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A three-dimensional real-space model has been created for complex hierarchical materials by matching observed and simulated small-angle X-ray scattering patterns. The simulation is performed by arranging the positions of small primary particles and constructing an aggregate structure in a finite-sized cell., A three-dimensional real-space model has been created for hierarchical materials by matching observed and simulated small-angle X-ray scattering patterns. The simulation is performed by arranging the positions of small primary particles and constructing an aggregate structure in a finite-sized cell. In order to avoid the effect of the finite size of the cell, the cell size is extended to infinity by introducing an asymptotic form of the long-range correlations among the primary particles. As a result, simulations for small-angle X-ray scattering patterns can be performed correctly in the low-wavenumber regime (

Background: Selective targeting of malignant cells is the ultimate goal of anticancer studies around the world. There are some modalities for cancer therapy devastating tumor size and growth rate, meanwhile attacking normal cells. Utilizing appropriate ligands, like folate, allow the delivery of therapeutic molecules to cancer cells selectively. There are a variety of photosensitizers, like gold nanorods (GNRs), capable of absorbing the energy of light and converting it to heat, evidently build a photothermal procedure for cancer therapy. Objective: To develop a one-step approach for calculating the temperature distribution by solving the heat transfer equation with multiple heat sources originating from NIR laser-exposed GNRs. Material and Methods: In this experimental study, we simulated NIR laser heating process in a single cancer cell, with and without incubation with folate conjugated PEG-GNRs. This simulation was based on a real TEM image from an experiment with the same setup. An in vitro experiment based on aforesaid scenario was performed to validate the simulated model in practice. Results: According to the simplifications due to computational resource limits, the resulting outcome of simulation showed significant compatibility to the supporting experiment. Both simulation and experimental studies showed a similar trend for heating and cooling of the cells incubated with GNRs and irradiated by NIR laser (5 min, 1.8 W/cm2). It was observed that temperature of the cells in microplate reached 53.6 °C when irradiated by laser. Conclusion: This new method can be of great application in developing a planning technique for treating tumors utilizing GNP-mediated thermal therapy.

Colloidal systems are composed of big particles — colloids, whose size ranges from 1 nm to 1 μm approximately — dispersed in a medium of smaller particles. As a consequence, colloids interact not only with the solvent particles, resulting in a stochastic dynamics called Brownian motion, but also with each other. The emerging collective behaviour is surprisingly rich and diverse. Remarkably, the phase behaviour and the self-assembly processes of colloidal systems are strikingly analogous to those of atoms and molecules, but on larger scales. Among the many self-assembly processes displayed by colloidal systems, one of the most common and certainly one of paramount importance is nucleation. Nucleation is the process through which a first-order phase transition happens, namely with the birth of a microscopic nucleus of the embryo phase inside the parent phase, which in some conditions is able to grow out and become macroscopic. Nucleation is an ubiquitous event in nature, and hence understanding its mechanism would generate remarkable breakthroughs in very diverse areas of science such as optics, pharmaceutics, and climate science. In the field of soft matter, nucleation constitutes an extremely broad topic, with many open, challenging, and fascinating questions. With the current thesis, we aim to address some of these questions by means of numerical simulations and machine learning algorithms. We try to understand its underlying mechanisms for several systems, and we pay special attention to the inhibitory factors as well as the optimal conditions for nucleation to happen.

Computer simulations of vehicle dynamics become more complex when a vehicle movement takes place on the uneven road surface. In such a case two problems must be solved. The first one concerns a way of road surface modeling, and the second one a way of precisely determining a place of interaction of reaction forces of the road on the vehicle wheels. In this paper triangular irregular networks (TIN) surface was used for modeling surface unevenness, and the author’s algorithm based on the efficient kd-tree data structure was developed for determining a place of an application road surface reaction forces. For calculating the reaction forces including rolling resistance force the Pacejka Magic Formula tire model was used. The solution presented in the paper is computing efficient and for this reason it can be used in the in real-time simulations not only for a vehicle dynamics but for any objects moving over an uneven surface road.

Colloidal suspensions of two species have the ability to form binary crystals under certain conditions. The hunt for these functional materials and the countless investigations on their formation process are justified by the plethora of synergetic and collective properties these binary superlattices show. Among the many crystal structures observed over the past decades, the highly exotic colloidal icosahedral AB13 crystal was predicted to be stable in binary hard-sphere mixtures nearly 30 years ago, yet the kinetic pathway of how homogeneous nucleation occurs in this system is still unknown. Here we investigate binary nucleation of the AB13 crystal from a binary fluid phase of nearly hard spheres. We calculate the nucleation barrier and nucleation rate as a function of supersaturation and draw a comparison with nucleation of single-component and other binary crystals. To follow the nucleation process, we employ a neural network to identify the AB13 phase from the binary fluid phase and the competing fcc crystal with single-particle resolution and significant accuracy in the case of bulk phases. We show that AB13 crystal nucleation proceeds via a coassembly process where large spheres and icosahedral small-sphere clusters simultaneously attach to the nucleus. Our results lend strong support for a classical pathway that is well-described by classical nucleation theory, even though the binary fluid phase is highly structured and exhibits local regions of high bond orientational order.

This study investigates the formation of microstructured macromaterials from thermo- and pH-sensitive microgels based on interpenetrating networks of poly-N-isopropylacrylamide (PNIPAM) and polyacrylic acid (PAA). Macromaterials are produced as a result of the deposition of microgel particles and subsequent crosslinking of polyacrylic acid subnetworks to each other due to the formation of the anhydride bonds during annealing. Since both PNIPAM and PAA are environment-sensitive polymers, one can expect that their conformational state during material development will affect its resulting properties. Thus, the influence of conditions of preparation for annealing (pH of the solution, the temperature of preliminary drying) on the swelling behavior, pH- and thermosensitivity, and macromaterial inner structure was investigated. In parallel, the study of the effect of the relative conformations of the IPN microgel subnetworks on the formation of macromaterials was carried out by the computer simulations method. It was shown that the properties of the prepared macromaterials strongly depend both on the temperature and pH of the PNIPAM-PAA IPN microgel dispersions. This opens up new opportunities to obtain materials with pre-chosen characteristics and environmental sensitivity.

The challenge of optimizing the pore size distribution of porous electrodes for different electrolytes is encountered in supercapacitors, lithium-ion capacitors and hybridized battery-supercapacitor devices. A volume-averaged continuum model of ion transport, taking into account the pore size distribution, is employed for the design of porous electrodes for electrochemical double-layer capacitors (EDLCs) in this study. After validation against experimental data, computer simulations investigate two types of porous electrodes, an activated carbon coating and an activated carbon fabric, and three electrolytes: 1.5 M TEABF4 in acetonitrile (AN), 1.5 M TEABF4 in propylene carbonate (PC), and 1 M LiPF6 in ethylene carbonate:ethyl methyl carbonate (EC:EMC) 1:1 v/v. The design exercise concluded that it is important that the porous electrode has a large specific area in terms of micropores larger than the largest desolvated ion, to achieve high specific capacity, and a good proportion of mesopores larger than the largest solvated ion to ensure fast ion transport and accessibility of the micropores.

The paper focuses on thermal and mechanical analysis of Periodic Surface Structure (PSS). PSS is a continuous surface with a specific topology that is mathematically formulated by geometric factors. Cubic P-surface (&ldquo, primitive&rdquo, ), D-surface (&ldquo, diamond&rdquo, ), and G-surface (&ldquo, gyroid&rdquo, ) structures were simulated under load and heat transport using a numerical approach. We conducted our study by solving the stress and heat equations using the Finite Element Method (FEM). We achieved results using our software module, which generates PSS and simulates stress and temperature distribution. The stress model defined by dependence between stress and strain, gained from an experiment, and correlation of strain and displacement, gained from geometric conditions, was used in numerical experiments. The influence of geometric factors on the thermal and mechanical behavior of PSS was qualitatively determined. We showed decreasing effective stress values with an increased number of cells in the cubic domain for concerned PSS. It is important, because the increase in the number of cells does not increase the structure&rsquo, s volume.

The Ce$_2$Fe$_{17}$ intermetallic compound has been studied intensely for several decades; its low-temperature state is reported experimentally either as ferromagnetic or antiferromagnetic by different authors, with a measured ordering temperature ranging within a hundred Kelvin. The existing theoretical investigations overestimate the experimental total magnetic moment of Ce$_2$Fe$_{17}$ by 20-40 % and predict a ferromagnetic ground state. By means of first-principle electronic structure calculations, we show that the total magnetic moment of Ce$_2$Fe$_{17}$ can be reproduced within the Local Density Approximation while functionals based on the Generalized Gradient Approximation fail. Atomistic spin dynamics simulations are shown to capture the change in the magnetic state of Ce$_2$Fe$_{17}$ with temperature, and closely replicate the reported helical structure that appears in some of the experimental investigations.

In this work we constructed a detailed phase diagram for the solutions of ideal diblock-copolymers and compared such diagram with that obtained during polymerization-induced self-assembly (PISA), a wide range of polymer concentrations as well as chain compositions was studied. As the length of the solvophobic block nB increases (the length of the solvophilic block nA was fixed), the transition from spherical micelles to cylinders and further to vesicles (lamellae) occurs. We observed a rather wide transition region between the spherical and cylindrical morphology in which the system contains a mixture of spheres and short cylinders, which appear to be in dynamic equilibrium, the transition between the cylinders and vesicles was found to be rather sharp. Next, upon increasing the polymer concentration in the system, the transition region between the spheres and cylinders shifts towards lower nB/nA values, a similar shift but with less magnitude was observed for the transition between the cylinders and vesicles. Such behavior was attributed to the increased number of contacts between the micelles at higher polymer volume concentrations. We also found that the width of the stability region of the cylindrical micelles for small polymer volume concentrations is in good quantitative agreement with the predictions of analytical theory. The obtained phase diagram for PISA was similar to the case of presynthesized diblock copolymer, however, the positions of the transition lines for PISA are slightly shifted towards higher nB/nA values in comparison to the presynthesized diblock copolymers, which is more pronounced for the case of the cylinders-to-vesicles transition. We believe that the reason for such behavior is the polydispersity of the core-forming blocks: The presence of the short and long blocks being located at the micelle interface and in its center, respectively, helps to reduce the entropy losses due to the insoluble block stretching, which leads to the increased stability of more curved micelles.

The design of colloidal interactions to achieve target self-assembled structures has especially been done for compact objects such as spheres with isotropic interaction potentials, patchy spheres and other compact objects with patchy interactions. Inspired by the self-assembly of collagen-I fibrils and intermediate filaments, we here consider the design of interaction patterns on semiflexible chains that could drive their staggered assembly into regular (para)crystalline fibrils. We consider semiflexible chains composed of a finite number of types of interaction beads (uncharged hydrophilic, hydrophobic, positively charged and negatively charged) and optimize the sequence of these interaction beads with respect to the interaction energy of the semiflexible chains in a number of target-staggered crystalline packings. We find that structures with the lowest interaction energies, that form simple lattices, also have low values of L/D (where L is chain length and D is stagger). In the low interaction energy sequences, similar types of interaction beads cluster together to form stretches. Langevin Dynamics simulations confirm that semiflexible chains with optimal sequences self-assemble into the designed staggered (para)crystalline fibrils. We conclude that very simple interaction patterns should suffice to drive the assembly of long semiflexible chains into staggered (para)crystalline fibrils.

A short experimental activity aimed at upper level undergraduate students or beginner researchers is presented to introduce the concepts of edge effects and hemispherical diffusion at ultramicroelectrodes. Students will perform simple cyclic voltammetry experiments varying the scan rate and using disk electrodes with different radii. They are then asked to interpret the results based on their previous knowledge. Simulations are also performed, which provide a clear visual interpretation of the underlying diffusion process and show the transition between linear and hemispherical diffusion regimes. The simulations are also presented as a tool to extend the study beyond the range of experimentally accessible conditions. The interplay between voltammetry experiments and simulations allows a natural comprehension of these concepts without the need of a previous rigorous theoretical introduction.

Inorganic phosphors based on monoclinic Y2WO6 doped with Sm3+ ions were prepared via conventional solid-state reactions at high temperature. A total of six samples were obtained with different Sm3+ concentrations (0–9%). The purity of the as-prepared phases was checked by powder X-ray diffraction (PXRD). The excitation, emission, and time-resolved emission spectra were examined in detail. The experimental decay curves were fitted to the Inokuti–Hirayama model, showing that the Sm3+ ions form clusters at all compositions. Periodic hybrid density functional theory calculations were also carried out on the undoped material and on 144-atom supercells of stoichiometry Y1.9375Sm0.0625WO6 and Y1.875Sm0.125WO6. The different coordination environments at the Y1, Y2 and Y3 sites are analysed in detail. The calculated structure and band gap of Y2WO6 are in good agreement with experiment with one potentially important discrepancy in a Y3-O bond length. The thermodynamically favoured substitution sites for Sm, Y2 and Y3, in the supercell are not those observed under the preparation conditions used here, since the experimental Rietveld analysis suggests occupation of Y1 at all concentrations. Analogous calculations for the Eu-doped system highlight marked differences between Eu and Sm despite their similar ionic sizes. The calculateddensities of states show the position of the 4f levels in the band gap depend on thesites occupied by the dopants and thus we expect marked differences in the luminescencespectra, opening up possibilities for tuning device performance.

The study presents the results of an experimental and computational study of the high-velocity impact of low-density aluminum foam into a rigid wall. It is shown that the aluminum foam samples deformed before hitting the rigid wall because of the high inertial forces during the acceleration. During the impact, the samples deformed only in the region contacting the rigid wall due to the high impact velocity, the inertial effects dominated the deformation process. However, the engineering stress&ndash, strain relationship retains its typical plateau shape until the densification strain. The experimental tests were successfully reproduced with parametric computer simulations using the LS-DYNA explicit finite element code. A unique computational lattice-type model was used, which can reproduce the randomness of the irregular, open-cell structure of aluminum foams. Parametric computer simulations of twenty different aluminum foam sample models with randomly generated irregular lattice structures were carried out at different acceleration levels to obtain representative statistical results. The high strain-rate sensitivity of low-density aluminum foam was also observed. A comparison of experimental and computational results during aluminum foam sample impact shows very similar deformation behavior. The computational model correctly represents the real impact conditions of low-density aluminum foam and can be recommended for use in similar high-velocity impact investigations.

International audience; Diffusion of interstitial carbon atoms in iron is the rate-limiting phenomenon of a number of phase transitions in body-centered (bcc) and body-centered tetragonal (bct) phases such as ferrite and martensite. These phases being rarely stress-free and undeformed, the influence of stress/strain on the diffusivity of carbon is essential, although scarcely documented. We developed a model of carbon elastodiffusion in bct-iron. We combined anisotropic linear elasticity theory of point defects, the dilute approximation of regular solutions and the multisite model of random walk into a coherent mean-field theory. The model allows predicting the effects of composition, temperature and mechanical loading on the anisotropy of carbon diffusion. Density functional theory calculations have provided most of the materials parameters. The predictions were successfully tested against kinetic Monte Carlo simulations. Our results show that compression of the crystal increases carbon diffusivity, while tension has the opposite effect. Axial straining is accompanied by a large anisotropy of diffusion. This effect could be exploited to produce stress-controlled diffusion channeling for the engineering of anisotropic microstructures during thermal ageing of martensitic Fe-C alloys.

A combined experimental and novel theoretical ab initio structural and electronic study was performed in order to characterize ZnO semiconductor nanopowders doped with Al atoms. For this, powder mixtures of ZnO and metallic Al in adequate proportions yielding different contents of Al (5, 10, and 30 at. %) were prepared by mechanical milling. The systems were characterized by X-ray diffraction and positron annihilation lifetime spectroscopy measurements. Additionally, combining two first-principles methods based on the Density Functional Theory (DFT) we calculated the final equilibrium structures for different concentrations of Al dopants and Zn vacancies in ZnO, predicting afterwards the characteristic positron annihilation lifetimes at these equilibrium structures. In addition to the structural relaxations, the ab initio predictions of the electronic properties in the studied systems help us to understand deeper the origin and characteristics of different positrons traps. This experimental and ab initio/DFT combined study allows to verify the dopant incorporation into the ZnO wurtzite structure and to extract the maximum information from the experimental data, giving an insight into the different defect complexes and their influence in the structural and electrical properties. Fil: Damonte, Laura Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina Fil: Darriba, German Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina Fil: Rentería, Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina

We use coarse-grained molecular dynamics simulations to study adsorption on ligand-tethered particles. Nanoparticles with attached flexible and stiff ligands are considered. We discuss how the excess adsorption isotherm, the thickness of the polymer corona, and its morphology depend on the number of ligands, their length, the size of the core, and the interaction parameters. We investigate the adsorption-induced structural transitions of polymer coatings. The behavior of systems involving curved and flat “brushes” is compared.

To date, it has been reliably shown that the lipid bilayer/water interface can be thoroughly characterized by a sophisticated so-called “dynamic molecular portrait”. The latter reflects a combination of time-dependent surface distributions of various physicochemical properties, inherent in both model lipid bilayers and natural multi-component cell membranes. One of the most important features of biomembranes is their mosaicity, which is expressed in the constant presence of lateral inhomogeneities, the sizes and lifetimes of which vary in a wide range—from 1 to 103 nm and from 0.1 ns to milliseconds. In addition to the relatively well-studied macroscopic domains (so-called “rafts”), the analysis of micro- and nanoclusters (or domains) that form an instantaneous picture of the distribution of structural, dynamic, hydrophobic, electrical, etc., properties at the membrane-water interface is attracting increasing interest. This is because such nanodomains (NDs) have been proven to be crucial for the proper membrane functioning in cells. Therefore, an understanding with atomistic details the phenomena associated with NDs is required. The present mini-review describes the recent results of experimental and in silico studies of spontaneously formed NDs in lipid membranes. The main attention is paid to the methods of ND detection, characterization of their spatiotemporal parameters, the elucidation of the molecular mechanisms of their formation. Biological role of NDs in cell membranes is briefly discussed. Understanding such effects creates the basis for rational design of new prospective drugs, therapeutic approaches, and artificial membrane materials with specified properties.

This work aims to compare the ultrasonic inspection of 9%Ni steel joints welded with the Gas Metal Arc Welding (GMAW) process and Shielded Metal Arc Welding (SMAW) process. These are the two most widely used processes used to weld pipes for CO2 injection units for floating production storage and offloading (FPSO) in the Brazilian oil and gas industry. The SMAW equipment is simple and portable, which is convenient for the FPSO, however, the GMAW process has the advantage of welding with high productivity. In this study we performed a numerical simulation using the software CIVA, 11th version, to analyze the behavior of ultrasonic longitudinal wave beams through GMAW and SMAW dissimilar weld joints. Ultrasonic tests were performed on calibration blocks drawn from both welded joints to evaluate the simulation results. The results are discussed with regard to the microstructure of the weld metal via electron backscatter diffraction (EBSD) analyses. The SMAW process presented better inspection performance than the GMAW process in terms of attenuation and dispersion effects. Although the SMAW had a better outcome, for both processes the configuration of 16 active elements and a scanning angle of 48&deg, resulted in an optimized inspection of the entire joint.

Background Transcranial direct current stimulation (tDCS) modulates neural networks. Computer simulations, while used to identify how currents behave within tissues of different conductivity properties, still need to be complemented by physical models. Objective/hypothesis To better understand tDCS effects on biology-mimicking tissues by developing and testing the feasibility of a high-fidelity 3D head phantom model that has sensing capabilities at different compartmental levels. Methods Models obtained from MRI images generated 3D printed molds. Agar phantoms were fabricated, and 18 monitoring electrodes were placed on specific phantom brain areas. Results When using rectangular electrodes, the measured and simulated voltages at the monitoring electrodes agreed reasonably well, except at excitation locations. The electric field distribution in different phantom layers appeared better confined with circular electrodes compared to rectangular electrodes. Conclusion The high-fidelity 3D head model was found to be feasible and comparable with computer-based electrical simulations, with high correlation between simulated and measured brain voltages. This feasibility study supports testing to further assess the reliability of this model.

New skeletal chemical kinetic models have been obtained by reducing a detailed model for the gas-phase combustion of Douglas Fir pyrolysis products. The skeletal models are intended to reduce the cost of high-resolution wildland fire simulations, without substantially affecting accuracy. The reduction begins from a 137 species, 4533 reaction detailed model for combustion of gas-phase biomass pyrolysis products, and is performed using the directed relation graph with error propagation and sensitivity analysis method, followed by further reaction elimination. The reduction process tracks errors in the ignition delay time and peak temperature for combustion of gas-phase products resulting from the pyrolysis of Douglas Fir. Three skeletal models are produced as a result of this process, corresponding to a larger 71 species, 1179 reaction model with less than 1\% error in ignition delay time compared to the detailed model, an intermediate 54 species, 637 reaction model with 24\% error, and a smaller 54 species, 204 reaction model with 80\% error. Using the skeletal models, peak temperature, volumetric heat release rate, premixed laminar flame speed, and diffusion flame extinction temperatures are compared with the detailed model, revealing an average maximum error in these metrics across all conditions considered of less than 1\% for the larger skeletal model, 10\% for the intermediate model, and 24\% for the smaller model. All three skeletal models are thus sufficiently accurate and computationally efficient for implementation in high-resolution wildland fire simulations, where other model errors and parametric uncertainties are likely to be greater than the errors introduced by the reduced kinetic models presented here.

In this article, an analysis of heat transfer in a porcelain-housed ZnO surge arrester is presented. Due to the fact that ZnO-based surge arresters are key components for protection and reliability of electrical systems, it is necessary to seek techniques to assure correct assessment. In porcelain-housed arresters, the air gap leads to an increased thermal resistance between the ambient and the varistor column. Consequently, a thermal analysis must consider convection and radiation heat transfer mechanisms, besides heat conduction. This study proposes the use of computational simulations in combination with thermography as a tool for a temperature-based estimation of the varistor state. For the analysis, temperature rise tests were performed in a 69-kV ceramic-housed arrester to measure material emissivity and produce data to fit the simulated response. Furthermore, the thermal response of the surge arresters subject to an impulsive energy input was evaluated. The simulations allow to relate varistors temperature and housing temperature with regard to a specified amount of dissipated power. The obtained results show that the used technique can be an effective method for arrester monitoring and may allow to define assessing criteria for a porcelain-housed arrester based on housing temperature measurements.

Thermoresponsive copolymer microgels based on the biocompatible monomer N-vinylcaprolactam (VCL) and the hydrophobic comonomer 4-tert-butylcyclohexylacrylate (TBCHA) with highly tunable comonomers ratio were for the first time synthesized by miniemulsion polymerization. Their physical properties in aqueous solution and at the solid interface were characterized using dynamic light scattering (DLS), atomic force microscopy (AFM) and dissipative particle dynamics (DPD) simulations. The results show a significant decrease of the swelling rate of the obtained microgels with an increase of the amount of the hydrophobic comonomer. In the case when the fraction of TBCHA is equal or higher than the fraction of VCL, the microgels become almost insensitive to the temperature changes, and the amount of water inside the microgels appeared to be diminishingly small. In the opposite case, if the VCL fraction is major, the copolymer microgels preserve their softness and deformability while being adsorbed onto a solid surface. At the same time, all samples have shown a good colloidal stability and a low polydispersity in size. Thus, the presented polymerization technique is applicable for the fabrication of microgels using hydrophobic monomers, which are not accessible by conventional precipitation polymerization. We demonstrate that the mechanical properties and the temperature-responsiveness of the copolymer microgels can be precisely adjusted by the content of the hydrophobic comonomer. (C) 2020 Elsevier Inc. All rights reserved.

Besides the dynamical slowing down signaled by an enormous increase of the viscosity approaching the glass transition, structural glasses show interesting anomalous thermodynamic features at low temperatures that hint at peculiar deviations from Debye's law at low enough frequencies. Theory, numerical simulations, and experiments suggest that deviation from Debye's law is due to soft-localized glassy modes that populate the low-frequency spectrum. We study the localization properties of the low-frequency modes in a three-dimensional supercooled liquid model. The density of states $D(\omega)$ is computed considering the inherent structures of configurations well thermalized at parental temperatures close to the dynamical transition $T_\text d$. We observe a crossover in the probability distribution of the inverse of the participation ratio that happens approaching $T_\text d$ from high temperatures. We show that a similar crossover is observed at high parental temperature when the translational invariance of the system is explicitly broken by a random pinning field., Comment: 10 pages, 7 figures

We report the results of the Stark profile studies of the 696.543 nm Ar I spectral line in laser-induced plasma generated by a nanosecond Nd:YAG laser radiation at 532 nm in argon at reduced pressure. Plasma diagnostics was performed with the use of the laser Thomson scattering method, free from assumptions about the plasma thermodynamic equilibrium, its composition but also independently of plasma emission spectra. The profiles were investigated in wide range of electron densities and temperatures, from 2.81 · 1022 m − 3 to 5.69 · 1023 m − 3 and from 10 430 K to 73 400 K, respectively. Stark profiles were calculated using a semi-classical method as well as by N-body numerical simulations assuming a plasma in local thermodynamic equilibrium. Our studies show agreement within 20% between experimental Stark widths and those calculated by the semi-classical method while much bigger discrepancies were found with computer simulated ones. Importantly, Stark profiles of the investigated spectral line, both experimentally determined and computed, are highly sensitive to electron temperature.

One of the biggest unresolved problems in crystallization phenomena is the significant discrepancy in the nucleation rate between experiments and simulations even for the simplest liquid, i.e., the hard-sphere system. A popular explanation for this discrepancy is the neglect of hydrodynamic interactions (HI) in simulation studies. By comparing simulations with and without HI, we show that the long-time diffusive dynamics of the colloids is slowed down more rapidly by hydrodynamic lubrication effects with increasing volume fraction. We find that the kinetics of both nucleation and growth are controlled by this long-time diffusion and that it is possible to account for most of the effects of HI by rescaling with this timescale. Therefore, we conclude that HI is not the primary cause of the accelerated nucleation rates observed in experiments.

The authors thank Eugene Kotomin and V. Kuzovkov for fruitful discussions and valuable suggestions. A.I.P thanks A.Moskina for the technical assistance in preparation of the manuscript. A.I.P also gratefully acknowledges a project LZP-2018/1-0214 from the Latvian Council of Science for partial support., The paper presents the results of first-principles computer simulations of the band structure, the density of states, and the total energy of NaCl (NaCl, Na2Cl2, Na3Cl3, Na4Cl4, Na6Cl6) linear chains of atoms. Modelling of the specified characteristics is realised in the computer code Atomistix ToolKit combined with Virtual NanoLab. The total energy depends on the number of ions in the nanoobject under study, but practically does not depend on the geometric arrangement of ions., Latvian Council of Science LZP-2018/1-0214; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

With numerical simulations of the mW model of water, we investigate the energetic stability of crystalline clusters both for Ice I (cubic and hexagonal ice) and for the metastable Ice 0 phase as a function of the cluster size. Under a large variety of forming conditions, we find that the most stable cluster changes as a function of size: at small sizes, the Ice 0 phase produces the most stable clusters, while at large sizes, there is a crossover to Ice I clusters. We further investigate the growth of crystalline clusters with the seeding technique and study the growth patterns of different crystalline clusters. While energetically stable at small sizes, the growth of metastable phases (cubic and Ice 0) is hindered by the formation of coherent grain boundaries. A fivefold symmetric twin boundary for cubic ice, and a newly discovered coherent grain boundary in Ice 0, promotes cross nucleation of cubic ice. Our work reveals that different local structures can compete with the stable phase in mW water and that the low energy cost of particular grain boundaries might play an important role in polymorph selection.

During the manufacture of a composite cathode for lithium-sulfur (Li-S) batteries it is important to realize homogeneous infiltration of a specified amount of sulfur, targeted to be at least 5 mg cm−2 to achieve good battery performance in terms of high energy density. A model of the sulfur infiltration is presented in this study, taking into account the pore size distribution of the porous cathode host, phase transitions in sulfur, and formation of different sulfur allotropes, depending on pore size, formation energy and available thermal energy. Simulations of sulfur infiltration into an activated carbon fabric at a hot-plate temperature of 175 °C for two hours predicted a composite cathode with 41 wt% sulfur (8.3 mg cm−2), in excellent agreement with the experiment. The pore size distribution of the porous carbon host proved critical for both the extent and form of retained sulfur, where pores below 0.4 nm could not accommodate any sulfur, pores between 0.4 and 0.7 nm retained S4 and S6 allotropes, and pores between 0.7 and 1.5 nm contained S8.

We discuss two procedures to obtain empirical potentials from ab initio trajectories. The first method consists in adjusting the parameters of an empirical pair potential so that the radial distribution functions extracted from classical simulations using this potential match the ones extracted from the ab initio simulations. As a case study, we consider the example of amorphous silica, a material that is highly relevant in the field of glass science as well as in geology. With our approach we are able to obtain an empirical potential that gives a better description with respect to structural and thermodynamic properties than the potential proposed by van Beest, Kramer, and van Santen, and that has been very frequently used as a model for amorphous silica. The second method is the so-called “force matching” approach proposed by Ercolessi and Adams to obtain an empirical potential. We demonstrate that for the case of silica this method does not yield a reliable potential and discuss the likely origin for this failure.

In order to estimate theoretical stability of the perovskite structure for synthesized Ca 1− x Gd x MnO 3 ( x = 0.05, 0.1, 0.15, 0.2) nanopowders, the Goldschmidt tolerance factor G t and global instability index GII were calculated. Furthermore, we have performed structure prediction of Ca 1− x Gd x MnO 3 perovskites and found several possible perovskite-related phases. The influence of gadolinium amount on Mn─O bond angles and distances, tilting of MnO 6 octahedra around all three axes and deformation due to the presence of the Jahn–Teller distortion around Mn 3+ cation, as well as the influence of the amount of Mn 3+ cation on Ca 1− x Gd x MnO 3 compound, was examined. Ion Mn valence states were determined by bond valence calculations (BVC). Infrared active phonon modes in Ca 1− x Gd x MnO 3 were studied by infrared reflection spectroscopy and magnetic properties were studied by using EPR (electron paramagnetic resonance) measurements.

We investigated the phenomenon of carbon supersaturation and carbon clustering in bainitic ferrite with atom probe tomography (APT) and ab-initio density functional theory (DFT) calculations. The experimental results show a homogeneous distribution of silicon in the microstructure, which contains both ferrite and retained austenite. This distribution is mimicked well by the computational approach. In addition, an accumulation of C in certain regions of the bainitic ferrite with C concentrations up to 13 at % is observed. Based on the DFT results, these clusters are explained as strained, tetragonal regions in the ferritic bainite, in which the solution enthalpy of C can reach large, negative values. It seems that Si itself only has a minor influence on this phenomenon., APT measurements and analyses were conducted at ORNL's Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy, Office of Science User Facility. The authors gratefully acknowledge the support of the Research Fund for Coal and Steel for funding this research under the Contract RFSR-CT- 2012-00017.

In perovskite-type strontium titanate (SrTiO 3 ) 〈110〉 dislocations, which are the main carriers of plastic flow at low temperature, lose their mobility as temperature increases, leading to brittle failure above 1050 K. We present theoretical evidence for a change in their core structure into a sessile, climb-dissociated configuration at high temperature. This mechanism is shown to operate in both SrTiO 3 and MgSiO 3 , indicating that it may be a general feature of perovskite-type materials. It follows that the activity of the 〈110〉 slip system depends critically on the strain rate-temperature couple, e T .

Experiments showed that multiwalled carbon nanotubes (MWCNT) can be used as masks gainst irradiation to create metallic nanowires in a substrate. In order to understand the limitations of this application, it is interesting to know the energy and number of carbon atoms emerging from the MWCNT after the irradiation and how the structure of the MWCNT is modified. Using a molecular dynamics code that we have previously developed, we have simulated the continuous irradiation of MWCNT with carbon and argon projectiles. We have obtained that the use of carbon instead of argon to irradiate the MWCNT increases de effectiveness of the MWCNTs as masks, due to the ability of the carbon projectiles to be part of the MWCNT structure and partially mend the damage produced during irradiation. We have analyzed the number, energy, and spatial distribution of the recoils generated during irradiation and the change of the MWCNT structure as a function of the incident energy (100 and 500 eV), fluence (up to 4:5 · 1015 ions=cm2), and number of shells (up to 5-shells) of the MWCNT. These results determine the effectiveness of MWCNT as a mask, being useful to understand whether the atoms emerging from the MWCNT produce damage in the substrate or not. We find that for carbon projectiles the efficiency of MWCNT as masks does not depend much on the fluence, but on the number of nanotube shells and projectile incident energy. On the other hand, for a given nanotube and fluence, we observe a threshold incident energy below which the nanotube acts as a perfect mask. This work has been financially supported by the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund (Project FIS2010-17225).

We present a combined theoretical/experimental study to investigate the effect of selective solvent vapor annealing treatment on the obtainment of highly ordered morphologies of symmetric poly(styrene-b-methyl methacrylate) diblock copolymer (PS-b-PMMA DBC) films loaded with compatibilized magnetic (Fe3O4) nanoparticles (NPs). Different amounts of NPs were considered (1, 2, and 5 wt %) to study the effect of the inorganic content on the final properties of Fe3O4/PS-b-PMMA films. A precise control of the DBC nanostructure could be obtained by very simple and cost-effective fabrication steps, compatible with current industrial processes. Moreover, the modified NPs could be selectively placed into the PMMA domains of the DBC up to NP concentration of 5 wt % while preserving the corresponding DBC lamellar morphology.

Using Molecular Dynamics simulations, we examine structural and dynamical properties of supercritical CO2 confined within cylindrical hydrophobic nanopores of diameters 38 and 10 Å. Computer simulations were performed along the isotherm T = 315 K, spanning CO2 densities from ρ/ρc = 2.22 down to ρ/ρc = 0.22. Radial and orientational distribution functions, analysis of interfacial dynamic properties, and estimatons for local diffusion and orientational relaxation times are presented. In agreement with previous experimental data, our simulation results reveal the presence of a dense phase adsorbed within the pores. The combination of low CO2 bulk densities and narrow pores leads to ρint/ρblk ≈ 5-fold enhancement of the global density of the confined fluid. These density increments gradually become much less marked as the external phase becomes denser. Contrasting, in that latter limit, we found that the trapped fluid may become less dense than the bulk phase. Adsorption behavior of CO2 onto hydrophilic-like and rugged pore surfaces were also exmined. In these cases, we observed a global slowdown in both translational and rotational motions for the trapped CO2, the largest retardations being those associated with spatial domains of the fluid located near the silica interface. Fil: Elola, Maria Dolores. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Constituyentes); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Rodriguez, Javier. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Constituyentes); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina

We present a Discrete Element study of the behavior of magnetic core-shell particles in which the properties of the core and the shell are explicitly defined. Particle cores were considered to be made of pure iron and thus possessed ferromagnetic properties, while particle shells were considered to be made of silica. Core sizes ranged between 0.5 and 4.0 μm with the actual particle size of the core-shell particles in the range between 0.6 and 21 μm. The magnetic cores were considered to have a magnetization of one tenth of the saturation magnetization of iron. This study aimed to understand how the thickness of the shell hinders the formation of particle chains. Chain formation was studied with different shell thicknesses and particle sizes in the presence and absence of an electrical double layer force in order to investigate the effect of surface charge density on the magnetic core-shell particle interactions. For core sizes of 0.5 and 4.0 μm the relative shell thicknesses needed to hinder the aggregation process were approximately 0.4 and 0.6 respectively, indicating that larger core sizes are detrimental to be used in applications in which no flocculation is needed. In addition, the presence of an electrical double layer, for values of surface charge density of less than 20 mC/m2, could stop the contact between particles without hindering their vertical alignment. Only when the shell thickness was considerably larger, was the electrical double layer able to contribute to the full disruption of the magnetic flocculation process.

Significance Water is the most common and yet least understood material on Earth. Despite its simplicity, water tends to form tetrahedral order locally by directional hydrogen bonding. This structuring is known to be responsible for a vast array of unusual properties, e.g., the density maximum at 4 °C, which play a fundamental role in countless natural and technological processes, with the Earth’s climate being one of the most important examples. By systematically tuning the degree of tetrahedrality, we succeed in continuously interpolating between water-like behavior and simple liquid-like behavior. Our approach reveals what physical factors make water so anomalous and special even compared with other tetrahedral liquids., Tetrahedral interactions describe the behavior of the most abundant and technologically important materials on Earth, such as water, silicon, carbon, germanium, and countless others. Despite their differences, these materials share unique common physical behaviors, such as liquid anomalies, open crystalline structures, and extremely poor glass-forming ability at ambient pressure. To reveal the physical origin of these anomalies and their link to the shape of the phase diagram, we systematically study the properties of the Stillinger–Weber potential as a function of the strength of the tetrahedral interaction λ. We uncover a unique transition to a reentrant spinodal line at low values of λ, accompanied with a change in the dynamical behavior, from non-Arrhenius to Arrhenius. We then show that a two-state model can provide a comprehensive understanding on how the thermodynamic and dynamic anomalies of this important class of materials depend on the strength of the tetrahedral interaction. Our work establishes a deep link between the shape of the phase diagram and the thermodynamic and dynamic properties through local structural ordering in liquids and hints at why water is so special among all substances.

Thermal analysis is a fundamental issue for the proper evaluation of the performance of lithium ion batteries. Thus, this work reports on the theoretical simulation of the effect of different thermal conditions on the performance of batteries with conventional and non-conventional geometries.The investigated geometries include conventional geometries (layer by layer), interdigitated, horse-shoe, spiral, ring, antenna and gear that can be fabricated by printed technologies for flexible/wearable electronic device applications. The thermal conditions are isothermal, adiabatic and environmental conditions and the computational simulations are based on the electrochemical (Newman/Doyle/Fuller) model.Generally, the best battery performance is obtained for interdigitated and gear geometries, regardless of thermal conditions. The dissipated ohmic heat is mainly influenced by the maximum distance that the ions move until their intercalation and the thickness of the separator. The present work allows the proper design of the batteries in order to optimize performance for specific applications., This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013. The authors thank FEDER funds through the COMPETE 2020 Programme and National Funds through FCT under the projects PTDC/CTM-ENE/5387/2014 and UID/CTM/50025/2013 and grant SFRH/BPD/112547/2015 (C.M.C.). Financial support from the Basque Government Industry Department under the ELKARTEK Program is also acknowledged., info:eu-repo/semantics/publishedVersion

The ability of Bader's charge density topology analysis to explain various material properties has been examined for simple ionic systems of alkali halides and alkali hydrides. It was established that despite the fact that most of them share the same rock salt crystal structure phase, some of them belong to different topological classes. This fact was used to explain various experimentally observed properties of these materials, and to discuss their deviations from expected trends. Some phase transitions observed in these systems, and their possible relation to changes in the charge density topology have been also investigated from the same point of view. Reasons for anion-anion bond formation in some of them and its features are discussed, as well.

This paper presents a finite-element analysis of honeycomb and re-entrant honeycomb structures made of a two-phase composite material which is optimized with respect to selected parameters. It is shown that some distributions of each phase in the composite material result in the counter-intuitive mechanical behaviour of the structures. In particular, negative values of effective Poisson's ratio, i.e., effective auxeticity, can be obtained for a hexagonal honeycomb, whereas re-entrant geometry can be characterized by positive values. Topology optimization by means of the method of moving asymptotes (MMA) and solid isotropic material with penalization (SIMP) was used to determine the materials' distributions.

The percolation behavior of alumina suspensions is studied by computer simulations. The percolation threshold phi(c), is calculated, determining the key factors that affect its magnitude: the strength of colloid-colloid attraction and the presence of hydrodynamic interactions (Hls). To isolate the effects of His, we compare the results of Brownian Dynamics, which do not include hydrodynamics, with those of Stochastic Rotation Dynamics-Molecular Dynamics, which include hydrodynamics. Our results show that phi(c), decreases with the increase of the attraction between the colloids. The inclusion of His always leads to more elongated structures during the aggregation process, producing a sizable decrease of phi(c) when the colloid-colloid attraction is not too strong. On the other hand, the effects of His on phi(c) tend to become negligible with increasing attraction strength. Our phi(c) values are in good agreement with those estimated by the yield stress model by Flatt and Bowen. (C) 2015 Published by Elsevier inc.

The k.p method and the effective mass theory are applied to compute valence-band electronic structure and optical properties of ZnO1-xSx ternary alloys under biaxial strain. A significant modification of the band structure with increasing sulfur content is revealed. Features of wave-functions and matrix elements in the transverse electrical (TE) and transverse magnetic (TM) regimes for three valence subbands are studied and discussed. The results of calculations of interband transition energy and spontaneous emission spectra are in agreement with experimental data for ZnO1-xSx films grown by radio-frequency magnetron sputtering technique. (C) 2015 Elsevier B.V. All rights reserved.

The role of porosity on the low and high field dielectric properties was studied in Ba 0.70 Sr 0.30 TiO 3 ceramics with various porosity levels obtained by using lamellar graphite as sacrificial template. The permittivity decreases with increasing porosity, from around e ∼ 7690 (dense ceramic) down to 380 (ceramic with 29% porosity), while preserving the Curie temperature at about 35 °C. The effective permittivity was discussed by using Effective Medium Approximation and Finite Element Method approaches. The role of porosity and specific microstructural characteristics induced by the pore forming addition, from closed porosity (0–3) towards a combined (0–3, 2–2) with lamellar-type of microstructures for the most porous ceramics was taken into consideration. All the investigated ceramics preserve a high level of tunability as in the dense material, irrespective of the porosity level, while the zero field permittivity was decreased to a few hundreds.

Titanium alloys are ideally suited for use as lightweight structural materials, but their use at high temperature is severely restricted by oxidation. Niobium is known to confer oxidation-resistance, and here we disprove the normal explanation, that Nb5+ ions trap oxygen vacancies. Using density functional theory calculation, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) we show that Nb is insoluble in TiO2. In fact, the Ti-Nb surface has three-layer structure: the oxide itself, an additional Nb-depleted zone below the oxide and a deeper sublayer of enhanced Nb. Microfocussed X-ray diffraction also demonstrates recrystallization in the Nb-depleted zone. We interpret this using a dynamical model: slow Nb-diffusion leads to the build up of a Nb-rich sublayer, which in turn blocks oxygen diffusion. Nb effects contrast with vanadium, where faster diffusion prevents the build up of equivalent structures.

Having plastic material for the stress analysis of structural connections seems to be a crucial point to obtain reliable results of the solution as it helps to smooth the local concentration of stress. The paper presents application of orthotropic plastic material to define material characteristics of timber structure of joint. To put that into perspective, the comparison with application of elastic material was done.