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In order to reduce aviation's CO 2 emissions and comply with current climate targets, the European Union plans a mandatory quota of 2 % sustainable aviation fuel (SAF) by 2025, rising up to ≥70 % SAF by 2050. In addition to a reduction of life cycle CO 2 emissions, the use of SAF can also have a positive impact on particle emissions and contrail properties. In this study we present observations from the ECLIF3 (Emission and CLimate Impact of alternative Fuels) aircraft campaign, which investigated exhaust and contrail characteristics of an Airbus A350-941 equipped with Rolls-Royce Trent XWB-84 engines. For the first time, non-volatile and total particle emissions of 100 % HEFA-SPK (hydroprocessed esters and fatty acids–synthetic paraffinic kerosene) SAF, a blended fuel and a reference Jet A-1 fuel were measured in flight. A maximum reduction in non-volatile particle number emissions of ∼41 % compared to the reference Jet A-1 fuel was measured at low cruise engine power settings when using 100 % HEFA-SPK. The reduction decreases to ∼29 % for typical cruise engine settings and to ∼22 % at high cruise engine power settings. The size of non-volatile particles was slightly smaller for HEFA-SPK compared to Jet A-1. We show a comprehensive analysis of the hydrogen content of globally available fuels. Our results demonstrate the impact of the fuel composition in terms of its aromatic, hydrogen, and sulfur content as well as of the effect of engine power settings on particle emissions. We demonstrate that the use of HEFA-SPK can significantly reduce particle emissions and thus contrail ice particles and therefore can provide an aviation climate benefit. [ABSTRACT FROM AUTHOR]

In order to reduce aviation's CO2 emissions and comply with current climate targets, the European Union plans a mandatory quota of 2% sustainable aviation fuel (SAF) by 2025, rising up to ≥ 70% SAF by 2050. In addition to a reduction of life cycle CO2-emissions the use of SAF can also have a positive impact on particle emissions and contrail properties. In this study we present observations from the ECLIF3 (Emission and CLimate Impact of alternative Fuels) aircraft campaign, which investigated exhaust and contrail characteristics of an Airbus A350-941 equipped with Rolls-Royce Trent XWB-84 engines. For the first time, non-volatile and total particle emissions of 100% HEFA-SPK (Hydro-processed Esters and Fatty Acids - Synthetic Paraffinic Kerosene) SAF, a blended fuel and a reference Jet A-1 were measured in flight. A maximum reduction in non-volatile particle number emissions of ~41 % compared to the reference Jet A-1 fuel was measured at low cruise engine power settings when using 100% HEFA-SPK. The reduction decreases to ~29% for typical cruise engine settings and to ~22% at high cruise engine power settings. The size of non-volatile particles was slightly smaller for HEFA-SPK compared to Jet A-1. We show a comprehensive analysis of the hydrogen content of globally available fuels. Our results demonstrate the impact of the fuel composition in terms of its aromatic, hydrogen and sulfur content as well as of the effect of engine power settings on particle emissions. We demonstrate that the use of HEFA-SPK can significantly reduce particle emissions and thus contrail ice particles, and therefore can provide an aviation climate benefit. [ABSTRACT FROM AUTHOR]

Powering aircraft by sustainable aviation fuels (SAFs) is a pathway to reduce the climate impact of aviation by lowering aviation lifecycle CO2 emissions and by reducing ice crystal numbers and radiative forcing from contrails. While the effect of SAF blends on contrails has been measured previously, here we present novel measurements on particle emission and contrails from 100 % SAF combustion. During the ECLIF3 (Emission and CLimate Impact of alternative Fuels) campaign, a collaboration between the Deutsches Zentrum für Luft- und Raumfahrt (DLR), Airbus, Rolls-Royce, and Neste, the DLR Falcon 20 research aircraft performed in situ measurements following an Airbus A350-941 source aircraft powered by Rolls-Royce Trent XWB-84 engines in 1 to 2 min old contrails at cruise altitudes. Apparent ice emission indices of 100 % HEFA-SPK (hydro-processed esters and fatty acids–synthetic paraffinic kerosene) were measured and compared to Jet A-1 fuel contrails at similar engine and ambient ice-supersaturated conditions within a single flight. A 56 % reduction in ice particle numbers per mass of burned fuel was measured for 100 % HEFA-SPK compared to Jet A-1 under engine cruise conditions. The measured 35 % reduction in soot particle numbers suggests reduced ice activation by the low-sulfur HEFA fuel. Contrail properties are consistently modeled with a contrail plume model. Global climate model simulations for the 2018 fleet conservatively estimate a 26 % decrease in contrail radiative forcing and stronger decreases for larger particle reductions. Our results indicate that higher hydrogen content fuels as well as clean engines with low particle emissions may lead to reduced climate forcing from contrails. [ABSTRACT FROM AUTHOR]

Nitrogen oxides, emitted from air traffic, are of concern due to their impact on climate by changing atmospheric ozone and methane levels. Using the DLR research aircraft Falcon, total reactive nitrogen (NOy) measurements were carried out at high altitudes to characterize emissions in the fresh aircraft exhaust from the latest generation Rolls-Royce Trent XWB-84 engine aboard the long-range Airbus A350-941 aircraft. The impact of different engine thrust settings, monitored in terms of combustor inlet temperature, pressure, and engine fuel flow, was tested for two different fuel types: Jet A-1 and for the first time a 100% sustainable aviation fuel (SAF) under similar atmospheric conditions. During ground emission measurements, a range of combustor temperatures and an additional blended SAF were tested. We confirm that the NOx emission index increases with increasing combustion temperature, pressure and fuel flow. We find that as expected, the fuel type has no measurable effect on the NOx emission index. These measurements are used to compare to cruise NOx emission index estimates from three engine emission models. Our measurements thus help to understand the ground to cruise correlation of current emission models while serving as input for climate modelling, and extending the extremely sparse data set on in-flight aircraft NOx emissions to newer engine generations. [ABSTRACT FROM AUTHOR]

Nitrogen oxides, emitted from air traffic, are of concern due to their impact on climate by changing atmospheric ozone and methane levels. Using the DLR research aircraft Falcon, total reactive nitrogen (NOy) measurements were carried out at high altitudes to characterize emissions in the fresh aircraft exhaust from the latest generation Rolls-Royce Trent XWB-84 engine aboard the long-range Airbus A350-941 aircraft. The impact of different engine thrust settings, monitored in terms of combustor inlet temperature, pressure, and engine fuel flow, was tested for two different fuel types: Jet A-1 and for the first time a 100 % sustainable aviation fuel (SAF) under similar atmospheric conditions. During ground emission measurements, a range of combustor temperatures and an additional blended SAF were tested. We confirm that the NOx emission index increases with increasing combustion temperature, pressure and fuel flow. We find that as expected, the fuel type has no measurable effect on the NOx emission index. These measurements are used to compare to cruise NOx emission index estimates from three engine emission models. Our measurements thus help to understand the ground to cruise correlation of current emission models while serving as input for climate modelling, and extending the extremely sparse data set on in-flight aircraft NOx emissions to newer engine generations. [ABSTRACT FROM AUTHOR]

Powering aircraft by sustainable aviation fuels (SAF) is a pathway to reduce the climate impact of aviation by lowering aviation life-cycle CO2 emissions and by reducing ice crystal numbers and radiative forcing from contrails. While the effect of SAF blends on contrails has been measured previously, here we present novel measurements on particle emission and contrails from 100% SAF combustion. During the ECLIF3 (Emission and CLimate Impact of alternative Fuels) campaign, a collaboration between DLR, AIRBUS, ROLLS-ROYCE and NESTE, the DLR Falcon 20 research aircraft performed in situ measurements following an Airbus A350-941 source aircraft powered by Rolls-Royce Trent XWB-84 engines in 1 to 2 min old contrails at cruise altitudes. Apparent ice emission indices of 100% HEFA-SPK (Hydro-processed Esters and Fatty Acids - Synthetic Paraffinic Kerosene) were measured and compared to Jet A-1 fuel contrails at similar engine and ambient ice-supersaturated conditions within a single flight. A 56% reduction of ice particle numbers per mass of burned fuel was measured for 100% HEFA-SPK compared to Jet A-1 at engine cruise conditions. The measured 35% reduction in soot particle numbers suggest reduced ice activation by the low sulfur HEFA fuel. Contrail properties are consistently modelled with a contrail plume model. Global climate model simulations for the 2018 fleet conservatively estimate a 26% decrease in contrail radiative forcing and stronger decreases for larger particle reductions. Our results indicate that higher hydrogen content fuels as well as clean engines with low particle emissions may lead to reduced climate forcing from contrails. [ABSTRACT FROM AUTHOR]

Powering aircraft by sustainable aviation fuels (SAF) is a pathway to reduce the climate impact of aviation by lowering aviation life-cycle CO2 emissions and by reducing ice crystal numbers and radiative forcing from contrails. While the effect of SAF blends on contrails has been measured previously, here we present novel measurements on particle emission and contrails from 100 % SAF combustion. During the ECLIF3 (Emission and CLimate Impact of alternative Fuels) campaign, a collaboration between DLR, AIRBUS, ROLLS-ROYCE and NESTE, the DLR Falcon 20 research aircraft performed in situ measurements following an Airbus A350-941 source aircraft powered by Rolls-Royce Trent XWB-84 engines in 1 to 2 min old contrails at cruise altitudes. Apparent ice emission indices of 100 % HEFA-SPK (Hydro-processed Esters and Fatty Acids - Synthetic Paraffinic Kerosene) were measured and compared to Jet A-1 fuel contrails at similar engine and ambient ice-supersaturated conditions within a single flight. A 56 % reduction of ice particle numbers per mass of burned fuel was measured for 100 % HEFA-SPK compared to Jet A-1 at engine cruise conditions. The measured 35 % reduction in soot particle numbers suggest reduced ice activation by the low sulfur HEFA fuel. Contrail properties are consistently modelled with a contrail plume model. Global climate model simulations for the 2018 fleet conservatively estimate a 26 % decrease in contrail radiative forcing and stronger decreases for larger particle reductions. Our results indicate that higher hydrogen content fuels as well as clean engines with low particle emissions may lead to reduced climate forcing from contrails. [ABSTRACT FROM AUTHOR]

The live fuel moisture content (LFMC) is an important precondition for wildfire activity, yet it remains challenging to predict LFMC due to the dynamic interplay between atmospheric and hydrological conditions that determine the plant's access to, and loss of water.We monitored LFMC and a range of plant water‐use traits (predawn and midday leaf water potentials [Ψleaf]), leaf traits (specific leaf area [SLA]), hydrological status (soil water content [SWC] in the shallow layer and full profile) and atmospheric variables (air temperature, vapour pressure deficit [VPD], CO2 concentrations) in a mature eucalypt woodland at the Eucalyptus Free‐Air CO2 Enrichment (EucFACE) facility during a drought.We combined plant traits, hydrological status and atmospheric variables into a biophysical model to predict LFMC dynamics, and compared these with predictions of LFMC based on a satellite model and established relationships between Ψleaf and LFMC from pressure–volume curves.Predawn Ψleaf could be well predicted from changes in SWC, but variation in midday Ψleaf and LFMC were more responsive to atmospheric than hydrological variables. The biophysical model explained up to 89% of variability in LFMC and outperformed established approaches to predict LFMC. SLA was the single most important variable to predict LFMC, followed by VPD, which explained 33% of the remaining variability in LFMC.Our study demonstrates that the co‐variation of plant traits and atmospheric and hydrological conditions affect LFMC during drought, suggesting a new way forward for predicting LFMC by combining biophysical and satellite‐based models of LFMC with seasonal forecasts of meteorological and hydrological variables. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

The origin of both weak temperature dependence and packing fraction dependence of T1/4η3/2 in the thermal conductivity of the simple Lennard-Jones (LJ) liquid is explored. In order to discuss the relative contributions from attractive or repulsive part of the interaction potential separately, the thermal conductivity of a series of Weeks-Chandler-Anderson (WCA) fluids is calculated by molecular dynamics simulations. The results show that the repulsive part plays the main role in the heat conduction, while the attractive part has no direct effect on the thermal conductivity for a given packing fraction. By investigating WCA fluids with potentials of varying softness, we explain the difference observed between the LJ liquids such as argon and Coulombic liquids such as NaCl. [ABSTRACT FROM AUTHOR]

The transport properties of molten LiF-YF3 mixtures have been studied by pulsed field gradient nuclear magnetic resonance spectroscopy, potentiometric experiments, and molecular dynamics simulations. The calculated diffusion coefficients and electric conductivities compare very well with the measurements across a wide composition range. We then extract static (radial distribution functions, coordination numbers distributions) and dynamic (cage correlation functions) quantities from the simulations. Then, we discuss the interplay between the microscopic structure of the molten salts and their dynamic properties. It is often considered that variations in the diffusion coefficient of the anions are mainly driven by the evolution of its coordination with the metallic ion (Y3+ here). We compare this system with fluorozirconate melts and demonstrate that the coordination number is a poor indicator of the evolution of the diffusion coefficient. Instead, we propose to use the ionic bonds lifetime. We show that the weak Y-F ionic bonds in LiF-YF3 do not induce the expected tendency of the fluoride diffusion coefficient to converge toward one of the yttrium cation when the content in YF3 increases. Implications on the validity of the Nernst-Einstein relation for estimating the electrical conductivity are discussed. [ABSTRACT FROM AUTHOR]

In models of Pt 111 and Pt 100 surfaces in water, motions of molecules in the first hydration layer are spatially and temporally correlated. To interpret these collective motions, we apply quantitative measures of dynamic heterogeneity that are standard tools for considering glassy systems. Specifically, we carry out an analysis in terms of mobility fields and distributions of persistence times and exchange times. In so doing, we show that dynamics in these systems is facilitated by transient disorder in frustrated two-dimensional hydrogen bonding networks. The frustration is the result of unfavorable geometry imposed by strong metal-water bonding. The geometry depends upon the structure of the underlying metal surface. Dynamic heterogeneity of water on the Pt 111 surface is therefore qualitatively different than that for water on the Pt 100 surface. In both cases, statistics of this ad-layer dynamic heterogeneity responds asymmetrically to applied voltage. [ABSTRACT FROM AUTHOR]

We revisit the statistical mechanics of charge fluctuations in capacitors. In constant-potential classical molecular simulations, the atomic charges of electrode atoms are treated as additional degrees of freedom which evolve in time so as to satisfy the constraint of fixed electrostatic potential for each configuration of the electrolyte. The present work clarifies the role of the overall electroneutrality constraint, as well as the link between the averages computed within the Born–Oppenheimer approximation and that of the full constant-potential ensemble. This allows us in particular to derive a complete fluctuation–dissipation relation for the differential capacitance, that includes a contribution from the charge fluctuations (around the charges satisfying the constant-potential and electroneutrality constraints) also present in the absence of an electrolyte. We provide a simple expression for this contribution from the elements of the inverse of the matrix defining the quadratic form of the fluctuating charges in the energy. We then illustrate numerically the validity of our results, and recover the expected continuum result for an empty capacitor with structureless electrodes at large inter-electrode distances. By considering a variety of liquids between graphite electrodes, we confirm that this contribution to the total differential capacitance is small compared to that induced by the thermal fluctuations of the electrolyte. [ABSTRACT FROM AUTHOR]

Dipole polarizabilities of a series of ions in aqueous solutions are computed from first-principles. The procedure is based on the study of the linear response of the maximally localized Wannier functions to an applied external field, within density functional theory. For most monoatomic cations (Li+, Na+, K+, Rb+, Mg2+, Ca2+ and Sr2+) the computed polarizabilities are the same as in the gas phase. For Cs+ and a series of anions (F-, Cl-, Br- and I-), environmental effects are observed, which reduce the polarizabilities in aqueous solutions with respect to their gas phase values. The polarizabilities of H(aq)+, OH(aq)- have also been determined along an ab initio molecular dynamics simulation. We observe that the polarizability of a molecule instantaneously switches upon proton transfer events. Finally, we also computed the polarizability tensor in the case of a strongly anisotropic molecular ion, UO22+. The results of these calculations will be useful in building interaction potentials that include polarization effects. [ABSTRACT FROM AUTHOR]

Expressions for the energy current of a system of charged, polarizable ions in periodic boundary conditions are developed in order to allow the thermal conductivity in such a system to be calculated by computer simulation using the Green–Kubo method. Dipole polarizable potentials for LiCl, NaCl, and KCl are obtained on a first-principles basis by “force matching” to the results of ab initio calculations on suitable condensed-phase ionic configurations. Simulation results for the thermal conductivity, and also other transport coefficients, for the melts are compared with experimental data and with results obtained with other interaction potentials. The agreement with experiment is almost quantitative, especially for NaCl and KCl, indicating that these methodologies, perhaps with more sophisticated forms for the potential, can be used to predict thermal conductivities for melts for which experimental determination is very difficult. It is demonstrated that the polarization effects have an important effect on the energy current and are crucial to a predictive scheme for the thermal conductivity. [ABSTRACT FROM AUTHOR]

The calculation of the Marcus free energy curves for electron transfer events between a redox species and a metallic electrode in an atomistic simulation designed to model the electrochemical interface with an ionic liquid is described. The calculation is performed on a system comprising a molten salt mixture confined between model metallic electrodes [Reed et al., J. Chem. Phys. 126, 084704 (2007)] which are maintained at a constant electrical potential. The calculation therefore includes a self-consistent description of the screening of the electrode potential by the liquid and the polarization of the electrode by the ions (image charge effects). The purpose of the study was to examine how the Marcus curves depend on the applied potential and on the distance of the redox species from an electrode. The pronounced oscillations in the mean electrical potential seen in molten salt systems in the “double-layer” region are not reflected in the reaction free energy for the electron transfer event. The reorganization energy depends markedly on the distance of the redox ion from the electrode surface because of image charge effects. [ABSTRACT FROM AUTHOR]

The observation of a very sharp low frequency spike in the hyper-Rayleigh spectrum (HRS) of strongly dipolar fluids, such as acetonitrile and water, has been interpreted as reflecting a very slowly relaxing component in the transverse dipole density. This suggestion is at variance with the expectation of the dielectric theory for an isotropic fluid and has led to the speculation that the slow relaxation is associated with the reorganization of ferroelectric domains. Very large-scale molecular-dynamics simulation (∼28 000 molecules) have been carried out using a three-site potential model of acetonitrile. The simulated fluid shows no suggestion of strong dipole correlations and domain structure. The dipole density correlations behave as predicted by the normal dielectric theory and their spectra do not show the low-frequency feature seen in the HRS. In order to examine the characteristics of the spectra which would be seen in a ferroelectric domain, the acetontrile model was transmuted to more closely resemble a Stockmayer-type fluid with the same dipole density and a ferroelectric phase was observed. In this phase the dielectric spectra show (i) a high-frequency spectral feature due to librational motion of the molecules within a domain, and (ii) slowly-relaxing longitudinal and transverse polar modes, again at variance from the experimental HRS characteristics. [ABSTRACT FROM AUTHOR]

A molecular dynamics simulation model for an electroactive interface in which a metallic electrode is maintained at a preset electrical potential is described. The model, based on earlier work of Siepmann and Sprik [J. Chem. Phys. 102, 511 (1995)], uses variable charges whose magnitudes are adjusted on-the-fly according to a variational procedure to maintain the constant potential condition. As such, the model also allows for the polarization of the electrode by the electrolyte, sometimes described by the introduction of image charges. The model has been implemented in a description of an electrochemical cell as a pair of parallel planar electrodes separated by the electrolyte using a two-dimensional Ewald summation method. The method has been applied to examine the interfacial structure in two ionic liquids, consisting of binary mixtures of molten salts, chosen to exemplify the influences of dissimilar cation size and charge. The stronger coordination of the smaller and more highly charged cations by the anions prevents them from approaching even the negatively charged electrode closely. This has consequences for the capacitance of the electrode and will also have an impact on the rates of electron transfer processes. The calculated capacitances exhibit qualitatively the same dependence on the applied potential as has been observed in experimental studies. [ABSTRACT FROM AUTHOR]

A method is presented to allow the calculation of the dipole polarizabilities of ions and molecules in a condensed-phase coordination environment. These values will be useful for understanding the optical properties of materials and for developing simulation potentials which incorporate polarization effects. The reported values are derived from plane wave density functional theory calculations, though the method itself will apply to first-principles calculations on periodic systems more generally. After reporting results of test calculations on atoms to validate the procedure, values for the polarizabilities of the oxide ion and various cations in a range of materials are reported and compared with experimental information as well as previous theoretical results. [ABSTRACT FROM AUTHOR]

Theoretical Raman spectra of the elpasolite-structured crystal Cs2NaLaCl6 and of molten mixtures of LaCl6 with NaCl and CsCl have been obtained from computer simulations in order to examine how the Raman spectra reflect the coordination structure around the La3+ ions. This system is a model for many other trivalent metal halides and for examining how the network structure of the pure melts is broken down by the addition of alkali halides with different structure-breaking powers. The results suggest a way of reconciling the conclusions of Raman studies about the structures of the melts with those of neutron and x-ray-diffraction studies, which have already been examined with the same simulation methods. The Raman spectra, both polarized and depolarized, are calculated from a model for the dependence of the polarizability of the system on the ionic coordinates which was inspired by electronic structure calculations of the polarizabilities of ions in a condensed phase environment. Some results on the lifetimes of the coordination complexes responsible for the appearance of the discrete Raman bands are discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Theoretical Raman spectra of the complex-forming ionic liquids LaCl[sub 3] and ScCl[sub 3], derived from molecular dynamics computer simulations, are presented. These simulations, which use polarizable ion interaction models, have previously been shown to predict structural properties in excellent agreement with diffraction experiments. The dependence of the polarizability of the melt on the ionic positions, which determines the Raman spectrum through the time dependence of the polarizability correlation function, is modeled on the basis of ab initio electronic structure calculations carried out on alkali chlorides. New simulation techniques are introduced in order to allow the spectrum to be calculated with acceptable statistics. The calculated spectra are in semiquantitative agreement with experimental data. The distinctive bands which appear in the spectra of such complex melts are linked to the vibrations of the transient coordination complexes which form in these melts and new interpretations for the origin of several well-known features are proposed. The simulations thus enable a link between the structure of a melt as perceived through Raman spectroscopy and through diffraction experiments to be made. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The dynamical properties of ionic melts formed from mixtures of LiCl and KCl have been studied across the full composition range in computer simulations of sufficient length to enable reliable values for such collective transport coefficients as the viscosity, conductivity, and internal mobilities to be determined reliably. Interest centers on the nontrivial concentration dependence exhibited by these transport coefficients, which agrees well with that observed experimentally, and in relating this to the strength of the association between an ion and its first coordination shell. The relationships between the various transport coefficients, such as those between the diffusion coefficient and the viscosity (Stokes–Einstein) and the conductivity (Nernst–Einstein) also exhibit composition dependences that reflect this association. The connection between the internal mobility and two measures of the coordination shell dynamics (the cage relaxation time and the self-exchange velocity) is explored; it is shown that the self-exchange velocity follows the composition and temperature dependence of the internal mobility very well. Finally, it is shown that allowing for anion polarization in the interaction model increases the mobility of all species without changing the structure of the melt discernibly, with the largest effect being found for the Li[sup +] ion. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ewald summation expressions are derived for the energy, interatomic forces, pressure tensor, electric fields, and electric field gradients in a periodic computer simulation system of molecules with charges, induced dipoles, and quadrupoles. The full expressions including quadrupolar multipole interactions are given; those involving dipoles are included for completeness. The expressions apply not only to molecules with permanent multipoles, but also to systems of polarizable ions where the multipoles are induced by the interionic interactions. The expressions which allow for this generalization consider the ions to be spherically polarizable, but include the consequences of the coupling between dipolar and quadrupolar induction. The phonon dispersion curves of MgO and the structural lattice constants of Al[sub 2]O[sub 3] in its corundum phase are discussed as specific examples. In simulations with a dipole- and quadrupole-polarizable interaction model, a full Ewald summation of quadrupolar interactions is shown to have a significant effect. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Transferable potential models of interatomic interactions in CaO, SrO, and BaO are obtained by fitting the forces and stress tensor given by the aspherical ion model (AIM) [J. Chem. Phys. 108, 10209 (1998)] to those obtained from the ab initio molecular dynamics code CASTEP on condensed phase ion configurations generated at different values of pressure, temperature, and coordination environment. The AIM allows for dipole and quadrupole polarization of the ions as well as for ion-shape deformation due to short-range interactions. The potentials produce thermal expansivities, elastic properties, and phonon dispersion curves of these materials in excellent agreement with experiment. The BaO potential is also found to reproduce the complicated pressure-driven phase transitions observed in experiments on this material, even though these structures were not represented in the fitting procedure. The fitting process shows the increasing significance of cation polarization and shape deformation for the interionic interactions on descending the alkaline earth group, and this becomes an essential feature to account for the stability of the observed high-pressure phases of BaO. [ABSTRACT FROM AUTHOR]

An aspherical ion model (AIM) description of interatomic interactions in alkaline earth oxides MgO, CaO, SrO, and BaO has been obtained. The parameters were determined by matching the forces predicted by the models to those calculated from an ab initio dynamics calculation in finite temperature simulations. The models were shown to be transferable in the sense that they offered equally accurate descriptions of the pure materials over very wide ranges of temperature and pressure and in phases with different coordination number. In the present paper, more wide-ranging transferability considerations are pursued. First, we check transferability between chemically related substances: we transform the model for CaO into a potential for BeO by scaling parameters according to the changes in ion sizes and polarizabilities. Second, we test transferability upon compound formation, by combining the MgO and CaO potentials in order to describe the interatomic interactions in MgO-CaO solid binary mixtures. The results show that the proposed models are able to provide a good description of interatomic interactions in both cases. The calculations demonstrate that the AIM represents the different contributions to the interionic forces faithfully and that the force-matching procedure finds physically meaningful values for the parameters therein. [ABSTRACT FROM AUTHOR]

The structure and surface tension of the liquid-vapor interface of pure LiC1 and KC1 molten salts and of LiC1-KC1 binary mixtures of different concentrations have been studied by using molecular dynamics simulations and a slab geometry. For the surface tension and its temperature and composition dependences, good agreement with experimental determinations is achieved. A comparison of the structure of LiC1 and KC1 interfaces allows us to discuss the relevance of size asymmetry effects on interfacial properties. These effects are apparent in the structure of the LiC1 interface, but only when a description of polarization interactions is included in the potential model. Polarization facilitates the formation of a displacement dipole moment across the interface by allowing an opposing electronic dipole moment of approximately the same magnitude, so that the total dipole moment is always small and thus not unfavorable from an electrostatic point of view. The study of the binary mixtures shows that the surface tension is relatively insensitive to the specific LiC1 concentration for a broad range of compositions. This is explained by potassium segregation towards the surface. In these cases, where segregation effects are important, we have found that very long simulations (several nanoseconds long) are needed in order to obtain converged density profiles. For all the systems studied, the local ion coordination number reduces to 50% of its bulk value only when the ion density has reduced to less than 5% of its bulk value, showing the importance of clustering effects in this kind of interface. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are used to calculate the surface tension γ and study the structural properties of the liquid–vapor interface of the simple molten salt KI. The focus of the present paper is the effect on the calculated surface tension of different terms in the interionic potential and of the way that long-ranged interactions are treated. Specifically, we analyze the dependence of γ on: (a) boundary conditions employed in the Ewald summations of Coulomb interactions; (b) truncation of dispersion interactions; (c) inclusion of polarization effects. Our results show that (a) the use of vacuum boundary conditions in the direction perpendicular to the interface helps to maintain the mechanical equilibrium of the interface; (b) an Ewald summation of dispersion interactions is necessary to avoid substantial truncation effects; (c) polarization tends to decrease γ by significant amounts, and improves the agreement with experiment. In all cases, a reduction of γ comes with a corresponding increase of the interfacial width. As a structural indicator, the tangential pair distribution functions at the interface are compared with those of the bulk liquid. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An examination of the finite system size effects on the calculated interfacial properties of the molten salt KI is described, as an extension of the work described in the preceding paper [J. Chem. Phys. 115, 8603 (2001)]. It is shown that, for system sizes beyond ∼1000 ions, the finite size effects are accounted for by the predictions of capillary wave (CW) theory, as in van der Waals liquids. Hence, there do not appear to be additional long-range effects arising from the Coulombic interactions. Techniques used to avoid truncation effects in the Coulombic and dispersion interactions appear to have eliminated system size dependent artefacts from these sources. The scaling behavior predicted from CW theory is used to predict the bulk surface tension for the chosen interaction potential, which is then compared with experimental values, and very good agreement found. Examination of the interfacial layers show that the local structure remains strongly charge ordered, but the surface is highly roughened by clustering and, on longer length-scales, by the effect of capillary waves. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the contributions of three-body triple dipole and dipole-dipole-quadrupole dispersion interactions to the thermodynamic properties of liquid argon. Use of a simulation scheme which contains a quantum mechanical representation of the electronic structure; Representation of three-body effects in an effective pair potential.

The general firm/trade union bargaining literature is brought to bear on a specific North American sports league model, where talent supply is perfectly inelastic and profit-maximizing clubs receive local (gate) revenue plus an equal share of league broadcasting revenue. Club and player representatives negotiate a collective bargaining agreement (CBA) on the levels of local revenue sharing, salary cap, and salary floor. Results characterize the set of efficient bargains and the Nash bargaining solution and show how they are affected by increases in broadcasting market size, focusing on player salaries, competitive balance, the content of CBA documents, and comparisons with laissez-faire. [ABSTRACT FROM AUTHOR]

Discusses computer simulations of the short-time, vibrational dynamics of the network-forming ionic melts and their mixtures with network-breaking alkali halides. Description of high frequency peaks in the vibrational density of states; Strong aspect of vibrational motions; Effects of network-induced coupling between the vibrations of different units.

Simulations of the superionic conductor CaF[SUB2] have been undertaken, with a model for the interionic interactions derived directly from electronic structure calculations. The model includes such many-body effects as polarization and the adaptation of the size of the anion to its instantaneous environment ("compression"). Physical properties of CaF[SUB2] accurately reproduced include the phonon frequencies, the fluorite → α-PbCl[SUB2]-structure phase transition and the solid-state diffusion. Analysis shows that the compression effect is much less important for fluorides than oxides but, nevertheless, significantly affects the phase transition pressure. Polarization effects, particularly of the cations, play a crucial role in allowing the anion diffusion, and the importance of a short-range contribution to the cation polarization is highlighted. These findings are contrasted with previous work using empirically parametrized shell and pair potentials, which suggest that other interactions play the dominant role. [ABSTRACT FROM AUTHOR]

An approach, based upon the Car–Parrinello method, for finding the electronic ground state for a self-interaction corrected density functional theory is described. The influence of the self-interaction correction for the ground-state properties and for predicted equilibrium molecular structures is illustrated with reference to calculations on small clusters of sodium. [ABSTRACT FROM AUTHOR]

The problem of keeping the electronic state at its adiabatic value in the course of ab initio molecular dynamics runs with the Car–Parrinello method is discussed. Attention is focused on the difficulties which arise when chemical bonds are broken and formed in the course of the atomic motion. A solution to the problems is the coupling of independent Nosé–Hoover thermostats to the up and down spin orbitals. The choice of suitable parameters to control the thermostats is discussed. The success of the method is illustrated in studies of the dissociation/recombination of Na2 and the isomerization of the Na3 molecule by a process of pseudorotation. [ABSTRACT FROM AUTHOR]

A new ‘‘ab initio’’ method is presented which is designed to simulate highly asymmetric systems of charged particles such as micellar solutions and charge-stabilized colloidal suspensions. The hybrid description considers the macroion degrees of freedom explicitly, while the microscopic counterions are treated within the framework of density functional theory. The counterion density profile is treated as a dynamical variable which is coupled to the macroion positions; the corresponding equation of motions are derived from a Lagrangian which contains a fictitious kinetic energy term associated with the inhomogeneous counterion density, with a fictitious mass chosen so that the counterions stay as close as possible to the surface of lowest free energy (adiabatic condition). The discontinuous behavior of the counterion density profile at the macroion surfaces is suppressed by the use of a classical pseudopotential scheme without spoiling the rapid variation of the counterion density profile outside the macroion cores. The ab initio method is implemented in Molecular and Brownian Dynamics simulations of concentrated colloidal suspensions, and the results are compared to the predictions of much simpler simulations based on the pairwise additive effective Derjaguin–Landau–Verwey–Overbeek (DLVO) potential between macroions. The density profiles calculated from the DLVO model differ considerably from the predictions of the ab initio simulations, but the macroion pair structures are in reasonable agreement. Recent ‘‘improvements’’ of the standard DLVO theory are found to overestimate or underestimate the pair structure considerably. The density functional formalism may be used to derive systematic many-body corrections to the effective DLVO pair potential. The extension of the ab initio method to treat colloidal suspensions in the presence of added salt is briefly sketched. [ABSTRACT FROM AUTHOR]

The time dependence of the refractive index change induced in an absorbing colloidal suspension by a nanosecond laser pulse is studied by the four-wave mixing method. A very large transient is observed even in very dilute suspensions whose amplitude oscillates on a time scale much shorter than the laser pulse duration; the effect is found in a variety of systems. The behavior of the transient suggests that it is associated with an acoustic wave in the suspending fluid excited by an explosive event at the surface of the particles. By comparing the predictions of various hydrodynamic models with the observations and by studying the effect of changing the experimental conditions on the form of the transient, it is proposed that the behavior arises from the very rapid growth of vapor bubbles around those particles which are heated sufficiently strongly; the four-wave mixing signal monitors the coherent superposition of the resulting pressure pulses in the fluid. [ABSTRACT FROM AUTHOR]

The kinetics of the heat and mass transport involved in vapor bubble formation around a colloidal particle which has been heated rapidly to high temperatures are examined with a theoretical model. It is argued that the likely mechanism of bubble formation on the nanosecond time scale is a spinodal decomposition of the liquid at the particle surface to the low density (vapor) phase. This process is shown to give rise to extremely rapid changes in the density and pressure fields of the fluid. The existence of such rapid events has been invoked to explain experimental observations of acoustic shocks generated in laser-pulse-heated colloidal suspensions. [ABSTRACT FROM AUTHOR]

The collision-induced depolarized light scattering spectrum arising from the dipole–induced dipole (DID) interactions in atomic fluids has been calculated using kinetic theory methods. The theory contains no adjustable parameters and requires only the temperature, density, and collision diameter as input. Above 25 cm-1, the calculated line shape was found to be in excellent agreement with the spectrum obtained from a hard-sphere molecular dynamics simulation, with the same model for the interaction-induced polarizability. The domain of applicability of the approximations used in reducing the theory to a tractable form was carefully evaluated. The methods developed should be applicable to other intermolecular correlation functions, such as those observed in vibrational relaxation and interaction-induced infrared spectroscopy. [ABSTRACT FROM AUTHOR]

Objective: To identify and define clinically meaningful type 1 diabetes outcomes beyond hemoglobin A1c (HbA1c) based upon a review of the evidence, consensus from clinical experts, and input from researchers, people with type 1 diabetes, and industry. Priority outcomes include hypoglycemia, hyperglycemia, time in range, diabetic ketoacidosis (DKA), and patient-reported outcomes (PROs). While priority outcomes for type 1 and type 2 diabetes may overlap, type 1 diabetes was the focus of this work.Research and Methods: A Steering Committee-comprising representatives from the American Association of Clinical Endocrinologists, the American Association of Diabetes Educators, the American Diabetes Association, the Endocrine Society, JDRF International, The Leona M. and Harry B. Helmsley Charitable Trust, the Pediatric Endocrine Society, and the T1D Exchange-was the decision-making body for the Type 1 Diabetes Outcomes Program. Their work was informed by input from researchers, industry, and people with diabetes through Advisory Committees representing each stakeholder group. Stakeholder surveys were used to identify priority outcomes. The outcomes prioritized in the surveys were hypoglycemia, hyperglycemia, time in range, DKA, and PROs. To develop consensus on the definitions of these outcomes, the Steering Committee relied on published evidence, their clinical expertise, and feedback from the Advisory Committees.Results: The Steering Committee developed definitions for hypoglycemia, hyperglycemia, time in range, and DKA in type 1 diabetes. The definitions reflect their assessment of the outcome's short- and long-term clinical impact on people with type 1 diabetes. Knowledge gaps to be addressed by future research were identified. The Steering Committee discussed PROs and concluded that further type 1 diabetes-specific development is needed.Conclusions: The Steering Committee recommends use of the defined clinically meaningful outcomes beyond HbA1c in the research, development, and evaluation of type 1 diabetes therapies. [ABSTRACT FROM AUTHOR]

The article focuses on an introduction of Non-Hydrostatic Icosahedral Model (NIM) with analysis of massively parallel fine grain (MPFG) performance over high-performance computing (HPC). Topics discussed include consideration of weather prediction models development for application in processors as Many Integrated Core (MIC); observation of NIM's performance of graphic processing unit (GPU); and illustration of cost–benefit analysis for NIM model accelerators.

Driskill and Vrooman have recently provided an interesting argument for a Cournot-based approach to modeling duopsony sports leagues with perfectly inelastic talent supply (the usual assumption for major North American sports league), quite different from the suggestion made by this author (and others) that specifications where talent expenditures are strategic variables (rather than Cournot talent levels) are most appropriate for the context. This comment offers some clarifications and comparisons of the merits of the alternative approaches; they continue to point toward the talent expenditure approach as the most fruitful for the leagues under investigation and probably more generally. [ABSTRACT FROM AUTHOR]

The article presents a discussion on chemical phenomena and processes including the addition of fluoride (F) ions into chloride molten salt, the impact of the interaction of titanium (Ti) ions and F ions to Ti reduction, and the use of disproportionation reactions of Ti ions in producing Ti powder.

The article presents a discussion concerning the development of nuclear reactors and processing of spent fuels.

The article presents a conversation regarding molten salts, environmental impact, and the benefits to energy efficiency.

The article presents a conversation concerning the improvements of energy storage and conversion.

Mixtures of trivalent metal halides with alkali halides are involved in many technologies but, from a more fundamental and general perspective, are worthy of study as interesting systems in which to examine the relationship between atomic-scale structure and physical properties. Here we examine the relationship between the viscosity and local and longer range structural measures in such mixtures where the trivalent metal cations span a significant size range and exhibit different behaviours in the dependence of their viscosity on the mixture composition. We characterise the structure and dynamics of the first coordination shell and the relationship between its structural relaxation time and the shear relaxation time of the mixture (the Maxwell relaxation time). We are then led to an examination of the structure of the networks which progressively form between the trivalent metal cations as their concentration increases in the mixtures. Here we find significant differences between small and larger cations, sufficient to explain the different behaviour of their viscosities. We draw attention to the similarities and differences of these networks with those which form in highly viscous, glass-forming materials like BeF2:LiF. [ABSTRACT FROM AUTHOR]

We perform molecular dynamics simulations of a system consisting of Eu3+and Eu2+species dissolved in a high-temperature KCl electrolyte between two metallic electrodes. The interaction potential includes ion polarisation effects, and a constant electric potential is maintained within the electrodes by allowing the atomic charges to fluctuate in response to the environment. This setup allows us to study the electrochemical Eu3+/Eu2+reaction in the framework of Marcus theory. Numerous studies have pointed to the highly structured nature of ionic liquids and molten salts close to solid surfaces which is not accounted for in the conventional mean-field description of this interface that underpins the theories of electrochemical reaction rates. Here we examine the influence on the kinetics of the charge-transfer event of the electrical potential across the electrode–electrolyte interface and on the effect of the presence of charged surface on the coordination structure and energetics of the ions in the region important for the charge-transfer event. [ABSTRACT FROM PUBLISHER]

A hydrostatic global weather prediction model based on an icosahedral horizontal grid and a hybrid terrain-following/isentropic vertical coordinate is described. The model is an extension to three spatial dimensions of a previously developed, icosahedral, shallow-water model featuring user-selectable horizontal resolution and employing indirect addressing techniques. The vertical grid is adaptive to maximize the portion of the atmosphere mapped into the isentropic coordinate subdomain. The model, best described as a stacked shallow-water model, is being tested extensively on real-time medium-range forecasts to ready it for possible inclusion in operational multimodel ensembles for medium-range to seasonal prediction. [ABSTRACT FROM AUTHOR]