Radial Distribution Analysis Research Articles

On the role of geometrically necessary dislocations in void formation and growth in response to shock loading conditions in wrought and additively manufactured Ta

This study investigates the role of geometrically necessary dislocations (GNDs) and microstructure on void nucleation and growth in wrought and additively manufactured (AM) tantalum subjected to high-strain rate loading. Multi-modal 3D data was collected using TriBeam tomography to calculate GND densities and their spatial relationship to voids. A microstructural comparison between the wrought and AM samples identified distinct void shapes and locations, with intragranular voids and more spherical voids frequently observed in the AM dataset. Results indicate that voids preferentially form at both high-angle grain boundaries and low-angle subgrain boundaries, the latter of which are frequently observed in the AM material. Through a radial distribution analysis of all voids in the datasets, significant GND localization to near-void-surface regions was observed in both samples. 3D crystal plasticity simulations were employed to extend the experimental observations, revealing higher void growth rates in [111] oriented grains when compared to [001] grains. The simulations also suggest that GNDs can be generated as part of the void growth process, with more GND accumulation for growth in a [111] grain than a [001] grain. These findings provide valuable insights into the links between nanoscale void nucleation, mesoscale void growth, and microstructural effects in dynamically loaded tantalum.

Enhancing Zn (II) recovery efficiency: Bi-divalent nickel–cobalt ferrite spinel NiXCo1-xFe2O4 as a Game-changing Adsorbent—an experimental and computational study

This study presents a comprehensive investigation into NiXCo1-xFe2O4 (x = 0.5) spinel nanoparticles synthesized through a one-pot hydrothermal method using Co(NO3)2.6H2O and Ni(NO3)2.6H2O salts. XRD, FTIR, FESEM, and VSM analyses confirmed a cubic structure of NiXCo1-xFe2O4 (x = 0.5) nanoparticles without impurities. These nanoparticles exhibit efficient Zn (II) adsorption characteristics, following Langmuir isotherm and pseudo-second-order kinetics. The maximum adsorption capacity was measured to be 666.67 mg g−1 at pH = 7, with mechanisms involving both electrostatic attraction and cation exchange. Desorption studies indicate more than 75% Zn (II) recovery in an acidic environment (pH = 2) after three cycles. Computational analysis was used to validate the experimental results through Molecular Dynamics simulations, initially focusing on NiXCo1-xFe2O4 (x = 0.5). Further exploration involved variations in x at 0.25 and 0.75 to identify the optimal Ni and Co ratio in this bivalent cation spinel ferrite. Computational analyses reveal the superior performance of NiXCo1-xFe2O4 (x = 0.75) in Zn (II) removal, supported by radial distribution analysis, VdW energy, Coulombic energy, mean square displacement (MSD), root mean square displacement (RMSD), and interaction energy. This comprehensive study provides valuable insights into the adsorption behavior and structural stability of NiXCo1-xFe2O4 nanoparticles, showcasing potential applications in Zn (II) removal.

Study on the influence of temperature and strain rate on the tensile behavior of Ti–5Mo–5Cu alloy biomaterial alloy: a molecular dynamics simulation

The development of efficient biomedical bone tissue implants has invoked significant impact in the biomedical research fields and aids the aged populated peoples. In this examination, the mechanical features of implant material (Ti–5Mo–5Cu alloy) has been investigated using the molecular dynamics method under varying temperature and strain rate to understand its physical phenomenon and through this study, it is found that the strain rate has offered a complex beneficial impact over the material characteristics such as yield stress and yield strain, owing to its higher impact over the restraining behavior between various atoms and strain toughening effect related to the temperature effect. Furthermore, the shear strain and point defect analysis has confirmed that the structural alteration and the establishment of multiple dislocations lead to induce the deformation behavior of Ti–5Mo–5Cu biomaterial alloy. Additionally, the radial distribution analysis has stated that the introduction of higher ambient temperature leads to invoking multiple dislocations which are responsible for the deformation behavior and cause the major reduction in tensile properties.

An Amine-Functionalized Ultramicroporous Metal–Organic Framework for Postcombustion CO2 Capture

Among the most promising methods by which to capture CO2 from flue gas, the emission of which has accelerated global warming, is energy-efficient physisorption using metal-organic framework (MOF) adsorbents. Here, we present a novel cuprous-based ultramicroporous MOF, Cu(adci)-2 (adci- = 2-amino-4,5-dicyanoimidazolate), which was rationally synthesized by combining two strategies to design MOF physisorbents for enhanced CO2 capturing, i.e., aromatic amine functionalization and the introduction of ultramicroporosity (pore size <7 Å). Synchrotron powder X-ray diffraction and a Rietveld analysis reveal that the Cu(adci)-2 structure has one-dimensional square-shaped channels, in each of which all affiliated ligands, specifically NH2 groups at the 2-position of the imidazolate ring, have the same orientation, with a pair of NH2 groups therefore facing each other on opposite sides of the channel walls. While Cu(adci)-2 exhibits a high CO2 adsorption capacity (2.01 mmol g-1 at 298 K and 15 kPa) but a low zero-coverage isosteric heat of adsorption (27.5 kJ mol-1), breakthrough experiments under dry and 60% relative humidity conditions show that its CO2 capture ability is retained even in the presence of high amounts of moisture. In a Monte Carlo simulation and a radial distribution analysis, the preferential CO2 binding site of Cu(adci)-2 was predicted to be between two ligands, forming a sandwich-like structure and implying that its CO2 adsorption properties originate from the enhancement of Lewis base-acid and London dispersion interactions due to the amino groups and ultramicroporosity, respectively.

On the randomness and correlation in the trajectories of alpha particle emitted from 241Am: statistical inference based on information entropy

Most particle detectors are based on the hypothesis that particles are emitted randomly upon nuclear decay. In the present work, we tested the hypothesis of the existence of correlation in the random trajectories of alpha particles emitted from {}^{241}Am source and the null hypothesis of random trajectories. The trajectories were clued through the registration of track in a solid-state nuclear track detector. The experimental parameters were optimized to identify the possible sources of correlation in the track registration and the detector conditions upon exposure and etching to avoid misleading results. The optimization included authentication of linearity in registration efficiency with exposure time to prevent coalescence of registered tracks. The statistical inference processes were based upon adaptive quadrates analysis of the spatial data, and entropy and divergence analysis of the quadrate data together with the null hypothesis of Poisson distribution of random trajectories. The clustering and dispersion analysis were performed with central deviation tendency, empirical K-function, radial distribution analysis, and proximity Analysis. Results showed a pattern of gained information within the registered tracks that may be attributed to the alteration in the alpha particles’ trajectories induced by the strong electric field due to atoms in the source compound and encapsulation film.

X-ray nanotomography uncovers morphological heterogeneity in a polymerization catalyst at multiple reaction stages

During olefin polymerization on supported catalysts, the controlled morphological evolution of the catalyst particle is vital for ensuring optimal product properties and high catalyst activity. We employed non-destructive hard X-ray holotomography to quantitatively assess the 3D morphology of multiple silica-supported hafnocene-based catalyst particles during the early stages of gas-phase ethylene polymerization. Image processing and pore network modeling revealed clear variations in the dimensions and interconnectivity of pristine particles' macropore networks. This, together with apparent differences in the fragmentation behavior of pre-polymerized particles, suggests that the reactivity and morphological evolution of individual particles are largely dictated by their unique support and pore space architectures. By minimizing the structural heterogeneity among pristine catalyst particles, more uniform particle morphologies may be obtained. Significant polymerization activity, observed in the particles' interiors, further implies that appropriate polymerization conditions and catalyst kinetics can guarantee sufficiently high particle accessibilities and thus more homogeneous support fragmentation. • 3D X-ray nanotomography on metallocene-based polymerization catalyst particles • Inter- and intraparticle heterogeneity observed at an advanced pre-polymerization stage • Pristine catalyst support structure strongly affects morphological evolution • Significant involvement of the layer-by-layer fragmentation mechanism postulated Our society's demand for polyolefins, such as polyethylene, is steadily rising. To improve the physicochemical properties of these high-performance materials, strict morphological control is required during the polymerization of related catalysts, especially at reaction onset. By assessing the 3D morphology of multiple catalyst particles during the early stages of ethylene polymerization, we were able to identify and correlate morphological differences to the initial catalyst particle support structure. Based on this, we believe that the implementation of structurally more uniform catalyst supports, in combination with controlled pre-polymerization procedures, may help optimize the performance of relevant catalysts. Our multi-particle approach also paves the way for other industrial heterogeneous catalysts, where the spatial distribution of catalytically relevant phases and/or carbon-based products is to be investigated in a representative number of catalyst particles. The morphology of an industrial-grade ethylene polymerization catalyst was investigated at multiple reaction stages using X-ray holotomography, a high-resolution 3D imaging technique. Image processing, radial phase distribution analysis, and pore network modeling revealed significant inter- and intraparticle heterogeneity in both pristine and pre-polymerized particles. Differences in the fragmentation and reactivity of individual catalyst particles can be attributed to the particles' unique support architectures. Mild reaction conditions ensured a high accessibility of the catalyst particles' interiors and more homogeneous support fragmentation.

Structural Change of TiAl Alloy under Uniaxial Tension and Compression in the &lt;001&gt; Direction: A Molecular Dynamics Study

TiAl alloys can be used in aircraft and high-performance vehicle engines owing to their structural stability at high temperatures and their light weight. Although many studies have focused on developing this alloy material, there is still a lack of information about the changes in the structure of TiAl alloys under tensile and compressive loading. Therefore, we performed molecular dynamics simulations of the tensile and compressive loading of TiAl alloys in the &lt;001&gt; direction at temperatures of 10 and 300 K. From our simulation results, we found that the tensile and compressive strengths of TiAl alloys are significantly affected by temperature. It was found that TiAl alloys can withstand greater compression loading than tensile loading. This is due to the change in the crystal structure of TiAl alloys after being deformed to a strain of 0.4 by compressive loading, according to the analysis of structural changes under loading conditions. From the radial distribution analysis results, there was a change in the orientation of the face-centered cubic-like structure as it reached the maximum compressive stress compared to the initial structure.

The cooperative effect between cyclic naphthenic acids and surfactant enhances the separation efficiency

Naphthenic Acids (NAs) are responsible for corrosion, produced water pollution, and are toxic to marine life. Therefore, more efficient NAs extraction techniques, such Micellar-Enhanced Ultrafiltration (MEUF), have been developed. In this work, Molecular Dynamics simulations were employed to deepen the comprehension of the behavior and properties of NA in interfacial systems and micellar systems. The calculated distribution coefficient (log D) in different water/oil interfaces demonstrated the greater affinity between NA and cyclic structures, showing a more negative free energy in the systems with toluene. Furthermore, simulations with different NAs and surfactant showed that micelle is effective in NAs carriage by two different interaction conformations, both by intercalation and adsorption of NAs on micelle surfaces, guiding to a micelle increase of about 5%. Radial distribution, hydrogen-bond, and non-bonded analysis indicated that NAs affect interactions between surfactant molecules' by diminishing the Lennard-Jones contribution. Moreover, the incorporated alicyclic molecules are responsible for facilitating the absorption of more NAs by the micelle. So, to enhance NAs separation from oil or produced water, cyclic molecular systems may be employed.

Insights into the intraparticle morphology of dendritic mesoporous silica nanoparticles from electron tomographic reconstructions

HypothesisAlthough many synthetic pathways allow to fine-tune the morphology of dendritic mesoporous silica nanoparticles (DMSNs), the control of their particle size and mesopore diameter remains a challenge. Our study focuses on either increasing the mean particle size or adjusting the pore size distribution, changing only one parameter (particle or pore size) at a time. The dependence of key morphological features (porosity; pore shape and pore dimensions) on radial distance from the particle center has been investigated in detail. ExperimentsThree-dimensional reconstructions of the particles obtained by scanning transmission electron microscopy (STEM) tomography were adapted as geometrical models for the quantification of intraparticle morphologies by radial porosity and chord length distribution analyses. Structural properties of the different synthesized DMSNs have been complementary characterized using TEM, SEM, nitrogen physisorption, and dynamic light scattering. FindingsThe successful independent tuning of particle and pore sizes of the DMSNs could be confirmed by conventional analysis methods. Unique morphological features, which influence the uptake and release of guest molecules in biomedical applications, were uncovered from analyzing the STEM tomography-based reconstructions. It includes the quantification of structural hierarchy, identification of intrawall openings and pores, as well as the distinction of pore shapes (conical vs. cylindrical).

Theoretical insight on the solvation properties of Zn2+ in pure liquid ammonia: A quantum mechanical molecular charges field molecular dynamics (QMCF-MD) study

In this work, the structural and dynamical properties of Zn2+ in pure liquid ammonia have been investigated via a quantum mechanical charge field molecular dynamics (QMCF MD) simulation approach. The average equilibrium Zn–N distance in the first solvation shell resulting from the radial distribution analysis is 2.15 Å. Even though the complex displays a high rate of ligand exchange compared to Zn2+ in aqueous solution, the result imply that NH3 is the preferred ligand compared to H2O. This result of this simulation studies provide a fundamental understanding of the characteristic of this metal ion in pure liquid ammonia, which is inter alia essential in the development of applications for CO2 capture based on Zn2+-containing NH3 solutions.

Urea-water solvation of protein side chain models

Aqueous urea stabilizes the unfolded states of protein due to their ability to solvate both hydrophilic and hydrophobic residues favorably. The nature of interactions that stabilize different types of amino acid side chains in their solvent exposed state is still not understood. To gain insights into the molecular level details of urea interactions with proteins in their unfolded states, we have performed atomistic molecular dynamics simulations and free energy calculations using the thermodynamic integration method on model systems representing side chains of all amino acids in different solvent environments (water and varying concentrations of aqueous urea). A systematic analysis of structural, energetic and dynamic parameters has been done to understand the detailed atomistic mechanism. The main aim of the current study is to unravel the nature of urea-amino acid interactions by emphasizing on the chemical nature of amino acid side chain models. The preferential interactions of urea over water with each side chain and backbone model systems in various concentrations of aqueous urea were quantified using the two-domain model, and it is validated by mean lifetime calculations. Interestingly, almost all amino acids showed a preference for urea over water. The order of preferences depending on the chemical nature of the amino acids is obtained with the aromatic groups exhibiting the highest preferences followed by hydrophobic groups, followed by amides and basic groups, and the least by nucleophilic groups. The extensive energetic analysis revealed, these preferential interactions are enthalpically and entropically driven and are dominated by dispersion effects. Spatial density distributions and radial distribution analyses provide insights to understand the different modes and urea orientation towards preferred sites of interactions by which urea-protein interactions stabilize proteins in their unfolded states by forming favorable interactions with exposed amino acids side chains.

Hyperosmotic stress: in situ chromatin phase separation

ABSTRACT Dehydration of cells by acute hyperosmotic stress has profound effects upon cell structure and function. Interphase chromatin and mitotic chromosomes collapse (“congelation”). HL-60/S4 cells remain ~100% viable for, at least, 1 hour, exhibiting shrinkage to ~2/3 their original volume, when placed in 300mM sucrose in tissue culture medium. Fixed cells were imaged by immunostaining confocal and STED microscopy. At a “global” structural level (μm), mitotic chromosomes congeal into a residual gel with apparent (phase) separations of Ki67, CTCF, SMC2, RAD21, H1 histones and HMG proteins. At an “intermediate” level (sub-μm), radial distribution analysis of STED images revealed a most probable peak DNA density separation of ~0.16 μm, essentially unchanged by hyperosmotic stress. At a “local” structural level (~1-2 nm), in vivo crosslinking revealed essentially unchanged crosslinked products between H1, HMG and inner histones. Hyperosmotic cellular stress is discussed in terms of concepts of mitotic chromosome structure and liquid-liquid phase separation.

The physical structure and surface reactivity of graphene oxide

The structural configuration of graphene oxide and its surface reactivity were investigated experimentally and clarified on the bases of time-independent density functional calculations (DFT). The physical structure was examined by transmission electron microscopy, infrared absorption, and X-ray diffraction parallel to radial distribution analysis. Surface reactivity was examined using N2-adsorption at 77 K and the kinetic of the adsorption of Ni2+, Cd2+, and Pb2+ ions at 300 K. The lattice structure of the material was hexagonal with unit cell a = 2.455 Å and c = 8.64 Å and with layer-layer distance of 4.32 Å. This structure is undulated in response to existence of oxygen atoms that shape surface topological imperfections and breaks the planner regularity. The undulation distance comprises 0.3 Å. The specific surface area was found 60.3 m2/g with about 50% of this area were available to adsorption of 2+ ions due to surface polarization. The vibration frequencies observed in FTIR are identified by DFT calculations and showed that the structure acts as an extended quantum system for which Pauli blocking prevents existence of two modes of marginal hydrogen vibrations within the same sheet.

Molecular dynamics of acetate-based ionic liquids

A radial distribution analysis of pairs between the constituent atoms of protic ionic 2-(hydroxy)ethylammonium acetate was performed with molecular dynamics technique (MDT). The ionic liquid structure will help us in different engineering applications, as emulsification process (petroleum industry). The results presented here show that the development of force field to predict the high interaction behaviour between the cation and the anion, as well as the formation of ion-pair dispersed aggregates. These results can contribute to help the different applications of ionic liquids.

A novel flexible cuff-like microelectrode for dual purpose, acute and chronic electrical interfacing with the mouse cervical vagus nerve

Objective. Neural reflexes regulate immune responses and homeostasis. Advances in bioelectronic medicine indicate that electrical stimulation of the vagus nerve can be used to treat inflammatory disease, yet the understanding of neural signals that regulate inflammation is incomplete. Current interfaces with the vagus nerve do not permit effective chronic stimulation or recording in mouse models, which is vital to studying the molecular and neurophysiological mechanisms that control inflammation homeostasis in health and disease. We developed an implantable, dual purpose, multi-channel, flexible ‘microelectrode’ array, for recording and stimulation of the mouse vagus nerve. Approach. The array was microfabricated on an 8 µm layer of highly biocompatible parylene configured with 16 sites. The microelectrode was evaluated by studying the recording and stimulation performance. Mice were chronically implanted with devices for up to 12 weeks. Main results. Using the microelectrode in vivo, high fidelity signals were recorded during physiological challenges (e.g potassium chloride and interleukin-1β), and electrical stimulation of the vagus nerve produced the expected significant reduction of blood levels of tumor necrosis factor (TNF) in endotoxemia. Inflammatory cell infiltration at the microelectrode 12 weeks of implantation was limited according to radial distribution analysis of inflammatory cells. Significance. This novel device provides an important step towards a viable chronic interface for cervical vagus nerve stimulation and recording in mice.

Effect of copper film catalyst substrate thickness on atomic diffusion time at the initiation of the recrystallization stage: a molecular dynamics study

Copper film growth using thermal evaporation and annealing methods were studied using molecular dynamics simulations. The AlSiMgCuFe modified embedded atom method potential was used to describe the interaction of Cu–Cu, Si–Si and Cu–Si atoms. The annealing process, which was limited to atomic diffusion, repaired the crystal structure of the copper film. Our results showed that the thickness of the copper film catalyst substrate affected the initiation of the recrystallization process. A change of phase transition of copper atoms was observed after annealing. These phenomena were supported by knowledge of the radial distribution function and analysis of the crystal structure.

Computer aided simulation of thermoplastic elastomer from poly (vinylidene fluoride)/hydrogenated nitrile rubber blend and its experimental verification

Theoretical understanding of thermoplastic elastomers (TPEs) from rubber-plastics blends is still obscure due to their complexities. Computer simulation would be a very promising method to understand miscibility, thermal transitions and polymer chain dynamics in these systems. As a representative example, novel TPEs prepared from poly (vinylidene fluoride) (PVDF) and hydrogenated nitrile rubber (HNBR) blends were investigated by atomistic and mesoscopic simulations and the results were compared with experiments. The specific volume of PVDF, HNBR and their blends was studied at various temperatures by atomistic simulation to estimate the glass-rubber transition. The estimated glass transition temperatures (Tg) showed good agreement with the experiments. In the blends, two Tgs were observed from both simulation and experiments, which in turn indicated immiscibility of the pristine polymers in the present compositions. Interaction parameter (χ) also suggested the immiscibility for both the blends. Dynamics of polymer chain indicated the lower relaxation rate of PVDF in the blends with respect to the pristine one, which is reflected in reduction of crystallization temperature for the blends. Radial distribution function revealed the separation of PVDF and agglomeration of HNBR chains in the blends owing to the formation of biphasic morphology. Morphology predicted by the Dissipative Particle Dynamics simulation was also in accord with the radial distribution analysis. This was further verified experimentally from microscopic analysis.

Transport Diffusion of Light Gases in Polyethylene Using Atomistic Simulations.

We explore the temperature dependence of the self-, corrected-, and transport-diffusivities of CO2, CH4, and N2 in a polyethylene (PE) polymer membrane through equilibrium molecular dynamics simulations. We also investigate the morphology of the polymer membrane based on the intermolecular radial distribution function, free volume, and pore size distribution analysis. The results indicate the existence of 1.5-3 Å diameter pores in the PE membrane, and with the increase in the temperature, the polymer swells linearly with changing slope at 450 K in the absence of gas and exponentially in the presence of gas. The gas adsorption isotherms extracted via a two-step methodology, considering the dynamics and structural transitions in the polymer matrix upon gas adsorption, were fitted using a "two-mode sorption" model. Our results suggest that CO2 adsorbs strongly, whereas N2 shows weak adsorption in PE. The results demonstrate that CO2 is more soluble, whereas N2 is least soluble. Further, it is found that an increase in the temperature negatively impacts the solubility of CO2 and CH4 but positively for N2; this reverse solubility behavior is due to increased availability of pores accessible to N2, which are kinetically closed at the lowest temperatures. The reported self-diffusivities of the gases from our simulations are on the order of 10-6 cm2/s, consistent with the experimental evidence, whereas transport-diffusivities are 2 orders of magnitude higher than self-diffusivities. Furthermore, the temperature dependence of the self-diffusivity follows Arrhenius behavior, whereas the transport-diffusivity follows non-Arrhenius behavior having different activation energies in low and high temperature regions. Also, it is seen that loading has little effect on the self- and corrected-diffusion coefficients of all gases in the PE membrane.

Molecular dynamics on the self-assembly of mesogenic graphene precursors

We characterize the spontaneous aggregation of Disodium Cromoglycate (DSCG) in the isotropic phase of aqueous solutions, which is an archetypical mesogenic precursor for the supramolecular synthesis of graphenic carbons, using molecular dynamics simulations and thermodynamic scaling. DSCG belongs to a broader family of mesogenic precursors called lyotropic chromonic liquid crystals (LCLC). Previously reported experimental self-assembly features were quantitatively reproduced using a full atomistic representation. We find that the formation of hydrogen bonds between solvent water and mesogenic molecules strongly contributes to the self-assembly, a new discovery in LCLC self-assembly. We propose that aggregation is energetically driven by entropic forces which favor the formation of π-π interactions within mesogens' polyaromatic cores by reorienting DSCG hydrophilic groups towards solvent molecules. We carried out different quantitative characterizations that support this mechanism, such as radial distribution function and hydrogen bond distribution analysis. Furthermore, conformation stability calculations were studied using metadynamics sampling technique. These results provide a significant contribution to the ongoing understanding of the self-assembly of LCLC required for the characterization and synthesis of highly ordered supramolecular graphenic materials.

The Simulation of Loop Flow in Radial Distribution Analysis Programs

Distribution systems are typically composed of radial feeders. Radial means that there is only one path of current flow to each of the loads on the feeder. There are times when it becomes necessary to form a loop in a feeder by closing switches. This may be because of an outage or a new load that will cause the radial current to exceed the conductor current rating or violate the American National Standards Institute voltage requirement. This paper will present a method for simulating the loop flow using an injection current technique. A simple single-phase circuit is used to demonstrate the steps in the simulation. Following that, the IEEE 13 bus test feeder will be studied as it is right now, followed by the addition of a new three-phase load at one bus and a new single-phase load added at another bus. Both of these loads are going to require the addition of new lines and the capability of operating the feeder with one or two closed loops. The process for simulating the closed loops will be presented.