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Monte carlo

Saeideh Tasharrofi, Hossein Taghdisian, Abdollah Golchoobi
In this study, pure and ternary adsorption of hydrogen sulfide (H2 S), ethylbenzene (EB), and carbon monoxide (CO) on different arrays of zigzag double wall carbon nanotube was investigated using grand canonical Monte Carlo simulations. The internal diameters of nanotube were fixed at 2r = 50.17 Å while nanotube wall distances were different values from d = 0 Å to d = 150 Å. Pure simulation results indicated that adsorption quantity of H2 S and EB in low pressure ranges of P = 1.9 bar to P = 3...
March 2, 2018: Journal of Molecular Graphics & Modelling
Eric C Andrade, José A Hoyos, Stephan Rachel, Matthias Vojta
We study the impact of quenched disorder (random exchange couplings or site dilution) on easy-plane pyrochlore antiferromagnets. In the clean system, order by disorder selects a magnetically ordered state from a classically degenerate manifold. In the presence of randomness, however, different orders can be chosen locally depending on details of the disorder configuration. Using a combination of analytical considerations and classical Monte Carlo simulations, we argue that any long-range-ordered magnetic state is destroyed beyond a critical level of randomness where the system breaks into magnetic domains due to random exchange anisotropies, becoming, therefore, a glass of spin clusters, in accordance with the available experimental data...
March 2, 2018: Physical Review Letters
David Vernez, Sandrine Fraize-Frontier, Raymond Vincent, Stéphane Binet, Christophe Rousselle
OBJECTIVES: Assessment factors (AFs) are commonly used for deriving reference concentrations for chemicals. These factors take into account variabilities as well as uncertainties in the dataset, such as inter-species and intra-species variabilities or exposure duration extrapolation or extrapolation from the lowest-observed-adverse-effect level (LOAEL) to the noobserved- adverse-effect level (NOAEL). In a deterministic approach, the value of an AF is the result of a debate among experts and, often a conservative value is used as a default choice...
March 15, 2018: International Journal of Occupational Medicine and Environmental Health
Thomas Tängdén, Pier Giorgio Cojutti, Jason A Roberts, Federico Pea
BACKGROUND AND OBJECTIVES: Valganciclovir is used as oral prophylaxis for cytomegalovirus (CMV) infection in kidney transplant recipients. However, limited pharmacokinetic data exist to guide dosing in this patient group. This study aimed to describe the population pharmacokinetics of valganciclovir in a large sample of kidney transplant recipients and predict optimal dosing based on Monte Carlo simulations. METHODS: Therapeutic drug monitoring (TDM) data from adult kidney transplant recipients who received valganciclovir prophylaxis during a 10-year study period were collected retrospectively...
March 15, 2018: Clinical Pharmacokinetics
Andras P Durko, Ruben L Osnabrugge, Nicolas M Van Mieghem, Milan Milojevic, Darren Mylotte, Vuyisile T Nkomo, A Pieter Kappetein
Aims: The number of transcatheter aortic valve implantation (TAVI) procedures is rapidly increasing. This has a major impact on health care resource planning. However, the annual numbers of TAVI candidates per country are unknown. The aim of this study was to estimate current and future number of annual TAVI candidates in 27 European countries, the USA and Canada. Methods and results: Systematic literature searches and meta-analyses were performed on aortic stenosis (AS) epidemiology and decision-making in severe symptomatic AS...
March 12, 2018: European Heart Journal
J Vedelago, F Mattea, M Valente
The use and implementation of nanoparticles in medicine has grown exponentially in the last twenty years. Their main applications include drug delivery, theranostics, tissue engineering and magneto function. Dosimetry techniques can take advantage of inorganic nanoparticles properties and their combination with gel dosimetry techniques could be used as a first step for their later inclusion in radio-diagnostics or radiotherapy treatments. The present study presents preliminary results of properly synthesized and purified silver nanoparticles integration with Fricke gel dosimeters...
March 1, 2018: Applied Radiation and Isotopes
Shuai Zhang, Burkhard Militzer, Lorin X Benedict, François Soubiran, Philip A Sterne, Kevin P Driver
Carbon-hydrogen plasmas and hydrocarbon materials are of broad interest to laser shock experimentalists, high energy density physicists, and astrophysicists. Accurate equations of state (EOSs) of hydrocarbons are valuable for various studies from inertial confinement fusion to planetary science. By combining path integral Monte Carlo (PIMC) results at high temperatures and density functional theory molecular dynamics results at lower temperatures, we compute the EOSs for hydrocarbons from simulations performed at 1473 separate (ρ, T)-points distributed over a range of compositions...
March 14, 2018: Journal of Chemical Physics
Christopher Robertson, Scott Habershon
We present an approximation to the thermal symmetric form of the quantum time-correlation function in the standard position path-integral representation. By transforming to a sum-and-difference position representation and then Taylor-expanding the potential energy surface of the system to second order, the resulting expression provides a harmonic weighting function that approximately recovers the contribution of the phase to the time-correlation function. This method is readily implemented in a Monte Carlo sampling scheme and provides exact results for harmonic potentials (for both linear and non-linear operators) and near-quantitative results for anharmonic systems for low temperatures and times that are likely to be relevant to condensed phase experiments...
March 14, 2018: Journal of Chemical Physics
Giovanni Rillo, Miguel A Morales, David M Ceperley, Carlo Pierleoni
We performed simulations for solid molecular hydrogen at high pressures (250 GPa ≤ P ≤ 500 GPa) along two isotherms at T = 200 K (phase III) and at T = 414 K (phase IV). At T = 200 K, we considered likely candidates for phase III, the C2c and Cmca12 structures, while at T = 414 K in phase IV, we studied the Pc48 structure. We employed both Coupled Electron-Ion Monte Carlo (CEIMC) and Path Integral Molecular Dynamics (PIMD). The latter is based on Density Functional Theory (DFT) with the van der Waals approximation (vdW-DF)...
March 14, 2018: Journal of Chemical Physics
E Curotto, M Mella
We have computed ground state energies and analyzed radial distributions for several gas phase and adsorbed D2 (H2 )n and HD(H2 )n clusters. An external model potential designed to mimic ionic adsorption sites inside porous materials is used [M. Mella and E. Curotto, J. Phys. Chem. A 121, 5005 (2017)]. The isotopic substitution lowers the ground state energies by the expected amount based on the mass differences when these are compared with the energies of the pure clusters in the gas phase. A similar impact is found for adsorbed aggregates...
March 14, 2018: Journal of Chemical Physics
Shinichi Miura
In this paper, the ground state of para-hydrogen clusters for size regime N ≤ 40 has been studied by our variational path integral molecular dynamics method. Long molecular dynamics calculations have been performed to accurately evaluate ground state properties. The chemical potential of the hydrogen molecule is found to have a zigzag size dependence, indicating the magic number stability for the clusters of the size N = 13, 26, 29, 34, and 39. One-body density of the hydrogen molecule is demonstrated to have a structured profile, not a melted one...
March 14, 2018: Journal of Chemical Physics
Luis M Sesé
The problem of the equilibrium triplet structures in fluids with quantum behavior is discussed. Theoretical questions of interest to the real space structures are addressed by studying the three types of structures that can be determined via path integrals (instantaneous, centroid, and total thermalized-continuous linear response). The cases of liquid para-H2 and liquid neon on their crystallization lines are examined with path-integral Monte Carlo simulations, the focus being on the instantaneous and the centroid triplet functions (equilateral and isosceles configurations)...
March 14, 2018: Journal of Chemical Physics
Joseph R Cendagorta, Zlatko Bačić, Mark E Tuckerman
We introduce a scheme for approximating quantum time correlation functions numerically within the Feynman path integral formulation. Starting with the symmetrized version of the correlation function expressed as a discretized path integral, we introduce a change of integration variables often used in the derivation of trajectory-based semiclassical methods. In particular, we transform to sum and difference variables between forward and backward complex-time propagation paths. Once the transformation is performed, the potential energy is expanded in powers of the difference variables, which allows us to perform the integrals over these variables analytically...
March 14, 2018: Journal of Chemical Physics
Massimo Boninsegni
The momentum distribution and atomic kinetic energy of the two isotopes of helium in a liquid mixture at temperature T = 2 K are computed by quantum Monte Carlo simulations. Quantum statistics is fully included for4 He, whereas3 He atoms are treated as distinguishable. Comparison of theoretical estimates with a collection of the most recent experimental measurements shows reasonable agreement for the energetics of4 He and pure3 He. On the other hand, a significant discrepancy (already observed in previous studies) is reported between computed and measured values of the3 He kinetic energy in the mixture, especially in the limit of low3 He concentration...
March 14, 2018: Journal of Chemical Physics
B P Abolins, R E Zillich, K B Whaley
The quantum phase transitions of dipoles confined to the vertices of two-dimensional lattices of square and triangular geometry is studied using path integral ground state quantum Monte Carlo. We analyze the phase diagram as a function of the strength of both the dipolar interaction and a transverse electric field. The study reveals the existence of a class of orientational phases of quantum dipolar rotors whose properties are determined by the ratios between the strength of the anisotropic dipole-dipole interaction, the strength of the applied transverse field, and the rotational constant...
March 14, 2018: Journal of Chemical Physics
Yongbing Song, Teng Xie, Run Jiang, Zheng Wang, Yuhua Yin, Baohui Li, An-Chang Shi
The self-assembly behaviors of two block copolymers with the same chain length but different chain architectures (cyclic AB, linear ABA) in B-selective solvents are investigated using Monte Carlo simulations. A morphological transition sequence, from spherical micelles to cylindrical micelles, to vesicles and then to multicompartment vesicles, is observed for both copolymer systems when the interaction between the solvophobic A-block and the solvent is increased. In particular, toroidal micelles could be formed in triblock systems due to the presence of the bridging chains at the parameter region between cylindrical micelles and vesicles whereas disk-like micelles are formed in cyclic systems...
March 15, 2018: Langmuir: the ACS Journal of Surfaces and Colloids
Franck Maunoury, Aurore Clément, Chizoba Nwankwo, Laurie Levy-Bachelot, Armand Abergel, Vincent Di Martino, Eric Thervet, Isabelle Durand-Zaleski
OBJECTIVE: To assess the cost-effectiveness of the elbasvir/grazoprevir (EBR/GZR) regimen in patients with genotype 1 chronic hepatitis C virus (HCV) infection with severe and end-stage renal disease compared to no treatment. DESIGN: This study uses a health economic model to estimate the cost-effectiveness of treating previously untreated and treatment experienced chronic hepatitis C patients who have severe and end stage renal disease with the elbasvir-grazoprevir regimen versus no treatment in the French context...
2018: PloS One
Seungtaik Hwang, Arun Gopalan, Maximilian Hovestadt, Frank Piepenbreier, Christian Chmelik, Martin Hartmann, Randall Q Snurr, Jörg Kärger
Molecular diffusion is commonly found to slow down with increasing molecular size. Deviations from this pattern occur in some host materials with pore sizes approaching the diameters of the guest molecules. A variety of theoretical models have been suggested to explain deviations from this pattern, but robust experimental data are scarcely available. Here, we present such data, obtained by monitoring the chain length dependence of the uptake of n- alkanes in the zeolitic imidazolate framework ZIF-4. A monotonic decrease in diffusivity from ethane to n- butane was observed, followed by an increase for n- pentane, and another decrease for n- hexane...
March 15, 2018: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Lucy Kerns
In risk assessment, it is often desired to make inferences on the risk at certain low doses or on the dose(s) at which a specific benchmark risk (BMR) is attained. At times, [Formula: see text] dose levels or BMRs are of interest, and some form of multiplicity adjustment is necessary to ensure a valid [Formula: see text] simultaneous inference. Bonferroni correction is often employed in practice for such purposes. Though relative simple to implement, the Bonferroni strategy can suffer from extreme conservatism (Nitcheva et al...
March 15, 2018: Journal of Biopharmaceutical Statistics
Shengfeng Yang, Naixie Zhou, Hui Zheng, Shyue Ping Ong, Jian Luo
First-order interfacial phaselike transformations that break the mirror symmetry of the symmetric ∑5 (210) tilt grain boundary (GB) are discovered by combining a modified genetic algorithm with hybrid Monte Carlo and molecular dynamics simulations. Density functional theory calculations confirm this prediction. This first-order coupled structural and adsorption transformation, which produces two variants of asymmetric bilayers, vanishes at an interfacial critical point. A GB complexion (phase) diagram is constructed via semigrand canonical ensemble atomistic simulations for the first time...
February 23, 2018: Physical Review Letters
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