar pressure (184%), based on the inspiratory occlusion pressure measurement. These changes indicate a compensatory increase in the inspiratory muscle contraction force. A stable level of minute ventilation during CHV was an effect of increased EMG activity of parasternal muscles more than twice (P<0.01). A contribution of the diaphragm and scalene muscles to ventilation during spontaneous breathing in HDT was reduced. An increase of genioglossus contractile activity during HDT contributed to the stabilization of airway patency. These results suggest that a coordinated modulation of inspiratory muscles activity allows preserving a constant level of minute ventilation during a short-time intrathoracic blood volume expansion. The mechanisms of respiratory load compensation seem to be mediated by afferent information from the lung and respiratory muscle receptors and from the segmentary reflexes and intrinsic properties of the muscle fibers.

  13. MRI Measurements and Granular Dynamics Simulation of Segregation of Granular Mixture

    NASA Technical Reports Server (NTRS)

    Nakagawa, M.; Moss, Jamie L.; Altobelli, Stephen A.

    1999-01-01

    the deep core region, which is untouched by the flowing layer, also completely disappear. Usually, the dynamics angle of repose are uniquely defined for individual species to characterize particle properties, and the dynamic angle of repose thus defined provides little information for the dynamic angle of repose of the mixture since the concentration ratio and the internal packing structure do not remain the same during the segregation processes. Under microgravity environment, the dynamics angle of repose argument does not hold since there is simply no flowing layer to influence/determine the preferred directions of segregation. We have thus designed an experiment so that the effects of the dynamic angle of repose can be minimized by filling the cylinder almost completely full. Small particles still formed a radial core and also migrated to form axial bands. As ground based experiments we have designed and conducted both 2D and 3D segregation experiments. The 2D experiments are performed using a thin cylinder (the gap between two end caps is about 5 mm) filled with different combinations of particles. The 3D experiments are conducted with a long cylinder of its length and diameter of 27cm and 7cm, respectively. Results of 2D experiments indicate that different mechanisms govern particle motion in regions near and far from the axis of rotation. Results of 3D experiments indicate that a series of collapses of microstructures of particle packing (micro-collapses) may be responsible for the creation of voids for small particles to migrate through in the axial direction. We have successfully eliminated the dynamic angle of repose as a cause for segregation, however, by almost completely filling the cylinder with the particles, we have lost an opportunity to investigate a possibility of particle "mobility" being a cause for segregation which requires a flowing surface but not the difference in the angle of repose. This is currently being investigated.

  14. Binary mixtures of two anionic polysaccharides simulating the rheological properties of oxidised starch

    NASA Astrophysics Data System (ADS)

    Sikora, Marek; Dobosz, Anna; Adamczyk, Greta; Krystyjan, Magdalena; Kowalski, Stanisław; Tomasik, Piotra; Kutyła-Kupidura, Edyta M.

    2017-01-01

    Modifications of starches are carried out to improve their industrial usefulness. However, the consumers prefer natural products. For this reason, various methods of starch properties modification are applied to replace those requiring the use of chemical reagents. The aim of this study was to determine whether it is possible to use binary pastes, containing normal potato starch and xanthan gum, as substitutes of chemically modified starches (with oxidised starch E 1404 pastes as an example). Flow curves with hysteresis loops, apparent viscosity at constant shear rate of 50 s-1 and in-shear structural recovery test with pre-shearing were applied to study the rheological properties of the pastes. It was found that two anionic hydrocolloids, potato starch and xanthan gum, can form binary systems with thickening properties, provided that their proportions are adequately adjusted. Some of the binary pastes under investigation exhibited rheological properties resembling pastes of starch oxidised with hypochlorite (E 1404). The way of tailoring the binary pastes properties is presented.

  15. Impact of an equality constraint on the class-specific residual variances in regression mixtures: A Monte Carlo simulation study.

    PubMed

    Kim, Minjung; Lamont, Andrea E; Jaki, Thomas; Feaster, Daniel; Howe, George; Van Horn, M Lee

    2016-06-01

    Regression mixture models are a novel approach to modeling the heterogeneous effects of predictors on an outcome. In the model-building process, often residual variances are disregarded and simplifying assumptions are made without thorough examination of the consequences. In this simulation study, we investigated the impact of an equality constraint on the residual variances across latent classes. We examined the consequences of constraining the residual variances on class enumeration (finding the true number of latent classes) and on the parameter estimates, under a number of different simulation conditions meant to reflect the types of heterogeneity likely to exist in applied analyses. The results showed that bias in class enumeration increased as the difference in residual variances between the classes increased. Also, an inappropriate equality constraint on the residual variances greatly impacted on the estimated class sizes and showed the potential to greatly affect the parameter estimates in each class. These results suggest that it is important to make assumptions about residual variances with care and to carefully report what assumptions are made.

  16. Modeling the adsorption of PAH mixture in silica nanopores by molecular dynamic simulation combined with machine learning.

    PubMed

    Sui, Hong; Li, Lin; Zhu, Xinzhe; Chen, Daoyi; Wu, Guozhong

    2016-02-01

    The persistence of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils is largely controlled by their molecular fate in soil pores. The adsorption and diffusion of 16 PAHs mixture in silica nanopore with diameter of 2.0, 2.5, 3.0 and 3.5 nm, respectively, were characterized by adsorption energy, mean square displacement, free surface area and free volume fraction using molecular dynamic (MD) simulation. Results suggested that PAHs adsorption in silica nanopores was associated with diffusion process while competitive sorption was not the dominant mechanism in context of this study. The partial least squares (PLS) regression and machine learning (ML) methods (i.e. support vector regression, M5 decision tree and multilayer perceptrons) were used to correlate the adsorption energy with the pore diameter and PAH properties (number of carbon atoms, aromatic ring number, boiling point, molecular weight, octanol-water partition coefficient, octanol-organic carbon partition coefficient, solvent accessible area, solvent accessible volume and polarization). Results indicated that the PAH adsorption could not be predicted by linear regression as the R(2)Y and Q(2)Y coefficients of PLS analysis was 0.375 and 0.199, respectively. The nonlinearity was well recognized by ML with correlation coefficient up to 0.9. Overall, the combination of MD simulation and ML approaches can assist in interpreting the sequestration of organic contaminants in the soil nanopores.

  17. One-dimensional turbulence model simulations of autoignition of hydrogen/carbon monoxide fuel mixtures in a turbulent jet

    SciTech Connect

    Gupta, Kamlesh G.; Echekki, Tarek

    2011-02-15

    The autoignition of hydrogen/carbon monoxide in a turbulent jet with preheated co-flow air is studied using the one-dimensional turbulence (ODT) model. The simulations are performed at atmospheric pressure based on varying the jet Reynolds number and the oxidizer preheat temperature for two compositions corresponding to varying the ratios of H{sub 2} and CO in the fuel stream. Moreover, simulations for homogeneous autoignition are implemented for similar mixture conditions for comparison with the turbulent jet results. The results identify the key effects of differential diffusion and turbulence on the onset and eventual progress of autoignition in the turbulent jets. The differential diffusion of hydrogen fuels results in a reduction of the ignition delay relative to similar conditions of homogeneous autoignition. Turbulence may play an important role in delaying ignition at high-turbulence conditions, a process countered by the differential diffusion of hydrogen relative to carbon monoxide; however, when ignition is established, turbulence enhances the overall rates of combustion of the non-premixed flame downstream of the ignition point. (author)

  18. The Standardization of Linear and Nonlinear Effects in Direct and Indirect Applications of Structural Equation Mixture Models for Normal and Nonnormal Data

    PubMed Central

    Brandt, Holger; Umbach, Nora; Kelava, Augustin

    2015-01-01

    The application of mixture models to flexibly estimate linear and nonlinear effects in the SEM framework has received increasing attention (e.g., Jedidi et al., 1997b; Bauer, 2005; Muthén and Asparouhov, 2009; Wall et al., 2012; Kelava and Brandt, 2014; Muthén and Asparouhov, 2014). The advantage of mixture models is that unobserved subgroups with class-specific relationships can be extracted (direct application), or that the mixtures can be used as a statistical tool to approximate nonnormal (latent) distributions (indirect application). Here, we provide a general standardization procedure for linear and nonlinear interaction and quadratic effects in mixture models. The procedure can also be applied to multiple group models or to single class models with nonlinear effects like LMS (Klein and Moosbrugger, 2000). We show that it is necessary to take nonnormality of the data into account for a correct standardization. We present an empirical example from education science applying the proposed procedure. PMID:26648886

  19. Deciding on the Number of Classes in Latent Class Analysis and Growth Mixture Modeling: A Monte Carlo Simulation Study

    ERIC Educational Resources Information Center

    Nylund, Karen L.; Asparouhov, Tihomir; Muthen, Bengt O.

    2007-01-01

    Mixture modeling is a widely applied data analysis technique used to identify unobserved heterogeneity in a population. Despite mixture models' usefulness in practice, one unresolved issue in the application of mixture models is that there is not one commonly accepted statistical indicator for deciding on the number of classes in a study…

  20. Normal mode energetics and error analysis of GLA GCM simulations with different horizontal resolutions during a winter month

    NASA Technical Reports Server (NTRS)

    Tanaka, H. L.; Kung, E. C.; Baker, W. E.

    1989-01-01

    Comparative energetics is presented for a series of four general circulation model simulations for January 1979 conducted by the Goddard Laboratory for Atmospheres. The simulations include cases of coarse and fine horizontal model resolutions with two slightly different initial conditions. Using a three-dimensional normal mode expansion, it is found that the gravity-mode energy levels are significantly reduced in the higher wavenumbers and in the higher-order internal vertical modes by the increase of horizontal model resolution.

  1. Mass Transport Properties of LiD-U Mixtures from Orbital Free Molecular Dynamics Simulations and a Pressure-Matching Mixing Rule

    SciTech Connect

    Burakovsky, Leonid; Kress, Joel D.; Collins, Lee A.

    2012-05-31

    Mass transport properties for LiD-U mixtures were calculated using a pressure matching mixture rule for the mixing of LiD and of U properties simulated with Orbital Free Molecular Dynamics (OFMD). The mixing rule was checked against benchmark OFMD simulations for the fully interacting three-component (Li, D, U) system. To obtain transport coefficients for LiD-U mixtures of different (LiD){sub x}U{sub (1-x)} compositions as functions of temperature and mixture density is a tedious task. Quantum molecular dynamics (MD) simulations can be employed, as in the case LiD or U. However, due to the presence of the heavy constituent U, such simulations proceed so slowly that only a limited number of numerical data points in the (x, {rho}, T) phase space can be obtained. To finesse this difficulty, transport coefficients for a mixture can be obtained using a pressure-matching mixing rule discussed. For both LiD and U, the corresponding transport coefficients were obtained earlier from quantum molecular dynamics simulations. In these simulations, the quantum behavior of the electrons was represented using an orbital free (OF) version of density functional theory, and ions were advanced in time using classical molecular dynamics. The total pressure of the system, P = nk{sub B}T/V + P{sub e}, is the sum of the ideal gas pressure of the ions plus the electron pressure. The mass self-diffusion coefficient for species {alpha}, D{sub {alpha}}, the mutual diffusion coefficient for species {alpha} and {beta}, D{alpha}{beta}, and the shear viscosity, {eta}, are computed from the appropriate autocorrelation function. The details of similar QMD calculations on LiH are described in Ref. [1] for 0.5 eV < T < 3 eV, and in Ref. [2] for 2 eV < T < 6 eV.

  2. Mechanistic simulation of normal-tissue damage in radiotherapy—implications for dose-volume analyses

    NASA Astrophysics Data System (ADS)

    Rutkowska, Eva; Baker, Colin; Nahum, Alan

    2010-04-01

    A radiobiologically based 3D model of normal tissue has been developed in which complications are generated when 'irradiated'. The aim is to provide insight into the connection between dose-distribution characteristics, different organ architectures and complication rates beyond that obtainable with simple DVH-based analytical NTCP models. In this model the organ consists of a large number of functional subunits (FSUs), populated by stem cells which are killed according to the LQ model. A complication is triggered if the density of FSUs in any 'critical functioning volume' (CFV) falls below some threshold. The (fractional) CFV determines the organ architecture and can be varied continuously from small (series-like behaviour) to large (parallel-like). A key feature of the model is its ability to account for the spatial dependence of dose distributions. Simulations were carried out to investigate correlations between dose-volume parameters and the incidence of 'complications' using different pseudo-clinical dose distributions. Correlations between dose-volume parameters and outcome depended on characteristics of the dose distributions and on organ architecture. As anticipated, the mean dose and V20 correlated most strongly with outcome for a parallel organ, and the maximum dose for a serial organ. Interestingly better correlation was obtained between the 3D computer model and the LKB model with dose distributions typical for serial organs than with those typical for parallel organs. This work links the results of dose-volume analyses to dataset characteristics typical for serial and parallel organs and it may help investigators interpret the results from clinical studies.

  3. Numerical simulations of electric field driven hierarchical self-assembly of monolayers of binary mixtures of particles

    NASA Astrophysics Data System (ADS)

    Amah, Edison; Musunuri, Naga; Hossain, Shahadat; Fischer, Ian; Singh, Pushpendra

    2016-11-01

    We numerically study the process of self-assembly of particle mixtures on fluid-liquid interfaces when an electric field is applied in the direction normal to the interface. Lateral forces cause particles to self-assemble into molecular-like hierarchical arrangements consisting of composite particles arranged in a pattern. As in experiments, if the particles sizes differ by a factor of two or more, the composite particle has a larger particle at its core with several smaller particles forming a ring around it. Approximately same sized particles form chains (analogous to polymeric molecules) in which positively and negatively polarized particles alternate when their concentrations are approximately equal, but when their concentrations differ substantially the particles whose concentration is larger form rings around the particles whose concentration is smaller. In some instances, particle chains with a positively polarized particle at one end and a negatively particle at the other folded to form circular chains. For submicron particles, only when the electric field intensity is larger than a critical value required for overcoming Brownian forces, a hierarchical pattern consisting of composite particles will form. The work was supported by National Science Foundation.

  4. UV-VIS backscattering measurements on atmospheric particles mixture using polarization lidar coupled with numerical simulations and laboratory experiments

    NASA Astrophysics Data System (ADS)

    Miffre, Alain; Francis, Mirvatte; Anselmo, Christophe; Rairoux, Patrick

    2015-04-01

    As underlined by the latest IPCC report [1], tropospheric aerosols are nowadays recognized as one of the main uncertainties affecting the Earth's climate and human health. This issue is not straightforward due to the complexity of these nanoparticles, which present a wide range of sizes, shapes and chemical composition, which vary as a function of altitude, especially in the troposphere, where strong temperature variations are encountered under different water vapour content (from 10 to 100 % relative humidity). During this oral presentation, I will first present the scientific context of this research. Then, the UV-VIS polarimeter instrument and the subsequent calibration procedure [2] will be presented, allowing quantitative evaluation of particles backscattering coefficients in the atmosphere. In this way, up to three-component particles external mixtures can be partitioned into their spherical and non-spherical components, by coupling UV-VIS depolarization lidar measurements with numerical simulations of backscattering properties specific to non-spherical particles, such as desert dust or sea-salt particles [3], by applying the T-matrix numerical code [4]. This combined methodology is new, as opposed to the traditional approach using the lidar and T-matrix methodologies separately. In complement, recent laboratory findings [5] and field applications [6] will be presented, enhancing the sensitivity of the UV-VIS polarimeter. References [1] IPCC report, Intergovernmental Panel on Climate Change, IPCC, (2013). [2] G. David, A. Miffre, B. Thomas, and P. Rairoux: "Sensitive and accurate dual-wavelength UV-VIS polarization detector for optical remote sensing of tropospheric aerosols," Appl. Phys. B 108, 197-216 (2012). [3] G. David, B. Thomas, T. Nousiainen, A. Miffre and P. Rairoux: "Retrieving simulated volcanic, desert dust, and sea-salt particle properties from two / three-component particle mixtures using UV-VIS polarization Lidar and T-matrix," Atmos. Chem Phys

  5. Li+ solvation and transport properties in ionic liquid/lithium salt mixtures: a molecular dynamics simulation study.

    PubMed

    Li, Zhe; Smith, Grant D; Bedrov, Dmitry

    2012-10-25

    Molecular dynamics simulations of N-methyl-N-propylpyrrolidinium (pyr(13)) bis(trifluoromethanesulfonyl)imide (Ntf(2)) ionic liquid [pyr(13)][Ntf(2)] mixed with [Li][Ntf(2)] salt have been conducted using a polarizable force field. Mixture simulations with lithium salt mole fractions between 0% and 33% at 363 and 423 K yield densities, ion self-diffusion coefficients, and ionic conductivities in very good agreement with available experimental data. In all investigated electrolytes, each Li(+) cation was found to be coordinated, on average, by 4.1 oxygen atoms from surrounding anions. At lower concentrations (x ≤ 0.20), the Li(+) cation was found to be, on average, coordinated by slightly more than three Ntf(2) anions with two anions contributing a single oxygen atom and one anion contributing two oxygen atoms to Li(+) coordination. At the highest [Li][Ntf(2)] concentration, however, there were, on average, 3.5 anions coordinating each Li(+) cation, corresponding to fewer bidendate and more monodentate anions in the Li(+) coordination sphere. This trend is due to increased sharing of anions by Li(+) at higher salt concentrations. In the [pyr(13)][Ntf(2)]/[Li][Ntf(2)] electrolytes, the ion diffusivity is significantly smaller than that in organic liquid electrolytes due to not only the greater viscosity of the solvent but also the formation of clusters resulting from sharing of anions by Li(+) cations. The ionic conductivity of the electrolytes was found to decrease with increasing salt concentration, with the effect being greater at the higher temperature. Finally, we found that the contribution of Li(+) to ionic conductivity does not increase proportionally to Li(+) concentration but saturates at higher doping levels.

  6. Monte Carlo simulations of the solid-liquid transition in hard spheres and colloid-polymer mixtures.

    PubMed

    Zykova-Timan, T; Horbach, J; Binder, K

    2010-07-07

    Monte Carlo simulations at constant pressure are performed to study coexistence and interfacial properties of the liquid-solid transition in hard spheres and in colloid-polymer mixtures. The latter system is described as a one-component Asakura-Oosawa (AO) model where the polymer's degrees of freedom are incorporated via an attractive part in the effective potential for the colloid-colloid interactions. For the considered AO model, the polymer reservoir packing fraction is eta(p) (r)=0.1 and the colloid-polymer size ratio is q[triple bond]sigma(p)/sigma=0.15 (with sigma(p) and sigma as the diameter of polymers and colloids, respectively). Inhomogeneous solid-liquid systems are prepared by placing the solid fcc phase in the middle of a rectangular simulation box, creating two interfaces with the adjoined bulk liquid. By analyzing the growth of the crystalline region at various pressures and for different system sizes, the coexistence pressure p(co) is obtained, yielding p(co)=11.576 k(B)T/sigma(3) for the hard-sphere system and p(co)=8.00 k(B)T/sigma(3) for the AO model (with k(B) as the Boltzmann constant and T as the temperature). Several order parameters are introduced to distinguish between solid and liquid phases and to describe the interfacial properties. From the capillary-wave broadening of the solid-liquid interface, the interfacial stiffness is obtained for the (100) crystalline plane, giving the values gamma approximately 0.49 k(B)T/sigma(2) for the hard-sphere system and gamma approximately 0.95 k(B)T/sigma(2) for the AO model.

  7. Monte Carlo simulations of the solid-liquid transition in hard spheres and colloid-polymer mixtures

    NASA Astrophysics Data System (ADS)

    Zykova-Timan, T.; Horbach, J.; Binder, K.

    2010-07-01

    Monte Carlo simulations at constant pressure are performed to study coexistence and interfacial properties of the liquid-solid transition in hard spheres and in colloid-polymer mixtures. The latter system is described as a one-component Asakura-Oosawa (AO) model where the polymer's degrees of freedom are incorporated via an attractive part in the effective potential for the colloid-colloid interactions. For the considered AO model, the polymer reservoir packing fraction is ηpr=0.1 and the colloid-polymer size ratio is q ≡σp/σ=0.15 (with σp and σ as the diameter of polymers and colloids, respectively). Inhomogeneous solid-liquid systems are prepared by placing the solid fcc phase in the middle of a rectangular simulation box, creating two interfaces with the adjoined bulk liquid. By analyzing the growth of the crystalline region at various pressures and for different system sizes, the coexistence pressure pco is obtained, yielding pco=11.576 kBT/σ3 for the hard-sphere system and pco=8.00 kBT/σ3 for the AO model (with kB as the Boltzmann constant and T as the temperature). Several order parameters are introduced to distinguish between solid and liquid phases and to describe the interfacial properties. From the capillary-wave broadening of the solid-liquid interface, the interfacial stiffness is obtained for the (100) crystalline plane, giving the values γ˜≈0.49 kBT/σ2 for the hard-sphere system and γ˜≈0.95 kBT/σ2 for the AO model.

  8. Modeling and simulation of cooling-induced residual stresses in heated particulate mixture depositions in additive manufacturing

    NASA Astrophysics Data System (ADS)

    Zohdi, T. I.

    2015-10-01

    One key aspect of many additive manufacturing processes is the deposition of heated mixtures of particulate materials onto surfaces, which then bond and cool, leading to complex microstructures and possible residual stresses. The overall objective of this work is to construct a straightforward computational approach that researchers in the field can easily implement and use as a numerically-efficient simulation and design tool. Specifically because multifield coupling is present, a recursive, staggered, temporally-adaptive, finite difference time domain scheme is developed to resolve the internal microstructural thermal and mechanical fields, accounting for the simultaneous elasto-plasticity and damage. The time step adaptation allows the numerical scheme to iteratively resolve the changing physical fields by refining the time-steps during phases of the process when the system is undergoing large changes on a relatively small time-scale and can also enlarge the time-steps when the processes are relatively slow. The spatial discretization grids are uniform and dense. The deposited microstructure is embedded into spatial discretization. The regular grid allows one to generate a matrix-free iterative formulation which is amenable to rapid computation and minimal memory requirements, making it ideal for laptop computation. Numerical examples are provided to illustrate the approach. This formulation is useful for material scientists who seek ways to deposit such materials while simultaneously avoiding inadvertent excessive residual stresses.

  9. A Method for Simulating Correlated Non-Normal Systems of Statistical Equations.

    ERIC Educational Resources Information Center

    Headrick, Todd C.; Beasley, T. Mark

    Real world data often fail to meet the underlying assumptions of normal statistical theory. Many statistical procedures in the psychological and educational sciences involve models that may include a system of statistical equations with non-normal correlated variables (e.g., factor analysis, structural equation modeling, or other complex…

  10. Molecular Dynamics Simulation Study of the Capacitive Performance of a Binary Mixture of Ionic Liquids near an Onion-like Carbon Electrode.

    PubMed

    Li, Song; Feng, Guang; Fulvio, Pasquale F; Hillesheim, Patrick C; Liao, Chen; Dai, Sheng; Cummings, Peter T

    2012-09-06

    An equimolar mixture of 1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C3mpy][Tf2N]), 1-methyl-1-butylpiperidinium bis(trifluoromethylsulfonyl)imide ([C4mpip][Tf2N]) was investigated by classic molecular dynamics (MD) simulation. Differential scanning calorimetry (DSC) measurements verified that the binary mixture exhibited lower glass transition temperature than either of the pure room-temperature ionic liquids (RTILs). Moreover, the binary mixture gave rise to higher conductivity than the neat RTILs at lower temperature range. In order to study its capacitive performance in supercapacitors, simulations were performed of the mixture, and the neat RTILs used as electrolytes near an onion-like carbon (OLC) electrode at varying temperatures. The differential capacitance exhibited independence of the electrical potential applied for three electrolytes, which is in agreement with previous work on OLC electrodes in a different RTILs. Positive temperature dependence of the differential capacitance was observed, and it was dominated by the electrical double layer (EDL) thickness, which is for the first time substantiated in MD simulation.

  11. Molecular Dynamics Simulations of the Ionic Liquid 1-n-Butyl-3-Methylimidazolium Chloride and Its Binary Mixtures with Ethanol.

    PubMed

    Chen, Mo; Pendrill, Robert; Widmalm, Göran; Brady, John W; Wohlert, Jakob

    2014-10-14

    Room temperature ionic liquids (ILs) of the imidazolium family have attracted much attention during the past decade for their capability to dissolve biomass. Besides experimental work, numerous compuational studies have been concerned with the physical properties of both neat ILs and their interactions with different solutes, in particular, carbohydrates. Many classical force fields designed specifically for ILs have been found to yield viscosities that are too high for the liquid state, which has been attributed to the fact that the effective charge densities are too high due to the lack of electronic polarizability. One solution to this problem has been uniform scaling of the partial charges by a scale factor in the range 0.6-0.9, depending on model. This procedure has been shown to improve the viscosity of the models, and also to positively affect other properties, such as diffusion constants and ionic conductivity. However, less attention has been paid to how this affects the overall thermodynamics of the system, and the problems it might create when the IL models are combined with other force fields (e.g., for solutes). In the present work, we employ three widely used IL force fields to simulate 1-n-butyl-3-methyl-imidazolium chloride in both the crystal and the liquid state, as well as its binary mixture with ethanol. Two approaches are used: one in which the ionic charge is retained at its full integer value and one in which the partial charges are uniformly reduced to 85%. We investigate and calculate crystal and liquid structures, molar heat capacities, heats of fusion, self-diffusion constants, ionic conductivity, and viscosity for the neat IL, and ethanol activity as a function of ethanol concentration for the binary mixture. We show that properties of the crystal are less affected by charge scaling compared to the liquid. In the liquid state, transport properties of the neat IL are generally improved by scaling, whereas values for the heat of fusion are

  12. Nonequilibrium Mixed Quantum-Classical simulations of Hydrogen-bond Structure and Dynamics in Methanol-d Carbon tetrachloride liquid mixtures and its spectroscopic signature

    NASA Astrophysics Data System (ADS)

    Kwac, Kijeong; Geva, Eitan

    2011-03-01

    Liquid mixtures of methanol-d and carbon tetrachloride provide attractive model systems for investigating hydrogen-bond structure and dynamics. The hydrogen-bonded methanol oligomers in these mixtures give rise to a very broad hydroxyl stretch IR band (~ 150 cm-1). We have employed mixed quantum-classical molecular dynamics simulations to study the nature of hydrogen- bond structure and dynamics in this system and its spectroscopic signature. In our simulations, the hydroxyl stretch mode is treated quantum mechanically. We have found that the absorption spectrum is highly sensitive to the type of force fields used. Obtaining absorption spectra consistent with experiment required the use of corrected polarizabile force fields and a dipole damping scheme. We have established mapping relationships between the electric field along the hydroxyl bond and the hydrogen-stretch frequency and bond length thereby reducing the computational cost dramatically to simulate the complex nonequilibrium dynamics underlying pump-probe spectra.

  13. Predicting the apparent viscosity and yield stress of mixtures of primary, secondary and anaerobically digested sewage sludge: Simulating anaerobic digesters.

    PubMed

    Markis, Flora; Baudez, Jean-Christophe; Parthasarathy, Rajarathinam; Slatter, Paul; Eshtiaghi, Nicky

    2016-09-01

    Predicting the flow behaviour, most notably, the apparent viscosity and yield stress of sludge mixtures inside the anaerobic digester is essential because it helps optimize the mixing system in digesters. This paper investigates the rheology of sludge mixtures as a function of digested sludge volume fraction. Sludge mixtures exhibited non-Newtonian, shear thinning, yield stress behaviour. The apparent viscosity and yield stress of sludge mixtures prepared at the same total solids concentration was influenced by the interactions within the digested sludge and increased with the volume fraction of digested sludge - highlighted using shear compliance and shear modulus of sludge mixtures. However, when a thickened primary - secondary sludge mixture was mixed with dilute digested sludge, the apparent viscosity and yield stress decreased with increasing the volume fraction of digested sludge. This was caused by the dilution effect leading to a reduction in the hydrodynamic and non-hydrodynamic interactions when dilute digested sludge was added. Correlations were developed to predict the apparent viscosity and yield stress of the mixtures as a function of the digested sludge volume fraction and total solids concentration of the mixtures. The parameters of correlations can be estimated using pH of sludge. The shear and complex modulus were also modelled and they followed an exponential relationship with increasing digested sludge volume fraction.

  14. Two-phase flow properties in aperture-based fractures under normal deformation conditions: Analytical approach and numerical simulation

    NASA Astrophysics Data System (ADS)

    Ye, Zuyang; Liu, Hui-Hai; Jiang, Qinghui; Liu, Yanzhang; Cheng, Aiping

    2017-02-01

    A systematic method has been proposed to estimate the two-phase flow properties of horizontal fractures under normal deformation condition. Based on Gaussian aperture distributions and the assumption of local parallel plate model, a simple model was obtained in closed form to predict the capillary pressure-saturation relationships for both wetting and non-wetting phases. Three conceptual models were also developed to characterize the relative permeability behaviors. In order to investigate the effect of normal deformation on two-phase flow properties, the normal deformation could be represented with the maximum void space closure on the basis of penetration model. A rigorous successive random addition (SRA) method was used to generate the aperture-based fractures and a numerical approach based on invasion percolation (IP) model was employed to model capillary-dominated displacements between wetting and non-wetting phases. The proposed models were partially verified by a laboratory dataset and numerical calculations without consideration of deformation. Under large normal deformations, it was found that the macroscopic model is in better agreement with simulated observations. The simulation results demonstrated that the two-phase flow properties including the relationships between capillary pressure, relative permeability and saturation, phase interference, phase structures, residual-saturation-rated parameters and tortuosity factor, were highly sensitive to the spatial correlation of aperture distribution and normal deformation.

  15. Simulations of exercise and brain effects of acute exposure to carbon monoxide in normal and vascular-diseased persons.

    PubMed

    Benignus, Vernon A; Coleman, Thomas G

    2010-04-01

    At some level, carboxyhemoglobin (COHb) due to inhalation of carbon monoxide (CO) reduces maximum exercise duration in both normal and ischemic heart patients. At high COHb levels in normal subjects, brain function is also affected and behavioral performance is impaired.These are findings from published experiments that are, due to ethical or practical considerations, incomplete in that higher or lower ranges of COHb, and exercise have not been well studied. To fill in this knowledge base, a whole-body human physiological model was used to make estimates of physiological functioning by the simulation of parametric exposures to CO and various exercise levels. Ischemic heart disease was simulated by introducing a stenosis in the left heart arterial supply. Brain blood flow was also limited by such a stenosis. To lend credibility to such estimation, the model was tested by simulating experiments from the published literature. Simulations permitted several new conclusions. Increases in COHb produced the largest decreases in exercise duration when exercise was least strenuous and when COHb was smallest. For ischemic heart disease subjects, the greatest change in exercise duration produced by COHb increase was when ischemia and COHb was smallest. Brain aerobic metabolism was unaffected until COHb exceeded 25%, unless the maximum brain blood supply was limited by a stenosis greater than 50% of normal. For higher levels of stenosis, aerobic brain metabolism was reduced for any increase in COHb level, implying that behavior would be impaired with no "threshold" for COHb.

  16. Mineral Trioxide Aggregate Mixed with Normal Saline, Calcium Chloride or KY Jelly as Apical Plug in Simulated Open Apices: An In vitro Microleakage Study

    PubMed Central

    Mehrvarzfar, Payman; Akhavan, Hengameh; Ghasemi, Sara; Khodaei, Fatemeh; Tour Savadkouhi, Sohrab; Dianat, Omid

    2014-01-01

    Introduction: Mineral trioxide aggregate (MTA) mixed with normal saline has short working time, delayed setting time, and poor consistency when used as an apical plug. A preliminary study suggested that substituting normal saline with KY Jelly or 5% calcium chloride (CaCl2) as a vehicle expedites the setting time of MTA. The present in vitro study compared the microleakage of ProRoot MTA mixed with normal saline (MS) to that of ProRoot MTA mixed with KY Jelly and/or 5% CaCl2 in simulated canals with open apices. Materials and methods: Thirty six single-rooted extracted human teeth were cleaned and shaped with ProTaper rotary system to make 36 standardized artificially created open apices. Teeth were randomly divided into three experimental groups (n=10) and two control groups (n=3). In group 1, MTA was mixed with normal saline (MS) and placed into the canals to form 4 to 5 mm apical plugs. In group 2, MTA was mixed with 5% CaCl2 (MC) and in group 3, MTA was mixed with KY Jelly (MK). The other two groups served as positive and negative controls. The remaining canal spaces in the experimental groups were backfilled with thermoplasticized gutta-percha without sealer. Dye penetration and clearing was used to evaluate the sealing ability of each group. The samples were then examined under stereomicroscope to measure the microleakage of different MTA mixtures in mm. Data were statistically analyzed using One-Sample Kolmogorov-Smirnov test for determination of normal distribution and then by one-way ANOVA and Tukey’s tests to detect any significance. Results: Positive and negative controls responded as expected. The MS group showed the least mean dye penetration value. There was a significant difference between MS with other groups (P<0.05) but no difference was found between MC and MK groups. Conclusion: Within the limitations of this in vitro study, we can conclude that among these three vehicles, normal saline mixed with ProRoot MTA has the least amount of

  17. Effects of temperature on the thermodynamic and dynamical properties of glycerol-water mixtures: a computer simulation study of three different force fields.

    PubMed

    Akinkunmi, Frederick O; Jahn, David A; Giovambattista, Nicolas

    2015-05-21

    Glycerol-water solutions are relevant in technological and scientific applications, such as in the preservation of biomolecules and tissues at low temperatures. We perform molecular dynamics simulations of glycerol-water mixtures with glycerol molar fractions of χg = 0-100% at P = 0.1 MPa and T = 210-460 K. We focus on the effects of temperature and concentration on the thermodynamic (density ρ, thermal expansion coefficient αP, isobaric specific heat cP, compressibility κT) and dynamical (glycerol and water diffusion coefficients, Dg and Dw) properties of the mixtures. In particular, we test the sensitivity of computer simulation results to the glycerol force field and water model (TIP3P and TIP4P/2005) employed. All mixture models underestimate ρ at high T and tend to overestimate ρ at low T; only the mixture model based on TIP4P/2005 water exhibits a density maximum at low χg, as expected. All models overestimate αP, cP, and κT; they are able to reproduce qualitatively the T dependence of αP and κT but fail in the case of cP. In all cases, Dg and Dw follow the Vogel-Tamman-Fulcher equation and decouple at low T, with Dw/Dg increasing upon cooling. Overall, the mixture based on TIP4P/2005 water provides better thermodynamic and dynamical properties than the mixtures based on TIP3P water, even at χg = 20%.

  18. Phase-coexistence simulations of fluid mixtures by the Markov Chain Monte Carlo method using single-particle models

    SciTech Connect

    Li, Jun; Calo, Victor M.

    2013-09-15

    We present a single-particle Lennard–Jones (L-J) model for CO{sub 2} and N{sub 2}. Simplified L-J models for other small polyatomic molecules can be obtained following the methodology described herein. The phase-coexistence diagrams of single-component systems computed using the proposed single-particle models for CO{sub 2} and N{sub 2} agree well with experimental data over a wide range of temperatures. These diagrams are computed using the Markov Chain Monte Carlo method based on the Gibbs-NVT ensemble. This good agreement validates the proposed simplified models. That is, with properly selected parameters, the single-particle models have similar accuracy in predicting gas-phase properties as more complex, state-of-the-art molecular models. To further test these single-particle models, three binary mixtures of CH{sub 4}, CO{sub 2} and N{sub 2} are studied using a Gibbs-NPT ensemble. These results are compared against experimental data over a wide range of pressures. The single-particle model has similar accuracy in the gas phase as traditional models although its deviation in the liquid phase is greater. Since the single-particle model reduces the particle number and avoids the time-consuming Ewald summation used to evaluate Coulomb interactions, the proposed model improves the computational efficiency significantly, particularly in the case of high liquid density where the acceptance rate of the particle-swap trial move increases. We compare, at constant temperature and pressure, the Gibbs-NPT and Gibbs-NVT ensembles to analyze their performance differences and results consistency. As theoretically predicted, the agreement between the simulations implies that Gibbs-NVT can be used to validate Gibbs-NPT predictions when experimental data is not available.

  19. Structural anomaly and dynamic heterogeneity in cycloether/water binary mixtures: Signatures from composition dependent dynamic fluorescence measurements and computer simulations

    NASA Astrophysics Data System (ADS)

    Indra, Sandipa; Guchhait, Biswajit; Biswas, Ranjit

    2016-03-01

    We have performed steady state UV-visible absorption and time-resolved fluorescence measurements and computer simulations to explore the cosolvent mole fraction induced changes in structural and dynamical properties of water/dioxane (Diox) and water/tetrahydrofuran (THF) binary mixtures. Diox is a quadrupolar solvent whereas THF is a dipolar one although both are cyclic molecules and represent cycloethers. The focus here is on whether these cycloethers can induce stiffening and transition of water H-bond network structure and, if they do, whether such structural modification differentiates the chemical nature (dipolar or quadrupolar) of the cosolvent molecules. Composition dependent measured fluorescence lifetimes and rotation times of a dissolved dipolar solute (Coumarin 153, C153) suggest cycloether mole-fraction (XTHF/Diox) induced structural transition for both of these aqueous binary mixtures in the 0.1 ≤ XTHF/Diox ≤ 0.2 regime with no specific dependence on the chemical nature. Interestingly, absorption measurements reveal stiffening of water H-bond structure in the presence of both the cycloethers at a nearly equal mole-fraction, XTHF/Diox ˜ 0.05. Measurements near the critical solution temperature or concentration indicate no role for the solution criticality on the anomalous structural changes. Evidences for cycloether aggregation at very dilute concentrations have been found. Simulated radial distribution functions reflect abrupt changes in respective peak heights at those mixture compositions around which fluorescence measurements revealed structural transition. Simulated water coordination numbers (for a dissolved C153) and number of H-bonds also exhibit minima around these cosolvent concentrations. In addition, several dynamic heterogeneity parameters have been simulated for both the mixtures to explore the effects of structural transition and chemical nature of cosolvent on heterogeneous dynamics of these systems. Simulated four-point dynamic

  20. Non-equilibrium Simulation of CO­2-hydrate Phase Transitions from Mixtures of CO2 and N2 Gases

    NASA Astrophysics Data System (ADS)

    Qorbani Nashaqi, K.

    2015-12-01

    Storage of CO2 in aquifers is one of several options for reducing the emissions of CO2 to the atmosphere. Generally this option requires sealing integrity through layers of clay or shale. Many reservoirs have regions of temperature and pressure inside hydrate formation conditions. Whether hydrate formation can provide long term extra sealing still remains unverified in view of all co-existing phases that affect hydrate stability. Yet another storage option for CO2 is in the form of hydrate through exchange of in situ CH4 hydrate. Injection of CO2 into hydrate filled sediments is challenging due to the partial filling of pores with hydrate which results in low porosity and low permeability. Formation of new hydrate from injected CO2 will enhance these problems, Mixing N2 gas with the CO2 will increase permeability and will reduce driving forces for formation of new hydrate from pore water and injection gas. Hydrate can generally not reach thermodynamic equilibrium due to Gibbs' phase rule and the combined first and second laws of thermodynamics. These thermodynamic constraints on distribution of masses over co-existing phases are dynamically coupled to local mass- and heat-transport. Reservoir simulations are one possible method for investigation of possible scenarios related to injection of CO2 with N2 into aquifers containing CH4 hydrate. In this work we have developed prevoiusly modified RetrasoCodeBrite (RCB) simulator to handle injection of CO2/N2 gas mixtures. Hydrate formation and dissociation were determined by investigating Gibbs free energy differences between hydrate and hydrate formers. Gibbs free energy differences were calculated from changes in chemical potentials, which were obtained using non-equilibrium thermodynamic approach. Further extension of RCB has been implemented in this work through adding on-the-fly thermodynamic calculations. Correspondingly, hydrate phase transitions are calculated directly inside the code as a result of super

  1. Effects of clove oil-phospholipid mixtures on rheology of gum tragacanth - possible application for surfactant action on mucus gel simulants.

    PubMed

    Banerjee, R; Puniyani, R R

    2000-01-01

    The present study evaluates the effectiveness of specialised biomaterials consisting of clove oil- phospholipid mixtures as possible substitute surfactants in diseases of altered mucus viscosity by studying their effect on the viscosity of mucus gel simulants in vitro. Test surfactants consisting of phospholipid-clove oil mixtures in the ratio of 1 part of oil to 9 parts of phospholipid were prepared. The phospholipids used were dipalmitoyl phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) and binary mixtures of PC: PE and PC: PG in the ratio of 2 parts of PC to 3 parts of PE or PG. The effects of the phospholipid-clove oil mixtures on the viscosity of mucus gel simulant (MGS: a polymeric gel consisting predominantly of gum tragacanth and simulating respiratory mucus), was studied by application of steady shear rates ranging from 0.512 to 51.2/s in a concentric cylinder viscometer at 37 degrees C. The change in MGS viscosity, after incubation with surfactants, was found to have a non-Newtonian character and to follow the power law model with R2 values >0.8. The addition of clove oil-phospholipid mixtures caused a decrease in the MGS viscosity when compared with the effect of the phospholipid alone at low shear rates in case of PC, PG and PCPG. The combination of PC : PG with clove oil caused ratios of change in MGS viscosity < 1 i.e., caused a decrease in the MGS viscosity. PC: PG with clove oil was capable of lowering MGS viscosity and should be further researched as possible therapies for diseases of altered mucus rheology.

  2. Vibrational spectra, normal coordinate treatment and simulation of the vibrational spectra of piperazine glyoxime and its Co(III) complex

    NASA Astrophysics Data System (ADS)

    Özpozan, T.; Küçükusta, D.; Büyükmumcu, Z.

    2003-12-01

    Newly synthesized Co(III) complexes of piperazine glyoxime (PGO) are examined from the vibrational spectroscopy point of view. A complete interpretation of the vibrational spectra of both the ligand and the complex has been carried out on the basis of normal coordinate analysis. A valence force field has been developed for both of the compounds. The vibrational spectra of the compounds are simulated by a visual basic program prepared to run on an MS Excel data sheet.

  3. Velocity and normal tyre force estimation for heavy trucks based on vehicle dynamic simulation considering the road slope angle

    NASA Astrophysics Data System (ADS)

    Ma, Zeyu; Zhang, Yunqing; Yang, James

    2016-02-01

    A precise estimation of vehicle velocities can be valuable for improving the performance of the vehicle dynamics control (VDC) system and this estimation relies heavily upon the accuracy of longitudinal and lateral tyre force calculation governed by the prediction of normal tyre forces. This paper presents a computational method based on the unscented Kalman filter (UKF) method to estimate both longitudinal and lateral velocities and develops a novel quasi-stationary method to predict normal tyre forces of heavy trucks on a sloping road. The vehicle dynamic model is constructed with a planar dynamic model combined with the Pacejka tyre model. The novel quasi-stationary method for predicting normal tyre forces is able to characterise the typical chassis configuration of the heavy trucks. The validation is conducted through comparing the predicted results with those simulated by the TruckSim and it has a good agreement between these results without compromising the convergence speed and stability.

  4. Impact of simulated microgravity on the normal developmental time line of an animal-bacteria symbiosis.

    PubMed

    Foster, Jamie S; Khodadad, Christina L M; Ahrendt, Steven R; Parrish, Mirina L

    2013-01-01

    The microgravity environment during space flight imposes numerous adverse effects on animal and microbial physiology. It is unclear, however, how microgravity impacts those cellular interactions between mutualistic microbes and their hosts. Here, we used the symbiosis between the host squid Euprymna scolopes and its luminescent bacterium Vibrio fischeri as a model system. We examined the impact of simulated microgravity on the timeline of bacteria-induced development in the host light organ, the site of the symbiosis. To simulate the microgravity environment, host squid and symbiosis-competent bacteria were incubated together in high-aspect ratio rotating wall vessel bioreactors and examined throughout the early stages of the bacteria-induced morphogenesis. The host innate immune response was suppressed under simulated microgravity; however, there was an acceleration of bacteria-induced apoptosis and regression in the host tissues. These results suggest that the space flight environment may alter the cellular interactions between animal hosts and their natural healthy microbiome.

  5. The structure of molten AgCl, AgI and their eutectic mixture as studied by molecular dynamics simulations of polarizable ion model potentials.

    PubMed

    Alcaraz, Olga; Bitrián, Vicente; Trullàs, Joaquim

    2011-01-07

    The structure of molten AgCl, AgI, and their eutectic mixture Ag(Cl(0.43)I(0.57)) is studied by means of molecular dynamics simulations of polarizable ion model potentials. The corresponding static coherent structure factors reproduce quite well the available neutron scattering data. The qualitative behavior of the simulated partial structure factors and radial distribution functions for molten AgCl and AgI is that predicted by the reverse Monte Carlo modeling of the experimental data. The AgI results are also in qualitative agreement with those calculated from ab initio molecular dynamics.

  6. Gene Expression Profile Analysis as a Prognostic Indicator of Normal Tissue Response to Simulated Space Radiations

    NASA Technical Reports Server (NTRS)

    Story, Michael; Stivers, David N.

    2004-01-01

    This project was funded as a pilot project to determine the feasibility of using gene expression profiles to characterize the response of human cells to exposure to particulate radiations such as those encountered in the spaceflight environment. We proposed to use microarray technology to examine the gene expression patterns of a bank of well-characterized human fibroblast cell cultures. These fibroblast cultures were derived from breast or head and neck cancer patients who exhibited normal, minimal, or severe normal tissue reactions following low LET radiation exposure via radiotherapy. Furthermore, determination of SF2 values from fibroblasts cultured from these individuals were predictive of risk for severe late reactions. We hypothesized that by determining the expression of thousands of genes we could identify gene expression patterns that reflect how normal tissues respond to high Z and energy (HZE) particles, that is, that there are molecular signatures for HZE exposures. We also hypothesized that individuals who are intrinsically radiosensitive may elicit a unique response. Because this was funded as a pilot project we focused our initial studies on logistics and appropriate experimental design, and then to test our hypothesis that there is a unique molecular response to specific particles, in this case C and Fe, for primary human skin fibroblasts.

  7. Identification of musical instruments by normal-hearing subjects listening through a cochlear-implant simulation

    NASA Astrophysics Data System (ADS)

    Reich, Rebecca D.; Eddington, Donald

    2002-05-01

    Signal processing in a cochlear implant (CI) is primarily designed to convey speech and environmental sounds, and can cause distortion of musical timbre. Systematic investigation of musical instrument identification through a CI has not yet revealed how timbre is affected by the implant's processing. In this experiment, the bandpass filtering, rectification, and low-pass filtering of an implant are simulated in MATLAB. Synthesized signals representing 12 common instruments, each performing a major scale, are processed by simulations using up to 8 analysis channels. The unprocessed recordings, together with the 8 simulation conditions for 12 instruments, are presented in random order to each of the subjects. The subject's task is to identify the instrument represented by each item. The subjects also subjectively score each item based on similarity and pleasantness. We anticipate performance using the simulation will be worse than the unprocessed condition because of the limited information delivered by the envelopes of the analysis channels. These results will be analyzed as a confusion matrix and provide a basis for contrasting the information used by subjects listening to the unprocessed and processed materials. Understanding these differences should aid in the development of new processing strategies to better represent music for cochlear implant users.

  8. Generating Non-normal Data for Simulation of Structural Equation Models Using Mattson's Method.

    ERIC Educational Resources Information Center

    Reinartz, Werner J.; Echambadi, Raj; Cin, Wynne W.

    2002-01-01

    Tested empirically the applicability of a method developed by S. Mattson for generating data on latent variables with controlled skewness and kurtosis of the observed variables. Monte Carlo simulation results suggest that Mattson's method appears to be a good approach to generate data with defined levels of skewness and kurtosis. (SLD)

  9. Detection of fallen trees in ALS point clouds by learning the Normalized Cut similarity function from simulated samples

    NASA Astrophysics Data System (ADS)

    Polewski, P.; Yao, W.; Heurich, M.; Krzystek, P.; Stilla, U.

    2014-08-01

    Fallen trees participate in several important forest processes, which motivates the need for information about their spatial distribution in forest ecosystems. Several studies have shown that airborne LiDAR is a valuable tool for obtaining such information. In this paper, we propose an integrated method of detecting fallen trees from ALS point clouds based on merging small segments into entire fallen stems via the Normalized Cut algorithm. A new approach to specifying the segment similarity function for the clustering algorithm is introduced, where the attribute weights are learned from labeled data instead of being determined manually. We notice the relationship between Normalized Cut's similarity function and a class of regression models, which leads us to the idea of approximating the task of learning the similarity function with the simpler task of learning a classifier. Moreover, we set up a virtual fallen tree generation scheme to simulate complex forest scenarios with multiple overlapping fallen stems. The classifier trained on this simulated data yields a similarity function for Normalized Cut. Tests on two sample plots from the Bavarian Forest National Park with manually labeled reference data show that the trained function leads to high-quality segmentations. Our results indicate that the proposed data-driven approach can be a successful alternative to time consuming trial-and-error or grid search methods of finding good feature weights for graph cut algorithms. Also, the methodology can be generalized to other applications of graph cut clustering in remote sensing.

  10. Air Distribution Effectiveness for Residential Mechanical Ventilation: Simulation and Comparison of Normalized Exposures

    SciTech Connect

    Petithuguenin, T.D.P.; Sherman, M.H.

    2009-05-01

    The purpose of ventilation is to dilute indoor contaminants that an occupant is exposed to. Even when providing the same nominal rate of outdoor air, different ventilation systems may distribute air in different ways, affecting occupants' exposure to household contaminants. Exposure ultimately depends on the home being considered, on source disposition and strength, on occupants' behavior, on the ventilation strategy, and on operation of forced air heating and cooling systems. In any multi-zone environment dilution rates and source strengths may be different in every zone and change in time, resulting in exposure being tied to occupancy patterns.This paper will report on simulations that compare ventilation systems by assessing their impact on exposure by examining common house geometries, contaminant generation profiles, and occupancy scenarios. These simulations take into account the unsteady, occupancy-tied aspect of ventilation such as bathroom and kitchen exhaust fans. As most US homes have central HVAC systems, the simulation results will be used to make appropriate recommendations and adjustments for distribution and mixing to residential ventilation standards such as ASHRAE Standard 62.2.This paper will report on work being done to model multizone airflow systems that are unsteady and elaborate the concept of distribution matrix. It will examine several metrics for evaluating the effect of air distribution on exposure to pollutants, based on previous work by Sherman et al. (2006).

  11. In vitro cardiovascular system emulator (bioreactor) for the simulation of normal and diseased conditions with and without mechanical circulatory support.

    PubMed

    Ruiz, Paula; Rezaienia, Mohammad Amin; Rahideh, Akbar; Keeble, Thomas R; Rothman, Martin T; Korakianitis, Theodosios

    2013-06-01

    This article presents a new device designed to simulate in vitro flow rates, pressures, and other parameters representing normal and diseased conditions of the human cardiovascular system. Such devices are sometimes called bioreactors or "mock" simulator of cardiovascular loops (SCVLs) in literature. Most SCVLs simulate the systemic circulation only and have inherent limitations in studying the interaction of left and right sides of circulation. Those SCVLs that include both left and right sides of the circulation utilize header reservoirs simulating cycles with constant atrial pressures. The SCVL described in this article includes models for all four chambers of the heart, and the systemic and pulmonary circulation loops. Each heart chamber is accurately activated by a separate linear motor to simulate the suction and ejection stages, thus capturing important features in the perfusion waveforms. Four mechanical heart valves corresponding to mitral, pulmonary, tricuspid, and aortic are used to control the desired unidirectional flow. This SCVL can emulate different physiological and pathological conditions of the human cardiovascular system by controlling the different parameters of blood circulation through the vascular tree (mainly the resistance, compliance, and elastance of the heart chambers). In this study, four cases were simulated: healthy, congestive heart failure, left ventricular diastolic dysfunction conditions, and left ventricular dysfunction with the addition of a mechanical circulatory support (MCS) device. Hemodynamic parameters including resistance, pressure, and flow have been investigated at aortic sinus, carotid artery, and pulmonary artery, respectively. The addition of an MCS device resulted in a significant reduction in mean blood pressure and re-establishment of cardiac output. In all cases, the experimental results are compared with human physiology and numerical simulations. The results show the capability of the SCVL to replicate various

  12. Mixture Experiments

    SciTech Connect

    Piepel, Gregory F.

    2007-12-01

    A mixture experiment involves combining two or more components in various proportions or amounts and then measuring one or more responses for the resulting end products. Other factors that affect the response(s), such as process variables and/or the total amount of the mixture, may also be studied in the experiment. A mixture experiment design specifies the combinations of mixture components and other experimental factors (if any) to be studied and the response variable(s) to be measured. Mixture experiment data analyses are then used to achieve the desired goals, which may include (i) understanding the effects of components and other factors on the response(s), (ii) identifying components and other factors with significant and nonsignificant effects on the response(s), (iii) developing models for predicting the response(s) as functions of the mixture components and any other factors, and (iv) developing end-products with desired values and uncertainties of the response(s). Given a mixture experiment problem, a practitioner must consider the possible approaches for designing the experiment and analyzing the data, and then select the approach best suited to the problem. Eight possible approaches include 1) component proportions, 2) mathematically independent variables, 3) slack variable, 4) mixture amount, 5) component amounts, 6) mixture process variable, 7) mixture of mixtures, and 8) multi-factor mixture. The article provides an overview of the mixture experiment designs, models, and data analyses for these approaches.

  13. Size evolution of normal and compact galaxies in the EAGLE simulation

    NASA Astrophysics Data System (ADS)

    Furlong, M.; Bower, R. G.; Crain, R. A.; Schaye, J.; Theuns, T.; Trayford, J. W.; Qu, Y.; Schaller, M.; Berthet, M.; Helly, J. C.

    2017-02-01

    We present the evolution of galaxy sizes, from redshift 2 to 0, for actively star forming and passive galaxies in the cosmological hydrodynamical 1003 cMpc3 simulation of the EAGLE project. We find that the sizes increase with stellar mass, but that the relation weakens with increasing redshift. Separating galaxies by their star formation activity, we find that passive galaxies are typically smaller than active galaxies at a fixed stellar mass. These trends are consistent with those found in observations and the level of agreement between the predicted and observed size-mass relations is of the order of 0.1 dex for z < 1 and 0.2-0.3 dex from redshift 1 to 2. We use the simulation to compare the evolution of individual galaxies with that of the population as a whole. While the evolution of the size-stellar mass relation for active galaxies provides a good proxy for the evolution of individual galaxies, the evolution of individual passive galaxies is not well represented by the observed size-mass relation due to the evolving number density of passive galaxies. Observations of z ˜ 2 galaxies have revealed an abundance of massive red compact galaxies, which depletes below z ˜ 1. We find that a similar population forms naturally in the simulation. Comparing these galaxies with their z = 0 descendants, we find that all compact galaxies grow in size due to the high-redshift stars migrating outwards. Approximately 60 per cent of the compact galaxies increase in size further due to renewed star formation and/or mergers.

  14. Computer simulation analysis of normal and abnormal development of the mammalian diaphragm

    PubMed Central

    Fisher, Jason C; Bodenstein, Lawrence

    2006-01-01

    Background Congenital diaphragmatic hernia (CDH) is a birth defect with significant morbidity and mortality. Knowledge of diaphragm morphogenesis and the aberrations leading to CDH is limited. Although classical embryologists described the diaphragm as arising from the septum transversum, pleuroperitoneal folds (PPF), esophageal mesentery and body wall, animal studies suggest that the PPF is the major, if not sole, contributor to the muscular diaphragm. Recently, a posterior defect in the PPF has been identified when the teratogen nitrofen is used to induce CDH in fetal rodents. We describe use of a cell-based computer modeling system (Nudge++™) to study diaphragm morphogenesis. Methods and results Key diaphragmatic structures were digitized from transverse serial sections of paraffin-embedded mouse embryos at embryonic days 11.5 and 13. Structure boundaries and simulated cells were combined in the Nudge++™ software. Model cells were assigned putative behavioral programs, and these programs were progressively modified to produce a diaphragm consistent with the observed anatomy in rodents. Homology between our model and recent anatomical observations occurred under the following simulation conditions: (1) cell mitoses are restricted to the edge of growing tissue; (2) cells near the chest wall remain mitotically active; (3) mitotically active non-edge cells migrate toward the chest wall; and (4) movement direction depends on clonal differentiation between anterior and posterior PPF cells. Conclusion With the PPF as the sole source of mitotic cells, an early defect in the PPF evolves into a posteromedial diaphragm defect, similar to that of the rodent nitrofen CDH model. A posterolateral defect, as occurs in human CDH, would be more readily recreated by invoking other cellular contributions. Our results suggest that recent reports of PPF-dominated diaphragm morphogenesis in the rodent may not be strictly applicable to man. The ability to recreate a CDH defect

  15. Molecular simulation of fluids with non-identical intermolecular potentials: Thermodynamic properties of 10-5 + 12-6 Mie potential binary mixtures

    SciTech Connect

    Stiegler, Thomas; Sadus, Richard J.

    2015-02-28

    General methods for combining interactions between particles characterised by non-identical intermolecular potentials are investigated. The combination methods are tested by performing molecular dynamics simulations to determine the pressure, energy, isochoric and isobaric heat capacities, thermal expansion coefficient, isothermal compressibility, Joule-Thomson coefficient, and speed of sound of 10-5 + 12-6 Mie potential binary mixtures. In addition to the two non-identical Mie potentials, mixtures are also studied with non-identical intermolecular parameters. The combination methods are compared with results obtained by simply averaging the Mie exponents. When either the energy or size parameters are non-identical, very significant differences emerge in the thermodynamic properties predicted by the alternative combination methods. The isobaric heat capacity is the thermodynamic property that is most affected by the relative magnitude of the intermolecular potential parameters and the method for combining non-identical potentials. Either the arithmetic or geometric combination of potentials provides a simple and effective way of performing simulations involving mixtures of components characterised by non-identical intermolecular potentials, which is independent of their functional form.

  16. Molecular simulation of fluids with non-identical intermolecular potentials: Thermodynamic properties of 10-5 + 12-6 Mie potential binary mixtures

    NASA Astrophysics Data System (ADS)

    Stiegler, Thomas; Sadus, Richard J.

    2015-02-01

    General methods for combining interactions between particles characterised by non-identical intermolecular potentials are investigated. The combination methods are tested by performing molecular dynamics simulations to determine the pressure, energy, isochoric and isobaric heat capacities, thermal expansion coefficient, isothermal compressibility, Joule-Thomson coefficient, and speed of sound of 10-5 + 12-6 Mie potential binary mixtures. In addition to the two non-identical Mie potentials, mixtures are also studied with non-identical intermolecular parameters. The combination methods are compared with results obtained by simply averaging the Mie exponents. When either the energy or size parameters are non-identical, very significant differences emerge in the thermodynamic properties predicted by the alternative combination methods. The isobaric heat capacity is the thermodynamic property that is most affected by the relative magnitude of the intermolecular potential parameters and the method for combining non-identical potentials. Either the arithmetic or geometric combination of potentials provides a simple and effective way of performing simulations involving mixtures of components characterised by non-identical intermolecular potentials, which is independent of their functional form.

  17. Molecular simulation of fluids with non-identical intermolecular potentials: thermodynamic properties of 10-5 + 12-6 Mie potential binary mixtures.

    PubMed

    Stiegler, Thomas; Sadus, Richard J

    2015-02-28

    General methods for combining interactions between particles characterised by non-identical intermolecular potentials are investigated. The combination methods are tested by performing molecular dynamics simulations to determine the pressure, energy, isochoric and isobaric heat capacities, thermal expansion coefficient, isothermal compressibility, Joule-Thomson coefficient, and speed of sound of 10-5 + 12-6 Mie potential binary mixtures. In addition to the two non-identical Mie potentials, mixtures are also studied with non-identical intermolecular parameters. The combination methods are compared with results obtained by simply averaging the Mie exponents. When either the energy or size parameters are non-identical, very significant differences emerge in the thermodynamic properties predicted by the alternative combination methods. The isobaric heat capacity is the thermodynamic property that is most affected by the relative magnitude of the intermolecular potential parameters and the method for combining non-identical potentials. Either the arithmetic or geometric combination of potentials provides a simple and effective way of performing simulations involving mixtures of components characterised by non-identical intermolecular potentials, which is independent of their functional form.

  18. The zoom lens of attention: Simulating shuffled versus normal text reading using the SWIFT model.

    PubMed

    Schad, Daniel J; Engbert, Ralf

    2012-04-01

    Assumptions on the allocation of attention during reading are crucial for theoretical models of eye guidance. The zoom lens model of attention postulates that attentional deployment can vary from a sharp focus to a broad window. The model is closely related to the foveal load hypothesis, i.e., the assumption that the perceptual span is modulated by the difficulty of the fixated word. However, these important theoretical concepts for cognitive research have not been tested quantitatively in eye movement models. Here we show that the zoom lens model, implemented in the SWIFT model of saccade generation, captures many important patterns of eye movements. We compared the model's performance to experimental data from normal and shuffled text reading. Our results demonstrate that the zoom lens of attention might be an important concept for eye movement control in reading.

  19. Table and charts of equilibrium normal-shock properties for hydrogen-helium mixtures with velocities to 70 km/sec. Volume 1: 0.95 H2-0.05 He (by volume)

    NASA Technical Reports Server (NTRS)

    Miller, C. G., III; Wilder, S. E.

    1976-01-01

    Equilibrium thermodynamic and flow properties are presented in tabulated and graphical form for moving, standing, and reflected normal shock waves into hydrogen-helium mixtures representative of postulated outer planet atmospheres. These results are presented in four volumes and the volmetric compositions of the mixtures are 0.95H2-0.05He in Volume 1, 0.90H2-0.10He in Volume 2, 0.85H2-0.15He in Volume 3, and 0.75H2-0.25He in Volume 4. Properties include pressure, temperature, density, enthalpy, speed of sound, entropy, molecular-weight ratio, isentropic exponent, velocity, and species mole fractions. Incident (moving) shock velocities are varied from 4 to 70 km/sec for a range of initial pressure of 5 N/sq m to 100 kN/sq m. Results are applicable to shock-tube flows and for determining flow conditions behind the normal portion of the bow shock about a blunt body at high velocities in postulated outer planet atmospheres. The document is a revised version of the original edition of NASA SP-3085 published in 1974.

  20. Simulating Geologic Co-sequestration of Carbon Dioxide and Hydrogen Sulfide using a Peng-Robinson Equation of State for Fluid Mixtures

    NASA Astrophysics Data System (ADS)

    Ramanathan, R.; Bacon, D. H.

    2011-12-01

    CO2 streams from coal-fired power plants may contain impurities, including H2S, SOx, NOx, O2, N2, Ar, CO, and Hg. Co-sequestered impurities could affect geologic storage, causing changes in pH and oxidation state which affect dissolution and precipitation reactions and the mobility of metals present in the reservoir rocks. Sequestration of CO2 in depleted natural gas reservoirs or in enhanced gas recovery requires the capability to simulate gas mixtures. To better simulate these conditions, we have developed a variable component, non-isothermal simulator, STOMP-WNSE (Water, N-component, Salt and Energy), which simulates multiphase flow gas mixtures in deep saline reservoirs, and the resulting reactions with reservoir minerals. The simulator is based on the Peng-Robinson cubic equation of state (EOS) with a flash equilibrium model where phase composition is defined through fugacity equilibria. The Peneloux volume correction is used to improve density predictions and the Friction Theory model improves our predictions of viscosity at high pressure. Equilibrium partitioning of components between the non-aqueous and aqueous phases is achieved using a successive substitution approach. Solubility of the components in various brine compositions is calculated accurately using binary interaction coefficients that are a function of temperature and salinity, which have been calibrated to match experimental data. We compare the fluid properties predicted by the Peng-Robinson EOS with more specialized empirical equations of state developed specifically for CO2, H2S and CH4. We validate the predictions of this new simulator using experimental results of co-sequestration of CO2 and H2S in sand. We compare the speed of execution of a field scale simulation of CO2 sequestration using the Peng-Robinson EOS and the more specialized Span & Wagner equation of state, and demonstrate the impact of adding H2S to the injected CO2.

  1. How Well Does Growth Mixture Modeling Identify Heterogeneous Growth Trajectories? A Simulation Study Examining GMM's Performance Characteristics

    ERIC Educational Resources Information Center

    Peugh, James; Fan, Xitao

    2012-01-01

    Growth mixture modeling (GMM) has become a more popular statistical method for modeling population heterogeneity in longitudinal data, but the performance characteristics of GMM enumeration indexes in correctly identifying heterogeneous growth trajectories are largely unknown. Few empirical studies have addressed this issue. This study considered…

  2. A Mixture Rasch Model with a Covariate: A Simulation Study via Bayesian Markov Chain Monte Carlo Estimation

    ERIC Educational Resources Information Center

    Dai, Yunyun

    2013-01-01

    Mixtures of item response theory (IRT) models have been proposed as a technique to explore response patterns in test data related to cognitive strategies, instructional sensitivity, and differential item functioning (DIF). Estimation proves challenging due to difficulties in identification and questions of effect size needed to recover underlying…

  3. Molecular Dynamic Simulation Insights into the Normal State and Restoration of p53 Function

    PubMed Central

    Fu, Ting; Min, Hanyi; Xu, Yong; Chen, Jianzhong; Li, Guohui

    2012-01-01

    As a tumor suppressor protein, p53 plays a crucial role in the cell cycle and in cancer prevention. Almost 50 percent of all human malignant tumors are closely related to a deletion or mutation in p53. The activity of p53 is inhibited by over-active celluar antagonists, especially by the over-expression of the negative regulators MDM2 and MDMX. Protein-protein interactions, or post-translational modifications of the C-terminal negative regulatory domain of p53, also regulate its tumor suppressor activity. Restoration of p53 function through peptide and small molecular inhibitors has become a promising strategy for novel anti-cancer drug design and development. Molecular dynamics simulations have been extensively applied to investigate the conformation changes of p53 induced by protein-protein interactions and protein-ligand interactions, including peptide and small molecular inhibitors. This review focuses on the latest MD simulation research, to provide an overview of the current understanding of interactions between p53 and its partners at an atomic level. PMID:22949826

  4. "Partial Panel" Operator Training: Advanced Simulator Training to Enhance Situational Awareness in Off-Normal Situations

    SciTech Connect

    Dagle, Jeffery E.

    2006-06-01

    On August 14, 2003, the largest blackout in the history of the North American electricity grid occurred. The four root causes identified by the blackout investigation team were inadequate system understanding, inadequate situational awareness, inadequate tree trimming, and inadequate reliability coordinator diagnostic support. Three of these four root causes can be attributed to deficiencies in training, communication, and the tools used by the control room operators. Using the issues revealed in the August 14, 2003 blackout, and addressing concerns associated with the security of control systems, the Pacific Northwest National Laboratory (PNNL) developed a hands-on training curriculum that utilizes a dispatcher training simulator to evoke loss of situational awareness by the dispatcher. PNNL performed novel changes to the dispatcher training software in order to accomplish this training. This presentation will describe a vision for a future training environment that will incorporate hands-on training with a dispatcher training simulator in a realistic environment to train operators to recognize and respond to cyber security issues associated with their control systems.

  5. Elastic-wave propagation and site amplification in the Salt Lake Valley, Utah, from simulated normal faulting earthquakes

    USGS Publications Warehouse

    Benz, H.M.; Smith, R.B.

    1988-01-01

    The two-dimensional seismic response of the Salt Lake valley to near- and far-field earthquakes has been investigated from simulations of vertically incident plane waves and from normal-faulting earthquakes generated on the basin-bounding Wasatch fault. The plane-wave simulations were compared with observed site amplifications in the Salt Lake valley, based on seismic recordings from nuclear explosions in southern Nevada, that show 10 times greater amplification with the basin than measured values on hard-rock sites. Synthetic seismograms suggest that in the frequency band 0.3 to 1.5 Hz at least one-half the site amplitication can be attributed to the impedance contrast between the basin sediments and higher velocity basement rocks. -from Authors

  6. Effect of potassium depletion in normal males - An Apollo 15 simulation

    NASA Technical Reports Server (NTRS)

    Hyatt, K. H.; Hulley, S. B.; Vogel, J. M.; Spears, C. P.; Johnson, P. C.; Hoffler, G. W.; Rambaut, P. C.; Rummel, J. A.; Huntoon, C.

    1975-01-01

    In the course of Apollo 15, physiologic abnormalities, manifested by ectopic activity on the ECG and unusual alterations in exercise tolerance, occurred in the crew of the Lunar Excursion Module. These were associated with decreases in total body potassium, measured by K-42, of 10% and 15%. The possibility of inadequate potassium (K+) intake existed. A simulation study was performed prior to Apollo 16, corresponding in duration to Apollo 15. Subjects endured the same sleep aberrations and caloric expenditure as the Apollo 15 astronauts. Subjects consumed a diet containing only 15 mEq/d of K+ during the entire 12 days of absolute bedrest. Study implications and reasons for discrepancies between K+ loss measured by balance techniques and K-42 are reviewed.

  7. Comparison of Ejecta Distributions from Normal Incident Hypervelocity Impact on Lunar Regolith Simulant

    NASA Technical Reports Server (NTRS)

    Edwards, David L.; Cooke, William; Scruggs, Rob; Moser, Danielle E.

    2008-01-01

    The National Aeronautics and Space Administration (NASA) is progressing toward long-term lunar habitation. Critical to the design of a lunar habitat is an understanding of the lunar surface environment; of specific importance is the primary meteoroid and subsequent ejecta environment. The document, NASA SP-8013, was developed for the Apollo program and is the latest definition of the ejecta environment. There is concern that NASA SP-8013 may over-estimate the lunar ejecta environment. NASA's Meteoroid Environment Office (MEO) has initiated several tasks to improve the accuracy of our understanding of the lunar surface ejecta environment. This paper reports the results of experiments on projectile impact into powered pumice and unconsolidated JSC-1A Lunar Mare Regolith stimulant (JSC-1A) targets. The Ames Vertical Gun Range (AVGR) was used to accelerate projectiles to velocities in excess of 5 km/s and impact the targets at normal incidence. The ejected particles were detected by thin aluminum foil targets placed around the impact site and angular distributions were determined for ejecta. Comparison of ejecta angular distribution with previous works will be presented. A simplistic technique to characterize the ejected particles was formulated and improvements to this technique will be discussed for implementation in future tests.

  8. Dangerous mixture of household detergents in an old-style toilet: a case report with simulation experiments of the working environment and warning of potential hazard relevant to the general environment.

    PubMed

    Minami, M; Katsumata, M; Miyake, K; Inagaki, H; Fan, X H; Kubota, H; Yamano, Y; Kimura, O

    1992-01-01

    A housewife cleaned toilet porcelain connected directly to a sewage storage tank with a mixture of cleaning agents; sodium hypochlorite (NaOCl) and hydrochloric acid (HCl) solutions. She complained of insomnia on the night after cleaning and suffered from severe metabolic acidosis with extremely low blood pH, PCO2 and bicarbonate values. She recovered from the acidosis after bicarbonate transfusion, plasmapheresis and plasma exchange. Permanent blindness ensued, however, from the third day after the event. These clinical symptoms suggested that the toxic substances responsible were chloramine and methyl chloride. Their generation was confirmed by in-vitro experiments, mixing NaOCl, HCl and pooled urine from normal people. In the simulation, the methyl chloride level far exceeded (100,000 ppm) the maximal allowable concentration recommended (ca 400 ppm) by the American Conference of Governmental Industrial Hygienists (ACGIH). Chloramine's toxic actions were confirmed using purified enzyme assay, and the inhibition of carbonic anhydrase and aldehyde dehydrogenase and the enhancement of superoxide dismutase activity were confirmed in neutral pH. The patient's clinical symptoms suggested that insomnia and permanent blindness seemed to be partly ascribable to chronic repetitive exposure to methyl chloride; catching a cold, drug intake and alcohol intake, in addition, precipitated the patient's visual loss. The possibility of this kind of intoxication with such a mixture of agents may lie latent in any situation where sewage or garbage are exposed to the open air.

  9. Molecular dynamics simulations of the structure and single-particle dynamics of mixtures of divalent salts and ionic liquids

    NASA Astrophysics Data System (ADS)

    Gómez-González, Víctor; Docampo-Álvarez, Borja; Cabeza, Oscar; Fedorov, Maxim; Lynden-Bell, Ruth M.; Gallego, Luis J.; Varela, Luis M.

    2015-09-01

    We report a molecular dynamics study of the structure and single-particle dynamics of mixtures of a protic (ethylammonium nitrate) and an aprotic (1-butyl-3-methylimidazolium hexaflurophosphate [BMIM][PF6]) room-temperature ionic liquids doped with magnesium and calcium salts with a common anion at 298.15 K and 1 atm. The solvation of these divalent cations in dense ionic environments is analyzed by means of apparent molar volumes of the mixtures, radial distribution functions, and coordination numbers. For the protic mixtures, the effect of salt concentration on the network of hydrogen bonds is also considered. Moreover, single-particle dynamics of the salt cations is studied by means of their velocity autocorrelation functions and vibrational densities of states, explicitly analyzing the influence of salt concentration, and cation charge and mass on these magnitudes. The effect of the valency of the salt cation on these properties is considered comparing the results with those for the corresponding mixtures with lithium salts. We found that the main structural and dynamic features of the local solvation of divalent cations in ionic liquids are similar to those of monovalent salts, with cations being localized in the polar nanoregions of the bulk mixture coordinated in monodentate and bidentate coordination modes by the [NO3]- and [PF6]- anions. However, stronger electrostatic correlations of these polar nanoregions than in mixtures with salts with monovalent cations are found. The vibrational modes of the ionic liquid (IL) are seen to be scarcely affected by the addition of the salt, and the effect of mass and charge on the vibrational densities of states of the dissolved cations is reported. Cation mass is seen to exert a deeper influence than charge on the low-frequency vibrational spectra, giving a red shift of the vibrational modes and a virtual suppression of the higher energy vibrational modes for the heavier Ca2+ cations. No qualitative difference with

  10. Molecular dynamics simulations of the structure and single-particle dynamics of mixtures of divalent salts and ionic liquids

    SciTech Connect

    Gómez-González, Víctor; Docampo-Álvarez, Borja; Gallego, Luis J.; Varela, Luis M.; Lynden-Bell, Ruth M.

    2015-09-28

    We report a molecular dynamics study of the structure and single-particle dynamics of mixtures of a protic (ethylammonium nitrate) and an aprotic (1-butyl-3-methylimidazolium hexaflurophosphate [BMIM][PF{sub 6}]) room-temperature ionic liquids doped with magnesium and calcium salts with a common anion at 298.15 K and 1 atm. The solvation of these divalent cations in dense ionic environments is analyzed by means of apparent molar volumes of the mixtures, radial distribution functions, and coordination numbers. For the protic mixtures, the effect of salt concentration on the network of hydrogen bonds is also considered. Moreover, single-particle dynamics of the salt cations is studied by means of their velocity autocorrelation functions and vibrational densities of states, explicitly analyzing the influence of salt concentration, and cation charge and mass on these magnitudes. The effect of the valency of the salt cation on these properties is considered comparing the results with those for the corresponding mixtures with lithium salts. We found that the main structural and dynamic features of the local solvation of divalent cations in ionic liquids are similar to those of monovalent salts, with cations being localized in the polar nanoregions of the bulk mixture coordinated in monodentate and bidentate coordination modes by the [NO{sub 3}]{sup −} and [PF{sub 6}]{sup −} anions. However, stronger electrostatic correlations of these polar nanoregions than in mixtures with salts with monovalent cations are found. The vibrational modes of the ionic liquid (IL) are seen to be scarcely affected by the addition of the salt, and the effect of mass and charge on the vibrational densities of states of the dissolved cations is reported. Cation mass is seen to exert a deeper influence than charge on the low-frequency vibrational spectra, giving a red shift of the vibrational modes and a virtual suppression of the higher energy vibrational modes for the heavier Ca{sup 2

  11. Comparing normal walking and compensated walking: their stability and perturbation resistance. A simulation study.

    PubMed

    Yu, W; Ikemoto, Y; Acharya, R; Unoue, J

    2010-01-01

    People usually develop different kinds of compensated gait in response to local function deficits, such as muscle weakness, spasticity in specific muscle groups, or joint stiffness, in order to overcome the falling risk factors. Compensated walking has been analysed empirically in the impaired gait analysis area. However, the compensation could be identified spatially and temporally. The stability and perturbation resistance of compensated walking have not been analysed quantitatively. In this research, a biomimetic human walking simulator was employed to model one individual paraplegic subject with plantarflexor spasticity. The pes equinus was expressed by biasing the outputs of plantarflexor neurons corresponding to the spastic muscles. Then, the compensatory mechanism was explored by adjusting the outputs of the other muscles. It was shown that this approach can be used for quantitative analysis of the spastic gait and compensated walking. Thus, this research can improve the understanding of the behaviour of compensated walking, bringing insights not only for building useful walking assist systems with high safety but also for designing effective rehabilitation interventions.

  12. Effect of potassium depletion in normal males: an Apollo 15 simulation.

    PubMed

    Hyatt, K H; Johnson, P C; Hoffler, G W; Rambaut, P C; Rummel, J A; Hulley, S B; Vogel, J M; Huntoon, C; Spears, C P

    1975-01-01

    In the course of Apollo 15, physiologic abnormalities, manifested by ectopic activity on the ECG and unusual alterations in excerise tolerance, occurred in the crew of the Lunar Excursion Module. These were associated with decreases in total body potassium, measured by 42K, of 10% and 15%. The possibility of inadequate potassium (K plus) intake existed. A simulation study was performed prior to Apollo 16, corresponding in duration to Apollo 15. Subjects endured the same sleep aberrations and caloric expenditure as the Apollo 15 astronauts. Subjects consumed a diet containing only 15 mEq/d of K plus during the entire 12 d of absolute bedrest. ECG was continuously monitored, body fluid compartments and total body K plus were measured at intervals by radionuclide methods, electrolyte balance was determined daily, and excercise and orthostatic tolerances were determined prior to and after bedrest. In spite of decreases in total body K plus measured by 42K of 14.5% and 10.5%, and by potassium balances of 3.3% and 6.5%, respectively, neither of the two subjects developed symptomatic hypokalemia. Minor ECG abnormalities were noted in one subject. Orthostatic and exercise tolerance showed only those changes expected as a result of bedrest. Muscle strength was unaffected. Study implications and reasons for discrepancies between K plus loss measured by balance techniques and 42K are reviewed.

  13. Normal Performance on a Simulated Gambling Task in Treatment-Naïve Alcohol Dependent Individuals

    PubMed Central

    Fein, George; McGillivray, Shannon; Finn, Peter

    2007-01-01

    Background Research suggests that substance abusers make more disadvantageous decisions on the simulated gambling task (SGT); such decisions are associated with deviance proneness and antisocial symptoms. This study examines decision-making on the SGT in young adults with alcohol dependence that are treatment-naïve (TxN). Methods 116 subjects (58 controls, 58 TxNs) were tested on the SGT, where participants choose cards from 4 different decks that vary in terms of the magnitude of the immediate gain (large/small) and the magnitude of long-term loss (larger/smaller). Participants also were assessed on measures of externalizing symptoms, personality traits reflecting social deviance, neuropsychological function, and the density of the family history of alcoholism. Results TxNs did not differ from controls on measures of SGT decision-making. SGT performance was not associated with externalizing symptoms, social deviance proneness, or a familial density of alcoholism. Although, TxNs had higher levels of externalizing symptoms, social deviance and familial density of alcoholism compared with controls, these variables were only modestly elevated compared with previous samples of long-term abstinent alcohol dependent individuals who showed decision-making deficits on the SGT. Conclusions The results suggest that our sample of young adult TxN adults with alcohol dependence do not have global deficits in decision-making as measured by the SGT, and that their poor decisions regarding their alcohol consumption are more specific to drinking. PMID:16737453

  14. Non-monotonic dynamics of water in its binary mixture with 1,2-dimethoxy ethane: A combined THz spectroscopic and MD simulation study

    NASA Astrophysics Data System (ADS)

    Das Mahanta, Debasish; Patra, Animesh; Samanta, Nirnay; Luong, Trung Quan; Mukherjee, Biswaroop; Mitra, Rajib Kumar

    2016-10-01

    A combined experimental (mid- and far-infrared FTIR spectroscopy and THz time domain spectroscopy (TTDS) (0.3-1.6 THz)) and molecular dynamics (MD) simulation technique are used to understand the evolution of the structure and dynamics of water in its binary mixture with 1,2-dimethoxy ethane (DME) over the entire concentration range. The cooperative hydrogen bond dynamics of water obtained from Debye relaxation of TTDS data reveals a non-monotonous behaviour in which the collective dynamics is much faster in the low Xw region (where Xw is the mole fraction of water in the mixture), whereas in Xw ˜ 0.8 region, the dynamics gets slower than that of pure water. The concentration dependence of the reorientation times of water, calculated from the MD simulations, also captures this non-monotonous character. The MD simulation trajectories reveal presence of large amplitude angular jumps, which dominate the orientational relaxation. We rationalize the non-monotonous, concentration dependent orientational dynamics by identifying two different physical mechanisms which operate at high and low water concentration regimes.

  15. Solvation Structure of Imidazolium Cation in Mixtures of [C4mim][TFSA] Ionic Liquid and Diglyme by NMR Measurements and MD Simulations.

    PubMed

    Shimomura, Takuya; Kodama, Daisuke; Kanakubo, Mitsuhiro; Tsuzuki, Seiji

    2017-04-06

    Interactions of 1-butyl-3-methylimidazolium cation ([C4mim](+)) with bis(trifluoromethanesulfonyl)amide anion ([TFSA](-)) and diethyleneglycol dimethyl ether (diglyme) in mixtures of [C4mim][TFSA] ionic liquid and diglyme have been investigated using (1)H and (13)C NMR spectroscopy and molecular dynamics (MD) simulations. The results of NMR chemical shift measurements and MD simulations showed that the diglyme oxygen atoms have contact with the imidazolium hydrogen atoms of [C4mim](+) in the mixtures. The contact between the hydrogen atoms of imidazolium and the oxygen atoms of [TFSA](-) remains even when the diglyme mole fraction (xdiglyme) increases up to 0.9. However, the coordination numbers of the hydrogen atoms of [C4mim](+) with oxygen atoms of diglyme increase with xdiglyme. The [TFSA](-) anions around [C4mim](+) are not completely replaced by diglyme even at xdiglyme > 0.9. The MD simulations revealed that the diglymes also have contact with the butyl group of [C4mim](+). The methyl groups of diglyme prefer to have contact with the terminal methyl group of the butyl group, whereas the diglyme oxygen atoms prefer to have contact with the methylene group connected to the imidazolium ring of [C4mim](+).

  16. Study of coherent structures of turbulence with large wall-normal gradients in thermophysical properties using direct numerical simulation

    NASA Astrophysics Data System (ADS)

    Reinink, Shawn K.; Yaras, Metin I.

    2015-06-01

    Forced-convection heat transfer in a heated working fluid at a thermodynamic state near its pseudocritical point is poorly predicted by correlations calibrated with data at subcritical temperatures and pressures. This is suggested to be primarily due to the influence of large wall-normal thermophysical property gradients that develop in proximity of the pseudocritical point on the concentration of coherent turbulence structures near the wall. The physical mechanisms dominating this influence remain poorly understood. In the present study, direct numerical simulation is used to study the development of coherent vortical structures within a turbulent spot under the influence of large wall-normal property gradients. A turbulent spot rather than a fully turbulent boundary layer is used for the study, for the coherent structures of turbulence in a spot tend to be in a more organized state which may allow for more effective identification of cause-and-effect relationships. Large wall-normal gradients in thermophysical properties are created by heating the working fluid which is near the pseudocritical thermodynamic state. It is found that during improved heat transfer, wall-normal gradients in density accelerate the growth of the Kelvin-Helmholtz instability mechanism in the shear layer enveloping low-speed streaks, causing it to roll up into hairpin vortices at a faster rate. It is suggested that this occurs by the baroclinic vorticity generation mechanism which accelerates the streamwise grouping of vorticity during shear layer roll-up. The increased roll-up frequency leads to reduced streamwise spacing between hairpin vortices in wave packets. The density gradients also promote the sinuous instability mode in low-speed streaks. The resulting oscillations in the streaks in the streamwise-spanwise plane lead to locally reduced spanwise spacing between hairpin vortices forming over adjacent low-speed streaks. The reduction in streamwise and spanwise spacing between

  17. Mixture Factor Analysis for Approximating a Nonnormally Distributed Continuous Latent Factor with Continuous and Dichotomous Observed Variables

    ERIC Educational Resources Information Center

    Wall, Melanie M.; Guo, Jia; Amemiya, Yasuo

    2012-01-01

    Mixture factor analysis is examined as a means of flexibly estimating nonnormally distributed continuous latent factors in the presence of both continuous and dichotomous observed variables. A simulation study compares mixture factor analysis with normal maximum likelihood (ML) latent factor modeling. Different results emerge for continuous versus…

  18. Detoxification and decolorization of a simulated textile dye mixture by phytoremediation using Petunia grandiflora and, Gailardia grandiflora: a plant-plant consortial strategy.

    PubMed

    Watharkar, Anuprita D; Jadhav, Jyoti P

    2014-05-01

    In vitro grown Petunia grandiflora and Gaillardia grandiflora plantlets showed 76 percent and 62 percent American Dye Manufacturers Institute value (color) removal from a simulated dyes mixture within 36h respectively whereas their consortium gave 94 percent decolorization. P. grandiflora, G. grandiflora and their consortium could reduce BOD by 44 percent, 31 percent and, 69 percent and COD by 58 percent, 37 percent and 73 percent respectively. Individually, root cells of P. grandiflora showed 74 and 24 percent induction in the activities of veratryl alcohol oxidase and laccase respectively; whereas G. grandiflora root cells showed 379 percent, 142 percent and 77 percent induction in the activities of tyrosinase, riboflavin reductase and lignin peroxidase respectively. In the consortium set, entirely a different enzymatic pattern was observed, where P. grandiflora root cells showed 231 percent, 12 percent and 65 percent induction in the activities of veratryl alcohol oxidase, laccase and 2, 6-dichlorophenol-indophenol reductase respectively, while G. grandiflora root cells gave 300 percent, 160 percent, 79 percent and 55 percent inductions in the activities of lignin peroxidase, riboflavin reductase, tyrosinase and laccase respectively. Because of the synergistic effect of the enzymes from both the plants, the consortium was found to be more effective for the degradation of dyes from the mixture. Preferential dye removal was confirmed by analyzing metabolites of treated dye mixture using UV-vis spectroscopy, FTIR and biotransformation was visualized using HPTLC. Metabolites formed after the degradation of dyes revealed the reduced cytogenotoxicity on Allium cepa roots cells when compared with untreated dye mixture solution. Phytotoxicity study exhibited the less toxic nature of the metabolites.

  19. Characteristics of surface-wave plasma with air-simulated N2 O2 gas mixture for low-temperature sterilization

    NASA Astrophysics Data System (ADS)

    Xu, L.; Nonaka, H.; Zhou, H. Y.; Ogino, A.; Nagata, T.; Koide, Y.; Nanko, S.; Kurawaki, I.; Nagatsu, M.

    2007-02-01

    Sterilization experiments using low-pressure air discharge plasma sustained by the 2.45 GHz surface-wave have been carried out. Geobacillus stearothermoplilus spores having a population of 3.0 × 106 were sterilized for only 3 min using air-simulated N2-O2 mixture gas discharge plasma, faster than the cases of pure O2 or pure N2 discharge plasmas. From the SEM analysis of plasma-irradiated spores and optical emission spectroscopy measurements of the plasmas, it has been found that the possible sterilization mechanisms of air-simulated plasma are the chemical etching effect due to the oxygen radicals and UV emission from the N2 molecules and NO radicals in the wavelength range 200-400 nm. Experiment suggested that UV emission in the wavelength range less than 200 nm might not be significant in the sterilization. The UV intensity at 237.0 nm originated from the NO γ system (A 2Σ+ → X 2Π) in N2-O2 plasma as a function of the O2 percentage added to N2-O2 mixture gas has been investigated. It achieved its maximum value when the O2 percentage was roughly 10-20%. This result suggests that air can be used as a discharge gas for sterilization, and indeed we have confirmed a rapid sterilization with the actual air discharge at a sample temperature of less than 65 °C.

  20. Human Peripheral Blood Mononuclear Cells Cultured in Normal and Hyperglycemic Media in Simulated Microgravity Using NASA Bioreactors

    NASA Technical Reports Server (NTRS)

    Lawless, DeSales

    2003-01-01

    We sought answers to several questions this summer at NASA Johnson Space Center. Initial studies involved the in vitro culture of human peripheral blood mononuclear in cells in different conditioned culture media. Several human cancer clones were similarly studied to determine responses to aberrant glycosylation by the argon laser. The cells were grown at unit gravity in flasks and in simulated microgravity using NASA bioreactors. The cells in each instance were analyzed by flow cytometry. Cell cycle analysis was acquired by staining nuclear DNA with propidium iodide. Responses to the laser stimulation was measured by observing autofluorescence emitted in the green and red spectra after stimulation. Extent of glycosylation correlated with the intensity of the laser stimulated auto-fluorescence. Our particular study was to detect and monitor aberrant glycosylation and its role in etiopathogenesis. Comparisons were made between cells known to be neoplastic and normal cell controls using the same Laser Induced Autofluorescence technique. Studies were begun after extensive literature searches on using the antigen presenting potential of dendritic cells to induce proliferation of antigen specific cytotoxic T-cells. The Sendai virus served as the antigen. Our goal is to generate sufficient numbers of such cells in the simulated microgravity environment for use in autologous transplants of virally infected individuals including those positive for hepatitis and HIV.

  1. Mathematical Simulation of Unsteady-State Gas-Liquid Mixture Flow in a Bed-Well System

    NASA Astrophysics Data System (ADS)

    Abbasov, É. M.; Imamaliev, S. A.

    2016-09-01

    Based on theoretical investigations, the influence of various forms of pressure variation at the wellhead with a nonstationary flow of a two-phase fluid in a bed-well system on the character of change in the bottom-hole pressure has been investigated, which makes it possible to determine this pressure from the wellhead operation parameters. The trapezoidal form of the change in pressure is considered as an example. The coupled equations of filtration and the equations describing nonstationary motion of a gas-liquid mixture in a pipeline have been solved jointly. Analytical formulas have been obtained allowing one to determine the bottom-hole pressure from the technological parameters at the wellhead with account for the dynamic connection of the bed-well system at different forms of change in the wellhead pressure. The influence of the wellhead pressure pulsation frequencies on the bottom-hole pressure dynamics has been established.

  2. Comparing sound localization deficits in bilateral cochlear-implant users and vocoder simulations with normal-hearing listeners.

    PubMed

    Jones, Heath; Kan, Alan; Litovsky, Ruth Y

    2014-11-10

    Bilateral cochlear-implant (BiCI) users are less accurate at localizing free-field (FF) sound sources than normal-hearing (NH) listeners. This performance gap is not well understood but is likely due to a combination of compromises in acoustic signal representation by the two independent speech processors and neural degradation of auditory pathways associated with a patient's hearing loss. To exclusively investigate the effect of CI speech encoding on horizontal-plane sound localization, the present study measured sound localization performance in NH subjects listening to vocoder processed and nonvocoded virtual acoustic space (VAS) stimuli. Various aspects of BiCI stimulation such as independently functioning devices, variable across-ear channel selection, and pulsatile stimulation were simulated using uncorrelated noise (Nu), correlated noise (N0), or Gaussian-enveloped tone (GET) carriers during vocoder processing. Additionally, FF sound localization in BiCI users was measured in the same testing environment for comparison. Distinct response patterns across azimuthal locations were evident for both listener groups and were analyzed using a multilevel regression analysis. Simulated implant speech encoding, regardless of carrier, was detrimental to NH localization and the GET vocoder best simulated BiCI FF performance in NH listeners. Overall, the detrimental effect of vocoder processing on NH performance suggests that sound localization deficits may persist even for BiCI patients who have minimal neural degradation associated with their hearing loss and indicates that CI speech encoding plays a significant role in the sound localization deficits experienced by BiCI users.

  3. Adsorption of xenon and CH4 mixtures in zeolite NaA. 129Xe NMR and grand canonical Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Jameson, Cynthia J.; Jameson, A. Keith; Kostikin, Pavel; Baello, Bernoli I.

    2000-01-01

    Investigation of competitive adsorption is carried out using the Xe-CH4 mixture in zeolite NaA as a model system. The Xen clusters are trapped in the alpha cages of this zeolite for times sufficiently long that it is possible to observe individual peaks in the NMR spectrum for each cluster while the CH4 molecules are in fast exchange between the cages and also with the gas outside. The 129Xe nuclear magnetic resonance spectra of nine samples of varying Xe and CH4 loadings have been observed and analyzed to obtain the 129Xe chemical shifts and the intensities of the peaks which are dependent on the average methane and xenon occupancies. The distributions Pn, the fraction of cages containing n Xe atoms, regardless of the number of CH4 molecules are obtained directly from the relative intensities of the Xen peaks. From the observed 129Xe chemical shift of each Xen peak can be obtained the average number of CH4 molecules in the same cavity as n Xe atoms. Grand canonical Monte Carlo (GCMC) simulations of mixtures of Xe and CH4 in a rigid zeolite NaA lattice provide the detailed distributions and the average cluster shifts, as well as the distributions Pn. The agreement with experiment is reasonably good for all nine samples. The calculated absolute chemical shifts for the Xen peaks in all samples at 300 K range from 80 to 230 ppm and are in good agreement with experiment. We also consider a very simple strictly statistical model of a binary mixture, derived from the hypergeometric distribution, in which the component molecules are distinguishable but equivalent in competition for eight lattice sites per cage under mutual exclusion. The latter simple model provides a limiting case for the distributions, with which both the GCMC simulations and the properties of the actual Xe-CH4 system are compared. The ideal adsorbed solution theory gives a first approximation to the selectivity of the adsorption of the Xe and CH4 from a mixture of gases, but starts to fail at high

  4. Predicting the excess solubility of acetanilide, acetaminophen, phenacetin, benzocaine, and caffeine in binary water/ethanol mixtures via molecular simulation.

    PubMed

    Paluch, Andrew S; Parameswaran, Sreeja; Liu, Shuai; Kolavennu, Anasuya; Mobley, David L

    2015-01-28

    We present a general framework to predict the excess solubility of small molecular solids (such as pharmaceutical solids) in binary solvents via molecular simulation free energy calculations at infinite dilution with conventional molecular models. The present study used molecular dynamics with the General AMBER Force Field to predict the excess solubility of acetanilide, acetaminophen, phenacetin, benzocaine, and caffeine in binary water/ethanol solvents. The simulations are able to predict the existence of solubility enhancement and the results are in good agreement with available experimental data. The accuracy of the predictions in addition to the generality of the method suggests that molecular simulations may be a valuable design tool for solvent selection in drug development processes.

  5. Predicting the excess solubility of acetanilide, acetaminophen, phenacetin, benzocaine, and caffeine in binary water/ethanol mixtures via molecular simulation

    NASA Astrophysics Data System (ADS)

    Paluch, Andrew S.; Parameswaran, Sreeja; Liu, Shuai; Kolavennu, Anasuya; Mobley, David L.

    2015-01-01

    We present a general framework to predict the excess solubility of small molecular solids (such as pharmaceutical solids) in binary solvents via molecular simulation free energy calculations at infinite dilution with conventional molecular models. The present study used molecular dynamics with the General AMBER Force Field to predict the excess solubility of acetanilide, acetaminophen, phenacetin, benzocaine, and caffeine in binary water/ethanol solvents. The simulations are able to predict the existence of solubility enhancement and the results are in good agreement with available experimental data. The accuracy of the predictions in addition to the generality of the method suggests that molecular simulations may be a valuable design tool for solvent selection in drug development processes.

  6. Mixture models for distance sampling detection functions.

    PubMed

    Miller, David L; Thomas, Len

    2015-01-01

    We present a new class of models for the detection function in distance sampling surveys of wildlife populations, based on finite mixtures of simple parametric key functions such as the half-normal. The models share many of the features of the widely-used "key function plus series adjustment" (K+A) formulation: they are flexible, produce plausible shapes with a small number of parameters, allow incorporation of covariates in addition to distance and can be fitted using maximum likelihood. One important advantage over the K+A approach is that the mixtures are automatically monotonic non-increasing and non-negative, so constrained optimization is not required to ensure distance sampling assumptions are honoured. We compare the mixture formulation to the K+A approach using simulations to evaluate its applicability in a wide set of challenging situations. We also re-analyze four previously problematic real-world case studies. We find mixtures outperform K+A methods in many cases, particularly spiked line transect data (i.e., where detectability drops rapidly at small distances) and larger sample sizes. We recommend that current standard model selection methods for distance sampling detection functions are extended to include mixture models in the candidate set.

  7. Solid-phase microextraction low temperature plasma mass spectrometry for the direct and rapid analysis of chemical warfare simulants in complex mixtures.

    PubMed

    Dumlao, Morphy C; Jeffress, Laura E; Gooding, J Justin; Donald, William A

    2016-06-21

    Solid-phase microextraction (SPME) is directly integrated with low temperature plasma ionisation mass spectrometry to rapidly detect organophosphate chemical warfare agent simulants and their hydrolysis products in chemical mixtures, including urine. In this sampling and ionization method, the fibre serves: (i) to extract molecules from their native environment, and (ii) as the ionization electrode that is used to desorb and ionize molecules directly from the SPME surface. By use of a custom fabricated SPME fibre consisting of a stainless steel needle coated with a Linde Type A (LTA) zeolitic microporous material and low temperature plasma mass spectrometry, protonated dimethyl methylphosphonate (DMMP), diethyl ethylphosphonate (DEEP) and pinacolyl methylphosphonic acid (PinMPA) can be detected at less than 100 ppb directly in water and urine. Organophosphates were not readily detected by this approach using an uncoated needle in negative control experiments. The use of the LTA coating significantly outperformed the use of a high alumina Zeolite Socony Mobil-5 (ZSM-5) coating of comparable thickness that is significantly less polar than LTA. By conditioning the LTA probe by immersion in an aqueous CuSO4 solution, the ion abundance for protonated DMMP increased by more than 300% compared to that obtained without any conditioning. Sample recovery values were between 96 and 100% for each analyte. The detection of chemical warfare agent analogues and hydrolysis products required less than 2 min per sample. A key advantage of this sampling and ionization method is that analyte ions can be directly and rapidly sampled from chemical mixtures, such as urine and seawater, without sample preparation or chromatography for sensitive detection by mass spectrometry. This ion source should prove beneficial for portable mass spectrometry applications because relatively low detection limits can be obtained without the use of compressed gases, fluid pumps, and lasers. Moreover, the

  8. Two-dimensional simulation of the development of an inhomogeneous volume discharge in a Ne/Xe/HCl gas mixture

    SciTech Connect

    Bychkov, Yu. I. Yampolskaya, S. A.; Yastremskii, A. G.

    2013-05-15

    The kinetic processes accompanying plasma column formation in an inhomogeneous discharge in a Ne/Xe/HCl gas mixture at a pressure of 4 atm were investigated by using a two-dimensional model. Two cathode spots spaced by 0.7 cm were initiated by distorting the cathode surface at local points, which resulted in an increase in the field strength in the cathode region. Three regimes differing in the charging voltage, electric circuit inductance, and electric field strength at the local cathode points were considered. The spatiotemporal distributions of the discharge current; the electron density; and the densities of excited xenon atoms, HCl(v = 0) molecules in the ground state, and HCl(v > 0) molecules in vibrational levels were calculated. The development of the discharge with increasing the electron density from 10{sup 4} to 10{sup 16} cm{sup -3} was analyzed, and three characteristic stages in the evolution of the current distribution were demonstrated. The width of the plasma column was found to depend on the energy deposited in the discharge. The width of the plasma column was found to decrease in inverse proportion to the deposited energy due to spatiotemporal variations in the rates of electron production and loss. The calculated dependences of the cross-sectional area of the plasma column on the energy deposited in the discharge agree with the experimental results.

  9. Different percentages of false-positive results obtained using five methods for the calculation of reference change values based on simulated normal and ln-normal distributions of data.

    PubMed

    Lund, Flemming; Petersen, Per Hyltoft; Fraser, Callum G; Sölétormos, György

    2016-11-01

    Background Reference change values provide objective tools to assess the significance of a change in two consecutive results for a biomarker from an individual. The reference change value calculation is based on the assumption that within-subject biological variation has random fluctuation around a homeostatic set point that follows a normal (Gaussian) distribution. This set point (or baseline in steady-state) should be estimated from a set of previous samples, but, in practice, decisions based on reference change value are often based on only two consecutive results. The original reference change value was based on standard deviations according to the assumption of normality, but was soon changed to coefficients of variation (CV) in the formula (reference change value = ± Z ċ 2(½) ċ CV). Z is being dependent on the desired probability of significance, which also defines the percentages of false-positive results. The aim of this study was to investigate false-positive results using five different published methods for calculation of reference change value. Methods The five reference change value methods were examined using normally and ln-normally distributed simulated data. Results One method performed best in approaching the theoretical false-positive percentages on normally distributed data and another method performed best on ln-normally distributed data. The commonly used reference change value method based on two results (without use of estimated set point) performed worst both on normally distributed and ln-normally distributed data. Conclusions The optimal choice of method to calculate reference change value limits requires knowledge of the distribution of data (normal or ln-normal) and, if possible, knowledge of the homeostatic set point.

  10. Response of selected plant and insect species to simulated solid rocket exhaust mixtures and to exhaust components from solid rocket fuels

    NASA Technical Reports Server (NTRS)

    Heck, W. W.; Knott, W. M.; Stahel, E. P.; Ambrose, J. T.; Mccrimmon, J. N.; Engle, M.; Romanow, L. A.; Sawyer, A. G.; Tyson, J. D.

    1980-01-01

    The effects of solid rocket fuel (SRF) exhaust on selected plant and and insect species in the Merritt Island, Florida area was investigated in order to determine if the exhaust clouds generated by shuttle launches would adversely affect the native, plants of the Merritt Island Wildlife Refuge, the citrus production, or the beekeeping industry of the island. Conditions were simulated in greenhouse exposure chambers and field chambers constructed to model the ideal continuous stirred tank reactor. A plant exposure system was developed for dispensing and monitoring the two major chemicals in SRF exhaust, HCl and Al203, and for dispensing and monitoring SRF exhaust (controlled fuel burns). Plants native to Merritt Island, Florida were grown and used as test species. Dose-response relationships were determined for short term exposure of selected plant species to HCl, Al203, and mixtures of the two to SRF exhaust.

  11. Nitriding kinetics of Si-SiC powder mixtures as simulations of reaction bonded Si3N4-SiC composites

    NASA Technical Reports Server (NTRS)

    Lightfoot, A.; Sheldon, B. W.; Flint, J. H.; Haggerty, J. S.

    1989-01-01

    The nitriding kinetics of Si and Si plus SiC powder mixtures were studied to simulate the fabrication of RBSN-SiC ceramic matrix composites. Very clean, assynthesized, and solvent-exposed powders were studied; C-rich and Si-rich SiC 0.04-0.05 micron diameter powders were mixed in varying concentrations with SiH4-derived 0.2-0.3 micron diameter Si powder. Complete nitridation is achieved with C-rich SiC powders in 140 min at 1250 C, and in the centers of Si-rich SiC powders in 15 min. The effects on the incubation periods, fast reaction periods, and slow reaction periods that characterize these nitriding processes were studied to explain unusual reverse reaction gradients and other effects of contamination.

  12. Organic tank safety project: Preliminary results of energetics and thermal behavior studies of model organic nitrate and/or nitrite mixtures and a simulated organic waste

    SciTech Connect

    Scheele, R.D.; Sell, R.L.; Sobolik, J.L.; Burger, L.L.

    1995-08-01

    As a result of years of production and recovery of nuclear defense materials and subsequent waste management at the Hanford Site, organic-bearing radioactive high-level wastes (HLW) are currently stored in large (up to 3. ML) single-shell storage tanks (SSTs). Because these wastes contain both fuels (organics) and the oxidants nitrate and nitrite, rapid energetic reactions at certain conditions could occur. In support of Westinghouse Hanford Company`s (WHC) efforts to ensure continued safe storage of these organic- and oxidant-bearing wastes and to define the conditions necessary for reactions to occur, we measured the thermal sensitivities and thermochemical and thermokinetic properties of mixtures of selected organics and sodium nitrate and/or nitrite and a simulated Hanford organic-bearing waste using thermoanalytical technologies. These thermoanalytical technologies are used by chemical reactivity hazards evaluation organizations within the chemical industry to assess chemical reaction hazards.

  13. Pulsed two-frequency capacitively coupled plasma simulation with H_2/N2 mixtures for the etching of low-k materials

    NASA Astrophysics Data System (ADS)

    Shon, C. H.; Makabe, T.

    2002-10-01

    As the critical dimension of integrated circuit is scaled down, the resistance-capacitance (RC) delay of signals through interconnection materials becomes important. As a solution, the new materials like Cu and low-k dielectric polymers have been used to reduce the signal delay in interconnect. As a result, low-k materials etching becomes a big issue in the plasma etching process. In this research, we present the simulation results of a pulsed two-frequency capacitively coupled plasma (2f-CCP)[1,2] based on relaxation continuum (RCT) model[3,4] in H_2/N2 mixtures. The electrons, ions of each gas and NHx radicals are followed in the model. The characteristics of a pulsed plasma are investigated. In addition, the flux of ions and radicals toward the biased substrate which has great importance in etching process is also discussed. sep = -1mm [[1

  14. Physalis method for heterogeneous mixtures of dielectrics and conductors: Accurately simulating one million particles using a PC

    NASA Astrophysics Data System (ADS)

    Liu, Qianlong

    2011-09-01

    Prosperetti's seminal Physalis method, an Immersed Boundary/spectral method, had been used extensively to investigate fluid flows with suspended solid particles. Its underlying idea of creating a cage and using a spectral general analytical solution around a discontinuity in a surrounding field as a computational mechanism to enable the accommodation of physical and geometric discontinuities is a general concept, and can be applied to other problems of importance to physics, mechanics, and chemistry. In this paper we provide a foundation for the application of this approach to the determination of the distribution of electric charge in heterogeneous mixtures of dielectrics and conductors. The proposed Physalis method is remarkably accurate and efficient. In the method, a spectral analytical solution is used to tackle the discontinuity and thus the discontinuous boundary conditions at the interface of two media are satisfied exactly. Owing to the hybrid finite difference and spectral schemes, the method is spectrally accurate if the modes are not sufficiently resolved, while higher than second-order accurate if the modes are sufficiently resolved, for the solved potential field. Because of the features of the analytical solutions, the derivative quantities of importance, such as electric field, charge distribution, and force, have the same order of accuracy as the solved potential field during postprocessing. This is an important advantage of the Physalis method over other numerical methods involving interpolation, differentiation, and integration during postprocessing, which may significantly degrade the accuracy of the derivative quantities of importance. The analytical solutions enable the user to use relatively few mesh points to accurately represent the regions of discontinuity. In addition, the spectral convergence and a linear relationship between the cost of computer memory/computation and particle numbers results in a very efficient method. In the present

  15. Model Misspecification: Finite Mixture or Homogeneous?

    PubMed Central

    Tarpey, Thaddeus; Yun, Dong; Petkova, Eva

    2007-01-01

    A common problem in statistical modelling is to distinguish between finite mixture distribution and a homogeneous non-mixture distribution. Finite mixture models are widely used in practice and often mixtures of normal densities are indistinguishable from homogenous non-normal densities. This paper illustrates what happens when the EM algorithm for normal mixtures is applied to a distribution that is a homogeneous non-mixture distribution. In particular, a population-based EM algorithm for finite mixtures is introduced and applied directly to density functions instead of sample data. The population-based EM algorithm is used to find finite mixture approximations to common homogeneous distributions. An example regarding the nature of a placebo response in drug treated depressed subjects is used to illustrate ideas. PMID:18974843

  16. Simulation for Large-Area, Inductively-Coupled Plasma Systems Using an Ar/Cl2 Gas Mixture.

    PubMed

    Oh, Seon-Geun; Lee, Young-Jun; Jeon, Jae-Hong; Kim, Young-Jin; Seo, Jong-Hyun; Choe, Hee-Hwan

    2015-11-01

    As research and development of high-performance devices are becoming increasingly important in the flat panel display industry, new structures and processes are essential to improve the performance of the TFT backplane. Also, high-density plasma systems are needed for new device fabrications. Chlorine-based, inductively-coupled plasma systems are widely used for highly-selective, anisotropic etching of polysilicon layers. In this paper, a plasma simulation for a large-area ICP system (8th glass size and 9 planar antenna set) was conducted using Ar/Cl2 gas. Transport models and Maxwell Equations were applied to calculate the plasma parameters such as electron density, electron temperature and electric potential. In addition, the spatial distribution of ions such as Ar+, Cl2+, Cl-, Cl+ were investigated respectively.

  17. Prediction of the bubble point pressure for the binary mixture of ethanol and 1,1,1,2,3,3,3-heptafluoropropane from Gibbs ensemble Monte Carlo simulations using the TraPPE force field

    SciTech Connect

    Rai, N; Rafferty, J L; Maiti, A; Siepmann, I

    2007-02-28

    Configurational-bias Monte Carlo simulations in the Gibbs ensemble using the TraPPE force field were carried out to predict the pressure-composition diagrams for the binary mixture of ethanol and 1,1,1,2,3,3,3-heptafluoropropane at 283.17 and 343.13 K. A new approach is introduced that allows to scale predictions at one temperature based on the differences in Gibbs free energies of transfer between experiment and simulation obtained at another temperature. A detailed analysis of the molecular structure and hydrogen bonding for this fluid mixture is provided.

  18. The Unified Gravel-Sand (TUGS) Model: Simulating the Transport of Gravel-Sand Mixtures in Rivers

    NASA Astrophysics Data System (ADS)

    Cui, Y.

    2006-12-01

    TUGS Model was developed by employing the surface-based bedload equation of Wilcock and Crowe (2003) and linking grain size distributions in the bedload, surface layer, and subsurface sediment deposit with the gravel transfer function of Hoey and Ferguson (1994) and Toro-Escobar et al. (1996), and a hypothetical sand transfer function. The unmodified model was applied to simulate the sedimentation process in Marmot Reservoir, Sandy River, Oregon and produced similar stratified sediment deposit as observed through coring exercises. The model was also examined with three runs of large-scale flume experiments conducted at St. Anthony Falls Laboratory (SAFL) by Seal et al. (1995). With a very minor modification to Wilcock and Crowe (2003) equation, the model excellently reproduced the longitudinal profiles, gravel grain size distributions and sand fractions in the deposits for all the three SAFL runs. Following its examination, TUGS model was applied to simulate the sediment transport dynamics in the Sandy River, Oregon under a few hypothetical scenarios, focusing on the dynamics of sand fractions in gravel-bedded channel deposits. Results of the exploratory runs on the Sandy River indicate that (a) surface and subsurface sand fractions generally increase in the downstream direction, similar to observed in the field; (b) sand fraction in the deposit is positively correlated with sand supply as expected; (c) extremely high sand supply under similar gravel supply and hydrologic conditions can transform the river into predominantly sand-bedded; (d) increased discharge under the same sand and gravel supply conditions results in decreased sand fraction in the deposit as expected; and (e) there can be significant increase in surface and subsurface sand fractions in the backwater zones near the mouth of the river as expected.

  19. The structure and the percolation behavior of a mixture of carbon nanotubes and molecular junctions: a Monte Carlo simulation study.

    PubMed

    Kwon, Gyemin; Jung, Hyun Tae; Shin, Kwanwoo; Sung, Bong June

    2011-05-01

    The structure and the percolation behavior of the composite of carbon nanotubes (CNTs), CNT molecular junctions and polymers are studied using Monte Carlo (MC) simulations. We model a CNT as a rigid rod composed of hard spheres. "X" and "Y" molecular junctions of CNTs are constructed by joining four and three segments of CNTs, respectively. The model system consists of CNTs mixed with either "X" or "Y" molecular junctions. The system is equilibrated using Monte Carlo simulations and the equilibrated configurations are used to locate the clusters of connected molecules via a recursive algorithm. The fraction (P(perc)) of configurations with a percolating cluster is then estimated for a given total volume fraction (phi(t)) of molecules. When P(perc) reaches 0.5, phi(t) of the system is considered a percolation threshold concentration (phi(c)). The percolation behavior is found to be sensitive to the aspect ratio of CNTs and the concentration and the shape of molecular junctions. phi(c) is decreased with an increase in the aspect ratio of CNTs. As the mole fraction of molecular junctions is increased, phi(c) is decreased significantly, which suggests that molecular junctions could enhance the electric conductivity of CNT-polymer composites. X junctions are found to construct a percolating network more effectively than Y junctions. More interestingly, even though molecular junctions change the percolation behavior significantly, the site-site pair correlation functions of CNTs hardly show any difference as the mole fraction of molecular junctions is increased. This implies that the percolation of CNTs is determined by the subtle many-body correlation of CNTs that is not captured by the site-site pair correlation functions.

  20. Molecular responses to stress induced in normal human caucasian melanocytes in culture by exposure to simulated solar UV.

    PubMed

    Marrot, Laurent; Belaïdi, Jean-Philippe; Jones, Christophe; Perez, Philippe; Meunier, Jean-Roch

    2005-01-01

    Melanocytes play a central role in the response of skin to sunlight exposure. They are directly involved in UV-induced pigmentation as a defense mechanism. However, their alteration can lead to melanoma, a process where the role of sun overexposure is highly probable. The transformation process whereby UV damage may result in melanoma initiation is poorly understood, especially in terms of UV-induced genotoxicity in pigmented cells, where melanin can act either as a sunscreen or as a photosensitizer. The aim of this study was to analyze the behavior of melanocytes from fair skin under irradiation mimicking environmental sunlight in terms of spectral power distribution. To do this, normal human Caucasian melanocytes in culture were exposed to simulated solar UV (SSUV, 300-400 nm). Even at relatively high doses (until 20 min exposure, corresponding to 12 kJ/m2 UV-B and 110 kJ/m2 UV-A), cell death was limited, as shown by cell viability and low occurrence of apoptosis (caspase-3 activation). Moreover, p53 accumulation was three times lower in melanocytes than in unpigmented cells such as fibroblasts after SSUV exposure. However, an important fraction of melanocyte population was arrested in G2-M phase, and this correlated well with a high induction level of the gene GADD45, 4 h after exposure. Among the genes involved in DNA repair, gene XPC was the most inducible because its expression increased more than two-fold 15 h after a 20 min exposure, whereas expression of P48 was only slightly increased. In addition, an early induction of Heme Oxygenase 1 (HO1) gene, a typical response to oxidative stress, was also observed for the first time in melanocytes. Interestingly, this induction remained significant when melanocytes were exposed to UV-A radiation only (320-400 nm), and stimulation of melanogenesis before irradiation further increased HO1 induction. These results were obtained with normal human cells after exposure to SSUV radiation, which mimicked natural sunlight

  1. Dynamic Contact Stress Patterns on the Tibial Plateaus during Simulated Gait: A Novel Application of Normalized Cross Correlation

    PubMed Central

    Wang, Hongsheng; Chen, Tony; Torzilli, Peter; Warren, Russell; Maher, Suzanne

    2014-01-01

    The spatial distribution and pattern of local contact stresses within the knee joint during activities of daily living have not been fully investigated. The objective of this study was to determine if common contact stress patterns exist on the tibial plateaus of human knees during simulated gait. To test this hypothesis, we developed a novel normalized cross-correlation (NCC) algorithm and applied it to the contact stresses on the tibial plateaus of twelve human cadaveric knees subjected to multi-directional loads mimicking gait. The contact stress profiles at different locations on the tibial plateaus were compared, where regions with similar contact stress patterns were identified across specimens. Three consistent regional patterns were found, among them two most prominent contact stress patterns were shared by 9 to 12 of all the knees and the third pattern was shared by 6 to 8 knees. The first pattern was located at the posterior aspect of the medial tibial plateau and had a single peak stress that occurred during the early stance phase. The second pattern was located at the central-posterior aspects of the lateral plateau and consisted of two peak stresses coincident with the timing of peak axial force at early and late stance. The third pattern was found on the anterior aspect of cartilage-to-cartilage contact region on the medial plateau consisted of double peak stresses. The differences in the location and profile of the contact stress patterns suggest that the medial and lateral menisci function to carry load at different points in the gait cycle: with the posterior aspect of the medial meniscus consistently distributing load only during the early phase of stance, and the posterior aspect of the lateral meniscus consistently distributing load during both the early and late phases of stance. This novel approach can help identify abnormalities in knee contact mechanics and provide a better understanding of the mechanical pathways leading to post

  2. Molecular dynamics simulations and Kelvin probe force microscopy to study of cholesterol-induced electrostatic nanodomains in complex lipid mixtures

    NASA Astrophysics Data System (ADS)

    Drolle, E.; Bennett, W. F. D.; Hammond, K.; Lyman, E.; Karttunen, M.; Leonenko, Z.

    The molecular arrangement of lipids and proteins within biomembranes and monolayers gives rise to complex film morphologies as well as regions of distinct electrical surface potential, topographical and electrostatic nanoscale domains. To probe these nanodomains in soft matter is a challenging task both experimentally and theoretically. This work addresses the effects of cholesterol, lipid composition, lipid charge, and lipid phase on the monolayer structure and the electrical surface potential distribution. Atomic Force Microscopy (AFM) was used to resolve topographical nanodomains and Kelvin Probe Force Microscopy (KPFM) to resolve electrical surface potential of these nanodomains in lipid monolayers. Model monolayers composed of dipalmitoylphosphatidylcholine (DPPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1,2-dioleoyl-sn-glycero-3-[phospho-rac-(3-lysyl(1-glycerol))] (DOPG), sphingomyelin, and cholesterol were studied. It is shown that cholesterol changes nanoscale domain formation, affecting both topography and electrical surface potential. The molecular basis for differences in electrical surface potential was addressed with atomistic molecular dynamics (MD). MD simulations qualitatively match the experimental results, with 100s of mV difference in electrostatic potential between liquid-disordered bilayer (Ld, less cholesterol and lower chain order) and a liquid-ordered bilayer (Lo, more cholesterol and higher chain order). Importantly, the difference in electrostatic properties between Lo and Ld phases suggests a new mechanism by which membrane composition couples to membrane function.

  3. Molecular dynamics simulations on desulfurization of n-octane/thiophene mixture using silica filled polydimethylsiloxane nanocomposite membranes

    NASA Astrophysics Data System (ADS)

    Shariatinia, Zahra; Mazloom Jalali, Azin; Afshar Taromi, Faramarz

    2016-03-01

    Molecular dynamics (MD) simulations were performed at 298.15 K and 1 atm in order to study microstructure and transport behaviors of polydimethylsiloxane (PDMS) membranes containing 0%-8% SiO2 nanoparticles used for the separation of thiophene from n-octane. It was found that the fractional free volume (FFV) of 0% SiO2 was the highest (47.24%) among five nanocomposite membranes and addition of 2%-8% silica nanoparticles led to dramatic decrease in the FFV of the cells. The x-ray diffraction (XRD) patterns of all membranes showed that they had a semi-crystalline structure containing a broad peak around 15°-18°. The radial distribution function (RDF) analysis proved that the smallest C(CH2-octane)-O(SiO2), C(PDMS)-O(SiO2) and H(thiophene)-O(SiO2) distances were present in 4% SiO2 membrane reflecting the silica-octane, silica-polymer and silica-thiophene interactions were the strongest in this membrane. The mean squared displacement (MSD) and diffusion coefficients of n-octane were both small in the 6% silica membrane but they were high for thiophene suggesting this membrane was the most suitable for the desulfurization process and separation of thiophene from n-octane.

  4. Evaluating the Effects of Tri-Butyl Phosphate and Normal Paraffin Hydrocarbon in Simulated Low-Activity Waste Solution on Ion Exchange

    SciTech Connect

    Adu-Wusu, K.

    2003-05-13

    Ultrafiltration and ion exchange are among the pretreatment processes selected for the WTP at the Hanford Site. This study is the second part of a two-part study on Evaluating the Effects of Tri-Butyl Phosphate and Normal Paraffin Hydrocarbon in Simulated Low-Activity Waste Solution on Ultrafiltration and Ion Exchange.

  5. 14 CFR 27.1147 - Mixture controls.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Mixture controls. 27.1147 Section 27.1147... STANDARDS: NORMAL CATEGORY ROTORCRAFT Powerplant Powerplant Controls and Accessories § 27.1147 Mixture controls. If there are mixture controls, each engine must have a separate control and the controls must...

  6. 14 CFR 27.1147 - Mixture controls.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Mixture controls. 27.1147 Section 27.1147... STANDARDS: NORMAL CATEGORY ROTORCRAFT Powerplant Powerplant Controls and Accessories § 27.1147 Mixture controls. If there are mixture controls, each engine must have a separate control and the controls must...

  7. 14 CFR 27.1147 - Mixture controls.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Mixture controls. 27.1147 Section 27.1147... STANDARDS: NORMAL CATEGORY ROTORCRAFT Powerplant Powerplant Controls and Accessories § 27.1147 Mixture controls. If there are mixture controls, each engine must have a separate control and the controls must...

  8. 14 CFR 27.1147 - Mixture controls.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Mixture controls. 27.1147 Section 27.1147... STANDARDS: NORMAL CATEGORY ROTORCRAFT Powerplant Powerplant Controls and Accessories § 27.1147 Mixture controls. If there are mixture controls, each engine must have a separate control and the controls must...

  9. 14 CFR 27.1147 - Mixture controls.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Mixture controls. 27.1147 Section 27.1147... STANDARDS: NORMAL CATEGORY ROTORCRAFT Powerplant Powerplant Controls and Accessories § 27.1147 Mixture controls. If there are mixture controls, each engine must have a separate control and the controls must...

  10. Simulations of exercise and brain effects of acute exposure to carbon monoxide in normal and vascular-diseased persons.

    EPA Science Inventory

    At some level, carboxyhemoglobin (RbCO) due to inhalation of carbon monoxide (CO) reduces maximum exercise duration in normal and ischemic heart patients. At high RbCO levels in normal subjects, brain function is also affected and behavioral performance is impaired. These are fin...

  11. Hip range-of-motion (ROM) is less than normal after rotational acetabular osteotomy for developmental dysplasia of the hip: A simulated ROM analysis.

    PubMed

    Hamada, Hidetoshi; Takao, Masaki; Nakahara, Ichiro; Sakai, Takashi; Nishii, Takashi; Sugano, Nobuhiko

    2016-02-01

    The optimal reorientation of the acetabulum for developmental dysplasia of the hip (DDH) is unknown in terms of hip range-of-motion (ROM). The simulated ROMs of 52 DDHs after rotational acetabular osteotomy (RAO) with several patterns of femoral head coverage and those of 73 normal hips were analyzed using computer models reconstructed from CT images. After RAO with a lateral center edge angle (LCEA) of 30° and an anterior center edge angle (ACEA) of 55° producing coverage similar to that of normal hips, the maximal flexion and maximal internal rotation at 110° flexion with 20° adduction were significantly smaller than those of the normal group. To achieve ROMs after RAO similar to those of the normal group, an LCEA of 30° with an ACEA of 45°, an LCEA of 25° with an ACEA of 45° to 50°, and an LCEA of 20° with an ACEA of 50° could be preferred angles to target, even though they provided smaller coverage than that of normal hips. After RAO producing femoral head coverage similar to that of normal hips, the maximal flexion and the maximal internal rotation at 110° flexion with 20° adduction were significantly smaller than those of the normal group.

  12. On the calculation of solubilities via direct coexistence simulations: Investigation of NaCl aqueous solutions and Lennard-Jones binary mixtures.

    PubMed

    Espinosa, J R; Young, J M; Jiang, H; Gupta, D; Vega, C; Sanz, E; Debenedetti, P G; Panagiotopoulos, A Z

    2016-10-21

    Direct coexistence molecular dynamics simulations of NaCl solutions and Lennard-Jones binary mixtures were performed to explore the origin of reported discrepancies between solubilities obtained by direct interfacial simulations and values obtained from the chemical potentials of the crystal and solution phases. We find that the key cause of these discrepancies is the use of crystal slabs of insufficient width to eliminate finite-size effects. We observe that for NaCl crystal slabs thicker than 4 nm (in the direction perpendicular to the interface), the same solubility values are obtained from the direct coexistence and chemical potential routes, namely, 3.7 ± 0.2 molal at T = 298.15 K and p = 1 bar for the JC-SPC/E model. Such finite-size effects are absent in the Lennard-Jones system and are likely caused by surface dipoles present in the salt crystals. We confirmed that μs-long molecular dynamics runs are required to obtain reliable solubility values from direct coexistence calculations, provided that the initial solution conditions are near the equilibrium solubility values; even longer runs are needed for equilibration of significantly different concentrations. We do not observe any effects of the exposed crystal face on the solubility values or equilibration times. For both the NaCl and Lennard-Jones systems, the use of a spherical crystallite embedded in the solution leads to significantly higher apparent solubility values relative to the flat-interface direct coexistence calculations and the chemical potential values. Our results have broad implications for the determination of solubilities of molecular models of ionic systems.

  13. On the calculation of solubilities via direct coexistence simulations: Investigation of NaCl aqueous solutions and Lennard-Jones binary mixtures

    NASA Astrophysics Data System (ADS)

    Espinosa, J. R.; Young, J. M.; Jiang, H.; Gupta, D.; Vega, C.; Sanz, E.; Debenedetti, P. G.; Panagiotopoulos, A. Z.

    2016-10-01

    Direct coexistence molecular dynamics simulations of NaCl solutions and Lennard-Jones binary mixtures were performed to explore the origin of reported discrepancies between solubilities obtained by direct interfacial simulations and values obtained from the chemical potentials of the crystal and solution phases. We find that the key cause of these discrepancies is the use of crystal slabs of insufficient width to eliminate finite-size effects. We observe that for NaCl crystal slabs thicker than 4 nm (in the direction perpendicular to the interface), the same solubility values are obtained from the direct coexistence and chemical potential routes, namely, 3.7 ± 0.2 molal at T = 298.15 K and p = 1 bar for the JC-SPC/E model. Such finite-size effects are absent in the Lennard-Jones system and are likely caused by surface dipoles present in the salt crystals. We confirmed that μs-long molecular dynamics runs are required to obtain reliable solubility values from direct coexistence calculations, provided that the initial solution conditions are near the equilibrium solubility values; even longer runs are needed for equilibration of significantly different concentrations. We do not observe any effects of the exposed crystal face on the solubility values or equilibration times. For both the NaCl and Lennard-Jones systems, the use of a spherical crystallite embedded in the solution leads to significantly higher apparent solubility values relative to the flat-interface direct coexistence calculations and the chemical potential values. Our results have broad implications for the determination of solubilities of molecular models of ionic systems.

  14. Three-Dimensional Numerical Simulation of Pure Solutocapillary Flow in a Shallow Annular Pool for Mixture Fluid with High Schmidt Number

    NASA Astrophysics Data System (ADS)

    Chen, Jie-Chao; Zhang, Li; Li, You-Rong; Yu, Jia-Jia

    2016-04-01

    In order to understand the characteristics of pure solutocapillary flow in a shallow annular pool subjected to a constant radial solutal gradient, a series of three-dimensional numerical simulations were performed. The annular pool was filled with the toluene/n-hexane mixture fluid with the Schmidt number of 142.8. The inner and outer cylinders were respectively maintained at low and high solutal concentrations. Aspect ratio of the annular pool is fixed at ɛ = 0.15 or 0.05. Results indicate that the solutocapillary flow is steady and axisymmetric at a small solutal capillary Reynolds number. The surface fluid flows radially from the inner cylinder toward the outer cylinder and a return flow exists near the bottom. With the increase of the solutal capillary Reynolds number, an axisymmetric oscillatory flow firstly appears and then becomes a three-dimensional oscillatory flow at ɛ = 0.15. Whereas at ɛ = 0.05 a direct transition from the steady and axisymmetric flow to the three-dimensional oscillatory flow is observed. Three types of the flow instabilities are the standing wave, hydrosolutal wave and source/sink type wave instabilities. Furthermore, the physical mechanism of the flow destabilization is analyzed.

  15. Use of Finite Difference Time Domain Simulations and Debye Theory for Modelling the Terahertz Reflection Response of Normal and Tumour Breast Tissue

    PubMed Central

    Fitzgerald, Anthony J.; Pickwell-MacPherson, Emma; Wallace, Vincent P.

    2014-01-01

    The aim of this work was to evaluate the capabilities of Debye theory combined with Finite Difference Time Domain (FDTD) methods to simulate the terahertz (THz) response of breast tissues. Being able to accurately model breast tissues in the THz regime would facilitate the understanding of image contrast parameters used in THz imaging of breast cancer. As a test case, the model was first validated using liquid water and simulated reflection pulses were compared to experimental measured pulses with very good agreement (p = 1.00). The responses of normal and cancerous breast tissues were simulated with Debye properties and the correlation with measured data was still high for tumour (p = 0.98) and less so for normal breast (p = 0.82). Sections of the time domain pulses showed clear differences that were also evident in the comparison of pulse parameter values. These deviations may arise from the presence of adipose and other inhomogeneities in the breast tissue that are not accounted for when using the Debye model. In conclusion, the study demonstrates the power of the model for simulating THz reflection imaging; however, for biological tissues extra Debye terms or a more detailed theory may be required to link THz image contrast to physiological composition and structural changes of breast tissue associated with differences between normal and tumour tissues. PMID:25010734

  16. Breakdown electric fields in dissociated hot gas mixtures of sulfur hexafluoride including teflon: Calculations with experimental validations and utilization in fluid dynamics arc simulations

    NASA Astrophysics Data System (ADS)

    Yousfi, M.; Merbahi, N.; Reichert, F.; Petchanka, A.

    2017-03-01

    Measurements of breakdown voltage Vb, gas temperature Tg, and density N and the associated critical electric field Ecr/N are performed in hot dissociated SF6 highly diluted in argon and in hot dissociated SF6 mixed with PTFE (Polytetrafluoroethylene or C2F4) also highly diluted in argon. Gases are heated using a microwave source and optical emission spectroscopy is used for measurements of Tg and N while Vb is measured from a specific inter-electrode arrangement placed inside of the cell of the hot gas conditioning. The experimental Ecr/N data in the numerous considered cases of gas temperatures and compositions have been used to evaluate and validate the sets of the collision cross sections of the 11 species involved in hot dissociated SF6 (i.e., SF6, SF5, SF4, S2F2, SF3, SF2, SF, S2, F2, F, and S), the 13 additional species involved either in hot C2F4 or CF4 (C2F6, C2F4, C2F2, CF4, CF3, CF2, CF, F2, F and carbon species as C, C2, C3, C4) and also the 2 further species (CS and CS2) present only in the considered mixtures SF6 + C2F4. The fitted sets of collision cross sections of all these 26 species are then used without argon dilution in hot SF6 and hot SF6 + C2F4 mixtures to calculate and to analyze the Ecr/N data obtained for a wide range of gas temperature (up to 4000 K) and gas pressure (8 bar and more) using a rigorous multi-term solution of the Boltzmann equation for electron energy distribution function and standard calculations of hot gas composition for the species proportions. Such Ecr/N data have been then successfully used to evaluate from a Computational Fluid Dynamics model the switching capacity at terminal fault from a coupled simulation of the electrostatic field and the hot gas flow after current zero.

  17. Determine the permeability of an amorphous mixture of polydimethylsiloxane and dealuminated zeolite ZSM-5 to various ethanol-water solutions using molecular simulations.

    EPA Science Inventory

    An amorphous mixture of PDMS and multi-cellular fragments of ZSM-5 is brought together to approximate the properties of a mixed matrix membrane of PDMS with ZSM-5. The permeability coefficient of the amorphous mixture for pure water is the product of the diffusion coefficient of...

  18. A piloted simulation investigation of the normal load factor and longitudinal thrust required for air-to-air acquisition and tracking

    NASA Technical Reports Server (NTRS)

    Whalley, Matthew S.

    1993-01-01

    A piloted simulation study was performed by the U.S. Army Aeroflighydynamics Directorate to develop insight into the maneuverability requirements for aggressive helicopter maneuvering tasks such as air-to-air combat. Both a conventional helicopter and a helicopter with auxiliary thrust were examined. The aircraft parameters of interest were the normal and longitudinal load factor envelopes. Of particular interest were the mission performance and handling qualities tradeoffs with the parameters of interest. Two air-to-air acquisition and tracking tasks and a return-to-cover task were performed to assess mission performance. Results indicate that without auxiliary thrust, the ownship normal load factor capability needs to match that of the adversary in order to provide satisfactory handling qualities. Auxiliary thrust provides significant handling qualities advantages and can be substituted to some extent for normal load factor capability. Auxiliary thrust levels as low as 0.2 thrust/weight can provide significant handling qualities advantages.

  19. Thrust Augmentation of a Turbojet Engine at Simulated Flight Conditions by Introduction of a Water-Alcohol Mixture into the Compressor

    NASA Technical Reports Server (NTRS)

    Useller, James W.; Auble, Carmon M.; Harvey, Ray W., Sr.

    1952-01-01

    An investigation was conducted at simulated high-altitude flight conditions to evaluate the use of compressor evaporative cooling as a means of turbojet-engine thrust augmentation. Comparison of the performance of the engine with water-alcohol injection at the compressor inlet, at the sixth stage of the compressor, and at the sixth and ninth stages was made. From consideration of the thrust increases achieved, the interstage injection of the coolant was considered more desirable preferred over the combined sixth- and ninth-stage injection because of its relative simplicity. A maximum augmented net-thrust ratio of 1.106 and a maximum augmented jet-thrust ratio of 1.062 were obtained at an augmented liquid ratio of 2.98 and an engine-inlet temperature of 80 F. At lower inlet temperatures (-40 to 40 F), the maximum augmented net-thrust ratios ranged from 1.040 to 1.076 and the maximum augmented jet-thrust ratios ranged from 1.027 to 1.048, depending upon the inlet temperature. The relatively small increase in performance at the lower inlet-air temperatures can be partially attributed to the inadequate evaporation of the water-alcohol mixture, but the more significant limitation was believed to be caused by the negative influence of the liquid coolant on engine- component performance. In general, it is concluded that the effectiveness of the injection of a coolant into the compressor as a means of thrust augmentation is considerably influenced by the design characteristics of the components of the engine being used.

  20. On the phase and interface behavior along the three-phase line of ternary Lennard-Jones mixtures: a collaborative approach based on square gradient theory and molecular dynamics simulations.

    PubMed

    Garrido, José Matías; Quinteros-Lama, Héctor; Piñeiro, Manuel M; Mejía, Andrés; Segura, Hugo

    2014-07-07

    This work focuses on the application of a two-way approach, where Molecular Dynamics (MD) simulations and the Square Gradient Theory (SGT) have been used for describing the phase and interface behavior of binary and ternary Lennard-Jones (LJ) mixtures, along a condition of three-phase equilibrium. The unequivocal correspondence between MD and SGT has been achieved by using the global phase diagram of binary mixtures composed by equally sized Lennard-Jones molecules, from which representative molecular parameters for Type-I, Type-II, and Type-III systems have been determined. The so selected binaries have been used then to scale the behavior of a ternary mixture characterized by complex phase equilibrium patterns. For the case of the theoretical SGT approach applied to the Lennard-Jones equation of state was used for predicting phase equilibrium and interfacial properties. In addition the corresponding MD simulations of these macroscopic properties have been conducted for the LJ potential by using equivalent molecular parameters and conditions than in the theoretical approach. Excellent agreement has been observed between the predictions obtained from theory and simulations. Particularly, our results concerning the characterization of the three phase line of a binary Type-III mixture indicate that the bulk liquid (α) and the bulk gas (G) regions are sharply separated by a bulk liquid region (β) for all the explored temperature, pressure, and concentration conditions. The structural analysis of these bulk phases reveals that a secondary liquid phase (β) perfectly wets the liquid-gas interface (α-G), as previously found for Type-II mixture [A. Mejía and L. F. Vega, J. Chem. Phys. 124, 244505 (2006)]. The exploration along the three-phase line for the ternary mixture shows good agreement between SGT and MD. Particularly, we observed the specific influence of a third component in the phase and interface behavior. From all the previous results, we conclude that the

  1. Effects of Pleiotrophin Overexpression on Mouse Skeletal Muscles in Normal Loading and in Actual and Simulated Microgravity

    PubMed Central

    Liantonio, Antonella; De Bellis, Michela; Cannone, Maria; Sblendorio, Valeriana; Conte, Elena; Mele, Antonietta; Tricarico, Domenico; Tavella, Sara; Ruggiu, Alessandra; Cancedda, Ranieri; Ohira, Yoshinobu; Danieli-Betto, Daniela; Ciciliot, Stefano; Germinario, Elena; Sandonà, Dorianna; Betto, Romeo; Desaphy, Jean-François

    2013-01-01

    Pleiotrophin (PTN) is a widespread cytokine involved in bone formation, neurite outgrowth, and angiogenesis. In skeletal muscle, PTN is upregulated during myogenesis, post-synaptic induction, and regeneration after crushing, but little is known regarding its effects on muscle function. Here, we describe the effects of PTN on the slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles in mice over-expressing PTN under the control of a bone promoter. The mice were maintained in normal loading or disuse condition, induced by hindlimb unloading (HU) for 14 days. Effects of exposition to near-zero gravity during a 3-months spaceflight (SF) into the Mice Drawer System are also reported. In normal loading, PTN overexpression had no effect on muscle fiber cross-sectional area, but shifted soleus muscle toward a slower phenotype, as shown by an increased number of oxidative type 1 fibers, and increased gene expression of cytochrome c oxidase subunit IV and citrate synthase. The cytokine increased soleus and EDL capillary-to-fiber ratio. PTN overexpression did not prevent soleus muscle atrophy, slow-to-fast transition, and capillary regression induced by SF and HU. Nevertheless, PTN exerted various effects on sarcolemma ion channel expression/function and resting cytosolic Ca2+ concentration in soleus and EDL muscles, in normal loading and after HU. In conclusion, the results show very similar effects of HU and SF on mouse soleus muscle, including activation of specific gene programs. The EDL muscle is able to counterbalance this latter, probably by activating compensatory mechanisms. The numerous effects of PTN on muscle gene expression and functional parameters demonstrate the sensitivity of muscle fibers to the cytokine. Although little benefit was found in HU muscle disuse, PTN may emerge useful in various muscle diseases, because it exerts synergetic actions on muscle fibers and vessels, which could enforce oxidative metabolism and ameliorate muscle

  2. Effects of pleiotrophin overexpression on mouse skeletal muscles in normal loading and in actual and simulated microgravity.

    PubMed

    Camerino, Giulia Maria; Pierno, Sabata; Liantonio, Antonella; De Bellis, Michela; Cannone, Maria; Sblendorio, Valeriana; Conte, Elena; Mele, Antonietta; Tricarico, Domenico; Tavella, Sara; Ruggiu, Alessandra; Cancedda, Ranieri; Ohira, Yoshinobu; Danieli-Betto, Daniela; Ciciliot, Stefano; Germinario, Elena; Sandonà, Dorianna; Betto, Romeo; Camerino, Diana Conte; Desaphy, Jean-François

    2013-01-01

    Pleiotrophin (PTN) is a widespread cytokine involved in bone formation, neurite outgrowth, and angiogenesis. In skeletal muscle, PTN is upregulated during myogenesis, post-synaptic induction, and regeneration after crushing, but little is known regarding its effects on muscle function. Here, we describe the effects of PTN on the slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles in mice over-expressing PTN under the control of a bone promoter. The mice were maintained in normal loading or disuse condition, induced by hindlimb unloading (HU) for 14 days. Effects of exposition to near-zero gravity during a 3-months spaceflight (SF) into the Mice Drawer System are also reported. In normal loading, PTN overexpression had no effect on muscle fiber cross-sectional area, but shifted soleus muscle toward a slower phenotype, as shown by an increased number of oxidative type 1 fibers, and increased gene expression of cytochrome c oxidase subunit IV and citrate synthase. The cytokine increased soleus and EDL capillary-to-fiber ratio. PTN overexpression did not prevent soleus muscle atrophy, slow-to-fast transition, and capillary regression induced by SF and HU. Nevertheless, PTN exerted various effects on sarcolemma ion channel expression/function and resting cytosolic Ca(2+) concentration in soleus and EDL muscles, in normal loading and after HU. In conclusion, the results show very similar effects of HU and SF on mouse soleus muscle, including activation of specific gene programs. The EDL muscle is able to counterbalance this latter, probably by activating compensatory mechanisms. The numerous effects of PTN on muscle gene expression and functional parameters demonstrate the sensitivity of muscle fibers to the cytokine. Although little benefit was found in HU muscle disuse, PTN may emerge useful in various muscle diseases, because it exerts synergetic actions on muscle fibers and vessels, which could enforce oxidative metabolism and ameliorate muscle

  3. Impact of simulated ostracism on overweight and normal-weight youths' motivation to eat and food intake.

    PubMed

    Salvy, Sarah-Jeanne; Bowker, Julie C; Nitecki, Lauren A; Kluczynski, Melissa A; Germeroth, Lisa J; Roemmich, James N

    2011-02-01

    There is growing evidence that the experience of being ostracized can impair individuals' abilities to self-regulate, which in turn, leads to negative health behaviors, such as increased unhealthy eating. Research has focused on adults, but deficits in eating regulation in response to ostracism may be particularly detrimental for overweight or obese youth. This study examines the effects of a brief episode of ostracism on the motivation to eat and food intake of overweight and normal-weight young adolescents (M age=13.6 years). A computerized ball-tossing game (Cyberball) was used to induce ostracism or inclusion. Following the inclusion/ostracism manipulation, all participants completed an operant computer task to earn points exchangeable for portions of food or for time socializing with an unfamiliar peer. Participants' responses for food and their subsequent energy intake were recorded. As hypothesized, ostracized overweight participants responded more for food and had a greater energy intake than overweight participants in the inclusion/control condition; whereas this was not the case for normal-weight participants. These results are important as studies indicate that overweight and obese youth may be at risk of social isolation and peer difficulties. Social adversity, if left unchanged, may increase the difficulty of promoting long-term changes in overweight youths' health behaviors.

  4. Impact of Simulated Ostracism on Overweight and Normal-Weight Youths’ Motivation to Eat and Food Intake

    PubMed Central

    Salvy, Sarah-Jeanne; Bowker, Julie C.; Nitecki, Lauren A.; Kluczynski, Melissa A.; Germeroth, Lisa J.; Roemmich, James N.

    2010-01-01

    There is growing evidence that the experience of being ostracized can impair individuals abilities to self-regulate, which in turn, leads to negative health behaviors, such as increased unhealthy eating. Research has focused on adults, but deficits in eating regulation in response to ostracism may be particularly detrimental for overweight or obese youth. This study examines the effects of a brief episode of ostracism on the motivation to eat and food intake of overweight and normal-weight young adolescents (M age = 13.6 years). A computerized ball-tossing game (Cyberball) was used to induce ostracism or inclusion. Following the inclusion/ostracism manipulation, all participants completed an operant computer task to earn points exchangeable for portions of food or for time socializing with an unfamiliar peer. Participants’ responses for food and their subsequent energy intake were recorded. As hypothesized, ostracized overweight participants responded more for food and had a greater energy intake than overweight participants in the inclusion/control condition; whereas this was not the case for normal-weight participants. These results are important as studies indicate that overweight and obese youth may be at risk of social isolation and peer difficulties. Social adversity, if left unchanged, may increase the difficulty of promoting long-term changes in overweight youths’ health behaviors. PMID:21094193

  5. TMVOC-MP: a parallel numerical simulator for Three-PhaseNon-isothermal Flows of Multicomponent Hydrocarbon Mixtures inporous/fractured media

    SciTech Connect

    Zhang, Keni; Yamamoto, Hajime; Pruess, Karsten

    2008-02-15

    TMVOC-MP is a massively parallel version of the TMVOC code (Pruess and Battistelli, 2002), a numerical simulator for three-phase non-isothermal flow of water, gas, and a multicomponent mixture of volatile organic chemicals (VOCs) in multidimensional heterogeneous porous/fractured media. TMVOC-MP was developed by introducing massively parallel computing techniques into TMVOC. It retains the physical process model of TMVOC, designed for applications to contamination problems that involve hydrocarbon fuels or organic solvents in saturated and unsaturated zones. TMVOC-MP can model contaminant behavior under 'natural' environmental conditions, as well as for engineered systems, such as soil vapor extraction, groundwater pumping, or steam-assisted source remediation. With its sophisticated parallel computing techniques, TMVOC-MP can handle much larger problems than TMVOC, and can be much more computationally efficient. TMVOC-MP models multiphase fluid systems containing variable proportions of water, non-condensible gases (NCGs), and water-soluble volatile organic chemicals (VOCs). The user can specify the number and nature of NCGs and VOCs. There are no intrinsic limitations to the number of NCGs or VOCs, although the arrays for fluid components are currently dimensioned as 20, accommodating water plus 19 components that may be either NCGs or VOCs. Among them, NCG arrays are dimensioned as 10. The user may select NCGs from a data bank provided in the software. The currently available choices include O{sub 2}, N{sub 2}, CO{sub 2}, CH{sub 4}, ethane, ethylene, acetylene, and air (a pseudo-component treated with properties averaged from N{sub 2} and O{sub 2}). Thermophysical property data of VOCs can be selected from a chemical data bank, included with TMVOC-MP, that provides parameters for 26 commonly encountered chemicals. Users also can input their own data for other fluids. The fluid components may partition (volatilize and/or dissolve) among gas, aqueous, and NAPL

  6. Scale Mixture Models with Applications to Bayesian Inference

    NASA Astrophysics Data System (ADS)

    Qin, Zhaohui S.; Damien, Paul; Walker, Stephen

    2003-11-01

    Scale mixtures of uniform distributions are used to model non-normal data in time series and econometrics in a Bayesian framework. Heteroscedastic and skewed data models are also tackled using scale mixture of uniform distributions.

  7. SIMULATION OF NON-AZEOTROPIC REFRIGERANT MIXTURES FOR USE IN A DUAL-CIRCUIT REFRIGERATOR/FREEZER WITH COUNTERCURRENT HEAT EXCHANGES

    EPA Science Inventory

    The paper discusses a refrigerator/freezer (RF) system that has two complete and independent refrigeration cycles for the two compartments. It uses a non-azeotropic refrigerant mixture (NARM) in each cycle and countercurrent heat exchangers throughout. This RF is housed in a stan...

  8. Unrestricted Mixture Models for Class Identification in Growth Mixture Modeling

    ERIC Educational Resources Information Center

    Liu, Min; Hancock, Gregory R.

    2014-01-01

    Growth mixture modeling has gained much attention in applied and methodological social science research recently, but the selection of the number of latent classes for such models remains a challenging issue, especially when the assumption of proper model specification is violated. The current simulation study compared the performance of a linear…

  9. Pharmacokinetic evaluation of doxorubicin plasma levels in normal and overweight patients with breast cancer and simulation of dose adjustment by different indexes of body mass.

    PubMed

    Barpe, Deise Raquel; Rosa, Daniela Dornelles; Froehlich, Pedro Eduardo

    2010-11-20

    Although being used for decades in the treatment of several types of cancer, either alone or in association, only a few data about the pharmacokinetics of doxorubicin (DOX) in humans are available. DOX is frequently used in association with other anticancer drugs in the management of breast cancer. Pharmacokinetic data available in the literature show that after i.v. administration DOX follows a two-compartment open model, with a fast distribution phase followed by a very slow elimination phase. The objective of this work is to perform a pilot study in order to verify if the usual dose adjustment based on body surface area (BSA) would be producing the same plasma concentration-time profiles in patients with normal (<25) and above normal (>25) body mass index (BMI). In order to assess the pharmacokinetics of DOX after a short-term i.v. infusion of 60mg/m(2) of BSA, an experimental design using only five plasma samples of each patient was applied. Samples were collected at 0.00, 0.66 (right after the end of infusion), 1.66, 8.66, and 24.66h. DOX pharmacokinetic profiles were evaluated after quantification of DOX using a new HPLC method developed and validated. Pharmacokinetic parameters (AUC(0-24.66) and C(max)) were analyzed by non-compartmental and compartmental approaches. Significant differences (α=0.05) between overweight and normal weight groups were found with respect to AUC and C(max). After adjustment of dose by weight and by BMI, the compartmental model was used to simulate plasma concentrations and new values for C(max) and AUC(0-24.66) were calculated. The new values obtained using both body weight (BW) and BMI were closer to the normal group than those obtained with BSA. According to the simulation, the differences of AUC and C(max) between the overweight group and the group of patients with normal weight were lower when the dose was adjusted by BW and BMI. These results suggest that more studies must be conducted, with more patients, in order to

  10. Borehole Plugging Program (waste disposal). Report 2. Petrographic examination of several four-year-old laboratory developed grout mixtures

    SciTech Connect

    Rhoderick, J E; Buck, A D

    1981-09-01

    Specimens from five grout mixtures had been stored in either simulated brine groundwater at 73/sup 0/F or in laboratory air for approximately 4 years. The variables included type of cement, use of a natural pozzolan, and use of salt in two mixtures. Available specimens were inspected; a specimen stored wet and one stored dry from each grout mixture were examined by x-ray diffraction for phase composition and by scanning electron microscopy to study microstructure. The results showed that: cracking of specimens was common; it was believed to be due mainly to temperature change and/or moisture change effects; the mixture variables were generally not recognizable; and the phase composition and microstructure of the five grout mixtures were considered normal.

  11. Thermal Analysis of Various Epoxy Mixtures.

    DTIC Science & Technology

    1986-03-01

    Dicyandiamide Thermal analysis Accelerator r20 ABSTRAC r (Continue on revre side If necesary and identif by. block riimeyp.) 4 4 (SEE REVERSE SIDE...mixed with Monuron. Also, three-component mixtures, epoxide + Dicy/Monuron, were prepared with dicyandiamide . The mixtures were cured by differential... dicyandiamide and Monuron, on the curing process, was simulated by the isothermal reaction of two mixtures. A type of reaction kinetics having the

  12. Mixtures and Mineral Reactions

    NASA Astrophysics Data System (ADS)

    Rumble, D.

    The monograph Mixtures and Mineral Reactions contains a large amount of information of value to mineralogists, petrologists, and geochemists. The first four chapters are a succinct account of the thermodynamic description of crystalline solutions. In these early chapters a comparison is made between different mathematical treatments of activitycomposition models, there is a discussion of the unmixing by exsolution of a single solution into two phases, and methods of computing phase equilibria in assemblages of different minerals are given. If the reader is perplexed by the discussion of standard states (cf. Figure 1.3), not to worry. That is a normal condition for anyone forced to choose between equivalent reference frames yet knowing, somewhere down the line, that the choice will ultimately make one's computational life more or less difficult.

  13. Normal Shock Vortex Interaction

    DTIC Science & Technology

    2003-03-01

    Figure 9: Breakdown map for normal-shock vortex-interaction. References [1] O. Thomer, W. Schroder and M. Meinke , Numerical Simulation of Normal...and Oblique-Shock Vortex Interaction, ZAMM Band 80, Sub. 1, pp. 181-184, 2000. [2] O. Thomer, E. Krause, W. Schroder and M. Meinke , Computational

  14. Gaussian-mixture umbrella sampling

    PubMed Central

    van der Vaart, Arjan; Karplus, Martin

    2009-01-01

    We introduce the Gaussian-mixture umbrella sampling method (GAMUS), a biased molecular dynamics technique based on adaptive umbrella sampling that efficiently escapes free energy minima in multi-dimensional problems. The prior simulation data are reweighted with a maximum likelihood formulation, and the new approximate probability density is fit to a Gaussian-mixture model, augmented by information about the unsampled areas. The method can be used to identify free energy minima in multi-dimensional reaction coordinates. To illustrate GAMUS, we apply it to the alanine dipeptide (2D reaction coordinate) and tripeptide (4D reaction coordinate). PMID:19284746

  15. Reflectance spectroscopy and GEX simulation of palagonite and iron-rich montmorillonite clay mixtures: Implications for the surface composition of Mars

    NASA Technical Reports Server (NTRS)

    Orenberg, J. B.; Handy, J.; Quinn, R.

    1992-01-01

    Because of the power of remote sensing reflectance spectroscopy in determining mineralogy, it has been used as the major method of identifying a possible mineral analogue of the martian surface. A summary of proposed martian surface compositions from reflectance spectroscopy before 1979 was presented by Singer et al. Since that time, iron-rich montmorillonite clay, nanocrystalline or nanophase hematite, and palagonite have been suggested as Mars soil analogue materials. Palagonite in petrological terms is best described as an amorphous, hydrated, ferric iron, silica gel. Montmorillonite is a member of the smectite clay group, and its structure is characterized by an octahedral sheet in coordination with two tetrahedral sheets in which oxygen atoms are shared. The crystal unity of montmorillonite is well defined in contrast to palagonite where it is considered amorphous or poorly crystalline at best. Because of the absence of the diagnostic strong 2.2-micron reflectance band characteristic of clays in the near-infrared (NIR) spectrum of Mars and palagonite and based upon a consideration of wide wavelength coverage (0.3-50 microns), Roush et al. concluded that palagonite is a more likely Mars surface analogue. In spite of the spectral agreement of palagonite and the Mars reflectance spectrum in the 2.2-micron region, palagonite shows poor correspondence with the results of the Viking LR experiment. In contrast, iron-rich montmorillonite clays show relatively good agreement with the results of the Viking LR experiment. This spectral study was undertaken to evaluate the spectral properties of mixtures of palagonite and Mars analogue iron-rich montmorillonite clay (16-18 wt. percent Fe as Fe2O3) as a Mars surface mineralogical model. Mixtures of minerals as Mars surface analogue materials have been studied before, but the mixtures were restricted to crystalline clays and iron oxides.

  16. Mapping of quantitative trait loci using the skew-normal distribution*

    PubMed Central

    Fernandes, Elisabete; Pacheco, António; Penha-Gonçalves, Carlos

    2007-01-01

    In standard interval mapping (IM) of quantitative trait loci (QTL), the QTL effect is described by a normal mixture model. When this assumption of normality is violated, the most commonly adopted strategy is to use the previous model after data transformation. However, an appropriate transformation may not exist or may be difficult to find. Also this approach can raise interpretation issues. An interesting alternative is to consider a skew-normal mixture model in standard IM, and the resulting method is here denoted as skew-normal IM. This flexible model that includes the usual symmetric normal distribution as a special case is important, allowing continuous variation from normality to non-normality. In this paper we briefly introduce the main peculiarities of the skew-normal distribution. The maximum likelihood estimates of parameters of the skew-normal distribution are obtained by the expectation-maximization (EM) algorithm. The proposed model is illustrated with real data from an intercross experiment that shows a significant departure from the normality assumption. The performance of the skew-normal IM is assessed via stochastic simulation. The results indicate that the skew-normal IM has higher power for QTL detection and better precision of QTL location as compared to standard IM and nonparametric IM. PMID:17973340

  17. Polyacrylamide gel substrates that simulate the mechanical stiffness of normal and malignant neuronal tissues increase protoporphyin IX synthesis in glioma cells

    NASA Astrophysics Data System (ADS)

    Niu, Carolyn J.; Fisher, Carl; Scheffler, Kira; Wan, Rachel; Maleki, Hoda; Liu, Haijiao; Sun, Yu; Simmons, Craig A.; Birngruber, Reginald; Lilge, Lothar

    2015-09-01

    Protoporphyrin IX (PPIX) produced following the administration of exogenous 5d-aminolevulinic acid is clinically approved for photodynamic therapy and fluorescence-guided resection in various jurisdictions around the world. For both applications, quantification of PPIX forms the basis for accurate therapeutic dose calculation and identification of malignant tissues for resection. While it is well established that the PPIX synthesis and accumulation rates are subject to the cell's biochemical microenvironment, the effect of the physical microenvironment, such as matrix stiffness, has received little attention to date. Here we studied the proliferation rate and PPIX synthesis and accumulation in two glioma cell lines U373 and U118 cultured under five different substrate conditions, including the conventional tissue culture plastic and polyacrylamide gels that simulated tissue stiffness of normal brain (1 kPa) and glioblastoma tumors (12 kPa). We found that the proliferation rate increased with substrate stiffness for both cell lines, but not in a linear fashion. PPIX concentration was significantly higher in cells cultured on tissue-simulating gels than on the much stiffer tissue culture plastic for both cell lines. These findings, albeit preliminary, suggest that the physical microenvironment might be an important determinant of tumor aggressiveness and PPIX synthesis in glioma cells.

  18. Generalized Beta Mixtures of Gaussians.

    PubMed

    Armagan, Artin; Dunson, David B; Clyde, Merlise

    2011-01-01

    In recent years, a rich variety of shrinkage priors have been proposed that have great promise in addressing massive regression problems. In general, these new priors can be expressed as scale mixtures of normals, but have more complex forms and better properties than traditional Cauchy and double exponential priors. We first propose a new class of normal scale mixtures through a novel generalized beta distribution that encompasses many interesting priors as special cases. This encompassing framework should prove useful in comparing competing priors, considering properties and revealing close connections. We then develop a class of variational Bayes approximations through the new hierarchy presented that will scale more efficiently to the types of truly massive data sets that are now encountered routinely.

  19. Impact of injected dose and acquisition time on a normal database by use of 3D-SSP in SPECT images: quantitative simulation studies.

    PubMed

    Onishi, Hideo; Hatazawa, Jun; Nakagawara, Jyoji; Ito, Kengo; Ha-Kawa, Sang Kil; Masuda, Yasuhiko; Sugibayashi, Keiichi; Takahashi, Masaaki; Kikuchi, Kei; Katsuta, Noboru

    2015-07-01

    The present study aimed to validate the accuracy of normal databases (NDBs) with respect to variable injected doses and acquisition times by use of three-dimensional stereotactic surface projections (3D-SSP) in N-isopropyl-p-[123I]-iodoamphetamine (I-123-IMP) brain perfusion images. We constructed NDBs based on brain SPECT images obtained from 29 healthy volunteers. Each NDB was rebuilt under simulated unique conditions by use of dynamic acquisition datasets and comprised injected doses (222, 167, and 111 MBq) and acquisition times (30, 20, and 15 min). We selected seven of 29 datasets derived from the volunteers to simulate patients' data (PD). The simulated PD were designed to include regions of hypoperfusion. The study comprised protocol A (same conditions for PD and NDB) and protocol B (mismatched conditions for PD and NDB). We used 3D-SSP to compare with the Z score and detection error. The average Z scores were decreased significantly in protocol A [PD (High)-NDB (High) vs. PD (Low)-NDB (Low); PD (30 m)-NDB (30 m) vs. PD (15 m)-NDB (15 m) and PD (20 m)-NDB (20 m)].The average Z scores of PD (High) and PD (Medium) with NDB (High) did not differ significantly in protocol B, whereas all others were decreased significantly. The error of detection increased 6.65 % (protocol A) and 32.05 % (protocol B). The Z scores were specific to the injected dose and acquisition time used in 3D-SSP studies, and the calculated Z scores were affected by mismatched injected doses and acquisition times between PD and selected NDBs.

  20. Molecular dynamics simulation of the structure and interfacial free energy barriers of mixtures of ionic liquids and divalent salts near a graphene wall.

    PubMed

    Gómez-González, Víctor; Docampo-Álvarez, Borja; Méndez-Morales, Trinidad; Cabeza, Oscar; Ivaništšev, Vladislav B; Fedorov, Maxim V; Gallego, Luis J; Varela, Luis M

    2016-12-21

    A molecular dynamics study of mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) with magnesium tetrafluoroborate (Mg[BF4]2) confined between two parallel graphene walls is reported. The structure of the system is analyzed by means of ionic density profiles, lateral structure of the first layer close to the graphene surface and angular orientations of imidazolium cations. Free energy profiles for divalent magnesium cations are calculated using two different methods in order to evaluate the height of the potential barriers near the walls, and the results are compared with those of mixtures of the same ionic liquid and a lithium salt (Li[BF4]). Preferential adsorption of magnesium cations is analyzed using a simple model and compared to that of lithium cations, and vibrational densities of states are calculated for the cations close to the walls analyzing the influence of the graphene surface charge. Our results indicate that magnesium cations next to the graphene wall have a roughly similar environment to that in the bulk. Moreover, they face higher potential barriers and are less adsorbed on the charged graphene walls than lithium cations. In other words, magnesium cations have a more stable solvation shell than lithium ones.

  1. In-simulator assessment of trade-offs arising from mixture of color cuing and monocular, binoptic, and stereopsis cuing information

    NASA Technical Reports Server (NTRS)

    Williams, Steven P.; Parrish, Russell V.

    1990-01-01

    The use of monochrome Helmet Mounted Display (HMD) systems is becoming prevalent in today's complex flight mission environment. These HMD systems can provide stereopsis cueing as an almost natural byproduct for binocular helmet systems of an additional image generation source is provided. The addition of color cueing capability is much more difficult. The application of stereopsis cueing to advanced HMD and heads-down flight display concepts has demonstrated gains in pilot situation awareness and improved task performance. To provide stereopsis, binocular HMD systems must trade some of the total field-of-view (FOV) available from their two monocular fields to obtain a partial overlap region. The visual field then provides a mixture of cues, with monocular regions on both peripheries, and, in the overlapped center, a binoptic (the same image to both eyes) or, if lateral disparity is introduced to produce two images, a stereo region. The goal of this research was to assess the trade-offs arising from the mixture of color cueing and monocular, biocular, and stereopsis cueing information in peripheral monitoring displays as encountered in HMD systems. The accompanying effect of stereopsis cueing in the foveal display of tracking information was also assessed.

  2. Bayesian Kernel Mixtures for Counts.

    PubMed

    Canale, Antonio; Dunson, David B

    2011-12-01

    Although Bayesian nonparametric mixture models for continuous data are well developed, there is a limited literature on related approaches for count data. A common strategy is to use a mixture of Poissons, which unfortunately is quite restrictive in not accounting for distributions having variance less than the mean. Other approaches include mixing multinomials, which requires finite support, and using a Dirichlet process prior with a Poisson base measure, which does not allow smooth deviations from the Poisson. As a broad class of alternative models, we propose to use nonparametric mixtures of rounded continuous kernels. An efficient Gibbs sampler is developed for posterior computation, and a simulation study is performed to assess performance. Focusing on the rounded Gaussian case, we generalize the modeling framework to account for multivariate count data, joint modeling with continuous and categorical variables, and other complications. The methods are illustrated through applications to a developmental toxicity study and marketing data. This article has supplementary material online.

  3. Hybrid Solution-Adaptive Unstructured Cartesian Method for Large-Eddy Simulation of Detonation in Multi-Phase Turbulent Reactive Mixtures

    DTIC Science & Technology

    2012-03-27

    an AMR approach would reach a steady state despite the unsteadiness in the flow (bluff-body stabilized flames, rocket combustors , swirl combustors , etc...influence the ac - curacy of the simulation and the resulting vortex structure. Both the IDW and MLS interpolation methods are used and the tunable param...Menon. Simulation of sprayturbulenceflame interactions in a lean direct injection combustor . Combustion and Flame, 153(12):228 – 257, 2008. [34] Nayan

  4. Dynamical response of the Galileo Galilei on the ground rotor to test the equivalence principle: Theory, simulation, and experiment. I. The normal modes

    NASA Astrophysics Data System (ADS)

    Comandi, G. L.; Chiofalo, M. L.; Toncelli, R.; Bramanti, D.; Polacco, E.; Nobili, A. M.

    2006-03-01

    Recent theoretical work suggests that violation of the equivalence principle might be revealed in a measurement of the fractional differential acceleration η between two test bodies—of different compositions, falling in the gravitational field of a source mass—if the measurement is made to the level of η ≃10-13 or better. This being within the reach of ground based experiments gives them a new impetus. However, while slowly rotating torsion balances in ground laboratories are close to reaching this level, only an experiment performed in a low orbit around the Earth is likely to provide a much better accuracy. We report on the progress made with the "Galileo Galilei on the ground" (GGG) experiment, which aims to compete with torsion balances using an instrument design also capable of being converted into a much higher sensitivity space test. In the present and following articles (Part I and Part II), we demonstrate that the dynamical response of the GGG differential accelerometer set into supercritical rotation—in particular, its normal modes (Part I) and rejection of common mode effects (Part II)—can be predicted by means of a simple but effective model that embodies all the relevant physics. Analytical solutions are obtained under special limits, which provide the theoretical understanding. A simulation environment is set up, obtaining a quantitative agreement with the available experimental data on the frequencies of the normal modes and on the whirling behavior. This is a needed and reliable tool for controlling and separating perturbative effects from the expected signal, as well as for planning the optimization of the apparatus.

  5. Dynamical response of the Galileo Galilei on the ground rotor to test the equivalence principle: Theory, simulation, and experiment. I. The normal modes

    SciTech Connect

    Comandi, G.L.; Chiofalo, M.L.; Toncelli, R.; Bramanti, D.; Polacco, E.; Nobili, A.M.

    2006-03-15

    Recent theoretical work suggests that violation of the equivalence principle might be revealed in a measurement of the fractional differential acceleration {eta} between two test bodies-of different compositions, falling in the gravitational field of a source mass--if the measurement is made to the level of {eta}{approx_equal}10{sup -13} or better. This being within the reach of ground based experiments gives them a new impetus. However, while slowly rotating torsion balances in ground laboratories are close to reaching this level, only an experiment performed in a low orbit around the Earth is likely to provide a much better accuracy. We report on the progress made with the 'Galileo Galilei on the ground' (GGG) experiment, which aims to compete with torsion balances using an instrument design also capable of being converted into a much higher sensitivity space test. In the present and following articles (Part I and Part II), we demonstrate that the dynamical response of the GGG differential accelerometer set into supercritical rotation-in particular, its normal modes (Part I) and rejection of common mode effects (Part II)-can be predicted by means of a simple but effective model that embodies all the relevant physics. Analytical solutions are obtained under special limits, which provide the theoretical understanding. A simulation environment is set up, obtaining a quantitative agreement with the available experimental data on the frequencies of the normal modes and on the whirling behavior. This is a needed and reliable tool for controlling and separating perturbative effects from the expected signal, as well as for planning the optimization of the apparatus.

  6. Used Nuclear Fuel Loading and Structural Performance Under Normal Conditions of Transport - Modeling, Simulation and Experimental Integration RD&D Plan

    SciTech Connect

    Adkins, Harold E.

    2013-04-01

    Under current U.S. Nuclear Regulatory Commission regulation, it is not sufficient for used nuclear fuel (UNF) to simply maintain its integrity during the storage period, it must maintain its integrity in such a way that it can withstand the physical forces of handling and transportation associated with restaging the fuel and moving it to treatment or recycling facilities, or a geologic repository. Hence it is necessary to understand the performance characteristics of aged UNF cladding and ancillary components under loadings stemming from transport initiatives. Researchers would like to demonstrate that enough information, including experimental support and modeling and simulation capabilities, exists to establish a preliminary determination of UNF structural performance under normal conditions of transport (NCT). This research, development and demonstration (RD&D) plan describes a methodology, including development and use of analytical models, to evaluate loading and associated mechanical responses of UNF rods and key structural components. This methodology will be used to provide a preliminary assessment of the performance characteristics of UNF cladding and ancillary components under rail-related NCT loading. The methodology couples modeling and simulation and experimental efforts currently under way within the Used Fuel Disposition Campaign (UFDC). The methodology will involve limited uncertainty quantification in the form of sensitivity evaluations focused around available fuel and ancillary fuel structure properties exclusively. The work includes collecting information via literature review, soliciting input/guidance from subject matter experts, performing computational analyses, planning experimental measurement and possible execution (depending on timing), and preparing a variety of supporting documents that will feed into and provide the basis for future initiatives. The methodology demonstration will focus on structural performance evaluation of

  7. Multi-scaled normal mode analysis method for dynamics simulation of protein-membrane complexes: A case study of potassium channel gating motion correlations

    SciTech Connect

    Wu, Xiaokun; Han, Min; Ming, Dengming

    2015-10-07

    Membrane proteins play critically important roles in many cellular activities such as ions and small molecule transportation, signal recognition, and transduction. In order to fulfill their functions, these proteins must be placed in different membrane environments and a variety of protein-lipid interactions may affect the behavior of these proteins. One of the key effects of protein-lipid interactions is their ability to change the dynamics status of membrane proteins, thus adjusting their functions. Here, we present a multi-scaled normal mode analysis (mNMA) method to study the dynamics perturbation to the membrane proteins imposed by lipid bi-layer membrane fluctuations. In mNMA, channel proteins are simulated at all-atom level while the membrane is described with a coarse-grained model. mNMA calculations clearly show that channel gating motion can tightly couple with a variety of membrane deformations, including bending and twisting. We then examined bi-channel systems where two channels were separated with different distances. From mNMA calculations, we observed both positive and negative gating correlations between two neighboring channels, and the correlation has a maximum as the channel center-to-center distance is close to 2.5 times of their diameter. This distance is larger than recently found maximum attraction distance between two proteins embedded in membrane which is 1.5 times of the protein size, indicating that membrane fluctuation might impose collective motions among proteins within a larger area. The hybrid resolution feature in mNMA provides atomic dynamics information for key components in the system without costing much computer resource. We expect it to be a conventional simulation tool for ordinary laboratories to study the dynamics of very complicated biological assemblies. The source code is available upon request to the authors.

  8. Evaluation of scatter-to-primary ratio, grid performance and normalized average glandular dose in mammography by Monte Carlo simulation including interference and energy broadening effects

    NASA Astrophysics Data System (ADS)

    Cunha, D. M.; Tomal, A.; Poletti, M. E.

    2010-08-01

    In this work, a computational code for the study of imaging systems and dosimetry in conventional and digital mammography through Monte Carlo simulations is described. The developed code includes interference and Doppler energy broadening for simulation of elastic and inelastic photon scattering, respectively. The code estimates the contribution of scattered radiation to image quality through the spatial distribution of the scatter-to-primary ratio (S/P). It allows the inclusion of different designs of anti-scatter grids (linear or cellular), for evaluation of contrast improvement factor (CIF), Bucky factor (BF) and signal difference-to-noise ratio improvement factor (SIF). It also allows the computation of the normalized average glandular dose, \\bar{D}_{g,N} . These quantities were studied for different breast thicknesses and compositions, anode/filter combinations and tube potentials. Results showed that the S/P increases linearly with breast thickness, varying slightly with breast composition or the spectrum used. Evaluation of grid performance showed that the cellular grid provides the highest CIF with smaller BF. The SIF was also greater for the cellular grid, although both grids showed SIF < 1 for thin breasts. Results for \\bar{D}_{g,N} showed that it increases with the half-value layer (HVL) of the spectrum, decreases considerably with breast thickness and has a small dependence on the anode/filter combination. Inclusion of interference effects of breast tissues affected the values of S/P obtained with the grid up to 25%, while the energy broadening effect produced smaller variations on the evaluated quantities.

  9. Multi-scaled normal mode analysis method for dynamics simulation of protein-membrane complexes: A case study of potassium channel gating motion correlations

    NASA Astrophysics Data System (ADS)

    Wu, Xiaokun; Han, Min; Ming, Dengming

    2015-10-01

    Membrane proteins play critically important roles in many cellular activities such as ions and small molecule transportation, signal recognition, and transduction. In order to fulfill their functions, these proteins must be placed in different membrane environments and a variety of protein-lipid interactions may affect the behavior of these proteins. One of the key effects of protein-lipid interactions is their ability to change the dynamics status of membrane proteins, thus adjusting their functions. Here, we present a multi-scaled normal mode analysis (mNMA) method to study the dynamics perturbation to the membrane proteins imposed by lipid bi-layer membrane fluctuations. In mNMA, channel proteins are simulated at all-atom level while the membrane is described with a coarse-grained model. mNMA calculations clearly show that channel gating motion can tightly couple with a variety of membrane deformations, including bending and twisting. We then examined bi-channel systems where two channels were separated with different distances. From mNMA calculations, we observed both positive and negative gating correlations between two neighboring channels, and the correlation has a maximum as the channel center-to-center distance is close to 2.5 times of their diameter. This distance is larger than recently found maximum attraction distance between two proteins embedded in membrane which is 1.5 times of the protein size, indicating that membrane fluctuation might impose collective motions among proteins within a larger area. The hybrid resolution feature in mNMA provides atomic dynamics information for key components in the system without costing much computer resource. We expect it to be a conventional simulation tool for ordinary laboratories to study the dynamics of very complicated biological assemblies. The source code is available upon request to the authors.

  10. Converging Stereotactic Radiotherapy Using Kilovoltage X-Rays: Experimental Irradiation of Normal Rabbit Lung and Dose-Volume Analysis With Monte Carlo Simulation

    SciTech Connect

    Kawase, Takatsugu; Kunieda, Etsuo Deloar, Hossain M.; Tsunoo, Takanori; Seki, Satoshi; Oku, Yohei; Saitoh, Hidetoshi; Saito, Kimiaki; Ogawa, Eileen N.; Ishizaka, Akitoshi; Kameyama, Kaori; Kubo, Atsushi

    2009-10-01

    Purpose: To validate the feasibility of developing a radiotherapy unit with kilovoltage X-rays through actual irradiation of live rabbit lungs, and to explore the practical issues anticipated in future clinical application to humans through Monte Carlo dose simulation. Methods and Materials: A converging stereotactic irradiation unit was developed, consisting of a modified diagnostic computed tomography (CT) scanner. A tiny cylindrical volume in 13 normal rabbit lungs was individually irradiated with single fractional absorbed doses of 15, 30, 45, and 60 Gy. Observational CT scanning of the whole lung was performed every 2 weeks for 30 weeks after irradiation. After 30 weeks, histopathologic specimens of the lungs were examined. Dose distribution was simulated using the Monte Carlo method, and dose-volume histograms were calculated according to the data. A trial estimation of the effect of respiratory movement on dose distribution was made. Results: A localized hypodense change and subsequent reticular opacity around the planning target volume (PTV) were observed in CT images of rabbit lungs. Dose-volume histograms of the PTVs and organs at risk showed a focused dose distribution to the target and sufficient dose lowering in the organs at risk. Our estimate of the dose distribution, taking respiratory movement into account, revealed dose reduction in the PTV. Conclusions: A converging stereotactic irradiation unit using kilovoltage X-rays was able to generate a focused radiobiologic reaction in rabbit lungs. Dose-volume histogram analysis and estimated sagittal dose distribution, considering respiratory movement, clarified the characteristics of the irradiation received from this type of unit.

  11. Production of Normal Mammalian Organ Culture Using a Medium Containing Mem-Alpha, Leibovitz L 15, Glucose Galactose Fructose

    NASA Technical Reports Server (NTRS)

    Goodwin, Thomas J. (Inventor); Wolf, David A. (Inventor); Spaulding, Glenn F. (Inventor); Prewett, Tacey L. (Inventor)

    1999-01-01

    Normal mammalian tissue and the culturing process has been developed for the three groups of organ, structural and blood tissue. The cells are grown in vitro under micro- gravity culture conditions and form three dimensional cells aggregates with normal cell function. The microgravity culture conditions may be microgravity or simulated microgravity created in a horizontal rotating wall culture vessel. The medium used for culturing the cells, especially a mixture of epithelial and mesenchymal cells contains a mixture of Mem-alpha and Leibovits L15 supplemented with glucose, galactose and fructose.

  12. Non-equilibrium molecular dynamics simulations of the transient Ludwig-Soret effect in a binary Lennard-Jones/spline mixture.

    PubMed

    Hafskjold, Bjørn

    2017-01-01

    A binary isotope mixture of Lennard-Jones/spline particles at equilibrium was perturbed by a sudden change in the system's boundary temperatures. The system's response was determined by non-equilibrium molecular dynamics (NEMD). Three transient processes were studied: 1) The propagation of a pressure (shock) wave, 2) heat diffusivity and conduction, and 3) thermal diffusion (the Ludwig-Soret effect). These three processes occur at different time scales, which makes it possible to separate them in one single NEMD run. The system was studied in liquid, supercritical, and dense gas states with various forms and strengths of the thermal perturbation. The results show that heat was initially transported by two separate mechanisms: 1) heat diffusion as described by the transient heat equation and 2) as a consequence of a pressure wave. The pressure wave travelled faster than the speed of sound, generating a shock wave in the system. Local equilibrium was found in the transient phase, even with very strong perturbations and in the shock front. Although the mass separation due to the Ludwig-Soret effect developed much slower than the pressure and temperature fields in the system at large, it was found that the Soret coefficient could be accurately determined from the initial phase of the transient and close to the heat source. This opens the possibility of a new way to analyse results from transient experiments and thereby minimize effects of gravity and convection due to buoyancy.

  13. Investigation of Jet Plume Effects on the Longitudinal Stability Characteristics of a Body of Revolution with Various Fin Configurations at Mach Numbers from 0.2 to 2.3 (Normal Jet Plume Simulator)

    DTIC Science & Technology

    1976-02-20

    configurations to investinate jet plune effects on missile longitudinal stability. A scries of cold air normal jets located downstream of the base... missile body. Thus, based on avail- able data, the desired unstable transonic-stable supersonic stability characteristics can be attained. Previous...as follows: Fin Chord ( in ) Semi span ( in ) Fl 5,0 2.5 F2 3.0 2.5 The plume simulator consisted of 24 sonic jets normal to the sting center- line

  14. Tracing Dynamics, Self-Diffusion, and Nanoscale Structural Heterogeneity of Pure and Binary Mixtures of Ionic Liquid 1-Hexyl-2,3-dimethylimidazolium Bis(fluorosulfonyl)imide with Acetonitrile: Insights from Molecular Dynamics Simulations.

    PubMed

    Kowsari, Mohammad H; Tohidifar, Leila

    2016-10-07

    All-atom molecular dynamics (MD) simulations of the ionic liquid (IL) 1-hexyl-2,3-dimethylimidazolium bis(fluorosulfonyl)imide ([C6mmim][FSI]) and its binary mixtures with acetonitrile (ACN) have been reported for the first time. The presence of ACN as a cosolvent, similar to the effect of increasing temperature, causes enhancements in the ion translational motion and fluidity of the IL, leading to significant improvement of ionic conductivity and self-diffusion, which is well explained by a microscopic structural analysis. In neat IL and a concentrated IL mixture, self-diffusion of the cation is higher than that of the corresponding anion; however, further addition of ACN into the diluted mixtures with IL molar fractions (xIL's) below 0.50 results in more weakened interactions among the nearest ACN-anion neighbors compared to those among the ACN-cation neighbors so that the number of isolated anions is more than that of isolated cations under this condition, and the anions diffuse faster than the cations, as expected on the basis of their relative sizes. The velocity autocorrelation function analysis indicates an inverse relation between xIL and the mean collision time of each species. Additionally, at a fixed xIL, both the mean collision time and velocity randomization time of ACN are shorter than those of the ions. Gradual addition of ACN changes the morphology of nanosegregated domains and tends to disrupt ionic clusters (i.e., it scatters and decomposes both the polar and nonpolar domains) compared with pure IL, whereas both the radial and spatial distribution functions show the stabilization role of ACN in the close-contact ion-pair association. On the other hand, increasing ACN causes weakening of the structural correlations of the cation-cation and anion-anion neighbors in the solutions. ACN molecules appeared as a bridge, with balanced affinities between the polar and nonpolar domains, and no indication was observed for aggregation of ACN molecules in the

  15. Mock-up tests on the combustion of hydrogen air mixture in the vertical tube simulating the CNS channel of the CARR

    NASA Astrophysics Data System (ADS)

    Yu, Qingfeng; Feng, Quanke; Kawai, Takeshi; Xu, Jian

    2007-01-01

    A two-phase thermo-siphon loop for removing nuclear heating and maintaining the stable liquid level in the moderator cell was adopted for the cold neutron source (CNS) of the China advanced research reactor (CARR). The moderator is liquid hydrogen. The two-phase thermo-siphon loop consists of the crescent-shape moderator cell, the moderator transfer tube, and the condenser. The hydrogen is supplied from the buffer tank to the condenser. The main feature of the loop is that the moderator cell is covered by the helium sub-cooling system. The cold helium gas from the helium refrigerator is firstly introduced into the helium sub-cooling system and then flows up through the tube covering the moderator transfer tube into the condenser. The main part of this system is installed in the CNS vertical channel made of aluminum alloy 6061 T6 (Al-6061-T6) of 6 mm in thickness, 270 mm in outer diameter and about 6 m in height. For confirming the safety of the CNS channel, the combustion tests using a tube compatible with the CNS channel were carried out using the hydrogen-air mixture under which air is introduced into the tube at 1 atmosphere, and then hydrogen gas is supplied from the gas cylinder up to the test pressures. And maximum test pressure is 0.14 MPa G. This condition is involved with the maximum design basis accident of the CARR-CNS. The peak pressure due to combustion was 1.09 MPa, and the design pressure of the CNS channel is 3 MPa. The safety of the CNS was thus verified even if the maximum design basis accident occurs. The pressure and stress distributions along the axial direction and the displacement of the tube were also measured.

  16. Orthogonal optical force separation simulation of particle and molecular species mixtures under direct current electroosmotic driven flow for applications in biological sample preparation.

    PubMed

    Staton, Sarah J R; Terray, Alex; Collins, Greg E; Hart, Sean J

    2013-04-01

    Presented here are the results from numerical simulations applying optical forces orthogonally to electroosmotically induced flow containing both molecular species and particles. Simulations were conducted using COMSOL v4.2a Multiphysics® software including the particle tracking module. The study addresses the application of optical forces to selectively remove particulates from a mixed sample stream that also includes molecular species in a pinched flow microfluidic device. This study explores the optimization of microfluidic cell geometry, magnitude of the applied direct current electric field, EOF rate, diffusion, and magnitude of the applied optical forces. The optimized equilibrium of these various contributing factors aids in the development of experimental conditions and geometry for future experimentation as well as directing experimental expectations, such as diffusional losses, separation resolution, and percent yield. The result of this work generated an optimized geometry with flow conditions leading to negligible diffusional losses of the molecular species while also being able to produce particle removal at near 100% levels. An analytical device, such as the one described herein with the capability to separate particulate and molecular species in a continuous, high-throughput fashion would be valuable by minimizing sample preparation and integrating gross sample collection seamlessly into traditional analytical detection methods.

  17. Optimized Mie potentials for phase equilibria: Application to noble gases and their mixtures with n-alkanes.

    PubMed

    Mick, Jason R; Soroush Barhaghi, Mohammad; Jackman, Brock; Rushaidat, Kamel; Schwiebert, Loren; Potoff, Jeffrey J

    2015-09-21

    Transferrable force fields, based on n-6 Mie potentials, are presented for noble gases. By tuning the repulsive exponent, ni, it is possible to simultaneously reproduce experimental saturated liquid densities and vapor pressures with high accuracy, from the normal boiling point to the critical point. Vapor-liquid coexistence curves for pure fluids are calculated using histogram reweighting Monte Carlo simulations in the grand canonical ensemble. For all noble gases, saturated liquid densities and vapor pressures are reproduced to within 1% and 4% of experiment, respectively. Radial distribution functions, extracted from NVT and NPT Monte Carlo simulations, are in similarly excellent agreement with experimental data. The transferability of the optimized force fields is assessed through calculations of binary mixture vapor-liquid equilibria. These mixtures include argon + krypton, krypton + xenon, methane + krypton, methane + xenon, krypton + ethane, and xenon + ethane. For all mixtures, excellent agreement with experiment is achieved without the introduction of any binary interaction parameters or multi-body interactions.

  18. Mixture of Skewed α-Stable Distributions

    NASA Astrophysics Data System (ADS)

    Shojaei, S. R. Hosseini; Nassiri, V.; Mohammadian, Gh. R.; Mohammadpour, A.

    2011-03-01

    Expectation maximization (EM) algorithm and the Bayesian techniques are two approaches for statistical inference of mixture models [3, 4]. By noting the advantages of the Bayesian methods, practitioners prefer them. However, implementing Markov chain Monte Carlo algorithms can be very complicated for stable distributions, due to the non-analytic density or distribution function formulas. In this paper, we introduce a new class of mixture of heavy-tailed distributions, called mixture of skewed stable distributions. Skewed stable distributions belongs to the exponential family and they have analytic density representation. It is shown that skewed stable distributions dominate skew stable distribution functions and they can be used to model heavy-tailed data. The class of skewed stable distributions has an analytic representation for its density function and the Bayesian inference can be done similar to the exponential family of distributions. Finally, mixture of skewed stable distributions are compared to the mixture of stable distributions through a simulations study.

  19. Uphill diffusion in multicomponent mixtures.

    PubMed

    Krishna, Rajamani

    2015-05-21

    Molecular diffusion is an omnipresent phenomena that is important in a wide variety of contexts in chemical, physical, and biological processes. In the majority of cases, the diffusion process can be adequately described by Fick's law that postulates a linear relationship between the flux of any species and its own concentration gradient. Most commonly, a component diffuses down the concentration gradient. The major objective of this review is to highlight a very wide variety of situations that cause the uphill transport of one constituent in the mixture. Uphill diffusion may occur in multicomponent mixtures in which the diffusion flux of any species is strongly coupled to that of its partner species. Such coupling effects often arise from strong thermodynamic non-idealities. For a quantitative description we need to use chemical potential gradients as driving forces. The transport of ionic species in aqueous solutions is coupled with its partner ions because of the electro-neutrality constraints; such constraints may accelerate or decelerate a specific ion. When uphill diffusion occurs, we observe transient overshoots during equilibration; the equilibration process follows serpentine trajectories in composition space. For mixtures of liquids, alloys, ceramics and glasses the serpentine trajectories could cause entry into meta-stable composition zones; such entry could result in phenomena such as spinodal decomposition, spontaneous emulsification, and the Ouzo effect. For distillation of multicomponent mixtures that form azeotropes, uphill diffusion may allow crossing of distillation boundaries that are normally forbidden. For mixture separations with microporous adsorbents, uphill diffusion can cause supra-equilibrium loadings to be achieved during transient uptake within crystals; this allows the possibility of over-riding adsorption equilibrium for achieving difficult separations.

  20. High-Resolution Numerical Simulation and Analysis of Mach Reflection Structures in Detonation Waves in Low-Pressure H 2 –O 2 –Ar Mixtures: A Summary of Results Obtained with the Adaptive Mesh Refinement Framework AMROC

    DOE PAGES

    Deiterding, Ralf

    2011-01-01

    Numerical simulation can be key to the understanding of the multidimensional nature of transient detonation waves. However, the accurate approximation of realistic detonations is demanding as a wide range of scales needs to be resolved. This paper describes a successful solution strategy that utilizes logically rectangular dynamically adaptive meshes. The hydrodynamic transport scheme and the treatment of the nonequilibrium reaction terms are sketched. A ghost fluid approach is integrated into the method to allow for embedded geometrically complex boundaries. Large-scale parallel simulations of unstable detonation structures of Chapman-Jouguet detonations in low-pressure hydrogen-oxygen-argon mixtures demonstrate the efficiency of the described techniquesmore » in practice. In particular, computations of regular cellular structures in two and three space dimensions and their development under transient conditions, that is, under diffraction and for propagation through bends are presented. Some of the observed patterns are classified by shock polar analysis, and a diagram of the transition boundaries between possible Mach reflection structures is constructed.« less

  1. Multivariate normality

    NASA Technical Reports Server (NTRS)

    Crutcher, H. L.; Falls, L. W.

    1976-01-01

    Sets of experimentally determined or routinely observed data provide information about the past, present and, hopefully, future sets of similarly produced data. An infinite set of statistical models exists which may be used to describe the data sets. The normal distribution is one model. If it serves at all, it serves well. If a data set, or a transformation of the set, representative of a larger population can be described by the normal distribution, then valid statistical inferences can be drawn. There are several tests which may be applied to a data set to determine whether the univariate normal model adequately describes the set. The chi-square test based on Pearson's work in the late nineteenth and early twentieth centuries is often used. Like all tests, it has some weaknesses which are discussed in elementary texts. Extension of the chi-square test to the multivariate normal model is provided. Tables and graphs permit easier application of the test in the higher dimensions. Several examples, using recorded data, illustrate the procedures. Tests of maximum absolute differences, mean sum of squares of residuals, runs and changes of sign are included in these tests. Dimensions one through five with selected sample sizes 11 to 101 are used to illustrate the statistical tests developed.

  2. Packed-Bed Reactor Study of NETL Sample 196c for the Removal of Carbon Dioxide from Simulated Flue Gas Mixture

    SciTech Connect

    Hoffman, James S.; Hammache, Sonia; Gray, McMahan L.; Fauth Daniel J.; Pennline, Henry W.

    2012-04-24

    An amine-based solid sorbent process to remove CO2 from flue gas has been investigated. The sorbent consists of polyethylenimine (PEI) immobilized onto silica (SiO2) support. Experiments were conducted in a packed-bed reactor and exit gas composition was monitored using mass spectrometry. The effects of feed gas composition (CO2 and H2O), temperature, and simulated steam regeneration were examined for both the silica support as well as the PEI-based sorbent. The artifact of the empty reactor was also quantified. Sorbent CO2 capacity loading was compared to thermogravimetric (TGA) results to further characterize adsorption isotherms and better define CO2 working capacity. Sorbent stability was monitored by periodically repeating baseline conditions throughout the parametric testing and replacing with fresh sorbent as needed. The concept of the Basic Immobilized Amine Sorbent (BIAS) Process using this sorbent within a system where sorbent continuously flows between the absorber and regenerator was introduced. The basic tenet is to manipulate or control the level of moisture on the sorbent as it travels around the sorbent circulation path between absorption and regeneration stages to minimize its effect on regeneration heat duty.

  3. Continuous recovery of valine in a model mixture of amino acids and salt from Corynebacterium bacteria fermentation using a simulated moving bed chromatography.

    PubMed

    Park, Chanhun; Nam, Hee-Geun; Jo, Se-Hee; Wang, Nien-Hwa Linda; Mun, Sungyong

    2016-02-26

    The economical efficiency of valine production in related industries is largely affected by the performance of a valine separation process, in which valine is to be separated from leucine, alanine, and ammonium sulfate. Such separation is currently handled by a batch-mode hybrid process based on ion-exchange and crystallization schemes. To make a substantial improvement in the economical efficiency of an industrial valine production, such a batch-mode process based on two different separation schemes needs to be converted into a continuous-mode separation process based on a single separation scheme. To address this issue, a simulated moving bed (SMB) technology was applied in this study to the development of a continuous-mode valine-separation chromatographic process with uniformity in adsorbent and liquid phases. It was first found that a Chromalite-PCG600C resin could be eligible for the adsorbent of such process, particularly in an industrial scale. The intrinsic parameters of each component on the Chromalite-PCG600C adsorbent were determined and then utilized in selecting a proper set of configurations for SMB units, columns, and ports, under which the SMB operating parameters were optimized with a genetic algorithm. Finally, the optimized SMB based on the selected configurations was tested experimentally, which confirmed its effectiveness in continuous separation of valine from leucine, alanine, ammonium sulfate with high purity, high yield, high throughput, and high valine product concentration. It is thus expected that the developed SMB process in this study will be able to serve as one of the trustworthy ways of improving the economical efficiency of an industrial valine production process.

  4. Near azeotropic mixture substitute

    NASA Technical Reports Server (NTRS)

    Jones, Jack A. (Inventor)

    1996-01-01

    The present invention comprises a refrigerant mixture consisting of a first mole fraction of 1,1,1,2-tetrafluoroethane (R134a) and a second mole fraction of a component selected from the group consisting of a mixture of CHClFCF.sub.3 (R124) and CH.sub.3 CClF.sub.2 (R142b); a mixture of CHF.sub.2 CH.sub.3 (R152a) and CHClFCF.sub.3 (R124); a mixture of CHF.sub.2 CH.sub.3 (R152a) and CH.sub.3 CClF.sub.2 (R142b); and a mixture of CHClFCF.sub.3 (R124), CH.sub.3 CClF.sub.2 (R142b) and CHF.sub.2 CH.sub.3 (R152a).

  5. Adaptation to New Microphones Using Tied-Mixture Normalization

    DTIC Science & Technology

    1994-01-01

    and WSJ1 corpora with 12 and 50 hours of recorded speech respectively. We trained two sets of phonetic models using the WSJ0 corpus and the com...speech. However the error rate reduces by a factor of 2 for some con- ditions by adding 50 hours of training high quality recorded speech...under Contract Nos. N00014-91-C-0115, and N00014-92-C-0035. References 1. A. Acero , and R.M. Stem, "Environmental Robustness in Au- tomatic Speech

  6. Perception of trigeminal mixtures.

    PubMed

    Filiou, Renée-Pier; Lepore, Franco; Bryant, Bruce; Lundström, Johan N; Frasnelli, Johannes

    2015-01-01

    The trigeminal system is a chemical sense allowing for the perception of chemosensory information in our environment. However, contrary to smell and taste, we lack a thorough understanding of the trigeminal processing of mixtures. We, therefore, investigated trigeminal perception using mixtures of 3 relatively receptor-specific agonists together with one control odor in different proportions to determine basic perceptual dimensions of trigeminal perception. We found that 4 main dimensions were linked to trigeminal perception: sensations of intensity, warmth, coldness, and pain. We subsequently investigated perception of binary mixtures of trigeminal stimuli by means of these 4 perceptual dimensions using different concentrations of a cooling stimulus (eucalyptol) mixed with a stimulus that evokes warmth perception (cinnamaldehyde). To determine if sensory interactions are mainly of central or peripheral origin, we presented stimuli in a physical "mixture" or as a "combination" presented separately to individual nostrils. Results showed that mixtures generally yielded higher ratings than combinations on the trigeminal dimensions "intensity," "warm," and "painful," whereas combinations yielded higher ratings than mixtures on the trigeminal dimension "cold." These results suggest dimension-specific interactions in the perception of trigeminal mixtures, which may be explained by particular interactions that may take place on peripheral or central levels.

  7. Robust nonlinear system identification: Bayesian mixture of experts using the t-distribution

    NASA Astrophysics Data System (ADS)

    Baldacchino, Tara; Worden, Keith; Rowson, Jennifer

    2017-02-01

    A novel variational Bayesian mixture of experts model for robust regression of bifurcating and piece-wise continuous processes is introduced. The mixture of experts model is a powerful model which probabilistically splits the input space allowing different models to operate in the separate regions. However, current methods have no fail-safe against outliers. In this paper, a robust mixture of experts model is proposed which consists of Student-t mixture models at the gates and Student-t distributed experts, trained via Bayesian inference. The Student-t distribution has heavier tails than the Gaussian distribution, and so it is more robust to outliers, noise and non-normality in the data. Using both simulated data and real data obtained from the Z24 bridge this robust mixture of experts performs better than its Gaussian counterpart when outliers are present. In particular, it provides robustness to outliers in two forms: unbiased parameter regression models, and robustness to overfitting/complex models.

  8. SEPARATION OF FLUID MIXTURES

    DOEpatents

    Lipscomb, R.; Craig, A.; Labrow, S.; Dunn, J.F.

    1958-10-28

    An apparatus is presented for separating gaseous mixtures by selectively freezing a constituent of the mixture and subsequently separating the frozen gas. The gas mixture is passed through a cylinder fltted with a cooling jacket, causing one gas to freeze on the walls of the cylinder. A set of scraper blades are provided in the interior of the cyllnder, and as the blades oscillate, the frozen gas is scraped to the bottom of the cylinder. Means are provided for the frozen material to pass into a heating chamber where it is vaporized and the product gas collected.

  9. Numerical modelling of continuous spin detonation in rich methane-oxygen mixture

    NASA Astrophysics Data System (ADS)

    Trotsyuk, A. V.

    2016-10-01

    A numerical simulation of a two-dimensional structure of the detonation wave (DW) in a rich (equivalence ratio φ=1.5) methane-air mixture at normal initial condition has been conducted. The computations have been performed in a wide range of channel heights. From the analysis of the flow structure and the number of primary transverse waves in the channel, the dominant size of the detonation cell for studied mixture has been determined to be 45÷50 cm. Based on the fundamental studies of multi-front (cellular) structure of the classical propagating DW in methane mixtures, numerical simulation of continuous spin detonation (CSD) of rich (φ=1.2) methane-oxygen mixture has been carried out in the cylindrical detonation chamber (DC) of the rocket-type engine. We studied the global flow structure in DC, and the detailed structure of the front of the rotating DW. Integral characteristics of the detonation process - the distribution of average values of static and total pressure along the length of the DC, and the value of specific impulse have been obtained. The geometric limit of stable existence of CSD has been determined.

  10. Carbonaceous materials water mixtures

    SciTech Connect

    Papalos, J.G.; Sinka, J.V.

    1985-04-30

    Particulate carbonaceous materials water mixtures are prepared by adding a condensate which is a condensation product of an aldehyde having from about 1 to about 7 carbon atoms, a benzene derivative such as benzene sulfonic acid, an alkyl benzene sulfonic acid having at least one alkyl group of from about 1 to about 20 carbon atoms and mixtures thereof, and optionally, and a naphthalene derivative such as naphthalene sulfonic acid, an alkyl naphthalene sulfonic acid having at least one alkyl group of from about 1 to about 12 carbon atoms and mixtures thereof. The condensate is added in an amount sufficient to reduce viscosity of the water mixture of carbonaceous materials, to stabilize carbonaceous materials in the water network and to improve pumpability. An acid form of the condensate or a salt may be added.

  11. Condensate Mixtures and Tunneling

    SciTech Connect

    Timmermans, E.

    1998-09-14

    The experimental study of condensate mixtures is a particularly exciting application of the recently developed atomic-trap Bose-Einstein condensate (BEC) technology: such multiple condensates represent the first laboratory systems of distinguishable boson superfluid mixtures. In addition, as the authors point out in this paper, the possibility of inter-condensate tunneling greatly enhances the richness of the condensate mixture physics. Not only does tunneling give rise to the oscillating particle currents between condensates of different chemical potentials, such as those studied extensively in the condensed matter Josephson junction experiments, it also affects the near-equilibrium dynamics and stability of the condensate mixtures. In particular, the stabilizing influence of tunneling with respect to spatial separation (phase separation) could be of considerable practical importance to the atomic trap systems. Furthermore, the creation of mixtures of atomic and molecular condensates could introduce a novel type of tunneling process, involving the conversion of a pair of atomic condensate bosons into a single molecular condensate boson. The static description of condensate mixtures with such type of pair tunneling suggests the possibility of observing dilute condensates with the liquid-like property of a self-determined density.

  12. Capillary condensation and adsorption of binary mixtures.

    PubMed

    Weinberger, B; Darkrim-Lamari, F; Levesque, D

    2006-06-21

    The adsorption of equimolar binary mixtures of hydrogen-carbon dioxide, hydrogen-methane, and methane-carbon dioxide in porous material models is determined by grand canonical Monte Carlo simulations. The material models have an adsorbent surface similar to that of nanofibers with a herringbone structure. Our main result, which is relevant for hydrogen purification and carbon dioxide capture, is that the adsorption selectivities calculated for the mixtures can differ significantly from those deduced from simulations of the adsorption of pure gases, in particular, when one of the adsorbed gases presents a capillary condensation induced by confinement within the pore network. A comparison of our data is also made with theoretical models used in the literature for predicting the properties of the mixture adsorption.

  13. Mixtures of planetary ices at extreme conditions.

    PubMed

    Lee, Mal-Soon; Scandolo, Sandro

    2011-02-08

    The interiors of Neptune and Uranus are believed to be primarily composed of a fluid mixture of methane and water. The mixture is subjected to pressures up to several hundred gigapascal, causing the ionization of water. Laboratory and simulation studies so far have focused on the properties of the individual components. Here we show, using first-principle molecular dynamic simulations, that the properties of the mixed fluid are qualitatively different with respect to those of its components at the same conditions. We observe a pressure-induced softening of the methane-water intermolecular repulsion that points to an enhancement of mixing under extreme conditions. Ionized water causes the progressive ionization of methane and the mixture becomes electronically conductive at milder conditions than pure water, indicating that the planetary magnetic field of Uranus and Neptune may originate at shallower depths than currently assumed.

  14. Phase separations in a copolymer copolymer mixture

    NASA Astrophysics Data System (ADS)

    Zhang, Jin-Jun; Jin, Guojun; Ma, Yuqiang

    2006-01-01

    We propose a three-order-parameter model to study the phase separations in a diblock copolymer-diblock copolymer mixture. The cell dynamical simulations provide rich information about the phase evolution and structural formation, especially the appearance of onion-rings. The parametric dependence and physical reason for the domain growth of onion-rings are discussed.

  15. A Bayesian mixture of semiparametric mixed-effects joint models for skewed-longitudinal and time-to-event data.

    PubMed

    Chen, Jiaqing; Huang, Yangxin

    2015-09-10

    In longitudinal studies, it is of interest to investigate how repeatedly measured markers in time are associated with a time to an event of interest, and in the mean time, the repeated measurements are often observed with the features of a heterogeneous population, non-normality, and covariate measured with error because of longitudinal nature. Statistical analysis may complicate dramatically when one analyzes longitudinal-survival data with these features together. Recently, a mixture of skewed distributions has received increasing attention in the treatment of heterogeneous data involving asymmetric behaviors across subclasses, but there are relatively few studies accommodating heterogeneity, non-normality, and measurement error in covariate simultaneously arose in longitudinal-survival data setting. Under the umbrella of Bayesian inference, this article explores a finite mixture of semiparametric mixed-effects joint models with skewed distributions for longitudinal measures with an attempt to mediate homogeneous characteristics, adjust departures from normality, and tailor accuracy from measurement error in covariate as well as overcome shortages of confidence in specifying a time-to-event model. The Bayesian mixture of joint modeling offers an appropriate avenue to estimate not only all parameters of mixture joint models but also probabilities of class membership. Simulation studies are conducted to assess the performance of the proposed method, and a real example is analyzed to demonstrate the methodology. The results are reported by comparing potential models with various scenarios.

  16. Shear viscosity for a heated granular binary mixture at low density.

    PubMed

    Montanero, José María; Garzó, Vicente

    2003-02-01

    The shear viscosity for a heated granular binary mixture of smooth hard spheres at low density is analyzed. The mixture is heated by the action of an external driving force (Gaussian thermostat) that exactly compensates for cooling effects associated with the dissipation of collisions. The study is made from the Boltzmann kinetic theory, which is solved by using two complementary approaches. First, a normal solution of the Boltzmann equation via the Chapman-Enskog method is obtained up to first order in the spatial gradients. The mass, heat, and momentum fluxes are determined and the corresponding transport coefficients identified. As in the free cooling case [V. Garzó and J. W. Dufty, Phys. Fluids 14, 1476 (2002)], practical evaluation requires a Sonine polynomial approximation, and here it is mainly illustrated in the case of the shear viscosity. Second, to check the accuracy of the Chapman-Enskog results, the Boltzmann equation is numerically solved by means of the direct simulation Monte Carlo method. The simulation is performed for a system under uniform shear flow, using the Gaussian thermostat to control inelastic cooling. The comparison shows an excellent agreement between theory and simulation over a wide range of values of the restitution coefficients and the parameters of the mixture (masses, concentrations, and sizes).

  17. I. Cognitive and instructional factors relating to students' development of personal models of chemical systems in the general chemistry laboratory II. Solvation in supercritical carbon dioxide/ethanol mixtures studied by molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Anthony, Seth

    likely to appear in students' post-laboratory refined models. These discussions during the laboratory period are primarily prompted by factors external to the students or their laboratory groups such as questions posed by the instructor or laboratory materials. Part II. Solvation of polar molecules within non-polar supercritical carbon dioxide is often facilitated by the introduction of polar cosolvents as entrainers, which are believed to preferentially surround solute molecules. Molecular dynamics simulations of supercritical carbon dioxide/ethanol mixtures reveal that ethanol molecules form hydrogen-bonded aggregates of varying sizes and structures, with cyclic tetramers and pentamers being unusually prevalent. The dynamics of ethanol molecules within these mixtures at a range of thermodynamic conditions can largely be explained by differences in size and structure in these aggregates. Simulations that include solute molecules reveal enhancement of the polar cosolvent around hydrogen-bonding sites on the solute molecules, corroborating and helping to explain previously reported experimental trends in solute mobility.

  18. Quantifying surface normal estimation

    NASA Astrophysics Data System (ADS)

    Reid, Robert B.; Oxley, Mark E.; Eismann, Michael T.; Goda, Matthew E.

    2006-05-01

    An inverse algorithm for surface normal estimation from thermal polarimetric imagery was developed and used to quantify the requirements on a priori information. Building on existing knowledge that calculates the degree of linear polarization (DOLP) and the angle of polarization (AOP) for a given surface normal in a forward model (from an object's characteristics to calculation of the DOLP and AOP), this research quantifies the impact of a priori information with the development of an inverse algorithm to estimate surface normals from thermal polarimetric emissions in long-wave infrared (LWIR). The inverse algorithm assumes a polarized infrared focal plane array capturing LWIR intensity images which are then converted to Stokes vectors. Next, the DOLP and AOP are calculated from the Stokes vectors. Last, the viewing angles, θ v, to the surface normals are estimated assuming perfect material information about the imaged scene. A sensitivity analysis is presented to quantitatively describe the a priori information's impact on the amount of error in the estimation of surface normals, and a bound is determined given perfect information about an object. Simulations explored the impact of surface roughness (σ) and the real component (n) of a dielectric's complex index of refraction across a range of viewing angles (θ v) for a given wavelength of observation.

  19. Determining inert content in coal dust/rock dust mixture

    DOEpatents

    Sapko, Michael J.; Ward, Jr., Jack A.

    1989-01-01

    A method and apparatus for determining the inert content of a coal dust and rock dust mixture uses a transparent window pressed against the mixture. An infrared light beam is directed through the window such that a portion of the infrared light beam is reflected from the mixture. The concentration of the reflected light is detected and a signal indicative of the reflected light is generated. A normalized value for the generated signal is determined according to the relationship .phi.=(log i.sub.c `log i.sub.co) / (log i.sub.c100 -log i.sub.co) where i.sub.co =measured signal at 0% rock dust i.sub.c100 =measured signal at 100% rock dust i.sub.c =measured signal of the mixture. This normalized value is then correlated to a predetermined relationship of .phi. to rock dust percentage to determine the rock dust content of the mixture. The rock dust content is displayed where the percentage is between 30 and 100%, and an indication of out-of-range is displayed where the rock dust percent is less than 30%. Preferably, the rock dust percentage (RD%) is calculated from the predetermined relationship RD%=100+30 log .phi.. where the dust mixture initially includes moisture, the dust mixture is dried before measuring by use of 8 to 12 mesh molecular-sieves which are shaken with the dust mixture and subsequently screened from the dust mixture.

  20. Use of log-skew-normal distribution in analysis of continuous data with a discrete component at zero.

    PubMed

    Chai, High Seng; Bailey, Kent R

    2008-08-15

    The problem of analyzing a continuous variable with a discrete component is addressed within the framework of the mixture model proposed by Moulton and Halsey (Biometrics 1995; 51:1570-1578). The model can be generalized by the introduction of the log-skew-normal distribution for the continuous component, and the fit can be significantly improved by its use, while retaining the interpretation of regression parameter estimates. Simulation studies and application to a real data set are used for demonstration.

  1. Thermophysical Properties of Fluids and Fluid Mixtures

    SciTech Connect

    Sengers, Jan V.; Anisimov, Mikhail A.

    2004-05-03

    The major goal of the project was to study the effect of critical fluctuations on the thermophysical properties and phase behavior of fluids and fluid mixtures. Long-range fluctuations appear because of the presence of critical phase transitions. A global theory of critical fluctuations was developed and applied to represent thermodynamic properties and transport properties of molecular fluids and fluid mixtures. In the second phase of the project, the theory was extended to deal with critical fluctuations in complex fluids such as polymer solutions and electrolyte solutions. The theoretical predictions have been confirmed by computer simulations and by light-scattering experiments. Fluctuations in fluids in nonequilibrium states have also been investigated.

  2. One- and multi-component theories of mixtures

    SciTech Connect

    Ree, F.H.

    1993-07-01

    We describe one-component statistical mechanical theories and van der Waal`s effective one-component mixture model. We then show how to apply them to mixtures (containing CO{sub 2}) to extract reliable unlike-pair potential involving CO{sub 2} molecules as well as their dissociation products. A more fundamental approach will require the development of a perturbation or variational theory of mixtures based on a non-additive hard-sphere mixture reference system. Recent progresses made in this direction by means of an integral equation and computer simulations is described.

  3. SIMULATION-BASED WEATHER NORMALIZATION APPROACH TO STUDY THE IMPACT OF WEATHER ON ENERGY USE OF BUILDINGS IN THE U.S.

    SciTech Connect

    Makhmalbaf, Atefe; Srivastava, Viraj; Wang, Na

    2013-08-05

    Weather normalization is a crucial task in several applications related to building energy conservation such as retrofit measurements and energy rating. This paper documents preliminary results found from an effort to determine a set of weather adjustment coefficients that can be used to smooth out impacts of weather on energy use of buildings in 1020 weather location sites available in the U.S. The U.S. Department of Energy (DOE) commercial reference building models are adopted as hypothetical models with standard operations to deliver consistency in modeling. The correlation between building envelop design, HVAC system design and properties for different building types and the change in heating and cooling energy consumption caused by variations in weather is examined.

  4. Mixture models for estimating the size of a closed population when capture rates vary among individuals

    USGS Publications Warehouse

    Dorazio, R.M.; Royle, J. Andrew

    2003-01-01

    We develop a parameterization of the beta-binomial mixture that provides sensible inferences about the size of a closed population when probabilities of capture or detection vary among individuals. Three classes of mixture models (beta-binomial, logistic-normal, and latent-class) are fitted to recaptures of snowshoe hares for estimating abundance and to counts of bird species for estimating species richness. In both sets of data, rates of detection appear to vary more among individuals (animals or species) than among sampling occasions or locations. The estimates of population size and species richness are sensitive to model-specific assumptions about the latent distribution of individual rates of detection. We demonstrate using simulation experiments that conventional diagnostics for assessing model adequacy, such as deviance, cannot be relied on for selecting classes of mixture models that produce valid inferences about population size. Prior knowledge about sources of individual heterogeneity in detection rates, if available, should be used to help select among classes of mixture models that are to be used for inference.

  5. Detailed Kinetic Modeling of Gasoline Surrogate Mixtures

    SciTech Connect

    Mehl, M; Curran, H J; Pitz, W J; Westbrook, C K

    2009-03-09

    Real fuels are complex mixtures of thousands of hydrocarbon compounds including linear and branched paraffins, naphthenes, olefins and aromatics. It is generally agreed that their behavior can be effectively reproduced by simpler fuel surrogates containing a limited number of components. In this work, a recently revised version of the kinetic model by the authors is used to analyze the combustion behavior of several components relevant to gasoline surrogate formulation. Particular attention is devoted to linear and branched saturated hydrocarbons (PRF mixtures), olefins (1-hexene) and aromatics (toluene). Model predictions for pure components, binary mixtures and multi-component gasoline surrogates are compared with recent experimental information collected in rapid compression machine, shock tube and jet stirred reactors covering a wide range of conditions pertinent to internal combustion engines. Simulation results are discussed focusing attention on the mixing effects of the fuel components.

  6. Bayesian meta-analysis for longitudinal data models using multivariate mixture priors.

    PubMed

    Lopes, Hedibert Freitas; Müller, Peter; Rosner, Gary L

    2003-03-01

    We propose a class of longitudinal data models with random effects that generalizes currently used models in two important ways. First, the random-effects model is a flexible mixture of multivariate normals, accommodating population heterogeneity, outliers, and nonlinearity in the regression on subject-specific covariates. Second, the model includes a hierarchical extension to allow for meta-analysis over related studies. The random-effects distributions are decomposed into one part that is common across all related studies (common measure), and one part that is specific to each study and that captures the variability intrinsic between patients within the same study. Both the common measure and the study-specific measures are parameterized as mixture-of-normals models. We carry out inference using reversible jump posterior simulation to allow a random number of terms in the mixtures. The sampler takes advantage of the small number of entertained models. The motivating application is the analysis of two studies carried out by the Cancer and Leukemia Group B (CALGB). In both studies, we record for each patient white blood cell counts (WBC) over time to characterize the toxic effects of treatment. The WBCs are modeled through a nonlinear hierarchical model that gathers the information from both studies.

  7. Lateral organization of complex lipid mixtures from multiscale modeling

    NASA Astrophysics Data System (ADS)

    Tumaneng, Paul W.; Pandit, Sagar A.; Zhao, Guijun; Scott, H. L.

    2010-02-01

    The organizational properties of complex lipid mixtures can give rise to functionally important structures in cell membranes. In model membranes, ternary lipid-cholesterol (CHOL) mixtures are often used as representative systems to investigate the formation and stabilization of localized structural domains ("rafts"). In this work, we describe a self-consistent mean-field model that builds on molecular dynamics simulations to incorporate multiple lipid components and to investigate the lateral organization of such mixtures. The model predictions reveal regions of bimodal order on ternary plots that are in good agreement with experiment. Specifically, we have applied the model to ternary mixtures composed of dioleoylphosphatidylcholine:18:0 sphingomyelin:CHOL. This work provides insight into the specific intermolecular interactions that drive the formation of localized domains in these mixtures. The model makes use of molecular dynamics simulations to extract interaction parameters and to provide chain configuration order parameter libraries.

  8. On the ideality of binary mixtures of ionic liquids.

    PubMed

    Brüssel, Marc; Brehm, Martin; Pensado, Alfonso S; Malberg, Friedrich; Ramzan, Muhammad; Stark, Annegret; Kirchner, Barbara

    2012-10-14

    In this work, structural and dynamical properties of the binary mixture of 1-ethyl-3-methyl-imidazolium chloride and 1-ethyl-3-methyl-imidazolium thiocyanate are investigated from ab initio molecular dynamics simulations and compared to the pure ionic liquids. Furthermore, the binary mixture is simulated with two different densities to gain insight into how the selected density affects the different properties. In addition, a simple NMR experiment is carried out to investigate the changes of the chemical shifts of the hydrogen atoms due to the composition of the mixture.

  9. Enhancement of iron(II)-dependent reduction of nitrite to nitric oxide by thiocyanate and accumulation of iron(II)/thiocyanate/nitric oxide complex under conditions simulating the mixture of saliva and gastric juice.

    PubMed

    Takahama, Umeo; Hirota, Sachiko

    2012-01-13

    Iron(III) ingested as a food component or supplement for iron deficiencies can react with salivary SCN(-) to produce Fe(SCN)(2+) and can be reduced to iron(II) by ascorbic acid in the stomach. Iron(II) generated in the stomach can react with salivary nitrite and SCN(-) to produce nitric oxide (NO) and FeSCN(+), respectively. The purpose of this investigation is to make clear the reactions among nitrite, SCN(-), iron ions, and ascorbic acid under conditions simulating the mixture of saliva and gastric juice. Iron(II)-dependent reduction of nitrite to NO was enhanced by SCN(-) in acidic buffer solutions, and the oxidation product of iron(II) reacted with SCN(-) to produce Fe(SCN)(2+). Almost all of the NO produced was autoxidized to N(2)O(3) under aerobic conditions. Iron(II)-dependent production of NO was also observed in acidified saliva. Under anaerobic conditions, NO transformed Fe(SCN)(2+) and FeSCN(+) to Fe(SCN)NO(+) in acidic buffer solutions. Fe(SCN)NO(+) was also formed under aerobic conditions when excess ascorbic acid was added to iron(II)/nitrite/SCN(-) systems in acidic buffer solutions and acidified saliva. The Fe(SCN)NO(+) formed was transformed to Fe(SCN)(2+) and iron(III) at pH 2.0 and pH 7.4, respectively, by O(2). Salivary glycoproteins could complex with iron(III) in the stomach preventing the formation of Fe(SCN)(2+). Ascorbic acid reduced iron(III) to iron(II) to react with nitrite and SCN(-) as described above. The above results suggest (i) that iron(II) can have toxic effects on the stomach through the formation of reactive nitrogen oxide species from NO when supplemented without ascorbic acid and through the formation of both reactive nitrogen oxide species and Fe(SCN)NO(+) when supplemented with ascorbic acid, and (ii) that the toxic effects of iron(III) seemed to be smaller than and similar to those of iron(II) when supplemented without and with ascorbic acid, respectively. Possible mechanisms that cause oxidative stress on the stomach

  10. Prevalence Incidence Mixture Models

    Cancer.gov

    The R package and webtool fits Prevalence Incidence Mixture models to left-censored and irregularly interval-censored time to event data that is commonly found in screening cohorts assembled from electronic health records. Absolute and relative risk can be estimated for simple random sampling, stratified sampling, and two-phase stratified sampling. Non-parametric (absolute risks only), semi-parametric, weakly-parametric (using B-splines), and some fully parametric (such as the logistic-Weibull) models are supported.

  11. Evaporation of Liquid Hydrocarbon Mixtures on Titan

    NASA Astrophysics Data System (ADS)

    Luspay-Kuti, Adrienn; Chevrier, V. F.; Rivera-Valentin, E. G.; Singh, S.; Roe, L. A.; Wagner, A.

    2013-10-01

    Besides Earth, Titan is the only other known planetary body with proven stable liquids on its surface. The hydrological cycle of these liquid hydrocarbon mixtures is critical in understanding Titan’s atmosphere and surface features. Evaporation of liquid surface bodies has been indirectly observed as shoreline changes from measurements by Cassini ISS and RADAR (Hayes et al. 2011, Icarus 211, 655-671; Turtle et al. 2011, Science 18, 1414-1417.), but the long seasons of Saturn strongly limit the time span of these observations and their validity over the course of an entire Titan year. Using a novel Titan simulation chamber, the evaporation rate of liquid methane and dissolved nitrogen mixture under Titan surface conditions was derived (Luspay-Kuti et al. 2012, GRL 39, L23203), which is especially applicable to low latitude transient liquids. Polar lakes, though, are expected to be composed of a variety of hydrocarbons, primarily a mixture of ethane and methane (e.g. Cordier et al. 2009, ApJL 707, L128-L131). Here we performed laboratory simulations of ethane-methane mixtures with varying mole fraction under conditions suitable for the polar regions of Titan. We will discuss results specifically addressing the evaporation behavior as the solution becomes increasingly ethane dominated, providing quantitative values for the evaporation rate at every step. These laboratory results are relevant to polar lakes, such as Ontario Lacus, and can shed light on their stability.

  12. Spinodal decomposition of chemically reactive binary mixtures

    NASA Astrophysics Data System (ADS)

    Lamorgese, A.; Mauri, R.

    2016-08-01

    We simulate the influence of a reversible isomerization reaction on the phase segregation process occurring after spinodal decomposition of a deeply quenched regular binary mixture, restricting attention to systems wherein material transport occurs solely by diffusion. Our theoretical approach follows a diffuse-interface model of partially miscible binary mixtures wherein the coupling between reaction and diffusion is addressed within the frame of nonequilibrium thermodynamics, leading to a linear dependence of the reaction rate on the chemical affinity. Ultimately, the rate for an elementary reaction depends on the local part of the chemical potential difference since reaction is an inherently local phenomenon. Based on two-dimensional simulation results, we express the competition between segregation and reaction as a function of the Damköhler number. For a phase-separating mixture with components having different physical properties, a skewed phase diagram leads, at large times, to a system converging to a single-phase equilibrium state, corresponding to the absolute minimum of the Gibbs free energy. This conclusion continues to hold for the critical phase separation of an ideally perfectly symmetric binary mixture, where the choice of final equilibrium state at large times depends on the initial mean concentration being slightly larger or less than the critical concentration.

  13. Intersection patterns of normal faults in the Lufeng Sag of Pearl River Mouth Basin, China: Insights from 4D physical simulations

    NASA Astrophysics Data System (ADS)

    Yu, Fusheng; Koyi, Hemin; Zhang, Xiangtao

    2016-12-01

    Interpretation of seismic data from the Lufeng Sag of the Pearl River Mouth Basin (PRMB) in the northern part of South China Sea shows that different intersection patterns developed in the cover units above basement normal faults. A series of analogue models are used to investigate the intersection patterns and deformation in the sedimentary cover sequences above a basement horst bounded by two non-parallel faults. Modelling results show that during their upward propagation, the basement faults may intersect within the cover sequences and form a graben above the basement horst. Length and width of the graben increase with cover thickness. The strike and dip intersection points are controlled directly by the thickness of the cover sequences, dip and strike of the basement faults, and width of the basement horst. The intersection point migrates along the axis of the graben toward the wide end of the basement horst, when the cover sequence thickens. In contrast, it migrates toward the narrow end of the basement horst, where both fault dip and angle of strike difference increase. The intersection point moves upward with increasing width of the basement horst crest. Model profiles also indicate that in the presence of a ductile layer between the cover and basement such intersection patterns do not form. Interpretation of seismic data and model results show that the intersection pattern developed in the Lufeng Sag is a result of propagation of basement faults into cover units during different extension stages of the basin. Results of this study can be applied to many other sedimentary basins where such fault intersection patterns are likely to form when non-parallel conjugate basement faults are active during sedimentation.

  14. Quantification of furanic compounds in coated deep-fried products simulating normal preparation and consumption: optimisation of HS-SPME analytical conditions by response surface methodology.

    PubMed

    Pérez-Palacios, T; Petisca, C; Melo, A; Ferreira, I M P L V O

    2012-12-01

    The validation of a method for the simultaneous quantification of furanic compounds in coated deep-fried samples processed and handled as usually consumed is presented. The deep-fried food was grinded using a device that simulates the mastication, and immediately analysed by headspace solid phase microextraction coupled to gas chromatography-mass spectrometry. Parameters affecting the efficiency of HS-SPME procedure were selected by response surface methodology, using a 2(3) full-factorial central composite design. Optimal conditions were achieved using 2g of sample, 3g of NaCl and 40min of absorption time at 37°C. Consistency between predicted and experimented values was observed and quality parameters of the method were established. As a result, furan, 2-furfural, furfuryl alcohol and 2-pentylfuran were, for the first time, simultaneously detected and quantified (5.59, 0.27, 10.48 and 1.77μgg(-1) sample, respectively) in coated deep-fried fish, contributing to a better understanding of the amounts of these compounds in food.

  15. A numerical study of laminar flames propagating in stratified mixtures

    NASA Astrophysics Data System (ADS)

    Zhang, Jiacheng

    Numerical simulations are carried out to study the structure and speed of laminar flames propagating in compositionally and thermally stratified fuel-air mixtures. The study is motivated by the need to understand the physics of flame propagation in stratified-charge engines and model it. The specific question of interest in this work is: how does the structure and speed of the flame in the stratified mixture differ from that of the flame in a corresponding homogeneous mixture at the same equivalence ratio, temperature, and pressure? The studies are carried out in hydrogen-air, methane-air, and n-heptane-air mixtures. A 30-species 184-step skeletal mechanism is employed for methane oxidation, a 9-species 21-step mechanism for hydrogen oxidation, and a 37-species 56-step skeletal mechanism for n-heptane oxidation. Flame speed and structure are compared with corresponding values for homogeneous mixtures. For compositionally stratified mixtures, as shown in prior experimental work, the numerical results suggest that when the flame propagates from a richer mixture to a leaner mixture, the flame speed is faster than the corresponding speed in the homogeneous mixture. This is caused by enhanced diffusion of heat and species from the richer mixture to the leaner mixture. In fact, the effects become more pronounced in leaner mixtures. Not surprisingly, the stratification gradient influences the results with shallower gradients showing less effect. The controlling role that diffusion plays is further assessed and confirmed by studying the effect of a unity Lewis number assumption in the hydrogen/air mixtures. Furthermore, the effect of stratification becomes less important when using methane or n-heptane as fuel. The laminar flame speed in a thermally stratified mixture is similar to the laminar flame speed in homogeneous mixture at corresponding unburned temperature. Theoretical analysis is performed and the ratio of extra thermal diffusion rate to flame heat release rate

  16. On the abiotic formation of amino acids. I - HCN as a precursor of amino acids detected in extracts of lunar samples. II - Formation of HCN and amino acids from simulated mixtures of gases released from lunar samples

    NASA Technical Reports Server (NTRS)

    Yuasa, S.; Flory, D.; Basile, B.; Oro, J.

    1984-01-01

    Two studies on the abiotic formation of amino acids are presented. The first study demonstrates the role of hydrogen cyanide as a precursor of amino acids detected in extracts of lunar samples. The formation of several amino acids, including glycine, alanine, aspartic acid, and glutamic acid, under conditions similar to those used for the analysis of lunar samples is demonstrated. The second study investigates the formation of hydrogen cyanide as well as amino acids from lunar-sample gas mixtures under electrical discharge conditions. These results extend the possibility of synthesis of amino acids to planetary bodies with primordial atmospheres less reducing than a mixture of methane, ammonia, hydrogen and water.

  17. Ethane-xenon mixtures under shock conditions

    NASA Astrophysics Data System (ADS)

    Flicker, Dawn; Magyar, Rudolph; Root, Seth; Cochrane, Kyle; Mattsson, Thomas

    2015-06-01

    Mixtures of light and heavy elements arise in inertial confinement fusion and planetary science. We present results on the physics of molecular scale mixing through a validation study of equation of state (EOS) properties. Density functional theory molecular dynamics (DFT/QMD) at elevated-temperature and pressure is used to obtain the properties of pure xenon, ethane, and various compressed mixture compositions along their principal Hugoniots. To validate the QMD simulations, we performed high-precision shock compression experiments using Sandia's Z-Machine. A bond tracking analysis of the simulations correlates the sharp rise in the Hugoniot curve with completion of dissociation in ethane. DFT-based simulation results compare well with experimental data and are used to provide insight into the dissociation as a function of mixture composition. Interestingly, we find that the compression ratio for complete dissociation is similar for ethane, Xe-ethane, polymethyl-pentene, and polystyrene, suggesting that a limiting compression exists for C-C bonded systems. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, Security Administration under contract DE-AC04-94AL85000.

  18. Measurement and Structural Model Class Separation in Mixture CFA: ML/EM versus MCMC

    ERIC Educational Resources Information Center

    Depaoli, Sarah

    2012-01-01

    Parameter recovery was assessed within mixture confirmatory factor analysis across multiple estimator conditions under different simulated levels of mixture class separation. Mixture class separation was defined in the measurement model (through factor loadings) and the structural model (through factor variances). Maximum likelihood (ML) via the…

  19. Numerical Prediction of Radiation Measurements Taken in the X2 Facility for Mars and Titan Gas Mixtures

    NASA Technical Reports Server (NTRS)

    Palmer, Grant; Prabhu, Dinesh; Brandis, Aaron; McIntyre, Timothy J.

    2011-01-01

    Thermochemical relaxation behind a normal shock in Mars and Titan gas mixtures is simulated using a CFD solver, DPLR, for a hemisphere of 1 m radius; the thermochemical relaxation along the stagnation streamline is considered equivalent to the flow behind a normal shock. Flow simulations are performed for a Titan gas mixture (98% N2, 2% CH4 by volume) for shock speeds of 5.7 and 7.6 km/s and pressures ranging from 20 to 1000 Pa, and a Mars gas mixture (96% CO2, and 4% N2 by volume) for a shock speed of 8.6 km/s and freestream pressure of 13 Pa. For each case, the temperatures and number densities of chemical species obtained from the CFD flow predictions are used as an input to a line-by-line radiation code, NEQAIR. The NEQAIR code is then used to compute the spatial distribution of volumetric radiance starting from the shock front to the point where thermochemical equilibrium is nominally established. Computations of volumetric spectral radiance assume Boltzmann distributions over radiatively linked electronic states of atoms and molecules. The results of these simulations are compared against experimental data acquired in the X2 facility at the University of Queensland, Australia. The experimental measurements were taken over a spectral range of 310-450 nm where the dominant contributor to radiation is the CN violet band system. In almost all cases, the present approach of computing the spatial variation of post-shock volumetric radiance by applying NEQAIR along a stagnation line computed using a high-fidelity flow solver with good spatial resolution of the relaxation zone is shown to replicate trends in measured relaxation of radiance for both Mars and Titan gas mixtures.

  20. Concrete mixture characterization. Cementitious barriers partnership

    SciTech Connect

    Langton, C.; Protiere, Yannick

    2014-12-01

    This report summarizes the characterization study performed on two concrete mixtures used for radioactive waste storage. Both mixtures were prepared with approximately 425 kg of binder. The testing protocol mostly focused on determining the transport properties of the mixtures; volume of permeable voids (porosity), diffusion coefficients, and water permeability were evaluated. Tests were performed after different curing durations. In order to obtain data on the statistical distribution of transport properties, the measurements after 2 years of curing were performed on 10+ samples. Overall, both mixtures exhibited very low tortuosities and permeabilities, a direct consequence of their low water-to-binder ratio and the use of supplementary cementitious materials. The data generated on 2-year old samples showed that porosity, tortuosity and permeability follow a normal distribution. Chloride ponding tests were also performed on test samples. They showed limited chloride ingress, in line with measured transport properties. These test results also showed that both materials react differently with chloride, a consequence of the differences in the binder chemical compositions.

  1. Modeling the chemistry of complex petroleum mixtures.

    PubMed

    Quann, R J

    1998-12-01

    Determining the complete molecular composition of petroleum and its refined products is not feasible with current analytical techniques because of the astronomical number of molecular components. Modeling the composition and behavior of such complex mixtures in refinery processes has accordingly evolved along a simplifying concept called lumping. Lumping reduces the complexity of the problem to a manageable form by grouping the entire set of molecular components into a handful of lumps. This traditional approach does not have a molecular basis and therefore excludes important aspects of process chemistry and molecular property fundamentals from the model's formulation. A new approach called structure-oriented lumping has been developed to model the composition and chemistry of complex mixtures at a molecular level. The central concept is to represent an individual molecular or a set of closely related isomers as a mathematical construct of certain specific and repeating structural groups. A complex mixture such as petroleum can then be represented as thousands of distinct molecular components, each having a mathematical identity. This enables the automated construction of large complex reaction networks with tens of thousands of specific reactions for simulating the chemistry of complex mixtures. Further, the method provides a convenient framework for incorporating molecular physical property correlations, existing group contribution methods, molecular thermodynamic properties, and the structure--activity relationships of chemical kinetics in the development of models.

  2. Modeling the chemistry of complex petroleum mixtures.

    PubMed Central

    Quann, R J

    1998-01-01

    Determining the complete molecular composition of petroleum and its refined products is not feasible with current analytical techniques because of the astronomical number of molecular components. Modeling the composition and behavior of such complex mixtures in refinery processes has accordingly evolved along a simplifying concept called lumping. Lumping reduces the complexity of the problem to a manageable form by grouping the entire set of molecular components into a handful of lumps. This traditional approach does not have a molecular basis and therefore excludes important aspects of process chemistry and molecular property fundamentals from the model's formulation. A new approach called structure-oriented lumping has been developed to model the composition and chemistry of complex mixtures at a molecular level. The central concept is to represent an individual molecular or a set of closely related isomers as a mathematical construct of certain specific and repeating structural groups. A complex mixture such as petroleum can then be represented as thousands of distinct molecular components, each having a mathematical identity. This enables the automated construction of large complex reaction networks with tens of thousands of specific reactions for simulating the chemistry of complex mixtures. Further, the method provides a convenient framework for incorporating molecular physical property correlations, existing group contribution methods, molecular thermodynamic properties, and the structure--activity relationships of chemical kinetics in the development of models. PMID:9860903

  3. Toxicological approaches to complex mixtures.

    PubMed Central

    Mauderly, J L

    1993-01-01

    This paper reviews the role of toxicological studies in understanding the health effects of environmental exposures to mixtures. The approach taken is to review mixtures that have received the greatest emphasis from toxicology; major mixtures research programs; the toxicologist's view of mixtures and approaches to their study; and the complementary roles of toxicological, clinical, and epidemiological studies. Studies of tobacco smoke, engine exhaust, combustion products, and air pollutants comprise most of the past research on mixtures. Because of their great experimental control over subjects, exposures, and endpoints, toxicologists tend to consider a wider range of toxic interactions among mixture components and sequential exposures than is practical for human studies. The three fundamental experimental approaches used by toxicologists are integrative (studying the mixture as a whole), dissective (dissecting a mixture to determine causative constituents), and synthetic (studying interactions between agents in simple combinations). Toxicology provides information on potential hazards, mechanisms by which mixture constituents interact to cause effects, and exposure dose-effect relationships; but extrapolation from laboratory data to quantitative human health risks is problematic. Toxicological, clinical, and epidemiological approaches are complementary but are seldom coordinated. Fostering synergistic interactions among the disciplines in studying the risks from mixtures could be advantageous. PMID:7515806

  4. Coupled gas flow/solid dynamics model for predicting the formation of fracture patterns in gas well simulation experiments. [Propellant mixture used instead of explosives to fracture rock surrounding borehole

    SciTech Connect

    Taylor, L.M.; Swenson, D.V.; Cooper, P.W.

    1984-07-01

    A two-dimensional finite element model for predicting fracture patterns obtained in high energy gas fracture experiments is presented. In these experiments, a mixture of propellants is used instead of explosives to fracture the rock surrounding the borehole. The propellant mixture is chosen to tailor the pressure pulse so that multiple fractures emanate from the borehole. The model allows the fracture pattern and pressure pulse to be calculated for different combinations of propellant mixture, in situ stress conditions, and rock properties. The model calculates the amount of gas generated by the burning propellants using a burn rate given by a power law in pressure. By assuming that the gas behaves as a perfect gas and that the flow down the fractures is isothermal, the loss of gas from the borehole due to flow down the cracks is accounted for. The flow of gas down the cracks is included in an approximate manner by assuming self-similar pressure profiles along the fractures. Numerical examples are presented and compared to three different full-scale experiments. Results show a good correlation with the experimental data over a wide variety of test parameters. 9 reference, 10 figures, 3 tables.

  5. Ethane-xenon mixtures under shock conditions

    DOE PAGES

    Magyar, Rudolph J.; Root, Seth; Mattsson, Thomas; ...

    2015-04-22

    Mixtures of light elements with heavy elements are important in inertial confinement fusion. We explore the physics of molecular scale mixing through a validation study of equation of state (EOS) properties. Density functional theory molecular dynamics (DFT-MD) at elevated temperature and pressure is used to obtain the thermodynamic state properties of pure xenon, ethane, and various compressed mixture compositions along their principal Hugoniots. In order to validate these simulations, we have performed shock compression experiments using the Sandia Z-Machine. A bond tracking analysis correlates the sharp rise in the Hugoniot curve with the completion of dissociation in ethane. Furthermore, themore » DFT-based simulation results compare well with the experimental data along the principal Hugoniots and are used to provide insight into the dissociation and temperature along the Hugoniots as a function of mixture composition. Interestingly, we find that the compression ratio for complete dissociation is similar for several compositions suggesting a limiting compression for C-C bonded systems.« less

  6. Ethane-xenon mixtures under shock conditions

    SciTech Connect

    Magyar, Rudolph J.; Root, Seth; Mattsson, Thomas; Cochrane, Kyle Robert; Flicker, Dawn G.

    2015-04-22

    Mixtures of light elements with heavy elements are important in inertial confinement fusion. We explore the physics of molecular scale mixing through a validation study of equation of state (EOS) properties. Density functional theory molecular dynamics (DFT-MD) at elevated temperature and pressure is used to obtain the thermodynamic state properties of pure xenon, ethane, and various compressed mixture compositions along their principal Hugoniots. In order to validate these simulations, we have performed shock compression experiments using the Sandia Z-Machine. A bond tracking analysis correlates the sharp rise in the Hugoniot curve with the completion of dissociation in ethane. Furthermore, the DFT-based simulation results compare well with the experimental data along the principal Hugoniots and are used to provide insight into the dissociation and temperature along the Hugoniots as a function of mixture composition. Interestingly, we find that the compression ratio for complete dissociation is similar for several compositions suggesting a limiting compression for C-C bonded systems.

  7. Personal Exposure to Mixtures of Volatile Organic Compounds: Modeling and Further Analysis of the RIOPA Data

    PubMed Central

    Batterman, Stuart; Su, Feng-Chiao; Li, Shi; Mukherjee, Bhramar; Jia, Chunrong

    2015-01-01

    known to affect VOC exposures, many personal, environmental, and socioeconomic determinants remain to be identified, and the significance and applicability of the determinants reported in the literature are uncertain. To help answer these unresolved questions and overcome limitations of previous analyses, this project used several novel and powerful statistical modeling and analysis techniques and two large data sets. The overall objectives of this project were (1) to identify and characterize exposure distributions (including extreme values), (2) evaluate mixtures (including dependencies), and (3) identify determinants of VOC exposure. METHODS VOC data were drawn from two large data sets: the Relationships of Indoor, Outdoor, and Personal Air (RIOPA) study (1999–2001) and the National Health and Nutrition Examination Survey (NHANES; 1999–2000). The RIOPA study used a convenience sample to collect outdoor, indoor, and personal exposure measurements in three cities (Elizabeth, NJ; Houston, TX; Los Angeles, CA). In each city, approximately 100 households with adults and children who did not smoke were sampled twice for 18 VOCs. In addition, information about 500 variables associated with exposure was collected. The NHANES used a nationally representative sample and included personal VOC measurements for 851 participants. NHANES sampled 10 VOCs in common with RIOPA. Both studies used similar sampling methods and study periods. Specific Aim 1 To estimate and model extreme value exposures, extreme value distribution models were fitted to the top 10% and 5% of VOC exposures. Health risks were estimated for individual VOCs and for three VOC mixtures. Simulated extreme value data sets, generated for each VOC and for fitted extreme value and lognormal distributions, were compared with measured concentrations (RIOPA observations) to evaluate each model’s goodness of fit. Mixture distributions were fitted with the conventional finite mixture of normal distributions and the

  8. Linear spectral mixture analysis with the Open Leontief Input-Output Model

    NASA Astrophysics Data System (ADS)

    Lijiang, Zhu

    2014-03-01

    Commonly, it requires two constraints imposed on the linear spectral mixture analysis (LSMA). One constraint is the abundance of sum-to-one, which requires the abundance fractions of materials presented in an image pixel to be one and is easy to deal with. The other constraint is that any abundance fractions are always nonnegative and difficult to solve with analytical solution. Most of approaches that provide the solution for the latter problem of LSMA use an optimization or maximization procedure. The results of solution resort to optimization strategies. The Leontief input-output model, of which parameters are very similar to LSMA, is represented by a linear system of equations and the system has a unique nonnegative solution. In this paper, we considered how to determine the parameters of LSMA model, and based on the open Leontief input-output model, we presented a fully constrained linear spectral (FCLS) mixture analysis method for estimating material abundance in spectral mixture pixel. The new FCLS method can not only make the abundance fractions of materials be nonnegative, but also keep them less than one, that always obtained by normalizing procedure in other methods. We also examine a number of approaches, previous FCLS and non-negative matrix factorization (NMF) spectral un-mixing, closely related. A series of computer simulations are conducted to demonstrate the performance of the proposed method in material quantification.

  9. Renormalized jellium model for colloidal mixtures

    NASA Astrophysics Data System (ADS)

    García de Soria, María Isabel; Álvarez, Carlos E.; Trizac, Emmanuel

    2016-10-01

    In an attempt to quantify the role of polydispersity in colloidal suspensions, we present an efficient implementation of the renormalized jellium model for a mixture of spherical charged colloids. The different species may have different size, charge, and density. Advantage is taken from the fact that the electric potential pertaining to a given species obeys a Poisson's equation that is species independent; only boundary conditions do change from one species to the next. All species are coupled through the renormalized background (jellium) density, that is determined self-consistently. The corresponding predictions are compared to the results of Monte Carlo simulations of binary mixtures, where Coulombic interactions are accounted for exactly, at the primitive model level (structureless solvent with fixed dielectric permittivity). An excellent agreement is found.

  10. Supervised and Unsupervised Classification Using Mixture Models

    NASA Astrophysics Data System (ADS)

    Girard, S.; Saracco, J.

    2016-05-01

    This chapter is dedicated to model-based supervised and unsupervised classification. Probability distributions are defined over possible labels as well as over the observations given the labels. To this end, the basic tools are the mixture models. This methodology yields a posterior distribution over the labels given the observations which allows to quantify the uncertainty of the classification. The role of Gaussian mixture models is emphasized leading to Linear Discriminant Analysis and Quadratic Discriminant Analysis methods. Some links with Fisher Discriminant Analysis and logistic regression are also established. The Expectation-Maximization algorithm is introduced and compared to the K-means clustering method. The methods are illustrated both on simulated datasets as well as on real datasets using the R software.

  11. A note on mixture bivariate model

    NASA Astrophysics Data System (ADS)

    Cao, Hanwen; Tian, Wei; Deng, Chengzhi

    2011-10-01

    L. Sendur and I. W. Selesnick suggest four jointly non-Gaussian bivariate models to characterize the dependency between a coefficient and its parent, and respectively derive the corresponding MAP estimators based on noisy wavelet coefficients in detail in [6]. Among the four models, the second is a mixture model and it is quite complicated to evaluate parameters, so L. Sendur and I.W. Selesnick didn't give a concrete method. In this letter, a concrete mixture bivariate model will be described by drawing inspiration from Model 2. Expectation maximization (EM) algorithm is employed to find the parameters of new model. The simulation results show that the values of PSNR have a bit improvement compared with Model 1. The results can be viewed as a supplementary of model 2 in [6].

  12. Renormalized jellium model for colloidal mixtures.

    PubMed

    García de Soria, María Isabel; Álvarez, Carlos E; Trizac, Emmanuel

    2016-10-01

    In an attempt to quantify the role of polydispersity in colloidal suspensions, we present an efficient implementation of the renormalized jellium model for a mixture of spherical charged colloids. The different species may have different size, charge, and density. Advantage is taken from the fact that the electric potential pertaining to a given species obeys a Poisson's equation that is species independent; only boundary conditions do change from one species to the next. All species are coupled through the renormalized background (jellium) density, that is determined self-consistently. The corresponding predictions are compared to the results of Monte Carlo simulations of binary mixtures, where Coulombic interactions are accounted for exactly, at the primitive model level (structureless solvent with fixed dielectric permittivity). An excellent agreement is found.

  13. Bioassay of complex mixtures of indoor air pollutants. Chapter 7

    SciTech Connect

    Lewtas, J.; Claxton, L.; Mumford, J.; Lofroth, G.

    1990-01-01

    There are several strategies for conducting bioassay studies of indoor air pollutant mixtures. One approach is to generate indoor pollutants from sources under laboratory conditions suitable for human, animal, or in vitro bioassay studies. This approach was used extensively to evaluate tobacco smoke and to a lesser extent for other indoor combustion sources such as kerosene heaters. A second approach is to simulate these complex mixtures by simpler mixtures of pure chemicals which can be used in biological studies. The third approach, which is described in more detail here, is to use bioassays in the direct evaluation of complex mixtures of indoor air pollutants. The mixtures of organics found indoors from combustion sources, building materials, household products and human activities are extremely complex. They consist of thousands of components which are not well characterized or quantified. Many of these mixtures and certain components are potential human carcinogens. The development of short-term bioassays to detect mutagens and potential carcinogens has facilitated studies of complex mixtures including air pollutants and combustion emissions. Chapter 7 will focus on the development and application of bacterial mutagenicity assays to complex mixtures of indoor air pollutants.

  14. Characterization of the homogeneous tissue mixture approximation in breast imaging dosimetry

    SciTech Connect

    Sechopoulos, Ioannis; Bliznakova, Kristina; Qin Xulei; Fei Baowei; Feng, Steve Si Jia

    2012-08-15

    Purpose: To compare the estimate of normalized glandular dose in mammography and breast CT imaging obtained using the actual glandular tissue distribution in the breast to that obtained using the homogeneous tissue mixture approximation. Methods: Twenty volumetric images of patient breasts were acquired with a dedicated breast CT prototype system and the voxels in the breast CT images were automatically classified into skin, adipose, and glandular tissue. The breasts in the classified images underwent simulated mechanical compression to mimic the conditions present during mammographic acquisition. The compressed thickness for each breast was set to that achieved during each patient's last screening cranio-caudal (CC) acquisition. The volumetric glandular density of each breast was computed using both the compressed and uncompressed classified images, and additional images were created in which all voxels representing adipose and glandular tissue were replaced by a homogeneous mixture of these two tissues in a proportion corresponding to each breast's volumetric glandular density. All four breast images (compressed and uncompressed; heterogeneous and homogeneous tissue) were input into Monte Carlo simulations to estimate the normalized glandular dose during mammography (compressed breasts) and dedicated breast CT (uncompressed breasts). For the mammography simulations the x-ray spectra used was that used during each patient's last screening CC acquisition. For the breast CT simulations, two x-ray spectra were used, corresponding to the x-ray spectra with the lowest and highest energies currently being used in dedicated breast CT prototype systems under clinical investigation. The resulting normalized glandular dose for the heterogeneous and homogeneous versions of each breast for each modality was compared. Results: For mammography, the normalized glandular dose based on the homogeneous tissue approximation was, on average, 27% higher than that estimated using the

  15. Lattice model for water-solute mixtures

    NASA Astrophysics Data System (ADS)

    Furlan, A. P.; Almarza, N. G.; Barbosa, M. C.

    2016-10-01

    A lattice model for the study of mixtures of associating liquids is proposed. Solvent and solute are modeled by adapting the associating lattice gas (ALG) model. The nature of interaction of solute/solvent is controlled by tuning the energy interactions between the patches of ALG model. We have studied three set of parameters, resulting in, hydrophilic, inert, and hydrophobic interactions. Extensive Monte Carlo simulations were carried out, and the behavior of pure components and the excess properties of the mixtures have been studied. The pure components, water (solvent) and solute, have quite similar phase diagrams, presenting gas, low density liquid, and high density liquid phases. In the case of solute, the regions of coexistence are substantially reduced when compared with both the water and the standard ALG models. A numerical procedure has been developed in order to attain series of results at constant pressure from simulations of the lattice gas model in the grand canonical ensemble. The excess properties of the mixtures, volume and enthalpy as the function of the solute fraction, have been studied for different interaction parameters of the model. Our model is able to reproduce qualitatively well the excess volume and enthalpy for different aqueous solutions. For the hydrophilic case, we show that the model is able to reproduce the excess volume and enthalpy of mixtures of small alcohols and amines. The inert case reproduces the behavior of large alcohols such as propanol, butanol, and pentanol. For the last case (hydrophobic), the excess properties reproduce the behavior of ionic liquids in aqueous solution.

  16. Nonequilibrium multiphase mixture modeling of energetic material response

    SciTech Connect

    Baer, M.R.; Hertel, E.; Bell, R.

    1995-12-31

    To model the shock-induced behavior of porous or damaged energetic materials, a nonequilibrium mixture theory has been developed and incorporated into the shock physics code, CTH. Foundation for this multiphase model is based on a continuum mixture formulation given by Baer and Nunziato. In this nonequilibrium approach, multiple thermodynamic and mechanics fields are resolved including the effects of material relative motion, rate-dependent compaction, drag and heat transfer interphase effects and multiple-step combustion. Benchmark calculations are presented which simulate low-velocity piston impact on a propellant porous bed and experimentally-measured wave features are well replicated with this model. This mixture model introduces micromechanical models for the initiation and growth of reactive multicomponent flow which are key features to describe shock initiation and self-accelerated deflagration-to-detonation combustion behavior. To complement one-dimensional simulation, two dimensional numerical simulations are presented which indicate wave curvature effects due to the loss of wall confinement.

  17. Thermophysical Properties of Hydrocarbon Mixtures

    National Institute of Standards and Technology Data Gateway

    SRD 4 NIST Thermophysical Properties of Hydrocarbon Mixtures (PC database for purchase)   Interactive computer program for predicting thermodynamic and transport properties of pure fluids and fluid mixtures containing up to 20 components. The components are selected from a database of 196 components, mostly hydrocarbons.

  18. Familial searching on DNA mixtures with dropout.

    PubMed

    Slooten, K

    2016-05-01

    Familial searching, the act of searching a database for a relative of an unknown individual whose DNA profile has been obtained, is usually restricted to cases where the DNA profile of that person has been unambiguously determined. Therefore, it is normally applied only with a good quality single source profile as starting point. In this article we investigate the performance of the method if applied to mixtures with and without allelic dropout, when likelihood ratios are computed with a semi-continuous (binary) model. We show that mixtures with dropout do not necessarily perform worse than mixtures without, especially if some separation between the donors is possible due to their different dropout probabilities. The familial searching true and false positive rates of mixed profiles on 15 loci are in some cases better than those of single source profiles on 10 loci. Thus, the information loss due to the fact that the person of interest's DNA has been mixed with that of other, and is affected by dropout, can be less than the loss of information corresponding to having 5 fewer loci available for a single source trace. Profiles typed on 10 autosomal loci are often involved in familial searching casework since many databases, including the Dutch one, in part consist of such profiles. Therefore, from this point of view, there seems to be no objection to extend familial searching to mixed or degraded profiles.

  19. Behavior of detonation propagation in mixtures with concentration gradients

    NASA Astrophysics Data System (ADS)

    Hall, Brian C.; Kirwin, William D.

    2007-08-01

    Behavior of detonation waves in mixtures with concentration gradients normal to the propagation direction was studied experimentally. Mixtures with various concentration gradients were formed by sliding the separation plate which divides a detonation chamber from a diffusion chamber in which a diffusion gas was initially introduced. A stoichiometric hydrogen oxygen mixture was charged in the detonation chamber, while oxygen or nitrogen was filled in the diffusion gas chamber. Temporal concentration measurement was conducted by the infrared absorption method using ethane as alternate of oxygen. Smoked foil records show a deformation of regular diamond cells to parallelogram ones, which well corresponds to local mixture concentration. Schlieren photographs reveal the tilted wave front whose angle is consistent with the deflection angle of the detonation front obtained from trajectories of the triple point. The local deflection angle increases with increase in local concentration gradient. Calculation of wave trajectory based on the ray tracing theory predicts formation of the tilted wave front from an initial planar front.

  20. SGC tests for influence of material composition on compaction characteristic of asphalt mixtures.

    PubMed

    Chen, Qun; Li, Yuzhi

    2013-01-01

    Compaction characteristic of the surface layer asphalt mixture (13-type gradation mixture) was studied using Superpave gyratory compactor (SGC) simulative compaction tests. Based on analysis of densification curve of gyratory compaction, influence rules of the contents of mineral aggregates of all sizes and asphalt on compaction characteristic of asphalt mixtures were obtained. SGC Tests show that, for the mixture with a bigger content of asphalt, its density increases faster, that there is an optimal amount of fine aggregates for optimal compaction and that an appropriate amount of mineral powder will improve workability of mixtures, but overmuch mineral powder will make mixtures dry and hard. Conclusions based on SGC tests can provide basis for how to adjust material composition for improving compaction performance of asphalt mixtures, and for the designed asphalt mixture, its compaction performance can be predicted through these conclusions, which also contributes to the choice of compaction schemes.

  1. Maximum Likelihood and Minimum Distance Applied to Univariate Mixture Distributions.

    ERIC Educational Resources Information Center

    Wang, Yuh-Yin Wu; Schafer, William D.

    This Monte-Carlo study compared modified Newton (NW), expectation-maximization algorithm (EM), and minimum Cramer-von Mises distance (MD), used to estimate parameters of univariate mixtures of two components. Data sets were fixed at size 160 and manipulated by mean separation, variance ratio, component proportion, and non-normality. Results…

  2. ECG Beats Classification Using Mixture of Features

    PubMed Central

    Ari, Samit

    2014-01-01

    Classification of electrocardiogram (ECG) signals plays an important role in clinical diagnosis of heart disease. This paper proposes the design of an efficient system for classification of the normal beat (N), ventricular ectopic beat (V), supraventricular ectopic beat (S), fusion beat (F), and unknown beat (Q) using a mixture of features. In this paper, two different feature extraction methods are proposed for classification of ECG beats: (i) S-transform based features along with temporal features and (ii) mixture of ST and WT based features along with temporal features. The extracted feature set is independently classified using multilayer perceptron neural network (MLPNN). The performances are evaluated on several normal and abnormal ECG signals from 44 recordings of the MIT-BIH arrhythmia database. In this work, the performances of three feature extraction techniques with MLP-NN classifier are compared using five classes of ECG beat recommended by AAMI (Association for the Advancement of Medical Instrumentation) standards. The average sensitivity performances of the proposed feature extraction technique for N, S, F, V, and Q are 95.70%, 78.05%, 49.60%, 89.68%, and 33.89%, respectively. The experimental results demonstrate that the proposed feature extraction techniques show better performances compared to other existing features extraction techniques. PMID:27350985

  3. Pycnonuclear reaction rates for binary ionic mixtures

    NASA Technical Reports Server (NTRS)

    Ichimaru, S.; Ogata, S.; Van Horn, H. M.

    1992-01-01

    Through a combination of compositional scaling arguments and examinations of Monte Carlo simulation results for the interparticle separations in binary-ionic mixture (BIM) solids, we have derived parameterized expressions for the BIM pycnonuclear rates as generalizations of those in one-component solids obtained previously by Salpeter and Van Horn and by Ogata et al. We have thereby discovered a catalyzing effect of the heavier elements, which enhances the rates of reactions among the lighter elements when the charge ratio exceeds a critical value of approximately 2.3.

  4. Environmental complex mixture toxicity assessment.

    PubMed

    Gardner, H S; Brennan, L M; Toussaint, M W; Rosencrance, A B; Boncavage-Hennessey, E M; Wolfe, M J

    1998-12-01

    Trichloroethylene (TCE) was found as a contaminant in the well supplying water to an aquatic testing laboratory. The groundwater was routinely screened by a commercial laboratory for volatile and semivolatile compounds, metals, herbicides, pesticides, and polychlorinated biphenyls using U.S. Environmental Protection Agency methods. Although TCE was the only reportable peak on the gas chromatograph, with average concentrations of 0.200 mg/l, other small peaks were also present, indicating the possibility that the contamination was not limited to TCE alone. A chronic 6-month carcinogenicity assay was conducted on-site in a biomonitoring trailer, using the Japanese medaka fish (Oryzias latipes) in an initiation-promotion protocol, with diethylnitrosamine (DEN) as the initiator and the TCE-contaminated groundwater as a promoter. Study results indicated no evidence of carcinogenic potential of the groundwater without initiation. There was, however, a tumor-promotional effect of the groundwater after DEN initiation. A follow-up laboratory study was conducted using reagent grade TCE added to carbon-filtered groundwater to simulate TCE concentrations comparable to those found in the contaminated groundwater. Study results indicated no promotional effects of TCE. These studies emphasize the necessity for on-site bioassays to assess potential environmental hazards. In this instance, chemical analysis of the groundwater identified TCE as the only reportable contaminant, but other compounds present below reportable limits were noted and may have had a synergistic effect on tumor promotion observed with the groundwater exposure. Laboratory toxicity testing of single compounds can produce toxicity data specific to that compound for that species but cannot take into account the possible toxic effects of mixtures of compounds.

  5. Environmental complex mixture toxicity assessment.

    PubMed Central

    Gardner, H S; Brennan, L M; Toussaint, M W; Rosencrance, A B; Boncavage-Hennessey, E M; Wolfe, M J

    1998-01-01

    Trichloroethylene (TCE) was found as a contaminant in the well supplying water to an aquatic testing laboratory. The groundwater was routinely screened by a commercial laboratory for volatile and semivolatile compounds, metals, herbicides, pesticides, and polychlorinated biphenyls using U.S. Environmental Protection Agency methods. Although TCE was the only reportable peak on the gas chromatograph, with average concentrations of 0.200 mg/l, other small peaks were also present, indicating the possibility that the contamination was not limited to TCE alone. A chronic 6-month carcinogenicity assay was conducted on-site in a biomonitoring trailer, using the Japanese medaka fish (Oryzias latipes) in an initiation-promotion protocol, with diethylnitrosamine (DEN) as the initiator and the TCE-contaminated groundwater as a promoter. Study results indicated no evidence of carcinogenic potential of the groundwater without initiation. There was, however, a tumor-promotional effect of the groundwater after DEN initiation. A follow-up laboratory study was conducted using reagent grade TCE added to carbon-filtered groundwater to simulate TCE concentrations comparable to those found in the contaminated groundwater. Study results indicated no promotional effects of TCE. These studies emphasize the necessity for on-site bioassays to assess potential environmental hazards. In this instance, chemical analysis of the groundwater identified TCE as the only reportable contaminant, but other compounds present below reportable limits were noted and may have had a synergistic effect on tumor promotion observed with the groundwater exposure. Laboratory toxicity testing of single compounds can produce toxicity data specific to that compound for that species but cannot take into account the possible toxic effects of mixtures of compounds. Images Figure 2 PMID:9860885

  6. Shear of ordinary and elongated granular mixtures

    NASA Astrophysics Data System (ADS)

    Hensley, Alexander; Kern, Matthew; Marschall, Theodore; Teitel, Stephen; Franklin, Scott

    2015-03-01

    We present an experimental and computational study of a mixture of discs and moderate aspect-ratio ellipses under two-dimensional annular planar Couette shear. Experimental particles are cut from acrylic sheet, are essentially incompressible, and constrained in the thin gap between two concentric cylinders. The annular radius of curvature is much larger than the particles, and so the experiment is quasi-2d and allows for arbitrarily large pure-shear strains. Synchronized video cameras and software identify all particles and track them as they move from the field of view of one camera to another. We are particularly interested in the global and local properties as the mixture ratio of discs to ellipses varies. Global quantities include average shear rate and distribution of particle species as functions of height, while locally we investigate the orientation of the ellipses and non-affine events that can be characterized as shear transformational zones or possess a quadrupole signature observed previously in systems of purely circular particles. Discrete Element Method simulations on mixtures of circles and spherocylinders extend the study to the dynamics of the force network and energy dissipated as the system evolves. Supported by NSF CBET #1243571 and PRF #51438-UR10.

  7. Statistical mechanical theory of fluid mixtures

    NASA Astrophysics Data System (ADS)

    Zhao, Yueqiang; Wu, Zhengming; Liu, Weiwei

    2014-01-01

    A general statistical mechanical theory of fluid mixtures (liquid mixtures and gas mixtures) is developed based on the statistical mechanical expression of chemical potential of components in the grand canonical ensemble, which gives some new relationships between thermodynamic quantities (equilibrium ratio Ki, separation factor α and activity coefficient γi) and ensemble average potential energy u for one molecule. The statistical mechanical expressions of separation factor α and activity coefficient γi derived in this work make the fluid phase equilibrium calculations can be performed by molecular simulation simply and efficiently, or by the statistical thermodynamic approach (based on the saturated-vapor pressure of pure substance) that does not need microscopic intermolecular pair potential functions. The physical meaning of activity coefficient γi in the liquid phase is discussed in detail from a viewpoint of molecular thermodynamics. The calculated Vapor-Liquid Equilibrium (VLE) properties of argon-methane, methanol-water and n-hexane-benzene systems by this model fit well with experimental data in references, which indicates that this model is accurate and reliable in the prediction of VLE properties for small, large and strongly associating molecules; furthermore the statistical mechanical expressions of separation factor α and activity coefficient γi have good compatibility with classical thermodynamic equations and quantum mechanical COSMO-SAC approach.

  8. Mixtures with relatives: a pedigree perspective.

    PubMed

    Egeland, Thore; Dørum, Guro; Vigeland, Magnus Dehli; Sheehan, Nuala A

    2014-05-01

    DNA mixture evidence pertains to cases where several individuals may have contributed to a biological stain. Statistical methods and software for such problems are available and a large number of cases can be handled adequately. However, one class of mixture problems remains untreated in full generality in the literature, namely when the contributors may be related. Disregarding a plausible close relative of the perpetrator as an alternative contributor (identical twin is the most extreme case) may lead to overestimating the evidence against a suspect. Existing methods only accommodate pairwise relationships such as the case where the suspect and the victim are siblings, for example. In this paper we consider relationships in full generality, conveniently represented by pedigrees. In particular, these pedigrees may involve inbreeding, for instance when the parents of an individual of interest are first cousins. Furthermore our framework handles situations where the opposing parties in a court case (prosecution and defence) propose different family relationships. Consequently, our approach combines classical mixture and kinship problems. The basic idea of this paper is to formulate the problem in a way that allows for the exploitation of currently available methods and software designed originally for linkage applications. We have developed a freely available R package, euroMix based on another package, paramlink, and we illustrate the ideas and methods on real and simulated data.

  9. Environmentally-assisted cracking behaviour in the transition region of an Alloy182/SA 508 Cl.2 dissimilar metal weld joint in simulated boiling water reactor normal water chemistry environment

    NASA Astrophysics Data System (ADS)

    Seifert, H. P.; Ritter, S.; Shoji, T.; Peng, Q. J.; Takeda, Y.; Lu, Z. P.

    2008-08-01

    The stress corrosion cracking (SCC) and corrosion fatigue behaviour perpendicular and parallel to the fusion line in the transition region between the Alloy 182 Nickel-base weld metal and the adjacent SA 508 Cl.2 low-alloy reactor pressure vessel (RPV) steel of a simulated dissimilar metal weld joint was investigated under boiling water reactor normal water chemistry conditions. A special emphasis was placed to the question whether a fast growing interdendritic SCC crack in the highly susceptible Alloy 182 weld metal can easily cross the fusion line and significantly propagate into the adjacent low-alloy RPV steel. Cessation of interdendritic SCC crack growth was observed in high-purity or sulphate-containing oxygenated water under constant or periodical partial unloading conditions for those parts of the crack front, which reached the fusion line. In chloride containing water, on the other hand, the interdendritic SCC crack in the Alloy 182 weld metal very easily crossed the fusion line and further propagated with a very high rate as a transgranular crack into the heat-affected zone and base metal of the adjacent low-alloy steel. The observed SCC cracking behaviour at the interface correlates excellently with the field experience of such dissimilar metal weld joints, where SCC cracking was usually confined to the Alloy 182 weld metal.

  10. Rheology of binary granular mixtures in the dense flow regime

    NASA Astrophysics Data System (ADS)

    Tripathi, Anurag; Khakhar, D. V.

    2011-11-01

    We study the rheology of granular mixtures in a steady, fully developed, gravity-driven flow on an inclined plane, by means of discrete element method (DEM) simulations. Results are presented for a single component system and binary mixtures with particles of different size and density. Inclination angles, composition, size ratios and density ratios are varied to obtain different segregated configurations at equilibrium. Steady state profiles of the mean velocity, volume fractions, shear stress, shear rate, inertial number and apparent viscosity across the depth of the flowing layer are reported for the different cases. The viscosity varies with height and is found to depend on the local bulk density and composition, which, in turn, depend on the size ratio, the mass ratio and the degree of segregation. For a single component system, a viscoplastic rheological model [P. Jop et al., Nature 441, 727 (2006)] describes the data quite well. We propose a modification of the model for the case of mixtures. The mixture model predicts the viscosity for both well-mixed and segregated granular mixtures differing in size, density or both, using the same model parameters as obtained for the single component system. The predictions of a model for the volume fraction of the mixtures also agree well with simulation results.

  11. Multinomial mixture model with heterogeneous classification probabilities

    USGS Publications Warehouse

    Holland, M.D.; Gray, B.R.

    2011-01-01

    Royle and Link (Ecology 86(9):2505-2512, 2005) proposed an analytical method that allowed estimation of multinomial distribution parameters and classification probabilities from categorical data measured with error. While useful, we demonstrate algebraically and by simulations that this method yields biased multinomial parameter estimates when the probabilities of correct category classifications vary among sampling units. We address this shortcoming by treating these probabilities as logit-normal random variables within a Bayesian framework. We use Markov chain Monte Carlo to compute Bayes estimates from a simulated sample from the posterior distribution. Based on simulations, this elaborated Royle-Link model yields nearly unbiased estimates of multinomial and correct classification probability estimates when classification probabilities are allowed to vary according to the normal distribution on the logit scale or according to the Beta distribution. The method is illustrated using categorical submersed aquatic vegetation data. ?? 2010 Springer Science+Business Media, LLC.

  12. Some results on Gaussian mixtures

    NASA Astrophysics Data System (ADS)

    Felgueiras, Miguel; Santos, Rui; Martins, João Paulo

    2014-10-01

    We investigate Gaussian mixtures with independent components, whose parameters are numerically estimated. A decomposition of a Gaussian mixture is presented when the components have a common variance. We introduce a shifted and scaled t-Student distribution as an approximation for the distribution of Gaussian mixtures when their components have a common mean and develop a hypothesis test for testing the equality of the components means. Finally, we analyse the fitness of the approximate model to the logarithmic daily returns of the Portuguese stock index PSI-20.

  13. Characteristics of dynamic triaxial testing of asphalt mixtures

    NASA Astrophysics Data System (ADS)

    Ulloa Calderon, Alvaro

    Due to the increasing traffic loads and tire pressures, a serious detrimental impact has occurred on flexible pavements in the form of excessive permanent deformation once the critical combination of loading and environmental conditions are reached. This distress, also known as rutting, leads to an increase in road roughness and ultimately jeopardizes the road users' safety. The flow number (FN) simple performance test for asphalt mixtures was one of the final three tests selected for further evaluation from the twenty-four test/material properties initially examined under the NCHRP 9-19 project. Currently, no standard triaxial testing conditions in terms of the magnitude of the deviator and confining stresses have been specified. In addition, a repeated haversine axial compressive load pulse of 0.1 second and a rest period of 0.9 second are commonly used as part of the triaxial testing conditions. The overall objective of this research was to define the loading conditions that created by a moving truck load in the hot mixed asphalt (HMA) layer. The loading conditions were defined in terms of the triaxial stress levels and the corresponding loading time. Dynamic mechanistic analysis with circular stress distribution was used to closely simulate field loading conditions. Extensive mechanistic analyses of three different asphalt pavement structures subjected to moving traffic loads at various speeds and under braking and non-braking conditions were conducted using the 3D-Move model. Prediction equations for estimating the anticipated deviator and confining stresses along with the equivalent deviator stress pulse duration as a function of pavement temperature, vehicle speed, and asphalt mixture's stiffness have been developed. The magnitude of deviator stress, sigmad and confining stress, sigmac, were determined by converting the stress tensor computed in the HMA layer at 2" below pavement surface under a moving 18-wheel truck using the octahedral normal and shear

  14. Evaluating differential effects using regression interactions and regression mixture models

    PubMed Central

    Van Horn, M. Lee; Jaki, Thomas; Masyn, Katherine; Howe, George; Feaster, Daniel J.; Lamont, Andrea E.; George, Melissa R. W.; Kim, Minjung

    2015-01-01

    Research increasingly emphasizes understanding differential effects. This paper focuses on understanding regression mixture models, a relatively new statistical methods for assessing differential effects by comparing results to using an interactive term in linear regression. The research questions which each model answers, their formulation, and their assumptions are compared using Monte Carlo simulations and real data analysis. The capabilities of regression mixture models are described and specific issues to be addressed when conducting regression mixtures are proposed. The paper aims to clarify the role that regression mixtures can take in the estimation of differential effects and increase awareness of the benefits and potential pitfalls of this approach. Regression mixture models are shown to be a potentially effective exploratory method for finding differential effects when these effects can be defined by a small number of classes of respondents who share a typical relationship between a predictor and an outcome. It is also shown that the comparison between regression mixture models and interactions becomes substantially more complex as the number of classes increases. It is argued that regression interactions are well suited for direct tests of specific hypotheses about differential effects and regression mixtures provide a useful approach for exploring effect heterogeneity given adequate samples and study design. PMID:26556903

  15. High/variable mixture ratio O2/H2 engine

    NASA Technical Reports Server (NTRS)

    Adams, A.; Parsley, R. C.

    1988-01-01

    Vehicle/engine analysis studies have identified the High/Dual Mixture Ratio O2/H2 Engine cycle as a leading candidate for an advanced Single Stage to Orbit (SSTO) propulsion system. This cycle is designed to allow operation at a higher than normal O/F ratio of 12 during liftoff and then transition to a more optimum O/F ratio of 6 at altitude. While operation at high mixture ratios lowers specific impulse, the resultant high propellant bulk density and high power density combine to minimize the influence of atmospheric drag and low altitude gravitational forces. Transition to a lower mixture ratio at altitude then provides improved specific impulse relative to a single mixture ratio engine that must select a mixture ratio that is balanced for both low and high altitude operation. This combination of increased altitude specific impulse and high propellant bulk density more than offsets the compromised low altitude performance and results in an overall mission benefit. Two areas of technical concern relative to the execution of this dual mixture ratio cycle concept are addressed. First, actions required to transition from high to low mixture ratio are examined, including an assessment of the main chamber environment as the main chamber mixture ratio passes through stoichiometric. Secondly, two approaches to meet a requirement for high turbine power at high mixture ratio condition are examined. One approach uses high turbine temperature to produce the power and requires cooled turbines. The other approach incorporates an oxidizer-rich preburner to increase turbine work capability via increased turbine mass flow.

  16. Vibrational properties of bioprotectant mixtures of trehalose and glycerol.

    PubMed

    Magazù, Salvatore; Migliardo, Federica; Parker, Stewart F

    2011-09-22

    In this work vibrational spectra of mixtures of two glass-forming bioprotectant systems, i.e., trehalose and glycerol, are collected at very low temperature by using the indirect geometry time-of-flight (t.o.f.) TOSCA spectrometer at the ISIS Pulse Neutron Facility (Rutherford Appleton Laboratory, Oxford, U.K.). The main aim of this work is to investigate, through inelastic neutron scattering (INS), the vibrational behavior of trehalose and its mixtures with glycerol at different concentration values in order to characterize the changes induced by glycerol on the trehalose hydrogen bonded network. The obtained experimental findings, which are discussed and interpreted in the framework of previous INS, quasi elastic neutron scattering (QENS) and molecular simulation data obtained on trehalose/glycerol mixtures at different concentration and temperature values, will be linked to the different mixtures bioprotectant effectiveness.

  17. On thermal conductivity of gas mixtures containing hydrogen

    NASA Astrophysics Data System (ADS)

    Zhukov, Victor P.; Pätz, Markus

    2016-12-01

    A brief review of formulas used for the thermal conductivity of gas mixtures in CFD simulations of rocket combustion chambers is carried out in the present work. In most cases, the transport properties of mixtures are calculated from the properties of individual components using special mixing rules. The analysis of different mixing rules starts from basic equations and ends by very complex semi-empirical expressions. The formulas for the thermal conductivity are taken for the analysis from the works on modelling of rocket combustion chambers. H_2- O_2 mixtures are chosen for the evaluation of the accuracy of the considered mixing rules. The analysis shows that two of them, of Mathur et al. (Mol Phys 12(6):569-579, 1967), and of Mason and Saxena (Phys Fluids 1(5):361-369, 1958), have better agreement with the experimental data than other equations for the thermal conductivity of multicomponent gas mixtures.

  18. Dynamic thermodiffusion model for binary liquid mixtures

    NASA Astrophysics Data System (ADS)

    Eslamian, Morteza; Saghir, M. Ziad

    2009-07-01

    Following the nonequilibrium thermodynamics approach, we develop a dynamic model to emulate thermo-diffusion process and propose expressions for estimating the thermal diffusion factor in binary nonassociating liquid mixtures. Here, we correlate the net heat of transport in thermodiffusion with parameters, such as the mixture temperature and pressure, the size and shape of the molecules, and mobility of the components, because the molecules have to become activated before they can move. Based on this interpretation, the net heat of transport of each component can be somehow related to the viscosity and the activation energy of viscous flow of the same component defined in Eyring’s reaction-rate theory [S. Glasstone, K. J. Laidler, and H. Eyring, The Theory of Rate Processes: The Kinetics of Chemical Reactions, Viscosity, Diffusion and Electrochemical Phenomena (McGraw-Hill, New York, 1941)]. This modeling approach is different from that of Haase and Kempers, in which thermodiffusion is considered as a function of the thermostatic properties of the mixture such as enthalpy. In simulating thermodiffusion, by correlating the net heat of transport with the activation energy of viscous flow, effects of the above mentioned parameters are accounted for, to some extent of course. The model developed here along with Haase-Kempers and Drickamer-Firoozabadi models linked with the Peng-Robinson equation of sate are evaluated against the experimental data for several recent nonassociating binary mixtures at various temperatures, pressures, and concentrations. Although the model prediction is still not perfect, the model is simple and easy to use, physically justified, and predicts the experimental data very good and much better than the existing models.

  19. Dynamic thermodiffusion model for binary liquid mixtures.

    PubMed

    Eslamian, Morteza; Saghir, M Ziad

    2009-07-01

    Following the nonequilibrium thermodynamics approach, we develop a dynamic model to emulate thermo-diffusion process and propose expressions for estimating the thermal diffusion factor in binary nonassociating liquid mixtures. Here, we correlate the net heat of transport in thermodiffusion with parameters, such as the mixture temperature and pressure, the size and shape of the molecules, and mobility of the components, because the molecules have to become activated before they can move. Based on this interpretation, the net heat of transport of each component can be somehow related to the viscosity and the activation energy of viscous flow of the same component defined in Eyring's reaction-rate theory [S. Glasstone, K. J. Laidler, and H. Eyring, (McGraw-Hill, New York, 1941)]. This modeling approach is different from that of Haase and Kempers, in which thermodiffusion is considered as a function of the thermostatic properties of the mixture such as enthalpy. In simulating thermodiffusion, by correlating the net heat of transport with the activation energy of viscous flow, effects of the above mentioned parameters are accounted for, to some extent of course. The model developed here along with Haase-Kempers and Drickamer-Firoozabadi models linked with the Peng-Robinson equation of sate are evaluated against the experimental data for several recent nonassociating binary mixtures at various temperatures, pressures, and concentrations. Although the model prediction is still not perfect, the model is simple and easy to use, physically justified, and predicts the experimental data very good and much better than the existing models.

  20. Cultured normal mammalian tissue and process

    NASA Technical Reports Server (NTRS)

    Goodwin, Thomas J. (Inventor); Prewett, Tacey L. (Inventor); Wolf, David A. (Inventor); Spaulding, Glenn F. (Inventor)

    1993-01-01

    Normal mammalian tissue and the culturing process has been developed for the three groups of organ, structural and blood tissue. The cells are grown in vitro under microgravity culture conditions and form three dimensional cell aggregates with normal cell function. The microgravity culture conditions may be microgravity or simulated microgravity created in a horizontal rotating wall culture vessel.

  1. Semi-parametric estimation in failure time mixture models.

    PubMed

    Taylor, J M

    1995-09-01

    A mixture model is an attractive approach for analyzing failure time data in which there are thought to be two groups of subjects, those who could eventually develop the endpoint and those who could not develop the endpoint. The proposed model is a semi-parametric generalization of the mixture model of Farewell (1982). A logistic regression model is proposed for the incidence part of the model, and a Kaplan-Meier type approach is used to estimate the latency part of the model. The estimator arises naturally out of the EM algorithm approach for fitting failure time mixture models as described by Larson and Dinse (1985). The procedure is applied to some experimental data from radiation biology and is evaluated in a Monte Carlo simulation study. The simulation study suggests the semi-parametric procedure is almost as efficient as the correct fully parametric procedure for estimating the regression coefficient in the incidence, but less efficient for estimating the latency distribution.

  2. Simulating Combustion

    NASA Astrophysics Data System (ADS)

    Merker, G.; Schwarz, C.; Stiesch, G.; Otto, F.

    The content spans from simple thermodynamics of the combustion engine to complex models for the description of the air/fuel mixture, ignition, combustion and pollutant formation considering the engine periphery of petrol and diesel engines. Thus the emphasis of the book is on the simulation models and how they are applicable for the development of modern combustion engines. Computers can be used as the engineers testbench following the rules and recommendations described here.

  3. Distillation of binary mixtures with capillary porous plates

    SciTech Connect

    Abu Al-Rub, F.A.; Akili, J.; Datta, R.

    1998-07-01

    Distillation of liquid mixtures using capillary porous plates is a new process which depends upon the use of the intermolecular interactions between solids and liquids to alter the normal vapor-liquid equilibrium of a given mixture. Distillation of different binary mixtures, namely ethanol-water, ethanol-benzene, and acetone-ethanol systems, of different compositions was experimentally studied in a continuous distillation column equipped with four, five, or six porous sintered stainless steel fractionating plates of 13.5 {micro}m pore diameter as well as six normal sieve plates. The results showed that the main factors affecting the separation efficiency in a given porous plate are the polarization of the pure liquids and the polarization difference between the mixture components. For the ethanol-water system, the results showed that while no separation was achieved in a distillation column with conventional stages, the zeotropic point of this system was broken in the distillation column with porous plates. A distillate of about 94 mol% ethanol was obtained for a feed of the zeotropic composition, i.e., 89.7 mol% ethanol. For the ethanol-benzene system, the azeotropic point was shifted from 40 mol% ethanol to about 30 mol% ethanol. For the acetone-ethanol system, there was no significant difference between the results obtained with normal stages and those with the porous plates. These results are in agreement with the developed theory.

  4. Advocating for Normal Birth With Normal Clothes

    PubMed Central

    Waller-Wise, Renece

    2007-01-01

    Childbirth educators need to be aware that the clothes they wear when teaching classes send a nonverbal message to class participants. Regardless of who wears the clothing or what is worn, clothes send a message; thus, both the advantages and disadvantages related to clothing choice should be considered. Ultimately, the message should reflect the values of supporting normal birth. For childbirth educators who are allowed to choose their own apparel to wear in their classes, street clothes may be the benchmark for which to strive. This article discusses the many nonverbal messages that clothes convey and provides support for the choice of street clothes as the dress for the professional childbirth educator; thus, “normal clothes to promote normal birth.” PMID:18408807

  5. Normal probability plots with confidence.

    PubMed

    Chantarangsi, Wanpen; Liu, Wei; Bretz, Frank; Kiatsupaibul, Seksan; Hayter, Anthony J; Wan, Fang

    2015-01-01

    Normal probability plots are widely used as a statistical tool for assessing whether an observed simple random sample is drawn from a normally distributed population. The users, however, have to judge subjectively, if no objective rule is provided, whether the plotted points fall close to a straight line. In this paper, we focus on how a normal probability plot can be augmented by intervals for all the points so that, if the population distribution is normal, then all the points should fall into the corresponding intervals simultaneously with probability 1-α. These simultaneous 1-α probability intervals provide therefore an objective mean to judge whether the plotted points fall close to the straight line: the plotted points fall close to the straight line if and only if all the points fall into the corresponding intervals. The powers of several normal probability plot based (graphical) tests and the most popular nongraphical Anderson-Darling and Shapiro-Wilk tests are compared by simulation. Based on this comparison, recommendations are given in Section 3 on which graphical tests should be used in what circumstances. An example is provided to illustrate the methods.

  6. Wavelength and energy dependent absorption of unconventional fuel mixtures

    NASA Astrophysics Data System (ADS)

    Khan, N.; Saleem, Z.; Mirza, A. A.

    2005-11-01

    Economic considerations of laser induced ignition over the normal electrical ignition of direct injected Compressed Natural Gas (CNG) engines has motivated automobile industry to go for extensive research on basic characteristics of leaner unconventional fuel mixtures to evaluate practical possibility of switching over to the emerging technologies. This paper briefly reviews the ongoing research activities on minimum ignition energy and power requirements of natural gas fuels and reports results of present laser air/CNG mixture absorption coefficient study. This study was arranged to determine the thermo-optical characteristics of high air/fuel ratio mixtures using laser techniques. We measured the absorption coefficient using four lasers of multiple wavelengths over a wide range of temperatures and pressures. The absorption coefficient of mixture was found to vary significantly over change of mixture temperature and probe laser wavelengths. The absorption coefficients of air/CNG mixtures were measured using 20 watts CW/pulsed CO2 laser at 10.6μm, Pulsed Nd:Yag laser at 1.06μm, 532 nm (2nd harmonic) and 4 mW CW HeNe laser at 645 nm and 580 nm for temperatures varying from 290 to 1000K using optical transmission loss technique.

  7. Structure of molecular liquids: hard rod-disk mixtures.

    PubMed

    Cheung, David L; Anton, Lucian; Allen, Michael P; Masters, Andrew J

    2008-01-01

    The structure of hard rod-disk mixtures is studied using Monte Carlo simulations and integral equation theory, for a range of densities in the isotropic phase. By extension of methods used in single component fluids, the pair correlation functions of the molecules are calculated and comparisons between simulation and integral equation theory, using a number of different closure relations, are made. Comparison is also made for thermodynamic data and phase behavior.

  8. Modeling and analysis of personal exposures to VOC mixtures using copulas

    PubMed Central

    Su, Feng-Chiao; Mukherjee, Bhramar; Batterman, Stuart

    2014-01-01

    Environmental exposures typically involve mixtures of pollutants, which must be understood to evaluate cumulative risks, that is, the likelihood of adverse health effects arising from two or more chemicals. This study uses several powerful techniques to characterize dependency structures of mixture components in personal exposure measurements of volatile organic compounds (VOCs) with aims of advancing the understanding of environmental mixtures, improving the ability to model mixture components in a statistically valid manner, and demonstrating broadly applicable techniques. We first describe characteristics of mixtures and introduce several terms, including the mixture fraction which represents a mixture component's share of the total concentration of the mixture. Next, using VOC exposure data collected in the Relationship of Indoor Outdoor and Personal Air (RIOPA) study, mixtures are identified using positive matrix factorization (PMF) and by toxicological mode of action. Dependency structures of mixture components are examined using mixture fractions and modeled using copulas, which address dependencies of multiple variables across the entire distribution. Five candidate copulas (Gaussian, t, Gumbel, Clayton, and Frank) are evaluated, and the performance of fitted models was evaluated using simulation and mixture fractions. Cumulative cancer risks are calculated for mixtures, and results from copulas and multivariate lognormal models are compared to risks calculated using the observed data. Results obtained using the RIOPA dataset showed four VOC mixtures, representing gasoline vapor, vehicle exhaust, chlorinated solvents and disinfection by-products, and cleaning products and odorants. Often, a single compound dominated the mixture, however, mixture fractions were generally heterogeneous in that the VOC composition of the mixture changed with concentration. Three mixtures were identified by mode of action, representing VOCs associated with hematopoietic, liver

  9. Modeling and analysis of personal exposures to VOC mixtures using copulas.

    PubMed

    Su, Feng-Chiao; Mukherjee, Bhramar; Batterman, Stuart

    2014-02-01

    Environmental exposures typically involve mixtures of pollutants, which must be understood to evaluate cumulative risks, that is, the likelihood of adverse health effects arising from two or more chemicals. This study uses several powerful techniques to characterize dependency structures of mixture components in personal exposure measurements of volatile organic compounds (VOCs) with aims of advancing the understanding of environmental mixtures, improving the ability to model mixture components in a statistically valid manner, and demonstrating broadly applicable techniques. We first describe characteristics of mixtures and introduce several terms, including the mixture fraction which represents a mixture component's share of the total concentration of the mixture. Next, using VOC exposure data collected in the Relationship of Indoor Outdoor and Personal Air (RIOPA) study, mixtures are identified using positive matrix factorization (PMF) and by toxicological mode of action. Dependency structures of mixture components are examined using mixture fractions and modeled using copulas, which address dependencies of multiple variables across the entire distribution. Five candidate copulas (Gaussian, t, Gumbel, Clayton, and Frank) are evaluated, and the performance of fitted models was evaluated using simulation and mixture fractions. Cumulative cancer risks are calculated for mixtures, and results from copulas and multivariate lognormal models are compared to risks calculated using the observed data. Results obtained using the RIOPA dataset showed four VOC mixtures, representing gasoline vapor, vehicle exhaust, chlorinated solvents and disinfection by-products, and cleaning products and odorants. Often, a single compound dominated the mixture, however, mixture fractions were generally heterogeneous in that the VOC composition of the mixture changed with concentration. Three mixtures were identified by mode of action, representing VOCs associated with hematopoietic, liver

  10. Thermal behavior of crumb-rubber modified asphalt concrete mixtures

    NASA Astrophysics Data System (ADS)

    Epps, Amy Louise

    Thermal cracking is one of the primary forms of distress in asphalt concrete pavements, resulting from either a single drop in temperature to an extreme low or from multiple temperature cycles above the fracture temperature of the asphalt-aggregate mixture. The first mode described is low temperature cracking; the second is thermal fatigue. The addition of crumb-rubber, manufactured from scrap tires, to the binder in asphalt concrete pavements has been suggested to minimize both types of thermal cracking. Four experiments were designed and completed to evaluate the thermal behavior of crumb-rubber modified (CRM) asphalt-aggregate mixtures. Modified and unmodified mixture response to thermal stresses was measured in four laboratory tests. The Thermal Stress Restrained Specimen Test (TSRST) and the Indirect Tensile Test (IDT) were used to compare mixture resistance to low temperature cracking. Modified mixtures showed improved performance, and cooling rate did not affect mixture resistance according to the statistical analysis. Therefore results from tests with faster rates can predict performance under slower field rates. In comparison, predicted fracture temperatures and stresses (IDT) were generally higher than measured values (TSRST). In addition, predicted fracture temperatures from binder test results demonstrated that binder testing alone is not sufficient to evaluate CRM mixtures. Thermal fatigue was explored in the third experiment using conventional load-induced fatigue tests with conditions selected to simulate daily temperature fluctuations. Test results indicated that thermal fatigue may contribute to transverse cracking in asphalt pavements. Both unmodified and modified mixtures had a finite capacity to withstand daily temperature fluctuations coupled with cold temperatures. Modified mixtures again exhibited improved performance. The fourth experiment examined fracture properties of modified and unmodified mixtures using a common fracture toughness test

  11. Computations of fluid mixtures including solid carbon at chemical equilibrium

    NASA Astrophysics Data System (ADS)

    Bourasseau, Emeric

    2013-06-01

    One of the key points of the understanding of detonation phenomena is the determination of equation of state of the detonation products mixture. Concerning carbon rich explosives, detonation products mixtures are composed of solid carbon nano-clusters immersed in a high density fluid phase. The study of such systems where both chemical and phase equilibriums occur simultaneously represents an important challenge and molecular simulation methods appear to be one of the more promising way to obtain some answers. In this talk, the Reaction Ensemble Monte Carlo (RxMC) method will be presented. This method allows the system to reach the chemical equilibrium of a mixture driven by a set of linearly independent chemical equations. Applied to detonation product mixtures, it allows the calculation of the chemical composition of the mixture and its thermodynamic properties. Moreover, an original model has been proposed to take explicitly into account a solid carbon meso-particle in thermodynamic and chemical equilibrium with the fluid. Finally our simulations show that the intrinsic inhomogeneous nature of the system (i.e. the fact that the solid phase is immersed in the fluid phase) has an important impact on the thermodynamic properties, and as a consequence must be taken into account.

  12. Studies of Particle Packings in Mixtures of Pharmaceutical Excipients

    NASA Astrophysics Data System (ADS)

    Bentham, Craig; Dutt, Meenakshi; Hancock, Bruno; Elliott, James

    2005-03-01

    Pharmaceutical powder blends used to generate tablets are complex multicomponent mixtures of the drug powder and excipients which facilitate the delivery of the required drug. The individual constituents of these blends can be noncohesive and cohesive powders. We study the geometric and mechanical characteristics of idealized mixtures of excipient particle packings, for a small but representative number of dry noncohesive particles, generated via gravitational compaction followed by uniaxial compaction. We discuss particle packings in 2- and 3- component mixtures of microcrystalline cellulose (MCC) & lactose and MCC, starch & lactose, respectively. We have computed the evolution of the force and stress distributions in monodisperse and polydisperse mixtures comprised of equal parts of each excipient; comparisons are made with results for particles packings of pure blends of MCC and lactose. We also compute the stress-strain relations for these mixtures. In order to obtain insight into details of the particle packings, we calculate the coordination number, packing fraction, radial distribution functions and contact angle distributions for the various mixtures. The numerical experiments have been performed on spheroidal idealizations of the excipient grains using Discrete Element Method simulations (Dutt et al., 2004 to be published).

  13. Bayesian analysis of nonlinear mixed-effects mixture models for longitudinal data with heterogeneity and skewness.

    PubMed

    Lu, Xiaosun; Huang, Yangxin

    2014-07-20

    It is a common practice to analyze complex longitudinal data using nonlinear mixed-effects (NLME) models with normality assumption. The NLME models with normal distributions provide the most popular framework for modeling continuous longitudinal outcomes, assuming individuals are from a homogeneous population and relying on random-effects to accommodate inter-individual variation. However, the following two issues may standout: (i) normality assumption for model errors may cause lack of robustness and subsequently lead to invalid inference and unreasonable estimates, particularly, if the data exhibit skewness and (ii) a homogeneous population assumption may be unrealistically obscuring important features of between-subject and within-subject variations, which may result in unreliable modeling results. There has been relatively few studies concerning longitudinal data with both heterogeneity and skewness features. In the last two decades, the skew distributions have shown beneficial in dealing with asymmetric data in various applications. In this article, our objective is to address the simultaneous impact of both features arisen from longitudinal data by developing a flexible finite mixture of NLME models with skew distributions under Bayesian framework that allows estimates of both model parameters and class membership probabilities for longitudinal data. Simulation studies are conducted to assess the performance of the proposed models and methods, and a real example from an AIDS clinical trial illustrates the methodology by modeling the viral dynamics to compare potential models with different distribution specifications; the analysis results are reported.

  14. Dipole oscillations in fermionic mixtures

    SciTech Connect

    Chiacchiera, S.; Macri, T.; Trombettoni, A.

    2010-03-15

    We study dipole oscillations in a general fermionic mixture. Starting from the Boltzmann equation, we classify the different solutions in the parameter space through the number of real eigenvalues of the small oscillations matrix. We discuss how this number can be computed using the Sturm algorithm and its relation with the properties of the Laplace transform of the experimental quantities. After considering two components in harmonic potentials having different trapping frequencies, we study dipole oscillations in three-component mixtures. Explicit computations are done for realistic experimental setups using the classical Boltzmann equation without intraspecies interactions. A brief discussion of the application of this classification to general collective oscillations is also presented.

  15. 14 CFR 23.1147 - Mixture controls.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Mixture controls. 23.1147 Section 23.1147... Accessories § 23.1147 Mixture controls. (a) If there are mixture controls, each engine must have a separate control, and each mixture control must have guards or must be shaped or arranged to prevent confusion...

  16. 14 CFR 23.1147 - Mixture controls.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Mixture controls. 23.1147 Section 23.1147... Accessories § 23.1147 Mixture controls. (a) If there are mixture controls, each engine must have a separate control, and each mixture control must have guards or must be shaped or arranged to prevent confusion...

  17. 16 CFR 1500.5 - Hazardous mixtures.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 16 Commercial Practices 2 2010-01-01 2010-01-01 false Hazardous mixtures. 1500.5 Section 1500.5... HAZARDOUS SUBSTANCES AND ARTICLES; ADMINISTRATION AND ENFORCEMENT REGULATIONS § 1500.5 Hazardous mixtures. For a mixture of substances, the determination of whether the mixture is a “hazardous substance”...

  18. 16 CFR 1500.5 - Hazardous mixtures.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 16 Commercial Practices 2 2011-01-01 2011-01-01 false Hazardous mixtures. 1500.5 Section 1500.5... HAZARDOUS SUBSTANCES AND ARTICLES; ADMINISTRATION AND ENFORCEMENT REGULATIONS § 1500.5 Hazardous mixtures. For a mixture of substances, the determination of whether the mixture is a “hazardous substance”...

  19. 16 CFR 1500.5 - Hazardous mixtures.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 16 Commercial Practices 2 2014-01-01 2014-01-01 false Hazardous mixtures. 1500.5 Section 1500.5... HAZARDOUS SUBSTANCES AND ARTICLES; ADMINISTRATION AND ENFORCEMENT REGULATIONS § 1500.5 Hazardous mixtures. For a mixture of substances, the determination of whether the mixture is a “hazardous substance”...

  20. 16 CFR 1500.5 - Hazardous mixtures.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 16 Commercial Practices 2 2013-01-01 2013-01-01 false Hazardous mixtures. 1500.5 Section 1500.5... HAZARDOUS SUBSTANCES AND ARTICLES; ADMINISTRATION AND ENFORCEMENT REGULATIONS § 1500.5 Hazardous mixtures. For a mixture of substances, the determination of whether the mixture is a “hazardous substance”...

  1. 14 CFR 23.1147 - Mixture controls.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Mixture controls. 23.1147 Section 23.1147... Accessories § 23.1147 Mixture controls. (a) If there are mixture controls, each engine must have a separate control, and each mixture control must have guards or must be shaped or arranged to prevent confusion...

  2. 16 CFR 1500.5 - Hazardous mixtures.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 16 Commercial Practices 2 2012-01-01 2012-01-01 false Hazardous mixtures. 1500.5 Section 1500.5... HAZARDOUS SUBSTANCES AND ARTICLES; ADMINISTRATION AND ENFORCEMENT REGULATIONS § 1500.5 Hazardous mixtures. For a mixture of substances, the determination of whether the mixture is a “hazardous substance”...

  3. 14 CFR 23.1147 - Mixture controls.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Mixture controls. 23.1147 Section 23.1147... Accessories § 23.1147 Mixture controls. (a) If there are mixture controls, each engine must have a separate control, and each mixture control must have guards or must be shaped or arranged to prevent confusion...

  4. 14 CFR 23.1147 - Mixture controls.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Mixture controls. 23.1147 Section 23.1147... Accessories § 23.1147 Mixture controls. (a) If there are mixture controls, each engine must have a separate control, and each mixture control must have guards or must be shaped or arranged to prevent confusion...

  5. Microstructure and hydrogen bonding in water-acetonitrile mixtures.

    PubMed

    Mountain, Raymond D

    2010-12-16

    The connection of hydrogen bonding between water and acetonitrile in determining the microheterogeneity of the liquid mixture is examined using NPT molecular dynamics simulations. Mixtures for six, rigid, three-site models for acetonitrile and one water model (SPC/E) were simulated to determine the amount of water-acetonitrile hydrogen bonding. Only one of the six acetonitrile models (TraPPE-UA) was able to reproduce both the liquid density and the experimental estimates of hydrogen bonding derived from Raman scattering of the CN stretch band or from NMR quadrupole relaxation measurements. A simple modification of the acetonitrile model parameters for the models that provided poor estimates produced hydrogen-bonding results consistent with experiments for two of the models. Of these, only one of the modified models also accurately determined the density of the mixtures. The self-diffusion coefficient of liquid acetonitrile provided a final winnowing of the modified model and the successful, unmodified model. The unmodified model is provisionally recommended for simulations of water-acetonitrile mixtures.

  6. Effect of the NACA Injection Impeller on the Mixture Distribution of a Double-row Radial Aircraft Engine

    NASA Technical Reports Server (NTRS)

    Marble, Frank E.; Ritter, William K.; Miller, Mahlon A.

    1946-01-01

    For the normal range of engine power the impeller provided marked improvement over the standard spray-bar injection system. Mixture distribution at cruising was excellent, maximum cylinder temperatures were reduced about 30 degrees F, and general temperature distribution was improved. The uniform mixture distribution restored the normal response of cylinder temperature to mixture enrichment and it reduced the possibility of carburetor icing, while no serious loss in supercharger pressure rise resulted from injection of fuel near the impeller outlet. The injection impeller also furnished a convenient means of adding water to the charge mixture for internal cooling.

  7. Vapor-alcohol control tests with compressed ethanol-gas mixtures: scientific basis and actual performance.

    PubMed

    Dubowski, K M; Essary, N A

    1996-10-01

    Commercial compressed vapor-alcohol mixtures ("dry gas") were evaluated to ascertain their suitability for control tests in breath-alcohol analysis. Dry gas control tests were conducted at nominal vapor-alcohol concentrations (VACs) of 0.045, 0.085, and 0.105 g/210 L (n = 50 at each VAC) with Alcotest 7110 MK III and Intoxilyzer 1400 evidential breath-alcohol testers. The measurement results were analyzed by standard statistical methods, and their correlation with certified dry gas VAC target values was examined. Also measured and examined statistically were the VACs of National Institute of Standards and Technology-traceable Research Gas mixtures (dry gas) ethanol standards at 97.8 and 198 ppm (n = 30-50 at each VAC). With the Alcotest 7110 MK III programmed to report VACs normalized to standard atmospheric pressure at 760 torr and the intoxilyzer 1400 programmed to report VACs at ambient atmospheric pressure, the predicted effects of ambient atmospheric pressure were confirmed experimentally. We developed and validated the following conversion factor for VAC units at 34 degrees C and 760 torr: ppm/2605 = g/210 L and g/210 L x 2605 = ppm. We found that the dry gas vapor-alcohol control samples conformed to established formal specifications and concluded that they compared favorably with simulator effluents for control tests of breath-alcohol analyzers, which are capable of adjusting VAC results for ambient atmospheric pressure.

  8. Taylor dispersion analysis of mixtures.

    PubMed

    Cottet, Hervé; Biron, Jean-Philippe; Martin, Michel

    2007-12-01

    Taylor dispersion analysis (TDA) is a fast and simple method for determining hydrodynamic radii. In the case of sample mixtures, TDA, as the other nonseparative methods, leads to an average diffusion coefficient on the different molecules constituting the mixture. We set in this work the equations giving, on a consistent basis, the average values obtained by TDA with detectors with linear response functions. These equations confronted TDA experiments of sample mixtures containing different proportions of a small molecule and a polymer standard. Very good agreement between theory and experiment was obtained. In a second part of this work, on the basis of monomodal or bimodal molar mass distributions of polymers, the different average diffusion coefficients corresponding to TDA were compared to the z-average diffusion coefficient (D(z)) obtained from dynamic light scattering (DLS) experiments and to the weight average diffusion coefficient (D(w)). This latter value is sometimes considered as the most representative of the sample mixture. From these results, it appears that, for monomodal distribution and relatively low polydispersity (I = 1.15), the average diffusion coefficient generally derived from TDA is very close to Dw. However, for highly polydisperse samples (e.g., bimodal polydisperse distributions), important differences could be obtained (up to 35% between TDA and D(w)). In all the cases, the average diffusion coefficient obtained by TDA for a mass concentration detector was closer to the Dw value than the z-average obtained by DLS.

  9. Electrochemical signatures of multivitamin mixtures.

    PubMed

    Mohan, A M Vinu; Brunetti, Barbara; Bulbarello, Andrea; Wang, Joseph

    2015-11-21

    The ability of cyclic square wave voltammetry to identify distinct fingerprints of multiple vitamins, in a single voltammetric run, is demonstrated. This method represents an efficient alternative to more common techniques for fast screening of complex vitamin mixtures or commercial tablets due to its low cost, high speed and sensitivity.

  10. Genetic Analysis of Plant Mixtures

    PubMed Central

    Griffing, B.

    1989-01-01

    Plant mixtures are difficult to analyze genetically because of possible interactions between neighboring plants (i.e., between plants in the same biological group). However, a genetic modeling scheme has been devised which, theoretically, can accommodate such interactions. This study was an attempt to put the theoretical modeling procedure to an experimental test. To this end an experimental procedure was devised that generated biological groups from a well defined base population. A cultural system was used which permitted growing plant mixtures in controlled environmental facilities. This allowed the experiment to be conducted over a wide range of temperature and nutrient conditions. Application of the theoretical gene model to the experimental data permitted identification of those classes of gene effects that were responsible for genetic variation exhibited by the mixtures. Adequacy of the genetic modeling description was corroborated by precise prediction of an independent genetic response. The genetic analyses also identified statistically significant temperature-and nutrient-dependent forms of heterosis. It was concluded that the study demonstrated the suitability of the theoretical group gene model for describing complexities inherent in plant mixtures. PMID:17246509

  11. Normalized medical information visualization.

    PubMed

    Sánchez-de-Madariaga, Ricardo; Muñoz, Adolfo; Somolinos, Roberto; Castro, Antonio; Velázquez, Iker; Moreno, Oscar; García-Pacheco, José L; Pascual, Mario; Salvador, Carlos H

    2015-01-01

    A new mark-up programming language is introduced in order to facilitate and improve the visualization of ISO/EN 13606 dual model-based normalized medical information. This is the first time that visualization of normalized medical information is addressed and the programming language is intended to be used by medical non-IT professionals.

  12. Molecular Simulation Of Nonequilibrium Hypersonic Flows

    NASA Astrophysics Data System (ADS)

    Schwartzentruber, T. E.; Valentini, P.; Tump, P.

    2011-05-01

    Large-scale conventional time-driven molecular dynamics (MD) simulations of normal shock waves are performed for monatomic argon and argon-helium mixtures. For pure argon, near perfect agreement between MD and direct simulation Monte Carlo (DSMC) results using the variable-hard-sphere model are found for density and temperature profiles as well as for velocity distribution functions throughout the shock. MD simulation results for argon are also in excellent agreement with experimental shock thickness data. Preliminary MD simulation results for argon-helium mixtures are in qualitative agreement with experimental density and temperature profile data, where separation between argon and helium density profiles due to disparate atomic mass is observed. Since conventional time-driven MD simulation of dilute gases is computationally inefficient, a combined Event-Driven/Time-Driven MD algorithm is presented. The ED/TD-MD algorithm computes impending collisions and advances molecules directly to their next collision while evaluating the collision using conventional time-driven MD with an arbitrary interatomic potential. The method timestep thus approaches the mean-collision- time in the gas, while also detecting and simulating multi-body collisions with a small approximation. Extension of the method to diatomic and small polyatomic molecules is detailed, where center-of-mass velocities and extended cutoff radii are used to advance molecules to impend- ing collisions. Only atomic positions are integrated during collisions and molecule sorting algorithms are em- ployed to determine if atoms are bound in a molecule after a collision event. Rotational relaxation to equilibrium for a low density diatomic gas is validated by comparison with large-scale conventional time-driven MD simulation, where the final rotational distribution function is verified to be the correct Boltzmann rotational energy distribution.

  13. Assessing variation in life-history tactics within a population using mixture regression models: a practical guide for evolutionary ecologists.

    PubMed

    Hamel, Sandra; Yoccoz, Nigel G; Gaillard, Jean-Michel

    2016-03-01

    Mixed models are now well-established methods in ecology and evolution because they allow accounting for and quantifying within- and between-individual variation. However, the required normal distribution of the random effects can often be violated by the presence of clusters among subjects, which leads to multi-modal distributions. In such cases, using what is known as mixture regression models might offer a more appropriate approach. These models are widely used in psychology, sociology, and medicine to describe the diversity of trajectories occurring within a population over time (e.g. psychological development, growth). In ecology and evolution, however, these models are seldom used even though understanding changes in individual trajectories is an active area of research in life-history studies. Our aim is to demonstrate the value of using mixture models to describe variation in individual life-history tactics within a population, and hence to promote the use of these models by ecologists and evolutionary ecologists. We first ran a set of simulations to determine whether and when a mixture model allows teasing apart latent clustering, and to contrast the precision and accuracy of estimates obtained from mixture models versus mixed models under a wide range of ecological contexts. We then used empirical data from long-term studies of large mammals to illustrate the potential of using mixture models for assessing within-population variation in life-history tactics. Mixture models performed well in most cases, except for variables following a Bernoulli distribution and when sample size was small. The four selection criteria we evaluated [Akaike information criterion (AIC), Bayesian information criterion (BIC), and two bootstrap methods] performed similarly well, selecting the right number of clusters in most ecological situations. We then showed that the normality of random effects implicitly assumed by evolutionary ecologists when using mixed models was often

  14. Sliding-surface-liquefaction of sand-dry ice mixture and submarine landslides

    NASA Astrophysics Data System (ADS)

    Fukuoka, H.; Tsukui, A.

    2010-12-01

    In the historic records of off-shore mega-earthquakes along the subduction zone offshore Japan, there are a lot of witnesses about large-scale burning of flammable gas possibly ejected from sea floor. This gas was supposed to be the dissolved methane hydrates (MH), which have been found in the soundings of IODP and other oceanology projects. Since the vast distribution of the BSR in the continental margins, a lot of papers have been published which pointed out the possibilities of that gasification of those hydrates could have triggered gigantic submarine landslides. Global warming or large earthquake or magma intrusion may trigger extremely deep gigantic landslides in continental margins that which could cause catastrophic tsunami. However, recent triaxial compression tests on artificially prepared sand-MH-mixture samples revealed that the they have slightly higher strength than the ones of only sands and MH’s endothermal characteristics may resist against accelerating shear and large-displacement landslides as well. While, the stress-controlled undrained ring shear apparatuses have been developed by Sassa and Fukuoka at Disaster Prevention Research Institute, Kyoto University to reproduce subaerial landslides induced by earthquakes and rainfalls. Using the apparatuses, they found localized liquefaction phenomenon along the deep saturated potential sliding surface due to excess pore pressure generation during the grain crushing induced bulk volume change. This phenomenon was named as “sliding surface liquefaction.” Similar sudden large pore pressure generation was observed in pore pressure control test simulating rain-induced landslides. In this paper, authors examined the shear behavior of the dry sand-dry ice mixture under constant normal stress and shear speed control tests using the latest ring shear apparatus. Sample was mixture of silica sands and dry-ice pellets (frozen carbon-dioxide). Those mixtures are often used for studying the mechanism of the

  15. Composition measurements of binary mixture droplets by rainbow refractometry

    SciTech Connect

    Wilms, J.; Weigand, B

    2007-04-10

    So far, refractive index measurements by rainbow refractometry have been used to determine the temperature of single droplets and ensembles of droplets. Rainbow refractometry is, for the first time, to the best of our knowledge, applied to measure composition histories of evaporating, binary mixture droplets. An evaluation method is presented that makes use of Airy theory and the simultaneous size measurement by Mie scattering imaging. The method further includes an empirical correction function for a certain diameter and refractive index range. The measurement uncertainty was investigated by numerical simulations with Lorenz-Mie theory. For the experiments, an optical levitation setup was used allowing for long measurement periods. Temperature measurements of single-component droplets at different temperature levels are shown to demonstrate the accuracy of rainbow refractometry. Measurements of size and composition histories of binary mixture droplets are presented for two different mixtures. Experimental results show good agreement with numerical results using a rapid-mixing model.

  16. Viscosity minima in binary mixtures of ionic liquids + molecular solvents.

    PubMed

    Tariq, M; Shimizu, K; Esperança, J M S S; Canongia Lopes, J N; Rebelo, L P N

    2015-05-28

    The viscosity (η) of four binary mixtures (ionic liquids plus molecular solvents, ILs+MSs) was measured in the 283.15 < T/K < 363.15 temperature range. Different IL/MS combinations were selected in such a way that the corresponding η(T) functions exhibit crossover temperatures at which both pure components present identical viscosity values. Consequently, most of the obtained mixture isotherms, η(x), exhibit clear viscosity minima in the studied T-x range. The results are interpreted using auxiliary molecular dynamics (MD) simulation data in order to correlate the observed η(T,x) trends with the interactions in each mixture, including the balance between electrostatic forces and hydrogen bonding.

  17. Chemical kinetic modeling of component mixtures relevant to gasoline

    SciTech Connect

    Mehl, M; Curran, H J; Pitz, W J; Westbrook, C K

    2009-02-13

    Real fuels are complex mixtures of thousands of hydrocarbon compounds including linear and branched paraffins, naphthenes, olefins and aromatics. It is generally agreed that their behavior can be effectively reproduced by simpler fuel surrogates containing a limited number of components. In this work, a recently revised version of the kinetic model by the authors is used to analyze the combustion behavior of several components relevant to gasoline surrogate formulation. Particular attention is devoted to linear and branched saturated hydrocarbons (PRF mixtures), olefins (1-hexene) and aromatics (toluene). Model predictions for pure components, binary mixtures and multi-component gasoline surrogates are compared with recent experimental information collected in rapid compression machine, shock tube and jet stirred reactors covering a wide range of conditions pertinent to internal combustion engines. Simulation results are discussed focusing attention on the mixing effects of the fuel components.

  18. Thermodynamic properties and diffusion of water + methane binary mixtures

    SciTech Connect

    Shvab, I.; Sadus, Richard J.

    2014-03-14

    Thermodynamic and diffusion properties of water + methane mixtures in a single liquid phase are studied using NVT molecular dynamics. An extensive comparison is reported for the thermal pressure coefficient, compressibilities, expansion coefficients, heat capacities, Joule-Thomson coefficient, zero frequency speed of sound, and diffusion coefficient at methane concentrations up to 15% in the temperature range of 298–650 K. The simulations reveal a complex concentration dependence of the thermodynamic properties of water + methane mixtures. The compressibilities, heat capacities, and diffusion coefficients decrease with increasing methane concentration, whereas values of the thermal expansion coefficients and speed of sound increase. Increasing methane concentration considerably retards the self-diffusion of both water and methane in the mixture. These effects are caused by changes in hydrogen bond network, solvation shell structure, and dynamics of water molecules induced by the solvation of methane at constant volume conditions.

  19. Simple and complex disorder in binary mixtures with benzene as a common solvent.

    PubMed

    Požar, Martina; Seguier, Jean-Baptiste; Guerche, Jonas; Mazighi, Redha; Zoranić, Larisa; Mijaković, Marijana; Kežić-Lovrinčević, Bernarda; Sokolić, Franjo; Perera, Aurélien

    2015-04-21

    Substituting benzene for water in computer simulations of binary mixtures allows one to study the various forms of disorder, without the complications often encountered in aqueous mixtures. In particular, we study the relationship between the local order generated by different types of molecular interactions and the nature of the global disorder, by analyzing the relationship between the concentration fluctuations and the correlation functions and the associated structure factors. Alkane-benzene mixtures are very close to ideal mixtures, despite appreciable short range shape mismatch interactions, acetone-benzene mixtures appear as a good example of regular mixtures, and ethanol-benzene mixtures show large micro-segregation. In the latter case, we can unambiguously demonstrate, unlike in the case of water, the appearance of domain-domain correlations, both in the correlation functions and the structure factor calculated in computer simulations. This finding helps to confirm the existence of a pre-peak in the structure factor associated with the micro-heterogeneity, which was speculated from several of our previous simulations of aqueous-alcohol mixtures. The fact that benzene as a solvent allows us to solve some of the problems that could not be solved with water points towards some of the particularities of water as a solvent, which we discuss herein. The concept of molecular emulsion put forward in our earlier work is useful in formulating these differences between water and benzene through the analogy with direct and inverse micellar aggregates.

  20. Normality in Analytical Psychology

    PubMed Central

    Myers, Steve

    2013-01-01

    Although C.G. Jung’s interest in normality wavered throughout his career, it was one of the areas he identified in later life as worthy of further research. He began his career using a definition of normality which would have been the target of Foucault’s criticism, had Foucault chosen to review Jung’s work. However, Jung then evolved his thinking to a standpoint that was more aligned to Foucault’s own. Thereafter, the post Jungian concept of normality has remained relatively undeveloped by comparison with psychoanalysis and mainstream psychology. Jung’s disjecta membra on the subject suggest that, in contemporary analytical psychology, too much focus is placed on the process of individuation to the neglect of applications that consider collective processes. Also, there is potential for useful research and development into the nature of conflict between individuals and societies, and how normal people typically develop in relation to the spectrum between individuation and collectivity. PMID:25379262

  1. Normal Pressure Hydrocephalus

    MedlinePlus

    ... techniques and neuroimaging, and finding improved treatments and preventions. Information from the National Library of Medicine’s MedlinePlus Normal Pressure Hydrocephalus × What research is being ...

  2. Normal Functioning Family

    MedlinePlus

    ... Spread the Word Shop AAP Find a Pediatrician Family Life Medical Home Family Dynamics Adoption & Foster Care ... Español Text Size Email Print Share Normal Functioning Family Page Content Article Body Is there any way ...

  3. MULTIVARIATE KERNEL PARTITION PROCESS MIXTURES

    PubMed Central

    Dunson, David B.

    2013-01-01

    Mixtures provide a useful approach for relaxing parametric assumptions. Discrete mixture models induce clusters, typically with the same cluster allocation for each parameter in multivariate cases. As a more flexible approach that facilitates sparse nonparametric modeling of multivariate random effects distributions, this article proposes a kernel partition process (KPP) in which the cluster allocation varies for different parameters. The KPP is shown to be the driving measure for a multivariate ordered Chinese restaurant process that induces a highly-flexible dependence structure in local clustering. This structure allows the relative locations of the random effects to inform the clustering process, with spatially-proximal random effects likely to be assigned the same cluster index. An exact block Gibbs sampler is developed for posterior computation, avoiding truncation of the infinite measure. The methods are applied to hormone curve data, and a dependent KPP is proposed for classification from functional predictors. PMID:24478563

  4. Thermodynamic properties of model CdTe/CdSe mixtures

    SciTech Connect

    van Swol, Frank; Zhou, Xiaowang W.; Challa, Sivakumar R.; Martin, James E.

    2015-02-20

    We report on the thermodynamic properties of binary compound mixtures of model groups II–VI semiconductors. We use the recently introduced Stillinger–Weber Hamiltonian to model binary mixtures of CdTe and CdSe. We use molecular dynamics simulations to calculate the volume and enthalpy of mixing as a function of mole fraction. The lattice parameter of the mixture closely follows Vegard's law: a linear relation. This implies that the excess volume is a cubic function of mole fraction. A connection is made with hard sphere models of mixed fcc and zincblende structures. We found that the potential energy exhibits a positive deviation from ideal soluton behaviour; the excess enthalpy is nearly independent of temperatures studied (300 and 533 K) and is well described by a simple cubic function of the mole fraction. Using a regular solution approach (combining non-ideal behaviour for the enthalpy with ideal solution behaviour for the entropy of mixing), we arrive at the Gibbs free energy of the mixture. The Gibbs free energy results indicate that the CdTe and CdSe mixtures exhibit phase separation. The upper consolute temperature is found to be 335 K. Finally, we provide the surface energy as a function of composition. Moreover, it roughly follows ideal solution theory, but with a negative deviation (negative excess surface energy). This indicates that alloying increases the stability, even for nano-particles.

  5. Thermodynamic properties of model CdTe/CdSe mixtures

    DOE PAGES

    van Swol, Frank; Zhou, Xiaowang W.; Challa, Sivakumar R.; ...

    2015-02-20

    We report on the thermodynamic properties of binary compound mixtures of model groups II–VI semiconductors. We use the recently introduced Stillinger–Weber Hamiltonian to model binary mixtures of CdTe and CdSe. We use molecular dynamics simulations to calculate the volume and enthalpy of mixing as a function of mole fraction. The lattice parameter of the mixture closely follows Vegard's law: a linear relation. This implies that the excess volume is a cubic function of mole fraction. A connection is made with hard sphere models of mixed fcc and zincblende structures. We found that the potential energy exhibits a positive deviation frommore » ideal soluton behaviour; the excess enthalpy is nearly independent of temperatures studied (300 and 533 K) and is well described by a simple cubic function of the mole fraction. Using a regular solution approach (combining non-ideal behaviour for the enthalpy with ideal solution behaviour for the entropy of mixing), we arrive at the Gibbs free energy of the mixture. The Gibbs free energy results indicate that the CdTe and CdSe mixtures exhibit phase separation. The upper consolute temperature is found to be 335 K. Finally, we provide the surface energy as a function of composition. Moreover, it roughly follows ideal solution theory, but with a negative deviation (negative excess surface energy). This indicates that alloying increases the stability, even for nano-particles.« less

  6. The use of gaseous fuels mixtures for SI engines propulsion

    NASA Astrophysics Data System (ADS)

    Flekiewicz, M.; Kubica, G.

    2016-09-01

    Paper presents results of SI engine tests, carried on for different gaseous fuels. Carried out analysis made it possible to define correlation between fuel composition and engine operating parameters. Tests covered various gaseous mixtures: of methane and hydrogen and LPG with DME featuring different shares. The first group, considered as low carbon content fuels can be characterized by low CO2 emissions. Flammability of hydrogen added in those mixtures realizes the function of combustion process activator. That is why hydrogen addition improves the energy conversion by about 3%. The second group of fuels is constituted by LPG and DME mixtures. DME mixes perfectly with LPG, and differently than in case of other hydrocarbon fuels consists also of oxygen makes the stoichiometric mixture less oxygen demanding. In case of this fuel an improvement in engine volumetric and overall engine efficiency has been noticed, when compared to LPG. For the 11% DME share in the mixture an improvement of 2% in the efficiency has been noticed. During the tests standard CNG/LPG feeding systems have been used, what underlines utility value of the research. The stand tests results have been followed by combustion process simulation including exhaust forming and charge exchange.

  7. Multisubstrate biodegradation kinetics of naphthalene, phenanthrene, and pyrene mixtures

    SciTech Connect

    Guha, S.; Peters, C.A.; Jaffe, P.R.

    1999-12-05

    Biodegradation kinetics of naphthalene, phenanthrene and pyrene were studied in sole-substrate systems, and in binary and ternary mixtures to examine substrate interactions. The experiments were conducted in aerobic batch aqueous systems inoculated with a mixed culture that had been isolated from soils contaminated with polycyclic aromatic hydrocarbons (PAHs). Monod kinetic parameters and yield coefficients for the individual parameters and yield coefficients for the individual compounds were estimated from substrate depletion and CO{sub 2} evolution rate data in sole-substrate experiments. In all three binary mixture experiments, biodegradation kinetics were comparable to the sole-substrate kinetics. In the ternary mixture, biodegradation of naphthalene was inhibited and the biodegradation rates of phenanthrene and pyrene were enhanced. A multisubstrate form of the Monod kinetic model was found to adequately predict substrate interactions in the binary and ternary mixtures using only the parameters derived from sole-substrate experiments. Numerical simulations of biomass growth kinetics explain the observed range of behaviors in PAH mixtures. In general, the biodegradation rates of the more degradable and abundant compounds are reduced due to competitive inhibition, but enhanced biodegradation of the more recalcitrant PAHs occurs due to simultaneous biomass growth on multiple substrates. In PAH-contaminated environments, substrate interactions may be very large due to additive effects from the large number of compounds present.

  8. Prediction of trapping rates in mixtures of partially absorbing spheres

    NASA Astrophysics Data System (ADS)

    Kansal, Anuraag R.; Torquato, Salvatore

    2002-06-01

    The combined effects of diffusion and reaction in heterogeneous media govern the behavior of a wide variety of physical and biological phenomena, including the consumption of nutrients by cells and the study of magnetic relaxation in tissues. We have considered the so-called "trapping problem," in which diffusion takes place exterior to a collection of fixed traps while reaction occurs at their surface. A simulation technique for predicting the overall trapping rate for systems of partially absorbing spherical traps based on the first-passage spheres method is presented. Using data obtained by applying this simulation technique, we then consider the problem of mixtures of partially absorbing traps. By hypothesizing a method for reducing a general mixture of traps to a mixture of perfect absorbers and perfect reflectors (i.e., reducing the dimensionality of the space of variables), we are able to accurately predict the effective surface rate constant and the trapping rate for an arbitrary mixture of partially absorbing traps. Remarkably, we find that a single, nearly universal curve allows accurate predictions to be made over a wide range of trap volume fractions and even for different trap distributions.

  9. Apparent diffusion coefficient normalization of normal liver

    PubMed Central

    Zhu, Jie; Zhang, Jie; Gao, Jia-Yin; Li, Jin-Ning; Yang, Da-Wei; Chen, Min; Zhou, Cheng; Yang, Zheng-Han

    2017-01-01

    Abstract Apparent diffusion coefficient (ADC) measurement in diffusion-weighted imaging (DWI) has been reported to be a helpful biomarker for detection and characterization of lesion. In view of the importance of ADC measurement reproducibility, the aim of this study was to probe the variability of the healthy hepatic ADC values measured at 3 MR scanners from different vendors and with different field strengths, and to investigate the reproducibility of normalized ADC (nADC) value with the spleen as the reference organ. Thirty enrolled healthy volunteers received DWI with GE 1.5T, Siemens 1.5T, and Philips 3.0T magnetic resonance (MR) systems on liver and spleen (session 1) and were imaged again after 10 to 14 days using only GE 1.5T MR and Philips 3.0T MR systems (session 2). Interscan agreement and reproducibility of ADC measurements of liver and the calculated nADC values (ADCliver/ADCspleen) were statistically evaluated between 2 sessions. In session 1, ADC and nADC values of liver were evaluated for the scanner-related variability by 2-way analysis of variance and intraclass correlation coefficients (ICCs). Coefficients of variation (CVs) of ADCs and nADCs of liver were calculated for both 1.5 and 3.0-T MR system. Interscan agreement and reproducibility of ADC measurements of liver and related nADCs between 2 sessions were found to be satisfactory with ICC values of 0.773 to 0.905. In session 1, the liver nADCs obtained from different scanners were consistent (P = 0.112) without any significant difference in multiple comparison (P = 0.117 to >0.99) by using 2-way analysis of variance with post-hoc analysis of Bonferroni method, although the liver ADCs varied significantly (P < 0.001). nADCs measured by 3 scanners were in good interscanner agreements with ICCs of 0.685 to 0.776. The mean CV of nADCs of both 1.5T MR scanners (9.6%) was similar to that of 3.0T MR scanner (8.9%). ADCs measured at 3 MR scanners with different field strengths and vendors

  10. Variable mixture ratio performance through nitrogen augmentation

    NASA Technical Reports Server (NTRS)

    Beichel, R.; Obrien, C. J.; Bair, E. K.

    1988-01-01

    High/variable mixture ratio O2/H2 candidate engine cycles are examined for earth-to-orbit vehicle application. Engine performance and power balance information are presented for the candidate cycles relative to chamber pressure, bulk density, and mixture ratio. Included in the cycle screening are concepts where a third fluid (liquid nitrogen) is used to achieve a variable mixture ratio over the trajectory from liftoff to earth orbit. The third fluid cycles offer a very low risk, fully reusable, low operation cost alternative to high/variable mixture ratio bipropellant cycles. Variable mixture ratio engines with extendible nozzle are slightly lower performing than a single mixture ratio engine (MR = 7:1) with extendible nozzle. Dual expander engines (MR = 7:1) have slightly better performance than the single mixture ratio engine. Dual fuel dual expander engines offer a 16 percent improvement over the single mixture ratio engine.

  11. A Bayesian spatial temporal mixtures approach to kinetic parametric images in dynamic positron emission tomography

    PubMed Central

    Zhu, W.; Ouyang, J.; Rakvongthai, Y.; Guehl, N. J.; Wooten, D. W.; El Fakhri, G.; Normandin, M. D.; Fan, Y.

    2016-01-01

    Purpose: Estimation of parametric maps is challenging for kinetic models in dynamic positron emission tomography. Since voxel kinetics tend to be spatially contiguous, the authors consider groups of homogeneous voxels together. The authors propose a novel algorithm to identify the groups and estimate kinetic parameters simultaneously. Uncertainty estimates for kinetic parameters are also obtained. Methods: Mixture models were used to fit the time activity curves. In order to borrow information from spatially nearby voxels, the Potts model was adopted. A spatial temporal model was built incorporating both spatial and temporal information in the data. Markov chain Monte Carlo was used to carry out parameter estimation. Evaluation and comparisons with existing methods were carried out on cardiac studies using both simulated data sets and a pig study data. One-compartment kinetic modeling was used, in which K1 is the parameter of interest, providing a measure of local perfusion. Results: Based on simulation experiments, the median standard deviation across all image voxels, of K1 estimates were 0, 0.13, and 0.16 for the proposed spatial mixture models (SMMs), standard curve fitting, and spatial K-means methods, respectively. The corresponding median mean squared biases for K1 were 0.04, 0.06, and 0.06 for abnormal region of interest (ROI); 0.03, 0.03, and 0.04 for normal ROI; and 0.007, 0.02, and 0.05 for the noise region. Conclusions: SMM is a fully Bayesian algorithm which determines the optimal number of homogeneous voxel groups, voxel group membership, parameter estimation, and parameter uncertainty estimation simultaneously. The voxel membership can also be used for classification purposes. By borrowing information from spatially nearby voxels, SMM substantially reduces the variability of parameter estimates. In some ROIs, SMM also reduces mean squared bias. PMID:26936707

  12. Analysis of gamma-ray burst duration distribution using mixtures of skewed distributions

    NASA Astrophysics Data System (ADS)

    Tarnopolski, M.

    2016-05-01

    Two classes of gamma-ray bursts (GRBs) have been confidently identified thus far and are prescribed to different physical scenarios - neutron star-neutron star or neutron star-black hole mergers, and collapse of massive stars, for short and long GRBs, respectively. A third, intermediate in duration class, was suggested to be present in previous catalogues, such as Burst Alert and Transient Source Explorer (BATSE) and Swift, based on statistical tests regarding a mixture of two or three lognormal distributions of T90. However, this might possibly not be an adequate model. This paper investigates whether the distributions of log T90 from BATSE, Swift, and Fermi are described better by a mixture of skewed distributions rather than standard Gaussians. Mixtures of standard normal, skew-normal, sinh-arcsinh and alpha-skew-normal distributions are fitted using a maximum likelihood method. The preferred model is chosen based on the Akaike information criterion. It is found that mixtures of two skew-normal or two sinh-arcsinh distributions are more likely to describe the observed duration distribution of Fermi than a mixture of three standard Gaussians, and that mixtures of two sinh-arcsinh or two skew-normal distributions are models competing with the conventional three-Gaussian in the case of BATSE and Swift. Based on statistical reasoning, and it is shown that other phenomenological models may describe the observed Fermi, BATSE, and Swift duration distributions at least as well as a mixture of standard normal distributions, and the existence of a third (intermediate) class of GRBs in Fermi data is rejected.

  13. A radiation damage repair model for normal tissues

    NASA Astrophysics Data System (ADS)

    Partridge, Mike

    2008-07-01

    A cellular Monte Carlo model describing radiation damage and repair in normal epithelial tissues is presented. The deliberately simplified model includes cell cycling, cell motility and radiation damage response (cell cycle arrest and cell death) only. Results demonstrate that the model produces a stable equilibrium system for mean cell cycle times in the range 24-96 h. Simulated irradiation of these stable equilibrium systems produced a range of responses that are shown to be consistent with experimental and clinical observation, including (i) re-epithelialization of radiation-induced lesions by a mixture of cell migration into the wound and repopulation at the periphery; (ii) observed radiosensitivity that is quantitatively consistent with both rate of induction of irreparable DNA lesions and, independently, with the observed acute oral and pharyngeal mucosal reactions to radiotherapy; (iii) an observed time between irradiation and maximum toxicity that is consistent with experimental data for skin; (iv) quantitatively accurate predictions of low-dose hyper-radiosensitivity; (v) Gomperzian repopulation for very small lesions (~2000 cells) and (vi) a linear rate of re-epithelialization of 5-10 µm h-1 for large lesions (>15 000 cells).

  14. Elusiveness of Fluid-Fluid Demixing in Additive Hard-Core Mixtures

    NASA Astrophysics Data System (ADS)

    Lafuente, Luis; Cuesta, José A.

    2002-09-01

    The conjecture that when an additive hard-core mixture phase separates when one of the phases is spatially ordered, well supported by considerable evidence, is in contradiction with some simulations of a binary mixture of hard cubes on cubic lattices. By extending Rosenfeld's fundamental measure theory to lattice models we show that the phase behavior of this mixture is far more complex than simulations show, exhibiting regions of stability of several smectic, columnar, and solid phases, but no fluid-fluid demixing. A comparison with the simulations show that they are, in fact, compatible with a fluid-columnar demixing transition, thus bringing this model into the same demixing scheme as the rest of additive hard-core mixtures.

  15. Stratification dynamics in drying colloidal mixtures.

    PubMed

    Howard, Michael P; Nikoubashman, Arash; Panagiotopoulos, Athanassios Z

    2017-03-28

    Stratification in binary colloidal mixtures was investigated using implicit-solvent molecular dynamics simulations. For large particle size ratios and film Péclet numbers greater than unity, smaller colloids migrated to the top of the film, while big colloids were pushed to the bottom, creating an "inverted" stratification. This peculiar behavior was observed in recent simulations and experiments conducted by Fortini et al. (Phys. Rev. Lett. 2016, 116, 118301). To rationalize this behavior, particle size ratios and drying rates spanning qualitatively different Péclet number regimes were systematically studied, and the dynamics of the inverted stratification were quantified in detail. The stratified layer of small colloids was found to grow faster and to larger thicknesses for larger size ratios. Interestingly, inverted stratification was observed even at moderate drying rates where the film Péclet numbers were comparable to unity, but the thickness of the stratified layer decreased. A model based on dynamical density functional theory is proposed to explain the observed phenomena.

  16. Nanostructural organization and anion effects in the optical Kerr effect spectra of binary ionic liquid mixtures.

    PubMed

    Xiao, Dong; Rajian, Justin Rajesh; Hines, Larry G; Li, Shengfu; Bartsch, Richard A; Quitevis, Edward L

    2008-10-23

    This article reports a study of the effect of anions on the optical Kerr effect (OKE) spectra of binary ionic liquid mixtures with one mixture comprising the 3-methyl-1-pentylimidazolium ([C 5mim] (+)) cation and the anions PF 6 (-) and CF 3CO 2 (-) (TFA (-)), and another mixture comprising the [C 5mim] (+) cation and the anions Br (-) and bis(trifluomethanesulfonyl)imide (NTf 2 (-)). The spectra were obtained by the use of optical heterodyne-detected Raman-induced Kerr Effect Spectroscopy at 295 K. The OKE spectra of the mixtures are compared with the calculated mole-fraction weighted sum of the normalized OKE spectra of the neat liquids. The OKE spectra are nearly additive for [C 5mim]Br/[C 5mim][NTf 2] mixtures, but nonadditive for [C 5mim][PF 6]/[C 5mim][TFA] mixtures. In the case of the equimolar [C 5mim][PF 6]/[C 5mim][TFA] mixture, the nonadditivity is such that the experimental OKE spectrum is narrower than the calculated OKE spectrum. The additivity or nonadditivity of OKE spectra for IL mixtures can be explained by assuming ionic liquids are nanostructurally organized into nonpolar regions and ionic networks. The ionic networks in mixtures will be characterized by "random co-networks" for anions that are nearly the same in size (PF 6 (-) and TFA (-)) and by "block co-networks" for anions that differ greatly in size (Br (-) and NTf 2 (-)).

  17. 21 CFR 82.6 - Certifiable mixtures.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... and, in the case of mixtures which are aqueous solutions or aqueous pastes, sodium benzoate in a... 21 Food and Drugs 1 2011-04-01 2011-04-01 false Certifiable mixtures. 82.6 Section 82.6 Food and... PROVISIONALLY LISTED COLORS AND SPECIFICATIONS General Provisions § 82.6 Certifiable mixtures. (a) A batch of...

  18. 21 CFR 82.6 - Certifiable mixtures.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... and, in the case of mixtures which are aqueous solutions or aqueous pastes, sodium benzoate in a... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Certifiable mixtures. 82.6 Section 82.6 Food and... PROVISIONALLY LISTED COLORS AND SPECIFICATIONS General Provisions § 82.6 Certifiable mixtures. (a) A batch of...

  19. 14 CFR 25.1147 - Mixture controls.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Mixture controls. 25.1147 Section 25.1147... STANDARDS: TRANSPORT CATEGORY AIRPLANES Powerplant Powerplant Controls and Accessories § 25.1147 Mixture controls. (a) If there are mixture controls, each engine must have a separate control. The controls must...

  20. 14 CFR 25.1147 - Mixture controls.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Mixture controls. 25.1147 Section 25.1147... STANDARDS: TRANSPORT CATEGORY AIRPLANES Powerplant Powerplant Controls and Accessories § 25.1147 Mixture controls. (a) If there are mixture controls, each engine must have a separate control. The controls must...