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Literatura académica sobre el tema "Dispersion interaction density"

Autor: Grafiati

Publicado: 4 de junio de 2021

Última modificación: 13 de febrero de 2022

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Artículos de revistas sobre el tema "Dispersion interaction density"

Becke, Axel D. y Erin R. Johnson. "A density-functional model of the dispersion interaction". Journal of Chemical Physics 123, n.º 15 (15 de octubre de 2005): 154101. http://dx.doi.org/10.1063/1.2065267.

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Tang, Hong y Jianmin Tao. "Long-range dispersion-corrected density functional for noncovalent interactions". International Journal of Modern Physics B 33, n.º 26 (20 de octubre de 2019): 1950300. http://dx.doi.org/10.1142/s0217979219503004.

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Noncovalent interactions are important in determining structures and properties of molecular complexes and biological molecules, and for understanding adsorption processes in chemistry and biological science, and are still challenging to conventional density functional theories. In this work, the recently developed Tao-Mo (TM) meta-GGA (generalized gradient approximation) functional is combined with the D3 scheme of long-range van der Waals (vdW) interaction correction and the parameters of damping function are optimized with the S66[Formula: see text]×[Formula: see text]8 set. The resulting TM-D3 method is applied to the medium-sized molecular set S22 and large size molecular complexes set L7 to calculate intramolecular interaction energies. The TM-D3 method produces the best accuracy for the S22 set with a MAE of 0.2 kcal/mol, improving upon the PBE-D3 (MAE[Formula: see text]=[Formula: see text]0.5 kcal/mol), PBE0-D3 (MAE[Formula: see text]=[Formula: see text]0.5 kcal/mol), TPSS-D3 (MAE[Formula: see text]=[Formula: see text]0.4 kcal/mol), M06L (MAE[Formula: see text]=[Formula: see text]0.8 kcal/mol), and SCAN-D3 (MAE[Formula: see text]=[Formula: see text]0.4 kcal/mol) methods. For the large size set L7, the TM-D3 (MAE[Formula: see text]=[Formula: see text]2.1 kcal/mol) also performs better than the PBE-D3 (MAE[Formula: see text]=[Formula: see text]2.6 kcal/mol), SCAN-D3 (2.5 kcal/mol) and M06L (3.0 kcal/mol), but not accurate than the PBE0-D3 (MAE[Formula: see text]=[Formula: see text]0.8 kcal/mol) and TPSS-D3 (MAE[Formula: see text]=[Formula: see text]1.1 kcal/mol). However, overall, the TM-D3 method performs very well with an error of 2.7% of mean binding of the S22 set and an error of 12.6% of the mean binding of the L7 set for the two typical and important medium and large size molecular complex sets. The success of the dispersion-corrected TM functional benefits from the ability of the plain TM functional to capture the short-range vdW interaction or extend the short-range interaction to the middle range, and the right coupling between the TM and the long-range vdW correction D3 scheme, leading to the improved description of noncovalent interactions.

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BARCI, DANIEL G., C. A. LINHARES, A. F. DE QUEIROZ y J. F. MEDEIROS NETO. "FUNCTIONAL BOSONIZATION OF NONRELATIVISTIC FERMIONS IN 2+1 DIMENSIONS". International Journal of Modern Physics A 15, n.º 29 (20 de noviembre de 2000): 4655–79. http://dx.doi.org/10.1142/s0217751x00002032.

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We analyze the universality of the bosonization rules in nonrelativistic fermionic systems in (2+1)d. We show that, in the case of linear fermionic dispersion relations, a general fermionic theory can be mapped into a gauge theory in such a way that the fermionic density maps into a magnetic flux and the fermionic current maps into a transverse electric field. These are universal rules in the sense that they remain valid whatever the interaction considered. We also show that these rules are universal in the case of nonlinear dispersion relations provided we consider only density–density interactions. We apply the functional bosonization formalism to a nonrelativistic and nonlocal massive Thirring-like model and evaluate the spectrum of collective excitations in several limits. In the large mass limit, we are able to exactly calculate this spectrum for arbitrary density–density and current–current interactions. We also analyze the massless case and show that it has no collective excitations for any density–density potential in the Gaussian approximation. Moreover, the presence of current interactions may induce a gapless mode with a linear dispersion relation.

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Kooi, Derk Pieter y Paola Gori-Giorgi. "London dispersion forces without density distortion: a path to first principles inclusion in density functional theory". Faraday Discussions 224 (2020): 145–65. http://dx.doi.org/10.1039/d0fd00056f.

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We analyse a path to construct density functionals for the dispersion interaction energy from an expression in terms of the ground state densities and exchange–correlation holes of the isolated fragments.

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Prakash, Ved, Suresh C. Sharma, Vijayshri y Ruby Gupta. "Surface wave excitation by a density modulated electron beam in a magnetized dusty plasma cylinder". Laser and Particle Beams 31, n.º 3 (17 de junio de 2013): 411–18. http://dx.doi.org/10.1017/s0263034612001048.

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AbstractThis paper studies the surface plasma wave excitation via Cerenkov and fast cyclotron interaction by a density modulated electron beam propagating through a magnetized dusty plasma cylinder. The dispersion relation of surface plasma waves has been derived and it has been shown that the phase velocity of waves increases with increase in relative density δ(= nio/ne0, where ni0 is the ion plasma density and ne0 is the electron plasma density) of negatively charged dust grains. The beam radius is taken slightly less than the radius of dusty plasma cylinder. The frequency and the growth rate of the unstable wave instability increases with increase in the value of δ and normalized frequency ω/ωpe. The growth rate of the instability increases with the beam density and scales as one-third power of the beam density in Cerenkov interaction and square root of beam density in fast cyclotron interaction. The dispersion relation of surface plasma waves has been retrieved from the derived dispersion relation by considering that the beam is absent and there are no dust grains in the plasma cylinder.

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Ciuffoli, Emilio, Jarah Evslin, Xiaojun Bi y Xinmin Zhang. "Neutrino Splitting and Density-Dependent Dispersion Relations". ISRN High Energy Physics 2012 (4 de noviembre de 2012): 1–20. http://dx.doi.org/10.5402/2012/436580.

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We show that particles are unstable with respect to a splitting process, which is the quantum analog of the modulational instability in anomalous dispersive media, only when their group velocity exceeds their phase velocity. In the case of a neutrino, when the concavity results from a term E(P)~Pk, the neutrino will decay to two neutrinos and an antineutrino after traveling a distance proportional to E2+3k. Unlike the Cohen-Glashow instability, the splitting instability exists even if all particles involved in the interaction have the same dispersion relations at the relevant energy scales. We show that this instability leads to strong constraints even if the energy E is a function of both the momentum P and also of the background density ρ; for example, we show that it alone would have been sufficient to eliminate any model of the MINOS/OPERA velocity anomaly which modifies the neutrino dispersion relation while leaving those of other particles intact.

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Yuan, Chengqian, Haiming Wu, Meiye Jia, Peifeng Su, Zhixun Luo y Jiannian Yao. "A theoretical study of weak interactions in phenylenediamine homodimer clusters". Physical Chemistry Chemical Physics 18, n.º 42 (2016): 29249–57. http://dx.doi.org/10.1039/c6cp04922b.

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Utilizing dispersion-corrected density functional theory (DFT) calculations, we demonstrate the weak intermolecular interactions of phenylenediamine dimer (pdd) clusters, emphasizing the local lowest energy structures and decomposition of interaction energies by natural bond orbital (NBO) and atoms in molecule (AIM) analyses.

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Stöhr, Martin y Alexandre Tkatchenko. "Quantum mechanics of proteins in explicit water: The role of plasmon-like solute-solvent interactions". Science Advances 5, n.º 12 (diciembre de 2019): eaax0024. http://dx.doi.org/10.1126/sciadv.aax0024.

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Quantum-mechanical van der Waals dispersion interactions play an essential role in intraprotein and protein-water interactions—the two main factors affecting the structure and dynamics of proteins in water. Typically, these interactions are only treated phenomenologically, via pairwise potential terms in classical force fields. Here, we use an explicit quantum-mechanical approach of density-functional tight-binding combined with the many-body dispersion formalism and demonstrate the relevance of many-body van der Waals forces both to protein energetics and to protein-water interactions. In contrast to commonly used pairwise approaches, many-body effects substantially decrease the relative stability of native states in the absence of water. Upon solvation, the protein-water dispersion interaction counteracts this effect and stabilizes native conformations and transition states. These observations arise from the highly delocalized and collective character of the interactions, suggesting a remarkable persistence of electron correlation through aqueous environments and providing the basis for long-range interaction mechanisms in biomolecular systems.

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Briggs, Edward A. y Nicholas A. Besley. "Modelling excited states of weakly bound complexes with density functional theory". Phys. Chem. Chem. Phys. 16, n.º 28 (2014): 14455–62. http://dx.doi.org/10.1039/c3cp55361b.

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Sahu, S., Y. Hardalupas y A. M. K. P. Taylor. "Interaction of droplet dispersion and evaporation in a polydispersed spray". Journal of Fluid Mechanics 846 (3 de mayo de 2018): 37–81. http://dx.doi.org/10.1017/jfm.2018.247.

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The interaction between droplet dispersion and evaporation in an acetone spray evaporating under ambient conditions is experimentally studied with an aim to understand the physics behind the spatial correlation between the local vapour mass fraction and droplets. The influence of gas-phase turbulence and droplet–gas slip velocity of such correlations is examined, while the focus is on the consequence of droplet clustering on collective evaporation of droplet clouds. Simultaneous and planar measurements of droplet size, velocity and number density, and vapour mass fraction around the droplets, were obtained by combining the interferometric laser imaging for droplet sizing and planar laser induced fluorescence techniques (Sahuet al.,Exp. Fluids, vol. 55, 1673, 2014b, pp. 1–21). Comparison with droplet measurements in a non-evaporating water spray under the same flow conditions showed that droplet evaporation leads to higher fluctuations of droplet number density and velocity relative to the respective mean values. While the mean droplet–gas slip velocity was found to be negligibly small, the vaporization Damköhler number ($Da_{v}$) was approximately ‘one’, which means the droplet evaporation time and the characteristic time scale of large eddies are of the same order. Thus, the influence of the convective effect on droplet evaporation is not expected to be significant in comparison to the instantaneous fluctuations of slip velocity, which refers to the direct effect of turbulence. An overall linearly increasing trend was observed in the scatter plot of the instantaneous values of droplet number density ($N$) and vapour mass fraction ($Y_{F}$). Accordingly, the correlation coefficient of fluctuations of vapour mass fraction and droplet number density ($R_{n\ast y}$) was relatively high (${\approx}0.5$) implying moderately high correlation. However, considerable spread of the$N$versus$Y_{F}$scatter plot along both coordinates demonstrated the influence on droplet evaporation due to turbulent droplet dispersion, which leads to droplet clustering. The presence of droplet clustering was confirmed by the measurement of spatial correlation coefficient of the fluctuations of droplet number density for different size classes ($R_{n\ast n}$) and the radial distribution function (RDF) of the droplets. Also, the tendency of the droplets to form clusters was higher for the acetone spray than the water spray, indicating that droplet evaporation promoted droplet grouping in the spray. The instantaneous group evaporation number ($G$) was evaluated from the measured length scale of droplet clusters (by the RDF) and the average droplet size and spacing in instantaneous clusters. The mean value of$G$suggests an internal group evaporation mode of the droplet clouds near the spray centre, while single droplet evaporation prevails near the spray boundary. However, the large fluctuations in the magnitude of instantaneous values of$G$at all measurement locations implied temporal variations in the mode of droplet cloud evaporation.

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Tesis sobre el tema "Dispersion interaction density"

Edwards, Angela Celeste. "Probing the Hydrogen Bonding Interaction at the Gas-Surface Interface using Dispersion Corrected Density Functional Theory". Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/71784.

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he interactions of the chemical warfare agent sulfur mustard with amorphous silica were investigated using electronic structure calculations. In this thesis, the binding energies of sulfur mustard and mimic species used in the laboratory were calculated using density functional theory and fully ab initio calculations. The wB97XD and B97D functionals, which include functions to account for long-range dispersion interactions, were compared to experimental trends. The hydroxylated amorphous silica surface was approximated using a gas-phase silanol molecule and clusters containing a single hydroxyl moiety. Recent temperature programmed desorption experiments performed in UHV concluded that sulfur mustard and its less toxic mimics undergo molecular adsorption to amorphous silica. Hydrogen bonding can occur between surface silanol groups and either the sulfur or chlorine atom of the adsorbates, and the calculations indicate that the binding energies for the two hydrogen bond acceptors are similar. The adsorption of sulfur mustard and its mimics on silica also exhibits the presence of significant van der Waals interactions between alkyl of the adsorbates and the surface. These interactions, in combination with the formation of a hydrogen bond between a surface silanol group and the Cl or S atoms of the adsorbates, provide remarkably large binding energies.
Master of Science

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Wuttke, Axel. "Computational Study of Dispersion Interactions through Local Orbital Analysis". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2019. http://hdl.handle.net/11858/00-1735-0000-002E-E606-7.

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Tuma, Christian. "A QM/QM hybrid method for MP2/Plane-Wave-DFT studies of extended systems". Doctoral thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=983810583.

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Johnson, Erin R. "A density-functional theory including dispersion interactions". Thesis, Kingston, Ont. : [s.n.], 2007. http://hdl.handle.net/1974/926.

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Mussard, Bastien. "Modélisation quantochimiques des forces de dispersion de London par la méthode des phases aléatoires (RPA) : développements méthodologiques". Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0292/document.

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Dans cette thèse sont montrés des développements de l'approximation de la phase aléatoire (RPA) dans le contexte de théories à séparation de portée. On présente des travaux sur le formalisme de la RPA en général, et en particulier sur le formalisme "matrice diélectrique" qui est exploré de manière systématique. On montre un résumé d'un travail sur les équations RPA dans le contexte d'orbitales localisées, notamment des développements des orbitales virtuelles localisées que sont les "orbitales oscillantes projetées" (POO). Un programme a été écrit pour calculer des fonctions telles que le trou de d'échange, la fonction de réponse, etc... sur des grilles de l'espace réel (grilles parallélépipédiques ou de type "DFT"). On montre certaines de ces visualisations. Dans l'espace réel, on expose une adaptation de l'approximation du dénominateur effectif (EED), développée originellement dans l'espace réciproque en physique du solide. Également, les gradients analytiques des énergies de corrélation RPA dans le contexte de la séparation de portée sont dérivés. Le formalisme développé ici à l'aide d'un lagrangien permet une dérivation tout-en-un des termes courte- et longue-portée qui émergent dans les expressions du gradient, et qui montrent un parallèle intéressant. Des applications sont montrées, telles que des optimisations de géométries aux niveaux RSH-dRPA-I et RSH-SOSEX d'un ensemble de 16 petites molécules, ou encore le calcul et la visualisation des densités corrélées au niveau RSH-dRPA-I
In this thesis are shown developments in the random phase approximation (RPA) in the context of range-separated theories. We present advances in the formalism of the RPA in general, and particularly in the "dielectric matrix" formulation of RPA, which is explored in details. We show a summary of a work on the RPA equations with localized orbitals, especially developments of the virtual localized orbitals that are the "projected oscillatory orbitals" (POO). A program has been written to calculate functions such as the exchange hole, the response function, etc... on real space grid (parallelepipedic or of the "DFT" type) ; some of those visualizations are shown here. In the real space, we offer an adaptation of the effective energy denominator approximation (EED), originally developed in the reciprocal space in solid physics. The analytical gradients of the RPA correlation energies in the context of range separation has been derived. The formalism developed here with a Lagrangian allows an all-in-one derivation of the short- and long-range terms that emerge in the expressions of the gradient. These terms show interesting parallels. Geometry optimizations at the RSH-dRPA-I and RSH-SOSEX levels on a set of 16 molecules are shown, as well as calculations and visualizations of correlated densities at the RSH-dRPA-I level

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Hermann, Jan. "Towards unified density-functional model of van der Waals interactions". Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/18706.

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Van der Waals-Wechselwirkungen (vdW) sind allgegenwärtig und spielen eine zentrale Rolle in einer großen Anzahl biologischer und moderner synthetischer Materialien. Die am weitesten verbreitete theoretische Methode zur Berechnung von Materialeigenschaften, die Dichtefunktionaltheorie (DFT) in semilokaler Näherung, vernachlässigt diese Wechselwirkungen jedoch größtenteils, was zur Entwicklung vieler verschiedener vdW-Modelle führte. Die hier vorgestellte Arbeit ebnet den Weg hin zu einem vereinheitlichten vdW-Modell welches die besten Elemente der unterschiedlichen Klassen von vdW-Modellen vereint. Zu diesem Zweck haben wir einen vereinheitlichten theoretischen Rahmen geschaffen, der auf dem Reichweite-separierten Adiabatischer-Zusammenhang-Fluktuations-Dissipations-Theorem aufbaut und die meisten existierenden vdW-Modelle umfasst. Wir analysieren die MBD-korrelierte Wellenfunktion am prototypischen Beispiel von π–π-Wechselwirkungen in supramolekularen Komplexen und stellen fest, dass diese Wechselwirkungen größtenteils durch delokalisierte kollektive Ladungsfluktuationen entstehen. Um zu dem langreichweitigen vdW-Modell ein ausgewogenes kurzreichweitiges Dichtefunktional zu identifizieren, präsentieren wir eine umfassende Untersuchung zum Zusammenspiel der kurz- und langreichweitigen Energiebeiträge in acht semilokalen Funktionalen und drei vdW-Modellen für eine große Spanne von Systemen. Die Bindungsenergieprofile vieler der DFT+vdW-Kombinationen unterscheiden sich sowohl quantitativ als auch qualitativ stark voneinander. Schließlich untersuchen wir die Performance des Vydrov–Van Voorhis-Polarisierbarkeitsfunktionals über das Periodensystem der Elemente hinweg und identifizieren eine systematische Unterschätzung der Polarisierbarkeiten und vdW-C₆-Koeffizienten für s- und d-Block-Elemente. Als Lösung entwickeln wir eine orbitalabhängige Verallgemeinerung des Funktionals.
The ubiquitous long-range van der Waals interactions play a central role in nearly all biological and modern synthetic materials. Yet the most widely used theoretical method for calculating material properties, the density functional theory (DFT) in semilocal approximation, largely neglects these interactions, which motivated the development of many different vdW models. The work in this thesis paves way towards a unified vdW model that combines best elements from the different classes of the vdW models. To this end, we developed a unified theoretical framework based on the range-separated adiabatic-connection fluctuation--dissipation theorem that encompasses most existing vdW models. We analyze the MBD correlated wave function on the prototypical case of π–π interactions in supramolecular complexes and find that these interactions are largely driven by delocalized collective charge fluctuations. To identify a balanced short-range density functional to accompany the long-range vdW model, we present a comprehensive study of the interplay between the short-range and long-range energy contributions in eight semilocal functionals and three vdW models on a wide range of systems. The binding-energy profiles of many of the DFT+vdW combinations differ both quantitatively and qualitatively, and some of the qualitative differences are independent of the choice of the vdW model. Finally, we investigate the performance of the Vydrov—Van Voorhis polarizability functional across the periodic table, identify systematic underestimation of the polarizabilities and vdW C₆ coefficients for s- and d-block elements, and develop an orbital-dependent generalization of this functional to resolve the issue.

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Veit, Max David. "Designing a machine learning potential for molecular simulation of liquid alkanes". Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/290295.

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Molecular simulation is applied to understanding the behaviour of alkane liquids with the eventual goal of being able to predict the viscosity of an arbitrary alkane mixture from first principles. Such prediction would have numerous scientific and industrial applications, as alkanes are the largest component of fuels, lubricants, and waxes; furthermore, they form the backbones of a myriad of organic compounds. This dissertation details the creation of a potential, a model for how the atoms and molecules in the simulation interact, based on a systematic approximation of the quantum mechanical potential energy surface using machine learning. This approximation has the advantage of producing forces and energies of nearly quantum mechanical accuracy at a tiny fraction of the usual cost. It enables accurate simulation of the large systems and long timescales required for accurate prediction of properties such as the density and viscosity. The approach is developed and tested on methane, the simplest alkane, and investigations are made into potentials for longer, more complex alkanes. The results show that the approach is promising and should be pursued further to create an accurate machine learning potential for the alkanes. It could even be extended to more complex molecular liquids in the future.

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Sulzer, David. "Modélisation des interactions faibles en théorie de la fonctionnelle de la densité". Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00945896.

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Les descriptions des interactions faibles et notamment de la dispersion représentent un problème majeur pour la théorie de la fonctionnelle de la densité. En effet, le caractère fortement local des fonctionnelles rend problématique la description des interactions à longue-portée. Aussi, plusieurs stratégies sont envisagées: des corrections des fonctionnelles existantes ou une introduction de méthodes post-Hartree-Fock par séparation de portée. Des résultats dans les deux cas sont exposés. Tout d'abord, la méthodologie hybride est appliquée à des dimères de métaux de transition (Cr2, Mn2 et Zn2). Ensuite, le calcul de coefficients de corrections pour la dispersion dans un cadre relativiste est présenté. Enfin, les interactions faibles peuvent également résulter de l'interaction d'une molécule avec un champ magnétique. Dans ce cadre, une modélisation de la modification de la densité électronique dans les systèmes aromatiques sous l'influence d'un champ magnétique extérieur est présentée.

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Petrović, Predrag. "Experimental and theoretical investigations of intermetallic in transition metal coordination and organometallic complexes". Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAF029.

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Ce travail de thèse démontre l’importance d’intégrer des outils théoriques à des observations expérimentales dans le but d’étudier le rôle des interactions non-covalentes et plus précisément de la dispersion dans la chimie des métaux de transition. Plusieurs thèmes ont ainsi été abordés comme les interactions d’empilement entre chélates de métaux de transition à l’état solide; l’influence de la chiralité sur l’oligomérisation en solution de complexes plans carrés de Rh(I) isonitrile; la stabilité et inactivité inhabituelles de complexes de type cis-platine en solution concentrée. Les résultats obtenus par titration calorimétrique isotherme ont permis d’évaluer la capacité de méthodes théoriques à reproduire avec précision les résultats expérimentaux. Les calculs ont démontré qu’un traitement théorique approprié des effets de la dispersion et de la solvatation, donne des valeurs cohérentes avec les résultats expérimentaux. Cependant, des améliorations supplémentaires sont nécessaires
This thesis has shown the importance of integration of theoretical calculations and experimental investigations in studying the role of non-covalent interactions and particularly dispersion interactions in transition metal chemistry. Several subjects were addressed, such as stacking interactions of chelates in transition metal complexes in solid state, influence of chirality on the oligomerization of Rh(I) isonitrile complexes in solution and the stability of the cis-platin type complexes in concentrated solutions. Isothermal titration calorimetry proved to be very useful in the studies by providing accurate experimental data on the thermochemistry of addressed processes. This data was used to gauge the ability of the theoretical methods to accurately reproduce the experimental results. Calculations have shown that the proper treatment of dispersion effects and solvation by theoretical models gives values in relatively good agreement with experiments, but further improvements are needed

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Brockbank, J. Wyatt. "Better Speakers Make More Friends: Predictors of Social Network Development Among Study-Abroad Students". BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2686.

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Social network development has been studied in the social sciences for the last several decades, but little work has applied social network theory to study-abroad research. This study seeks to quantitatively describe factors that predict social network formation among study-abroad students while in the host countries. Social networks were measured in terms of the number of friends the students made, the number of distinct social groups reported, and the number of friends within those groups. The Study Abroad Social Interaction Questionnaire was compared against these pre-trip factors: intercultural competence, target-language proficiency, prior missionary experience, gender, study-abroad program, neuroticism, extroversion, agreeableness, openness to new experience, agreeableness, and conscientiousness. Results showed that pre-trip oral proficiency in the target language was the strongest predictor of the number of friends made in-country. Certain programs showed stronger predictive statistics in terms of size of largest social group, number of social groups, and number of friends made. A distinction is made between total number of friends and number of friends who are more likely to be native speakers. Neither intercultural competence nor personality showed a significant correlation with the number of friendships made during study abroad.

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Libros sobre el tema "Dispersion interaction density"

Eriksson, Olle, Anders Bergman, Lars Bergqvist y Johan Hellsvik. Atomistic Spin Dynamics. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198788669.001.0001.

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The purpose of this book is to provide a theoretical foundation and an understanding of atomistic spin-dynamics, and to give examples of where the atomistic Landau-Lifshitz-Gilbert equation can and should be used. The contents involve a description of density functional theory both from a fundamental viewpoint as well as a practical one, with several examples of how this theory can be used for the evaluation of ground state properties like spin and orbital moments, magnetic form-factors, magnetic anisotropy, Heisenberg exchange parameters, and the Gilbert damping parameter. This book also outlines how interatomic exchange interactions are relevant for the effective field used in the temporal evolution of atomistic spins. The equation of motion for atomistic spin-dynamics is derived starting from the quantum mechanical equation of motion of the spin-operator. It is shown that this lead to the atomistic Landau-Lifshitz-Gilbert equation, provided a Born-Oppenheimer-like approximation is made, where the motion of atomic spins is considered slower than that of the electrons. It is also described how finite temperature effects may enter the theory of atomistic spin-dynamics, via Langevin dynamics. Details of the practical implementation of the resulting stochastic differential equation are provided, and several examples illustrating the accuracy and importance of this method are given. Examples are given of how atomistic spin-dynamics reproduce experimental data of magnon dispersion of bulk and thin-film systems, the damping parameter, the formation of skyrmionic states, all-thermal switching motion, and ultrafast magnetization measurements.

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Capítulos de libros sobre el tema "Dispersion interaction density"

Kryachko, Eugene S. "Density Functional Theory and Molecular Interactions: Dispersion Interactions". En Structure and Bonding, 65–96. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-32750-6_2.

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Assovskiy, Igor G. "Laser Ignition of Metalized Solid Propellants". En Energetic Materials Research, Applications, and New Technologies, 79–99. IGI Global, 2018. http://dx.doi.org/10.4018/978-1-5225-2903-3.ch004.

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This Chapter presents a theoretical analysis of radiation interaction with a semi-transparent metalized energetic material. Main regularities of the laser pulse interaction with metalized compositions are considered within the framework of non-resonant interaction of radiation with matter. The large variety of metalized composite propellants with different properties of the components, their ratio and dispersion can be divided into two classes, depending on the ratio of the laser irradiation's characteristic time (tr) and the thermal relaxation time of the propellant characteristic cell containing one metal particle (tm). Analysis of the role of metallic particles shape shows that in the case of spherical metal particles, duration of the laser pulse corresponds to the optimal size of particles, heated to a maximum temperature. In the case of flat metallic particles and constant pulse duration, the critical radiation flux and the critical density of ignition energy significantly decrease with decreasing thickness of the particle.

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Ullrich, Carsten A. "Long–range correlations and dispersion interactions". En Time-Dependent Density-Functional Theory, 333–50. Oxford University Press, 2011. http://dx.doi.org/10.1093/acprof:oso/9780199563029.003.0014.

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Singh, Sukhmander, Ashish Tyagi y Bhavna Vidhani. "Physics of Absorption and generation of Electromagnetic Radiation". En Electromagnetic Wave Propagation for Industry and Biomedical Applications [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.99037.

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The chapter is divided into two parts. In the first part, the chapter discusses the theory of propagation of electromagnetic waves in different media with the help of Maxwell’s equations of electromagnetic fields. The electromagnetic waves with low frequency are suitable for the communication in sea water and are illustrated with numerical examples. The underwater communication have been used for the oil (gas) field monitoring, underwater vehicles, coastline protection, oceanographic data collection, etc. The mathematical expression of penetration depth of electromagnetic waves is derived. The significance of penetration depth (skin depth) and loss angle are clarified with numerical examples. The interaction of electromagnetic waves with human tissue is also discussed. When an electric field is applied to a dielectric, the material takes a finite amount of time to polarize. The imaginary part of the permittivity is corresponds to the absorption length of radiation inside biological tissue. In the second part of the chapter, it has been shown that a high frequency wave can be generated through plasma under the presence of electron beam. The electron beam affects the oscillations of plasma and triggers the instability called as electron beam instability. In this section, we use magnetohydrodynamics theory to obtain the modified dispersion relation under the presence of electron beam with the help of the Poisson’s equation. The high frequency instability in plasma grow with the magnetic field, wave length, collision frequency and the beam density. The growth rate linearly increases with collision frequency of electrons but it is decreases with the drift velocity of electrons. The real frequency of the instability increases with magnetic field, azimuthal wave number and beam density. The real frequency is almost independent with the collision frequency of the electrons.

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Bunker, Bruce C. y William H. Casey. "The Colloidal Chemistry of Oxides". En The Aqueous Chemistry of Oxides. Oxford University Press, 2016. http://dx.doi.org/10.1093/oso/9780199384259.003.0014.

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Colloids are defined as suspensions of finely divided particles in a continuous medium that do not settle rapidly and are not readily filtered. To be more specific, the International Union of Pure and Applied Chemistry defines a colloid as any material for which one or more of its three dimensions lies within the size range of 1 to 1000 nm. As the nucleation and growth of oxides from aqueous solutions almost always produces suspensions containing submicron particles (see Chapter 7), typical oxide suspensions fall squarely within the colloidal domain. In this book, we consider colloidal particles to represent oxides or hydroxides that are small enough to stay in aqueous suspensions for more than a few hours, yet are larger and lacking in the specific molecular structures of typical hydrolysis products (see Chapter 5). Given the density range of most oxides (from around 2−10 g/cm3), the sizes of most colloidal oxides fall within the limits of the International Union of Pure and Applied Chemistry (see Section 8.4.5). Colloidal oxide particles suspended in water represent a complex chemical environment. At the molecular level, protons, ions, small molecules, and polymeric species interact with particle surfaces to create charged surface sites and promote adsorption and desorption phenomena (see Chapter 6). These modified surfaces perturb the adjacent liquid, creating ordered solvent layers and strong concentration gradients in ions and other dissolved species. These interfacial phenomena generate a range of forces called interaction potentials. Such forces determine whether particles repel each other (leading to stable suspensions) or are attracted to one another, resulting in agglomeration and sedimentation phenomena. The length scales of those components of the oxide–water interface that influence the interaction potentials to be discussed in this chapter are introduced in Figure 8.1. At the subatomic level, the correlated polarization of electron clouds gives rise to dispersion forces described by quantum mechanics that contribute to van der Waals interactions. At the atomic level, the inherent charge on each exposed oxygen anion that terminates the oxide surface is controlled by local chemical bonds to adjacent cations (see Chapter 6).

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Utkov, Hunter, Maura Livengood y Mauricio Cafiero. "Using Density Functional Theory Methods for Modeling Induction and Dispersion Interactions in Ligand–Protein Complexes". En Annual Reports in Computational Chemistry, 96–112. Elsevier, 2010. http://dx.doi.org/10.1016/s1574-1400(10)06007-x.

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"CONCLUSION While cleaned silica-based glass surfaces have similar surface compositions, their susceptibility to strongly adsorbing organic contaminant s depends strongly on the glass composition and the cleaning procedure. For the three glass species exam-ined: silica, aluminoborosilicate, and sodalime glass , the glass surfaces behave similarly after chromic acid cleaning. They show significant differences in their properties followin g a dry cleaning procedure, such as pyrolysis or UV/ozone cleaning. The cleaned silica surfaces show a high susceptibility to adsorbing or-ganic contamination following pyrolysis cleaning, while the pyrolyzed sodalime glass appears to be virtually immune to strongly adsorbing organic molecules. Py-rolyzed aluminoborosilicate glass shows an intermediate susceptibility to adsorb-ing organic contaminants. The chromic acid cleaned glass surfaces all show an in-termediate susceptibility to contamination by adsorbed organic molecules. Thus, it may be an oversimplification to consider a clean glass surface as a high energy substrate that is bound to attract ambient organic contamination. The wettability behavior of the cleaned glass surfaces showed features associ-ated with their exposed chemical functions. The non-dispersive interaction energy between glass and water as a function of pH showed evidence of charging of the surface silanol groups. The point of zero charge for these surface chemical func-tions was observed at pH 3. An estimate of the non-dispersive interaction energy between glass and water at the point of zero charge enables a reasonable estima-tion of the density of surface silanol groups on the cleaned glass. The trends ob-served for the surface charge as a function of pH correlate with the observed sus-ceptibility for adsorbing organic contamination to the cleaned glass surfaces. Charge-adsorbed surfactant monolayers indicated a negative surface charge on the cleaned glass, as expected for silica-based glass surfaces at neutral pH. The wettability of grafted self-assembled octadecylsilane monolayers indicated high quality coatings on the cleaned glass surfaces. The coating quality was identical for all three glass species following chromic acid cleaning. The UV/ozone cleaned glass surfaces showed the highest coating quality on the silica surface, followed by the aluminoborosilicate surface and the sodalime glass surface. The trends in coating quality for all chromic acid cleaned surfaces and UV/ozone cleaned surfaces correlate with those seen for susceptibility to organic contamina-tion of the cleaned glass surfaces exposed to unpurified liquid octane. REFERENCES". En Surface Contamination and Cleaning, 114–16. CRC Press, 2003. http://dx.doi.org/10.1201/9789047403289-17.

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Actas de conferencias sobre el tema "Dispersion interaction density"

Jin, Jae Sik y Joon Sik Lee. "Electron-Phonon Interaction Model and Thermal Transport Simulation During ESD Event in NMOS Transistor". En ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference collocated with the ASME 2007 InterPACK Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ht2007-32199.

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An electron-phonon interaction model is proposed and applied to the transient thermal transport simulation during electrostatic discharge (ESD) event in the NMOS transistor. The high electron energy induced by the ESD in the transistor is transferred to the lattice phonons through electron-phonon interaction in the local region of the transistor. Due to this fact, a hot spot turns up, the size of which is much smaller than the phonon mean free path in the silicon layer. The full phonon dispersion model based on the Boltzmann transport equation (BTE) with the relaxation time approximation is applied to describe the interactions among different phonon branches and different phonon frequencies. The Joule heating by the electronphonon scattering is modeled through the intervalley and intravalley processes by introducing the average electron energy. In the simulation, the electron-phonon interaction model is used in the hot spot region, and then after a quasi-equilibrium state is achieved there, the temperature of lattice phonons in the silicon is calculated by using the phonon-phonon interaction model. The revolution of peak temperature in the hot spot during the ESD event is simulated and compared to that obtained by the previous full phonon dispersion model which treats the electron-phonon scattering as a volumetric heat source. The results show that the lower group velocity phonon modes (i.e. higher frequency) and optical mode of negligible group velocity obtain the highest energy density from electrons during the ESD event, which induces the devices melting phenomenon. The thermal response of phonon is also investigated, and it is found that the ratio of the phonon group velocity to the phonon specific heat can account for the phonon thermal response. If the ratio is higher than 2, the phonon have a good response to the heat input changes.

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Kohli, Atul y David G. Bogard. "Effects of Very High Free-Stream Turbulence on the Jet-Mainstream Interaction in a Film Cooling Flow". En ASME 1997 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/97-gt-121.

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Dispersion of coolant jets in a film cooling flow field is the result of a highly complex interaction between the film cooling jets and the mainstream. Understanding this complex interaction, particularly near the injection location, is critical for improving the predictive capabilities of existing film cooling models, especially when very high free-stream turbulence levels exist. This study uses a high frequency response temperature sensor to investigate the mean and fluctuating thermal field of a film cooling flow for two vastly different free-stream turbulence levels (0.5% and 20%). The high frequency response temperature sensor provides new information about the film cooling flow in terms of actual rms levels (Θ′), probability density functions (pdf’s), and frequency spectra of the thermal field. Results are presented for both free-stream conditions using round holes inclined at 35°, at a momentum flux ratio of I = 0.156 and density ratio of DR = 1.05. The mean thermal field results show severe degradation of the film cooling jet occurs with very high free-stream turbulence levels. Temperature rms results indicate levels as high as Θ′ = 0.25 exist at the jet-mainstream interface. More information is provided by the temperature pdf’s which are able to identify differences in the jet-mainstream interaction for the two free-stream conditions. With small free-stream turbulence, strong intermittent flow structures generated at the jet-mainstream interface disperse the jet by moving hot mainstream fluid into the coolant core, and ejecting coolant fluid into the mainstream. When the free-stream has large scales and very high turbulence levels, the jet-mainstream interface is obliterated by large scale turbulent structures originating from the free-stream which completely penetrate the coolant jet causing very rapid dispersion of the film cooling jet.

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Kohli, Atul y David G. Bogard. "Fluctuating Thermal Field in the Near Hole Region for Film Cooling Flows". En ASME 1996 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1996. http://dx.doi.org/10.1115/96-gt-209.

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The film cooling flow field is the result of a highly complex interaction between the film cooling jets and the mainstream, Understanding this interaction is important in order to explain the physical mechanisms involved in the rapid decrease of effectiveness which occurs close to the hole exit. Not surprisingly, it is this region which is not modeled satisfactorily with current film cooling models. This study uses a high frequency response temperature sensor which provides new information about the film cooling flow in terms of actual turbulence levels and probability density functions of the thermal field. Mean and rms temperature results are presented for 35° round holes at a momentum flux ratio of I = 0.16, at a density ratio of DR = 1.05. Probability density functions of the temperature indicate penetration of the mainstream into the coolant core, and ejection of coolant into the mainstream. Extreme excursions in the fluctuating temperature measurements suggests existence of strong intermittent flow structures responsible for dilution and dispersion of the coolant jets.

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Pastor, J. M., J. M. Desantes, J. M. García-Oliver, A. Pandal, B. Naud, K. Matusik, D. Duke, A. Kastengren, C. Powell y D. P. Schmidt. "Modelling and validation of near-field Diesel spray CFD simulations based on the Σ -Y model". En ILASS2017 - 28th European Conference on Liquid Atomization and Spray Systems. Valencia: Universitat Politècnica València, 2017. http://dx.doi.org/10.4995/ilass2017.2017.4715.

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Diesel spray modelling still remains a challenge, especially in the dense near-nozzle region. This region is difficultto experimentally access and also to model due to the complex and rapid liquid and gas interaction. Modelling approaches based on Lagrangian particle tracking have struggled in this area, while Eulerian modelling has proven particularly useful. An interesting approach is the single-fluid diffuse interface model known as Σ-Y, based on scale separation assumptions at high Reynolds and Weber numbers. Liquid dispersion is modelled as turbulent mixing of a variable density flow. The concept of surface area density is used for representing liquid structures, regardless of the complexity of the interface.In this work, an implementation of the Σ-Y model in the OpenFOAM CFD library is applied to simulate the ECN Spray A in the near nozzle region, using both RANS and LES turbulence modelling. Assessment is performed with measurements conducted at the Advanced Photon Source at Argonne National Laboratory (ANL). The ultra-small- angle x-ray scattering (USAXS) technique has been used to measure the interfacial surface area, and x-rayradiography to measure the fuel dispersion, allowing a direct evaluation of the Σ-Y model predictions.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4715

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De, Ashoke, Akshay Dongre y Rakesh Yadav. "Numerical Investigation of Delft-Jet-in-Hot-Coflow (DJHC) Burner Using Probability Density Function (PDF) Transport Modeling". En ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-95390.

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In the present paper, the flames from DJHC burner, imitating MILD (Moderate and Intense Low Oxygen Dilution) combustion, are simulated using PDF transport modeling. Two different solution approaches have been used to resolve the joint composition PDF. First, a Lagrangian approach is used to solve the joint composition PDF, while in the second approach, the approximate solution is achieved by using presumed shape PDF and DQMOM-IEM modeling known as Multi-Environment Eulerian PDF (MEPDF). A quantitative comparison of the predictions from these two solution methods has been performed for two different jet Reynolds number, i.e. Re = 4100 & 8800. Moreover, the effect of molecular diffusion is also explored by comparing the predictions using different micro-mixing models such as Coalescence Dispersion (CD), Euclidean Minimum Spanning Tree (EMST), and Interaction-by-Exchange-with-Mean (IEM) model. The obtained numerical predictions from both approaches are compared with the experimental data to highlight the accuracy as well as the predictive capability of these models. In the case of low Reynolds number (Re = 4100), it is observed that the mean axial velocity and turbulent kinetic energy profiles are in good agreement with the measurements while the temperature profiles are slightly over-predicted in the downstream region. Although MEPDF results are in good agreement with the LPDF results, both the model predictions tend to exhibit discrepancies at higher Reynolds number.

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Satoh, Akira y Eiji Taneko. "Brownian Dynamics Simulations of a Dispersion Composed of Two-Types of Spherical Particles (for Development of a New Technology of Improving the Visibility of Rivers and Lakes)". En ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-67142.

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We have carried out Brownian dynamics simulations of sedimentation phenomena of a dispersion composed of two-kinds of spherical particles in water under the gravity field. This study may be the first step to develop a new technology which enables us to improve the visibility of rivers and lakes. In the present study, we have modeled sub-micrometer-dimension particles, or dirty particles in lakes, as small spherical particles, and capturing particles as large spherical particles; these two kinds of particles conduct Brownian motion in water, and large particles adsorb small particles to sediment gradually toward the bottom in the gravity field. From the results of Brownian dynamics simulations, the influences of Brownian motion, particle-particle interaction forces, the size of each particle, and the gravity force on the performance of the adsorption of large particles have been discussed. In addition, we have discussed what the most appropriate situation of large particles is to accomplish the most effective adsorption rate or improve the visibility of water most effectively in terms of capturing particles. The most important conclusion derived from the present results is that, in order to improve the capturing performance, the Brownian motion of large particles have to be activated in an appropriate number density without losing the influence of the gravity.

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Cai, Shuang, Chenhan Liu, Yi Tao, Zaoqi Duan, Yunfei Chen y Yun Dong. "Pressure Effects on the Thermal Properties of Graphite". En ASME 2016 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/imece2016-66379.

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In this paper, the thermal properties of graphite under external pressure were systematically investigated based on first-principles calculations and Boltzmann transport equation (BTE). This method is relatively simple and general to any other crystals. It was found that a compressive pressure can significantly increase the interaction between the layers in graphite and increase the phonon group velocity, the phonon mean free paths, thus the cross-plane thermal conductivity decreases. The effects of pressure on the in-plane thermal conductivity are much weaker than those on the cross-plane value. Our results indicate that the thermal properties of graphite can be strongly modulated by pressure engineering. Moreover we extracted the phonon dispersion and phonon lifetime of graphite under or without external pressure. And changes in the density of states and the cumulative thermal conductivity under 12GPa pressure are analyzed by comparing with no pressure. Our investigation here provides a physical insight into the modulation and heat transfer mechanism of graphite theoretically, which can help the design of graphite-like materials in experiment and practical application.

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Medlar, Michael P. y Edward C. Hensel. "Validation of an Enhanced Dispersion Algorithm for Use With the Statistical Phonon Transport Model". En ASME 2020 Heat Transfer Summer Conference collocated with the ASME 2020 Fluids Engineering Division Summer Meeting and the ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/ht2020-8926.

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Abstract Computer simulations of quasi-particle based phonon transport in semiconductor materials rely upon numerical dispersion relations to identify and quantify the discrete energy and momentum states allowable subject to quantum constraints. The accuracy of such computer simulations is ultimately dependent upon the fidelity of the underlying dispersion relations. Dispersion relations have previously been computed using empirical fits of experimental data in high symmetry directions, lattice dynamics, and Density Function Theory (DFT) or Density Functional Perturbation Theory (DFPT) approaches. The current work presents high fidelity dispersion relations describing full anisotropy for all six phonon polarizations with an adjustable computational grid. The current approach builds upon the previously published Statistical Phonon Transport Model (SPTM), which employed a first nearest neighbor lattice dynamics approach for the dispersion calculation. This paper extends the lattice dynamics approach with the use of both first and second nearest neighbors interactions that are quantified using published interatomic force constants calculated from DFT. The First Brillouin Zone (FBZ) is segmented into eight octants of high symmetry, and discretized in wave vector space with a 14 by 14 by 14 grid. This results in 65,586 states of unique wave vector and frequency combinations. Dispersion calculations are performed at each of the six faces of the wave vector space volume elements in addition to the centroid, resulting in 460,992 solutions of the characteristic equations. For the given grid, on the order of 108 computations are required to compute the dispersion relations. The dispersion relations thus obtained are compared to experimental reports available for high symmetry axes. Full anisotropic results are presented for all six phonon polarizations across the range of allowable wave vector magnitude and frequency as a comprehensive model of allowable momentum and energy states. Results indicate excellent agreement to experiment in high symmetry directions for all six polarizations and illustrate an improvement as compared to the previous SPTM implementation. Dispersion relations based on the lattice dynamic model with first and second nearest neighbor atomic interactions relying upon DFT calculated inter-atomic force constants provides an accurate high fidelity energy and momentum model for use in phonon transport simulations.

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Ofei, Titus Ntow, Itung Cheng, Bjørnar Lund, Arild Saasen y Sigbjørn Sangesland. "On the Stability of Oil-Based Drilling Fluid: Effect of Oil-Water Ratio". En ASME 2020 39th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/omae2020-19071.

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Abstract Drilling fluids are complex mixtures of natural and synthetic chemical compounds used to cool and lubricate the drill bit, clean the wellbore, carry drilled cuttings to the surface, control formation pressure, and improve the function of the drill string and tools in the hole. The two main types of drilling fluids are water-based and oil-based drilling fluids, where the oil-based also include synthetic-based drilling fluids. Many rheological properties of drilling fluids are key parameters that must be controlled during design and operations. The base fluid properties are constructed by the interaction of the emulsified water droplets in combination with organophilic clay particles. The rheological properties resulted from this combination, along with the particle size distribution of weight materials are vital in controlling the physical stability of the microstructure in the drilling fluid. A weak fluid microstructure induces settling and sagging of weight material particles. The presence of sag has relatively often been the cause for gas kicks and oil-based drilling fluids are known to be more vulnerable for sag than water-based drilling fluids. Hence, the shear-dependent viscosity and elasticity of drilling fluids are central properties for the engineers to control the stability of weight material particles in suspension. In this study, we examined the stability of typical oil-based drilling fluids made for North Sea oilfield drilling application with oil-water-ratios (OWR) of 80/20 and 60/40. The structural character of the fluid samples was analyzed both at rest and dynamic conditions via flow and viscosity curves, amplitude sweep, frequency sweep, and time-dependent oscillatory sweep tests using a rheometer with a measuring system applying a grooved bob at atmospheric conditions. A high precision density meter was used to measure the density of the drilling fluid samples before and after each test. The measurement criteria used to rank the fluids stability include the yield stress as measured from flow curves and oscillatory tests, flow transition index, mechanical storage stability index, and dynamic sag index. We observed that between the two drilling fluids, the sample with OWR = 60/40 showed a stable dispersion with stronger network structure as evidenced by higher yield stress and flow transition index values, while the mechanical storage stability index and dynamic sag index recorded lower values. The results of this study enable drilling fluid engineers to design realistic oil-based drilling fluids with stable microstructure to mitigate settling and sagging of weight material particles for North Sea drilling operation.

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Han, J., D. M. Wang y D. Filipi. "Numerical Simulation of Boiling Flows Using an Eulerian Multi-Fluid Model". En ASME 2005 Fluids Engineering Division Summer Meeting. ASMEDC, 2005. http://dx.doi.org/10.1115/fedsm2005-77239.

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A mathematical model to simulate boiling flows in industrial applications is presented. Following the Eulerian multifluid framework, separate sets of mass, momentum, and energy conservation equations are solved for liquid and vapor phases, respectively. The interactions between the phases are accounted for by including relevant mass, momentum, heat exchanges and turbulent dispersion effects. Velocity-pressure coupling is achieved through a multiphase version of the SIMPLE method and the standard k-ε turbulence model is employed. In order to validate and assess the accuracy of the boiling model, subcooled nucleate boiling flows in a vertical annular pipe are simulated in the steady-state mode. The computed axial velocities, volume fractions, temperature profiles are compared with available experimental data (Roy et al., ASME J. of Heat Transfer, Vol. 119, 1997). The result obtained by assuming a constant value for the bubble diameter shows a reasonable agreement, but several limitations are observed in the details. A more advanced mathematical model incorporating separate transport equations for the bubble number density and the interfacial area is suggested.

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